Dioxins Reassessed

A new draft reassessment of dioxins by the Environmental Protection Agency takes into account both cancerous and noncancerous health effects of this group of compounds. Released today, the long-awaited draft reassessment would also, for the first time, set a safe daily dose for the most toxic form of dioxin: 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Once finalized, the reassessment will affect a host of regulatory decisions affecting a group of compounds collectively called dioxins, including TCDD, polychlorinated biphenyls, and polychlorinated dibenzofurans. Most notable will be the amount of cleanup needed for river sediments contaminated with dioxins. The reassessment could also affect rules governing air and water pollution, as well as waste disposal.

For TCDD, the draft report would set the safe daily dose at 7 × 10-10 mg per kg of body weight per day. This dose is designed to protect people from adverse reproductive and developmental effects. The draft report would also classify TCDD as carcinogenic to humans.

The draft report updates the agency's first official risk estimates for dioxins, which were set in 1984 and are based solely on cancer concerns. The agency began reassessing those numbers in 1991 and has produced several drafts that suggest dioxins have health effects other than cancer.

In 2006, the National Research Council said EPA needed to refine its draft assessment by spelling out what is and isn't known about the risks from exposure to dioxins (C&EN, July 17, 2006, page 9). In the latest draft, EPA says it analyzed parts of its dose-response assessment for dioxins but "concludes that a comprehensive uncertainty analysis is infeasible at this time."

EPA's Science Advisory Board will review the draft in July. EPA says it will update the draft to incorporate comments from the advisers and the public. EPA Administrator Lisa P. Jackson has directed the agency to finalize dioxin reassessment by the end of 2010 (C&EN, June 1, 2009, page 5).

The draft is available through cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=222203.