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The study found one or more chemical compounds in 92.5 percent of all 709 samples taken, with mixtures of 10 or more compounds in 34 percent of samples. The Clinton River, at Auburn Hills, tested positive for 53 different compounds in a single sample. Among the compounds the USGS tested for were six PAHs. Findings showed 56 percent to 85 percent of samples were PAHs.

Steve Corsi, a research hydrologist with the USGS' Wisconsin Water Science Center who contributed to the study, said researchers at the time didn't focus on sources of contamination, but what contamination exists.

"There are all sorts of (PAHs) in sealcoat. The question is probably how are PAHs distributed. There are many that are in sealcoat, and many other sources in the environment," he said. "The distribution of concentrations for different PAHs is what changes from source to source."

The study cast a wide net on the collection of contaminants. Those results have now helped to determine future areas of study. For instance, Corsi said he and others are working on a study focusing on pesticides in Great Lakes tributaries. Next year, studies will focus on PAH levels and sources, with pharmaceuticals and personal care products the focus of study the following year.

The most recent study released, Corsi said, looked at only six PAHs.

"From those six, we can't do source apportionment. That just tells us if there could be problems from PAHs," he said. "The next sample we will do 40-plus, and we will have enough to do some sort of source apportionment, or fingerprinting, of PAHs."

The study of Great Lakes tributaries will be independent of USGS researchers in Texas, who determined that coal tar sealants were a main source of PAH contamination in stormwater sediments there.

Researchers in 2008 expanded their findings to test parking lots and adjacent ponds or lakes that may be effected by runoff from coal tar sealants. Those tests included nine cities in the United States, including lots in Commerce Township and sediments in South Commerce Lake, in western Oakland County.

Of the nine cities tested, PAH samples taken in Commerce Township showed the highest level of PAHs in the country, followed by samples in Chicago; Washington D.C.; Austin, Texas; New Haven, Connecticut; Minneapolis, Minnesota; Seattle, Washington; Salt Lake City, Utah; and Portland; Oregon. Cites west of the Rocky Mountains and the Continental Divide, where asphalt or petroleum-based sealcoat is primarily used, had drastically lower levels of PAH.

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