5540 905R78102
NATIONAL AMBIENT
AIR QUALITY STANDARD
FOR LEAD
September 1978
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air, Noise, and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
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TITLE 40 - PROTECTION OF ENVIRONMENT
CHAPTER 1 - ENVIRONMENTAL PROTECTION AGENCY
SUBCHAPTER C - AIR PROGRAMS
PART 50 - NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY STANDARDS
NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY STANDARDS FOR LEAD
AGENCY: Environmental Protection Agency.
ACTION: Final Rulemaking.
SUMMARY: EPA is setting a National Ambient Air Quality Standard for lead
at a level of 1.5 micrograms lead per cubic meter of air, (pg Pb/m ), averaged
over a calendar quarter. This final rulemaking follows a 1976 court order to
list lead as a criteria pollutant for the development of an ambient standard,
and the Agency's issuance of a proposed standard on December 14, 1977. In
response to comments received on the proposed standard, EPA has changed the
averaging period for the standard from a calendar month to a calendar quarter,
and has clarified the health basis used in selecting the standard level.
In establishing the level of the final standard, EPA has determined
that young children (age 1-5 years) should be regarded as a group within the
general population that is particularly sensitive to lead exposure. The
final standard for lead in air is based on preventing most children in
the United States from exceeding a blood lead level of 30 micrograms
lead per deciliter of blood (ng Pb/dl). Blood lead levels above 30 yg
Pb/dl are associated with the impairment of heme synthesis in cells indicated
by elevated erythrocyte protoporphyrin (EP), which EPA regards as adverse
to the health of chronically exposed children. There are a number of
other adverse health effects associated with blood lead levels above
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30 yg Pb/dl, in children as well as in the general population, including
the possibility that nervous system damage may occur in children even
without overt symptoms of lead poisoning.
After promulgation, States will have nine months to prepare and
submit to EPA plans for attainment of the standard by no later than October
of 1982. EPA's final regulations for the development of State implementation
plans appear elsewhere in this Federal Register.
FOR FURTHER INFORMATION CONTACT:
Mr. Joseph Padgett, Director
Strategies and Air Standards Division
Office of Air Quality Planning and Standards
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
Telephone: 919-541-5204
AVAILABILITY OF RELATED INFORMATION: A docket (Number OAQPS-77-1) containing
the information used by EPA in the development of the proposed standard is
available for public inspection and copying between 8:00 a.m. and 4:30 p.m.
Monday through Friday, at EPA's Central Docket Section, Room 2903B, Waterside
Mall, 401 M Street, SW, Washington, D.C. 20460.
The Federal Reference Method for collecting and measuring lead and its
compounds in the ambient air is published in Appendix G to this promulgation.
This Federal Register also contains proposed regulations under 40 CFR Parts 51
and 53 for equivalent lead air monitoring methods, final rules for the develop-
ment of State implementation plans promulgated under 40 CFR Part 51, and an
advance notice of proposed rulemaking under 40 CFR Part 51 for ambient monitoring
in the vicinity of certain industrial plants with lead emissions. Additional
information for the development of the State implementation plans is contained
in the document Supplementary Guidelines for Lead Implementation Plans. The
environmental and economic impacts of implementing this standard are described
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in an Environmental Impact Statement and an Economic Impact Assessment.
These documents are available for public inspection and copying at the
Central Docket Section (address above). Copies may be obtained upon request
from Mr. Joseph Padgett at the above address.
The documents Air Qua!ity Criteria for Lead and Control Techniques for
Lead Air Emissions were issued at the time of proposal. The Control Tech-
niques Document is available upon request from Mr. Joseph Padgett at the
above address. The Air Quality Criteria Document can be obtained from:
Mr. Michael Berry
Environmental Criteria and Assessment Office, MD-52
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
Telephone: 919-541-2266
SUPPLEMENTARY INFORMATION:
BACKGROUND
Lead is emitted to the atmosphere by vehicles burning leaded fuel and
by certain stationary sources. Lead enters the human body through ingestion
and inhalation with consequent absorption into the blood stream and distribution
to all body tissues. Clinical, epidemiological, and toxicological studies
have demonstrated that exposure to lead adversely affects human health.
EPA's initial approach to controlling lead in the air was to limit the
lead emissions from automobiles, the principal source of lead air emissions.
Regulations for the phasedown of lead in the total gasoline pool were
promulgated in 1973, and, following litigation, modified and put into effect
in 1976. The Agency has also established regulations requiring the
availability of no-lead gasoline for catalyst-equipped cars. EPA also
intended to control emissions from certain categories of industrial
point sources under Section 111 of the Clean Air Act.
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In 1975, the Natural Resources Defense Council (NRDC) and others
brought suit against EPA to list lead under Section 108 of the Clean Air Act
as a pollutant for which air quality criteria would be developed and a
National Ambient Air Quality Standard established under Section 109 of the Act.
The Court ruled in favor of NRDC. [ NRDC. Inc. et al. v. Train, 411 F.Supp. 864
(S.D.N.Y., 1976) aff'd 545 F.2d 320 (2nd Cir. 1976).] EPA listed lead on
March 31, 1976, and proceeded to develop air quality criteria and the proposed
standard.
On December 14, 1977, EPA proposed a standard of 1.5 u9 Pb/m , calendar
month average, proposed the Federal Reference Method for monitoring air lead
levels, issued the documents Air Quality Criteria for Lead and Control
Techniques for Lead Air Emissions and proposed regulations for State implementa-
tion plans. EPA invited public comments during the period from December 14, 1977,
to March 17, 1978,on the standard, reference method, and the SIP regulations.
Additional comments on these matters were provided to EPA at a public hearing
held on February 15-16, 1978.
LEGISLATIVE REQUIREMENTS FOR NATIONAL
AMBIENT AIR QUALITY STANDARDS
Sections 108 and 109 of the Clean Air Act govern the development of
National Ambient Air Quality Standards. Section 108 instructs EPA to document
the scientific basis for the standard:
"Sec. 108(a)(2) The Administrator shall issue air quality criteria
for an air pollutant within 12 months after he has included such pollutant
in a list under paragraph (1). Air quality criteria for an air pollutant
shall accurately reflect the latest scientific knowledge useful in indicating
the kind and extent of all identifiable effects on public health or
welfare which may be expected from the presence of such pollutant in the
ambient air, in varying quantities. The criteria for an air pollutant,
to the extent practicable, shall include information on --
(A) tnose variable factors (including atmospheric conditions) which
of themselves or in combination with other factors may alter the effects
on public health or welfare of such air pollutant;
(B) the types of air pollutants which, when present in the
atmosphere, may interact with such pollutant to produce an adverse effect
on public health or welfare; and
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(C) any known or anticipated adverse effects on welfare."
Section 109 addresses the actual setting of the standard:
"Section 109(b)(l) National primary ambient air quality standards,
prescribed under subsection (a) shall be ambient air quality standards
the attainment and maintenance of which in the judgment of the Adminis-
trator, based on such criteria and allowing an adequate margin of safety,
are requisite to protect the public health. Such primary standards may
be revised in the same manner as promulgated.
(2) Any national secondary ambient air quality standard prescribed,
under subsection (a) shall specify a level of air quality the attainment
and maintenance of which in the judgment of the Administrator, based on
such criteria, is requisite to protect the public welfare from any known
or anticipated adverse effects associated with the presence of such air
pollutant in the ambient air. Such secondary standards may be revised in
the same manner as promulgated."
In order to conform to the requirements of Section 109, EPA has
based the level of the lead air quality standard on information presented
in the criteria document pertaining to the health and welfare implications
of lead air pollution. This is in contrast to other sections of the Act
under which EPA considers economic costs and technical availability of
air pollution control systems in determining emissions limitations. It is
clear from Section 109 that the Agency should not attempt to place the
standard at a level estimated to be at the threshold for adverse health
effects, but should set the standard at a lower level in order to provide
a margin of safety. EPA believes that the extent of the margin of
safety represents a judgment in which the Agency considers the severity
of reported health effects, the probability that such effects may occur,
and uncertainties as to the full biological significance of exposure to
lead.
Comments resulting from external review of the air quality criteria
and the proposed standard highlight disagreements on a number of areas
critical to EPA's rationale for the standard. However, the scientific
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data base provided in the document Air Quality Criteria for Lead
is as extensive as that for any other regulated air pollutant. Also, at
every stage of development of the air quality criteria and the standard, EPA
has facilitated and received broad external participation. EPA regards as
inevitable the presence of scientific disagreement and uncertainty about key
factors relevant to environmental standards. Provisions of the Act requiring
timely promulgation of the standard, and requirements for periodic
future review of air quality criteria and standards indicate Congressional
intent that the Agency proceed even where scientific knowledge is not
complete or full scientific consensus is absent.
SUMMARY OF GENERAL FINDINGS FROM AIR QUALITY CRITERIA FOR LEAD
Following the listing of lead as a criteria pollutant, EPA developed
the document, Air Qua!ity Criteria for Lead. In the preparation of this
document, EPA provided opportunities for external review and comment on
three successive drafts. The document was reviewed at three meetings of the
Subcommittee on Scientific Criteria for Environmental Lead of EPA's Science
Advisory Board. Each of these meetings was open to the public and a number
of individuals presented both critical review and new information for EPA's
consideration. The final criteria document was issued on December 14, 1977.
From the scientific information in the criteria document, EPA draws con-
clusions in several key areas with particular relevance for the ambient
air quality standard for lead.
1. There are multiple sources of lead exposure. In addition to
air lead, these sources include: lead in paint and ink, lead in
drinking water, lead in pesticides, and lead in fresh and processed
food.
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2. Exposure to air lead can occur directly by inhalation, or indirectly
by ingestion of lead contaminated food, water, or non-food materials
including dust and soil.
3. There is significant individual variability in response to lead
exposure. Even within a particular population, individual response
to lead exposure may vary widely from the average response for the
same group. Certain subgroups within the general population are
more susceptible to the effects of lead or have greater exposure
potential. Of these, young children represent a population of fore-
most concern.
4. Three systems within the human body appear to be most sensitive
to the effects of lead -- the blood-forming or hematopoietic system,
the nervous system, and the renal system. In addition, lead has
been shown to affect the normal functions of the reproductive, endocrine,
hepatic, cardiovascular, immunologic, and gastrointestinal systems.
5. The blood lead level thresholds for various biologic effects range
from the risk of permanent, severe, neurological damage or death as
blood leads approach and exceed 80 to 100 yg Pb/dl in children down to
the inhibition of an enzymes system as low as 10 yg Pb/dl.
6. Lead is a stable compound, ubiquitously distributed, which persists
and accumulates both in the environment and in the human body.
In developing the proposed standard, EPA used these findings to
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arrive at a standard level of 1.5 yg Pb/m , calendar month average.
This level was derived from the Agency's judgment that the maximum safe
blood lead level (geometric mean) for a population of young children was
15 yg Pb/dl and, of this amount, 12 yg Pb/dl should be attributed to
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non-air sources. The difference of 3.0 yg Pb/dl was estimated to be the
allowable safe contribution to mean population blood lead from lead in
the air. With epidemiological data indicating a general relationship of
1:2 between air lead (yg Pb/m ) and blood lead (yg Pb/dl), EPA determined
that the level for the proposed standard should be 1.5 yg/m .
SUMMARY OF ANTICIPATED IMPACTS
While the level of the standard is based on health considerations,
EPA has conducted economic and environmental studies to assess the
potential impacts of the standard selected. EPA estimates that the
existing regulations for the phase-down of lead in gasoline, combined with
the increasing use of no-lead gasoline for catalyst-equipped cars, will
result in attainment of the standard in urban areas where automobile
exhaust is the dominant source of air lead. No additional pollution
controls are anticipated for these areas.
EPA's economic analysis does indicate that there may be significant
problems in attainment of the standard in the vicinity of non-ferrous
smelters and other large industrial sources of lead emissions. This
assessment is based, however, on studies using general emission factors
and plant configurations, combined with dispersion modeling. In the
development of State plans to implement the standard, EPA is encouraging
affected industries and State agencies to gather plant-specific technical
data, ambient air quality data, and assessments of alternative engineering
controls. With this information, the Agency will be able to more accurately
evaluate the impact of the standard and better consider approval of
alternative approaches to emission control in the State plans.
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Also, EPA is encouraging affected firms and State agencies to
evaluate in the early design phase, strategies which take into considera-
tion the work-place standard for airborne lead which will be promulgated
by the Occupational Health and Safety Administration (OSHA). EPA believes
that this approach will facilitate application of control technologies
which meet the requirements of both agencies. In working with OSHA to
estimate the combined impact of the OSHA and EPA standards, in coordinating
compliance strategies, and in reviewing State plans implementing the
ambient standard, EPA intends to avoid an approach which would foster
uncertainty in the investment decisions of affected firms.
The Agency will make every effort to insure that all opportunities
to avoid plant closures are examined, while at the same time assuring
protection from clear risks to the public health.
