Great Lakes Binational Toxics Strategy
U.S. Challenge on Alkyl-lead:
Report on
Use of Alkyl-lead in Automotive Gasoline
U.S. EPA
Great Lakes National Program Office
June 2000
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TABLE OF CONTENTS
1.0 Introduction 1
1.1 Alkyl-lead Challenge 1
1.2 Description of Alkyl-lead 2
1.3 Health Effects of Lead Exposure 3
2.0 Overview of Federal and State Regulations Governing Alkyl-lead
5
3.0 Status of Domestic Use of Gasoline Containing Alkyl-lead in On-
road Vehicles 7
3.1 Production of Gasoline Containing Alkyl-lead 7
3.2 Lead Emissions 8
4.0 Compliance and Enforcement 11
5.0 Conclusions 11
6.0 References 13
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LIST OF TABLES
Table 1. Properties of Tetraethyl Lead and Tetramethyl Lead 2
Table 2. 1995 and 1996 National Lead Emissions by Source Category
10
Table 3. Violations Issued for Excess Lead-levels in Gasoline... 11
LIST OF FIGURES
Figure 1. Relationship Between the Phase-out of Leaded Gasoline in
On-road Vehicles and the Decline in Children's Blood-lead
Levels in the U.S 3
Figure 2. Summary of Unleaded vs. Leaded Gasoline Production
1967-1991 7
Figure 3. Total Lead Emissions (Short Tons) by Year 8
Figure 4. Percentage of 1996 National Emission Estimates by Source
(Short Tons) 9
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1.0 Introduction
On April 7, 1997, the United States Environmental Protection Agency (USEPA) and
Environment Canada (EC) signed The Canada-United States Strategy for the Virtual Elimination
of Persistent Toxic Substances in the Great Lakes Basin (Binational Strategy) (1). This
agreement provided a framework for reducing or eliminating persistent toxic substances,
especially those that bioaccumulate, from the Great Lakes Basin. The Binational Strategy
established quantifiable pollution reduction challenges for the time frame 1997 to 2006 involving
twelve "Level I" substances: aldrin/dieldrin, chlordane, DDT, mirex, toxaphene, alkyl-lead,
benzo(a)pyrene, dioxins and furans, hexachlorobenzene, mercury, PCBs, and octachlorostyrene.
The Binational Strategy acknowledged and built on existing Canadian and U.S. regulatory
programs that address the targeted substances, and the two governments will continue to cooperate
on any new toxics reduction regulations. However, a cornerstone of the Binational Strategy is its
reliance on voluntary measures to dramatically reduce pollutant discharges to the Great Lakes
Basin. The Binational Strategy affirmed each country's commitment to virtually eliminating
discharge of the targeted substances to the Great Lakes Basin and outlined a framework by which
the countries can work together to achieve this objective.
1.1 Alkyl-lead Challenge
As part of the Binational Strategy, the United States and Canada have identified alkylated
lead compounds (or alkyl-lead) as a "Level I" substance. Therefore, the virtual elimination of
alkyl-lead, through pollution prevention and other incentive-based actions, is considered an
immediate priority for both governments. EC and the USEPA have accepted the following
challenges as significant milestones on the path toward virtual elimination of alkyl-lead emissions.
U.S. Challenge: Confirm by 1998, that there is no longer use of alkyl-lead in automotive
gasoline. Support and encourage stakeholder efforts to reduce alkyl-lead
releases from other sources.
Canadian Challenge: Seek by 2000, a 90 percent reduction in use, generation, or release of alkyl-
lead consistent with the 1994 Canada-Ontario Agreement Respecting the
Great Lakes Basin Ecosystem (COA).
This report addresses the first portion of the Alkyl-Lead Challenge for the United States —
use of alkyl-lead in automotive gasoline. "Automotive gasoline" is defined as gasoline used in on-
road vehicles (light and heavy gasoline vehicles, motorcycles, and gasoline trucks). Historically,
on-road automotive sources in the U.S. have been the major contributors of lead emissions to the
atmosphere (2). The second portion of the U.S. Alkyl-Lead Challenge — identifying and
encouraging stakeholder efforts to reduce alkyl-lead emissions from other sources — will be the
subject of a subsequent report.
