An   SAB   Synopsis
Volume 1 Number 2
                            A Summary of a Just-Released SAB Report
                        October 13,
                        1998
  Review of the Agency's Diesel Health Assessment Document
                          EPA-SAB-CASAC-99-001
   T1
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        •'he Clean Air Scientific Advisory Committee
        .(CASAC) of the Science Advisory Board
(SAB) of the US EPA (Agency) has completed a review
the Agency's assessment of the health effects of inhaling
diesel exhaust. While acknowledging the difficulty of the
task,  CASAC encourages the Agency to revise the
document, which was judged to be not acceptable as a
summary of the current knowledge of the health effects of
diesel exhaust inhaled in the environment.  Consequently,
in CASAC's view, it does not serve as an acceptable basis
for regulatory decision making, based on adverse health
effects.
      The CASAC's concerns are four-fold:
      1. Some of the information was judged  to
considerably out of date. For example, the changes in
diesel engines and their emissions that have occurred in
the 1990s is not reflected in the document.
      2. Neither of the two approaches employed by the
Agency to use animal data to generate estimates of human
risks associated with environmental exposure to diesel
exhaust was found to be supported by present knowledge.
      3. The document fails to distinguish the effects of
diesel  exhaust,  per se,  from the effects of PM 2.5
(particulate matter less than 2.5 microns in diameter), of
which it is a constituent.
      4.  The  human  epidemiological data  from
occupational exposures  present the  strongest  current
evidence for human cancer risk from  inhaled diesel
exhaust. However,  the  Agency's document does not
effectively address  ongoing debates about the existing
data. In the end the  CASAC could not reach a consensus
on whether a quantitative,  rather than a qualitative,
assessment can be scientifically justified at
this time.
      This marks the third time that the
CASAC has reviewed the Agency's health
risk assessment of diesel exhaust.  In its
prior review — in 1990 and 1995  — the
Committee  identified   a   number of
shortcomings, some of which persist in the
current document.
      The CASAC believes that a credible
document is within the Agency's grasp it
sufficient attention is given the matters
raised in this report.   The Agency is
encouraged  to  engage  CASAC  in a
discussion of its proposed  strategy for
remedying the document's deficiencies, prior
to completing the next revision.
   A complete copy of this report from the
SAB's  Clean  Air  Scientific  Advisory
Committee is available
      1. On the SAB Website
            [http :/www. epa.gov/sab]
      2. By request from the SAB office
            through   Email
            [pope.derrick@epa.gov], or
      3. By Fax [202-260-1889].
         Office of the Science Advisory Board, US Environmental Protection Agency
                            Website: www.epa.gov/sab

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