SUMMARY OF COMMENTS RECEIVED
During the comment period from December 14, 1977, to March 17, 1978,
and at the public meeting on February 15-16, 1978, EPA received 95
written and oral comments addressing the proposed standard or the
requirements for State implementation plans. All comments opposing the
standard as excessively stringent (25) came from representatives of
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affected industries, and twenty of these counter-proposed 5.0 yg Pb/m ,
calendar quarter average, as the appropriate level for the standard.
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COMMENTS RECEIVED OPPOSING THE PROPOSED STANDARD
OF 1.5 yg/m3 CALENDAR MONTH AVERAGE AS EXCESSIVELY STRINGENT
COMPANY OPPOSED 1.5 ug/m3, ENDORSED 5.0 yg/m3,
calendar month calendar quarter (or
other averaging period)
Amax Lead and Zinc, Inc. X X
American Mining Congress X X
American Petroleum Institute X
ASARCO X X
Associated Octel Company Limited X X
Battery Council International X X
Bethlehem Steel Corporation X X
Bunker Hill Company X X
C & D Batteries Division X X
E. I. DuPont de Nemours & Company, Inc. X X
ESA Laboratories, Inc. X X
Ethyl Corporation X X
General Battery Corporation X X
General Motors Corporation
Getty Refining and Marketing Company X
HECLA Mining Company X
Houston Chemical X X
Hunt Oil Company X
Kerr-McKee Corporation
Lead Industries Association X X
Nalco Chemical X X
N L Industries, Inc. X X
Prestolite Battery Division X X
Secondary Lead Smelters Association X X
Shell Oil Company X
St. Joe Minerals Corporation X X
Texaco, Inc. X X
United Machinery Group
Vulcan Materials Company
Summary: 45 comments received from 29 corporations or their representatives.
25 of the 29 firms oppo:
calendar month average;
20 endorsed an alternat'
quarter average (or other averaging period).
25 of the 29 firms opposed the proposed standard of 1.5 yg/m ,
20 endorsed an alternative standard of 5.0 yg/m , calendar
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Four comments opposed the proposed standard on the grounds that it was
not sufficiently protective of health.
COMMENTS RECEIVED OPPOSING PROPOSED LEAD AIR QUALITY
STANDARD OF 1.5 ug/m3, CALENDAR MONTH AVERAGE,
IN FAVOR OF A MORE STRINGENT STANDARD
Natural Resources Defense Council
Dr. Sergio Piomelli, Director, Pediatric Hematology, New York University Medical Center
Public Interest Campaign
University of Connecticut School of Medicine
Comments supporting the level of the proposed standard (17) came from
the medical community, Federal agencies, State and local public health
agencies, and public interest groups.
COMMENTS RECEIVED ENDORSING PROPOSED LEAD AIR QUALITY
STANDARD OF 1.5 yg/m3. CALENDAR MONTH AVERAGE
State and Local Agencies
California Department of Health
Massachusetts Department of Public Health
New York State Department of Environmental Conservation
New York City Department of Environmental Protection
Tennessee Department of Public Health
Wisconsin Department of Natural Resources
Federal Agencies
Center for Disease Control, Public Health Service
Department of Transportation
Food and Drug Administration
Occupational Safety and Health Administration
Public Interest Groups and the Medical Community
Committee on Environmental Hazards, American Academy of Pediatrics
D.C. Committee for Lead Elimination in the District
League of Women Voters of the U.S.
National Urban League
Herbert Needleman, Boston Children's Hospital Medical Center
University of North Carolina School of Public Health
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In addition, EPA has received numerous comments and correspondence
on the proposed standard after the official end of the comment period.
Though EPA does not have a legal obligation to review these documents,
it has, in the interest of fostering full public participation in the
rulemaking process, reviewed these comments and correspondence as time
permitted. As with all other documents considered or examined by EPA as
part of its decision process, these documents have been placed in the
public docket and have become part of the administrative record of this
decision.
The comments received by EPA did not challenge three aspects of the
proposed standard:
1. the basic structure of the rationale used by the Agency in
deriving the level of the proposed standard.
2. the selection of young children as a population particularly
at risk to lead exposure.
3. The attribution of 12 yg Pb/dl out of the target mean population
blood lead level of 15 yg Pb/dl to non-air sources of lead for the
purposes of setting the air standard.
Significant comments were received, however, on the following key areas
relating to the standard:
1. the elevation of erythrocyte protoporphyrin (EP) as the first
adverse health effect with increasing lead exposure rather than
the decline of hemoglobin levels.
2. the blood lead threshold level for elevated EP.
3. the incidence of health effects in populations residing in the
vicinity of industrial sources of lead particulate emissions.
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4. the relationship describing the response of lead in the blood
to lead in the air.
5. the statistical form and averaging period for the standard.
6. the appropriate margin of safety.
7. the limitation of the standard to the respirable fraction of
total air lead particles.
8. the economic impact of the standard.
9. the State implementation plan regulations.
10. the Federal Reference Method for monitoring lead air quality.
11. the administrative procedures employed by EPA in the development
of the standard and the provision for public participation.
A review of the comments received and their disposition has been placed
in the rulemaking docket (OAQPS-77-1) for public inspection. The following
paragraphs summarize the significant comments and present the Agency's findings.
The Health Significance of Erythrocyte Protoporphyrin Elevation
Ten commenters disagreed with EPA's conclusion that the impairment
of heme synthesis indicated by elevated erythrocyte protoporphyrin (EP)
constituted an adverse health effect. Reasons for this disagreement included:
1. An elevated level of EP is not itself toxic to the cells in
blood or other tissues.
2. EP elevation, while indicating a change in heme synthesis, does
not indicate an insufficient production of heme, or hemoglobin.
3. EP elevation and the alteration of heme synthesis does not imply
impairment of other mitochondrial functions.
4. EP elevation is not associated with impairment of other heme proteins,
particularly cytochrome P-450.
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5. Elevated EP may be caused by conditions other than exposure to
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lead, particularly iron deficiency.
Five commenters agreed with EPA's conclusions about the health
significance of elevated EP citing the following arguments:
1. the interference of lead in a fundamental cellular metabolic
function to the extent that there is accumulation of a substrate
is physiological impairment, even without the presence of clinical
evidence of disease.
2. it is prudent medical practice to intervene where subclinical
indicators of physiological impairment are present.
3. the impairment of heme synthesis resulting from genetic or dietary
factors places a child at enhanced risk to lead exposure.
4. there is evidence to suggest that impaired heme synthesis may affect
the function of neural or hepatic tissue iven at levels where heme
production is sufficient for hematopoiesis.
Agency Response
EPA agrees with the comments received that the initial elevation of EP
as a result of exposure to lead, while indicating an impairment of heme
synthesis, may not be a disease state or be seen as a clinically detectable
decline in performance. However, the Criteria Document points out (p. 1-13)
that this impairment does increase progressively with lead dose.
"The hematological effects described above are the earliest physiological
impairments encountered as a function of increasing lead exposures as
indexed by blood lead elevations; as such, those effects may be con-
sidered to represent critical effects of lead exposure. Although it may
be argued that certain of the initial hematological effects (such as
ALAD inhibition) constitute relatively mild, nondebilitating symptoms
at low blood lead levels, they nevertheless signal the onset of steadily
intensifying adverse effects as blood lead elevations increase. Eventually,
the hematological effects reach such magnitude that they are of clear-cut
medical significance as indicators of undue lead exposure."
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The fact that other conditions, such as iron deficiency, may also
impair heme synthesis, does not obviate concern that lead is interfering
with an essential biological function. There is the possibility that a
nutritional deficiency is an additional stress to the heme synthetic
system which may increase the sensitivity of a child to the adverse effects
of lead exposure.
EPA notes that there is general agreement that heme and heme-containing
proteins play important roles in the oxygen fixation pathways in all cells.
While the effects of low-level lead exposure on the heme synthetic pathway
in erythroid tissue have been extensively studied in part because of the ease
with which this tissue may be obtained, other cellular metabolic systems
utilizing heme are less well understood. EPA does not have sufficient
information to conclude that impairment of heme synthesis in other tissues
is not of concern until blood lead levels are reached greater than those
associated with hematological effects. The air quality Criteria Document
does point out that this effect has been established in other tissues
and that other dose-response factors may apply.
"The effect of lead on the formation of heme is not limited to the
hematopoietic system. Experimental animal studies have shown a
lead effect on the heme-requiring protein, cytochrome P-450, an
integral part of the hepatic mixed-function oxidase (Chapter 11),
the systemic function of which is detoxification of exogenous sub-
stances. Heme synthesis inhibition also takes place in neural
tissue." (p. 13-5)
In summary, the Criteria Document states:
"Elevation in protoporphyrin is considered not only to be a biological
indicator of impaired mitochondria! function of erythroid tissue but
also an indicator of accumulation of substrate for the enzyme
ferrochelatase. It therefore has the same pathophysiological
meaning as increased urinary s-ALA (vide supra). For these reasons,
accumulation of protoporphyrin has been taken to indicate physiological
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impairment in humans, and this clinical consensus is expressed in
the 1975 Statement of the Center for Disease Control (CDC), USPHS.
The criterion used by CDC to indicate an effect of lead on heme
function is an FEP level of 60 vg/dl in the presence of a blood lead
level above 30 pg/dl whole blood.
More recent information relating to threshold of lead effects indicates
that FEP levels begin to increase at a blood lead value of 15 to 20 pg Pb/dl
blood in children and women and, at a somewhat higher value, 20 to 25
yg Pb/dl blood, in adult men." (p. 13-5)
EPA concludes that the state of elevated EP must be regarded as potentially
adverse to the health of young children. While the onset or a mild experience
of this condition may be tolerated by an individual, as with other subclinical
manifestations of impaired function, it is a prudent public health practice
to exercise corrective action prior to the appearance of clinical symptoms.
The criteria document reports that symptoms of anemia in children may occur
at blood lead levels of 40 pg/dl. EPA has adopted 30 vg Pb/dl as a maximum
safe blood lead level for individual children.
The Blood Lead Threshold, for Elevated Erythrocyte Protoporphyrin
Comments provided by ten organizations challenged EPA's conclusion
that the threshold for the elevation of EP occurs in children at a blood
lead level of 15 vg/dl. Evidence offered for a higher threshold included:
1. the threshold accepted by EPA is based on a study in which an
inappropriate statistical technique, probit analysis, was employed.
2. application of a more appropriate technique, segmented line
analysis, results in a higher threshold.
3. the study in question excluded data on children with blood lead
levels in excess of 30 pg/dl.
4. other investigators have reported higher thresholds.
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Comments in support of the 15 yg/dl threshold maintained:
1. it is proper to exclude values considered abnormal if the intent
of the analysis is to determine an unbiased effect threshold.
2. other studies have reported thresholds with error bands which
include 15 yg/dl.
3. probit analysis is an appropriate technique and differs only
slightly from the results obtained from segmented line analysis.
Agency Response
EPA agrees that the segmented line technique provides a more accurate
estimate of the correlation threshold of EP elevation with increasing blood
lead, about 16.7 yg Pb/dl, and for this reason considered changing its
judgments as to the maximum safe blood lead level for a population of children.
However, as the target geometric mean for a population is increased, a greater
percentage of children in the population will exceed the maximum safe individual
level of 30 yg Pb/dl. EPA estimates that at a population geometric mean of
15 yg Pb/dl, 99.5 percent of children will be below 30 yg Pb/dl. At
16.7 yg Pb this percentage falls to 98.7. EPA regards the number of children
predicted to be below 30 yg Pb/dl as the critical health consideration. For
this reason, EPA has maintained its estimate of a geometric mean of 15 yg Pb/dl
as the target for population blood lead.
The Incidence of_ Health Effects in Populations Residing ijn the Vicinity
of_ Industrial Sources of_ Lead Particulate Emissions
Several comments cited situations in which proximity to significant
point sources of airborne lead emissions appear to have little or no
health impact on resident populations. This was taken to imply that the
air standard was not necessary to protect public health.
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Agency Response
EPA acknowledges the variability of the impact of exposure to air lead
on the potential for adverse health consequences. It is clear that
direct exposure to air lead is only one of the routes through which
human exposure occurs. It is for this reason that the Agency has accepted
the concept that only a portion of the safe population mean blood lead
level should be attributable to air lead exposure. The presence or
absence of health effects in an exposed population is influenced by a
variety of factors including: meteorology, terrain characteristics,
geological and anthropological history, personal and domestic hygiene,
the occupations of the population members, and the food and non-food
materials with which they come into contact. Taking into account such
variability, it remains the Agency's belief that airborne lead directly
and indirectly contributes to the risk of adverse health consequences
and that sufficient clinical and epidemiological evidence is available to form
a judgment as to the extent of this contribution. This evidence includes
epidemiological studies showing higher blood lead levels in urban areas
where air lead levels were elevated in comparison to rural areas. There
have also been a number of studies linking elevated blood lead levels to
industrial sources of lead emissions. With regard to the 1972 study at
El Paso, Texas, by the Center for Disease Control, the Criteria Document
reports:
"It was concluded that the primary factor associated with elevated
blood lead levels in the children was ingestion or inhalation of
dust containing lead. Data on dietary intake of lead were not
obtained because 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 and farther away were
significantly different." (p. 12-15)
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With regard to the report of Yankel et. al at Kellogg, Idaho, the Criteria
Document states:
"Five factors influenced, in a statistically significant manner, the
probability of a child developing an excessive blood lead level:
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1. Concentrations of lead in ambient air (yg/m ).
