ENVIRONMENTAL
NEWS
Long-running dioxin reassessment nears SAB review
E
PA's dioxin reassessment will be ready for public review this summer and should go before the agency's Science Advisory Board (SAB) this fall, according to EPA officials. The new draft is expected to include much stronger language on the carcinogenicity of the most notorious form of dioxin, 2378-tetrachlorodibenzo-p-dioxin, or TCDD, and a new chapter on toxic equivalency factors (TEF). EPA has finalized regulations for a number of dioxin sources, including medical waste incinerators, since the reassessment began in 1992. The reassessment nonetheless is eagerly anticipated by those concerned that EPA is operating without a clear policy on dioxin. The chapter on risk characterization, a summary of the 2200page document, is expected to include a determination that dioxin 2378-TCDD is a human carcinogen, said William Farland, director of EPA's National Center for Environmental Assessment. The World Health Organization's International Agency for Research on Cancer listed 2378-TCDD as a known carcinogen in 1997, and several groups in the U.S. Department of Health and Human Services plan to follow suit. "The case for referring to 2378TCDD as a human carcinogen is quite strong. The cases for other compounds are not as strong," said Farland, who has led the reassessment for six years. "The strength of our conviction of whether we know 2378-TCDD is carcinogenic in humans is not a matter of our looking at the epidemiological data and saying we can point to that as a definitive answer. It is a matter of looking at what is still limited epidemiological evidence and combining it with some animal and mechanism of action data to say we think there is enough here to push for a call of a known carcino-
There is enough data on 2378-TCDD to push EPA to list it as a known human carcinogen, said William Farland, director of the National Center for Environmental Assessment. (Photo courtesy EPA)
gen." The conclusion reached in 1994 remains that dioxins other than 2378-TCDD are probable carcinogens and some cancer and noncancer effects are seen at background levels. Calling dioxin 2378-TCDD a known carcinogen would be much stronger language than in the 1994 draft. Once such a determination is
The dioxin inventory lists data from over 50 source categories. made, it will be adopted as agency policy and will affect how EPA regulates dioxin sources, said Dave Cleverly in the Office of Research and Development. The risk characterization chapter is undergoing revisions, he said. A revised inventory of dioxin sources including updated emissions data from over 50 different source categories, such as pulp and paper mills and secondary lead smelters, was released in April. The inventory also takes into account the recycling of dioxin in the envi-
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ronment, said Cleverly, head of the inventory project. In 1995, the SAB had criticized the reassessment for not providing a detailed source apportionment to back up its assertions identifying certain sources as major dioxin emitters. The inventory catalogs all of the information that led up to the source determination and is available to the public on the Internet, said Cleverly. The SAB specifically criticized certain aspects of the reassessment, including EPA's reliance on toxic equivalency factors (ES&T, Nov. 1995, 492A). Since the 1980s, convention has suggested that by assigning a TEF to each dioxin congener in a mixture, one can calculate the likely cancer risk or relative margins of exposure for the entire mixture. Because using toxicity equivalency factors is still controversial, the team will devote an entire chapter to TEFs, including the theoretical strengths and weaknesses of relying on them and a discussion of the international consensus on this approach, said Farland. The reassessment will also include updates of the chapters on noncancer health endpoints, as well as a fair amount of new information on lower level noncancer health effects. Well-known studies, including a 1995 Dutch paper describing some neurobehavioral effects in children born to mothers exposed dioxin at typical background levels, have been incorporated. Once the risk characterization chapter is forwarded to the writing group for review this summer, "in essence the document would be out, and would be available to the public," Farland said. The dioxin source inventory is available on the Web (http://www.epa.gov/ ncea/dioxin.htm). —CATHERINE M. COONEY
0013-936X/98/0932-302A$15.00/0 © 1998 American Chemical Society