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1.2 Description of Alkyl-lead
Lead (CAS number 7439-92-1) is a naturally occurring, bluish-gray metal originating in the
earth's crust. Its atomic number is 82, and it has an atomic (molecular) weight of 207.20. Its
chemical abbreviation is Pb and other names for lead include C.I. 77575, C.I., pigment metal 4,
KS-4, Glover, Lead S2, Glow (Polish), plumbum, and Omaha. Metallic lead is odorless,
tasteless, and has no known physiological value. It does not dissolve in water and does not burn.
The vast majority of lead chemical compounds are inorganic. However, lead can be combined
with other chemicals to form lead compounds with very different characteristics from metallic
lead (3). Alkyl-leads are by far the predominate type of organic lead compounds.
Alkyl-lead compounds are compounds in which a carbon atom of one or more organic
molecules is bound to a metal atom. As with metallic lead, alkyl-lead compounds can occur
naturally; however, most are man-made compounds used for various purposes (primarily as an
"anti-knock" agent in gasoline). The most common alkyl-lead compound used as an anti-knock
agent in gasoline is tetraethyl lead. Tetramethyl lead is also used as an anti-knock agent.
Tetraethyl lead is also referred to as lead tetraethide, tetraethyllead, and
tetraethylplumbane and is commonly abreviated as TEL. It is a colorless, oily liquid, with a musty
odor, and is typically dyed red, orange, or blue, depending upon its use. Tetramethyl lead,
commonly abbreviated as TML, is also colorless and oily, with a musty odor. Table 1 summarizes
additional properties of tetraethyl and tetramethyl lead.
Table 1. Properties of Tetraethyl Lead and Tetramethyl Lead
Property
Chemical Formula
CAS Registry Number
Molecular Weight
Melting Point
Boiling Point
Liquid Density
Water Solubility
Tetraethyl Lead (TEL)
Pb(C2H5)4
78-00-2
323.45
-130 °C
200 °C
1.65g/cm3
0.29 mg/L
Tetramethyl Lead (TML)
Pb(CH3)4
75-74-1
267.35
-27 °C
108 °C
2.0 g/cm3
17.9 mg/L
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1.3 Health Effects of Lead Exposure
Alkyl-lead compounds added to gasoline combine with dichloroethane and dibromoethane
or other lead scavengers during the combustion process to form lead oxides that are subsequently
emitted as exhaust. Thus, very little alkyl-lead is emitted from gasoline combustion. The primary
direct exposure routes to alkyl-lead is through inhalation of evaporative emissions during fuel
refining, blending, and transportation, as well as during actual fueling or from dermal exposure to
leaded gasoline.
Although alkyl-lead is generally not emitted from gasoline engine exhaust, the lead forms
that are emitted add to total lead emissions. Inhalation of these airborne lead particles represents
one mechanism by which humans can be exposed to lead. Oral exposure mechanisms include
inadvertent ingestion of soil or dust that contains lead or ingestion of food or drinking water that
has been contaminated by lead. Alkyl-lead is easily absorbed through the skin (4), while the
possibility of dermal absorption of inorganic lead is considered to be low (5).
On a global basis, lead in gasoline has been estimated to contribute 95 percent of the lead
1
250 H
2OO-
150-
1OO-
5O-
AvBraga Blood— Laad Cancan tratToris
Load used In Gasoline
18
14
12
10
6 -^
1974 1976 1978 1980 19B2 1984 1986 1988 199O 1992
Figure 1. Relationship Between the Phase-out of Leaded Gasoline in On-road
Vehicles and the Decline in Children's Blood-lead Levels in the U.S. [Figure
Produced using data from National Health and Nutrition Examination Survey
(NHANES), Unpublished Gasoline Production from the DOE's Energy Information
Agency (EIA), and the Trends Procedure Document (8) for (lead content per
gallon)]
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air pollution found in the world's major cities (6). The United States, however, began phasing
lead out of automotive gasoline in the 1970's. The gradual phase-out of lead in automotive
gasoline has correlated with a dramatic decline in children's blood-lead concentrations as
illustrated in Figure 1. Other factors, including the ban on the use of lead in house paint and
reductions in dietary lead levels that took place during this time period (7), also likely contributed
to the declining blood-lead concentrations. With the reduction in leaded gasoline and dietary
intake, deteriorating lead-based paint in homes is now considered to be the primary source of lead
exposure for U.S. children (9). Nevertheless, air emissions of lead from both on-road and nonroad
vehicle emissions (as well as airborne sources such as lead smelters) contribute to childhood lead
exposure through a variety of pathways including migration of lead from exterior soil to interior
household dust.
