August 31, 1995
EPA-SAB-CASAC-LTR-95-005
Honorable Carol M. Browner
Administrator
U.S. Environmental Protection Agency
401 M Street SW
Washington, DC 20460
Re: Clean Air Scientific Advisory Committee
(CASAC) Comments on the April 1995 draft Air
Quality Criteria for Particulate Matter.
Dear Ms. Browner:
The Particulate Matter Criteria Document Review Panel of the
Clean Air Scientific Advisory Committee (CASAC) of EPA's Science
Advisory Board (SAB) reviewed the document entitled Air Quality
Criteria for Particulate Matter (PM) at a meeting on August 3 and
4, 1995. At that meeting and in subsequent written comments, the
Panel made numerous recommendations for improving the document,
and they have been forwarded to your staff. This report includes
input from the Particulate Matter Criteria Document Review Panel
and has been approved by the Clean Air Scientific Advisory
Committee.
The Panel was impressed with the breadth and scope of the
Criteria Document (CD) especially given the extremely tight
schedule imposed upon the Agency. The CD is a comprehensive
review of the PM literature. However, many of the CASAC panel
members expressed concerns that the Agency does not have
sufficient time to make the changes necessary for the document to
serve as a basis for regulatory decisions. Because the CD
requires such extensive revisions, the Panel recommends that it
be given the opportunity to review the revised draft. In reviews
of previous Criteria Documents, CASAC had the opportunity to
review the second, and in some cases the third draft. This was
done to yield a CD that was of sufficient scientific quality for
regulatory decision-making and one the CASAC could reach closure
on.
I will summarize the principal concerns expressed by Panel
members. It should be pointed out that not all of these concerns
were expressed by all the Panel members. However, in order for
the Panel to reach consensus on closure on the CD, EPA needs to
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address these concerns. In general, the concerns were expressed
by multiple Panel members who, because of their specific
expertise, were assigned to review the chapters on which they
commented.
Many Panel members expressed the view that the CD has not
adequately demonstrated several important linkages that are
crucial in relating PM to mortality and/or morbidity. The first
example occurs in Chapter 7 where the Agency attempts to
establish a link between personal exposure (PE - the exposure one
would measure with a personal PM monitor) and the exposure
estimated from a fixed-site monitor located at some central
monitoring (CM) site. This is a key issue because all of the
epidemiological studies linking PM to mortality/morbidity use
data from CM sites. In Chapter 7, fourteen studies are cited
which show no relationship or a poor relationship between PE and
exposures estimated from a CM for both PM10 and PM25. One other
study shows an excellent correlation between particulate sulfate
PE and outdoor concentrations which the Agency embraces. One
positive result out of 15 studies is not a strong case for the
relationship.
Second, the linkages between the animal studies and the
human clinical studies presented in Chapters 10 and 11 to the
epidemiological results in Chapter 12 are not established. In
fact, almost nothing from the encyclopedic Chapters 10 and 11 is
cited in Chapter 13, the integrated health effects synthesis
chapter, or Chapter 1, the Executive Summary. The focus of
Chapter 13 should be to take the exposure analysis, dosimetry,
toxicology, and epidemiology and integrate them into a
comprehensive review. Chapter 13 does contain a discussion about
the "coherence" of results among the excess daily mortality and
excess daily hospital admissions for respiratory disease.
However, this needs to be broadened to identify coherence among
the different types of epidemiological studies, as well as among
the toxicological and controlled human studies.
Third, a number of the Panel members indicated that the
confounding influences due to stressful meteorological conditions
on mortality/morbidity may not have been completely removed in
any of the epidemiological studies and that this could inflate
the mortality/morbidity ascribed to pollution. This is pointed
out in the CD on pages 12-32 to 12-36 and in the appendix for
chapter 12. However, it is ignored in the discussions of the
results of the PM-mortality/morbidity studies. Although it is
unlikely that all of the excess mortality/morbidity would be
ascribed to adverse meteorological conditions, it would be
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advantageous if a reanalysis was performed which removed the
meteorological influences using methodologies similar to those
recommended in the appendix.
The fourth and, perhaps the most important link that has not
been adequately discussed and is not established, is the link
between mortality/morbidity and a specific component of air
pollution. Although the studies show a consistent statistical
association between some measure of PM and mortality/morbidity,
it does not necessarily follow that PM is the responsible agent.
In fact, the inclusion of additional air pollutants (i.e., 03,
S02, N02, or CO) usually results in the additional pollutant(s)
accounting for some of the excess mortality/morbidity. The
recent reanalyses of the Philadelphia data set by the Health
Effects Institute (HEI) and Dr. Lester Lave presented at the
CASAC meeting underscores this point. The HEI report concludes:
"However, the findings do not clearly indicate that the increased
mortality associated with increasing indexes of air pollution can
be assigned to either TSP or S02 alone." Some individuals have
proposed that the PM is an indicator of air pollution and is not
necessarily the causative agent. Others have proposed that the
causative agent is some specific component of the PM. For
example, some argue that the acid sulfate component of the PM is
the causative agent. The CD considers this possibility as well,
but also considers a variety of other causative agents including
PM2 5 and ultrafine PM (PM with diameters less than about 0.1 //m) ,
and arguments are made for each. Unfortunately, there are only a
limited number of data sets that include measurements of PM25 or
ultrafine PM. Indeed, the number of data sets with PM10 is not
large. Consequently, we have a dilemma in not being able to
definitively identify the possible causative agent(s), and hence,
not being able to identify the air pollution component(s) that
needs to be reduced in order to reduce mortality/morbidity.
