-------
PRELIMINARY DRAFT
diameter (MMED), which is defined as the point in the size distribution of particles such that
half the mass lies on either side of the MMED value (National Air Pollution Control Adminis-
tration, 1970). Table 5-3 summarizes a recent study estimating the particulate emission rates
and particle composition for light-duty vehicles operated on a leaded fuel of 1.8 g Pb/gallon
(Hare and Black, 1981). Table 5-4 estimates particulate emission rates for heavy- duty
vehicles (trucks) operated on a leaded fuel of 1.8 g Pb/gallon (Hare and Black, 1981). The
lead content of 1.8 g Pb/gallon was chosen to approximate the lead concentration of leaded
gasoline during 1979 (Table 5-5). Another recent study utilizing similar composite emission
factors provides estimates of motor vehicle lead emissions for large areas (Provenzano, 1978).
Lead occurs, on the average, as PbBrCl in fresh exhaust particles (Hirschler et al. ,
1957). This lead compound is 64.2 percent lead by mass and is a common form of lead emitted
due to the presence of the scavengers ethylene dichloride and ethylene dibromide in normal
leaded fuel. PbBrCl has theoretical mass ratios for lead, bromine, and chlorine of 0.64,
0.25, and 0.11, respectively. The particle compositional data in Table 5-3 indicate that mass
ratios for lead, bromine, and chlorine are approximately 0.60, 0.30, and 0.10, respectively,
from both pre- and post-1970 vehicles. Data from another study (Lang et al., 1981), involving
1970-1979 vehicles, indicated that mass ratios for lead, bromine, and chlorine were 0.62,
0.30, and 0.08, respectively.
The fate of emitted lead particles depends upon their particle size (see Section 6.3.1).
Particles initially formed by condensation of lead compounds in the combustion gases are quite
small (well under 0.1 pm in diameter) (Pierson and Brachaczek, 1982). Particles in this size
category are subject to growth by coagulation and, when airborne, can remain suspended in the
atmosphere for 7 to 30 days and travel thousands of miles from their original source
(Chamberlain et al., 1979). Larger particles are formed as the result of agglomeration of
smaller condensation particles and .have limited atmospheric lifetimes (Harrison and Laxen,
1981). The largest vehicle-emitted particles, which are greater than 100 pm in diameter, may
be formed by materials flaking off- from the surfaces of the exhaust system. As indicated in
Table 5-3, the estimated mass median equivalent diameter of leaded particles from light-duty
vehicles is <0.25 pm, suggesting that such particles have relatively long atmospheric
lifetimes and the potential for long-distance transport. Similar values for MMED in
automobile exhausts were found in Britain (0.27 pm) (Chamberlain et al. 1979) and Italy (0.33
pm) (Facchetti and Geiss, 1982). Particles this small deposit by Brownian diffusion and are
generally independent of gravitation.
The size distribution of lead exhaust particles is essentially bimodal (Pierson and
Brachaczek, 1976) and depends on a number of factors, including the particular driving pattern
in which the vehicle is used and its past driving history (Ganley and Springer, 1974; Habibi,
023PB5/A 5-10 7/13/83
-------
PRELIMINARY DRAFT
TABLE 5-3. LIGHT-DUTY VEHICULAR PARTICULATE EMISSIONS*
Data by vehicle category
1970 & later
Rate or property Pre-1970 without catalyst
Exhaust particulate emissions, g/mi 0.29 0.13
Particle mass median equivalent diameter, |jm <0.25 <0.25
Percent of particulate mass as:
Lead (Pb)
22
or
greater
36
or
greater
Bromine (Br)
11
or
greater
18
or
greater
Chlorine (CI)
4
or
greater
• 6
or
greater
Trace metals
1
1
or
greater
Carbon (C), total
33
or
greater
33
or
less
Sulfate (S04~)
1.
3
1.3
or
greater
Soluble organics ~30 or less ~10
*Rate estimates are based on 1.8 Pb/gal fuel.
Source: Hare and Black (1981).
TABLE 5-4. HEAVY-DUTY VEHICULAR PARTICULATE EMISSIONS'1
Particulate emissions by model year
Heavy-duty category Pre-1970 1970 and later
Medium-duty trucks 0.50 0.40
(6,000 to 10,000 lb GVW)'
Heavy-duty trucks 0.76 0.60
(over 10,000 lb GVW)
*Rate estimates are based on 1.8 g Pb/gal fuel, units are g/mi.
Source: Hare and Black (1981).
023PB5/A 5-11 7/13/83
276*:
-------
PRELIMINARY DRAFT
TABLE 5-5. RECENT AND PROJECTED CONSUMPTION OF GASOLINE LEAD
Average lead content
(g/gal)
Sales
Total
lead
Air-lead
Gasoli ne
volume
weighted
(103t)
(|jg/m3)d
Calendar
(billions o
f gallons)
total
0.5 gpg
1.1 gpg
year
Total
Leaded
pool
Leaded
pooled std
leaded std
1975a
102.3
92.5
1.62
1.81
165.6
—
1.23
1976
107.0
87.0
1.60
1.97
171.0
—
1.22
1977
113.2
79.7
1.49
2.12
168.7
—
1.20
1978
115.8
75.0
1.32
2.04
153.3
—
1.13
1979
111.2
58.1
1.16
1.90
129.5
—
0.93
1980
110.8
57.5
0.71
1.37
78.5
—
0.60
1981
102.6
51.0
0.59
1.19
61.0
—
0.47
1982
100.0
40.6
0.64
1.44
62.0
—
0.45C
1983
96.1
41.7
48.1
47.0
1984
92.3
35.4
0.50
1.10
'46.1
39.0
1985
89.2
29.7
0.50
1.10
44.6
32.7
1986
86.1
25.3
0.50
1.10
43.0
27.8
1987
83.8
22.1
0.50
1.10
41.9
24.3
1988
81.5
19.5
0.50
1.10
40.7
21.4
1989
79.2
17.0
0.50
1.10
39.6
18.7
1990
77.7
14.7
0.50
1.10
38.8
16.2
a
Data for the years 1975-1982 are taken from U.S. Environmental Protection Agency
(1983b), in which data for 1975-1981 are actual consumption of lead and for 1982,
estimates of consumption.
^Data for 1983-1990 are estimates taken from F.R. (1982 October 29).
Estimated (this work)
^Data from Hunt and Neligan (1982), discussed in Chapter 7, are the maximum
quarterly average lead levels from a composite of sampling sites.
023PB5/A 5-12 7/13/83
Z77
-------
PRELIMINARY DRAFT
1973; 1970; Ter Haar et al., 1972; Hirschler and Gilbert, 1964; Hirschler et al. , 1957). As
an overall average, it has been estimated that during the lifetime of the vehicle,
approximately 35 percent of the lead contained in the gasoline burned by the vehicle will be
emitted as small particles (<0.25 pm MMED), and approximately 40 percent will be emitted as
larger particles (>10 pm MMED) (Ter Haar et al., 1972). The remainder of the lead consumed in
gasoline combustion is deposited in the engine and exhaust system. Engine deposits are, in
part, gradually transferred to the lubricating oil and removed from the vehicle when the oil
is changed. A flow chart depicting lead-only emissions per gallon of fuel charged into the
engine is shown in Figure 5-4. It is estimated that 10 percent of the lead consumed during
combustion is released into the environment via disposal of used lubricating oil (Piver,
1977). In addition, some of the lead deposited in the exhaust system gradually flakes off, is
emitted in the exhaust as extremely large particles, and rapidly falls into the streets and
roads where it is incorporated into the dust and washed into sewers or onto adjacent soil.
Although the majority (>90 percent on a mass basis) of vehicular lead compounds are
emitted as inorganic particles (e.g., PbBrCl), some organolead vapors (e.g., lead alkyls) are
also emitted. The largest volume of organolead vapors arises from the manufacture, transport,
and handling of leaded gasoline. Such vapors are photoreactive, and their presence in local
atmospheres is transitory, i.e., the estimated atmospheric half-lives of lead alkyls, under
typical summertime conditions, are less than half a day (Nielsen, 1982). Organolead vapors
are most likely to occur in occupational settings (e.g., gasoline transport and handling
operations, gas stations, parking garages) and have been found to contribute less than 10
percent of the total lead present in the atmosphere (Gibson and Farmer, 1981; National Academy
of Sciences, 1972).
The use of lead additives in gasoline, which increased in volume for many years, is now
decreasing as automobiles designed to use unleaded fuel constitute the major portion of the
automotive population (Table 5-1). The decline in the use of leaded fuel is the result of two
regulations promulgated by the U.S. Environmental Protection Agency (F.R., 1973 December 6).
The first required the availability of unleaded fuel for use in automobiles designed to meet
federal emission standards with lead-sensitive emission control devices (e.g., catalytic
converters); the second required a reduction or phase-down of the lead content in leaded
gasoline. Compliance with the phase-down of lead in gasoline has recently been the subject of
proposed rulemakings. The final action (F.R., 1982 October 29) replaced the present 0,5 g/gal
standard for the average lead content of all gasoline with a two-tiered standard for the lead
content of leaded gasoline. Under this proposed rule, large refineries would be required to
meet a standard of 1.10 g/gal for leaded gasoline while certain small refiners would be
subject to a 1.90 g/gal standard until July 1, 1983, at which time they were made subject to
the 1.10 g/gal standard.
023PB5/A 5-13 7/13/83
Z? 8<
-------
^35%
LEADED FUEL ^
(Pb = 1.0 g/gal)
1000 ma (100%)-
TOTAL MASS OF LEAD
CHARGED INTO THE
ENGINE
AUTO
ENGINE
TAILPIPE DEPOSITION ^ 15%
150 mg RETAINED ON
INTERIOR SURFACES OF
ENGINE AND EXHAUST
SYSTEM
7
^10%
^40%
350 mg Pb EMITTED !
TO ATMOSPHERE AS
LEAD AEROSOL WITH !
MASS MEDIAN DIAMETER
OF <0.25 fjm. POTENTIAL
FOR LONG RANGE
TRANSPORT/POLLUTION.
400 mg Pb EMITTED TO
ROADWAY AS PARTICLES
WITH MASS MEDIAN
DIAMETERS >10 pm
LOCALIZED POLLUTION.
100 mg Pb RETAINED BY
LUBRICATING OIL
EXHAUST PRODUCTS
^75% (750 mg TOTAL
Pb EMITTED)
Figure 5-4. Estimated lead-only emissions distribution per gallon of combusted fuel.
-------
PRELIMINARY DRAFT
The trend in lead content for U.S. gasolines is shown in Figure 5-5 and Table 5-5. Of
the total gasoline pool, which includes both leaded and unleaded fuels, the average lead
content has decreased 63 percent, from an average of 1.62 g/gal in 1975 to 0.60 g/gal in 1981
(Table 5-5, Figure 5-5). Accompanying the phase-down of lead in leaded fuel has been the
increased consumption of unleaded fuel, from 11 percent of the total gasoline pool in 1975 to
50 percent in 1981 (Table 5-5 and Figure 5-6).. Since 1975, when the catalytic converter was
introduced by automobile manufacturers for automotive exhaust emissions control, virtually all
new passenger cars have been certified on unleaded gasoline (with the exception of a few
diesels and a very few leaded-gasoline vehicles). Because of the yearly turnover rate in the
vehicle fleet, the demand for unleaded gasoline is forecast to increase to 58 percent of the
total gasoline pool in 1982 and -75 percent by 1985. As the demand for unleaded fuel
increases, it may become uneconomical to distribute leaded gasoline for light-duty vehicles in
low-volume localities.
The lead content of leaded gasoline (Table 5-5) is forecast to increase from 1.19 to 1.44
g/gal in 1982 (DuPont de Nemours, 1982). The reason for this increase is that under the 1982
0.5 g/gal total pool standard, refiners could add ever-increasing amounts of lead to each
gallon of leaded gasoline (up to the level at which it would no longer be economically
justified) as the amount of unleaded gasoline produced by the refinery increases. Thus, as
the amount of unleaded gasoline increased, the amount of lead in leaded gasoline could also
increase under the former regulations. The recent EPA decision (F.R., 1982 October 29)
eliminated this practice, thereby ensuring that the amount of lead used in gasoline will
decline after 1982 to 1.1 g/gal. Further decreases in lead emissions from gasoline combustion
will depend on continued reductions in the sales of leaded gasoline.
Data describing the lead consumed in gasoline and average ambient lead levels (composite
of maximum quarterly values) versus calendar year are listed in Table 5-5 and plotted in
Figure 5-7. The 1975 through 1979 composite quarterly lead averages are based on 105
lead-monitoring sites, primarily urban. The 1980 composite average is based on 58 sites with
valid annual data. The EPA National Aerometric Data Base is still receiving the 1980 data.
The linear correlation (Figure 5-8) between lead consumed in gasoline and the composite
maximum average quarterly ambient average lead level is very good with r2 = 0.99. The 1981
and 1982 composite averages shown in Table 5-5 and Figures 5-7 and 5-8 are derived using the
linear equation of Figure 5-6. Between 1975 and i960, the lead consumed in gasoline decreased
52 percent (from 165,577 metric tons to 78,679 metric tons) while the corresponding composite
maximum quarterly average of ambient lead decreased 51 percent (from 1.23 pg/m3 to 0.60
ng/m3). This indicates that control of lead in gasoline over the past several years has
effected a direct decrease in peak ambient lead concentrations, at least for this group of
monitoring sites.
023PB5/A 5-15 7/13/83
280"=
-------
2.40
2.00
CO
UJ
o
co
<
<3
uj
=>
u.
O
LLI
H
Z
o
o
Q
«
o
<
DC
LLI
>
«
1.50
1.00
0.50
0.00
PRELIMINARY DRAFT
! 1—
LEADED FUEL
SALES-WEIGHTED TOTAL
GASOLINE POOL
(LEADED AND UNLEADED
"AVERAGE")
UNLEADED FUEL
±
±
1975
1976
1977
1981
1982'
1978 1979 1980
CALENDAR YEAR
Figure 5-5. Trend in lead content of U.S. gasolines, 1975-1982. {DuPont, 1982).
•1982 DATA ARE FORECASTS.
023PB5/A
5-16
7/01/83
281-
-------
PRELIMINARY DRAFT
! 1 1 1—!—r
TOTAL GASOLINE SALES
yZZZ// '
UNLEADED :/%
LEADED REGULAR
LEADED PREMIUM
CALENDAR YEAR
Figure 5-6. Trend In U.S. gasoline sales, 1975-1982. (DuPont, 1982).
•1982 DATA ARE FORECASTS.
023PB5/A 5-17 7/01/83
282c:
-------
c
o
H
u
'5
e
s
%
o
W
<
<3
200
180
160
140
120
O
iu
5
5> 100
Z
o
o
Q
u 80
60
40
20
M
C
£
c
o
¦C
w
%
200
180
160
140
120
100
80
60
40
20
AMBIENT LEAD CONCENTRATION
LEAD CONSUMED IN GASOLINE
1.20
1.10
1.00
0.90
0.80
0.70
0.80
0.50
0.40
0.30
o
o
2
3
tfl
q
m
3
5
3
c
2
D
c
>
30
H
m
33
r-
<
3D
>
O
55
o
(/)
x
co
1975 1976 1977 1978 1979
CALENDAR YEAR
1980
198 V
1982"
Figure 5-7. Lead consumed in gasoline (Du Pont, 1982) and ambient lead con-
centrations, 1975-1982. (Hunt and Neligan, 1982).
'DASHED LINES ARE ESTIMATES.
5-18
283-
7/01/83
-------
AVEHAGE Pb = 6.93 x 10* (Pb CONSUMED) + 0.05
• 1975
£ 120
.•1980
0.20 0.40 0.60 0.80 1 00 1.20
COMPOSITE MAXIMUM QUARTERLY AVERAGE LEAD LEVELS, fig/m"
Figure 5-B. Relationship between lead consumed in gasoline and composite maximum
quarterly average lead levels, 1975-1980.
*1981 AND 1982 DATA ARE ESTIMATES.
5-19
7/01/83
284*=:
-------
PRELIMINARY DRAFT
Furthermore, the equation in Figure 5-8 implies that the complete elimination of lead
from gasoline might reduce the composite average of the maximum quarterly lead concentrations
at these stations to 0.05 pg/m3, a level typical of concentrations reported for nonurban
stations in the U.S. (see Chapter 7). Even this level of 0.05 pg/m3 is regarded as evidence
of human activity since it is at least two orders of magnitude higher than estimates of
geochemical background lead concentrations discussed in Section 5.2.
5.3.3.2 Stationary Sources. As shown in Table 5-2 (based on 1982 emission estimates), solid
waste incineration and combustion of waste oil are the principal contributors of lead
emissions from stationary sources, accounting for two-thirds of stationary source emissions.
The manufacture of consumer products such as lead glass, storage batteries, and lead additives
for gasoline also contributes significantly to stationary source lead emissions. Since 1970,
the quantity of lead emitted from the metallurgical industry has decreased somewhat because of
the application of control equipment and the closing of several plants, particularly in the
zinc and pyrometallurgical industries.
A new locus for lead emissions emerged in the mid-1960s with the opening of the "Viburnum
Trend" or "New Lead Belt" in southeastern Missouri. The presence of ten mines and three
accompanying lead smelters in this area makes it the largest lead-producing district in the
world and has moved the United States into first place among the world's lead-producing
nati ons.
Although some contamination of soil and water occurs as a result of such mechanisms as
leaching from mine and smelter wastes, quantitative estimates of the extent of this
contamination are not available. Spillage of ore concentrates from open trucks and railroad
cars, however, is known to contribute significantly to contamination along transportation
routes. For example, along two routes used by ore trucks in southeastern Missouri, lead
levels in leaf litter ranged from 2000 to 5000 |jg/g at the roadway, declining to a fairly
constant 100 to 200 pg/g beyond about 400 ft from the roadway (Wixson et al., 1977).
Another possible source of land or water contamination is the disposal of particulate
lead collected by air pollution control systems. The potential impact on soil and water
systems from the disposal of dusts collected by these control systems has not been quantified.
5.4 SUMMARY
There is no doubt that atmospheric lead has been a component of the human environment
since the earliest written record of civilization. Atmospheric emissions are recorded in
glacial ice strata and pond and lake sediments. The history of these global emissions seems
closely tied to production of lead by industrially oriented civilizations.
023PB5/A
5-20
285^
7/13/83
-------
PRELIMINARY DRAFT
Although the amount of lead emitted from natural sources is a subject of controversy,
even the most liberal estimate (25 X 103 t/year) is dwarfed by the global emissions from
anthropogenic sources (450 X 103 t/year).
Production of lead in the United States has remained steady at about 1.2 X 106 t/year for
the past decade. The gasoline additive share of this market has dropped from 18 to 9.5
percent during the period 1971 to 1981. The contribution of gasoline lead to total
atmospheric emissions has remained high, at 85 percent, as emissions from stationary sources
have decreased at the same pace as from mobile sources. The decrease in stationary source
emissions is due primarily to control of stack emissions, whereas the decrease in mobile
source emissions is a result of switchover to unleaded gasolines. The decreasing use of lead
in gasoline is projected to continue through 1990.
023PB5/A 5-21 7/13/83
286<
-------
PRELIMINARY DRAFT
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023PB5/A
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Nielsen, T. (1982) Atmospheric occurence of organolead compounds. In: Grandjean, P., ed. Bio-
logical effects of organolead compounds. Boca Raton, FL: CRC Press; PAGES. (IN PRESS)
Nriagu, J. 0. (1979) Global inventory of natural and anthropogenic emissions of trace metals
to the atmosphere. Nature (London) 279: 409-411.
Patterson, C. C. (1965) Contaminated and natural lead environments of man. Arch. Environ.
Health. 11: 344-360.
Patterson, C. C. (1980) An alternative perspective - lead pollution in the human environment:
origin, extent and significance. In: National Academy of Sciences, Committee on Lead in
the Human Environment. Lead in the human environment. Washington, DC: National Academy of
Sciences; pp. 265-350.
Patterson, C. C. (1983) Criticism of "Flow of metals into the global atmosphere [Letter].
Geochim. Cosmochim. Acta 47: 1163-1168.
Pierson, W. R. ; Brachaczek, W. W. (1976) Particulate matter associated with vehicles on the
road. Warrandale, PA: Society of Automotive Engineers; SAE technical paper no. 760039.
SAE transactions 85: 209-227.
Pierson, W. R. ; Brachaczek, W. W. (1982) Particulate matter associated with vehicles on the
road II. J. Aerosol Sci. VOL: PAGES. (IN PRESS)
Piver, W. T. (1977) Environmental transport and transformation of automotive-emitted lead.
Environ. Health Perspect. 19: 247-259.
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Provenzano, G. (1978) Motor vehicle lead emissions in the United States: an analysis of
important determinants, geographic patterns and future trends. J. Air Pollut. Control
Assoc. 28: 1193-1199.
Rolfe, G. L. (1974) Lead distribution in tree rings. For. Sci. 20: 283-286.
Servant, J. (1982) Atmospheric trace elements from natural and industrial sources. London,
United Kingdom: University of London, Monitoring and Assessment Research Centre.
Settle, D. M. ; Patterson, C. C. (1980) Lead in albacore: guide to lead pollution in Americans.
Science (Washington D.C.) 207: 1167-1176.
Shacklette, H. T. ; Hamilton, J. C. ; Boerngen, J. G. ; Bowles, J. M. (1971) Elemental composi-
tion of surficial materials in the conterminous United States: an account of the amounts
of certain chemical elements in samples of soils and other regoliths. Washington, DC:
U.S. Department of the Interior, Geological Survey; Geological Survey professional paper
no. 574-D.
Shirahata, H. ; Elias, R. W. ; Patterson, C. C. ; Koide, M. (1980) Chronological variations in
concentrations and isotopic compositions of anthropogenic atmospheric lead in sediments
of a remote subalpine pond. Geochim. Cosmochim. Acta 44: 149-162.
Symeonides, C. (1979) Tree-ring analysis for tracing the history of pollution: application to
a study in northern Sweden. J. Environ. Qual. 8: 482-486.
Ter Haar, G. L. ; Lenane, D. L.; Hu, J. N.; Brandt, M. (1972) Composition, size, and control of
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U.S. Bureau of Mines. (1972-1982) Lead. In: Minerals yearbook. Volume I: Metals and minerals.
Washington, DC: U.S. Government Printing Office.
U.S. Environmental Protection Agency. (1977a) Control techniques for lead air emissions:
volumes I and II. Durham, NC: U.S. Environmental Protection Agency, Office of Air Quality
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Available from: NTIS, Springfield, VA; PB80-197544 and PB80-197551.
U.S. Environmental Protection Agency, Health Effects Research Lab. (1977b) Air quality cri-
teria for lead. Research Triangle Park, NC: U.S. Environmental Protection Agency,
Criteria and Special Studies Office; EPA report no. EPA-600/8-77-017. Available from:
NTIS, Springfield, VA; PB 280411.
U.S. Environmental Protection Agency. (1978) Air quality data for metals 1975 from the
National Air Surveillance Networks. Research Triangle Park, NC: U.S. Environmental
Protection Agency; Office of Research and Development; EPA report no. EPA-600/4-78-059.
Available from: NTIS, Springfield, VA; PB 293106.
U.S. Environmental Protection Agency. (1979) Air quality data for metals 1976 from the
National Air Surveillance Networks. Research Triangle Park, NC: U.S. Environmental
Protection Agency, Office of Research and Development; EPA report no. EPA-600/4-79-054.
Available from NTIS, Springfield, VA; PB80-147432.
U.S. Environmental Protection Agency. (1983) Summary of lead additive reports for refineries.
Washington, DC: U.S. Environmental Protection Agency, Office of Mobile Source: draft
report.
023PB5/A 5-25 7/13/83
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United Kingdom Department of the Environment, Central Unit on Environmental Pollution. (1974)
Lead in the environment and its significance to man. London, United Kingdom: Her
Majesty's Stationery Office; pollution paper no. 2.
Wixson, B. G. ; Bolter, E. ; Gale, N. L. ; Hemphill, D. D. ; Jennett, J. C. (1977) The Missouri
lead study: an interdisciplinary investigation of environmental pollution by lead and
other heavy metals from industrial southeastern Missouri: vols. 1 and 2. Washington, DC:
National Science Foundation. Available from: NTIS, Springfield, VA: PB 281859 and PB
274242.
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6. TRANSPORT AND TRANSFORMATION
6.1 INTRODUCTION
This chapter describes the transition from the emission of .lead particles into the
atmosphere to their ultimate deposition on environmental surfaces, i.e., vegetation, soil, or
water. At the source, lead emissions are typically around 10,000 pg/m3 (see Section'. 5.3.3),
while in city air, lead values are usually between 0.1 and 10 pg/m3 (Dzubay et al., 1979;
Reiter et al., 1977; also see Chapter 7). These reduced concentrations are the result of
dilution of effluent gas with clean air and the removal of particles by wet or dry deposition.
Characteristically, lead concentrations are highest in confined areas close to sources and are
progressively reduced by dilution or deposition in districts more removed from sources.
At any particular location and time, the concentration of lead found in the atmosphere
depends on the proximity to the source, the amount of lead emitted from sources, and the
degree of mixing provided by the motion of the atmosphere. It is possible to describe
quantitatively the physics of atmospheric mixing in a variety of ways and, with some limiting
assumptions, to develop simulation models that predict atmospheric lead concentrations. These
models are not sensitive to short-term variations in air motion over a period of weeks or
months because these variations are suppressed by integration over long periods of time.
In highly, confined areas such as parking garages or tunnels, atmospheric lead
concentrations can be ten to a thousand times greater than values measured near roadways or in
urban areas. In turn, atmospheric lead concentrations are usually about 24 times greater in
the central city than in residential suburbs. Rural areas have even lower concentrations.
Because lead emissions in the United States have declined dramatically in the past few
years, the older lead concentration data on which recent dispersion studies are based may seem
not to be pertinent to existing conditions. Such studies do in fact illustrate principles of
atmospheric dispersion and may validly be applied to existing concentrations of lead, which
are described in Section 7.2.1.1.
Transformations which may occur during dispersion are physical changes in particle size
distribution, chemical changes from the organic to the inorganic phase, and chemical changes
in the inorganic phase of lead particles. Particle size distribution stabilizes within a few
hundred kilometers of the sources, although atmospheric concentration continues to decrease
with distance. Concentrations of organolead compounds are relatively small (1 to 6 percent of
total lead) except in special situations where gasoline is handled or where engines are
started cold within confined areas. Ambient organolead concentrations decrease more rapidly
than inorganic lead, suggesting conversion from the organic to the inorganic phase during
transport. Inorganic lead appears to convert from lead halides and oxides to lead sulfates.
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Lead is removed from the atmosphere by wet or dry deposition. The mechanisms of dry
deposition have been incorporated into models that estimate the flux of atmospheric lead to
the Earth's surface. Of particular interest is deposition on vegetation surfaces, since this
lead may be incorporated into food chains. Between wet and dry deposition, it is possible to
calculate an atmospheric lead budget that balances the emission inputs discussed in Section
5.3.3. with deposition outputs.
6.2 TRANSPORT OF LEAD IN AIR 8Y DISPERSION
6.2.1 Fluid Mechanics of Dispersion
Particles in air streams are subject to the same principles of fluid mechanics as
particles in flowing water (Friedlander, 1977). On this basis, the authors of several texts
have described the mathematical arguments for the mixing of polluted air with clean air
(Benarie, 1980; Dobbins, 1979; Pasquill, 1974). The first principle is that of diffusion
along a concentration gradient. If the airflow is steady and free of turbulence, the rate of
mixing is determined by the diffusivity of the pollutant. In the case . of gases, this
diffusivity is an inherent property of the molecular forces between gases. For particles,
diffusivity is a property of Brownian movement, hence a function of particle size and
concentration. For both cases, the diffusivity for dilute media is a constant (Dobbins,
1979).
If the steady flow of air is interrupted by obstacles near the ground, turbulent eddies
or vortices may be formed. Diffusivity is no longer constant but may be influenced by factors
independent of concentrations, such as windspeed, atmospheric stability, and the nature of the
obstacle. By making generalizations of windspeed, stability, and surface roughness, it is
possible to construct models using a variable transport factor called eddy diffusivity (K), in
which K varies in each direction, including vertically. There is a family of K-theory models
that describe the dispersion of particulate pollutants.
The simplest K-theory model assumes that the surface is uniform and the wind is steady;
thus, turbulence is predictable for various conditions of atmospheric stability (Pasquill,
1974). This model produces a Gaussian plume, called such because the concentration of the
pollutant decreases according to a normal or Gaussian distribution in both the vertical and
horizontal directions. These models have some utility and are the basis for most of the air
quality simulations performed to date (Benarie, 1980). However, the assumptions of steady
windspeed and smooth surface place constraints on their utility.
Several approaches have been used to circumvent the constraints of the Gaussian models.
Some have been adapted for studying long range transport (LRT) (more than 100 km) of
pollutants. Johnson (1981) discusses 35 LRT models developed during the 1970s to describe the
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dispersion of atmospheric sulfur compounds. A few models that address specific problems of
local and regional transport merit further discussion because they emphasize the scope of the
modeling problem.
One family of models is based on the conservative volume element approach, where volumes
of air are seen as discrete parcels having conservative meteorological properties, such as
water vapor mixing ratio, potential temperature, and absolute vorticity (Benarie, 1980). The
effect of pollutants on these parcels is expressed as a mixing ratio. These parcels of air
may be considered to move along a trajectory that follows the advective wind direction. These
models are particularly suitable for dealing with surface roughness, but they tend to
introduce artifact diffusion or pseudodiffusion, which must be suppressed by calculation (Egan
and Mahoney, 1972; Liu and Seinfeld, 1975; Long and Pepper, 1976).
An approach useful for estimating dispersion from a roadway derives from the similarity
approach of Prandtl (1927). A mixing length parameter is related to the distance traveled by
turbulent eddies during which violent exchange of material occurs. This mixing length is
mathematically related to the square root of the shear stress between the atmosphere and the
surface. Richardson and Procter (1925) formulated these concepts in a law of atmospheric
diffusion which was further extended to boundary layer concepts by Obukhov (1941). At the
boundary layer, the turbulent eddy grows and its energy decreases proportionately with time
and distance away from the source.
Although physical descriptions of turbulent diffusion exist for idealized circumstances
such as isolated roadways and flat terrain, the complex flow and turbulence patterns of cities
has defied theoretical description. The permeability of street patterns and turbulent eddy
development in street canyons are two major problem areas that make modeling urban atmospheres
difficult. Kotake and Sano (1981) have developed a simulation model for describing air flow
and pollutant dispersion in various combinations of streets and buildings on two scales. A
small scale, 2 to 20 m, is used to define the boundary conditions for 2 to 4 buildings and
associated roadways. These subprograms are combined on a large scale of 50 to 500 meters.
Simulations for oxides of nitrogen show nonlinear turbulent diffusion, as would be expected.
The primary utility of this program is to establish the limits of uncertainty, the first step
toward making firm predictions. It is likely that the development of more complete models of
dispersion in complex terrains will become a reality in the near future.
An important point in this discussion is that none of the models described above have
been tested for lead. The reason for this is simple. All of the models require sampling
periods of 2 hours or less in order for the sample to conform to a well-defined set ot
meteorological conditions. In most cases, such a sample would be below the detection limits
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for lead. The common pollutant used to test models is S02, which can be measured over very
short, nearly instantaneous, time periods. The question of whether gaseous S02 can be used as
a surrogate for particulate lead in these models remains to be answered.
6.2.2 Influence of Dispersion on Ambient Lead Concentrations
Dispersion within confined situations, such as parking garages, residential garages and
tunnels, and away from expressways and other roadways not influenced by complex terrain
features depends on emission rates and the volume of clean air available for mixing. These
factors are relatively easy to estimate and some effort has been made to describe ambient lead
concentrations which can result under selected conditions. On an urban scale, the routes of
transport are not clearly defined, but can be inferred from an isopleth, i.e., a plot
connecting points of identical ambient concentrations. These plots always show that lead
concentrations are maximum where traffic density is highest.
Dispersion beyond cities to regional and remote locations is complicated by the fact that
there are no monitoring network data from which to construct isopleths, that removal by
deposition plays a more important role with time and distance, and that emissions from many -
different geographic location's sources converge. Some techniques of source reconciliation
are described, but these become less precise with increasing distance from major sources of
lead. Dispersion from point sources such as smelters and refineries is described with
isopleths in the manner, of urban dispersion, although the available data are notably less
abundant.
6.2.2.1 Confined and Roadway Situations. Obviously, the more source emissions are diluted by
clean air, the lower ambient air concentrations of lead will be. Ingalls and Garbe (1982)
used a variety of box and Gaussian plume models to calculate typical levels of automotive air
pollutants that might be present in microscale (within 100 meters of the source) situations
with limited ventilation. Table 6-1 shows a comparison of six exposure situations, recomputed
for a flat-average lead emission factor of 6.3 mg/km for roadway situations and 1.0 mg/min for
garage situations. The roadway emission factor chosen corresponds roughly to values chosen by
Dzubay et al. (1979) and Pierson and Brachaczek (1976) scaled to 1979 lead-use statistics.
The parking garage factor was estimated from roadway factors by correction for fuel
consumption (Ingalls and Garbe, 1982).
Confined situations, with low air volumes and little ventilation, allow automotive
pollutant concentrations to reach one to three orders of magnitude higher than are found in
open air. Thus, parking garages and tunnels are likely to have considerably higher ambient
lead concentrations than are found in expressways with high traffic density or in city
streets. Purdue et al. (1973) found total lead levels of 1.4 to 2.3 pg/m3 in five of six U.S.
cities in 1972. In similar samples from an underground parking garage, total lead was 11 to
12 (jg/m3.
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Table 6-1 also shows that the high concentration of automotive lead near roadways
declines significantly at distances greater than 100 meters. Dzubay et al. (1979) found lead
concentrations of 4 to 20 pg/m3 in air over Los Angeles freeways in 1976; at nearby sites off
the freeways, concentrations of 0.3 to 4.7 pg/m3 were measured.
TABLE 6-1. SUMMARY OF MICROSCALE CONCENTRATIONS
Data are recalculated from Ingalls and Garbe (1982) using 1979 lead emission factors. They
show that air lead concentrations in a garage or tunnel can be two or three orders of magni-
tude higher than on streets or expressways. Typical conditions refer to neutral atmospheric
stability and average daily traffic volumes. Severe conditions refer to maximum hourly
traffic volume with atmospheric inversion. Data are in jjg/m3. Emission rates are given in
parentheses.
Si tuation
Air lead
concentration
Residential garage (1 mg Pb/min)
Typical (30 second idle time)
Severe (5 min idle time)
' H ¦
80
670
Parking garage
Typical
Severe
Roadway tunnel
Typical
Severe
(1 mg Pb/min)
(6.3 mg Pb/km)
Street canyon (sidewalk receptor) (6.3 mg Pb/km)
Typical a) 800 vehicles/hr
b) 1,600 vehicles/hr
Severe a) 800 vehicles/hr
b) 1,600 vehicles/hr
On expressway (wind: 315 deg. rel., 1 m/sec) (6.3 mg Pb/km)
Typical
Typical
Severe
Beside expressway (6.3 mg Pb/km)
Severe 1 meter
10 meters
100 meters
1,000 meters
30 min
~5
6
2
0.25
40
560
11
29
0.4
0.9
1.4
2.8
2.4
10
Annual
1.2
1.0
0.3
0.03
average
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Tiao and Hillmer (1978) and Ledolter and Tiao (1979) have analyzed 3 years (1974-1977) of
ambient air lead data from one site on the San Diego Freeway in Los Angeles, California.
Particulate lead concentrations were measured at five locations: in the median strip and at
distances of 8 and 30 to 35 meters from the road edge on both sides of>the road. Average lead
concentrations at the 35 meter point were two- to four-fold lower than at the 8 meter location
(Tiao and Hillmer, 1978). An empirical model involving traffic count and traffic speed, which
are related to road emissions, required only windspeed as a predictor of dispersion
conditions.
Witz et al. (1982) found that meteorological parameters in addition to windspeed, such as
inversion frequency, inversion duration, and temperature, correlate well with ambient levels
of lead. At a different site near the San Diego freeway in Los Angeles, monthly ambient
particulate lead concentrations and meteorological variables were measured about 100 meters
from the roadway through 1980. Multiple linear regression analysis showed that temperature at
6 AM, windspeed, wind direction, and a surface-based inversion factor were important variables
in accurately predicting monthly average lead concentrations. In this data set, lead values
for December were about five-fold higher than those measured in the May to September summer
season, suggesting that seasonal variations in,, wind direction and the occurrence of
surface-based inversions favor high winter lead values. Unusually high early morning
temperatures and windspeed during the winter increased dispersion and reduced lead
concentration. The success of this empirical model depends on the interplay of windspeed and
atmospheric stability (Witz et al., 1982).
6.2.2.2 Dispersion of Lead on an Urban Scale. In cities, air pollutants including lead that
are emitted from automobiles tend to be highest in concentration in high traffic areas. Most
U.S. cities have a well-defined central business district (CBD) where lead concentrations are
highest. To illustrate the dispersion of lead experienced in cities, two cases are presented
below.
Trijonis et al. (1980) reported lead concentrations for seven sites in St. Louis,
Missouri; annual averages for 1977 are shown in Figure 6-1. Values around the CBD are
typically two to three times greater than those found in the outlying suburbs in St. Louis
County to the west of the city. Bradow (1980) presented results from the Regional Air
Monitoring System Gaussian plume model (Turner, 1979) for St. Louis for the 1977 calendar
year. Figure 6-1 also presents isopleths for lead concentration calculated from that model.
The general picture is one of peak concentrations within congested commercial districts which
gradually decline in outlying areas. However, concentration gradients are not steep, and the
whole urban area has levels of lead above 0.5 (jg/ro3-
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ST. CHARLES COUNTY. MO
92.954 . _
MADISON COUNTY. ILL
250.934
EDWARDSVILLE
ST. LOUIS COUNTY. MO
951,353
-GRANITE
CITY
COLLINSVILLE
ST. LOUIS CITY.1
I M° /
622,236 I
ST. CLAIR COUNTY
2B6.176
2 8
2.2
EAST ST LOUIS
1 70
0.56/
18,831
MONROE COUNTY
Figure 6-1. Isopleths are shown for annual average particulate lead in ^g/m3.
RAM Model calculations predict lead concentrations in St. Louis for 1977.
Numerical values below place names are 1970 population counts for these
areas.
Source: Calculated from Bradow (1980) on the basis of a fleet average lead
emissions factor of 54 mg/mile for 1977.
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For the South Coast Basin of Southern California, the area of high traffic density is
more widespread than is characteristic of many cities. Ambient concentrations of lead tend to
be more uniform. For example, Figures 6-2 and 6-3 show the average daily traffic by grid
square and the contour plots of annual average lead concentration, respectively, for 1969
(Kawecki, 1978). In addition, Figure 6-3 shows annual average lead measured at eight sites in
the Basin for that year. It is clear that the central portion had atmospheric particulate
lead concentrations in the range of 3 pg/m3; the outer areas were about 1 to 2 Mg/m3.
Reiter et al. (1977) have shown similar results for the town of Fort Collins, Colorado,
for a 5.5-hr period in May of 1973. In that study, modeling results showed maximum lead
concentrations in the center of town around 0.. 25 (jg/m3, which decreased to 0.1 pg/m3 in the
outermost region. Presumably, still lower values would be found at more remote locations.
Apparently, then, lead in the air decreases 2^-fold from maximum values in center city
areas to well populated suburbs, with a further 2-fold decrease in the outlying areas. These
modeling estimates are generally confirmed by measurement in the cases cited above and in the
data presented in Section 7.2.1.
6.2.2.3 Dispersion from Smelter and Refinery Locations. The 15 mines and 7 primary smelters
and refineries shown in Figure 5-3 are not located in urban areas. Most of the 56 secondary
smelters and refineries are likewise non-urban. Consequently, dispersion from these point
sources should be considered separately, but in a manner similar to the treatment of urban
regions. In addition to lead concentrations in air, concentrations in soil and on vegetation
surfaces are often used to determine the extent of dispersion away from smelters and
refineries.
6.2.2.4 Dispersion to Regional and Remote Locations. Beyond the immediate vicinity of urban
areas and smelter sites, lead in air declines rapidly to concentrations of 0.1 to 0.5 yg/m3.
Two mechanisms responsible for this change are dilution with clean air and removal by
deposition (Section 6.4). In the absence of monitoring networks that might identify the
sources of lead in remote areas, two techniques of source identification have been used.
Vector gradient analysis was attempted by Everett et al. (1979) and source reconciliation has
been reported by Sievering et al. (1980) and Cass and McRae (1983). A third technique, isoto-
pic composition, has been used to identify anthropogenic lead in air, sediments, soils,
plants, and animals in urban, rural, and remote locations (Chow et al. 1975), but this
technique is not discussed here because it provides no information on the mechanism of
transport.
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342
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207
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Figure 6-2. Spatial distribution of surface street and freeway traffic in the Los
Angeles Basin (103 VMT/day) for 1979.
Source: Kawecki 11978).
023PB6/A 6-9 7/01/83
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KEY TO CONTOUR CONCENTRATIONS
Figure 6-3. Annual average suspended lead concentrations for 1969 in the Los
Angeles Basin, calculated from the model of Cass (1975). The white zones between
the patterned areas are transitional zones between the indicated concentrations.
Source: Kawecki (1978).
023P86/A 6-10 7/01/83
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In vector gradient analysis, the sampler is oriented to the direction of the incoming
wind vector, and samples are taken only during the time the wind is within a 30° arc of that
vector. Other meteorological data are taken continuously. As the wind vector changes, a
different sampler is turned on. A 360° plot of concentration vs. wind direction gives the
direction from which the pollutant arrives at that location. Only one report of the use of
this technique for lead occurs in the literature (Everett et al., 1979), and analysis of this
experiment was complicated by the fact that in more than half the samples, the lead con-
centrations were below the detection limit. The study was conducted at Argonne National
Laboratory and the results reflected the influence of automobile traffic east and northeast of
this location.
Source reconciliation is based on the concept that each type of natural or anthropogenic
emission has a unique combination of elemental concentrations. Measurements of ambient air,
properly weighted during multivariate regression analysis, should reflect the relative amount
of pollutant derived from each of several sources (Stolzenberg et al., 1982). Sievering et
al. (1980) used the method of Stolzenberg et al. (1982) to analyze the transport of urban air
from Chicago over Lake Michigan. They found that 95 percent of the lead in Lake Michigan air
could be attributed to various anthropogenic sources, namely coal fly ash, cement manufacture,
iron and steel manufacture, agricultural soil dust, construction soil dust, and incineration
emissions. This information alone does not describe transport processes, but the study was
repeated for several locations to show the changing influence of each source.
Cass and McRae (1983) used source reconciliation in the Los Angeles Basin to interpret
1976 NFAN data (see Sections 4.2.1 and 7.2.1.1) based on emission profiles from several
sources. They developed a chemical element balance model, a chemical tracer model, and a
multivariate statistical model. The chemical element balance model showed that 20 to 22
percent of the total suspended particle mass could be attributed to highway sources. The
chemical tracer model permitted the lead concentration alone to represent the highway profile,
since lead comprised about 12 percent of the mass of the highway generated aerosol. The
multivariate statistical model used only air quality data without source emission profiles to
estimate stoichiometric coefficients of the model equation. The study showed that single
element concentrations can be used to predict the mass of total suspended particles.
A type of source reconciliation, chemical mass balance, has been used for many years
by geochemists in determining the anthropogenic influence on the global distribution of ele-
ments. Two studies that have applied this technique to the transport of lead to remote
areas are Murozumi et al. (1969) and Shirahata et al. (1980). In these studies, the influence
of natural or crustal lead was determined by mass balance, and the relative influence of
023PB6/A 6-11 7/13/83
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PRELIMINARY DRAFT
anthropogenic leaa was determined. In the Shirahata et al. (1980) study, the influence of
anthropogenic lead was confirmed quantitatively by analysis of isotopic compositions in the
manner of Chow et al. (1975).
Harrison and Williams (1982) determined air concentrations, particle size distributions,
and total deposition flux at one urban and two rural sites in England. The urban site, which
had no apparent industrial, commercial or municipal emission sources, had an air lead
concentration of 3.8 pg/m3, whereas the two rural sites were about 0.15 pg/m3. The average
particle size became smaller toward the rural sites, as the mass median equivalent diameter
(MMED) shifted downward from 0.5 to 0.1 (jm. The total deposition flux will be discussed
in Section 6.4.2.
Knowledge of lead concentrations in the oceans and glaciers provides some insight into
the degrees of atmospheric mixing and long range transport. Tatsumoto and Patterson (1963),
Chow and Patterson (1966), and Schaule and Patterson (1980) measured dissolved lead
concentrations in sea water off the coast of California, in the Central North Atlantic (near
Bermuda), and in the Mediterranean, respectively. The profile obtained by Schaule and
Patterson (1980) is shown in Figure 6-4. Surface concentrations in the Pacific (14 ng/kg)
were found to be higher than those of the Mediterranean or the Atlantic, decreasing abruptly
with depth to a relatively constant level of 1 to 2 ng/kg. The vertical, gradient was found to
be much less in the Atlantic. Tatsumoto and Patterson (1963) had earlier estimated an average
surface lead concentration of 200 ng/kg in the northern hemispheric oceans. Chow and
Patterson (1966) revised this estimate downward to 70 ng/kg. Below the mixing layer, there
appears to be no difference between lead concentrations in the Atlantic and Pacific. These
investigators calculated that industrial lead currently is being added to the oceans at about
10 times the rate of introduction by natural weathering, with significant amounts being
removed from the atmosphere by wet and dry deposition directly into the ocean. Their data
suggest considerable contamination of surface waters near shore, diminishing toward the open
ocean (Chow and Patterson, 1966).
Duce et al. (1975), Taylor (1964), and Maenhaut et al. (1979) have investigated trace
metal concentrations (including lead) in the atmosphere in remote northern and southern
hemispheric sites. The natural sources for such atmospheric trace metals include the oceans
and the weathering of the Earth's crust, while the anthropogenic source is particulate air
pollution. Enrichment factors for concentrations relative to standard values for the oceans
and the crust were calculated (Table 6-2); the mean crustal enrichment factors for the
North Atlantic and the South Pole are shown in Figures 6-5 and 6-6. The significance
of the comparison in Figure 6-6 is that 90 percent of the particulate pollutants in the global
023PB6/A
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PRELIMINARY DRAFT
1000
• DISSOLVED Pb
~ PARTICULATE Pb
0)
2000
a
E
z
I-
£L
Q 3000
4000
~ < >
5000
0
2 4
6 8 10 12 14 16 0
CONCENTRATION, ng Pb/kg
Figure 6-4. Profile of lead concentrations in the
central northeast Pacific. Values below 1000 m are
an order of magnitude lower than reported by
Tatsumoto and Patterson (1963) and Chow and
Patterson (1966).
Source: Schaule and Patterson (1980).
023PB6/A 6-13 7/01/83
304<
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023PB6/A
PRELIMINARY DRAFT
80'w 60 40" 20°
60° N
50°
40°
30®
20°
Figure 6-5. Midpoint collection locetlon for at-
mospheric samples collected from R.V. Trident
north of 30 N, 1970-1972.
Source: Duce et al. (1975); Zoller et al. (1974).
105
ic'
a 10
c
~
ai
a
10'
10 1
ICELAND
GREENLAND
NORTH ATLANTIC
• AZORES
«;•
"NORTH ATLANTIC WESTERLIES
SOUTH POLE _ ®e4f
Pbf-U
ELEMENT
Figure 6-6. The EFcrust values for atmospheric
trace metals collected in the North Atlantic
westerlies and at the South Pole. The horizontal
bars represent the geometric mean enrichment fac-
tors, and the vertical bars represent the geometric
standard deviation of the mean enrichment factors.
The EFcrust for lead at the South Pole is based on
the lowest lead concentration (0.2 mg/scm).
Source: Duce et al. (1975); Zoller et al. (1974).
6-14 7/01/83
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PRELIMINARY DRAFT
troposphere are injected in the northern hemisphere (Robinson and Robbins, 1971). Since the
residence times for particles in the troposphere (Poet et al., 1972) are much less than the
interhemispheric mixing time, it is unlikely that significant amounts of particulate
pollutants can migrate from the northern to the southern hemisphere via the troposphere;
however, this does not rule out stratospheric transfer.
TABLE 6-2. ENRICHMENT OF ATMOSPHERIC AEROSOLS OVER CRUSTAL ABUNDANCE
Using the crustal abundances of Taylor (1964), the enrichment of atmospheric aerosols, rela-
tive to aluminum, has been calculated by Duce et al. (1975). An enrichment factor signifi-
cantly above one implies a source other than crustal rock for the element in question.
Element
Concentration
range, ng/m3
Enrichment
factor
Al
8-370
1. 0
Si
0:0008-0.011
0.8
Fe
3.4-220
1.4
Co
0.006-0.09
2.4
Mn
0.05-5.4
2.6
Cr
0.07-1.1
11
V
0.06-14
17
Zn
0.3-27
110
Cu
0.12-10
120
Cd
0.003-0.62
730
Pb
0.10-64
2,200
Sb
0.05-0.64
2,300
Se
0.09-0.40
10,000
aBased on the geometric mean of the concentration.
Murozumi et al. (1969) have shown that long range transport of lead particles emitted
from automobiles has significantly polluted the polar glaciers. They collected samples of
snow and ice from Greenland and the Antarctic. As shown in Figure 6-7, they found that the
concentration of lead varied inversely with the geological age of the sample. The authors
023PB6/A
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7/13/83
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PRELIMINARY DRAFT
0 20
cr
s
o
Z 0 12
m
9)
0 10
J
Q
< 0.08
UJ
o_
0 06
0.02 —
1950
1850
1900
1800
1750
A D.
AGE OF SAMPLES
Figure 6-7. Lead concentration profile in snow
strata of Northern Greenland.
Source: Murozumi et al. (1969).
attribute the gradient increase after 1750 to the Industrial Revolution and the accelerated
increase after 1940 to the increased use of lead alkyls in gasoline. The most recent levels
found in the Antarctic snows were, however, less than those found in Greenland by a factor of
10 or more. Before 1940 the concentrations in the Antarctic were below the detectable level
(<0.001 pg/kg) and have risen to 0.2 pg/kg in recent snow.
Jaworowski (1967) found that lead concentrations in two glaciers have increased by a
factor of 10 during the last century. The concentrations in the most recent ice layers were
extremely high (148 pg/kg). Jaworowski et al. (1975) also studied stable and radioactive
pollutants from ice samples from the Storbreen glaciers in Norway. -The mean stable lead
concentration in Storbreen glacier ice in the 12th century was 2.1 pg/kg. The mean for more
recent samples was 9.9 pg/kg. Around 1870 the average lead concentration in Norwegian glacier
ice was 5.9 pg/kg, whereas that for glaciers in Poland was 5.0 pg/kg. A century later, the
mean concentration in the Norwegian glacier was 9.9 pg/kg, while the mean concentration in the
Polish glacier reached 148 pg/kg. Jaworowski et al. (1975) attributed the large increase of
lead concentrations in the Polish glacier to local sources.
023PB6/A 6-16 7/01/83
3
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PRELIMINARY.DRAFT
Evidence from remote areas of the world suggests that lead and other fine particle
components are transported substantial distances, up to thousands of kilometers, by general
weather systems. The degree of surface contamination of remote areas with lead depends both
on weather influences and on the degree of air contamination. However, even in remote areas,
man's primitive activities can play an important role in atmospheric lead levels. Davidson et
al. (1982) have shown that there are significant levels of fine particle lead, up to 0.5
pg/m3, in remote villages in Nepal. The apparent source is combustion of dried yak dung,
which contains small amounts of naturally occurring lead derived from plant life in those
remote valleys.
6.3 TRANSFORMATION OF LEAD IN AIR
6.3.1 Particle Size Distribution
Whitby et al. (1975) placed atmospheric particles into three' different size regimes: the
nuclei mode (<0.1 pm), the accumulation mode (0.1 to 2 pm) and the large particle mode (>2
pm). At the source, lead particles are generally in the nuclei and large particle modes.
Large particles are removed by deposition close to the source and particles in the nuclei mode
diffuse to surfaces or agglomerate while airborne to form larger .particles of the accumulation
mode. Thus it is in the accumulation mode that particles are dispersed great distances.
In Figure 6-8, size distributions for lead particles in automobile exhaust are compared
with those found in air samples at a receptor site in Pasadena, California, "not in the
immediate influence of traffic" (Huntzicker et al., 1975). The authors. conclude that the
large particle mode found in exhaust (>9 pm) is severely attenuated in ambient air samples.
Therefore, large particle lead must be deposited near roadways. Similar data and conclus.ions
had been reported earlier by Daines et al. (1970).
Pierson and Brachaczek (1976) reported particle size distributions that were larger in
ambient air than in a roadway tunnel, where vehicle exhaust must be dominant (see Figure 6-9).
The large particles may have.been deposited in the roadway itself and small particles may have
agglomerated during transport from the roadway to the immediate roadside. Since 40 to 1,000
pm particles are found in gutter debris (Figure 6-10), deposition of large particles appears
confirmed. , .
Little and Wiffen (1977, 1978) reported a MMED for lead of 0.1 pm in the roadway but
0.3 pm 1 meter from the road edge in an intercity expressway in England. Further, particle
size distributions reported by Huntzicker et al. (1975) show bimodal distributions for on-
roadway samples, with peak mass values at about 0.1 and 10 pm. For off-roadway Pasadena
samples, there is no evidence of bimodality and only a broad maximum in lead mass between 0.1
and 1 pm.
023PB6/A
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PRELIMINARY DRAFT
4.0
2.0
t—T
i—T
10.0 —
8.0
6.0 —
AUTO EXHAUST
Pb
1.0
0.8
0.6
PASADENA Pb
(11/72)
(2/74)
0.4
J_l I I I L
20 40 60 80 90 95 98
MASS IN PARTICLES < D .percent
P
Figure 6-8. Cumulative mass distribution for lead particles in
auto exhaust and at an urban site in Pasadena, Calif, some
distance from high traffic density roadways.
Source: Huntzicker et al. (1975).
023PB6/A
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309<
7/01/83
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PRELIMINARY DRAFT
10
8
Pb
6
4
AMBIENT AEROSOL Pb
2
1
0.8
0.6
VEHICLE AEROSOL Pb
0.4
0.2
0.1
10
1
90 95 98 99
SO
80
% OF MASS IN PARTICLES SMALLER THAN STATED p'^d
Figure 6-9. Particulate lead size distribution measured at the
Allegheny Mountain Tunnel, Pennsylvania Turnpike, 1975.
Source; Pierson and Brachaczek (1976).
023PB6/A . 6-19 7/01/83
310<
-------
PRELIMINARY DRAFT
0)
c
o
in
5
«
o
in
1000
500 —
= 100 I—-
GC
<
£L
50 —
GROSS
10
J_
I I I I
0.1 1 2 5 10 50 90 95 9B 99
PERCENT OF MASS IN PARTICLES SMALLER THAN STATED SIZE
99.9
Figure 6-10. Particle size distributions of substances in gutter
debris. Rotunda Drive, Dearborn, Michigan.
Source: Pierson and Brachaczek (1976).
023PB6/A
6-20
31^
7/01/83
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PRELIMINARY DRAFT
In cities or in rural areas, there is a remarkable consistency in lead particle size
range. For example, Robinson and Ludwig (1964) report cascade impactor MMED values for lead
ranging from 0.23 to 0.3 pm in six U.S. cities and three rural areas as shown in Table 6-3.
Stevens et al. (1978) have reported dichotomous sampler data for six U.S. cities, as shown in
Table 6-4, and Stevens et al. (1980, 1982) have reported similar results for remote locations.
Virtually every other study reported in the literature for Europe, South America, and Asia has
cone to the conclusion that ambient urban and rural air contains predominantly fine particles
(Cholak et al., 1968; De Jonghe and Adams, 1980; Durando and Aragon, 1982; Lee et al., 1968;
Htun and Ramachandran, 1977).
TABLE 6-3. COMPARISON OF SIZE DISTRIBUTIONS OF LEAD-CONTAINING
PARTICLES IN MAJOR SAMPLING AREAS
Distribution by particle size,
Mm
25%a
MMED
75%a
No. of
Sample area samples
Avg.
Range
Avg.
Range
Avg.
Range
Chicago
12
0.19(7)b
0.10-0.29
0.30
0.16-0.64
0.40(10)
0.28-0.63
Ci nci nnati
7
0.15(3)
0.09-0.24
0.23
0.16-0.23
0.44
0.30-0.68
Phi 1adelphia
7
0.14(3)
0.09-0.25
0.24
0.19-0.31
0.41
0.28-0.56
Los Angeles
8
0.16(7)
0.10-0.22
0.26
0.19-0.29
0.49(7)
0.39-0.60
Pasadena
7
0.18
0.05-0.25
0.24
0.08-0.32
0.48(6)
0.13-0.67
San Francisco
3
0.11
0.06-0.13
0.25
0.15-0.31
0.45(2)
0.44-0.46
Vernon (rural)
5
0.17(4)
0.12-0.22
0.24
0.18-0.32
0.40
0.28-0.47
Cherokee (rural)
1
0.25
0. 31
0.71
Mojave (rural)
1
-
0.27
0. 34
^ refers to the percentile of the mass distribution. Thus in the column labeled 25% are the
particle sizes at which 25% of the particle mass is in smaller sizes. Similarly, the 75%
.column contains values of particle sizes at which.75% of the mass is in smaller sizes.
Numbers in parentheses indicate number of samples available for a specific value when dif-
ferent from total number of samples. -
Source: Robinson and Ludwig (1964).
023PB6/A 6-21 7/13/83
312<
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PRELIMINARY DRAFT
TABLE 6-4. DISTRIBUTION OF LEAD IN TWO SIZE FRACTIONS AT
SEVERAL SITES IN THE UNITED STATES
((j g/m3)
Location
Date
Fi ne
Coarse
F/C ratio
New York, NY
2/1977
1.1
0.18
6.0
Philadelphia, PA
2-3/1977
0.95
0.17
5.6
Charlestown, W. WA
4-8/1976
0.62
0.13
4.6
St. Louis, MO
12/1975
0.83
0.24
3.4
Portland, OR
12/1977
0.87
0.17
5.0
Glendora, CA
3/1977
0.61
0.09
6.7
Average
5.2
Source: Stevens et
al. (1978).
It appears that lead particle size distributions are stabilized close to roadways and
remain constant with transport into remote environments (Gillette and Winchester, 1972).
6.3.2 Organic (Vapor Phase) Lead in Air
Although lead additives used in gasoline are less volatile than gasoline itself (see
Section 3.4), small amounts may escape to the atmosphere by evaporation from fuel systems or
storage facilities. Tetraethyllead (TEL) and tetramethyllead (TML) photochemically decompose
when they reach the atmosphere (Huntzicker et al., 1975; National Air Pollution Control
Administration, 1965). The lifetime of TML is longer than that of TEL. Laveskog (1971) found
that transient peak concentrations of organolead up to 5,000 pg/m3 in exhaust gas may be
reached in a cold-started, fully choked, and poorly tuned vehicle. If a vehicle with such
emissions were to pass a sampling station on a street where the lead level might typically be
0.02 to 0.04 fjg/m3, a peak of about 0.5 pg/m3 could be measured as the car passed by. The
data reported by Laveskog were obtained with a procedure that collected very small (100 ml),
short-time (10 min) air samples. Harrison et al. (1975) found levels as high as 0.59 fjg/m3
(9.7 percent of total lead) at a busy gasoline service station in England. Grandjean and
Nielsen (1977), using GC-MS techniques, found elevated levels (0.1 pg/m3) of TML in city
streets in Denmark and Norway. These authors attributed these results to the volatility of
TML compared with TEL.
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PRELIMINARY DRAFT
A number of studies have used gas absorbers behind filters to trap vapor-phase lead
compounds. Because it is not clear that all the lead captured in the backup traps is, in
fact, in the vapor phase in the atmosphere, "organic" or "vapor phase" lead is an operational
definition in these studies. Purdue et al. (1973) measured both particulate and organic lead
in atmospheric samples. They found that the vapor phase lead was about 5 percent of the total
lead in most samples. The results are consistent with the studies of Huntzicker et al. (1975)
who reported an organic component of 6 percent of the total airborne lead in Pasadena for a
3-day period in June, 1974, and of Skogerboe (1975), who measured fractions in the range of 4
to 12 percent at a site in Fort Collins, Colorado. It is noteworthy, however, that in an
underground garage, total lead concentrations were approximately five times those in ambient
urban atmospheres, and the organic lead increased to approximately 17 percent.
Harrison et al. (1979) report typical organolead percentages in ambient urban air of 1 to
6 percent. Rohbock et al. (1980) reported higher fractions, up to 20 percent, but the data
and interpretations have been questioned by Harrison and Laxen (1980). Rohbock et al. (1980)
and De Jonghe and Adams (1980) report one to two orders of magnitude decrease in organolead
concentrations from the central urban areas to residential areas.
6.3.3 Chemical Transformations of Inorganic Lead in Air
Lead is emitted into the air from automobiles as lead halides and as double salts with
ammonium halides (e.g., PbBrCl • 2NH4C1). From mines and smelters, PbS04, Pb0-PbS04, and PbS
appear to be the dominant species. In the atmosphere, lead is present mainly as the sulfate
with minor amounts of halides. It is not completely clear just how the chemical composition
changes in transport.
Biggins and Harrison (1978, 1979) have studied the chemical composition of lead particles
in exhaust and in city air in England by X-ray diffractometry. These authors reported that
the dominant exhaust forms were PbBrCl, PbBrCl•2NH4C1 , and a-2PbBrCl•NH4C1, in agreement with
the earlier studies of Hirschler and Gilbert (1964) and Ter Haar and Bayard (1971).
At sampling sites in Lancaster, England, Biggins and Harrison (1978, 1979) found
PbS04•(NH4)2S04, and PbS04 • (NH4)2BrCl together with minor amounts of the lead halides and
double salts found in auto exhaust. These authors suggested that emitted lead halides react
with acidic gases or aerosol components (S02 or H2S04) on filters to form substantial levels
of sulfate salts. It is not clear whether reactions with S04 occurs in the atmosphere or on
the sample filter.
023PB6/A 6-23 7/13/83
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/
PRELIMINARY DRAFT
The ratio of Br to Pb is often cited as an indication of automotive emissions. From the
mixtures commonly used in gasoline additives, the mass Br/Pb ratio should be about 0.386 if
there has been no fractionation of either element (Harrison and Sturges, 1983). However,
several authors have reported loss of halide, preferentially bromine, from lead salts in
atmospheric transport (Dzubay and Stevens, 1973; Pierrard, 1969; Ter Haar and Bayard, 1971).
Both photochemical decomposition (Lee et al., 1971; Ter Haar and Bayard, 1971) and acidic gas
displacement (Robbins and Snitz, 1972) have been postulated as mechanisms. Chang et al.
(1977) have reported only very slow decomposition of lead bromochloride in natural sunlight;
currently the acid displacement of halide seems to be the most likely mechanism. O'Connor
et al. (1977) have reported no loss in bromine in comparison of roadside and suburban-rural
aerosol samples from western Australia; low levels of S02 and sulfate aerosol could account
for that result. Harrison and Sturges (1983) warn of several other factors that can alter the
Br/Pb ratio. Bromine may pass through the filter as hydrogen bromide gas, lead may be
retained in the exhaust system, or bromine may be added to the atmosphere from other sources,
such as marine aerosols. They concluded that Br/Pb ratios are only crude estimates of
automobile emissions, and that this ratio would decrease with distance from the highway from
0.39 to 0.35 less proximate sites and 0.25 in suburban residential areas.
Habibi et al. (1970) studied the composition of auto exhaust particles as a function of
particle size. Their main conclusions follow:
1. Chemical composition of emitted exhaust particles is related to
particle size.
a. Very large particles greater than 200 jjm have a
composition similar to lead-containing material deposited
in the exhaust system, confirming that they have been
emitted from the exhaust system. These particles contain
approximately 60 to 65 percent lead salts, 30 to 35
percent ferric oxide (Fe203), and 2 to 3 percent soot and
carbonaceous material. The major lead salt is lead
bromochloride (PbBrCl), with (15 to 17 percent) lead oxide
(PbO) occurring as the 2PbO-PbBrCl double salt. Lead
sulfate and lead phosphate account for 5 to 6 percent of
these deposits. (These compositions resulted from the
combustion of low-sulfur and low-phosphorus fuel.)
b. PbBrCl is the major lead salt in particles of 2 to 10 pm
equivalent diameter, with 2PbBrCl-NH4C1 present as a minor
constituent.
c. Submicrometer-sized lead salts are primarily 2PbBrCl¦NH4C1.
023PB6/A
6-24
7/13/83
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PRELIMINARY DRAFT
2. Lead-halogen molar ratios in particles of less than 10 pm MMED
indicate that much more halogen is associated with these solids
than the amount expected from the presence of 2PbBrCl-NH4C1, as
identified by X-ray diffraction. This is particularly true for
particles in the 0.5 to 2 pm size range.
3. There is considerably more soot and carbonaceous material
associated with fine-mode particles than with coarse mode
particles re-entrained after having been deposited after
emission from the exhaust system. This carbonaceous material
accounts for 15 to 20 percent of the fine particles.
4. Particulate matter emitted under typical driving conditions is
rich in carbonaceous material. There is substantially less
such material emitted under continuous hot operation.
5. Only small quantities of 2PbBrCl-NH4C1 were found in samples
collected at the tailpipe from the hot exhaust gas. Its
formation therefore takes place primarily during cooling and
mixing of exhaust with ambient air.
Foster and Lott (1980) used X-ray diffractometry to study the composition of lead
compounds associated with ore handling, sintering, and blast furnace operations-around a lead
smelter in Missouri. Lead sulfide was the main constituent of those samples associated with
ore handling and fugitive dust from open mounds of ore concentrate. The major constituents
from sintering and blast furnace operations appeared to be PbS04 and Pb0-PbS04, respectively.
6.4 REMOVAL OF LEAD FROM THE ATMOSPHERE
Before atmospheric lead can have any effect on organisms or ecosystems, it must be
transferred from the air to a surface. For natural ground surfaces and vegetation, this
process may be either dry or wet deposition.
6.4.1 Dry Deposition
6.4.1.1 Mechanisms of Dry Deposition. Transfer by dry deposition requires that the particle
move from the main airstream through the boundary layer to a surface. The boundary layer is
defined as the region of minimal air flow immediately adjacent to that surface. The thickness
of the boundary layer depends mostly oh the windspeed and roughness of the surface.
Airborne particles do not follow a smooth, straight path in the airstream. On the
contrary, the path of a particle may be affected by micro-turbulent air currents, gravitation,
or its own inertia. There are several mechanisms which alter the particle path sufficient to
cause transfer to a surface. These mechanisms are a function of particle size, windspeed, and
surface characteristics.
023PB6/A
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PRELIMINARY DRAFT
Particles larger than a few micrometers in diameter are influenced primarily by
sedimentation, where the particle accelerates downward until aerodynamic drag is exactly
balanced by gravitational force. The particle continues at this velocity until it reaches a
surface. Sedimentation is not influenced by windspeed or surface characteristics. Particles
moving in an airstream may be removed by impaction whenever they are unable to follow the
airstream around roughness elements of the surface, such as leaves, branches, or tree trunks.
In this case, the particle moves parallel to the airstream and strikes a surface perpendicular
to the airstream. A related mechanism, turbulent inertial deposition, occurs when a particle
encounters turbulence within the airstream causing the particle to move perpendicular to the
airstream. ]t may then strike a surface parallel to the airstream. In two mechanisms, wind
eddy diffusion and interception, the particle remains in the airstream until it is transferred
to a surface. With wind eddy diffusion, the particle is transported downward by turbulent
eddies. Interception occurs when the particle in the airstream passes within one particle
radius of a surface. This mechanism is more a function of particle size than windspeed. The
final mechanism, Brownian diffusion, is important for very small particles at very low
windspeeds. Brownian diffusion is motion, caused by random collision with molecules, in the
direction of a decreasing concentration gradient.
Transfer from the main airstream to the boundary layer is usually by sedimentation or
wind eddy diffusion. From the boundary layer to the surface, transfer may be by any of the
six mechanisms, although those which are independent of windspeed (sedimentation,
interception, Brownian diffusion) are more likely.
6.4.1.2 Dry deposition models. A particle influenced only by sedimentation may be considered
to be moving downward at a specific velocity usually expressed in cm/sec. Similarly,
particles transported to a surface by any mechanism are said to have an effective deposition
velocity (V^), which is measured not by rate of particle movement but by accumulation on a
surface as a function of air concentration. This relationship is expressed in the equation:
where J is the flux or accumulation expressed in ng/cm2*s and C is the air concentration in
ng/cm3. The units of become cm/sec.
Several recent models of dry deposition have evolved from the theoretical discussion of
Fuchs (1964) and the wind tunnel experiments of Chamberlain (1966). From those early works,
it was obvious that the transfer of particles from the atmosphere to the Earth's surface
involved more than rain or snow. The models of Slinn (1982) and Davidson et al. (1982)
are particularly useful for lead deposition and were strongly influenced by the theoretical
023PB6/A 6-26 7/13/83
Vd = J/C
-------
PRELIMINARY DRAFT
discussions of fluid dynamics by Friedlander (1977). Slinn's model considers a multitude of
vegetation parameters to find several approximate solutions for particles in the size range of
0.1 to 1.0 pm. In the absence of appropriate field studies, Slinn (1982) estimates deposition
velocities of 0.01 to 0.1 cm/sec.
The model of Davidson et al. (1982) is based on detailed vegetation measurements and wind
data to predict a of 0.05 to 1.0 cm/sec. Deposition velocities are specific for each
vegetation type. This approach has the advantage of using vegetation parameters of the type
made for vegetation analysis in ecological studies (density, leaf area index (LAI), height,
diameter) and thus may be applicable to a broad range of vegetation types for which data are
already available in the ecological literature.
Both models show a decrease in deposition velocity with decreasing particle size down to
about 0.1 to 0.2 pm, followed by an increase in Vd with decreasing diameter from 0.1 to 0.001
cm/sec. On a log plot of diameter vs. this curve is v-shaped, and the plots of several
vegetation types show large changes (10X) in minimum V^, although the minima commonly occur at
about the same particle diameter (Figure 6-11).
In summary, it is not correct to assume that air concentration and particle size alone
determine the flux of lead from the atmosphere to terrestrial surfaces. The type of vegetation
canopy and the influence of the canopy on windspeed are important predictors of dry
deposition. Both of these models predict deposition velocities more than one order of
magnitude lower than reported in several earlier studies (e.g., Sehmel and Hodgson, 1976).
6.4.1.3 Calculation of Dry Deposition. The data required for calculating the flux of lead
from the atmosphere by dry deposition are leaf area index, windspeed, deposition velocity, and
air concentration by particle size. The LAI should be total surface rather than upfacing
surface, as used in photosynthetic productivity measurements. Leaf area indices should also
be expressed for the entire community rather than by individual plant, in order to incorporate
variations in density. Some models use a more generalized surface roughness parameter, in
which case the deposition velocity may also be different.
The value selected for Vd depends on the type of vegetation, usually described as either
short (grasses or shrubs) or tall (forests). For particles with an MMED of about 0.5, Hicks
(1980) gives values for tall vegetation deposition velocity from 0.1 to 0.4 cm/sec. Lannefors
and Hansson (1983) estimated values of 0.2 to 0.5 cm/sec in the particle size range of 0.06 to
2.0 pm in a coniferous forest. For lead, with an MMED of 0.55 pm, they measured a deposition
velocity of 0.41.
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10
* 10"
>
u
o
>
z
o
-------
PRELIMINARY DRAFT
6.4.1.4 Field Measurements of Dry Deposition on Surrogate and Natural Surfaces. Several in-
vestigators have used surrogate surface devices similar to those described in Section 4.2.2.4.
These data are summarized in Table 6-5. The few studies available on deposition to vegetation
surfaces show deposition rates comparable to those of surrogate surfaces and deposition velo-
cities in the range predicted by the models discussed above, In Section 6.4.3, these data are
used to show that global emissions are in approximate balance with global deposition. It is
reasonable that future refinements of field measurements and model calculations will permit
more accurate estimates of dry deposition in specific regions or under specific environmental
conditions.
TABLE 6-5. SUMMARY OF SURROGATE AND VEGETATION SURFACE DEPOSITION OF LEAD
Depositional surface ng
Flux
Pb/cm2-day
Air cone
ng/m3
Deposition velocity
cm/sec
Reference
Tree leaves (Paris)
0.38
...
0.086
1
Tree leaves (Tennessee)
0.29-1.2
—
—
2
Plastic disk (remote
Cali fornia)
0.02-0.08
13-31
0.05-0.4
3
Plastic plates
(Tennessee)
0.29-1.5
110
0.05-0.06
4
Tree leaves (Tennessee)
—
110
0.005
4
Snow (Greenland)
0.004
0.1-0.2
0.1
5
Grass (Pennsylvania)
—
590
0.2-1.1
6
Coniferous forest (Sweden)
0.74
21
0.41
7
1. Servant, 1975.
2. Lindberg et al., 1982.
3. Elias and Davidson, 1980.
4. Lindberg and Harriss, 1981.
5. Davidson et al., 1981.
6. Davidson et al., 1982.
7. Lannefors et al., 1983.
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6.4.2 Wet Deposition
Wet deposition includes removal by rainout and washout. Rainout occurs when particulate
matter is present in the supersaturated environment of a growing cloud. The small particles
(0.1 to 0.2 ^im) act as nuclei for the formation of small droplets, which grow into raindrops
(Junge, 1963). Droplets also collect particles under 0.1 pm by Brownian motion and by the
water-vapor gradient. The nucleation process may also occur on particulate matter present
below cloud level, producing droplets large enough to be affected by sedimentation. These
processes are referred to as rainout. Washout, on the other hand, occurs when falling
raindrops collect particles by diffusion and impaction on the way to the ground. Although
data on the lead content of precipitation are rather limited, those that do exist indicate a
high variability.
Results on lead scavenging by washout are conflicting. In a laboratory study employing
simulated rainfall, Edwards (1975) found that less than 1 percent of auto exhaust lead
particles could be removed by washout. However, Ter Haar et al. (1967) found that intense
rainfall removed most of the atmospheric lead. As a result, the lead content of rain water is
smaller for intense rainfall than in steady showers, presumably because the air contains
progressively less lead. It is not clear which of the two phenomena, nucleation or washout,
is responsible.
Lazrus et al. (1970) sampled precipitation at 32 U.S. stations and found a correlation
between gasoline used and lead concentrations in rainfall in each area. Similarly, there is
probably a correlation between lead concentration in rainfall and distance from large
stationary point sources. The authors pointed out that at least twice as much lead is found
in precipitation as in water supplies, implying the existence of a process by which lead is
removed from the soil solution after precipitation reaches the ground. Russian studies
(Konovalov et al., 1966) point to the insolubility of lead compounds in surface waters and
suggest removal by natural sedimentation and filtration.
Atkins and Kruger (1968) conducted a field sampling program in Palo Alto, California, to
determine the effectiveness of sedimentation, impaction, rainout, and washout in removing lead
from the atmosphere. Rainfall in the area averages approximately 33 cm/year and occurs
primarily during the late fall and winter months. Airborne concentrations at a freeway site
varied from 0.3 pg/m3 to a maximum of 19 pg/m3 in the fall and winter seasons, and were a
maximum of 9.3 pg/m3 in the spring. During periods of light rainfall in the spring, the
maximum concentration observed was 7.4 pg/m3. More than 90 percent of the lead reaching the
surface during the one-year sampling period was collected in dry fallout. Wet deposition
accounted for 5 to 10 percent of the lead removal at the sampling sites.
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Andren et al. (1975) evaluated the contribution of wet and dry deposition of lead in a
study of the Walker Branch Watershed in Oak Ridge, Tennessee, during the period June 1973 to
July 1974. The mean precipitation in the area is approximately 130 cm/yr. Results reported
for the period January through June 1974 are presented in Table 6-6. Wet deposition
contributed approximately 67 percent of the total deposition for the period.
TABLE 6-6. DEPOSITION OF LEAD AT THE WALKER BRANCH WATERSHED, 1974
Lead deposition (g/ha)
Peri od
Wet
Dry
January
34.1
<16.7
February
6.7
< 3.3
March
21.6
<10.6
Apri 1
15.4
< 7.5
/
May
26.5
<13.0
June
11.1
< 5.4
Total
115.4
56.5
Average
19.2
9.4
aTotal deposition ^172 g/ha. Wet deposition ^67 percent of total.
Source: Andren et al., 1975.
6.4.3 Global Budget of Atmospheric Lead
The geochemical mass balance of lead in the atmosphere may be determined from
quantitative estimates of inputs and outputs. Inputs are from natural and anthropogenic
emissions described in Section 5.2 and 5.3. They amount to 450,000 to 475,000 metric tons
annually (Nriagu, 1979). There are no published estimates of global deposition from the
atmosphere, but the data provided in Sections 6.4.1 and 6.4.2 can provide a reasonable basis
on which to make such an estimate. Table 6-7 shows an average concentration of 0.4 pg Pb/kg
precipitation. The total mass of rain and snowfall is 5.2 x 107 kg, so the amount of lead
removed by wet deposition is approximately 208,000 t/yr. For dry deposition, a crude estimate
may be derived by dividing the surface of the Earth into three major vegetation types based on
surface roughness or LAI. Oceans, polar regions, and deserts have a very low surface rough-
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TABLE 6-7. ESTIMATED GLOBAL DEPOSITION OF ATMOSPHERIC LEAD
Deposition from atmosphere
Mass Concentration Deposition
1017 kg/yr 10 6 g/kg 106 kg/yr
Wet
To "oceans 4.1 0.4 164
To continents 1.1 0.4 44
Area Deposition rate Deposition
Dry ( 1012 km2 10 3 q/m2-yr 10G kg/yr
To oceans, ice caps, deserts 405 0.2 89
Grassland, agricultural
areas, and tundra 46 0.71 33
Forests 59 1.5 80
Total dry: 202
Total wet: 208
Global: 410
Source: This report.
ness and can be assigned a deposition velocity of 0.01 cm/sec, which gives a flux of 0'. 2
pg/m2,yr assuming 75 ng Pb/m3 air concentration. Grasslands, tundra, and other areas of
low-lying vegetation have a somewhat higher deposition velocity; forests would have the
highest. Values of 0.3 and 0.65 can be assigned to these two vegetation types, based on the
data of Davidson et al. (1982). Whittaker (1975) lists the global surface area of each of the
three types as 405, 46, and 59 x 1012 km2, respectively. In the absence of data on the global
distribution of air concentrations of lead, an average of 0.075 pg/m3 is assumed. Multiplying
air concentration by deposition velocity gives the deposition flux for each vegetation type
shown on Table 6-7. The combined wet and dry deposition is 410,000 metric tons, which
cpmpares favorably with the estimated 450,000 to 475,000 metric tons of emissions.
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Mass balance calculations of this type serve to accentuate possible errors in the data
which are not otherwise obvious. The data used above arei not held to be absolutely firm.
Certainly, more refined estimates of air concentrations and deposition velocities can be made
in the future. On the other hand, the calculations above show some published calculations to
be unreasonable. In particular, values of 36 MQ/kQ rain reported by Lazrus (1970) would
account for more than 50 times the total global emissions. Likewise, deposition fluxes of
0.95 pg/cm2-yr reported by Jaworowski et al. (1981) would account for 10 times global
emissions. Chemical budgets are an effective means of establishing reasonable limits to
environmental lead data.
6.5 TRANSFORMATION AND TRANSPORT IN OTHER ENVIRONMENTAL MEDIA
6.5.1 Soil
Soils have both a liquid and solid phase, and trace metals are normally distributed
between these two phases. In the liquid phase, metals may exist as free ions or as soluble
complexes with organic or inorganic ligands. Organic ligands are typically humic substances
such as fulvic or humic acid, and the inorganic ligands may be iron or manganese hydrous
oxides. Since lead rarely occurs as a free ion in the liquid phase (Camerlynck and Kiekens,
1982), its mobility in the soil solution depends on the availability of organic or inorganic
ligands. The liquid phase of soil often exists as a thin film of moisture in intimate contact
with the solid phase. The availability of metals to plants depends on the equilibrium between
the liquid and solid phase.
In the solid phase, metals may be incorporated into crystalline minerals of parent rock
material, into secondary clay minerals, or precipitated as insoluble organic or inorganic
complexes. They may also be adsorbed onto the surfaces of any of these solid forms. Of these
categories, the most mobile form is in soil moisture, where lead can move freely into plant
roots or soil microorganisms with dissolved nutrients. The least mobile is parent rock
material, where lead may be bound within crystalline structures over geologic periods of time.
Intermediate are the lead complexes and precipitates. Transformation from one form to another
depends on the chemical environment of the soil. For example at pH 6 to 8, insoluble
organic-Pb complexes are favored if sufficient organic matter is available; otherwise hydrous
oxide complexes may form or the lead may precipitate with the carbonate or phosphate ion. In
the pH range of 4 to 6, the organic-Pb complexes become soluble. Soils outside the pH range
of 4 to 8 are rare. The interconversion between soluble and insoluble organic complexes
affects the equilibrium of lead between the liquid and solid phase of soil.
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Even though the equilibrium may shift toward the insoluble form so strongly that 99.9
percent of the lead may be immobilized, 0.01 percent of the lead in total soil can have a
significant effect on plants and microorganisms if the soils are heavily contaminated with
lead (Chapter 8).
The water soluble and exchangeable forms of metals are generally considered available for
plant uptake (Camerlynck and Kiekens, 1982). These authors demonstrated that in normal soils,
only a small fraction of the total lead is in exchangeable form (about 1 pg/g) and none exists
as free lead ions. Of the exchangeable lead, 30 percent existed as stable complexes, 70
percent as labile complexes. The organic content of these soils was low (3.2 percent clay,
8.5 percent silt, 88.3 percent sand). In heavily contaminated soils near a midwestern
industrial site, Miller and McFee (1983) found that 77 percent of the lead was in
exchangeable or organic form, although still none could be found in aqueous solution. Soils
had a total lead content from 64 to 360 pg/g and an organic content of 7 to 16 percent.
Atmospheric lead may enter the soil system by wet or dry deposition mechanisms described
earlier. There is evidence that this lead enters as PbS04 or is rapidly converted to PbS04 at
the soil surface (Olson and Skogerboe, 1975). Lead sulfate is relatively soluble and thus
could remain mobile if not transformed. Lead could be immobilized by precipitation as less
soluble compounds [PbC03, Pb(P04)2], by ion exchange with hydrous oxides or clays, or by
chelation with humic and fulvic acids. Santi11an-Medrano and Jurinak (1975) discussed the
possibility that the mobility of lead is regulated by the formation of Pb(0H)2, Pb3(P04)2,
Pb5(P04)30H, and PbC03, This model, however, did not consider the possible influence of
organic matter on lead immobilization. Zimdahl and Skogerboe (1977), on the other hand, found
lead varied linearly with cation exchange capacity (CEC) of soil at a given pH, and linearly
with pH at a given CEC (Figure 6-12). The relationship between CEC and organic carbon is
discussed below.
Some of the possible mechanisms mentioned above can be eliminated by experimental
evidence. If surface adsorption on clays plays a major role in lead immobilization, then the
capacity to immobilize should vary directly with the surface-to-volume ratio of clay. Two
separate experiments using the nitrogen BET method for determining surface area and size
fractionation techniques to obtain samples with different surface-to-volume ratios, Zimdahl
and Skogerboe (1977) demonstrated that this was not the case. They also showed that precipi-
tation as lead phosphate or lead sulfate is not significant, although carbonate precipitation
\ -
can be important in soils that are are carbonaceous in nature or to which lime (CaC03) has
been added.
023PB6/A
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Of the two remaining processes, lead immobilization is more strongly correlated with
organic chelation than with iron and manganese oxide formation (Zimdahl and Skogerboe, 1977).
It is possible, however, that chelation with fulvic and humic acids is catalyzed by the
presence of iron and manganese oxides (Saar and Weber, 1982). This would explain the positive
correlation for both mechanisms observed by Zimdahl and Skogerboe (1977). The study of Miller
and McFee (1983) discussed above seemed to indicate that atmospheric lead added to soil is
distributed to organic matter (43 percent) and ferro-manganese hydrous oxides (39 percent),
with 8 percent found in the exchangeable fraction and 10 percent as insoluble precipitates.
If organic chelation is the correct model of lead immobilization in soil, then several
features of this model merit further discussion. First, the total capacity of soil to
immobilize lead can be predicted from the linear relationship developed by Zimdahl and
Skogerboe (1977) (Figure 6-12) based on the equation:
N = 2.8 x 10"6 (A) + 1.1 x 10"5 (B) - 4.9 x ID*5
where N is the saturation capacity of the soil expressed in moles/g soil, A is the CEC of the
soil in meq/100 g soil, and B is the pH. Because the CEC of soil is more difficult to
determine than total organic carbon, it is useful to define the relationship between CEC and
organic content. Pratt (1957) and Klemmedson and Jenny (1966) found a linear correlation
between CEC and organic carbon for soils of similar sand, silt, and clay content. The data of
Zimdahl and Skogerboe (1977) also show this relationship when grouped by soil type. They show
that sandy clay loam with an organic content of 1.5 percent might be expected to have a CEC of
12 meq/100 g. From the equation, the saturation capacity for lead in soil of pH 5.5 would be
45 (jmoles/g soil or 9,300 mQ/Q- The same soil at pH 4.0 would have a total capacity of 5,900
Mg/g-
The soil humus model also facilitates the calculation of lead in soil moisture using
values available in the literature for conditional stability constants with fulvic acid. The
term conditional is used to specify that the stability constants are specific for the
conditions of the reaction. Conditional stability constants for HA and FA are comparable.
The values reported for log K are linear in the pH range of 3 to 6 (Buffle and Greter, 1979;
Buffle et al., 1976; Greter et al., 1979), so that interpolations in the critical range of pH
4 to 5.5 are possible (Figure 6-12). Thus, at pH 4.5, the ratio of complexed lead to ionic
lead is expected to be 3.8 x 10a. For soils of 100 \ig/q, the ionic lead in soil moisture
solution would be 0.03 |jg/g. The significance of this ratio is discussed in Section 8.2.1.
It is also important to consider the stability constant of the Pb-FA complex relative to
-f
other metals. Schnitzer and Hansen (1970) showed that at pH 3, Fe3 is the most stable in the
023PB6/A
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c
PRELIMINARY DRAFT
x
£
x
_ct>
o
E
o
<
a.
<
o
z
o
p
<
ae
3
i-
<
(/)
25
50
75
100
125
CEC. meq/100 g
Figure 6-12. Variation of lead saturation capacity with cation exchange
capacity in soil at selected pH values.
Source: Data from Zimdahl and Skogerboe (1977).
023PB6/A
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7/01/83
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PRELIMINARY DRAFT
sequence Fe3+ > Al3+ > Cu2 > Ni2 > Co2 > Pb2+ > Ca2+ > Zn2+ > Mn2+ > Mg2+. At pH 5, this
sequence becomes Ni2 = Co2 > Pb2 > Cu2 > Zn2 = Mn2 > Ca2 > Mg2 . This means that at
normal soil pH levels of 4.5 to 8, lead is bound to FA + HA in preference to many other metals
that are known plant nutrients (Zn, Mn, Ca, and Mg). Furthermore, if lead displaces iron in
this scheme, an important function of FA may be inhibited at near saturation capacity. Fulvic
acid is believed to play a role in the weathering of parent rock material by the removal of
iron from the crystalline structure of the minerals, causing the rock to weather more rapidly.
In the absence of this process, the weathering of parent rock material and the subsequent
release of nutrients to soil would proceed more slowly.
6.5.2 Water
6.5.2.1 Inorganic. The chemistry of lead in an aqueous solution is highly complex because
the element can be found in a multiplicity of forms. Hem and Durum (1973) have reviewed the
chemistry of lead in water in detail'; the aspects of aqueous lead chemistry that are germane
to this document are discussed in Section 3.3.
Lead in ore deposits does not pass easily to ground or surface water. Any lead dissolved
from primary lead sulfide ore tends to combine with carbonate or sulfate ions to (1) form
insoluble lead carbonate or lead sulfate, or (2) be absorbed by ferric hydroxide (Lovering,
1976). An outstanding characteristic of lead is its tendency to form compounds of low
solubility with the major anions of natural water. Hydroxide, carbonate, sulfide, and more
rarely sulfate may act as solubility controls in precipitating lead from water. The amount of
lead that can remain in solution is a function of the pH of the water and the dissolved salt
content. Equilibrium calculations show that at pH > 5.4, the total solubility of lead in hard
water is about 30 pg/1 and about 500 pg/1 in soft water (Davies and Everhard, 1973). Lead
sulfate is present in soft water and limits the lead concentration in solution. Above pH 5.4,
PbC03 and Pb2(0H)2C03 limit the concentration. The carbonate concentration is in turn
dependent on the partial pressure of C02 as well as the pH. Calculations by Hem and Durum
(1973) show that many river waters in the United States have lead concentrations near the
solubility limits imposed by their pH levels and contents of dissolved C02. Because of the
influence of temperature on the solubility of C02, observed lead concentrations may vary sig-
nificantly from theoretically calculated ones.
Lazrus et al. (1970) calculated that as much as 140 g/ha*mo of lead may be deposited by
rainfall in some parts of the northeastern United States. Assuming an average annual rainfall
runoff of 50 cm, the average concentration of lead in the runoff would have to be about
330 pg/1 to remove the lead at the rate of 140 g/ha-mo. Concentrations as high as 330 jjg/1
023PB6/A 6-37 7/13/83
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PRELIMINARY DRAFT
could be stable in water with pH near 6.5 and an alkalinity of about 25 ng bicarbonate ion/1
of water. Water having these properties is common in runoff areas of New York State and New
England; hence, the potential for high lead concentrations exists there. In other areas, the
average pH and alkalinity are so high that maximum concentrations of lead of about 1 pg/1
could be retained in solutions at equilibrium (Lovering, 1976).
A significant fraction of the lead carried by river water may be in an undissolved state.
This insoluble lead can consist of colloidal particles in suspension or larger undissolved
particles of lead carbonate, -oxide, -hydroxide, or other lead compounds incorporated in other
components of particulate lead from runoff; it may occur either as sorbed ions or surface
coatings on sediment mineral particles or be carried as a part of suspended living or
nonliving organic matter (Lovering, 1976). A laboratory study by Hem (1976) of sorption of
lead by cation exchange indicated that a major part of the lead in stream water may be
adsorbed on suspended sediment. Figure 6-13 illustrates the distribution of lead outputs
between filtrate and solids in water from both urban and rural streams, as reported by Rolfe
and Jennett (1975). The majority of lead output is associated with suspended solids in both
urban and rural streams, with very little dissolved in the filtrate. The ratio of lead in
suspended solids to lead in filtrate varies from 4:1 in rural streams to 27:1 in urban
streams.
Soluble lead is operationally defined as that fraction which is separated from the
insoluble fraction by filtration. However, most filtration techniques do not remove all
colloidal particles. Upon acidification of the filtered sample, which is usually done to
preserve it before analysis, the colloidal material that passed through the filter is
dissolved and is reported as dissolved lead. Because the lead in rainfall can be mainly
particulate, it is necessary to obtain more information on the amounts of lead transported in
insoluble form (Lovering, 1976) before a valid estimate can be obtained of the effectiveness
of runoff in transporting lead away from areas where it has been deposited by atmospheric
fallout and rain.
6.5.2.2 Organic. The bulk of organic compounds in surface waters originates from natural
sources. (Neubecker and Allen, 1983). The humic and fulvic acids that are primary complexing
agents in soils are also found in surface waters at concentrations from 1 to 5 mg/1,
occasionally exceeding 10 mg/1. (Steelnik, 1977), and have approximately the same chemical
characteristics (Reuter and Perdue, 1977). The most common anthropogenic organic compounds
are NTA and EDTA (Neubecker and Allen, 1983). There are many other organic compounds such as
oils, plasticizers, and polymers discharged from manufacturing processes that may complex with
lead.
023P86/A
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PRELIMINARY DRAFT
c
01
o
0)
a
z~
o
<
tr
H
2
IXI
O
z
o
u
a
<
LU
100
75
50
25
suspended solids
FILTRATE
URBAN
RURAL
Figure 6-13. Lead distribution between filtrate and suspended
solids in stream water from urban and rural compartments.
Source: Hem (1976); Rolfe and Jennett (1975).
023PB6/A
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PRELIMINARY DRAFT
The presence of fulvic acid in water has been shown to increase the rate of solution of
lead sulfide 10 to 60 times over that of a water solution at the same pH that did not contain
fulvic acid (Bondarenko, 1968; Lovering, 1976). At pH values near 7, soluble lead-fulvic acid
complexes are present in solution. At initial pH values between 7.4 and about 9, the
lead-fulvic acid complexes are partially decomposed, and lead hydroxide and carbonate are
precipitated. At initial pH values of about 10, the lead-fulvic acid complexes again
increase. This increase is attributed to dissociation of phenolic groups at high pH values,
which increases the complexing capacity of the fulvic acid. But it also may be due to the
formation of soluble 1ead-hydroxy1 complexes.
The transformation of inorganic lead, especial 1-y in sediment, to tetramethyllead (TML)
has been observed and biomethylation has been postulated (Schmidt and Huber, 1976; Wong et
a 1., 1975). However, Reisinger et al. (1981) have reported extensive studies of the
methylation of lead in the presence of numerous bacterial species known to alkylate mercury
and other heavy metals. In these experiments no biological methylation of lead was found
under any condition. Chemical alkylation from methylcobalamine was found to occur in the
presence of sulfide or of aluminum ion; chemical methylation was independent of the presence
of bacteria.
Jarvie et al. (1977, 1981) have recently shown that tetraalkyllead (TEL) compounds are
unstable in water. Small amounts of Ca2+ and Fe2+ ions and sunlight have been shown to cause
decomposition of TEL over time periods of 5 to 50 days. The only product detected was
triethyl lead, which appears to be considerably more stable than the TEL. Tetramethyllead is
decomposed much more rapidly than TEL in water, to form the trimethyl lead ion. Initial
4
concentrations of 10 molar were reduced by one order of magnitude either in the dark or
light in one day, and were virtually undetectable after 21 days. Apparently, chemical
methylation of lead to the trialkyllead cation does occur in some water systems, but evolution
of TML appears insignificant.
Lead occurs in riverine and estuarial waters and alluvial deposits. Laxen and Harrison
(1977) and Harrison and Laxen (1981) found large concentrations of lead (~1 mg/1) in rainwater
runoff from a roadway; but only 5 to 10 percent of this is soluble in water. Concentrations
of lead in ground water appear to decrease logarithmically with distance from a roadway.
Rainwater runoff has been found to be an important'transport mechanism in the removal of lead
from a roadway surface in a number of studies (Bryan, 1974; Harrison and Laxon, 1981; Hedley
and Lockley, 1975; Laxen and Harrison, 1977).
023PB6/A
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Apparently, only a light rainfall, 2 to 3 mm, is sufficient to remove 90 percent of the lead
from the road surface to surrounding soil and to waterways (Laxen and Harrison, 1977).
The Applied Geochemistry Research Group (1978) has reported elevated lead concentrations
(40 |jg/g and above) in about 30 percent of stream bed sediment samples from England and Wales
in a study of 50,000 such samples. Abdullah, and Royle (1973) have reported lead levels- .in
coastal areas of the Irish sea of 400 pg/g and higher.
Evidence for the sedimentation of lead in freshwater streams may be found in several
reports. Laxen and Harrison (1983) found that lead in the effluent of a lead-acid battery
plant near Manchester, England, changed drastically in particle size. In the plant effluent,.
53 percent of the lead was on particles smaller than 0.015 ^im and 43 percent on particles
greater than 1 pm. Just downstream .o,fi Jthejuplant, 91 percent of the lead was on particles
greater ihan 1 pm and only 1 percent on particles smaller than 0.015 pm. Under these,
conditions, lead formed or attached to large particles at a rate exceeding that of Cd, Cu, Fe
or Mn.
The lead concentrations in off-shore sediments often show a marked increase corresponding
i
to anthropogenic activity in the region (Section 5.1). Rippey et al. (1982) found such
increases recorded in the sediments of Lough Neagh, Northern Ireland, beginning during the
1600's and increasing during the late 1800's. Corresponding increases were also observed for
Cr, Cu, Zn, Hg, P, and Ni. For lead, the authors found an average anthropogenic flux of 72
mg/m2-yr, of which 27 mg/m2-yr could be attributed to direct atmospheric deposition. Prior to
1650, the total flux was 12 mg/m2-yr, so there has been a 6-fold increase since that time. •
Ng and Patterson (1982) found prehistoric fluxes of 1 to 7 mg Pb/m2-yr to three offshore
basins in southern California, which have now increased 3 to 9-fold to 11 to 21 mg/m2*yr.-
Much of this lead is deposited directly from sewage outfalls, although at least 25 percent
probably comes from the atmosphere.
6.5.3 Vegetation Surfaces
The deposition of lead on the leaf surfaces of plants where the particles are often-
retained for a long time must also be considered (Dedolph et al., 1970; Gange and Joshi, 1971;
Schuck and Locke, 1970). Several studies have shown that plants near roadways exhibit
considerably higher levels of lead than those further away. In most instances, the higher
concentrations were due to lead particle deposition on plant surfaces (Schuck and Locke,
1970). Studies have shown that particles deposited on plant surfaces are difficult to remove
by typical kitchen washing techniques. (Arvik and Zimdahl, 1974; Gange and Joshi, 1971;
Lagerwerff et al., 1973). Leaves with pubescent surfaces seem able to attract and retain
023PB6/A 6-41 7/13/83
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332-:
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PRELIMINARY DRAFT
particles via an electrostatic mechanism.. Other types of leaves are covered with a cuticular
wax sufficiently sticky to retain particles. Thus, rainfall does not generally remove the
deposited particles (Arvik and Zimdahl, 1974). Animals or humans consuming the leafy portions
of such plants can certainly be exposed to higher than normal levels of lead. Fortunately, a
major fraction of lead emitted by automobiles tends to be deposited inside a highway
right-of-way, so at least part of this problem is alleviated.
Tlje particle deposition on leaves has led some investigators to stipulate that lead may
enter plants through the leaves. This would typically require, however, that the lead
particles be dissolved by constituents of the leaf surface and/or converted to the ionic form
via contact with water. The former possibility is not considered likely since cuticular waxes
are relatively chemically inert. Arvik and Zimdahl (1974) have shown that entry of ionic lead
through plant leaves is of minimal importance. Using the leaf cuticles of several types of
plants essentially as dialysing membranes, they found that even high concentrations of lead
ions would not pass through the cuticles into distilled water on the opposite side.
The uptake of soluble lead by aquatic plants can be an important mechanism for depleting
lead concentrations in downstream waterways. Gale and Wixson (1979) have studied the
influence of algae, cattails, and other aquatic plants on lead and zinc levels in wastewater
in the New Lead Belt of Missouri. These authors report that mineral particles become trapped
by roots, stems, and filaments of aquatic plants. Numerous anionic sites on and within cell
+ + +
walls participate in cation exchange, replacing metals such as lead with Na , K , and H ions.
Mineralization of lead in these Missouri waters may also be promoted by water alkalinity.
However, construction of stream meanders and settling ponds have greatly reduced downstream
water concentrations of lead, mainly because of absorption in aquatic plants (Gale and Wixson,
1979).
6.6 SUMMARY
From the source of emission to the site of deposition, lead particles are dispersed by
the flow of the airstream, transformed by physical and chemical processes, and removed from
the atmosphere by wet or dry deposition. Under the simplest of conditions (smooth, flat
terrain), the dispersion of lead particles has been modeled and can be predicted (Benarie,
1980). Dispersion modeling in complex terrains is still under development and these models
have not been evaluated (Kotake and Sano, 1981).
Air lead concentrations decrease logarithmically away from roadways (Edwards, 1975) and
smelters (Roberts et al., 1974). Within urban regions, air concentrations decrease from the
central business district to the outlying residential areas by a factor of 2 to 3. In moving
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from urban to rural areas, air concentrations decrease from 1 to 2 mq/"1"1 down to 0.1 to 0.5
pg/m3 (Chapter 7). This decrease is caused by dilution with clean air and removal by
deposition. During dispersion to remote areas, concentrations decrease to 0.01 pg/m3 in the
United States (Elias and Davidson, 1980), to 0.001 pg/m3 in the Atlantic Ocean (Duce et al.,
1975), and to 0.000076 pg/m3 in Antarctica (Maenhaut et al., 1979).
Physical transformations of lead particles cause a shift in the particle size
distribution. The bimodal distribution of large and small particles normally found on the
roadway changes to a single mode of intermediate sized particles with time and distance
(Huntzicker et al., 1975). This is probably because large particles deposit near roadways and
small particles agglomerate to medium sized particles with an MMED of about 0.2 to 0.3 pm.
Particles transform chemically from lead halides to lead sulfates and oxides. Organolead
compounds usually constitute 1 to 6 percent of the total airborne lead in ambient urban air
(Harrison et al., 1979).
Wet deposition accounts for about half of the removal of lead particles from the
atmosphere. The mechanisms may be rainout, where the lead may be from another region, or
washout, where the source may be local. The other half of the atmospheric lead is removed by
dry deposition. Mechanisms may be gravitational for large particles or a combination of
gravitational and wind-related mechanisms for small particles (Elias and Davidson, 1980).
Models of dry deposition predict deposition velocities as a function of particle size,
windspeed, and surface roughness. Because of their large surface area/ground area ratio,
vegetation surfaces receive the bulk of dry deposited particles over continental areas. Wet
and dry deposition account for the removal of over 400,000 t/year of the estimated 450,000
t/yr emissions (Nriagu, 1979).
Lead enters soil as a moderately insoluble lead sulfate and is immobilized by
complexation with humic and fulvic acids. This iimrobi 1 ization is a function of pH and the
concentration of humic substances. At low pH (*4) or low organic content (<5 percent),
immobilization of lead in soil may be limited to a few hundred pg/g (Zimdahl and Skogerboe,
1977), but at 20 percent organic content and pH 6, 10,000 Pb/g soil may be found.
In natural waters, lead may precipitate as lead sulfate or carbonate, 'or it may form a
complex with ferric hydroxide (Lovering, 1976). The solubility of lead in water is a function
of pH and hardness (a combination of Ca and Mg content). Below pH 5.4, concentrations of
dissolved lead may vary from 30 jjg/1 in hard water to 500 pg/1 in soft water at saturation
(Lovering, 1976).
Particles deposited by dry deposition on vegetation surfaces (leaves and bark) are
retained for the lifetime of the plant part. The particles are not easily washed off by rain
nor are they taken up directly by the leaf (Arvik and Zimdahl, 1974).
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D06REF/A 6-53 7/14/83
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PRELIMINARY DRAFT
7. ENVIRONMENTAL CONCENTRATIONS AND POTENTIAL PATHWAYS TO HUMAN EXPOSURE
7.1 INTRODUCTION
In general, typical levels of human lead exposure may be attributed to four components of
the human environment: food, inhaled air, dusts of various types, and drinking water. This
chapter presents information on the ranges and temporal trends of concentrations in ambient
air, soil, and natural waters, and discusses the pathways from each source to food, inhaled
air, dust, and drinking water. The ultimate goal is to quantify the contribution of anthropo-
genic lead to each source and the contribution of each source to the total lead consumed by
humans. These sources and pathways of human lead exposure are diagrammed in Figure 7-1.
Chapters 5 and 6 discuss the emission, transport, and deposition of lead in ambient air.
Some information is also presented in Chapter 6 on the accumulation of lead in soil and on
plant surfaces. Because this accumulation is at the beginning of the human food chain, it is
critical to understand the relationship between this lead and lead in the human diet. It is
also important where possible to project temporal trends.
In this chapter, a baseline level of potential human exposure is determined for a normal
adult eating a typical diet and living in a non-urban community. This baseline exposure is
deemed to be unavoidable by any reasonable means. Beyond this level, additive exposure factor
s can be determined for other environments (e.g., urban, occupational, smelter communities),
for certain habits and activities (e.g., pica, smoking, drinking, and hobbies), and for varia-
tions due to age, sex, or socioeconomic status.
7.2 ENVIRONMENTAL CONCENTRATIONS
Quantifying human exposure to lead requires an understanding of ambient lead levels in
environmental media. Of particular importance are lead concentrations in ambient air, soil,
and surface or ground water. The following sections discuss environmental lead concentrations
in each of these media in the context of anthropogenic vs. natural origin, and the contribu-
tion of each to potential human exposure.
7.2.1 Ambient Air
Ambient airborne lead concentrations may influence human exposure through direct inhala-
tion of lead-containing particles and through ingestion of lead which has been deposited from
the air onto surfaces. Although a plethora of data on airborne lead is now available, our
understanding of the pathways to human exposure is far from complete because most ambient mea-
surements were not taken in conjunction with studies of the concentrations of lead in man or
in components of his food chain. However, that is the context in which these studies must now
PB7/A 7-1 7/14/83
345c
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! PRELIMINARY DRAFT
AUTO
EMISSIONS
CRUSTAL
WEATHERING
INDUSTRIAL
EMISSIONS
PLANTS
MAN
FOOD
ANIMALS
DUSTS
INHALED
AIR
DRINKING
WATER
AMBIENT
AIR
SOIL
SURFACE AND
GROUND WATER
Figure 7-1. Pathways of lead from the environment to human consumption. Heavy
arrows are those pathways discussed in greatest detail in this chapter.
PB7/A
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7/1/83
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PRELIMINARY DRAFT
be interpreted to shed the most light possible on the concentrations likely to be encountered
in various environmental settings.
The most complete set of data on ambient air concentrations may be extracted from the
National Filter Analysis Network (NFAN) and its predecessors (see Section 4.2.1). These data,
which are primarily for urban regions, have been supplemented with published data from rural
and remote regions of the United States. Because some stations in the network have been in
^ r\-~' , . .
place for about 15 years, information on temporal trends is available but sporadic. Ambient
air concentrations in the United States are comparable to other industrialized nations. -In
remote regions of the world, air concentrations are two or three orders of magnitude lower,
lending credence to estimates of the concentration of natural lead in the atmosphere. In the
context of the NFAN data base, the conditions are considered which modify ambient air, as
measured by the monitoring networks, to air as inhaled by humans. Specifically, these
conditions are changes in particle size distributions, changes with vertical distance above
ground, and differences between indoor and outdoor concentrations.
7.2.1.1 Total Airborne Lead Concentrations. A thorough understanding of human exposure to
airborne lead requires detailed knowledge of spatial and temporal variations in ambient con-
centrations. The wide range of concentrations is apparent from Table 7-1, which summarizes
data obtained from numerous independent measurements. Concentrations vary from 0.000076 pg/ni3
in remote areas to over 10 ^g/m3 near sources such as smelters. Many of the remote areas are
far from human habitation and therefore do not reflect human exposure. However, a few of the
regions characterized by low lead concentrations are populated by individuals with primitive
lifestyles; these data provide baseline airborne lead data to which modern American lead expo-
sures can be compared. Examples include some of the data from South America and the data from
Nepal.
Urban, rural, and remote airborne lead concentrations in Table 7-1 suggest that human ex-
posure to lead has increased as the use of lead in inhabited areas has increased. This is
consistent with published results of retrospective human exposure studies. For example,
Ericson et al. (1979) have analyzed the teeth and bones of Peruvians buried 1600 years ago.
Based on their data, they estimate that the skeletons of present-day American and British
adults contain roughly 500 times the amount of lead which would occur naturally in the absence
of widespread anthropogenic lead emissions. Grandjean et al. (1979) and Shapiro et al. (1980)
report lead levels in teeth and bones of contemporary populations to be elevated 100-fold over
levels in ancient Nubians buried before 750 A.D. On the other hand, Barry and Connolly (1981)
report excessive lead concentrations in buried medieval English skeletons; one cannot discount
the possibility that the lead was absorbed into the skeletons from the surrounding soil.
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PRELIMINARY DRAFT
TABLE 7-1. ATMOSPHERIC LEAD IN URBAN, RURAL,
AND REMOTE AREAS OF THE WORLD
Location
Sampling period Lead conc. (pg/m3) Reference
Urban
Miami
New York
Boston
St. Louis
Houston
Chicago
Salt Lake City
Los Angeles
Ottowa
Toronto
Montreal
Berli n
Vienna
Zuri ch
Brussels
Turin
Rome
Pari s
Rio de Janeiro
Rural
New York Bight
Framingham, MA
Chadron, NE
United Kingdom
Italy
Belgium
Remote
White Mtn., CA
High Sierra, CA
Olympic Nat. Park, WA
Antarctica
South Pole
Thule, Greenland
Thule, Greenland
Prins Christian-
sund, Greenland
Dye 3, Greenland
Eniwetok, Pacific Ocean
Kumjung, Nepal
Bermuda
Spi tsbergen
1974
1978-79
1978-79
1973
1978-79
1979
1974
1978-79
1975
1975
1975
1966-67
1970
1970
1978
1974-79
1972-73
1964
1972-73
1974
1972
1973-74
1972
1976-80.
1978
1969-70
1976-77
1980
1971
1974
1965
1978-79
1978-79
1979
1979
1979
1973-75
1973-74
1.3
1.1 '
0.8
1.1
0.9
0.8
0.89
1.4
1.3
1.3
2.0
3.8
2.9
3.8
0.5
4.5
4.5
4.6
0.8
0.13
0.9
0.045
0.13
0.33
0.37
0.008
0.021
0.0022
0.0004
0.000076
0.0005
0.008
0.018
0.00015
0.00017
0.00086
0.0041
0.0058
HASL, 1975
see Table 7-3
see Table 7-3
see Table 7-3
see Table 7-3
see Table 7-3
HASL, 1975
see Table 7-3
NAPS, 1975
NAPS, 1975
NAPS, 1975
Blokker, 1972
Hartl and Resch, 1973
Hogger, 1973
Roels et al., 1980
Facchetti and Geiss, 1982
Colacino and Lavagnini, 1974
Blokker, 1972
Branquinho and Robinson, 1976
Duce et al., 1975
0'Brien et al., 1975
Struempler, 1975
Cawse, 1974
Facchetti and Geiss, 1982
Roels et al. 1980
Chow et al., 1972
Elias and Davidson, 1980
Davidson et al., 1982
Duce, 1972
Maenhaut et al., 1979
Murozumi et al., 1969
Heidam, 1981
Heidam, 1981
Davidson et al., 1981c
Settle and Patterson, 1982
Davidson et al., 1981b
Duce et al., 1976
Larssen, 1977
Source; Updated from Nriaga, 1978
PB7/A
7-4
346*-
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PRELIMINARY DRAFT
The remote area concentrations reported in Table 7-1 do not necessarily reflect natural,
preindustrial lead. Murozumi et al. (1969) and Ng and Patterson (1981) have measured a 200-
fold increase over the past 3000 years in the lead content of Greenland snow. In the opinion
of the authors, this lead originates in populated raid-latitude regions, and is transported
over thousands of kilometers through the atmosphere to the Arctic. All of the concentrations
in Table 7-1, including values for remote areas, have been influenced by anthropogenic lead
emi ssions.
Studies referenced in Table 7-1 are limited in that the procedures for determining the
quality of the data are generally not reported. In contrast, the two principal airborne lead
data bases described in Section 4.2.1 include measurements subjected to documented quality as-
surance procedures. The U.S. Environmental Protection Agency's National Filter Analysis Net-
work (NFAN) provides comprehensive nationwide data on long-term trends. The second data base,
EPA's National Aerometric Data Bank, contains information contributed by state and local
agencies, which monitor compliance with the current ambient airborne standard for lead (1.5
pg/m3 averaged over a calendar quarter) promulgated in 1978.
7.2.1.1.1 Distribution of air lead in the United States. Figure 7-2 categorizes the urban
sites with valid annual averages (4 valid quarters) into several annual average concentration
ranges (Akland, 1976; Shearer et al. 1972; U.S. Environmental Protection Agency, 1970, 1979;
Quarterly averages of lead from NFAN, 1982). Nearly all of the sites reported annual averages
below 1.0 jjg/m3. Although the decreasing number of monitoring stations in service in recent
years could account for some of the shift in averages toward lower concentrations, trends at
individual urban stations, discussed below, confirm the apparent national trend of decreasing
lead concentration.
The data from these networks show both the maximum quarterly average to reflect compli-
ance of the station to the ambient airborne standard (1.5 ^jg/m3), and quarterly averages to
show trends at a particular location. Valid quarterly averages must include at lease five
24-hour sampling periods evenly spaced throughout the quarter. The number of stations comply-
ing with the standard has increased, the quarterly averages have decreased, and the maximum
24-hour values appear to be smaller since 1977.
Table 7-2 provides cumulative frequency distributions of all quarterly lead concentra-
tions for urban NFAN stations (1st quarter = Jan-Mar, etc.). Samples collected by the NFAN
from 1970 through 1976 were combined for analysis into quarterly composites. Since 1977, the
24-hour samples have been analyzed individually and averaged arithmetically to determine
the quarterly average. These data show that the average lead concentration has dropped
markedly since 1977. An important factor in this evaluation is that the number of reporting
stations has also decreased since 1977. Stations may be removed from the network for several
PB7/A
7-5
7/14/83
-------
PRELIMINARY DRAFT
100
(A
Z
o
H
<
H
(A
_l
<
H
O
>-
LL
O
< 0.5
0.5-0.9 ^g/m3
1.0-1.9
2.0-3.9
L_
1966 67 68 69 70
(95) (146) (159)
71 72 73 74
(180) (130)
YEAR
PB7/A
Figure 7-2. Percent of urban 9tation9 reporting indicated concentration interval.
7-6 7/1/83
350<
-------
TABLE 7-2. CUMULATIVE FREQUENCY DISTRIBUTIONS OF URBAN AIR LEAD CONCENTRATIONS*
Year
No. of
Station
Reports
10
Percentile
30
50
70
90
95
99
Ari thmetic
Max.
Qtrly.
Avg
Mean
Std.
dev.
Geometric
Mean
Std.
dev.
1970
797
0.47
0.75
1.05
1.37
2.01
2.59
4.14
5.83
1.19
0.80
0.99
1.80
1971
717
0.42
0.71
1.01
1.42
2.21
2.86
4.38
6.31
1.23
0.87
1.00
1.89
1972
708
0.46
0.72
0.97
1.25
1.93
2.57
3.69
6.88
1.13
0.78
0.93
1.87
1973
559
0.35
0.58
0.77
1.05
1.62
2.08
3.03
5.83
0.92
0.64
0.76
1.87
1974
594
0.36
0.57
0.75
1.00
1.61
1.97
3.16
4.09
0.89
0.57
0.75
1.80
1975
695
0.37
0.58
0.78
0.96
1.54
2.02
3.15
4.94
0.89
0.59
0.74
1.82
1976
670
0.37
0.58
0.74
0.96
1.41
1.72
3.07
4 . 54
0.85
0.55
0.72
1.80
1977
533
0.37
0.57
0.75
0.95
1.67
2.13
3.29
3.96
0.91
0.80
0.68
1.79
1978
282
0.27
0.43
0.57
0.74
1.19
1.49
2.40
3.85
0.68
0.64
0.50
t 1.87
1979
167
0.22
0.33
0.43
0.63
1.09
1.33
2.44
3.59
0.56
0.58
0.39
1.89
1980
220
0.14
0.21
0.30
0.38
0.55
0.66
0.84
1.06
0.32
0.27
0.24
1.88
*The data reported here are all valid quarterly averages reported from urban stations from 1970 to 1980,
in pg/m3. The vertical line marks compliance with the 1978 1.5 pg/m3 EPA National Ambient Air Quality
Standard. In 1980, the quarterly average for all but the highest 1 percent of the stations was 0.84. The
sources of the data are Akland, 1976; U.S. EPA, 1978, 1979; Quarterly averages of lead from NFAN, 1982.
-------
PRELIMINARY DRAFT
reasons, the most common of which is that the locality has now achieved compliance status and
fewer monitoring stations are required. It is likely that none of the stations removed from
the network were in excess of 1.5 pg/m3, and that most were below 1:0 |jg/Tna.
The summary percentiles and means for urban stations (Table 7-2) have decreased over the
period from 1970 to 1980, with most of the decrease occurring since 1977; the 1980 levels are
in the range of one-third to one-fourth of the values in 1970. The data from non-urban loca-
tions are given in Appendix 7A. While the composite nonurban lead concentrations are approxi-
mately one-seventh of the urban concentrations, they exhibit the same relative decrease over
the 1979-1980 period as the urban sites.
Long-term trends and seasonal variations in airborne lead levels at urban sites can be
seen in Figure 7-3. The 10th, 50th, and 90th percentile concentrations are graphed, using
quarterly composite and quarterly average data from an original group of 92 urban stations
(1965-1974) updated with data for 1975 through 1980. Note that maximum lead concentrations
typically occur in the winter, while minima occur in the summer. In contrast, automotive
emissions of lead would be expected to be greater in the summer for two reasons: (1) gasoline
usage is higher in the summer, and (2) lead content is raised in summer gasolines to replace
some of the more volatile high-octane components that cannot be used in summertime gasolines.
The effect is apparently caused by the seasonal pattern of lower dispersion capacity in
winter, higher capacity in summer.
Figure 7-3 also clearly portrays the significant decrease in airborne lead levels over
the past decade. This trend is attributed to the decreasing lead content of regular and pre-
mium gasoline, and to the increasing usage of unleaded gasoline. The close parallel between
these two parameters is discussed in detail in Chapter 5. (See Figure 5-4 and Table 5-5.)
The decrease in lead concentrations, particularly in 1979 and 1980, was not caused by the
disappearance from the network of monitoring sites with characteristically high concentra-
tions; the quarterly values for sites in six cities representing the east coast, the central,
and the western sections of the country (Figure 7-4) indicate that the decrease is widespread
and real.
Table 7-3 shows lead concentrations in the atmospheres of several major metropolitan
areas of epidemiological interest. Some of the data presented do not meet the stringent re-
quirements for quarterly averages and occasionally there have been changes in site location or
sampling methodology. Nevertheless, the data are the best available for reporting the history
of lead contamination in these specific urban atmospheres. Further discussions of these data
appear in Chapter 11.
PB7/A
7-8
7/14/83
-------
TABLE 7-3. AIR LEAD CONCENTRATIONS IN MAJOR METROPOLITAN AREAS (pg/m3) (quarterly averages)
Boston
New York
Phi la. Wash.
Delroi t
Chicago
Houston
Dal las/Ft.Worth
Los Anneles
MA
NY
PA DC
Ml
IL
1X
TX
CA
Station
lype
1
1
1 4 1
1
1 2 3
1
4
1
2 4
1
2
Year
Quarter
1970
0.8
1.2
0.9
1.2
1.8
3.8
5.7
3.2
2
1.5
0.9
1.4
2.0
2.3
3.5
2.2
3
1.2
1.9
1.4
1.9
2.8
5.1
3.3
4
1.2
1.4
1.2
1.3
2.5
3.7
3.9
1.9
1971
1
1.6
1.1
1.0
1.9
3.4
6.0
2
0. 7
1.8
1.3
1.8
1.6
1.8
2.9
3
1.3
1.6
1.7
2.5
3.3
4
1.7
2.1
2.2
2.7
2.7
6.3
1972
1
1.0
0.9
1. 7
2.3
3.4
3 1
0.6
1.3
1. 2
1.0
1.8
2.0
1.6
3
2.5.
1.0
0.9
2.2
2.6
1.5
4
1.1
1.1
2.3
2.8
4. 7
2.1
1973
1
2.9
1.9
2.7
1.6
2
0.8
1.8
1.3
2.0
2.5
3
0.6
1.3
1.7
2.7
4
0.9
1.7
1.9
1974
0.5
0.5
1.8
1.3
1.9
1.6
2
0.9
1.1
2.0
0.6a
1.4
0.2a
2.0
1.7
3
1.0
0.9
0.9
1.8
0.6
2.8
0.4
1.4
1.9
4
0.9
0.9
2.6
0.5
3.3
0.6
3.2
2.6
1975
1
1.2
0.8
1.1
0.8
2.1a
0.7
2.9
0.3
1.7
2
0.6a
0.8
0.7
1.7
0.7
2.3
0.3
1.2
1.2
3
1.0a
1.0
1.2
2.1
0.6
3.0
0.4
1.9
1.7
4
0.9a
1.1
1.2
2.4
1.1
2.9
0.5 0.3
3.2
2.2
-------
TABLE 7-3. (continued)
Boston
MA
Station Type 1
Year Quarter
New York
NY
1
0. 6a
0. 7
0.8
1.0a
0.9
1.3
1.0
0.4
0.6
0.8a
0.9a
0.5
0.6
0.4
0.3
1.0
1.3
1.0a
0.9
0.5
0.5
0.8a
Phi la.
PA
1 4
Wash.
DC
1
Oetro'it
HI
1
Chicago
1L
1 2 3
Houston
IX
1 4
Oallas/Ft.
IX
1 2
Worth
1
Los Angeles
CA
1 2
-0.8a 0.5
0. 7a
0. 3
0.2
1.2a
0.7a 0.5
0. 7 •
0. 3
0.4
1.4
1.1 0.7
1. la
0.3
0.3
0.4a
4. 1
3.0
1.3
1.0
1.2
1. 1
2.3
3.3
2 4
1. 6
0.8
0.9
• 0.3a 0.2
1. 2
0.2
0.2
1. 7
1.4
1.4
0.9
0.9a
1.0
0.8 0.3
1. 1
0.2
0.2
1.8
1.6
1. 3
1.0
2.1
1.3 0.7
1.6a
0.5
0.5
3.8
2.9
1.2
0.8
2.2
1.0 0.5
1. 7a
0.4
0.3
2.2a
16
1.1
0. 7
1. 1
0.8 0.4
1. 1
0.4
0.3
1.4
0. 7
1. 1
0.8 0.5
1.3
0.4
0.3
1.6
1. 6
1.2
3.3
1.7 0.9
1. 7
0.5
0.6
1.9
1.1
0. 7
1.8
0.9 0.4
1.2a
0.4
0.4
1.5
1.2
0.6
1. 3
0. 7
0.9
0.8
0.8 0.4
0.6a
0.2
0.3
0.9
1.0
0. 6
1.6
0.5
0.6
0.8
0.5a 0.6a
1. la
0.4
0.6
1.0a
1.2
0.8
1. 9
0.7a 0.5
0.5a
0.3
0.4
0.6a
0. 7
0.4
0.3
0.4
0.3
0.3
0.6a 0.3
0. 3a
0.3
0.2
0. 7
1.1
0.4
0.4
0.3
0.7
0.4
0.6
0. 3a 0. 3a
0.6a
0. 1
0.2
0.8
0. 7
0.4
0.3
1.0
0.5
0.5
0.2
0.3
0.1
0.1
1. la
1.0
0.7
0.5
0.4a
0.5
0.4
0.4
0.4
0.4
0.3
0.3
1.7
0.5
0.4a
0.3
0.2
0.3
0.2
0.7 0.5
0.6
0.3
0.3
1.3
1.0
0.4
0.3
0. 3
0.4
0. 3
0.3
0.2 0.2
0.3
0.1
0.2
0.7
0. 7
0.4
0.2
0.3
0.3
0.3
0.2
0.5 0.3
0.2
0.3
0.8
0.8
0.4
0. 3
0.3a
0.4
0.2a
0.3
0.8 1.0a
0.3
0.4
1.3
1.1
0.3
0.4
0.3
0.3
0.8
0. 7
0.3
0.2
0.4
0.3
0.5
0.3
0.3
0. 3
0.2
0.8
0.4
0.4
0.3
0.3
1.1
0.6
Station type: 1. center city commercial
2. center city residential
3. center city industrial
4. suburban residential
a: less than required number of 24-hour sampling periods to meet composite criteria
-------
PRELIMINARY DRAFT
4.0
n
E
o»
3 3.0
-------
I I I I
TUCSON, AZ
i
cn
o>
a.
Z
o
~-
<
QC
o
z
o
o
Q
<
UJ
_i
DC
5
1.4
1.2
1.0
0.8
0.6
0.4
0.2
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
WORCHESTER. MA
NEWARK. NJ
DES MOINES, IA
AKRON, OH —
J_J I I l
PB7/A
1975 76 77 78 79 80 1975 76 77 78 79 80
YEAR
Figure 7-4. Time trends in ambient air lead at selected urban sites.
7-12 7/1/83
356^
-------
PRELIMINARY DRAFT
Another approach to determining natural concentrations is to estimate global emissions
from natural sources. Nriagu (1979) estimated emissions at 24.5 x 106 kg/yr, whereas Settle
and Patterson (1980) estimated a lower value of 2 x 106 kg/yr. An average troposheric volume,
to which surface generated particles are generally confined, is about 2.55 x 1010m3. Assuming
a residence time of 10 days (see Section 6.3), natural lead emissions during this time would
be 6.7 x 1014 |jg. The air concentrations would be 0.000263 using the values of Nriagu (1979)
or 0.0000214 pg/m3 using the data of Settle and Patterson (1980). It seems likely that the
concentration of natural lead in the atmosphere is between 0.00002 and 0.00007 pg/m3. A value
of 0.00005 pg/m3 will be used for calculations regarding the contribution of natural air lead
to total human uptake in Section 7.3.1.
7.2.1.2 Compliance with the 1978 Air Quality Standard. Table 7-4 lists stations operated by
state and local agencies where one or more quarterly averages exceeded 1.0 pg/m3 or the cur-
rent standard of 1.5 pg/m3 in 1979 or 1980. A portion of each agency's compliance monitoring
network consists of monitors sited in areas expected to yield high concentrations associated
with identifiable sources.. In the case of lead, these locations are most likely to be near
stationary point sources such as smelters or refineries, and near routes of high traffic den-
sity. Both situations are represented in Table 7-4; e.g., the Idaho data reflect predominant-
ly stationary source emissions, whereas the Washington, D.C. data reflect predominantly
vehicular emissions.
Table 7-5 summarizes the maximum quarter lead values for those stations reporting 4 valid
quarters in 1979, 1980, and 1981, grouped according to principal exposure orientation or in-
fluence—population, stationary source, or background. The sites located near stationary
sources clearly dominate the concentrations over 2.0 pg/m3; however, new siting guidelines,
discussed in Section 7.2.1.3.2, will probably effect some increase in the upper end of the
distribution of values from population-oriented sites by adding sites closer to traffic emis-
sions.
The effect of the 1978 National Ambient Air Quality Standard for Lead has been to reduce
the air concentration of lead in major urban areas. Similar trends may also be seen in urban
areas of lower population density (Figure 7-4). Continuous monitoring at non-urban stations
has been insufficient to show a trend at more than a few locations.
7.2.1.3 Changes in Air Lead Prior to Human Uptake. There are many factors which can cause
differences between the concentration of lead measured at a monitoring station and the actual
inhalation of air by humans. The following sections show that air lead concentrations usually
decrease with vertical and horizontal distance from emission sources, and are generally lower
indoors than outdoors. A person working on the fifth floor of an office building would be ex-
posed to less lead than a person standing on a curb at street level. The following dis-
cussions will describe how these differences can affect individual exposures in particular
circumstances.
P07/A 7-13 7/14/83
357
-------
TABLE 7-4. STATIONS WITH AIR LEAD CONCENTRATIONS GREATER THAN 1.0 pg/m3
Data are listed from all stations, urban and rural, reporting valid quarterly averages greater than 1.0
pg/m3. Some stations have not yet reported data for 1981.
1979
Max
1980
Max
1981
Max
No. of Quarters
Qtrly
No. of Quarters
Qtrly
No of Quarters
Qtrly
Station #
>1.0
>1.5
Ave
>1.0
>1.5
Ave
>1.0
>1.5
Ave
Troy, AL
(003)
2
2
2.78
2
0
1.13
2
2
4.32
Glendale, AZ
(001)
1
0
1.06
Phoenix, AZ
(002A)
1
1
1.54
2
0
1.29
1
0
1.17
II II
(002G)
2
2.59
2
0
1.49
2
0
1.39
II II
(004)
2
0
1.48
1
0
1.04
II II
(013)
2
1.55
1
0
1.06
Scottsdale, AZ
(003)
2
0
1.41
1
0
1.13
1
0
1.08
Tucson, AZ
(009)
1
0
1.18
Nogales, AZ
(004)
1
0
1.10
Los Angeles, CA
(001)
1
1
1.51
2
0
1.43
Anaheim, CA
(001)
1
0
1.11
Adams Co, CO
(001)
2
1
1.77
Arapahoe Co, CO
(001)
1
0
1.10
Arvada, CO
(001)
1
1
1.60
•
Brighton, CO
(001)
1
0
1.17
Colorado Springs,CO
(004)
1
0
1.37
Denver, CO
(001)
2
1
1.70
II II
(002)
4
3
3.47
2
1
1. 53
II II
(003)
3
1
2.13
1
0
1.03
II II
(009)
1
1
1.57
2
0
1.23
II II
(010)
2
1
1.67
II II
(012)
2
1
1.67
1
0
1.10
Englewood, CO
(001)
1
1
1.80
Garfield, CO
(001)
1
0
1.20
Grand Junction, CO
(010)
2
1
1.53
1
0
1.27
Longmont, CO
(001)
2
0
1.07
Pueblo, CO
(001)
1
0
1.03
II II
(003)
1
0
1.03
Routt Co, CO
(003)
1
0
1.33
New Haven, CT
(123)
3
1.57
Waterbury, CT
(123)
2
0
1.41
Wilmington, DE
(002)
2
0
1.21
-------
TABLE 7-4. (continued)
1979
Max
1980
Max
1981
Max
No. of Quarters
Qtrly
No. of Quarters
Qtrly
No of Quarters
Qtrly
Station #
>1.0
>1.5
Ave
>1.0
>1.5
Ave
>1.0
>1.5
Ave
Washington, DC
(005)
1
0
1.49
II II
(007)
4
1.89
II II
(008)
1
1
1.90
II II
(011)
2
0
1.44
II II
(015)
2
0
1.06
II II
(017)
1
0
1.45
Dade Co, FL
(020)
1
0
1.16
Miami, FL
(016)
3
0
1.46
2
0
1.10
Perrine, FL
(002)
1
0
1.01
Hillsborough, FL
(082)
2
0
1.31
1
0
1.09
Tampa, FL
(043)
3
1.60
1
0
1.07
Boise, ID
(003)
1
0
1.01
Kellogg, ID
(004)
4
9.02
2
6.88
II II
(006)
4
4
8.25
4
4
8.72
4
4
6.67
Shoshone Co, ID
(015)
2
0
1.21
II II
(016)
1
1
2.27
1
0
1.02
II II
(017)
4
4.57
3
3.33
2
2
1.54
II II
(020)
2
4.11
2
2.15
1
0
1.49
II II
(021)
4
4
13.54
4
4
13.67
4
4
11.82
II II
(027)
4
10.81
3
7.18
Chicago, IL
(022)
1
0
1.02
II II
(030)
1
0
1.06
II II
(005)
1
0
1.05
II II
(036)
1
0
1.02
II II
, (037)
1
0
1.14
Cicero, IL
(001)
1
0
1.00
Elgin, IL
(004)
1
1
1.95
Granite City, IL
(007)
1
0
1.04
II II
(009)
4
0
1.15
II II
(010)
4
4
3.17
3
2
2.97
4
3
7.27
II II
(011)
4
0
1.33
1
0
1.43
1
0
1.13
Jeffersonvilie,
IN (001)
3
0
1.38
East Chicago, IL
(001)
2
2.19
II II
(003)
2
0
1.42
II II
(004)
1
1
1.67
II II
(006)
2
0
1.34
1
0
1.04
-------
TABLE 7-4. (continued)
1979 Max 1980 Max 1981 Max
No. of Quarters Qtrly No. of Quarters Qtrly No of Quarters Qtrly
Station # >1.0 >1.5 Ave >1.0 >1.5 Ave >1.0 >1.5 Ave
Hammond, IN
(004)
2
0
1.18
II II
(006)
1
0
1.46
Indianapolis, IN
(030)
1
0
1.16
Des Moines, IA
(051)
1
0
1.30
Buechel, KY
(001)
1
0
1.41
Covington, KY
(001)
2
0
1.12
II II
(008)
1
0
1.16
Greenup Co, KY
(003)
1
0
1.42
Jefferson Co, Ky
(029)
1
0
1.05
1
1
1.78
Louisville, KY
(004)
1
0
1.01
1
1
2.41
II II
(009)
1
1
1.75
II II
(019)
1
1
1.59
II II
(020)
1
1
2.52
II II
(021)
1
0
1.29
1
1
1.42
II II
(028)
1
0
1.06
Newport, KY
(002)
1
0
1.06
Okolona, KY
(001)
1
1
1.51
2
1
2.31
Paducha, KY
(004)
1
0
1.41
II II '
(020)
1
0
1.22
St. Matthews, KY
(004)
1
0
1.20
1
1
1.83
Shively, KY
(002)
1
1
1.56
Baton Rouge, LA
(002)
1
1
1.57
Portland, ME
(009)
2
0
1.02
Anne Arundel Co,
MD (001)
1
0
1.27
II II
(003)
2
0
1.45
Baltimore, MD
(001)
2
0
1.06
II II
(006)
1
0
1.09
II II
(008)
1
0
1.24
II II
(009)
1
0
1.08
II II
(018)
2
0
1.12
Cheverly, MD
(004)
4
1
1.51
-
Essex, MD
(001)
2
0
1.15
Hyattsville, MD
(001)
2
0
1.18
Springfield, MA
(002)
1
1
1.68
1
0
1.04
Boston, MA
(012)
1
0
1.01
-------
TABLE 7-4. (continued)
1979
Max
1980
Max
1981
Max
No.
of Quarters
Qtrly
No. of Quarters
Qtrly
No of Quarters
Qtrly
Station 0 >1. C
>1.5
Ave
>1.0
>1.5
Ave
>1.0 >1.5
Ave
Minneapolis, MN
(027) 1
1
2.44
II II
(055)
3
2.41
3 1
1.52
Richfield, MN
(004) 4
1.95
2
0
1.18
St. Louis Park, MN
(007) 2
2.87
4
3.04
St. Paul, MN
(031) 1
0
1.04
II II
(038 1
0
1.36
3
1.82
2 2
3.11
Lewis & Clark Co, MT (002) 4
4.19
4
2.75
2 2
3.19
II II
(008)
1
0
1.19
Omaha, NE
(034) 1
0
1.08
Las Vegas, NV
(001) 1
0
1.15
Newark, NJ
(001) 1
0
1.17
Perth Amboy, NJ
(001) 1
0
1.08
Paterson, NJ
(001) 1
0
1.42
Elizabeth, NJ
(002) 1
0
1.16
Yonkers, NY
(001) 1
0
1.08
Cincinnatti, OH
(001) 1
0
1.15
Laureldale, PA
(717) 4
3.30
2
1.86
4 3
2.18
Reading, PA
(712) 1
0
1.11
E.Conemaugh, PA
(804) 3
0
1.28
Throop, PA
(019) 3
0
1. 13
Lancaster City, PA
(315) 1
0
1.18
New Castle, PA
(015) 1
0
1.01
Montgomery Co, PA
(103) 1
0
1.23
Pottstown, PA
(101) 1
0
1.16
Phi la. , PA
(026) 3
0
1.21
II II
(028) 4
2.71
3
0
1.26
1 0
1. 30
II II
(031) 2
0
1.29
II II
(038) 1
0
1.06
Guaynabo Co, PR
(001) 2
1.60
1
0
1.06
1 0
1.02
Ponce, PR
(002) 1
0
1.08
San Juan Co. , PR
(003) 4
3. 59
E.Providence, RI
(008) 2
0
1.10
Providence, RI
(007) 4
1.92
2
0
1.16
II II
(015) 1
0
1.34
Greenville, SC
(001) 2
0
1.38
-------
TABLE 7-4. (continued)
1979
Max
1980
Max
1981 Max
No. of Quarters
Qtrly
No. of Quarters
Qtrly
No of Quarters Qtrly
Station #
>1.0
>1.5
Ave
>1.0 >1.5
Ave
>1.0 >1.5 Ave
Nas hv i11e/Dav i dson,
TN
(006)
1
0
1.05
San Antonio, TX
(034)
1
0
1.23
Dallas, TX
(018)
1
1
1.59
II II
(029)
1
0
1.07
II II
(035)
1
0
1.12
II II
(046)
1
0
1.22
II II
(049)
1
0
1.01
II II
(050)
0
1.13
El Paso, TX
(002A)
1
1.90
2.12
II II
(002F)
1
1
1.90
4 1 1.79
II II
(002G)
4
2.60
II II
(018)
2
1.91
II II
(021)
1
0
1.02
II II
(022)
2
1.84
II II
(023)
2
2.12
II II
(027)
2
2.15
2 Y
1.74
4 2 1.75
II II
(028)
1 0
1.16
II II
(030)
1
0
1.02
II II
(031)
1
1
2.47
II II
(033)
1
1
1.97
Houston, TX
(001)
2
0
1.35
II II
(002)
2
0
1.39
II II
(037)
1
0
1.26
II II
(049)
3
0
1.13
1 1 1.96
Ft. Worth, TX
(003)
2
0
1.14
Seattle, WA
(057)
1
0
1.36
Tacoma, WA
(004)
1
0
1.06
Charleston, WV
(001)
1
0
1.09
-------
PRELIMINARY. DRAFT
TABLE 7-5. DISTRIBUTION OF AIR LEAD CONCENTRATIONS BY TYPE OF SITE
Concentration ranges
(pg/m3)
Site-type
g. 5
>.5
<1.0
>1.0
<1.5
>1.5
<2.0
>2.0
Total no.of
site-years
Populati on
300
173
46
7
5
531
Stationary
source
50
12
10
2
21
95
Background
21
0
0
0
0
21
Total
(si te-years)
371
185
56
9
26
647
Percent of sites
in concentration
range
57%
29%
9%
1%
4%
100%
Data are the number of site years during 1979-81 falling within the designated quarterly aver-
age concentration range. To be included, a site year must have four valid quarters of data.
7.2.1.3.1 Airborne particle size distributions. The effects of airborne lead on human health
and welfare depend upon the sizes of the lead-containing particles. As discussed in Chapter
6, large particles are removed relatively quickly, from the atmosphere by dry and wet deposi-
tion processes. Particles with diameter smaller than a few micrometers tend to remain
airborne for long periods (see Section 6.3.1).
Figure 7-5 summarizes airborne lead particle size data from the literature. Minimum and
maximum aerodynamic particle diameters of 0.05 pm and 25 pm, respectively, have been assumed
unless otherwise specified in the original reference. Note that most of the airborne lead
mass is associated with small particles. There is also a distinct peak in the upper end of
many of the distributions. Two separate categories of sources are responsible for these dis-
tributions: the small particles result from nucleation of vapor phase lead emissions (pre-
dominantly automotive), while the larger particles represent primary aerosol emitted from com-
bustion or from mechanical processes (such as soil erosion, abrasion of metal products, re-
suspension of automobile tailpipe deposits, and flaking of paint).
Information associated with each in the distributions in Figure 7-5 may be found in Table
7A-1 of Appendix 7A. The first six distributions were obtained; by an EPA cascade Impactor
network established in several cities during the calendar year 1970 (Lee et al., 1972). These
PB7/A 7-19 7/14/03
363<
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PRELIMINARY DRAFT
distributions represent the most extensive size distribution data base available. However,
the impactors were operated at excessive air flow rates that most likely resulted" in particle
bounceoff, biasing the data toward smaller particles (Dzubay et a 1., 1976). Many of the later
distributions, although obtained by independent investigators with unknown quality control,
were collected using techniques which minimize particle bounceoff and hence may be more reli-
able. It is important to note that a few of the distributions were obtained without backup
filters that capture the smallest particles. These distributions are likely to be inaccurate,
since an appreciable fraction of the airborne lead mass was probably not sampled. The distri-
butions of Figure 7-5 have been used with published lung deposition data to estimate the frac-
tion of inhaled airborne lead deposited in the human respiratory system (see Chapter 10).
7.2.1.3.2 Vertical gradients and siting guidelines. New guidelines for placing ambient air
lead monitors went into effect in July, 1981 (F.R., 1981). "Microscale" sites, placed between
5 and 15 meters from thoroughfares and 2 to 7 meters above the ground, are prescribed, but
until now few monitors have been located that close to heavily traveled roadways. Many of
these microscale sites might be expected to show higher lead concentrations than that measured
at nearby middlescale urban sites, due to vertical gradients in lead concentrations near the
source. One study (PEDCo, 1981) gives limited insight into the relationship between a micro-
scale location and locations further from a roadway.' The data in Table 7-6 summarize total
suspended particulates and particulate lead concentrations in samples collected in Cincinnati,
Ohio, on 21 consecutive days in April and May, 1980, adjacent to a 58,500 vehicles-per-day
expressway connector. Simple interpolation indicates that a microscale monitor as close as 5
meters from the roadway and 2 meters above the ground would record concentrations some 20 per-
cent higher than those at a "middle scale" site 21.4 meters from the roadway. On the other
hand, these data also indicate that although lead concentrations very close to the roadway
(2.8 m setback) are quite dependent on the height of the sampler,.the averages at the three
selected heights converge rapidly with increasing distance from the roadway. In fact, the
average lead concentration (1.07 pg/m3) for the one monitor (6.3 m height, 7.1 « setback) that
satisfies the microscale site definition proves not to be significantly different from the
averages for its two companions at 7.1 m, or from the averages for any of the three monitors
at the 21.4 m setback. It also appears that distance from the source, whether vertical or
horizontal, can be the primary determining factor for changes in air lead concentrations. At
7.1 m from the highway, the 1.1 and 6.3 m samplers would be about 7 and 11 meters from the
road surface. The values at these vertical distances are only slightly lower than the
corresponding values for comparable horizontal distances.
PB7/A
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PRELIMINARY DRAFT
i 'f I—n—r
1 CHICAGO IL
I ! I I
9 Alton, il
ii tii i
l II! Ill—»'ll
17 S.E. MISSOURI.
NEAR SMELTER
"i—m—m—r-r^—r
28 GREAT SMOKIES
NAT I PARK. TN
33 ANN Anioh. Ml'
1.00
0.75
0.60
0.25
0
1.00
0.75
0.60
0.26
0
1.00
0,76
0.50
0.26
0
1 00
a 0.75
' 0.50
2 0 26
18 S.E MISS
FAR FROM
SMELTER
TER f*l
oDir
2 CINCINNATI, OH
10 CENTRE VILL6. IL
nj*i.
HJU1
26 PITTSBURGH. PA
3 DENVER. CO
11 COLUNSVILLE. IL
IL
34 ANN ARBOR. MS
rU
19 NEW BRUNSWICK. NJ
HIGHWAY
27 NEPAL mm HIMALAYAS
35 CHICAGO. IL
4 PHILADELPHIA. PA
12 KMOX
RADIO
TRANSMITTER.
IL
20 SAN FRANCISCO. CA
28 EXPORT, PA
36 LINCOLN, NE
O 1.00
9 0.75
0.60
0.26
0
1.00
075
0.60
0.25
0
1.00
0.76
0.60
0.25
0
1.00
0,76
0 60
0.26
B ST. LOUIS. MO
MARQUETTE
13 PEHE
PARK. IL
1« WOOD
RIVER. IL
21 LOS ANGELES. CA
I
29 PACKWOOD, WA
r-rL
37 TALLAHAS9EE. FL
1608
6 WASHINGTON. O.C.
22 LOS ANGELES. CA
FREEWAY
30 OLYMPIC NAT L
PARK. WA
38 CHILTON. ENGLAND
-~"rAjL|
f CINCINNATI. OH
15 CINCINNATI. OH
FREEWAY
23 PASADENA CA
31 BERMUDA
:yh=.
8 FAIRFAX. OH
18 GLASGOW. SCOTLANO
24 PASADENA. CA
j=!L
32 BERMUDA
39 TREBANOS. ENGLAND
40 NEW YORK. NY
J-
» ' ' ' ' ' '1 ¦ I I ' ' ' ' ' ll I I L
J ' ' ' ''
' ' 1 ¦ ¦ ' ¦ ' 1 ™ i
0.01 0.1 1 10 0.01 0.1 1 10 0.01 0.1 1 10 0.01 0.1 1 10 0.01 0.1 1 10
dp, Mm
Figure 7-5. Airborne mass size distributions for lead taken from the literature. AC represents
the airborne lead concentration in each size range. Cj is the total airborne lead concentra-
tion in all size ranges, and dp is the aerodynamic particle diameter. A density of 6 g/cm3 for
lead-containing particles has been used to convert aerodynamic to physical diameter when
applying the lower end of the lung deposition curves of Figures 7-3 through 7-5.
PB7/A
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365
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PRELIMINARY DRAFT
TABLE 7-6. VERTICAL DISTRIBUTION OF LEAD CONCENTRATIONS
Effective1
di stance
Setback
from
Air lead
Ratio to
di stance
Height
source
conc.
source
(m)
(m)
(m)
(pg/m3)
Kansas City
east of road
3.0*
6.1
6.4
1.7
0.85
1.5
3.2
2.0
S
Kansas City
west of road
3.0*
6.1
6.4
1.5
0.88
1.5
3. 2
1.7
S
Ci nci nnati
east of road
3.0*
6.1
6.4
0.9
0.64
1.5
3.2
1.4
S
Ci nci nnati
west of road
3.0*
6.1
6.4
0. 6
0. 75
1.5
3.2
0.8
S
Ci ncinnati
2.8
10.5
10.4
0.81
0.61
6.3
6.4
0.96
0.72
1.1
2.9
1.33
S
Ci nci nnati
7.1
10.5
12.3
0.93
0.69
6.3
9.2
1.07
0.80
1.1
7.1
1.16
0.87
Ci nci nnati
21.4
10. 5
23.6
0.90
0.68
6.3
22.2
0.97
0.73
1.1
21.4
1.01
0.77
S = Station closest
to source used
to calculate
ratio.
'Effective distance
was calculated
assuming the
source was
the edge of
the roadway at a height
of 0.1 m.
*Assumed setback distance of 3.0 m.
Other urban locations around the country with their own characteristic wind flow patterns
and complex settings, such as multiple roadways, may produce situations where the microscale
site does not record the highest concentrations. Collectively, however, the addition of these
microscale sites to the nation's networks can be expected to shift the distribution of
reported quarterly averages toward higher values. This shift will result from the change in
composition of the networks and is a separate phenomenon from downward trend at long estab-
lished sites described above, reflecting the decrease in lead additives used in gasoline.
PB7/A 7-22 7/14/83
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PRELIMINARY DRAFT
Two other studies show that lead concentrations decrease with vertical distance from the
source. PEDCo-Environmental (1977) measured lead concentrations at heights of 1.5 and 6.1 m
at sites in Kansas City, MO and Cincinnati, OH. The sampling sites in Kansas City were des-
cribed as unsheltered, unbiased by local pollution influences, and not immediately surrounded
by large buildings. The Cincinnati study was conducted in a primarily residential area with
one commercial street. Samplers were operated for 24-hour periods; however, a few 12-hour
samples were collected from 8 AM to 8 PM. Data were obtained in Kansas City on 35 days and in
Cincinnati on 33 days. The range and average values reported are shown in Table 7-7. In all
cases except two, the measured concentrations were greater at 1.5 meters than at 6.1 meters.
Note that the difference between the east side and west side of the street was approximately
the same as the difference between 1,5 m and 5.1 m in height.
Sinn (1980) investigated airborne lead concentrations at heights of 3 and 20 m above a
road in Frankfurt, Germany. Measurements conducted in December 1975, December 1976, and Janu-
ary 1978 gave monthly mean values of 3.18, 1.04, and 0.65 |jg/m3, respectively, at 3 m. The
corresponding values at 20 m were 0.59, 0.38, and 0.31 |jg/m3, showing a substantial reduction
at this height. The decrease in concentration over the 2-year period was attributed to a de-
crease in the permissible lead content of gasoline from 0.4 to 0.15 g/liter beginning in Janu-
ary 1976.
Two reports show no relationship between air concentration and vertical distance. From
August 1975 to July 1976, Barltrop and Strehlow (1976) conducted an air sampling program in
London at a proposed nursery site under an elevated motorway. The height of the motorway was
9.3 m. Air samplers were operated at five to seven sites during the period from Monday to
Friday, 8 AM to 6 PM, for one year. The maximum individual value observed was 18 pg/m3. The
12 month mean ranged from 1.35 |jg/m3 to 1.51 pg/m3, with standard deviations of 0.91 and 0.66,
respectively. The authors reported that the airborne concentrations were independent of height
from ground level up to 7 m.
Ter Haar (1979) measured airborne lead at several heights above the ground, using
samplers positioned 6 m from a heavily traveled road in Detroit. A total of nine 8-hour day-
time samples were collected. The overall average airborne lead concentrations at heights of
0.3, 0.9, 1.5, and 3.0 m were 4.2, 4.8, 4,7, and 4.6 pg/m3, respectively, indicating a uniform
concentration over this range of heights at the measurement site. It should be noted that at
any one height, the concentration varied by as much as a factor of 10 from one day to the
next; the importance of simultaneous sampling when attempting to measure gradients is clearly
demonstrated.
Data that show variations with vertical distance reflect the strong influence of the geo-
metry of the boundary layer, wind, and atmospheric stability conditions on the vertical gradi-
ent of lead resulting from automobile emissions. The variability of concentration with height
PB7/A 7-23 7/14/83
367 <
-------
PRELIMINARY DRAFT
is further complicated by the higher emission elevation of smokestacks. Concentrations
measured from sampling stations on the roofs of buildings several stories high may not reflect
actual human exposure conditions, but neither would a single sampling station located at
ground level in a building complex. The height variation in concentration resulting from
vertical diffusion of automobile emissions is likely to be small compared to temporal and
spatial variations resulting from surface geometry, wind, and atmospheric conditions. Our
understanding of the complex factors affecting the vertical distribution of airborne lead is
extremely limited, but the data of Table 7-6 indicate that air lead concentrations are pri-
marily a function of distance from the source, whether vertical or horizontal.
7.2.1.3.3 Indoor/outdoor relationships. Because people spend much of their time indoors, am-
bient air data may not accurately indicate actual exposure to airborne lead. Table 7-7 sum-
marizes the results of several indoor/outdoor airborne lead studies. In nearly all cases, the
indoor concentration is substantially lower than the corresponding value outdoors; the only
indoor/outdoor ratio exceeding unity is for a high-rise apartment building, where air taken in
near street level is rapidly distributed through the building air circulation system. Some of
the studies in Table 7-7 show smaller indoor/outdoor ratios during the winter, when windows
and doors are tightly closed. Overall, the data suggest indoor/outdoor ratios of 0.6 to 0.8
are typical for airborne lead in houses without air conditioning. Ratios in air conditioned
houses are expected to be in the range of 0.3 to 0.5 (Yocum, 1982).
The available data imply that virtually all airborne lead found indoors is associated
with material transported from the outside. Because of the complexity of factors affecting
infiltration of air into buildings, however, it is difficult to predict accurately indoor lead
concentrations based on outdoor levels. Even detailed knowledge of indoor and outdoor air-
borne lead concentrations at fixed locations may still be insufficient to assess human expo-
sure to airborne lead. The study of Tosteson et al. (1982) in Table 7-7 included measurement
of airborne lead concentrations using personal exposure monitors carried by individuals going
about their day-to-day activities. In contrast to the lead concentrations of 0.092 and 0.12
pg/m3 at fixed locations, the average personal exposure was 0.16 pg/m3. The authors suggest
this indicates an inadequacy of using fixed monitors at either indoor or outdoor locations to
assess exposure.
7.2.2 Lead in Soil
Much of the lead in the atmosphere is transferred to terrestrial surfaces where it is
eventually passed to the upper layer of the soil surface. The mechanisms which determine the
transfer rate of lead to soil are described in Section 6.4.1 and the transformation of lead in
PB7/A
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7/14/83
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PRELIMINARY DRAFT
TABLE 7-7. COMPARISON OF INDOOR ANO OUTDOOR AIRBORNE LEAD CONCENTRATIONS
Airborne lead concentration
Indoor/outdoor
Type of building Indoor Outdoor ratio Location Ref
Library
1.12
2.44
0.46
Hartford, CT (1)
City hall
1.31
1.B7
0.70
II
Office building 1
0. 73
1.44
0. 51
II
Office building 2
0.55
1.09
0. 51
It
House 1
1.37
2.48
0. 55
11
House 2
0.94
1.34
0.70
<1
Apartment building 1
Second floor
1.46
2.67
0.55
New York, NY (2)
Roof
1. 50
1.38
1.09
M
Apartment building 2
Third floor
1.21
II
Eleventh floor
1. 68
—
II
Eighteenth floor
1.86
—
--
II
Roof
1.42
--
"
New air conditioned
0.12-0.40
0.13-0.50
0.82
New York, NY (3)
apartment
Older non-air condi-
tioned apartment
0.14-0.51
0.17-0.64
0.87
II
Air conditioned public
0.15-0.79
0.33-1.IB
0.63
II
bui1di ng
Non-air conditioned
storeroom in public
0.45-0.9B
0.38-1.05
0.81
II
building
Houses
—
--
0.53
Pittsburgh, PA (4)
University buildings
--
--
0.28
"
Public schools
—
--
0.28
Store
...
--
0.31
n
Commercial office
--
--
0.27
H
Houses
0. 092
0.12
0. 74
Topeka, KS (5)
Houses with gas stoves
--
--
0. 65
Boston, MA (6)
Houses with electric
--
-- ¦
0. 68
"
stoves
Office buildings
--
0.42
H
House 1
Before energy conser-
0 . 039
0.070
0.56
Medford, OR (7)
vation retrofit
After energy conser-
vation retrofit
0.037
0.084
0.44
II
House 2
Before energy
conservation retrofit
0.035
0.045
0.78
After energy
conservation retrofit
0.038
0.112
0.34
II
1. Yocum et al., 1971.
2. General Electric Company, 1972.
3. Halpern, 19>8.
4. Cohen and Cohen, 1980.
5. Tosteson et al., 19B2.
6. Maschandreas et al., 1981.
7. Berk et al., 1981.
7-25
369<
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PRELIMINARY DRAFT
soil in Section 6.5.1. The uptake of lead by plants and its subsequent effect on animals may
be found in Section 8.2. The purpose of this section is to discuss the distribution of lead
in U.S. soils and the impact of this lead on potential human exposures.
7.2.2.1. Typical Concentrations of Lead in Soil.
7.2.2.1.1 Lead in urban, smelter, and rural soils. Shacklette et al. (1971) sampled soils at
a depth of 20 cm to determine the elemental composition of soil materials derived from the
earth's crust, not the atmosphere. The range of values probably represent natural levels of
lead in soil, although there may have been some contamination with anthropogenic lead during
collection and handling. Lead concentrations in soil ranged from less than 10 tc greater than
70 pg/g. The arithmetic mean of 20 and geometric mean of 16 pg/g reflect the fact that most
of the 863 samples were below 30 pg/g at this depth. McKeague and Wolynetz (1980) found the
same arithmetic mean (20 pg/g) for 53 uncultivated Canadian soils. The range was 5 to 50 pg/g
and there was no differences with depth between the A, B and C horizons in the soil profile.
Studies discussed in Section 6.5.1 have determined that atmospheric lead is retained in
the upper two centimeters of undisturbed soil, especially soils with at least 5 percent
organic matter and a pH of 5 or above. There has been no general survey of this upper 2 cm of
the soil surface in the United States, but several studies of lead in soil near roadsides and
smelters and a few studies of lead in soil near old houses with lead-based paint can provide
the backgound information for determining potential human exposures to lead from soil.
Because lead is immobilized by the organic component of soil (Section 6.5.1), the concen-
tration of anthropogenic lead in the upper 2 cm is determined by the flux of atmospheric lead
to the soil surface. Near roadsides, this flux is largely by dry deposition and the rate de-
pends on particle size and concentration. These factors vary with traffic density and average
vehicle speed (see Section 6.4.1). In general, deposition flux drops off abruptly with
increasing distance from the roadway. This effect is demonstrated in studies which show that
surface soil lead decreases exponentially up to 25 m from the edge of the road. The original
work of Quarles et al. (1974) showed decreases in soil lead from 550 to 40 pg/g within 25 m
alongside a highway with 12,500 vehicles/day in Virginia. Their findings were confirmed by
Wheeler and Rolfe (1979), who observed an exponential decrease linearly correlated with traf-
fic volume. Agrawal et al (1981) found similar correlations between traffic density and road-
side proximity in Baroda City, as did Garcia-Miragaya et al. (1981) in Venzuela and Wong and
Tam (1978) in Hong Kong. The extensive study of Little and Wiffen (1978) is discussed in
Chapter 6. These authors found additional relationships between particle size and roadside
proximity and decreases with depth in the soil profile. The general conclusion from these
studies is that roadside soils may contain atmospheric lead from 30 to 2000 pg/g in excess of
natural levels within 25 meters of the roadbed, all of which is in the upper layer of the soil
PB7/A
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7/14/83
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PRELIMINARY DRAFT
profile. It is assumed that particles deposited directly on the roadway are washed to the
edge of the pavement, but do not migrate beyond the shoulder.
Near primary and secondary smelters, lead in soil decreases exponentially within a 5 to
10 km zone around the smelter complex. Soil lead contamination varies with the smelter emis-
sion rate, length of time the smelter has been in operation, prevailing windspeed and direc-
tion, regional climatic conditions, and local topography (Roberts, 1975).
Little and Martin (1972) observed decreases from 125 to 10 pg/g in a 6 km zone around a
smelting complex in Great Britain; all of the excess lead was in the upper 6 cm of the soil
profile. Roberts (1975) reported soil lead between 15,000 and 20,000 pg/g near a smelter in
Toronto. Kerin (1975) found 5,000 to 9,000 pg/g adjacent to a Yugoslavian smelter; the con-
tamination zone was 7 km in radius. Ragaini et al. (1977) observed 7900 pg/g near a smelter
in Kellogg, Idaho; they also observed a 100-fold decrease at a depth of 20 cm in the soil pro-
file. Palmer and Kucera (1980) observed soil lead in excess of 60,000 pg/g near two smelters
in Missouri, decreasing to 10 pg/g at 10 km.
Urban soils may be contaminated from a variety of atmospheric and non-atmospheric
sources. The major sources of soil lead seem to be paint chips from older houses and deposi-
tion from nearby highways. Lead in soil adjacent to a house decreases with distance from the
house; this may be due to paint chips or to dust of atmospheric origin washing from the
rooftop (Wheeler and Rolfe, 1979).
Andresen et al. (1980) reported lead in the litter layer of 51 forest soils in the north-
eastern United States. They found values from 20 to 700 pg/g, which can be compared only
qualitatively to the soil lead concentration cited above. This study clearly shows that the
major pathway of lead to the soil is by the decomposition of plant material containing high
concentrations of atmospheric lead on their surface. Because this organic matter is a part of
the. decomposer food chain, and because the organic matter is in dynamic equilibrium with soil
moisture, it is reasonable to assume that lead associated with organic matter is more mobile
than lead tightly bound within the crystalline structure of inorganic rock fragments. This
argument is expressed more precisely in the discussions below.
i
Finally, a definitive study which describes the source of soil lead was reported by
Gulson et al. (1981) for soils in the vicinity of Adelaide, South Australia. In an urban to
rural transect, stable lead isotopes were measured in the top 10 cm of soils over a 50 km dis-
tance. By their isotopic compositions, three sources of lead were identified: natural, non-
automotive industrial lead from Australia, and tetraethyl lead manufactured in the United
States. The results indicated that most of the soil surface lead originated from leaded gaso-
line. Similar studies have not been conducted in the United States.
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PRELIMINARY DRAFT
7.2.2.1.2 Natural and anthropogenic sources of soil lead. Although no study has clearly
identified the relative concentrations of natural and anthropogenic lead in soil, a few clari-
fying statements can be made with some certainty. Lead may be found in inorganic primary
minerals, on humic substances, complexed with Fe-Mn oxide films, on secondary minerals or in
5oi1 moisture. All of the lead in primary minerals is natural and is bound tightly within the
crystalline structure of the minerals. Most of this lead can be released only by harsh treat-
ment with acids. The lead on the surface of these minerals is leached slowly into the soil
moisture. Atmospheric lead forms complexes with humic substances or on oxide films that are
in equilibrium with soil moisture, although the equilibrium strongly favors the complexing
agents. Consequently, the ratio of anthropogenic to natural lead in soil moisture depends
mostly on the amounts of each type of lead in the complexing agents and very little on the
concentration of natural lead in the inorganic minerals.
F.xcept near roadsides and smelters, only a few py of atmospheric lead have been added-to
each gram of soil. Several studies indicate that this lead is available to plants (Section
8.3.1.1) and that even with small amounts of atmospheric lead, about 75 percent of the lead in
soil moisture is of atmospheric origin, A conservative estimate of 50 percent is used in the
discussions in Section 7.3.1.2. A breakdown of the types of lead in soil may be found in
Table 7-8.
TABLE 7-8. SUMMARY OF SOIL LEAD CONCENTRATIONS!
Natural
Atmospheri c
Total
1 ead
lead
lead
Matrix
Rural Urban
Rural
Urban
Total soil
8-25
3 50-150
10-30
150-300
Primary minerals
8-25
-
8-25
8-25
Humic substances*
20
60 2000
80
2000
Soil moisture
0.0005
0.0005 0.0150
0.001
0.0155
t All values in pg/g.
*Assumes 5% organic matter, ph 5.0; may also include lead in Fe-Mn oxide films.
Source: Section 6.5.1
7.2.2.2 Pathways of Soil Lead to Human Consumption.
7.2.2.2.1 Crops. Lead on the surfaces of vegetation may be of atmospheric origin, or a com-
bination of atmospheric and soil in the internal tissues. As with soils, lead on vegetation
surfaces decreases exponentially with distance away from roadsides and smelters (Cannon and
Bowles, 1962; see also Chapter 8). This deposited lead is persistent. It is neither washed
PB7/A
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PRELIMINARY DRAFT
off by rain nor taken up through the. l.eaf^.s.urface. For many years, plant surfaces have been
used as indicators of lead pollution (Garty and Fucns, 1982; Pilegaard, 1978; Ratcliffe, 1975;
Ruhling and Tyler, 1969; Tanaka and Ichikuni, 1982). These studies all show that lead on the
surface of leaves and bark is proportional to traffic density and distance from the highway,
or more specifically, to air lead concentrations and particle size distributions. Other
factors such as surface roughness, wind direction and speed are discussed in Chapter 6. The
data also show that lead in internal plant tissues is directly related to lead in soil.
In a study to determine the background concentrations of lead and other metals in agri-
cultural crops, the Food and Drug Administration (Wolnik et aT., 1983), in cooperation with
the U.S. Department of Agriculture and the U.S. Environmental Protection Agency, analyzed over
1500 samples of the most common crops taken from a cross section of geographic locations.
Collection sites were remote from mobile or stationary sources of lead. Soil lead concentra-
tions were within the normal range (8-25 pg/g) of U.S. soils. Extreme care was taken to avoid
contamination during collection, transportation, and analysis. The concentrations of lead in
crops found by Wolnik et al. (1983) are shown as "Total" concentrations in Table 7-9. The
breakdown by source of lead is discussed below. The total concentration data should probably
be seen as representing the lowest concentrations of lead in food available to Americans. It
is likely that lead concentrations in crops harvested by farmers are somewhat higher for
several reasons: some crops are grown closer to highways and stationary sources of lead than
those sampled by Wolnik et al. (1983); some harvest techniques used by farmers might add more
lead to the crop than did Wolnik et al.; and some crops are grown on soils significantly
higher in lead than those of the Wolnik et al. study because of a history of fertilizer ad-
ditions or sludge applications.
Because the values reported by Wolnik et al. are of better quality than previously
reported data for food crops, it is necessary to disregard many other reports as being either
atypical or erroneous. Studies that specifically apply to roadside or stationary source con-
ditions, however, may be applicable if the data are placed in the context of these recent
findings by Wolnik et al. (1983). Studies of the lead associated with crops near highways
have shown that both lead taken up from soil and aerosol lead delivered by deposition are
found with the edible portions of common vegetable crops. However, there is enormous vari-
ability in the amount of lead associated with such crops and in the relative amounts of lead
in the plants versus on the plants. The variability depends upon several factors, the most
prominent of which are the plant species, the traffic density, the meteorological conditions,
and the local soil conditions (Welch and Dick, 1975; Rabinowitz, 1974; Arvik, 1973; Dedolph et
PB7/A 7-29 7/14/83
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PRELIMINARY DRAFT
TABLE 7-9. BACKGROUND LEAD IN BASIC FOOD CROPS AND MEATS+
Crop
Natural
Pb
Indi rect
atmospheri c
Di rect
atmospheric
Total^
Wheat
0.0015
0.0015
0.034
0.037
Potatoes
0.0045
0.0045
--
0.009
Field corn
0.0015
0.0015
0.019
0.022*
Sweet corn
0.0015
0.0015
--
0.003
Soybeans
0.021
0.021
--
0.042
Peanuts
0.050
0.050
—
0.100
Onions
0.0023
0.0023
--
0.0046*
Ri ce
0.0015
0.0015
0.004
0.007*
Carrots
0.0045
0.0045
¦ --
0.009*
Tomatoes
0. 001
0.001
--
0.002*
Spi nach
0.0015
0.0015
0.042
0.045*
Lettuce
0.0015
0.0015
0.010
0.013'
Beef (muscle)
0.0002
0.002
0.02
0.02**
Pork (muscle)
0.0002
0. 002
0. 06
0.06**
ifAll units are in pg/g fresh weight.
Except as indicated, data are from Wolnick et al. (1983).
*Preliminary data provided by the Elemental Analysis Research Center, Food and Drug Adminis-
tration, Cincinnati, OH.
**Data from Penumarthy et al. (1980).
al,, 1970; Motto et al., 1970; Schuck and Locke, 1970; Ter Haar, 1970). These factors,
coupled with the fact that many studies have neglected differentiation between lead on plants
versus lead in plants, make it difficult to generalize. Data of Schuck and Locke (1970)
suggest that in some cases (e.g., tomatoes and oranges) much of the surface lead is readily
removed by washing. But as noted in Section 6.4,3, this is not universally true; in some
cases, much more vigorous washing procedures are necessary.
Ter Haar (1970) found that inedible portions of several plants (bean leaves, corn husks,
soybean husks, and chaff from oats, wheat, and rice) had two to three times the lead concen-
tration when grown near a busy highway compared with similar plants grown in a greenhouse sup-
plied with filtered air. The edible portions of these and other plants showed little or no
difference in lead content between those grown in ambient air and those grown in the filtered
air. However, the lead concentrations found by Ter Haar (1970) for edible portions of crops
grown in filtered air in the greenhouse were one to two orders of magnitude higher than those
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of the same types of crops taken from actual agricultural situations by Wolnik et al. (1983).
Dedolph et al. (1970) found that while ryegrass and radish leaves grown near a busy highway
contained deposited airborne lead, the edible portion of the radish was unaffected by varia-
tions in either soil lead or air lead.
To estimate the distribution of natural and atmospheric lead in food crops (Table 7-9),
it is necessary to recognize that some crops of the Wolnik et al. study have no lead from
direct atmospheric deposition, that all lead comes through soil moisture. The lowest concen-
trations of lead are found in those crops where the edible portion grows above ground and is
protected from atmospheric deposition (sweet corn and tomatoes). Belowground crops are also
protected from atmospheric deposition but have slightly higher concentrations of lead, partly
because lead accumulates in the roots of plants (potatoes, onions, carrots). Leafy above-
ground plants (lettuce, spinach, wheat) have even higher lead concentrations presumably
because of exposure to atmospheric lead. The assumption that can be made here is that, in the
absence of atmospheric deposition, exposed aboveground plant parts would have lead concentra-
tions similar to protected aboveground parts.
The data on these ten crops suggest that root vegetables have lead concentrations between
0.0046 and 0.009 pg/g, all soil lead, which presumably is half natural and half anthropogenic
(called indirect atmospheric lead here). Aboveground parts not exposed to significant amounts
of atmospheric deposition (sweet corn and tomatoes) have less lead internally, also equally
divided between natural and indirect atmospheric lead. If it is assumed that this same con-
centration is the internal concentration for aboveground parts for other plants, it is ap-
parent that five crops have direct atmospheric deposition in proportion to surface area and
estimated duration of exposure. The deposition rate of 0.04 ng/cm2,day in rural environments
(see Section 6.4.1) could account for these amounts of direct atmospheric lead.
In this scheme, soybeans and peanuts are anomalously high. Peanuts grow underground in a
shell and should be of a lead concentration similar to potatoes or carrots, although peanuts
technically grow from the stem of a plant. Soybeans grow inside a sheath and should have an
internal lead concentration similar to corn. The fact that both soybeans and peanuts are
legumes,may indicate species differences.
The accumulation of lead in edible crops was measured by Ter Haar (1970), who showed that
edible plant parts not exposed to air (potatoes, corn, carrots, etc.) do not accumulate atmo-
spheric lead, while leafy vegetables do. Inedible parts, such as corn husks, wheat and oat
chaff, and soybean hulls were also contaminated. These results were confirmed by McLean and
Shields (1977), who found that most of the lead in food crops is on leaves and husks. The
general conclusion from these studies is that lead in food crops varies according to exposure
to the atmosphere and in proportion to the effort taken to separate husks, chaff, and hulls
from edible parts during processing for human or animal consumption.
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These discussions lead to the conclusion that-root parts and protected aboveground parts
of edible crops contain natural lead and indirect atmospheric lead, both derived from the
soil. For exposed aboveground parts, any lead in excess of the average found on unexposed
aboveground parts is considered to be the result of direct atmospheric deposition.
Near smelters, Merry et al. (1981) found a pattern different from roadside studies cited
above. They observed that wheat crops contained lead in proportion to the amount of soil
lead, not vegetation surface contamination. A similar effect was reported by Harris (1981).
7.2.2.2.2 Livestock. Lead in forage was found to exceed 950 pg/g within 25 m of roadsides
with 15,000 or more vehicles per day (Graham and Kalman, 1974. At lesser traffic densities,
200 pg/g were found. Other reports have observed 20 to 660 pg/g with the same relationship to
traffic density and distance from the road (see review by Graham and Kalman, 1974). A more
recent study by Crump and Barlow (1982) showed that the accumulation of lead in forage is di-
rectly related to the deposition rate, which varied seasonally according to traffic density.
The deposition rate was measured using the moss bag technique, in which bags of moss are
exposed and analyzed as relative indicators of deposition flux. Rain was not effective in
removing lead from the surface of the moss.
7.2.3 Lead in Surface and Ground Water
Lead occurs in untreated water in either dissolved or particulate form. Dissolved lead is
operationally defined as that which passes through a 0.45 membrane filter. Because atmos-
pheric lead in rain or snow is retained by soil, there is little correlation between lead in
precipitation and lead in streams which drain terrestrial watersheds. Rather, the important
factors seem to be the chemistry of the stream (pH and hardness) and the volume of the stream
flow. For groundwater, chemistry is also important, as is the geochemical composition of the
water-bearing bedrock.
Of the year-round housing units in the United States, 84 percent receive their drinking
water from a municipal or private supply of chemically treated surface or ground water. The
second largest source is privately owned wells (Bureau of the Census, 1982). In some communi-
ties, the purchase of untreated bottled drinking water is a common practice. The initial con-
centration .of lead in this water, depends largely on the source of the untreated water.
7.2.3.1. Typical Concentrations of Lead in Untreated Water.
7.2.3.1.1 Surface water. Durum et al. (1971) reported a range of 1 to 55 pg/1 in 749 surface
water samples in the United States. Very few samples were above 50 pg/1 , and the average was
3.9 pg/1. Chow (1978) reviewed other reports with mean values between 3 and 4 pg/1. The
National Academy of Sciences (1980) reported a mean of 4 pg/1 with a range from below
detection to 890 pg/1. Concentrations of 100 pg/l were found near sites of sewage treatment,
urban runoff, and industrial waste disposal.
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Because 1 pg/1 was at or below the detection limit of most investigators during the
1970's, it is likely that the mean of 3 to 4 pg/1 was unduly influenced by a large number of
erroneously high values at the lower range of detection. On the other hand, Patterson (1980)
reports values of 0.006 to 0.05 pg/1 for samples taken from remote streams. Extreme care was
taken to avoid contamination and analytical techniques sensitive to less than 0.001 pg/1 were
used.
Streams and lakes are influenced by their water chemistry and the lead content of their
sediments. At neutral pH, lead moves from the dissolved to the particulate form and the part-
icles eventually pass to sediments. At low pH, the reverse pathway generally takes place.
Hardness, which is a combination of the Ca and Mg concentration, also can influence lead con-
centrations. At higher concentrations of Ca and Mg, the solubility of lead decreases.
Further discussion of the chemistry of lead in water may be found in Sections 6.5.2.1 and
8.2.2.
7.2.3.1.2 Ground water. Municipal and private wells account for a large percentage of the
drinking water supply. This water typically has a neutral pH and somewhat higher hardness
than surface water. Lead concentrations are not influenced by acid rain, surface runoff, or
atmospheric deposition. Rather, the primary determinant of lead concentration is the geo-
chemical makeup of the bedrock that is the source of the water supply. Ground water typically
ranges from 1 to 100 pg Pb/1 (National Academy of Sciences, 1980). Again, the lower part of
the range may be erroneously high due to difficulties of analysis. It is also possible that
the careless application of fertilizers or sewage sludge to agricultural lands can cause con-
tamination of ground water supplies.
7.2.3.1.3 Natural vs. anthropogenic lead in water. Although Chow (1978) reports that the na-
tural lead concentration of surface water is 0.5 jjg/1, this value may be excessively high. In
a discussion of mass balance considerations (National Academy of Sciences, 1980), natural lead
was suggested to range from 0.005 to 10 |jg/1. Patterson (1980) used further arguments to
establish an upper limit of 0.02 pg/1 for natural lead in surface water. This upper limit
will be used in further discussions of natural lead in drinking water.
Because ground water is free of atmospheric lead, lead in ground water should probably be
considered natural in origin as it occurs at the well head, unless there is evidence of
surface contamination.
7.2.3.2 Human Consumption of Lead in Water. Whether from surface or ground water supplies,
municipal waters undergo extensive chemical treatment prior to release to the distribution
system. There is no direct effort to remove lead from the water supply. However, some treat-
ments, such as flocculation and sedimentation, may inadvertently remove lead along with other
undesirable substances. On the other hand, chemical treatment to soften water increases the
solubility of lead and enhances the possibility that lead will be added to water as it passes
through the distribution system.
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7.2.3.2.1 Contributions to drinking water. For samples taken at the household tap, lead con-
centrations are usually higher in the initial volume (first daily flush) than after the tap
has been running for some time. Water standing in the pipes for several hours is intermediate
between these two concentrations (Sharrett et'al. , 1982; Worth et a.l. , 1981). Common plumbing
materials are galvanized and copper pipe; lead solder is usually used to seal the joints of
copper pipes. Lead pipes are seldom in service in the United States, except in the New
England states (Worth et al., 1981).
Average lead content of running water at the household tap is generally lower (fi g/1)
than in some untreated water sources (25 to 30 pg/1) (Sharrett et al., 1982). This implies
either that treatment can remove a portion of the lead or that measurements of untreated water
are erroneously high. If first flush or standing water is sampled, the lead content may be
considerably higher. Sharrett et al. (1982) showed that in both copper and galvanized pipes,
lead concentrations were increased by a factor of two when the sample was taken without first
flushing the line (see Section 7.3.1.3).
The age of the plumbing is an important factor. New copper pipes with lead solder ex-
posed on the inner surface of the joints produce the- highest amount of lead in standing water.
After six years, this lead is leached away and copper pipes subsequently have less lead in
standing water than galvanized pipes. Because lead pipes are rarely used in the United
States, exposure from this source will be treated as a special case in Section 7.3.2.1. The
pH of the water is also important; the acid water of some eastern United States localities can
increase the leaching rate of lead from lead pipes or lead solder joints and prevent the
buildup of a protective coating of calcium carbonate plaque.
Table 7-10 summarizes the contribution of atmospheric lead to drinking water. In this
determination, the maximum reported value for natural lead (0.02 pg/1) was used, all ad-
ditional lead in untreated water is considered to be of atmospheric origin, and it is assumed
that treatment removes 85 percent of the original lead, and that any lead added during distri-
bution is non-atmospheric anthropogenic lead.
7.2.3.2.2 Contributions to food. The use of treated water in the preparation of food can be
a significant source of lead in the human diet. There are many uncertainties in determining
this contribution, however. Water used in food processing may be from a municipal supply or a
private well. This water may be used to merely wash the food, as with fruits and vegetables,
or as an actual ingredient. Water lead may remain on food that is partially or entirely de-
hydrated during processing (e.g., pasta). Water used for packing or canning may be used with
the meal or drained prior to preparation. It is apparent from discussions in Section 7.3.1.3
that, considering both drinking water and food preparation, a significant amount of lead can
be consumed by humans from treated water. Only a small fraction of this lead is of atmo-
spheric origin, however.
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PRELIMINARY DRAFT
TABLE 7-10.
SUMMARY OF
LEAD IN DRINKING
WATER SUPPLIES*
Indi rect
Di rect
Non-atmospheri c
Natural
atmospheri c
atmospheri c
anthropogenic
Total
Pb
Pb
Pb
Pb
Pb
Untreated
Lakes
0.02
15
10
--
25
Ri vers
0.02
15
15
--
30
Streams
0.02
2.5
2.5
--
5
Groundwater
3
--
--
3
T reated
Surface
0.003
2.5 ¦
1.5
4
8
Ground
0.45
--
- -
7.5
8
*units are pg/1.
7.2.4 Summary of Environmental Concentrations of Lead
Lead concentrations in environmental media that are in the pathway to human consumption
are summarized on Table 7-11. These values are estimates derived from the preceding discus-
sions. In each category, a single value is given, rather than a range, in order to facilitate
further estimates of actual human consumption. This use of a single value is not meant to
imply a high degree of certainty in its determination or homogeneity within the human popula-
tion. The units for water are converted from |jg/l as in Table 7-10 to pg/g to facilitate the
discussions of dietary consumption of water and beverages.
TABLE 7-11. SUMMARY OF ENVIRONMENTAL CONCENTRATIONS OF LEAD
Natural
Atmospheric
Total
Medi um
Pb
Pb
Pb
Air urban (pg/m3)
0.00005
0.8
0.8
rural (pg/m3)
0.00005
0.2
0.2
Soil total (pg/g)
8-25
3.0
15.0
Food crops (pg/g)
0.0025
0.027
0.03
Surface water (pg/g)*
0.00002
0.005
0.005
Ground water (pg/g)*
0.003
--
0.003
*note change in units
from Table 7-12.
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Because concentrations of natural lead are generally three to four orders of magnitude
lower than anthropogenic lead in ambient rural or urban air, all atmospheric contributions of
lead are considered to be of anthropogenic origin. Natural soil lead typically ranges from 10
to 30 |jg/g, but much of this is tightly bound within the crystalline matrix of soil minerals
at normal soil pHs of 4 to 8. Lead in the organic fraction of soil is part natural and part
atmospheric. The fraction derived from fertilizer is considered to be minimal. In undis-
turbed rural and remote soils, the ratio of natural to atmospheric lead is about 1:1, perhaps
as high as 1:3. This ratio persists ^'n soil moisture and in internal plant tissues. Thus,
some of the internal lead in crops is of anthropogenic origin, and some is natural. Informa-
tion on the effect of fertilizer on this ratio is not available. Lead in untreated surface
water is 99 percent anthropogenic, presumably atmospheric except near municipal waste out-
falls. It is possible that 75 percent of this lead is removed during treatment. Lead in un-
treated ground water is probably all natural.
In tracking air lead through pathways to human exposure, it is necessary to distinguish
between lead of atmospheric origin that has passed through the soil (indirect atmospheric
lead), and atmospheric lead that has deposited directly or crops or water. Because indirect
atmospheric lead will remain in the soi] for many decades, this source is insensitive to pro-
jected changes in atmospheric lead concentrations. Regulation of ambient air lead concentra-
tions will not affect indirect atmospheric lead concentrations over the next several decades.
The method of calculating the relative contribution of atmospheric lead to total poten-
tial human exposure relies heavily on the relationship between air concentration and deposi-
tion flux described on Section 6.4. Estimates of contributions from other sources are usually
based on the observed value for total lead concentration from which the estimated contribution
of atmospheric lead is subtractea. Except for t'h'e contribution of lead solder in food cans
and paint pigments in dust, there is little or no direct evidence for the contribution of non-
atmospheric anthropogenic lead to the total lead consumption of humans.
7.3 POTENTIAL PATHWAYS TO HUMAN EXPOSURE
The preceding section discussed ambient concentrations of lead in the environment, focus-
ing on levels in the air, soil, food crops, and water. In this section, environmental lead
concentrations are examined from the perspective of pathways to human exposure (Figure 7-1).
Initially, a current baseline exposure scenario is described for an individual with a minimum
amount of daily lead consumption. This person would live and work in a nonurban environment,
eat a normal diet of food taken from a typical grocery shelf, and would have no habits or ac-
tivities that would tend to increase lead exposure. Lead exposure at the baseline level is
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PRELIMINARY DRAFT
considered unavoidable without further reductions of lead in the atmosphere or in canned
foods. Most of the baseline lead is of anthropogenic origin, although a portion is natural,
as discussed in Section 7.3.1.5.
7.3.1 Baseline Human Exposure
To arrive at a minimum or baseline exposure for humans, it is necessary to begin with the
environmental components, air, soil, food crops, and water, which are the major sources of
lead consumed by humans (Table 7-11). These components are measured frequently, even
monitored routinely in the case of air, so that many data are available on their concentra-
tions. But there are several factors which modify these components prior to actual human ex-
posure. We do not breathe air as monitored at an atmospheric sampling station, we may be
closer to or farther from the source of lead than is the monitor. We may be inside a
building, with or without filtered air; the water we drink, does not come directly from a
stream or river. It has passed through a chemical treatment plant and a distribution system.
A similar type of processing has modified the lead levels present in our food.
Besides the atmospheric lead in environmental components, there are two other sources
that contribute to this baseline of human exposure: paint pigments and lead solder (Figure
7-6). Solder contributes directly to the human diet through canned food and copper water dis-
tribution systems. Chips of paint pigments are discussed later under special environments.
But paint and solder are also a source of lead-bearing dusts. The most common dusts in the
baseline human environment are street dusts and household dusts. They originate as emissions
from mobile or stationary sources, as the oxidation products of surface exposure, or as pro-
ducts of frictional grinding processes. Dusts are different from soil in that soil derives
from crustal rock and typically has a lead concentration of 10 to 30 (jg/g, whereas dusts come
from both natural and anthropogenic sources and vary from 1,000 to 10,000 |jg/9-
The discussion of the baseline human exposure traces the sequence from ambient air to in-
haled air, from soil to prepared food, from natural water to drinking water, and from paint,
solder and aerosol particles to dusts. At the end of this section, Table 7-24 summarizes the
four sources by natural and anthropogenic contributions, with the atmospheric contribution to
the anthropogenic fraction identified. Reference to this table wi.1,1 guide the discussion of
human exposure in a logical sequence that ultimately presents an estimate of the exposure of
the human population to atmospheric lead. To construct this table, it was necessary to make
decisions based on sound scientific judgment, occasionally in the absence of conclusive data.
This method provides a working approach to identifying sources of lead that can be easily
modified as more accurate data become available.
PB7/A
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~u
CO
I
U>
00
&
A
AUTO
EMISSIONS
CRUSTAL
WEATHERING
INDUSTRIAL
EMISSIONS
PAINT
PIGMENTS
SOLDER
o
70
MAN
ANIMALS
FOOD
PLANTS
INHALED
AIR
DUSTS
DRINKING
WATER
AMBIENT
AIR
SOIL
SURFACE AND
GROUND WATER
-a
to
CO
co
atmntnho 'i P'SJ^ents and solder are two additional sources of patential lead exposure which are not of
taJhm h. °r'9m- Solder ,s common even in baseline exposures and may represent 30 to 45 percent of the
houses consumption. Paint pigments are encountered in older houses and in soils adjacent to older
-------
PRELIMINARY DRAFT
7-3.1.1 Lead in Inhaled Air. A principal determinant of atmospheric lead is distance from
the source. At more than 100 m from a major highway or more than 2 km from a stationary
source, lead concentrations generally drop to constant levels (see Section 6.3), and the par-
ticle size distribution shifts from a bimodal distribution to a unimodal one with a mass
median equivalent diameter of about 0.2 (Jin. Because the concentration of atmospheric lead at
nonurban stations is generally from 0.05 to 0.15 pg/ma, a value of 0.1 pg/m3 may reasonably be
assumed. A correction can be made for the indoor/outdoor ratio assuming the average individ-
ual spends 20-22 hours/day in an unfiltered inside atmosphere and the average indoor/outdoor
ratio for a nonurban location is 0.5 (Table 7-7). The adjusted air concentration becomes 0.05
pg/m3 for baseline purposes.
The concentration of natural lead in the atmosphere, discussed in Section 7.2.1.1.3, is
probably about 0.00005 pg/m3. This is an insignificant amount compared to the anthropogenic
contribution of 0.2 pg/m3. A summary of lead in inhaled air appears in Table 7-12.
TABLE 7-12. SUMMARY OF INHALED AIR LEAD EXPOSURE
Adjusted
Total
Natural
Direct
air Pb
Amount
lead
Pb
atmospheri c
conc.1
i nhaled
exposure
(pg/day)
Pb
pg/m3
(m3/day)
(pg/day)
(pg/day)
Children (2 year-old)
0.05
10
0.5
0.001
0.5
Adult-working inside
0.05
20
1.0 •
0.002
1.0
Adult-working outside
0.10
20
2.0
0.004
2.0
1Values adjusted for indoor/outdoor ratio of lead concentrations and for daily time spent
outdoors.
7.3.1.2 Lead in Food. The route by which many people receive the largest portion of their
daily lead intake is through foods. Several studies have reported average dietary lead inakes
in the range 100 to 500 pg/day for adults, with individual diets covering a much greater range
(Schroeder and Tipton, 1968; Tepper, 1971; Mahaffey, 1978; Nutrition Foundation, Inc/ 1982).
Gross (1981) analyzed results of the extensive lead mass balance experiments described by
f
Kehoe (1961), which were conducted from 1937 to 1972. According to these data, total dietary
lead intake decreased from approximately 300 pg/day in 1937 to 100 pg/day in 1970, although
there is considerable variability in the data. Only a fraction of this lead is absorbed, as
discussed in Chapter 10.
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The amount of lead typically found in plants and animals is discussed in Section 1.2.2.2.
The sources of this lead are air, soil, and untreated waters (Figure 7-1). Food crops and
livestock contain lead in varying proportions from the atmosphere and natural sources. From
the farm to the dinner table, lead is added to food as it is harvested, transported, pro-
cessed, packaged, and prepared. The sources of this lead are dusts of atmospheric and indus-
trial origin, metals used in grinding, crushing, and sieving, solder used in packaging, and
water used in cooking.
The American diet is extremely complex and variable among individuals. Pennington (1983)
has described the basic diets, suppressing individual variation but identifying 234 typical
food categories, for Americans grouped into eight age/sex groups (Table 7-13). These basic
diets are the foundation for the Food and Drug Administration's revised Total Diet Study,
often called the market basket study, beginning in April, 1982. The diets used for this dis-
cussion include food, beverages and drinking water for a 2-year-old child, the adult female 25
to 30 years of age and the adult male 25 to 30 years of age. The 234 typical foods that com-
prise the basic diets approximate 90 percent or more of the food actually consumed by partici-
pants in the two surveys which formed the basis of the Pennington study. These 234 categories
have been further reduced to 26 food categories (Table 7-13) and 6 beverage categories (Table
7-20) based on known or presumed similarities in lead concentration, and a weighted average
lead concentration has been assigned to each category from available literature data. A com-
plete list of the Pennington categories and the rationale for grouping into the categories of
Tables 7-13 and 7-20 appears in Tables 7D-1 and 7D-2 of Appendix 7D.
Milk and foods are treated separately from water and other beverages because the pathways
by which lead enters these dietary components are substantially different (Figure 7-1), as
solder and atmospheric lead contribute significantly to each. Data for lead concentrations on
Tables 7-13 and 7-20 came from a preliminary report of the 1982 Total Diet Study provided by
the U.S. Food and Drug Administration (1983) for the purpose of this document. In 1982, the
Nutrition Foundation published an exhaustive study of lead in foods, using some data from the
National Food Processors Assocation and some data from Canadian studies by Kirkpatrick et al.
(1980) and Kirkpatrick and Coffin (1974, 1977). A summary of the available data for the
period 1973 to 1980 was prepared in an internal report to the FDA prepared by Beloian (1980).
Portions of these reports were used to interpret the contributions of lead to food during
processing.
Many of the food categories in Table 7-13 correspond directly to the background crop and
meat data presented in Table 7-9. The following section evaluates the amounts of lead added
during each step of the. process from the field to the dinner table. In the best case, re-
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liable data exist for the specific situation in question and conclusions are drawn. In some
cases, comparable data can be used with a few reasonable assumptions to formulate acceptable
estimates of lead contributions. For a portion of the diet, there are no acceptable data and
the contributions of lead must, for the time, be listed as of undetermined origin.
TABLE 7-13. LEAD CONCENTRATIONS IN MILK AND FOODS
Dietary consumption
(g/day)
Lead
Summary
Child
Adult
Adult
concentration*
food
(2
-yr-old)
female
male
Cpg/g)
category
in Table 7-16
Milk
350
190
280
0.01
A
Dairy products
24
36
49
0. 03
A
Milk as ingredient
7
11
15
0.01
A
Beef
33
61
120
0.035
B
Pork
12
21
40
0.06
B
Chicken
12
20
29
0.02
B
Fish
5
15
18
0.09
B
Prepared Meats
14
11
23
0.013
B
Other Meats
1
7
5
0.07
B
Eggs
33
34
53
0.017
B
Bread
42
56
75
0.015
C
Flour as ingredient
23
26
79
0.013
C
Non-wheat cereals
33
13
34
0.025
C
Corn flour
14
12
20
0.025
C
Leafy vegetables
7
39
38
0.05
C
Root vegetables
3
7
7
0.025
C
Vine vegetables
19
49
62
0.025
c
Canned vegetables
39
53
62
0.25
D
Sweet corn
4
6
7
0.01
C
Canned sweet corn
5
4
7
0.21
D
Potatoes
38
52
85
0.02
C
Vegetable oil
5
12
15
0.03
C
Sugar
15
21
34
0.03
C
Canned fruits
14
11
13
0.22
D
Fresh fruits
49
57
49
0.02
C
Pureed baby food
11
--
--
0.03
Subtotal
812
824
1219
Water and
beverages
647
1286
1804
See Table 7-21
Total
1459
2110
3023
• -N .
"Data are summarized from preliminary data provided by the U.S. FDA; complete data appear in
Appendix 7D.
PB7/A 7-41 7/14/83
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PRELIMINARY.DRAFT
7.3.1.2.1 Lead added during handling and transportation to processor. Between the field and
the food processor, lead is added to the food crops. It is assumed that this lead is all of
direct atmospheric origin. Direct atmospheric lead can be lead deposited directly on food
materials by dry deposition, or it can be lead on dust which has collected on other surfaces,
then transferred to foods. For the purposes of this discussion, it is not necessary to dis-
tinguish between these two forms, as both are a function of air concentration.
There are no clear data on how much lead is added during transportation, but some obser-
vations are worth noting. First, some fresh vegetables (e.g., potatoes, lettuce, carrots,
onions) undergo no further processing other than trimming, washing and packaging. If washed,
water without soap is used; no additives or preservatives are used. An estimate of the amount
of atmospheric lead added during handling and transportation of all food crops can be made
from the observed increases in lead on those fresh vegetables where handling and transpor-
tation would be the only source of added lead. Because atmospheric lead deposition is a
function of time, air concentration, and exposed surface area, there is an upper limit to the
maximum amount of direct atmospheric lead that can be added, except by the accumulation of
atmospheric dusts.
7.3.1.2.2 Lead added during preparation for packaging. For some of the food items, data are
available on lead concentrations just prior to the filling of cans. In the case where the
food product has not undergone extensive modification (e.g., cooking, added ingredients), the
added lead was most likely derived from the atmosphere or from the machinery used to handle
the product. As with transportation, the addition of atmospheric lead is limited to reason-
able amounts that can be added during exposure to air, and reasonable amounts of atmospheric
dust accumulation on food processing surfaces. One process that may increase the exposure of
the food to air is the use of air in separating food items, as in wheat grains from chaff.
Where modification of the food product has occurred, the most common ingredients added
are sugar, salt, and water. It is reasonable that water has a lead concentration similar to
drinking water reported in Section 7,3.1.3 (0.008 |jg/g) and that sugar (Boyer and Johnson,
1982) and salt have lead concentrations of 0.01 m9/Q- Grinding, crushing, chopping, and
cooking may add lead from the metallic parts of machinery and fromcindustrial greases. A
summary of the data (Table 7-14) indicates that about 30 percent of the total lead in canned
goods is the result of prepacking processes.
7.3.1.2.3 Lead added during packaging. From the time a product is packaged in bottles, cans
or plastic containers, until it is opened in the kitchen, it may be assumed that no food item
receives atmospheric lead. Most of the lead which is added during this stage comes from the
solder used to seal some types of cans. Estimates by the U.S. FDA, prepared in cooperation
A
f
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PRELIMINARY DRAFT
with the National Food Processors Association, suggest that lead in solder contributes more
than 66 percent of the lead in canned foods where a lead solder side seam was used. This lead
was thought to represent a contribution of 20 percent to the total lead consumption in foods
(F.R. , 1979 August 31).
TABLE 7-14. ADDITION OF LEAD TO FOOD PRODUCTS
Food
In the
field
After
preparation
for packaging
After
packaging
After
kitchen
preparation
Total Pb
added
after harvest
Soft Packaged
Wheat
0.037
0.065
--
--
Field corn
0.022
0.14
0.025
0.003
Potatoes
0.009
0.018
0.02
0.011
Lettuce
0.013
0.07
0.015
0.002
Rice
0.007
0.10
0.084
0.077
Carrots
0.009
0,05
0.017
0.008
Beef
0.01
0.07
0.035
0.025
Pork
0.06
0.10
0.06
Metal cans
Sweet corn
0.003
0.04
0.27
0.28
0.28
Tomatoes
0.002
0.06
0.29
—
Spi nach
0.045
0.43
0.68
0.86
0.82
Peas
0.08
0.19
0.22
0.14
Applesauce
0.08
0.24
0.17
0.09
Apricots
0.07
0.17
--
0.10
Mixed fruit
0.08
0.24
0.20
0.12
Plums
0.09
0.16
0.07
Green beans
0.16
0.32
0.16
This table summarizes the stepwise addition of lead to food products at several stages between
the field and the dinner table. Data are in jjg/g fresh weight.
The full extent of the contribution of the canning process to overall lead levels in
albacore tuna was reported in a benchmark study by Settle and Patterson (1980). Using rigor-
ous clean laboratory procedures, these investigators analysed lead in fresh tuna, as well as
in tuna packaged in soldered and unsoldered cans. The data, presented in Table 7-15, show
that lead concentrations in canned tuna are elevated above levels in fresh tuna by a factor of
4,000, and by a factor of 40,000 above natural levels of lead inrtiina. Nearly all of the in-
crease results from leaching of the lead from the soldered seam of the can; tuna from an
unsoldered can is elevated by a factor of only 20 compared with tuna fresh from the sea. Note
PB7/A 7-43 7/14/83
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PRELIMINARY DRAFT
that when fresh tuna is dried and pulverized, as in the National Bureau of Standards reference
material, lead levels are seen to increase by a factor of 400 over fresh sea tuna. Table 7-15
also shows the results of analyses conducted by the National Marine Fisheries Service.
TABLE 7-15. PREHISTORIC
AND MODERN CONCENTRATIONS
IN HUMAN FOOD
FROM
A MARINE FOOD CHAIN1
" "= 1'-
Estimated
: 1- - — -=
prehi stori c
Modern
Surface seawater
0.0005
0.005
Albacore muscle, fresh
0.03
0. 3
Albacore muscle from die-punched
unsoldered can
- ~
7.0
Albacore muscle, lead-soldered can
, --
1400
Anchovy from albacore stomach
2.1
21
Anchovy from lead-soldered can
--
4200
Values are ng/g fresh weight.
Source: Settle and Patterson (1980).
7.3.1.2.4 Lead added during kitchen preparation and storage. Although there have been
several studies of the lead concentrations in food after typical meal preparation, most of the
data are not amenable to this analysis. As a part of its compliance program, the U.S. FDA has
conducted the Total Diet Study of lead and other trace contaminants in kitchen-prepared food
each year since 1973. Because the kitchen-prepared items were composited by category, there
is no direct link between a specific food crop and the dinner table. Since April, 1982, this
survey has analyzed each food item individually (Pennington, 1983).
Other studies which reflect contributions of lead added during kitchen preparation have
been conducted. Capar (1978) showed that lead in acidic foods that are stored refrigerated in
open cans can increase by'a factor of 2 to 8 in five days if the cans have a lead-soldered
side seam not protected by an interior lacquer coating. Comparable products in cans with the
lacquer coating or in glass jars showed little or no increase.
f
PB7/A " 7-44 7/14/83
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4 PRELIMINARY DRAFT
7.3.1.2.5 Recent changes of lead in food. As a part of its program to reduce the total lead
intake by children (0 to 5 years) to less than 100 pg/day by 1988, the U.S. FDA estimated lead
intakes for individual children in a large-scale food consumption survey (Beloian and
McDowell, 1981). To convert the survey of total food intakes into lead intake, 23 separate
government and industry studies, covering the period from 1973 to 1978, were statistically
analyzed. In spite of the variability that can occur among individuals grouped by age, the
authors estimated a baseline (1973-78) daily lead intake of 15 ^g/day for infants aged 0 to 5
months, 59 pg/day for children 6 to 23 months, and 82 pg/day for children 2 to 5 years. Bet-
ween 1973 and 1978, intensive efforts were made by the food industry to remove sources of lead
from infant food items. By 1980, there had been a 47 percent reduction in the lead consump-
tion of the age group 0 to 5 months and a 7 percent reduction for the 6 to 23 month age group
(Table 7-16). Most of this reduction was accomplished by the discontinuation of soldered cans
used for infant formula.
TABLE 7-16. RECENT TRENDS OF LEAD CONCENTRATIONS IN FOOD ITEMS
Early 70's 1976-77 1980-81 1982
(pg/g) (^g/g) (pg/g) (pg/g)
Canned food1
Green beans
Beans w/pork
Peas
Tomatoes
Beets
Tomato juice
Applesauce
Citrus juice
Infant food2
0.32
0.64
0.43
0.71
0.38
0.34
0.32
0.14
data
not
available
0.32
0.26
0.19
0.29
0.24
0.08
0.04
0.11
0.16
0.17
0.22
0.12
0.067
0.17
0.04
Formula concentrate 0.10
Juices 0.30
Pureed foods 0.15
Evaporated milk 0.52
0.055
0.045
0.05
0.10
0.01
0.015
0.02
0.07
:Boyar and Johnson (1982); 1982 data from U.S. Food and Drug Administration (1983).
2Pre-1982 data from early 70's and 1976-79 from Jelinek (1982); 1980-81 data from Schaffner
et al. (1983).
The 47 percent reduction in dietary lead achieved for infants prior to 1980 came about
largely because there are relatively few manufacturers of foods for infants and it was compar-
atively simple for this industry to mount a coordinated program in cooperation with the U.S.
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PRELIMINARY. DRAFT"
FDA. There has not yet been a similar decrease in adult foods (Table 7-16) because only a few
manufacturers have switched to non-lead cans. As the switchover increases, lead in canned
food should decrease to a level as low as 30 percent of the pre-1978 values, and there should
be a corresponding decrease of lead in the total adult diet, perhaps as much as 25 to 30 per-
cent. The use of lead-soldered cans in the canning industry has decreased from 90 percent in
1979 to 63 percent in 1982. By the end of 1984, the two leading can manufacturers expect to
produce no more lead-soldered cans for the food industry. A two-year time lag.is expected
before the last of these cans disappears from the grocery shelf. Some of the 23 smaller
manufacturers of cans have announced similar plans over a longer period of time. It is likely
that any expected decrease in the contribution of air lead to foods will be complemented by a
decrease in lead from soldered cans.
7.3.1.2.6 Summary of lead in food. The data of Table 7-13 have been condensed to four cate-
gories from the 26 categories of food in Table 7-17. The total lead concentrations are
weighted according to consumption from Table 7-13, then broken down by source based on the in-
formation provided in Tables 7-9 and 7-14, which show estimates of the atmospheric lead added
before and after harvest. The same weighted total lead concentrations are used to estimate
milk and food lead consumption in Table 7-18 for three age/sex categories. The total dietary
lead consumption is then broken down by source in Table 7-19, using the distributions of Table
7-17. Because the percent.distribution by source is approximately the same for the three age/
sex categories, only the data for adult males are shown.
TABLE 7-17. SUMMARY OF LEAD CONCENTRATIONS IN MILK AND FOODS BY SOURCE*
Pb of .
%
Major
Di rect
Pb from
undeter-
Di rect
food
Total
atmospheri c
solder-'S ^ n<
¦ mi ned
atmospheri c
category
lead
lead
other metals
on gi n
lead
A. Dairy
0.013
0.007
--
0.007
54%
B. Meat
0.036
0.02
0.02
0.016
56%
C. Food crops
0.022
0.016
--
0.002
73%
D. Canned food
0.24
0.016
0.20
0.02
7%
*Foods have been categorized from Table 7-13. Data are in \iq/q. The natural and indirect
atmospheric lead concentrations in dairy and meat products are estimated to be 0.0002 hq/Q
from each source. In food crops and canned foods, these values are 0.002 pg/g.
PB7/A
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It is apparent that at least 35 percent of lead in milk and food can be attributed to
direct atmospheric deposition, compared to 26 percent from solder or other metal sources. Of
the remaining 34 percent for which the source is as yet undetermined, it is likely that
further research will show this lead tobe part atmospheric in origin and part from solder and
other industrial metals.
This dietary lead consumption is used to calculate the total baseline human exposure in
Section 7,3.1.5 and is the largest baseline source of lead. Possible additions to dietary
lead consumption are discussed in Section 7.3.2.1.1 with respect to urban gardens.
TABLE 7-18. SUMMARY BY AGE AND SEX OF ESTIMATED AVERAGE LEVELS
OF LEAD INGESTED FROM MILK AND FOODS
Dietary consumption
(g/day)
Lead conc.
in food
Lead consumption
(jg/ day
2-yr-old Adult
child female
Adult
male
M9 Pb/g*
2-yr-old Adult
child female
Adult
male
A. Dairy
381
237
344
0.013
5.0 3.1
4.5
B. Meat
113
169
288
0.036
4.1 6.1
10.4
C. Food crops
260
350
505
0.022
5.7 7.7
11.1
D. Canned food
58
68
82
0.24
13.9 16.3
19.7 .
Total
812
824
1219
28.7 33.2
45.6
^Weighted average lead concentration in foods from Table 7-13.
Because the U.S. FDA is actively pursuing programs to remove lead from adult foods, it is
probable that there will be a decrease in total dietary lead consumption over the next decade
independent of projected decreases in atmospheric lead concentration. With both sources of
lead minimized, the lowest reasonable estimated dietary lead consumption would be 10 to 15
|jg/day for adults and children. This estimate is based on the assumption that about 90 per-
cent of the direct atmospheric lead, solder lead and lead of undetermined origin would be re-
moved from the diet, leaving 8 pq/day from these sources and 3 pg/day of natural and indirect
atmospheric lead.
7.3.1.3 Lead in Drinking Water. The U.S. Public Health Service standards specify that lead
~
levels in drinking water should not exceed 50 The presence of detectable amounts of
lead in untreated public water supplies was shown by Durum (1971) to be widespread, but only a
few samples contained amounts above the 50 pg/1 standard.
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PRELIMINARY.DRAFT
The major source of lead contamination in drinking water is the water supply system it-
self, Water that is corrosive can leach considerable amounts of lead from lead plumbing and
lead compounds used to join pipes. Moore (1977) demonstrated the effect of water standing in
pipes overnight. Lead concentrations dropped significantly with flushing at 10 1/min for five
minutes (Figure 7-7). Lead pipe currently is in use in some parts of New England for water
service lines and interior plumbing, particularly in older urban areas. The contributions of
lead plumbing to potential human exposure are considered additive rather than baseline and are
discussed in Section 7.3.2.1.3.
There have been several studies in North America and Europe of the sources of lead in
drinking water. A recent study in Seattle, WA by Sharrett et al. (1982) showed that the age
of the house and the type of plumbing determined the lead concentration in tap water. Stand-
ing water in copper pipes from houses newer than five years averaged 31 (Jg/1 ; those less than
18 months average about 70 (jg/1. Houses older than five years and houses with galvanized pipe
averaged less than 6 The source of the water supply, the length of the pipe and the use
of plastic pipes in the service line had little or no effect on the lead concentrations. It
appears certain that the source of lead in new homes with copper pipes is the solder used to
join these pipes, and that this lead is eventually leached away with age.
The Sharrett et al. (1982) study of the Seattle population also provided data on water
and beverage consumption which extended the scope of the Pennington (1983) study of all Ameri-
cans. While the total amount of liquids consumed was slightly higher in Seattle (2200 g/day
vs. 1800 g/day for all Americans), the breakdown between water consumed inside and outside the
home can prove useful. Men, women and children consume 53, 87, and 87 percent respectively of
their water and beverages within the home.
Bailey and Russell (1981) have developed a model for population exposure to lead in home
drinking water. The model incorporates data for lead concentration as a function of stagna-
tion time in the pipes, as well as probability distributions for times of water use throughout
the day. Population surveys conducted as part of the United Kingdom Regional Heart Survey
provided these water-use distributions.
Other studies have been conducted in Canada and Belgium. Lead levels in water boiled in
electric kettles were measured in 574 households in Ottawa (Wigle and Charlebois, 1978). Con-
centrations greater than 50 (jg/1 were observed in 42.5 percent of the households, and ex-
cessive lead levels were associated with kettles more than five years old.
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PRELIMINARY DRAFT
S
a.
Z
o
<
DC
I-
Z
HI
o
z
o
o
D
<
UJ
_i
cc
LU
I-
<
$
TIME OF FLUSHING, minutes
Figure 7-7. Change in drinking water lead concentration in a house with
lead plumbing for the first use of water in the morning. Flushing rate was
10 liters/minute.
Source: Moore (1977).
023PB8/B .
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PRELIMINARY DRAFT
TABLE 7-19.
SUMMARY
BY SOURCE
OF LEAD CONSUMED FROM
MILK AND FOODS
*
Total
Natural
Atmospheric
1 ead
Pb from
Lead of
1 ead
lead
solder and
undeter-
Indi rect
Di rect
other ..
mi ned
lead
1 ead
metals
origin
A. Dairy
4. 5
0.1
0.1
2.3
__
2.0
B. Meat
10.4
0.1
0. 1
5.7
--
4.5
C. Food crops
11.1
1.0
1.0
8.1
— .
1.0
D. Canned foods
19.7
0.2
0.2
1.3
16.4
1.6
Total
45. 7
1.4
1.4
17.4
16.4
9.1
% of total
100%
3.1%
3.13!
38.1%
35.9%
19. 9%
*Distribution based on adult male diet. Data are in pg/day. There may be some direct
atmospheric lead and solder lead in the category of undetermined origin.
The potential exposure to lead through water and beverages is presented in Tables 7-20,
7-21 and 7-22. In Table 7-20, typical concentrations of lead in canned and bottled beverages
and in beverages made from tap water (e.g., coffee, tea, drinking water) are shown by source.
The baseline concentration of water is taken to be 0.01 pg/g, although 0.006 to 0.008 are
often cited in the literature for specific locations. It is assumed that 2/3 of the original
lead is lost during water treatment and that only 0.005 ng/g remains from direct atmospheric
deposition. The water distribution system adds 0.001 pg/g, shown here as lead of undetermined
origin. The source appears to be the pipes or the solder used to seal the pipes. These
values are used for water in canned and bottled beverages, with additional amounts added from
solder and other packaging procedures.
The lead concentrations in beverages are multiplied by total consumption to get daily
lead consumption in Table 7-21 for 3 age/sex categories. For adult males, these are
summarized by source of lead in Table 7-22; distribution by source would be proportional for
children and adult females. The data of Table 7-22 are used for the overall summary of base-
line human exposure in Section 7.3.1.5.
7.3.1.4 Lead in Dusts. By technical definition, dusts are solid particles produced by the
disintegration of materials (Friedlander, 1977) and appear to have no size limitations.
Although dusts are of complex origin, they may be placed conveniently into a few categories
relating to human exposure. Generally, the most convenient categories are household dusts,
soil dust, street dusts and occupational dusts. It is a characteristic of dust particles that
they accumulate on exposed surfaces and are trapped in the fibers of clothing and carpets.
Ingestion of dust particles, rather than inhalation, appears to be the greater problem in the
baseline environment, especially ingestion during meals and playtime activity by small chil-
dren.
023PB8/B 7-50 7/14/83
39^
-------
TABLE 7-20. SUMMARY BY SOURCE OF LEAD CONCENTRATIONS IN WATER
AND BEVERAGES*
Di rect
Lead from
Percent
Total
atmospheric
solder and
di rect
lead
lead
other metals
atmospheric
Canned juices
0.052
0.0015
0.048
2.9%
Frozen juices
0.02
0.0015
0.014
7.5
Canned soda
0.033
0.0015
0.029
4.5
Bottled soda
0.02
0.0015
0.014
7.5
Canned beer
0.017
0.0015
0.013
8.8
Water & beverages
0.008
0.0015
0.004
18.9
*Data are in \ig/g. Natural and indirect atmospheric lead are estimated to be 0.00002 and
0.0025 [ig/g respectively, for all beverage types.
-------
TABLE 7-21. DAILY CONSUMPTION AND POTENTIAL LEAD EXPOSURE FROM
WATER AND BEVERAGES
Beverage
2 yr old
chi Id
Consumption*
(g/day)
Adul t
female'
Beverage
lead
Adult conc.t
male (pg/g)
Lead consumption
(ng/day)
2 yr old Adult Adult
child female male
Canned juices
53
28
20
0.052
2.8
1.5
1.0
Frozen juices
66
66
73
0.02
1. 3
1. 3
1.5
Canned soda
75
130
165
0.033
2.5
4.3
5.4
Bottled soda
75
130
165
0.02
1.5
2.6
3.3
Coffee
2
300
380
0.01
-
3.0
3.8
Tea
32
160
140
0.01
0.3
1.6
1.4
Canned beer
-
35
300
0.017
-
0.6
5.1
Wi ne
-
35
11
0.01
-
0.1
0.1
Whi skey
-
5
9
0.01
-
0.1
0.1
Water
320
400
510
0.008
2.6
2.6
3.2
Water as ingredient
24
20
31
0.008
0.2
0.2
0.2
Total
647
1286
1804
11.2
17.9
25.1
* Data from Pennington, 1983.
t Data from U.S. Food and Drug Administration, 1983.
-------
PRELIMINARY DRAFT
TABLE 7-22.
SUMMARY BY
SOURCE OF LEAD
CONSUMED IN WATER AND BEVERAGES*
Total
Pb
Natural and
i ndi rect
atmospheric
Pb
Lead in
Direct solder and
atmospheric other metals
Pb Pb
Canned juices
1.0
0.05
0.03 0.92
Frozen juices
1.5
0.18
0.11 1.2
Canned soda
5.4
0.42
0.25 4.7
Bottled soda
3.3
0.50
0.3 2.5
Canned beer
5.1
0.8
0.5 3.8
Water &
beverages
8.8
2.8
1.6 4.4
Total
Percent
25. 1
100%
4.8
19.1%
2.8 17.5
11.IX 69. 7%
*Data are for adult males, expressed in pg/day. Percentages are the same for children
and adult females. Total consumption for children and adult females shown on Table 7-21.
Two other features of dust are important. First, they must be described in both concen-
tration and amount. The concentration of lead in street dust may be the same in a rural and
urban environment, but the amount of dust may differ by a wide margin. Secondly, each cate-
gory represents some combination of sources. Household dusts contain some atmospheric lead,
some paint lead and some soil lead. Street dusts contain atmospheric, soil, and occasionally
paint lead. This apparent paradox does not prevent the evaluation of exposures to dust, but
it does confound efforts to identify the amounts of atmospheric lead contributed to dusts.
For the baseline human exposure, it is assumed that workers are not exposed to occupational
dusts, nor do they live in houses with interior leaded paints. Street dust, soil dust and
some household dust are the primary sources for baseline potential human exposure.
In considering the impact of street dust on the human environment, the obvious question
arises as to whether lead in street dust varies with traffic density. Nriagu (1970) reviewed
several studies of lead in street dust. The source of lead was probably flue dust from burn-
ing coal. Warren et al. (1971) reported lead in street dust of 20,000 vg/g in a heavily traf-
ficked area. In the review by Nriagu (1978), street dust lead concentrations ranged from 300
023PB8/B 7-53 7/14/83
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/
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PRELIMINARY DRAFT
to 18,000 pg/g in several cities in the United States. In Hong Kong, lead in street dust
ranged from 960 to 7400 pg/g with no direct relationship to traffic volume (Ho, 1979). In
other reports from Hong Kong, Lau and Wong (1982) found values from 130 pg/g at 20 vehicles/
day to 3,900 pg/g at 37,000 vehicles/day. Fourteen sites in this study showed close correla-
tion with traffic density.
In the United Kingdom, lead in urban and rural street dusts was determined to be 970 and
85 pg/g, respectively, by Day et al. (1975). A later report by this group (Day et al. , 1979)
discusses the persistency of.lead dusts in rainwashed areas of the United Kingdom and New
Zealand and the potential health hazard due to ingestion by children. They concluded that,
whereas the acidity of rain was insufficient to dissolve and transport lead particles, the
potential health hazard lies with the ingestion of these particles during the normal play
activities of children residing near these areas. A child playing at a playground near a
roadside might consume 20 to 200 pg lead while eating a single piece of candy with unwashed
hands. It appears that in nonurban environments, lead in street dust ranges from 80 to 130
pg/g, whereas urban street dusts range from 1,000 to 20,000 pg/g. For the purpose of esti-
mating potential human exposure, an average lead value of 90 pg/g in street dust is assumed
for baseline exposure on Table 7-23, and 1500 pg/g in the discussions of urban environments in
Section 7.3.2.1.
Dust is also a normal component of the home environment. It accumulates on all exposed
surfaces, especially furniture, rugs and windowsills. For reasons of hygiene and respiratory
health, many homemakers take-great care to remove this dust from the household. Because there
are at least two circumstances where these measures are inadequate, it is important to
consider the possible concentration of lead in these dusts in order to determine potential ex-
posure to young children. First, some households do not practice regular dust removal, and
secondly, in some households of workers exposed occupationally to lead dusts, the worker may
carry dust home in amounts too small for efficient removal but containing lead concentrations
much higher than normal baseline values.
In Omaha, Nebraska, Angle and Mclntire (1979) found that lead in household dust ranged
from 18 to 5600 pg/g. In Lancaster, England, a region of low industrial lead emissions,
Harrison (1979) found that household dust ranged from 510 to 970 pg/g, with a mean of 720
pg/g. They observed soil particles (10 to 200 pm in diameter), carpet and clothing fibers,
animal and human hairs, food particles, and an occasional chip of paint. The previous Lead
Criteria Document (U.S. Environmental Protection Agency, 1977) summarized earlier reports of
lead in .household dust showing residential suburban areas ranging from 280 to 1,500 pg/g,
urban residential from 600 to 2,000-pg/g, urban industrial from 900 to 16,000 pg/g. In El
Paso, Texas, lead in household dust ranged from 2,800 to 100,000 pg/g within 2 km of a smelter
(Landrigan et al. 1975).
023PB8/B 7-54 7/14/83
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It appears that most of the values for lead in dust in nonurban household- environments
fall in the range of 50 to 500 pg/g. A mean value of 300 pg/g is assumed. The only natural
lead in dust would be some fraction of that derived from soil lead. A value of 10 pg/g seems
reasonable, since some of the soil lead is of atmospheric origin. Since very little paint
lead is included in the baseline estimate, most of the remaining dust lead would be from the
atmosphere. Table 7-23 summarizes these estimates of human exposure to dusts for children and
adults. It assumes that children ingest about 5 times as much dust as adults, most of the ex-
cess being street dusts from sidewalks and playgrounds. Exposure of children to occupational
lead would be through contaminated clothing brought home by parents. Most of this lead is of
undetermined origin because no data exist on whether the source is dust similar to household
dust or unusual dust from the grinding and milling activities of factories.
7.3.1.5 Summary of Baseline Human Exposure to Lead. The values derived or assumed in the
preceeding sections are summarized on Table 7-24. These values represent only consumption,
not absorption of lead by the human body. The key question of what are the risks to human
health from these baseline exposures is addressed in Chapter 13. The approach used here to
evaluate potential human exposure is similar to that used by the""National Academy of Sciences
(1980) and the Nutrition Foundation (1982) in their assessments of the impact of lead in the
human environment.
TABLE 7-23. CURRENT BASELINE ESTIMATES OF POTENTIAL HUMAN EXPOSURE TO DUSTS
Dust
lead
conc.
^g/g
Dust
i ngested
g/day
Dust
lead
consumed
pg/day
Natural
Source of lead f^q/day)
Atmos. Undetermined
Child
Household dusts
Street dust
Occupational dust
Total
Percent
300
90
150
0.05
0.04
0.01
0.10
15
4. 5
1.5
21.0
100%
0.5
0.1
0.6
2.8
14. 5
4.5
19.0
90. 5
1.4
1.4
6.7
Adult
Household dusts
Street dust
Occupational dust
Total
Percent
300
90
150
0. 01
0.01
0.02
3
1.5
4.5
100%
0.1
0.1
0.2
4.5
2.9
2.9
64.4
1.4
1.4
31.1
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TABLE 7-24. SUMMARY OF BASELINE HUMAN EXPOSURES TO LEADT
Source
Total
lead
consumed
Natural
lead
consumed
So i 1
Indi rect
atmospheric
lead*
Di rect
atmospheric
lead*
Lead from
solder or
other metals
Lead of
undetermined
origin
Child-2 yr old
Inhaled air
0.5
0.001
-
0.5
-
-
Food
28. 7
0.9
0.9
10.9
10. 3
17 6
Water & beverages
11.5
0.01
2.1
1.2
7.8
-
Dust
21.0
Li
_I_
19.0
1.4
Total
61.4
1.5
3.0
31.6
18.1
19.0
Percent
100%
2.4%
4.9%
51.5%
29.5%
22.6%
Adult female
Inhaled air
1.0
0.002
-
1.0
-
-
Food
33.2
1.0
1.0
12.6
11.9
21.6
Water & beverages
17. 9
0.01
3.4
2.0
12.5
-
Dust
4.5
0.2
—_
2.9
-
1.4
Total
56.6
1.2
4.4
18.5
24.4
23.0
Percent
100% •
2. IX
7.8%
32.7%
43,1%
26.8%
Adult nale
Inhaled air
1.0
0.002
-
1.0
-
-
Food
45.7
1.4
1.4
17.4
16.4
31.5
Water & beverages
25.1
0.1
4.7
2.8
17.5
-
Dust
4 5
0.2
2.9
—I—
1.4
Total
76 3
1.7
6.1
24.1
33.9
32.9
Percent
100%
2.2%
e.o%
31.6%
44.4%
27.1%
"Indirect atmospheric lead has been previously incorporated into soil, and will probably remain in the
soil for decades or longer. Direct atmospheric lead has been deposited on the surfaces of vegetation
.and living areas or incorporated during food processing shortly before human consumption.
Units are in pg/day.
7.3.2 Additive Exposure Factors
There are many conditions, even in nonurban environments, where an individual may
increase his lead exposure by choice, habit, or unavoidable circumstance. The following sec-
tions describe these conditions as separate exposures to be added as appropriate to the base-
line of human exposure described above. Most of these additive exposure clearly derive from
air or dust, while few derive from water or food.
7.3.2.1 Living and Working Environments With Increased Lead Exposure. Ambient air lead con-
centrations are typically higher in an urban than a rural environment. This factor alone can
contribute significantly to the potential lead exposure of Americans, through increases in
023PB8/B 7-56 7/14/83
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inhaled air and consumed dust. Produce from urban gardens may also increase the daily con-
sumption of lead. Some environmental exposures may not be related only to urban living, such
as houses with interior lead paint or lead plumbing, residences near smelters or refineries,
or family gardens grown on high-lead soils. Occupational exposures may also occur in an urban
or rural setting. These exposures, whether primarily in the occupational environment or
secondarily in the home of the worker, would be additive with other exposures in an urban
location or with special cases of lead-based paint or plumbing.
7.3.2.1.1 Urban atmospheres. Urban atmospheres have more airborne lead than do nonurban
atmospheres, therefore there are increased amounts of lead in urban household and street dust.
Typical urban atmospheres contain 0.5 to 1.0 pg Pb/m3. Other variables are the amount of in-
door filtered air breathed by urban residents, the amount of time spent indoors, and the
amount of time spent on freeways. Dusts vary from 500 to 3000 ^ig Pb/g in urban environments.
It is not known whether there is more or less dust in urban households and playgrounds than in
rural environments. Whereas people may breathe the same amount of air, eat and drink the same
amount of food and water, it is not certain that urban residents consume the same amount of
dust as nonurban. Nevertheless, in the absence of more reliable data, it has been assumed
that urban and nonurban residents consume the same amount of dusts.
The indoor/outdoor ratio of atmospheric lead for urban environments is about 0.8 (Table
7-7). Assuming 2 hours of exposure/day outdoors at a lead concentration of 0.75 pg/m3, 20
hours indoors at 0.6 pg/m3, and 2 hours in a high traffic density area at 5 pg/m3, a weighted
mean air exposure of 1.0 ^ig/m3 appears to be typical of urban residents.
7.3.2.1.2 Houses with interior lead paint. In 1974, the Consumer Product Safety Commission
collected household paint samples and analyzed them for lead content (National Academy of
Sciences; National Research Council, 1976). Analysis of 489 samples showed that 8 percent of
the oil-based paints and 1 percent of the water-based paints contained greater than 0.5
percent lead (5000 pg Pb/g paint, based on dried solids), which was the statutory limit at the
time of the study. The current statutory limit for Federal construction is 0.06 percent. The
greatest amounts of leaded paint are typically found in the kitchens, bathrooms, and bedrooms
(Tyler, 1970; Laurer et al., 1973; Gilbert et al. , 1979).
Some investigators have shown that flaking paint can cause elevated lead concentrations
in nearby soil. For example, Hardy et al. (1971) measured soil lead levels of 2000 pg/g next
to a barn in rural Massachusetts. A steady decrease in lead level with increasing distance
from the barn was shown, reaching 60 pg/g at fifty feet from the barn. Ter Haar (1974)
reported elevated soil lead levels in Detroit near eighteen old wood frame houses painted with
lead-based paint. The average soil lead level within two feet of a house was just over 2000
pg/g; the average concentration at ten feet was slightly more than 400 pg/g. The same author
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reported smaller soil lead elevations in the vicinity of eighteen brick veneer houses in
Detroit. Soil lead levels near painted barns located in rural areas were similar to urban
soil lead concentrations near painted houses, suggesting the importance of leaded paint at
both urban and rural locations. The baseline lead concentration for household dust of 300
pg/g was increased to 2000 pg/g for houses with interior lead based paints. The additional
1700 pg/g would add 85 pg Pb/day to the potential exposure of a child (Table 7-25). This in-
crease would occur in an urban or nonurban environment and would be in addition to the urban
residential increase if the lead-based painted house were in an urban environment.
7.3.2.1.3 Family gardens. Several studies have shown potentially higher lead exposure
through the consumption of home-grown produce from family gardens grown on high lead soils or
near sources of atmospheric lead. Kneip (1978) found elevated levels of lead in leafy vege-
tables, root crops, and garden fruits associated qualitatively with traffic density and soil
lead. Spittler and Feder (1978) reported a linear correlation between soil lead (100 to 1650
pg/g) and leafy or root vegetables. Preer et al. (1980) found a three-fold increase in lead
concentrations of leafy vegetables (from 6 to 16 pg/g) ln the soil lead range from 150 to 2200
pg/g. In none of these studies were the lowest soil lead concentrations in the normal range
of 10 to 25 pg/g, nor were any lead concentrations reported for vegetables as low as those of
Wolnik et al. (1983) (see Table 7-9).
In family gardens, lead may reach the edible portions of vegetables by deposition of at-
mospheric lead directly on aboveground plant parts or on soil, or by the flaking of lead-
containing paint chips from houses. Traffic density and distance from the road are not good
predictors of soil or vegetable lead concentrations (Preer et al., 1980). Air concentrations
and particle size distributions are the important determinants of deposition on soil or vege-
tation surfaces. Even at relatively high air concentrations (1.5 pg/m3) and deposition velo-
city (0.5 cm/sec) (see Section 6.4,1), it is unlikely that surface deposition alone can
account for more than 2-5 pg/g lead on the surface of lettuce during a 21-day growing period.
It appears that a significant fraction of the lead in both leafy and root vegetables derives
from the soil.
Using the same air concentration and deposition velocity values, a maximum of 1000 pg
lead has been added to each cm2 of the surface of the soil over the past 40 years. With cul-
tivation to a depth of 15 cm, it is not likely that atmospheric lead alone can account for
more than a few hundred pg/g of soil in urban gardens. Urban soils with lead concentrations
of 500 pg/g or more must certainly have another source of lead. In the absence of a nearby
(<5 km) stationary industrial source, paint chips seem the most likely explanation. Even if
the house no longer stands at the site, the lead from paint chips may still be present in the
soil.
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TABLE 7-25. SUMMARY OF POTENTIAL ADDITIVE EXPOSURES TO LEAD
Total
Atmospheric
Other
1 ead
lead
1 ead
consumed
consumed
sources
(|jg/day)
(pg/day)
(pg/day)
Baseline exposure:
Chi 1 d
Inhaled air
0.5
0.5 . „
-
Food, water & beverages
39.9
12.1
27.8
Dust
21.0
19.0
2.0
Total baseline
61.4
31. 6
29.8
Additional exposure due to;
Urban atmospheres1
99
98
Family gardens2
800
200
600
Interior lead paint3
85
85
Residence near smelter'1
1300
1300
Secondary occupational5
150
Baseline exposure:
Adult male
Inhaled air
1.0
1.0
-
Food, water & beverages
70.8
20.2
50.6
Dust
4.5
2.9
1.6
Total baseline
76.3
24.1
52.2
Additonal exposure due to:
Urban atmospheres1
28
28
Family gardens2
2000
500
1500 '
Interior lead paint3
17
17
Residence near smelter4
370
370
Occupati onal6
1100
1100
Secondary occupational 5
21
Smoki ng
30
27
3
Wine consumption
100
?
?
1 includes lead from household and street dust (1000 pg/g) and inhaled air (.75 pg/m3).
2assumes soil lead concentration of 2000 vq/q\ all fresh leafy and root vegetables, sweet corn
of Table 7-13 replaced by produce from garden. Also assumes 25% of soil lead is of atmos-
pheric origin.
3assumes household dust rises from 300 to 2000 |-ig/g. Dust consumption remains the same as
baseli ne.
"•assumes household and street dust increases to 25,000 pg/g.
5assumes household dust increases to 2400 pg/g.
Gassumes 8 hr shift at 10 pg Pb/m3 or 90% efficiency of respirators at 100 pg Pb/m3, and occu-
pational dusts at 100,000 |jg/m3.
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Studies of family gardens do not agree on the concentrations of lead in produce. At the
higher soil concentrations, Kneip (1978) reported G.2 to 1 |jg/g in vegetables, Spittler and
Feder (1978) reported 15 to 90 pg/g, and Preer et al. (1980) found 2 to 16 pg/g. Since the
Spittler and Feder (1978) and Preer et al. (198G) studies dealt with soils in the range of
2000 (jg/g, these data can be used to calculate a worst case exposure of lead from family
gardens. Assuming 15 pg/g for the leafy and root vegetables [compared to 0.01 to 0.05 pg/g of
the Wolnik et al. (1983) study] family gardens could add 2000 pg/day if the 137 g of leafy and
root vegetables, sweet corn and potatoes consumed by adult males (Table 7-13) were replaced by
family garden products. Comparable values for children and adult females would be 800 and
1600 |jg/day, respectively. No conclusive data are available for vine vegetables, but the
ranges of 0.08 to 2 pg/g for tomatoes suggest that the contamination by lead from soil is much
less for vine vegetables than for leafy or root vegetables.
7.3.2.1.4 Houses, with lead plumbing. The Glasgow Duplicate Diet Study (United Kingdom
Department of the Environment, 1982) reports that children approximately 13 weeks old living
in houses with lead plumbing consume 6 to 480 |jg Pb/day. Water lead levels in the 131 homes
studied ranged from less than 50 to over 500 pg/1. Those children and mothers living in the
ho/nes containing high water-lead levels generally had greater total lead consumption and
higher blood lead levels, according to the study. Breast-fed infants were exposed to much
less lead than bottle-fed infants. Because the project was designed to investigate child and
mother blood lead levels over a wide range of water lead concentrations, the individuals
studied do not represent a typical cross-section of the population. However, results of the
study suggest that infants living in homes with lead plumbing may have exposure to consid-
erable amounts of lead. This conclusion was also demonstrated by Sherlock et al. (1982) in a
duplicate diet study in Ayr, Scotland.
7.3.2.1.5 Residences near smelters and refineries. Air concentrations within 2 km of lead
smelters and refineries average 5 to 15 pg/m3. Assuming the same indoor/outdoor ratio of
atmospheric lead for nonurban residents (0.5), residents near smelters would be exposed to in-
haled air lead concentrations of about 6 pg/m3, compared to 0.05 pg/m3 for the background
levels. Household dust concentrations range from 3000 to 100,000 pg/g (Landrigan et al.,
1975). A value of 25,000 pg/g is assumed for household dust near a smelter. Between inhaled
air and dust, a child in this circumstance would be exposed to 1300 pg Pb/day above background
levels. Exposures for adults would be much less, since they consume only 20 percent of the
dusts children consume.
7.3.2.1.6 Occupational exposures. The highest and most prolonged exposures to lead are found
among workers in the lead smelting, refining, and manufacturing industries (World Health
Organization, 1977). In all work areas, the major route of lead exposure is by inhalation and
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ingestion of lead-bearing dusts and fumes. Airborne dusts settle out of the air onto food,
water, the workers' clothing, and other objects, and may be transferred subsequently to the
mouth. Therefore, good housekeeping and good ventilation have a major impact on exposure. It
has been found that levels might be quite high in one factory and low in another solely
because of differences in ventilation, or differences in custodial practices and worker edu-
cation. The estimate of additional exposure on Table 7-25 is for an 8 hour shift at 100 (jg
Pb/m3. Occupational exposure under these conditions is primarily determined by occupational
dust consumed. Even tiny amounts (e.g., 10 mg) of dust containing 100,000 pg Pb/g dust can
account for 1,000 pg/day exposure.
7.3.2.1.6.1 Lead mining, smelting, and refining. Roy (1977) studied exposures during mining
and grinding of lead sulfide at a mill in the Missouri lead belt. Primary smelting operations
were 2.5 miles from the mill, hence the influence of the smelter was believed to be negligible.
The total airborne lead levels were much greater than the concentrations of respirable lead,
indicating a predominance of coarse material.
The greatest potential for high-level exposure exists in the process of lead smelting and
refining (World Health Organization, 1977). The most hazardous operations are those in which
molten lead and lead alloys are brought to high temperatures, resulting in the vaporization of
lead. This is because condensed lead vapor or fume has, to a substantial degree, a small
(respirable) particle size range. Although the total air lead concentration may be greater in
the vicinity of ore-proportioning bins than it is in the vicinity of a blast furnace in a
smelter, the amount of particle mass in the respirable size range may be much greater near the
furnace.
A measure of the potential lead exposure in smelters was obtained in a study of three
typical installations in Utah (World Health Organization, 1977). Air lead concentrations near
all major operations, as determined using personal monitors worn by workers, were found to
vary from about 100 to more than 4000 pg/nr'5. Obviously, the hazard to these workers would be
extremely serious if it were not for the fact that the use of respirators is mandatory in
these particular smelters. Maximum airborne lead concentrations of about 300 pg/m3 were mea-
sured in a primary lead-zinc smelter in the United Kingdom (King et al., 1979). These authors
found poor correlations between airborne lead and blood lead in the smelter workers, and con-
cluded that a program designed to protect these workers should focus on monitoring of biologi-
cal parameters rather than environmental levels.
Spivey et al. (1979) studied a secondary smelter in southern California which recovers
lead mainly from automotive storage batteries. Airborne lead concentrations of 10 to 4800
pg/m^ were measured. The project also involved measurement of biological parameters as well
as a survey of symptoms commonly associated with lead exposure; a poor correlation was found
023PB8/B 7-61 7/14/83
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PRELIMINARY DRAFT
between indices of lead absorption and symptom reporting. The authors suggested that such
factors as educational level, knowledge of possible symptoms, and biological susceptibility
may be important factors in influencing symptom reporting. In a second article covering this
same study, Brown et al. (1980) reported that smokers" working at a smelter had greater blood
lead levels than nonsmokers. Furthermore, smokers who brought their cigarettes into the work-
place had greater blood lead levels than those who left their cigarettes elsewhere. It was
concluded that direct environmental contamination of the cigarettes by lead-containing dust
may be a major exposure pathway for these individuals '(See Section 7.3.2.3.1).
Secondary lead smelters in Memphis, Tennessee and Salt Lake City, Utah were studied by
Baker et al. (1979). The former plant extracted lead principally from automotive batteries,
producing 11,500 metric tons of lead in the eleven months preceding the measurements. The
latter plant used scrap to recover 258 metric tons of lead in the six months preceding the
measurements. Airborne concentrations of lead in the Tennessee study exceeded 200 pg/m3 in
some instances, with personal air sampler data ranging from 120 pg/m3 f°r a battery wrecker to
350 pg/m3 for two yard workers. At the Utah plant, airborne lead levels in the office, lunch-
room, and furnace room (furnace not operating) were 60, 90, and 100 pg/m3, respectively. When
charging the furnace, the last value increased to 2650 pg/m3. Personal samplers yielded con-
centrations of 17 pg/m3 for an office worker, 700 pg/m3 for two welders, and 2660 pg/m3 for
two furnace workers. Some workers in both plants showed clinical manifestations of lead poi-
soning; a significant correlation was found between blood lead levels and symptom reporting.
High levels of atmospheric lead are also found in foundries in which molten lead is al-
loyed with other metals. • Berg and Zenz (1967) found in one such operation that average con-
centrations of lead in various work areas were 280 to 600 pg/m3. These levels were sub-
sequently reduced to 30 to 40 pg/m3 with the installation of forced ventilation systems to
exhaust the work area atmosphere to the outside.
7.3.2.1.6.2 Welding and cutting of metals containing lead. When metals that contain lead or
are protected with a lead-containing coating are heated in the process of welding or cutting,
copious quantities of lead in the respirable size range may be emitted. Under conditions of
poor ventilation, electric arc welding of zinc silicate-coated steel (containing 4.5 mg Pb/cm2
of coating) produced breathing-zone concentrations of lead reaching 15,000 pg/m3, far in
excess of 450 pg/m3, which is the current occupational short-term exposure limit (STEL) in
the United States (Pegues, 1960). Under good ventilation conditions, a concentration of
140 pg/m3 was measured (Tabershaw et al., 1943).
In a study of salvage workers using oxyacetylene cutting torches on lead-painted struc-
tural steel under conditions of good ventilation, breathing-zone concentrations of lead aver-
aged 1200 pg/m3 and ranged as high as 2400 pg/m3 (Rieke, 1969). Lead poisoning in workers
023PB8/B
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dismantling a painted bridge has been reported by Graben et al. (1978). Fischbein et al.
(1978) discuss the exposure of workers dismantling an elevated subway line in New York City,
where the lead content of the paint is as great as 40 percent. The authors report that one
mm3 of air can contain 0.05 g lead at the source of emission. Similarly, Grandjean and Kon
(1981) report elevated lead exposures, of welders and other employees in a Baltimore, Maryland
shipyard.
7.3.2.1.6.3 Storage battery industry. At all stages in battery manufacture except for
final assembly and finishing, workers are exposed-to high air lead concentrations, particular-
ly lead oxide dust. For example, Boscolo et al. (1978) report air lead concentrations of
16-100 pg/m3 in a battery factory in.Italy, while values up to 1315 gg/m3 have been measured
by Richter et al. (1979) in an Israeli battery factory. Excessive concentrations, as great as
5400 pg/m3, have been reported by the World Health Organization (1977).
7.3.2.1.6.4 Printing industry. The use of lead in typesetting machines has declined in
recent years. Air concentrations of 10 to.30 pg/m3 have been reported where this technique is
used (Parikh et al., 1979). Lead is also a component of inks and dyes used in the printing
industry, and consequently can present a hazard to workers handling these products.
7.3.2.1.6.5 Alkyl lead manufacture. Workers involved in the manufacture of alkyl lead
compounds are exposed to both inorganic and alkyl lead. Some exposure also occurs at the
petroleum refineries where the two compounds are blended into gasoline, but no data are avail-
able on these blenders. . •
The major potential hazard in the manufacture of tetraethyl lead and tetramethyl lead is
from skin absorption, which is minimized by the use of protective clothing. Linch et al.
(1970) found a correlation between an index of organic plus inorganic lead concentrations in a
plant and the rate of lead excretion in the urine of workers. Significant concentrations of
organic lead in the urine were found in workers involved with both tetramethyl lead and tetra-
ethyl lead; lead levels in the tetramethyl lead workers were slightly higher because the reac-
tion between the organic reagent and lead alloy takes place at a somewhat higher temperature
and pressure than that employed in tetraethyl lead production.
Cope et al. (1979) used personal air samplers to assess exposures of five alkyl lead
workers exposed primarily to tetraethyl lead. Blood and urine levels were measured over a
six-week period. Alkyl lead levels ranged from 1.3 to 1249 pg/m3, while inorganic lead varied
from 1.3 to 62.6 pg/m3. There was no significant correlation between airborne lead (either
alkyl or inorganic) and blood or urine levels. The authors concluded that biological monito-
ring, rather than airborne lead monitoring, is a more reliable indicator of potential exposure
problems.
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7.3,2,1.6.6 Other occupations. In both the rubber products industry and the plastics
industry there are potentially high exposures to lead. The potential hazard of the use of
lead stearate as a stabilizer in the manufacture of polyvinyl chloride was noted in the 1971
Annual Report of the British Chief Inspector of Factories (United Kingdom Department of
Employment, Chief Inspector of Factories 1972). The inspector stated that the number of
reported cases of lead poisoning in the plastics industry was second only to that in the lead
smelting industry. Scarlato et al. (1969) reported other individual cases of exposure. The
source of this problem is the dust that is generated when the lead stearate is milled and
mixed with the polyvinyl chloride and the plasticizer. An encapsulated stabilizer which
greatly reduces the occupational hazard is reported by Fischbein et al. (1982).
Sakurai et al. (1974), in a study of bioindicators of lead exposure, found ambient air
concentrations averaging 58 pg/m3 in the lead-covering department of a rubber hose manufactu-
ring plant. U nfortunately, no ambient air measurements were taken for other departments or
the control group.
The manufacture of cans with leaded seams may expose workers to elevated ambient lead
levels. Bishop (1980) reports airborne lead concentrations of 25 to 800 pg/m3 in several can
manufacturing plants in the United Kingdom. Between 23 and 54 percent of the airborne lead
was associated with respirable particles, based on cyclone sampler data.
Firing ranges may be characterized by high airborne lead concentrations, hence instruc-
tors who spend considerable amounts of time in such areas may be exposed to lead, For exam-
ple, Smith (1976) reports airborne lead concentrations of 30 to 160 p/m3 at a firing range in
the United Kingdom. Anderson et al. (1977) discuss lead poisoning in a 17 year old male
employee of a New York City firing range, where airborne lead concentrations as great as 1000
pg/m3 were measured during sweeping operations. Another report from the same research group
presents time-weighted average exposures of instructors of 45 to 900 pg/m3 in three New York
City firing ranges (Fischbein et al., 1979).
Removal of leaded paint from walls and other surfaces in old houses may pose a health
hazard. Feldman (1978) reports an airborne lead concentration of 510 pg/m3, after 22 minutes
of sanding an outdoor post coated with paint containing 2.5 mg Pb/cm2. After only five min-
utes of sanding an indoor window sill containing 0.8 to 0.9 mg Pb/cm2, the air contained 550
pg/m3. Homeowners who attempt to remove leaded paint themselves may be at risk of excessive
lead exposure. Garage mechanics may be exposed to excessive lead concentrations. Clausen and
Rastogi (1977) report airborne lead levels of 0.2 to 35.5 pg/m3 in ten garages in Denmark; the
greatest concentration was measured in a paint workshop. Used motor oils were found to con-
tain 1500 to 3500 pg Pb/g, while one brand of unused gear oil contained 9280 pg Pb/g. The
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authors state that absorption through damaged skin could be an important exposure pathway.
Other occupations involving risk of lead exposure include stained glass manufacturing and re-
pair, arts and crafts, and soldering and splicing.
7.3.2.1.7 Secondary occupational exposure. Winegar et al. (1977) examined environmental con-
centrations as well as biological indicators and symptom reporting in workers in a secondary
lead smelter near St. Paul, Minnesota. The smelter recovers approximately 9000 metric tons of
lead per year from automotive batteries. The lead concentrations in cuff dust from trousers
worn by two workers were 60,000 and 600,000 mq/9- The amount of lead contained in pieces of
cloth 1 cm2 cut from the bottoms of trousers worn by the workers ranged from 110 to 3000 M9>
with a median of 410 pg. In all cases, the trousers were worn under coveralls. Dust samples
from 25 households of smelter workers ranged from 120 to 26,000 pg/g, with a median of 2400
pg/g. No significant correlations were found between dust lead concentrations and biological
indicators, or between symptom reporting and biological indicators. However, there was an in-
creased frequency of certain objective physical signs, possibly due to lead toxicity, with in-
creased blood lead level. The authors also concluded that the high dust lead levels in the
workers' homes are most likely due to lead originating in the smelter.
7.3.2.2 Additive Exposure Due to Age, Sex, or Socio-Economic Status.
7.3.2.2.1 Quality and quantity of food. The quantity of food consumed per body weight varies
greatly with age and somewhat with sex. A 14 kg, 2-year-old child eats and drinks 1.5 kg food
and water per day. This is 110 g/kg, or 3 times the consumption of an 80 kg adult male, who
eats 39 g/kg. Teenage girls consume less than boys and elderly women eat more than men, on a
body weight basis.
It is likely that poor people eat less frozen and pre-prepared foods, more canned foods.
Rural populations probably eat more home-grown foods and meats packed locally.
7.3.2.2.2 Mouthing behavior of children. Children place their mouths on dust collecting sur-
faces and lick non-food items with their tongues. This fingersucking and mouthing activity
are natural forms of behavior for young children which expose them to some of the highest con-
centrations of lead in their environment. A single gram of dust may contain ten times more
lead than the total diet of the child.
7.3.2.3 Special Habits or Activities.
7.3.2.3.1 Smoking. Lead is also present in tobacco. The World Health Organization (1977)
estimates a lead content of 2.5 to 12.2 pg per cigarette; roughly two to six percent of this
lead may be inhaled by the smoker. The National Academy of Sciences (1980) has used these
data to conclude that a typical urban resident who smokes 30 cigarettes per day may inhale
roughly equal amounts of lead from smoking and from breathing urban air.
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7.3.2.3.2 Alcoholic beverages. Reports of lead in European wines (Olsen et al., 1981;
Boudcne et al., 1975; Zurlo and Graffini, 1973) show concentrations averaging 100 to 200 (jg/1
and ranging as high as 300 |jg/l. Measurements of lead in domestic wines were in the range of
10C to 3C0 (jg/1 tor California wines with and without lead foil caps. The U.S. Food and Drug
Administration (1983) found 30 pg/1 in the 1982 Market Basket Survey. The average adult con-
<
sumption of table wine in the U.S. is about 12 g. Fven with a lead content of 0.1 |jg/g, which
is ten times higher than drinking water, wine does not appear to represent a significant
potential exposure to lead. At one i/day. however, lead consumption would be greater than the
total basel-'ne consumption.
McDonald (1981) points out that older wines with lead foil caps mey represent a hazard,
especially if they have been damaged or corroded. Wai et al. (1979) found that the lead con-
tent of wine rose from 200 to 1200 mq/ 1 when the wine was allowed to pass over the thin ring
of residue left by the corroded lead foil cap. Newer wines (1971 and later) use other means
of sealing. If a lead foil is used, the foil is tin-plated and coated with an acid-resistant
substance. Lead levels in beer are generally smaller than those in wine; Thalacker (1980)
reports a maximum concentration of 80 mq/1 in several brands of German beer. The U.S. Food
and Drug Administration (1983) found 13 pg/1 in beer consumed by Americans.
7.3.2.3.3 Pica. Pica is the compulsive, habitual consumption of non-food items, such as
paint chips and soil. This habit can present a significant lead exposure to the afflicted
person, especially to children, who are more apt to'have pica. There are very little data on
the amounts of paint or soil eaten by children with varying degrees of pica. Exposure can
only be expressed on a unit basis. Billick and Gray. (1978) report lead concentrations of 1000
to 5000 M9/cm2 in lead-based paint pigments. A single chip of paint can represent greater ex-
posure than any other source of lead to a child who has pica. A gram of urban soil may have
150 to 2000 [jg lead.
7.3.2.3.4 Glazed earthenware vessels. Another potential source of dietary lead poisoning is
the use of inadequately glazed earthenware vessels for food storage and cooking. An example
of this danger involved the severe poisoning of a family in Idaho which resulted from drinking
orange juice that had been stored in an earthenware pitcher (Block, 1969). Similar cases,
sometimes including fatalities, have involved other relatively acidic beverages such as fruit
juices and soft drinks, and have been documented by other workers (Klein et al,, 1970; Harris
and Elsen, 1967). Because of these incidents, the U.S. Food and Drug Administration (1979)
has established a maximum permissible concentration of 7 (jg Pb/g in solution after leaching
with 4 percent acetic acid in the earthenware vessel for 24 hours.
Inadequately glazed pottery manufactured in other countries continues to pose a signifi-
cant health hazard. For example, Spielholtz and Kaplan (1980) report 24 hour acetic
acid-leached lead concentrations as great as 4400 pg/g in Mexican pottery. The leached lead
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decreased with exposure time, and after several days appears to asymptotically approach a
value which may be as great as 600 pg/g. These investigators have also measured excessive
lead concentrations leached into acidic foods cooked for two hours in the same pottery.
Similarly, Acra et al. (1981) report that 85 percent of 275 earthenware vessels produced in
primitive Lebanese potteries had lead levels above the 7 jjg/g limit set by the U.S. FDA. How-
ever, only 9 percent of 75 vessels produced in a modern Beirut pottery exceeded the limit.
Cubbon et al. (1981) have examined properly glazed ceramic plates in the United Kingdom, and
have found a decrease in leached lead with exposure time down to very low levels. The authors
state that earthenware satisfying the 7 pg/g limit will contribute about 3 pg/day to the
dietary intake of the average consumer.
7.3.2.3.5 Hobbies. There are a few hobbies where the use of metallic lead or solder may pre-
sent a hazard to the user. Examples are electronics projects, stained glass window construc-
tion, and firing range ammunition recovery. There are no reports in which the exposure to
lead has been quantified during these activities.
7.3.3 Summary of Additive Exposure Factors
Beyond the baseline level of human exposure, additional amounts of lead consumption are
largely a matter of individual choice or circumstance. Many of these additional exposures
arise from the ingestion of atmospheric lead in dust. In one or more ways probably 90 percent
of the American population are exposed to lead at greater than baseline levels. A summary of
the most common additive exposure factors appears on Table 7-25. In some cases, the additive
exposure can be fully quantified and fhe.amount of lead consumed can be added to the baseline
consumption. These may be continuous (urban residence), or seasonal (family gardening) expo-
sures. Some factors can be quantified only on a unit basis because of wide ranges in exposure
duration or concentration. For example, factors affecting occupational exposure are air lead
concentrations (10 to 4000 MQ/m3), use and efficiency of respirators, length of time of expo-
sure, dust control techniques, and worker training in occupational hygiene.
