But a spokeswoman for a trade group of companies that apply the coal tar sealants said research has not been comprehensive enough to justify such bans. Anne P. LeHuray, director of the Pavement Coatings Technology Council, said people who advocate bans are looking for a “magic bullet” to solve a complicated problem.

She points out that cancer-causing chemicals contained in the pavement sealants also get into cities and suburbs from a number of other sources, including motor oil, vehicle exhaust and tires.

“Right now the research is not that convincing that this is that important a source of PAHs relative to all the other sources that are out there,” LeHuray said. “They didn’t look at all the potential sources.”

A tiny toxic creek
The path that led to the discovery of the toxic dirt inside Americans’ homes traces back to a tiny creek in Austin, Texas.

When researcher Mahler saw test results on dirt scooped from the bottom of a tributary of Barton Creek in 2001, the pollution readings were so high she felt certain someone had made an error. The concentrations found in a drainage ditch leading from a parking lot to Barton Creek were higher than levels typically measured at toxic-waste sites — higher even than Boston’s notoriously polluted Charles River, where PAHs are listed as among the “contaminants of concern” on that major industrial waterway.

Further testing showed the high readings were accurate. But what was the source?

Barton Creek feeds Barton Springs, a public bathing site cherished by Austin residents because it offers a cool respite from tyrannically hot Texas summers. Levels of PAHs measured in Barton Springs were high enough that the Austin American-Statesman dispatched reporters to track down what was suspected to be a hidden toxic waste dump.

On Aug. 16, 2002, Tom Bashara of Austin’s Watershed Protection Department went to check spots along Barton Creek where city biologists had pinpointed extremely high levels of PAHs.

“I spent a good half an hour walking around looking for cars gushing out fluid or someone dumping stuff, but none of that was happening,” Bashara recalls.

He did notice that the parking lot was rich black color. Then he noticed the deep black color had been rubbed off by cars’ tires in some places. So it was newly sealed.

He moved on to other pollution hotspots on the creek, where he found more parking lots colored the same deep, rich black.

“That’s when it dawned on me: There’s some connection between the sealcoat and the hotspots,” Bashara said.