2. Concentration of lead in soil (ppm).
3. Age (years).
4. Cleanliness of the home (subjective evaluation coded 0, 1, and 2,
with 2 signifying dirtiest).
5. General classification of the parents' occupation (dimensionless).
Although the strongest correlation found was between blood lead levels
and air lead level, the authors concluded that it was unlikely that
inhalation of contaminated air alone could explain the elevated blood
lead levels observed." (p. 12-16)
The Appropriate Relationship Between Lead !n_ Air and Lead in^ Blood
Several commenters questioned the Agency's estimate that, for children,
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one microgram of lead per cubic meter air (yg Pb/m ) results in an
increase of two micrograms lead per deciliter blood (pg Pb/dl).
Agency Response:
EPA has reviewed the studies discussed in the criteria document which
report changes in blood lead levels with different air lead levels. The Agency
believes that one of the strongest epidemiological studies is that by Azar et al
in which personal dosimeters were used to measure lead intake. This eliminated
some of the uncertainty about the extent to which air quality observations
accurately reflect actual exposure. From the Azar data, the relationship
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of lead in the air to lead in the blood, evaluated at 1.5 ug Pb/m , was
1:1.8. The Azar study was, however, limited to an adult population.
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A clinical study of adults, Griffin ejt al_, gives roughly the same con-
clusion for a group of adults confined to a chamber with controlled exposure
to lead aerosol. This study was conducted over a three month period with control
over lead ingestion. As air lead levels in the chamber were increased from
3 3
0.15 yg Pb/m to 3.2 yg Pb/m , the air lead to blood lead relationship was
1:1.7.
Because children are known to have greater net absorption and retention
of lead than adults, it is reasonable to assume that the air lead to blood lead
relationship for this sensitive population, exposed to air lead levels in the
range of the proposed standard, is equal to if not greater than for adults.
EPA also notes that the air lead to blood lead relationship is non-linear and
may result in a higher ratio at lower air levels.
In an epidemiological study of children near a smelter, Yankel et al.
the response of blood lead to air lead, averaged over the exposure range, was
1.9. EPA believes that these studies as well as others reported in the Criteria
Document, support the criteria document's conclusion that:
"Ratios between blood lead levels and air lead exposures were shown
to range generally from 1:1 to 2:1. These were not, however, constant
over the range of air lead concentrations encountered. There are
suggestive data indicating that the ratios for children are in the
upper end of the range and may even be slightly above it. There is
also some slight suggestion that the ratios for males are higher
than those for females." (p. 12-38)
The Statistical Form and Period of the Standard
One commenter expressed the view that, due to the lognormal distribution
of measured air lead, a not-to-be-exceeded standard of 1.5 pg/m , calendar
month average, would require sources of air lead to achieve control of their
3
emissions to a geometric monthly mean of 0.41 ug/m in order to prevent the
occurrence of a violation. Another comment expressed the opinion that,
with the normal operation of a six day sampling schedule, the number of
samples which could be collected in the course of a calendar month would not
20
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provide a statistically valid estimate of the actual lead air quality for
the period.
Several comments questioned the health basis for the selection of the
calendar month averaging period.
EPA Response
EPA accepts the consensus of comments received on the scientific and
technical difficulties presented by the selection of a calendar month
averaging period. The Agency believes that the key criterion for the
averaging period is the protection of health of the sensitive population.
3
In proposing the 1.5 yg/m standard, EPA concluded that this air level
as a ceiling would be safe for indefinite exposure of young children. The
critical question in the determination of the averaging period is the
health significance of possible elevations of air lead above 1.5 yg/m
3
which could be sustained without violation of the average of 1.5 yg/m . In
the proposed standard, EPA chose a monthly averaging period on the basis
of a study showing an adjustment period of blood lead level with a
change of exposure (Griffin et al_). Because of the scientific and
technical difficulties of the monthly standard, EPA has reexamined this
question and concludes that there is little reason to expect that the
slightly greater possibility of elevated air lead levels within the
quarterly period is significant for health. This conclusion is based,
on the following points:
(1) from actual ambient measurements, the distribution of air lead
levels is such that where the quarterly standard is achieved,
there is little possibility that there could be sustained
periods greatly above the average value.
21
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(2) while it is difficult to relate the extent to which a monitoring
network actually represents the exposure situation for young children,
it seems likely that where elevated air lead levels do occur, they
will be close to point or mobile sources of lead air pollution.
Typically, young children will not encounter such levels for the
full twenty-four hour period reported by the monitor.
(3) there is medical evidence indicating that blood lead levels
reequilibrate slowly to changes in air exposure. This serves
to dampen the impact of a short-term period of exposure to
elevated air lead.
(4) direct exposure to air is only one of several routes of total
exposure. This lessens the impact of a change in air lead on
blood lead levels.
On balance, the Agency concludes that a requirement for the averaging
of air quality data over calendar quarter will improve the validity of air
quality data gathered without a significant reduction in the protect!veness
of the standard.
The Appropriate Margin of Safety
Several comments received by the Agency criticized the proposed standard
for incorporating an excessive margin of safety. This criticism was based
either on the view that the critical health effect, impaired heme synthesis,
was not of health significance or on the view that EPA had employed
conservative estimates of the several factors used in calculating the
standard which, when combined, resulted in an excessively stringent standard.
22
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Other comments were received which expressed concern that the standard
had little or no margin of safety, particularly for certain subgroups within
the general population of young children.
Agency Response
EPA does not agree that the impairment of heme synthesis is a
physiological response to lead exposure that is without health signifi-
cance. While EPA does not find that this impairment is necessarily
serious to health at the point at which it first can be detected by the
elevation of erythrocyte protoporphyrin, at a threshold in a range of
15-20 yg Pb/dl, the Agency does believe that above blood lead levels of
30 ug Pb/dl this effect has progressed to the extent that it should be re-
garded as an adverse health effect.
In determining the final ambient air standard for lead, EPA has used
margin of safety considerations principally in establishing a maximum safe
blood lead level for individual children at 30 pg Pb/dl and in determining
the percentage of children to be placed below this maximum level, about 99.5
percent. Using these factors, results in a target geometric mean population
blood lead of 15 yg Pb/dl.
In establishing other factors used in calculating the standard, EPA
has used margin of safety in the sense of making careful judgments
based on available data, but these judgments have not been at the pre-
cautionary extreme of the range of data available to the Agency. In the
case of the geometric standard deviation (GSD), studies reviewed in the
criteria document showed a range of 1.3 to 1.5. A standard based on a
1.5 GSD would be far more stringent than using 1.3. EPA took the
23
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1.3, however, because of its concern that the total geometric standard
deviation contains variation attributable to monitoring and analytical
methodology. In estimating the relationship between air lead and blood
lead to be 1:2, the Agency used an epidemiological study of children near
a smelter, Yankel et_._ aj_._, where response of blood lead to air lead
averaged over the exposure range was 1 to 1.9. In adopting 12 pg Pb/dl
as the part of blood lead attributable to non-air sources, EPA is
concerned that typical levels for this component may be much greater, and
that regulatory actions by other public health programs may be necessary
to achieve a 12 pg level.
Because of the variability between individuals in a population ex-
periencing a given level of lead exposure, EPA finds it is impossible
to provide the same amount of margin of safety for all members in the
sensitive population, or to define the margin of safety in the standard as
a simple percentage. EPA does believe that the factors it has used in
designing the standard provide an adequate margin of safety for a large
proportion of the sensitive population. The Agency does not believe
that this margin is excessively large or on the other hand that the air
standard can protect everyone from elevated blood lead levels.
The Importance of_ the Respirable Fraction of Total Air Lead Level
The Agency received a number of comments expressing concern that,
because only a fraction of airborne particulate matter is respirable, an
air standard based on total air lead is unnecessarily stringent.
Agency Response
EPA agrees that some lead particles are too small or too large to be
deposited in the respiratory system. EPA cannot conclude, however, that
24
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particles outside of the respirable range do not represent an exposure
hazard. A significant component of exposure can be ingestion of materials
contaminated by deposition of lead from the air. In addition to the
indirect route of ingestion and absorption from the gastrointestinal
tract, non-respirable lead in the environment may, at some point, become
respirable through weathering or mechanical action. EPA concludes,
therefore, that total airborne lead, both respirable and non-respirable
fractions, should be addressed by the air standard.
The Economi c Impact of the Proposed Standard
A number of commenters were critical of the Agency's Economic Impact
Assessment, and argued that the forecast underestimated the severity of the
economic impact to certain lead industries.
Agency Response
The comments critical of the draft impact statement did not include data
which would allow EPA to confirm the possibility of more severe economic
impacts on certain source categories including primary and secondary lead
smelters which could have difficulty in limiting emissions sufficiently to
assure attaining the standard in their immediate vicinity. Under the Clean Air
Act, the primary responsibility for implementing the standard is assigned to
the States and each State is required to submit a plan to EPA demonstrating
how attainment is to be achieved. The actual economic impacts of implementation
are difficult to estimate at this time since, following promulgation, States
will have nine months to develop and submit these plans to EPA. The plans must
demonstrate attainment as soon as practicable, but no later than three years
following the date of plan approval. However, under certain circumstances, Stat
may request up to a two-year extension of this deadline. Other sections of the
25
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Clean Air Act may be used with the Administrator's discretion to grant further
extensions of compliance deadlines for impacted industrial facilities.
EPA cannot at this time accurately predict the impact of this standard,
but with the timetable in the Act, sees no reason to expect imminent closure
of any facility. The Agency is committed to developing accurate data for
specific plants in cooperation with the industry and State agencies in order
to avoid the imposition of unnecessary controls. EPA's principal concern, however,
must be to follow the mandate of the Clean Air Act relating to the protection of
the public health.
EPA believes that the Economic Impact Assessment is a reasonable
forecast of the economic consequences of implementation of the standard.
The Proposed State Implementation Plan (SIP) Regulations
A summary of comments and the Agency response is included in the preamble
to the final regulations published elsewhere in this Federal Register.
The Federal Reference Method for Monitoring Lead Air Qua!ity
A summary of comments and the Agency's disposition is included in the
preamble to the final method published elsewhere in this Federal Register.
The Administrative Procedures Employed by_ EPA in_ the Development of the
Proposed Standard and the Provision for Public Participation
Two commenters requested that cross examination of witnesses be
allowed in the post-proposal public hearing on the proposed standard and
implementation regulations. EPA also received a request to postpone the public
hearing and to e-xtend the comment period, citing the need to complete ongoing
studies.
26
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Agency Response
Both the request for cross-examination and the extension of the comment
period were denied by the Agency. With regard to the request for cross-
examination, the Agency determined that, in light of the extensive review
already conducted, cross-examination was not likely to produce new
information or results that would justify such a significant departure from
the normal rulemaking process. Also the existence of the normal comment
period was sufficient to allow interested members of the public to raise
questions concerning the Agency's determinations. Further, due to the
extensive review opportunities available at all stages of the regulatory
development, an extension of the comment period was not believed to be
sufficiently necessary to further delay the schedule for preparation of
the final rule.
Clarification of_ Elements of_ the_ Standard
From reviewing the comments received, EPA wishes to clarify the following
points in the presentation of the rationale for the final standard:
(1) EPA is making a distinction between the blood lead level that
is the threshold for detection of the biological effect, impaired
heme synthesis, and the blood lead level at which this effect
has progressed to an extent that it is regarded as
adverse to health.
(2) EPA is making a distinction between estimating a maximum safe
blood lead level for an individual child, and establishing a
population target geometric mean blood lead level for the
sensitive population.
(3) EPA is making a distinction between what the contribution to
blood lead levels from non-air sources actually may be, and
attributing a contribution from non-air sources for the purpose
of standard-setting.
27
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DERIVATION OF THE NUMERICAL LEVEL OF THE FINAL STANDARD
EPA's objective in setting the level of the standard is to estimate
the concentration of lead in the air to which all groups within the general
population can be exposed for protracted periods without an unacceptable
risk to health.
This estimate is based on EPA's judgment in four key areas:
(1) determining the "sensitive population" as that group within
the general population which has the lowest threshold for adverse
effects or greatest potential for exposure. EPA concludes
that young children, aged 1-5, are the sensitive population.
(2) determining the safe level of total lead exposure for the
sensitive population, indicated by the concentration of lead in the blood.
