UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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- ' October 13, 1983
OFFICE OF
THE ADMINISTRATOR
Honorable William D. Ruckelshaus
Administrator
U.S. Environmental Protection Agency
401 M Street, S.w.
Washington, D.C. 20460
Dear MJT. Ruckelshaus?
The Environmental Health Committee of the Science Advisory
Board has completed its review of a revised Draft Health
Assessment Document for Acrylonitrile prepared by the Agency's
Office of Research and Development. The major conclusion of
the document was that, in combining the animal and human
evidence, acrylonitrile would be placed in group 2A of the
International Agency for Research on Cancer's (IARC) classifi-
cation system. Osing' the IARC criteria acrylonitrile is
characterized as probably carcinogenic in humans, where the
evidence for human carcinogenicity is almost sufficient. The
Committee concurs with this statement and concludes that the
health assessment document is scientifically adequate for use
in regulatory decision-making*
The revised Draft Health Assessment Do'cuMentf ~f or' Acrylo—
nitrile has been reviewed by the Science Advisory Board on
August 3 and December 9, 1982, and June 10, 1983. Agency
staff have proven responsive to SAS, requests for revisions,
particularly in the development of a quantitative risk
assessment* As a result, the Board is satisfied that the
November 1982 draft document presents a-thorough analysis of
existing information -concerning the sources of acrylonitrile
in the environment and the consequences'~to "animal and human
populations of exposure to this pollutant..
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Additional comments and recommendations are summarized in
the attached report. The Environmental Health Committee
appreciates the opportunity to provide its advice on this
important issue.
Herschel
C hairpian
Environmental Health Committee
farnest P. Gi|oyna
hairman
Science Advisory Board
Attachment
cc: Mr. Alvin Aim
Dr. Courtney Riordan
Dr. Terry F. Yosie
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Environmental Health Committee Key Findings and
Conclusions on the Revised Draft Health
Assessment Document for Acrylonitrile (November 1982)
1. The chapters on air quality have been revised to
incorporate more recently available data on acrylonitrile
sources, emission estimates and ambient air concentrations
based upon a comparison between monitoring data and data
generated from air quality dispersion modeling. Such revisions
are appropriate and present a more complete profile of
acrylonitrile in the environment.
2. Acrylonitrile exposures to humans are associated with
health effects such as irritation of the eyes and nose, central
nervous system impairment and cancer. The earcinogenigity of
acrylonitrile has been assessed in seven cancer bioassays in
rats, and ten human epidemiological studies, published and
unpublished, were discussed in the .document. The_.Commit tee
i
found the Agency's analyses of this information both balanced
and thorough. •'" ....._.... . . -
%The findings of these studies related to cancer include a
•* ,
significantly.increased risk of cancer of_the stomach antl of
the lymph system and a statistically significant risk of lung
cancer in the populations studied. Comparing these results
with the criteria for carcinogenicity developed by the
International Agency for Research on Cancer (IARC), the Agency
concluded that the animal data presented "sufficient" evidence
of carcinogenicity and the human data constituted "limited to
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sufficient" evidence of carcinogenicity. Combining these two
data sets, the document asserts that acrylonitrile should be
classified as 2A, the category of the IARC criteria which reads
"probably carcinogenic in humans, where the evidence for human
carcinogenicity is almost sufficient." The Committee concurs
with this assessment as well as the scientific rationale
developed in the document to support it.
3. The section of the document that was vastly improved
was the presentation of the quantitative information that
addressed cancer risk. Several particular areas of improvement
included:
o clear presentation and discussion of the basis for
use of the linear non-threshold multistage model, the
mathematical assumptions associated with utilization of
the model, and use of particular studie's from which the
gg.• unit risk numbers for the linear model were generated.
important were the caveats explaining that the
~~2 ' Itirear non-threshold model, at best, provided a rough but
let""bound limit of the cancer risk, i.e., it is not
likely that the true risk would be higher•than the estimate,
but it could be lower.
o discussion of the potency of acrylonitrile compared
to other suspected carcinogens. Table 13-161, which
illustrates this comparison, is a particularly effective
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. '• -3-
display of the relative potencies of these substances and
their estimated unit risks. The Agency agreed to modify
Table 13-161 to indicate that the values stated are upper
bound risk estimates,
o agreement by the Agency to include in the document
information presented to the Committee on estimates of
unit risk derived from using three models that are
alternatives to the linear non-threshold multistage model.
These include the Logitr Probit and Weibull models. The
inclusion of these alternative methodological approaches
will considerably clarify the Agency's rationale for its
risk assessment approach,
The Committee made additional suggestions for improving
the final health assessment document for acrylonttrile- which are
i
.included in the transcripts of the Committee's meetings. With
the understanding that, these" changes will "be incorporated in
the ""final document, the Environmental Health -Committee has
unanimously concluded that the document is scientifically
adequate ..for use in regulatory decision-making.
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