New research shows sealed asphalt may cause cancer

By Kayla Reeves

Is pavement the new bogeyman?

Research completed by Dr. Spencer Williams, assistant research scientist, and Barbara Mahler, a research hydrologist at the U.S. Geological Survey, suggests it might be so; sealed pavement might be dangerous to children.

Williams and Mahler have been researching the levels of polycyclic aromatic hydrocarbons in pavement.

Carcinogenic polycyclic aromatic hydrocarbons are complex organic chemicals that are known to cause cancer, and yet they are located almost everywhere in the environment. Because they are unavoidable, humans take in some of the chemicals every day, mostly through what they eat, Williams said.

The typical human diet contains less than two parts of polycyclic aromatic hydrocarbons per billion parts of food, which is not enough to cause harm, said the Agency for Toxic Substances & Disease Registry.

A study done by Mahler’s survey group researched the levels of polycyclic aromatic hydrocarbons present in pavement sealant and the effects they have once when the sealant wears out.

Sealants are used to make parking lots and other asphalt surfaces look new and last longer, but they contain very high levels of polycyclic aromatic hydrocarbons because they are made from coal tar, a waste product from the steel industry. Coal tar can contain up to 50 percent of carcinogenic polycyclic aromatic hydrocarbons, Mahler said.

The U.S. Geological Survey attempted to discover the source of these chemicals in the environment by taking samples in different areas. Higher levels of polycyclic aromatic hydrocarbons were found near sealed parking lots. This discovery sparked Williams’ interest and subsequent research on the subject of children’s exposure to the chemicals.

Williams concluded children who live near coal tar-sealed pavement receive a significantly higher dose of the chemicals than those who do not, because they receive them from the asphalt and not just from their diet.

As the friction of car tires and other things begins to wear the surface of the pavement, the sealant is ground to dust.

“The dust gets into the air, rain carries it into lakes, and it can stick to your shoes and get in your house,” Mahler said. And since young children tend to put their hands in their mouths more than adults, they tend to consume more of that dust, including ground sealant from pavement. This is where Williams’ study comes in, said Mahler.

Both researchers said they are unable to comment on exactly how dangerous the sealant is until further research is completed.

“My goal is to do the best science I can,” Williams said. “In the future, we may be interested in looking at health issues for humans.”

Mahler said her team at the U.S. Geological Survey will soon start studying at how much of the chemicals escape into the air and comparing coal-tar sealants to an oil-based sealant that has much lower polycyclic aromatic hydrocarbon levels.