Unites) Stat» Office o* th« Admindtrator EPA-SAe-CASAC-ii-Q if
Environmental Prettetlon Seltne* Advisory lotrcf April 1389
Agtncy Wasftinften, OC 20460
Clean Air Scientific
Advisory Committee
(CASAC)
Review of the Lead
NAAQS Exposure
Analysis Methodology
and Validation
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SI-,,
UNITED STATES ENVIRONMENTAL PROTECTION AGtNCY
WASHINGTON. O C 20-160
April 27, 1989
The Honorable William Reilly
Administrator
U.S. Environmental Protection Agency
401 M Street, SW
Washington, DC 20460
Dear Mr, Reilly;
We are pleased to transmit via this letter the advice of the
Clean Air Scientific Advisory Committee (CASAC) concerning its
review of the EPA document "Review of the National Ambient Air
Quality Standards for Lead; Exposure Analysis Methodology and
Validation" {August 1988) .
This document was reviewed by the Lead Exposure Subcommittee
of CASAC on October 23, 1988. It was the unanimous consensus of the
Subcommittee that the document is scientifically adequate for use
in the standard setting process for lead as an ambient air
pollutant. The CASAC hereby endorses the report of its
Subcommittee. A detailed presentation of our views are contained
in the attached report.
We appreciate the opportunity to provide advice on this
important issue. Further advice concerning the lead national
ambient air quality standards will be contained in our closure
letter on the Lead Staff Paper.
Sincerely ,
Timothy Larson
Chairman, Lead Exposure
;omiitt**
Roger 0. McClellan
Chairman, Clean Air Scientific
Advisory Committee
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ABSTRACT
This report presents the views of the EPA1a Clean Air
Scientific Advisory Committee on its review of the Agency's
document entitled* "Review of the National Ambient Air Quality
Standards for Leads Estposure Analysis Methodology and Validation".
The Committee concurred with the general modeling framework
presented in the report and endorsed the use of the biokinetic
model in children under .six years of age, and the use of the
disaggregate approach in adults. The Committee cautioned that
these modeling predictions were not valid for pregnant women and
their fetuses due to a lack of information on this subpopulation.
The use of the Mokinetic model for metals other than lead was not
recommended.
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NOTICE
This report has been written as part of the activities of the
Science Advisory Board, a public advisory group providing
extramural scientific information and advice to the Administrator
and other officials off the Environmental Protection Agency. The
Board is structured to provide a balanced expert assessment of
scientific matters related to problems facing the Agency. This
report has not been reviewed for approval by the Agency; and,
hence, the contents of this report do not necessarily represent the
views and policies of the Environmental Protection Agency or other
agencies in the Federal Government. Mention of trade names or
commercial products does not constitute a recommendation for use.
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U, S. Environmental protection Agency
Science Advisory Board
Clean Air Scientific Advisory Coaoaittea
EXPOSURE SUBCOMMITTEE
Chairman
Dr. Timothy Larson, Environmental Engineering; and Science
Program, Department of civil Engineering,
University of Washington, Seattle, Washington
Members
Dr. J. Julian chisola, Jr., Associate Professor, Johns Hopkins
School of Medicine, Francis Scott Key Medical Center,
Baltimore, Maryland
Dr. Scott Clark, Professor of Environmental Health, Department
of Environmental Health, University of Cincinnati Medical
Center, Cincinnati, Ohio
Dr. Ian von Lindern, President, Terragraphics Environmental
Engineering, Moscow, Idaho
Dr. Kathryn R. Mahaffey, Science Advisor, Office of the
Director, NIEHS, University of Cincinnati Medical Center,
Cincinnati, Ohio
Dr. M. Granger Morgan, Head, Department of Engineering and
Public Policy, Carnegie Mellon University, Pittsburgh,
Pennsylvania
Dr. Paul Mushak, Consultant and Adjunct Professor, University
of North Carolina, Durham, North Carolina
Dr. Michael B. Rabinowitz, Investigator, Marine Biological
Laboratory, Woods Hole, Massachusetts
Dr. Robert D, Rove, Senior Vice President, RCG/Haglor, Bailly
Inc., Boulder, Colorado
Executive Secretary
Mr. A. Rotwrt Flaafc, Environmental Scientist, science Advisory
Board (A-101F) , U.S. Environmental Protection Agency,
401 M Street, SW, Washington, DC 20460
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U.S. ENVIRONMENTAL, PROTECTION AGENCY
SCIENCE ADVISOR* BOARD
CLEAN AIR SCIENTIFIC ADVISORY
Chairman
Or, Roger 0, Mceiellan, President, Chemical Industry Institute
of Toxicology, Research Triangle Park, North Carolina
Members
Dr. Timothy Larson, Environmental Engineering and Science Program,
Department of civil Engineering, University of Washington,
Seattle, Washington
Dr. Gilbert S, Omenn, trofessor of Medicine and of Environmental
Health, Dean, School of Public Health and community Medicine,
University of Washington, Seattle, Washington
Dr. Marc B. Schenker, Director, Occupational and Environmental
Health Unit, University of California* Davis, California
Dr, Mark J.~Utell, Professor of Medicine and Toxicology,
co-Director, Pulmonary Disease Unit, University of Rochester
School of Medicine, Rochester, New York
Dr. Jerome J. Wesolowski, Chief, Air and Industrial Hygiene
Laboratory, California Department of Health, Berkeley,
California
Dr, George T. Wolff, Principal Scientist, General Motors
Research Labs, Environmental Science Department,
Warren, Michigan
Executive Secretary
Mr, A. Robert Flamk, Environmental Scientist, Science Advisory
Board (A-101P), U,S. Environmental Protection Agency,
401 II Street, sw, Washington, D.C* 20460
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REPORT OP THg CLEAN AIR SCIENTIFIC ADVISORY COMMITTEE
. ON ITS REVIEW OF
"REVIEW OF THE NATIONAL AMBIENT AIR QUALITY STANDARDS FOR LEAD;
EXPOSURE ANALYSIS METHODOLOGY AND VALIDATION"
With the dramatic decline in the emissions of lead from mobile
sources, there has been increased interest in airborne lead near
stationary sources. Given a proposed change in lead concentrations
near stationary sources due to reduced emissions, will there be
predictable changes in blood lead levels in the surrounding
population? Exposure models are currently the only practical tool
that can address this question within the framework of the national
ambient air quality standard (NAAQS) setting process. The
scientific framework for such modeling is the basis of the document
