Augusts, 1995
EPA-SAB-CASAC-LTR-95-003
Honorable Carol M. Browner
Administrator
U.S. Environmental Protection Agency
401 M Street, SW
Washington, DC 20460
Subject: Review of the Diesel Health Assessment Document
A Panel of the Clean Air Scientific Advisory Committee (CASAC) met on May 4-
5, 1995 to review the scientific and technical adequacy of the Agency's "Health
Assessment Document for Diesel Emissions." Specifically, the Agency asked us the
following questions: 1) Does the document accurately represent the key literature on
diesel emissions? 2) Are the cancer and non-cancer hazard identification and dose-
response assessments scientifically appropriate? In particular: a) Is the application of
dosimetry modeling scientifically sound? b) Are the modes of action appropriately
identified and applied to the health assessment? c) Are the qualitative and quantitative
cancer risk estimates scientifically appropriate? d) Is the diesel reference
concentration scientifically appropriate? and, 3) Is it possible to improve the diesel risk
characterization in the document, given the inadequate exposure information to
compare to the quantitative health assessment?
It was the consensus of the Panel that the present document is not scientifically
adequate for making regulatory decisions concerning the use of diesel-powered
engines. It is outdated and needs to be substantially revised and re-reviewed before
the CASAC can come to closure. The Panel members provided the Agency with
extensive comments on the document at the meeting and subsequently in writing.
Because of the rapid rate of change of relevant knowledge, the document is
considerably out of date. A number of important new studies have not been included or
adequately considered, and the Panel felt that their inclusion would change the focus
and conclusions of the report. For example, EPA's quantitative risk assessment for
lung cancer is based on animal carcinogenicity data for only one species, the rat, with
no comparable response in two other species. The cancer-causing mechanism in the
rat may be unique to the rat and does not appear to occur in other species including
humans. The mechanism in rats is apparently related to particulate overload followed
by a sequence of events beginning with inflammation and ending in tumorigenesis.
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These events are conditional upon particle overload which also occurs in rats
exposed to high concentrations of inert dusts as well. Consequently, it appears that
these studies are not relevant for human risk assessments.
We appreciate the opportunity to assist the Agency, and we look forward to
receiving the revised version when it is available.
Sincerely,
Augusts. 1995
Dr. George T. Wolff *S Date
Chair, Clean Air Scientific Advisory Committee
Science Advisory Board
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