7.4 SUMMARY
Ambient airborne lead concentrations have shown no marked trend from 1965 to 1977. Over
the past five years, however, distinct decreases have occurred. The mean urban air concentra-
tions has dropped from 0.91 jjg/m3 in 1977 to 0.32 Mg/ro3 in 19B0. These decreases reflect the
smaller lead emissions from mobile sources in recent years. Airborne size distribution data
indicate that most of the airborne lead mass is found in submicron particles.
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Atmospheric lead is deposited on vegetation and soi" surfaces, entering the human food
chain through contamination of grains and leafy vegetables, of pasture lands, and of soil
moisture taken up by all crops. Lead contamination of drinking water supplies appears to
originate mostly from within the distribution system.
Most people receive the largest portion of their lead intake through foods. Unprocessed
foods such as fresh fruits and vegetables receive lead by atmospheric deposition as well as
uptake from soil; crops grown near heavily traveled roads generally have greater lead levels
than those grown at greater distances from traffic. For many crops the edible internal por-
tions of the plant (e.g., kernels of corn and wheat) have considerably less lead than the
outer, more exposed parts such as stems, leaves, and husks. Atmospheric lead accounts for
about 30 percent of the total adult lead exposure, and 50 percent of the exposure for chil-
dren. Processed foods have greater lead concentrations than unprocessed foods, due to lead
inadvertently added during processing. Foods packaged in soldered cans have much greater lead
levels than foods packaged in other types of containers. About 45 percent of the baseline
adult exposure to lead results from the use of solder lead in packaging food and distributing
drinking water.
Significant amounts of lead in drinking water can result from contamination at the water
source ana from the use of lead solder in the water distribution system. Atmospheric deposi-
tion has been shown to increase lead in rivers, reservoirs, and other sources of drinking
water; in some areas, however, lead pipes pose a more serious problem. Soft, acidic water in
homes with lead plumbing may have excessive lead concentrations. Besides direct consumption
of the water, exposure may occur when vegetables and other foods are cooked in water contain-
ing lead,
All of the categories of potential lead exposure discussed above may influence or be in-
fluenced by dust and soil. For example, lead in street dust is derived primarily from vehic-
ular emissions, while leaded house dust may originate from nearby stationary or mobile
sources. Food and water may include lead adsorbed from soil as well as deposited atmospheric
material. Flaking leadbased paint has been shown to increase soil lead levels. Natural con-
centrations of lead in soil average approximately 15 |jg/g'» this natural lead, in addition to
anthropogenic lead emissions, influences human exposure.
Americans living in rural areas away from sources of atmospheric lead consume 50 to 75 pg
Pb/day from all sources. Circumstances which can increase this exposure are: urban residence
(25 to 100 pg/day), family garden on high-lead soil (800 to 2000 pg/day), houses with interior
lead-based paint (20 to 85 pg/day), and residence near a smelter (400 to 1300 |jg/day). Occu-
pational settings, smoking, and wine consumption also can increase consumption of lead accord-
ing to the degree of exposure.
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A number of manmade materials are known to contain lead, the most important being paint
and plastics. Lead-based paints, although no longer used, are a major problem in older homes.
Small children who ingest paint flakes can receive excessive lead exposure. Incineration of
plastics may emit large amounts of lead into the atmosphere. Because of the increasing use of
plastics, this source is likely to become more important. Other manmade materials containing
lead include colored dyes, cosmetic products, candle wicks, and products made of pewter and
silver.
The greatest occupational exposures are found in the lead smelting and refining indus-
tries. Excessive airborne lead concentrations and dust lead levels are occasionally found in
primary and secondary smelters; smaller exposures are associated with mining and processing of
the lead ores. Welding and cutting of metal surfaces coated with lead-based paint may also
result in excessive exposure. Other occupations with potentially high exposures to lead in-
clude the manufacture of lead storage batteries, printing equipment, alkyl lead, rubber pro-
ducts, plastics, and cans; individuals removing lead paint from walls and those who work in
indoor firing ranges may also be exposed to lead.
Environmental contamination by lead should be measured in terms of the total amount of
lead emitted to the biosphere. American industry contributes several hundred thousand tons of
lead to the environment each year: 35,000 tons from petroleum additives, 50,000 tons from am-
munition, 45,000 tons in glass and ceramic products, 16,000 tons in paint pigments, 8,000 tons
in food can solder, and untold thousands of tons of captured wastes during smelting, refining,
and coal combustion. These are uses of lead which are generally not recoverable, thus they
represent a permanent contamination of the human or natural environment. Although much of
this lead is confined to municipal and industrial waste dumps, a large amount is emitted to
the atmosphere, waterways, and soil, to become a part of the biosphere.
Potential human exposure can be expressed as the concentrations of lead in these environ-
mental components (air, dust, food, and water) that interface with man. It appears that, with
the exception of extraordinary cases of exposure, about 100 pg of lead are consumed daily by
each American. This amounts to only 8 tons for the total population, or less than 0.01 per-
cent of the total environmental contamination.
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E07REF/A
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PRELIMINARY DRAFT
APPENDIX 7A
SUPPLEMENTAL AIR MONITORING INFORMATION
7A.1 AIRBORNE LEAD SIZE DISTRIBUTION
In Section 7.2.1.3.1, several studies of the particle size distributions for atmospheric
lead were discussed. The distributions at forty locations were given in Figure 7-5. Supple-
mentary information from each of these studies is given in Table 7A-1.
7A.2 NONURBAN AIR MONITORING INFORMATION
Section . 7.2.1.1.1 describes ambient air lead concentrations in the United States,
emphasizing monitoring network data from urban stations. Table 7-2 gives the cumulative fre-
quency distributions of quarterly averages for urban stations. Comparable data for nonurban
stations are given in Table 7A-2. The trends shown by the two tables are similar, but the
numbers of reports for nonurban stations has decreased markedly since 1977. Table 7A-2 does
not include nonurban stations located near specific point sources. The detection limit has
decreased over the years, thus there are fewer reports of air concentrations below the
detection limit since 1975.
The distributions of annual averages among specific concentration intervals are given in
Table 7A-3 for nonurban stations. Comparable data were presented graphically in Figure 7-2
for urban stations.
7APPB/B
7A-1
43i<
7/1/83
-------
PRELIMINARY DRAFT
TABLE 7A-1. INFORMATION ASSOCIATED WITH THE AIRBORNE LEAD SIZE
DISTRIBUTIONS OF FIGURE 7-5
C
Graph ^ Approx.
no. Reference Dates of sampling Location of sampling Type of sampler pg/m3 MMD pm
Lee et al. (1972)
Jan. - Dec. 1970
Average of 4 quarterly
composited samples,
representing a total of
21 sampling periods of
24 hours each
Chicago, Illinois
Modified Anderson
impactor with backup
fiIter
3.2
0.68
Lee et al. (1972)
Lee et al. (1972)
Lee et al. (1972)
Mar. - Dec. 1970
Same averaging as
Graph 1, total of 18
sampling periods
Jan. - Dec. 1970
Same averaging as
Graph 1, total of
21 sampling periods
Mar. - Dec. 1970
Same averaging as
Graph 1, total of 20
sampline periods
Cincinnati, Ohio
Denver, Colorado
Philadelphia,
Pennsylvania
Modified Andersen 1.8
impactor with backup
filter
Modified Andersen 1.8
impactor with backup
fiIter
Modified Andersen 1.6
impactor with backup
fi1ter
0.48
0.50
0.47
Lee et al. (1972)
Lee et al. (1972)
Jan. - Dec. 1970
Same averaging as
Graph 1, total of 22
sampling periods
Jan. - Dec. 1970
Same averaging as
Graph 1, total of 23
sampling periods
St. Louis, Missouri
Washington, D.C.
Modified Andersen 1.8
impactor with backup
fiIter
Modified Andersen 1.3
impactor with backup
filter
0.69
0.42
-------
PRELIMINARY DRAFT
Graph
no Reference
Dates of sampling
Lee et al. (1968)
September 1966
Average of 14 runs,
24 hours each
10
11
12
13
14
Lee et al. (1968)
Peden (1977)
Peden (1977)
Peden (1977)
Peden (1977)
Peden (1977)
Peden (1977)
February 1967
.Average of 3 runs
,4 days each
Sumner 1975
Average of 4 runs,
average 8 days each
Summer 1972
Average of 3 runs,
average 10 days eacn
Summer 1973
Average of 2 runs
average 5 days each
Summer 1973
Average of 2 runs,
average 6 days each
Summer 1972
Average of 9 runs,
average 9 days each
Summer 1975
Average of 4 runs,
average 8 days each
TABLE 7A-1. (continued)
Location of sampling
Type of sampler
T
(jg/ra3
Approx.
HMO pm
Cincinnati, Ohio
Fairfax, Ohio
suburb of Cincinnati
Alton, Illinois,
industrial area near
St. Louis
Centreville, Illinois,
downwind of a zinc
smelter
Col 1insvi1le, Illinois
industrial area near
St. Louis
KMOX radio transmitter,
Illinois, industrial
area near St. Louis
Andersen impactor with 2.8
backup filter, 1.2m
above the ground
Andersen impactor with 0.69
backup filter, 1.2m
above the ground
Andersen impactor 0.24
no backup filter
Andersen impactor 0.62
with backup fiIter
Andersen impactor 0.67
with backup fiIter
Andersen impactor 0.60
wi th backup fi1ter
0.29
0.42
2.1
0.41
0.24
0.31
Pere Marquette State
Park, 111i on is. upwind
of St. Louis
Andersen impactor
with backup filter
0.15
0.51
Wood River, Illinois,
industrial area near
St. Louis
Andersen impactor,
no backup filter
0.27
1.8
-------
PRELIMINARY DRAFT
TABLE 7A-1 (continued)
C
Graph T Approx.
no Reference Dates of sampling Location of sampling Type of sampler pg/m3 MMD pm
15
16
17
18
19
20
21
22
Cholak et al.
(1968)
McDonald and
Duncan (1979)
Dorn et al. (1976)
Dorn et al. (1976)
Daines et al.
(1970)
Martens et al.
(1973)
Lundgren (1970)
Huntzicker et al.
(1975)
April 1968
average of several runs,
3 days each
June 1975
One run of 15 days
Winter, spring,
summer 1972
Average of 3 runs,
27 days each
Winter, spring,
summer 1972
Average of 3 runs,
14 days each
1968
Average of continuous
1-week runs over an
8-nonth period
July 1971
One run of 4 days
November 1968
Average of 10 runs,
16 hours each
May 1973
One run of 8 hours
3 sites: 10,400 and
3300m from Interstate
75, Cincinnati, Ohio
Glasgow, Scotland
Southeast Missouri,
800m from a lead
smelter
Southeast Missouri,
75 km from the lead
smelter of Graph 17
3 sites: 9, 76, and
530m from U.S. Route 1,
New Brunswick,
New Jersey
9 sites throughout
San Francisco area
Riverside, California
Shoulder of Pasadena
Freeway near downtown
Los Angeles, California
Andersen impactor
with backup filter
"i
Casella impactor
with backup fiIter,
30m above the ground
Andersen impactor,
no backup filter,
1.7m above the ground
Andersen impactor,
no backup filter,
1.7m above the ground
7.8*
1.7
1.1
0.53
1.0
0.11
Cascade impactor with 4.5
backup filter 2.2
1.5
Andersen impactor 0.84
with backup filter
Lundgren impactor 0.59
Andersen impactor 14.0
with backup filter,
2m above the ground ...
0.32
0.51
3.8
2.4
0.35
0.49
0.50
0.32
-------
PRELIMINARY DRAFT
Graph
no Reference Dates of sampling
23
Huntzicker et al.
(1975)
Februray 1974
One run of 6 days
24
Davidson (1977)
May and July 1975
Average of 2 runs,
61 hours each
25
Davidson et al.
(19B0)
October 1979
One run of 120 hours
26
Davidson et al.
(1981a)
July-Sep. 1979
Average of 2 runs,
90 hours each
27
Davidson et al.
(1981b)
December 1979
One run of 52 hours
28
GooId and
Davidson (1982)
June 1980
One run of 72 hours
29
Goold and
Davidson (1982)
July 1980
One run of 34 hours
TABLE 7A-1 (continued)
C
I Approx.
Location of sampling Type of sampler pg/m3 MMD pm
Pasadena, California
Pasadena, California
Clingman's Dome
Great Smokies National
Park, elev. 2024m
Andersen impactor 3.5
with backup filter,
on roof of 4 story
building
Modified Andersen 1.2
impactor with backup
filter on roof of 4
story building
2 Modified Andersen 0.014
impactors with backup
filters, 1.2m above
the ground
0. 72
0.97
1.0
Pittsburgh, Pennsylvania
Nepal Himalayas
elev. 3962m
Modified Andersen 0.60
impactor with backup
filter, 4m above the
ground
Modified Andersen 0.0014
impactor with backup
filter, 1.2m above
the ground
0.56
0.54
Export, Pennsylvania
rural site 40 km
east of Pittsburgh
Packwood, Washington
rural site in Gifford
Pinchot National Forest
2 Modified Andersen 0.111
impactors with backup
filters, 1.2m above
the ground >
Modified Andersen 0.016
impactor with backup
fiIter, 1.5m above
the ground 1
1.2
0.40
-------
PRELIMINARY DRAFT
Graph
no Reference Dates of sampling
30
Goold and
Davidson (1982)
July-Aug. 1980
One run of 92 hours
31
Ouce et at
(1976)
May - June 1975
One run of 112 hours
32
Ouce et al.
(1976)
July 1975
One run of 79 hours
33
Harrison et al.
(1971)
April 1968
Average of 21 runs,
2 hours each
34
Gillette and
Winchester (1972)
Oct. 1968
Average of 15 runs,
24 hours each
35
Gillette and
Winchester (1972)
May - Sept. 1968
Average of 10 runs,
8 hours each
36 Gillette and
Winchester (1972)
Oct. 1968
Average of 3 runs,
24 hours each
37
Johansson et al.
(1976)
June - July 1973
Average of 15 runs,
average 50 hr each
TABLE 7A-1 (continued)-
Location of sampling
Type of sampler
C
T
pg/m-'1
Approx.
MMD pm
Hurricane Ridge
Olympic National
Park elev. 1600m
Southeast coast of
Bermuda
Southeast coast of
Bermuda
Ann Arbor, Michigan
Ann Arbor, Michigan
Modified Andersen 0.0024
impactor with backup
fiIter, 1.5m above
the ground
Sierra high-volume 0.0085
impactor with backup
filter, 20m above the
ground
Sierra high-volume 0.0041
impactor with backup
filter. 20m above the
ground
Modified Andersen 1.8
impactor with backup
filter, 20m above the
ground
Andersen impactor with 0.82
backup filter
0.87
0.57
0.43
0. 16
0.28
Chicago, Illinois
Andersen impactor with
backup filter
1.9
0. 39
Lincoln, Nebraska
Andersen impactor with 0.14
backup filter
0.42
2 sites in Tallahassee,
Florida
Delron Battelle-type 0.24
impactor, no backup
filter, on building roofs
0.62
-------
PRELIMINARY DRAFT
TABLE 7A-1 (continued)
C
Graph
T
Approx.
no
Reference
Dates of sampling
Location of sampling
Type of sampler
(jg/m3
MMD pm
38
Cawse et a).
July - Dec. 1973
Chilton, England
Andersen impactor with
0.16
0.57
(1974)
backup filter, 1.5m above
the ground
39
Pattenden et al.
May - Aug. 1973
Trebanos, England
Andersen Impactor with
0.23
0.74
(1974)
Average of 4 runs,
backup filter, 1.5m above
I month each
the ground
40
Bernstein and
Aug. 1976
New York City
Cyclone sampling
1.2
0.64
Rahn (1979)
Average of 4 runs,
system with backup
1 week each
filter, on roof on
15 story building
"Airborne concentrations for filters run at the sane sites as the impactor, but during different tine periods.- Inpactor'concentrations not available.
-------
TABLE 7A-2. CUMULATIVE FREQUENCY DISTRIBUTIONS OF QUARTERLY LEAD MEASUREMENTS
AT NONURBAN STATIONS BY YEAR, 1970 THROUGH 1980
(pg/m3)
_ . Arithmetic Geometric
Percent!le —
Std. Std.
Year No. of Minimum 10 30 50 70 90 95 99 Max. Mean dev. Mean dev.
station qtrly. qtrly.
reports avg. avg.
1970
124
LD
LD
LD
LD
LD
0.267
0. 383
0.628
1.471
--
--
--
--
1971
85
LD
LD
LD
LD
LD
0. 127
0.204
0.783
•1.134
•—
--
--
--
1972
137
LD
LD
LD
0.107
0.166
0.294
0.392
0.950
1.048
0. 139
0.169
0.90
2. 59
1973
100
LD
LD
LD
LD
0. 132
0.233
0. 392
0.698
0.939
—
--
--
--
1974
79
LD
LD
0.053
0.087
0.141
0.221
0.317
0.496
0.534
0. Ill
0.111
0.083
2.30 ,
1975
98
LD
LD
LD
LD
0. 144
0.255
0.311
0.431
0.649
--
—
— ¦
--
1976
98
LD
LD
LD
LD
0.105
0.240
0.285
0.336
0.483
--
--
—
1977
84
0.006
0.01
0. 04
0.08
0. 11
0.18
0.20
0.25
0.40
0.09
0. 10
0.07
3. 19
1978
20
0.002
0.007
0.04
0.06
0.09
0.24
0.33
0 . 33
0. 33
0.08
0.10
0.07
2.84
1979
16
LD
0.02
0.02
0.10
0. 14
0.21
0.27
0.32
0.11
0.11
0.13
0. 11
3.45
1980
12
LD
0.01
0.005
0.03
0.05
0.11
0.13
0.13
0. 13
0.04
0.06
0.05
3. 33
Sources: Akland (1976); U.S. Environmental Protection Agency (1978; 1979); Quarterly averages of Lead from NFAN
(1982).
-------
Year
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
Sour*
PRELIMINARY DRAFT
TABLE 7A-3. NUMBER OF NASN NONURBAN STATIONS WHOSE DATA FALL WITHIN
SELECTED ANNUAL AVERAGE LEAD CONCENTRATION INTERVALS, 1966-1980
Concentration interval, pg/m3
<0.03
0.03-0.096
0.10-0.19
0.20-0.45
Tota
No. stations
• »
10
6
3
19
Percent
52
32
16
100
No. stations
1
7
10
2
20
Percent
5
- 35
50
10
100
No. stations
1
15
4
20
Percent
5
75
20
—
100
No. stations
11
9
1
21
Percent
—
52
43
5
100
No. stations
7
3
10
Percent
¦
70
30
100
No. stations
10
4
9
11
34
Percent
29
12
26
33
100
No. stations
9
7
6
1
23
Percent
39
31
26
4
100
No. stations
3
5
6
2
16
Percent
19
31
38
12
100
No. stations
0
0
1
4
5
Percent
0
0
20
80
100
No. stations
0
0
3
3
6
Percent
0
0
50
50
100
No. stations
5
8
7
1
21
Percent
24
38
33
5
100
No. stations
1.
3
1
0
5
Percent
' 20
60
20
0
100
No. stations
1
1
1
1
4
Percent
25
. 25
25
25
100
No. stations
1
2
0
0
3
Percent
33
67
0
0
100
Akland (1976); Shearer et al. (1972); U.S. Environmental Protection Agency (1978;
1979); Annual averages of lead from NFAN (1982).
7A-9 7/1/83
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APPENDIX 7B
SUPPLEMENTAL SOIL AND DUST INFORMATION
Lead in soil, and dust of soil origin, is discussed in Section 7.2.2. The data shov.
average soil concentrations are 8 to 25 pg/g, and dust from this soil rarely exceeds 80 to 100
|jg/g. Street dust, household dust and occupational dusts often exceed this level by one to
two orders of magnitude. Tables 7B-1 and 7B-2 summarizes several studies of sjtreet dust.
Table 7B-3 shows data on household and residential soil dust. These data support the
estimates of mean lead concentrations in dust discussed in Section 7.3.1.4. Table 7B-4 gives
airborne lead concentrations for an occupational setting, which are only qualitatively related
to dust lead concentrations.
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TABLE 7B-1. LEAD OUST
ON AND NEAR HEAVILY
TRAVELED ROADWAYS
Sampling site
Concentration,
M9 Pb/g
Reference
Washington, DC:
Busy intersection
Many sites
13,000
4000-8000
Fritsch and Prival (1972)
Chicago:
Near expressway
6600
Phi 1adelphia:
Near expressway
3000-800D
Kennedy (1973)
Brooklyn:
Near expressway
900-4900
Lombardo (1973)
New York City:
Near expressway
2000
Pinkerton et al. (1973)
Detroi t:
Street dust
970-1200
Ter Haar and Aronow (1974)
Phi 1adelphia:
Gutter (low pressure)
Gutter (high pressure)
1500
210-2600
3300
280-8200
Shapiro et al. (1973)
Shapiro et al. (1973)
Miscellaneous U.S. Cities:
Highways and tunnels
10,000-20,000
Buckley et al. (1973)
Netherlands:
Heavily traveled roads
5000
Rameau (1973)
TABLE 7B-2. LEAD CONCENTRATIONS IN STREET OUST IN
LANCASTER, ENGLAND
No. of Range of
Site samples concentrations.
Standard
Mean deviation
Car parks 4 39,700 - 51,900
16 950 - 15,000
46,300 5,900
4,560 3,700
Garage forecourts 2 44,100 - 48,900
7 1,370-4,480
46,500
2,310 1,150
Town centre streets 13
840 - 4,530
2,130 960
Main roads 19
740 - 4,880
1,890 1,030
Residential areas 7
620 - 1,240
850 230
Rural roads 4
410 - 870
570 210
Source: Harrison (1979).
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TABLE 7B-3.
LEAD DUST IN,RESIDENTIAL
AREAS
Sampling site
Concentrate on,
pg Pb/g
Reference
Philadelphia:
CIassroom
Playground
Window frames
2000
3000
1750
Shapiro et al.
(1973)
Boston and New York:
House dust
1000-2000
Needleman and Scanlon (1973)
Brattleboro, VT:
In home
500-900
Darrow and Schroeder (1974)
New York City:
Middle Class
Residential
"610-740
Pinkerton et al
. (1973)
Philadelphia:
Urban industrial
Residential
Suburban
3900
930-16,000
610
290-1000
830
. 280-1500
Needleman et al
Needleman et al
Needleman et al
. (1974)
. (1974)
. (1974)
Derbyshire, England:
Low soil lead area
High soil lead area
"M^o-
130-3000
4900
1050-28,000
Barltrop et al.
Barltrop et al.
(1975)
(1975)
TABLE 7B-4. AIRBORNE LEAD CONCENTRATIONS BASED ON PERSONAL SAMPLERS, WORN BY
EMPLOYEES AT A LEAD MINING AND GRINDING OPERATION IN THE MISSOURI
LEAD BELT
Air lead concentration (pg/m3)
Occupati on
N
'¦High
Low
Mean
Mill operator
6 . .
300
50
180
Flotation operator
4 .
.750
100
320
Filter operator
4
2450
380
1330
Crusher operator
4
590
20
190
Sample finisher
2
10,000
7070
8530
Crusher utility
1
--
--
70
Shift boss
5
560
110
290
Equipment operator
1
--
--
430
N denotes number of air samples.
Source: Roy (1977).
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APPENDIX 7C
STUDIES OF SPECIFIC POINT SOURCES
OF LEAD
This collection of studies is intended to extend and detail the general picture of lead
concentrations in proximity to identified major point sources as portrayed in Chapter 7.
Because emissions and control technology vary between point sources, each point source is
unique in the degree of environmental contamination. The list is by no means all-inclusive,
but is intended to be representative and to supplement the data cited in Chapter 7. In many
of the studies, blood samples of workers and their families were taken. These studies are
also discussed in Chapter 11.
7C.1 SMELTERS AND MINES
7C.1.1 Two Smelter Study
The homes of workers of two unidentified secondary lead smelters in different geograph-
ical areas of the United States were studied by Rice et al. (1978). Paper towels were used to
collect dust from surfaces in each house, following the method of Vostal et al. (1974). A
total of 33 homes of smelter workers and 19 control homes located in the same or similar
neighborhoods were investigated. The geometric mean lead levels on the towels were 79.3 jjg
(smelter workers) versus 28.8 pg (controls) in the first area, while in the second area mean
values were 112 pg versus 9.7 pg. Also in the second area, settled dust above doorways was
collected by brushing the dust into glassine envelopes for subsequent analysis. The geometric
mean lead content of this dust in 15 workers' homes was 3300 pg/g, compared with 1200 pg/g
in eight control homes. Curbside dust collected near each home in the second area had a
geometric mean lead content of 1500 jjg/g. with no significant difference between worker and
control homes. No significant difference was reported in the paint lead content between
worker and control homes. The authors concluded that lead in dust carried home by these
workers contributed to the lead content of dust in their homes, despite showering and changing
clothes at the plant, and despite work clothes being laundered by the company. Storage of
employee street clothes in dusty lockers, walking across lead-contaminated areas on the way
home, and particulate settling on workers' cars in the parking lot may have been important
factors. Based on measurement of zinc protoporphyrin levels in the blood of children in these
homes, the authors also concluded that the greater lead levels in housedust contributed to in-
creased child absorption of lead.
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7C.1.2 British Columbia, Canada
Neri et al. (1978) and Schmitt et al. (1979) examined environmental lead levels in the
vicinity of a lead-zinc smelter at Trail, British Columbia. Total emissions from the smelter
averaged about 135 kg Pb/day. Measurements were conducted in Trail (population 12,000), in
Nelson, a control city 41 kilometers north of Trail (population 10,000), and in Vancouver.
The annual mean airborne lead concentrations in Trail and in Nelson were 2.0 and 0.5 pg/m3,
respectively. Mean lead levels in surface soil were 1320 pg/g in Trail (153 samples), 192
pg/g in Nelson (55 samples), and 1545 pg/g in Vancouver (37 samples).
Blood lead measurements shows a positive correlation with soil lead levels for children
aged 1-3 years and for first graders, but no significant correlation for ninth graders. The
authors concluded that small children are most likely to ingest soil dust, and hence deposited
smelter-emitted lead may pose a potential hazard for the youngest age group.
7C.1.3 Netherlands
Environmental lead concentrations were measured in 1978 near a secondary lead smelter in
Arnhem, Netherlands (Diemel et al., 1981). Air and dust were sampled in over 100 houses at
distances of 450 to 1000 meters from the smelter, with outdoor samples of air, dust, and soil
collected for comparison. Results are presented in Table 7C-1. Note that the mean indoor
concentration of total suspended particulates (TSP) is greater than the mean outdoor concen-
tration, yet the mean indoor lead level is smaller than the corresponding outdoor level. The
authors reasoned that indoor sources such as tobacco smoke, consumer products, and decay of
furnishings are likely to be important in affecting indoor TSP; however, much of the indoor
lead was probably carried in from the outside by the occupants, e.g., as dust adhering to
shoes. The importance of resuspension of indoor particles by activity around the house was
also discussed.
7C.1.4 Belgium
Roels et al. (1978; 1980) measured lead levels in the air, in dust, and on childrens1
hands at varying distances from a lead smelter in Belgium (annual production 100,000 metric
tons). Blood data from children living near the smelter were also obtained. Air samples were
collected nearly continuously beginning in September 1973. Table 7C-2 lists the airborne con-
centrations recorded during five distinct population surveys between 1974 and 1978, while
Figure 7C-1 presents air, dust, and hand data for Survey #3 in 1976. Statistical tests showed
that blood lead levels were better correlated with lead on childrens1 hands than with air
lead. The authors suggested that ingestion of contaminated dust by hand-to-mouth activities
7APPB/D
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such as nail-biting and thumb-sucking, as well as eating with the hands, may be an important
exposure pathway. It was concluded that intake from contaminated hands contributes at least
two to four times as much lead as inhalation of airborne material.
TABLE 7C-1. LEAD CONCENTRATIONS IN INDOOR AND OUTDOOR AIR, INDOOR AND OUTDOOR
DUST, AND OUTDOOR SOIL NEAR THE ARNHEM, NETHERLANDS SECONDARY LEAD SMELTER
(INDOOR CONCENTRATIONS)
Arithmetic
*
Parameter
mean
Range
n
Suspended particulate matter
dust concentration (pg/m3)
140
20-570
101
lead concentration (pg/m3)
0.27
0.13-0.74
101
dust lead content (pg/kg)
2670
400-8200
106
Dustfal1
dust deposition (mg/m3iday)
15.0
1.4-63.9
105
lead deposition (pg/m3-day)
9.30
1.36-42.4
105
dust lead content (mg/kg)
1140
457-8100
105
Floor dust
amount of dust (mg/m3)
356
41-2320
107
amount of lead (pg/m3)
166
18-886
101
Dust lead content (mg/kg)
in "fine" floor dust
1050
463-4740
107
in "coarse" floor dust
370
117-5250
101
*N number of houses.
(OUTDOOR CONCENTRATIONS)
Parameter
Arithmetic mean
Range
Suspended particles
dust concentration (pg/m3)
lead concentraton (pg/m3)
(high-volume samplers, 24-hr
samples, 2 months' average)
Lead in dustfal1
(pg/m3-day)
(deposit gauges, weekly
samples, 2 months' average)
Lead in soil
(mg/kg 0-5 cm)
Lead 1n streetdust
(mg/kg <0.3 mm)
64.5
0.42
508
322
860
53.7-73.3
0.28-0.52
208-2210
21-1130
77-2670
Source: Dlemel et al (1981).
7APPB/D
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Pb IN AIR | | | |
0 12 3 MQ/m'
Pb IN DUST L I I I
0 760 1500 2260 Mfl'a
Pb ON HAND I ; I I I
0 160 300 460 pg/hand
AT LESS THAN 1km FROM LEAD SMELTER
1
' 111
II
1
1 1
II
1
fill
—1
AT 25 km FROM LEAD SMELTER
26 cr
16
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PRELIMINARY DRAFT
TABLE 7C-2. AIRBORNE CONCENTRATIONS OF LEAD DURING FIVE
POPULATION SURVEYS NEAR A LEAD SMELTER IN BELGIUM*
Pb-Ai r
Study populations (|jg/f3)
1
Survey
<1 km
4.06
(1974)
2.5 km
1.00
Rural
0.29
2
Survey
<1 km
2.94
(1975)
2.5 km
0.74
Rural
3
Survey
<1 km
3.67
(1976)
2.5 km
0.80
Urban
0.45
Rural
0.30
4
Survey
<1 km
3.42
(1977)
2.5 km
0.49
5
Survey
<1 km
2.68
(1978)
2.5 km
0.54
Urban
0.56
Rural
0.37
^Additional airborne data in rural and urban areas obtained as controls are also shown.
Source: Roels et al. (1980).
7C.1.5 Meza River Valley, Yugoslavia
In 1967, work was initiated in the community of Zerjav, situated in the Slovenian Alps on
the Meza River, to investigate contamination by lead of the air, water, snow, soil, vegeta-
tion, and animal life, as well as the human population. The mselter in this community pro-
duces about 20,000 metric tons of lead annually; until 1969 the stack emitted lead oxides
without control by filters or other devices. Five sampling sites with high-volume samplers
operating on a 24-hr basis were established in the four principal settlements within the Meza
River Valley (Figure 7C-2): (1) Zerjav, in the center, the site of the smelter, housing 1503
inhabitants, (2) Rudarjevo, about 2 km to the south of Zerjav with a population of 100;
(3) Crna, some 5 km to the southwest, population 2198, where there are two sites (Crna-SE and
Crna-W); and (4) Mezica, a village about 10 km to the northwest of the smelter with 2515
7APPB/D 7C-5 7/1/83
447<
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PRELIMINARY DRAFT
inhabitants. The data in Table 7C-3 are sufficient to depict general environmental contami-
nation of striking proportions.
7C.1.6 Kosova Province, Yugoslavia
Popovac et al. (1982) discuss lead exposure in an industrialized region near the town of
Kosova Mitrovica, Yugoslavia, containing a lead smelter and refinery, and a battery factory.
In 1979, 5800 kg of lead were emitted daily from the lead smelter alone. Ambient air concen-
trations in the town were in the range 21.2 to 29.2 pg/m3 in 1980, with levels occasionally
reaching 70 pg/m3. The authors report elevated blood lead levels in most of the children
tested; some extremely high values were found, suggesting the presence of congenital lead
poi soni ng.
7C.1.7 Czechoslovak!" a
Wagner et al. (1981) measured total suspended particulate and airborne lead concentra-
tions in the vicinity of a waste lead processing plant in Czechoslovakia. Data are shown in
Table 7C-4. Blood lead levels in 90 children living near the plant were significantly greater
than in 61 control children.
7C.1.8 Australia
Heyworth et al. (1981) examined child response to lead in the vicinity of a lead sulfide
mine in Northhamptom Western Australia. Two samples of mine tailings measured in 1969
contained 12,000 pg/g and 28,000 pg/g lead; several additional samples analyzed in 1978 con-
tained 22,000 pg/g to 157,000 pg/g lead. Surface soil from the town boundry contained 300
pg/g, while a playground and a recreational area had soil containing 11,000 pg/g and 12,000
pg/g lead respectfully.
Blood lead levels measured in Northhamptom children, near the mine, were slightly greater
than levels measured in children living a short distance away. The Northhampton blood lead
levels were also slightly greater than those reported for children in Victoria, Australia
(DeSilva and Donnan, 1980). Heyworth et al. concluded that the mine tailings could have
increased the lead exposure of children living in the area.
7C.2 BATTERY FACT0RIE5
7C.2.1 Southern Vermont
Watson et al. (1978) investigated homes of employees of a lead storage battery plant in
southern Vermont in August and September, 1976. Lead levels in household dust, drinking
water, and paint were determined for 22 workers' homes and 22 control homes. The mean lead
7APPB/D 7C-6 7/1/83
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t )'J A v A W j
D SMi i iiNii Plant
PRIST AV A
— Rivl AS
mnup it III I Ml NT S
Figure 7C-2. Schematic plan of lead mine and smelter from Meza Valley,
Yugoslavia, study.
Source: Fugas(1977).
7APPB/D 7C-7 7/1/83
443<
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PRELIMINARY DRAFT _
Table 7C-3. ATMOSPHERIC LEAD CONCENTRATIONS (24-hour) IN THE
MEZA VALLEY, YUGOSLAVIA, NOVEMBER 1971 TO AUGUST 1972
Pb concentration, nQ/m3
Site Minimum Maximum Average
Mezica
0.1
236.0
24.2
Zerjav
0.3
216.5
29.5
Rudarjevo
0.5
328.0
38.4
Crna SE
0.1
258.5
33.7
Crna W
0.1
222.0
28.4
Source: Fugas (1977).
TABLE 7C-4. CONCENTRATIONS OF TOTAL AIRBORNE DUST AND OF AIRBORNE LEAD IN THE
VICINITY OF A WASTE LEAD PROCESSING PLANT IN CZECHOSLOVAKIA,
AND IN A CONTROL AREA INFLUENCED PREDOMINANTLY BY AUTOMOBILE EMISSIONS
TSP
Lead
Exposed
n
300
303
x (pg/m3)
113.6
1.33
S
83.99
1.9
range
19.7-553.4
0.12-10.9
95% c.i.
123.1-104.1
1.54-1.11
Control
n
56.0
87
x (pg/m3)
92.0
0.16
S
40.5
0.07
range
10-210
0.03-0.36
95% c.i.
102.7-81.3
0.17-0.14
n = number of samples; x = mean of 24~hour samples;
s = standard deviation; 95% confidence interval.
Source: Wagner et al. (1981).
/
7APPB/D 7C-8 7/1/83
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concentration in dust in the workers' homes was 2,200 pg/g, compared with 720 pg/g in the
control homes. Blood lead levels in the workers' children were greater than levels in the
control children, and were significantly correlated with dust lead concentrations. No sig-
nificant correlations were found between drinking water lead and blood lead, or between paint
lead and blood lead. It is noteworthy that although 90 percent of the employees showered and
changed clothes at the plant, 87 percent brought their work clothes home for laundering. The
authors concluded that dust carried home by the workers contributed to increased lead absorp-
tion in their children.
7C.2.2 North Carolina
Several cases of elevated environmental lead levels near point sources in North Carolina
have been reported by Dolcourt et al. (1978; 1981). In the first instance, dust lead was
measured in the homes of mothers employed in a battery factory in Raleigh; blood lead levels
in the mothers and their chldren were also measured. Carpet dust was found to contain 1,700
to 4-8,000 pg/g lead in six homes where the children had elevated blood lead levels (>40
|jg/dl). The authors concluded that lead carried home on the mothers' clothing resulted in
increased exposure to their children (Dolcourt et al., 1978). In this particular plant, no
uniforms or garment covers were provided by the factory; work clothing was worn home.
In a second case, discarded automobile battery casings from a small-scale lead recovery
operation in rural North Carolina were brought home by a worker and used in the family's
wood-burning stove (Dolcourt et al. , 1981). Two samples of indoor dust yielded 13,000 and
41,000 |jg/g lead. A three-year-old girl living in the house developed encephalopathy
resulting in permanent brain damage.
In a third case, also in rural North Carolina, a worker employed in an automobile battery
reclamation plant was found to be operating an illicit battery recycling operation in his
home. Reclaimed lead was melted on the kitchen stove. Soil samples obtained near the house
measured as high as 49 percent lead by weight; the driveway was covered with fragments of
battery casings. Although no family member had evidence of lead poisoning, there were
unexplained deaths among chickens who fed where the lead waste products were discarded
(Dolcourt et al., 1981).
7C.2.3 Oklahoma
Morton et al. (1982) studied lead exposure in children of employees at a battery manu-
facturing plant in Oklahoma. A total of 34 lead-exposed children and 34 control children were
examined during February and March, 1978; 18 children in the lead-exposed group had elevated
blood lead levels (>30 |jg/dl), while none of the controls were in this category.
7APPB/D
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7/1/83
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preliminary draft
It was found that many of the battery factory employees also used lead at home, such as
casting lead into fishing sinkers and using leaded ammunition. A significant difference in
blood lead levels between the two groups of children was found even when families using lead
at home were deleted from the data set. Using the results of personal interviews with the
homemaker in each household, the authors concluded that- dust carried home by the employees
resulted in increased exposure of their children. Merely changing clothes at the plant was
deemed insufficient to avoid transporting appreciable amounts of lead home: showering and
shampooing, in addition to changing clothes, was necessary.
7C.2.4 Oakland, California
Environmental lead contamination at the former site of wet-cell battery manufacturing
plant in Oakland, California was reported by Wesolowski et al. (1979). The plant was opera-
tional from 1924 to 1974, and was demolished in 1976. Soil lead levels at the site measured
shortly after demolition are shown in Table 7C-5. The increase in median concentrations with
depth suggested that the battery plant, rather than emissions from automobiles, were respons-
ible for the elevated soil lead levels. The levels decreased rapidly below 30 cm depth. The
contaminated soil was removed to a sanitary landfill and replaced with clean soil; a park has
subsequently been constructed at the site.
TABLE 7C-5. LEAD CONCENTRATIONS IN SOIL AT THE FORMER SITE OF A WET-CELL
BATTERY MANUFACTURING PLANT IN OAKLAND, CALIFORNIA
Depth
N
Range
Mean
Medi an
Cmg/g)
(pg/g)
(pg/g)
Surface
24
57-96,000
4300
200
15 cm
23
13-4200
370
200
30 cm
24
13-4500
1100
360
Source: Wesolowski et al. (1979).
7C.2.5 Manchester, England
Elwood et al. (1977) measured lead concentrations in air, dust, soil, vegetation, and tap
water, as well as in the blood of children and adults, in the vicinity of a large battery
factory near Manchester. It was found that lead levels in dust, soil, and vegetation
decreased with increasing distance from the factor. Airborne lead concentrations did not show
a consistent effect with downwind distance, although higher concentrations were found downwind
7APPB/D
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PRELIMINARY DRAFT
compared with upwind of the factor. Blood lead levels were greatest in the households of
battery factor employees: other factors such as distance from the factory, car ownership, age
of house, and presence of lead water pipes were outweighed by the presence of a leadworker in
the household. These results strongly suggest that lead dust carried home by the factor
employees is a dominant exposure pathway for their families. The authors also discussed the
work of Burrows (1976), who demonstrated experimentally that the most important means of lead
transport from the factory into the home is via the workers' shoes.
7APPB/D
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I
1 '
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APPENDIX 7D
SUPPLEMENTAL DIETARY INFORMATION FROM THE
U.S. FDA TOTAL DIET STUDY
The U.S. Food and Drug Administration published a new Total Diet Food List (Pennington,
1983) based on over 100,000 daily diets from 50,000 participants. Thirty five hundred
categories of foods were condensed to 201 adult food categories for 8 age/sex groups.
Summaries of these data were used in Section 7.3.1.2 to arrive at lead exposures through food,
water, and beverages. For brevity and continuity with the crop data of Section 7.2.2.2.1, it
was necessary to condense the 201 categories of the Pennington study to 25 categories in this
report.
The preliminary lead concentrations for all 201 items of the food list were provided by
U.S. Food and Drug Administration (1983). These data represent three of the four Market
Basket Surveys, the fourth to be provided at a later time. Means of these values have been
calculated by EPA, using one-half the detection limit for values reported be-low detection
limit. These data appear in Table 7D-1.
In condensing the 201 categories of Table 7D-1 to the 2b categories of Table 7-15,
combinations and fractional combinations of categories were made according to the scheme of
Table 7D-2. In this way, specific categories of food more closely identified with farm
products were summarized. The assumptions made concerning the ingredients in the final
product, (mainly water, flour, eggs, and milk) had little influence on the outcome of the
summarization.
7APPB/E
7D-1
454 <
7/1/83
-------
; i
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
PRELIMINARY'DR'AFTron
TABLE 7D-1. FOOD LIST AND PRELIMINARY LEAD CONCENTRATIONS
Food Lead concentration* Mean*
(ng/g)
Whole milk
0.01
Low fat milk
0.02
T
T
0.017
Chocolate milk
0.04
0.02
Skim milk
0.01
Butter milk
0.01
Yogurt, plain
0.01
Mi 1kshake
0.06
0.05 .
0.04
Evaporated milk
0.08
0.07
0.18
0.11
Yogurt, sweetened
0.04
0.02
Cheese, American
0.03
0.97
Cottage cheese
0.05
0.023
Cheese, Cheddar
0.04
0.020
Beef, ground
0.11
0.043
Beef, chuck roast
0.09
0.03
0.043
Beef, round steak
0.01
Beef, sirloin
0. 01
Pork, ham
0.03
0.017
Pork chop
0.03
0.017
Pork sausage
0.03
0.05
0.030
Pork, bacon
0.05
0.22 .
0.093
Pork roast
0.01
Lamb chop
0.03
0.017
Veal cutlet
0.01
Chicken, fried
0.04
0.020
Chicken, roasted
0.01
Turkey, roasted
0.01
Beef liver
0.11
0.12
0.08
Frankfurters
0.01
Bologna
0.02
0.013
Salami
0.01
Cod/haddock filet
0.07
0.03
Tuna, canned
0.18
0.27
0.08
0.18
Shrimp
0.10
0.04
Fish sticks, frozen
0.03
0.017
Eggs, scrambled
0.01
Eggs, fried
0.03.
0.017
Eggs, soft boiled
0.01
Pinto beans, dried
0.04
0.02
0.023
Pork and beans, canned
0.41
0.07
0.04
0.17
Cowpeas, dried
0.01
Lima beans, dried
0.03 .
0.017
Lima beans, frozen
0.03
0.017
Navy beans, dried
0.03
0. 017
Red beans, dried
0.02
0.06
0.03
7D-2 7/1/83
-------
Cat'
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
PREtl.Ml NARY DRAFT
TABLE 7D-1. (continued)
+
Food Lead concentration* Mean
(pg/g)
Peas, green, canned
0.14
0.28
0.25
0.22
Peas, green, frozen
0.03
. 0.08
0.04
Peanut butter
0.15
0.56
Peanuts
0. 01
Pecans
0.03
0.017
Rice, white
0.05
0.19
0. 084
Oatmeal
0.06
0.027
Fari na
0.03
0.017
Corn grits
0.01
Corn, frozen
T
T
0.013
Corn, canned
0.22
0.56
0.06
0. 28
Corn, cream style, canned
0.09
0.06
0.11
0. 09
Popcorn
0.07
0.08
0.053
White bread
0.01
Rolls, white
0.03
0.06
0.02
0.037
Cornbread
0.01
Bi scuits
0.04
0. 02
0. 023
Whole wheat bread
0.05 '
0.03
0.03
Tortilla
0.02
0.03
0.02
0.023
Rye bread
0.03
0.02
0.02
Muff i ns
0.01
Crackers, sal tine
0.03
0.017
Corn chips
0.04
0.02
Pancakes
0. 03
0.017
Noodles
0.04
0.05
0.033
Macaroni
0.02
0.013
Corn flakes
0.04
0.02
Pre-sweetened cereal
0.06
0.03
0.033
Shredded wheat cereal
0.01
Raisin bran cereal
0.03
0.017
Crisped rice cereal
0.02
0.013
Granola
0.03
0.02
0.02
Oat ring cereal
0.03
0.02
0.04
0.03
Apple, raw
0.04
0.04
0.03
Orange, raw
0.03
0.02
0.02
Banana, raw
0.01
Watermelon, raw
0.02
0.013
Peach, canned
0.18
0 . 23
0.28
0.23
Peach, raw
0.02
0.04
0.023
Applesauce, canned
0.21
v 0.19
0.10
0.17
Pear, raw
0.02
0.03
0.02
Strawberries, raw
0.03
0.017
Fruit cocktail, canned
0.23
0.24
0.13
0.20
Grapes, raw
0.02
0.013
Cantaloupe, raw
0.03
0.08
0.04
Pear, canned
0.24
0.22
0.17
0.31
Plums, raw
T
0.012
Grapefruit, raw
0.03
0.017
Pineapple, canned
0.10
0.08
0.05
0.08
7D-3
456*:
-------
Cati
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
125
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
PRELIMINARY DRAFT
TABLE 7D~1. (continued)
Food Lead concentration* Mean+
(M9/g)
Cherries, raw
0.03
0.017
Raisins, dried
0.04
0.04
0.03
Prunes, dried
0.05
0.04
0.033
Avocado, raw
0.03
0.07
0. 037
Orange juice, frozen
0.02
0.013
Apple juice, canned
0.06
0.09
0.02
0.054
Grapefruit juice, frozen
0.03
0.04
0.027
Grape juice, canned
0.06
0.11
0.04
0.07
Pineapple juice, canned
0.08
0.02
0.05
0.05
Prune juice, bottled
0.02
0.02
0. 017
Orange juice, canned
0.05
0.03
0.02
0.033
Lemonade, frozen
0.04
0.07
0.03
Spinach, canned
0.80
1.65
0.12
0.86
Spinach, frozen
0.05
0.10
0.06
0.07
Collards, frozen
0.05
0.27
0.04
0.12
Lettuce, raw
0.01
Cabbage, raw
0.03
0.017
Coleslaw
0.13
0.05
Sauerkraut, canned
0.77
0.39
0.12
0.43
Broccoli, frozen
0.04
0.03
0.027
Celery, raw
0.01
Asparagus, frozen
0.02
0.013
Cauliflower, frozen
0.01
Tomato, raw
0.03
0.017
Tomato juice, canned
0.16
0.04
T
0.072
Tomato sauce, canned
0.26
0.31
0.12
0.23
Tomatoes, canned
0.19
-
0.23
0.21
Beans, snap green, frozen
0.03
0.02
0.02
Beans, snap green, canned
0.14
0.23
0.12
0.16
Cucumber, raw
T
0.012
Squash, summer, frozen
0.04
0.02
0.023
Pepper, green, raw
0. 07
0.02
0.033
Squash, winter, frozen
0.02
0.013
Carrots, raw
0.03
0.017
Onion, raw
0.05
0.02
0.027
Vegetables, mixed, canned
0.17
0.06
0.08
Mushrooms, canned
0.25
0.25
0.12
0.21
Beets, canned
0.17
0.11
0.08
0.12
Radish, raw
0. 03
0.03
0.023
Onion rings, frozen
0.07
0.02
0.033
French fries, frozen
T
0.012
Mashed potatoes, instant
0.11
0.043
Boiled potatoes, w/o peel
0.02
0.013
Baked potato, w/ peel
0.04
0.02
0.023
Potato chips
0.03
0.017
Scalloped potatoes
0.04
0.02
0.023
Sweet potato, baked
0.05
0.04
0.033
Sweet potato, candied
0.04
0.04
0.02
0.033
Spaghetti, w/ meat sauce
0.11
0.12
0.08
0.10
Beef and vegetable stew
T
0.012
7D-4 7/1/83
45*7 ^
-------
PRELIMINARY DRAFT
TABLE 7D-1. (continued)
Category Food Lead concentration* Means*
(pg/g) . .
144
Pizza, frozen
0.06
0. 03
0.033
145
Chi 1i , beef and beans
0.12
0.05
0.06
146
Macaroni and cheese
0. 01
147
Hamburger sandwich
0.02
0.013
148
Meatloaf
0.06
0.46
0.17
149
Spaghetti in tomato sauce,
canned
0.06
0.02
0.03
150
Chicken noodle casserole
0.04
0. 02
151
Lasagne
0.11
0.06
o: 03
0.067
152
Potpie, frozen
0. 04
0.03
0.027
153
Pork chow mein
0.32
0.03
0.04
0.13
154
Frozen dinner
0. 01
155
Chicken noodle soup, canned
0.02
0.02
0.06
0.033
156
Tomato soup, canned
0.07
0.02
T
0.035
157
Vegetable beef soup, canned
0.04
0.04
0.04
0.04
158
Beef bouillon, canned
0.02
0.013
159
Gravy mix
0.02
0.013
160
White sauce
0.05
0.02
0.027
161
Pickles
0.10
0.09
0.67
162
Margari ne
0.06
0.06
0.043
163
Salad dressing
0.03
0.06
0.033
164
Butter
0.14
0.053
165
Vegetable oil
0.01
166
Mayonnai se
0.01
167
Cream
0.06
0.027
168
Cream substitute
0.10
0.04
0.05
169
Sugar
0.07
0.05
0.043
170
Syrup
0.06
0.027
171
Jel ly
0.05
0.023
172
Honey
0.12
0.06
0.063
173
Catsup
0.02
0.013
174
Ice cream
0.03
0.02
0.03
0.027
175
Pudding, instant
0.01
176
Ice cream sandwich
0.05
0.02
0.027
177
Ice milk
0.07
0.04
0.02
0.043
178
Chocolate cake
0.13
0.03
0.057
179
Yellow cake
0,16
0.06
180
Coffee cake
0.04
0.03
0.05 '
0.04
181
Doughnuts
0.02
0.013
182
Danish pastry
0.06
0.037
183
Cookies, choc, chip
0.04
0.03
0.03
0.033
184
Cookies, sandwich type
0.03
0.03
0.04
0.027
185
Apple pie, frozen
0.04
0.02
0.023
186
Pumpkin pie
0.05
0.02
0.03
0.033
187
Candy, milk chocolate
0.09
0.04
0.09
0.07
188
Candy, caramels
0.04
0.04
0.03
189
Chocolate powder
0.06
0.03
0.08
0.06
190
Gelatin dessert
0.02
T
0.015
191
Soda pop. cola, canned
0.02
0.013
7APPB/E 7D-5 7/1/83
458'
-------
PRELIMINARY DRAFT
TABLE 7D-1. (continued)
Category
Food
Lead
concentrati on*
(Mg/g)
+
Mean
192
Soda pop lemon-lime, canned
0.13
0.02 0.02
0.06
193
Soft drink powder
0.02
0.013
194
Soda pop, cola, low cal.,
canned
0.05
0.02
0.027
195
Coffee, instant
0.01
196
Coffee, instant, decaf.
0.02
0.013
197
Tea
0.01
198
Beer, canned
0.02
0.02
0.17
199
Wi ne
0.03
0.03 0.03
0.03
200
Wh i s key
0.02
0.013
201
Water
T
0.012
^Individual values for three Market Basket Surveys. "T" means only a trace detected, missing
+value means below detection limit.
Means determined by EPA using 0.01 (H of detection limit) for missing values and
0.015 for "T".
7APPB/E
7D-6
45^
7/1/83
-------
PRELIMINARY DRAFT
TABLE 7D-2. CONDENSATION, TO 25 CATEGORIES, OF THE
2D1 CATEGORIES OF FOOD
Table 7-13
category
Categories and fractional categories*
from Pennington (1983) (Table 7D-1)
Milk
1-6, 9
Dairy Products
7, 10-12, 164, 167, 174, 176, 177
Milk as ingredient
0.5(156), 0.2(178-187)
Beef
13-16, 0.1(143), 0.3(145), 0.6(147, 0.4(142, 149)
Pork
17-21
Chicken
24-26
Fi sh
31-34
Prepared meats
28-30
Other meats
22-23, 27
Eggs
35-37, 0.15(142, 144, 146, 149), 0.2(178-187), 0.3(69,
Bread
58, 59, 61, 62, 65, 66, 0.4(147)
Flour as ingredient
159, 160, 0.3(142, 144, 146, 149, 178-187), 0.6(69, 70)
Non-wheat cereals
50-52, 64, 75-77
Corn flour
53, 60, 63, 67, 71
Leafy vegetables
107-111, 113-116
Root vegetables
127, 128, 132
Vine vegetables
38, 40-44, 46, 117, 121, 123-126, 161, 173
Canned vegetables
39, 45, 106, 112, 118-120, 122, 129-131, 0.1(142, 145, :
0.2(144), 0.5(155-157)
Sweet corn
54
Canned sweet corn
55, 56
Potatoes
134-141
Vegetable oil
162, 163, 165, 166
Sugar
169-172, 188, 0.3(178-187)
Canned fruits
82, 84, 87, 90, 93
Fresh fruits
78-81, 83, 85, 86, 88, 89, 91, 92, 94-97
*In some cases, only a fraction of a category, e.g. , milk in tomato soup, was used, and this
fraction is indicated by a decimal fraction before the category number in parenthesis.
7APPB/E 7D-7 7/1/83
46CK
-------
r
-------
PRELIMINARY DRAFT
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conference on trace substances in environmental health]; June; Columbia, M0. Columbia,
M0: University of Missouri-Columbia; pp. 403-410.
Pattenden, N. J. (1974) Atmospheric concentrations and deposition rates of some trace elements
measured in the Swansea/Neath/Port Talbot area. Harwell, United Kingdom: Atomic Energy
Research Establishment, Environment and Medical Sciences Division. Available from: NTIS,
Springfield, VA; AERE-R7729.
Peden, M. E. (1977) Flameless atomic absorption determinations of cadmium, lead, and manganese
in particle size fractionated aerosols. In: Kirchhoff, W. H. , ed. Methods and standards
for environmental measurement: proceedings of the 8th materials research symposium;
September 1976; Gaithersburg, MD. Washington, DC: U.S. Department of Commerce, National
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Pennington, J. A. T. (1983) Revision of the total diet study food list and diets. J. Am. Diet.
Assoc. 82: 166-173.
Pinkerton, C. ; Creason, J. P.; Hammer, D. I.; Colucci, A. V. (1973) Multi-media indices of
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Ganther, H. E. ; Mertz, W. , eds. Trace element metabolism in animals-2: proceedings of
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Popovac, D. ; Graziano, J.; Seaman, C. ; Kaul , B. ; Colakovic, B. ; Popovac, R. ; Osmani, I.;
Haxhiu, M. ; Begraca, M. ; Bozovic, Z. ; Mikic, M. (1982) Elevated blood lead in a popula-
tion near a lead smelter in Kosovo, Yugoslavia. Arch. Environ. Health 37: 19-23.
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at: U.S. Environmental Protection Agency, Environmental Criteria and Assessment Office,
Research Triangle Park, NC.
Rameau, J. T. L. B. (1973) Lead as an environmental pollutant. In: Proceedings, international
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1972. Luxembourg: Commission of the European Communities; pp. 189-200.
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8. EFFECTS OF LEAD ON ECOSYSTEMS
8.1 INTRODUCTION
8.1.1 Scope of Chapter 8
This chapter describes the potential effects of atmospheric lead inputs on several types
of ecosystems. An effect is any condition attributable to lead that causes an abnormal phy-
siological response in individual organisms or that perturbs the normal processes of an eco-
system. A distinction is made among natural, cultivated, and urban ecosystems, and extended
discussions are included on the mobility and bioavailability of lead in ecosystems.
There are many reports on the effects of lead on individual populations of plants and
animals and a few studies on the effects of lead in simulated ecosystems or microcosms.
However, the most realistic studies are those that examine the effects of lead on entire
ecosystems, as they incorporate all of the ecological interactions among the various popu-
lations and all of the chemical and biochemical processes relating to lead (National Academy
of Sciences, 1981). Unfortunately, these studies have also had to cope with the inherent
variability of natural systems and the confounding frustrations of large scale projects.
Consequently, there are only a handful of ecosystem studies on which to base this report.
The principle sources of lead entering an ecosystem are: the atmosphere (from automotive
emissions), paint chips, spent ammunition, the application of fertilizers and pesticides, and
the careless disposal of lead-acid batteries or other industrial products. Atmospheric lead
is deposited on the surfaces of vegetation as well as on ground and water surfaces. In
terrestrial ecosystems, this lead is transferred to the upper layers of the soil surface,
where it may be retained for a period of several years. The movement of lead within eco-
systems is influenced by the chemical and physical properties of lead and by the biogec-
chemical properties of the ecosystem. Lead is non-degradable, but in the appropriate chemical
environment, may undergo transformations which affect its solubility (e.g., formation of lead
sulfate in soils), its bioavailability (e.g., chelation with humic substances), or its toxi-
city (e.g., chemical methylation).
The previous Air Quality Criteria for Lead (U.S. Environmental Protection Agency, 1977)
recognized the problems of atmospheric lead exposure incurred by all organisms including man.
Emphasis in the chapter on ecosystem effects was given to reports of toxic effects on specific
groups of organisms, e.g. domestic animals, wildlife, aquatic organisms, and vascular and non-
vascular plants. Forage containing lead at 80 pg/g dry weight was reported to be lethal to
horses, whereas 300 ng/g dry weight caused lethal clinical symptoms in cattle. This report
will attempt to place the data in the context of sublethal effects of lead exposure, to extend
the conclusions to a greater variety of domestic animals, and to describe the types and ranges
of exposures in ecosystems likely to present a problem for domestic animals.
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Research on lead in wildlife has traditional ly fallen into the following somewhat arti-
ficial categories: waterfowl; birds and small mammals; fish; and invertebrates. In all these
categories, no correlation could be made in the 1977 report between toxic effects and environ-
mental concentrations. Some recent toxicity studies have been completed on fish and inverte-
brates and the data are reported below, but there is still little information on the levels of
lead that can cause toxic effects in small mammals or birds.
Information on the relationship between soil lead and plants can be expanded somewhat
beyond the 1977 report, primarily due to a better understanding of the role of humic sub-
stances in binding lead. Although the situation is extremely complex, it is reasonable to
state that most plants cannot survive in soil containing 10,000 yg/g dry weight if the pH is
below 4.5 and the organic content is below 5 percent. The specifics of this statement are
discussed more extensively in Section 8,3.1.2.
Before 1977, natural levels of lead in environmental media other than soil were not well
known. Reports of sublethal effects of lead were sparse and there were few studies of total
ecosystem effects. Although several ecosystem studies have been completed since 1977 and many
problems have been overcome, it is still difficult to translate observed effects under speci-
fic conditions directly to predicted effects in ecosystems. Some of the known effects, which
are documented in detail in the appropriate sections, are summarized here:
PI ants. The basic effect of lead on plants is to stunt growth.
This may be through a reduction of photosynthetic rate,
inhibition of respiration, cell elongation, or root deve-
lopment, or premature senescence. Some genetic effects
have been reported. All of these effects have been ob-
served in isolated cells or in hydroponically-grown plants
in solutions comparable to 1 to 2 pg/g soil moisture.
These concentrations are well above those normally found
in any ecosystem except near smelters or roadsides.
Terrestrial plants take up lead from the soil moisture and
most of this lead is retained by the roots. There is no
evidence for foliar uptake of lead and little evidence
that lead can be translocated freely to the upper portions
of the plant. Soil applications of calcium and phosphorus
may reduce the uptake of lead by roots.
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Animals. Lead affects the central nervous system of animals and
their ability to synthesize red blood cells. Blood con-
centrations above 0.4 ppm (40 pg/dl) can cause observable
clinical symptoms in domestic animals. Calcium and phos-
phorus can reduce the intestinal absorption of lead. The
physiological effects of lead exposures in laboratory
animals are discussed in extensive detail in Chapters 10
and 12 of this document.
Microorgani stns.There is evidence that lead at environmental concen-
trations occasionally found near roadsides and smelters
(10,000 to 40,000 pg/g dw) can eliminate populations of
bacteria and fungi on leaf surfaces and in soil. Many of
those micoorganisms play ,key roles in the decomposition
food chain. It is likely that the affected microbial
populations are replaced by others of the same or differ-
ent species, perhaps less efficient at decomposing organic
matter. There is also evidence that microorganisms can
mobilize lead by making it more soluble and more readily
taken up by plants. This process occurs when bacteria
exude organic acids that lower the pH in the immediate
vicinity of the plant root.
Ecosystems. There are three known conditions under which lead may
perturb ecosystem processes. At soil concentrations of
1,000 pg/g or higher, delayed decomposition may result
from the elimination of a single population of decomposer
microorganisms. Secondly, at concentrations of 500 to
1,000 pg/g, populations of plants, microorganisms, and
invertebrates may shift toward lead tolerant papulations
of the same or different species. Finally, the normal
biogeochemical process which purifies and repurifies
calcium in grazing and decomposer food chains may be
circumvented by the addition of lead to vegetation and
animal surfaces. This third effect can be measured at all
ambient atmospheric concentrations of lead.
Some additional effects may occur due to the uneven dis-
tribution of lead in ecosystems. It' is known that lead
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accumulates in soil, especially soil with high organic
content. Although no firm documentation exists, it is
reasonable to assume from the known chemistry of lead in
soil that: 1) other metals may be displaced from the
binding sites on the organic matter; 2) the chemical
breakdown of inorganic soil fragments may be retarded by
the interference of lead on the action of fulvic acid on
iron bearing crystals; and 3) lead in soil may be in
equilibrium with moisture films surrounding soil particles
and thus available for uptake by plants.
To aid the reader in understanding the effects of lead on ecosystems, sections have been
included that discuss such important matters as how ecosystems are organized, what processes
regulate metal cycles, what criteria are valid in interpreting ecosystem effects, and how soil
systems function to regulate the controlled release of nutrients to plants. The informed
reader may wish to turn directly to Section 8.3, where the discussion of the effects of lead
on organisms begins.
8.1.2 Ecosystem Functions
8.1.2.1 Types of Ecosystems. Based on ambient concentrations of atmospheric lead and the dis-
tribution of lead in the soil profile, it is useful to distinguish among three types of eco-
systems: natural, cultivated, and urban. Natural ecosystems include aquatic and terrestrial
ecosystems that are otherwise unperturbed by man, and those managed ecosystems, such as com-
mercial forests, grazing areas, and abandoned fields, where the soil profile has remained un-
disturbed for several decades. Cultivated ecosystems include those where the soil profile is
frequently disturbed and those where chemical fertilizers, weed killers, and pest-control
agents may be added. In urban ecosystems, a significant part of the exposed surface includes
rooftops, roadways, and parking lots from which runoff, if not channeled into municipal waste
processing plants, is spread over relatively small areas of soil surface. The ambient air
concentration of lead in urban ecosystems is 5 to 10 times higher than in natural or culti-
vated ecosystems (See Chapter 7), Urban ecosystems may also be exposed to lead from other
than atmospheric sources, such as paint, discarded batteries, and used motor oil. The effects
of atmospheric lead depend on the type of ecosystems examined.
8.1.2.2 Energy Flow and Biogeochemical Cycles. Two principles govern ecosystem functions:
1) energy flows through an ecosystem; and 2) nutrients cycle within an ecosystem. Energy
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usually enters the ecosystem in the ,form of sunlight and leaves as heat of respiration.
Stored chemical energy may be transported into or out of an ecosystem (e.g., leaf detritus in
a stream) or be retained by the ecosystem for long periods of time (e.g., tree trunks).
Energy flow through an ecosystem may give structure to the ecosystem by establishing food webs
which efficiently regulate the transfer of energy. Segments of these food webs are called
food chains. Energy that flows along a grazing food chain is diverted at each step to the
detrital food chain.
Unlike energy, nutrient and non-nutrient elements are recycled by the ecosystem and
transferred from reservoir to reservoir in-a pattern usually referred to as a biogeochemical
cycle (Brewer, 1979, p. 139). The reservoirs correspond approximately to the food webs of
energy flow. Although elements may enter (e.g., weathering of soil) or leave the ecosystem
(e.g., stream runoff), the greater fraction of the available mass of the element is usually
cycled within the ecosystem.
Two important characteristics of a reservoir are the amount of the element that may be
stored in the reservoir and the rate at which the element enters or leaves the reservoir.
Some reservoirs may contain a disproportionately large amount of a given element. For exam-
ple, most of the carbon in a forest is bound in the trunks and roots of trees, whereas most of
the calcium may be found in the soil (Smith, 1980, p. 316). Some large storage reservoirs,
such as soil, are not actively involved in the rapid exchange of the nutrient element, but
serve as a reserve source of the element through the slow exchange with a more active reser-
voir, such as soil moisture. When inputs exceed outputs, the size of the reservoir increases.
Increases of a single element may reflect instability of the ecosystem. If several elements
increase simultaneously, this expansion may reflect stable growth of the community.
Reservoirs are connected by pathways which represent real ecosystem processes. Figure
8-1 depicts the biogeochemical reservoirs and pathways of a typical terrestrial ecosystem.
Most elements, especially those with no gaseous phase, do not undergo changes in oxidation
state and are equally available for exchange between any two reservoirs, provided a pathway
exists between the two reservoirs. The chemical environment of the reservoir may, however,
regulate the availability of an element by controlling solubi1ity or binding strengths. This
condition is especially true for soils.
Ecosystems have boundaries. These boundaries may be as distinct as the border of a pond
or as arbitrary as an imaginary circle drawn on a map. Many trace metal studies are conducted
in watersheds where some of the boundaries are determined by topography. For atmospheric
inputs to terrestrial ecosystems, the boundary is usually defined as the surface of vegeta-
tion, exposed rock, or soil. The water surface suffices for aquatic ecosystems.
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GRAZERS
HERBIVORES
CARNIVORES
CARNIVORES
PRIMARY
PRODUCERS
DECOMPOSERS
DETRITUS
INORGANIC
NUTRIENTS
Figure 8-1. This figure depicts cycling processes within the major components of a
terrestrial ecosystem, i.e. primary producers, grazers and decomposers. Nutrient and
non-nutrient elements are stored in reservoirs within these components. Processes
that take place within reservoirs reguiate the flow of elements between reservoirs
along established pathways. The rate of flow i3 in part a function of the concentra-
tion in the preceding reservoir. Lead accumulates in decomposer reservoirs which
have a high binding capacity for this metal. 3t is likely that the rate of flow away
from these reservoirs has increased in past decades and will continue to increase for
some time until the decomposer reservoirs are in equilibrium with the entire
ecosystem. Inputs to and outputs from the ecosystem as a whole are not shown.
Source; Adapted from Swift et al. (1979).
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Non-nutrient elements differ little from nutrient elements in their biogeochemical cy-
cles. Quite often, the cycling patterns are similar to those of a major nutrient. In the
case of lead, the reservoirs and pathways are very similar to those of calcium.
The important questions are: Does atmospheric lead interfere with the normal mechanisms
of nutrient cycles? How does atmospheric lead influence the normal lead cycle in an eco-
system? Can atmospheric lead interfere with the normal flow of energy through an ecosystem?
8.1.2.3 Bioqeochemistry of Lead. Naturally occurring lead from the earth's crust is commonly
found in soils and the atmosphere. Lead may enter an ecosystem by weathering of parent rock
or by deposition of atmospheric particles. This lead becomes a part of the nutrient medium of
plants and the diet of animals. All ecosystems receive lead from the atmosphere. More than
99 percent of the current atmospheric lead deposition is now due to human activities (National
Academy of Sciences, 1980). In addition, lead shot from ammunition may be found in many
waterways and popular hunting regions, leaded paint chips often occur in older urban regions
and lead in fertilizer may contaminate the soil in agricultured regions.
In prehistoric times, the contribution of lead from weathering of soil was probably about
4 g Pb/ha-yr and from atmospheric deposition about 0.02 g Pb/ha*yr, based on estimates of
natural and anthropogenic emissions in Chapter 5 and deposition rates discussed in Chapter 6.
Weathering rates are presumed to have remained the same, but atmospheric inputs are believed
to have increased to 180 g/ha-yr in natural and some cultivated ecosystems, and 3,0C0 g/ha*yr
in urban ecosystems and along roadways (see Chapter 6). In every terrestrial ecosystem of the
Northern Hemisphere, atmospheric lead deposition now exceeds weathering by a factor of at
least 10, sometimes by as much as 1,000.
Many of the effects of lead on plants, microorganisms, and ecosystems arise from the fact
that lead from atmospheric and weathering inputs is retained by soil. Geochemical studies
show that less than 3 percent of the inputs to a watershed leave by stream runoff (Siccama and
Smith, 1978; Shirahata et al., 1980). In prehistoric times, stream output nearly equalled
weathering inputs and the lead content of soil probably remained stable, accumulating at an
annual rate of less than 0.1 percent of the original natural lead (reviewed by Nriagu, 1978).
Due to human activity, lead in natural soils now accumulates on the surface at an annual rate
of 5 to 10 percent of the natural lead. One effect of cultivation is that atmospheric lead is
mixed to a greater depth than the 0 to 3 cm of natural soils.
Most of the effects on grazing vertebrates stem from the deposition of atmospheric parti-
cles on vegetation surfaces. Atmospheric deposition may occur by either of two mechanisms.
Wet deposition (precipitation scavenging through rainout or washout) generally transfers lead
directly to the soil. Dry deposition transfers particles to all exposed surfaces. Large
particles (>4 pm) are transferred by gravitational mechanisms, small particles (<0.5 m"1) are
also deposited by wind-related mechanisms.
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About half of the foliar dry deposition remains on leaf surfaces following normal rain-
fall (Elias et al., 1976; Peterson, 1978), but heavy rainfall may transfer the lead to other
portions of the plant (Elias and Croxdale, 1980). Koeppe (1981) has reviewed the literature
and concluded that less than 1 percent of the surface lead can pass directly into the internal
leaf tissues of higher plants. The cuticular layer of the leaves is an effective barrier to
aerosol particles and even to metals in solution on the leaf surface (Arvik and Zimdahl,
1974), and passage through the stomata cannot account for a significant fraction of the lead
inside leaves (Carlson et al., 1976; 1977).
When particles attach to vegetation surfaces, transfer to soil is delayed from a few
months to several years. Due to this delay, large amounts of lead are diverted to grazing
food chains, bypassing the soil moisture and plant root reservoirs (Elias et al. , 1982).
8.1.3 Criteria for Evaluating Ecosystem Effects
As it is the purpose of this chapter to describe the levels of atmospheric lead that may
produce adverse effects in plants, animals, and ecosystems, it is necessary to establish the
criteria for evaluating these effects. The first step is to determine the connection between
air concentration and ecosystem exposure. If the air concentration is known, ecosystem inputs
from the atmosphere can be predicted over time and under normal conditions. These inputs and
those from the weathering of soil determine the concentration of lead in the nutrient media of
plants, animals, and microorganisms. It follows that the concentration of lead in the nutri-
ent medium determines the concentration of lead in the organism and this in turn determines
the effects of lead on the organism.
The fundamental nutrient medium of a terrestrial ecosystem is the soil moisture film
which surrounds organic and inorganic soil particles. This film of water is in equilibrium
with other soil components and provides dissolved inorganic nutrients to plants. It is chemi-
cally different than ground water or rain water and there is little reliable information on
the relationship between lead in soil and lead in soil moisture. Thus, it appears impossible
to quantify all the steps by which atmospheric lead is transferred to plants. Until mora
information is available on lead in soil moisture, another approach may be more productive.
This involves determining the degree of contamination of organisms by comparing the present
known concentrations with calculated prehistoric concentrations.
Prehistoric concentrations of lead have been calculated for only a few types of organ-
isms. However, the results are so low that any normal variation, even of an order of magni-
tude, would not seriously alter the degree of contamination. The link between lead in the
prehistoric atmosphere and in prehistoric organisms may allow us to predict concentrations of
lead in organisms based on present or future concentrations of atmospheric lead.
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It is reasonable to infer a relationship between degree of contamination and physio-
logical effect. It seems appropriate to assume that natural levels of lead which were safe
for organisms in prehistoric times would also be safe today. It is also reasonable that some
additional atmospheric lead can be tolerated by all populations of organisms with no ill
effects, that some populations are more tolerant than others, and that some individuals within
populations are more tolerant of lead effects than others.
For nutrient elements, the concept of tolerance is not new. The Law of Tolerance
(illustrated in Figure 8-2) states that any nutrient may be present at concentrations either
too low or too high for a given population and that the ecological success of a population is
greatest at some optimum concentration of the nutrient (Smith, 1980, .p. 35). In a similar
manner, the principle applies to non-nutrient elements. Although there is no minimum concen-
tration below which the population cannot survive, there is a concentration above which the
success of the population will decline (point of initial response) and a concentration at
which the entire population will die (point of absolute toxicity). In this respect, both
nutrients and non-nutrients behave in a similar manner at concentrations above some optimum.
Certain variables make the points of initial response and absolute toxicity somewhat
imprecise. The point of initial response depends on the type of response investigated. This
response may be at the molecular, tissue, or organismic level, with the molecular response
occurring at the lowest concentration. Similarly, at the point of absolute toxicity, death
may occur instantly at high concentrations or over a prolonged- period of time at somewhat
lower concentrations. Nevertheless, the gradient between these two points remains an appro-
priate basis on which to evaluate known environmental effects, and any information which
correctly positions this part of the tolerance curve will be of great value.
The normal parameters of a tolerance curve, i.e., concentration and ecological success,
can be replaced by degree of contamination and percent physiological dysfunction, respectively
(Figure 8-3). Use of this method of expressing degree of contamination should not imply that
natural levels are the only safe levels. It is likely that some degree of contamination can
be tolerated with no physiological effect.
Data reported by the National Academy of Sciences (1980) are used to determine the typi-
cal natural lead concentrations shown in various compartments of ecosystems in Table 8-1.
These data are from a variety of sources and are simplified to the most probable value within
the range reported by NAS. The actual prehistoric air concentration was probably near the low
end of the range (0.02-1.0 ng/m3), as present atmospheric concentrations of 0.3 ng/m3 in the
Southern Hemisphere and 0.07 ng/m3 at the South Pole (Chapter 5), would seem to preclude natu-
ral lead values higher than this.
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NON-NUTRIENT
INITIAL
RESPONSE
I NUTRIENT
in
ABSOLUTE
TOXICITY
LOW
HIGH
CONCENTRATION OF ELEMENT
Figure 8-2. The ecological success ol a population depends in part on the availability
of all nutrients at some optimum concentration. The dashed line ol this diagram
depicts the rise and decline of ecological success (the ability of a population to grow,
survive and reproduce) over a wide concentration range of a single element. The
curve need not be symmetrically bell-shaped, but may be skewed to the right or left.
Although the range in concentration that permits maximum success may be much
wider then shown here, the important point is that at some high concentration, the
nutrient element becomes toxic. The tolerance of populations for high concentrations
of non-nutrients (solid line) is similar to that of nutrients, although there is not yet
any scientific basis for describing the exact shape of this portion of the curve.
Source: Adapted from Smith (19(H)).
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z
o
z
D
li.
W
>
a
<
o
5
o
o
>
z
n.
#
100
1 10 100 1.000 10.000
OBSERVED CONC 'NATURAL CONC-
Figure 8-3. This figure attempts to reconstruct the right portion of a tolerance curve, similar to
Figure 8-2 but plotted on a semilog scale, for a population using a limited amount of information.
H the natural concentration is known for a population and if it is arbitrarily assumed that 10k
natural concentration is also safe, then the zone of assumed safe concentration defines the
region.
TABLE 8-1. ESTIMATED NATURAL LEVELS OF LEAD IN ECOSYSTEMS
Component
Range
Best estimate
Ai r
0.01-1.0 ng/m3
0.07
Soi 1
Inorganic
5-25 gg/g
12.0
Organic
1 MQ/g
1.0
Soil moisture
0.0002 pg/g
0.0002.
Plant leaves
0.01-0.1 gg/g dw
0.05
Herbivore bones
0.04-0.12 gg/g dw
0.12
Carnivore bones
0.01-0.03 gg/g dw
0.03
Source: Ranges are from the
in the text. Units
National Academy of Sciences,(19801*best estimates are discussed
for best estimates are the same as for ranges.
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T
ARBITRARY ZONE OF ASSUMED
SAFE CONCENTRATION
NATURAL
CONCENTRATION
Ax
IMlTIAL v
RESPONSE V
vo
OBSERVED N .
DYSFUNCTION Q
- DEGREE OF CONTAMINATION *0
S
s
\
s
S v ABSOLUTE
\ TOXICITY
XV
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PRELIMINARY DRAFT
In prehistoric times, the rate of entry of lead into the nutrient pool available to
plants was predominantly determined by the rate of weathering of inorganic minerals in frag-
ments of parent rock material. Geochemical estimates of denudation and adsorption rates
(Chapter 6) suggest a median value of 12 pg/g as the average natural lead content of total
soil, with the concentration in the organic fraction at approximately 1 pg/g.
Studies have shown the lead content of leafy vegetation to be 90 percent anthropogenic,
even in remote areas (Crump and Barlow, 1980; Elias et al., 1976, 1978). The natural lead
content of nuts and fruits may be somewhat higher than leafy vegetation, based on internal
lead concentrations of modern samples (Elias et al., 1982). The natural lead concentrations
of herbivore and carnivore bones were .reported by Elias et al. (Elias and Patterson, 1980;
Elias et al., 1982). These estimates are based on predicted Pb/Ca ratios calculated from the
observed biopurification of calcium reservoirs with respect to Sr, Ba, and Pb, on the system-
atic evaluation of anthropogenic lead inputs to the food chain (Section 8.5.3), and on
measurements of prehistoric mammalian bones.
8.2 LEAD IN SOILS AND SEDIMENTS
8.2.1 Distribution of Lead in Soils
Because lead in soil is the source of most effects on plants, microorganisms, and eco-
systems, it is important to understand the processes that control the accumulation of lead in
soil. The major components of soil are: 1) fragments of inorganic parent rock material;
2) secondary inorganic minerals; 3) organic constituents, primarily humic substances, which
are residues of decomposition or products of decomposer organisms; 4) Fe-Mn oxide films, which
coat the surfaces of all soil particles and appear to have a high binding capacity for metals;
5) soil microorganisms, most commonly bacteria and fungi, although protozoa and soil algae may
also be found; and 6) soil moisture, the thin film of water surrounding soil particles which
is the nutrient medium of plants. Some watershed studies consider that fragments of inorganic
parent rock material lie outside the forest ecosystem, because transfer from this compartment
is so slow that much of the material remains inert for centuries.
The concentration of lead ranges from 5 to 30 pg/g in the top 5 cm of most soils not
adjacent to sources of industrial lead, although 5 percent of the soils contain as much as
800 pg/g (Chapter 5). Aside from surface deposition of atmospheric particles, plants in North
America average about 0.5 to 1 pg/g dw (Peterson, 1978) and animals roughly 2 pg/g (Forbes and
Sanderson, 1978). Thus, soils contain the greater part of total ecosystem lead. In soils,
lead in parent rock fragments is tightly bound within the crystalline structures of the
inorganic soil minerals. It is released to the ecosystem only by surface contact with soil
moisture films.
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Hutchinson (1980) has reviewed the effects of acid precipitation on the ability of soils
to retain cations. Excess calcium and other metals are leached from the A horizon of soils by
rain with a pH more acidic than 4.5. Most soils in the eastern United States are normally
acidic (pH 3.5 to 5.2) and the leaching process is a part of the complex equilibrium main-
tained in the soil system. By increasing the leaching rate, acid rain can reduce the availa-
bility of nutrient metals to organisms dependent on the top layer of soil. Tyler (1978)
reports the effect of acid rain on the leaching rate (reported as residence time) for lead and
other metals. Simulated rain of pH 4.2 to 2.8 showed the leaching rate for lead increases
with decreasing pH, but not nearly as much as that of other metals, especially Cu, Mn, and Zn.
This would be as expected from the high stability constant of lead relative to other metals in
humic acids (see Section 6.5.1). It appears from this limited information that acidification
of soil may increase the rate of removal of lead from the soil, but not before several major
nutrients are removed first. The effect of acid rain on the retention of lead by soil mois-
ture is not known.
8.2.2 Origin and Availability of Lead in Aquatic Sediments
Atmospheric lead may enter aquatic ecosystems by wet or dry deposition (Dolske and
Sievering, 1979) or by the erosional transport of soil particles (Baier and Healy, 1977). In
waters not polluted by industrial, agricultural, or municipal effluents, the lead concentra-
tion is usually less than 1 ng/1• Of this amount, approximately 0.02 pg/1 is natural lead and
the rest is anthropogenic lead, probably of atmospheric origin (Patterson, 1980). Surface
waters mixed with urban effluents may frequently reach lead concentrations of 50 |jg/1 , and
occasionally higher (Bradford, 1977).
In aqueous solution, virtually all lead is divalent, as tetravalent lead can exist only
under extremely oxidizing conditions (reviewed by Rickard and Nriagu, 1978; Chapter 3). At pH
higher than 5, divalent lead can form a number of hydroxyl complexes, most commonly PbOH+,
Pb(0H)2, and Pb(0H)3 . At pH lower than 5, lead exists in solution as hydrated Pb. In still
water, lead is removed from the water column by the settling of lead-containing particulate
matter, by the formation of insoluble complexes, or by the adsorption of lead onto suspended
organic particles. The rate of sedimentation is determined by temperature, pH, oxidation-
reduction potential, ionic competition, the chemical form of lead in water, and certain bio-
logical activities (Jenne and Luoma, 1977). McNurney et al. (1977) found 14 pg Pb/g in stream
sediments draining cultivated areas and 400 pg/g in sediments associated with urban eco-
systems. Small sediment grain size and high organic content contributed to increased reten-
tion in sediments.
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8.3 EFFECTS OF LEAD ON PLANTS
8.3.1 Effects on Vascular Plants and Algae
Some physiological and biochemical effects of lead on vascular plants have been detected
under laboratory conditions at concentrations higher than normally found in the environment.
The commonly reported effects are the inhibition of photosynthesis, respiration or cell
elongation, all of which reduce the growth of the plant (Koeppe, 1981). Lead may also induce
premature senescence, which may affect the long-term survival of the plant or the ecological
success of the plant population. To provide a meaningful evaluation of these effects, it is
necessary to examine the correlation between laboratory conditions and typical conditions in
nature with respect to form, concentration, and availability of lead. First, the reader must
understand what is known of the movement of lead from soil to the root to the stem and finally
to the leaf or flower. Most notably, there are specific barriers to lead at the soil:soil
moisture interface and at the root:shoot interface which retard the movement of lead and
reduce the impact of lead on photosynthetic and meristematic (growth and reproduction) tissue.
8.3.1.1 Uptake by Plants. Most of the lead in or on a plant occurs on the surfaces of leaves
and the trunk or stem. The surface concentration of lead in trees, shrubs, and grasses
exceeds the internal concentration by a factor of at least five (Elias et al, 1978). There is
little or no evidence of lead uptake through leaves or bark. Foliar uptake, if it does occur,
cannot account for more than 1 percent of the uptake by roots, and passage of lead through
bark tissue has not been detected (Arvik and Zimdahl, 1974; reviewed by Koeppe, 1981; Zimdahl,
1976). Krause and Kaiser (1977) were able to show foliar uptake and translocation of lead
mixed with cadmium, copper, and manganese oxides when applied in large amounts (122 mg/m2)
directly to leaves. This would be comparable to 100,000 days accumulation at a remote site
(0.12 ng/cm2*d) (Elias et al. , 1978). The uptake of lead was less than that of other metals
and application of sulfur dioxide did not increase the foilar uptake of these metals. The
major effect of surface lead at ambient concentrations seems to be on subsequent components of
the grazing food chain (Section 8.4.1) and on the decomposer food chain following litterfall
(Elias et al., 1982). (See also Section 8.4.2.)
Uptake by roots is the only major pathway for lead into plants. The amount of lead tnat
enters plants by this route is determined by the availability of lead in soil, with apparent
variations according to plant species. Soil cation exchange capacity, a major factor, is
determined by the relative size of the clay and organic fractions, soil pH, and the amount of
Fe-Mn oxide films present (Nriagu, 1978). Of these, organic humus and high soil pH are the
dominant factors in immobilizing lead (Chapter 6). Under natural conditions, most of the
total lead in soil would be tightly bound within the crystalline structure of inorganic soil
fragments, unavailable to soil moisture. Available lead, bound on clays, organic colloids,
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and Fe-Mn films, would be controlled by the slow release of bound lead from inorganic rock
sources. Since before 3000 B.C., atmospheric lead inputs through litter decomposition have
increased the pool of available lead bound on organic matter within the soil reservoir (see
Section 5.1). "
Because lead is strongly immobilized by humic substances, only a small fraction (perhaps
0.01 percent in soils with 2G percent organic matter, pH 5.5) is released to soil moisture
(see Chapter 6). In soil moisture, lead may pass along the pathway of water and nutrient
uptake on either a cellular route through the cell membranes of root hairs (symplastic route)
or an extracellular route between epidermal cells into the intercellular spaces of the root
cortex (apoplastic route) (Foy et al., 1978). Lead probably passes into the symplast by mem-
brane transport mechanisms similar to the uptake of calcium or other bivalent cations.
At 500 |jg Pb/g nutrient solution, lead has been shown to accumulate in the cell walls of
germinating Raphinus sativus roots (Lane and Martin, 1982). This concentration is much higher
than that found by Wong and Bradshaw (1982) to cause inhibition of germinating root elongation
(less than 2.5 pg/g), absence of root growth (5 pg/g), or 55 percent inhibition of seed ger-
mination (20 to 40 pg/g) in the rye grass, Col i um perenne. Lane and Martin (1982) also
observed lead in cytoplasmic organelles which appeared to have a storage function because of
their osmiophi11ic properties. It was suggested that the organelles eventually emptied their
contents into the tor.oplast.
The accumulation of lead in cell walls and cytoplasmic bodies has also been observed in
blue green algae by Jensen et al. (1982), who used X-ray energy dispersive analysis in con-
junction with scanning electron microscopy to observe high concentrations of lead and other
metals in these single celled procaryotic organisms. They found the lead concentrated in the
third of the four layered cell wall and in polyphosphate bodies (not organelles, since they
are not membrane-bound) which appeared to be a storage site for essential metals. The nutri-
ent solution contained 100 pg Pb/g. The same group (Rachlin et al., 1982) reported morpholo-
gical changes in the same blue green alga (Plectonema boryanum). There was a significant
increase in cell size caused by the lead, which indicated that the cell was able to detoxify
its cytoplasm by excreting lead with innocuous cell wall material.
It appears that two defensive mechanisms may exist in the roots of plants for removing
lead from the stream of nutrients flowing to the above ground portions of plants. Lead may be
deposited with cell wall material exterior to the individual root cells, or may be sequestered
in organelles within the root cells. Any lead not captured by these mechanisms would likely
move with nutrient metals cell-to-cell through the symplast and into the vascular system.
Uptake of lead by plants may be enhanced by symbiotic associations with mycorrhizal fungi
The three primary factors that control the uptake of nutrients by plants are the surface area
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of the roots, the ability of the root to absorb particular ions, and the transfer of ions
through the soil. The symbiotic relationship between mycorrhizal fungi and the roots of
higher plants can increase the uptake of nutrients by enhancing all three of these factors
(Voigt, 1969). The typical ectomycorrhiza consist's of "''a mantle or sheath of mycelia that com-
pletely surrounds the root. The physical extension of the sheath may increase the volume of
the root two to three times (Voigt, 1969). Mycorrhizal roots often show greater affinities
for nutrients than do uninfected roots of the same species grown in the same conditions. In
many soil systems, where the bulk of the nutrients are bound up in parent rock material, effi-
cient uptake of these nutrients by plants depends on the ability of organisms in the rhizo-
sphere (plant roots, soil fungi, and bacteria) to increase the rates of weathering. Mycorrhi-
zal fungi are known to produce and secrete into their environment many different acidic com-
pounds (e.g., malic and oxalic acids). In addition, mycorrhizal roots have been shown to
release more carbon dioxide into the rhizosphere than do non-mycorrhizal roots as a result of
their increased rates of respiration. Carbon dioxide readily combines with soil moisture to
produce carbonic acid. All of these acids are capable of increasing the weathering rates of
soil particles such as clays, and altering the binding capacity of organic material, thereby
increasing the amount of nutrients in the soil solution. Mycorrhizae are known to enhance the
uptake of zinc by pine roots (Bowen et al. , 1974), and it is likely that lead uptake is simi-
larly increased, by inference to the ability of mycorrhizae to enhance the uptake of calcium
by pine roots (Melin and Hilsson, 1955; Melin et al., 1958).
The translocation of lead to aboveground portions of the plant is not clearly understood.
Lead may follow the same pathway and be subject to the same controls as a nutrient metal such
as calcium. This assumption implies that the plant root has no means of discriminating
against lead during the uptake process, and it is not known that any such discrimination
mechanism exists. There may be several mechanisms, however, that excrete lead back out of the
root or that prevent its translocation to other plant parts. The primary mechanisms may be
storage in cell organelles or adsorption on cell walls. The apoplast contains an important
supply of plant nutrients, including water. Lead in the apoplast remains external to the
cells and cannot pass to vascular tissue without at least passing through the cell membranes
of the endodermis. Because this extracellular region is bounded on all sides by cell walls,
the surface of which is composed of layers of cellulose strands, the surface area of the
apoplast is comparable to a sponge. It is likely that much of the lead in roots is adsorbed
to the apoplast surface. Dictyosomes, cytoplasmic organelles which contain cell wall
material, may carry lead from inside the cell through the membrane to become a part of the
external cell wall (Malone et al., 1974), possibly replacing calcium in calcium pectate. Lead
may also be stored and excreted as lead phosphate in dictyosome vesicles (Malone et al.,
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1974). Nevertheless, some lead does pass into the vascular tissue, along with water and
dissolved nutrients, and is carried to physiologically active tissue of the plant.
Evidence that lead in contaminated soils can enter the vascular system of plants and be
transported to aboveground parts may be'-found in the analysis of tree rings. RoTfe (1974)
found four-fold increases in both rural and urban trees using 10 year increments of annual
rings for the period 1910-20 and comparing these to annual rings of the period 1963-73.
Symeonides (1979) found a two-fold increase from 1907-17 to 1967-77 in trees at a high-lead
site, with no increase in trees from a low-lead site. Finally, Baes and Ragsdale (1981),.
using only ring porous species, found significant post-1930 increases in Quercus and Carya
with high lead exposure, but only in Carya with low lead exposure. These chronological
records confirm that lead can be translocated from roots to the upper portions of the plant
and that the amounts translocated are in proportion to the concentrations of lead in soil.
B.3.1.2 Physiological Effects on Plants. Because most of the physiologically active tissue of
plants is involved in growth, maintenance, and photosynthesis, it is expected that lead might
interfere with one or more of these processes. Indeed, such interferences have been observed
in laboratory experiments at lead concentrations greater than those normally found in the
field, except near smelters or mines (Koeppe, 1981). It is likely that more is known of these
effects because these are the physiological processes studied more vigorously than others.
Studies of other plant processes, especially maintenance, flowering, and hormone development,
have not been conducted and no conclusion can be reached concerning possible lead effects on
these processes.
Inhibition of photosynthesis by lead may be by direct interference with the light reac-
tion or the indirect interference with carbohydrate synthesis. At 21 pg Pb/g reaction solu-
tion, Miles et al. (1972) demonstrated substantial inhibition of photosystem II near the site
of water splitting, a biochemical process believed to require manganese. Homer et al. (1979)
found a second effect on photosystem II at slightly higher concentrations of lead. This
effect was similar to that of DCMU [3-(3,4-dichlorophenyl)-l,1-dimethylurea], a reagent com-
monly used to uncouple the photosynthetic. electron transport system. Bazzaz and Govindjee
(1974) suggested that the mechanism of lead inhibition was a change in the conformation of the
thylakoid membranes, separating and isolating pigment systems I and II. Wong and Govindjee
(1976) found that lead also interferes with P700 photooxidation and re-reduction, a part of
the photosystem 1 light reaction. Homer et al. (1981) found a lead tolerant population of the
grass Phalaris arundinacea had lowered the ratio of chlorophyll a/chlorophyll b, believed to
be a compensation for photosystem II inhibition. There was no change in the total amount of
chlorophyll, but the mechanism of inhibition was considered different than that of Miles et
al. (1972). Hampp and Lendzian (1974) found that lead chloride inhibits the synthesis of
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chlorophyll b more than that of chlorophyll a at concentrations up to 100 mg Pb/g. Devi
Prasad and Devi Prasad (1982) found 10 percent inhibition of pigment production in three spe-
cies of green algae at 1 pg/g, increasing to 50 percent inhibition at 3 pg/g. Bazzaz et al.
(1974, 1975) observed reduced net photosynthesis which may have been caused indirectly by
inhibition of carbohydrate synthesis. Without carbohydrates, stomatal guard cells remain
flaccid, transpiration ceases, carbon dioxide fixation decreases', ar.d further carbohydrate
synthesis is inhibited.
The stunting of plant growth may be by the inhibition of the growth hormone IAA (indole-
3-ylacetic acid). Lane et al. (1978) found a 25 percent reduction in elongation at 10 jjg/g
lead as lead nitrate in the nutrient medium of wheat coleoptiles. This effect could be re-
versed with the addition of calcium at 18 pg/g. Lead may also interfere with plant growth by
reducing respiration or inhibiting cell division. Miller and Koeppe (1970) and Miller et al.
(1975) showed succinate oxidation inhibition in isolated mitochondria as well as stimulation
of exogenous NADH oxidation with related mitochondrial swelling. Hassett et al. (1976),
Koeppe (1977), and Malone et al. (1978) described significant inhibition of lateral root
initiation in corn. Inhibition increased with the simultaneous addition of cadmium.
Sung and Yang (1979) found that lead at 1 pg/g can complex with and inactivate ATPase to
reduce the production and utilization of ATP in kidney bean (Phaseolus vulgaris) and buckwheat
leaves (Faqopyruni esculentum). The lead was added hydroponically at concentrations up to
1,000 pg/g. Kidney bean ATPase showed a continued response from 1 to 1,000 pg/g, but buck-
wheat leaves showed little further reduction after 10 pg/g. Neither extracted ATP nor chemi-
cally added ATP could be used by the treated plants. Lee et al. (1976) found a 50 percent
(
increase in the activity of several enzymes related to the onset of senescence in soybean
leaves when lead was added hydroponically at 20 pg/g. These enzymes were acid phosphatase,
peroxidase, and alpha-amylase. A build-up of ammonia was observed along with a reduction in
nitrate, calcium, and phosphorus. Glutamine synthetase activity was also reduced by 65 per-
cent. Continued increases in effects were observed up to 100 pg/g, including a build-up of
soluble protein. Paivoke (1979) also observed a 60 percent increase in acid phosphatase acti-
vity during the first 6 days of pea seedling germination (Pisum sativum) at 2 pg/g, under low
nutrient conditions. The accumulation of soluble protein was observed and the effect could be
reversed with the addition of nutrients, including calcium.
The interaction of lead with calcium has been shown by several authors, most recently by
Garland and Wilkins (1981), who demonstrated that barley seedlings (Hordeum vulgare), which
were growth inhibited at 2 pg Pb/g sol. with no added calcium, grew at about half the control
rate with 17 pg Ca/g sol. This relation persisted up to 25 pg Pb/g sol. and 500 pg Ca/g sol.
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These studies of the physiological effects of lead on plants ail show some effect at
concentrations from 2 to 10 pg/g in the nutrient medium of nydroponically-grown agricultural
plants. It is certain that no effects would have been observed at these concentrations had
the lead solutions been added to normal soil, where the lead wou:d have been bound by humic
substances. There is no firm relationship between soil lead and soil moisture lead, because
each soil type has a unique capacity to retain lead and to release that lead to the soil
moisture film surrounding the soil particle. Once in soil moisture, lead seems to pass freely
to the plant root according to the capacity of the plant root to absorb water and dissolved
substances (Koeppe, 1981).
Chapter 6 discusses the many parameters controlling the release of lead from soil to soil
moisture, but so few data are available on observed lead concentrations in soil moisture that
no model can be formed. It seems reasonable that there may be a direct correlation between
lead in hydroponic media and lead in soil moisture, Hydroponic media typically have an excess
of essential nutrients, including calcium and phosphorus, so that movement of lead from hydro-
ponic media to plant root would be equal to or slower than movement from soil moisture to
plant root. Hughes (1981) adopted the general conclusion that extractable soil lead is typi-
cally 10 percent of total soil lead. However, this lead was extracted chemicaJly under lab-
oratory conditions more rigorous than the natural equilibrium between soil and soil moisture.
Ten percent should therefore be considered the upper limit, where the ability of soil to
retain lead is at a minimum. A lower limit of 0.01 percent is based on the only known report
of lead in both soil and soil moisture (16 pg/Q soil, 1.4 jjg/g soil moisture; Elias et al. ,
1982). This single value shows neither trends with different soil concentrations nor the soil
component (organic or inorganic) that provides the lead to the soil moisture. But the number
(0.01 percent) is a conservative estimate of the ability of soil to retain lead, since the
conditions (pH, organic content) were optimum for retaining lead. A further complication is
that atmospheric lead is retained at the surface (0-2 cm) of the soil profile (Martin and
¦ Coughtrey, 1981), whereas most reports of lead in soil pertain to samples from 0 to 10 cm as
the "upper" layer of soil. Any plant that absorbs solely from the top few centimeters of soil
obviously is exposed to more lead than one with roots penetrating to a depth of 25 cm or more.
Agricultural practices that cultivate soil to a depth of 25 cm blend in the upper layers with
lower to create a soil with average lead content somewhat above background.
These observations lead to the general conclusion that even under the best of conditions
where soil has the highest capacity to retain lead, most plants would experience reduced
growth rate (inhibition of photosynthesis, respiration, or cell elongation) in soils of 10,000
pg Pb/g or greater. Concentrations approaching this value typically occur around smelters
(Martin and Coughtrey, 1981) and near major highways (Wheeler and Rolfe, 1979). These con-
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elusions pertain to soil with the ideal composition and pH to retain the maximum amount of
lead. Acid soils or soils lacking organic matter would inhibit plants at much lower lead
concentrations.
The rate at which atmospheric lead accumulates in soil varies from 1.1 mg/m2-yr average
global deposition (Table 6-7) to 3,000 rng/m2-yr near a smelter (Patterson et a 1. , 1975).
Assuming an average density of 1.5 g/cm3, undisturbed soil to a depth of 2 cm (20,000 cm3/m2)
would incur an increase in lead concentration at a rate of 0.04 to 100 pg/g soil-yr. This
means remote or rural area soils may never reach the 10,000 |jg/g threshold but that undis-
turbed soils closer to major sources may be within range in the next 50 years.
8.3.1.3 Lead Tolerance in Vascular Plants. Some plant species have developed populations
tolerant to high lead soils (Antonovics st al., 1971). In addition to Homer et al. (1981)
cited above, Jowett (1964) found populations of Agrostis tenuis in pure stands on acidic spoil
banks near an abandoned mine. The exclusion of other species was attributed to root inhibi-
tion. Populations of A. tenuis from low-lead soils had no tolerance for the high lead soils.
Several other studies suggest that similar responses may occur in populations growing in
lead-rich soils (reviewed in Peterson, 1978). ' A few have suggested that crops may be culti-
vated for their resistance to high lead soils (Gerakis et al., 1980; John, 1977).
Using populations taken from mine waste and uncontaminated control areas, some authors
have quantified the degree of tolerance of Agrostis tenuis (Karataglis, 1982) and Festuca
rubra (Wong, 1982) under controlled laboratory conditions. Root elongation was used as the
index of tolerance. At 36 pg Pb/g nutrient solJutn>ny al 1 populations of A. tenuis were com-
pletely inhibited. At 12 pg Pb/g, the control populations from low lead soils were completely
inhibited, but the populations from mine soils achieved 30 percent of their normal growth
(growth at no lead in nutrient solution). At 6 pg/g, the control populations achieved 10 per-
cent of their normal growth, tolerant populations achieved 42 percent. There were no measure-
ments below 6 pg/g. Wong (1982) measured the index of tolerance at one concentration only,
2.5 pg Pb/g nutrient solution, and found that non-adapted populations of Festuca rubra which
had grown on soils with 47 pg/g total lead content were completely inhibited, populations from
soils with 350 to 650 pg/g achieved 3 to 7 percent of normal growth, and populations from
5,000 pg/g soil achieved nearly 40 percent of normal growth.
These studies support the conclusion that inhibition of plant growth begins at a lead
concentration of less than 1 |jg/g soil moisture and becomes completely inhibitory at a level
between 3 and 10 pg/g. Plant populations that are genetically adapted to high lead soils may
achieve 50 percent of their normal root growth at lead concentrations above 3 pg/g. These
experiments did not show the effect of reduced root growth on total productivity, but they did
show that exposure to high lead soils is a requirement for genetic adaptation and that, at
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least in the case of F. rubra, plant lead concentrations increase with increasing concentra-
tions i n the soi1.
8.3.1.4 Effects of Lead on Forage Crops. In the 1977 Criteria Document (U.S. Environmental
Protection Agency, 1977), there was a general awareness that most of the lead in plants was
surface lead from the atmosphere. Most studies since then have addressed the problem of dis-
tinguishing between surface and internal plant lead. The general conclusion is that, even in
farmlands remote from major highways or industrial sources, 90 to 99 percent of the total
plant lead is of anthropogenic origin (National Academy of Sciences, 1980). Obviously, the
critical agricultural problem concerns forage crops and leafy vegetables. In Great Britain,
Crump and Barlow (1982) determined that within 50 m of the highway, surface deposition is the
major source of lead in forage vegetation. Beyond this range, seasonal effects can obscure
the relative contribution of atmospheric lead. The atmospheric deposition rate appears to be
much greater in the winter than in the summer. Two factors may explain this difference.
First, deposition rate is a function of air concentration, particle size distribution, wind-
speed, and surface roughness. Of these, only particle size distribution is likely to be inde-
pendent of seasonal effects. Lower windspeeds or air concentration during the summer could
account for lower deposition rates. Second, it may be that the deposition rate only appears
to change during the summer. With an increase in biomass and a greater turnover in biomass,
the effective surface area increases and the rate of deposition, which is a function of sur-
face area, decreases. During the summer, lead may, not build up on the surface of leaves as it
does in winter, even though the f 1 ux.pep ,uni% ..of ground area may be the same.
8.3.1.5 Summary of Plant Effects. When soil conditions allow lead concentrations in soil
moisture to exceed 2 to 10 pg/g, most plants experience reduced growth due to the inhibition
of one or more physiological processes. Excess calcium or phosphorus may reverse the effect.
Plants that absorb nutrients from deeper soil layers may receive less lead. Acid rain is not
likely to release more lead until after major nutrients have been depleted from the soil. A
few species of plants have the genetic capability to adapt to high lead soils.
8.3.2 Effects on Bacteria and Fungi
8.3.2.1 Effects on Decomposers. Tyler (1972) explained three ways in which lead might inter-
fere with the normal decomposition processes in a terrestrial ecosystem. Lead may be toxic to
specific groups of decomposers, it may deactivate enzymes excreted by decomposers to break
down organic matter, or it may bind with the organic matter to render it resistant to the
action of decomposers. Because lead in litter may selectively inhibit decomposition by soil
bacteria at 2,000 to 5,000 pg/g (Smith, 1981, p. 160), forest floor nutrient cycling processes
may be seriously disturbed near lead smelters (Bisessar, 1982; Watson et al., 1976). This, is
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especially important because approximately 70 percent of plant biomass enters the decomposer
food chain (Swift et al. , 1979, p. 6). If decomposition of the biomass is inhibited, then
much of the energy and nutrients remain unavailable to subsequent components of the food
chain. There is also the possibility that the ability of soil to retain lead would be re-
duced, as humic substances are byproducts of bacterial decomposition.
During decomposition, plant tissues are reduced to resistant particulate matter, as solu-
ble organic and inorganic compounds are removed by the chemical action of soil moisture and
the biochemical action of microorganisms (Odum and Drifmeyer, 1978). Each group of micro-
organisms specializes in the breakdown of a particular type of organic molecule. Residual
waste products of one group become the food for the next group. Swift et al. (1979, p. 101)
explained this relationship as a cascade effect with the following generalized pattern (Figure
8-4). Organisms capable of penetrating hard or chemically resistant plant tissue are the
primary decomposers. These saprotrophs, some of which are fungi and bacteria that reside on
leaf surfaces at the initial stages of senescence, produce a wide rar.ge of extracellular
enzymes. Others may reside in the intestinal tract of millipedes, beetle larvae, and termites
capable of mashing plant tissue into small fragments. The feces and remains of this group and
the residual plant tissue are consumed by secondary decomposers, i.e., the coprophilic fungi,
bacteria, and invertebrates (including protozoa) specialized for consuming bacteria. These
are followed by tertiary decomposers. Microorganisms usually excrete enzymes that carry out
this digestive process external to their cells. They are often protected by a thick cell
coat, usually a polysaccharide. Because they are interdependent, the absence of one group in
this sequence seriously affects the success of subsequent groups, as well as the rate at which
plant tissue decomposes. Each group may be affected in a different way and at different lead
concentrations. Lead concentrations toxic to decomposer microbes may be as low as 1 to 5 pg/g
or as high as 5,000 (jg/g (Doelman, 1978).
Under conditions of mild contamination, the loss of one sensitive bacterial population
may result in its replacement by a more lead-tolerant strain. Inman and Parker (1978) found
that litter transplanted from a low-lead to a high-lead site decayed more slowly than high-
lead litter, suggesting the presence of a lead sensitive microorganism at the low-lead site.
When high-lead litter was transplanted to the low-lead site, decomposition proceeded at a rate
faster than the low-lead litter at the low-lead site. In fact, the rate was faster than the
high-lead litter at the high*lead site, suggesting even the lead tolerant strains were some-
what inhibited. The long term effect is a change in the species composition of the ecosystem,
which will be considered in greater detail in Section 8.5.2.
Delayed decomposition has been reported near smelters (Jackson and Watson, 1977), mine
waste dumps (Williams et al., 1977), and roadsides (Inman and Parker, 1978). This delay is
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GROUP I
RAW
DETRITUS
GROUP II
GROUP III
INORGANIC
NUTRIENTS
Figure 8-4. Within the decomposer food chain, detritus is progressively broken down
in a sequence of steps regulated by specific groups of decomposers. Because of the
cascade effect of this process, the elimination of any decomposer interrupts the sup-
ply of organic nutrients to subsequent groups and reduces the recycling of inorganic
nutrients to plants. Undecomposed litter would accumulate at the stages preceding
the affected decomposer.
Source: Adapted from Swift et al. (1979).
generally in the breakdown of litter from the first stage (Oj) to the second (02) with intact
plant leaves and twigs accumulating at the soil surface. The substrate concentrations at
which lead inhibits decomposition appear to be very low. Williams et al. (1977) found inhibi-
tion in 50 percent of the bacteria and fungal strains at 50 ^9 Pb/ml nutrient solution. The
community response time for Introducing lead tolerant populations seems very fast, however.
Doelman and Haanstra (1979a,b) found lead-tolerant strains had replaced non-tolerant bac-
teria within 3 years of lead exposure. These new bacteria were predominately thick-coated
gram negative strains and their effectiveness in replacing lead-sensitive strains was not
evaluated in terms of soil decomposition rates.
Tyler (1982) has also shown that many species of wood-decaying fungi do not accumulate
Pb, Ca, Sr, or Mn as strongly as they do other metals, even the normally toxic metal, cadmium.
. .v- n :. A
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Accumulation was expressed as the ratio of the metal concentration in the fungus to its sub-
strate. A ratio of greater than one implies accumulation, less than one, exclusion. Of 11
species, manganese was excluded by ten, strontium by nine, lead by eight., and calcium by
seven. Potassium, at the,other end of the spectrum, was not excluded by any species. The
species which appeared to accumulate calcium and lead were described as having harder, less
ephemoral tissues.
This relationship among calcium, strontium, and lead is consistent with the phenomenon of
biopurification described in Section 8.5.2. From the date of Tyler (1982) it appears that
some of the species of fungi receive lead from a source other than the nutrient medium, per-
haps by direct atmospheric deposition.
8.3.2.2 Effects on Nitrifying Bacteria. The conversion of ammonia to nitrate in soil is a
two-step process mediated by two genera of bacteria, Nitrosomonas and Nitrobacter. Nitrate is
required by all plants, although some maintain a symbiotic relationship with nitrogen-fixing
bacteria as an alternate source of nitrogen. Those which do not would be affected by a loss
of free-living nitrifying bacteria, and it is known that many trace metals inhibit this nitri-
fying process (Liang and Tabatabai, 1977,1978). Lead is the least of these, inhibiting nitri-
fication 14 percent at concentrations of 1,000 pg/g soil. Many metals, even the nutrient
metals, manganese and iron, show greater inhibition at comparable molar concentrations.
Nevertheless, soils with environmental concentrations above 1,000 pg Pb/g are frequently found,
Even a 14 percent inhibition of nitrification can reduce the potential success of a plant
population, as nitrate is usually the limiting nutrient in terrestrial ecosystems. In cul-
tivated ecosystems, nitrification inhibition is not a problem if nitrate fertilizer is added
to soil, but could reduce the effectiveness of ammonia fertilizer if the crops rely on nitri-
fying bacteria for conversion to nitrates.
8.3.2.3 Methylation by Aquatic Microorganisms. While methyl lead is not a primary form of
environmental lead, methylation greatly increases the toxicity of lead to aquatic organisms
(Wong and Chau, 1979). There is some uncertainty about whether the mechanism of methylation
is biotic or abiotic. Some reports (Wong and Chau, 1979, Thompson and Crerar, 1980) conclude
that lead in sediments can be methylated by bacteria. Reisinger et al. (1981) report that
biomethylation of lead under aerobic or anaerobic conditions does not occur and such reports
are probably due to sulfide-induced chemical conversion of organic lead salts. These authors
generally agree that tetramethyl lead can be formed under environmental conditions when
another tetravalent organolead compound is available, but methylation of divalent lead salts
such as Pb(N03)2 does not appear to be significant.
8.3.2.4 Summary of Effects on Microorganisms. It appears that microorganisms are more sen-
sitive than plants to soil lead pollution and that changes in the composition of bacterial
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PRELIMINARY DRAFT
populations may be an early indication of lead effects. Delayed decomposition may occur at
750 |jg Pb/g soil and nitrification inhibition at 1,000 pg/g. Many of the environmental vari-
ables which can raise or lower these estimates are not yet known. In certain chemical en-
vironments, the highly toxic tetramethyllead can be formed, but this; process does not appear
to be mediated by aquatic microorganisms.
8.4 EFFECTS OF LEAD ON DOMESTIC AND WILD ANIMALS
8.4.1 Vertebrates
8.4.1.1 Terrestrial Vertebrates. Forbes and Sanderson (1978) have reviewed reports of lead
toxicity in domestic and wild animals. Lethal toxicity can usually be traced to consumption
of lead battery casings, lead-based paints, oil wastes, putty, linoleum, pesticides, lead shot,
or forage near smelters. Except for lead shot ingestion, these problems can be solved by pro-
per management of domestic animals. However, the 3,000 tons of lead shot distributed annually
along waterways and other hunting grounds continues to be a problem. Of the estimated 80 to
90 million waterfowl in North America, 3.5 million die of poisoning from lead shot annually
(U.S. Fish and Wildlife Service, 1976).
A single pellet of lead shot weighs about 110 mg, and 70 percent of this may be eroded in
ringed turtle dove gizzards over a period of 14 days (Kendall et at., 1982). Their data
showed an immediate elevation of blood lead and reduction of ALA-D activity within 1 day of
swallowing two pellets.
Awareness of the routes of uptake is important in interpreting the exposure and accumula-
tion in vertebrates. Inhalation rarely accounts for more than 10 to 15 percent of the daily
intake of lead (National Academy of Sciences, 1980). Much of the inhaled lead is trapped on
the walls of the bronchial tubes and passes to the stomach embedded in swallowed mucus.
Because lead in lakes or running stream water is quite low, intake from drinking water may
also be insignificant unless the animal drinks from a stagnant or otherwise contaminated
source.
Food is the largest contributor of lead to animals. The type of food an herbivore eats
determines the rate of lead ingestion. More than 90 percent of the total lead in leaves and
bark may be surface deposition, but relatively little surface deposition may be found on some
fruits, berries, and seeds which have short exposure times. Roots intrinsically have no sur-
face deposition. Similarly, ingestion of lead by a carnivore depends mostly on deposition on
herbivore fur and somewhat less on lead in herbivore tissue.
The type of food eaten is a major determinant of lead body burdens in small mammals.
Goldsmith and Scanlon (1977) and Scanlon (1979) measured higher lead concentrations in insect-
ivorous species than in herbivorous species, confirming the earlier work of Quarles et al.
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(1974), which showed body burdens of granivores < herbivores < insectivores, and Jeffries and
French (1972) that granivores < herbivores. Animals in these studies were analyzed whole
minus the digestive tract. It is likely that observed diet-related differences were somewhat
diluted by including fur in the analysis, because fur-lead might be similar for small mammals
from the same habitats with different feeding habits.
Since 1977, there has been a trend away from whole body analyses toward analysis of iso-
lated tissues, especially bones and blood. Bone concentrations of lead are better than blood
as indicators of long term exposure. Because natural levels of blood lead are not wel.l known
for animals and blood is not a good indicator of chronic exposure, blood lead is poorly suited
for estimating total body burdens. One experiment with sheep shows the rapid response of
blood to changes in lead ingestion and the relative contribution of food and air to the total
blood level. Ward et al. (1978) analyzed the blood in sheep grazing near a highway (0.9 (jg/g
ml) and in an uncontaminated area (0.2 pg/ml). When sheep from the uncontaminated area were
allowed to graze near the roadway, their blood levels rose rapidly (within 1 day) to about
3.0 jjg/ml, then decreased to 2.0 pg/ml during the next 2 days, remaining constant for the
remainder of the 14-day period. Sheep from the contaminated area were moved to the uncon-
taminated area, where upon their blood dropped to 0.5 pg/ml in 10 days and decreased to 0.3
pg/ml. during the next 180 days. Sheep in the uncontaminated area that were fed forage from
the roadside experienced an increase in blood lead from 0.2 to 1.1 pg/ml in 9 days. Con-
versely, sheep from the uncontaminated area moved to the roadside but fed forage only from the
uncontaminated site experienced an increase from 0.2 to 0.5 pg/ml in 4 days. These data
show that both air and food contribute to lead in blood and that blood lead concentrations are
a function of both the recent history of lead exposure and the long term storage of lead in
bone tissue.
Chmiel and Harrison (1981) showed that the highest concentrations of lead occurred in the
bones of small mammals (Table 8-2), with kidney and liver concentrations somewhat less. They
also showed greater bone concentrations in insectivores than herbivores, both at the control
and contaminated sites. Clark (1979) found lead concentrations in shrews, voles, and brown,
bats from roadside habitats near Washington, D.C., to be higher than any previously reported.
His estimates of dosages (7.4 mg Pb/kg-day) exceed those that normally cause mortality or
reproductive impairment in domestic mammals (1.5-9 mg Pb/g-day) (Hammond and Aronson, 1964;
James et al., 1966; Kelliher et al., 1973). Traffic density was the same as reported by Chmiel
and Harrison (1981), nearly twice that of Goldsmith and Scanlon (1977) (See Table 8-2). The
body lead burden of shrews exceeded mice, which exceeded voles. Beresford et al. (1981) found
higher lead in box turtles within 500 m of a lead smelter than in those from control sites.
Bone lead exceeded kidney and liver lead as in small mammals.
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There are few studies reporting lead in vertebrate tissues from remote sites. Elias et
al. (1976, 1982) reported tissue concentrations in voles, shrews, chipmunks, tree squirrels,
and pine martens from the remote High Sierra. Bone concentrations were generally only 2
percent of those reported from roadside studies and 10 percent of the controls of roadside
studies (Table 8-2), indicating the controls were themselves contaminated to a large degree.
Furthermore, biogeochemical calculations suggest that even animals in remote areas have bone
lead concentrations 50 to 500 times natural background levels. The natural concentration of
lead in the bones of herbivores is about 0.04 ng/g dry weight (Table 8-1). This value may
vary regionally with geochemical anomalies in crustal rock, but provides a reasonable indica-
tor of contamination. Natural levels of lead in carnivore bone tissue should be somewhat
lower, with omnivores generally in between (Elias and Patterson, 1980; Elias et al., 1982).
Table 8-2 shows the results of several studies of small animal bone tissue. To convert
reported values to a common basis, assumptions were made of the average water content, calcium
concentration, and average crustal concentration. Because ranges of natural concentrations of
lead in bones, plants, soils, and air are known with reasonable certainty (Table 8-1), it is
possible to estimate the degree of contamination of vertebrates from a wide range of habitats.
It is important to recognize that these are merely estimates that do not allow for possible
errors in analysis or anomalies in regional crustal abundances of lead.
8.4.1.2 Effects on Aquatic Vertebrates. Two requirements limit the evaluation of literature
reports of lead effects on aquatic organisms. First, any .laboratory study should incorporate
the entire life cycle of the organism studied. It is clear that certain stages of a life
cycle are more vulnerable than others (Hodson, 1979, Hodson et al., 1979). For fish, the egg
or fry is usually most sensitive. Secondly, the same index must be used to compare results.
Christensen et al. (1977) proposed three indices useful for identifying the effects of lead on
organisms. A molecular index reports the maximum concentration of lead causing no significant
biochemical change; residue index is the maximum concentration showing no continuing increase
of deposition in tissue; and a bioassay index is the maximum concentration causing no mortal-
ity, growth change, or physical deformity. These indices are comparable to those of physio-
logical dysfunction (molecular, tissue, and organismic) discussed in Section 8.1.4.
From the standpoint of environmental protection, the most useful index is the molecular
index. This index is comparable to the point of initial response discussed previously and is
equivalent to the "safe concentration" originally described by the U.S. Environmental
Protection Agency (Batelle, 1971) as being the concentration that permits normal reproduction,
growth, and all other life-processes of all organisms. It is unfortunate that very few of the
toxicity studies in the aquatic literature report safe concentrations as defined above.
Nearly all report levels at which some or all of the organisms die.
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TABLE 8-2. ESTIMATES OF THE DEGREE OF CONTAMINATION OF HERBIVORES,
OMNIVORES, AND CARNIVORES
Data are based on published concentrations of lead in bone tissue (corrected to dry weight as
indicated). Degree of contamination is calculated as observed/natural Pb. Natural lead con-
centrations are from Table 8-1. Concentrations are in (jg Pb/g dw.
Estimated degree of
Bone contamination
Organism Pb conc. Ref. bone
Herbivores
Vole-roadside
38
1
320
Vole-roadside
17
2
140
-control
5
2
42
Vole-orchard
73
5
610
-control
9
5
75
Vole-remote
2
11
17
Deer mouse-roadside
25
2
210
-control
5.7
2
48
Deer mouse-roadside
29
3
240
-control
7.2
3
60
Deer mouse-roadside
52
4
430
-control
5
4
42
Mouse-roadside
19
2
160
-control
9.3
2
78
Mouse-roadside
1D9
2
910
-control
18
2
150
Average herbivore
roadside (7)
41
340
control (7)
8.5
71
remote (2)
2
17
nni vores/frugi vores
Woodmouse-roadsi de
67
1
840
-control
25
1
• 310
Composite-roadside
22
7
280
-control
3
37
Chipmunk-remote
2
1
25
Tree squirrel-remote
1.3
11
16
Feral pigeon-urban
670
6
8400
-rural
5.7
6
71
Feral pigeon-urban
250
12
3100
-suburan
33
12
410
-rural
12
12
150
Starling-roadside
210
7
2600
-control
13
7
160
(continued)
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TABLE 8-2. (continued)
Organi sui
Bone
Pb conc.
Ref.
Estimated degree of
contamination
bone
Robin-roadside
130
7
1600
-control
41
7
510
Sparrow-roadsi de
130
7
1600
-control
17
7
200
B1ackbi rd-roadsi de
90
7
1100
-control
7
7
88
Grackle-roadside
63
790
-control
22a
7
280
Rats-roadside
310
9
10000
-control
15
9
500
Average omnivore
*
roadside (7)
102
1260
urban (1)
670
8400
control (7)
18
230
remote (2)
1.7
21
Carnivores
Box turtle-smelter
91' a
8
3000
-control
V
8
190
Egret-rural
12a
10
400
Gul1-rural
lla
10
370
Shrew-roadside
67
2
2200
-control
12
2
400
Shrew-roadside
193
1
6400
-control
41
1
1400
Shrew-remote
4.6
1
150
Pine marten-remote
1.4
11
47
Average carnivore
roadside (3)
190
6200
smelter (1)
91
3000
rural (2)
11
385
control (4)
18
620
remote (2)
• 3
' 99
aDry weight calculated from published fresh weights assuming 35 percent water.
1. Chmiel and Harrison, 1981 /
2. Getz et al., 1977b
3. Welch and Dick, 1975
4. Mierau and Favara, 1975
5. Elfving et al., 1978
6. Hutton and Goodman, 1980
7. Getz et al., 1977a
8. Beresford et al. , 1981
9. Mouw et al. , 1975
10. Hul se et al., 1980
11. Elias et al., 1982
12. Johnson et al., 1982b
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Hematological and neurological responses are the most commonly reported effects of
extended lead exposures in aquatic vertebrates. Hematological effects include the disabling
and destruction of mature red blood cells and the inhibition of the enzyme ALA-D required for
hemoglobin synthesis. At low exposures, fish compensate by forming additional red blood
cells. These red blood cells often do not reach maturity. At higher exposures, the fish
become anemic. Symptoms of neurological responses are difficult to detect at low exposure,
but higher exposure can induce neuromuscular distortion, anorexia, and muscle tremors. Spinal
curvature eventually occurs with time or increased concentration (Hodson 1979; Hodson et al.,
1977). Weis and Weis (1982) found spinal curvature in developing eggs of killifish when the
embryos had been exposed to 10 pg Pb/ml during the first 7 days after fertilization. All
batches showed some measure of curvature, but those that were most resistant to lead were
least resistant to the effects of methylmercury.
The biochemical changes used by Christensen et al. (1977) to determine the molecular
index for brook trout were 1) increases in plasma sodium and chloride and 2) decreases in
glutamic oxalacetic transaminase activity and hemoglobin. They observed effects at 0.5 fjg/1»
which is 20-fold less than the lower range (10 pg/1) suggested by Wong et al. (1978) to cause
significant detrimental effects. Hodson et al. (1978a) found tissue accumulation and blood
parameter changes in rainbow trout at 13 pg/1. This was the lowest experimental level, and
only slightly above the controls, which averaged 4 pg/1. They concluded, however, that
because spinal curvature does not occur until exposures reach 120 pg/1, rainbow trout are ade-
quately protected at 25 pg/1.
Aside from the biochemical responses discussed by Christensen et al. (1977), the lowest
reported exposure concentration that causes hematological or neurological effects is 8 \iq/\
(Hodson, 1979). Christensen's group dealt with subcellular responses, whereas Hodson's group
dealt primarily with responses at the cellular or higher level. Hodson et al. (1978a) also
reported that lead in food is not available for assimilation by fish, that most of their lead
comes from water, and that decreasing the pH of water (as in acid rain) increases the uptake
of lead by fish (Hodson et al., 1978b). Patrick and Loutit (1978), however, reported that
tissue lead in fish reflects the lead in food if the fish are exposed to the food for more
than a few days. Hodson et al. (1980) also reported that, although the symptoms are similar
(spinal deformation), lead toxicity and ascorbic acid deficiency are not metabolically
related.
8.4.2 Invertebrates
Insects have lead concentrations that correspond to those found in their habitat and diet.
Herbivorous invertebrates have lower concentrations than do predatory types (Wade et al.,
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1980). Among the herbivorous groups, sucking insects have lower lead concentrations than
chewing insects, especially in regions near roadsides, where more lead is found on the sur-
faces of vegetation. Williamson and Evans (1972) found gradients away from roadsides are not
the same as with vertebrates, in that invertebrate lead decreases more slowly than vertebrate
lead relative to decreases in soil lead. They also found great differences between major
groups of invertebrates. Wood lice in the same habitat, eating the same food, had eight times
more lead than millipedes.
The distribution of lead among terrestrial gastropod tissues was reported by Ireland
(1979). He found little difference among the foot, skin, mantle, digestive gland, gonad, and
intestine. There are no reports of lead toxicity in soil invertebrates. In a feeding experi-
ment, however, Coughtrey et al. (1980) found decreased tolerance for lead by microorganisms
from the guts of insects at 800 ^g Pb/g food. Many roadside soils fall in this range.
Cepaea hortensis, a terrestrial snail, Williamson (1979) found most of the lead in the
digestive gland and gonadal tissue. He also determined that these snails can lose 93 percent
of their whole body lead burden in 20 days when fed a low-lead diet in the laboratory. Since
no analyses of the shell were reported, elimination of lead from thistissue cannot be evalu-
ated. A continuation of the study (Williamson, J980) showed that body weight, age, and day-
length influenced the lead concentrations in soft tissues.
Beeby and Eaves (1983) addressed-^the -question of whether uptake of lead in the garden
snail, Helix aspersa, is related to the nutrient requirement for calcium during shell forma-
tion and reproductive activity. They found both metals were strongly correlated with changes
in dry weight and little evidence for correlation of lead with calcium independent of weight
gain or loss. Lead in the diet remained constant.
Gish and Christensen (1973) found lead in whole earthworms to be correlated with,soil
lead, with little rejection of lead by earthworms. Consequently, animals feeding on earth-
worms from high lead soils might receive toxic amounts of lead in their diets, although there
was no evidence of toxic effects on the earthworms (Ireland, 1977). Ash and Lee (1980)
cleared the digestive tracts of earthworms and still found direct correlation of lead in
earthworms with soil lead; in this case, soil lead was inferred from fecal analyses. These
authors found differences among species of earthworms. Ireland and Richards (1977) also found
species differences in earthworms, as well as some localization of lead in subcellular organ-
elles of chloragogue and intestinal tissue. In view of the fact that chloragocytes are be-
lieved to be involved with waste storage and glycogen synthesis, the authors concluded that
this tissue is used to sequester lead in the manner of vertebrate livers. Species differences
in whole body lead concentrations could not be attributed to selective feeding or differential
absorption, unless the differential absorption occurs only at elevated lead concentrations.
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The authors suggested that the two species have different maximum tolerances for body lead but
gave no indication of physiological dysfunction when the maximum tolerance was reached. In
soils with a total lead concentration of 1,800 (jg/g dry weight (Ireland, 1975), Lumbricus
rube 11 us had a whole body concentration of 3,600 pg/g, while Dendrobaene rubida accumulated
7,600 pg/g in the same location (Ireland and Richards, 1977). Because this difference was not
observed at the control site (15 (jg/g soil), it can be assumed that at some soil concentration
between 15 and 1,800 pg/g, different species of earthworms begin to accumulate different
amounts of lead. The authors concluded that D. rubida can simply tolerate higher tissue lead
concentrations, implying that soil concentrations of 1,800 pg/g are toxic to I. rubel lus. This
concentration would be considerably lower than soil lead concentrations that cause effects in
plants, and similar to that which can affect soil microorganisms.
-Aquatic insects appear to be resistant to high levels of lead in water. To be conclu-
sive,' toxicity studies must observe invertebrates through an entire life cycle, although this
is infrequently done. Anderson et al. (1980) found LC5o's for eggs and larvae of Tanytarsus
dissimilis, a chironomid, to be 260 pg/1. This value is 13 to 250 times lower than previously
reported by Warnick and Bell (1969), Rehwoldt et al. (1973), and Nehring (1976). However,
Spehar et al. (1978) found that mature amphipods (Gammarus pseudolimnaeus) responded nega-
tively to lead at 32 jjg/1. Fraser et al. (1978) found that adult populations of a freshwater
isopod (Asel 1 us aquaticus) have apparently developed a genetic tolerance for lead in river
sediments.
Newman and Mcintosh (1982) investigated freshwater gastropods, both grazing and burrow-
ing. Lead concentrations in the grazers (Physa integra, Pseudosuccinea columella, and Helisoma
trivolvis) were more closely correlated with water concentrations than with lead in the food.
Lead in the burrowing species, Campeloma decisum, was not correlated with any environmental
factor. These authors (Newman and Mcintosh, 1983) also reported that both Physa integra and
Campeloma decisum are able to eliminate lead from their soft tissue when transferred to a
low-lead medium, but that tissue lead stabi1ized"at a level higher than found in populations
living permanently in the low-lead environment. This would seem to indicate the presence of a
persistent reservoir of lead in the soft tissues of these gastropods.
Borgraann et al. (1978) found increased mortality in a freshwater snail, Lymnaea palutris,
associated with stream water with a lead content as low as 19 pg/1. Full life cycles were
studied to estimate population productivity. Although individual growth rates were not af-
fected, increased mortality, especially at the egg hatching stage, effectively reduced total
biomass production at the population level. Production was 50 percent at 36 pg/1 and 0 per-
cent at 48 pg Pb/1.
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The relationship between LC50 and initial physiological response is not immediately
obvious. It is certain that some individuals of a population experience physiological dys-
function well before half of them die. For example, Biesinger and Christensen (1972) observed
minimum reproductive impairment in Daphnia at 6 percent of the LC50 (450 pg/1) for this
species.
8.4.3 Summary of Effects on Animals
While it is impossible to establish a safe limit of daily lead consumption, it is reason-
able to generalize that a regular diet of 2 to 8 nig Pb/kg*day body weight over an extended
period of time (Botts, 1977) will cause death in most animals. Animals of the grazing food
chain are affected most directly by the accumulation of aerosol particles on vegetation sur-
faces and somewhat indirectly by the uptake of lead through plant roots. Many of these
animals consume more than 1 mg Pb/kg-day in habitats near smelters and roadsides, but no toxic
effects have been documented. Animals of the decomposer food chain are affected indirectly by
lead in soil which can eliminate populations of microorganisms preceeding animals in the food
chain or occupying the digestive tract of animals and aiding in the breakdown of organic
matter. Invertebrates may also accumultate lead at levels toxic to their predators.
Aquatic animals are affected by lead at water concentrations lower than previously con-
sidered safe (50 pg Pb/1) for wildlife. These concentrations occur commonly, but the contri-
bution of atmospheric lead to specific sites of high aquatic lead is not clear.
8.5 EFFECTS OF LEAD ON ECOSYSTEMS
There 1s wide variation in the mass transfer of lead from the atmosphere to terrestrial
ecosystems. Even within the somewhat artificial classification of undisturbed, cultivated,
and urban ecosystems, reported fluxes in undisturbed ecosystems vary by nearly 20-fold. Smith
and Siccama (1981) report 270 g/ha-yr in the Hubbard Brook forest of New Hampshire; Lindberg
and Harriss (1981) found 50 g/ha-yr -i,n .the.Walker Branch watershed of Tennessee; and Elias et
al. (1976) found 15 g/ha-yr in a remote subalpine ecosystem of California. Jackson and Watson
(1977) found 1,000,000 g/ha-yr near a smelter in southeastern Missouri. Getz et al. (1979)
estimated 240 g/ha-yr by wet precipitation alone 1n a rural ecosystem largely cultivated and
770 g/ha-yr in an urban ecosystem.
One factor causing great variation is remoteness from source, which translates to lower
air concentrations, smaller particles, and greater dependence on wind as a mechanism of depo-
sition (Elias and Davidson, 1980). Another factor is type of vegetation cover. Deciduous
leaves may, by the nature of their surface and orientation in the wind stream, be more suit-
able deposition surfaces than conifer needles. Davidson et al. (1982) discussed the influence
of leaf surface on deposition rates to grasses.
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The history of lead contamination in roadside ecosystems has been reviewed by Smith
(1976). Recent studies hsve shown three areas of concern where the effects of lead on eco-
systems may be extremely sensitive (Martin and Coughtrey, 1981; Smith, 1981). First, decom-
position is delayed by lead, as some decomposer microorganisms and invertebrates are inhibited
by soil lead. Secondly, the natural processes of calcium biopurification are circumvented by
the accumulation of lead on the surfaces of vegetation and in the soil reservoir. Thirdly,
some ecosystems experience subtle shifts toward lead tolerant plant populations. These pro-
blems all arise because lead in ecosystems is deposited on vegetation surfaces, accumulates in
the soil reservoir, and is not removed with the surface and ground water passing out of the
ecosystem. Other potential effects are discussed that may occur because of the longterm
build-up of lead in soil.
8.5.1 Delayed Decomposition
The flow of energy through an ecosystem is regulated largely by the ability of organisms
to trap energy in the form of sunlight and to convert this energy from one chemical form to
another (photosynthesis). Through photosynthesis, plants convert light to stored chemical
energy. Starch is only a minor product of this energy conversion. The most abundant sub-
stance produced by net primary production is cellulose, a structural carbohydrate of plants.
Terrestrial ecosystems, especially forests, accumulate, a tremendous amount of cellulose as
woody tissue of trees. Few animals can digest cellulose and most of these require symbiotic
associations with specialized bacteria. It is no surprise then, that most of this cellulose
must eventually pass through the decomposer food chain. Litter fall is the major route for
this pathway. Because 80 percent or more of net primary production passes through the decom-
posing food chain (Swift et al., 1979), the energy of this litter is vital to the rest of the
plant community and the inorganic nutrients are vital to plants.
The amount of lead that causes litter to be resistant to decomposition is not known.
Although laboratory studies show that 50 |jg Pb/ml nutrient medium definitely inhibits soil
bacterial populations, field studies indicate little or no effect at 600 pg/g litter (Do&lman
and Haanstra, 1979b). One explanation is that the lead in the laboratory nutrient medium was
readily available, while the lead in the litter was chemically bound to soil organic matter.
Indeed, Doelman and Haanstra (1979a) demonstrated the effects of soil lead content on delayed
decomposition: sandy soils lacking organic complexing compounds showed a 30 percent inhibition
of decomposition at 750 pg/g, including the complete loss of major bacterial species, whereas
the effect was reduced in clay soils and non-existent in peat soils. Organic matter maintains
the cation exchange capacity of soils. A reduction 1n decomposition rate was observed by
Doelman and Haanstra (1979a) even at the lowest experimental concentration of lead, leading to
the conclusion that some effect might have occurred at even lower concentrations.
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When decomposition is delayed, nutrients may be limiting to plants. In tropical regions
or areas with sandy soils, rapid turnover of nutrients is essential for the success of the
forest community. Even in a mixed deciduous forest, a significant portion of the nutrients,
especially nitrogen and sulfur, may be found in the litter reservoir (Likens et al. 1977).
Annual litter inputs of calcium and nitrogen to the soil account for about 60 percent of root
uptake. With delayed decomposition, plants must rely on precipitation and soil weathering for
the bulk of their nutrients. Furthermore, the organic content of soil may decrease, reducing
the cation exchange capacity of soil.
8.5.2 Circumvention of Calcium Biopurification
Biopurification is a process that regulates the relative concentrations of nutrient to
non-nutrient elements in biological components of a food chain. In the absence of absolute
knowledge of natural lead concentrations, biopurification can be a convenient method for esti-
mating the degree of contamination. Following the suggestion by Comar (1966) that carnivorous
animals show reduced Sr/Ca ratios compared to herbivorous animals which, in turn show less
than plants, Elias et al. (1976, 1982) developed a theory of biopurification, which hypothe-
sizes that calcium reservoirs are progressively purified of Sr, Ba, and Pb in successive
stages of a food chain. In other words, if the Sr/Ca and 3a/Ca ratios are known, the natural
Pb/Ca ratio can be predicted and the observed Pb/Ca to natural Pb/Ca ratio is an expression of
the degree of contamination. Elias et al. (1976, 1982) and Elias and Patterson (1980)
observed continuous biopurification of calcium in grazing and detrital food chains by the pro-
gressive exclusion of Sr, Ba, and Pb (Figure 8-5). It is now believed that members of grazing
and decomposer food chains are contaminated by factors of 30 to 500, i.e., that 97 percent to
99.9 percent of the lead in organisms is of anthropogenic origin. Burnett and Patterson
(1980) have shown a similar pattern for a marine food chain.
The mechanism of biopurification relies heavily on the selective transport of calcium
across membranes, the selective retention of non-nutrients at physiologically inactive binding
sites, and the reduced solubility of non-nutrient elements in the nutrient medium of plants
and animals. For example, lead is bound more vigorously to soil organic complexes and is less
soluble in soil moisture (Section 6.5.1). Lead is also adsorbed to cell walls in the root
apoplast, is excluded by the cortical cell membrane, and is isolated as a precipitate in sub-
cellular vesicles of cortical cells (Koeppe, 1981). Further selectivity at the endodermis
results in a nutrient solution of calcium in the vascular tissue which is greatly purified of
lead. Similar mechanisms occur in the stems and leaves of plants, in the digestive and circu-
latory systems of herbivores and carnivores, and in the nutrient processing mechanisms of
insects.
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ROCKS SOIL PLANT HERBI CARNI
MOISTURE LEAVES VORES VORES
Figure 8-5. The atomic ratios Sr/Ca, Ba/Ca and Pb/Ca (O)
normally decrease by several orders of magnitude from the
crustal rock to ultimate carnivores in grazer and decomposer
food chains. Anthropogenic lead in soil moisture and on the
surfaces of vegetation and animal fur interrupt this process
to cause elevated Pb/Ca ratios (•) at each stage of the
sequence. The degree of contamination is the ratio of Total
Pb/Ca vs. Natural Pb/Ca at any stage. Ba/Ca and Sr/Ca ratios
are approximate guidelines to the expected natural Pb/Ca
ratio.
Source: Adapted from Elias et al. (1982).
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Atmospheric lead circumvents the natural biopurification of calcium. Deposition on plant
surfaces, which accounts for 90 percent of the total plant lead, increases the ratio of Pb/Ca
in the diet of herbivores. Deposition on animal fur increases the Pb/Ca ratio in the diet of
carnivores. Atmospheric lead consumed by inhalation or grooming, possibly 15 percent of the
total intake of lead, represents sources of lead which were non-existent in prehistoric times
and therefore were not present in the food chain.
8.5.3 Population Shifts Toward Lead Tolerant Populations
It has been observed that plant communities near smelter sites are composed mostly of
lead tolerant plant populations (Antonovics et al., 1971). In some cases, these populations
appear to have adapted to high-lead soils, since populations of the same species from low-lead
soils often do not thrive on high-lead soils (Jowett, 1964). Similar effects have been ob-
served for soils enriched to 28,000 jjg/g dry weight with ore lead CH
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This organic layer becomes a natural site for the accumulation of lead and other non-nutrient
metals which might otherwise interfere with the uptake and utilization of nutrient metals.
But the rate accumulation of lead in this reservoir may eventually exceed the capacity of the
reservoir. Johnson et al. (1982a) have established a baseline of 80 stations in forests of
the' northeast United States. In the litter component of the forest floor, they measured an
average lead concentration of 150 pg/g. Near a smelter, they measured 700 pg/g and near a
highway, 440 pg/g. They presented some evidence from buried litter that predevelopment con-
centrations were 24 pg/g. On an area basis, the present concentrations range from 0.7 to
1.8 g Pb/m2. Inputs of 270 g/ha-yr measured in the Hubbard Brook forest (see Section 8.5)
would account for 1.0 g Pb/m2 in forty years if all of the lead were retained. The 80 sta-
tions will be monitored regularly to show temporal changes. Evidence for recent changes in
litter lead concentrations is documented in the linear relationship between forest floor lead
concentration and age of forest floor, up to 100 years.
Lead in the detrital reservoir is determined by the continued input of atmospheric lead
from the litter layer, the passage of detritus through the decomposer food chain, and the rate
of leaching into soil moisture. There is strong evidence that soil has a finite capacity to
retain lead (Zimdahl and Skogerboe, 1977). Harrison et al. (1981) observed that most of the
lead in roadside soils above 200 pg/g is found on Fe-Mn oxide films or as soluble lead car-
bonate. Elias et al. (1982) have shown that soil moisture lead is derived from the leachable/
organic fraction of soil, not the inorganic fraction. Lead is removed from the detrital
reservoir by the digestion of organic particles in the detrital food chain and by the release
of lead to soil moisture. Both mechanisms result in a redistribution of lead among all of the
reservoirs of the ecosystem at a very slow rate. A closer look at the mechanisms whereby lead
is bound to humic and fulvic acids leads to the following conclusions: 1) because lead has a
higher binding strength than other metals, lead can displace other metals on the organic
molecule (Schnitzer and Khan, 1978); 2) if calcium is displaced, it would be leached to a
lower soil horizon (B), where it may accumulate as it normally does during the development of
the soil profile; and 3) if other nutrient metals, such as iron.or manganese, are displaced,
they may become unavailable to roots as they pass out of the soil system.
Fulvic acid plays an important role in the development of the soil profile. This organic
acid has the ability to remove iron from the -lattice structures of inorganic minerals, result-
ing in the decomposition of these minerals as a part of the weathering process. This break-
down releases nutrients for uptake by plant roots. If all binding sites on fulvic acid are
occupied by lead, the role of fulvic acid in providing nutrients to plants will be circum-
vented. While it is reasonably certain that such a process is possible, there is no informa-
tion about the soil lead concentrations that would cause such an effect.
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Ecosystem inputs of lead by the atmospheric route have established new pathways and
widened old ones. Insignificant amounts of lead are removed by surface runoff or ground water
seepage. It is likely that the ultimate fate of atmospheric lead will be a gradual elevation
in lead concentration of all reservoirs in the system, with most of the lead accumulating in
the detrital reservoir.
8.6 SUMMARY
Because there is no protection from industrial lead once it enters the atmosphere, it is
important to fully understand the effects of industrial lead emissions. Of the 450,000 tons
emitted annually on a global basis, 115,000 tons of lead fall on terrestrial ecosystems.
Evenly distributed, this would amount to 0.1 g/ha«yr, which is much lower than the range of
15 to 1,000,000 g/ha-yr reported in ecosystem studies in the United States. Lead has per-
meated these ecosystems and accumulated in the soil reservoir where it will remain for decades
(Chapter 6). Within 20 meters of every major highway, up to 10,000 |jg Pb have been added to
each gram of surface soil since 1930 (Getz et al., 1979). Near smelters, mines, and in urban
areas, as much as 130,000 jjg/g have been observed in the upper 2.5 cm of soil (Jennett et al.,
1977). At increasing distances up to 5 kilometers away from sources, the gradient of lead
added since 1930 drops to less than 10 pg/g (Page and Ganje, 1970), and 1 to 5 |jg/g have been
added in regions more distant than 5 kilometers (Nriagu, 1978). In undisturbed ecosystems,
atmospheric lead is retained by soil organic matter in the upper layer of soil surface. In
cultivated soils, this lead is mixed with soil to a depth of 25 cm.
Because of the special nature of the soil reservoir, it must not be regarded as an infi-
nite sink for lead. On the contrary, atmospheric lead which is already bound to soil will
continue to pass into the grazing and detrital food chains until equilibrium is reached,
whereupon the lead in all reservoirs will be elevated proportionately higher than natural
background levels. This conclusion applies also to cultivated soils, where lead bound within
the upper 25 cm is still within the root zone.
Few plants can survive at soil concentrations in excess of 20,000 |jg/g, even under opti-
mum conditions. Some key populations of soil microorganisms and invertebrates die off at 1000
pg/g. Herbivores, in addition to a normal diet from plant tissues, receive lead from the sur-
faces of vegetation in amounts that may be 10 times greater than from internal plant tissue.
A diet of 2 to 8 mg/daykg body weight seems to initiate physiological dysfunction in many
vertebrates.
Whereas previous reports have focused on possible toxic effects of lead on plants,
animals, and humans, it is essential to consider the degree of contamination as one measure of
safe concentration. Observed toxic effects occur at environmental concentrations well above
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levels that cause no physiological dysfunction. Small animals in undisturbed ecosystems are
contaminated by factors of 20 to 600 over natural background levels, and in roadside and urban
ecosystems by 300 to 6200. Extrapolations based on sublethal effects may become reliable when
these measurements can be made with controls free of contamination. The greatest impact may
be on carnivorous animals, which generally have the lowest concentrations of natural lead, and
may thus havet he greatest percent increase when the final equilibrium is reached.
Perhaps the most subtle effect of lead is on ecosystems. The normal flow of energy
through the decomposer food chain may be interrupted, the composition of communities may shift
toward more lead-tolerant populations, and new biogeochemical pathways may be opened, as lead
flows into and throughout the ecosystem. The ability of an ecosystem to compensate for atmos-
pheric lead inputs, especially in the presence of other pollutants such as acid precipitation,
depends not so much on factors of ecosystem recovery, but on undiscovered factors of ecosystem
stability. Recovery implies.that inputs of the perturbing pollutant have ceased and that the
pollutant is being removed from the ecosystem. In the case of lead, the pollutant is not
being eliminated from the system nor are the inputs ceasing. Terrestrial ecosystems will
never return to their original, pristine levels of lead concentrations.
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. U
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*uAOO>piM*prrwwTwQ(»wcE. im - 661-^55/1001
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Draft
Do Not Quote or Cite
EPA-6OO/B-03-O2BA
August 19B3
External Review Draft No. 1
Air Quality Criteria
for Lead
Volume III of IV
NOTICE
This document is a preliminary draft. It has not been formally released by EPA and should not at this stage
be construed to represent Agency policy. It is being circulated for comment on its technical accuracy and
policy implications.
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Office of Health and Environmental Assessment
Environmental Criteria and Assessment Office
Research Triangle Park, NC 27711
517 <
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NOTICE
Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
518 "
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ABSTRACT
The document evaluates and assesses scientific information on the health
and welfare effects associated with exposure to various concentrations of lead
in ambient air. The literature through 1983 has been reviewed thoroughly for
information relevant to air quality criteria, although the document is not
intended as a complete and detailed review of all literature pertaining to
lead. An attempt has been made to identify the major discrepancies in our
current knowledge and understanding of the effects of these pollutants.
Although this document is principally concerned with the health and
welfare effects of lead, other scientific data are presented and evaluated in
order to provide a better understanding of this pollutant in the environment.
To this end, the document includes chapters that discuss the chemistry and
physics of the pollutant; analytical techniques; sources, and types of
emissions; environmental concentrations and exposure levels; atmospheric
chemistry and dispersion modeling; effects on vegetation; and respiratory,
physiological, toxicological, clinical, and epidemiological aspects of human
exposure.
ii1
519<
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PRELIMINARY DRAFT
CONTENTS
Pa^e
VOLUME I
Chapter 1. Executive Summary and Conclusions 1-1
VOLUME II
Chapter 2. Introduction 2-1
Chapter 3. Chemical and Physical Properties *. 3-1
Chapter 4. Sampling and Analytical Methods for Environmental Lead 4-1
Chapter 5. Sources and Emissions 5-1
Chapter 6. Transport and Transformation 6-1
Chapter 7. Environmental Concentrations and Potential Pathways to Human Exposure .. 7-1
Chapter 8. Effects of Lead on Ecosystems 8-1
VOLUME III
Chapter 9. Quantitative Evaluation of Lead and Biochemical Indices of Lead
Exposure in Physiological Media 9-1
Chapter 10. Metabolism of Lead 10-1
Chapter 11. Assessment of Lead Exposures and Absorption in Human Populations 11-1
Volume IV
Chapter 12. Biological Effects of Lead Exposure 12-1
Chapter 13. Evaluation of Human Health Risk Associated with Exposure to Lead
and Its Compounds 13-1
iv
TCPBA/H 8/8/83
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TABLE OF CONTENTS
Page
9. QUANTITATIVE EVALUATION OF LEAD AND BIOCHEMICAL INDICES OF LEAD EXPOSURE
IN PHYSIOLOGICAL MEDIA 9-1
9.1 INTRODUCTION 9-1
9.2 DETERMINATIONS OF LEAD IN BIOLOGICAL MEDIA 9-2
9.2.1 Sampling and Sample Handling Procedures for Lead
in Biological Media 9-2
9.2.1.1 Blood Sampling 9-3
9.2.1.2 Urine Sampling 9-4
9.2.1.3 Hair Sampling 9-4
9.2.1.4 Mineralized Tissue 9-4
9.2.1.5 Sampling Handling in the Laboratory 9-5
9.2.2 Methods of Lead Analysis 9-6
9.2.2.1 Lead Analysis in Whole Blood 9-7
9.2.2.2 Lead in Plasma 9-10
9.2.2.3 Lead in Teeth 9-12
9.2.2.4 Lead in Hair 9-13
9.2.2.5 Lead in Urine 9-13
9.2.2.6 Lead in Other Tissues 9-14
9.2.3 Quality Assurance Procedures in Lead Analysis 9-15
9.3 DETERMINATION OF ERYTHROCYTE PORPHYRIN (FREE ERYTHROCYTE
PROTOPOPHYRIN, ZINC PROTOPORPHYRIN) 9-19
9.3.1 Methods of Erythrocyte Porphyrin Analysis 9-19
9.3.2 Interlaboratory Testing of Accuracy and Precision in
EP Measurement 9^23
9.4 MEASUREMENT OF URINARY COPROPORPHYRIN 9"24
9.5 MEASUREMENT OF DELTA-AMINOLEVULINIC ACID DEHYDRATASE ACTIVITY 9-24
9.6 MEASUREMENT OF DELTA-AMINOLEVULINIC ACID IN URINE AND OTHER MEDIA 9-26
9.7 MEASUREMENT OF PYRIMIDINE-51-NUCLEOTIDASE ACTIVITY 9-27
9.8 SUMMARY 9-29
9.8.1 Determinations of Lead in Biological Media 9-29
9.8.1.1 Measurements of Lead in Blood 9-29
9.8.1.2 Lead in Plasma 9-31
9.8.1.3 Lead in Teeth .". 9-31
9.8.1.4 Lead in Hair 9-31
9.8.1.5 Lead in Urine 9-31
9.8.1.6 Lead in Other Tissues 9-32
9.8.1.7 Quality Assurance Procedures in Lead Analyses 9-32
9.8.2 Determination of Erythrocyte Porphyrin (Free Erythrocyte
Protoporphyrin, Zinc Protoporphyrin) 9-33
9.8.3 Measurement of Urinary Coproporphyrin 9-34
9.8.4 Measurement of Delta-Aminolevulinic Acid Dehydratase Activity 9-34
9.8.5 Measurement of Delta-Aminolevulinic Acid in Urine and Other Media ... 9-35
9.8.6 Measurement of Pyrimidine-5'-Nucleotidase Activity 9-36
9.9 REFERENCES 9"37
10. METABOLISM OF LEAD 10-1
10.1 INTRODUCTION 10-1
10.2 LEAD ABSORPTION IN HUMANS AND ANIMALS 10-1
10.2.1 Respiratory Absorption of Lead 10-1
10.2.1.1 Human Studies 10-2
10.2.1.2 Animal Studies 10r5
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PRELIMINARY DRAFT
TABLE OF CONTENTS (continued).
Page
10.2.2 Gastrointestinal Absorption of Lead 10-6
10.2.2.1 Human Studies 10~6
10.2.2.2 Animal Studies 10-10
10.2.3 Percutaneous Absorption of Lead 10-12
10.2.4 Transplacental Transfer of Lead 10-12
10.3 DISTRIBUTION OF LEAD IN HUMANS AND ANIMALS 10-13
10.3.1 Lead in Blood 10-14
10.3.2 Lead Levels in Tissues 10-15
10.3.2.1 Soft Tissues 10-16
10.3.2.2 Mineralizing Tissue 10-19
10.3.3 Chelatable Lead 10-20
10.3.4 Mathematical Descriptions of Physiological Lead Kinetics 10-22
10.3.5 Animal Studies 10-23
10.4 LEAD EXCRETION AND RETENTION IN HUMANS AND ANIMALS 10-24
10.4.1 Human Studies 10-24
10.4.2 Animal Studies 10-28
10.5 INTERACTIONS OF LEAD WITH ESSENTIAL METALS AND OTHER FACTORS 10-31
10.5.1 Human Studies 10-31
10.5.2 Animal Studies 10-33
10.5.2.1 Interactions of Lead with Calcium 10-34
10.5.2.2 Interactions of Lead with Iron 10-38
10.5.2.3 Lead Interactions with Phosphate 10-38
10.5.2.4 Interactions of Lead with Vitamin D 10-39
10.5.2.5 Interactions of Lead with Lipids 10-39
10.-5.2.-6 - Lead Interaction with Protein 10-39
10.5.2.7 Interactions of Lead with Milk Components 10-40
10.5.2.8 Lead Interactions with Zinc and Copper 10-40
10.6 INTERRELATIONSHIPS OF LEAD EXPOSURE, EXPOSURE INDICATORS,
AND TISSUE LEAD BURDENS 10-41
10.6.1 Temporal Characteristics of Internal Indicators
of Lead Exposure 10-41
10.6.2 Biological Aspects of External Exposure-Internal
Indicdt;(5P0Relationships 10-42
10.6.3 Internal Indicator-Tissue Lead Relationships 10-43
10.7 METABOLISM OF LEAD ALKYLS 10-45
10.7.1 Absorption-of Lead Alkyls in Humans and Animals 10-46
10.7.1.1 Gastrointestinal Absorption 10-46
10.7.1.2 Percutaneous Absorption of Lead Alkyls ....;; 10-46
10.7.2 Biotransformation and Tissue Distribution of Lead Alkyls 10-46
10.7.3 Excretion of Lead Alkyls 10-48
10.8 SUMMARY - 10-49
10.8.1 Lead Absorption in Humans and Animals 10-49
10.8.1.1 Respiratory Absorption of Lead 10-49
10.8.1.2 Gastrointestinal Absorption of Lead 10-50
10.8.1.3 Percutaneous Absorption of Lead 10-51
10.8.1.4 Transplacental Transfer of Lead 10-51
10.8.2 Distribution of Lead in Humans and Animals 10-51
10.8.2.1 Lead in Blood 10-51
10.8.2.2 Lead Levels in Tissues 10-52
10.8.3 Lead Excretion and Retention in Humans and Animals 10-54
10.8.3.1 Human Studies 10-54
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PRELIMINARY DRAFT
TABLE OF CONTENTS (continued).
Page
10.8.3.2 Animal Studies 10-55
10.8.4 Interactions of Lead with Essential Metals and Other Factors 10-56
10.8.4.1 Human Studies 10-56
10.8.4.2 Animal Studies 10-56
10.8.5 Interrelationships of Lead Exposure with Exposure Indicators
and Tissue Lead Burdens 10-57
10.8.5.1 Temporal Characteristics of Internal Indicators of
Lead Exposure 10-57
10.8.5.2 Biological Aspects of External Exposure-Internal
Indicator Relationships ¦ 10-58
10.8.5.3 Internal Indicator-Tissue Lead Relationships 10-58
10.8.6 Metabolism of Lead Alkyls 10-59
10.8.6.1 Absorption of Lead Alkyls in Humans and Animals 10-59
10.8.6.2 Biotransformation and Tissue Distribution of
Lead Alkyls 10-59
10.8.6.3 Excretion of Lead Alklys 10-59
10.9 REFERENCES 10-60
11. ASSESSMENT OF LEAD EXPOSURES AND ABSORPTION IN HUMAN POPULATIONS 11-1
11.1 INTRODUCTION 11-1
11.2 METHODOLOGICAL CONSIDERATIONS 11-4
11.2.1 Analytical Problems 11-4
11.2.2 Statistical Approaches 11-5
11.3 LEAD IN HUMAN POPULATIONS 11-6
11.3.1 Introduction ;,.... 11-6
11.3.2 Ancient and Remote Populations (Low Lead Exposures) 11-6
11.3.2.1 Ancient Populations .• 11-8
11.3.2.2 Remote Populations 11-8
11.3.3 Levels of Lead and Demographic Covariates in U.S. Populations 11-10
11.3.3.1 The NHANES II Study 11-10
11.3.3.2 The Childhood Blood Lead Screening Programs 11-15
11.3.4 Time Trends '. ... 11-19
11.3.4.1 Time Trends in the Childhood Lead Poisoning Screening
Programs 11-19
11.3.4.2 Newark 11-22
11.3.4.3 Boston 11-24
. 11.3.4.4. NHANES II ! 11-24
11.3.4.5, Other Studies 11-24
11.3.5 Distributional Aspects of Population Blood Lead Levels 11-24
11.3.6 Exposure Covariates of Blood Lead Levels in Urban Children 11-31
11.3.6.1 Stark Study 11-32
11.3.6.2 Charney Study 11-33
11.3.6.3 Hammond Study 11-34
11.3.6.4 Gilbert Study 11-35
11.4 STUDIES RELATING EXTERNAL DOSE TO INTERNAL EXPOSURE 11-36
11.4.1 Air Studies 1 11-37
11.4.1.1 The Griffin et al. Study 11-30
11.4.1.2 The Rabinowitz et al. Stutty 11-47
11.4.1.3 The Chamberlain et al. Study 11-50
11.4.1.4 The Kehoe Study 11-52
11.4.1.5 The Azar et al. Study '... 11-53
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TABLE OF CONTENTS (continued)
Page
11.4.1.6 Silver Valley/Kellogg, Idaho Study 11-58
11.4.1.7 Omaha, Nebraska Studies 11-65
11.4.1.8 Roels et al. Studies 11-67
1114.1.9 Other Studies Relating Blood Lead Levels to
Air Exposure 11-70
11.4.1.10 Summary of Blood Lead vs. Inhaled Air Lead Relations ..... 11-74
11.4.2 Dietary Lead Exposures Including Water 11-80
11.4.2.1 Lead Ingestion from Typical Diets 11-81
11.4.2.2 Lead Ingestion from Experimental Dietary Supplements 11-90
11.4.2.3 Inadvertent Lead Ingestion From Lead Plumbing 11-93
11.4.2.4 Summary of Dietary Lead Exposures Including Water 11-97
11.4.3 Studies Relating Lead in Soil and Dust to Blood Lead 11-105
11.4.3.1 Omaha Nebraska Studies 11-105
11.4.3.2 The Stark Study 11-106
11.4.3.3 The Silver Valley/Kellogg Idaho Study 11-106
11.4.3.4 Charleston Studies 11-106
11.4.3.5 Barltrop Studies 11-107
11.4.3.6 The British Columbia Studies 11-108
11.4.3.7 Other Studies of Soil and Dusts 11-109
11.4.3.8 Summary of Soil and Dust Lead 11-113
11.4.4 Paint Lead Exposures 11-115
11.5 SPECIFIC SOURCE STUDIES 11-121
11.5.1 Combustion of Gasoline Antiknock Compounds 11-121
11.5.1.1 Isotope Studies 11-121
11.5.1.2 Studies of Childhood Blood Lead Poisoning
Control Programs 11-130
11.5.1.3 NHANES II 11-133
11.5.1.4 Frankfurt, West Germany 11-136
11.5.2 Primary Smelters Populations 11-137
11.5.2.1 El Paso, Texas 11-137
11.5.2.2 CDC-EPA Study 11-139
11.5.2.3 Meza Valley, Yugoslavia , 11-139
11.5.2.4 "Kosovo Province, Yugoslavia 11-140
11.5.2.5 The Cavalleri Study 11-141
11.5.3 Battery Plants 11-142
11.5.4 Secondary Smelters 11-145
11.5.5 Secondary Exposure of Children 11-145
11.5.6 Miscellaneous Studies 11-152
11.5.6.1 Studies Using Indirect Measures of Air Exposure 11-152
11.5.6.2 Miscellaneous Sources of Lead 11-156
11.6 SUMMARY 11-158
11.7 REFERENCES 11-166
APPENDIX 11A 11A-1
APPENDIX 11B 11B-1
APPENDIX 11C 11C-1
APPENDIX 11D 11D-1
vii i
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PRELIMINARY DRAFT
LIST OF FIGURES
Figure
10-1 Effect of particle size on lead deposition rate in the lung 10-4
11-1 Pathways of lead from the environment to man 11-3
11-2 Estimate of world-wide lead production and lead concentrations in
bones (pg/gm) from 5500 years before present to the present time 11-7
11-3 Geometric mean blood lead levels by race and age for younger children
in the NHANES II study 11-16
11-4 Geometric means for blood lead values by race and age for younger
children in the New York City screening program (1970-1976) 11-20
11-5 Time dependence of blood lead for blacks, aged 24 to 35 months,
in New York City and Chicago 11-23
11-6 Modeled umbilical cord blood lead levels by date of sample collection
for infants in Boston 11-25
11-7 Average blood lead levels of U.S. population 6 months - 74 years,
United States, February 1976 - February 1980, based on dates of
examination of NHANES II examinees with blood lead determinations 11-26
11-8 Histograms of blood lead levels with fitted lognormal curves for
the NHANES II study 11-30
11-9 Graph of the average normalized increase in blood lead for subjects
exposed to 10.9
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PRELIMINARY DRAFT
LIST OF FIGURES (continued).
Figure Page
11-28 Geometric mean blood levels for blacks and Hispanics in the 25-to-36-
month age group and rooftop quarterly averages for ambient citywide
1 ead levels 11-134
11-29 Time dependence of blood lead and gas lead -for blacks, ages 24 to 35
months, in New York 11-135
11-30 Arithmetic mean air lead levels by traffic volume, Dallas, 1976 11-154
11-31 Blood lead concentration and traffic density by sex and age, Dallas, 1976 ...... 11-155
11-32 Geometric mean blood lead levels by race and age for younger children in
the NHANES II study, and the Kellogg/Silver Valley and the New York
childhood screening studies .... 11-159
11B-1 Residual sum of squares for nonlinear regression models for Azar data
(N=149) 11-170
11B-2 Hypothetical relationship between blood lead and air lead by inhalation
and non-inhalation 11-172
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PRELIMINARY DRAFT
LIST OF TABLES
Table Page
10-1 Deposition of lead in the human .respiratory, tract 10-3
10-2 Regional distribution of lead in humans and animals 10-17
10-3 Comparative excretion and retention rates in adults and infants 10-25
10-4 Effect of nutritional factors on lead uptake in animals 10-35
11-1 Studies of past exposures to lead 11-9
11-2 NHANES II blood lead levels of persons 6 months-74 years, with weighted
arithmetic mean, standard error of the mean, weighted geometric mean,
median, and percent distribution, by race and age, United States,
1976-80 11-12
11-3 NHANES II blood lead levels of males 6 months-74 years, with weighted
arithmetic mean, standard error of the mean, weighted geometric mean,
median, and percent distribution, by race and age, United States,
1976-80 11-13
11-4 NHANES II blood lead levels of females 6 months-74 years, with weighted
arithmetic mean, standard error of the mean, weighted geometric mean,
median, and percent distribution, by race and age, United States,
1976-80 11-14
11-5 Weighted geometric mean blood lead levels from NHANES II survey by
degree of urbanization of place of residence in the U.S. by age
and race, United States 1976-80 11-17
11-6 Annual geometric mean blood lead levels from the New York blood lead
screening studies. Annual geometric means are calculated from
quarterly geometric means estimated by the method of
Hasselblad et al. (1980) 11-18
11-7 Characteristics of childhood lead poisoning screening data 11-21
11-8 Distribution of blood lead levels for 13 to 48 month old blacks
by season and year for New York screening data 11-21
11-9 Summary of unweighted blood lead levels in whites not living in an
SMSA with family income greater than $6,000 11-28
11-10 Summary of fits to NHANES II blood lead levels of whites not
living in an SMSA, income greater than $6,000, for five
different two parameter distributions 11-29
11-11 Estimated mean square errors resulting from analysis of variance on
various subpopulations of the NHANES II data using unweighted data 11-31
11-12 Multiple regression models for blood lead of children in
New Haven, Connecticut, September 1974 - February 1977 11-33
11-13 Griffin experiments - subjects exposed to air lead both years 11-43
11-14 Griffin experiments - controls used both years 11-44
11-15 Griffin experiment - subjects exposed to air lead one year only 11-45
11-16 Inhalation slope estimates 11-47
11-17 Mean residence time in blood 11-47
11-18 Air lead concentrations (^g/m3) for two subjects in the
Rabinowitz studies 11-48
11-19 Estimates of inhalation slope for Rabinowitz studies 11-49
11-20 Linear slope for blood lead vs. air lead at low air lead
exposures in Kehoe's subjects 11-53
11-21 Geometric mean air and blood lead levels (jjg/100 g) for five city-
occupation groups 11-56
11-22 Geometric mean blood lead levels by area compared with estimated
air-lead levels for 1- to 9-year-old children living near Idaho
smelter 11-61
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PRELIMINARY DRAFT
LIST OF TABLES (continued).
Table Page
11-23 Geometric mean blood lead levels by age and area for subjects
living near the Idaho smelter 11-61
11-24 Age specific regression coefficients for the analysis of log-blood-
lead levels in the Idaho smelter study 11-62
11-25 Estimated coefficients and standard errors for the Idaho
smelter study 11-63
11-26 Air, dustfall and blood lead concentrations in Omaha, NE, study, —
1970-1977 11-66
11-27 Mean airborne and blood lead levels recorded during five distinct
surveys (1974 to 1978) for study populations of 11-year old
children living less than 1 km or 2.5 km from a lead smelter,
or living in a rural or urban area 11-69
11-28 Geometric mean air and blood lead values for 11 study populations 11-71
11-29 Mean air and blood lead values for five zones in Tokyo study 11-71
11-30 Blood lead-air lead slopes for several population studies as
calculated by Snee 11-73
11-31 A selection of recent analyses on occupational 8-hour exposures
to high air lead levels 11-74
11-32 Cross-sectional observational study with measured individual air
lead exposure 11-75
11-33 Cross-sectional observational studies on children with estimated
air exposures 11-76
11-34 Longitudinal experimental studies with measured .individual
air lead exposures 11-77
11-35 Blood lead levels and lead intake values for infants
in the study of Ryu et al 11-82
11-36 Influence of level of lead in water on blood lead level in
blood and placenta 11-84
11-37 Blood lead and kettle water lead concentrations for adult
women living in Ayr 11-85
11-38 Relationship of blood lead (pg/dl) and water lead (pg/1) in 910
men aged 40-59 from 24 British towns 11-88
11-39 Dose response analysis for blood leads in the Kehoe study as
analyzed by Gross 11-90
11-40 Blood lead levels of 771 persons in relation to lead content of
drinking water, Boston, Mass 11-99
11-41 Studies relating blood lead levels (jjg/dl) to dietary intakes (pg/day) 11-100
11-42 Studies relating blood lead levels (pg/dl) and experimental
dietary intakes 11-101
11-43 Studies relating blood lead levels (pg/dl) to
first-flush water lead 11-102
11-44 Studies relating blood lead levels (pg/dl) to running water
lead (pg/1) 11-104
11-45 Mean blood and soil lead concentrations in English study 11-108
11-46 Lead concentration of surface soil and children's blood
by residential area of trail, British Columbia. 11-110
11-47 Analysis of relationship between soil lead and blood lead in children 11-113
11-48 Estimates of the contribution of soil lead to blood lead 11-114
11-49 Estimates to the contribution of housedust to blood lead in children 11-115
11-50 Results of screening and housing inspection in childhood lead
poisoning control project by fiscal year 11-120
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PRELIMINARY DRAFT
LIST OF TABLES (continued).
Table Page
11-51 Estimated contribution of leaded gasoline to blood lead by inhalation
and non-inhalation pathways 11-124
11-52 Assumed air lead concentration,for model 11-125
11-53 Regression model for blood lead attributable to gasoline 11-127
11-54 Rate of change of 266Pb/2d4Pb and 206Pb/207Pb in air and blood, and
percentage of airborne lead in blood of subjects 1, 3, 5, 6 and 9 11-128
11-55 Calculated blood lead uptake from air lead using Manton isotope study 11-129
11-56 Mean air lead concentrations during the various blood sampling periods
at the measurement sites described in the text (|jg/m3) 11-136
11-57 Mean blood lead levels in selected Yugoslavian populations, by
estimated weekly time-weighted air lead exposure 11-140
11-58 E nvironmental parameters and methods: Arnhem lead study, 1978 11-144
.11-59 Geometric mean blood lead levels for children based on reported
occupation of father, history of pica, and distance of residence
from smelter 11-146
11-60 Sources of lead 11-157
11-61 Summary of pooled geometric standard deviations and estimated
analytic errors 11-160
11-62 Summary of blood inhalation slopes, (p)|jg/dl per pg/m3 11-161
11-63 Estimated contribution of leaded gasoline to blood lead by
inhalation and non-inhalation pathways 11-165
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PRELIMINARY DRAFT
LIST OF ABBREVIATIONS
AAS
Ach
ACTH
ADCC
ADP/O ratio
AIDS
AIHA
All
ALA
ALA-D
ALA-S
ALA-U
APDC
APHA
ASTM
ASV
ATP
B-cel15
Ba
BAL
BAP
BSA
BUN
BW
C.V.
CaBP
CaEDTA
CBD
Cd
CDC
CEC
CEH
CFR
CMP
CNS
CO
COHb
CP-U
C u
cBa
D.F.
DA
OCMU
DDP
DNA
DTH
EEC
EEG
EMC
EP
EPA
Atomic absorption spectrometry
Acetylcholine
Adrenocoticotrophic hormone
Antibody-dependent eel1-mediated.cytotoxicity
Adenosine d1phosphate/oxygen ratio
Acquired immune deficiency syndrome
American Industrial Hygiene Association
Angiotensin II
Aminolevulinic
Ami nolevuli ni c
Aminolevulinic
Ami nolevulini c
aci d
aci d
acid
acid
dehydrase
synthetase
in urine
Ammoniurn pyrrolidine-dithiocarbamate
American Public Health Association
Araercian Society for Testing and Materials
Anodic stripping voltaminetry -
Adenosine triphosphate
Bone marrow-derived lymphocytes
Bari um
British anti-Lewisite (AKA dimercaprol)
benzo(a)pyrene
Bovine serum albumin
Blood urea nitrogen
Body weight
Coefficient of variation
Calcium binding protein
Calcium ethylenediaminetetraacetate
Central business district
Cadmium
Centers for Disease Control
Cation exchange capacity
Center for Environmental Health
reference method
Cytidine monophosphate
Central nervous system
Carbon monoxide
Carboxyhemoglobin
Urinary coproporphyrin
plasma clearance of p-aminohippuric acid
Copper
Degrees of freedom
Dopamine
[3-(3,4-dichlorophenyl)-1,1-dimethyl urea
Differential pulse polarography
Deoxyribonucleic acid
Delayed-type hypersensitivity
European Economic Community
Electroencephalogram
Encephalomyocardi ti s
Erythrocyte protoporphyrin
U.S. Environmental Protection Agency
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PRELIMINARY DRAFT
LIST OF ABBREVIATIONS (continued).
FA Fulvic acid
FDA Food and Drug Administration
Fe Iron
FEP Free erythrocyte protoporphyrin
FY Fiscal year
G.M. Grand mean -M-^r •
G-6-PD G1ucose-6-phosphate dehydrogenase
GABA Gamma-aminobutyric acid
GALT Gut-associated lymphoid tissue
GC Gas chromatography
GFR Glomerular filtration rate •
HA Humic acid
Hg Mercury
hi-vol High-volume air sampler
HPLC High-performance liquid chromatography
i.m. Intramuscular (method of injection)
i.p. Intraperitoneally (method of injection)
i.v. Intravenously (method of injection)
IAA Indol-3-ylacetic acid
IARC International Agency for Research on Cancer
ICD International classification of diseases
ICP Inductively coupled plasma •
IDMS Isotope dilution mass spectrometry
IF Interferon
ILE Isotopic Lead Experiment (Italy)
IRPC International Radiological Protection Commission
K Potassium
LAI Leaf area index
LDH-X Lactate dehydrogenase isoenzyme x
LCj-fl Lethyl concentration (50 percent)
LD50 Lethal dose (50 percent)
LH Luteinizing hormone
LIP0 Laboratory Improvement Program Office
In National logarithm
LPS Lipopolysaccharide
LRT Long range transport
mRNA Messenger ribonucleic acid
ME Mercaptoethanol
MEPP Miniature end-plate potential
MES Maximal electroshock seizure
MeV Mega-electron volts
MLC Mixed lymphocyte culture
MMD Mass median diameter
MMED Mass median equivalent diameter
Mn Manganese
MND Motor neuron disease
MSV Moloney sarcoma virus
MTD Maximum tolerated dose
n Number of subjects
N/A Not Available
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PRELIMINARY DRAFT
LIST OF ABBREVIATIONS
NA Not Applicable
NAAQS National ambient air quality standards
NADB National Aerometric Data Bank
HAMS National Air Monitoring Station
NAS National Academy of Sciences
NASN National Air Surveillance Network
UBS National Bureau of Standards
NE Norepinephrine
NFAN National Filter Analysis Network
NFR-82 Nutrition Foundation Report of 1982
NHANES II National Health Assessment and Nutritional Evaluation Survey II
Ni Nickel
OSHA Occupational Safety and Health Administration
P Potassium
p Significance symbol
PAH Para-aminohippuric acid
Pb Lead
PBA Air lead
PbCAc)^ Lead acetate
PbB concentration of lead in blood
PbBrCl Lead (II) bromochloride
PBG Porphobilinogen
PFC Plaque-forming cells
pH Measure of acidity
PHA Phytohemagglutinin
PHZ Polyacrylami de-hydrous-zi rconia
PIXE Proton-induced X-ray emissions
PMN Polymorphonuclear leukocytes
PND Post-natal day
PNS Peripheral nervous system
ppm Parts per million
PRA Plasma renin activity
PRS Plasma renin substrate
PWM Pokeweed mitogen
Py-5-N Pyrirm'de-5'-nucleotidase
RBC Red blood cell; erythrocyte
RBF Renal blood flow
RCR Respiratory control ratios/rates
redox Oxidation-reduction potential
RES Reticuloendothelial system
RLV Rauscher leukemia virus
RNA Ribonucleic acid
S-HT Serotonin
SA-7 Simian adenovirus
scm Standard cubic meter
S.D. Standard deviation
SDS Sodium dodecyl sulfate
S.E.M. Standard error of the mean
SES Socioeconomic status
SGOT Serum glutamic oxaloacetic transaminase
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PRELIMINARY DRAFT
LIST OF ABBREVIATIONS (continued).
sig
SLAMS
SMR
Sr
SRBC
SRMs
STEL
SW voltage
T-cells
t-tests
TBL
TEA
TEL
TIBC
TML
TMLC
TSH
TSP
U.K.
UMP
USPHS
VA
!ir
WHO
XBF
X^
Zn
ZPP
Surface immunoglobulin
State and local air monitoring stations
Standardized mortality ratio
Strontium
Sheep red blood eel Is
Standard reference materials
Short-term exposure limit
Slow-wave vol.tage
Thymus-derived lymphocytes
Tests of significance
Tri-n-butyl lead
Tetraethyl-ammoni um
Tetraethyllead
Total iron binding capacity
Tetramethyllead
Tetramethyllead chloride
Thyroid-stimulating hormone
Total suspended particulate
United Kingdom
Uridine monophosphate
U.S. Public Health Service
Veterans Administration
Deposition velocity
Visual evoked response
World Health Organization
X-Ray fluorescence
Chi squared
Zinc
Erythrocyte zinc protoporphyrin
MEASUREMENT ABBREVIATIONS
dl deciliter
ft feet
g gram
g/gal gram/gallon
g/ha-mo gram/hectare-month
km/hr kilometer/hour
1/min liter/minute
mg/km milligram/kilometer
pg/m3 microgram/cubic meter
mm millimeter
pmol micrometer
ng/cm2 nanograms/square centimeter
nm namometer
nM nanomole
sec second
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AUTHORS, CONTRIBUTORS, AND REVIEWERS
Chapter 9: Quantitative Evaluation of Lead and Biochemical Indices of Lead
Exposure in Physiological Media
Principal Author
Dr. Paul Mushak
Department of Pathology
School of Medicine
University of North Carolina \
Chapel Hill, NC 27514
The following persons reviewed this chapter at EPA's request. The evaluations
and conclusions contained herein, however, are not necessarily those of the
reviewers.
Dr. Carol Angle
Department of Pediatrics
University of Nebraska
College of Medicine
Omaha, NE 68105
Dr. Lee Annest
Division of Health Examin. Statistics
National Center for Health Statistics
3700 East-West Highway
Hyattsville, MD 20782
Dr. Donald Barltrop
Department of Child Health
Westminister Children's Hospital
London SW1P 2NS
England
Dr. Irv Billick
Gas Research Institute
8600 West Bryn Mawr Avenue
Chicago, IL 60631
Dr. Joe Boone
Clinical Chemistry and
Toxicology Section
Centers for Disease Control
Atlanta, GA 30333
Dr. A. C. Chamberlain
Environmental and Medical
Sciences Division
Atomic Energy Research
Establi shment
Harwell 0X11
England
Dr. Neil Chernoff
Division of Developmental Bioloqy
MD-67
U.S. Environmental Protection
Agency
Research Triangle Park, NC 27711
Dr. Julian Chisolm
Baltimore City Hospital
4940 Eastern Avenue
Baltimore, MD 21224
Mr. Jerry Cole
International Lead-Zinc Research
Organization
292 Madison Avenue
New York, NY 10017
Dr. Max Costa
Department of Pharmacology
University of Texas Medical
School
Houston, TX 77025
Dr. Robert Bornschein
University of Cincinnati
Kettering Laboratory
Cincinnati, OH 45267
Dr. Anita Curran
Commissioner of Health
Westchester County
White Plains, NY 10607
xvi i i
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Dr. Jack Dean
Immunobiology Program and
Immunotoxicology/Cell Biology program
CUT
P.O. Box 12137
Research Triangle Park, NC 27709
Dr. H. T. Delves
Chemical Pathology and Human
Metabolism
Southampton General Hospital
Southampton S09 4XY
England
Dr. Fred deSerres
Assoc. Director for Genetics
NIEHS
P.O. Box 12233
Research Triangle Park, NC 27709
Dr. Robert Dixon
Laboratory of Reproductive and
Developmental Toxicology
NIEHS
P.O. Box 12233
Research Triangle Park, NC 27709
Dr. Claire Ernhart
Department of Psychiatry
Cleveland Metropolitan General Hospital
Cleveland, OH 44109
Dr. Sergio Fachetti
Section Head - Isotope Analysis
Chemistry Division
Joint Research Center
121020 Ispra
Varese, Italy
Dr. Virgil Ferm
Department of Anatomy and Cytology
Dartmouth Medical School
Hanover, NH 03755
Dr. ATf Fischbein
Environmental Sciences Laboratory
Mt. Sinai School of Medicine
New York, NY 10029
Dr. Jack Fowle
Reproductive Effects Assessment Group
U.S. Environmental Protection Agency
RD-689
Washington, DC 20460
Dr. Bruce Fowler
Laboratory of Pharmacology
NIEHS
P.O. Box 12233
Research Triangle Park, NC 27709
Dr. Warren Galke
Department of Biostatisties
and Epidemiology
School of Allied Health
East Carolina University
Greenville, NC 27834
Mr. Eric Goldstein
Natural Resources Defense
Council, Inc.
122 E. 42nd Street
New York, NY 10160
Dr. Harvey Gonick
1033 Gayley Avenue
Suite 116
Los Angeles, CA 90024
Dr. Robert Goyer
Deputy Director
NIEHS
P.O. Box 12233
Dr. Stanley Gross
Hazard Evaluation Division
Toxicology Branch
U.S. Environmental Protection
Agency
Washington, DC 20460
Dr. Paul Hammond
University of Cincinnati
Kettering Laboratory
Cincinnati, OH 45267
Dr. Ronald D. Hood
Department of Biology
The University of Alabama
University, AL 35486
Dr. V. Houk
Centers for Disease Control
1600 Clifton Road, NE
Atlanta, GA 30333
xix
535v
-------
Dr. Loren D. Koller
School of Veterinary Medicine
University of Idaho
Moscow, ID 83843
Dr. Kristal Kostial
Institute for Medical Research
and Occupational Health
Yu-4100 Zagreb
Yugoslavia
Dr. Lawrence Kupper
Department of Biostatisties
UNC School of Public Health
Chapel Hill, NC 27514
Dr. Phillip Landrigan
Division of Surveillance,
Hazard Evaluation and Field Studies
Taft Laboratories - NIOSH
Cincinnati, OH 45226
Dr. David Lawrence
Microbiology and Immunology Dept.
Albany Medical College of Union
University
Albany, NY 12208
Dr. Jane Lin-Fu
Office of Maternal and Child Health
Department of Health and Human Services
Rockville, MD 20857
Dr. Don Lynajn
Air Conservation
Ethyl Corporation
451 Florida Boulevard
Baton Rouge, LA 70801
Dr. Kathryn Mahaffey
Division of Nutrition
Food and Drug Administration
1090 Tusculum Avenue
Cincinnati, OH 45226
Dr. Ed McCabe
Department of Pediatrics
University of Wisconsin
Madison, WI 53706
Dr. Chuck Nauman
Exposure Assessment Group
U.S. Environmental Protection
Agency
Washington, DC 20460
Dr. Herbert L. Needleman
Children's Hospital of Pittsburgh
Pittsburgh, PA 15213
Dr. H. Mitchell Perry
V.A. Medical Center
St. Louis, M0 63131
Dr. Jack Pierrard
E.I. duPont de Nemours and
Company, Inc.
Petroleum Laboratory
Wilmington, DE 19898
Dr. Sergio Piomelli
Columbia University Medical School
Division of Pediatric Hematology
and Oncology
New York, NY 10032
Dr. Magnus Piscator
Department of Environmental Hygiene
The Karolinska Institute 104 01
Stockholm
Sweden
Dr. Robert Putnam
International Lead-Zinc
Research Organization
292 Madison Avenue
New York, NY 10017
Dr. Michael Rabinowitz
Children's Hospital Medical
Center
300 Longwood Avenue
Boston, MA 02115
xx
53G<
-------
Dr. Harry Roels
Unite de Toxicologie
Industrie"!le et Medicale
Universite de Louvain
Brussels, Belgium
Dr. John Rosen
Division of Pediatric Metabolism
Albert Einstein College of Medicine
Montefiore Hospital and Medical Center
111 East 210 Street
Bronx, NY 10467
Dr. Michael Rutter
Department of Psychology
Institute of Psychiatry
DeCrespigny Park
London SE5 8AL
England
Dr. Stephen R. Schroeder
Division for Disorders
of Development, and Learning
Biological Sciences Research Center
University of North Carolina
Chapel Hill, NC 27514
Dr. Anna-Maria Seppalainen
Institutes of Occupational Health
Tyoterveyslaitos
Haartmaninkatu 1
00290 Helsinki 29
Fi nland
Dr. Ellen Silbergeld
Environmental Defense Fund
1525 18th Street, NW
Washington, DC 20036
Dr Ron Snee
E.I. duPont Nemours and
Company, Inc.
Engineering Department L3167
Wilmington, DE 19898
Dr. Gary Ter Haar
Toxicology and Industrial
Hygiene
Ethyl Corporation
451 Florida Boulevard
Baton Rouge, LA 70801
Mr. Ian von Lindern
Department of Chemical Engineering
University of Idaho
Moscow, Idaho 83843
Dr. Richard P. Wedeen
V.A. Medical Center
Tremont Avenue
East Orange, MJ 070i9
xx i
537--
-------
Chapter 10: Metabolism of Lead
Principal Author
Dr. Paul Mushak
Department of Pathology
School of Medicine
University of North Carolina
Chapel Hill, NC 27514
Contributing Author
Dr. Michael Rabinowitz
Children's Hospital Medical Center
300 Longwood Avenue
Boston, MA 02115
The following persons reviewed this chapter at EPA1s request. The evaluations
and conclusions contained herein, however, are not necessarily those of the
revlewers.
Dr. Carol Angle
Department of Pediatrics
University of Nebraska
College of Medicine
Omaha, NE 68105
Dr. Robert Bornschein
University of Cincinnati
Kettering Laboratory
Cincinnati, OH 45267
Dr. Lee Annest
Division of Health Examin. Statistics
National Center for Health Statistics
3700 East-West Highway
Hyattsvilie, MD 20782
Dr. Donald Barltrop
Department of Child Health
Westminister Children's Hospital
London SW1P 2NS
England
Dr. Irv Billick
Gas Research Institute
8600 West Bryn Mawr Avenue
Chicago, IL 60631
Dr. Joe Boone
Clinical Chemistry and
Toxicology Section
Centers for Disease Control
Atlanta, GA 30333
Dr. A. C. Chamberlain
Environmental and Medical
Sciences Division
Atomic Energy Research
Establishment
Harwell 0X11
England
Dr. Neil Chernoff
Division of Developmental Biology
MD-67
U.S. Environmental Protection
Agency
Research Triangle Park, NC 27711
Dr. Julian Chisolm
Baltimore City Hospital
4940 Eastern Avenue
Baltimore, MD 21224
Mr. Jerry Cole
International Lead-Zinc Research
Organization
292 Madison Avenue
New York, NY 10017
xx i i
538<
r ,
-------
Dr. Max Costa
Department of Pharmacology
University of Texas Medical School
Houston, TX 77025
Dr. Anita Curran
Commissioner of Health
Westchester County
White Plains, NY 10607
Dr. Jack Dean
Immunobiology Program and
Immunotoxicology/Cel 1 Biology program
CUT
P.O. Box 12137
Research Triangle Park, NC 27709
Dr. H.T. Delves
Chemical Pathology and Human Metabolism
Southampton General Hospital
Southampton S09 4XY
England
Dr. Fred deSerres
Assoc. Director for Genetics
NIEHS
P.O. Box 12233
Research Triangle Park, NC 27709
Dr. Robert Dixon
Laboratory of Reproductive and
Developmental Toxicology
NIEHS
P.O. Box 12233
Research Triangle Park, NC 27709
Dr. Claire Ernhart
Department of Psychiatry
Cleveland Metropolitan General Hospital
Cleveland, OH 44109
Dr. Sergio Fachetti
Section Head - Isotope Analysis
Chemistry Division
Joint Research Center
121020 Ispra
Varese, Italy
Dr. Virgil Ferm
Department of Anatomy and Cytology
Dartmouth Medical School
Hanover, NH 03755
XXI 11
Dr. Alf Fischbein
Environmental Sciences Laboratory
Mt. Sinai School of Medicine
New York, NY 10029
Dr. Dr. Jack Fowle
Reproductive Effects Assessment
Group
U.S. Environmental Protection
Agency
RD-689
Washington, DC 20460
Dr. Bruce Fowler
Laboratory of Pharmacology
NIEHS
P.O. Box 12233
Research Triangle Park, NC 27709
Dr. Warren Galke
Department of Biostatisties
and Epidemiology
School of Allied Health
East Carolina University
Greenville, NC 27834
Mr. Eric Goldstein
Natural Resources Defense
Council, Inc.
122 E. 42nd Street
New York, NY 10158
Dr. Harvey Gonick
1033 Gayley Avenue
Suite 116
Los Angeles, CA 90024
Dr. Robert Goyer
Deputy Director
NIEHS
P.O. Box 12233
Research Triangle Park, NC 27709
Dr. Stanley Gross
Hazard Evaluation Division
Toxicology Branch
U.S. Environmental Protection
Agency
Washington, DC 20460
Dr. Paul Hammond
University of Cincinnati
Kettering Laboratory
Cincinnati, OH 45267
5353-:
-------
Dr. Ronald D. Hood
Department of Biology
The University of Alabama
University, AL 35486
Dr. V. Houk
Centers for Disease Control
1600 Clifton Road, NE
Atlanta, GA 30333
Dr. Loren D. Koller
School of Veterinary Medicine
University of Idaho
Moscow, ID 83843
Dr. Kristal Kostial
Institute for Medical Research
and Occupational Health
Yu-4100 Zagreb
Yugoslavia
Dr. Lawrence Kupper
Department of Biostatisties
UNC School of Public Health
Chapel Hill, NC 27514
Dr. Phillip Landrigan
Division of Surveillance,
Hazard Evaluation and Field Studies
Taft Laboratories - NIOSH
Cincinnati, OH 45226
Dr. David Lawrence
Microbiology and Immunology Dept.
Albany Medical College of Union
University
Albany, NY 12208
Dr. Jane Lin-Fu
Office of Maternal and Child Health
Department of Health and Human Services
Rockville, MD 20857
Dr. Don Lynam
Air Conservation
Ethyl Corporation
451 Florida Boulevard
Baton Rouge, LA 70801
Dr. Kathryn Mahaffey
Division of Nutrition
Food arid Drug Administration
1090 Tusculum Avenue
Cincinnati, OH 45226
xx iv
Dr. Ed McCabe
Department of Pediatrics
University of Wisconsin
Madison, WI 53706
Dr. Chuck Nauman
Exposure Assessment Group
U.S. Environmental Protection Agency
Washington, DC 20460
Dr. Herbert L. Neddleman
Children's Hospital of Pittsburgh
Pittsburgh, PA 15213
Dr. H. Mitchell Perry
V.A. Medical Center
St. Louis, M0 63131
Dr. Jack Pierrard
E.I. duPont de Nemours and
Company, Inc.
Petroleum Laboratory
Wilmington, DE 19898
Dr. Sergio Piomelli
Columbia University Medical School
Division of Pediatric Hematology
and Oncology
New York, NY 10032
Dr. Magnus Piscator
Department of Environmental Hygiene
The Karolinska Institute 104 01
Stockholm
Sweden
Dr. Robert Putnam
International Lead-Zinc
Research Organization
292 Madison Avenue
New York, NY 10017
Dr. Harry Roels
Unite de Toxicologic
Industrielle et Medicale
Universite de Louvain
Brussels, Belgium
Dr. John Rosen
Division of Pediatric Metabolism
Albert Einstein College of Medicine
Montefiore Hospital and Medical Center
111 East 210 Street
Bronx, NY 10467
540<
-------
Dr. Michael Rutter
Department of Psychology
Institute of Psychiatry
DeCrespigny Park
London SE5 8AL
England
Dr. Stephen R. Schroeder
Division for Disorders
of Development and Learning
Biological Sciences Research Center
University of North Carolina
Chapel Hill, NC 27514
Dr. Anna-Maria Seppalainen
Institutes of Occupational Health
Tyoterveyslaitos
Haartmaninkatu 1
00290 Helsinki 29
Finland
Dr. Ellen Silbergeld
Environmental Defense Fund
1525 18th Street, NW
Washington, DC 20036
Dr. Ron Snee
E.I. duPont Nemours and
Company, Inc.
Engineering Department L3167
Wilmington, DE 19898
Dr. Gary Ter Haar
Toxicology and Industrial
Hygiene
Ethyl Corporation
451 Florida Boulevard
Mr. Ian von Lindern
Department of Chemical
Engineering
University of Idaho
Moscow, ID 83843
Dr. Richard P. Wedeen
V.A. Medical Center
Tremont Avenue
East Orange, NJ 07019
xxv
541*:
-------
Chapter 11: Assessment of Lead Exposures and Absorption in Human Populations
Principal Authors
Dr. Warren Galke
Department of Biostatistics and Epidemiology
School of Allied Health
East Carolina University
Greenville, NC 27834
Dr. Alan Marcus
Department of Mathematics
Washington State University
Pullman, Washington 99164-2930
Dr. Vic Hasselblad
Biometry Division
MD-55
U.S. Environmental Protection
Agency
Research Triangle Park, NC 27711
Contributing Author:
Dr. Dennis Kotchmar
Environmental Criteria and Assessment Office
MD-52
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
The following persons reviewed this chapter at EPA's request. The evaluations
and conclusions contained herein, however, are not necessarily those of the
reviewers.
Dr. Carol Angle
Department of Pediatrics
University of Nebraska
College of Medicine
Omaha, NE 68105
Dr. Lee Annest
Division of Health Examin. Statistics
National Center for Health Statistics
3700 East-West Highway
Hyattsville, MD 20782
Dr. Donald Barltrop
Department of Child Health
Westminister Children's Hospital
London SW1P 2NS
England
Dr. Irv Bi11ick
Gas Research Institute
8600 West Bryn Mawr Avenue
Chicago, IL 60631
Dr. Joe Boone
Clinical Chemistry and
Toxicology Section
Centers for Disease Control
Atlanta, GA 30333
Dr. Robert Bornschein
University of Cincinnati
Kettering Laboratory
Cincinnati, OH 45267
Dr. A. C. Chamberlain
Environmental and Medical
Sciences Division
Atomic Energy Research
Establi shraent
Harwell 0X11
England
Dr. Neil Chernoff
Division of Developmental Biology
MD-67
U.S. Environmental Protection
Agnecy
Research Triangle Park, NC 27711
xxvi
5425
-------
Dr. Julian Chisolm
Baltimore City Hospital
4940 Eastern Avenue
Baltimore, MD 21224
Mr. Jerry Cole
International Lead-Zinc Research Organization
292 Madison Avenue
New York, NY 10017
Dr. Max Costa
Department of Pharmacology
University of Texas Medical School
Houston, TX 77025
Dr. Anita Curran
Commissioner of Health
Westchester County
White Plains, NY 10607
Dr. Jack Dean
Immunobiology Program and
Immunotoxicology/Cel1 Biology Program
CIIT
P.O. Box 12137
Research Triangle Park, NC 27709
Dr. Fred deSerres
Assoc. Director for Genetics
NIEHS
P.O. Box 12233
Research Triangle Park, NC 27709
Dr. Robert Dixon
Laboratory of Reproductive and
Developmental Toxicology
NIEHS
P.O. Box 12233
Research Tn'angle Park, NC 27709
Dr. Claire Ernhart
Department of Psychiatry
Cleveland Metropolitan General Hospital
Cleveland, OH 44109
Dr. Sergio Fachetti
Section Head - Isotope Analysis
Chemistry Division
Joint Research Center
121020 Ispra
Varese, Italy
xxv i i
Dr. Virgil Ferm
Department of Anatomy and Cytology
Dartmouth Medical School
Hanover, NH 03755
Dr. Alf Fischbein
Environmental Sciences Laboratory
Mt. Sinai School of Medicine
New York, NY 10029
Dr. Jack Fowle
Reproductive Effects Assessment
Group
U.S. Environmental Protection
Agency
RD-689
Washington, DC 20460
Dr. Bruce Fowler
Laboratory of Pharmocology
NIEHS
P.O. Box 12233
Research Triangle Park, NC 27709
Mr. Eric Goldstein
Natural Resources Defense
Council, Inc.
School of Allied Health
122 E. 42nd Street
New York, NY 10168
Dr. Harvey Gonick
1033 Gayley Avenue
Suite 116
Los Angeles, CA 90024
Dr. Robert Goyer
Deputy Director
NIEHS
P.O. Box 12233
Research Triangle Park, NC 27709
Dr. Stanley Gross
Hazard Evaluation Division
Toxicology Branch
U.S. Environmental Protection
Dr. Paul Hammond
University of Cincinnati
Kettering Laboratory
3223 Eden Avenue
Cincinnati, OH 45267
543<
-------
Dr. Ronald D. Hood
Department of Biology
The University of Alabama
University, AL 35486
Dr. V. Houk
Centers for Disease Control
1600 Clifton Road, NE
Atlanta, GA 30333
Dr. Loren Koller
School of Veterinary Medicine
University of Idaho
Moscow, ID 83843
Dr. Kristal Kostial
Institute for Medical Research
and Occupational Health
Yu-4100 Zagreb
Yugoslavia
Dr. Lawrence Kupper
Department of Biostatistics
UNC School of Public Health
Chapel Hill, NC 27514
Dr. Phillip Landrigan
Division of Surveillance,
Hazard Evaluation and Field Studies
Taft Laboratories - NIOSH
Cincinnati, OH 45226
Dr. David Lawrence
Microbiology and Immunology Dept.
Albany Medical College of Union
University
Albany, NY 12208
Dr. Jane Lin-Fu
Office of Maternal and Child Health
Department of Health and Human Services
Rockville, MD 20857
Dr. Don Lynam
Air Conservation
Ethyl Corporation
451 Florida Boulevard
Baton Rouge, LA 70801
Dr. Kathryn Mahaffey
Division of Nutrition
Food and Drug Administration
1090 Tusculum Avenue
Cincinnati, OH 45226
Dr. Ed McCabe
Department of Pediatrics
University of Wisconsin
Madison, WI 53706
Dr. Paul Mushak
Department of Pathology
UNC School of Medicine
Chapel Hill, NC 27514
Dr. Chuck Nauman
Exposure Assessment Group
U.S. Environmental Protection
Agency
Washington, DC 20460
Dr. Herbert L. Needleman
Children's Hospital of Pittsburgh
Pittsburgh, PA 15213
Dr. H. Mitchell Perry
V.A. Medical Center
St. Louis, M0 63131
Dr. Jack Pierrard
E.I. duPoint de Nemours and
Company, Inc.
Petroleum Laboratory
Wilmington, DE 19898
Dr. Sergio Piomelli
Columbia University Medical School
Division of Pediatric Hematology
and Oncology
New York, NY 10032
Dr. Magnus Piscator
Department of Environmental Hygiene
The Karolinska Institute 104 01
Stockholm
Sweden
xxv1i i
541
-------
Dr. Robert Putnam
International Lead-Zinc
Research Organization
292 Madison Avenue
New York, NY 10017
Dr. Michael Rabinowitz
Children's Hospital Medical Center
300 Longwood Avenue
Boston, MA 02115
Dr. Harry Roels
Unite de Toxicologic
Industrielle et Medicale
Universite de Louvain
Brussels, Belgium
Dr. John Rosen
Division of Pediatric Metabolism
Albert Einstein College of Medicine
Montefiore Hospital and Medical Center
111 East 210 Street
Bronx, NY 10467
Dr. Stephen R. Schroeder
Division for Disorders
of Development and Learning
Biological Sciences Research Center
University of North Carolina
Chapel Hill, NC 27514
Dr. Anna-Maria Seppalainen
Institutes of Occupational Health
Tyoterveyslaitos
Haartmaninkatu 1
00290 Helsinki 29
Finland
Dr. Ellen Silbergeld
Environmental Defense Fund
1525 18th Street, NW
Washington, DC 20036
Dr. Ron Snee
E.I. duPont Nemours and
Company, Inc.
Engineering Department L3267
Wilmington, DE 19898
Dr. Gary Ter Haar
Toxicology and Industrial
Hygiene
Ethyl Corporation
451 Florida Boulevard
Baton Rouge, LA 70801
Mr. Ivon von Lindern
Department of Chemical Engineering
University of Idaho
Moscow, ID 83843
Dr. Richard P. Weeden
V.A. Medical Center
Tremont Avenue
East Orange, NJ 07019
xx ix
545<
-------
-------
PRELIMINARY DRAFT
9. QUANTITATIVE EVALUATION OF LEAD AND BIOCHEMICAL INDICES
OF LEAD EXPOSURE IN PHYSIOLOGICAL MEDIA
9.1 INTRODUCTION
In order to completely understand a given agent's effects on an organism, e.g., dose-
effect relationships, a quantitative evaluation of the substance in some indicator medium and
knowledge of the physiological parameters associated with exposure is vital. This said, two
questions follow:
1) What are the most accurate, precise, and efficient ways to
carry out such measurements?
2) In the case of lead (lead itself or biological indicators),
which measurement methods in which media are most appropri-
ate for each particular exposure?
Under the rubric of "analysis" are a number of discrete steps, all of which are important
contributors to the quality of the final result: (1) collection of samples and transmission
to the laboratory; (2) laboratory manipulation of samples, physically and chemically, before
analysis by instruments; (3) instrumental analysis and quantitative measurement; and (4)
establishment of relevant criteria for accuracy and precision, namely, internal and external
quality assurance checks. Each of these steps is discussed in this chapter.
It is clear that the definition of "satisfactory analytical method" for lead has been
changing over the years in ways paralleling (1) the evolution of more sophisticated instrumen-
tation and procedures, (2) a greater awareness of such factors as background contamination and
loss of element from samples, and (3) development of new statistical methods to analyze data.
For example, current methods of lead analysis, such as anodic stripping voltammetry, back-
ground-corrected atomic absorption spectrometry, and isotope dilution mass spectrometry (par-
ticularly the latter), are more sensitive and specific than the older classical approaches.
Increasing use of the newer methods would tend to result in lower lead values being reported
for a given sample. Whether this trend in analytical improvement can be isolated from such
other variables- as temporal changes in exposure is another matter.
Since lead is ubiquitously distributed as a contaminant, the constraints (i.e., ultra-
clean, ultra-trace analysis) placed upon a laboratory attempting analysis of geochemical
samples of pristine origin, or of extremely low lead levels in biological samples such as
plasma, are quite severe. Very few laboratories can credibly claim such capability. Ideally,
similar standards of quality should be adhered to across the rest of the analytical spectrum.
With many clinical, epidemiological, and experimental studies, however, this may be unrealis-
tic, given practical limitations and objectives of the studies. Laboratory performance is but
23PB12/C 9-1 7/1/83
546<
-------
PRELIMINARY DRAFT
one part of the quality equation; the problems of sampling are equally important but less sub-
ject to tight control. The necessity of rapidly obtaining a blood sample in cases of suspec-
ted lead poisoning, or of collecting hundreds or thousands of blood samples in urban popu-
lations, limits the number of sampling safeguards to those that can be realistically achieved.
Sampling in this context will always be accompanied by a certain amount of analytical
"suspicion." Furthermore, a certain amount of biological lead analysis data is employed for
comparative purposes, as in experimental studies concerned with the relative increase in tis-
sue burden of lead associated with increases in doses or severity of effects. In addition,
any major compromise of an analytical protocol may be statistically discernible. Thus, anal-
ysis of biological media for lead must be done under protocols that minimize the risk of in-
accuracy. Specific accuracy and precision characteristics of a method in a particular report
should be noted to permit some judgment on the part of the reader about the influence of
methodology on the reported results.
The choice of measurement method (see Question 2) and medium for analysis is dictated
both by the type of information desired and by technical or logistical considerations. As
noted elsewhere in this document, whole blood lead reflects recent or continuing exposure,
whereas lead in mineralized tissue, such as deciduous teeth, reflects an exposure period of
months and years. While urine lead values are not particularly good correlates of lead ex-
posure under steady-state conditions in populations at large, such measurements may be of con-
siderable clinical value. In acquisition of blood samples, the choice of venipuncture or
finger puncture will be governed by such factors as cost and feasibility, contamination risk,
the biological quality of the sample, etc. The use of biological Indicators that strongly
correlate with lead burden may be more desirable since they provide evidence of actual re-
sponse and, together with blood lead data, provide a less risky diagnostic tool for assessment
of lead exposure.
9.2 DETERMINATIONS OF LEAD IN BIOLOGICAL MEDIA
9.2.1 Sampling and Sample Handling Procedures for Lead in Biological Media
Lead analysis in biological media requires careful collection and handling of samples for
two special reasons: (1) lead occurs at trace levels in most indicators of subject exposure,
even under conditions of high lead exposure, and (2) such samples must be obtained against a
backdrop of pervasive contamination, the full extent of which may still be unrecognized by
many laboratories.
The reports of Speecke et al. (1976), Patterson and Settle (1976), Murphy (1976), Berman
(1976), and Settle and Patterson (1980) review detailed aspects of the problems of sampling
and subsequent sample handling in the laboratory. It is clear from these discussions that the
23PB12/C 9-2 7/1/83
547
-------
PRELIMINARY DRAFT
normal precautions taken in the course of sample acquisition (detailed below for clinical and
epidemiological studies) should not be taken as absolute, but rather as what is practical and
feasible. Furthermore, it may also be the case that the inherent sensitivity or accuracy of a
given methodology or instrumentation is less of a determining factor in the overall analysis
than is quality of sample collection and handling.
9.2.1.1 Blood Sampling. Samples for blood lead determination may be collected by venipunc-
ture (venous blood) or finger tip puncture (capillary blood). Collection of capillary vs.
venous blood is normally decided by a number of factors, including the feasibility of obtain-
ing samples during screening of many subjects and the difficulty of securing subject compli-
ance, particularly in the case of children and their parents. Furthermore, capillary blood
may be collected as discrete quantities in small-volume capillary tubes or as spots on filter
paper disks. With capillary tubes, obtaining good mixing with anticoagulant to avoid clotting
is important, as is the problem of lead contamination of the tube. The use of filter paper
requires the selection of paper with uniform composition, low lead content, and uniform blood
dispersal.characteristics.
Whether venous or capillary blood is collected, much care must be exercised in cleaning
the site before puncture as well as in selecting lead-free receiving containers. Cooke et al.
(1974) employed vigorous scrubbing with a low-lead soap solution and deionized water rinsing,
while Marcus et al. (1975) carried.out preliminary cleaning with an ethanolic citric acid
solution followed by 70 percent ethanol rinsing. The vigor in cleaning the puncture site is
probably as important as any particular choice of cleaning agent. Marcus et al. (1977) noted
that in one procedure for puncture site preparation, where the site is covered with wet paper
towels, contamination will occur if the paper towels are made from recycled paper, owing to
significant lead retention in recycled paper.
In theory, capillary and venous blood lead levels should be virtually identical, although
the available literature indicates that some differences, which mainly reflect problems of
sampling, do arise in the case of capillary blood. A given amount' of contaminant has a
greater impact on a 100 |jl fingerstick sample than on a 5 ml sample of venous blood. Finger
coating techniques may reduce some of the contamination problem (Mitchell et al., 1974). An
additional problem is the presence of lead in the anticoagulants used to coat capillary tubes.
Also, lower values of capillary vs. venous blood lead may reflect "dilution" of the sample by
extracellular fluid owing to excessive compression of the puncture site. When Joselow and
Bogden (1972) compared a method using finger puncture and spotting onto filter paper with a
procedure using venous blood and Hessel's procedure (1968) for flame atomic absorption spec-
trometry, they obtained a correlation coefficient of r = 0.9 (range, 20-46 gg/dl). Similarly,
Cooke et al. (1974) found an r value of 0.8 (no range given), while Mitchell et al. (1974)
23PB12/C
9-3
7/1/83
-------
PRELIMINARY DRAFT
obtained a value of 0.92 (10-92 |jg/dl). Mahaffey et al. (1979) found that capillary blood
levels in a comparison test were approximately 20 percent higher than corresponding venous
blood levels in the same subjects, presumably reflecting sample contamination. Similar eleva-
tions have been described by DeSilva and Donnan (1980). Carter (1978) has found that blood
samples with lower hemoglobin levels may spread onto filter paper differently from normal
hemoglobin samples, requiring correction in quantification to obtain values that are reliable.
This complication should be kept in mind when considering children, who are frequently prone
to iron-deficiency anemia.
The relative freedom of the blood container from interior surface lead and the amount of
lead in the anticoagulant used are important considerations in venous sampling. For studies
focused on "normal" ranges, such tubes may add some lead to blood and still meet certification
requirements. The "low-lead" heparinized blood tubes commercially available (blue stopper
Vacutainer, Becton-Dickinson) were found to contribute less than 0.2 ^ig/dl to whole blood
samples (Rabinowitz and Needleman, 1982). Nackowski et al. (1977) surveyed a large variety of
commercially available blood tubes for lead and other metal contamination. Lead uptake by
blood over time from the various tubes was minimal with the "low-lead" Vacutainer tubes and
with all but four of the other tube types. In the large survey of Mahaffey et al. (1979),
5-ml Monoject (Sherwood) or 7-ml lavender-top Vacutainer (Becton-Dickinson) tubes were found
satisfactory. However, when more precision is needed, tubes are best recleaned in the labor-
atory and lead-free anticoagulant added (although this would be less convenient for sampling
efficiency than the commercial tubes). In addition, blank levels for every batch of samples
should be verified.
9.2.1.2 Urine Sampling. Urine samples require collection in lead-free containers and caps as
well as the addition of a low-lead bacteriocide if samples are to be stored for any period of
time. While not always feasible, 24-hour samples should be obtained, as such collection would
level out any effect of variation in excretion over time. If spot sampling is done, lead
levels should be expressed per unit creatinine. For 24-hour collections, corrections must be
made for urine density.
9.2.1.3 Hair Sampling. The usefulness of hair lead analysis depends on the manner of samp-
ling. Hair samples should be removed from subjects by some consistent method, either by a
predetermined length measured from the skin or by using the entire hair. Hair should be
placed in air-tight containers for shipment or storage. For segmental analysis, the entire
hair length is required.
9.2.1.4 Mineralized Tissue. An important consideration in deciduous tooth collection is
consistency in the type of teeth collected from various subjects. Fosse and Justesen (1978)
reported no difference in lead content between molars and incisors, and Chatman and Wilson
(1975) reported comparable whole tooth levels for cuspids, incisors, and molars. On the other
hand, Mackie et al. (1977) and Lockeretz (1975) noted levels varying with tooth type, with a
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statistically significant difference (Mackie et al., 1977) between second molar (lowest
levels) and incisors (highest levels). The fact that the former two studies found rather low
overall lead levels across groups, while Mackie et al. (1977) reported higher values, suggests
that dentition differences in lead content may be magnified at relatively higher levels of ex-
posure. Delves et al. (1982), comparing pairs of central incisors or pairs of central and
lateral incisors from the same child, found that lead levels may even vary within a specific
type of tooth. These data suggest the desirability of acquiring two teeth per subject to get
an average lead value.
Teeth containing fillings or extensive decay are best eliminated from analysis. Mackie
et al. (1977) discarded decayed teeth if the extent of decay exceeded approximately 30 per-
cent.
9.2.1.5 Sample Handling in the Laboratory. With blood samples, there is the potential prob-
lem of the effect of storage on the lead content. It is clear that dilute aqueous solutions
of lead will surrender a sizable portion of the lead content to the container surface, whether
glass or plastic (Issaq and Zielinski, 1974; Linger and Green, 1977); whether there is a com-
parable effect, or the extent of such an effect, with blood is not clear. Unger and Green
(1977) claim that lead loss from blood to containers parallels that seen with aqueous solu-
tions, but their data do not support this assertion. Moore and Meredith (1977) used isotcpic
lead spiking (203Pb) with and without carrier in various containers at differing temperatures
to monitor lead stability in blood over time. The only material loss occurred with soda glass
at room temperature after 16 days. Nackowski et al. (1977) found that "low-lead" blood tubes,
while quite satisfactory in terms of sample contamination, began to show transfer of lead to
the container wall after four days. Meranger et al. (1981) studied movement of lead, spiked
to various levels, to containers of various composition as a function of temperature and time.
In all cases, reported lead loss to containers was significant. However, there are problems
with the above reports. Spiked samples probably are not incorporated into the same biochemi-
cal environment as lead inserted j_n vivo. The Nackowski et al. (1977) study did not indicate
whether the blood samples were kept frozen or refrigerated between testing intervals.
Mitchell et al. (1972) found that the effect of blood storage depends on the method of anal-
ysis, with lower recoveries of lead from aged blood being seen using the Hessel (1968) method.
Lerner (1975) collected blood samples (35 originally) from a single subject into lead-
free tubes and, after freezing, forwarded them in blind fashion to a certified testing labor-
atory over a period of 9 months. Four samples were lost, while one was rejected as being
grossly contaminated (4 standard deviations from mean). Of the remaining 30 samples, the mean
was 18.3 |jg/d1 with a standard deviation (S.D.) of 3.9. The analytical method had a precision
of ±3.5 pg Pb/dl (1 = S.D.) at normal levels of lead, suggesting that the overall stability of
the samples in terms of lead content, was good. Boone et al. (1979), reported that samples
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frozen for periods of less than a year showed no effect of storage, while Piscator (1982)
noted no change in low levels (<10 pg/dl) when samples were stored at -20°C for 6 months.
Based on the above data, it appears that blood samples to be stored for any period of time
should be frozen rather than refrigerated, with care taken to prevent breaking of the tube
during freezing. Teeth and hair samples, when stored in containers to minimize contamination,
are indefinitely stable.
The actual site of analysis should be as lead-free as possible. Given the uncommon
availability of an "ultra-clean" facility such as that described by Patterson and Settle
(1976), the next desirable level of laboratory cleanliness is the "Class 100" facility, in
which there are fewer than 100 airborne particles >0.5 pm. These facilities employ high ef-
ficiency particulate air filtering and laminar air flow (with movement away from sample
handling areas). Totally inert surfaces in the working area and an antechamber for removing
contaminated clothes, appliance cleaning, etc. are other necessary features.
All plastic and glass ware coming into contact with samples should be rigorously cleaned
and stored away from dust contact; materials such as ashing vessels should permit minimal lead
leaching. In this regard, Teflon and quartz ware is more desirable than other plastics or
borosilicate glass (Patterson and Settle, 1976).
Reagents, particularly for chemical degradation of biological samples, should be both
certified and periodically tested for retention of quality. Several commercial grades of re-
agents are available, although precise work may require doubly purified materials from the
National Bureau of Standards. These reagents should be stored with a minimum of surface con-
tamination around the top of the containers.
For a more detailed discussion of appropriate laboratory practices, the reader may con-
sult LaFleur (1976).
9.2.2 Methods of Lead Analysis
Detailed technical discussion of the array of instruments available to measure lead in
blood and other media is outside the scope of this Chapter (see Chapter 4). This discussion
is structured more appropriately to those aspects of methodology dealing with relative sensi-
tivity, specificity, accuracy and precision. While there is increasing acceptance of interna-
tional standardized units (SI units) for expressing lead levels in various media, units famil-
iar to clinicians and epidemiologists will be used here. (To convert |jg Pb/dl blood to SI
units (Mmoles/1iter), multiply by 0.048.)
Many reports over the years have purported to offer satisfactory analysis of lead in bio-
logical media, but in fact have shown rather meager adherence to criteria for accuracy and
precision or have shown a lack of demonstrable utility across a wide spectrum of analytical
applications. Therefore, discussion in this section is confined to "definitive" and reference
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methods for lead analysis, except for a brief treatment of the traditional but now widely sup-
planted colorimetric method.
Using the definition of Cali and Reed (1976), a definitive method is one in which all
major or significant parameters are related by solid evidence to the absolute mass of the ele-
ment with a high degree of confidence. A reference method, by contrast, is one of demonstra-
ted accuracy, validated by a definitive method and arrived at by consensus through performance
testing by a number of different laboratories. In the case of lead in biological media, the
definitive method is isotope-dilution mass spectrometry (IDMS). IDMS accuracy comes from the
fact that all manipulations are on a weight basis involving simple procedures. The measure-
ments entail only ratios and not the absolute determinations of the isotopes involved, which
greatly reduces instrumental corrections or errors. Reproducible results to a precision of
one part in 104 or 10s are routine with specially designed instruments.
In terms of reference methods for lead in biological media, such a label cannot techni-
cally be attached to atomic absorption spectrometry in its various instrumentation/
methodology configurations or to the electrochemical technique, anodic stripping voltammetry.
However, these have been termed reference methods insofar as their precision and accuracy can
be verified or calibrated against IDMS.
Other methods that are recognized for trace metal analysis in general are not fully ap-
plicable to biological lead or have inherent shortcomings. X-ray fluorescence analysis lacks
the requisite sensitivity for media with low lead content and the associated sample prepara-
tion may present a high contamination risk. A notable exception may be X-ray fluorescence
analysis of teeth or bone i_n situ as discussed below. Neutron activation analysis is the
method of choice with many elements, but is not technically feasible for lead analysis because
of the absence of long-lived isotopes.
9.2.2.1 Lead Analysis in Whole Blood. The first generally accepted technique for quantifying
lead in whole blood and other biological media was a colorimetric method that involved spec-
trophotometry measurement based on the binding of lead to a chromogenic agent to yield a
chromophobe complex. The complexing agent has typically been dithizone, 1,5-diphenylthio-
carbazone, yielding a lead complex that is spectrally measured at 510 nm.
Two variations of the spectrophotometry technique used when measuring low levels of lead
have been the USPHS (National Academy of Sciences, 1972) and APHA (American Public Health
Association, 1955) procedures. In both, venous blood or urine is wet ashed using concentrated
nitric acid of low lead content followed by adjustment of the ash with hydroxylamine and so-
dium citrate to a pH of 9-10. Cyanide ion is added and the solution extracted with dithizone
in chloroform. Back extraction removes the lead into dilute nitric acid; the acid layer is
treated with ammonia, then cyanide, and re-extracted with dithizone in chloroform. The
extracts are read in a spectrophotometer at 510 nm. Bismuth interference is handled (APHA
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variation) by removal with dithizone at pH 3.4. According to Lerner (1975), the analytical
precision in the "normal" range is about ±3.5 |jg Pb/dl (1 = S.D.), using 5 ml of sample.
The most accurate and precise method for lead measurement in blood is isotope dilution
mass spectrometry. As typified by the report of Machlan et al. (1976), whole blood samples
are accurately weighed, and a weighed aliquot of 206Pb-enriched isotope solution is added.
After sample decomposition with ultra-pure nitric and perchloric acids, samples are evapo-
rated, residues are taken up in dilute lead-free hydrochloric acid, and lead is isolated using
anion-exchange columns. Column eluates are evaporated with the above acids, and lead is
deposited onto high purity platinum wire from dilute perchloric acid. The 206Pb/208Pb ratio
is then determined by thermal ionization mass spectrometry. Samples without added isotope and
reagent blanks are also carried through the procedure. In terms of precision, the 95 percent
confidence level for lead samples overall is within 0.15 percent. Due to the expense incurred
by the requirements for operator expertise, the amount of time involved, and the high standard
of laboratory cleanliness, IDMS is mainly of practical value in the development of standard
reference materials and for the verification of other analytical methods.
Atomic absorption spectrometry (AAS) is widely used for lead measurements in whole blood,
with sample analysis involving analysis of venous blood with chemical degradation, analysis of
liquid samples with or without degradation, and samples applied to filter paper. It is thus
the most flexible for samples already collected or subject to manipulation.
By means of a flame or electrothermal excitation, ionic lead in some matrix is first vapor-
ized and then converted to the atomic state, followed by resonance absorption from either a
hollow cathode or electrodeless discharge lamp generating lead absorption lines at 217.0 and
283.3 nm. After monochrometer separation and photomultiplier enhancement of the differential
signal, it is measured electronically.
The earliest methods of atomic absorption spectrometric analysis involved the aspiration
into a flame of ashed samples of blood, usually subsequent to extraction into an organic sol-
vent to enhance sensitivity by preconcentration. Some methods did not involve digestion steps
prior to solvent extraction (Kopito et al. , 1974). Of these various flame AAS methods, that
of Hessel's (1968) technique continues to be used with some frequency.
Currently, lead measurement in blood by AAS employs several different methods that permit
greater sensitivity, precision, and economy of sample and time. The flame method of Delves
(1970), called the "Delves cup" procedure, usually involves delivery of discrete small samples
(S100 |jl) of unmodified whole blood to nickel cups, with subsequent drying and peroxide decom-
position of organic content before positioning in the flame. The marked enhancement of sen-
sitivity over conventional flame aspiration is due to immediate, total consumption of the
sample and the generation of a localized population of atoms. In addition to discrete blood
volumes, blood-containing filter paper disks have been used (Joselow and Bogden, 1972; Cernil
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and Sayers, 1971; Piomelli et al., 1980). 5everal modifications of the Delves method include
that of Ediger and Coleman (1972), in which dried blood samples in the cups are pre-ignited to
destroy organic matter by placement near the flame in a precise, repeatable manner, and the
variation of Barthel et al. (1973), in which blood samples are mixed with dilute nitric acid
in the cups followed by drying in an oven at 200°C and charring at' 450°C on a hot plate. A
number of laboratories eschew even these modifications and follow dispensing and drying with
direct placement of the cup into the flame (e.g., Mitchell et al., 1974). The Delves cup pro-
cedure may require correction for background spectral interference, which is usually achieved
by instrumentation equipped at a non-resonance absorption line. While the 217.0 nm line of
lead is less subject to such interference, precise work is best done with correction. This
method as applied to whole blood lead appears to have an operational sensitivity down to 1.0
pg Pb/dl, or somewhat below when competently employed, and a relative precision of approxi-
mately 5 percent in the range of levels encountered in the United States.
AAS methods using electrothermal (furnace) excitation in lieu of a flame can be approxi-
mately 10-fold more sensitive than the Delves procedure. A number of reports describing whole
blood lead analysis have appeared in the literature (Lawrence, 1982, 1983). Because of in-
creased sensitivity, the "flameless" AAS technique permits the use of small blood volumes
(1-5 pi) with samples undergoing drying and dry ashing in situ. Physicochemical and spectral
interferences are inherently severe with this approach, requiring careful background cor-
rection. In one flameless AAS configuration, background correction exploits the Zeeman
effect, where correction is made at the specific absorption line of the element and not over a
band-pass region, as is the case with the deuterium arc. While control of background inter-
ference up to 1.5 molecular absorbence is claimed with the Zeeman system (Koizumi and Yasuda,
1976), it is technically preferable to employ charring before atomization. Hinderberger et
al. (1981) used dilute ammonium phosphate solution to minimize chemical interference in their
furnace AAS method.
Precision can be a problem in the flameless technique unless careful attention is paid to
the problem of sample diffusibi1ity over and into the graphite matrix of the receiving recep-
tacle -- tube, cup, or rod. With the use of diluted samples and larger applied volumes, the
relative precision of this method can approach that of the Delves technique (Delves, 1977).
In addition to the various atomic absorption spectral methods noted above, electro-
chemical techniques have been applied to blood lead analysis. Electrochemical methods, in
theory, differ from AAS methods in that the latter are "concentration" methods regardless of
sample volumes available, while electrochemical analysis involves bulk consumption of sample
and hence would have infinite sensitivity, given an infinite sample volume. This intrinsic
property is of little practical advantage given usual sample volume, instrumentation design,
and blank 1imits.
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The most widely used electrochemical method for lead measurement in whole blood and other
biological media is anodic stripping voltammetry (ASV) which is also probably the most sensi-
tive, as it involves an electrochemical preconcentration (deposition) step in the analysis
(Matson and Roe, 1966; Matson et al., 1970). In this method, samples such as whole blood
(50-100 pi), are preferably but not commonly wet ashed and reconstituted in dilute acid or
made electro-available with metal exchange reagents. Using freshly prepared composite elec-
trodes of mercury film deposited on carbon, lead is plated out from the solution for a speci-
fic amount of time and at a selected negative voltage. The plated lead is then reoxidized in
the course of anodic sweeping, generating a current peak that may be recorded on a chart or
displayed on commercial instruments as units of concentration (pg/dl).
One alternative to the time and space demands of wet ashing blood samples is the use of
metal exchange reagents that displace lead from binding sites in blood by competitive binding
(Morell and Giridhar, 1976; Lee and Meranger, 1980). In one commercial preparation, this re-
agent consists of a solution of calcium, chromium, and mercuric ions. Use of the metal ex-
change reagent adds a chemical step that must be carefully controlled for full recovery of
lead from the sample.
The working detection limit of ASV for blood is comparable to that of the AAS flameless
methods while the relative precision is best with prior sample degradation, approximately 5
percent, but less when the blood samples are run directly with the ion exchange reagents
(Morrell and Giridhar, 1976), particularly at the low end of "normal" blood lead values.
While AAS methods require attention to various spectral interferences to achieve satisfactory
performance, electrochemical methods such as ASV require consideration of such factors as the
effects of co-reducible metals and agents that complex lead and alter its reduction-oxidation
(redox) potential properties. Chelants used in therapy, particularly penicillamine, may in-
terfere, as does blood copper, which may be elevated in pregnancy and such disease states as
leukemia, lymphoma, and hyperthyroidism (Berinan, 1981). At very low levels of lead in blood,
then, ASV may pose more problems than atomic absorption spectrometric techniques.
Correction of whole blood lead values for hematocrit, although carried out in the past,
is probably not appropriate and not commonly done at present. While the erythrocyte is the
carrier for virtually all lead, in blood, the saturation capacity of the red blood cell for
lead is so high that it can still carry lead even at highly toxic levels (Kochen and Greener,
1973). Kochen and Greener (1973) also showed that acute or chronic dosing at a given lead
level in rats with a wide range of hematocrits (induced by bleeding) gave similar blood lead
values. Rosen et al. (1974), based on studies of hematocrit, plasma, and whole blood lead in
children, noted hematocrit correction was not necessary, a view supported by Chisolm (1974).
9.2.2.2 Lead in Plasma. While virtually all of the lead present in whole blood is bound to
the erythrocyte (Robinson et al., 1958; Kochen and Greener, 1973), lead in plasma is trans-
ported to affected tissues. It is very important, therefore, that every precaution be taken
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to use non-hemolyzed blood samples for plasma isolation. The very low levels of lead in
plasma require that more attention be paid to "ultra clean" methods.
Rosen et al. (1974) used flameless atomic absorption spectrometry and microliter samples
of plasma to measure plasma lead, with background correction for the smoke signal generated
for the unmodified sample. Cavalleri et al. (1978) used a combination of solvent extraction
of modified plasma with preconcentrating and flameless atomic absorption. These authors noted
that the method used by Rosen et al. (1974) permitted less precision and accuracy than did
their technique, because a significantly smaller amount of lead was delivered to the furnace
accessory.
DeSilva (1981) used a technique similar to that of Cavalleri et al. (1978), but collected
samples in heparinized tubes, claiming that the use of EDTA as anticoagulant disturbs the
cell-plasma distribution of lead enough to yield erroneous data. Much more care was given in
this procedure to background contamination. In both cases, increasing levels of plasma lead
were measured with increasing whole blood lead, suggesting an equilibrium ratio in contradic-
tion to the data of Rosen et al. (1974), who found a fixed level of 2-3 pg Pb/dl plasma over a
wide range of blood lead. However, the actual levels of lead in plasma in the DeSilva (1981)
study were much lower than those reported by Cavalleri et al. (1978).
Using isotope-dilution mass spectrometry and sample collection/manipulation in an
"ultra-clean" facility, Everson and Patterson (1980) measured the plasma lead levels in two
subjects, a control and a lead-exposed worker. The control had a plasma lead level of 0.002
pg Pb/dl, several orders of magnitude lower than that seen with studies using less precise
analytical approaches. The lead-exposed worker had a plasma level of 0.2 |jg Pb/dl. Several
other reports in the literature using isotope-dilution mass spectrometry noted somewhat higher
values of plasma lead (Manton and Cook, '1979; Rabinowitz et al., 1974), which Everson and
Patterson (1980) have ascribed to problems of laboratory contamination. Utilizing tracer lead
to minimize the impact of contamination results in a value of 0.15 pg/dl (Rabinowitz et al.,
1974).
With appropriate plasma lead methodology, reported lead levels are extremely low, the de-
gree varying with the methods used to measure such concentrations. While the data of Everson
and Patterson (1980) were obtained from only two subjects, it seems unlikely that using more
subjects would result in a plasma lead range extending upward to the levels seen with ordinary
methodology in ordinary laboratory surroundings. The above considerations are necessary when
discussing appropriate methodology for plasma analysis, and the Everson and Patterson (1980)
report indicates that some doubt surrounds results obtained with conventional methods. Al-
though not the primary focus of their study, the values obtained by Everson and Patterson
(1980) for whole blood lead, unlike the data for plasma, are within the ranges for unexposed
(11 pg Pb/dl) and exposed (80 pg Pb/dl) subjects generally reported with other methods. This
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would suggest that, for the most part, reported values do actually reflect i_n vivo blood lead
levels rather than sampling problems or inaccurate methods.
9.2.2.3 Lead in Teeth. When carrying out analysis of shed deciduous or extracted permanent
teeth, some reports have used the whole tooth after surface cleaning to remove contaminating
lead (e.g., Moore et al., 1978; Fosse and Justesen, 1978; Mackie et al., 1977), while others
have measured lead in dentine (e.g., Shapiro et al., 1973; Needleman et al. , 1979; Al-Naimi et
al., 1980). Several reports (Grandjean et al., 1978; Shapiro et al., 1973) have also de-
scribed the analysis of secondary (circumpulpal) dentine, that portion of the tooth found to
have the highest relative fraction of lead. Needleman et al. (1979) separated dentine by em-
bedding the tooth in wax, followed by thin central sagittal sectioning. The dentine was then
isolated from the sawed sections by careful chiseling.
The mineral and organic composition of teeth and their components requires the use of
thorough chemical decomposition techniques, including wet ashing and dry ashing steps, sample
pulverizing or grinding, etc. In the procedure of Steenhout and Pourtois (1981), teeth are
dry ashed at 450°C, powdered, and dry ashed again. The powder is then dissolved in nitric
acid. Fosse and Justesen (1978) reduced tooth samples to a coarse powder by crushing in a
vise, followed by acid dissolution. Oehme and Lund (1978) crushed samples to a fine powder in
an agate mortar and dissolved the samples in nitric acid. Mackie et al. (1977) and Moore et
al. (1978) dissolved samples directly in concentrated acids. Chatman and Wilson (1975) and
Needleman et al. (1974) carried out wet ashing with nitric acid followed by dry ashing at
450°C. Oehme and Lund (1978) found that acid wet ashing of tooth samples yielded better re-
sults if carried out in a heated Teflon bomb at 200°C.
With regard to methods of measuring lead in teeth, atomic absorption spectrometry and
anodic stripping voltammetry have been employed.,most., often. With the AAS methods, the high
mineral content of teeth tends to argue for isolating lead from this matrix before analysis.
In Needleman et al.'s (1974) and Chatman and Wilson's (1975) method, ashed residues in nitric
acid were treated with ammonium nitrate and ammonium hydroxide to a pH of 2.8, followed by
dilution and extraction with a methylisobutylketone solution of ammonium pyrrolidine-
carbodithioate. Analysis is by flame AAS using the 217.0 nm lead absorption line. A similar
procedure was employed by Fosse and Justesen (1978).
Anodic stripping voltammetry has been successfully used in tooth lead measurement
(Shapiro et al., 1973; Needleman et al., 1979; Oehme and Lund, 1978). As typified by the
method of Shapiro et al. (1973), samples of dentine were dissolved in a small volume of low-
lead concentrated perchloric acid and diluted (5.0 ml) with lead-free sodium acetate solution.
With deoxygenation, samples were analyzed in a commercial ASV unit, using a plating time of 10
minutes at a plating potential of -1.05 V. Anodic sweeping was at a rate of 60 irV/sec with a
variable current of 100-500 pA.
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Since lead content of teeth is higher than in most samples of biological mecia, the rela-
tive precision of analysis with appropriate accommodation of the matrix effect, such as the
use of matrix-matched standards, in tne better studies indicates a value of aporoximately 5-7
percent.
All of the above methods involve 'shed or extracted teeth and consequently provide a ret-
rospective determination of lead exposure. In Bloch et al.'s (1976) procedure, tooth lead is
measured _i_n situ using an X-^ay fluorescence technique. A col "!inated beam of radiation from
57Co was allowed to irradiate the uoper central incisor teeth of the subject. Using a rela-
tive'y safe 100-second irradiation time and measurement of K , ana K lead lines via a ger-
J al az 3
manium diode and a pulse height analyzer for signal processing, lead levels of 15 ppm or
higher could be measured. Multiple measurement by this method would be very useful in pros-
pective studies because it would show the 'on-going" rate of increase in body lead burden.
Furthermore. when combined with serial blood sanipli-g, it would provide data for blood lead-
tootr lead relationships.
9.2.2.4 Lead in Hair. Hair constitutes a non-invasive sampling source with virtually no
problems with sample stability on extended storage. However, the advantages of accessibility
and stability are offset by the problem of assessing external contamination of the hair sur-
face by atmospheric fallout, hand dirt, lead in hair preoaratio.ns, etc. Thus, such samples
are probably of less value overall than those 'rom otrer media.
The various methods that have been employed for removal of external lead have been
reviewed (Chatt et al., 1980; Gibson, 1980; Chattopadhyay et a:., 1977). Cleaning techniques
obviously should be vigorous enough to remove surface lead but not so vigorous as to remove
the endogenous fraction. To date, it remains to be demonstrated that any published cleaning
p^ocedu^e is reliable enough to permit acceptance of reported levels of : ead in hair. Such a
demonstration would have to use lead isotopic studies with both surface and endogenous
-'sotopic lead removal monitored as a 'unction of a particular clearing technique.
9.2.2.5 Lead in Urine. Analysis of lead i.n urine is complicated by its relatively low con-
centrations (lower than in blood in many cases) as well as by the complex mixture of mineral
elements present. Lead levels are higher, of course, in cases where lead mobilization or
therapy wi t.h chelants is in progress, but in these cases samples must be analyzed to account
for lead bound to chelants such as EDTA. This requires either sanple ashing or the use of
standards containing the chelant. Although analytical methods have been published for the
direct analysis of lead in urine, samples are probably best wet ashed before analysis, using
the usual mixtures of nitric plus sulfuric and/or perchloric acids.
Both atomic absorption spectrometric and anodic stripping voltammetric methods have been
applied to urine lead analyses, the former employing either direct analysis of ashed residues
or a preliminary che 1 ation-extraction step. With flame AAS, ashed urine samples must invari-
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ably be extracted with a chelant such as ammonium pyrroliciinecarbodithioate in methy1isobutyl-
ketone to achieve reasonably satisfactory resuHs. Direct analysis, furtnermore, creates me-
chanical problems with burner operation, due to the high mineral content of urine, and results
in considerable maintenance problems with equipment. The procedure of Lauwerys et al. (197b)
is typical of fame AAS methoas with preliminary lead separation. Owing zo the relatively
greater sensitivity of graphite furnace (flameless) AAS, this variation of the method has been
applied to urine analysis in scattered reports where it appears that adequate performance for
direct sample analysis requires steps to minimize ,natr;x interference. A typical example of
one of the better direct analyses methods is that of Hodges and Skeldirg (1981). Urine
samples were mixed with iodine solution and heated, then diluted with a special *~eagent con-
taining ammonium molybdate, phosphoric acid, and ascorbic acid. Small aliquots (5 |jl) were
delivered to the furnace accessory of an AAS unit containing a graphite tube pretreated with
ammonium molybdate. The relative standard deviation of the method is reported to be about 6
percent. In the method of Legotte et al. (1980), such tube treatment and sample rrodifications
were not employed and the average precision figure was 13 percent.
Compared with various atomic absorption spectrometric methods, anodic stripping voltam-
metry has been less frequently employed for urine lead analysis, and it would appear from
available electrochemical methods in general that such techniques applied tc urine require
further development. Franke and de Zeeuw (1977) used differentia1 pulse anodic stripping vol-
tammetry as a screening tool for lead and other elements in urine. Jagner et a". (1979) de-
scribed analyses of urine lead using potentionetric stripping. In their procedure the element
was pre-concentrated at a thin-film mercury electrode as in conventional ASV, but deoxygenated
samples were reoxidized with either oxygen or mercuric ions a^ter the circuitry was disconnec-
ted.
As noted in Section 9.1.1.2, spot sampling of lead in urine should be expressed per unit
creatinine, if it is not possible to obtain 24-hour collection.
9,2.2.6 Lead in Other Tissues. Bone samples of experimental animal or human autopsy origin
require preliminar.y cleaning procedures for removal of muscle and connective tissue, with care
being taken to minimize sample contamination. As is the case with teeth, samples must be che-
mically decomposed before analysis. Satisfactory instrumental methods for bone lead analysis
comprise a much smaller literature than is tne case for other media.
Wittmers et al. (1981) have described the measurement of lead in dry-ashed (450°C) bone
samples using flameless atomic absorption spectrometry. Ashed samples were weighed and dis-
solved in dilute nitric acid containing lanthanum ion, the latter being used to suppress in-
terference from bone elements. Small volumes (20 pi) and high calcium content required that
atomization be done at 2400°C to avoid condensation of calcium within the furnace. Quantifi-
cation was by the method of additions. Relative precision was 6-8 percent at relatively high
lead content (60 pg/g ash) and 10-12 percent at levels of 14 pg/g ash or less.
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Ahlgren et al. (1S80) described the application of X-ray fluorescence analysis to i_n vivo
lead measurement ;n the tiLman skeleton, using tibia and pha'anges. In this technique, ir-
radiation is carried out wHh dual S7Co gamna ray source. The generated K x and K 2 lead
lines are detected witr a lithium-drifted germanium detector. The detection limit is 20 parts
oer mi 11 ion.
So't organs differ from other biological media in the extent of anatomic heterogeneity as
well as lead distribution, e.g., bra1-n vs. kidney. Hence, sanple analysis involves either
discrete regional sarr.pl irg cr the homogenizing of an organ. The efficiency of the latter can
vary considerably, depending on the density of the homogenate, the efficiency of rupture of
the formed elements, and other factors. Glass-on-glass homogenizing is to be avoided because
'ead is liberated from the glass matrix with abrasion.
Atomic absorption spectrometry, in its flame or flameless variations, appears to be tie
method of choice in many studies. In the procedure of Slavin et al. (1975), tissues were wet
ashed and the residues taKen up in dilute acid and analyzed with the furnace accessory of an
AAS unit. A large number of reports representing slight variations of this basic technique
have aopeared ever the yea>-s (Lawrence, 1982, 1983). Flame procedures, being less sensitive
than the graohite furnace method, require more sample than may 3e available or are restricted
to measurement ir tissues where levels are relatively high, e.g.. kidney. In the method of
Farris et al. (1978), samples of brain, liver, lung, or spleen (as discrete segments) were
lyophilized and so'ubi 1 i zee: at room temperature with nitric acid. Following neutralization,
lead was extracted into methylisobutylketone with ammonium pyrrolidinecarbodithioate and
aspirated into the flame of an AAS unit. The reported relative orecision was 8 percent.
9.2.3 Quality Assurance Procedures In Lead Analysis
Regardless of technical differences among the different methodologies for lead analysis,
one can define the quality of such techniques as being of: (I) poor accuracy and poor pre-
cision; (2) poor accuracy and good precision; or (3) good accuracy and good precision. In
terms of available information, the major focus in assessing quality has been on olood lead
determi nati ons.
According to Boutwell (1976), the use of quality control testing for lead measurement
rests on four assumptions; (1) the validity of the specific procedure for lead in some matrix
has been established; (2) the stability of the factors making up the method has been both es-
tablished and manageable; (3) the validity of the calibration process and the calibrators with
respect to the media being analyzed has been established; and (4) surrogate quality control
materials of reliably determined analyte content can be provided. These assumptions, when
translated into practice, revolve around steps employed within the laboratory, using a battery
of "internal checks" and a further reliance on "external checks" such as a formal, well-
organized, irulti-laboratory proficiency testing program.
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Analytical qjal ,-ty protocol s can oe further divided into start-up and routine procedures,
the former entailing the establishment, of detection limits, "within-run" and "between-run'1
precision, recovery of analyte, etc. When ?. new method is adopted for some specific analyti-
cal advantage, the urocedure is usually testec in the laboratory or outside the laboratory for
comparative pe-rormance. For example, Hicks et al. (1973) and Kubasik et al. (1972) reported
that flameless techniques for measuring lead in whole blcod were fcund tc have a satisfactory
correlation with resLlts using conventional flame procedures. Matson et al. (197C) noted a
good agreement between anodic stripping voltanmetry and both atomic absorpt;on spectral and
dithizone co1orimetric techniques. Tne problem with such comparisons is that the reference
method is assumed to be accurate for the particular level of lead "n a given matrix. High
correlations obtained in this manner may simply indicate that two inaccurate methods are
simultaneously performing with the same level of precision.
Preferable approaches for assessing accuracy are the use of certified sanp'es determined
by a definitive method, or a direct comparison of different techniques with a definitive pro-
cecure. For example, E'ler and Hartz (1977) comparoc the precision and accuracy of five
available netrods for measuring lead in Mood: dithizone spectrometry, extraction and tanta-
lum boat AA5, extraction and flane aspiration AAS, direct aspiration AAS, anc graphite furnace
AAS techniques. Porc;ne whole blood certified by the National Sureau of Standards (NBS) using
isotope-di1uticn mass spectrometry at 1.00 p9 Pb/g (±0.023) was tested and all methods were
found to be equally accurate. 'tie tantalum boat technique was found to be the 'east precise.
The obvious limitation of these data is that they relate to a high olood lead content, suit-
able for use in measuring the exposure of lead workers or in some othe" occupational context,
but less appropriate for clinical or epidemiological investigations.
Boone et al. (1979) compared the analytical performance of 113 laboratories using various
methods and 12 whole blood samples (blood from cows fed a lead salt) certified as to lead con-
tent using isotooe-dilution mass spectrometry at the NBS. Lead content ranged from 13 to 102
pg Pb/dl , determined by anodic stripp-'ng voltanmetry-arid five variations of AAS. The order of
agreement w'th NBS values, i.e., relative accuracy, was: extraction > ASV > tantalum strip >
graphite furnace > Delves cup > carbon rod. The AAS methods a'l tended to show bias, being
positive at values less than 40 pg Pb/dl and negative at levels greater than 50 pg Pb/dl. ASV
tended to show less of a positive bias problem-, although it was not bias-free within either of
the blood lead ranges. In terms of relative precision, the ranking was: ASV > Delves cup >
tantalum strip > graphite furnace > extraction > carbon rod. The overall ranking ir accuracy
and precision indicated: ASV > Delves cup > extraction > tantalum strip > graphite furnace >
carbon rod. As the authors cautioned,' the above data should not be taken to indicate that any
established laboratory using one particular techniqje would not perform better than this;
rather, it should be used as a guide for newer facilities choosing among methods.
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There are a number of necessary>steps in quality assurance pertinent to the routine
measurement of lead that should be used in an ongoing program. With respect to internal
checks of routine performance, these include calibration and precision and accuracy testing.
With biological matrices, the use of matrix-matched standards is quite important, as is an
understanding of the range of linearity and variation of calibration curve slopes from day to
day. It is common practice to analyze a given sample in duplicate, further replication being
carried out if the first two determinations vary beyond a predetermined range. A second de-
sirable step is the analysis of samples collected in duplicate but analyzed "blind" to avoid
bias.
Monitoring of accuracy within the laboratory is limited to the availability of control
samples having a certified lead content in the same medium as the samples being analyzed.
Controls should be as physically close to the media being analyzed as possible. Standard re-
ference materials (SRMs), such as orchard leaves and lyophilized bovine liver, are of help in
some cases, but there is need for NBS-certified blood samples for the general laboratory com-
munity. There are commercially available whole blood samples, prepared and certified by the
marketing facility (TOX-EL, A. R. Smith Co., Los Angeles, CA; Kaulson Laboratories, Caldwell,
NJ; Behringwerke AG, Marburg, W. Germany; and Health Research Institute, Albany, NY). With
these samples, attention must be paid to the reliability of the methods used by reference
laboratories. The use of such materials, from whatever source, must minimize bias; for exam-
ple, the attention given control specimens should be the same as that given routine samples.
Finally, the most important form of quality assurance is the ongoing assessment of lab-
oratory performance by proficiency testing programs using externally provided specimens for
analysis. Earlier interlaboratory surveys of lead measurement in blood and in urine indicated
that a number of laboratories had performed unsatisfactorily, even at high levels of lead
(Keppler et al., 1970; Donovan et al., 1971; Berlin et al., 1973), although there may have
been problems in the preparation and status of the blood samples during and after distribution
(World Health Organization, 1977). These earlier tests for proficiency indicated that: (1)
many laboratories were able to achieve a good degree of precision within their own facilities;
(2) the greater the number of samples routinely analyzed by a facility, the better the per-
formance; and (3) 30 percent of the laboratories routinely analyzing blood lead repprted
values differing by more than 15 percent from the true level (Pierce et al., 1976).
In the more recent, but very limited, study of Paulev et al. (1978), five facilities par-
ticipated in a survey, using samples to which known amounts of lead were added. For lead in
both whole blood and urine, the interlaboratory coefficient of variation was reported to be
satisfactory, ranging from 12.3 to 17.2 percent for blood and urine samples.- Aside from its
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limitation of scope, this study used "spiked'1 instead of j_n vivo lead, so that extraction
techniques used in most of the laboratories surveyed would have given misleadingly better
results in terms of actual recovery.
Maher et al. (1979) described the outcome of a proficiency study involving up to 38 lab-
oratories that analyzed whole blood pooled from a large number of samples submitted for blood
lead testing. The Delves cup technique was the most heavily represented, followed by the
chelation-extraction plus flame AAS method and the graphite furnace AAS method. Anodic strip-
ping voltammetry was used by only approximately 10 percent of the laboratories, so that the
results basically portray AAS methods. All laboratories had about the same degree of ac-
curacy, with no evidence of consistent bias, while the interlaboratory coefficient of
variation was approximately 15 percent. A subset of this group, certified by the American
Industrial Hygiene Association (AIHA) for air lead, showed a corresponding precision figure of
approximately 7 percent. Over time, the subset of AIHA-certified laboratories remained about
the same in proficiency, while the other facilities showed continued improvement in both ac-
curacy and precision. This study indicates that program participation does help the per-
formance of a laboratory doing blood lead determinations.
The most comprehensive proficiency testing program is that carried out by the Centers for
Disease Control of the U.S. Public Health Service. This consists of two operationally and ad-
ministratively distinct subprograms, one conducted by the Center for Environmental Health
(CEH) and the other by the Licensure and Proficiency Testing Division, Laboratory Improvement
Program Office (LIP0). The CEH program is directed at facilities involved in lead poisoning
prevention and screening, while LIP0 is concerned with laboratories seeking certification
under the Clinical Laboratories Improvement Act of 1967 as well as under regulations of the
Occupational Safety and Health Administration (OSHA). Both the CEH and LIPO protocols involve
the use of bovine whole blood certified as to content by reference laboratories (6 in the CEH
program, 20-23 in LIPO) with an ad hoc target range of ±6 ^g Pb/dl for values of 40 (jg Pb/dl
or less and ±15 percent for higher levels. Three samples are provided monthly from CEH, for
a total of 36 yearly, while LIPO participants receive 3 samples quarterly (12 samples yearly).
Use of a fixed range rather than a standard deviation has the advantage of allowing the moni-
toring of overall laboratory improvement.
For Fiscal Year (FY) 1981, 114 facilities were in the CEH program, 92 of them partici-
pating for the entire year. Of these, 57 percent each month reported all three samples within
the target range, and 85 percent on average reported two out of three samples correctly. Of
the facilities reporting throughout the year, 95 percent had a 50 percent or better perfor-
mance, i.e., 18 blood samples or better. If one compares these summary data for FY 1981 with
earlier annual reports, it would appear that there has been considerable improvement in the
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number of laboratories achieving higher levels of proficiency. For the interval FY 1977-79,
there was a 20 percent increase in the number correctly analyzing more than 80 percent of all
samples and a 33 percent decrease in those reporting less than 50 percent correct. In the
last several years, FY 1979-81, overall performance appears to have more or less stabilized.
With the LIPO program for 1981 (Dudley, 1982), the overall laboratory performance
averaged across all quarters was 65 percent of the laboratories analyzing all samples cor-
rectly and approximately 80 percent performing well with two of three samples. Over the four
years of this program, an increasing ability to correctly analyze lead in blood appears to
have been demonstrated. Dudley's survey (1982) also indicates that reference laboratories in
the LIPO program are becoming more accurate relative to isotope-dilution mass spectrometry
values, i.e., bias over the blood lead range is contracting.
Current OSHA criteria for certification of laboratories measuring occupational blood lead
levels require that eight of nine samples be correctly analyzed in the previous quarter (U.S.
Occupational Safety and Health Administration, 1982). These criteria appear to reflect the
ability of a number of laboratories to perform at this level.
It should be noted that most proficiency programs, including the CEH and LIPO surveys,
are appropriately concerned with blood lead levels encountered in such cases as pediatric
screening for excessive exposure to lead or in occupational exposures. As a consequence,
there does appear to be an underrepresentation of lead values in the low end of the "normal"
range. In the CEH distribution for FY 1981, four samples (11 percent) were below 25 pg Pb/dl.