EPA concludes that the maximum safe level of blood lead for an
individual child is 30 yg Pb/dl and the'- population blood lead,
measured as the geometric mean, must be 15 yg Pb/dl in order to
place 99.5 percent of children in the United States below
30 yg Pb/dl.
(3) attributing the contribution to blood lead from non-air pollution
sources. EPA concludes that 12 yg Pb/dl of population blood
lead for children should be attributed to non-air exposure.
(4) determining the air lead level which is consistent with main-
tainining the mean population blood lead level at 15 yg Pb/dl.
Taking into account exposure from other sources (12 yg Pb/dl)
EPA has designed the standard to limit air contribution after
28
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achieving the standard to 3 yg Pb/dl. On the basis of an estimated
relationship of air lead to blood lead of 1 to 2, EPA concludes
3
that the ambient air standard should be 1.5 ug Pb/m .
Each of these four areas is discussed further in the following sections.
SENSITIVE POPULATION
EPA believes that the health of young children is at particular risk from
lead exposure. This is because children have a greater physiological
sensitivity to the effects of lead than do adults and may have greater
exposure to environmental lead from playing in contaminated areas. Other
sensitive populations identified by EPA include those occupationally
exposed, and pregnant women and their fetuses. Comments received on the
proposed standard did not challenge EPA's position that young children
are the most sensitive population for determining the standard. A
number of comments did point out that within the general population of
children there were subgroups with enhanced risk due to genetic factors,
dietary deficiencies, or residence in urban areas. EPA acknowledges the
higher risk status of such groups but does not have information either
in the air quality criteria or in the comments received for estimating a
threshold for adverse effects separate from that of all young children.
Concern about these high risk subgroups has, however, influenced EPA's
determination of the percentage of the population of children (99.5
percent) to be maintained below 30 yg Pb/dl.
EPA continues to be concerned about the possible health risk of
lead exposure for pregnant women and their fetuses. The stress of
pregnancy may place pregnant women in a state more susceptible to the
29
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effects of lead, and transplacental transfer of lead may effect the
prenatal development of the child. There is, however, insufficient
scientific information for EPA to either confirm or dismiss this sug-
gestion, or to establish that pregnant women and fetuses are more at
risk than young children.
THE MAXIMUM SAFE EXPOSURE FOR CHILDREN
In determining the maximum safe exposure to lead for children, EPA has
taken the measurement of blood lead as the indicator of total lead dose.
There are other possible indicators of exposure, for example the level
of zinc protoporphyrin (ZPP), but most health studies reported in the
criteria document utilize blood lead levels as indications of the mobile
body burden of lead. The criteria document reports the following table
of effect thresholds for children with increasing blood lead levels.
Summary of Lowest Observed Effee4 Levels in Young Children
S-ALAD inhibition 10 yg Pb/dl
Erythrocyte protoporphyrin elevation 15-20 yg Pb/dl
Increased urinary 6-ALA excretion 40 yg Pb/dl
Anemia 40 yg Pb/dl
Coproporphyrin elevation 40 yg Pb/dl
Cognitive (CNS) deficits 50-60 yg Pb/dl
Peripheral neuropathies 50-60 yg Pb/dl
Encephalopathic symptoms 80-100 yg Pb/dl
(p. 13-8)
The first physiological effect associated with increasing blood lead levels
is the inhibition of the enzyme 6-aminolevulinic acid dehydratase
(6-ALAD), both in red blood cells (erythrocytes), and in cells in other
tissues. This enzyme catalyzes the condensation of two molecules of
6-aminolevulinic acid (6-ALA) to form porphobilinogen, one of the components
involved in the cellular synthesis of heme. The criteria document reports
that the threshold for 6-ALAD inhibition in children is 10 yg Pb/dl.
30
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At blood lead levels above 10 yg Pb/dl, the function of 6-ALAD is
increasingly inhibited by lead. The criteria document states that
40 yg Pb/dl is the threshold for elevation of 6-ALA recognized as
6-ALA in the urine or 6-ALA-U, an indication that 6-ALA has begun to
accumulate in cells.
EPA does not regard the inhibition of 6-ALAD above 10 yg Pb/dl
as adverse to health because of the absence of evidence that there is
an impairment of heme synthesis until a threshold of 40 yg Pb/dl is reached.
The accumulation of 6-ALA above normal levels, indicated by 6-ALA-U,
is regarded as adverse to health, both because of impaired heme synthesis,
and the possibility that 6-ALA accumulation is itself toxic to cells.
The criteria document reports that above a threshold of 15-20 yg Pb/dl
there is an elevation of protoporphyrin in erythrocytes. Protoporphyrin
is an organic chemical compound used by all cells in the production of
heme. In the final stage of heme synthesis, erythrocyte protoporphyrin
(EP) and iron are brought together in the cell mitochondria. In the
presence of lead, this step is blocked, possibly by inhibition of the
enzyme ferrochelatase or by interference in the transport of iron across
the mitochondria! membrane. Without incorporation into heme, the levels
of protoporphyrin in the cell become elevated.
From review of the information provided by the air quality criteria
document as well as the evidence and arguments offered by medical pro-
fessionals commenting on the proposed standard, EPA has concluded that
the effects of lead on the cellular synthesis of heme, as indicated by
31
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elevated erythrocyte protoporphyrin, are potentially adverse to the health of
young children. This appears, however, to be a question of the degree to which
the effect has progressed. EPA does not believe that there is significant
risk to health at the point where the elevation of EP can first be correlated
with an increase in blood lead (15 to 20 yg Pb/dl). On the other hand, EPA
regards as clearly adverse to health the impairment of heme synthesis, and
other effects of lead which result in clinical symptoms of anemia above
40 yg Pb/dl. These effects are followed quickly by the risk of nervous
system deficits for some children with blood lead levels of 50 yg Pb/dl.
EPA has concluded that the maximum safe blood lead level for an
individual child is 30 yg Pb/dl. This is based on the following factors:
(1) the maximum safe blood lead level should be somewhat lower
than the threshold for a decline in hemoglobin levels (40 yg Pb/dl).
(2) the maximum safe blood lead level should be at an even greater
distance below the threshold for risks of nervous system deficits
(50 ug Pb/dl).
(3) the maximum safe blood lead level should be no higher than the
blood lead range characterized as undue exposure by the Center
for Disease Control of the Public Health Service, as endorsed by
the American Academy of Pediatrics, because of elevation of
erythrocyte protoporphyrin (above 30 yg Pb/dl).
(4) the maximum safe blood lead level for an individual need not
be as low as the detection point for the initial elevation of
EP (15-20 yg Pb/dl).
The criteria document points out that data from epidemiological
studies show that the log values of measured individual blood lead values
in a uniformly-exposed population are normally distributed with a geometric
32
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standard deviation (GSD) of 1.3 to 1.5. Using standard statistical techniques,
it is possible to use the geometric standard deviation to calculate the mean
population blood lead level which vould place a given percentage of the
population below the level of an effects threshold. A GSD of 1.5 would result
in a lower geometric mean, and a more stringent standard. However, because
some of the variability in the GSD is from measurement systems, EPA has used
a GSD of 1.3.
Recently, analysis of the data collected by New York City's Bureau of
Lead Poisoning has shown that populations of children in the New York area
consistently have distributions of blood lead values with a GSD of 1.4 to
1.5. With a geometric mean of 15.0 yg Pb/dl, a GSD of 1.4 results in about
two percent of the population over levels of 30 yg Pb/dl. A GSD of 1.5
would place more than four percent over 30 yg Pb/dl. EPA is concerned
that such results may imply that the standard is not as precautionary as it
would be if the actual GSD is 1.3. However, the Agency's best estimate is
that some of the GSD is from analytical and monitoring variance, and for
this reason, EPA is using the 1.3 value in calculating the final standard.
In EPA's view, use of the 99.5 percent range is not excessive. From
1970 statistics, there are approximately 20 million children in the
United States below the age of 5 years, 12 million in urban areas, and 5
million in center cities where lead exposure may be high. Again,
knowledge that there are special high risk groups of children within the
general population deters EPA from considering lower percentages.
CONTRIBUTION TO TOTAL LEAD EXPOSURE FROM NON-AIR SOURCES
In the proposed standard, EPA argued that the air standard should take
into account the contribution to blood lead levels from lead sources unrelated
to air pollution. No comments were received challenging this argument.
EPA continues to base its calculation of the ambient air standard on the
33
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assumptions that, to an extent, the lead contribution to blood lead from non-
air sources should be subtracted from the estimate of safe mean population
blood lead. Without this subtraction, the combined exposure to lead from
air and non-air sources would result in a blood lead concentration exceeding
the safe level.
EPA notes that the level of the standard is strongly influenced by
judgments about non-air contribution to total exposure, and that there
are difficulties in attempting to estimate exposure from various lead
sources. Studies reviewed in the Criteria Document do not provide detailed
or widespread information about the relative contribution of various sources
to children's blood lead levels. Estimates can only be made by inference
from other empirical or theoretical studies, usually involving adults.
Also, it can be expected that the contribution to blood lead levels from
non-air sources can vary widely, is probably not in constant proportion
to air lead contribution, and in some cases may alone exceed the target
mean population blood lead level.
In spite of these difficulties, EPA has attempted to assess available
information in order to estimate the general contribution to population
blood lead levels from air and non-air sources. This has been done with
evaluation of evidence from general epidemiological studies, studies showing
decline of blood lead levels with decrease in air lead, studies of blood lead
levels in areas with low air lead levels, and isotopic tracing studies.
Studies reviewed by the Criteria Document show that the geometric mean
blood lead levels for populations of children are frequently above 15 yg Pb/dl.
In studies reported, the range of mean population blood lead levels for
children was from 16.5 yg Pb/dl to 46.4 yg Pb/dl with most studies showing
mean levels greater than 25 yg Pb/dl (Fine, 1972; Landrigan, 1975; von
Lindern, 1975). EPA believes that, for many of these populations, the contri-
bution to blood lead levels from non-air sources may exceed the desired
target mean blood lead level.
34
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In a number of studies, reduction in air lead levels resulted in a
decline in children's blood lead levels. A study of blood lead levels in
children in New York City showed that children's mean blood lead levels
declined from 30.5 ug Pb/dl to 21.0 yg Pb/dl from 1970 to 1976, while during
the same period air lead levels at a single monitoring site fell from 2.0 yg Pb/dl
to 0.9 yg/Pb (Billick, 1977). Studies at Omaha, Nebraska (Angle, 1977) and
Kellogg, Idaho (Yankel, von Lindern, 1977) also show a drop in mean blood lead
levels with declines in air lead levels. As air lead levels decline there
appears to be a rough limit to the drop in blood lead levels.
EPA has also examined epidemiological studies in the Criteria Document where
air lead exposure is low, and can be assumed to be a minor contributor to blood
lead. These studies provide an indication of blood lead levels resulting from
a situation where non-air sources of lead are predominant.
Studies Reporting Blood Lead Levels in Children Exposed to Moderate to Low
Air Lead Levels
Investigator
Blood lead (in
micrograms of
lead per
deciliter)
Air lead (in
micrograms of
lead per cubic
meter)
Comment
Hammer ,
Angle,
1972
1974
Goldsmith, 1974
Johnson
, Tillery, 1975
11.
14.
13.
10.
6
4
7
2
0.
0.
0.2 -
0.3 -
0.
1
14
0.7
0.6
6
Children
Montana
Suburban
ages 1 to
Children
Children
in
Helena,
children
4 in Omaha
in
in
Benecia,
Crocket,
CA
CA
Female children - mean
age 9 in Lancaster, CA
35
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The range of mean blood lead levels in those studies is from 10.2 yg Pb/dl
to 14.4 pg Pb/dl, with an average at 12.7 yg Pb/dl.
In addition to epidemiological investigations, EPA has reviewed studies
that examine the source of blood lead by detecting characteristic lead
isotopes. A study using isotopic tracing (Manton, 1977) suggests that for
several adults in Houston, Texas, 7 to 41 percent of blood lead could be
attributed to air lead sources. An earlier isotopic study (Rabinowitz, 1974)
concluded that for two adult male subjects studied, approximately one-third
of total daily intake of lead could be attributed to exposure to air lead
levels of 1-2 yg Pb/m . While these results cannot be directly related to
children, it is reasonable to assume that children may exhibit the same or
higher percentages of air lead contribution to blood lead level because of
a greater potential for exposure to indirect air sources, soil and dust.
From reviewing these areas of evidence, EPA concludes that:
1. In studies showing mean blood lead levels above 15 yg Pb/dl, it
is probable that both air and non-air sources of lead contribute significantly
to blood lead with the possibility that contributions from non-air sources
exceed 15 yg Pb/dl.
2. Studies showing a sustained drop in air lead levels show a correspond-
ing drop in blood lead levels, down to an apparent limit in the range of
10.2 to 14.4 yg Pb/dl.
3. Isotopic tracing studies show air contribution to blood lead to
be 7-41 percent in one study and about 33 percent in another study.
