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By Pat Rizzuto
The Environmental Protection Agency established its first-ever “safe dose” for dioxins Feb. 17 as part of an updated health assessment that determined current levels of exposure to dioxins do not pose a significant health risk.
The “safe dose,” properly called a reference dose, or RfD, is to help health officials determine when exposure levels might lead to thyroid, fertility, dental, immunological, and other health problems other than cancer.
EPA set the RfD at 0.7 picogram of dioxins per kilogram bodyweight per day. That compares to individuals' estimated intake of dioxins in food and water of about 0.6 picogram per day, EPA told Bloomberg BNA in an e-mail.
“Today's findings show that generally, over a person's lifetime, current exposure to dioxins does not pose a significant health risk,” the agency said in its announcement of the document.
“The non-cancer health assessment for dioxin released today could be considered in a range of agency activities, from establishing cleanup levels at superfund sites, to reviewing the dioxin drinking water standard as part of EPA's regularly scheduled review process, to evaluating whether additional Clean Air Act limits on dioxin emissions are warranted,” EPA said.
EPA has said it would complete the cancer portion of its dioxins assessment as soon as possible following the release of the non-cancer analysis (169 DEN A-8, 8/31/11).
Rep. Edward Markey (D-Mass.) said EPA “has taken a major step toward protecting the public from dioxin by shining light on some of the health impacts this dangerous chemical has on the public.”
“By releasing this important part of the scientific assessment, we can begin to develop a cohesive plan to safeguard American families from dioxin exposure. It is also time for industry groups and chemical companies to stop their efforts to block completion of this important public health document. I urge EPA to continue this progress forward by moving quickly to finalize the cancer portion of the dioxin assessment as well as its cleanup goals for soil at waste sites containing dioxin,” Markey said.
EPA issued its first assessment of dioxins in 1985 after the chemical had been discovered in the herbicide Agent Orange, which the U.S. military extensively sprayed during the Vietnam War. That assessment also followed discovery of dioxins in Love Canal in Niagara Falls, N.Y., in 1978 and in 1983 on the streets of Times Beach, Mo., where it prompted EPA to buy out a town of 2,000 residents.
The agency has repeatedly been challenged by experts, regulated parties, and other interested groups as it has sought to update its assessment in the intervening years.
The American Chemistry Council promptly voiced concerns about EPA's analysis in a Feb. 17 statement.
The trade association criticized EPA for releasing the non-cancer analysis of its dioxins assessment separately from its analysis of the chemicals' carcinogenic effects, saying the agency ignored recommendations by the National Academy of Sciences to issue a complete assessment.
“Furthermore, it is not clear why the agency set a dioxin level [RfD] that is three times more stringent than other countries and the World Health Organization if the EPA contends that current levels of dioxin do not pose a health concern,” the council said.
“We are disappointed with the EPA's decision to publish a scientifically flawed dioxin reassessment that provides no defined public health benefit,” the council said.
ACC referred to the agency's RfD as “overly stringent,” council spokesman Scott Jensen told Bloomberg BNA. If dioxins pose no risk to human health, as the agency says, it is unclear why future regulations need to be considered, he said.
Meanwhile environmental health advocacy groups praised the agency for releasing this portion of its assessment.
“We applaud EPA,” Jennifer Sass, a senior scientist with the Natural Resources Defense Council, told Bloomberg BNA.
“EPA's effort to assess the risks of dioxin have been delayed time and time again despite overwhelming scientific evidence supporting EPA's assessment, and approval in 2010 by EPA's independent Scientific Advisory Board,” she said.
“The chemical industry has been in a lather over EPA's decision to release the non-cancer portion of its assessment of dioxin with a non-cancer risk estimate (i.e. reference dose, RfD), rather than waiting until completion of its cancer assessment.
“However, EPA's procedural decision to issue the portion of the assessment it has completed will provide the public and regulators with a clear consensus statement on the most current estimated risk associated with dioxin exposure, and the supporting scientific evidence and rationale,” Sass said.
The term “dioxins” refers to a family of 30 chemicals that are not deliberately manufactured, but occur as byproducts of incomplete incineration, paper production, and forest fires. After release into the environment, they can bioaccumulate in the food chain. They also can be detected as residual contaminants in some soils.
The toxicity of the dioxin family is based on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most-studied dioxin and the compound believed to be the most toxic.
Reference doses are EPA's estimate of a daily ingestion level below which human health would not be harmed.
Although EPA analyzes available animal and human toxicity, it generally bases its RfDs on those toxicological studies that have found a problem at the lowest dose.
In the case of this dioxins reassessment, EPA based its RfD on two human studies that found young children and infants exposed in the womb might have the levels of their thyroid hormone disrupted or decreased sperm levels and decreased sperm motility.
The RfD is intended to be low enough that these effects should not occur even in vulnerable portions of the population.
EPA's assessment and related documents are available at http://www.epa.gov/iris/supdocs/1024index.html.
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