The relative performance of the 114 facilities with these samples indicates outcomes much
better than with the whole sample range.
9.3 DETERMINATION OF ERYTHROCYTE PORPHYRIN (FREE ERYTHROCYTE PROTOPORPHYRIN,
ZINC PROTOPORPHYRIN)
9.3.1 Methods of Erythrocyte Porphyrin Analysis
Lead exposure results in inhibition of the final step in heme biosynthesis, the insertion
of iron into protoporphyrin IX to form heme. This leads to an accumulation of the porphyrin,
with zinc (II) occupying the position normally filled by iron. Depending on the particular
method of analysis, zinc protoporphyrin (ZPP) itself or the metal-free form, free erythrocyte
protoporphyrin (FEP), is measured. FEP generated as a consequence of chemical manipulation
should be kept distinct from the metal-free form biochemically produced in the porphyria,
erythropoietic protoporphyria. The chemical or "wet" methods measure free erythrocyte
porphyrin or zinc protoporphyrin, depending upon the relative acidity of the extraction
medium. The hematofluorometer in its commercially available form measures zinc proto-
porphyri n.
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Porphyrins are labile due to photochemical decomposition; hence, samples must be pro-
tected from light during collection and handling and analyzed as soon as possible.
Hematocrits must also be obtained to adjust for anemic subjects.
In terms of methodological approaches for EP analysis, virtually all methods now in use
exploit the ability of porphyrins to undergo intense fluorescence when excited at the appro-
priate wavelength of light. Such fluorometric techniques can be further classified as wet
chemical micromethods or as micro methods using a recently developed instrument, the hemato-
fluorometer. The latter involves direct measurement in whole blood. Because the mammalian
erythrocyte contains all of the EP in whole blood, either packed cells or whole blood may be
used, although the latter is more expedient.
Due to the relatively high sensitivity of fluorometric measurement for FEP or ZPP,
laboratory methods for spectrof1uorometric analysis require a relatively small sample of
blood; hence, microtechniques are currently the most popular in most laboratories. These in-
volve either liquid samples or blood collected on filter paper, the latter of use particularly
in field sampling.
As noted above, chemical methods for EP analysis measure either free erythrocyte proto-
porphyrin, where zinc is chemically removed, or zinc protoporphyrin, where zinc is retained.
The procedures of Piomelli and Davidow (1972), Granick et al., (1972), and Chisholm and Brown
(1975) typify "free" EP methods, while those of Lamola et al. (1975), Joselow and Flores
(1977), and Chisholm and Brown (1979) involve measurement of zinc-EP.
In Piomelli and Davidow's (1972) micro procedure, small volumes of whole blood, analyzed
either directly or after collection on filter paper, were treated with a suspension of Celite
in saline followed by a 4:1 mixture of ethyl acetate to glacial acetic acid. After agitation
and centrifugation, the supernatant was extracted with 1.5N HC1. The acid layer was analyzed
fluorometrically using an excitation wavelength of 405 nm and measurement at 615 nm. Blood
collected on filter paper discs was first eluted with 0.2 ml H20. The filter paper method was
found to work just as well as liquid samples of whole blood. Protoporphyrin IX was employed
as a quantitative standard. Granick et al. (1972) use similar microprocedure, but it differs
in the concentration of acid employed and the use of a ratio of maxima.
In Chisolm and Brown's (1975) variation, volumes of 20 m1 of whole blood were treated
with ethyl acetate/acetic acid (3:1) and briefly mixed. The acid extraction step was done
with 3N HCl, followed by a further dilution step with more acid if the value was beyond the
range of the calibration curve. In this procedure, protoporphyrin IX was used as the working
standard, with coproporphyrin used to monitor the calibration of the fluorometer and any
variance with the protoporphyrin standard.
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The above microf1uorometric methods all involve double extraction. In the single-
extraction variation of Orfanos et al. (1977), liquid samples of whole blood (40 pi) or blood
on filter paper were treated with acidified ethanol, the mixtures agitated and centrifuged,
and the supernatants analyzed directly in fluorometer cuvettes. For blood samples on filter
paper, blood was first leached from the paper with saline by soaking for 60 minutes. Copro-
porphyria was used as the quantitative standard. The correlation coefficient with the
Piomelli and Davidow (1972) procedure (see above) over the range 40-650 pg EP/dl RBCs was
r = 0.98.
Lamola et al. (1975) analyzed the zinc protophyrin as such in their procedure. Small
volumes of blood (20 pi) were worked up in a detergent (dimethyl dodecylamine oxide) and
phosphate buffer solution, and fluorescence measured at 594 nm with excitation at 424 nm. In
the variation of Joselow and Flores (1977), 10 pi of whole blood was diluted 1000-fold, along
with protoporphyrin (Zn) standards, with the detergent-buffer solution. It should be noted
that it is virtually impossible to obtain the ZPP standard in pure form, and Chisolm and Brown
(1979) reported the use of protoporphyrin IX plus very pure zinc salt for such standards.
Regardless of the extraction methods used, some instrumental parameters are of impor-
tance, including the variation between cut-offs in secondary emission filters and variation
among photomultiplier tubes in the red region of the spectrum. Hanna et al. (1976) compared
four micromethods for EP analysis: double extraction with ethyl acetate/acetic acid and HC1
(Piomelli and Davidow, 1972), single extraction with either ethanol or acetone (Chisolm et
al. , 1974), and direct solubilization with detergent (Lamola et al. , 1975). Of these, the
ethyl acetate and ethanol procedures were satisfactory; complete extraction occurred only with
the ethylacetate/acetic acid method. In the method of Chisholm et al. (1974), it appears that
the choice of acid and its concentration is more significant than the choice of organic
solvent.
The levels of precision with these wet micromethods appears to differ with the specifics
of analysis. Piomelli (1973) reported a coefficient of variation (C.V.) of 5 percent, com-
pared to Herber's (1980) observation of 2-4 percent for the methods per se and 6-11 percent
total C.V., which included precision of samples, standards, and day-to-day variation. The
Lamola et al. (1975) method for ZPP measurement was found to have a C.V. of 10 percent (same
day, presumably), whereas Herber (1980) reported a day-to-day C.V. of 9.3-44.6 percent.
Herber (1980) also found that the wet chemical micro method of Piomelli (1973) had a detection
limit of 20 pg EP/dl whole blood, while that of Lamola et al. (1975) was sensitive to 50 pg
EP/dl whole blood.
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The recent development of direct instrumental measurement of ZPP with the hematof1uoro-
meter has added a dimension to the use of EP measurement for field screening the lead exposure
of large groups of subjects. As originally developed by Bell Laboratories (Blumberg et al.,
1977) and now produced commercially, the apparatus employs front-face optics, in which exci-
tation of the fluorophore is at an acute angle to the sample surface, with emitted light
emerging from the same surface and thus being detected. Routine calibration requires a stable
fluorescing material with spectra comparable to ZPP; the triphenylmethane dye Rhodamine B is
used for this purpose. Absolute calibration requires adjusting the microprocessor-controlled
readout system to read the known concentration of ZPP in reference blood samples, the latter
calibration being performed as frequently as possible.
Hematof1uorometers are designed for the measurement of EP in samples containing oxyhemo-
globin, i.e., capillary blood. Venous blood, therefore, must first be oxygenated, usually by
moderate shaking for approximately 10 minutes (Blumberg et al. , 1977; Grandjean and Lintrup,
1978). A second problem with hematof1uorometer use, in contrast to wet chemical methods, is
interference by bilirubin (Karacic et al., 1980; Grandjean and Lintrup, 1978); this would oc-
cur with relatively low levels of EP. At levels normally encountered in lead workers or sub-
jects with anemia or nonoccupational lead exposure, the degree of such interference is not
considered significant (Grandjean and Lintrup, 1978). Karacic et al. (1980) have found that
carboxyhemoglobin (COHb) may pose a potential problem, but its relevance to EP levels of sub-
jects exposed to lead has not been fully elucidated. Background fluorescence in cover glass
may be a problem and should be tested in advance. Finally, the accuracy of the hematof1uoro-
meter appears to be affected by hemolyzed blood.
Competently employed, the hematof1uorometer appears to be reasonably precise but its ac-
curacy may still be biased (see below). Blumberg et al. (1977) reported a C.V. of 3 percent
over the entire range of ZPP values measured when using a prototype apparatus. Karacic et al.
(1980) found the relative standard deviation to vary from 1 percent (0.92 mM ZPP/M Hb) to 5
percent (0.41 mM ZPP/M Hb) depending on concentration. Grandjean and Lintrup (1978) obtained
a day-to-day C.V. of 5 percent using blood samples refrigerated for up to 9 weeks. Herber
(1980) obtained a total C.V. of 4.1-11.5 percent.
A number of investigators have compared EP measured by the hematof1uorometer with the
laboratory or wet chemical techniques, ranging from a single, intralaboratory comparison to
interlaboratory performance testing. The latter included the EP proficiency testing program
of the Centers for Disease Control. Working with prototype instrumentation, Blumberg et al.
(1977) obtained correlation coefficients of r = 0.98 (range: 50-800 pg EP/dl RBCs) and 0.99
(range: up to 1000 ng EP/dl RBCs) for comparisons with the Granick and Piomelli methods,
respectively. Grandjean and Lintrup (1978), Castoldi et al. (1979) and Karacic et al. (1980)
have achieved equally good correlation results.
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Several reports (Culbreth et al. , 1979; Scoble et al. , 1981; Smith et al. , 1980) have
described the application of high-performance liquid chromatography (HPLC) to the analysis of
either free or zinc protoporphyrin in whole blood. In one of the studies (Scoble et al.,
1981), the protoporphyrins as well as coproporphyrin and mesoporphyrin IX were reported to be
determined on-line f1uorometrically in less than 6 minutes using 0.1 ml of blood sample. The
HPLC approach remains to be tested in interlaboratory proficiency programs.
9.3.2 Interlaboratory Testinq of Accuracy and Precision in EP Measurement
— i, m i m ¦ i,
In a relatively early attempt to assess interlaboratory proficiency in EP measurement,
Jackson (1978) reported results of a survey of 65 facilities that analyzed 10 whole blood
samples by direct measurement with the hematofluorometer or by one of the wet chemical
methods. In this survey, the instrumental methods had a low bias compared to the extraction
techniques but tended to show better interlaboratory correlation.
At present, CDC's ongoing EP proficiency testing program constitutes the most comprehen-
sive assessment of laboratory performance (U.S. Centers for Disease Control, 1981). Every
month, three samples of whole blood prepared at the University of Wisconsin Laboratory of
Hygiene are forwarded to participants. Reference means are determined by a group of reference
laboratories with a target range of ±15 percent across the whole range of EP values. For
Fiscal Year 1981, of the 198 laboratories participating, 139 facilities were involved for the
entire year. Three of the 36 samples in the year were not included. Of the 139 year-long
participants, 93.5 percent had better than half of the samples within the target range, 84.2
percent performed satisfactorily with 70 percent or more of the samples within range, and 50.4
percent of all laboratories had 90 percent or more of the samples yielding the correct re-
sults. The participants as a whole showed greater proficiency than in the previous year. Of
the various methods currently used, the hematofluorometer direct measurement technique was
most heavily represented. For example, the January 1982 survey of the three major techniques
154 participants used the hematofluorometer, 30 used the Piomelli method, and 7 used the
Chisolm/Brown method.
The recent survey of Balamut et al. (1982) raises the troublesome observation that the
use of commercially available hematofluorometers may yield satisfactory proficiency results
but still be inaccurate when compared to the wet chemical method using freshly-drawn whole
blood. Two hematof1uorometers in wide use performed well in proficiency testing but showed an
approximately 30 percent negative bias with clinical samples analyzed by both instrument and
chemical microtechniques. This bias leads to false negatives when used in screening. It ap-
pears that periodic testing of split samples by both fluorometer and chemical means is neces-
sary to monitor, and correct for, instrument negative bias. The basis of the bias is much
more than can be explained by the difference between FEP and IIP.
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9.4 MEASUREMENT OF URINARY COPROPORPHYRIN
The elevation of urinary coproporphyrin (CP-U) with lead intoxication served as a useful
indicator of such intoxication in children and lead workers for many years. Although analysis
of CP-U has declined considerably in recent times with the development of other testing
methods, such as measurement of erythrocyte protoporphyrin, it still possesses the advantage
of showing active intoxication (Piomelli and Graziano, 1980).
The standard method of CP-U determination is the f1uorometric procedure described by
Schwartz et al. (1951). Urine samples are treated with acetate buffer and aqueous iodine, the
latter converting coproporphyrinogen to CP. The porphyrin is partitioned into ethyl acetate
and back-extracted (4 X) with 1.5N HC1. Coproporphyrin is employed as the quantitative stan-
dard. Working curves are linear below 5 (jg CP/1 urine.
In the absorption spectrometric technique of Haeger-Aronsen (1960), iodine is also used
to convert coproporphyrinogen to CP. The extractant is ethyl ether, from which the CP is re-
moved with 0.1N HC1. Absorption is read at three wavelengths, 380, 430, and the Soret maximum
at 402 nm; and quantification is carried out using an equation involving the three wave
lengths.
9.5 MEASUREMENT OF DELTA-AMINOLEVULINIC ACID DEHYDRASE ACTIVITY
Delta-aminolevulinic acid dehydrase (5-aminolevulinate hydrolase; porphobilinogen
synthetase; E.C. 4.2.1.24; ALA-D) is an allosteric sulfhydryl enzyme that mediates the con-
version of two units of 6-aminolevulinic acid to porphobilinogen, a precursor in the heme bio-
synthetic pathway to the porphyrins. Lead's inhibition of the activity of this enzyme is the
enzymological basis of ALA-D's diagnostic utility in assessing lead exposure using erythro-
cytes.
A number of sampling precautions are necessary when measuring this enzyme's activity.
ALA-D activity is modified by the presence of zinc as well as by lead. Consequently, blood
collection tubes that have high background zinc content, mainly in the rubber stoppers, must
be avoided completely or care' taken to avoid stopper contact with blood. Nackowski et al.
(1977) observed that the presence of zinc in blood collection tubes is a pervasive problem,
and it appears that plastic-cup tubes are the only practical means to avoid it. To guard
against zinc in the tube itself, it would appear prudent to determine the extent of zinc
leachability by blood and to use one tube lot, if possible. Heparin is the anticoagulant of
choice, as the lead binding agent, EDTA, or other chelants would affect the lead-enzyme inter-
action. The relative stability of the enzyme in blood makes rapid determinations of activity
necessary, preferably as soon after collection as possible. Even with refrigeration, analysis
of activity should be done within 24 hours (Berlin and Schaller, 1974). Furthermore, porpho-
bilinogen is light-labile, which requires that the assay be done under restricted light.
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Various procedures for ALA-D activity measurement are chemically based on measurement of
porphobilinogen generated from the substrate, 6-ALA porphobilinogen is condensed with p-di-
methylaminobenzaldehyde (Ehrlich's reagent) to yield a chromophore measured at 553 nm in a
spectrophotometer. In the European Standardized Method for ALA-D activity measurement (Berlin
and Schaller, 1974), developed with the collaboration of nine laboratories for use with blood
samples having relatively low lead content, triplicate blood samples (0.2 ml) are hemolyzed,
along with a blood blank, with water for 10 minutes at 37°C. Samples are then mixed with
6-ALA solution followed by a 60-minute incubation. The enzyme reaction is terminated by ad-
dition of a solution of mercury (II) in trichloroacetic acid, followed by centrifugation and
filtration. Filtrates are mixed with modified Ehrlich's reagent (p-dimethylaminobenzalehyde
in trichloroacetic/perchloric acid mixture) and allowed to react for 5 minutes, followed by
chromophore measurement in a spectrophotometer at 555 nm. Activity is quantified in terns of
pM 6-ALA/min-l erythrocytes. It should be noted that the amount of phosphate for Solution A
in Berlin & Schaller's report should be 1.78 g, not the 1.38 g stated. In a micro scale
variation, Granick et al. (1973) used only 5 |jl of blood and terminated the assay by tri-
chloroacetic acid.
In comparing various reports concerning the relationship between lead exposure and ALA-D
inhibition, attention should be paid to the units of activity measurement employed with the
different techniques. Berlin and Schaller's (1974) procedure expresses activity as pM
ALA/min/1 cells, while Tomokuni's (1974) method expresses activity as pM porphobi1inogen/hr/ml
cells. Similarly, when comparing the Bonsignore et al. (1965) procedure to that of Berlin and
Schaller (1974), a conversion factor of 3.8 is necessary when converting from Bonsignore to
European Standard Method units (Trevisan et al,, 1981).
Several factors have been shown to affect ALA-D activity. Rather than measuring enzyme
activity in blood once, Granick et al. (1973) measured activity before and after treatment
with dithiothreitol, an agent that reactivates the enzyme by complexing lead. The ratio of
activated to unactivated enzymes vs. blood lead levels accommodates inherent differences in
enzyme activity among individuals due to genetic factors and other;, reasons. Other agents for
such activation include zinc (Finelli et al., 1975) and zinc plus glutathione (Mitchell et
al., 1977). In the Mitchell et al. (1977) study, non-physiological levels of zinc were used.
Wigfield and Farant (1979) found that enzyme activity is related to assay pH; thus, reduced
activity from such a pH-activity relationship could be misinterpreted as lead inhibition.
These researchers find that pH shifts away from optimal, in terms of activity, as blood lead
content increases and the incubation step proceeds.
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9.6 MEASUREMENT OF DELTA-AMINOLEVULINIC ACID IN URINE AND OTHER MEDIA
Delta-aminolevulinic acid (6-ALA) levels increase with elevated lead exposure, due to the
inhibitory effect of lead on the activity of ALA dehydrase and/or the increase of ALA synthe-
tase activity by feedback derepression. The result is that this intermediate in heme bio-
synthesis rises in the body and eventually results in increased urinary excretion. The meas-
urement of this metabolite in urine provides an indication of the level of lead exposure.
The ALA content of urine samples is stable for approximately 2 weeks or more if urine
samples are acidified with tartaric or acetic acid and kept refrigerated. Values of ALA-U are
adjusted for urine density, if concentration is expressed in mg/1 or is measured per gram
creatinine. As noted in the case of urinary lead measurement, 24-hour collection is more de-
sirable than spot sampling.
Five manual and one automated procedure for urinary ALA measurement are most widely used.
Mauzerall and Granick (1956) and Davis and Andelman (1967) described the most involved proce-
dures, requiring the initial chromatographic separation of ALA. The approach of Grabecki et
al. (1967) omitted chromatographic isolation, whereas the automated variation of Lauwerys et
al. (1972) omitted prechromatography but included the use of an internal standard. Tomokuni
and Ogata (1972) omitted, chromatography but employed solvent extraction to isolate the pyr-
role intermediate.
Mauzerall and Granick (1956) condensed ALA with a p-dicarbonyl compound, acetylacetone,
at pH 4.6 to yield a pyrrole intermediate (Knorr condensation reaction), which was further re-
acted with p-dimethylaminobenzaldehy.de in perchloric/acetic acid. The' samples were then read
in a spectrophotometer at 553 nra 15 minutes after mixing. In this method, there is separation
of both porphobilinogen and ALA from urine by means of a dual column configuration of cation
and anion exchange resins. The latter retains the porphobilinogen and the former separates
ALA from urea. The detection limit is 3 (jmoles/1 urine. In the modification of this method
by Davis and Andelman (1967), disposable cation/anion resin cartridges were used, in a
sequential configuration, to expedite chromatographic separation and increase sample analysis
rate. Commercial (Bio-Rad) disposable columns based on this design are now available and
appear satisfactory.
In these two approaches (Mauzerall and Granick, 1956; Davis and Andelman, 1967), the pro-
blem of interference due to aminoacetone, a metabolite occurring in urine, is not taken into
account. However, Marver et al. (1966) used Dowex-1 in a chromatographic step subsequent to
the condensation reaction to form the pyrrole. This separates the ALA derivative from that of
the aminoacetone. Similarly, Schlenker et al. (1964) used an IRC column to retain amino-
acetone.
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Tomokuni and Ogata (1972) condensed ALA with ethylacetoacetate and extracted the re-
sulting pyrrole with ethyl acetate. The extract was then treated with Ehrlich's reagent and
the resulting chromophore measured spectrophotometrical ly. Lauwerys et al. (1972) developed
an automated ALA analysis method for lead worker screening, in which ALA was added in known
amount as an internal standard and the pre-chromatography avoided. They reported a high cor-
relation (r = 0.98, no range available) with the procedure of Mauzerall and Granick (1956).
Roels et al. (1974) compared the relative proficiency of four methods — those of
Mauzerall and Granick (1956), Davis and Andelman (1967), the Lauwerys et al. (1972) automated
version, and the Grabecki et al. (1967) method, which omits chromatographic separation and is
normally used with occupational screening. The chromatographic methods gave identical results
over the range of 0-60 mg ALA/1 urine, while the automated method showed a positive bias at <6
mg/1. The Grabecki et al. (1967) technique was the least satisfactory of the procedures com-
pared. Roels et al. (1974) also noted that commercial ion-exchange columns resulted in low
variability (<10 percent).
Del la-Fiorentina et al. (1979) combined the Tomokuni and Ogata (1972) extraction method
with a correction equation for urine density. Up to 25 mg ALA/1, the C.V. was £4 percent
along with a good correlation (r = 0.937) with the Davis and Andelman (1967) technique. While
there is a time saving in avoiding prechromatography, it is necessary to prepare a curve re-
lating urine density to a correction factor for quantitative measurement.
Although ALA analysis is normally done with urine as the indicator medium, Haeger-Aronsen
(1960) reported a similar colorimetric method for blood and MacGee et al. (1977) described a
gas-liquid chromatographic method for ALA in plasma as well as urine. Levels of ALA in plasma
are much lower than those in urine. In the latter method, ALA was isolated from plasma, re-
acted with acetyl-acetone, and partitioned into a solvent (trimethylphenylhydroxide), which
also served for pyrolytic methylation in the injection port of the gas-liquid chromatograph,
the methylated pyrrole being more amenable to chromatographic isolation than the more polar
precursor. For quantification, an internal standard, 6-amino-5-oxohexanoic acid, was used.
The sample requirement is 3 ml plasma. Measured levels ranged from 6.3 to 73.5 ng ALA/ml
plasma, and yielded values that were approximately 10-fold lower than the colorimetric techni-
ques (01Flaherty et al., 1980).
9.7 MEASUREMENT OF PYRIMIDINE-5'-NUCLEOTIDASE ACTIVITY
Erythrocyte pyrimidine-5'-nucleotidase (5'-ribonucleotide phosphohydrolase, E.C. 3.1.3.5,
Py5N) catalyzes the hydrolytic dephosphorylation of the pyrimidine nucleotides uridine mono-
phosphate (UMP) and cytidinemonophosphate (CMP) to uridine and cytidine (Paglia and Valentine,
1975). Enzyme inhibition by lead in humans and animals results in incomplete degradation of
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reticulocyte RNA fragments, accumulation of the nucleotides, and increased cell hemolysis
(Paglia et a 1. , 1975; Paglia and Valentine, 1975; Angle and Mclntire, 1978; George and Duncan,
1982). ¦ ¦
There are two methods for measurement of Py5N activity. One is quite laborious in terms
of time and manipulation, while the other is shorter but requires the use of radioisotopes and
radiometric measurement. In Paglia and Valentine's (1975) method, heparinized venous blood
was filtered through cotton or a commercial cellulose preparation to separate erythrocytes
from platelets and leukocytes. Cells were given multiple saline washings, packed lightly, and
subjected to freeze hemolysis. The hemolysates were dialyzed against a saline-Tris buffer
containing MgCl2 and EDTA to remove nucleotides and other phosphates. The assay system con-
sists of dialyzed hemolysate, MgC12, Tris buffer at pH 8.0, and either UMP or CMP; incubation
is for 2 hours at 37°C. Activity is terminated by treatment with 20 percent trichloroacetic
acid, followed by centrifugation. The supernatant inorganic phosphate, P., is measured by the
classic method of Fiske and Subbarow (1925), the phosphomolybdic acid complex being measured
spectrophotometrical ly at 660 nm. A unit of enzyme activity is expressed as pmol P./hr/g
hemoglobin. Hemolysates appear to be stable (90 percent) with refrigeration at 4°C for up to
6 days, provided that mercaptoethanol is added at the time of assay. Like the other method,
activity measurement requires the determination of hemoglobin.
In the simpler approach of Torrance et al. (1977), which can be feasibly applied to much
larger numbers of samples, erythrocytes were separated from leukocytes and platelets with a
1:1 mixture of microcrystal1ine and alphacellulose, followed by saline washing and hemolysis
with a solution of mercaptoethanol and EDTA. Hemolysates were incubated with a medium con-
taining purified 14C-CMP and MgC12 30 minutes at 37°C. The reaction was terminated by
sequential addition of barium hydroxide and zinc .sulfate solution. Proteins and unreacted'
nucleotide were precipitated, leaving the labeled cytidine in the supernatant. Aliquots were
measured for 14C activity in a liquid scintillation counter. Enzyme activity was expressed as
nM CMP/min/g hemoglobin. The blank activity was determined for each sample by carrying out
the precipitation step as soon as the hemolysate was mixed with the labeled CMP, i.e., t = 0.
This procedure shows a good correlation (r = 0.94; range: 135-189 enzyme units) with the
method of Paglia and Valentine (1975). The two methods express units of enzyme activity dif-
ferently, so that one must know which method is used when comparing enzyme activity.
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9.8 SUMMARY
The sine qua non of a complete understanding of a toxic agent's effects on an organism,
e.g., dose-effect relationships, is quantitative measurement of either that agent in some bio-
logical medium or a physiological parameter associated with exposure to the agent. Quantita-
tive analysis involves a number of discrete steps, all of which contribute to the overall
reliability of the final analytical result: sample collection and shipment, laboratory
handling, instrumental analysis, and criteria for internal and external quality control.
From a historical perspective, it is clear that the definition of "satisfactory analyt-
ical method" for lead has been steadily changing as new and more sophisticated equipment
becomes available and understanding of the hazards of pervasive contamination along the
analytical course increases. The best example of this is the use of the definitive method for
lead analysis, isotope-dilution mass spectrometry in tandem with "ultra-clean" facilities and
sampling methods, to demonstrate conclusively not only the true extent of anthropogenic input
of lead to the environment over the years but also the relative limitations of most of the
methods for lead measurement used today.
9.8.1 Determinations of Lead in Biological Media
The low levels of lead in biological media, even in the face of excessive exposure, and
the fact that sampling of such media must be done against a backdrop of pervasive lead contam-
. ination necessitates that samples be carefully collected and handled. Blood lead sampling is
»„• best done by venous puncture and collection into low-lead tubes after careful cleaning of the
.puncture site. The use of finger puncture^as an alternative method of sampling should be
avoided, if feasible, given the risk of contamination associated with the practice in indus-
trialized areas. While collection of blood on.to filter paper enjoyed some popularity in the
past, paper deposition of blood requires special correction for hematrocrit/hemoglobin level.
Urine sample collection requires the use of lead-free containers as well as addition of a
bacteriocide. If feasible, 24-hour sampling is preferred to spot collection. Deciduous teeth
vary in lead content both within and across type of dentition. Thus a specific tooth type
should be uniformly obtained for all study subjects and, if possible, more than a single
sample should be obtained from each subject.
Measurements of Lead in Blood. Many reports over the years have purported to offer
satisfactory analysis of lead in blood and other biological media, often with severe inherent
limitations on accuracy and precision, meager adherence to criteria for accuracy and pre-
cision, and a limited utility across a spectrum of analytical applications. Therefore, it is
only useful to discuss'"definitive" and, comparatively speaking, "reference" methods presently
used.
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In the case of lead in biological media, the definitive method is isotope-dilution mass
spectrometry (IDMS). The accuracy and unique precision of IDMS arise from the fact that all
manipulations are on a weight basis involving simple procedures, and measurements entail only
lead isotope ratios and not the absolute determinations of the isotopes involved, greatly re-
ducing instrumental corrections and errors. Reproducible results to a precision of one part
in 104_105 are routine with appropriately designed and competently operated instrumentation.
Although this methodology is still not recognized in many laboratories, it was the first
breakthrough, in tandem with "ultra-clean" procedures and facilities, to definitive methods
for indexing the progressive increase in lead contamination of the environment over the
centuries. Given the expense, required level of operator expertise, and time and effort
involved for measurements by IDMS, this methodology mainly serves for analyses that either
require extreme accuracy and precision, e.g., geochronometry, or for the establishment of
analytical reference material for general testing purposes or the validation of other
methodologies.
While the term "reference method" for lead in biological media cannot be rigorously ap-
plied to any procedures in popular use, the technique of atomic absorption spectrometry in its
various configurations or the electrochemical method, anodic stripping voltammetry, come
closest to meriting the designation. Other methods that are generally applied in metal anal-
yses are either limited in sensitivity or are not feasible for use on theoretical grounds for
lead analysis.
Atomic absorption spectrometry (AAS) as applied to analysis of whole blood generally in-
volves flame or flameless micromethods. One macromethod, the Hessel procedure, still enjoys
some popularity. Flame microanalysis, the Delves cup procedure, applied to blood lead appears
to have an operational sensitivity of about 10 pg Pb/dl blood and a relative precision of
approximately 5 percent in the range of blood lead seen in populations in industrialized
areas. The flameless, or electrothermal, method of AAS enhances sensitivity about 10-fold,
but precision can be more problematical because of chemical and spectral interferences.
The most widely used and sensitive electrochemical method for lead in blood is anodic
stripping voltammetry (ASV). For most accurate results, chemical wet ashing of samples must
be carried out, although this process is time-consuming and requires the use of lead-free
reagents. The use of metal exchange reagents has been employed in lieu of the ashing step to
liberate lead from binding sites, although this substitution is associated with less
precision. For the ashing method, relative precision is approximately 5 percent. In terms of
accuracy and sensitivity, it appears that there are problems at low levels, e.g., 5 pg/dl or
below, particularly if samples contain elevated cooper levels.
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Lead in Plasma. Since lead in whole blood is virtually all confined to the erythrocyte,
plasma levels are quite low and it appears that extreme care must be employed to reliably
measure plasma levels. The best method for such measurement is 1DMS, in tandem with ultra-
clean facility use. Atomic absorption spectrometry is satisfactory for comparative analyses
across a range of relatively high whole blood values.
Lead in Teeth. Lead measurement in teeth has involved either whole tooth sampling or
analysis of specific regions, such as primary or circumpulpal dentine. In either case, sam-
ples must be solublized after careful surface cleaning to remove contamination; solubilization
is usually accompanied by either wet ashing directly or ashing subsequent to a dry ashing
step.
Atomic absorption spectrometry and anodic stripping have been employed more frequently
for such determinations than any other method. With AAS, the high mineral content of teeth
argues for preliminary isolation of lead via chelation-extraction. The relative precision of
analysis for within-run measurement is around 5-7 percent, with the main determinant of vari-
ance in regional assay being the initial isolation step. One change from the usual methods
for such measurement is the i_n situ measurement of lead by X-ray fluorescence spectrometry in
children. Lead measured in this fashion allows observation of on-going lead accumulation,
rather than waiting for exfoliation.
Lead in Hair. Hair as an exposure indicator for lead offers the advantages of being non-
invasive and a medium of indefinite stability. However, there is still the crucial problem of
external surface contamination, which is such that it is still not possible to state that any
cleaning protocol reliably differentiates between external and internally deposited lead.
Studies that demonstrate a correlation between increasing hair lead and increasing sever-
ity of a measured effect probably support arguments for hair being an external indicator of
exposure. It is probably also the case, then, that such measurement, using cleaning protocols
that have not been independently validated, will overstate the relative accumulation of "in-
ternal" hair lead in terms of some endpoint and will also underestimate the relative sensiti-
vity of changes in internal lead content with exposure. One consequence of this would be, for
example, an apparent threshold for a given effect in terms of hair lead which is significantly
above the actual threshold. Because of these concerns, hair is best used with the simultan-
eous measurement of blood lead.
Lead in Urine. Analysis of lead in urine is complicated by the relatively low levels of
the element in this medium as well as the complex mixture of mineral elements present. Urine
lead levels are most useful and also somewhat easier to determine in cases of chelation mobil-
ization or chelation therapy, where levels are high enough to permit good precision and dilu-
tion of matrix interference.
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Samples are probably best analyzed by prior chemical wet ashing, using the usual mixture
of acids. Both anodic stripping voltammetry and atomic absorption spectrometry have been
applied to urine analysis, with the latter more routinely used and usually with a chelation/
extraction step.
Lead in Other Tissues. .Bone samples require cleaning procedures for removal of muscle
and connective tissue and chemical solubilization prior to analysis. Methods of analysis are
comparatively limited and it appears that flameless atomic absorption spectrometry is the
technique of choice.
Lead measurements in bone, i_n vivo, have been reported with lead workers, using X-ray
fluorescence analysis and a radioisotopic source for excitation. One problem with this
approach with moderate lead exposure is the detection limit, approximately 20 ppm. Soft organ
analysis poses a problem in terms of heterogeneity in lead distribution within an organ (e.g.,
brain and kidney. In such cases, regional sampling or homogenization must be carried out.
Both flame and flameless atomic absorption spectrometry appear to be satisfactory for soft
tissue analysis and are the most widely used.
Quality Assurance Procedures in Lead Analyses. In terms of available information, the
major focus in establishing quality control protocols for lead has involved whole blood meas-
urements. Translated into practice, quality control revolves around steps employed within the
laboratory, using a variety of internal checks, and the further reliance on external checks,
such as a formal continuing multi-laboratory proficiency testing program.
Within the laboratory, quality assurance protocols can be divided into start-up and rou-
tine procedures, the former involving establishment of detection limits, within-run and
between-run precision, analytical recovery, and comparison with some reference technique
within or outside the laboratory. The reference method is assumed to be accurate for the par-
ticular level of lead in some matrix at a particular point in time. Correlation with such a
method at a satisfactory level, however, may simply indicate that both methods are equally
inaccurate but performing with the same level of precision proficiency. More preferable is
the use of certified samples having lead at a level established by the definitive method.
For blood lead, the Centers for Disease Control periodically survey overall accuracy and
precision of methods used by reporting laboratories. In terms of overall accuracy and preci-
sion, one such survey found that anodic stripping voltammetry as well as the Delves cup and
extraction variations of atomic absorption spectrometry performedbetter than other proce-
dures. These results do not mean that a given laboratory cannot perforin better with a partic-
ular technique; rather, such data are of assistance for new facilities choosing among methods.
Of particular value to laboratories carrying out blood lead analysis are the external
quality assurance programs at both the state and federal levels. The most comprehensive
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proficiency testing program is that,carried, out by the Centers for Disease Control, USPHS.
This program actually consists of two subprograms, one directed at facilities involved in lead
poisoning prevention and screening (Cente,r ^or Environmental Health) and the other concerned
with laboratories seeking certification under the Clinical Laboratories Improvement Act of
1967 as well as under regulations of the Occupational Safety and Health Administration's
(OSHA) Laboratory Improvement Program Office. Overall, the proficiency testing programs have
served their purpose well, judging from the relative overall improvements in reporting
laboratories over the years of the programs' existence. In this regard, OSHA criteria for
laboratory certification require 8 of 9 samples be correctly analyzed for the previous
quarter. This level of required proficiency reflects the ability of a number of laboratories
to actually perform at this level.
9.8.2 Determination of Erythrocyte Porphyrin (Free Erythrocyte Protoporphyrin, Zinc
Protoporphyrin)
With lead exposure, there is an accumulation of erythrocyte protoporphyrin IX, owing to
impaired placement of divalent iron to form heme. Divalent zinc occupies the place of the na-
tive iron. Depending upon the method of analysis, either metal-free erythrocyte porphyrin or
zinc protoporphyrin (ZPP) is measured, the former arising from loss of zinc in the chemical
manipulation. Virtually all methods now in use for EP analysis exploit the ability of the
porphyrin to undergo intense fluorescence when excited by ultraviolet light. Such fluoro-
metric methods can be further classified as wet chemical micromethods or direct measuring
fluorometry using the hematofluorometer. Owing to the high sensitivity of such measurement,
relatively small blood samples are required, with liquid samples or blood collected on filter
paper.
The most common laboratory or wet chemical procedures now in use represent variations of
several common chemical procedures: 1) treatment of blood samples with a mixture of ethyl
acetate/acetic acid followed by a repartitioning into an inorganic acid medium, or 2) solu-
bilization of a blood sample directly into a detergent/buffer solution at a high dilution.
Quantification has been done using protoporphyrin, coproporphyrin, or zinc protoporphyrin IX
plus pure zinc ion. The levels of precision for these laboratory techniques vary somewhat
with the specifics of analysis. The Piomelli method has a coefficient of variation of 5
percent, while the direct ZPP method, using buffered detergent solution is higher and more
variable.
The recent development of the hematofluorometer has made it possible to carry out EP
measurements in high numbers, thereby making population screening feasible. Absolute calibra-
tion is necessary and requires periodic adjustment of the system using known concentrations of
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EP in reference blood samples. Since these units are designed for oxygenated blood, i.e.,
capillary blood, use of venous blood requires an oxygenation step, usually a moderate shaking
for several minutes. Measurement of low or moderate levels of EP can be affected by interfer-
ence with bilirubin. Competently employed, the hematofluorometer appears to be reasonably
precise, showing a total coefficient of variation of 4.11-11.5 percent. While the comparative
accuracy of the unit has been reported to be good relative to the reference wet chemical tech-
nique, a very recent study has shown that commercial units carry with them a significant nega-
tive bias, which may lead to false negatives in subjects having only moderate EP elevation.
Such a bias in accuracy has been difficult to detect in existing EP proficiency testing
programs. It appears that, by comparision to wet methods, the hematofluorometer should be
restricted to field use rather than becoming a substitute in the laboratory for chemical meas-
urement, and field use should involve periodic split-sample comparison testing with the wet
method.
9.8.3 Measurement of Urinary Coproporphyrin
Although EP measurement has largely supplanted the use of urinary coproporphyrin analysis
(CP-U) to monitor excessive lead exposure in humans, this measurement is still of value in
that it reflects active intoxication. The standard analysis is a fluoroinetric technique,
whereby urine samples are treated with buffer, and an oxidant (iodine) is added to generate CP
from its precursor. The CP-U is then partitioned into ethyl acetate and re-extracted with
dilute hydrochloric acid. The working curve is linear below 5 pg CP/dl urine.
Measurement of Delta-Aminolevulinic Acid Dehydrase Activity
Inhibition of the activity of the erythrocyte enzyme, delta-aminolevulinic acid dehydra-
tase (ALA-D), by lead is the basis for using such activity in screening for excessive lead
exposure. A number of sampling and sample handling precautions attend such analysis. Since
zinc (II) ion will offset the degree of activity inhibition by lead, blood collecting tubes
must have extremely low zinc content. This essentially rules out the use of rubber-stoppered
blood tubes. Enzyme stability is such that the activity measurement is best carried out
within 24 hours of blood collection. Porphobilinogen, the product of enzyme action, is light-
labile and requires the assay be done in restricted light. Various procedures for ALA-D meas-
urement are based on measurement of the level of'the chromophoric pyrrole (approximately
555 nm) formed by condensation of the porphobilinogen with p-dimethylaminobenzaldehyde.
In the European Standardized Method for ALA-D activity determination, blood samples are
hemolyzed with water, ALA solution added, followed by incubation at 37°C, and the reaction
terminated by a solution of mercury (II) in trichloroacetic acid. Filtrates are treated with
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modified Ehrlich's reagent (p-dimethylaminobenzaldehyde) in trichloroacetic/perchloroacetic
acid mixture. Activity is quantified in terms of micromoles ALA/min/liter erythrocytes.
One variation in the above procedure is the initial use of a thio
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In the older method, heparinized venous blood is filtered through cellulose to separate
erythrocytes from platelets and leukocytes. Cells are then freeze-fractured and the hemo-
lysates dialyzed to remove nucleotides and other phosphates. This dialysate is then incubated
in the presence of a nucleoside monophosphate and cofactors, the enzyme reaction being termi-
nated by treatment with- trichloroacetic acid. The inorganic phosphate isolated from added
substrate is measured colorimetrically as the phosphomolybdic acid complex.
In the radiometric assay, hemolysates obtained as before are incubated with pure 14C-CMP.
By addition of a barium hydroxide/zinc sulfate solution, proteins and unreacted nucleotide are
precipitated, leaving labeled cytidine in the supernatant. Aliquots are measured for 14C ac-
tivity in a liquid scintillation counter. This method shows a good correlation with the ear-
lier technique.
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9.9 REFERENCES
Ahlgren, L.; Haeger-Aronsen, B.; Mattson, S.; Schutz, A. (1980) In vivo determination of lead
in the skeleton after occupational exposure to lead. Br. J. Ind. Med. 37: 109-113.
Al-Naimi, T. ; Edmonds, M. I.; Fremlin, J. H. (1980) The distribution of lead in human teeth,
using charged particle activation analysis. Phys. Med. Biol. .25:-.719-726.
American Public Health Association, Committee on Clinical Procedures. (1955) Methods for
determining lead in air and biological materials. New York, NY: American Public Health
Associati on.
Angle, C. R. ; Mclntire, M. S. (1978) Low level lead and inhibition of erythrocyte pyrimidine
nucleotidase. Environ. Res. 17: 296-302.
Balamut, R.; Doran, 0. ; Giridhar, G. ; Mitchell, D.; Soule, S. (1982) Systematic error between
erythrocyte protoporphyrin in proficiency test samples and patients' samples as measured
with two hematofluorometers. Clin. Chem. (Winston Salem N.C.) 28: 2421-2422.
Barthel, W. F. ; Smrek, A. L. ; Angel, G. P.; Liddle, J. A.; Landrigan, P. J.; Gehlbach, S. H.;
Chisolm, J. J. (1973) Modified Delves cup atomic absorption determination of lead in
blood. J. Assoc. Off. Anal. Chem. 56: 1252-1256.
Berlin, A.; Schaller, K. H. (1974) European standardized method for the determination of
6-aminolevulinic acid dehydratase activity in blood. Z. Klin. Chem. Klin. Biochem. 12:
389-390.
Berlin, A.; Del Castilho, P.; Smeets, J. (1973) European intercomparison programmes. In:
Barth, D. ; Berlin, A.; Engel, R. ; Recht, P.; Smeets, J., eds. Environmental health
aspects of lead: proceedings, international symposium; October 1972; Amsterdam, The
Netherlands. Luxembourg: Commission of the European Communities, Centre for Information
and Documentation; pp. 1033-1046.
Berman, E. (1976) The challenge of getting the lead out. In: LaFleur, P. D. , ed. Accuracy in
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Science (Washington D.C.) 207: 1167-1176.
Shapiro, I. M. ; Dobkin, B. ; Tuncay, 0. C.; Needleman, H. L. (1973) Lead levels in dentine and
circumpulpal dentine of deciduous teeth of normal and lead poisoned children. Clin. Chim.
Acta 46: 119-123. .
Slavin, S. ; Peterson, G. E. ; Lindahl, P. C. (1975) Determination of heavy metals in meats by
atomic absorption spectrometry. At. Absorp. Newsl. 14: 57-59.
Smith, R. M. ; Doran, D. ; Mazur, M. ; Bush, B. (1980) High performance liquid chromatographic
determination of protoporphyrin and zinc protoporphyrin in blood. J. Chromatogr. 181:
319-327.
SRD13REF/E 9-45 7/1/83
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I
PRELIMINARY DRAFT
Speecke, A.; Hoste, J.; Versieck, J. (1976) Sampling of biological materials. In: LaFleur,
P. D. , ed. Accuracy in trace analysis: sampling, sample handling, analysis - volume 1.
Proceedings of the 7th materials research symposium; October 1974; Gaithersburg, MD.
Washington, DC: U.S. Department of Commerce, National Bureau of Standards; NBS special
publication no. 422; pp. 299-310.
Steenhout, A.; Pourtois, M. (1981) Lead accumulation in teeth as a function of age with dif-
ferent exposures. Br. J. Ind. Med. 38: 297-303.
Tomokuni, K. (1974) 6~aminolevulinic acid dehydratase test for lead exposure. Arch. Environ.
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Tomokuni, K. ; Ogata, M. (1972) Simple method for determination of urinary 6-aminolevulinic
acid as an index of lead exposure. Clin. Chem. (Winston Salem N.C.) 18: 1534-1536.
Torrance, J.; West, C. ; Beutler, E. (1977) A simple rapid radiometric assay for pyrimidine-
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Trevisan, A.; Buzzo, A,; Scarpa, F. M. (1981) Studio comparativo delie metodiche di deter-
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U.S. Occupational Safety and Health Administration. (1982) OSHA criteria for laboratory pro-
ficiency in blood lead analysis. Arch. Environ. Health 37: 58-60.
Unger, B. C. ; Green. V. A. (1977) Blood lead analysis—lead loss to storage containers. Clin.
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Wigfield, D. C. ; Farant, J-P. (1979) Factors influencing the pH-activity relationship of
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assay. J. Anal. Toxicol. 3: 161-168.
Wittmers, L. E. , Jr.; Alich, A.; Aufderheide, A..C. (1981) Lead in bone. 1: Direct analysis
for lead in milligram quantities of bone ash by graphite furnace atomic absorption
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SRD13REF/E 9-46 7/1/83
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6EPA
United States
Environmental Protection
Agency
Environmental Criteria and
Assessment Office
Research Triangle Park NC 27711
EPA-600/8-83-028A
October 1983
External Review Draft
Research and Development
Quality
Criteria for Lead
Volume I — IV
Review
Draft
(Do Not
Cite or Quote)
NOTICE
This document is a preliminary draft. It has not been formally
released by EPA and should not at this stage be construed to
represent Agency policy. It is being circulated for comment on its
technical accuracy and policy implications.
-------
)
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PRELIMINARY DRAFT
10. METABOLISM OF LEAD
10.1 INTRODUCTION
The absorption, distribution, retention, and excretion of lead in humans and animals as
well as the various factors that mediate the extent of toxicokinetic processes are discussed
in this chapter. While inorganic lead is the form of the element that has been most heavily
studied, organolead compounds are also emitted into the environment and, as they are quite
toxic, they are also included in the discussion. Since the preparation of the 1977 Air
Quality Criteria Document for Lead (U.S. Environmental Protection Agency, 1977), a number of
reports have appeared that have proved particularly helpful in both quantifying the various
processes to be discussed in this chapter and assessing the interactive impact of factors such
as nutritional status in determining internal exposure risk.
10.2 LEAD ABSORPTION IN HUMANS AND ANIMALS
The amounts of lead entering the bloodstream from various routes of absorption are deter-
mined not only by the levels of the element in the particular media, but also by the various
physical and chemical parameters that characterize lead. Furthermore, specific host factors,
such as age and nutritional status, are important, as is interindividual variability. Addi-
tionally, in order to assess absorption rates, it is necessary to know whether or not the sub-
ject is in "equilibrium" with respect to a given level of lead exposure.
10.2.1 Respiratory Absorption of Lead
The movement of lead from ambient air to the bloodstream is a two-part process: a frac-
tion of air lead is deposited in the respiratory tract and, of this deposited amount, some
fraction is subsequently absorbed directly into the bloodstream or otherwise cleared from the
respiratory tract. At present, enough data exist to make some quantitative statements about
both of these components of respiratory absorption of lead.
The 1977 Air Quality Criteria Document for Lead described the model of the International
Radiological Protection Commission (IRPC) for the deposition and removal of lead from the
lungs and the upper respiratory tract (International Radiological Protection Commission,
1966). Briefly, the model predicts that 35 percent of lead inhaled from ambient air is depos-
ited in the airways, with most of this going to the lung. The IRPC model predicts a total de-
position of 40-50 percent for particles with an aerodynamic diameter of 0.5 pm and indicates
that the absorption rate would vary, depending on the solubility of the particular form.
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10.2.1.1 Human Studies. Table 10-1 tabulates the various studies of human subjects that pro-
vide data on the deposition of inorganic lead in the respiratory tract. Studies of this type
have involved diverse methodology to characterize the inhaled particles in terms of both size
(and size ranges) and fractional distribution. ' The use of radioisotopic or stable lead iso-
topes to directly or indirectly measure lead deposition and uptake into the bloodstream has
been particularly helpful in quantifying these processes.
From the studies of Kehoe (1961a,b,c) and their update by Gross (1981) as well as data
from Chamberlain et al. (1978), Morrow et al. (1980), and Nozaki (1966), it appears that the
respiratory deposition of airborne lead as encountered in the general population is approx-
imately 30-50 percent, depending on particle size and.venti1ation rates. Ventilation rate is
particularly important with submicron particles, where Brownian diffusion governs deposition,
since a slower breathing rate enhances the frequency of collisions of particles w;th the alve-
olar wal 1.
Figure 10-1 ¦reproduces a composite figure of Chamberlain et al. (1978) that compares
data, both calculated and experimentally measured, on the relationship of percentage deposi-
tion to particle size. With increasing particle size, deposition rate decreases to a minimum
over the range where Brownian diffusion predominates, followed by an increase in deposition
with size (>0.5 pm MMAD) as impaction and sedimentation become the main deposition factors.
In contrast to the ambient air or chamber data tabulated in Table 10-1, higher deposition
rates in some occupational settings are associated with relatively large particles. However,
much of this deposition will be in the upper respiratory tract, with eventual moverrent to the
gastrointestinal tract by ciliary action and swallowing. Mehani et al. (1966) measured depo-
sition rates in battery workers and workers in marine scrap yards and observed total depositon
rates of 28-70 percent. Charrberlain and Heard (1981) calculated an absorption rate fcr parti-
cle sizes encountered in workplace air of appproximately 47 percent.
Systemic absorption of lead from the lower respiratory tract occurs directly, while much
of the absorption from the upper tract involves swallowing and some uptake in the gut. From
the radioactive isotope data of Chamberlain et al. (1978) and Morrow et al. (1980), and the
stable isotope studies of Rabinowitz et al. (1977), it can be concluded that lead deposited in
the lower respiratory tract is quantitatively absorbed.
Chamberlain et al. (1978) used 2
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TABLE 10-1. DEPOSITION OF LEAD IN THE HUMAN RESPIRATORY TRACT
Form
Particle
size
Exposure
Percent
deposi tion
Reference
Pb203 aerosols
from engine*
exhaust
0. 05 (jm medi an
count diameter
in 38 studies;
5 subjects
exposed to average
of 0.9 pm
Lead "fumes" 0.05-1.0 pm mean
made in indue- diameter
tion furnace
203Pb-labeled
Pb203 aerosol
Ambient air
lead near
motorway and
other urban
areas in U.K.
203Pb-labeled
Pb(0H)2 or
PbC12 aero-
sols
Lead in work-
place air;
battery
factory and
shipbreaking
operations
Mean densities
of 0.02,- 0.04,
0. 09 pm
Mainly 0.1 pm
Both forms at
0.25 pm MMA0
Not determined;
defined as fumes,
fine dust, or
coarse dust
Chamber studies; 10, 20,
or 150 pg/m3; 3 hr on
alternate days;
12 subjects
Mouthpiece/aerosol chamber;
10 mg/m3; adult subjects
Mouthpiece/aerosol chamber;
adult subjects
2-10 pg/m3; adult subjects
50 1 iters air; 0.2 pCi/
liter; adult subjects
3 adult groups:
23 pg/m3 - controls
86 pg/m3 - battery workers
180 pg/m3 - scrap yard
30-70% (mean: 48%)
for mainly
0.05 pm particles
42% 0.05 pm;
63% 1.0 pm
80% 0.02 pm;
45% 0.04 pm;
30% 0.09 pm
60%, fresh exhaust;
50% other urban
area
23%, chloride;
26%, hydroxide
47%, battery workers;
39%, shipyard and
controls
Kehoe, 1961a,b,c;
Gross, 1981
Nozaki, 1966
Chamberlain et al. ,
1978
Chamberlain et al. ,
1978
Morrow et al., 1980
Mehani, 1966
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PRELIMINARY DRAFT
Pb DATA (VT = 1000 cm3)
HEYDER 1975 (VT = 1000 cm3)
MITCHELL 1977
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PRELIMINARY DRAFT
Rabinowitz et al. (1977) administered 204Pb tracer to young adult volunteers and were
able to determine by isotope tracer as well as balance data that 14 pg of lead was absorbed by
these subjects daily at ambient air lead levels of 1-2 pg/m3. Assuming a daily ventilation
rate of 20 m3 a deposition rate of 50 percent of ambient air (Chamberlain et al., 1978), and a
mean air lead level of 1.5 pg/m3 (2.0 pg/m3 outside the study unit, 1.0 pg/m3 inside, as de-
termined by the authors), then 15 pg lead was available for absorption. Hence, better than 90
percent of deposited lead was absorbed daily.
Morrow et al. (1980) followed the systemic uptake of 203Pb-1abeled lead in 17 adult sub-
jects using either lead chloride or lead hydroxide aerosols with an average size of 0.25
(±0.1) pm MMAD. Half of the deposited fraction of either aerosol was absorbed in 14 hours or
less. The radiolabel data described above are consistent with the results of Hursh and Mercer
(1970), who studied the systemic uptake of 212Pb on a carrier aerosol.
Given the apparent invariance of absorption rate for deposited lead in the above studies
as a function of chemical form of the element (Chamberlain et al., 1978; Morrow et al., 1980),
it seems that inhaled lead lodging deep in the respiratory tract is absorbed equally, regard-
less of form. Supporting evidence for total human systemic uptake of lead comes from autopsy
tissue analysis for lead content. Barry (1975) found that lead was not accumulated in the
lungs o* lead workers. This may also be seen in the data of Gross et al. (1975) for non-occu-
pational ly exposed subjects.
All of'the available data for lead deposition and uptake from the respiratory tract in
humans have been obtained with adults, and quantitative comparisons with the same exposures in
children are not possible. Although children 2 years of age weigh one-sixth as much as an
adult, they inhale 40 percent as much air lead as adults (Barltrop, 1972). James (1978) has
also taken into account differences in airway dimensions in adults vs. children, and has es-
timated that, often controlling for weight, the 10-year-old child has a deposition rate 1.6-
to 2.7-fold higher than the adult.
10.2.1.2 Animal Studies. Experimental animal data for quantitative assessment of lead de-
position and absorption for the lung and upper respiratory tract are limited. The available
information does, however, support the finding that respired lead is extensively and rapidly
absorbed.
Morgan and Holmes (1978) exposed adult rats, by nose-only technique, to a 203Pb-1abeled
engine exhaust aerosol generated in the same manner as by Chamberlain et al. (1978) over a
period of 8 days. Exposure was at a level of 21.9-23.6 nCi label/liter chamber air. Ad-
justing for deposition on the animal pelt, 20-25 percent of the label was deposited in the
lungs. Deposited lead was extensively taken up in blood: 50 percent within 1 hour and, 98
percent within 7 days. The absorption rate kinetic profile was similar to that reported for
humans (Chamberlain et al., 1978).
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Boudene et al. (1977) exposed rats to 210Pb-1abeled aerosols at a level of 1 pg label/m3
and 10 pg/rn3, the majority of the particles being 0.1-0.5 pm in size. At 1 hour, 30 percent
of the label had left the lung; by 48 hours 90 percent was gone.
Bianco et al. (1974) used 2l2Pb aerosol (SO. 2 pm) inhaled briefly by dogs arid found a
clearance half-time from the lung of approximately 14 hours. Greenhalgh et al. (1979) found
that direct instillation of 203Pb-1abeled lead nitrate solution into the lungs of rats led to
an uptake of approximately 42 percent within 30 minutes, compared with an uptake rate of 15
percent within 15 minutes in the rabbit. These instillation data are consistert with the
report of Pott and Brockhaus (1971), who noted that intratracheal instillation of lead in
solution (as bromide) or suspension (as oxide) serially over 8 days resulted in systerric lead
levels in tissues indistinguishable from injected lead. Rendall et al. (1975) found that the
movement of lead into blood of baboons inhaling a lead oxide (Pb304) was more rapid and
resulted in higher levels when coarse (1.6 |jm mean diameter) rather than fine (0.8 pm mean
diameter) particles were used. This suggests that considerable fractions of both size parti-
cles were eventually lodged in the gut, where absorption of lead tends to be higher in baDcons
than in other animal species (Pounds et al., 1978). In addition, the larger particles appear
to move more rapidly to the gut.
10.2.2 Gastrointestinal Absorption of Lead
Gastrointestinal absorption of lead mainly involves uptake from food and beverages as
well as lead deposited in the upper respiratory tract and eventually swallowed. It a]so in-
cludes ingestion of non-focd material, primarily in children via normal mouthing activity and
pica. Two issues of concern with lead uptake from the gut a^e the comparative rates cf such
absorption in developing vs. adult organisms, including hLmans, and how the bioavailability cf
lead affects such uptake.
10.2.2.1 Human Studies. Based on the long-term metabolic studies with adult volunteers,
Kehoe (1961a,b,c) estimated that approximately 10 percent of dietary lead is absorbed from the
gut of humans. According to Gross (1981), there can be considerable variation of various
balance parameters among subjects. These studies did not take into account the contribution
of biliary clearance of lead into the gut, which would have affected measurements for both
t
absorption and total excretion. Chamberlain et al. (1978) also determined that the level of
endogenous fecal lead is approximately 50 percent of urinary lead values. Chamberlain et al.
(1978) have estimated that 15 percent of dietary lead is absorbed, if the amount of endogenous
fecal lead is taken into account.
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PRELIMINARY DRAFT
Following the Kehoe studies, a number of reports determined gastrointestinal (GI) absorp-
tion using both stable and radioisotopic labeling of dietary lead. Generally, these reports
support the observation that in the adult human there is limited absorption of lead when taken
with food. Harrison et al. (1969) determined a mean absorption rate of 14 percent for three
adult subjects ingesting 203Pb-labeled lead in diet, a figure in accord with the results of
Hursh and Suomela (1968). Chamberlain et al. (1978) studied the absorption of 203Pb in two
forms (as the chloride and as the sulfide) taken with food. The corresponding absorption
rates were 6 percent (sulfide) and 7 percent (chloride), taking into account endogenous fecal
excretion. Using adult subjects who ingested the stable isotope 204Pb in their diet,
Rabinowitz et al. (1974) reported an average gut absorption of 7.7 percent. In a later study,
Rabinowitz et al. (1980) measured an absorption rate of 10.3 percent.
A number of recent studies indicate that lead ingested under fasting conditions is absor-
bed to a much greater extent than when it is taken with or incorporated into food. For exam-
ple, Blake (1976) measured a mean absorption rate of 21 percent when 11 adult subjects in-
gested 203Pb-labeled lead chloride several hours after breakfast. Chamberlain et al. (1978)
found that lead uptake in six subjects fed 203Pb as the chloride was 45 percent after a fast-
ing period, compared to 6 percent with food. Heard and Chamberlain (1982) obtained a rate of
63.3 percent using a similar procedure with eight subjects. Rabinowitz et al. (1980) reported
an absorption rate of 35 percent in five subjects when 204Pb was ingested after 16 hours of
fasting. To the extent that lead in beverages is ingested between meals, these isotope
studies support the observations of Barltrop (1975) and Garbc" and Wei (1974) that beverage
lead is absorbed to a greater extent than is lead in food.
The relationship of lead bioavailability in the human gut to the chemical/biochemical
form of lead can be determined from available data, although interpretation is complicated by
the relatively small amounts given and the presence of various components of food already pre-
sent in the gut. Harrison et al. (1969) found no difference in lead absorption from the human
gut when lead isotope was given either as the chloride or incorporated into alginate. Cham-
berlain et al. (1978) found that labeled lead as the chloride or sulfide was absorbed to the
same extent when given with food, while the sulfide form was absorbed at a rate of 12 percent
compared with 45 percent for the chloride when given under fasting conditions. Rabinowitz et
al. (19S0) obtained similar absorption rates for the chloride, sulfide, or cysteine conplex
forms when administered with food or under fasting conditions. Heard and Chamberlain (1982)
found no difference in absorption rate when isotopic lead (203Pb) was given with unlabeled
liver and kidney or when the label was first incorporated into these organs.
Three studies have focused on the question of differences in gastrointestinal absorption
rates between adults and children. Alexander et al. (1973) carried out 11 balance studies
with 8 children, aged 3 months to 8 years. Intake averaged 10.6 |.ig Pb/kg body weight/day
NEW10A/A 10-7 7/1/83
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PRELIMINARY DRAFT
(range 5-17); the mean absorption rate determined from metabolic balance studies was 53 per-
cent. Ziegler et al. (1978) carried out a total of 89 metabolic balance studies with 12 nor-
mal infants aged 2 weeks to 2 years. Diets were closely controlled and lead content was
measured. Two discrete studies were carried out and in the first, 51 balance studies using 9
children furnished a mean absorption rate of 42.7 percent. In the second study, 6 children
were involved in 38 balance studies involving dietary lead intake at 3 levels. For all daily
intakes of 5 Pb/kg/day or higher, the mean absorption rate was 42 percent. At low levels
of lead intake data were variable, with some children apparently in negative balance, probably
due to the difficulty in controlling low lead intake.
In contrast to these studies, Barltrop and Strehlow (1978) found that with children hos-
pitalized as orthopedic or "social" admissions, the results were highly variable. A total of
104 balance studies were carried out in 29 children ranging in age from 3 weeks to 14 years.
Fifteen of the subjects were in net negative balance, with an average dietary absorption of
-40 percent and, when weighted by number of balance studies, -16 percent.
It is difficult to closely compare these data with those of Ziegler et al. (1978). Sub-
jects were inpatients, represented a much greater age range, and were not classified in terms
of mineral nutrition or weight change status. As an urban pediatric group, the children in
this study may have had higher prior lead exposure so that the "washout" phenomenon (Kehoe,
1961a,b,c; Gross, 1981) may have contributed to the highly variable results. The calculated
mean daily lead intake in the Barltrop and Strehlow group (6.5 pg/kg/day) was lower than those
for all but one study group described by Ziegler et al. (1978). In the latter study it ap-
pears that data for absorption became more variable as the daily lead intake was lowered.
Finally, in those children classified as orthopedic admissions, it is not clear that skeletal
trauma was without effect on lead equilibrium between bone and other body compartments.
As typified by the results of the NHANES II survey (Mahaffey et al. , 1979), children at
2-3 years of age show a small peak in blood lead during childhood. The question arises
whether this peak indicates"an intrinsic biological factor, such as increased absorption or
retention when compared with older children, or whether this age group is exposed to lead in
sone special way. Several studies are relevant to the question. Zielhuis et al. (1978) re-
ported data for blood lead levels in 48 hospitalized Dutch children ranging in age from 2
months to 6 years. Children up to 3 years old had a mean blood lead level of 11.9 pg/dl vs. a
level of 15.5 in children aged 4-6 years. A significant positive relationship between child
age and blood lead was calculated (r - 0.44, p <0.05). In the Danish survey by Nygaard et al.
(1977), a subset of 126 children representing various geographical areas and age groups
yielded the following blood lead values by mean age group: children (N = 8) with a mean age of
1.8 years had a mean blood lead of 4.3 pg/dl; those with a mean age of 3.7-3.9 had values
ranging from 5.6 to 8.3 (jg/dl children 4.6-4.8 years of age had a range of 9.2 to 10 pg/dl.
NEW10A/A 10-8 7/1/83
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PRELIMINARY DRAFT
These authors note that the youngest group was kept at a nursery whereas the older kindergar-
ten children had more interaction with the outside environment. Sartor and Rondia (1981) sur-
veyed two population groups in Belgium, one of which consisted of groups of children aged 1-4,
5-8, and 9-14 years. Children under the age of 1 had a mean blood lead of 10.7 pg/dl; the 1-4
and 5-8 age groups were comparable, 13.9 and 13.7 pg/dl respectively; and those 9-14 years old
had a blood lead of 17.2 pg/dl. In this study, all of the children were hospital patients.
While these European studies suggest that any significant restriction of children in terms of
environmental interaction, e.g., hospitalization or nurseries, is associated with an apparen-
tly different age-blood lead relationship than the U.S. NHANES II subjects, it remains to be
demonstrated that European children in the 2-3 year age group show a similar peak. The issue
merits further study.
The normal mouthing activity of young children, as well as the actual ingestion of non-
food items, i.e., pica, is a major concern in pediatric lead exposure, particularly in urban
areas with deteriorating housing stock and high automobile density and in non-urban areas
contiguous to lead production facilities. The magnitude of such potential exposures is dis-
cussed in Chapter 7, while an integrated assessment of impact on human intake appears in
Chapter 13. Such intake is intensified for children with pica and would include paint, dust
and dirt.
Drill et al. (1979), using data from Day et al. (1975) and Lepow et al. (1974), have at-
tempted to quantify the daily intake of soil/dust in young children from such mouthing acti-
vities as thumb sucking and finger licking. A total of 100 mg/day was obtained for children
2-3 years old, with the amount of lead in this ingested quantity varying considerably from
site to site. In the report, a gastrointestinal absorption rate of 30 percent was taken for
lead in soil and dust. Of relevance to this estimate of absorption rate in children are the
animal data discussed in the next section, which show that lead of variable chemical form in
soil or dust is as available for absorption as food lead. The i_n vitro studies relating lead
solubility .in street dusts With acidity clearly demonstrate that the acidity of the human
stomach is adequate to extensively solubilize lead assimilated from soil and dust. To the
extent that ingestion of such material by children occurs other than at mealtime, the fasting
factor in enhancing lead absorption from the human gastrointestinal tract (vides supra) must
also be considered. Hence, a factor of 30 percent for lead absorption from dusts and soils is
not an unreasonable value.
Paint chip ingestion by children with pica has been estimated in the NAS report on lead
poisoning in children to be considerable (National Academy of Sciences, 1976). In the case of
paint chips, Drill et al. (1979) estimated an absorption rate as.high as 17 percent.. This
value may be compared with the animal data in Section 10.2.2.2 which indicate that lead in old
paint films can undergo significant absorption in animals.
NEW10A/A 10-9 7/1/83
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PRELIMINARY DRAFT
10.2.2.2 Animal Studies. Lead absorption via the gut of various adult experimental animal
species appears to resemble that for the adult human, on the order of 1-15 percent in most
cases. Kostial and Kello (1979), Kostial et al. (1978), and Kostial et al. (1971) reported a
value of 1 percent or less in adult rats maintained on commercial rat chow. These studies
were carried out using radioisotopic tracers. Similarly, Barltrop and Meek (1975) reported an
absorption rate of 4 percent in control diets, while Aungst et al. (1981) found the value to
range froin 0.9 to 6.9 percent, depending on the level of lead given in the diet. In these rat
studies, lead was given with food. Quarterman and Morrison (1978) administered 203Pb label in
small amounts of food to adult rats and found an uptake rate of approximately 2 percent at 4
months of age. Pounds et al. (1978) obtained a value of 26.4 percent with four adult Rhesus
monkeys given 210Pb by gastric intubation. The higher rate, relative to the rat, may reflect
various states of fasting at time of intubation or differences in dietary composition (vide
infra), two factors that affect rates of absorption.
As seen above with human subjects, fasting appears to enhance the rate of lead uptake in
experimental animals. Garber and Wei (1974) found that fasting markedly enhanced gut uptake
of lead in rats. Forbes and Reina (1972) found that lead dosing by gastric intubation of rats
yielded an absorption rate of 16 percent, which is higher than other data for the rat. It is
likely that intubation was done when there was little food in the gut. The data of Pounds et
al. (1978), as described above, may also suggest a problem with giving lead by gastric intuba-
tion or with water as opposed to mixing it with food.
The bioavailabi1ity of lead in the gastrointestinal tract of experimental animals has
been the subject of a number of reports. The designs of these studies differed in accordance
with how "bioavailability" is defined by different investigators. In some cases, the dietary
matrix was kept constant, or nearly so, while the chemical or physical form of the lead was
varied. By contrast, other data described the effect of changes in bioavailability as the
basic diet matrix was changed. The latter case is complicated by the simultaneous operation
of lead-nutrient interactive relationships, which are described in Section 10.5.2 within this
chapter.
Allcroft (1950) observed comparable effects when calves were fed lead in the form of the
phosphate, oxide, or basic carbonate (PbC03-Pb(0H)2), or incorporated into wet or dry paint.
By contrast, lead sulfide "'in-the form of finely ground galena ore was less toxic. Criteria
for relative effect included kidney and blood lead levels and survival rate over time.
In the rat, Barltrop and Meek (1975) carried out a comparative absorption study using
lead in the form of the acetate as the reference substance. The carbonate and thai late were
absorbed to the greatest extent, while absorption of the sulfide, chromate, napthenate, and
octoate was 44i67 percent"*of the reference agent. Gage and Litchfield (1968, 1969) found
that lead napthenate and chromate can undergo considerable absorption from the rat gut when
NEW10A/A 10-10 7/1/83
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PRELIMINARY DRAFT
incorporated into dried paint films, although less than when given with other vehicles. Ku et
al. (1978) found that lead in the form of the acetate or as a phospholipid complex was equally
absorbed from the GI tract of both adult and young rats at a level of 300 pprr. Uptake was
assessed by weight change, tissue levels of lead, and urinary aminolevulinic acid levels.
In a study relevant to the problem of lead bioavailability in soils and dusts, particu-
larly in exposed children, Dacre and Ter Haar (1977) compared the effects of lead as acetate
with lead contained in roadside soil and in house paint soil, at a level of approximately 50
ppm, in commercial rat chow. Uptake of lead was indexed by weight change, tissue lead con-
tent, and inhibition of ALA-D activity. There was no significant difference in any of these
parameters across the three groups, suggesting that neither the geochemical matrix in the
soils or the various chemical forms—basic carbonate in paint soil, and the oxide, carbonate,
and basic carbonate in roadside soil--affect lead uptake.
These data are consistent with the behavior of lead in dusts upon acid extraction as re-
ported by Day et al. (1979), Harrison (1979), and Duggan and Williams (1977). In the Day et
al. study, street dust samples from England and New Zealand were extracted with hydrochloric
acid over the pH range of 0-5. At an acidity that may be equalled by gastric secretions,
i.e., pH of 1, approximately 90 percent of the dust lead was solubilized. Harrison (1979)
noted that at this same acidity, up to 77 percent of Lancaster, England, street dust lead was
soluble, while an average 60 percent solubility was seen in London dust sanples (Duggan and
Williams, 1977). Because gastric solubilization must occur for lead in these media to be ab-
sorbed, the above data are useful in determining relative risk.
Kostial and Kello (1979) compared the absorption of 203Pb from the gut of rats maintained
on commercial rat chow vs. rats fed such "human" diets as baby foods, porcine liver, bread,
and cow's milk. Absorption in the latter cases varied from 3 to 20 percent, conpared with
<1.0 percent with rat chow. This range of uptake for the non-chow diet compares closely with
that reported for human subjects (vide supra). Similarly, Jugo et al. (1975a) observed that
rats maintained on fruit .diets. had an absorption rate of 18-20 percent. It would appear,
then, that the generally observed lower absorption of lead in the adult rat vs. the adult
human is less reflective of a species "difference than of a dietary difference.
Barltrop and Meek (1979) studied the relationship of particle size of lead in two
forms—as the metal or as lead octoate or chromate in powdered paint-films--tc the amount of
gut absorption in the rat and found that there was an inverse relationship between uptake and
particle size for both forms.
A number of studies have documented that the developing animal absorbs a relatively
greater fraction of ingested lead than does the adult, thus supporting those studies that have
shown this age dependency in humans. For example, the adult rat absorbs approximately 1 per-
cent lead or less when contained in diet vs. a corresponding value 40-50 times greater in the
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PRELIMINARY DRAFT
rat pup (Kostial et al., 1971, 1978; Forbes and Reina, 1972). In the rat, this difference
persists through weaning (Forbes and Reina, 1972), at which point uptake resembles that of
adults. Part of this difference can be ascribed to the nature of the diet (mother's milk vs.
regular diet), although it should be noted that the extent of absorption enhancement with milk
vs. rat chow in the adult rat (Kello and Kostial, 1973) falls short of what is seen in the
neonate. An undeveloped, less selective intestinal barrier may also exist in the rat neonate.
In non-human primates, Munro et al. (1975) observed that infant monkeys absorbed 65-85 percent
via the gut vs. 4 percent in adults. Similarly, Pounds et al. (1978) noted that juvenile
Rhesus monkeys absorbed approximately 50 percent more lead than adults.
The question of the relationship of level of lead intake through the GI tract and rate of
lead absorption was addressed by Aungst et al. (1981), who exposed adult and suckling rats to
doses of lead by intubation over the range 1-100 mg Pb/kg or by variable concentrations in
drinking water.. With both age groups and both forms of oral exposure, lead absorption as a
percentage of dose decreased, suggesting a saturation phenomenon for lead transport across the
gut wal1.
10.2.3 Percutaneous Absorption of Lead
Absorption of inorganic lead compounds through the skin appears to be considerably less
significant than the respiratory and gastrointestinal routes of uptake. This is in contrast
to the observations for lead alkyls and other organic derivatives (U.S. Environmental
Protection Agency, 1977). Uptake of alkyl lead through the skin is discussed in Section 10.7.
Rastogi and Clausen (1976) found that cutaneous or subcutaneous administration of lead
napthenate in rat skin was associated with higher tissue levels and more severe toxic effects
than was the case for lead acetate. Laug and Kunze (1948) applied lead as the acetate, ortho-
arsenate, oleate, and ethyl lead to rat skin and determined that the greatest levels of kidney
lead were associated with the alkyl contact.
Moore et al. (1980) studied the percutaneous absorption of 203Pb-labeled lead acetate in
cosmetic preparations using eight adult volunteers. Applied in wet or dry forms, absorption
was indexed by blood, urine, and whole body counting. Absorption rates ranged from 0 to 0.3
percent, with the highest values obtained when the application sites were scratched. These
researchers estimated that the normal use of such preparations would result in an absorption
of approximately 0.06 percent.
10.2.4 Transplacental Transfer of Lead
Lead uptake by the human and animal fetus occurs readily, based on such indices as fetal
tissue lead measurements and, in the human, cord blood lead levels. Barltrop (1969) and
Horiuchi et al. (1959) demonstrated by fetal tissue analysis that placental transfer in the
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human occurs by the 12th week of gestation, with increasing fetal lead uptake throughout deve-
lopment. Highest levels occur in bone, kidney, and liver, followed by blood, brain, and
heart. Cord blood contains significant amounts of lead, generally correlating w,-th maternal
blood values and being slightly but significantly lower than mothers' in concentration
(Scanlon, 1971; Harris and Holley, 1972; Gershanik et al., 1974; Buchet et a 1 - , 1978;
Alexander and Delves, 1981; Rabinowitz and Needleman, 1982).
A cross-sectional study of maternal blood lead carried out by Alexander and Delves (1981)
showed that a significant decrease in maternal blood lead occurs throughout pregnancy, a de-
crease greater than the dilution efffect of the concurrent increase in plasma volume. Hence,
during pregnancy there is either an increasing deposition of lead in placental or fetal tissue
or an increased loss of body lead via other routes. Increasing absorption by the fetus during
gestation, as demonstrated by Barltrop (1969), suggests that the former explanation is a
likely one. Hunter (1978) found that summer-born children showed a trend to higher blood lead
than those born in the spring, suggesting increased fetal uptake in the summer due to in-
creases in circulating maternal lead. This observation was confirmed in the report of
Rabinowitz and Needleman (1982). Ryu et al. (1978) and Singh et al. (1978) both reported that
infants born to women having a history of lead exposure had significantly elevated blood lead
values at birt1-
.10.3 DISTRIBUTION OF LEAD IN HUMANS AND ANIMALS
A quantitative understanding of the sequence of changes in levels of lead in various body
pools and tissues is essential in interpreting measured levels of lead with respect to past
exposure as well as present and future risks of toxicity. This section discusses the dis-
tribution kinetics of lead in various portions of the b'ody~-blood, soft tissues, calcified
tissues, and the "chelatable" or toxicologically active body burden--as a function of such
parameters as exposure history and age.
A given quantity of lead taken up from the GI tract or the respiratory tract into the
bloodstream is initially distributed according to the rate of delivery by blood to the various
organs and systems. Lead is then redistributed to organs and systems in proportion to their
respective affinities for the element. With consistent exposure for an extended period, a
near steady-state of intercompartmental distribution is achieved.
Fluctuations in the near steady-state will occur whenever short-term lead exposures are
superimposed on a long-term uptake pattern. Furthermore, the steady-state description is im-
perfect because on a very short (hourly) time scale, intake is not constant. Lead intake with
meals and changes in ambient air lead--outside to inside and vice versa--will cause quick
changes in exposure levels which may be viewed as short-term alterations in the small, labile
NEW10A/A 10-13 7/1/83
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604c:
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PRELIMINARY DRAFT
lead pool. Metabolic stress could remobilize and redistribute body stores, although documen-
tation of the extent to which this happens is very limited (Chisolm and Harrison, 1956).
10.3.1 Lead in Blood
Viewed from different time scales, lead in whole blood may be seen as residing in seve-al
distinct, interconnected pools. More than 99 percent of blood lead is associated with the
erythrocytes (DeSilva, 1981; Everson and Patterson, 198Q.Manton and Cook, 1979) unaer typical
conditions, but it is the very small fraction, of lead transported in plasma and extracellular
fluid that provides lead to the various body organs (Bdloh, 1974).
Most of the erythrocyte lead is bound within the cell, although toxicity of the element
to the erythrocyte (Raghavan et al., 1981) is mainly associated with membrane lead content.
Within erythrocytes from non-exposed subjects, lead is primarily bound to hemoglobin, ir par-
ticular HbA2i which binds approximately 50 percent of cell lead although it comprises on^y 1-2
percent of total hemoglobin (Bruenger et al., 1973). A further 5 percent is bound to a
10,000-dalton molecular weight fraction, about 20 percent to a much heavier molecule, a^ti
about-25 percent is considered "free" or bound to lower weight molecules (Ong and Lee, 1980a;
Raghavan and Gonick, 1977). Raghavan et al. (1980) have observed that, among workers exposed
to lead, those who develop signs of toxicity at relatively ¦ low blood lead levels seem to have
a diminished binding of intracellular lead with the 10,000-da1 ton fraction, suggesting an im-
paired biosynthesis of a protective species. According to Ong and Lee (1980b), fetal hemo-
globin has a higher affinity for lead than adult- hemoglobin. Whole blood lead in daily equi-
librium with other compartments was found to have a mean life of 35 days (25-day half-life)
and a total content of 1.9 mg, based on studies with a small number of subjects (Rabinowitz et
al., 1976). Chamberlain et al. (1978) established a similar half-time for 203Pb in blood when
volunteers were given the label by ingestion, inhalation, or injection. The inhaled lead
studies in adults, described by Griffin et al,. (1975), permit calculation of half-tines of 28
and 26 days for inhalation of 10.4 and 3.1 pg Pb/m3 respectively.
Alterations in blood lead levels in response to abrupt changes in exposure apparently oc-
cur over somewhat different periods, depending on whether the direction of change is g-eater
or smaller. With increased lead intake, blood lead achieves a new value in approximately 60
days (Griffin et al., 1975; Tola et al., 1973), while a decrease may involve a longer period
of time, depending on the magnitude of the past higher exposure (O'Flaherty et al., 1982;
Rabinowitz et al. 1977; Gross, 1981). With age, there appears to be a modest increase in
blood lead, Awad et al. (1981) reporting an-increase of 1 pg for each 14 years of age. In the
latter case, particularly with occupational exposure, it appears that the time for re-estab-
lishing near steady-state is more dependent upon the extent of lead resorption from bone and
the total quantity deposited, extending the "washout".interval.
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PRELIMINARY DRAFT
Lead levels in newborn children are similar to but somewhat lower than those of their
mothers: B.3 vs. 10.4 pg/dl (Buchet et al. , 1978) and 11.0 vs. 12.4 pg/dl (Alexander and
Delves, 1981). Alexander and Delves (1981) also reported that maternal blood lead levels de-
crease throughout pregnancy, such decreases being greater than the expected dilution via the
concurrent increase in plasma volume. These data are consistent with increasing fetal uptake
during gestation (Barltrop, 1969). Increased tissue retention may also be a factor.
Levels of lead in blood are sex-related, adult women invariably showing lower levels than
adult males (e.g., Mahaffey et al., 1979). Of interest in this regard is the study of Stuik
(1974) showing lower blood lead response in women than in men for an equivalent level of lead
intake.
The small but biologically significant lead pool in blood plasma has proven technically
difficult to measure reliable values have become available only recently, and (see Chapter 9).
Chamberlain et al. (1978) found that injected 203Pb was removed from plasma (and, by infer-
ence, extracellular fluid) with a half-life of less than 1 hour. These data support the ob-
servation of DeSilva (1981) that lead is rapidly cleared from plasma. Ong and Lee (1980a), in
their i_n vitro studies, found that 203PB is virtually all bound to albumin ard that only trace
amounts are bound to high weight globulins. It is not possible to state which binding form
constitutes an "active" fraction for movement to tissues.
Although Rosen et al. (1974) reported that plasma lead was invariant across a range of
whole blood levels, the findings of Everson and Patterson (1980), DeSilva (1981), and
Cavalleri et al. (1978) indicate that there is an equilibrium between red cell and plasma,
such that levels in plasma rise with levels in whole blood. This is consistent with the data
of Clarkson and Kench (1958) who found that lead in the red cell is relatively lab-'le to ex-
change and a logical prerequisite for a dose-effect relationship in various organs. Ong anc
Lee (1980c), furthermore, found that plasma calcium is capable of displacing RBC menbrane
lead, suggesting that plasma calcium is a factor in the cell-plasma lead equilibrium.
10.3.2 Lead Levels in Tissues
Of necessity, various relationships of tissue lead to exposure and toxicity in humans
generally must be obtained from autopsy samples, although in some studies biopsy data have,
been described. There is, then, the inherent question of how such samples adequately repre-
sent lead behavior in the living population, particularly in cases where death was preceded by
prolonged illness or disease.states. Also, victims-of fatal accidents are not well character-
ized as to exposure status", and are usually described as having no "known" lead exposures.
Finally, these studies are necessarily cross-sectional in design, and in the case of body
accumulation of lead it is assumed that. different age groups have been similarly exposed.
Some important aspects of the avai1able-data include the distribution of lead between soft and
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PRELIMINARY DRAFT
calcifying tissue, the effect of age and development on lead content of soft and mineral tis-
sue, and the relationship between total and "active" lead burdens in the body.
10.3.2.1 Soft Tissues. In humans after age 20 most soft tissues do not show age-related
changes in lead levels, in contrast to the case with bone (Barry and Mossman, 1970; Barry,
1975, 1981; Schroeder and Tipton, 1968; Butt et al., 1964). Kidney cortex also shows in-
creases in lead with age that may be associated with formation of lead nuclear inclusion
bodies (Indraprasit et al., 1974). Based on these rates of accumulation, the total body bur-
den may be divided into pools that behave differently: the largest and kinetically slowest
pool is the skeleton, which accumulates lead with age; and the much more labile lead pool is
in soft tissue.
Soft tissue levels generally stabilize in early adult life and show a turnover rate
similar to blood, sufficient to prevent accumulation except in the renal cortex, which may be
reflecting formation of lead-containing nuclear inclusion bodies (Cramer et al., 1974;
Indraprasit et al., 1974). The data of Gross et al. (1975) and Barry (1975) indicate that
aortic levels appear to rise with age, although this may reflect entrapment of lead in athero-
sclerotic deposits. Biliary and pancreatic secretions, while presumably reflecting some of
the organ levels, have tracer lead concentrations distinct from either blood or bone pools
(Rabinowitz et al., 1973).
For levels of lead in soft tissue, the reports of Barry (1975, 1981), Gross et al. (1975)
and Horiuchi et al. (1959) indicate that soft tissue lead content generally is below 0.5 pg/g
wet weight, with higher values for aorta and kidney cortex. The higher values in aorta may or
may not reflect lead in plaque deposits, while higher kidney levels may be associated with the
presence of 1ead-accumulating tubular cell nuclear inclusions. The relatively constant lead
concentration "in lung tissue across age groups suggests no accumulation of respired lead and
is consistent with data for deposition and absorption (see Section 10.2.2). Brain tissue was
generally under 0.2 ppm wet weight and appeared to show no change with increasing age. Since
these data were collected by cross-sectional study, age-related changes in the low levels of
lead in brain would have been difficult to discern. Barry (1975) found that tissues in a
small group of samples from subjects with known or suspected occupational exposure showed
higher lead levels in aorta, liver, brain, skin, pancreas, and prostate.
Levels of lead in whole brain are less illuminating to the issue of sensitivity of cer-
tain regions within the organ to toxic effects of lead than is regional analysis. The distri-
bution of lead across brain regions has been reported from various laboratories and the
relevant data for humans and animals are set forth in Table 10-2. The data of Grandjean
(1978) and Niklowitz and Mandybur (1975) for human adults, and those of Okazaki et al. (1963)
for autopsy samples from young children who died of lead poisoning, are consistent in showing
that lead is selectively accumulated in the hippocampus. The correlation of lead level with
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TABLE 10-2. REGIONAL DISTRIBUTION OF LEAD IN HUMANS AND ANIMALS
Species
Humans
Exposure status
Relative distribution
Reference
CD
C
GO
A
Adult Males
Chi 1dren
Adults
Animals
Adult rats
Adult rats
Unexposed
Fatal lead poisoning
Child, 2 yrs? old Fatal lead poisoning
3 subjects unexposed;
1 subject with lead
poisoning as child
Unexposed
Unexposed
Hippocampus = amygdala > medulla
oblongata > half brain > optic
tract ~ corpus callosum. Pb
correlated with K.
Hippocampus > frontal cortex >>
occipital white matter, pons
Cortical gray matter > basal
gangli > cortical white matter
Hippocampus > cerebellum ~ temporal
lobes > frontal cortex in 3
unexposed subjects; temporal
lobes > frontal cortex >
hippocampus > cerebellum > in
case with prior exposure
Hippocampus > amygdala >> whole
brai n
Hippocampus had 50 percent of
brain lead with a 4:1 ratio
of hippocampus:whole brain
Grandjean, 1978
Okazaki et al., 1963
Klein et al., 1970
Niklowitz and
Mandybur, 1975
Danscher et al., 1975
Fjerdingstad et al.,
1974
TD
TO
TO
-<
O
TO
-------
Species
Exposure status
Neonatal rats
Young dogs
Controls and
daily i.p. injection
5.0 or 7.5 mg/kg
Contrpls and dietary
exposure, 100 ppm;
12 weeks of exposure
TABLE 10-2 (continued)
Relative distribution Reference
In both treated and control Klein and Koch, 1981
animals: cerebellum > cerebral
cortex > brainstem + hippocampus
Controls: cerebellum ~ medulla > Stowe et al., 1973
caudate > occipital gray > frontal
gray
Exposed: occipital gray > frontal
gray - caudate > occipital
white = thalamus > medulla > cerebellum
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PRELIMINARY DRAFT
potassium level suggests that uptake of lead is greater in cellulated areas. The involvement
of the cerebellum in lead encephalopathy in children (see Section 12.4) and in adult intoxica-
tion from occupational exposure indicates that the sensitivity of various brain regions to
lead as well as their relative uptake characteristics are factors in lead neuropathology.
In adult rats, selective uptake of lead is shown by the hippocampus (Fjerdingstad et a 1.,
1974; Danscher et al., 1975) and the amygdala (Danscher et al., 1975). By contrast, lead-
exposed neonate' rats show greatest uptake of lead into cerebellum, followed by cerebral cor-
tex, then brainstem plus hippocampus. Hence, there is a developmental difference in lead dis-
tribution in the rat with or without increased lead exposure (Klein and Koch, 1981).
In studies of young dogs, unexposed animals showed highest levels in the cerebellurr,
while lead exposure was associated with selective uptake into gray matter; cerebellar levels
were relatively low. Unlike the young rat, then, the distribution of lead in brain regions of
dogs appears to be dose-dependent (Stowe et al., 1973).
Barry (1975, 1981) compared lead levels in soft tissues of children vs. adults. Tissue
lead of infants' under 1 year old was generally lower than in older children, while children
aged 1-16 years had values that were comparable to adult women. In the Barry (1981) study,
the absolute concentration of lead in brain cortex or the ratios of brain cortex to blood lead
levels did not appear to be different in infants or older children compared to adults. Such
direct co.nparisons do not account for relative tissue mass changes with age, but this factor
is comparatively less with soft tissue than with the skeletal system (see Section 10.4).
Subcellular distribution of lead in soft tissue is not uniform,, with high amounts of lead
being sequestered in the mitochondria and nucleus. Cramer et al. (1974) studied renal biopsy
tissue in lead workers having exposures of variable duration and observed lead-binding nuclear
inclusion bodies in renal proximal tubules of subjects having short exposure, with all slowing
mitochondrial changes. A considerable body of animal data (see Section 10.3.5) docunents the
selective uptake of lead into these organelles. Pounds and Wright (1982) describe these
organellar pools in kinetic terms as haying half-lives of comparatively short duration in cul-
tured rat hepatocytes, while McLachlin $t al. (1980) found that rat kidney epithelial cells
form lead-sequestering nuclear inclusions within 24 hours.
10.3.2.2 Mi nerali zi ng Ti ssue. Biopsy and autopsy data have shown that lead becomes localized
and accumulates in human calcified tissues, i.e., bones and teeth. The accumulation begins
with fetal development (Barltrop, 1969; Horiuchi et al., 1959).
Total lead content in bone may exceed 200 mg in men aged 60 to 70 years, but in women the
accumulation is somewhat lower. Various investigators (Barry, 1975; Horiguchi and Utsonorriya,
1973; Schroeder and Tipton, 1968; Horiuchi et al., 1959) have documented that approximately 95
percent of total body lead is lodged in bone. These reports not only establish the affinity
of bone for lead, but also pro»ide evidence that lead increases in bone until 50-60 years, the
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PRELIMINARY DRAFT
later fall-off reflecting some combination of diet and mineral metabolism changes. Tracer
data show accumulation in both trabecular and compact bone (Rabinowitz et al., 1976).
In adults, bone lead is the most inert pool as well as the largest, and accumulation can
serve to maintain elevated blood lead levels years after past, particularly occupational, ex-
posure has ended. This accounts for the observation that duration of exposure correlates with
the rate of reduction of blood lead after termination of exposure (O'Flaherty et al., 1982).
The proportion of body lead lodged in bone is reported to be lower in children than in adults',
although concentrations of lead in bone increase more rapidly than in soft tissue during
childhood (Barry, 1975, 1981). In 23 children, bone, lead was 9 mg, or 73 percent of total
body burden vs. 94 percent in adults. Expression of lead in bone in terms of concentration
across age groups, however, does not accommodate the "dilution" factor, which is quite large
for the skeletal system in children (see Section 10.4).
The isotope kinetic data of Rabinowitz et al. (1976) and Holtzman (1978) indicate biolo-
gical half-times of lead in bone on the order of several decades, although it appears that
there are two bone compartments, ona of which is a repository for relatively labile lead
(Rabinowitz et al., 1977).
Tooth lead levels also increase with age at a rate proportional to exposure (Steenhout
and Pourtois, 1981), and are also roughly proportional to-blood lead levels in man (Winneke et
al., 1S81) and experimental animals (Kaplan et al., 1980). Dentine lead is perhaps the most
responsive component of teeth to lead exposure since it is laid down from the time of eruption
until the tooth is shed. Needleman and Shapiro (1974) have documented the utility of dentine
lead as an indicator of the degree of subject exposure. Fremlin and Edmonds (1980), using
alpha particle excitation and micro-autoradiography, have shown dentine zones of lead enrich-
ment related to abrupt changes in exposure. The rate of lead deposition in teeth appears to
vary with the type of tooth, being highest in the central incisors and lowest in the molars, a
difference that must be taken into account when using tooth lead data for exposure assessment,
particularly for low levels of lead exposure (Mackie et al., 1977; Delves et al., 1982).
10.3.3 Chelatable Lead
Mobile lead in organs and systems is potentially more "active" toxicologically in terms
of being available to sites of action. Hence, the presence of diffusible, mobilizable, or ex-
changeable lead may be a more significant predictor of imminent toxicity or recent exposure
than total body or whole blood burdens. In reality, however, these would be quite difficult
assays.
In this regard, "chelatable" urinary lead has been shown to provide an index of this
mobile portion of total body burden. Chelation challenge is now viewed as the most useful
probe of undue body burden in children and adults (U.S. Centers for Disease Control, 1978;
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PRELIMINARY DRAFT
World Health Organization, 1977; Chisolm and Barltrop, 1979; Chisolm et a 1., 1976; Saenger et
al., 1982; Hansen et a 1. , 1981), based mainly on the relationship of chelatable lead to in-
dices of heme biosynthesis impairment. In general, the amount of plumburesis associated with
chelant challenge is related to the dose and the schedule of administration.
A quantitative description of inputs to the fraction of body lead that is chelatable from
various body compartments is difficult to fully define, but it very likely includes a sizable,
fairly mobile compartment within bone as well as soft tissues this assertion is based on: 1)
the fact that the amount of lead mobilized by chelation is age dependent in non-exposed adults
(Araki, 1973; Araki and Ushio, 1982) while blood and soft tissue lead levels are not (Barry,
1975), indicating a lead pool labile to chelation but kinetically distinct from soft tissue;
2) the studies of chelatable lead in animals (Hammond, 1971, 1973) suggesting removal of some
bone lead fraction and the response of explanted fetal rat bone lead to chelants (Rosen and
Markowitz, 1980); 3) the tracer modeling estimates of Rabinowitz et al. (1977) which suggest a
mobile bone compartment; and 4) the complex, non-linear relationship of lead intake by air,
-food, and water (see Chapter 11) to blood lead, as well as the exponential relationship of
chelatable lead to blood lead (Chisolm et al., 1976).
The logarithmic relationship of chelatable lead to blood lead in children (Chisolm et
al., 1976) is consistent with the studies of Saenger et al. (1982), who reported that levels
of mobilizable lead in "asymptomatic" children with moderate elevations in blood lead were
quite similar in many cases to those values obtainednn children with signs of overt toxicity.
Hansen et al. (1981) reported that lead workers challenged with CaNa2EDTA showed 24-hour urine
lead levels that in many cases exceeded the accepted limit levels even though blood lead was
only moderately elevated in many of those workers. The action level corresponded, on the re-
gression curve, to a blood value of 35 (jg/dl.
Several reports provide insight into the behavior of labile lead pools in children
treated with chelating agents over varying periods of time. Treatment regimens using
CaNa2EDTA or CaNazEDTA + BAL for up to 5 days have been invariably associated with "rebound"
in blood lead, ascribed to a redistribution of lead among mobile lead compartments (Chisolm
and Barltrop, 1979). Marcus (1982) reported that 41 children given oral D-penici11 amine for 3
months showed a significant drop in blood lead by 2 weeks (mean initial value of 53.2 pg/dl)
then a slight rise that was within measurement error with a peak at 4 weeks, and a fall at 6
weeks, followed by no further change at a blood lead of 36 ^g/dl. Hence, there was a near
steady-state at an elevated level for 10 of the 12 weeks with continued treatment. This pb-
servation may indicate that re-exposure was occurring, with oral penicillamine and ingested
lead leading to increased lead uptake, as seen by Jugo et al. (1975a). However, Marcus
states that an effort was made to limit further lead intake as much as possible.. From these
reports, it appears that a re-equilibration does occur, varying in characteristics with type
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PRELIMINARY DRAFT
and duration of chelation. The rebound seen in short-term treatment with CaNa2EDTA or
CaNa2EDTA + BAL, although attributed to soft tissue, could well include a shift of lead from a
larger mobile bone compartment to soft tissues and blood. The apparent steady state between
the blood lead pool and other compartments that is achieved in the face of plumburesis, in-
duced by D-penicillamine (Marcus, 1982), suggests a rather sizable labile body pool which, in
quantitative terms, would appear to exceed that of soft tissue alone.
10.3.4 Mathematical Descriptions of Physiological Lead Kinetics
In order to account for observed kinetic data and make predictive statements, a variety
of mathematical models have been suggested, including those describing "steady state" condi-
tions. Tracer experiments have suggested compartmental models of lead turnover based on a
central blood pool (Holtzman, 1978; Rabinowitz et a 1. , 1976; Batschelet et al. , 1979). These
experiments have hypothesized well-mixed, interconnected pools and have utilized coupled dif-
ferential equations with linear exponential solutions to predict blood and tissue lead ex-
change rates. Were lead to be retained in these pools in accordance with a power-law distri-
bution of residence times, rather than being uniform, a semi-Markov model would be mere appro-
priate (Marcus, 1979).
Lead pools with more rapid turnover than whole blood (on the order of minutes) have been
detected within isolated cells (Pounds and Wright, 1982). Evidence of an extracellular lead
pool in hurr.ans exists in observations of lead plasma (DeSilva, 1981) and urine (Rabinowitz et
al., 1974) after oral lead exposure, as well as from 203Pb studies using injection, ingestion,
and inhalation exposure routes (Chamberlain and Heard, 1981). No single model has been deve-
loped to utilize what has been learned about lead behavior in these highly labile pools
existing around and within permanent and concentrated sites.
Extant steady-state models are also deficient, not only because they are based on small
numbers of subjects but also because there may be a dose dependency for some of the interpool
transfer coefficients. In this case, a non-linear dose-indicator response model would be more
appropriate when considering changes in blood lead levels. For example, the relationship
between blood lead and air lead (Hammond et al., 1981) as well as that for diet (United
Kingdom Central Directorate on Environmental Pollution, 1982) and tap drinking water (Sherlock
et al., 1982) are all non-linear in mathematical form. In addition, alterations in
nutritional status or the onset of metabolic stresses can complicate steady-state relation-
ships.
The above discussions of both the non-linear relationship of intake to the blood lead
pool and the non-1inear-relationship of chelatable, or toxicologically active, lead to blood
levels logically indicate that intake at elevated levels can add substantially to this
chelatable pool and be substantially unrecognized in blood lead measurements.
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10.3.5 Animal 5tudies
The relevant questions to be asked of animal data are those that cannot be readily or
fully satisfied in human subjects: (1) What is the effect of exposure level'on distribution
within the body at specific time points? (2) What is the relationship of age or developmental
stage on the distribution of lead in organs and systems, particularly the nervous system?
(3) What are the relationships of physiological stress and nutritional status to the redistri-
bution kinetics? (4) Can the relationship of chelatable lead to such indicator lead pools as
blood be defined better?
Administration of a single dose of lead to rats produces high initial lead concentrations
in soft tissues, which then fall rapidly as the result of excretion and transfer to bone
(Hammond, 1971), while the distribution of lead appears to be independent of the dose.
Castellino and Aloj (1964) reported that single dose exposure of rats to lead was associated
with a fairly constant ratio of red cell to plasma, a rapid distribution to tissues and rela-
tively higher uptake in liver, kidney, and particularly bone. Lead loss from organs and tis-
sues follow first-order kinetics except for bone. The data of Morgan et al. (1577),
Castellino and Aloj (1964), and Keller and Doherty (1980a) document that the skeletal system
in rats and mice is the kinetically rate-limiting step in whole-body lead clearance.
Subcellular distribution studies involving either tissue fractionation after i_n vivo lead
exposure or i_n vitro data document that lead is preferentially sequestered in the nucleus
(Castellino and Aloj, 1964; Goyer et al., 1970) and mitochondrial fractions (Castellino and
Aloj, 1964; Barltrop et al., 1974) of cells from lead-exposed animals. Lead enrichment in the
mitochondrion is consistent with the high sensitivity of this organelle to the toxic effects
of lead.
The neonatal animal seems to retain proportionately higher levels of tissue lead compared
with the adult (Goldstein et al., 1974; Momcilovic and Kostial, 1974; Mykkanen et al., 1979;
Klein and Koch, 1981) and shows slow decay of brain lead levels while other tissue levels sig-
nificantly decrease over time. This appears to be the result of enhanced entry by lead due to
a poorly developed brain barrier system in the developing animals, as well as enhanced body
retention in the young animals. The effects of such changes as metabolic stress and nutri-
tional status have been noted in the literature. Keller and Doherty (1980b) have documented
that tissue redistribution of lead, specifically bone lead mobilization, occurs in lactating
female mice, both lead and calcium transfer occurring from mother to pups. Changes in lead
movement from body compartments, particularly bone, with changes in nutrition are described in
Section 10.5.
In studies with rats that are relevant both to the issue.of chelatable lead vs. lead in-
dicators in humans and to the relative lability of lead in the young vs. the adult, Jugo et
al. (1975b) and Jugo (1980) studied the chelatabi1ity of lead in neonate vs. adult rats and
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its lability in the erythrocyte. Challenging young rats with metal chelants yielded propor-
tionately lower levels of urinary lead than in the adult, a finding that has been ascribed to
tighter binding of iead in" the young animal (Jugo et al., 1975b). In a related observation,
the chelatable fraction of lead bound to erythrocytes of young animals given 203Pb was approx-
imately 3-fold greater than in the adult rat (Jugo, 1980), although the fraction of dose in
the cells was higher in the suckling rat. The difference in the suckling rat erythrocyte re-
garding the binding of lead and relative content compared with the adult may be compared with
the Ong and Lee's (1980b) observation that human fetal hemoglobin binds lead more avidly than
does mature hemoglobin.
10.4 LEAD EXCRETION AND RETENTION IN HUMANS AND ANIMALS
Dietary lead in humans and animals that is not absorbed passes through the gastro-
instestinal tract and is eliminated with feces, as is that deposited fraction of air lead that
is swallowed and not absorbed. Lead absorbed into the blood stream and not retained is excre-
ted through the renal and gastrointestinal tracts, the latter by biliary clearance. The
amounts appearing in urine and feces appear to be a function of such factors as species, age,
and differences in dosing.
10.4.1 Human Studies
Booker et al. (1969) found that 212Pb injected into two adult volunteers led to initial
appearance of the label first in urine (4.4 percent of dose in 24 hours), then in both urine
and feces in approximately equal amounts. By use of the stable isotope 204Pb, Rabinowitz et
al. (1973) reported that urinary and fecal excretion of the label amounted to 38 and 8 pg/day
in adult subjects, accounting for 76 and 16 percent, respectively, of the measured recovery.
Fecal excretion was thus approximately twice that of all the remaining modes of excretion:
hair, sweat, and nails (8 percent).
Perhaps the most detailed study of lead excretion in adult humans was done by Chamberlain
et al. (1978), who used Z03Pb administered by injection, inhalation and ingestion. Following
injection or oral intake, the amounts in urine (Pb~U) and feces (Pb-Fe, endogenous fecal lead)
were compared for the two administration routes. Endogenous fecal lead was 50 percent of that
in urine, or a 2:1 ratio of urinary/fecal lead, after allowing for increased transit time of
fecal lead through the 61 tract. .
Based on the metabolic balance and isotope excretion data of Kehoe (1961a,b,c),
Rabinowitz et al. (1976), and Chamberlain et al. (1978), as well as some recalculations of the
Kehoe and Rabinow.itz data by Chamberlain et al. (1978), it appears that short-term lead excre-
tion amounts to 50-60 percent of the absorbed fraction, the balance moving primarily to bone
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TABLE 10-3. COMPARATIVE EXCRETION AND RETENTION
RATES IN ADULTS AND INFANTS
Chi 1 dren'3
Adul t
group A
Adult .
~ d
group B
Dietary intake (|jg/kg)
10.76
3.63
3.86
p
Fraction absorbed
0.46 (0.55)f
0.159
0.159
Diet lead absorbed (pg/kg)
4.95 (5.92)
0.54
0.58
Air lead absorbed (pg/kg)
0.20
0.21
0.11
Total absorbed lead (pg/kg
5.15 (6.12)
0.75
0.60
Daily urinary Pb (pg/kg)
1.00
0.47
0.34
Ratio: urinary/absorbed Pb
0.19 (0.16)
0.62
0.50
Endogenous fecal Pb.
0.5 (1.56)h
0.241
¦0.171
Total excreted Pb
1.50 (2.56)
0.71
0.51
Ratio: total excreted/
absorbed Pb
0.29 (0.42)
0.92
0.75
Fraction of intake retained
0.34 (0.33)
0.01
0.04
.pg/kg-day.
Ziegler et al., 1978.
^Rabinowitz et al., 1977. . „
Thompson, 1971, and estimates of Chamberlain et al., 1978'. "
^Corrected for endogenous fecal Pb; Pb-Fe = 0.5 x Pb-U.
Corrected for endogenous fecal Pb at extrapolated value from
Ziegler et al., 1978.
^Corrected for Pb-Fe.
•Extrapolated value for endogenous fecal Pb of 1.56.
Vor a ratio of 0.5, Pb-Fe/Pb-U. . -
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with some subsequent fraction, (approximately half) of this stored amount eventually being
excreted. The rapidly excreted fraction was determined by Chamberlain et al. (1978) to have
an excretion half-time of about 19 days. This is consistent with the estimates of Rabinowitz
et al. (1976), who expressed clearance in terms of mean-times. Mean-times are multiplied by
In 2 (0.693) to arrive at half-times. The similarity of blood 203Pb half-times with that of
body excretion noted by Chamberlain et al. (1978) indicates a steady rate of clearance from
the body.
The age dependency of lead excretion rates in humans, has not been well studied, for all
of the above lead excretion data involved only adults. Table 10-3 combines available data
from adults and infants for purposes of comparison. Intake, urine, fecal, and endogenous
fecal lead data from two studies involving adults and one, report with infants are used. For
consistency in the adult data, 70 kg is used as an average adult weight, and a Pb-Fe/Pb-U
value of 0.5 used. Lead intake, absorption, and excretion are expressed as pg Pb/kg/day. For
the Ziegler et al. (1978) data with infants, endogenous fecal lead excretion is calculated
using the adult ratio as well as the extrapolated value of 1.5 pg Pb/kg/day. The respiratory
intake value for the infants is an upper value (0.2 pg Pb/m3), since Ziegler et al. found air
lead to be <0.2 pg/m3. In comparison with the two representative adult groups, infants appear
to have a lower total excretion rate, although the excretion of endogenous fecal lead may be
higher than for adults.
Lead is accumulated in the human body with age, mainly in bone, up to approximately 60
years of age, when a decrease occurs with changes in intake as well as in bone mineral
metabolism. Total accumulation by 60 years of age ranges up to approximately 200 mg (see
review by Barry, 1978), although occupational exposure can raise this figure several-fold
(Barry, 1975). Holtzman (1978) has reviewed the available literature on studies of lead
retention in bone. In normally exposed humans a biological half-time of approximately 17
years has been calculated, while data for uranium miners yield a range of 1320-7000 days (4-19
years). Chamberlain et al.,(1978) have estimated life-time averaged daily retention at 9.5 pg
using data of Barry (1975). Within shorter time frames, however, retention can vary con-
siderably due to such factors as disruption of the individual's equilibrium with lead intake
at a given level of exposure, the differences between children and adults, and, in elderly
subjects, the presence of osteoporosis (Gross and Pfitzer, 1974).
Lead labeling experiments, such as those of Chamberlain et al. (1978), indicate a short-
term or initial retention of approximately 40-50 percent of the fraction absorbed, much of
which is by bone. It is difficult to determine how much lead resorption from bone will even-
tually occur using labeled lead, given the extremely small fraction of labeled to unlabeled
lead (i.e.r label dilution) that would exist. Based on the estimates of Kehoe (1961a,b,c),
the Gross (1981) evaluation of the Kehoe studies, the Rabinowitz et al. (1976) study, the
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Chamberlain et al. (1978) assessments of the aforementioned reports, and the data of Thompson
(1971), approximately 25 percent of the lead absorbed daily undergoes long-term bone storage.
The above estimates relate either to adults or to long-term retention over most of an
individual's lifetime. Studies with children and developing animals (see Section 10.4.2)
indicate lead retention in childhood can be higher than in adults. By means of metabolic
balance studies, Ziegler et al. (1978) obtained a retention figure (as percentage of total
intake) of 31.5 percent for infants, while of Alexander et al. (1973) provided an estimate of
18 percent. Corrected retention data for both total and absorbed intake for the pediatric
subjects of Ziegler et al. (1978) are shown in Table 10.3, using the two values for endogenous
fecal excretion as noted. Barltrop and Strehlow (1978) calculated a net negative lead reten-
tion in their subjects, but problems in comparing this report with the others were noted
above. Given the increased retention of lead in children relative to adults, as well as the
greater rate of lead intake on a body weight basis, increased uptake in soft tissues and/or
bone is indicated.
Barry (1975, 1981) measured the lead content of soft and mineral tissue in a small group
of autopsy samples from children 16 years of age and under, and noted that average soft tissue
values were comparable to those in female adults, while mean bone lead values were lower than
in adults. This suggests that bone in children has less retention capacity for lead than
adults. It should be noted, however, that "dilution" of bone lead will occur because of the
significant growth rate of the skeletal system through childhood. Trotter and Hixon (1974)
¦ studied changes in skeletal mass, density, and mineral content as a function of age, and noted
that skeletal mass increases exponentially in children until the early teens, increases less
v up to the early 20s, levels off in adulthood, and then slowly decreases. From infancy to the
late teens, bone rrass increases up to 40-fold. Barry (1975) noted an approximate doubling in
bone lead concentration over this interval, indicating that total skeletal lead had actually
increased 80-fold, and obtained a mean total bone lead content up to 16 years of approximately
8 mg, compared with a value of approximately 18 mg estimated from both the bone concentrations
in his study at different ages and the bone growth data of Trott'er!and Hixon (1974). In a
later study (Barry, 1981), autopsy samples from infants and children between 1 and 9 years old
showed an approximate 3.5-fold increase in mean bone concentrations across the three bone
types studied, compared with a skeletal mass increase from 0-6 mos. to 3-13 years old of
greater than 10-fold, for an estimated increase in total lead of approximately 35-fold. Five
reports (see Barry, 1981) noted age vs. tissue lead relationships indicating that overall bone
lead levels in infants and children were less than in adults, whereas while 4 reports observed
comparable levels in children and adults.
If one estimates total daily retention of lead in the infants studied by Ziegler et al.
(1978), using a mean body weight of approximately 10 kg and the corrected retention rate in
Table 10.3, one obtains a total daily retention of approximately 40 pg Pb. By contrast, the
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total reported or estimated skeletal lead accumulated between 2 and 14 years is 8-18 mg (vi de
supra), which averages out to a daily long-term retention of 2.0-4.5 pg/day or 6-13 percent of
total retention. It may be the case that lead retention is highest in infants up to about 2
years of age (the subjects of the Ziegler et al. study), then decreases in older children.
The mean retention in the Alexander et al. (1973) study was 18 percent, about half that seen
by Ziegler et al. (1978). This difference is possibly due to the greater age range in the
former study.
"Normal" blood lead levels in children either parallel adult males or are approximately
30 percent greater than adult females (Chamberlain et al., 1978), indicating (1) that the soft
tissue lead pool in very young children is not greatly elevated and thus, (2) that there is a
huge labile lead pool in bone which is still kinetically quite distinct from soft tissue lead
or (3) that in young children, blood lead is a much less reliable indicator of greatly ele-
vated soft tissue or labile bone lead than is the case with adults. Barry (1981) found that
soft tissue lead levels were comparable in infants SI year old and children 1-5 and 6-9 years
old.
Given the implications of the above discussion, that retention of lead in the young child
is higher than in adults and possibly older children, while at the same time their skeletal
system is less effective for long-term lead sequestration, the very young child is at greatly
elevated risk to a toxicologically "active" lead burden. For a more detailed discussion, see
Chapter 13.
10.4.2 Animal Studies
In rats and other experimental animals, both urinary and fecal excretion appear to be
important routes of lead removal from the organism; the relative partitioning between the two
modes is species and dose dependent. Morgan et al. (1977), injected 203Pb into adult rats and
noted that lead initially appeared in urine, followed by equivalent elimination by both
routes; by 5 days, lead was proportionately higher in feces. Castellino and Aloj (1964),
using 210Pb, observed that fecal excretion was approximately twice that of urine (35.7 vs.
15.9 percent) by 14 days. In the report of Klaassen and Shoeman (1974), relative excretion by
the two routes was seen to be dose-dependent up to 1.0 mg/kg, being much higher by biliary
clearance into the gut. At 3.0 mg/kg, approximately 90 percent of the excreted amount was
detected in feces. The relatively higher proportion appearing in feces in the studies of
Castellino and Aloj (1964) and Klaassen and Shoeman (1974), compared with the results of
Morgan et al. (1977), is possibly due to the use of carrier dosing, since Morgan et al. (1977)
used carrier-free injections. Hence, it appears that increasing dose does favor biliary excre-
tion, as noted by Klaassen and Shoeman (1974).
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With regard to species differences, Klaassen and Shoeman (1974) found that the amount of
biliary clearance in dogs was about 2 percent of that in rats, while rabbits showed 50 percent
of the rate of the rat at equivalent dosing. These data for the dog are in contrast to the
results of Lloyd et al. (1975), who observed 75 percent of the excreted lead eliminated
through biliary clearance. It should be noted that the latter researchers used carrier-free
label while the other investigators used injections with carrier at 3.0 mg Pb/kg levels. In
mice, Keller and Doherty (1980a) observed that the cumulative excretion rate of 210Pb in urine
was 25-50 percent of that in feces. In nonhuman primates, Cohen (1970) observed that baboons
excreted lead at the rate of 40 percent in feces and 60 percent in urine. Pounds et al.
(1978) noted that the Rhesus monkey lost 30 percent of lead by renal excretion and 70 percent
in feces. This may also be reflecting a carrier dosing difference.
The extent of total lead excretion in experimental animals given labeled lead orally or
parenterally varies, in part due to the time frames for post-exposure observation. In the
adult rat, Morgan et al. (1977) found that 62 percent of injected 203Pb was excreted by 6
days. By 8 days, 66 percent of injected 203Pb was eliminated in the adult rats studied by
Momcilovic and Kostial (1974), while the 210Pb excretion data of Castellino and Aloj (1964)
for the adult rat showed 52 percent excreted by 14 days. Similar data were obtained by
Klaassen and Shoeman (1974). Lloyd et al. (1975) found that dogs excreted 52 percent of
injected lead label by 21 days, 83 percent by 1 year, and 87 percent by 2 years. In adult
mice (Keller and Doherty, 1980a), 62 percent of injected lead label was eliminated by 50 days.
In the nonhuman primate, Pounds et al. (1978) measured approximately 18 percent excretion in
adult Rhesus monkeys by 4 days.
Kinetic studies of lead elimination in experimental animals indicate that excretion is
described by two or more components. From the elimination data of Momcilovic and Kostial
(1974), Morgan et al. (1977) estimated that in the rat the excretion curve obeys a two-compo-
nent exponential expression with half-times of 21 and 280 hours. In dogs, Lloyd et al. (1975)
found that excretion could be described by three components, i.e., a sum of exponentials with
half-times of 12 days, 184 days, and 4951 days. Keller and Doherty (1980a) reported that the
half-time of whole-body clearance of injected 203Pb consisted of an initial rapid and a much
slower terminal component, the latter having a half-time of 110 days in the adult mouse.
The excretion rate dependency on dose level has been investigated in several studies.
Although Castellino and Aloj (1964) saw no difference in total excretion rate when label was
injected with 7 or 100 pg of carrier, Klaassen and Shoeman (1974) did observe that the excre-
tion rate by biliary tract was dose dependent at 0.1, 1.0, and 3.0 mg Pb/kg (urine values were
not provided for obtaining estimates of total excretion). Momcilovic and Kostial (1974) saw
increased rate of excretion into urine over the added carrier range of 0.1 to 2.0 |.ig Pb with
no change in fecal excretion. In the report of Aungst et al. (1981) there was no change in
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PRELIMINARY DRAFT;*..
excretion rate in the rat over the injected lead dosing range of 1.0 to 15.0 mg/kg. It thus
appears that rat urinary excretion rates are dose-dependent over a narrow range less than <7
(jg, while elimination of lead through biliary clearance is dose-dependent up to an exposure
level pf 3 mg Pb/kg.
Lead movement from lactating animals to their offspring via milk constitutes both a route
of excretion for the mother and a route of exposure to lead for the young. Investigations
%
directed at this phenomenon have examined both prior-plus-ongoing maternal lead exposure
during lactation and the effects of immediate prior treatment. Keller and Doherty (1980b)
exposed two groups of female rats to 210Pb-labeled lead: one group for 105 days before mat-
ing; the second before and during gestation and nursing. During lactation, there was an over-
all loss of lead from the bodies of the lactating females compared with controls while the
fenur ash weights were inversely related to level of lead excretion, indicating that such
enhancement is related to bone mineral metabolism. Lead transfer via milk was approximately
3 percent of maternal body burden, increasing with continued lead exposure during lactation.
Lorenzo et al. (1977) found that blood lead in nursing rabbits given injected lead peaks
rather rapidly (within 1 hour), while milk lead shows a continuous increase for about 8 days,
at which point its concentration of lead is 8-fold higher than blood. This indicates that
lead transfer to milk can occur against a concentration gradient in blood. Momcilovic* (1978)
and Kostial and Momcilovic (1974) observed that transfer of 203Pb in the late stage of lacta-
tion occurs readily in the rat, with higher overall excretion of lead in nursing vs. control
females. Furthermore, it appeared that the rate of lead movement to milk was dose-dependent
over the added lead carrier range of 0.2-2.0 (jg Pb.
The comparative retention of lead in developing vs. adult animals has been investigated
in several studies using rats, mice, and nonhuman primates. Momcilovic and Kostial (1974)
compared the kinetics of lead distribution- in suckling vs. adult rats after injection of
203Pb. Over an 8-day interval, 85 percent of the label was retained in the suckling rat,
compared with 34 percent in the adult. Keller and Doherty (1980a) compared the levels of
210Pb in 10-day-old mice and adults, noting from the clearance half-times (vide supra) that
lead retention was greater in the suckling animals than in the adults. In both adult and
young mice, the rate of long-term retention was governed by the rate of release of lead from
bone, indicating that in the mouse, skeletal, lead retention in the young is greater than in
the adult. With infant and adult monkeys orally exposed to 2l0Pb, Pounds et al. (1978)
observed that at 23 days the corresponding amounts of initial dose retained were 92.7 and 81.7
percent, respectively.
The studies of Rader et al. (1981; 1982) are of particular interest as they not only
demonstrate that young experimental animals continue-^to show greater retention of lead in
tissue when exposure occurs after weaning, but also that such retention occurs in terms of
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PRELIMINARY DRAFT
either uniform exposure (Rader et al., 1981) or uniform dosing (Rader et al., 1982) when com-
pared with adult animals. With uniform exposure, 30-day-old rats given lead in drinking water
showed significantly higher lead levels in blood and higher percentages of dose retained in
brain, femur, and kidney, as well as higher indices (ALA-U, EP) of hematopoietic impairment
when compared with adult animals. As a percentage of dose retained, tissues in the young ani-
mals were approximately 2-3-fold higher. In part, the difference is due to a higher ingestion
rate of lead. However, in the uniform dosing study where this was not the case, an increased
retention of lead still prevailed, the amount of lead in brain being approximately 50 percent
higher in young vs. adult animals. Comparison of values in terms of percent retained is more
meaningful for such assessments, because the factor of changes in organ mass (see above) is
taken into account. Delayed excretion in the young animal may reflect an immature excretory
system or a tighter binding of lead in various body compartments.
10.5 INTERACTIONS OF LEAD WITH ESSENTIAL METALS AND OTHER FACTORS
Deleterious agents, particularly toxic metals such as lead, do not express their toxico-
kinetic or toxicological behavior in a physiological vacuum, but rather are affected by inter-
actions of the agent with a variety of biochemical factors such as nutrients. Growing recog-
nition of this phenomenon and its implications for lead toxicity in humans have prorrpted a
number of studies, many of them recent, that address both the scope and mechanistic nature of
such interactive behavior. ' r "
10.5.1 Human Studies
In humans, the interactive behavior of lead and various nutritional factors is appropri-
ately viewed as being particularly - significant.for children, since this age group is not only
particularly sensitive to lead's effects, but also represents the time of greatest flux in
relative nutrient status. Such interactions occur against a backdrop of rather widespread
deficiencies in a number of nutritional, components in children. While such deficiencies are
"¦ore pronounced in lower income groups, they exist in all socioeconomic strata. Mahaffey and
Michaelson (1980) have summarized the three nutritional status surveys carried out in the
United States for infants and young children: the Preschool Nutrition Survey, the Ten State
Nutrition Survey, and the National Health Assessment and Nutritional Evaluation Survey (NHANES
I). The most recent body of data of this type is the NHANES II study (Mahaffey et al., 1979),
although the dietary information from it has yet is to be reported. In the older surveys,
iron deficiency was the most common nutritional deficit in children under 2 years of age,
particularly children from low-income groups. Reduced vitamin C intake was noted in about
one-third of the children, while sizable numbers of them had significantly reduced intakes of
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PRELIMINARY DRAFT
calcium. Owen and Lippmann (1977) reviewed the regional surveys of low-inccme groups within
Hispanic, white, and black populations. In these groups, iron deficiency was a common
finding, while low intakes of calcium and vitamins A and C were observed regularly. Hambidge
(1977) concluded that zinc intake in low-income groups is generally inadequate, relative to
recommended daily allowances.
Available data from a number of reports document the association of lead absorption with
suboptimal nutritional status. Mahaffey et al. (1976) summarized their studies showing that
children with blood lead greater than 40 pg/dl had significantly (p <0.01) lower intake of
phosphorus and calcium compared with a control group, while iron intake in the two groups was
comparable. This study involved children 1-4 years old from an inner-city, low-income popula-
tion, with close matching for all parameters .except the blood lead level. Sorrell et al.
(1977), in their nutritional assessment of 1- to 4-year-old children with a range of blood
lead levels, observed that blood lead content was inversely correlated with calcium intake,
while children with blood lead levels >60 pg/dl had significantly (p <0.001) lower intakes of
calcium and vitamin D.
Rosen et al. (1981) found that children with elevated blood lead (33-120 pg/dl) had sig-
nificantly lower serum concentrations of the vitamin D metabolite 1,25-(0H)2D (p <0.001) com-
pared with age-matched controls, and showed a negative correlation of serum 1,25-(0H)2D with
lead over the range of blood leads measured. These observations and animal data (Barton et
al., 1978a, see Section 10.5.2) may suggest an increasingly adverse interactive cycle of
1,25—(OH)2D, lead, and calcium in which lead re(3iices~bio's'ynthesis of the vitamin D metabolite.
This then leads to reduced induction of calcium binding protein (CaBP), less absorption of
calcium from the gut, and greater uptake of lead, thus increasing uptake of lead and further
reducing metabolite levels. Barton et al. (1978a) isolated two mucosal proteins in rat intes-
tine, one of which bound mainly lead and was not vitamin D-stimulated; the second bound mainly
calcium and was under vitamin control. The authors suggested direct site binding competition
between lead and calcium in these proteins. Hunter (1978) investigated the possible inter-
active role of seasonal vitamin D biosynthesis in adults and children; it is a common obser-
vation that lead poisoning occurs more often in summer than in other seasons (see Hunter,
1977, for review). In children, seasonality accounts for 16 percent of explained variance
of blood lead in black children, 12 percent in Hispanics, and 4 percent in whites. More
recently, it has been documented that there, is no seasonal variation in circulating levels of
1,25-(0H)2D the metabolite that affects the rate of lead absorption from the GI tract (Chesney
et al., 1981). These results suggest that seasonality is related to changes in exposure.
Johnson and Tenuta (1979) determined that calcium intake was negatively correlated
(r = -0.327, p <0.05) with blood lead in 43 children s'ged 1-6 years. The high lead group also
consumed less zinc than children with lower blood levels. Yip et al. (1981) found that 43
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children with elevated blood lead (>30 MQ/dl) and EP (>35 pg/dl) had an increased prevalence
of iron deficiency as these two parameters increased. Children classed as COC lb and I] had a
79 percent deficiency rate, while those in Class III were all iron-deficient. Chisolm (1981)
demonstrated an inverse relationship between "chelatable" iron and chelatable body lead levels
as indexed by urinary ALA levels in 66 children with elevated blood lead. Watson et al.
(1980) reported that adult subjects who were iron-deficient (determined from serum ferritin
measurement) showed a lead absorption rate 2-3 times greater than subjects who were iron
replete. In a group of 13 children, Markowitz and Rosen (1981) reported that the mean serum
zinc levels in children with plumbism were significantly below the values seen in normal chil-
dren. Chelation therapy reduced the mean level even further. Chisolm (1981) reported that
there was an inverse relationship between ALA-U and the amount of "chelatable" or systemically
active zinc in 66 children challenged with EDTA and having blood lead levels ranging from 45
to 60 pg Pb/dl. These two studies suggest that zinc status is probably as important an inter-
active modifier of lead toxicity as is either calcium or iron.
The role of nutrients in lead absorption has been reported in several metabolic balance
studies for both adults and children. Ziegler et al. (1978), in their investigations of lead
absorption and retention in infants, observed that lead retention, was inversely correlated
with calcium intake, expressed either as intake percentage (r = -0.284,.p <0.01) or on a
weight basis (r = -0.279, p <0.01). Of interest is the fact that the range of calcium intake
measured was within the range considered adequate for infants and toddlers by the National
Research Council (National Academy of Sciences, National Research Council, 1974). These data
also support the premise that savere deficiency need not be present for an interactive rela-
tionship to occur. Using adults, Heard and Chamberlain (1982) monitored the uptake of 203Pb
from the gut in eight subjects as a function of the amounts of dietary calcium and phosphorus.
Without supplementation with either of these minerals in fasting subjects, the label absorp-
tion rate was approximately 60 percent, compared with 10 percent with 200 mg calcium plus
140 mg phosphorus, the amounts present in an average meal. Calcium alone reduced uptake by a
factor of 1.3 and phosphorus alone by 1.2; both together yielded a reduction factor of .6.
This work suggests that insoluble calcium phosphate is formed and co-precipitates any lead
present. This interpretation is supported by animal data (see Section 10.5.2).
10.5.2 Animal Studies
Reports of lead-nutrient interactions in experimental animals have generally described
such relationships in terms of a single nutrient, using relative absorption or tissue reten-
tion in the animal to index the effect. Most of the recent data are concerned with the impact
of dietary levels of calcium, iron, phosphorus, and vitamin D. Furthermore, some investigat-
ors have attempted to elucidate the . site(s) . of- interaction as well as the mechanism(s)
NEW10A/A 10-33 7/1/83
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PRELIMINARY DRAFT
governing the interactions. Lead's interactions involve the effect of the nutrient on lead
uptake, as well as lead's effect on nutrients; the focus of this discussion is on the former.
These interaction studies are tabulated in Table 10-4.
10.5.2.1 Interactions of Lead with Calcium. The early report of Sobel et al. (1940) noted
that variation of dietary calcium and other nutrients affected the uptake of lead by bone and
blood in animals. Subsequent studies by Mahaffey-Six and Goyer (1970) in the rat demonstrated
that a considerable reduction in dietary calcium was necessary from (0.7 percent to 0.1 per-
cent), at which level blood lead was increased 4-fold, kidney lead content was elevated 23-
fold, and relative toxicity (Mahaffey et al., 1973) was increased. The changes in calcium
necessary to alter lead's effects in the rat appear to be greater than those seen by Ziegler
et al. (1978) in young children, indicating species differences in terms of sensitivity to
basic dietary differences, as well as to levels of all interactive nutrients. These observa-
tions in the rat have been confirmed by Kostial et al. (1971), Quarterman and Morrison (1975),
Barltrop and Khoo (1975), and Barton et al. (1978a). The inverse relationship between dietary
calcium and lead uptake has also been noted in the pig (Hsu et al., 1975), horse (Willoughby
et al., 1972), lamb (Morrison et al., 1977), and domestic fowl (Berg et al., 1980).
The mechanism(s) governing lead's interaction with calcium operate at both the gut wall
and within body compartments. Barton et al. (1978a), using everted duodenal sac preparations
in the rat, reported that: (1) interactions at the gut wall require the presence of intubated
calcium to affect lead label absorption - (pre-existing calcium deficiency in the animal and
no added calcium have no effect on lead transport); (2) animals having calcium deficiency show
increased retention of lead rather than absorption-(confirmed by Quarterman et al., 1973); and
(3) lead transport may be mediated by two mucosal proteins, one of which has high molecular
weight, a high proportion of bound lead, and, is affected in extent of lead binding with
changes in lead uptake. The second protein binds mainly calcium and is vitamin D-dependent.
Smith et al. (1978) found that lead is taken up at a different site in the duodenum of
rats than is calcium but absorption does occur at the site of phosphate uptake, suggesting a
complex interaction of phosphorus, calcium, and lead. This is consistent with the data of
Barltrop and Khoo (1975) for rats and the data of Heard and Chamberlain (1982) for humans,
thus showing that the combined action of the two mineral nutrients is greater than the sum of
either's effects.
Mykkanen and Wassermann (1981) observed that lead uptake in the intestine of the chick
occurs in 2 phases: a rapid uptake (within 5 minutes) followed by a rate-1imi ting slow trans-
fer of lead into blood. Conrad and Barton (1978) have observed a similar process in the rat.
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TABLE 10-4. EFFECT OF NUTRITIONAL FACTORS ON LEAD UPTAKE IN ANIMALS
Factor Species Index of effect Interactive effect Reference
Calci um
Calcium
Calcium
Calcium .
Calcium
Iron
I ron
Iron
Rat
Pig
i
Horse
Lamb
Rat
Rat
Rat
Mouse
Lead in tissues and
effect severity at
low levels of dietary
calci um
Lead in tissues at
low levels of
dietary calcium
Lead in tissues at
low levels of
dietary calcium
Lead in tissue at
low levels of
dietary calcium
Lead retention
Tissue levels and
relative toxicity
of lead
Lead absorption in
everted duodenal
sac preparation
Lead retention
Low dietary calcium (0.1%)
increases lead absorption
and severity of effects
Increased absorption of
lead with low dietary
calci um
Increased absorption of
lead with low dietary
calcium
Increased absorption of
lead with low dietary
calcium
Retention increased in
calcium deficiency
Iron deficiency increases
lead absorption and
toxicity
Reduction in intubated
iron increases lead
absorption; increased
levels decrease lead uptake
Iron deficiency has no
effect on lead
retention
Mahaffey-Six and Goyer,
1970; Mahaffey et al.,
1973
Hsu et al., 1975
Willoughby et al., 1972
Morrison et al. , 1977
Barton et al., 1978a
Mahaffey-Six and Goyer,
1972
Barton et al., 1978b
Hamilton, 1978
-------
TABLE 10-4. (continued)*
Factor Species Index of effect Interactive effect Reference
Iron
Phosphorus
Phosphorus
Phosphorus
Vitamin D
Vitamin D
Lipid
Protei n
Rat
Rat
Rat
Rat
Rat
Rat
Rat
Rat
In utero or mi 1k
transfer of lead in
pregnant or lactating
rats
Lead uptake in tissues
Lead retention
Lead retention
Lead absorption
using everted sac
techni ques
Lead absorption
using everted sac
techniques
Lead absorption
Lead uptake by tissues
Iron deficiency increases
both j_n utero and milk
transfer of lead to
suckli ngs
Reduced P increased
203Pb uptake 2.7-fold
Low dietary P enhances
lead retention; no
effect on lead resorption
i n bone
Low dietary P enhances
both lead retention "and
deposition in bone
Increasing vitamin D
increases intubated
lead abosrption
Both low and excess
levels of vitamin D
increase lead uptake
by affecting motility
Increases in lipid (corn
oil) content up to
40.percent enhances lead
absorption
Both low and high protein
in diet increase lead
absorption
Cerklewski, 1980
Barltrop and Khoo, 1975
Quarterman and Morrison,
1975
Barton and Conrad, 1981
Smi th et al1978 ,
Barton et al., 1980
Barltrop and Khoo, 1975
Barltrop and Khoo, 1975
-------
TABLE 10-4. (continued)
Factor
Species Index of effect
Interactive effect
Reference
Protein
Rat
Body lead retention
Low dietary protein either
reduces or does not affect
retention in various
ti ssues
Quarterman et al., 1978b
Protein
Rat
Milk components Rat
Tissue levels of
lead
Lead absorption
Casein in diet increases
lead uptake compared to
soybean meal
Lactose-hydrolyzed milk
does not increase lead
absorption, but ordinary
mi 1k does
Anders et al., 1982
Bell and Spickett, 1981
Milk components Rat
Zinc/Copper
Zinc/Copper
Rat
Rat
Lead absorption
Lead absorption
Lead transer i n
utero and in mi lk
during lactation
Lactose in diet enhances
lead absorption compared
to glucose
Low zinc in diets
increases lead absorption
Low-zinc diet of mother
increases lead transfer
in utero and in maternal
mi lk
Bushnell and DeLuca, 1981
Cerklewski and Forbes,
1976; El-Gazzar et al.,
1978
Cerklewski, 1979
Zinc/Copper
Rat
Lead absorption
Low copper -in diet
increases lead absorption
Klauder et a 1., 1973;
Klauder and Petering, 1975
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PRELIMINARY DRAFT
Hence, there is either a saturation process occurring, i.e., carrier-mediated transport, or
simply lead precipitation in the lumen. In the former case, calcium interacts to saturate the
carrier proteins as isolated by Barton et al. (1978a) or may precipitate lead in the lumen by
initial formation of calcium- phosphate.
Quarterman et al. (1978a) observed that calcium supplementation of the diet above normal
also resulted in increased body retention of lead in the rat. Because both deficiency (Barton
et al., 1978a) and excess in calcium intake enhance retention, two sites of influence on
retention are suggested. Goyer (1978) has suggested that body retention of lead in calcium
deficiency, i.e., reduced excretion rate, may be due to renal impairment, while Quarterman et
al. (1978a) suggest that excess calcium suppresses calcium resorption from bone, hence also
reducing lead release.
10.5.2.2 Interactions of Lead with Iron. Mahaffey-Six and Goyer (1972) reported that iron-
deficient rats had increased tissue levels of lead and manifested greater toxicity compared
with control animals. This uptake change was seen with but minor alterations in hematocrit,
indicating a primary change in lead absorption over the time of the study. Barton et al.
(1978b) found that dietary restriction of iron, using 210Pb and everted sac preparations in
the rat, led to enhanced absorption of iron; iron loading suppressed the extent of lead
uptake, using normal intake levels of iron. This suggests receptor binding competition at a
common site, consistent with the isolation by these workers of two iron-binding mucosa frac-
tions. While iron level of diet affects lead absorption, the effect of changes in lead con-
tent in the gut on iron absorption is not clear. Barton et al. (1978b) and Dobbins et al.
(1978) observed no effect of lead in the gut on iron absorption in the rat, while Flanagan et
al. (1979) reported that lead reduced iron absorption in mice.
In the mouse, Hamilton (1978) found that body retention of 2U3Pb was unaffected by iron
deficiency, using intraperitoneal administration of the label, while gastric intubation did
lead to increased retention. Animals with adequate iron showed no changes in lead retention
at intubation levels of 0.01 to 10 nM. Cerklewski (1980) observed that lead transfer both in
utero and in milk to nursing rats was enhanced when dams were maintained from gestation
through lactation on low iron diets compared with controls.
10.5.2.3 Lead Interactions with Phosphate. The early studies of Shelling (1932), Grant et
al. (1938), and Sobel et al. (1940) documented that dietary phosphate influenced the extent of
lead toxicity and tissue retention of lead in animals, with low levels enhancing those para-
meters while excess intake retarded the effects. More recently, Barltrop and Khoo (1975)
reported that reduced phosphate increased the uptake of 203Pb approximately 2.7-fold compared
with controls. Quarterman and Morrison (1975) found that low dietary phosphate enhanced lead
retention in rats but had no effect on skeletal lead mobilization nor was injected lead
label affected by such restriction. In a related study, Quarterman et al. (1978a) found that
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PRELIMINARY DRAFT
doubling of the nutrient over normal levels resulted in lowering of lead absorption by appro-
ximately half. Barton and Conrad (1981) found that reduced dietary phosphorus increased the
retention of labeled lead and deposition in bone, in contrast to the results of Quarterman and
Morrison (1975). Increasing the intraluminal level of phosphorus reduced lead absorption,
possibly by increasing intraluminal precipitation of lead as the mixed lead/calcium phosphate.
Smith et al. (1978) reported that lead uptake occurs at the same site as phosphate, suggesting
that lead absorption may be more related to phosphate than calcium transport.
10.5.2.4 Interactions of Lead with Vitamin D. Several studies had earlier indicated that a
positive relationship might exist between dietary vitamin D and lead uptake, resulting in
either greater manifestations of lead toxicity or a greater extent of lead uptake (Sobel et
al. , 1938, 1940). Using the everted sac technique and testing with 210Pb, Smith et al. (1978)
observed that increasing levels of intubated vitamin D in the rat resulted in increased
absorption of the label, with uptake occurring at the distal end of the rat duodenum, the site
of phosphorus uptake and greatest stimulation by the vitamin. Barton et al. (1980) used 2l0Pb
to monitor lead absorption in the rat under conditions of normal, deficient, and excess
amounts of dietary vitamin D. Lead absorption is increased with either low or excess vitamin
D. This apparently occurs because of increased retention time of fecal mass containing the
lead due to alteration of intestinal motility rather than because of direct enhancement of
mucosal uptake rate. Hart and Smith (1981) reported that vitamin D repletion of diet enhanced
lead absorption (210Pb) in the rat, while also enhancing femur and kidney lead uptake when the
label was given by injection.
10.5.2.5 Interactions of Lead with Lipids. Barltrop and Khoo (1975) observed that varying
the lipid (corn oil) content of rat diet from 5 up to 40 percent resulted in an increase of
lead in blood 13.6-fold higher compared with the normal level. Concomitant increases were
observed in lead levels in kidney, femur, and carcass. Reduction of dietary lipid below the
5 percent control figure was without effect on lead absorption rate. As an extension of this
earlier work, Barltrop (1982) has noted that the chemical composition of the lipid is a signi-
ficant factor in affecting lead absorption. Study of triglycerides of saturated and unsatura-
ted fatty acids showed that polyunsaturated, trilinolein increased lead absorption by 80 per-
cent in rats, when given as 5 or 10 percent loadings in diet, compared with monounsaturated
triolein or any of the saturates in the series tricaproin to tristearin.
10.5.2.6 Lead Interaction with Protein. Quarterman et al. (1978b) have drawn attention to
one of the inherent difficulties of measuring lead-protein interactions, i.e., the effect of
protein on both growth and the toxicokinetic parameters of lead. Der et al. (1974) found that
reduction of dietary protein, from 20 to 4 percent, led to increased uptake of lead in rat
tissues, but the approximately 6-fold reduction in body weight over the interval of the study
makes it difficult to draw any firm conclusions. Barltrop and Khoo (19/5) found that lead
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PRELIMINARY DRAFT
(203Pb) uptake by rat tissue could be enhanced with either suboptimal or excess levels of pro-
tein in diet. Quarterman et al. (1978b) reported that retention of labeled lead in rats main-
tained on a synthetic diet containing approximately 7 percent protein was either unaffected or
reduced compared with controls, depending on tissues taken for study.
It appears that not only levels of protein but also the type of protein affects tissue
levels of lead. Anders et al. (1982) found that rats maintained on either of two synthetic
diets varying only as to having casein or soybean meal as the protein source showed signifi-
cantly higher lead levels in the casein group.
10.5.2.7 Interactions of Lead with Milk Components. For many years, milk was recommended
prophylactically for lead poisoning among lead workers (Stephens and Waldron, 1975). More
recent data, however, suggest that milk may actually enhance lead uptake. Kello and Kostial
(1973) found that rats maintained on milk diets absorbed a greater amount of 203Pb than those
having access to commercial rat chow. This was ascribed to relatively lower levels of certain
nutrients in milk compared with the rat chow. These observations were confirmed by Bell and
. - ypi'u ¦ ¦
Spickett (1981), who also observed that lactose-hydrolyzed milk was less effective than the
ordinary form in promoting lead absorption, suggesting that lactose may be the enhancing prin-
ciple. Bushnell and DeLuca (1981) demonstrated that lactose significantly increased lead
(2i°pb) absorption and tissue retention by weanling rats by comparing diets identical in all
respects except for carbohydrate source. These results provide one rationale for why nursing
mammals tend to absorb greater quantities of lead than adults; lactose is the major carbohy-
drate source in suckling rats and is known to enhance the uptake of many essential metals.
10.5.2.8 Lead Interactions with Zinc and Copper. The studies of Cerklewski and Forbes (1976)
and El-Gazzar et al. (1978) documented that zinc-deficient diets promote lead absorption in
the rat, while repletion with zinc reduces lead uptake. The interaction continues within the
body, particularly with respect to ALA-D activity (see Chapter 11). In a study of zinc-lead
interactions in female rats during gestation and lactation, Cerklewski (1979) observed that
zinc-deficient diets resulted in more transfer of lead through milk to the pups as well as
reduced litter body weights.
Klauder et al. (1973) reported that low dietary copper enhanced lead absorption in rats
fed a high lead diet (5000 ppm). These observations were confirmed by Klauder and Petering
(1975) at a level of 500 ppm lead in diet. These researchers subsequently observed that
reduced copper enhanced the hematological effects of lead (Klauder and Petering, 1977), and
that both copper and iron deficiencies must be corrected to restore hemoglobin levels to-
normal .
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PRELIMINARY DRAFT
10.6 INTERRELATIONSHIPS OF LEAD EXPOSURE, EXPOSURE INDICATORS, AND TISSUE LEAD BURDENS
Information presented so far in this chapter sets forth the quantitative and qualitative
aspects of lead toxicokinetics, including the compartmental modeling of lead distribution in
vivo, and leads up to the critical issue of the various interrelationships of lead toxico-
kinetics to lead exposure, toxicant levels in indicators of such exposure, and exposure-target
tissue burdens of lead.
Chapter 11 (Sections 11.4, 11.5, 11.6) discusses the various experimental and epidemiolo-
gical studies relating the relative impact of various routes of lead exposure on blood lead
levels in human subjects, including the description of mathematical models for such relation-
ships. In these sections, the basic question is: what is the mathematical relationship¦of
lead in air, food, water, etc. to lead in blood? This question is descriptive and does not
address the biological basis of the observed relationships. Nor does it consider the impli-
cations for adverse health risk in the sequence of exposure leading from external lead to lead
in some physiological indicator to lead in target tissues.
For purposes of discussion, this section separately considers 1) the temporal character-
istics of physiological indicators of lead exposure, 2) the biological aspects of the rela-
tionship of external exposure to internal indicators of exposure, and 3) internal indicator-
tissue lead relationships, including both steady-state lead exposure and abrupt changes in
lead exposure. The relationship of internal indicators of body lead, such as blood lead, to
biological indicators such as EP or urinary ALA is discussed in Chapter 13, since any compara-
tive assessment of the latter should follow the chapter on biological effects, Chapter 12.
10.6.1 Temporal Characteristics of Internal Indicators of Lead Exposure
The biological half-time for blood lead or the non-retained fraction of body lead is
relatively short (see Sections 10.3 and 10.4); thus, a given blood or urine lead value
reflects rather recent exposure. In cases where lead exposure can be reliably assumed to have
occurred at a given level, a blood lead value is more useful than in cases where some inter-
mittent, high level of exposure may have occurred. The former most often occurs with occupa-
tional exposure, whi1e.the fatter is of particular relevance to young children.
Accessible mineralizing tissue, such as shed teeth, extend the time frame for assessing
lead exposure from weeks or several months to years (Section 10.3), since teeth accumulate
lead up to the time of shedding or extraction. Levels of lead in teeth increase with age in
proportion to exposure (Steenhout and Pourtois, 1981). Furthermore, tooth levels are propor-
tional to blood lead levels in humans (Shapiro et a 1. , 1978) and animals (Kaplan et al.,
1980). The technique of Fremlin and Edmonds (1980), employing micro-autoradiography of
irradiated teeth, permits the identification of dentine zones high in lead content, thus
allowing the disclosure of past periods of abrupt increases in lead intake.
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PRELIMINARY DRAFT
While levels of lead in shed teeth are more valuable than blood lead in assessing expo-
sure at more remote time points, such information is retrospective in nature and would not be
of use in monitoring current exposure. In this case, serial blood lead measurements must be
employed. With the development of methodology for j_n 5itu measurement of tooth lead in chil-
dren (described in Chapter,9), serial i_n si tu tooth analysis in tandem with serial blood lead
determining would provide comparative data for determination of both time-concordant blood/
tooth relationships as well as which measure is the better indicator of ongoiny exposure.
Given the limitations of an indicator such as blood lead in reflecting lead uptake in target
organs, as discussed below, it may well be the case that the rate of accumulation of lead in
teeth, measured i_n s i tuis -a better index of ongoing tissue lead uptake than is blood lead.
This aspect merits further study, especially as Shapiro et al. (1978) were able to demonstrate
the feasibility of using _in situ tooth lead analysis in a large group of children screened for
lead exposure.
10.6.2 Biological Aspects of External Exposure-Interna 1 Indicator Relationships
Information provided in Chapter 11 as well as the critique of Hammond et al. (1981) indi-
cate that the relationship of levels of lead in air, food, and water to lead in blood is
curvilinear, w-th the result that as "baseline" blood lead rises, i.e., as one moves up the
curve, the relative change in the dependent variable, blood lead, per unit change of lead in
some intake medium (such as air) becomes smaller. Conversely, as one proceeds down the curve
with reduction in "baseline" lead, the corresponding change in blood lead becomes larger. One
assumption in this "single medium" approach is that the baseline is not integrally related to
the level of lead in the particular medium being studied. This assumption is not necessarily
appropriate in the case of air vs. food lead, nor, in the case of young children, air lead vs.
total oral intake of the element.
Hammond et al. (1981) have noted that the shape of the blood lead curves seen in human
subjects is similar to that discernible in certain experimental animal studies with dogs,
rats, and rabbits (Azar et al., 1973; Prpic'-Majic et al., 1973). Also, Kimmel et al . (1980)
exposed adult female rats to lead at four levels in drinking water for 6-7 weeks and reported
values of blood lead that showed curvilinear relationship to the dose levels. Cver the dosing
range of 5 to'250 ppm in water, the blood lead range was 8.5 to 31 pg/dl. In a related study
(Grant et al., 1980) rats were exposed to lead i_n utero, through weaning, and up to 9 months
of age at the dosing range used in the Kimmel et al. study the weanlings, 0.5 to 250 ppm in
the dams' drinking water until weaning of pups; then the same levels in the weanlings' drink-
ing water) showed a blood lead range of 5 to 67 pg/dl. It may be assumed in all of the above
studies that lead in the various dosing groups was near or at equilibrium within the various
body compartments.
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PRELIMINARY DRAFT
The biological basis of the curvilinear relationship of blood lead to lead intake does
not appear to be due to reduced absorption or enhanced excretion of the element with changes
in exposure level. In other words, a decrease in the ratio of blood lead to medium lead as
blood lead increases cannot be taken to indicate reduced uptake rate of lead into target tis-
sues. In the study of Prpic-Majic et al. (1973), dosing was by..injection so that the GI
absorption rate of lead was not a factor. Azar et al. (1973) reported values for urirary lead
across the dosing groups that indicated the excretion rate for the 10, 50, 100, and. 500 ppm
dietary lead groups was fairly constant. As suggested by Hammond et al. (1981), the shape of
the blood lead curves in the context of external exposure, is probably related to the tissue
distribution of lead. Other supporting evidence is the relations.hip. of blood lead to chela-
table lead and that of tissue burden to dosing level as discussed below.
10.6.3 Internal Indicator-Tissue Lead Relationships
In living human subjects it is not possible to directly determine tissue burdens of lead
(or relate these levels to adverse effects associated with target tissue) as a function of
lead intake. Instead, measurement of lead in an accessible indicator such as Diocd, along
with determination of some biological indicator of impairment, e.g., ALA-U or EP, is used.
Evidence continues to accumulate in both the clinical and experimental animal literature
that the use of blood lead as an indicator has limitations in reflecting both the amounts of
lead in target tissues and the temporal changes in tissue lead with changes in exposure. Per-
haps the best example of the problem is the relationship of blood lead to chelatable lead (see
Section 10.3.3). Presently, measurement of the plunburesis associated with challenge by a
single dose of a chelating agent such as CaNa2EDTA is considered the best measure of the mo-
bile, potentially tcxic, fraction of body lead in children and adults (Chisolm et al., 1976;
U.S. Centers for Disease Control, 1978; Chisolm and Barltrop, 1979; Hansen et al., 19B1).
Chisolm et al. (1975) have documented that the relationship of blood lead to chelatable
lead is curvilinear, such that a given incremental increase in blood lead is associated with
an increasingly larger increment of mobilizable lead. The problems associated with this cur-
vilinear relationship: ir. exposure assessment are typified by the recent reports of Saenger et
al. (1982) concernirg children and Hansen et al. (1981) concerning on adult lead workers. In
the former study, it was noted that significant percentages of children having mild to moder-
ate lead exposure, as discernible by blood lead and EP measurements, were found to have uri-
nary outputs of lead upon challenge with CaNa2EDTA qualifing them for chelation therapy under
CDC guidelines. In adult workers, Hansen et al. (1981) observed that a sizable fraction of
subjects with only modest elevations in blood lead excreted lead upon CaNa^EDTA challenge sig-
nificantly exceeding the upper end of normal. This occurred at blood lead levels of 35 pg/dl
and above.
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PRELIMINARY DRAFT
The biological basis for the non-linearity of the relationship between blood lead and
chelatable lead, appears in a major part, to be the existence of a sizeble pool of lead in
bone that is labile to chelation. Evidence pointing to this was summarized in Section 10.3.3.
The question of how long any lead in this compartment of bone remains labile to chelation has
been addressed by several investigators in studies of both children and adults. The question
is relevant to the issue of the utility of EDTA challenge in assessing evidence for past lead
exposure.
Chisolmet al. (1976) found that a group of adolescent subjects (N = 55; 12-22 yrs old),
who had a clinical history of lead poisoning as young children and whose mean blood lead was
22.1 (jg/d 1 at the time
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PRELIMINARY DRAFT
Finally, there is the question of how adequately an internal indicator such as blood lead
reflects changes in tissue burden when exposure changes abruptly. In the study of Bjorklund
et al. (1981), lead levels in both blood and brain were monitored over a 6-week period in rats
exposed to lead through their drinking water. Blood lead rose rapidly by day 1, during which
time brain lead content was only slightly elevated. After day 1, the rate of increase in
blood lead began to taper off while brain lead began to rise in a near-linear fashion up to
the end of the experiment. From day 7 to 21, blood lead increased from approximately .45 to 55
pg/dl, while brain lead increased approximately 2-fold.
Abrupt reduction in exposure similarly appears to be associated with a more rapid
response in blood than in soft tissues, particularly brain. Goldstein and Diamond (1974)
reported that termination of intravenous administration of lead to 30-day-old rats resulted in
a 7-fold drop of lead in blood by day 7. At the same time, there was no significant decrease
in brain lead. A similar difference in brain vs. blood response was reported by Momcliovic
and Kostial (1974).
In all of the above studies, it may be seen that blood lead was of limited value in
reflecting changes in the brain, which is, for children, the significant target organ fcr lead
exposure. With abrupt increases in exposure level, the problem concerns a much more rapid
approach to steady-state in blood than in brain. Conversely, the biological half-time for
lead clearance from blood in the young rats of both the Goldstein and Diamond (1974) and
Momcilovic and Kostial (1974) studies was much less than it appeared to be for lead movement
from brain.
Despite the limitations in indexing tissue burden and exposure changes, blood lead
remains the one measure that can reliably demonstrate the relationship of various effects.
10.7 METABOLISM OF LEAD ALKYLS
The lower alkyl lead compounds used as gasoline additives, tetraethyl lead (TEL) and
tetramethyl lead (TML), are much more toxic, i.e., neurotoxic, on an equivalent dose basis
than inorganic lead. These agents are emitted in auto exhaust and their rate of environmental
degradation depends on such factors as sunlight, temperature, and ozone levels. There is also
some concern that organolead compounds may result from biomethylation in the environment (see
Chapter 6). Finally, there appears to be a problem with the practice among children of snif-
fing leaded gasoline. The available information dealing with metabolism of lead alkyls is
derived mainly from experimental animal studies, workers exposed to the agents and cases of
lead alkyl poisoning.
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PRELIMINARY DRAFT
10.7.1 Absorption of Lead Alkyls in Humans and Animals
The respiratory intake and absorption of TEL and TML in the vapor state was investigated
by Heard et al. (1979), who used human volunteers inhaling 203Pb-labeled TEL and TML. Initial
lung deposition rates were 37 and 51 percent foa?TEL'and.iTML, respectively. Of these amounts,
40 percent of TEL was lost by exhalation within 48 hours, while the corresponding figure for
TML was 20 percent. The remaining fraction was absorbed. The effect of gasoline vapor on
these parameters was not investigated. In this study Mortensen (1942) reported that adult
rats inhaling TEL labeled with 203Pb (0.07-7.00 irg TEL/1) absorbed 16-23 percent of the frac-
tion reaching the alveoli. Gasoline vapor had no effect on the absorption rates.
Respiratory absorption of organolead bound to particuTate matter has not been specif-
ically studied as such. According to Harrison and Laxen (1978), TEL or TML does not adher to
particulate matter to any significant extent, but tne toxicologically equivalent trialky1
derivatives, formed from photolytic dissociation or ozonolysis in the atmosphere, may do so.
10.7.1.1 Gastrointestinal Absorption. Information on the rate of absorption of lead alkyls
through the gastrointestinal tract is not available in the literature. Given the level of
gastric acidity (pH 1.0) in humans, one would expect TML and TEL to be rapidly converted tc
the corresponding trialkyl forms, which are comparatively more stable (Baae and Huber, 1970).
Given the similarity of the chemical and biochemical behavior of trialkyl leads to their Group
IV analogs, the trialkyltins, the report of Barnes and Stoner (1958) that triethyltin is
qualitatively absorbed from the GI tract indicates that triethyl and trimethyllead would be
extensively absorbed via this route.
10.7.1.2 Percutaneous Absorption of Lead Alkyls. In contrast to inorganic lead salts, both
TEL and TML are rapidly and extensively absorbed through the skin in rabbits and rats (Kehoe
and Thamann, 1931; Laug and Kunze, 1948), and lethal effects can be rapidly induced in these
animals by merely exposing the skin. Laug and Kunze (1948) observed that systemic uptake of
TEL was still 6.5 percent even though rrost of the TEL was seen to have evaporated from the
skir. surface. The rate of passage of tml was somewhat slower than that of TEL in the study of
Davis et al. (1963); absorption of either agent was retarded somewhat when applied in gaso-
line.
10-7.2 Biotransformation and Tissue Distribution of Lead Alkyls
In order to have an understanding of the i_n vivo fate of lead alkyls, it is useful to
first discuss the biotransformation processes of lead alkyls known to occur in mammalian
systems. Tetraethyl and tetramethyl lead both undergo oxidative dealkylation in mammals to
the triethyl or trimethyl metabolites, which are now accepted as the actual toxic forms of
these alkyls.
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Studies of the biochemical mechanisms for these transformations, as noted by Kimmel et
al. (1977), indicate a dealkylation mediated by a P-450 dependent mono-oxygenase system in
liver microsomes, with intermediate hydroxylation. In addition to rats (Cremer, 1959; Stevens
et al., 1960; Bolanowska, 1968), mice j.(Hayakawa, 1972), and rabbits (Bolanowska and
Garczyriski, 1968) this transformation ,also occurs in humans accidentally poisoned with TEL
(Bolanowska et al., 1967) or workers chronically exposed to TEL (Adamiak-Ziemka and
Bolanowska, 1970).
The rate of hepatic oxidative de-ethylation of TEL in mammals appears to be rather rapid;
Cremer (1959) reported a maximum conversion rate of approximately 200 pg TEL/g rat liver/hour.
In comparison with TEL, TML may undergo transformation at either a slower rate (in rats) or
more rapidly (in mice), according to Cremer and Calloway (1961) and Hayakawa (1972).
Other transformation steps involve conversion of triethyl lead to diethyl form, the pro-
cess appearing to be species-dependent. Bolanowska (1968) did not report the formation of
diethyl lead in rats, while significant amounts of it are present in the urine of rabbits
(Arai et al., 1981) and humans (Chiesura, 1970). Inorganic lead is formed in various species
treated with tetraethyl lead, which may arise from degradation of the diethyl lead metabolite
or some other direct process (Bolanowska, 1968). The latter process appears to occur in rats,
as little or no diethyllead is found, whereas significant amounts of inorganic lead are
present. formation of inorganic lead with lead alkyl exposure may account for the hematolo-
gical effects seen in humans chronically exposed to the lead alkyls (see Section 12.3),
including children who inhale leaded gasoline vapor.
Partitioning of triethyl or trimethyl lead, the corresponding active metabolites of TEL
and TML, between the erythrocyte and plasma appears to be species-dependent, Byington et al.
(1980) studied the partitioning of triethyl lead between cells and plasma i_n vitro using
washed human and rat erythrocytes and found that human cells had a very low affinity for the
alkyl lead while rat cells bound the alkyl lead in the globin moiety at a ratio of three mole-
cules per Hb tetramer. Similarly, it was found that injected triethyl lead was associated
with whole blood levels approximately 10-fold greater than in rat plasma. The available
literature on TEL poisoning in humans concurs, as significant plasma values of lead have been
routinely reported (Boeckx et al. , 1977; Golding and Stewart, 1982). These data indicate that
the rat is a poor model to use in studying the adverse effects of lead alkyls in human sub-
jects.
The biological half-time in blood for the lead alkyls depends on whether clearance of the
tetraalkyl or trialkyl forms is being observed. Heard et al. (1979) found that ^3Pb-labeled
TML and TEL inhaled by human volunteers was rapidly cleared from blood (by 10 hours), followed
by a reappearance of lead. The fraction of lead in plasma initially was quite high, approxi-
mately 0.7, suggesting tetra/trialkyl lead; but the subsequent rise in blood lead showed all
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of it essentially present in the call, which would indicate inorganic or possibly diethyl
lead. Triethyl lead in rabbits was more rapidly cleared from the blood of rabbits (3-5 days)
than was the trimethyl form (15 days) when administered as such (Hayakawa, 1972).
Tissue distribution of lead in both humans" and animals exposed to TEL and TML primarily
involves the trialkyl metabolites. Levels are highest in liver, followed by kidney, then
brain (Bolanowska et al., 1967; Grandjean and Nielsen, 1979). Nielsen et al. (1978) observed
that measurable amounts of trialkyl lead were present in samples of brain tissue from subjects
with no known occupational exposure.
The available studies on tissue retention of triethyl or trimethyl lead provide variable
findings. Bolanowska (1968) noted that tissue levels of triethyl lead in rats were almost
constant for 16 days after a singla injection of TEL. Hayakawa (1972) found that the half-
time of triethyl lead in brain was 7-8 days for rats; the half-time for trimethyl lead was
much longer. In humans, Yamamura et al. (1975) reported two tissue compartments for triethyl
lead having half-times of 35 and 100 days (Yamamura et al., 1975).
10.7.3 Excretion of Lead Alkyls
Excretion of lead through the renal tract is the main route of elimination in various
species exposed to lead alkyls (Grandjean and Nielsen, 197S). The chemical forms of lead in
urine suggest that the differing amounts of the various forms are species-dependent. Arai et
al. (1981) found that rabbits given TEL parenterally excreted lead primarily in the form of
diethyl lead (69 percent) and inorganic lead (27 percent), triethyl lead accounting only for 4
percent. In rats, Bolanowska and Garczynski (1968) found that levels of triethyl lead were
somewhat higher in urine than was the case for rabbits. In humans, Chiesura (1970) found that
trialkyl lead never was greater than 9 percent of total lead content in workers with heavy TEL
exposure. Adamiak-Ziemka and Bolanowska (1970) reported similar data; the fraction of tri-
ethyl lead in the urine was approximately 10 percent of total lead.
The urinary rates of lead excretion in human subjects with known levels of TEL exposure
were also reported by Adamiak-Ziemka and Bolanowska (1970). In workers involved with the
blending and testing of leaded gasoline, workplace air levels of lead (as TEL) ranged from
0.037 to 0.289 mg Pb/m3 and the corresponding urine levels ranged from 14 to 49 jjg Pb/1, of
which approximately 10 percent was triethyl lead.
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10.8 SUMMARY
Toxicokinetic parameters of leed absorption, distribution, retention, and excretion con-
necting external environmental lead exposure to various adverse effects are discussed in this
section. Also considered are various influences on these parameters, e.g., nutritional
status, age, and stage of development.
A number of specific issues in lead metabolism by animals and humans merit special focus
and these include:
1. How does the developing organism from gestation to maturity differ from the adult in
toxicokinetic response to lead intake?
2. What do these differences in lead metabolism portend for relative risk for adverse
effects?
3. What are the factors that significantly change the toxicokinetic parameters in ways
relevant to assessing health risk?
4. How do the various interrelationships among body compartments for lead translate to
assessment of internal exposure and changes in internal exposure?
10.8.1 Lead Absorption in Humans and Animals
The amounts of lead entering the bloodstream via various routes of absorption are influ-
enced not only by the levels of the element in a given medium but also by various physical and
chemical parameters and specific host factors, such as age and nutritional status.
10.6.1.1 Respiratory Absorption of Lead. The movement of lead from ambient air to the blood-
stream is a two-part process: deposition of some fraction of inhaled air lead in the deeper
part of the respiratory tract and absorption of the deposited fraction. For adult humans, the
deposition rate of particulate airborne lead as likely encountered by the general population
is around 30-50 percent, with these rates being modified by such factors as particle size and
ventilation rates. It also appears that essentially all of the lead deposited in the lower
respiratory tract is absorbed, so that the overall absorption rate is governed by the deposi-
tion rate, i.e., approximately 30-50 percent. Autopsy results showing no lead accumulation in
the lung indicate quantitative absorption of deposited lead.
All of the available data for lead uptake via the respiratory tract in humans have been
obtained with adults. Respiratory, uptake of lead in children, while not fully quantifiable,
appears to be comparatively greater on a body weight basis, compared to adults. A second fac-
tor influencing the relative deposition rate in children has to do with airway dimensions.
One report has estimated that the 10-year-old child has a deposition rate 1.6- to 2.7-fold
higher than the adult on a weight basis.
It appears that the chemical form of the lead compound inhaled is not a major determinant
of the extent of alveolar absorption of lead. While experimental animal data for quantitative
assessment of lead deposition and absorption for the lung and upper respiratory tract are
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limited, available information from th,? rat, rabbit, dog, and nonhuman primate support the
findings that respired lead in humans is extensively and rapidly absorbed.
10.8.1.2 Gastrointestinal Absorption of Lead. Gastrointestinal absorption of lead mainly
involves lead uptake from food and beverages as well as lead deposited in the upper respira-
tory tract which is eventually swallowed. It also includes ingestion of non-food material,
primarily in children via normal mouthing activity and pica. Two issues of concern with lead
uptake from the gut are the comparative rates of such absorption in developing vs. adult
organisms, including humans, and how the relative bioavailability of lead affects such uptake.
By use of metabolic balance and isotopic (radio-isotope or stable isotope) studies, var-
ious laboratories have provided estimates of lead absorption in the human adult on the order
of 10-15 percent. This rate can be significantly increased under fasting conditions to 45
percent, compared to lead ingested with food. The latter figure also suggests that beverage
lead is absorbed to a greater degree since much beverage ingestion occurs between meals.
The relationship of the chemical/biochemical form of lead in the gut to absorption rate
has been studied, although interpretation is complicated by the relatively small amounts given
and the presence of various components in food already present in the gut. In general, how-
ever, chemical forms of lead or their incorporation into biological matrices seems to have a
minimal impact on lead absorption in the human gut.-' Several studies have focused on the ques-
tion of differences in gastrointestinal absorption rates for lead between children and adults.
It would appear that such rates for children are considerably higher than for adults: 10-15
percent for adults vs. approximately 50 percent fdr"clVildren. Available data for the absorp-
tion of lead from non-food items such as dust and dirt on hands are limited, but one study has
estimated a figure of 30 percent. For paint chips, a value of about 17 percent has been esti-
mated.
Experimental animal studies show that, like humans, the adult absorbs much less lead from
the gut than the developing animal. Adult rats maintained on ordinary rat chow absorb 1 per-
cent or less of the dietary lead. Various animal species studies make it clear that the new-
born absorbs a much greater amount of lead than the adult, supporting studies showirg this age
dependency in humans. Compared to an absorption rate of about 1 percent in adult rats, the
rat pup has a rate 40-50 times greater. Part, but not most, of the difference can be ascribed
to a difference in dietary composition. In nonhuman primates, infant monkeys absorb 65-85
percent of lead from the gut, compared to 4 percent for the adults.
The bioavailability of lead in the gastrointestinal (GI) tract as a factor in its absorp-
tion has been the focus of a number of experimental studies. These data show that: 1) lead
in a number of forms is absorbed about equally, except for the sulfide; 2) lead in dirt and
dust and as different chemical forms is absorbed at about the same rate as pure lead salts
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added to diet; 3) lead in paint chips undergoes significant uptake from the gut; and 4) in
some cases, physical size of particulate lead can affect the rate of GI absorption.
10.8.1.3 Percutaneous Absorption of Lead. Absorption of inorganic lead compounds through the
skin is of much less significance than through the respiratory and gastrointestinal routes.
This is in contrast to the case with lead alkyls (See Section 1.10.6). One recent study using
human volunteers and 203Pb-labeled lead acetate showed that under normal conditions, absorp-
tion approaches 0.06 percent.
10.8.1.4 Transplacental Transfer of Lead. Lead uptake by the human and animal fetus readily
occurs, such transfer going on by the 12th week of gestation in humans, with increasing fetal
uptake throughout development. Cord blood contains significant amounts of lead, correlating
with but somewhat lower than maternal blood lead levels. Evidence for such transfer, besides
lead content of cord blood, includes fetal tissue analyses and reduction in maternal blood
lead during pregnancy. There also- appears to be a seasonal effect on the fetus, summer-born
children showing a trend to higher blood lead levels than those born in the spring.
10.8.2 Distribution of Lead in Humans and Animals
In this subsection, the distributional characteristics of lead in various portions of the
body--blood, soft tissue, calcified, tissue, and the "chelatable" or potentially toxic body
burden--are discussed as a function of such variables as exposure history and age.
10.8.2.1 Lead in Blood. More than 99 percent of blood lead is associated with the erythro-
cyte in humans under steady state conditions, but it is the very small fraction transported in
plasma and extracellular fluid that provides lead to the various body organs. Most ("-50 per-
cent) of erythrocyte lead is bound within the cell, primarily associated with hemoglobin (par-
ticularly HbA2), with approximately 5 percent bound to a 10,000-dal ton fraction, 20 percent to
a heavier molecule, and 25 percent to lower weight species.
Whole blood lead in daily equilibrium with other compartments in adult humans appears to
have a biological half-time of 25-28 days and comprises about 1.9 mg in total lead content.
Human blood lead responds rather quickly to abrupt changes in exposure. With increased lead
intake, blood lead achieves a new value in approximately 40-60 days, while a decrease in expo-
sure may be associated with variable new blood values, depending upon the exposure history.
This dependence presumably reflects lead resorption from bone. With age, furthermore, there
appears to be little change in blood lead during adulthood. Levels of lead in blood of child-
ren tend to show a peaking trend at 2-3 years of age, probably due to mouthing activity, fol-
lowed by a decline. In older children and adults, levels of lead are sex-related, females
showing lower levels than men even at comparable levels of exposure.
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In plasma, lead is virtually all bound to albumin and only trace amounts to high weight
globulins. It is not possible to state which binding form constitutes an "active" fraction
for movement to tissues. The most recent studies of the erythrocyte-plasma relationship in
humans indicate that there is an equilibrium between these blood compartments, such that
levels in plasma rise with levels in whole blood.
10.8.2.2 Lead Levels in Tissues. Of necessity, various relationships of tissue lead to expo-
sure and toxicity in humans must generally be obtained from autopsy samples. Limitations on
such data include questions of how samples represent lead behavior in the living population,
particularly with reference to prolonged illness and disease states. The adequate characteri-
zation of exposure for victims of fatal accidents is a problem, as is the fact that such
studies are cross-sectional in nature, with different age groups assumed to have had similar
exposure in the past.
10.8.2.2.1 Soft tissues. After age 20, most soft tissues in humans do not show age-related
changes, in contrast to bone. Kidney cortex shows increase in lead with age which may be
associated with formation of nuclear inclusion bodies. Absence of lead accumulation in most
soft tissues is due to a turnover rate for lead which is similar to that in blood.
Based on several autopsy studies, it appears that soft tissue lead content for individ-
uals net occupationally exposed is generally below 0.5 pg/g wet weight, with higher values for
acrta and kidney cortex. Brain tissue lead level is generally below 0.2 ppm wet weight with
no change with increasing age, although the cross-sectional nature of these data would make
changes in low brain lead levels difficult to discern. Autopsy data for both children and
adults indicate that lead is selectively accumulated in the hippocampus, a finding that is
also consistent with the reginal distribution in experimental animals.
Comparisons of lead levels in soft tissue autopsy samples from children with results from
adults indicate that such values are lower in infants than in older children, while children
aged 1-16 years had levels comparable to -adult women. In one study, lead content of brain
regions did not materially differ for infants and older children compared to adults. Compli-
cating these data somewhat are changes in tissue mass with age, although such changes are less
than for the skeletal system.
Subcellular distribution of lead in soft tissue is not uniform, with high amounts of lead
being sequestered in the mitochondria and nucleus. Nuclear accumulation is consistent with
the existence of lead-containing nuclear inclusions in various species and a large body of
data demonstrating the sensitivity of mitochondria to injury by lead.
10.8.2.2.2 Mineralizing tissue. Lead becomes localized and accumulates in human calcified
tissues, i.e., bones and teeth. This accumulation in humans begins with fetal development and
continues to approximately 60 years of age. The extent of lead accumulation in bone ranges up
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to 200 mg in men ages 60-70 years, while in women lower values have been measured. Based upon
various studies, approximately 95 percent of total body lead is lodged in the bones of human
adults, with uptake distributed, over trabecular and compact bone. In the human adult, bone
lead is both the most inert and largest body pool, and accumulation can serve to maintain ele-
vated blood lead levels years after exposure, particularly occupational exposure, has ended.
Compared to the human adult, 73 percent of body lead is lodged in the bones of children,
which is consistent with other information that the skeletal system of children is more meta-
bolically active than in the adult. While the increase in bone lead across childhood is mod-
est, about 2-fold if expressed as concentration, the total accumulation rate is actually 80-
fold, taking into account a 40-fold increase in skeletal mass. To the extent that some sig-
nificant fraction of total bone lead in children and adults is relatively labile, it is more
appropriate in terms of health risk for the whole organism to consider the total accumulation
rather than just changes in concentration.
The traditional view that the skeletal system was a "total" sink for body lead (and by
implication a biological safety feature to permit significant exposure in industrialized popu-
lations) never did accord with even older information on bone physiology, e.g., bone remodel-
ling, and is now giving way to the view that there are at least several bone compartments for
lead, with different mobility profiles. It would appear, then, that "bone lead" may be more
of an insidious source of long-term internal exposure than a sink for the element. This
aspect of the issue is summarized more fully in the next section. Available information from
studies of such subjects as uranium miners and human volunteers ingesting stable isotopes
indicates that there is a relatively inert bone compartment for lead, having a half-time of
several decades, and a rather labile compartment which permits an equilibrium between bone and
tissue lead.
Tooth lead also increases with age at a rate proportional to exposure and roughly propor-
tional to blood lead in humans and experimental animals. Dentine lead is perhaps the most
responsive component of teeth to lead exposure since it is laid down from the time of eruption
until shedding. It is this characteristic which underlies the utility of dentine lead levels
in assessing long-term exposure.
10.8.2.2.3 Chelatable lead. Mobile lead in organs and systems is potentially more .active
toxicologically in terms of being available to biological sites of action. Hence, this frac-
tion of total body lead burden is a more significant predictor of imminent toxicity. In
reality, direct measurement of such a fraction in human subjects would not be possible. In
this regard, "chelatable" lead, measured as the extent of plumburesis in response to admini-
stration of a chelating agent, is not viewed as the most useful probe of undue body burden in
children and adults.
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A quantitative description of the inputs to the body lead fraction that is chelant-
mobilizable is difficult to fully define, but it most likely includes a labile lead compart-
ment within bone as well as in soft tissues. Support for this view includes: 1) the age
dependency of chelatable lead, but not lead in blood or soft tissues; 2) evidence of removal
of bone lead in chelation studies with experimental animals; 3) i_n vitro studies of1 lead
mobilization in bone organ explants under closely defined conditions; 4) tracer modelling
estimates in human subjects; and 5) the complex nonlinear relationship of blood lead and lead
intake through various media. Data for children and adults showing a logarithmic relationship
of chelatable lead to bloodr,l"ead and the phenomenon of "rebound" in blood lead elevation after
chelation therapy regimens (without obvious external re-exposure) offer further support.
10.8.2.2.4 Animal studies. Animal studies have been of help in sorting out some of the rela-
tionships of lead exposure to i_n vivo distribution of the element, particularly the impact of
skeletal lead on whole body retention. In rats, lead administration results in an initial
increase in soft tissues, followed by loss from soft tissue via excretion and transfer to
bone. Lead distribution appears to be relatively independent of dose. Other studies have
shown that lead loss from organs follows first-order kinetics except for bone, and the skele-
tal system in rats and mice is the kinetically rate-limiting step in whole-body lead clear-
ance.
The neonatal animal seems to retain proportionally higher levels of tissue lead compared
to the adult and manifests slow decay of brain lead levels while showing a significant decline
over time in other tissues. This appears to be the result of enhanced lead entry to the brain
because of a poorly developed brain barrier system as well as enhanced body retention of lead
by young animals.
The effects of such changes'as metabolic stress and nutritional status on body redistri-
bution of lead have been noted. Lactating mice, for example, are known to demonstrate tissue
redistribution of lead, specifically bone lead resorption with subsequent transfer of both
lead and calcium from mother to pups.
10.8.3 Lead Excretion and Retention in Humans and Animals
10.8.3.1 Human Studies. Dietary lead in humans and animals that is net absorbed passes
through the gastrointestinal tract and is eliminated with feces, as is the fraction of air
lead that is swallowed and not absorbed. Lead entering the bloodstream and not retained is
excreted through the renal and GI tracts, the latter via biliary clearance. The amounts
excreted through these routes are a function of such factors as species, age, and exposure
characteristics.
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Based upon the human metabolic balance data and isotope excretion findings of various
investigators, it appears that short-term lead excretion in adult humans amounts to 50-60 per-
cent of the absorbed fraction, with the balance moving primarily to bone and some fraction
(approximately half) of this stored amount eventually being excreted. This overall retention
figure of 25 percent necessarily assumes that isotope clearance reflects that for body lead in
all compartments. The rapidly excreted fraction has a biological half-time of 20-25 days,
similar to that for lead removal from blood. This similarity indicates a steady rate of lead
clearance from the body. In terms of partitioning of excreted lead between urine and bile,
one study indicates that the biliary clearance is about 50 percent-that of renal clearance.
Lead is accumulated in the human body with age, mainly in bone, up to around 60 years of
age, when a decrease occurs with changes in intake as well as in bone mineral metabolism. As
noted earlier, the total amount of lead in long-term retention can approach 200 mg, and even
much higher in the case of occupational exposure. This corresponds to a lifetime average
retention rate of 9-10 pg Pg/day. Within shorter time frames, however, retention will vary
considerably due to such factors as development, disruption in the individuals' equilibrium
with lead intake, and the onset of such states as osteoporosis.
The age dependency of lead retention/excretion in humans has not been well studied, but
most of the available information indicates that children, particularly infants, retain a sig-
nificantly higher amount of lead. While autopsy data indicate that pediatric subjects at iso-
lated points in time actually have a lower fraction of body lead lodged in bone, a full under-
standing of longer-term retention over childhood must consider the exponential growth rate oc-
curring in a child's skeletal system over the time period for which bone lead concentrations
have been gathered. This parameter itself represents a 40-fold mass increase. This signifi-
cant skeletal growth rate has an impact on an obvious question: if children take in more lead
on a body weight basis than adults, absorb and retain more lead than adults, and show only
modest elevations in blood lead compared to adults in the face of a more active skeletal sys-
tem, where does the lead go? A second factor is the assumption that blood lead in children
relates to body lead burden in the same quantitative fashion as in adults, an assumption that
remains to be adequately proven.
10.8.3.2 Animal Studies. In rats and other experimental animals, both urinary and fecal
excretion appear to be important routes of lead removal from the organism; the relative parti-
tioning between the two modes is species- and dose-dependent. With regard to species differ-
ences, biliary clearance of lead in the dog is but 2 percent of that for the rat, while such
excretion in the rabbit is 50 percent that of the rat.
Lead movement from laboratory animals to their offspring via milk constituents is a route
of excretion for the mother as well as an exposure route for the young. Comparative studies
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of lead retention in developing vs. adult animals, e.g., rats, mice, and non-human primates,
make it clear that retention is significantly greater in the young animal. These observations
support those studies showing greater lead retention in children. Some recent data indicate
that a differential retention of lead in young rats persists into the post-weaning period,
calculated as either uniform dosing or uniform exposure.
10.8.4 Interactions of Lead with Essential Metals and Other Factors
Toxic elements such as lead are affected in their toxicokinetic or toxicological behavior
by interactions with a variety of biochemical factors such as nutrients.
10.8.4.1 Human Studies. In humans the interactive behavior of lead and various nutritional
factors is expressed most significantly in young children, with such interactions occurring
against a backdrop of rather widespread deficiencies in a number of nutritional components.
Various surveys have indicated that deficiency in iron, calcium, zinc, and vitamins are wide-
spread among the pediatric population, particularly the poor. A number of reports have docu-
mented the association of lead absorption with suboptimal nutritional states for iron and cal-
cium, reduced intake being associated with increased lead absorption.
10.8.4.2 Animal Studies. Reports of lead-nutrient interactions in experimental animals have
generally described such relationships for a single nutrient, using relative absorption or
tissue retention in the animal to index the effect. Most of the recent data are for calcium,
iron, phosphorus, and vitamin D. Many studies have established that diminished dietary calci-
um is associated with increased blood and soft tissue lead content in such diverse species as
the rat, pig, horse, sheep, and domestic fowl. The increased body burden of lead arises from
both increased GI absorption and increased retention, indicating that the lead-calcium inter-
action operates at both the gut wall and within body compartments. Lead appears to traverse
the gut via both passive and active transfer, involves transport proteins normally operating
for calcium transport, and is taken up at the site of phosphorus, not calcium, absorption.
Iron deficiency is associated with an increase in lead of tissues and increased toxicity,
an effect which is expressed at the level of lead uptake by the gut wall. hi vitro studies
indicate an interaction through receptor binding competition at a common site. This probably
involves iron-binding proteins. Similarly, dietary phosphate deficiency enhances the extent
of lead retention and toxicity via increased uptake of lead at the gut wall, both lead and
phosphate being absorbed at the same site in the small intestine. Results of various studies
of the resorption of phosphate along with lead as one further mechanism of elevation of tissue
lead have not been conclusive. Since calcium plus phosphate retards lead absorption to a
greater degree than simply the sums of the interactions, it has been postulated that an insol-
uble complex of all these elements may be the basis of this retardation.
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Unlike the inverse relationship existing for calcium, iron, and phosphate vs. lead
uptake, vitamin D levels appear to be directly related to the rate of lead absorption from the
GI tract, since the vitamin stimulates the same region of the duodenum where lead is absorbed.
A number of other nutrient factors are known to have an interactive relationship with lead:
1. Increases in dietary lipids increase the extent of lead absorption, with the extent
of the increase being highest with polyunsaturates and lowest with saturated fats,
e.g., tristearin.
2. The interactive relationship of lead and dietary protein is not clearcut, and either
suboptimal or excess protein intake will increase lead absorption.
3. Certain milk components, particularly lactose, will greatly enhance lead absorption
in the nursing animal.
4. Zinc deficiency promotes lead absorption as does reduced dietary copper.
10.8.5 Interrelationships of Lead Exposure with Exposure Indicators and Tissue Lead Burdens
There are three issues involving lead toxicokinetics which evolve toward a full connec-
tion between lead exposure and its adverse effects: 1) the temporal characteristics of inter-
nal indices of lead exposure; 2) the biological aspects of the relationship of lead in vari-
ous media to various indicators in internal exposure; and 3) the relationship of various
internal indicators of exposure to target tissue lead burdens.
10.8.5.1 Tenporal Characteristics of Internal Indicators of Lead Exposure. The biological
half-time for newly absorbed lead in blood appears to be of the order of weeks or several
months, so that this medium reflects relatively recent exposure. If recent exposure is fairly
representative of exposure over a considerable period of time, e.g., exposure of lead workers,
then blood lead is more useful than for cases where exposure is intermittent or different
across time, as in the case of lead exposure of children. Accessible mineralized tissue, such
as shed teeth, extend the time frame back to years of exposure, since teeth accumulate lead
with age and as a function of the extent of exposure. Such measurements are, however, retro-
spective in nature, in.that identification of excessive exposure occurs after the fact and
thus limits the possibility of timely medical intervention, exposure abatement, or regulatory
policy concerned with ongoing control strategies.
Perhaps the most practical solution to the dilemma posed by both tooth and blood lead
analyses is J_n situ measurement of lead in teeth or bone during the time when active accumu-
lation occurs, e.g., 2-3-year-old children. Available data using X-ray fluorescence analysis
do suggest that such approaches are feasible and can be reconciled with such issues as accept-
able radiation hazard risk to subjects.
10.8.5.2 Biological Aspects of External Exposure-Internal Indicator Relationships. It is
clear from a reading of the literature that the relationship of lead in relevant media for
human exposure to blood lead is curvilinear when viewed over a relatively broad range of blood
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lead values. This implies that the unit change in blood lead per unit intake of lead in some
medium varies across this range of exposure, with comparatively smaller blood lead changes as
internal exposure increases.
Given our present knowledge, such a relationship cannot be taken to mean that body uptake
of lead is proportionately lower at higher exposure, for it may simply mean that blood lead
becomes an increasingly unreliable measure of target tissue lead burden with increasing expo-
sure. While the basis of the curvilinear relationship remains to be identified, available
animal data suggest that it does not reflect exposure-dependent absorption or excretion rates.
10.8.5.3 Internal Indicator-Tissue Lead Relationships. In living human subjects, it is not
possible to directly determine tissue lead burdens or how these relate to adverse effects in
target tissues; some- accessible indicator, e.g., lead in a medium such as blood or a biochem-
ical surrogate of lead such as EP, must be employed. While blood lead still remains the only
practical measure of excessive lead exposure and health risk, evidence continues to accumulate
that such an index has limitations in either reflecting tissue lead burdens or changes in such
tissues with changes in exposure.
At present, the measurement of plumburesis associated with challenge by a single dose of
a lead chelating agent such as CaNa2EDTA is considered the best indicator of the mobile,
potentially toxic fraction of body lead. Chelatable lead is logarithmically related to blood
lead, such that incremental increase in blood lead is associated with an increasingly larger
increment of mobilizable lead. The problems associated with this logarithmic relationship may
be seen in studies of children and lead workers in whom moderate elevation in blood lead can
disguise levels of mobile body lead. This reduces the margin of protection against severe
intoxication. The biological basis of the logarithmic chelatable lead-blood lead relationship
rests, in large measure, with the existence of a sizable bone lead compartment that is mobile
enough to undergo chelation removal and, hence, potentially mobile enough to move into target
ti ssues.
Studies of the relative mobility of chelatable lead over time indicate that, in former
lead workers, removal from exposure leads to a protracted washing out of lead (from bone
resorption of lead) to blood and tissues, with preservation of a bone burden amenable to sub-
sequent chelation. Studies with children are inconclusive, since the one investigation
directed to this end employed pediatric subjects who all underwent chelation therapy during
periods of severe lead poisoning. Animal studies demonstrate that changes in blocd lead with
increasing exposure do not agree with tissue uptake in a time-concordant fasion, nor does
decrease in blood lead with reduced exposure signal a similar decrease in target tissue, par-
ticularly in the brain of the developing organism.
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10.6.6 Metabolism of Lead Alkyls
The lower alkyl lead components used as gasoline additives, tetraethyl lead (TEL) and
tetramethyl lead (TML), may themselves poise a toxic risk to humans. In particular, there is
among children a problem of sniffing leaded gasoline.
10.8.6.1 Absorption of Lead Alkyls in Humans and Animals. Human volunteers inhaling labeled
TEL and TML show lung deposition rates for the lead alkyls of 37 and 51 percent, respectively,
values which are similar to those for particulate inorganic lead. Significant portions of
these deposited amounts were eventually absorbed. Respiratory absorption of organolead bound
to particulate matter has not been specifically studied as such.
While specific data for the GI absorption of lead alkyls in humans and animals are not
available, their close similarity to organotin compounds, which are- quantitatively absorbed,
would argue for extensive GI absorption. In contrast to inorganic lead salts, the lower lead
alkyls are extensively absorbed through the skin and animal data show lethal effects with per-
cutaneous uptake as the sole route of exposure.
10.8.6.2 Biotransformation and Tissue Distribution of Lead Alkyls. The lower lead alkyls TEL
and TML undergo monodealky1ation in the liver of mammal ian spheres'via- the P-450-dependent
mono-oxygenase enzyme system. Such transformation is very rapid. Further transformation
involves conversion to the dialky1 and inorganic lead forms, the latter accounting for the
effects on heme biosynthesis and erythropoiesis observed in alkyl lead intoxication. Alykl
lead is rapidly cleared from blood, shows a higher partitioning into plasma than inorganic
lead with triethyl lead clearance being more rapid than the methyl analog.
Tissue distribution of alkyl lead in humans and animals primarily involves the trialkyl
metabolites. Levels are highest in liver, followed by kidney, then brain. Of interest is the
fact that there are detectable amounts of trialkyl lead from autopsy samples of human brain
even in the absence of occupational exposure. In humans, there appear to be two tissue com-
partments for triethyl lead, having half-times of 35 and 100 days.
10.8.6.3 Excretion of Lead Alkyls. With alkyl lead exposure, excretion of lead through the
renal tract is the main route; of elimination. The chemical forms being excreted appear to be
species-dependent. In humans, trialkyl lead in workers chronically exposed to alkyl lead is a
minor component of urine lead, approximately 9 percent.
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I: Influence of calcium, phosphorus, and vitamin D on lead in blood and bone. J. Biol.
Chem. 132: 239-265. Reprinted (1981) in Nutr. Rev. 39: 374-377.
Sorrell, M.; Rosen, J. F. ; Roginsky, M. (1977) Interactions of lead, calcium, vitamin D, and
nutrition in lead-burdened children. Arch. Environ. Health 32: 160-164.
Steenhout, A.; Pourtois, M. (1981) Lead accumulation in teeth as a function of age with dif-
ferent exposures. Br. J. Ind. Med. 38: 297-303.
:obsvu. ' '•
Stephens, R. ; Waldron, H. A. (1975) The influence of milk and related dietary constituents on
lead metabolism. Food Cosmet. Toxicol: 13: 555-563.
Stevens, C. D. ; Feldhake, C. J.; Kehoe, R: A. (1960) Isolation of triethyllead ion from liver
after inhalation of tetraethyllead. J. Pharmacol. Exp. Ther. 128: 90-94.
Stowe, H. D. ; Goyer, R. A.; Krigman, M. M. ; Wilson, M. ; Cates, M. (1973) Experimental oral
lead toxicity in young dogs: clinical and morphologic effects. Arch. Pathol. 95:
106-116.
Stuik, E. J. (1974) Biological response of male and female volunteers to inorganic lead. Int.
Arch. Arbeitsmed. 33: 83-97.
Thompson, J. A. (1971) Balance between intake and output of lead in normal individuals. Br. J.
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Tola, S.; Hernberg, S. ; Asp, S. ; Nikkanen, J. (1973) Parameters indicative of absorption and
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134-141.
Trotter, M. ; Hixon, B, B. (1974) Sequential changes in weight, density, and percentage ash
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Willoughby, R. A.; Thirapatsakun, T. ; McSherry, B. J. (1972) Influence of rations low in
calcium and phosphorus on blood and tissue lead concentrations in the horse. Am. J. Vet.
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Neuropsychological comparison of children with different tooth-lead levels: preliminary
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Netherlands. Edinburgh, United Kingdom: CEP Consultants, Ltd.; pp. 553-556.
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poisoning caused by cleaning work in the aviation fuel tank. Jpn. J. Ind. Health 17:
223-235.
Yip, R. ; Norris, T. N. ; Anderson, A. S. (1981) Iron status of children with elevated blood
lead concentrations. J. Pediatr. (St. Louis) 98: 922-925.
Ziegler, E. E.; Edwards, B. B.; Jensen, R. L.; Mahaffey, K. R.; Fomon, S. J. (1978) Absorption
and retention of lead by infants. Pediatr. Res. 12: 29-34.
Zielhuis, R. L.; del Castilho, P.; Herber, R. F. M; Wibowo, A. A. E. (1978) Levels of lead and
other metals in human blood: suggestive relationships, determining factors. Environ.
Health Perspect. 25: 103-109.
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11. ASSESSMENT OF LEAD EXPOSURES AND ABSORPTION IN HUMAN POPULATIONS
11.1 INTRODUCTION
The purpose of this chapter is to.describe effects on internal body burdens of lead in
human populations resulting from exposure to lead in their environment. This chapter dis-
cusses changes in various internal exposure indices that follow changes in external lead
exposures. The main index of internal lead exposure focused on herein is blood lead
levels, although other indices, such as levels of lead in teeth and bone are also briefly dis-
cussed. As noted in Chapter 10, blood lead levels most closely reflect recent exposures to
environmental lead. On the other, hand, teeth and bone lead levels better reflect or index
cumulative exposures.
The following terms and definitions will be used in this chapter. Sources of lead are
those components of the environment (e.g., gasoline combustion, smelters) from which signifi-
cant quantities of lead are released into various environmental media of exposure. Environ-
mental media are direct routes by which humans become exposed to lead (e.g., air, soil, water,
dust). External exposures are levels at which lead is present in any or all of the environ-
mental media. Internal exposures are the amounts of lead present at various sites within the
body.
The present chapter is organizationally structured so as to achieve the following four
main objectives:
(1) Elucidation of patterns of absorbed lead in U.S. populations and identifi-
cation of important demographic covariates.
(2) Characterization of relationships between external and internal exposures
by exposure medium (air, food, water or dust).
(3) Identification of specific sources of lead which result in increased
internal exposure levels.
(4) Estimation of the relative contributions of various sources of lead in the
environment to total internal exposure.
The existing scientific literature must be examined in light of the investigators' own
objectives and the quality of the scientific investigations performed. Although all studies
need to be evaluated in regard to their methodology, the more quantitative studies are evalu-
ated here in greater depth. A discussion of the main types of methodological points con-
sidered in such evaluations is presented in Section 11.2.
After discussing methodological aspects, patterns of internal exposure to lead in human
populations are delineated in Section 11.3. This begins with a brief examination of the
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historical record of internal lead exposure in human populations. These data serve as a back-
drop against which recent U.S. levels can be contrasted and defines the relative magnitude of
external lead exposures in the past and presents The contrast is structured as follows: his-
torical data, recent data from populations thought to be isolated from urbanized cultures, and
then U.S. populations showing various degrees of.urbanization and industrialization.
Recent patterns of internal exposure in U.S. populations are discussed in greater detail.
Estimates of internal lead exposure and identification of demographic covariates are made.
Studies examining the recent past for evidence of change in levels in internal exposure are
presented; A discussion follows regarding exposure covariates of blood lead levels in urban
U.S.- children, who are at special risk for increased internal exposure.
The statistical treatment of distributions of blood lead levels in human populations is
the next topic discussed. As part of that discussion, the empirical characteristics of blood
lead distributions in well defined homogeneous populations are denoted. Important issues
addressed include the proper choice of estimators of central tendency and dispersion, estima-
tors of percentile values and the potential influence of errors in measurement on statistical
estimation involving blooc! lead data.
Section 11.4- focuses on general relationships between external exposures a^d levels of
internal exposure. The distribution of lead in man is diagramatically depicted by the compo-
nent, model shown in Figure 1. Of particular importance for this document is the relationship
between lead in air and lead in blood. If lead in air were the only medium of exposure, then
the interpretation of a statistical relationship between lead in air and lead in blood would
.be relatively simple. However, this is not the case. Lead is present in a number of environ-
mental media, as described in Chapter 7 and summarized in Figure 11-1. There are relation-
ships between lead levels in air and lead concentrations in food, soil, dust and water. As
shown in Chapters 6, 7 and 8, lead emitted into the atmosphere ultimately comes back to con-
taminate the earth. However, only limited data are currently available that provide a quan-
titative estimate of the magnitude of this secondary lead exposure. The implication is that
an analysis involving estimated lead levels in all environmental media may prodjce an under-
estimate of the relationship between lead in blood and lead in air.
The discussion of relationships between external exposure and internal absorption com-
mences with air lead exposures. Both experimental and epidemiological studies are discussed.
Several studies are identified as being of most importance in determining the quantitative
relationship between lead in blood and lead in air. The shape of the relationship between
blood lead and air lead is of particular interest and importance.
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AUTO
EMISSIONS
INDUSTRIAL
EMISSIONS
CRUSTAL
WEATHERING
LIVER
KIDNEY
" S \
FECES URINE
SOFT
TISSUE
BONES
BLOOD
MAN
FOOD
PLANTS
DUSTS
INHALED
AIR
DRINKING
WATER
ANIMALS
AMBIENT
AIR
SOIL
SURFACE AND
GROUND WATER
Figure 11-1. Pathways of lead from the environment to man.
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After discussion of air lead vs. blood lead relationships, the chapter next discusses the
relationship of blood lead to atmospheric lead found in other environmental media. Section
11.5 describes studies of specific lead exposure situations useful in identifying specific
environmental sources of lead that contribute to elevated body burdens of lead. The chapter
concludes with a summary of key information and conclusions derived from the scientific evi-
dence reviewed.
11.2 METHODOLOGICAL CONSIDERATIONS
11.2.1 Analytical Problems
Internal lead exposure levels in human populations have been estimated by analyses of a
variety of biological tissue matrices (e.g., blood, teeth, bone, and hair). Lead levels in
each of these matrices have particular biological meanings with regard to external exposure
status; these relationships are discussed in Chapter 10. The principal internal exposure
index discussed in this chapter is blood lead concentration. Blood lead concentrations
are most reflective of recent exposure to lead and bear a consistent relationship to levels of
lead in the external environment if the latter have been stable, Blood lead "levels are vari-
ously reported as pg/100 g, pg/100 ml, jjg/dl , ppm, ppb, and jjm/1. The first four measures are
roughly equivalent, whereas ppb values are simply divisible by 1000 to be equivalent. Actual-
ly there is a small but not meaningful difference in blood lead levels reported on a per
volume vs. per weight difference. The difference results from the density of blood being
slightly greater than 1 g/ml. For the purposes of this chapter, data reported on a weight cr
volume basis are considered equal. On the other hand, blood lead data reported on a pmo1/1
basis must be multiplied by 20.72 to get the equivalent pg/dl value. Data reported originally
as pmol/1 in studies reviewed here are converted to pg/dl in subsequent sections of this
chapter.
As discussed in Chapter 9, the measurement of lead in blood has been accomplished via a
succession of analytical procedures over the years. The first reliable analytical methods
available were wet chemistry procedures that have been succeeded by increasingly automated in-
strumental procedures. With these changes in technology there has been increasing recognition
of the importance of controlling for contamination in the sampling and analytical procedures.
These advances, as well as institution of external quality control programs, have resulted in
markedly improved analytical results. Data summarized in Chapter 9 show that a generalized
improvement in analytical results across many laboratories occurred during Fede-al Fiscal
Years 1977 to 1979. No futher marked improvement was seen during Federal Fiscal Years 1979 to
1981.
As difficult as getting accurate blood lead determinations is, the achievement of accu-
rate lead isotopic determinations is even more difficult. Experience gained from the isotonic
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lead experiment (ILE) in Italy (reviewed in detail in Section 11.5.1.1.1) has indicated that
extremely aggressive quality control and contamination control programs must be implemented to
achieve acceptable results. With proper procedures, meaningful differences on the order of a
single nanogram are achievable.
11,2.2 Statistical Approaches
Many studies summarize the distribution of lead levels in- humans. These studies usually
report measures of central tendency (means) and dispersion (variances). In this chapter, the
term "mean" refers to the arithmetic mean unless stated otherwise. This measure is always an
estimate of the average value, but it estimates the center of the distribution (50th percen-
tile) only for symmetric distributions. Many authors provide geometric means, which estimate
the center of the distribution if the distribution is lognormal. Geometric means are influ-
enced less by unusually lerge values than are arithmetic means. A complete discussion of the
lognormal distribution is given by Aitchison- and :Brown (1966), including formulas for conver-
ting from arithmetic to geometric means.
Most studies also give sample variances" c"r standard deviations in addition to. the means.
If geometric means are given, then the correspond! ng measure of dispersion is the geometric
standard deviation. Aitchison and Brown (1966) give formulas for the geometric stardard devi-
ation and, also, explain how to estimate percentiles and construct confidence intervals. All
of the measures of dispersion actually include three sources of variation: population varia-
tion, measurement variation and variation due to sampling error. Values for these components
are needed in order to evaluate a study correctly.
A separate issue is the form of the distribution of blood lead values. Although the nor-
mal and lognorrral distributions are commonly used, there are many other possible distribu-
tions. The form is important for two reasons: 1) it determines which is more appropriate,
the arithmetic or geometric mean, and 2) it determines estimates of the fraction of a popula-
tion exceeding given internal lead levels under various external exposures. Both of these
questions arise in the discussion of the distribution of hunan blood lead levels.
Many studies attempt to relate blood lead levels to an estimate of dose such as lead
levels in air. Standard regression techniques should be used with caution, since they assume
that the dose variable is measured without error. The dose variable is an estimate of the
actual lead intake and has inherent inaccuracies. As a result, the slopes tend to be under-
estimated; however, it is extremely difficult to quantify the actual amount of this bias.
Multiple regression analyses have additional problems. Many of the covariates that measure
external exposures art highly correlated with each other. For example, much of the soil lead
and house dust lead comes from the air. The exact effect of such high correlations with each
other on the regression coefficients is not clear.
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11.3 LEAD IN HUMAN POPULATIONS
11.3.1 Introduction
This section is designed to provide insight into current levels of lead absorption in the
U.S. and other countries, and how they differ from "natural" levels, to examine the influence
of demographic factors, and to describe the degree of internal exposure in selected population
subgroups. This section will also examine time trend studies of blood lead levels.
11.3.2 Ancient and Remote Populations
A question of major interest in understanding environmental pollutants is the extent to
which current ambient exposures exceed background levels.. -Because lead is a naturally occur-
ring element it can be surmised that some level has been and will always be present in the
human body; the question of interest is what is the difference in the levels of current sub-
groups of the United States population from those "natural" levels. Information regarding this
issue has been developed from studies of populations that lived in the past and populations
that currently live in remote areas far from the influence of industrial and urban lead ex-
posures.
Man has used lead since antiquity for a variety of purposes. These uses have afforded
the opportunity for some segments of the human population to be exposed to lead and subse-
quently absorb it into the body. Because lead accumulates over a lifetime in bones and teeth
and because bones and teeth stay intact for extremely long times, it is possible to estimate
the extent to which populations in the past have been exposed to lead.
Because of the problems of scarcity of sampl es""arTd little knowledge of how representative
the samples are of conditions at the time, the data from these studies provide only rough es-
timates of the extent of absorption. Further complicating the interpretation of these data
are debates over proper analytical procedures and the question of whether skeletons and teeth
pick up or release lead from or to the soil in which.they are interred.
Despite these difficulties, several studies provide data by which to estimate internal
\
exposure patterns among ancient populations, and some studies have included data from both
past and current populations for comparisons. Figure 11-2, which is adapted from Angle (1982)
displays a historical view of the estimated lead usage and data from ancient bone and teeth
lead levels. There is a reasonably good fit. There appears to be an increase in both lead
usage and absorption over the time span covered. - Specifics of these studies of bone ard teeth
will be presented in Section 11.3.2.1. In contrast to the study of ancient populations using
bone and teeth lead levels, several studies have looked at the issue of lead contamination
from the perspective of comparing current remote and urbanized populations. These studies
have used blood lead levels as an indicator and found mean blood concentrations in remote
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6
o
~
O
PERU
EGYPT
NUBIA
DENMARK
BRITAIN-ROMAN,
ANGLO SAXON
U.S.
BRITAIN
104
WORLDWIDE LEAD
PRODUCTION
2 10s
Z
o
u
D
Q
O
oe
o.
D
<
111
10"
10s
10
101
USE OF
SILVER COINS,
m
NEW
WORLD
SILVER
DEPLETION OF
ROMAN MINES
DOMINANCE OF
ATHENS ROME
LEAD CONCENTRATION
IN BONES
5000 4500 4000 3500 3000 2500 2000 1500 1000 500 PRESENT
YEARS BEFORE PRESENT
Figure 11-2. Estimate of world-wide lead production and lead concentrations
in bones (/jg/gm) from 5500 years before present to the present time.
Source: Adapted from Angle and Mclntire (1982).
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populations between 1 and 5 pg/dl, which is an order of magnitude below current U.S. urban
population means. These studies are presented in detail in Section 11.3.2.2.
11.3.2.1 Ancient Populations. Table 11-1 presents summaries of several studies that analyzed
bones and teeth to yield approximate estimates cf lead absorption in the past. Some of these
studies also analyzed contemporary current samples so that a comparison between past a^d pre-
sent could be made.
Samples from the Sudan (ancient Nubians) were collected fron several different periods
(Grandjean et a 1., 1978). The oldest sample (3300-2900 B.C.) averaged 0.6 pg/g for bone and
0.9 pg/g for teeth. Data from the later time of 1650-1350 B.C. show a substantial increase in
absorbed lead. Comparison of even the most recent ancient samples with a current Danish sam-
ple show a 4- to 8-fold increase over time.
Similar data were also obtained from Peruvian and Pennsylvania samples (Becker et al.,
1968). The Peruvian and Pennsylvania samples were approximately from the same era (^1200-1400
A.D..). Little lead was used in these cultures as reflected by chemical analyses of bone lead
content. The values were less than 5 pg/g for both samples. In contrast, modern samples from
Syracuse, New York, ranged from 5 to 110 pg/g. ¦ -
Fosse and Wesenberg (1981) reported a>study of Norwegian samples from several eras. The
oldest material was significantly lower in lead than modern samples. Ericso.net al. (1979)
also analyzed bone specimens from ancient Peruvians. Samples from 4500-3000 years ago to
about 1400 years ago were reasonably constant (<0.2 pg/g).
Aufderheide et al. (1981) report a study of 16 skeletons from colonial America. Two
social groups, identified as plantation proprietors' and laborers, had distinctly different
diet exposures to lead as shown by the analyses of the skeletal samples. The proprietor
group averaged 185 pg/g bone ash while the laborer group averaged 35 pg/g.
Shapiro et al. (1975) report a study that contrasts teeth lead content cf ancient popula-
tions with that of current remote populations and, also, with current urban populations. The
ancient Egyptian samples (1st and 2nd millenia) exhibited the lowest teeth lead levels, mean
of 9.7 pg/g. The more recent Peruvian Indian samples (12th Century) had similar levels
(13.6 pg/g). The contemporary Alaskan Eskimo samples had a mean of 55.0 mQ/Q while
Philadelphia samples had a mean of 188.3 pg/g. These data suggest an increasing pattern of
lead absorption from ancient populations to current remote and urban populations.
11.3.2.2 Remote Populations. Several studies have looked at the blood lead levels in current
remote populations (Piomelli et al., 1980; Poole and Srnythe, 1980). These studies are impor-
tant in defining the baseline level of internal lead exposures found in the world today.
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TABLE 11-1. STUDIES OF PAST EXPOSURES TO LEAD
Index of
Populati on
Age of
Exposure Method of
Lead
Studi ed
Sample
Used Analysis
Levels
Pb
|jg/g dry wt.
Nub i ans1
3300 B.C. to 750 A.D.
Teeth FASS
Bone Tooth
vs. Modern
(5000 yrs. old)
(circum- ASV
Danes
pupi 1
Nubi ans
denti ne)
A-group
3300 to 2900 B.C.
Bone (temporal)
0.6 0.9
C-group
2000 to 1600 B.C.
1.0 2.1
Pharoni c
1650 to 1350 B.C.
2.0 5.0
Meroti c,
X-group &
Chri 51ians
1 to 750 A.D.
1.2 3.2
Danes
Contemporary
5.5 25.7
Bone
pg/g
Ancient
500-600 yrs. old
Bone Arc emission
Peruv i ans2
(Tibia) spectroscopy
Peru <5
Ancient Penn-
500 yrs. old
(Femur)
sylvanian .
Penn. N.D.
Indi ans
Recent
Contemporary
Modern 110, 75,
Syracuse,NY
5, 45, 16
Tooth
Uvdal3
Buried from before
Teeth AAS
^g/g
1200 A.D. to 1804
(Whole
1. 22
Modern
Contemporary
teeth, but
4.12
Buskend County
values
Bryggen
•>
corrected for
1.81
(medieval Bergen)
enamel and
Norway
Contemporary
denti ne)
3.73
'Grandjean, P.; Nielsen, O.V.; Shapiro, I.M. (1978) Lead retention in ancient Nubian and
contemporary populations. J. Environ. Pathol. Toxicol. 2: 781-7B7.
2Becker, R.O.; Spadaro, J.A.; Berg, E.W. (1968) The trace elements in human bone. J. Bone
Jt. Surg. 50A: 326-334.
3Fosse, G.; Wesenberg, G.B.R. (1981) Lead, cadmium, zinc and copper in deciduous teeth of
Norwegian children in the pre-industrial age. Int. J. Environ. Stud. 16: 163-170.
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Piomelli et al. (1900) report a study of blood lead levels of natives in a remote (far
from industrialized regions) section of Nepal. Portable air samplers were used to determine
the air leaa exposure in the region. The lead content of the air samples proved to be less
than the detection limit, 0.004 |jg/m^. A later study by Davidson et al. (1981) from Nepal
confirmed the low air lead levels reported by Piomelli et al. (1980). Davidson et al. (1981)
3
found an average air lead concentration of 0.00086 pg/m .
Blood lead levels reported by Piomelli et al. (1980) for the Nepalese natives were low;
the geometric mean blood lead for this population was 3.4 pg/dl. Adult males had a geometric
mean of 3.8 pg/dl and adult females, 2.9 jjg/dl. Children had a geometric mean blood lead of
3.5 pg/dl. Only 10 of 103 individuals tested had a blood lead level greater than 10 pg/dl.
The blood samples, which were collected on filter paper discs, were analyzed by a modification
of the Delves Cup Atomic Absorption Spectrophotometric method. Stringent quality control pro-
cedures were followed for both the blood and air samples.
To put these Nepalese values in perspective, Piomelli et al. (1980) reported analyses of
blood samples collected and analyzed by the same methods from Manhattan, New York. New York
blood leaas averaged about lb pg/dl, a 5-fold increase over the Nepalese values.
Po.ole and 5nythe (-1980) reported another study of a remote population, using contam-
ination-free micro-blood sampling and chemical analysis techniques. They reported acceptable
precision at blood lead concentrations as low as 5 pg/dl, using spectrophotometry. One hun-
dred children were sampled from a remote area of Papua, New Guinea. Almost all of the chil-
dren cane from families engaging in subsistence agriculture. The children ranged from 7 to 10
years and included both sexes: • Blood lead levels ranged from 1 to 13 |jg/d1 with a mean of
5.2. Although the data appear to be somewhat skewed to the right, they are in good agreement
with those of Piomelli for Nepalase suDjects.
11.3.3 Levels of Lead and Demographic Covariates in U.S. Populations
11.3.3.1 The NHANES II Study. The National Center for Health Statistics has provided the
best currently available picture of blood lead levels among United States residents as part of
the second National Health and Nutrition Examination Study (NHANES II) conducted from February
1976 to February 1980 (Mahaffey et al., 1982; McDowell et al., 1981; Annest et al., 1982).
These are the first national estimates of lead levels in whole blood from a representative
sample of the non-instituticnalized U.S. civilian population aged 6 months to 74 years of age.
From a total of 27,801 persons identified through a stratified, multi-stage probability
cluster sample of households throughout the U.S., blood lead determinations were scheduled for
16,563 persons including all children ages 6 months to 6 years, and one-half of all persons
ages 7 to 74. Sampling was scheduled in 64 sampling areas over the 4-year period according to
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a previously determined itinerary to maximize operational efficiency and response of partici-
pants. Because of the constraints of cold weather, the examination trailers traveled in the
moderate climate areas during the winter, and the more northern areas during the sumner
(McDowell et al., 1981).
All reported blood lead levels were based on samples collected by venipuncture. Blood
lead levels were determined by atomic absorption spectrophotometry using a modified Delves Cup
micro-method. Specimens were analyzed in duplicate, with both determinations done independ-
ently in the same analytical run. Quality control was maintained by two systerrs, a bench
system and a blind insertion of samples. If the NHANES II replicates differed by more than
7 pg/dl, the analysis was repeated for the specimen (about 0.3 percent were reanalyzed). If
the average of the replicate values of either "bench" or "blind" control specimens fell out-
side previously established 95 percent confidence limits, the entire run was repeated. The
estimated coefficient of variation for the "bench" quality control ranged from 7 to 15 percent
(Mahaffey et al., 1979).
The reported blood lead levels were based on the average of the replicates. Blood lead
levels and related data were reported as population estimates; findings for each person were
inflated by the reciprocal of selection probabilities, adjusted" rto- account for persons whc
were not examined and poststratified by race, sex and age. The final estimates closely
approximate the U.S. Bureau of Census estimates for the civilian non-institutionalized popula-
tion of the United States as of March 1, 1978, aged 1/2 to 74 years.
Participation rates varied across age categories; the highest non-response rate (51
percent) was for the youngest age group, 6 months through 5 years. Among medically examined
persons, those with missing blood lead values were randomly distributed by race, sex, degree
of urbanization and annual family income. These data are probably the best estimates now
available regarding the degree of lead absorption in the general United States population.'
Forthofer (1983) has studied the potential effects of non-response bias in the NHANES II
survey and found no large biases in the health variables. This was based on the excellent
agreement of the NHANES II examined data, which had a 27 percent non-response rate, with the
National Health Interview Survey data, which had a 4 percent non-response rate.
The national estimates presented below are based on 9,933 persons whose blood lead levels
ranged from 2.0 to 66.0 (jg/dl. The median blood lead for the entire U.S. population is 13.0
pg/dl. It is readily apparent that blacks have a higher blood lead level than whites (medians
for blacks and whites were 15.0 and 13.0 jjg/d-1, respectively).
Tables 11-2 through 11-4 display the observed distribution of measured blood lead levels
by race, sex and age. The possible influence of measurement error on the percent distribution
estimates is discussed in Section 11.3.5. Estimates of mean blood lead levels differ sub-
stantially with respect to age, race and sex. Blacks have higher levels than whites, the
PB11A2/B 11-11 7/29/63
678<
-------
PRELIMINARY DRAFT
TABLE 11-2. NHANES II BLOOD LEAD LEVELS OF PERSONS 6 MONTHS-74 YEARS,,WITH WEIGHILD ARITHMETIC MEAN, STANDARD ERROR OF THE
MIAN, WLIGHTID GEOMETRIC MEAN, MEDIAN, AND PI RCENT. DISTRIBUTION, BY RACE AND AGE, UNITED STATES, 1976-80
Race and age
Estimated
population
i n
thousands
Number
examined
Ar i th-
metic
Mean
Blood lead level Qjq/dl)
Standard
error of
the mean
Geometric
Mean
Less
than
Median 10
10-19
20-29
30-39
40+
All races
All ages ....
6 months-5 years
6-17 years . . .
18-74 years. . .
203,554
16,852
44,964
141,728
9,933
2,372
1,720
5,841
13.9
16.0
12. 5
14.2
0.24
0.42
0. 30
0.25
12.8
14.9
11. 7
13. 1
13.0
15.0
12.0
13.0
22. 1
12.2
27.6
21.2
Percent distribution
62.9
63. 3
64.8
62. 3
13.0
20. 5
7.1
14. 3
1.6
3.6
0.5
1.8
0. 3
0.4
0.4
Whi te
A11 ages ....
6 months-5 years
6-17 years . . .
18-74 years. . .
Black
All ages ....
6 months-5 years
6-17 years . . .
18-74 years. . .
174,528
13,641
37,530
123,357
23,853
2,584
6,529
14,740
8,369
1,8/6
1,424
5,069
1,332
419
263
650
13. 7
14.9
12. 1
14. 1
15. 7
20.9
14.8
15.5
0.24
12.6
13.0
23.3
62.8
12.2
1.5
0.3
0.43
14.0
14.0
14. 5
67. 5
16. 1
1.8
0.2
0. 30
11.3
11.0
30.4
63.4
b. 8
0.4
-
0.25
12.9
13.0
21.9
62. 3
13. 7
1.8
0.4
0.48
14.6
15.0
13.3
63. 7
20.0
2.3
0.6
0.61
19 6
20.0
2.5
45.4
39.9
10.2
2.0
0.53
14.0
14.0
12.8
70.9
15.6
0. 7
-
0.54
14.4
14.0
14. 7
62 9
19.6
2.0
0.9
At the midpoint of the survey, March 1, 1978.
''with lead determinations from blood specimens drawn by venipuncture,
includes date for races not shown separately.
^Numbers may not add to 100 percent due to rounding.
-------
PRE I IMINARY DRAFT
TABLE 11-3. NHANES II BLOOD ItAO LEVELS OK MALES 6 MONTHS-74 YIARS, WITH WEIGHTED ARITHMETIC MEAN, STANDARD ERR(3 OF THE
MEAN, WEIGHTED GEOMETRIC Mt AN, MEDIAN, AND PERCfNT D1STRIBUI ION, BY RACE AND AGE, UNITED SIATES, 19/6-80
Blood lpad level (|j(|/dl)
Race and age
Estimated
popu1 at ion
in
thousands
Number
exami ned
Ari th-
met ic
Menn
Standard
error of
the mean
Geometric
Mean
Median
1 PSS
than
10
10-19
20-29
30-39
40*
All racesC
Percent distribution
d
All ages
99,062
4,945
16. 1
0.26
15.0
15.0
10.4
65.4
20.8
2.8
0.5
6 months-5 years . . . .
8,621
1,247
10. 3
0.46
15. 1
15.0
110
63. 5
21.2
4.0
0.3
6-17 years
22,887
902
13.6
0. 32
12.8
13.0
19. 1
70. 1
10.2
0. 7
-
18"74 years
67,555
2,796
16.8
0.28
lb.8
16.0
7.6
64. 1
24.2
3.4
0.6
Whi te
All ages
85,112
4,153
15.8
0.27
14.7
15.0
11.3
66.0
19.6
2.6
0.4
6 months-5 years . . . .
6,910
969
15.2
0.4b
14.2
14.0
13.0
67.6
17.3
2.0
0. 1
6-17 years
19,060
753
13. 1
0.33
12.4
13.0
21.4
69.5
8.4
0. 7
-
18-74 years
59,142
2,431
16.6
0.29
15.6
16.0
8. 1
64.8
23. 3
3.3
0.6
Black
All ages
11,171
664
18. 3
0.52
17.3
1/.0
4.0
59.6
31.0
4.1
1.3
6 months-5 years . . . .
1,307
231
20. 7
0. 74
19.3
19.0
2.7
48.8
35. 1
11.1
2.4
6-17 years
3,272
129
lb. 0
0.62
15. 3
15.0
8.0
69.9
21. 1
1.0
-
18-74 years
6,592
304
19. 1
0. 70
18. 1
18.0
2. 3
56.4
34.9
4.5
1.8
aAt the midpoint of the survey, March 1, 1978.
bWith lead determinations from blood specimens drawn by venipuncture.
clncludes date for races not shown separately.
dNumbers may not add to 100 percent due to rounding.
-------
PRELIMINARY ORAIT
TABLE
11-4. NHANES
11 BLOOD LEAD
IEVFLS
OF FtMALfS 6
MONTHS-74
YFARS,
WITH WEIGHTED ARI THEME TIC MEAN,
STANDARD ERROR OF
THE MEAN, WEIGHTED GEOMETRIC
Mf AN,
MEDIAN, AND 1
PERCENT 01SIRIBUTION, BV RACE AND AGE,
UNITED STATES,
1976-80
-
Blood 1
pad level
(.[jq/dl)
Estimated
o
population
Ari th-
Standard
Less
-¦
ln a
Number ^
metic
error of
Geometri
c
than
Race and age
thousands
examined
Mean
the mean
Mean
Median 10
10-19
20-29
30-39
40+
All races'"
~
Percent
. distribution''
All ages
104,492
4,988
11.9
0.23
11.1
11.0
33. 3
60.5
5. 7
0.4
0.2
6 months-5 years ....
8,241
1,125
15.8
0.42
14.6
15.0
13.5
63.2
19.8
3.0
0.5
6-17 years
22,077
818
11.4
0.32
10.6
11.0
36.6
59.3
3.9
0.2
-
18-74 years
74,173
3,045
11.8
0.22
11.0
11.0
33.7
60.6
5.2
0.3
0.2
Whi te
All ages
89,417
4,216
11.7
0.23
10.9
11.0
34.8
59.6
5.0
0.4
0.2
6 months-5 years ....
6,732
907
14. 7
0.44
13. 7
14.0
16. 1
67. 3
14.8
1.6
0.2
6-17 years
18,470
671
11.0
0. 31
10.3
11.0
40.0
56.9
2.9
0.2
-
18-74 years
64,215
2,638
11. 7
0.23
10.9
11.0
34.6
59.9
5.0
0.4
0.2
Black
All ages
12,682
668
13.4
0.45
12.6
13.0
21.5
67.3
10.3
0. 7
0.1
6 months-5 years ....
1,277
188
21.0
0.69
19.8
20.0
2.2
41.6
45.3
9.2
1. 7
6-17 years
3,256
134
13.6
0.64
12.8
13.0
17.7
71.9
10.0
0.4
-
18-74 years
8,148
346
12. 7
0.44
12.0
12.0
24. 7
68. 1
7.2
-
-
At the midpoint of the survey, March 1, 1978.
''with lead determinations from blood specimens drawn by venipuncture.
cIncludes date for races not shown separately.
^Numbers may not add to 100 percent due to rounding.
-------
PRELIMINARY DRAFT
6-month to 5-year group is higher than the older age groups, and men are higher than women.
Overall, younger children show only a slight age effect, with 2- to 3-year-olds having slig.ht-
ly higher blood lead levels than older children or adults (see Figure 11-3).. In the 6-17 year
grouping there is a decreasing trend in lead levels with increasing age. Holding age constant,
there are significant race and sex differences; as age increases, the difference in mean blood
leads between males and females increases.
For adults 18-74 years, males have greater blood lead levels than females for both whites
and blacks. There is a significant relationship between age and blood lead, but it differs
for whites and blacks. Whites display increasing blood lead levels until 35-44 years of age
and then a decline, while blacks have increasing blood lead levels until 55-64.
This study showed a clear relationship between blood lead level and family income group.
For both blacks and whites, increasing family income is associated with lower blood lead level.
At the highest income level the difference betwee.n blacks and whites is the smallest, although
blacks still have significantly higher blood lead levels than whites. The racial difference
was greatest for the 6-month to 5-year age range.
The NHANES II blood lead data were also examined with respect to the degree of urbaniza-
tion at the place of residence. The three categories used were urban areas with population
greater than one million, urban areas with population less than one million and rural areas.
Geometric mean blood lead levels increased with degree of urbanization for all race-age groups
except for blacks 18-74 years of age (see Table 11-5). Most importantly, urban black children
aged 6 months to 5 years appeared to have distinctly higher mean blood lead levels than any
other population subgroup.
11.3.3.2 The Childhood Blood Lead Screening Programs. In addition to the nationwide picture
presented by the NHANES II (Annest et al., 1982) study regarding important demographic corre-
lates of blood lead levels, Billick et al. (1979, 1982) provide large scale analyses of blood
lead values in specific cities that also address this issue.
Billick et al. (1979) analyzed data from New York City blood lead screening programs from
1970 through 1976. . The. data include age in months, sex, race, residence expressed as health
district, screening information and blood lead values expressed in intervals of 10 mg/dl.
Only the venous blood lead data (178,588 values), clearly identified as coming from the first
screening of a given child, were used. All blood lead determinations were done by the same
laboratory. Table 11-6 presents the geometric means of the children's blood lead levels by
age, race and year of collection. The annual means were calculated from the four quarterly
means which were estimated by the method of Hasselblad et al. (1980).
PB11A2/B 11-15 7/29/83
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PRELIMINARY DRAFT
B lack
White
AGE, years
Figure 11-3. Geometric mean blood lead levels by race and age for younger children in
the NHAIMES II study. The data were furnished by the National Center of Health
Statistics.
PB11A2/B
11-16
68^<
7/29/83
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PRELIMINARY DRAFT
TABLE 11-5. WEIGHTED GEOMETRIC MEAN BLOOD LEAD LEVELS
FROM NHANES II SURVEY BY DEGREE OF URBANIZATION OF PLACE OF
RESIDENCE IN THE U.S. BY AGE AND RACE, UNITED STATES 1976-80
Degree of urbanization
Urban,
Urban,
Race and age
n
mi 11 ion
<1 mi 11i on
Rural
All races
Geometric mean (pg/dl)
All ages
14.0
(2,395)a
12.8 (3,869)
11. 9
(3,669)
6 months-5 years
16.8
(544)
15.3 (944)
13.1
(884)
6-17 years
13.1
(414)
11.7 (638)
1C.7
(668)
18-74 years
14. 1
(1,437)
12.9 (2,287)
12. 2
(2,117)
Whi tes
All ages
14.0
(1,767)
12.5 (3,144)
11.7
(3,458)
6 months-5 years
15.6
(358)
14.4 (699)
12.7
(819)
6-17 years
12. 7
(294)
11.4 (510)
10.5
(620)
18-74 years
14. 3
(1,115)
12.7 (1,935)
12.1
(2,019)
Blacks
All ages
14.4
(570)
14.7 (612)
14.4
(150)
6 months-5 years
20.9
(172)
19.3 (205)
, 16.4
(42)
6-17 years
14.6
(111)
13.6 (113)
12!9
(39).
18-74 years
13.9
(287)
14.7 (294)
14.9
(69)
aNumber with lead determinations from blood specimens drawn by venipuncture.
Source: Annest et al., 1982.
PB11A2/B
11-17
7/29/83
-------
TABLE 11-6. ANNUAL GEOMETRIC MEAN BLOOD LEAD LEVELS FROM THE NEW YORK BLOOD LEAD SCREENING STUDIES
OF BILLICK ET AL. (1979). ANNUAL GEOMETRIC MEANS ARF CALCULATED FROM QUARTERLY
GEOMETRIC MEANS ESTIMATED BY THE METHOD OF HASSELBLAD ET AL. (1980)
Ethnic group
Year
Geometric mean blood
lead level
, pq/100 ml
1-12 mo
13-24 mo
25-36 mo
37-48 mo
49-60 mo
61-72 mo
73- mo
All ages
Black
1970
25.2
28.9
30.1
28.3
27.8
26.4
25.9
27.5
1971
24.0
29.3
29.9
29.3
28.2
27.2
26. 5
27.7
1972
22.2
26.0
26.3
25.4
24.7
23.9
23.3
24.5
1973
22.9
26.6'
26.0
25.3
24.4
24.1
23.3
24.6
1974
22.0
25.5
25.4
24.3
23.4
21.8
21.9
23.4
1975
19.8
22.4
22.4
21.9
21.2
21.4
18.9
21.1
1976
16.9
20.0
20.6
20.2
19.5
18.2
18.4
19.1
Hi spanic
1970
20.8
23.8
24.5
24.7
23.8 .
23.6
' 23.0
¦*3.4
1971
19.9
22.6
24.6
24.4
23.9
23.4
23. 5
=23.1
1972
18.7
20.5
21.8
22.2
21.8
21.8
21.0
-21.1
1973
20.2
21.8
22.5
22.8
22.0
21.5
21.7
i21.8
1974
19.8
21.5
22.7
22.5
21.9
20.5
20.2
"21.3
1975
16.3
18. 7
19.9
20.1
19.8
19.2
17.2
°18. 7
1976
16.0
17.4
18.1
18.2
18.0
16.7
17.2
17.4
Whi te
1970
21.1
25.2
26.0
24.8
26.0
22.6
21.3
23.8
1971
22.5
22.7
22.7
23. 5
21.6
21.3
19. 5
21. 9
1972
20.1
21.6
20.7
20.8
21.0
20.2
17.3
20.2
1973
21.5
21.8
21. 7
20.2
21.3
20. 7
18.4
20.8
1974
20.4
21. 7
21.3
21.1
20.6
19. 5
17.3
20.2
1975
19.3
17.9
16.1
18.5
16.8
15.4
15.9
17. 1
1976
15.2
18.2
17.1
16.6
16.2
15.9
8.8
15.1
-------
PRELIMINARY DRAFT
All racial/ethnic groups show an increase in geometric mean blood level with age for the
first two years and a general decrease' in' the' older age groups. Figure 11-4 shows the trends
for all years (1970-1976) combined.
The childhood screening data described by Billick et al. (1979) show higher geometric
mean blood lead values for blacks than for Hispanics or for whites. Table 11-6 also presents
these geometric means for the three racial/ethnic groups for seven years. Using the method of
Hasselblad et al. (1980), the estimated geometric standard deviations were 1.41, 1.42 and 1.42
for blacks, Hispanics and whites, respectively.
11.3.4 Time Trends
In the past few years a number of reports have appeared that examined trends in blood
lead levels during the 1970's. In several of these reports some environmental exposure esti-
mates are available.
11.3.4.1 Time Trends in the Childhood Lead Poisoning Screening Programs. Billick and col -
leagues have analyzed the results of blood lead screening programs conducted by the City of
New York (Billick et al., 1979; Billick 1982). Most details regarding this data set were al-
ready described, but Table 11-7 summarizes .relevant methodologic information for these
analyser and for analyses done on a similar data base from Chicago, Illinois. The discussion
of the New York data below is limited to an exposition of the time trend in blood lead levels
from 1970 to 1977.
Geometric mean blood lead levels decreased for all three racial groups and for almost all
age groups in the period 1970-76 (Table 11-6). Table 11-8 shows that the downward trend
covers the entire range of the frequency distribution of blood lead levels. The decline in
blood lead levels showed seasonal variability, but the decrease in time was consistent for
each season. The 1977 data were supplied, to EPA by Dr. Billick.
In addition to this time trend observed in New York City, Billick (1982) examined similar
data from Chicago and Louisville. The Chicago data set was much more complete than the Louis-
ville one, and was much more methodologically consistent. Therefore, only the Chicago data
will be discussed here. The lead poisoning screening program in Chicago may be the longest
continuous program in the United States. Data used in this report covered the years 1967-1980.
Because the data set was so large, only a 1 in 30 sample of laboratory records was coded for
statistical analysis (similar to procedures used for New York described above).
The blood lead data for Chicago contains samples that may be repeats, confirmatory analy-
ses, or even samples collected during treatment, as well as initial screening samples. This
is a major difference from the New York City data, which had initial screening values only.
PB11A2/B
11-19
7/29/83
-------
PRELIMINARY DRAFT
30
25
3 20
01
a.
C/3
—I
HI
>
HI
-• 15
Q
O
o
—I
CQ
2
a io
5
o
1 2 3 4 5 6 7
AGE, years
Figure 11-4. Geometric mean blood lead values by race and age for younger children
in the New York City screening program (1970-1976).
G Blacks
O Whites
A Hispanics
PB11A2/B
11-20
68? <
7/29/83
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PRELIMINARY DRAFT
TABLE 11-7. CHARACTERISTICS OF CHILDHOOD LEAD POISONING SCREENING OATA
New York Chicago
Time period
1970 - 1979
1967 - 1980 ,(QTR 2)
Sampling technique
Venous
Venous
Analytic technique
AAS
(Hasel method)
AAS
(Hasel method)
Laboratory
In house
In house
Screening status
Avai1able/unknown
Unavai1able
Race classification
and total number of
samples used in
analysi s*
Unknown 69,658
White 5,922
Black 51,210
Hispanic 41,364
Other 4,398
TOTAL 172,552
Nonblack 6,459
Black 20,353
TOTAL 26,812
Raw data
Decade grouped
Ungrouped
Gasoline data
Tri-state (NY, NJ, CT)
1970 - 1979
SMSA 1974 - 1979
SMSA
*New York data set only includes first screens while Chicago includes also
confirmatory and repeat samples.
TABLE 11-8. DISTRIBUTION OF BLOOD LEAD LEVELS FOR 13 TO 48
MONTH OLD BLACKS BY SEASCN AND YEAR* FOR NEW YORK SCREENING DATA
Year
<15pg/dl
January - March
Percent
15 to 34|jg/dl
>34^g/dl
July - September
Percent
<15|jg/dl 15 to 34pg/dl
> 34(jg/d 1
1970
(insufficient sample
size)
3.4 54.7
42.0
1971
3.8
69. 5
26.7
1.3 56.0
42. 7
1972
4.4
76.1 ,
19.5
4.3 72.2
23.4
1973
7. 3
80. 3
12.4
2.7 62.4
34. 9
1974
9.2
73.8
17.0
8.2 65.4
26.4
1975
11.1**
77.5**
11.4**
7.3** 81.3**
11.4**
1976
21.1
74.1
4.8
11.9 75.8
12. 3
1977
28.4
66.8
4.8
19.9 72.9
7.2
* data provided by I.H. Billick
**Percents estimated using interpolation assuming a lognormal distribution.
PB11A2/B 11-21 7/29/83
K88-c
-------
PRELIMINARY DRAFT
Chicago blood lead levels were all obtained on venous samples and were analyzed by one labora-
tory, the Division of Laboratories, Chicago Department of Health. Lead determinations were
done by atomic absorption. Racial composition was described in more detail than for New York,
but analysis showed there was no difference among the non-blacks, so they were pooled in the
final analysis.
Table. 11-7 displays important characteristics of the Chicago and New York screening pro-
grams, including the number of observations involved in these studies. From tables in the ap-
pendices of the report (Billick, 1982), specific data on geometric mean blood lead values,
race, sex and sampling data for both cities are available. Consistency of the data across
cities is depicted in Figure 11-5. The long-term trends are quite consistent, although the
seasonal peaks are somewhat less apparent.
11.3.4.2 Newark. Gause et al. (1977) present data from Newark, New Jersey, that reinforce
the findings of Billick and coworkers. Gause et al. studied the levels of blood lead among 5-
and 6-year-old children tested by the Newark Board of Education during the academic years
1973-74, 1974-75 and 1975-76. All Newark schools participated in all years. Participation
rates were 34, 33 and 37 percent of the eligible children for the three years, respectively.
Blood samples were collected by fingerstick onto filter paper. The samples were then
analyzed for lead by atomic absorption spectrophotometry. The authors point out that finger-
stick samples are more subject to contamination than venous samples; and that because erythro-
cyte protoporphyrin confirmation of blood lead values greater than 50 pg/dl was not done until
1974, data from earlier years may contain somewhat higher proportions of false positives than
later years.
Blood lead levels declined markedly during this 3-year period. In the three years covered
by the study the percentage of children with blood lead levels less than 30 pg/dl went from 42
percent for blacks in 1973-74 to 71 percent in 1975-76; similarly, the percentages went from
56 percent to 85 percent in whites. The percentage of high risk children (>49 pg/dl) dropped
from 9 to 1 percent in blacks and from 6 to 1 percent in whites during the study period.
Unfortunately, no companion analysis was presented regarding concurrent trends in en-
vironmental exposures. However, Foster et al. (1979) reported a study from Newark that exam-
ined the effectiveness of the city's housing deleading program, using the current blood lead
status of children who had earlier been identified as having confirmed elevated blood lead
levels; according to the deleading program, these children's homes should have been treated to
alleviate the lead problem. After intensive examination, the investigators found that 31 of
the 100 children studied had lead-related symptoms at the time of Foster's study. Examination
of the records of the program regarding the deleading activity indicated a serious lack of
compliance with the program requirements. Given the results of Foster's study, it seems un-
likely that the observed trend was caused by the deleading program.
PB11A2/B 11-22 7/29/83
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PRELIMINARY DRATT
60
40
E
8
"3b
3.
Q
<
a
o
o
2
a
E
t
2
o
iii
o
20
10
CHICAGO
NEW VORK
2 I'll.' Pi.
1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980
YEAR (Beginning Jan. 1)
Figure 11-5. Time dependence of blood lead for blacks, aged 24 to 35
months, in New York City and Chicago.
Source: Adapted from Billick (1982).
PB11A2/B
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11.3.4.3 Boston. Rabinowitz and Needleman (1982) report a study of umbilical cord blood lead
levels from 11,837 births between April 1979 and April 1981 in the Boston area. These repre-
sent 97 percent of the births occurring in a hospital serving a diverse population. Blood
samples were analyzed for lead by anodic stripping voltammetry after stringent quality control
procedures were used. External quality control checks were done by participation in the Blood
Lead Reference Program, conducted by the Centers for Disease Control. The average difference
between the investigators' results and the reference lab was 1.4 pg/dl.
The overall mean blood lead concentration was 6.56 ± 3.19 (standard deviation) with a
range from 0.0 to 37.0 pg/dl. A downward trend in umbilical cord blood lead levels (-0.89
pg/dl/yr) was noted over the two years of the study (see Figure 11-6).
11.3.4.4 NHANES II. Blood lead data from NHANES II (see Section 11.3.3.1) also show a signi-
ficant downward trend over time (Annest et a1., 1983). Predicted mean blood lead levels
dropped from 14.6 pg/dl in February 1976 to 9.2 pg/dl in February of 1980. Mean values from
these national data presented in 28 day intervals from February 1976 to February 1980 are dis-
played in Figure 11-7.
The decreases in average blood lead levels were found for both blacks and whites, all age
groups and both sexes. Further statistical analysis suggested that the decline was not en-
tirely due to season, income, geographic region or urban-rural differences. The analyses of
the quality control data showed no trend in the blind quality control data.
A review panel has examined this data, and a report of their findings is in Appendix 11-D.
The panel concluded that there was strong evidence of a downward trend during the period of
the study. The panel further stated that the magnitude of this drop could be estimated, and
that it appeared not only in the entire population, but in some major subgroups as well.
11.3.4.5 Other Studies. Oxley (1982) reported an English study that locks at the recent past
time trend in blood lead levels. Preemployment physicals conducted in 1967-69 and 1978-80
provided the subjects for the study. Blood samples were collected by venipuncture. Different
analytical procedures were used in the two surveys, but a comparison study showed that the
data from one procedure could be reliably adjusted to the other procedure. The geometric mean
blood lead levels declined from 20.2 to 16.6 pg/dl.
11.3.5 Distributional Aspects of Population Blood Lead Levels
The importance of the distribution form of blood lead levels was briefly discussed in
Section 11.2.3. The distribution form determines which measure of central tendency (arith-
metic mean, geometric mean, median) is most appropriate. It is even more important in esti-
mating percentiles in the upper tail of the distribution, an issue of much importance in esti-
mating percentages (or absolute numbers) of individuals in specific population groups likely
to be experiencing various lead exposure levels.
PB11A2/B 11-24 7/29/83
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PRELIMINARY DRAFT
12.0
5 10.0
8.0
6.0
4.0
Model Predicted
Actual Data
J
4179 779 10,79 1/B0 4/80
TIME, days
7/80
10/80
1/81
4/81
Figure 11-6. Modeled umbilical cord blood lead levels by date of sample collection
for infants in Boston.
Source: Rabinowitz and Needleman (1982).
PB11A2/B 11-25 7/P9/S3
692-c
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"O
CD
3>
f\j
ID Z
W i\>
A 01
o
<
O
O
O
_j
CD
LU
O
<
cc
U1
>
<
25
5 20
o>
3.
WINTER 1976
(FEB.)
WINTER 1977
(FEB.)
WINTER 1978
(FEB.)
FALL 1978
(OCT.)
WINTER 1979
FEB.
15 —
WINTER 1980
(FEB.
10 —
5 —
TO
O
TO
3>
10 15 20 25 30 35
CHRONOLOGICAL ORDER, 1 unit = 28 days
40
45
50
55
Figure 11-7. Average blood lead levels of U.S. population 6 months—74 years. United States,
February 1976—February 1980, based on dates of examination of NHANES II examinees with
blood lead determinations.
Source: Annest et al. (1983).
r\>
CO
u>
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PRELIMINARY DRAFT
Distribution fitting requires large numbers of samples taken from a relatively homo-
geneous population. A homogeneous population is one in which the distribution of values
remains constant when split into subpopulations. These subpopulations could be defined by
demographic factors such as race, age, sex, income, degree of urbanization, and by degree of
exposure. Since these factors always have some effect, a relatively homogeneous population
will be defined as one with minimal effects from any factors that contribute to differences in
blood lead levels.
Several authors have suggested that the distribution of blood lead levels for any rela-
tively homogeneous population closely follows a lognormal distribution (Yankel et al., 1977;
Tepper and Levin, 1975; Azar et al., 1975). Lognormality has been noted for other metals,
such as eoSr, l44Ce, Pu and Ti in various tissues of human populations (Cuddihy et al., 1979;
Schubert et al., 1967). Yankel et al. (1977), Tepper and Levin (1975) and Angle and Mclntire
(1979) all found their blood lead data to be lognormally distributed. Further analysis by EPA
of the Houston study of Johnson et al. (1974), the study of Azar et al. (1975) and the New
York children screening program reported by Billick et al. (1979) also demonstrated that a
lognormal distribution provided a good fit to the data.
The only nationwide survey of blood lead levels in the U.S. population is the NHANES II
Su'vey CA~nest et al., 1982). In order to obtain a relatively homogeneous subpopulation of
lower environmental exposure, the analysis was restricted to whites not living in an SMSA with
a family income greater than $6,000 per year, the poverty threshold for a family of four at
the midpoint of study as determined by the U.S. Bureau of Census. This subpopulation was
split into four subgroups based on age and sex. The summary statistics for these subgroups
are in Table 11-9.
Each of these four subpopulations were fitted to five different distributions: normal,,
lognormal, gamma, Weibull and Wald (Inverse Gaussian) as shown in Table 11-10. Standard chi-
square goodness-of-fit tests were computed after collapsing the tails to obtain an expected
cell size of five. The goodness-of-fit test and likelihood functions indicate that the log-
normal distribution provides a better fit than the normal, gamma or Weibull. A histogram and
the lognormal fit for each of the four subpopulations appear in Figure 11-8. The Wald distri-
bution is quite similar to the lognormal distribution and appears to provide almost as good a
fit. Table 11-10 also indicates that the lognormal distribution estimates the 99th percentile
as well as any other distribution.
Based on the examination of the NHANES II data, as well as the results of several other
papers, it appears that the lognormal distribution is the most appropriate for describing the
distribution blood lead levels in homogeneous populations with relatively constant exposure
1evels.
PB11A2/8 11-27 7/29/83
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The lognormal distribution appears to fit well across the entire range of the distribution,
including the right tail. It should be noted, however, that the data being fitted are the
result of both measurement variation and population variation. The measurement variation
alone does not follow a lognormal distribution, as was shown by Saltzman et al., 1983.
TABLE 11-9. SUMMARY OF UNWEIGHTED BLOOD LEAD LEVELS IN WHITES
NOT LIVING IN AN SMSA WITH FAMILY INCOME GREATER THAN $6,000
Unweighted Mean
Sample
Arith.
Geom.
Sample
99th
Ari th.
Geom.
Subgroup
Si ze
Mean
Mean
Medi an
%t lie
Std, Dev.
Std. Dev.
pg/dl
pg/dl
pg/dl
yg/di
pg/di
pg/dl
,age 1/2 to 6
752
13.7
12.9
13.0
32.0
5.03
1.43
age 6 to 18
573
11.3
10.6
10.0
24.0
4.34
1.46
age 18+,men
922
15.7
14.7
15. 0
35.8
5.95
1.44
age 18+,women
927
10.7
10.0
10. 0
23.0
4.14
1.46
It is obvious that even relatively homogeneous populations have considerable variation
among individuals. The estimation of this variation is important for determination of the
upper tail of the blood lead distribution, the group at highest risk. The NHANES 'II study
provides sufficent data to estimate this variation. In order to minimize the effects of loca-
tion, income, sex and age, an analysis of variance procedure was used to estimate the varia-
tion for several age-race groups. The variables just mentioned were used as main effects, and
the resulting mean square errors of the logarithms are in Table ll-l'l. The estimated
geometric standard deviations represent the estimated variances for subgroups with comparable
sex, age, income and place of residence. These are not necessarily representative of the
variances seen for specific subgroups described in the NHANES II study.
Analytical variation, which exists in any measurement of any kind, has an impact on the
bias and precision of statistical estimates. For this reason, it is important to estimate the
magnitude of variation. Analytical variation consists of both measurement variation (vari-
ation between measurements run at the same time) and variation created by analyzing samples at
different times (days). This kind of variation for blood lead determinations has been dis-
cussed by Lucas (1981).
The NHANES II survey is an example of a study with excellent quality control data. The
analytical variation was estimated specifically for this study by Annest et al. (1S83). The
analytical variation was estimated as the sum of components estimated from the high and low
PB11A2/B 11-28 7/29/83
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TABLE 11-10. SUMMARY OF FITS TO NHANES II BLOOD LEAD LEVELS
OF WHITES NOT LIVING IN AN SMSA, INCOME GREATER THAN $6,000,
FOR FIVE DIFFERENT TWO-PARAMETER DISTRIBUTIONS
Chi 1dren <6 years
deviation*
1 og-
at
Chi - square
D.F.
p-value
1i keli hood
99 Xtile
Normal
75. 52
8
0.0000
-2280.32
6. 61
Lognormal
14.75
10
0.1416
-2210.50
2. 57
Gamma
17.51
9
0.0413
-2216.51
4.68
Weibul1
66. 77
8
0.0000
-2271.57
5. 51
Wal d
15.71
10
0.1083
-2211.83
2.76
Children 6S years 517
' ~'
devi ati on*
log-
at
Chi-square
D.F.
p-value
1i keli hood
99 %t1le
Normal
39.58
6
0.0000
-1653.92
2 . 58
Lognormal
3.22
8
0.9197
-1607.70
-1.50
Gamma
4.88
7
0.6745
-1609.33
-0.64
Wei bul1
24.48
6
0.0004
-1641.35
1.72
Wald
2.77
8
0.9480
-1609.64
-1.30
Men S18 years
devi ati on*
log-
at
Chi-square
D.F. ¦
p-value
1i keli hood
99 %t i1e
Normal
156.98
10
0.0000
-2952.85
6 . 24
Lognormal
12.22
13
0.5098
-2854.04
1.51
Gamma
34.26
12
0.0006
-2864.79
4. 00
Weibul1
132.91
11
0.0000
-2934.14
4.8B
Wal d
14.42
13
0.3450
-2855.94
1.72
Men §18 years
deviation*
1 og-
at
Chi-square
D.F.
p-value
1i keli hood
99 %tile
Normal
66. 31
5
0.0000
-2631.67
2.6B
Lognormal
7.70
8
0.4632
-2552.12
-1.18
Gamma
11.28
7
0.1267
-2553.34
0.90
Weibul1
56.70
6
0.0000
-2611.78
1.73
Wald
10.26
8
0.2469
-2556.B8
-1.01
^observed
99th sample percentile
minus predicted 99th percentile
PB11A2/B
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PRELIMINARY DRAFT
BLOOD LEAD LEVELS (fjg/dl)
FOR 6 MONTHS TO 6 YEAR OLD CHILDREN
BLOOD LEAD LEVELS l^g/dl)
FOR 6 TO 17 YEAR OLD CHILDREN
7.5
15.5
23 5
31.5
7.5
15.5
23.5
31.5
BLOOD LEAD LEVELS l^g/dl)
FOR MEN >18 YEARS OLD
BLOOD LEAD LEVELS (Hg/dl)
FOR WOMEN ?1B YEARS OLD
Figure 11-8. Histograms of blood lead levels with fitted lognormal curves for the IMHANES II
study. All subgroups are white, non-SMSA residents with family incomes greater than $6000.
PB11A2/B
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69"
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PRELIMINARY DRAFT
TABLE 11-11. ESTIMATED MEAN SQUARE ERRORS RESULTING FROM
ANALYSIS OF VARIANCE ON VARIOUS SUBPOPULATIONS
OF THE NHANES II DATA USING UNWEIGHTED DATA
Age
Whi te,
Non SMSA
White, SMSA,
not central city
Whi te,
central city
Black,
central city
0.5 to 6
0.0916
0.0839
0.1074
0.0978
(1.35)*
(1.34)
(1.39)
(1.37)
6 to 18
0.0814
0.0724
0.0790
0.0691
(1.33)
(1-31)
(1.33)
(1.30)
18+, men
0.1155
0.0979
0.1127
0.1125
(1.40)
(1.37)
(1.40)
|
(1.40)
18+, women
0.1083
0.0977
0.0915
0.0824
(1-39)
(1.37)
(1.35)
(1.33)
Note: Mean square errors are based on the logarithm of the blood lead levels.
*Estimated geometric standard deviations are given in parentheses.
blind pool and from the replicate measurements in the study of Griffin et al. (1975). The
overall estimate of analytical variation for the NHANES II study was 0.02083.
Analytical variation causes a certain amount of misclassification when estimates of the
percent of individuals above or below a given threshold are made. This is because the true
value of a person's blood lead could be below the threshold, but the contribution from analy-
tical variation may push the observed value over the threshold. The reverse is also possible.
These two types of misclassifications do not necessarily balance each other.
Annest et al. (19B3) estimated this misclassification rate for several subpopulations in
the NHANES II data using a threshold value of 30 pg/dl. In general, the percent truly greater
than this threshold was approximately 24 percent less than the prevalence of blood lead levels
equal to or greater than 30 pg/dl, estimated from the weighted NHANES II data. This is less
than the values predicted by Lucas (1981) which were based on some earlier studies.
11.3.6 Exposure Covariates of Blood Lead Levels in Urban Children
Results obtained from the NHANES II study show that urban children generally have the
highest blood lead levels of any non-occupationally exposed population group. Furthermore,
black urban children have significantly higher blood lead levels than white urban children.
Several studies have been reported in the past few years that look at determinants of blood
PB11A2/B
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7/29/83
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PRELIMINARY DRAFT
lead levels in urban children (Stark et al., 1982; Charney et al., 1980; Hammond et a 1. , 1980;
Gilbert et al., 1979).
11.3.6.1 Stark Study. Stark et al. (1982) used a large scale lead screening program in New
Haven, Connecticut, during 1974-77 as a means of identifying study subjects. The screening
program had blood lead levels on 8289 children ages 1-72 months, that represented about 80
percent of the total city population in that age group. From this initial population, a much
smaller subset of children was identified for a detailed environmental exposure study. Using
the classifying criteria of residential stability and repeatable blood lead levels (multiple
measurements fell into one of three previously defined blood lead concentration categories), a
potential study population of 784 was identified. Change of residence following identifica-
tion and refusal to let sanitarians make inspections resulted in 407 children being dropped;
the final study population contained 377 children.
With the exception of dietary lead intake, each child's potential total lead exposure was
assessed. Information was obtained on lead in air, house dust, interior and exterior paint
and soil near and far from the home. A two percent sample of homes with children having
elevated lead levels had tap water lead levels assessed. No water lead levels above the
public health service standard of 50 ng/1 were found. Socioeconomic variables were also
obtai ned.
For all children in the study, micro blood samples were taken and analyzed for lead by
AAS with Delves cup attachment. Blood lead values were found to follow a lognormal distri-
bution. Study results were presented using geometric means and geometric standard deviation.
Among the various environmental measurements a number of significant correlation coefficients
were observed. However, air lead levels were independent of most of the other environmental
variables. Environmental levels of lead did not directly follow socioeconomic status. Most
of the children, however, were in the lower socioeconomic groups.
