After the city of Austin, Texas, banned a pavement sealant, the levels of a group of cancer-causing compounds dropped significantly in its lake.Photo credit: LoneStarMike, Wikimedia CommonsThey published their study, which could have broad implications for other jurisdictions and public health, in the American Chemical Society journal Environmental Science & Technology.

Peter C. Van Metre and Barbara J. Mahler point out that in 2005, researchers figured out that pavement sealants made from coal tar were contributing high levels of polycyclic aromatic hydrocarbons (PAHs) to the environment. This is a serious public concern because studies have shown that PAHs cause cancer in animals, and they likely impact human health as well. In the meantime, U.S. developers and residents are still coating driveways and parking lots with millions of gallons of coal-tar sealants every year. Some local and state governments have banned coal-tar sealants, but no one knew what kind of effect the interdictions were having. To find out, Mahler and Van Metre’s team decided to investigate whether Austin’s ban was in fact lowering local PAH levels.

They sampled the mud at the bottom of Lady Bird Lake, which receives much of the water running off Austin’s streets and parking lots. Using historic data and their new analyses, the scientists found that after a 40-year rise in PAHs in the lake’s sediments, the ban knocked levels down by about half. Concentrations are still continuing to decline, they say.

The authors acknowledge funding from the U.S. Geological Survey.