matched the chemical fingerprint of PAHs in New Zealand streams to coal tar in older roads repaved with asphalt. jor source [of PAHs to streams],” Suburbia, beware. Vast stretches of “There’s no regulation of how Van Metre says. parking lots in the U.S. are coated much [coal-tar sealant] is used or Coal tar is the most common with toxic coal tar that is slowly the PAH content of sealants,” sealant east of the Continental Dicrumbling into dust. Coal-tar-based adds Tom Ennis, environmental vide, the study shows, whereas sealants, which give the lots an resource manager for Austin’s low-PAH asphalt sealants dominate ebony finish, produce dust containWatershed Protection and Develin the West. This pattern is consising 100 to 1000 times higher PAH opment Review Department. Entent with industry information and levels than unsealed lots, according nis’s research group to new research published recommended the Austin in ES&T (DOI 10.1021/ ban after finding biological es802119h). Many PAHs are effects such as altered carcinogenic and harm growth, survival, and deaquatic life, and runoff velopment in amphibians from the lots could be a exposed to sediment conmajor source of urban wataining coal-tar sealant. ter contamination, the sciPAHs are not the only entists report. pollutants that wash off The sealants first drew pavement. “The dominant attention in Austin, Texas, hydrology of urban areas when city workers discovis storm water,” says Aliered high PAH levels in son Watts of the Universediments near Barton sity of New Hampshire Springs, a popular swim(UNH) Stormwater Center. ming spot and home to an Coal-tar sealants are sprayed onto parking lots and driveways to give the surface a new appearance and protect Storm water sends large endangered salamander pulses of runoff, loaded species. Scientists from the underlying asphalt. with various contamiU.S. Geological Survey nants, into streams. The research corresponds with the availability of (USGS) first reported in ES&T in center is now continuously monicoal tar, which is a byproduct of 2005 that runoff from Austin parktoring runoff water quality from steel manufacturing. ing lots sealed with coal tar conthree parking lotssunsealed as Other sources of PAHs, such as tained 65 times more PAHs than well as coal-tar- and asphaltexhaust particles, tire-wear resirunoff from unsealed lots. Since sealed. due, and motor oil, could not acthen, Austin and Dane County, Van Metre, Watts, and environcount for the high levels found on Wisc., home to the city of Madison, mental scientist Mateo Scoggins of and near coal-tar-sealed parking have banned coal-tar sealants. Now Austin’s watershed department lots, Van Metre says. “Even if the the USGS team, led by research have briefed the U.S. EPA and lawsoil was made completely of tire hydrologist Peter Van Metre, has makers on their results. The EPA’s rubber or motor oil, it wouldn’t compared lots sealed with coal tar maximum soil screening level for reach these PAH levels,” he says. and with asphalt in nine U.S. cities. one PAH, benzo[a]pyrene, is 0.09 No one knows how much coal-tar Pavement sealants, used to premg/kg, 5300 times lower than the sealant is used nationally, but acvent cracks from freezing and level in dust from coal-tar-sealed cording to industry estimates, thawing, are most often used on driveways sampled in suburban about 600,000 gallons of sealant, parking lots rather than roads and Chicago. However, EPA’s stormor about 1 gallon per person, are are ground into dust as vehicles water program, which could help applied annually in the Austin drive over them. In the new study, control non-point-source pollution area alone. researchers compared PAHs in dust from parking lots, was recently “America is doing the worst from sealed and unsealed parking criticized as ineffective in a report possible thing by putting down a lots. Dust from sealed lots in the by the National Research Council. material with extremely high PAH central and eastern U.S. contained Because the sealants are used on levels on the surface, where it an average of 2200 milligrams per some playgrounds and driveways, flakes off and wears down,” says kilogram (mg/kg) of 12 PAHs, comVan Metre says, the human-health Craig Depree, an environmental pared with 27 mg/kg in unsealed effects of coal-tar dust should be chemist at the National Institute lots. “There is evidence, at least studied further. of Water and Atmospheric Requalitatively, that where coal tar is search (New Zealand). Depree has in use in urban settings it’s the ma—ERIKA ENGELHAUPT UNH STORMWATER CENTER
Parking lots create sticky pollution problem
10.1021/es803118b
2009 American Chemical Society
Published on Web 11/19/2008
January 1, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 3
