EPA Advisers Move Closer to Approval Of Revised Arsenic Cancer Risk Estimate

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An advisory board of scientists moved a step closer Nov. 22 to completing a review that would allow the Environmental Protection Agency to issue a new assessment for the risk of cancer from arsenic in drinking water, possibly in the next six months.

The EPA Science Advisory Board gave its conditional approval to a review that would recommend clarifications, but no basic changes, to EPA's draft Toxicological Review of Inorganic Arsenic, which contains a much higher estimate of risk.

In a wide-ranging teleconference, the board suggested the panel writing the review make some alterations that would sharpen the language of the document and avoid ambitious suggestions about updating research.

The board voted its conditional approval after hearing sometimes scathing comments by independent scientists and industry representatives who argued that EPA's cancer risk assessment was poorly done.

Members of the Science Advisory Board expressed some discomfort over those comments, but in the end decided to stick to a narrow interpretation of their task--to critique any perceived flaws in the panel's review but not spend time debating the fundamentals of the science behind the EPA assessment.

The draft cancer risk assessment from EPA's National Center for Environmental Assessment would increase the estimated risk of cancer about 17 times from its current level, as measured by a “cancer slope factor,” which charts cancer risk at various levels of exposure.

Such a change could have costly implications for drinking water utilities, companies involved in waste management, waste site cleanups, and other organizations. Agricultural companies have expressed fears about public perceptions of food safety, given the fact that arsenic is a naturally occurring substance can be found at low levels in some food and water.

Criticism of EPA's Science

The Science Advisory Board heard scientists argue that EPA had botched the job of estimating the risk of cancer at low levels--levels typically encountered in the United States.

EPA mishandled data from southwestern Taiwan in ways that blur the distinction between low-exposure village data and other data, and in some cases misclassify a high-dose village as a low-dose village, said Steven H. Lamm, an independent epidemiologist. It may be that arsenic is a carcinogen at high levels but not at low levels, according to Lamm. But the EPA draft relies on a “linear” extrapolation of risk that assumes a steady decline in risk by level of exposure, with no elimination of risk above zero exposure.

Samuel M. Cohen, a University of Nebraska professor who specializes in cancer research, said all postulated modes of action for arsenic to cause cancer point to a risk assessment that could include a threshold below which arsenic is not carcinogenic. The “linear” extrapolation by EPA, allowing for risk even below the regulated permissible U.S. levels, flies in the face of that reality, he argued.

EPA is relying entirely on southwestern Taiwan studies for its arsenic risk assessment. Former EPA toxicologist Barbara Beck, now a principal at consulting firm Gradient Corp., said EPA should have reconciled contrasting arsenic research by using a weight-of-evidence analysis for all of the better low-dose studies together, not just the Taiwan research in isolation.

Kevin Bromberg, an attorney for the U.S. Small Business Administration's Office of Advocacy, said there is little evidence that the SAB's review panel has responded to the criticisms from non-EPA experts. The advisory board should at least discuss the criticisms, he argued.

Substance of Criticism Not Addressed

The board members expressed uneasiness about the criticisms, but did not address the substance of the comments. They praised the review panel, which has tentatively supported the EPA work (41 ER 2416, 10/29/10).

The review panel had discussed the idea that EPA consider some type of “reality check,” possibly a review of bladder and lung cancer rates in the United States to see whether the new estimate of arsenic cancer risk could be reconciled with the statistics on U.S. cancer. But the panel was tentative in its discussion, and that section of the review was criticized during the board meeting, making it doubtful that the idea would survive to the final version of the review.

Deborah Swackhamer, a University of Minnesota professor and SAB chairwoman, asked EPA's John Vandenberg what the agency's next steps might be.

Cautioning that he was offering his own guess, Vandenberg said EPA would take four to six months to consider the Science Advisory Board's comments, make final changes, and issue the assessment as an update to EPA's Integrated Risk Information System.

By Alan Kovski  


Information on the Nov. 22 teleconference of the EPA Science Advisory board meeting to consider the draft cancer risk assessment for inorganic arsenic is available at http://yosemite.epa.gov/sab/sabproduct.nsf/MeetingCal/138473F4B37B3225852577B300516041?OpenDocument.