In considering this evidence, EPA notes that if, from the isotopic
studies, approximately two-thirds of blood lead is typically derived from
non-air sources, a mean blood lead target of 15 yg Pb/dl would attribute
36
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10 yg Pb/dl to non-air sources. On the other hand, the average blood lead
level from the limited studies available where air exposure was low is
12.7yg Pb/dl. In the absence of more precise information, EPA is cal-
culating the lead standard based on the attribution of 12 yg Pb/dl of the
blood lead level in children to lead sources unaffected by the lead air quality
standard. EPA is aware that actual population blood lead levels, either
individually or as a population mean, may exceed this benchmark. However,
if EPA were to use a larger estimate of non-air contribution to blood lead,
the result would be an exceptionally stringent standard, which would not
address the principal source of lead exposure.
THE RELATIONSHIP BETWEEN AIR LEAD EXPOSURE AND RESULTING BLOOD LEAD LEVEL
EPA has reviewed the studies discussed in the criteria document
which report changes in blood lead levels with different air lead levels.
The Agency believes that one of the strongest epidemiological studies is
that by Azar ejt;al_ which used personal dosimeters to measure lead intake.
Tins eliminated some of the uncertainty about the extent to which air quality
observations accurately reflect actual exposure. From the Azar data, the
3
relationship of lead in the air to lead in the blood, evaluated at 1.5 yg Pb/m ,
VKIS 1:1.8. The Azar study was, however, limited to an adult population.
A clinical study of adults, Griffin ejt al_, gives roughly the same
conclusion for a group of adults confined to a chamber with controlled ex-
posure to lead aerosol. This study was conducted over a three month period
with control over lead ingestion. As air lead levels in the chamber were
3 3
increased from 0.15 yg Pb/m to 3.2 yg Pb/m , the air lead to blood lead
relationship was 1:1.7.
37
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Because children are known to have greater net absorption and retention
of lead than adults, it is reasonable to assume that the air lead to blood
lead relationship for this sensitive population, exposed to air lead levels
in the range of the proposed standard, is equal to if not greater than
for adults. EPA also notes that the air lead to blood lead relationship
is non-linear which will result in a higher ratio at lower air levels.
In an epidemiological study of children near a smelter, Yankel e^t a!,
the response of blood lead to air lead, averaged over the exposure range,
was 1.95. This study provided information on the relationship of blood lead
to air lead over a very large range of air lead values. The air lead values
in the study are the result of a model calibrated by monitoring data. The
relative error of the individual values, especially in the low range is larger
than in the AZAR study.
The authors of the study, Yankel and von Lindern, chose a log-linear model
which provided a good fit to the data and gave an estimated slope of about
1.2 at an air lead of 1.5. However, EPA sees a problem with a log-linear
model in that it forces a lower slope at low air lead values and a higher slope
at higher lead values. This is in direct contradiction to the AZAR and the
Griffin studies, both of which indicate higher slopes at lower air lead values.
Because of the uncertainties in the low air lead values in the Idaho study,
EPA felt that the calculation of an average slope or ratio over the entire range
of data would be a moderate compromise. The calculation of an average slope
gives a value of 1.95. EPA believes that these studies as well as others
reported in the Criteria Document support the document's conclusion that:
38
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"ratios between blood lead levels and air lead exposures were shown to
range generally from 1:1 to 2:1. These were not, however, constant over
the range of air lead concentrations encountered. There are suggestive
data indicating that the ratios for children are in the upper end of the
range and may even be slightly above it. There is also some slight
suggestion that the ratios for males are higher than those for females."
(p. 12-38)
CALCULATION OF THE AIR STANDARD
EPA has calculated the standard based on the conclusions reached in the
previous sections;
1. Sensitive population: children, ages 1-5.
2. Health basis: maximum safe blood lead level for individual children
is 30 yg Pb/dl based on concern for impaired heme synthesis above
30 yg Pb/dl and margin of safety for anemia above 40 ug Pb/dl and
nervous system deficits above 50 ug Pb/dl.
3. Maximum safe geometric mean blood lead for children
based on placing 99.5 percent of the sensitive population
below the 30 yg/dl level of concern: 15 yg Pb/dl.
4. Estimate of blood lead level attributed to non-air sources: 12 yg Pb/dl
5. Allowable contribution to blood lead from air sources after
achieving the standard: 15 yg Pb/dl - 12 yg Pb/dl = 3 yg Pb/dl.
6. Air lead concentration consistent with blood lead contribution
from air sources:
3 yg Pb/dl x 1 yg Pb/m3 air = 1.5 yg Pb/m3
2 yg Pb/dl blood
SELECTION OF THE AVERAGING PERIOD FOR THE STANDARD
Based on comments received and consideration by the Agency, the
proposed averaging period of a calendar month is extended to a calendar
quarter. EPA believes that this change will significantly improve the
validity of lead air quality data which will be gathered to monitor progress
towards attainment without placing an undue burden on State and local
environmental agencies, or significantly reducing the protectiveness of
39
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the standard.
The Agency believes that the key criteria for the averaging period
is the protection of the health of the sensitive population. In proposing
3
the 1.5yg Pb/m standard, EPA concluded that this air level was safe
for young children with an indefinite exposure period. The critical
factor in the determination of the averaging period is the health significance
of possible elevations of air lead above 1.5 yg Pb/m which could be
encountered for short periods without causing average levels to exceed
the standard. In the proposed standard, EPA chose a calendar month averaging
period on the basis of a study (Griffin et^ al_J showing an adjustment
period of blood lead level with a change in exposure. Because of the
scientific and technical difficulties of the monthly standard, EPA has
reexamined this question and concluded that there is little reason to
expect that the slightly greater possibility of elevated air lead levels
sustainable by the calendar quarter standard is significant for health.
This conclusion is based on the following factors:
(1) from actual ambient measurements, there is evidence that the
distribution of air lead levels is such that if the quarterly
average was achieved there is little possibility that there
could be sustained periods greatly above the average value.
(2) while it is difficult to relate the extent to which a monitoring
network actually represents the exposure situation for young
children, it seems likely that where elevated air lead levels
do occur, they will be close to point or mobile sources. Typically,
young children will not enccunter such levels for the full
twenty-four hour period reported by the monitor.
(3) there is medical evidence indicating that blood lead levels
reequilibrate slowly to changes in air exposure. This serves to
40
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dampen the impact of a short-term period of exposure to elevated
air lead.
(4) direct exposure to air is only one of several routes of total
exposure. This lessens the impact of a change in air lead on
blood lead levels.
On balance, the Agency concludes that a requirement for the averaging
of air quality data over a calendar quarter will improve the validity of
air quality data gathered without a significant reduction in the pro-
tectiveness of the standard.
MARGIN OF SAFETY
The Clean Air Act instructs EPA to set the level of an ambient air
quality standard at a level which protects the public health with a margin
of safety. One approach to using margin of safety is to estimate the
air concentration of a pollutant that is the threshold for the first
adverse effect detected with increasing air levels, and then set the
air standard at a somewhat lower level. The extent of the safety margin between
the standard and the estimated threshold for adverse effects is influenced
by such factors as the severity or irreversibility of effects, the degree of
uncertainty about known or suspected health effects, the size of the popula-
tion at risk, and possible interactions of several pollutants in potentiating
health effects. While the margin of safety is based on available scientific
information, this factor is judgmental in that the Administrator must weigh
the acceptability of estimated risk.
Estimating an appropriate margin of safety for the air lead standard
is complicated by the multiple sources and media for lead exposure.
Because of this, EPA has elected to use margin of safety considerations in
estimating the maximum safe level for blood lead, and the percentage of the
sensitive population to be placed below this level, rather than making
a final adjustment to concentration of lead in the air. EPA has adopted
41
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30 vg Pb/dl as the maximum safe blood lead level for individual children,
and the air standard is calculated to maintain most children below this
target. On the basis of information developed in the criteria document
and from public comment, blood lead levels between 30 and 40 yg Pb/dl
are associated with impairments of the heme synthetic pathway which EPA
regards as adverse to health. Blood lead levels above 40 yg Pb/dl are
associated with a decline in hemoglobin levels, and levels above 50 yg
Pb/dl are associated with the risk of nervous system deficits for some
children. With a geometric mean population blood of 15 yg Pb/dl lead,
most children will be well below these thresholds, but a small percentage
can be expected to have blood lead levels of concern.
Because of the variability between individuals in a population experiencing
a given level of lead exposure, EPA finds that it is not possible to provide
the same amount of margin of safety for all members in the sensitive population,
or to define a margin of safety in this standard -s a simple percentage. In
developing the numerical level of the standard, EPA used evidence in the Criteria
Document that the blood lead levels for individuals in a given population of
children are log-normally distributed. The statistical properties of this dis-
tribution make it possible to calculate the percentage of the population which
will fall below any given blood lead level. Individuals at each of these
levels would have a different margin of safety below the maximum safe blood
lead level. As a rough example, with a population of children with a geometric
mean blood lead of 15 yg Pb/dl, 86 percent of the children would be below
20 yg Pb/dl, 97.5 percent would be below 25 yg Pb/dl and 99.5 percent would
be below 30 yg Pb/dl. Assuming a population of children in central urban areas
where air lead was at the standard level, 693,000 children would be over
20 yg Pb/dl, 126,500 over 25 yg Pb/dl, and 20,605 above 30 yg Pb/dl.
42
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In determining the appropriate margin of safety, the Agency has also
included consideration of the following factors:
(1) in addition to the health effects discussed, the "Air Quality
Criteria for Lead" report multiple biological involvements of
lead in practically all cell types, tissues, and organ systems.
The significance for health of these has not been fully studied.
(2) there are no beneficial effects of lead at current environmental
levels.
(3) EPA has incomplete data about the extent to which children are
indirectly exposed to lead from air lead which moves to other
environmental media, such as water, soil and dirt, and food.
(4) lead is chemically persistent and with continued uncontrolled emissions
will continue to accumulate both in human tissue and in the
environment.
(5) there is a possibility that lead exposure resulting in blood lead
levels previously considered safe may in fact influence the
neurological development and learning abilities of the young
child. EPA does not have evidence, however, that provides
more than a suggestion that this could occur at blood lead levels
below 30 Pb/dl for individual children.
Impact of Lead Dustfall on Blood Lead
In the preamble for the proposed air standard for lead, EPA pointed
out that the significance of dust and soil lead as indirect routes of exposure
has been of particular concern in the case of young children. Play habits
and mouthing behavior between the ages of one and five have led to the
conclusion that greater potential may exist in these children for ingestion
and inhalation of the lead available in contaminated dust and soil. EPA is
also concerned that the deposition of lead particles can lead to general
43
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contamination of the environment and increased lead exposure from surface
waters and foodstuffs.
Studies reviewed in the Criteria Document indicate a correlation between
soil and dust levels and childrens1 blood lead levels in highly contaminated
environments (Yankel and von Lindern, 1977; Barltrop, 1974; Galke, in press).
The lead threshold for concern has been reported as 1,000 parts per million (ppm)
in soil (Yankel and von Lindern, 1977). At levels of between 500 and 1,000 ppm
soil, the Criteria Document concludes that blood lead levels begin to increase.
A two-fold increase in soil concentration in this range is predicted to result in
a 3-6 percent rise in blood lead levels. Below 500 ppm lead in soil,
no correlation has been observed with blood lead levels.
The normal background for lead in soil is cited in the Criteria Document
as 15 ppm. Due to human activities, the average levels in most areas of the
U.S. are considerably higher. Soil studies conducted by EPA's Office of
Pesticides Programs from 1974-1976 in 17 urban areas reported only 3 cities
with arithmetic mean concentrations in excess of 200 ppm, with the highest
value 537 ppm. Concentrations in the soils surrounding large point sources
of lead emissions, or heavily-travel led roads may reach many thousand ppm.
Because of the many factors involved, EPA is unable to predict the
relationship between air lead levels, dustfall rates, and resulting soil
accumulation. Complicating factors include: particle size distribution,
rain-out, other meteorological factors, topographical features affecting
deposition, and removal mechanisms.
EPA believes, however, that significant impacts on blood lead of
soil and dust lead are mainly limited to areas of high soil concentration
(in excess of 1,000 ppm) around large point sources and heavily- travelled roads.
Evidence suggests that soil lead levels in areas with air lead levels in the
range of the standard are below the threshold for lead health impact
44
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(Johnson, Tillery, 1975; Johanson, 1972; EPA, 1975 Air Quality Data and
Soil Levels).
Comments received on the proposed standard argued that the lead air
standard should be limited to respirable size lead particulate matter, as
larger particles would fall to the ground without being deposited or absorbed
in the lung. EPA has decided not to accept this recommendation because, as
discussed above, larger particles can contribute to lead dose by human
ingestion of airborne particles, by contamination of other environmental
media, or by eventual reduction to respirable size by mechanical action or weathering.
