CORVALLIS, Ore., April 27 (UPI) -- A new study of coal tar sealcoats used to extend the lifespan of asphalt driveways and parking lots shows they are significantly more toxic than previous studies have found.
Researchers at Oregon State University found polycyclic aromatic hydrocarbons, products of combustion, at levels higher than had previously been seen, and types that researchers say had not been detected before.
Coal tar sealcoats, products based on coal tar emulsions, are used throughout the East and Midwest regions of the United States, while asphalt-based sealcoats are far more common throughout the West.
Studies by the U.S. Geological Survey have shown PAHs are toxic to animals and humans, though they have been disputed as overstating any health risks posed by coal tar sealcoats.
A 2013 report from USGS found coal tar sealants were responsible for about half the hazardous chemicals in 40 lakes around the country, spurring several states to ban or restrict use of the sealants. Many cities and towns have also banned them as municipalities have had to fund the cleanup of the deadly chemicals.
In addition to the sealcoats chipping off and blowing into waterways, they give off PAHs -- which cause the scent of newly repaved parking lots -- which are toxic and can increase the risk for a wide range of cancers, including blood, kidney, liver, lung, scrotal, skin and stomach.
A program at OSU studying PAHs can identify and analyze more than 150 types of the chemicals, more than studies by the USGS are capable of, researchers at the university said.
"Our study is consistent with previous findings made by the USGS," said Staci Simonich, a professor in the departments of Environmental and Molecular Toxicology and Chemistry at Oregon State University said in a press release. "But we were able to study a much wider number of PAH compounds than they did. As a result, we found even higher levels of toxicity in coal-tar based sealcoats than has previously been suspected."
For the study, published in the journal Environmental Science and Technology, researchers found 146 PAHs in coal tar- and asphalt-based sealcoat products, well beyond the number found in previous studies.
Although many PAHs were present in asphalt-based products, researchers report levels of the chemicals were much higher in coal tar sealcoats. The chemicals caused development toxicity in zebrafish embryos as well, chosen as an animal model for the study because their reaction is similar to that of humans.
When compared to previous analyses, some PAHs in coal tar sealcoat were 30 times more toxic than compounds analyzed in the 2011 USGS study. The chemicals were also shown to be 4 percent to 40 percent more carcinogenic than previous studies have shown, with 11 PAH derivative compounds that were not detected in previous studies.
"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," Simonich said. "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."