According to researchers at the U.S. Gelological Survey (USGS), elevated levels of polycyclic aromatic hydrocarbons (PAHs) in house dust has been linked to coal-tar-based sealcoat, the black, shiny substance sprayed or painted on many parking lots, driveways, and playgrounds. PAHs are an environmental health issue because several are probable human carcinogens and they are toxic to fish and other aquatic life.

Coal tar is a byproduct of the coking of coal, and can contain 50 percent or more PAHs by weight. Coal-tar-based pavement sealants therefore have very high levels of PAHs compared to other PAH sources (e.g., soot, vehicle emissions, used motor oil).

The USGS study found that apartments adjacent to coal-tar-sealcoated parking lots contained concentrations of PAHs in house dust with that were 25 times higher than in house dust from apartments with concrete, asphalt, or asphalt-based sealcoat parking lot surfaces. The study also found that dust directly on the coal-tar-sealcoated parking lots had PAH concentrations that were 530 times higher than in dust on the parking lots without coal-tar sealcoat. Researchers conducting the study surmised that small particles of sealcoat, which contains extremely high concentrations of PAHs, likely are tracked indoors by residents after they walk across the parking lot.

In the past, several factors have been thought to affect PAH concentrations in house dust, including tobacco smoking and frequency of vacuuming. Researchers have had little success, however, demonstrating a relation between any of those factors and PAH concentrations.

The study is published online in Environmental Science and Technology.