PhotoYou might not think of your driveway as toxic, but maybe you should. That's the upshot of an Oregon State University study that found sealcoat products are much more toxic and mutagenic than previously suspected.

Most worrisome are sealcoat products based on coal tar emissions. The researchers said tests on zebrafish, which closely resemble humans in their reaction to toxins, showed developmental effects on embryos.

Sealcoating is usually brushed or sprayed onto asphalt pavements to extend their lifespan and make them look better. Coal tar is generally used in products distributed east of the U.S. continental divide, and those based on asphalt are most common west of the divide.

The main concern is a group of chemicals known as polycyclic aromatic hydrocarbons, or PAHs. They are products of combustion, and have been shown to be toxic to birds, fish, amphibians, plants, and mammals, including humans.

30 times more toxic

While there are many different kinds of PAHs, the researchers found that the ones used in coal tar sealcoats -- those used in the East -- were 30 times more toxic than one of the most common PAH compounds that was studied previously in these products by the U.S. Geological Survey.

The OSU study also showed that new PAH compounds found in coal tar sealcoats had a carcinogenic risk that was between 4% and 40% higher than any study had previously found.

By contrast, the study showed that sealcoats based on asphalt -- mostly used in the West -- were still toxic, but far less than those based on coal tar.

"This should assist individuals and municipalities to make more informed decisions about the use of sealcoats and weigh their potential health risks against the benefits of these products," said Staci Simonich, an OSU professor and one of the authors of the study. "And if a decision is made to use sealcoats, we concluded that the products based on asphalt are significantly less toxic than those based on coal tar."

Some states and many municipalities around the nation have already banned the use of coal tar-based sealcoats, due to the human, wildlife, and environmental health concerns. In the European Union, use of coal tar-based sealcoats is limited or banned.

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