Dow-Funded Dioxin Study Of Limited Value

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Cheryl Hogue/C&EN

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Signs posted by the state like this one warn against consuming fish from waterways downstream of Dow's headquarters in Midland, Mich.

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A major scientific study of human exposure to dioxins downstream of Dow's flagship plant is of "limited value" to regulators, according to EPA.

The study by researchers at the University of Michigan was conducted in 2004 and 2005. The principal investigator has told C&EN that the study finds that living on dioxin-contaminated soil does not contribute to the level of dioxins in people's blood. Dow funded the investigation in an unrestricted grant (C&EN, Oct. 20, 2008, page 7).

The results of the study were expected to influence the extent of cleanup Dow will conduct in the Tittabawassee River, Saginaw River, and Saginaw Bay downstream of the company's plant in Midland, Mich. The chemical maker's past operations contaminated the waterways with chlorinated furans and dioxins (C&EN, Aug. 11, page 15).

The University of Michigan study, EPA says, was well-conducted and provided useful, scientifically credible information. But several significant issues limit the usefulness of the study for the agency's evaluation of people's exposure to dioxins, according to EPA.

The study did not include children, who touch and ingest more soils and dusts than do adults and thus tend to have higher exposures to contaminants, EPA says.

In addition, the agency says it is unclear to what extent the investigation included people whose activities, such as eating local fish and game, could boost the levels of dioxins in their bodies. Also unclear, EPA says, is whether the study included a sufficient number of contaminated properties. There are a number of highly contaminated properties along the two Michigan rivers, it adds.

Dow is reviewing EPA's critique of the University of Michigan study in detail, says Mary Draves, a company spokeswoman.

According to David H. Garabrant, an emeritus professor of environmental health sciences and epidemiology who led the study, children were left out because it is not safe to take a large enough blood sample from small children to detect key dioxin congeners. "This is not a deficiency of our study; it is a limitation of science," he tells C&EN.

Garbrant contends that there were an adequate number of people studied who were living on contaminated land to estimate the association between the concentrations of dioxins in the soil and their blood. And, he says, researchers are still studying fish consumption data. "EPA is drawing conclusions that the study is irrelevant before we have had the opportunity to complete the analyses," he says.

EPA and Dow are working out a cleanup plan for the area and are expected to announce a proposed agreement in mid-October.

The website for the study is at www.sph.umich.edu/dioxin.

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