Tadpoles in toxic Dixie Cups

A series of scientific studies followed.

In one, Mahler and her colleagues demonstrated that the particles of dirt in water running off a parking lot with coal tar sealant had PAH levels about 65 times higher than those from water running off lots where no sealant had been applied.

In another, tadpoles were put into containers with high, medium and low levels of pollution. The tadpoles in the cups with the highest concentration all died within six days, said Mateo Scoggins, a City of Austin biologist. The ones exposed to medium and low levels of PAHs, comparable to the concentration in Barton Creek, showed stunted growth.

Researchers from the city of Austin and Texas Tech University also looked at how the PAH pollution was affecting life in the creeks in Austin, and found a reduced number of insects available for birds, frogs and other creatures to eat.

That, said Scoggins, indicated that “there is more of a problem . . . than we thought.”

Sweeping the parking lot

Scientists from the USGS Texas Water Science Center involved in the Barton Creek findings measured pollution in lakes around the country, noting an increase in PAHs. In the next phase of their inquiry, they swept up dust in parking lots in Seattle, Portland, Salt Lake City, Minneapolis, Austin, Chicago, Detroit, Washington, D.C. and New Haven, Conn.

Coal tar sealants are used predominantly in the East, and that’s where the highest PAH readings were found — roughly 1,000 times higher than those in the West, where it’s much more likely that a driveway or parking lot will be coated with an asphalt sealant.

That figures, because the levels of PAHs in coal tar sealants is about 1,000 times what it is in asphalt sealants, researchers have found. One parking lot near Seattle had high pollution levels, while the other Western readings were relatively low.

The big question is how do parking lots figure into the big picture on these growing levels of PAH contamination?

U.S.G.S. researchers, led by hydrologist Peter Van Metre, expect they will soon have an answer. Research expected to be finalized in coming months will analyze the “fingerprint” of PAHs in various lakes to determine the source of the chemicals.

“We’re able to isolate the (parking lot) sealcoat in some of these settings as the only really logical source,” Van Metre said.

The “poster child,” he said, may be Lake in the Hills, a town northwest of Chicago. In the last two decades it went from a small town amid cornfields to a sprawling suburb dotted with big box stores. Roughly 40 percent of the paved areas that drain into the town’s manmade lake had been covered with sealcoating. PAH pollution levels in the lake went up tenfold, Van Metre said, and the contamination included the two homes with PAH levels in their driveways at thousands of times the amount that would trigger a toxic-waste site cleanup.