By David J. Wilson, PhD
Van Buren Township
Recently the Independent published an article that discussed the various health and environmental hazards resulting from the use of coal tar-based driveway sealers.
It also provided background information on these materials and the carcinogenic polycyclic aromatic hydrocarbons (PAHs) they contain.
Here I shall focus on the health aspects of these sealers. This information is drawn from an article, You’re Standing on It! Health Risks of Coal-Tar Pavement Sealcoat, posted on the web on March 28, 2013 and authored by Spencer Williams (Baylor University) and by Barbara Mahler, Pete Van Metre, and Jennifer LaVista, all of the U.S. Geological Survey.
Coal tar-based driveway sealers, used on driveways, parking lots, and sometimes on playgrounds, are a major source of PAHs to air, soils, streams and lakes (including stormwater management facilities), and our homes.
Coal tar-based sealers typically contain 20-35% coal tar pitch and some 50,000 to 100,000 milligrams per kilogram (mg/kg, parts per million) PAHs, about 1,000 times higher than PAH concentrations in asphalt-based sealers and hundreds of times higher than the PAH levels in tire particles, used motor oil, and other sources.
A new (as of 2013) study by these researchers at Baylor and the USGS found that living next to a coal tar-sealed driveway is associated with significant increases in estimated excess lifetime cancer risk, and that much of this increase occurs during early childhood.
Weathering and tire abrasion gradually convert the seal coat into small particles; dust on coal tar-sealed pavement contains PAHs at concentrations hundreds of times higher than those in dust on concrete or unsealed asphalt pavement. This contaminated dust is then transported by wind, rain, and tracking to nearby soil, and some is tracked into homes.
People, especially children, are exposed to PAHs in soil and house dust through “incidental ingestion” when we (and our children) put hands or objects into our mouths. The researchers focused on the incidental ingestion of seven cancer-causing PAHs.
They found that the estimated lifetime PAH dose for someone living adjacent to coal tar-sealed pavement was 38 times greater than that for someone living adjacent to unsealed asphalt pavement. About half of that dose occurs during childhood (0-6 years of age).
The estimated lifetime cancer risk is substantially higher for people living near coal tar-sealed pavement. For someone who spends their entire lifetime (70 years) living adjacent to coal tar-sealed pavement, these researchers estimated that the average excess lifetime cancer risk is 38 times higher than that for normal urban background exposure.
Most of this (84%) is from ingestion of soil. The estimated lifetime cancer risk is also increased markedly for someone who spends just the first 6 years of life living adjacent to coal tar-sealed pavement; it is some 25 times higher than that resulting from urban background exposure.
For someone who lives next to coal tar-sealed pavement for either their entire lifetime or for just the first 6 years, the excess lifetime cancer risk is estimated to be greater than 1 in 10,000. The U.S. EPA generally considers excess cancer risks greater than 1 in 10,000 to be large enough so that some sort of remediation is desirable.
In our situation, remediation is simple and quite cheap. First, a program of public education on the problem, already initiated by the Independent, the Van Buren Township environmental commission, and by the Huron River Watershed Council. Second, an ordinance banning the sale and use of coal tar-based sealers in our community, as safe alternatives are readily available.
If you are concerned about this readily solved problem, please, PLEASE discuss it with your friends and neighbors and with our local political leaders. Thanks.
Editor’s Note: Dr. Wilson has been invited to speak to the Belleville Rotary Club about his coal-tar driveway sealer findings.