Pollution from pavements to people

April 2012 » Columns » BEYOND WORDS
Bob Drake

Research, detailed in a recent article in the journal Environmental Science & Technology, found that coal-tar-based pavement sealcoat, common on asphalt driveways and parking lots throughout the nation, has significant health and ecosystem implications. Sealcoat is made of either an asphalt emulsion or a refined coal-tar pitch emulsion. The two sealcoats are similar in appearance and cost, but concentrations of polycyclic aromatic hydrocarbons (PAHs), a group of organic compounds known to be detrimental to human and ecosystem health, are about 1,000 times higher in coal-tar-based sealcoats than those based in asphalt.

University of New Hampshire research on coal-tar-based pavement sealcoat has contributed to growing concern about the substance’s impact on human and environmental health.
Photo: UNH Stormwater Center

Alison Watts, research assistant professor of civil engineering at the University of New Hampshire (UNH) and a researcher with the UNH Stormwater Center (www.unh.edu/unhsc), conducted side-by-side studies of coal-tar-based sealcoated and nonsealcoated asphalt pavement at parking lots at the edge of the UNH campus. She found that soil at the edge of the sealcoated lot contained several hundred parts per million (ppm) of PAHs, compared with less than 10 ppm from the lot without sealcoating. In addition, soil samples taken three years after the initial application of sealcoat remained high in PAHs.

The problem may be even more pronounced in New England: PAHs move into the environment as the sealcoat wears off, a process that snowplows seem to accelerate, Watts noted. According to the U.S. Geological Survey (USGS), an estimated 85 million gallons of coal-tar-based sealant are used each year, primarily in the central and eastern United States.

Unlike many complex environmental issues, however, this one has a relatively painless fix: Avoid coal-tar-based sealcoats in favor of asphalt-based ones, or no sealcoat at all. According to the USGS, 15 municipalities and two counties in four states (Minnesota, New York, Texas, and Wisconsin), the District of Columbia, and the state of Washington all have enacted some type of ban on coal-tar-based sealcoats.

The journal article, "Coal-Tar-Based Pavement Sealcoat and PAHs: Implications for the Environment, Human Health, and Stormwater Management," was co-authored by Watts; Barbara J. Mahler, USGS; Peter C. Van Metre, USGS; Judy L. Crane, Minnesota Pollution Control Agency; Mateo Scoggins, city of Austin, Texas; and E. Spencer Williams, Baylor University. The authors discuss the potential human health effects of coal-tar-based sealcoat, which is associated with elevated concentrations of PAHs in house dust, soil, air, water, and sediment. Studies at the Columbia Center for Children’s Health have found that PAHs in homes can contribute to delays in cognitive development, asthma and other respiratory symptoms, obesity and metabolic disorders, or changes at the molecular level that could increase children’s cancer risk.

"The value of this research is that it identifies the pathways by which PAHs move from pavements to people and measures the contribution in relation to other sources," said USGS Director Marcia McNutt. "The most striking finding is that pavement sealcoat contaminates virtually every part of our every-day surroundings, including our air and our homes."

Learn more about PAHs in sealcoat, including links to articles in peer-reviewed scientific journals, at http://tx.usgs.gov/coring/allthingssealcoat.html.

Information for this article was provided by the University of New Hampshire and the U.S. Geological Survey.

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