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U.S.: Sealant Runoff Kills Aquatic Life

Friday, May 8, 2015

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RESTON, VA—Confirming 10 years of earlier research, new studies by the U.S. Geological Survey report toxic effects on aquatic life in the runoff from pavement sealcoated with coal tar.

The studies were undertaken to address concerns by environmental and health groups that rainfall runoff after sealant application might be toxic to fish and other organisms.

And the concern proved founded: When exposed to runoff from coal-tar sealant, fish cells showed damaged DNA and impaired ability to repair that damage, according to the USGS. In some species, the exposure was fatal.

coal-tar-sealant runoff
Photos: USGS

Runoff collected from pavement with coal-tar sealcoating was toxic to test organisms up to as much as 111 days after application, the USGS found.

An estimated 85 million gallons of coal-tar-based sealant are applied to pavement each year, primarily east of the Continental Divide in the U.S. and parts of Canada, according to the USGS.

'Important Implications'

"The simultaneous occurrence of DNA damage and impairment of DNA repair has important implications for cell health," said Sylvie Bony, who led one of the studies at Ecole Nationale des Travaux Publics de I'Etat (ENTPE), a research agency based in Lyon, France.

Pavement sealants that contain coal tar, a known human carcinogen, have extremely high levels of polycyclic aromatic hydrocarbons (PAHs). Several PAHs are probable human carcinogens, and some are toxic to fish and other aquatic life.

Coal-tar sealants have "significantly" higher levels of PAHs and related compounds compared to asphalt-based pavement sealants and other urban sources, such as vehicle emissions and used motor oil, according to the USGS.

100% Mortality

The two studies collected and tested simulated runoff at various times, from just hours after application of coal-tar sealant to 111 days later.


DNA damage from runoff continues many after sealcoat application, the USGS has found.

According to the USGS, rainwater runoff collected up to three months after application caused 100 percent mortality to minnows and water fleas when they were exposed to ultra-violet radiation to simulate sunlight.

The studies were published in the scientific journal Science of the Total Environment and the American Chemical Society's journal Environmental Science & Technology.

A Decade of Research

"The USGS has been studying coal-tar-sealcoat as a source of PAHs for 10 years, and findings from these two studies are consistent with what is known about toxicity and genotoxicity of these chemicals," said Barbara Mahler, a USGS scientist.

In February 2014, the USGS published findings that concentrations of PAHs in runoff from pavement with coal-tar-based sealcoat remain elevated for months after application.

That study found concentrations of PAHs and chemically similar azaarenes in runoff from pavement sealcoated with coal tar were about 20 times higher than in runoff from asphalt sealcoating and about 40 times higher than in runoff from unsealed asphalt.

USGS coal tar sealant study

An estimated 85 million gallons of coal-tar-based sealant are applied to pavement each year. Pictured: Runoff from a sealcoated parking lot in central Texas stains the gutter black as it flows to a nearby creek.

A 2013 human health-risk analysis, done in partnership with Baylor University, found an elevated risk of cancer in people living near pavement sealed with coal-tar products.

The USGS reported in 2010 that a study of 40 urban lakes revealed coal-tar-based sealant as the largest source of PAHs.


Tagged categories: Asphalt; Coal tar epoxy; Construction; Good Technical Practice; Government; North America; Research; Sealant; Toxicity

Comment from Sarah Geary, (5/8/2015, 8:23 AM)

It would be interesting to read about their method of UV radiation exposure and how it correlates to actual radiation from sunlight.

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