Defense Environment Alert
an exclusive biweekly report on defense policies
for cleanup, compliance and pollution prevention
Vol. 12, No. 22--November 2, 2004
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 boosts 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 an "incorrect assumption."
But the new findings could help clear the way for final release of EPA's
dioxin risk review, which could be used to establish Superfund and other
waste site cleanup levels 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 cancer responses in a test group exposed to a mixture
of dioxins, PCBs and furans could be predicted based on the responses of
groups exposed to a single chemical in the mixture. The researchers conclude
that EPA's 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. Relevant
documents are available on InsideEPA. com. Seepage 2 for details.
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 Nov. 22 to consider the scope of its upcoming review. The
NAS was asked to conduct the study to help resolve interagency squabbling
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 host of cleanups at state, federal
and military sites where officials have been awaiting the government's final
conclusions. The 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 the study contradicts EPA's position that no
"safe" level of dioxin exposure exists. That position 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 show 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 & 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.