Thursday, September 8, 2016
Don’t Use Coal Tar Based Sealcoat on Your Driveway
Sealcoat used in the central, southern, and eastern U.S. commonly contains coal-tar pitch. Polycyclic aromatic hydrocarbons (PAHs) escape from coal tar based sealcoat and other pavement materials when they are scraped, washed or blown by wind carried into stormwater and snow runoff. There is a concern that these chemicals may enter the nation’s water supply and through dust be ingested by children. At least seven of the two hundred PAHs are known to cause mutagenic/carcinogenic behavior in human cells. A recent study by scientists at Baylor University and the U.S. Geological Survey (USGS) found that living adjacent to a coal tar sealed driveways, roadways or playgrounds is associated with a significant increase in lifetime cancer risk. In addition, previous studies have found that PAHs carried by stormwater build up in the sediments of rivers streams and lakes and impact our water resources.
Coal-tar-based sealcoat usually contain 20-35% coal-tar pitch and contains from 50,000 to 100,000 milligrams per kilogram (or parts per million) PAHs which is about 1,000 times higher than PAH concentrations in asphalt-based sealcoat products used in the western states, and hundreds of times higher than PAH concentrations that appear in tire particles, used motor oil, or other urban sources.
Friction from car and truck tires grinds pavement sealcoat into small particles, which are incorporated into the dust on the pavement surface. Testing has shown that dust on coal-tar-sealed pavement contains PAHs at concentrations that are hundreds of times higher than those in dust on concrete or unsealed asphalt pavement. Not only is the transported dust carried by wind and stormwater to our waterways, but it is also carried on our clothes and shoes into our homes where it becomes part of the household dust.
Incidental ingestion is a pathway to exposure to many chemicals, especially for children. The USGS/ Baylor study focused on incidental ingestion of the seven cancer-causing PAHs. The scientists only looked at the concentration of the seven PAHs that have quantitative evidence of probable carcinogenic impact. They found that the average estimated lifetime dose for someone living adjacent to coal-tar-sealcoated driveway or road was 38 times greater than for someone living adjacent to unsealed asphalt pavement. About more than half of the exposure occurs before the age of six. The estimated lifetime cancer risk for someone who spends just the first 6 years of their life living adjacent to coal-tar-sealed pavement is about 25 times higher than urban background exposure.
In addition, in sediment studies in the eastern half of the U.S., the USGS found that of PAHs in stormwater ponds, and streams traceable to coal tar sealcoats ranging from 21% to 54%. While there are other active sources of PAH contamination such as wood fires, tires and vehicle emissions, coal tar sealcoat is one of the more easily preventable sources. In addition, safer substitutes are now available which are comparable in performance and price. Most highway departments have not used coal tar products on asphalt pavement for many years; and use is banned in part or all of 19 states, though not Virginia. You should avoid sealing your driveway with coal tar based sealcoats to protect our water resources and our children. Use instead asphalt-based sealcoat emulsions with the asphalt concentration (the binder) to be 25-30%. There are also no-PAH options including acrylic-based and agricultural oil-based sealcoats, and cement-based micro-layers; however, durability can be an issue with these products and they are not as readily available.