Multiple regression analyses were performed by Stark et al. (1982) and by EPA*. Stark
and coworkers derived a log-log model with R2 = 0.11, and no significant effects of race or
age were found. EPA fitted a linear exposure model in logarithmic form with results shown in
Table 11-12. Significant differences among age groups were noted, with considerably improved
predictability (R2 = 0.29, 0.30, 0.14 for ages 0-1, 2-3, and 4-7). Sex was not a significant
variable, but race equal black was significant at ages 4-7. Air lead did not significantly
improve the fit of the model when other covariates were available, particularly dust, soil,
paint and housekeeping quality. However, the range of air lead levels was small (0.7-1.3
pg/m3) and some of the inhalation effect may have been confounded with dust and soil inges-
tion. Seasonal variations were important at all ages.
*N0TE: The term EPA analyses refers to calculations done at EPA. A brief discussion of the
methods used is contained in Appendix 11-B; more detailed information is available at EPA
upon request.
PB11A2/B 11-32 7/29/83
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TABLE 11-12. MULTIPLE REGRESSION MODELS FOR BLOOD LEAD
OF CHILDREN IN NEW HAVEN, CONNECTICUT,
SEPTEMBER 1974 - FEBRUARY 1977
Regression Coefficients and Standard Errors
Age group, years ' 0-T-""" 2-3 4-7
Summer - Winter
6.33
±
2.11*
3.28
±
1. 30*
2.43
+
1.38*
Dust, pg/g
0.00402
±"
0". 00170*
'0.00182
±
0.00066*
0.00022
+
0.00077
Housekeeping Quality
4.38
±
2.02*
1.75
±
1.17
-1.61
+
1.12
Soil near house, pg/g
0.00223
±
0.00091*
-0.00016
t
0.00042
0.00060
+
0.00041
Soil at curb, pg/g
0.00230
±
0.00190
0.00203
±
0.00082*
0.00073
+
0.00079
Paint, child's bedroom
0.0189
±
0.0162
0.0312
±
0.0066*
0.0110
±
0.0064*
Paint outside house
-0.0023
t
0.0138
0.0200
±
0.0069*
0.0172
+
0.0067*
Paint quality
0.89
±
1. 71
3. 38
+
0. 96*
4.14
±
1.15*
Race = Black
2.16
±
2.05
0.07
+
1.09
5.81
+
1.00*
Re::d'jal Standard Deviations 0.1299 0.0646 0.1052
Multiple R2 0.289 0.300 0.143
Sample size (blood samples) 153 334 439
*Significant positive coefficient, one-tailed p <0.05
11.3.6.2 Charney Study. Charney et al. (1980) conducted a case control study of children 1.5
to 6 years of age with highly elevated and non-elevated blood lead levels. Cases and controls
were initially identified from the lead screening programs of two Rochester, New York, health
facilities. Cases were defined as.children who had at least two blood lead determinations
between 40 and 70 pg/dl and FEP values greater than 59 pg/dl during a 4-month period. Con-
trols were children who had blood lead levels equal to or less than 29 pg/dl and FEP equal to
or less than 59 High level children were selected first and low level children were
group matched on age, area of residence, and social class of the family. Home visits were
made to gain permission as well as to gather questionnaire and environmental data. Lead anal-
yses of the various environmental samples were done at several different laboratories. No
specification was provided regarding the analytical procedures followed.
The matching procedure worked well for age, mother's educational level and employment
status. There were more blacks in the high lead group as well as more Medicaid support. These
factors were then controlled in the analysis; no differences were noted between the high and
PB11A2/B 11-33 7/29/83
70(K
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PRELIMINARY DRAFT
low blood lead groups regarding residence on high traffic density streets (>10,000 vehicles/
day) or census tract of residence.
The two groups differed regarding mean house dust lead levels (1265 pg/sample for high
and 123 pg/sample for low). Median values also differed, 149 vs. 55 pg/sample. One-third of
tne children in the low blood lead group had house dust lead samples with more lead than those
found in any middle class home previously investigated:^.
There were considerably greater quantities of lead on the hands of the high blood lead
group compared with the low group (mean values were 49 pg/sample and 21 pg/sample, respective-
ly). Hand and house dust lead levels were correlated (r = 0.25) but the relationship was not
linear. At the low end of the house dust lead values, hand dust was always low but the con-
verse was not true: not every child exposed to high house dust lead had high hand dust levels.
In addition to hand and house dust lead,, other factors differentiated the high and low
blood lead groups. Although both groups had access to peeling paint in their homes (-^2/3),
paint lead concentrations exceeding 1 percent were found'more frequently in the high as oppo-
sed to the low group. Pica (as defined in Chapter Seven) was more prevalent in the high lead
group as opposed to the low lead group.
Since the data suggested a multifactorial contribution of lead, a multiple regression
analysis was undertaken. The results suggest that hand lead level, house dust lead level,
lead in outside soil, and history of pica are very important in explaining the observed vari-
ance in blood lead levels.
11.3.6.3 Hammond Study. Hammond et al. (1S80) conducted a study of Cincinnati children with
the dual purpose of determining whether inner city children with elevated blood lead levels
have elevated fecal lead and whether fecal lead correlates with lead-base paint hazard in the
home or traffic density as compared with blood lead.
Subjects were recruited primarily to have high blood lead levels. Some comparison chil-
dren with low blood lead levels were also identified. The three comparison children had to be
residentially stable so that their low blood lead levels were reflective of the lead intake of
their current environment. The subjects from the inner city were usually from families in
extremely depressed socio-economic circumstances.
Stool samples were collected on a daily basis for up to 3 weeks, then analyzed for lead.
2
Fecal lead levels were expressed both as mg/kg day and as mg/m day.
An environmental assessment was made at the home of each child. Paint lead exposure was
rated on a three-point scale (high, medium and low) based on paint lead level and integrity of
the painted wall. Air lead exposure was assessed by the point scale (high, medium and low)
based on traffic density, because there are no major point sources of lead in the Cincinnati
area.
PB11A2/B 11-34 7/29/83
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Blood samples were collected on an irregular basis but were taken sufficiently often to
havp at least one sample from a child from every house studied. The blood samples were ana-
lyzed for lead by two laboratories that had different histories of performance in the CDC pro-
ficiency testing program. All blood lead levels used in the statistical analysis were ad-
justed to a common base. Because of the variable number of fecal and blood lead levels, the
data were analyzed using a nested analysj s.i o,f, ya.riance.
The homes of the children were found to be distributed across the paint and traffic lead
exposure categories. Both fecal lead levels and blood lead levels were positively associated
with interior paint lead hazard. A marginal association between fecal lead levels and
exterior paint hazard was also obtained. Neither fecal lead or blood lead was found to be
associated with traffic density; the definition of the high traffic density category, however,
began at a low level of traffic flow (7500 cars/day).
Examination of fecal and blood lead levels by sex and race showed that black males had
the highest fecal lead excretion rates•followed -by white males and black females. White-fe-
males were only represented by two subjects, both of whom had high fecal lead excretion.
Blood lead levels were more influenced by race than by sex. The results suggested that chil-
dren in high and medium paint hazard homes (high = at least 1 surface >0.5 percent Pb, peeling
or loose) were probably ingesting paint in some form. This could not be confirmed, however,
by finding physical evidence in the stools.
Long term stool collection in a subset of 13 children allowed a more detailed examination
of the pattern of fecal lead excretion. Two patterns of elevated fecal lead excretion were
noted. The first was a persistent elevation compared with controls; the second was markedly
elevated occasional spikes against a normal background.
One family moved from a high hazard home to a low one during the course of the study.
This allowed a detailed examination of the speed of deleading of fecal and blood lead level.
The fecal levels decreased faster than the blood lead levels. The blood leads were still
elevated at the end of the collection.
11.3.6.4 Gilbert Study. Gilbert et al. (1979) studied a population of Hispanic youngsters in
Springfield, Massachusetts, in a case control study designed to compare the presence of
sources of lead in homes of lead poisoned children and appropriately matched controls. Cases
were defined as children having two consecutive blood lead levels greater than 50 jjg/dl. Con-
trols were children with blood lead levels less than or equal to 30 pg/dl who had no previous
history of lead intoxication and were not siblings of children with blood lead levels greater
than 30 pg/dl. Study participants had to be residential ly stable for at least 9 months and
not have moved into their current home from a lead contaminated one. All blood lead levels
were analyzed by Delves cup method of AAS. Cases and controls were matched by age (±3 months),
PB11A2/B 11-35 7/29/83
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PRELIMINARY DRAFT
sex and neighborhood area. The study population consisted of 30 lead intoxication cases and
30 control subjects.
Home visits were undertaken to gather interview information and conduct a home in-
spection. Painted surfaces were assessed for integrity of the surface and lead content. Lead
content was measured by X-ray fluorimetry. A surface was scored as positive if the lead con-
tent exceeded 1.2 mg/cm2. Drinking water lead was assessed for each of the cases and was
found to contain less than 50 pg/1, sufficiently low so as not to constitute a hazard. Tap
water samples were not collected in the homes of the controls. Soil samples were collected
from three sites in the yard and analyzed for lead by X-ray f 1 uorometry.
Cases and controls were compared on environmental lead exposures and interview data using
McNemar's test for pair samples. The odds ratio was calculated as an estimator of the rela-
tive risk on all comparisons. Statistically significant differences between cases and con-
trols were noted for lead in paint and the presence of loose paint. Large odds ratios (>10)
were obtained; there appeared to be little influence of age or sex on the odds ratios.
Significant differences between cases and controls were obtained for both intact and
loose paint by individual surfaces within specific living areas of the home. Surfaces acces-
sible to children were significantly associated with lead poisoning status while inaccessible
surfaces generally were not. Interestingly, the odds ratios tended to be larger for the in-
tact surface analysis than for the loose paint one.
Median paint lead levels in the homes of cases were substantially higher than those in
the homes of controls. The median paint lead for exterior surfaces in cases was about 16-20
mg/cm2 and about 10 mg/cm2 for interior surfaces. Control subjects lived in houses in which
the paint lead generally was less than 1.2 mg/cm2 except for some exterior surfaces.
Soil lead was significantly associated with lead poisoning; the median soil lead level
for homes of cases was 1430 pg/g, while the median soil lead level for control homes was
440 (jg/g.
11.4 STUDIES RELATING EXTERNAL DOSE TO INTERNAL EXPOSURE
The purpose of this section is to assess the importance of environmental exposures in
determining the level of lead in human populations. Of prime interest are those studies that
yield quantitative estimates of the relationship between air lead exposures and blood lead
levels. Related to this question is the evaluation of which environmental sources of airborne
lead play a significant role in determining the overall impact of air lead exposures on blood
lead levels.
A factor that complicates the analysis presented here is that lead does not remain sus-
pended in the atmosphere but rather falls to the ground, is incorporated into soil, dust, and
PB11A2/B
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PRELIMINARY DRAFT
water, and enters the food chain over time (see Figure 11-1). Since man is exposed to lead
from all of these media, as will be demonstrated below, studies that relate air lead levels to
blood lead levels (especially experimental exposure studies) may underestimate the overall
impact of airborne lead on blood lead levels. In observational studies, the effects of air
lead will thus be confounded with lead exposures from other pathways. The simultaneous pre-
sence of lead in multiple environmental media requires the use of multiple variable analysis
techniques or surrogate assessment of all other external exposures. Virtually no assessments
of simultaneous exposures to all media have been done.
Although no study is ever done perfectly, there are several key factors that are present
in good studies relating external exposure to internal exposure of lead:
(1) The study population is well-defined.
(2) There is a good measure of the exposure of each individual.
(3) The response variable (blood lead) is measured with adequate quality control,
preferably with replicates.
(4) The statistical analysis model is biologically plausible and is consistent with
the data.
(5) The important covariates are either controlled for or measured.
'f " - ' •
Even studies of considerable importance do not address all of these factors adequately.
We have selected as key studies (for discussion below) those which address enough of these
factors sufficiently well to establish meaningful relationships.
11.4.1 Air Studies
The studies emphasized in this section are those most relevant to answering the following
question: If there is moderate change in average ambient air lead concentrations due to
changes in environmental exposure (at or near existing EPA air lead standards), what changes
are expected in blood lead levels of individual adults and children in the population? Longi-
tudinal studies in which changes in blood lead can be .measured in single individuals as
responses to changes in air lead are discussed first. The cross-sectional relationship
between blood lead and air lead levels in an exposed population provides a useful but differ-
ent kind of information, since the population "snapshot" at some point in time does not direc-
tly measure changes in blood lead levels or responses to changes in air lead exposure. We
have also restricted consideration to those individuals without known excessive occupational
or personal exposures (except, perhaps, for some children in the Kellogg/Silver Valley study).
The previously published analyses of relevant studies have not agreed on a single form
for the relationship between air lead and blood lead. All of the experimental studies have at
least partial individual air lead exposure measures, as does the cross-sectional observational
PB11A2/B 11-37 7/29/83
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PRELIMINARY DRAFT
study of Azar et al. (197b) The 1974 Kellogg/Silver Valley study (Yankel et a 1., 1977) has
also been analyzed using several models. Other population cross-sectional studies have been
analyzed by Snee (1981). The most convenient method for summarizing these diverse studies and
their several analyses is by use of the blood lead-air lead slope (p), where p measures the
change in blood lead that is expected for a unit change in air lead. If determined for indi-
vidual subjects in a study population, this slope is denoted p.. If the fitted equation is
linear, then p or is the slope of the straight line relationship at any air lead level. If
the fitted relationship is nonlinear, then the slope of the relationship measures the expected
effect on blood lead of a small change in air lead at some given air lead value and thus will
be somewhat different at different air lead levels. It is necessary to compare the slopes of
the nonlinear relationships at the same value., of .air .lead or change in air lead. A discussion
of the linear, nonlinear and compartment models is in Appendix 11A-B.
Snee (1982b,c) has indicated that inclusion of additional sources of lead exposure im-
proves biological plausibility of the models. It is desirable that these sources be as spe-
cific to site, experiment and subject as possible.
11.4.1.1 The Griffin et al. Study. In two separate experiments conducted at the Clinton
Correctional Facility in 1971 and 1972, adult male prisoner volunteers were seqjestered in a
prison hospital unit and exposed to approximately constant levels of lead oxide (average
10.9 pg/m3 in the first study and 3.2 pg/m3 in the "second). Volunteers were exposed in an ex-
posure chamber to an artificially generated aerosol of submicron-sized particles of lead
dioxide. All volunteers were introduced into the chamber 2 weeks before the initiation of the
exposure; the lead exposures were scheduled to last 16 weeks, although the volunteers could
drop out whenever they wished. Twenty-four volunteers, including 6 controls, participated in
the 10.9 pg/rr3 exposure study. Not all volunteers completed the exposure regimen. Blood lead
levels were found to stabilize after approximately 12 weeks. Among 8 men exposed to 10.9
pg/rr3 for at least 60 days, a stabilized mean level of 34.5 ± 5.1 pg/dl blood was obtained, as
compared with an initial level of 19.4 ± 3.3 pg/dl. All but two of the 13 men exposed at 3.2
pg/m3 for at least 60 days showed increases and an overall stabilized level of 25.6 ± 3.9
pg/dl was found, compared with an initial level of 20.5 ± 4.4 |jg/dl. This represented an in-
crease of about 25 percent above the base level.
The aerosols used in this experiment were somewhat less complex chemically, as well as
somewhat smaller, than those found in the ambient environment. Griffin et al. (1S75),
however, pointed out that good agreement was achieved on the basis of the comparison o* their
observed blood lead levels with those predicted by Goldsmith and Hexter's (1967) equation;
that is, log^ blood lead = 1.265 + 0.2433 atmospheric air lead. The average diet con-
tent of lead was measured and blood lead levels were observed at 1- or 2-week intervals for
PB11A2/B
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PRELIMINARY DRAFT
several months. Eight subjects received the maximum 4-month exposure to 10.9 pg/m3; nine sub-
jects were exposed for 1 to 3 months. Six subjects had the maximum 4-month exposure to 3.2
pg/nr'1, and eight others had shorter exposures.
Compartnental models have been fitted to these data by 0'Flaherty et al. (1982) and by
EPA. The basis of these models is that the mass of lead in each of several distinct pools or
conpartments within the body changes according to a system of coupled first-order linear dif-
ferentia1 equations with constant fractional transfer rates (Batschelet et al., 1979; Rabino-
witz et al., 1976). Such a model predicts that when the lead intake changes from one constant
level to another, then the relationship between the mass of lead in each compartment and time
with constant intake has a single exponential term.
The subjects at 3.2 pg/m3 exhibited a smaller increase in blood lead, with corres-
pondingly less accurate estimates of the parameters. Several of the lead-exposed subjects
failed to show an.increase.
Figure 11-9 shows a graph of the blood lead.levels for the 10.9 pg/^3 exposure by length
of exposure. Each person's values are individually normalized, and then averaged across
PB11A2/B
0 10 20 30 40 50 60 70 SO 90 1 00 110 120
DAY OF EXPOSURE
Figure 11-9. Graph of the average normalized increase in biood lead for subjects exposed to
10.9 yg/m3 of lead in Griffin et al. study (19751.
11-39 7/29/83
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PRELIMINARY DRAFT
subjects for each time period. The smooth curve shows a fitted one-compartment model, assum-
ing pre-exposure equilibrium and constant lead intake during exposure.
EPA has reanalyzed these data using a two-compartment model for two reasons:
(1) Semi logarithmic plots of blood lead vs. time for most subjects showed a two-
component exponential decrease of blood lead during the postexposure or washout
phase of the experiments. Rabinowitz et al. (1977) show that at least two
.pools are necessary to model blood lead kinetics accurately. The first pool is
tentatively identified with blood and the most labile soft tissues. The second
pool probably includes soft tissues and labile bone pools.
(2) Kinetic models are needed to account for the subjects' lead burdens not being
in equilibrium at any phase of the experiments.
The pre-exposure decline in Figure 11-9 is apparently real and suggests a low pre-exposure
lead intake. The deviation from the fitted curve after about 50 days suggests a possible
change in lead intake at that time.
Previously published analyses have not used data for all 43 subjects, particularly for
the same six subjects (labeled 15 to 20 in both, experiments) who served as controls both
years. These subjects establish a baseline for non-inhalation exposures to lead, e.g., in
diet and water, and allow an independent assessment of within-subject variability over time.
EPA analyzed data for these subjects as well as-others'who received lead exposures of shorter
duration.
The estimated blood lead inhalation slope, p, was calculated for each individual subject
according to the formula:
(Change in intake, pg/day) x (mean residence time in blood, day)
p = 3
(Change in air exposure, pg/m ) x (Volume of distribution, dl)
The mean values of these parameters are given in Tables 11-13 through 11-15. The changes in
air exposure were 10.9 - 0.15 = 10.75 pg/m"^ for 1970-71 and 3.2 - 0.15 = 3.05 pg/m^ in 1971-
72. Paired sample t-tests of equal means were carried out for the six controls and five sub-
jects with exposure both years, and independent sample t-tests were carried out comparing the
remaining 12 subjects the first year and nine different subjects the next year. All standard
error estimates include within-subject parameter estimation uncertainties as well as between
subject differences. The following are observations.
(1) Non-inhalation lead intake of the control subjects varied substantially during the
second experiment at 3.2 pg/m^, with clear indication of low intake during the 14-day pre-
exposure period (net decrease of blood lead), see Figure 11-10. There was an increase in lead
intake (either equilibrium or net increase of blood lead) during the exposure period.
PB11A2/B 11-40 7/29/83
707•==
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PRELIMINARY DRAFT
KEY
~ Subject 15
A Subject 16
A Subject 17
Subject 18
O Subject 19
9 Subject 20
* -A. 16
40 60 80 100
EXPOSURE
140 160 180 200
POST-EXPOSURE
EXPOSURE
TIME, days
Figure 11-10. Control subjects in Griffin experiment at 3.2 Mg'm3-
PB11A/B
11-41
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708<
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PRH IMINARY DRAFT
TABLE 11-13. GRIFMN EXPERIMLNTS - SUBJECTS EXPOSED TO AIR LEAD BOTH YEARS
Change in Intake, Inhalation slo^e,
Subject Mean Residence Time.d. Post-Pre-exposure, pq/d* pg/dJ per jjg/m *
At 3.2 At 10.9 At 3.2 At 10.9 At 3.2 At 10.9 At 3.2 At 10.9
1
3
42.1 + 17.4
55.
2 ± 27.2
-4.4 ~ 13.8
-3.0
1 12.2
0.92
± 1.94
1.09
± 0.80
2
13
47.6 ± 21.4
38.4 > 14.5
3. 1 t 14. 1
3.8
± 14.6
3.95
~ 3.44
1.27
± 0. 79
3
14
48.0 ± 21.7
40.
1 i 15.8
3. 3 < 13. 1
11. 6
~ 13.4
2.50
± 2.20
1 -88
i 1.03
4
7
42.5 ± 17.6
50.
1 ± 22 5
12.0 t 14.2
5. 1
i 13.6
3.36
± 2.49
1.57
i 0.99
5
4 >
43.6 ± 18.2
35.
9 i 12.8
0.6 i 19.3
-9. 5
i 14.3
3.76
± 2.93
1.29
± 0.68
Mean 44.7 ! 8.7
Mean w/o
subject 1 at 3.2
*Assumed volume of blood pool is 75 dl.
43.
9 ± 9.4
2 9 i 7.2
1.6
± 7.1
2.90
3.39
~ 1.31
i 1.44
1.42
±."0.41
TARIf 11-14.
GRIFFIN EXPERIMENTS -
SUBJECTS EXPOSED
TO AIR LEAD BOTH YEARS
Subject
At 3.2
Mean Residence
At 3.2
T i me,d.
At 10.9
Change in Intake,
Post.-Pre-exposure, (iq/d*
At 3.? At lfi
1.9
At 3.
Inhalation sloge,
pg/d8 per pq/m *
2 At 10.
,9
15
28.6 ~ 10.4
38.3 i
21.8
18.6 t 11.3
-
1.76 i
1.17
-0. 16 ±
0.46
16
36.2 ± 14.6
35.2 ±
16.8
5.0 1 11.6
4.8 *
ll.fi
1.57 ±
1.31
0.14 ±
0.35
17
33.5 ~ 14.0
44.2 ±
20. 7
7.9*12.1
8.6 i
13.5
1.25 i
1.43
-0.7b ±
0.68
18
34.4 i 15.7
36.3 ±
18.2
-
2.1 t
12.1
0.67 ±
1. 11
0.09 ±
0.38
19
36.8 + 19.6
49.1 i
27.3
-
3.1 i
15.6
0.73 i
2.82
-0.2b i
0. 73
20
34.0 t 17 8
4 7 5 1
24.0
-
7.2 -
14 5
2.90 i
2.46
-0.29 ±
0. 70
Mean ± s
*Assumed
. e. m.
volume of
34.6 i 6.5
blood pool is /5 dP..
41.8 '
9 2 ¦
•10. b 1 7 9
2.4 t
6.6
1.48 i
0.84
-0.20 ±
0.27
-------
Sub ji
6
7
8
9
10
11
12
14
21
Mean
Mean
PRELIMINARY DRAFT
TABLE 11-15. GRIFFIN EXPIRI ML N r - SUBJECTS EXPOSED TO AIR LEAD ONE YEAR ONLY
Time, d.
At 3.2 (second year only)
Intake Change (ig7d.
S lope
49.4 ± 26.1
34.6 ± 11.9
38.0 ± 15.2
29.7 ±9.7
40.4 ± 16.9
37.5 ± 15.3
43.3 i 17.3
37.9 t 14.7
36.8 ± 15.6
3.9 ± 20.1
7.0 ± 15.6
9.4 ± 15.6
3.3 ± 14.8
5.7 ± 13.9
7.4 ± 14.6
-1.4 ± 16.6
-7.7 ± 22.5
0.52 ± 3.29
4.35 ± 2.48
3.33 ± 2.33
3.26 ± 1.59
2.08 i 1.95
3.93 i 2.50
4.62 ~ 2.81
3.32 ± 2.25
2.06 ± 3.19
Subject
1
2
5
6
8
9
10
11
12
Time, d.
At 10 9 (first year only)
Intake Difference, pg/d Slope
2. 17 ±1.22
1.57 ± 0,95
1.08 ± 0.62
1.42 ± 0.76
1.90 ± 1.05
1.67 ± 0.84
0.65 ± 1.06
1.36 ± 1.05
2.09 ± 1.39
38.6 ± 5.8
3.5 ± 6.3
3.05 ± 0.95
3.37 ± 0.92
21
23
24
Mean
39.3 ±
1.80 ± 1.40
2.04 ± 0.97:
1.80 ±0.65
1.63 ± 0.32
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PRELIMINARY DRAFT
Subjects 16 and 20 had substantial increases, subjects 15 and 19 had moderate increases and
subject 18 had no increase in blood lead during exposure. Subject 17 had a marked decline in
blood lead, but the rate of decrease was much faster in the pre-exposure period, suggesting an
apparent increase of intake during exposure periods even for this subject. These subjects had
not apparently achieved equilibrium in either blood or tissue compartments. Even though these
subjects were not exposed to air lead, the estimated difference between blood lead intake be-
fore and during exposure of the other subjects was used to calculate the apparent inhalation
slope at that exposure. The pooled inhalation slope estimated for all six controls (1.48 ±
0.82 s.e.) was significantly positive (2 = 1.76, one-tailed p <0.05), as shown in Table 11-16.
No explanation for the increased lead intake during the winter of 1971-72 can be advanced at
this time, but factors such as changes in diet or changes in resorption of bone lead are
likely to have had equal effect on the lead-exposed subjects.
No statistically significant changes in the controls were found during the first experi-
ment at 10.9 pg/m^.
(2) Among the controls, the estimated mean residence time in pool 1 was slightly longer
for the first year than the second year, 41.8 ±9.2 days vs. 34.6 ±6.5 days, but a paired
sample Z-test found that the mean difference for the controls (7.2 i 11.2 days) was not signi-
ficantly different from zero (see Table 11-17).
3 3
(3) Among the five subjects exposed to 10.9 pg/m the first year and 3.2 pg/m the
second year, the mean residence time in blood was almost identical (43.9 ± 9.4 vs. 44.7 ± 8.7
days).
(4) The average inhalation slope for all 17 subjects exposed to 10.9 pg/m^ is 1.77 ±
0.37 when the slope for the controls is subtracted. The corrected inhalation slope for all 14
subjects exposed to 3.2 pg/m3 is 1.52 ± 1.12, or 1.90 ± 1.14 without subjects 1 and 6 who were
"non-responders." These are not significantly different. The pooled slope estimate for all
subjects is 1.75 + 0.35. The pooled mean residence time for all subjects is 39.9 ±2.5 days.
Thus, in spite of the large estimation variability at the lower exposure level, the aver-
age inhalation slope estimate and blood lead half-life are not significantly different at the
two exposure levels. This suggests that blood lead response to small changes in air lead in-
halation is approximately linear at typical ambient levels.
11.4.1.2 The Rabinowitz et al. Study. The use of stable lead isotopes avoids many of the
difficulties encountered in the analysis of whole blood lead levels in experimental studies.
Five adult male volunteers were housed in the metabolic research wards of the Sepulveda and
Wadsworth VA hospitals in Los Angeles for extended periods (Rabinowitz et al. , 1974; 1976;
1977). For much of the time they were given low-lead diets with controlled lead content, sup-
plemented by tracer lead salts at different times.
PB11A/B 11-44 7/29/83
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TABLE 11-16.
INHALATION SLOPE ESTIMATES
Group
At 3.2 pq/m3
At 10.9 pg/m
Controls
1.48 ± 0.82
-0.20 ± 0.27
All exposed
3.00 ± 0.76
1.57 ± 0.26
Di fference
1.52 ± 1.12
1.77 ± 0.37
(Exposed-
control s)
Without sub-
jects 1, 6
3.38 ± 0.79
Di fference
1.90 ±1.14
(Exposed w/o
1,6 - control)
Pooled: (all subjects)
1.75 ± 0.35
(without subjects 1,6)
1.78 ± 0.35
TABLE 11-17.
MEAN RESIDENCE TIME IN BLOOD
3.2 pg/m3
10.9 pg/m3
Experi ment
Experi ment
Control 34.6
±6.5 days
41.B ±9.2 days
Exposed 40.8
±4.4 days
40.6 ± 3.6 days
Four subjects were initially observed in the ward for several weeks. Each subject was in
the semi-controlled ward about 14 hours per day and was allowed outside for 10 hours per day,
allowing the blood lead concentration to stabilize.
Subjects B, D and E then spent 22 to 24 hours per day for 40, 25 and 50 days, respec-
¦- v ' > . »
tively, in a low lead.room with total particulate and vapor lead concentrations that were much
lower than in the metabolic wards or outside (see Table 11-18). The subjects were thereafter
exposed to Los Angeles air with much higher air lead concentrations than in the ward.
The calculated changes in lead intake upon entering and leaving the low-lead chamber are
shown in Table 11-19. These were based on the assumption that the change in total blood lead
was proportional to the change in tracer lead. The change in calculated air lead intakes
(other than cigarettes) due to removal to the clean room were also calculated independently by
the lead balance and labeled tracer methods (Rabinowitz et al., 1976) and are consistent with
\
these direct estimates.
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712
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PRELIMINARY DRAFT
TABLE 11-18. AIR LEAD CONCENTRATIONS (pg/m3) FOR TWO SUBJECTS
IN THE RABINOWITZ STUDIES
Subject A
outside (Sepulveda VA)
Average
1.8
Range
(1.2-2.4)
inside (Sepulveda VA,
airconditioned without
fiIter)
1.5
(1.0-2.7)
inside (Wadsworth VA,
open air room)
2.1
(1.8-2.6)
Subject B
(Wadsworth VA)
outside
2.0
(1.6-2.4)
in room (air conditioner
with filter, no purifier)
0. 91
(C.4-2.1)
in room (with purifiers,
"clean air")
0.072
(0.062-0.087)
open-air room
1.9
(1.8-1.9)
organic vapor lead
outside
0.10
-
"clean air"
0.05
-
* 5-20 days exposure for each particulate lead filter
Rabinowitz and coworkers assumed that the amount of lead in compartments within the body
evolved as a coupled system of first-order linear differential equations with constant frac-
tional transfer rates. .This compartmental model was fitted to the data. This method of
analysis is described in Appendix 11A.
Blood lead levels calculated from the three compartment model adequately predicted the
observed blood lead levels over periods of several hundred days. There was no evidence to
suggest homeostasis or other mechanisms of lead metabolism not included in the model. There
was some indication (Rabinowitz et al., 1976) that gut absorption may vary from time to time.
The calculated volumes of the pool with blood lead (Table 11-19) are much larger than the
body mass of blood (about 7 percent of body weight, estimated respectively as 4.9, 6.3, 6.3,
4.6 and 6.3 kg for subjects A-E). The blood lead compartment must include a substantial mass
of other tissue.
PB11A/B 11-46 7/29/83
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PRELIMINARY DRAFT
TABLE 11-19. ESTIMATES OF INHALATION
SLOPE FOR RABINOWITZ STUDIES
Subject
Chanqes in
Intake*,
pg/day
Volume**,
kg
Resi dencef
Time, days
Changes in
Air Lead-t
pg/ir.3
Inhalationt
Slope pg/df
per pg/m3
Maxi mum++
Slope
A
17 ± 5*
7.4 ± 0.6
34 ± 5
2. 5TT
2.98 ± 1.06
4.38 ± 1.55
B
16+3
10.0 + 0.8
40 + 5
2. 0
3.56 ± 0.93
5.88 ± 1.54
C
15 ± 5*
10.1 ± 1**
37 + 5
2.2ft
2.67 ± 1.04
4. 16 ± 1.62
D
9 ± 2
9.9 ± 1.2
40 + 5
2.0
2.02 ± 0.60
3.34 ± 0.99
E
12 + 2
11.3 ± 1.4
27 + 5
2.0
1.5-9 + 0.47
2.63 ± 0.78
*Fron (Rabinowitz et al., 1977) Table VI. Reduced intake by low-lead method for subjects
B, D, E, tracer method for A, balance method for C. Standard error for C is assumed by EPA
tc be same as A.
*AFrom (Rabinowitz et al., 1976) Table II. EPA has assumed standard error with coefficient
of variation same as that for quantity of tracer absorbed in Table VI, except for subject C.
tEstimates frorr (Rabinowitz et al., 1976) Table II. Standard error estimate from combined
sample.
TTSee text, For A and C, estimated from average exposure. For B, D, E reduced by 0.2 pg/rn3,
for clean room exposure. Coefficient of variation assumed to be 10%.
-•Assumed density of blood 1.058 g/cm3.
++AsSLiring outside air exposure is 2.1 pg/m3 rather than 4 pg/rn3 for 10 hours.
The mean residence time in blood in Table 11-IS includes both loss of lead-from blood to
urine and transfer of a fraction of blood lead to other tissue pools. This parameter reflects
the speed with which blood lead concentrations approach a new quasi-equi1ibrium level. Many
years may be needed before approaching a genuine equilibrium level that includes lead that can
be mobilized from bones.
One of the greatest difficulties in using these experiments is that the air lead ex-
posures of the subjects were not measured directly, either by personal monitors or by restric-
ting the subjects to the metabolic wards. The times when the subjects were allowed outside
the wards included possible exposures to ground floor and street level air, whereas the outside
air lead monitor was mounted outside the third-floor window of the ward. The VA hospitals are
not far from major streets and the subjects' street level exposures could have been much
higher than those measured at about 10 m elevation (see Section 7.2.1.3). Some estimated
ratios between air concentrations at elevated and street level sites are given in Table 7.6.
A second complication is that the inside ward value of 0.97 mq/"1 (Rabinowitz et al.,
1977) used for subject B may be appropriate for the Wadsworth VA hospital, but not for subject
PB11A/B 11-47 7/29/83-.
714^
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PRELIMINARY DRAFT
A in the Sepulveda VA hospital (see Table 11-18). The change in air lead values shown in
Table 11-19 is thus nominal, and is likely to have systematic inaccuracies much larger than
the nominal 10 percent coefficients of variation stated. The assumption is that for subjects
B, D and E, the exposure to street level air for 10 hours per day was twice as large as the
3
measured roof level air, i.e., 4 pg/m I and the remaining 14 hours per day was at the ward
level of 0.97 pg/m^; thus the time-averaged level was (10 x 4 + 14 x 0.97)/24 = 2.23 pg/m^.
The average controlled exposure during the "clean room" part of the experiment was 23, 22 and
24 hours respectively for subjects B, D, E; thus averaged exposures were 0.19, 0.28, and 0.12
3 3
pg/m , and reductions in exposure were about 2.0 pg/m . This value is used to calculate the
slope. For subject A, the total intake due to respired air is the assumed indoor average of
3
1.5 pg/m for the Sepulveda VA hospital, combining indoor and outdoor levels (10 x 4 + 14 x
I.5)/24 = 2.54 pg/m''. For subject C we use the Wadsworth average. Apart from uncertainties in
the air lead concentration, the inhalation slope estimates for Rabinowitz's subjects have less
internal uncertainty than those calculated for subjects in Griffin's experiment.
The inhalation slopes thus calculated are the lowest that can be reasonably derived from
this experiment, since the largest plausible air lead concentrations have been assumed. The
third-floor air monitor average of 2.1 pg/m3 is a plausible minimum exposure, leading to the
higher plausible maximum inhalation slopes in the last column of Table 11-19. These are based
on the assumption that the time-averaged air lead exposure is smaller by 10x(4-2.l)/24 = 0.79
pg/m3 than assumed previously. It is also possible that some of this difference can be
attributed to dust ingestion while outside the metabolic ward.
II.4.1.3 The Chamberlain et al. Study. A series of investigations were carried out by
A.C. Chamberlain et al. (1975a,b; 1978) at the U.K. Atomic Energy Research Establishment in
Harwell, England. The studies included exposure of up to 10 volunteer subjects to inhaled,
ingested and injected lead in various physical forms. The inhalation exposures included labo-
ratory inhalation of lead aeroso.ls generated in a wind tunnel, or box, of various particle
sizes and chemical compositions (lead oxide and lead nitrate). Venous blood samples were
taken at several times after inhalation of 203Pb. Three subjects also breathed natural high-
way exhaust fumes at various locations for times up to about 4.5 hours.
The natural respiratory cycles in the experiments varied from 5.7 to 17.6 seconds (4 to
11 breaths per minute) and tidal volumes from 1.6 to 2.3 liters. Lung deposition of lead-
bearing particles depended strongly on particle size anc composition, with natural exhaust
particles being more efficiently retained by the lung (30 to 50 percent) than were the chem-
ical compounds (20 to 40 percent).
The clearance of lead from the lungs was an extended process over time and depended on
particle size and composition, leaving only about 1 percent of the fine wind tunnel aerosols
PB11A/B 11-48 7/29/83
7l5<
-------
PRELIMINARY DRAFT
in the lung after 100 hours, but about 10 percent of the carbonaceous exhaust aerosols. The
203Pb isotope reached a peak blood level about 30 hours after inhalation, the blood level then
representing about 60 percent of the initial lung burden.
A substantial fraction of the lead deposited in the lung appears to be unavailable to the
blood pool in the short term, possibly due to rapid transport to and retention in other tis-
sues including skeletal tissues. In long term balance studies, some of this lead in deep tis-
sue compartment would return to the blood compartment.
Lead kinetics were also studied by use of injected and ingested tracers, which suggested
that in the short term, the mean residence time of lead in blood could be calculated from a
one-pool model analysis.
Chamberlain et al. (1978) extrapolated these high level, short term exposures to longer
term ones. The following formula and data were used to calculate a blood-to-air level ratio:
[Tjyg] [% Deposition] [% Absorption] [Daily ventilation]
^ [Blood volume] [0.693]
where. = biological half life
With an estimated value of T^ = 18 days (mean residence time T^2/0.693 _ days), with 50
percent for deposition in lung for ordinary urban dwellers, and 55 percent of- the lung lead
retained in the blood lead compartment (all based on Chamberlain's experiments), with an
3
assumed ventilation of 20 m /day over blood volume 5400 ml (Table 10.20' in Chamberlain et
al. , 1978), then
26 day X 0.50 X 0.55 X 20 m3/day „ _3yj,
p - - t. / m /d l
54 dl
This value of (3 could vary for the following reasons,
1. The absroption from lung to blood used here, 0.55, refers to short term kine-
tics. In the long term, little lead is lost through biliary or pancreatic
secretions, nails, hair and sweat, so that most of the body lead is available to
the blood pool even if stored in the skeleton from which it may be resorbed.
Chamberlain suggests an empirical correction to 0.55 X 1.3 = 0.715 absorption.
2. The mean residence time, 26 days, is shorter than in Rabinowitz's subjects, and
the blood volume is less, 54 dl. It is possible that in the Rabinowitz study,
PB11A/B 11-49 7/29/83
716^
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PRELIMINARY DRA^T
the mean times are longer and the blood poo] size (100 dl) is larger than here
because Rabinowitz et al. included•relati'vely less labile tissues such as kidney
and liver in the pool. Assuming 40 days mean residence time and 100 dl blood
volume the slope can be recalculated,
p =
_ 40 d X 0.50 X 0.55 X 20 m3/d
100 dl. '
= 2.2 m3/dl
3. The breathing rate could be much less, for inactive people.
11.4.1.4 The Kehoe Study. Between 1950 and 1971, Professor R. A. Kehoe exposed 12 subjects
to various levels of air lead under a wide variety of conditions. Four earlier subjects had
received oral Pb during 1937-45. The inhalation experiments were carried out in an inhalation
chamber at the University of Cincinnati, in which the subjects spent varying daily time
periods over extended intervals. The duration was- typically 112 days for each exposure level
in the inhalation studies, at the end of this period it was assumed the blood lead concentra-
tion had reached a near equilibrium level. The experiments are described by Kehoe (1961a,b,c)
and the data and their analyses by Gross (1981) and Hammond et al. (1981). The studies most
relevant to this document are those in which only particles of lead sesquioxide aerosols in
the submicron range were used, so that there was at least one air lead exposure (other than
control) for which the time-averaged air lead concentration did not exceed 10 pg/m3. Only six
subjects met these criteria: LD (1960-63), J0S^Yl96ci-o3), NK (1S63-66), SS (1963-68), HR
(1966-67) and DH (1967-69). Subject DH had a-rather high initial lead concentration (30
pg/dl) that fell during the course of the experiment to 28 pg/d1; apparently daily detention
in the inhalation chamber altered DH's normal pattern of lead exposure to one of lesser total
exposure. The Kehoe studies did not measure non-experimental airborne lead exposures, and
did not measure lead exposures during "off" periods. Subject HR received three exposure
levels from 2.4 to 7.5 pg/m3, subject NK seven exposure levels from 0.6 to 4.2 pg/'m3 and sub-
jects SS 13 exposure levels from 0.6 to 7.2.pg/m3. _ LD and JOS were each exposed to about 9,
19, 27 and 36 pg/ir.3 during sequential periods of 109-113 days.
A great deal of data on lead content i;n blood, feces, urine and diet were obtained in
these studies and are exhibited graphically in Gross. (1979) (see Figure 11-11). Apart from
the quasi-equilibrium blood lead values and balances reported in Gross (1979; 1981), there has
been little use of these data to study the uptake and distribution kinetics of lead in man.
EPA analyses used only the summary data in Gross (1981).
Data from Gross (1981) were fitted by least squares linear and quadratic regression
models. The quadratic models were not significantly better than the linear model except for
PB.11A/B
11-50
7/29/83
71*7 «=
-------
05
/I
~u
CD
3>
N
133
SUBJECT - SS
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00
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<
o
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o
2
5
o
o
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ffi
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2
1.00
0.60
0.20
-0.20
-0.60
-1.00
2.00
1.60
1.20
0.80
0.40
0.00
1.00
0.80
0.60
0.40
0.20
0.00
0.10
0.08
0.06
0.04
0.02
0.00
0.10
0.08
0.06
0.04
0.02
0.00
BALANCE
• • .•
FECES
. t i
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t.
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URINE
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7rt-™(r' •>?
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r-i'. i
4^ h
¦'^55,
J*
i : •-*-
i*. J...,.- ii\
100.
200. 300
ft
< '
Q!
400. 500. 600
i.J
. in in
:Z
:<
700. j 800. 900. 1000. 1100. 1200. 1300. 1400.] 1500 )1600. (1700.0
t <£>'
(/> 2
2 £
? <
:z
:<
t f
(A V)
> >
<<
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in o
fN fN
+ +
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: o)
$
X
;CC
• Z
ic
;«
->
O
<
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CM
n
n
TIME (days)
Figure 11-11. Data plots for individual subjects with time for kehoe data as presented by Gross.
TD
TO
J>
TO
-<
O
TO
J>
-------
V
PRELIMINARY DRAFT
subjects LD and JOS, who were exposed to air levels above 10 pg/m3. The linear terms predomi-
nate in all models for air lead concentrations below 10 pg/m3 and are reported in Table 11-20.
These data represent most of the available experimental evidence in the higher range of
ambient exposure levels, approximately 3 to 10 pg/m3.
Data for the four subjects with statistically significant relationships are shown in
Figure 11-12, along with the fitted regression curve and its 95 percent confidence band.
TABLE 11-20. LINEAR SLOPE FOR BLOOD LEAD VS. AIR LEAD AT
LOW AIR LEAD EXPOSURES IN KEHOE'S SUBJECTS
LINEAR SLOPES p, m3/dl, ± s.e. RANGE
SUBJECT LINEAR MODEL QUADRATIC MODEL AIR* BLOOD
DH3
-0. 34
+
0.28
0.14
+
1.25
5.6 - 8.8
26 - 31
HRa
0.70
+
0.46
0. 20
+
2.14
2.4 - 7.5
21 - 27
$
0.67
+
0.07
1.01
+
0.19
9.4 - 35.7
21 - 46
0.64
+
0.11
1.29
±
0.06
9.3 - 35.9
18 - 41
NKC
2.60
+
0.32
1. 55
±
1.28
0.6 - 4.0
20 - 30
ssc
1. 31
+
0.20
1.16
±
0.78
0.6 - 7.2
18 - 29
*Al50 control = 0
aNo statistically significant relationship between air and blood lead.
^High exposures. Use linear slope from quadratic model.
cLow exposures. Use linear slope from linear model.
11.4.1.5 The Azar et al. Study. Thirty adult- male subjects were obtained from each of five
groups: 1) Philadelphia cab drivers; 2) DuPont employees in Starke, Florida; 3) DuPont
employees in Barksdale, Wisconsin; 4) Los Angeles cab drivers; and 5) Los Angeles office
workers (Azar et al., 1975). Subjects carried air lead monitors in their automobiles and in
theirs breathing zones at home and work. Personal variables (age, smoking habits, water
samples) were obtained from all subjects, except for water samples from Philadelphia cab
drivers. Blood lead, ALAD urine lead and other variables were measured. From two to eight
blood samples were obtained from each subject during the air monitoring phase. Blood lead
determinations were done in duplicate. Table 11-21 presents the geometric means for air lead
and blood lead.for the five groups. The geometric means were calculated by EPA from the raw
data presented in the authors' report (Azar et al., 1975).
The Azar study has played an important role'in setting standards because of the care used
in measuring air lead in the subjects' breathing zone. Blood lead levels change in response
to air lead levels, with typical time constants of 20 to 60 days. One must assume that the
subjects' lead exposures during preceding months had been reasonably similar to those during
PB11A/B
11-52
7/29/83
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PRtLIMINARY' CRAFT
~
<
a
o
o
5
a
3.
a
<
~
Q
O
SUBJECT NK
1 2 3
AIR LEAD, ug/m1
AIR LEAD, (jg'm1
SUBJECT JOS S
SUBJECT LD
0 5 10 15 20 25 30 35
AIR LEAD, ^ig/m'
0 5 10 15 20 25 30 35
AIR LEAD, (ig/m1
Figure 11-12. Blood level vs. air lead relationships for kehoe inhalation studies: line.i- rela-
tion for low exposures, quadratic for high exposures, with 95% confidence bands
PB11A/B
11-53
7/29/33
720<
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PRELIMINARY DRAFT
TABLE 11-21. GEOMETRIC MEAN AIR AND BLOOD LEAD LEVELS (|jg/100 g)
FOR FIVE CITY-OCCUPATION GROUPS (DATA CALCULATED BY EPA)
Geometric mean Geometric mean
air lead, blood lead, Sample
Group |jg/m3 GSD pg/100 g GSD size Code
Cab drivers
Philadelphia, PA
2.59
1.16
22.1
1.16
30
C1
Plant employees
Starke, FL
0.59
2.04
15.4
1.41
29
C2
Plant employees
Barksdale, WI
0.61
2.39
12.8
1.43
30
C3
Cabdrivers
Los Angeles, CA
6.02
1.18
24.2
1.20
30
C4
Office workers
Los Angeles, CA
2.97
1.29
18.4
1.24
30
C5
Source: Azar et al. (1975).
the study period. Models have been proposed for these data by Azar et al. (1975), Snee (1981;
1983b) and Hammond et al. (1981) including certain nonlinear models.
Azar et al. (1975) used a log-log model for their analysis of the data. The model in-
cluded dummy variables, C^, CC^, C^, C^, which take on the value 1 for subjects in that
group and 0 otherwise (see Table 11-21 for the definitions of these dummy variables). The
fitted model using natural logarithms was
log (blood Pb) = 2.951 Cj + 2.818 C? +
2.627 C3 + 2.910 C4 + 2.821 C5 + 0.153 log (air Pb)
This model gave a residual sum of squares of 9.013, a mean square error of 0.63 (143 degrees
of freedom), and a multiple R2 of 0.502. The air lead coefficient had a standard error of
0.040. The fitted model is nonlinear in air lead, and so the slope depends on both air lead
and the intercept. Using an average intercept value of 1.226, the curve has a slope ranging
3 3
from 10.1 at an air lead level of 0.2 pg/m to .0.40 ,at ,an air lead level of 9 jjg/m .
PB11A/B
11-54
7/29/83
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PRELIMINARY DRAFT
Snee (1982b) reanalyzed the same data and fitted the following power function model,
. 'JO'JJfci -"A ¦ -
log (blood Pb) = log [12.1 (air Pb + 6.00 + 1.46
n
- 0.44 C3 + 2.23 + 6.26 Cg) ]
This model gave a residual sum of squares of 9.101, a mean square error of 0.064 (142 degrees
of freedom) and a multiple R2 of 0.497. Using an average constant value of 3.28, the slope
ranges from 1.29 at an air lead of 0.2 to 0.51 at an air lead of 9.
An important extension in the development of models for the data was the inclusion cf
separate ncn-air contributions or background exposures for each separate group. The coeffi-
cients of the group variables, C j , in the lead exposure model may be interpreted as measures
of total exposure of that group to non-air~ external sources (cigarettes, food, dust, water)
and to endogenous sources (lead stored in skeleton). Water and smoking variables were used to
estimate some external sources. (This required deleting another observation fcr a subject
with unusually high water lead.) The effect of endogenous lead was estimated using subject
age as a surrogate measure of cumulative exposure, since lead stored in skeleton is known to
increase approximately linearly with age, for ages 20 to 60 (Gross et a 1., 1975; Barry, 1975;
Steenhout, 1982) in homogeneous populations.
In order to facilitate comparison with the constant 0 ratios calculated from the clinical
studies, EPA f-'tted a linear exposure model to the Azar data. The model was fitted on a loga-
rithmic scale to facilitate comparison of goodness of fit with other exposure models and to
produce an approximately normal pattern of regression residuals. Neither smoking nor water
lead providec significantly better fits to the log (blood lead) measurements after the effect
of age was removed.
Age and air lead may be confounded to some extent because the regression coefficient for
.u
age may include the effects of prior air lead exposures on skeletal lead buildup. This would
have the effect of reducing the estimated apparent slope p.
Geometric mean regressions of blood lead on air lead were calculated by EPA for several
assumptions: (i) A linear model analogous to Snee's exposure model, assuming different non-
air contributions in blood lead for each of the five subgroups; (ii) linear model in which age
of the subject is also used as a surrogate measure of the cumulative body burden of lead that
provides an endogenous source of blood lead; (iii) linear mcdel similar to (ii), in which the
change of blood lead with age is different in'different subgroups, but it is assumed that the
non-air contribution is the same in all five groups (as was assumed in the 1977 criteria docu-
ment); (iv) linear model in which both the non-air background and the change in blocdlead
PB11A/B
•11-55
7/29/83
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PRELIMINARY DRAFT
with age may differ by group; and (v) nonlinear model similar to (iv). None of the fitted
models are significantly different from each other using statistical tests of hypotheses about
parameter subsets in nonlinear regression (Gallant, 1975).
11.4.1.6 Silver Valley/Kellogg, Idaho Study. In 1970, EPA carried out a study of a lead
smelter in Kellogg, Idaho (Hammer et al., 1972; U.S. Environmental Protection Agency, 1972).
The study was part of a national effort to determine the effects of sulfur dioxide, total sus-
pended particulate and suspended sulfates, singly and in combination with other pollutants, on
human health. It focused on mixtures of the sulfur compounds and metals. Although it was
demonstrated that children had evidence of lead absorption, insufficient environmental data
were reported to allow further quantitative analyses.
In 1974, following the hospitalization of two children from Kellogg with suspected acute
leaa poisoning, the CDC joined the State of Idaho in a comprehensive study of children in the
Silver Valley area of Shoshone County, Idaho, near the Kellogg smelter (Yankel et al., 1977;
Land'-igan et al., 1976).
The principal source of exposure was a smelter whose records showed that emissions aver-
aged 8.3 metric tons per month from 1955 to 1964 and 11.7 metric tons from 1965 to September
1973. After a September 1973 fire extensively damaged the smelter's main emission filtration
facility, emissions averaged 35.3 metric tons from October 1973 to September 1974 (Landrigan
et al., 1976). The smelter operated during the fall and winter of 1973-74 with severely limited
air pollution control capacity. Beginning in 1971, ambient concentrations of lead in the
vicinity of the smelter were determined from particulate matter collected by Hi-Vol air
samples. Data indicated that monthly average levels measured in 1974 (Figure 11-13) were
three to four times the levels measured in 1971 (von Lindern and Yankel, 1976). Individual
exposures of study participants to lead in the air were estimated by interpolation from these
data. Air lead exposures ranged from 1.5 jjg/m3 to 30 ng/m3 monthly average (see Figure 11-13).
Soil concentrations were as high as 24,000 (jg/g and averaged 7000 pg/g within one mile of the
smelter. House dusts were found to contain as much as 140,000 pg/g and averaged 11,000 |jg/g
in homes within one mile of the complex.
The study was initiated in May of 1974 and the blood samples were collected in August
1974 from children 1 to 9 years old in a door-to-door survey (greater than 90 percent partici-
pation). Social, fairily and medical histories were conducted by interview. Paint, house
dust, yard and garden soils, grass, and garden vegetable samples were collected. At that
time, 385 of the 919 children examined (41.9 percent) had blood lead levels in excess of 40
Mg/dl , 41 children (4.5 percent) had levels greater than 80 pg/dl. All but 2 of the 172
children living within 1.6 km of the smelter had levels greater than or equal to 40 mg/d1.
Those two children had moved into the area less than six months earlier and had blood lead
PB11A/B
11-56
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7/29/83
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PRELIMINARY DRAFT
1974
TIME, year
1975
Figure 11-13. Monthly ambient air lead concentrations in Kellogg, Idaho,
1971 through 1975.
PB11A/B
11-57
7/29/83
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PRELIMINARY DRAFT
levels greater than 35 pg/dl. Both the mean blood lead concentration and the number of chil-
dren classified as exhibiting excess absorption, decreased with distance from the smelter
(Table 11-22). Blood lead levels were consistently higher in 2- to 3-year-old children than
they were in other age groups (Table 11-23). A significant negative relationship between
blood lead level and hematocrit value was found. Seven of the 41 children (17 percent) with
blood lead levels greater than 80 pg/d 1 were diagnosed as being anemic on the basis of
hematocrit less than 33 percent, whereas only 16 of 1006 children (1.6 percent) with blood
lead levels less than 80 (.jg/d 1 were so diagnosed. Although no overt disease was observed in
children with higher lead intake, differences were found in nerve conduction velocity.
Details of this finding are discussed in chapter 12.
Yankel et al. (1977) fitted the data to the following model:
In (blood lead) = 3.1 + 0.041 air lead + 2.1 x 10 ^ soil lead
+ 0.087 dustiness - 0.018 age
¦t- 0. 024 occupation
where air lead was in pg/m3; soil lead was in pg/g; dustiness was 1, 2 or 3; age was in years;
and occupation was a Hollingshead index. The analysis included 879 subjects, had a multiple
R of 0.622 and a residual standard deviation of 0.269 (geometric standard deviation of 1.31).
Walter et al. (1980) used a similar model to examine age specific differences of the re-
gression coefficients for the different variables. Those coefficients are summarized in Table
11-24. The variable that was most significant overall was air lead; its coefficient was ap-
proximately the same for all ages, corresponding to a change in blood lead of about 1 pg/dl
per unit increase of air lead (in pg/m3) at an air exposure of 1 pg/m3 and about 2.4 jjg/d1 per
unit increase in air at an air exposure of 22 pg/m3.
The next most important variable that attained significance at a variety of ages was the
household dustiness level (coded as low = 0, medium - 1 or high = 2), showing a declining ef-
fect with age. and being significant for ages 1 to 4 years. This suggested age-related hygiene
behavior and a picture of diminishing home orientation as the child develops. For ages 1 to 4
years, the coefficient indicates the child in a home with a "medium" dust level would have a
blood lead level ~ 10 percent higher than a child in a home with a "low" dust level, other
factors being comparable.
The coefficients for soil lead-blood lead relationships exhibited a fairly regular pat-
tern, being highly significant (p <0.01) for ages 3 to 6 years, and significant (p <0.05) at
ages 2 to 6 years. The maximum coefficient (at age 6) indicates a 4 percent increase in blood
lead per 1000 pg/g increase in soil lead.
PB11A/B
11-58
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PRELIMINARY DRAFT
TABLE 11-22. GEOMETRIC MEAN BLOOD LEAD LEVELS BY AREA COMPARED WITH
ESTIMATED AIR-LEAD LEVELS FOR 1- TO 9-YEAR-OLD CHILDREN
LIVING NEAR IDAHO SMELTER. (GEOMETRIC STANDARD DEVIATIONS
SAMPLE SIZES AND DISTANCES FROM SMELTER ARE ALSO GIVEN)3
Area
Geometric mean
blood lead,
Mg/dl
GSD
Sample
si ze
% blood
1 ead
>40|jg/dl
Estimated
air lead,
^ig/m3
Distance from
smelter, km
1
65.9
1.30
170
98.9
18.0
O
1
cr>
2
47.7
1.32
192
72.6
14.0
1.6- 4.0
3
33.8
1.25
174
21.4
6.7
4.0-10.0
4
32. 2
1.29
156
17.8
3.1
10.0-24.0
5
27.5
1.30
188
8.8
1.5
24.0-32.0
6
21.2
1.29
90
1.1
1.2
about 75
aEPA analysis of data from Yankel et al. (1977).
TABLE 11-23. GEOMETRIC MEAN BLOOD LEAD LEVELS BY AGE AND AREA FOR
SUBJECTS LIVING NEAR THE IDAHO SMELTER
Area
1
2
3
4
5
Age Group
6 7 8
9
Teenage
Adult
1
69*
72
75
75
68
66
63
60
57
39
37
2
50
51
55
46
49
50
47
42
40
33
33
3
33
36
36
35
35
35
31
32
32
28
' 30
4
31
35
34
31
31
35
30
32
30
34
5
27
35
29
29
29
28
25
27
24
*
32
6
21
25
22
23
20
22
20
22
17
7
28
30
28
32
30
26
37
30
20
35
32
*error in original publication (Yankel et al., 1977).
¦ .01.-1 oc,
PB11A/B 11-59 7/29/83
726 v
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PRELIMINARY DRAFT
TABLE 11-24. AGE SPECIFIC REGRESSION COEFFICIENTS FOR THE ANALYSIS OF
LOG-BLOOD-LEAD LEVELS IN THE IDAHO SMELTER STUDY
Age Air
Dust Occupation Pica Sex Soil (xlO4) Intercept N
1 0.0467* 0.119?
2 0.0405* 0.106+
3 0.0472* 0.108+
4 0.0366* 0.107+
5 0.0388* 0.052
6 0.0361* 0.070
7 0.0413* 0.053
8 0.0407* 0.051
9 0.0402* 0.081?
0.0323 0.098 0.055 3.5
0.0095 0.225* 0.002 20.6?
0.0252 0.077 0.000 24.2*
0.0348 0.117 0.032 32.1*
0.0363? 0.048 -0.081 23.4*
0.0369? 0.039 -0.092 38.4*
0.0240 0.106 -0.061 21.3?
0.0422? 0.010 -0.106? 16.2
0.0087 0.108 -0.158* 11.6
3.017 98
3.567 94
3.220 115
3.176 104
3.270 130
3.240 120
3.329 113
3.076 105
3.477 104
* p <0.01
? p <0.05
Pica (coded absent = 0, present = 1) had a significant effect at age 2 years, but was in-
significant elsewhere; at age 2 years, an approximate 25 percent elevation in blood lead is
predicted in a child with pica, compared with an otherwise equivalent child without pica.
Occupation was significant at ages 5, 6 and 8 years; at the other ages, however, the sign
of the coefficient was always positive, consistent with a greater lead burden being introduced
into the home by parents working in the smelter complex.
Finally, sex (coded male = 0; female = 1) had a significant negative coefficient for ages
8 and 9 years, indicating that boys would have lead levels 15 percent higher than girls at
this age, on the average. This phenomenon is enhanced by similar, but nonsignificant, nega-
tive coefficients for ages 5 to 7 years.
Snee (1982c) also reanalyzed the Idaho smelter data using a log-linear model. He used
dummy variables for age, work status of the father, educational level of the father, and
2
household dust level (cleanliness). The resulting model had a multiple R of 0.67 and a resi-
dual standard deviation of 0.250 (geometric standard deviation of 1.28). The model showed
that 2-year-olds had the highest blood lead levels. The blood lead inhalation slope was es-
sentially the same as that of Yankel et al. (1977) and Walter et al. (1980).
The above non-linear analyses of the Idaho smelter study are the only analyses which sug-
gest that the blood lead to air lead slope increases with increasing air lead, a finding in
counterdistinction to the findings of decreasing slopes seen at high air lead exposures in
other studies.. A" alternative to this would be to attempt to fit a linear model as described
in Appendix 11-B. Exposure coefficients were estimated for each of the factors shown in
Table 11-25. The results for the different covariates are similar to those of Snee (1982c)
and Walter et al. (1980).
PB11A/B
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TABLE 11-25. ESTIMATED COEFFICIENTS* AND STANDARD
ERRORS FOR THE IDAHO SMELTER STUDY
Asymptoti c
Factor Coefficient Standard Error
Intercept (pg/dl)
13.19
1.90
Air lead (pg/m3)
1.53
0.064
Soil lead (1000 pg/g)
1.10
0.14
Sex (male=l, female=0)
1. 31
0.59
Pica (eaters=l, noneaters=0)
2.22
0.90
Education (graduate training=0)
-
At least high school
3.45
1.44
No high school
4.37
1.51
Cleanliness of home (clean=0)
-
Moderately clean
3.00
0.65
Di rty
6.04
1.06
Age (1 year olds-0)
-
2 years olds
4.66
1.48
3 years olds
5.48
1.32
4 years olds
3.16
1.32
5 years olds
2.82
1.25
6 years olds
2. 74
1.24
7 years olds
0.81
1.23
8 years olds
-0.19
1.28
9 years olds
-1.50
1.21
Work status (no exposure-0)
-
Lead or zinc worker
3.69
0.61
Residual standard deviation = 0.2576 (geometric standard deviation = 1.29)
Multiple R2 = 0.662
Number of observations = 860
Calculations made by EPA
Because the previous analyses noted above indicated a nonli'near' relationship, a similar
model with a quadratic air lead term added was also fitted. The coefficients for the other
factors remained about the same, and the improvement in the model was marginally significant
3
(p = 0.05). This model gave a slope of 1.16 at an air lead of 1 pg/m , and 1.39 at an air
lead of 2 pg/m3. Both the linear and quadratic models, along with Snee's (1982) model are
shown in Figure 11-14. The points represent mean blood lead levels adjusted for the factors
in Table 11-25 (except air lead) for each of the different exposure subpopulations.
PB11A/B 11-61 7/29/83
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PRELIMINARY DRAFT
Yankel et al. (1977), Walter et al. (1980) and Snee (1982c) make reference to a follow-up
study conducted in 1975. The second study was undertaken to determine the effectiveness of
control and remedial measures instituted after the 1974 study. Between August 1974 and August
1975; the mean annual air lead levels decreased at all stations monitored. In order of in-
creasing distance from the smelter, the annual mean air lead levels for the one year preceding
each drawing were 18.0 to 10.3 ng/m3, 14.0 to 8.5 jjg/m3, 6.7 to 4.9 pg/mfl and, finally 3.1 to
2.5 (jg/m3 at 10 to 24 km. Similar reductions were noted in house dust lead concentrations.
In a separate report, von Lindern and Yankel (1976) described reductions in blood lead levels
of children for whom determinations were made in both years. The results demonstrated that
significant decreases in blood lead concentration resulted from exposure reductions.
80
~9
3.
6
<
UJ
-J
Q
O
O
O
UJ
&
-l
a
<
20
10
0
n
11 i i i i i i i i i i i i i \.r
LINEAR (EPA)
- - — QUADRATIC (EPA)
LOG-LINEAR (SNEE)
i ii i i i i i i i i i r
10 15
AIR LEAD, ^g/m1
20
25
Figure 11-14. Fitted equations to Kellogg Idaho/Silver Valley
adjusted blood lead data.
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PRELIMINARY DRAFT
11.4.1.7 Ciraha, Nebraska Studies. Exposure from both a primary and secondary smelter in the
inner city area of Omaha, Nebraska, has been reported in a series of publications (Angle et
al., 1974; Angle and Mclntire, 1977; Mclntire and Angle, 1973). During 1970 to 1977 children
were studied from: an urban school at a site immediately adjacent to a small battery plant
and downwind from two other lead emission sources; from schools in a mixed commercial-residen-
tial area; and from schools in a suburban setting. Children's blood lead levels were obtained
by macro technique for 1970 and 1971, but Delves micro assay was used for 1972 and later. The
differences for the change in techniques were taken into account in the presentation of the
data. A-'r lead values were obtained by Hi-Vol samplers and dustfall va-ues were also moni-
tored. Table 11-26 presents the authors' summary of the entire data set, showing that as air
lead values decrease and then increase, dustfall and blood lead values follow. The authors
used regression models, both log-linear and semilog, to calculate (air lead)/'(blcod lead).
Specific reports present various aspects of the work. Black children in the two ele-
mentary schools closest to the battery plant had higher blood leads (34.1 pg/dl) than those in
elementary and junior high schools farther away (26.3 pg/dl). Best estimates of the air ex-
3
posures were 1.65 and 1.48 pc/m , respectively (Mclntire and Angle, 1973). The latter study
compared three populations: urban vs. suburban high school students, ages 14 and 18; urban
black children, ages 10 to 12, vs. suburban whites, age 10 to 12; and blacks ages 10 to 12
with blood lead levels over 20 pg/dl vs. schoolmates with blood lead levels below 20 pg/dl
(Angle et al., 1974). The urban vs. suburban high school children did not differ significan-
tly, 22.3 ± 1.2 and 20.2 ± 7.0 pg/dl, respectively, with mean values of air lead concentra-
tions of 0.43 and 0.29 pg/m^. For 15 students who had environmental samples taken from their
hones, correlation coefficients between blood lead levels and soil and housedust leac levels
were 0.31 and 0.29, respectively.
Suburban 10-to-12-year-olds haa lower blood lead levels than their urban counterparts,
17.1 ± 0.7 versus 21.7 ± 0.5 pg/dl (Angle et al., 1974). Air lead exposures were higher in
the urban than in the suburban population, although the average exposure remained less than 1
3 2
pg/m . Djstfall lead measurements, however, were very much higher; 32.96 mg/m /month for
2
urban 10-to-12-year-olds vs. 3.02 mg/m /month for suburban children.
Soil lead and house dust lead exposure levels were significantly higher for the urban
black high lead group than for the urban low lead group. A significant correlation (r = 0.49)
between blood lead and soil lead levels was found.
Angle has reanalyzed the Omaha study using all of the data on children. There were 1075
samples from which blood lead (pg/dl), air (pg/m3), soil (pg/g) and house dust (pg/g) lead
were available. The linear regression model, fitted in logarithmic form, was
PB11A/B 11-63 7/29/83
730<
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PRELIMINARY DRAFT
Pb-Blood = 15.'67 + 1.92 Pb-Air + 0.00680 Pb-Soil + 0.00718 Pb-House Dust
(±0.40) (±0.60) (±0.00097) (±0.00090)
(N = 1075, R2 = 0.20, S2 = 0.0901, GSD = 1.35)
Similar models fitted by age category produced much more variable results, possibly due to
small ranges of variation in air lead within certain age categories.
TABLE 11-26. ArR, DUSTFALL AND BLOOD LEAD CONCENTRATIONS IN
OMAHA, NE STUDY, 1970-19773
Air Dustfall, Blood,
Group (N)b pg/m^ - mo (N)c Mg/dl (N)d
All urban children, mixed commercial and residential site
1970-71
1.48 ± 0.14(7;65)
--
31.4
+
0.7(168)
1972-73
0.43 ± 0.08(8;72)
10.6 ± 0.3(6)
23.3
+
0.3(211)
1974-75
0.10 ± 0.03(10;72)
6.0 ± 0.1(4)
20.4
+
0.1(284)
1976-77
0.52 ± 0.07(12;47)
8.8 (7)
22.8
+
0.7(38)
Children at school in
a commercial site
1970-71
1.69 ± 0.11(7;67)
--
34.6
+
1.5(21)
1972-73
0.63 ± 0.15(8;74)
25.9 ± 0.6(5)
21.9
+
0.6(54)
1974-75
0.10 ± 0.03(10;70)
14.3 ± 4.1(4)
19.2
+
0.9(17)
1976-77
0.60 + 0.10(12;42)
33.9 (7)
22.8
+
0.7(38)
All suburban children
in a residential site
1970-71
0.79 ± 0.06(7;65)
--
--
1972-73
0.29 ± 0.04(8;73)
4.6 t 1.1(6)
19.6
+
0.5(81)
1974-75
0.12 ± 0.05(10,73)
2.9 ± 0.9(4)
14.4
+
0.6(31)
1976-77
• -•
18.2
+
0.3(185)
aBlood lead 1970-71 is by the macro technique, corrected for an established
laboratory bias of 3 (jg/dl, macro-micro; all other values are by Delves micro
assay.
bN = Number of months; number of 24-hour samples.
CN = Number of months.
- Number of blood samples.¦- -
Source: Adapted from Angle and Mclntire, 1977.
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PRELIMINARY DRAFT
11.4.1.8 Roels et al. Studies. Roels et al. (1976, 1978, 1980) have conducted a series of
studies in the vicinity of a lead smelter in Belgium. Roels et al. (1980) reports a follow-up
study (1975) that included study populations from a rural-nonindustrialized area as well as
from the lead smelter area. The rural group consisted of 45 children (11-14 years). The
smelter area group consisted of 69 school children from three schools. These children, were
divided into.two groups; group A (aged 10-13) lived less than 1 km from the smelter and their
schools were very close to the smelter; group B consisted of school children living more than
1.5 km from the smelter and attending a school more distant from the smelter.
In 1974 the smelter emitted 270 kg of lead and the air lead levels were 1 to 2 orders of
magnitude greater than the current Belgian background concentration for air lead (0.23 pg/m^).
Soil and vegetation were also contaminated with lead; within 1 km the soil lead level was
12,250 (jg/g. The concentration of lead in drinking water was less than 5 MS/1-
Environmental assessment included air, soil and dust. Air monitoring for lead had been
continuous since September 1973 at two sites, one for each of the two groups. In the rural
area, air monitoring was done at two sites for five days using membrane pumps. Lead was ana-
lyzed by flameless atomic absorption spectrophotometry. Dust and soil samples were collected
at the various school playgrounds. The soil sample was analyzed by flameless atomic absorp-
t j np
A 25 ml blood sample was collected from each child and immediately divided among three
tubes. One tube was analyzed for lead content by flaneless atomic absorption with background
correction. Another tube was analyzed for ALA-D activity while the third was analyzed for FEP.
FEP was determined by the Roels modification of the method of Sassa. ALA-D was assayed by the
European standard method.
Air lead levels decreased from area A to area B. At both sites the airborne lead levels
declined over the two years of monitoring. The amount of lead produced at this smelter during
this time remained constant, about 100,000 tons/year. The median air lead level at the closer
3
site (A) dropped from 3.2 to 1.2 |jg/m H.wfo-i 1 e at> the far site (B) the median went from 1.6 to
3 ...
0.5-0.8 pg/m . The rural area exposure levels did not vary over the study period, remaining
rather constant at about 0.30 |jg/ni^.
Both smelter vicinity groups showed signs of increased lead absorption relative to the
rural population. Blood lead levels for group A were about three times those for the rural
population (26 pg/dl vs. 9 pg/dl). The former blood lead levels were associated with about a
50 percent decrease in ALA-D activity and a 100 percent increase in FEP concentration. How-
ever, FEP levels were not different for group B and rural area residents.
Later surveys of children (Roels et al., 1980) were conducted in 1976, 1977 and 1978; the
former two in autumn, the latter in spring. In total there were five surveys conducted yearly
from 1974 to 1978. A group of age-matched controls from a rural area was studied each time
except 1977. In 1976 and 1978 an urban group of children was also studied.
PB11A/B 11-65 7/29/83
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PRELIMINARY DRAFT
The overall age for the different groups ranged from 9 to 14 years (mean 11-12). The
length of residence varied from 0.5 to 14 years (mean 7-10 years). The subjects were always
recruited from the same five schools: one in the urban area, one in the rural area and three
in the smelter area (two <1 km and one, 2.5 km away). Air lead levels decreased from 1977 to
1S73. However, the soil lead levels in the vicinity of the smelter were still elevated (<1
km, soil lead 2000-6000 pg/g). Dustfall lead in the area of the near schools averaged
2 2 2
16.4-22.0 mg/m -day at 500 m from the stack, 5.8-7.2 mg/m -day at 700 m, about 2 mg/m -day at
2
1000 m and fluctuating around 0.5-1 mg/m -day at 1.5 km and beyond. The particle size was
predominantly 2 pm in diameter with a secondary peak between 4 and 9 pm. The particle size
declined with increasing distance from the smelter (0.7-2.4 km).
In all, 661 children (328 beys and 333 girls) were studied over the years. Two hundred
fourteen children came from less than 1 km from the smelter, 16S children fron 1.5 to 2.5 km
from the p^nt, 55 children lived in the urban area and 223 children lived in the rural area.
The air lead and blocd lead results for the five years are presented as Table 11-27. The
reported air leads are not calendar year averages. The table shows that blood lead levels
(electrothermal atomic absorption spectrophotometry) are lower in the girls than the boys.
Within 1 km o* the smelter no consistent improvement in air lead levels was noted over the
years of the study. The mean blood leads for the children living at about 2.5 kjn from the
smelter never exceeded 20 pg/dl since 1975, although they were higher than for urban and rural
cni1dren.
The researchers then investigated the importance of the various sources of lead in
determining blood lead levels. Data were available from the 1976 survey on air, dust and hand
lead levels. Boys had higher hand dust lead than girls. Unfortunately, the regression analy-
ses performed on these data were based on the group means of four groups.
EPA has reanalyzed the 1976 study using original data provided by Dr. Roels on the 148
children. The air lead, playground dust lead, and hand lead concentrations were all highly
correlated with each other. The hand lead measurements are used here with due regard for
their limitations, because day-to-day variations in hand lead for individual children are
believed to be very large. However, even though repeated measurements were not available,
this is among the most usable quantitative evidence on the role of ingested hand dust in
childhood 1ead absorption.
Total lead content per hand is probably more directly related to ingested lead than is
the lead concentration in the hand dust. The linear regression model used above was fitted by
EPA using lead in air (pg/m3), lead in hand dust (pg/hand), lead in playground dust (pg/g) and
sex as covariates of blood lead. The lead variables were highly correlated, resulting in a
PB11A/B 11-66 7/29/83
733<
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PRELIMINARY DRAFT
TABLE 11-27. MEAN AIRBORNE AND BLOOD LEAD LEVELS RECORDED DURING FIVE DISTINCT SURVEYS
(1974 to 1978) FOR STUDY POPULATIONS OF 11-YEAR-OLD CHILDREN LIVING LESS THAN 1 km
OR 2.5 km FROM A LEAD SMELTER, OR LIVING IN A RURAL OR URBAN AREA
Blood lead concentration (nq/dl)
Study Pb-Air Total Population Boys Girl s
populations (Mg/m3) n Mean ± SD n Mean + SD n Mean ± SD
1 Survey
<1 km
4.06
37
30.1
+
5.7
14
31.0
+
5.5
23
29.6
±
5.9
(1974)
2.5 km
1.00
—
--
14
21.1
+
3.4
--
--
Rural
0.29
92
9.4
+
2.1
28
9.7
+
1.6
64
9.3
+
2.2
2 Survey
<1 k/n
2.94
40
26.4
+
7.3
19
27.4
+
6. 5
21
25.4
+
8.1
(1975)
2.5 km
0.74
29
13.6
+
3.3
17
14.8
+
3.6
12
11.9
+
1.9
Rural
0. 31
45
9.1
+
3.1
14
8.2
+
2.1
31
9. 5
3.4
3 Survey
<1 km
3.67
38
24.6
+
8.7
18
28.7
+
8.0
20
20.8
+
7.6
(1976)
2.5 km
0.80
40
13.3
+
4.4
24
15.6
+
2.9
16
9.8
+
3.8
Urban
0.45
26
10.4
+
2.0
17
10. 6
+
2.0
9
9.9
+
2.0
Rural
0.30
44
9.0
+
2.0
21
9.2
2.3
23
8.7
+
1.7
4 Survey
<1 km
3.42
56
28.9
+
6.5
27
31.7
+
9.5
29
26.4
+
8.7
(1977)
2.5 km
0.49
50
14.8
+
4.7
34
15.7
+
4.8
16
13.0
+
4.3
5 Survey
1 km
2.68
43
27.8
+
9.3
20
29.3
+
9.8
23
26.5
+
8.9
(1978)
2.5 km
0. 54
36
16. 0
+
3.8
26
16.6
+
3.5
10
14.3
+
4.2
Urban
0.56
29
12.7
+
3.1
18
13.4
+
2.3
11
11.5
+
4.0
Rural
0.37
42
10.7
+
2.8
17
11.9
3.0
25
10.0
+
2.4
Source: Roels et al. 1980.
statistically significant regression but not statistically significant coefficients. Thus the
playground dust measurement was dropped and the following model obtained with almost as small
-&0 . £.11! I- . -
a residual sum of squares,
1n(Pb-Blood) = ln(7.37 + 2.46 Pb-Air + 0.0195 Pb-Hand + 2.10 Male)
(±.45) '(±.58) ( + .0062) (±0.56)
The fitted model for the 148 observations gave an R2 of 0.654 and a mean square error (S2) of
0.0836 (GSD = 1.335). The significance of the estimated coefficient establishes that intake
of lead-bearing dust from the hands of children does play a role in childhood lead absorption
over and above the role t.hat can be "assigned to inhalation of air lead. Individual habits of
mouthing probably also affect lead absorption along this pathway. Note too that the estimated
inhalation slope, 2.46, is somewhat larger than most estimates for adults. However, the ef-
fect of ingestion of hand dust appears to be almost as large as the effect of air lead in-
halation in children of this age (9-14 years). Roels et al. (1980), using group means,
PB11A/B 11-67 7/29/83
^34*:
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PRELIMINARY DRAFT
concluded that the quantitative contribution of hand lead to children's blood lead levels was
far greater than that of air lead.
¦ i.'r-r.
The high mutual correlations among air, hand, and dust lead suggest the use of their
principal components or principal factors as predictors. Only the first principal component
(which accounted for 91£ of the total variance in lead exposure) proved a statistically sig-
nificant covariate of blood lead. In this form the model could be expressed as
ln(Pb-Blood) = ln(7.42 + 1.56Pb-Air + 0.0120Pb-Hand + 0.00212Pb~Dust + 2.29 Male)
The estimated standard error on the inhalation slope is ±0.47. The difference between these
inhalation slope and hand lead coefficients is an example of the partial attribution of the
effects of measured lead exposure sources to those sources that are not measured.
11.4.1.9 Other Studies Relating Blood Lead Levels to Air Exposure. The following studies
also provide information on the relationship of blood lead to air lead exposures, although
they are less useful in accurately estimating the slope at lower exposure levels. The first
group of studies are population studies with less accurate estimates of individual exposures.
The second group of studies represent industrial exposures at very high air lead levels in
which the response of blood lead appears to be substantially different than at ambient air
levels.
The Tepper and Levin (1975) study included both air and blood lead measurements. House-
wives were recruited from locations in the vicinity of air monitors. Table 11-28 presents the
geometric mean air lead and adjusted geometric mean blood lead values for this study. These
values were calculated by Hasselblad and Nelson (1975). Geometric mean air lead values ranged
from 0.17 to 3.39 pg/m , and geometric mean blood lead values ranged from 12.7 to 20.1 pg/dl.
Nordman (1975) reported a population study from Finland in which data from five urban and
two rural areas were compared. Air lead data were collected by stationary samplers. All
levels were comparatively low, particularly in the rural environment, where a concentration of
3 3
0.025 pg/m was seen. Urban-suburban levels ranged from 0.43 to 1.32 pg/m .
A study was undertaken by Tsuchiya et al. (1975) in Tokyo using male policemen who
worked, but not necessarily lived, in the vicinity of air samplers. In this study, five zones
were established, based on degree of urbanization, ranging from central city to suburban. Air
monitors were established at various police station's within each zone. Air sampling was con-
ducted from September 1971 to September 1972; blood and urine samples were obtained from 2283
policemen in August and September 1971. Findings are presented in Table 11-29.
Goldsmith (1974) obtained data for elementary school (9- and 10-year-olds) and high
school students in 10 California communities. Lowest air lead exposures were 0.28 pg/m^ and
3
highest were 3.4 ^g/m . For boys in elementary school, blood lead levels ranged from 14.3 to
PB11A/B 11-68 7/29/83
735--
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PRELIMINARY DRAFT
TABLE 11-28. GEOMETRIC MEAN AIR LEAD AND ADJUSTED BLOOD LEAD
LEVELS FOR 11 COMMUNITIES IN STUDY OF
TEPPER AND LEVIN (1975) AS REPORTED BY
HASSELBLAD AND NELSON (1975)
Communi ty
Geometric mean
air lead,
pg/m3
Age and smoking
adjusted geometric
mean blood lead,
pg/dl
Sample
size
Los Alamos, NM
0.17
15.1
185
Okeana, OH
0.32
16.1
156
Houston, TX
0.85
12.7
186
Port Washington, NY
1.13
15.3
196 -
Ardmore, PA
1.15
17.9
148
Lombard, IL
1.18
• 14.0
204
Washington, DC
1.19
18.7
219
Philadelphia, PA
1.67
20.1
136
Bridgeport, IL
1.76
17.6
146
Greenwich Village, NY
2.08
16.5
139
Pasadena, CA
3.39
17.6
194
Multiple R2 = 0.240
Residual standard deviation = 0.262 (geometric standard deviation = 1.30)
TABLE 11-29. MEAN AIR AND BLOOD LEAO VALUES FOR
FIVE ZONES IN TOKYO STUDY
Zones
Air lead,
pg/m3 -
Blood lead,
pg/100 g
1
0.024
17.0
2
' r 0.198
17.1
3
0.444
16.8
4
0.831
18.0
5
1.157
19.7
Source: Tsuchiya et al. 1975.
PB11A/B 11-69 7/29/83
736'
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PRELIMINARY DRAFT
23.3 pg/dl; those for girls ranged from 13.8 to 20.4 pg/dl for the same range of air lead ex-
posures. The high school student population was made up of only males from some of the 10
towns. The air lead range was 0.77 to 2.75 pg/m , and the blood lead range was 9.0 to 12.1
pg/dl. The high school students with the highest blood lead levels did not come from the town
with the highest air lead value. However, a considerable lag time occurred between the col-
lection and analysis of the blood samples. In one of the communities the blood samples were
refrigerated rather than frozen.
Another California study (Johnson et al., 1975, 1976) examined blood lead levels in rela-
tion to exposure to automotive lead in two communities, Los Angeles and Lancaster (a city in
the high desert). Los Angeles residents studied were individuals living in the vicinity of
heavily traveled freeways within the city. They included groups of males and females, aged 1
through 16, 17 through 34, and 34 and over. The persons selected from Lancaster represented
similar age and sex distributions. On two consecutive days, blood, urine and fecal samples
were collected. Air samples were collected from one Hi-Vol sampler in Los Angeles, located
near a freeway, and two such samplers in Lancaster. The Los Angeles sampler collected for 7
days; the two in Lancaster operated for 14 days. Soil samples were collected in each area in
the vicinity of study subjects,
3
Lead in ambient air along the Los Angeles freeway averaged 6.3 ± 0.7 pg/m and, in the
3
Lancaster area, the average was 0.6 ± 0.2 pg/m . The mean soil lead in Los Angeles was 3633
pg/g, whereas that found in Lancaster was 66.9 pg/g. Higher blood lead concentrations were
found in Los Angeles residents than in individuals living in the control area for all age
groups studied. Differences between Los Angeles and Lancaster groups were significant with
the sole exception of the older males. Snee (1981) has pointed out a disparity between blood
samples taken on consecutive days from the same child in the study. This calls into question
the validity of using this study to quantify the air lead to blood lead relationship.
Daines et al. (1972) studied black women living near a heavily traveled highway in New
Jersey. The subjects lived in houses on streets paralleling the highway at three distances:
3.7, 38.1 and 121.9 m. Air lead as well as blood lead levels were measured. Mean annual air
3
lead concentrations were 4.60, 2.41 and 2.24 pg/m , respectively, for the three distances.
The mean air lead concentration for the area closest to the highway was significantly dif-
S ¦ C'- •
ferent from that in both the second and third, but the mean air lead concentration of the
third area was not significantly different from that of the second. The results of the blood
lead determinations paralleled those of the air lead. Mean blood lead levels of the three
groups of women, in order of increasing distance, were 23.1, 17.4 and 17.6 pg/dl, respec-
tively. Again, the first group showed a.significantly, higher mean than the other two, but the
second and third groups' blood lead levels were similar to each other. Daines et al. (1972),
in the same publication, reported a second study in which the distances from the highway were
33.5 and 457 meters and in which the subjects were white upper middle class women. The air
PB11A/B 11-70 7/29/63
737'-
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PRELIMINARY DRAFT
lead levels were trivially different at these two distances, and the blood lead levels did not
differ either. Because the residents nearest the road were already 33 m from the highway, the
differences in air lead may have been insufficient to be reflected in the blood lead levels.
(See Chapter 7)
A summary of linear relationships for other population studies has been extracted fron
Snee (1981) and is shown in Table 11-30. The Fugas study is described later in Section
11.5.2.3. There is a large range of slope values (-0.1 to 3.1) with most studies in the range
of 1.0 to 2.0. Additional information on the more directly relevant studies is given in tne
Summary Section 11.4.1.10.
TABLE 11-30. BLOOD LEAD-AIR LEAD SLOPES FOR SEVERAL POPULATION
STUDIES AS CALCULATED BY SNEE
Study
No.
Subjects
Sex
Slope
95% confidence
Intervals
Tepper & Levin
1935
Female
1.1
±1.8
(1975)
Johnson et al.
65
Male
0.8
±0.7
(1975)
96
Female
0.8
±0.6
Nordnan (1975)
536
Mai e
1.2
±1.0
478
Female
0.6
±0.9
Ts'-chiya et al. (1975)
537
Mai e
3. 1
±2.2
Goldsmith (1974)
89
Male
-0.1
+0.7
79
Female
0. 7
±0.7
Fugas (1977)
352
Mai e
2.2
±0.7
Daines et al. (1972)
61 .• '
Female
(spring)
1.6
±1.7
88
Female (fall)
2.4
±1.2
Johnson et al.
37a
Mai e
(1975)
(chi1dren)
1.4
±0. 6
43
Female
(chi1dren)
1.1
±0.6
Goldsmith (1974)
486
Male & Feirale
(children)
2.0
±1.3
a0utlier results for four subjects deleted.
Source: Snee, 1981.
There is a great deal of information on blood lead responses to air lead exposures of
workers in lead-related occupations. Almost all such exposures are at air lead levels far in
excess of typical non-occupational- exposuries. The blood lead vs. air lead slope p is very
much siral1er at high blood and air levels. Analyses of certain studies are shown in Table
11-31. '
s-'iew
PB11A/B 11-71 7/29/83
738c
-------
PRELIMINARY DRAF-T-
TABLE 11-31. A SELECTION
OF RECENT ANALYSES
ON OCCUPATIONAL
8-HOUR EXPOSURES
TO HIGH AIR LEAD
LEVELS
Analysis
Study
A
Air Lead
Blood Lead
P
(jg/m3
|j g/d 1
(slope)
Ashfora et al.
Wi11iams et al.(1969)
50-300
40-90
0.19
(1977)
Globe Union
0.10
Delco-Remy
0.05
King et al.
Factory 1, 1975
35-1200
25-90
0.032
(1979)
Factory 2a, 1975
0.07
Factory 3a, 1975
0.068
Garts i de
Delco-Remy,
10-350
22-72
0.0514
et al. (1982)
1974-1976
Nonlinear:
at 50:
Bishop and
Battery plants A
20-170
12-50
0.081
Hill (1983)
1975-1981 B
2-200
18-72
0.045
C
7-170
22-60
0.046
D
7-195
24-75
0.022
E
20-140
18-60
0.045
F
4-140
15-53
0.101
*Assume
-------
TABLE 11-32. CROSS-SECTIONAL OBSERVATIONAL STUDY WITH MEASUREO INDIVIDUAL AIR LEAD FXPOSURE
Study
Analysis
Model
Mode I Slope at an air lead of
d.f. 1.0 pg/in^ 2.0 ijg/m:i
Azar et al. (1975)
Azar et al. (1975)
In (PBB)
= 0.153 In (PBA) ~ separate intercepts tor each group
0.50?
6
2.57
143
Study done in
(1.23, 3.91)
(0.64, 2.30)
1970-1971 in five
U.S. cities, total
Snee (1982b)
In (PBB)
= 0.2669 In (PBA ~ separate background for each group)
0.497
7
1.12
0.96
sample size = 149.
~ 1.0842
(0.29, 1.94)
(0.25, 1.66)
Blood leads ranged
from 8 to 40 pg/dl.
Hammond et al.
(PBB)"1'
= 0.179 (PBA ~ separate background for each group)"'
0.49
8
1.08
1.07
Air leads ranged
(1981)
-0.098
from 0.2 to 9.1
(jg/m3
EPA
1n(PB8)
= ln(1.318 PBA ~ separate background for each group)
p
0.491
6
1.32
(0.46, 2.17)
1.32
(0.46, 2.17)
EPA
ln(PBB)
= ln(2.902 PBA - 0.257 PBA ~ separate background
for each group)
0.504
7
2. 39
1.87
EPA
ln(PBB)
= 1n(1.342 PBA ~ separate background ~ age slope x age)
0.499
7
1. 34
(0.32, 2.37)
1. 34
(0.32, 2.37)
EPA
ln(PB8)
= ln(1.593 PBA = common intercept ~ age x separate age
slope)
0.489
7
1.59
(0.76, 2.42)
1.59
(0.76, 2.42)
EPA
)n(PBB)
= ln(1.255 PBA ~ separate background ~ age ~ separate
age slope)
0.521
11
1.26
(0.46, 2.05)
1.26
(0.46, 2.05)
EPA
ln(PBB)
= 0.25 ln-(P8A ~ separate background ~ age x separate
age slope)
0.514
12
about 1.0
(varies by
city)
about 1.0
(varies by
city)
Z
3>
73
-<
O
73
>
Note: PBB stands for blood lead (pg/dl); PBA stands for air lead (pg/m3); slope means rate of change of blood lead per unit change in air lead at the
stated air lead value. The 95 percent confidence intervals for the slope are given in parentheses. OThese are approximate and should be used
with caution. The analyses labelled "EPA" are calculated from the original authors' data. r.i\-
-------
TABLF 11-33. CROSS-SEC!IONAL OBStRVATIONAL SlUOIfS ON CH1IDRLN WITH E51IMATED AIR IXPOSURES
Study
Analysis
Mode 1
Mode) Slope at an air lend of
R^ d. f. 1. 0 pq/m-1 5.0
Kellogg Idaho/Silver
Yankel et al.
ln(PBB) = 0.011 PDA «¦
7.1x10 soil ~ 0.087 dust -
• 0.622
6
1.
16
1. 37
Valley study conducted
(1977)
- 0.018 age +
0 024 occupation « 3.14
(1.09,
1 23)
(1.27, 1.46)
in 1971 based on about
c
880 children. Air
Snee (1982c)
ln(PBB) - 0.039 PBA •
0.065 In (soil) + terms for sex,
0. 666
25
1.
13
1.32
leads ranged from
occupat ion,
cleanliness, education, pica
(1.06,
1.70)
(1 23, 1.47)
0.5 to 22 pg/m3.
EPA
ln(PBB) = ln(l 52 PBA
to 0.0011 soil ~ terms for sex,
—" 0. 655
18
1
52
1 52
Blood leads ranged
otcupation,
c1ean1i ness,.educat i on, pica)
~ 0 026 PBA + terms for soil, sex,
from 11 to 164
FPA
ln(PBB) = ln(1 13 PBA
0.656
19
1.
16
1 39
occupation, cleanliness,
Walter et al.
(1980)
ln(PBB) - separate slopes for air, dust
sex and soil by age
education, pica)
occupation, pica
0.56 to 0 70
1.01 to 1.26 1.18 to 1.48
Kellogg Idaho/Silver
Valley study as above
restricted to 537 chil-
dren with air leads
hp 1 nw lfl i in /m-1
Snee (1982a) ln(PBB) - 0.039 PBA < 0.055 In (soil) ~ terms for sex, occupation
cleanliness, education, pica
0.317
2b
1.07 1.75
(0.89, 1.25) (1.01. 1.50)
"O
33
Roels et al.
(1980)
Roels et al.
(1980) based
on B groups
PBB = 0.007 PBA ~ 11.50 log(PB-Hand) - 4.27
- 4.27
0.65
3
0.007
0. 007
1
EPA analysis
on 148 subjects
ln(PBB) = ln(2.46 PBA ~ 0.0195 (Pb-Hand) ~ 2.1 (Male) ~ 7.37)
0.654
4
2.46
(1.31,3.61)
2.46
(1 31,3.61)
Angle and Mclntire
(1979)
Angle and
Mclntire (1979)
on 832 samples
ayes 6-18
ln(PBB) = ln(8.1) » 0.03 In (PBA) ~ 0.10 In (PB-Soil)
~ 0.07 In (Pb-House Dust)
0.21
4
0.6
0. 14
Angle et al.
(1903) on 1074
samples for ages
1-18
ln(PBB) = ln(l.92 PBA ~ 0.00680 Pb-Soil
+ 0.00718 Ph-House Dust ~ 15 67)
0 199
4
1.9^
(0.74,3.10)
1.92
(0.74,3.10)
832 samples ages
6 to 18
ln(PBB) ^ In (4 40 PBA to .00457 Pb-Soil
< 0.00336 Ph-House Dust ~ 16 21)
0.262
4
4 . 40
(3.20,5.60)
4.40
(3,20,5.60)
3>
TO
-<
O
TO
Note: PBB stands for blood lead (pg/dl); PBA stands for air lead (pq/m-1); slope means rate of change of blood lead per unit change in air lead at the
stated air lead value. The 95 percent confidence intervals for the slope are given in parentheses Ihese are approximate and should be used
with caution. The analyses labelled "EPA" are calculated from the original authors' data.
-------
TABLE 11-34. LONGITUDINAL EXPERIMENTAL STUDIES WITH MEASURED INDIVIDUAL AIR LEAD EXPOSURE
.
A
Experiment
Analysis
Model
Air Lead
Blood Lead
pg/m3
Mg/dl
Kehoe 1950-1971
Gross (1981)
A
PBB = 0
57 A PBA
0.6 to 36
18 to 41
1960-1969
Hammond et a 1.(1981)
A
PBB = p
A PBA, p^ by subject
from -0. 6 to 2. 94
"
"
Snee (1981)
A
PBB = p
A PBA, by subject
from 0. 4 to 2.4
II
"
EPA
PBB = p
PBA + background, p.
by subject from -.34 to 2.60
0.6 to 9
18 to 29
CP
Griffin et al. Knelson et al.(1973) A PBB = 0.327 PBA ~ 3.236 ~ (2.10 PBA ~ 1.96) (In PBA ~ p.) by subject 0.15, 3.2
1971-1972 Hammond et al.(1981) A PBB = p A PBA, p = 1.90 at 3.2 and p = 1.54 at 10.9 0.15, 10.9
Snee (1981) A PBB = p. A PBA, p. by subject, p = 2.3 at 3.2 and p = 1.5 at 10.9
EPA A PBB = pj A PBA, p. by subject, mean p = 1.52 at 3.2
and p = 1.77 at 10.9
11 to 32
14 to 43
-o
yO
>
yO
-<
o
JO
3>
Chamberlain et
al. 1973-1978
Chamberlain et al.
(1978)
EPA
A PBB = p APBA, p = 1.2 calculated
A PBB = p APBA, p = 2.7 calculated
Rabinowitz
et al. 1973-1974
Snee (1981)
EPA
A PBB = 0^ APBA, p. by subject from 1.7 to 3.9
A PBB = p. APBA, 0^ by subject from 1.59 to 3.56
0.2 to 2
14 to 28
-------
PRELIMINARY DRAFT
The blood lead inhalation slope estimates vary appreciably from one subject to another in
experimental and clinical studies, and from one study to another. The weighted slope and
standard error estimates from the Griffin study in Table 11-16 (1.75 ± 0.35) were combined
with those calculated similarly for the Rabinowitz study in Table 11-19 (2.14 ± 0.47) and the
Kehoe study in Table 11-20 (1.25 ± 0.35 setting DH = 0), yielding a pooled weighted slope es-
3
timate of 1.64 ± 0.22 jjg/d1 per yg/m . There are some advantages in using these experimental
studies on adult males, but certain deficiencies need to be acknowledged. The Kehoe study ex-
posed subjects to a wide range of exposure levels while in the exposure chamber, but did not
control air lead exposures outside the chamber. The Griffin study provided reasonable control
of air lead exposure during .the experiment, but difficulties in defining the non-inhalation
baseline for blood lead (especially in the important experiment at 3.2 pg/m^) add much uncer-
tainty to the estimate. The Rabinowitz study controlled well for diet and othe" factors and
since they used stable lead isotope tracers, they had nc baseline problem. However, the
actual air lead exposure of these subjects outside the metabolic ward was not well determined.
Among population studies, only the Azar study provides a slope estimate in which air lead
exposures are known for individuals. However, there was no control of dietary lead intake or
other factors that affect blood lead levels, and slope estimates assuming only air lead and
location as covariables (1.32 ± 0.38) are not significantly different from the pooled experi-
mental studies.
Snee and Pfeifer (1983) have extensively analyzed the observational studies, tested the
equivalence of slope estimates using pooled within-study and between-study variance com-
ponents, and estimated the common slope. The result of five population studies on adult males
(Azar, Johnson, Nordnan, Tsuchiya, ,Fugas) was an inhalation slope estimate ±95 percent
confidence limits of 1.4 ± 0.6. For six populations of adult females [Tepper-Levin, Johnson,
Nordman, Goldsmith, Daines (spring), Daines (fall)], the slope was 0.9 ± 0.4. For four
populations of children [Johnson (male), Johnson (female), Yankel, Goldsmith], the slope
estimate was 1.3 ± 0.4. The between-study variance component was not significant for any
group so defined, and when these groups were pooled and combined with the Griffin subjects,
the slope estimate for all subjects was 1.2 ± 0.2.
The Azar slope estimate was not combined with the experimental estimates because of the
lack of control on non-inhalation exposures. Similarly, the other population studies in Table
11-30 were not pooled because of the uncertainty about both inhalation and non-inhalation lead
exposures. These studies, as a group, have, lower slope estimates than the individual experi-
mental studies.
There are no experimental inhalation studies on adult females or on children. The inha-
lation slope for women should be roughly the same as that for men, assuming proportionally
smaller air intake and blood volume. The assumption of proportional' size is less plausible
PB11A/B 11-76 7/29/83
7-13^
-------
PRELIMINARY DRAFT
for children. Slope estimates for children from population studies have been used in which
some other important covariates of lead absorption were controlled or measured, e.g., age,
sex, dust exposure in the environment or on the hands. Inhalation slopes were estimated for
the studies of Angle and Mclntire (1.92 ± 0.60), Roels (2.46 ± 0.58) and Yankel et al. (1.53 ±
(J.0b4). ii.e standard error of the Yankel study is extremely low and a weighted pooled slope
estimate for children would reflect essentially that study alone. In this case the small
standard error estimate is attributable to the very large range of air lead exposures of
children in the Silver Valley (up to 22 pg/m^). The relationship is in fact not linear, but
increases more rapidly in the upper range of air lead exposures. The slope estimate at lower
air lead concentrations may not wholly reflect uncertainty about the shape of the curve at
higher concentrations. The unweighted mean slope of the three studies and its standard error
estimate are 1.97 ± 0.39.
This estimate was not combined with the child population studies of Johnson or Goldsmith.
The Johnson study slope estimate used air lead measured at only two sites and is sensitive to
assumptions about data outliers (Snee, 1981), which adds a large non-statistical uncertainty
to the slope estimate. The Goldsmith slope estimate for children (2.0 ± 0.65) is close to
the estimate derived above, but was not used due to non-statistical uncertainties about blood
lead collection and storage.
One can summarize the situation briefly:
3
(1) The experimental studies at lower air lead levels, 3.2 pg/m or less, and lower
blood levels, typically 30 pg/dl or less, have linear blood lead inhalation
relationships with slopes p. of 0 to 3.6 for most subjects. A typical value of
1.64 ± 0.22 may be assumed tor adults.
(2) Population cross-sectional studies at lower air lead and blood lead levels are
approximately linear with slopes p of 0.8 to 2.0.
(3) Cross-sectional studies ioccupational exposures in which air lead levels are
higher (much abo've'l'O (jg/rn ) and blood lead levels are higher (above 40 |jg/dl),
show a much more shallow linear blood lead inhalation relation. The slope p is
in the range 0.03 to 0.2.
(4) Crosr.-sectional and experimental studies at levels of air lead somewhat above
the higher ambient exposures (9 to 36 pg/m ) and blood leads of 30 to 40 (jg/dl
can be described either by a nonlinear relationship with decreasing slope or by
a linear relationship with intermediate slope, approximately p = 0.5. Several
biological mechanisms for these differences have been discussed (Hammond et
al., 1981; O'Flaherty et al., 1982; Chamberlain, 1983; Chamberlain and Heard,
1981). Since no explanation for the decrease in steepness of the blood lead
inhalation response to higher air lead levels has been generally accepted at
this time, there is little basis on which to select an interpolation formula
from low air lead to high air lead exposures. The increased steepness of the
inhalation curve for the Silver Valley/ Kellogg study is inconsistent with the
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11-77
7/29/83
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PRELIMINARY DRAFT
other studies presented. It may be that smelter situations are unique and must
be analyzed differently, or it may be that the curvature is the result of
imprecise exposure estimates.
(5) The blood-lead inhalation slope for children is at least as steep as that for
adults, with an estimate of 1.97 + 0.39 from three major studies (Yankel et
al., 1977; Roels, et al. (1980); Angle and Mclntire, 1979).
11.4.2 Dietary Lead Exposures Including Water
Another major pathway by which lead enters the body is by ingestion. As noted in Chap-
ters 6 and 7, the recycling of both natural and anthropogenic lead in the environment results
in a certain•amount¦of -lead, being found in the food we eat and the water we drink. Both of
these environmental media provide external exposures to lead that ultimately increase internal
exposure levels in addition to internal lead elevations caused by direct inhalation of lead in
air. The Nutrition Foundation Report (1982) presents a compilation of recent estimates of
dietary intakes in the United States and Canada. The report gives information on relation-
ships between external lead exposures and blood lead levels. The mechanisms and absorption
rates for uptake of lead from food and water are described in Chapter 10. The purpose of the
present section is to establish (analogously to Section 11.4.1) the relationships between
external exposures to lead in food and drinking water and resulting internal lead exposures.
The establishment of these external and internal lead exposure relationships for the en-
vironmental media of food and water, however, is complicated by the inherent relationship be-
tween food and water. First, the largest component of food by weight is water. Second,
drinking water is used for food preparation and, as shown in Section 7.3.1.3 provides addi-
tional quantities of lead that are appropriately included as part of external lead exposures
ascribed to food. Third, the quantity of liquid consumed daily by people varies greatly and
substitutions are made among different sources of liquid: soft drinks, coffee, tea, etc., and
drinking water. Therefore, at best, any values of water lead intake used in drinking water
calculations are somewhat problematic.
A further troubling fact is the influence of lead in the construction of plumbing facil-
ities. Studies discussed in Section 7.3.2.1.3 have pointed out the substantial lead exposures
in drinking water that can result from the use of lead pipes in the delivery of water to the
tap. This problem is thought to occur only in limited geographic areas in the U.S. However,
where the problem is present, substantial water lead exposures occur. In these areas one can-
not make a simplifying assumption that the lead concentration in the water component of food
is similar to that of drinking water. But rather one is adding a potentially major additional
lead exposure to the equation.
PB11A/B 11-78 7/29/83
745-'
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PRELIMINARY DRAFT
Studies that have attempted to relate blood lead levels to ingested lead exposures have
uifcJ three approaches to estimate the external lead exposures involved: duplicate meals, fe-
cal lead determinations, and market basket surveys. In duplicate diet studies, estimated lead
exposures are assessed by having subjects put aside a duplicate of what they eat at each meal
fc- 3 limited period of time. These studies probably provide a good, but short term, estimate
of the ingestion intake. However, the procedures available to analyze lead in foods have his-
torically been subject to inaccuracies. Hence, the total validity of data from this approach
has not been established. Studies relying on the use of fecal lead determinations face two
major difficulties. First, this procedure involves the use of a mathematical estimate of the
overall absorption coefficient from the gut to estimate the' external' exposure'. Until re-
cently, these estimates have not been well documented and were assumed to be relatively con-
stant. Newer data discussed later show a much wider variability in the observed absorption
coefficients than was thought to be true. These new observations cloud the utility of studies
using this method to establish external/internal exposure relationships. Second, it is dif-
ficult to collect a representative sample. ' kssf
The last approach is the market basket approach. This approach uses the observed lead
concentrations for a variety of food items coupled with estimated dietary consumption of the
particular food items. Some studies use national estimates of typical consumption patterns
upon which to base the estimated exposures. Other studies actually record the daily dietary
intakes. This approach faces similar analytic problems to those found in the duplicate diet
pproach. It also faces the problem of getting accurate estimates of dietary intakes. The
n ;st current total diet study (Pennington, 1983) is described in Section 7.3.1.2.
Exposures to lead in the diet are thought to have decreased from the 1940's. Estimates
>om that period were in the range of 400-500 pg/day for U.S. populations. Current estimates
ar U.S. populations are under 100 pg/day for adults. Unfortunately, a good historical record
regarding the time course of dietary exposures is not available. In the years 1978-82, ef-
forts have been made by the American food canning industry in cooperation with the FDA to re-
duce the lead contamination of canned food. Data presented in Section 7.3.1.2.5 confirm the
success of this effort.
The specific studies available for review regarding dietary exposures will be organized
into three major divisions: lead ingestion from typical diets, lead ingestion from experi-
mental dietary supplements and inadvertent lead ingestion from lead plumbing.
11.4.2.1 Lead Ingestion from Typical Diets.
11.4.2.1.1 Ryu study on infants and toddlers. Ryu et al. (1983) reported a study of four
breast-fed infants and 25 formula-fed infants from 8 days to 196 days of age. After 112 days,
the formula-fed infants were separated into a group of 10 who received carton milk and a
PB11B/A 11-79 7/29/83
746 v
-------
PRELIMINARY DRAFT
second group of seven who received either canned formula or heat-treated milk in cans.. In ad-
dition to food concentrations, data were collected on air, dust and water lead. Hemoglobin
and FEP were also measured.
The trends in blood lead for the formula-fed infants are shown in Table 11-35. The re-
sults up to day 112 are averaged for all 25 infants. The estimated average intake was 17
pg/day for this time period. After day 112, the subgroup of seven infants fed either canned
formula or heat-treated cow's milk in cans (higher lead), had average estimated lead intake of
61 pg/day. This resulted in an increase of 7.2 pg/dl in the average blood lead for an in-
crease of 45 pg/day in lead intake. The estimated slope from this data is 0.16.
TABLE 11-35. BLOOD LEAD LEVELS AND LEAD INTAKE VALUES
FOR INFANTS IN THE STUDY OF RYU ET AL.
Age i n
Blood
lead of combined
Average lead intake of
Days
...group (pg/dl)
combined group (pg/day)
8
f! f: c
8.9
17
28
5.8
17
56
5.1
17
84
5.4
112
6.1
17
Lower Lead
Higher Lead
Lower Lead Higher Lead
140
6.2
9.3
16 61
168
7.0
12.1
16 61
196
7.2
14.4
16 61
Source: Ryu et al. (1983).
11.4.2.1.2 Rabinowitz study. This study on male adults was described in Section 11.4.1 and
in Chapter 10, where ingestion experiments were analyzed in more detail (Rabinowitz et al.,
1980). As in other studies, the fraction of ingested stable isotope lead tracers absorbed
into the blood was much lower when lead was consumed with meals (10.3 ± 2.2 percent) than
between meals (35 ± 13 percent). Lead nitrate, lead sulfide and lead cysteine as carriers
made little difference. The much higher absorption of lead on an empty stomach implies
greater significance of lead ingestion from leaded paint and from dust and soil when consumed
between meals, as seems likely to be true for children.
11.4.2.1.3 Hubermont study. Hubermont et al. (1978) conducted a study of pregnant women
living in rural Belgium because their drinking water was suspected of being lead contaminated.
This area was known to be relatively free of air pollution. Seventy pregnant women were
PB11B/A
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747 <
7/29/83
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PRELIMINARY DRAFT
recruited and were asked to complete a questionnaire. Information was obtained on lifetime
residence history, occupational history, smoking and drinking habits. First flush tap water
samples were collected from each home with the water lead level determined by flameless atomic
absorption spectrophotometry. Biological samples for lead determination were taken at
delivery. A venipuncture blood sample was collected from the mother as was a fragment of the
placenta. An umbilical cord blood sample was used to estimate the newborn's blood lead
status.
For the entire population, first flush'^tap water samples ranged from 0.2 to 1228.5 M9/1-
The mean was 109.4 while the median was 23.2. The influence of water lead on the blood lead
of the mother and infants was examined by categorizing the subjects on the basis of the lead
level of the water sample, below or above 50 pgV 1." Table 11-36 presents the results of this
study. A significant difference in blood lead levels of mothers and newborns was found for
the water lead categories. Placenta lead levels also differed significantly between water
lead groups, The fitted regression equation of blood lead level for mothers is given in
summary Table 11-42.
11.4.2.1.4 Sherlock study. Sherlock et al. (1982) reported a study from Ayr, Scotland, which
considered both dietary and drinking water lead exposures for mothers and children living in
the area. In December 1980, water lead concentrations were determined from kettle water from
114 dwellings in which the mother and child lived less than 5 years. The adult women had
venous blood samples taken in early 1981 as part of a European Economic Community (EEC) survey
on blood lead levels. A duplicate diet survey was conducted on a random sample of these 114
women stratified by kettle water lead levels.
A study population of 11 mothers, with infants less than 4 months of age agreed to
participate in the infant survey. A stratified sample of 31 of 47 adult volunteers was
selected to participate in the duplicate diet study.
Venous blood samples for adults were analyzed for lead immediately before the duplicate
diet study; in some instances additional samples were taken to give estimates of long term ex-
posure. Venous samples were taken from the infants immediately after the duplicate diet week.
--Blood lead levels were determined by AAS with graphite furnace under good quality control.
Two other laboratories analyzed each sample by different methods. The data reported are based
on the average value of the three methods.
Dietary intakes for adults and children were quite different; adults had higher intakes
than children. Almost one third of the adults had intakes greater than 3 mg/week while only
20 percent of the infants had that level of intake. Maximum values were 11 mg/week for adults
and 6 mg/week for infants.
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The observed blood lead values in the dietary study had the following distributions:
>20 (jg/dl >30 (jg/dl >35 |jg/dl
Adults
Infants
EEC Directive
55%
100%
50%
16%
55%
10%
2%
36%
2%
TABLE 11-36. INFLUENCE OF LEVEL OF LEAD IN WATER
ON BLOOD LEAD LEVEL IN BLOOD AND PLACENTA
Compari son
Water
Mean
Median
Range
Si gnificance
Group
Level
- .. .
Low**
25.6
- - 24-
- 18-41
NS*
Age (Years)
High***
26.3
25
20-42
Pb-B mother
Low
10.6
9.9
5.1-21.6
<0.005
(pg/di)
High
13.8
13.1
5.3-26.3
Pb-B newborn
Low
8.8
8.5
3.4-24.9
<0.001
((jg/dl)
High
12.1
11.-9
2.9-22.1
Pb placenta
Low
9.7
8.2
4.4-26.9
<0.005
(|jg/100 g)
High
13.3
12.0
7.1-28
Water Pb
Low
11.8
6.3
0.2-43.4
(pg/1)
High
247.4
176.8
61.5-1228.
5
Source: Hubermont et al. (1978)
*NS means not significant
**Water Lead <50 (jg/1
***Water Lead >50 pg/1
Table 11-37 presents the crosstabulation of drinking water lead and blood lead level for
the 114 adult women in the study. A strong trend of increasing blood lead levels with in-
creasing drinking water lead levels is apparent. A curvilinear regression function fits the
data better than a linear one. A similar model including weekly dietary intake was fitted to
the data for adults and infants. These models are in summary Tables 11-41 and 11-44.
The researchers also developed a linear model for the relationship between dietary intake
and drinking water lead. The equation indicates that, when the concentration of lead in water
was about 100 pg/1, approximately equal amounts of lead would be contributed to the total
PB11B/A 11-82 7/29/83
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PRELIMINARY- DRAFT
TABLE
11-37.
BLOOD
FOR
LEAD AND KETTLE WATER
ADULT WOMEN LIVING IN
LEAD CONCENTRATIONS
AYR
B1 ood
(jg per
1 ead
100 ml
Water
lead (fjg/1)
<10
11-
99
100-
299
300'
499
500-
999
1000-
1499
>1500
Total
<10
11-15
16-20
21-25
26-30
31-35
36-40
>40
8
4
1
5
7
3
4
3-,
12
9
2
2
n i^\2-; i
3 '
7
4
1
1
1
i :.p
3
' 5
4
2
1
4
2
2
1
3
1
3
1
3
13
17
22
25
12
10
4
11
Total
13
19
28
.19
19
8
8
114
week's intake from water and from~the~diet;" as water lead concentrations increase from this
value, the principal contributor would be water.
11.4.2.1.5 Central Directorate on Environmental Pollution study. The United Kingdom Central
Directorate on Environmental Pollution (1982) studied the relationship between blood lead
level and dietary and drinking water lead in infants. Subjects were first recruited by
soliciting participation of all pregnant women attending two hospitals and residing within a
single water distribution system. Each woman gave a blood sample and a kettle water sample.
The women were then allocated to one of six potential study groups based on the concentration
of water lead.
At the start of the second phase (duplicate diet) a total of 155 women volunteered
(roughly 17 to 32 per water lead level category). During the course of the study, 24 mothers
withdrew; thus a final study population of 131 mothers was achieved.
At 13 weeks of age, duplicate diet for a week's duration was obtained for each infant.
Great care was exerted to allow collection of the most accurate sample possible. Also, at
this time a variety of water samples were collected for subsequent lead analysis.
Blood samples were collected by venipuncture from mothers before birth, at delivery, and
about the time of the duplicate diet. A specimen was also collected by venipuncture from the
infant at the time of the duplicate diet. The blood samples were analyzed for lead by graph-
ite furnace AAS with deuterium background correction. Breast milk was analyzed analogously to
the blood sample after pretreatment for the different matrix. Water samples were analyzed by
flame atomic absorption. Food samples were analyzed after ashing by flameless atomic absorp-
tion.
PB11B/A 11-83 7/29/B3
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Both mothers and infants exhibited increased lead absorption by EEC directive standards.
The infants generally had higher blood leads than the mothers. However, in neither population
was there evidence of substantial lead absorption.
Water lead samples ranged from less than 50 fjg/1 to greater than 5D0 pg/1 , which was ex-
pected due to the sampling procedure used. First draw samples tended to be higher than the
other samples. The composite kettle samples and the random daytime samples taken during the
duplicate diet week were reasonably similar: 59 percent of the composite kettle samples con-
tained up to 150 pg/1 as did 66 percent of the random daytime samples.
Lead intakes from breast milk were lower than from duplicate diets. The lead intakes
• - .-A
estimated by duplicate diet analysis ranged from 0.04 mg/week to 3.4 mg/week; about 1/4 of the
diets had intakes less than 1,0 mg/week. The minimum intakes were truncated, as the limit of
detection for lead was 10 pg/kg and the most common diets weighed 4 kg or more.
The authors used both linear and cube root'models to describe their data. Models rela-
ting blood lead levels of infants to dietary intake are in Table 11-41. Models relating blood
lead levels for both mothers and infants to first flush water lead levels and running water
lead levels are in Tables 11-43 and 11-44, respectively. In most cases, the nonlinear (cubic)
model provided the best fit. Figure 11-15 illustrates the fit for the two models showing
infant blood lead levels vs. dietary lead intake.
11.4.2.1.6 Pocock study. Pocock et al. (1983) have recently reported an important study ex-
amining the relationship in middle aged men of blood lead level and water lead levels. Men
aged 40 to 59 were randomly selected from the registers of general practices located in 24
British towns. Data were obtained between January 1978 and June 1980.
Blood lead levels were obtained on 95 percent of the 7378 men originally selected. The
levels were determined by microatomic absorption spectrophotometry. A strict internal and ex-
ternal quality control program was maintained on the blood lead determinations for the entire
study period. Tap water samples were obtained on a small subset of the population. About 40
men were chosen in each of the 24 towns to participate in the water study. First draw samples
were collected by the subjects themselves, while a grab daytime and flushed sample were col-
lected hy study personnel. These samples were analyzed by several methods of AA5 depending
on the concentration range of the samples.
Blood lead and water lead levels were available for a total of 910 men from 24 towns.
Table 11-38 displays the association between blood lead levels and water lead levels. Blood
lead levels nearly doubled from the lowest to highest water lead category.
The investigators analyzed their data further by examining the form of the relationship
between blood and water lead. This was done by categorizing the water lead levels into nine
intervals of first draw levels. The first group (<6 (.ig/1) had 473 rren while the remaining
PB11B/A
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LINEAR
EQUATION .
CUBE ROOT
EQUATION
E •
O 30 —
? •
^ (
3.
Q
<
• •
LU
Q
O
O
• ••
ffl
2*
0
1-0
20
30
LEAD INTAKE, mg/wk
Figure 11-15. Blood-lead concentrations versus weekly lead
intake for bottle-fed infants.
PB11B/A 11-85 7/29/83
752<
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PRELIMINARY DRAFT
TABLE 11-38.
AND WATER LEAD (pg/dl)
RELATIONSHIP OF
IN 910 MEN AGED
BLOOD
40-59
LEAD (pg/dl)
FROM 24 BRITISH
TOWNS
First Draw
Water Lead
(pg/i)
Number of
Men
Mean Blood
Lead
(pg/dl)
Standard
Devi ation
% with
Blood Lead
>35 pg/dl
<50
789
15.06
5.53
0.7
50-99
69
18.90
7.31
4.3
100-299
40
21.65
7.83
7.5
^300
12
34.19 "
15.27
41.7
Total
910
15.89
6.57
1. 9
Daytime
Watc Lead
(|jg/i)
<50
845
15.31
5.64
0.7
50-99
36
19.62
7.89
8.3
100-299
23
24.78
9.68
17.4
5300
5
39.78
15.87
60.0
Total
909
15.85
6.44
1.8
Source: Pocock et al. (1983).
eight intervals had ~ 50 men each. Figure 11-16 presents the results of this analysis. "The
impression is that mean blood lead increases linearly with first draw water lead except for
the last group with very high water concentrations." The regression line shown in the figure
is only for men less than 100 (jg/1, and is given in Table 11-43. A separate regression was
done for the 49 men whose water lead exposures were greater than 10D pg/1. The slope for the
second line was only 23 percent of the first line.
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Additional analyses were done examining the possible influence of water hardness on blood
lead levels. A strong negative relationship (r = -0.67) was found between blood lead level
and water hardness. There is a possibility that the relationship between blood lead and water
hardness was due to the relationship of water hardness and water lead. It was found that a
relationship with blood lead and water hardness still existed after controlling for water lead
level.
The authors come to the following conclusion regarding the slope of the relationship
between blood lead and water lead:
This study confirms that the relation is not linear at higher levels. Previous
research had suggested a power function relationship—for example, blood lead in-
creases as the cube root of water lead. Our data, based on a large and more
representative sample of men, do not agree with such a curve, particularly at low
concentrations of water lead.
1.25
1.2
0
1 0.9
Q
«
hi
_i
O
O
o
_l
O.B
m
0.7
320
50
350
100
0
FIRST DRAW WATER LEAD (Mg/1)
61 52
473 6 0 51 50 65 49 49
Figure 11-16. Mean blood lead for men grouped by first draw water concentra-
tion.
Source: Pocock et al. (19831.
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754^
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PRELIMINARY DRAFT
11.4.2.2. Lead Ingestion from Experimental Dietary Supplements.
11.4.2.2.1 Kehoe study. Experimental studies have been used to study the relationship of
food lead and blood lead levels. Gross (1981) reanalyzed the results of Kehoe. Oral doses of
lead included 300, 1000, 2000, and 3000 pg/day. Each subject had a control period and an ex-
posure period. Some also had a post-exposure period. Blood samples were collected by veni-
puncture and analyzed by spectrograph^ and dithi2one methods during the study years. The
ingestion doses were in addition to the regular ingestion of lead from the diet. The results
of the dose response analysis for blood lead concentrations are summarized in Table 11-39.
Both subjects MR and EB had long exposure periods, during which time their blood lead
levels increased to equilibrium averages of 53 and 60 pg/dl, respectively. The exposure for
IF was terminated early before his blood lead had achieved equilibrium. No response in blood
lead was seen for subject SW whose supplement was 300 (jg/day.
TABLE 11-39. DOSE RESPONSE ANALYSIS FOR BLOOD LEAD LEVELS IN THE KEHOE STUDY
AS ANALYZED BY GROSS (1981)
Subject
Added lead
(pg/day)
Diet
(pg/day)
Di fference
Feces¦
(pg/day)
from control
Urine
(pg/day)
B1 ood
(pg/dl)
SW
300
308
208
3
-1
MR
1000
1072
984
55
17
EB
2000
1848
1547
80
33
IF*
3000
2981
2581
49
19
*Subject did not reach equilibrium.
11.4.2.2.2 Stuik study. Stuik (1974) administered lead acetate in two dose levels (20 and 30
pg/kg body weight-day) to volunteers. The study was conducted in two phases. The first
phase was conducted for 21 days during February-March 1973. Five males and five females aged
2+
18-26 were exposed to a daily dose of 20 pg Pb /kg of body weight. Five males served as
2+
controls. In the second phase, five females received 20 pg Pb /kg body weight and five males
2+
received 30 (jg Pb /kg body weight. Five females served as controls. Pre-exposure values
were established during the week preceding the exposures in both phases. Blood lead levels
were determined by Hessel's method.
The results of phase I for blood lead levels are presented in Figure 11-17. Blood lead
levels appeared to achieve an equilibrium after 17 days of exposure. Male blood lead levels
went from 20.6 pg/g to 40.9 pg/g while females went from 12.7 to 30.4 pg/g. The males seemed
to respond more to the same body weight dose.
PB11B/A 11-88 7/29/83
r:^;<
75b
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PRELIMINARY DRAFT
T~1 TT
500
CONTROL GROUP
EXPOSED MALE SUBJECTS: 20 ug/kg.'day
EXPOSED FEMALE SUBJECTS. 20 ^g'kg'dsy
.~
a
a
m
n
a.
300
___ ~
/
/
J
V
100
¦Pb EXPOSURE-
C»¦EDTA
Ca-EDTA
.MALE GROUP FEMALE GROUP
1_J ; l
13 8 10 15 17 22 29 31
DAYS
Figure 11-17. Average PbB levels, Exp. I.
Source: Stuik (1974).
38
46
CONTROL GROUP
500 \— ——— EXPOSED MALE SUBJECTS 30 ^g/kgiday
• EXPOSED FEMALE SUBJECTS 20 kg day
: 300
¦ Pb EXPOSURE-
J L
Ca EDTA
MALE GROUP
11 14 18 21
DAYS
25 27
34
PB11B/A
Figure 11-18. Average PbB levels, Exp. II.
Source: Stuik (1974)
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756•=:
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PRELIMINARY DRAFT
In phase I], males were exposed to a higher lead dose (30 |jg/kg*day). Figure 11-19 dis-
plays these results. Male blood lead rose higher than in the first study (46.2 vs. 40.9
M9/g); furthermore, there was no indication of a leveling off. Females also achieved a higher
blood lead level (41.3 vs. 30.4), which the author could not explain. The pre-exposure level,
however, was higher for the second phase than the first phase (12.7 vs. 17.3 [ig/g)-
11.4.2.2.3 Cools study. Cools et al. (1976) extended the research of Stuik (1974) by ran-
domly assigning 21 male subjects to two groups. The experimental group was to receive a 30
pg/kg body weight dose of oral lead acetate long enough to achieve a blood lead level of 30.0
pg/g, when the lead dose would be adjusted downward to attempt to maintain the subjects at a
blood lead level of 40.0 yg/g. The other group received a placebo.
In the pre-exposure phase, blood lead levels were measured three times, while during ex-
posure they were measured once a week, except for the first three weeks when they were deter-
mined twice a week. Blood lead was measured by flame AAS according to the Westerlund modifi-
cation of Hessel's method.
Pre-exposure blood lead values for the 21 volunteers averaged 172 ppb. The effect of
ingestion of lead acetate on blood lead is displayed in Figure 11-19. After 7 days mean blood
lead levels had increased from 17.2 to 26.2 pg/g. The time to reach a blood lead level of
35.0 |jg/g took 15 days on the average (range 7-40 days).
11.4.2.2.4 Schlegel study. Schlegel and Kufner (1979) report an experiment in which two sub-
+ ^
jects received daily oral doses of 5 mg Pb as an aqueous solution of lead nitrate for 6 and
13 weeks, respectively. Blood and urine samples were taken. Blood lead uptake (from 16 to 60
pg/dl in 6 weeks) and washout were rapid in subject HS, but less so in subject GK (from 12 to
29 pg/dl in 6 weeks). Time series data on other heme system indicators (FEP, 6-ALA-D,
6-ALA-U, coproporphyrin III) were also reported.
11.4.2.2.5 Chamberlain study. This study (Chamberlain et al., 1978) was described in Section
11.4.1, and in Chapter 10. The ingestion studies on six subjects showed that the gut absorp-
tion of lead was much higher when lead was ingested between meals. There were also dif-
ferences in absorption of lead chloride and lead sulfide.
11.4.2.3 Inadvertent Lead Ingestion from Lead Plumbing.
11.4.2.3.1 Early studies. Although the use of lead piping has been largely prohibited in
recent construction, occasional episodes of poisoning from this lead source still occur.
These cases most frequently involve isolated farms or houses in rural areas, but a surprising
urban episode was revealed in 1972 when Beattie et al. (1972a,b) showed the seriousness of the
situation in Glasgow, Scotland, which had very pure but soft drinking water as its source.
The researchers demonstrated a clear association between blood lead levels and inhibition of
the enzyme ALA-D in children living in houses with (1) lead water pipes and lead water tanks,
PB11B/A 11-90 7/29/83
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PRELIMINARY DRAFT
450
PREEXPOSURE
EXPOSURE
400
350
# EXPOSED (n = 11)
O CONTROLS In = 10!
300
200
100
5 7 12 14 19
28
42
14
0
35
30
20
LEAD DOSE
10
0
•14 0 49
DAYS
Figure 11-19. Lead in blood (mean values and range) in volunteers. In
the lower curve the average daily lead dose of the exposed group is
shown.
Source: Cools (1976).
PB1IB/A 11-91 7/29/63
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PRELIMINARY DRAFT
(2) no lead water tank but with more than 60 ft of lead piping and (3) less than 60 ft of lead
piping. The mean lead content of the water as supplied by the reservoir was 17.9 pg/1; those
taken from the faucets of groups 1, 2 and 3 were 934, 239 and 108 pg/1, respectively.
Another English study (Crawford and Crawford, 1969) showed a clear difference between the
bone lead contents of the populations of Glasgow and London, the latter having a hard, nonsol-
vent water supply.
In a study of 1200 blood donors in Belgium (DeGraeve et al., 1975), persons from homes
with lead piping and supplied with corrosive water had significantly higher blood lead levels.
11.4.2.3.2 Moore studies. M. R. Moore and colleagues have reported on several studies rela-
ting blood lead levels to water lead levels. Moore (1977) studied the relationship between
blood lead level and drinking water lead in residents of a Glasgow tenement. The tenement was
supplied with water from a lead-lined water tank carried by lead piping. Water samples were
collected during the day. Comparative water samples were collected from houses with-copper
pipes and from 15 lead plumbed houses. Blood samples were taken wherever possible from all
inhabitants of these houses. The data indicated that if a house has lead lined pipes, it is
almost impossible to reach the WHO standard for lead in water. Linear regression equations
relating blood lead levels to first flush and running water lead levels are in Tables 11-43
and 11-44.
Moore et al. (1977) also reported the analysis of blood lead and water lead data col-
lected over a four year period for different sectors of the Scottish population. The combined
data showed consistent increases in blood lead levels as a function of first draw water lead,
but the equation was nonlinear at the higher range. The water lead values were as high as
2000 jjg/-l. The fitted regression equation for the 949 subjects is in Table 11-43.
Moore et al. (1981a,b) reported a study of the effectiveness of control measures for
piumbosolvent water supplies. In autumn and winter of 1977, they studied 236 mothers aged 17
to, 37 in a post-natal ward of a hospital in Glasgow with no historical occupational exposure.
Blood lead and tap water samples from the home were analyzed for lead by AAS under a quality
control program.
A skewed distribution of blood lead levels was obtained with a median value of 16.6
pg/dl; 3 percent of the values exceeding 41 pg/dl. The geometric mean was 14.5 pg/dl. A
curvilinear relationship between blood lead level and water lead level was found. The log of
the maternal blood lead varied as the cube root of both first flush and running water lead
concentrations. In Moore et al. (1979) further details regarding this relationship are
provided. Figure 11-20 presents the observed relationship between blood lead and water lead.
In April 1978 a closed loop lime dosing system was installed. The pH of the water was
raised from 6.3 to 7.8. Before the treatment, more than 50 percent of random daytime water
samples exceeded 100 pg of Pb/1, the WHO standard. After the treatment was implemented, 80
PB11B/A 11-92 7/29/83
•759*?
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PRELIMINARY DRAFT
2
2
a.
Q
<
LU
_l '
Q
O
O
_i
00
23.5
25
24 26 25
24
2 3 4
WATER LEAD, >iM
23
UP TO 1(VM
NO. IN
GROUP
Figure 11-20. Cube root regression of blood lead on first flush water lead.
This shows mean ± S.D. of blood lead for pregnant women grouped in 7:
intervals of first flush water lead.
PB11B/A
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PRELIMINARY DRAFT
percent of random samples were less than 100 |jg/l. It was found, however, that the higher pH
was not maintained throughout the distribution system. Therefore, in August 1980, the pH was
raised to 9 at the source,'thereby maintaining the tap water at 8. At this time more than 95
percent of random daytime samples were less than 100 jjg/1.
In the autumn and winter of 1980, 475 mothers from the same hospital were studied. The
median blood lead was 6.6 pg/dl and the geometric mean was 8.1 g/d1. Comparison of the fre-
quency distributions of blood lead between these two blood samplings show a remarkable drop.
No other source of lead was thought to account for the observed change.
11.4.2.3.3 Thomas study. Thomas et al. (1979) studied women and children residing on two
adjacent housing estates. One estate was serviced by lead pipes for plumbing while the other
was serviced by copper pipe. In five of the homes in the lead pipe estate, the lead pipe had
been replaced with copper pipe. The source water is soft, acidic and lead-free.
Water samples were collected from the cold tap in the kitchen in each house on three oc-
casions at two-week intervals. The following water samples were collected: daytime - first
water out of tap at time of visit; running - collected after tap ran moderately for 5 minutes
after the daytime sample; and first flush - first water out of tap in morning (collected by
residents). Lead was analyzed by a method (unspecified in report) that was reportedly under
quality control.
Blood samples were collected from adult females (2.5 ml venipuncture) who spent most of
the time in the home and from the youngest child (capillary sample). Blood samples were ana-
lyzed for lead by a quality controlled unspecified method. Blood lead levels were higher in
the residents of the lead estate homes than in the residents of the copper estate homes.
Median levels for adult females were 39 jjg/d1 and 14.5 gg/d1 for the lead and copper estate
homes, respectively. Likewise, children's blood lead levels were 37 |jg/dl and 16.6 ng/dl,
respectively. Water lead levels were substantially higher for the lead estate than for the
copper estate. This was true for all three water samples.
The researchers then monitored the effectiveness of replacing the lead pipe on reducing
both exposure to lead in drinking water and ultimately blood lead levels.1 This monitoring was
done by examining subsamples of adult females for up to 9 months after the change was
implemented. Water lead levels became indistinguishable from those found in the copper estate
homes. Blood lead levels declined about 30 percent after 3 to 4 months and 50 percent at 6
and 9 months. At 6 months the blood lead levels reached those of women living in the copper
estates. A small subgroup of copper estate females was also followed during this time. No
decline was noted among them. Therefore, it was very likely that the observed reduction in
blood lead levels among the other women was due to the changed piping.
PB11B/A 11-94 7/29/83
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PRELIMINARY DRAFT
The researchers then analyzed the fortr, of the relationship between blood lead levels and
water lead levels. They tried several different shapes for the regression line. Curvilinear
models provided better fits. Figure 11-21 depicts the scatter di as,r;.am: of bl ood lead and water
lead. An EPA analysis of the data is in Table 11-43.
A later publication by Thomas (1980) extended his earlier analysis. This more extensive
analysis was limited to lead estate residents. Subjects who did.not consume the first draw-
water from the tap had significantly lower blood lead levels than those who did (10.4 pg/dl
difference/. No gradient was noted in blood lead levels with increasing water consumption.
Furthermore, no gradient in blood lead levels was noted' with total beverage consumption (tea
ingestion frequency). -
11.4.2.3.4 Worth stucy. In Boston, Massachusetts an investigation was made of wate" distri-
bution via lead pipes. In addition to the data on lead in water, account was taken of socio-
economic and demographic factors as well as other sources of lead in the environment (Worth et
a 1. , 1981). Participants, 771 persons from 383 households, were classified into age groups of
less than 6, 6 to 20, and greater than 20 years of age for analysis. A clear association
between water lead and blood lead was apparent (Table 11-40). For children unde^ 6 years of
age, 34.6 percent of those consuming water with lead above the U.S. standard of 50 pg/1 had a
blood lead value greater than or equal to 35 pg/dl , whereas only 17.4 percent of those con-
suming water within the standard had blcod lead values of greater than or equal to 35 pg/d1.
Worth et al. (1981) have published an extensive regression analysis of these data. Blood
lead levels were found to be significantly related to ace, education of head of household, sex
and water lead exposure. Of the two types of water samp^s taken, standing grab sample and
running grab sample, the former was shown to be more closely related to blcod lead levels than
the latter. Regression equations are given in Tables 11-43 and 11-44.
11.4.2.4 Summary of Dietary Lead Exposures Including Water. It is difficult to obtain accu-
rate dose-response relationships between blood lead levels and lead levels in. food or water.
Dietary intake must be estimated, by duplicate diets or fecal lead determinations. Water lead
levels can be determined with- some accuracy, but the varying amounts of water consumed by dif-
ferent individuals adds to the uncertainty of the estimated relationships.
Studies relating blood lead levels to dietary lead intake are compared in Table 11-41.
Most of the subjects in the Sherlock et al. (1982) and United Kingdom Central Directorate on
Environmental Pollution (1982) studies received quite high dietary lead levels (>300 pg/day).
The fitted cubic equations give high slopes at lower dietary lead levels. On the other hand,
the linear slope of the United Kingdom Central Directorate on Environmental Pollution (1982)
study is probably an underestimate of the slope at lower dietary lead levels. For these
PB11B/A 11-95 7/29/83
'62
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PRELIMINARY DRAFT
MAXIMUM WATER LEAD
LEVELS ON COPPER' ESTATE
MEDIAN WATER LEAD
LEVELS ON LEAD' ESTATE
FIRST FLUSH WATER LEAD, mg/liter
Figure 11-21. Relation of blood lead (adult female) to first flush water lead in
combined estates. (Numbers are coincidental points: 9 = 9 or more.) Curve a,
present diata; curve b, data of Moore et at.
PB11B/A
11-96
7/29/83
763^
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'PRELIMINARY' DRAFT
TABLE 11-40. BLOOD LEAD LEVELS OF 771 PERSONS IN RELATION
TO LEAD CONTENT OF DRINKING WATER, BOSTON, MA
Persons consuming water (standing grab samples)
<50 ug Pb/1 =?50 uq Pb/1
Blood lead
levels, mg/d 1
No.
Percent
No.
Percent
Total
<35
622
91
68
77.3
690
>35
61
9
20
22. 7
81
Total
683
100
88
100.0
771
X2 = 14.35; df = 1.
P <0.01.
Source: Worth et al. (1981).
reasons, the Ryu et al. (1983) study is the most believable, although it only applies to in-
fants. Estimates for adults should be taken from the experimental studies or calculated from
assumed absorption and half-life values.
The experimental studies are summarized in Table 11-42. Most of the dietary intake sup-
plements were so high that many of the subjects had blood lead concentrations much in excess
of 30 |jg/dl for a considerable part of the experiment. Blood lead levels thus may not
completely reflect lead exposure, due to the previously noted nonlinearity of blood lead re-
sponse at high exposures. The slope estimates for adult dietary intake are about 0.02 (jg/dl
increase in blood lead per pg/day intake, but consideration of blood lead kinetics may in-
crease this value greatly. Such values are a bit lower than those estimated from the popu-
lation studies extrapolated to typical dietary intakes in Table 11-41, about 0.05 |jg/dl per
|jg/day. The value for infants is much larger.
The studies relating first flush and running water lead levels to blood lead levels are
in Tables 11-43 and 11-44, respectively. Many of the authors chose to fit cube root models to
their data, although polynomial and logarithmic models were also used. Unfortunately, the
form of the model greatly influences the estimated contributions to blood lead levels from
relatively low water lead concentrations.
The models producing high estimated contributions are the cube root models and the loga-
rithmic models. These models have a slope that approaches infinity as water lead concentra-
tions approache zero. All other ar,e,. polynomial models, either linear, guadratic or cubic.
The slopes of these models tend to be relatively, constant at the origin.
PB11B/A
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TABLE 11-41. STUDIES RELATING BLOOD IEAD LEVELS (pg/dl) TO DIETARY INTAKES (pg/day)
Study
Analysis
Model
Model
D.E.
Estimated Predicted blood lead
Blood contribution (pg/dl) for
lead at a given dietary intake
0 H.^0 Pb (pg/day)
Slope from 100 to 200
pg/d. , pg/dl per pg/d
Sherlock et al.
(1982) study of
31 adult women
in Ayr
I,
Sherlock'iet al.
(1982) study of
infants in Ayr
combi ned'Jwi th U.K.
Central Directorate
Study
U.K. Central
D i rectorate
(1982) Study
of infants in
Glasgow
Ryu et al. (1983)
study of infants
Sherlock et al.
(1982)
Sherlock et al.
(1982)
U.K. Central
Di rectorate
on Environmental
Pollution
(1982)
EPA
PBB = -1.4 ~ 3.6 V PBO 0 52
P8B = 2.5 ~ 5.0 V PBO
PBB = 17.1 ~ .056(PBO) 0.39
or 3
PBB = 3.9 ~ 4.6 V PBO 0.43
PBB = A ~ .16PBD
-1.4
2.5
17. 1
3.9
100
16. 7
23.2
200
?1. 1
29.2
300
24.1
33.5
5.6 11.2 16.8
21.4 26.9 30.8
16.0 32.0 48.0
0.034
"O
JO
0.060
¦3»
-JO
T-C
0.056
0.053
0.16
-jo
-------
TABLE 11-42. STUOIfS 1NV0LVING BLOOD LEAD IFVFIS (tjg/d 1)
AND EXPERIMENTAL OlFIARY INIAKES
Study Subjects Exposure Torm of Lead Blood Lead Slope* pg/dl
Initial TTnal per pg/d.
Stuik (1974)
Study 1
5 adult male students
5 adult female students
5 adult male students
20 |ig Ph/k(|/d.iy - 21 d.
20 pg Pb/kg/day - 21 d
Controls - 21 d.
Lead acetate
lead acetate
Placebo
20 6
12. 1
20.6
40.9
30.4
1ft. 4
0.017**,***
0.018**,***
"D
30
Study II
.111 J.
Cools et ;a>l.
(1976) ji
''f;
Schlegel*and
Kufner (1979)
5 adult female students
b adult male students
5 adult female students
20 pg Pb/kg/day
30 pg Pb/kg/day
Controls
Lead acetate
lead acetate
Placebo
17. 3
16. 1
-17.0
41.3
46.2
-17.0
0.022
0.014
T—
3C
z
11 adult males
10 ^ult males
30 pg Pb/kg/day -7 days
Controls
1ead acetate
Placebo
1 /. 2
26 2
-19.0
0.027***
-<
O
1 adult-male
1 adult male
50 pg Ph/kg/day - 6 wk.
70 pg Pb/kg/day -13 wk.
Lead nitrate
Lead nitrate
16.5
12.4
64.0
30.4
0.014
0.004****
3D
>
n
—K
Gross (1979)
analysis of
Kehoe1 s
experiments
1 adult male
1 adult male
1 adult male
1 adult male
300 pg/day
1000 pg/day
2000 pg/day
3000 pg/day
Lead acetate
Lead acetate
Lead acetate
Lead acetate
-1
+ 17
~33
~19
[0]
0.017
0.016
0.006*****
* Exposure (pg/d) = Exposure (pg/kg/day) x 70 kg (or males, 55 kg for females. Slope = (Final - Initial Blood Lead)/Exposure (pg/d).
** Corrected for decrease of 2.2 pg/dl in control males.
*** Assumed mean life 40d. This increases slope estimate for short-term studies. Stuik Study 1 would be 0.042, 0.044 respectively for males, females.
•••• Assumed limited absorption of lead.
«««* Removed from exposure before equilibrium.
-------
TABLE 11-43. STUDIES RELATING BLOOD LEAD LEVELS (Mg/dl) TO FIRST-FLUSH WATER LEAD (Mg/1)
Estimated
Predi
icted blood lead
Blood
contribution
(Mg/di
for
Model
lead at
a given water
lead (
k-g/i)
Study
Analysis
Model
R2
O.F.
0 H20 Pb
5
10
25
50
Worth et al. (1981) study of 524
Worth et al. (1981)
In (PBB) = 2.729 PBW - 4.699
(PBW)2 ~
0.18
14
20. 5
0.3
0.6
1.4
2. 7
subjects in greater Boston. Water
2.116 (PBW)3 + other terms for age,
leads (standing water) ranged from
sex, education, dust (PBW is
in mg/1)
<13 to 110B (jg/1. Blood leads
ranged from 6 to 71.
EPA
ln(PBB) = In (40.69 PBW - 21.
.89 (PBW)2
0. 18
11
21.1
0.2
0.4
1.0
2. 1
+ other terms tor age, sex, i
education,
dust) (PBW is in mg/1)
Moore et al. (1979) study of 949
Moore et al. (1979)
PBB = 11.0,+ 2.36 (PBW)1/3
2
11.0
4.0
5. 1
6.9
8.7
subjects from different areas of
Scotland. Water leads were as
high as 2000 pg/1.
Hubermont et al. (1978) study of
Hubermont et al.
PBB = 9.62 + 0.756 fn (PBW)
0.14
2
8.4"
2.4
3.0
3.7
4.2
70 pregnant women in rural Belgium.
(1978)
Water leads ranged from 0.2 to
1228.5 (jg/1. Blood leads ranged
¦ .
from 5.1 to 26. 3 jjg/dl.
U.K.'Central Directorate (198?)
U.K. Central
PBB = 13.2 ~ 1.8 (PBW)1/3
0,11
V . 2 ,
13.2
3.1
3.9
5.3
6.6
study of 128 mothers in greater
Directorate on
PBB = 18.0 ~ 0.009 PBW
V
0.05
2
18.0
O.'O
0. 1
0.2
! 0.4
Glasgow. Water leads ranged from
Environmental
• ;
under 50 ^jg/1 (35%) to over 500
Pollution
pg/1 (11%). Blood leads ranged
(1982)
from under 5 jjg/dl (2%) to over
' .
35 Hg/dl (5%).
U.K. Central Directorate (1982)
U.K. Central
PBB = 9.4 ~ 2.4 (PBW)1/3
0. 17
2
9.4
4.1
5.2
7.0
8.8
study of 126 infants (as above).
Directorate on
PBB = 17.1 ~ 0.018 PBW
0.12
2
17.1
0. 1
0.2
0.4
0.9
Blood leads ranged from under 5
Envi ronmental
pg/dl (4%) to over 40 pg/d1 (4%).
Pollution
(1982)
Thomas et al. (1979) study of 115
EPA
In (PBB) = [14.9 + 0.041 PBW
- 0.000012
0.61
3
14.9
0.2
0.4
1.0
2.0
adult Welsh females. Water leads
(PBW)2]
ranged from <10 to 2800 pg/dl.
Blood leads ranged from 5 to 65
(_jg/d 1.
Moore (1977) study of 75 residents
Moore (19/7)
PBB = 15.7 + 0.015 PBW
0.34
2
15.7
0.1
0.2
0.4
0.8
of a Glasgow tenement
Pocock et al. (1983) study of 7735
Pocock et al. (1983)
PBB = 14.48 + 0.062 PBW
2
14.5
0.3
0.6
1.6
3. 1
men aged 40-59 in Great Britain.
Water leads restricted to <100 |ig/l.
'minimum water lead of 0.2 pg/dl used instead of 0
-------
TABLF 11-44. STUOIFS RIIATINfi HI OOO IEAD LIVFLS ((ig/dl) TO RUNNING WAH.R Lt AD (|ig/l)
Study
Worth et al. (1981) study of 524 sub-
jects in greater Boston. Water leads
ranged from <13 to 208 jjg/dl. Blood
leads ranged from 6 to 71.
Worth et al. (1981) study restricted
to 390 subjects aged 20 or older.
Worth et al. (1981) study restricted
to 249 females ages 20 to 50.
U.K. Central Directorate (1982)
study of 128 mothers in greater
Glasgow. Water leads ranged from
under 50 jjg/1 (61%) to over 500
jjg/dl (5%). Blood leads ranged
from under 5 jjg/dl (2%) to over
35 Mg/dl (5%).
U.K. Central Directorate (1982)
study of 126 infants in greater
Glasgow. Water leads ranged from
under 50 jjg/1 (61%) to over 500
jjg/dl (5%). Blood leads ranged
from under 5 pg/dl (4%) to over
40 pg/dl (4%).
Moore (1977) study of 75 residents
of a Glasgow tenement.
Sherlock et al. (1982) study of 114
adult women. Blood leads ranged
<5 to >61 jjg/dl. Kettle water leads
ranged from <10 to >2570 uq/1.
Analys i s
EPA
U.S. EPA (1980)
EPA
I
, ,U.S.l,rEPA (1980)
t tPA
EPA
U.K. Central
Di rectorate on
Envi ronmental
Pollution "
(1982)
U.K. Central
Directorate on
Envi ronmental
Pollution
(1982)
Moore (1977)
Sherlock et al.
(1982)
In (P8B)
age, sex,
Mode 1
(0 042b PliW ~ other terms for
education, and dust)
.1/3
PB8 - 14.33 ~ 2.541 (PBW)*
FPA In (PBB) ~'ln (18.6 ~ 0.0/1 PBW)
In (PBB) = In (0.073 PBW ~ other terms
for sex, education, and dust)
1/3
PBB = 13:3B ~ 2.487 (PHW-) . , v.
In (PBB) = In (17.6 ~ 0-067 PBW)
In (PBB) = (0.067 PBW ~ other terms
for education and dust)
PBB - 12.8 ~ 1.8 (PBW)1/3
PBB = 18.1 ~ .014 PBW
PBB - 7.6 ~ 2. 3 (PBW)
PBB = 16.7 + 0.033 PBW
1/3
PBB = 16.6 ~ 0.02 PBW
PBB = 4.7 ~ 2.78 (PBW)
1/3
Model
R* OF.
0.153
0.030
0.032
0.091
0.12
0.06
0.22
0.12
0.27
0.56
10
0.023 2
0.028 2
0 153 7
Fstimated
Blood
lead at
0 H.^,0 Pb
21.3
14 3
18. 6
18 8
13.4
17.6
1/.6
12.8
18. 1
7.6
16. 7
16.6
4.7
Predicted blood lead
contribution (tjg/dl) for
a given water lead (iuj/1)
0.2
4 4
0.4
0.4
4. 3
0. 3
0. 3
10
0.4
25
50
1.1 2.1
5.4 7.4
0 7 1.8
0.7 1.8
5.4 7.3
0.7 1.7
0.7 1.7
9.4
3.6
3. 7
9 2
3.4
3.4
3.1 3.9 5.3 6.6
0.1 0.1 0.4 0.7
3.9 5.0 6.7 8.5
0.2 0.3 0.8 1.6
0.1 0.2 0.5 1.0
4.8 6.0 8.1 10 2
-------
PRELIMINARY DRAFT
The problem of determining the most appropriate model(s) is essentially equivalent to the
low dose extrapolation problem, since most data sets estimate a relationship that is primarily
based on water lead values from 50 to 2000 pg/dl. The only study that determines the re-
lationship based on lower water lead values (<100 ng/1) is the Pocock et al. (1983) study.
The data from this study, as well as the authors themselves, suggest that in this lower range
of water lead levels, the relationship is linear. Furthermore, the estimated contributions to
blood lead levels from this study are quite consistent with the polynomial models from other
studies, such as the Worth et al. (1981) and Thomas et al. (1979) studies. For these reasons,
the Pocock et al. (1983) slope of 0.06 is thought to represent the current best estimate. The
possibility still exists, however, that the higher estimates of the other studies may be cor-
rect in certain situations, especially at higher-water lead levels (>100 pg/1).
11.4.3 Studies Relating Lead in Soil and Dust to Blood Lead
The relationship of exposure to lead contained in soil and house dust, and the amount of
lead absorbed by humans, particularly children, has been the subject of scientific investi-
gation for some time (Duggan and Williams, 1977; Barltrop, 1975; Creason et al., 1975; Barl-
trop et al., 1974; Roberts et al., 1974; Sayre et al., 1974; Ter Haar and Aronow, 1974; Fairey
and Gray, 1970). Duggan and Williams (1977) published an assessment of the risk of increased
blood lead resulting from the ingestion of lead in dust. Some of these studies have been con-
cerned with the effects of such exposures (Barltrop, 1975; Creason et al, , 1975; Barltrop et
al., 1974; Roberts et al., 1974; Fairey and Gray, 1970); others have concentrated on the means
by which the lead in soil and dust becomes available to the body (Sayre et al., 1974; Ter Haar
and Aronow, 1974).
11.4.3.1 Omaha Nebraska Studies. The Omaha studies were described in Section 11.4.1.7. Soil
samples were 2-inch cores halfway betweenthe bu^ljdipg and the lot line. Household dust was
collected from vacuum cleaner bags. The ufo,l lowing analysis was provided courtesy of Dr.
Angle. The model is also described in Section 11.4.1.8, and provided the following coeffi-
cients and standard errors:
Factor
Coefficient
Asymptoti c
Standard Error
Intercept (jjg/dl)
Air lead (pg/m3)
Soil lead (mg/g)
House dust (mg/g)
15.67
1.92
6.80
7.18
0.398
0.600
0.966
0.900
Multiple R2 = 0.198
Sample size = 1075
Residual standard deviation = 0.300 (geometric standard deviation = 1.35)
PB11B/A
11-102
7/29/83
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PRELIMINARY DRAFT
11.4.5.2 ihf Stark Study. EPA analyses of data from children in New Haven (Stark et a 1.,
196^) found substantial evidence for aust and soil lead contributions to blood lead, as well
as evidence for increased blood lead due to decreased household cleanliness. Tnese factor's
are somewhat correlated with each other,' but the separate roles of increasec concentration and
co:.l ' J could be distinguished. The fitted models were summarized ear'ier (Section
11.3.6.1).
11.4.3.3 The Silver Va11ey/Ke'1oqq Icaho Study. The Silver Valley Kellogg Idaho stucy was
discussed in section 11.4.1.5. Yan
-------
PRELIMINARY DRAFT
paint, and lead in soil were all independently and significantly related to blood lead levels.
Using the model described in Appendix 11B, the following coefficients and standard errors were
obtai ned:
Multiple R2 = 0.386
Residual standard deviation = 0.2148 (geometric standard deviation = 1.24)
11.4.3.5 Barltrop Studies. Barltrop et al. (1974) described two studies in England investi-
gating the soil lead to blood lead relationship. In the first study, children aged 2 and 3
and their mothers from two towns chosen for their soil lead content had their blood lead
levels determined from a capillary sample. Hair samples were also collected and analyzed for
lead. Lead content of the suspended particulate matter and soil was measured. Soil samples
for each home were a composite of several 2-inch core samples taken from the yard of each
home. Chemical analysis of the lead content of soil, in the two towns showed a 2- to 3-fold
difference, with the values in the control town about 200 to 300 (jg/g compared with about 700
to 1000 (jg/g in the exposed town. A difference was also noted in the mean air lead content of
the two towns, 0.60 ^ig/m3 compared with 0.29 pg/m2. Although this difference existed, both
air lead values were thought low enough not to affect the blood level values differentially.
Mean surface soil lead concentrations for- the two communities were statistically different,
the means for the high and low community being 909 and 398 M9/g> respectively. Despite this
difference, no statistically significant differences3in;maternal blood lead levels or chil-
dren's blood or hair lead levels were noted. Furtherpsta.tistical analysis of the data, using
correlational analysis on either raw or log-transformed blood lead data, likewise failed to
show a statistical relationship of soil lead with either blood lead or hair lead.
The second study was reported in both preliminary and final form (Barltrop et al., 1974;
Barltrop, 1975). In the more detailed report (Barltrop, 1975), children's homes were clas-
sified by their soil lead content into three groups, namely. less than 1,000; 1,000 to
10,000; and greater than 10,000 pg/g. As shown in Table 11-45, children's mean blood lead
levels increased correspondingly from 20.7 to 29.0 pg/dl. Mean soil lead levels for the low
and high soil exposure groups were 420 and 13,969 \iq/q, respectively. Mothers' blood levels,
Factor
Coefficient
Asymptoti c
Standard Error
Intercept (pg/dl)
Pica (1 = eater, 0 = otherwise)
Traffic Pattern (1 = high, 0 = low)
Siding paint (mg/cm2)
Door paint (mg/cm2)
Soil lead (mg/g)
25.92
7. 23
7.11
0.33
0.18
1.46
1.61
1.60
1.48
0.11
0.12
0.59
PB11B/A
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7/29/83
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PRELIMINARY DRAFT
howeve-, did not reflect this trend; nor were the children's fecal lead levels different
across the soil exposure areas.
An analysis of the data in Table 11-45 gives the following model:
blood lead (pg/dl) = 0.64 soil lead (1000 pg/g) + 20.98
No confidence intervals were calculated since the calculations were based on means.
TABLE 11-45. MEAN BLOOD AND SOIL LEAD
CONCENTRATIONS IN ENGLISH STUDY
Category
Chi 1dren's
of soil lead,
Sample
blood lead,
Soil lead,
pg/g
si ze
pg/di
pg/g
<1000
29
20.7
420
1000-10000
43
23.8
3390
>10000
10
29.0
13969
Source: Barltrop, 1975.
11.4.3.6 The British Columbia Studies. Neri et al. (1978) studied blood leaa levels in chil-
dren living in Trail, British Columbia. These blood lead measurements were made by the
capillary method. An episode of poisoning of horses earlier had been traced to ingestion of
lead. Environmental monitoring at that time did not suggest that a human health risk existed.
However, it was later thought wise to conduct a study of lead absorption in the area.
Trail had been the site of a smelter since the turn of the century. The smelter had
undergone numerous changes for reasons of both health and productivity. At the tiir.e of the
blood lead study, the smelter was emitting 300 pounds of lead daily, with ambient air lead
3
levels at about 2 pg/m in 1975. Nelson, BC was chosen as the control city. The cities are
reasonably close (--30 miles distant), are similar in population, and served by the same water
basin. The average air lead level in Nelson during the study was 0.5 pg/m^.
Initial planning called for the sampling of 200 children in each of three age groups (1-3
years, 1st grade and 9th grade) from each of the two sites. A strike at the smelter at the
onset of the study caused parts of the Trail population to move. Hence, the recruited sample
deviated from the planned one. School children were sampled in May 1975 at their schools
while the 1- to 3-year olds were sampled in September 1975 at a clinic or home. This delayed
sampling was intentional to allow those children to be exposed to the soil and dust for the
entire su.nmer. Blood and hair samples were collected from eacli child.
PB11B/A
11-105
772^
7/29/83
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PRELIMINARY DRAFT
Blood samples were analyzed for lead by anodic stripping voltammetry. The children in
the younger age groups living in Trail had higher blood lead levels than those living' in
Nelson, An examination of. the frequency distributions of the blood lead levels shewed that
the entire frequency of the distribution shifted between the residents of the two cities.
Interestingly,- there was no difference in the ninth grade children.
Table 11-46 displays the results of the soil lead levels along with the blocd lead levels
obtained in the earlier study. Blood leac levels were higher for 1- to 3-year olds and first
graders in r-the- two, •• nearest-to-smelter categories than in the far-from-smelter category.
Again, no difference was noted for the ninth graders.
An EPA analysis of the Neri et al. (1978) data gives the following models for children 1-
to 3-years old:
Blocd lead (pg/dl) = 0.0076 soil lead (jjg/g) ~ 15.43, and
Blood lead ((.ig/dl) = 0.0C46 soil lead (jg/g) + 16.37
for children in grade one. No confidence intervals were calculated since the analysis was
based on means.
TABLE 11-46. LEAD CONCENTRATION OF SURFACE SOIL AND CHILDREN'S
BLOOD BY RESIDENTIAL AREA OF TRAIL, BRITISH COLUMBIA
Blood lead concentration
Mean (pg/dl), mean ± standard
soil lead error (and no. of children)
concentration ((jg/g)
Residential i standard error 1- to 3- Grade one
area(s) (ard no. of samples) year olds children
1 and
9
c-
225
+
39 (26)
17.2
+
1.1 (27)
18.0
+
1.9 (18)
5
777
+
239 (12)
19.7
+
1.5 (11)
18.7
+
2.3 (12)
S
570
+
143 (11)
20.7
+
1.6 (19)
19. 7
±
1.0 (16)
3, 4,
and 8
1674
183 (53)
27.7
+
1.8 (14)
23. 8
+
1.3 (31)
6 and
7
1800
+
212 (51)
30.2
+
3.0 (16)
25.6
+
1.5 (25)
Total
1320
+
212 (153)
22.4
±
1.0 (87)
21.9
+
0.7 (103)
Source: Schmitt et al., 1979.
11.4.3.7 Other Studies of Soil and Dusts. Lepow et al. (1975) studied the lead content of
air, house dust and dirt, as well as the lead content of dirt on hands, food and wate^, to
determine the cause of chronically elevated blood lead levels in 10 children 2- to 6-years-old
PB11B/A ll-106ry^3<: 7/29/83
-------
PRELIMINARY DRAFT
in Hartford, Connecticut. Lead-based paints had been eliminated as a significant source of
lead for these children. Ambient air lead concentrations varied from 1.7 to 7.0 pg/rr.^. The
mean lead concentration in dirt was 1,200 pg/g and in dust, 11,000 .pg'/gv Themean concentra-
tion of lead in dirt on children's hands was 2,400 pg/g. The mean weight of samples of dirt
fraii: hands was 11 mg, which represented only a small fraction of the total dirt on hards. Ob-
servation of the mouthing behavior in these young children led to the conclusion that the
hands-in-mouth exposure route was the principal cause of excessive lead accumulation.
Several studies have investigated the mechanism by which lead'from soil and dust- gets in-
to the body (Sayre et a 1. , 1974; Ter Haar and Aronow, 1974). Sayre et al. (1974) in
Rochester, New York, demonstrated the feasibility of house dust as a source of lead for chil-
dren. Two groups of houses, one inner city and the other suburban, were chcsen for the study.
Lead-free sanitary paper towels were used to collect dust samples from house surfaces and the
hands of children (Vostal et al., 1974). The medians for the hand and household samples were
used as the cutpoints in the chi-square contingency analysis. A statistically significant
difference between the urban and suburban homes for dust levels was noted, as was a relation-
ship between household dust levels and hand dust levels (Lepow et al., 1975).
Ter Haar and Arcnow (1974) investigated lead absorption in children that can be at-
tributed to ingestion cf dust and dirt. They reasoned that because the proportion of the
naturally occurring isotope of 210Pb varies for paint chips, airborne particulates, fallout
dust, house dust, yard dirt and street dirt, it would be possible to identify the sources of
ingested lead. They collected 24-hour excreta from eight hospitalized children on the first
day cf hospitalization. These children, 1- to 3-years old, were suspected of having elevated
body burdens of lead, and one criterion for the suspicion was a history of pica. Ten children
of the same age level, who lived in good housing in Detroit and the suburbs, were selected as
controls and 24-hour excreta were collected from them. The excreta were dried and stable lead
as well as 210Pb content determined. For seven hospitalized children, the stable lead mean
value was 22.43 pg/g dry excreta, and the eighth child had a value of 1640 pg/g. The con-
trols' mean for stable lead was 4.1 pg/g dry excreta. However, the respective means for 210Pb
expressed as pCi/g dry matter were 0.044 and 0.040. The authors concluded that because there
is no significant difference between these means for 21uPb, the hypothesis that young children
with pica eat dust is not supported. The authors further concluded that children with
evidence of high lead intake did not have dust and air suspended particulate as the sources of
their lead. It is clear that air suspended particulate did net account for the lead levels in
the hospitalized children. However, the 21uPb concentrations in dust and feces were similar
for all children, making it difficult to estirrate the dust contribution.
Hoyworth et al. (1981) studied a population of children exposed to lead in mine tailings.
These tailings were used in foundations and playgrounds, and had a lead content ranging from
PB11B/A 11-107 7/29/83
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PRELIMINARY DRAFT
10,000 to 15,000 pg/g. In December 1979 venous blood samples and hair were collected from 181
of 346 children attending two schools in Western Australia. One of the schools was a primary
school; the other was a combined primary and secondary school. Parents completed question-
naires covering background information as well as information regarding the children's expo-
sure to the tailings. Blood lead levels were determined by the AAS method of Farrely and
Pybos. Good quality control measures were undertaken for the study, especially for the blood
lead levels. B^ood leac! levels were higher in beys vs. girls (mean values were 14.0 and 10.4
pg/dl, respectively). This difference was statistically significant. Five percent of the
children (n = 9) had blood lead levels greater than 25 pg/dl. Five of the children had blood
lead levels greater than 30 |jg/dl. Blood lead levels decreased significantly with age and
were slightly lower in children living on properties on which tailings were used. However,
they were higher for children attending the school that used the tailings in the playground.
Landrigan et al. (1982) studied the impact on soil and dust lead levels on removal of
leaded paint from the Mystic River Bridge in Masschusetts. Environmental studies in 1977 in-
dicated that surface soil directly beneath the bridge had a lead content ranging frcrc 1300 to
1800 pg/g. Analysis of concomitant trace elements showed that the lead came from the bridge.
A concurrent survey of children living in Chelsea (vicinity of bridge) found that 49 percent
of 109 children had blood lead levels greater than or equal to 30 pg/d1. Of children living
more distant from the bridge "only" 37 percent had that level of blood lead.
These findings prompted the Massachusetts Port Authority to undertake a program to delead
the bridge. Paint on parts of the bridge that extended over neighborhoods was removed by
abrasive blasting and replaced by zinc primer. Some care was undertaken to minimize both the
occupational as well as environmental exposures to lead as a result of the blasting process.
Concurrently with the actual deleading work, a program of air monitoring was established
to check on the environmental lead exposures being created. In June 1980 four air samples
taken at a point 27 meters from the bridge had a mean lead content of 5.32 pg/m^. As a result
of these findings air pollution controls were tightened; mean air lead concentrations 12
3
meters from the bridge in July were 1.43 pg/m .
Samples of the top 1 cm of soil were obtained in July 1980 from within 30, 30 to 80, and
100 meters from the bridge. Comparison samples from outside the area were also obtained.
Samples taken directly under the bridge had a mean lead content of 8127 pg/g.
Within 30 meters of the bridge, the mean content was 3272 pg/g, dropping to 457 pg/g at 30 to
80 meters. At 100 meters the soil lead level dropped to 197 pg/g. Comparison samples ranged
from 83 to 165 pg/g depending on location.
Fingerstick blood samples were obtained on 123 children 1-5 years of age living within
0.3 km of the bridge in Charlestown. Four children (3.3 percent) had blood lead levels
PB11B/A
11-108
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7/29/83
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PRELIMINARY DRAFT
greater than 30 jjg/d 1 with a maximum of 35 pg/d 1. All four children lived within two blocks
of the bridge. Two of the four had lead paint in their horres but it was intact. None of the
76 children living more than two blocks from the bridge had blood leads greater than or equal
to 30 pg/dl, a statistically significant difference.
5iic 11 j ear' s (1973) case report from New Zealand ascribes a medically diagnosed case of
lead poisoning to high soil lead content in the child's home environment. Shellshear et al.
(1975) followed up his case report of increased lead absorption resulting from exposure to
lead contaninated soil with a study carried out in Christchurch, New Zealand. Two related
activities comprised the study. First, from May 1973 to November 1973, a random study of
pediatric admissions to a local hospital was made. Blood samples were taken and analyzed for
lead. Homes were visited and soil samples were collected and analyzed for lead. Lead anal-
yses for both soil and blood were conducted by AAS. Second, a soil survey of the area was
undertaken. Whenever a soil lead value greater than 300 pg/g was found and a child aged one
to five was present, the child was referred for blood testing.
The two methods of subject recruitment yielded a total of 170 subjects. Eight (4.7 per-
cent) of the children had blood lead equal to or greater than 40 (jg/d1, and three of them had
a blood lead equal to or greater than 80 pg/dl. No correlation with age was noted. The mean
tf.ood lead of the pediatric admissions was 17.5 pg/d 1 with an extremely large range (4 to 170
pg/dl). The mean blood lead for soil survey children was 19.5 pg/dl.
Christchurch was divided into two sections based on the date of development of the area.
The inner area had developed earlier and a higher level of lead was used there in the house
paints. The frequency distribution of soil lead levels showed that the inner zone samples had
much higher soil lead levels than the outer zone. Furthermore, analysis of the soil lead
levels by type of exterior surface of the residential unit showed that painted exteriors had
higher soil lead values than brick, stone or concrete block exteriors.
Analysis of the relationship between soil lead and blood lead was restricted to children
from the sampled hospital who had lived at their current address for at least 1 year. Table
11-47 presents the analysis'of these results. Although the results were not statistically
significant, they are suggestive of an association.
Analysis of the possible effect of pica on blood lead levels showed tie mean blood lead
for children with pica to be 32 jj g/d 1 while those without pica had a mean of 16.8 j.ig/dl. The
pica blood lead mean was statistically significantly higher than the non-pica mean.
Wedeen et al. (1978) reported a case of lead nephropathy in a black female who exhibited
geophagia. The patient, who had undergone chelation therapy, eventually reported that she had
a habit of eating soil from her garden in East Orange, New Jersey. During spring and summer,
she continuously kept soil from her garden in her mouth while gardening. She even put a sup-
ply away for winter. The soil was analyzed for lead and was found to contain almost 700 pg/g.
P611B/A 11-109 7/29/83
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TABLE 11-47. ANALYSIS OF RELATIONSHIP BETWEEN SOIL LEAD AND BLOOD
LEAD IN CHILDREN
Soi 1
lead (pg/q)
Blood lead pq/dl)
Area of city
Mean
Range n
Mean
Range
Inner zone
1950
30-11000 21
25.4
4-170
Outer zone
150
30-1100 47
18.3
5-84
Source: Shellshear (1973).
The authors estimated that the patient consumed 100 to 500 mg of lead each year. One month
after initial hospitalization her blood lead level was 70 |jg/d1.
11.4.3.8 Summary of Soil and Dust Lead . Studies relating soil lead to blood lead levels are
difficult to compare. The relationship obviously depends on depth of soil lead, age of the
children, sampling method, cleanliness of the home, mouthing activities of the children, and
possibly many other factors. Table 11-48 gives some estimated slopes taken from several dif-
ferent studies. The range of these values is quite large, ranging from C.6 to 7.6. The
values from the Stark et al. (1980) study of about 2 jjg/d 1 per mg/g represent a reasonable
median estimate.
The relationship of house dust lead to blood lead is even more difficult tc obtain.
Table 11-49 contains some values for three studies that give data permitting such caculations.
The median value of 1.8 pg/dl per mg/g for 2-3 years old in the Stark study may also represent
a reasonable value for use here.
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TABLE 11-48. ESTIMATES OF THE CONTRIBUTION OF SOIL LEAD
TO BLOOD LEAD
Range of soil
lead values
Depth of
Estimated ,
Sample
9
Study
(pg/g)
sample
slope (X10 )
size
R
Angle and Mclntire
16 to 4792
2"
6:8
1075
. 198
(193?) study of
children in
Omaha, NE
Stark et al.
30 to 7000
h"
2.2
153
.289
(1982) study
(age 0-1)
of children
New Haven, CT
30 to 7600
• 2.0
334
.300
(age 2-3)
Yankel et al.
50 to 24,600
3/4"
1.1
860
.662
(1977) study
of children
in Kellogg, ID
Gcike etc .
9 to 7890
2"
1.5
194
. 385
(1975)
study of
chilren in
Charleston, SC
Barltrop et
420 to 13,969
2"
0.6 ,
. 82
NA*
al. (1975)
(group means)
stuay of
children in
Engl and
Neri et al.
225-1800
NA
7.6
87
NA
(1978) stuay
(group rreans,
of children
age 1-3)
in British
Col urcbi'a
225-1800
NA
4.6
103
NA
(group means,
age 2-3)
*NA means Not Available.
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TABLE 11-49. ESTIMATES OF THE
CONTRIBUTION OF
HOUSEDUST TO
BLOOD LEAD IN
CHILDREN
Range of dust
Age range
Estimated ,
Sample
•)
Study
Lead values (pg/g)
in years
slope (X10J)
Size
R
Angle and Mclntire
18-5571
1-18
7.18
1074
.198
(1979) study in
6-18
3.36
832
.262
Omaha, NE
Stark et al. (1982)
70-7600
0-1
4.02
153
.289
study in New Haven,
40-7600
2-3
1.82
334
.300
CT
9-4900
4-7
0.02
439
.143
Yankel et al. (1977)
50-35,600
0-4
0.19
185
.721
study in Kellogg,
5-9
0.20
246
.623
ID
11.4.4 Paint Lead Exposures
A major source of environmental lead exposure for the general population conies from lead
contained in both interior and exterior paint on dwellings. The amount of lead present, as
well as its accessibility, depends upon the age of the residence (because older buildings
contain paint manufactured before lead content was regulated) and the physical condition of
the paint. It is generally accepted by the public and by health professionals that lead-based
paint is one major source of overtly symptomatic pediatric lead poisoning in the United States
(Lin-Fu, 1973).
The level and distribution of lead paint in a dwelling is a complex function of history,
geography, economics, and the decorating habits of its residents. Lead pigments were the
first pigments produced on a large commercial scale when the paint industry began its growth
in the early 1900's. In the 19301s lead pigments were gradually replaced with zinc and other
opacifiers. By the 1940's, titanium dioxide became available and is -now the most commonly
used pigment for residential coatings. There was no regulation of the use of lead in house
paints until 1955, when the paint industry adopted a voluntary standard that limited the lead
content in interior paint to no more than 1 percent by weight of the nonvolatile solids. At
about the same time, local jurisdictions began adopting codes and regulations that prohibited
the sale and use of interior paints containing more than 1 percent lead (Berger, 1973a,b).
In spite of the change in paint technology and local regulations governing its use, and
contrary to popular belief, interior paint with significant amounts of lead was still availa-
ble in the 1970's. Studies by the National Bureau of Standards (1973) and by the U.S.
PB11B/A 11-112 7/29/83
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Consumer Product Safety Commission (1974) showed a continuing decrease in the number of in-
terior paints with lead levels greater than 1 percent. By 1974, only 2 percent of the in-
terior paints sampled were found to have greater than 1 percent lead in the dried film (U.S.
Consumer Product Safety Commission, 1974).
I
The level of lead in paint in a residence that should be considered hazardous remains in
question. Not only is the total amount of lead in paint important, but also the accessibility
of the painted surface to a child, as well as the frequency of ingestion must be considered.
Attempts to set an acceptable lead level, j_n situ, have been unsuccessful, and preventive con-
trol measures of lead paint hazards has been concerned with lead levels in currently manu-
factured paint. In one of its reviews, the NAS concluded: "Since control of the lead paint
hazard is difficult to accomplish once multiple layers have been applied in homes over two to
three decades, and since control is more easily regulated at the time of manufacture, we re-
commend that the lead content of paints be set and enforced at time of manufacture" (National
Academy of Sciences, 1976).
Legal control of lead paint hazards- is being attempted by local communities through
health or housing codes and regulations. At the. Federal level, the Department of Housing and
Urban Development has issued regulations for lead hazard abatement in housing units assisted
or supported by its programs. Generally, the lead level considered hazardous ranges from 0.5
2
to 2.5 mg/cm , but the level of lead content selected appears to depend more on the sensiti-
vity of field measurement (using X-ray fluorescent lead detectors) than on direct biological
dose-response relationships. Regulations also require lead hazard abatement when the paint is
loose, flaking, peeling or broken, or in some cases when it is on surfaces within reach of a
chiId's mouth.
Some studies have been carried out to determine the distribution of lead levels in paint
in residences. A survey of lead levels in 2370 randomly selected dwellings in Pittsburgh pro-
vides some indication of the lead levels to be found (Shier and Hall, 1977). Figure 11-22
shows the distribution curves for the highest lead level found in dwellings for three age
groupings. The curves bear out the statement often made that paint with high levels of lead
is most frequently found in pre-1940 residences. One cannot assume, however, that high lead
paint is absent in dwellings built after 1940. In the case of the houses surveyed in
Pittsburgh, about 20 percent of the residences built after 1960 have at least one surface with
2
more than 1.5 mg/cm .
The distribution of lead within an individual dwelling varies considerably. Lead paint
2
is most frequently found on doors and windows where lead levels greater than 1.5 mg/cm were
found on 2 percent of the surfaces surveyed, whereas only about 1 percent of the walls had
2
lead levels greater than 1.5 mg/cm (Shier and Hall, 1977).
PB11B/A
11-113
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PRELIMINARY DRAFT
LEAD LEVEL (X),
Figure 11-22. Cumulative distribution of lead levels in dwelling units.
PB11B/A
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Tn a review of the literature (Lin-Fu, 1973) found general acceptance that the presence
of lead in paint is necessary but not sufficient evidence of a hazard. Accessibility in
terms of peeling, flaking or loose paint also provide evidence for the presence of a hazard.
Of the total samples surveyed, about 14 percent of the residences had accessible paint with a
2
lead content greater than 1.5 mg/cm . As discussed in Section 7.3.2.1.2, one must note that
lead oxides of painted surfaces contribute to the lead level of house dust.
It is not possible to extrapolate the results of the Pittsburgh survey nationally; how-
ever, additional data from a pilot study of 115 residences in Washington, DC, showed similar
results (Hall 1974).
An attempt was made in the Pittsburgh study to obtain information about the correlation
between the quantity and condition of lead paint in buildings, and the blood lead of children
who resided there (Urban, 1976). Blood lead analyses and socioeconomic data for 456 children
were obtained, along with the information about lead levels in the dwelling. Figure 11-23 is
a plot of the blood lead levels vs. the fraction of surfaces within a dwelling with lead
2
levels of at least 2 mg/cm . Analysis of the data shows a low correlation between the blood
2
lead levels of the children and fraction of surfaces with lead levels above 2 mg/crr, , but
there is a stronger correlation between the blood lead levels and the condition of the painted
;u,faces "n the dwellings in which children reside. This latter correlation appeared to be
independent of the lead levels in the dwellings.
Two other studies have attempted to relate blood lead levels and paint lead as determined
by X-ray fluorescence. Reece et al. (1972) studied 81 children from two lower socioeconomic
corrmunities in Cincinnati. Blood leads were analyzed by the dithizone method. There was con-
siderable lead in the hone environment, but it was not reflected in the children's blood lead.
Analytical procedures used to test the hypothesis were not described; neither were the raw
data presented.
Galke et al. (1975), in their study of inner city black children measured the paint lead,
both interior and exterior, as well as soil and traffic exposure. In a multiple regression
analysis, exterior siding paint lead was found to be significantly related to blood lead
1evels.
Evidence indicates that a source of exposure in childhood lead poisoning is peeling lead
paint and broken 1 ead-impregnated plaster found in poorly maintained houses. There are also
reports of exposure cases that cannot be equated with the presence of lead paint. Further,
the analysis of paint in homes of children with lead poisoning has not consistently revealed a
hazardous lead content (Lin-Fu, 1973). For example, one paper reported 5466 samples of paint
obtained from the home environment of lead poisoning cases in Philadelphia between 1964 and
1968. Among these samples of paint, 67 percent yielded positive findings, i.e., paint with
more than 1 percent lead (Tyler, 1970).
PB11B/A 11-115 7/29/83
782^
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o>
¦ a.
c/5
z
LU
oc
o
_l
X
u
w 30
HI
>
LU
_l
Q
<
LU
Q
o
O
_i
00
25
20
15
~i 1 1 1 1 1 1 r
SURFACES IN BAD CONDITION, i.e., PEELING,
CHALKING, OR POOR SUBSTRATE
ALL SURFACES
ny
e
,1
1
1
1
1
1
s
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
FRACTIONS OF SURFACES WITH LEAD >2 mg/cm2
Figure 11-23. Correlation of children's blood lead levels with fractions of surfaces
within a dwelling having lead concentrations > 2 mg Pb/cm3.
PB115/A-
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PRELIMINARY DRAFT
Data published or made available by the Centers for Disease Control also show that a sig-
nificant number of children with undue lead absorption occupy buildings that were inspected
for lead-based paint hazards, but in which no hazard could be demonstrated (U.S. Centers for
Disease Control, 1977a; Hopkins and Houk, 1976). Table 11-50 summarizes the data obtained
fi;:; the HEV/ funded lead-based paint poisoning control projects for Fiscal Years 1981, 1979,
1978, 1975, and 1974. These data show that in Fiscal Years 1974, 1975, and 1978, about 40 to
50 percent of confirmed cases of elevated blood lead levels, a possible source of lead paint
hazard could not be located. In fiscal year 1981, the U.S. Centers for Disease Control
(1982a,b), screened 535,730 children and found 21,897 with lead toxicity. Of these, 15,472
dwellings were inspected and 10,666 or approximately 67 percent were found to have leaded
paint. The iirplications of these findings are not clear. The findings are presented in order
to place in proper perspective both the concept of total lead exposure and the concept that
lead paint is one source of lead that contributes to the total body load. The background con-
tribution of lead from other sources is still not known, even for those children for whom a
potential lead paint hazard has been identified; nor is it known what proportion of lead cane
from which source.
TABLE 11-50. RESULTS OF SCREENING AND HOUSING INSPECTION IN CHILDHCOD LEAD
POISONING CONTROL PROJECT BY FISCAL YEAR
Fiscal Year
Results
1981
1979
1978
1975
1974
Chi 1dren screened
535,730
464,751
397,963
440,650
371,955
Children with elevated
lead exposure
21,897
32,537
25,801
28,597a
16,228a
Dwellings inspected
15,472
17,911
36,138
30,227
23,096
Dwellings with
lead hazard
10,666
12,461
18,536
17,609
13,742
aConfirmed blood lead level >40 pg/dl.
Source: U.S. Centers for Disease .Control (1977a, 1979, 1980, 1982a,b);
Hopkins and Houk, 1976.
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11.5 SPECIFIC SOURCE STUDIES
The studies reviewed in this section all provide important information regarding specific
environmental sources of airborne lead that play a significant role in population blood lead
levels. These studies also illustrate several interesting approaches to this issue.
11.5.1 Combustion of Gasoline Antiknock Compounds
11.5.1.1 Isotope Studies. Two field investigations have attempted to derive estimates of
the amount of lead from gasoline that is absorbed by the blood of individuals. Both of these
investigations used the fact that non-radioactive isotopes of lead are stable. The varying
proportions of the isotopes present in blood and environmental samples can indicate the source
of the lead. The Isotopic Lead Experiment (ILE) is an extensive study that attempted to use
differing proportions of the isotopes in geologic formations to infer the proportion of lead
in gasoline that is absorbed by the body. The other study utilized existing natural shifts in
isotopic proportions in an attempt to do the same thing.
11.5.1.1.1 Italy. The ILE is a large scale community study in which the geologic source of
lead for antiknock compounds in gasoline was manipulated to change the isotopic composition of
the atmosphere (Garibaldi et al., 1975; Facchetti, 1979). Preliminary investigation of the
environment of Northwest Italy, and the blood of residents there, indicated that the ratio of
lead 206/207 in blooc was a constant, about 1.16, and the ratio in gasoline was about 1.18.
This preliminary study also suggested that it would be possible to substitute for the curren-
tly used geologic sources of lead for antiknock production, a geologically distinct source of
lead from Australia that had an isotopic 206/207 ratio of 1.04. It was hypothesized that the
resjlting change in blood lead 206/207 ratios (from 1.16 to a lower value) would indicate the
proportion of lead in the blood of exposed human populations attributable to lead in the air
contributed by gasoline combustion in the study area.
Baseline sampling of both the environment and residents in the geographic area of the
study was conducted in 1974-75. The sampling included air, soil, plants, lead stock, gasoline
supplies, etc. Human blood sampling was done on a variety of populates within the area.
Both environmental and human samples were analyzed for lead concentrations as well as isotopic
205/207 composition.
In August 1975 the first switched (Australian lead labelled) gasoline was introduced;
although it was originally intended to get a 100 percent substitution, practical and logisti-
cal problems resulted in only a 50 percent substitution being achieved by this time. By May
1977, these problems were worked out and the substitution was practically complete. The sub-
stitution was maintained until the end of 1979, when a partial return to use of the original
sources of lead began. Therefore, the project had four phases: phase zero - background;
phase one - partial switch; phase two - total switch; and phase three - switchback.
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Airborne lead measurements were collected in a number of sites to generate estimates of
the lead exposure that was experienced by residents of the area. Turin, the major city of the
region, was found to have a much greater level of atmospheric lead than the surrounding
countryside. There also appeared to be fairly wide seasonal fluctuations.
The isotopic lead ratios obtained in the samples analyzed are displayed in Figure 11-24.
It can easily be seen that the airborne particulate lead rapidly changed its isotope ratio in
line with expectations. Changes in the isotope ratios of the blood samples appeared to lag
somewhat behind. Background blood lead ratios for adults were 1.1591 ± 0.0043 in rural areas
and 1.1627 + 0.0022 in Turin in 1975. For Turin adults, a mean isotopic ratio of 1.1325 was
obtained in 1979, clearly less than background. Isotopic ratios for Turin schoolchildren,
obtained starting in 1977, tended to be somewhat lower than the ratios for Turin adults.
Preliminary analysis of the isotope ratios in air lead allowed for the estimation of the
fractional contribution of gasoline in the city of Turin, in small communities within 25 km of
Turin, and in small communities beyond 25 km (Facchetti and Geiss, 1982). At the time of
maximal use of Australian lead isotope in gasoline (1978-79), about 87.3 percent of the air
lead in Turin and 58.7 percent of the air lead in the countryside was attributable to
gasoline. The determination of lead isotope ratios was essentially independent of air lead
3
concentrations. During that time, air lead averaged about 2.0 |jg/m in Turin (from 0.88 to
3 3
4.54 pg/m depending on location of the sampling site), about 0.56 pg/m in the nearby com-
3 3
munities (0.30 to 0.67 pg/m ) and about 0.30 pg/m in more distant (> 25 km) locations.
Blood lead concentrations and isotope ratios for 35 adult subjects were determined on two
or more occasions during phases 0-2 of the study (see Appendix C). Their blood lead isotope
ratios decreased over time and the fraction of lead in their blood attributable to the
Australian 1ead-1abelled gasoline could be estimated independently of blood lead concentration
(see Appendix C for estimation method). The mean fraction of blood lead attributable to the
Australian 1ead-1 abel led gasoline ranged from 23.7 ± 5,4 percent in Turin to 12.5 ± 7.1 per-
cent in the nearby (< 25 km) countryside and 11.0 ± 5.8 percent in the remote countryside.
These likely represent minimal estimates of fractions of blood lead derived from gasoline due
to: (1) use of some non-Australian 1ead-1abel1ed gasoline brought into the study area from
outside; (2) probable insufficient time to have achieved steady-state blood lead isotope
ratios by the time of the switchback; (3) probable insufficient time to fully reflect delayed
movement of the Australian lead from gasoline via environmental pathways in addition to air.
These results can be combined with the actual blood lead concentrations to estimate the
fraction of gasoline uptake attributable or not attributable to direct inhalation. The
results are shown in Table 11-51 (based on a suggestion by Dr. Facchetti). From Section
11.4.1, we conclude that an assumed value of |J=1.6 is plausible for predicting the amount of
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PRELIMINARY DRAf-T
I I I I I I I I I I I I I I I
•J BASED ON A LIMITED NUMBER OF SAMPLES
Pb 206!Pb 207
• ADULTS < 25 km
BLOOD a ADULTS > 25 km
O ADULTS TURIN
~ TRAFFIC WARDENS TURIN
¦ SCHOOL CHILDREN-TURIN
1.20
1.18
1.16
1.14
1.12
1.10
1.0B
1.06
A
AIRBORNE
PARTICULATE
• TURIN
A COUNTRYSIDE
O PETROL
Phase 0 Phase 1 Phase 2
4*
Phase 3
I I I I I I I I I I I I
74
75 76
77
78
79
80
81
Figure 11-24. Change in Pb-206/Pb-207 ratios in petrol, airborne particulate,
and blood from 1974 to 1981.
Source: Facchetti and Geiss (1982).
PB11C/A
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TABLE 11-51. ESTIMATED CONTRIBUTION OF LEADED GASOLINE TO BLOOD LEAD
BY INHALATION AND NON-INHALATION PATHWAYS
Estimated
Fracti on
Gas-Lead
Locati on
Turin 0.873 2.0 0.237 21.77 5.16 2.79 2.37 0.54
<25 km 0.587 0.56 0.125 25.06 3.13 0.53 2.60 0.17
>25 km 0.587 0.30 0.110 31.78 3.50 0.28 3.22 0.08
(a) Fraction of air lead in Phase 2 attributable to lead in gasoline.
(b) Mean air lead in Phase 2,
(c) Mean fraction of blood lead in Phase 2 attributable to lead in gasoline.
(d) Mean blood lead concentration in Phase 2, pg/dl.
(e) Estimated blood lead from gasoline = (c) x (d)
(f) Estimated blood lead from gas inhalation = f! x (a) x (b), {3 = 1.6. .
(g) Estimated blood lead from gas, non-inhalation = (f)-(e)
(h) Fraction of blood lead uptake from gasoline attributable to direct inhalation = (f)/(e)
Data: Facchetti and Geiss (1982), pp. 52-56.
3
lead absorbed into blood at air lead concentrations less than 2.0 (jg/m . The predicted values
for lead from gasoline in air (in the ILE) range from 0.28 to 2.79 jjg/dl in blood due to
direct inhalation. The total contribution of blood lead from gasoline is much larger, from
3.50 to 5.16 |jg/dl, suggesting that the non-inhalation contribution of gasoline increases from
2.37 |jg/dl in Turin to 2.60 pg/d1 in the near region and 3.22 pg/dl in the more distant region.
The non-inhalation sources include ingestion of dust and soil lead, and lead in food and
drinking water. Efforts are being made to quantify the magnitude of these sources. The aver-
age direct inhalation of lead in the air from gasoline is 8 to 17 percent of the total
intake attributable to gasoline in the countryside and an estimated 68 percent in the city
of Turin.- Note that i_n this sample, the blood lead concentrations are least in the city and
highest in the more remote areas. This-is not obviously attributable to sex because the city
sample was all male. A more detailed statistical investigation is needed.
Air Lead _ Blood Pb Blood PB Non-
Fraction Mean Fraction Mean PB From Inhaled
From Air From Blood From Gaso- Pb From
Gaso7,x Lead ,Gaso? Lead ,.s Gaso; * line Gaso? *
1ine Cone. 1ine Conc.(d) line**0 In Air(f) line(9)
(Mg/m3) (ug/dl) (ug/dl) (ug/dl) (ug/dl)
PB11C/A 11-121 7/29/83
788^
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PRELIMINARY DRAFT
Lead uptake may also be associated with occupation, sex, age, smoking and drinking
habits. The linear exposure model used in Section 11.4 was also used here to estimate the
fraction uf labelled blood lead from gasoline attributable to exposure via direct inhalation
and other pathways. EPA used blood lead measurements in Phase 2 for the 35 subjects for whom
repeated measurements allowed estimation of the change in isotope ratios in the blood. Their
blood lead concentrations in Phase 2 were also determined, allowing for estimation of the total
gasoline contribution to blood lead. Possible covariates included sex, age, cigarette
smoking, drinking alcoholic beverages, occupation, residence location and work location. In
order to obtain some crude comparisons with the inhalation exposure studies of Section 11.4.1,
EPA analysis assigned the air lead values listed in Table 11-52 to various locations. Lowe*"
values for air lead in Turin would increase the estimated blood lead inhalation s'ope above
the estimated value.1.70. Since the fraction of time subjects were exposed to workplace air
was not known, tr.is was also estimated froir the data as about 41 percent (i.e., 9.8 hou-s/day).
The results are shown in Figure 11-25 and Taole 11-53. Of all the available variables, only
location, sex and inhaled air lead from gasoline proved statistically significant in predic-
2
ting blood lead attributable to gasonne. The model predictability is fairly gooc, R = 0.654.
It should be noted that a certain amount of confounding of variables was unavoidable in this
small set of preliminary data, e.g., no female subjects in Turin or in occupations of traffic
wardens, etc. There was a systematic increase in estimated non-inhalation contribution fror
gasoline increase for reinote areas, but the cause is unknown. Nevertheless, the estimated
non-inhalation contribution of gasoline to blood lead in the ILE study is significant (i.e.
1.8 to 3.4 pg/dl).
TABLE 11-52. ASSUMED AIR LEAD CONCENTRATIONS FOR MODEL
Residence or workplace code 1-4 5 6
Location outside Turin Turin residential Turin central
Air lead concentration (a) 1.0 |jg/m^b^ 2.5 (ig/n3^
(a) Use value for community air load, 0.16 to 0.G7 pg/m^.
(b) Intermediate between average traffic areas (1.71 g/m ) and low traffic areas (0.88 g/m )
in Turin.
(c) Intermediate between average traffic areas (1.71 (jg/in ) and heavy traffic areas (4.54
g/m ) in, Turin.
PBUC/A
11-122
7/29/83
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PRELIMINARY DRAFT
Ine preliminary linear analysis of the overall ILE data set (2161 observations) found
that total blood lead levels depended on other covariates for which there were plausible
mechanisms of lead exposure, including location, smoking, alcoholic beverages, age and occu-
pation (Facchetti and Geiss 1982). The difference between total blood lead uptake and blood
3
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O
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<
u
a
<
(-
3
m
Q
O
O
z
<
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2
Total contribution of
gasoline iBad to
blood lead in
Italian men
Non-inhalation contribution
of gasoline to blood lead
in Italian men.
Contribution to blood lead
by direct inhalation from
air lead attributable to
gasoline
< *¦ ~
~
<
>28km <25km
AVERAGE AIR LEAD CONCENTRATION ATTRIBUTABLE TO GASOLINE
fifl/m1
Figure 11-25. Estimated direct and indirect contributions of lead in
gasoline to blood lead in Italian men, based on EPA analysis of
ILE data (Table 11-53).
lead uptake attributable to gasoline lead has yet to be analyzed in detail, but these analyses
suggest that certain important differences may be found. Some reservations have been expres-
sed about the ILE study, both by the authors themselves and by Elwood (1983). These include
unusual conditions of meteoro'logy and traffic in Turin, and demographic characteristics of the
35 subjects measured repeatedly that may restrict the generalizabi1ity of the study. However,
it is clear that changes in air lead attributable to gasoline were tracked by changes in blood
PB11C/A 11-123 7/29/83
790<
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PRELIMINARY DRAFT
TABLE 11-53. REGRESSION MODEL FOR BLOOD LEAD ATTRIBUTABLE TO GASOLINE
Variable
Coefficient ± Standard Error
Air lead from gas
1.70 ± 1.04 jjg/dl per pg/m3
LOCATION
Turin
<25 km
>25 km
1.82 ± 2.01 (jg/dl
2.56 ± 0.59 (jg/dl
3.42 ± 0.85 pg/dl
Sex
-2.03 ± 0.48 jjg/d 1 for women
lead in Turin residents. The airborne particulate lead isotope ratio quickly achieved new
equilibrium levels as the gasoline isotope ratio was changed, and maintained that level during
the 2h years of Phase 2. The blood lead isotope ratios fell slowly during the changeover
period, and rose again afterwards as shown in Figure 11-24. Equilibrium was not clearly
achieved for blood lead isotope ratios, possibly due to large endogenous pools of old lead
stored in the skeleton and slowly mobilized over time. Even with such reservations, this
study provides a useful basis for relating blood lead and air lead derived from gasoline com-
busti on.
11.5.1.1.2 United States. Manton (1977) conducted a long term study of 10 subjects whose
blood lead isotopic composition was monitored for comparison with the isotopic composition of
the air they breathed. Manton had observed that the ratio of 2°6Pb/2°4Pb in the air varied
with seasons in Dallas, Texas; therefore, the ratio of those isotopes should vary in the
blood. By comparing the observed variability, estimates could then be made of the amount of
lead in air that is absorbed by the blood.
Manton took monthly blood samples from all 10 subjects from April 1974 until June 1975.
The blood samples were analyzed for both total lead and isotopic composition. The recruited
volunteers included a mix of males and females, and persons highly and moderately exposed to
3
lead. However, none of the subjects was thought to be exposed to more than 1 (jg/m of lead in
air. Lead in air samples was collected by Hi-Vol samplers primarily from one site in Dallas.
That site, however, had been shown earlier to vary in isotopic composition paralleling another
site some 16 miles away. All analyses were carried out under clean conditions with care and
caution being exercised to avoid lead contamination.
The isotope ratio of lead 2o6Pb/204Pb increased linearly With time from about 18.45 to
19.35, approximately a 6 percent increase. At least one of the two isotopic lead ratios in-
creased linearly in 4 of the 10 subjects. In one other, they increased but erratically. In
PB11C/A
11-124
7/29/83
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PRELIMINARY DRAFT
the remainder of the subjects, the isotopic ratios followed smooth curves showing inflection
points. The curves obtained for the two subjects born in South Africa were 6 months out of
phase with the curves of the native-born Americans. The fact that the isotope ratios in 9 of
the 10 subjects varied regularly was thought to indicate that the, non-airborne.sources of lead
varied in isotopic composition very slowly.
The blood lead levels exhibited a variety of patterns, although none of the subjects
showed more than a 25 percent change from initial levels. This suggests a reasonably steady
state external environment.
Manton carried his analyses further to estimate the percentage of -lead, in blood that
comes from air. He estimated that the percentage varied from 7 to 41 percent, assuming that
dietary sources of lead had a constant isotopic ratio while air varied. He calculated the
percent contribution according to the following equation:
9 = _iL t where
100+q a
b = rate of change of an isotope ratio in blood,
a = rate of change of the same ratio in the air,
q = constant - the number of atoms of the isotope in the denominator
of the airborne lead ratio mixed with 100 atoms of the same iso-
tope of lead from non-airborne sources.
The results are shown in Table 11-54. Slopes were obtained by least squares regression.
Percentages of airborne lead in blood varied between 7+3 and 41+3.
TABLE 11-54. RATE OF CHANGE OF 206Pb/201Pb AND 206Pb/2o7Pb
IN AIR AND BLOOD, AND PERCENTAGE OF AIRBORNE
..LEAD IN BLOOD OF SUBJECTS 1, 3, 5, 6 AND 9
Subject Rate of Change per Day Percentage of Airborne Lead in Blood
20*pb/2o4pb 206Pb/207Pb From 20BPb/2C!4Pb From 2u6Pb/2u7Pb
X 10"4 X io"5
(Air)
17.60 ± 0.77
9.97
±
0.42
1
• . .
0.70
±
0.30
7 ± 3
3
5.52 ± 0.55
.
31.4 ± 3.4
.
5
• • •
3.13
±
0.34
• . -
31.4 +
3.7
6
6.53 ± 0.49
4.10
~
0.25
37.1 ± 2.8
41.1 ±
3.0
9*
3.25
2.01
18.5
20.0
Note: Errors quoted are one standard deviation
"From slope of tangent drawn to the minima of subject's blood curves. Errors
cannot realistically be assigned.
PB11C/A 11-125 7/29/83
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PRELIMINARY DRAFT
Stephens (1981) has extended the analysis of data in Manton's study (Table 11-55). He
used the observed air lead concentrations based on actual 24-hour air lead exposures in three
adjlts. He assumed values for breathing rate, lung deposition and absorption into l>lcod to
estimate the blood lead uptake attributable to ^04Pb by the direct inhalation pathway. Sub-
jects 5, 6 and 9 absorbed far more air lead in fact than was calculated using the values in
Table 11-54. The total air lead contribution was 8.4, 4.4 and 7.9 tir.es larger than the
direct inhalation. These estimates are sensitive to the assurred parameter values.
In surrmary, the direct inflation pathway accounts fcr cnly a fraction of the total a^r
lead contribution to blood,- the direct inhalation contribution being on the order of 12 to 23
percent of the total uptake of lead attributable to gasoline, using Stephen's assumotions.
This is consistent with estimates (i.e. 8 to 54 percent) from the ILE study, taking into
account the much higher air lead levels in Turin.
11.5.1.2 Studies of Childhood Blood Lead Poisoning Control Programs. Billick et al. (1979)
presented several possible explanations for the observed decline in blood lead levels in New
York City children as well as evidence supporting and refuting each. The suggested contribu-
ting factors include the active educational and screening prograrr of the New York City Bjreaj
of Lead Poisoning Control, and the decrease in the arrourt of lead-based paint exposure as a
result of rehabilitation or removal of older housing or changes in environmental lead exposure.
Information was on'y available to partially evaluate the last source of leac exposure and
particularly only for a-nb^'ent air lead levels. Air lead measurements were available during
the entire study period for only one station which was located on the west side of Manhattan
at a height of 56 m. Superposition of the air "lead and blood lead levels indicated a
similarity in cycle and decline. The authors cautioned against overinterpretation by assuming
that one air monitoring site was representative o* the air lead exposure of New York City
residents. With this in mind, the investigators fitted a multiple regression model to the
data to try to define the important determinants of blood lead levels for this population.
Age, ethnic group and air lead level were all found to be significant determinants of blood
lead levels. The authors further point out the possibility of a change in the nature of the
population being screened before and after 1973. They reran this regression analysis sepa-
rately for years both before and after 1973. The sane results were still obtained, although
the exact coefficients varied.
Billick et al. (1983) extended their previous analysis of the data from the single moni-
toring site mentioned earlier. The investigators examined the possible relationship between
blood lead level and the amount of lead in gasoline used in the area. Figures 11-26 and 11-27
present illustrative trend lines in blood leads for blacks and Hispanics, vs. air lead and
PB11C/A
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TABLE 11-55
. CALCULATED BLOOD LEAD UPTAKE
USING MANTON ISOTOPE STUDY
FROM AIR LEAD
Blood Uptake from Air
Sub-
ject
Concen-
trati on
Expo-
sure*
Deposi-
ti on
Absorp-
ti on
Calcu-
1 ated
Inhala-
tion
Observed
Fraction of lead
uptake from gasoline
by direct inhalation
5
0.22 pg/m3
15 m3/day
37%
50%
0. 61 jjg/d
5.1 pg/d
0.120
6
3
1.09 pg/m
15 m3/day
37%
50%
3.0 pg/d
13.2 pg/d
0.229
9
0.45 pg/m3
15 m3/day
37%
50%
1.2 pg/d
9.9 H9/d
0.126
"¦assumed rather than measured exposure, deposition and absorption.
Source: Stephens, 1981, based on Manton, 1977; Table III.
gasoline lead, respectively. Several different measures of gasoline lead were tried: mid-
Atlantic Coast (NY, NJ, Conn), New York, New York plus New Jersey and New York plus
Connecticut. The lead in gasoline trend line appears to fit the blood lead trend line better
than the air lead trend, especially in the summer of 1973.
Multiple regression analyses were calculated using six separate models. The best fitting
2
model had an R - 0.745. Gasoline lead content was included rather than air lead. The gaso-
line lead content coefficient was significant for all three racial groups. The authors state
a number of reasons for gasoline lead providing a better fit than air lead, including the fact
that the single monitoring site might not be representative.
Nathanson and Nudelman (1980) provide more detail regarding air lead levels in New York
City. In 1971, New York City began to regulate the lead content of gasoline sold. Lead in
gasoline was to be totally banned by 1974, but supply and distribution problems delayed the
effect of the ban. Ultimately regulation of lead in gasoline was taken over by the U.S.
Environmental Protection Agency.
New York City measured air lead levels during the periods June 1969 to September 1973 and
during 1978 at multiple sites. The earlier monitoring was done by 40 rooftop samples using
cellulose filters analyzed by AAS. The latter sampling was done by 27 rooftop samplers using
glass fiber filters analyzed by X-ray fluorescence (XRF). There was excellent agreement
between the XRF and atomic absorption analyses for lead (r = 0.985). Furthermore, the XRF
analyses were checked against EPA AAS and again excellent agreement was found. The authors
did, however, point out that cellulose filters are not as efficient as glass fiber filters.
Therefore, the earlier results tend to be underestimates of air lead levels.
PB11C/A 11-127 7/29/83
794 <
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PRELIMINARY DRAFT
I I I | I I I | I I I | I I I | II I [ I I I | 1 I I
35 —
30
BLACK
HISPANIC
. AIR LEAD
25
20
15
10
i/i I i A „
\ \> - \/\ A
\l i v v \
/
2.5
2.0
1.5
1.0
>
<
m
a
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m
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jj
r-
m
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O
r-
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<
m
r
"C
nf I I I t I t I I I I I I I I I I I II I II I \ \ I I ton
1970 1971 1972 1973 1974 1975 1976
QUARTERLY SAMPLING DATE
Figure 11-26. Geometric mean blood lead levels of New York City
children (aged 25-36 months) by ethnic group, and ambient air lead
concentration versus quarterly sampling period, 1970-1976.
Source: Billick (1980).
PB11C/A
11-128
795-=
7/29/83
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E
s
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4
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u
£
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1 1 M 1 1 1 I
BLACK
— HISPANIC
GASOLINE LEAD
a
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a
3
u
nT I I I I I I I I I I I I I I I I I I I I I I I I I I I To o
1970 1971 1972 1973 1974 1975 1976
QUARTERLY SAMPLING DATE
Figure 11-27. Geometric mean blood lead levels of New York City
children (aged 25-36 months) by ethnic group, and estimated
amount of lead present in gasoline sold in New York, New Jersey,
and Connecticut versus quarterly sampling period, 1970-1976.
Source: Billick (1980).
PB11C/A
11-129
7/29/83
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PRELIMINARY DRAFT
Quarterly citywide air lead averages generally declined during the years 1969-1978. The
3
maximum quarterly citywide average obtained was about 2.5 pg/m for the third quarter of 1970.
The citywide trend corresponds to the results obtained from the single monitoring site used in
Billick et al.'s analysis. The citywide data suggest that the single monitoring site in Man-
hattan is a responsible indicator of air lead level trends. The graph in Figure 11-28 rein-
forces this assertion by displaying the geometric mean blood lead levels for blacks and
Hispanics in the 25 to 36-month age groups and the quarterly citywide air lead levels for the
periods of interest. A good correspondence was noted.
As part of a detailed investigation of the relationship of blood lead levels and lead in
gasoline covering three cities, Billick (1982) extended the time trend analyses of New York
City blood lead data. Figure 11-29 presents the time trend line for geometric mean blood
leads for blacks age 24-35 months extended to 1979. The downward trend noted earlier was
still continuing, although the slopes for both the blood and gasoline lead seem to be somewhat
shallower toward the most recent data. A similar picture is presented by the percent of chil-
dren with blood lead levels greater than 30 pg/dl. In the early 70's, about 60 percent of the
screened children had these levels; by 1979 the percent had dropped between 10 and 15 percent.
11.5.1.3 NHANES II. Blood lead data from the second National Health and Nutrition Examina-
tion Survey has been described in sections 11.3.3.1 and 11.3.4.4. The report by Annest et al.
(1983) found highly significant associations between amounts of lead used in gasoline produc-
tion in the U.S. and blood lead levels. The associations persisted after adjusting for race,
sex, age, region of the country, season, income and degree of urbanization.
Various analyses of the relationship between blood lead values in the NHANES II sample
and estimated gasoline lead usage were also reviewed by an expert panel (see Appendix 11-D).
They concluded that the correlation between gasoline lead usage and blood lead levels was con-
sistent with the hypothesis that gasoline lead is an important causal factor, but the analyses
did not actually confirm the hypothesis.
11.5.1.4 Frankfurt, West Germany, Sinn (1980; 1981) conducted a study specifically examining
the environmental and biological impact of the gasoline lead phasedown implemented in West
Germany on January 1, 1976. Frankfurt am Main provided a good setting for such a study
because of its physical character.
Air and dustfall lead levels at several sites in and about the city were determined be-
fore and after the phasedown was implemented. The mean air lead concentrations obtained
during the study are presented in Table 11-56. A substantial decrease in air lead levels was
noted for the low level high traffic site (3.18 pg/m3 in 1975-76 to 0.68 pg/m3 in 1978-79).
No change was noted for the background site while only minor changes were observed for the
other locations. Dustfall levels fell markedly (218 mg/cm2-day for 1972-73 to 128 mg/cm2*day
PB11C/A
11-130
7
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PRELIMINARY DRAFT
O)
3.
Q
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QC
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35
30
25
20
15
10
II I | I ! I | M I | I I I | I I I | I II | M I
BLACK
— — —- HISPANIC
— • — • AIR LEAD
2.5
2.0
1.5
1.0
<
~
m
P
C
>
X
H
m
X
r-
<
>
<
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in
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to
nT I I l I I I I I I I I I I I l I I I I I I 1 I I I I I fnn
1970 1971 1972 1973 1974 1975 1976
QUARTERLY SAMPLING DATE
Figure 11-28. Geometric mean blood levels for blacks and
Hispanics in the 25-to-36-month age group and rooftop
quarterly averages for ambient citywide lead levels.
Source: Nathanson and Nudelman (1980).
PB11C/A 11-131 7/29/83
798<
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PRELIMINARY DRAFT
50
40
o>
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<
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—I
a
z
<
5-0*
2 o
U*~
LU lu
o»
Hi <
oo
GEO MEAN BLOOD Ph
GAS LEAD
TRISTATE X 4
SMSA X 20
65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81
YEAR
Figure 11-29. Time dependence of blood lead and gas lead for blacks, aged 24 to
35 months, in New York.
So *ce: Billick (1982).
Source: Billick (1982).
PB11C/A
11-132
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7/29/83
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TABLE 11-56. MEAN AIR LEAD CONCENTRATIONS DURING THE VARIOUS BLOOD SAMPLING
PERIODS AT THE MEASUREMENT SITES DESCRIBED IN THE TEXT ((jg/m3)
Residenti al
High Traffic
High Traffic
Background
Low Traffic
(>20m)
(3m)
Site
1975-1976
0.57
0.59
3.18
0.12
1976-1977
0.39
0.38
1.04
0.09
1977-1978
0.32
0.31
0.66
0.10
1978-1979
0.39
0.31
0.68
0.12
Source: Sinn (1980, 1981).
for 1977-78). Traffic counts were essentially unchanged in the area during the course of
study.
A number of population groups were included in the study of the blood lead levels; they
were selected for having either occupational or residential exposure to high density automo-
bile traffic. Blood samples were taken serially throughout the study (three phases in
December-January 1975-76, December-January 1976-77 and December-January 1977-78). Blood
samples were collected by venipuncture and analyzed by three different laboratories. All the
labs used AAS although sample preparation procedures varied. A quality control program across
the laboratories was conducted. Due to differences in laboratory analyses, attrition and loss
of sample, the number of subjects who could be examined throughout the study was considerably
reduced from the initial number recruited (124 out of 300).
Preliminary analyses indicated that the various categories of subjects had different
blood lead levels, and that males and females within the same category differed. A very com-
plicated series of analyses then ensued that made it difficult to draw conclusions because the
various years' results were displayed separately by each laboratory performing the chemical
analysis and by different groupings by sex and category. In Sinn's later report (1981) a
downward trend was shown to exist for males and females who were in all years of the study and
whose blood levels were analyzed by the same laboratory.
11.5.2 Primary Smelters Populations
Most studies of nonindustry-employed populations living in the v.icinity of industrial
sourcesof lead pollution were triggered because evidence of severe health impairment had been
found. Subsequently, extremely high exposures and high blood lead concentrations were found.
The following studies document the excessive lead exposure that developed, as well as some of
the relationships between environmental exposure and human response.
PB11C/A ... = 11-133 7/29/83
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11.5.2.1 El Paso. Texas. In 1972, the Centers for Disease Control studied the relationships
between blood lead levels and environmental factors in the vicinity of a primary smelter lo-
cated in El Paso, Texas emitting lead, copper and zinc. The smelter had been in operation
since the late 1800's (Landrigan et al., 1975; U.S. Centers for Disease Control, 1973). Daily
3
Hi-Vol samples collected on 86 days between February and June 1972 averaged 6.6 yg/m . These
air lead levels fell off rapidly with distance, reaching background values approximately 5 km
from the smelter. Levels were higher downwind, however. High concentrations of lead in soil
and house dusts were found, with the highest levels occurring near the smelter. The geometric
means of 82 soil and 106 dust samples from the sector closest to the smelter were 1791 and
4022 |jg/g, respectively. Geometric means of both soil and dust lead levels near the smelter
were significantly higher than those in study sectors 2 or 3 km farther away.
Sixty-nine percent of children 1- to 4-years old living near the smelter had blood lead
levels greater than 40 Mg/dl, and 14 percent had blood lead levels that exceeded 60 pg/dl.
Concentrations in older individuals were lower; nevertheless, 45 percent of the children 5- to
9-years old, 31 percent of the individuals 10- to 19-years old and 16 percent of the in-
dividuals above 19 had blood lead levels exceeding 40 )jg/dl. The data presented preclude cal-
culations of means and standard deviations. ¦
Data for people aged 1 to 19 years of age living near the smelter showed a relationship
between blood lead levels and concentrations of lead in soil and dust. For individuals with
blood lead levels greater than 40 jjg/d1, the geometric mean concentration of lead in soil at
their homes was 2587 pg/g, whereas for those with a blood lead concentration less than 40
jjg/d1, home soils had a geometric mean of 1419 pg/g. For house dust, the respective geometric
means were 6447 and 2067 pg/g. Length of residence was important only in the sector nearest
the smelter.
Additional sources of lead were also investigated. A relationship was found between
blood lead concentrations and lead release from pottery, but the number of individuals exposed
to lead-glazed pottery was very small. No relationships were found between blood lead levels
and hours spent out of doors each day, school attendance, or employment of a parent at the
smelter. The reported prevalence of pica also was minimal.
Data on dietary intake of lead were not obtained because there was no food available from
sources near the smelter since the climate and proximity to the smelter prevented any farming
in the area. It was unlikely that the dietary lead intakes of the children from near the
smelter or farther away were significantly different. It was concluded that the primary
factor associated with elevated blood lead levels in the children was ingestion or inhalation
of dust containing lead.
Morse et al. (1979) conducted a follow-up investigation of the El Paso smelter to deter-
mine whether the environmental controls instituted following the 1972 study had reduced the
PB11C/A 11-134 gOl.< 7/29/83
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' PRELIMINARY DRAFT
lead problem described. In November 1977, all children 1- to 18-years old living within
1.6 km of the smelter on the U.S. side of the border were surveyed. Questionnaires were ad-
ministered to the parents of each participant to gather background data.
Venous blood samples were drawn and analyzed for lead by modified Delves cup spectropho-
tometry. House dust and surface soil samples, as well as sample pottery items were taken from
each participant's residence. Dust and soil samples were analyzed for lead by AAS. Pottery
lead determinations were made by the extraction technique of Klein. Paint, food, and water
specimens were not collected because the earlier investigations of the problem had demon-
strated these media contributed little to the lead problem in El Paso.
Fifty-five of 67 families with children (82 percent) agreed to participate in the study.
There were 142 children examined in these homes. The homes were then divided into two groups.
Three children lived in homes within 0.8 km "of the smelter. Their mean blood lead level in
1977 was 17.7 tjg/d1. By contrast, the mean blood lead level of 160 children who lived within
0.8 km of the smelter in 1972 had been 41.4 pg/dl. In 1977, 137 children lived in homes' lo-
cated 0.8 to 1.6 km from the smelter. Their mean blood lead level was 20.2 pg/dl. The mean
blood level of 96 children who lived in that same area in 1972 had been 31.2 pg/dl.
Environmental samples showed a similar improvement. Dust lead fell from 22,191 pg/g to
I,479 jjg/g while soil lead fell from 1,791 pg/g to 427 pg/g closest to the smelter. The mean
3
air lead concentration at 0.4 km from the smelter decreased from 10.0 to 5.5 pg/m and at 4.0
3
km from 2.1 to 1.7 pg/m . Pottery was not found to be a problem.
II.5.2.2 CDC-EPA Study, Baker et al. (1977b), in 1975, surveyed 1774 children 1 to 5 years
old, most of whom lived within 4 miles of lead, copper or zinc smelters located in various
parts of the United States. Blood lead levels were modestly elevated near 2 of the 11 copper
and 2 of the 5 zinc smelters. Although blood lead levels in children were not elevated in the
vicinity of three lead smelters, their FEP levels were somewhat higher than those found in
controls. Increased levels of lead and cadmium in hair samples were found near lead and zinc
smelters; this was considered evidence of external exposure. No environmental determinations
were made for this study.
11.5.2.3 Meza Valley, Yugoslavia. A series of Yugoslavian studies investigated exposures to
lead from a mine and a smelter in the Meza Valley over a period of years (Fugas et al., 1973;
Graovac-Leposavic et al. 1973; Mi lie et al., 1973; Djuric et al., 1971, 1972). In 1967,
24-hour lead concentrations measured on 4 different days varied from 13 to 84 pg/m^ in the
village nearest the smelter, and concentrations of up to 60 pg/m^ were found as far as 5 km
from the source. Mean particle size in 1968 was less than 0.8 pm. Analysis of some common
foodstuffs showed "concentrations that were 10 to 100 times higher than corresponding food-
stuffs from the least exposed area (Mezica) (Djuric et al., 1971). After January 1969, when
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partial control of emissions was established at the smelter, weighted average weekly exposure
was calculated to be 27 pg/m in the village near the smelter. In contrast to this, the city
of Zagreb (Fugas et al., 1973), which has no large stationary source of lead, had an average
3
weekly air lead level of 1.1 (jg/m .
In 1968, the average concentration of ALA in urine samples from 912 inhabitants of 6 vil-
lages varied by village from 9.8 to 13 mg/1. A control group had a mean ALA of 5.2 mg/1.
Data on lead in blood and the age and sex distribution of the villagers were not given (Djuric
et al., 1971).
Of the 912 examined, 559 had an ALA level greater than 10 mg/1 of urine. In 1969, a more
extensive study of 286 individuals with ALA greater than 10 mg/1 was undertaken (Graovac-
Leposavic et al. 1973). ALA-U increased significantly from the previous year. When the
published data were examined closely, there appeared to be some discrepancies in inter-
pretation. The exposure from dust and from food might have been affected by the control de-
vices, but no data were collected to establish this. In one village, Zerjua, ALA-U dropped
from 21.7 to 9.4 mg/1 in children 2 to 7 years of age. Corresponding ALA-U values for 8- to
15-year-olds and for adult men and women were reduced from 18.7 to 12.1, from 23.9 to 9.9 and
from 18.5 to 9.0 mg/1, respectively. Because lead concentrations in air (Fugas et al., 1973),
even after 1969, indicated an average exposure of 25 pg/m^, it is possible that some other
explanation should be sought. The author indicated in the report that the decrease in ALA-U
showed "the dependence on meteorologic, topographic, and technological factors" (Graovac-
Leposavic et al., 1973).
Fugas (1977) in a later report estimated the time-weighted average exposure of several
populations studied during- the course of this project. Stationary samplers as well as
personal monitors were used to estimate the exposure to airborne lead for various parts of the
day. These values were then coupled with estimated proportions of time at which these expo-
sure held. In Table 11-57, the estimated time-weighted air lead values as well as the ob-
served mean blood lead levels for these studied populations are presented. An increase in
blood lead values occurs with increasing air lead exposure.
11.5.2.4 Kosovo Province, Yugoslavia. Residents living in the vicinity of the Kosovo smelter
were found to have elevated blood lead levels (Popovac et al., 1982). In this area of
Yugoslavia, five air monitoring stations had been measuring air lead levels since 1973. Mean
air lead varied from 7.8 to 21.7 pg/m^ in 1973; by 1980 the air lead averages ranged from 21.3
3
to 29.2 ng/m . In 1978 a pilot study suggested that there was a significant incidence of ele-
vated blood lead levels in children of the area. Two major surveys were then undertaken.
In August 1978 letters were sent to randomly selected families from the business commu-
nity, hospitals or lead-related industries in the area. All family members were asked to come
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TABLE 11-57. MEAN BLOOD LEAD LEVELS IN SELECTED YUGOSLAVIAN
POPULATIONS, BY ESTIMATED WEEKLY TIME-WEIGHTED AIR LEAD EXPOSURE
Time-weighted3
Blood
lead level,
Populati on
N
air lead, pg/m
pg/dl
SD
Rural I
49
0.079
7.9
4.4
Rural II
47
0.094
11.4
4.8
Rural III
45
0.146
10.5
4.0
Postmen
44
1.6
18.3
9.3
Customs officers
75
1.8
10.4
3.3
Street car drivers
43
2.1
24.3
10.5
Traffic policemen
24
3.0
12.2
5.1
Source: Fugas, 1977.
to a hospital for primary screening by erythrocyte protoporphyrin. A central population of
comparable socioeconomic and dietary background was collected from a town without lead emis-
sions. Blood levels were determined primarily for persons with greater than yg/g Hgb. EP was
measured by a hematof1uorimeter, while blood lead was determined by the method of Fernandez
using atomic absorption with graphite furnace and background correction.
Mean EP values were higher in the 1978 survey for exposed residents compared to controls
in the average age group. EP values seemed to decline with age. Similar differences were
noted for blood lead levels. The observed mean blood leads, ranging from 27.6 in the greater
than 15-year age group to 50.9 ^g/dl in the 5- to 10-year group, suggest substantial lead ex-
posure of these residents. In the control group the highest blood lead level was 19
In December 1980 a second survey was conducted to obtain a more representative sample of
persons residing in the area. Letters were sent again, and 379 persons responded. EP levels
were higher in all ages in 1980 vs. 1978, although the differences were not statistically sig-
nificant. The air lead levels Increased from 14.3 ng/m^ in 1978 to 23.8 (jg/m^ in 1980.
Comparing the 1980 blood lead results with the 1978 control group shows that the 1980
levels were higher in each age group. Males older than 15 years had higher mean blood lead
levels than the females (39.3 vs. 32.4 |jg/dl).
11.5.2.5 The Cavalleri Study. Cavalleri et al. (1981) studied children in the vicinity of a
lead smelter and children from a control area (4 km from the smelter). The exposed population
consisted of 85 children aged 3 to 6 attending a nursery school and 80 primary school children
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aged 8 to 11. The control population was 25 nursery school children aged 3 to 6 and 64 pri-
mary school children aged 8 to 11. Since the smelter had installed filters 8 years before the
study, the older children living in the smelter area had a much higher lifetime exposure.
Blood lead analysis was performed on venous samples using anodic stripping voltammetry by
Morrell's method. Precision was checked over the range 10 to 100 pg/dl. Reported reproduci-
bility was also good. All samples were subsequently reanalyzed by AAS using graphite furnace
and background correction by the method of Volosen. The average values obtained by the
second method were quite similar to those of the first (average difference 1.4 pg/dl; cor-
relation coefficient, 0.962).
Air was sampled for lead for 1 month at three sampling sites. The sites were located at
150 m, 300 m and 4 km from the wall of the lead smelter. The average air lead levels were
3
2.32, 3.43 and 0.56 pg/m , respectively.
A striking difference in blood lead levels of the exposed and control populations was ob-
served; levels in the exposed population were almost twice that in the control population.
There was no significant difference between nursery school and primary school children. The
geometric mean for nursery school children was 15.9 and 8.2 for exposed and control, respecti-
vely. For primary school it was 16.1 and 7.0 pg/dl. In the exposed area 23 percent of the
subjects had blood lead levels between 21 and 30 jjg/dl and 3 percent greater than 31 pg/dl.
3
No control children had PbB greater than 20 jjg/dl. The air leads were between 2 to 3 ^ig/m in
3
the exposed and 0.56 pg/m in the control cases.
11.5.3 Battery Plants
5tudies of the effects of storage battery plants have been reported from France and Italy
(Dequidt et al., 1971; De Rosa and Gobbato, 1970). The French study found that children from
an industrialized area containing such a plant excreted more ALA than those living in a diffe-
rent area (Dequidt et al., 1971). Increased urinary excretion of lead and coproporphyrins was
found in children living up to 100 m from a battery plant in Italy (De Rosa and Gobbato,
1970). Neither study gave data on plant emissions or lead in air.
Zielhius et al. (1979) studied children living in the vicinity of the Arnhem secondary
lead smelter. In 1976 they recruited children to serve as subjects and controls. The chil-
dren chosen were 2 and 3 years old. Parents were asked to complete a questionnaire for back-
ground information. Two ml venous samples were collected from 17 children living less than 1
km, from 54 children living 1 to 2 km, and from 37 children living greater than 2 km from the
smelter (control group). Blood samples were analyzed for lead by graphite furnace AAS and for
FEP by the method of Piomelli. Air measurements for lead were made in autumn 1976. Samples
were established about 2 km northeast and about 0.4 km north of the plant. Air lead levels
ranged from 0.8 to 21.6 (jg/m^ northeast and from 0.5 to 2.5 |jg/m^ north of the plant.
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Blood leads were statistically significantly higher closer to the smelter. For all chil-
dren the mean blood lead level was 19.7 pg/d 1 for the less than 1 km and 11.8 pg/dl for the
controls (>2 km). Similarly, FEP levels were higher for the closer (41.9 (jg/100 ml RBC)
children as opposed to the control (32.5 (jg/100 ml RBC). Higher blood levels were associated
with lower socioeconomic status.
Further investigation of this smelter was undertaken by Brunekreef et al. (1981) and
Diemel et al. (1981). In May 1978 venipuncture blood samples were collected from 95 one- to
three-year old children living within 1 km of the smelter. Blood leads were determined by
graphite AAS.
Before the blood sampling, an environmental sampling program was conducted. The samples
collected are listed in Table 11-58. Questionnaires were administered to collect background
and further exposure information. A subset of 39 children was closely observed for 1 or 2
days for mouthing behavior. Table 11-58 also presents the overall results of the environ-
mental sampling. As can be readily seen, there is a low exposure to airborne lead (G.M.
3 3
0.41 ^jg/m with a range of 0.28 to 0.52 yiq/m ). Soil exposure was moderate, although high.
Interior dust was high in lead, geometric mean of 967 pg/g with a maximum of 4741 |jg/g. In a
few homes, high paint lead levels were found. Diemel et al. (1981) extended the analysis of
the environmental samples. They found that indoor pollution was lower than outside. In
Arnhem, it was found that lead is carried into the homes in particulate form by sticking to
shoes. Most of the lead originated from soil from gardens and street dust.
Simple correlation coefficients, were calculated to investigate the relationship between
log blood lead and the independent variables. Significantly, correlations were found with
quantity of house dust, quantity of deposited lead indoors, observational score of dustiness,
age of child and the average number of times an object is put in the mouth. Multiple regre-
ssion analyses were calculated on four separate subpopulations. Among children living in
houses with gardens, the combination of soil lead level and educational level of the parents
explained 23 percent of the variations of blood lead. In children without gardens, the amount
of deposited lead indoors explained 26 percent of the variance. The authors found that an
increase in soil lead level from 100 to 600 jjg/g results in an increase in blood lead of
53 pg/dl.
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TABLE 11-58. ENVIRONMENTAL PARAMETERS AND METHODS: ARNHEM LEAD STUDY, 19783-'
Parameter Method Geometric Mean Range
1. Lead in-ambient air
(|jg/m )
High volume samples; 24-hr measurements
at 6 sites, continuously for 2 months
0.41
0.28-0.52
2. Lead in^dustfall
(Mg/m -day)
Standard deposit gauges; 7-day measurements
at 22 sites, semi continuously for 3 months
467
108-2210
3. Lead in soil
(Mg/g)
Sampling in gardens of study populations;
analysis of layers from 0 to 5 cm and
5 to 20 cm
240
21-1126
4. Lead in street dust
(Mg/g)
Samples at 31 sites, analysis of fraction
<0.3mm
690
77-2667
5. Lead in„indoor air
(pg/m )
Low volume samples; 1-month measurements
in homes of study population, continuously
for 2 months
0.26
0.13-0.74
1
6. Lead in dustfalj
indoors (pg/m -day)
Greased glass plates of 30 x 40 cm; 1-month
measurements in homes of study population,
continuously for 3 months
7.34
1.36-42.35
7. Lead in floor dust
(Mg/g)
Vacuum cleaner with special filter
holder; 5 samples, collected on 3 different
occasions; with intervals of approximately
1 month, in homes of study populations
fine 957
course 282
463-4741
117-5250
8. Easily available
lead indoors
Wet tissues, 1 sample in homes of study
population
85% of samples
<20 pg Pb/tissue
9. Lead in tapwater
Proportional samples, during 1 week in
homes of study population
5.0 (arthimetic)
mean
<0.5-90.0
10. Dustiness of homes
Visual estimation, on a simple scale ranging
from 1 (clean) to 3 (dusty); 6 observations
in homes of study population
All lead analyses were performed by atomic absorption spectrophotometry, except part of the tapwater analysis
which was performed by anodic stripping voltametry. Lead in tapwater analyzed by the National Institute of
Drinking Water Supply in Leidscherdam. Soil and street dust analyzed by the Laboratory of Soil and Plant
Research in Oosterbeek. (Zielhuis, et. al., 1979; Diemel, et. al., 1981)
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11.5.4 Secondary Smelters
In a Dallas, Texas, study of two secondary lead smelters, the average blood lead levels
of exposed children was found to be 30 jjg/d 1 vs. an average of 22 pg/dl in control children
(Johanson and Luby, 1972). For the two study populations, the air and soil lead levels were
3
3.5 and 1.5 (jg/ro and 727 and 255 pg/g, respectively.
In Toronto, Canada the effects of two secondary lead smelters on the blood and hair lead
levels of nearby residents have been extensively studied (Ontario Ministry of the Environment,
1975; Roberts et al., 1974). In a preliminary report, Roberts et al. (1974) stated that blood
and hair lead levels were higher in children living near the two smelters than in children
living in an urban control area. Biologic and environmental lead levels were reported to de-
crease with increasing distance from the base of the smelter stacks.
A later and more detailed report identified a high rate of lead fallout around the two
secondary smelters (Ontario Ministry of the Environment, 1975). Two groups of children living
within 300 rff of each of the smelters had geometric mean blood lead levels of 27 and 28 pg/dl,
respectively; the geometric mean for 1231 controls was 17 |jg/dl. Twenty-eight percent of the
sample children tested near one smelter during the summer and 13 percent of the sample chil-
dren tested near the second smelter during the winter had blood lead levels greater than 40
pg/dl. Only 1 percent of the controls had blood lead levels greater than 40 MQ/dl• For chil-
dren, blood lead concentrations increased with proximity to both smelters, but this trend did
not hold for adults, generally. The report concluded that soil lead levels were the main de-
terminant of blood lead levels; this conclusion was disputed by Horn (1976).
^ Blood lead levels in 293 Finnish individuals, aged 15 to 80, were significantly cor-
related with distance of habitation from a secondary lead smelter (Nordman et al., 1973). The
geometric mean blood lead concentration for 121 males was 18.1 pg/dl; for 172 females, it was
14.3 pg/dl. In 59 subjects who spent their entire day at home, a positive correlation was
found between blood lead and distance from the smelter up to 5 km. Only one of these 59 in-
dividuals had a blood lead greater than 40 pg/dl , and none exceeded 50 Mg/dl•
11.5.5 Secondary Exposure of Children
Excessive intake and absorption of lead on the part of children can result when parents
who work in a dusty environment with a high lead content bring dust home on their clothes,
shoes or even their automobiles. Once they are home, their children are exposed to the dust.
Landrigan et al. (1976) reported that the 174 children of smelter workers who lived with-
in 24 km of the smelter had significantly higher blood lead levels, a mean of 55.1 pg/dl, than
the 511 children of persons in other occupations who lived in the same areas whose mean
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blood lead levels were 43.7 yq/dl. Analyses by EPA of the data collected in Idaho showed that
employment of the father at a lead smelter, at a zinc smelter, or in a lead mine resulted in
higher blood lead levels in the children living in the same house as opposed to those children
whose fathers were employed in different locations (Table 11-59). The effect associated with
parental employment appears to be much more prominent in the most contaminated study areas
nearest to the smelter. This may be the effect of an intervening socioeconomic variable: the
lowest paid workers, employed in the highest exposure areas within the industry, might be ex-
pected to live in the most undesirable locations, closest to the smelter.
TABLE 11-59. GEOMETRIC MEAN BLOOD LEAD LEVELS FOR CHILDREN
BASED ON REPORTED OCCUPATION OF FATHER, HISTORY
OF PICA, AND DISTANCE OF RESIDENCE FROM SMELTER
Area
Di stance
from
smelter, km
Lead
smelter
worker
Lead/zinc mine
worker
Zinc smelter
worker
Other
occupati ons
Pi ca
No
Pica
Pica
No
Pica
Pica
No
Pica
Pica
No
Pica
1
1.6
78.7
74.2
75. 3
63. 9
69.7
59.1
70.8
59.9
2
1.6 to 4.0
50.2
52.2
46.9
46.9
62.7
50.3
37.2
46.3
3
4.0 to 10.0
33.5
33. 3
36.7
33.5
36.0
29.6
33.3
32.6
4
10.0 to 24.0
-
30.3
38.0
32.5
40.9
36.9
-
39.4
5
24.0 to 32.0
-
24.5
31.8
27.4
-
-
28.0
26.4
6
75
-
-
-
-
-
-
17.3
21.4
Source: Landrigan et al. 1976.
Landrigan et al. (1976) also reported a positive history of pica for 192 of the 919 chil-
dren studied in Idaho. This history was obtained by physician and nurse interviews of
parents. Pica was most common among 2-year old children and only 13 percent of those with
pica were above age 6. Higher blood lead levels were observed in children with pica than in
those without pica. Table 11-59 shows the mean blood lead levels in children as they were af-
fected by pica, occupation of the father and distance of residence from the smelter. Among
the populations living nearest to the smelter environmental exposure appears to be sufficient
at times to more than overshadow the effects of pica, but this finding may also be caused by
inadequacies inherent in collecting data on pica.
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These data indicate that in a heavily contaminated area, blood lead levels in children
may be significantly increased by the intentional ingestion of nonfood materials having a high
lead content.
Data on the parents' occupation are, however, more reliable. It must be remembered also
that the study areas were not homogeneous socioeconomically. In addition, the specific type
of work an individual does in an industry is probably much more important than simply being
employed in a particular industry. The presence in the home of an industrial employee exposed
occupational ly to lead may produce increases in the blood lead levels ranging from 10 to 30
percent.
The importance of the infiltration of lead dusts onto clothing, particularly the under-
garments, of lead workers and their subsequent transportation has been demonstrated in a
number of studies on the effects of smelters (Martin et al., 1975). It was noted in the
United Kingdom that elevated blood lead levels were found in the wives and children of
workers, even though they resided some considerable distance from the facility. It was most
prominent in the workers themselves who had elevated blood lead levels. Quantities of lead
dust were found in workers' cars and homes. It apparently is not sufficient for a factory
merely to provide outer protective clothing and shower facilities for lead workers. In
another study in Bristol, from 650 to 1400 pg/g of lead was found in the undergarments of
workers as compared with 3 to 13 pg/g in undergarments of control subjects. Lead dust will
remain on the clothing even after laundering: up to 500 mg of lead has been found to remain
on an overall garment after washing (Lead Development Association, 1973).
Baker et al. (1977a) found blood lead levels greater than 30 pg/dl in 38 of 91 children
whose fathers were employed at a secondary lead smelter in Memphis, TN, House dust, the only
source of lead in the homes of these children, contained a mean of 2687 pg/g compared with 404
ng/g in the homes of a group of matched controls. Mean blood lead levels in the workers'
children were significantly higher than those for controls and were closeiy correlated with
the lead content of household dust. In homes with lead in dust less than 1000 pg/g, 18 chil-
dren had a mean blood lead level of 21.8 ± 7.8 pg/dl , whereas in homes where lead in dust was
greater than 7000 pg/g. 6 children had mean blood lead levels of 78.3 ± 34.0 pg/dl. See
Section 7.3.2.1.6 for a further discussion of household dust.
Other studies have documented increased lead absorption in children of families where at
least one member was occupational ly exposed to lead (Fischbein et al., 1980a). The occupa-
tional exposures involved battery operations (Morton et al., 1982; U.S. Centers for Disease
Control, 1977b; Dolcourt et al., 1978, 1981; Watson et al., 1978; Fergusson et al. , 1981) as
well as other occupations (Snee, 1982b; Rice et al., 1978).
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In late summer of 1976, a battery plant in southern Vermont provided the setting for the
first documented instance of increased lead absorption in children of employees in the battery
industry. The data were first reported by U.S. Centers for Disease Control (1977b) and more
completely by Watson et al. (1978).
Reports of plant workers exposed to high levels of lead stimulated a study of plant
employees and their children in August and September 1975. In the plant, lead oxide powder is
used to coat plates in the construction of batteries. Before the study, the work setting of
all 230 employees of the plant had been examined and 62 workers (22 percent) were identified
as being at risk for high lead exposure. All of the high risk workers interviewed reported
changing clothes before leaving work and 90 percent of them reported showering. However, 87
percent of them stated that their work clothes were washed at home.
Of the high risk employees, 24 had children between the ages of 1 and 6 years. A case-
control study was conducted in the households of 22 of these employees. Twenty-seven children
were identified. The households were matched with neighborhood controls including 32 control
children. None of the control family members worked in a lead industry. Capillary blood
specimens were collected from all children and the 22 battery plant employees had venous spec-
imens taken. All blood samples were analyzed for lead by AAS. Interviewers obtained back-
ground data, including an assessment of potential lead exposures.
About 56 percent of the employees' children had blood leads greater than 30 |jg/d1 com-
pared with about 13 percent of the control children. Mean blood lead levels were stat-
istically significantly different, 31.8 pg/dl and 21.4 pg/dl, respectively. Blood lead levels
in children were significantly correlated with employee blood lead levels.
House dust lead levels were measured in all children's homes. Mean values were 2239.1
pg/g and 718.2 pg/g for employee and control homes, respectively; this was statistically sig-
nificant. Examination of the correlation coefficient between soil lead and blood lead levels
in the two sets of homes showed a marginally significant coefficient in the employee household
but no correlation in the control homes. Tap water and paint lead levels did not account for
the observed difference in blood leads between children of workers and neighborhood controls.
It is significant that these findings were obtained despite the changing of clothes at the
pi ant.
Morton et al. (1982) conducted their study of children of battery plant workers and con-
trols during February-March 1978. Children were included in the study if one parent had at
least 1 year of occupational exposure, if they had lived at the same residence for at least 6
months, and if they were from 12-83 months of age. Children for the control group had to have
no parental occupational exposure to lead for 5 years, and had to have lived at the same ad-
dress at least 6 months.
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Thirty-four children were control matched to the exposed group by neighborhoods and age
(±1 year). No matching was thought necessary for sex because in this age group blood lead
levels are unaffected by sex. The selection of the control population attempted to adjust for
both socioeconomic status as well as exposure to automotive lead.
Capillary blood specimens were collected concurrently for each matched pair. Blood lead
levels were measured by the CDC lab using a modified Delves cup AAS procedure. Blood lead
levels for the employees for the previous year were obtained from company records. Question-
naires were administered at the same time as the blood sampling to obtain background informa-
tion. The homemaker was asked to complete the interview to try to get a more accurate picture
of the hygiene practices followed by the employees.
Children's blood lead levels differed significantly between the exposed and control
groups. Fifty-three percent of the employees' children had blood lead levels greater than 30
pg/dl, while no child in the control population had a value greater than 30 pg/dl. The mean
blood lead for the children of the employees was 49.2 pg/dl with a standard deviation of 8.3
pg/dl. These data represent the population average for yearly individual average levels. The
employees had an average greater than 60 pg/dl. Still, this is lower than the industry
average. Of the eight children with blood levels greater than 40 gg/dl , seven had fathers
with blood lead greater than 50 pg/dl. Yet there was not a significant correlation between
children's blood lead level and father's blood lead level.
Investigations were made into the possibility that other lead exposures could account for
the observed difference in blood lead levels between children of employees and control chil-
dren. In 11 of the 33 pairs finally included in the study, potential lead exposures other
than fathers' occupations were found in the employee child of the matched pair. These in-
cluded a variety of lead sources such as- automobile body painting, casting of lead, and
playing with spent shell casings. The control and exposed populations were again compared
after removing these 11 pairs from consideration. There was still a statistically significant
difference in blood lead level between the two groups of children.
An examination of personal hygiene practices of the workers showed that within high ex-
posure category jobs, greater compliance with recommended lead containment practices resulted
in lower mean blood lead levels in children. Mean blood leads were 17.3, 36.0 and 41.9
for good, moderately good and poor compliance groups, respectively. In fact, there was only a
small difference between the good hygiene group within the high exposure category and the mean
of the control group (17.3 pg/dl vs. 15.9 pg/dl). Insufficient sample sizes were available to
evaluate the effect of compliance on medium and low lead exposures for fathers.
Dolcourt et al. (1978) investigated lead absorption in children of workers in a plant
that manufactures lead-acid storage batteries. The plant became known to these researchers as
a result of finding an elevated blood lead level in a 20-month-old child during routine
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screening. Although the child was asymptomatic, his motner proved not to be. Two siblings
were also found to have elevated blood lead levels. The mother was employed by the plant; her
work involved much hard labor and brought her into continual contact with powdery lead oxide.
No uniforms or garment covers were provided by the company. As a result of these findings,
screening was offered to all children of plant employees.
During February to May 1977, 92 percent of 63 eligible children appeared for screening.
Age ranged from 10 montns to 15 years. About equal numbers of girls and boys underwent
screening. Fingerstick blood samples were collected on filter paper and were analyzed for
lead by AAS. Children with blood lead levels equal to or greater than 40 pg/dl were referred
for more detailed medical evaluation including an analysis of a venous blood specimen for
lead. ' Dust samples were collected from carpeting in each home and analyzed for lead by gra-
phite furnace AAS. Home tap water was analyzed for lead by AAS, and house paint was analyzed
for lead by XRF.
Of the 58 children who had the initial fingerstick blood lead elevation, 69 percent had
blood lead levels equal to or greater than 30 (jg/d1. Ten children from six families had blood
lead levels equal to or greater than 40 pg/dl , and blood lead levels were found to vary
markedly with age. The 0- to 3-year old category exhibited the highest mean with the 3- to
6-year-olds the next highest (39.2 pg/dl). Lowest mean values were found in the equal to or
greater than 10-year-old group (26.7 pg/dl).
More detailed investigation of the six families with the highest blood lead levels in
their children revealed the following: five of the six- lived in rural communities, with no
pre-existing source of lead from water supply, house paint, industrial emissions or heavy
automobile traffic. However, dust samples from the carpets exhibited excessively high lead
concentrations. These ranged from 1700 to 84,050 pg/g. (
Fergusson et al. (1981) sampled three population groups: general population, employees
of a battery plant, and children of battery plant employees, using hair lead levels as indices
of lead. Hair lead levels ranged from 1.2 to 110.9 pg/g in the 203 samples from the general
population. The distribution of hair lead levels was nearly lognormal. Employees of the bat-
tery factory had the highest hair lead levels (median ~250 pg/g) while family members (median
~40 pg/g) had a lesser degree of contamination and the general population (median ~5 pg/g)
still less. . ..
Analysis of variance results indicated a highly significant difference between mean lead
levels of the general survey and family members of the employees, and a significant difference
between the mean lead levels in the hair of the employees and their families. No significant
differences were found comparing mean hair lead levels among family members in terms of age
and sex. The analyses of the house dust suggested that the mechanism of exposure of family
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members is via the lead in dust that is carried home. Mean dust lead levels among the homes
of factory employees was 5580 ng/g while the dust inside of houses along a busy road was only
1620 pg/g. Both of these concentrations are for particles less than 0.1 mm.
Dolcourt et al. (1981) reported two interesting cases of familiar exposure to lead caused
by recycling of automobile storage batteries. The first case was of a 22 member, 4 generation
family living in a three bedroom house in rural eastern North Carolina. The great grandfather
of the index case worked at a battery recycling plant. He had two truckloads of spent casings
delivered to the home to serve as fuel for the wood stove; the casings were burned over a 3-
month period.
The index case presented with classic signs of acute lead encephalopathy, the most severe
and potentially fatal form of acute lead poisoning. The blood lead level was found to be 220
pg/dl. Three months after initial diagnosis and after chelation therapy, she continued to
have seizures and was profoundly mentally retarded. Dust samples were obtained by vacuum
cleaner and analyzed for lead by flameless AAS. Dust from a sofa near the wood stove con-
tained 13,283 pg/g lead while the kitchen floor dust had 41,283 mq/Q- There was no paint
lead. All other members of the family had elevated blood lead levels ranging from 27-256
pg/dl.
The other case involved a truck driver working in. a low exposure area of a battery re-
cycling operation in rural western North Carolina. He was operating an illegal battery re-
cycling operation in his home by melting down reclaimed lead on the kitchen stove. No family
member was symptomatic for lead symptoms but blood lead levels ranged from 24 to 72 pg/dl.
Soil samples taken from the driveway, which was paved with fragments of the discarded battery
casing, contained 12-13 percent lead by weight.
In addition to families being exposed as a result of employment at battery plants, stu-
dies have been reported recently for smelter worker families (Rice et al., 1978; Snee, 1982c).
Rice et al. studied lead contamination in the homes of secondary lead smelters. Homes of em-
ployees of secondary smelters in two separate geographic areas of the country were examined to
determine whether those homes had a greater degree of lead contamination than homes of workers
in the same area not exposed to lead. Both sets of homes ( area I and II) were examined at
the same time of the year.
Thirty-three homes of secondary smelter employees were studied; 19 homes in the same or
similar neighborhoods were studied as controls. Homes studied were in good condition and were
one or two family dwellings. Blood lead levels were not obtained for children in these homes.
In the homes of controls, a detailed occupational history was obtained for each employed
person. Homes where one or more residents were employed in a lead contaminated environment
were excluded from the analysis.
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House dust samples were collected by Vostal's method and were analyzed for lead by AA5.
In one of the areas, samples of settled dust were collected from the homes of employees and
controls. Dust was collected over the doorways. In homes where the settled dust was col-
lected, zinc protoporphyrin (ZPP) determinations were made in family members of the lead
workers and in the controls.
In both areas the wipe samples were statistically significantly higher in the homes of
employees compared to controls (geometric mean 79.3 ± 61.8 pg/g vs. 28.8 ± 7.4 (jg/g Area I;
112.0 ± 2.8 pg/g vs- 9.7 ± 3.9 (jg Area II). No significant differences were found between
workers' homes or controls between Area I and Area II. Settled dust lead was significantly
higher in the homes of employees compared to controls (3300 vs. 1200 pg/g). Lead content of
particulate matter collected at the curb and of paint chips collected in the home was not sig-
nificantly different between employee homes and controls. Zinc protoporphyrin determinations
were done on 15 children, 6 years or younger. ZPP levels were higher in employee children
than in control children. Mean levels were 61.4 pg/ml and 37.6 |jg/ml, respectively.
It should be noted again that the wipe samples were not different between employee homes
in the two areas. Interviews with employees indicated that work practices were quite similar
in the two areas. Most workers showered and changed before going home. Work clothes were
washed by the company. Obviously much closer attention needs to be paid to other potential
sources of lead introduction into the home (e.g., automobile surfaces).
11.5.6 Miscellaneous Studies
11.5.6.1 Studies Using Indirect Measures of Air Exposure.
11.5.6.1.1 Studies in the United States. A 1973 Houston study examined the blood lead levels
of parking garage attendants, traffic policemen, and adult females living near freeways
(Johnson et al. , 1974). A control group for each of the three exposed populations was selec-
ted by matching for age, education and race. Unfortunately, the matching was not altogether
successful; traffic policemen had less education than their controls, and the garage employees
were younger than their controls. Females were matched adequately, however. It should be
noted that the mean blood lead values for traffic policemen and parking garage attendants, two
groups regularly exposed to higher concentrations of automotive exhausts, were significantly
higher than the means for their relevant control groups. Statistically significant dif-
ferences in mean values were not found, however, between women living near a freeway, and con-
trol women living at greater distances from the freeway.
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A study of the effects of lower level urban traffic densities on blood lead levels was
undertaken in Dallas, Texas, in 1976 (Johnson et al., 1978). The study consisted of two
phases. One phase measured air lead values for selected traffic densities and conditions,
ranging from equal to or less than l,000"to about 37,000 cars/day. The second phase consisted
of an epidemiological study of traffic density and blood lead levels among residents. Figure
11-30 shows the relationship between arithmetic means of air lead and traffic density. As can
be seen from the graph, a reasonable fit was obtained.
In addition, for all distances measured (1.5 to 30.5 m from the road), air lead concen-
trations declined rapidly with distance from the street. At 15 m, concentrations were about
55 percent of the street concentrations. In air lead collections from 1.5 to 30.5 m from the
street, approximately 50 percent of the airborne lead was in the respirable range (<1 pm), and
the proportions in each size class remained approximately the same as the distance from the
street increased.
Soil lead concentrations were higher in areas with greater traffic density, ranging from
73.6 (jg/g at less than 1,000 cars per day to a mean of 105.9 at greater than 19,500 cars per
day. The maximum soil level obtained was 730 \iq/q.
Dustfall samples for 28 days from 9 locations showed no relationship to traffic
densities, but outdoor levels were at least 10 times the indoor concentration in nearby
residences.
In the second phase, three groups of subjects, 1- to 6-years-old, 18- to 49-years old and
50 years and older, were selected in each of four study areas. Traffic densities selected
were less than 1,000, 8,000 to 14,000, 14,000 to 20,000 and 20,000 to 25,000 cars/day. The
study groups averaged about 35 subjects, although the number varied from 21 to 50. The
smallest groups were from the highest traffic density area. No relationship between traffic
density and blood lead levels in any of the age groups was found (Figure 11-31). Blood lead
levels were significantly higher in children, 12 to 18 pg/dl, than in adults, 9 to 14 pg/dl.
Caprio et al. (1974) compared blood lead levels and proximity to major traffic arteries
in a study reported in 1971 that included 5226 children in Newark, New Jersey. Over 57 per-
cent of the children living within 30.5 m of roadways had blood lead levels greater than 40
pg/dl. For those living between 30.5 and 61 m from the roadways, more than 27 percent had
such levels, and at distances greater than 61 m, 31 percent exceeded 40 pg/dl. The effect of
automobile traffic was seen only in the group that lived within 30.5 m of the road.
No other sources of lead were considered in this study. However, data from other studies
on mobile sources indicate that it is unlikely that the blood lead levels observed in this
study resulted entirely from automotive exhaust emissions.
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2.0
I I I 1 T
III!
A
5
o
oc
1.6
<
0
z
z
1.2
_
0 O
o
o
o
<
Q
0
a.
t-
0.8
0
-
z
Q
0
Y = 0.659B + 0.0263 X
LU
a
D
X = TRAFFIC COUNT/1000
z
0.4
_
0
u
a
<
11
0
1 1 t I I
1 I I I
0 4,000 8,000 12.000 16,000 20,000 24,000 28,000 32,000 36,000 38,000
TRAFFIC VOLUME, cars/day
»
Figure 11-30. Arithmetic mean of air lead levels by traffic volume,
Dallas, 1976.
