updated 5/26/2009 8:06:35 PM ET 2009-05-27T00:06:35

The federal government will speed up a long-delayed assessment of how chemicals called dioxins affect human health, Environmental Protection Agency head Lisa Jackson said Tuesday.

Jackson promised the quickened timetable while also announcing a revised strategy for planning cleanup of one of the nation's biggest dioxin pollution zones: a 50-mile section of Lake Huron watershed near a Dow Chemical Co. plant in Michigan.

Dioxins are toxic byproducts from manufacturing chemicals. In a 2003 report, EPA labeled some dioxins as causing cancer and said virtually any level of exposure posed at least some danger.

The National Research Council, an affiliate of the National Academies, agreed in 2006 that dioxins were a likely carcinogen but questioned how EPA estimated risks from low doses.

Jackson said in a phone interview with The Associated Press the agency would issue a draft report on the matter by Dec. 31 and a final version within a year later.

"This will be important for a bunch of sites around the country," she said.

In an open letter to Michigan communities affected by pollution from the Dow plant, Jackson said scientific findings about dioxins' health and ecological effects "will obviously play an important role in our decisions" about the cleanup.

EPA considers a dioxin reading of 1,000 parts per trillion or higher in neighborhood soils cause for cleanup or at least more intense study. But many states have established different thresholds, creating regulatory confusion.

Michigan's is 90 parts per trillion, although it applies to long-term exposure, while the federal standard deals with short-term exposure. EPA has yet to complete its evaluation of long-term risk.

"A lot of people have been calling for that assessment to be finished for years," said Robert McCann, spokesman for the Michigan Department of Environmental Quality. "We need standard criteria."

Hot spots
The extent of the health threat is among many issues that have delayed action at the Michigan site, which includes the city of Midland near the Dow plant, plus the Tittabawassee and Saginaw rivers and Lake Huron's Saginaw Bay.

Dow acknowledges polluting the region with dioxins for much of the 20th century. The company has spent about $40 million on studies, sediment sampling and other preliminary work and has removed tainted soil from a number of "hot spots" with particularly high dioxin readings.

Even so, the chemical giant contends the pollution hasn't harmed people or wildlife and has argued with state and federal regulators since the 1990s over how to design a comprehensive cleanup.

Shortly after her appointment as EPA chief this year, Jackson halted talks and sent a fact-finding team to Michigan.

Under the revised negotiating framework, the Michigan DEQ will be in charge of the area immediately around the Dow plant while EPA oversees the rivers and bay.

No Superfund classification
EPA decided against adding the area to the Superfund list of top-priority toxic sites, which would trigger federal funding. Instead, it will require Dow to pay the costs while meeting Superfund cleanup standards. If the company falls short, it could be penalized under the same law.

"These strong enforcement tools will assure progress here after a history of delay in accomplishing significant cleanup," Jackson said. She promised to set benchmarks for finishing the job, which will be presented during a June 17 public meeting.

Activist groups have demanded a seat at the table as regulators and the company negotiate cleanup details. Jackson told the AP it was standard procedure for such talks to be confidential.

But the public will be informed of topics under negotiation and regular progress reports will be issued, she said. Before an agreement is signed, a draft will be issued for public comment.

"This is an unprecedented degree of transparency and goes well beyond the opportunities or public participation typically provided at this phase at other (Superfund) sites," Jackson said.

The Lone Tree Council and the Ecology Center, environmental groups that have long accused Dow of stalling, said they would await more details about EPA's plans before passing judgment.

"While optimistic, we remain guarded given the history of this site," spokeswoman Michelle Hurd Riddick said.

Dow spokeswoman Mary Draves said, "We are prepared to move forward with this systematic approach EPA has outlined."

More on: Superfund

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