GovernmentInvestigative Reports

New studies: Toxic asphalt sealants threaten kids, cause air pollution

By February 17, 2012November 21st, 20236 Comments

When you think of pollution, you might picture an industrial center like Camden, N.J., or Jersey City. But new research shows that when it comes to a potent class of cancer-causing toxic chemicals, many American parking lots are a lot worse.

New studies paint an increasingly alarming picture – particularly for young children – about how these chemicals are being spread across big swaths of American cities and suburbs by what may seem an unlikely source – a type of asphalt sealer. These sealants are derived from an industrial waste, coal tar.

Four new studies announced this week further implicate coal tar-based asphalt sealants as likely health risks.  The creosote-like material typically is sprayed onto parking lots and driveways in an effort to preserve the asphalt. It also gives the pavement a dark black coloring that many people find attractive.

Coal tar is a byproduct of the steelmaking industry. In 1992, the U.S. Environmental Protection Agency declared that it would not be classified as a hazardous waste, even though it met the characteristics of one, because it could be recycled for uses including coating asphalt. That meant steel mills didn’t have to pay for costly landfilling or incineration of the waste.

Only in recent years have scientists discovered the ill effects of this practice.

Coal tar sealants are used most heavily in the eastern United States, but have been used in all 50 states until Washington State banned the products last year as a result of reporting by InvestigateWest. More than a dozen local governments, including Washington, D.C., and Austin, Texas, also have banned the coal tar sealants in favor of the other major type of sealant, which is asphalt-based.

Asphalt-based sealants contain about 1/1000th the concentration of the cancer-causing chemicals that coal tar-based products do. Home Depot and Lowe’s stores have dropped the coal tar sealants from their product lines, but still some 85 million gallons of the coal tar-based sealants are applied annually in the United States.

The new research, published in peer-reviewed science journals, focuses on a class of chemicals found in coal tar and known as “polycyclic aromatic hydrocarbons,” or PAHs. Previously, researchers believed that people’s exposure to PAHs came primarily through food, which contains trace amounts produced primarily from smoking food or cooking it at high temperatures in practices such as grilling, roasting, and frying. PAHS are produced when any organic matter burns.

The new research shows:

  • It appears that children – especially those from 3 to 5 years old – living by coal tar-sealed parking lots and driveways are getting a bigger dose of PAHs from house dust than from their food. The kids who put their hands in their mouths most often are likely receiving 9 ½ times more exposure through house dust than through food, according to research led by E. Spencer Williams, a Baylor University human health risk assessment expert. That’s just from the house dust. When the kids are outside in the yard or playing on coal tar-sealed pavement, they likely are picking up much larger doses.
  • Concentrations measured four feet above the coal tar-sealed lots in some cases exceeded health-protection guidelines recommended by a European Union science panel to protect against cancer. The United States has no similar guidelines.
  • While researchers previously theorized that airborne PAHs come mostly from power plants, factories and cars’ and trucks’ tailpipe emissions, U.S. Geological Survey researchers measured large amounts vaporizing into the air off coal tar-sealed parking lots. The concentrations coming off parking lots in suburban Austin, where the researchers are based, were higher than in centers of heavy industry including Jersey City and Camden, N.J.; Chicago; London and Manchester, England; and Guangzhou, China. The Austin parking lots tested were three to eight years old. Much more off-gassing occurs in the first few years after the sealants are applied, researchers said.
  • Extrapolating from the 85 million gallons of coal tar sealants laid down annually and the out-gassing rates measured in Austin, Geological Survey researchers calculated that nationwide, more PAHs are getting into the air from coal tar-sealed parking lots, driveways and playgrounds than from all the auto and truck exhaust.

Before this week, researchers had previously shown that coal tar-sealed parking lots were shedding tiny bits of material, which was washed by rain into nearby waterways — killing, sickening and maiming aquatic creatures such as salamanders, minnows and, importantly, bugs at the base of the food chain. the chemicals kill tadpoles, cause tumors on fish, stunt growth of aquatic creatures and reduce the number of species able to live in a waterway.

As a result of being washed into waterways by stormwater, these chemicals’ concentrations have been rising over the last two decades, even as levels of most contaminants are headed down, Geological Survey researchers showed.

The chemicals are getting into the house dust, researchers think, when small bits are eroded off pavement and tracked into nearby homes on people’s shoes and pets’ paws.

Scientists also had previously demonstrated that toxic constituents of coal tar were showing up in the dust of homes adjacent to parking lots and driveways, raising questions about health effects on children in those homes, especially toddlers who frequently put their hands in their mouths. Coal tar is known to cause cancer in humans, as well as genetic mutations in lab animals.

One of the new studies helps quantify that risk. Kids who are average in terms of how often they put their hands into their mouths are getting 2 ½ times as many PAHs from house dust as from food, while those in the 95th percentile of hand-to-mouth behavior – they do it more than 94 percent of other kids – get 9 ½ times as much from the dust.

Researchers still would like to know how much of a toxic dose those same kids are getting when they play outside in yards next to coal tar-sealed asphalt, or on the asphalt itself. The level of cancer-causing chemicals in the dust on the asphalt has been measured at about 37 times the levels found in house dust.

“Those concentrations are a good bit higher and this study doesn’t include that at all,” said Williams, the Baylor researcher. “That may be important because just one little fingerful could be a relevant dose,” meaning one that worries health experts.

While researchers have known about contamination of water and dust, the findings about air pollution are new. Significant amounts of PAHs continue to vaporize off coal tar-sealed lots even years after the sealant is put down.

