National Academies Questions EPA Assessment of Dioxin

A panel of the National Academies of Science (NAS) has concluded that low doses of dioxin might not be as carcinogenic as the U.S. Environmental Protection Agency (EPA) claimed in a 2003 draft risk assessment. When EPA first published an assessment of dioxin, in 1985, it labeled the chemical a “probable human carcinogen.” EPA upgraded the threat, however, to “carcinogenic to humans,” in a draft reassessment published in 2003. The Interagency Working Group on Dioxin, including representatives of seven federal agencies, recommended further review, a move critics contend was intended to stall federal action based on its conclusions. The NAS panel tasked with reviewing the reassessment took issue with EPA’s decision to rely on a linear model, which assumes the risk of cancer is directly proportional to dose at all exposure levels. NAS argued that some evidence points to a nonlinear model, with a threshold below which dioxin has no impact on cancer risk. The report recommends that EPA estimate the cancer risk resulting from both models and describe the strengths and weaknesses of each. The full report, including this and several other recommendations, is online at www.nationalacademies.org/morenews/20060711c.html.