In 1964, Thomas et al. (1967) investigated blood lead levels in 50 adults who had lived
for at least 3 years within 76 m of a freeway (Los Angeles) and those of 50 others who had
lived for a similar period near the ocean or at least 1.6 km from a freeway. Mean blood lead
levels for those near the freeway were 22.7 ±5.6 for men and 16.7 ±7.0 pg/dl for women.
These concentrations were higher than for control subjects living near the ocean; 16.0 ±8.4
pg/dl for men and 9.9 ± 4.9 jjg/d 1 for women. The higher values, however, were similar to
those of other Los Angeles populations. Measured mean air concentrations of lead in Los
Angeles for October 1964 were 12.25 ± 2.70 pg/ni3 at a location 9 m from the San Bernardino
freeway; 13.25 ± 1.90 (jg/m3 at a fourth floor location 91.5 m from the freeway; and 4.60 ±
1.92 pg/m3 1.6 km from the nearest freeway. The investigators concluded that the differences
observed were consistent with coastal inland atmospheric and blood lead gradients in the Los
Angeles basin and that the effect of residential proximity to a freeway (7.6 to 76 m) was not
demonstrated.
Ter Haar and Chadzynski report a study of blood lead levels of children living near three
heavily travelled streets in Detroit (Ter Haar, 1981; Ter Haar and Chadzynski, 1979). Blood
lead levels were not found to be related to distance from the road but were related to condi-
tions of housing and age of the child after multiple regression analyses.
PB11C/A 11-150 7/29/83
8 Y7<
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25
¦o
o>
d
Z
o
P
<
oc
I-
z
UJ
(J
z
o
u
o
<
LU
_i
Q
O
O
_i
ffl
20
15
10
1 1 1
1
A
/ s
' FEMALES<
9
/ n n
y /\ \
MALES <9
' / \ \
\
/
f
1
1
X>
MALES >49
a.
»
FEMALES 19-49 _
-O
FEMALES >49
1 1 1
I
1,000 1,000 13,500
13,500
19,500
TRAFFIC DENSITY, cars/day
19,500
38.000
Figure 11-31. Blood lead concentration and traffic density by sex and
age, Dallas, 1976.
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11.5.6.1.2 British Studies. In a Birmingham, England study, mean blood lead levels in 41
males and 58 females living within 800 m of a highway interchange were 14.41 and 10.93 jjg/d1,
respectively, just before the opening of the interchange in May 1972 (Waldron, 1975). From
October 1972 to February 1973, the respective values for the same individuals were 18.95 and
14.93 pg/dl. In October 1973 they were 23.73 and 19.21 pg/dl. The investigators noted dif-
ficulties in the blood collection method during the baseline period and changed from capillary
to venous blood collection for the remaining two samples. To interpret the significance of
the change in blood collection method, some individuals gave both capillary and venous blood
at the second collection. The means for both capillary and venous bloods were calculated for
the 18 males and 23 females who gave both types of blood samples (Barry, 1975). The venous
blood mean values for both these males and females were lower by 0.8 and 0.7 pg/dl, respec-
tively. If these differences were applied to the means of the third series, the mean for
males would be reduced to 24.8 pg/dl and that for the females to 18.7 pg/dl. These adjusted
means still show an increase over the means obtained for the first series. Comparing only the
means for venous bloods, namely series two and three, again shows an increase for both groups.
The increase in blood lead values was larger than expected following the model of Knelson et
al. (1973), because air lead values near the road were approximately 1 pg/m3. The investi-
gators concluded that either the lead aerosol of very small particles behaved more like a gas
so that considerably more than 37 percent of inhaled material was absorbed or that ingestion
of lead contaminated dust might be responsible.
Studies of taxicab drivers have employed different variables to represent the drivers'
lead exposure (Flindt et al., 1976; Jones et al., 1972): one variable was night vs. dayshift
drivers (Jones et al., 1972); the other, mileage driven (Flindt et al., 1976). No difference
was observed, in either case.
The studies reviewed show that automobiles produce sufficient emissions to increase air
and nearby soil concentrations of lead as well, as increase blood lead concentrations in chil-
dren and adults. The problem is of greater importance when houses are located within 100 ft
(30 m) of the roadway.
11.5.6.2 Miscellaneous Sources of Lead. The habit of cigarette smoking is a source of lead
exposure. Shaper et al. (1982) report that blood lead concentration is higher for smokers
than nonsmokers and that cigarette smoking makes a significant independent contribution to
blood lead concentration in middle-aged men in British towns. A direct increase in lead in-
take from cigarettes is thought to be responsible. Hopper and Mathews (1983) comment that
current smoking has a significant effect on blood lead level, with an average increase of 5.8
percent in blood lead levels for every 10 cigarettes smoked per day. They also report that
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past smoking history had' no measurable effect on blood lead levels. Hasselblad and Nelson
(1975) report an average increase in women's blood lead levels of 1.3 pg/dl in' the study of
Tepper and Levin (1975).
Although no studies are available, it is conceivable that destruction of lead-containing
plastics (to recover copper), which has caused cattle poisoning, also could become a source of
lead exposure for humans. Waste disposal is a more general problem because lead-containing
materials may be incinerated and may thus contribute to increased air lead levels. This
source of lead has not been studied in detail. Tyrer (1977) cautions of the lead hazard in
the recycling of waste.
The consumption of illicitly distilled liquor has been shown to produce clinical cases of
lead poisoning. Domestic and imported earthenware (De Rosa et al., 1980) with improperly
fired glazes have also been related to clinical lead poisoning. This source becomes important
when foods or beverages high in acid are stored in earthenware containers, because the acid
releases lead from the walls of the containers.
Particular cosmetics, popular among some Oriental and Indian ethnic groups, contain high
percentages of lead that sometimes are absorbed by users in quantities sufficient to be toxic.
Ali et al. (1978) and Attenburrow et al. (1980) discuss the practice of surma and lead poison-
ing. Other sources of lead are presented in Table 11-60.
TABLE 11-60. SOURCES OF LEAD
Source
Gasoline Sniffing
Colored Gift Wrapping
Gunshot Wound
Drinking Glass Decorations
Electric Kettles
Hair dye
Snuff use
Firing ranges
References
Kaufman and Wiese (1978)
Coodin and Boeckx (1978)
Hansen and Sharp (1978)
Bertagnolli and Katz (1979)
Dillman et al. (1979)
Anonymous (1979)
Wigle and Charlebois (1978)
Searle and Harnden (1979)
Filippini and Simmler (1980)
Fischbein et al. (1979, 1980b)
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11.6 SUMMARY AND CONCLUSIONS
Studies of ancient populations using bone and teeth show that levels of internal exposure
of lead today are substantially elevated over past levels. Studies of current populations
living in remote areas far from urbanized cultures show blood lead levels in the range of 1 to
5 pg/dl. In contrast to the blood lead levels found in remote populations, data from current
U.S. populations have geometric means ranging from 10 to 20 |jg/dl depending on age, race, sex
and degree of urbanization. These higher current exposure levels appear to be associated with
industrialization and widespread commercial use of lead, e.g. in gasoline combustion.
Age appears to be one of the single most important demographic covariates of blood lead
levels. Blood lead levels in children up to six years of age are generally higher than those
in non-occupational ly exposed adults. Children aged two to three years tend to have the high-
est levels as shown in Figure 11-32. Blood lead levels in non-occupationally exposed adults
may increase slightly with age due to skeletal lead accumulation.
Sex has a differential impact on blood lead levels depending on age, No significant dif-
ferences exist between males and females less than seven years of age. Males above the age of
seven generally have higher blood lead levels than females.
Race also plays a role, in that blacks generally have higher blood lead levels than
either whites or Hispanics and urban black children (aged 6 mo. to 5 yr.) have markedly higher
blood lead concentrations than any other racial or age group. Possible genetic factors asso-
ciated with race have yet to be fully disentangled from differential exposure levels as im-
portant determinants of blood lead levels.
Blood lead levels also generally increase with degree of urbanization. Data from NHANES
II show blood lead levels in the United States, averaged from 1976 to 1980, increasing from a
geometric mean of 11.9 pg/dl in rural populations to 12.8 pg/d"I in urban populations less than
one million, increasing again to 14.0 (jg/dl in urban populations of one million or more.
Recent U.S. blood lead levels show a downward trend occurring consistently across race,
age and geographic location. The downward pattern commenced in the early part of the 19701s
and has continued into 1980. The downward trend has occurred from a shift in the entire dis-
tribution and not through a truncation in the high blood lead levels. This consistency sug-
gests a general causative factor, and attempts have been made to identify the causative ele-
ment. Reduction in lead emitted from the combustion of leaded gasoline is a prime suspect, but
at present no causal relationship has been established.
Blood lead levels, examined on a population basis, have similarly skewed distributions.
Blood lead levels, from a population thought to be homogenous in terms of demographic and lead
exposure characteristics, approximately follow a lognormal distribution. The geometric stan-
dard deviations, an estimation of dispersion, for four different studies are shown in Table
11-61. The values, including analytic error, are about 1.4 for children and possibly somewhat
PB11C/A 11-154 7/29/83
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40
35
30
25
o>
a.
ri
uj 20
O
O
O
15
10
/
/
/
/
IDAHO STUDY
NEW YORK SCREENING - BLACKS
NEW YORK SCREENING WHITES
NEW YORK SCREENING ¦ HISPANICS
NHANES II STUDY BLACKS
NHANES II STUDY - WHITES
10
AGE IN YEARS
Figure 11-32. Geometric mean blood lead levels by race and age for younger children in the
NHANES II study, and the Kellogg/Silver Valley and New York Childhood Screening Studies.
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TABLE 11-61. SUMMARY OF POOLED GEOMETRIC STANDARD
DEVIATIONS AND ESTIMATED ANALYTIC ERRORS
Study
Pooled Geometric Standard Deviations
Estimated
Inner City
Black Children
Inner City
White Children
Adults
Females
Adul t
Males
Analytic
Error
NHANES II
1.37
1.39
1. 36a
1. 40a
0.021
N.Y. Childhood
Screening Study
1.41
1.42
-
-
(b)
Tepper-Leven
-
-
1.30
-
0.056°
Azar et al.
-
-
-
1.29
0.042°
2
Note: To calculate an estimated person-to-person GSD, compute Exp [((ln(GSD)) -
Analytic Error)4]
apooled across areas of differing urbanization
not known, assumed to be similar to NHANES II
Ctaken from Lucas (1981).
smaller for adults. This allows an estimation of the upper tail of the blood lead distri-
bution, the group at higher risk.
Because the main purpose of this chapter is to examine relationships of lead in air and
lead in blood under ambient conditions, the results of studies most appropriate to this area
have been emphasized. A summary of the most appropriate studies appears in Table 11-62. At
3
air lead exposures of 3.2 jjg/m or less, there is no statistically significant difference be-
tween curvilinear and linear blood lead inhalation relationships. At air lead exposures of 10
3
pg/m or more, either nonlinear or linear relationships can be fitted. Thus, a reasonably
consistent picture emerges in which the blood-lead air-lead relationship by direct inhalation
3
was approximately linear in the range of normal ambient exposures of 0.1 - 2.0 pg/m (as dis-
cussed in Chapter 7). Differences among individuals in a given study (and among several
studies) are large, so that pooled estimates of the blood lead inhalation slope depend upon
the the weight given to various studies. Several studies were selected for analysis, based
upon factors described earlier. EPA analyses* of experimental and clinical studies (Griffin
et al. 1975; Rabinowitz et al., 1974, 1976, 1977; Kehoe 1961a,b,c; Gross 1981; Hammond et al. ,
1981) suggest that blood lead in adults increases by 1.64 ± 0.22 (jg/dl from direct inhalation
"Note: The term EPA analyses refers to calculations done at EPA. A brief discussion of the
methods used is contained in Appendix 11-B; more detailed information is available at EPA upon
request.
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TABLE 11-62. SUMMARY OF BLOOD INHALATION SLOPES, (?)
pg/dl per pg/m
Population
Study
Study
Type
N
(P)
Slope
pg/dl per pg/m3
Model Sensitivity
Of Slope*
Children
Angle and
Mclntire, 1979
Omaha, NE
Populati on
1074
1.92
1 9 •s
(1.40 - 4.40) ' '
Roels et al.
(1980)
Belgi um
Populati on
148
2.46
(1.55 - 2.46)1'2
Yankel et al.
(1977); Walter
et al. (1980)
Idaho
Populati on
879
1.52
12 3
(1.07 - 1.52) ' '
Adult Males
Azar et al.
(1975). Five
groups
Population
149
1.32
(1.08 " 2.39)2,3
Gri ffi n et al.
(1975), NY
pri soners
Experiment
43
1.75
(1.52 - 3.38)4
Gross
(1979)
Experiment
6
1.25
(1.25 - 1.55)2
Rabinowitz et
al. (1973,1976,
1977)
Experiment
5
2.14
(2.14 - 3.51)5
*Selected from amogg the most plausible statistically equivalent models. For nonlinear models,
slope at 1.0 pg/m .
^"Sensitive to choice of other correlated predictors such as dust and soil lead.
2
Sensitive to linear vs. nonlinear at low air lead.
3 . .
Sensitive to age as a covariate.
4
Sensitive to baseline changes in controls.
^Sensitive to assumed air lead exposure.
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of each additional ng/m of air lead. EPA analyses of population studies (Yankel et al.,
1977; Roels et al., 1980; Angle and Mclntire, 1979) suggest that, for children, the blood lead
3
increase is 1.97 ± 0.39 pg/dl per pg/m for air lead. EPA anaylsis of Azar's population study
(Azar et al., 1975) yields a slope of 1.32 ± 0.38 for adult males.
These slope estimates are based on the assumption that an equilibrium level of blood lead
is achieved within a few months after exposure begins. This is only approximately true, since
lead stored in the skeleton may return to blood after some years. Chamberlain et al. (1978)
suggest that long term inhalation slopes should be about 30 percent larger than these
estimates. Inhalation slopes quoted here are associated with a half-life of blood lead in
adults of about 30 days. O'Flaherty et al. (1982) suggest that the blood-lead half-life may
increase slightly with duration of exposure, but this has not been confirmed (Kang et al.,
1983).
One possible approach would be to regard all inhalation slope studies as equally infor-
mative and to calculate an average slope using reciprocal squared standard error estimates as
weights. This approach has been rejected for two reasons. First, the standard error estima-
tes characterize only the internal precision of an estimated slope, not its representativeness
(i.e., bias) or predictive validity. Secondly, experimental and clinical studies obtain more
information from a single individual than do population studies. Thus, it may not be appro-
priate to combine the two types of studies.
Estimates of the inhalation slope for children are only available from population
studies. The importance of dust ingestion as a non-inhalation pathway for children is estab-
lished by many studies. A slope estimate has been derived for air lead inhalation based on
those studies (Angle and Mclntire 1979; Roels et al., 1980; Yankel et al., 1977) from which
the air inhalation and dust ingestion contributions can both be estimated.
While direct inhalation of air lead is stressed, this is not the only air lead contribu-
tion that needs to be considered. Smelter studies allow partial assessment of the air lead
contributions to soil, dust and finger lead. Conceptual models allow preliminary estimation
of the propagation of lead through the total food chain as shown in Chapter 7. Useful mathe-
matical models to quantify the propagation of lead through the food chain need to be
developed. The direct inhalation relationship does provide useful information on changes in
blood lead as responses to changes in air lead on a time scale of several months. The in-
direct pathways through dust and soil and through the food chain may thus delay the total
blood lead response to changes in air lead, perhaps by one or more years. The Italian ILE
study facilitates partial assessment of this delayed response from leaded gasoline as a
source.
Dietary absorption of lead varies greatly from one person to another and depends on the
physical and chemical form of the carrier, on nutritional status, and on whether lead is
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ingested with food or between meals. These distinctions are particularly important for con-
sumption by children of leaded paint, dust and soil. Typical values of 10 percent absorption
of ingested lead into blood have been assumed for adults and 25 to 50 percent for children.
It is difficult to obtain accurate dose-response relationships between blood lead levels
and lead levels in food or water. Dietary intake must be estimated by duplicate diets or
fecal lead determinations. Water lead levels can be determined with some accuracy, but the
varying amounts of water consumed by different individuals adds to the uncertainty of the es-
timated relationships.
Quantitative analyses relating blood lead levels and dietary lead exposures have been re-
ported. Studies on infants provide estimates that are in close agreement. Only one indi-
vidual study is available for adults (Sherlock et al. 1982); another estimate from a number of
pooled studies is also available. These two estimates are in good agreement. Most of the
subjects in the Sherlock et al. (1982) and United Kingdom Central Directorate on Environmental
Pollution (1982) studies received quite high dietary lead levels ,(>300 pg/day). The fitted
cube root equations give high slopes at lower dietary lead levels. On the other hand, the
linear slope of the United Kingdom Central Directorate on Environmental Pollution (1982) study
is probably an underestimate of the slope at lower dietary lead levels. For these reasons,
the Ryu et al. (1983) study is the most believable, although it only applies to infants.
Estimates for adults should be taken from the experimental studies or calculated.from assumed
absorption and half-life values. Most of the dietary intake supplements were so high that
3
many of the subjects had blood lead concentrations much in excess of 30 pg/m for a considera-
ble part of the experiment. Blood lead levels thus may not completely reflect lead exposure,
due to the previously noted nonlinearity of blood lead response at high exposures. The slope
estimates for adult dietary intake are about 0.02 pg/dl increase in blood lead per |jg/day in-
take, but consideration of blood lead kinetics may increase this value to about 0.04. Such
values are a bit lower than slopes of about 0.05 |jg/d 1 per pg/day estimated from the popula-
tion studies extrapolated to typical dietary intakes. The value for infants is larger.
The relation between blood;,:]ead and water lead is not clearly defined and is often de-
scribed as nonlinear. Water lead intake varies greatly from, one person to another. It has
been assumed that children can absorb 25 to 50 percent of lead in water. Many authors chose
to fit cube root models to their data, although polynomial and logarithmic models were also
used. Unfortunately, the form of the model greatly influences the estimated contributions to
blood leads from relatively low water lead concentration.
Although there is close agreement in the quantitative analyses of the relationship bet-
ween blood lead level and dietary lead, there is a larger degree of variability in results of
the various water lead studies. The relationship is curvilinear, but its exact form is yet to
be determined. At typical levels for U.S. populations, the relationship appears linear. The
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only study that determines the relationship based on lower water lead values (<100 ^g/1) is
the Pocock et al. (1983) study. The data from this study, as well as the authors themselves,
suggest that in this lower range of water lead levels, the relationship is linear. Further-
more, the estimated contributions to blood lead levels from this study are quite consistent
with the polynomial models from other studies. For these reasons, the Pocock et al. (1983)
slope of 0.06 is considered to represent the best estimate. The possibility still exists,
however, that the higher estimates of the other studies may be correct in certain situations,
especially at higher water lead levels (>100 mg/1).
Studies relating soil lead to blood lead levels are difficult to compare. The relation-
ship obviously depends on depth of soil lead, age of the children, sampling method, cleanli-
ness of the home, mouthing activities of the children, and possibly many other factors. Var-
ious soil sampling methods and sampling depths have been used over time, and as such they may
not be directly comparable and may produce a dilution effect of the major lead concentration
contribution from dust which is located primarily in the top 2 cm of the soil. Increases in
soil dust lead significantly increase blood lead in children. From several studies (Yankel et
al., 1977; Angle and Mclntire, 1979) EPA estimates an increase of 0.6 to 6.8 pg/dl in blood
lead for each increase of 1000 pg/g in soil lead concentration. Values of about 2.0 pg/dl per
1,000 Mg/g soil lead from the Stark et al. (1982) study may represent a reasonable median
estimate. The relationship of housedust lead to blood lead is difficult to obtain. House-
hold dust also increases blood lead, children from the cleanest homes in the Silver Valley/
Kel 1 ogg*Study having 6 pg/d 1 less lead in blood, on average, than those from the households
with the most dust.
A number of specific environmental sources of airborne lead have been evaluated for pot-
ential direct influence on blood lead levels. Combustion of leaded gasoline appears to be the
largest contributor to airborne lead. Two studies used isotope ratios of lead to.estimate the
relative proportion of lead in the blood coming from airborne lead. From one study, by
Manton, it can be estimated that between 7 and 41 percent of the blood lead in study subjects
in Dallas resulted from airborne lead. Additionally, these data provide a means of estimating
the indirect contribution of air lead to blood lead. By one estimate, only 10 to 20 percent
of the total airborne contribution in Dallas is from direct inhalation.
From the ILE data in Facchetti and Geiss (1982), as shown in Table 11-63, the direct in-
halation of air lead may account for 54 percent of the total adult blood lead uptake from
leaded gasoline in a large urban center, but inhalation is a much less important pathway in
suburban parts of the region (17 percent of the total gasoline lead contribution) and in the
rural parts of the region (8 percent of the total gasoline lead contribution). EPA analyses
of the preliminary results from the ILE study separated the inhalation and non-inhalation con-
tributions of leaded gasoline to blood lead into the following three parts: (1) An increase
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of about 1.7 ng/dl in blood lead per |jg/m^ of air lead, attributable to direct inhalation of
the combustion products of leaded gasoline; (2) a sex difference of about 2 |jg/dl attributable
to lower exposure of women to indirect (non-inhalation) pathways for gasoline lead; and (3) a
non-inhalation background attributable to indirect gasoline lead pathways, such as ingestion
of dust and food, increasing from about 2 |.ig/dl in Turin to 3 pg/dl in remote rural areas.
The non-inhalation background represents only two to three years of environmental accumulation
at the new experimental lead isotope ratio. It is not clear how to extrapolate numerically
these estimates to U.S. subpopulations; but it is evident that even in rural and suburban
parts of a metropolitan area, the indirect (non-inhalation) pathways for exposure to leaded
gasoline make a significant contribution to blood lead. This can be seen in Table 11-63. It
should also be noted that the blood lead isotope ratio responded fairly rapidly when the lead
isotope ratio returned to its pre-experiment.al value, but it is not yet possible to estimate
the long term change in blood lead attributable to persistent exposures to accumulated envi-
ronmental lead.
Studies of data from blood lead screening programs suggest that the downward trend in
blood lead levels noted earlier is due to the reduction in air lead levels, which has been at-
tributed to the reduction of lead in gasoline.
TABLE 11-63. ESTIMATED CONTRIBUTION OF LEADED GASOLINE TO BLOOD LEAD
BY INHALATION AND NON-INHALATION PATHWAYS
Air Lead
Fracti on
From
Gasoli ne
(a)
Blood
Lead
Fracti on
From
Gasoli ne
(b)
Bl ood
"From
Gasoli
In Air
pg/dl
Pb
K)
Blood Lead
Not Inhaled
From,Gaso-
1 i ne
pg/dl
Estimate
Fraction
Gas-Lead
Inhalati on
(e)
Location
Turi n
<25 km
>25 km
0.873
0.587
0.587
0.237
0.125
0.110
2.79
0. 53
0.28
2.37
2.60
3.22
0.54
0.17
0.08
(a) Fraction of air lead in Phase 2 attributable to lead in gasoline.
(b) Mean fraction of blood lead in Phase 2 attributable to lead in gasoline.
(c) Estimated blood lead from gas inhalation : p x (a) x (b), p = 1.6.
(d) Estimated blood lead from gas, non-inhalation = (f)-(e)
(e) Fraction of blood lead uptake from gasoline attributable to direct inhalation = (f)/(e)
Source: Facchetti and Geiss (1982), pp. 52-56.
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Primary lead smelters, secondary lead smelters and battery plants emit lead directly into
the air and ultimately increase soil and dust lead concentrations in their vicinity. Adults,
and especially children, have been shown to exhibit elevated blood lead levels when living
close to these sources. Blood lead levels in these residents have been shown to be related to
air, as well as to soil or dust exposures.
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Tyler, R. L. (1970) Philadelphia combats "silent epidemic" in the "ghetto" lead poisoning
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Tyrer, F. H. (1977) A cautionary tale of a lead hazard in recycling of waste. J. Soc. Occup.
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U.S. Centers for Disease Control. (1973) Human lead absorption - Texas. Morbidity and Mortality
Weekly Report 22: 405-407.
U.S. Centers for Disease Control. (1977a) Surveillance of childhood lead poisoning - United
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U.S. Centers for Disease Control. (1977b) Increased lead absorption in children of lead workers
- Vermont. Morbidity and Mortality Weekly Report 26: 61-62.
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U.S. Centers for Disease Control. (1982c) Surveillance of childhood lead poisoning - United
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I11REF/A
11-176
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U.S. Environmental Protection Agency. (1980) Ambient water quality criteria for lead.
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Concentrations of lead and other metals in blood of two and three year-old children living
near a secondary smelter. Int. Arch. Occup. Environ. Health 42: 231-239.
IllREF/A 11-177 7/29/83
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/
PRELIMINARY DRAFT
APPENDIX 11A
COMPARTMENTAL ANALYSIS
Many authors have noted that under conditions of constant lead exposure, blood lead con-
centrations change from one level to another apparent equilibrium level over a period of
several months. A mathematical model is helpful in estimating the new apparent equilibrium
level even when the duration of the experiment is not sufficiently long for this equilibrium
level to have been achieved. The model assumes that lead in the body is held in some number
of homogeneous and well-mixed pools or compartments. The compartments have similar kinetic
properties and may or may not correspond to identifiable organ systems. In a linear kinetic
model it is assumed that the rate of change of the mass of lead in compartment i at time t,
denoted X..(t), is a linear function of the mass of lead in each compartment. Denote the frac-
tional rate of transfer of lead into compartment i from compartment j by (fraction per
day), and let I.(t) be the total external lead input into compartment i at time t in units
such as jjg/day. The elimination rate from compartment i is denoted The compartmental
model is:
dX.(t)/dt = I.(t) ~ Ku Xl(t)* * ' * ~ KinXn(t) - (Koi * KX1 ~ " " " ~ Wt)
for each of the n compartments. If the inputs are all constant, then each X.(t) is the sum of
(at most) n exponential functions of time (see for example, Jacquez, 1972).
For the one-compartment model:
dX.(t)/dt = Ix - K01 xx(t)
with an initial lead burden X^(0) at time 0,
Xx(t) = Xx(0) exp(-KQ1t) + [(I1/K01) (l-exp(-K01t)]
The mass of lead at equilibrium is ^9- ^'c may think of this pool as "blood lead". If
tne pool has volume then the equilibrium concentration is ^ MQ/dl. Intake from
several pathways will have the form:
1^ = (Pb-Air) + A^ (Pb-Diet)+
so that the long term concentration is
VK01 V1 = (A1/K01V1} Pb~Air + '
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The inhalation coefficient is 3 = A^/K^V^. The blood lead half-life is 0.693/K01-
Models with two or more compartments will still have equilibrium concentrations in blood
and other compartments that are proportional to the total lead intake, and thus increase
linearly with increasing concentrations in air, dust, and diet. The relationship between the
exponential parameters and the fractional transfer coefficients will be much more complicated,
however.
Models with two or three pools have been fitted by Rabinowitz et a!. (1976, 1977) and by
Batschelet et al. (1979). The pools are tentatively identified as ma i nly blood, soft tissue
and bone. But as noted in Section 11.4.1.1, the "blood" pool is much larger than the volume
of blood itself, and so it is convenient to think of this as the effective volume of distri-
bution for pool 1. A five-pool model has been proposed by Bernard (1977), whose pools are
mainly blood, liver, kidney, soft bones and hord bone.
The major conclusion of this Appendix is that linear kinetic mechanisms imply linear
relationships between blood lead and lead concentrations in environmental media. Any extended
discussion of nonlinear kinetic mechanisms is premature at this point, but it is of some
interest that even simple nonlinear kinetic models produce plausible nonlinear blood lead vs.
concentration relationships. For example, if the rate of blood lead excretion into urine or
storage "permanently" in bone increases linearly with blood lead, then at high blood lead
levels, blood increases only as the square root of lead intake. Let M denote the mass of lead
in pool 1 at which excretion rate doubles. Then:
dX1(t)/dt = Ij - K01(l ~ x1(t)/M1)xJ(t)
has an equilibrium level:
Xx - HjCV 1 + 4Ii/KoiMi " V/2
This is approximately linear in intake I when 1^ is small, but a square root function of in-
take when it is large. Other plausible models can be constructed.
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APPENDIX 11B
FITTING CURVES TO BLOOD LEAD DATA
The relationship between blocd lead and the concentration of lead in various environ-
mental media is a principal concern of this chapter. It is generally accepted t^at the geo-
metric mean blood lead is some function, f, of the concentration of air lead and of lead in
diet, dus*„, soil and other media. It has been observed that blood lead levels have a highly
skewed distribution even for populations with relatively homogeneous exposure, and that the
variability in bloor, lead is roughly proportional to the geometric mean blood lead or to the
arithmetic mean (constart coefficient of variation). Thus, instead of the usual nodel in
which randorr. variations are normally distributed, a model is assumed here in which the random
deviations are multiplicative and lognormally distributed with geometric mean 1 and geometric
standard deviation (GSD) e°. Tre model is written
Pb-Blood = f (Pb-Air, etc.) eoz
w: cs z is a random variable with mean 0 and standard deviation 1. It has a Gaussian or
normal di stri bjtion. The model is fitted to data in 1 ogari th ,
f = (P Pb-Air + Pq + Pb"Du5t- + • • • )^
These functions can all be fitted to data using nonlinear regression techniques. Even when
the nonlinear shape parameter A has a sma". 1 statistical uncertainty or standard error as-
sociated with it, a highly variable data set may not clearly distinguish the linear function
(A. = 1) frorr a nonlinear function (A i- 1). In particular, for the Azar data set, the residual
sum of squares is shown as a function of the shape parameter A, in Figure 1IB-1. Wher only a
PB11D/D 11B-1 7/29/83
847<
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PRELIMINARY DRAFT
\
9.3
2 9-1
oc
<
a
w 9.0
LL
o
s
w 0.9
<
3
q
[2 8.8
oc
8.7
8.6
i—i—i—r
MINIMUM SIGNIFICANT
DIFFERENCE FOR 1 DF
i—i—r—r
SSE FOR In |Pb-Blood) = A In (/? Pb-Air + I/?. C.I
j = U J
A = 0.26
MINIMUM SIGNIFICANT
DIFFERENCE FOR 5 DF
5 5
SSE FOR In (Pb-Blood) = A In (0 Pb-Air + 1/3. C. +1 /?'. C. Age)
1 J J 1 J J
A = 1
1 I
J L
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
POWER EXPONENT. A
Figure 11 B-1. Residual sum of squares for nonlinear regression models for Azar
data (N = 149).
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PRELIMINARY DRAFT
senarate intercept (background) is assumed for each subpopu1ation, the best choice is A =
D 2S: but when age is also used as a covariate for each subpopulation, then the linear rrodel
is better. However, the approximate size of the difference, in residual surr of squares
required to decide at the 5 percent significance level that a nonlinear model is better (or
wo-se) than a linear model, is larger than the observed difference in sum of squares for any
A>0.2 (Gallant, 1975). Therefore a linear model is used unless evidence of no^linearity is
very strong, as with some of Kehoe's studies and the Silver Valley/Kellogg study. Non-
linearity is detectable only when blood lead is high (much above 35 or 40 pg/dl), and intake
is high, e.g., air lead much above 10 pg/m3. Additional research is needed on the relation-
ship between lead levels and lead intake from all environmental pathways.
The "background" or intercept term in irost models requires sorre comment. As the
Mantcn and Italian lead isotope studies show, lead added to a regional environment by corrbus-
tion of gasoline accumulates a large non-inhalation component even after only 2 years (see
Figure 11-26). The non-inhalation contribution in the Turin region was nearly independent of
location (air lead). It is not possible to assign causes, e.g., ingestion of food, dust, or
water by adults, so no .direct extrapolation to U.S. populations is possible at this time due
to unknown differences in non-air exposures between the U.S. and Italy. It is probable that
the ncn-inhalation contribution to blood lead increases with time as lead accumulates in the
environment. After many years, one might ODtain a figure like Figure 11B-2. Another concept
is that such a curve should predict zero blooc lead increase at zero air lead. If the blood
lead curve is forced to pass through 0 when air lead - 0, a nonlinear curve is required. It
has been concluded that a positive intercept term is needed to account for intake from
accumulated lead in the environment, which precludes fully logarithmic models such as
In (Pb-Blood) - In (p^) +¦ p In (Pb-Air) + In (Pb-Dust) + ...
It must be acknowledged that such models may provide useful interpolations over a range o*7 air
lead levels; e.g., the Goldsmith-Hexter equation predicts blood lead 3.4 pg/dl at an air lead
<0.004 pg/rr.3 in the Nepalese subjects in Piomelli et al. (1980).
The final concern is that the intercept term may represent indirect sources of lead expo-
sure that include previous air lead exposures. To the extent t.hat present and previous air
lead exposures are correlated, the intercept or background term may introduce apparent curvi-
linearities in the population studies of inhalation. The magnitude of this effect is unknown.
PB11D/D 11B-3 7/29/83
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PRELIMINARY DRAFT
TOTAL CONTRIBUTION OF AIR LEAD AFTER
LONG INTERVAL OF EXPOSURE AND DEPOSITION
z
o
H
<
0c
H
Z
UJ
u
z
o
u
Q
Q
O
O
V
NONINHALATION
BACKGROUND
CONCENTRATION
AFTER LONG
INTERVAL
OF AIR LEAD
EXPOSURE AND
DEPOSITION ^
TOTAL CONTRIBUTION OF AIR
LEAD AFTER SHORT INTERVAL
OF EXPOSURE AND DEPOSITION
L
NONINHALATION
BACKGROUND
CONCENTRATION
AFTER SHORT
INTERVAL OF
AIR LEAD
EXPOSURE AND
DEPOSITION.
DIRECT INHALATION
OF AIR LEAD FROM
CURRENT EXPOSURE
1.
AIR LEAD CONCENTRATION
Figure 11 B-2. Hypothetical relationship between blood lead and air lead by
inhalation and non-inhalation.
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APPENDIX 11C
ESTIMATION OF GASOLINE LEAD CONTRIBUTIONS TO ADULT
BLOOD LEAD BURDENS BASED ON ILE STUDY RESULTS
As discussed in Chapter 11 (pp. 11-118 to 11-123) the results of the Isotopic Lead Ex-
periment (ILE) carried out in Northern Italy provide one basis by which to estimate contribu-
tions of lead in gasoline to blood lead burdens of populations exposed in the ILE study area.
Figures 1 to 5 of this appendix, reprinted from the ILE Status Report (1982) illustrate
changes in isotopic lead (206/207) ratios for 35 adult subjects, for whom repeated measure-
ments were obtained over time during the ILE study. The percent of total blood lead in those
subjects contributed by Australian lead-labelled gasoline (petrol) used in automotive vehicles
in the ILE study area was estimated by the approach reprinted below verbatim from Appendix 17
of the ILE Status Report (1982):
The main purpose of the ILE project was the determination of the contribution of petrol
lead to total lead in blood. A rough value for the fraction of petrol lead in blood can be
derived from the following equations;
each of them referring to a given time- at which equilibrium conditions hold.
R1 and R" represent the blood lead isotopic ratios measured at each of the two times; if
R-^ and represent the local petrol lead isotopic ratios measured at the same times, X is the
fraction of local petrol lead in blood due to petrols affected by the change in the lead iso-
topic ratio, irrespective of its pathway to the blood i.e. by inhalation and ingestion (e.g.
from petrol lead fallout). The term (1-X) represents the fraction of the sum of all other
external sources of lead in the blood (any <> petrol lead included), factor f being the
unknown isotopic ratio of the mixture of these sources. It is assumed that X and f remained
constant over the period of the experiment, which implies a reasonable constancy of both the
lead contributing sources in the test areas and the living habits which, in practice, might
not be entirely the case.
Data from individuals sampled at the initial and final equilibrium phases of the ILE
study together with petrol lead isotopic ratios measured at the same times, would ideally pro-
vide a means to estimate X for Turin and countryside adults. However, for practical reasons,
calculations were based on the initial and final data of the subjects whose first sampling was
R: X + f (1-X) = R1
R2 X + f (1-X) = R"
(1)
(ID
DUP11/B
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PRELIMINARY- DRAFT
done not later than 1975 and the final one during phase 2. Their complete follow-up data are
shown in Table 27. For and the values measured in the phases 0 and 2 of ILE were used
(R^ = 1.186, R,, = 1.060). Hence, as averages of the individual X and f results, we obtain:
Turin x. - 0.237 ±0.054 i.e 24%
fj = 1.1560 ± 0,0033
countryside X = 0.125 ± 0.071 i.e. 12%
<25 km - f2 = 1.1542 ± 0.0036
countryside X = 0.110 ± 0.058 i.e 11%
>25 km f| = 1.1576 i 0.0019
6-;
«-
114-
r
• PhlSt1
Phase I
Fig. I. Individual values of blood Pb-206.'Pb-20? ratio for subjects follow-up in Turin (12 subjects)
DUP11/B 11C-2 7/29/83
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PRELIMINARY DRAFT
Pb 206/Pti207
Phase 2
Phase 0
I ig. 2. Individual values in blood Ph-206/Pb-20'' ratio for subjects follow-up in Castagneto (4 subjects)
Pb206/Pb207
116-
1.15
I.U
113
112
--O--DRUEHT0
— •—flANO
Phase 0
Phase I
Phase 2
T
79 1 80
U 75 I 76 ' 11 78 >
Fig. 3. Individual values of blood Pb-206/Pb-207 ratio Tor subjects follow-up in Druento and FiaJio (6 subjects)
11C-3 7/29/83
853<
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PRELIMINARY DRAFT
I
Pb206/Pt?07
1.15-
—SANTENA
--o-- nole
Phase D
Phase 1
— j- -
r
74
1
75
76
Phase?
11
78
79
80
Fig. 4. Individual values of blood Pb-206/Pb-207 ratio for subjects follow-up in Nole and Santena (9 subjects)
Pfa206/Pb207
Phase 0
Phase 2
Fig. S. Individual values of blood Pb-206/Pb-207 ratio for subjects follow-up in Viu (4 subjects)
DUP11/B
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APPENDIX 11-D
REPORT
OF THE
NHANES II TIME TREND ANALYSIS REVIEW GROUP
June 15, 1983
SRD/NHANES
(11D-1)
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Environmental Criteria and Assessment Office (MD-B2J
Research Triangle Park, North Carolina 27711
The materials contained in this report were generated as the result of critical
evaluations and deliberations by members (listed below) of the NHANES II Time Trend
Analysis Review Group. All members of this Review Group unanimously concur with
and endorse the findings and recommendations contained in the present report as
representing the collective sense of the Review Group.
Dr. Joan Rosenblatt (Chairman)
Deputy Director
Center for Applied Mathematics
National Bureau of Standards
Washington, D. C. 20234
Dr. Harry Smith, Professor
Chairman, Department of
Biomathematical Science
Mt. Sinai School of Medicine
New York, New York 10029
Dr. Richard Royall, Professor
Department of Biostatisties
Johns Hopkins University
615 North Wolfe Street
Baltimore, Maryland 21205
Dr. Roderick Little
American Statical Assoc. Fellow
Bureau of Census
Department of Commerce
Washington, D. C.
Dr. J. Richard Landis, Professor
Department of Biostatisties
School of Public Health II
University of Michigan
Ann Arbor, Michigan 18109
(11D-2)
856 ^
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Table of Contents
Summary ii
Introduction 1
Time Trends in Blood-Lead Values 2
Measurement Quality Control 2
Nonresponse 3
Survey Design . . 3
Sample Weights 5
Estimated Time Trends 6
Summary 6
Correlation Between Blood-Lead and Gasoline-Lead Levels 7
Preliminary Remarks 7
Variables Used in the Analyses 8
Statistical Techniques Used in the Analyses 11
Models Used in the Analyses 11
Gasoline Lead as a Causal Agent for the Decline
in Blood-Lead Levels 12
Use of NHANES II Data for Forecasting Results of
Alternative Regulatory Policies 13
Summary 13
References 14
Appendix 01 - Questions for the Review Group 15
Appendix D2 - Documents Considered by the Review Group 16
Appendix D3 - List of Attendees at Review Group Meetings 19
(11D-3)
857¦=:
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Sumnary
The Review Group finds strong evidence that there was a substantial dtcline in
the average level of blood lead in the U.S. population during the NHANES II
survey period. After adjustment for relevant demographic covariables, the
magnitude of the change can be estimated for the total U.S. population and for
some major subgroups, provided careful attention is given to underlying model
assumptions.
The Review Group also finds a strong correlation between gasoline-1eaj usage
and blood-lead levels. In the absence of scientifically plausible alternative
explanations, the hypothesis that gasoline lead is an important causal factor
for blcod-lead levels must receive serious consideration. Nevertheless,
despite the strong association between the decline in gasoline-lead usage anc
the decline in blood-lead levels, the survey results and statistical analyses
do not confirm the causal hypothesis. Rather, this finding is based on the
qualitatively consistent results of extensive analyses done in different but
comp1enentary ways.
The gasoline lead coefficient in regressions of blood-lead levels on that
variable, adjusted for observed covariates, has been used to quantify the
causal effect of gasoline lead on blood-lead levels. The Review Group
considers that such inferences require strong assurrptions about the absence of
effects from other unmeasured lead sources, the adequacy of national gasoline
lead usage as a proxy for local exposure, and the adequacy of a sarnie design
which does not measure changes in blood-lead levels for individuals in the
sample. The validity of these assumptions could not be determined f^or. the
NhA'
-------
Introducti on
This Review Group was appointed in February, 1983 by the Director of the
Environmental Criteria and Assessment Office, U.S. Environmental Protection
Agency (EPA), to consider a series of questions about the interpretation of
data from the second National Health and Nutrition Examination Survey (NHANES
II) to evaluate relationships over time between blood-lead levels and gasoline
lead usage. The questions addressed to the Review Group are listed in full in
Appendix Dl.
Documents describing NHANES II, analyses of the survey data, and analyses of
the relationships between blood-lead values and gasoline lead usage were
furnished for review. In two meetings, on March 10-11 and March 30-31, 1983,
the Review Group discussed these materials with officials of the EPA, and with
specialists from the several institutions that had conducted these studies.
The documents provided for review are listed in Appendix D2. The individuals
who attended the two meetings are listed in Appendix D3.
The panel members of the Review Group are statisticians with experience in
applications of statistics in the physical, biomedical, and social sciences,
but had no previous involvement in analyses of data about blood lead or
gasoline lead. The affiliations of the panel members are listed in Appendix
D3 for identification; views expressed by the panel in this report are their
own and not those of the institutions.
Agencies involved in the conduct of the NHANES II were the National Center for
Health Statistics (NCHS), the Centers for Disease Control (CDC) where the
chemical analyses were done, and the Food and Drug Administration (FDA).
Contributors to the analysis of the association between blood lead and
gasoline lead usage, in addition to NCHS and CDC, are E. I. DuPont de Nemours
& Co. (DuPont), The Ethyl Corporation (Ethyl), and the EPA Office of Policy
Analysis working in collaboration with ICF Incorporated (1CF) and Energy and
Resource Consultants, Inc. (ERC).
This report contains two major sections. The first, on time trends in
blood-lead levels, addresses a set of questions about the use of NHANES II
data to estimate changes over time. The second addresses statistical aspects
of evaluating the relationship of changes in blood-lead levels to gasoline
lead usage.
-1- 7/29/83
(11D-5)
859
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Time Trends In Blood-lead Values
At its first meeting on March 10-11, 1983, the Review Group considered only
the first of the set of questions presented to it (see Appendix Dl), namely
questions about the extent to which the NHANES II data could be used to
"determine time trends for changes in nationally representative blood-lead
values for the years of the study (1976-1980)."
The phrases "define time trends" and "determine time trends ... (1976-1980)"
are interpreted throughout this report to mean "estimate changes in blood-lead
values during the survey period." In particular, such changes are not to be
interpreted as trends that might be extrapolated.
The Group recognizad that the survey was designed as a cross-sectional survey,
and specifically inquired into three general kinds of possible sources of
time-related bias:
- the measurement quality control,
- the nonresponse experience, and
- the survey design.
As would be expected, only incomplete evidence could be made available in each
of these areas. The following assessment of this evidence indicates where it
depends on the expert opinion of others.
Measurement Quality Control
In order to analyze the time trends in NHANES II data, one must assume that
the procedures for collecting, handling, and analyzing blood specimens did not
change during the survey years. The.Review Group is aware that contamination
can produce spuriously high values in determination of trace elements, and
sought evidence that quality control procedures were equally stringent at all
times.
Although no quality control specimens were prepared at the medical examination
sites, the Review Group has been assured that training, periodic retraining,
materials, equipment, and procedures were designed to prevent contamination,
and not changed. There was some turnover of personnel.
The CDC laboratory established and documented the results of extensive quality
control sampling (App. D2, item 14). The data on lead levels in the "blind"
samples, from two pools of bovine blood, exhibit essentially constant means
and standard deviations. The coefficient of variation for measurement error
was found to be about 17 percent for blood-lead levels near 13 pg/dL; it was
smaller, about 13 percent, for higher blood-lead levels near 25
Additional evidence of the constancy of quality control is that data from
other analyses of the blood specimens (zinc, for example) exhibit little or no
change over time.
The Review Group finds no evidence that field and laboratory quality control
changes could account for the observed change in blood-lead levels.
-2-
7/29/83
(11D-6)
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Nonresponse
Nonresponse is an important potential source of bias in sample surveys. It is
of particular concern in the blood-lead analysis of the NHANES II since the
nonresponse rate is high—39.3 percent of sampled persons had missing lead
values due to nonresponse at various stages of participation in the survey
(App. D2, item 14, p.9). The NCHS attempted to adjust for nonresponse by
weighting responding individuals by estimates of the probability of response,
calculated within subclasses of the population formed by joint levels of age,
income, SMSA/non-SMSA, and region.
This is a standard adjustment method for unit nonresponse in surveys. The
method adjusts for differential nonresponse across the subclasses used to
calculate the weight, but does not account for residual association between
nonresponse and tine and blood-lead level, which are the variables of primary
interest in the analysis under consideration. Thus there is the possibility
that nonresponse bias is a contributory factor to the trend in blood-lead
levels across time.
In order for nonresponse to have this effect it is necessary that, after
adjusting for the socioeconomic variables used to define the weights,
nonresponse be related to blood-lead level, and further'that this relationship
change over time, so that a differential bias in the mean blocd-levels of
respondents exists across time. Clearly this question cannot be addressed
directly, since tne blood-lead levels of nonrespondents are not measured.
However, the Review Group considered such an interaction to be hignly
unlikely, for the following reasons:
° Nonresponse rates did not vary in a consistent way across
time. Examination of changes in response rates does not
incicate any relationship of importance (App. D2, item 18).
° There does not appear"to- be¦evidence that the conditions of
the survey changed significantly across time, so that any bias
introduced by an association between nonresponse and
blood-lead level is unlikely to change across time.
Accordingly, the Review Group, rejected nonresponse as a likely explanation for
the trend observed in the data/ ' ' "
Survey Design
The NHANES II was designed to provide U.S. national prevalence rates for a
wide range of characteristies and health conditions. Due to financial and
logistical constraints, the survey design required a four-year data collection
period. Consequently, the sample quantities, such as the blood-lead levels,
necessarily will provide period prevalence estimators, rather than point
prevalence estimators of the underlying population parameters. In general
practice, a fundamental assumption underlying the use of period data to
generate prevalence estimators is that the condition under investigation
remains relatively constant throughout the survey period.
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Even though the NHANES II was not designed to detect and estimate changes in
prevalence throughout the survey period, one must consider the possibility
that the level of a particular target characteristic, such as blcod lead,
actually may be changing over time. Consequently, one cannot ignore evidence
suggesting that the level of lead in blood in the U.S. population was
decreasing during the data collection period simply because the survey design
was cross-sectional, rather than longitudinal. Rather, the difficult question
is to what extent, if any, can these NHANES II data be used to determine time
trends.
Although a cross-sectional design such as the one utilized in the NHANES II
certainly is not optimal for investigating time trends, one can consider
making adjustments within the sample for the effects of relevant covar'ables
such as age, sex, race, residence, and income, if the distributions of these
covariables are not highly confounded with time. An additional requirement
for making adjustments is that there be reasonably large numbers of sample
persons for different covariable levels at various times. These internal
adjustments permit one to examine whether the decline in blood-lead levels can
be accounted for by differing proportions of individuals from subgroups
determined by relevant covariables. The extent of this type of selection bias
over time relative to primary demographic characteristics can be summarized
(App. D2, item 20, Tables M7, M8 for whites, and M13, M14 for blacks).
The Review Group considered carefully the potential bias due to changing
composition of the sample over time, especially since this had been emphasized
by Ethyl (App. D2, itens 25, 26). The most striking problem occurs with urban
vs. ru>~al groups. The fractions of blood samples obtained from white urban
residents are shown as follows:
Thus, there has been a striking decrease in the nunber of bloods taken from
white urbanites across the four years. If one assumes that exposure to lead
from gasoline is more prevalent in urban areas, then (without adjustment) the
observed mean blood levels across the four years would be biased because of
the NHANES II schedule.
Further examination of the CDC tabulation (App.'D2, item 20) indicates sparse
information on blacks. The numbers are so small that time trend inferences
for blacks can be estimated with confidence only for overall mean blood-lead
level results without regard to sex, place of residence, and age.
% urban bloods
Sample size
Jan - Jun 1976
Jul - Dec 1976
Jan - Jun 1977
Jul - Dec 1977
Jan - Jun 1978
Jul - Dec 1978
Jan - Jun 1979
Jul - Dec 1979
Jar, 1980
64.2
36.9
44.6
57.3
46.3
40.6
31.6
20.7
0.0
795
1255
935
1010
1056
981
1228
842
267
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The Review Group finds that despite obvious trends over time for such
characteristics as degree of urbanization and the proportion of children aged
0.5 to 5 years, the sample size is distributed across the grid of covariable
levels sufficiently to permit reasonable adjustments. In support of this
finding, the Review Group notes that similar trends appeared whenever
demographic subgroups were examined separately. These subgroups included
white males, white females, white children, white teenagers, white adults, and
blacks, as well as breakdowns by income and urban-rural status.
Sample Weights
Another possibility is that the sample mean blood-lead level changes resulted
from trends in mors subtle statistical characteristics of the sample over
time, such as characteristics related to the way sample weights are used to
calculate averages. But this explanation appears to be inconsistent with the
fact that analyses of the unweighted NHANES II data lead to essentially the
same results as the weighted data and analysis.
In response to questions raised by both industry representatives and other
observers, the Review Group explored the effects of the complex weighting
scheme inherent in all the CDC and EPA/ICF analyses. Each sample observation
has both a basic weight (related to the probability of selection), a final
weight (reflecting additional adjustments to the basic weight accounting for
nonresponse patterns of selected demographic subgroups), and a final examined
lead subsapple weight (corresponding to the entire set of adjustments due to
the probability of selection, nonresponse, and post-stratification, and the
subsampling of individuals selected for the measurement of blood lead). All
the weighted analyses in the CDC and EPA/ICF reports were conducted relative
to the final examined lead subsample weight.
One potential problem associated with this final lead subsample weight is the
possibility that differential nonresponse patterns for various demographic
subgroups may lead to marked differences between the basic weight (without
nonresponse adjustments) and this final weight. For that reason, the Review
Group requested a data display of the total nonresponse rate and the average
blood-lead levels by the 64 separate stands using three different weighting
schemes in computing the averages:
i) unweighted;
ii) basic weights;
iii) final lead subsampling weights.
As shown in Table 1, item 18 of.App. D2, the average blood-lead levels are
quite consistent under each weighting scheme for each of the 64 stands.
Furthermore, there is no apparent trend in the nonresponse rate across time.
Consequently, one would expect that an analysis of these data under the basic
weights also would parallel the results obtained in the CDC and the ICF
reports.
These findings, in conjunction with the similarities between the weighted and
unweighted analyses, lend additional support to the overall consensus among
panel members that these data analyses are not dependent on the particular
choice of weights, including the. i ntermedi.ate basic weights.
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Estimated Time Trends
There seems to be no doubt that, qualitatively, a downward trend of blood-lead
levels has been observed during the NHANES II survey.
The data appear to support reasonably precise estimates of the magnitude of
t change fcr a few major subgroups of the population. In particular, the
change in mean blood-lead levels during the survey period can be estimated for
the population as a whole and for population sectors grouped by age, sex,
race, urban/rural, and income, if each of these demographic categories is
considered separately.
For estimating changes in mean blood-lead levels for combinations of
demographic factors, sufficient data appeared to be available for white-by-sex
and white-by-age breakdowns. These estimated changes, and others that might
be considered, can be made on the basis of a linear model that provides
adjustments for demographic and socioeconomic covariables that are known or
believed to be associated with blood-lead levels.
For finer subdivisions, estimates of change are subject to large sampling
error and are sensitive to correct specification of the regression model.
Hence, caution must be exercised in their interpretation. It is not possible
to show time changes in mean blood levels for specific cities, towns, or
locales using the NHANES II data, since no city or locale was sampled more
than once. No data which would allow estimates of time trends in mean
Llcod-lc-ad levels for different occupational categories were shown to the
Review Group. The only socioeconomic variable considered was income.
Estimates of change, e.g., those reported by CDC (App. D2, item 14, Table 6,
page 44), should be accompanied by standard errors. There should be
discussions of the use cf regression diagnostics to evaluate the adequacy of
the model, and the possibility that a few observations exert an excessive
influence on the result. The calculation of standard errors should use
procedures that take into account the stratification and clustering properties
of the survy design. In response to the Review Group's questions, CDC
provided a document presenting standard errors and the methodology used to
estimate them (App. D2, item 38). The size of these standard errors suggests
that there are only weak indications of differences between subgroups with
respect to the percent drop in the average blood-lead level.
Summary
Although the survey was not specifically designed to measure trends, data from
the NHANES II can be used to estimate changes in blood-lead levels during the
four-year period, 1976-1980, of the survey. Changes can be estimated for tne
U.S. population and for major population subgroups, as specified in the
previous subsection. Because of sampling error, laboratory measurement error,
a high nonresponse rate, and the need to adjust for tine-related imbalance in
the survey design, such estimated changes should be interpreted with caution.
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Correlation Between Blood-Lead and Gasoline-Lead Changes
At its second meeting on March 30-3i, 1983, the Review Group considered three
sets of studies that examine the association between changes in blood-lead
levels estimated from the NHANES II data and changes in the use of leaded
gasoli ne:
- the Ethyl Corp. analysis (App. D2, items 25, 26)
- the ICF/EPA analysis (App. D2, items 11, 22, 23, 24), and
- the CDC/NCHS analysis (App. D2, item 14 and appendices).
The following discussions summarize the Review Group's assessment of the
strengths and weaknesses of the analyses.
Preliminary Remarks
The analyses propose and evaluate models for the relationship between
blood-lead levels and gasoline-lead usage. All of these analyses rely on
multiple linear regression methods, whose limitations with respect to
establishing causal relations are well known (See, e.g., reference 1). The
statistician-reviewer may adopt one or the other of two approaches in
considering the strengths and weaknesses of the several analyses:
(1) Assume (on external authority) the existence of a causal
relationship between gascline lead usage and blood lead levels. Consider the
variables and models used to analyze the strength of the association and to
estimate the effect of gasoline-lead changes on blood-lead changes. In this
approach, the possible effects of other changes over time that affect
blood-lead levels are treated as second-order effects. CDC urges this
approach.
(2) Adopt a neutral position as to the causal relationships, and examine
the associations among the variables studied. In this approach, "time" serves
as a proxy for the combined effect of whatever changes affected blood-lead
lev/els and it is left to the interpreter of the analyses to assign relative
importance among suggested explanations for changes over time. DuPont and
Ethyl suggest this approach.
The ICF and CCC analyses both found a clear relationship between gasoline lead
and blooa lead. The Ethyl analysis found no evidence of association between
these variables. The purpose of this commentary is to discuss the important
differences between the analyses and to assess their utility in establishing
or contradicting the hypothesized relationship between the decline in
blood-lead levels and the decline in gasoline lead emissions over the period
of 1he NHANES II Survey.
Table I (next page) classifies the three analyses by six factors which capture
the main differences between them, namely: 1) the choice of measure of
gasoline lead, 2) the scale of blood lead variable, raw or logarithrr, 3) the
unit of analysis, 4) control variables in the regression, and in particular
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the inclusion or omission of a time variable, 5) the weighting used in the
regressions, and 6) the method used to calculate standard errors. The panel
concludes that of these factors only (1) and (4) had a substantial impact on
the final results.
Table 1
1) measure of gasoline
lead
2) scale of dependent
variable
3) unit of analysis
4) control variables
include time
5) weighting by
selection probs.
6) design based
standard errors
CDC
quarterly
log
individual
no
both
yes
ICF
monthly sales
x lead conc.
raw
individual
time, season,
lagged gas
yes
yes
Et^yl
pop. density
local lead usage
raw
individual stage 1
locality stage 2
ti me
no
no
The first three factors are discussed under the heading "Variables Used in the
Analyses". Factors (4), (5), and (6) are discussed under "Statistical
Techniques Used in the Analyses". Factor (4) is considered further in the
assessment of "Models Used in the Analyses".
Variables Used in the Analyses
Detiographic and socioeconomic covariables were used as defined for the NHANES
II Survey. Differences between the analyses occurrec in the choice of
specific representations for blcod-lead levels and gasoline lead usage.
Blood Lead. All the studies used blood-lead values for individuals from the
NHANES II Public Use Data Tape, with associated demographic, econonic, time,
and sampling-weights data.
Ethyl calculated adjusted blood-lead values for its principal analysis by
fitting a linear model to adjust for age, sex, race, and income to obtain the
residuals from this analysis. Ethyl did not adjust the individual data for
the effect of the degree of urbanization, a factor recognized to be related to
blood-lead levels. Averages of the adjusted values for 55 of the 64
examination sites were used in the principal (second-stage) analysis.
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ICF used the NHANES II blood leads without adjustment or transformation.
Adjustment for socio-demographic variables was achieved by including these
variables as covariates in regression models for individual blood leads.
CDC adopted a similar approach, but used the natural logarithms of the NHANES
II blood leads, on the basis of an analysis showing that the distribution of
the values themselves was skewed and that the transformation successfully
corrected for the skewness.
The scale of the dependent variable (raw or logarithm) does not appear to have
a great influence on the final results. With the exception of race, the
blood-lead/gasoline-lead slope in the CDC and ICF analyses appeared stable
across demographic factors, whether the raw or log scale was used for the
dependent variable. The logarithm scale has the advantage of being more
likely to yield normal residuals.
The unit of analysis (factor 3) received a considerable amount of discussion
by reviewers. In particular, the Ethyl two-stage analysis was subjected to
some criticism. At the first stage, the blood lead variable was adjusted for
differences in the distributions of demographic variables by an indiviudal
level regression on NHANES II data. At the second stage, the adjusted
locality mean blood-lead values were regressed on proxies for gasoline lead
which had not themselves been adjusted for the demographic variables. This
two-step regression procedure leads to bias (see reference 2), but the bias
does not appear important, as Ethyl later corrected the analysis with no
substantial change in the results.
Gasoline Lead Usage/Exposure. There were several different approaches to
defining variables that could be interpreted as indexes of the amount of lead
present in the environment at the time when blood samples were taken, as well
as during the antecedent months. Clearly, no index number or set of index
numbers can serve as an ideal surrogate for a measurement of the exposure
experiences of sampled persons. The Review Group recognizes the complexity of
the mixture of lead sources and uptake pathways.
The large differences between the results of the ICF/CDC analyses and the
Ethyl analysis are caused by different measures of gasoline lead exposure.
ICF and CDC used national period measures-quarterly EPA lead additive data for
CDC and adjusted monthly gasoline sales data for ICF, whereas Ethyl used two
proxy measures for lead exposure at each locality—population density and lead
use per unit area.
A fundamental assumption underlying the creation of a 1 oca! estimate of
gasoline lead exposure is the notion that the volume of leaaed gasoline
consumed locally, with the resulting "fallout", is the primary source of lead
in human blood. Although this determination requires substantive expertise
beyond that on our Review Group, the choice of a 1ocal vs. a global measure of
exposure is a pivotal one in all these analyses. If, in fact, lead enters the
human blood system via imported fallout through the food chain (and other
sources), as well as the inhalation of local "fallout", then ideally one would
require a summary measure of exposure which captures both of these sources.
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CDC used data from the quarterly EPA Lead Additive Reports (App. D2, item 14,
pages 37-40 and Appendix H). These are national values of the total amount
(by weight) of lead used in gasoline production. The series exhibits seasonal
fluctuations in gasoline production in addition to a general downward- trend.
ICF developed a monthly series of national values of the average amount (by
weight) per day of lead used in gasoline, as follows: Monthly average
gasoline use (liquid volume per day) was obtained from the DOE Monthly Energy
Review. Quarterly values of the concentration of lead in gasoline (grams per
gallon, based on refiner reports) were obtained from EPA (App. D2, item 11).
The product of these produced a monthly series. This series, if aggregated to
a quarterly series, would be closely related to the series used by CDC.
The measures of lead use used by CDC and ICF capture the downward trend in
gasoline lead over time, but they suffer from specification error in that they
are national rather than localized measures of gasoline lead exposure. The
defect has two consequences:
(a.) The gasoline lead use variable does not capture variation in gasoline
lead exposure between localities.
(b. ) The lead use variable can be only partially adjusted for correlations
with the demographic covariates.
The CDC analysis partially corrects for (a) by aggregating the gasoline lead
exposure over all sampled localites in a six month period of sampling. The
second problem remains, however. The panel does not believe that these
deficiencies invalidate the qualitative findings of a relationship between
lead usage and blood lead. However, the impact on the coefficient of lead
usage in the CDC analysis is not clear.
Ethyl adopted a different approach, seeking to represent gasoline-lead usage
at the survey locations and also to consider separately the effects of lead in
air and lead fallout. The variables used to represent the two kinds of lead
exposure were, respectively, population density and gasoline lead usage per
square mile for the sampled localities.
The Review Group applauded the intention of the Ethyl effort, but the
variables selected appear to be inappropriate. In the Ethyl discussion (App.
D2, item 26, Appendix page A-3) it is pointed out that population density is
strongly related to degree of urbanization, a factor for which adjustment is
made in the CDC and ICF analyses, but not in the Ethyl analysis. Furthermore,
Ethyl calculated population density by interpolation between censuses and it
is doubtful that it would reflect changes (if any) in the concentration, of
lead in air within the four-year survey period.
Ethyl represented lead usage per unit area by annual values by state.
Department of Transportation reports of annual gasoline sales (by state) and
annual Ethyl estimates of the amount of lead in gasoline being sold (by state)
produced state estimates of annual totals of lead used. These were then
divided by the area of the state. Examination of the resulting values (App.
D2, item 26, Table 6, page 23) reveals anomalies. For example, the 1979 lead
usage value for Washington, DC, is 5 times larger than that for any other
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location. The second-1 argest value is the one for New Jersey in 1977, used
for locations adjacent to New York City; it is more than 4 times the 1977
value used for both New York City and its Westchester County suburbs. As
another example, the computed exposure for Houston, TX (ID no. 28) is 101,
compared to 7174 for Washington, DC (ID no. 33). The naive implication of
these two data points is that persons living in Washington, DC received a
71-fold (7174/101) increase in dosage of air-lead (or food chain lead)
compared to persons living in Houston, TX. Whether we view this dosage as
exposure through air or food, this extreme differential is highly unlikely.
This variable appears to represent chiefly the statewide average population
density. The Review Group cannot accept it as an indicator of gasoline lead
usage at the sample locations.
Statistical Techniques Used in the Analyses
All final models reported by EPA/1CF and CDC were fitted to the NHANES II data
using the SURREGR procedure available in SAS. This computing software permits
sample weights and cluster design effects to be incorporated into the
variance-covariance estimators of the model parameters. Although unweighted
and weighted ordinary least squares model fitting provided the same
conclusions, SURREGR provides better estimates of standard errors for these
complex survey data. Tnis estimation and hypothesis testing strategy is the
most conservative approach, since it will produce larger standard errors for
the parameter estimates due to the clustering in the data. Extensive
empirical investigations of the role of weights and design effects in the
NHANES I survey demonstrated that test statistics are decreased when including
weights, and decreased even further when adjusting for design effects (see
reference 3).
The two-stage procedure adopted by Ethyl was described in the preceding
subsection.
Models Used in the Analyses
There is no unique correct approach to analyzing the relationships within the
NHANES II data or between the NHANES II and other data sets. For this reason,
it has been useful to compare and contrast a variety of approaches and models.
All of the models have the general character that a measure of blood lead is
expressed as a linear combination of a measure (or measure) of exposure to
gasoline lead with various demographic and socioecononic covariables and
(sometimes) time.
The primary difficulty with the Ethyl analyses (App. D2, item 26) lies in the
choice of constructed gasoline-1ead variables. Neither the population density
variable (C19) nor the lead usage variable (C16) is an acceptable measure of
gasoline lead exposure.
The Ethyl report concludes with the observation
In summary, our analysis of the NHANES II data has shown that time
rf) is the major contributor to differences in food lead between
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1976 and 1980 ... The major contribution of time to the decrease in
blood lead indicates that other factors that vary with time are the
major causes of the 1976 to 1980 decrease in blood lead and not
gasoli ne 1ead usage.
Ironically, national gasoline lead usage (as defined in the CDC or ICF
analysis) is such a variable that varies with time and is known to be
causative of some portion of the lead in blood. The constructed variable
(C16) does not display a similar relationship with time.
The CDC and ICF/EPA analyses are similar in their general approach'. In each
case, a variety of models was considered (adding and deleting various subsets
of the covariables and interaction terms). These variations had only minor
impact on the value of the coefficient for the lead usage variable.
Although both the CDC and EPA/ICF analyses used national data on leaded
gasoline sales, the EPA/ICF models utilized a gasoline lead use variable which
was estimated at each month of the survey (App. 02, item 11, Table 1, pp.
13-14). Consequently, since the data collection period for most of the 64
stands in the NHANES II survey spanned across two months, the gasoline lead
use variable could, and in some cases did, assume two different values for the
same site, according to the month of examination. Investigations of the
relationships between time and blood-lead levels involved comparisons within
sites (due to spanning two months), as well as among sites. Thus, even though
there is a high degree of correlation between time and gasoline lead usage,
these two variables are not completely confounded with the 64 different sites.
It is, nevertheless, a significant question whether the time variable is
included in the model as a covariate. The ICF analysis included a linear time
covariable and seasonal effects in the model, "to give the models the ability
to attribute temporal variations in blood lead to effects other than gasoline
lead" (App. D2, item 11, p. 8). Variables for time and gasoline lead were not
included simultaneously in the CDC analysis.
The intent of the ICF procedure is reasonable, but the confounding between
time and gasoline lead in the data make the simultaneous inclusion of these
variables in the model questionable. The data do not allow the relationship
between gasoline lead and blood lead to be estimated at any particular time
point. Thus the attempt to adjust for time is highly dependent on the
specification of the time effects in the model. Despite these problems, two
aspects of the ICF analysis yielded some circumstantial evidence that gasoline
lead is an important agent of the trend in blood lead. The gasoline lead
variable accounted for seasonal variation in blood lead, and the lagged
gasoline lead variables provided a plausible lag structure: the one-month
lagged variable had the strongest association with blood lead.
Gasoline Lead as a Causal Agent for the Decline in Blood-Lead Levels
The CDC and ICF analyses provide strong evidence that gasoline lead is a major
contributor to the decline in blood lead over the period of the NHANES study.
DuPont stressed the limitations of statistical theory and methods as tools for
assessing causal relationships.
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Analysis of the NHANES II data cannot prove whether changes in the use of
leaded gasoline caused a change in average blood-lead levels. Variables X and
Y can be correlated because changes in X cause changes in Y, or vice versa, or
because some third factor, Z, affects both X and Y. There are many other
possibilities as well, but these are enough for this discussion. If X stands
for some measure of average blood lead concentration and Y stands for the
amount of lead in gasoline, we can dismiss the first possibility as absurd.
But the relative plausibility of the other two is a matter for expert
scientific judgement. To date, no hypothesis of the third form which could
explain the NHANES II data has been presented to the panel. One hypothesis of
this form has been discussed. This hypothesis has 2 representing regulatory
changes and publicity aimed at reducing lead exposure generally. This could
result in reductions in gas lead, lead in food, lead in paint, etc., and it
could be that the gas lead change had little effect on blood-lead levels --
the blood-lead changes might have been caused by the other factors (food,
paint, etc.). Although this hypothesis cannot be disregarded entirely, it
does not seem to explain the blood-lead drop adequately. We have seen little
evidence that food lead has dropped by a factor large enough to explain a
sizable part of the drop in blood lead. In fact, the FDA diet lead values
shown in the ICF Report (App. D2, item 11, Table 2) were increasing during the
study period. That changes in exposure to leaded paint caused the decrease in
blood-lead observed over all age and sex groups seems highly unlikely. The
existence of influences (other than gasoline lead usage) that are not included
in the models must be recognized as a limiting factor in the evaluation of all
of the analyses.
Use of NHANES II Data for Forecasting Results of Alternative Regulatory Policies
Regression models have been used in all three analyses to see if the NHANES II
time trend in average blood-lead levels can be explained in terms of changes
in demographic variables or in terms of changes in gas and lead usage.
Extension of the use of these and other statistical techniques "to estimate
the distribution of blood-lead levels of whites, blacks, and black children
and to forecast the results of alternative regulations," as in Section III of
the ICF Report of December, 1982 (App. D2, item 11), raises questions and
involves assumptions that go much further than those the Review Group was able
to consider. In general, the Review Group would warn that the weaknesses that
have been discussed in the context of analyzing relationships within the
four-year survey period become enormously greater in any attempt to
extrapolate beyond that period. For example, the cautions mentioned in the
ERC review (App. D2, item 22, p. 6) of the ICF analysis probably do not go far
enough.
Summary
In general, there is a significant correlation between gasoline-lead levels
and blood-lead levels in persons examined in the NHANES II Survey. Major
obstacles interfere with the use of the available data to describe the
relationship. They are: the need to perform model-based adjustments to
compensate for imbalance in the design of the NHANES II, the possibility of
specification error in the regression models, and the lack of a satisfactory
measure of individual or local exposure to gasoline lead, in addition to
sampling error, laboratory measurement error, and the high nonresponse rate.
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The Review Group finds that the Ethyl analyses contribute little to
understanding the association between blood lead and gasoline lead because the
variables adopted to represent lead exposure are deemed inappropriate.
The CDC and 1CF/EPA analyses relating the NHANES II blood-lead data to a
national measure of the amount of lead used in gasoline indicate that the drop
in average blood-lead levels can be explained, in large part, by the
.concurrent drop in gasoline lead. This by no means confirms the hypothesis
that the blood lead decrease was caused by the decrease in gasoline lead but,
in the absence of scientifically plausible alternative explanations, that
hypothesis must receive serious consideration.
References
Literature cited in this report, in addition to the documents furnished by the
EPA which are listed in Appendix D2.
(1) Ling, R. F. (1982). A review of Correlation and Causation by David A. Kenny,
John Wiley & Sons. J. Am. Statis. Assoc. 77, 490-491.
(2) Goldberger, A. S. (1961). Step wise Least Squares: Residual Analysis and
Specification Error. J. Am. Statis. Assoc. 56, 998-1000.
(3) Landis, J. R., Lepkowski, J. M., Eklund, S. A. and Stehouwer, S. A. (1982).
A General Methodolody for the Analysis of Data from the NHANES I Survey.
Vital and Health Statistics, NCHS Series 2; No^ 92. DHHS Publ No. (PHS)
82-1366. Washington. U.S. Government PrTnting Office.
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Appendix D1
Questions for the Review Group
The following questions were stated in letters to members of the Review Group
from Dr. Lester D. Grant, Director of the EPA Environmental Criteria and
Assessment Office, February 17, 1983.
1. To what extent is it valid to use the NHANES II data to determine time
trends for changes in nationally representative blood-lead values for the
years of the study (1976-1980)? More specifically, to what extent can the
NHANES II data appropriately be used to define time trends for blood-lead
levels (aggregated on an annual, semiannual, or any other time-related basis)
for the total NHANES II sample (all ages, sexes, races, etc.) or for
subsamples defined by the following demographic variables: (1) age (e.g.,
children <6 years old, children 6-12 years old, adults by 10- or 20- year age
groups); (2) sex; (3) race; (4) geographic location (e.g., urban vs. rural
residence; Northeast vs. Southeast, Midwest, or other large regional areas of
the U.S.; residence in specific cities, towns, or rural locales); (5)
socioeconomic status; (6) occupation of respondants or their parents/head of
'household at main residence; or (7) any combination of such demographic
variables (e.g., black children <6 years or white children <6 years old living
in urban or rural areas, etc.).
2. If it is indeed possible to derive such time trends from the NHANES II
data, to what extent can the changes in NHANES II blood-lead levels over time
be correlated credibly with changes in the usage of leaded gasoline over the
same time period (i.e., the years 1976-1980)? Several analyses of this type
have already been conducted and submitted to us, and we would appreciate your
evaluation of those analyses.
3. Are there any other appropriate credible statistical approaches or
analyses, besides those alluded to as already having been done, that might be
carried out with the NHANES II data to evaluate relationships over time
between blood-lead levels and gasoline lead usage?
-15- 7/29/83
(110-191
873^
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Appendix D2
Documents Considered by
NHANES II TIME TREND ANALYSIS REVIEW GROUP
1. Plan and Operation of the Second National Health and Nutrition Examina-
tion Survey. {1976-1980) National Center for Health Statistics, Series 1,
No. 15. July, 1981.
2. Public Use Data Tape Documentation. Hematology and Biochemistry, catalog
number 5411. NHANES II Survey, 1976-1980, NCHS. July, 1982.
3. NHANES II Weight Deck (one record for each SP). Deck #502. Attachment
I, NCHS.
4. NHANES II Sampling Areas. Document furnished by NCHS during site visit,
March 10, 1983.
5. Steps in Selection of PSU's for the NHANES II Survey. Document furnished
by NCHS during site visit, March 10, 1983.
6. Location of Primary Sampling Units (PSU) chronologically by pair of cara-
vans: NHANES II Survey, 1976-80. Document furnished by NCHS during site
visit, March 10, 1983.
7. Annest, J. L. et al. (1982) Blood lead levels for person 6 months - 74
years of age: United States, 1976-1980. NCHS ADVANCEDATA, No. 79, May 12,
1982.
8. Mahaffey, K. R. et al. (1982) National estimates of blood lead levels:
United States, 1976-1980. Association with selected demographic and socio-
economic factors. New England Journal of Medicine 307: 573-579.
9. Average Blood Lead Levels for White Persons, 6 months - 74 years strat-
ified chronologically by PSU's: NHANES II, 1976-80 by caravan. "Graph"
furnished by NCHS, March 17, 1983.
10. Schwartz, J. The use of NHANES II to investigate the relationship between
gasoline lead and blood lead. Memo to David Weil (ECA0) (March 3, 1983).
11. ICF Report: The Relationship between Gasoline Lead Usage and Blood Lead
Levels in Americans: A Statistical Analysis of the NHANES II Data..
December 1982.
12. Annest, J. L. et al. (1983) The NHANES II study. Analytic error and its
effect on national estimates of blood lead levels.
13. Pirkle, J. L. Comments on the Ethyl Corp. analysis of the NHANES II data
submitted to EPA October 8, 1982 (Feb. 26, 1983).
14. Pirkle, J. L. Chronological trend in blood lead levels of the second
NHANES, Feb. 1976-Feb. 1980 (Feb. 26, 1983).
-16- 7/29/83
(11D-20)
-------
15
16
17
18
19
20
21
22
23
24
25
26
27.
28
Lynam, D. R. Letter to David Weil dated October 15, 1982 containing ad-
ditional comments on NHANES II data.
E. I. OuPont de Nemours & Co., Inc. Supplementary statement presented to
EPA in the matter of regulation of fuel and fuel additives - lead phase-
down regulations proposed rulemaking (Oct. 8, 1982).
Pirkle, J. L. An expanded regression model of the NHANES II blood lead
data including more than 100 variables to explain the downward trend from
Feb., 1976-Feb. , 1980 (Dec. 23, 1982).
Annest, J. L. et al. Table 1. Average blood lead levels and total non-
response rates for persons ages 6 months - 74 years stratified chrono-
logically by primary sampling unit (PSU): NHANES II, 1976-1980 (Corrected
version; April 8, 1983).
Pirkle, J. L. (1983). Duplicate measurements differing by. more than 7
mg/dl in the lead measurements done in NHANES II Survey. Document fur-
nished by CDC at Panels request, March 18, 1983.
Pirkle, J. L. Appendix M: Tabulation by demographic variables (March 18,
1983).
Pirkle, J. L. Appendix N: Regression analysis of urban and rural popu-
lation subgroups (March 18, 1983).
Miller, C. and Violette, D. Comments on studies using the NHANES II data
to relate human blood lead levels to lead use as a gasoline additive
(March, 1983).
Miller, C. and Violette, D. (March 4, 1983). The Usefulness of the
NHANES II Data for Discerning the Relationship between Gasoline Lead
Levels and Blood Lead Levels in Americans and a Review of ICF's Analysis
using the NHANES II Data. Energy and Resource Consultants, Inc.;
Boulder, Colorado.
Schwartz, J. Analysis of NHANES II data to determine the relationship be-
tween gasoline lead and blood lead. Memo to David Weil (ECA0). (March
18, 1983).
Excerpt - (Section I. C. - "Discussion of NHANES II Blood Lead Data")
from the Ethyl submission to the EPA's docket on the Lead Phasedown dated
May 14, 1982.
Excerpt - (Section III. A. - entitled "Correlation of Blood Lead to Gaso-
line Lead" and Appendix "Discrete Linear Regression Study") from the
Ethyl submission to EPA's docket on the Lead Phasedown. (October 8, 1982)
Ethyl Analyses of the NHANES II Data. This item was distributed at the
Criteria Document meeting held on January 18-20, 1983.
Comments by Dr. Norman R. Draper on Ethyl Corporation's comments and ICF,
Inc.'s comments.
-17t 7/29/83
(11D-21)
875-c
-------
25. Comments by Dr. Ralph A. Bradley entitled "A Discussion of Issues and
Conclusions on Gasoline Lead Use and Human Blood Lead Levels".
30. Comments by Dr. Ralph A. Bradley in a letter to B. F. Fort. (Ethyl Corp.)
31. Ethyl Corp. NHANES II - blood lead data correlation with air lead concen-
tration data.
32. Ethyl Corp. Summary of analyses of the NHANES II blood lead data (Janu-
ary, 1983).
33. E. I. DuPont de Nemours & Co. Comments submitted March 21, 1983.
34. E. I. DuPont de Nemours & Co. Comments by R. Snee and C. Pfieffer on
paper by Annest et al. on analytic error (see item #5).
35. Pirkle, J. L. The relationship between EPA air lead levels and population
density. (March, 1983).
36. Pirkle, J. Consecutive numbering of points on plots of 6-month average
NHANES II blood lead levels versus 6-month total lead used in gasoline
(April 11, 1983).
37. Pirkle, J. L. Distribution of the NHANES II lead subsample "weight" vari-
able (April 11, 1983).
38. Pirkle, J. L. Appendix 0: Propagation of error in calculating the percent
decrease in blood lead levels over the NHANES II survey period (April 11,
1983).
39. Pirkle, J. L. Appendix P: Regressing In (blood lead) on the demographic
covariates and then regressing the residuals on GASQ compared to regres-
sing In (blood lead) simultaneously on the demoqraphic covariates + GASQ
(April 11, 1983).
40. Pirkle, J. L. Appendix Q: Regression of In (blood lead) on the demo-
graphic covariates only and subsequently adding GASQ: F statistics, R
square and Mallows C (p) (April 11, 1983).
-18-
(llb-22)
S7(i«
7/29/83
-------
Appendix D3
List of Attendees at March 10-11 and March 30-31, 1983
meeting of
NHANES II TIME TREND ANALYSIS REVIEW GROUP
Panel Members
Joan Rosenblatt (Chairman)
National Bureau of Standards
J. Richard Landis
University of Michigan
Roderick Little
Bureau of the Census
Richard Royall
Johns Hopkins University
Harry Smith, Jr.
Mt. Sinai School of Medicine
David Weil (Co-chairman)
U.S. EPA
Observers
Dennis Kotchmar*
U.S. EPA
Vic Hasselblad
U.S. EPA
Allen Marcus
U.S. EPA
George Provenzano
U.S. EPA
Joel Schwartz
U.S. EPA
Earl Bryant*
NCHS
Trena Ezzote*
NCHS
J. Lee Annest
NCHS
Mary Kovar*
NCHS
Bob Casady*
NCHS
Jean Roberts*
NCHS
*attendcd March 10-11 meeting only,
tattended March 30-31 meeting only.
-19
• j i acWBMUWT pnwnwa omcc. ion - 66t-?M/loot ( 1 1 D"
Robert Murphy
NCHS
Vernon Houkt
Centers for Disease Control
James Pirkle
Centers for Disease Control
Don Lynam
Ethyl Corporation
Ben Forte
Ethyl Corporation
Jack Pierrard*
DuPont
Chuck Pfieffer
DuPont
Ron Snee
DuPont
Asa Janney
ICF
Kathryn Mahaffey*
FDA
7/29/83
23)
877'<
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Draft
Do Not Quote or Cite
EPA-600/8-83-028A
October 1983
External Review Draft
Air Quality Criteria
for Lead
Volume IV
NOTICE
This document is a preliminary draft. It has not been formally released by EPA and should not at this stage
be construed to represent Agency policy. It is being circulated for comment on its technical accuracy and
policy implications.
Environmental Criteria and Assessment Office
Office of Health and Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
S78<
-------
NOTICE
Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
i i
-------
ABSTRACT
The document evaluates and assesses scientific information on the health
and welfare effects associated with exposure to various concentrations of lead
in ambient air. The literature through 1983 has been reviewed thoroughly for
information relevant to air quality criteria, although the document is not
intended as a complete and detailed review of all literature pertaining to
lead. An attempt has been made to identify the major discrepancies in our
current knowledge and understanding of the effects of these pollutants.
Although this document is principally concerned with the health and
welfare effects of lead, other scientific data are presented and evaluated in
order to provide a better understanding of this pollutant in the environment.
To this end, the document includes chapters that discuss the chemistry and
physics of the pollutant; analytical techniques; sources, and types of
emissions; environmental concentrations and exposure levels; atmospheric
chemistry and dispersion modeling; effects on vegetation; and respiratory,
physiological, toxicological , clinical, and epidemiological aspects of human
exposure.
i i l
88Q<
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PRELIMINARY DRAFT
CONTENTS
Page
VOLUME I
Chapter 1. Executive Summary and Conclusions 1-1
VOLUME II
Chapter 2. Introduction ' 2-1
Chapter 3. Chemical and Physical Properties 3*1
Chapter 4. Sampling and Analytical Methods for Environmental Lead 4-1
Chapter 5. Sources and Emissions 5-1
Chapter 6. Transport and Transformation 6-1
Chapter 7. Environmental Concentrations and Potential Pathways to Human Exposure .. 7-1
Chapter 8. Effects of Lead on Ecosystems 8-1
VOLUME III
Chapter 9. Quantitative Evaluation of Lead and Biochemical Indices of Lead
Exposure in Physiological Media 9-1
Chapter 10. Metabolism of Lead 10-1
Chapter 11. Assessment of Lead Exposures and Absorption in Human Populations 11-1
Volume IV
Chapter 12. Biological Effects of Lead Exposure 12-1
Chapter 13. Evaluation of Human Health Risk Associated with Exposure to Lead
and Its Compounds 13-1
iv
88l<
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PRELIMINARY DRAFT
TABLE OF CONTENTS
Page
LIST OF FIGURES ix
LIST OF TABLES ix
12. BIOLOGICAL EFFECTS OF LEAD EXPOSURE 12-1
12.1 INTRODUCTION .• 12-1
12.2 SUBCELLULAR EFFECTS OF LEAD IN HUMANS AND EXPERIMENTAL ANIMALS 12-3
12.2.1 Effects of Lead on the Mitochondrion • ... 12-4
12.2.1.1 Effects of Lead on Mitochondrial Structure 12-4
12.2.1.2 Effects of Lead on Mitochondrial Function 12-4
12.2.1.3 hi Vivo Studies 12-4
12.2.1.4 Ij] Vitro Studies 12-6
12.2.2 Effects of Lead on the Nucleus 12-7
12.2.3 Effects of Lead on Membranes 12-8
12.2.4 Other Organellar Effects of Lead 12-9
12.2.5 Summary of Subcellular Effects of Lead 12-9
12.3 EFFECTS OF LEAD ON HEME BIOSYNTHESIS AND ERYTHROPOIESIS/ERYTHROCYTE
PHYSIOLOGY IN HUMANS AND ANIMALS 12-12
12.3.1 Effects of Lead on Heme Biosynthesis 12-12
12.3.1.1 Effects of Lead on 6-Aminolevulinic Acid Synthetase 12-13
12.3.1.2 Effects of Lead on 6-Aminolevulinic Acid Dehydrase and
ALA Accumulation/Excretion 12-14
12.3.1.3 Effects of Lead on Heme Formation from Protoporphyrin ... 12-19
12.3.1.4 Other Heme-Related Effects of Lead 12-24
12.3.2 Effects of Lead on Erythropoiesis and Erythrocyte Physiology 12-25
12.3.2.1 Effects of Lead on Hemoglobin Production 12-25
12.3.2.2 Effects of Lead on Erythrocyte Morphology and Survival- .. 12-26
12.3.2.3 Effects of Lead on Pyrimidine-51-Nucleotidase Activity
and Erythropoietic Pyrimidine Metabolism 12-28
12.3.3 Effects of Alkyl Lead on Heme Synthesis and Erythopoiesis 12-30
12.3.4 The Interrelationship of Lead Effects on Heme Synthesis and
the Nervous System 12-30.
12.3.5 Summary and Overview 12-33
12.3.5.1 Lead Effects on Heme Biosynthesis 12-33
12.3.5.2 Lead Effects on Erythropoiesis and
Erythrocyte Physiology 12-37
12.3.5.3 Effects of Alkyl Lead Compounds on Heme Biosynthesis
and Erythropoiesis 12-38
12.3.5.4, Relationships of Lead Effects on
Heme Synthesis and Neurotoxicity 12-38
12.4 NEUROTOXIC EFFECTS QF LEAD 12-40
12.4.1 introduction 12-40
12.4.2 Human Studies 12-41
12.4.2.1 Neurotoxic Effects of Lead Exposure in Adults 12-44
12.4.2.2 Neurotoxic Effects of Lead Exposure in Children 12-50
12.4.3 Animal Studies 12-76
12.4.3.1 Behavioral Toxicity: Critical Periods for Exposure and
Expression of Effects 12-77
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PRELIMINARY DRAFT
TABLE OF CONTENTS (continued).
Page
12.4.3.2 Morphological Effects 12-100
12.4.3.3 Electrophysiological Effects 12-102
12.4.3.4 Biochemical Alterations 12-105
12.4.3.5 Accumulation and Retention of Lead in the Brain 12-110
12.4.4 Integrative Summary of Human and Animal Studies of Neurotoxicity .. 12-110
12.4.4.1 Internal Exposure Levels at Which Adverse
Neurobehavioral Effects Occur 12-114
12.4.4.2 The Question of Irreversibility 12-115
12.4.4.3 Early Development and the Susceptibility to
Neural Damage 12-116
12.4.4.4 Utility of Animal Studies in Drawing Parallels
to the Human Condition 12-116
12.5 EFFECTS OF LEAD ON THE KIDNEY 12-121
12.5.1 Historical Aspects 12~121
12.5.2 Lead Nephropathy in Childhood 12-121
12.5.3 Lead Nephropathy in Adults 12-122
12.5.3.1 Lead Nephropathy Following Childhood Lead Poisoning 12-122
12.5.3.2 "Moonshine" Lead Nephropathy 12-124
12.5.3.3 Occupational Lead Nephropathy 12-124
12.5.3.4 Lead and Gouty Nephropathy 12-129
12.5.3.5 Lead and Hypertensive Nephrosclerosis 12-132
12.5.3.6 General Population Studies 12-133
12.5.4 Mortality Data 12-134
12.5.5 Experimental Animal Studies of the Pathophysiology of
Lead Nephropathy 12-135
12.5.5.1 Lead Uptake By the Kidney 12-135
12.5.5.2 Intracellular Binding of Lead in the Kidney 12-137
12.5.5.3 Pathological Features of Lead Nephropathy 12-137
12.5.5.4 Functional Studies 12-139
12.5.6 Experimental Studies of the Biochemical Aspects of
Lead Nephrotoxicity 12-140
12.5.6.1 Membrane Marker Enzymes and Transport Functions 12-140
12.5.6.2 Mitochondrial Respiration/Energy-Linked
Transformation 12-140
12.5.6.3 Renal Heme Biosynthesis 12-141
12.5.6.4 Lead Alteration of Renal Nucleic Acid/Protein
Synthesis •,•••.•. 12-142
12.5.6.5 Lead Effects on the Renin-Angiotension System 12-144
12.5.6.6 Effects of Lead on Uric Acid Metabolism 12-145
12.5.6.7 Effects of Lead on Vitamin D Metabolism in the Kidney ... 12-145
12.5.7 General Summary and Comparison of Lead Effects in Kidneys of
Humans and Animal Models 12-146
12.6 EFFECTS OF LEAD ON REPRODUCTION AND DEVELOPMENT 12-147
12.6.1 Human Studies 12-147
12.6.1.1 Historical Evidence 12-147
12.6.1.2 Effects of Lead Exposure on Reproduction 12-148
12.6.1.3 Placental Transfer of Lead 12-152
12.6.1.4 Effects of Lead on the Developing Human 12-152
12.6.1.5 Summary of the Human Data 12-156
12.6.2 Animal Studies 12-156
12.6.2.1 Effects of Lead on Reproduction 12-156
12.6.2.2 Effects of Lead on the Offspring 12-160
vi
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PRELIMINARY DRAFT
TABLE OF CONTENTS (continued).
Page
12.6.2.3 Effects of Lead on Avian Species 12-171
12.6.3 Summary 12-171
12.7 GENET0X1C AND CARCINOGENIC EFFECTS OF LEAD 12-173
12.7.1 Introduction 12-173
12.7.2 Carcinogenesis Studies with Lead and its Compounds 12-176
12.7.2.1 Human Epidemiological Studies 12-176
12.7.2.2 Induction of Tumors in Experimental Animals 12-180
12.7.2.3 Cell Transformation 12-185
12.7.3 Genotoxicity of Lead 12-188
12.7.3.1 Chromosomal Aberrations 12-188
12.7.3.2 Effect of Lead on Bacterial and Mammalian
Mutagenesis Systems 12-193
12.7.3.3 Effect of Lead on Parameters of DNA
Structure and Function 12-194
12.7.4 Summary and Conclusions 12-195
12.8 EFFECTS OF LEAD ON THE IMMUNE SYSTEM 12-196
12.8.1 Development and Organization of the Immune System 12-196
12.8.2 Host Resistance 12-197
12.8.2.1 Infectivity Models 12-198
12.8.2.2 Tumor Models and Neoplasia 12-200
12.8.3 Humoral Immunity 12-200
12.8.3.1 Antibody Titers 12-200
12.8.3.2 Enumeration of Antibody Producing Cells
(Plaque-Forming Cells) 12-202
12.8.4 Cell-Mediated Immunity 12-204
12.8.4.1 Delayed-Type Hypersensitivity 12-204
12.8.4.3 Interferon 12-206
12.8.5 Lymphocyte Activation by Mitogens 12-206
12.8.5.1 _l_n Vivo Exposure 12-206
12.8.5.2 In Vitro Exposure 12-208
12.8.6 Macrophage Function 12-209
12.8.7 Mechanisms of Lead Immunomodulation 12-211
12.8.8 Summary 12-211
12.9 EFFECTS OF LEAD ON OTHER ORGAN SYSTEMS 12-212
12.9.1 The Cardiovascular System 12-212
12.9.2 The Hepatic System 12-214
12.9.3 The Endocrine System 12-216
12.9.4 The Gastrointestinal System 12-218
12.10 CHAPTER SUMMARY 12-218
12.10.1 Introduction 12-218
12.10.2 Subcellular Effects of Lead ,. .. 12-218
12.10.3 Effects of Lead on Heme Biosynthesis, Erythropoiesis, and
Erythrocyte Physiology in Humans and Animals 12-221
12.10.4 Neurotoxic Effects of Lead 12-227
12.10.4.1 Internal Exposure Levels at Which Adverse
Neurobehavioral Effects Occur 12-228
12.10.4.2 The Question of Irreversibility 12-229
12.10.4.3 Early Development and the Susceptibility to Neural
Damage 12-230
12.10.4.4 Utility of Animal Studies in Drawing Parallels to the
Human Condition 12-230
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PRELIMINARY DRAFT
TABLE OF CONTENTS (continued).
Page
12.10.5 Effects of Lead on- the Kidney 12-232
12.10.6 Effects of Lead on Reproduction and Development 12-233
12.10.7 Genotoxic and Carcinogenic Effects of Lead 12-234
12.10.8 Effects of Lead on the Immune System 12-234
12.10.9 Effects of Lead on Other Organ Systems 12-235
12.11 REFERENCES 12-236
APPENDIX 12-A •. . . 12A-1
APPENDIX 12-B 12B-1
APPENDIX 12-C TftA
APPENDIX 12-D 12D-1
13.1 INTRODUCTION 13-1
13.2 EXPOSURE ASPECTS 13-2
13.2.1 Sources of Lead Emission in the United States 13-2
13.2.2 Environmental Cycling of Lead 13-4
13.2.3 Levels of Lead in Various Media of Relevance to Human Exposure 13-5
13.2.3.1 Ambient Air Lead Levels 13-6
13.2.3.2 Levels of Lead in Dust 13-6
13.2.3.3 Levels of Lead in Food 13—7
13.2.3.4 Lead Levels in Drinking Water 13-7
13.2.3.5 Lead in Other Media 13-11
13.2.3.6 Cumulative Human Lead Intake From Various Sources 13-11
13.3 LEAD METABOLISM: KEY ISSUES FOR HUMAN HEALTH RISK EVALUATION 13-11
13.3.1 Differential Internal Lead Exposure Within Population Groups 13-12
13.3.2 Indices of Internal Lead Exposure and Their Relationship to External
Lead Levels and Tissue Burdens/Effects 13-13
13.4 DEMOGRAPHIC CORRELATES OF HUMAN LEAD EXPOSURE AND RELATIONSHIPS BETWEEN
EXTERNAL AND INTERNAL LEAD EXPOSURE INDICES 13-16
13.4.1 Demographic Correlates of Lead Exposure 13-16
13.4.2 Relationships Between External and Internal Lead Exposure Indices 13-18
13.4.3 Proportional Contributions of Lead in Various Media to Blood Lead in
Human Populations 13-23
13.5 BIOLOGICAL EFFECTS OF LEAD RELEVANT TO THE GENERAL HUMAN POPULATION 13-27
13.5.1 Introduction 13-27
13.5.2 Dose-Effect Relationship for Lead-Induced Health Effects 13-29
13.5.2.1 Human Adults ! 13-29
13.5.2.2 Children 13-31
13.6 DOSE-RESPONSE RELATIONSHIPS FOR LEAD IN HUMAN POPULATIONS 13-36
13.7 POPULATIONS AT RISK 13-40
13.7.1 Children as a Population at Risk 13-40
13.7.1.1 Inherent Susceptibility of the Young 13-40
13.7.1.2 Exposure Consideration 13-41
13.7.2 Pregnant Women and the Conceptus as a Population at Risk 13-41
13.7.3 Description of the United States Population in Relation to Potential
Lead Exposure Risk 13-42
13.8 SUMMARY AND CONCLUSIONS 13-44
13-9 REFERENCES 13-46
v i l i
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PRELIMINARY DRAFT
LIST OF FIGURES
Figure Page
12-1 Lead effects on heme biosynthesis 12-13
12-2 Maximal motor nerve conduction velocity (NCV) of the median nerve plotted
against the actual Pb-B level (pg/100 ml) for 78 workers occupationally
exposed to lead and for 34 control subjects 12-49
12-3 (a) Predicted SW voltage and 95% confidence bounds in 13- and 75-month-old
children as a function of blood lead level, (b) Scatter plots of SW data
from children aged 13-47 months with predicted regression lines for ages
18, 30, and 42 months, (c) Scatter plots for children aged 48-75 months
with predicted regression lines for ages 54 and 66 months. These graphs
depict the linear interaction of blood lead level and age 12-73
12-4 Peroneal nerve conduction velocity versus blood lead level, Idaho, 1974 12-75
12-5 Probit plot of incidence of renal tumors in male rats 12-186
t
13-1 Pathways of lead from the environment to man 13-3
13-2 Geometric mean blood lead levels by race and age for younger children in the
NHANES II study, and the KelTogg/Si1ver Valley and New York childhood
screening studies 13-17
13-3 Dose-response for elevation of EP as a function of blood lead level using
probit analysis 13-38
13-4 Dose-response curve for FEP as a function of blood lead level;
in subpopulations 13-38
13-5 EPA calculated dose-response curve for ALA-U 13-39
LIST OF TABLES
Table Page
12-1 Summary of results of human studies on neurobehavioral effects 12*55
12-2 Effects of lead on activity in rats and mice 12-81
12-3 Recent animal toxicology studies of lead effects on learning in rodent
species 12-83
12-4 Recent animal toxicology studies of lead effects on learning in primates 12-89
12-5 Summary of key studies of morphological effects of _i_n vivo lead exposure 12-101
12-6 Summary of key studies of electrophysiological effects of i_n vivo
lead exposure 12-103
12-7 Summary of key studies on biochemical effects of i_n vi vo lead exposure 12-106
12-8 Index of blood lead and brain lead levels following exposure 12-111
12-9 Summary of key studies of i_n vitro lead exposure 12-119
12-10 Morphological features of lead nephropathy in various species 12-138
12-11 Effects of lead exposure on renal heme biosynthesis 12-143
12-12 Statistics on the effect of lead on pregnancy 12-148
12-13 Effects of prenatal exposure to lead on the offspring of laboratory and
domestic animals 12-161
12-14 Effects of prenatal lead exposure on offspring of laboratory animals 12-163
12-15 Reproductive performance of Fx lead-intoxicated rats 12-166
ix
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PRELIMINARY DRAFT
LIST OF TABLE5 (continued).
Table Page
12-16 Expected and observed deaths for malignant neoplasms Jan. 1, 1947 -
Dec. 31, 1979 for lead smelter and battery plant workers 12-177
12-17 Expected and observed deaths resulting from specified malignant neoplasms
for lead smelter and battery plant workers and levels of significance by
type of statistical analysis according to one-tailed tests 12-178
12-18 Examples of studies on the incidence of tumors in experimental animals
exposed to lead compounds 12-181
12-19 Mortality and kidney tumors in rats fed lead acetate for two years 12-185
12-20 Cytogenetic investigations of cells from individuals exposed to lead:
10 positive studies 12-189
12-21 Cytogenetic investigations of cells from individuals exposed to lead:
6 negative studies 12-190
12-22 Effect of lead on host resistance to infectious agents 4 12-197
12-23 Effect of lead on antibody titers 12-200
12-24 Effect of lead on the development of antibody-producing cells (PFC) 12-202
12-25 Effect of lead on cell-mediated immunity 12-204
12-26 Effect of lead exposure on mitogen activation of lymphocytes 12-206
12-27 Effect of lead on macrophage and reticuloendothelial system function 12-209
12-B Tests commonly used in a psycho-educational battery for children 12-B2
13-1 Summary of baseline human exposures to lead 13-8
13-2 Relative baseline human lead exposures expressed per kilogram body weight 13-9
13-3 Summary of potential additive exposures to lead 13-11
13-4 Summary of blood inhalation slopes, (p) 13-19
13-5 Estimated contribution of leaded gasoline to blood lead by inhalation and
non-inhalation pathways 13-22
13-6 Direct contributions of air lead to blood lead in adults at fixed inputs of
water and food lead 13-24
13-7 Direct contributions of air lead to blood lead in children at fixed inputs
of food and water lead 13-25
13-8 Contributions of dust/soil lead to blood lead in children at fixed inputs
of air, food, and water lead 13-26
13-9 Summary of lowest observed effect levels for key lead-induced health effects
in adults 13-30
13-10 Summary of lowest observed effect levels for key lead-induced health effects
in children 13-32
13-11 EPA-estimated percentage of subjects with ALA-U exceeding limits for various
blood lead levels 13-39
13-12 Provisional estimate of the number of individuals in urban and rural
population segments at greatest potential risk to lead exposure 13-43
x
23PB13/D 9/20/83
887<
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PRELIMINARY DRAFT
LIST OF ABBREVIATIONS
AAS
Atomic absorption spectrometry
Ach
Acetylcholine
ACTH
Adrenocoticotrophic hormone
ADCC
Antibody-dependent eel 1-mediated cytotoxicity
ADP/0 ratio
Adenosine diphosphate/oxygen ratio
AIDS
Acquired immune deficiency syndrome
AIHA
American Industrial Hygiene Association
All
Angiotensin II
ALA
Aminolevulinic acid
ALA-D
Aminolevulinic acid dehydrase
ALA-S
Aminolevulinic acid synthetase
ALA-U
Aminolevulinic acid in urine
APDC
Ammonium pyrrolidine-dithiocarbamate
APHA
American Public Health Association
A5TM
Amercian Society for Testing and Materials
ASV
Anodic stripping voltammetry
ATP
Adenosine triphosphate
B-cells
Bone marrow-derived lymphocytes
Ba
Bari um
BAL
British anti-Lewi site (AKA dimercaprol)
BAP
benzo(a)pyrene
BSA
Bovine serum albumin
BUN
Blood urea nitrogen
BW
Body weight
C.V.
Coefficient of variation
CaBP
Calcium binding protein
CaEDTA
Calcium ethylenedi" amine tetraacetate
CBD
Central business district
Cd
Cadmi um
CDC
Centers for Disease Control
CEC
Cation exchange capacity
CEH
Center for Environmental Health
CFR
reference method
CMP
Cytidine monophosphate
CNS
Central nervous system
CO
Carbon monoxide
COHb
Carboxyhemoglobin
CP-U
Urinary coproporphyrin
C .
plasma clearance of p-aminohippuric acid
cBah
Copper
D. F.
Degrees of freedom
DA
Dopami ne
DCMU
[3-C3,4-dichlorophenyl)-1,1-dimethyl urea
DDP
Differential pulse polarography
DNA
Deoxyribonucleic acid
DTH
Delayed-type hypersensitivity
EEC
European Economic Community
EEG
Electroencephalogram
EMC
Encephalomyocardi ti s
EP
Erythrocyte protoporphyrin
EPA
U.S. Environmental Protection Agency
xi
TCPBA/D 9/20/83
888^
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PRELIMINARY DRAFT
LIST OF ABBREVIATIONS (continued).
FA Fulvie acid
FDA Food and Drug Administration
Fe Iron
FEP Free erythrocyte protoporphyrin
FY Fiscal year
G.M. Grand mean
G-6-PD G1ucose-6-phosphate dehydrogenase
GABA Gamma-aminobutyric acid
GALT Gut-associated lymphoid tissue
GC Gas chromatography
GFR Glomerular filtration rate
HA Humic acid
Hg Mercury
hi-vol High-volume air sampler
HPLC High-performance liquid chromatography
i.m. Intramuscular (method of injection)
i.p. Intraperitoneally (method of injection)
i.v. Intravenously (method of injection)
IAA Indol-3-ylacetic acid
IARC International Agency for Research on Cancer
ICD International classification of diseases
ICP Inductively coupled plasma
IDMS Isotope dilution mass spectrometry
IF Interferon
ILE Isotopic Lead Experiment (Italy)
IRPC International Radiological Protection Commission
K Potassium
LAI Leaf area index
¦ LDH-X Lactate dehydrogenase isoenzyme x
LC™ Lethyl concentration (50 percent)
LDj.0 Lethal dose (50 percent)
LH Luteinizing hormone
LIP0 Laboratory Improvement Program Office
In National logarithm
LPS Lipopolysaccharide
LRT Long range transport
mRNA Messenger ribonucleic acid
ME Mercaptoethanol
MEPP Miniature end-plate potential
MES Maximal electroshock seizure
MeV Mega-electron volts
MLC Mixed lymphocyte culture
MMD Mass median diameter
MMED Mass median equivalent diameter
Mn Manganese
MND Motor neuron disease
MSV Moloney sarcoma virus
MTD Maximum tolerated dose
n Number of subjects
N/A Not Available
xi i
TCPBA/D 9/20/83
889<
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PRELIMINARY DRAFT
LIST OF ABBREVIATIONS
NA Not Applicable
NAAQS National ambient air quality standards
NADB National Aerometric Data Bank
NAMS National Air Monitoring Station
NAS National Academy of Sciences
NASN National Air Surveillance Network
NBS National Bureau of Standards
NE Norepinephrine
NFAN National Filter Analysis Network
NFR-82 Nutrition Foundation Report cf 1982
NHANES II National Health Assessment and Nutritional Evaluation Survey II
Ni Nickel
OSHA Occupational Safety and Health Administration
P Potassium
p Significance symbol
PAH Para-aminohippuric acid
Pb Lead
PBA Air lead
Pb(Ac)2 Lead acetate
PbB concentration of lead in blood
PbBrCl Lead (II) bromochloride
PBG Porphobilinogen
PFC Plaque-forming eel 1s
pH Measure of acidity
PHA Phytohemagglutinln
PHZ Polyacrylamide-hydrous-zi rconia
PIXE Proton-induced X-ray emissions
PMN Polymorphonuclear leukocytes
PND Post-natal day
PNS Peripheral nervous system
ppm Parts per million
PRA Plasma renin activity
PRS Plasma renin substrate
PWM Pokeweed mitogen
Py-5-N Pyrimide-5'-nucleotidase
RBC Red blood cell; erythrocyte
RBF Renal blood flow
RCR Respiratory control ratios/rates
redox Oxidation-reduction potential
RES Reticuloendothelial system
RLV Rauscher leukemia virus
RNA Ribonucleic acid
S-HT Serotonin
SA-7 Simian adenovirus
scm Standard cubic meter
S.D. Standard deviation
SDS Sodium dodecyl sulfate
S.E.M. Standard error of the mean
SES Socioeconomic status
SGOT Serum glutamic oxaloacetic transaminase
x i i i
TCPBA/D 9/20/83
890<
-------
PRELIMINARY DRAFT
LIST OF ABBREVIATIONS (continued).
sig
SLAMS
SMR
S r
SRBC
SRMs
STEL
SW voltage
T-cells
t-tests
TBL
TEA
TEL
TIBC
TML
TMLC
TSH
TSP
U.K.
UMP
USPHS
VA
vf-R
WHO
XBF
2n
ZPP
Surface immunoglobulin
State and local air monitoring stations
Standardized mortality ratio
Stronti urn
Sheep red blood eel Is
Standard reference materials
Short-term exposure limit
Slow-wave voltage
Thymus-derived lymphocytes
Tests of significance
Tri-n-butyl lead
Tetraethyl-ammonium
Tetraethyllead
Total iron binding capacity
Tetramethyl1ead
Tetramethyl1ead chloride
Thyroid-stimulating hormone
Total suspended particulate
United Kingdom
Uridine monophosphate
U.S. Public Health Service
Veterans Administration
Deposition velocity
Visual evoked response
World Health Organization
X-Ray fluorescence
Chi squared
Zi nc
Erythrocyte zinc protoporphyrin
MEASUREMENT ABBREVIATIONS
dl deciliter
ft feet
g gram
g/gal gram/gallon
g/ha-mo gram/hectare-month
km/hr kilometer/hour
1/min liter/minute
mg/km milligram/kilometer
(jg/m3 microgram/cubic meter
mm millimeter
jjmol micrometer
ng/cm2 nanograms/square centimeter
nm namometer
nM nanomole
sec second
xiv
TCPBA/D 9/20/82
831-
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Chapter 12: Biological Effects of Lead Exposure
Contributing Authors
Dr. Max Costa
Department of Pharmacology
University of Texas Medical School
Houston, TX 77025
Dr. J. Michael Davis
Environmental Criteria and Assessment Office
MD-52
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Dr. Jack Dean
Immunobiology Program and Immunotoxicology/
Cell Biology Program
CIIT
P.O. Box 12137
Research Triangle Park, NC 27709
Dr. Bruce Fowler
Laboratory of Pharmacology
NIEHS
P.O. Box 12233
Research Triangle Park, NC 27709
Dr. Lester Grant
Director, Environmental Criteria and
Assessment Office
MD-52
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Dr. Ronald D. Hood
Department of Biology
The University of Alabama
P.O. Box 1927
University, AL 35486
Dr. Loren Koller
School of Veterinary Medicine
University of Idaho
Moscow, ID 83843
Dr. David Lawrence
Microbiology and Immunology
Department
Albany Medical College of Union
Uni versi ty
Albany, NY 12208
Dr. Paul Mushak
Department of Pathology
UNC School of Medicine
Chapel Hill, NC 27514
Dr. Dr. David Otto
Clinical Studies Division
MD-58
U.S. Environmental Protection
Agency
Research Triangle Park, NC 27711
Dr. Magnus Piscator
Department of Environmental Hygiene
The Karolinska Institute 104 01
Stockholm
Sweden
Dr. Stephen R. Schroeder
Division for Disorders of
Development and Learningv
Biological Sciences Research Center
University of North Carolina
Chapel Hill, NC 27514
Dr. Richard P. Wedeen
V.A. Medical Center
Tremont Avenue
East Orange, NJ 07019
Dr. David Weil
Environmental Criteria and
Assessment Office
MD-52
U.S. Environmental Protection
Agency
Research Triangle Park, NC 27711
xv
-------
The following persons reviewed this chapter at EPA'5 request. The evaluations
and conclusions contained herein, however, are not necessarily those of the
reviewers.
Dr. Carol Angle
Department of Pediatrics
University of Nebraska
College of Medicine
Omaha, NE 68105
Dr. Lee Annest
Division of Health Examin. Statistics
National Center for Health Statistics
3700 East-West Highway
Hyattsville, MD 20782
Dr. Donald Barltrop
Department of Child Health
Westminister Children's Hospital
London SW1P 2NS
England
Dr. Irv Billick
Gas Research Institute
8600 West Bryn Mawr Avenue
Chicago, IL 60631
Dr. Joe Boone
Clinical Chemistry and
Toxicology Section
Center for Disease Control
Atlanta, GA 30333
Dr. Robert Bornschein
University of Cincinnati
Kettering Laboratory
Cincinnati, OH 45267
Dr. A. C. Chamberlain
Environmental and Medical Sciences Division
Atomic Energy Research Establishment
Harwell 0X11
Engl and
Dr. Neil Chernoff
Division of Developmental Biology
MD-67
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Dr. Julian Chisolm
Baltimore City Hospital
4940 Eastern Avenue
Baltimore, MD 21224
Dr. Jerry Cole
International Lead-Zinc Research
Organization
292 Madison Avenue
New York, NY 10017
Dr. Anita Curran
Commissioner of Health
Westchester County
White Plains, NY 10607
Dr. Cliff Davidson
Department of Civil Engineering
Carnegie-Mellon University
Schenley Park
Pittsburgh, PA 15213
Dr. H. T. Delves
Chemical Pathology and Human
Metaboli sm
Southampton General Hospital
Southampton S09 4XY
England
Dr. Fred deSerres
Associate Director for Genetics
NIEHS
P.O. Box 12233
Research Triangle Park, NC 27709
Dr. Joseph A. DiPaolo
Laboratory of Biology, Division
of Cancer Cause and Prevention
National Cancer Institute
Bethesda, MD 20205
Dr. Robert Dixon
Laboratory of Reproductive and
Developmental Toxicology
NIEHS
P.O. Box 12233
Research Triangle Park, NC 27711
xv i
893-^
-------
Dr. Clair Ernhart
Department of Psychiatry
Cleveland Metropolitan General Hospital
3395 Scranton Road
Cleveland, OH 44109
Dr. Sergio Fachetti
Section Head - Isotope Analysis
Chemistry Division
Joint Research Center
121020 Ispra
Varese, Italy
Dr. Virgil Ferm
Department of Anatomy and Cytology
Dartmouth Medical School
Hanover, NH 03755
Dr. Alf Fischbein
Environmental Sciences Laboratory
Mt. Sinai School of Medicine
New York, NY 10029
Dr. Jack Fowle
Reproductive Effects Assessment Group
U.S. Environmental Protection Agency
RD-689
Washington, DC 20460
Dr. Robert Goyer
Deputy Director
NIEHS
P.O. Box 12233
Research Triangle Park, NC 27711
Dr. Phi 1ippe. Grandjear
Department of Environmental Medicine
Institute of Community Health
Odense University
Denmark
Dr. Stanley Gross
Hazard Evaluation Division
Toxicology Branch
U.S. Environmental Protection
Agency
Washington, DC 20460
Dr. Paul Hammond
University of Cincinnati
Kettering Laboratory
Cincinnati, OH 45267
Dr. Kari Hemminki
Institute of Occupational Health
Tyoterveys1 a itos-Haartmani nkatu
1 SF-00290 Helsinki 29
Fi nland
Dr. Bruce Fowler
Laboratory of Pharmocology
NIEHS
P.O. Box 12233
Research Triangle Park, NC 27709
Dr. Warren Galke
Department of Biostatisties and Epidemiology
School of Allied Health
East Carolina University
Greenville, NC 27834
Mr. Eric Goldstein
Natural Resources Defense Council, Inc.
122 E. 42nd Street
New York, NY 10168
Dr. Harvey Gonick
1033 Gayley Avenue
Suite 116
Los Angeles, CA 90024
Dr. V. Houk
Center for Disease Control
1600 Clifton Road, NE
Atlanta, GA 30333
Dr. Carole A. Kimmel
Perinatal and Postnatal Evaluation
Branch
National Center for Toxicological
Research
Jefferson, AR 72079
Dr. Kristal Kostial
Institute for Medical Research
and Occupational Health
YU-4100 Zagreb
Yugoslavia
Dr. Lawrence Kupper
Department of Biostatistics
UNC School of Public Health
Chapel Hill, NC 27514
xvi i
894<
-------
Dr. Phillip Landrigan
Division of Surveillance,
Hazard Evaluation and Field Studies
Taft Laboratories - NIOSH
Cincinnati, OH 45226
Dr. Alais-Yves Leonard
Centre Betude De L'Energie Nucleaire
B-1040 Brussels
Be 1g ium
Dr. Jane Lin-fu
Office of Maternal and Child Health
Department of Health and Human Services
Rockville, MD 20857
Dr. Don Lynam
Air Conservation
Ethyl Corporation
451 Florida Boulevard
Baton Rouge, LA 70801
Dr. Kathryn Mahaffey
Division of Nutrition
Food and Drug Administration
1090 Tusculum Avenue
Cincinnati, OH 45226
Dr. Ed McCabe
Department of Pediatrics
University of Wisconsin
Madison, WI 53706
Dr. Chuck Nauman
Exposure Assessment Group
U.S. Environmental Protection Agnecy
Washington, DC 20460
Dr. Herbert L. Needleman
Children's Hospital of Pittsburgh
Pittsburgh, PA 15213
Dr. Forrest H. Nielsen
Grand Forks Human Nutrition Research Center
USDA
Grand Forks, ND 58202
Dr. Stephen Overman
Toxicology Institute
New York State Department of
Health
Empire State Plaza
Albany, NY 12001
Dr. H. Mitchell Perry
V.A. Medical Center
St. Louis, M0 63131
Dr. Jack Pierrard
E.I. duPont de Nemours and
Company, Inc.
Petroleum Laboratory
Wilmington, DE 19898
Dr. Sergio Piomelli
Columbia University Medical School
Division of Pediatric Hematology
and Oncology
New York, NY 10032
Dr. Robert Putnam
International Lead-Zinc
Research Organization
292 Madison Avenue
New York, NY 10017
Dr. Rabinowitz
Children's Hospital Medical Center
300 Longwood Avenue
Boston, MA 02115
Dr. Dr. Larry Reiter
Neurotoxicology Division
MD-74B
U.S. Environmental Protection
Agency
Research Triangle Park, NC 27711
Dr. Cecil R. Reynolds
Department of Educational Psychology
Texas A & M University
College Station, TX 77843
Dr. Patricia Rodier
Department of Anatomy
University of Rochester Medical
Center
Rochester, NY 14642
xv i i i
895^
-------
\
Dr. Harry Roels
Unite de Toxicologie Industrielle et
Universite de Louvain
Brussels, Belgium
Dr. John Rosen
Head, Division of Pediatric Metabolism
Montefiore Hospital and Medical Center
111 East 210 Street
Bronx, NY 10467
Dr. Michael Rutter
Department of Psychology
Institute of Psychiatry
DeCrespigny Park
London SE5 SAL
England
Dr. Anna-Maria Seppalainen
Institutes of Occupational Health
Tyoterveyslaitos
Haartmanikatu 1
00290 Helsinki 29
Fi nland
Dr. Ellen Silbergeld
Environmental Defense Fund
1525 18th Street, NW
Washington, DC 20036
Dr. Ron Snee
icale E.I. duPont de Nemours and
Company, Inc.
Engineering Department L3167
Wilmington, DE 19898
Dr. J. William Sunderman, Jr.
Department of Pharmacology
University of Connecticut
School of Medicine
Farmington, CT 06032
Dr. Gary Ter Haar
Toxicology and Industrial
Hygiene
Ethyl Corporation
451 Florida Boulevard
Baton Rouge, LA 70801
Dr. Hugh A. Tilson
Laboratory of Behavioral and
Neurological Toxicology
NIEHS
Research Triangle Park, NC 27709
Mr. Ian von Lindern
Department of Chemical Engineering
University of Idaho
Moscow, ID 83843
xi x
896*:
-------
Chapter 13: Risk Assessment
Principal Authors
Dr. Lester Grant
Director, Environmental Criteria and
Assessment Office
MD-52
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Contributing Authors
Dr. Robert Eli as
Environmental Criteria and Assessment Office
MD-52
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Or. Vic Hasselblad
Biometry Division
MD-55
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Dr. Paul Mushak
Department of Pathology
UNC School of Medicine
Chapel Hill, NC 27514.
Dr. Alan Marcus
Department of Mathematics
Washington State University
Pullman, Washington 99164-2930
Dr. David Weil
Environmental Criteria and
Assessment Office
U.S Environmental Protection
Agency
Research Triangle Park, NC 27711
Dr. Dennis Kotchmar
Environmental Criteria and Assessment Office
MD-52
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
897-
XX
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PRELIMINARY DRAFT
12. BIOLOGICAL EFFECTS OF LEAD EXPOSURE
12.1 INTRODUCTION
As noted in Chapter 2, air quality criteria documents evaluate scientific knowledge of
relationships between pollutant concentrations and their effects on the environment and public
health. Early chapters cf this document (Chapters 3-7) discuss: physical and chemical pro-
perties of lead; measurement methods for lead in environmental media; sources of emissions;
transport, transformation, and fate; and ambient concentrations and other aspects of the ex-
posure of the U.S. population to lead in the environment. Chapter 8 evaluates the projected
impact of lead on ecosystems. Chapters 9-11, immediately proceeding this one, discuss:
measurement techniques for lead in biologic media; aspects related to the uptake, distribu-
tion, toxicokinetics, and excretion of lead; and the relationship of various external and
internal lead exposure indices to each other. This chapter assesses information regarding
biological effects of lead exposure, with emphasis on (1) the qualitative characterization of
various lead-induced effects and (2) the delineation of dose-effect relationships for key
effects most likely of health concern at ambient exposure levels presently encountered by the
general population of the United States.
In discussing biological effects of lead, one should note at the outset that, to date,
lead has not been demonstrated to have any beneficial biological effect in humans. Some in-
vestigators have hypothesized that lead may serve as an essential element in certain mammalian
species (e.g., the rat) and have reported experimental data interpreted as supporting such an
hypothesis. However, a critical evaluation of these studies presented in Appendix. 12-A of
this chapter raises serious questions regarding interpretation of the reported findings; and
the subject studies are currently undergoing intensive evaluation by an expert committee con-
vened by EPA. Therefore, pending the final report from that expert committee, the present
chapter does not address the issue of potential essentiality of lead.
It is clear from the evidence evaluated in this chapter that there exists a continuum of
biological effects associated .with lead across a broad range of exposure. At rather low
levels of lead exposure, biochemical changes, e.g., disruption of certain enzymatic activities
involved in heme biosynthesis and erythropoietic pyrimidine metabolism, are detectable. With
increasing lead exposure, there are sequentially more pronounced effects on heme synthesis and
a broadening of lead effects to additional biochemical and physiological mechanisms in various
tissues, such that increasingly more severe disruption of the normal functioning of many dif-
ferent organ systems becomes apparent. In addition to impairment of heme biosynthesis, signs
of disruption of normal functioning of the erythropoietic and nervous systems are among the
earliest effects observed in response to increasing lead exposure. At increasingly higher
exposure levels, more severe disruption of the erythropoietic and nervous systems occurs; and
APB12/A 12-1 9/20/83
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PRELIMINARY DRAFT
other organ systems are also affected so as to result in the manifestation of renal effects,
disruption of reproductive functions, impairment of immunological functions, and many other
biological effects. At sufficiently high levels of exposure, the damage to the nervous system
and other effects can be severe enough to result in death or, in some cases of non-fatal lead
poisoning, long-lasting sequelae such as permanent mental retardation.
The etiologies of many of the different types of functional disruption of various mamma-
lian organ systems derive (at least in their earliest stages) from lead effects on certain
subcellular organelles, which result in biochemical derangements (e.g., disruption of heme
synthesis processes) common to and affecting many tissues and organ systems. Some major
effects of lead on subcellular organelles common to numerous organ systems in mammalian spe-
cies are discussed below in Section 12.2, with particular emphasis on lead effects on mito-
chondrial functions. Subsequent sections of the chapter discuss biological effects of lead in
terms of various organ systems affected by that element and its compounds (except for Section
12.7, which assesses genotoxic and carcinogenic effects of lead). Additional cellular and
subcellular aspects of the biological effects of lead are discussed within respective sections
on particular organ systems.
Sections 12.3 to 12.9 have been sequenced generally according to the degree of known vul-
nerability of each organ system to lead. Major emphasis is placed first on discusssion of the
three systems classically considered to be most sensitive to lead (i.e., the hematopoietic,
the nervous, and the renal systems). The next sections then discuss the effects of lead on
reproduction and development (in view of the impact of lead on the fetus and pregnant women),
as well as gametotoxic effects of lead. Genotoxic effects of lead and evidence for possible
carcinogenic effects of lead are then reviewed, followed by discussion of lead effects on the
immune system and, lastly, other organ systems.
This chapter is subdivided mainly according to organ systems to facilitate presentation
of information. It must be noted, however, that, in reality, all systems function in delicate
concert to preserve the physiological integrity of the whole organism and all systems are in-
terdependent. Thus, not only do effects in a critical organ often exert impacts on other
organ systems, but low-level effects that might be construed as unimportant,in a single speci-
fic system may be of concern in terms of their cumulative or aggregate impact.
Special emphasis is placed on the discussion of lead exposure effects in children. They
are particularly at risk due to sources of exposure, mode of entry, rate of absorption and re-
tention, and partitioning of lead in soft and hard tissues. The greater sensitivity of
children to lead toxicity, their inability to recognize symptoms, and their dependence on par-
ents and health care professionals all make them an especially vulnerable population requiring
special consideration in developing criteria and standards for lead.
APB12/A
12-2
9/20/83
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PRELIMINARY DRAFT
12.2 SUBCELLULAR EFFECTS OF LEAD IN HUMANS AND EXPERIMENTAL ANIMALS
The biochemical or molecular basis for lead toxicity is the ability of the toxicant, as a
metallic cation, to bind to ligating groups in biomolecular substances crucial to normal phy-
siological functions, thereby interfering with these functions via such mechanisms as competi-
tion with native essential metals for binding sites, inhibition of enzyme activity, and
inhibition or other alterations of essential ion transport. The relationship of this basis
for lead toxicity to organ- and organelle-specific effects is modulated by: (1) the inherent
stability of such binding sites for lead; (2) the compartmentalization kinetics governing lead
distribution among body compartments, among tissues, and within cells; and (3) differences in
biochemical and physiological organization across tissues and cells due to their specific
function. Given complexities introduced .by factors 2 and 3, it is not surprising that no
single, unifying mechanism of lead toxicity has been demonstrated to apply across all tissues
and organ systems.
In the 1977 Air Quality Criteria Document for Lead, cellular and subcellular effects of
lead were discussed, including effects on various classes of enzymes. Much of the literature
detailing the effects of lead on enzymes £er se has entailed study of relatively pure enzymes
.in vitro in the presence of added lead. This was the case for data discussed in the earlier
document and such information continues to appear in the literature. Much of this material is
of questionable relevance for effects of lead j_n vivo. On the other hand, lead effects on
certain enzymes or enzyme systems are recognized as integral mechanisms of action underlying
the impact of lead on tissues i_n vivo and are logically discussed in later sections below on
effects at the organ system level.
This subsection is mainly concerned with organellar effects of lead, especially those
that provide some rationale for lead toxicity at higher levels of biological organization.
While a common mechanism at the subcellular level that would account for all aspects of lead
toxicity has not been identified, one fairly common cellular response to lead is the impair-
ment of mitochondrial structure and function; thus, mitochondrion effects are accorded major
attention here. Lead effects on other organelles have not been as extensively studied as
mitochondrion effects; and,' in" some cases, it is not clear how the available information,
e.g., that on lead-containing nuclear inclusion bodies, relates to organellar dysfunction.
12.2.1 Effects of Lead on the Mitochondrion
The mitochondrion is clearly the target organelle for toxic effects-of lead on many tis-
sues, the characteristics of vulnerability varying somewhat with cell type. Given early re-
cognition of this sensitivity, it is not surprising that an extensive body of in vivo and i_n
vitro data has accumulated, which can be characterized as evidence of: (1) structural injury
to the mitochondrion; (2) impairment of basic cellular energetics and other mitochondrial
functions; and (3) uptake of lead by mitochondria jn vivo and in vitro.
APB12/A 12-3 9/20/83
SOOc
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PRELIMINARY DRAFT
12.2.1.1 Lead Effects on Mitochondrial Structure. Changes in mitochondrial morphology with
lead exposure have been well documented in humans and experimental animals and, in the case of
the kidney, are a rather early response to such exposure. Earlier studies have been reviewed
by Goyer and Rhyne (1973), followed by later updates by Fowler (1978) and Bull (1980).
Chronic oral exposure of adult rats to lead (1 percent lead acetate in diet) results in
structural changes in renal tubule mitochondria, including swelling with distortion or loss of
cristae (Goyer, 1968). Such changes have also been documented in renal biopsy tissue of lead
workers (Wedeen et a 1., 1975; Biagini et al., 1977) and in tissues other than kidney, i.e.,
heart (Malpass et al., 1971; Moore et al., 1975b), liver (Hoffman et al., 1972), and the cen-
tral (Press, 1977) and peripheral (Brashear et al., 1978) nervous systems.
While it appears that relatively high level lead exposures are necessary to detect struc-
tural changes in mitochondria in som^ animal models (Goyer, 1968; Hoffman et al., 1972),
changes in rat heart mitochondria have been seen at blood lead levels as low as 42 |jg/dl.
Also, in the study of Fowler et al. (1980), swollen mitochondria or renal tubule cells were
seen in rats chronically exposed to lead from gestation to 9 months of age at a dietary lead
dosing level as low as 50 ppm and a median blood lead level of 26 pg/dl (range 15-41 pg/dl).
Taken collectively, these differences point out relative tissue sensitivity, dosing protocol,
and the possible effect of developmental status (Fowler et al., 1980) as important factors in
determining lead exposure levels at which mitochondria are affected in various tissues.
12.2.1.2 Lead Effects on Mitochondrial Function. Both hi vivo and i_n vitro studies dealing
with such effects of lead as the impact on energy metabolism, intermediary metabolism, and
intracellular ion transport have been carried out in various experimental animal models. Of
particular interest for this section are such effects of lead in the developing versus the
adult animal, given the greater sensitivity of the young organism to lead.
12.2.1.3 In Vivo Studies. Uncoupled energy metabolism, inhibited cellular respiration using
succinate and NAD-linked substrates, and altered kinetics of intracellular calcium have all
been documented for animals exposed to lead i_n vivo, as reviewed by Bull (1980).
Adult rat kidney mitochondria, following chronic oral feeding of lead in the diet (1 per-
cent lead acetate, 10 or more weeks) showed a marked sensitivity of the pyruvate-NAD reductase
system (Goyer, 1971), as indicated by impairment of pyruvate-dependent respiration indexed by
ADP/0 ratio and respiratory control rates (RCRs). Succinate-mediated respiration in these
animals, however, was not different from controls. In contrast, Fowler et al. (1980) found in
rats exposed j_n utero (dams fed 50 or 250 ppm lead) and for 9 months postnatal ly (50 or 250
ppm lead in their diet) renal tubule mitochondria that exhibited decreased state 3 respiration
and RCRs for both succinate and pyruvate/malate substrates. This may have been due to longer
exposure to lead or a differential effect of lead exposure during early development.
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Intraperitoneal administration of lead to adult rats at doses as low as 12 mg/kg over 14
days was associated with inhibition of potassium-stimulated respiration in cerebral cortex
slices with impairment of NAD(P)H oxidation using glucose but not pyruvate as substrate (Bull
et al., 1975). This effect occurred at a corresponding blood lead of 72 pg/dl and a brain
lead content of 0.4 pg/g, values below those associated with overt neurotoxicity. Bull
(1977), in a later study, demonstrated that the respiratory response of cerebral cortical tis-
sue from lead-dosed rats receiving a total of 60 mg Pb/kg (10 mg/kg x 6 dosings) over 14 days
was associated with a marked decrease in turnover of intracellular calcium in a cellular com-
partment that appears to be the mitochondrion. This is consistent with the observation of
Bouldin et al. (1975) that lead treatment leads to increased retention of calcium in guinea
pig brain.
Numerous studies have evaluated relative effects of lead on mitochonodria of developing
vs. adult animals, particularly in the nervous system. Holtzman and Shen Nsu (1976) exposed
rat pups at 14 days of age to lead via milk of mothers fed lead in the diet (4 percent lead
carbonate) with exposure lasting for 14 days. A 40 percent increase in state 4 respiratory
rate of cerebellar mitochonodria was seen within one day of treatment and was lost at the end
of the exposure period. However, at this later time (28 days of age), a substantial inhibi-
tion of state 3 respiration was observed. This early effect of lead on uncoupling oxidative
phosphorylation is consistent with the results of Bull et al. (1979) and McCauley et al.
(1979). In these investigations, female rats received lead in drinking water (200 ppm) from
14 days before breeding through weaning of the pups. At 15 days of age, cerebral cortical
slices showed alteration of potassium-stimulated respiratory response and glucose uptake.
Holtzman et al. (1980a) compared mitochondrial respiration in cerebellum and cerebrum in
rat pups exposed to lead beginning at 14 days of age (via milk of mothers fed 4 percent lead
carbonate) and in adult rats maintained cn the same diet. Cerebellar mitochondria showed a
very early loss (by 2 days of exposure) of respiratory control in the pups with inhibition of
phosphorylation-coupled respiration for NAD-linked substrates but not for succinate. Such
changes were less pronounced in mitochondria of the cerebrum and were not seen for either
brain region in the adult rat. This regional and age dependency of mitochondrial impairment
parallels features of lead encephalopathy.
In a second study addressing this issue, Holtzman et al. (1981) measured the cytochrome
contents of cerebral and cerebellar mitochondria from rat pups exposed either from birth or at
14 days of age via the same dosing protocol noted above. These were compared to adult animals
exposed in like fashion. Pups exposed to lead from birth showed statistically significant
reductions of cytochrome b, cytochromes c + cL, and cytochromes a + a3 in cerebellum by 4
weeks of exposure. Changes in cerebral cytochromes, in contrast, were marginal. When lead
exposure began at 14 days of age, little effect was observed, and adult rats showed little
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change. This study indicates that the most vulnerable period for lead effects on developing
brain oxidative metabolism is the same period where a major burst in such activity begins.
Related to effects of lead on energy metabolism in the developing animal mitochondrion is
the effect on brain development. In the study of Bull et al. (1979) noted earlier, cerebral
cytochrome c + Ci levels between 10 and 15 days of age decreased in a dose-dependent fashion
at all maternal dosing levels (5-100 mg Pb/1iter drinking water) and corresponding blood lead
values for the rat pups (11.7-35.7 pg/dl). Delays in synaptic development in these pups also
occurred, as indexed by synaptic counts taken in the parietal cortex. As the authors con-
cluded, uncoupling of energy metabolism appears to be causally related to delays in cerebral
cortical development.
Consistent with the effects of lead on mitochondrial structure and function are i_n vivo
data demonstrating the selective accumulation of lead in mitochondria. Studies in rats using
radioisotopic tracers ^iUPb (Castal 1 ino and Aloj, 1969) and *U3Pb (Barltrop et al., 1971)
demonstrate that mitochondria will accumulate ^ead in significant relative amounts, the nature
of the accumulation seeming to vary with the dosing protocol. Sabbioni and Marafante (1976)
as well as Murakami and Hurosawa (1973) also found that lead is selectively lodged in mito-
chondria. Of interest in regard to the effects of lead on brain mitochondria are the data of
Moore et al. (1975a) showing uptake of lead by guinea pig cerebral mitochondria, and the
results of Krigman et al. (1974c) demonstrating that mitochondria in brain from 6-month-old
rats exposed chronically to lead since birth showed the highest uptake of lead (34 percent),
followed by the nuclear fraction (31 percent). While the possibility of translocation of lead
during subcellular fractionation can be raised, the distribution pattern seen in the reports
of Barltrop et al. (1971) and Castallino and Aloj (1969) over multiple time points make this
unlikely. Also, findings of i_n vivo uptake of lead in brain mitochondria are supported by i_n
vitro data discussed below.
12.2.1.4 In Vitro Studies. I_n vitro studies of both the response of mitochondrial function
to lead and its accumulation by the organelle have been reported, using both isolated mito-
chondria and tissues. Bull (1980) reviewed such data published up to 1979.
Significant reductions in mitochondrial respiration, using both NAD-1 inked and succinate
substrates have been reported for isolated heart and brain mitochondria. The lowest levels of
lead associated with such effects appear to be 5 pM or, in some cases, less. Available evi-
dence suggests that the sensitive site for lead in isolated mitochondria is before cytochrome
b in the oxidative chain and involves either tricarboxylic acid enzymes or non-heme protein/
ubiquinone steps. If substrate specificity is compared, e.g., succinate vs. glutamate/malate
oxidation, there appear to be organ-specific differences. As Bull (1980) noted, tissue-
specific effects of lead on cellular energetics may be one bases for differences in toxicity
across organs. Also, several enzymes involved in intermediary metabolism in isolated mito-
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chonaria have been observed to undergo significant inhibition in activity in the presence of
lead, and these have been tabulated by Bull (1980).
One focus of studies dealing with lead effects on isolated mitochondria has been ion
transport—particularly that of calcium. Scott et al. (1971) have shown that lead movement
into rat heart mitochondria involves active transport, with characteristics similar to those
of calcium, thereby establishing a competitive relationship. Similarly, lead uptake into
brain mitochondria is also energy dependent (Holtzman et al., 1977; Goldstein et al., 1977).
The recent elegant studies of Pounds and coworkers (Pounds et al., 1982a,b), using labeled
calcium or lead and desaturation kinetic studies of these labels in isolated rat hepatocytes,
have elucidated the intracellular relationship of lead to calcium in terms of cellular com-
partmentalization. In the presence of graded amounts of lead (10, 50, or 100 pM), the kinetic
analysis of desaturation curves of calcium-45 label showed a lead dose-dependent increase in
the size of all three calcium compartments within the hepatocyte, particularly that deep com-
partment associated with the mitochondrion (Pounds et al., 1982a). Such changes were seen to
be relatively independent of serum calcium or endogenous regulators of systemic calcium meta-
bolism. Similarly, the use of lead-210 label and analogous kinetic analysis (Pounds et al.,
1982b) showed the same three compartments of intracellular distribution as noted for calcium,
including the deep component (which has the mitochondrion). Hence, there is striking overlap
in the cellular metabolism of calcium and lead. These studies not only further confirm easy
entry of lead into cells and cellular compartments, but also provide a basis for perturbation
by lead of intracellular ion transport, particularly in neural cell mitochondria, where there
is a high capability for calcium transport. Such capability is approximately 20-fold higher
than in heart mitochondria (Nicholls, 1978).
Given the above observations, it is not surprising that a number of investigators have
noted the i_n vitro uptake of lead into isolated mitochondria. Walton (1973) noted that lead
is accumulated within isolated rat liver mitochondria over the range of 0.2-100 nM lead; and
Walton and Buckley (1977) extended this observation to mitochondria in rat kidney cells in
culture. Electron microprobe analyses of isolated rat synaptosomes (Silbergeld et al., 197.7)
and capillaries (Silbergeld et al., 1980b) incubated with lead ion have established that sig-
nificant accumulation of lead, along with calcium, occurs in the mitochondrion. These obser-
vations are consistent with the kinetic studies of Pounds et al. (1982a,b), and the in vitro
data for isolated capillaries are in accord with the observations of Toews et al. (1978), who
found significant lead accumulation in brain capillaries of the suckling rat.
12.2.2 Effects of Lead on the Nucleus
With lead exposure, a cellular reaction typical of many species (including humans) is the
formation of intranuclear lead-containing inclusion bodies, early data for which have been sum-
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marized by Goyer and Moore (1974). In brief, these" lead-bearing inclusion bodies: (1) have
been verified as to lead content by X-ray microanalysis (Carroll et al., 1970); (2) consist
of a rather dense core encapsulated by a fibrillary envelope; (3) are a complex of lead and
the acid fractions of nuclear protein; (4) can be disaggregated _i_n vitro by EDTA; (5) can
appear very rapidly after lead exposure (Choie et al., 1975); (6) consist of a protein moiety
in the complex which is synthesized de novo; and (7) have been postulated to serve a protec-
tive role in the cell, given the relative amounts of lead accumulated and presumably rendered
toxicologically inert.
Based on renal biopsy studies, Cramer et al. (1974) concluded that such inclusion body
formation in renal tubule cells in lead workers is an early response to lead entering the kid-
ney, in view of decreased presence as a function of increased period of employment. Schumann
et al. (1980), however, observed a continued exfoliation of inclusion-bearing tubule cells
into urine of workers havinp a variable employment history.
Any protective role played by the lead inclusion body appears to be an imperfect one, to
the extent that both subcellular organelle injury and lead uptake occur simultaneously with
such inclusion formation, often in association with severe toxicity at the organ system level.
For example, Osheroff et al. (1982), observed lead inclusion bodies in the anterior horn cells
of the cervical spinal cord and neurons of the substantia nigra (as well as in renal tubule
cells) in the adult rhesus monkey, along with damage to the vascular walls and glial processes
and ependymal cell degeneration. At the light- and electron-microscope level, there ware no
signs of neuronal damage or altered morphology except for the inclusions. As noted by the
authors, these inclusions in the large neurons of the. substantia nigra show that the neuron
will take up and accumulate lead. In the study of Fowler et al. (1980), renal tubule inclu-
sions were observed simultaneously with evidence of structural and functional damage to the
mitochondrion, all at relatively low levels of lead. Hence,-it appears that a limited pro-
tective role for these inclusions may extend across a range of lead exposure.
Chromosomal effects and other indices of genotoxicity in humans and animals are discussed
in Section 12.7 of this chapter.
12.2.3 Effects of Lead on Membranes
In theory, the cell membrane is the first organelle to encounter lead, and it is not sur-
prising that cellular effects can be ascribed to interactions at cellular and intracellular
membranes, mainly appearing to be associated with ion transport processes across membranes.
In Section 12.3 a more detailed discussion is accorded the effects of lead on the membrane as
they relate to the erythrocyte in terms of increased cell fragility and increased osmotic
resistance. These effects can be rationalized, in large part, by the documented inhibition by
lead of erythrocyte membrane (Na , K )-ATPase.
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Lead also appears to interfere with the normal processes of calcium transport across mem-
branes of various tissue types. Silbergeld and Adler (1978) have described lead-induced
retardation of the release of the neurotransmitter, acetylcholine, in peripheral cholinergic
synaptosomes, due to a blockade of calcium binding to the synaptosomal membrane reducing
calcium-dependent choline uptake and subsequent release of acetylcholine from the nerve ter-
minal. Calcium efflux from neurons is mediated by the membrane (Na+, K+)-ATPase via an ex-
change process with sodium. Inhibition of the enzyme by lead, as also occurs with the
erythroctye (see above), increases the concentration of calcium within nerve endings (Goddard
and Robinson, 1976). As seen from the data of Pounds et al. (1982a), lead can also elicit
retention of calcium in neural cells by easy entry into the cell and by directly affecting the
deep calcium compartment within the cell, of which the mitochondrion is a major component.
12.2.4 Qtner Qrganellar Effects of Lead
Studies of morphological alterations of renal tubule cells in the rat (Chang et al.,
\
1981) and rabbit (Spit et al., 1981) with varying lead treatments have demonstrated lead-
induced lysosomal changes. In the rabbit, with relatively modest levels of lead exposure
(0.25 or 0.5 mg Pb/kg, 3 times weekly over 14 weeks) and corresponding blood lead values of 50
and 60 |jg/dl, there was a dose-dependent increase in the amount of lysosomes in proximal con-
voluted tubule cells, as well as increased numbers of lysosomal inclusions. In the rat, expo-
sure to 10 mg Pb/kg i.v. (daily over 4 weeks) resulted in the accumulation of lysosomes, some
gigantic, in the pars recta segment of renal tubules. These animal data are consistent with
observations made in lead workers (Cramer et al., 1974; Wedeen et al. , 1975) and appear to
represent a disturbance in normal lysosomal function, with the accumulation of lysosomes being
due to enhanced degradation of proteins arising from effects of lead elsewhere within the
cell.
12.2.5 Summary of Subcellular Effects of Lead
The biological basis of lead toxicity is closely linked to the ability of lead to bind to
ligating groups in biomolecular substances crucial to normal physiological functions. This
binding interferes with physiological processes by such mechanisms as: competition with
native essential metals for binding sites; inhibition of enzyme activity; and inhibition or
other changes in essential ion transport.
The main target organelle for lead toxicity in a variety of cell and tissue types clearly
is the mitochondrion, followed probably by cellular and intracellular membranes. Mitochon-
drial effects take the form of structural changes and marked disturbances in mitochondrial
function within Lhe cell, especially energy metabolism and ion transport. These effects are
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associated, in turn, with demonstrable accumulation of lead in mitochondria, both i_n vivo and
i_n vitro. Structural changes include mitochondrial swelling in many cell types, as well as
distortion and loss of cristae, which occur at relatively moderate levels of lead exposure.
Similar changes have been documented in lead workers across a wide range of exposure levels.
Uncoupled energy metabolism, inhibited'-eel l-u'lar respiration using both succinate and
nicotinamide adenine dinucleotide (NAD)-linked substrates, and altered kinetics of intracellu-
lar calcium have been demonstrated hi vivo using mitochondria of brain and non-neural tissue.
In some cases, relatively moderate lead exposure levels have been associated with such
changes, and several studies have documented the relatively greater sensitivity of this organ-
elle in young versus adult animals in terms of mitochondrial respiration. The cerebellum
appears to be particularly sensitive, providing a connection between mitochondrial impairment
and lead encephalopathy. Impairment by lead of mitochondrial function in the developing brain
has also been associated with delayed brain development, as indexed by content of various
cytochromes. In the rat pup, ongoing lead exposure from birth is required for this effect to
be expressed, indicating that such exposure must occur before, and is inhibitory to, the burst
of oxidative metabolism activity that normally occurs in the young rat during 10 to 21 days
postnatally.
Ii2 V1V0 lead exposure of adult rats has also been observed to markedly inhibit cerebral
cortex intracellular calcium turnover (in a cellular compartment that appears to be the mito-
chondrion) at a brain lead level of 0.4 ppm. These results are consistent with a separate
study showing increased retention of calcium in the brain of lead-dosed guinea pigs. A number
of reports have described the i_n vivo accumulation of lead in mitochondria of kidney, liver,
spleen, and brain tissue, with one study showing that such uptake was slightly more than
occurred in the nucleus. These data are not only consistent with the various deleterious ef-
fects of lead on mitochondria but are also supported by other, i_n vitro findings.
Significant decreases in mitochondrial respiration i_n vitro using both NAD-linked and
succinate substrates have been observed for brain and non-neural tissue mitochondria in the
presence of lead at micromolar levels. There appears to be substrate specificity in the inhi-
bition of respiration across different tissues, which may be a factor in differential organ
toxicity. Also, a number of enzymes involved in intermediary metabolism in isolated mitochon-
dria have been observed to undergo significant inhibition of activity with lead.
A major focus of research on lead effects on isolated mitochondria has concerned ion
(especially calcuim) transport. Lead movement into brain and other tissue mitochondria, as
does calcium movement, involves active transport. Recent sophisticated kinetic analyses of
desaturation curves for radiolabeled lead or calcium indicate that there is striking overlap
in the cellular metabolism of calcium and lead. These studies not only establish a basis for
easy entry of lead into cells and cell compartmentsj but also provide a basis for impairment
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by lead of intracellular ion transport,- particularly in neural cell mitochondria, where the
capacity for calcium transport is 20-fold higher than even in heart mitochondria.
Lead is also selectively taken up in isolated mitochondria _i_n vitro, including the mito-
chondria of synaptosohies and brain capillaries. Given the diverse and extensive evidence of
lead's impairment of mitochondrial structure and function as viewed from a subcellular level,
it is not surprising that these derangements are logically held to be the basis of dysfunction
of heme biosynthesis, erythropoiesis, and the central nervous system. Several key enzymes in
the heme biosynthetic pathway are intramitochondrial, particularly ferrochelatase. Hence, it
is to be expected that entry of lead into mitochondria will impair overall heme biosynthesis,
and in fact this appears to be the case in the developing cerebellum. Furthermore, the levels
s. '
of lead exposure associated with entry of lead into mitochondria and expression of mitochon-
drial injury can be relatively moderate.
Lead exposure provokes a typical cellular reaction in human and other species that has
been morphologically characterized as a lead-containing nuclear inclusion body. Although it
has been postulated that such inclusions constitute a cellular protection mechanism, such a
mechanism is an imperfect one. Other organelles, e.g., the mitochondrion, also take up lead
and sustain injury in the presence of nuclear inclusion bodies. Chromosomal effects and other
indices of genotoxicity in humans and animals are considered later, in Section 12.7.
In theory, the cell membrane is the first organelle to encounter lead and it is not sur-
prising that cellular effects of-lead can be ascribed to interactions at cellular and intra-
cellular membranes in the form of distrubed ion transport. The inhibition of membrane
(Na+,K+)-ATPase of erythrocytes as, a factor in lead-impaired erythropoiesis is noted else-
where. Lead also appears to interfere-with the normal processes of calcium transport across
membranes of different tissues. In peripheral cholinergic synaptosomes, lead is associated
with retarded release of acetylcholine owing to. a blockade of calcium binding to the membrane,
while calcium accumulation within nerve endings can be ascribed to inhibition of membrane
(Na+,K+)-ATPase.
Lysosomes accumulate in renal proximal convoluted tubule cells of rats and rabbits given
lead over a wide range of dosing. This also appears to occur in the kidneys of lead workers
and seems to represent a disturbance, in normal lysosomal function, with the accumulation of
lysosomes being due to enhanced degradation of proteins because of the effects of lead else-
where within the eel 1.
In so far as effects of lead on the activity of various enzymes are concerned, many of
the available studies concern i_n vitro behavior of relatively pure enzymes with marginal rele-
vance to various effects i_n vivo. On the other hand, certain enzymes are basic to the effects
of lead at the organ or organ system level, and discussion is best reserved for such effects
in ensuing sections of the document dealing with these systems.
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12.3 EFFECTS OF LEAD ON HEME BIOSYNTHESIS AND ERYTHROPOIESIS/ERYTHROCYTE PHYSIOLOGY IN HUMANS
AND ANIMALS
Lead has well-recognized effects not only on heme biosynthesis, a crucial process common
to many organ systems, but also on erythropoiesis and erythrocyte physiology. This section is
therefore divided for purposes of discussion into: (1) effects of lead on heme biosynthesis
and (2) effects of lead on erythropoiesis and erythrocyte physiology. Discussion of the
latter is further subdivided into effects of lead on hemoglobin production, cell morphology
and survival, and erythropoietic nucleotide metabolism. The interrelationship of effects of
lead on heme biosynthesis and neurotoxic effects of lead are discussed in a final subsection.
Attention is accorded to discussion of effects of both inorganic lead and alkyl lead compounds
used as gasoline additives.
12.3.1 Effects of Lead on Heme Biosynthesis
The effects of lead on heme biosynthesis are very well known because of both their prom-
inence and the large number of studies of these effects in humans and experimental animals.
In addition to being a constituent of hemoglobin, heme is a prosthetic group of a number of
tissue hemoproteins having diverse functions, such as myoglobin, the P-450 component of the
mixed function oxidase system, and the cytochromes of cellular energetics. Hence, any effects
of lead on heme biosynthesis will, perforce, pose the potential for multi-organ toxicity.
At present, much of the available information concerning the effects of lead on heme bio-
synthesis have been obtained by measurements in blood, due in large part to the relative ease
of assessing such effects via measurements in blood and in part to the fact that blood is the
vehicle for movement of metabolites from other organ systems. On the other hand, a number of
reports have been concerned with lead effects on heme biosynthesis in tissues such as kidney,
liver, and brain. In the discussion below, various steps in the heme biosynthetic pathway
affected by lead are discussed separately, with information describing erythropoietic effects
usually appearing first, followed by studies involving other tissues.
The process of heme biosynthesis results in formation of the porphyrin, protoporphyrin
IX, starting with glycine and succinyl-coenzyme A. It culminates with the insertion of iron
at the center of the porphyrin ring. As may be noted in Figure 12-1, lead interferes with
heme biosynthesis by disturbing the activity of three major enzymes: (1) it indirectly stim-
ulates, by feedback derepression, the mitochondrial enzyme delta-aminolevulinic acid synthe-
tase (ALA-S), which mediates the condensation of glycine and succinyl-coenzyme A to form
delta-aminolevulinic acid (6-ALA); (2) it directly inhibits the cytosolic enzyme delta-amino-
levulinic acid dehydrase (ALA-D), which catalyzes the cyclocondensation of two units of ALA to
porphobilinogen; (3) it disturbs the mitochondrial enzyme ferrochelatase, found in liver, bone
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MiTOCHONDRAIL MEMBRANE
MITOCHONDRION
GLYCINE
+
SUCCINYL-CoA
FERRO
CHELATASE
Pb
HEME
A
Fe + PROTOPORPHYRIN || Fb
d-ALA SYNTHETASE
(INCREASEI
Pb (DIRECTLY OR BY
DEREPRESSION)
d-ALA
d-ALA
DEHYDRASE
(DECREASE)
Pb
'jggS*
J <3— Pb
COPROPORPHYRIN
(INCREASEI
PORPHOBILINOGEN (PBG)
Figure 12-1. Lead effects on heme biosynthesis.
marrow, and other tissues, by either direct inhibition or alteration of intermitochondrial
transport of iron ferrochelatase, which catalyzes the insertion of iron (II) into the proto-
porphyrin ring to form heme, the enzyme situated in mammals in the inner mitochondrial mem-
brane (McKay et al., 1969).
12.3.1.1 Effects of Lead on 6-Aminolevulinic Acid Synthetase. The activity of the enzyme
ALA-S is the rate-limiting step in the heme biosynthetic pathway. With decreased heme forma-
tion at other steps downstream or with increased heme oxygenase activity, compensatory
increase of ALA-S activity occurs through feedback derepression and enhances the rate of heme
formation. Hence, excess ALA formation is due to both stimulation of ALA-S and direct inhibi-
tion of ALA-D (see below).
Increased ALA-S activity has been reported in lead workers (Takaku et al., 1973; Campbell
et al., 1977; Meredith et al., 1978), with leukocyte ALA-S stimulated at a blood lead value of
40 pg/dl (Meredith et al., 1978), a level at which ALA-D activity is significantly inhibited.
To the extent that mitochondria in leukocytes show a dose-effect relationship comparable to
the bone marrow and hepatic systems, it appears that most of the excess ALA formation below
the observed threshold value is due to ALA-D inhibition. From the authors' data, blood ALA
had increased about 2-fold in these workers over the blood lead range 18 pg/d 1 to 40 pg/dl.
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l_n vitro and i_n vivo experimental data have provided mixed results in terms of the direc-
tion of the effect of lead on ALA-S activity. Silbergeld et al. (1982) observed that ALA-S
activity was increased in kidney with acute lead exposure in rats, while chronic treatment was
associated with increased activity of the enzyme in spleen. In liver, however, ALA-S activity
was reduced under both acute and chronic dosing. Fowler et al. (1980) reported that renal
ALA-S activity was significantly reduced in rats continuously exposed to lead i_n utero,
through development, and up to 9 months of age. Meredith and Moore (1979) noted a steady in-
crease in hepatic ALA-S activity when rats were given lead parenterally over an extended
period of time. Maxwell and Meyer (1976) and Goldberg et al. (1978) also noted increased
ALA-S activity in rats given lead parenteral ly. It appears that the type and time-frame of
dosing influences the observed effect of lead on the enzyme activity. Using a rat liver cell
line (RLC-GAI) in culture, Kusel 1 et al. (1978) demonstrated that lead could produce a time-
dependent increase in ALA-S activity. Stimulation of activity was observed at lead levels as
. t> .
low as 5 x 10 M, with maximum stimulation at 10 M. The authors report that the activity
increase was associated with biosynthesis of more enzyme, rather than stimulation of the pre-
existing enzyme. Lead-stimulated ALA-S formation was also not limited to liver cells; rat
gliomas and mouse neuroblastomas showed similar results.
12.3.1.2 Effects of Lead on 6-Aminolevulinic Acid Dehydrase and ALA Accumulation/Excretion.
Delta-aminolevulinic acid dehydrase (5-aminolevulinate hydrolase; porphobilinogen synthetase;
E.C. 4.2.1.24; ALA-D) is a sulfhydryl, zinc-requiring allosteric enzyme in the heme biosynthe-
tic pathway which catalyzes the conversion of two units of ALA to porphobilinogen. The
enzyme's activity is very sensitive to inhibition by lead, the inhibition being reversed by
reactivation of the sulfhydryl group with agents such as dithiothreitol (Granick et al. ,
1973), zinc (Finelli et al., 1975), or zinc plus glutathione (Mitchell et al. , 1977).
The activity of ALA-D appears to be inhibited at virtually all blood lead levels studied
so far, and any threshold for this effect remains to be identified (see discussion below).
Dresner et al. (1982) found that ALA-D activity in rat bone marrow suspensions was signifi-
_ (
cantly inhibited to 35 percent of control levels in the presence of 5 x 10 M (0.5 |jM) lead.
This potency, on a comparative molar basis, was unmatched by any other metals tested.
Recently, Fujita et al. (1981) showed evidence of an increase in the amount of ALA-D in ery-
throcytes in lead-exposed rats, ascribed to an increased rate of ALA-D synthesis in bone
marrow cells. Hence, the commonly observed net inhibition of activity occurs even in the face
of an increase in ALA-D synthesis.
Hernberg and Nikkanen (1970) found that enzyme activity was correlated inversely with
(logarithmic) blood lead values in a group of urban, non-exposed subjects. Enzyme activity
inhibition was 50 percent at a blood lead level of 16 pg/dl. Other reports have confirmed
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these observations across age groups and exposure categories (Alessio et al., 1976b; Roels et
al., 1975b; Nieberg et al. , 1974; Wada et al. , 1973). A ratio of activated to inhibited en-
zyme activity (versus a single activity measurement, which does not accommodate intersubject
genetic variability) measured against blood lead in children with values between 20 and 90
pg/dl was employed by Granick et al. (1973) to obtain an estimated threshold of 15 pg/dl for
an effect of lead. On the other hand, Hernberg and Nikkanen (1970) observed no threshold in
their subjects, all of whom were at or below 16 pg/dl. The lowest blood lead actually mea-
sured by Granick et al. (1973) was higher than the values measured by Hernberg and Nikkanen
(1970).
Kuhnert et al. (1977) reported that ALA-D activity measures in erythrocytes from both
pregnant women and cord blood of infants at delivery are correlated with the corresponding
blood lead values, using the activated/inhibited activity ratio method of Granick et al.
(1973). The correlation coefficient of activity with lead level was higher in fetal erythro-
cytes (r = -0.58, p <0.01) than in the mothers (r = -0.43, p <0.01). The mean inhibition
level was 28 percent in mothers vs. 12 percent in the newborn. A £tudy by Lauwerys et al.
(1978) in 100 pairs of pregnant women and infant cord blood samples confirms this observation,
i.e., for fetal blood r = 0.67 (p <0.001) and for maternal blood r = -0.56 (p <0.001).
While several factors other than lead may affect the activity of erythrocyte ALA-D, much
of the available information suggests that most of these factors do not materially compromise
the interpretation of the relationship between enzyme activity and lead or the use of this
relationship for screening purposes. Border et al. (1976) questioned the reliability of ALA-D
activity measurement in subjects concurrently exposed to both lead and zinc, since zinc also
affects the activity of the enzyme. The data of Meredith and Moore (1980) refute this objec-
tion. In subjects without exposure, having serum zinc values of 80-120 |jM, there was only a
minor activating effect with increasing zinc when contrasted to the correlation of activity
and blood lead in these same subjects. In workers exposed to both lead and zinc, serum zinc
values were greater than in subjects with just lead exposure, but the mean level of enzyme ac-
tivity was still much lower than in controls (p <0.001).
The preceding discussion indicates that neither differences within the normal range of
physiological zinc in humans nor combined excessive zinc and lead exposure in workers materi-
ally affects ALA-D activity. The obverse of this, lead exposure in the presence of zinc defi-
ciency, is probably the more significant issue, but one that has not been well studied. Since
ALA-D is a zinc-requiring enzyme, one would expect that optimal activity would be governed by
j_n vivo zinc availability. Furthermore, zinc deficiency could potentially have a dual dele-
terious effect on ALA-D activity, first by reduced activity with reduced zinc availability and
second, by enhanced lead absorption in the presence of zinc deficiency (see Section 10.5), the
increased lead burden further inhibiting ALA-D activity.
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The recent study of Roth and Kirchgessner (1981) indicates that ALA-D activity is signi-
ficantly decreased in the presence of zinc deficiency. In zinc-deficient rats showing reduced
serum and urinary zinc levels, the level of erythrocyte ALA-D activity was only 50 percent
that of pair-fed controls, while urinary ALA was significantly elevated. Although these in-
vestigators did not measure blood lead in deficient and control animal groups, it would appear
that the level of inhibition is more than could be accounted for just on the basis of in-
creased lead absorption from diet. Given the available information documenting zinc defi-
ciency in children (Section 10.5) as well as the animal study of Roth and Kirchgessner (1981),
the relationship of lead, zinc deficiency, and ALA-D activity in young children merits fur-
ther, careful study.
Moore and Meredith (1979) noted the effects of carbon monoxide on the activity of ALA-D,
comparing moderate or heavy smokers with non-smokers. At the highest level of carboxyhemoglo-
bin measured in their smoker groups, the depression of ALA-D activity was 2.1 percent. In
these subjects, a significant inverse correlation of ALA-D activity and blood lead existed,
but there was no significant correlation of such activity and blood carboxyhemoglobin levels.
While blood ethanol has been reported to affect ALA-D activity (Moore et al. , 1971;
Abdulla et al., 1976), its effect is significant only with intake corresponding to acute alco-
hol intoxication. Hence, relevance of this observation to screening is limited, particularly
in children. The effect is reversible, declining with clearing of alcohol from the blood
stream.
The inhibition of ALA-D activity in erythrocytes by lead apparently reflects a similar
effect in other tissues. Secchi et al. (1974) observed that there was a clear correlation in
26 lead workers between hepatic and erythrocyte ALA-D activity as well as the expected inverse
correlation between such activity and blood lead in the range 12-56 |jg/dl. In suckling rats,
Millar et al. (1970) noted decreased enzyme activity in brain and liver as well as red cells
when lead was administered orally. In the study of Roels et al. (1977), tissue ALA-D changes
were not observed when dams were administered 1, 10, or 100 ppm lead in drinking water. How-
ever, the recent report of Silbergeld et al. (1982) described moderate inhibition of ALA-D
activity in brain and significant inhibition in kidney, liver, and spleen when adult rats were
acutely exposed to lead given intraperitoneal^; chronic exposure was associated with reduced
activity in kidney, liver, and spleen. Gerber et al. (1978) found that neonatal mice exposed
to lead from birth through 17 days of age at a level of 1.0 mg/ml in water showed significant
decreases in brain ALA-D activity (p <0.01) at all time points studied. These results support
the data of Millar et al. (1970) for the suckling rat. In this study by Millar et al., rats
exposed from birth through adulthood only showed significant decreases of brain ALA-D activity
at 15 and 30 days, which also supports other data for the developing rodent. It would appear,
therefore, that brain ALA-D activity is more sensitive to lead in the developing animal than
in the adult.
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The study of Dieter and Finley (1979) sheds light on the relative sensitivity of ALA-D
activity in several regions of the brain and permits comparison of blood vs. brain ALA-D acti-
vity as a function of lead level. Mallard ducks given a single pellet of lead showed, by 4
weeks, 1 ppm lead in blood, 2.5 ppm lead in liver, and 0.5 ppm lead in brain. Cerebellar
ALA-D activity was reduced by 50 percent at a lead level below 0.5 ppm; erythrocyte enzyme
activity was lowered by 75 percent. Hepatic ALA-D activity was comparable to cerebellar acti-
vity or somewhat less, although the lead level in the liver was 5-fold higher. Cerebellar
ALA-D activity was significantly below that for cerebrum. In an avian species, then, at
blood lead levels where erythrocyte ALA-D activity is significantly depressed, activity of the
enzyme in cerebellum v/as even more affected relative to lead concentration. The Roels et al.
(1977) data may reflect a lower effective dose delivered to the rat pups in maternal milk as
well as the dose taken in by the dams themselves, since they similarly showed no tissue enzyme
activity changes.
The inhibition of ALA-D is reflected by increased levels of its substrate, ALA, in urine
(Haeger, 1957) as well as in whole blood or plasma (Meredith et al., 1978; MacGee et al.,
1977; Chisolm, 1968; Haeger-Aronsen, 1960). The detailed study of Meredith et al. (1978),
which involved both control subjects and lead workers, indicated that in elevated lead expo-
sure the increase in urinary ALA is preceded by a significant rise in circulating levels of
ALA. The overall relationship of plasma ALA to blood lead was exponential and showed a per-
ceptible continuation of an ALA-blood lead correlation into the control group to include the
lowest value, 18 pg/dl. The relationship of plasma ALA to urinary levels of the precursor was
found to be exponential, indicating that as plasma ALA increases, a greater proportion under-
goes excretion into urine. Inspection of the plot of urinary vs. plasma ALA in these subjects
shows that the correlation persists down to the plasma ALA concentration corresponding to the
lowest blood lead level, 18 pg/dl. Cramer et al. (1974) have demonstrated that ALA clearance
into urine parallels glomerular filtration rate across a range of lead exposures, suggesting
that increased urinary output with increasing circulating ALA is associated with decreased tu-
bular reabsorption (Moore et al., 1980). This study employed the method of Haeger-Aronsen
(1960), which does not account for the presence of ami no-acetone. If amino-acetone were in-
terfering at low blood lead levels, however, one might expect an obliteration of the associa-
tion, since this metabolite is not affected by lead exposure and its concentration should be
randomly distributed in plasma and urine of'the subjects.
Urinary ALA has been employed extensively as an indicator of excessive lead exposure,
particularly in occupational settings (e.g., Davis et al., 1968; Selander and Cramer, 1970;
Alessio et al., 1976a). The reliability of this test in initial screening of children for
lead exposure has been questioned by Specter et al. (1971) and Blanksma et al. (1969), who
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pointed out the failure of urinary ALA analysis to detect lead exposure when compared with
blood lead values. This is due to the fact that an individual subject will show a wide vari-
ation in urinary ALA with random sampling. Chisolm et al. (1976) showed that reliable levels
could only be obtained with 24-hour collections. In children with blood lead levels above 40
pg/dl the relationship of ALA in urine to blood lead becomes similar to that observed in lead
workers (see below).
A correlation exists between blood lead and the logarithm of urinary ALA in workers
(Meredith et al., 1978; Alessio et al., 1976a; Roels et al. , 1975a; Wada et al., 1973;
Selander and Cramer, 1970) and in children (National Academy of Sciences, 1972). Selander and
Cramer (1970) reported that two different correlation curves were obtained, one for individ-
uals below 40 (jg/d1 blood lead, and a different one for values above this, although the degree
of correlation was less than with the entire group. A similar observation has been reported
by Lauwerys et al. (1974) from a study of 167 workers (10-75 pg/dl). Meredith et al. (1978)
found that the correlation curve for blood ALA vs. urinary ALA was linear below a blood lead
of 40 (jg/dl, as was the relationship of blood ALA to blood lead. Hence, there was also a
linear relationship between blood lead and urinary ALA below 40 pg/dl, i.e., a continuation of
the correlation below the commonly accepted threshold blood lead value of 40 (jg/dl (see
below). Tsuchiya et al. (1978) have questioned the relevance of using single correlation
curves to describe the blood lead-urinary ALA relationship across a broad range of exposure,
because they found that this relationship in workers showing moderate, intermediate, and high
lead exposure could be described by three correlation curves of differing slope. This finding
is consistent with the observations of Selander and Cramer (1970) as well as the results of
Meredith et al. (1978) and Lauwerys et al. (1974). Chisolm et al. (1976) described an expo-
nential correlation between blood lead and urinary ALA in children 5 years old or younger,
with blood lead ranging from 25 to 75 pg/dl. In adolescents with blood lead below 40 pg/dl,
no clear correlation was observed.
It - is apparent from the above reports (Tsuchiya et al., .1978; Meredith et al., 1978;
Selander and Cramer, 1970) that circulating ALA and urinary ALA are elevated and correlated at
blood lead values below 40 |jg/dl in humans. This is consistent, as in the Meredith et al.
study, with the significant and steady increase in ALA-D inhibition concomitant with rising
blood levels of ALA, even at blood lead values considerably below 40 pg/dl. Increases of ALA
in tissues of experimental animals exposed to lead have also been documented. In the study of
Silbergeld et al. (1982), acute administration of lead to adult rats was associated with an
elevation in spleen and kidney ALA vs. that of controls, while in chronic exposure there was a
moderate increase in ALA in the brain and a large increase (9-15 fold) in kidney and spleen.
Liver levels with either, form of exposure were not materially affected, although there was
inhibition of liver ALA-D, particularly in the acute dose group.
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12.3.1.3 Effects of Lead on Heme Formation from Protoporphyrin. The accumulation of proto-
porphyrin in the erythrocytes of individuals with lead intoxication has been recognized since
the 1930s (Van den Bergh and Grotepass, 1933), but it has only recently been possible to study
this effect through the development of sensitive and specific analytical techniques that per-
mit quantitative measurement. In particular, the development of laboratory microtechniques
and the hematofluorometer have allowed the determination of dose-effect relationships as well
as the use of such measurements to screen for lead exposure.
In humans under normal circumstances, about 95 percent of the protoporphyrin in cir-
culating erythrocytes is zinc protoporphyrin (ZPP) with the remaining 5 percent present as
"free" protoporphyrin (Chisolm and Brown, 1979). Accumulation of protoporphyrin IX in the
erythrocytes is the result of impaired iron (II) placement in the porphyrin moiety to form
heme, an intramitochondrial process. In lead exposure, the porphyrin acquires a zinc ion, in
lieu of the native iron, with the resulting ZPP tightly bound in the available heme pockets
for the life of the erythrocyte, about 120 days (Lamola et al., 1975a,b).
In lead poisoning, the accumulation of protoporphyrin differs from that seen in the con-
genital disorder, erythropoietic protoporphyria. In the latter case, there is a defect in
/
ferrochelatase function, leading to loose attachment of the porphyrin, accumulated without up-
take of zinc, on the surface of the hemoglobin. Loose attachment permits diffusion into
plasma and ultimately into the skin, where photosensitivity is induced. This behavior is ab-
sent in lead-associated porphyrin accumulation. The two forms of porphyrin, free and zinc-
containing, differ sufficiently in fluorescence spectra to permit a laboratory distinction.
With iron deficiency, there is also accumulation of protoporphyrin in the heme pocket as the
zinc complex, resembling in large measure the characteristics of lead intoxication.
The elevation of erythrocyte ZPP has been extensively documented as being exponentially
correlated with blood lead in children (Piomel1i et al., 1973; Kammholz et al., 1972; Sassa et
al., 1973; Lamola et al., 1975a,b; Roels et al., 1976) and in adult workers (Valentine et al.,
1982; Lilis et al. , 1978; Grandjean and Lintrup, 1978; Alessio.-et.al., 1976b•.Roels et al.,
1975a, 1979; Lamola et al., 1975a,b). Reigart and Graber (1976) and Levi et al. (1976) have
demonstrated that ZPP elevation can predict which children tend to increase their blood lead
levels, a circumstance which probably rests on the nature of chronic lead exposure in certain
groups of young children where a pulsatile blood lead curve is superimposed on some level of
ongoing intake of lead which continues to elevate the ZPP values.
Accumulation of ZPP only occurs in erythrocytes formed during lead's presence in erythro-
poietic tissue, resulting in a lag of several weeks before the fraction of new ZPP-rich cells
is large enough to influence total cell ZPP level. On the other hand, elevated ZPP in ery-
throcytes long after significant lead exposure has ceased appears to be a better indicator of
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resorption of stored lead in bone than other measurements. Alessio et al. (1976b) reported
that former lead workers, removed from exposure at the workplace for more than 12 months in
all cases, still showed the typical logarithmic correlation with blood or urinary lead. How-
ever, the best correlation was observed between ZPP and chelatable lead, that fraction of
total body burden considered toxicologically active (see Chapter 10). This post-exposure re-
lationship for adults clearly indicates that significant levels of hematologically toxic lead
continue to circulate long after exposure to lead has ceased.
In a report relevant to the problem of multi-indicator measurement to assess the degree
of lead exposure, Hesley and Wimbish (1981) studied changes in blood lead and ZPP in two
groups, newly exposed lead workers or those removed from significant exposure. In new
workers, blood lead achieved a plateau at 9-10 weeks, while ZPP continued to rise over the
entire study interval of 24 weeks. Among workers removed from exposure, both blood lead and
ZPP values remained elevated up to the end of this study period (33 weeks), but the decline in
ZPP concentration lagged behind blood lead in reaching a plateau. These investigators logi-
cally concluded that the difficulty in demonstrating reliable blood lead-ZPP relationships may
reflect differences in when the two measures reach plateau. Similarly, more reliance should
be placed on ZPP vs. blood lead levels before permitting re-entry into areas of elevated lead
exposure.
The threshold for the effect of lead on ZPP accumulation is affected by the relative
spread of blood lead values and the corresponding concentrations of ZPP. In many cases these
range from "normal" levels in non-exposed subjects up to values reflecting considerable expo-
sure. Furthermore, iron deficiency is also associated with ZPP elevation, particularly in
children 2-3 years or younger.
In adults, Roels et al. (1975b) found that a cutoff for the relationship of erythrocyte
protoporphyrin (EP) elevation to blood lead was 25-30 [jg/dl, confirmed by the log-transformed
data of Joselow and Flores (1977), Grandjean and Lintrup (1978), Odone et al. (1979), and
Herber (1980).
In older children, 10-15 years of age, the data of Roels et al. (1976) indicate a thres-
hold for effect of 15.5 pg/dl. The population dose-response relationship between EP and blood
lead in these children indicated that EP levels were significantly higher (>2 SDs) than the
reference mean in 50 percent of the children at a blood lead level of 25 ng/dl. In the age
range of children studied here, iron deficiency is uncommon and these investigators did not
note any significant hematocrit change in the exposure group. In fact, it was lower in the
control group, although these subjects had lower ZPP levels. In this study, then, iron defi-
ciency was unlikely to be a confounding factor in the primary relationship. Piomelli et al.
(1977) obtained a comparable threshold value (15.5 pg/dl) for lead's effect on ZPP elevation
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in children who were older than 4 years as well as those who were 2-4 years old. Were iron
deficiency a factor in the results for this large study population (1816 children), one would
expect a greater impact in the younger group, where the deficiency is more common.
Within the blood lead range considered "normal," i.e., below 30-40 pg/dl, assessment of
any ZPP-blood lead relationship is strongly influenced by the relative analytical proficiency
of the laboratory carrying out both measurements, particularly for blood lead at lower values.
The type of statistical treatment of the data is also a factor, as are some biological sources
of variability. With respect to subject variability, Grandjean (1979) has documented that ZPP
increases throughout adulthood while hemoglobin remains relatively constant. Hence, age
matching is a prerequisite. Similarly, the relative degree of ZPP response is sexually dicho-
tomous, being greater in females for a given blood lead level (see discussion below).
Suga et al. (1981) claimed no apparent correlation between blood lead levels below
40 pg/dl and blood ZPP content in an adult population of 395 male and female subjects. The
values for males and females were combined, based on no measured differences in ZPP response,
which is at odds with the studies of Stuik (1974), Roels et al. (1975b), Zielhuis et al.
(1978), Odone et al. (1978), and Toriumi and Kawai (1981). Also, EP was found to increase
with increasing age, despite the fact that the finding of no correlation between blood lead
and ZPP was based on a study population with all age groups combined.
Piomelli et al. (1982) investigated both the threshold for the effect of lead on ZPP ac-
cumulation and a dose-response relationship in 2004 children, 1852 of whom had blood lead
values below 30 pg/dl. In this study, blood lead and EP measurements were done in facilities
with a high proficiency for both blood lead and ZPP analyses. The study employed two statis-
tical approaches (segmental line techniques and probit analysis), both of which revealed an
average threshold blood lead level of 16.5 pg/dl in either the full group or the children with
blood values below 30 pg/dl. In this report, the effect of iron deficiency and other non-lead
factors was tested and removed using the Abbott formula (Abbott, 1925). With respect to popu-
lation dose-response relationships, it was found that blood lead values corresponding to sig-
nificant EP elevation at more than 1 or 2 standard deviations above a reference mean in 50
percent of the subjects were 28.6 or 35.6 pg/dl blood lead, respectively. At a blood lead
level of 30 jjg/dl » furthermore, it was determined that 27 percent of children would have an EP
greater than 53 pg/dl.
Comparison of ZPP elevation among adult males and females and children at a given blood
lead level generally indicates that children and adult females are more sensitive to this ef-
fect of lead. Lamola et al. (1975a,b) demonstrated that the slope of ZPP vs. blood lead was
steeper in children than in adults. Roels et al. (1976) found that women and children were
equally more sensitive in response than adult males, a finding also observed in the population
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studied by Odone et al. (1979). Other comparisons between adults, either as groups studied at
random or in a voluntary lead exposure study, also document the sensitivity of females vs.
males to this effect of lead (Stuik, 1974; Roels etal., 1975b, 1976, 1979; Toriumi and Kawai,
1981). The heightened response of females to lead-associated EPP elevation was investigated
in rats (Roels et al., 1978a) and shown to relate to hormonal interactions with lead, con-
firming the human data of Roels et al. (1975b, 1976, 1979) that iron status is not a factor in
the phenomenon.
The effect of lead on iron incorporation into protoporphyrin in the heme biosynthetic
pathway is not restricted to the erythropoietic system. Evidence of a generalized effect of
lead on tissue heme synthesis at low levels of lead exposure comes from the recent studies of
Rosen and coworkers (Rosen et al., 1980, 1981; Mahaffey et al., 1982). Children with blood
lead levels in the range 12-120 pg/dl showed a strong negative correlation (r = -0.88) with
serum 1,25-dihydroxy vitamin D (1,25-(0H)2D). The slopes of the regression lines for subjects
having blood lead below 30 pg/dl were not materially different from those over this level.
Furthermore, when lead-intoxicated children were subjected to chelation therapy, it was
observed that the depressed levels of serum 1,25-(OHD returned to normal, while values of
serum 25-hydroxy vitamin D (the precursor to 1,25-(0H)ZD) remained the same. This indicates
that lead has an inhibitory effect on renal 1-hydroxylase, a cytochrome P-450 mediated mito-
chondrial enzyme system that converts 25-(0H)D to 1,25-(0H)2D. The low end of the blood lead
range associated with lowered l,25-(0H)-(yD levels and accompanying 1-hydroxylase activity inhi-
bition corresponds to the lead level associated with the onset of EP accumulation in erythro-
poietic tissue (see above). Sensitivity of renal mitochondrial 1-hydroxylase activity to lead
is consistent with a large body of information showing the susceptibility of renal tubule cell
mitochondria to injury by lead and with the chronic lead exposure animal model of Fowler et
al. (1980), discussed in more detail below.
Formation of the heme-containing protein cytochrome P-450, which is an integral part of
the hepatic mixed function oxygenase system, has been documented as being affected by lead
exposure, particularly acute lead intoxication, in animals (Alvares et al., 1972; Scappa et
al., 1973; Chow and Cornish, 1978; Goldberg et al. , 1978; Meredith and Moore, 1975) and humans
(Alvares et al., 1975; Meredith et al., 1977.; Fischb.ein et al., 1977). Many of these studies
used altered drug detoxification rates as a functional measure of such effects. In the work
of Goldberg et al. (1978), increasing level of lead exposure in rats was correlated with both
steadily decreasing P-450 content of hepatic microsomes and decreased activity in the detoxi-
fying enzymes aniline hydroxylase and aminopyrine demethylase, while the data of Meredith and
Moore (1979) showed that continued dosing of rats with lead results in steadily decreased
microsomal P-450 content, decreased total heme content of microsomes, and increased ALA-S
activity.
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Of interest in this regard are data relating to neural tissue. Studies of organotypic
chick dorsal root ganglion in culture document that the nervous system has heme biosynthetic
capability (Whetsell et al. , 1978) and that this cell system, in the presence of lead, elabo-
rates increased porphyrinic material (Sassa et al. , 1979). Chronic administration of lead to
neonatal rats indicates that at low levels of exposure, with modest elevations of blood lead,
there is a retarded growth in the respiratory chain hemoprotein cytochrome C and disturbed
electron transport function in the developing rat cerebral cortex (Holtzman and Shen Hsu,
1976; Bull et al., 1979). These effects on the developing organism are accentuated by in-
creased whole body lead retention in both developing children and experimental animals, as
well as by higher retention of lead in brain of suckling rats compared with adults (see
Chapter 10).
Heme oxygenase activity is elevated in lead-intoxicated animals (Maines and Kappas, 1976;
Meredith and Moore, 1979) in which relatively high dosing is employed, indicating that normal
repression of this enzyme's activity is lost, further adding to heme reduction and loss of
regulatory control on the heme biosynthetic pathway.
The mechanism(s) underlying derangement of heme biosynthesis leading to ZPP accumulaton
in lead intoxication rests with either ferrochelatase inhibition, impaired mitochondrial
transport of iron, or a combination of both. Inferentially, the resemblance of lead-associ-
ated ZPP accumulation to a similar effect of iron deficiency is consistent with the unavaila-
bility of iron to ferrochelatase rather than direct enzyme inhibition, while the porphyrin
pattern seen in the congenital disorder, erythropoietic porphyria, where ferrochelatase itself
is affected, is different from that seen in lead intoxication. Similarly, lead-induced
effects on mitochondrial morphology and function are well known (Goyer and Rhyne, 1973;
Fowler, 1978), and such disturbances may include impaired iron transport (Borova et al.,
1973).
Several animal studies indicate that the effects of lead on heme formation may involve
both ferrochelatase inhibition and impaired mitochondrial transport of iron. Hart et al.
(1980) observed that acute lead exposure in rabbits is associated with a two-stage hemato-
poietic response, the earlier one resulting in significant formation of free vs. zinc proto-
porphyrin with considerable hemolysis,. and a later phase (where ZPP is formed) which otherwise
resembles the common features of lead intoxication. Subacute exposure shows more of the typi-
cal porphyrin response reported with lead. These data may suggest that acute lead poisoning
is quite different from chronic exposure in terms of the nature of hematological derangement.
Fowler et al. (1980) maintained rats on a regimen of oral lead, starting with exposure of
their dams to lead in water and continuing through 9 months after birth at levels up to 250
ppm lead. The authors observed that the activity of kidney mitochondrial ALA-S and ferro-
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chelatase, but not that of the cytosolic enzyme ALA-D, was inhibited. Ferrochelatase activity
was inhibited at 25, 50, and 250 ppm exposure levels, being 63 percent of the control values
at the 250 ppm level. Depression of state-3 respiration control ratios was observed for both
succinate and pyruvate. Ultrastructurally, the mitochondria were swollen and lysosomes were
rich in iron. In this study, reduced ferrochelatase activity was observed while there was
concomitant mitochondrial injury and disturbance of function. The accumulation of iron may be
the result of phagocytized dead mitochondria or it may represent intracellular
accumulation of iron owing to the inability of mitochondria to use the element. Ibrahim et
al. (1979) have shown that excess intracellular iron under conditions of iron overload is
stored in cytoplasmic lysosomes. The observation of disturbed mitochondrial respiration sug-
gests, as do the mitochondrial function data of Holtzman and Shen Hsu (1976) and Bull et al.
(1979) for the developing nervous system, that intramitochondrial transport of iron would be
impaired. Flatmark and Romslo (1975) demonstrated that iron transport in mitochondria is
energy linked and requires an intact respiration chain at the level of cytochrome C, whereby
iron (III) on the C-side of the mitochondrial inner membrane is reduced before transport to
the M-side and utilization in heme formation.
The above results are particularly interesting in terms of relative tissue response.
While the kidney was affected, there was no change in blood indices of hematological derange-
ment in terms of inhibited ALA-D activity or accumulation of ZPP. This suggests that there is
a difference in dose-effect functions among different tissues, particularly with lead exposure
during development of the organism. It appears that while indices of erythropoietic effects
of lead may be more accessible, they may not be the most sensitive as indicators of heme bio-
synthesis derangement in other organs.
12.3.1.4 Other Heme-Related Effects of Lead. An increased excretion of coproporphyria in the
urine of lead workers and children with lead poisoning has long been recognized, and urinary
coproporphyrin measurement has been used as an indicator of lead poisoning. The mechanism of
such accumulation is not understood in terms of differentiating among direct enzyme inhibi-
tion, accumulation of substrate secondary to inhibition of heme formation, or impaired move-
ment of the coproporphyrin intramitochondrially. Excess coproporphyrin excretion differs as
an indicator of lead exposure from EP accumulation in that the former is a measure of ongoing
lead intoxication without the lag in response seen with EP (Piomelli and Graziano, 1980).
In lead intoxication, there is an accumulation of porphobilinogen with elevated excration
in- urine, owing to inhibition by lead of the enzyme uroporphyrinogen URO-I-svnthetase (Piper
and Tephly, 1974). hi vitro studies of Piper and Tephly.(1974) using rat and human erythro-
cyte and liver preparations indicate that it is the erythrocyte URO-I-synthetase in both rats
and humans that is sensitive to the inhibitory effect of lead; activity of the hepatic enzyme
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is relatively insensitive. Significant inhibition of the enzyme's activity occurs at 5 pM
_ 4
lead with virtually total inhibition of activity in human red cell hemolysates at 10 M. Ac-
cording to Piper and van Lier (1977), the lower sensitivity of hepatic URO-I-synthetase activ-
ity to lead is due to a protective effect afforded by a pteridine derivative, pteroylpolyglu-
tamate. It appears that the protection does not occur through lead chelation, since hepatic
ALA-D activity was reduced in the presence of lead. The studies of Piper and Tephly (1974)
indicate that it is inhibition of URO-I-synthetase in erythroid tissue or erythrocytes that
accounts for the accumulation of its substrate, porphobilinogen.
12.3.2 Effects of Lead on Erythropoiesis and Erythrocyte Physiology
12.3.2.1 Effects of Lead on Hemoglobin Production. Anemia is a manifestation (sometimes an
early one) of chronic lead intoxication. Typically, the anemia is mildly hypochromic and usu-
ally normocytic. It is associated with reticulocytosis, owing to shortened cell survival, and
the irregular presence of basophilic stippling. Its genesis lies in both decreased hemoglobin
production and increased rate of erythrocyte destruction. Not only is anemia commonly seen in
children with lead poisoning, but it appears to be more severe and frequent among those with
severe lead intoxication (World Health Organization, 1977; National Academy of Sciences, 1972;
Lin-Fu, 1973; Betts Gt al., 1973).
While the anemia associated with lead intoxication in children shows features of iron-
deficiency anemia, there are differences in cases of severe intoxication. These differences
include reticulocvtosis, basophilic stippling, and a significantly lower total iron binding
capacity (T1BC). These latter features suggest that iron-deficiency anemia in young children
is exacerbated by lead. The reverse is also true.
In young children, iron deficiency occurs at a significant rate, based on national
(Mahaffey and Michael son, 1980) and regional (Owen and Lippman, 1977) surveys and is known to
be correlated with increased lead absorption in humans (Yip et al., 1981; Chisolm, 1981;,
Watson et al., 1980; Szold, 1974; Watson et al., 1958) and animals (Hamilton, 1978; Barton et
al., 1978; Mahaffey-Six and Goyer, 1972). Hence, prevalent iron deficiency can be seen to
potentiate the effects of lead in reduction of hemoglobin by both increasing lead absorption
and exacerbating the degree of anemia'.
Also in young children, there is a negative correlation between hemoglobin level and
blood lead levels (Adebonojo, 1974; Rosen et al. , 1974; Betts et al. , 1973; Pueschel et al. ,
1972). These studies generally involvea children under 6 years of age where iron deficiency
may have been a factor. In adults, a negative correlation at blood lead values usually below
80 (jg/dl has been observed (Grandjean, 1979; Li lis et al. , 1978; Roels et al., 1975a; Wada,
1976), while several studies did not report any relationship below 80 |jg/dl (Valentine et al.,
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1982; Roels et al., 1979; Ramirez-Cervantes et al., 1978). In adults, iron deficiency would
be expected to play less of a role in this relationship; Lilis et al. (1978) reported that the
significant correlation between lead in blood and hemoglobin level was observed in workers
where serum iron and TIBC were indistinguishable from controls.
The blood lead threshold for effects on hemogloblin has not been conclusively estab-
lished. In children, this value appears to be about 40 |jg/dl (World Health Organization,
1977), which is somewhat lower than in adults (Adebonojo, 1974; Rosen et al., 1974; Betts et
al., 1973; Pueschel et al., 1972). Tola et al. (1973) observed no effect of lead on new work-
ers until the blood lead had risen to a value of 50 pg/dl after about 100 days. The regres-
sion analysis data of Grandjean (1979), Lilis et al. (1978), and Wada (1976) show persistence
of the negative correlation of blood lead and hemoglobin below 50 pg/dl. Human population
dose-response data for the lead-hemoglobin relationship are limited. For lead workers, Bake,'
et al. (1979) have calculated the corresponding dose-response (<14.0 g Hb/dl): 5 percent at
blood lead of 40-59 pg/dl; 14 percent at blood lead of 60-79 pg/dl; and 36 percent at values
above 80 (jg/dl. In 202 lead workers, Grandjean (1979) noted the following percentage of
workers having a hemoglobin level below 14.4 g/dl as a function of blood lead: <25 pg/dl, 17
percent; 25-60 }jg/d 1, 26 percent; >60 pg/dl, 45 percent.
The underlying mechanisms of lead-associated anemia appear to be a combination of reduced
hemoglobin production and shortened erythrocyte survival because of direct cell damage. Ef-
fects of lead on hemoglobin production, furthermore, rest with disturbances of both heme and
globin biosynthesis.
Biosynthesis of globin, the protein moiety of hemoglobin, also appears to be inhibited in
lead exposure (Dresner et al. , 1982; Wada et al., 1972; White and Harvey, 1972; Kassenaar et
al., 1957). White and Harvey (1972) reported a decrease of globin synthesis in reticulocytes
j_n vitro in the presence of lead at levels as low as 1.0 pM, corresponding to a blood lead
level of 20 |jg/dl. These data are in accord with the observation of Dresner et al. (1982),
who noted a reduced globin synthesis (76 percent of controls) in rat bone marrow suspensions
exposed to 1.0 pM lead. White and Harvey (1972) also noted that there was a decreased synthe-
sis of alpha chains vs. beta chains.
Disturbance of globin biosynthesis is a consequence of lead's effects on heme formation
since cellular heme regulates protein synthesis in erythroid cells (Levere and Granick, 1967)
and regulates the translation of globin messenger RNA (Freedman and Rosman, 1976). The dis-
turbance in the translation of mRNA in erythroid tissue may also reflect the effect of lead on
pyrimidine metabolism.
12.3.2.2 Effects of Lead on Erythrocyte Morphology and Survival. It is clear that there is a
hemolytic component to lead-induced anemia in humans owing to shortened erythrocyte survival,
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and the various aspects of this effect have been reviewed by Waldron (1966), Goldberg (1968),
Moore et a "I. (1980), Valentine and Paglia (1980), and Angle and Mclntire (1982).
The relevant studies of shortened cell life with lead intoxication include observations
of the behavior of red cells to mechanical and osmotic stress under _i_n vivo and i_n vitro con-
ditions. Waldron (1966) has discussed the frequent reports of increased mechanical fragility
of erythrocytes from lead-poisoned workers, beginning with the work of Aub et al. (1926). In-
creased osmotic resistance of erythrocytes from subjects with lead intoxication is a parallel
finding, both i_n vivo (Aub and Reznikoff, 1924; Harris and Greenberg, 1954; Horiguchi et al.,
1974) and i_n vitro (Qazi et al., 1972; Waldron, 1964; Clarkson and Kench, 1956). Using an ap-
paratus called a coil planet centrifuge, Karai et al. (1981) studied erythrocytes of lead
workers and found significant increases in osmotic resistance; at the same time mean corpuscu-
lar volume and reticulocyte counts were not different from controls. Karai et al. suggest
that one mechanism of increased resistance involves impairment of hepatic lecithin-cholesterol
acyltransferase, leading to a build-up of cholesterol in the cell membrane. This resembles
the increased osmotic resistance seen in obstructive jaundice where increased membrane choles-
terol has been observed (Cooper et al. , 1975). Karai et al. (1981) also reported an increased
choiesterol-phospholipid ratio in lead workers' erythrocytes.
Erythrokinetic data in lead workers and children with lead-associated anemia have been
reported. Shortening of erythrocyte survival has been demonstrated by Hernberg et al. (1967a)
using tritium-labeled dif1uorophosphonate. Berk et al. (1970) used detailed isotope studies
of a subject with severe lead intoxication to determine shorter erythrocyte life span, while
Lei ken and Eng (1963) observed shortened cell survival in three of seven children. These
studies, as well as the reports of Landaw et al. (1973), White and Harvey (1972), Albaharry
(1972), and Dagg et al. (1965), indicate that hemolysis is not the exclusive mechanism of ane-
mia and that diminished erythrocyte production also plays a role.
The molecular basis for increased cell destruction with lead exposure includes the inhi-
bition by lead of the activities of the enzymes (Na+, K+)-ATPase and' pyrimidine-5'-nucleoti-
dase. Erythrocyte membrane (Na , K+)-ATPase is a sulfhydryl enzyme and inhibition of its ac-
tivity by lead has been well documented (Raghavan et al., 1981; Secchi et al., 1968; Hasan et
al., 1967; Hernberg et al., 1967b). In the study of Raghavan et al. (1981), enzyme activity
was inversely correlated with membrane lead content (p <0.001) in lead workers with or without
symptoms of overt lead toxicity, while correlation with whole blood lead was poor. With en-
zyme inhibition, there is irreversible loss of potassium ion from the cell with undisturbed
input of sodium into the cell, resulting in a relative increase in sodium. Since the cells
"shrink," there is a net increase in sodium concentration, which likely results in increased
mechanical fragility and cell lysis (Moore et al., 1980).
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Both with lead exposure and in subjects with a genetic deficiency of the enzyme pyrimi-
dine-5'~nucleotidase, activity is reduced, leading to impaired phosphorolysis of the nucleo-
tides cytidine and uridine phosphate, which are then retained in the cell, causing interfer-
ence with the conservation of the purine nucleotides necessary for cellular energetics (Angle
and Mclntire, 1982; Valentine and Paglia, 1980). A more detailed discussion of lead's inter-
action with this enzyme is presented in Section 12.3.2.3.
In a series of studies dealing with the hemolytic relationship of lead and vitamin E
deficiency in animals, Levander et al. (1980) observed that lead exposure exacerbates the
experimental hemolytic anemia associated with vitamin E deficiency by enhancing mechanical
fragility, i.e., retarded cell deformabi1ity. These workers note that vitamin E deficiency is
seen with children having elevated blood lead levels, especially subjects having glucose-6-
phosphate dehydrogenase (G-6-PD) deficiency, indicating that the synergistic relationship seen
in animals may exist in humans.
Glutathione is a necessary factor in erythrocyte function and structure. In workers ex-
posed to lead, Roels et al. (1975a) found that there is a moderate but significant decrease in
red cell glutathione compared with controls. This appears to reflect lead-induced impairment
of glutathione synthesis.
12.3.2.3 Effects of Lead on P.yrimidine-51-Nucleotidase Activity and Erythropoietic Pyrimidine
Metabolism. The presence in lead intoxication of basophilic stippling and an anemia of hemo-
lytic nature is similar to what is seen in subjects having a congenital deficiency of
pyrimidine-5'-nucleotidase (Py-5-N), an enzyme mediating the phosphorolysis of the pyrimidine
nucleotides, cytidine and uridine phosphates. With inhibition these nucleotides accumulate in
the red cell or reticulocyte, there is a retardation of ribonuclease-mediated ribosomal RNA
catabolism in maturing cells, and the resulting accumulation of aggregates of incompletely de-
graded ribosomal fragments accounts for the phenomenon of basophilic stippling.
In characterizing the enzyme Py-5-N, Paglia and Valentine (1975) observed that its
activity was particularly sensitive to inhibition by certain metals, particularly lead,
prompting further investigation of the interplay between lead intoxication and disturbances of
erythropoietic pyrimidine metabolism. Paglia et al. (1975) observed that in subjects occupa-
tionally exposed to lead but having no evidence of basophilic stippling or significant fre-
quency of anemia, the activity of Py-5-N was reduced to about 50 percent of control subjects
and was most impaired in one worker with anemia, about 11 percent of normal. There was a
general inverse correlation between enzyme activity and blood lead level. In this report,
normal erythrocytes incubated with varying levels of lead showed detectable inhibition at
levels as low as 0.1-1.0 pM, with consistent 50 percent inhibition at about 10 |jM. Subse-
quently, these investigators (Valentine et al. , 1976) observed that an individual with severe
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lead intoxication had an 85 percent decrease, in Py-5-N activity, basophilic stippling, and
accumulation of.pyrimidine nucleotides, mainly cytidine triphosphate. Since these parameters
approached values seen in the congenital deficiency of Py-5-N, the data suggest a common eti-
ology for the hemolytic anemia and stippling in both lead poisoning and the congenital dis-
order.
Several other reports of investigations of Py-5-N activity and pyrimidine nucleotide
levels in lead workers have been published (Paglia et al., 1977; Buc and Kaplan, 1978). In
nine workers having overt lead intoxication and blood lead values of 80-160 (jg/dl, Py-5-N
activity was significantly inhibited while the pyrimidine nucleotides comprised 70-80 percent
of the total nucleotide pool, in contrast to trace levels in unexposed individuals (Paglia
et al., 1977). In the study of Buc and Kaplan (1978), lead workers with or without overt lead
intoxication all showed reduced activity of Py-5-N, which was inversely correlated with blood
lead when the activity was expressed as a ratio with G-6-PD activity to accommodate an
enhanced population of young cells due to hemolytic anemia. Enzyme inhibition was observed
even when other indicators of lead exposure were negative.
Angle and Mclntire (1978) observed that in 21 children 2-5 years old, with blood lead
levels of 7-80 (jg/dl, there was a negative linear correlation between Py-5-N activity and
blood lead (r = -0.60, p <0.01). Basophilic stippling was only seen in the child with the
highest blood lead value and only two subjects had reticulocytosis. While adults tended to
show a threshold for inhibition of Py-5-N at a blood lead level of 44 pg/dl or higher,
there was no clear response threshold in these children. In a related investigation with 42
children 1-5 years old having blood lead levels of <10 to 72 (jg/dl, Angle et al. (1982) noted
that there was: (1) an inverse correlation (r = -0.64, p <0.001) between the logarithm of
Py-5-N activity and blood lead; (2) a positive log-log correlation between cytidine phosphates
and blood lead in 15 of these children (r = 0.89, p <0.001); and (3) an inverse relationship
in 12 subjects between log of enzyme activity and cytidine phosphates (r = -0.796, p'<0.001).
Study of the various relationships at low levels was made possible by the use of anion-
exchange high performance liquid chromatography. In these studies, there was no threshold of
effects of lead on either enzyme activity or cell nucleotide content even below 10 pg/dl.
Finally, there was a significant positive correlation of pyrimidine nucleotide accumulation
and the accumulation of ZPP.
In subjects undergoing therapeutic chelation with EDTA, Py-5-N activity increased, while
there was no effect on pyrimidine nucleotides (Swanson et al., 1982), indicating that the py-
rimidine accumulation is associated with the reticulocyte.
The metabolic significance of Py-5-N activity inhibition and nucleotide accumulation with
lead exposure is derived from its effects on red cell membrane stability and survival by al-
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teration of cellular energetics (Angle and Mclntire, 1982), leading to cell lysis. A further
consequence may be feedback inhibition of mRNA and protein synthesis, in that denatured mRNA
may alter globin mRNA or globin chain synthesis. It was noted earlier that disturbances in
heme production also affect the translation of globin mRNA (Freedman and Rosman, 1976).
Hence, these two lead-associated disturbances of erythroid tissue function potentiate the ef-
fects of each other.
12.3.3 Effects of Alkyl Lead on Heme Synthesis and Erythropoiesis
In the Section 10.7 discussion of alkyl lead metabolism, it was noted that transforma-
tions of tetraethyl and tetramethyl lead i_n vivo result in generation not only of neurotoxic
trialkyl lead metabolites but also of products of further dealkylation, including inorganic
lead. One would therefore expect alkyl lead exposure to be associated with, in addition to
other effects, some of those effects classically related to inorganic lead exposure.
Chronic gasoline sniffing has been recognized as a problem habit among children in rural
or remote areas (Boeckx et al., 1977; Kaufman, 1973). When such practice involves leaded gas-
oline, the potential exists for lead intoxication. Boeckx et al. (1977) conducted surveys of
children in remote Canadian communities in regard to the prevalence of gasoline sniffing and
indications of chronic lead exposure. In one group of 43 children, all of whom sniffed gaso-
line, mean ALA-D activity was only 30 percent that of control subjects, with a significant
correlation between the decrease in enzyme activity and the frequency of sniffing. A second
survey of 50 children revealed similar results. Two children having acute lead intoxication
associated with gasoline sniffing showed markedly lowered hemoglobin, elevated urinary ALA,
and. elevated urinary coproporphyrin. The authors estimated that more than half of disadvan-
taged children residing in rural or remote areas of Canada may have chronic lead exposure via
this habit, consistent with the estimate of Kaufman (1973) of 62 percent for children in rural
American Indian communities in the Southwest.
Robinson (1978) described two cases of pediatric lead poisoning due to habitual gasoline
sniffing, one of which showed basophilic stippling. Hansen and Sharp (1978) reported that a
young adult with acute lead poisioning due to chronic gasoline sniffing not only had basophi-
lic stippling, but a 6-fold increase in urinary ALA, elevated urinary coproporphyria and an
EP level about 4-fold above normal. In the reports of Boeckx et al. (1977) and Robinson
(1978), increased lead levels were measured in urine in the course of chelation therapy, indi-
cating that significant amounts of inorganic lead were present.
12.3.4 The Interrelationship of Lead Effects on Heme Synthesis and the Nervous System
Lead-associated disturbances in heme biosynthesis as a possible factor in the neurologi-
cal effects of lead have been studied because of (1) the recognized similarity between
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classic signs of lead neurotoxicity and many, but not all, of the neurological components of
the congenital disorder, acute intermittent porphyria, and (2) some unusual aspects of lead
neurotoxicity. Both acute attack porphyria and lead intoxication with neurological symptoms
are variably accompanied by abdominal pain, constipation, vomiting, paralysis or paresis,
demyelination, and psychiatric disturbances (Dagg et al., 1965; Moore et al., 1980; Silbergeld
and Lamon, 1980). According to Angle and Mclntire (1982), some of the unusual features of
lead neurotoxicity are consistent with deranged hematopoiesis: (1) a lag in production of
neurological symptoms; (2) the incongruity of early deficits in affective and cognitive func-
tion with the regional distribution of lead in the brain; and (3) a better correlation of neu-
robehavioral deficits with erythrocyte protoporphyrin than with blood lead. Item 3, it should
be noted, is not universally the case (Hammond et al., 1980; Spivey et al., 1979).
While the nature and pattern of the derangements in heme biosynthesis in acute attack
porphyria and lead intoxication differ in many respects, both involve excessive systemic ac-
cumulation and excretion of ALA, and this common feature has stimulated numerous studies of a
connection between hemato- and neurotoxicity. Hi vitro data (Whetsell et al., 1978) have
shown that the nervous system is capable of heme biosynthesis in the chick dorsal root gan-
glion. Sassa et al. (1979) found that the presence of lead in these preparations increases
production of porphyrinic material, i.e., there is disturbed heme biosynthesis with accumula-
tion of one or more porphyrins and, presumably, ALA. Millar et al. (1970) reported inhibited
brain ALA-D activity in suckling rats exposed to lead, while Silbergeld et al. (1982) observed
similar inhibition in brains of adult rats acutely exposed to lead. In the latter study,
chronic lead exposure was also associated with a moderate increase in brain ALA without inhi-
bition of ALA-D, suggesting an extra-neural source of the heme precursor. Moore and Meredith
(1976) administered ALA to rats and observed that exogenous ALA can penetrate the blood-brain
barrier. These reports suggest that ALA can either be generated i_n situ in the nervous system
or can enter the nervous system from elsewhere.
Neurochemical investigations of ALA action in the nervous system have evaluated interac-
tions with the neurotransmitter gamma-aminobutyric acid (GABA). Interference with GABAergic
function by exposure to lead is compatible with such clinical and experimental signs of lead
neurotoxicity as excitability, hyperactivity, hyperreactivity, and, in severe lead intoxica-
tion, convulsions (Silbergeld and Laraon, 1980). Of particular interest is the similarity in
chemical structure between ALA and GABA, which differ only in that ALA has a carbonyl group on
the alpha carbons, and GABA has a carbonyl group on the beta carbon.
While chronic lead exposure appears to alter neural pathways involving GABA function
(Piepho et al., 1976; Silbergeld et al., 1979), this effect cannot be duplicated i_n vitro
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using various levels of lead (Silbergeld et a 1. , 1980). This suggests that lead does not
impart the effect by direct interaction or an intact multi-pathway system is required. In
vitro studies (Silbergeld et al. , 1980a; Nicoll, 1976) demonstrate that ALA can displace GABA
from synaptosomal membranes associated with synaptic function of the neurotransmitter on the
GABA receptor, but that it is less potent than GABA by a factor of 10a-104, suggesting that
levels of ALA achieved even with severe intoxication may. not be effectively competitive.
A more significant role for ALA in lead neurotoxicity may well be related to the observa-
tion that GABA release is subject to negative feedback control through presynaptic receptors
on GABAergic terminals (Snodgrass, 1978; Mitchell and Martin, 1978). Brennan and Cantrill
(1979) found that ALA inhibits K -stimulated release of GABA from pre-loaded synaptosomes by
functioning as an agonist at the presynaptic receptors. The effect is evident at 21.0 pM ALA,
while the inhibiting effect is abolished by the GABA antagonists bicuculline and picrotoxin.
Of interest also is the demonstration (Silbergeld et al., 1980a) that synaptosomal release of
preloaded ^H-GABA, both resting and K -stimulated, is also inhibited in animals chronically
treated with lead, paralleling the i_n vitro data of Brennan and Cantrill (1979) using ALA.
Silbergeld et al. (1982) described the comparative effects of lead and the agent succi-
nylacetone, given acutely or chronically to adult rats, in terms of disturbances in heme syn-
thesis and neurochemical indices. Succinylacetone, a metabolite that can be isolated from the
urine of patients with hereditary tyrosinemia (Lindblad et al. , 1977) is a potent inhibitor of
heme synthesis, exerting its effect by ALA-D inhibition and derepression of ALA synthetase
(Tschudy et al., 1980, 1983). Both agents, i_n vivo, showed significant inhibition of high
affinity Na+-dependent uptake of 14C-GABA by cortex, caudate, and substantia nigra. However,
neither agent affected GABA uptake, in vitro. Similarly, both chronic or acute lead treatment
and chronically administered succinylacetone reduced the seizure threshold to the GABA antago-
nist, picrotoxin. While these agents may involve entirely different mechanisms of toxicity to
the GABAergic pathway, the fact remains that two distinct potent inhibitors of the heme bio-
synthetic pathway and ALA-D, which do not impart a common neurochemical effect by direct
action on a neurotransmitter function, have a common neurochemical action i_n vivo.
Human data relating the hemato- and neurotoxicity of lead to each other are limited.
Hammond et al. (1980) reported that the best correlates of the frequency of neurological symp-
toms in 28 lead workers were urinary and plasma ALA, which showed a higher correlation than
EP. These data support a connection between heme biosynthesis impairment and neurological
effects of ALA. Of interest here is the clinical report of Lamon et al. (1979) describing the
effect of hematin [Fe(III)-heme] given parenterally to a subject with lead intoxication. Over
the course of treatment (16 days), urinary coproporphyrin and ALA significantly dropped
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and such neurological symptoms as lower extremity numbness and aching diminished. Blood lead
levels were not altered during the treatment. Although remission of symptoms in this subject
may have been spontaneous, the outcome parallels that observed in hematin treatment of sub-
jects with acute porphyria in terms of similar reduction of heme indicators and relief of
symptoms (Lamon et al., 1979).
Taken collectively, all of the available data strongly suggest that ALA, formed in situ
or entering the brain, is neurotoxic to GABAergic function in particular. It inhibits
K -stimulated GABA release by interaction with presynaptic receptors, where ALA appears to be
particularly potent at very low levels, based on i_n vitro results. As described in the sec-
tion on heme biosynthesis, lead can affect both cellular respiration and cytochrome C levels
in the nervous system of the developing rat, which may contribute to manisfestation of some
symptoms of lead neurotoxicity. Hence, more than the issue of ALA neurotoxicity should be
considered in assessing connections between lead-induced hemato- and neurotoxicity.
12.3.5 Summary and Overview
12.3.5.1 Lead Effects on Heme Biosynthesis. Lead effects on heme biosynthesis are well known
because of both their prominence and numerous studies of such effects in humans and experimen-
tal animals. The process of heme biosynthesis starts with glycine and succinyl-coenzyme A,
proceeds through formation of protoporphyrin IX, and culminates with the insertion of divalent
iron into the porphyrin ring, thus forming heme. In addition to being a constituent of hemo-
globin, heme is the prosthetic group of many tissue hemoproteins having variable functions,
such as myoglobin, the P-450 component of the mixed function oxygenase system, and the cyto-
chromes of cellular energetics. Hence, disturbance of heme biosynthesis by lead poses the
potential for multi-organ toxicity.
At present, steps in the heme synthesis pathway that have been best studied in regard to
lead effects involve three enzymes: (1) stimulation of mitochondrial delta-aminolevulinic
acid synthetase (ALA-S), which mediates formation of delta-aminolevulinic acid (ALA); (2) di-
rect inhibition of the cytosolic enzyme, delta-aminolevulinic acid dehydrase (ALA-D), which
catalyzes formation of porphobilinogen from two units of ALA; and (3) inhibition of insertion
of iron (II) into protoporphyrin IX to form heme, a process mediated by ferrochelatase.
Increased ALA-S activity has been found in lead workers as well as lead-exposed animals,
although the converse, an actual decrease in enzyme activity, has also been observed in
several experimental studies using different exposure methods. It appears, then, that enzyme
activity increase via feedback derepression or activity inhibition may depend on the nature of
the exposure. Using rat liver cells in culture, ALA-S activity was stimulated i_n vitro at
levels as low as 5.0 or 1.0 fjg Pb/g preparation. The increased activity was seen to be due
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to biosynthesis of more enzyme. The threshold for lead stimulation of ALA-S activity in
humans, based on a study using leukocytes from lead workers, appears to be about 40 |jg Pb/dl.
The generality of this apparent threshold to other tissues depends on how well the sensitivity
of leukocyte mitochondria mirrors that in other systems. The relative impact of ALA-S activi-
ty stimulation on ALA accumulation at lower lead exposure levels appears to be much less than
the effect of ALA-D activity inhibition, to the extent that at ALA-D activity is significantly
depressed at 40 (jg/dl blood lead, where ALA-S activity only begins to be affected.
Erythrocyte ALA-D activity is very sensitive to lead inhibition, which is reversed by re-
activation of the sulfhydryl group with agents such as dithiothreitol, zinc, or zinc plus glu-
tathione. Zinc levels that achieve reactivation, however, are well above physiological
levels. Although zinc appears to offset inhibitory effects of lead observed in human eryth-
rocytes i_n vitro and in animal studies, lead workers exposed to both zinc and lead do not show
significant changes in the relationship of ALA-D activity to blood lead compared with just
lead exposure; nor dees the range of physiological zinc in non-exposed subjects affect the
activity. In contrast zinc deficiency in animals significantly inhibits activity, with con-
comitant accumulation of ALA in urine. Since zinc deficiency has also been demonstrated to
increase lead absorption, the possibility exists for dual effects of such deficiency on ALA-D
activity: (1) a direct effect on activity due to reduced zinc availability; and (2) increased
lead absorption leading to further inhibition of activity.
Erythrocyte ALA-D activity appears to be inhibited at virtually all blood lead levels
measured so far, and any threshold for this effect in either adults or ch'ildren remains to be
determined. A further measure of this enzyme's sensitivity to lead is a report that rat bone
marrow suspensions show inhibition of ALA-D activity by lead at a level of 0.1 |jg/g suspen-
sion. Inhibition of ALA-D activity in erythrocytes apparently reflects a similar effect in
other tissues. Hepatic ALA-D activity was inversely correlated in lead workers with both
erythrocyte activity as well as blood lead levels. Of significance are experimental animal
data showing that (1) brain ALA-D activity is inhibited with lead exposure and (2) this inhi-
bition appears to occur to a greater extent in developing vs; adult animals, presumably re-
flecting. greater.retention of lead in developing animals. In the avian brain, cerebellar
ALA-D activity is affected to a greater extent than that of the cerebrum and, relative to lead
concentration^ shows inhibition approaching that occurring in erythrocytes.
Lead inhibition of- ALA-D activity is reflected by elevated levels of its substrate, ALA,
in blood, urine, and soft tissues. In one study, increases in urinary ALA were preceded by a
rise in circulating levels of the metabolite. Blood ALA was elevated at all corresponding
blood lead values down to the lowest determined (18 |jg/dl), while urinary ALA increased expo-
nentially with blood ALA.
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Urinary ALA is employed extensively as an indicator of excessive lead exposure in lead
workers. The value of this measurement in pediatric screening, however, is diagnostically
limited if only spot urine collection is done, more satisfactory data being obtainable with
24-hour collections. Numerous independent studies document a direct correlation between blood
lead and the logarithm of urinary ALA in human adults and children; the threshold for urinary
ALA increases is commonly accepted as being 40 (jg/dl. However, several studies of lead
workers indicate that the correlation of urinary ALA with blood lead continues below this
value, and one study found that the slope of the dose-effect curve in lead workers is depen-
dent upon level of exposure.
The health significance of lead-inhibited ALA-D activity and accumulation of ALA at lower
lead exposure levels is controversial, to the extent that the "reserve capacity" of ALA-D
activity is such that only the level of inhibition associated with marked accumulation of the
enzyme's substrate, ALA, in accessible indicator media may be significant. However, it is not
possible to quantify, at lower levels of lead exposure, the relationship of urinary ALA to
target tissue levels nor to relate the potential neurotoxicity of ALA at any accumulation
level to levels in indicator media; i.e., the blood lead threshold for neurotoxicity of ALA
may be different from that associated with increased urinary excretion of ALA.
Accumulation of protoporphyrin in erythrocytes of lead-intoxicated individuals has been
recognized since the 1930s, but it has only recently been possible to quantitatively assess
the nature of this effect via development of sensitive, specific microanalysis methods. Accu-
mulation of protoporphyrin IX in erythrocytes results from impaired placement of iron (II) in
the porphyrin moiety to form heme, an intramitochondrial process mediated by ferrochelatase.
In lead exposure, the porphyrin acquires a zinc ion in lieu of native iron, thus forming zinc
protoporphyrin (ZPP), and is tightly bound in available heme pockets for the life of the ery-
throcytes. This tight sequestration contrasts with the relatively mobile non-metal, or free,
protoporphyrin (FEP) accumulated in the congenital disorder erythropoietic protoporphyria.
Elevation of erythrocyte ZPP has been extensively documented as being exponentially cor-
related with blood lead in' children and adult lead workers and is presently considered one of
the best indicators of undue lead exposure. Accumulation of ZPP only-occurs in erythrocytes
formed during lead's presence in erythroid tissue, resulting in a lag of at least several
weeks before such build-up can be measured. The level of such accumulation in erythrocytes of
newly employed lead workers continues to increase when blood lead has already reached a pla-
teau. This influences the relative correlation of ZPP and blood lead in workers with short
exposure histories. In individuals removed from occupational exposure, the ZPP level in blood
declines much more slowly than blood lead, even years after removal from exposure or after a
drop in blood lead. Hence, ZPP level appears to be a more reliable indicator of continuing
intoxication from lead resorbed from bone.
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- The threshold for detection of lead-induced ZPP accumulation is affected by the relative
spread of blood lead and corresponding ZPP values measured. In young children (< 4 yr old),
the ZPP elevation associated with iron-deficiency anemia must also be considered. In adults,
numerous studies indicate that the blood lead threshold for ZPP elevation is about 25-30
Mg/dl. In children 10-15 years old, the threshold is about 16 pg/dl; in this age group, iron
deficiency is not a factor. In one study, children over 4 years old showed the same thresh-
old, 15.5 ng/dl, as a second group under 4 years old, indicating that iron deficiency was not
a factor in the study. Fifty percent of the children had significantly elevated EP levels (2
standard deviations above reference mean EP) at 25 pg/dl blood lead.
At blood lead levels below 30-40 pg/dl, any assessment of the ZPP-blood lead relationship
is strongly influenced by the relative analytical proficiency for measurement of both blood
lead and EP. The types of statistical analyses used are also important. In a recent detailed
statistical study involving 2004 children, 1852 of whom had blood lead values below 30 pg/dl,
segmental line and probit analysis techniques were employed to assess the dose-effect thres-
hold and dose-response relationship. An average blood lead threshold for the effect using
both statistical techniques yielded a value of 16.5 pg/dl for either the full group or those
subjects with blood lead below 30 ^ig/dl. The effect of iron deficiency was tested for and
removed. Of particular interest was the finding that the blood lead values corresponding to
EP elevations more than 1 or 2 standard deviations above the reference mean in 50 percent of
the children were 28.6 or 35.7 pg Pb/dl, respectively. Hence, fully half of the children had
significant elevations of EP at blood lead levels around 30 jjg/dl, the currently accepted cut-
off value for undue lead exposure. From various reports, children and adult females appear to
be more sensitive to lead effects on EP accumulation at any given blood lead level, with
children being somewhat more sensitive than adult females.
Lead effects on heme formation are not restricted to the erythropoietic system. Recent
studies show that the reduction of serum l,25-(0H)liD seen with even low level lead exposure is
apparently the result of lead inhibition of the activity of renal 1-hydroxylase, a cytochrome
P-450 mediated enzyme. This heme-containing protein, cytochrome P-450 (an integral part of
the hepatic mixed function oxygenase system), is affected in humans and animals by lead expo-
sure, especially acute intoxication. Reduced P-450 content correlates with impaired activity
of detoxifying enzyme systems such as aniline hydroxylase and aminopyrine demethylase.
Studies of organotypic chick dorsal root ganglion in culture show that the nervous system
not only has heme biosynthetic capability but such preparations elaborate porphyrinic material
in the presence of lead. In the neonatal rat, chronic lead exposure, resulting in moderately
elevated blood lead, is associated with retarded increases in the hemoprotein, cytochrome C,
and disturbed electron transport in the developing cerebral cortex. These data parallel ef-
fects of lead on ALA-D activity and ALA accumulation in neural tissue. When both these
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effects are viewed in the toxicokinetic context of increased retention of lead in both devel-,
oping, animals and children, there is an obvious, serious potential for impaired heme-based
metabolic function in the nervous system of lead-exposed children.
As can be concluded from the above discussion, the health significance of ZPP accumula-
tion rests with the fact that it is evidence of impaired heme and hemoprotein formation in
many tissues, arising from entry of lead into mitochondria. Such evidence for reduced heme
synthesis is consistent with much data documenting lead-associated effects on mitochondria.
The relative value of the lead-ZPP relationship in erythropoietic tissue as an index of this
effect in other tissues hinges on the relative sensitivity of the erythropoietic system com-
pared with other organ systems. One study of rats exposed to low levels of lead over their
lifetime demonstrated that protoporphyrin accumulation in renal tissue was already significant
at levels of lead exposure where little change was seen in erythrocyte porphyrin levels.
Other, steps in the heme biosynthesis pathway are also known to be affected by lead, al-
though these have not been as well studied on a biochemical or molecular level. Coproporphy-
ria levels are increased in urine, reflecting active lead intoxication. Lead also affects the
activity of the enzyme uroporphyrinogen-I-synthetase, resulting in an accumulation of its sub-
strate, porphobilinogen. The erythrocyte enzyme has been reported to be much more sensitive
to lead than the hepatic species, presumably accounting for much of the accumulated substrate.
Ferrochelatase is an intramitochondrial enzyme, and impairment of its activity, either di-
rectly by lead or via impairment of iron transport to the enzyme, is evidence of the presence
of lead in mitochondria.
12.3.5.2 Lead Effects on Erythropoiesis and Erythrocyte Physiology. Anemia is a manifesta-
tion of chronic lead intoxication, being characterized as mildly hypochromic and usually nor-
mocyte. It is associated with reticulocytosis, owing to shortened cell survival, and the
variable presence of basophilic stippling. Its occurrence is due to both decreased production
and increased rate of destruction of erythrocytes. In young children (< 4 yr old) iron
deficiency anemia is exacerbated by lead effects, and vice versa. Hemoglobin production is
negatively correlated with blood lead in young children, where iron deficiency may be a con-
founding factor, as well as in lead workers. In one study, blood lead values that Were
usually below 80 jjg/dl were inversely correlated with hemoglobin content. In these subjects,
no iron deficiency was found. The blood lead threshold for reduced hemoglobin content is
about 50 ng/dl in adult lead workers and somewhat lower (40 |jg/dl) in children.
The mechanism of lead-associated anemia appears to be a combination of reduced hemoglobin
production and shortened erythrocyte survival because of direct cell injury. Lead effects on
hemoglobin production involve disturbances of both heme and globin biosynthesis. The hemoly-
tic component to lead-induced anemia appears to be due to increased cell fragility and in-
creased osmotic resistance. In one study using rats, the hemolysis associated with vitamin E
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deficiency, via reduced cell deformability, was exacerbated by lead exposure. The molecular
basis for increased cell destruction rests with inhibition of (Na+, K+)-ATPase and pyrimidine-
5'~nucleotidase. Inhibition of the former enzyme leads to cell "shrinkage" and inhibition of
the latter results in impaired pyrimidine nucleotide phosphorolysis and disturbance of the
activity of the purine nucleotides necessary for cellular energetics.
12.3.5.3 Effects of Alkyl Lead Compounds on Heme Biosynthesis and Erythropoiesis. Tetraethyl
lead and tetramethyl lead, components of leaded gasoline, undergo transformation i_n vivo to
neurotoxic trialky1 metabolites as well as further conversion to inorganic lead. Hence, one
might anticipate that exposure to such agents may show effects commonly associated with inor-
ganic lead in terms of heme synthesis and erythropoiesis. Various surveys and case reports
show that the habit of sniffing leaded gasoline is associated with chronic lead intoxication
in children from socially deprived backgrounds in rural or remote areas. Notable in these
subjects is evidence of impaired heme biosynthesis as indexed by significantly reduced ALA-D
activity. In several case reports of frank lead toxicity from habitual leaded gasoline
sniffing, effects such as basophilic stippling in erythrocytes and significantly reduced hemo-
globin have also been noted.
12.3.5.4 Relationships of Lead Effects on Heme Synthesis to Neurotoxicity. The role of lead-
associated disturbances of heme biosynthesis as a possible factor in neurological effects of
lead is of considerable interest because of: (1) similarities between classical signs of lead
neurotoxicity and several neurological components of the congenital disorder, acute intermit-
tent porphyria; and (2) some of the unusual aspects of lead neurotoxicity. There are two
possible points of connection between lead effects on heme biosynthesis and the nervous
system. Associated with both lead neurotoxicity and acute intermittent porphyria is the
common feature of excessive systemic accumulation and excretion of ALA. Secondly, lead neuro-
toxicity reflects, to some degree, impaired synthesis of heme and hemoproteins involved in
crucial cellular functions. Available information indicates that ALA levels are elevated in
the brain of lead-exposed animals, arising via j_n situ inhibition of brain ALA-D activity or
via transport to the brain after formation in other tissues. ALA is known to traverse the
blood-brain barrier. Hence, ALA is accessible to, or formed within, the brain during lead
exposure and may express its neurotoxic potential.
Based on various in vitro and j_n vivo data obtained in the context of neurochemical
studies of lead neurotoxicity, it appears that ALA can readily play a role in GABAergic func-
tion, particularly inhibiting release of the neurotransmitter GABA from presynaptic receptors,
where ALA appears to be very potent even at low levels. In an i_n vitro study, agonist behav-
ior by ALA was demonstrated at levels as low as 1.0 pM ALA. This ijn vitro observation sup-
ports results of a study using lead-exposed rats in which there was reported inhibition of
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both resting and K+-stimulated release of preloaded ^H-GABA from nerve terminals. Further
evidence for an effect of some agent other than lead acting directly is the observation that
i_n vivo effects of lead on neurotransmitter function cannot be duplicated with in vitro pre-
parations to which lead is added. Human .data on lead-induced associations between disturbed
heme synthesis and neurotoxicity, while limited, also suggest that ALA may function as a neu-
rotoxicant.
The connection of impaired heme and hemoprotein synthesis in the neonatal rat brain was
noted earlier, in terms of reduced cytochrome C production and impaired operation of the cyto-
chrome C respiratory chain. Hence, one might expect that such impairment would be most promi-
nent in areas of relatively greater eel 1ularization, such as the hippocampus. As noted in
Chapter 10, these are also regions where selective lead accumulation occurs.
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12.4 NEUROTOXIC EFFECTS OF LEAD
12.4.1 Introduction
Historically, neurotoxic effects have long been recognized as being among the more severe
consequences of human lead exposure (Tanqueral Des Planches, 1839; Stewart, 1895; Prendergast,
1910; Oliver, 1911; Blackfan, 1917). Since the early 190C's, extensive research has focused on
the elucidation of lead exposure levels associated with the induction of various types of neu-
rotoxic effects and related issues, e.g. critical exposure periods for their induction and
their persistence or reversibility. Such research, spanning more than 50 years, has provided
expanding evidence indicating that progressively lower lead exposure levels, previously accep-
ted as "safe," are actually sufficient to cause notable neurotoxic effects of lead.
The neurotoxic effects of extremely high exposures resulting in blood lead levels in ex-
cess of 80-100 (jg/dl, have been well documented—especially in regard to increased risk for
fulminant lead encephalopathy (a well-known clinical syndrome characterized by overt symptoms
such as gross ataxia, persistent vomiting, lethargy, stupor, convulsions, and coma of such
severity that immediate medical attention is required). The persistence of neurological
sequelae in cases of non-fatal lead encephalopathy has also been well established. The neuro-
toxic effects of subencephalopathic lead exposures in both human adults and childran, however,
continues to represent a major area of controversy and interest. Reflecting this, much
research during the past 10-15 years has focussed on the delineation of exposure-effect rela-
tionships for: (1) the occurrence of overt signs and symptoms of neurotoxicity in relation to
other indicators of subencephalopathic overt lead intoxication; and (2) the manifestation of
more subtle, often difficult-to-detect indications of altered neurological functions in appar-
ently asymptomatic (i.e., not overtly lead-poisoned) individuals.
The present assessment critically reviews the available scientific literature on the neu-
rotoxic effects of lead, first evaluating the results of human studies bearing on the subject
and then focusing on pertinent animal toxicology studies. The discussion of human studies is
divided into two major subsections focusing on neurotoxic effects of lead exposure in (1)
adults and (2) children. Both lead effects on the central nervous system (CNS) and the peri-
pheral nervous system (PNS) are discussed in each case. In general, only relatively brief
overview summaries are provided in regard to findings bearing on the effects of extremely high
level exposures resulting in encephalopathy or other frank signs or symptoms of overt lead in-
toxication. Studies concerning the effects of lower- level lead exposures are assessed in
more detail, especially those dealing with non-overtly lead intoxicated children. As for the
animal toxicology studies, particular emphasis is placed on the review of studies that help to
address certain important issuss raised by the human research findings, rather than attempting
an exhaustive review of all animal toxicology studies concerning the neurotoxic effects of
lead.
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12.4.2 Human Studies
Defining exposure-effect or dose-response relationships between lead and particular
neurotoxic responses in humans involves two basic steps. First, there must be an assessment
of the internal lead burden resulting from external doses of lead received via various routes
of exposure (such as air, water, food, occupational hazards, house dust, etc.). Internal lead
burdens may be indexed by lead concentrations in blood, teeth, or other tissue, or by other
biological indicators. The second step involves an assessment of the relationship of internal
exposure indices to behavioral or other types of neurophysiological responses. The difficulty
of this task is reflected by current controversies over existing data. Studies vary greatly
in the quality of design, precision of assessment instruments, care in data collection, and
appropriateness of statistical analyses employed. Many of these methodological problems are
broadly common to research on toxic agents in general and not just to lead alone.
Although epidemiological studies of lead effects have immediate environmental relevance
at the human level, difficult problems are often associated with the interpretation of the
findings, as noted in several reviews (Bornschein et al., 1980; Cowan and Leviton, 1980;
Rutter, 1980; Valciukas and Li lis, 1980; Neddleman and Landrigan, 1981. The main problems
are; (1) inadequate markers of exposure to lead; (2) insensitive measures of performance; (3)
bias in selection of subjects; (4) inadequate handling of confounding covariates; (5) inappro-
priate statistical analyses; (6) inappropriate generalization and interpretation of results;
and (7) the need for ''blind" evaluations by experimenters and technicians. Each of these pro-
blems are briefly discussed below.
Each major exposure route—food, water, air, dust, and soil--contributes to a person's
total daily intake of lead (see Chapters 7 and 11 of this document). The relative contribu-
tion of each exposure route, however, is difficult to ascertain; neurotoxic endpoint measure-
ments, therefore, are most typically evaluated in relation to one or another indicator of
overall internal lead body burden. Subjects in epidemiological studies may be misclassified
as to exposure level unless careful choices of exposure indices are made based upon the hypo-
theses to be tested, the accuracy and precision of the biological media assays, and the
collection and assay procedures employed. Chapter 9 of this document evaluates different
measures of internal exposure to lead and their respective advantages and disadvantages. The
most commonly used measure of internal dose is blood lead concentration, which varies as a
function of age, sex, race, geographic location, and exposure. The blood lead level is a use-
ful marker of current exposure but generally does not reflect cumulative body lead burdens as
we'll as lead levels in teeth. Hair lead levels, measured in some human studies, are not
viewed as reliable indicators of internal body burdens at this time. Future research may
identify a more standard exposure index, but it appears that a risk classification similar to
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that of the U.S. Centers for Disease Control (1978) in terms of blood lead and FEP levels will
continue in the foreseeable future to be the standard approach most often used for lead expo-
sure screening and evaluation. Much of the discussion below is, therefore, focused on
defining dose-effect relationships for human neurotoxic effects in terms of blood lead levels;
some ancillary information on pertinent teeth lead levels is also discussed.
The frequency and timing of sampling for internal lead burdens represent another impor-
tant factor in evaluating studies of lead effects on neurological and behavioral functions.
For example, epidemiological studies often rely on blood lead and/or erythrocyte protoporphy-
rin (EP) levels determined at a single point in time to retrospectively estimate or character-
ize internal exposure histories of study populations that may have been exposed in the past to
higher levels of lead than those indicated by a single current blood sample. Relatively few
prospective studies exist that provide highly reliable estimates of critical lead exposure
levels associated with observed neurotoxic effects in human adults or children, especially in
regard to the effects of subencephalopathic lead exposures. Some prospective longitudinal
studies on the effects of lead on early development of infants and young children (e.g.,
Bornschein, 1983) are currently in progress, but the results of these studies are not yet
available. The present assessment of the neurotoxic effects of lead in humans must, there-
fore, rely heavily on published epidemiological studies which typically provide exposure
history information of only limited value in defining exposure-effect relationships.
Key variables that have emerged in determining effects of lead on the nervous system in-
clude (1) duration and intensity of exposure and (2) age at exposure. Evidence suggest that
young organisms with developing nervous systems are more vulnerable than adults with fully
matured nervous systems. Particular attention is, therefore, accorded below to discussion of
neurotoxic effects of lead in children as a special group at risk.
Precision of measurement is a critical methodological issue, especially when research on
neurotoxicity leaves the laboratory setting. Neurotoxicity is often measured indirectly with
psychometric or neurometric techniques in epidemiological studies (Valciukas and Lilis, 1980).
The accuracy with which these tests reflect what they purport to measure (validity) and the
degree to which they are reproducible (reliability) are issues central to the science of mea-
surement theory. Many cross-sectional population studies make use of instruments that are
only brief samples of behavior thought to be representative of some relatively constant
underlying traits, such as intelligence. Standardization of tests is the subject of much
research in psychometrics. The quality and precision of specific test batteries have been
particularly controversial issues in evaluating possible effect levels for neurotoxic effects
of lead exposure in children. Table 12B (Appendix 12B) lists some of the major tests used,
together with their advantages and weaknesses. The-following review places most weight on
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results obtained with age-normed, standardized psychometric test instruments and well-
controlled, standardized nerve conduction velocity (NCV) tests. Other measures, such as reac-
tion time, finger tapping, and certain electrophysiological measures (e.g., cortical evoked
and slow-wave potentials) are potentially more sensitive indices, but are still experimental
measures whose clinical utility and psychometric properties with respect to the neuro-
behavioral toxicity of lead remain to be more fully explored.
Selection bias is a critical issue in epidemiological studies in which attempts are made
to generalize from a small sample to a large.population. Volunteering to participate in a
study and attendance at special clinics or schools are common forms of selection bias that
often limit how far the results of such studies can be generalized. These factors may need to
be balanced in lead neurotoxicity research since reference groups are often difficult to find
because of the pervasiveness of lead in the environment and the many non-lead covariates that
also affect performance. Selection bias and the effects of confounding can be reduced by
choosing a more homogeneous stratified sample, but the generalizability of the results of such
cohort studies is thereby limited.
Perhaps the greatest methodological concern in epidemiological studies is controlling for
confounding covariates, so that residual effects can be more confidently attributed to lead.
Among adults, the most important covariates are age, sex, race, educational level, exposure
history, alcohol intake, total food intake, dietary calcium and iron intake, and urban vs.
rural styles of living (Valciukas and Li lis, 1980). Among children, a number of developmental
covariates are additionally important: parental socioeconomic status (Needleman et al.,
1979); maternal IQ (Perino and Ernhart, 1974); pica (Barltrop, 1966); quality of the care-
giving environment (Hunt et al., 1982; Milar.et al., 1980); dietary iron and calcium intake,
vitamin D levels, body fat and nutrition (Mahaffey and Michael son, 1980; Mahaffey, 1981); and
age at exposure. Preschool children below the age of 3-5 years appear to be particularly vul-
nerable, in that the rate of accumulation- of. even a low body-lead burden is higher for them
than for adults (National Academy of Sciences, Committee on Lead in the Human Environment,
1980). Potential confounding effects of covariates become particularly important when trying
to interpret threshold effects of lead exposure. Each covariate alone may not be significant,
but, when combined, may interact to pose a cumulative risk which could result in under- or
overestimation of a small effect of lead.
Statistical considerations important not only to lead but to all epidemiological studies
include adequate sample size (Hill, 1966), the use of multiple comparisons (Cohen and Cohen,
1975), and the use of multivariate analyses (Cooley and Lohnes, 1971). Regarding sample size,
false negative conclusions are at times drawn from small studies with low statistical power.
:t is often difficult and expensive to use-:large sample sizes in complex research such as that
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on lead neurotoxicity. This fact makes it all the more important to use sensitive assessment
instruments which have a high level of discriminating power and can be combined into factors
for multivariate analysis. Mul tipl e .statistical comparisons can then be made while reducing
the likelihood of finding a certain number of significant differences by chance alone. This
is a serious problem, because near-threshol d effects are often small and variable.
A final crucial issue in this and other research revolves around the care taken to assure
that investigators are isolated from information that might identify subjects in terms of
their lead exposure levels at the time of assessment and data recording. Unconscious biases,
nonrandom errors, and arbitrary data correction and exclusion can be ruled out only if a study
is performed under blind conditions or, preferably, double-blind conditions.
With the above methodological considerations in mind, the following sections evaluate
pertinent human studies, including an overview of lead exposure effects in adults, followed by
a more detailed assessment of neurotoxic effects of lead exposures in children.
12.4.2.1 Neurotoxic Effects of Lead Exposures in Adults.
12.4.2.1.1 Overt lead intoxication in adults. Severe neurotoxic effects of extreme exposures
to high levels of lead, especially for prolonged periods that produce overt signs of acute
lead intoxication, are well documented in regard to both adults and children. The most pro-
found (CNS) effects in adults have been referred to for many years as the clinical syndrome of
lead encephalopathy, described in detail by Aub et al. (1926), Cantarow and Trumper (1944),
Cumings (1959), and Teisinger and Styblova (1961). Early features of the syndrome that may
develop within weeks of initial exposure include dullness, restlessness, irritability, poor
attention span, headaches, muscular tremor, hallucinations, and loss of memory. These symp-
toms may progress to delirium, mania, convulsions, paralysis, coma, and death. The onset of
such symptoms can often be quite abrupt, with convulsions, coma, and even death occurring very
rapidly in patients who shortly before appeared to exhibit much less severe or no symptoms of
acute lead intoxication (Cumings, 1959; Smith et al., 1938). Symptoms of lead encephalopathy
indicative of severe CNS damage and posing a threat to life are generally not seen in adults
except at blood lead levels well in excess of 120 pg/dl (Kehoe, 1961a,b,c). Other data
(Smith et al., 1938) suggest that acute lead intoxication, including severe gastrointestinal
symptoms and/or signs of encephalopathy can occur in some adults at blood lead levels around
100 pg/dl, but ambiguities make this data difficult to interpret.
In addition to the above CNS effects, lead also clearly damages peripheral nerves at tox-
ic, high exposure levels that predominantly affect large myelinated nerve fibers (Vasilescu,
1973; Feldman et al., 1977; Englert, 1980). Pathologic changes in peripheral nerves, as shown
in animal studies, can include both segmental demyelination and, in some fibers, axonal degen-
eration (Fullerton, 1966). The former types of changes appear to reflect lead effects on
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Schwann cells, with concomitant endoneural edema and disruption of myelin membranes
(Windebank and Dyck, 1981). Apparently lead induces a breakdown in the blood-nerve barrier
which allows lead-rich edema fluid to enter the endoneurium (Dyck et al. , 1980; Windebank
et al., 1980). Remyelination observed in animal studies suggests either that such lead
effects may be reversible or that not all Schwann cells are affected equally (Lampert and
Schochet, 1968; Ohnishi and Dyck, 1981). Reports of plantar arch deformities due to old per-
ipheral neuropathies (Emmerson, 1968), however, suggest that lead-induced neuropathies of
sufficient severity in human adults could result in permanent peripheral nerve damage. Mor-
phologically, peripheral neuropathies are usually detectable only after prolonged high expo-
sure to lead, with distinctly different sensitivities and histological differences existing
among mammalian species. In regard to man, as an example, Buchthal and Behse (1979, 1981),
using nerve biopsies from a worker with frank lead neuropathy (blood lead = 150 pg/dl), found
histological changes indicative of axonal degeneration in association in NCV reductions that
corresponded to loss of large fibers and decreased amplitude of sensory potentials.
Data from certain studies provide a basis by which to estimate lead exposure levels at
which adults exhibit overt signs or symptoms of neurotoxicity and to compare such levels with
those associated with other types of signs and symptoms indicative of overt lead intoxication
(Lilis et al., 1977; Irwig et al., 1978; Dahlgren et al., 1978; Baker et al., 1979; Hanninen
et al., 1979; Spivey et al., 1979; Fischbein et al., 1980; Hammond et al., 1980). These
studies evaluated the incidence of various clinical signs and symptoms of lead intoxication
across a wide range of lead exposures among occupationally exposed smelter and battery plant
workers. The reported incidences of particular types of signs and symptoms, both neurological
and otherwise, and associated lead exposure levels varied considerably from study to study,
but they collectively provide evidence indicating that overt neurological, gastrointestinal,
and other lead-related symptoms can occur among adults starting at blood lead levels as low as
40-60 pg/dl. Considerable individual biological variability is apparent, however, among vari-
ous study populations and individual workers in terms of observed lead levels associated with
overt signs and symptoms of lead intoxication, based on comparisons of exposure-effect and
dose-response data from the above studies. Irwig et al (1978), for example, report data for
black South African lead workers indicative of clearly increased prevalence of both neurologi-
cal and gastrointestinal symptoms at blood lead levels over 80 jjg/d'l. Analogously, Hammond
et al. (1980) reported significant increases in neurological (both CNS and PNS) and gastro-
intestinal symptoms among American smelter workers with blood lead levels often exceeding
80 pg/dl, but not among workers whose exposure histories did not include levels above 80
pg/dl--findings in contrast to the results of several other studies. Lilis et al. (1977), for
instance, found that CNS symptoms (tiredness, sleeplessness, irritability, headaches) were
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reported by 55 percent and muscle or joint pain by 39 percent of a group of lead smelter
workers whose blood lead levels had never been found to exceed 80 (jg/dl. Low hemoglobin
levels (<14g/dl) were found in more than 33 percent of these workers. Also, Spivey et al.
(1977) reported significantly increased neurological (mainly CNS, but some PNS) symptoms and
joint pain among a group of 69 lead workers with mean + standard deviation blood lead levels
of 61.3 ± 12.8 pg/dl in comparison to a control group with 22.0 ± 5.9 ^g/dl blood lead values.
Hanninen et al. (1979) similarly reported finding significantly increased neurological (both
CNS and PNS) and gastrointestinal symptoms among 25 lead workers with maximum observed blood
lead levels of 50-69 pg/dl and significantly increased CNS symptoms among 20 lower exposure
workers with maximum blood lead values below 50 pg/dl, compared in each case against a refer-
ent control group (N = 23) with blood lead values of 11.9 ± 4.3 pg/dl (mean ± standard devia-
tion).
Additional studies provide evidence of overt signs or symptoms of neurotoxicity occurring
at still lower lead exposure levels than those indicated above. Baker et al. (1979) studied
dose-response relationships between clinical signs and symptoms of lead intoxication among
lead workers in two smelters. No toxicity was observed at blood lead levels below 40 (jg/dl.
However, 13 percent of those workers with blood lead values in the range 40-79 pg/dl had
extensor muscle weakness or gastrointestinal symptoms; and anemia occurred in 5 percent of the
workers with 40-59 jjg/dl blood lead levels, in 14 percent with levels of 60-79 pg/dl, and in
36 percent with blood lead levels exceeding 80 pg/dl. Also, Fischbein et al. (1980), in a
study of 90 cable splicers intermittently exposed to lead, found higher zinc protoporphyrin
levels (an indicator of impaired heme synthesis associated with lead exposure) among workers
reporting CNS or gastrointestinal symptoms than among other cable splicers not reporting such
symptoms. Only 5 percent of these workers had blood lead levels in excess of 40 pg/dl, and
the mean ± standard deviation blood lead levels for the 26 reporting CNS symptoms were 28.4
±7.6 pg/dl and 30 ±9.4 jjg/dl for the 19 reporting gastrointestinal symptoms. Caution must be
exercised in accepting these blood levels as being representative of average or maximum lead
exposures of this worker population, however, in view of the highly intermittent nature of
their exposure and probable much higher resulting peaks in their blood lead levels than those
coincidentally measured at the time of their blood sampling.
Overall, the above results appear to support the following conclusions: (1) overt signs
and symptoms of neurotoxicity in adults are manifested at roughly comparable lead exposure
levels as other types of overt signs and symptoms of lead intoxication, such as gastrointesti-
nal complaints; (2) the neurological signs and symptoms are indicative of both central and
peripheral nervous system effects; (3) such overt signs and symptoms, both neurological and
otherwise, occur at markedly lower blood lead levels than the 60 or 80 ^ig/dl criteria levels
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previously established or recently discussed as being "safe" for occupationally exposed
adults; and (4) lowest observed effect levels for the neurological signs and symptoms can most
credibly be stated to be in the 40 to 60 pg/dl range. Insufficient information exists pre-
sently by which to estimate with confidence to what extent or for how long such overt signs
and symptoms persist in adults after termination of precipitating external lead exposures, but
at least one study (Dahlgren, 1978) reports evidence of abdominal pain persisting for as long
as 29 months after exposure termination among 15 smelter workers, including four whose blood
lead levels were between 40 and 60 pg/dl while working.
12.4.2.1.2 Non-Overt lead intoxication in adults. Of special importance for establishing
standards for exposure to lead is the question of whether exposures lower than those producing
overt signs or symptoms of lead intoxication result in less obvious neurotoxic effects in
otherwise apparently healthy individuals. Attention has focused in particular on whether ex-
posures leading to blood lead levels below 80-100 pg/dl may lead to behavioral deficits or
other neurotoxic effects in the absence of classical signs of overt lead intoxication.
In adults, if such neurobehavioral deficits occurred with great frequency, one might ex-
pect this to be reflected by performance measures in the workplace, such as higher rates of
absences or reduced psychomotor performances among occupationally exposed lead workers. Some
epidemiological studies have investigated possible relationships between elevated blood lead
and general health as indexed by records of sick absences certified by physicians (Araki et
a 1., 1982; Robinson, 1976; Shannon et al., 1976; Tola and Nordman, 1977). However, sickness
absence rates are generally poor epidemiologic outcome measures that may be confounded by many
variables and are difficult to relate specifically to lead exposure levels. Much more useful
are studies discussed below which evaluate lead exposures in relation to direct measurements
of CNS or peripheral neurological functions.
Only a few studies have employed sensitive psychometric and/or neurological testing
procedures in an effort to demonstrate specific lead-induced neurobehavioral effects in
adults. For example, Morgan and Repko (1974) reported deficits in hand-eye coordination and
reaction time in an extensive study of behavioral functions in 190 lead-exposed workers (mean
blood lead level = 60.5 ± 17.0 pg/dl). The majority of the subjects were exposed between 5
and 20 years. In a similar study, Milburn et al. (1976) found no differences between control
and lead-exposed workers on numerous psychometric and other performance tests. On the other
hand, several recent studies (Arnvig et al., 1980; Grandjean et al. , 1978; Hanninen et al.,
1978; Mantere et al., 1982; Valciukas et al., 1978) have found disturbances in visual motor
performance, IQ test performance, hand dexterity, mood, nervousness, and coping in lead
workers with blood lead levels of 50-80 ^ig/d1. A graded dose-effect relationship for non-
overt CNS lead effects in otherwise apparently asymptomatic adults is indicated by such
studies.
2BPB12/B 12-47 9/20/83
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PRELIMINARY DRAFT
In addition to the above studies indicative of CNS dysfunctions in non-overtly lead
intoxicated adults, numerous investigations have provided electrophysiological data indicating
that peripheral nerve dysfunction in apparently asymptomatic adults can be associated with
blood lead values below 80 pg/dl. Such peripheral nerve deficits, i.e. slowed nerve conduc-
tion veolocity (NCV), were established by Seppalainen et al. (1975) for lead workers whose
blood lead levels were as low as 50 (jg/dl and had never exceeded 70 (jg/dl during their entire
exposure period (mean = 4.6 years), as determined by regular monitoring. Similar results were
obtained in a study by Melgaard et al. (1976) on automobile mechanics exposed to TEL and other
lead compounds in lubricating and high-pressure oils. Results of an analysis of the workers'
blood for lead, chromium, copper, nickel, and manganese indicated a clear association between
lead exposure and peripheral nerve dysfunction. Half of the workers (10 to 20) had elevated
blood lead levels (60-120 pg/dl) and showed definite electromyographic deficits. The mean
blood lead level for the control group was 18.6 pg/dl. Melgaard et al. (1976) reported addi-
tional results on associating lead exposures with polyneuropathy of unknown etiology in 10
cases from the general population. Another study reported by Araki and Honma (1976) provided
further confirmation of the Seppalainen et al. (1975) and Melgaard et al. (1976) findings in
that evidence for peripheral neuropathy effects were reported for lead industry workers with
blood lead values of 29 to 70 ng/dl.
More recent studies by Araki et al (1980), Ashby (1980), Bordo et al. (1982), Johnson
et al. (1980), Seppalainen et al. (1979), and Seppalainen and Hernberg (1980, 1982) have con-
firmed a dose-dependent slowing of NCV in lead workers with blood lead levels below 70 to 80
(jg/dl. Seppalainen et al. (1979) observed NCV slowing in workers with blood lead levels
across a range of 29 to 70 (jg/dl (Figure 12-2); and Seppalainen and Hernberg (19B0, 1982)
found NCV slowing in workers with maximum blood lead levels of 30 to 48 pg/d 1, but not among
workers with levels below 30 MQ/dl. Buchthal and Behse (1979), Lilis et al. (1977), and
Paulev et al. (1979), in contrast, found no signs of neuropathy below 80 pg/dl. Reports of
low blood lead levels (below 50 (jg/dl) in some of the above studies should be viewed with cau-
tion until further confirmatory data are reported for larger samples using well verified blood
assay results. Nonetheless, these studies are consistent with a continuous dose-response
relationship between blood lead concentration and extent and degree of peripheral nerve dys-
function in non-overtly lead intoxicated adults.
The above studies on nerve conduction velocity provide convergent evidence for peripheral
nerve dysfunctions occurring in adults with blood lead levels in the 30-70 |jg/d1 range but not
exhibiting overt signs of lead intoxication. Furthermore, although it might be argued that
peak levels of lead may have been significant and that substantially higher lead body burdens
existing before the time of some of the studies were actually responsible for producing the
dysfunctions, it appears that in several cases (Seppalainen et al., 1975; Seppalainen and
2BPB12/B
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9/20/83
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80 —
o
«
in
>
DC
LU
70
#• ® 8 e
• •
>
u
50
40 —
* V
-------
PRELIMINARY DRAFT
Hernberg, 1980) blood levels that had never exceeded 70 |Jg/d1 were related to increased peri-
pheral nerve dysfunction; and, in the Seppalainen and Hernberg (1982) study, NCV slowing was
associated with maximum levels of 30-48 (jg/dl. The studies by Seppalainen and her co-workers
are generally methodologically sound, having been well controlled for the possible effects of
extraneous factors such as history, length, and type of exposure, multiple assessments of dif-
ferent nerves, temperature differences at the NCV assessment sites, plus relevant confounding
covariates. Thus, when the Seppalainen et al. (1975) results are viewed collectively with
the data from other studies reviewed here, substantial evidence can be stated to exist for
peripheral nerve dysfunctions occurring in adults at blood lead levels of as low as 30 to 50
pg/dl. The question as to whether these reflect mild, reversible effects (Buchthal and Behse,
1981) or are true early warning signals of progressively more serious peripheral neuropathies
important in the diagnosis of otherwise unrecognized toxic effects of lead (Feldman et. al.,
1977; Seppalainen and Hernberg, 1980) is still a matter of some dispute. Nevertheless, it is
clear that these effects represent departures from normal neurologic functioning and their
potential relationship to other extremely serious effects (see, for example, the next para-
graph) argues for prudence in interpreting their potential health significance.