Lead absorbed by the body is distributed through the blood to "soft tissues" (e.g., liver,
kidneys, muscles, brain) and, over the course of several weeks, moves to and accumulates in "hard
tissues" (e.g., bones, teeth). Lead stored in hard tissues can be mobilized back into soft tissues
over time, particularly during periods of physiological stress. Lead in soft-tissues is thought to
have a half-life of 35 to 40 days. Lead in hard tissues (about 90 percent of the total body-burden
of lead) has a half-life of about 20 years (10).
The effects of lead are the same regardless of the source of exposure (inhalation, ingestion,
or absorption). These effects are modulated by lead's distribution in the body, its affinity for
various binding sites, and differences in cellular composition and structure within tissues and
organs. Once lead enters the body, it interferes with normal cell function and with a number of
physiologic processes. Lead primarily affects the peripheral and central nervous systems, the
blood cells, and metabolism of vitamin D and calcium. Lead also causes reproductive toxicity
(11).
Blood-lead concentration is a commonly used measure of body lead burden. An extensive
body of research relates the health effects of lead exposure to blood-lead concentration. For
example, lead-related reductions in intelligence, impaired hearing acuity, and interference with
vitamin D metabolism have been documented in children at blood-lead concentrations as low as
10 to 15 |ig/dL, with no apparent threshold. At higher exposure levels, these effects become more
pronounced, and other adverse health effects are observed in a broader range of body systems.
Increased blood pressure, delayed reaction times, anemia, and kidney disease may become
apparent at blood-lead concentrations between 20 and 40 |ig/dL. Symptoms of very severe lead
poisoning, such as kidney failure, abdominal pain, nausea and vomiting, and pronounced mental
retardation can occur at blood-lead levels as low as 60 |ig/dL. At even higher levels, convulsions,
coma, and death may result (3,12). Children are particularly at risk from lead exposure due to
their low body weight and maturing neurological system.
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2.0 Overview of Federal and State Regulations Governing Alkyl-lead
Alkylated lead compounds were included in gasoline soon after the anti-knock properties
of alkyl-lead compounds were first discovered in 1921 (13). It was not until 1970, almost fifty
years later, that the Clean Air Act (CAA) was introduced as the first legislative effort to reduce the
amount of lead in gasoline. In the early 1970s, USEPA issued two regulations under the statutory
authority of the 1970 CAA. First, USEPA required major gasoline retailers to begin selling one
grade of unleaded gasoline by July 1, 1974. This mandate was primarily focused on preventing the
deterioration, as a result of leaded gasoline, of emissions control systems (e.g., catalytic
converters) in motor vehicles so equipped. In developing these regulations, USEPA first
established the working definition of "unleaded" gasoline as "gasoline containing not more than
0.05 gram of lead per gallon and not more than 0.005 gram of phosphorus per gallon" [38FR1255,
January 10, 1973]. USEPA issued a regulation calling for the gradual phase-out of leaded
gasoline. The schedule for reduction of lead content in automobile gasoline was 1.7 grams per
gallon (g/gal) in 1975, to 1.4 g/gal in 1976, 1.0 g/gal in 1977, 0.8 g/gal in 1978, and 0.5 g/gal in
1979 [38FR33741, December 6, 1973]. Subsequent regulations reduced the allowable lead
content to 0.1 g/gal in 1986 [50FR9397, March 7, 1985], and prohibited leaded gas use after 1995
[61FR3837, February 2, 1996].
Most recently, alkylated lead compounds have been regulated under the 1990 Clean Air
Act Amendments (CAAA). The following components of the 1990 CAAA relate to alkyl-lead:
1. Emissions for Nonroad Vehicles. Section 213 of the 1990 CAAA requires USEPA
to consider regulating emissions from off-highway vehicles1 (construction
equipment, boats, farm equipment, lawn equipment, etc.). Currently, these vehicles
are permitted to use leaded gasoline, but may be regulated in the future.
2. Misfueling with Leaded Gasoline. Section 21 l(g) of the 1990 CAAA prohibits
misfueling vehicles built after 1990 (or vehicles designated solely for unleaded
gasoline) with leaded gasoline.
3. Prohibition on the Use of Leaded Gasoline in On-Road Vehicles. Section 21 l(n) of
the 1990 CAAA states: "After December 31, 1995, it shall be unlawful for any
person to sell, offer for sale, supply, offer for supply, dispense, transport, or
introduce into commerce, for use as fuel in any motor vehicle (as defined in
Section 219(2)) any gasoline which contains lead or lead additives." This
provision applies only to on-road vehicles. Enacting regulations were promulgated
[61FR3837, February 2, 1996].
