In 1994, the Environmental Protection Agency (EPA) issued its Dioxin Reassessment in draft form for peer review. Since that time, the understanding of dioxin science has continued to advance, and the document has been the subject of study and debate. In October 2004, EPA delivered its updated draft dioxin reassessment to the National Academy of Sciences (NAS) for review.
On July 11, 2006, the NAS issued a report on its review of the EPA DRAFT dioxin reassessment. According to the NAS review committee, “Although the U.S. Environmental Protection Agency presented a comprehensive review of the scientific literature in its 2003 draft reassessment of the risks of dioxin, the agency did not sufficiently quantify the uncertainties and variabilities associated with the risks, nor did it adequately justify the assumptions used to estimate them.” The committee recommended that EPA better estimate the risks using several different assumptions and communicate the uncertainties in all estimates. The essence of the NAS panel’s findings is that the Draft Dioxin Reassessment overstated the risks from dioxin exposure and that the scientific information combined with the use of probabilistic risk assessment methods would support a different estimate of the theoretical risk.
We are encouraged by our review of the expert panel's report. Overall, the NAS panel was critical of EPA’s approach and encouraged EPA to use a more robust range of models and more current data. Specifically the committee found compelling data to justify the use of threshold (nonlinear) methods for estimating cancer risk at relatively low levels of exposure, which would result in a lower estimate of risk than in EPA's DRAFT reassessment. The report recommends that cancer risks be estimated using several models, describing the strengths and weaknesses of each. The report also recommended that EPA write a more thorough chapter on risk characterization that includes a comprehensive discussion of uncertainties of their risk assessment. The NAS panel also criticized the methods used by EPA for characterizing theoretical non-cancer risks for dioxins. In addition, the NAS panel strongly endorsed the use of probabilistic methods for evaluating the risk related to dioxins. The NAS panel made many other constructive comments regarding EPA”s risk characterization that should result in a much more accurate and robust derivation of the risk characterization for dioxin.
However the NAS panel’s task was not to provide actual dioxin risk assessment guidance. It is up to the agencies to set policy. Regulatory agencies will now evaluate the panel's findings to determine how to incorporate them into their own policies and regulations. And much work remains to ensure EPA incorporates the committee's findings into a finalized dioxin risk assessment in a timely fashion.
It is important to note that industrial dioxin releases continue to decline. Today, average dioxin levels in foods such as meat, fish, poultry and dairy products, have returned to the low levels measured in foods stored from the early 1900s prior to the industrial expansion of the 20th century. This success is due to a combination of government regulations and voluntary industry efforts.