There are several reports of previous overexposure to heavy metals in amyotrophic lateral
sclerosis (ALS) patients and patients dying of motor neuron disease (MND). Conradi et al.
(1976, 1978a,b, 1980) found elevated cerebrospinal fluid lead levels in ALS patients as com-
pared with controls. Thus, the possible pathogenic significance of lead in ALS needs to be
further explored. In addition, Kurlander and Patten (1978) found that lead levels in spinal
cord anterior horn cells of MND patients were nearly three times that of control subjects and
that lead levels correlated with illness durations. Despite chelation therapy for about a
year, high lead levels remained in their tissue.
12.4.2.2 Neurotoxic Effects of Lead Exposure in Children.
12.4.2.2.1 Overt lead intoxication in children. Symptoms of encephalopathy similar to those
that occur in adults have been reported to occur in infants and young children (Prendergast,
1910; Oliver and Vogt, 1911; Blackfan, 1917; McKahann and Vogt, 1926; Giannattasio et al.,
1952; Cumings, 1959; Tepper, 1963; Chisolm, 1968), with a markedly higher incidence of severe
encephalopathic symptoms and deaths occurring among them than in adults. This may reflect the
greater difficulty in recognizing early symptoms in young children, thereby allowing intoxica-
tion to proceed to a more severe level before treatment is initiated (Lin-Fu, 1973). In
regard to the risk of death in children, the mortality rate for encephalopathy cases was
approximately 65 percent prior to the introduction of chelation therapy as standard medical
practice (Greengard et al., 1965; National Academy of Sciences, 1972; Niklowitz, 1975;
Niklowitz and Mandybur, 1975). The following mortality rates have been reported for children
2BPB12/B 12-50 9/20/83
947<
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PRELIMINARY DRAFT
experiencing lead encephalopathy since the inception of chelation therapy as the standard
treatment approach: 39 percent (Ennis and Harrison, 1950); 20 to 30 percent (Agerty, 1952);
24 percent (Mellins and Jenkins, 1955); 18 percent (Tanis, 1955); and 5 percent (Lewis et al.,
1955). These data, and those tabulated more recently (National Academy of Sciences, 1972),
indicate that once lead poisoning has progressed to the point of encephalopathy, a life-
threatening situation clearly exists and, even with medical intervention, is apt to result in
a fatal outcome. Historically there have been three stages of chelation therapy. Between
1946 and 1950, dimercaprol (BAL) was used. From 1950 to 1960, calcium disodium ethylenedia-
minetetraacetate (CaEDTA) completely replaced BAL. Beginning in 1960, combined therapy with
BAL and CaEDTA (Chisolm, 1968) resulted in a very substantial reduction in mortality.
Determining precise values for lead exposures necessary to produce acute symptoms, such
as lethargy, vomiting, irritability, loss of appetite, dizziness, etc., or later neurotoxic
sequelae in humans is difficult in view of the usual sparsity o.f data on environmental lead
exposure levels, period(s) of exposure, or body burdens of lead existing prior to manifesta-
tion of symptoms. Nevertheless, enough information is available to permit reasonable esti-
mates to be made regarding the range of blood lead levels associated with acute encephalo-
pathy symptoms or death. Available data indicate that lower blood lead levels among children
than among adults are associated with acute encephalopathy symptoms. The most extensive
compilation of information on a pediatric population is a summarization (National Academy of
Sciences, 1972) of data from Chisolm (1962, 1965) and Chisolm and Harrison (1956). This data
compilation relates occurrence of acute encephalopathy and death in children in Baltimore to
blood lead levels determined by the Baltimore City Health Department (using the dithizone
method) between 1930 and 1970. Blood lead levels formerly regarded as "asymptomatic" and
other signs of acute lead poisoning were also tabulated. Increased lead absorption in the
absence of detected symptoms was observed at blood lead levels ranging from 60 to 300 pg/dl
(mean = 105 pg/dl). Acute lead poisoning symptoms other thah signs of encephalopathy were
observed from approximately 60 to 450 jjg/dl (mean = 178 pg/dl). Signs of encephalopathy
(hyperirritabi1ity, ataxia, convulsions, stupor, and coma) were associated with blood lead
levels of approximately 90 to 700 or 800 pg/dl (mean = 330 pg/dl). The distribution of blood
lead levels associated with death (mean = 327 pg/dl) was essentially the same as for levels
yielding encephalopathy. These data suggest that blood lead levels capable of producing death
in children are essentially identical to those associated with acute encephalopathy and that
such effects are usually manifested in children starting at blood lead levels of approximately
100 pg/dl. Certain other evidence from scattered medical reports (Gant, 1938; Smith et al.,
1938; Bradley et al., 1956; Bradley and Baumgartner, 1958; Cumings, 1959; Rummo et al. , 1979),
however, suggests that acute encephalopathy in the most highly susceptible children may be
associated with blood lead levels in the range of 80-100 pg/dl. These latter reports are
evaluated in detail in the 1977 EPA document Air Qua1ity Criteria for Lead (U.S. EPA, 1977).
2BPB12/B 12-51 9/20/83
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PRELIMINARY DRAFT
From the preceding discussion, it can be seen that severity of symptoms varies widely for
different adults or children as a function of increasing blood lead levels. Some show irre-
versible CNS damage or death at blood lead levels around 100 pg/dl, whereas others may not
show any of the usual clinical signs of lead intoxication even at blood lead levels in the 100
to 200 jjg/d 1 or higher range. This diversity of response may be due to: (1) individual bio-
logical variation in lead uptake or susceptibility to lead effects; (2) changes in blood lead
values from the time of initial damaging intoxication; (3) greater tolerance for a gradually
accumulating lead burden; (4) other interacting or confounding factors, such as nutritional
state or inaccurate determinations of blood lead; or (5) lack of use of blind evaluation pro-
cedures on the part of the evaluators. It should also be noted that a continuous gradation of
frequency and severity of neurotoxic symptoms extends into the lower ranges of lead exposure.
Morphological findings vary in cases of fatal lead encephalopathy among children
(Blackman, 1937; Pentschew, 1965; Popoff et al., 1963). Reported neuropathologic findings are
essentially the same for adults and children. On macroscopic examination the brains are often
edematous and congested. Microscopically, cerebral edema, altered capillaries (endothelial
hypertrophy and hyperplasia), and perivascular glial proliferation often occur. Neuronal
damage is variable and may be caused by anoxia. However, in some cases gross and microscopic
changes are minimal (Pentschew, 1965). Pentschew (1965) described neuropathology findings for
20 cases of acute lead encephalopathy in infants and young children. The most common finding
was activation of intracerebral capillaries characterized by dilation of the capillaries, with
swelling of endothelial cells. Diffuse astrocytic proliferation, an early morphological
response to increased permeability of the blood-brain barrier, was often present. Concurrent
with such alterations, especially evident in the cerebellum, were changes that Pentschew
(1965) attributed to hemodynamic disorders, i.e., ischemic changes manifested as cell
necrosis, perineuronal incrustations, and loss of neurons, especially in isocortex and basal
ganglia.
Attempts have been made to understand better brain changes associated with encephalopathy
by studying animal models. Studies of lead intoxication in the CNS of developing rats have
shown vasculopathic changes (Pentschew and Garro, 1966), reduced cerebral cortical thickness
and reduced number of synapses per neuron (Krigman et al., 1974a), and reduced cerebral axonal
size (Krigman et al., 1974b). Biochemical changes in the CNS of lead-treated neonatal rats
have also demonstrated reduced lipid brain content but no alterations of neural lipid composi-
tion (Krigman et al., 1974a) and a reduced cerebellar DNA content (Michaelson, 1973). In
cases of lower level lead exposure, subjectively recognizable neuropathologic features may not
occur (Krigman, 1978). Instead there may be subtle changes at the level of the synapse
(Silbergeld etal., 1980a) or dendritic field, myelin-axon relations, and organization of
2BPB12/B
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9/20/83
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PRELIMINARY DRAFT
synaptic patterns (Krigman, 1978). Since the nervous system is a dynamic structure rather
than a static one, it undergoes compensatory changes (Norton and Culver, 1977), maturation and
aging (Sotelo and Pal ay, 1971), and structural changes in response to environmental stimuli
(Coss and Glohus, 1978). Thus, whereas massive structural damage in many cases of acute
encephalopathy would be expected to lead to lasting neurotoxic sequalae, some other CNS
effects due to severe early lead insult might be reversible or compensated for, depending upon
age and duration of toxic exposure. This raises the question of whether effects of early
overt lead intoxication are reversible beyond the initial intoxication or continue to persist.
In cases of severe or prolonged nonfatal episodes of lead encephalopathy, there occur
neurological sequelae qualitatively similar to those often seen following traumatic or infec-
tious cerebral injury, with permanent sequelae being more common in children than in adults
(Mel 11ns and Jenkins, 1955; Chisolm, 1962, 1968). The most severe sequelae in children are
cortical atrophy, hydrocephalus, convulsive seizures, and severe mental retardation (Mellins
and Jenkins, 1955; Perlstein and Attala, 1966; Chisolm, 1968). Children who recover from
acute lead encephalopathy but are re-exposed to lead almost invariably show evidence of per-
manent central nervous system damage (Chisolm and Harrison, 1956). Even if further lead expo-
sure is minimized, 25 to 50 percent show severe permanent sequelae, such as seizure disorders,
blindness, and hemiparesis (Chisolm and Barltrop, 1979).
s
Lasting neurotoxic sequelae of overt lead intoxication in children in the absence of
acute encephalopathy have also been reported. Byers and Lord (1943), for example, reported
that 19 out of 20 children with previous lead poisoning later made unsatisfactory progress-in
school, presumably due to sensorimotor deficits, short attention span, and behavioral dis-
orders. These latter types of effects have since been confirmed in children with known high
exposures to lead, but without a history of life-threatening forms of acute encephalopathy
(Chisolm and Harrison, 1956; Cohen and Ahrens, 1959; Kline, 1960). Perlstein and Attala
(1966) also reported neurological sequelae in 140 of 386 children (37 percent) following lead
poisoning without encephalopathy. Such sequelae included mental retardation, seizures, cere-
bral palsy, optic atrophy, and visual-perceptual problems in some children with minimal intel-
lectual impairment. The severity of sequelae was related to severity of earlier observed
symptoms. For 9 percent of those children who appeared to be without severe symptoms at the
time of diagnosis of overt lead poisoning, mental retardation was observed upon later follow-
up. The conclusion of the neurological effects observed by Perlstein and Attala (1966) being
persisting effects of earlier overt lead intoxication without encephalopathy might be ques-
tioned in view of no control group having been included in the study; however, it is extremely
unlikely that 37 percent of any randomly selected control group from the general pediatric
population would exhibit the types of neurological problems observed in that proportion of the
cohort of children with earlier lead intoxication studied by Perlstein and Attala (1966).
2BPB12/B
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9/20/83
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PRELIMINARY DRAFT
Numerous studies (Cohen et al., 1976; Fejerman et.al., 1973; Pueschel et al., 1972; Sachs
et al., 1978, 1979, 1982) suggest that, in the absence of encephalopathy, chelation therapy
may ameliorate the persistence of neurotoxic effects of overt lead poisoning (especially cog-
nitive, perceptual, and behavioral deficits). On the other hand, one recent study found a
residual effect on fine motor performance even after chelation (Kirkconnell and Hicks, 1980).
In summary, pertinent literature definitively demonstrates that lead poisoning with
encephalopathy results in a greatly increased incidence of permanent neurological and cogni-
tive impairments. Also, several studies further indicate that children with symptomatic lead
poisoning in the absence of encephalopathy also show a later increased incidence of neurologi-
cal and behavioral impairments.
12.4.2.2.2 Non-Overt lead intoxication in children
In addition to neurotoxic effects associated with overt lead intoxication in children,
growing evidence indicates that lead exposures not.leading to overt lead intoxication in
children can induce neurological dysfunctions. This issue has attracted much attention and
generated considerable controversy during the past 10 to 15 years. However, the evidence for
and against the occurrence of significant neurotoxic deficits at relatively low levels of lead
exposure is quite mixed and largely interpretable only after a thorough critical evaluation of
methods employed in the various important studies on the subject. Based on the five criteria
listed earlier (i.e., adequate markers of exposure to lead, sensitive measures, appropriate
subject selection, control of confounding covariates, and appropriate statistical analysis),
the 20 population studies summarized in Table 12-1 were conducted rigorously enough to warrant
at least some consideration here. Even so, no epidemiological study is completely flawless
and, therefore, overall interpretation of such findings must be based on evaluation of:
(1) the internal consistency and quality of each study; (2) the consistency of results ob-
tained across independently conducted studies; and (3) the plausibility of results in view of
other available information.
Rutter (1980) has classified studies evaluating neurobehavioral effects of lead exposure
in non-overtly lead intoxicated children according to several types, including four categories
reviewed below: (1) clinic-type studies of children thought to be at risk because of high lead
levels; (2) other studies of children drawn from general (typically urban or suburban) pedia-
tric populations; (3) samples of children living more specifically in close proximity to lead
emitting smelters; and (4) studies of mentally retarded or behaviorally deviant children.
Major attention is accorded here to studies falling under the first three categories. As
will be seen, quite mixed results have emerged from the studies reviewed.
12.4.2.2.2.1 Clinic-type studies of children with high lead levels. The clinic-type
studies are typified by evaluation of children with relatively high lead body burdens as
identified through lead screening programs or other large-scale programs focussing on mother-
infant health relationships and early childhood development.
2BPB12/B 12-54 9/20/83
951«=
-------
TABLE 12-1. SUMMARY OF PUBLISHED RESULTS FROM STUDIES OF LEAD EFFECTS ON NEUROBEHAVIORAL FUNCTIONS
OF NON-OVERTLY LEAD INTOXICATED CHILDREN
Reference
Population
studied
N/group
Age at
testing, yr
Blood lead,
pg/dl
Psychometric
tests employed
Summary of results
(C-control; Pb=lead)a
Levels of
signi ficance
Clinic-type Studies of Children with High Lead Levels
De la Burde and
Inner city
Control
72
4
Choate (1972)
(Richmond, VA)
Lead
=
70
4
De la Burde and
Foilow-up
Control
—
67
7
Choate (1975)
same subjects
Lead
=
70
7
Rummo et al.
Inner city
Control Ss
_
45
4-8
C* =
= 5.8)
(1974, 1979)
(Providence, RI)
:
Short Pb Ss
=
15
4-8
(i =
= 5.6)
/
Long Pb Ss
=
20
4-8
(I =
= 5.6)
Post enceph Pb
=
10
4-8
(~x =
= 5.3)
Kotok (1972)
Inner city
Control =
25
1.1
-5 .
5 (x
(New Haven, CT)
Lead =
24
1.0
- 5.8 (X :
Kotok et al.
Inner city
Control =
36
1.9
- 5.
6 {'*
(1977)
(Rochester, NY)
Lead =
31
1.7
- 5.
4 (- =
Peri no and
Ernhart (1974)
Ernhart et al.
(1981)
Not assayed
40-100°
See above®
See above
x = 23 ± 8
x = 61 ± 7
x = 68 ± 13
x - 88 ± 40
20-55
58-137
11-40
61-200
Inner city
(New York, NY)
Follow-up same
subjects
Control = 50
Lead
30
Control = 31
Lead = 32
3-6
3-6
8-13
10-30
40-70
21.3+3.71
32.4±5.3
Stanford-Binet IQ
Other measures
WISC Full Scale IQ
Neurologic exam
Other measures
McCarthy General
Cogni tive
McCarthy Subscales
Neurologic exam
rating
Objective neurologic
tests
Denver Developmental
Scale
IQ Equivalent for
six abiIity classes:
Social maturity;
Spatial relations;
Spoken vocab;
Info, comprehension;
Visual attention;
Auditory memory
McCarthy General
Cognitive
McCarthy Subscales
McCarthy General Cog-
nitive Index
McCarthy Subscales
Reading Tests
Exploratory Tests
(Bender Gestalt,
Draw-A-ChiId)
Conners Teachers Rating
Scale
C = 94 Pb = 89
C > Pb on 3/4 tests
C = 90 Pb = 87
C better than Pb
C > Pb on 9/10 tests
C = 93; S = 94;
L = 88; P = 77
C+S > L > P on 5/5
tests
C+S > L > P on ratings
C+S > L > P on 3/12
tests
C > Pb on 1/3 Subscales
IQ Equivalent for
each:
C
C
C
C
C
C
126 Pb = 124
101 Pb = 92;
93 Pb = 92;
96 Pb = 95;
93 Pb = 90
100 Pb = 93
C = 90 Pb = 80
C > Pb on 5/5 scales
Shared Variance =
(2/5) 8.0, 7.4
1.3
7
7. 7
p <0.05
N.S.-p <0.01
p <0.01
p <0.01
N.S.-p <0.001
N.S.-p <0.01
(P vs C)
N.S.-p <0.01
(P vs C)
N.S.
N.S.-p <0.01
(P vs C)
N.S.
p <0.10 for
spatial
p >0.10 for al1
other ability
classes
p <0.01
N.S.-p <0.01
p <0.05
(i <0.05
N.S.
N.S.
N.S.
-------
TABLE 12-1. (continued)
Reference
Population
studied
N/group
Age at
testing, yr
Blood lead,
ljg/dl
Psychometric
tests employed
Summary of results
(C=control; Pb=lead)s
Levels of b
significance
to
W-
.A
General Population Studies
Needleaan et al.
(1979)
General population
(Boston, HA area)
Control = 100
Lead = 58
PbT
PbT
10 ppm WISC Full scale IQ
20 ppm WISC Verbal IQ
WISC Performance IQ
Seashore Rhythm Test
Token Test
Sentence Repetition Test
Delayed Reaction Time
Teacher's Behavior
Rati ng
c
=
106.6
Pb = 102.1
p < 0.03
c
=
103.9
Pb = 99.3
p <0.03
c
=
108.7
Pb = 104.9
N.S.
c
=
21.6
Pb = 19.4
p <0.002
c
=
24.8
Pb = 23.6
N.S.
c
=
12.6
Pb = 11.3
p <0.04
c
>
Pb on
3/4 blocks
p <0.01
c
=
9.5
Pb = 8.2
p <0.02
ro
i
cn
en
HcBride
et al.
Urban and suburban Moderate = C.
100 4,5
19-30 pg/dl
Peabody Picture.Voc.
C =
105 Pb = 104
' N: S.
(1982)
(Sydney, Australia)
Test
i
Low = C.100
4.5
0.5-9 pg/dl
Fine Motor Tracking ¦
C >
Pb 1/4 comparisons
p <0.05
Pegboard
C =
20 Pb = 20
N.S.
Tapping Test
C =
30 Pb = 31
N.S.
Beam Walk
C =
5 Pb = 4
N.S.
'
Standing Balance
C >
Pb 1/4 comparisons
p <0.05
Rutter Activity Scale
C =
1.9 Pb - 2.1
N.S.
Yule et
al.
Urban Group 1 = 20
9
8.8j
WISC-R Full Scale IQ
Gpl
< Gp2 > Gp3 > Gp4
• p <0.029
(1981)
(London, England) Group 2=29
9
11.6
Verbal IQ
Gpl
< Gp2 > Gp3 > Gp4
p <0.04
Group 3 = 29
8
14.5
Performance IQ .
Gpl
< Gp2 > Gp3 > Gp4
N.S.
Group 4 = 21
8
19.6
Vernon Spelling Test k
Gpl
> Gp2 > Gp3 > Gp4
p <0.001
Vernon Arithmetic lest
Gpl
< Gp2 > Gp3 > Gp4
N.S.
Neale Reading Test
Gpl
< Gp2 > Gp3 > Gp4
p <0.001
Yule et
al.
Same subjects Sane
Same
Same
Needleman Teacher's
Linear Trend 3/4 items
p <0.05
(1983)
Behavior Ratings
Conners Teachers
Gpl
< Gps2-4
p <0.05
Questionnaire
Factors 1,2,4,5
Rutter Teacher Rating
Scale for Activity
Linear Trend 25/36 items N.S.
"O
ZJO
3»
•JO
-c
C3
JO
3»
-------
Table 12-1.
(continued)
cs
C/T
/I
<_n
Population
Age at
Blood lead,
Psychometric
Summary of results
Levels of^- b
Reference studied
N/group
testing, yr
Mg/dl
tests employed
(C=control; Pb=lead)a
signi ficance
HIGH
MED LOW
Smith et al. Urban
Hi = 155
6.7
PbT 2 8.0
WISC-R Full Scale
105
105 107
N.S.
(1983) (London, UK)
Med = 103
6,7
PbT = 5-5.5
Verbal IQ
103
103 105
N. S.
Low = 145
6,7
PbT <2.5
Performance IQ
106
106 108
N.S.
(All in yg/g)
x PbB = 13.1
1
MS/dl
Word Reading.Test
40
42 45
N.S.
Seashore Rhythm Test
20
20 21
N.S.
-
Visual Sequential Memory
20
19 20
N. S.
Sentence Memory
9
9 9
N.S.
Shape Copying
14
14 14
N.S.
v. 0 o
'
1 *
Mathematics
15
15 16
N.S.
1
*
Mean Visual RT (sees)
.39
.37 .37
N.S.
)
'¦
. ' •
Conners Teachers Ratings
13
11 11
N.S.
Low
Hi
fule and Lansdown Urban
80
9
7-12
WISC-R Full Scale
107
105
N. S.
(1983) (London, UK)
82
9
13-24
Verbal IQ
104
103
N.S.
Performance IQ
108
106
N.S.
Neale Reading Acc.
114
111
N.S.
Neale Reading Comp.
113
109
N.S.
Vernon Spel1ing
101
99
N.S.
Vernon Math
100
99
N.S.
Harvey et al. Urban
189
2.5
15.5
British Ability Scales
Regression F Ratio
N.S.
(1983) (Birmingham, UK)
Naming
<1
N.S.
Recal1
1.26
N.S.
Comprehension
<1
N.S.
Recognition
<1
N.S.
IQ
<1
N.S.
Stanford-Binet Items
Shapes
<1
N.S.
Blocks
2.34
N. S.
Beads
2.46
N.S.
Playroom Activity
7
N.S.
73
-<
o
-------
Table 12-1. (continued)
Population Age at Blood lead, Psychometric Summary of results Levels of b
Reference studied N/group testing, yr ng/dl tests employed (C=control; Pb=lead)a significance
Smelter Area Studies
Landrigan et al.
(1975)
McNeil and Ptasnik
(1975)
Ratcliffe (1977)
Winneke et al.
(1982a)
Smelter area
Control = 46
3-15 (x =
9.3)
<40
WISC Full Scale IQ
C
=
93 Pb = 87
N.S.
(El Paso, TX)
Lead = 78
3-15 (x =
8.3)
40-68
WPPSI Full Scale IQU
c
=
91 Pb = 86
N. S.
WISC ~ WPPSI Combined
c
=
93 Pb = 88
P
<0.01
WISC ~ WPPSI Subscales
c
>
Pb on 13/14 scales
N.S.
-p <0.01
Neurologic testing
c
>
Pb on 4/4 tests
N.S.
-p <0.001
Smelter area
Control = 61-152
1.5 -
18(Mdn = 9)
<40
McCarthy General
(El Paso, TX)
Lead = 23-161
1.5 -
18(Hdn = 9)
>40
Cognitive
c
=
82 Pb = 81
N. S.
WISC-WAIS Full Scale
IQ
c
=
89 Pb = 87
N.S.
Oseretsky Motor Level
c
=
101 Pb = 97
N.S.
California Person-
ality
c
>
Pb, 6/10 items
p <0.05
Frostig Perceptual
Quotient
c
=
100 Pb = 103
N.S.
Finger-Thumb
/
Apposition
c
=
27 Pb = 29
N.S.
Smelter area
Control = 23
4-7
28.2
Griffiths Mental Dev.
c
=
101-111 Pb = 97-107
N.S.
Manchester, Eng.
Lead = 24
4-8
44.4
Frostig Visual
Perception
c
=
14.3 Pb = 11.8
N.S.
Pegboard Test
c
=
17.5 Pb = 17.3
N.S.
c
=
19.5 Pb = 19.8
N.S.
Smelter area
(Duisburg, FRG)
Control =,26
Lead - 26
Winneke et al.
(1982b)
Smelter area
(Stolburg, FRG)
89
9.4
PbT =2.4 ppm German WISC Full Scale C = 122 Pb = 117 N.S.
PbT =9.2 ppm Verbal 1Q C = 130 Pb = 124 N.S.
No PbB Performance IQ C = 130 Pb = 123 N.S.
Bender Gestalt Test C = 17.2 Pb = 19.6 p <0.05
Standard Neurological C = 2.7 Pb = 7.2 N.S.
Tests
Conners Teachers Rating C = ? Pb = ? N.S.
Scale
PbT = 6.16 ppm
PbB = 14.3 pg/dl
German WISC Full Scale Prop.
of Variance=-0.0
N.S.
IQ
Verbal 0
-0.5
N.S.
Performance IQ
~0.6
N.S.
Bender Gestalt Test
~ 2.1
p <0.05
Standard Neurological
~ 1.2
N.S.
Tests
Conners Teachers Rating
0.4-1.3
N.S.
Scale
Wiener Reaction Performance
~2.0
N. S.
¦o
TO
TO
-c
o
TO,
^lean test scores for control children indicated by C = x; mean scores for respective lead-exposed groups indicated by Pb = x, except for Rummno (1979)
study where C = control, S = short-term lead-exposed subjects, L = long-term lead-exposed group, and P = post-encephalopathy lead group. N.S. = non-
significant, i.e. p >0.05. Note exception of £ <0.10 listed for spacial ability results in Kotok et al. (1977) study. Significance levels are those found
after partialing out confounding covariates. Urinary coproporphyrin levels were not elevated. Or ?30 jjg/d1 with positive radiologic findings, suggesting
earlier exposure in excess of 50-60^ng/dl. Assays for lead in teeth showed the Pb-exposed group to be approximately tw'ce as high as controls (20?
jjg/g vs..112 Mg/g. respectively). Used for children over 5 years of age. ^Used for children under 5 years of age. Main measure was dentine lead
(PbT). Dentine levels not reported for statistical reasons. ^Blood lead levels taken 9-12 months prior to testing; none above 33 pg/dl. Data not
corrected for age.
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PRELIMINARY DRAFT
Of the several pediatric studies presenting evidence for CNS deficits beincj associated
with lead exposure in asymptomatic children, most all are either retrospective or cross-
sectional studies except the work of De la Burde and Choate (1972, 1975). De la Burde and
Choate (1972) observed neurological dysfunctions, fine motor dysfunction, impaired concept
formation, and altered behavioral profiles in 70 preschool children exhibiting pica and ele-
vated blood lead levels (in all cases above 30 |jg/d 1; mean = 59 pg/dl) in comparison with
matched control subjects not engaging in pica. Subjects were drawn from the Collaborative
Study of Cerebral Palsy, Mental Retardation, and Other Neurologic Disorders of Infancy and
Childhood (Broman et al . , 1975), which was conducted in Richmond, Virginia, and had a total
population of 3400 mothers. The De la Burde and Choate study population was drawn from this
group, in which all mothers were followed throughout pregnancy and all children were post-
natally evaluated by regular pediatric neurologic examinations, psychological testing, and
medical interviews. All children subject to prenatal, perinatal, and early postnatal insults
were excluded from the study, and all had to have normal neurologic examinations and Bayley
tests at eight to nine months of age. These are important points which add value to the study.
It is unfortunate that blood lead data were not regularly obtained; however, at the time of
the study in the late 1960s, 10 to 20 ml of venous blood was required for a blood lead deter-
mination and such samples usually had to be obtained by either jugular or femoral puncture.
The other control features (housing location and repeated urinary coproporphyrin tests) would
be considered the state of the art for such a study at the time that it was carried out.
In a follow-up study on the same children (at 7 to 8 years old), De la Burde and Choate
(1975) reported continuing CNS impairment in the lead-exposed group as assessed by a variety
of psychological and neurological tests. In addition, seven times as many lead-exposed
children were repeating grades in school or being referred to the school psychologist, despite
many of their blood lead levels having by then dropped significantly from the initial study.
In general, the De la Burde and Choate (1972, 1575) studies appear to be methodologically
sound, having many features that strengthen the case for the validity of their findings. For
example, there were appreciable numbers of children (67 lead-exposed and 70 controls) whose
blood lead values were obtained in preschool years and who were old enough (7 years) during
the follow-up study to cooperate adequately for reliable psychological testing. The psycho-
metric tests employed were well standardized and acceptable as sensitive indicators of neuro-
behavioral dysfunction, and the testing was carried out in a blind fashion (i.e., without the
evaluators knowing which were control or lead-exposed subjects).
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The De la Burde and Choate (1972, 1975) studies might be criticized on several points,
but none provide sufficient grounds for rejecting their results: One difficulty is that blood
lead values were not determined for control subjects in the initial study; but the lack of
history of pica, as well as tooth lead analyses done later for the follow-up study, render it
improbable that appreciable numbers of lead-exposed subjects might have been wrongly assigned
to the control group. Subjects in the control group did have a history of pica, but not for
paint. Also, results indicating no measurable coproporphyrins in the urine of control sub-
jects at the time of initial testing further confirm proper assignment of those children to
the nonexposed control group. A second point of criticism is the use of multiple chi-square
statistical analyses, but the fact that the control subjects did significantly better on vir-
tually every measure makes it unlikely that all of the observed effects were due to chance
alone. One last problem concerns ambiguities in subject selection which complicate interpre-
tation of the results obtained. Because the lead-exposed group included children with blood
lead levels of 40 to 100 ^jg/dl, or of at least 30 pg/dl with "positive radiographic findings
of lead lines in the long bones, metallic deposits in the intestines, or both," observed defi-
cits might be attributed to blood lead .levels as low as 30 fjg/dl. Other evidence (Betts et
a 1. , 1973), however, suggests that such a simple interpretation is probably not accurate.
That is, the Betts et al. (1973) study indicates that lead lines are usually seen only if
blood levels exceed 60 g/d 1 for most children -at some time during exposure, although some
(about 25 percent) may show lead lines at blood lead levels of 40 to 60 |jg/dl. In view of
this, the de la Burde and Choate results can probably be most reasonably interpreted as
showing persisting neurobehavioral deficits at blood lead levels of 40 to 60 pg/dl or higher.
; In another clinic-type child study, Rummo et al. (1974, 1979), found significant neuro-
behavioral deficits (hyperactivity, lower scores on McCarthy scales of cognitive function,
etc.) among Providence, Rhode Island, inner-city children who had previously experienced high
levels of lead exposure that had produced acute lead encephalopathy. Mean maximum blood lead
levels recorded for those children at the time of encephalopathy were 88 ± 40 pg/dl. However,
children with moderate blood lead elevation but not manifesting symptoms of encephalopathy
were not significantly different (at p <0.05) from controls on any measure of cognitive func-
tioning, psychomotor performance, or hyperactivity. Still, when the data from the Rummo et
al. (1979) study for performance on the McCarthy General Cognitive Index or several McCarthy
Subscales are compared (see Table 12-1), the scores for long-term moderate-exposure subjects
consistently fall below those for control subjects and lie between the latter and the encepha-
lopathy group scores. Thus, it appears that long-term moderate lead exposure may have, in
fact, exerted dose-related neurobehavioral effects. The overall dose-response trend might
have been shown to be statistically significant if other types of analyses were used or if
2BPB12/B 12-60 9/20/83
957<
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PRELIMINARY DRAFT
larger samples were assessed. However, control for confounding variables in the different
exposure groups would also have to be considered. Note that (1) the maximum blood lead levels
for the short-term and long-term exposure subjects were all greater than 40 pg/d1 (means =
61 ± 7 and 68 ± 13 pg/dl, respectively), whereas control subjects all had blood lead levels
below 40 pg/dl (mean = 23 ± 8 jjg/d 1), and (2) the control and lead-exposed subjects were
inner-city children well matched for socioeconomic background, parental 'education levels,
incidence of pica, and other pertinent factors, but not parental IQ.' '
A somewhat similar pattern of results emerged from a study by Kotok et al. (1977) in
which 36 Rochester, New York, control-group children with blood lead levels less than 40 (jg/d1
were compared with 31 children having distinctly elevated blood lead levels (61 to 200 pg/dl)
but no classical lead intoxication symptoms. Both groups were well matched on important back-
ground factors, notably including their propensity to exhibit pica. Again, no clearly statis-
tically significant differences between the two groups were found on numerous tests of cogni-
tive and sensory functions. However, mean scores of control-group children were consistently
higher than those of the lead-exposed group for all six of the ability classes listed. Kotok
(1972) had reported earlier that developmental deficiencies (using the comparatively insen-
sitive Denver Development Screening test) in a group of chi ldren ¦ having elevated lead levels
(58 to 137 pg/dl) were identical to those in a control group similar in age, sex, race,
environment, neonatal condition, and presence of pica, but whose blood lead levels were lower
(20 to 55 (jg/dl). Children in the lead-exposed group, however, had blood lead levels as high
as 137 pg/dl, whereas some control children had blood lead levels as high as 55 pg/dl. Thus,
the study essentially compared two groups with different degrees of markedly elevated lead
exposure rather than one of lead-exposed vs. nonexposed control children.
Perino and Ernhart (1974) reported a relationship between neurobehavioral deficits and
blood lead levels ranging from 40 to 70 pg/dl in a group of 80 inner-city preschool black
children, based on the results of a cross-sectional study including children detected as
having elevated lead levels via the New York City lead screening program. One key result
reported was that the high-lead children had McCarthy Scale IQ scores markedly lowe than those
of the low-lead group (mean IQ = 90 vs 80, respectively). Also, the normal correlation of
0.52 between parents' intelligence and that of their offspring was found to be reduced to only
0.10 in the lead-exposed group, presumably because of the influence of another factor (lead)
that interfered with the normal intellectual development of the lead-exposed children. One
obvious possible alternative explanation for the reported results, however, might be differ-
ences in the educational backgrounds of parents of the control subjects when compared with
lead-exposed subjects, because parental education level was found to be significantly nega-
tively related to blood lead levels of the children participating in the Perino and Ernhart
2BPB12/B 12-61 9/20/83
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PRELIMINARY DRAFT
(1974) study. The importance of this point lies in the fact that several other studies
(McCall et al. , 1972; Elardo et a 1. , 1975; Ivanans, 1975) have demonstrated that higher paren-
tal education levels are associated with more rapid development and higher intelligence quo-
tients (IQs) for their children.
Ernhart et al. (1981) were able to follow up 63 of the 80 preschool children of the
Perino and Ernhart (1974) study once they reached school age, using the McCarthy IQ scales,
various reading achievement-tests, the Bender-Gestalt test, the Draw-A-Child test, and the
Conners Teacher's Questionnaire for hyperactivity. The children's blood lead levels cor-
related significantly with FEP (r = 0.51) and dentine lead levels (r = 0.43), but mean blood
lead levels of the moderately elevated group had decreased after five years. When control
variables of sex and parent IQ were extracted by multivariate analyses, the observed differ-
ences were reported to be greatly reduced but remained statistically significant for three of
seven tests on the McCarthy scales in relation to concurrently measured blood lead levels but
not in relation to the earlier blood lead levels for the same children. This led Ernhart et
al. (1981) to reinterpret their 1974 (Perino and Ernhart, 1974) IQ results (in which they
had not controlled for parental education) as either not likely being due to lead or, if due
to lead, then representing un'l-y minimal effects on intelligence.
The Perino and Ernhart (1974) and Ernhart et al. (1981) studies were intensively reviewed
by an expert committee convened by EPA in March, 1983 (see Appendix 12-C). The committee
found that blood lead measurements used in the Perino and Ernhart (1974) study were of accep-
table reliability and the psychometric measures for children were acceptable. However, the
IQ measure used for their parents was of questionable utility, other confounding variables
may not have been adequately measured, and the statistical analyses did not deal adequately
with confounding variables. As for the Ernhart et al. (1981) follow-up study, the committee
found the psychometric measures to be acceptable, but the blood lead sampling method raised
questions about the reliability of the reported blood lead levels and the statistical analyses
did not adequately control for confounding factors. The committee concluded, therefore, that
the Perino and Ernhart (1974) and Ernhart et al. (1981) study results, as published, neither
confirm nor refute the hypothesis of associations between neuropsychologic deficits and low-
level lead exposures in children. It was also recommended that the entire Ernhart data set be
reanalyzed, using statistical analyses that better control for confounding factors and includ-
ing longitudinal analyses of data for subjects that were evaluated in both the Perino and
Ernhart (1974) and the Ernhart et al. (1981) studies. A sample longitudinal analysis provided
by one committee member, using uncorrected blood lead values and unadjusted psychometric
scores from such subjects, suggested that an association may exist between changes in blood
lead levels and changes in IQ scores from the first to the second sampling point.
2BPB12/B
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PRELIMINARY DRAFT
Two recent reports of a study of 193 children from the Philadelphia cohort of the Collab-
orative Perinatal Project at age seven years examined the persistence of lead-related neuro-
psychological deficits using circumpulpal rather than primary dentine lead assays at ages
10-14 years (Shapiro and Ma^ecek, 1983, Marecek et al., 1983). Performance differences on
several subtests of the Wechsler Intelligence Scale for Children (WISC) and Bender-Gestalt
Test were found to persist after four years, these effects being more evident when related
to circumpulpal than to primary dentine lead levels. Methodologically,1 this study suffers
from sampling bias, subject ascertainment bias, poor control of covarying social factors, and
use of different testers at different testing periods, with no notation as to their blindess.
Odenbro et al. (1983) studied psychological development of children (aged 3-6 yr) seen
in Chicago Department of Health Clinics (August, 1976 - February, 1977), evaluating Denver
Development Screening test (DDST) and Wechsler IQ scales (WPPSI) scores in relation to blood
lead levels obtained by repeated sampling during the three previous years. A significant cor-
relation (r - -0.435, p <0.001) was reported between perceptual-visual-motor ability and mean
blood levels measured. Statistically significant (p <0.005) deficits in verbal productivity
and perceptual visual motor performance (measured by the WPPSI) were found for children with
mean blood lead levels of 30-40 (jg/d1 versus control children with mean1 blood lead levels
<25 pg/dl, using two-tailed Student's t-tests. These results are highly suggestive of neuro-
psychologic deficits being associated with blood lead levels of 30-60 pg/dl in preschool
children. However, questions can be raised regarding the adequacy of the statistical analyses
employed, especially in regard to sufficient control for confounding covariates, e.g., parental
IQ, education, and socioeconomic status.
The above studies generally found higher lead-exposure groups to do more poorly on IQ or
other types of psychometric tests. However, many studies did not control for importtant con-
founding variables or, when such were taken into account, differences between lead exposed and
control subjects were often no longer statistically significant. Still, the consistency of
finding lower IQ values among at-risk higher lead children across the studies lends credence
to cognitive deficits occurring in apparently asymptomatic children with relatively high blood
lead levels. The De la Burde studies in particular point to 40*60 |jg/d1 as likely lowest
observed effect levels among such children.
12.4.2.2.2.2 General population studies. These studies evaluated samples of non-overtly
lead intoxicated children drawn from and thought to be representative of the general pediatric
population. They generally aimed to evaluate asymptomatic children with lower lead body bur-
dens than those of children in most of the above clinic-type studies.
A pioneering, general population study was reported by Needleman et al. (1979), who used
shed deciduous teeth to index lead exposure. Teeth were donated from 70 percent of a total
population of 3329 first and second grade children from two towns near Boston. Almost all
2BPB12/B 12-63 9/20/83
960<
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PRELIMINARY DRAFT
children who donated teeth (2146) were rated by their teachers on an eleven-item classroom
behavior scale devised by the authors to assess attention disorders. An apparent dose-response
function was reported for ratings on the behavior scale not taking potentially confounding
variables into- account. After excluding various subjects for control reasons, two groups
(<10th and >90th percentiles of primary dentine lead levels) were provisionally selected for
further in-depth neuropsychologic testing. Later, some provisionally eligible children were
also excluded -for -various- reas'ons, leaving 100 low-lead (<10 ppm dentine lead) children for
comparison with 58 high-lead (>20 ppm dentine lead) children in statistical analyses reported
by Needleman et al. (1979). A preliminary analysis on 39 non-lead variables showed significant
differences between the low- high-lead groups for age, maternal IQ and education, maternal
age at time of birth, paternal SES, and paternal education. Some of these variables were
entered as covariates into an analysis of covariance along with lead. Significant effects
(p <0.05) were reported for full-scale WISC-R IQ scores, WISC-R verbal scales scores, for 9 of
11 classroom behavior scale items, and several experimental measures of perceptual-motor
behavior.
Additional papers published by Needleman and coworkers report on results of the same or
further analyses -of the data discussed in the initial paper by Needleman et al. (1979). For
example, a paper by Needleman (1982) provided a summary overview of findings from the Needleman
et al. (1979) study and findings reported by Burchfiel et al. (1980) that are discussed later
in this section concerning EEG patterns for a subset of children included in the 1979 study.
Needleman (1982) summarized results of an additional analysis of the 1979 data set reported
elsewhere by Needleman, Levitan and Bellinger (1982). More specifically, cumulative frequency
distributions of verbal IQ scores for low- and high-lead subjects from the 1979 study were
reported by Needleman et al. (1982), and the key point made was that the average IQ deficit of
four points demonstrated by the 1979 study did not just reflect children with already low IQs
having their cognitive abilities further impaired. Rather the entire distribution of IQ scores
across all IQ levels was shifted downward in the high-lead group, with none of the children in
that group having verbal IQs over 125. Another paper, by Bellinger and Needleman (1983), pro-
vided still further follow-up analyses of the 1979 N. Eng. J. Med. data set, focusing mainly
on comparison of the low- and high-lead children's observed versus expected IQs based on their
mother's IQ. Bellinger and Needleman reported that regression analyses showed that IQs of
children with elevated levels of dentine-lead (>20 ppm) fell below those expected based on
their mothers' IQs and the amount by which a child's IQ falls below the expected value in-
creases with increasing dentine-lead levels in a nonlinear fashion. Scatter plots of IQ
residuals by dentine-lead levels, as illustrated and discussed by Bellinger and Needleman
(1983), indicated that regressions for children with 20-29.9 ppm dentine lead in the high-lead
2BPB12/B
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PRELIMINARY DRAFT
group did not reveal significant associations between increasing lead levels in that range and
IQ residuals, in contrast to statistically significant (p <0.05) correlations between IQ resi-
duals ana dentine-lead for high-lead group children with 30-39.9 ppm dentine lead levels.
The Needleman et al. (1979) study and spin-off analyses published later by Needleman and
coworkers were critically evaluated by the same expert committee noted above that was convened
by EPA in March, 1983, and which evaluated the Perino and Ernhart (1974) and Ernhart et al.
(1981) studies (see Appendix 12-C). In regard to the original study reported by Needleman
et al. (1979), the expert committee found that dentine-lead was adequately determined as a
measure of cumulative lead exposure and the psychometric data for'the subject children ge.rier11
ally appeared to be adequately collected and of acceptable reliability. However, the commit-
tee concluded that the reported dose-response relationship between dentine-lead levels and
teachers' ratings of classroom behavior cannot be accepted as valid, due to: (*1) serious res-
ervations regarding the adequacy of classification of subjects into lead exposure categories
using only the first dentine-lead level obtained for each child and (2) failure to control for
effects of confounding variables. The committee also found that the reported statistically
significant effects of lead on IQ and other behavioral neuropsychologic abilities measured for
the low- and high-lead groups could not be accepted as valid, due to: (1) errors made in cal-.
culations of certain parental IQ scores entered as a control variable in analyses of covari-
ance; (2) failure to take age and father's education into account adequately--in the analyses,
of covariance; (3) use of a forward elimination approach rather than a backwards elimination
strategy in statistical analyses; (4) concerns regarding the basis for classification of
children in terms of dentine-lead levels; and (5) questions about possible bias due to exclu-
sion of data for large numbers of provisionally eligible subjects from statistical analyses.
The committee concluded, therefore, that the study results, as published by Needleman et al.
(1979), neither confirm nor refute the hypothesis of associations between neuropsychologic
deficits and low-level lead exposure in non-overtly lead intoxicated children. In regard to
the publications by Needleman (1982), Needleman et al. (1982), and Bellinger and Needleman
(1983) describing further analyses of the same data set reported on by Needleman et al.
(1979), the committee concluded that the findings reported in these later papers also cannot
be accepted as valid, in view'of the above reservations regarding the basic analyses reported
by Needleman et al. (1979) and additional problems with the later "spin-off" analyses. The
committee also recommended that the entire Needleman data set be reanalyzed, correcting for
errors in data calculation and entry, using better Pb exposure classification, and appropri-
ately adjusting for confounding factors.
A recent study of urban children in Sydney, Australia (McBride et al., 1982) involved 454
preschoolers (aged 4-5 yr) with blood lead levels of 2 to 29 (jg/dl. Children born at the
Women's Hospital in Sydney were recruited via personal letter. No blood lead measures were
2BPB12/B 12-65 9/20/83
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PRELIMINARY DRAFT
available on non-participants. Blood levels were evaluated after neurobehavioral testing, but
earlier exposure history was apparently not assessed. Using a multiple statistical comparison
procedure and Bonferroni correction to protect against study-wise error, no statistically
significant differences were found between two groups with blood lead levels more than one
standard deviation above and below the mean (>19 |jg/dl vs. <9 pg/dl) on the Peabody Picture
Vocabulary IQ Test, on a parent rating scale of hyperactivity devised by Rutter, or on three
tests of motor ability (pegboard, standing balance, and finger tapping). In one test of fine
motor coordination (tracking), five-year old boys in the higher lead group performed worse
than'boys in the- 1 ower- 'lead- group.' In one test of gross motor skill (walking balance), results
for the two age groups were conflicting. This study suffers from many methodological weak-
nesses and cannot be regarded as providing evidence for or against an effect of low-level lead
exposures in non-overtly lead intoxicated children. For example, a comparison of socioeconomic
status (father's occupation and mother's education) of the study sample with the general popu-
lation showed that it was higher than Bureau of Census statistics for the Australian work force
as a whole. There was apparently some self-selection bias due to a high proportion of profes-
sionals living near the hospital. Also, other demographic variables such as mother's IQ, pica,
and caregiving environment were not evaluated.
Another recent large scale study (Smith et al., 1983) of tooth lead, behavior, intelli-
gence and a variety of other-psychological skills was carried out in a general population sam-
ple of over 4000 children aged 6 to 7 years in three London boroughs, 2663 of whom donated
shed teeth for analysis. Of these, 403 children were selected to form six groups, one each of
high (8 pg/g or more), intermediate (5-5.5 pg/g), and low (2.5 pg/g or less) tooth lead levels
for two socioeconomic groups (manual vs. non-manual workers). Parents were intensively inter-
viewed at home regarding parental interest and attitudes toward education and family charac-
teristics and relationships. The early history of the child was then studied in school using
tests of intelligence (WISC-R), educational attainment, attention, and other cognitive tasks.
Teachers and parents completed the Conners behavior questionnaires. Results showed that in-
telligence and other psychological measures were strongly related to social factors, especi-
ally social grouping. Lead level was linked to a variety of factors in the home, especially
the level of cleanliness, and to a lesser extent, maternal smoking. There was no statisti-
cally significant link between lead level and IQ or academic performance. However, when rated
by teachers (but not by parents), there were small, reasonably consistent (but not statisti-
cally significant) tendencies for high-lead children to show more behavioral problems after
the different social covariables were taken into account statistically. The Smith et al.
(1983) study has much to recommend it: (1) a well-drawn sample of adequate size; (2) three
tooth "lead groupings based on well-defined classifications minimizing possible overlaps of
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exposure groupings using whole tooth lead values, including quality-controlled replicate ana-
lyses comparisons for the same tooth and duplicate analyses comparisons across multiple teeth
from the same child; (3) blood lead levels on a subset of 92 children (averaging 13.1 M9/dl),
which correlated reasonably well with tooth "ead levels (r = 0.45); (4) cross-stratified
design of social groups; (5) extensive information on social covariates and exposure sources;
and (6) statistical control for potentially confounding covariates in the analsyes of study
results. However, one possible source of selection bias was that tooth donors had a signifi-
cantly higher social status than non-donors. Thus, the reported results may be less generali-
zable to the lower socioeconomic working classes, where one,might expect the. effects of- lead
exposure to be greater (Yule and Lansdown, 1983).
Harvey et al. (1983) also recently reported that blood lead made no significant contri-
bution to IQ decrements after appropriate allowance had been made for social factors. This
study involved 189 children, average age 2.5 years and 15.5 pg/dl blood lead, of middle class
workers from the inner city of Birmingham, England. The investigators utilized a wide range
of behavioral measures of activity level and psychomotor performance. Strengths of this study
are: (1) a well-drawn sample, (2) extensive evaluation of 15 confounding social factors, (3)
a wide range of abilities evaluated, and (4) blind evaluations. However, evaluation of lead
burden was based on only a single venous blood sample, so that exposure history was not docu-
mented as well as in the study by Smith et al. (1983). Nevertheless, a stronger correlation
between IQ and blood lead levels was found in children of manual workers (r - -0.32) than in
children of non-manual workers (r = -0.06), consistent with findings from the Yule and
Lansdown (1983) study discussed below.
Yule et al. (1981) carried out a pilot study on the effects of low-level lead exposure on
85 percent of a population of 195 children aged 6-12 years, whose blood lead concentrations
had been determined some nine months earlier as part of a European Economic Community survey.
The blood lead concentrations ranged from 7 to 32 pg/dl , and the children were assigned to
four quartiles encompassing the following values: 7 to 10 pg/dl; 11 to 12 pg/dl; 13 to .16
pg/dl; and 17 to 32 pg/dl. The tests of achievement and intelligence were similar to those
used in the Lansdown et al .- (1974) and Needleman et al. (1979) studies. There were signifi-
cant associations between blood lead levels and scores on tests of reading, spelling, and in-
telligence, but not on mathematics (Yule et al. , 1981). These differences in performance
largely remained after age, sex, and father's occupation were taken into account. However,
other potentially confounding social factors were not controlled in.this study. Another paper
by Yule et al. (1983) dealt with the results pertinent to attention deficits. While there
were few differences between groups on the Rutter Scale, the summed scores on the Needleman
questionnaire across the blood lead groupings approached significance (p = 0.096). Three of
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the questionnaire items showed a significant dose-response function ("Day Dreamer," "Does not
Follow Sequence of Direction," "Low Overall Functioning"). Nine of 11 items were highly cor-
related with children's IQ. Therefore, the Needleman questionnaire may be tapping IQ-related
attention deficits as opposed to measures of conduct disorder and socially maladaptive behav-
ior (Yule et al. , 1983). The hyperactivity factors on the Conners and Rutter scales were
reported to be related to blood lead levels (7-12 vs. 13-32 M9/dl), but the authors noted that
caution is necessary in interpreting their findings in view of the crude measures of social
factors available and differences between countries in diagnosing attention deficit disorders.
Moreover, -since the blood'1ead-values reported were determined only once (nine months before
psychological testing), earlier lead exposures may not be fully reflected and the reported
blood lead levels cannot be accepted confidently as those with which any behavioral effects
might be'associated. Also, home environment and parental IQ and education were not evaluated.
Yule and Lansdown (1983) reported a second, better designed study with similar methods
and procedures using 194 children living in a predominantly lower-middle-class area of London
near a busy roadway. In this study, a lengthy structured interview yielded data on sources of
exposure, medical history, and many potentially confounding variables. Parental IQ was also
examined. In contrast to the first pilot study, no statistically significant relationships
were found even before social class was controlled for in the statistical analyses. Still,
the authors stated that there- was some evidence of weak associations between lead level and
intelligence in working-class groups but whether these are of a causal nature in either direc-
tion is unclear.
Two studies by. Winneke and colleagues, the first a pilot study (Winneke et al., 1982a)
and the second an extended study (Winneke et al., 1982b) discussed later, employed teeth lead
analyses analogous to some of the above studies. In the pilot study, incisor teeth were
donated by 458 children aged 7 to 10 years in Duisburg, Germany, an industrial city with air-
borne lead concentrations between 1.5 and 2.0 (jg/m3. Two extreme exposure groups were formed,
a low-lead group with 2.4 (jg/g mean tooth lead level (n = 26) and another, high-lead group
with 7 pg/g mean, tooth lead level (n = 16), and matched for age, sex, and father's occupa-
tional status. The two groups did not differ significantly on confounding covariates, except
that the high-lead group showed more perinatal risk factors. Parental IQ and quality of the
home environment were not among the 52 covariables examined. The authors found a marginally
significant decrease (p <0.10) of '5-7 IQ points and a significant decrease in perceptual-
motor integration (p <0.05), but no significant differences in hyperactivity as measured by
the Conners Teachers' Questionnaire administered during testing. As with the Yule et al.
(1981) study, the inadequacy of the background social measures (e.g., parental IQ, caregiving
environment, and pica), and group differences in perinatal factors weaken this study.
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None of the general population studies reviewed provide strong evidence for neuropsycho-
logic deficits being associated with relatively low body lead burdens in non-overtly lead
intoxicated children representative of general pediatric populations. All of the studies
reporting statistically significant associations between cognitive (IQ) or other behavior
(e.g., attentional) deficits have methodological weaknesses, especially inadequate control for
confounding covariates such as parental IQ or socioeconomic status. On the other hand, in
view of the consistent pattern of results from such studies showing relationships between lead
and neuropsychologic deficits before major confounding variables are controlled for, one
cannot completely rule out the possibility tha£ lead may be contributing to the observed
deficits, especially given the cross-sectional design used in such studies (see Appendix 12-C
introduction). The findings of no significant associations between lead and cognitive/behav-
ioral deficits in several recently reported studies (generally controlling better for con-
founding variables) may not be incompatible with this possibility, in view of the latter
studies apparently having evaluated children with lead body burdens likely generally lower
than the former studies reporting at least suggestive evidence for lead effects on cognitive
and behavioral functions. «.
12.4.2.2.2.3 Smelter area studies. These studies evaluated children with elevated lead
exposures associated with residence in close proximity to lead emitting smelters.
For example, Lansdown et al. (1974) reported a relationship between blood lead level in
children and the distance they lived from lead-processing facilities, but no relationship
between blood lead level and mental functioning. However, only a minority of the lead-exposed
cohort had blood lead levels over 40 pg/dl. Furthermore, this study failed to consider ade-
quately social factors such as socioeconomic status.
In another study, Landrigan et al. (1975) found that lead-exposed children living near an
El Paso, Texas, smelter scored significantly lower than matched controls on measures of per-
formance IQ and finger-wrist tapping. The control children in this study were, however, not
well matched by age or sex to the lead-exposed group, although the results remained statisti-
cally significant after adjustments were attempted for age differences. McNeil and Ptasnik
(1975) found negative results in another sample of children living near the same lead smelter
in El Paso who were generally comparable medically and psychologically to matched controls
living elsewhere in the same city, except for the direct effects of lead (blood lead level,
free erythrocyte protoporphyrin levels, and X-ray findings). An extensive critique of these
two studies made by another expert committee (see Appendix 12-D) found that no reliable con-
clusions could be based on either of the two El Paso smelter studies in view of various metho-
dological and other problems affecting the conduct of the studies.
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A later study by Ratcliffe (1977) of children living near a battery factory in Manchester,
England, found no relation between their blood levels taken at two years of age (28 |.ig/d 1 vs.
44 (jg/dl in low- vs. high-lead groups) and testing done at age five on the Griffiths Mental
Development Scales, the Frostig Developmental Test of Visual Perception, a pegboard test, or a
behavioral questionnaire. The differences in scores, although small, favored the low-lead
exposure children, i.d., they had somewhat better scores than the higher exposure group. The
failure to repeat blood lead assays at age five weakens this otherwise adequate study; poten-
tially higher blood lead levels occurring after age two'among control children may have less-
ened exposure differences between the low- and high-lead groups.
Winneke et al. (1982b) carried out a study which involved 115 children aged 9.4 years
living in the lead smelter town of Stolberg. Tooth lead (X - 6.16 ppm, range = 2.0-38.5 ppm)
and blood lead levels (X = 13.4 pg/dl; range - 6.8-33. 8'pg/dl were significantly correlated
(r = 0.47; p <0.001) for the children studied. Using stepwise multiple regression analysis,
the authors found significant (p <0.05) or marginally significant (p <0.10) associations be-
tween tooth lead levels and measures of perceptual-motor integration, reaction time perfor-
mance, and four behavioral rating dimensions, including distractibi1ity. This was true even
after taking into account age, sex, duration of labor at birth, and socio-heredity background
as covariates. However, the proportion of explained variance due to lead never exceeded
6 percent for any of these outcomes, and no significant association was found between tooth
lead and WI5C verbal-IQ after the effects of socio-hereditary background were eliminated.
The above smelter area studies, again, do not provide strong evidence for cognitivie or
behavior deficits being associated with lead exposure in nonovertly lead exposed children.
At the same time, the possibility of such deficits being associated with lead exposure in
apparently asymptomatic children cannot be ruled out, either, given the overall pattern of
results obtained with the cross sectional study design typically employed (see Appendix 12-C
i ntroduction).
Several studies have also reported significant associations between hair lead levels and
behavioral or cognitive testing endpoints (Pihl and Parkes, 1977; Hole et al., 1979; Hansen
et al., 1980; Capel et al., 1981; Ely et al., 1981; Thatcher et al., 1982a,b; Marlowe et al.,
1982, 1983; Marlowe and Errera, 1982). Measures of hair lead are easily contaminated by ex-
ternal exposure and are generally questionable in terms of accurately reflecting internal body
burdens (see Chapter 9). Such data, therefore, cannot be credibly used to evaluate relation-
ships between absorbed lead and nervous system effects and are not discussed further.
12.4.2.2.2.4 Studies of mentally retarded or behaviorally abnormal children. Other stu-
dies, of mentally retarded or autistic individuals and infants, have shown such abnormal popu-
lations to have somewhat higher lead levels than the control groups (Beattie et al., 1975;
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David et al. , 1972, 1976,, 1979a,b, 1982a,b, 1983; Moore et a1., 1977). However, whether dis-
orders such as mental retardation, hyperactivity, autism, etc. are the causes or the effects
of lead exposure is a difficult, issue to resolve, and most of the studies cited employed
study designs not capable of achieving such resolution. Still, results of at least one study
(David et al. , 1983) indicate that chelation therapy leading to reduced lead levels resulted
in some improvement in behavior among a group of retarded individuals, suggesting that lead
may contribute to deviant behavior patterns among such behaviorally abnormal populations, even
if lead was not the key etiological-factor originally causing the retardation or other behav-
ioral abnormalities. , .
12.4.2.2.2.5 Electrophysiological studies of lead effects in children. In addition to
studies using psychometric and behavioral testing approaches, electrophysiological studies of
CNS lead neurotoxicity in non-overtly lead-intoxicated children have been conducted.
Burchfiel et al. (1980) used computer-assisted spectral analysis of a standard EEG exam-
ination on 41 children from the Needleman et al. (1979) study and reported significant EEG
spectrum differences in percentages of - low-frequency delta activity and in alpha activity in
spontaneous EEGs of the high-lead children. Percentages of alpha and delta frequency EEG
activity and results for several psychometric and behavioral testing variables (e.g., WISC-R
full-scale IQ and verbal IQ, reaction, time under varying delay, etc.) for the same children
were then employed as input variables.(or "features") in direct and stepwise discriminant anal-
yses. The separation determined by these analyses for combined psychological and EEG variables
(p <0.005) was reported to be strikingly better than the separation of low-lead from high-lead
children using either psychological (p <0.041) or EEG (p <0.079) variables alone. Unfortun-
ately, no dentine lead or blood lead values were reported for the specific children from the
Needleman et al. (1979) study who underwent the EEG evaluations reported by Burchfiel et al.
(1980), and making it impossible to estimate lead-exposure levels associated with observed EEG
effects. (See also Appendix 12-C).
The relationship between low-level lead exposure and neurobehavioral function (including
electrophysiological responses) in children aged 13-75 months was extensively explored in
another study, conducted at the University of North Carolina in collaboration with the U.S.
Environmental Protection Agency. Psychometric evaluation (Milar et al., 1980, 1981a) revealed
lower IQ scores for children with elevated blood lead levels of 30 pg/dl or higher compared
with children with levels under 30 fjg/dl , but the observed IQ deficits were confounded by
poorer home caregiver environment scores in children with elevated blood lead levels (Milar
et al., 1980); and no relationship between blood lead and hyperactive behavior (as indexed by
standardized playroom measures and parent-teacher rating scales) was observed in these child-
ren (Milar et al., 1981a). On the other hand, electrophysiological assessments, including
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analyses of slow cortical potentials during sensory conditioning (Otto et a 1. , 1981) and EEG
spectra (Benignus et a 1. , 1981), did provide evidence of CNS effects of lead in the same
children. In contrast to psychometric and behavioral findings, a significant linear relation-
ship between blood lead (ranging from 6 to 59 (jg/d 1) and slow wave voltage (SW) was observed
(Otto et a 1. , 1981) as depicted in Figure 12~3. Analyses of quadratic and cubic trends in SW
voltage, moreover, did not reveal any evidence of a threshold for this effect. The slope of
the blood lead x SW voltage function, however, varied systematically with age. No effect of
blood lead on EEG power spectra or coherence measures'was observed, but the relative amplitude
of synchronized EEG between left and right hemispheres (gain spectra) increased relative to
blood lead levels (Benignus et al., 1981). A significant cubic trend for gain between the
left and right parietal lobes was found with a major inflection point at 15 |jg/d1. This
finding suggests that EEG gain is altered at blood lead levels as low as 15 pg/dl, although
the clinical and functional significance of this. measure has not been established. A follow-
up study of slow cortical potentials and EEG spectra in a subset (28 children aged 35 to 93
months) of the original sample was carried out two years later (Otto et al., 1982). Slow wave
voltage during sensory conditioning again varied as a linear function of blood lead, even
though the mean lead level had declined by 11 (jg/d 1 (from 32.5 |jg/d 1 to 21.1 mg/d 1). The
similarity of SW results obtained at initial and follow-up assessments suggests that the ob-
served alterations in this parameter of CNS function are persistent, despite a significant
decrease in the mean blood lead level during the two-year interval.
Results of the neurobehavioral study and two-year follow-up described above are important
for several reasons. First, no significant relationship between child IQ and EEG measures was
found in the initial (Benignus et al. , 1981; Otto-et al., 1981) or follow-up study. SW volt-
age and EEG gain thus appear to provide CNS indices of lead exposure effects that may be both
more sensitive than and independent of standardized psychometric measures used in other stud-
ies. Electrophysiological measures such as these hold considerable promise as indicators of
CNS function that are free of cultural bias and other linguistic and motor constraints atten-
dant to traditional paper-and-penci1 or behavioral tests. Observation of a linear relation-
ship between SW voltage and blood lead within a range of 6 to 59 M9/dl, without evidence of
any threshold effect level, is also provocative, particularly in view of the apparent persis-
tence of the effect over a two-year interval. The inflection point in the EEG gain function
at 15 pg/dl provides additional evidence of the effect of lead exposure of CNS function in
young children at levels considerably below those previously considered to be safe (30 pg/dl).
Interpretation of these electrophysiological data, however, must be carefully tempered in view
of: (1) SW voltage and EEG gain are both experimental measures, the clinical and functional
significance of which is presently unknown; (2) estimated effective blood lead levels associ-
ated with the EEG effects are somewhat probalematic because the effects might have resulted
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MONTHS
-^p.vTv.v.v.
-10
-20
MONTHS
-30
-40
20
"i—rn—1—i—r
i—r
ui
<
t-
_i
MONTHS
O
>
"J -10
<
§
-20
AGE, months
• 12 23
¦ 24-35
a 3647
5
o
_l
w -30
20
1—r
(c) ~
10 -
o 48 59
~ 60-75
-20
5 10 15 20 25 30 35 40 45 50 55
PbB LEVEL, ^g.'dl
Figure 12-3. (a) Predicted SW voltage and 95% confidence
bounds in 13- and 75-month-old children as a function of
blood lead level, lb) Scatter plots of SW data from children
aged 13-47 months with predicted regression lines for
ages 18. 30, and 42 months, (c) Scatter plots for children
aged 48-75 months with predicted regression lines for
ages 54 and 66 months. These graphs depict the linear in-
teraction of blood lead and age.
Source: Otto et al. (1981).
12-73
970c
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PRELIMINARY DRAFT
from higher blood lead levels prior to the reported studies; and (3) the study sample was rela
tively small (n - 43 for the original and 28 for the follow-up SW analyses). In view of these
caveats, these findings need to be replicated in an independent sample. Nevertheless, they
provide clear evidence cf a-tered CNS functioning being associated with relatively low level
lead exposure of non-overtly lead intoxicated children and at least lead levels likely well
below 30 j.jg/d 1.
The adverse effects of lead on peripheral nerve function in children remain to be consi-
dered. Lead-induced peripheral neuropathies, although often seen in adults after prolonged
exposures, are rare in children. Several articles (Anku and Harris, 1974; Erenberg et al. ,
1974; Seto and Freeman, 1964), however, describe case histories of children with lead-induced
peripheral neuropathies, as indexed by electromyography, assessment of nerve conduction ve-
locity, and observation of other overt neurological signs, such as tremor and wrist or foot
drop. Frank neuropathic effects have been observed at blood lead levels of 60 to 80 pg/dl
(Erenberg et al. , 1974). In other cases, signs indicative of peripheral neuropathy have been
reported to be associated with blood lead values of 30 pg/dl. In these latter cases, however,
lead lines in long bones suggest probable past exposures leading to peak blood lead levels at
least as high as 40 to 60 ^g/dl and probably in excess .of 60 pg/dl (based cn the data of Betts
et al., 1973). In each of these case' studies, s.pme,-if not complete, recovery of affected
motor functions was reported after treatment for lead poisoning. A tentative association has
also been hypothesized between sickle cell disease and increased risk of peripheral neuropathy
as a consequence of childhood lead exposure. Half of the cases reported (10 out of 20) in-
volved inner-city black children, several with sickle cell anemia (Anku and Harris, 1974;
Feldman et al., 1973; Lampert and Schochet, 1968; Seto and Freeman, 1964; Imbus et al., 1978).
In summary, (1) evidence exists for frank peripheral neuropathy in children, and (2) such
neuropathy can be associated with blood lead levels at least as low as 60 pg/dl and, possibly,
as low as 40-60 pg/dl.
Further evidence for lead-induced peripheral nerve dysfunction in children is provided by
the data from two studies by Feldman et al. (1972, 1977) of inner city children and from a
study by Landrigan et al. (1976) of children living in close proximity to a smelter in Idaho.
The nerve conduction velocity results from this latter study are presented in Figure 12-4 in
the form of a scatter diagram relating peroneal nerve conduction velocities to blood lead
levels. No clearly abnormal conduction velocities were observed, although a statistically
significant negative correlation was found between peroneal NCV and blood lead levels
(r = -0.38, p <0.02 by one-tailed t-test). These results, therefore, provide evidence for
significant slowing of nerve conduction velocity (and, presumably, for advancing peripheral
neuropathy as a function of increased blood lead levels), but do not allow clear statements to
be made regarding a threshold for pathologic slowing of NCV.
2BPB12/B 12-74 9/20/83
971<
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88.00
82 90
77.60
u
01
72.40
E
>
- 67.20
O
o
LU
> 62.00
Z
o
y 56.80
D
O
z
o 51.60
46.40
41.20
36.00
0 15 30 45 60 75 90 105 120 135 150
BLOOD LEAD, ^g/dl
Figure 12-4. Peroneal nerve conduction velocity versus blood lead level, Idaho.
1974.
Source: Landrigan et al. (1976).
12-75
T i r
Y(CONDUCTION VELOCITY)
(r = —0.38Hn 2021
54.8 - .045 x (BLOOD LEAD)
• •
• 9 • t **
•J # • , •
• • • •
• • • •
• • "
• •
972 c
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PRELIMINARY DRAFT
12.4.3 Animal Studies
The following sections focus on recent experimental studies of lead effects on behavioral,
morphological, physiological, and biochemical parameters of nervous system development and
function in laboratory animals. Several basic areas or "issues are addressed: (1) behaviorial
toxicity, including the question of critical exposure periods for concurrent induction or
later expression of behavioral dysfunction in motor development, learning performance, and
social interactions; (?) alterations in morphology, including synaptogenesis, dendritic deve-
lopment, myelination, and fiber tract formation; (3) perturbations in various electrophysiolo-
gical parameters, e.g., ionic mechanisms of neurotransmission or conduction velocities in
various tracts; (4) disruptions of biochemical processes such as energy metabolism and
chemical neurotransmission; (5) the persistence or reversibility of the above types of effects
beyond the cessation of external lead exposure; and (6) the issue of "threshold" for neuro-
toxic effects of lead.
Since the initial description of lead encephalopathy in the developing rat (Pentschew and
Garro, 1966), considerable effort has been made to define more closely the extent of nervous
system involvement at subencephalopathic levels of lead exposure. This experimental effort
has focused primarily on exposure of the developing organism. The interpretation of a large
number of studies dealing with early ijn vivo exposure to lead has, however, been made diffi-
cult by variations in certain important experimental design factors across available studies.
One of the more notable of the experimental shortcomings of some studies has been the
occurrence of undernutrition in experimental animals (U.S. Environmental Protection Agency,
1977). Conversely, certain other studies of lead neurotoxicity in experimental animals have
been confounded by the use of nutritionally fortified diets, i.e., most commercial rodent
feeds (Michaelson, 1980). In general, deficiencies of certain minerals result in increased
absorption of lead, whereas excesses of these minerals result in decreased uptake (see Chapter
10). Commercial feeds may also be contaminated by variable amounts of heavy metals, including
as much as 1.7 ppm of lead (Michaelson, 1980). Questions have also been raised about possible
nutritional confounding due to the acetate radical in lead acetate solutions, which are often
used as the source of lead exposure in experimental animal studies ( Barrett and Livesey,
1982).
Another important factor that varies among many studies is the route of exposure to lead.
Exposure of the suckling animal via the dam would appear to be the most "natural" method, yet
may be confounded by lead-induced chemical changes in milk composition. On the other hand,
intragastric gavage allows one to determine precisely the dose and chemical form of admini-
stered lead, but the procedure is quite stressful to the animal and does not necessarily
reflect the actual amount of lead absorbed by the gut. Injections of lead salts (usually
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performed intraperitoneally) do not mimic natural exposure routes and can be complicated by
local tissue calcinosis at the site of repeated injections.
Another variable in experimental animal studies that merits attention concerns species
and strains of experimental subjects used. Reports by Mykkanen et al. (1980) and Overmann et
al. (1981) have suggested that hooded rats and albino rats may differ in their sensitivity to
the toxic effects of lead, possibly because of differences in their rates of maturation and/or
rates of lead absorption. Such differences may account for variability of lead effects
and exposure-response relationships between different species as well.
Each of the above factors may lead to widely variable internal lead burdens in the same
or different species exposed to roughly comparable amounts of lead, making comparison and
interpretation of results across studies difficult. The force of this discussion, then, is to
emphasize the importance of measurements of blood and tissue concentrations of lead in experi-
mental studies. Without such measures, attempts to formulate dose-response relationships are
futile. This problem is particularly evident in later sections dealing with the morpholo-
gical, biochemical, and electrophysiological aspects of lead neurotoxicity. I_n vitro studies
accorded attention in those sections, in contrast to jn vivo studies, are of limited relevance
in dose-response terms. The j_n vitro studies, however, provide valuable information on basic
mechanisms underlying the neurotoxic effects of lead.
The following sections discuss and evaluate the most recent studies of nervous system in-
volvement at subencephalopathic exposures to lead. Older studies reviewed in the previous
Air Quality Criteria Document for Lead (U.S. Environmental Protection Agency, 1977) are cited
as needed to illustrate particular points but, in general, the discussion below focuses on
more recent work.
12.4.3.1 Behavioral Toxicity: Critical Periods for Induction and Expression of Effects. The
1977 EPA review (U.S. Environmental Protection Agency, 1977) of animal behavioral studies and
a number of articles since then (e.g., Shigeta et al., 1977; Zenick et al., 1979; Crofton et
al., 1980; Kimmel , 1983) have pointed to the perinatal period of ontogeny as a particularly
critical time for the induction of behavioral effects due to lead exposure. Such findings are
consistent with the general pattern of development of the nervous system in the experimental
animals that have been investigated (see Reiter, 1982) and are reviewed in some detail in the
ensuing sections of this chapter.
Alterations in the behavior of rats exposed after weaning or after maturation have also
been reported (Angel 1 and Weiss, 1982; Cory-Slechta. and Thompson, 1979; Cory-Slechta et al. ,
1981; Donald et al., 1981; Geist and Mattes, 1979; Lanthorn and Isaacson, 1978; Nation et al.,
1982; Shapiro et al. , 1973). These findings stand in contrast to results from other studies
showing some effects in rats as being produced only by early perinatal exposure (e.g., Brown,
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1975; Brown et a 1. , 1971; Padich and Zenick, 1977; Shigeta et al., 1977; Snowdon, 1973).
Nevertheless, behavioral effects of relatively low-level exposure to lead have also been noted
in adult subjects of other species, including pigeons (Barthalmus et al., 1977; Dl'etz et al.,
1979) and fish (Weir and Hine, 1970), and the effects of lead exposure during adulthood are
not to be dismissed as inconsequential, although the present evaluation focuses mainly on the
effects of lead exposure early in development.
12.4.3.1.1 Development of motor function and reflexes. A variety of methods have been used
to assess the effect of lead on the ability of experimental animals to respond appropriately,
either by well defined motor responses or gross movements, to a defined stimulus. Such
responses have been variously described as reflexes, kineses, taxes, and "species-specific"
behavior patterns. The air righting reflex, which refers to the ability to orient properly
with respect to gravity while falling through the air and to land on one's feet, is only one
of several commonly used developmental markers of neurobehavioral function (Tilson and Harry,
1982). Overmann et al. (1979) found that development of this particular reflex was slowed in
rat pups exposed to lead via their dams (0.02 or 0.1 percent lead as lead acetate in the dams'
drinking water). However, neither the auditory startle reflex nor the ability to hang
suspended by the front paws was affected.
Grant et al. (1980) exposed rats indirectly to lead j_n utero and during lactation through
the mothers' milk and, after weaning, directly through drinking water containing the same
lead concentrations their respective dams had been given. In addition to morphological and
physical effects [see Sections 12.5, 12.6, and 12.11 for discussions of this work as reported
by Kimmel et al. (1980), Fowler et al. (1980), Faith et al. (1979), and Luster et al. (1978)],
there were delays in the development of surface righting and air righting reflexes in subjects
exposed under the 0.005 and 0.025 percent lead conditions; other reflexive patterns showed no
effect. The median blood lead concentration for the 0.005-percent subjects at postnatal day
(PND) 11 was 35 ng/dl; the median brain lead concentration was 0.07 (jg/g- Locomotor develop-
ment generally showed no significant alteration due to lead exposure. Body weight was signif-
icantly depressed for the most part in the 0.005- and 0.025-percent pups.
The ontogeny of motor function was also investigated by Overmann et al. (1981). Exposure
of pups to lead was limited to the period from parturition to weaning and occurred through
adulteration of the dams' drinking water with lead acetate (0.01 or 0.1 percent lead acetate).
The development of swimming performance was assessed on alternate days from PND 6 to 24. No
alterations in swimming ability were found. Rotorod performance was also tested at PND 21,
30, 60, 90, 150, and 440. Overall, the ability to remain on a rotating rod was significantly
impaired (p <0.01) at 0.1 percent and tended to be impaired (0.10 > p > 0.05) at 0.1 percent
(blood lead values were not reported). However, data for individual days were statistically
BPB12/A
12-78
975<
9/20/83
-------
PRELIMINARY DRAFT
significant only on PND-60 and 150. An adverse effect of lead exposure on rotorod performance
at PND 30-70 was also found in an earlier study by Overmann (1977) at a higher exposure level
of 30 mg/kg lead acetate by intubation (average PbB value at PND 21 was 173.5 ± 32.0 pg/dl).
At blood lead concentrations averaging 33.2 ± 1.4 pg/dl, however, performance was not
impaired. Moreover, other studies using rotorods at average blood lead concentrations of
approximately 61 pg/dl (Zenick et al., 1979) and 30 to 48 pg/dl (Grant et a 1., 1980) have not
found significant effects of lead on such performance when tested at PND 21 and 45, respec-
tively. Comparisons between studies are confounded by differences in body weight and age at
time of testing and by differences in speed and size of the rotorod apparatus (Zenick et al.,
1979).
Delays in the development of gross activity in rat pups have been reported by Crofton et
al. (1980) and by Jason and Kellogg (1981). It should be noted that very few studies have
been designed to measure the rate of development of activity. Ideally, subjects should be
assessed daily over the entire period of development in order to detect any changes in the
rate at which a behavior pattern occurs and matures. In the study by Crofton et al. (1980),
photocell interruptions by pups as they moved through small passageways into an "exploratory
cage" adjacent to the home cage were automatically counted on PND 5 to 21. Pups exposed in
utero through the dams' drinking water (0.01 percent solution of lead as lead chloride) lagged
controls by approximately one day in regard to characteristic changes in daily activity count
levels starting at PND 16. (81ood lead concentrations at PND 21 averaged 14.5 ± 6.8 pg/dl for
representative pups exposed to lead i_n utero and 4.8 ±1.5 pg/dl for controls.) Another form
of developmental lag in gross activity around PND 15-18, as measured in an automated activity
chamber, was reported by Jason and Kellogg (1981). Rats were intubated on PND 2-14 with lead
at 25 mg/kg (PbB = 50.07 ± 5.33 pg/dl ) and 75 mg/kg (PbB = 98.. 64 ± 9.89 fjg/dl). In this case,
the observed developmental lag was in the characteristic decrease in activity that normally
occurs in pups at that age (Campbell et al. , 1969; Melberg et al. , 1976); thus, lead-exposed
pups were significantly more active than control subjects at PND 18.
One question that arises when ontogenetic effects are discovered concerns the possible
contribution of the lead-exposed dam to her offsprings' slowed development through, for exam-
ple, reduced or impaired maternal care giving behavior. A detailed assessment of various
aspects of maternal behavior in chronically lead-exposed rat dams by Zenick et al. (1979),
discussed more fully in Section 12.4.3.1.4, and other studies using cross-fostering techniques
(Crofton et al., 1980; Mykkanen et al., 1980) suggest that the deleterious effects observed in
young rats exposed to lead via their mothers' milk are not ascribable to alterations in the
dams' behavior toward their offspring. Chronically lead-exposed dams may, if anything, tend
to respond adaptively to their developmentally retarded pups by, for example, more quickly
retrieving them to the nest (Davis, 1982).
BPB12/A 12-79 9/20/83
376<
-------
PRELIMINARY.DRAFT
12.4.3.1.2 Locomotor activity. The spontaneous activity of laboratory animals has been meas-
ured frequently and in various ways as a behavioral assay in pharmacology and toxicology
(Reiter and MacPhail, 1982). Such activity is sometimes described as gross motor activity or
exploratory behavior, and is distinguished from the motor function tests noted in the previous
section by the lack of a defined eliciting stimulus for the activity. With reports of hyper-
activity in lead-exposed children (see Section 12.4.2), there has naturally been considerable
interest in the spontaneous activity of laboratory animals as a model for human neurotoxic
effects of lead (see Table 12-2). As the 1977 review (U.S. Environmental Protection Agency,
1977) of this material demonstrated, however, and as other reviews (e.g., Jason and Kellogg,
1980; Michaelson, 1980; Mullenix, 1980) have since confirmed, the use of activity measures as
an index of the neurotoxic effects of lead has been fraught with difficulties.
First, there is no unitary behavioral endpoint that can be labeled "activity." Activity
is, quite obviously, a composite of many different motor actions and can comprise diverse be-
havior patterns including (in rodents) ambulation, rearing, sniffing, grooming, and, depending
on one's operational definition, almost anything an animal does. These various behavior pat-
terns may vary independently, so that any gross measure of activity which fails to differen-
tiate these components will be susceptible to confounding. Thus, different investigators'
definitions of activity are critical to interpreting and comparing these findings. When these
definitions are sufficiently explicit operationally (e.g., activity as measured by rotations
of an "activity wheal"), they are frequently not comparable with other operational definitions
of activity (e.g., movement in an open field as detected by photocell interruptions). More-
over, empirical comparisons show that different measures of activity do not necessarily cor-
relate with one another quantitatively (e.g., Copobianco and Hamilton, 1976; Tapp, 1969).
In addition to these rather basic difficulties, activity levels are influenced greatly by
numerous variables such as age, sex, estrous cycle, time of day, novelty of environment, and
food deprivation. If not controlled properly, any of these variables can confound measure-
ments of activity levels. Also, nutritional status has been a frequent confounding variable
in experiments examining the neurotoxic effects of lead on activity (see the review by U.S.
Environmental Protection Agency, 1977; Jason and Kellogg, 1980; Michaelson, 1980). In
general, it appears that rodents exposed neonatally to sufficient concentrations of lead
experience undernutrition and subsequent retardation in growth; and, as Loch et al. (1978)
have shown, retarded growth per se can induce increased activity of the same types that were
attributed to lead alone in some earlier studies.
In view of the various problems associated with the use of activity measures as a behav-
ioral assay of the neurotoxic effects of lead, the discrepant findings summarized in Table
12-2 should come as no surprise. Until the measurement of "activity" can be better
BPB12/A
12-80
9/20/83
-------
PRELIMINARY DRAFT
TABLE
12-2. EFFECTS OF LEAD ON ACTIVITY
IN RATS AND MICE
Age-dependent,
qualitative, nixed or
Increased
Decreased
no change
Dn'scoll and Steqner
Dn'scoll and Stegner
Barrett and Livesey (1982)
(1978)
(1976)
Brown (1975)
Goiter and Michaelson
Flynn et al. (1979)
(1975)
Crofton et al. (1980)
Gray and Reiter (1977)
Kostas et ,al. (1976)
Cutler (1977)
Reiter et al. (1975)
Overmann (1977)
Dolinsky et al. (1981)
Verlangieri (1979)
Petit and Alfano (1979)
Dubas and Hrdina (1978)
Sauerhoff and Michaelson
Geist and Balko (1980)
(1973)
Geist and Praed (1982)
Silbergeld and Goldberg
(1973, 1974a,b)
Grant et al. (1980)
Weinreich et al. (1977)
Gross-Selbeck and
Gross-Selbeck (1981)
Winneke et al. (1977)
Hastings et al. (1977)
Jason and Kellogg (1981)
Kostas et al. (1978)
Krehbiel et al. (1976)
Loch et al. (1978)
Minsker et al. (1982)
Mullenix (1980)
Ogilvie and Martin (1982)
Rafales et al. (1979)
Schlipkoter and Winneke (1980)
Sobotka and Cook (1974)
Sobotka et al. (1975)
Zimering et al. (1982)
BPB12/A
12-81
9/20/83
978<
-------
PRELIMINARY DRAFT
standardized, there appears to be little basis for comparing or utility in further discussing
the results of studies listed in Table 12-2.
12.4.3.1.3 Learning ability. When animal learning studies related to the neurotoxic effects
of lead were reviewed in 1977 (U.S. Environmental Protection Agency, 1977), a number of criti-
cisms of existing studies were noted. A major limitation of early work in this field was the
lack of adequate information on the exposure regimen (dosage of lead, how precisely adminis-
tered, timing of exposure) and the resulting body burdens of lead in experimental subjects
(concentrations of lead in blood, brain, or other tissue; time course of blood or tissue lead
values, etc.). A review of studies appearing since 1977 reveals a notable improvement in this
regard. A number of more recent studies have also attempted to control for the confounding
factors of litter effects and undernutrition--variables that were generally not controlled in
earlier studies.
Unfortunately, other criticisms are still valid Loday. The reliability and validity of
behavioral assays remain to be established adequately, although progress is being made. The
reliability of a number of common behavioral assays for neurotoxicity is currently being de-
termined by several independent U.S. laboratories (Kimmel et al., 1982). The results of this
program should he 1, standardize some behavioral testing procedures and perhaps create some
reference methods in behavioral toxicology. Also, as wel1-described studies are replicated
within and between laboratories, the reliability of certain experimental paradigms for demon-
strating neurotoxic effects is effectively established.
Some progress is also being made in dealing with the issue of the validity of animal be-
havioral assays. As the neurological and biochemical mechanisms underlying reliable behavi-
oral effects become better understood, the basis for extrapolating from one species to another
becomes stronger and more meaningful. An awareness of different species' phylogenetic, evo-
lutionary, and ecological relationships can also help elucidate the basis for comparing
behavioral effects in one species with those observed in another (Davis, 1982).
Tables 12-3 and 12-4 summarize exposure conditions, testing conditions, and results of a
number of recent studies of animal learning (see U.S. Environmental Protection Agency, 1977,
for a summary of earlier studies). Some general issues emerge from an examination of these
studies. One point of obvious interest is the lowest level of exposure at which behavioral
effects are clearly evident. Such a determination is best done on a species-by-species basis.
Rats seem to be the species of choice for the great majority of the behavioral studies,
despite the concerns that have repeatedly been expressed concerning the appropriateness of
this species as a subject for behavioral investigation (e.g., Lockard, 1968, 1971; Zeigler,
1973). Of the studies not obviously confounded by nutritional or litter effects, those by
Winneke et al. (1977, 1982c) and by Cory-Slechta and Thompson (1979) report alterations in
BPB12/A
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9/20/83
-------
TABLE 12-3. RECENT ANIMAL TOXICOLOGY STUDIES OF LEAD EFFECTS ON LEARNING IN RODENT SPECIES
Reference
Experimental
animal
(species
or strain)
Lead exposure
Pb conc.
(medium)
period
(route)
Treatment
groups
(n)
Li tters
per
group
Tissue lead
(age measured)
Aye at
testing
Testi ng
paradigm
(task)
Non-
behavioral
effects
Behavioral
results
Hastings
et al.
(1977)
Rat
(L-E)
0.01
or
0. 05%
(water)
PND 0-
21
(dam's
mi Ik)
C (12)
Pb, (12)
Pb2 (12)
Random
selection
from 9
1itters
PbB
(20 d):
C: 11 pg/dl
Pb,: 29
Pb2: 42
(60 d):
C: 4
Pb,: 5
Pb,: 9
-90-
186 d
Operant
(successive
brightness
di scrim.)
None
No sig. differences
between Pb-Ss
and C-Ss in
learning original
or reversed
discrim. task.
CO
O
A
Overmann
(1977)
00
CO
Rat
(L-E)
10,
30, or
90 rag/kg
(gavage)
PND 3-21
(di rect)
C
Pb,
Pb2
Pb3
12-
25
ea.
PbB (21 d)
C: 15 pg/dl
Pb,
Pb2
Pb,
33.2
173.5
226. 1
26-29 d
67-89 d
79-101 d
83-105 d
95-117 d
Aversi ve
conditioning
(1) active
2) passive)
Operant
(inhibit
response)
E-maze
(di scrim.:
1) spatial
2) tactile
3) visual)
None
Pbj-Ss sig. slower
in acquisition and
extinction of active
avoidance response;
no sig. diffs. for
passive avoidance.
All Pb groups failed
to inhibit responses
as well as C-Ss.
No sig. diffs. on E"
maze tasks, except
Pb2l3-Ss sig. worse
than C-Ss when on
tactile discrim.
-o
23
>
33
-e
o
23
>
Padich
and Zenick
(1977)
Rat
(CD)
375
mg/kg
(water)
Preconception
to
a) Weaning
(via dam)
or
b) termination
(via dam
and direct);
or
Weaning to
termination
(direct only)
0-0 (10)
0-Pb (10)
Pb-0 (10)
Pb-Pb (10)
42-
? d
Operant
(FR 20)
Body wt.
of Pb-Ss
< 0-Ss from
birth to
weaning.
Pb-Pb group
had sig. fewer
rewarded responses
even though
responding at
sig. higher rate.
Winneke
et al.
(1977)
Rat
(W)
372
mg/kg
(food)
Preconception
- Testing
(via dam
and
di rect)
C (20)
Pb (20)
(random
selection
from
110 male
pups)
PbB
(-16 d):
C: 1.7 pg/dl
Pb. 26.6
(-190 d)
Pb: 28.5
100-
200 d
Lashley
jumping
stand
(visual
discrim.
of stimulus:
1) orientation
2) size)
Body wt. of
Pb-Ss > C-Ss;
however, size
of Pb-Ss
1i tters
< C-S
1i tters.
Pb-Ss sig. slower
to learn size
di scrimination;
no diff. between
Pb and C groups
on orientation
discrim. (a rela-
tively easy task).
-------
TABLE 12-3. (continued)
Reference
Experimental
animal
(species
or strain)
Lead exposure
Pb conc.
(medium)
period
(route)
Treatment
groups
(n)
Litters
per
group
Tissue lead
(age measured)
Age at
testing
Testing
paradigm
(task)
Non-
behavioral
effects
Behavioral
results
ID
OP
r\}
i
00
Dietz
et al.
(1978)
Rat
Expt. l(L-E)
Expt. 2(CQ)
Lanthorn
& Isaacson
(1978)
Rat
(L-E)
Cory-
Schlecta
&
Thompson
(1979)
Rat
(S-D)
Cory-
Schlecta
et al.
(1981)
Rat
(S-D)
200
mg/kg
(gavage)
0.01%
(water)
PNO
3-30
(direct)
C (6)
Pb (7)
Preconcep-
tion to
termination
(via dam
until weaning,
then direct)
C (4)«
Pb (4)
0.27%
(water)
Adult
(direct)
(1) 0.005, PND
(2) 0.03, 20-
or
(3) 0.1%
(water)
(1) 0.01
or
(2) 0.03%
(water)
PND
21-?
C (4)
Pb (6)
(a) 70
or
(b) 150
(direct)
la:
C (4)*
Pb (5)
lb:
C (4)*
Pb (6)
2:
C (3)*
Pb (4)
3:
C (4)*
Pb (5)
C (4)
Pb, (5)
Pb2 (5)
2, split
random
assign-
ment
random
assign-
ment
PbB (150 d):
C: -6 pg/dl
la: ~3
lb: ~7
2: -27
3: -42
Brain-Pb
(post-test):
C: 14-26 ng/g
Pb,: 40-142
Pb2: 320-1080
3 mo
or
21 mo
8 mo
Adul t
55-
140 d
55-
? d
Operant
(minimum
20-sec pd.
between
bar-presses)
T-maze
(1) spontan.
alternation
2) light
di scrim.
3) spatial
di scrim.)
Operant
(FI-
30 sec)
Operant
(m i n i mum
duration
bar-press)
None
Pb-body
wt. lower
1 wk. prior
to test; C
reduced to
same wt. at
test.
C-Ss
pai r-fed
to control
for loss
of body
wt.
None
None
Short IRTs (S4 sec)
more prevalent in
Pb-Ss than in
C-Ss, but did not
result in different
reward rates; Pb-Ss
showed higher varia-
bility in response-
rate under d-amphet-
amine treatment.
Pb-Ss had sig.
lower rate of
spontaneous alterna-
tion; Pb-Ss sig.
slower than C-Ss
only on 1st spatial
discrim. task.
"O
33
l»
vo
-<
o
vo
I»
Increased response
rate and inter-S
variability in groups
Pb] b and Pb2; de-
creased response rate
in group Pbj, effects
in Pb, reversed after
exposure terminated.
Pb groups impaired:
decreased response
durations; increased
response latencies;
failure to improve
performance by
external stimulus
control.
*Weight-matched controls
-------
Experimental
animal Lead exposure Treatment
(species Pb conc. period groups
Reference or strain) (medium) (route) (n)
Ge i s t
& Mattes
(1979)
Rat
(S-D)
0.001
or
0.0025%
(water)
PND 23-
termination
(di rect)
C (7)
Pb, (7)
Pb2 (7)
Flynn Rat
et al. (L-E)
(1979) Expt. 1
0.25%
(water)
Preconception
- PND 22
(via dam)
C (8)
Pb (10)
Expt. 2
i-o
i
00
cn
Expt. 3
0. IX
(water),
225 mg/kg
(gavage),
0.25%
(water)
same
as above
except 90
rag/ky
(gavage)
Preconception
- Birth
(via dam),
Birth -
Weani ng
(di rect),
Weaning
- termination
(direct)
same as
above except
stopped at
PND 33
C (12)
Pb (12)
C (10)
Pb (10)
Petit
& Alfano
(1979)
Rat
(L-E)
0.2 or
2%
(food)
PND
1-25
C, (22)
C' (22)
PB,. (22)
PL,' (22)
Pb,® (22)
PbJ (22)
TABLE 12-3. (continued)
Litters
per
group
Tissue Lead
(age measured)
Aye at
testing
Testi ng
paradigm
(task)
Non-
behavioral
effects
Behavioral
results
8
10
Brain-Pb (3 d):
C: ~0
Pb: 0.174 ug/g
(30-34 d):
no sig. diffs.
(75-76 d):
C: 0.13 pg/g
Pb: 1.85
58-
? d
49-
58 d
Hebb-
Wi11iams
maze
(find way
to goal
box)
Radial
arm maze
(spontaneous
al ternation)
Passive
avoidance
(remain
in 1 of 2
compartments
to avoid
elect, shock)
None
Brain wts.
of Pb-Ss
< C-Ss;
no other
differences.
None
Pb,- and Pb2-Ss
made sig. more
errors than C-Ss;
Pb^-Ss slower
than C-Ss to
traverse maze.
No sig. difference
between Pb-Ss
and C-Ss.
No sig. difference
in trials to criterion,
but Pb-Ss made
sig. fewer partial
excursions from
"safe" compartment.
see above
58-
60 d
Shuttle-box
signal led
avoidance
(move from one
compartment to
other to avoid
elect, shock)
None
No sig. difference
between Pb-Ss
and C-Ss.
~7
each;
spl i t
for "i"
(isola-
tion and
"e" (en-
richment)
condi tions
PbB
(25 d):
C: 2 ug/dl
Pb,: 331
Pbz: 1297
66-
115 d
Hebb-
Wi 11iams
maze
(find way
to goal
box)
¦Passive
avoidance
(remain
in compart-
ment to
avoid shock)
Body wts.
of Pb^-Ss
< C-Ss,
Pb,-Ss
> C-Ss;
gross
toxicity
in Pbjj-Ss;
lower
brain
wts. in
Pb-Ss
No sig. diff.
between Pb- and C-
Ss in maze learning;
Isolation-reared
Pb-Ss less success-
ful than C-Ss
on passive-avoidance
task; enrichment-
reared Pb,-Ss = C -Ss
but Pb2 -Ss sig. e
worse ofi passive
avoidance.
-------
TAB Lt 12-3 (continued)
Reference
Experimental
animal
(species
or strain)
Lead exposure
Pb conc.
(medium)
period
(route)
Treatment
groups
(n)
Li tters
per
group
Tissue lead
(age measured)
Age at
testi ng
Testing
paradi gm
(task)
Non-
behavioral
effects
Behavioral
results
Zenick
et al.
(197B)
Rat
(CD)
500
mg/kg
(water)
Preconception
- Weaning
(via dam)
C (10)
Pb (10)
30-
40 d
55-
63 d
Water T-maze
1) black-white
di scrim.
2) shape
discrim.
Body wt. of
Pb-Ss <
C-Ss from
birth to
50 d.
On both discrim.
tasks, Pb-Ss
made sig. more
errors with sig
shorter response
Zenick
et al.
(1979)
Rat
(CD)
375 Preconception 0-0 (?)
mg/kg to Pb-0 (?)
(water) a) Weaning Pb-Pb (?)
(via dam)
or
b) termination
(via dam and direct)
42-
? d
Operant
(FI -1 m i n)
Body wt.
of Pb-Ss
< 0-Ss
from birth
to weaning.
Pb-Pb group had sig.
fewer rewarded
responses across
sessions than Pb-0
or 0-0 groups.
Hastings
et al.
(1979)
Rat
(L-E)
CO
cri
W
A
Schlipkoter Rat
& Winneke (?)
(1980) Expt. 1
Expt. 2
Expt. 3
Expt. 4
0.01
or
0.1%
(water)
0.23%
(food)
0.075%
(food)
PN0 0
- 21
(dam's
milk)
C (23)
Pb, (11)
Pb2 (13)
Preconception
- PND 120
(via dam
and direct)
a) Prenatal-
7 mo
(via dam
and direct)
b) Prenatal-
Weaning
(via dam)
-Same as Expt. 2-
0.025
or
0.075%
(food)
Prenatal
- 7 mo
(via dam
and direct)
Random
selection
from
15
litters
C (?)
Pb, (18)
C (10)
Pb2 (10)
Pb.,* (10)
C (14)
Pba, (14)
Pba* d")
C (10)
Pb4 (10)
Pb^ (10)
PbB (20 d):
C: 11 Mg/dl
Pb,
Pbj
29
65
Brain-Pb
(20 d):
C: 12.5 pg%
Pb,
Pb2
29
65
PbB
all C: <5 pg/dl
Pb, (120 d):
39.5
(8 mo):
12.0
Pb2 :
(21 d) 29.2
(7 mo) 27.0
PtV
(21 d) 29.2
(7 mo) 5.2
Pb:,d:
(21 d) 29.9
(7 mo) 30.8
PbV
(21 d) 29.9
(7 mo) 1.8
(120 d)
Pb4
b'
17.8
28.6
120 d
270 d
330 d
7 mo
(1) Operant
(simult. vis.
di scrim. )
(2) T-maze
(success, vis.
di scrim.)
(3) Operant
(go/no-go task)
Lashley
jumping
stand
(cue -
size
di scrim.)
None
Water
maze
(spatial
di scrim. )
Pb2-Ss sig. slower
to reach criterion
than C-Ss on
simultaneous visual
discrimination task;
no sig. differences
on successive and
go/no-go discrim.
tasks.
Sig. increase in
error repetition
by Pb,-Ss.
Non-sig. (p <0.10)
increase in error
repetition by Pb2-Ss.
No sig. di ffs.
between Pb3-Ss
and C-Ss.
35% of Pb4-Ss failed
to reach criterion
(vs. 10% C-Ss); 35%
also failed retest
after 1 wk (vs. 0%
C-Ss).
"D
X)
3»
X)
-c
o
TO
3»
-------
PRELIMINARY DRAFT
TABLE 12-3. (continued)
Reference
Experimental
animal
(species
or strain)
Lead exposure
Pb conc. period
(medium) (route)
T reatment
groups
(n)
Litters
per
group
Tissue lead
(age measured)
Gross-
Selbeck
& Gross-
Selbeck
(1981)
Angel 1
& Weiss
(1982)
Rat F,
(W)
Rat
(L-E)
OS g/kg Postweaning C (6)
(food) - termination Pb (6)
(direct)
0. IX
(water)
Preconception
- Weaning
(via dam)
PND 3-21
(dam's
mi lk)
and/or
21-130
(direct)
C (6)
Pb (6)
0-0 (20)
0-Pb (20) •
Pb-0 (24)
Pb-Pb (24)
5, split
6, split
PbB
(-180 d):
C: 6.2 pg/dl
Pb: 22.7
(-110 d):
C: 3.7
Pb: 4.6
PbB(130d):
0-0: 2 pg/dl
0-Pb: 66
Pb-0: 9
Pb-Pb: 64
Hilar Rat 25, 100, PND 4-31 C (10) 3 PbB (32 d)
et al. (L-E) or 200 (direct) Pb, (5) 4 C: 5 pg/dl
(1981b) mg/kg Pbz (4) 4 Pb,: 26
Nation Rat 10 mg/kg PNO 100- C (8)
et- al. (S-D) (food) termina- Pb (8)
(1982) tion
(direct)
Pb.: 123
Winneke Rat
et al. (W)
(1982c) Expt. 1
0.004,
0.012,
or
0.037%
(food)
Preconception C(16)
- Testing
(via dam
and
direct)
Pb, (16)
Pb2
Pb,
Random
selection
(16) from 5-6
(16) litters
per condi-
tion
Expt. 2 -Continuation of Expt. 1- C (10) (females
Pb2 (10) dropped;
Pb3 (10) no Pb, group
for Expt. 2)
Testing Non-
Age at paradigm behavioral Behavioral
testing (task) effects results
Adul t
3-4
mo
Operant
(DRH)
None
Both F, and F2
(especially F2)
Pb-Ss had greater
% rewarded responses
than C-Ss, i.e.,
Pb-Ss bar-pressed
at higher rate
than C-Ss.
58-
130 d
Operant
(Mult
FI-TO-
FR-TO)
Pb-Pb Ss
sig. lower
body wt.
postweaning
Groups exposed post-
weaning (0-Pb, Pb-
Pb) had longer
Inter-Response
Times; group ex-
posed preweaning
(Pb-0) had
shorter IRTs.
50 d
156 d
70-
100 d
Operant
(spatial
alternation
levers)
Operant
(conditioned
suppression
of respond-
ing on mult.
VI schedule)
Shuttle-box
signalled
avoidance
(move from
one compart-
ment to avoid
elect, shock)
Pb2-Ss
sig.
slower
rate
None
ALA-D at
90 d:
C: 7.05 U/l
Pb,: 4.26
Pb2:
Pb'i
1.92
1.18
No sig. differences 3:
between C-Ss 5
and Pb-Ss.
-c
Presentation of tone
associated with
electrical shock
disrupted steady-
state responding
more in PB-Ss than
in C-Ss.
Expt. 1 Pb-Ss sig.
faster than C-Ss to
learn avoidance
response.
190-
250 d
Lashley
jumping stand
(size discrim.)
Expt. 2 Pb-Ss
sig. slower than
C-Ss to learn
s ize discrim.
-------
TABLE 12-3 (continued)
Reference
Experimental
animal
(species
or strain)
lead exposure
Pb conc.
(medium)
period
(route)
Treatment
groups
(n)
Li tters
per
group
Tissue lead
(age measured)
Age at
testing
Testi ng
paradigm
(task)
Non-
behavioral
effects
Behavioral
results
CO
CO
Taylor
et al.
(1982)
Kowalski
et al.
(1982)
McLean
et al.
(1982)
Rat
(CO)
House
(Wistar)
House
(Swiss)
0.01
or
0.02%
(water)
0.0002%
(water)
0.002 or
0.2%
(water)
Preconception
- Weaning
(via dam)
Adult
(direct)
Adul t
(direct)
C (12)
Pb, (16)
C2 (4)
Pb2 (4)
C (16)
Pb (16)
C (16)
Pb, (16)
Pb2 (16)
PbB (21 d)
C: 3.7 Mg/dl
Pb,: 38.2
Pb2: 49.9
11 d Runway None
(traverse
alley to
reach dam
and dry
suckle)
(13 d Water T-maze None
after (spatial
start of discrim.)
exposure)
(10 d Water T-maze None
after (spatial
start of discrim.)
expos.)
No sig. diffs.
in acquisition of
response, but
both Pb groups
sig. slower to
extinguish when
response no longer
rewarded.
Pb-Ss made more
errors than C-Ss;
food deprivation
exacerbated effect.
Pb-Ss showed no
improvement in
performance com-
pared to C-Ss.
"Inferred from information in report.
"O
TO
3>
TO
-C
o
TO
3>
Abbreviations:
? information not given in report
ALA-0 delta Aminolevulinic Acid Dehydrase
C Control group
CD substrain of Sprague Dawley
DRH Differential Reinforcement of High response rates
F, 1st Filial generation
F2 2nd Filial generation
FI Fixed Interval
FR Fixed Ratio
IRT Inter Response Time
L"E Long Evans
N/A Not Applicable
NaAc
sodium acetate
Pb
lead-exposed group
Pb(Ac)2
lead acetate
PbB
blood lead
PND
Post-Natal Day
S
Subject
S-D
Sprague Oawley
TO
Time Out
U/l
pmol ALAD/min x liter erythrocytes
VI
Variable Interval
W
Wi star
WGTA
Wisconsin General Testing Apparatus
X
experimental group
-------
TABLE 12-4. RECENT ANIMAL TOXICOLOGY STUDIES OF LEAD EFFECTS ON LEARNING IN PRIMATES
Experimental
anioal
(species
Reference or strain)
Lead exposure
Pb conc.
(medium)
period
(route)
Treatment
groups
(n)
Li tters
per
group
Tissue lead
(age measured)
Age at
testing
Testing
paradigm
(task)
Non-
behavioral
effects
Behavioral
results
Bushnel1
& Bowman
(1979a)
Monkey
(Macaca
nulatta)
Expt. 1
~0.07 or
0.16%
(milk)
adjusted
to main-
tain tar-
get PbB
Daily for
1st yr
(di rect)
C (4)
Pb, (3)
Pb2 (3)
N/A
PbB (1st yr):
C: ~5 pg/dl*
Pb,: 37*
Pb2: 58*
5-
10 mo
WGfA (form
discrim.
reversal
learning)
None
Both Pb-exposed
groups retarded
in reversal learn-
ing; Pb-,,-Ss
especially impaired
on 1st reversal
following over-
training.
Expt. 2
Test 1
oo
lO
Test 2
--same as Expt. 1— C (4)
Pb, (4)
Pb2 (4)
N/A
-Continuation of Expt. 2-
PbB (1st yr):
C: ~4 pg/dl*
Pb,: 32*
Pb2: 65*
1.5-
4. 5 mo
5-
12 mo
2-choice
maze
(discr.
reversal
learni ng)
non-food
reward
WGTA
(series
of 4
rpyor«a i
discr.
problems)
None
None
Pb2-Ss sig.
retarded on 1st
reversal (confirms
Expt. 1 using di ft
task and reward to
control for possible
confounding by motiva
tional or motor
factors).
Both Pb groups
retarded in
reversal learning;
PD-~
impaired on 1st
reversals regard-
less of prior over-
training.
Test 3
Continuation of Expt. 2
after exposure terminated at 12 mo
PbB (16
mo):
C: -5 pg/dl
Pb,: 19
Pb2: 46
15
mo
WGTA
(di scr.
reversal
learning,
more
None
Pb2-Ss retarded
on 1st reversal.
Bushnel1
& Bowman
(1979b)
Monkey
(Macaca
mulatta)
--Continuation of Bushnel1 & Bowman (1979a)--
PbB (56
mo):
C: 4 jjg/dl
Pb,: 5
Pb2: 6
49-
55 mo
WGTA
(spatial
di scr.
reversal
learning)
None
Both Pb-exposed
groups retarded
in reversal learn-
ing; 3 Pb2-Ss
failed to retain
motor pattern for
operating WGTA
from 2 yrs
earlier.
"Corrected annual averages obtained from Bushnel 1 (1978)
-------
Experimental
animal Lead exposure Treatment
(species Pb conc. period groups
Reference or strain) (medium) (route) (n)
Rice Monkey 500 Daily C (4)
& Willes (Macaca pg/kg for 1st Pb (4)
(1979) fascicu- (milk) year
laris) (direct)
Rice Continuation of Rice & Willes (1979)
et al.
(1979)
1 <3 F
on §
/\
Abbreviations:
7
information not given in report
ALA-D
delta Aminolevulinic Acid Dehydrase
C
Control group
CD
substrain of Sprague Dawley
DRH
Differential Reinforcement of High response rates
fx
1st Filial generation
f2
2nd Filial generation
FI
Fixed Interna)
FR
Fixed Ratio
IRT
Inter Response Time
L-E
Long Evans
N/A
Not Applicable
TABLE 12-4 (continued)
Li tters
per
group
Tissue lead
(age measured)
Age at
testing
Testing
paradigm
(task)
Non-
behavioral
effects
Behavioral
results
N/A
PbB
(200 d):
C: <5 pg/dl
Pb: 35-70
(400 d):
Pb: 20-50
421-
714 d
WGTA
(form
discrim.
reversal)
None
Pb-Ss slower
to learn successive
reversals.
PbB (400i- d):
20-30 HQ/dl
2. h-
3 yr
Operant
(mult. FI-
T0)
None
Pb-Ss responded
at higher rates, had
shorter IRTs, 2?
' m
and tended to r—
respond more during
time-out (unrewarded) i—i
z
XI
-<
o
XI
3>
NaAc sodium acetate
Pb lead-exposed group
Pb(Ac)2 lead acetate
PbB blood lead
PND Post-Natal Day
S Subject
S-D Sprague Dawley
TO Tine Out
U/l pmol ALAD/min x liter erythrocytes
VI Variable Interval
W Wistar
WGTA Wisconsin General Testing Apparatus
X experimental group
-------
PRELIMINARY DRAFT
learning task performances by rats with blcod lead levels below 30 (jg/dl. Winneke et al.
(1977) exposed Wistar rats J_n utero and postnatally to a diet containing D.07 percent lead as
lead acetate. Between PND 100 and 200 the subjects were tested on two types of visual discri-
mination learning tasks using either "easy" stimuli (vertical vs. horizontal stripes) or
"difficult" stimuli (white circles or differing diameters). Blood lead concentrations were
measured at about PND 16 (26.6 pg/dl) and PND 190 (28.5 pg/dl). Although there were no
significant differences between lead-exposed and control subjects on the easy discrimination
task, the lead-exposed subjects performed significantly (p <0.01) worse than controls on the
size discrimination task. The performance of the lead group continued around change level
(50 percent correct) essentially throughout the 4-week training period; control subjects began
to improve after about 2 weeks of training and reached an error rate of about 15 percent by 3
to 4 weeks. Stated differently, 8 out of 10 control animals reached criterion performance
levels within 27 days, whereas only one of the lead-exposed subjects did (p <0.01).
More recently, Winneke et al. (1982c) repeated the size discrimination experiment and
added another test involving shock avoidance. As in the earlier study, exposure started in
utero and continued through behavioral testing. Different concentrations of lead acetate in
the diet were used to yield average blood lead levels of 18.3 and 31.2 pg/dl after 130 days of
feeding, compared to 5 |.ig/dl for control subjects. These values were not determined directly
from the subjects in this study but were based on separate work by Schlipkoter and Winneke
(1980). However, ALA-D activity was measured directly in selected female subjects at
PND-90 and was found to be inhibited 73 percent and 83 percent, respectively, for the
different levels of lead exposure. Consistent with their earlier findings, Winneke et al.
(1982c) found that lead-exposed subjects were significantly slower to reach criterion perfor-
mance levels on the size discrimination task. However, on the shock avoidance task, the lead-
exposed subjects were significantly quicker than control subjects to reach the criterion of
successful performance. Although seemingly incongruous with the impairment found in the
discrimination task, the latter finding is consistent with results obtained by Driscoll and
Stegner (1976), who found performance on a shock avoidance task enhanced by lead exposure at a
level high enough (~0.15 percent lead in dams' drinking water) to cause a 20 percent weight
reduction in the subjects prior to weaning. Both the size discrimination deficits and the
enhanced avoidance performance are indicative of alterations in normal neural functioning
consequent to lead exposure.
Cory-Slechta and Thompson (1979) exposed Sprague-Dawley rats to 0.0025, 0.015, or 0.05
percent drinking water solutions of lead as lead acetate starting at PND 20-22. Operant con-
ditioning on a fixed-interval 30-second schedule of reinforcement (food pel 1et delivered upon
the first bar-press occurring at least 30 sec after preceding pellet delivery) began at PND
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PRELIMINARY DRAFT
55-60. Blood lead concentrations measured at approximately PND 150 were reported in graphical
form roughly as follows: 0.0025-percent solution group, 5 to 10 pg/dl PbB; 0.015-percent
group, 25 to 30 pg/d 1 PbB; 0.05-percent group, 40 to 45 pg/dl PbB. Subjects exposed to 0.0025
or 0.015 percent lead solutions showed a "significantly" (no probability value reported)
higher median response rate than matched controls during the first 30 sessions of training;
response rates continued to be significantly higher over the next 60 sessions for the 0.0025-
percent group and over the next 30 sessions for the 0.015-percent group (at which points
training terminated for each group). Moreover, latencies to the first response in the 30-sec
interval (the beginning of the typical "fixed-interval scallop" cumulative response pattern)
were significantly shorter in the 0.0025- and 0.015-percent groups. However, response rates
for the group exposed to the 0.05 percent solution were significantly lower than the control
group's rates for the first 40 sessions; correspondingly, response latencies were longer for
the highest exposure group.
Other work by Cory-Slechta et al. (1981) repeated the earlier study's exposure regimen
(using 0.005 and 0.015 percent solutions) and examined the effects on another aspect of oper-
ant performance. In this study the subjects were required to depress a bar for a specified
minimum duration (0.5 to 3.0 sec) before a food pellet could be delivered. Intersubject vari-
ability increased greatly in the lead-exposed groups (see also, e.g., Cory-Slechta and
Thompson, 1979; Dietz et al., 1978; Hastings et al., 1979). In general, though, treated sub-
jects tended to shorten their response durations (p = 0.04 for the 0.005-percent group;
p = 0.03 for the 0.015-percent group). This tendency would contribute toward a reduced rate
of reinforcement, which is associated with (and perhaps accounts for) an observed tendency
toward increased response latencies in the lead-exposed subjects (p = 0.04 in the 0.015-
percent group). Although blood lead values were not reported by Cory-Slechta et al. (1981),
brain lead concentrations at approximately PND 200 ranged from 40 to 142 ng/g for the 0.005-
percent group and 320 to 1080 ng/'g for the 0.015-percent group. Given the same exposure regi-
mens in the two studies, blood lead values should be comparable.
The Gross-Selbeck and Gross-Selbeck (1981) study (partly described below in Section
12.4.3.1.5) also tested Wistar rats exposed post-weaning to a diet containing 0.05 percent
lead daily until completion of behavioral testing at -180 days of age, at which time the
average blood lead level was 22.7 (jg/dl. Although no differences were apparent in preliminary
operant barpress training, differences between lead-treated and control groups did appear when
the subjects were required to bar-press at a very high rate (e.g., 2 presses per second). The
lead-treated subjects outperformed, i.e., bar-pressed more rapidly than, the control subjects.
Except for monkeys, few other species have recently been studied in sufficient detail to
warrant discussion here. One of the primate studies, that by Bushnell and Bowman (1979b),
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PRELIMINARY DRAFT
is discussed under Section 12.4.3.1.5 because it examined learning ability some time after
neonatal exposure to lead had terminated. In brief, that study showed impaired discrimination
reversal learning performance at 40 months of age, even though lead exposure was limited to
the first 12 months and the mean blood lead level was about 32 pg/dl for the "low-lead" group
during that period. When measured following behavioral testing, average blood lead concentra-
tions were similar to control levels, i.e., 5-6 pg/dl.
Other studies of nonhuman primates, however, have examined learning ability while lead
exposure was ongoing. In a more comprehensive report, to which the above-described study
(Bushnell and Bowman, 1979b) was a follow-up, Bushnell and Bowman (1979a) ran a series of
tests on discrimination reversal learning in rhesus monkeys over the second through sixteenth
months of life. Lead acetate was fed to the subjects during the first 12 months so as to
maintain nominal blood lead levels of 50 and 80 pg/dl in the low-lead and high-lead groups
(actual blood lead concentrations varied considerably during the first year, particularly for
the high-lead groups). Although lead dosing was terminated at 12 months, blood lead levels
were still somewhat elevated over control levels at the completion of behavioral testing
(18.75 ± 2.87 pg/dl, low-lead group; 46.25 ± 6.74 pg/dl, high-lead group). The basic finding
that appeared consistently throughout this series of tests, including two separate experiments
involving different groups of subjects (see Table 12-4), was that young rhesus monkeys with
blood lead levels on the order of 30 to 50 pg/dl, compared to control groups with levels of
approximately 5 pg/dl, were significantly retarded in their ability to learn a visual discri-
mination task in which the cues were reversed from time to time according to specified
criteria. In addition, the higher exposure subjects were especially slow in mastering the
first reversal problem, following extended training on the original discrimination task.
Rice and Willes (1979) attempted to replicate the Bushnell and Bowman (1979a) findings.
They fed Rhesus monkeys lead acetate from day one of life and obtained blood lead concentra-
tions in their four experimental subjects between 35 and 70 pg/dl around PND 200, which
dropped to 20-50 pg/dl by PND 400; the four control subjects' levels were generally 5 pg/dl or
lower. At 2-3 years of age, while lead exposure continued, the subjects were trained on a
WGTA form-discrimination task similar to that used by Bushnell and Bowman (1979a). Consistent
with the latter study, Rice and Willes (1979) used a reversal-learning paradigm in which the
correct discriminative cue was reversed once the task was mastered. Although initially the
lead-treated monkeys performed better than cortrols (fewer trials to criterion and fewer
errors), over successive reversals (4 through 12) the control subjects made fewer errors and
required fewer trials to reach criterion performance in each daily session. This difference
disappeared following session 12, which was extended 500 trials beyond the criterion level
("overtraining"). Overall, the lead-treated subjects appeared to make more errors in per-
BPB12/A 12-93 9/20/83
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PRELIMINARY' DRAFT
forming the reversal tasks; analysis of variance yielded a significant main effect (p = 0.05),
but this applied only to sessions 6 through 12, which would seem to be a somewhat arbitrary
selection of data for analysis. The authors did note, however, that the success of the lead-
treated monkeys in the first few trials appeared to result from the treated subjects' reluc-
tance to manipulate the novel negative stimulus after 100 pretraining trials in which only the
positive stimulus was presented. Thus, the unexpected initial success of the lead-exposed
subjects may have been an artifact of the pretraining procedure. By this interpretation, the
lead-treated monkeys in Rice and Wilies' (1979) study and the high-lead group of monkeys in
Bushnell and Bowman's (1979a) study were both showing perturbed behavior, that is, refractori-
ness to alter their behavior under changed conditions.
Rice and her coworkers studied the same two groups of subjects at 2-3 years of age on an
operant conditioning task involving a multiple fixed-interval/tlme-out schedule of reinforce-
ment (Rice et a 1. , 1979). This schedule alternated a 10- to 90-sec time-out period, during
which responses were unrewarded, with an 8-min fixed interval, at the end of which a push on a
lighted disk was rewarded. The lead-treated monkeys, whose blood-lead levels had by then sta-
bilized at 20*30 pg/dl , showed a higher response rate than controls during the fixed interval
and shorter pauses between responses (lower median interresponse times). The treated monkeys
also tended to respond more during the time-out period, even though responses were not reward-
ed.
In conclusion, it appears that alterations in behavior in rats and monkeys occur as a
consequence of chronic exposure to dietary lead resulting in blood lead levels on the order of
30-50 MQ/dl. These alterations in behavior are clearly indicative of altered neural function-
ing, especially in the CNS in view of certain of the tasks employed. Another question that
arises, however, is whether such alterations represent impairment in overall functioning of
the lead-exposed subjects. As some studies indicate, lead-treated subjects may actually per-
form better than non-treated control subjects on certain learned tasks. For example, in the
Winneke et al. (1982c) study, the task on which lead-exposed rats excelled required the sub-
jects to move from one compartment to the other in a two-compartment shuttle box in order to
avoid receiving an electrical shock to the feet. A successful avoidance response had to occur
within 5 seconds after the onset of a warning stimulus. Similar findings have been reported
by Driscoll and Stegner (1976) for shock-avoidance performance. As previously described, a
study by Gross-Selbeck and Gross-Selbeck (1981) required rats to press a bar for food under an
operant conditioning schedule that rewarded only high rates of responding. By responding more
rapidly, the lead-treated subjects were more successful than untreated control subjects in
maximizing their rewards.
BPB12/A
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99 V
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PRELIMINARY DRAFT
Because of the contingencies of reinforcement specified in the just-cited experiments, a
tendency to resaond with greater alacrity or less hesitation was properly adaptive for the
subjects. Other conditions, however, could make the same tendency unadaptive, as, for exam-
ple, in the study by Cory-Slechta et al. (1981), which required rats to press a bar and hold
it down longer than rats are normally inclined to do. In that case the 1ead-treated subjects
were less successful than untreated controls. Thus, success or failure (or enhancement or
impairment of performance) may be misleading designations for the behavioral alterations mea-
sured under arbitrary experimental conditions (cf. Penzien et al., 1982). Of greater impor-
tance may be the underlying tendency to respond more rapidly or "excessively," regardless of
whether or not such responding is appropriate for the reinforcement contingencies of an
experiment. Such a tendency may be inferred from results of other studies of the neurotoxic
effects of lead (e.g., Angel 1 and Weiss, 1982; Overmann, 1977; Rice et al., 1979). Taken
together, these reports might be interpreted as suggesting a possible "hyper-reactivity"
(cf. Winneke et al. , 1982c) in lead-treated animals. They and others (e.g., Petit and Alfano,
1979) have noted the commonality of such types of behavioral deficits with experimental
studies of lesions to the hippocampus (see also Sections 12.4.3.2.1 and 12.4.3.5.).
12.4.3.1.4 Effects of lead on social behavior. The social behavior and organization of even
phylogenetically closely related species may be widely divergent. For this and other reasons,
there is little or no basis to assume that, for example, aggressiveness in a lead-treated
Rhesus monkey provides a model of aggressiveness in a lead-exposed human child. However,
there are other compelling grounds for including animal social behavior in the present review.
As in the case of nonsocial behavior patterns, characteristics of an animal's interactions
with conspecifics may reflect neurological (especially CNS) impairment due to toxic exposure.
Also, certain aspects of animal social behavior have evolved for the very purpose (in a non-
teleological sense) of indicating an individual's physiological state or condition (Davis,
1982). Such behavior could potentially provide a sensitive and convenient indicator of toxi-
cological impairment.
Two early reports (Silbergeld and Goldberg, 1973; Sauerhoff and Michaelson, 1973) sug-
gested that lead exposure produced increased aggressiveness in rodents. Neither report, how-
ever, attempted to quantify these observations of increased aggression. Later, Hastings et
al. (1977) examined aggressive behavior in rats that had been exposed to lead via their dams'
milk. Solutions containing 0, 0.01, or 0.05 percent lead as lead acetate constituted the dams'
drinking water from parturition to weaning at PND 21, at which time exposure was terminated.
This lead treatment produced no change in growth of the pups. Individual pairs of male off-
spring (from the same treatment groups) were tested at PND 60 for shock-elicited aggression.
Both lead-exposed groups (average blood-lead levels of 5 and 9 ng/dl and brain lead levels of
BPB12/A 12-95 9/20/83
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PRELIMINARY DRAFT
8 and 14- pg/lOOg) showed significantly less aggressive behavior than the control group. There
were no significant differences among the groups in the flinch/jump thresholds to shock, which
suggests that the differences seen in shock-elicited aggression were not caused by differences
in sensitivity to shock.
A study by Drew et al. (1979) utilized apomorphine to induce aggressive behavior in 90-
day-old rats and found that earlier lead exposure attenuated the drug-induced aggressiveness.
Lead exposure occurred between birth and weaning primarily through the dams' milk or through
food containing 0.05 percent lead as lead acetate. No blood or tissue concentrations of lead
were measured. There were no significant differences in the weights of the lead-treated and
control animals at PND 10, 20, 30, or 90.
Using laboratory mice exposed as adults, Ogilvie and Martin (1982) also observed reduced
levels of aggressive behavior. Since the same subjects showed no differences in vitality or
open field activity measures, the reduction in aggressiveness did not appear to be due to a
general effect of lead on motor activity. Blood lead levels were estimated from similarly
treated groups as being approximately 160 pg/dl after 2 weeks of exposure and as 101 pg/dl
after 4 weeks of exposure.
Cutler (1977) used ethological methods to assess the effects of lead exposure on social
behavior in laboratory mice. Subjects were exposed from birth (via their dams' milk) and
post-weaning to a 0.05 percent solution of lead as lead acetate (average brain lead concentra-
tions were 2.45 nmol/g for controls and 4.38 nmol/g for experimental subjects). At 8 weeks of
age social encounters between subjects from the same treatment group were analyzed in terms of
numerous specified, identifiable behavioral and postural elements. The frequency and dura-
tion of certain social and sexual investigative behavior patterns were significantly lower in
lead-treated mice of both sexes than in controls. Lead-exposed males also showed significant-
ly reduced agonistic behavior compared with controls. Overall activity levels (nonsocial as
well as social behavior) were not affected by the lead treatment. Average body weights did
not differ for the experimental and control subjects at weaning or at the time of testing.
A more recent study by Cutler and coworkers (Donald et al., 1981) used a similar
paradigm of exposure and behavioral evaluation, except that exposure occurred either only pre-
natal ly or postnatally and testing occurred at two times, 3-4 and 14-16 weeks of age. Sta-
tistically significant effects were found only for the postnatal exposure group. Although
total activity in postnatally exposed mice did not differ from that of controls at either age
of testing, the incidence of various social activities did differ significantly. As juveniles
(3-4 weeks old), lead-treated males (and to some extent, females) showed decreased social in-
vestigation of a same-sex conspecific. This finding seems to be consistent with Cutler's
(1977) earlier observations made at 8 weeks of age. Aggressive behavior, however, was almost
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PRELIMINARY DRAFT
nonexistent in both control and lead-treated subjects in the later study, and so could not be
compared meaningfully. Although the authors do not comment on this aspect of their study, it
seems likely that differences in the strains of laboratory mice used as subjects could well
have been responsible for the lack of aggressive behavior in the Donald et al.'s (1981) study
(cf., e.g., Adams and Boice, 1981). Later testing eit 14 to 16 weeks revealed that lead-exposed
female subjects engaged in significantly more investigative behavior of a social or sexual
nature than did control subjects, while males still showed significant reductions in such
behavior when encountering another mouse of the same sex. This apparent disparity between
male and female mice is one of relatively few reports of gender differences in sensitivity to
lead's effects on the nervous system (cf. Cutler, 1977; Verlangieri, 1979). In this case,
Donald et al. (1981) hypothesized that the disparity might have been due to differences in
brain lead concentrations: 74.7 pmo1/kg in males versus 191.6 |jmol/kg in females (blood lead
concentrations were not measured). The Donald et al. (1981) study, along with the above-
mentioned study of Ogilvie and Martin (1982), point out the importance of not focusing exclu-
sively on perinatal exposure in assessing neurotoxic effects of chronic lead exposure.
The social behavior of rhesus monkeys has also been evaluated as a function of early lead
exposure. A study by Allen et al. (1974) reported persistent perturbations in various aspects
of the social behavior of lead-exposed infant and juvenile monkeys, including increased cling-
ing, reduced social interaction, and increased vocalization. However, exposure conditions
varied considerably in the course of this study, with overt toxicity being evident as blood
lead levels at times ranged higher than 500 |jg/dl.
A more recent study consisting of four experiments (Bushnell and Bowman, 1979c) also
examined social behavior in infant Rhesus monkeys, but under more systematically varied expo-
sure conditions. In experiments 1 and 2, daily "ingestion of lead acetate during the first
year of life resulted in blood lead levels of 30-100 |jg/dl, with consequent suppression of
play activity, increased clinging, and greater disruption of social behavior when the play
environment was altered. Experiment 3, a comparison of chronic and acute lead exposure (the
latter resulting in a peak blood lead concentration of 250-300 pg/d1 during weeks 6-7,of
life), revealed little effect of acute exposure except in the disruption that occurred when
the play environment was altered. Otherwise, only the chronically exposed subjects differed
significantly from controls in various categories of social behavior. Experiment 4 of the
study showed that prenatal exposure alone, with blood lead concentrations of exposed infants
ranging between 33 and 98 pg/dl at birth, produced no detectable behavioral effects under the
same procedures of evaluation. Overall, neither aggressiveness nor dominance was clearly
affected by lead exposure.
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PRELIMINARY DRAFT
Another aspect of social behavior--interaction between mothers and their offspring—was
examined in lead-exposed rats by Zenick et al. (1979). Dams chronically received up to 400
mg/kg lead acetate in their drinking water on a restricted daily schedule (blood lead concen-
trations averaged 96.14 ± 16.54 pg/dl in the high-exposure group at day 1 of gestation). Dams
and their litters were videotaped on PND 1-11, and the occurrence of certain behavior patterns
(e.g., lying with majority of pups, lying away from pups, feeding) was tabulated by the exper-
imenters. In addition, dams were tested for their propensity to retrieve pups removed from
the nest. Neither analysis revealed significant effects of lead exposure on the behavior of
the dams. However, restricted access to drinking water (whether lead-treated or not) appeared
to confound the measures of maternal behavior.
The above studies suggest that aggressive behavior in particular is, if anything, reduced
in laboratory animals as a result of exposure to lead. Certain other aspects of social behav-
ior in laboratory mice, namely components of sexual interaction and social investigation, also
appear to be reduced in lead-treated subjects, although there may be gender differences in
this regard following chronic post-maturational exposure. Young rhesus monkeys also appear to
be sensitive to the disruptive effects of lead on various aspects of social behavior. All of
these alterations in social behavior are indicative of altered neural functioning as a conse-
quence of lead exposure in several mammalian species.
12.4.3.1.5 Persistence of neonatal exposure effects. The specific question of persisting,
long-term consequences of lead effects on the developing organism has been addressed in a
number of studies by carrying out behavioral testing some time after the termination of lead
exposure. Such evidence of long-term effects has been reported for rhesus monkeys by Bushnell
and Bowman (1979b). Their subjects were fed lead acetate so as to maintain blood lead (PbB)
levels of either 50 ± 10 (low-lead) or 80 ± 10 pg/dl (high-lead) throughout the first year of
life (actual means and standard errors for the year were reported as 31.71 ± 2.75 and 65.17 ±
6.28 (jg/d1). Lead treatment was terminated at 12 months of age, after which blood lead levels
declined to around 5-6 pg/dl at 56 months. At 49 months of age the subjects were re-
introduced to a discrimination reversal training procedure using new discriminative stimuli.
Despite their extensive experience with the apparatus (Wisconsin General Test Apparatus)
during the first two years of life, most of the high-lead subjects failed to retain the simple
motor pattern (pushing aside a small wooden block) required to operate the apparatus.
Remedial training largely corrected this deficit. However, both high- and low-lead groups
required significantly more trials than the control group (p <0.05) to reach criterion per-
formance levels. This difference was found only on the first discrimination task and nine
reversals of it. Successive discrimination problems showed no differential performance
effects, which indicates that with continued training the lead-treated subjects were able to
achieve the same level of performance as controls.
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PRELIMINARY DRAFT
Studies using rats have also suggested that behavioral perturbations may be evident some
time after the termination of exposure to lead. Hastings et al. (1979) exposed rat pups to
lead through their mothers' milk by providing the dams 0.01 or 0.1 percent solutions of lead
as lead acetate for drinking water. Exposure was stopped at weaning, at which time average
blood-lead values were 29 (± 5) and 65 (± 25) pg/dl, respectively. At 120 days of age the
subjects were placed on an operant conditioning simultaneous visual discrimination task.
Although Hastings et al. (1979) did not actually measure blood lead levels in adult subjects
at the time of behavioral testing, they presumed that the levels for control and experimental
groups were by then probably quite similar, i.e., on the order of 10 pg/dl , based on prior
work (Hastings et al. , 1977.) Forty-six percent of the high-lead group and 37 percent of the
low-lead group failed to learn the task within 60 days; only 4 percent of the control group
failed to reach criterion. In terms of time to reach criterion, controls required a mean of
23 days while the low-lead subjects required 32 days and the high-lead rats 39 days (high-lead
vs. controls, ,p <0.01). Additional testing on a successive discrimination task at 270 days of
age and a go/no-go discrimination task at 330 days revealed no significant differences between
controls and lead-treated subjects. Since the three tests were not counter-balanced in pres-
entation, there is no way to determine whether the lack of effects in the two latter tests may
have been a function of the order of testing or age at the time of testing or, more simply, a
function of the latter tests' lack of sensitivity to neurotoxic effects.
Gross-Selbeck and Gross-Selbeck (1981) also found alterations in the operant behavior of
adult rats after perinatal exposure to lead via mothers whose blood lead levels averaged 20.5
pg/dl. At the time of testing (3 to 4 months postnatally) the lead-exposed subjects' blood
lead levels averaged 4.55 pg/dl, compared to 3.68 pg/dl in control subjects. Although the two
groups appeared qualitatively similar in their behavior in an open-field test and in prelimi-
nary bar-press training, the lead-exposed subjects tended to respond at a much higher rate
than did control subjects when rewarded for responding quickly. Since the schedule differen-
tially reinforced high response rates, the lead-exposed subjects performed more successfully
than did the control subjects. This was true for three different variations on the basic
schedule examined by the authors. As noted earlier, in this case, the heigtened response rate
was adaptive within the context of the particular task used but may not have been under other
contingencies. Most importantly here, it is indicative of altered CNS function persisting for
months beyond the cessation of lead exposure early in development.
Results from the above studies indicate thot behavioral effects may exist as sequelae to
past lead exposure early in development of mammalian species, even though blood lead levels at
the time of later behavioral assessment are essentially "normal."
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PRELIMINARY DRAFT
12.4.3.2 Morphological Effects
12.4.3.2.1 In vivo studies. Recent key findings on the morphological effects of in vivo lead
exposure on the nervous system are summarized in Table 12-5. It would appear that certain
types of glial cells are sensitive to lead exposure, as Reyners et al. (1979) found a
decreased density of ol igodendrocytes in cerebral cortex of young rats exposed from birth to
0.1 percent lead in their food. Higher exposure concentrations (0.2-0.4 percent lead salts),
especially during the prenatal period (Bull et al., 1983), can reduce synaptogenesis and
retard dendritic development in the cerebral cortex (McCauley and Bull, 1978; McCauley et al.,
1979, 1982) and the hippocampus of developing rats (Campbell et al., 1982, and Alfano and
Petit, 1982). Some of these effects, e.g. on cerebral cortex appear to be transient (McCauley
et al., 1979, 1982). Suckling rats subjected to increasing exposures of lead exhibit more
pronounced effects, such as reduction in the number and average diameter of axons in the optic
nerve at 0.5 percent lead acetate exposure (Tennekoon et al. , 1979). a general retardation of
cortical synaptogenesis at 1.0 percent lead carbonate exposure (Averill and Needleman, 1980),
or a reduction in cortical thickness at 4.0 percent lead carbonate exposure (Petit and
LeBouti11ier, 1979). This latter exposure concentration also causes a delay in the onset and
peak of Schwann cell division and axonal regrowth in regenerating peripheral nerves in chroni-
cally exposed adult rats (Ohnishi and Dyck, 1981). In short, both neuronal and glial compo-
nents of the nervous system appear to be affected by neonatal or chronic lead exposure.
Organolead compounds have also been demonstrated to have a deleterious effect on the mor-
phological development of the nervous system. Seawright et al. (1980) administered triethyl
lead acetate (Et3Pb) by gavage to weanling (40-50 g) and "young adult" (120-150 g) rats.
Single doses of 20 mg EtsPb/kg caused impaired balance, convulsions, paralysis, and coma in
both groups of treated animals. Peak levels in blood and brain were noted two days after ex-
posure, with extensive neuronal necrosis evident in several brain regions by three days post-
treatment. Weekly exposures to 10 mg Et3Pb/kg for 19 weeks resulted in less severe overt
signs of intoxication (from which the animals recovered) and moderate to severe loss of
neurons in the hippocampal region only.
12.4.3.2.2 In vitro studies. Bjorklund et al. (1980) placed tissue grafts of developing ner-
vous tissue in the anterior eye chambers of adult rats. When the host animals were given 1 or
2 percent lead acetate in their drinking water, the growths of substantia nigral and hippocam-
pal , but not cerebellar, grafts were retarded. Grafts of the developing cerebral cortex in
host animals receiving 2 percent lead exhibited a permanent 50 percent reduction in size
(volume), whereas 1 percent lead produced a slight increase in size in this tissue type. The
authors felt that this anomalous result might be explained by a hyperplasia of one particular
cell type at lower concentrations of lead exposure.
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preliminary draft
TABLE 12-5. SlfMARY OF KEY STUDIES OF MCRPHOtOGiXAL EFFECTS OF IN VIVO -EAD EXPOSURE
Speci es
Exposure protocol
Peak blood
lead level
Observed
effect
Reference
YoLng rats
0.1% Pb
PND 0-90
in chew
0. 1% Pb(Ac)2 in
dams' drinking
water PND 0-22
0. 2% PbC'i2 in dams'
drinking water from
gestation thru PN30
0.2% Pb(Ac)j ;n
dams' drinking
water PND 0-25
0.4% PbC03 in
dams' drinking
water PND 0-3G
0 5% =b(Ac)2 in
dams' drinking
water "ND 0-21
80 (-?/d"
at b1rth
Gi:cr eased censity of
cligadendrocytes in cerebral
cc.rtex
Significant inhibition in
myelin deposition and
Tituration in whole brain
L'jss mature synoptic profile
i:< cerebral cortex at PND-
li
30% reduction in synoDtic
density ir cerebral cortex
at 3N015 (returned to normal
at PND21)
15-30% "reduction in
synaptic profiles in
h'ppocampus
Ratjrdation in temporal
sequence of hippocampal
cendritic development
10-15% reduction in number
of axons in optic nerve;
skewing of fiber ciaTete'-s
to smal1er si zes
Reyners et al. (1979)
Stephens ard
Gerber (1981)
McCauley and Bu"1
(1978)
McCaLley et al. (1979)
McCauley et al. (1982)
Corppel1 et al. (1982)
Al 'ano and Pet^ t
(1962)
Ternekoon et al.
(1S79)
1% PbC03
PND C-60
385 pg/dl
(PND 21)
".etardaf!on of cortical
synaptogenesis over and
r.bove any nutritional
effects
AveriH and Needleraan
(I960)
Adult rats
4% PbCOj in dams'
chow PND 0-28
4% PbCOj in dams'
chow PND 0-25
4% PbC0a in chow
for 3 mos.
4% PBCO3 in chow
PND 0-150
258 jjg/d 1
(PND 28)
PND:
Pb(Ac)2:
PbC03:
post-natal day
lead acetate
lead carbonate
300 pg/dl
(PND 150)
13% reduction in
coctical thickness
and total brain weight;
reduction in synaptic
;iensity
deduction in hippccampal
length and width; similar
reduction in afferent
projection to hippocampus
lie lay in onset and peak
}f Schwann cell division
and axonal regrowth in
regenerating nerves
Demyelination of peri-
pheral nerves beginning
PND 20-35
Pet;t and
LeBojtillier (1979)
Al fano et al. (1982)
Ohnishi and Dyck
(1981)
Wi ndebank et al.
1980
12-101
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PRELIMINARY DRAFT
Organoleaa compounds have also been demonstrated to affect neuronal growth (Grundt et
al. , 1981). Cultured cells from embryonic chick brain were exposed to 3.16 mM trielhyllead
chloride in the incubation mediu.n for 48 hr, resulting in a 50 percent reduction in the number
of cells exhibiting processes. There was no observed effect on glial morphology.
Other investigations have focused on morphological aspects of the blood-brain barrier and
its possible disruption by lead intoxication (Kolber et al., 1980). Capillary endothelial
cells isolated from rat cerebral cortex and exposed to 100 jjM lead acetate j_n vitro
(Silbergeld et al., 1980b) were examined by electron microscopy and X-ray microprobe analysis.
Lead deposits were found to be sequestered preferentially in the mitochondria of these cells
in much the same manner as calcium. This affinity may be the basis for lead-induced disrup-
tion of transepithelial transport of Ca^+ and other ions.
12.4.3.3 Electrophysiological Effects.
12.4.3.3.1 In vivo studies. Recent key findings on the electrophysiological effects of in
vivo lead exposure are summarized below in Table 12-6. The visual system appears to be par-
ticularly susceptible to perturbation by neonatal lead exposure. Suckling rats whose dams
were given drinking water containing 0.2 percent lead acetate had significant alterations in
their visual evoked responses (VER) and decreased visual acuity at PND 21, at which time their
blood lead levels were 65 pg/dl (Cooper et al., 1980; Fox et al., 1977; Impelman et al., 1982;
Fox and Wright, 1982; Winneke, 1980). Both of these observations are indicative of depressed
conduction velocities in the visual pathways. These same exposure levels also increased the
severity of the maximal electroshock seizure (MES) response in weanling rats who exhibited
blood lead levels of 90 pg/dl (Fox et al., 1978, 1979). The authors speculated that neonatal
lead exposure acts to increase the ratio of excitatory to inhibitory systems in the developing
cerebrospinal axis. Such exposure can also lead to lasting effects on the adult nervous
system, as indicated by persistent decreases in visual acuity and spatial resolution in 90-day
old rats exposed only from birth to weaning to 0.2 percent lead acetate (Fox et al., 1982).
The adult nervous system is also vulnerable to lead-induced perturbation at low levels of
exposure. Hietanen et al. (1980) found that chronic exposure of adult rabbits to 0.2 percent
lead acetate in drinking water resulted in an 85 percent inhibition of motor conduction velo-
city in the sciatic nerve.
12.4.3.3.2 In vitro studies. Palmer et al. (1981) and Olson et al. (1981) looked at intrao-
cular grafts of cerebellar tissue from 14- to 15-day-old rats in host animals treated for 2
months with drinking water containing 1 percent lead acetate, followed by plain water for 4-5
months. They found no alterations in total growth or morphology of grafts in treated vs.
control hosts, yet the Purkinje neurons in the lead-exposed grafts had almost no spontaneous
activity. Host cerebellar neurons, on the other hand, and both host and graft neurons in
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TABLE 12-6.
Species Exposure protocol
Suckling rat 0.2% Pb(Ac)2 in
dams' drinking water
PND 0-20
0.2% Pb(Ac)2 in
dams' drinking water
PND 0-21
ro
i
Young rhesus
monkeys
Pb(Ac)z solutions
in food
PN0 0-365
Adult rabbit 0.2% Pb(Ac)2 in
drinking water for
4 weeks
PND: post-natal day
PbCAc)^: lead acetate
MES: maximal electroshock seizure
VER: visual evoked response
SUMMARY OF KEY STUDIES OF ELECTROPHYSIOLOGICAL
EFFECTS OF IN VIVO LEAD EXPOSURE
Peak blood
lead level
Observed
effect
Reference
90 ng/dl
(PND 20)
65 pg/dl
(PN0 21)
300 ng/dl
(PND 60)
85 pg/dl
More rapid appearance
and increased severity of
MES response
1) Increased latencies and
decreased amplitudes of
primary and secondary
components of VER;
2) decreased conduction
velocities in visual
pathways;
3) 25-50% decrease in
scotopic visual acuity
4) persistent decreases
in visual acuity and
spatial resolution d'c
PND 90
Severe impairment
of discrimination
accuracy; loss of
scotopic function
85% reduction in motor
conduction velocity of
sciatic nerve
Fox et al.
(1978, 1979)
Fox et al.
(1977);
Impelman et al.
(1982);
Cooper et al.
(1980);
Winneke (1980);
Fox and Wright
(1982)
Fox et al. (1982)
Bushnel1 et al
(1977)
Hietanen et al.
(1980)
-------
PRELIMINARY DRAFT
control animals, all exhibited significant levels of spontaneous activity. Taylor et al.
(1978) recorded extracel1ularly from cerebellar Purkinje cells in adult rats both i_n s i tu and
in intraocular grafts in an effort to determine what effect lead had on the norepinephrine
(NE)-induced inhibition of Purkinje cell spontaneous discharge. Application of exogenous NE
to both i_n si tu and i_n ocul o cerebellum produced 61 and 49 percent inhibitions of spontaneous
activity, respectively. The presence of 5-10 pM lead reduced this inhibition to 28 and 13
percent, respectively. This "disinhibition" was specific for NE, as responses to both cho-
linergic and parallel fiber stimulation in the same tissue remained the same. Furthermore,
application of lead itself did not affect spontaneous activity, but did inhibit adenylate
cyclase activity in cerebellar homogenates at the same concentration required to disinhibit
the NE-induced reduction of spontaneous activity (3 to 5 pM).
Fox and Sillman (1979) looked at receptor potentials in the isolated, perfused bullfrog
retina and found that additions of lead chloride caused a reversible, concentration-dependent
depression of rod (but not cone) receptor potentials. Concentrations of 5 pM produced an
average 16 percent depression, while 12.5 pM produced an average 23 percent depression.
Evidence that lead does indeed resemble other divalent cations, in that it appears to
interfere with chemically mediated synaptic transmission, has been obtained in studies of
peripheral nerve function. For example, lead is capable of blocking neural transmission at
peripheral adrenergic synapses (Cooper and Steinberg, 1977). Measurements of the contraction
force of the rabbit saphenous artery following stimulation of the sympathetic nerve endings
indicated that lead blocks muscle contraction by an effect on the nerve terminals rather than
by an effect on the muscle. Since the response recovered when the Ca2+ concentration was in-
creased in the bathing solution, il was concluded that lead does not deplete transmitter
stores in the nerve terminals, but more likely blocks NE release.
It has also been demonstrated that lead depresses synaptic transmission at the peripheral
neuromuscular junction by impairing acetylcholine' (ACh) release from presynaptic terminals
(Kostial and Vouk, 1957; Manalis and Cooper, 1973; Cooper and Manalis, 1974). This depression
of neurotransmitter release evoked by nerve stimulation is accompanied by an increase in the
spontaneous release of ACh, as evidenced by the increased frequency of spontaneous miniature
endplate potentials (MEPPs). Kolton and Yaari (1982) found that this increase in MEPPs in the
frog nerve/muscle preparation could be induced by lead concentrations as low as 5 pM.
The effects of lead on neurotransmission within the central nervous system have also been
studied. For example, Kim et al. (1980) fed adult rabbits 165 mg lead carbonate per day for
five days and looked at Ca2 + retention in brain slices. Treated animals showed a 75 percent
increase in Ca2+ retention time, indicating that lead inhibited the mediated efflux of Ca2
from the incubated brain slice. Investigation of the |n vitro effects of lead on Ca2 binding
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PRELIMINARY.DRAFT
was carried out by Silbergeld and Adler (1978) on caudate synaptosomes. They determined that
50 pM lead caused an 8-fold increase in 45Cas+ binding and that in both control and lead-
treated preparations the addition of ATP increased binding, while ruthenium red and Caz+
decreased it. Further findings in this series of experiments demonstrated that lead inhibits
the Na+-stimul ated loss of Ca2+ by mitochondria and that blockade of dopamine (DA) uptake by 5
pM benz-tropine reversed the lead-stimulated increase in Ca2+ uptake by synaptosomes. The
authors concluded that lead affects the normal mecnanisms of Ca2+ binding and uptake, perhaps
by chelating with DA in order to enter the -erve terminal. By inhibiting the release of Ca2+
bound to mitochondria there, lead essentially causes an increase in the Ca2+ concentration
gradient across the nerve terminal membrane. As a result, more Ca2+ would be expected to
enter the nerve terminal during depolarization, thus, effectively increasing synaptic neuro-
transmission at dopaminergic terminals without altering neuronal firing rates.
12.4.3.4 Biochemical Alterations. The majority of previous investigations of biochemical
alterations in the nervous system following exposure to lead have focused on perturbations of
various neurotransmitter systems, probably because of the documentation extant on the neuro-
physiological and behavioral roles played by these transmitters. Recently, however, somewhat
more attention has been centered on the impact of lead exposure on energy metabolism and other
cellular homeostatic mechanisms such as protein synthesis and glucose transport. A signifi-
cant portion of this work has, however, been conducted i_n vitro.
12.4.3.4.1 In vivo studies. Recent key findings on the biochemical effects of i_n vivo expo-
sure are summarized in Table 12-7. Although the majority of recent work has continued to
focus on neurotransmitter function, it appears that the mechanisms of energy metabolism are
also particularly vulnerable to perturbation by lead exposure. McCauley, Bull, and coworkers
have demonstrated that exposure of prenatal rats; to 0.02 percent lead chloride in their dams'
drinking water leads to a marked reduction in cytochrome content in cerebral cortex, as well
as a possible uncoupling of energy metabolism. Although the reduction in cytochrome content
is transient and disappears by PND 30, it occurs at blood lead levels as low as 36. jjg/dl
(McCauley and Bull, 1978; Bull et al. , 1979); celays in the development of energy metabolism
may be seen as late as PND 50 (Bull, 1983).
There does not appear to be a selective vulnerability of any particular neurotransmitter
system to the effects of lead exposure. Pathways utilizing dopamine (DA), norepinephrine
(NE), serotonin (5-HT), and y-aminobutyric acid (GABA) are all affected in neonatal animals at
lead-exposure concentrations of 0.2-2.0 percent lead salts in dams' drinking water. Although
the blood lead values reported following exposure to the lower lead concentrations (0.2-0.25
percent lead acetate or lead chloride) range from 47 (jg/dl (Goldman et at., 1980) to 87 ^ig/dl
(Govoni et al., 1980), a few general reservations can be made:
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PRELIMINARY DRAFT
TABLE 12-7. SUMMARY OF KEY STUDIES ON BIOCHEMICAL
EFFECTS OF IN VIVO LEAD EXPOSURE
Speci es
Exposure protocol
Peak blood
lead level
Observed
effect
Reference
Suckling rat 0.004% Pb(Ac)2 in
dams' drinkinq water
PND 0-35
0.02% PbC 12 in dams' 80 |jg/d 1
drinking water from (at birth)
gestation thru PND 36 pg/dl
0-21 (PND 21)
0.2% Pb(Ac)2 in 47 |jg/dl
dams' drinking water (PND 21)
PND 0-21
Decline in synthesis and
turnover of striatal DA
1) Transient 30% reduction
in cytochrome content of
cerebral cortex;
2) possible uncoupling of
energy metabolism
3) delays in development of
energy metabolism
1) 23% decrease in NE levels
of hypotholamus and
striatum;
2) increased turnover of
NE in brainstem
Govoni et al.
(1979, 1980);
Memo et al.
(1980a, 1981)
McCauley and
Bull (1978);
McCauley et
al. (1979);
Bull et al.
(1979)
Bull (1983)
Goldman et al,
(1980)
0.25% Pb(Ac)2 in
dams' drinking water
PND 0-35
0.25% Pb(Ac)2 in
dams' drinking water
PND 0-35
0.25% Pb(Ac)-) in
dams' drinking water
PND 0-35
0.25% Pb(Ac)2 in 87 (jg/dl
dams' drinking water (PND 42)
PND 0-42
Decline in synthesis
and turnover of striatal
DA
Govoni et al
(1978a)
Increase in DA synthesis
in frontal cortex and
nuc. accumbens(10-30%
and 35-45%, respectively)
1) 50% increase in DA
binding to striatal
D2 receptors;
2) 33% decrease in DA binding
to nuc. accumbens D2 receptors
1) 31% increase in GABA
specific binding in
cerebellum; 53% increase
in GMP activity;
2) 35% decrease in GABA-
specific binding in striatum;
47% decrease in GMP activity
Govoni et al.
(1979, 1980);
Memo et al.
(1980a, 1981)
Lucchi et al.
(1981)
Govoni et al.
(1978b, 1980)
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PRELIMINARY DRAFT
TABLE 12-7. (continued)
Species
Exposure protocol
Peak blooc
lead level
Observed
effect
Reference
Young rat
0.25% Pb(Ac)2 in
dam's drinking water
PND 0-21; 0.004% or
0.25% until PND 42
0.5-1% Pb(Ac)2 in
drinking water
PND 0-60
0.25-1% Pb(Ac)2 in
drinking water
PND 0-60
75 mg,Pb(Ac)2/kg
b.w./day via
gastric intubation
PND 2-14
72-91 g/dl
(PND 21)
98 |jg/dl
(PND 15)
7% Pb(Ac)2 in dam's
drinking water PND 0-21
then 0.002-0.008% until
PND 56
1) 12 and 34% elevation of Memo et al.
GABA binding in cerebellum (1980b)
for 0.004% and 0.25%, respec-
tively;
2) 20 and 45% decreases in GABA
binding in striatum for 0.004%
and 0.25%, respectively
Si 1bergeld
et al.
(1979, 1980a)
1) Increased sensitivity
to seizures induced
by GABA blockers;
2) increase in GABA synthesis
in cortex and striatum;
3) inhibition of GABA uptake
and release by synaptosomes
from cerebellum and basal
gangli a;
4) 70% increase in GABA-
specific binding in
cerebel1 urn
1) 40-50% reduction of
whole-brain ACh by PND 21;
2) 36% reduction by PND 30
(return to normal values
by PND 60)
1) 20% decline in striatal
DA levels at PND 35;
2) 35% decline in striatal DA
turnover by PND 35;
3) Transient depression of DA
uptake at PND 15;
4) Possible decreased DA
terminal density
1) non-dose-dependent Dubas et al.
elevations of NE in (1978)
midbrain (60-90%) and
DA and 5-HT in midbrain,
striatum and hypothalamus
(15-30%);
2) non-dose-dependent depression
of NE in hypothalamus and
striatum (20-30%).
Modak et al
(1978)
Jason and
Kellogg (1981)
PND:
Pb(Ac)z;
PbCl2:
NE:
BPB12/A
post-natal day
lead acetate
lead chloride
norepi nephri ne
DA: dopamine
GABA: \-aminobutyric acid
GMP: guanosine monophosphate
5-HT: serotonin
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(1). Synthesis and turnover of DA and NE are depressed in the striatum, and elevated in mid-
brain, frontal cortex, and nucleus accumbens. This seems to be paralleled by concomitant
increases in DA-specific binding in striatum and decreases in DA-specific binding in
nucleus accumbens, possibly involving a specific subset (Dj.) of DA receptors (Lucchi
et al., 1981). These findings are probably reflective of sensitization phenomena result-
ing from changes in the availability of neurotransmitter at the synapse.
(2). The findings for pathways utilizing GABA show similar parallels. Increases in GABA syn-
thesis in striatum are coupled with decreases in GABA-specific binding in that region,
while the converse holds true for the cerebellum. In these cases, cyclic GMP activity
mirrors the apparent changes in receptor function. This increased sensitivity of cere-
bellar postsynaptic receptors (probably a response to the lead-induced depression of pre-
synaptic function) is likely the basis for the finding that lead-treated animals are more
susceptible to seizures induced by GABA-blocking agents such as picrotoxin or strychnine
(Silbergeld et al., 1979).
12.4.3.4.2 In vitro studies. Any alterations in the integrity of the blood-brain barrier can
have serious consequences for the nervous system, especially in the developing organism.
Kolber et al. (1980) examined glucose transport in isolated microvessels prepared from the
brains of suckling rats given 25, 100, 200, or 1000 mg lead/kg body weight daily by intra-
gastric gavage. On PND 25, they found that ev2n the lowest dose blocked specific transport
sites for sugars and damaged the capillary endothelium. _In vitro treatment of the preparation
with concentrations of lead as low as 0.1 pM produced the same effects.
Purdy et al. (1981) examined the effects in rats of varying concentrations of lead ace-
tate on the whole-brain synthesis of tetrahydrobiopterin (BH4), a cofactor for many important
enzymes, including those regulating catecholamine synthesis. Concentrations of lead as low as
0.01 pM produced a 35 percent inhibition of BH4 synthesis, while 100 pM inhibited the BH4 sal-
vage enzyme, dihydropteridine reductase, by 40 percent. This would result in a decreased con-
version of phenylalanine to tyrosine and thence to D0PA (the initial steps in dopamine synthe-
sis), as well as decreases in the conversion of trytophan to its 5-hydroxy form (the initial
step in serotonin synthesis). These decrements, if occurring j_n vivo, could not be ameliora-
ted by increased dietary intake of BH4, as it does not cross the blood-brain barrier.
Lead has also been found to have an inhibitory effect on mitochondrial respiration in the
cerebrum and cerebellum of immature or adult rats at concentrations greater than 50 pM
(Holtzman et al . , 1978b). This effect, which was equivalent in both brain regions at both
ages studied, is apparently due to an inhibition of nicotinamide adenine dinucleotide (NAD)-
linked dehydrogenases within the mitochondrial matrix. These same authors found that this
lead-induced effect, which is an energy-dependent process, could be blocked i_n vi tro by
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PRELIMINARY DRAFT
addition cf ruthenium red to the incubation medium (Holtzman et al., 1980b). In view of the
fact that Ca2+ uptake and entry into the mitochondrial matrix is also blocked by ruthenium
red, it is possible that both lead and Caz+ shara the same binding site/carrier in brain mito-
chondria. These findings are supported by the work of Gmerek et al. (1981) on adult rat
cerebral mitochondria, with the exception that they observed respiratory inhibition at 5 pM
lead acetate, which is a full order of magnitude lower than the Holtzman et al. (1978b, 1980b)
studies. Gmerek and co-workers offer the possibility that this discrepancy may have been due
to the inadvertent presence of EDTA in the incubation medium used by Holtzman et al.
Organolead compounds have also been demonstrated to have a deleterious effect on cellular
metabolism in the nervous system. For example, Grundt and Neskovic (1980) found that concen-
trations of triethyl lead chloride as low as 5-7 pM caused a 40 percent decrease in the incor-
poration of S04 or serine into myelin galacto-1ipids in cerebellar slices from 2-week-old
rats. Similarly, Konat and coworkers (Konat and Clausen, 1978, 1980; Konat et al., 1979) ob-
served that 3 pM triethyl lead chloride preferentially inhibited the incorporation of leucine
into myelin proteins in brain stem and forebrain slices from 22-day-old rats. This apparent
inhibition of myelin protein synthesis was two-fold greater than that observed for total pro-
tein synthesis (approximately 10 vs. 20 percent, respectively). In addition, acute intoxica-
tion of these animals by i.p. injection of triethyl lead chloride at 8 mg/kg produced- equiva-
lent results accompanied by a 30 percent reduction in total forebrain myelin content.
Interestingly, while a suspension of cells from the forebrain of these animals (Konat et
al., 1978) exhibited a 30 percent inhibition of total protein synthesis at 20 pM triethyl lead
chloride (the lowest concentration examined), a cell-free system prepared from the same tissue
was not affected by triethyl lead chloride concentrations as high as 200 pM. This result,
coupled with a similar, although not as severe, inhibitory effect of triethyl lead chloride on
oxygen consumption in the cell suspension (20 percent inhibition at 20 pM) would tend to indi-
cate that the inhibition of rat forebrain protein synthesis is related to an inhibition of
cellular energy-generating systems.
The effects of organolead compounds on various neurotransmitter systems have been inves-
tigated in adult mouse brain homogenates. Bondy et al. (1979a,b) demonstrated that micromolar
concentrations (5 pM) of tri-n-butyl lead (TBL) acetate were sufficient not only to cause a 50
percent decline in the high affinity uptake of GABA and DA in such homogenates, but also to
stimulate a 25 percent increase in GABA and DA release. These effects were apparently selec-
tive for DA neurons at lower concentrations, as only DA uptake or release was affected at 0.1
pM, albeit mildly so. The effect of TBL acetate on 0A uptake appears to be specific, as there
is a clear dose-response relationship down to 1 pM TBL (Bondy and Agarwal, 1980) for inhibi-
tion (0-60 percent) of spiroperidol binding to rat striatal DA receptors. A concomitant
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PRELIMINARY DRAfT
inhibition of adenyl cyclase in this dose range (50 percent) suggests that TBL may affect the
entire postsynaptic binding site for DA.
12.4.3.5 Accumulation and Retention of Lead in the Brain. All too infrequently, experimen-
tal studies of the neurotoxic effects of lead exposure do not report the blood-lead levels
achieved by the exposure protocols used. Even less frequently reported are the concomitant
tissue levels found in brain or other tissues. From the recent information that is available,
however, it is possible to draw some limited conclusions about the relationship of exposure
concentrations to blood and brain lead concentrations. Table 12-8 calculates the blood lead/
brain lead ratios found in recent studies where such information was available. It can be
seen that, at exposure concentrations greater than 0.2 percent and for exposure periods longer
than birth until weaning (21 days in rats), the ratio generally falls below unity. This
suggests, that, even as blood lead levels reach a steady state and then fall due to excretion
or some other mechanism, lead continues to accumulate in brain.
Further evidence bearing on this was derived from a set of studies by Goldstein et al.
(1974), who reported that administration of a wide range of doses of radioactive lead nitrate
to one-month-old rats resulted in parallel linear increases in both blood and brain lead
levels during the ensuing 24 hours. This suggests that deposition of lead in brain occurs
without threshold and that, at least initially, it is proportional to blood lead concentra-
tion. However, further studies by Goldstein et al. (1974) followed changes in blood and brain
1ead concentrations after cessation of lead exposure and found that, whereas blood lead levels
decreased dramatically (by an order of magnitude or more) during a 7-day period, brain lead
levels remained essentially constant over the one-week postexposure period. Thus, with even
intermittent exposures to lead, it is not unexpected that brain concentrations would tend to
remain the same or even to increase although blood lead levels may have returned to "normal"
levels. Evidence confirming this comes from findings of: (1) Hammond (1971), showing that
EDTA administration causing marked lead excretion in urine of young rats did not significantly
lower brain lead levels in the same animals; and (2) Goldstein et al. (1974), showing that
although EDTA prevented the j_n vitro accumulation of lead into brain mitochondria, if lead was
added first then EDTA was ineffective in removing lead from the mitochondria. These results,
overall, indicate that, although lead may enter the brain in rough proportion to circulating
blood lead concentrations, it is then taken up by brain cells and tightly bound into certain
subcellular components (such as mitochondrial membranes) and retained there for quite long
after initial external exposure ceases and blood lead levels markedly decrease. This may help
to account for the persistence of neurotoxic effects of various types noted above long after
the cessation of external lead exposure.
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TABLE 12-8. INDEX OF BLOOD LEAD AND BRAIN LEAD LEVELS FOLLOWING EXPOSURE
Species Tine of Blood lead Brain lead Bloodtbrain
(strain) Exposure assay (uq/d 1 > (no/lOOq) lead ratio Reference
Suckling rat
(Charles
3iver-CD)
0.0005% PbC1^
1n water
PND 0-21
PND 21
12
8
1 5
Btl' et al.
(1979)
0.003% PoCl2
in water
PND 0-21
PND 21
21
11
1.9
Sjckling rat
(Cnarles
River)
0.005% Pd(Ac)2
in water from
conception
PND 11
PND 30
22
18
3
11
7.0
1.6
Grant et al.
(1983)
0.01% Pb(Ac)2
in water from
conception
PND 11
PND 30
35
46
7
22
5.0
2.2
Suckling rat
(Charles
River-CD)
0.02% PbC12
in water
PND 0-21
PND 21
36
25
1.4
Bull et al.
(1979)
SuckV.ng rat
(Long-Evans)
0 02% Pb(Ac)2
ir water
PND 0-21
PND 10
PND 21
21.7
25.2
6.3
13
3.4
1.9
Fox et al.
(1979)
Stckl"ig rat
(Long-Evans)
0.02% Pb(Ac)2
in water froi.
PND 0-21
PND 21
29
29
1.0
Hasti ngs
et al. (1979)
Suckling rat
(Holtzraar-
a^bino)
0.05% Pb(Ac)2
in water
PND 0-21
PND 21
12
20
0.6
Goldman et al.
(1980)
0.1% Pb(Ac)2
in water
PND 0-21
PND 21
20
50
0.4
Suck'ing -at
0.2% ®b(Ac)2
in water
PND 0-21
PND 21
65
65
1.0
Hastings et
al. (1979)
Suckling rat
(Hoitzman-
albi no)
0.2% Pb(Ac)^
i n wate-
PND 0-21
PND 21
47
80
0.6
Goldman et al.
(1980)
Suckling rat
(Long-Evans)
0.2% Pb(Ac)i:
in water
PND 0-21
PND 1C
PND 21
49.5
69.4
1?
82
2.6
1.1
Fox et al.
(1979)
Suckling rat
(Long-Evans)
D.2% Pb(Ac)2
in water
PND 0-21
PND 21
65.0
53
1.2
Fox et al.
(1977)
SjCKlirg rat
(Long-Evans)
0.2% Pb(Ac)2
1n water
PND 0-21
PND 21
65.1
5?
1.2
Cooper et al.
(19e3)
SucKling mice
(ICR Swiss
albino)
0 25% Pb(Ac)2
in water
PND 0-21
PND 21
72
230
D. 3
Modak et al.
(1978)
Suckling rat
(Wistar)
D.2% Pb(Ac)2
in water
PND 2-60
PND 30
PN0 60
115*
35*
84
99
_
Shigeta et al.
(1979)
0.5% Pb(AC)2
in water
PND 2-60
PND 30
PND 60
308*
73*
172
222
i2-m, . .
; •" ' L-008<
• • j
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PRELIMINARY DRAFT
Table 12-8. (continued)
Speci es
(strain)
Exposure
Time of
assay
load lead Brain lead Blood:brain
(M/fl) (M/1009) lead ratio
Reference
Suckling rat
(Sp^ague-
Dawley)
Suckling rat
(Sprague-
Dawley)
Suckling rat
(Long-Evans)
Young mice
(ICR Swiss
albino)
0.25% Pb(Ac)2
in water from
gestation until
PND 42
0.5% Pb(Ac)2
in water
PND 0-21
1% Pb(Ac)j
in water
PND 0-21
0.25% Pb(Ac),
in water
PND 0-60
0.5% Pb(Ac)2
in water
PND 0-60
PND 42
PND 21
PND 21
4% PbC03 PND 27
in water
PND 0-27
25 mg/kg Pb(Ac)j PND 15
by gavage
PND 2-14
75 mg/kg Pb(Ac)2 PND 15
by gavage
PND 2-14
PND 50
PNC 60
87
70
91
50
98
91
194
85
280
270
1.36
40
60
410
360
1.0
0.25
0.3
1. 3
1.6
0.2
0.5
Govani et al.
(1960)
Wi nee et al
(1980)
Jason and
Kellogg (1981)
Modak et a'.
(1978)
Adult rat
(Charles
River-CD)
Adult rat
(Wi star)
1% Pb(Ac)2 PND 60
in water PND 0-60
0.0005% Pb(Ac)j
in water for 21 days
0.003% Pb(Ac)2
in water for 21 days
0.02% Pb(Ac)2
in water for 21 days
0.15% Pb(Ac)2
in water for 3 months
0.4% Pb(Ac)2
in water for 3 months
1% Pb(Ac)2
in water for 3 months
223
11
29
31
69
122
810
10
12
100
12-18
(dependi ng
on region)
16-34
(depend!ng
on region)
37-72
(depending
on region)
PND: post-natal day
Pb(Ac)2: lead acetate
PbCl2: lead chloride
'Expressed as pg Pb/lOOg blood.
0.3
0.9
0.9
0.29
2.6-1.7
(depending
011 region)
4. 3-2.0
(depending
on region)
3.3-1.7
(depending
on region)
Bull et al.
(1979) .
Ewers and
Erbe (1980)
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/oo
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The uptake of lead into specific neural and non-neuronal elements of the brain has also
been studied and provides insight into possible morphological correlates of certain lead
effects discussed above and below as beinq observed in vivo or in vitro. For example, Stumpf
710—
et al. (1980), via autoradiographic localization nf Pb, found that ependymal cells, glial
cells, and endothelial cells of brain capillaries concentrate and retain lead above background
levels for several days after injections of tracer amounts of the elements. These cells are
non-neural elements of brain important in the maintenance of "blood-brain barrier" functions,
and their uptake and retention of lead, even with tracer doses, provides evidence of a mor-
phological basis by which lead effects on blood-brain barrier functions may be exerted.
Again, the retention of lead in these non-neuronal elements for at least several days after
original exposure points towards the plausibility of lead exerting effects on blood-brain
barrier functions long after external exposure ceases and blood lead levels decrease back
toward normal levels. Uptake and concentration of lead in the nuclei of some cortical neurons
210
even several days after administration of only a tracer dose of Pb was also observed by
Stumpf et al. (1980) and provide yet another plausible morphological basis by which neurotoxic
effects might be exerted by lead long after external exposure terminates and blood lead levels
return to apparently "normal" levels.
12.4.4 Integrative Summary of Human and Animal Studies of Neurotoxicity
An assessment of the impact of lead on human and animal neurobehavioral function raises a
number of issues. Among the key points addressed here are: (1) the internal exposure levels,
as indexed by blood lead levels, at which various adverse neurobehavioral effects occur; (2)
the reversibility of such deleterious effects; an£ (3) the populations that appear to be most
susceptible to neural damage. In addition, the question arises as to the utility of using
animal studies to draw parallels to the human condition.
12.4.4.1 Internal Exposure Levels at Which Adverse Neurobehavioral Effects Occur. Markedly
elevated blood lead levels are associated with neurotoxic effects of lead exposure (including
severe, irreversible 'brain damage as indexed by the occurrence of acute and/or chronic enceph-
alopathy symptoms) in both humans and and animals. For most adult humans, such damage typi-
cally does not occur until blood lead levels exceed 120 pg/dl. Evidence does exist, however,
for acute encephalopathy and death occurring in some human adults at blood lead levels below
120 jjg/dl. In children, the effective blood lead level for producing encephalopathy or death
is lower, starting at approximately 100 pg/dl. Again, however, evidence exists for encepha-
lopathy occurring in some children at lower blood lead levels, i.e., at 80-100 pg/dl.
It should be emphasized that, once encephalop«thy occurs, death is not an improbable out-
come, regardless of the quality of medical treatment available at the time of acute crisis.
BPB12/A 12-113 9/20/83
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it Id
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In fact, certain diagnostic or treatment procedures themselves tend to exacerbate matters and
push the outcome toward fatality if the nature and severity of the problem a^e not fully rec-
ognized or properly diagnosed. It is also crucial to note the rapidity with which acute
encephalopathy symptoms can develop or death can occur in apparently asymptomatic individuals
or in those apparently only mildly affected by elevated body burdens of lead. It is not
unusual for rapid deterioration to occur, with convulsions or coma suddenly appearing and with
progression to death within 48 hours. This strongly suggests that, even in apparently asymp-
tomatic individuals, rather severe neural damage probably does exist at high blood lead levels
even though it is not yet overtly manifested in obvious encephalopathy symptoms. This con-
clusion is further supported by numerous studies showing that children with high blood lead
levels (over 80-100 |jg/dl), but not observed to manifest acute encephalopathic symptoms, are
permanently cognitively impaired, as are most children who survive acute episodes of frank
lead encephalopathy.
Other evidence, tends to confirm that some type of neural dysfunction exists in apparently
asymptomatic children, even at much lower levels of blood lead. The body of studies on 1 ow-
or moderate-level lead effects on neurobehavioral functions, as summarized in Table 12-1, pre-
sents a rather impressive array of data pointing to that conclusion. Several well-controlTed
studies have found effects that are clearly statistically significant, whereas others have
found nonsignificant but borderline effects. Even certain studies reporting generally non-
significant findings at times contain data confirming some statistically significant effects,
which the authors attribute to various extraneous factors. It should also be noted that,
given the apparent non-specific nature of some of the behavioral or neural effects probable at
low levels of lead exposure, one would not expect to find striking differences in every
instance. The lowest blood lead levels associated with significant neurobehavioral (e.g.
cognitive) deficits both in apparently asymptomatic children and in developing rats and
monkeys generally appear to be in the range of 30-50 pg/dl. Also, certain behavioral and
electrophysiological effects indicative of CNS deficits have been reported at lower levels,
supporting a continuous . dose-response relationship between lead, and neurotoxicity. Such
effects, when combined with adverse social factors (such as low parental IQ, low socioeconomic
status, poor nutrition, and poor quality of the caregiving environment) can place children,
especially those below the age of three years, at significant risk. However, it must be
acknowledged that nutritional covariates, as well as demographic social factors, have been
poorly controlled in many of the pediatric neurobehavioral studies reviewed above. Socio-
economic status also is a crude measure of parenting and family structure that requires fur-
ther assessment as a possible contributor to observed results of neurobehavioral studies.
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Timing, type, and duration of exposure are also important factors in both animal and
human studies. It is often uncertain whether observed blood lead levels represent the levels
that were responsible for observed behavioral deficits. Monitoring of lead exposures in human
subjects in all cases has been highly intermittent or non-existent during the period of life
preceding neurobehavioral assessment. In most human studies, only one or two blood lead
values arc provided per subject. Tooth lead may be an important cumulative exposure index;
but its modest, highly variable correlation to blood lead or FEP and to external exposure
levels makes findings from various studies difficult tc compare quantitatively. The com-
plexity of the many important covariates and their interaction with dependent measures of
modest validity, e.g., 1Q tests, may also account for many of the discrepancies among the dif-
ferent studies.
The precise medical or health significance of the neuropsychological and electrophysio-
logical effects associated with low-level lead exposure as reported in the above studies is
difficult to state with confidence at this time. Observed IQ deficits and other behavioral
changes, although statistically significant in some- studies, tend to be relatively small as
reported by the investigators, but nevertheless may still affect the intellectual development,
school performance, and social development of the affected children sufficiently to be regard-
ed as adverse. This would be especially true if such impaired intel1ectual development or
school performance and disrupted social development were reflective of persisting, long-term
effects of low-level lead exposure in early childhood. The issue of persistence of such lead
effects, however, remains to be more clearly resolved. Still, some study results reviewed
above suggest that significant low-level lead-induced neurobehavioral and EEG affects may, in
fact, persist at least into later childhood, and a number of animal studies demonstrate long-
term persistence into adulthood of neurologic dysfunctions induced by relatively moderate or
low level lead exposures early in postnatal development of mammalian species.
12.4.4.2 The Question of Irreversibility. Little research on humans is available on persis-
tence of effects. Some work suggests the possibility of reversing mild forms of peripheral
neuropathy in lead workers,¦ but>1ittle is known regarding the reversibility of lead effects on
central nervous system function in humans. A recent two-year follow-up study of 28 children
of battery factory workers found a persistent relation between blood lead and altered slow
wave voltage of cortical slow wave potentials. Current human psychometric studies, however,
will have to be supplemented by prospective longitudinal studies of the effects of lead on
development in order to better elucidate persistence or reversibility of neurotoxic effects of
lead exposure early in infancy or childhood.
Various animal studies provide evidence that alterations in neurobehavioral function may
be long-lived, with such alterations being evident long after blood lead levels have returned
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PRELIMINARY DRAFT
to control levels. These persistent effects have been demonstrated in monkeys as well as rats
under a variety of learning performance test paradigms. Such results are also consistent with
morphological, electrophysiological, and biochemical studies on animals that suggest lasting
changes in synaptogenesis, dendritic development, myelin and fiber tract formation, ionic
mechanisms of neurotransmission, and energy metabolism.
12.4.4.3 Early Development and Susceptibility to Neural Damage. On the question of early
childhood vulnerability, the neurobehavioral data are consistent with morphological and bio-
chemical studies of the susceptibility of the heme biosynthetic pathway to perturbation by
lead. Various lines of evidence suggest that the order of susceptibility neurotoxic effects of
lead is: young > adult; female > male. Animal studies also have pointed to the perinatal
period of ontogeny as a particularly critical time for a variety of reasons: (1) it is a
period of rapid development of the nervous system; (2) it is a period where good nutrition is
particularly critical; and (3) it is a period where the caregiver environment is vital to nor-
mal development. However, the precise boundaries of a critical period for lead exposure are
not yet clear and may vary depending on the species and function or endpoint that is being
assessed. Nevertheless, there is general agreement that human infants and toddlers below the
age of three years are at special risk because of i_n utero exposure, increased opportunity for
exposure because of normal mouthing behavior of lead-containing objects, and increased rates
of lead absorption due to various factors, e.g., iron and calcium deficiencies.
12.4.4.4 Utility of Animal Studies in Drawing Parallels to the Human Condition. Animal
models are used to shed light on questions where it would be impractical or ethically unaccep-
table to use human subjects. This is particularly true in the case of exposure to environmen-
tal toxins such as lead. In the case of lead, it has been most effective and convenient to
expose developing animals via their mothers' milk or by gastric gavage, at least until
weaning. Very often, the exposure is continued in the water or food for some time beyond
weaning. This approach does succeed in simulating at least two features commonly found in
human exposure: oral intake and exposure during early development. The preweaning postnatal
period in rats and mice is of particular relevance in terms of parallels with the first two
years or so of human brain development.
However, important questions exist concerning the comparability of animal models to
humans. Given differences between humans, rats, and monkeys in heme chemistry, metabolism,
and other aspects of physiology and anatomy, it is difficult to state what constitutes an
equivalent internal exposure level (much less an equivalent external exposure level). For
example, is a blood lead level of 30 jjg/dl in a suckling rat equivalent to 30 pg/dl in a
three-year-old child? Until an answer is available to this question, i.e., until the function
describing the relationship of exposure indices in different species is avai 1 abl ethe utility
of animal models for deriving dose-response functions relevant to humans will be limited.
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Questions also exist regarding the comparability of nejrobehavioral effects in animals
with human behavior and cognitive function. One difficulty in comparing behavioral endpoints
such as locomotor activity is the lack of a consistent operational definition. In addition to
the lack of standardized methodologies, behavior is notoriously difficult to "equate" or com-
pare meaningfully across species because behavioral analogies do not demonstrate behavioral
homologies. Thus, it is improper to assume, without knowing more about the responsib-le
underlying neurological structures and processes, that a rat's performance on an operant
conditioning schedule or a monkey's performance on a stimulus discrimination task necessarily
corresponds directly to a child's performance on a cognitive function test. Nevertheless,
deficits in performance by mammalian animals on such tasks are indicative of likely altered
CNS functions, which is reasonable to assume will likely parallel some type of altered CNS
function in humans as well.
In terms of morphological findings, there are reports of hippocampal lesions in both
lead-exposed rats and humans that,are consistent w'th a nunber of independent behavioral find-
ings suggesting an impaired ability tc respond appropriately to altered contingencies • for
rewards. That is, subjects with hippocampal damage tend to persist in certain patterns of
behavior even when changed conditions make the behavior inappropriate; the same sort of ten-
dency seems to be common to a number of lead-induced behavioral effects. Other morphological
findings in animals, such as denyelination and glial cell decline, are comparable to human
neuropathologic observations only at relatively high exposure levels.
Another neurobehavioral endpoir.t of interest in comparing human and animal neurotoxicity
of lead is electrophysiological function. Alterations of electroencephalographic patterns and
cortical slow wave voltage have been reported for lead-exposed children, and various electro-
physiological alterations both j_n vivo (e.g., in rat visual evoked response) and i_n vitro
(e.g., in frog miniature endplate potentials) have also been noted in laboratory animals.
Thus, far, however, these lines of work have not converged sufficiently to allow for much in
the way of definitive conclusions regarding electrophysiological aspects of lead neuro-
toxicity.
Biochemical approaches to the experimental study of lead effects on the nervous system
have been basically limited to laboratory animal subjects Although their linkage to human
neurobehavioral function is at this point somewhat speculative, such studies do provide in-
sight on possible neurochemical intermediaries of lead neurotoxicity. No single neurotrans-
mitter system has been shown to be particularly sensitive to the effects of lead exposure;
lead-induced alterations have been demonstrated in various neurotransmitters, including
dopamine, norepinephrine, serotonin, and gamma-aminobutyric acid. In addition, lead has been
shown to have subcellular effects in the central nervous system at the level of mitochondrial
function and protein synthesis. In particular, the work of McCauley, Bull, and co-workers has
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PRELIMINARY DRAFT
indicated that delays seen in cortical synoptcgenesis and metabolic maturation following pre-
natal lead exposure may well underly the delayed development of exploratory and locomoter
function seen in other studies of the neurobehavioral effects of lead.
Given the difficulties in formulating a comparative basis for internal exposure levels
among different species, the primary value of many animal studies, particularly j_n vitro
stucies, may be in the information they can provide on basic mechanisms involved in lead
neurotoxicity. A number of key i_n vi tro studies are summarized in Table 12-9. These stu-
dies show that significant, potentially deleterious effects on nervous system function occur
at i_n 5itu lead concentrations of 5 pM and possibly lower. This suggests that, at least
intracel1ularly or on a molecular level, there may exist essentially no threshold for certain
neurochemical effects of lead. The relationship between blood lead levels and lead concen-
trations at extra- or intracellular sites of action, however, remains to be determined.
Despite the problems in generalizing from animals to humans, both the animal and the
human studies show considerable internal consistency in that they both support a continuous
dose-response functional relationship between lead and neurotoxic biochemical, morphological,
electrophysiological, and behavioral effects.
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TABLE 12-9. SUMMARY OF KEY STUDIES OF IN VITRO LEAD EXPOSURE
Preparation
Adult rat brain
Isolated microvessels
from rat brain
Exposure
concentration
0.1 pM Pb(Ac)2
0.1 pM Pb(Ac)2
Adult mouse
brain homogenate
0.1-5 (jM tri-n-butyl
lead (TBL)
Adult rat striatum
1-5 pM TBL
Embryonic chick
brain cell culture
Brainstem and forebrain
slices from PND-22 rats
3 pM (Et3Pb)Cl2
3 pM (Et3Pb)Cl2
Adult rat 3-5 pM Pb
cerebellar homogenates
Adult rat 5 pM Pb(Ac)2
cerebellar mitochondria
Adult frog 5 pM Pb++
nerve/muscle preparation
Isolated, perfused
bullfrog retina
5 pM Pb
Results
Reference
35% inhibition of whole-
brain BH4 synthesis
Blockade of sugar-specific
transport sites in capi-
llary endothelial cells
1) 50% decline in high
affinity uptake of DA;
2) 25% increase in
release of DA
0-60% inhibition of spiro-
peridal binding to DA
receptors
50% reduction in no. of
cells exhibiting processes
Inhibition of leucine in-
corporation into myelin
protei ns
Inhibition of adenylate
cyclase activity
Inhibition of respiration
Increase in frequency of
MEPP's (indicative of
depression of synaptic
transmission)
Depression of rod (but not
cone) receptor potentials
Purdy et al.
(1981)
Kolber et al,
(1980)
Bondy et al.
(1979a,b)
Bondy and Agarwal
(1980)
Grundt et al.
(1981)
Konat and Clausen
(1978, 1980)
Konat et al.
(1979)
Taylor et al.
(1978)
Gmerek et al.
(1981)
Kolton and Yaari
(1982)
Fox and Sillman
(1979)
-------
TABLE 12-9. (continued)
Preparation
Exposure
concentration
Cerebellar slices
from PND-14 rats
5-7 pM (Et3Pb)Cl;
In oculo culture of
cerebellar tissue
from PND-15 rats
5-10 pM Pb
++
©
3
A
[NJ
I
[NJ
O
Cell suspension from
forebrain of PND-22 rats
Adult rat cerebral
and cerebellar mitochondria
Adult rat caudate
synaptosomes
20 pM (Et-jPbJClj,
50 pM Pb(Ac)2
50 pM PbCl2
Capillary endothelial
cells from rat cere-
cortex
100 pM Pb(Ac)z
Results
Reference
Inhibition of incorporation
of S04 and serine into
myelin galactolipids
"Disinhibition" of NE-
induced inhibition of
spontaneous activity in
Purkinje eel 1s
30% inhibition of total
protein synthesis
Inhibition of respiration
8-fol
TO
-C
o
TO
J>
Silbergeld et al,
(1980b)
PND: post-natal day
Pb(Ac)2: lead acetate
PbC12: lead chloride
Et3Pb: triethyl lead
TBL: tri-n-butyl lead
DA: dopamine
NE: norepinephrine
BH4: tetrahydrobiopterin
MEPP's: miniature endplate potentials
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PRELIMINARY DRAFT
12.5 EFFECTS OF LEAD ON THE KIDNEY
12.5.1 Historical Aspects
The first description of renal disease due to lead was published by Lancereaux (1862).
In a painter with lead encephalopathy and gout, Lancereaux noted tubulo-interstitial disease
of the kidneys at autopsy. Distinctions between glomerular and tubulo-interstitial forms of
kidney disease were not, however, clearly defined in the mid-nineteenth century. Ollivier
(1863) reported observations in 37 cases of lead poisoning with renal disease and thus intro-
duced the idea that lead nephropathy was a proteinuric disease, a confusion with primary
glomerular disease that persisted for over a century. Under the leadership of Jean Martin
Charcot, interstitial nephritis characterized by meager proteinuria in lead poisoning was
widely publicized (Charcot, 1868; Charcot and Gombault, 1881) but not always appreciated by
contemporary physicians (Danjoy, 1864; Gepper, 1882; Lorimer, 1886).
More than ninety years ago, the English toxicologist Thomas Oliver (1885, 1891) distin-
guished acute effects of lead on the kidney from lead-induced chronic nephropathy. Acute
renal effects of lead were seen in persons dying of lead poisoning and were usually restricted
to non-specific changes in the renal proximal tubular lining cells. Oliver noted that a
"true interstitial nephritis" developed later, often with glomerular involvement.
In an extensive review of the earlier literature, Pejic (1928) emphasized that changes in
the proximal tubules, rather than the vascular changes often referred to in earlier studies
(Gull and Sutton, 1872), constitute the primary injury to the kidney in lead poisoning. Many
subsequent studies have shown pathological alterations in the renal tubule with onset during
the early or acute phase of lead , intoxication. These include the formation of inclusion
bodies in nuclei of proximal tubular cells (Blackman, 1936) and the development of functional
defects as well as ultrastructural changes, particularly in renal tubular mitochondria.
12.5.2 Lead Nephropathy in Childhood
Dysfunction of the proximal tubule was first noted as glycosuria in the absence of hyper-
glycemia in childhood pica (McKhann, 1926). Later it was shown that the proximal tubule
transport defect included aminoaciduria (Wilson et al. , 1953). Subsequently, Chisolm et al.
(1955) found that the full Fanconi syndrome was present: glycosuria, aminoaciduria, phos-
phaturia (with hypophosphatemia), and rickets, Proximal tubular transport defects appeared
only when blood lead levels exceeded 80 ng/dl. Generalized aminoaciduria was ,seen more con-
sistently in Chi solm's (1962, 1968) studies than were other manifestations of renal dysfunc-
tion. The condition was related to the severity of clinical toxicity, with the complete
Fanconi syndrome occurring in encephalopathy children when blood lead concentrations exceeded
150 pg/dl (National Academy of Sciences, 1972). Children who were under three years of age
excreted 4 to 12.8 mg of lead chelate during the first day of therapy with CaEDTA at 50 mg/kg
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day. The aminoaciduria disappeared after treatment with chelating agents and clinical remis-
sion of other symptoms of lead toxicity (Chisolm, 1962). This is an important observation
relative to the long-term or chronic effects of lead on the kidney.
In a group of children with slight lead-related neurological signs reported by Pueschel
et al. (1972), generalized aminoaciduria was found in 8 of 43 children with blood lead levels
of 40 to 120 pg/dl. It should be noted that the children reported to have aminoaciduria in
this study were selected because of a blood lead level of ^50 |jg/dl or a provocative chelation
test of >500 |jg of lead chelate per 24 hours.
Although children are considered generally to be more susceptible than adults to the
toxic effects of lead, the relatively sparse literature on childhood lead nephropathy probably
reflects a greater clinical concern with the life-threatening neurologic symptoms of lead in-
toxication than with the transient Fanconi syndrome.
12.5.3 Lead Nephropathy in Adults
. There is convincing evidence in the literature that prolonged lead exposure in humans can
result in chronic lead nephropathy in adults. This evidence is reviewed below in terms of six
major categories: (1) lead nephropathy following childhood lead poisoning; (2) "moonshine"
lead nephropathy; (3) occupational lead nephropathy; (4) lead and gouty nephropathy; (5) lead
and hypertensive nephrosclerosis; and (6) general population studies.
12.5.3.1 Lead Nephropathy Following Childhood Lead Poisoning. Reports from Queensland,
Australia (Gibson et al., 1892; Nye, 1933; Henderson, 1954; Emmerson, 1963) points to a strong
association between severe childhood lead poisoning, including central nervous system
symptoms, and chronic nephritis in early adulthood. The Australian children sustained acute
lead poisoning when confined to the enclosed, raised terraces peculiar to the houses around
Brisbane. The houses were painted with white lead, which the children ingested by direct con-
tamination of their fingers or by drinking lead-sweetened rain water as it flowed over the
weathered surfaces. Two fingers brushed against the powdery paint were shown to pick up about
2 mg of lead (Murray, 1939). Henderson (1954) followed up 401 untreated children who had been
diagnosed as having lead poisoning in Brisbane between 1915 and 1935. Of these 401 subjects,
death certificates revealed that 165 had died under the age of 40, 108 from nephritis or
hypertension. This is greatly in excess of expectation. Information was obtained from 101 of
the 187 survivors, and 17 of these had hypertension and/or albuminuria.
In a more recent study, Emmerson (1963) presented a criterion for implicating lead as an
etiological factor in such patients: the patients should have an excessive urinary excretion
of lead following administration of CaEDTA. Leckie and Tompsett (1958) had shown that
increasing the CaEDTA dosage above 2 g/day intravenously had little effect on the amount of
lead chelate excreted by adults. They observed little difference in chelatable lead excretion
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when 1 g was compared with 2 g (i.v.). Similarly, the magnitude of lead chelated when 1 g is
given i.v. or 2 g i.m. (over 12 hr) appears to be the same (Albahary et al., 1961; Emmerson,
1963; Wedeen et al., 1975). Adult control subjects without undue lead absorption excrete less
than 650 ng lead chelate during the first post-injection day if renal function is normal, or
over 4 days if renal function is severely reduced. The level of reduction of glomerular fil-
tration rate (GFR) at which the EDTA lead-mobilization test is no longer reliable has not been
precisely defined but probably exceeds a reduction of 85 percent (serum creatinine concentra-
tions in excess of about 6 mg/dl). In Emmerson's (1963) study 32 patients with chronic renal
disease attributable to lead poisoning had elevated excretion of lead chelate. Intranuclear
inclusions are associated with recent acute exposure but are often absent in chronic lead
nephropathy or after the administration of CaNa^EDTA (Goyer and Wilson, 1975).
The Australian investigators established the validity of the EDTA lead-mobilization test
for the detection of excessive past lead absorption and further demonstrated that the body
lead stores were retained primarily in bone (Emmerson, 1963; Henderson, 1954; Inglis et al.,
1978). Bone lead concentration averaged 94 pg/g wet weight in the young adults dying of lead
nephropathy in Australia (Henderson and Inglis, 1957; Inglis et al., 1978), compared with mean
values ranging from 14 to 23 jjg/g wet weight in bones from non-exposed individuals (Barry,
1975; Emmerson, 1963; Gross et al. , 1975; Wedeen, 1982).
Attempts to confirm the relationship between childhood lead intoxication and chronic
nephropathy have not been successful in at least two studies in the United States. Tepper
(1963) found no evidence of increased chronic renal disease in 139 persons with a well-
documented history of childhood plumbism 20 to 35 years earlier at the Boston Children's
Hospital. The study population was 165 patients (after review of 524 case records) who met
any two of the following criteria: 1) a definite history of pica or use of lead nipple
shields; 2) X-ray evidence of lead-induced skeletal alterations; or 3) characteristic
symptoms. No uniform objective measure of lead absorption was reported in this study. In 42
of the 139 subjects clinical studies of renal function were performed and included urinalysis,
endogenous creatinine clearance, urine culture, urine concentrating ability, 24-hour protein
excretion, and phenolsulfonphthalein excretion. Only one patient was believed to have died of
lead nephropathy; three with creatinine clearances under 90 ml/min were said to have had
inadequate urine collections. Insufficient details concerning past lead absorption and
patient selection were provided to permit generalized conclusions from this report.
Chisolm et al. (1976) also found no evidence of renal disease (as judged by routine
urinalysis, blood urea nitrogen, serum uric acid, and creatinine clearance) in 55 adolescents
known to have been treated for lead intoxication 11 to 16 years earlier. An important dis-
tinction between the Australian group and those patients in the United States studied by
Chisolm et al. (1976) was that none of the latter subjects showed evidence of increased
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residual body lead burden by the EDTA lead-mobilization test. This U.S. study was carried out
on adolescents between 12 and 22 years of age in the late 1960s. During acute toxicity in
early childhood, blood lead levels had ranged from 100 to 650 (jg/dl; all received immediate
chelation therapy. Follow-up chelation tests performed with 1 g EDTA i.m. (with procaine)
approximately a decade later resulted in 24-hour lead-chelate excretion of less than 600 pg in
45 of 52 adolescents. The absence of renal disease in this study led Chisolm et al. to sug-
gest that lead toxicity in the Australian children may have been of a different type, with a
more protracted course than that experienced by the American children. On the other hand,
chelation therapy of the American children may have removed lead stored in bone and thus pre-
vented the development of renal failure later in life. Most children in the United States who
suffer from overt lead toxicity do so early in childhood, between the ages of 1 and 4, the
source often being oral ingestion of flecks of wall paint and plaster containing lead.
12.5.3.2 "Moonshine" Lead Nephropathy. In the United States, chronic lead nephropathy in
adults was first noted among illicit whiskey consumers in the southeastern states. The pre-
revolutionary tradition of homemade whiskey ("moonshine") was modernized during the Prohibi-
tion era for large scale production. The copper condensers traditionally used in the illegal
stills were replaced by truck radiators with lead-soldered parts. Illegally produced whiskey
might contain up to 74 mg of lead per liter (Eskew et al., 1961). The enormous variability in
moonshine lead content has recently been reiterated in a study of 12 samples from Georgia, of
which five contained less than 10 pg/1 but one contained 5.3 mg/1 (Gerhard! et al., 1980).
Renal disease often accompanied by hypertension and gout was common among moonshiners
(Eskew et al., 1961; Morgan et al. , 1966; Ball and Sorenson, 1969). These patients usually
sought medical care because of symptomatic lead poisoning characterized by colic, neurological
disturbances, and anemia, although more subtle cases were sometimes detected by use of the
i.v. EDTA lead-mobilization test (Morgan, 1968; Morgan and Burch, 1972). While acute sympto-
matology, including azotemia, sometimes improved during chelation therapy, residual chronic
renal failure, gout, and hypertension frequently proved refractory, thus indicating underlying
chronic renal disease superimposed on acute renal failure due to lead (Morgan, 1975).
12.5.3.3 Occupational Lead Nephropathy. Although rarely recognized in the United States
(Brieger and Reiders, 1959; Anonymous, 1966; Greenfield and Gray, 1950; Johnstone, 1964;
Kazantzis, 1970; Lane, 1949; Malcolm, 1971; Mayers, 1947), occupational lead nephropathy,
often associated with gout and hypertension, was widely identified in Europe as a sequela to
overt lead intoxication in the industrial setting (Albahary et al., 1961, 1965; Cramer et al.,
1974; Danilovic, 1958; Galle and Morel-Maroger, 1965; Lejeune et al. , 1969; Lilis et al., 1967,
1968; Radosevic et al., 1961; Radulescu et al., 1957; Richet et al., 1964, 1966; Tara and
Francon, 1975; Vigdortchik, 1935). Some important recent studies are summarized here.
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Richet et al. (1964) reported renal findings in eight lead workers, all of whom had
repeated episodes of lead poisoning, including colic. Intravenous EDTA lead-mobilization
tests ranged from 587 to 5930 fjg lead-chelate excretion per 24 hours. Four of these men had
reduced glomerular filtration rates, one had hypertension with gout, one had hypertension
alone, and one had gout alone. Proteinuria exceeded 200 mg/day in only one patient. Five of
seven renal biopsies were abnormal showing minor glomerular sclerosis but severe interstitial
nephritis and vascular sclerosis by light microscopy. The one patient with proteinuria of 1.7
gin/day showed extensive glomerular hyalinization. Electron microscopy showed intranuclear and
cytoplasmic inclusions and ballooning of mitochondria in proximal tubule cells. The presence
of intranuclear inclusion bodies is helpful in establishing a relationship between renal
lesions and lead toxicity, but inclusion bodies are not always present in persons with chronic
lead nephropathy (Cramer et al., 1974; Wedeen et al., 1975, 1979).
Richet et al. (1966) subsequently recorded renal findings in 23 symptomatic lead workers
in whom blcod lead levels ranged from 30 to 87 |jg/dl. Six had diastolic pressures over 90
mm Hg, three had proteinuria exceeding 200 mg/day, and five had gout. In 5 of 21 renal biop-
sies, glomeruli showed minor hyalinization, but two cases showed major glomerular disease
(their creatinine clearances were 20 and 33 ml/min, respectively). Interstitial fibrosis and
arteriolar sclerosis were seen in all but two biopsies. Intranuclear inclusion bodies were
noted in 13 cases. Electron jnicroscopy showed loss of brush borders, iron-staining intra-
cellular vacuoles, and ballooning of mitochondria in proximal tubule epithelial cells.
Effective renal plasma flow (Cp^. plasma clearance of p-aminohippuric acid) by the
single injection disappearance technique was measured in 14 lead-poisoned Rumanian workers be-
fore and after chelation therapy by Li lis et al. (1967). Cpa^ increased from a pre-treatment
mean of 428 ml/min (significantly less than the control mean of 580 ml/min) to a mean of 485
ml/min after chelation therapy (p <0.02). However, no significant increase in GFR (endogenous
creatinine clearance) was found. Lilis et al. interpreted the change in effective renal
plasma flow as indicating reversal of the renal vasoconstriction that accompanied acute lead
toxicity. Although neither blood lead concentrations nor long-term follow-up studies of renal
function were provided, it seems likely that most of these patients suffered from acute,
rather than chronic, lead nephropathy.
In a subsequent set of 102 cases of occupational lead poisoning studied by Lilis et al.
(1968), seven cases of clinically verified chronic nephropathy were found. In this group, en-
dogenous creatinine clearance was less than 80 ml/min two weeks or more after the last episode
of lead colic. The mean blood lead level approximated 80 ng/dl (range 42 to 141 ng/dl.) All
patients excreted more than 10 mg lead chelate over 5 days during therapy consisting of 2 g
CaNa-^EDTA i.v. daily. Nephropathy was more common among those exposed to lead for more than
10 years than among those exposed for less than 10 years. Most of the Rumanian lead workers
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PRELIMINARY DRAFT
had experienced lead colic, and 13 of 17 had persistent hypertension that followed the appear-
ance of renal failure by several years. Proteinuria was absent except in two individuals who
excreted 250 and 500 mg/1. Hyperuricemia was not evident in the absence of azotemia. In both
studies by Lillis, reduced urea clearance preceded reduced creatinine clearance.
Cramer et al. (1974) examined renal biopsies from five lead workers exposed for 0.5 to 20
years in Sweden. Their blood lead levels ranged from 71 to 138 ng/dl , with GFR ranging from
65 to 128 ml/min, but C ^ exceeding 600 ml/min in all. Although plasma concentrations of
valine, tyrosine, and phenylalanine were reduced, excretion of these amino acids was not sig-
nificantly different from controls. A proximal tubular reabsorptive defect might, therefore,
have been present without increased amino acid excretion because of low circulating levels:
increased fractional excretion may have occurred without increased absolute amino acid ex-
cretion. Albuminuria and glycosuria were not present. Glomeruli were normal by electron
microscopy. Intranuclear inclusions in proximal tubules were found in two patients with nor-
mal GFRs, and peritubular fibrosis was present in the remaining three patients who had had the
longest occupational exposure (4 to 20 years).
Wedeen et al. (1975, 1979) reported on renal dysfunction in 140 occupationally exposed
men. These investigators used the EDTA lead-mobilization test (1 g CaEDTA with 1 ml of 2 per-
cent procaine given i.m. twice, 8 to 12 hr apart) to detect workers with excessive body lead
stores. In contrast to workers with concurrent lead exposure (Alessio et al., 1979), blood
lead measures have proven unsatisfactory for detection of past lead exposure (Baker et al.,
1979; Havelda et al., 1980; Vitale et al., 1975). Of the 140 workers tested, 113 excreted
1000 |jg or more of lead-chelate in 24 hr compared with a normal upper limit of 550 ^g/day
(Albahary et al., 1961; Emmerson, 1973; Wedeen et al., 1975). Glomerular filtration rates
measured by lliaI-iothalamate clearance in 57 men with increased mobilizable lead revealed
reduced renal function in 21 (GFR less than 90 ml/min per 1.73 m* body surface area). When
workers over age 55 or with gout, hypertension, or other possible causes of renal disease were
excluded, 15 remained who had previously unsuspected lead nephropathy. Their GFRs ranged
between 52 and 88 ml/min per 1.73 m*. Only three of the.men with occult renal failure had
ever experienced symptoms attributable to lead poisoning. Of the 15 lead nephropathy
patients, one had a blood lead level over 80 ng/dl, three repeatedly had blood levels under 40
pg/dl, and eleven had blood levels between 40 and 80 pg/dl at the time of the study. Thus,
blood lead levels were poorly correlated with degree of renal dysfunction. The failure of
blood lead level to predict the presence of lead nephropathy probably stems from the indepen-
dence of blood lead from cumulative bone lead stores (Gross, 1981; Saenger et al., 1982a,b).
Percutaneous renal biopsies from 12 of the lead workers with reduced GFRs revealed focal
interstitial nephritis in six. Non-specific changes were present in proximal tubules, includ-
ing loss of brush borders, deformed mitochondria, and increased lysosomal bodies. Intra-
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PRELIMINARY DRAFT
nuclear inclusion bodies were not found in the renal biopsies from these men who had experi-
enced long-term occupational exposure and who had had chelation tests shortly before biopsy.
In experimental animals, chelation results in the rapid disapperance of lead-induced intra-
nuclear inclusions (Goyer and Wilson, 1975). The presence of a variety of irrmiunoglobulin
deposits by fluorescent microscopy suggests (but does not prove) the possibility that some
stages of lead nephropathy in adults may be mediated by immune mechanisms.
Eight patients with pre-azotemic occupational lead nephropathy were treated with 1 g
CaEDTA (with procaine) i.m. three times weekly for 6 to 50 months. In four patients, GFR rose
by 20 percent or more by the time the EDTA test had fallen to less than 850 (jg Pb/day. The
rise in GFR was paralleled by increases in effective renal plasma flow (Cpah) during CaEDTA
treatment. These findings indicate that chronic lead nephropathy may be reversible by chela-
tion therapy, at least during the pre-azotemic phase of the disease (Wedeen et al., 1979).
However, much more information will have to be obtained on the value of long-term, low-dose
chelation therapy before this regimen can be widely recommended. There is, at present, no
evidence that interstitial nephritis itself is reversed by chelation therapy. It may well be
that only functional derangements are corrected and that the improvement in GFR is not accom-
panied by disappearance of tubulo-interstitial changes in kidney. Chronic volume depletion,
for example, might be caused by lead-induced depression of the renin-angiotension-aldosterone
system (McAllister et al., 1971) or by direct inhibition of (Na+, K+)ATPase-mediated sodium
transport (Nechay and Williams, 1977; Nechay and Saunders, 1978a,b,c; Raghavan et al., 1981;
Secchi et al. , 1973). On the other hand, volume depletion would be expected to produce pre-
renal azotemia, but this was not evident in these patients. The value of chelation therapy in
chronic lead nephropathy once azotemia is established is unknown.
The prevalence of azotemia among lead workers has recently been confirmed in health sur-
veys conducted at industrial sites (Baker et al. , 1979; Hammond et al. , 1980; Landrigan et
al. , 1982; Lilis et al., 1979, 1980). Interpretation of these data is, however, hampered by
the weak correlation generally found between blood lead levels and chronic lead nephropathy in
adults, the absence of matched prospective controls, and the lack of detailed diagnostic in-
formation on the workers found to have renal dysfunction. Moreover, blood serum urea nitrogen
(BUN) is a relatively poor indicator of renal function because it is sensitive to a variety of
physiological variables other than GFR, including protein anabolism, catabolism, and hydra-
tion. Several other measures of renal function are more reliable than the BUN, including in
order of increasing clinical reliability: serum creatinine, endogenous creatinine clearance,
and 11!bI-iothalamate or inulin clearance. It should be noted that none of these measures of
GFR can be considered reliable in the presence of any acute illness such as lead colic or
encephalopathy. Elevated BUN in field surveys may, therefore, sometimes represent transient
acute functional changes rather than chronic intrinsic renal disease.
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PRELIMINARY DRAFT
The variable susceptibility of the kidneys to the nephrotoxic effects of lead suggests
that environmental factors in addition to lead may participate in the expression of renal
damage. Industrial workers are often exposed to a variety of toxic materials, some of which,
such as cadmium (Buchet et al. , 1980), are themselves nephrotoxic. In contrast to cadmium,
lead does not increase urinary excretion of beta-2-microglobulins (Batuman et al., 1981;
Buchet et al., 1980) or lysozyme (Wedeen et al., 1979). Multiple interactions between en-
vironmental toxins may enhance susceptibility to lead nephrotoxicity. Similarly, nephro-
toxicity may be modulated by reductions in 1,25-dihydroxy vitamin D^, increased 6-beta-hydro-
xycortisol production (Saenger et al., 1981, 1982a,b), or immunologic alterations
(Gudbrandsson et al., 1981; Koller and Brauner, 1977; Kristensen, 1978; Kristensen and
Andersen, 1978). Reductions in dietary intake of calcium, copper, or iron similarly appear to
increase susceptibility to lead intoxication (Mahaffey and Michaelson, 1980).
The slowly progressive chronic lead nephropathy resulting from years of relatively low-
dose lead absorption observed in adults is strikingly different from the acute lead nephro-
pathy arising from the relatively brief but intense exposure arising from childhood pica.
Typical acid-fast intranuclear inclusions are, for example, far less common in the kidneys of
adults (Cramer et al. , 1974; Wedeen et al. , 1975). Although aminoaciduria has been found to
be greater in groups of lead workers than in controls (Clarkson and Kench, 1956; Goyer et al.,
1972), proximal tubular dysfunction is more difficult to demonstrate in adults with chronic
lead nephropathy than in acutely exposed children (Cramer et al. , 1974). It should be remem-
bered, however, that children with the Fanconi syndrome have far more severe acute lead intox-
ication than is usual for workmen on the job. In contrast to the reversible Fanconi syndrome
associated with childhood lead poisoning, proximal tubular reabsorptive defects in occupa-
tionally exposed adults are uncommon and subtle; clearance measurements are often required to
discern impaired tubular reabsorption in chronic lead nephropathy. Hyperuricemia is frequent
among lead workers (Albahary et al., 1965; Garrod, 1859; Hong et al., 1980; Landrigan et al.,
1982), presumably a consequence of specific lead inhibition of uric acid excretion, increased
uric acid production (Emmerson et al., 1971; Granick et al. , 1978; Ludwig, 1957), and pre-
renal azotemia from volume depletion. The hyperuricemia in adults contrasts with the reduced
serum uric acid levels usually associated with the Fanconi syndrome in childhood lead
poisoning. Although aminoaciduria and glycosuria are unusual in chronic lead nephropathy,
Hong et al. (1980) reported a disproportionate reduction in the maximum reabsorptive rate for
glucose compared with para-aminohippuric acid (PAH) in five of six lead workers they studied.
PAH transport has not been consistently altered beyond that expected in renal failure of any
etiology (Hong et al., 1980; Wedeen et al., 1975). Biagini et al. (1977) have, however,
reported a good negative linear correlation between the one-day EDTA lead-mobilization test
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PRELIMINARY DRAFT
and C ^ in 11 patients with histologic evidence of lead-induced ultrastructural abnormalities
in proximal tubules.
The differences between lead nephropathy in children and adults would not appear to be a
consequence of the route of exposure, since a case of pica in an adult (geophagic lead nephro-
pathy) studied by Wedeen et al. (1978) showed the characteristics of chronic rather than acute
lead nephropathy; intranuclear inclusions were absent and the GFR was reduced out of propor-
tion to the effective renal plasma flow.
12.5.3.4 Lead and Gouty Nephropathy. Renal disease in gout can often be attributed to well
defined pathogenetic mechanisms including urinary tract stones and acute hyperuricemic nephro-
pathy with intratubular uric acid deposition (Bluestone et al., 1977). In the absence of
intra- or extra-renal urinary tract obstruction, the frequency, mechanism, and even the exist-
ence of a renal disease peculiar to gout remains in question. While some investigators have
described "specific" uric acid-induced histopathologic changes in both glomeruli and tubules
(Gonick et al., 1965; Sommers and Churg, 1982), rigorously defined controls with comparable
degrees of renal failure were not studied simultaneously. Specific histologic changes in the
kidneys in gout have not been found by others (Pardo et al. , 1968; Bluestone et al. , 1977).
Glomerulonephritis, vaguely defined "pyelonephritis" (Heptinstal1, 1974), or intra- and extra-
renal obstruction may have sometimes been confused with the gouty kidney, particularly in
earlier studies (Fineberg and Altschul, 1956; Gibson et al. , 1980b; Mayne, 1955; McQueen,
1951; Schnitker and Richter, 1936; Talbott and Terplan, 1960; Williamson, 1920).
The histopathology of interstitial nephritis in gout appears to be non-specific and can-
not usually be differentiated from that of "pyelonephritis," nephrosclerosis, or lead nephro-
pathy on morphologic grounds alone (Barlow and Beilin, 1968; Bluestone et al., 1977; Greenbaum
et al., 1961; Heptinstall, 1974; Inglis et al. , 1978). Indeed, renal histologic changes in
non-gouty hypertensive patients have been reported to be identical to those found in gout
patients (Cannon et al. , 1966). In these hypertensive patients, serum uric acid levels paral-
leled the BUN.
Confusion between glomerular and interstitial nephritis can in part be explained by the
tendency of proteinuria to increase as renal failure progresses, regardless of the underlying
etiology (Batuman et al. , 1981). In the absence of overt lead intoxication it may, there-
fore, be difficult to recognize surreptitious lead absorption as a factor contributing to
renal failure in gouty patients. Further, medullary urate deposits, formerly believed to be
characteristic of gout (Brown and Mallory, 1950; Mayne, 1955; McQueen, 1951; Fineberg and
Altschul, 1956; Talbott and Terplan, 1960), have more recently been reported in end-stage
renal disease patients with no history of gout (Cannon et al., 1966; Inglis et al., 1978;
Linnane et al., 1981; Ostberg, 1968; Verger et al., 1967). Whether such crystalline deposits
contribute to, or are a consequence of, renal damage cannot be determined with confidence. In
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the presence of severe hyperuricemia (serum uric acid greater than 20 (jg/dl), intraluminal
crystal deposition may produce acute renal failure because of tubular obstruction (Emmerson,
1980) associated with grossly visible medullary streaks. In chronic renal failure without
gout or massive hyperuricemia, the functional significance of such medullary deposits is un-
clear (Linnane et al., 1981). Moreover, medullary microtophi, presumably developing around
intraluminal deposits, may extend into the renal interstitium, inducing foreign body reactions
with giant cell formation. Such amorphous deposits may require alcohol fixation and
deGalantha staining for identification (Verger et al. , 1967). Because of the acid milieu,
medullary deposits are usually uric acid, while microtophi developing in the neutral pH of the
renal cortex are usually monosodium urate. Both amorphous and needle-like crystals have been
demonstrated in kidneys of non-gout and hyperuricemic patients frequently in association with
arteriolonephrosclerosis (Inglis et al. , 1978; Cannon et al., 1966; Ostberg, 1968). Urate
deposits therefore, are not only not diagnostic, but may be the result, rather than the
cause, of interstitial nephritis. The problem of identifying unique characteristics of the
gouty kidney has been further confounded by the coexistence of pyelonephritis, diabetes
mellitis, hypertension, and the aging process itself.
Although the outlook for gout patients with renal disease was formerly considered grim
(Talbott, 1949; Talbott and Terplan, 1960), more recent long-term follow-up studies suggest a
benign course in the absence of renovascular or other supervening disease (Fessel, 1979; Yli
and Berger, 1982; Yu, 1982). Over the past four decades the reported incidence of renal
disease has varied from greater than 25 percent (Fineberg and Altschul , 1956; Henck et al. ,
1941; Talbott, 1949; Talbott and Terplan, 1960; Wyngaarden, 1958) to less than 2 percent, as
observed by Yii (1982) in 707 patients followed from 1970 to 1980. The low incidence of renal
disease in some hyperuricemic populations does not support the view that elevated serum uric
acid levels of the degree ordinarily encountered in gout patients is harmful to the kidneys
(Emmerson, 1980; Fessel, 1979; Ramsey, 1979; Reif.et al., 1981). Similarly, the failure of
the xanthine oxidase inhibitor, allopurinol, to reverse the course of renal failure in gout
patients despite marked reductions in the serum uric acid (Bowie et al., 1967; Levin and
Abrahams, 1966; Ogryzlo et al., 1966; Rosenfeld, 1974; Wilson et' al., 1967) suggests that
renal disease in gout may be due in part to factors other than uric acid. Some studies have,
however, suggested a possible slowing of the rate of progression of renal failure in gout by
allopurinol (Gibson et al., 1978, 1980a,b; Briney et al., 1975). While the contribution of
uric acid to the renal disease of gout remains controversial, the hypothesized deleterious
effect of hyperuricemia on the kidney has no bearing on other potential mechanisms of renal
damage in these patients.
Although hyperuricemia is universal in patients with renal failure, gout is rare in such
patients except when the renal failure is due to lead. Gout occurs in approximately half of
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the patients with lead nephropathy (Emmerson, 1963, 1973; Ball and Sorenson, 1969; Richet et
al. , 1965). Moreover, among gout patients in Scotland without known lead exposure, blood lead
levels were found to be higher than in non-gouty controls (Campbell et al. , 1978). The long
association of lead poisoning with gout raises the possibility that lead absorption insuffi-
cient to produce overt lead intoxication may, nevertheless, cause gout with slowly progressive
renal failure. Garrod (1859), Ball and Sorenson (1969), and Emmerson et al., (1971) demon-
strated that lead reduces uric acid excretion, thereby creating the internal milieu in which
gout can be expected. The mechanism of hyperuricemia in lead poisoning is, however, unclear.
Serum uric acid levels would be expected to rise in association with lead induced pre-renal
azotemia; increased proximal tubule reabsorption of uric acid could result from reduced glo-
merular filtration rate due to chronic volume depletion. Increased tubular reabsorption of
uric acid in lead nephropathy was suggested by the pyrazinamide suppression test (Emmerson,
1971), but interpretation of this procedure has been questioned (Holmes and Kelly, 1974).
Lead inhibition of tubular secretion of uric acid, therefore, remains another possible mecha-
nism of reduced uric acid excretion. In addition, some investigators have found increased
uric acid excretion in saturnine gout patients, thereby raising the possibility that lead in-
creases uric acid production in addition to reducing uric acid excretion (Emmerson et al. ,
1971; Ludwig, 1957; Granick et al., 1978).
Having specifically excluded patients with gout or hypertension from their study of occu-
pational lead nephropathy, Wedeen and collaborators examined the possible role of lead in the
etiology of the gouty kidney (Batuman et al., 1981). To test the hypothesis that surrepti-
tious lead absorption may sometimes contribute to renal failure in gout, 44 armed service
veterans with gout were examined by the EDTA lead-mobilization test. Individuals currently
exposed to lead (including lead workers) were specifically excluded. Collection of urine dur-
ing the EDTA lead-mobilization test was extended to three days because reduced GFR delays
excretion of the lead chelate (Emmerson, 1963). Note that the EDTA test does not appear to be
nephrotoxic even for patients with preexisting renal failure (Wedeen et al. , 1983). Half of
the gout patients had normal renal function and half had renal failure as indicated by serum
creatinines over 1.5 mg/dl"(mean = 3.0; standard error = 0.4 mg/dl), reflecting approximately
70 percent reduction in renal function. The groups were comparable in regard to age, duration
of gout, incidence of hypertension, and history of past lead exposure. The mean (and standard
error) blood lead concentration was 26 (± 3) |jg/dl in the patients with reduced renal function
and 24 (± 3) pg/dl in the gout patients with normal kidney function. The gout patients with
renal dysfunction, however, excreted significantly more lead chelate than did those without
renal dysfunction (806 ± 90 and 470 ± 52 pg Pb over 3 days, respectively).
Ten control patients with comparable renal failure excreted 424 ± 72 pg lead during the
3-day EDTA test (2 g i.m.). The non-gout control patients with renal failure had normal lead
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stores (Emmerson, 1973; Wedeen et al. , 1975), indicating that the excessive mobilizable lead
in the gout patients with renal failure was not a consequence of reduced renal function per
se. These studies suggest that excessive lead absorption may sometimes be responsible for the
gouty kidney in contemporary patients, as appeared to be the case in the past (Wedeen, 1981).
While the EDTA lead-mobilization test cannot prove the absence of other forms of renal
disease, when other known causes are excluded by appropriate diagnostic studies, a positive
EDTA test can indicate that lead may be a contributing cause of renal failure.
The source of lead exposure in these armed service veterans could not be determined with
confidence. A history of transient occupational exposure and occasional moonshine consumption
was common among all the veterans, but the medical histories did not correlate with either the
EDTA lead-mobilization test or the presence of renal failure. The relative contributions of
airborne lead, industrial sources, and illicit whiskey to the excessive body lead stores dem-
onstrated by the EDTA lead-mobilization test could not, therefore, be determined.
12.5.3.5 Lead and Hypertensive Nephrosclerosis. Hypertension is another putative complica-
tion of excessive lead absorption that has a long and controversial history. Hypertension has
often been associated with lead poisoning, frequently together with renal failure (Beevers et
al., 1980; Dingwall-Fordyce and Lane, 1963; Emmerson, 1963; Legge, 1901; Lorimer, 1886;
Morgan, 1976; Oliver, 1891; Richet et al., 1966; Vigdortchik, 1935). However, a number of in-
vestigators have failed to find such an association (Belknap, 1936; Brieger and Rieders, 1959;
Cramer and Dahlberg, 1966; Fouts and Page, 1942; Malcolm, 1971; Mayers, 1947; Ramirez-
Cervantes et al., 1978). Because of the absence of both uniform definitions of excessive lead
exposure and prospective control populations, the true contribution of lead to hypertension at
various levels and durations of exposure is unknown. Similarly, it is not clear whether
lead-induced hypertension is mediated by renal disease, vascular effects, or mechanisms invol-
ving vasoactive hormones or sodium transport. Definitive epidemiological studies remain to be
performed, but the etiologic role of lead in hypertension is likely to remain clouded as long
as the etiology of "essential" hypertension is unknown.
Among non-occupationally exposed individuals, hypertension and serum uric acid levels
have been found to correlate with blood lead levels (Beevers et al., 1976). Moreover, the
kidneys of patients with chronic lead nephropathy may show uric acid microtophi and the vas-
cular changes of "benign essential hypertension" even in the absence of gout and hypertension
(Cramer et al., 1974; Inglis et al., 1978; Morgan, 1975; Wedeen et al., 1975). In a long-term
follow-up study of 624 patients with gout, Yii and Berger (1982) reported that while hyper-
uricemia alone had no deleterious effect on renal function, decreased renal function was more
likely to occur in gout patients with hypertension and/or ischemic heart disease than in those
with uncomplicated gout.
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Like gout, hypertension was specifically excluded from the study of occupational lead
nephropathy by Wedeen et al. (1975, 1979) in order to isolate lead-induced renal disease.
Hypertension by itself is widely accepted as a cause of renal failure. Currently, however,
the renal sequelae of moderate hypertension appear to be less dramatic than in the past
(Kincaid-Smith, 1982). In order to determine if unsuspected excessive body lead stores might
contribute to the renal disease of hypertension, 3-day EDTA (2 g i.m.) lead mobilization tests
were performed in hypertensive armed service veterans with and without renal failure (Batuman
et al. , 1983). A significant increase in mobilizable lead was found in hypertensive subjects
with renal disease compared to those without renal disease. Control patients with renal fail-
ure again demonstrated normal mobilizable lead, thereby supporting the view that renal
failure is not responsible for the excess mobilizable lead in patients with hypertension and
renal failure. These findings suggest that patients who would otherwise be deemed to have
essential hypertension with nephrosclerosis can be shown to have underlying lead nephropathy
by the EDTA lead-mobilization test when other renal causes of hypertension are excluded.
The mechanism whereby lead induces hypertension remains unclear. Although renal disease,
particularly at the end-stage, is a recognized cause of hypertension, renal arteriolar histo-
logic changes may precede both hypertension and renal disease (Wedeen et al., 1975). Lead may
therefore induce hypertension by direct or indirect effects on the vascular system.
Studies of hypertension in moonshine consumers have indicated the presence of hyporenin-
emic hypoaldosteronism. A blunted plasma renin response to salt depletion has been described
in lead poisoned patients; this response can be restored to normal by chelation therapy
(McAllister et al., 1971; Gonzalez et al., 1978; Sandstead et al. , 1970a). The diminished
renin-aldosterone responsiveness found in moonshine drinkers could not, however, be demon-
strated in occupationally exposed men with acute lead intoxication (Campbell et al. , 1979).
Although the impairment of the renin-aldosterone system appears to be independent of renal
failure and hypertension, hyporeninemic hypoaldosteronism due to lead might contribute to the
hyperkalemia (Morgan, 1976) and the exaggerated natriuresis (Fleischer et al., 1980) of some
patients with "benign essential hypertension." Since urinary kallikrein excretion is reduced
in lead workers with hypertension, it has been suggested that the decrease in this vasodilator
may contribute to lead-induced hypertension (Boscolo et al., 1981). The specificity of kalli-
krein suppression in the renal and hypertensive manifestions of excessive lead absorption can-
not, however, be determined from available data, because lead workers without
hypertension and essential hypertensive patients without undue lead absorption also have
reduced urinary kallikrein excretion.
12.5.3.6 General Population Studies. Few studies have been performed to evaluate the possi-
ble harmful effects of lead on the kidneys in populations without suspected excessive lead
absorption from occupational or moonshine exposure.
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An epidemiological survey in Scotland of households with water lead concentrations in ex-
cess of WHO recommendations (100 mq/I) revealed a close correlation between water lead content
and blood lead and serum urea concentrations (Campbell et al., 1977). In 970 households lead
concentrations in drinking water ranged from <0.1 to >8.0 mg/1. After clinical and biochemi-
cal screening of 283 subjects from 136 of the households with water lead concentrations in
excess of 100 pg/1, a subsample of 57 persons with normal blood pressure and elevated serum
urea (40 pg/dl) was compared with a control group of 54 persons drawn from the study group
with normal blood pressure and normal serum urea. The frequency of renal dysfunction in indi-
viduals with elevated blood lead concentratons (>41 ng/dl) was significantly greater than that
of age- and sex-matcheci controls.
Since 62 general practitioners took part in the screening, the subsamples may have come
from many different areas; however, it was not indicated if matching was done for place of re-
sidence. The authors found a significantly larger number of high blood lead concentrations
among the persons with elevated serum urea and claimed that elevated water lead concentration
was associated with renal insufficiency as reflected by raised serum urea concentrations.
This is difficult to accept since serum urea is not the method of choice for evaluating renal
function. Despite reservations concerning use of the BUN for assessing renal function (de-
scribed above), these findings are consistent with the view that excessive lead absorption
from household water causes renal dysfunction. However, the authors used unusual statistical
methods and could not exclude the reverse causal relationship, i.e., tnat renal failure had
caused elevated blood lead levels in their study group. A carefully matched control popula-
tion of azotemic individuals from low. lead households would have been helpful for this
purpose. A more convincing finding in another subsample was a strong association between
hyperuricemia and blood lead level. This was also interpreted as a sign of renal insuffici-
ency, but it may have represented a direct effect of lead on uric acid production or renal
excretion.
These investigators have also found a statistically significant correlation between blood
lead concentration and hypertension. Tap-water lead did not, however, correlate with blood
lead among the hypertensive group, thus suggesting that other environmental sources of lead
may account for the presence of high blood lead concentrations among hypertensive persons in
Scotland (Beevers et al., 1976, 1980).
12.5.4 Mortality Data
Cooper and Gaffey (1975) analyzed mortality data available from 1267 death certificates
for 7032 lead workers who had been hired by 16 smelting or battery plants between 1900 and
1969. Standardized mortality ratios revealed an excess of observed over predicted deaths from
"other hypertensive disease" and "chronic nephritis and other renal sclerosis." The authors
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I
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PRELIMINARY DRAFT
concluded that "high levels of lead absorption such as occurred in many of the workers in this
series, can be associated with chronic renal disease.11 Although renal carcinomas have been
observed in lead poisoned rats, no increase in cancer rates was evident in this study of lead
workers (Cooper, 1976; see Section 12.7). Reports of renal carcinoma among lead workers are
distinctly unusual (Baker et al., 1980).
In a more limited study of 241 Australian smelter employees who were diagnosed as lead
poisoned between 1928 and 1959 by a government medical board, 140 deaths were identified
between 1930 and 1977 (McMichael and Johnson, 1982). Standard proportional mortality rates of
the lead-exposed workers compared with 695 non-lead-exposed employees revealed an overall
three-fold excess in deaths due to chronic nephritis and a two-fold excess in deaths due to
cerebral hemorrhage in the lead-exposed workers. Over the 47 years of this retrospective
study the number of deaths from chronic nephritis decreased from an initial level of 36 per-
cent to 4.6 percent among the lead-exposed workers, compared with a drop from 8.7 percent to
2.2 percent among controls. From 1965 to 1977 the age-standardized mortality rates from
chronic nephritis were the same for the lead-worker and control groups, although both rates
were higher than the proportional mortality rate for the general population of Australian
males. The latter observation indicated that the excessive deaths from chronic nephritis
among lead-poisoned workers at the smelter had declined in recent decades.
Despite substantial evidence that lead produces interstitial nephritis in adults, the im-
pact of chronic lead nephropathy on the general population is unknown. The diagnosis of lead
nephropathy is rarely made in dialysis patients in the United States. The absence of the
diagnosis does not, however, provide evidence for the absence of the disease. Advanced renal
failure is usually encountered only many years after excessive lead exposure. Moreover, acute
intoxication may never have occurred, and neither heme enzyme abnormalities nor elevated blood
lead levels may be present at the time renal failure becomes apparent. The causal relation-
ship between lead absorption and renal disease may therefore not be evident. It is likely
that such cases of lead nephropathy have previously been included among other diagnostic
categories such as pyelonephritis, interstitial nephritis, gouty nephropathy, and hypertensive
nephrosclerosis. Increasing proteinuria as lead nephropathy progresses may also cause con-
fusion with primary glomerulonephritis. It should also be noted that the End Stage Renal
Disease Program (Health Care Financing Administration, 1982) does not even include the diag-
nosis of lead nephropathy in its reporting statistics, regardless of whether the diagnosis is
recognized by the attending nephrologist.
12.5.5 Experimental Animal Studies of the Pathophysiology of Lead Nephropathy
12.5.5.1 Lead Uptake by the Kidney. Lead uptake by the kidney has been studied j_n vivo and
i_n vitro using renal slices. Vander et al. (1977) performed renal clearance studies in dogs
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two hours after a single i.v. dose of 0.1 or 0,5 mg lead acetate containing 1-3 mCi of 20aPb
or 1 hour after continous i\v. infusion of 0.1-0.15 mg/kg-hour. These investigators reported
that 43-44 percent of the plasma lead was ultrafiltrable, with kidney reabsorption values of
89*94 percent for the ultrafiltrable fraction. A subsequent stop-flow analysis investigation
by Victery et al. (1979a), using dogs given a single i.v. dose of lead acetate at 0.2 or 10.0
mg/kg, showed both proximal and distal tubular reabsorption sites for lead. Distal reabsorp-
tion was not linked to sodium chloride or calcium transport pathways. Proximal tubule reab-
sorption was demonstrated in all animals tested during citrate or bicarbonate infusion.
Another experiment (Victery et al., 1979b) examined the influence of acid-base status on renal
accumulation and excretion of lead in dogs given 0.5-50 pg/kg hr as an infusion or in rats
given access to drinking water containing 500 ppm Pb for 2-3 months. These showed that
alkalosis increased lead entry into tubule cells via both luminal and basolateral membranes,
with a resultant increase in both renal tissue accumulation and urinary excretion of lead.
Similarly, acutely induced alkalosis increased lead excretion in rats previously given access
to drinking water containing 500 ppm lead for 2-3 months. These authors also concluded that
the previously reported acute exposure experiments concerning the renal handling of lead were
at least qualitatively similar to results of the chronic exposure experiments and that rats
were an acceptable model for investigating the effects of alkalosis on the excretion of lead
following chronic exposure.
In vitro studies (Vander et al. , 1979) using slices of rabbit kidney incubated with -,iU3Pb
acetate at lead concentrations of 0.1 or 1.0 pM over 180-minute time intervals showed that a
steady-state uptake of i!u3Pb by slices (ratio of slice: medium uptake in the range of 10-42)
was reached after 90 minutes and that lead could enter the slices as a free ion. Tissue slice
uptake was reduced by a number of metabolic inhibitors, thus suggesting a possible active
transport mechanism. Tin (Sn IV) was found to markedly reduce ^^Pb uptake into the slices
but not to affect lead efflux or para-aminohippurate accumulation. This finding raises the
possibility that Pb and Sn (IV) compete for a common carrier.
Subsequent studies also using rabbit kidney slices (Vander and Johnson, 1981) showed that
co-transport of '^u;1Pb into the slices in the presence of organic anions such as cysteine,
citrate, glutathione, histidine, or serum ultrafiltrate was relatively small compared with up-
take due to ionic lead.
In summary, it is clear from the above i_n vivo and i_n vitro studies on several different
animal species that renal accumulation of lead is an efficient process that occurs in both
proximal and distal portions of the nephron and at both luminal and basolateral membranes.
The transmembrane movement of lead appears to be mediated by an uptake process that is subject
to inhibition by several metabolic inhibitors and the acid-base status of the organism.
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12.5.5.2 Intracellular Binding of Lead in the Kidney. The bioavailability of lead inside
renal tubule cells under low or ^^Pb tracer exposure conditions is mediated in part by bind-
ing to several high affinity cytosolic binding proteins (Oskarsson et al., 1982; Mistry et
al., 1982) and, at higher exposure conditions, by the formation of cytoplasmic and intra-
nuclear inclusion bodies (Goyer et al. , 1970a). These inclusion bodies have been shown by
both cell fractionation (Goyer et al., 1970a) and X-ray microanalysis (Fowler et al., 1980) to
contain the highest intracellular concentrations of lead. Saturation analysis of the renal
63,000 dalton (63K) cytosolic binding protein has shown that it possesses an approximate dis-
sociation constant (Kd) of 10 M (Mistry et al., 1982). These data quantify the high af-
finity nature of this protein for lead and explain the previously reported finding (Oskarsson
et al., 1982) th^t this protein constitutes a major intracellular lead-binding site in the
kidney cytosol. Biochemical studies on the protein components of isolated rat kidney intra-
nuclear inclusion bodies have shown that the main component has an approximate molecular
weight of 27K (Moore et al., 1973) or 32K (Shelton and Eg 1e, 1982) and that it is rich in the
dicarboxylic amino acids glutamate and aspartate (Moore et al., 1973). The isoelectric point
of the main nuclear inclusion body protein has been reported to be pi = 6.3 and appeared from
two-dimensional gel analysis to be unique to nuclei of lead-injected rats (Shelton and Egle,
1982). The importance of the inclusion bodies resides with the suggestion (Goyer et al. ,
1970a; Moore et al., 1973; Goyer and Rhyne, 1973) that, since these structures contain the
highest intracellular concentrations of lead in the kidney proximal tubule and hence account
for much of the total cellular lead burden, they sequester lead to some degree away from
sensitive renal organelles or metabolic (e.g., heme biosynthetic) pathways until their capac-
ity is exceeded. The same argument would apply to the high affinity cytosolic lead-binding
proteins at lead exposure levels below those that cause formation of inclusion bodies. It is
currently unclear whether lead-binding to these proteins is an initial step in the formation
of the cytoplasmic or nuclear inclusion bodies (Oskarsson et al. , 1982).
12.5.5.3 Pathological Features of Lead Nephropathy. The main morphological effects of lead
in the kidney are manifested in renal proximal tubule cells and interstitial spaces between
the tubules. A summary of morphological findings from some recent studies involving a number
of animal species is given in Table 12-10. In all but one of these studies, formation of
intranuclear inclusion bodies is a common pathognomic feature for all species examined. In
addition, proximal tubule cell cytomegaly and swollen mitochondria with increased numbers of
lysosomes were also observed in two of the chronic exposure studies (Fowler et al., 1980; Spit
et al., 1981). Another feature reported in three of these studies (Hass et al., 1964; White,
1977; Fowler et al., 1980) was the primary localization of morphological changes in the
straight (S3) segments of the proximal tubule, thereby indicating that not all cell types of
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TABLE 12-10. MORPHOLOGICAL FEATURES OF LEAD NEPHROPATHY IN VARIOUS SPECIES
Morphological findi
1
H
Species
Increased
Nuclear mitochondrial
Pb dose regimen inclusions swelling
Increased
lysosomes
Interstitial
fibrosis
Reference
Rabbit
0.5% Pb acetate in ~ —
diet for up to 55
weeks
--ND
+
Hass et al., 1964
Rat
1% Pb in d.w. for + +
9 weeks
NO
+
Goyer, 1971
Dog
50 pg Pb/kg for 5 weeks* +
— ND
ND
White, 1977
Monkey
0, 1.5, 6.0, 15 pg Pb/day** +
6 days/week for 9 months
---NO
ND
Colle et al., 1980
Rat
0, 0.5, 5, 25, 50, 250 + +
ppm Pb**
--
—
Fowler et al., 1980
Rabbit
0, 0.25, 0.50 pg Pb/kg***
3 days/wk for 14 weeks
+
--
Spit et al., 1981
Ringed
dove
100 pg Pb/ml** ~ +
—
Kendall et al. , 1981
* Dosed by oral gavage
** Drinking water ad libitum
***Subcutaneous injection
ND - Not determined
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PRELIMINARY DRAFT
the kidney are equally involved in the toxicity of lead to this organ. Interstitial fibrosis
has also been reported in rabbits (Hass et al., 1964) given diets containing 0.5 parcent lead
acetate for up to 55 weeks and in rats (Goyer, 1971) given drinking water containing lead ace-
tate for 9 weeks.
12.5.5.4 Functional Studies.
12.5.5.4.1 Renal blood flow and glomerular filtration rate. Studies by Aviv et al. (1980)
concerning the impact of lead on renal function as assessed by renal blood flow (RBF) and
glomerular filtration rate (GFR) have reported significant (p <0.01) reductions in both of
these parameters in rats at 3 and 16 weeks after termination of exposure to 1 percent lead
acetate in drinking water. Statistically significant (p <0.05) reduction of GFR has also been
recently described (Victery et al., 1981) in dogs 2.5-4 hours after a single i.v. dose of 3.0
mg Pb/kg. In contrast, studies by others (Johnson and Kleinman, 1979; Hammond et al., 1982)
were not able to demonstrate reduction in GFR or RBF using the rat as a model. The reasons
behind these reported differences are presently unclear but may be related to differences in
experimental design, age, or other variables.
12.5.5.4.2 Tubular function. Exposure to lead has also been reported to produce tubular dys-
function (Studnitz and Haeger-Aronsen, 1962; Goyer, 1971; Mouw et al., 1978; Suketa et al.,
1979; Victery et al., 1981, 1982a,b, 1983). An early study (Studnitz and Haeger-Aronsen,
1962) reported aminoaciduria in rabbits given a single dose of lead at 125 mg/kg, with urine
collected over a 15-hour period. Goyer et al. (1970b) described aminoaciduria in rats follow-
ing exposure to 1 percent lead acetate in the diet for 10 weeks. Wapnir et al, (1979) con-
firmed a mild hyperaminoaciduria in rats injected with lead at 20 mg/kg five times a week for
six weeks but found no changes in urinary excretion of phosphate or glucose.
Other studies (Mouw et al., 1978; Suketa et al. , 1979; Victery et al., 1981, 1982a,b,
1983) have focused attention on increased urinary excretion of electrolytes. Mouw et al.
(1978) reported increased urinary excretion of sodium, potassium, calcium, and water in dogs
given a single i.v. injection of lead at 0.6 or 3.0 mg/kg over a 4-hour period despite a con-
stant GFR, indicating decreased tubular reabsorption of these substances. Suketa et al.
(1979) treated rats with a single oral dose of lead at 0, 5, 50, or 200 mg/kg and killed the
animals at 0, 6, 12, or 24 hours after treatment. A dose-related increase in urinary sodium,
potassium, and water was observed over time. Victery et al. (1981, 1982a,b, 1983) studied
zinc excretion in dogs over a 4-hour period following an i.v. injection of lead at 0.3 or 3.0
mg/kg. These investigators reported maximal increases in zinc excretion of 140 ng/min at the
0.3 mg/kg dose and 300 ng/min at the 3.0 mg/kg dose at the end of the 4-hour period. In con-
trast, in studies by Mouw et al. (1978) no changes in urinary excretion of sodium or potassium
were noted. Urinary protein or magnesium excretion were also unchanged.
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1 The results of the above studies indicate that acute or chronic lead treatment is capable
of producing tubular dysfunction in several species of animals, as manifested by increased
urinary excretion of amino acid nitrogen and some ions such as Zn , Ca , Na , K , and water.
12.5.6 Experimental Studies of the Biochemical Aspects of Lead Nephrotoxicity
12.5.6.1 Membrane Marker Enzymes and Transport Functions. The biochemical effects of lead in
the kidney appear to be preferentially localized in the cell membranes and mitochondrial and
nuclear compartments following either acute or chronic lead exposure regimens.
Oral exposure of rats to lead acetate in the diet at concentrations of 1-2 percent for
10-40 weeks was found to produce no significant changes in renal slice water content or in
accumulation of paraminohippurate (PAH) or tetraethyl-ammonium (TEA). However, tissue glucose
synthesis at 40 weeks and pyruvate metabolism were both significantly (p <0.05) reduced
(Hirsch, 1973).
Wapnir et al. (1979) examined biochemical effects in kidneys of rats injected with lead
acetate (20 mg/kg) five days per week for six weeks. They observed a significant (p <0.05)
reduction in renal alkaline phosphatase activity and an increase in (Mg )-ATPase, but no sig-
nificant changes in (Na+,K+)-ATPase, glucose-6-phosphatase, fructose 1-6 diphosphatase, tryp-
tophan hydroxylase, or succinic dehydrogenase. These findings indicated that preferential
effects occurred only in marker enzymes localized in the brush border membrane and mitochon-
drial inner membrane. Suketa et al. (1979) reported marked (50-90 percent) decreases in renal
(Na ,K )-ATPase at 6-24 hours following a single oral administration of lead acetate at a dose
of 200 mg/kg. A later study (Suketa et al., 1981) using this regi-men showed marked decreases
in renal (Na , K )-ATPase but no significant changes in (Mg )-ATPase after 24 hours, thus in-
dicating inhibition of a cell membrane marker enzyme prior to changes in a mitochondrial
marker enzyme.
12.5.6.2 Mitochondrial Respiration/Enerqy-Linked Transformation. Effects of lead on renal
mitochondrial structure and function have been studied by a number of investigators (Goyer,
1968; Goyer and Krai 1, 1969a,b; Fowler et al., 1980, 1981a,b). Examination of proximal tubule
cells of rats exposed to drinking water containing 0.5-1.0 percent lead acetate for 10 weeks
(Goyer, 1968; Goyer and Krai 1, 1969a,b) or 250 ppm lead acetate for 9 months (Fowler et al.,
1980) has shown swollen proximal tubule cell mitochondria i_n situ. Common biochemical find-
ings in these studies were decreases in respiratory control ratios (RCR) and inhibition of
state-3 respiration, which was most marked for NAD-linked substrates such as pyruvate/malate.
Goyer and Krall (1969a,b) found these respiratory effects to be associated with a decreased
capacity of mitochondria to undergo energy-linked structural transformation.
.4
In vitro studies (Garcia-Cafiero et al. , 1981) using 10 M lead demonstrated decreased
renal mitochondrial membrane transport of pyruvate or glutamate associated with decreased res-
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piration for these two substrates. Other i_n vitro studies (Fowler et al., 1981a,b) have shown
decreased renal mitochondrial membrane energization as measured by the fluorescent probes
l-anilino,-8 napthalenesulfonic acid (ANS) or ethidium bromide following exposure to lead
_5 _3
acetate at concentrations of 10 to 10 M lead. High amplitude mitochondrial swelling was
also observed by light scattering.
The results of the above studies indicate that lead produces mitochondrial swelling both
i_n situ and i_n vitro, associated with a decrease in respiratory function that is most marked
for RCR and state-3 respiration values. The structural and respiratory changes appear to be
linked to lead-induced alteration of mitochondrial membrane energization.
12.5.6.3 Renal Heme Biosynthesis. There are several reports concerning the effects of lead
on renal heme biosynthesis following acute or chronic exposure. Silbergeld et al. (1982) in-
jected rats with lead at 10 pM/kg per day for three days and examined effects on several tis-
sues including kidney. These investigators found an increase in 6-aminolevulinic acid syn-
thetase (ALA-S) following acute injection and no change following chronic exposure (first in-
directly via their dams' drinking water containing lead at 10 mg/ml until 30 days of age and
then directly via this drinking water to 40-60 days of age). Renal tissue content of 6-amino-
levulinic acid (ALA) was increased in both acutely and chronically exposed rats. Renal
6-aminolevulinic acid dehydrase (ALA-D) was found to be inhibited in both acute and chronic
treatment groups. Gibson and Goldberg (1970) injected rabbits s.c. with lead acetate at doses
of 0, 10, 30, 150, or 200 mg Pb/week for up to 24 weeks. The mitochondrial enzyme ALA-S in
kidney was found to show no measurable differences from control levels. Renal ALA-D, which is
found in the cytosol fraction, showed no differences from control levels when glutathione was
present but was significantly reduced (p <0.05) to 50 percent of control values for the pooled
lead-treated groups when glutathione was absent. Mitochondrial heme synthetase (ferrochel-
atase) was not significantly decreased in lead-treated versus control rabbits, but this enzyme
.4
in the kidney was inhibited by 72 and 94 percent at lead-acetate concentrations of 10 and
10 M lead, respectively. Accumulation (12-15 fold) of both ALA and porphobilinogen (PBG)
was also observed in kidney tissue of lead-treated rabbits relative to controls. Zawirska and
Medras (1972) injected rats with lead acetate at a dose of 3 mg Pb/day for up to 60 days and
noted a similar renal tissue accumulation of uroporphyrin, coproporphyria, and protoporphyrin.
A study by Fowler et al. (1980) using rats exposed through 9 months of age to 50 or 250 ppm
lead acetate in drinking water showed significant inhibition of the mitochondrial enzymes
ALA-S and ferrochelatase but no change in the activity of the cytosolic enzyme ALA-D. Similar
findings have been reported for ALA-D following acute i.p. injection of lead acetate at doses
of 5-100 mg Pb/kg at 16 hours prior to sacrifice (Woods and Fowler, 1982). In the latter two
studies, reduced glutathione was present in the assay mixture.
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To summarize the above studies (also see Table 12-11), the pattern of alteration of renal
heme biosynthesis by lead is somewhat different from that usually observed with this agent in
other tissues (see Section 12.3). A general lack of lead-induced inhibition of renal ALA-D is
one frequently reported observation in this tissue except under conditions of high-level expo-
sure. Such a finding could result from the presence of the recently described high affinity
cytosolic lead-binding proteins (Oskarsson et al., 1982; Mistry et al., 1982) in the kidney
and/or the formation of lead-containing intranuclear inclusion bodies in this tissue (Goyer,
1971; Fowler et al., 1980), which would sequester most of the intracellular lead away from
other organelle compartments until the capacity of these mechanisms is exceeded. Based on the
observations of Gibson and Goldberg (1970), tissue or assay concentrations of glutathione may
also be of importance to the effects of lead on this enzyme. The observed lack of ALA-S in-
duction in kidney mitochondria reported in the above studies may have been caused by decreased
mitochondrial protein synthesis capacity or, as previously suggested (Fowler et al., 1980), by
overwhelming inhibition of this enzyme by lead, such that any inductive effects were not mea-
surable. Further research is needed to resolve these questions.
12.5.6.4 Lead Alteration of Renal Nucleic Acid/Protein Synthesis. A number of studies have
shown marked increases in renal nucleic acid or protein synthesis following acute or chronic
exposure to Pb acetate. One study (Choie and Richter, 1972a) conducted on rats given a single
intraperitoneal injection of lead acetate showed an increase in 3H-thymidine incorporation. A
subsequent study (Choie and Richter, 1972b) involved rats given intraperitoneal injections of
1-7 mg lead.once per week over a 6-month period. Autoradiography of 3H-thymidine incorpora-
tion into tubule cell nuclei showed a 15-fold increase in proliferative activity in the lead-
treated rats relative to controls. The proliferative response involved cells both with and
without intranuclear inclusions. Follow-up autoradiographic studies in rats given three
intraperitoneal injections of lead acetate (0.05 mg Pb/kg) 48 hours apart showed a 40-fold
increase in ^H-thymidine incorporation 20 hours after the first lead dose and 6 hours after
the second and third doses.
Choie and Richter (1974a) also studied mice given a single intracardiac injection of lead
(5 Pb/g) and demonstrated a 45-fold maximal increase in DNA synthesis in proximal tubule
cells as judged by aH-thymidine autoradiography 33 hours later. This increase in DNA synthe-
sis was preceded by a general increase in both RNA and protein synthesis (Choie and Richter,
1974b). The above findings were essentially confirmed with respect to lead-induced increases
in nucleic acid synthesis by Cihak and Seifertova (1976), who found a 13-fold increase in
3H-thymidine incorporation into kidney nuclei of mice 4 hours after an intracardiac injection
(5 pg Pb/g) of lead acetate. This finding was associated with a 34-fold increase in the
mitotic index but no change in the activities of thymidine kinase or thymide monophosphate
kinase. Stevenson et al. (1977) have also reported a 2-fold increase in ^H-thynridine or
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TABLE 12-11. EFFECTS OF LEAD EXPOSURE ON RENAL HEME BIOSYNTHESIS
Species
Pb dose regimen
ALA-S
ALA-D
FC*
Renal tissue
porphyrins
Reference
Rabbi t
10, 30, 150, 200
mg Pb/kg/wk (s.c.)
NC**
±4-
NC
t ALA, PBG
(12-15 x)
Gibson and
Goldberg, 1970
Rat
3 mg Pb/day
(s.c.)
NM***
NM
NM
t uro-,
copro-, proto-
porphyrins
Zawirska and
Medras, 1972
Rat
10, 100, 1000,
5000 ppm Pb i n
d.w. for 3 wks
NM
i
NM
t at 1000 and
5000 ppm
t ALA-urine
Buchet et al.,
1976
Rat
(dams)
10 ppm in d.w.
duri ng:
3 wks before mating
3 wks of pregnancy
3 wks after delivery
NM
NC
NM
NC
Hubermont
et al., 1976
(newborns)
NM
NC
NM
t
Rat
(dams)
100 ppm Pb
in d.w. for
3 wks
NM
NC
NM
NC
Roels et al.,
1977
i
(suckling)
NM
±+
NM
*
Rat
0.5, 5, 25, 50, 250
ppm Pb in d.w. for
9 months
*
NC
i
NM
Fowler et al. ,
1980
Rat
5, 25, 50, 100 mg
Pb/kg (i.p.) 16 hrs.
prior to sacrifice
NM
NC
NM
NM
Woods and
Fowler, 1982
Rat
10 pM Pb/kg/3 day
(i.p.)
10 mg Pb/ml in d.w.
for 10-30 days
t ,
NC
i
+
NM
NM
tALA
tALA
Silbergeld
et al., 1982
*FC - Ferro
chelatase "NC - Not changed
relative
to controls ***NM - Not
measured
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14C-orotic acid incorporation into kidney DNA or RNA of rats given a single intraperitoneal
injection of lead chloride three days earlier.
The above studies clearly demonstrate that acute or chronic administration of lead by
injection stimulates renal nucleic acid and protein synthesis in kidneys of rats and mice.
The relationship between this proliferative response and formation of intranuclear inclusion
bodies is currently unknown; nor is the basic mechanism underlying this response and the
formation of renal adenomas in rats and mice following chronic lead exposure understood.
12.5.6.5 Lead Effects on the Renin-Anqiotension System. A study by Mouw et al. (1978) used
dogs given a single intravenous injection of lead acetate at doses of 0.6 or 3.0 mg Pb/kg and
observed over a 4-hour period. Subjects showed a small but significant decrease in plasma
renin activity (PRA) at 1 hour, followed by a large and significant (p <0.05) increase from
2.5 to 4.0 hours. Follow-up work (Goldman et al. , 1981) using dogs given a single intravenous
injection of lead acetate at 3.0 mg Pb/kg showed changes in the renin-angiotensin system over
a 3-hour period. The data demonstrated an increase in PRA, but increased renin secretion oc-
curred in only three of nine animals. Hepatic extraction of renin was virtually eliminated in
all animals, thus providing an explanation for the increased blood levels of renin. Despite
the large observed increases in PRA, blood levels of angiotensin II (All) did not increase
after lead treatment. This suggests that lead inhibited the All converting enzyme.
