Polyaromatic hydrocarbons (PAHs) are a group of chemicals that have caused cancer, birth defects and other problems in animals. Long term exposure to PAHs is also associated with development of cancer in people (Poirier, M.C.). A new study in the journal Environmental Science & Technology finds that high concentrations of PAHs from coal tar sealants, used for driveways and parking lots, make their way into homes.
Coal tar sealants are the sticky black coatings that are put over asphalt to give an attractive finish to driveways, parking lots, and sometimes playgrounds or basketball courts. Coal tar contains more than 50 percent PAHs by weight and coal tar sealants contain 15 to 35 percent of coal tar according to the National Institute of Standards and Technology. Dust derived from coal tar sealants contains a surprising high concentration of PAHs. Researchers in the new study analyzed the settled dust in apartments that were next to coal tar sealed parking lots and compared the dust to dust from similar apartments that were not near coal tar sealed parking lots. Carpeting, cooking and vacuum habits and other potential factors did not impact the concentrations of PAHs. The concentration of PAHs in dust from apartments with coal tar sealed parking lots was 25 fold higher than in the dust from apartments without coal tar sealed parking lots. The dust, sitting right on the surface of the coal tar sealed parking lot had on average 530 times greater concentrations of PAHs than parking lots with asphalt based sealers, unsealed asphalt or concrete (Mahler et al.).
Although we are exposed to PAHs from many other sources, the high concentrations in household dust and on coal tar sealed surfaces are alarming. Small children spend more time on the floor and are more likely to ingest or breathe in PAH-laden household dust. Children also play and spend significant amounts of time on driveways and the hard surfaces of playgrounds. Previous studies have shown that run-offs from coal tar sealed surfaces contained extremely high concentrations of PAHs. In response, some states and areas have outlawed coal tar sealants.
So what are the alternatives? If you want to seal your black top driveway, use an asphalt type sealer, making sure no coal tar is in it. Some experts note that asphalt sealers are not as resistant to oil or gasoline stains as coal tar sealants. But that is a small price to pay for your health. If you are redoing your driveway or installing a new black top area, an even more environmentally friendly option is to use porous material like gravel or pavers, which will prevent run-offs and allow rainwater to sink into the ground.
Mahler, B.J. et al. Coal-Tar-Based Parking Lot Sealcoat: An Unrecognized Source of PAH to Settled House Dust. Environmental Science & Technology (2010) DOI: 10.1021/es902533r
Poirier, M.C. Chemical-induced DNA damage and human cancer risk. Nature Reviews Cancer (2004) 4:630