WELFARE EFFECTS
Comments received on the proposed lead air quality standard did not
address the issue of welfare effects or the need for a secondary air
quality standard more restrictive than the primary standard. EPA maintains
its position that the primary air quality standard will adequately protect
against known and anticipated adverse effects on public welfare. EPA does not
have evidence that a more restrictive secondary standard would be justified.
Available evidence cited in the criteria document indicates that animals
do not appear to be more susceptible to adverse effects from lead than man,
nor do adverse effects in animals occur at lower levels of exposure than
comparable effects in humans.
Lead is absorbed but not accumulated to any great extent by
plants from soil. Lead is either unavailable to plants or is fixed in
the roots and only small amounts are transported to the above ground portions.
Lead may be deposited on the leaves of plants and present a hazard to grazing
animals. Although some plants may be susceptible to lead in the natural
environment, it is generally in a form that is largely non-available to them.
There is no evidence to indicate that ambient levels of lead result
in significant damage to man-made materials. Effects of lead on
visibility and climate are minimal.
45
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Based on such data, EPA promulgates the secondary air quality standard
3
for lead at 1.5 yg Pb/m , calendar quarter average.
ECONOMIC IMPACT ASSESSMENT
As required by Executive Orders 11821 and 12044, EPA has conducted
a general analysis of the economic impact which might result from the
implementation of the lead regulations. This analysis was not intended
for nor was it used in the development or promulgation of the standard,
and was issued for informational purposes only.
The Economic Impact Assessment points out that the categories of
sources likely to be affected by control of lead emissions are primary
lead and copper smelters, secondary lead smelters, gray iron foundries,
gasoline lead additive manufacturers, and lead storage battery manufacturers.
This analysis further indicates that some primary and secondary lead
smelters and copper smelters may be severely strained economically in
achieving emission reductions that may be required in -.implementing the
proposed air quality standard.
There are, however, uncertainties associated with evaluating the
impact of attaining the standard. For smelters and foundries, attaining
the standard may require control of fugitive lead emissions, i.e., those
emissions escaping from individual process operations, other than emissions
from smoke stacks. Fugitive emissions are difficult to estimate, measure,
and control; and it is also difficult to predict their impact on air quality
near the facility. From the information available to EPA, non-ferrous
smelters may have great difficulty in achieving lead air quality levels
consistent with the proposed standard in areas immediately adjacent to
the smelter complex.
The change in averaging time from a monthly average to a calendar quarter
average will affect the economic impacts associated with the lead standard because
for a given level of the standard, a longer averaging period is theoretically less
stringent than a shorter averaging period.
46
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OTHER LEAD REGULATORY AND CONTROL PROGRAMS
EPA's ambient air quality standard is only one of a number of Federal,
State, and local programs designed to limit exposure to lead.
In 1975, EPA promulgated the national interim primary drinking water
regulation, setting a maximum contaminant level for lead. The standard, aimed
at protecting children from undue lead exposure, was set at 50 yg Pb/liter.
In 1977, the National Academy of Sciences concluded that a lead level at which
adverse health effects are observed cannot be set with assurance at any
value greater than 25 yg Pb/liter. The Office of Drinking Water is currently
considering the need to revise the interim drinking water standard for lead.
Based on its toxicity, EPA has included lead on its list of priority
water pollutants for which effluent guidelines are being developed under the
Clean Water Act. Effluent guidelines are being developed for lead for
non-ferrous smelters, based on achievement of best available technology.
EPA's Office of Pesticide Programs has promulgated regulations based
on the toxicity of lead which require the addition of coloring agents to
the pesticide lead arsenate and specify disposal procedures for lead
pesticides. Use of lead in pesticides is a small and decreasing proportion
of total lead consumption in the U.S.
The Resource Conservation and Recovery Act (RCRA) of 1976, through which
EPA is to establish standards on how to treat, dispose, or store hazardous
wastes, provides a means for specifying how used crankcase oil and other
waste streams containing lead should be recycled or safely disposed of.
47
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Regulatory actions related to wastes containing lead are currently
being developed under Subtitle C of RCRA.
EPA has regulations for reducing the average lead content in the total
gasoline pool to 0.5 grams/gallon by October 1, 1979, and regulations
providing for lead-free gasoline required for cars equipped with catalytic
converters and other vehicles certified for use of unleaded fuel. The
former regulations are based on reducing exposure to airborne lead to
protect public health. Other EPA actions which result in the reduction
of airborne lead levels include ambient standards and State implementation
plans for other pollutants such as particulate matter and sulfur dioxide
and new source performance standards limiting emissions of such pollutants.
Existing and new sources of particulate matter emissions generally use
control techniques which reduce lead emissions as one component of
particulate matter.
The Occupational Safety and Health Administration proposed regulations
3
in 1975 to limit occupational exposure to lead to 100 yg Pb/m , 8-hour
time-weighted average. The exposure limit was based on protecting
against effects, clinical or subclinical, and the mild symptoms which
may occur below 80 yg Pb/dl, providing an adequate margin of safety.
3
The level of 100 yg Pb/m is anticipated to limit blood lead levels in
workers to a mean 40 yg Pb/dl and a maximum of 60 yg Pb/dl. OSHA is
presently reviewing the latest information on lead exposure and health
effects in preparation for promulgation of the workplace standard for
lead.
The Department of Housing and Urban Development (HUD) has requirements
for reducing human exposure to lead through the prevention of lead
poisoning from ingestion of paint from buildings, especially residential
dwellings. Their activities include (1) prohibition of the use of lead-based
48
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paints on structures constructed or rehabilitated through Federal funding
and on all HDD-associated housing; (2) the elimination of the immediate
hazard from lead-based paint; (3) notification of purchases of HUD-
associated housing constructed prior to 1950 which may contain lead-
based paint; and (4) research activities to develop improved methods of
detection and elimination of lead-based paint hazards, and the nature
and extent of lead poisoning.
The Consumer Product Safety Commission (CPSC) promulgated regulations
in September 1977 which ban: (1) paint and other surface coating materials
containing more than 0.06 percent lead; (2) toys and other articles intended
for use by children bearing paint or other similar surface coating
material containing more than 0.06 percent lead; and (3) furniture coated
with materials containing more than 0.06 percent lead. These regulations
are based on CPSC's conclusion that it is in the public interest to reduce
the risk of lead poisoning to young children from ingestion of paint and
other similar surface-coating materials.
The Food and Drug Administration (FDA) adopted in 1974 a proposed
tolerance for lead of 0.3 ppm in evaporated milk and evaporated skim
milk. This tolerance is based on maintaining children's blood lead
levels below 40 pg Pb/dl. FDA has also proposed an action level of 7
ug Pb/ml for Teachable lead in pottery and enamelware, although the
exact contribution of such exposure to total human dietary intake has
not been established.
The Center for Disease Control (CDC) concluded in 1975 that undue
or increased lead absorption exists when a child has confirmed blood
lead levels of 30-70 ug Pb/dl or an EP elevation of 60-189 yg Pb/dl
except where the elevated EP level is caused by iron deficiency.
49
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In developing the lead air standard, EPA has estimated both individual
and population blood lead levels which it regards as safe targets. The
Agency believes that these targets do not necessarily serve as precedents
for other regulatory programs. There are three reasons for this view:
(1) these targets were selected on the basis of what the Clean
Air Act requires. Other programs have other legislative requirements
which would lead to adoption of different but equally legitimate goals.
(2) the scientific data provided by the air quality criteria allow
comparison of air levels with blood lead levels, but analagous
information is not available for other media. At this time, there
does not appear to be the same extent of information about the
impact on blood lead of lead in food, water, and non-food ingested
items. Because of this, FDA, CPSC and other EPA standards have
been based on estimates of acceptable daily c'jse rather than on
blood lead targets.
(3) studies currently underway may provide new information relevant
to estimating safe levels of lead exposure.
COMMENTS BY OTHER FEDERAL AGENCIES
Comments on the proposed lead air quality standard were received from
eight Federal agencies. Five of the agencies endorsed the air standard
while three of the agencies commented on specific issues and neither endorsed
nor opposed the standard. The Center for Disease Control and the U.S.
Public Health Service voiced support for the proposed standard of 1.5 yg Pb/m
and urged basing the decision on the standard solely on considerations of public
health. CDC is fully satisfied that EP elevation does indeed
represent a subclinica"! manifestation of lead toxicity and that young
50
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children are the population most at risk from lead exposure, while some
subgroups of children are at special risk to lead because of conditions
such as malnutrition, genetic factors, or iron deficiency.
The Consumer Product Safety Commission endorsed the approach and
some of the judgments made in arriving at the proposed air standard. CPSC
concurred with the position that children are the population at enhanced
risk to lead exposure, and that the goal of a mean population blood
lead level for children of 15 yg Pb/dl is sufficiently low to be protective
of the population at enhanced risk of exposure. CPSC views the selection
of EP elevation as the adverse health effect of concern as open to challenge
and suggests basing the standard on a more generally recognized severe health
effect. CPSC concurs that the contribution of non-air sources to lead body
burden must be evaluated in setting the air standard and suggests that a
larger non-air contribution, such as 13.5 yg Pb/dl used in the California
standard, might be considered.
The Food and Drug Administration commended EPA's proposal of an ambient
air quality standard for lead. FDA agrees that children aged 1-5 years
old comprise the most critically sensitive population. FDA concurs that
15 yg Pb/dl is a reasonable maximum blood lead level to use as an average
national goal for children aged 1 to 5, although FDA suggests that for young
children the margin of safety is disturbingly narrow. The division of the
15 yg Pb/dl into 12 yg Pb/dl for non-air sources and 3 yg Pb/dl for air
sources was not unreasonable in FDA's view.
The Occupational Safety and Health Administration endorsed EPA's
proposed standard for lead and agrees with EPA that 15 yg Pb/dl as an
average national blood lead level goal for young children is reasonable.
3
OSHA views their proposed standard of 100 yg Pb/m , 8-hour time-weighted
51
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average, and their establishment of 40 pg Pb/dl as the threshold effect
level for workers as consistent with the EPA proposed standard.
The Department of Transportation (DOT) endorsed the proposed standard
3
of 1.5 pg Pb/m . Based on an analysis of the impact of the proposed
standard on the highway program, DOT concluded that it is highly probable
that transportation-related violations of the proposed standard would be
limited to large urban areas.
In commenting on the proposed standard, the Department of the Interior
(DOI) expressed concern that the burden for meeting the proposed standard
will fall primarily on lead and copper smelters and battery manufacturers,
and commented on the impact of lead dustfall on ground water quality.
The Tennessee Valley Authority provided specific comments on the proposed
State implementation plan regulations and the proposed Federal Reference
Method. The Department of Commerce offered comments on the potential
impacts of the standard, pointing out that more consideration should be
given to the potential impact of the standard on the petroleum industry.
THE FEDERAL REFERENCE METHOD
The Reference Method for the Determination of Lead in Suspended
Particulate Matter Collected from Ambient Air describes the appropriate
techniques for determining the concentration of lead and its compounds as
measured as elemental lead in the ambient air. A total of eight organiza-
tions submitted written comments on the method and two persons made
comments at EPA's February public hearing on the proposed air quality
standard. Since proposal of the Federal Reference Method for lead, EPA has
completed additional testing of the method and added new information on
the precision of the extraction analysis procedure.
Two of the commenters recommended the addition of a nitric plus
hydrochloric acid extraction procedure. The extraction procedure of the
52
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proposed method contains only nitric acid. Use of a mixed acid procedure
would permit the analyst to quantitatively extract more metals than just
lead, thereby allowing him to analyze the same extract for more than one
metal. The analysis for lead would not be affected. EPA agrees that a
mixed acid extraction procedure should be added, and the revised method
contains a mixed nitric-hydrochloric acid extraction procedure.
One commenter questioned the reliability of the air volume measured
in the sampling procedure because of differences between initial and
final flow rates caused by build-up of particulate matter on the collecting
filter. The method of sampling specifies that initial and final flow
rates must fall between 40 and 60 cubic feet per minute and variations
within this range cause only a slight error. If the flow rate specification
is not met, the sample should be voided. For these reasons, EPA believes the
air volume measurement does not suffer unduly from inaccuracies.
A question was raised as to the effect of variation in lead content
across the filter of the collected sample on lead analysis, since the
method calls for analysis of only one strip or one-twelfth of the
filter. Our work has shown that strips taken from different positions
within the filter can, on occasion, produce different lead values, but the
effect appears to be significant only when sampling near a heavily traveled
roadway. The proposed method recommends analyzing additional strips, when
sampling near a roadway, to minimize this error.
One commenter pointed out that the proposed sampling procedure does
not collect gaseous (organic) lead compounds and recommended that EPA consider
requiring the use of a method for monitoring gaseous lead. As the criteria
document states, reported ambient levels of gaseous lead are very low and EPA
53
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has determined that the effort required to carry out the difficult task of
monitoring for ambient gaseous lead is not justified in view of the extremely
low concentration.
