Expert report on EPA dioxin reassessment suggests improvements

Kathie Marchlewski, Midland Daily News

07/12/2006

The long-awaited and objective third-party review of the Environmental Protection Agency's reassessment of dioxin released Tuesday creates more work and more questions, but both The Dow Chemical Co. and Michigan Department of Environmental Quality agree the dialogue it creates is valuable.

The National Academies' National Research Council report confirms that dioxin is toxic, but questions the level at which it is harmful and the methods used to figure it out.

"The interpretation is controversial," said Dow Toxicologist Bob Budinsky. "Overall, I think it's an objective critique of how to conduct a dioxin risk assessment."

Equally important to the local contamination situation, Dow officials say, is this month's World Health Organization downgrading of the toxicity of the Tittabawassee River's primary contaminant, known as 2,3,7,8 pentachlorodibenzo furan. The furan makes up about 50 percent of the mix of dioxins and furans in river sediment, and a smaller percentage, about 5 percent, of what is in Midland-area soils.

Previously, the furan had been considered half as toxic as the most potent from of dioxin, TCDD, but now is considered less than one-third as toxic, and has been assigned a "toxic equivalency factor" in relation to TCDD of 0.3.

The lowered toxicity doesn't mean there will be changes to the way the state calculates its 90 parts per trillion direct contact criteria. Instead it could mean adjustments to the way dioxin in soil is measured. A soil sample containing 1,000 ppt of the dioxin/furan mix, for example, depending on the portion that is the penta furan, might now be recalculated to 800.

DEQ spokesman Robert McCann said the department will take the change into consideration for samples that have been analyzed to determine the variety and extent of each dioxin and furan congener.

He pointed out that when properties have contamination levels in the thousands -- some along the flood plain do -- the difference will be slight. "Does it lower the toxicity? Sure," McCann said. "But it doesn't suggest that now there's nothing to worry about."

The DEQ will be looking to the EPA for guidance on how to incorporate the report. EPA is reviewing the report and preparing a response, Project Manager Gregory Rudloff said.

"The report doesn't change anything," DEQ spokesman Robert McCann said. "It basically just tells the EPA they need to finish their reassessment."

In the report, the committee took issue with the way EPA estimated cancer risk, with the spectrum of studies it chose to rely on, and the extent to which -- or lack thereof -- it explains uncertainty that still exists.

Because the data indicating cancer and immune system health risk come from occupational and animal studies where exposure was higher than normal, models are used to extrapolate the effects of lower exposures. The committee said those models should be expanded and better explained.

According to the committee, the "linear" slope of risk EPA uses -- one in which the risk of cancer increases at the same rate as the level of exposure increases -- might not be the best method. EPA had said there was a lack of data to support another approach, but the committee pointed to recently released animal data from the National Toxicology Program to justify the use of nonlinear methods. The report recommends that EPA estimate cancer risk using both methods and thoroughly explain the pros and cons of each.

Dow officials agree. "Fundamentally, there's nothing in this report that is inconsistent with what Dow has been trying to implement as part of the framework process," Dow spokesman John Musser said. Dow's human health risk assessment proposal, not yet approved by the DEQ for the Tri-City areas, includes the use of a non-linear approach as well as a probabilistic risk method, both of which are endorsed by the report.

Midland State Rep. John Moolenaar, who successfully introduced legislation in the House last month requiring the DEQ to incorporate the committee's report into its work with Dow on local contamination remediation, said it, along with the U-M study, will be important to a local resolution.

The bill is expected to make it to the Senate by fall and was passed unanimously in the House. Moolenaar acknowledged the DEQ's agreement to use the report's suggestions, and said the bill provides legislative clarity.

"Where the science is going, that's where policy ought to be," he said.

Copies of the report, titled "Health Risks from Dioxin and Related Compounds: Evaluation of the EPA Reassessment," are available by calling the National Academies Press at (202) 334-3313 or 1-800-624-6242 or on the Internet at www.nap.edu.

©Midland Daily News 2006
 

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