Oregon State University
The pavement sealcoat products used widely around the nation on
thousands of asphalt driveways and parking lots are significantly more toxic
and mutagenic than previously suspected, according to a new paper published
this week by researchers from Oregon State University.
Of
particular concern are the sealcoat products based on use of coal tar
emulsions, experts say. Studies done with zebrafish -- an animal model that
closely resembles human reaction to toxic chemicals -- showed developmental
toxicity to embryos.
Sealcoats
are products often sprayed or brushed on asphalt pavements to improve their
appearance and extend their lifespan. Products based on coal tar are most
commonly used east of the U.S. continental divide, and those based on asphalt
most common west of the divide.
The
primary concern in sealcoats are polycyclic aromatic hydrocarbons, or PAHs,
which are common products of any type of combustion, and have been shown to be
toxic to birds, fish, amphibians, plants and mammals, including humans.
There are many different types of PAHs. This study was able to examine the presence and biologic activity of a much greater number of them in sealcoats than has been done in any previous research.
The OSU program studying PAHs is one of the
most advanced of its type in the world, and can identify and analyze more than
150 types of PAH compounds.
It
found some PAHs in coal tar sealcoats that were 30 times more toxic than one of
the most common PAH compounds that was studied previously in these products by
the U.S. Geological Survey.
The
OSU study also showed that new PAH compounds found in coal tar sealcoats had a
carcinogenic risk that was 4 percent to 40 percent higher than any study had
previously showed. Among the worst offenders were a group of 11 "high
molecular weight" PAH derivative compounds, of which no analysis had
previously been reported.
By
contrast, the study showed that sealcoats based on asphalt, more commonly used
in the West, were still toxic, but far less than those based on coal tar. Use
of coal tar sealcoats, which are a byproduct of the coal coking process, is
most common in the Midwest and East.
The
research was reported this week in Environmental
Science and Technology Letters, in work supported by the National
Institute of Environmental Health Science's Superfund Research Program, and
done by researchers in the OSU College of Agricultural Sciences and OSU College
of Science.
"Our
study is consistent with previous findings made by the USGS," said Staci
Simonich, a professor with appointments in OSU's departments of Environmental
and Molecular Toxicology and Chemistry. "But we were able to study a much
wider number of PAH compounds than they did. As a result, we found even higher
levels of toxicity in coal-tar based sealcoats than has previously been
suspected."
"This
should assist individuals and municipalities to make more informed decisions
about the use of sealcoats and weigh their potential health risks against the
benefits of these products," said Simonich, the corresponding author on
the study. "And if a decision is made to use sealcoats, we concluded that
the products based on asphalt are significantly less toxic than those based on
coal tar."
The
previous research done by the USGS about the potential health risks of sealcoat
products has been controversial, with some industry groups arguing that the
federal government agency overstated the risks. The new OSU study indicates
that previous research has, if anything, understated the risks.
A
2011 report from the USGS outlined how PAH compounds from sealcoat products can
find their way into soils, storm waters, ponds, streams, lakes, and even house
dust, as the compounds are tracked by foot, abraded by car tires, washed by
rain and volatilize into the air.
They reported that the house dust in
residences adjacent to pavement that had been treated with a coal tar-based
sealcoat had PAH concentrations 25 times higher than those normally found in
house dust.
Some
states and many municipalities around the nation have already banned the use of
coal tar-based sealcoats, due to the human, wildlife and environmental health
concerns. In the European Union, use of coal tar-based sealcoats is limited or
banned.
