UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
"' '''
WASHINGTON, D,C- 20460
NOVEMBER 23, 19S3
OFFICE OP
THE
Mr. William D. Ruckelshaus
Administrator
U.S. Environmental Protection Agency
401 H Street, S.W*
Washington, D,C. 20460
Dear Mr. luckelshaus;
The Environmental Health Committee of the Science Advisory
Board has completed its review of revised drafts of the
Health Assessment Document for 1,1,l-*Trichloroethane (Methyl
Chloroform) prepared by the Agency's Office of Research
and Development. The major conclusions of the document state
that in tests conducted to date, there is no adequate scientific
basis for determining the carcinogenicity of Methyl Chloroform
CMC}, Recent information available on the biologic effects
of MC and its role in contributing to an increased incidence
of skin cancer as a result of ozone depletion also downplays
the potential role of this chemical. As a result, a definitive
evaluation of MC and its contribution to health hazards in
the workplace or as the result of ambient exposures is not
possible at the present time.
Drafts of the Health Assessment Document for Methyl
Chloroform have been formally reviewed by the Committee on
September 28-29, 1982 and December 8, 1982. In addition, a
revised draft dated May 1983 has been discussed with the
Committee at a public meeting on June 10, 1983. The Committee
understands that the May 1983 draft will be further changed
to reflect the most current status of the National Toxicology
Program (NTP) 1983 rat study.
Agency staff have adequately responded to Committee
advice for revising the document in terras of the discussion
of the carcinogenicity issue as well as other issues. The
Committee is satisfied that the revisions to the November 1982
and May 1983 documents present a thorough and balanced
treatment of the existing scientific literature concerning
this pollutant.
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Committee comments and recommendations on these successive
drafts of the document ar© summarized in the attached report.
A full record of the Committee's review of Methyl Chloroform
is contained in 'the transcripts on file at the Science Advisory
Board* With the understanding that the final document will
incorporate the further changes discussed with Agency staff,
the Committee unanimously concludes that the assessment
document is scientifically adequate.
Sincerely,
Herschel E, Grifl
Chairman
Environmental Health Committee
Science Advisory Board
Attachment
ccs Mr* Alvin Aim
Mr. Joseph Cannon
Dr. Bernard Goldstein
Dr. Lester Grant
Dr. Terry Yosie
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Environmental Health Committee Key Findings, Conclusions
and Recommendations on the Revised Draft Health
Assessment Document for l,lrl-Trichloroethane
(Methyl Chloroform) (May 1983)
1. The Summary and Conclusions chapter has been revised
in response to recommendations made by the Committee, In the
Committee's view these revisions have enhanced the quality of
this chapter by;
* expanding the discussion of directly-induced
health effects to delineate No-Observed Effects Level
(NOEL) estimates from Lowest-Observed Effects Level (LOEL)
numbers for Methyl Chloroform, These estimates have in
turn been contrasted with 'the generally much lower level
ambient Methyl Chloroform exposures.
* clarifying the role of Methyl Chloroform as a
contributing factor to ozone layer depletion and to a
consequent rise in the incidence of skin cancer. Recent
evaluations of this issue by the world Meterological
Organization and the National Research Council suggest
that the potential role for MC is smaller than indicated
in previous drafts of this document.
2. The document and EPA staff discussion of the issue
of the carcinogenicity of Methyl Chloroform is more straight-
forward in presenting and assessing the current state of
knowledge* Staff have indicated that there is no adequate
basis at the present time for evaluating the carcinogenicity
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of this chemical. Acknowledgment is given to previous
assessments of MC carcinogenic!ty and why those assessments
have proven inconclusive.
The Cancer Assessment Group's (CAG) evaluation of the
carcinogenicity of MC will not include a discussion in the
document of the results of the lifetime animal bioassay
carried out under the auspices of the National Toxicology
Program (NTP), CAG staff have informed the Committee they
will evaluate the results of this study when they are finalized
and available from NTP. In the meantime, they and their
colleagues in the Office of Research and Development plan to
finalize the Health Assessment Document for Methyl Chloroform
and to incorporate information on the current status of the
NTP work. The need to modify or issue an addendum to the
document to incorporate NTP results will be determined by
EPA staff at the time of final issuance of the NTP results.
The Environmental Health Committee concurs with the judgment
reached by Agency staff on these matters.
3. The discussion of the biotransformation of Methyl
Chloroform to reactive intermediate metabolites overstates
the case* There is insufficient scientific evidence to
support the EPA position as stated in the document. The final
document should incorporate a revised statement that indicates
that this issue has not been resolved. EPA staff have
concurred with this recommendation.
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4, Information has been added in several of the chapters
that strengthen the document. This includes: updating of
information on sources, emissions and ambient concentrations
of MC (chapter 3); and including recent studies on metabolism
and pharmacokineties (chapter 4)f and neurotoxicology,
behavioral toxicology and mutagenicity (chapter 5).
5. As part of the overall assessment of Methyl Chloroform,
major information gaps or research needs should be briefly
identified.
The Committee made additional suggestions for improving
the final document which are included in the transcripts of
the Committee's meetings. With the understanding that these
and other changes identified in this report will be incorporated
in the final Health Assessment Document for Methyl Chloroform
the Environmental Health Committee unanimously concludes that
the document is scientifically adequate.
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