reviewed by the Clean Air Scientific Advisory Committee's (CASAC)
Lead Exposure subcommittee. In addition to discussing various
modeling approaches, the document also presents several validation
studies in order to compare these modeling approaches with actual
observations of blood lead levels near several point sources of
lead. It was the unanimous consensus of this subcommittee that the
document is scientifically adequate and that the EPA staff's
proposed changes to the document discussed at the meeting
appropriately address the written comments 'of the Subcommittee'
members. The Clean Air Scientific Advisory Committee (CASAC)
hereby endorses this report of its Lead Exposure Subcommittee,
The validation studies presented convincing evidence for a
decrease in blood lead levels with increasing distance (out to
several kilometers) from a point source. The subcommittee agreed
with the conclusion that any attempt to predict blood lead levels
must include all the important 'exposure pathways and that the
direct inhalation route of airborne lead is a relatively minor
pathway in children. The validation studies also provided
additional information on the lead levels of other important
exposure media, including soil, house dust, food and water.
Therefore, these studies provide a unique opportunity to test the
ability of various exposure/uptake models to predict mean values
of blood lead from various routes of exposure. Blood lead levels
were predicted using both a disaggregate approach as well as a
biokinetic approach. The Subcommittee recognized that several of
the inputs to the exposure models are uncertain, but felt that this
uncertainty was adequately recognized in the document. More
important, the Subcommittee concurred with the general modeling
framework and endorsed the use of the biokinetic model, in children
under six years of age and the use of the disaggregate approach in
adults. The Subcommittee also strongly emphasized that these
modeling predictions were not valid for pregnant women and their
fetuses due to a lack of information on this potentially important
subpopulation* The Subcommittee also recommended that the
exposure model outputs include not only the predicted mean blood
lead levels as a function of downwind distance but also the
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corresponding lead levels In all exposure media including air,
soil, dust, food and water. These outputs would provide an
additional basis for evaluating model performance.
Given a. predicted mean blood lead level, another important
component of the exposure mod*! is the prediction of maximum blood
lead levels in exposed individuals. EPA's approach is to use
empirical estimates of the variance of blood lead levels in the
general population, as well as those in populations living near
lead point sources, as a predictor of peak to mean values. The
document correctly recognized that the population variance
estimates depend on many different factors (e.g., biological,
climatic, behavioral) that exposure modeling cannot fully capture
at this time. Given the uncertainties, the Subcommittee agreed
that the only reasonable assumption is to use the range of variance
estimates from the empirical data. However, because this is a
sensitive parameter, we felt the additional concern that as blood
lead levels continue to decrease in the future, the assumption of
a constant proportional variance (log-normality assumption) may be
compromised by analytical uncertainties in the measurement of blood
lead, but the Subcommittee felt that this issue was adequately
addressed in the document.
The Subcommittee felt very strongly that the results of this
modeling exercise not be taken out of context. for example,
because the available data on lead in drinking water for the'
validation studies was limited, the biokinetic model in this
application was used to calculate average drinking water exposures
over tin*. However, the biokinetic model is sensitive to total
intake from this route and can account for variations in water lead
exposure where appropriate data are available. While the model can
be used now to evaluate relative changes in blood lead levels from
changes in water lead levels, it has not been calibrated for
absolute assessments of risk from drinking water in the same way
as done for other routes of exposure. Use of the model for other
metals was also not recommended at this time. in addition,
although the Subcommittee agreed that an appropriate application
of this approach might be for prediction of offsite lead exposures
from fugitive dust emissions, there was concern that until non-
linearities in the relationship between lead exposure and blood
lead are incorporated into the model, the model be limited to use
in areas where soil lead levels do not exceed 4000 ppm. In
addition, th* model should not be used in areas where ingestion
(pica) of paint fragments is an important route of intake because
this variable was not considered in the case study validation.
Finally, the biokinetic model should not be used for predicting
adult blood lead levels at this time due to limited data regarding
historical exposures and the possible confounding factor of blood
lead coming from bone.
The Subcommittee was also asked for guidance on several
technical Issues that are summarized below* As to the range of
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F
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dirt ingestion rates used in the report (55-135 mg/day depending
on ag«), the Subcommittee agreed that this is a relatively poorly
defined parameter subject to climatic variations. Some members
felt that tft* value of*1QQ mg/day represented an upper limit for
a high risJe child, whereas others felt that the use of the Binder
et al. and Clausing et al. studies was as good a choice as any
until further data are available. All members agreed that this is
an important paraneter in determining total intake and that the
uncertainties have been adequately discussed in the document, in
this regard, there was agreement that the emphasis in future
research should focus on the lead levels in the surface layer of
the soil and not on the older, deeper layers. There was general
agreement that the model use a constant soil lead level in
predicting future scenarios, but that the house dust component
should track the air lead value. Finally, the approach of
interfacing the biokinetic and disaggregate models for intermediate
age groups was judged acceptable by the Subcommittee in the absence
oŁ any other available information to the contrary.
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