EPA Releases IRIS Assessment of Dioxin Non-Cancer Risks

Matt Shudtz

Feb. 17, 2012

Today EPA released the first part of its long-awaited reassessment of the human health risks posed by 2,3,7,8-tetrachlorodibenzo-p-dioxin, a chemical considered to be the most toxic of the dioxin compounds and the stuff that made Agent Orange so bad for its victims.  It’s bittersweet news: on the one hand, the decades-long stretch between EPA’s first look at dioxin and this document is something we don’t like to see, while on the other, today marks an enormous step forward. The document released today focuses only on non-cancer effects and sets an oral reference dose—the level of exposure below which key health impacts are unlikely to occur.  Past EPA assessments looked only at dioxin’s carcinogenic risks, so it is an important development that today’s release looks at the many other adverse health outcomes that might occur, such as “chloracne, developmental and reproductive effects, damage to the immune system, interference with hormones, skin rashes, skin discoloration, excessive body hair, and possibly mild liver damage.”

As Ben Somberg noted here in December, the American Chemistry Council tried to convince EPA that a rider to the FY2012 omnibus spending bill required the agency to pull back the dioxin assessment.  CPR President Rena Steinzor and I wrote a letter to EPA Administrator Lisa Jackson to correct the record on ACC’s false claim.  The letter explained how the House had earlier considered a version of the bill that required EPA to rework all draft and final IRIS assessment due out in FY 2012, but ultimately went with a bill that requires revision of only the draft assessments and not the final assessments.

Good for EPA for calling the chemical industry’s bluff!

The most important part of EPA’s dioxin risk assessment is still in the works.  The cancer-focused part of the assessment continues to be under review.  The National Academy of Sciences undertook a two-year review of EPA’s draft dioxin assessment (both the non-cancer and cancer analyses) in 2004-2006.  There’s no question that dioxin is a carcinogen.  This protracted fight over the cancer part of the assessment revolves around exactly how dioxin and related compounds cause cancer.  It matters because the mode of action determines the shape of the dose-response curve, which will ultimately impact EPA’s best guess as to the “safe” level of dioxin exposure.  The lower the level, the more expensive Superfund cleanups become and the more likely it is that guidelines for meat and dairy consumption will have to be rethought.  (Dioxin bioaccumulates in fat, resulting in the public’s primary routes of exposure being beef, dairy, and freshwater fish consumption.)

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