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The Science Advisory Board (SAD) recently endorsed the U.S. Environmental Protection Agency's (EPA) long-awaited Dioxin Reassessment. The SAB endorsement was accompanied by some serious criticisms concerning the “gaps in the science”, but it was, nonetheless, an endorsement that allows EPA to move to complete the Reassessment within the next few months. The implications for the regulated community are likely to be far-reaching. While the Dioxin Reassessment is a scientific document and has no direct authority over the host of rules and regulations the Agency is currently drafting, ii will govern many of the options EPA can consider when proposing and promulgating those rules. The Biosolids Part 503 rule, in particular, will be one of the first such test cases where the science will guide EPA's decisions.

The Dioxin Reassessment contains information on sources of emissions, environmental pathways that will serve as a road map for exposure risk assessments, and, a risk characterization that suggests adverse health effects may be occurring at background levels of exposure In the human population. The cancer risks, although not very specific in terms of target organs, are estimated to be an order of magnitude greater than previously thought. The non-cancer health effects are based primarily on extrapolation from animal studies to humans, and the SAB panel pointed out that some of the effects are merely biochemical reactions, but some are clinically significant.

The EPA intends to propose specific program actions to control releases to air and water, as well as for contamination of land and products. The Agency will also address cross-media transfers of dioxin in the environment. Additionally, the United States Department of Agriculture and the Food and Drug Administration has requested the National Academy of Sciences to conduct a review of dioxin levels in the nation's food supply. More than 95 percent of the human body burden or dioxin and dioxin-like compounds is attributed to the food supply.

These findings do not bode well for a number of industrial activities in the United States. EPA considers the land application of biosolids as an uncontrolled release of dioxin into the environment. The industry has begun the difficult task of describing the various forms of biosolids management in the U.S. and its relatively low contribution of dioxin in the overall inventory. Another difficult task before the industry is the development of a fact-based rationale that explains why land application practices are an insignificant source of dioxin contamination compared to air deposition sources. Some recent literature describes the increment to human exposure from biosolids land application, through the food chain, is well within background levels and does not pose additional health threats. This message must be well documented and presented in a timely manner if it is to influence the EPA's decisions relative to the Part 503 regulatory effort.

Document Type: Research Article


Publication date: January 1, 2001

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