It was pointed out in the preamble to the proposed method that other
analytical principles would probably be handled by provision for approval
of the equivalent methods (40 CFR Part 53) proposed elsewhere in this
Federal Register. Two organizations submitted requests that alternate
methods (x-ray fluorescence and anodic stripping voltametry) for lead analysis
be declared equivalent to the reference method. These requests will be
considered when the procedures for determining equivalency are promulgated.
The final Federal Reference Method is based on measuring the lead con-
tent of suspended particulate matter on glass fiber filters using high
volume sampling. The lead is then extracted from the particulate matter with
nitric acid facilitated by heat or by a mixture of nitric acid and hydro-
chloric acid facilitated by ultrasonication. Finally, the lead content is
measured by atomic absorption spectrometry.
The reference method specified for lead measures the lead for a
single sampling period by extraction of a portion of a high-volume glass
fiber filter used to collect particulate matter over a 24-hour period. Some
agencies may prefer to composite filter strips from a number of sampling
periods and extract and analyze it for lead. This procedure is acceptable
provided the Agency shows that the compositing procedure results in the
same average lead value as would be obtained from averaging individual values.
Date Administrator
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40 CFR Part 50 is amended by adding a new §50.12 and a new Appendix G as
follows:
§50.12 National primary and secondary ambient air quality standards
for lead and its compounds, measured as elemental lead by a reference
method based on Appendix G to this Part, or by an equivalent method,
are: 1.5 micrograms per cubic meter, maximum arithmetic mean
averaged over a calendar quarter.
(Sections 109 and 301(a) of the Clean Air Act as amended
(42 U.S.C. 7409, 7601(a)).)
REFERENCES
Angle, C. R. and M. S. Mclntire. Environmental controls and the de-
cline of blood lead. Arch. Environ. Hlth. (in press.) 1977.
Azar, A., R. D. Snee, and K. Habibi. An Epidemiologic Approach to
Community Air Lead Exposure Using Personal Air Samplers. Environmental
Quality and Safety, Supplement Vol II—Lead 254-288 (1975).
Barltrop, D., C. D. Strehlow, J. Thornton, and J. S. Webb. Significance
of high soil concentrations for childhood lead burdens. Environ. Hlth. Persp.
Expt. Iss. 7:75-84. 1974.
Billick, I. A. Curran, and D. Shier. Presentation to the U.S. EPA Lead
Subcommittee of the Science Advisory Board, Washington, D.C., October 7, 1977.
Fine, P. R., C. W. Thomas, R. H. Suho, R. E. Cohnberg, and B. A. Flashner.
Pediatric Blood Lead Levels A Study in 14 Illinois Cities of Intermediate
Population. JAMA 221:1475-1479, September 25, 1972.
Johanson, W. C. and J. P. Luby. A Report on a Study to Determine the
Blood Lead Levels in Dallas Children. Dallas Health Department, Dallas,
Texas 1972.
Johnson, D. E., J. B. Tillery, and R. J. Prevost. Levels of platinum,
palladium and lead in populations of Southern California. Environ. Health
Persp. 12:27-33, 1975.
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Landrigan, P. J., S. H. Gehlbach, B. F. Rosenblum, J. M. Shoults, et.
al. Epidemic Lead Absorption Near an Ore Smelter. The role of particulate
lead. New England J. Med. 292:123-129, 1975.
Manton, W. I. Sources of Lead in Blood. Arch. Environmental Health,
32:149-156, 1977.
Rabinowitz, M. B. Lead contamination of the biosphere by human activity.
A stable isotope study, PhD Thesis, University of California, Los Angeles,
1974, 120 pp.
U. S. Environmental Protection Agency. Air Quality Criteria for Lead
Office of Research and Development. Washington, D.C. 20460. EPA-450/8-77-
017, December, 1977.
von Lindern, I. and A. J. Yankel. Presentation to the Shoshone Heavy
Metals Project Committee by Idaho Deparment of Health and Welfare, Boise,
Idaho, September 4, 1975.
Yankel, A. J. and I. von Lindern. The Silver Valley lead study. The
relationship of childhood lead poisoning and environmental exposure.
J. Air Pollut. Cont. Ass., August, 1977.
APPENDIX G
REFERENCE METHOD FOR THE DETERMINATION OF LEAD IN
SUSPENDED PARTICULATE MATTER COLLECTED FROM AMBIENT AIR
1. Principle and Applicability
1.1 Ambient air suspended particulate matter is collected on a
glass-fiber filter for 24-hours using a high volume air sampler.
1.2 Lead in the particulate matter is solubilized by extraction with
nitric acid (HNO-J, facilitated by heat or by a mixture of HNOg and hydrochloric
acid (HC1) facilitated by ultrasonication.
1.3 The lead content of the sample is analyzed by atomic absorption
spectrometry using an air-acetylene flame, the 283.3 or 217.0 nm 1iad absorption
line, and the optimum instrumental conditions recommended by the manufacturer.
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1.4 The ultrasonication extraction with HN03/HC1 will extract metals
other than lead from ambient particulate matter.
2. Range, Sensitivity and Lower Detectable Limit
The values given below are typical of the methods capabilities. Absolute
values will vary for individual situations depending on the type of instrument
used, the lead line, and operating conditions.
3
2.1 Range. The typical range of the method is 0.07 to 7.5 yg Pb/m
assuming an upper linear range of analysis of 15 yg/ml and an air volume of
2400 m3.
2.2 Sensitivity. Typical sensitivities for a 1% change in absorption
(0.0044 absorbance units) are 0.2 and 0.5 yg Pb/ml for the 217.0 and 283.3 nm
lines, respectively.
2.3 Lower Detectable Limit (LDL). A typical LDL is 0.07 yg Pb/m3.
The above value was calculated by doubling the between-laboratory standard
deviation obtained for the lowest measurable lead concentration in a colla-
15 3
borative test of the method. An air volume of 2400 m was assumed.
3. Interferences
Two types of interferences are possible: chemical, and light scattering.
12345
3.1 Chemical. Reports on the absence ' ' * ' of chemical inter-
ferences far outweigh those reporting their presence, therefore, no correction
for chemical interferences is given here. If the analyst suspects that the
sample matrix is causing a chemical interference, the interference can be
verified and corrected for by carrying out the analysis with and without the
method of standard additions.
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3.2 Light Scattering. Non-atomic absorption or light scattering,
produced by high concentrations of dissolved solids in the sample, can produce
2
a significant interference, especially at low lead concentrations. The inter-
ference is greater at the 217.0 nm line than at the 283.3 nm line. No inter-
ference was observed using the 283.3 nm line with a similar method.
Light scattering interferences can, however, be corrected for
instrumentally. Since the dissolved solids can vary depending on the origin
of the sample, the correction may be necessary, especially when using the
217.0 nm line. Dual beam instruments with a continuum source give the most
accurate correction. A less accurate correction can be obtained by using a
non-absorbing lead line that is near the lead analytical line. Information
on use of these correction techniques can be obtained from instrument manu-
facturers' manuals.
If instrumental correction is not feasible, the interference can
be eliminated by use of the ammonium pyrrolidinecarbodithioate-methylisobutyl
Q
ketone, chelation-solvent extraction technique of sample preparation.
4. Precision and Bias
4.1 The high-volume sampling procedure used to collect ambient air particulate
matter has a between-laboratory relative standard deviation of 3.7% over the range
3 g
80 to 125 pg/m . The combined extraction - analysis procedure has an average with-
in-laboratory relative standard deviation of 5 to 6% over the range 1.5 to 15 yg
Pb/ml, and an average between laboratory relative standard deviation of 7 to 9% over
the same range. These values include use of either extraction procedure.
4.2 Single laboratory experiments and collaborative testing indicate that
there is no significant difference in lead recovery between the hot and ultrasonic
15
extraction procedures.
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5. Apparatus
5.1 Sampling.
5.1.1 High-volume sampler. Use and calibrate the sampler as described
in reference 10.
5.2 Analysis.
5.2.1 Atomic Absorption Spectrophotometer. Equipped with lead hollow
cathode or electrode!ess discharge lamp.
5.2.1.1 Acetylene. The grade recommended by the instrument manufacturer
should be used. Change cylinder when pressure drops below 50-100 psig.
5.2.1.2 Air. Filtered to remove particulate, oil and water.
5.2.2 Glassware. Class A borosilicate glassware should be used through-
out the analysis.
5.2.2.1 Beakers. 30 and 150 ml. graduated, Pyrex.
5.2.2.2 Volumetric flasks. 100-ml.
5.2.2.3 Pipettes. To deliver 50, 30, 15, 8, 4, 2, 1 ml.
5.2.2.4 Cleaning. All glassware should be scrupulously cleaned. The
following procedure is suggested. Wash with laboratory detergent, rinse, soak
for 4 hours in 20% (w/w) HNO.,, rinse 3 times with distilled-deionized water,
and dry in a dust free manner.
5.2.3 Hot plate.
5.2.4 Ultrasonication water bath, unheated. Commercially available
laboratory ultrasonic cleaning baths of 450 watts or higher "cleaning power", i.e.,
actual ultrasonic power output to the bath have been found satisfactory.
5.2.5 Template. To aid in sectioning the glass-fiber filter. See
Figure 1 for dimensions.
59
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5.2.6 Pizza cutter. Thin wheel. Thickness <1 mm.
5.2.7 Watch glass.
5.2.8 Polyethylene bottles. For storage of samples. Linear polyethylene
gives better storage stability than other polyethylenes and is preferred.
5.2.9 Parafilm "M".* American Can Company, Marathon Products, Nennah,
Wisconsin, or equivalent.
6. Reagents
6.1 Sampling
6.1.1 Glass fiber filters. The specifications given below are intended
to aid the user in obtaining high quality filters with reproducible properties.
These specifications have been met by EPA contractors.
6.1.1.1 Lead content. The absolute lead content of filters is not critical,
but low values are, of course, desirable. EPA typically obtains filters with a
lead content of <75 yg/filter.
It is important that the variation in lead content from filter to
filter, within a given batch, be small.
6.1.1.2 Testing.
6.1.1.2.1 For large batches of filters ( > 500 filters) select at random
20 to 30 filters from a given batch. For small batches (< 500 filters) a lesser
number of filters may be taken. Cut one 3/4" x 8" strip from each filter any-
where in the filter. Analyze all strips, separately, according to the directions
in Sections 7 and 8.
*Mention of commercial products does not imply endorsement by the U.S. Environmental
Protection Agency.
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6,1.1.2.2 Calculate the total lead in each filter as
c nk/ i 100 ml 12 strips
V ^ Pb/ml x itRF" X filter
where:
F.= Amount of lead per 72 square inches of filter, yg.
6.1.1.2.3 Calculate the mean, F^, of the values and the relative standard
deviation (standard deviation/mean x 100). If the relative standard deviation
is high enough so that, in the analysts opinion, subtraction of F^, (Section 10.3)
3
may result in a significant error in the pg Pb/m , the batch should be rejected.
6.1.1.2.4 For acceptable batches, use the value of F, to correct all lead
analyses (Section 10.3) of particulate matter collected using that batch of filters.
If the analyses are below the LDL (Section 2.3) no correction is necessary.
6.2 Analysis
6.2.1 Concentrated (15.6 M_) HN03. ACS reagent grade HN03 and commer-
cially available redistilled HN03 has been found to have sufficiently low lead con-
centrations.
6.2.2 Concentrated (11.7 M.) HC1. ACS reagent grade.
6.2.3 Distilled-deionized water. (D.I. water).
6.2.4 3 M HN03. This solution is used in the hot extraction procedure.
To prepare, add 192 ml of concentrated HNO-, to D.I. water in a 1 £ volumetric
flask. Shake well, cool, and dilute to volume with D.I. water. CAUTION: Nitric
Acid Fumes Are Toxic. Prepare in a well ventilated fume hood.
6.2.5 0.45 M^ HN03< This solution is used as the matrix for calibration
standards when using the hot extraction procedure. To prepare, add 29 ml of con-
centrated HN03 to D.I. water in a 1 a volumetric flask. Shake well, cool, and
dilute to volume with D.I. water.
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6.2.6 2.6 M_ HN03 + 0 to 0.9 M_ HC1. This solution is used in the ultra-
sonic extraction procedure. The concentration of HC1 can be varied from 0 to
0.9 M_. Directions are given for preparation of a 2.6 f4 HNO-, + 0.9 M_ HC1 solution.
Place 167 ml of concentrated HN03 into a 1 a volumetric flask and add 77 ml of
concentrated HC1. Stir 4 to 6 hours, dilute to nearly 1 £ with D.I. water, cool
to room temperature, and dilute to l£.
6.2.7 0.40 M_ HN03 + X M^ HC1. This solution is used as the matrix
for calibration standards when using the ultrasonic extraction procedure. To
prepare, add 26 ml of concentrated HNO,, plus the ml of HC1 required, to a U
volumetric flask. Dilute to nearly In with D.I. water, cool to room temperature,
and dilute to l£. The amount of HC1 required can be determined from the follow-
ing equation:
_7_7 ml x 0.15 x
0.9 M
where:
y = ml of concentrated HC1 required
x = molarity of HC1 in 6.2.6
0.15 = dilution factor in 7.2.2
6.2.8 Lead Nitrate, Pb(N03)2. ACS reagent grade, purity 99.0%. Heat
for 4-hours at 120°C and cool in a desiccator.
