After researching the question for seven years, a U.S. government agency said Wednesday it cannot draw broad conclusions about how industrial pollution in the Great Lakes region has affected human health.

The Agency for Toxic Substances and Disease Registry called for more study — and better organization and analysis of information — so the area's citizens and governments can deal with potential dangers from environmental contaminants.

The ATSDR is affiliated with the U.S. Centers for Disease Control, which released an updated version of a report by agency scientists about health problems in 26 highly polluted "areas of concern" around the lakes.

"The major conclusion of this report is that we need better data to allow us to assess threats to human health," said Dr. Howard Frumkin, director of the CDC's Agency for Toxic Substances and Disease Registry.

It is impossible to know the extent of the problem from currently available information, he said.

The report had been scheduled for release in July 2007, but was withheld after senior officials questioned its methodology and conclusions. The delay drew accusations of a coverup from members of Congress.

"The fact that this report was delayed for almost a year raises serious questions about whether this is another example of the administration suppressing science for political purposes," said U.S. Representative John Dingell, a Michigan Democrat who is chairman of the House of Representatives' energy and commerce committee.

That was not the intention, said Dr. Henry Falk, who oversees CDC research on environmental health hazards. Critics had noted problems in the report that needed fixing — particularly its use of data that might have implied unproven cause-and-effect relationships between toxins and illness in the area, he said.

"We're being as open and co-operative as we can," Falk said.

CDC officials have asked the Institute of Medicine, an independent scientific advisory organization, to review the report's various drafts and assess their quality. The panel's first session begins Thursday.

After getting feedback from the institute and the public, the CDC will produce a final version.

The study originally was requested in 2001 by the International Joint Commission, a U.S.-Canadian agency that advises the two countries on issues affecting the Great Lakes and other boundary waters.

It didn't generate new data but pulled together existing information from a variety of sources, including the U.S. Environmental Protection Agency's Toxic Release Inventory and state reports on how pollution has degraded resources such as wildlife and water.

Correlations between disease, toxins questioned

Earlier drafts noted elevated levels of cancer, premature births and other health concerns in counties where some heavily tainted sites are located.

But Falk said those drafts made flawed correlations between countywide health data and environmental measures drawn from areas sometimes larger or smaller than a county.

The new version removes some material senior agency scientists decided was irrelevant or misleading — including the countywide health statistics — while updating or improving other data, Falk said.

The only health data it includes comes from previous ATSDR assessments of about 150 hazardous-waste sites within the areas of concern. Of those, 86 were described as posing a potential problem; 47 were classified as hazards and two were labelled "urgent" hazards.

But that information provides little insight about whether people were actually exposed to toxins, the report acknowledges.

"For exposure to occur, there needs to be a completed pathway from a source to people's bodies," it says.

"Discharge of a pollutant into a stream … does not mean that people are exposed to that pollutant, or if so, how much. Use of a chemical in a factory … does not mean that people are exposed to the chemical, or if so, to what extent."