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Overall, dust swept from parking lots in six cities east of the Continental Divide had a median PAH concentration of 2200 parts per million, with unsealed parking lot dust registering a median of 27 parts per million. In western states, the parking lot dust of asphalt-based sealcoat was 2.1 parts per million, and .8 parts per million for unsealed parking lots. Dust samples taken in Commerce Township had a cumulative average of 3,400 parts per million from coal tar sealed parking lots, and 47 parts per million on non-sealcoated parking lots.

"The other sources of PAHs, such as fallout of industrial emissions, exhaust particles, tire-wear residue or leaking motor oil, because PAHs from such sources are equally likely to occur on both unsealcoated and sealcoated lots," the researchers said in the report.

The study also stated that lakes sampled east of the Continental Divide had higher levels of PAH concentrations.

"Lakes in the central and eastern cities where pavement was sampled have bottom sediments with higher PAH concentrations than do those in western cities relative to degree of urbanization," the study states. "Bottom-sediment PAH assemblages are similar to those of sealcoated pavement dust regionally, impacting coal tar-based sealcoat as a PAH source to the central and eastern lakes."

PAH in dust poses a greater risk to humans than PAHs that settle in water. That is because PAHs tend to bind to particulates in the air, or in the soil or sediments, rather than is found independent in the air or water table. PAHs in raw water tends to absorb particulate matter and are removed by filtration before reaching the tap, according to the EPA.

Nicholas Schroeck, director of the Transnational Environmental Law Clinic at Wayne State University, said he receives calls from the community about whether coal tar sealants are harmful.

"Certainly, with the coal tar sealant, the answer is 'yes,'" he said. "They contain enough PAHs that it is something that you should be concerned with. There are more PAHs in the sealant than in asphalt or oil."

Schroeck said he expects more communities in Michigan will consider restricting or banning the use of coal tar sealants.

"The potential threat to the rivers, lakes and streams in the Great Lakes state is what I would be concerned about. It runs off the pavement and into waterbodies, and the concentrations in those waterbodies pose a health risk to aquatic life.

"In Oakland County, with so many inland lakes, it's something that people should be aware of and look for an alternative. It's definitely providing a pollution load every time it washes off."

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