Exposure of rats to drinking water containing 0.5 mg Pb/ml for three weeks to five months
(Fleischer et al., 1980) produced an elevation of PRA after six weeks of exposure in those
rats on a sodium-free diet. No change in plasmairenin substrate (PRS) was observed. At five
months, PRA was significantly higher in the lead-treated group on a 1-percent sodium chloride
diet, but the previous difference in renin levels between animals on an extremely low-sodium
(1 meq) vs. 1-percent sodium diet had disappeared. The lead-treated animals had a reduced
ability to decrease sodium excretion following removal of sodium from the diet.
Victery et al. (1982a) exposed rats to lead utero and to drinking water solution con-
taining 0, 100, or 500 ppm lead as lead acetate for six months. Male rats on the 100 ppm lead
dose became significantly hypertensive at 3.5 months and remained in that state until termi-
nation of the experiment at six months. All female rats remained normotensive as did males at
the 500-ppm dose level. PRA was found to be significantly reduced in the 100-ppm treatment
males and normal in the 500-ppm treatment groups of both males and females. Dose-dependent
decreases in AII/PRA ratios and renal renin content were also observed. Pulmonary All con-
verting enzyme was not significantly altered. It was concluded that, since the observed
hypertension in the 100-ppm group of males was actually associated with reduction of PRA and
All, the renin-angiotensin system was probably not directly involved in this effect.
Webb et al. (1981) examined the vascular responsiveness of helical strips of tail
arteries in rats exposed to drinking water containing 100 ppm lead for seven months. These
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investigators found that the mild hypertension associated with this regimen was associated
with increased vascular responsiveness to a-adrenergic agonists.
Male rats exposed to lead i_n utero and prior to weaning indirectly by their dams' drink-
ing water containing 0, 5, or 25 ppm lead as lead acetate, followed by direct exposure at the
same levels for five months (Victery et al., 1982b), showed no change in systolic blood pres-
sure. Rats exposed to the 25 ppm dose showed a significant (p <0.05) decrease in basal PRA.
Stimulation of renin release by administration of polyethylene glycol showed a significant
increase in PRA but low All values. These yielded a significant (p <0.001) decrease in the
AII/PRA ratio. Basal renal renin concentrations were found to be significantly reduced in
both the 5 ppm (p <0.05) and 25 ppm (p <0.01) dose groups relative to controls.
Victery et al. (1983) exposed rats in utero to lead by maternal administration of 0, 5,
25, 100, or 500 ppm lead as lead acetate. The animals were continued on their respective dose
levels through one month of age. All exposure groups had PRA values significantly (p <0.05)
elevated relative to controls. Renal renin concentration was found to be similar to controls
in the 5 and 25 ppm groups but significantly increased (p <0.05) in the 100 and 500 ppm
groups. The plasma All/PRA ratio was similar to controls in the 100 ppm group but was signi-
ficantly reduced (p <0.05) in the 500 ppm group.
It appears from the above studies that lead exposure at even low dose levels is capable
of producing marked changes in the renin-angiotension system and that the direction and mag-
nitude of these changes is mediated by a number of factors, including dose level, age, and sex
of the species tested, as well as dietary sodium content. Lead also appears capable of
directly altering vascular responsiveness to a-adrenergic agents. The mild hypertension ob-
served with chronic low level lead exposure appears to stem in part from this effect and not
from changes in the renin-angiotensin system. (See also Section 12.9.1 for a discussion of
other work on the hypertensive effects of lead.)
12.5.6.6 Lead Effects on Uric Acid Metabolism. A report by Mahaffey et al. (1981) on rats
exposed concurrently to lead, cadmium, and arsenic alone or in combination found significantly
(p <0.05) increased serum concentrations of uric acid in the lead-only group. While the bio-
chemical mechanism of this effect is not clear, these data support certain observations in
humans concerning hyperuricemia as a result of lead exposure (see Section 12.5.3) and, also,
confirm an earlier report by Goyer (1971) showing increased serum uric acid concentration in
rats exposed to 1 percent lead acetate in drinking water for 84 weeks.
12.5.6.7 Lead Effects on Kidney Vitamin D Metabolism. Smith et al. (1981) fed rats vitamin
D-deficient diets containing either low or normal calcium or phosphate for two weeks. The
animals were subsequently given the same diets supplemented with 0.82 percent lead as lead
acetate. Ingestion of lead at this dose level significantly reduced plasma levels of 1,25
dihydrocholecalciferol in cholecalciferol-treated rats and in rats fed either a low phospho-
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rous or low calcium diet while it had no effect in rats fed either a high calcium or normal
phosphorous diet. These data suggest decreased production of 1,25-dihydrocholecalciferol in
the kidney in response to lead exposure in concert with dietary deficiencies.
12.5.7 General Summary: Comparison of Lead Effects in Kidneys of Humans and Animal Models
It seems clear from the preceding review that, in general, results of experimental animal
studies have confirmed findings reported for human kidney function in individuals exposed to
lead for prolonged time periods and that these studies have helped illuminate the mechanisms
underlying such effects. Similar morphological changes are found in kidneys of humans and
animals following chronic lead exposure, including nuclear inclusion bodies, cytomegaly,
swollen mitochondria, interstitial fibrosis, and increased numbers of iron-containing lyso-
somes in proximal tubule cells. Physiological renal changes observed in humans have also been
confirmed in animal model systems in regard to increased excretion of amino acids and elevated
serum urea nitrogen and uric acid concentrations. The inhibitory effects of lead exposure on
renal blood flow and glomerular filtration rate are currently less clear in experimental model
systems; further research is needed to clarify the effects of lead on these functional para-
meters in animals. Similarly, while lead-induced perturbation of the renin-angiotensin system
has been demonstrated in experimental animal models, further research is needed to clarify the
exact relationships among lead exposure (particularly chronic low-level exposure), alteration
of the renin-angiotensin system, and hypertension in both humans and animals.
On the biochemical level, it appears that lead exposure produces changes at a number of
sites. Inhibition of membrane marker enzymes, decreased mitochondrial respiratory function/
cellular energy production, inhibition of renal heme biosynthesis, and altered nucleic acid
synthesis are the most marked changes thus far reported. The extent to which these mito-
chondrial alterations occur is probably mediated in part by the intracellular bioavailability
of lead, which is determined by its binding to high affinity kidney cytosolic binding proteins
and deposition within intranuclear inclusion bodies.
Recent studies in humans have indicated that the EDTA lead-mobilization test is the most
reliable technique for detecting persons at risk for chronic nephropathy. Blood lead measure-
ments are a less satisfactory indicator because they may not accurately reflect cumulative
absorption some time after exposure to lead has terminated.
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12.6 EFFECTS OF LEAD ON REPRODUCTION AND DEVELOPMENT
Data from human and animal studies indicate that lead may exert gametotoxic, embryotoxic,
and (according to animal studies) teratogenic effects that could influence the survival and
development of the fetus and newborn. It appears that prenatal viability and development may
also be affected by lead indirectly, via effects on various health parameters of the expectant
mother. The vulnerability of the conceptus to such effects of lead has contributed to concern
that the unborn may constitute a group at risk for lead health effects. Also, certain infor-
mation regarding lead effects on male reproductive functions has led to concern regarding the
impact of lead on men.
12.6.1 Human Studies
12,6.1.1 Historical Evidence. Findings suggesting that lead exerts adverse effects on human
reproductive functions have existed in the literature since before the turn of the century.
For example, Paul (1860) observed that severely lead-poisoned pregnant women were likely to
abort, while those less severely intoxicated were more likely to deliver stillborn infants.
Legge (1901), in summarizing the reports of 11 English factory inspectors, found that of 212
pregnancies in 77 female lead workers, only 61 viable children were produced. Fifteen workers
never became pregnant; 21 stillbirths and 90 miscarriages occurred. Of 101 children born, 40
died in the first year. Legge also noted that when lead was fed to pregnant animals, they
typically aborted. He concluded that maternal exposure to lead resulted in a direct action of
the element on the fetus.
Four years later, Hall and Cantab (1905) discussed the increasing use of lead in nostrums
sold as abortifacients in Britain. Nine previous reports of the use of diachylon ("lead plas-
ter") in attempts to cause miscarriage were cited and 30 further cases of known or apparent
use of lead in attempts to terminate real or suspected pregnancy listed. Of 22 cases de-
scribed in detail, 12 resulted in miscarriage and all 12 exhibited marked signs of plumbism,
including a blue gum line (in eight cases the women were known to have attempted to induce
abortion). Hall's report was soon followed by those of Cadman (1905) and Eales (1905), who
described three more women who miscarried following consumption of lead-containing pills.
Oliver (1911) then published statistics on the effect of lead on pregnancy in Britain
(Table 12-12). These figures showed that the miscarriage rate was elevated among women em-
ployed in industries in which they were exposed to lead. Lead compounds were said by Taussig
(1936) to be known for their embryotoxic properties and their use to induce abortion.
In a more recent study by Lane (1949), women exposed to lead levels of 750 pg/m3 were ex-
amined for effects on reproduction. Longitudinal data on 15 pregnancies indicated an increase
in the number of stillbirths and abortions. No data were given on urinary lead in women, but
men in this sample had urinary levels of 75 to 100 pg/liter.
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TABLE 12-12. STATISTICS ON THE EFFECT OF LEAD ON PREGNANCY
Number of
Number of
abortions and
neonatal deaths
stillbirths per
(first year) per
Sample
1000 females
1000 females
Housewives
43.2
150
Female workers (mill work)
47.6
214
Females exposed to lead premaritally
86.0
157
Females exposed to lead after marriage
133.5
271
Source: Oliver (1911).
The above studies clearly demonstrate an adverse effect of lead at high levels on human
reproductive functions, and include evidence of increased incidence of miscarriages and still-
births when women are exposed to lead during pregnancy. The mechanisms underlying these ef-
fects are unknown at this time. Many factors could contribute to such results, ranging from
lead effects on maternal nutrition or hormonal state before or during pregnancy to more direct
gametotoxic, embryotoxic, fetotoxic, or teratogenic effects that could affect parental fertil-
ity or offspring viability during gestation. Pregnancy is a stress that may place a woman at
higher risk for toxic lead exposure. Both iron deficiency and calcium deficiency increase sus-
ceptibility to lead, and women have an increased risk of both deficiencies during pregnancy
and postpartum (Rom, 1976).
Such studies as those of Legge, Hall, and Oliver suffer from methodological inadequacies.
They must be mentioned, however, because they provide evidence that effects of lead on repro-
duction occurred at times when women were exposed to high levels of lead. Nevertheless, evi-
dence for adverse reproductive outcomes in women with obvious lead poisoning is of little help
in defining the effects of lead at significantly lower exposure levels. Efforts have been
made to define more precisely the points at which lead may affect reproductive functions in
both the human female and male, as well as in animals, as reviewed below.
12.6.1.2 Effects of Lead Exposure on Reproduction.
12.6.1.2.1 Effects associated with exposure of women to lead. Since the time of the above
reports, women have been largely, though not entirely (Khera et al., 1980), excluded from oc-
cupational exposure to lead; and lead is no longer used to induce abortion. Thus, little new
information is available on reproductive effects of chronic exposure of women to lead. Vari-
ous reports (Pearl and Boxt, 1980; Qazi et al., 1980; Timpo et al., 1979; Singh et al., 1978;
Angle and Mclntire, 1964) suggest that relatively high prenatal lead exposures do not invari-
ably result in abortion or in major problems readily detectable in the first few years of life
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These findings are based on only a few case histories, however, and are obviously not an ade-
quate sample. The data are confounded by numerous variables, and longer follow-ups are
needed.
In a sample population exposed to lead and to other toxic agents (including arsenic and
sulfur dioxide) from the Ronnskar smelter, Nordstrom et al. (1978b) found an increased fre-
quency of spontaneous abortions among women living closest to the smelter. In addition to the
exposure to multiple environmental toxins, however, the study was confounded by failure to
match exposed and control populations for socioeconomic status. A further study by the same
authors (Nordstrom et al. , 1979a) determined that female smelter workers at the Ronnskar
smelter had an increased frequency of spontaneous miscarriage when the mother was employed by
the smelter during pregnancy or had been so employed prior to pregnancy and still lived near
the smelter. Also, women who worked in more highly polluted areas of the smelter were more
likely to have aborted than were other employees. This report, however, suffers from the same
deficiencies as the earlier study.
In regard to potential lead effects on ovarian function in human females, Panova (1972)
reported a study of 140 women working in a printing plant for less than one year (1 to 12
months) where ambient air levels were <7 |jg Pb/m3. Using a classification of various age
groups (20-25, 26-35, and 36-40 yr) and type of ovarian cycle (normal, anovular, and disturbed
lutein phase), Panova claimed that statistically significant differences existed between the
lead-exposed and control groups in the age range 20 to 25 years. Panova1s report, however,
does not show the age distribution, the level of significance, or data on the specificity of
her method for classification. Zielhuis and Wibowo (1976), in a critical review of the above
study, concluded that the study design and presentation of data were such that it is difficult
to evaluate the author's conclusions. It should also be noted that no consideration was given
to the dust levels of lead, an important factor in print shops.
Unfortunately, little else besides the above study appears to exist in regard to assess-
ing the effects of lead on human ovarian function or other factors affecting female fertility.
Studies offering firm data on maternal variables, e.g., hormonal state, that are known to af-
fect the ability of the pregnant woman to carry the fetus full term are also lacking.
12.6.1.2.2 Effects associated with exposure of men to lead. Lead-induced effects on male re-
productive functions have been reported in several instances. Among the earliest of these was
the review of Stofen (1974), who described data from the'work of Neskov in the USSR involving
66 workers exposed chiefly to lead-containing gasoline (organic lead). In 58 men there was a
decrease or disappearance of erection, in 41 there was early ejaculation, and in 44 there were
a diminished number of spermatocytes. These results were confounded, however, by the presence
of the other constituents of gasoline.
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Lancranjan et al. (1975) reported lead-related interference with male reproductive func-
tions. A group of 150 workmen who had long-term exposure to lead in varying degrees was
studied. Clinical and toxicological criteria were used to categorize the men into four
groups: lead-poisoned workmen (mean blood lead level = 74.5 pg/dl) and those showing moderate
(52.8 |jg/dl), slight (41 pg/dl), or "physiologic" (23 (jg/dl) exposure to lead. Moderately
increased lead absorption (52.8 pg/dl) was said to result in gonadal impairment. The effects
on the testes were believed to be direct, in that tests for impaired hypothalamopituitary
influence were negative. Also, semen analysis revealed asthenospermia and hypospermia in all
groups except those with "physiologic" absorption levels, and increased teratospermia was seen
in the two highest lead exposure groups.
An apparently exposure-related increase in erectile dysfunction was also found by
Lancranjan et al. (1975). Problems with ejaculation and libido were said to be more common in
the lead exposed groups, but their incidences did not seem to be dose-dependent. Control in-
cidences of these difficulties were invariably lower than those of the lead exposed groups,
however, so the lack of a clear cut dose-response relationship may have merely been due to in-
appropriate assignment of individuals to the high, moderate, and low exposure groups.
The Lancranjan et al. (1975) study has been criticized by Zielhuis and Wibowo (1976), who
stated that the distributions of blood lead levels appeared to be skewed and that exposure
groups overlapped in terms of lead intake. Thus, the means for each putative exposure group
may not have been representative of the individuals within a group. It is difficult to dis-
cern, however, if the men were improperly assigned to exposure level groups, as blood lead
levels may have varied considerably on a short term basis. Zielhuis and Wibowo also stated
that the measured urinary ALA levels were unrealistically high for individuals with the stated
blood lead levels. This suggests that if the ALA values were correct, the blood lead levels
may have been underestimated. Other deficiencies include failure to use matched controls and
exclusion of different proportions of individuals per exposure group for the semen analyses.
Plechaty et al. (1977) measured lead concentrations in the semen of 21 healthy men.
Semen lead levels were generally less than blood lead levels, and no correlation was found be-
tween lead content of the semen and sperm counts or blood lead levels in this small sample.
Hypothalamic-pituitary-testicular relationships were investigated by Braunstein et al.
(1978) in men occupationally exposed at a lead smelter. Six subjects had 2-11 years of expo-
sure to lead and exhibited marked symptoms of lead toxicity. All had received one or more
courses of EDTA chelation therapy. This group was referred to as "lead-poisoned" (LP). Four
men from the same smelter had no signs of lead toxicity, but had been exposed for 1-23 years
and were designated "lead-exposed" (LE). The control (C) group consisted of nine volunteers.
Mean (± standard error) blood lead levels for the LP, LE, and C groups were 38.7 (± 3),
29.0 (± 5), and 16.1 (± 1.7) (jg/d1, respectively, at the time of the study. Previously, how-
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ever, the LP and LE groups had exhibited values as high as 88.2 (± 4) and 80 (± 0) ug/dl ,
respectively. All three groups were chelated and 24-hour urinary lead excretion values were
999 (+ 141), 332 (+ 17), and 225 (± 31) pg for the LP, LE, and C groups, respectively. Fre-
quency of intercourse was significantly less in both lead-exposed groups than in controls.
Sperm concentrations in semen of the LP and LE men ranged from normal to severely oligosper-
mic, and one from the LP group was unable to ejaculate. Testicular biopsies were performed on
"the two most severely lead-poisoned men," one with aspermia and one with testicular pain.
Both men showed increased peritubular fibrosis, decreased spermatogenesis, and Sertoli cell
vacuolization. The two lead groups exhibited reduced basal serum testosterone levels, but
displayed a normal increase in serum testosterone following stimulation with human chorionic
gonadotroph!-n. A similar rise in serum follicle-stimulating hormone was seen following treat-
ment with clomiphene citrate or gonadotroph!-n releasing hormone, although the LP men exhibited
a lower than expected increase in luteinizing hormone (LH). The LE men also appeared to have
a decreased LH response, but the difference was not significant.
The results of the Braunstein et al. (1978) study suggest that lead exposure at high
levels may result in a defect in regulation of LH secretion at the hypothalamic-pituitary
level, resulting in abnormal dynamics of LH secretion. They also indicate a likely direct
effect on the testes, resulting in oligospermia and peritubular fibrosis. Nevertheless, the
possibility remains that such effects may have been precipitated by the EDTA chelation ther-
apy, and the numbers of men studied were quite small.
More recently, Wildt et al. (1983) compared two groups of men exposed to lead in a
Swedish battery factory. The 29 high-lead group men had had blood lead levels >50 pg/dl at
least once prior to the study, while the 30 "controls" seldom exceeded 30 pg/dl. There were
two test periods eight months apart. For the first test, 15 men were in the high lead and 24
in the control groups, respectively, and 17 were in each group for the second test. Fourteen
and 15 of these men from the high lead and control groups, respectively, took part in both
tests. Blood lead values were obtained periodically over a six-month period. For the two
high lead groups, blood lead values were 46.1 and 44.6 pg/dl, respectively (range 25-75);
corresponding values for the controls were 31.1 and 21.5 pg/dl (range 8-39). The high lead
men tended to exhibit decreased function of the prostate and/or seminal vesicles, as measured
by seminal plasma constituents (fructose, acid phosphatase, Mg, and Zn); however, a signifi-
cant difference was seen only in the case of zinc. More men in the high lead than in the
control group had low semen volume values, but the numbers of individuals did not allow a
reliable statistical analysis. The heads of sperm of high lead individuals were more likely
to swell when exposed to a detergent solution, viz. sodium dodecyl sulfate (SDS), a test of
functional maturity, but the values were still in a normal range. Conversely, the leakage of
lactate dehydrogenase isoenzyme X (LDH-X) was greater in control semen samples.
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The values for live and for motile sperm were lower in the control group. The data were
skewed, however, by the presence of several of the same men with low values in the control
groups for both sampling times. Another confounding factor was the fact that the high lead
and control groups differed in a significant way: ten of the control men had present or past
urogenital tract infections versus none in the high lead group, possibly explaining the inci-
dence of control samples with lowered sperm motility and viability. The observed decrease in
SDS resistance in sperm of high lead group men may have been related to their apparent abnor-
mal prostatic function, or to an effect of lead on sperm maturation. In evaluating the above
results, it must also be noted that even the "controls" had elevated blood lead levels.
12.6.1.3 Placental Transfer of Lead. The transfer of lead across the human placenta and its
potential threat to the conceptus have been recognized for more than a century (Paul, 1860).
Documentation of placental transfer of lead to the fetus and data on resulting fetal blood
lead levels help to build the case for a potential, but as yet not clearly defined, threat of
subtle embryotoxicity or other deleterious health effects.
The placental transfer of lead has been established, in part, by various studies that
have disclosed measurable quantities of lead in human fetuses or newborns, as well as off-
spring of experimental animals. The relevant data on prenatal lead absorption have been re-
viewed in Chapter 10, Section 2.4 of this document, and thus work dealing only with lead
levels will not be discussed further here.
12.6.1.4 Effects of Lead on the Developing Human.
12.6.1.4.1 Effects of lead exposure on fetal metabolism. Prenatal exposure of the conceptus
to lead, even in the absence of overt teratogenicity, may be associated with other health
effects. This is suggested by studies relating fetal and cord-blood levels to changes in
fetal heme synthesis. Haas et al. (1972) examined 294 mother-infant pairs for blood lead and
urinary ALA levels. The maternal blood lead mean was 16.89 pg/dl; and the fetal blood lead
mean was 14.98 pg/dl, with a correlation coefficient of 0.54 (p <0.001). In the infants,
blood lead levels and urinary ALA were positively correlated (r = 0.19, p <0.01), although the
data were based on spot urines (which tends to limit their value). The full biological signi-
ficance of the elevated ALA levels is not clear, but the positive correlation between lead in
blood and urinary ALA for the group as a whole indicates that increased susceptibility of heme
synthesis occurs at relatively low blood lead levels in the fetus or newborn infant.
Subsequently, Kuhnert et al. (1977) measured ALA-D activity and levels of erythrocyte
lead in pregnant urban women and their newborn offspring. Cord erythrocyte lead levels ranged
from 16 to 67 pg/100 ml of cells, with a mean of 32.9. Lead levels were correlated with in-
hibition of ALA-D activity (r = -0.58, p <0.01), suggesting that typical urban lead exposures
could affect fetal enzyme activity. Note, however, that ALA-D activity is related to blood
cell age, being highest in the younger cells. Thus, results obtained with cord blood, with
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its high percentage of immature cells, are not directly comparable to those obtained with
adult blood. In a later study, Lauwerys et al. (1978) found no lead-related increase in
erythrocyte porphyrin levels in 500 mothers or their offspring. They did, however, report
negative correlations between ALA-D activity and blood lead levels in both mothers and their
newborns. Maternal blood lead levels averaged 10.2 (jg/dl (range 3.1-31 ng/dl). Corresponding
values for the newborns were 8.4 jjg/dl and 2.7-27.3. Such results indicate that ALA-D activ-
ity may be a more sensitive indicator of fetal lead toxicity than erythrocyte porphyrin or
urinary ALA levels.
12.6.1.4.2 Other toxic effects of intrauterine lead exposure. Fahim et al. (1976), in a
study on maternal and cord-blood lead levels, determined blood lead values in women having
preterm delivery and premature membrane rupture. Such women residing in a so-called "lead
belt" (mining and smelting area) had significantly higher blood lead levels than women from
the same area delivering at full term. Fahim et al. (1976) also noted that among 249 pregnant
women in a control group outside the lead belt area, the percentages of women having preterm
deliveries and premature rupture were 3 and 0.4, respectively, whereas corresponding values
for the lead area (n = 253) were 13.04 and 16.99, respectively. A confusing aspect of this
study, however, is the similarity of blood lead levels in women from the nonlead and lead belt
areas. In fact, no evidence was presentee that women in the lead belt group had actually
received a greater degree of lead exposure during pregnancy than did control individuals.
Also, questions exist regarding analytical aspects of this study. Specifically, other workers
(e.g., see summary table in Clark, 1977) have typically found blood lead levels in mothers and
their newborn offspring to be much more similar than those of Fahim et al. (1976).
In another study, Clark (1977) detected no effects of prenatal lead exposure in newborns
with regard to birth weight, hemoglobin, or hematocrit. He compared children born of 122
mothers living near a Zambian lead mine with 31 controls from another area. Maternal and
infant blood lead levels for the mine area were 41.2 (± 14.4) and 37.9 (± 15.3) fjg/dl, respec-
tively. Corresponding values for control mothers and offspring were 14.7 (± 7.5) and 11.8 (±
5.6) ufl/dl.
There is also some evidence that lead levels in bone samples from stillborn children are
higher than would be expected (Khera et al., 1980; Bryce-Smith et al., 1977), but the data are
i nconclusive.
Nordstrom et al. (1979b) examined birth weight records for offspring of female employees
of the Ronnsk3r smelter and found decreased birth weights related to: (1) employment of the
mothers at the smelter during pregnancy, (2) distance that the mothers lived from the smelter,
and (3) proximity of the mother's job to the actual smelting process. Similar results were
also seen for children born to mothers merely living near the smelter (Nordstrom et al.,
1978a). Nordstrom et al. (1979b) also investigated birth defects in offspring of the female
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smelter workers and in populations living at various distances from the Ronnskar smelter.
They concluded that the frequencies of both single and multiple malformations were increased
when the mother worked at the smelter during pregnancy.
The number of smelter workers with malformed offspring was relatively small (39/1291).
The incidence of children with birth defects whose mothers worked while pregnant was 5.8 per-
cent (17 of 291). Five of the six offspring with multiple malformations were in this group,
suggesting that the observed effect may have been a real one. Nevertheless, the crucial
factor in evaluating all of the Ronnskar studies is the exposure of workers and the nearby
population to a number of toxic substances including not only lead, but arsenic, mercury, cad-
mium, and sulfur dioxide as well.
Alexander and Delves (1981) found that the mean blood lead concentrations of pregnant and
non-pregnant control women living in an urban area of England were approximately 4 pg/dl
higher than those for similar groups living in a rural area. The mean concentrations for the
urban and rural pregnant women were 15.9 and 11.9 pg/dl, respectively (p <0.001), but there
were no demonstrable effects of the higher maternal blood lead levels on any aspect of peri-
natal health. The rate for congenital abnormality was higher in the rural area, suggesting
that whatever the cause, it was unlikely to be related to maternal levels of lead.
Additional studies of placental lead and stillbirths have not clarified the situation.
Khera et al. (1980) measured placental and stillbirth tissue lead in occupationally exposed
women in the United Kingdom. Regardless of the incidence of stillbirths, placental lead con-
centrations were found to increase with duration of occupational exposure, from 0.29 pg/g at
<1 yr exposure to 0.48 pg/g at >6 yr exposure for a group of 26 women aged 20-29 years. Pla-
cental lead concentrations also increased with age of the mother, independently of time of oc-
cupational exposure, and ranged from 0.30 (± 0.16) pg/g for those <20 yrs old to 0.51 (± 0.44)
pg/g for those £30 yrs old. Average placental lead concentrations for 20 occupationally ex-
posed women whose babies were stillborn were higher [0.45 (± 0.32) pg/g] than the average
level of 0.29 (± 0.09) pg/g for placentas from eight mothers who had not been occupational ly
exposed for at least two years. The authors noted, however, that it was not possible to say
whether occupational exposure caused any of the stillbirths or whether the high lead levels
were merely consequential to the fetal death. It is somewhat disconcerting that the placental
lead concentrations were about three times lower than those reported earlier by this group
(Wibberley et al., 1977). These differences were attributed to methodological changes and to
changes in concentration during storage of placentas at -20°C (Khera et al., 1980).
The placental lead concentrations reported by Alexander (1982) are, however, similar to
the earlier results of Wibberley et al. (1977), with mean values of 1.34 (± 0.15) pg/g for
seven stillbirths and 1.27 (i 0.48) pg/g for seven matched healthy controls. The wide range
of concentrations reported for the controls (0.34-5.56 pg/g) and the differences in concentra-
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tion with site of sampling makes it difficult to draw any useful conclusions from the results
presented by Alexander. Clearly these analytical discrepancies in placental lead measurements
must be resolved if any interpretation of their significance is to be made.
An additional study by Roels et al. (1978b) reported placental lead values of 0.08
(± 0.05) (jg/g (range = 0.01-0.40 ng/g) from a variety of locations in Belgium, but these data
indicated no correlation between lead concentration and birth weight. In contrast, placental
lead has been reported to be associated with decreased activity of a placental enzyme, steroid
sulfatase (Karp and Robertson, 1977). A similar association was found for mercury, suggesting
that either metal or both together could have affected the enzyme activity or that the authors
had merely uncovered a spurious correlation.
12.6.1.4.3 Paternally mediated effects of lead. There is increasing evidence that exposure
of male laboratory animals to toxic agents can result in adverse effects on their offspring,
including decreased litter size, birth weight, and survival. Mutagenic effects are the most
likely cause of such results, but other mechanisms have been proposed (Soyka and Joffe, 1980).
In the following cases, exposure of human males to lead has been implicated as the cause of
adverse effects on the conceptus.
According to Koinuma (1926) in a brief report, 24.7 percent of workmen exposed to lead in
a storage battery plant had childless marriages, while the value for men not so exposed was
14.8 percent. Rates for miscarriages or stillbirths in wives of lead-exposed men and controls
were 8.2 and 2.8 percent, respectively, while corresponding figures for neonatal deaths were
24.2 and 19.2 percent. These comparisons were based on 170 lead-exposed and 128 control men.
These differences in fertility and prenatal mortality, while not dramatic, are suggestive of a
male-mediated lead effect; however, the reliability of the methodology used in this study can-
not be determined, due to the brevity of the report.
In a study of the pregnancies of 104 Japanese women before and after their husbands began
lead-smelter work, miscarriages increased to 8.30 percent of pregnancies from a pre-exposure
rate of 4.70 percent (Nogaki, 1957). The miscarriage rate for 75 women whose husbands were
not occupational ly exposed to lead was 5.80 percent. In addition, exposure to lead was
related to a significant increase in the ratio of male to female offspring at birth. Lead
content of paternal blood ranged from 11 to 51.7 pg/dl [mean - 25.4 (± 1.26) pg/dl], but was
not correlated with reproductive outcome, except in the case of the male to female offspring
ratio. The reported blood lead levels appear low, however, in view of the occupational expo-
sure of these men, and were similar to those given for controls [mean = 22.8 (± 1.63)
pg/dl]. Also, maternal age and parity appear not to have been well controlled for in the
analysis of the reproductive data. Another report (Van Assen, 1958) on fatal birth defects in
children conceived during a period when their fathers were lead poisoned (but neither before
nor after) also hints at paternally-mediated effects of lead.
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In the above study by Nordstrom et al. (1979b), women employed at the Ronnskar smelter
were found to have higher abortion rates if their husbands were also employed at the smelter.
This was true only of their third or later pregnancies, however, suggesting that the effect
was related to long-term exposure of the male gametogenic stem cells. Whether this was a lead
effect or that of other toxins from the smelter is not clear.
12.6.1.5 Summary of the Human Data. The literature on the effects of lead on human reproduc-
tion and development leaves little doubt that lead can, at high exposure levels, exert signi-
ficant adverse health effects on reproductive functions. Most studies, however, only looked
at the effects of prolonged moderate to high exposures to lead, e.g., those encountered in
industrial situations, and many reports do not provide definite information on exposure levels
or blood lead levels at which specific effects were observed. Also the human data were
derived from studies involving relatively small numbers of individuals and therefore do not
allow for discriminating statistical analysis. These reports are often additionally con-
founded by failure to obtain appropriate controls and, in some cases, by the presence of addi-
tional toxic agents or disease states. These and other factors obviously make interpretation
of the data difficult. It appears possible that effects on sperm or on the testis may occur
due to chronic exposure resulting in blood lead values of 40-50 ng/dl, based on the Lancranjan
et al. (1975) and Wildt et al. (1983) studies, but additional data are greatly needed. Expo-
sure data related to reproductive functions in the female are so lacking that even a rough
estimate is impossible. Data on maternal exposure levels at which effects may be seen in
human fetuses or infants are also quite meager, although the results of Haas et al. (1972),
Kuhnert et al. (1977), and Lauwerys et al. (1978) suggest possible perinatal effects on heme
metabolism at maternal blood levels considerably below 30 jjg/dl. The human data on actual
absorbed doses are even more lacking than those on blood lead values, adding to the impreci-
sion of conclusions relating lead exposure to reproductive outcome.
12.6.2 Animal Studies
12.6.2.1 Effects of Lead on Reproduction.
12.6.2.1.1 Effects of lead on male reproductive functions. Among the first investigators to
report infertility in male animals due to lead exposure were Puhac et al. (1963), who exposed
rats to lead via their diet. Ability to sire offspring returned, however, 45 days after ces-
sation of treatment. More recently, Varma et al. (1974) gave a solution of lead subacetate in
drinking water to male Swiss mice for four weeks (mean total intake of lead = 1.65 g). The
fertility of treated males was reduced by 50 percent. Varma and coworkers calculated the
mutagenicity index (number of early fetal deaths/total implants) to be 10.4 for lead-treated
mice versus 2.98 for controls (p <0.05). The major differences in fecundity appeared to have
been due to differing pregnancy rates, however, rather than prenatal mortality. Impairment of
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male fertility by lead rather than lead-induced mutagenicity was thus likely to have been the
primary toxic effect observed. Additionally, it has been suggested by Leonard et al. (1973),
that effects seen following administration of lead acetate in water may be due to resulting
acidity, rather than to lead. Also, Eyden et al. (1978) found no decrease in fertility of
male mice fed 0.1 percent lead acetate in the diet for 64 weeks.
Several animal studies have found lead-associated damage to the testes or prostate,
generally at relatively high doses. Golubovich et al. (1968) found a decrease in normal sper-
matogonia in the testes of rats gavaged for 20 days with lead (2 mg/kg/day). Desquamation of
the germinal epithelium of the seminiferous tubules was also increased, as were degenerating
spermatogonia. Hilderbrand et al. (1973) also noted testicular damage in male rats given oral
lead (100 pg/day for 30 days). Egorova (cited in Stofen, 1974) injected lead at a dose of 2
pg/kg six times over a ten-day period and reported testicular damage.
Ivanova-Chemishanska et al. (1980) investigated the effect of lead on male rats adminis-
tered 0.0001 or 0.01 percent solutions of lead acetate over a four-month period. The authors
reported that changes in enzymatic activity and in levels of disulfide and ATP were observed
in testicular homogenates. No histopathological changes in testicular tissue were found, but
the fertility index for treated males was decreased. Offspring of those males exhibited post-
partum "failure to thrive" and stunted growth. Such data suggest biological effects due to
chronic lead exposure of the male, but the study is difficult to evaluate due to limited in-
formation on the experimental methods, particularly the dose levels actually received.
In a more recent study of lead effects on the male reproductive tract, no histopathologi-
cal changes were seen during an examination of the testes of rabbits (Willems et al., 1982).
Five males per group were dosed subcutaneously with up to 0.5 mg/kg lead acetate three times
weekly for 14 weeks. Blood lead levels at termination of treatment were 6.6 and 61.5 pg/dl
for control and high dose rabbits, respectively.
Lead-related effects on spermatozoa have also been published. For example, Stowe et al.
(1973) reported the results of a low calcium and phosphate diet containing 100 ppm lead (as
acetate) fed to dogs from 6 to 18 weeks of age. This dose resulted in a number of signs of
toxicity, including spermatogonia with hydropic degeneration. In the Maisin et al. (1975)
study, male mice received up to 1 percent lead in the diet, and the percentage of abnormal
spermatozoa increased with increasing lead exposure. Eyden et al. (1978) also fed 1 percent
lead acetate- in the diet to male mice. By the eighth week, abnormal sperm had increased;
however, the affected mice showed weight loss and other signs of general toxicity. Thus, the
spermatogenesis effect was not indicative of differential sensitivity of the gonad to lead.
Krasovskii et al. (1979) observed decreased motility, duration of motility, and osmotic
stability of sperm from rats given 0.05 mg/kg lead orally for 20-30 days. Damage to gonadal
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blood vessels and to Leydig cells was also seen. Rats treated for 6-12 months exhibited ab-
normal sperm morphology and decreased spermatogenesis. In the report of Willems et al. (1982)
described above, however, no effects on sperm count or morphology were seen in rabbits.
Lead acetate effects on sperm morphology were also tested in mice given about one six-
teenth to one half an LD5o dose by i.p. injection on five consecutive days (Bruce and Heddle,
1979; Wyrobek and Bruce, 1978; Heddle and Bruce, 1977). The two lowest doses (apparently 100
and 250 mg/kg) resulted in only a modest increase in morphologically abnormal sperm 35 days
after treatment, but the 500 or 900 mg/kg doses resulted in up to 21 percent abnormal sperm.
That lead could directly affect developing sperm or their cellular precursors is made
more plausible by the data of Timm and Schulz (1966), who found lead in the seminiferous
tubules of rats and in their sperm. The mechanisms for lead effects on the male gonad or
gamete are unknown, however, although Golubovich et al. (1968) found altered RNA levels in the
testes of lead exposed rats. They suggested that testicular damage was related to diminished
ribosomal activity and inhibition of protein synthesis. As noted above, Ivanova-Chemishanska
et al. (1980) observed biochemical changes in testes of lead-treated mice. Nevertheless, such
observations are only initial attempts to determine a mechanism for observed lead effects. A
more likely mechanism for such effects on the testis may be found in the work of Donovan et
al. (1980), who found that lead inhibited androgen binding by the cytosolic receptors of mouse
prostate. This could provide a mechanism for the observation of Khare et al. (1978), who
found that injection of lead acetate into the rat prostate resulted in decreased prostatic
weight; no such changes were seen in other accessory sex glands or in the testes.
Effects on hormonal production or on hormone receptors could also explain the results of
Maker et al. (1975), who observed a delay in testicular development and an increase in age of
first mating in male mice of two strains whose dams were given 0.08 percent lead (C57B1/6J) or
0.5 percent lead (Swiss-Webster albino) during pregnancy and lactation. The weanling males
were fed these same doses in their diets through 60 days of age.
Another potential mechanism underlying lead effects on sperm involves its affinity for
sulfhydryl groups. Mammalian sperm possess high concentrations of sulfhydryls believed to be
involved in the maintenance of motility and maturation via regulation of stability in sperm
heads and tails (Bedford and Calvin, 1974; Calvin and Bedford, 1971). It has also been found
that blockage of membrane thiols inhibits sperm maturation (Reyes et al. , 1976).
12.6.2.1.2 Effects associated with exposure of females to lead. Numerous studies have
focused on lead exposure effects in females. For example, effects of lead on reproductive
functions of female rats were studied by Hilderbrand et al. (1973), using animals given lead
acetate orally at doses of 5 and 100 ijg for 30 days. Control rats of both sexes had the same
blood lead levels. Blood lead levels of treated females were higher than those of similarly
treated males: 30 versus 19 |jg/dl at the low dose, and 53 versus 30 ng/dl at the high dose.
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The females exhibited irregular estrus cycles at both doses. When blood lead levels reached
50 pg/dl, they developed ovarian follicular cysts, with reductions in numbers of corpora
1utea.
In a subsequent study (Der et al. , 1974), lead acetate (100 pg lead per day) was injected
s.c. for 40 days in weanling female rats. Treated rats received a low-protein (4 percent) or
adequate-protein (20 percent) diet; controls were given the same diets without lead. Females
on the low protein, high lead diet did not display vaginal opening during the treatment period
and their ovaries decreased in weight. No estrous cycles were observed in animals from either
low protein group; those of the adequate diet controls were normal, while those of the rats
given adequate protein plus lead were irregular in length. Endometrial proliferation was also
inhibited by lead treatment. Blood lead levels were 23 vjg/dl in the two control groups, while
values for the adequate and low protein lead-treated groups were 61 and 1086 pg/dl, respec-
tively. The reports of Hilderbrand et al. (1973) and Der et al. (1974) suggest that lead
chronically administered in high doses can interfere with sexual development in rats and the
body burden of lead is greatly increased by protein deprivation.
Maker et al. (1975) noted a delay in age at first conception in female mice of two
strains exposed to 0.08 percent (C57B1/6J) or 0.5 percent lead (Swiss-Webster) indirectly via
the maternal diet (while i_n utero and nursing) and directly up to 60 days of age. These
females were retarded in growth and tended to conceive only after reaching weights approxi-
mating those at which untreated mice normally first conceive. Litters from females that had
themselves been developmentally exposed to at least 0.5 percent lead had lower survival rates
and retarded development. More recently, Grant et al. (1980) reported delayed vaginal opening
in rats whose mothers were given 25, 50, or 250 ppm lead (as lead acetate) in their drinking
water during gestation and lactation followed by equivalent exposure of the 9ffspring after
weaning. The vaginal opening delays in the 25 ppm females occurred in the absence of any
growth retardation or other developmental delays, in association with median blood lead levels
of 18-29 jjg/dl.
Although most animal studies have used rodents, Vermande-Van Eck and Meigs (1960) admin-
istered lead chloride i.v. to female rhesus monkeys. The monkeys were given 10 mg/ week for
four weeks and 20 mg/week for the next seven months. Lead treatment resulted in cessation of
menstruation, loss of color of the "sex skin" (presumably due to decreased estrogen produc-
tion), and pathological changes in the ovaries. One to five months after lead treatment
ceased menstrual periods resumed, the sex skin returned to a normal color, and the ovaries
regained their normal appearance. Thus, there was an apparent reversal of lead effects on
female reproductive functions, although there were no confirmatory tests of fertility.
The above studies indicate that pre- and/or post-natal exposure of female animals to lead
can affect pubertal progression and hypothalamic-pituitary-ovarian-uterine functions. The
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observations of delayed vaginal opening may reflect delayed ovarian estrogen secretion,
suggesting toxicity to the ovary, hypothalamus, or pituitary. One study has demonstrated
decreased levels of circulating follicle-stimulating hormone (Petrusz et al., 1979), and
others discussed previously have shown lead-induced ovarian atrophy (Stowe and Goyer, 1971;
Vermande-Van Eck and Meigs, 1960), again suggesting toxicity involving the hypothalamic-
pitui tary-ovarian-endometrial axi s.
12.6.2.2 Effects of Lead on the Offspring. This section discusses developmental studies of
offspring whose parents (one or both) were exposed to lead. Possible male-mediated effects as
well as effects of exposure during gestation are reviewed. Results obtained for offspring of
females given lead following implantation or throughout pregnancy are summarized in Tables
12-13 and 12-14.
12.6.2.2.1 Male mediated effects. A few studies have focused on male-mediated lead effects
on the offspring, suggesting that paternally transmitted effects of lead may cause reductions
in litter size, offspring weight, and survival rate.
Cole and Bachhuber (1914), using rabbits, were the first to report paternal effects of
lead intoxication. In their study, the litters of dams sired by lead-intoxicated male rabbits
were smaller than those sired by controls. Weller (1915) similarly demonstrated reduced birth
weights and survival among offspring of lead-exposed male guinea pigs.
Offspring of lead-treated males from the Ivanova-Chemishanska et al. (1980) study de-
scribed above were affected in a variety of ways, e.g. they exhibited "failure to thrive" and
lower weights than did control progeny at one and three weeks postpartum. These results are
difficult to interpret, however, without more specific information on the experimental methods
and dosing procedures.
12.6.2.2.2 Results of lead exposure of both parents. Only a few studies have assessed the
effects of lead exposure of both parents on reproduction. Schroeder and Mitchener (1971)
found a reduction in the number of offspring of rats and mice given drinking water containing
25 ppm lead. According to the data of Schroeder et al. (1970), however, animals in the 1971
study may have been chromium deficient, and the Schroeder and Mitchener (1971) results are in
marked contrast to those of an earlier study by Morris et al. (1938), who reported no signifi-
cant reduction in weaning percentage among offspring of rats fed 512 ppm lead.
In another study, Stowe and Goyer (1971) assessed the relative paternal and maternal
effects of lead as measured by effects on the progeny of lead-intoxicated rats. Female rats
fed diets with or without 1 percent lead were mated with normal males. The pregnant rats were
continued on their respective rations with or without lead throughout gestation and lactation.
Offspring of these matings, the Fj generation, were fed the rations of their dams and were
mated in combinations as follows: control female to control male (CF-CM), control female to
DPB12/G
12-160
9/20/83
-------
TABLE 12-13. EFFECTS OF PRENATAL EXPOSURE TO LEAD ON THE OFFSPRING OK LABORATORY AND DOMESTIC ANIMALS:
STUDIES USING ORAL OR INHALATION ROUIES OF EXPOSURE
Treatment Effect on the offspring3
Test agent
Ooseb and mode
Timingc
Mortality
Fetotoxicity
Mai formation
Reference
Lead acetate
512 ppm in diet
all
-
-
7
Morris et al. (1938)
10,000 ppm in diet
all
+
7
Stowe and Goyer (1971)
Lead acetate
45.2 ;mg/kg/day, po
45. 5'-mg/kg/day, po
31.9-47.8 mg/kg/day, po
63.7 mg/kg/day, po
6-16
6-B
all
all
~
+
+
-
Kennedy et al. (1975)
Miller et al. (1982)
150 mg'/kg/day, po
6-18
~
-
Wardel1 et al. (1982)
255-478 mg/kg/day in
water
all,LAC
+d
?
Murray et al. (1978)
31.9-319 ppm in water
all
±e
+
-
Oilts and Ahokas (1979, 1980)
0.32-159 ppm in water
all
-
+
-
Kimmel et al. (1980)
Tetraethyl lead
1.6-3.2 mg/kg/day, po
9-11 or 12-14
±
+
-
McClain and Becker (1972)
0.064 mg/kg/day, po
0.64 mg/kg/day, po
6.4 mg/kg/day, po
6-16
6-16
6-8
+
+
+
~
-
Kennedy et al. (1975)
Tetramethyl lead
10-28.7 mg/kg/day, po
9-11 or 12-14
±
+
-
McClain and Becker (1972)
Trimethyl lead
chloride
3.6-7.2 mg/kg/day, po
9-11 or 12-14
"
+
-
Lead nitrate
1 ppm in water
10 ppm in water
all
all
-
+ f-9
7
7
Hubermont et al. (1976)
Lead (aerosol)
1 or 3 mg/m3, inhaled
10 mg/m3, inhaled
1-21
1-21
?
?
+h
7
7
Prigge and Greve (1977)
Lead acetate
3,185 ppm in diet
1-7
+
N/A
Jacquet (1977)
780-1,593 ppm in diet
3,185 ppm in diet
1-16,17, or 18
1-16,17, or 18
0
1
7
7
Jacquet et al. (1977b)
1,593-6,370 ppm in diet
1-15,16, or 17
+k
7
Gerber and Maes (1978)
1,595-3,185 ppm in diet
7-16,17, or 18
7
+ 1
7
Gerber et al. (1978)
45.3 mg/kg/day, po
455 mg/kg/day, po
6-16
6-8
+
-
Kennedy et al. (1975)
-------
TABLE 12-13. (continued)
Treatment
Effect on the offspring
Species
Test agent
Dose'3 and mode
T - C
Timing
Mortality
Fetotoxicity Malformation
Reference
House
0.1-1.0 g/1 in water
all
-
? ?
Leonard et al. (1973)
637-3,185 ppm in diet
1-18
+
? ?
Maisin et al. (197b)
1,593 ppm in diet
1-16,17, or
18
+
-
Jacquet et al. (1975)
3,185 ppm in diet
1-16,17, or
18
+
~
1,250 ppm in diet
all
-
+
3,185 ppm in diet
1-16,17, or
18
+
+
1,250 ppm in diet
all
-
+
2,500-5,000 ppm
all
+
+
Jacquet (1976)
in diet
1,250 ppm in diet
all
-
+
Tetraethyl lead
0.06 mg/kg/day, po
6-16
-
-
Kennedy et al. (1975)
0.64 mg/kg/day, po
6-16
+
+
6.4 mg/kg/day, po
6-8
+
+
Sheep
Lead powder
0.5-16 mg/kg/day, in
all
+
?
Sharma and Buck (1976)
diet'
£
o
cn
to
A
CTl
ro
+ - present; - = effect not seen; l = ambiguous effect; ? = effect not examined or insufficient data.
^ As elemental lead.
cSpecific gestation days when exposed; LAC = also during lactation.
^Decreased numbers of dendritic spines and malformed spines at day 30 postpartum.
Litter size values for high dose group suggestive of an effect.
*ALAD activity was decreased.
^Free tissue porphyrins increased in kidneys.
^Hematocrit was decreased.
1 Fetal porphyrins were increased, except in the low dose fetuses assayed on gestation day 18.
^Decreased heme and fetal weight,
k
Incorporation of Fe into heme decreased, and growth was retarded.
Decreased placental blood flow.
-o
TO
TO
-c
ZD
TO
-------
TABLE 12-14. EFFECTS OF PRENATAL IEAO EXPOSURE ON OFFSPRING OF LABORATORY ANIMALS:
RESULTS OF STUOIES EMPLOYING ADMINISTRATION OF LEAO BY INJECTION
CO
Treatment
Effect on the offspring3
Species
Test agent
Doseb and
mode
T c
Timing
Mortality Fetotoxicity Malformation
Reference
Rat
Lead acetate
15.9 mg/kg.
ip
9
+ + +
Zegarska et al. (1974)
Lead nitrate
31.3 mg/kg,
31.3 mg/kg.
31.3 mg/kg,
iv
iv
iv
8
9 or 16
10-14,
15,17
- + +
+ + +
+d
McClain and Becker (1975)
3.13 mg/kg,
15.6 mg/kg,
15.6 mg/kg,
iv
iv
iv
9 or 15
9
15
+ + +
~ ? ?
Hackett et al. (1978a,b)
-
unknown, iv
8 or 9
~ ? +
Coro Antich and Amoedo Hon
(1980)
31.3 mg/kg,
15.6 mg/kg.
iv
iv
17
17
+ +
Minsker et al. (1982)
5 mg/kg, iv
25 mg/kg, iv
9 or 15
9 or 15
+ + +,-e
Hackett et al. (1982)
Lead chloride
7.5 mg/kgff
75 mg/kg,
9
9
± ~
+ +
McLellan et al. (1974)
Trimethyl lead
chloride
20.2 mg/kg,
23.8 mg/kg,
iv
iv
12
9,10,13, or 15
^ I :
House
Lead acetate
9.56-22.3 mg/kg,
9.56 mg/kg, ip
22.3 mg/kg, ip
22.3 mg/kg, ip
ip 8
9
9
10 or 12
- + +
+ - +
+ + +
Jacquet and Gerber (1979)
Lead chloride
29.8 mg/kg,
29.8 mg/kg,
iv
iv
3 or 4
6
~ ? ?
+ N/A N/A
Wide and Nilsson (1977)
-o
JO
3>
JO
-c
o
TO
3>
-------
TABLE 12-14.
(continued)
Treatment
Effect on the offspring
Species
Test agent
Dose'' and mode
T. . c
Timing
Mortality Fetotoxicity Malformation
Reference
Hamster
Lead acetate
31.9 mg/kg, iv
8
~ ? ~
Ferm (1969)
Lead acetate or
chloride
31.9 or 37.3 mg/kg, iv
8
? ? ~
Ferm and Carpenter (1967)
Lead nitrate
31.3 mg/kg, iv
7, 8, or 9
? ? ~
Ferm and Carpenter (1967)
15.6-31.3 mg/kg, iv
8 or 9
+ ? ~
Ferm and Ferm (1971)
31.3 mg/kg, iv
8
+ + *
Carpenter and Ferm (1977)
31.3 mg/kg, iv
8
h
~ + ~
Gale (1978)
~ - effect present; - = effect not seen; ± = ambiguous effect; ? = effect not examined or insufficient data.
As elemental lead.
cSpecific gestation days when exposed.
'Hjith the exception of day 17.
eNo fetuses survived to be examined for malformation.
fNo dosage route specified.
®0nly after day 10 treatment.
^Delayed ossification (fetal weights not given).
'Dosage was varied daily to maintain a blood lead level of = 40 pg/dl (range = 30 to 70 \ig/d\).
-o
XD
J»
va
CD
XD
J»
-------
PRELIMINARY DRAFT
lead-intoxicated male (CF-PbM), 1ead-intoxicated female to control male (PbF-CM), and lead-
intoxicated female to lead-intoxicated male (PbF-PbM). The results are shown in Table 12-15.
The paternal effects of lead included reductions of 15 percent in the number of pups per
litter, 12 percent in mean pup birth weight, and 18 percent in pup survival rate. The mater-
nal effects of lead included reductions of 26 percent in litter size, 19 percent in pup birth
weight, and 41 percent in pup survival. The combined male and female effects of lead toxicity
resulted in reductions of 35 percent in the number of pups per litter, 29 percent in pup birth
weight, and 67 percent in pup survival to weaning. Stowe and Goyer classified the effects of
lead upon reproduction as gametotoxic, intrauterine, and extrauterine. The gametotoxic ef-
fects of lead seemed to be irreversible and had additive male and female components. Intra-
uterine effects were presumed to be due to lead uptake by the conceptus, plus gametotoxic ef-
fects. The extrauterine effects were due to the passage of lead from the dam to the nursing
pups, adding to the gametotoxic and intrauterine effects.
Leonard et al. (1973), however, found no effect on the reproductive performance of groups
of 20 pairs of mice given lead in their drinking water over a nine-month period. Lead doses
ranged from 0.1 to 1.0 g/1. A total amount of 31 g/kg was ingested at the high dose, equiva-
lent to ingestion of 2.2 kg lead by a 70 kg man over the same time period.
12.6.2.2.3 Lead effects on implantation and early development. Numerous studies have been
performed to elucidate mechanisms by which lead causes prenatal death. They suggest two
mechanisms of action for lead, one on implantation and the other (mainly at higher doses) on
fetal development. The latter is discussed primarily in Section 12.6.2.2.4.5.
Maisin et al . (1975) exposed female mice to dietary lead for 18 days after mating; both
the number of pregnancies and surviving embryos decreased. Similarly, exposure of female mice
to lead via their diet (0.125-1.00 percent) from mating to 16-18 days afterward (Jacquet,
1976; Jacquet et al., 1975) resulted in decreased pregnancy incidence and number of corpora
lutea; increased number of embryos dying after implantation at the highest dosages; decreased
body weights of surviving fetuses; and treated dam fatalities at the high dose.
Jacquet and co-workers also described effects of maternal dietary lead exposure on pre-
implantation mouse embryos (Jacquet, 1976; Jacquet et al., 1976). They found lead in the diet
to be associated with retardation of cleavage in embryos, failure of trophoblastic giant cells
to differentiate, and absence of an uterine decidual reaction. Maisin et al. (1978) also
found delayed cleavage in embryos of mice fed lead acetate prior to mating and up to 7 days
afterwards.
Giavini et al. (1980) further confirmed the ability of lead to affect the preimplantation
embryo in studies of rats transplacentally exposed to lead nitrate, and Wide and Nilsson
(1977, 1979) reported that inorganic lead had similar effects on mice. Jacquet (1978) was
able to force implantation in that species by use of high doses of progesterone, while Wide
DPB12/G 12-165 9/20/83
1062<
-------
TABLE 12-15. REPRODUCTIVE PERFORMANCE OF F, LEAD-INTOXICATED RATS
Parameter Type of mat1n9
CF-CM CF-PbM PbF-CM PbF-PbM
Litters observed
22
24
36
16
Pups per litter
11.90 ±
0.403
10.10 ±
0.50
8.78 +
0.30b
7.75
± 0.50C
Pup birth weight, g
6.74 +
0. 15
5.92 ±
0. 13C
5.44 +
0.13C'd
4.80
± 0.19C,d,e
Weaned rats per litter
9.84 ±
0. 50
7.04 ±
0.77C
5.41 +
0.74C'd
2. 72
± 0.70C,d'e
Survival rate, %
89.80 ±
3.20
73.70 ±
7.90
52.60 ±
7.20
30.00"
± 8.20C,d'f
Litter birth weight, „
0am breeding weight
28.04 ±
1.30
22.30 ±
0. 90C
19.35 ±
1 ,ooc
15. 38
± 1.ioc'd'f
Litter birth weight, ^
0am whelping weight
19.09 ±
0.80
15.97 ±
0. 58C
14.28 ±
0.66C
11.58
± 0.78C,d,f
Gestational gain,
Pups per litter ^
11.54 ±
0.60
11.20 ±
0. 74
11.17 ±
0.54
12.34
±1.24
Nonfetal gestational
gain per fetus, g
3.93 ±
0.38
4.83 +
0.47
4. 15 ±
0.42
3.96
+ 0.46
aMean + S.E.M.
^Significantly (p <0.05) less than mean for CF-CM.
CSignificantly (p <0.01) less than mean for CF-CM.
dSignificantly (p <0.01) less than mean for CF-PbM.
eSignificantly (p <0.01) less than mean for PbF-CM.
fSignificantly (p <0.05) less than mean for PbF-CM.
Source: Stowe and Goyer (1971).
-------
PRELIMINARY DRAFT
(1980) determined that administration of estradiol-17p and progesterone could reverse the ef-
fects of lead on implantation. Wide suggested that the lead-induced implantation blockage was
mediated by a decrease in endometrial responsiveness to both sex steroids. Jacquet (1976) and
Jacquet et al. (1977b) had attributed lead-induced prevention of implantation in the mouse to
a lack of endogenous progesterone alone, stating that estrogen levels were unaffected. Later,
however, Jacquet et al. (1977a) stated that estrogen levels also decreased, a finding not sup-
ported by Wide and Wide (1980). The latter authors did find a lead-induced increase in
uterine estradiol receptors, but no change in binding affinities.
In order to examine lead effects early in gestation, Wide and Nilsson (1977) examined
embryos from untreated mice and from mothers given 1 mg lead chloride on days 3, 4, or 6 of
pregnancy. Embryonic mortality was greater in lead-treated litters; in the day-6 group some
abnormal embryos were observed by day 8. In a later experiment, Wide (1978) removed blasto-
cysts from lead-treated mice. She found that they attached and grew normally during three
days of i_n vitro culture. Other blastocysts from untreated mothers were cultured in media
containing lead, and a dose-dependent decrease in the number of normally developing embryos
was seen.
A study employing domestic sheep was reported by Sharma and Buck (1976), who fed lead
powder to pregnant ewes throughout gestation. Levels in the diet were varied from 0.5 to 16
mg/kg/day in an effort to keep blood lead levels near 40 pg/dl (actual levels ranged from 30
to 70 (jg/dl). Such treatment resulted in a greatly decreased lambing percentage but no gross
malformations. However, the number of subjects was small.
12.6.2.2.4 Teratogenicity and prenatal toxicity of lead in animals.
12.6.2.2.4.1 High dose effects on the conceptus. Teratogenic effects refer to physical
defects (malformations) in the developing offspring. Prenatal toxicity (embryotoxicity, feto-
toxicity) includes premature birth, prenatal death, stunting, histopathological effects, and
transient biochemical or physiological changes. Behavioral teratogenicity, consisting of be-
havioral alterations or functional (e.g., motor, sensory) deficits resulting from i_n utero
exposure, is dealt with in Section 12.4 of this chapter.
Teratogenicity of lead, at high exposure levels, has been demonstrated in rodents and
birds, with some results suggesting a species-related specificity of certain gross teratogenic
effects. Ferm and Carpenter (1967), as well as Ferm and Ferm (1971), reported increased
embryonic resorption and malformation rates when various lead salts were administered i.v. to
pregnant hamsters. Teratogenic effects were largely restricted to the tail region, including
malformations of sacral and caudal vertebrae resulting in absent or stunted tails. Gale
(1978) found the same effects plus hydrocephalus, among six strains of hamsters and noted dif-
ferences in susceptibility, suggesting a genetic component in lead-induced teratogenicity.
DPB12/G 12-167 9/20/83
1064^
-------
PRELIMINARY DRAFT
Zegarska et al. (1974) performed a study with rats injected with lead acetate at midges-
tation. They reported embryonic mortality and malformations, McClain and Becker (1975) sub-
sequently administered lead nitrate i.v. to rats on one of days 8-17 of gestation, producing
malformations and embryo- and feto-toxicity. Hackett et al. (1978, 1982a,b) also gave lead
i.v. to rats and found-malformations and high incidences of prenatal mortality. Minsker et
al. (1982) gave lead i.v. to dams on day 17 of gestation and observed decreased birth weights,
as well as decreased weight and survival by postpartum day 7.
In another study, Miller et al. (1982) used oral doses of lead acetate up to 100 mg/kg
given daily to rats before breeding and throughout pregnancy and found fetal stunting at the
high dose, but no other effects. Maternal blood lead values ranged from 80 to 92 pg/dl prior
to mating and from 53 to 92 (jg/dl during pregnancy. Pretreatment and control blood lead
levels averaged 6 to 10 pg/dl. Also, Wardell et al. (1982) gavaged rats daily with lead doses
of up to 150 mg/kg from gestation day 6 through day 18 and observed decreased prenatal surviv-
al at the high dose, but no malformations.
Ferm (1969) reported that teratogenic effects of i.v. lead in hamsters are potentiated in
the presence of cadmium, leading to severe caudal dysplasia. This finding was duplicated by
Ht1 be link (1980). In addition to caudal malformations, lead appears to influence the morphol-
ogy of the developing brain. For example, Murray et al. (1978) described a significant
decrease in number of dendritic spines and a variety of morphological abnormalities of such
spines in parietal cortex of 30-day-old rat pups exposed to lead during gestation and nursing,
during the postweaning period only, or during both periods. Morphometric analysis of rats
transplacentally exposed to lead indicated that cellular organelles were altered as a function
of dose and stage of development at exposure (Klein et al. , 1978). These results indicate
that morphologically apparent effects of lead on the brain could be produced by exposure dur-
ing pregnancy alone, a question not addressed by Murray et al. (1978).
A variety of studies relating neurobehavioral effects to prenatal lead exposure have also
been published. These studies are discussed in Section 12.4.3 of this chapter.
12.6.2.2.4.2 Low dose effects on the conceptus. There is a paucity of information re-
garding the teratogenicity and developmental toxicity of prolonged low-level lead exposure.
Kimmel et al. (1980) exposed female rats chronically to lead acetate via drinking water (0.5,
5, 50, and 250 pg/g) froni weaning through mating, gestation, and lactation. They observed a
decrease in fetal body length of female offspring at the high dose, and the female offspring
from the 50 and 250 |jg/g groups weighed less at weaning and showed delays in physical develop-
ment. Maternal toxicity was evident in the rats given 25 pg/g or higher doses, corresponding
to blood lead levels of 20 pg/dl or higher. Reiter et al. (1975) observed delays in the
development of the nervous system in offspring exposed to 50 pg/g lead throughout gestation
DPB12/G 12-168 9/20/83
-------
"PRELIMINARY DRAFT
and lactation. Whether these delays in development resulted from a direct effect of lead on
the nervous system of the pups or reflect secondary changes (resulting from malnutrition, hor-
monal imbalance, etc.) is not clear. Whatever the mechanisms involved, these studies suggest
that low-level, chronic exposure to lead may induce postnatal developmental delays.
12.6.2.2.4.3 Prenatal effects of orqanolead compounds. In an initial study of the ef-
fects of organolead compounds in animals, McClain and Becker (1972) treated rats orally with
7.5-30 mg/kg tetraethyl lead, 40-160 mg/kg tetramethyl lead, or 15-38 mg/kg trimethyl lead
chloride, given in three divided doses on gestation days 9-11 or 12-14. The last compound was
also given i.v. at doses of 20 to 40 mg/kg on one of days 8-15 of pregnancy. The highest dose
of each agent resulted in maternal death, while lower doses caused maternal toxicity. At all
dose levels, fetuses from dams given multiple treatment weighed less than controls. Single
treatments at the highest doses tended to have similar effects. In some cases delayed ossifi-
cation was observed. In addition, direct intra-amniotic injection of trimethyl lead chloride
at levels up to 100 yjg per fetus caused increasing fetal mortality.
Kennedy et al. (1975) administered tetraethyl lead by gavage to mice and rats during the
period of organogenesis at dose levels up to 10 mg/kg. Maternal toxicity, prenatal mortality,
and developmental retardation were noted at the highest doses in both species, although mater-
nal treatment was discontinued after only three days due to excessive toxicity. In a subse-
quent study involving alkyl lead, Odenbro and Kihlstrom (1977) treated female mice orally with
triethyl lead at doses of up to 3.0 mg/kg/day on days 3 to 5 following mating. The highest
treatment levels resulted in decreased pregnancy rates, while at 1.5 mg/kg, lower implantation
rates were seen. In order to elucidate the mechanism of implantation failure in organolead-
intoxicated mice, Odenbro et al. (1982) measured plasma sex steroid levels in mice five days
after mating. Levels of both estradiol and progesterone, but not estrone, were decreased
following intraperitoneal triethyl lead chloride on days three and four of gestation. Such
results suggest a hormonal mechanism for blockage of implantation, a finding also suggested
for inorganic lead (Wide, 1980; Jacquet et al., 1977a).
12.6.2.2.4.4 Effects of lead on fetal physiology and'metabol ism. Biochemical indicators
of developmental toxicity have been the subject of a number of investigations, as possible in-
dicators of subtle prenatal effects. Hubermont et al. (1976) exposed female rats to lead in
drinking water before mating, during pregnancy, and after delivery. In the highest exposure
group (10 ppm), maternal and offspring blood lead values were elevated and approached 68 and
42 Mg/dl, respectively. Inhibition of ALA-D and elevation of free tissue porphyrins were also
noted in the newborns. Maternal diets containing up to 0.5 percent lead were associated with
increased fetal porphyrins and decreased ALA-D activity by Jacquet et al. (1977a). Fetuses in
the high dose group had decreased weights, but no data were presented on maternal weight gain
or food consumption (which could have influenced fetal weight).
DPB12/G 12-169 9/20/83
1066^
-------
PRELIMINARY DRAFT
In the only inhalation exposure study (Prigge and Greve, 1977), rats were exposed
throughout gestation to an aerosol containing 1, 3, or 10 mg Pb/m3 or to a combination of 3 mg
Pb/m3 and 500 ppm carbon monoxide CO. Both maternal and fetal ALA-D activities were strongly
inhibited by lead exposure in a dose-related manner. In the presence of lead plus CO, how-
ever, fetal (but not maternal) ALA-D activity was higher than in the group given lead alone,
possibly due to the increase in total ALA-D seen in the CO-plus-lead treated fetuses. Fetal
body weight and hematocrit were decreased in the high-dose lead group, while maternal values
were unchanged, thus suggesting that the fetuses were more sensitive to lead effects than were
the mothers. Granahan and Huber (1978) also reported decreased hematocrit, as well as reduced
hemoglobin levels, in fetal rats from lead intoxicated dams (1000 ppm in the diet throughout
gestation).
Gerber and Maes (1978) fed pregnant mice diets containing up to one percent lead from day
7 to 18 of pregnancy and determined levels of heme synthesis. Incorporation of iron into
fetal heme was inhibited, but glycine incorporation into heme and protein was unaffected.
Gerber et al. (1978) also found that dietary lead given late in gestation resulted in dimin-
ished placental blood flow but did not decrease uptake of a non-metabolizable amino acid,
alpha-amino isobutyrate. The authors could not decide whether lead-induced fetal growth
retardation was due to placental insufficiency or to the previously described reduction in
heme synthesis (Gerber and Maes, 1978). They did not mention the possibility that the treated
mothers may have reduced their food consumption, resulting in a reduced nutrient supply to the
fetus, regardless of fetal ability to absorb nutrients.
More recently, Wardell et al. (1982) exposed rat fetuses i_n utero to lead by gavaging
their pregnant mothers with 150 mg/kg lead from gestation days 6 to 18. On day 19, fetal limb
cartilage was tested for ability to synthesize protein, DNA, and proteoglycans, but no adverse
effects were seen.
12.6.2.2.4.5 Possible mechanisms of lead-induced teratogenesis. The reasons for the
localization of many of the gross teratogenic effects of lead are unknown at this tima. Ferm
and Ferm (1971) have suggested that the observed specificity could be explained by an inter-
ference with specific enzymatic events. Lead alters mitochondrial function and enhances or
inhibits enzymes (Vallee and Ulmer, 1972); any or all such effects could interfere with normal
development. Similarly, inhibition of ALA has been suggested as a mechanism of teratogenesis
by Cole and Cole (1976).
In an attempt to study the mechanics of lead induction of sacral-tail region malforma-
tions, Carpenter and Ferm (1977) examined hamster embryos treated at mid-gestation during the
critical stage for response to teratogens in this species. The initial effects were edema of
the tail region of embryos 30 hours after maternal exposure, followed by blisters and hema-
DPB12/G 12-170 9/20/83
10G7<
-------
PRELIMINARY DRAFT
tomas. These events disrupted normal caudal development, presumably by mechanical displace-
ment. The end results seen in surviving fetuses were missing, stunted, or malformed tails and
anomalies of the lower spinal cord and adjacent vertebrae.
12.6.2.2.4.6 Maternal factors in lead-induced teratogenesis and fetotoxicity. Nutri-
tional factors may also have a beaming on the prenatal toxicity of lead. Jacquet and Gerber
(1979) reported increased mortality and defects in fetuses of mice given i.p. injections of
lead while consuming a calcium deficient diet during gestation. In several treatment groups,
lead-treated calcium deficient mothers had low blood calcium levels, while controls on the
same diet had normal values. It is not certain how meaningful these data are, however, as
there was no clear dose-response relationship within diet groups. In fact, fetal weights were
said to be significantly higher in two of the lead-treated groups (on the normal diet) than in
the untreated controls. Another problem with the study was that litter numbers were small.
Another study on interactions of lead with other elements was done by Dilts and Ahokas
(1979), who exposed rats to lead in their drinking water throughout gestation. Controls were
pair-fed or fed ad 1ibiturn. Lead treatment was said to result in decreased fetal weight, and
dietary z^'nc supplementation was claimed to be associated with a protective effect against
fetal stunting. The data presented do not allow differentiation of effects due to maternal
stress (e.g., decreased food consumption) from direct effects on the fetus. Litter numbers
were small, and some of the data were confusing (e.g., a lead-treated and a pair-fed group
with very similar litter sizes and total litter weights, but rather dissimilar average fetal
weights; live litter weight divided by live litter size does not give the authors' values for
average fetal. weight). Also, no data were given on maternal or fetal lead or zinc levels. In
a further report on apparently the same animals as above, Dilts and Ahokas (1980) found that
lead inhibited cell division and decreased protein contents of the fetal placentas, evis-
cerated carcasses, and livers. Such lead-related effects were not influenced by maternal zinc
supplementation.
12.6.2.3 Effects of Lead on Avian Species. The effects of lead on the reproduction and
development of various avian species have been studied by a number of investigators, primarily
out of interest in the effects of lead shot ingested by wildlife or out of interest in an
avian embryo model for the experimental analysis of ontogenetic processes. The relevance of
such studies to the health effects of lead on humans is not clear. Consequently, these
studies are not discussed further here.
12.6.3 Summary
The most clear-cut data described in this section on reproduction and development are de-
rived from studies employing high lead doses in laboratory animals. There is still a need for
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more critical research to evaluate the possible subtle toxic effects of lead on the fetus,
using biochemical, ultrastructural , or behavioral endpoints. An exhaustive evaluation of
lead-associated changes in offspring will require consideration of possible additional effects
due to paternal lead burden. Neonatal lead intake via consumption of milk from lead-exposed
mothers may also be a factor at times. Also, it must be recognized that lead effects on re-
production may be exacerbated by other environmental ' factors (e.g., dietary influences,
maternal hyperthermia, hypoxia, and co-exposure to other toxins).
There are currently no reliable data pointing to adverse effects in human offspring fol-
lowing paternal exposure to lead, and the early studies of high dose exposure in pregnant
women indicate toxic—but not teratogenic--effects on the conceptus. Effects on reproductive
performance in women are not well documented, but industrial exposure of men to lead at levels
resulting in blood lead values of 40-50 Mg/dl appear to have resulted in altered testicular
function. Unfortunately, the human data regarding lead effects during development currently
do not lend themselves to accurate estimation of no-effect levels.
The paucity of human exposure data forces an examination of the animal studies for indi-
cations of threshold levels for effects of lead on the conceptus. It must be noted that the
animal data are almost entirely derived from rodents. Based on these rodent data, it seems
likely that fetotoxic effects have occurred in animals at chronic exposures to 600-1000 ppm
lead in the diet. Subtle effects appear to have been observed at 10 ppm in the drinking water,
while effects of inhaled lead have been seen at levels of 10 mg/m3. With acute exposure by
gavage or by injection, the values are 10-16 mg/kg and 16*30 mg/kg, respectively. Since
humans are most likely to be exposed to lead in their diet, air, or water, the data from other
routes of exposure are of less value in estimating harmful exposures. Indeed, it seems likely
that teratogenic effects occur only when the maternal dose is given by injection.
Although human and animal responses may be dissimilar, the animal evidence does document
a variety of effects of lead exposure on reproduction and development. Measured or apparent
changes in production of or response to reproductive hormones, toxic effects on the gonads,
and toxic or teratogenic effects on the conceptus have all been reported. The animal data
also suggest subtle effects on such parameters as metabolism and cell structure that should be
monitored in human populations. Well-designed human epidemiological studies involving large
numbers of subjects are still needed. Such data could clarify the relationship of exposure
levels and durations to blood lead values associated with significant effects and are needed
for estimation of no-effect levels.
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12.7 GENOTOXIC AND CARCINOGENIC EFFECTS OF LEAD
12.7.1 Introduction
Potential carcinogenic, gsnotoxic (referring to alteration in structure or metabolism of
DNA), and mutagenic roles of lead are considered here. Epidemiological studies of occupation-
ally exposed populations are considered first. Such studies investigate possible associations
of lead with induction of human neoplasia. Epidemiological studies are important because they
assess the incidence of disease in humans under actual ambient exposure conditions. However,
such studies have many limitations that make it difficult to assess the carcinogenic activity
of any specific agent. These include general problems in accurately determining the amount
and nature of exposure to a particular chemical agent; in the absence of adequate exposure
data it is difficult to determine whether each individual in a population was equally exposed
to the agent in question. It is also often difficult to assess other factors, such as expo-
sure to carcinogens in the diet, and to control for confounding variables that may have con-
tributed to the incidence of any neoplasms. These factors tend to obscure the effect of lead
alone. Also, in an occupational setting a worker is often exposed to various chemical com-
pounds, making it more difficult to assess epidemiologically the injurious effect resulting
specifically from exposure to one, such as lead.
A second approach considered here examines the ability of specific lead compounds to in-
duce tumors in experimental animals. The advantage of these studies over epidemiological in-
vestigations is that a specific lead compound, its mode of administration, and level of expo-
sure can be well defined and controlled. Additionally, many experimental procedures can be
performed on animals that for ethical reasons cannot be performed on humans, thereby allowing
a better understanding of the course of chemically induced injury. For example, animals may
be sacrificed and necropsies performed at any desired time during the study. Factors such as
diet and exposure to other environmental conditions can be well controlled, and genetic vari-
ability can be minimized by use of well established and characterized animal lines. One
problem with animal studies is the difficulty of extrapolating such data to humans; however,
this drawback is perhaps more important in assessing the toxicity of organic chemicals than in
assessing inorganic agents. The injury induced by many organic agents is highly dependent
upon reactive intermediates formed i_n vivo by the action of enzymatic systems (e.g., micro-
somal enzymes) upon the parent compound. Both qualitative and quantitative differences be-
tween the metabolic capabilities of humans and experimental animals have been documented
(Neal , 1980). With inorganic compounds of lead, however, the element of interest undergoes
little alteration j_n vi vo and, therefore, the ultimate toxic agent is less likely to differ
between experimental animals and humans (Costa, 1980). The carcinogenic action of most
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organic chemicals is dependent upon activation of a parent pro-carcinogen, whereas most metal-
lic carcinogens undergo little alteration j_n vi vo to produce their oncogenic effects (Costa,
1980).
A third approach discussed below is i_n vitro studies. Animal carcinogen bioassays are
presently the preferred means for assessing carcinogenic activity but they are extremely ex-
pensive and time consuming. As a result, much effort has been directed toward developing
suitable j_n v i t.ro tests to complement _in vi vo animal studies in evaluating potential oncogen-
icity of chemicals. The cell transformation assay has as its endpoint neoplastic transforma-
tion of mammalian cells and is among the most suitable i_n vitro systems because it examines
cellular events closely related to carcinogenesis (Heck and Costa, 1982a). A general problem
with this assay system, which is less troublesome with reference to metal compounds, is that
it employs fibroblastic cells in culture, which lack many j_n vi vo metabolic systems. Since
lead is not extensively metabolized _in vi vo, addition of liver microsomal extracts (which has
been attempted in this and similar systems) is not necessary to generate ultimate carcino-
gen(s) from this metal (see above). However, if other indirect factors are involved with lead
carcinogenesis _i_n vi vo, then these might be absent in such culture systems (e.g., specific
lead-binding proteins that direct lead interactions i_n vivo with oncogenically relevant
sites). There are also technical problems related to the culturing of primary cells and dif-
ficulties with the final microscopic evaluation of morphological transformations, which are
prone to some subjectivity. However, if the assay is performed properly it can be very relia-
ble and reproducible. Modifications of this assay system (i.e., exposure of pregnant hamsters
to a test chemical followed by culturing and examination of embryonic cells for transplacen-
tally induced transformation) are available for evaluation of i_n vivo metabolic influences,
provided that the test agent is transported to the fetus. Additionally, cryopreservation of
primary cultures isolated from the same litter of embryos can control for variation in cell
populations exposed to test chemicals and give more reproducible responses in replicate ex-
periments (Pienta, 1980). A potential advantage of the cell transformation assay system is
the possibility that-cultured human cells can be transformed i_n vi tro. Despite numerous at-
tempts, however, no reproducible human-cell transformation system has yet been sucessfully
established which has been evaluated with a number of different chemicals of defined carcino-
genic activity.
Numerous processes have been closely linked with oncogenic development, and specific
assay systems that utilize events linked mechanistically with cancer as an endpoint have been
developed to probe whether a chemical agent can affect any of these events. These systems in-
clude assays for mutations, chromosomal aberrations, development of micronuclei, enhancement
of sister chromatid exchange, effects on DNA structure, and effects on DNA and RNA polymerase.
These assay systems have been used to examine the genotoxicity of lead and facilitate the
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assessment of possible lead carcinogenicity. Chromosomal aberration studies are useful
because human lymphocytes cultured from individuals after exposure to lead allow evaluation of
genotoxic activity that occurred under the influence of an i_n vivo metabolic system. Such
studies are discussed below in relationship to genotoxic effects of lead. However, a neo-
plastic change does not necessarily result, and evaluations of some less conspicuous types of
chromosomal aberrations are somewhat subjective since microscopy is exclusively utilized in
the final analyses. The sensitivity of detection of chromosomal changes also tends to be less
than other measurable DNA effects, e.g., the induction of DNA repair. However, it is reason-
able to assume that if an agent produces chromosomal aberrations it may have potential carcin-
ogenic activity. Many carcinogens are also mutagenic and this fact, combined with the low
cost and ease with which bacterial mutation assays can be performed, has resulted in wide use
of these systems in determining potential carcinogenicity of chemicals. Mutation assays can
also be performed with eukaryotic cells and several studies are discussed below that examined
the mutagenic role of lead in these systems. However, in bacterial systems such as the Ames
test, metal compounds with known human carcinogenic activity are generally negative and,
therefore, this system is not useful for determining the potential oncogenicity of lead.
Similarly, even in eukaryotic systems, metals with known human cancer-causing activity do not
produce consistent mutagenic responses. Reasons for this lack of mutagenic effect remain un-
clear, and it appears that mutagenicity studies of lead cannot be weighed heavily in assessing
its genotoxicity.
Other test systems that probe for effects of chemical agents on DNA structure may be use-
ful in assessing the genotoxic potential of lead. Sister chromatid exchange represents the
normal movement of DNA in the genome and enhancement of this process by potentially carcino-
genic agents is a sensitive indicator of genotoxicity (Sandberg, 1982). However, these
studies usually involve tissue cultures; consequently, i_n vivo interactions related to such
effects have not been addressed with this system. Numerous recently developed techniques can
be used to assess DNA damage induced by chemical carcinogens. One of the most sensitive is
alkaline elution (Kohn et al., 1981), which may be used to study DNA lesions produced j_n vi vo
or in cell culture. This technique can measure DNA strand breaks or crosslinks in DNA, as
well as repair of these lesions, but lead compounds have not been studied with this technique.
Assessment of the induction of DNA repair represents one of the most sensitive techniques for
probing genotoxic effects. The reason for this is that the other procedures measure DNA
lesions that have persisted either because they were not recognized by repair enzymes or
because their number was sufficiently great to saturate DNA repair systems. Measurement of
DNA repair activation is still possible even if the DNA lesion has been repaired, but effects
of lead compounds on DNA repair have not been studied. There are a few isolated experiments
within publications that examined the ability of lead compounds to induce DNA damage, but this
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line of investigation requires further work. There are some well-conducted studies of the
effect of lead along with other water soluble metals on isolated DNA and RNA polymerases,
which suggest mutagenic mechanisms occurring in intact cells. The ability of lead to affect
the transcription of DNA and RNA merits concern in regard to its potential oncogenic and muta-
genic properties.
12.7.2 Carcinogenesis Studies with Lead and its Compounds
12.7.2.1 Human Epidemiological Studies. Epidemiological studies of industrial workers, where
the potential for lead exposure is usually greater than for a "normal population," have been
conducted to evaluate the role of lead in the induction of human neoplasia (Cnoper, 1976,
1981; Cooper and Gaffey, 1975; Chrusciel , 1975; Dingwall-Fordyce and Lane, 1963; Lane, 1964;
McMichael and Johnson, 1982; Neal et al. , 1941; Nelson et al., 1982). In general, these
studies made no attempt to consider types of lead compounds to which workers were exposed or
to determine probable routes of exposure. Some information on specific lead compounds encoun-
tered in the various occupational settings, along with probable exposure routes, would have
made the studies more interpretable and useful. As noted in Chaptar 3, with tha exception of
lead nitrate and lead acetate, many inorganic lead salts are relatively water insoluble. If
exposure occurred by ingestion, the ability of water-insoluble lead salts (e.g., lead oxide
and lead sulfide) to dissolve in the gastrointestinal tract may contribute to understanding of
their ultimate systemic effects in comparison to their local actions in the gastrointestinal
tract. Factors such as particle size are also important in the dissolution of any water in-
soluble compounds in the gastrointestinal system (Mahaffey, 1983). When considering other
routes of exposure (e.g., inhalation), the water solubility of the lead compound in-question,
as well as the particle size, are extremely important, both in terms of systemic absorption
and contained injury in the immediate locus of the retained particle (see Chapter 10). A
hypothetical example is the inhalation of an aerosol of lead oxide versus a 'vater soluble lead
salt such as lead acetate. Lead oxide particlas having a diameter of <5 pm would tend to
deposit in the lung and remain in contact with cells there until they dissolved, while soluble
lead salts would dissipate systemically at a much more rapid rate. Therefore, in the case of
inhaled particulate compounds, localized exposure to lead might produce injury primarily in
respiratory tissue, whereas with soluble salts systemic (i.e., CNS, kidney, and erythropoie-
tic) effects might predominate.
The studies of Cooper and Gaffey (1975) and Cooper (1976, 1981) examined the incidence of
cancer in a large population of industrial workers exposed to lead. Two groups of individuals
were identified as the lead-exposed population under consideration: smelter workers from six
lead production facilities and battery plant workers (Cooper and Gaffey, 1975). The authors
reported (see Table 12-16) that total mortality from cancer was higher in lead smelter workers
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than in a control population in two ways: (1) the difference between observed and expected
values for the types of malignancies reported; and (2) the standardized mortality ratio, which
indicates a greater than "normal" response if it is in excess of 100 percent. These studies
report not only an excess of all forms of cancer in smelter workers but also a greater level
of cancer in the respiratory and digestive systems in both battery plant and smelter workers.
The incidence of urinary system cancer was also elevated in the smelter workers (but not in
the battery plant workers), although the number of individuals who died from this neoplasm was
very small. As the table indicates, death from neoplasm at other sites was also elevated com-
pared with a normal population, but these results were not discussed in the report. Kang et
al. (1S80) examined the Cooper and Gaffey (1975) report and noted an error in the statistical
equation used to assess the significance of excess cancer mortality. Table 12-17, from Kang
et al., 1980, shows results based on a corrected form of the statistical equation used by
Cooper and Gaffy; it also employed another statistical test claimed to be more appropriate.
Statistical significance was observed in every category listed with the exception of battery
plant workers, v/hose deaths from all forms of neoplasia were not different from a control
population.
TABLE 12-16. EXPECTED AND OBSERVED DEATHS FOR MALIGNANT NEOPLASMS
JAN. 1, 1947 - DEC. 31, 1979 FOR LEAD SMELTER AND BATTERY PLANT WORKERS
Causes.of Death
Smelters
Battery plant
(ICDT Code)
Obs
Exp
SMR*
Obs
Exp
SMR+
All malignant neoplasms (140-205)
69
54.95
133
186
180.34
111
Buccal cavity & pharynx (140-248)
0
1.89
--
6
6.02
107
Digestive organs peritoneum (150-159)
25
17.63
150
70
61.48
123
Respiratory system (160-164)
22
15.76
148
61
49. 51
132
Genital organs (170-179)
4
4.15
101
8
18.57
46
Urinary organs (180-181)
5
2.95
179
5
10.33
52
Leukemia (204)
2
2.40
88
6
7.30
88
Lymphosarcoma lymphatic and
hematopoietic (200-203, 205)
3
3.46
92
7
9.74
77
Other sites
8
6.71
126
23
17.39
142
^International Classification of Diseases.
Correction of +5.55% applied for 18 missing death certificates.
+Correction of +7.52% applied for 71 missing death certificates.
Source: Cooper and Gaffey (1975).
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TABLE 12-17. EXPECTED AND OBSERVED DEATHS RESULTING FROM SPECIFIED MALIGNANT NEOPLASMS
FOR LEAD SMELTER AND BATTERY PLANT WORKERS AND LEVELS OF SIGNIFICANCE BY
TYPE OF STATISTICAL ANALYSIS ACCORDING TO ONE-TAILED TESTS
Probability
Causestof death Number of deaths This Cooper
(ICD code) Ob- Ex- SMR* Pois- anal- and
served pected son** ysis*** Gaffey****
Lead smelter workers:
All malignant neoplasms
(140-205)
Cancer of the digestive organs
peritoneum (250-159)
Cancer of the respiratory system
(160-164)
Battery plant workers:
All malignant neoplasms
(140-205)
Cancer of the digestive organs,
peritoneum (150-159)
Cancer of the respiratory system
(160-164)
^International Classification of Diseases.
*SMR values were corrected by Cooper and Gaffey for missing death certificates under the
assumption that distribution of causes of death was the same in missing certificates as in
those that were obtained.
AA0bserved deaths were recalculated as follows: adjusted observed deaths = (given SMR/100) x
expected deaths.
***Given z = (SMR - 100) v'expected/100.
*A**Given z = (SMR - 100)/Vl00 x SMR/expected.
Source: Kang et al. (1980).
Cooper and Gaffey (1975) did not discuss types of lead compounds that these workers may
have been exposed to in smelting operations, but workers thus employed likely ingested or
inhaled oxides and sulfides of lead. Since these and other lead compounds produced in the in-
dustrial setting are not readily soluble in water it could be that the cancers arising in res-
piratory or gastrointestinal systems were caused by exposure to water-insoluble lead com-
pounds. Although the Cooper and Gaffey (1975) study had a large sample (7032), only 2275 of
the workers (32.4 percent) were employed when plants monitored urinary lead. Urinary lead
values were available for only 9.7 percent of the 1356 deceased employees on whom the cancer
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69 54.95
25 17.63
22 15.76
186 180.34
70 61.48
61 49.51
133 <0.02
150 <0.03
148 <0.05
111 >0.05
123 <0.05
132 <0.03
<0.01 <0.02
<0.02 <0.05
<0.03 >0.05
>0.05 >0.05
<0.04 >0.05
<0.02 <0.03
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mortality data were based. Only 23 (2 percent) of the 1356 decedents had blood lead levels
measured. Cooper and Gaffey (1975) did report some average urinary and blood lead levels,
where 10 or more urine or at least three blood samples were taken (viz., battery plant
workers: urine lead = 129 pg/1, blood lead = 67 |jg/d1; smelter workers: urine lead = 73
pg/1, blood lead = 79.7 yg/dl). Cooper (1976) noted that these workers were potentially
exposed to other materials, including arsenic, cadmium, and sulfur dioxide, although no data
on such exposures were reported. In these and other epidemiological studies in which selec-
tion of subjects for monitoring exposure to an agent such as lead is left to company discre-
tion, it is possible that individual subjects are selected primarily on the basis of obvious
signs of lead exposure, while other individuals who show no symptoms of lead poisoning would
not be monitored (Cooper and Gaffey, 1975). It is also not clear from these studies when the
lead levels were measured, although the timing of measurement would make little difference
since no attempt was made to match an individual's lead exposure to any disease process.
In a follow-up study of the same population of workers, Cooper (1981) concluded that lead
had no significant role in the induction of neoplasia. However, he did report standardized
mortality ratios (SMRs) of 149 percent and 125 percent for all types of malignant neoplasms in
lead battery plant workers with < 10 and > 10 years of employment, respectively. SMR is a
percentage value that is based upon comparison of an exposed population relative to a control
population. If the value exceeds 100 percent, the incidence of death is greater than normal
but not necessarily statistically significant. In battery workers employed for 10 years or
•more there was an unusually high incidence of cancer listed as "other site" tumors (SMR = 229
percent; expected = 4.85, observed = 16). Respiratory cancers were elevated in the battery
plant workers employed for less than 10 years (SMR - 172 percent). Similarly, in workers in-
volved with lead production facilities for more than 10 years the SMR was 151 percent. Again,
in the absence of good lead exposure documentation, it is difficult to assess the contribution
of lead to the observed results. Cooper (1981) suggested that the excess of respiratory
cancers could have been due to a lack of correction for smoking histories.
A recent study (McMichael and Johnson, 1982) examined the historical incidence of cancers
in a population of smelter workers diagnosed as having lead poisoning. The incidence of can-
cer in a relatively small group of 241 workers was compared with 695 deceased employees from
the same company. The control group had been employed during approximately the same period
and was asserted to be free from lead exposure, although there were no data to indicate lead
levels in either the control or the experimental group. Based upon diagnoses of lead poison-
ing made in the 1920s and 1930s for a majority of the deaths, the authors concluded that there
was a considerably lower incidence of cancer in lead-poisoned workers. However, there is no
indication of how lead poisoning was diagnosed. It is difficult to draw any conclusions from
this study with regard to the role of lead in human neoplasia.
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Evaluation of the ability of lead to induce human neoplasia must await further epidemio-
logical studies in which other factors that may contribute to the observed effects are well
controlled for and the disease process is assessed in individuals with well documented expo-
sure histories. Little can now be reliably concluded from available epidemiological studies.
12.7.2.2 Induction of Tumors in Experimental Animals. As discussed in the preceding sections
it is difficult to obtain conclusive evidence of the carcinogenic potential of an agent using
only epidemiological studies. Experiments testing the ability of lead to cause cancer in
experimental animals are an essential aspect of understanding its oncogenicity in humans.
However, a proper lifetime animal feeding study to assess the carcinogenic potential of lead
following National Cancer Institute guidelines (Sontag et al., 1976) has not been conducted.
The cost of such studies exceed $1 million and consequently are limited only to those agents
in which sufficient evidence based upon i_n vitro or epidemiological studies warrants such an
undertaking. The literature on lead carcinogenesis contains many smaller studies where only
one or two dcses were employed and where toxicological monitoring of experimental animals ex-
posed to lead was generally absent. Some of these studies are summarized in Table 12-18.
Most mainly serve to illustrate that numerous different laboratories have induced renal tumors
in rats by feeding them diets containing 0.1 percent or 1.0 percent lead acetate. In some
cases, other lead formulations were tested, but the dosage selection was not based upon lethal
dose values. In most cases, only one dose level was used. Another problem with many of these
studies was that the actual concentrations of lead administered and internal body burdens
achieved were not measured. Some of these studies are discussed very briefly; others are
omitted entirely because they contribute little to our understanding of lead carcinogenesis.
Administration of 1.0 percent lead acetate (10,000 ppm) resulted in kidney damage and a
high incidence of mortality in most of the studies in Table 12-18. However, kidney tumors
were also evident at lower dosages (e.g., 0.1 percent lead acetate in the diet), which pro-
duced less mortality among the test animals. As discussed in Section 12.5, renal damage is
one of the primary toxic effects of lead. At 0.1 percent lead acetate (1000 ppm) in the diet,
the concentration of lead measured in the kidney was 30 pg/g while 1 percent lead acetate
resulted in 300 pg/g of lead in the kidneys of necropsied animals (Azar et al., 1973). In
most of the studies with rats fed 0.1 or 1.0 ,percent lead in the diet, the incidence of kidney
tumors increased between the lower and higher dosage, suggesting a relationship between the
deposition of lead in the kidney and the carcinogenic response. Renal tumors were also
induced in mice at the 0.1 percent oral dosage of lead subacetate but not in hamsters that
were similarly exposed to this agent (Table 12-18).
Other lead compounds have also been tested in experimental animals, but in these studies
only one or two dosages (generally quite high) were employed, making it difficult to assess
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TABLE 12-18. EXAMPLES OF STUDIES ON THE INCIDENCE OF TUMORS IN EXPERIMENTAL
ANIMALS EXPOSED TO LEAD COMPOUNDS
Species Pb compound Dose and mode
Incidence (and type) of
neoplasms
Reference
Rat
Rat
Rat
Mouse
Rat
Rat
Rat
Mouse
Rat
Hamster
Mouse
Rat
Rat
Pb phosphate
Pb acetate
Pb
subacetate
Pb
naphthenate
Pb phosphate
Pb
subacetate
Pb
subacetate
Tetraethyl
lead in
tri capryli n
Pb acetate
Pb
subacetate
Pb
subacetate
Pb nitrate
Pb acetate
120-680 mg
(total dose s.c.)
1% (in diet)
0.1% and
1.0% (in diet)
20% in benzene
(dermal 1-2
times weekly)
1.3 g (total
dosage s.c.)
0.5 - 1%
(in diet)
1% (in diet)
0.6 mg (s.c.)
4 doses between
birth and 21 days
3 mg/day for
2 months;
4 mg/day for
16 months (p.o. )
1.0% (in
0.5% diet)
0.1% and
1.0% (in diet)
25 g/1 in
drinking water
3 mg/day (p.c.)
19/29 (renal tumors)
15/16 (kidney tumors)
14/16 (renal carcinomas)
11/32 (renal tumors)
13/24 (renal tumors)
5/59 (renal neoplasms)
(no control with
benzene)
29/80 (renal tumors)
14/24 (renal tumors)
31/40 (renal tumors)
5/41 (lymphomas)
in females, 1/26 in
males, and 1/39 in
controls
72/126 (renal tumors)
23/94 males (testicular
[Leydig cell] tumors)
No significant incidence
of renal neoplasms
7/25 (renal carcinomas)
at 0.1%
Substantial death at 1.0%
No significant incidence
of tumors
89/94 (renal, pituitary,
cerebral gliomas,
adrenal, thyroid, pro-
static, mammary tumors)
Zollinger
(1953)
Boyland et
al. (1962)
Van Esch
et al. (1962)
Baldwin et
al. (1964)
Balo et al.
(1965)
Hass et al.
(1967)
Mao and
Molnar (1967)
Epstein and
Mantel (1968)
Zawirska and
Medras (1968)
Van Esch and
Kroes (1969)
Van Esch and
Kroes (1969)
Schroeder et
al. (1970)
Zawi rska
and
Medras, 1972
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TABLE 12-18. (continued)
Species
Pb
Compound
Dose and mode
Incidence (and type) of
neoplasms
Reference
Rat
Pb
acetate
0, 10, 50, 100,
1000, 2000 ppm
(in diet) for
2 yr
No tumors 0-100 ppm;
5/50 (renal tumors) at
500 ppm; 10/20 at 1000 ppm;
16/20 males, 7/20 females
at 2000 ppm
Azar et al.
(1973)
Hamster
Pb
oxi de
10 intratracheal
admi ni strati ons
(1 mg)
0/30 without benzopyrene,
12/30 with benzopyrene
(lung cancers)
Kobayashi
and
Okamoto (1974)
Rat
Pb
powder
10 mg orally 2 times
each month
10 mg/monthly
for 9 months;
then 3 monthly
injections of 5 mg
5/47 (1 lymphoma,
4 leukemias)
1/50 (fibrosarcoma)
Furst et al.
(1976)
the potential carcinogenic activity of lead compounds at relatively nontoxic concentrations.
It is also difficult to assess the true toxicity caused by these agents, since properly
designed toxicity studies were generally not performed in parallel with these cancer studies.
As shown in Table 12-18, lead nitrate produced no tumors in rats when given at very low
concentrations, but lead phosphate administered subcutaneously at relatively high levels in-
duced a high incidence of renal tumors in two studies. Lead powder administered orally
resulted in lymphomas and leukemia; when given intramuscularly only one fibrosarcoma was pro-
duced in 50 animals. Lead naphthenate applied as a 20 percent solution in benzene two times
each week for 12 months resulted in the development of four adenomas and one renal carcinoma
in a group of 50 mice (Baldwin et al. , 1964). However, in this study control mice were not
painted with benzene. Tetraethyl lead at 0.6 mg given in four divided doses between birth and
21 days to female mice resulted in 5/36 surviving animals developing lymphomas while 1/26
males treated similarly and 1/39 controls developed lymphomas (Epstein and Mantel, 1968).
Lead subacetate has also been tested in the mouse lung adenoma bioassay (Stoner et al.,
1976). This assay measures the incidence of nodules forming in the lung of strain A/Strong
mice following parenteral administration of various test agents. Nodule formation in the lung
does not actually represent the induction of lung cancer but merely serves as a general meas-
ure of carcinogenic potency independent of lung tissue (Stoner et al., 1976). Lead subacetate
was administered to mice at 150, 75, and 30 mg (total dose), which represented the maximum
CPB12/A 12-182 9/20/83
10*7^
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PRELIMINARY DRAFT
tolerated dose (MTD), 1/2 MTD,' and 1/5 MTD, respectively, over a 30-week period using 15 sepa-
rate i.p. injections (Stoner et al., 1976), Survivals at the three doses were 15/20 (MTD),
12/20 (1/2 MTD), and 17/20 (1/5 MTD), respectively, with 11/15, 5/12, and 6/17 survivors
having lung nodules. Only at the highest doses was the incidence of nodules greater than in
the untreated 1 or 2 highest groups. However, these authors concluded that on a molar-dose
basis lead subacetate was the most potent of all the metallic compounds examined. Injection
of 0.13 mmol/kg lead subacetate was required to produce one lung tumor per mouse, indicating
that this compound was about three times more potent than urethane (at 0.5 mmol/kg) and
approximately 10 times more potent than nickelous acetate (at 1.15 mmol/kg). The mouse lung
adenoma bioassay has been one of the most utilized systems for examining carcinogenic activity
in experimental animals and is well recognized as a highly accurate test system for assessing
potential carcinogenic hazard (Stoner et al., 1976). Lead oxide combined with benzopyrene
administered intratracheally resulted in 11 adenomas and 1 adenocarcinoma in a group of 15
hamsters, while no lung neoplasias were observed in groups receiving benzopyrene or lead oxide
alone (Kobayashi and Okamoto, 1974).
Administration of lead acetate to rats has been reported to produce other types of
tumors, e.g., testicular, adrenal, thyroid, pituitary, prostate, lung (Zawirska antf Medras,
1968), and cerebral gliomas (Oyasu et al. , 1970). However, in other animal species, such as
dogs (Azar et al. , 1973; Fouts and Page, 1942) and hamsters (Van Esch and Kroes, 1969), lead
acetate induced either no tumors or only kidney tumors (Table 12~18).
The above studies seem to implicate some lead compounds as carcinogens in experimental
animals but were not designed to address the question of lead carcinogenesis in a definitive
manner. In contrast, a study by Azar et al. (1973) examined the oncogenic potential of lead
acetate at a number of doses and in addition monitored a number of toxicological parameters in
the experimental animals. Azar et al. (1973) gave 0, 10, 50, 100, 1000 and 2000 ppm dose
levels of lead (as lead acetate) to rats during a two-year feeding study. Fifty rats of each
sex were utilized at doses of 10 to 500 ppm, while 100 animals of each sex were used as con-
trols. After the study was under way for a few months, a second 2-year feeding study was ini-
tiated using 20 animals of each sex in groups given doses of 0, 1000, or 2000 ppm. The study
also included four male and four female beagle dogs at each dosage of lead ranging from 0 to
500 ppm in a 2-year feeding study. During this study, the clinical appearance and behavior of
the animals were observed, and food consumption, growth, and mortality were recorded. Blood,
urine, fecal, and tissue lead analyses were done periodically using atomic absorption spectro-
photometry. A complete blood analysis was done periodically, including blood count, hemo-
globin, hematocrit, stippled cell count, prothrombin time, alkaline phosphatase, urea nitro-
gen, glutamic-pyruvate transaminase, and albumin-to-globulin ratio. The activity of the
enzyme alpha-aminolevulinic acid dehydrase (ALA-D) in the blood and the excretion of its sub-
CPB12/A 12-183 9/20/83
'1080*:
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PRELIMINARY DRAFT
strate, delta-aminolevulinic acid (6-ALA) in the urine were also determined. A thorough na-
cropsy, including both gross and histologic examination, was performed on all animals. Repro-
duction was also assessed (see Section 12.6).
Table 12-19 depicts the mortality and incidence of kidney tumors reported by Azar et al.
(1973). At 500 ppm (0.05 percent) and above, male rats developed a significant number of re-
nal tumors. Female rats did not develop tumors except when fed 2000 ppm lead acatate. Two
out of four male dogs fed 500 ppm developed a slight degree of cytomegaly in the proximal con-
voluted tubule but did not develop any kidney tumors. The number of stippled red blood cells
increased at 10 ppm in the rats but not until 500 ppm in the dogs. ALA-D was decreased at 50
ppm in the rats but not until 100 ppm in the dogs. Hemoglobin and hematocrit, however, were
not depressed in the rats until they received a dose of 1000 ppm lead. These results illus-
trate that the induction of kidney tumors coincides with moderate to severe toxicological
doses of lead acetate, for it was at 500-1000 ppm lead in the diet that s significant
increase in mortality occurred (see Table 12-19). At 1000 and 2000 ppm lead, 21-day-old wean-
ling rats showed no tumors but did show histological changes in the kidney comparable to those
seen in adults receiving 500 ppm or more lead in their diet. Also of interest from the Azar
et al. (1973) study is the direct correlation obtained in dogs between blood lead level and
kidney lead concentrations. A dietary lead level of 500 ppm produced a blood lead concentra-
tion of 80 pg/dl , which corresponds to a level at which humans often show clinical signs of
lead poisoning (see Section 12.4.1). The kidney lead concentration corresponding to this
blood lead level was 2.5 (jg/g (wet weight), while at 50 pg/dl in blood the kidney lead levels
were 1.5 mq/9- Presumably blood and kidney lead were determined at about the same time,
although this was not clear from the report. At this level of lead, kidney tumors were in-
duced. in the rats but not the dogs. However, it is apparent from the above differences in
hematological parameters that dogs tolerate higher levels of lead than rats. As shown in
Figure 12-5, the induction of renal tumors by lead acetate was linearly proportional to the
dietary levels of lead fed to male rats. It may be concluded, therefore, that chronic lead
exposure of rats producing blood lead levels comparable to those at which clinical signs of
toxicity would be evident in humans results in a significant elevation in the incidence of
kidney tumors.
Animal carcinogenesis studies conducted with lead and its compounds are numerous; how-
ever, with the exception of the study by Azar et al., (1973) they do not provide much useful
information. Most of the studies shown in Table 12-18 were conducted with only one lead com-
pound in one animal species, the rat. In cases where other lead compounds were tested or where
other animal species were used, only a single high dosage level was administered, and para-
meters of toxicity such as those monitored in the Azar et al. (1973) study were not measured.
Although it is clear from these studies as a whole that lead is a carcinogen in experimental
CPB12/A 12-184 9/20/03
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TABLE 12-19. MORTALITY AND KIDNEY TUMORS IN RATS FED LEAD ACETATE FOR TWO YEARS
Nominal (actual)9
h
concentration in
No. of rats
% Mortal
i ty
% Kidney tumors
ppm of Pb in diet
of each sex
Mai e
Female
Mai e
Female
• 0 (5)
100
37
34
0
0
10 (18)
50
36
30
0
0
50 (62)
50
36
28
0
0
100 (141)
50
36
28
0
0
500 (548)
50
52
36
10
0
0 (3)
20
50
35
0
0
1000 (1130)
20
50
50
50
0
2000 (2102)
20
80
35
80
35
aM,easured concentration of lead in diet.
^Includes rats that either died or were sacrificed i_n extremis.
Source: Azar et al. (1973).
animals, until more investigations such as that of Azar et al. (1973) are conducted it is
difficult to determine the relative carcinogenic potency of lead. There remains a need to
test thoroughly the carcinogenic activity of lead compounds in experimental animals. These
tests should include several modes of administration, many dosages spanning non-toxic as well
as toxic levels, and several different lead compounds or at least a comparison of a relatively
water-soluble form such as lead acetate with a less soluble form such as lead oxide.
12.7.2.3 Cell Transformation. Although cell transformation is an i_n vitro experimental
system, its end point is a neoplastic change. There are two types of cell transformation
assays: (1) those employing continuous cell lines, and (2) those employing cell cultures pre-
pared from embryonic tissue. Use of continuous cell lines has the advantage of ease in prepa-
ration of the cell cultures, but these cells generally have some properties of a cancer cell.
The absence of a few characteristics of a cancer cell in these continuous cell lines allows
for an assay of cell transforming activity. End points include morphological transformation
(ordered cell growth to disordered cell growth), ability to form colonies in soft agar-con-
taining medium (a property characteristic of cancer cells), and ability of cells to form
tumors when inoculated into experimental animals. Assays that utilize freshly isolated embry-
onic cells are generally preferred to those that use cell lines, because embryonic cells have
not yet acquired any of the characteristics of a transformed cell. The cell transformation
assay system has been utilized to examine the potential carcinogenic activity of a number of
chemical agents, and the results seem to agree generally with the results of carcinogenesis
CPB12/A 12-185 9/20/83
10S2<
-------
99
c
m
u
Si
a
0
C
O
90
80
50
DC
Z
10
0.1 0.2 0.5 1 2 5
DIETARY LEAD, 103 ppm
Figure 12-5. Probit plot of incidence of renal tumors in male rats.
Source; U.S. Environmental Protection Agency 11980) based on
Azar et al. (1973).
CPB12/A 12-186 9/20/83
1083'-
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PRELIMINARY DRAFT
tests using experimental animals. Cell transformation assays can be made quantitative by
assessing the percentage of surviving colonies exhibiting morphological transformation.
Verification of a neoplastic change can be accomplished by cloning these cells and testing
their ability to form tumors in animals.
Lead acetate has been shown to induce morphological transformation in Syrian hamster em-
bryo cells following a continuous exposure to 1 or 2.5 |jg/m1 of lead in culture medium for
nine days (Dipaolo et al., 1978). The incidence of transformation increased from 0 percent in
untreated cells to 2.0 and 6.0 percent of the surviving cells, respectively, following treat-
ment with lead acetate. Morphologically transformed cells were capable of forming fibrosarco-
mas when cloned and administered to "nude" mice and Syrian hamsters, while no tumor growth
resulted from similar inoculation with untreated cells (Dipaolo et al . , 1978). In the same
study lead acetate was shown to enhance the incidence of simian adenovirus (SA-7) induction of
Syrian hamster embryo cell transformation. Lead acetate also caused significant enhancement
(~2-3 fold) at 100 and 200 pg/ml following three hours of exposure. In another study (Casto
et al., 1979), lead oxide also enhanced SA-7 transformation of Syrian hamster embryo cells
almost 4 fold at 50 pM following three hours of exposure (Casto et al., 1979). The signifi-
cance of enhanced virally induced carcinogenesis in relationship to the carcinogenic potential
of an agent is not well understood.
Morphological transformation induced by lead acetate was correlated with the ability of
the transformed cells to form tumors in appropriate hosts (see above), indicating that a truly
neoplastic change occurred in tissue culture. The induction of neoplastic transformation by
lead acetate suggests that this agent is potentially carcinogenic at the cellular level. How-
ever, with j_n vitro systems such as the cell transformation assay it is essential to compare
the effects of other, similar types of carcinogenic agents in order to evaluate the response
and to determine the reliability of the assay. The incidence of transformation obtained with
lead acetate was greater than the incidence following similar exposure to NiCl2, but less than
that produced by CaCr04 (Heck and Costa, 1982a). Both nickel and chromium have been impli-
cated in the etiology of human cancer (Costa, 1980). These results thus suggest that lead
acetate has effects similar to those caused by other metal carcinogens. In particular, the
ability of lead acetate to induce neoplastic transformation in cells in a concentration-depen-
dent manner is highly suggestive of potential carcinogenic activity. It should also be noted
that lead acetate induced these transformations at concentrations that decreased cell survival
by only 27 percent (Heck and Costa, 1982a). Further studies from other laboratories utilizing
the cell transformation assay and other lead compounds are needed.
CPB12/A 12-187 9/20/83
i If ft 4^
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PRELIMINARY DRAFT
12.7.3 Genotoxicity of Lead
Since cancer is known to be a disease of altered gene expression, numerous studies have
evaluated changes in DNA consequent to exposure to suspected carcinogenic agents. The general
response associated with such alterations in regulation of DNA function has been called geno-
toxicity. Various assay systems developed to examine specific changes in DNA structure and
function caused by carcinogenic agents include assays that evaluate chromosomal aberrations,
sister chromatid exchange, mutagenicity, and functional and structural features of DNA meta-
bolism. Lead effects on these parameters are discussed below.
12.7.3.1 Chromosomal Aberrations. Two approaches have been used in the analysis of effects
of lead on chromosomal structure. The first approach involves culturing lymphocytes either
from humans exposed to lead or from experimental animals given a certain dosage of lead. The
second approach involves exposing cultured lymphocytes directly to lead. For present pur-
poses, emphasis will not be placed on the type of chromosomal aberration induced, since most
of the available studies do not appear to associate any specific type of chromosomal aberra-
tion with lead exposure. It should be noted, however, that moderate aberrations include gaps
and fragments, whereas severe aberrations include dicentric rings, translocations, and ex-
changes. Little is known of the significance of chromosomal aberrations in relationship to
cancer, except that in a number of instances genetic diseases associated with chromosomal
aberrations often enhance the probability of neoplastic disease. However, implicit in a mor-
phologically distinct change in genetic structure is the possibility of an alteration in gene
expression that represents a salient feature of neoplastic disease.
Contradictory reports exist regarding lead effects in inducing chromosomal aberrations
(Tables 12-20 and 12-21). These studies have been grouped in two separate tables based upon
their conclusions. Those studies reporting a positive effect of lead on chromosomal aberra-
tions are indexed in Table 12-20, whereas studies reporting no association between lead expo-
sure and chromosomal aberrations are indexed in Table 12-21. Unfortunately, these studies are
difficult to evaluate fully because of many unknown variables (e.g., absence of sufficient
evidence of lead intoxication, no dose-response relationsiiip, and absence of information
regarding lymphocyte culture time). To illustrate, in a number of the studies where lead ex-
posure correlated with an increased incidence of chromosomal aberrations (Table 12-20), lym-
phocytes were cultured for 72 hours. Most cytogenetic studies have been conducted with a
maximum culture time of 48 hours to avoid high background levels of chromosomal aberrations
due to multiple cell divisions during culture. Therefore, it is possible that the positive
effects of lead on chromosomal aberrations may have been due to the longer culture period.
Nonetheless, it is evident that in the negative studies the blood lead concentration was gen-
erally lower than in the studies reporting a positive effect of lead on chromosomal aberra-
tions, although in many of the latter instances blood lead levels indicated severe exposure.
CPB12/A
12-188
9/20/83
-------
TABLE 12-20. CYTOGENETIC INVESTIGATIONS OF CELLS FROM INDIVIDUALS EXPOSED TO LEAD: POSITIVE STUDIES
Number of Cell Blood (pg/dl)
exposed Number of culture or urine
subjects controls time (hrs.)
I
oo
vx>
11 (before
and after ex-
posure)
48
72
68-70
155-720
(urine)
11.6-97.4
mean, 37.7
(blood)
34.-64.
(blood)
Workers in a zinc
plant, exposed to
fumes & dust of
cadmium, zinc &
lead
Blast-furnace work-
ers, metal grin-
ders, scrap metal
processers
Workers in a
lead-acid battery
plant and a lead
foundry
Gaps, fragments,
exchanges, dicen-
trics, rings
"Structural ab-
normalities,"
gaps, breaks,
hyperploidy
Gaps, breaks,
fragments
Thought to be caused
by lead, not cadmium
or zinc
No correlation with
6-ALA excretion or
blood lead levels
No correlation
with ALA-D activity
in red eel Is
Deknudt et
al. (1973)
Schwanitz et
al. (1975)
Forni et al.
(1976)
"O
ja
z
J»
TO
-c
TO
J»
44
15
72
30.-75.
(blood)
Individuals in a
lead oxide fac-
tory
Chromatid and
chromosome
aberrations
Positive correlation
with length of expo-
sure
Garza-Chapa
et al. (1977)
23
20
48
44.-95.
(not given)
Lead-acid battery
me Iters, tin workers
Dicentrics,
rings, fragments
Factors other than
lead exposure may be
required for severe
aberrations
Deknudt et al.
(1977b)
20
26 (4 low,
16 medium,
6 high ex-
posure)
20
not
given
46-48
72
53.-100.
(blood)
22.5-65.
(blood)
Ceramic, lead &
battery workers
Smelter workers
Breaks, frag-
ments
Gaps, chroma-
tid and chro-
mosome aberra-
tions
Positive correlation
with blood lead levels
Positive correlation
with blood lead levels
Sarto et al.
(1978)
Nordenson et al.
(1978)
12
18
48-72
24-49
(blood)
Electrical storage
battery workers
Chromatid and
chromosome aberra-
tions
Forni et al. (1980)
Source:
International Agency for Research on Cancer (1980), with modifications.
-------
TABLE 12-21.
CYTOGENETIC INVESTIGATIONS OF CELLS FROM INDIVIDUALS EXPOSED TO LEAD: NEGATIVE STUDIES
Number of
exposed subjects
Number of
controls
Cell culture
time (hrs.)
Blood lead
level (pg/dl)
Exposed subjects
References
&
M
1
GO
VO
*
1 \
29
32
35
24
20
20
35
15
46-48
46-48
45-48
48
30
20
72
48
Not given, stated
to be 20-30%
higher than controls
Range not given;
highest level was
590 mg/1 [sic]
Control, <4.; ex-
posed, 4. - >12.
19.3 (lead)
0.4 (cadmium)
40.0 ±
weeks
Control,
exposed,
5.0, 7
11.8-13.2;
29-33
Policemen "permanently in
contact with high levels of
automotive exhaust"
Workers in lead manufacturing
industry; 3 had acute lead
intoxication
Shipyard workers employed as
"burners" cutting metal struc-
tures on ships
Mixed exposure to zinc, lead,
and cadmium in a zinc-smelting
plant; significant increase in
chromatid breaks and exchanges.
Authors suggest that cadmium
was the- major cause of this
damage
Volunteers ingested capsules
containing lead acetate
Children living near a lead
smelter
Bauchinger et a I.
(1972)
Schmid et al. (1972)
O'Riordan and Evans
(1974)
8auchinger et al.
(1976)
Bulsma & De France
(1976)
Bauchinger et al.
(1977)
3>
JO
-c
CD
JO
3>
Source: International Agency for Research on Cancer (1980).
-------
PRELIMINARY DRAFT
In some of these positive studies there was a correlation in the incidence of gaps, fragments,
chromatid exchanges, and other chromosomal aberrations with blood lead levels (Sarto et al.,
1978; Nordenson et al. , 1978). However, as indicated in Table 12-20, in other studies there
were no direct correlations between indices of lead exposure (i.e., 6-ALA excretion) and
2 +
numbers of chromosomal aberrations. Nutritional factors such as Ca levels i_n vivo or in
vitro are also important since it is possible that the effects of lead on cells may be antag-
onized by Ca (Mahaffey, 1983). As is usually the case in studies of human populations ex-
posed to lead, exposure to other metals (zinc, cadmium, and copper) that may produce chromoso-
mal aberrations was prevalent. None of the studies attempted to determine the specific lead
compound that the individuals were exposed to.
In a more recent study by Forni et al. (1980), 18 healthy females occupationally exposed
to lead were evaluated for chromosomal aberrations in their lymphocytes cultured for 48 or 72
hours. There were more aberrations at the 72-hour culture time compared with the 48-hour cul-
ture period in both control and lead-exposed groups, but this difference was not statistically
significant. However, statistically significant differences from the 72-hour controls were
noted in the 72-hour culture obtained from the lead exposed group. These results demonstrate
that the extended 72-hour culture time results in increased chromosomal aberrations in the
control lymphocytes and that the longer culture time was apparently necessary to detect the
effects of lead on chromosomal structure. However, the blood lead levels in the exposed fe-
males ranged from 24 to 59 pg/dl , while control females had blood lead levels ranging from 22
to 37 |jg/d1. Thus, there was a marginal effect of lead on chromosomal aberration, but the two
groups may not have been sufficiently different in their lead exposure to show clear differ-
ences in frequency of chromosomal aberrations.
Some studies have also been conducted on the direct effect of soluble lead salts on cul-
tured human lymphocytes. In a study by Beek and Obe (1974), longer (72-hr) culture time was
used and lead acetate was found to induce chromosomal aberrations at 100 pM. Lead acetate had
no effect on chromatid aberrations induced with X-rays or alkylating agents (Beek and Obe,
1975). In another study (Deknudt and Deminatti, 1978), lead acetate at 1 and 0.1 mM caused
minimal chromosomal aberrations. Both cadmium chloride (CdCl2) and zinc chloride (ZnCl2) were
more potent than lead acetate in causing these changes; however, both CdCl2 and ZnCl2 also
displayed greater toxicity than lead acetate.
Chromosomal aberrations have been demonstrated in lymphocytes from cynomolgus monkeys
treated chronically with lead acetate (6 mg/day, 6 days/week for 16 months), particularly when
they were kept on a low calcium diet (Deknudt et al., 1977a). These aberrations accompanying a
2 +
low Ca diet were characterized by the authors as severe (chromatid exchanges, dispiraliza-
tion, translocations, rings, and polycentric chromosomes). Similar results were observed in
mice (Deknudt and Gerber, 1979). The effect of low calcium on chromosomal aberrations induced
CPB12/A 12-191 9/20/83
iOSSv
-------
PRELIMINARY DRAFT
2 + 2 +
by lead is most likely due to interaction of Ca and Pb at the level of the chromosome
(Mahaffey, 1983). Leonard and his coworkers found no effect of lead on the incidence of
chromosomal aberrations in accidentally intoxicated cattle (Leonard et al., 1974) or in mice
given 1 gram of lead per liter of drinking water for 9 months (Leonard et al., 1973). How-
ever, Muro and Goyer (1969) found gaps and chromatid aberrations in bone marrow cells cultured
for four days after isolation from mice that had been maintained on 1 percent dietary lead
acetate for two weeks. Chromosomal loss has been reported (Ahlbert et al., 1972) in Droso-
phila exposed to triethyl lead (4 mg/1), but inorganic lead had no effect (Ramel, 1973). Lead
acetate has also been shown to induce chromosomal aberrations in cultured cells other than
lymphocytesviz. Chinese hamster ovary cells (Bauchinger and Schmict, 1972).
These studies demonstrate that under certain conditions lead compounds are capable of in-
ducing chromosomal aberrations _i_n vivo and in tissue cultures. The ability of lead to induce
these chromosomal changes appears to be concentration-dependent and highly influenced by cal-
cium levels. In lymphocytes isolated from patients or experimental animals, relatively long
(72-hr) culture conditions are required for the abnormalities to be expressed.
Sister chromatid exchange represents the normal movement of DNA in the genome. The sister
chromatid exchange assay offers a very sensitive probe for the effects of genotoxic compounds
on DNA rearrangement, as a number of chemicals with carcinogenic activity are capable of in-
creasing these exchanges (Sandberg, 1982). The effect of lead on such movement has been exam-
ined in cultured lymphocytes (Beek and Obe, 1975), with no increase in exchanges observed at
lead acetate concentrations of 0.01 mM. However, one study with lead at one dose in one sys-
tem is not sufficient to rule out whether lead increases the incidence of these exchanges.
The ability of agents such as lead to cause abnormal rearrangements in the structure of
DNA, as revealed by the appearance of chromosomal aberrations, and sister chromatid exchanges
has become an important focus in carcinogenesis research. Current theories suggest that can-
cer may result from an abnormal expression of oncogenes (genes that code for protein products
associated with virally induced cancers). Numerous oncogenes are found in normal human DNA,
but the genes are regulated such that they are not expressed in an carcinogenic fashion.
Rearrangement of these DNA sequences within the genome can lead to oncogenic expression. Evi-
dence has been presented suggesting that chromosomal aberrations such as translocations are
associated with certain forms of cancer and with the movement of oncogenes in regions of the
DNA favoring their expression in cancer cells (Shen-Ong et al., 1982). By inducing aberra-
tions in chromosomal structure, lead may enhance the probability of an oncogenic event.
12.7.3.2 Lead Effects on Bacterial and Mammalian Mutagenesis Systems. Bacterial and mamma-
lian mutagenesis test systems examine the ability of chemical agents to induce changes in DNA
sequences of a specific gene product that is monitored by selection procedures. They measure
the potential of a chemical agent to produce a change in DNA, but this change is not likely to
CPB12/A 12-192 9/20/83
1069*=
-------
PRELIMINARY DRAFT
b» the same alteration in gene expression that occurs during oncogenesis. However, if an
agent affects the expression of a particular gene product that is being monitored, then it
could possibly affect other sequences which may result in cancer. Since many carcinogens are
also mutagens, it is useful to employ such systems to evaluate genotoxic effects of lead.
Use of bacterial systems for assaying metal genotcxicity must await further development
of bacterial strains that are appropriately responsive to known mutagenic metals (Rosenkranz
and Poirier, 1979; Simmon, 1979; Simmon et al., 1979; Nishioka, 1975; Nestmann et al., 1979).
Mammalian cell mutagenic systems that screen for specific alterations in a defined gene muta-
tion have not been useful in detecting mutagenic activity with known carcinogenic metals (Heck
and Costa, 1982b). In plants, however, chromosomal aberrations in root tips (Mukherji and
Maitra, 1976) and other mutagenic activity, such as chlorophyll mutations (Reddy and Vaidya-
nath, 1978), have been demonstrated with lead.
12.7.3.3 Lead Effects on Parameters of DMA Structure and Function. There are a number of
very sensitive techniques for examining the effect of metals on DNA structure and function in
intact cells. Although these techniques have not been extensively utilized with respect to
metal compounds, future research will probably be devoted to this area. Considerable work has
been done to understand the effects of metals on enzymes involved in DNA transcription.
Sirover artd Loeb (1976) examined effects of lead and other metal compounds upon the
fidelity of transcription of DNA by a viral DNA polymerase. High concentrations of metal ions
(in some cases in the millimolar range) were required to decrease the fidelity of transcrip-
tion, but there was a good correlation between metal ions that are carcinogenic or mutagenic
and their activity in decreasing the fidelity of transcription. This assay system measures
the ability of a metal ion to incorporate incorrect (non-homologous) bases using a defined
polynucleotide template. In an intact cell, this would cause the induction of a mutation if
the insertion of an incorrect base is phenotypically expressed. Since the interaction of
metal ions with cellular macromolecules is relatively unstable, misincorporation of a base
during semi-conservative DNA replication or during DNA repair synthesis following breakage of
DNA with a metal could- alter the base sequence of DNA in an intact cell. Lead at 4 mM was
among the metals listed as mutagenic or carcinogenic that caused a decrease in the fidelity of
transcription (Sirover and Loeb, 1976). Other metals active in decreasing fidelity included:
+ 2 + 2+ 2+ 2+ 3+ 2 + 2+ 2 +
Ag , Be , Cd , Co , Cr , Cr , Cu , Mn , and Ni . No change in fidelity was produced
3+ 2+ 2+ 3+ + + 2+ + 2+ 2+ ^ +
by Al , Ba , Ca , Fe , K , Rb , Mg , Mg , Se , Sr , and Zn . Metals that decreased
fidelity are metals also implicated as carcinogenic or mutagenic (Sirover and Loeb, 1976).
In a similar study, Hoffman and Niyogi (1977) demonstrated that lead chloride was the
2+ 2+ 2+ 2^.
most potent of 10 metals tested in inhibiting RNA synthesis (i.e., Pb > Cd > Co > Mn >
Li+ > Na+ > K+) for both types of templates tested, i.e., calf thymus DNA and T4 phage DNA.
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PRELIMINARY DRAFT
These results were explained in terms of the binding of these metal ions more to the bases
+¦ ^ +¦ + +
than to the phosphate groups of the DNA (i.e., Pb > Cd > Zn > Mn > Mg > Li = Na =
K+). Additionally, metal compounds sucn as lead chloride with carcinogenic o^ mutagenic
activity were found to stimulate mRNA chain initiation at 0.1 mM concentrations.
These well-conducted mechanistic studies provide evidence that lead can affect a molecu-
lar process associated with normal regulation of gene expression. Although far removed from
the intact cell situation, these effects suggest that lead may be genotoxic.
12.7.4 Summary and Conclusions
It is evident from studies reviewed above that, at relatively high concentrations, lead
displays some carcinogenic activity in experimental animals (e.g. the rat). An agent may act
as a carcinogen in two distinct ways: (1) as an initiator or (2) as a promoter (Weisburger
and Williams, 1980). By definition, an initiator must be able to interact with DNA to produce
a genetic alteration, whereas a promoter acts in a way that allows the expression of an
altered genetic change responsible for cancer. Since lead is capable of transforming cells
directly in culture and affecting DNA-to-DNA and DNA-to-RNA transcription, it may have some
initiating activity. Its ability to induce chromosomal aberrations is also indicative of
initiating activity. There are no studies that implicate or support a promotional activity of
lead; however, its similarity to Ca suggests that it may alter regulation of this cation in
processes (e.g., cell growth) related to promotion. Intranuclear lead inclusion bodies in the
kidney may pertain to lead's carcinogenic effects, since both the formation of these bodies
and the induction of tumors occur at relatively high doses of lead. The interaction of lead
with key non-histone chromosomal proteins in the nucleus to form the inclusion bodies or the
presence of inclusion bodies in the nucleus may alter genetic function, thus leading to cell
transformation. Obviously, elucidating the mechanism of lead carcinogenesis requires further
research efforts and only theories can be formulated regarding its oncogenic action at
present.
It is hard to draw clear conlusions concerning what role lead may play in the induction
of human neoplasia. Epidemiological studies of lead-exposed workers provide no definitive
findings. However, statistically significant elevations in respiratory tract and digestive
system cancer in workers exposed to lead and other agents warrant concern. Also, since lead
acetate can produce renal tumors in some experimental animals, it may be prudent to assume
that at least that lead compound may be carcinogenic in humans. However, this statement is
qualified by noting that lead has been observed to increase tumorogenesis rates in animals
only at relatively high concentrations, and therefore does not appear to be an extremely
potent carcinogen. hi vitro studies further support the genotoxic and carcinogenic role of
lead, but also indicate that lead is not extremely potent in these systems either.
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PRELIMINARY DRAFT
12.8 EFFECTS OF LEAD ON THE IMMUNE SYSTEM
12.8.1 Development and Organization of the Immune System
Component cells of the immune system arise from a pool of pluripotent stem cells in the
yolk sack and liver of the developing fetus and in the bone marrow and spleen of the adult.
5tem cell differentiation and maturation follows one of several lines to produce lymphocytes,
macrophages, and polymorphonuclear leukocytes. These cells have important roles in immunolog-
ical function and host defense.
The predominant lymphocyte class develops in the thymus, which is derived from the third
and fourth pharyngeal pouches at 9 weeks of gestation in man (day 9 in mice). In the thymus
microenvironment they acquire characteristics of thymus-derived lymphocytes (T-eel Is), then
migrate to peripheral thymic-dependent areas of the spleen and lymph nodes. T-cells are
easily distinguished from other lymphocytes by genetically defined cell surface markers that
allow them to be further subdivided into immunoregulatory amplifier cells (helper T-cells) and
suppressor T-cells that regulate immune responses. T-cells also participate directly as cyto-
lytic effector cells against virally infected host cells, malignant cells, and foreign tissues
as well as in delayed-type hypersensitivity (DTH) reactions where they elaborate lymphokines
that modulate the inflammatory response. T-cells are long-lived lymphocytes and are not read-
ily replaced. Thus, any loss or injury to T-cells may be detrimental to the host and result
in increased susceptibility to viral, fungal, bacterial, or parasitic diseases. Individuals
with acquired immune deficiency syndrome (AIDS) are examples of individuals with T-cell dys-
function. There is ample evidence that depletion by environmental agents of thymocytes or
stem cell progenitors during lymphoid organogenesis can produce permanent immunosuppression.
The second major lymphocyte class differentiates from a lymphoid stem-cell in a yet un-
defined site in man, which would correspond functionally to the Bursa of Fabricius in avian
species. In man, B-lymphocyte maturation and differentiation probably occur embryological ly
in gut-associated lymphoid tissue (GALT) and fetal liver, as well as adult spleen and bone
marrow. This is followed by the peripheral population of thymic-independent areas of spleen
and lymph nodes. Bone marrow-derived lymphocytes (B-cells), which mature independently of the
thymus, possess specific immunoglobulin receptors on their surfaces. The presence of cell
surface immunoglobulin (slg) at high density is the major characteristic separating B-cells
from T-cells. Following interaction with antigens and subsequent activation, B-lymphocytes
proliferate and differentiate into antibody-producing plasma cells. In contrast to the long-
lived T-cell, B-cells are rapidly replaced by newly differentiating stem cells. Therefore,
lesions in the B-cell compartment may be less serious than those in the T-cell compartment
since they are more easily reversed. Insult to B-cells at the stem cell or terminal matura-
tion stage can result in suppression of specific immunoglobulin and enhanced susceptibility to
infectious agents whose pathogenesis is limited by antibodies.
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Pluripotent stem cells also give rise to lymphocytes whose lineages are still unclear.
Some possess natural cytolytic activity for tumor cells (natural killer cell activity), while
others, devoid of T- and B-cell surface markers (null cells), participate in antibody-depen-
dent cell-mediated cytotoxicity (ADCC). The pluripotent stem cell pool also contains precur-
sors of monocyte-macrophages and polymorphonuclear leukocytes (PMN). The macrophage has a
major role in presentation and processing of certain antigens, in cytolysis of tumor target
cells, and in phagocytosis and lysis of persistent intracellular infectious agents. Also, it
actively phagocytizes and kills invading organisms. Defects in differentiation or function of
PMNs or macrophages predispose the host to infections by bacteria and other agents.
This introduction should make it evident that the effects of an element such as lead on
the immune system may be expressed in complex or subtle ways. In some cases, lead might pro-
duce a lesion of the immune system not resulting in markedly adverse health effects, espe-
cially if the lesion did not occur at an early stem cell stage or during a critical point in
lymphoid organogenesis. On the other hand, some lead-induced immune system effects might
adversely affect health through increasing susceptibility to infectious agents or neoplasti-
cally transformed cells if, for example, they were to impair cytocidal or bactericidal
function.
12.8.2 Host Resistance
One way of ascertaining if a chemical affects the immune response of an animal is to
challenge an exposed animal with a pathogen such as an infectious agent or oncogen. This pro-
vides a general approach to determine if the chemical interferes with host immune defense
mechanisms. Host defense is a composite of innate immunity, part of which is phagocyte activ-
ities, and acquired immunity, which includes B- and T-lymphocyte and enhanced phagocyte reac-
tivities. Analysis of host resistance constitutes a holistic approach. However, dependent on
the choice of the pathogen, host resistance can be evaluated somewhat more selectively.
Assessment of host resistance to extracellular microbes such as Staphylococci, Salmonel1 a
typhimurium, Escherichia coli, or Streptococcus pneumoniae and to intracellular organisms such
as Listeria monocytogenes or Candida albicans primarily measures intact humoral immunity and
cell-mediated immunity, respectively. Immune defense to extracellular organisms requires
T-lymphocyte, B-lymphocyte, and macrophage interactions for the production of specific anti-
bodies to activate the complement cascade and to aid phagocytosis. Antibodies can also
directly neutralize some bacteria and viruses. Resistance to intracellular organisms requires
T-lymphocyte and macrophage interactions for T-lymphocyte production of lymphokines, which
further enhance immune mechanisms including macrophage bactericidal activities. An additional
T-lymphocyte subset, the cytolytic T-cell, is involved in resistance to tumors; immune
defenses against tumors are also aided by NK- and K-lymphocytes and macrophages.
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PRELIMINARY DRAFT
12.8.2.1 Infectivity Models. Numerous studies designed t.o assess the influence of lead on
host resistance to infectious agents consistently have shown that lead impairs host resis-
tance, regardless of whether the defense mechanisms are predominantly dependent on humoral- or
eel 1-mediated immunity (Table 12-22).
TABLE 12-22. EFFECT OF LEAD ON HOST RESISTANCE TO INFECTIOUS AGENTS
Species
Infectious agent
Lead dose
Lead exposure
Mortalitya
Reference
Mouse
S. typhi murium
200 ppm
i.p.; 30 days
54%
(13%)
Hemphill et al. (1971)
Rat
E. co1i
2 mg/100 g
i.v. ; 1
day
96%
(0%)
Cook et al. (1975)
Rat
S. epidermidis
2 mg/100 g
i.v.; 1
day
80%
(0%)
Cook et al. (1975)
Mouse
L. monocytogenes
80 ppm
orally;
4 wk
100%
(0%)
Lawrence (1981a)
Mouse
EMC virus
2000 ppm
orally;
2 wk
100%
(19%)
Gainer (1977b)
Mouse
EMC virus
13 ppm
orally;
10 wk
80%
(50%)
Exon et al. (1979)
Mouse
Langat virus
50 mg/kg
orally;
2 wk
68%
(0%)
Thind and Kahn (1978)
aThe percent mortality is reported for the lowest dose of lead in the study that significantly
altered host resistance. The percent mortality in parentheses is that of the non-lead-treated,
infected control group.
Mice (Swiss Webster) injected i.p. for 30 days with 100 or 250 jjg (per 0.5 ml) of lead
nitrate and inoculated with Salmonella typhimuriurn had higher mortality (54 and 100 percent,
respectively) than non-1ead-injected mice (13 percent) (Hemphill et al., 1971). These concen-
trations of lead, by themselves, did not produce any apparent toxicity. Similar results were
observed in rats acutely exposed to lead (one i.v. dose of 2 mg/100 g) and challenged with
Escherichia col i (Cook et al., 1975). In these two studies, lead could have interfered with
the clearance of endotoxin from the S^ typhimurium or E. col i, and the animals may have died
from endotoxin shock and not septicemia due to the lack of bacteriostatic or bactericidal
activities. However, the study by Cook et al. (1975) also included a non-endotoxin-producing
gram-positive bacterium, Staphylococcus epi dermi di s, and lead still impaired host resistance.
In another study, lead effects on host resistance to the intracellular parasite Listeria
monocytogenes were monitored (Lawrence, 1981a). CBA/J mice orally exposed to 16, 80, 400, and
2000 ppm lead for four weeks were assayed for viable Listeria after 48 and 72 hours, and for
mortality after 10 days. Only 2000 ppm lead caused significant inhibition of early bacteri-
cidal activity (48-72 hr), but 80-2000 ppm lead produced 100 percent mortality, compared with
0 percent mortality in the 0-16 ppm lead groups. Other reports have suggested that host
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resistance is impaired by lead exposure of rodents. Salaki et al. (1975) indicated that lead
lowered resistance of mice to Staphylococcus aureus, Listeria, and Candida; and observed
higher incidence of inflammation of the salivary glands in lead-exposed rats (Grant et al. ,
1980) may be due, in part, to lead-induced increased susceptibility to infections.
Inhalation of lead has also been reported to lower host resistance to bacteria.
SchlipkSter and Frieler (1979) exposed NMRI mice to an aerosol of 13-14 pg/m3 lead chloride
and clearance of Serratia marcesens in the lungs was reduced significantly. Microparticles of
lead in lungs of mice were also shown to lower resistance to Pasteurel 1 a multocida, in that
6 pg of lead increased the percentage of mortality by 27 percent (Bouley et al., 1977).
Lead has also been shown to increase host susceptibility to viral infections. CD-I mice,
administered 2,000 and 10,000 ppm lead in drinking water for two weeks and subsequently inocu-
lated with encephalomyocarditis (EMC) virus, had a significant increase in mortality (100 per-
cent at 2,000 ppm; 65 percent at 10,000 ppm) compared with control EMC virus-infected mice (13
percent) (Gainer, 1977b). In another study (Exon et al., 1979), Swiss Webster mice were ex-
posed to 13, 130, 1300, or 2600 ppm lead for 10 weeks in their drinking water and were infec-
ted with EMC virus. Although as low as 13 ppm lead caused a significant increase in mortality
(80 percent) in comparison with the non-1ead-treated EMC virus-infected mice (50 percent),
there were no dose-response effects, in that 2600 ppm lead resulted in only 64 percent mortal-
ity. The lack of a dose-response relationship in the two studies with EMC virus (Gainer,
1977b; Exon et al., 1979) suggests that the higher doses of lead may directly inhibit EMC
infectivity as well as host defense mechanisms. Additional studies have confirmed that lead
inhibits host resistance to viruses. Mice treated orally with lead nitrate (10-50 mg/kg/ day)
for two weeks had suppressed antibody titers to Langat virus (Type B arbovirus) and increased
titers of the virus itself (Thind and Singh, 1977), and the lead-inoculated, infected mice had
higher mortalities (25 percent at 10 mg/kg; 68 percent at 50 mg/kg) than the non-lead-infected
mice (0 percent) (Thind and Khan, 1978).
The effects of lead on bacterial and viral infections in humans have never been studied
adequately; there is only suggestive evidence that human host resistance may be lowered by
lead. Children with persistently high blood lead levels who were infected with Shigella
enteritis had prolonged diarrhea (Sachs, 1978). In addition, lead workers with blood lead
levels of 22-89 pg/dl have been reported to have more colds and influenza infections per year
(Ewers et al. , 1982). This study also indicated that secretory IgA levels were suppressed
significantly in lead workers with a median blood lead level of 55 pg/dl. Secretory IgA is a
major factor in immune defense against respiratory as well as gastrointestinal infections.
Hicks (1972) points out that there is need for systematic epidemiological studies on the
effects of elevated lead levels on the incidence of infectious diseases in humans. The cur-
rent paucity of information precludes formulation of any clear dose-response relationship for
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PRELIMINARY DRAFT
humans. Epidemiological investigations may help to determine if lead alters the immune system
of man and consequently increases susceptibility to infectious agents and neoplasia.
12.8.2.2 Tumor Models and Neoplasia. The carcinogenicity of lead has been studied both as a
direct toxic effect of lead (see Section 12.7) and as a means of better understanding the
effects of lead on the body's defense mechanisms. Studies by Gainer (1973, 1974) demonstrated
that exposure of CD-I mice to lead acetate potentiated the oncogenicity of a challenge with
Rauscher leukemia virus (RLV), resulting in enhanced splenomegaly and higher virus titers in
the spleen presumably through an immunosuppressive mechanism. Recent studies by Kerkvliet and
Baecher-Steppan (1982) revealed that chronic exposure of C57BL/6 mice to lead acetate in
drinking water at 130-1300 ppm enhanced the growth of primary tumors induced by Moloney sar-
coma virus (MSV). Regression of MSV-induced tumors was not prevented by lead exposure, and
lead-treated animals resisted late sarcoma development following primary tumor resistance.
Depressed resistance to transplantable MSV tumors was associated with a reduced number of
macrophages, which also exhibited reduced phagocytic activity.
In addition to enhancing the transplantabi1ity of tumors or the oncogenicity of leukemia
viruses, lead has also been shown to facilitate the development of chemically induced tumors.
Kobayashi and Okamoto (1974) found that intratracheal dosing of benzo(a)pyrene (BaP) combined
with lead oxide resulted in an increased frequency of lung adenomas and adenocarcinomas over
mice exposed to BaP alone. Similarly, exposure to lead acetate enhanced the formation of
N(4'-fluoro-4-biphenyl) acetamide-induced renal carcinomas from 70 to 100 percent and reduced
the latency to tumor appearance (Hinton et al,, 1980). Recently, Koller et al. (1983) found
that exposure to lead for 18 months increased the frequency of spontaneous tumors, predomi-
nantly renal carcinomas, in rats. Similarly, Schrauzer et al. (1981) found that adding lead
at 5 ppm to drinking water of C3H/St mice infected with Bittner milk factor diminished the up-
take of selenium and reduced its anticarcinogenic effects, causing mammary tumors to appear at
the same high incidence as in selenium-unsupplemented controls. Lead likewise significantly
accelerated tumor growth and shortened survival in this model.
The above studies on host susceptibility to various pathogens, including infectious
agents and tumors, indicate that lead could be detrimental to health by methods other than di-
rect toxicity. In order to understand the mechanisms by which lead suppresses host resistance
maintained by phagocytes, humoral immunity, and/or cell-mediated immunity, the immune system
must be dissected into its functional components and the effects of lead on each, separately
and combined, must be examined in order that the mechanism(s) of the immunomodulatory poten-
tial of lead can be understood.
12.8.3 Humoral Immunity
12.8.3.1 Antibody Titers. A low antibody titer in animals exposed to lead could explain the
increased susceptibility of animals to extracellular bacteria and some viruses (see Table
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PRELIMINARY DRAFT
12-23), as well as to endotoxins (Selye et al., 1966; Filkins, 1970; Cook et a 1. , 1974;
Schumer and Erve, 1973; Rippe and Berry, 1973; Truscott, 1970). Specific antibodies can
directly neutralize pathogens, activate complement components to induce lysis, or directly or
indirectly enhance phagocytosis via Fc receptors or C3 receptors, respectively. Studies in
animals and humans have assayed the effects of lead on serum immunoglobulin levels, specific
antibody levels, and complement levels. Analysis of serum immunoglobulin levels is not a good
measure of specific immune reactivity, but it would provide evidence for an effect on B-
lymphocyte development.
TABLE 12-23. EFFECT ON LEAD ON ANTIBODY TITERS
Lead dose and
Species
Antigen
exposure
Effect
Reference
Rabbit
Pseudorabies virus
2500 ppm; 10 wk
Decrease
Koller (1973)
Rat
S. typhimurium
5000-20000 ppm; 3 wk
Decrease
Stankovid and Jugo
(1976)
Rat
Bovine serum albumin
10-1000 ppm; 10 wk
Decrease
Koller et al.
(1983)
Mouse
Sheep red blood cells
0.5-10 ppm3; 3 wk
Decrease
Biakley et al.
(1980)
aLead was administered as tetraethyl lead; other studies used inorganic forms.
Lead had little effect on the serum immunoglobulin levels in rabbits (Fonzi et al.,
1967a), children with blood lead levels of 40 pg/dl (Reigart and Garber, 1976), or lead
workers with 22-89 pg/dl (Ewers et al., 1982). On the other hand, most studies have shown
that lead significantly impairs antibody production. Acute oral lead exposure (50,000 ppm/kg)
produced a decreased titer of anti-typhus antibodies in rabbits immunized with Typhus vaccine
(Fonzi et al., 1967b). In New Zealand white rabbits challenged with pseudorabies virus, lead
(oral exposure to 2500 ppm for 70 days) caused a 9-fold decrease in antibody titer to the
virus (Koller, 1973). However, lead has not always been shown to reduce titers to virus.
Vengris and Mare (1974) did not observe depressed antibody titers to Newcastle disease virus
in lead-treated chickens, but their lead treatment was only for 35 days prior to infection.
Lead-poisoned children also had normal anti-toxoid titers after booster immunizations with
tetanus toxoid (Reigart and Garber, 1976). In another study, Wistar rat dams were exposed to
5,000, 10,000, or 20,000 ppm lead for 20 days following parturition (Stankovid and Jugo,
1976). The progeny were weaned at 21 days of age and given standard laboratory chow for an
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PRELIMINARY DRAFT
additional month.- At that time, they were injected wi Lh Salmonel1 a typhimuri urn", and serum
antibody titers were assessed. Each dosage of lead resulted in significantly reduced antibody
titers. More recently, rats (Sprague-Dawley) given 10 ppm lead acetate orally for 10 weeks
had a significant suppression in antibody titers when challenged with tovine serum albumin
(BSA) and compared with BSA-immunized non-1ead-exposed rats (Koller et al., 1983). Develop-
ment of a highly sensitive, quantitative, enzyme-linked immunosorbent assay (ELISA) contrib-
uted to detecting the immunosuppressive activity of lead at this dosage.
Tetraethyl lead also has been responsible for reduced antibody titers in Swiss-cross mice
(Blakley et al., 1980). The mice were exposed orally to 0.5, 1.0, and 2.0 ppm tetraethyl lead
for 3 weeks. A significant reduction in hemagglutination titers to sheep red blood cells
(SRBC) occurred at all levels of exposure.
12.8.3.2 Enumeration of Antibody Producing Cells (Plaque-Forming Cells). From the above re-
sults, it appears that lead inhibits antibody production. To evaluate this possible effect at
the cellular level, the influence of lead on the number of antibody producing cells after pri-
mary or secondary immunization can be assessed. In primary humoral immune responses (mostly
direct), IgM plaque-forming cells (PFC) are measured, whereas in secondary or anamnestic
responses (mostly indirect), IgG PFC are counted. The primary immune response represents an
individual's first contact with a particular antigen. The secondary immune response repre-
sents re-exposure to the same antigen weeks, months, or even years after the primary antibody
response has subsided. The secondary immune response is attributed to persistence, after
initial contact with the antigen, of a substantial number of antigen-sensitive memory cells.
Impairment of the memory response, therefore, results in serious impairment of humoral immun-
ity in the host.
Table 12-24 summarizes the effects of lead on IgM or IgG PFC development. Mice exposed
orally to tetraethyl lead (0.5, 1, or 2 ppm) for three weeks produced a significant reduction
in the development of IgM and IgG PFC (Blakley et al., 1980). Mice (Swiss Webster) exposed
orally to 13, 137, or 1375 ppm inorganic lead for eight weeks had reduced numbers of IgM PFC
in each lead-exposed group (Koller and Kovacic, 1974). Even the lowest lead group (13 ppm)
had a decrease. The secondary response (IgG PFC, induced By a second exposure to antigen SRBC
seven days after the primary immunization) was inhibited to a greater extent than the primary
response. This study indicated that chronic exposure to lead produced a significant decrease
in the development of IgM PFC and IgG PFC. When Swiss Webster mice were exposed to 13, 130,
and 1300 ppm lead for 10 weeks and hyperimmunized by SRBC injections at week 1, 2, and 9, the
memory response as assessed by the enumeration of IgG PFC was significantly inhibited at 1300
ppm (Koller and Roan, 1980a). This suggests that the temporal relationships between lead
exposure and antigenic challenge may be critical. Other studies support this interpretation.
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TABLE 12-24. EFFECT OF LEAD ON THE DEVELOPMENT OF ANTIBODY-PRODUCING CELLS (PFC)
Speci es
/ii.- 3
Antigen
Lead dose and exposure
Effectb
Reference
Mouse
SRBC
(in
vivo)
13-1370 ppm; 8 wk
IgM
IgG
PFC
PFC
(D)
(D)
Koller and
Kovacic (1974)
Mouse
SRBC
(_i_n
vivo)
0.5-2 ppm tetraethyl lead;
3 wk
IgM
IgG
PFC
PFC
(D)
(D)
Blakley et al.
(1980)
Mouse
SRBC
(io
vivo)
13-1370 ppm; 10 wk
IgG
PFC
(D)
Kol1er and
Roan (1980a)
Mouse
SRBC
(in
vi vo)
4 mg (i.p. or orally)
IgM
IgG
PFC
PFC
(I)
(D)
Koller et al.
(1976)
Mouse
SRBC
SRBC
(in
(in
vivo)
vitro +
2-ME)
16-2000 ppm; 1-10 wk
16-80 ppm; 4 wk
2000 ppm; 4 wk
IgM
IgM
IgM
PFC
PFC
PFC
(N)
(I)
(D)
Lawrence
(1981aj
Rat
SRBC
(in
vi vo)
25-50 ppm; pre/postnatal
IgM
PFC
(D)
Luster et al.
(1978)
Mouse
SRBC
SRBC
(in
(in
vitro)
vitro +
2-ME)
50-1000 ppm; 3 wk
50-1000 ppm; 3 wk
IgM PFC
IgM PFC
(N or
(D)
I)
Blakley and
Archer (1981)
Mouse
SRBC
(in
vitro +
2-ME)
2-20 ppm (in vitro)
IgM
PFC
(I)
Lawrence
(1981b,c)
aThe antigenic challenge with sheep red blood cells (SRBC) was i_n vivo or i_n vitro after in
vi vo exposure to lead unless otherwise stated. The iji vi tro assays were performed in the
presence or absence of 2-mercaptoethanol (2-ME).
^The letters in parentheses are defined as follows: D = decreased response; N = unaltered
response; I = increased response.
Female Sprague-Dawley rats with pre- and post-natal exposure to lead (25 or 50 ppm) had a
significant reduction in IgM PFC (Luster et al. , 1978). In contrast, CBA/J mice exposed
orally to 15-2000 ppm lead for 1-10 weeks did not have altered IgM PFC responses to SRBC
(Lawrence, 1981a). Furthermore, when Swiss Webster mice were exposed to an acute lead dose (4
mg lead orally or i.p.), the number of IgG PFC was suppressed, but the number of IgM PFC was
enhanced (Koller et al., 1976).
The influence of lead on the development of PFC in mice was assessed further by i_n vi vo
exposure to lead, removal of spleen cells, and i_n vi tro analysis of PFC development. Initi-
ally it appeared that low doses of lead (16 and 80 ppm) enhanced development, and only a high
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PRELIMINARY DRAFT
dose (2000 ppm) inhibited the development of IgM PFC (Lawrence, 1981a). However, a later
study by Blakley and Archer (1981) indicated that 50-1000 ppm lead consistently inhibited IgM
PFC. Through the analysis of mixed cultures of lead-exposed lymphocytes (nonadherent cells)
and unexposed macrophages (adherent cells), and vice versa, as well as of i_n vitro responses
to antigens that do not require macrophage help (i.e., 1ipopolysaccharide, LPS), their data
indicated that the effects of lead may be at the level of the macrophage. This was substan-
tiated by the fact that 2-mercaptoethanol (2-ME, a compound that can substitute for at least
one macrophage activity) was able to reverse the inhibition by lead. This may explain why in
vi vo lead exposure (16 and 80 ppm) appeared to enhance the i_n vi tro IgM PFC responses in the
study by Lawrence (1981a), because 2-ME was present in the j_n vi tro assay system. Further-
more, i_n vitro exposure to lead (2 or 20 ppm) in spleen cell cultures with 2-ME enhanced the
development of IgM PFC (Lawrence, 1981b,c).
These experiments indicate that lead modulates the development of antibody-producing
cells as well as serum antibody titers, which supports the notion that lead can suppress hu-
moral immunity. However, it should be noted that the dose and route of exposure of both lead
and antigen may influence the modulatory effects of lead. The adverse effects of lead on hu-
moral immunity may be due more to lead's interference with macrophage antigen processing
and/or antigen presentation to lymphocytes than to direct effects on B-lymphocytes. These
mechanisms require further investigation.
12.8.4 Cell-Mediated Immunity
12.8.4.1 Delayed-Type Hypersensitivity. T-lymphocytes (T-helper and T-suppressor cells) are
regulators of humoral and cell-mediated immunity as well as effectors of two aspects of cell-
mediated immunity. T-cells responsive to delayed-type hypersensitivity (DTH) produce lym-
phokines that induce mononuclear infiltrates and activate macrophages, which are aspects of
chronic inf 1 arrmatory responses. In addition, another subset of T-cells, cytolytic T-cells,
cause direct lysis of target cells (tumors or antigenically modified autologous cells) when in
contact with the target. To date, the effects of lead on cytolytic T-cell reactivity have not
been measured, but the influence of lead on inducer T-cells has been studied (Table 12-25).
Groups of mice injected i.p. daily for 30 days with 13.7 to 137 ppm lead were subsequently
sensitized i.v. with SRBC. The DTH reaction was suppressed in these animals in a dose-related
fashion (Miiller et a 1., 1977). The secondary DTH response was inhibited in a similar fashion.
In another study (Faith et al. , 1979), the effects of chronic low level pre- and post-natal
lead exposure on cellular immune functions in Sprague-Dawley rats was assessed. Female rats
were exposed to 25 or 50 ppm lead acetate continuously for seven weeks before breeding and
through gestation and lactation. The progeny were weaned at three weeks of age and continued
on the respective lead exposure regimen of their mothers for an additional 14 to 24 days.
CPB12/B 12-203 9/20/83
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PRELIMINARY DRAFT
TABLE 12-25. EFFECT OF LEAD ON CELL-MEDIATED IMMUNITY
Species Lead dose and exposure Parameter* Effect Reference
Mouse 13.7-137 ppm; 4 wk DTH Decrease MLiller et al. (1977)
Rat 25-50 ppm; 8 wk DTH Decrease Faith et al. (1979)
Mouse 13-1300 ppm; 10 wk MLC None Koller and Roan (1980b)
Mouse .16-2000 ppm; 4 wk MLC Decrease Lawrence (1981a)
*DTH =delayed-type hypersensitivity; MLC = mixed lymphocyte culture.
Thymic weights and DTH responses were significantly decreased by both lead dosages. These
results indicate that chronic low levels of lead suppress eel 1-mediated immune function.
The i_n vitro correlete of the analysis of DTH responsive T-cells j_n vivo is the analysis
of nixed lymphocyte culture (MLC) responsive T-cells. When two populations of allogeneic lym-
phoid cells are cultured together, cellular interactions provoke blast cell transformation and
proliferation of a portion of the cultured cells (Cerottini and Brunner, 1974; Bach et al . ,
1976). The response can be made ons-way by irradiating one of the two allogeneic prepara-
tions, in which case the irradiatad cells are the stimulators (allogeneic B-cells and macro-
phages) and the responders (T-cells) are assayed for their proliferation. The mixed lympho-
cyte reaction is an i_n vi tro assay of eel 1 -medi ated immunity analogous to i_n vivo host versus
graft reactions.
Mice (DBA/2J) fed 13, 130, or 1300 ppm lead for 10 weeks were evaluated for responsive-
ness in mixed lymphocyte cultures. The 130-ppm lead dose tended to stimulate the lymphocyte
reaction, although no change was observed at the other dose levels (Koller and Roan, 1980b).
In another study (Lawrence, 1981a), mice (CBA/J) were fed 16, 80, 400, or 2000 ppm lead for
four weeks. The 16 and 80 ppm doses slightly stimulated, while the 2000 ppm dose suppressed,
the mixed lymphocyte reaction. It is important to note that in these i_n vi tro MLC assays,
2-ME was present in the culture medium, and the 2-ME may have reversed the i_n vi vo effects of
lead, as was observed for the ijn vi tro RFC responses (Blakley and Archer, 1981).
The data on the effects of lead on humoral and cell-mediated immunity indicate that i_n
vivo lead usually is immunosuppressive, but additional studies are necessary to fully under-
stand the temporal and dose relationship , of lead's immunomodulatory effects. The i_n vi tro
analysis of immune cells exposed to laad i_n vi vo suggest that the major cell type modified is
the macrophage; the suppressive effects of lead may be readily reversed by thiol reagents
possibly acting as chelators.
CPB12/B 12-204 9/20/83
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PRELIMINARY DRAFT
12.8.4.3 Interferon. Interferons (IF) are a family of low molecular weight proteins which
exhibit antiviral activity in sensitive cells through processes requiring new cellular RNA and
protein synthesis (Stewart, 1979). It has been speculated that the enhanced susceptibility of
lead-treated mice to infectious virus challenge might be due to a decreased capacity of these
animals to produce viral or immune interferons or to respond to them. Studies by Gainer
(1974, 1977a) appeared to resolve this question and indicated that exposure of CD-I mice to
lead does not inhibit the antiviral action of viral IF jkj vivo or i_n vitro. In the later of
the two studies, lead exposure inhibited the protective effects of the IF inducers Newcastle
disease virus and poly I:poly C against encephalomyocarditis virus (EMC)-induced mortality.
These data suggest that, although lead did not directly interfere with the antiviral activity
of interferon, it might suppress viral IF production in vivo. Recently, Blakley et al. (1982)
re-examined this issue and found that female BDF! mice exposed to lead acetate in drinking
water at concentrations ranging from 50 to 1000 pg/ml for three weeks produced amounts of IF
similar to controls given a viral IF inducer, Tilorone. Similarly, the i_n vitro induction of
immune IF by the T-cell mitogens phytohemagglutinin, concanavalin A, and staphylococcal
enterotoxin in lymphocytes from lead-exposed mice were unaltered compared with controls
(Blakley et al., 1982). Thus, lead exposure does not appear to significantly alter the lym-
phocyte's ability to produce immune interferon. Therefore, it must be assumed that increased
viral susceptibility associated with chronic lead exposure in rodents is by mechanisms other
than interference with production of or response to interferon.
12.8.5 Lymphocyte Activation by Mitogens
Mitogens are lectins that induce activation, blast-cell transformation, and proliferation
in resting lymphocytes. Certain lectins bind specifically to (1) T-cells (i.e., phytohemag-
glutinin [PHA] and concanavalin A [Con A]), (2) B-cells (i.e., 1ipopolysaccharide [LPS] of
gram-negative bacteria) or (3) both (i.e., pokeweed mitogen [PWM]). The blastogenic response
produced can be used to assess changes in cell division of T- and B-lymphocytes. The biologi-
cal significance of the following studies is difficult to interpret since exposure to lead was
either i_n vi vo or i_n vi tro at different doses and for different exposure periods.
12.8.5.1 In Vivo Exposure. Splenic lymphocytes from Swiss Webster mice exposed orally to
2000 ppm lead for 30 days had significantly depressed proliferative responses to PHA (Table
12-26) which were not observed after 15 days of exposure (Gaworski and Sharma, 1978). Sup-
pression was likewise observed with PWM, a T- and B-cell mitogen. These observations with
T-cell mitogens were confirmed in Sprague-Dawley rats exposed orally to 25 or 50 ppm lead pre-
and postnatally for seven weeks (Faith et si., 1979). Splenic T-cell responses to Con A and
PHA were significantly diminished. A similar depression of Con A and PHA responses occurred
CPB12/B 12-205 9/20/83
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TABLE 12-26. EFFECT OF LEAD EXPOSURE ON MITOGEN ACTIVATION OF LYMPHOCYTES
Species Lead dose Mitogen Effect Reference
Mice
In vivo, 250 and 2000
ppm, 30 days
PHA
PWM
(T-Cell)
(T and B-Cell)
Significantly depressed at
2000 ppm on day 30 only1
Significantly depressed at
2000 ppm on both days 15
and 301
Gaworski and
Sharma (1978)
Mice
In vivo, 13, 130 and 1300
ppm, 10 weeks
Con
LPS
A (T-Cell)
(B-Cell)
No effect
No effect
Koller et al. (1979)
Rats
In vivo, pre/postnatal
25 and 50 ppm, 7 weeks
Con
PHA
A
Significantly depressed at
25 and 50 ppm
Significantly depressed at
50 ppm only
Faith et al. (1979)
T3
TO
m
Mice
In vivo, .08 - 10 mM, 4 weeks
Con
LPS
A, PHA
No effect
Depressed at 2 and 10 mM
Lawrence (1981c)
r~
~—<
~—<
Mice
In vivo, 1300 ppm, 8 weeks
Con
LPS
A, PHA
Significantly depressed
No effect
Neilan et al. (1980)
3>
>o
-<
Mice
In vivo, 50. 200 and 1000 ppm
3 weeks
Con
LPS
A, PHA, SEA
Increased to all2
No effect
Blakley and Archer (1982)
TO
3>
-n
—\
Mice
In vitro, 10 ^ - 10 ^ for
full culture period
Con
LPS
A, PHA
Slightly increased at
highest dose at day 2, no
effect at day 3.5
Increased up to 245%*
Lawrence (1981a,b)
Mice
In vitro, 0.1, 0.5. 1.0 mM
for full culture period
PHA
PWM
Increased at all doses by
up to 453%3
Increased by approximately
250% at 0.1 and 0.5 mM only
Gaworski and
Sharma (1978)
Mice
In vitro. 10"3 - 10~7 M
LPS
Increased by up to 312%
Shenker et al. (1977)
Gallagher et al. (1979)
1. Difficult to interpret since data were reported only as % of control response rather than CPM of 3H-TdR incorporation.
2. Untreated control values unusually low for T-cell response. Lead treated had much higher response with highest dose
showing cytotoxicity.
3. Noted white precipitate thought to be lead carbonate in cultures.
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PRELIMINARY DRAFT
in lymphocytes from C57B1/6 mice exposed to 1300 ppm lead for 8 weeks (Neilan et al. , 1980).
Lead impaired blastogenic transformation of lymphocytes by both T-cell mitogens, although the
B-cell proliferative response to LPS was not impaired.
In contrast to reports that lead exposure suppressed the blastogenic response of T-cells
to mitogens, several laboratories have reported that lead exposure does not suppress T-cell
proliferative responses (Koller et al. , 1979; Lawrence, 1981c; Blakley and Archer, 1982).
These differences are not easily reconciled since analysis of the lead dose employed and ex-
posure period (Table 12-25) provides little insight into the observed differences in T-cell
responses. In one case, a dose of 2000 ppm for 30 days produced a clear depression while a
lesser dose of 1300 ppm produced no effect at 10 weeks in another laboratory. These data are
confusing and may reflect technical differences in performing the T-cell blastogenesis assay
in different laboratories, a lack of careful attention to lectin response kinetics, or the
influence of suppressor macrophages. Thus, no firm conclusion can be drawn regarding the
ability of i_n vivo exposure to lead to impair the proliferative capacity of T-cells.
The blastogenic response of B-cells to LPS was unaffected in four different i_n vi vo stud-
ies at lead exposure levels from 25 to 1300 ppm (Koller et al., 1979; Faith et al., 1979;
Neilan et al., 1980; Blakley and Archer, 1982). Lawrence (1981c), however, reported that the
LPS response was suppressed after 4 weeks exposure at 2 and 10 mM lead. The weight of the
data suggests that the proliferative response of B-cells to LPS is probably not severely im-
paired by lead exposure.
12.8.5.2 In Vitro Exposure. The biological relevance of immunological studies in which lead
was added i_n vitro to normal rodent splenocytes in the presence of a mitogen (Table 12-26) is
questionable since differences probably reflect either a direct toxic or stimulatory effect by
the metal. These models may, however, provide useful information regarding metabolic and
functional responses in lymphocytes using lead as a probe.
.4 _5 _6
In one study, lymphocytes were cultured in the presence of lead (10 , 10 , and 10 M).
A- slight but significant increase in lymphocyte transformation occurred on day 2 at the high-
est lead dosage when stimulated with Con A or PHA (Lawrence, 1981b). In a follow-up study
.4 _s
where the kinetics of the lectin response were examined (Lawrence, 1981a), lead (10 , 10 ,
_6
and 10 M) significantly suppressed the Con A- and PHA-induced proliferative responses of
lymphocytes on day 2, but not on days 3 to 5. In yet another i_n vitro exposure study, lympho-
cytes cultured in the presence of 0.1, 0.5, or 1.0 mM lead had a significantly enhanced
response to PHA (Gaworski and Sharma, 1978). It should be kept in mind when considering these
in vitro exposure observations that lead has been demonstrated to be directly mitogenic to
lymphocytes (Shenker et al., 1977). The data discussed here suggest that lead may also be
slightly co-mitogenic with T-cell mitogens. Direct exposure of lymphocytes in culture to lead
can also result in decreased lymphocyte viability (Gallagher et al., 1979). Ijn vitro studies
CPB12/B 12-207 ' 9/20/83
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PRELIMINARY DRAFT
on the effect of lead on the B-cel 1 blastogenic response to LPS indicated that lead is
potently co-mitogenic with LPS and enhanced the proliferative response of B-cells by 245 per-
cent (Lawrence 1981b,c) to 312 percent (Shenker et a 1., 1977; Gallagher et al., 1979).
12.8.6 Macrophage Function
The monocyte/macrophage is involved with phagocytosis, bactericidal activity, processing
of complex antigens for initiation of antibody production, interferon production, endotoxin
detoxification, and iinmunoregulation. Since some of these functions are altered in lead-
treated rodents (Table 12-27), the monocyte/macrophage or comparable phagocytic cell in the
liver has been suggested as a possible cellular target for lead (Trejo et al., 1972; Cook et
al., 1974; Muller et al., 1977; Luster et al., 1978; Blakley and Archer, 1981).
Several laboratories have shown that a single i.v. injection of lead impaired the phago-
cytic ability of the reticuloendothelial system (RES) (Trejo et al., 1972; Cook et al., 1974;
Filkins and Buchanan, 1973). Trejo et al. (1972) found that an i.v. injection of 5 mg lead
impaired vascular clearance of colloidal carbon that resulted from an impaired phagocytic
ability of liver Kupffer cells. Similarly, others have confirmed that lead injected i.v. de-
pressed intravascular clearance of colloidal carbon (Filkins and Buchanan, 1973) as well as a
radiolabeled lipid emulsion (Cook et al., 1974). Opposite effects on RES function have been
seen when lead was given orally (Koller and Roan, 1977). Similarly, Schlick and Friedberg
(1981) noted that a 10-day exposure to 10-1000 pg lead enhanced RES clearance and endotoxin
hypersensitivity.
Lead has likewise been demonstrated to suppress macrophage-dependent immune responses
(Blakley and Archer, 1981). Exposure of BDFi mice to lead (50 ppm) for three weeks in drink-
ing water suppressed i_n vitro antibody PFC responses to the macrophage-dependent antigens,
sheep red blood cells or dinitrophenyl-Ficol1 , but not to the macrophage-independent antigen
E. col i 1ipopolysaccharide. The macrophage substitute 2-mercaptoethanol and macrophages from
non-exposed mice restored lead-suppressed response. Castranova et al. (1980) found that
cultured rat alveolar macrophages exposed to lead had depressed oxidative metabolism.
The effects of heavy metals on endotoxin hypersensitivity were first observed by Selye et
al. (1966), who described a 100,000-fold increase in bacterial endotoxin sensitivity in rats
given lead acetate. The increased sensitivity to endotoxin was postulated to be due to a
blockade of the RES. Filkins (1970) subsequently demonstrated that endotoxin detoxification
is primarily a hepatic macrophage-mediated event that is profoundly impaired by lead exposure
(Trejo and Di Luzio, 1971; Filkins and Buchanan, 1973). The several types of data described
above suggest that macrophage dysfunction may be contributing to impairment of immune func-
tion, endotoxin detoxification, and host resistance following lead exposure.
CPB12/B • 12-208 9/20/83
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TABLE 12-27. EFFECT OF LEAD ON MACROPHAGE AND RETICULOENDOTHELIAL SYSTEM FUNCTION
Species
Lead dose
and exposure
Parameter
Effect
Reference
Rat
Rat
Mouse
Guinea Pig
Rat
Mouse
Mouse
2. 25 pmol i.v. ,
single injection
5 mg i.v. ,
single injection
13, 130, 1300 ppm
oral, 10-12 weeks
io~3-io"6m
io 3-io~6m
50-1000 ppm oral,
3 weeks
10-1000 (jg,
10 days
Vascular clearance;
lipid emulsion
endotoxin sensitivity
Vascular clearance;
colloidal carbon
endotoxin sensitivity
Phagocytosi s
Macrophage migration
Macrophage oxygen
metaboli sm
Macrophage dependent
antigens PFC response
Vascular clearance
Depressed
Increased
Depressed
Increased
Depressed
Depressed
Depressed
Depressed
Enhanced at
10 days;
no effect
at >30 days.
Cook et al. (1974);
Trejo et al. (1972)
Trejo et al. (1972);
Filkins and
Buchanan (1973)
Kervliet and Braecher-
Steppan (1982)
Ki remi dj i an-
Schumacher et al. (1981)
Castranova et al. (1980)
Blakley and Archer
(1981)
Schlick and
Friedberg (1981)
"J.
"X
c
J
Endotoxin sensitivity
Increased
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PRELIMINARY DRAFT
12.8.7 Mechanisms of Lead Immunomodulation
The mechanism of toxic action of lead on cells is complex (see Section 12.2). Since lead
has a high affinity for sulfhydryl groups, a likely subcellular alteration accounting for the
immunomodulatory effects of lead on immune cells is its association with cellular thiols.
Numerous studies have indicated that surface and intracellular thiols are involved in lympho-
cyte activation, growth, and differentiation. Furthermore, the study by Blakley and Archer
(1981) suggests that lead may inhibit the macrophage's presentation of stimulatory products to
the lymphocytes. This process may rely on cellular thiols since the inhibitory effects of
lead can be overcome by an exogenous thiol reagent. Goyer and Rhyne (1973) have indicated
that lead ions tend to accumulate on cell surfaces, thereby possibly affecting surface recep-
tors and cell-to-cell communication. A study by Koller and Brauner (1977) indicated that lead
does alter C3b binding to its cell surface receptor.
12.8.8 Summary
Lead renders animals highly susceptible to endotoxins and infectious agents. Host sus-
ceptibility and the humoral immune system appear to be particularly sensitive. As postulated
in recent studies, the macrophage may be the primary immune target cell of lead. Lead-induced
immunosuppression occurs at low dosages that induce no evident toxicity and, therefore, may be
detrimental to the health of animals and perhaps of humans. The data accumulated to date pro-
vide good evidence that lead affects immunity, but additional studies are necessary to eluci-
date the actual mechanism by which lead exerts its immunosuppressive action. Knowledge of
lead effects of lead on the immune system of man is lacking and must be properly ascertained
in order to. determine permissible levels for human exposure. However, since this chemical
affects immunity in laboratory animals and is immunosuppressive at very low dosages, its
potential serious effects in man should be carefully considered.
CPB12/B 12-210 9/20/83
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PRELIMINARY DRAFT
12.9 EFFECTS OF LEAD ON OTHER ORGAN SYSTEMS
12.9.1 The Cardiovascular System
Since the best understood pathophysiologic mechanisms of hypertension in humans are those
resulting from renal disease, the clinical evidence for a relationship between lead and hyper-
tension is reviewed in Section 12.5.3.5 above. Under conditions of long-term lead exposure at
high levels, arteriosclerotic changes have been demonstrated in the kidney. Dingwal1-Fordyce
and Lane (1963) reported a marked increase in the cerebrovascular mortality rate among heavily
exposed lead workers as compared with the expected rate. These workers were exposed to lead
during the first quarter of this century when working conditions were quite bad. There has
been no similar increase in the mortality rate for men employed in recent times.
There are conflicting reports regarding whether lead can cause atherosclerosis in experi-
mental animals. Scroczynski et al. (1967) observed increased serum lipoprotein and choles-
terol levels and cholesterol deposits in the aortas of rats and rabbits receiving large doses
of lead. On the other hand, Prerovska (1973), using similar doses of lead given over an even
longer period of time, did not produce atherosclerotic lesions in rabbits.
Structural and functional changes have been noted in the myocardium of children with
acute lead poisoning, but to date the extent of such studies has been limited. Cases have
been described in adults and in children, always with clinical signs of poisoning. There is,
of course, the possibility that the coexistence of lead poisoning and myocarditis is coinci-
dental. In many cases in which encephalopathy is present, the electrocardiographic abnorma-
lities disappeared with chelation therapy, suggesting that lead may have been the original
etiological factor (Freeman, 1965; Myerson and Eisenhauer, 1963; Silver and Rodriguez-Torres,
1968). Silver and Rodriguez-Torres (1968) noted abnormal electrocardiograms in 21 of 30 chil-
dren (70 percent) having symptoms of lead toxicity. After chelation therapy, the electro-
cardiograms remained abnormal in only four (13 percent) of the patients. Electron microscopy
of the myocardium of lead-intoxicated rats (Asokan, 1974) and mice (Khan et al. , 1977) have
shown diffuse degenerative changes. Kopp and coworkers have demonstrated depression of con-
tractility, isoproterenol responsiveness, and cardiac protein phosphorylation (Kopp et al.,
1980a), as well as high energy phosphate levels (Kopp et al., 1980b) in hearts of lead-fed
rats. Similarly, persistent increased susceptibility to norepinephrine-induced arrhythmias
has been observed in rats fed lead during the first three weeks of life (Hejtmancik and
Williams, 1977, 1978, 1979a,b; Williams et al., 1977a,b).
In a review of five fatal cases of lead poisoning in young children, degenerative changes
in heart muscle were reported to be the proximate cause of death (Kline, 1960). It is not
clear that such morphological changes are a specific response to lead intoxication. Kosmider
and Petelnz (1962) examined 38 adults over 46 years of age with chronic lead poisoning. They
CPB12/C 12-211 9/20/83
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PRELIMINARY DRAFT
found that 66 percent had electrocardiographic changes, a rate that was four times the expec-
ted rate for that age group.
The cardiovascular effects of lead in conjunction with cadmium have been studied in rats
following chronic low level exposure by Perry and coworkers (Perry and Erlanger, 1978; Kopp
et al. , 1980a,b). Perry and Erlanger (1978) exposed female weanling Long-Evans rats to
cadmium, lead, or cadmium plus lead (as acetate salts) at concentrations of 0.1, 1.0, or 5.0
ppm in deionized drinking water for up tc 18 months. These authors reported statistically
significant increases in systolic blood pressure for both cadmium and lead in the range of
15-20 mm Hg. Concomitant exposure to both cadmium and lead usually doubled the pressor ef-
fects of either metal alone. A subsequent study (Kopp et al. , 1980a) using weanling female
Long-Evans rats exposed to 5.0 ppm cadmium, lead, or lead plus cadmium in deionized drinking
water for 15 or 20 months showed similar pressor effects of these two metals alone or in com-
bination on systolic blood pressure. Electrocardiograms performed on these rats demonstrated
statistically significant prolongation of the mean PR interval. Bundle electrograms also
showed statistically significant prolongations. Other parameters of cardiac function were not
markedly affected. Phosphorus-31 nuclear magnetic resonance (NMR) studies conducted on
perchloric acid extracts of liquid nitrogen-frozen cardiac tissue from these animals disclosed
statistically significant reductions in adenosine triphosphate (ATP) levels and concomitant
increases in adenosine diphosphate (ADP) levels. Cardiac glycerol 3-phosphoryl-choline (GPC)
were also found to be significantly reduced using this technique, indicating a general
reduction of tissue high-energy phosphates by lead or cadmium. Pulse-labeling studies using
32P demonstrated decreased incorporation of this isotope into myosin light-chain (LC-2) in all
lead or cadmium treatment groups relative to controls. The results of these studies indicate
that prolonged low-dose exposure to lead (and/or cadmium) reduces tissue concentrations of
high-energy phosphates in rat hearts and suggest that this effect may be responsible for
decreased myosin LC-2 phosphorylation and subsequent reduced cardiac contractility. Other
studies by these authors (Kopp et al., 1980b) were also conducted on isolated perfused hearts
of weanling female Long-Evans rats exposed to cadmium, lead, or lead plus cadmium in deionized
drinking water at concentrations of 50 ppm for 3-15 months. Incorporation of 32P into cardiac
proteins was studied following perfusion on inotropic perfusate containing isoproterenol at a
concentration of 7 x 10 M. Data from these studies showed a statistically significant reduc-
tion in cardiac active tension in hearts from cadmium- or lead-treated rats. Phosphorus-32
incorporation was also found to be signficantly reduced in myosin LC-2 proteins. The authors
suggested that the observed decrease in LC-2 phosphorylation could be involved in the observed
decrease in cardiac active tension in lead- or cadmium-treated rats.
CPB12/C
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PRELIMINARY DRAFT
Makasev and Krivdina (1972) observed a two-phase change in the permeability of blood ves-
sels (first increased, then decreased permeability) in rats, rabbits, and dogs that received a
solution of lead acetate. A phase change in the content of catecholamines in the myocardium
and in the blood vessels was observed in subacute lead poisoning in dogs (Mambeeva and
Kobkova, 1969). This effect appears to be a link in the complex mechanism of the cardiovas-
cular pathology of lead poisoning.
The susceptibility of the myocardium to toxic effects of lead was supported by i_n vitro
studies in rat mitochondria by Parr and Harris (1976). These investigators found that the
2 +
rate of Ca removal by rat heart mitochondria is decreased by 1 nmol Pb/mg protein.
12.9.2 The Hepatic System
The effect of lead poisoning on liver function has not been extensively studied. In a
study of 301 workers in a 1ead-smelting and refining facility, Cooper et al. (1973) found an
increase in serum glutamic oxaloacetic transaminase (SGOT) activity in 11.5 percent of
subjects with blood lead levels below 70 jjg/dl, in 20 percent of those with blood lead levels
of about 70 fjg/dl, and in 50 percent of the workers with blood lead levels of about 100 pg/dl.
The correlation (r = 0.18) between blood lead levels and SGOT was statistically significant.
However, there must also have been exposure to other metals, e.g., cadmium, since there was a
zinc plant in the smelter. In lead workers with moderate effects on the hematopoietic system
and no obvious renal signs, SGOT was not increased compared with controls on repeated examina-
tions (Hammond et al., 1980). In most studies on lead workers, tests for liver function are
not included.
The liver is the major organ for the detoxification of drugs. In Section 12.3.1.3 it is
mentioned that exposure to lead may cause altered drug detoxification rates as a result of in-
terference with the formation cf heme-containing cytochrome P-450, which is part of the
hepatic mixed function oxidase system. This enzyme system is involved in the.hepatic bio-
transformation of medicaments, hormones, and many environmental chemicals (Remmer et al.,
1966). Whereas a decrease in drug-metabolizing activity clearly has been demonstrated in
experimental animals given large doses of lead resulting in acute toxicity, the evidence for
effects of that type in humans is less consistent. Alvares et al. (1975) studied the effect
of lead exposure on drug metabolism in children. There were no differences between two normal
children and eight children with biochemical signs of lead toxicity in their capacities to
metabolize two test drugs, antipyrine and phenylbutazone. In two acutely poisoned children
in whom blood levels of lead exceeded 60 (jg/d1 , antipyrine half-lives were significantly
longer than normal, and therapy with EDTA led to biochemical remission of the disease and
restoration of deranged drug metabolism toward normal. One of the "normal" children in this
CPB12/C 12-213 9/20/83
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PRELIMINARY DRAFT
study had a blood lead level of 40 fjg/dl, but normal ALA-D and EP values. No data were given
on the analytical methods used for indices of lead exposure. Furthermore, the age of the
children varied from 1 to 7.5 years, which is significant because, as pointed out by the
authors, drug detoxification is age-c!ependent,
Meredith et al. (1977) demonstrated enhanced hepatic metabolism of antipyrine in lead-
exposed workers (PbB: 77-195 pg/dl) following chelation therapy. The significance of this
evidence of restored hepatic mixed oxidase function is, however, unclear because the pretreat-
ment antipyrine biologic half-life and clearance were not significantly different in lead-
exposed and control subjects. Moreover, there were more heavy smokers among the lead-exposed
workers than controls. Smoking increases the drug-metabolizing capacity and may thus counter-
act the effects of lead. Also, the effect of chelation on antipyrine metabolism in non-
exposed control subjects was not determined.
Hepatic drug metabolism in eight adult patients showing marked effects of chronic lead
intoxication on the erythropoietic system was studied by Alvares et al. (1976). The plasma
elimination rate of antipyrine, which, as noted above, is a drug primarily metabolized by he-
patic microsomal enzymes, was determined in eight subjects prior to and following chelation
therapy. In seven of eight subjects, chelation therapy shortened the antipyrine half-lives,
but the effect was minimal. The authors concluded that chronic lead exposure results in sig-
nificant inhibition of the heme biosynthetic pathway without causing significant changes in
enzymatic activities associated with hepatic cytochrome P-450.
A confounding factor in the above three studies may be that treatment with EDTA causes an
increase in the glomerular filtration rate (GFR) if it has been reduced by lead (Section
12.5.3.3). This may cause a decrease in the half-times of drugs. There are, however, no data
on the effect of chelating agents on GFR in children or adults with moderate signs of lead
toxicity.
In 11 children with blood lead levels between 43 and 52 pg/dl, Saenger et al. (1981)
found a decrease in 24-hour urinary 6-beta-hydroxycortisol excretion that correlated closely
(r = 0.85, p <0.001) with a standardized EDTA lead-mobilization test (1000 mg EDTA/m2 body
surface area). This glucocorticoid metabolite is produced by the same hepatic microsomal
mixed function oxidase system that hydroxylates antipyrine. The authors suggest that the
depression of 6-beta-hydroxylation of Cortisol in the liver may provide a non-invasive method
for assessing body lead stores in children (Saenger et al., 1981).
In a few animal studies special attention has been paid to morphological effects of lead
on the liver. White (1977) gave eight beagle dogs oral doses of lead carbonate, 50-100 mg
Pb/kg b.w., for 3-7 weeks. Lead concentrations were not measured in blood or tissues. In two
dogs exposed from 5 weeks of age to 50 mg/kg, morphological changes were noted. Changes in
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enzyme activities were noted in most exposed animals; for example, some dehydrogenases showed
increased activity after short exposure and decreased activity after longer exposures, mainly
in animals with weight losses. The small number of animals and the absence of data on lead
concentrations makes it impossible to use these results for risk evaluations.
Hoffmann et al. (1974) noted moderate to marked morphological changes in baboon livers
after a single intravenous injection of large doses of lead acetate (25 mg/kg b.w.). It can
be concluded that effects on the liver may be expected to occur only at high exposure levels.
If effects on more sensitive systems, viz., the nervous and hematopoietic systems, are pre-
vented, no adverse effects should be noted in the liver.
12.9.3 The Endocrine System
The effects of lead on the endocrine or hormonal system are not well defined at the pre-
sent time, but some evidence exists for such effects, at least at high levels of lead expo-
sure. Lead is thought, for example, to decrease thyroid function in man and experimental ani-
mals. Porritt (1931) suggested that lead dissolved from lead pipes by soft water was the
cause of hypothyroidism in individuals living in southwest England. Later, Kremer and Frank
(1955) reported the simultaneous occurrence of myxedema and plumbism in a house painter.
Monaenkova (1957) observed impaired concentration of 131I by thyroid glands in 10 of 41
patients with industrial plumbism. Subsequently, Zel'tser (1962) showed that in vivo 131I up-
take and thyroxine synthesis by rat thyroid were decreased by lead when doses of 2 and 5 per-
cent lead acetate solution were administered. Uptake of 131I, sometimes decreased in men with
lead poisoning, can be offset by treatment with thyroid-stimulating hormone (TSH) (Sandstead
et al., 1969; Sandstead and Galloway, 1967). Lead may act to depress thyroid function by in-
hibiting thiol groups or by displacing iodine in a protein sulfonyl iodine carrier (Sandstead
and Galloway, 1967), and the results suggest that excessive lead may act at both the pituitary
and the thyroid gland itself to impair thyroid function. None of these effects on the thyroid
system, however, have been demonstrated to occur in humans at blood lead levels below 30-40
|jg/dl.
Sandstead et al. (1970a) studied the effects of lead intoxication on pituitary and adre-
nal function in man and found that it may produce clinically significant hypopituitarism in
some. The effects of lead on adrenal function were less consistent, but some of the patients
showed a decreased responsiveness to an inhibitor (metapyrone) of 11-beta-hydroxylation in the
synthesis of Cortisol. This suggests a possible impact of lead on pituitary-adrenal hormonal
functions. That excessive oral ingestion of lead may in fact result in pathological changes
in the pituitary-adrenal axis is also supported by other reports of lead-induced decreased
metapyrone responsiveness, a depressed pituitary reserve, and decreased immunoreactive ACTH
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(Murashov, 1966; Pines, 1965). These same events may also affect adrenal gland function as
much as decreased urinary excretion of 17-hydroxy-corticosteroids was observed in these
patients. Also, suppression of responsiveness to exogenous ACTH in the zona fasciculata of
the adrenal cortex has been reported in lead-poisoned subjects (Makotchenko, 1965), and
impairment of the zona glom9rulosa of the adrenal cortex has also been suggested (Sandstead et
al. , 1970b). Once again, however, none of these effects on adrenal hormone function have been
shown to occur at blood lead levels as low as 30-40 |jg/dl.
Other studies provide evidence suggestive of lead exposure effects on endocrine systems
controlling reproductive functions (see also Section 12.6). For example, evidence of abnormal
luteinizing hormone (LH) secretory dynamics was found in secondary lsad smelter workers
(Braunstein et al., 1978). Reduced basal serum testosterone levels with normal basal LH
levels but a diminished rise in LH following stimulation indicated suppression of hypo-
thalamic-pituitary function. Testicular biopsies in two lead-poisoned workmen showed peritu-
bular fibrosis suggesting direct toxic effects of lead in the testes as well as effects at the
hypothalamic-pituitary level. Lancranjan et al. (1975) also reported lead-related interfer-
ence with male reproductive functions. Moderately increased lead absorption (blood lead mean
= 52.8 [jg/dl) among a group of 150 workmen who had long-term exposure to lead in varying
degrees was said to result in gonadal impairment. The effects on the testes were believed to
be direct, howevar, in that tests for hypothalamic-pituitary influence were negative.
In regard to effects of lead on ovarian function in human females, Panova (1972) reported
a study of 140 women working in a printing plant for 1 to 2 months, where ambient air lead
levels were <7 |jg/m3. Using a classification of various age groups (20-25, 26-35, and 36-40
yr) and type of ovarian cycle (normal, anovular, and disturbed lutein phase), Panova claimed
that statistically significant differences existed between the lead-exposed and control groups
in the age range 20-25 years. It should be noted that the report does not show the age dis-
tribution, the level of significance, or the data on specificity of the method used for class-
ification. Also, Zielhuis and Wibowo (1976), in a critical review of the above study, con-
cluded that the design of the study and presentation of data are such that it is difficult to
evaluate the author's conclusion that chronic exposure to low air lead levels leads to dis-
turbed ovarian function. Moreover, no consideration was given to the dust levels of lead, an
important factor ;n print shops. Unfortunately, little else besides the above report exists
in the literature in regard to assessing lead effects on human ovarian function or other fac-
tors affecting human female fertility. Studies offering firm data on maternal variables,
e.g., hormonal state, that are known to affect the ability of the pregnant woman to carry the
fetus full-term are also lacking, although certain studies do indicate that at least high-
level lead exposure induces stillbirths and abortions (see Section 12.6).
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One animal study (Petrusz et al., 1979) indicates that orally administered lead can exert
effects on pituitary and serum gonadotropins, which may represent one mechanism by which lead
affects reproductive functions. The blood lead levels at which alterations in serum and pitu-
itary follicle stimulating hormone were observed in neonatal rats, however, were well in ex-
cess of 100 (jg/dl.
12.9.4 The Gastrointestinal System
Colic is usually a consistent early symptom of lead poisoning, warning of much more seri-
ous effects that are likely to occur with continued or more intense lead exposure. Although
most commonly seen in industrial exposure cases, colic is also a lead-poisoning symptom pres-
ent in infants and young childran.
Beritic (1971) examined 64 men suffering from abdominal colic due to lead intoxication
through occupational exposure. The diagnosis of lead colic was based on the occurrence of
severe attacks of spasmodic abdominal pain accompanied by constipation, abnormally high copro-
porphyrinuria, excessive basophilic stippling, reticulocytosis, and some degree of anemia (all
clinical signs of lead poisoning). Thirteen of the 64 patients had blood lead levels of 40-
80 |jg/dl upon admission. However, the report did not indicate how recently the patients'
exposures had been terminated or provide other details of their exposure histories.
A more recent report by Dahlgren (1978) focused on the gastrointestinal symptoms of lead
smelter workers whose blocd lead levels were determined within two weeks of the termination of
their work exposure. Of 34 workers with known lead exposure, 27 (79 percent) complained of
abdominal pain, abnormal bowel movements, and nausea. Fiftaen of the 27 had abdominal pain
for more than 3 months after removal from the exposure to lead. The mean (and SD) blood lead
concentration for this group of 15 was 70 (± 4) pg/dl. There was, however, no correlation
between severity of symptoms and blood lead levels, as those experiencing stomach pain for
less than 3 months averaged 68 (± 9) pg/dl and the remaining 7 workers, reporting no pain at
all, averaged 76 (± 9) pg/dl.
Hanninen et al. (1979) assessed the incidence of gastrointestinal symptoms in 45 workers
whose blood lead levels had been regularly monitored throughout their exposure and had never
exceded 69 pg/d 1, A significant association between gastrointestinal symptoms (particularly
epigastric pain) and blood lead level was reported. This association was more pronounced in
subjects whose maximal blood' lead levels had reached 50-69 pg/dl, but was also noted in those
whose blood lead levels were bslow 50 |jg/d 1.
Other occupational studies have also suggested a relationship between lead exposure and
gastrointestinal symptoms (Lilis et al., 1977; Irwig et al., 1978; Fischbein et al., 1979,
1980). For demonstrating such a relationship, however, the most useful measure of internal
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exposure has not necessarily been blood lead concentrations. Fischbein et al. (1980) surveyed
a cross-section of New York City telephone cable splicers exposed to lead in the process of
soldering cables. Of the 90 workers evaluated, 19 (21 percent) reported gastrointestinal
symptoms re'ated to lead colic. The difference between mean blood lead levels in those re-
porting GI symptoms and those not reporting such symptoms (30 vs. 27 pg/dl) was not statis-
tically significant. However, mean zinc protoporphyrin concentrations (67 vs. 52 pg/dl) were
significantly different (p <0.02)
Although gastrointestinal symptoms of lead exposure are clinically evident in frank lead
intoxication and may even be present when blood lead levels approach the 30-80 [jg/dl range,
there is currently insufficient information to establish a clear dose-effect relationship for
the general population at ambient exposure levels.
12.10 CHAPTER SUMMARY
12.10.1 Introduction
Lead has diverse biological effects in humans and animals. Its effects are seen at the
subcellular level of organellar structures and processes as well as at the overall level of
general functioning that encompasses all systems of the body operating in a coordinated,
interdependent fashion. The present chapter not only categorizes and describes the various
biological effects of lead but also attempts to identify the exposure levels at which such
effects occur and the mechanisms underlying them. The dose-response curve for the entire
range of biological effects exerted by lead is rather broad, with certain biochemical changes
occurring at relatively low levels of exposure and perturbations in other systems, such as the
endocrine, becoming detectable only at relatively high exposure levels.
In terms of relative vulnerability to deleterious effects of lead, the developing organism
generally appears to be more sensitive than the mature individual. A more detailed and quan-
titative examination of overall exposure-effect relationships for lead is presented in
Chapter 13.
12.10.2 Subcellular Effects of Lead
The biological basis of lead toxicity is its ability to bind to ligating groups in bio-
molecular substances crucial to various physiological functions, thereby interfering with
these functions by, for example, competing with native essential metals for binding sites,
inhibiting enzyme activity, and inhibiting or otherwise altering essential ion transport.
These effects are modulated by: 1) the inherent stability of such binding sites for lead; 2)
the compartmentalization kinetics governing lead distribution among body compartments, among
tissues, and within cells; and 3) the differences in biochemical organization across cells and
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tissues due to their specific functions. Given the complexities introduced by items 2 and 3,
it is not surprising that no single unifying mechanism of lead toxicity across all tissues in
humans and experimental animals has yet been demonstrated.
In so far as effects of lead on activity of various enzymes are concerned, many of the
available studies concern J_n vitro behavior of relatively pure enzymes with marginal relevance
to various effects in vivo. On the other hand, certain enzymes are basic to the effects of
e
lead at the organ or organ system level, and discussion is best reserved for such effects in
the summary sections below dealing with lead effects on particular organ systems. This sec-
tion is mainly concerned with organellar effects of lead, expecially those which provide some
rationale for lead toxicity at higher levels of biological organization. Particular emphasis
is placed on the mitochondrion, because this organelle is not only affected by lead in numer-
ous ways but has also provided the most data bearing on the subcellular effects of lead.
The critical target organelle for lead toxicity in a variety of cell and tissue types
clearly is the mitochondrion, followed probably by cellular and intracellular membranes. The
mitochondrial effects take the form of structural changes and marked disturbances in mitochon-
drial function within the cell, particularly in energy metabolism and ion transport. These
effects in turn are associated with demonstrable accumulation of lead in mitochondria, both
in vivo and i_n vitro. Structural changes include mitochondrial swelling in a variety of cell
types as well as distortion and loss of cristae, which occur at relatively moderate lead
levels. Similar changes have also been documented in lead workers across a range of exposures.
Uncoupled energy metabolism, inhibited cellular respiration using both succinate and
nicotinamide adenine dinucleotide (NAO)-linked substrates, and altered kinetics of intracellu-
lar calcium have been demonstrated in vivo using mitochondria of brain and non-neural tissue.
In some cases, the lead exposure level associated with such changes has been relatively low.
Several studies document the relatively greater sensitivity of this organelle in young vs.
adult animals in terms of mitochondrial respiration. The cerebellum appears to be particular-
ly sensitive, providing a connection between mitochondrial impairment and lead encephalopathy.
Impairment by lead of mitochondrial function in the developing brain has also been consistent-
ly associated with delayed brain development, as indexed by content of various cytochromes.
In the rat pup, ongoing lead exposure from birth is required for this effect to be expressed,
indicating that such exposure must occur before, and is inhibitory to, the burst of oxidative
metabolism activity that occurs in the young rat at 10 to 21 days postnatally.
In vivo lead exposure of adult rats also markedly inhibits cerebral cortex intracellular
calcium turnover in a cellular compartment that appears to be the mitochondrion. The effect
was seen at a brain lead level of 0.4 ppm. These results are consistent with a separate study
showing increased retention of calcium in the brain of lead-dosed guinea pigs. Numerous
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reports have described the j_n vivo accumulation of lead in mitochondria of kidney, liver,
spleen, and brain tissue, with one study showing that such uptake was slightly more than
occurred in the call nucleus. These data are not only consistent with deleterious effects of.
lead on mitochondria but are also supported by other investigations i_n vitro.
Significant decreases in mitochondrial respiration iji vitro using both NAD-linked and
succinate substrates have been observed for Drain and non-neural tissue mitochondria in the
presence of lead at microinolar levels. There appears to be substrate specificity in the inhi-
bition of respiration across different tissues, which may be a factor in differential organ
toxicity. Also, a number of enzymes involved in intermediary metabolism in isolated mitochon-
dria have been observed to undergo significant inhibition of activity with lead.
Of particular interest regarding lead effects on isolated mitochondria are ion transport
effects, especially in regard to calcium. Lead movement into brain and other tissue mitochon-
dria involves active transport, as does calcium. Recent sophisticated kinetic analyses of
desaturation curves for radiolabeled lead or calcium indicate that there is striking overlap
in the cellular metabolism of calcium and lead. These studies not only establish the basis of
lead's easy entry into cells and cell compartments, but also provide a basis for lead's im-
pairment of intracellular ion transport, particularly in neural cell mitochondria, where the
capacity for calcium transport is 20-fold higher than even in heart mitochondria.
Lead is also selectively taken up in isolated mitochondria _in vi tro, including the mito-
chondria of synaptosomes and brain capillaries. Given the diverse and extensive evidence of
lead's impairment of mitochondrial structure and function as viewed from a subcellular level,
it is not surprising that these derangements are logically held to be the basis of dysfunction
of heme biosynthesis, erythropoiesis, and the central nervous system. Several key enzymes in
the heme biosynthetic pathway are intramitochondrial, particularly ferrochelatase. Hence, it
is to be expected that entry of lead into mitochondria will impair overall heme biosynthesis,
and in fact this appears to be the case in the developing cerebellum. Furthermore, lead
levels associated with entry of lead into mitochondria and expression of mitochondrial injury
can be relatively moderate.
Lead exposure provokes a typical cellular reaction in human and other species that has
been morphologically characterized as a lead-containing nuclear inclusion body. While it has
been postulated that such inclusions constitute a cellular protection mechanism, such a
mechanism is an imperfect one. Other organelles, e.g., the mitochondrion, also take up lead
and sustain injury in the presence of nuclear inclusion formations.
In theory, the cell membrane is the first organelle to encounter lead and it is not
surprising that cellular effects of lead can be ascribed to interactions at cellular and
intracellular membranes in the form of distrubed ion transport. The inhibition of membrane
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(Ma ,K )-ATPase of erythrocytes as a factor in lead-impaired erythropoiesis is noted else-
where. Lead also appears to interfere with the normal processes of calcium transport across
membranes of different tissues. In peripheral cholinergic synaptosomes, lead is associated
with retarded release of acetylcholine owing to a blockade of calcium binding to the membrane,
while calcium accumulation within nerve endings can be ascribed to inhibition of membrane
(Na+,K+)-ATPase.
Lysosomes accumulate in renal proximal convoluted tubule cells of rats and rabbits given
lead over a range of dosing. This also appears to occur in the kidneys of lead workers and
seems to represent a disturbance in normal lysosomal function, with the accumulation of
lysosomes being due to enhanced degradation of proteins because of the effects of lead else-
where within the cell.
12.10.3: Effects of Lead on Heme Biosynthesis, Erythropoiesis, and Erythrocyte Physiology in
Humans and Animals
The effects of lead on heme biosynthesis are well known both because of their prominence
and the large number of studies of these effects in humans and experimental animals. The
process of heme biosynthesis, starts with glycine and succinyl-coenzyme A, proceeds through
formation of protoporphyrin IX, and culminates with the insertion of divalent iron into the
porphyrin ring, thus forming heme. In addition to being a constituent of hemoglobin, heme is
the prosthetic group of numerous tissue hemoproteins having variable functions, such as myo-
globin, the P-450 component of the mixed function oxygenase system, and the cytochromes of
cellular energetics. Hence, disturbance of heme biosynthesis by lead poses ths potential for
multiple-organ toxicity.
The steps in the heme synthesis pathway that have been best studied in regard to lead
effects involve three enzymes: (1) stimulation of mitochondrial delta-aminolevulinic acid
synthetase (ALA-S), which mediates formation of delta-aminolevulinic acid (ALA); (2) direct
inhibition of the cytosolic enzyme, delta-aminolevulinic acid dehydrase (ALA-D), which cata-
lyzes formation of porphobilinogen from two units of ALA; and (3) inhibition of insertion of
iron (II) into protoporphyrin IX to form heme, a process mediated by the enzyme ferrochelatase.
Increased ALA-S activity has been documented in lead workers as well as lead-exposed ani-
mals, although the converse, an actual decrease in enzyme activity, has also been observed in
several experimental studies using different exposure methods. It would appear, then, that
enzyme activity increase via feedback derepression or that activity inhibition may depend on
the nature of the exposure. In an i_n vitro study'using rat liver cells in culture, ALA-S
activity could be stimulated at levels as low as 5.0 pM or 1.0 pg Pb/g preparation. In the
same study, increased activity was seen to be due to biosynthesis of more enzyme. The thres-
hold for lead stimulation of ALA-S activity in humans, based upon a study using leukocytes
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from lead workers, appears to be about 40 pg Pb/dl. The generality of this threshold level to
other tissues is dependent upon how well the sensitivity of leukocyte mitochondria mirrors
that in other systems. It would appear that the relative impact of ALA-S activity stimulation
on ALA accumulation at lower levels of lead exposure is considerably less than the effect of
ALA-D activity inhibition: at 40 jjg/d1 blood lead, ALA-D activity is significantly depressed,
while ALA-S activity only begins to be affected.
Erythrocyte ALA-D activity is very sensitive to lead inhibition, which is reversed by re-
activation of the sulfhydryl group with agents such as dithiothreitol, zinc, or zinc plus glu-
tathione. The zinc levels employed to achieve reactivation, however, are well above normal
physiological levels. Although zinc appears to offset the inhibitory effects of lead observed
in human erythrocytes j_n vitro and in animal studies, lead workers exposed to both zinc and
lead do not show significant changes in the relationship of ALA-D activity to blood lead con-
centration when compared to workers exposed only to lead. By contrast, zinc deficiency in
animals has been shown to significantly inhibit ALA-D activity, with concomitant accumulation
of ALA in urine. Since zinc deficiency has also been associated with increased lead absorp-
tion in experimental studies, the possibility exists for a dual effect of such deficiency on
ALA-D activity: (1) a direct effect on activity due to reduced zinc availability, as well as
(2) the effect of increased lead absorption leading to further inhibition of such activity.
The activity of erythrocyte ALA-D appears to be inhibited at virtually all blood lead
levels measured so far, and any threshold for this effect in either adults or children remains
to be determined. A further measure of this enzyme's sensitivity to lead comes from a report
noting that rat bone marrow suspensions show inhibition of ALA-D activity by lead at a level
of 0.1 |jg/g suspension. Inhibition of ALA-D activity in erythrocytes apparently reflects a
similar effect in other tissues. Hepatic ALA-D activity was inversely correlated in lead
workers with both the erythrocyte activity as well as blood lead. Of significance are the ex-
perimental animal data showing that (1) brain ALA-D activity is inhibited with lead exposure
and (2) inhibition appears to occur to a greater extent in the brain of developing vs. adult
animals. This presumably reflects greater retention of lead in developing animals. In the
avian brain, cerebellar ALA-D activity is affected to a greater extent than that of the
cerebrum and, relative to lead concentration, shows inhibition approaching that occurring in
erythrocytes.
The inhibition of ALA-D activity by lead is reflected in increased levels of its sub-
strate, ALA, in blood, urine, and tissues. In one investigation, the increase in urinary ALA
was seen to be preceded by a rise in circulating levels of the metabolite. Blood ALA levels
were elevated at all corresponding blood lead values down to the lowest value determined (18
pg/dl), while urinary ALA was seen to rise exponentially with blood ALA. Numerous independent
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studies have documented that there is a direct correlation between blood lead and the loga-
rithm of urinary ALA in adult humans and children, and that the threshold is commonly accepted
as being 40 |jg/dl. Several studies of lead workers also indicate that the correlation of
urinary ALA with blood lead continues below this value. Furthermore, one report has demon-
strated that the slope of the dose-effect curve in lead workers is dependent upon the level of
exposure.
The health significance of 1 ead-inhibited ALA-D activity and accumulation of ALA at low
levels of exposure has been an issue of some controversy. One view is that the "reserve
capacity" of ALA-D activity is such that only high accumulations of the enzyme's substrate,
ALA, in accessible indicator media would result in significant inhibition of activity. One
difficulty with this view is that it is not possible to quantify at lower levels of lead ex-
posure the relationship of urinary ALA to levels in target tissues nor to relate the potential
neurotoxicity of ALA at any level of build-up to levels in indicator media; i.e., the thres-
hold for potential neurotoxicity of ALA in terms of blood lead may be different from the level
associated with urinary accumulation.
Accumulation of protoporphyrin in the erythrocytes of individuals with lead intoxication
has been recognized since the 1930s, but it has only recently been possible to quantitatively
assess the nature of this effect via the development of specific, sensitive microanalysis
methods. Accumulation of protoporphyrin IX in erythrocytes is the result of impaired place-
ment of iron (II) in the porphyrin moiety to form heme, an intramitochondrial process mediated
by the enzyme ferrochelatase. In lead exposure, the porphyrin acquires a zinc ion in lieu of
native iron, thus forming zinc protoporphyrin (ZPP), and is tightly bound in available heme
pockets for the life of the erythrocytes. This tight sequestration contrasts with the rela-
tively mobile non-metal, or free, erythrocyte protoporphyrin (FEP) accumulated in the congen-
ital disorder erythropoietic protoporphyria.
Elevation of erythrocyte ZPP has been extensively documented as being exponentially cor-
related with blood lead in children and adult lead workers and is presently considered one of
the best indicators of undue lead exposure. Accumulation of ZPP only occurs in erythrocytes
formed during lead's presence in erythroid tissue, resulting in a lag of at least several
weeks before such build-up can be measured. It has been shown that the level of such accumu-
lation in erythrocytes of newly-employed lead workers continues to increase when blood lead
has already reached a plateau. This would influence the relative correlation of ZPP and blood
lead in workers with a short exposure history. In individuals removed from occupational expo-
sure, the ZPP level in blood declines much more slowly than blood lead, even years after re-
moval from exposure or after a drop in blood lead. Hence, ZPP level would appear to be a more
reliable indicator of continuing intoxication from lead resorbed from bone.
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The measurable threshold for lead-induced 2PP accumulation is affected by the relative
spread of blood lead and corresponding 2PP values measured. In young children (under four
years old) the ZPP elevation typically associated with iron-deficiency anemia should be taken
into account. In adults, several studies indicate that the threshold for ZPP elevation with
respect to blood lead is approximately 25-30 pg/dl. In children 10-15 years old the threshold
is about 16 pg/dl; in this age group, iron deficiency is not a factor. In one report, it was
noted that children over four years old showed the same threshold, 15.5 pg/dl, as a second
group under four years old, indicating that iron deficiency was not a factor in the study.
Fifty percent of.the children were found to have significantly elevated EP levels (2 standard
deviations above reference mean EP) or a dose-response threshold level of 25 pg/dl.
Within the blood lead range considered "normal," i.e., below 30-40 pg/dl, any assessment
of the ZPP-blood lead relationship is strongly influenced by the relative analytical profi-
ciency for measurement of both blood lead and EP. The types of statistical treatments
employed in analyzing the data are also important. In a recent detailed statistical study
involving 2004 children, 1852 of whom had blood lead values below 30 pg/dl, segmental line and
probit analysis techniques were employed to assess the dose-effect threshold and dose-response
relationship. An average blood lead threshold for the effect using both statistical tech-
niques yielded a value of 16.5 pg/dl for either the full group or those subjects with blood
lead levels below 30 pg/dl. The effect of iron deficiency was tested for and removed. Of
particular interest was the finding that the blood lead values corresponding to EP elevations
more than 1 or 2 standard deviations above the reference mean in 50 percent of the children
were 28.6 or 35.7 pg Pb/dl, respectively. Hence, fully half of the children were seen to have
significant elevations of EP at blood lead levels around the currently accepted cut-off value
for undue lead exposure, 30 pg/dl, From various reports, children and adult females appear to
be more sensitive to the effects of lead on EP accumulation at any given blood lead level,
with children being somewhat more sensitive than adult females.
Effects of lead on ZPP accumulation arid reduced heme formation are not restricted to the
erythropoietic system. Recent studies show that reduction of serum 1,25-dihydroxy vitamin D
seen with even low level lead exposure is apparently the result of lead's inhibition of the
activity of renal 1-hydroxylase, a cytochrome P-450 mediated enzyme. Cytochrome P-450, a
heme-containing protein, is an integral part of the hepatic mixed function oxygenase system
and is known to be affected in humans and animals by lead exposure, particularly acute intoxi-
cation. Reduced P-450 content has been found to be correlated with impaired activity of such
detoxifying enzyme systems as aniline hydroxylase and aminopyrine demethylase.
Studies of organotypic chick dorsal root ganglion in culture show that the nervous system
not only has heme biosynthetic capability but also such preparations elaborate porphyrinic ma-
terial in the presence of lead. In the neonatal rat, chronic lead exposure resulting in
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moderately elevated blood lead levels is associated with retarded growth in the hemoprotein
cytochrome C and with disturbed electron transport in the developing rat cerebral cortex.
These data parallel the effect of lead on ALA-D activity and ALA accumulation in neural
tissue. When these effects are viewed in the toxicokinetic context of increased retention of
lead in both developing animals and children, there is an obvious, serious' potential for
impaired heme-based metabolic function in the nervous system of lead-exposed children.
As can be seen from the above discussion, the health significance of ZPP accumulation
rests with the fact that such build-up is evidence of impaired heme and hemoprotein formation
in tissues, particularly the nervous system, arising- from entry of lead into mitochondria.
Such evidence for reduced heme synthesis is consistent with a diverse body of data documenting
lead-associated effects on mitochondria, including impairment of ferrochelatase activity. As
a mitochondrial enzyme, ferrochelatase activity may be inhibited either directly by lead or
indirectly by impairment of iron transport to the enzyme.
The relative value of the lead-ZPP relationship in erythropoietic tissue as an index of
this effect in other tissues hinges on the relative sensitivity of the erythropoietic system
compared with other systems. For example, one study of rats exposed to low levels of lead
over their lifetime demonstrated that protoporphyrin accumulation in renal tissue was already
significant at levels of lead exposure where little change was seen in erythrocyte porphyrin
levels. The issue of sensitivity is obviously distinct from the question of which system is
most accessible to measurement of the effect.
Other steps in the heme biosynthesis pathway are also known to be affected by lead, al-
though these have not been studied as much on a biochemical or molecular level. Levels of co-
proporphyria are increased in urine, reflecting active lead intoxication. Lead also affects
the activity of the enzyme uroporphyrinogen-I-synthetase, resulting in an accumulation of its
substrate, porphobilinogen. The erythrocyte enzyme is much more sensitive to lead than the
hepatic species and presumably accounts for much of the accumulated substrate.
Anemia is a manifestation of chronic lead intoxication, being characterized as mildly
hypochromic and usually normocytic. It is associated with reticulocytosis, owing to shortened
cell survival, and the variable presence of basophilic stippling. Its occurrence is due to
both decreased production and increased rate of destruction of erythrocytes. In children
under four years old, the anemia of iron deficiency is exacerbated by lead, and vice versa.
Hemoglobin production is negatively correlated with blood lead levels in young children, where
iron deficiency may be a confounding factor, as well as in lead workers. In one study, blood
lead values that were usually below 80 (jg/dl were inversely correlated with hemoglobin content.
In these subjects, iron deficiency was found to be absent. The blood lead threshold for
reduced hemoglobin content is about 50 (jg/dl in adult lead workers and somewhat lower in child-
ren, around 40 (jg/dl.
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The mechanism of lead-associated anemia appears to be a combination of reduced hemoglobin
production and shortened erythrocyte survival because of direct cell injury. Effects of lead
on hemoglobin production involve disturbances of both heme and globin biosynthesis. The hemo-
lytic component to lead-induced anemia appears to be due to increased cell fragility and in-
creased osmotic resistance. In one study using rats, it was noted that the reduced cell
deformabi1ity and consequent hemolysis associated with vitamin E deficiency is exacerbated by
lead exposure. The molecular basis for increased cell destruction rests with inhibition of
(Na , K )-ATPase and pyrimidine-5'-nucleotidase. Inhibition of the former enzyme leads to
cell "shrinkage," and inhibition of the latter results in impaired pyrimidine nucleotide phos-
phorolysis and disturbance of the activity of the purine nucleotides necessary for cellular
energetics.
Tetraethyl lead and tetramethyl lead, components of leaded gasoline, undergo transforma-
tion j_n vivo to the neurotoxic trialkyl metabolites as well as further conversion to inorganic
lead. Hence, one might anticipate that exposure to such agents may show effects commonly
associated with inorganic lead in terms of heme synthesis and erythropoiesis. Various surveys
and case reports make it clear that leaded-gasoline sniffing is associated with chronic lead
intoxication in children from socially deprived backgrounds in rural or remote areas. Notable
in these subjects is evidence of impaired heme biosynthesis as indexed by significantly
reduced ALA-D activity. In several case reports of frank lead toxicity from habitual sniffing
of leaded gasoline, such effects as basophilic stippling in erythrocytes and significantly
reduced hemoglobin have also been noted.
Lead-associated disturbances of heme biosynthesis as a possible factor underlying neuro-
logical effects of lead are of considerable interest because of (1) the recognized similarity
between the classical signs of lead neurotoxicity and numerous neurological components of the
congenital disorder known as acute intermittent porphyria, as well as (2) some unusual aspects
of lead neurotoxicity. There are two possible points of connection between lead effects on
both heme biosynthesis and the nervous system. Concerning the similarity of lead neurotoxi-
city to acute intermittent porphyria, there is the common feature of excessive systemic accum-
ulation and excretion of ALA. Second, lead neurotoxicity reflects, to some degree, impaired
synthesis of heme and hemoproteins involved in crucial cellular functions. Available informa-
tion indicates that ALA levels are elevated in the brain of lead-exposed animals, arising via
in situ inhibition of brain ALA-D activity or via transport to the brain after formation in
other tissues. ALA is known to traverse the blood-brain barrier. Hence, ALA is accessible
to, or formed within, the brain during lead exposure and may express its neurotoxic potential.
Based on various i_n vitro and i_n vivo data obtained in the context of neurochemical
studies of lead neurotoxicity, it appears that ALA can readily affect GABAergic function,
particularly inhibiting release of the neurotransmitter GABA from presynaptic receptors, where
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ALA appears to be very potent even at low levels. In an i_n vitro study, agonist behavior by
ALA was demonstrated at levels as low as 1.0 pM ALA. - This J_n vitro observation supports
results of a study using lead-exposed rats in which there was reported inhibition of both
resting and K+-stimulated preloaded ^H-GABA. Further evidence for an effect of some agent
other than lead acting directly is the observation that i_n vivo effects of lead on neurotrans-
mitter function cannot be duplicated with i_n vitro preparations to which lead is added. Human
data on lead-induced associations between disturbed heme synthesis and neurotoxicity, while
limited, also suggest that ALA may function as a neurotoxicant.
The connection between impaired heme and hemoprotein synthesis in the brain of the neo-
natal rat was noted earlier. In these studies there was reduced cytochrome C production and
impaired operation of the cytochrome C respiratory chain. Hence, one might expect that such
impairment would be most prominent in areas of relatively greater eellularization, such as the
hippocampus. As noted in Chapter 10, these are also regions where selective lead accumulation
appears to occur.
12.10.4 Neurotoxic Effects of Lead
An assessment of the impact of lead on human and animal neurobehavioral function raises a
number of issues. Among the key points addressed here are: (1) the internal exposure levels,
as indexed by blood lead levels, at which various neurotoxic effects occur; (2) the persis-
tence or reversibility of such effects; and (3) populations that appear to be most susceptible
to neural damage. In addition, the question arises as to the utility of using animal studies
to draw parallels to the human condition.
12.10.4.1 Internal Lead Levels at which Neurotoxic Effects Occur. Markedly elevated blood
lead levels are associated with the most serious neurotoxic effects of lead exposure
(including severe, irreversible brain damage as indexed by the occurrence of acute or chronic
encephalopathic symptoms, or both) in both humans and animals. For most adult humans, such
damage typically does not occur until blood lead levels exceed 120 |jg/dl. Evidence does
exist, however, for acute encephalopathy and death occurring in some human adults at blood
lead levels below 120 pg/dl. In children, the effective blood lead level for producing
encephalopathy or death is lower, starting at approximately 80-100 pg/dl. It should be
emphasized that, once encephalopathy occurs, death is not an improbable outcome, regardless of
the quality of medical treatment available at the time of acute crisis. In fact, certain
diagnostic or treatment procedures themselves may exacerbate matters and push the outcome
toward fatality if the nature and severity of the problem are not diagnosed or fully recog-
nized. It is also crucial to note the rapidity with which acute encephalopathy symptoms can
develop or death can occur in apparently asymptomatic individuals or in those apparently only
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mildly affected by elevated lead body burdens. Rapid deterioration often occurs, with
convulsions- or coma suddenly appearing with progression to death within 48 hours. This
strongly suggests that even in apparently asymptomatic individuals, rather severe neural
damage probably exists at high blood lead levels even though it is not yet overtly manifested
in obvious encephalopathy symptoms. This conclusion is further supported by numerous studies
showing that overtly lead intoxicated children with high blood lead levels, but not observed
to manifest acute encephalopathy symptoms, are permanently cognitively impaired, as are most
children who survive acute episodes of frank lead encephalopathy.
Recent studies show that overt signs and symptoms of neurotoxicity (indicative of both
CNS and peripheral nerve dysfunction) are detectable in some human adults at blood lead levels
as low as 40-60 pg/dl , levels well below the 60 or 80 jjg/d1 criteria previously discussed as
being "safe" for adult lead exposures. In addition, certain electrophysiological studies of
peripheral nerve function in lead workers, indicate that slowing of nerve conduction veloc-
ities in some peripheral nerves are associated with blood lead levels as low as 30-50 pg/dl
(with no clear threshold for the effect being evident). These results are indicative of
neurological dysfunctions occurring at relatively low lead levels in non-overtly lead intoxi-
cated adults.
Other evidence tends to confirm that neural dysfunctions exist in apparently asymptomatic
children, at similar or even lower levels of blood lead. The body of studies on low-or
moderate-level lead effects on neurobehavioral functions in non-overtly lead intoxicated child-
ren, as summarized in Table 12-1, presents an array of data pointing to that conclusion.
Several well-controlled studies have found effects that are clearly statistically significant,
whereas other have found nonsignificant but borderline effects. Even some studies reporting
generally nonsignificant findings at times contain data confirming some statistically signif-
icant effects, which the authors attribute to various extraneous factors. It should also be
noted that, given the apparent nonspecific nature of some of the behavioral or neural effects
probable at low levels of lead exposure, one would not expect to find striking differences in
every instance. The lowest observed blood lead levels associated with significant neurobehav-
ioral deficits indicative of CNS dysfunction, both in apparently asymptomatic children and in
developing rats and monkeys generally appear to be in the range of 30-50 pg/dl. However,
other types of neurotoxic effects, e.g., altered EEG patterns, have been reported at lower
levels, supporting a continuous dose-response relationship between lead and neurotoxicity.
Such effects, when combined with adverse social factors (such as low parental IQ, low socio-
economic status, poor nutrition, and poor quality of the caregiving environment) can place
children, especially those below the age of three years, at significant risk. However, it
must be acknowledged that nutritional covariates, as well as demographic social factors, have
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been poorly controlled in many of the human studies reviewed. Socioeconomic status also is a
crude measure of parenting and family structure that reauires further assessment as a possible
contributor to observed results of neurobehavioral studies.
Timing, type, and duration of exposure are important factors in both animal and human
studies. It is often uncertain whether observed blood lead levels represent the levels that
were responsible for observed behavioral deficits or electrophysiological changes. Monitoring
of lead exposures in human subjects in all cases has been highly intermittent or nonexistent
during the period of life preceding neurobehavioral assessment. In most human studies, only
one or two blood lead values are provided per subject. Tooth lead may be an important cumula-
tive exposure index, but its modest, highly variable correlation to blood lead or FEP and to
external exposure levels makes findings from various studies difficult to compare quantita-
tively. The complexity of the many important covariates and their interaction with dependent
variable measures of modest validity, e.g., IQ tests, may also account for many of the discrep-
ancies among the different studies.
12.10.4.2 Early Development and the Susceptibility to Neural Damage. On the question of
early childhood vulnerability, the neurobehavioral data are consistert with morphological and
biochemical studies of the susceptibility of the heme biosynthetic pathway to perturbation by
lead. Various lines of evidence suggest that the order of susceptibility to lead's effects
is: (1) young > adults and (2) female > male. Animal studies also have pointed to the peri-
natal period of ontogeny as a particularly critical time for a variety of reasons: (1) it is
a period of rapid development of the nervous system; (2) it is a period where good nutrition
is particularly critical; and (3) it is a period where the caregiver environment is vital to
normal development. However, the precise boundaries cf a critical period are not yet clear
and may vary depending on the species and function or endpoint that is being assessed. Never-
theless, there is genera1, agreement that human infants and toddlers below the age of three
years are at special risk because of j_n utero exposure, increased opportunity for exposure
because of normal mouthing behavior, and increased rates of lead absorption due to various
factors, e.g., nutritional deficiences.
12.10.4.3 The Question of Irreversibility. Little research on humans is available on persis-
tence of effects. Some work suggests that mild forms of peripheral neuropathy in lead workers
may be reversible after termination of lead exposure, but little is known regarding the rever-
sibility of lead effects on central nervous system function in humans. A recent two-year
follow-up study of 28 children of battery factory workers found a continuing relationship
between blood lead levels and altered slow wave voltage of cortical slow wave potentials "indic-
ative of persisting CNS effects of lead. Current population studies, however, will have to be
supplemented by prospective longitudinal studies of the effects of lead on development in
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order to address the issue of reversibility or persistence of lead neurotoxic effects in
humans more satisfactorily.
Various animal studies provide evidence that alterations in neurobehavioral function may
be long-lived, with such alterations being evident long after blood lead levels have returned
to control levels. These persistent effects have been demonstrated in monkeys as well as rats
under a variety of learning performance test paradigms. Such results are also consistent with
morphological, electrophysiological, and biochemical studies on animals that suggest lasting
changes in synaptogenesis, dendritic development, myelin and fiber tract formation, ionic
mechanisms of neurotransmission, and energy metabolism.
12.10.4.4 Utility of Animal Studies in Drawing Parallels to the Human Condition. Animal
models are used to shed light on questions where it is impractical or ethically unacceptable
to use human subjects. This is particularly true in the case of exposure to environmental
toxins such as lead. In the case of lead, it has been effective and convenient to expose
developing animals via their mothers' milk or by gastric gavage, at least until weaning. In
many studies, exposure was continued in the water or food for some time beyond weaning. This
approach simulates at least two features commonly found in human exposure: oral intake and
exposure during early development. The preweaning period in rats and mice is of particular
relevance to in terms of parallels with the first two years or so of human brain development.
However, important questions exist concerning the comparability of animal models to
humans. Given differences between humans, rats, and monkeys in heme chemistry, metabolism,
and other aspects of physiology and anatomy, it is difficult to state what constitutes an
equivalent internal exposure level (much less an equivalent external exposure level). For
example, is a blood lead level of 30 (jg/dl in a suckling rat equivalent to 30 pg/d1 in a
three-year-old child? Until an answer is available to this question, i.e., until the function
describing the relationship of exposure indices in different species is available, the utility
of animal models for deriving dose-response functions relevant to humans will be limited.
Questions also exist regarding the comparability of neurobehavioral effects in animals
with human behavior and cognitive function. One difficulty in comparing behavioral endpoints
such as locomotor activity is the lack of a consistent operational definition. In addition to
the lack of standardized methodologies, behavior is notoriously difficult to "equate" or com-
pare meaningfully across species because behavioral analogies do not demonstrate behavioral
homologies. Thus, it is improper to assume, without knowing more about the responsible under-
lying neurological structures and processes, that a rat's performance on an operant condition-
ing schedule or a monkey's performance on a stimulus discrimination task corresponds tc a
child's performance on a cognitive function test. Still deficits in performance on such tasks
are indicative of altered CNS function which is likely to parallel some type of altered human
CNS function as well.
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In terms of morphological findings, there are reports of hippocampal lesions in both
lead-exposed rats and humans that are consistent with a number of behavioral findings suggest-
ing an impaired ability to respond appropriately to altered contingencies for rewards. That
is, subjects tend to persist in certain patterns of behavior even when changed conditions make
the behavior inappropriate. Other morphological findings in animals, such as demyelination
and glial cell decline, are comparable to human neuropathologic observations mainly at rela-
tively high exposure levels.
Another neurobehavioral endpoint of interest in comparing human and animal neurotoxicity
of lead is electrophysiological function. Alterations of electroencephalographic patterns and
cortical slow wave voltage have been reported for lead-exposed children, and various electro-
physiological alterations both i_n vivo (e.g., in rat visual evoked response) and i_n vitro
(e.g., in frog miniature endplate potentials) have also been noted in laboratory animals. At
this time, however, these lines of work have not converged sufficiently to allow for strong
conclusions regarding the electrophysiological aspects of lead neurotoxicity.
Biochemical approaches to the experimental study of leads effects on the nervous system
have generally been limited to laboratory animal subjects. Although their linkage to human
neurobehavioral function is at this point somewhat speculative, such studies do provide in-
sight to possible neurochemical intermediaries of lead neurotoxicity. No single neurotrans-
mitter system has been shown to be particularly sensitive to the effects of lead exposure;
lead-induced alterations have been demonstrated in various neurotransmitters, including dopa-
mine, norepinephrine, serotonin, and gamma-aminobutyric acid. In addition, lead has been
shown to have subcellular effects in the central nervous system at the level of mitochondrial
function and protein synthesis.
Given the above-noted difficulties in formulating a comparative basis for internal expo-
sure levels among different species, the primary value of many animal studies, particularly in
vitro studies, may be in the information they can provide on basic mechanisms involved in lead
neurotoxicity. A number of j_n vitro studies show that significant, potentially deleterious
effects on nervous system function occur at i_n situ lead concentrations of 5 pM and possibly
lower, suggesting that no threshold may exist for certain neurochemical effects of lead on a
subcellular or molecular level. The relationship between blood lead levels and lead concen-
trations at such extra- or intracellular sites of action, however, remains to be determined.
Despite the problems in generalizing from animals to humans, both the animal and the human
studies show great internal consistency in that they support a continuous dose-response
functional relationship between lead and neurotoxic biochemical, morphological, electrophysio-
logical, and behavioral effects.
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12.10.5 Effects of Lead on the Kidney
It has been known for more than a century that kidney disease can result from lead
poisoning. Identifying the contributing causes and mechanisms of lead-induced nephropathy has
been difficult, however, in part because of the complexities of human exposure to lead and
other nephrotoxic agents.
Nevertheless, it is possible to.estimate at least roughly lead exposure ranges associated
with detectable renal dysfunction in both human, adults -and children. More specifically,
numerous studies of occupationally exposed workers have provided evidence for lead-induced
chronic nephropathy being associated with blood lead levels ranging from 40' to more than
100 pg/dl, and some are suggestive of renal effects possibly occurring even at:levels as low
as 30 pg/dl. Similarly, in children, the relatively sparse evidence available points to the
manifestation of renal dysfunction, as indexed for example by generalized aminoaciduria, at
blood lead levels across the range of 40 to more "than 100 ^ig/dl. The current lack of evidence
for renal dysfunction at lower blood lead levels in children may simply reflect the greater
clinical concern with neurotoxic effects of lead intoxication in children. The persistence of
lead-induced renal dysfunction in children also remains- to be more fully investigated, al-
though a few studies indicate that children diagnosed as being acutely lead poisoned experi-
ence lead nephropathy effects lasting throughout adulthood.
Parallel results from experimental animal studies reinforce the findings in humans and
help illuminate the mechanisms underlying such effects. For'example, a number of transient
effects in human and animal renal function are consistent with experimental findings of revers-
ible lesions such as nuclear inclusion bodies, cytomegaly, swollen mitochondria, and increased
numbers of iron-containing lysosomes in proximal tubule cells. Irreversible lesions such as
interstitial fibrosis are also well documented in both humans and animals following chronic
exposure to high doses of lead. Functional renal changes observed in humans have also been
confirmed in animal model systems with respect to increased excretion of amino -acids and
elevated serum urea nitrogen and uric acid concentrations. The inhibitory effects of lead
exposure on renal blood flow and glomerular filtration rate are currently less clear in exper-
imental model systems; further research is needed to clarify the effects of lead on these
functional parameters in animals. Similarly, while lead-induced perturbation of the renin-
angiotensin system has been demonstrated in experimental animal models, further research is
needed to clarify the exact relationships among lead exposure (particularly chronic low-level
exposure), alteration of the renin-angiotensin system, and hypertension in both humans and
animals.
On the biochemical level, it appears that lead exposure produces changes at a number of
sites. Inhibition of membrane marker enzymes, decreased mitochondrial respiratory function/
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cellular energy production, inhibition of renal heme biosynthesis, and altered nucleic acid
synthesis are the most marked changes to have been reported. The extent to which these mito-
chondrial alterations occur is probably mediated in part by the intracellular bioavailability
of lead, which is determined by its binding to high affinity kidney cytosolic binding proteins
and deposition within intranuclear inclusion bodies.
Recent studies in humans have indicated that the EDTA lead-mobilization test is the most
reliable technique for detecting persons at risk for chronic nephropathy. Blood lead measure-
ments are a less satisfactory indicator because they may not accurately reflect cumulative
absorption some time after exposure to lead has terminated.
A number of major questions remain to be more definitively answered concerning the effect
of lead on the kidney. ¦ Can a distinctive lead-induced renal lesion be identified either in
functional or histologic terms? What biologic measurements are most reliable for the predic-
tion of lead-induced nephropathy? What is the incidence of lead nephropathy in the general
population as well as among specifically defined subgroups with varying exposure? What is the
natural history of treated and untreated lead nephropathy? What is the mechanism of lead-
induced hypertension and renal injury? What are the contributions of environmental and
genetic factors to the appearance of renal injury due to lead? At what level of lead in blood
can the kidneys be affected? Is there a threshold for renal effects of lead? The most dif-
ficult question to answer may well be to determine the contribution of low levels of lead
exposure.to renal disease of non-lead etiologies. 4
12.10.6 Effects of Lead on Reproduction and Development
Data from human and animal studies indicate that lead may exert gametotoxic, embryotoxic,
and (according to some animal studies) teratogenic effects that may influence the survival and
development of the fetus and newborn. Prenatal viability and development, it appears, may
also be affected indirectly, contributing to concern for unborn children and, therefore, preg-
nant women or women of childbearing age being group at special risk for lead effects. Early
studies of quite high dose lead exposure in pregnant women indicate toxic--but not tera-
togenic—effects on the conceptus. Effects on reproductive performance in women at lower
exposure levels are not well documented. Unfortunately, currently available human data
regarding lead effects on the' fetus during development generally do not lend themselves to
accurate estimation, of lowest observed or no-effect levels. However, some studies have shown
that fetal heme synthesis is affected at maternal and fetal blood lead levels as low as
approximately 15 pg/dl, as indicated by urinary ALA levels and ALA-0 activity. This observed
effect level is consistant with lowest observed effect levels for indications of altered heme
synthesis seen at later ages for preschool and older children.
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There are currently no reliable data pointing to adverse effects in human offspring fol-
lowing paternal exposure to lead, but industrial exposure of men to lead at' levels resulting
in blood lead values of 40-50 pg/dl appear to have resulted in altered testicular function.
Also, another study provided evidence of effects of prostatic and seminal vesicle functions at
40-50 (jg/dl blood lead levels in lead workers.
The paucity of human exposure data force an examination of the animal studies for indica-
tions of threshold levels for effects of lead on the conceptus. It must be noted that the
animal data are almost entirely derived from rodents. Based on these rodent data, it seems
likely that fetotoxic effects have occurred in animals at chronic exposures to 600-1000 ppm
lead in the diet. Subtle effects on fetal physiology and metabolism appear to have been ob-
served in rats after chronic maternal exposure to 10 ppm lead in drinking water, while similar
effects of inhaled lead have been seen at chronic levels of 10 mg/m^. With acute exposure by
gavage or by injection, the values are 10-16 mg/kg and 16-30 mg/kg, respectively. Since
humans are most likely to be exposed to lead in their diet, air, or water, the data from other
routes of exposure are of less value in estimating harmful exposures. Indeed, it seems likely
that teratogenic effects occur only when the maternal dose is given by injection.
Although human and animal responses may be dissimilar, the animal evidence does document
a variety of effects of lead exposure on reproduction and development. Measured or apparent
changes in production of or response to reproductive hormones, toxic effects on the gonads,
and toxic or teratogenic effects on the conceptus have all been reported. The animal data
also suggest subtle effects on such parameters as metabolism and cell structure that should be
monitored in human populations. Well designed human epidemiological studies involving large
numbers of subjects are still needed. Such data could clarify the relationship of exposure
levels and durations to blood lead values associated with significant effects, and are needed
for estimation of no-effect levels.
Given that the most clear-cut data concerning the effects of lead on reproduction and
development are derived from studies employing high lead doses in laboratory animals, there is
still a need for more critical research to evaluate the possible subtle toxic effects of lead
on the fetus, using biochemical, ultrastructural, or neurobehavioral endpoints. An exhaustive
evaluation of lead-associated changes in offspring will require consideration of possible
additional effects due to paternal lead burden. Neonatal lead intake via consumption of milk
from lead-exposed mothers may also be a factor at times. Also, it must be recognized that
lead effects on reproduction may be exacerbated by other environmental factors (e.g., dietary
influences, maternal hyperthermia, hypoxia, and co-exposure to other toxins).
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12.10.7. Genotoxic and Carcinogenic Effects of Lead
It is difficult to conclude what role lead may play in the induction cf human neoplasia.
Epidemiological studies of lead-exposed workers provide no definitive findings. However, sta-
tistically significant elevations in cancer of the respiratory tract and digestive system in
workers exposed to lead and other agents warrant some concern. Since it is clear that lead
acetate can produce renal tumors in some experimental animals, it seems reasonable to conclude
that at least that particular lead compound should be regarded as a carcinogen and prudent to
treat it as if it were also human carcinogen (as per IARC conclusions and recommendations).
However, this statement is qualified by noting that lead has been seen to increase tumorogen-
esis rates in animals only at relatively high concentrations, and therefore does not seem to
be an extremely potent carcinogen. I_n vitro studies further support the genotoxic and carcin-
ogenic role of lead, but also indicate that lead is not extremely potent in these systems.
12.10.8. Effects of Lead on the Immune System
Lead renders animals highly susceptible to endotoxins and infectious agents. Host sus-
ceptibility and the humoral immune system appear to be particularly sensitive. As postulated
in recent studies, the macrophage may be the primary immune target cell of lead. Lead-induced
immunosuppression occurs at low lead exposures (blood lead levels in the 20-40 pg/dl range)
that, although they induce no overt toxicity, may nevertheless be detrimental to health.
Available data provide good evidence that lead affects immunity, but additional studies are
necessary to elucidate the actual mechanisms by which lead exerts its immunosuppressive action
Knowledge of lead effects on the human immune system is lacking and must be ascertained in
order to determine permissible levels for human exposure. However, in view of the fact that
lead affects immunity in laboratory animals and is immunosuppressive at very low dosages, its
potential for serious effects in humans should be carefully considered.
12.10.9 Effects of Lead on Other Organ Systems
The cardiovascular, hepatic, endocrine, and gastrointestional systems generally show
signs of dysfunction mainly at relatively high lead exposure levels. Consequently, in most
clinical and experimental studies attention has been primarily focused on more sensitive and
vulnerable target organs, such as the hematopoietic and nervous systems. However, it should
be noted that overt gastrointestinal symptoms associated with lead intoxication have been
observed in some recent studies to occur in lead workers at blood lead levels as low as AO-
GO (jg/dl , suggesting that effects on the gastrointestinal and the other above organ systems
may occur at relatively low exposure levels but remain to be demonstrated by future scientific
i nvesti gati ons.
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APPENDIX 12-A
ASSESSMENT OF STUDIES REPORTING THE POTENTIAL ESSENTIALITY OF LEAD
Available information concerning the potential essentiality of lead is quite limited, due
in part to the inherent difficulties surrounding such investigations. The presence of lead as
a ubiquitous contaminant requires that studies of the effects of lead deficiency use synthetic
or semi-synthetic diets prepared from components extremely low in lead or use chemical agents
to reduce the level of background lead in the diet components. Such procedures, particularly
the use of chelating agents to remove lead, can entail risk in terms of their potential effect
on the nutritional integrity of the particular diet used.
Schwarz (1975) used synthetic diets prepared from low-lead constituents with or without
lead supplementation to determine the effect of low lead on the growth rate of adult rats. It
was reported that lead supplementation, usually over the range of 0.5 to 2.5 ppm lead, was
associated with measurable enhancement in growth rate compared to low-lead animals. In a
critique of the Schwarz results, Nielsen (1980) pointed out that all of the animals in the
Schwarz study, both low-lead and supplementation groups, showed sub-optimal growth, which
could be ascribed to riboflavin deficiency (Morgan and Schwarz, 1978); hence, the question
remains as to what the effect of lead supplementation would be in animals not riboflavin-
deficient and growing optimally. Nielsen (1980) has also questioned the statistical methods
used in the Schwarz studies and pointed out that addition of lead to the diet was of no ap-
parent benefit to deficient controls in subsequent studies. Problems associated with lead
deprivation studies are exemplified by the inability of Schwarz to duplicate his growth rate
data over time. He attributed this to the inadvertent use of a dietary component with an
elevated lead content for diets of the low-lead animals.
In a series of recent reports, Reichlmayr-Lais and Kirchgessner have described results
showing that rats maintained on a semi-synthetic diet low in lead (to levels of either 18 or
45 ppb) over several generations showed reduced growth rate (Reichlmayr-Lais and Kirchgessner,
1981a), disturbances in hematological indices, tissue iron and iron absorption (Reichlmayr-
Lais and Kirchgessner, 1981b,c,d; Kirchgessner and Reichlmayr-Lais, 1981a,b), and changes in
certain enzyme activities and metabolite levels (Reichlmayr-Lais and Kirchgessner, 1981e;
Kirchgessner and Reichlmayr-Lais, 1982). Diets containing 18 ppb were associated with the
most pronounced effects on iron metabolism and growth as well as on enzyme activities and
metabolite levels. Animals maintained on a 45 ppb lead diet showed moderate changes in some
hematological indices in the F^group. In these studies, controls were maintained on the same
dietary matrix to which 1.0 ppm lead was added.
LEAD12/A
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In the above reports, EDTA was used to remove lead (and other elements) from casein, and
the chelating agent ammonium pyrrolidinodithiocarbamate (APDC) was employed to remove lead
from the starch and cellulose components to achieve the final diet level of 18 ppb. For the
45 ppb diet experiment, only the starch and cellulose components were treated with APDC
(Schnegg, 1975). Although the report of Reichlmayr-Lais and Kirchgessner (1981b) indicated
that the cellulose and starch extraction treatment was done on all of the material, a communi-
cation in this regard (Kirchgessner, 1982) noted that only a portion of the starch and cellu-
lose for the 45 ppb study was extracted with APDC. After chelant treatment, the components
were washed with solvents to remove the complexed metals originally present. Washing was also
assumed to remove the chelants.
Caution must be exercised in interpreting these studies as they currently stand, owing
to the use of the chelating agents EDTA and/or APDC. Retention of free chelating agent(s) in
the diets could potentially affect the bioavailability of certain metals. In the report of
Davis et al. (1962), it was noted that diets containing soybean protein that had been ex-
tracted with EDTA to lower iron content, followed by supplementation with iron and copper,
were associated with iron deficiency in chicks maintained on these diets when compared to
chicks fed the same level of iron and copper in untreated diets. Clearly, EDTA treatment of
the soybean protein affected iron bioavailability in this study. Subsequently, the authors
(Davis et al., 1964) attempted to determine the presence of EDTA in the diets by simulating
those used earlier. The crude methodology employed made accurate quantification difficult,
but the amounts of EDTA measured ranged up to 67 (jg/g diet. Other investigations through the
years have documented that EDTA will affect iron absorption/retention and utilization in
various species (e.g., Larsen et al., 1960; Brise and Hallberg, 1962; Saltman and Helbock,
1965; Gunther, 1969; Cook and Monson, 1976).
In this connection, retention of EDTA by proteins appears to be a general problem, based
on information available for casein (Hegenauer et al., 1979), transferrin (Price and Gibson,
1972), the enzyme alkaline phosphatase (Csopak and Szajn, 1973), photoprotein aequonin
(Shimomura and Shimomura, 1982), and human fibrinogen (Nieuwenhuizen et al., 1981). Further-
more, complete removal of EDTA from these rather diverse proteins is reported to involve
forcing conditions, and the washing procedure used by the authors of the studies in question
gives no assurance of being adequate for chelant removal.
Available information also suggests that diets retaining free EDTA and/or APDC, even at
quite low levels, may pose problems by affecting the bioavailability of the essential metal,
nickel. The studies of Schnegg and Kirchgessner (see review of Kirchgessner and Schnegg,
1980) have shown that nickel deficiency in rats followed over several generations is associ-
ated with reduced growth rate, disturbed hematological indices, lowered tissue iron, reduced
LEAD12/A
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PRELIMINARY DRAFT
iron absorption, and disturbances in enzyme activities and metabolite levels. According to
Nielsen (1980), nickel plays a role in the intestinal absorption of trivalent iron. In the
nickel deficiency studies-of Schnegg and Kirchgessner, low-nickel diets contained 15 ppb
nickel, while control groups were maintained on the same basal diet supplemented with 20 ppm
nickel. In the lead deficiency studies under discussion, nickel was added back to the treated
diets at a level of 1.0 ppm (Reichlmayr-Lais and Kirchgessner, 1981b; Kirchgessner and
Reichlmayr-Lais, 1981b).
The interaction of nickel with the chelants EDTA and/or APDC in the context of bioavail-
ability has been documented. Dithiocarbamates such as APDC are effective chelation therapy
agents in protecting against nickel toxicity (see review of Sunderman, 1981), while the report
of Solomons et al. (1982) described the significant effect of EDTA on nickel bioavailability
in human subjects., In the latter study, human volunteers ingested a single dose of 5 mg of
nickel, and the resulting effect on plasma nickel was monitored. When nickel was co-ingested
with EDTA (40 mg of Na2EDTA*H20, a 1.3:1 ratio of EDTA to Ni), not only was the rise in plasma
seen with just nickel abolished, but the plasma nickel level was reduced below the fasting
background level.
It is not possible to draw a ,close comparison of the data of Schnegg and Kirchgessner for
nickel deficiency with the potential effects of impaired nickel bioavailability in the lead
deficiency studies since 1) the actual level of bioavailable nickel in the studies cannot be
defined and 2) the age points for most of the effects seen in nickel deficiency are different
from those in the lead studies. Interestingly, one can calculate that the decrements in body
weight of animals of the Fj-generation in both groups of studies at various common time
points, e.g., 20, 22, 30, 38 days, are virtually identical.
Any mechanism by which lead supplementation at 1.0 ppm in the lead deficiency studies
would operate in a situtation of altered bioavailability of nickel or iron in the diets can
only be inferred, given the absence of any further experiemental data which would more fully
elucidate an essential vs. an artifactive role for lead.
In terms of any simple competitive binding mechanism involving lead, chelating agents,
and nickel or iron, the presence of lead at a level of 1.0 ppm would be seen to most immedi-
ately affect nickel bound up with EDTA (as the common 1:1 complex) or APDC (as the common 1:2
complex). Nickel was added back to the diets at a level of 1.0 ppm. Since the binding
constants for lead and nickel with EDTA are roughly comparable (Shapiro and Papa, 1959; Pribl,
1972), while complexes of lead with dithiocarbamates are vastly greater in stability than the
corresponding nickel complexes (Sastri et al., 1969), lead at 1.0 ppm can displace up to its
molar equivalent of nickel from complexation, which calculates to be 0.3 ppm nickel. This
amount of liberated nickel, 0.3 ppm, appears to be nutritionally adequate, since the minimal
LEAD12/A 12A-3 9/20/83
1202<
-------
PRELIMINARY DRAFT
nutritional requirement is noted to be around 50 ppb (Kirchgessner and Schnegg, 1980; Nielson,
1980). The corresponding amounts of APDC and EDTA required to bind up 1.0 ppm nickel cal-
culate to be 5.4 pg/g (1:2 complex, NiAPDC) and slightly under 5 (jg/g (1:1 complex, Ni-EDTA).
Hence, mere traces of free chelants could be a potential problem.
Similar direct competitive binding involving lead and iron cannot be invoked as likely;
given the relative amounts of iron and lead in lead-supplemented diets, although lead forms
more stable complexes than divalent iron with EDTA or APDC (Pribl, 1972; Sastri et al., 1969).
A cyclic mechanism would have to be invoked whereby Pb-EDTA is formed by exchange of ligand
from Fe-EDTA, is then dissociated i_n vivo, and the displacement process repeated.
Nickel supplementation at 20 ppm in the Schnegg and Kirchgessner studies, where a similar
APDC procedure was used to purify starch and cellulose components, as well as in the study of
Nielsen et al, (1979), where APDC at 10 ppm was employed to assess the role of nickel in iron
metabolism, do not permit comparison with the studies in question because of the 20-fold dis-
parity in the level of supplementation.
Given the above concerns, it would appear that: 1) further experiments, using methodol-
ogy such as scintillography and labeled chelants, are necessary to conclusively determine that
diet preparation in the Reichlmayr-Lais and Kirchgessner studies did not involve retention of
free chelating agents, 2) determination of levels of nickel and lead in tissues, blood, and
excreta would greatly help to elucidate the true role of lead, and 3) replication of the
results in the authors' or another laboratory, preferably with minimal chelant treatment of
components, should be done. It appears that the various reports describe basically single
experiments over several generations, one at a diet level of 18 ppb lead, and one at 45 ppb
lead.
LEAD12/A
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PRELIMINARY DRAFT
12A REFERENCES
Brise, H. ; Hallberg, L. (1962) Iron absorption studies: a method for comparative studies on
iron absorption in man using 2 radio-iron isotopes. Acta Med. Scand. 171 (Suppl.): 23-27.
Cook, J. D. ; Monsen, E. R. (1976) Food iron absorption by man. II: The effect of EDTA on
absorption of dietary non-heme iron. Am. J. Clin. Nutr. 29: 614-620.
Csopak, H. ; Szajn, H. (1973) Factors affecting the zinc content of E. coli alkaline phos-
phatase. Arch. Biochem. Biophys. 157: 374-379.
Davis, P. N. ; Norris, L. C. ; Kratzer, F. H. (1962) Iron deficiency studies in chicks using
treated isolated soybean protein diets. J. Nutr. 78: 445-453.
Davis, P. N.; Norris, L. C.; Kratzer, F. H. (1964) Iron deficiency studies in chicks. J. Nutr.
84: 93-94.
Gunther, R. (1969) Der Einfluss von chelatbildnern auf die Verteilung und Ausscheidung von
Radioeisen bei der Ratte. [Distribution and excretion of radioiron in the rat as
influenced by chelating agents.] Naunyn Schmiedebergs Arch. Pharmakol. Exp. Pathol. 262:
405-418.
Hegenauer, J.; Saltman, P.; Nace, G. (1979) Iron (Ill)-phosphoprotein chelates: stoichiometric
equilibrium constants for interaction of iron and phosphoryl serine residues of phosvitin
and casein. Am. J. Clin. Nutr. 32: 809-816.
Kirchgessner, M. (1982) [Letter to D. Weil]. October 6. Available for inspection at: U.S.
Environmental Protection Agency, Environmental Criteria and Assessment Office, Research
Triangle Park, NC.
Kirchgessner, M. ; Reichlmayr-Lais, A. M. (1982) Konzentrationen verschiedener Stoffwechsel-
metaboliten im experimentellen Bleimangel. [Concentrations of various metabolites with
experimental lead deficiency.] Ann. Nutr. Metab. 26: 50-55.
Kirchgessner, M. ; Schnegg, A. (1980) Biochemical and physiological effects of nickel defi-
ciency. In: Nriagu, J. 0. , ed. Nickel in the environment. New York, NY: John Wiley &
Sons; pp. 635-652.
Kirchgessner, M. ; Reichlmayr-Lais, A. M. (1981a) Changes of iron concentration and iron-
binding capacity in serum resulting from alimentary lead deficiency. Biol. Trace Elem.
Res. 3: 279-285.
Kirchgessner, M. ; Reichlmayr-Lais, A. M. (1981b) Retention, Absorbierbarkeit und intermeditare
Verfiigbarkeit von Eisen bei alimentarem Bleimangel. [Retention, absorbability and
intermediate availability of iron with alimentary lead deficiency.] Int. J. Vitam. Nutr.
Res. 51: 421-424.
Larsen, B. A.; Bidwell, R. G. S.; Hawkins, W. W. (1960) The effect of ingestion of disodium
ethylenediaminetetraacetate on the absorption and metabolism of radioactive iron by the
rat. Can. J. Biochem. Physiol. 38: 51-55.
B12REF/D 12A-5 9/20/63
1204^
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PRELIMINARY DRAFT
Morgan, J. K. ; Schwarz, K. (1978) Light sensitivity of riboflavin in amino acid diets. Fed.
Proc. Fed. Am. Soc. Exp. Biol. 37:671.
Nielsen, F. H. (1980) Effect of form of iron on the interaction between nickel and iron in
rats: growth and blood parameters. J. Nutr. 110: 965-973.
Nielsen, F. H. ; Zimmerman, T. J.; Collings, M. E. ; Myron, D. R. (1979) Nickel deprivation in
rats: nickel-iron interactions. J. Nutr. 109: 1623-1632.
