Image: Coal tar sealant applied in test
Peter Van Metre
Coal tar sealant is applied at a test site at the University of Austin in Texas, where it was studied for a year.
updated 5/5/2011 2:09:30 PM ET 2011-05-05T18:09:30

Washington state has become the first in the nation to ban toxic asphalt sealants made from cancer-causing industrial waste that have been spread over vast swaths of the nation’s cities and suburbs.

The toxic ingredients in coal tar-based sealants are turning up in ordinary house dust as well as in streams, lakes and other waterways at levels that concern government researchers.  The chemicals have been found in driveways at concentrations that could require treatment by moon-suited environmental technicians if detected at similar levels at a toxic-waste cleanup site. The sealants are also applied on playgrounds and parking lots.

Democratic Gov. Christine Gregoire signed the measure Thursday, making Washington the largest government to ban or restrict coal tar asphalt sealants. Last month, Prior Lake, Minn., joined a growing number of local governments to ban them.

Alternative asphalt-based sealants shed far fewer toxic particles, government tests show.

A federal scientist recently briefed congressional aides and others about threats to the environment and public health from sealing of driveways, parking lots and playgrounds with coal tar. The briefing was co-sponsored by U.S. Rep. Lloyd Doggett, D-Texas, who is seeking a nationwide ban on the toxic sealants.

The Washington state legislation and Doggett’s drive for a nationwide ban flowed from studies by the U.S. Geological Survey, which showed that components of the toxic sealants are increasing in many waterways, while levels of most pollutants are declining.

A 2009 Geological Survey study identified chemicals associated with the coal tar sealants in house dust at levels that worried researchers because they could contribute to long-term cancer risks, especially in young children who crawl through — and might accidentally ingest —  the toxic dust.

InvestigateWest and partnered last year to publish the first major national story examining the toxic sealants.

Washington’s move follows earlier bans. The first ban came in 2006 in Austin, Texas, site of the discovery of the link between toxic parking-lot sealants and waterway pollution.  Subsequent bans followed in Washington, D.C., and in Madison and surrounding Dane County, Wisconsin.

In the 16 months since the InvestigateWest/ story, bans or restrictions on the use of the sealants also have been adopted in several towns, mostly in the Midwest, where they have been heavily used. McHenry County, Ill., near Chicago, is studying whether to ban the coal tar sealants. That was where Geological Survey studies found constituents of coal tar sealants on driveways at levels thousands of times above what would trigger a hazardous-waste cleanup at a Superfund site.

“It is a very topical, hot issue in the Midwest now,” said Bob Newport, stormwater specialist in the U.S. Environmental Protection Agency’s Region 5 headquarters in Chicago. “It’s quite possible other states will follow.”

Washington’s law brings the number of Americans living in places where the coal tar sealants are banned to 8.7 million, according to the Coal Tar Free Americablog by Tom Ennis, an Austin city official who helped prompt research on the sealants.

The fact that a second kind of asphalt sealant without coal tar is widely available helped gain support in the Washington Legislature, said state Rep. David Frockt, D-Seattle, sponsor of the measure.

“When I started to understand the science, I concluded there is no reason to have this stuff,” Frockt said. “Nobody felt their business was going to be impacted if they had to go to the (other) sealants.”

In the end, though, “the human health aspect is what really hit home,” Frockt said.

The Pavement Coatings Technology Council, a Washington, D.C.,-area lobbying group representing companies that paint or spray on the deep black coal tar-based sealants, has launched scientific attacks on coal tar research.

The pavement council hired a Seattle-area scientist and consultant, who told Washington legislators he found flaws in the methods used by government researchers to produce a “chemical fingerprint.” The Geological Survey researchers say those chemical fingerprints implicate the parking-lot sealants as the largest source in many urban lakes of a class of toxic chemicals known as “polycyclic aromatic hydrocarbons,” or PAHs.

Industry officials’ main defense is that the PAH chemicals can come from a variety of sources other than the coal tar sealants.

"Their mathematical model that purports to apportion sources of PAHs is based on pre-selection of sources using cherry-picked data," Anne LeHuray, executive director of the pavement council, wrote in an email to InvestigateWest.

But Mo McBroom, a lobbyist for the Washington Environmental Council, said the new law protects health, saves money and  is supported by compelling scientific evidence.

“Dealing with the problem of toxic runoff is huge,” said McBroom, who brought the issue to Frockt’s attention based on the InvesigateWest/ story.  “This is a big step forward. We know that coal tar sealants are potential threats to public health and to water quality.”

The sealants are marketed as a way to extend the life of asphalt, while also restoring a rich dark color. The sealants usually are not applied to public streets.

The alternative to coal tar-based sealants is a class of asphalt-based sealants. Dust on parking lots using the coal tar sealants can contain hundreds or sometimes even thousands of times the concentration of toxic chemicals as dust from parking lots using the asphalt-based products, federal research indicates.

Story: Study sees parking lot dust as a cancer risk

The coal tar-based sealants typically are used more heavily east of the Rocky Mountains, in part because coal tar is a waste product of the steelmaking industry that was traditionally based in the Rust Belt. Both coal tar- and asphalt-based sealants are used in all 50 states.

Coal tar is a known human carcinogen. It caused scrotal cancer in London chimney sweeps in the 1700s and skin cancer in creosote workers in this country a century ago. Children exposed to these chemicals in the womb may be more prone to asthma and other health problems and may suffer from lowered IQs, emerging scientific evidence suggests. In men they can harm sperm and in pregnant women they can cause damage to the umbilical cord.

In streams, the chemicals have been shown to kill tadpoles, cause tumors on fish, stunt growth of aquatic creatures and reduce the number of species able to live in a waterway.

InvestigateWest is a nonprofit investigative journalism center covering the Pacific Northwest. For information on how you can support independent investigative reporting for the common good, go to


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