4. Prohibition on Production of Engines Requiring Leaded Gasoline. Section 218 of
the 1990 CAAA requires USEPA to promulgate rules that prohibit the
"manufacture, sale, or introduction into commerce of any engine that requires
1 Fuels for Race Cars or "Competition Use Vehicles" are exempted from regulation under the
Clean Air Act.
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leaded gasoline." Further, these rules apply to all motor vehicle engines and
nonroad engines manufactured after the 1992 model year.
5. Identification of Sources of Alkyl-Lead. Section 112(c)(6) of the 1990 CAAA
requires USEPA to identify sources of alkyl-lead (and six other chemicals). The
identified sources must account for at least 90 percent of the aggregate emissions
for alkyl-lead. In response, USEPA developed emission inventories of known
sources of each pollutant and added two source categories on April 3, 1998:
(1) open burning of scrap tires, and (2) gasoline distribution Stage I aviation
(including evaporative losses associated with the distribution and storage of
aviation gas containing lead).
Thus, the sale or use of gasoline containing alkyl-lead (greater than 0.05 grams of lead per
gallon) is now prohibited in on-road vehicles [40CFR Part 80.22].
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3.0 Status of Domestic Use of Gasoline Containing Alkyl-lead in On-road Vehicles
While the use of leaded gasoline in on-road vehicles is prohibited by the 1990 CAAA, the
production of leaded gasoline for other uses was not prohibited. For example, leaded gasoline is
a predominant fuel in the general aviation (piston engine) industry, and it is also used in farm
machinery and race cars. However, the introduction of unleaded gasoline in the late 1970s and
the enactment of the 1990 CAAA has caused production volumes of leaded gasoline to fall
dramatically. Consequently, lead emissions from the use of leaded gasoline in on-road vehicles
have also fallen dramatically.
3.1 Production of Gasoline Containing Alkyl-lead
The production of gasoline containing alkyl-lead has greatly diminished. As seen in Figure
(0
c
.o
15
O
.o
m
120
100 --
0
1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991
Year
•Leaded Gasoline
• Unleaded Gasoline
Figure 2. Summary of Unleaded vs. Leaded Gasoline Production 1967-1991.
[Figure produced using unpublished data, USEPA 1991 (14).]
2, the production of leaded gasoline has decreased from 77.5 billion gallons in 1967 to 3.1 billion
gallons in 1991 (14), or to 3% of all gasoline produced.
Conversely, the production of unleaded gasoline has risen sharply. In 1991, 94.9 billion gallons of
unleaded gasoline were produced, which represents approximately 97 percent of all gasoline
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produced. To complete the leaded gasoline phase-out picture, it would be desirable to obtain
more recent production information for leaded and unleaded automotive gasoline.
3.2 Lead Emissions
The overall amount of lead emissions (all forms of lead and lead compounds, including
alkyl-lead) in the U.S. has decreased by two orders of magnitude between 1970 (220,869 short
tons emitted) and 1996 (3,869 short tons emitted) (15) Figure 3 summarizes estimates of total lead
emissions by year. Most notable in Figure 3 is
250,000
200,000
^
° 150,000
o
in
v 100,000
TO
0)
50,000
1970
1975
1980
1985
1990
1995
Year
Figure 3. Total Lead Emissions (Short Tons) by Year.
[Figure reproduced from National Air Pollutant Emission Trends Report, 1900-1996
(15).]
that the greatest reduction in lead emissions occurred between 1970 and 1985. This large
reduction is a direct result of the regulated phase-out of leaded gasoline (reductions in both the
lead content per gallon and the total gallons produced) and the increased availability of unleaded
gasoline (3). Currently, there are several major sources of airborne lead emissions2, including
bulk production plants for aviation gasoline, nonroad vehicles, waste incinerators, metal
processing, and other fuel combustion (e.g., electrical utility, industrial). As seen in Figure 4, on-
road emissions, the predominant emissions source in the 1970s and 1980s, contributed less than
Through the combustion process in automotive engines, alkyl-lead compounds combine with fuel
scavengers to form lead oxides. Alkyl-lead is the only known significant source of lead in
gasoline. Typically, only a very small percentage (0.2%-0.4%) of alkyl-lead is exhausted
uncombusted when driving at constant speeds (16). Therefore, estimates of the total lead
emitted as exhaust from on-road vehicles will be used to characterize the decline in use of leaded
gasoline in on-road vehicles.
