Texas Water Science Center
Coal-tar-based sealcoat being applied to a test plot.
Pavement sealcoat, or sealant, is a black liquid that is sprayed or painted on asphalt pavement. It is marketed as protecting and beautifying the asphalt surface. Sealcoat is used commercially and by homeowners across the Nation.
Most sealcoat products have a coal-tar-pitch or asphalt base. Coal-tar-based sealcoat is most commonly used in the central, southern, and eastern U.S., and asphalt-based sealcoat is used predominantly in the western U.S.
Polycyclic aromatic hydrocarbons (PAHs) are a group of chemical compounds that form during the combustion of anything with a carbon base, from wood and gasoline to cigarettes and meat. PAHs also are found in products whose production involves the heating of hydrocarbons, such as automobile tires and coal-tar pitch.
PAHs are of environmental concern because several are toxic, carcinogenic, mutagenic, and(or) teratogenic (causing birth defects) to aquatic life and because several are probable human carcinogens.
Coal tar is a byproduct of the coking of coal, and can contain 50 percent or more PAHs by weight. Coal-tar pitch is known to cause cancer in humans (International Agency for Research on Cancer, 1985).
Coal-tar-based sealcoat products typically are 20 to 35 percent coal-tar pitch. Product analyses indicate that coal-tar-based sealcoat products contain about 1,000 times more PAHs than sealcoat products with an asphalt base (City of Austin, 2005).
PAH and Sealcoat Contacts
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USGS Water Science Centers are located in each state.
USGS Research: PAHs and Coal-Tar-Based Pavement Sealcoat
Partially sealcoated parking lot
Some USGS publications on PAHs and coal-tar-based pavement sealant have been subject to Information Quality Act correction requests. USGS Information Quality Guidelines, the correction requests, and USGS responses can be found at: http://tx.usgs.gov/infodata/infosealcoat.html