Coatings Industry News

Main News Page

USGS: Sealcoat Runoff Fatal to Fish

Wednesday, May 6, 2015

Comment | More

RESTON, VA—Runoff from pavement sealcoated with coal tar is toxic to aquatic life and has detrimental effects on DNA, according to two new studies by the U.S. Geological Survey.

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.

"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.

Known Carcinogen

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.

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.

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.

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.

USGS coal tar sealant study

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

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.

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; Government; Health & Safety; North America; Research; Sealant; Toxicity

Comment from Gary Burke, (5/6/2015, 7:37 AM)

I love what we keep on doing to our planet. Should we all just go ahead and commit suicide???

Comment from Thomas Ennis, (5/6/2015, 8:33 AM)

Thanks PaintSquare for this well-written article. There's another part of the story that should be told. Many of your readers are members of a national coating association which actively lobbies against regulations of this particular product. When approached about it, there was no comment. If it were my money going to that organization I would let them know my opinion. Just Google "American coating association coal tar lobby" and see for yourself.

Comment from Tom Schwerdt, (5/6/2015, 9:29 AM)

Yep, coal tar sealers are quite nasty stuff. This has been known for decades. Austin, TX banned it 10 years ago. I can't see a real justification for continuing to use coal tar for a simple pavement sealer when asphalt sealers are much safer and the cost difference is minimal.

Comment from Joe Miller, (5/6/2015, 11:14 AM)

There are alternatives to using coal tar surface treatments. They are Crystalline Penetrating Sealers that are very low viscosity and penetrate deep into the asphalt pavements. They crystallize within the pores and voids to form a barrier to water and water soluble compounds thus greatly reducing freeze-thaw damage in colder climates and salt and chemical ingress in all climates. They are made with moisture-insensitive, silicone-based compounds that rejuvenate the aromatic compounds within the asphalt substrates. So they extend the life of the asphalt, resist UV damage and restore the asphalt. No Toxic coal-tar compounds. Water run-off is safe, not harmful to fish, animals or humans. They can be used on Asphalt Parking Lots, Asphalt Bridge Decks, Residential Streets and Highways, Cart Paths and Pathways, Roofs and Airport Runways and Shoulders.

Comment from Andrew Piedl, (5/6/2015, 3:12 PM)

I've never been able to grasp the need to seal pavement.

Comment from Lydia Frenzel, (5/6/2015, 5:09 PM)

My husband (physicist)and I (Chemist) talked about this article when I read it. It's hard to believe that the federal government is just now finding that sealant has consequences as runoffs. Duh. My recollection is that back in the 1970's the coal tars were suspect. Why do I think this? At the time, I was formulating new organotin anti-foulants- as an academic study under a ONR grant. I was looking at slow release mechanisms and the effect on the environment. Thus I was in touch with environmental consequences. However, Barnie Appleman, at the time the Executive Director of SSPC, just set aside a standard on coal tar paint which had completed review by the respective committee. Appleman had some reservations about publishing current documents on coatings that he personally deemed less than desirable.

Comment from Tom Schwerdt, (5/7/2015, 8:26 AM)

Andrew: For parking lots, "sealing" is often an aesthetic issue. However, when any real cracks develop in a parking lot, road or other pavement - it is critical to seal them quickly (often with the aptly named "crack sealer" - squiggly black lines on the pavement.) Unsealed cracks allow water to penetrate into and below the pavement, dramatically speeding up the degradation of the roadway through a variety of mechanisms, the obvious ones being freeze-thaw damage and simply washing away the base underneath the pavement. Crack sealing is likely the most cost effective maintenance you can perform for pavement with regard to longevity. Sometimes whole-surface sealing or repaving is definitely justified as well.

Comment Join the Conversation:

Sign in to our community to add your comments.


Axxiom Manufacturing

KTA-Tator, Inc. - Corporate Office

Sauereisen, Inc.

Abrasives Inc.

HoldTight Solutions Inc.


Technology Publishing Co., 1501 Reedsdale Street, Suite 2008, Pittsburgh, PA 15233

TEL 1-412-431-8300  • FAX  1-412-431-5428  •  EMAIL

The Technology Publishing Network

PaintSquare the Journal of Protective Coatings & Linings Paint BidTracker

EXPLORE:      JPCL   |   PaintSquare News   |   Interact   |   Buying Guides   |   Webinars   |   Resources   |   Classifieds
REGISTER AND SUBSCRIBE:      Free PaintSquare Registration   |   Subscribe to JPCL   |   Subscribe to PaintSquare News
MORE:      About   |   Privacy Policy   |   Terms & Conditions   |   Support   |   Site Map   |   Search   |   Contact Us