EPA-CASAC-8.?-001
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. zo46Q
October 22, 1986
The Honorable Lee Thorns OFFICE or
Administrator
U.S. Environmental Protection
Agency
Washington, DC 20460
Dear Mr. Thomas:
The Clean Air Scientific Advisory Ccnroittee (CASAC) has completed
its review of the Air Quality Criteria for Ozone and Other Photochemical
Oxidants prepared by the Agency's Environmental Criteria and Assessment
Off ice (BCAO). The Comnitbee unanimously concluded that this document
represents a scientifically balanced and defensible summary of the extensive
scientific literature on these pollutants.
The CASAC's current review cycle for ozone and other photochemical
oxidants has included public meetings on March 4-6, 1985, and April 21-22,
1986. The Committee was impressed with the efforts of the staff of ECAO
in preparing a well written, integrated and thorough review of recent
relevant scientific studies.
It is evident that the Agency responded to CASAC's request to ECAO
that criteria documents contain health summary chapters that integrate
data from toxicological, epidemiological, and clinical studies. The summary
health chapter of this document approprlately emphasizes the singularly
important role of exercise as a factor in determining response to ozone.
Although somewhat understated in the criteria document, exercise is
clearly the dominant factor affecting the response to a specific ambient
concentration of ozone in acute exposures. Despite speculation regarding
variables, such as age, sex, smoking status, pre-existing lung disease,
nutritional status, arid red blood cell enzyme deficiencies, little conclusive
evidence is available to link these factors to ozone responsiveness.
As a corollary, although the identification of populations potentially
at risk from ozone exposure is of obvious importance, it is apparent that
at risk groups are not as well defined for ozone as they are for other
criteria pollutants. Wide variability of response from subject to subject
exists, while intrasubject variability is not as great. At the April
1986 review meeting, the Committee reeenroended that the document further
emphasize reproducibility of response in given individuals and the fact
that we cannot at this time define the parameters that lead to such a
response. Research should be undertaken to identify those factors and
mechanisms that can make a given individual susceptible to ozone.
-------
-2-
One of t±ie more controversial issues in the Criteria Document is how
to classify so-called "responders". This represents a key issue in the
evaluation of public health risks from ozone. This group is characterized
at present only by its response to ozone and possesses no other known
distinguishing characteristics. There is no consensus as to whether
"responders" constitute a specific pcpulation subgroup or siiflply_represent
the upper 5^20% of the ozone response distribution in the general population.
Several carefully executed investigations on animals provide cause
for concern over long term exposures to ambient ozone levels, ffiile it
is not possible at the present time to conclusively extrapolate the
quantitative results from animal studies to humans, the Committee reccraraended
at its review meeting that the Agency integrate the information derived
from animal studies into the health summary chapter, insofar as possible.
In addition, CASAC believes such toxicological information should be an
inportant basis for decisions on directions for future research.
The discussion of the effects of ozone and other photochemical
oxidants on vegetation provides a reasonably complete update and analysis
of the literature. The Conmittee acknowledges that the document accurately
describes the National Crop toss Assessment Network (NCIAN) studies and
that NCIAN data constitute the bulk of the agricultural crop data. The
results of NCLAN indicate that regionally elevated levels of ozone influence
the yield of several sensitive agricultural species. However, NCLM focuses
on agricultural crops of significant commercial value but does not evaluate
potential damage to forest systems or ornamentals. Consequentially, one
member of the Conmittee expressed major reservations regarding the regulatory
use of NCLAN data-
With respect to the influence of ozone on natural ecosystems, the
document accurately characterizes the potential for ozone to alter ecosystem
structure and function using the well documented studies in the San
Bernardino National Forest of California. The hypothesis that ozone is a
contributory factor underlying the reported declines in forest productivity
elsewhere in the United States has not been definitively evaluated and
warrants further investigation,
There is growing evidence that ozone is only one of several important
constituents in the complex and often non-linear chemical behavior of regionalr
as well as local air pollution. The Agency needs to pay careful attention
to understanding the nature and implications of these interactions in both
its future research and regulatory activities.
A separate report will be prepared reflecting the Committee's final
conclusions and recommendations on the National Ambient Air Quality Standards
(NAftOS) for Ozone when the Agency's Office of Air Quality Planning and
Standards completes the companion document, the Staff Paper for Ozone
(Review of the NAAQS for Ozone? Assessment of Scientific and Technical
Information).
-------
-3-
Thank you for the opportunity to present the Comnittee's views on
these important public health and welfare issues.
Sincerely,
cc: Mr. A. James Barnes
Mr. Donald Ehreth
Dr. Lester Grant
Dr. Vatm Newill
Mr. Craig Potter
Dr. Terry Yosie
tf/th- •—
Morton Lippmantff'Th.D.
Chairman
Clean Air Scientific Advisory
Committee
------- |