Nieuwenhuizen, W. ; Vermond, A.; Hermans, T. (1981) Human fibrinogen binds EDTA and citrate.
Thromb. Res. 22: 659-663.
Pribl, R. (1972) Analytical applications of EDTA and Related Compounds. New York, NY:
Pergamon Press; p. 27. (International series of monographs in analytical chemistry, v.
52.)
Price, E. M. ; Gibson, J. F. (1972) A re-interpretation of bicarbonate-free ferric transferrin
E.P.R. spectra. Biochem. Biophys. Res. Commun. 46: 646-651.
Reichlmayr-Lais, A. M. ; Kirchgessner, M. (1981a) Zur Essentialitat von Blei fur das tierische
Wachstum. [Why lead is essential for animal growth.] Z. Tierphysiol. Tierernaehr.
Futtermittelkd. 46: 1-8.
Reichlmayr-Lais, A. M. ; Kirchgessner, M. (1981b) Depletionsstudien zur Essentialitat von Blei
an wachsenden Ratten. [Depletion studies on the essentiality of lead in growing rats.]
Arch. Tierenaehr. 31: 731-737.
Reichlmayr-Lais, A. M. ; Kirchgessner, M. (1981c) Hamatologische Veranderungen bef alimentarem
Bleimangel. [Hematological changes with alimentary lead deficiency.] Ann. Nutr. Metab.
25: 281-288.
Reichlmayr-Lais, A. M.; Kirchgessner, M. (1981d) Eisen-,Kupfer- und Zinkgehalte in Neuge-
borenen sowie in Leber und Mi 1 z wachsender ratten bei alimentarem Blei-Mangel. [Iron,
copper and zinc contents in newborns as well as in the liver and spleen of growing rats
in the case of alimentary lead deficiency.] Z. Tierphysiol. Tierernaehr. Futtermittelkd.
46: 8-14.
Reichlmayr-Lais, A. M.; Kirchgessner, M. (1981e) Aktivitats-veranderungen verschiedener Enzyme
im alimentaren Blei-Mangel. [Activity changes of different enzymes in alimentary lead
deficiency.] Z. Tierphysiol. Tierernaehr. Futtermittelkd. 46: 145-150.
Saltman, P.; Helbock, H. (1965) The regulation and control of intestinal iron transport. In:
Proc. Symp. Radio-isotope Anim. Nutr. Physiol., Prague, Czeckoslovakia; pp. 301-317.
Sastri, V. S. ; Aspila, K. I.; Chakrabarti, C. L. (1969) Studies on the solvent extraction of
metal dithiocarbamates. Can. J. Chem. 47: 2320-2323.
Schnegg, A. (1975) [Dissertation.] Technische Universitat Munchen-Weihenstephan. [Technical
University, Munich-Weihenstephan, West Germany.] Available for inspection at: U.S.
Environmental Protection Agency, Environmental Criteria and Assessment Office, Research
Triangle Park, NC.
B12REF/D 12A-6 9/20/83
<>,05^
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PRELIMINARY DRAFT
Schwarz, K. (1975) Potential essentiality of lead. Arh. Rada Toksikol. 26 (Suppl): 13-28.
Shapiro, S. ; Papa, D. (1959) Heavy metal chelates and cesium salts for contrast radiography.
Ann. N.Y. Acad. Sci. 78: 756-763.
Shimomura, 0.; Shimomura, A. (1982) EDTA-binding and acylation of the Ca(2+)-sensitive photo-
protein aequorin. FEBS Lett. 138: 201-204.
Solomns, N. W.; Viteri, F.; Shuler, T. R.; Nielsen, F. H. (1982) Bio-availability of nickel in
men: effects of foods and chemically-defined dietary constituents on the absorption of
inorganic nickel. J. Nutr. 112: 39-50.
Sunderman, F. W. (1981) Chelation therapy in nickel poisoning. Ann. Clin. Lab. Sci. 11: 1-8.
B12REF/D
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PRELIMINARY DRAFT
APPENDIX 12-B
SUMMARY OF PSYCHOMETRIC TESTS USED TO ASSESS COGNITIVE
AND BEHAVIORAL DEVELOPMENT IN PEDIATRIC POPULATIONS
LEAD12/B
12B-1
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TABLE 12B. TESTS COMMONLY USED IN A PSYCWUE'DUCATIONAL BATTERY FOR CHILDREN
Age range
Norms
Scores
Advantages
Disadvantages
General Intelligence Tests
Stanford-Blnet (Fora l-N)
2 yrs - Adult 1972
Wechsler Preschool & Primary 4 - 6H yrs 1967
Scales of Intelligence (WPPSI) Best for 5-yr-olds
Wechsler Intelligence Scale 6-16 yrs
for Children-Revised (WISC-R)
1974
McCarthy Scales of Children's 2S - BH yrs 1972
Abilities (MSCA) Best for ages
4 - 6
Bayley Scales of Mental
Development
2-30 otos.
1969
1. Deviation IQ:
Mean = 100 SD = 16
2. Mental Age Equivalent
1. Oeviation IQ:
Mean = 100 SD = 15
2. Scaled Scores for
10 sub tests:
Mean = 10 SD = 3
1. Deviation IQ:
Mean = 100 SD = 15
2. Scaled Scores for
10 subtests: Mean = 10
SD = 3
1. General Cognitive Index:
Mean = 100 SD = 16
2. Scaled scores for 5
subtests: mean = 50
SD = 10 Age equivalents
can be derived.
1. Standard scores
(M = 100 SD = 16)
2. Mental Development
Psychomotor Index
1. Good reliability & validity
2. Predicts school performance
3. Covers a wide age range
1. Good reliability & validity
2. Predicts school performance
3. Gives a profile of verbal &
non-verbal skills.
4. Useful in early identifica-
tion of learning disability
1. Good reliability & validity
2. Predicts school performance
3. Gives a profile of verbal
and non-verbal skills
4. Useful in identification of
learning disabi1ity
1. Good reliability & validity
2. Good predictor of school
performance
3. Useful in identification of
learning disabilities when
given with a WISC-R or
Stanford-Binet
4. Gives good information for
educational programming
1. Norms are excellent
2. Satisfactory reliability
and validity
3. Best measure of infant
development
1. Tests mostly verbal skills
especially after 6 yrs
2. Does not give a profile
of skills
1. Narrow age range
2. Mentally retarded children
find this a disproportionate
difficult test
T3
TO
1. Gives a lower IQ than
Stanford-Binet for normal
and bright children
1.
Children score much lower
than on WISC-R or
Stanford-Binet
Narrow age range
zs.
3»
73
-< '
a
73
1.
Not a good predictor of-
later functioning In
average as in below average
children
-------
§
£o TAELE 12B (continued)
CD „===_=======^======
Age range Norms Scores Advantages Disadvantages
Slosson Intelligence Test
Infancy - 27 yrs
1963
1. Ratio IQ: is not
related to general
population
h*
O
,C£
A
Peabody Picture Vocabulary
Test
2H - 18 yrs
1959,rev.1981 1. Verbal iq
White, 2. Age equivalent
Middle class
sample
IV
< Visual-Hotor Tests
CD
CO
Frostig Developmental Test of
Visual Perception
3-8 yrs & older
learning disabled
(L.D.) children
1963
White, middle
class sample
1.
2.
3.
1. Good reliability & validity
2. Quick to administer. A
good screening test
1. Easily adxinistered
2. Does not require language
or motor skills
Perceptual Quotient:
Median = 100 Quartile
Deviation = 10
Perceptual Age Equivalent
Scaled Scores for 5 sub-
tests
1. Good reliability for L.D.
children
1. Many items taken from
Stanford Binet
2. Responses require good
language skills
3. Measures a narrow range
of skills
4. A screening test: not to
be used for classification
or placement
1.
4.
5.
Fair reliability and
validity
Tests only receptive
vocabulary
Lower class children score
lower
Mentally Retarded children
score higher than on other
tests
Not to be used for classi-
fication or placement.
Fair reliability for norma
children
Poor Validity
No known relationship to
reading or learning
Remedial program based on
test of questionable value
Not useful in identifying
children at risk for L.D.
~o
73
73
-<
' a
73
Bender-Gestalt
ro
o
oo
oo
4 yrs - Adult
1964
Normal and
Bra in-injured
Children
Beery-Buktenica
Developmental Test of
Visual Motor integration (VMI)
2 - 15 yrs
1967
1. Age equivalent
1. Age equivalent
1. Easily administered
2. Long history of research
makes it a good research
tool
1. Easily administered
2. Good normative sample
1. Fair reliabi1ity
2. Poor predictive and
validity
3. Responses influenced by
fatigue & variations in
administration
4. No known relationship to
reading or subtle neuro-
logical dysfunction
1. Moderate reliability and
validity
2. Correlates better with
mental age than chrono-
logical age
-------
ro
OJ
TABLE 12B (continued)
Age range
Norms
Scores
Advantages
Di sadvantages
Educational Tests
Wide Range Achievement Test
(WRAT)
5 yrs - Adult 1976 1. Standard Score:
Revised mean = 100 SO = IS
2. Grade equivalent
1. Good reliability & validity
Reading scores predict
grade level
2. Tasks similar to actual
work
1. Reading portion tests
word recognition only
2. Responses require good
organizational skills
(could be an advantage)
Peabody Individual
Achievement Test (PIAT)
5-10 yrs
1969
to Woodcock Reading
Mastery Tests
Spache Diagnostic
Reading Scales
Kgn - 12 grade
1st ' 8th grade
1971-72
adjusted for
social class
1972
o
A
1. Standard Scores:
Hean = 100 SD = 15
2. Grade equivalent
3. Age equivalent
1. Grade equivalent
2. Standard Score
3. Percentile Rank
1. Instructional level of
reading (grade equiva-
lent).
2. Independent level of
reading.
3. Potential level of
reading
1. Tests word recognition and
2. Breaks down skills into 5
areas
1. Moderate reliability. Low
stability for Kindergarten
2. No data on predictive
validity
3. A multiple choice test
requiring child to recog-
nize correct answer (could
be an advantage).
4. Heavily loaded on verbal
reasoning.
5. Factor structure changes
with age.
1. Good reliability
2. Breakdown of reading skills
useful diagnostically and 1n
planning remediation
3. Easy to administer and score
1. Independent level score
predicts gains following
remediation
2. Good breakdown of reading
skills
1. No data on validity
1. Fairly complex scoring
2. Moderate reliability
3. No good data on validity
¦o
73
73
-<
o
73
Key Math Diagnostic
Arithmetic Test
Pre-school - 6th
grade
1971
1. Grade equivalent
1. Excellent breakdown of math
skills
2. Easy to administer and
score
1. Moderate reliability
2. No data on validity
ro
o
00
OJ
-------
>
o
ro
\
00
TABLE 12B (continued)
Age range
Norms
Scores
Advantages
Oi sadvantages
A
Tests of Adaptive Functioning
Vineland Social Maturity Scale Birth - 25 yrs
1983
Revised
1. Social Quotient (Ratio)
2. Social Age Equivalent
AAMD Adaptive Behavior Scale
3 yrs - Adult
1974
Institu-
tional izeo
Retardates;
Public School
Children (1982)
1. Percentile Ranks
2. Scaled scores
Progress Assessment Chart of
Social Development (PAC)
~—*
ro
i
™ Developmental Profile
Conners Rating Scale
Birth - Adult
Birth - 12 yrs
3 yrs - 17 yrs
1976
1972
1978
No Scores
1. Age equivalents in 5
S areas
2. IQ equivalency (IQE)
1. Age equivalents
1. Easily administered
2. Good reliability for normal
and HR chidren
1. Discriminates between EMR
and regular classes
2. Useful for class placement
and monitoring progress
1. Useful for training and
assessing progress
2. Gives profile of skills
1. Good reliability and valid-
ity. Excellent study of
construct validity reported
in manual.
2. Gives a profile of skills
1. Host widely used measure of
attention deficit disorder
2. Four factors: conduct prob-
lems; hyperactivity;
inattentive-passive; hyper-
activity index
1. Poor norms
2. No data on validity
3. Items are limited past
preschool years
4. Scores decrease with age
for MR children
1. Moderate reliability for
independent living skills
scale. Poor reliability
for maladaptive behaviour
scale.
2. Lengthy administration
3. Items & scoring are not
behaviorally objective
1.
-o
TO
1. No data on reliability or
validity 3
>
IQE underestimates IQ of 5
above average children,
overestimates IQ of below §
average children. 3s
1. Parents' ratings don't pre-
dict as well as teachers'
ratings
2. Works best middle class
children
Werry-Weiss-Peters Hyperactivity 1 yr - 9 yrs
Scale
1974, 1977 1. Age equivalents
1. Good measure of hyperac-
tivity
2. Seven Factors
1. Limited age range
2. Standardized on middle
class children
io
\
ro
o
\
00
LO
-------
APPENDIX 12-C
KILL BE FORTHCOMING UNDER A SEPARATE COVER.
12C-1
1212<
-------
APPENDIX 12-D
ABSTRACT OF A REVIEW OF THREE STUDIES
ON THE EFFECTS OF LEAD SMELTER
EMISSIONS IN EL PASO, TEXAS
Presenled by Warren R. Muir
Council on Environmental Quality
Washington, D.C.
At Ihe International Conference on Heavy
Metals In the Environmeat
Toronto, Ontario, Canada
October 1975
The committee reviewed two independent studies conducted in 1973 by Dr. Landrigan (CDC) and Dr.
McNeil (ILZRO) to determine the effects of community lead exposures near the ASARCO smeller in El
Paso, Texas. The CDC study used a random sample approach to group participating children, and in the
ILZRO study match paired groups were selected on the basis of residence. In both studies the criteria for
subclassiHcation with regard to lead exposure were blood lead levels Neuropsychological dysfunction was
evaluated by several tests including W1SC, WPPSI. and McCarthy scales. Statistical differences in test results
could no: be directly correlated to blood lead levels
The opinion of the committee was that no firm conclusions could be drawn from the studies as lo whether or
not there are subclinical effects of lead on children in El Paso and that the reports and data made available
have not clearly demonstrated any psychologic or neurologic effects in the children under study. It noted the
absence of major chronic clinical effects, and concluded that these studies therefore do not bear upon the con-
clusions of other investigations under different conditions and those in which clinical effects have been con-
firmed. However, because of inherent problems of study design and the limitations in the tests used, this find-
ing should not lead to a conclusion that low levels of lead have no effectson neuropsychological performance.
Ellen Stlbergeld, Ph.D., NIH, Eileen Higham, Ph.D., and Mr. Russell Jobaris, Johns Hopkins University,
Department of Medical Psychology, served as special consultants.
The committee decided to limit its focus to a review of the three studies, and to attempt to account for and
interpret the differences between the studies. Thus, aspects not related to differences were not emphasized.
The committee limited its consideration to Ihe following materials: (1) reports of the three studies under
consideration; (2) other materials provided by the authors of the studies; (3) background information and
documents collected by Dr. Muir in El Paso. This presentation today consists of excerpts from a draft com-
mittee report.
D.l HISTORY
El Pasn is situated on the Mexican border in the western part of Texas A lead smelter owned by American
Smelling and Refining Company (ASARCO) has been located on the southwestern border of the city, on the
Rio Grande River, since 1 887. The area most conspicuously involved in Ihe sludies. Smelteriown, was a 2 x 6
block area located between the plant and the river. Smelteriown is no longer in existence, having been
destroyed in December 1972. About 2 km south of Smelteriown is Old Fori Bliss, a considerably smaller
community, whose inhabitants were considered in some, but not all, of the sludies.
The ASARCO smelter produces lead, zinc, copper, and cadmium. Particulate matter is removed from air-
borne wastes in a series of baghouses. remaining emissions contain approximately 40 lb of lead per day.
The El Paso City County Health Department began an investigation of the ASARCO smeller in early 1970,
in preparation for an air pollution suit filed by the city in April 1970. As part of this investigation. Dr.
12D-1
1213 ^
-------
Bertram Carnow was hired by (he ci(y as a consultant. At his suggestion, the city began.to sample the blood
lead levels of El Paso children to determine whether any had been over-exposed to lead. This included a large
number of Smeltertown children. Based upon early results in 1971, Br. Carnow visited El Paso, and saw a
selected group of children with high blood lead levels. He interviewed the children, and reviewed their medi-
cal records The information contained in the medical histories, and Dr. Carnow's interviews, constitute the
observations reported by Dr. Carnow in the paper presented to the American Pollution Control Association
(APCA). The clinical observations were in a paragraph of a paper o'.herwise devoted to a consideration of the
effects of the smelter on the environment as a whole, and the extent of its emissions. This report contains no
details on the age. exposures, individual signs and symptoms, or diagnostic criteria used in the ten cases re-
ported. Our committee focused its attention, therefore, upon the two full-scale follow-up epidemiological
studies conducted by Dr. Landrigan (CDC) and Dr. McNeil (ILZRO).
In 1973 ASARCO began a separate investigation of the population of Smeltertown, and asked Dr. James
McNeil of the International Lead Zinc Research Organization (ILZRO) for his assistance in the examination
and possible treatment of children with elevated blood levels greater than 60 mg/100 ml.
As a result of public concern over widespread lead poisoning throughout the city nf El Paso. the mayor re-
quested aid from the Federal Government. A separate protocol for a Center for Disease Control (CDC) study
was submitted to and approved by the Public Health Board in 1973 with the understanding that the two
studies would proceed independently, with those children in the ILZRO sponsored study being excluded
from the CDC study.
In the summer of 1973, CDC and ILZRO proceeded independently to collect data for iheir respective
studies. CDC's examinations were done in two weeks in June 1973, while McNeil's were carried out over the
course of the summer with the aid of the El Paso public school system.
The CDC group supplied to the Committee data in detail, which were sufHcient to allow the committee to
conduct statistical tests and analyze characteristics of groups. For the ILZRO study, this committee requested
data sufficient to carry out similar in-depth analyses. All of the requested data were supplied; however, they
were not in such a form as to allow recalculation of most of the statistical findings of the study or to allow
comparison with the CDC findings.
0 2 STUDY DESIGN
The environmental sampling that was performed was comrr.on for both of these studies. In the selection of
study and control populations, the Landrigan CDC study used a classical approach of a random sample
survey to determine the prevalence of abnormal blood lead values. The 13 census tracts mo:t adjacent to the
smeller were divided into three areas. The sampling frame was designed to obtain about 100 study subjects
from each area for various age groups. Of 833 occupied residences, interviews were obtained from 758 study
subjects in the 1-19 age group. The participating children were divided into a lead-absorption group (40-80
/ig/100 ml) of 46 and a control group ( < 40 /xg/100 ml) of 78. There is no detailed description as to how the
children were chosen.
CDC used these sanpe children as the basis for the later study of neuropsychological dysfunction. All but 3
children chosen for study came from the 1972 prevalence survey; 5 children with known preexisting defects
such as with a history of symptoms compatible with acute lead poisoning or acute lead encephalopathy and
those who had received chelation therapy were excluded.
While it is understood that a number of Smeltertown children with blood lead levels over 40 p'g/100 ml
were eventually involved in litigation, most of them look part in the studies. However, on the recommenda-
tion of the lawyers representing the children, at least one group of 18 did not participate in the ILZRO study.
In the absence of identification by names of the individuals in the three studies, it has been impossible to
evaluate the effects of non-participation.
The ILZRO study was very different; 138 children from Smeltertown agreed io participate in a study. Resi-
dence. not blood lead, was the selection criterion. Two control groups were chosen, and were reported to have
been matched on age, sex, ethnic background, and income, with one set chosen from-EI Paso and another set
for those 8 years of age or under from a rural area about I 2 miles from the smelter. This classification had the
effect of grouping together children who, under the CDC criteria, would have been in "lead" and "control"
groups.
Reproduced from
best available copy
12ll<
-------
The criteria used for subclassification nf children with regard to lead exposure were bated in both studies
on the blood lead level Whereas the CDC study utilized blood lead values obtained at only iwo points in
time. ILZRO. which was faced with the problem that many children had repeated blood lead measurements
with marked variations over a period of 18 months (the levels being generally lower after exposure was dis-
continued), classified children on the basis of the average of the "two highest" recorded values.
This criterion results in a substantial increase in the number of children in the apparently higher blood lead
category and a corresponding decrease in the number of those in the apparently lower blood lead level
category.
Although it is understandable that this type of selection was used to avoid underestimating the problem of
lead intoxicction in the population examined, it ultimately resulted in muddling of the separation between
groups (and possibly obscuring eventual differences). For example, the selection for analysis of children from
the same geographical area, subclassified according to blood lead level, in the ILZRO study, may give the im-
pression that the effects of lead itself ere being studied in a homogeneous population. However, since ex-
posure was geographically the same, other factors inherent to each individual child may be responsible for the
difference in blood lead level observed.
An additional method of classification could have been the use of free erythrocytic protoporphyrin
measurements (FEP) which have been shown to provide an indication of metabolic effects of lead absorption
on metabolism, particularly useful in blood lead level ranges (40-60 jig/100 ml) where analytical and
biological fluctuation may result in uncertain classification (The ILZRO study included this lest but did not
include i; as a basis for data analysis.) Absence of elevation of free erythrocytic protoporphyrin may indicate
those instances where high blood lead levels were spurious.
The following psychometric tests were employed by the two studies:
1. Wechsler Intelligence Scale for Children. WISC (CDC. ILZRO)
2. McCarthy Scales of Children's Abilities (ILZRO)
3. Wechsler Preschool and Primary Scale of Intelligence. WPPS1 (CDC)
4. Lincoln-Oseretsky Motor Development Scale (ILZRO)
5. California Test of Personality Adjustment (ILZRO)
6. Frosting Perceptual Quotient (ILZRO)
7. Bender Visual-Motor Gestah Test (CDC. ILZRO)
B. Peabody
9; WRAT
10. Wepman
11. Draw-a-person
All of tht tests selected by both studies were appropriate for the ages of the children to whom they were ad-
ministered. Since the common ground for these studies is the WISC test, with the WPPSI used by CDC and the
McCarthy Scales by ILZRO for the younger children in their studies, the Committee concentrated on these
three tests and the results obtained for them.
D.3 RESULTS
The study by CDC reports results for 27 children given the WPPSi (12 with blood lead levels 40-80 /ig'100
ml and ! 5 with blood lead levels less than 40 /igMOO ml) and for 97 children tested with the WISC (34 in the
"lead group" and 63 in the "control group"). Statistical analyses were performed on grouped data with one-
tailed tests. Significant differences between lead and control groups are reported in this study for the perfor-
mance IQ's of the WICS and WPPSI. In subtest scores, significant differences were found in Coding on the
WISC and Geometric Design on the WPPSI. When data from both tests are combined, a significant difference
between lead and control groups on performance IQ is found. No differences were found between groups in
verbal lQ's or full-scale IW's of the WISC or WPPS!
The ILZRO study based on match pairing solely by residences reports no significant differences in scores
on the WISC or McCarthy scales between groups with increased lead absorption and pair-matched controls.
Statistical analysis was by means of two-way analysis of variance by age and blond lead levels.
The two studies base much of iheir conclusions upon psychometric and neurological testing of children
from E! Paso and Smeltertown. The reported significant differences and psychometric and neuromotor func-
tions in the CDC study were clouded by potentially important methodological difficulties. These included
-------
age differences between case and control groups, limited statistical treatment of the psychometric data col-
lected, and. in the ILZRO study, the use of an average of the two highest blood lead levels to categorize lead
exposure.
In addition, both the studies shared the following inherent problems:
1. Non-random exclusion of large groups of children
2. Uncertainties as to the selection of control groups
3. Reliance upon blood lead as the indicator of lead exposure and intoxication in analyses of data
4. Measurement of a limited aspect of psychological behavior
5. Lack of consideration of the potentially disruptive influences on test taking of the raring of Smelter-
town, closing of its school, resettlement, litigation, and public controversy
6. Inability to rule out possible preexisting conditions
The Committee stressed the last issue, noting the likelihood that any behavioral or genetic factors that pre-
dispose an individual child to ingest or absorb more lead than another child equally exposed may itself be
correlated to he result of psychometric testing. In other words an increased blood lead level may reflect,
rather than cause, a preexisting difference in intelligence or behavior, an issue inherent in virtually all
retrospective studies of the effects of low level blood lead.
The opinion of the committee was that no firm conclusions could be drawn from the studies as to whether or
not there are subclinical effects of lead on children in El Paso and that the reports and data made available
have not clearly demonstrated any psychologic or neurologic effects in the children under study. It noted the
absence of major chronic clinical effects, and concluded that these studies therefore do not bear upon the con-
clusions of other investigations under different conditions and those in which clinical effects have been con-
firmed. However, because of inherent problems of study design and the limitations in the tests used, this find-
ing should not lead to a conclusion that low levels of lead have no effects on neuropsychological performance.
120-4
1216<
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PRELIMINARY DRAFT
13. EVALUATION OF HUMAN HEALTH RISKS ASSOCIATED WITH
EXPOSURE TO LEAD AND ITS COMPOUNDS
13.1 INTRODUCTION
This chapter attempts to integrate, concisely, key information and conclusions discussed
in preceding chapters into a coherent framework by which interpretation and judgments can be
made concerning the risk to human health posed by present levels of lead contamination in the
United States.
Towards this end, the chapter is organized into seven sections, each of which discusses
one or more of the following major components of the overall health risk evaluation: (1)
external and internal exposure aspects of lead; (2) lead metabolism, which determines the
relationship of external lead exposure to associated health effects of lead; (3) qualitative
and quantitative characterization of key health effects of lead; and (4) identification of
population groups at special risk for health effects associated with lead exposure.
The various aspects of lead exposure discussed include: (1) an historical perspective on
the input of lead into the environment as well as the nature and magnitude of current lead
input; (2) the cycling of lead through the various environmental compartments; and (3) levels
of lead in those media most relevant to lead exposure of various segments of the U.S. popula-
tion. These various aspects of lead exposure are summarized in Section 13.2.
With respect to lead metabolism, some of the relevant issues addressed include: (1) the
major quantitative characteristics of lead absorption, distribution, retention, and excretion
in humans and how these differ between adults and children; (2) the toxicokinetic bases for
external/internal lead exposure relationships with respect to both internal indicators and
target tissue lead burdens; and (3) the relationships between internal and external indices of
lead exposure, i.e., blood-lead levels in relation to lead concentrations in air, food, water,
dust/soil. Section 13.3 summarizes the most salient features of lead metabolism, whereas
Section 13.4 addresses experimental and epidemiological data concerning various blood lead-
environmental media lead relationships.
In regard to various health effects of lead, the main emphasis here is on the identifica-
tion of those effects most relevant to various segments of the general U.S. population and the
placement of such effects in a dose-effect/dose-response framework. In regard to the latter,
a crucial issue has to do with relative response of various segments of the population in
terms of effect thresholds as indexed by some exposure indicator. Furthermore, it is of
interest to assess the extent to which available information supports the notion of a conti-
nuum of effects as one proceeds across the spectrum of exposure levels. Finally, it is of
interest to ascertain the availability of data on the relative number or percentage of members
23PB13/A
13-1
9/20/83
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AUTO
EMISSIONS
INDUSTRIAL
EMISSIONS
CRUSTAL
WEATHERING
AMBIENT
AIR
SURFACE AND
GROUND WATER
SOIL
PLANTS
ANIMALS
PAINT
PIGMENTS
SOLDER
INHALED
AIR
DRINKING
WATER
FOOD
DUSTS
MAN
SOFT
TISSUE
BLOOD
LIVER
KIDNEY
* S\
FECES URINE
Figure 13 1. Pathways of lead from the environment to man.
13-3
1213-c
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PRELIMINARY DRAFT
urban air lead concentrations frequently approaching 1.0 ^9 Pb/m^. A recent measurement of
0.000076 pg Pb/m^ at the South Pole, using highly reliable lead analysis, suggests an anthro-
pogenic enrichment factor of 13,000-fold compared to the same urban air level of 1.0 pg Pb/m^.
Lead occupies an important niche in the U.S. economy, with consumption averaging 1.36 x
106 metric tons/year over the period 1971-1980. Of the various categories of lead consump-
tion, those of pigments, gasoline additives, ammunition, foil, solder and steel products are
widely dispersed and therefore unrecoverable. In the United States, about 41,000 tons are
emitted to the atmosphere each year, including 35,000 tons as gasoline additives. Lead and
its compounds enter the atmosphere at various points during mining, smelting, processing, use,
recycling, or disposal. Leaded gasoline combustion in vehicles accounted for 86 percent of
the total anthropogenic input into the atmosphere in the U.S. in 1981. Of the remaining 14
percent of total emissions from stationary sources, 7 percent was from the metallurgical
industry, 2 percent was from waste oil combustion, and 2 percent from coal combustion.
Atmospheric emissions have declined in recent years with the phase-down of lead in gasoline.
The fate of emitted particulate lead depends on particle size. It has been estimated
that, of the 75 percent of combusted gasoline lead which immediately departs the vehicle in
exhaust, 46 percent is in the form of particles <0.25 pm mass median equivalent diameter
(MMED) and 54 percent has an average particle size of >10 pm. The sub-micron fraction is in-
volved in long-range transport, whereas the larger particles settle mainly near the roadway.
13.2.2 Environmental Cycling of Lead
The atmosphere is the main conduit for movement of lead from emission sources to other
environmental compartments. Removal of lead from the atmosphere occurs by both wet and dry
deposition processes, each mechanism accounting for about one-half of the atmospheric lead
removed. The fraction of lead emitted as alkyl lead vapor (1 to 6 percent) undergoes subse-
quent transformation to other, more stable compounds such as triethyl- or trimethyl lead, as a
complex function of sunlight, temperature and ozone level.
Studies of the movement of lead emitted into the atmosphere indicate that air lead levels
decrease logarithmically with distance away from the source: (1) away from emission sites,
e.g., roadways and smelters; (2) within urban regions away from central business districts;
(3) from urban to rural areas; and (4) from developed to remote areas.
By means of wet and dry deposition, atmospheric lead is transferred to terrestrial sur-
faces and bodies of water. Transfer to water occurs either directly from the atmosphere or
through runoff from soil to surface waters. A sizeable fraction of water-borne lead becomes
lodged in aquatic sediments. Percolation of water through soil does not transport much lead
to ground water because most of the lead is retained at the soil surface.
23PB13/A 13-4 9/20/83
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PRELIMINARY DRAFT
The fate of lead particles on terrestrial surfaces depends upon such factors as the
mechanism of deposition, the chemical form of the particulate lead, the chemical nature of the
receiving soil, and the amount of vegetation cover. Lead deposited on soils is apparently
immobilized by conversion to the carbonate, by binding to humic or fulvic acids, or by ion
exchange on clays and hydrous oxides. In industrial, playground, and household environments,
atmospheric particles accumulate as dusts with lead concentrations often greater than 1000
pg/g. It is important to distinguish these dusts from windblown soil dust, which typically
has a lead concentration of 10 to 30 pg/g.
It has been estimated that soils adjacent to roadways have been enriched in lead content
by as much as 10,000 pg Pb/g soil since 1930, while in urban areas and sites adjacent to
smelters as much as 130,000 jjg Pb/g has been measured in the upper 2.5 cm layer of soil.
Soil appears to be the major sink for emitted lead, with a residency half-time of
decades; but soil as a reservoir for lead cannot be considered as an infinite sink, because
lead will continue to pass into the grazing and detrital food chains and sustain elevated lead
levels in them until equilibrium is reached. It was estimated in Chapters 7 and 8 that lead
in soils not adjacent to major sources such as highways and smelters contain 3 to 5 pg/g of
anthropogenic lead and that this lead has caused an increase of lead in soil moisture by a
factor of 2 to 4. Thus, movement of lead from soils to other environmental compartments is at
least twice the prehistoric rate and will continue to increase for the foreseeable future.
Lead enters the aquatic compartment by direct transfer from the atmosphere via wet and
dry precipitation as well as indirectly from the terrestrial compartment via surface runoff.
Water-borne lead, in turn, may be retained in some soluble fraction or may undergo sedimenta-
tion, depending on such factors as pH, temperature, suspended matter which may entrap lead,
etc. Present levels of lead in natural waters represent a 50-fold enrichment over background
content, from 0.02 to 1.0 pg Pb/1 , due to anthropogenic activity. Surface waters receiving
urban effluent represent a 2500-fold and higher enrichment (50 pg Pb/1 and higher).
13.2.3 Levels of Lead in Various Media of Relevance to Human Exposure
Human populations in the United States are exposed to lead in air, food, water, and dust.
In rural areas, Americans not occupationally exposed to lead consume 50 to 75 pg Pb/day. This
level of exposure is referred to as the baseline exposure because it is unavoidable except by
drastic change in lifestyle or by regulation of lead in foods or ambient air. There are
several environmental circumstances that can increase human exposures above baseline levels.
Most of these circumstances involve the accumulation of atmospheric dusts in the work and play
environments. A few, such as pica and family home gardening, may involve consumption of lead
from chips of exterior or interior house paint.
23PB13/A 13-5 9/20/83
1221<
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PRELIMINARY DRAFT
13.2.3.1 Ambient Air Lead Levels. Monitored ambient air lead concentration values in the
U.S. are contained in two principal data bases: (1) EPA's National Air Sampling Network
(NASN), recently renamed Nat"ional Filter Analysis Network (NFAN); and (2) EPA's National Aero-
metric Data Bank, consistting of measurements by state and local agencies in conjunction with
compliance monitoring for the current ambient air lead standard.
NASN data for 1982, the most current year in the annual surveys, indicate that most of
the urban sites show reported annual averages below C.7 |jg Pb/m^, while the majority of the
non-urban locations have annual figures below 0.2 pg Pb/m^. Over the interval 1976-1981,
there has been a downward trend in these averages, mainly attributable to decreasing lead
content of leaded gasoline and the increasing usage of lead-free gasoline. Furthermore,
examination of quarterly averages over this interval shows a typical seasonal variation,
characterized by maximum air lead values in winter and minimum values in summer.
With respect to the particle size distribution of ambient air lead, EPA studies using
cascade impactors in six U.S. cities have indicated that 60 to 75 percent of such air lead was
associated with sub-micron particles. This size distribution is significant in considering
the distance particles may be transported and the deposition of particles in the pulmonary
compartment of the respiratory tract. The relationship between airborne lead at the monitor-
ing station and the lead inhaled by humans is complicated by such variables as vertical
gradients, relative positions of the source, monitor, and the person, and the ratio of indoor
to outdoor lead concentrations. To obtain an accurate picture of the amount of lead inhaled
during the normal activities of an individual, personal monitors would probably be the most
effective. But the information gained would be insignificant, considering that inhaled lead
is only a small fraction of the total lead exposure, compared to the lead in food, beverages,
and dust. The critical question with respect to airborne lead is how much lead becomes
entrained in dust. In this respect, the existing monitoring network may provide an adequate
estimate of the air concentration from which the rate of deposition can be determined. The
percentage of ambient air lead which represents alkyl forms was noted in one study to range
from 0.3 to 2.7 percent, rising up to about 10 percent at service stations.
13.2.3.2 Levels of Lead In Dust. The lead content of dusts can figure prominently in the
total lead exposure picture for young children. Lead in aerosol particles deposited on rigid
surfaces in urban areas (such as sidewalks, porches, steps, parking lots, etc.) does not
undergo dilution compared to lead transferred by deposition onto soils. Dust can approach
extremely high concentrations. Dust lead can accumulate in the interiors of dwellings as well
as in the outside surroundings, particularly in urban areas.
Measurements of soil lead to a depth of 5 cm in areas of the U.S., using sites near road-
ways, were shown in one study to range fro.n 150 to 500 pg Pb/g dry weight close to roadways
23PB13/A 13-6 9/20/83
1SS2<
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PRELIMINARY DRAFT
(i.e., within 8 meters). By contrast, lead in dusts deposited on or near heavily traveled
traffic arteries show levels in major U.S. cities ranging up to 8000 |jg Pb/g and higher. In
residential areas, exterior dust lead levels are 1000 pg/g or less. Levels of lead in house
dust can be significantly elevated. A study of house dust samples in Boston and New York City
revealed levels of 1000 to 2000 pg Pb/g. Some soils adjacent to houses with exterior lead-
based paints may have lead concentrations greater than 10,000 pg/g.
Thirty-four percent of the baseline consumption of lead by children comes from the con-
sumption of 0.1 g of dust per day (Tables 13-1 and 13-2). Ninety percent of this dust lead is
of atmospheric origin. Dust also accounts for more than ninety percent of the additive lead
attributable to residences in an urban environment or near a smelter (Table 13-3).
13.2.3.3 Levels of Lead in Food. The route by wfnch adults and olaer children in the base-
line population of the U.S. receive the largest proportion of lead intake is through foods,
with reported estimates of the dietary lead intake for Americans ranging from 60 to 75 pg/day.
The added exposure from living in an urban environment is about 30 pg/day for adults and 100
pg/day for children, all of which can be attributed to atmospheric lead.
Atmospheric lead may be added to food crops in the field or pasture, during transporta-
tion to the market, during processing, and during kitchen preparation. Metallic lead, mainly
solder, may be added during processing and packaging. Other sources of lead, as yet undeter-
mined, increase the lead content of food between the field and dinner table. American
children, adult females, and adult males consume 29, 33 and 46 |jg Pb/day, respectively, in
milk and nonbeverage fooas. Of these amounts, 38 percent is of direct atmospheric origin, 36
percent is of metallic origin and 20 percent is of undetermined origin.
Processing of foods, particularly canning, can significantly add to their background lead
content, although it appears that the impact of this is being lessened with the trend away
from use of lead-soldered cans. The canning process can increase lead levels 8-to 10-fold
higher than for the corresponding uncanned food items. Home food preparation can also be a
source of additional lead in cases where food preparation surfaces are exposed to moderate
amounts of high-lead household dust.
13.2.3.4 Lead Levels in Drinking Water. Lead in drinking water may result from contamination
of the water source or from the use of lead materials in the water distribution system. Lead
entry into drinking water from the latter is increased in water supplies which are plumbo-
solvent, i.e., with a pH below 6.5. Exposure of individuals occurs through direct ingestion
of the water or via food preparation in such water.
The interim EPA drinking water standard for lead is 0.05 pg/g (50 pg/1) and several
extensive surveys of public water supplies indicate that only a limited number of samples ex-
ceeded this standard on a nationwide basis. For example, a survey of interstate carrier water
supplies conducted by EPA showed that only 0.3 percent exceeded the standard.
23PB13/A 13-7 9/20/83
±223<
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TABLE 13-1. SUMMARY OF BASELINE HUMAN EXPOSURES TO LEADt
Soil
Percent
Total
of
Natural
Indi rect
Di rect
Lead from
Lead of
Lead
Total
Lead
Atmospheric
Atmospheric
Solder or
Undetermi ned
Source
Consumed
Consumption
Consumed
Lead*
Lead*
Other Metals
Origin
Child 2-yr old
Inhaled Air
0.5
0.8%
0.001
-
0.5
-
-
Food
28.7
46. 7
0.9
0.9
10.9
10.3
17.6
Water & beverages
11.2
18.3
0.01
2.1
1.2
7.8
-
Dust
21.0
34.2
0.6
_I_
19.0
_
1.4
Total
61.4
1.5
3.0
31.6
18. 1
19.0
Percent
100%
2.4%
4.9%
51.5%
29.5%
22.6%
Adult female
Inhaled Air
1.0
1.8%
0.002
-
1.0
-
-
Food
33.2
58.7
1.0
1.0
12.6
11.9
21.6
Water & beverages
17.9
31.6
0.01
3.4
2.0
12.5
-
Dust
4.5
7.9
0.2
-
2.9
-
1.4
Total
56.6
1.2
4.4
18.5
24.4
23.0
Percent
100%
2.1%
7.8%
32.7%
43.1%
26.8%
Adult oale
Inahaled air
1.0
1.3%
0.002
-
1.0
-
-
Food
45.7
59.9
1.4
1.4
17.4
16.4
31.5
Water & beverages
25.)
32.9
0.1
4.7
2.8
17.5
-
Dust
_4
5.9
0.2
-
2.9
—I—
1.4
Total
'6.3
1. 7
6.1
24.1
33.9
32.9
Percent
100%
2.2%
8.0%
31.6%
44.4%
27.1%
"Indirect atmospheric lead has bee i previously incorporated into soil, and will probably remain in the soil for decades or
longer. Direct atmospheric lead has been deposited on the surfaces of vegetation and living areas or incorporated during
food processing shortly before human consumption. It may be assumed that 85 percent of direct atmospheric lead derives
from gasoline additives.
tunits are in pg/day.
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PRELIMINARY DRAFT
TABLE 13-2. RELATIVE
BASELINE HUMAN
LEAD EXPOSURES EXPRESSED PER
KILOGRAM BODY WEIGHT*
Total
Total Lead Consumed
Atmospheric Lead
Lead
Per Kg Body Wt
Per Kg Body Wt
Consumed
pg/Kg-Day
pg/Kg-Day
Child (2 yr old)
(pg/day)
Inhaled air
0.5
0.05
0.05
Food
28.7
2.9
1.1
Water and beverages
11.2
1.1
0.12
Dust
21. 0
2.1
1.9
Total
61.4
6.15
3.17
Adult female
Inhaled air
1.0
0.02
0.02
Food
33.2
0.66
0.25
Water and beverages
17.9
0.34
0.04
Dust
4.5
0.09
0.06
Total
56.6
1.13
0.37
Adult male
Inhaled air
1.0
0.014
0. 014
Food
45.7
0. 65
0.25
Water and beverages
25.1
0.36
0.04
Dust
4.5
0.064
0.04
Total
76.3
1.088
0.344
*Body weights: 2 year old child = 10/kg; adult female = 50 kg; adult male = 70 kg.
The major source of lead contamination of drinking water is the distribution system it-
self, particularly in older urban areas. Highest levels are encountered in "first-draw" sam-
ples, i.e., water sitting in the piping system for an extended period of time. In a large
community water supply survey of 969 systems carried out in 1969-1970, it was found that the
prevalence of samples exceeding 0.05 pg/g was greater where water was plumbo-solvent.
Most drinking water, and the beverages produced from drinking water, contain 0.008 to
0.02 pg Pb/g. The exceptions are canned juices and soda pop, which range from 0.033 to 0.052
pg/g. About 11 percent of the lead consumed in drinking water and beverages is of direct
atmospheric origin, 70 percent comes from solder and other metals.
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TABLE 13-3. SUMMARY OF POTENTIAL ADDITIVE EXPOSURES TO LEAD
Total
Atmospheri c
Other
Lead
Lead
Lead
Consumed
Consumed
Sources
(pg/day)
(pg/day)
(pg/day)
Baseline exposure:
Chi Id (2 yr Did)
Inhaled air
0.5
0.5
-
Food, water & beverages
39.9
12.1
27.8
Dust
21.0
19.0
2.0
Total baseline
61.4
31.6
29.8
Additional exposure due to:
urban atmospheres:1
air inhalation
7
7
0
dust
72
71
1
family gardens2
800
200
600
interior lead paint3
85
-
85
residence nea^ smelter:4
air inhalation
60
60
-
dust
2250
2250
-
secondary occupational5
150
-
-
Baseline exposure:
Adult Male
Inhaled air
1.0
1.0
-
Food, water & beverages
70.8
20.2
50.6
Dust
4.5
2.9
1.6
Total baseline
76.3
24.1
52.2
Additional exposure due to:
urban atmospheres: !
air inhalation
14
14
-
dust
7
7
-
family gardens2
2000
500
1500
interior lead paint3
17
-
17
residence near smelter:4
air inhalation
120
120
-
dust
250
250
-
occupational6
1100
1100
-
secondary occupational 5
21
-
-
smoki ng
30
27
3
wine consumption
100
¦>
¦>
Hncludes lead from household and street dust (1000 pg/g) and inhaled air (.75 pg/m3)
2assumes soil lead concentration of 2000 pg/g; all fresh leafy and root vegetables, sweet
corn of Table 7-15 replaced by produce from garden. Also assumes 25% of soil lead is of
atmospheric origin.
3assumes household dust rises from 300 tti 2000 pg/g. Dust consumption remains the same as
baseline. Does not include consumDtion of paint chips.
^assumes household and street dust increases to 25,000 pg/g, inhaled air increases to 6
pg/m3.
5assumes household dust increases to 2400 pg/g.
^assumes 8 hr shift at 10 pg Pb/m3 or 90% efficiency of respirators at 100 pg/ Pb/m3. and
occupational dusts at 100,000 pg/m3.
13-10
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PRELIMINARY DRAFT
13.2.3.5 Lead in Other Media. Flaking lead paint in deteriorated housing stock in urban
areas of the Northeast and Midwest has long been recognized as a major source of lead exposure
for young children residing in this housing stock, particularly for children with pica.
Individuals who are cigarette smokers may inhale significant amounts of lead in tobacco smoke.
One study has indicated that the smoking of 30 cigarettes daily results in lead intake. equiva-
lent to that of inhaling lead in ambient air at a level of 1.0 pg Pb/m3.
13.2.3.6 Cumulative Human Lead Intake From Various Sources.
Table 13-1 shows the baseline of human lead exposures as described in detail in Chapter
7. These data show that atmospheric lead accounts for at least 30 percent of the baseline
adult consumption and 50 percent of the daily consumption by a 2 yr old child. These percent-
ages are conservative estimates because a part of the lead of undetermined origin may
originate from atmospheric lead not yet accounted for.
From Table 13-2, it can be seen that young children have a dietary lead intake rate that
is 5-fold greater than for adults, on a body weight basis. To these observations must be
added that absorption rates for lead are higher in children than in adults by at least 3-fold.
Overall, then, the rate of lead entry into the blood stream of children, on a body weight
basis, is estimated to be twice that of adults from the respiratory tract and 6 and 9 times
greater from the GI tract. Since children consume more dust than adults, the atmospheric
fraction of the baseline exposure is ten-fold higher for children than for adults, on a body
weight basis. These differences generally tend to place young children at greater risk, in
terms of relative amounts of proportions of atmospheric lead absorbed per kg body weight, than
adults under any given lead exposure situation.
13.3 LEAD METABOLISM: KEY ISSUES FOR HUMAN HEALTH RISK EVALUATION
From the detailed discussion of those various quantifiable characteristics of lead toxi-
cokinetics in humans and animals presented in Chapter 10, several clear issues emerge as being
important for full evaluation of the human health risk posed by lead:
1) Differences in systemic or internal lead exposure of groups within the general popula-
tion in terms of such factors as age/development and nutritional status; and
2) The relationship of indices of internal lead exposures to both environmental levels of
lead and tissues levels/effects.
Item 1 provides the basis for identifying segments within human populations at increased
risk in terms of exposure criteria and is used along with additional information on relative
sensitivity to lead health effects for identification of risk populations. The chief concern
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PRELIMINARY DRAFT
with item 2 is the adequacy of current means for assessing internal lead exposure in terms of
providing adequate margins of protection from lead exposures producing health effects of con-
cern.
13.3.1 Differential Internal Lead Exposure Within Population Groups
Compared to adults, young children take in more lead through the gastrointestinal and
respiratory tracts on a unit body weight basis, absorb a greater fraction of this lead intake,
and also retain a greater proportion of the absorbed amount.
Unfortunately, such amplification of these basic toxicokinetic parameters in children vs.
adults also occurs at the time when: (1) humans are developmentally more vulnerable to the
effects of toxicants such as lead in terms of metabolic activity, and (2) the interactive re-
lationships of lead with such factors as nutritive elements are such as to induce a negative
course toward further exposure risk.
Typical of physiological differences in children vs. adults in terms of lead exposure im-
plications is a more metabolically active skeletal system in children. In children, turnover
rates of bone elements such as calcium and phosphorus are greater than in adults, with corre-
spondingly greater mobility of bone-sequestered lead. This activity is a factor in the obser-
vation that the skeletal system of children is relatively less effective as a depository for
lead than in adults.
Metabolic demand for nutrients, particularly calcium, iron, phosphorus, and the trace
nutrients, is such that widespread deficiencies of these nutrients exist, particularly among
poor children. The interactive relationships of these elements with lead are such that defi-
ciency states both enhance lead absorption/retention and, as in the case of lead-induced
reductions in 1,25-dihydroxyvitamin D, establish increasingly adverse interactive cycles.
Quite apart from the physiological differences which enhance internal lead exposure in
children is the unique relationship of 2- to 3-year-olds to their exposure setting by way of
normal mouthing behavior and the extreme manifestation of this behavior, pica. This behavior
occurs in the same age group which studies have consistently identified as having a peak in
blood lead. A number of investigations have addressed the quantification of this particular
route of lead exposure, and it is by now clear that such exposure will dominate other routes
when the child's surroundings, e.g., dust and soil, are significantly contaminated by lead.
Information provided in Chapter 10 also makes it clear that lead traverses the human pla-
cental barrier, with lead uptake by the fetus occurring throughout gestation. Such uptake of
lead poses a potential threat to the fetus via an impact on the embryo!ogical developement of
the central nervous and other systems. Hence, the only logical means of protecting the fetus
from lead exposure is exposure control during pregnancy.
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Within the general population, then, young children and pregnant women qualify as defin-
ale risk groups for lead exposure. Occupational exposure to lead, particularly among lead
workers, logically defines these individuals as being in a high-risk category; work place con-
tact is augmented by those same routes and levels of lead exposure affecting the rest of the
adult population. From a biological point of view, lead workers do not differ from the gene-
ral adult population with respect to the various toxicokinetic parameters and any differences
in exposure control — occupational vs. non-occupational populations—as they exist are based on
factors other than toxicokinetics.
13.3.2 Indices of Internal Lead Exposure and Their Relationship To External Lead Levels and
Tissue Burdens/Effects•
Several points are of importance in this area of lead toxicokinetics. They are: 1) the
temporal characteristics of indices of lead exposure; 2) the relationship of the indicators to
external lead levels; 3) the validity of indicators of exposure in reflecting target tissue
burdens; 4) the interplay between these indicators and lead in body compartments; and 5) those
various aspects of the issue with particular reference to children.
At this time, blood lead is widely held to be the most convenient, if imperfect, index of
both lead exposure and relative risk for various adverse health effects. In terms of ex-
posure, however, it is generally accepted that blood lead is a temporally variable measure
which yields an index of relatively recent exposure because of the rather rapid clearance of
absorbed lead from the blood. Such a measure, then, is of limited usefulness in cases where
exposure is variable or intermittent over time, as is often the case with pediatric lead ex-
posure.
Mineralizing tissue, specifically deciduous teeth, accumulate lead over time in propor-
tion to the degree of lead exposure, and analysis of this material provides an assessment
integrated over a.greater time period and of more value in detecting early childhood exposure.
These two methods of assessing internal lead exposure have obvious shortcomings. A blood
lead value will say little about any excessive lead intake at early periods, even though such
remote exposure may have resulted in significant injury. On the other hand, whole tooth or
dentine analysis is retrospective in nature and can only be done after the particularly vulne-
rable age in children under 4 to 5 years-- has passed. Such a measure, then provides little
utility upon which to implement regulatory policy or clinical intervention.
The dilemmas posed by these existing methods may be able to be resolved by i_n situ analy-
sis of teeth and bone lead, such that the intrinsic advantage of mineral tissue as a cumula-
tive index is combined with measurement which is temporally concordant with on-going exposure.
Work in several laboratories offers promise for such J_n situ analysis (See Chapters 9 and 10).
23PB13/A 13-13 9/20/83
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A second issue concerning internal indices of exposure and environmental lead is the
relationship of changes in lead content of some medium with changes in blood content. Much of
Chapter 11 was given over to description of the mathematical relationships of blood lead with
lead in some external medium— air, food, water, etc., without consideration of the biological
underpinnings for these relationships.
Over a relatively broad range of lead exposure through some medium, the relationship of
lead in the external medium to blood lead is curvilinear, such that relative change in blood
lead per unit change in medium level generally becomes increasingly less as exposure increases.
This behavior may reflect changes in tissue lead kinetics, reduced lead absorption, or in-
creased excretion. Limited animal data would suggest that changes in excretion or absorption
are not factors in this phenomenon. In any event, modest changes in blood levels with expo-
sure at the higher end of this range are in no way to be taken as reflecting concomitantly
modest changes in body or tissue lead uptake. Evidence continues to accumulate which suggests
that an indicator such as blood lead is an imperfect measure of tissue lead burdens and of
changes in such tissue levels in relation to changes in external exposure.
In Chapter 10, it was pointed out that blood lead is logarithmically related to chelata-
ble lead (the latter being a more useful measure of the potentially toxic fraction of body
lead), such that a unit change in blood lead is associated with an increasingly larger amount
of chelatable lead. One consequence of this relationship is that moderately elevated blood
lead values will tend to mask the "margin of safety" in terms of mobile body lead burdens.
Such masking is apparent in one study of children where chelatable lead levels in children
showing moderate elevations in blood lead overlapped those obtained in subjects showing frank
plumbism, i.e. overt lead intoxication.
Related to the above is the question of the source of chelatable lead. It was noted in
Chapter 10 that some sizable fraction of chelatable lead is derived from bone and this compels
reappraisal of the notion that bone is an "inert sink" for otherwise toxic body lead.
The notion of bone lead as toxicologically inert never did accord with what was known
from studies of bone physiology, i.e., that bone is a "living" organ, and the thrust of recent
studies of chelatable lead as well as interrelationships of lead and bone metabolism is more
to a view of bone lead as actually an insidious source of long-term systemic lead exposure
rather than evidence of a protective mechanism permitting significant lead contact in indus-
trialized populations.
The complex interrelationships of lead exposure, blood lead, and lead in body compart-
ments is of particular interest in considering the disposition of lead in young children.
Since children take in more lead on a weight basis, and absorb and retain more of this lead
than the adult, one might expect that either tissue and blood levels would be significantly
elevated or that the child's skeletal system would be more efficient in lead sequestration.
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Blood lead levels in young children are either similar to adults (males) or somewhat
higher (adult females). Limited autopsy data, furthermore, indicate that soft tissue levels
in children are not markedly different from adults, whereas the skeletal system shows an
approximate 2-fold increase in lead concentration from infancy to adolescence. Neglected in
this observation is the fact that the skeletal system in children grows at an exponential
rate, so that skeletal mass increases 40-fold during the interval in childhood when bone lead
levels increase 2-fold, resulting in an actual increase of approximately 80-fold in total ske-
letal lead. If the skeletal growth factor is taken into account, along with growth in soft
tissue and the expansion of vascular fluid volumes, the question of lead disposition in
children is better understood.
Finally, limited animal data indicate that blood lead alterations with changes in lead
exposure are poor indicators of such changes in target tissue. Specifically, it appears that
abrupt reduction of lead exposure will be more rapidly reflected in blood lead than in such
target tissues as the central nervous system, especially in the developing organism. This
discordance may underlie the observation that severe lead neurotoxicity in children is assoc-
iated with a rather broad range of blood lead values (see Section 12.4).
The above discussion of soma of the problems with the use of blood lead in assessing tar-
get tissue burdens or the toxicologically active fraction of total body lead is really a sum-
mary of the inherent toxicokinetic problems with use of blood lead levels in defining margins
of safety for avoiding internal exposure or undue risk of adverse effects.
If, for example, blood lead levels of 40-50 pg/dl in "asymptomatic" children are associ-
ated with chelatable lead burdens which overlap those encountered in frank pediatric plumbism,
as documented in one series of lead-exposed children, then there is no margin of safety at
these blood levels for severe effects which are not at all a matter of controversy. Were it
both logistically feasible to do so on a large scale and were the use of chelants free of
health risk to the subjects, serial provocative chelation testing would appear to be the
better indicator of exposure and risk. Failing this, the only prudent alternative is the use
of a large safety factor applied to blood lead which would translate to an "acceptable" chela-
table burden. It is likely that this blood lead value would lie well below the currently
accepted upper limit of 30 pg/dl, since the safety factor would have to be large enough to
protect against frank plumbism as well as more subtle health effects seen with rion-overt lead
intoxication. This rationale from the standpoint of lead toxicokinetics is in accord also
with the growing data base for dose-effect relationships of lead's effects on heme biosynthe-
sis, erythropoiesis, and the nervous system in humans as detailed in Sections 12.3 and 12.4.
The future developemant and routine use of i_n situ mineral tissue testing at time points
concordant with on-going exposure and the comparison of such results with simultaneous blood
23PB13/A 13-15 9/20/83
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PRELIMINARY DRAFT
lead and chelatable lead measurement would be of significant value in further defining what
level of blood lead is indeed an acceptable upper limit.
13.4 DEMOGRAPHIC CORRELATES OF HUMAN LEAD EXPOSURE AND RELATIONSHIPS BETWEEN EXTERNAL AND
INTERNAL LEAD EXPOSURE INDICES
13.4.1 Demographic Correlates of Lead Exposure
Studies of ancient populations using bone and teeth,show that levels of internal exposure
of lead today are substantially elevated over past levels. Studies of current populations
living in remote areas far from urbanized cultures show blood lead levels in the range of 1 to
5 pg/dl. In contrast to the blood lead levels found in remote populations, data from current
U.S. populations have geometric means ranging from 10 to 20 |jg/dl depending on age, race, sex
and degree of urbanization. These increases of current exposure appear to be associated with
industrialization and widespread commercial use of lead, for example gasoline combustion.
Age appears to be one of the single most important demographic covariate of blood lead
levels. Blood lead levels in children up to six years are generally higher than those in non-
occupational ly exposed adults. Children aged two to three years tend to have the highest
levels as shown in Figure 13-2. Blood lead levels in non-occupational ly exposed adults may
increase slightly with age due to skeletal lead accumulation.
Sex has a differential impact on blood lead levels depending on age. No significant dif-
ferences exist between males and females less than seven years of age. Males above the age of
seven generally have higher blood lead levels than females.
Race also plays a role, in that blacks have higher blood lead levels than either whites
or Hispanics. Race has yet to be fully disentangled from exposure.
Blood lead levels also seem to increase with degree of urbanization. Data from NHANES II
show that blood lead levels in the United States, averaged from 1976 to 1980, increase from a
geometric mean of 11.9 pg/dl in rural populations to 12.8 (jg/d1 in urban populations less than
one million, and increase again to 14.0 pg/dl in urban populations of one million or more.
Recent U.S. blood lead levels show a downward trend occurring consistently across race,
age and geographic location. The downward pattern commenced in the early part of the 1970's
and has continued into 1980. The downward trend has occurred from a shift in the entire dis-
tribution and not through a truncation in the high blood lead levels. This consistency sug-
gests a general causative factor, and attempts have been made to identify the causative ele-
ment. Reduction in lead emitted from the combustion of leaded gasoline is a prime candidate,
but at present no causal relationship has be«n definitively established.
23PB13/A 13-16 9/20/83
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40
35
30
25
20
15
10
5
0
IDAHO STUDY
NEW YORK SCREENING - BLACKS
NEW YORK SCREENING - WHITES
NEW YORK SCREENING HISPANICS
NHANES II STUDY BLACKS
NHANES II STUDY - WHITES
12 3 4 5 6 7 8 9 10
AGE IN YEARS
13 -2. Geometric mean blood lead levels by race and age for younger children in the
ES II study, and the Kellogg/Silver Valley and New York Childhood Screening Studies.
-------
PRELIMINARY DRAFT
Blood lead levels, examined on a population basis, have similarly skewed distributions.
Blood lead levels, from a population thought to be homogenous in terms of demographic and lead
exposure characteristics, approximately follow a lognormal distribution. Geometric standard
deviations, an estimation of dispersion, from four different studies discussed in Chapter 11,
including analytic error, are about 1.4 for children and possibly somewhat smaller for adults.
This allows an estimation of the upper tail of the blood lead distribution, which is the popu-
lation segment in the United States at higher risk.
13.4.2 Relationships Between External and Internal Lead Exposure Indices
Because one main purpose of this chapter is to examine relationships of lead in air and
lead in blood under ambient conditions, the results of studies most appropriate to this area
have been emphasized. A summary of the most appropriate studies appears in Table 13-4. At
air lead exposures of 3.2 fjg/m3 or less, there is no statistically significant difference be-
tween curvilinear and linear blood lead inhalation relationships. At air lead exposures at 10
Mg/m^ or more, either nonlinear or linear relationships can be fitted. Thus, a reasonably
consistent picture emerges in which the blood lead air lead relationship by direct inhalation
was approximately linear in the range of normal ambient exposures (0.1 - 2.0 fjg/m3) as dis-
cussed in Chapter 7. Differences among individuals in a given study, and among several
studies are large, so that pooled estimates of the blood lead inhalation slope depend upon the
the weight given to various studies. Several studies were selected for analysis, based upon
factors described earlier. EPA analyses of experimental and clinical studies (Griffin et al.,
1975; Rabinowitz et al., 1974, 1976, 1977; Kehoe 1961a,b,c; Gross 1981; Hammond et al. , 1981)
suggest that blood lead in adults increases by 1.64 ± 0.22 pg/dl from direct inhalation of
each additional pg/m3 of air lead. EPA analyses of population studies (Yankel et al., 1977;
Roels et al., 1980; Angle and Mclntire, 1979) suggest that, for children, the blood lead
increase is 1.97 ± 0.39 |jg/d 1 per mQ/1"3 air lead. EPA anaylsis of Azar's population study
(Azar et al., 1975) yields a slope of 1.32 ± 0.38 for adult males.
These slope estimates are based on the assumption that an equilibrium level of blood lead
is achieved within a few months after exposure begins. This is only approximately true, since
lead stored in the skeleton may return to blood after some years. Chamberlain et al. (1978)
suggest that long term inhalation slopes should be about 30 percent larger than these esti-
mates. Inhalation slopes quoted here are associated with a half-life of blood lead in adults
of about 30 days. O'Flaherty et al. (1982) suggest that the blood-lead half-life may increase
slightly with duration of exposure, but this has not been confirmed (Kang et al., 1983).
One possible approach would be to regard all inhalation slope studies as equally infor-
mative and to calculate an average slope using reciprocal squared standard error estimates as
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PRELIMINARY DRAFT
TABLE 13-4. SUMMARY OF BLOOD INHALATION SLOPES, (p)
pg/dl per pg/m3
POPULATION
STUDY
STUDY
TYPE
(P)
SLOPE
pg/dl per pg/ma
MODEL SENSITIVITY
OF SLOPE*
Children
Adult Males
Angle and
Mclntire, 1979
Omaha, NE
Roels et al.
(1980)
Belg iurn
Yankel et al.
(1977); Walter
et al. (1980)
Idaho
Azar et al.
(1975). Five
groups
Griffin et al.
(1975), NY
prisoners
Gross
(1979)
Rabinowitz et
al. (1973,1975,
1977)
Populati on
Population
Population
Population
Experi ment
Experiment
Experi ment
1074
148
879
149
43
1.92
2.46
1.52
1.32
1.75
1.25
2.14
(1.40 - 4.40)1,2,3
(1.55 - 2.46)1,2
(1.07 - 1.52)1'2,3
(1.08 - 2.39)2'3
(1. 52 3.38)4
(1.25 - 1.55)2
(2.14 - 3.51)5
"¦Selected from among the most plausible statistically equivalent models. For nonlinear models,
slope at 1.0 pg/m^.
''"Sensitive to choice of other correlated predictors such as dust and soil lead.
2
Sensitive to linear vs. nonlinear at low air lead.
3
Sensitive to age as a covariate.
4
Sensitive to baseline changes in controls.
^Sensitive to assumed air lead exposure.
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weights. This approach has been rejected for two reasons. First, the standard error estima-
tes characterize only the internal precision of an estimated slope, not its representativeness
(i.e., bias) or predictive validity. Secondly, experimental and clinical studies obtain more
information from a single individual than do population studies. Thus, it may not be appro-
priate to combine the two types of studies.
Estimates of the inhalation slope for children are only available from population
studies. The importance of dust ingestion as a non-inhalation pathway for children is estab-
lished by many studies. A slope estimate has been derived for air lead inhalation based on
those studies (Angle and Mclntire 1979; Roels et al., 1980; Yankel et al., 1977) from which
the air inhalation and dust ingestion contributions can both be estimated.
While direct inhalation of air lead is stressed, this is not the only air lead contribu-
tion that needs to be considered. Smelter studies allow partial assessment of the air lead
contributions to soil, dust and finger lead. Conceptual models allow preliminary estimation
of the propagation of lead through the total food chain as shown in Chapter 7. Useful mathe-
matical models to quantify the propagation of lead through the food chain need to be devel-
oped. The direct inhalation relationship does provide useful information on changes in blood
lead as responses to changes in air lead on a time scale of several months. The indirect
pathways through dust and soil and through the food chain may thus delay the total blood lead
response to changes in air lead, perhaps by one or more years. The Italian ILE study
facilitates partial assessment of this delayed response from leaded gasoline as a source.
Dietary absorption of lead varies greatly from one person to another and depends on the
physical and chemical form of the carrier, on nutritional status, and on whether lead is in-
gested with food or between meals. These distinctions are particularly important for con-
sumption by children of leaded paint, dust and soil. Typical values of 10 percent absorption
of ingested lead into blood have been assumed for adults and 25 to 50 percent for children.
It is difficult to determine accurate relationships between blood lead levels and lead
levels in food or water. Dietary intake must be estimated by duplicate diets or fecal lead
determinations. Water lead levels can be determined with some accuracy, but the varying
amounts of water consumed by different individuals adds to the uncertainty of the estimated
relationships.
Quantitative analyses relating blood lead levels and dietary lead exposures have been re-
ported. Studies on infants provide estimates that are in close agreement. Only one indi-
vidual study is available for adults (Sherlock et al. 1982); another estimate from a number of
pooled studies is also available. These two estimates are in good agreement. Most of the
subjects in the Sherlock et al. (1982) and United Kingdom Central Directorate on Environmental
Pollution (1982) studies received quite high dietary lead levels (>300 pg/day). The fitted
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PRELIMINARY DRAFT
cube root equations give high slopes at lower dietary lead levels. On the other hand, the
linear slope of the United Kingdom Central Directorate on Environmental Pollution (1982) study
is probably an underestimate of the slope at lower dietary lead levels. For these reasons,
the Ryu et al. (1983) study is the most believable, although it only applies to infants.
Estimates for adults should be taken from the experimental studies or calculated from assumed
absorbtion and half-life values. Most of the dietary intake supplements were so high that
many of the subjects had blood lead concentrations much in excess of 30 pg/m5 for a considera-
ble part of the experiment. Blood lead levels thus may not completely reflect lead exposure,
due to the previously noted nonlinearity of blood lead response at high exposures. The slope
estimates for adult dietary intake are about 0.02 pg/dl increase in blood lead per pg/day in-
take, but consideration of blood lead kinetics may increase this value to about 0.04. Such
values are a bit lower than those estimated from the population studies extrapolated to typi-
cal dietary intakes about 0.05 |jg/d1 per pg/day. The value for infants is much larger.
The relation between blood lead and water lead is not clearly defined and is often de-
scribed as nonlinear. Water lead intake varies greatly from one person to another. It has
been assumed that children can absorb 25 to 50 percent of lead in water. Many authors chose
to fit cube root models to their data, although polynomial and logarithmic models were also
used. Unfortunately, the form of the model greatly influences the estimated contributions to
blood lead levels from relatively low water lead concentration.
Although there is close agreement in the quantitative analyses of the relationship bet-
ween blood lead level and dietary lead, there is a larger degree of variability in results of
the various water lead studies. The relationship is curvilinear, but its exact form is yet to
be determined. At typical levels for U.S. populations, the relationship appears linear. The
only study that determines the relationship based on lower water lead values (<100 pg/1) is
the Pocock et al. (1983) study. The data from this study, as well as the authors themselves,
suggest that in this lower range of water lead levels, the relationship is linear. Further-
more, the estimated contributions to blood lead levels from this study are quite consistent
with the polynomial models from other studies. For these reasons, the Pocock et al. (1983)
slope of 0.06 is considered to represent the best estimate. The possibility still exists,
however., that the higher estimates of the other studies may be correct in certain situations,
especially at higher water lead levels (>100 pg/1).
Studies relating soil lead to blood lead levels are difficult to compare. The relation-
ship obviously depends on depth of soil lead, age of the children, sampling method, cleanli-
ness of the home, mouthing activities of the children, and possibly many other factors. Var-
ious soil sampling methods and sampling depths have been used over time, and as such they may
not be directly comparable and may produce a dilution effect of the major lead concentration
PB13B/C 13-21 9/20/83
123
~ <
-------
PRELIMINARY DRAFT
contribution from dust which is located primarily in the top 2 cm of the soil. Increases in
soil dust lead significantly increase blood lead in children. From several studies (Yankel et
al., 1977; Angle and Mclntire, 1979) EPA estimates an increase of 0.6 to 6.8 (jg/dl in blood
lead for each increase of 1000 \iq/q in soil lead concentration. The values from the Stark et
al. (1982) study of about 2, may represent a reasonable median estimate. The relationship of
housedust lead to blood lead is difficult to obtain. Household dust also increases blood
lead, children from the cleanest homes in the Silver Valley/Kellogg Study having 6 (jg/dl less
lead in blood, on average, than those from the households with the most dust.
A number of specific environmental sources of airborne lead have been evaluated for po-
tential direct influence on blood lead levels. Combustion of leaded gasoline appears to be the
largest contributor to airborne lead. Two studies used isotope ratios of lead to estimate the
relative proportion of lead in the blood coming from airborne lead.
From the Manton study it can be estimated that between 7 to 41 percent of the blood lead
in study subjects in Dallas resulted from airborne lead. Additionally, these data provide a
means of estimating the indirect contribution of air lead to blood lead. By one estimate,
only 10 to 20 percent of the total airborne contribution in Dallas is from direct inhalation.
From the ILE data of Facchetti and Geiss (1982), as shown in Table 13-5, the direct in-
halation of air lead may account for 54 percent of the total adult blood lead uptake from
leaded gasoline in a large urban center, but inhalation is a much less important pathway in
TABLE 13-5. ESTIMATED CONTRIBUTION OF LEADED GASOLINE TO BLOOD LEAD
BY INHALATION AND N0N-INHALATION PATHWAYS
Ai r Lead
Fracti on
From
Gasoli nee
B1 ood
Lead
Fracti on
From t
Gasoli ne
Blood
Lead
From
Gasoline
In Ai r
(Mg/dl)
Blood Lead
Net
Inhaled
From ^
Gasoli ne
(ng/dl)
Estimated
Fraction
Gas-Lead
Inhalation
Locati on
Turi n
<25 km
>25 km
0.873
0.587
0.587
0.237
0.125
0.110
2.79
0. 53
0.28
2.37
2.60
3.22
0.54
0.17
0.08
Fraction of air lead in Phase 2 attributable to lead in gasoline.
^Mean fraction of blood lead in Phase 2 attributable to lead in gasoline.
CEstimated blood lead from gas inhalation = p x (a) x (b), p = 1.6.
Estimated blood lead from gas, non-inhalation = (f)-(e)
eFraction of blood lead uptake from gasoline attributable to direct inhalation = (f)/(e)
Source: Facchetti and Geiss (1982), pp. 52-56.
23PB13/A 13-22
9/20/83
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PRELIMINARY DRAFT
suburban parts of the region (17 percent of the total gasoline lead contribution) and in the
rural parts of the region (8 percent of the total gasoline lead contribution). EPA analyses
of the preliminary results from the 1LE study separated the inhalation and non-inhalation con-
tributions of leaded gasoline to blood lead into the following three parts: (1) An increase
of about 1.7 pg/dl in blcod lead per pg/m3 of air lead, attributable to direct inhalation of
the combustion products of leaded gasoline; (2) a sex difference of about 2 pg/dl attributable
to lower exposure of women to indirect (non-inhalation) pathways for gasoline lead; and (3) a
non-inhalation background attributable to indirect gasoline lead pathways, such as ingestion
of dust and food, increasing from about 2 pg/dl in Turin to 3 ng/dl in remote rural areas.
The non-inhalation background represents only two to three years of environmental accumulation
at the new experimental lead isotope ratio. It is not clear how to numerically extrapolate
these estimates to U.S. subpopul ations; but it is evident that even in rural and suburban
parts of a metropolitan area, the indirect (non-inhalation) pathways for exposure to leaded
gasoline make a significant contribution to blood lead. This can be seen in Table 13-5. It
should also be noted that the blood lead isotope ratio responded fairly rapidly when the lead
isotope ratio returned to its pre-experimental value, but it is not yet possible t.o estimate
the long term change in blood lead attributable to persistent exposures to accumulated envi-
ronmental lead.
Studies of data from blood lead screening programs suggest that the downward trend in
blood lead levels noted earlier is due to the reduction in air lead levels, which has been at-
tributed to the reduction of lead in gasoline.
Primary lead smelters, secondary lead smelters and battery plants emit lead directly into
the air and ultimately increase soil and dust lead concentrations in their vicinity. Adults,
and especially children, have been shown to exhibit elevated blood lead levels when living
close to these sources. Blood lead levels in these residents have been shown to be related to
air, as well as to soil or dust exposures.
13.4.3 Proportional Contributions of Lead in Various Media to Blood Lead
in Human Populations
The various mathematical descriptions of the relationship of blood lead to lead in indi-
vidual media--air, food, water, dust, soil—were discussed in some detail in Chapter 11 and
concisely in the preceding section (13.4.2) of this chapter. Using values for lead intake/
content of these media which appear to represent the current exposure picture for human popu-
lations in the U.S., these relationships are further employed in this section to estimate
proportional inputs to total blood lead levels in U.S. populations. Such an exercise is of
help in providing an overall perspective on which routes of exposure are of most significance
in terms of contributions to blood lead levels seen in U.S. populations.
PB13B/C 13-23 9/20/83
1239-c
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PRFLIMINARY DRAFT
Table 13-6 tabulates the relative direct contributions (in percentages) of air lead to
blood lead at different air-lead levels for calculated typical background levels of lead from
food and water in adults. The blood lead contributions from diet are estimated using the
slope 0.02 (jg/dl increase in blood lead pg/cay intake as discussed in Section 11.4.2.4.
TABLE 13-6. DIRECT CONTRIBUTIONS OF AIR LEAD TO BLOOD LEAD (PbB)
IN ADULTS AT FIXED INPUTS OF WATER AND FOOD LEAD
Air Lead
(Mfl/m3)
0.1
1.0
1.5
PbB (Air)*
0.2
2.0
3.0
PbB (Food)
2.0
2.0
2.0
PbB (Water)c
0.6
0.6
0.6
% PbB
From Air
7.1
43.4
53.5
A PbB
t = 2.0 for 3.2 pg/m3 or less.
A Pb Air
""Assuming 100 [jg/day lead from diet and slope 0.02 as discussed in Section 11.4.2.4.
'Assuming 10 pg/£ water, Pocock et al. (1983).
In Table 13-7 are listed the direct contributions of air lead to blood lead at varying
air lead levels for children given calculated typical background levels of blood lead for food
and water. Diet contribution is based on the work of Ryu et al. (1983). Table 13-8 shows
the relative contributions of dust/soil to blood lead at varying dust/soil levels for children
given calculated background levels of blood lead from air, food, and water. Assuming that
virtually all soil/dust lead is due to atmospheric fallout of lead particles, the percentage
contribution of air directly and indirectly to blood lead becomes significantly greater than
when considering just the direct impact of inhaling lead in the ambient air.
23PB13/A 13-24 „ ^ 9/20/83
1210<
-------
A
TABLE 13-7. DIRECT CONTRIBUTIONS OF AIR LEAD TO BLOOD LEAD IN CHILDREN AT
FIXED INPUTS OF FOOD AND WATER LEAD
Air Lead . % PbB
(pg/m^) PbB (Air)a PbB (Food) PbB (Water) From Air
0.1 0.2 16.0 0.6 1.2
0.5 1.0 16.0 0.6 5.7
1.0 2.0 16.0 0.6 10.8
1.5 3.0 16.0 0.6 15.3
2.5 5.0 16.0 0.6 23.1
3 A PbB
A Pb A i r
b
j = 2.0 for 3.2 (jg/m^ or less.
Assuming 100 (jg Pb/day based upon Ryu et al. (1983).
c Assuming 10 (jg Pb/1 water, using Pocock et al. (1983).
TD
3D
^ 1.5 3.0 16.0 0.6 15.3 £
-<
o
TO
3>
-------
TABLE 13-8. CONTRIBUTIONS OF DUST/SOIL LEAD TO BLOOD LEAD IN CHILDREN AT
FIXED INPUTS OF AIR, FOOD, AND WATER LEAD
Dust-Soi1
(pg/g)
Air Lead
pg/m3
PbB (Air)'
PbB (Food)
PbB (Water)0
PbB
(Dust-Soi1)(
% PbB
From Dust/Soil
500
1000
2000
0.5
0.5
0.5
1.0
1.0
1.0
16.0
16.0
16.0
0.6
0.6
0.6
0.3/3.4
0.6/6.8
1.2/13.6
1. 7/16.2
3.3/27.8
6.4/43.6
A PbB _ , „ t ,3
A Pb Air~ 2.0 for 3.2 [ig/m or less.
Assuming 100 pg Pb/day based on Ryu et al. (1983).
"Assuming 10 pg Pb/1 water, based on Pocock et al. (1983).
Based on range 0.6 to 6.8 pg/dl for 1000 pg/g (Angle and Mclntire, 1979).
-------
PRELIMINARY DRAFT
13.5 BIOLOGICAL EFFECTS OF LEAD RELEVANT TO THE GENERAL HUMAN POPULATION
13.5.1 Introduction
It is clear from the wealth of available literature reviewed in Chapter 12, that there
exists a continuum of biological effects associated with lead across a broad range of expo-
sure. At rather low levels of lead exposure, biochemical changes, e.g., disruption of certain
enzymatic activities involved in heme biosynthesis and erythropoietic pyrimidine metabolism,
are detectable. Heme biosynthesis is a generalized process in mammalian species, including
man, with importance for normal physiological functioning of virtually all organ systems.
With increasing lead exposure, there are sequentially more intense effects on heme synthesis
and a broadening of lead effects to additional biochemical and physiological mechanisms in
various tissues, such that increasingly more severe disruption of the normal functioning of
many different organ systems becomes apparent. In addition to heme biosynthesis impairment at
relatively low levels of lead exposure, disruption of normal functioning of the erythropoietic
and the nervous systems are among the earliest effects observed as a function of increasing
lead exposure. With increasingly intense exposure, more severe disruption of the erythropoie-
tic and nervous systems occur and additional organ systems are affected so as to result, for
example, in the manifestation of renal effects, disruption of reproductive functions, and im-
pairment of immunological functions. At sufficiently high levels of exposure, the damage to
the nervous system and other effects can be severe enough to result in death or, in some cases
of non-fatal lead poisoning, long-lasting sequelae such as permanent mental retardation.
As discussed in Chapter 12 of this document, numerous new studies, reviews, and critiques
concerning Pb-related health effects have been published since the issuance of the earlier EPA
lead criteria document in 1977. Of particular importance for present criteria development
purposes are those new findings, taken together with information earlier available at the
writing of the 1977 Criteria Document, which have bearing on the establishment of quantitative
dose-effect or dose-response relationships for biological effects of lead potentially viewed
as adverse health effects likely to occur among the general population at or near existing
ambient air concentrations of lead in the United States. Key information regarding observed
health effects and their implications are discussed below for- adults and children.
For the latter group, children, emphasis is placed on the discussion of (1) heme biosyn-
thesis effects, (2) certain other biochemical and hematological effects, and (3) the disrup-
tion of nervous system functions. All of these appear to be among those effects of most con-
cern for potential occurrence in association with exposure to existing U.S. ambient air lead
levels of the population group (i.e., children ^6 years old) at greatest risk for lead-induced
health effects. Emphasis is also placed on the delineation of internal lead exposure levels,
as defined mainly by blood-lead (PbB) levels, likely associated with the occurrence of such
23PB13/A 13-27 9/20/83
I243<
-------
PRELIMINARY DRAFT
effects. Also discussed are characteristics of the subject effects that are of crucial impor-
tance in regard to the determination of which might reasonably be viewed as constituting
"adverse health effects" in affected human populations.
Over the years, there has been superimposed on the continuum of lead-induced biological
effects various judgments as to which specific effects observed in man constitute "adverse
health effects". Such judgments involve not only medical concensus regarding the health sig-
nificance of particular effects and their clinical management, but also incorporate societal
value judgments. Such societal value judgments often vary depending upon the specific overall
contexts to which they are applied, e.g., in judging permissible exposure levels for occupa-
tional versus general population exposures to lead. For some lead exposure effects, e.g.,
severe nervous system damage resulting in death or serious medical sequelae consequent to
intense lead exposure, there exists little or no disagreement as to these being significant
"adverse health effects." For many other effects detectable at sequentially lower levels of
lead exposure, however, the demarcation lines as to which effects represent adverse health
effects and the lead exposure levels at which they are accepted as occurring are neither sharp
nor fixed, having changed markedly during the past several decades. That is, from a histori-
cal perspective, levels of lead exposure deemed to be acceptable for either occupationally ex-
posed persons or the general population have been steadily revised downward as more sophisti-
cated biomedical techniques have revealed formerly unrecognized biological effects and concern
has increased in regard to the medical and social significance of such effects.
It is difficult to provide a definitive statement of all criteria by which specific bio-
logical effects associated with any given agent can be judged to be "adverse health effects".
Nevertheless, several criteria are currently wel1-accepted as helping to define which effects
should be viewed as "adverse". These include: (1) impaired normal functioning of a specific
tissue or organ system itself; (2) reduced reserve capacity of that tissue or organ system in
dealing with stress due to other causative agents; (3) the reversibi1ity/irreversibi1ity of
the particular effect(s); and (4) the cumulative or aggregate impact of various effects on
individual organ systems on the overall functioning and well-being of the individual.
Examples of possible uses of such criteria in evaluating lead effects can be cited for
illustrative purposes. For example, impairment of heme synthesis intensifies with increasing
lead exposure until hemeprotein synthesis is inhibited in many organ systems, leading to re-
ductions in such functions as oxygen transport, cellular energetics, and detoxification of
xenobiotic agents. The latter effect can also be cited as an example of reduced reserve capa-
city pertinent to consideration of effects of lead, the reduced capacity of the liver to deto-
xify certain drugs or other xenobiotic agents resulting from lead effects on hepatic detoxifi-
cation enzyme systems.
23PB13/A
13-28
9/20/83
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PRELIMINARY DRAFT
In regard to the issue of reversibi1ity/irreversibi1ity of lead effects, there are really
two dimensions to the issue that need to be considered, i.e.: (1) biological reversibility or
irreversibility characteristic of the particular effect in a given organism; and (2) the gene-
rally less-recognized concept of exposure reversibility or irreversibility. Severe central
nervous system damage resulting from intense, high level lead exposure is generally accepted
as an irreversible effect of lead exposure; the reversibi1ity/irreversibi1ity of certain more
difficult-to-detect neurological effects occurring at lower lead exposure levels, however,
remains a matter of some controversy. The concept of exposure reversibi 1 ity/irreversibi1ity
can be illustrated by the case of urban children of low socioecomomic status showing dis-
turbances in heme biosynthesis and erythropoiesis. Biologically, these various effects may be
considered reversible; the extent to which actual reversibility occurs, however, is determined
by the feasibility of removing these subjects from their particular lead exposure setting. If
such removal from exposure is unlikely or does not occur, then such effects will logically
persist and, defacto, constitute essentially irreversible effects.
13.5.2 Dose-Effect Relationships for Lead-Induced Health Effects
13.5.2.1 Human Adults
Table 13-9 concisely summarizes the lowest observed effect levels (in terms of blood lead
concentrations) thus far credibly associated with particular health effects of concern for
human adults in relation to specific organ systems or generalized physiological processes,
e.g. heme synthesis.
The most serious effects associated with markedly elevated blood lead levels are severe
neurotoxic effects that include irreversible brain damage as indexed by the occurrence of
acute or chronic encephalopathic symptoms observed in both humans and experimental animals.
For most human adults, such damage typically does not occur until blood lead levels exceed
100-120 pg/dl. Often associated with encephalopathic symptoms at such blood lead levels or
higher are severe gastrointestinal symptoms and objective signs of effects on several other
organ systems as well. The precise threshold for occurrence of overt neurological and gastro-
intestinal signs and symptoms of lead intoxication remains to be established but such effects
have been observed in adult lead workers at blood lead levels as low as 40-60 pg/dl, notably
lower than the 60 or 80 pg/dl levels previously established or discussed as being "safe" for
occupational lead exposure.
Other types of health effects occur coincident with the,above overt neurological and gas-
trointestinal symptoms indicative of marked lead intoxication. These range from frank peri-
pheral neuropathies to chronic renal nephropathy and anemia. Toward the lower range of blood
lead levels associated with overt lead intoxication or somewhat below, less severe but impor-
tant signs of impairment in normal physiological functioning in several organ systems are
evident, including: (1) slowed nerve conduction velocities indicative of peripheral nerve
23PB13/A 13-29 9/20/83
1245<
-------
TABLE 13-9. SUMMARY OF LOWEST OBSERVED EFFECT LEVELS FOR KEY LEAD-INDUCED HEALTH EFFECTS IN ADULTS
Lowest Observed
Effect Level (PbB)
Heme Synthesis and
Hematological Effects
Neurological
Effects
Renal System
Effects
Reproducti ve
Function Effects
Gastrointestinal
Effects
100-120 (jg/dl
60 pg/dl
60 pg/dl
co
o
V3 50 pg/dl
40 pg/dl
30 pg/dl
25-30 pg/dl
15-20 pg/dl
<10 pg/dl
Frank aneaia
Reduced hemoglobin
production
Increased urinary ALA and
elevated coproporphyrins
Erythrocyte protoporphyrin
(EP) elevation in Bales
Erythrocyte protoporphyrin
(EP) elevation in females
ALA-D inhibition
Encephalopathy signs
and symptoms
T>
Overt subencephalopathic
neurological symptoms
1?
Peripheral nerve dysfunction
(slowed nerve conduction)
Chronic renal
nephropathy
Altered testicular
function
1
Overt gastrointestinal
symptoms (colic, etc.)
Abbreviations: PbB = blood lead concentrations.
-------
•PRELIMINARY DRAFT
dysfunction (at 30-40 pg/dl, or possibly lower levels); (2) altered testicular function (at
40-50 pg/dl); and (3) reduced hemoglobin production (at approximately 50 pg/dl) and other
signs of impaired heme synthesis evident at still lower blood lead levels. All of these ef-
fects point toward a generalized impairment of normal physiological functioning across several
different organ systems, which becomes abundantly evident as adult blood lead levels approach
or exceed 30-40 pg/dl. Evidence for impaired heme synthesis effects in blood cells exists at
still lower blood lead levels in human adults and the significance of this and evidence of
impairment of other biochemical processes important in cellular energetics are the subject of
discussion below in relation to health effects observed in children.
13.5.2.2 Chi 1dren
Table 13-10 summarizes lowest observed effect levels for a variety of imporatnt health
effects observed in children. Again, as for adults, it can be seen that lead impacts many
different organ systems and biochemical/physiological processes across a wide range of expo-
sure levels. Also, again, the most serious of these effects is the severe, irreversible cen-
tral nervous system damage manifested in terms of encephalopathic signs and symptoms. In
children, effective blood lead levels for producing encephalopathy or death are lower than for
adults, starting at approximately 80-100 pg/dl. Other overt neurological symptoms are evident
at somewhat lower blood lead levels associated with lasting neurological sequalae. Colic and
other overt gastrointestinal symptoms clearly occur at similar or still lower blood lead
levels in children, at least down to GO pg/dl and, perhaps, below. Renal dysfunction is also
manifested along with the above overt signs of lead intoxication in children and has been
reported at blood lead levels as low as 40 pg/dl in some pediatric populations. Frank anemia
is also evident at 70 pg/dl, representing an extreme manifestation of reduced hemoglobin syn-
thesis observed at blood lead levels as low as 40 pg/dl along with other signs of marked heme
synthesis inhibition at that exposure level. Again, all of these effects are reflective of
widespread impact of lead on the normal physiological functioning of many different organ
systems in children at bloo'cf l^ad levels at least as low as 40 pg/dl.
Among the mos? important' and controversial of the issues discussed in Chapter 12 are the
evaluation of neuropsychological or electrophysiological effects associated with low-level
lead exposures in non-overtly lead intoxicated children. None of the available studies on the
subject, individually, can be said to prove conclusively that significant neurological effects
occur in children at blood-Pb levels <30 pg/dl. The collective neurobehavioral studies of CNS
(cognitive; IQ) effects, for example, can probably now be most reasonably interpreted as most
clearly being indicative of a likely association between neuropsychologic deficits and low-
level Pb-exposures in young children resulting in blood-Pb levels of approximately 30 to 50
pg/dl.
23PB13/A 13-31 9/20/83
1247<
-------
TABLE 13-10. SUMMARY OF LOWEST OBSERVED EFFECT LEVELS FOR KEY LEAD-INDUCED HEALTH EFFECTS IN CHILDREN
Lowest Observed
Effect Level (PbB)
Heme Synthesis and
Hematological Effects
Neurological
Effects
Renal System
Effects
Gastrointestinal
Effects
Other Biochemical
Effects
N
OD
A
80-100 pg/di
70 pg/dl
60 pg/dl
50 pg/dl
^ 40 pg/dl
CO
ro
30 pg/d1
15-20 pg/dl
10
Frank anemia
Reduced hemoglobin
Elevated coproporphyrin
Increased urinary ALA
Erythrocyte protoporphyin
elevation
ALA-D inhibition
Encephalopathy
signs and symptoms
T
Cognitive (CNS) deficts
Peripheral nerve dysfunction
(slowed NCV's)
CNS electrophysiological
deficits
Renal dys-
function
(aminoaciduria)
Colic, other overt
gastrointestinal symptoms
Vitamin D metabolism
interference
Py-5-N activity
inhibition
"D
x>
-<
o
;o
Abbreviations: PbB = blood lead concentrations; Py-5-N = pyrimidine-5'-nucleotidase.
-------
PRELIMINARY DRAFT
However, due to specific methodological problems with each of the various studies (as
noted in Chapter 12), much caution is warranted that precludes conclusive acceptance of the
observed effects being due to Pb rather than other (at times uncontrolled for) potentially
confounding variables.
Also of considerable importance are studies by by Benignus et al. (1981) and Otto et al,
(1981, 1982a,b), which provide evidence of changes in EEG brain wave patterns and CNS evoked
potential responses in non-overtly lead intoxicated children experiencing relatively low
blood-Pb levels. Sufficient exposure information was provided by Otto et al. (1981, 1982a,b);
and appropriate statistical analyses were carried out which demonstrated clear, statistically
significant associations between electrophysiological (SW voltage) changes and blood-Pb levels
in the range of 30 to 55 (jg/dl and probable analogous associations at blood-Pb levels below 30
pg/dl (with no evident threshold down to 15 pg/dl). In this case, the continued presence of
such electrophysiological changes upon follow-up two years later, suggests persistence of such
effects even in the face of later declines in blood-Pb levels and, therefore, possible non-
reversibility of the observed electrophysiological CNS changes. However, the reported elec-
trophysiological effects were not found to be significantly associated with IQ decrements.
The precise medical or health significance of the neuropsychological and electrophysiolo-
gical effects found by the above studies to be associated with low-level Pb-exposures is dif-
ficult to state with confidence at this time. The IQ deficits and other behavioral changes,
although statistically significant, are generally relatively small in magnitude as detected by
the reviewed studies, but nevertheless may still impact the intellectual development, school
performance, and social development of the affected children sufficiently so as to be regarded
as adverse. This would be especially true if such impaired intellectual development or school
performance and disrupted social development were reflective of persisting, long-term effects
of low-level lead exposure in early childhood. The issue of persistence of such lead effects,
however, remains to be more clearly resolved, with some study results reviewed in Chapter 12
and mentioned above suggesting relatively short-lived or markedly decreasing Pb-effects on
neuropsychological functions over" a few years from early to later childhood and other studies
suggesting that significant low-level Pb-induced neurobehavioral and EEG effects may, in fact,
persist into later childhood.
In regard to additional studies reviewed in Chapter 12 concerning the neurotoxicity of
lead, certain evidence exists which suggests that neurotoxic effects may be associated with
Pb-induced altered heme synthesis, which results in an accumulation of ALA in brain affecting
CNS GABA synthesis, binding, and/or inactivation by neuronal reuptake after synaptic release.
Also, available experimental data suggest that these effects may have functional significance
in the terms of this constituting one mechanism by which lead may increase the sensitivity of
23PB13/A 13-33 9/20/83
1249-:
-------
PRELIMINARY DRAFT
rats to drug-induced seizures and, possibly, by which GABA-related behavioral or physiological
control functions are disrupted. Unfortunately, the available research data do not allow cre-
dible direct estimates of blood-Pb levels at which such effects might occur in rats, other
non-human mammalian species, or man. Inferentially, however, one can state that threshold
levels for any marked Pb-induced ALA impact on CNS GABA mechanisms are most probably at least
as high as blood-Pb levels at which significant accumulations of ALA have been detected in
erythrocytes or non-blood soft tissues (see below). Regardless of any dose-effect levels in-
ferred, though, the functional and/or medical significance of Pb-induced ALA effects on CNS
mechanisms at low-levels of Pb-exposure remains to be more fully determined and cannot, at
this time, be unequivocably seen as an adverse health effect.
Research concerning Pb-induced effects on heme synthesis, also provides information of
importance in evaluating whether significant health effects in children are associated with
blood-Pb levels below 30 pg/dl. As discussed earlier, in Chapter 12, Pb affects heme synthe-
sis at several points in its metabolic pathway, with consequent impact on the normal func-
tioning of many body tissues. The activity of the enzyme, ALA-S, catalyzing the rate-limiting
step of heme synthesis does not appear to be significantly affected until blood-Pb levels
reach or exceed approximately 40 ng/dl• The enzyme ALA-D, which catalizes the conversion of
ALA to' porphobilinogen as a further step in the heme biosynthetic pathway, appears to be
affected at much lower blood-Pb levels as indexed directly by observations of ALA-D inhibition
or indirectly in terms of consequent accumulations of ALA in blood and non-blood tissues.
More specifically, inhibition of erythrocyte ALA-D activity has been observed in humans and
other mammalian species at blood-Pb levels even below 10 to 15 |jg/dl, with no clear threshold
evident. Correlations between erythrocyte and hepatic ALA-D activity inhibition in lead
workers at blood-Pb levels in the range of 12 to 56 nQ/dl suggest that ALA-D activity in soft
tissues (eg. brain, liver, kidney, etc.) may be inhibited at similar blood-Pb levels at which
erythrocyte ALA-D activity inhibition occurs, resulting in accumulations of ALA in both blood
and soft tissues.
It is now clear that significant increases in both blood and urinary ALA occur below the
currently commonly-accepted blood-Pb level of 40 |jg/dl and, in fact, such increases in blood
and urinary ALA are detectable in humans at blood-Pb levels below 30 pg/dl , with no clear
ft
threshold evident down to 15 to 20 pg/dl. Other studies have demonstrated significant eleva-
tions in rat brain, spleen and kidney ALA levels consequent to acute or chronic Pb-exposure,
but no clear blood-Pb levels can yet be specified at which such non-blood tissue ALA increases
occur in humans. It is reasonable to assume, however, that ALA increases in non-blood tissues
likely begin to occur at roughly the same blood-Pb levels associated with increases in eryth-
rocyte ALA levels.
23PB13/A 13-34 9/20/83
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PRELIMINARY DRAFT
Lead also affects heme synthesis beyond metabolic steps involving ALA, leading to the
accumulation of protoporphyrin in erythrocytes as the result of impaired iron insertion into
the porphyrin moiety to form heme. The porphyrin acquires a zinc ion in lieu of the native
iron, and the resulting accumulation of blood zinc protoporphyrin (ZPP) tightly bound to ery-
throcytes for their entire life (120 days) represents a commonly employed index of Pb-exposure
for medical screening purposes. The threshold for elevation of erythrocyte protoporphyrin
(EP) levels is well-established as being 25 to 30 MQ/dl in adults and approximately 15 (jg/dl
for young children, with significant EP elevations (>1 to 2 standard deviations above refer-
ence normal EP mean levels) occurring in 50 percent of all children studied as blood-Pb
approaches or moderately exceeds 30 g/d 1.
Medically, small increases in EP levels have generally not been viewed as being of great
concern at initial detection levels around 15 to 20 |jg/d1 in children, but EP increases become
more worrisome as markedly greater, significant EP elevations occur as blood-Pb levels
approach and exceed 30 (jg/dl and additional signs of significantly deranged heme synthesis
begin to appear along with indications of functional disruption of various organ systems.
Previously, such other signs of significant organ system functional disruptions had only been
credibly detected at blood-Pb levels somewhat in excess of 30 pg/dl, e.g., hemoglobin synthe-
sis inhibition starting at 40 (jg/dl and significant nervous system effects at 50-60 pg/dl.
This served as a basis for CDC establishment of 30 (jg/dl blood-Pb as a criteria level for
undue Pb exposure for young children and adoption by EPA of it as the "maximum safe" blood-Pb
level (allowing some margin(s) of safety before reaching levels associated with inhibition of
hemoglobin synthesis or nervous system deficits) in setting the 1978 NAAQS for lead.
To the extent that new evidence is now available, indicative of probable Pb effects on
nervous system functioning or other important physiological processes at blood-Pb levels below
30 to 40 pg/dl , then the rationale for continuing to view 30 |jg/d1 as a "maximum safe" blood-
Pb level is called into question and substantial impetus is provided for revising the criteria
level downward, i.e., to some blood-Pb level below 30 pg/dl- At this time, such impetus
toward revising the blood-Pb criteria level downward is" gaining momentum not only from new
neuropsychologic and electrophysiological findings of the type summarized above, but also from
growing evidence for Pb effects on other functional systems. These include, for example, the:
(1) disruption of formation of the heme-containing protein, cytochrome c, of considerable
importance in cellular energetics involved in mediation of the normal functioning of many dif-
ferent mammalian (including human) organ systems and tissues; (2) inhibition by Pb of the bio-
synthesis of globin, the protein moiety of hemoglobin, in the presense of Pb at concentrations
corresponding to a blood-Pb level of 20 pg/dl; (3) observations of significant inhibition of
pyrimidine-5'-nucleotidase (Py-5-N) activity in adults at blood-Pb levels ^44 ^ig/dl and in
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children down to blood-Pb levels of 10 pg/dl; and (4) observations of Pb interference with
vitamin D metabolism in children across a blood-Pb level range of 33 to 120 jjg/d1, with conse-
quent increasingly enhanced Pb uptake due to decreased vitamin D metabolism and likely asso-
ciated increasingly cascading effects on nervous system and other functions at sequentially
higher blood-Pb levels. Certain additional evidence for Pb effects on hormonal systems and
immune system components, thus far detected only at relatively high blood-Pb levels or at
least not credibly associated with blood-Pb levels as low as 30 to 40 pg/d 1, also contributes
to concern as blood-Pb levels exceed 30 (jg/dl.
Also adding to the concern about relatively low lead exposure levels are the results of
an expanding array of animal toxicology studies which demonstrate: (1) persistence of lead-
induced neurobehavioral alterations well into adulthood long after termination of perinatal
lead exposure early in development of several mammalian species; (2) evidence for uptake and
retention of lead in neural and non-neuronal elements of the CNS, including long-term persis-
tence in brain tissues after termination of external lead exposure and blood lead levels
return to "normal"; and (3) evidence from various in-vivo and in-vitro studies indicating
that, at least on a subcel1ular-molecular level, no threshold may exist for certain neuro-
chemical effects of lead.
13.6 DOSE-RESPONSE RELATIONSHIPS FOR LEAD EFFECTS IN HUMAN POPULATIONS
Information summarized in the preceding section dealt with the various biological effects
of lead germane to the general population and included comments about the various levels of
blood lead observed to be associated with the measurable onset of these effects in various
populations groups.
As indicated above, inhibition of ALA-D activity by lead occurs at virtually all blood
lead levels measured in subjects residing in industrialized countries. If any threshold for
ALA-D inhibition exists, it lies somewhere below 10 \ig Pb/dl in blood lead.
Elevation in erythrocyte porphyrin for a given blood lead level is greater in children
and women than in adult males, children being somewhat more sensitive than women. The thres-
hold for currently detectable EP elevation in terms of blood lead levels for children was
estimated at ca. 16 to 17 pg/dl in the recent studies of Piomelli et al. (1982). In adult
males, the corresponding blood lead value is 25 to 30 pg/dl.
Statistically significant reduction in hemoglobin production occurs at a lower blood lead
level in children, 40 pg/dl , than in adults, 50 pjg/dl.
It appears that urinary ALA shows a correlation with blood lead levels to below 40 pg/dl,
but since there is no clear agreement as to the meaning of elevated ALA-U below 40 pg/dl , this
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value is taken as the threshold for pronounced excretion of ALA into urine. This value
appears to apply to both children and adults. Whether this blood lead level represents a
threshold for the potential neurotoxicity of circulating ALA cannot now be stated and requires
further study.
Coproporphyria elevation in urine first occurs at a blood lead level of 40 pg/dl and this
threshold appears to apply for both children and adults.
A number of investigators have attempted to quantify more precisely dose-population
response relationships for some of the above lead effects in human populations. That is they
have attempted to define the proportion of a population exhibiting a particular effect at a
given blood lead level. To date, such efforts at defining dose-response relationships for
lead effects have been mainly limited to the following effects of lead on heme biosynthesis:
inhibition of ALA-D activity; elevation of EP; and urinary excretion of ALA.
Dose-population response relationships for EP in children has been analyzed in detail by
Piomelli and et al. (1982) and the corresponding plot at 2 levels of elevation (>1 S.D., >2
S.D.) is shown in Figure 13-3 using probit analysis. It can be seen that blood lead levels in
half of the children showing EP elevations at >1 and 2 S.D. 1 s closely bracket the blood lead
level taken as the high end of "normal" (i.e., 30 pg/dl). Dose-response curves for adult men
and women as well as children prepared by Roels et al. (1976) are set forth in Figure 13-4.
In Figure 13-4, it may be seen that the dose-response for children remains greater across the
blood-lead range studied, followed by women, then adult males.
Figure 13-5 presents dose-population response data for urinary ALA exceeding two levels
(at mean + 1 S.D. and mean + 2 S.D.), as calculated by EPA from the data of Azar et at.
(1975). The percentages of the study populations exceeding the corresponding cut-off levels
as calculated by EPA for the Azar data are set forth in Table 13-11. It should be noted that
the measurement of ALA in the Azar et al. study did not account for amino acetone, which may
influence the results observed at the lowest blood lead levels.
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99
95
t/l
90
<
3
Q
75
>
Q
Z
50
LL
O
>
u
25
z
LU
D
10
o
LU
IX
5
LL
1
I I
1
' / '
I I
EP>* + 1 SD
—
—
—
—
EP> x + 2 SD
—
—
O
* /
/ 1
II
NATURAL FREQUENCY
—
—
' i
I
I I I
—
10
20
50
60
70
30 40
BLOOD LEAD. Mg'dl
Figure 13-3. Dose-response for elevation of EP as a
function of blood lead level using probit analysis.
Geometric mean plus 1 S.D. = 33 ^jg/dl; geometric mean
plus 2 S.D. = 53 ptg/dl.
Source: Piomelli et al. 11982).
t/i
Hi
>
<
-------
(A
UJ
>
UJ
O
i/i
A
D
3
<
X
3
a.
o
a.
o
<
o
a.
100
90
80
70
= 60
I .
40
30
20
10
i~i—i—i—r
o MEAN + 1 S.D.
A MEAN + 2 S.D.
MEAN ALAU = 0.32 FOR
BLOOD LEAD < 13 Hg/dl
30 40 50 60 70
BLOOD LEAD LEVEL. Mg Pb/dl
80
90
Figure 13-5. EPA calculated dose-response curve for
ALA U.
Source: Azar et al. (1975).
TABLE 13-11. EPA-ESTIMATED PERCENTAGE OF SUBJECTS
WITH ALA-U EXCEEDING LIMITS FOR VARIOUS BLOOD LEAD LEVELS
Blood lead levels
(pg/dl)
10
20
30
40
50
60
70
Azar et al. (1975)
(Percent Population)
2
6
16
31
50
69
84
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13.7 POPULATIONS AT RISK
Population at risk is a segment of a defined population exhibiting characteristics asso-
ciated with significantly higher probability of developing a condition, illness, or other ab-
normal status. This high risk may result from either (1) greater inherent susceptibility or
(2) from exposure situations peculiar to that group. What is meant by inherent susceptibility
is a host characteristic or status that predisposes the host to a greater risk of heightened
response to an external stimulus or agent.
In regard to lead, two such populations are definable. They are preschool age children,
especially those living in urban, settings, and pregnant women, the latter group owing mainly
to the risk to the conceptus. Children are such a population for both of the reasons stated
above, whereas pregnant women are at risk primarily due to the inherent susceptibility of the
conceptus.
13.7.1 Children as a Population at Risk
Children are developing and growing organisms exhibiting certain differences from adults
in terms of basic physiologic mechanisms, capability of coping with physiologic stress, and
their relative metabolism of lead. Also, the behavior of children frequently places them in
different relationship to sources of lead in the environment, thereby enhancing the opportu-
nity for them to absorb lead. Furthermore, the occurrence of excessive exposure often is not
realized until serious harm is done. Young children do not readily communicate a medical his-
tory of lead exposure, the early signs of such being common to so many other disease states
that lead is frequently not recognized early on as a possible etiological factor contributing
to the manifestation of other symptoms.
13.7.1.1 Inherent Susceptibility of the Young. Discussion of the physiological vulnerability
of the young must address two discrete areas. Not only should the basic physiological differ-
ences be considered that one would expect to predispose children to a heightened vulnerability
to lead, but also the actual clinical evidence must be considered that shows such vulner-
ability does indeed exist.
In Chapter 10 and Section 13.2 above, differences in relative exposure to lead and body
handling of lead for children versus adults were pinpointed throughout the text. The signifi-
cant elements of difference include: (1) greater intake of lead by infants and young children
into the respiratory and gastro-intestinal tracts on a body weight basis compared to adults;
(2) greater absorption and retention rates of lead in children; (3) much greater prevalence of
nutrient deficiency in the case of nutrients which affect lead absorption rates from the GI
tract; (4) differences in certain habits, i.e., normal hand to mouth activity as well as pica
resulting in the transfer of lead-contaminated dust and dirt to the GI tract; (5) differences
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in the efficiency of lead sequestration in the bones of children, such that not only is less
of the body burden of lead in bone at any given time but the amount present may be relatively
more labile. Additional information discussed in Chapter 12 suggests that the blood-brain
barrier in children is less developed, posing the risk for greater entry of lead into the
nervous system.
Hematological and neurological effects in children have been demonstrated to have lower
thresholds in terms of blood lead levels than in adults. The extent of reduced hemoglobin
production and EP accumulation occur at relatively lower exposure levels in children than in
adults, as indexed by blood lead thresholds. With reference to neurologic effects, the onset
of encephalopathy and other injury to the nervous system appears to vary both regarding likely
lower thresholds in children for some effects and in the typical pattern of neurologic effects
presented, e.g., in encephalopathy or other CNS deficits being more common in children versus
peripheral neuropathy being more often seen in adults. Not only are the effects more acute in
children than in adults, but also the neurologic sequelae are usually much more severe in
chi1dren.
13.7.1.2 Exposure Consideration. The dietary habits of children as well as the diets them-
selves differ markedly from adults and, as a result, place children in a different relation-
ship to several sources of lead. The dominance of canned milk and processed baby food in the
diet of many young children is an important factor in assessing their exposure to lead since
both those foodstuffs have been shown to contain higher amounts of lead than components of the
adult diet. The importance of these lead sources is not their relationship to airborne lead
directly but, rather, their role in providing a higher baseline lead burden to which the air-
borne contribution is added.
Children ordinarily undergo a stage of development in which they exhibit normal mouthing
behavior, as manifested, for example, in the form of thumbsucking. At this time they are at
risk for picking up lead-contaminated soil and dust on their hands and hence into their mouths
where it can be absorbed. Scientific evidence documenting at least the first part of the
chain is available.
There is, however, an abnormal extension of mouthing behavior, called pica, which occurs
in some children. Although diagnosis of this is difficult, children who exhibit this trait
have been shown to purposefully eat nonfood items. Much of the lead-based paint problem is
known to occur because children actively ingest chips of leaded paint.
13.7.2 Pregnant Women and the Conceptus as a Population at Risk
There are some rather inconculsive data indicating that women may in general be somewhat
higher risk to lead than men. However, pregnant women and their concepti as a subgroup are
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demonstrably at higher risk. It should be pointed out that, in fact, it really is not the
pregnant woman per se who is at greatest risk but, rather, the unborn child she is carrying.
Because of obstetric complications, however, the mother herself can also be at somewhat
greater risk at the time of delivery of her child.
Studies have demonstrated that women in general, like children, tend to show a heightened
response of erythorcyte protoporphyrin levels upon exposure to lead. The exact reason for
this heightened response is not known but may relate to endocrine differences between men and
women.
As stated above, the primary reason pregnant women are a high-risk group is because of
the fetus each is carrying. In addition, there is some suggestive evidence that lead expo-
sures may also affect maternal complications at delivery. With reference to maternal compli-
cation at delivery, information in the literature suggests that the incidence of preterm deli-
very and premature membrane rupture relates to maternal blood lead level. Further study of
this relationship as well as studies relating to discrete health effects in the newborn are
needed.
Vulnerability of the developing fetus to lead exposure arising from transplacental trans-
fer of maternal lead was discussed in Chapter 10. This process starts at the end of the first
trimester, Umbilical cord blood studies involving mother-infant pairs have repeatedly shown a
correlation between maternal and fetal blood lead levels.
Further suggestive evidence, cited in Chapter 12, has been advanced for prenatal lead
exposures of fetuses possibly leading to later higher instances of postnatal mental retarda-
tion among the affected offspring. The available data are insufficient to state with any cer-
tainty that such effects occur or to determine with any precision what levels of lead exposure
might be required prior to or during pregnancy in order to produce such effects.
13.7.3 Description of the United States Population in Relation to Potential
Lead Exposure Risk
In this section, estimates are provided of the number of individuals in those segments of
the population which have been defined as being potentially at greatest risk for lead ex-
posures. These segments include pre-school children (up to 6 years of age), especially those
living in urban settings, and women of child-bearing age (defined here as ages 15-44). These
data, which are presented below in Table 13-12, were obtained from a provisional report by the
U.S. Census Bureau (1982), which indicates that approximately 61 percent of the populace lives
in urban areas (defined as central cities and urban fringe). Assuming that the 61 percent
estimate for urban residents also applies to children of preschool age, then approximately
14,206,000 children of the total listed in Table 13-12 would be expected to be at greater risk
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by virtue of higher lead exposures generally associated with thei^ living in urban versus non-
urban settings. (NOTE: The age distribution of the percentage of urban residents may vary
between SMSA1s.)
TABLE 13-12. PROVISIONAL ESTIMATE OF THE NUMBER OF INDIVIDUALS IN URBAN AND
RURAL POPULATION SEGMENTS AT GREATEST POTENTIAL RISK TO LEAD EXPOSURE
Total Number in U.S.
Actual Age
Populati on
Urban ,
Population Segment
(year)
(1981)
Populat ion
Pre-school children
0-4
16,939,000
10,333,000
5
3,201,000
1,953,000
6
3,147,000
1,920,000
Total
23,287,000
14,206,000
Women of
15-19
10,015,000
6,109,000
child-bearing age
20-24
10,818,000
6,599,000
25-29
10,072,000
6,144,000
30-34
9,463,000
5,772,000
35-39
7,320,000
4,465,000
40-44
6,147,000
3,749,000
Total
53,835,000
32,838,000
Source: U.S. Census Bureau (1982), Tables 18 and 31.
''"An urban/total ratio of 0.61 was used for all age groups. "Urban" includes central city
and urban fringe populations.
The risk encountered with exposure to lead may be compounded by nutritional deficits (see
Chapter 10). The most commonly seen of these is iron deficiency, especially in young children
less than 5 years of age (Mahaffey and Michaelson, 1980). Data available from the National
Center for Health Statistics for 1976-1980 (Fulwood et al., 1982) indicate that from 8 to 22
percent of children aged 3-5 may exhibit iron deficiency, depending upon whether this condi-
tion is defined as serum iron concentration (<40 MQ/dl) or as transferrin saturation (<16 per-
cent), respectively. Hence, of the 20,140,000 children ^5 years of age (Table 13-12), as many
as 4,431,000 would be expected to be at increased risk depending on their exposure to lead,
due to iron deficiency.
As pointed out in Section 13.7.2, the risk to pregnant women is mainly due to risk to the
conceptus. By dividing the total number of women of child-bearing age in 1981 (53,835,000)
into the total number of live births in 1981 (3,646,000; National Center for Health Statis-
tics, 1982), it may be seen that approximately 7 percent of this segment of the population
may be at increased risk at any given time.
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13.8 SUMMARY AND CONCLUSIONS
Among the most significant pieces of information and conclusions that emerge from the
present human health risk evaluation are the following;
(1) Anthropogenic activity has clearly led to vast increases of lead input into
those environmental compartments which serve as media (e.g., a~r, water, food,
etc.) by which significant human exposure to lead occurs.
(2) Emission of lead into the atmosphere, especially through leaded gasoline com-
bustion, is of major significance in terms of both the movement of lead to
other environmental compartments and the relative impact of such emissions on
the internal lead burdens in industrialized human populations. By means of
both mathematical modeling of available clinical/epidemiological data by EPA
and the isotopic tracing of lead from gasoline to the atmosphere to human blood
of exposed populations, the size of atmospheric lead contribution can be con-
fidently said to be 25-50 percent or probably somewhat higher.
(3) Given this magnitude of relative contribution to human external and internal
exposure, reduction in levels of atmospheric lead would then result in signifi-
cant widespread reductions in levels of lead in human blood (an outcome which
is supported by careful analysis of the NHANES II study data). Reduction of
lead in food (added in the course of harvesting, transport, and processing)
would also be expected to produce significant widespread reductions in human
blood lead levels in the United States.
(4) A number of adverse effects in humans and other species are clearly associated
with lead exposure and, from a historical perspective, the observed "thres-
holds" for these various effects (particularly neurological and heme biosynthe-
sis effects) continue to decline as more sophisticated experimental and clini-
cal measures are employed to detect more subtle, but. still significant effects.
These include significant alterations in normal physiological functions at
blood lead levels markedly below the currently accepted 30 pg/dl "maxim safe
level" for pediatric exposures.
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(5) Preceding chapters of this document demonstrate that young children are at
greatest risk for experiencing lead-induced health effects, particularly in the
urbanized, low income segments of this pediatric population. A second group at
increased risk are pregnant women, because of exposure of the fetus to lead in
the absence of any effective biological (e.g. placental) barrier during gestation.
(6) Dose-populatien response information for heme synthesis effects, coupled with
information from various blood lead surveys, e.g. the NHANES II study, indicate
that large numbers of American children (especially low income, urban dwellers)
have blood lead levels sufficiently high (in excess of 15-20 pg/dl) that they
are clearly at risk for deranged heme synthesis and, possibly, other health ef-
fects of growing concern as lead's role as a general systemic toxicant becomes
more fully understood.
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Effects of low to moderate lead exposure on slow cortical potentials in young children:
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Perino, J.; Ernhart, C. B. (1974) The relation of subclinical lead level to cognitive and
sensorimotor impairment in black preschoolers. J. Learn. Dis. 7: 616620.
Piomelli, S. ; Seaman, C. ; Zullow, D.; Curran, A. ; Davidow, B. (1982) Threshold for lead damage
to heme synthesis in urban children. Proc. Natl. Acad. Sci. U.S.A. 79: 3335-3339.
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Rabinowitz, M,; Wetherill, G. W. ; Kopple, J. D. (1974) Studies of human lead metabolism by
using stable isotope tracers. Environ. Health Perspect. 7: 145-152.
Rabinowitz, M. B. ; Wetherill, G. W. ; Kopple, J. D. (1976) Kinetic analysis of lead metabolism
in healthy humans. J. Clin. Invest. 58: 260-270.
Rabinowitz, M. B. ; Wetherill, G. W. ; Kopple, J. D. (1977) Magnitude of lead intake from res-
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PRELIMINARY DRAFT
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* J 3 OOv'e'HMLN: rWN'lNliOFHCE ' MJ - 662-CJ8/100J
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EPA-600/6-33-023A
APPENDIX 12-C
INDEPENDENT PEER REVIEW OF SELECTED STUDIES CONCERNING
NEUROBEHAVIORAL EFFECTS OF LEAD EXPOSURES IN NOMINALLY ASYMPTOMATIC CHILDREN
OFFICIAL REPORT OF FINDINGS AND RECOMMENDATIONS
OF AN INTERDISCIPLINARY EXPERT REVIEW COMMITTEE
Presented by
Expert Committee on Pediatric
Neurobehavioral Evaluations
To:
Dr. Lester D. Grant, Director
Environmental Criteria and Assessment Office
United States Environmental Protection Agency
Research Triangle Park, North Carolina
November 14, 1983
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The materials contained in this report were generated as a result of critical evaluations
and deliberations concerning the subject studies in the course of review of them by members of
the Expert Committee on Pediatric Neurobehavioral Evaluations. The members of the Committee
(listed below) unanimously concur with and endorse the findings and recommendations contained
in the present report as representing the collective sense of the Committee.
Expert Committee on Pediatric
Neurobehavioral Evaluations
Dr. Lyle Jones,
Alumni Distinguished Professor
Dept. of Psychology and
Director, L. L. Thurstone
Psychometric Laboratory
University of North Carolina
Chapel Hill, NC 27514
Dr. Richard Weinberg, Professor
Dept.of Educational Psychology
and Co-Director, Center for
Early Education and Development
University of Minnesota
Minneapolis, MN 55455
Dr. Lloyd Humphreys, Professor
Dept. of Psychology and
Educational Psychology
University of Illinois
Champaign, IL 61820
Dr. Larry Kupper, Professor
Dept. of Biostatisties
School of Public Health
University of North Carolina
Chapel Hill, NC 27514
Dr. Paul Mushak, Associate Professor
Dept. of Pathology and Co-Director,
Environmental Toxicology Research Program
University of North Carolina
Chapel Hill, NC 27514
Dr. Sandra Scarr, Commonwealth
Professor, Dept. of Psychology
University of Virginia
Charlottesville, VA 22901
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PREFACE
As part of the periodic (5-year) review and revision of criteria for the National Ambient
Air Quality Standards (NAAQS) for lead established in 1978, the EPA Environmental Criteria and
Assessment Office (ECAO/RTP) initiated in 1982 an intensive, critical evaluation of pertinent
scientific information concerning health effects associated with lead (Pb) exposure. Of con-
siderable importance in that regard are certain published (and related unpublished) studies
from several different research groups, which provide data that have been interpreted as
demonstrating significant associations between neuropsychologic deficits (e.g., impaired cog-
nitive development) or other neurobehavioral effects (e.g., poorer classroom behavior) and
lead exposures in otherwise apparently asymptomatic children. The findings and interpretation
of such studies have become a matter of great controversy, especially among those research
scientists directly involved in the conduct and reporting of the subject studies.
.In an effort to resolve major points of controversy concerning some of the most important
and controversial of the subject studies, an interdisciplinary Expert Committee on Pediatric
Neurobehavioral Evaluations was convened by Dr. Lester D. Grant (Director of ECAO/RTP) start-
ing in March, 1983, to provide independent peer review of selected studies and to make recom-
mendations concerning how particular study results should be most appropriately interpreted
or, possibly, reanalyzed before final interpretation. The Committee comprised internationally
recognized experts in t^e areas of: child development, psychometric techniques, biostatis-
tics, lead exposure measurement techniques, and overall aspects of lead pharmacokinetics and
toxicology. The present report contains a series of critiques of interrelated sets of selec-
ted studies conducted during the 1970s and early 1980s.
The Commi-ttee focused on answering the following four general questions in reviewing each
of the sets of studies:
(1) Were the studies appropriately designed and conducted (including data collec-
tion and statistical analyses) so as to allow for scientifically sound testing
of the main hypotheses posed regarding possible associations between lead expo-
sure and neurobehavioral effects (e.g., poorer classroom behavior, 1Q deficits,
etc.) in chi1dren?
(2) To what extent do the particular data, statistical analyses, and results ob-
tained support the conclusions stated in the published papers (or other related
materials regarding each study), and what caveats or limitations should most
appropriately be stated as applying to such conclusions?
(3) Are there other conclusions that might be appropriately drawn (given the parti-
cular design, data collection, and statistical analyses employed in each study)
and/or are there other appropriate approaches to the analysis of the data col-
lected that would be expected to yield further meaningful and important infor-
mation concerning the hypothesis that low-level lead exposure leads to neuro-
behavioral deficits in children?
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(4) To what extent do the published studies allow for meaningful conclusions to be
drawn regarding quantitative exposure-effect or dose-response relationships
between any observed neurobehavioral effects and specific levels of lead expo-
sure (as defined by either dentine or blood lead concentrations as indices of
exposure)?
In the course of deliberating on general issues such as those posed above, the Committee
considered more specific questions or points as appropriate for each of the studies reviewed.
Many of the specific questions posed were presented in letters from Dr. Grant to.the investi-
gators (see attachment to this report, for a listing of letters). At initial meetings of the
Committee in March, 1983, these and other questions were discussed with the senior in-
vestigators responsible for the conduct of particular studies, and some additional, unpublish-
ed information was provided by the investigators to the Committee to assist in accomplishing
as complete an evaluation of each study as possible at the time of review. A preliminary
draft of the Committee's report was provided to Drs. Ernhart and Needleman in September, 1983.
The Committee reconvened in October, 1983, at which time written comments submitted by
Drs. Ernhart and Needleman were considered by the Committee in making revisions in the report.
The Committee members thank the investigators for taking time to meet with us, for their
assistance in providing and discussing information beyond that included in the published
reports of their studies, and for calling to our attention certain factual errors in the pre-
liminary draft of our report. The Committee hopes that the ensuing critiques of specific
studies both (1) help to resolve legitimate controversy regarding the most appropriate inter-
pretation^) of the subject study results and (2) provide constructive criticisms and recom-
mendations that are of value in carrying out reanalysis of certain subject data sets which
hold promise for providing more definitive outcomes than those thus far reported for the
studies in the published literature.
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TABLE OF CONTENTS
SECTION PAGE
SUMMARY v
I. INTRODUCTION 1
A. Alternative Research Designs 1
1. Randomized Clinical Trials 1
2. Cross-Sectional Designs 1
3. Longitudinal Designs 4
4. Time-Series Designs 5
B. Additional Remarks 5
II. REVIEW OF STUDIES BY DR. CLAIRE ERNHART AND COLLEAGUES 6
A. Background Information 6
B. Comments on Peri no and Ernhart (1974) and Ernhart et al.
(1981) Studies 8
1. Indicators of Lead Exposure . 8
2. Psychometric Measurements and Procedures 12
3. Statistical Analyses 15
4. Committee Conclusions and Recommendations .. 17
C. Comments on Yamins (1976) Dissertation Study 18
1. Indicators of Lead Exposure 18
2. Psychometric Measurements and Procedures 19
3. Statistical Analyses 20
4. Committee Conclusions and Recommendations 21
III. REVIEW OF STUDIES BY DR. HERBERT NEEDLEMAN AND COLLEAGUES 22
A. Background Information 22
B. Comirents on Needleman et al. (1979) Study 28
1. Indicators of Lead Exposure 28
2. Psychometric Measurements and Procedures 31
3. Statistical Analyses 33
4. Committee Conclusions and Recommendations •. 37
C. Comments on Burchfiel et al. (1980) Study 38
D. Comments on Needleman (1982) Report 39
E. Comments on Bellinger and Needleman (1983) Study 39
F. Comments on Needleman (1981) Report 40
IV. POSTSCRIPT 41
V. REFERENCES 44
VI. ATTACHMENT I 47
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SUMMARY
The Expert Committee on Pediatric Neurobehavioral Evaluations reviewed two independent
sets of studies by: (1) Dr. Claire Ernhart and colleagues and (2) Dr. Herbert Needleman and
colleagues. The studies evaluated possible associations between low-level lead (Pb) exposures
and neuropsychological deficits in children who were otherwise apparently asymptomatic.
The Perino and Ernhart (1974) study evaluated relationships between blood Pb levels in a
sample of 80 inner city black children (aged 3-5 yr) and IQ scores determined by the McCarthy
Scales of Cognitive Abilities. Small but significant associations between lead exposure and
lower IQ scores were reported, based on regression analyses. The Committee found the blood Pb
measures were of acceptable reliability, as were also the psychometric measures for children.
However, errors now have been discovered in the data analyzed for that report. In addition,
confounding variables may not have been adequately measured, and the statistical analyses did
not deal adequately with confounding variables. The Committee concludes, therefore, that the
study results, as published by Perino and Ernhart (1974), neither confirm nor refute the hypo-
thesis that low-level Pb exposure in children leads to neuropsychologic deficits.
Ernhart et al. (1981), in a follow-up study, reassessed blood Pb levels and neuropsycho-
logic function in a subset of the same children 5 years later. The McCarthy Scales were again
used, along with school reading tests and teacher ratings of classroom behavior. Small but
statistically significant negative correlations were found between school-age blood Pb levels
and scores on some McCarthy subscales, controlling for certain confounders. No significant
associations remained if results were deleted for one "outlier" with markedly elevated dentine
Pb beyond other values for the higher Pb group. The Committee found the psychometric measures
to be acceptable, but the blood Pb sampling method raised questions about the reliability of
the reported blood Pb levels. In addition, the statistical analyses did not adequately con-
trol for confounding factors. The Committee concludes, therefore, that the Ernhart et al.
(1981) results neither confirm nor refute the hypothesis that low-level Pb exposure in chil-
dren is partially responsible for neuropsychologic deficits. The Committee recommends that
longitudinal analyses be carried out, using data from both the Perino and Ernhart (1974) and
Ernhart et al. (1981) follow-up studies.
The Committee also reviewed a doctoral dissertation prepared by J. Yamins (1976) under
Dr. Ernhart's direction. The Yamins study attempted to replicate certain aspects of the find-
ings reported by Perino and Ernhart (1974), but used different psychometric measures and a
different population of children. A major problem was the method of blood sampling, i.e.,
collection onto filter paper, which requires correction for hematocrit. Hematocrit levels
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apparently are not available for data reanalysis. Although Yamins reported small but signifi-
cant effecL? of lead exposure on some indices of cognitive functioning (taking age into
account), the Committee found it difficult to place much confidence in such findings because
of the failure to control adequately for confounding variables (besides age).
Results from an epidemiological study conducted by Needleman and colleagues were reported
or disc-jssed in: Needleman et al. (1979), Burchfiel et al. (1980), Needleman (1981), Needle-
man (1982), Needleman et al. (1982), Bellinger and Needleman (1983), and Needleman (1983).
The main set of analyses was presented by Needleman et al. (1979). The study entailed neuro-
psychologic evaluations for more than 2000 first- and second-grade (mainly white) students.
Lead exposure was indexed by dentine Pb in deciduous teeth. The classroom behavior of each
chi'd submitting a tooth was rated by the child's teacher. Some children, falling within the
highest and lowest deciles for dentine Pb measurea in one or more of their teeth, underwent
more in-depth neuropsychologic evaluations, including use of an individual standardized mea-
sure of intellectual abilities (the WISC-R) to estimate IQ levels and tests of academic
achievement,- auditory and language processing, visual-motor reflexes, attentional performance,
and motor coorcination.. Needleman et al. (1979) reported a relationship between first tooth
dentine Pb values and percentages of students receiving poor classroom behavior ratings, which
he has interpreted (Needleman, 1983) as "a strong dose-response relationship." Children in
the high-Pb group (top 10% of dentine Pb levels) were also reported to have statistically sig-
nificantly lower IQ scores (especially verbal IQ) than the low-Pb group (lowest 10% of dentine
Pb values), taking into account five covariates in an analysis of covariance. The high-Pb
children were also reported to do more poorly on certain other neurobehavioral tasks.
The Committee concludes that the relationship between dentine Pb levels and teachers'
ratings of classroom behavior cannot be safely attributed to the effects of Pb, due to:
(1) reservations regarding the adequacy of classification of subjects into Pb exposure cate-
gories using only the first dentine Pb value obtained for each child and (2) failure to con-
trol adequately for effects of confounding variables. The Committee also concludes that the
reported results concerning the effects of lead on IQ and other behavioral neuropsychologic
abilities measured for the low-Pb and high-Pb groups must be questioned, due to: (1) errors
made in calculations of certain parental IQ scores entered as a control variable in analyses
of covariance; (2) failure to take age and father's education into account adequately in the
analyses of covariance; (3) the failure to employ a reliable strategy for the control of con-
founding variables; (4) concerns regarding missing data for subjects included in the analyses;
and (5) questions about possible bias due to exclusion of large numbers of provisionally eli-
gible subjects from statistical analyses. The Committee concludes, therefore, that the study
results, as published Dy Needleman et al. (1979), neither confirm nor refute the hypothesis
that low-level Pb exposure in children leads to neuropsychologic deficits.
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The publications by Needleman (1982), Needleman et al. (1982), Bellinger and Needleman
(1983), and Needleman (1983) describe further analyses of the same data set reported by
Needleman et al. (1979). Burchfiel et al. (1980) reported analyses of certain psychometric
data together with additional data on electrophysiological (EEG) measures for a subset of the
high-Pb and low-Pb children from the Needleman et al. (1979) study. The above reservations
regarding the basic analyses reported by Needleman et al. (1979) apply also to the analyses
reported by Burchfiel et al. (1980), Needleman (1982), Needleman et al. (1982), Bellinger and
Needleman (1983), and Needleman (1983). Similar reservations apply to analyses of another
data set (Needleman, 1981). The Committee recommends that the entire Needleman data set be
reanalyzed, correcting for errors in data calculation and entry, using better Pb exposure
classification, and appropriately adjusting for confounding factors.
In addition to evaluating the studies of Ernhart and Needleman, the Committee reviewed
available reports (some published and others as yet unpublished) of other studies from the
United States and Europe. Although an exhaustive, in-depth evaluation of the world literature
on low-level Pb exposure was beyond the current charge to the Committee, we note that new
studies reported in the spring and summer of 1983, with only a few exceptions, failed to find
significant association between low-level Pb exposure and neuropsychologic deficits, once con-
trol variables were taken into account.
From its review of the recent research literature covered in this report, the Committee
concludes that: (1) in the absence of control for other variables, a negative association
between Pb exposure and neuropsychologic functioning has been established; (2) the extent of
this negative association is reduced or eliminated when confounding factors are appropriately
controlled; and (3) the Committee knows of no studies that, to date, have validly established
(after proper control for confounding variables) a relationship between low-level Pb exposure
and neuropsychologic deficits in children.
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INTRODUCTION
In approaching its task, the Committee was faced first with establishing criteria for
research studies, the results of which may be accepted as evidence pertinent to determining
the influence of Pb exposures on cognitive functioning in apparently asymptomatic children.
Because children live and mature in a complex socio-cultural milieu that affects them in many
diverse ways, isolation of a definitive cause, e.g., lead exposure, for neuropsychological
problems in children is extremely difficult. Under these circumstances, what kind of research
design is necessary or adequate to produce pertinent evidence?
The problem of determining the effects of Pb on cognitive functioning is viewed as an in-
stance of a general class of dosage-response problems. Alternative research designs with which
to approach such problems include:
(i) randomized clinical trials;
(ii) cross-sectional observational study of individuals from groups known to vary in
exposure (dosage);
(iii) longitudinal study of the same individuals over time;
(iv) a time series of observations on different sets of individuals who are members of
groups known to differ in exposure (dosage).
A, Alternative Research Designs
1. Randomized Clinical Trials
There is no question that randomized clinical trials, properly conducted, provide evi-
dence that is highly relevant to the research question. Neither is there any question that
the experimental administration of Pb to human subjects is unethical, and not to be con-
sidered. This highly effective research design, then, simply cannot be adopted to address the
question of the effect of Pb on human cognitive functioning.
2. Cross-Sectional Designs
The bulk of published work assessing Pb effects on human cognitive functioning has en-
tailed the cross-sectional study of a sample of children. A serious complicating feature of
the design results from typical empirical findings of association between low or moderate
levels of lead exposure, on the one hand, and such background variables as parental IQ, paren-
tal education, quality of home environment, family size, etc., all of which are known to be
1
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correlated with children's cognitive performance. Under what conditions, then, might this
design yield valid conclusions about the effect of Pb on cognition? Three possibilities appear
to exist, as follows:
(a) Were low or moderate levels of Pb consistently found to be negatively corre-
lated with cognitive performance, while all potential confounding background
variables were negligibly correlated with cognitive performance, then a valid
conclusion would be that Pb is responsible for the cognitive deficits. How-
ever, the premise generally appears to be false: published studies on Pb, con-
sistent with research literature in child psychology, report sizable correla-
tions between cognitive performance and a host of background variables.
(b) Were low or moderate levels of Pb consistently found to be negligibly corre-
lated with cognitive functioning, regardless of the pattern of association
between cognitive function and confounded background variables, then it would
be fairly safe to conclude that the differences in Pb levels are not important-
ly related to cognitive performance. Again, however, the premise generally
appears to be false: most published studies on Pb report significant correla-
tions between Pb and cognitive test scores unadjusted for other key con-
founders.
(c) Consider a study designed so as to provide a factor analysis of interrelations
among variables. It might be found that cognitive performance is represented
on one factor along with noncognitive variables that arie not appreciably
associated with cognitive performance in the absence of Pb. In the presence of
Pb, however, such noncognitive variables might be hypothesized tc be associated
with cognitive function. Lead would be the primary defining variable on such a
factor. Noncognitive variables that would be appropriate candidates for this
factor analysis include sensory discriminations and electroencephalograph^
(EEG) recordings. This finding would support the hypothesis that Pb was a par-
tial determinant of cognitive functioning.
The research studies of Pb effects on cognition of which the Committee is aware generally
fail to match any of the above conditions (a), (b), or (c). Rather, the studies mainly report
cross-sectional data for which: (1) Pb is correlated with cognitive test scores by a nonzero
but modest amount; (2) Pb is correlated with background variables; and (3) background vari-
ables are correlated with .cognitive performance. In most such studies, efforts are made to
separate the influence cf .Pb or cognitive functions from the influence'of confounding varia-
bles, using methods of statistical adjustment (e.g., regression analysis).-
2
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Statistical adjustment for confounding variables may reduce the residual relation between
Pb and cognition to a negligible value. If so, however, it would not necessarily follow that
cognitive functioning is not influenced by Pb; the effects of Pb might be masked by one or
more of the confounding variables. The research design is generally incapable of providing
evidence which permits a clear separation of the magnitude of effect of Pb from effects of the
confounding variables.
Statistical adjustment for confounding variables may leave a significant residual corre-
lation between Pb and cognition. If so, however, it would not necessarily follow that cogni-
tive function is influenced by Pb. Perhaps other background variables, not explicitly ad-
justed for, but correlated both with Pb and cognition, are the effective determinants of cog-
nitive differences. Or, perhaps, less fallible measures of the confounding variables would
have further reduced the correlation between Pb and cognition to a non-significant amount.
The research design is not sufficiently sensitive to provide guidance concerning which of
these alternative conclusions should be embraced.
The controversy over the interpretation of results from a series of recent studies may be
attributed to this intrinsic ambiguity regarding the assignment of causal status to the pre-
dictor variable of interest (Pb) or to confounding variables (e.g., home and parental mea-
sures). Some consider Pb to act as a surrogate for the confounding variables. Others con-
sider the confounding variables to act as a surrogate for Pb. There is no scientific basis
for accepting or rejecting either set of interpretations.
In view of these considerations, the Committee concludes that, no matter how carefully
designed and executed, cross-sectional studies of relationships between Pb and cognitive func-
tioning are not able to yield definitive conclusions regarding the influence of low-level Pb
exposures on human cognitive functioning, when measures of both are correlated with background
variables also known to influence cognitive development and performance. At best, such cross-
sectional studies may yield evidence suggestive of effects of low-level Pb exposures which
would need to be confirmed by studies using more definitive research designs.
The Committee has been charged with evaluating the research reports of Needleman and his
associates and of Ernhart and her associates. All of these reports concern essentially cross-
sectional studies (although some of the Ernhart data are amenable to longitudinal analysis, a
subject to which we return later). F.ach study is thus subject to the severe reservations ex-
pressed above: i.e., fron cross-sectional studies with confounding variables, it is not possi-
ble to draw definitive conclusions about the role of low-level Pb exposures as a determinant
of cognition. Nevertheless, we do present more detailed critiques of these studies in sec-
tions below, recognizing the importance of attempting to resolve apparent inconsistencies in
the results and conclusions presented by these sets of irvestigators and recognizing, also,
the value of accumulating even small or suggestive indications of possible relationships, or
lack thereof, between Pb and cognitive deficits.
3
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We have judged that, to assess effects of Pb on cognition, (i) randomized clinical trials
cannot be conducted and (ii) cross-sectional observational studies cannot adequately disentan-
gle effects of Pb from effects of confounding variables. We now comment on strengths and weak-
nesses of certain other research designs, longitudinal studies and time-series analyses, which
may be capable of yielding more definitive conclusions than cross-sectional designs.
3. Longitudinal Designs
A longitudinal design is characterized as a study of the same individuals over a period
of time. For the topic at hand, primary interest, would reside in changes over time in rela-
tive levels of cognitive functioning as a consequence of earlier levels of systemic Pb or of
changes in systemic Pb. Many (but not all) of the confounding variables are usually quite
stable over time, and thus may be assumed to have a similar influence on measures obtained at
different times. To that extent, the difficulty created by confounding variables will be at
least partially alleviated.
Documentation of the history of systemic Pb exposure should begin early, even prior to an
infant's birth. Cognitive performance also should be assessed early, as soon as 18 months
after birth. Measurements of both sets of variables should be repeated periodically for
several years, and other measures, e.g., dentine lead, might be obtained at appropriate times.
It is crucial that as complete a history as possible of Pb exposure (as indexed by changes in
internal indices) be obtained and that such indices of exposure be evaluated for relationships
to dependent variables indicative of cognitive/behavioral development both proximate and dis-
tant in time after the exposure measures are obtained. This is important both to increase
information on latency periods for Pb effects to be manifested and in regard to augmenting our
knowledge of reversibi1ity/irreversibi1ity of Pb effects.
In the study by Perino and Ernhart (1974) discussed below, the same sample of children
was assessed both for Pb exposure and cognitive performance at ages 4-5 years, and again five
years later, as reported by Ernhart et al. (1981). The authors did inquire about the relation-
ship between later cognitive measures and earlier Pb levels, but they failed to study the
possibly revealing relationship between change in cognitive score and change in Pb levels (see
comments on these studies in a later section of this report).
A longitudinal design reduces but does not necessarily totally avoid problems of con-
founding variables. Variables that remain stab^ over time for a given individual, while
creating difficulty in a cross-sectional design, may not be as much of a problem in a longitu-
dinal design. However, confounding variables that change over time would be troublesome in
longitudinal as well as in cross-sectional studies. Techniques for statistical adjustment may
(and usually should) be employed for such variables. To the degree that they a"-e prominently
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related to Pb levels and cognition or to changes in these variables, they are as troublesome
in longitudinal as in cross-sectional studies. The hope is that their effects will be far
smaller in longitudinal studies.
4. Time-Series Design
Fortuitous events, from the research perspective, may occasionally provide the opportuni-
ty for a time-series study of the effects of Pb on cognitive functioning. For example, it
might be recognized that an environmental change is imminent in Community A, a change antici-
pated to have a large effect on typical systemic Pb exposure in that community. Prior to that
change, Pb and cognitive measures might be obtained for a random sample of 5-year-olds (or 7-
or 9-year-olds) in community A, and also in community B, considered similar to A except for
the impending change. Later, after the environmental change and its effects have had an
opportunity to be exerted, similar measures are again collected on random samples at the same
age, in both communities. Differential changes in cognition as a function of different levels
of Pb may strongly suggest that Pb has influenced cognition. A specific example of where
such a research approach might be applied is a situation whereby an imminent governmental or
industry action is anticipated that would lead to substantial reductions in Pb exposure in a
particular geographic area.
B. Additional Remarks
The Committee cannot conclude these general introductory remarks without presenting an
additional caveat regarding the interpretation of even an unambiguous finding of a signifi-
cant negative relationship between low Pb levels and measures of children's IQ or other
behavioral variables, based on epidemiological observations. If an investigator is able to
discount the influence of confounding variables,' arid if no '"laws are found with the research
design employed or the conduct of the study, the temptation may exist to conclude that Pb is
responsible for the observed lowered IQ levels or other behavioral deficits. Note, however,
that such results are, in many cases, equally consistent with the conclusion that increased Pb
exposures and associated body burdens are a consequence of low IQ or other observed behavioral
deficits. Furthermore, Knowledge external to the research study generally would not be such
so as to provide an obvious basis for preferring one of these conclusions over the other.
5
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REVIEW OF STUDIES BY DR. CLAIRE ERNHART AND COLLEAGUES
A. Background Information
The Committee undertook detailed review of two studies published by Dr. Ernhart and col-
leagues (Perino and Ernhart, 1974; Ernhart et al. , 1981) and, also, preliminary review of a
third study reported in the 1976 doctoral dissertation of J. Yamins at Hofstra University.
(The latter doctoral research was conducted under Dr. Ernhart's direction but is not yet pub-
lished in the peer-reviewed literature).
In the first study, based on the doctoral research of J. Perino (under Dr. Ernhart's
direction), inner city black children of low socioeconomic status were recruited for study
based on blood Pb values obtained during screening for possible undue Pb exposure by the New
York City Health Department during 1972. Children were randomly selected to participate in
the study so as to represent a group of subjects with lead exposures ranging from low (<30
Mg/d£) to moderately elevated (40-70 pg/di.) according to then existing screening standards.
Because the study was designed to evaluate neuropsychologic deficits associated with moderate
lead exposures in non-overtly lead-poisoned children, children with histories of overt signs
or symptoms typical of Pb poisoning were excluded from the study. Eighty black children (41
boys and 39 girls) of preschool age (3 yr to 5 yr, 1 mo) from Queens, New York, were included
in the study. The McCarthy Scales of Children's Abilities (McCarthy, 1972) were administered
to the children in their homes by a trained school psychologist (J. Perino), to yield a
General Cognitive Scale score with norms obtained in the same manner as and roughly comparable
to IQ scores. The test also provided scores on several subscales, i.e. Verbal, Perceptual
Performance, Quantitative, and Motor Abilities. Parental IQ was measured by means of the
Quick Test (Ammons and Ammons, 1962) of gross intellectual level. Questions regarding other
covariates were administered to the parent by the school psychologist, following a standard-
ized format and recording answers on a typed questionnaire form. In general, the results of
the study were such so as to lead the authors to conclude that neuropsychologic deficits
(i.e., decreased cognitive, verbal, and perceptual performance abilities) were significantly
associated with Pb exposure in the otherwise asymptomatic children studied. The results have
also been interpreted (in Air Quality Criteria for Lead, U.S. EPA, 1977) as demonstrating such
deficits to be associated with Pb exposures resulting in blood Pb levels of 40-70 pg/d£.
The study by Ernhart et al. (1981) is a followup study, in which 63 children (30 boys, 33
girls) from the original cohort of 80 black children studied by Perino and Ernhart (1974) were
reexamined 5 years later. Scores were obtained for these school-age children on the McCarthy
Scales of Children's Abilities, school reading tests, teacher ratings of classroom behavior,
6
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arid several neurobehavioral exploratory measures. Hypothesized relationships between perfor-
mance on these neuropsychologic tests and childhood Pb exposures were first statistically
evaluated by means of omnibus multivariate tests (Hotel ling's T*), comparing test scores of
"low lead" versus "moderate lead" children defined in terms of (1) pre-school blood Pb levels
(low = 10-30 g/d 3. ; moderate = 40-70 p g/d£) and (2)school-age blood Pb levels (low S26
py/d£; moderate = 27-49 fjg/d£). Significant omnibus test results (p<0.0b) were obtained only
for reading scores related to both preschool and school-age Pb levels. Further multivariate
and univariate analyses were conducted for these significant neuropsychologic outcome vari-
ables. Univariate tests for differences on McCarthy scores between low and moderate Pb sub-
jects (ignoring control variables) suggested that the moderate Pb group performed more poorly
on the General Cognitive Index (GCI) and 3 of the 5 McCarthy Test subscales. However, multi-
variate (regression) analyses revealed that sex and parental IQ were control variables that
were significantly correlated with one or more outcome measures. When these control variables
were ignored in analyses including Pb exposure measures, preschool Pb was significantly nega-
tively related to scores on the GCI, 4 of 5 McCarthy subscales, and the reading tests. When
sex and parental IQ were taken into account, however, preschool Pb was not related to any
neuropsychologic outcome measure and school-age Pb was significantly related only to the
McCarthy GCI, verbal subscale, and motor subscale scores (with the variance attributable to
school-age Pb generally being less than half that found for the same outcome measures when the
control variables were excluded). Dentine Pb levels in shed deciduous teeth of 33 children
were not significantly related to any outcome measures, even when control variables were ig-
nored.
The Yamins (1976) dissertation study, in part, attempted to replicate the Perino and
Ernhart (1974) findings, using a different study population and psychometric tests. Preschool
children (aged 2 yr, 4 mo to 5 yr, 9 mo), including 80 black (38 girls, 42 boys) and 20 white
(10 girls, 10 boys) children from low to low-middle socioeconomic status communities in the
Nassau County (Long Island) Department of Health Clinics lead-screening program catchment area,
were included in the study. Children with overt signs or symptoms of Pb intoxication were ex-
cluded. Of the included children, 54 black subjects had blood Pb levels below 37 pg/d2 ,
whereas 26 fell in a 38-70 |jg/d£ range; of the 20 white children, 19 had blood Pb levels below
37 pg/d£. Cognitive performance and language development of the children were assessed by the
following tests administered in a set sequence in the home by a school psychologist blind as
to the children's Pb levels: a "nonverbal" IQ test (Peabody Picture Vocabulary Test; PPVT); a
general information test (Caldwell Preschool Inventory); a concepts test (Block Sort); a per-
ceptual-motor functioning test (Copy Forms); and a sentence repetition task designed for the
study. The Amnions Quick Test was used to measure parental IQ, and data were gathered on
several other background variables (parental education and occupation, quality of housing,
7
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child's medical history, number of siblings, etc.) by means of standardized questionnaire and
rating forms. Raw scores for all dependent variable measures were used in multiple regression
analyses, which took into account age as well as the other potentially confounding background
variables that were measured. For the black children, several such variables (e.g., parental
IQ and education, absence of father from home, etc.) were significantly negatively related to
children's Pb levels but positively related to each other and the children's cognitive and
language variables. Similar results were obtained for the white children. Stepwise multiple
regressions were then performed, excluding predictor variables contributing less than 1% of
the variance, entering the included predictor variables into the equation before Pb. With all
predictor variables controlled, for the black sample, Pb contributed 2.4% of the total vari-
ance for nonverbal intelligence (PPVT, p<0.05), 3.1^ for general information (Preschool Inven-
tory, p<0.01), 2.4% for overall level of acquired syntax (Total Repetition Score, p<0.05), and
2.5% for ability to repeat nongrammatical verbal stimuli (Ungrammatical Stimuli Test, p<0.05).
Lead did not contribute significantly to conceptual level (Block Sort), perceptual-motor, func-
tioning (Copy Forms), or ability to repeat grammatical stimuli (Grammatical Repetition) scores.
In order to evaluate critically the above studies, the Committee met with Dr. Ernhart at
EPA facilities in Research Triangle Park, NC on March 17-18, 1983. At that time, a>summary
overview presentation was made by Dr. Ernhart on the objectives, design, data collection and
analysis procedures, and results for each of the studies. Certain listings of raw- data values
(provided in coded form to protect the privacy of subjects) and other pertinent published and
unpublished materials were examined by the Committee and considered during discussions with
Dr. Ernhart regarding diverse aspects of the studies reviewed. Some additional, follow-up in-
formation was requested by the Committee and was provided to them subsequent to the March
17-18 meeting with Dr. Ernhart. See Attachment 1 for a list of materials examined by the Com-
mittee in connection with their review of the subject studies. The Committee1s comments
regarding the most salient points of concern and controversy related to methodological and
other features of the above studies by Ernhart and associates are presented below.
B. Comments on Perino and .Ernhart (1974) and Ernhart et al. (1981) Studies
1. Indicators of Lead Exposure
In the first two studies under consideration, Perino and Ernhart (1974) and Ernhart et
al. (1981), the major indicator of exposure was blood Pb, with additional use of erythrocyte
porphyrin (EP) measurements and a sub-group of dentine Pb samples in the follow-up study of
Ernhart et al. (1981).
8
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On the basis of current criteria of methodology assessment for Pb analyses as noted in
Chapter 9 of the EPA draft document Air Quality Criteria for Lead (U.S. EPA, 1983), it can be
said that the blood lead values in the Perino and Ernhart study are reasonably reliable. With
the follow-up study of Ernhart et al. (1981), blood lead accuracy becomes potentially problem-
atical, due both to: (1) a combined positive bias of capillary blood sampling and choice of
analysis, and (2) a bias of negative direction but of possibly variable size, owing to the
generally poorly recognized effect of whole blood hematocrit/hemoglobin on blood Pb measure-
ments using filter paper. The latter factor requires making use of the hematocrit measure-
ments for the subjects' blood (which presumably are available, since EP measurements also
require knowing the hematocrit) to correct for differential spread or diffusion of blood (and
concentration of Pb therein) on the filter paper matrix.
Measurement of Pb in dentine of shed teeth from the subjects in the Ernhart et al. (1981)
follow-up study was carried out in the laboratory which both pioneered the analysis of Pb in
teeth and probably has the most experience and proficiency with such analyses. The method of
analysis for dentine Pb is reasonably reliable, and it appears that analysis error in repli-
cate sampling is at the step of isolating the dentine zones from a given whole tooth sample.
Measurement of erythrocyte porphyrin involved blood collected on filter paper and subse-
quent elution and micro-fluorometric analysis. Such a "wet" or laboratory analysis is con-
sidered much more reliable than the use of the hematof1uorometer when applied to blood samples
of modest EP content. Analytical error was noted to be less than 15 percent.
Ir the study of Perino and Ernhart (1974) lead exposure in the pediatric subjects was in-
dexed by analysis of venous whole blood. Characteristics of the specific procedures employed
and pertinent evaluative comments are as follows:
(a) Venous blood samples we>"e collected by trained technicians in a lead screening
urogram and analyzed in the laboratory facilities of the New York City Depart-
ment of Health (NYCHD) during the summer of 1972. Sampling involved standard
precautions tc minimize sample contann natior and col'ection during the summer
months, wren blood lead values in the city are known to be maximal. Samples
were analyzed within 48 hours of co'Mecticn and refrigeration.
(b) As a lead analysis facility, the NYCHD laboratory has processed a large volume
of samples for lead content over many years, an important consideration in view
of the fact that laboratory proficiency is direcLly related to the level of Pb
analysis activity.
(c) The specific method of blood lead analysis employed was the Hessel extraction
variation of atomic absorption spectrometry (Hessel, 1968), a macro method
9
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using venous blood which still enjoys popularity up to the present time. The
periodic surveys by the Centers for Disease Control (CDC) of participating
laboratories in their proficiency programs indicate (see Boone et al., 1979)
that the Hessel method is somewhat more accurate than the Delves cup technique
and more accurate than the other variations of atomic absorption spectrometry.
Precision tends to be less than for the Delves cup procedure, consistent with
the reported analytical error of ±5-6 |jg Pb/dJ! for the NYCHD laboratory when
using the Hessel method (communication of B. Davidow to N.B. Schell, see
Ernhart, March 11, 1983: summary of conversation between N.B. Schell and C.
Ernhart). Compared to isotope dilution mass spectrometry (IDMS), the Hessel
method for the range of blood lead in the Perino and Ernhart study shows a
modest positive bias of 2.5 pg Pb/d2.
(d) At the time of data collection for the Perino and Ernhart study, it was the
practice of the NYCHD laboratory to report blood lead values rounded to the
nearest decile of blood lead. Hence, a subject blood Pb value of 40 pg/d£ in
the Perino and Ernhart (1974) report would have resulted from a reading of some
value between 35 and 44 pg Pb/di.
(e) Internal and external quality control protocols were in place in the NYCHD
laboratory at the time of the subject study. The latter consisted of partici-
pation in both the CDC and New York State proficiency testing programs, and the
NYCHD laboratory met acceptable proficiency standards.
(f) It appears that there are no major difficulties with methodological aspects of
the blood Pb data. The moderate positive bias in the Hessel procedure, if
corrected for among the Perino and Ernhart (1974) study data, would result in a
constant shift downward in all values. Since there was decile rounding, abso-
lute corrections for this bias would require having the original blood Pb
values.
(g) The full use of confidence bounds for the lead measurements, if employed in any
overall reanalysis of the data, would require havinq the original blood lead
values as well as taki.ny into account the analytical error noted above.
Lead exposure levels for subjects in the follow-up study of Ernhart et al. (1981) were
indexed via measurement of Pb in capillary blood (applied to filter paper) and free erythro-
cyte protoporphyrin (FEP) determination. A sub-group of the follow-up population furn'shed
shed teeth for dentine lead analysis. Characteristics of the procedures used and evaluative
comments are as follows:
10
1283<
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(a) Capillary blood samples were collected on filter paper and analyzed in the same
NYCHD laboratories (as noted above) that assayed blood Pb by the Delves cup
variation of atomic absorption spectrometry.
(b) It is now generally accepted that capillary blood samples, as compared to those
obtained by venous puncture, manifest a significant positive bias in lead level
even under relatively stringent sample collection conditions. The best data
base by which to estimate the magnitude of this positive bias is the NHANES II
survey, which indicated that for the Delves cup procedure used in the present
study under discussion capillary blood Pb was 6 pg/d£ higher than for venous
samples. An additional positive bias of approximately 3 pg/dJi exists for the
Delves cup analysis compared to the definitive IDM5 method.
(c) A generally unrecognized problem with the analysis of lead in blood using
filter paper spotting has to do with the close dependence of blood flow (on
filter paper) on hemoglobin/hematocrit content. The study of Carter (1978)
makes it clear that blood flow is increased on filter paper with decreasing
hematocrit, resulting in proportionately lower blood lead values contrasted to
venous blood analysis.
(d) In view of the documented problem of using blood on filter paper without
correction for hematocrit, blood lead values in the Ernhart et al. (1981)
report would have to be appropriately corrected, if this was not already done
initially by the NYCHD. It should be noted that Carter (1978) observed under-
estimation of lead content of blood on filter paper at hematocrit values that
would be considered in a normal range.
(e) Dentine lead levels were determined in the laboratories of Dr. Irving Shapiro,
School of Dental Medicine, University of Pennsylvania, a facility which
pioneered such analyses and is recognized as having the most proficiency in
such measures. In this study, dentine was isolated from a given whole tooth
sample.
(f) Samples of isolated dentine were dissolved in perchloric acid, buffer added,
and lead measured by an electrochemical technique, anodic stripping voltam-
metry. At the levels of lead being measured in the dentine samples, this tech-
nique provides reasonably reliable results for the solubilized analyte.
(g) From data of Shapiro et al. (1973), duplicate analysis of dentine with low and
elevated lead exposure of subjects indicates that the analytical error in-
creases with concentration, suggesting greater variation in replicate section-
ing than in the instrumental measurement itself.
11
:1284c
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(h) Identification of an "outlier" by Ernhart in further unpublished analyses of
data from the follow-up study (see following sections) was done on the basis of
a dentine lead value being 107.4 ppm Pb in the subject sample. A methodolo-
gical problem accounting for this high value has been discounted by Shapiro
(personal communication of I. M. Shapiro to C. B. Ernhart, see Ernhart,
February 3, 1983, letter to D. Weil), who indicated that any contamination of
the dentine section by inclusion of circumpulpal dentine, a region manyfold
higher in lead, would only account for 3-4 percent of the above dentine lead
level.
(i) Erythrocyte porphyrin analysis in the present study was carried out in the
NYCHD laboratory which simultaneously analyzed capillary blood for lead. It
was noted that analytical error was less than 15 percent, using a microfluoro-
metric analysis of blood samples eluted from the filter paper. This laboratory
employs internal and external quality control protocols for EP analyses, the
latter including the EP proficiency testing program of CDC.
2. Psychometric Measurements and Procedures
Comments on the psychometric measurements employed in the Perino and Ernhart (1974) study
and the results obtained are as follows:
(a) The study employed the McCarthy Scales to assess the intellectual development
of young children and the Amnions Quick Test to assess parents' IQ levels. The
Committee agreed that the McCarthy Scales were appropriate for assessing intel-
lectual abilities of the children in this sample, whose race, age range, and
socioeconomic status (SES) were represented in the standardization sample. The
Amnions Quick Test, however, has more questionable validity for two reasons:
(1) the content of the test is a very limited sample of adult intelligence,
and (2) the test was not standardized on low SES black subjects. The reliabil-
ity of the McCarthy Scales is satisfactory for the present research. The reli-
ability of the Quick Test, however, is only about .75, a low value for an adult
measure. More importantly, correlations with the Stanford-Binet and WISC range
from only .10 to .80, with a median in the .40 range. Large discrepancies have
been observed between Quick Test Scores and individual IQ test scores (Sattler,
1982). Although the Quick Test is considered useful in large scale research
studies, where a simple and quick assessment of average ability is needed, the
measure is less adequate in the Perino and Ernhart study where it was used as a
12
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control for individual differences. A measure such as the short form of the
WAIS or the WAIS vocabulary scale would have provided a better estimate of
parental IQ.
(b) The administration of the tests by the first author, a school psychologist, was
blind with respect to the children's blood Pb levels. Although the tests were
administered in the home, under nonstandard conditions, the Committee concluded
that the assessments were generally valid. Because of the training and clini-
cal experience of the investigator, the Committee thought it unlikely that the
assessments were seriously compromised.
(c) Birth weight, history of birth risk factors, and maternal education were
reported by the mothers in an interview, but were not verified by checking of
appropriate records. Maternal occupation was recorded from clinic records em-
ploying a 1950 census classification that was inadequate to differentiate among
urban blacks. Thus, nearly all families in this sample fell within two occupa-
tional classes. It is not known whether a finer SES scale would have resulted
in greater relations between SES and other variables in the study than those
reported by Perino (1973).
(d) In view of the limitations of the Quick Test and the measurements of some of
the control variables, it is especially important that new analyses of the data
(proposed below) be employed to maximize the efficiency of the control vari-
ables.
(e) Descriptions of quality control procedures by Dr. Ernhart regarding the check-
ing of data entries onto computer cards and/or tapes seemed to indicate that
reasonable care was taken to ensure accurate encoding of data for statistical
analyses. The Committee had no feasible way to confirm this independently, but
Dr. Ernhart, in responding to the Committee's request for reanalyses of the
data set, reported as follows: "In the course of conducting the reanalyses to
include parent education, we found several errors in the data and the previous
analyses. One child's age was incorrect by one year (38 months rather than 50
months). This changed his General Cognitive Index (GCI) from 50 to 86; other
scores were correspondingly affected. Another child's GC.I was incorrect by one
point. The degrees of freedom used and reported in the tests of significance
of the lead effect (regression analyses) should have been 1 and 75, not 4 and
75."
Comments on the psychometric assessment procedures used by Ernhart et al. (1981) in thfe
follow-up study are as follows:
13
1286^
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(a) Because this study is a follow-up of the Perino and Ernhart sample, many of the
issues raised about the original study apply here. Also, use of the McCarthy
Scales with age groups not included in the standardization sample is question-
able. More than half of the children were beyond the age range of the test,
and their test scores were determined by linear extrapolation. The Committee
believes that a better procedure would have been the use of residuals after
regressing raw McCarthy Scale scores on age at testing. The Committee acknow-
ledges that no subject reached the ceiling on the subtests and also that some
value exists in re-administering the same measure in a longitudinal study.
However, the Committee concludes that it would have been preferable to have
chosen an age-appropriate measure of intelligence, such as the WISC-R, which is
based on a suitable standardization sample and also taps cognitive performance
of older children. Despite reservations about the use of the McCarthy Scales in
the follow-up, the Committee does not believe that the assessment of intellec-
tual development was seriously compromised. Because the children in the study
were functioning at levels well below those of most children of their ages, the
test was more appropriate for them than for most children of the same age but
of average intelligence.
(b) Reading test scores were obtained from many different tests. The Committee
concludes, however, that the combination of multiple measures does not neces-
sarily compromise the assessment of reading achievement (Scarr and Yee, 1980).
The age correction used was appropriate.
(c) More than one psychologist collected the follow-up McCarthy data, generally
within the children's schools. The Committee believes that the administration
and scoring of the protocols were adequate. The testers were both blind as to
the children's Pb levels and well-trained in psychometric assessment.
(d) Correlations between the earlier and later administrations of the McCarthy
Scales, as reported in Ernhart et al. (1980), were in the moderate range (from
.24 to .61). The highest correlation is for the General Cognitive Index, which
. is considered by the Committee to be the most important cognitive measure in
the study. In light of developmental changes from preschool to school-age
skills, and the use of extrapolated scores, this relationship suggests consid-
erable reliablity for the McCarthy Scales in the follow-up study.
(e) The same comments regarding quality assurance checks for data entries as were
made under (e) above for the Perino and Ernhart (1974) study also apply here.
14
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3. Statistical Analyses
The Committee believes that the treatment of confounding factors can be handled in a
better way than as described in the 1974 and 1981 Ernhart papers. The analyses performed by
Ernhart and colleagues can be questioned in light of currently accepted statistical practices
for dealing with interaction and confounding, and they should be reworked.
The proper model for assessing the effect of Pb exposure on IQ is one which contains, in
addition to the Pb exposure variable, all factors deemed to be potentially confounding. A
potentially confounding factor is one which is correlated (in the population) with the expo-
sure variable (Pb) and for which there is reasonable evidence from previous research experi-
ence and knowledge that it is predictive (in its own right) of the outcome variable (IQ).
Thus, a procedure which chooses potential confounders via a forward selection procedure,
ignoring the Pb variable (as Ernhart did), can be misleading and can actually incorrectly drop
important confounders from consideration. A backward elimination strategy is designed to ob-
tain the most accurate estimate of the effects of the exposure variable adjusted for all key
confounders, whereas a forward selection approach is designed to predict the outcome variable
but does not assure an accurate estimate of the effects of the exposure variable.
As an example, parental education was eliminated by a forward selection approach not in-
volving the Pb exposure variable at all; in fact, it is a potential confounder, and should
only be eliminated from the full model if its elimination does not alter the Pb exposure
regression coefficient. Similarly, SES should be handled in the same fashion.
In theory, assuming that the data set is free from bias (i.e., is a random sample of the.
population under study), one can lose precision but not validity by including in the full
model a true non-determinant of the dependent variable under study. An example in the data
under consideration is the variable sex, which is generally agreed to be a predictor of motor
skills but not of the other outcome measures being studied. Its inclusion in the full model
(using any outcome variable other than motor skills) should not cause a validity problem (even
though it is correlated with Pb exposure); this can be demonstrated (assuming that the data
are representative of the population) by dropping the sex,variable from the full model and
noting that the Pb exposure coefficient does not materially change. With- motor skill as the
outcome variable, sex should be expected to be manifest as a real confounder in these data and
hence cannot be dropped from the model. In summary, then, a reanalysis of the Peri no and
Ernhart (1974) and Ernhart et al. (1981) data should be carried out, based on a model contain-
ing the Pb exposure variable and all available confounders measured.
In general, interaction effects between the Pb exposure variable and the ccvariates
should be assessed before confounding issues are considered. A qualitative assessment can be
lb - v- . ,
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done initially by stratifying on each of the covariates and determining whether the relation-
ship between Pb exposure and IQ is reasonably constant across strata of the covariate under
consideration. Nonconsistency suggests the need for one or more interaction terms in the
model under study. Ultimately, the modeling of interaction involves the use of cross-product
terms in regression models. A strategy for dealing with interaction and confounding in obser-
vational epidemiologic data is described by Kleinbaum et al. (1982). Possible interaction
effects were not really examined by Ernhart and colleagues, and the presence of any inter-
action^) would complicate data interpretation. However, given the highly variable nature of
the data and the limited sample size, it may be difficult to deal adequately with interaction
assessment for these data.
Comments on specific aspects of the statistical analyses employed in the 1974 and 1981
Ernhart studies include:
(a) Corrections for unreliability (i.e., measurement error) in the variables under
study should be made, especially concerning the Pb exposure indices. Such cor-
rections will adjust the observed correlations, and could have a major impact
on the ultimate conclusions drawn from the analyses. They provide a limit on
the strength of relationships by showing the relationship that would be expec-
ted were the measurements made and recorded without error.
(b) The outlier alluded to earlier in the Ernhart et al. (1981) data set should be
dropped from all analyses. The dentine Pb value provides enough evidence that,
in this case, the past Pb exposure was sufficiently high to conclude that the
subject may have earlier been overtly symptomatic but undiagnosed.
(c) It is important that the dependent variables be adjusted appropriately for age.
As a suggestion, one could use, for each child, the deviation from the linear
regression line of "raw score" on "age at testing".
(d) Dependent variable scores for a given individual on a series of intelligence
tests are obviously correlated. Multivariate analysis of covariance is one
option, but must be done very carefully. Certain assumptions (e.g., multivari-
ate normality) must hold at least approximately.
(e) Treating the Pb exposure variable as a continuous variable is preferable to
categorizing cases into high and low Pb groups.
(f) The Committee notes that, for the 62 children in the 1981 study (excluding the
outlier), significant correlations are seen between the identification number
I289<
16
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assigned to children and other variables of interest. Identification number
correlates -0.43 with 1972 level of blood Pb, 0.38 with parent IQ, 0.28 with
parent education, and 0.27 with 1972 GCI score from the McCarthy scale. These
results would be expected if identification numbers were assigned to children in
the order in which they were assessed (by Perino in 1972) and if the children
with higher Pb levels tended to be the earlier ones assessed. Results of the
Ernhart studies, particularly the one by Perino and Ernhart (1974), could be
affected by this nonrandom ordering of assessments, to the extent that any
aspects of the assessment process systematically changed over the course of the
studies.
An alternative research question to those addressed in the Perino and Ernhart (1974) and
Ernhart et al. (1981) analyses can be asked by considering data from the cases assessed both
in 1972 and in 1977: namely, is there a relationship between differences in cognitive scores
and differences in blood lead concentrations from 1972 to 1977? Do children whose blood lead
levels were higher in 1977 than expected from their 1972 levels display cognitive scores in
1977 that differ from those expected from their 1972 cognitive scores?
This question could be addressed by regression analyses. The 1977 Pb level could be pre-
dicted from its regression on the 1972 Pb level and residual values obtained. Similarly, the
1977 IQ value could be predicted from its regression on the 1972 IQ value and residual values
obtained. The correlation between IQ residuals and Pb residuals would indicate an association
between change in IQ and change in Pb. That correlation also could be adjusted for confound-
ers such as parental IQ, parental education, and 5ES. We would urge such a reanalysis of the
data from Perino and Ernhart and Ernhart et al. (after correction of the erroneous values
recently discovered in those data). Interpretation of results from such analyses must depend
upon careful inspection of the cross-lagged correlations on which the correlation of residuals
depends. In addition, of course, even the residual values may De acting as surrogates for un-
recognized confounding variables.
4. Committee Conclusions and Recommendations
The Committee's conclusions and recommendations regarding the Perino and Ernhart (1974)
study can be summarized as follows. Blood lead levels, as the main index of exposure, appear
to be of acceptable reliability. The psychometric measures for children are also acceptable,
but confounding variables rray not have been adequately measured. The statistical analyses do
not adequately deal with confounding variables. In the view of the Committee, the findings of
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this study, as reported, neither support nor refute the hypothesis that low to moderate lead
exposures are associated with cognitive impairments in apparently asymptomatic children. The
Committee recommends that the data from the Perino and Ernhart study be used in conjunction
with the 1981 Ernhart et al. follow-up study in longitudinal analyses.
The Committee's conclusions and recommendations concerning the Ernhart et al. (1981)
study include the following points. Given limitations in both the control and the outcome
measures, it is difficult to assess the possible role of less-than-ideal measures in contribu-
ting to the generally null results reported. When the authors conclude that there are no sig-
nificant effects, or very weak effects at best, then that outcome might also be reasonably
attributable to unreliable measures or other procedural problems. One major difficulty with
this study is the potential unreliability of the blood Pb level measurements, such that the
Committee recommends that the blood Pb values be corrected in the fashion specified earlier.
The psychometric data were adequately collected but should be readjusted for age. The crossr
sectional analyses suffer from the same problems as those of the previous (Perino and Ernhart,
1974) study. More importantly, the analyses failed to exploit fully the longitudinal aspects
of the study data set. In the view of the Committee, then, the findings of this study as
reported in the published form also neither support nor refute the hypothesis that the report-
ed blood lead levels are associated with cognitive impairments in children. The Committee
strongly recommends that longitudinal analyses of these data (from both Perino and Ernhart,
1974, and Ernhart et al., 1981) be carried out.
C.. Comments on Yamins (1976) Dissertation Study
1. Indicators Of Lead Exposure
Comments on specific aspects of the Pb exposure measurement methodology used in the
Yamins (1976) dissertation study are as follows:
(a) Blood Pb was sampled by finger puncture, using established techniques for blood
lead sampling, and the blood samples collected on filter paper presumably pro-
vided by the New York City Health Department. Upon collection, samples were
transported to the New York City Health Department for lead measurement.
(b) The use of filter paper for blood collection raises the same question that is
of concern in the Ernhart et al. follow-up study, i.e., the blood lead value
must be corrected for hematocrit. The problem here occurs, actually, with each
of the three indices (highest blood lead, mean blood lead, or most recent blood
lead), so that it is not possible to assess the actual blood lead level in each
18
12°>1 .<
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case nor to determine the suitability of selecting one exposure index over
another, since a given subject may have had variable hematocrit over the multi-
sampling time period.
(c) Measurement of EP was also carried out in the laboratories of the New York City
Health Department, quality control details for which were discussed among com-
ments on the studies of Ernhart and coworkers (vide supra).
2. Psychometric Measurements and Procedures
In the Yamins dissertation, a variety of psychometric measurement procedures were employ-
ed, including some standardized instruments such as the Caldwell Preschool Inventory and
other, more-or-less experimental measures such as the verbal repetition tasks.
Specific comments on the psychometric measurements utilized by Yamins (197G) include:
(a) This study employed the Peabody Picture Vocabulary Test (PPVT) to assess the
intellectual development of the children. The PPVT is not a nonverbal measure
' of intelligence; it provides a narrow assessment of verbal abilities. However,
the committee agreed that the PPVT was a reasonable measure of cognitive per-
formance to use in the study because the scores correlated well with the other
cognitive and experimental language measures, including the Caldwell Preschool
Inventory, which is an appropriate measure for this population.
: (b) The Amnions Quick Test was used to assess parental IQ in this study. As noted
earlier, this measure has questionable validity. However, the pattern of cor-
relations between the Quick Test scores and other variables does establish some
credibility for its use in the current study.
(c) The experimental measures of 1anguage ski 11 correlated with child's age, as one
would predict, and yet appear to measure skills already tapped by the cognitive
measures.
(d) There .is no obvious explanation for the correlation of 0.30 between parent
Quick Test scores and child's age. However, when age is partialled out, the
correlation between child IQ and parental IQ is approximately 0.35, a value
close to that found in other studies,
(e) The author (Yamins) administered all of the cognitive and language measures in
the children's homes and was blind as to Pb levels at the time. She appears to
have been appropriately trained and competent to collect the psychometric test
data. Quality assurance checks regarding data collection (e.g., scoring,
coding, and keypunching) could not be ascertained but are assumed to be the
same as for the above Ernhart studies,
19
1292c
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3. Statistical Analyses
Many of the same reservations expressed earlier regarding the analyses used in the 1974
and 1981 Ernhart studies also apply here. Specific concerns include the fdllowing:
(a) Stepwise multipie regression Was employed to choose the set of covariates to be
included in the final regression mode'i with mean lead level. In the Commit-
tee's view, this is not the appropriate way to deal with potentially confound-
ing factors. A backward elimination strategy starting with a model containing
lead and all potential confounders is recommended since confounding involves
association with both the outcome variable (e.g., a measure of learning perfor-
mance) and the exposure variable (e.g., mean lead level). A forward selection
approach, as was apparently employed by Yamins, igriores the relationship be-1
tween the potential confounders and the exposure variable in choosing an appro-
priate subset for control, and hence can lead to inappropriate adjustment.
(b) the strategy for analysis described oii pag'e 79 of the Yamiris (i976) disserta-
tion is not appropriate for valid control of confounding effects (see preceding
comment). Although it may produce the same results as a backward elimination
approach, one cannot know without trying both approaches. In this case, back-
ward elimination of variables does not markedly alter the outcome of the analy-
sis. One Committee member (LH) found that the association between Pb arid IQ
remained after controlling for father's absence, parental IQ, parental educa-
tion, birth order, and birth weight, using a backward elimination approach.
(c) The results displayed in table 9 (page4 82) of the dissertation do hot, in the
Committee's opinion, represent a strong indictment of lead exposure. Finding a
few significant partial correlations of lead exposure with various dependent
variables just by chance is riot at ait unlikely when performing several analy-
ses using mutually correlated dependent variablefs. Apparently, no multivariate
(as opposed to multivariable) analyses Were employed to account for such corre*1
lations.
(d) the results in table 10 (page 85) of the dissertation are based on a compari-
son of a "low lead" group to a "moderate l'e"a"d" group (after dichotomizing lead
exposure), with adjustment only for the covaria'te "age". Given that other
potential confounders were apparently ignored, and given that several compar-
isons were made involving correlated responses, not much importance can be
attached to the few significant findings reported.
-------
(e) Results presented in Tables 11 (page 86), 12 (page 88), 14 (page 91), and 15
(page 93) of the dissertation are also based on controlling only for age. The
Committee finds it difficult to place much importance on the findings presented
in these tables.
4. Committee Conclusions and Recommendations
The Committee concludes that, despite reservations expressed regarding psychometric mea-
surements employed in the Yamins study, the pattern of results obtained (including the inter-
correlations between different measurement outcomes and parental measures) lends credibility
to the psychometric results as reasonably reflective of the cognitive abilities of the sub-
jects tested. The blood lead data require correction for hematocrit because of the use of
filter paper for blood collection; unfortunately, the hematocrit values are not available to
make this correction. In addition, the Committee finds that specific statistical analyses
employed (including stepwise regressions and covariate analyses controlling only for age) are
not the most appropriate for analyzing the Yamins data set. Rather, multivariate analyses
should have been used that included other potential confounders besides age and, also, back-
ward elimination of variables having negligible impact on the variance attributed to Pb. The
Committee further finds that the very modest residual effects attributed to Pb based on the
reported analyses controlling only for age are not convincing evidence for a negative effect
of Pb on the cognitive abilities of the subject children.
21
1294^
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REVIEW OF STUDIES BY DR. HERBERT NEEDLEMAN AND COLLEAGUES
A. Background Information
The Committee undertook detailed review of an epidemiological study published in 1979 by
Dr. Herbert Needleman and associates (Needleman et al. , 1979). In addition, limited review
was carried out for several other reports (Burchfiel et al., 1980; Needleman, 1981; Needleman,
1982; Needleman, 1983; Bellinger and Needleman, 1983) published as follow-up analyses of the
same data set and/or new data constituting extensions of the 1979 study.
Approximately 3329 children attending first and second grades between 1975 and 1978 in
Chelsea and Somerville, Massachusetts, constituted the study population in the Needleman et
al. (1979) study. Children submitted shed teeth to their teacher, who verified the presence
of a fresh socket. The shed deciduous teeth were cleaned ultrasonically (discarding any con-
taining fillings), followed by dissection of a 1-mm central slice and•subsequent analysis of
Pb in dentine tissue by anodic stripping voltammetry. Teeth were donated from 70% of the
population sampled. Almost all children who donated teeth (2146) were rated by their
teachers on an eleven-item classroom behavior scale. The results obtained for the rated chil-
dren were reported to demonstrate a dose-response relationship be-tween increasing dentine Pb
levels and increasing percentages of students receiving negative (poorer) ratings on several
of the 11 categories of classroom behavior, as shown in Figure 1 below.
Following the teachers' ratings of classroom behavior, subsets of the rated students
(reported to represent polar groups of children with the lowest and highest 10 percent of den-
tine Pb levels) were recruited for further, extensive neuropsychological evaluation by means
of psychometric tests. Each subject whose initial tooth slice was in the highest 10th percen-
tile (>24 ppm) or lowest 10th percentile (<6 ppm) was provisionally classified as having high
or low lead levels, respectively. Repeat dentine lead samples from the same teeth were analy-
zed, when possible, and attempts were made to obtain and analyze other shed teeth from each
subject provisionally classified in either lead exposure group (with more than one analysis
being obtained for all but one subject). Parents of children provisionally classified as
having either high or low dentine Pb levels were invited to have their children participate
in further neuropsychological evaluations. Criteria were established for requisite agreement
between replicate dentine sample analyses before the data for a given subject were included in
the study; when requisite agreement was not found, then the subject was designated as "unclas-
sified" and excluded from data analyses. Other children were excluded from the study because:
(1) their parents were unable or unwilling to participate; (2) they came from bilingual homes;
12CJ5<
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DENTINE LEAD
CLASS
(ppm)
1
< 5.1
2
5.1 - 8.1
3
8.2 -11.8
4
11.9 -17.1
5
17.2 -27.0
6
>27.0
CLASS
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DISTRACT
123456
123456
123456
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IBLE PERSISTENT ORGANIZED ACTIVE
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IMPULSIVE
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TRATED
123456
123456
123456
123456
DAY SIMPLE SEQUENCES LOW
OREAMER DIREC OVERALL
TIONS FUNC
Lunable TO FOLLOW-^ T'ONING
Figure 1. Distribution of negative ratings by teachers on eleven classroom behaviors in relation
to dentine lead concentrations.
Source: IMeedleman et al. (1979).
-------
(3) they had been diagnosed as having been lead poisoned; or (4) their medical history indi-
cated a birth weight of <2500 g, delay in discharge beyond mother's discharge from hospital
after birth, or a record of noteworthy head injury (any of which can correlate with slower
neurobehavioral development). Table 1 from the Needleman et al. (1979) paper, reproduced
below, lists the number of provisionally eligible children, those excluded from neuropsycho-
logic testing, and those undergoing neuropsychologic testing who were retained or excluded
from data analyses.
TABLE 1. REASONS FOR EXCLUDING SUBJECTS AND DISTRIBUTION OF
FINAL DENTINE LEAD LEVELS IN INCLUDED AND EXCLUDED GROUPS
GROUP NO. DENTINE LEAD LEVEL
LOW HIGH UNCLASSIFIED
Provisionally eligible subjects: 524 258 187 79
Excluded from neuropsychologic testing: 254* 123 101 30
Bilingual home 84
Not interested 57
Moved 19
Othert 94
Total 254
Subjects tested 2701 135 86 49
Excluded from data analysis: 112 35 28 49
Later tooth discordant 36
Not discharged' from nursery with 76
mother, possible head injury,
reported to have plumbism or
bilingual home
Total 112
Cases scored and data analyzed 158 100 58
^Teachers' behavioral assessment available on 235.
tlnfant at home, two working parents, etc.
^Teachers' behavioral assessment available on 253.
Source: Needleman et al. (1979)
Mean dentine lead values for the 100 children included in the low-Pb and 58 in the high-
Pb exposure groups were not reported by Needleman et al. (1979). However, Bellinger and
Needleman (1983), who studied 141 of the 158 subjects of Needleman et al. (1979), reported
those subjects to have mean dentine Pb levels of 6,2 ppm and 31.4 ppm, respectively. Mean
blood Pb levels reported as having been assayed 4-5 years earlier for approximately 50% of
the children in these two groups were 23.8 ± 6.0 pg/dSL vs. 35.5 + 10.1 (jg/d£, respectively;
24
1297 <
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the highest blood-Pb level recorded was 54 p g/d £ . The low-Pb and high-Pb group children
underwent a comprehensive neuropsychologic evaluation, beginning with the Wechsler
Intelligence Scale for Chi 1 dren-Revised (WISC-R), with the examiners blind to. the Pb-exposure
status of the children. In addition to the WISC-R, the children were administered, in set
sequence, tests of: concrete operational intelligence; academic achievement (in mathematics,
reading recognition, and reading comprehension); auditory and language processing; visual-
motor reflexes; attentional performance; and motor coordination. While each child was being
tested, the parents filled out a comprehensive medical and social history, received a 58-item
questionnaire on parent attitudes, and took the Peabody Picture Vocabulary Test (PPVT). Also,
39 non-lead variables potentially affecting the children's development were scaled and coded,
e.g., estimation of parental socioeconomic status (SES) by a two-factor Hollingshead index.
The scores of the high-Pb and low-Pb children for each of 39 control variables were com-
pared statistically by the Student t-Test, with the two groups differing significantly on such
variables as age, father's social class and father's education. Scores from the neuropsycho-
logic evaluations of the high-Pb and low-Pb children were then compared statistically, using
an analysis of covariance with dentine-Pb level as the main independent variable and with the
fallowing five covariates: father's SES (composed of education and occupation score); mother's
age at subject's birth; number of pregnancies; mother's education-; and parental IQ score.
With the exception of these variables and age, the low-Pb and high-Pb groups were similar in
regard to most of the non-Pb control factors.
Results of the neuropsychologic evaluations for the low-pb and high-Pb groups can be sum-
marized as follows: children in the high-Pb group were reported to have performed signifi-
:~ntly less well on the WISC-R (especially on the verbal items), un three measures of auditory
and visual processing, on attentional performance as measured by reaction time under varying
ielay conditions, and on most items of the teachers' behavioral ratings. The high-Pb children
appeared to be particularly less competent in areas of verbal performance and auditory proces-
sing, having obtained lower scores, for example, on tasks requiring: response to verbal in-
structions of increasing complexity, immediate repetition of previously uttered sentences of
increasing complexity, and discrimination of tone sequences of increasing complexity as either
alike or different. Impaired focusing of attention (or distraction) of high-Pb children was
also reflected by a significantly higher percentage of high-Pb children rating items being
found to be significantly different (i.e., more negative) for high-Pb than low-Pb children at
p <0.05. Overall, the sum score (mean) of ratings of classroom behavior were found to be sig-
nificantly poorer for the high-Pb children based on an analysis of covariance.
Burchfiel et al. (1980); using computer-assisted spectral analysis of recordings from a
standard EEG examination on 41 (22 low-Pb and 19 high-Pb) children from the Needleman et al.
25
U'SSt
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(1979) study, reported significant increases in percentages of low frequency delta activity
and decreases in percentages of alpha activity in the spontaneous EEG cf the high-Pb children.
Percentages of alpha and delta frequency EEG activity and results for several psychometric and
behavioral testing variables (e.g., WISC-R full-scale IQ and verbal IQ, reaction time under
varying delay, etc.) obtained for the same children were then employed as input variables (or
"features") in direct and stepwise discriminant analyses. The separation determined by these
analyses for combined psychological and EEG variables (p<0.005) was strikingly better than the
separation of low-Pb from high-Pb children using either psychological (p <0.041) or EEG
(p<0.079) variables alone.
A more recent paper by Needleman (1982) provided a summary overview of findings from the
Needleman et al. (1979) study and findings reported by Burchfiel et al. (1980) concerning EEG
patterns for a small subset of the children included in the 1979 study. Needleman (1982)
also summarized results of an additional analysis of the Needleman et al. (1979) data reported
elsewhere by Needleman et al. (1982). More specifically, cumulative frequency distributions
of verbal IQ scores for the low-Pb and high-Pb subjects from the 1979 study were reported by
Needleman et al. (1982) and reprinted as Figure 2 of the Needleman (1982) paper, as shown
below in Figure 2. One key point made by Needleman (1982) was that the average IQ deficit of
four points demonstrated by the Needleman et al. ( 1979) study reflected not just further im-
pairment of cognitive abilities of children with already low IQs but rather a shift downward
in the entire distribution of IQ scores across all IQ levels in the high-Pb group, with none
of the children in that group having verbal IQs over 125.
The Bellinger and Needleman (1983) paper provided still further follow-up analyses of the
Needleman et al . (1979) data set, focusing mainly on comparison of the low-Pb and high-Pb
children's observed IQs versus their expected IQs based on their mothers' IQs. Bellinger and
Needleman reported that regression analyses showed that the IQs of children with elevated
levels of dentine Pb (>20 ppm) fell below those expected based on their mothers' IQs and that
the amount by which a child's IQ falls below the expected value increases with increasing den-
tine Pb levels in a nonlinear fashion (see Figure 3 below, showing plots of IQ residuals by
dentine Pb levels as illustrated in Figure 2 of the Bellinger and Needleman paper). In fact,
examination of the scatterplot shown in Figure 3 and the discussion of results provided by
Bellinger and Needleman (1983) indicate that regressions for the 20-29.9 ppm group did not
reveal significant associations between increasing Pb levels in that range and IQ residuals,
in contrast to statistically significant. (p<0.05) correlations found between IQ residuals and
dentine Pb in the 30-39.9 ppm range.
In order to evaluate critically the above studies, the Committee met with Dr. Needleman
at his University of Pittsburgh (Children's Hospital) office facilities in Pittsburgh, PA. on
26
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a LOW LEAD
90 100 110
VERBAL I.Q.
140
Figure 2. Cumulative frequency distributions of
verbal IQ scores in high and low lead subjects.
Source: Needleman (1982) and Needleman et al.
(1982).
I LOW I
DENTINE
LEAD
ELEVATED DENTINE LEAD
30
• •
20
••
••
•• •
••
• •
-10
• •
-20
-30
0
10
20
30
40
50
60
70
DENTINE LEAD LEVEL, ppm
Figure 3. Scatterplot of children's dentine lead level versus
residual. Regression lines are shown for four ranges of
lead level: low lead. 0.9 to 9.9 ppm; elevated lead, 20.0 to
66.0. 20.0 to 29.9. and 30.0 to 39.9 ppm.
Source: Bellinger and Needleman (1983).
-------
March 30-31, 1983. During that meeting, Dr. Needleman presented an overview focusing mainly
on the objectives, design, data collection and statistical analysis procedures, and findings
for the original study reported by Needleman et al. (1979). Dr. Needleman also provided addi-
tional information regarding follow-up analyses or extensions of the 1979 study either pub-
lished in other papers referred to above or expected to be published in the near future. This
additional information included comments regarding the conduct of a separate study involving
the evaluation of teachers' ratings of classroom behavior of children in Lowell, MA (a dif-
ferent population from the one sampled in the 1979 study). Certain listings of raw data
(provided in coded form to protect the privacy of subjects), computer printouts summarizing
data entries for statistical analyses or results of such analyses, and miscellaneous other
pertinent materials were discussed with Dr. Needleman during the March 30-31 meeting. Addi-
tional information was requested by the Committee in,order to clarify factual points or to
help resolve evaluative issues arising from the discussions in March with Dr. Needleman. A
portion of the information was provided during the 2-3 months following the March meeting.
(See Attachment 1 for a list of materials examined by the Committee in connection with the re-
view of the subject studies.) The Committee's comments regarding the most salient points of
concern and controversy related to methodological and other features of the above studies by
Needleman and colleagues are presented below.
B. Comments on Needleman et al. (1979) Study
1. Indicators of Exposure
In the principal study (Needleman et al. , 1979) as well as in subsequent reports on sub-
sets of subjects from- the initial population (e.g., Burchfiel et al., -1980; Bellinger and
Needleman, 1983), Pb exposure in the pediatric subjects was assessed by analysis of Pb in the
dentine of deciduous teeth. In contrast to blood Pb, which is an exposure marker for rela-
tively recent exposure, whole-tooth or tooth-region analysis for Pb content yields an index of
cumulative Pb exposure of the subject up to the time of exfoliation.
In the report of Needleman et al. (1979), blood Pb levels as an additional index of prior
exposure were reported as only being available for some (approximately 50%) of the subjects in
the highest/lowest deciles, and were discussed only in terms of group means. These measure-
ments were reported tc have been obtained as part of a blood screening program in the subject
communities 4-5 years prior to collection of tooth samples.
Observations and comments concerning specific aspects of the Pb exposure indices and
associated methodological procedures include:
28
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(a) Dentine was isolated from each tooth sample by a procedure described in an
earlier report in which the present principal investigator (Dr. Ncedleman) was
also heavily involved (Shapiro et a 1., 1973). In that procedure, very thin sec-
tions of tooth were carefully cut from the central sagittal plane, dentine
(coronal plus secondary) was mechanically separated from enamel and circumpul-
pal dentine, and the dentine samples were dissolved in acid and subsequently
analyzed by anodic stripping voltammetry (ASV) for Pb content.
(b) According to Dr. Need^man, the type of tooth selected for analysis was fairly
consistent: mainly the incisor, and some bicuspids. Hence, it appears that
any variation in Pb content which might arise from random selection of diverse
types of dentition (due to variation in Pb content across different types of
teeth) would have been minimal.
(c) Unlike blood Pb, there 1's nu external quality control framework by which to
evaluate the dentine Pb analyses such as were done in the subject studies. One
must therefore consider the specific steps in the analysis against a general
body of information. Two steps in the dentine Pb measurement need to be con-
sidered. According to Needleman, the homogeneity of dentine in terms of Pb
content for a given tooth can va^y sufficiently that tooth sectioning was con-
fined to an initial central sagittal sectioning in all cases, the sectioned
sample providing two (replicate) samples for analysis. Once dentine was iso-
lated, its subsequent analysis by ASV would be expected to be achieved with
good accuracy and precision, given available data for overall performance of
ASV assays of Pb in biological matrices and the fact t.nat such Pb levels are
relatively high. Since the major determinant of variance in the replicate
(single tooth)/duplicats (multiple teeth) analyses was the dentine isolation
step, Needleman et al. (1979) attempted to minimize unacceptable variance by
use of intra-sample concordance criteria in analyzing relationships between
dentine Pb levels and the results of the psychometric test battery.
(d) The impression gained fron close reading of the Needlciian and other reports, as
well as discussions with Needleman, is that, use of dentine Pb va'ues entails
methodological skill at the step cf dentine isolation. From the information
available tc the Committee as to actua1 variation in destine Pb across a given
tooth sample, it appears that illj% represents a reasonable specific est;mate o+"
variability for the dentine analysis for subjects from the lcw-Pb and high-Pb
groups incUjded in statistical analyses of neuropsychologic test outcomes
29
1302*:
-------
(i.e., for subjects with the greatest concordance among their dentine Pb
values). Much greater variation existed among replicate or duplicate dentine
Pb values for individuals from the low-Pb and high-Pb groups excluded from the
Statistical analyses. Examination of replicate/duplicate values for measure-
ments for all subjects in the study (including the 2000+ students for which
teachers' ratings were obtained) would be necessary to determine an overall
estimate of variance for dentine Pb measurements in the study.
(e) Whole-tooth analysis would be simpler technically and has been irore often
employed than specific tooth-region analysis. However, one can also expect
that such a measure would be less sensitive as a biological index of Pb expo-
sure due to the inclusion of enamel, a region that contributes significiantly
to tooth mass but has relatively invariant low Pb content regardless of expo-
sure. In the case of whole-tooth Pb, it is known that Pb content is linearly
related to age of the subject and that the values of the slopes of Pb content
vs. age are better indicators of Pb exposure than just the Pb concentrations
alone (Steenhout and Pourtois, 1981). Shapiro and coworkers (1978) have also
reported that there is a better correlation of tooth Pb concentration/year with
either .blood Pb or erythrocyte porphyrin than just Pb concentration unadjusted
for age. Expression of dentine Pb as a function of age in the present study
(pg Pb • g dentine ^ • yr ^) would be desirable, especially because the mean
age of the high-Pb subjects was greater than that of the low exposure group.
While this method of expressing Pb exposure would have minimal effect on the
categorization of subjects into high- and low-Pb groups, it might be expected
to influence relationships between Pb and other variables, e.g., in Figure 3
(above) from Bellinger and Needleman (1983).
(f) The relative quality of the earlier blood Pb determinations for some low-Pb and
high-Pb subjects cannot be ascertained and must be considered more suspect than
the main exposure measure used (i.e., dentine Pb). At the time blood Pb levels
were measured i-n the subjects, the quality control for the community Pb-screen-
ing programs was minimal, with sampling being done by finger puncture and trans-
fer to capillary tube (communication of V. N. Houk to H. 1. Needleman, see
Needleman, November 22, 1982: letter to L. D. Grant). These limitations on
the relative reliability of such measurements apparently were the reason for
Dr. Needleman's discussion of tnese values only in terms of group means for the
low-Pb and high-Pb subjects. Given present .Knowledge about the impact of sam-
pling protocols on the accuracy of blood Pb measurements, one can reasonably
say that finger puncture plus capillary tube versus venous puncture plus Icw-Pb
30
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blood tube would impart a significant positive bias to the blood Pb levels ob-
tained. Hence, the overall means reported for the low-Pb and high-Pb groups in
terms of blood Pb would, if anything, likely be higher than their true values
for the 50% of the low-Pb and high-Pb children sampled.
(g) Apart from the issue of reliability of the blood Pb measures under considera-
tion is the question of age of the children at the time of blood sampling rela-
tive to the known variation of blood Pb with age in children for a given expo-
sure setting: i.e., blood Pb levels in chi1dren generally tend to peak at 2-3
years of age and decline in subsequent years. Available information on the ages
of the children at the time of psychometric testing, the years when such test-
ing occurred, and the years when blood Pb measurements were made indicate that
the ages of some children at the time of blood Pb measurement were probably at
or not materially beyond the period of typical peaking in blood Pb, but others
may have been sampled at a later age within 1-2 years (during 1973-74) prior to
their participation in neuropsychologic testing while in first or second grade
(as early as during 1975-76). It would be necessary to know the ages of speci-
fic subjects when the blood lead determinations were done and their age at neu-
ropsychologic testing before reliable judgments could be made regarding the
representativeness of the reported mean blood Pb values for either the low-Pb
or high-Pb subjects.
2. Psychometric Measurements and Procedures
The study employed a comprehensive neuropsychological battery to assess 'the children's
behavioral functioning. The measures included the WISC-R, Piagetian tasks, and selected tests
of academic achievement, auditory and language processing, visual and motor performance, reac-
tion time, motor coordination, and teacher ratings of classroom behavior. Mothers' attitudes
toward child rearing .and parental IQ (indexed by the PPVT) wpre also assessed. The PPVT is a
narrow assessment of mothers' intelligence, but their PPVI scores correlated in expected ways
with other variables in the study.
Dr. Needleman administered the PPVT to the mothers, and three other exairiners adminis-
tered the WISC-R and other assessments of the children ir a fixed order. The examiners were
blind as to children's Pb levels and scored the test immediately after t.hp test session. It
is not known how qualified the examiners were to administer individual tests, but Dr. Needle-
man reported that the examiners were instructed on how to administer and score the test.
In a recent publication (Needleman, 1983, p. 243) additional details of the psychometric
procedures were reported. Children with low-Pb exposure were scheduled early in the study,
31
.1304^
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because "I wanted my technicians to get some experience with normal children." In addition,
Dr. Needleman told the Committee during the meeting in Pittsburgh that the study began with
three technicians, one of whom left during the study and was replaced by a fourth tester.
Results of the Needleman et al. (1979) and related publications using the psychometric test
scores could be affected by this nonrandom ordering of assessments.
Dr. Needleman reported that quality assurance procedures for ensuring the accuracy of
teachers' ratings and neuropsychologic test results used in statistical analyses included:
(1) summing of teacher ratings across items and entry of scores for each item and sum scores
onto computer cards, followed by verification and transfer onto magnetic tapes; (2) checking
of neuropsychologic test scores by a second examiner other than the one doing the original
scoring, followed by entry onto cards, verification, and transfer to magnetic tapes; (3) sub-
sequent 5% sampling of computer tape entries to check accuracy against original data listings,
with 12 errors in 15,600 columns of entries being found and corrected.
The Committee's inspection of raw data during the March visit with Dr. Needleman revealed
some problems of another kind, however. Printouts of parental IQ data for low- and high-Pb
subjects included in the statistical analyses (e.g., analyses of covariance) published in the
1979 article revealed errors in calculating parental IQ values for some subjects when their
fathers and mothers were both administered the Peabody Picture Vocabulary Test. Instead of an
average of mothers' and fathers' scores (.midparent IQ), the parents' IQ scores were evidently
combined by taking one-half of one parent's score and adding that value to the other parent's
score. This erroneous procedure resulted in some parental IQ values that lie well outside
probable values. These errors were confirmed later by Dr. Needleman in his letter of
October 4, 1983 to Dr. Bernard Goldstein. The impact of this is to introduce error into the
results of all of the published analyses of the data set where parental IQ was included as a
variable. Correcting these errors would alter the results of the analyses. The precise in-
fluence of the errors on the results can be determined only by reanalyzing the data, and the
Committee urges that this be done.
During inspection of raw data, the Committee also noted a seemingly higher proportion of
large discrepancies between the children's WISC-R Verbal and Performance Scale IQ scores than
would be expected in an unselected sample. The discrepancies seemed to be distributed across
the high-Pb and low-Pb groups. Neither sufficient time nor facilities were available during
the data inspection to carry out an adequate quantitative analysis of the relationship of the
verbal to performance IQs, but if the discrepancies are as large and/or numerous as they ap-
peared to be, this may raise questions about the validity of the WISC-R assessment as employed
in this study.
32
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3. Statistical Analyses
Comments on specific aspects of the statistical analyses employed in the Needleman et al.
(1979) study include the following:
(a) The statistical analyses for teachers' rating scores for classroom behavior
were based on classification of the children's Pb exposure levels in terms of
first dentine lead values obtained for the first tooth submitted by each of the
2146 subjects included in the analyses (vide supra). Six lead exposure cate-
gories were defined as indicated in Figure 1 (i.e., <5.1, 5.1-8.1, 8.2-11.8,
11.9-17.1, 17.2-27.0, and >27.0 ppm dentine Pb), with group boundaries chosen
to give symmetrical cell sizes around the median (i.e., 6.8% in Groups 1 and 6,
17.6% in Groups 2 and 5, and 25.6% in Group 4, respectively). However, no sta-
tistical analyses that take into account other potentially confounding vari-
ables were done on the teachers' rating data shown in Figure 1 and, thus, the
dose-response relationships shown in that figure cannot be attributed to Pb
• . - exposure alone.
In addition, questions arise regarding the appropriateness or accuracy of
classification of subjects in terms of the narrow dentine Pb ranges employed in
plotting the dose-response data shown in Figure 1. Given the 15% variability
noted for replicate analyses of teeth for those subjects with the most highly
concordant dentine Pb values, many subjects who were included in one or another
of the six exposure categories based on first dentine Pb analyses could be more
appropriately classified as belonging in a different exposure category, accord-
ing to later replicate/duplicate dentine Pb values. This is particularly
likely if the same or analogous concordance criteria used by Dr. Needleman to
select' low-Pb and high-Pb subjects for inclusion in statistical analyses of
later psychometric test scores were used, for the teachers' rating analyses.
Inspection of raw dentine Pb values for subjects provisionally classified as
low-Pb or high-Pb subjects for psychometric testing, but then excluded from
final statistical analyses of the psychometric test results because of non-
concordance of dentine Pb values, revealed that shifts across the six exposure
categories could be substantial if replicate or duplicate dentine Pb values
beyond the first dentine Pb value were taken into account.
(b) In regard to the statistical analysis of results from the subsequent psychome-
tric testing phase of the study, comparisons were made only between those
33
ISOGc
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children reported to be ranked in the highest 10th percentile for dentine Pb
concentrations and those in the lowest 10th percentile. This strategy certain-
ly maximizes the chances for finding significant differences. Reviewing Figure
1 of the 1979 report, the Committee notes that a group with "moderate" exposure
might serve to provide evidence for a dose-response relationship (which, if
found, would argue more strongly in favor of a causal connection than the polar
low-Pb vs. high-Pb group comparision used). An earlier report on the subject
(Needleman, 1977) suggests an intention to use low, medium, and high dentine Pb
groups, and a very recent report (Needleman, 1983; Table 6; p. 237) does show
some results on behavior ratings for a group of 13 subjects with "middle" den-
tine Pb levels. Psychological test scores have evidently been obtained for a
middle group of subjects (Needleman, 1983, p. 242). The Committee recommends
that analyses be undertaken to evaluate any available psychometric testing data
for "intermediate" lead-exposure subjects.
(c) Many questions about sampling procedures arise from the exclusion of large
numbers of potential participants in the psychometric testing phase of this
study. From 542 provisionally eligible participants, almost half were excluded
from neuropsychological assessment, and 41 percent of those tested were later
excluded from data analyses. Although reasons for the exclusions were given
(see Table 1 of the 1979 article), the distribution of demographic and psycho-
logical outcome measures for those excluded from the low- and high-Pb groups
was provided neither in the published article nor by the investigator to the
Committee. The Committee could not fully evaluate sources of possible bias due
to such exclusions in the selection of the sample reported in this paper and
other publications reviewed.
Some of the criteria used to define Pb exposure levels or to exclude sub-
jects from statistical analyses seemed arbitrary, and different results might
have been obtained with application of equally good or better alternative cri-
teria for classification of Pb exposure levels and groups. For example, some
subjects provisionally classified as low-Pb or high-Pb subjects based on ini-
tial dentine Pb values were excluded from final data analyses based on discor-
dances arising from later replicate or duplicate Pb values obtained for the
same or different teeth, although certain key "discordant" dentine Pb values
were not meaningfully different from the cut-off criteria levels for inclusion
as low-Pb or high-Pb subjects. Thus, exclusion of some subjects from the low-Pb
group for statistical analyses hinged on a single dentine Pb value (e.g., 10.1
34
-------
or 10.5 ppm) barely exceeding the 10 ppm criterion ultimately selected and
rigidly enforced as defining the low-Pb (or lowest decile) exposure group, al-
though such dentine Pb values were as likely to have true readings below 10 ppm
as were certain key values (e.g., 9.5 or 9.8 ppm) for some subjects included in
the low-Pb group likely to have true readings above 10 ppm. Also, since inclu-
sion or exclusion of subjects in the statistical analyses was based on dentine
Pb values for all teeth submitted by a given subject over the course of the
study, soine subjects may have been classified as high-Pb or low-Pb children (or
excluded from analysis) based on replicate or duplicate dentine Pb values ob-
tained for teeth shed up to 1-3 years after their psychometric testing. The
impact of this may not have been symmetrically exerted on the high-Pb and low-
Pb groups. That is, it is not likely that "actual"' high-Pb exposure children
at the time of psychometric testing would have distinctly lower later dentine
Pb values; but low-Pb children with initial values <10 ppm could have- experi-
enced lead exposures after psychometric testing that substantially increased
their later dentine Pb values and resulted in their exclusion from the low-Pb
group.
(d) Normalized outcomes for which age-normed scores were not available were con-
structed .by regressing on age before analysis of covariance. Assuming that age
effects were-accounted for, five covariates (namely, mother's age at subject's
birth, mother's educational level, father's socioeconomic status, number of
pregnancies, and parental IQ) were considered. Only five covariates were used
. because that is the limit dictated by a widely used computer software package
(SPSS). However, the.number of covariates considered should not be arbitrarily
dictated by the constraints of a packaged program but should be determined with
the goal of properly controlling confounding variables. Father's education
(grade) level was not included separately, although (as Dr. Needleman argued)
it is part of father's socioeconomic status. It would seem to be better, based
on the results shown in Table 5 of the 1979 report, to use father's education
directly rather than as part of a diluted "socioeconomic status" variable.
(e) The Committee reviewed computer printouts from numerous SPSS analysis of covar-
iance runs on psychometric testing data indicated by Dr. Needleman as forming
the basis for the results and conclusions presented in the 1979- report and
noticed many missing data points among the analyses. In fact,.the actual number
of data points used in certain regression analyses was sometimes as much as 20%
35
1308<
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fewer than those for the 158 cases claimed in the 1979 paper to have been
analyzed for the low-Pb and high-Pb subjects. For example, the analyses later
reported in the Bellinger and Needleman (1983) paper (on the same data set dis-
cussed in the 1979 article) are based on 17 fewer cases than the 158 stated to
have been included in the final statistical analyses of psychometric test
results appearing in the 1979 article, because of missing parental IQ data for
the 17 cases. Missing data, not alluded to in the 1979 report, can pose a
serious validity problem if the missing observations are not randomly distribu-
ted across the important variables. The effects of such missing data are
impossible to assess without detailed analysis of the available data set.
(f) Based upon cursory inspection of the numerous statistical analysis computer
runs provided by Dr. Needleman (which was all that was possible during the
limited time of access to the printouts), the Committee came away with the im-
pression that most runs led to non-significant findings. In a recent publica-
tion (Needleman, 1983), the investigator notes that of the 66 outcomes evalua-
ted, 15 were significantly different between the low- and high-lead groups,
given the control variables included in the analyses. He notes that 1 in 20
would be expected by chance, if the outcome variables were uncorrected. Of
course, most of the psychological assessments in this study are moderately to
highly correlated, so that this probability does not apply. In addition,
apparent group differences are affected by the method of handling important
covariates.
(g) Of special interest, printouts for several regression analyses in which child's
age was entered as a control variable showed reduced and generally non-signifi-
cant coefficients for Pb levels, but such findings are not presented in the
1979 report or later articles by Needleman and colleagues. This is in contrast
to the earlier reporting (Needleman et al., 1978) of statistically significant
Pb effects when age was included as a covariate in preliminary statistical
analyses performed when the collection of psychometric data for the study was
about one-half completed. The standardized psychometric measures with age norms
provided do not perfectly correct for age differences in a specific sample.
Because there^ are significant age differences between the high-Pb and low-Pb
groups in this study, the regressions of raw test scores on child's own age
would have been the more desirable analyses to report. The Committee has
reached this conclusion despite the principal investigator's (Dr. Needleman's)
argument that it is undesirable to "correct for age twice."
36
1309-:
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4. Committee Conclusions and Recoranendations
Estimation of Pb exposures by dentine Pb measurements is more appropriate than blood Pb
as an index of cumulative exposure, and the analytical determination of such dentine Pb levels
appears to have generally been done competently in the study. However, it is not possible to
estimate the variance of the dentine Pb measurements in replicate/duplicate analyses (beyond
the 15% estimate arrived at for replicate analyses for the most concordant samples) without
full access to the coded, raw data of all children who participated in the study. The blood
Pb measurements, obtained earlier for some of the children, are of unknown reliability.
Because the blood data appear to have been obtained at varying ages for the children sampled,
the reported blood Pb data probably do not uniformly assess peak exposure levels for them and
cannot be accepted as providing quantitive estimates of Pb levels associated with any neuro-
behavioral deficits demonstrated to exist among the children studied.
Teacher ratings of children's classroom behaviors were collected on more than 2000 chil-
dren who also contributed shed deciduous teeth for dentine Pb analyses. The failure to revise
the lead classification of the children based on discrepancies with later replicate/duplicate
dentine Pb values in the analysis of teachers' ratings contrasts sharply with the demand for
concordance of dentine Pb readings in the neuropsychological testing phase of the study.
Also, the failure to analyze for possible contributions of confounding factors or covariates
to the teachers' rating results is disturbing. (The covariance adjustment used for teachers'
ratings on the 158 children included in the neuropsychological testing phase of the study is
subject to the criticisms noted for other analyses of data for those groups.) The dose-
response relationships reported to exist between dentine Pb levels and teachers' rating
scores, therefore, cannot be accepted as valid based on the published analyses.
A comprehensive neuropsychological test battery was administered to the children defined
as beTonging in low-Pb or high-Ph subgroups. Serious questions exist regarding the basis for
classification of subjects in these groups or exclusion of others from them. Also, discrepan-
cies between WISC-R verbal and performance scores, if as large or numerous as they seem upon
cursory inspection, may raise questions about the test administration or the sample selection.
Errors in the calculation of some averaged parental IQ scores, evident in coded materials
provided to the Committee, introduced unknown errors into the regression analyses for the psy-
chometric testing results. The use of the PPVT for parental 1Q was not ideal, but was still
acceptable. Exclusion of large numoe^s of eligible participants prio^ to data analysis could
have resulted in systematic bias in the results. However, the Committee was unable to evaluate
this possibility fully, g'ven the limited information made available by the investigator.
37
13I0-:
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The treatment of covariates in the statistical analysis of the psychometric testing
results was unsatisfactory. The failure to report statistical analyses showing generally
reduced or non-significant negative correlations between dentine Pb levels and performance on
the psychometric tests also lessens the credibility of those few statistically significant
effects attributed to Pb in the published version(s) of the Needleman et al. (1979) study.
In summary, at this time, based on the questionable Pb exposure categorization and sub-
ject exclusion methods, problems with missing data, and concerns regarding the statistical
analyses employed and selected for reporting, the Committee concludes that the study results,
as reported in the Needleman et al. (1979) paper, neither support nor refute the hypothesis
that low or moderate levels of Pb exposure lead to cognitive or other behavioral impairments
in children. The Committee strongly recommends that the subject data set be reanalyzed to
correct for errors in data calculation and entry noted above, that the reanalysis be based on
better exposure classification of subjects, and that all potentially confounding variables
(including age) be assessed using a backwards elimination approach analogous to that recom-
mended earlier for the reanalysis of Ernhart data.
C. Comments on the Burchfiel et al. (1980) Study
The Committee carried out only a very preliminary review of the Burchfiel et al. (1980)
study, focusing mainly on consideration of Pb exposure, neuropsychologic testing, and statis-
tical analysis aspects of the study. Review of the electrophysiological recording aspects of
the study would require additional committee members or a separate review committee with
recognized expertise in elect^ophysiology and, in particular, electroencephalography.
In view of the fact that the Pb exposure and psychometric measurement data utilized in
the Burchfiel study are subsets of the data underlying the Needleman et al. (1979) article
discussed above, most of the preceding comments regarding those aspects apply here as well.
Only a few additional remarks are, therefore, felt to be necessary he^e. Specifically,
no definite dentine Pb or blood Pb values were reported for the specific children from the
Needleman et al. (1979) study who underwent the EEG evaluations reported by Burchfiel et al.
(1980). It is therefore impossible to determine with any confidence the specific Pb exposure
levels (including either blood Pb or dentine Pb values) that may have been associated with the
reported EEG effects. Nor is it possible to accept with much confidence any reported rela-
tionships between the observed brain wave alterations, the psychometric testing snores, and Pb
exposure classification as low-Pb or high-Pb, especially in view of the various problems noted
above regarding exposure classification, psychometric testing, and statistical treatment - of
covariates or- confounders that preclude acceptance of the findings reported i ri the 1979 publi-
cation.
38
1311<
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D. Comments on the Needleman (1982) Report
The 1982 report published by Needleman represents mainly a summary or restatement of
findings already reported in the earlier Needleman et al. (1979), Burchfiel et al. (1980), and
Needleman et al. (1982) publications. The comments provided above on the first two of the
earlier publications, obviously, also apply here.
One additional point worthy of discussion concerns the plot of cumulative frequency dis-
tributions of verbal 1Q scores for low-Pb and high-Pb subjects shown in Figure 2 of the
Needleman (1982) report, as reprinted from the Needleman et al. (1982) article. Given the
serious reservations expressed earlier by the Committee regarding the Pb-exposure classifica-
tion procedures, aspects of the psychometric testing, and statistical treatment of covariates
or confounding factors as employed in the analyses reported in the 1979 article, the particu-
lar cumulative distribution curves shown in the figure for verbal IQ scores among the low-Pb
and high-Pb subjects cannot be accepted at this time as being either qualitatively valid
(i.e., as demonstrating, lower IQs for high-Pb subjects than for low-Pb subjects) or quantita-
tively accurate (i.e., in terms of absolute decreases in IQ implied to be associated with Pb
exposure). Similarly, the Committee finds certain statements in the discussion (page 731 of
the 1982 Needleman paper) of the cumulative distribution curves to be somewhat misleading in
noting that none of the included high-Pb subjects had an IQ over 125 (while 5% of the low-Pb
subjects did) but failing to mention that at least one subject excluded because of overt plum-
bism had a full-scale WISC-R IQ over 125.
E. Comments on the Bellinger & Needleman (1983) Study
This paper reports two kinds of reanalyses of the data from the previous (Needleman et
al., 1979) report and, again, most of the comments made earlier on aspects of that study also
apply here. Certain additional comments are warranted, however. First, child IQ is regressed
on mother's IQ separately for the low-Pb and high-Pb groups. The results are that mother-
child IQ correlations do not differ for the two Pb exposure groups and the high-Pb group has
lower than predicted IQ scores (controlling for maternal IQ).
Second, the residuals of child's IQ regressed on mother's IQ from the first analysis were
regressed on dentine Pb levels, arranged by individual values. Four ranges of lead values
were used to estimate regression slopes of residual IQ on lead. The sample size for the low-
Pb group in this report was N=94; for high-Pb. N-47; and for two subsamples of the high-Pb
group, i.e., dentine Pb levels of 20.0-29.9 ppm, N=24, and for 30.0-39.9 ppm, N~17. The
39
1312c
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latter two groups are far too small to be used to estimate slopes that can be credibly gen-
eralized to other samples. The results for the regression of child's IQ residuals on lead in
the low-Pb group had, not surprisingly, a slope of zero because of extreme restriction of the
range of lead values. The slope far the high-Pb group was -0.36, significantly different from
zero. One serious problem in interpreting these results is that only maternal TQ was used as
a "covariate" for child IQ. No other background factors, as reported in the earlier paper,
were included as adjustments for the residualized IQ scores in this study.
To control, in part, for additional covariates that could affect the relationships
between residual IQ and lead level, a stepwise regression was done. Surprisingly, and con-
trary to all of their other analyses of these data, lead level was allowed to enter the equa-
tion second, before two of the three control variables. Table 111 of the Bellinger and
Needleman (1983) article reported results in the form of unstandardized regression coeffi-
cients without accompanying standard errors or significance levels. The F ratios reported
seemed to be those of the equations, not of the individual coefficients, except of course for
the first variable in the first step. Thus, it is not clear that the Pb coefficient is
actually reliably different from zero.
Given the above problems and concerns, the reanalyses of the Needleman data set presented
in the Bellinger and Needleman (1983) paper cannot be accepted as providing credible or reli-
able estimates of quantitative relationships between Pb exposure and neuropsychologic deficits
in children. Nor can the reported results be taken as either qualitatively supporting or
refuting the hypothesis of associations between low-level lead exposure and cognitive deficits
in children.
F. Comments on the Needleman (1981) Report
Shed teeth and teacher ratings were collected in 1977-1978 from a new sanple of about
1300 first-grade children in Lowell, MA. Children were classified into five groups according
to their dentine Pb levels: Group 1, S6.4 ppm; Group 2, 6.5 to 8.7 ppm; Group 3, 8.7] to 12
ppm; Group 4, 12.01 to 18.1 ppm; Group 5, 218.2 ppm. The association of teacher ratings on 11
behavior scales with Pb levels is displayed separately for males and females in Figures 4 and
5. No effort was made to control for confounding variables in this overall set of results.
Essentially complete follow-up data and Pb levels were obtained on 130 children of the
447 males selected far follow-up. Given the design of this study, the expected analysis would
investigate the relationship between teacher ratings and Pb level following adjustment for
confounding variables, collected on the follow-up sample. Such an analysis was not reported.
-------
In the Committee's view, these data should be reanalyzed to show clearly the form of the
relationship between Pb level and teacher ratings, with appropriate controls for the follow-
up subjects.
POSTSCRIPT
In addition to evaluation of the studies of Ernhart and Needleman, the Committee reviewed
available reports (some published and others as yet unpublished) of other studies from the
United States and Europe. These studies included, for example, those by: Winneke et al.
(1982, 1983), Winneke (1983), Yule et al. (1981), Lansdown et al. (1983), Smith (1983), and
Harvey et al. (1983). Although an exhaustive, in-depth evaluation of the world literature on
low-level Pb exposure was beyond the current charge to the Committee, we note that new stu-
dies reported in the spring and summer of 1983, with only a few exceptions, failed to find
significant association between low-level Pb exposure and neuropsychologic deficits, once con-
trol variables were taken into account.
From its review of the recent research literature covered in this report, the Committee
concludes that: (1) in the absence of control for otner variables, a negative• association
between Pb exposure and neuropsychologic functioning has been established; (2) the extent of
tlr's negative association is reduced or eliminated when confounding factors are appropriately
controlled; and (3) the Committee knows of no studies that, to date, have validly established
(after proper control for confounding variables) a relationship between low-level Pb exposure
and neuropsychologic deficits in children.
Research addressing possible dose-response relationships between lead and cognitive func-
tioning in children is a worthy effort, and the Committee hopes that future studies can gather
data that speak more adequately to this issue. In the view of the Committee, it is unlikely
that continued use of cross-sectional epidemiological analyses will produce much credible evi-
dence for or against the hypothesis that low to moderate levels of lead exposure are respon-
sible for neurobehavioral deficits in apparently asymptomatic children. The study design
generally does not allow for unambiguous disentangling of possible contributions of such lead
exposures to observed cognitive or behavioral deficits versus the contributions of numerous
other potentially confounding factors. There is a great need for longitudinal and time-series
analyses, which include detailed prospective measurements of Pb exposure indices from early
childhood onward and repeated sampling of neurobehavioral endpoints, both during preschool and
school-age years.
41
1314 <
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V.
It1
piii
MALES-LOWELL
DENTINE LEAD
1. < 6.4 ppm
2 6 5 - 8.7
3. 8 71 - 12
4 12 01 - 18 1
5. ? 18.2
A
J
L
Hi
rf
/i
*** -S O /$• _C<,9 Co" o
/
-------
60
50
40
30
20
10
FEMALES LOWELL
DENTINE LEAD
1. <6.4 ppm
2 6 5 - 8 7
3. 8.71 - 12
4. 12.01 - 18.1
5. > 18.2
/
j\ r
y\
£l
r
ji
/
£
o*
A.
/
/
*
J?
-------
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Perino, J.; Ernhart, C. B. (1974) The relation of subclinical lead level to cognitive and sen-
sorimotor impairment in black preschoolers. J. Learn. Dis. 7: 616-620.
Sattler, J. M. (1982) Assessment of children's intelligence and special abilities. 2ni
ed. Boston, MA: Allyn and Bacon.
Scarr, S. ; Yee, D. (1980) Heritability and educational policy: genetic and environmental ef
fects on IQ, aptitude and achievement. Educ. Psychol. 15:1-22.
Shapiro, I. M. ; Dobkin, B. ; Tuncay, 0. C. ; Needleman, H. L. (1973) Lead levels in dentine ar
circumpulpal dentine of deciduous teeth of normal and lead poisoned children. Clir
Chim. Acta 46: 119-123.
Shapiro, I. M. ; Burke, A.; Mitchell, G. ; Bloch, P. (1978) X-ray fluorescence ana^sis of lec!
in teeth of urban children i_n situ: correlation between the tooth lead level and concer
tration of blood lead and free erythroporphyrins. Environ. Res. 17: 46-52.
45
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Smith, M. ; Delves, T. ; Lansdown, R. ; Clayton, B. ; Graham, P. (1983) The effects of lead expo-
sure on urban children: the Institute of Child Health/Southampton study. London,
United Kingdom: Department of the Environment.
Steenhout, A.; Pourtois, M. (1981) Lead accumulation in teeth as a function of age with dif-
ferent exposures. Br. J. Ind. Med. 38: 297-303.
U.S. Environmental Protection Agency, Health Effects Research Laboratory (1977) Air quality
criteria for lead. Research Triangle Park, NC: U.S. Environmental Protection Agency,
Criteria and Special Studies Office; EPA report no. EPA-600/8-77-017. Available from:
NTIS, Springfield, VA; PB-280411.
U.S. Environmental Protection Agency. (August, 1983) Air quality criteria for lead. First Ex-
ternal Review Draft. Research Triangle Park, NC: U.S. Environmental Protection Agency,
Environmental Criteria and Assessment Office.
Winneke, G. (1983) Neurobehavioral and neuropsychological effects of lead. In: Rutter, M. ;
Russell Jones, R., eds. Lead versus health. New York, NY: John Wiley & Sons, Ltd.; pp.
249-265.
Winneke, G. ; Hrdina, K-G.; Brockhaus, A. (1982) Neuropsychological studies in children with
elevated tooth-lead concentrations. Part I: Pilot study. Int. Arch; Occup. Environ.
Health 51: 169-183.
Winneke, G. ; Kramer, U. ; Brockhaus, A.; Ewers, U.; Kujanek, G.; Lechner, H.; Janke, W. (1983)
Neuropsychological studies in children with elevated tooth lead concentrations. Part II:
Extended study. Int. Arch. Occup. Environ. Health 51: 231-252.
Yamins, J. (1976) The relationship of subclinical lead intoxication to cognitive .and language
functioning and preschool children. Hempstead, NY: Hofstra University. Dissertation.
Yule, W. ; Lansdown, R. ; Millar, I. B. ; Urbanowicz, M-A. (1981) The relationship between blood
lead concentrations, intelligence and attainment in a school population: a pilot study.
Dev. Med. Child Neurol. 23: 567-576.
46
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ATTACHMENT 1
Additional materials considered in review of studies by Dr. Claire Ernhart and colleaguts
1. Grant, L. D. (March 7, 1983) [Letter to C. Ernhart]. Available for inspection at: U.S.
Environmental Protection Agency, Environmental Criteria and Assessment Office,
Research Triangle Park, NC.
2. Ernhart, C. 6. Coded raw data entries of psychometric test scores and background variable
values (sex, parental IQ, etc.) for subjects evaluated in Perino and Ernhart (1974)
and Ernhart et al. (1981) studies. Submitted to Committee at March 17-18, 1901
meeting. Available for inspection at: U.S. Environmental Protection Agency, En-
vironmental Criteria and Assessment Office, Research Triangle Park, NC.
3. Ernhart, C. B. ; Landa, B. (1980) "Cumulative deficit," a longitudinal analysis of score;
on McCarthy scales. Psychol. Rep. 47: 283-286.
4. Ernhart, C. B.; Landa, B. ; Schell, N. B. (1981) Lead levels and intelligence [Letter].
Pediatrics 68: 903-904.
Spector, S. ; Brown, K. E. (1982) Lead study questioned [Letter]. Pediatrics 69: 134-135.
6. Ernhart, C. B.; Landa, B.; Schell, N. B. (1982) Lead study questioned: in reply [Letter],
Pediatrics 69: 135.
7. Ernhart, C. B. (1982) Lead results: no justification [Letter], Sci. News (Washington,
D.C.) 122: 3.
8. Ernhart, C. B. Scatter plots and associated coded data listings of residualized cognitive
test performance scores vs. blood lead levels for subjects used in Perino and
Ernhart (1979) study. Submitted to Committee at March 17-18, 1983 meeting. Avail-
able for inspection at: U.S. Environmental Protection Agency, Environmental Criteria
and Assessment Office, Research Triangle Park, NC.
9. Ernhart, C. B. Scatter diagram of parents' IQ vs. child's IQ for low and moderate lead
groups in Perino and Ernhart (1979) study (based on Perino dissertation). Submitted
to Committee at March 17-18, 1983 meeting. Available for inspection at: U.S. En-
vironmental Protection Agency, Environmental Criteria and Assessment Office,
Research Triangle Park, NC.
10. Ernhart, C. B. ; Landa, B.; Schell, N. B. (1983) Lead and intelligence - the effect of an
outlier. Pediatrics (Submitted for publication).
11. Ernhart, C. B. Summary of conversation between N. B. Schell and C. Ernhart on March 11,
1983. Submitted to Committee at March 17-18, 1983 meeting. Available for inspec-
tion at: U.S. Environmental Protection Agency, Environmental and Criteria and
Assessment Office, Research Triangle Park, NC.
12. Ernhart, C. B. (1983) Summary report: reanalysis of data of three studies: the effects
of lead on children. Available for inspection at: U.S. Environmental Protection
Agency, Environmental Criteria and Assessment Office, Research Triangle Park, NC.
47
1320c
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13. Ernhart, C. B. (October 7, 1983) Response to [preliminary draft of] Appendix 12-C.
Available for inspection at: U.S. Environmental Protection Agency, Environmental
Criteria and Assessment Office, Research Triangle Park, NC.
14. Ernhart, C. B. (October 25, 1983) [Letter to L. Grant]. Available for inspection at:
U.S. Environmental Protection Agency, Environmental Criteria and Assessment Office,
Research Triangle Park, NC.
Additional materials considered in review of studies by Dr. Herbert Needleman and colleagues
1. Grant, L. D. (October 25, 1982) [Letter to H. Needleman], Available for inspection at:
U.S. Environmental Protection Agency, Environmental Criteria and Assessment Office,
Research Triangle Park, NC.
2. Needleman, H. L. (November 22, 1982) [Reply to L. D. Grant]. Available for inspection
at: U.S. Environmental Protection Agency, Environmental and Criteria and Assessment
Office, Research Triangle Park, NC.
3. Needleman, H. L. (November 22, 1982) [List of 250 excluded subjects for Chelsea run].
Available for inspection at: U.S. Environmental Protection Agency, Environmental
Criteria and Assessment Office, Research Triangle Park, NC. Attachment to Item 2
above.
4. Needleman, H. L. (November 22, 1982) [Frequency distribution of psychometric scores for
high-lead subjects.] Available for inspection at: U.S. Environmental Protection
Agency, Environmental Criteria and Assessment Office, Research Triangle Park, NC.
Attachment to Item 2 above.
5. Needleman, H. L. (November 22, 1982) [Frequency distribution of psychometric scores for
low-lead subjects.] Available for inspection at: U.S. Environmental Protection
Agency, Environmental Criteria and Assessment Office, Research Triangle Park, NC.
Attachment to Item 2 above.
6. Needleman, H. L. (1977) Lead in the child's world, a model for action. In: Hemphill, D.
D. , ed. Trace substances in environmental health-XI: [proceedings of University of
Missouri's 11th annual conference on trace substances in environmental health];
June; Columbia, MO. Columbia, MO: University of Missouri-Columbia; pp. 229-235.
7.- Needleman, H. L. ; Leviton, A. (1979) Lead and neurobehavioral deficit in children
[Letter]. Lancet 2(8133): 104.
8. Needleman, H. L. (1980) Lead and neuropsychological deficit: finding a threshold. In:
Needleman, H. L. , ed. Low level lead exposure: the clinical implications of current
research. New York, NY: Raven Press; pp. 43-51.
9. Needleman, H. L. ; Landrigan, P. J. (1981) The health effects of low level exposure to
lead. Ann. Rev. Public Health 2: 277-298.
10. Needleman, H. L.; Bellinger, D.; Leviton, A. (1981) Does lead at low dose affect intel-
ligence in children? Pediatrics 68: 894-896.
11. Needleman, H. L. (1982) The lead debate: a response. Environ. Sci. Technol. 16: 208A.
12. Needleman, H. L. (1983) The prevention of mental retardation and learning disabilities
due to lead exposure. In: Jahiel , R. I., ed. The handbook of prevention of mental
retardation and learning disabilities. (In preparation)
48
1321<
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13. Grant, L. D. (March 14, 1983) [Letter to H. Needleman]. Available for inspection at:
U.S. Environmental Protection Agency, Environmental Criteria and Assessment Office,
Research Triangle Park, NC.
14. Jones, L. V. (March 23, 1983) [Letter to L. Kupper],
Environmental Protection Agency, Environmental
Research Triangle Park, NC.
15. Grant, L. D. (April 8, 1983) [Letter to H. Needleman].
Environmental Protection Agency, Environmental
Research Triangle Park, NC.
16. Needleman, H. L. (April 13, 1983) [Reply to L. Grant].
Environmental Protection Agency, Environmental
Research Triangle Park, NC.
Available for inspection at: U.S.
Criteria and Assessment Office,
Available for inspection at: U.S.
Criteria and Assessment Office,
Available for inspection at: U.S.
Criteria and Assessment Office,
17. Needleman, H. L. (May 26, 1983) [Lists of all dentine lead levels for included children
and for the 30 excluded from neuropsychological testing, and the unadjusted means,
SD's and t tests]. Available for inspection at: U.S. Environmental Protection
Agency, Environmental Criteria and Assessment Office, Research Triangle Park, NC.
18. Needleman, H. L. ; Rabinowitz, M. ; Leviton, A. (1983) The risk of minor congenital anoma-
lies in relation to umbilical cord blood lead levels. Pediatr. Res. 17: 300A.
19. Needleman, H. L. ; Bellinger, D. ; Leviton, A.; Rabinowitz, M. ; Nichols, M. (1983) Umbili-
cal cord blood lead levels and neuropsychological performance at 12 months of age.
Pediatr. Res. 17: 179A.
20. Needleman, H. L. (June 14, 1983) [Letter to L. Grant], Final complete dentine lead
levels on those subjects excluded because of discordant values. Available for in-
spection at: U.S. Environmental Protection Agency, Environmental Criteria and
Assessment Office, Research Triangle Park, NC.
21. Needelman, H. L. (1983) Listings of coded raw data for dentine lead levels of both
"included" and "excluded" subjects who underwent psychometric testing in Needleman
et al. (1979) study. Attachment to Item 20 above.
22. Needleman, H. L. (1983) Listings of coded raw data for psychometric test results and
background variables (e.g., sex, age, father's education, parental I.Q., etc.) for
"included" and "excluded" subjects in Needleman et al. (1979) study. Attachment to
Item 20 above.
23. Needleman, H. L. (1983) Computer printouts of frequency distribution of IQ scores and
other psychometric test results for high and low lead subjects in Needleman et al.
(1979) study. Inspected by Committee at H. L. Needleman1s facilities at University
of Pittsburgh (Children's Hospital), Pittsburgh, PA.
24. Needleman, H. L. (1983) Computer printouts of results of SPSS version of analysis of
covariance for psychometric test scores of high and low lead subjects of Needleman
et al. (1979) study, taking into account up to five covariates (including age as a
covariate in some runs). Inspected by Committee at H. L. Needleman1s facilities at
University of Pittsburgh (Children's Hospital), Pittsburgh, PA.
25. Needleman, H. L. (October 4, 1983) [Letter to L. Grant]. Available for inspection at:
U.S. Environmental Protection Agency, Environmental Criteria and Assessment Office,
Research Triangle Park, NC.
49
1322-r.
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26. Needleman, H. L. (October 4, 1983) [Letter to B. Goldstein]. Available for inspection
at: U.S. Environmental Protection Agency, Environmental Criteria and Assessment
Office, Research Triangle Park, NC.
27. Grant, L. D. (October 7, 1983) [Reply to H. L. Needleman]. Available for Inspection at:
U.S. Environmental Protection Agency, Environmental Criteria and Assessment Office,
Research Triangle Park, NC.
28. Needleman, H. L. (October 7, 1983) [Letter to L. Grant]. Available for inspection at:
U.S. Environmental Protection Agency, Environmental Criteria and Assessment Office,
Research Triangle Park, NC.
GU$ OOVliN'Mfll *5ifTINC (JfC* ISM &5^0l7vJ24C
50
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EPA-600/8-83-02BA
INDEPENDENT PEER REVIEW OF SELECTED STUDIES
BY DRS. KIRCHGESSNER AND REICHLMAYR-LAIS
CONCERNING THE POSSIBLE NUTRITIONAL ESSENTIALITY OF LEAD:
Official Report of Findings and Recommendations of an
Interdisciplinary Expert Review Committee
Presented by
Expert Committee an Trace Metal Essentiality
to
Dr. Lester D. Grant, Director
Environmental Criteria and Assessment Office
United States Environmental Protection Agency
Research Triangle Park, North Carolina
November, 1983
1321 <
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The materials contained in this report were generated as the result of
critical evaluations and deliberations by the members (listed below) of the
Expert Committee on Trace Metal Essentiality. All members concur with and
endorse the findings and recommendations contained in the present report as
representing the collective sense of the Committee.
Dr. F. William Sunderman, Jr. (Chairman)
Professor, Departments of Laboratory
Medicine and Pharmacology
University of Connecticut School of
Medici ne
Farmington, CT 06232
Dr. M. R. Spivey Fox
Chief, Nutrient Interaction Section
Division of Nutrition
U.S. Food and Drug Administration
Washington, DC 20204
Dr. Kathryn Mahaffey
Chief, Priorities and Research Analysis
National Institute of Occupational
Safety and Health
Cincinnati, OH 45226
Dr. Orville Levander
Research Chemist
Beltsville Human Nutrition
Research Center
U.S. Department of Agriculture
Beltsville, MD 20705
Dr. Walter Mertz
Director, Beltsville Human Nutrition
Research Center
U.S. Department of Agriculture
Beltsville, MD 20705
Dr. Ekhard Ziegler
Professor, Department of Pediatrics
University of Iowa Hospital
Iowa City, IA 52242
Dr. Forrest Nielsen
Research Chemist
Human Nutrition Research Center
U.S. Department of Agriculture
Box 7166 University Station
Grand Forks, ND 58202
1325< i i
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TABLE OF CONTENTS
PAGE
PREFACE 1
INTRODUCTION 2
CRITICAL COMMENTS 2
RECOMMENDATIONS AND CONCLUSIONS 3
ATTACHMENT 1 4
ATTACHMENT 2 7
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PREFACE
The Expert Committee on Trace Metal Essentiality was appointed in August,
1983 by the Environmental Criteria and Assessment Office (ECAO) of EPA, to
evaluate the studies of Drs. M. Kirchgessner and A. M. Reichlmayr-Lais on the
possible nutritional essentiality of lead. The Committee was provided with
all relevant papers by the authors, the critiques of these papers prepared by
Dr. Paul Mushak in his capacity as a consulting author of the revised Air
Qua!ity Criteria Document for Lead, and all correspondence between ECAO and
Drs. Kirchgessner and Reichlmayr-Lais. Attachment 1 contains a complete list
of the materials reviewed by the Committee.
The Committee convened on September 29, 1983 at the ECAO facilities in
Research Triangle Park, NC. Present at the meeting were all but one member of
the Committee (K.M.), Drs. Anna Reichlmayr-Lais and E. Grassmann (substituting
for Professor Kirchgessner), Dr. Mushak, EPA staff, and observers from various
interest groups. A complete list of attendees may be found in Attachment 2.
Following a presentation by Dr. Reichlmayr-Lais, in which she reviewed
her published data as well as experiments in progress, all meeting attendees
were given an opportunity to address the Committee. The Committee then pur-
sued specific lines of questioning to its satisfaction and retired to execu-
tive session to draft its final report.
The Committee was charged with critically evaluating the studies of
Kirchgessner and Reichlmayr-Lais and determining whether or not they supported
the concept of a nutritional essentiality of lead. Their findings and recom-
mendations are contained in this consensus report; views expressed by the
members of the Committee in this report are their own and are not necessarily
those of the institutions with which they are affiliated.
1
1327<
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INTRODUCTION
The Committee commends Drs. Kirchgessner and Reichlmayr-Lais for their
pioneering work, which is at the frontier of current research on trace metal
nutrition, and wishes to express their appreciation to them for their coopera-
tion in the Committee's efforts to assess their findings.
CRITICAL COMMENTS
The Reichlmayr-Lais and Kirchgessner data that were available for review
were derived from two experiments. Based upon the published and oral descrip-
tions of the experiments, members of the Committee expressed reservations
about specific facets of experimental design, execution, and documentation',
including the following:
(1) No selenium or chromium was added to the basal diet, nor were
the concentrations of selenium or chromium measured in the diet
to indicate nutritional adequacy of those essential elements.
(In discussion, Dr. Reichlmayr-Lais indicated that Se, Cr, and
other essential elements are being added to the diets in two
experiments that are currently in progress.)
(2) The sole source of fat in the basal diet was coconut oil, which '
might render the rats deficient in essential fatty acids. (In , .
discussion, Dr. Reichlmayr-Lais indicated that linoleic acid is .
being added to the diets in the experiments that are in pro-
gress.)
(3) The possibility exists that chelant residues (EDTA and APDC)
may persist in the basal diet despite the extensive extraction
procedures that were employed. Documentation of. the EDTA or
APDC concentrations was lacking and the Committee considered
that HPLC or radiotracer experiments would be advisable in order
to address these concerns.
(4) As the basal diet was prepared, iron supplements were added in
an aqueous mixture with several other inorganic ingredients
(e.g., KI, CuS04). Under the conditions of drying at 50°C,
oxidation-reduction reactions could occur that might affect
the bioavailability of iron. The Committee considered that
this potential problem should be addressed in future experi-
ments .
(5) The method of blood collection by decapitation and draining
into a test tube via a funnel raised concerns owing to the
potential for contamination by other body fluids (e.g., gastric
fluid, spinal fluid, lymph).
2
1328<
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(6) The results of lead analyses of blood and tissues of the ex-
perimental animals have not been reported. (Dr. Reichlmayr-
Lais indicated that such analyses are being attempted in cur-
rent experiments.)
(7) The possibility that lead supplementation of the basal diet
might affect its palatability was not addressed in the experi-
ments, either by pilot trials or by measurements of food intake.
(8) Lead supplementation of the basal diet was performed only at a
single (relatively high) concentration of 1 ppm. Further
experiments at graded levels of Pb supplementation are desira-
ble in order to establish a dose-effect relationship.
(9) The statistical methods that were used to analyze the data in
the two experiments were not described in sufficient detail; the
application of multiple t-tests may be a cause for concern, and
the various reports contain inconsistencies in numbers of
experimental animals per group. These matters might advantage-
ously be clarified in a consolidated report of each experiment.
(Dr. Reichlmayr-Lais indicated that such a consolidated report
is in press.)
RECOMMENDATIONS AND CONCLUSIONS
In view of the concerns that are listed above, the Committee reached
the following conclusions and recommendations:
.1. The Kirchgessner and Reichlmayr-Lais data furnish evidence that
is consistent with and, in some opinions, indicative of a nu-
tritional essentiality of lead for rats.
2. The. evidence is not sufficient to establish nutritional essen-
tiality of lead for rats.
3. . To address the basic issue of nutritional essentiality of lead,
additional evidence needs to be obtained under different condi-
tions in the laboratory of Kirchgessner-Reichlmayr-Lais, as
well as by independent investigators; additional species should
also be exami ned.
The Committee emphasizes the difference that apparently exists between
lead concentrations that are of concern from a toxicologic viewpoint and
those that might possibly be of nutritional concern. Hence the Committee does
not perceive any practical incompatibility between (a) efforts to reduce Pb in
the human environment to concentrations that are unassociated with toxic ef-
fects and (b) efforts to define the potential nutritional essentiality of
lead. The Committee recognizes that current public health concerns for
humans are those of lead toxicity.
3
1.329<
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ATTACHMENT 1
The following materials were considered by the Committee in their deli-
berati ons:
1. Reichlmayr-Lais, A. M. and Kirchgessner, M. (1981) Zur essentialitat von
blei fur das tierische Wachstum. [Why lead is essential for animal growth.]
Z. Tierphysiol. Tierernaehr. Futtermittelkd. 46:1_8.
2. Reichlmayr-Lais, A. M. and Kirchgessner, M. (1981) Depletions studien zur
essentialitat von blei an wachsenden ratten. [Depletion studies on the
essential nature of lead in growing rats.] Arch. Tierernaehr., 31:731-737.
3.' Reichlmayr-Lais, A. M. and Kirchgessner, M. (1981) Eisenkupfer- und
zinkgehalte in neugeborenen sowie in leber und milz wachsender ratten bei
alimentarem blei-mangel. [Iron-, copper- and zinc contents in newborns
as well as in the liver and spleen of growing rats in the case of alimen-
tary lead deficiency.] Z. Tierphysiol. Tierernaehr. Futtermittelkd.
46:8-14.
4. Kirchgessner, M. and Reichlmayr-Lais, A. M. (1980) Lead deficiency and
its effects on growth and metabolism. Presented at TEMA-4 Meeting; May;
Perth, Australia.
5. Reichlmayr-Lais, A. M. and Kirchgessner, M. (1981) Activities-veranderungen
verschiedener enzyme im alimentaren blei-mangel. [Activity changes of
different enzymes in alimentary lead deficiency.] Z. T i erphys iol.
Ti erernaehr. Futtermi ttelk 46:145-150.
6. Kirchgessner, M. and Reichlmayr-Lais, A. M. (1981) Changes of iron concen-
tration and iron-binding capacity in serum resulting from alimentary lead
deficiency. Biol. T race El em. Res. 3:279-285.
7. Kirchgessner, M. and Reichlmayr-Lais, A. M. (1981) Retention, absorbier-
barkeit und intermeditare neifugbarkeit von eisen bei alimentarem bleimangel.
[Retention, absorbability and intermediate availability of iron in the
case of alimentary lead deficiency.] Int. J. Vitam. Nutr. Res. 51:421-424.
8. Reichlmayr-Lais, A. M. and Kirchgessner, M. (1981) Katalase- und coerulo-
plasmin -acktivitat im blut bzw. serum von ratten in blei-mangel. [Catalase
and coeruloplasmin activity in blood and serum of rats with lead defici-
ency.] Zentral bl. Veteri naertned. Rei he A 28: 410-414.
9. Kirchgessner, M. and Reichlmayr-Lais, A. M. (1982) Konzentrationen ver-
scheidener stoffwechsel-metaboliten im experimentellen bleimangel. [Concen-
tration of different metabolites resulting from experimental lead defici-
ency] Ann. Nutr. Metab. 26:50-55.
10. Reichlmayr-Lai s, A. M. and Ki rchgessner, M. (1981) Hemat.ologi.sche veran-
derungen bei alimentarem blei mangel. [Hematological changes in the case
of alimentary lead deficiency.] Ann. Nutr. Metab. 25:281-288.
1330<
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11. Schwarz, K. (1973) New essential trace elements (Sn, V, F, Si): progress
report and outlook. Proceedings International Conference Trace Element
Metabolism in Animals (TEMA) II. Madison, Wisconsin. Edited by W. G.
Hoekstra, J. W. Suttie, H. E. Gantner, and W. Mertz, University Park
Press, Baltimore, MD.
12. Pallauf, J., and Kirchgessner, M. (1971) Herstellung der gereinigten
halbsynthetischen diat. [Production of the purified semi-synthetic
diet.] Z. Tierphysiol. Tierernaehr. Futtermittelkd. 23:128-139
13. Schnegg, A. (1975) Dissertation, T. U. Munchen. Excerpt on diet from
Mr. Schnegg's dissertation, provided by Professor Kirchgessner.
14. Kirchgessner, M. and Schwarz, W. A. (1976) Zum einfluss von zinkmangel
und unter-schiedlichen zinkzulagen auf resorption und retention des zinks
bei milchkuhen. [Concerning the influence of zinc deficiency and different
zinc additions on resorption and retention of zinc in milk cows.] Arch.
Tierernaehrung. 26:3-16.
15. Mertz, Walter (1981) The essential trace elements. Science (Washington,
D.C.) 213:1332-1338.
16. Mushak, P. (1982) [Appendix 11-A, draft Ai r Qua!i ty Cri teria Document for
Lead]. August 9. Assessment of studies reporting the potential essential-
ity of lead. Available for inspection at U.S. Environmental Protection
Agency, Environmental Criteria and Assessment Office, Research Triangle
Park, N.C.
17. Kirchgessner, M. and Reichlmayr-Lais, A. M. (1982) [Rebuttal to Appendix
11-A]. September 2. Available for inspection at U.S. Environmental
Protection Agency, Environmental Criteria and Assessment Office, Research
Triangle Park, N.C.
18. Weil, D. (1982) [Letter to M. Kirchgessner]. October 14. Available for
inspection at U.S. Environmental Protection Agency, Environmental Criteria
and Assessment Office, Research Triangle Park, N.C.
19. Kirchgessner, M. (1982) [Reply to 0. Weil], October 26. Available for
inspection at U.S. Environmental Protection Agency, Environmental Criteria
and Assessment Office, Research Triangle Park, N.C.
20. Mushak, P. (1983) [Appendix 12-A, draft Ai r Qual i t.y Cri teri a Document for
Lead]. January 5. Assessment of studies reporting data regarding the
potential essentiality of lead. Available for inspection at U.S. Environ-
mental Protection Agency, Environmental Criteria and Assessment Office,
Research Triangle Park, N.C.
21. Grant, L. D. (1983) [Letter to M. Kirchgessner]. February 15. Available
for inspection at U.S. Environmental Protection Agency, Environmental
Criteria and Assessment Office, Research Triangle Park, N.C.
22. Kirchgessner, M. (1983) [Reply to L. D. Grant]. March 28. Available
for inspection at U.S. Environmental Protection Agency, Environmental
Criteria and Assessment Office, Research Triangle Park, NC.
5
1331*:
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23.
24.
25.
26.
27.
28.
29.
30.
Grassmann, E., Kirchgessner, M. and Hampel, G. (1970) Zur kupferdepletion
bei ratten und kuten mit athylendiamin-tetraazetat und adenin. [Copper
depletion in rats and chicks as produced by ethyloned"5amine- tetraacetate
and adenine.] Arch. Tierernaehr. 20:537-544.
Grassmann, E. (1976). Zur verwertung verschiedener eisenverbindungen bei
der ratte. [.The utilization of various iron compounds in the rat.]
Zentra1b1. Veterinaermed. Reihe A 23:292-306.
Schnegg, A. and Kirchgessner, M. (1977) Zur differeritialdiagnose von Fe-
und Ni-mangel durch bestimmung einiger enzymabtivitaten. [Differential
diagnosis of Fe and Ni deficiencies by determining some enzyme activities. ]
Zentralbl. Veteri naermed. Rei he A 24:242-247.
Schnegg, A. and Kirchgesser, M. J. (1977) Aktivit.atsanderungen von enzymen
der leber und xiere im nickel-bzw. eisin-mangel. [Changes in liver and
kidney enzyme activities during nickel or iron deficiency.] Z. Tierphysiol.
Tierernaehr. Futtermittelkd. 38:300-205.
Schnegg, A. and Kirchgessner, M. (1977) Konzentrationsanderungen einiger
substrate in serum und leber bei Ni-bzw. Fe-mangel. [Concentration
changes in some serum and liver substrates with Ni and Fe deficiency]
Z. 1ierphysiol. Ti erernaehr. Futtermi ttelkd. 39:247-251.
Schnegg, A. and Kirchgessner, M. (1977) Alkalische und saure phosphatase-
ackivitat in leber und serum bei Ni-bzw. Fe-mangel. [Alkaline and acid
phosphatase activity in the liver and serum with Ni versus Fe deficiency.]
Int. Z. Vi tarn. Ernaehrungsforsch. 47:274-276.
Nielsen, F. (1983) [Letter to M. Davis], May 19. Available for inspection
at U.S. Environmental Protection Agency, Environmental Criteria and
Assessment Office, Research Triangle Park, NC.
Mushak, P. (1983) [Appendix 12"A, draft Air Qua!i ty Cri ter ia Document for
Lead], July 1. Assessment of studies reporting the potential essen-
tiality of lead. Available for inspection at U.S. Environmental Protection
Agency, Environmental Criteria and Assessment Office, Research Triangle,-
Park, NC.
6
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ATTACHMENT 2
List of attendees at September 29, 1983 meeting of the Expert Committee on
Trace Metal Essentiality:
PANEL MEMBERS
Dr. F. W. Sunderman, Jr. (Chairman)
University of Connecticut, School of
Medicine
Dr. Walter Mertz
USDA
Dr. Forrest Nielsen
USDA
Dr. M. R. Spivey Fox
FDA
Dr. Ekhard Ziegler
University of Iowa
Dr. Kathryn Mahaffey*
NIOSH
Dr. Orville Levander
USDA
INVITED DISCUSSANTS
Dr. Paul Mushak
University of North Carolina
Dr. Anna M. Reichlmayr-Lais
Technical University of Munich
Federal Republic of Germany
Dr. E. Grassmann (substituting for Dr. M. Kirchgessner*)
Technical University of Munich
Federal Republic of Germany
EPA STAFF
PUBLIC OBSERVERS
Dr. David Weil (Meeting Coordinator)
EPA/ECAO
Mr. Jeff Cohen
EPA/OAQPS
Dr. J. Michael Davis
EPA/ECAO
Dr. Gary Ter Haar
Ethyl Corporation
Dr. Elizabeth Lightfoot
Ethyl Corporation
Dr. Jerry Cole
ILZRO
Dr. Robert Elias
EPA/ECAO
Dr. Magnus Piscator
Karolinska Institute
Dr. Lester Grant
EPA/ECAO
*not present at meeting
.1333<
*.$ CCVtPNHif.' pqM.XSMiCt
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