6.3 Calibration Standards
6.3.1 Master standard, 1000 yg Pb/ml in HNCy Dissolve 1.598 g of
Pb(NOo)o in 0-45 M_ HNOo contained in a 1 a volumetric flask and dilute to volume
with 0.45 M_ HN03.
6.3.2 Master Standard, 1000 yg Pb/ml in HNCyHCl. Prepare as in
6.3.1 except use the HN03/HC1 solution in 6.2.7.
Store standards in a polyethylene bottle. Commercially avail-
able certified lead standard solutions may also be used.
62
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7. Procedure
7.1 Sampling. Collect samples for 24-hours using the procedure
described in reference 10 with glass-fiber filters meeting the specifications in
6.1.1. Transport collected samples to the laboratory taking care to minimize
contamination and loss of sample.
7.2 Sample Preparation.
7.2.1 Hot Extraction Procedure
7.2.1.1 Cut a 3/4" x 8" strip from the exposed filter using a template
and a pizza cutter as described in Figures 1 and 2. Other cutting procedures may
be used.
Lead in ambient particulate matter collected on glass fiber
1311
filters has been shown to be uniformly distributed across the filter ' '
12
suggesting that the position of the strip is unimportant. However, another study
has shown that when sampling near a road-way lead is not uniformly distributed across
the filter. The nonuniformity has been attributed to large variations in particle
size. Therefore, when sampling near a road-way, additional strips at different
positions within the filter should be analyzed.
7.2.1.2 Fold the strip in half twice and place in a 150-ml beaker. Add
15 ml of 3 M^ HN07 to cover the sample. The acid should completely cover the sample.
O
Cover the beaker with a watch glass.
7.2.1.3 Place beaker on the hot-plate, contained in a fume hood, and boil
gently for 30 min. Do not let the sample evaporate to dryness. CAUTION: Nitric
Acid Fumes Are Toxic.
7.2.1.4 Remove beaker from hot plate and cool to near room temperature'.
7.2.1.5 Quantitatively transfer the sample as follows:
7.2.1.5.1 Rinse watch glass and sides of beaker with D.I. water.
63
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7.2.1.5.2 Decant extract and rinsings into a 100-ml volumetric flask.
7.2.1.5.3 Add D.I. water to 40 ml mark on beaker, cover with watch glass,
and set aside for a minimum of 30 minutes. This is a critical step and cannot
be omitted since it allows the HNO, trapped in the filter to diffuse into the
rinse water.
7.2.1.5.4 Decant the water from the filter into the volumetric flask.
7.2.1.5.5 Rinse filter and beaker twice with D.I. water and add rinsings
to volumetric flask until total volume is 80 to 85 ml.
7.2.1.5.6 Stopper flask and shake vigorously. Set aside for approximately
5 minutes or until foam has dissipated.
7.2.1.5.7 Bring solution to volume with D.I. water. Mix thoroughly.
7.2.1.5.8 Allow solution to settle for one hour before proceeding with
analysis.
7.2.1.5.9 If sample is to be stored for subsequent analysis, transfer to
a linear polyethylene bottle.
7.2.2 Ultrasonic Extraction Procedure
7.2.2.1 Cut a 3/4" x 8" strip from the exposed filter as described in
Section 7.2.1.1.
7.2.2.2 Fold the strip in half twice and place in a 30 ml beaker. Add
15 ml of the HN03/HC1 solution in 6.2.6. The acid should completely cover the
sample. Cover the beaker with Parafilm.
The Parafilm should be placed over the beaker such that none of
the Parafilm is in contact with water in the ultrasonic bath. Otherwise, rinsing
of the Parafilm (Section 7.2.2.4.1) may contaminate the sample.
7.2.2.3 Place the beaker in the ultrasonication bath and operate for
30 minutes.
64
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7.2.2.4 Quantitatively transfer the sample as follows:
7.2.2.4.1 Rinse Parafilm and socles of beaker with D.I. water.
7.2.2.4.2 Decant extract and rinsings into a TOO ml volumetric flask.
7.2.2.4.3 Add 20 ml D.I. water to cover the filter strip, cover with para-
film, and set aside for a minimum of 30 minutes. This is a critical step and
cannot be omitted. The sample is then processed as in Sections 7.2.1.5.4 through
7.2.1.5.9. NOTE: Samples prepared by the hot extraction procedure are now in
0.45 M_ HN03. Samples prepared by the ultrasonication procedure are in 0.40 M_ HNO, +
X MHC1 .
8. Analysis
8.1 Set the wavelength of the monochromator at 283.3 or 217.0 nm.
Set or align other instrumental operating conditions as recommended by the manu-
facturer.
8.2 The sample can be analyzed directly from the volumetric flask, or
an appropriate amount of sample decanted into a sample analysis tube. In either
case, care should be taken not to disturb the settled solids.
8.3 Aspirate samples, calibration standards and blanks (Section 9.2)
into the flame and record the equilibrium absorbance.
8.4 Determine the lead concentration in ug Pb/ml, from the calibration
curve, Section 9.3.
8.5 Samples that exceed the linear calibration range should be diluted
with acid of the same concentration as the calibration standards and reanalyzed.
9. Calibration
9.1 Working Standard, 20 yg Pb/ml. Prepared by diluting 2.0 ml
of the master standard (6.3.1 if the hot acid extraction was used or 6.3.2 if
65
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the ultrasonic extraction procedure was used) to 100 ml with acid of the same
concentration as used in preparing the master standard.
9.2 Calibration standards. Prepare daily by diluting the working
standard, with the same acid matrix, as indicated below. Other lead concen-
trations may be used.
Volume of 20 yg/ml Final Concentration
Working Standard, ml Volume, ml yg Pb/ml
0 100 0.0
1.0 200 0.1
2.0 200 0.2
2.0 100 0.4
4.0 100 0.8
8.0 100 1.6
15.0 100 3.0
30.0 100 6.0
50.0 100 10.0
100 100 20.0
9.3 Preparation of calibration curve. Since the working range of
analysis will vary depending on which lead line is used and the type of instrument,
no one set of instructions for preparation of a calibration curve can be given.
Select standards (plus the reagent blank), in the same acid concentration as the
samples, to cover the linear absorption range indicated by the instrument manu-
facturer. Measure the absorbance of the blank and standards as in Section 8.0.
Repeat until good agreement is obtained between replicates. Plot absorbance
(y-axis) versus concentration in pg Pb/ml (x-axis). Draw (or compute) a straight
line through the linear portion of the curve. Do not force the calibration curve
through zero. Other calibration procedures may be used.
-------
To determine stability of the calibration curve, remeasure - alternately -
one of the following calibration standards for every 10th sample analyzed: con-
centration s 1 yg Pb/ml ; concentration < 10 yg Pb/ml . If either standard deviates
by more than 5% from the value predicted by the calibration curve, recalibrate
and repeat the previous 10 analyses.
10. Calculation.
10.1 Measured air volume. Calculate the measured air volume as
Qi t Qf
Vm - -V1 * T
where:
o
V = Air volume sampled (uncorrected), m
3
Q- = Initial air flow rate, m /min.
3
0~ = Final air flow rate, m /min.
T = Sampling Time, min.
The flow rates Q. and Qf should be corrected to the temperature and pressure
conditions existing at the time of orifice calibration as directed in addendum B
of reference 10, before calculation of Vm>
10.2 Air volume at STP. The measured air volume is corrected to reference
conditions of 760 mm Hg and 25°C as follows. The units are standard cubic meters,
sm3.
VSTP = Vm
Pl XT2
3
= Sample volume, sm , at 760 mm Hg and 298° K
V = Measured volume from 10.1
67
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?2 = Atmospheric pressure at time of orifice
calibration, mm Hg
PI = 760 mm Hg
T2 = Atmospheric temperature at time of orifice
calibration, °K
T1 = 298°K
10.3 Lead Concentration. Calculate lead concentration in the air sample,
(yg Pb/ml x 100 ml/strip x 12 strips/filter) - F.
VSTP
where:
3
C = Concentration, yg Pb/sm
yg Pb/ml = Lead concentration determined from Section 8
100 ml/strip = Total sample volume
. = Useable filter area, 7" x 9"
Exposed area of one strip, 3/4" x 7"
F. = Lead concentration of blank filter, yg, from Section
6.1.1.2.3
= Air volume from 10. 2
11. Quality Control
3/4" x 8" glass fiber filter strips containing 80 to 2000 yg Pb/strip
(as lead salts) and blank strips with zero Pb content should be used to
determine if the method - as being used - has any bias. Quality control charts
should be established to monitor differences between measured and true values.
The frequency of such checks will depend on the local quality control program.
68
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To minimize the possibility of generating unreliable data, the user should
13
follow practices established for assuring the quality of air pollution data,
and take part in EPA's semi-annual aucit program for lead analyses.
12. Trouble Shooting
1. During extraction of lead by the hot extraction procedure, it is
important to keep the sample covered so that corrosion products - formed on
fume hood surfaces which may contain lead - are not deposited in the extract.
2. The sample acid concentration should minimize corrosion of the
nebulizer. However, different nebulizers may require lower acid concentrations.
Lower concentrations can be used provided samples and standards have the same
acid concentration.
3. Ashing of particulate samples has been found, by EPA and contractor
laboratories, to be unnecessary in lead analyses by Atomic Absorption. Therefore,
this step was omitted from the method.
4. Filtration of extracted samples, to remove particulate matter, was
specifically excluded from sample preparation, because some analysts have observed
losses of lead due to filtration.
5. If suspended solids should clog the neublizer during analysis of samples,
centrifuge the sample to remove the solids.
13. Authority
(Section 109 and 301(a) of the Clean Air Act as amended, 42 U.S.C. 7409,
7601(a))
14. References
1. Scott, D. R. et al. Atomic Absorption and Optical Emission Analysis
of NASN Atmospheric Particulate Samples for Lead. Envir. Sci. and
Tech., 10, 877-880 (1976).
69
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2. Skogerboe, R. K. et al. Monitoring for Lead in the Environment.
pp. 57-66, Department of Chemistry, Colorado State University,
Fort Collins, Colorado 80523. Submitted to National Science
Foundation for publication, 1976.
3. Zdrojewski, A. et al. The Accurate Measurement of Lead in Airborne
Participates. Inter. J. Environ. Anal. Chem., 2, 63-77 (1972).
4. Slavin, W. Atomic Absorption Spectroscopy. Published by Inter-
science Company, New York, NY (1968).
5. Kirkbright, G. F., and Sargent, M. Atomic Absorption and Fluorescence
Spectroscopy. Published by Academic Press, New York, N.Y. 1974.
6. Burnham, C. D. et al. Determination of Lead in Airborne Particulates
in Chicago and Cook County, Illinois by Atomic Absorption Spectroscopy.
Envir. Sci. and Tech., 3_, 472-475 (1969).
7. Proposed Recommended Practices for Atomic Absorption Spectrometry.
ASTM Book of Standards, Part 30, pp. 1596-1608 (July 1973).
8. Koirttyohann, S. R., and Wen, J. W. Critical Study of the APCD-MIBK
Extraction System for Atomic Absorption. Anal. Chem., 45, 1986-1989
(1973).
9. Collaborative Study of Reference Method for the Determination of
Suspended Particulates in the Atmosphere (High Volume Method).
Obtainable from National Technical Information Service, Department
of Commerce, Port Royal Road, Springfield, Virginia 22151, as
PB-205-891.
10. Reference Method for the Determination of Suspended Particulates in
the Atmosphere (High Volume Method). Code of Federal Regulations, Title 40,
Part 50, Appendix B, pp. 12-16 (July 1, 1975).
70
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11. Dubois, L., et al. The Metal Content of Urban Air. JAPCA, 1_6_,
77-78 (1966).
12. EPA Report No. 600/4-77-034, June 1977. Los Angeles Catalyst Study
Symposium. Page 223.
13. Quality Assurance Handbook for Air Pollution Measurement Systems.
Volume 1 - Principles. EPA-600/9-76-005, March 1976.
14. Thompson, R. J. et al. Analysis of Selected Elements in Atmospheric
Participate Matter by Atomic Absorption. Atomic Absorption News-
letter, 9_, No. 3, May-June 1970.
15. To be published. EPA, QAB, EMSL, RTP, N.C. 27711
16. .Hirschler, D. A. et al. Particulate Lead Compounds in Automobile
Exhaust Gas. Industrial and Engineering Chemistry, 49, 1131-1142
(1957).
17. Quality Assurance Handbook for Air Pollution Measurement Systems.
Volume II - Ambient Air Specific Methods. EPA-600/4-77-027a, May 1977,
71
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