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100.0% -
yo.o%
on no/ -
oU.U/o
7n no/ .
/U.U /o
on no/
bU.Uyo
50.0% -
/in no/ .
4U.U70
on no/ -
oU.Uyo
on no/
ZU.UTO
10.0% '
.0% n
t>1.b"y%
20.01%
-I A 0<~)0/r
1070% 11.UJ,U
o.U.^70 0.49%
1 1 1 1 1 1
Metals Fuel Chemical On-road Nonroad All Other
Processing Combustion and Allied
(Other) Products
Figure 4. Percentage of 1996 National Emission Estimates by Source (Short Tons).
[Figure produced using data from National Air Pollutant Emission Trends Report,
1900-1996, EPA 1997 (15).]
one-half of one percent to the total emissions in 1996 (2, 15). In 1996, metals processing was
estimated to be the predominant source of lead emissions. Therefore, not only have total lead
emissions been reduced, but the relative contribution of on-road vehicles has also been reduced.
With the continued implementation of provisions of the 1990 CAAA, this trend is expected to
continue.
Table 2 summarizes the information contained in Figures 3 and 4. Emissions of lead
compounds from on-road vehicles were estimated by USEPA to be approximately 19 tons in 1996.
However, this estimate does not imply a widespread use of leaded gasoline as a fuel source for
on-road vehicles. Rather, this emission estimate incorporates the trace amount of lead remaining
in unleaded gasoline. This trace amount of lead is due to the sharing of distribution systems
utilized by gasoline manufacturers for the production of leaded and unleaded gasoline and residual
amounts of lead in crude oil. USEPA has determined that requiring manufacturers to eliminate this
trace amount is not economically feasible. As production of leaded gasoline has decreased, so too
has the trace amount of lead in unleaded gasoline.
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10
Table 2. 1995 and 1996 National Lead Emissions by Source Category
Source Category
Metals
Primary lead production
Secondary lead production
Gray iron production
All other
Fuel combustion other
Chemical and Allied Products (lead oxide and pigments)
On-road
Nonroad(a)
Nonroad gasoline
Aircraft
All other
Total
Emissions (short tons)
1995
2,067
674
432
366
595
414
144
19
545
0
545
754
3,943
1996
2,000
636
400
339
625
414
117
19
545
0
545
774
3,869
[Table reproduced from Table 2-1 in the National Air Pollutant Emission Trends Report, 1900-
1996, EPA 1997.]
(a) EPA did not develop estimates for Nonroad emissions (other than those for aviation)
because they were deemed to be extremely low relative to other sources.
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11
4.0 Compliance and Enforcement
Because leaded gasoline still is produced in the United States, is being used in nonroad
vehicles (primarily as aviation fuel, but also in farm machinery and race cars), and is dispensed by
private citizens, it is possible that illegal misfueling occurs. Historically, USEPA's Office of
Enforcement has not found this to be the case in public gasoline service stations. In previous years,
USEPA's Office of Enforcement screened for lead during routine inspections at service stations.
However, as leaded gasoline became increasingly scarce, the number of violations related to the
misuse of leaded gasoline dropped precipitously (see Table 3) (17). As a result of finding
virtually no cases of misfueling, USEPA's Office of Enforcement no longer routinely screens for
lead as part of the typical inspection process. It does continue to test for lead on a case-by-case
basis if illegal misfueling is suspected. Typically, very few cases of suspected misfueling with
leaded gasoline are investigated in a given year. No documentation of investigation of misfueling
of leaded fuel intended to fuel farm machinery or racing cars was found for this report.
Although it is possible for misfueling of on-road automobiles to occur using leaded racing
gasoline, such misfueling, if it occurs at all, is likely to be rare. Limited supply, limited
distribution, much higher cost, incompatibility with emission control systems on production
automobiles, and limited performance benefits in production automobiles designed for unleaded
gasoline all weigh against use of leaded racing gasoline in on-road automobiles.
