Driveway Coating May Raise Cancer Risk

Coal tar, a byproduct of steel manufacturing, is a common ingredient in sealants that are used in the Eastern part of the United States to refresh worn parking lots and driveways. The black sealcoats, however, are a concentrated source of polycyclic aromatic hydrocarbons (PAHs), a known group of cancer-causing chemicals. When tires drive across the sealcoat, they grind the surface to release particles and dust – which then can be carried into homes on shoes and hands, as well as wash into the surrounding soil and waterways after a rainstorm.  Barbara J. Mahler, from the US Geological Survey (Texas, USA), and colleagues compared the levels of PAHs in house dust swept from 23 ground-level apartments in Austin. About half of the apartments sat on parking lots that were coated with coal-tar sealants; the rest did not.  The researchers combined those levels with measurements of PAHs in soils sampled near parking lots with and without coal tar-based sealants in New Hampshire and Chicago.  The team then modeled the data to establish excess cancer risk, ie how many people would get cancer because of their exposure to PAHs who would otherwise not be expected to do so.  Based on the models, for every million people who live near unsealed asphalt for 70 years, or roughly their whole lives, the team revealed that there would be three extra cases of cancer because of exposure to PAHs. However, that risk is 38 times greater, for people living near asphalt sealed with coal tar: for every million people who spend 70 years living next to sealed pavement, researchers said they would expect about 110 cases of cancer because of the exposure to PAHs. Importantly, the investigators calculated that most of that risk appears to accrue in childhood:  50% of the cancer risk from PAHs in sealcoated asphalt is acquired within the first six years of life, and 80% of a person's risk adds up before age 18.  Writing that: “Our results indicate that the presence of coal-tar-based pavement sealants is associated with significant increases in estimated excess lifetime cancer risk for nearby residents,” the study authors warn that: “Much of this calculated excess risk arises from exposures to [polycyclic aromatic hydrocarbons] in early childhood (i.e., 0–6 years of age).”