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Federal Study Backs Controversial EPA Approach To Dioxin Mixtures

EPA scientists say a major new federally funded study on dioxin and
related compounds confirms the agency's risk assessment approach to
mixtures of the chemicals and provides a boost to its controversial
dioxin report just as the National Academy of Sciences (NAS) is beginning a
critical review of the document.

Industry has long challenged EPA's approach to dioxin mixtures, saying
in written comments to the agency last June that assuming the toxicity of
different dioxin-related chemicals can be added together is "incorrect."
But the new findings could help clear the way for final release of
EPA's dioxin risk review, which could be the basis of Superfund and other
waste site cleanups where dioxin, furans and polychlorinated biphenyls
(PCBs) are often found in mixtures.

The National Institute of Environmental Health Sciences released a
study Oct. 20 that found the pattern of cancer responses in a test group
exposed to a mixture of dioxins, PCBs and furans could be predicted based on
the pattern of responses by three groups exposed to each chemical in the
mixture. The researchers conclude that EPA reliance on "toxic equivalency
factors" (TEFs) in evaluating mixtures of dioxin, PCBs and furans is
valid. "These data support the use of the TEF approach for dioxin
cancer risk assessments," according to the study.

One EPA official says the study "blows a big hole in industry
arguments about the reliability of our approach to dioxin mixtures and adds
support to what we've been saying." The study was released just weeks before
the NAS holds a public meeting on Nov. 22 to examine the scope of its
upcoming review. The NAS was asked to conduct the study to help
resolve interagency squabbling within the administration over EPA's dioxin
risk review, which has been 15 years in the making.

NAS approval of EPA's risk conclusions could clear the way for release
of its dioxin report which could prompt a a host of cleanups at state,
federal and military sites where officials have been awaiting the
government's final conclusions. NAS must still form a study panel to
consider EPA's dioxin risk methods.

But industry sources say there are still problems with mixtures
analysis despite the new findings, and that the study contradicts EPA's
position that no "safe" level of dioxin exposure exists, a position which in
part prompted the NAS review because other federal agencies and
international organizations have found there is a safe level of exposure to the
group of compounds.

An official with the Chlorine Chemistry Council, which has questioned
EPA's dioxin risk methods, says the most important finding in the new
study is that dose-response patterns for each cancer observed
determined that there is a "safe" level of exposure, calling into question
another key aspect of EPA's risk assessment. The source says EPA's approach is
in the minority given that the federal Agency for Toxic Substances and
Disease Registry, the World Health Organization, and the European
Union all hold that a "safe" level of exposure exists, while EPA does not.

EPA scientists say the agency's stance on safe exposures to dioxin is
in part a "policy" rather than a purely scientific determination, and say
they look forward to receiving the results of the NAS review.

Source: http://environmentalnewsstand.com/epanewsstand_spclsubj.asp?s=toxics

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