“When we look at seal-coated parking lots, in any direction we look we see these really strongly elevated concentrations,” said Peter Van Metre, a U.S. Geological Survey scientist based in Austin. Of the dust on the coal tar-sealed pavement, he said: “It would just take a tiny amount of that to be a large enough dose for it to be significant.”

Companies that sell and use the coal tar sealants have previously disputed the growing body of evidence of the coal tar sealants’ danger being amassed by scientists from the Geological Survey, the University of New Hampshire, Baylor and other institutions.

Repeated attempts this week to reach an industry representative, Anne LeHuray, executive director of the Pavement Coatings Technology Council, for comment on the new studies were unsuccessful. In an email on Thursday, LeHuray said she was tied up at a meeting of the pavement council in Memphis.

Generally, though, the pavement council has attacked previous coal tar research on technical grounds.

The pavement council has fought bans – sometimes successfully – when they have been proposed by local and state governments. In addition to the local governments that have forbidden use of the coal tar sealants, some governments have placed restrictions on their use, including the state of Minnesota and the California Department of Transportation. Restrictions also are in effect in more than 40 Illinois municipalities.

U.S. Rep. Lloyd Doggett, a Democratic congressman from the Austin area, has previously filed legislation calling for a nationwide ban on coal tar sealants. He plans to refile the legislation, a Doggett spokeswoman said, but is currently embroiled in a redistricting fight.

Tom Ennis, an Austin city official who helped get coal tar sealants banned there, has now launched a campaign to support a nationwide ban.

“You’re looking at a big urban air quality” problem, Ennis said. “It’s completely unacceptable and something needs to be done.”

The studies announced this week appeared in the science journals Environmental Science and Technology, Chemosphere, Atmospheric Environment,  and  Environmental Pollution.

Robert McClure

Robert McClure

Robert is co-founder and executive editor of InvestigateWest. At the Seattle Post-Intelligencer, Robert exposed a major weakness in the Endangered Species Act and deficiencies in Puget Sound restoration efforts. His reporting on hard-rock mining won the John B. Oakes Award for Distinguished Environmental Journalism. A Pulitzer Prize finalist, Robert is a longtime former board member of the Society of Environmental Journalists; he currently serves as chair of the editorial board of SEJournal. Seattle Magazine in 2013 chose him as one of Seattle's "most influential" people.


  • M L Selz says:

    Thank you for an informative article. Helpful for me as I am about to have my driveway sealed and I will now know what not to use.

    I just wonder if you could have written the article without taking an unwarranted shot at New Jersey.

    Are you aware the Jersey City has some of the highest real estate values in the Northeast because it is a vibrant city with beautiful parks and a magnificent water front location? Or is it just practice in the Northwest to use New Jersey as the poster child for whatever ills you imagine befall the rest of the country?

    Really, don’t you think that an article intended to spread useful information could have been written without the ignorant comments about New Jersey? I bet you could if you tried.

    • robert mcclure says:

      You have a fair point. I’m actually from the east coast myself. Perhaps native Northwesterners would have been kinder? :>) We selected the two New Jersey cities from a list of locales mentioned deeper in the story whose PAH levels had been compared to the air above coal-tar-sealed parking lots tested near Austin. The others, as we said deeper in the story, were Chicago; London and Manchester, England; and Guangzhou, China. Looking over the list, we thought the two that would most telegraph “industrial” to the American reader were the two that were in New Jersey. It’s my understanding that the list of cities in the paper was determined in part by where measurements of PAHs in ambient air had been done, hence the rather short list of alternative. I’ll remember your comment and try to refrain from picking on New Jersey in the future.

  • Bailey Londagin says:

    Thank you for bringing to light the issue of asphalt sealant toxicity. However, I ask that you please correct the photo caption in your article on The photograph was taken at The University of Texas at Austin (not the University of Austin in Texas, which doesn’t exist.)

  • ru4democracy says:

    What’s pretty amazing is that the PAH load of 1 acre of Applied Refined Coal Tar Sealcoat = 2oz of Denorex Shampoo or BBQ’ing a 6 oz Pork Chop.

    Before this charade continues – Would greatly appreciate Someone, With Some Authority over the USGS to Show Testing Results that the Ban in Austin, Actually Reduced the PAH’s.

    Extrapolating – transitive and intransitive verb infer:
    To use assumed facts as the starting point from which to draw inferences or conclusions about something unknown. “Very Scientific”

  • Nick J. Constant says:

    Although reporting environmental issues and documenting field data and statistics is of great value to environmental advocates, enforcement of existing laws gets to be mind bungling obstruction with EPA bureaucracy.
    Worst, when an advocate goes after the environment offender, he or she encounters
    bureaucrats kicking the can down the bureaucratic alley so as no to make waves or risk their employment status quo. That includes local agents of the judicial system, judges.
    Some of the EPA and state environmental laws like CEQA seem to be unworthy of the paper they are written on. Some small cities, reminiscent of the old west days still carry on with the “cow boy mentality” defying environmental law.
    Former president R. Reagan would turn in his grave had he been around to witness blatant EPA violations. Violations done not by ignorant citizens but by public agency knuckle-heads which most often act like premadonas.
    The State Attorney General’s office is the enforcer of EPA in most states, but don’t bother much as they are busy with “real crimes” we are told.
    Fighting an uphill battle for an advocate may not be the thing to do What is left for advocates to do is to publicize environmental crime when seen. That is if their local newspaper does not mind rocking the boat or making “marketing” waves.
    Studies with scientific facts, substantiated with evidence can only serve as a back up.

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