Parking lot sealcoat: a major source of PAHs in urban and suburban environments.
Coal tar-based sealcoat--the black, shiny emulsion painted or
sprayed on asphalt pavement--has extremely elevated concentrations of
polycyclic aromatic hydrocarbons (PAHs) and can affect the quality of
downstream water resources, according to a recent joint study in Texas
by the USGS National Water-Quality Assessment (NAWQA) Program and the
city of Austin. PAHs are an environmental concern because they are toxic
to aquatic life and because several are suspected human carcinogens.
Small particles of sealcoat flake off as they are abraded by vehicle
tires and can wash into urban streams with rain and runoff. The study
found that particles in runoff from parking lots with coal tar-based
sealcoat have PAH concentrations that are about 65 times higher than
particles washed off parking lots that have not been sealcoated.
Particles in runoff from parking lots sealed with asphalt-based
sealcoat, the other major product on the market, have PAH concentrations
about 10 times higher than those from unsealed lots. The large
differences suggest that abraded sealcoat is a potentially dominant (and
heretofore unrecognized) source of PAHs in urban and suburban water
bodies. PAH concentrations have been increasing over the past 30 to 35
years in many urban and suburban lakes across the United States.
The findings of the study have been published in the August 2005
issue of Environmental Science & Technology (ES & T). For more
information about PAHs and to view the online abstract of the ES & T
article, visit http://water.usgs.gov/nawqa/asphalt_sealers.html.