Table 3. Violations Issued for Excess Lead-levels in Gasoline
[Source: USEPA(17)]
Year
1980
1981
1982
1983
1984
1985
1986
1987
Number of Service Station
Inspections
5,021
10,179
10,266
9,896
4,652
5,363
5,363
9,003
Number of
Violations Issued
83
73
60
41
24
30
8
4
Violation Rate
1 .65%
0.72%
0.5%
0.41%
0.52%
0.56%
0.15%
0.04%
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12
5.0 Conclusions
The 1990 Clean Air Act Amendments prohibit the use of leaded gasoline as fuel for on-
road automotive use. As a result of this prohibition and earlier CAA regulations, the production of
leaded gasoline and its use in on-road vehicles has declined dramatically, as have estimates of
lead emissions resulting from on-road vehicles. It is clear that the vast majority of on-road
vehicles use unleaded gasoline as their primary fuel. This can be verified by examining emission
and production estimates. In particular, the amount of leaded gasoline produced is not sufficient to
serve as fuel for a significant number of on-road vehicles. Further, emissions of lead have
decreased since leaded gasoline was phased out, and on-road vehicles are estimated by USEPA to
account for less than one-half of one percent of the total amount of lead emitted in 1996.
Leaded gasoline is still legally produced and used as fuel for a variety of other vehicles in
the United States (e.g., aviation, farm machinery, nonroad automotive). Although illegal misfueling
of on-road vehicles with leaded gasoline is possible, it is likely to be rare, if it occurs at all.
Based on the above, it is concluded that alkyl-lead has been virtually eliminated from use
in automotive gasoline. Further confirmation should be sought by collecting up-to-date leaded
gasoline production data. This could be done when a detailed inventory of all sources of alkyl-
lead is conducted as part of the Great Lakes Binational Toxics Strategy 4-Step Process to virtual
elimination.
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13
6.0 References
(1) USEPA, EC, "The Great Lakes Binational Toxics Strategy: Canada-United States Strategy
for the Virtual Elimination of Persistent Toxic Substances in the Great Lakes," April 7,
1997.
(2) USEPA, "National Air Quality and Emissions Trends Report, 1996," Office of Air Quality
Planning and Standards, U.S. Environmental Protection Agency, EPA-454-R-97-013,
January 1998.
(3) U.S. Department of Health and Human Services, Public Health Service, Agency for Toxic
Substances and Disease Registry, "Toxicological Profile for Lead, Draft for Public
Comment," August 1997.
(4) Bress, W.C., Bidanset, J.H., "Percutaneous in vivo and in vitro absorption of lead" Vet.
Hum. Toxicol. 33: 212-214, 1991.
(5) Moore, M.R., Meredith, P.A., Watson, W.S., Sumner, D.J., Taylor, M.K., and Goldberg, A.
"The Percutaneous Absorption of Lead-203 in Humans from Cosmetic Preparations
Containing Lead Acetate As Assessed by Whole-Body Counting and Other Techniques"
Food and Cosmetic Toxicology 18:399-405, 1980.
(6) USEPA, "Reducing Health Risks Worldwide: EPA's International Lead Risk Reduction
Program," EPA 160-K-98-001, March, 1998.
(7) USFDA, "Dangers of Lead Still Linger," FDA Consumer, January-February 1998.
(8) USEPA, "National Air Pollutant Emission Trends, Procedures Document, 1900-1996,"
Office of Air Quality Planning and Standards, EPA-454-R-98-008, May 1998.
(9) Centers for Disease Control and Prevention, "Screening Young Children for Lead
Poisoning," November, 1997.
(10) Lauwerys, R., "Inorganic and Organometallic Substances: Chapter II, Section 10. Lead",
Industrial Chemical Exposure, 1983.
(11) ATSDR, "Case Studies in Environmental Medicine: Lead Toxicity," U.S. Department of
Health and Human Services, Public Health Service, Agency for Toxic Substances and
Disease Registry.
(12) USEPA, "Risk Analysis to Support Standards for Lead in Paint, Dust, and Soil," Office of
Pollution Prevention and Toxics, EPA-745-R-97-005, April 1997.
(13) Nriagu, J., "The Rise and Fall of Leaded Gasoline," The Science of the Total
Environment, 92:13-28, 1990.
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14
(14) Unpublished Data, USEPA, 1991.
(15) USEPA, "National Air Pollutant Emission Trends Report, 1900-1996," Office of Air
Quality Planning and Standards, EPA-454-R-97-011, December, 1997.
(16) Grandjean, P., "Health Significance of Organolead Compounds," Lead Versus Health,
Edited by M. Rutter and R. Russell Jones, 1983 John Wiley & Sons Ltd.
(17) Personal communication with George Lawrence, USEPA, Office of Enforcement, 1998.
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