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Coal Tar-Based Pavement Sealcoat, Polycyclic Aromatic Hydrocarbons (PAHs), and Environmental Health

Several PAHs are suspected human carcinogens and are toxic to aquatic life.

USGS – March 23, 2011

Studies by the U.S. Geological Survey (USGS) have identified coal-tar-based sealcoat – the black, viscous liquid sprayed or painted on asphalt pavement such as parking lots – as a major source of polycyclic aromatic hydrocarbon (PAH) contamination in urban areas for large parts of the nation.

USGS Explanatory Graphic

Key Findings from USGS Studies

  • Dust from pavement with coal-tar-based sealcoat has PAH concentrations hundreds to thousands of times higher than dust from pavement with no sealcoat or with asphalt-based sealcoat.
  • Coal-tar pitch from sealcoat reaches streams and lakes in runoff and soils and unsealed pavement near sealed parking lots.
  • Coal-tar-based sealcoat was determined to be the largest source of PAH contamination to urban lakes.
  • Use of coal-tar-based sealcoat is the primary cause of upward trends in PAHs in urban lake sediment.
  • Residences adjacent to parking lots with coal-tar-based sealcoat have housedust with elevated concentrations of PAHs.

Polycyclic aromatic hydrocarbons, or PAHs, are a group of organic compounds composed of fused benzene rings. PAHs occur naturally in crude oil, coal, and tar, and are produced by the incomplete combustion of fossil fuels and biomass (wood, grass, tobacco). They are widely distributed in the environment and are of concern because they are toxic, mutagenic, teratogenic, and several are probable human carcinogens.

Pavement sealcoat (also called sealant) is a black liquid that is sprayed or painted on asphalt parking lots and driveways. It is marketed as protecting and beautifying the asphalt pavement. Sealcoat is used commercially and by homeowners across the Nation. It is applied to residential driveways, playgrounds, and parking lots associated with commercial businesses, apartment and condominium complexes, churches, schools, and business parks. Most sealcoat products have a coal-tar-pitch or asphalt base. Coal-tar-based sealcoat is commonly used in the central, southern, and eastern U.S.; asphalt-based sealcoat is commonly used in the western U.S.

Coal-tar pitch can contain 50 percent or more PAHs by weight and 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.

To view information on this topic in its entirety on the USGS "Texas Water Science Center" website, click here. The site includes a link to the latest seal coat fax sheet. We also have the latter archived here on the WorldSweeper site.

For additional information contact:
Director, Texas Water Science Center
U.S. Geological Survey
1505 Ferguson Lane
Austin, TX 78754-4501
Web: http://tx.usgs.gov/


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