Depending on the choice of a risk management strategy, this
dilemma may also exist if we accept the hypothesis that PM is an
indicator of overall pollution. It appears that EPA is leaning
towards PM25 as the constituent that needs to be addressed.
However, the scientific basis for this has not been established
in the CD or reflected in Chapter 13.
Fifth, the CD does not establish a link between evidence on
the biological mechanisms and the reported epidemiological
findings. The epidemiological studies, by themselves, do not
provide this knowledge, which some consider essential to
establish a cause and effect. Only an intervention study or an
experimental exposure study can demonstrate cause and effect.
The Agency needs to more adequately explore in the CD mechanisms
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of action as a basis for biological or clinical plausibility.
The results of this exploration need to be emphasized in the
introduction and conclusion of the Executive Summary and in
Chapters 10, 11, 12 and 13.
A number of the Panel members noted the absence of a sixth
link, namely the rationale for using a 24-hour averaging time for
the NAAQS (National Ambient Air Quality Standard). The
justification for using any specific averaging time, including a
24-hour averaging time, is not established
A number of Panel members also noted a deficiency in the CD
in that it did not include a discussion of biological aerosols in
either the indoor or outdoor environments. These would include
potential allergens like pollens, spores, molds, mites etc. If
these agents are to be excluded, the rationale for their
exclusion needs to be developed and stated.
In summary, a case can be made for concern for health
effects associated with particulate matter. However, information
presented in the CD does not provide a basis to select the agent
or agents which need to be regulated nor does it provide a basis
for predicting the health benefits of any control strategies.
The Panel urges that sufficient time be given to allow EPA staff
to make the necessary changes in the CD so that the CASAC can
come to closure on a document of acceptable scientific quality
for regulatory decision-making.
The Panel would welcome the opportunity to review another
version of the CD, and looks forward to reviewing the Staff
Position Paper on Particulate Matter. However, in closing, it
should be noted that it would be difficult to create an
acceptable Staff Position Paper absent a fully satisfactory
Criteria Document on Particulate Matter.
Sincerely,
Dr. George T. Wolff,
Clean Air Scientific Advisory
Committee
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U.S. Environmental Protection Agency
Science Advisory Board
Clean Air Scientific Advisory Committee
Particulate Matter Criteria Document Review Panel
Chairman
Dr. George T. Wolff
General Motors
Environmental & Energy Staff
Detroit, MI
Members
Dr. Stephen M. Ayres
Office of International
Programs
Virginia Commonwealth
University
/Medical College of Virginia
Richmond, VA
Dr. Jay S. Jacobson
Boyce Thompson Institute
Cornell University
Ithaca, NY
Dr. Joe L. Mauderly
Inhalation Toxicology Research
Institute
Lovelace Biomedical &
Environmental
Research Institute
Albuquerque, NM
Dr. Paulette Middleton
Science and Policy Assoc., Inc
Boulder, CO
Dr. James H. Price, Jr.
Texas Natural Resource
Conservation
Commission
Austin, TX
Harvard School of Public
Health
Boston, MA
Dr. Morton Lippmann
Institute of Environmental
Medicine
New York University
Tuxedo, NY
Dr. Kinley Larntz
Department of Applied
Statistics
University of Minnesota
St. Paul, MN
Dr. Allan Legge
Biosphere Solutions
Calgary, Alberta, Canada
Dr. Roger 0. McClellan
Chemical Industry Institute of
Toxicology
Research Triangle Park, NC
Dr. Daniel Menzel
Department of Community
and Environmental Medicine
University of California,
Irvine
Irvine, CA
Dr. William R. Pierson
Energy & Environmental
Engineering
Center
Desert Research Institute
Reno, NV
Consultants
Dr. Petros Koutrakis
Dr. Carl M. Shy
Department of Epidemiology
School of Public Health
University of North Carolina
Chapel Hill, NC
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Dr. John Samet
School of Hygiene & Public
Health
Johns Hopkins University
Baltimore, MD
Dr. Christian Siegneur
NSR Consulting & Engineering
Alameda, CA
Dr. Frank Speizer
Harvard Medical School
Channing Lab
Boston, MA
Dr. Jan Stolwijk
Yale University
New Haven, CT
Dr. Mark Utell
Pulmonary Disease Unit
University of Rochester
Medical Center
Rochester, NY
U.S. EPA
Science Advisory Board
Washington, DC
Mr. A. Robert Flaak
Designated Federal Official
U.S. EPA
Science Advisory Board
Washington, DC
Lori Anne Gross
Staff Secretary
U.S. EPA
Science Advisory Board
Washington, DC
August 1995
Dr. Warren White
Washington University
St. Louis, MO
Science Advisory Board Staff
Mr. Randall C. Bond
Designated Federal Official
U.S. EPA
Science Advisory Board
Washington, DC
Dr. Donald G. Barnes
Designated Federal Official
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NOTICE
This report has been written as a 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 of the Environmental Protection Agency. The
Board is structured to provide balanced expert assessment of
scientific matters related to problems faced by 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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