The Canary Report

Coal-tar sealcoat contains highly dangerous chemicals

Posted on Jan 24, 2009 by Susie Collins in Blog, Environment, Research

Parking lots treated with coal-tar-based sealcoats are a major source of cancer-causing contaminants that can pollute air, soil, water and wildlife, posing a significant health risk to humans who may breathe, drink or eat them in fish and other food.

Environmental Health News reports on a recent study that highlights the potential human health risk from coal-tar based products and shows a need to better understand and reduce use and impacts.

Coal-tar based sealcoats contain very high levels of polycyclic aromatic hydrocarbons (PAHs) — up to 30 percent by weight. PAHs are known to cause an array of health effects and pose a significant threat to wildlife and humans.

Sealcoats are not stable. The coatings break down over time, forming dust that moves the PAHs from the paved surfaces to surrounding areas, including soil, water and air.

Of particular concern are the levels found in residential driveways. PAH levels in the collected dust were above toxic guideline limits for indoor dust and soils. Potentially, the outside dust could pose a human health risk either directly, by someone touching the surface, or indirectly through objects that contact the surface, such as shoes or basketballs.

Hand to mouth contact is a major route of exposure for infants, children and adults. People can ingest contaminant-laden house dust by touching it then eating without washing their hands. Mouthing toys and other objects is another way babies are exposed (Stapleton et al. 2008).

Outdoor, PAH-laden dust could also be ingested by hand to mouth contact. The dust could be picked up on hands or carried indoors on the bottom of shoes. It could also be breathed in while working or playing outside (driveways, playgrounds, etc.).

PAHs in the lake sediments and surrounding soils is also a concern for wildlife and people. Humans could eat contaminated fish or agriculural crops grown on soils polluted with PAHs.

Clearly, the high levels of PAHs observed in these urban and suburban areas warrant further research as to the health risk of these common and widely used sealing products.

Coal-tar sealants are banned from use in some places. One simple solution is use asphalt containing sealcoats, particularly for residential use and playgrounds.

Background:

Parking lots and other paved areas are sometimes sealed to protect them from the elements. Two main sealants are used in the US: asphalt (crude oil base) and coal-tar base. Asphalt is more common in western states, while coal-tar base is the dominant form used in eastern and central states.

Coal-tar is formed when coal is coked, a process to prepare coal for use as a fuel.  Coal-tar base sealants contain high levels of a class of chemicals known as polycyclic aromatic hydrocarbons (PAHs). A mix of different types of PAHs are found in the sealant.

The long-lived PAHs widely pollute the environment, wildlife and people. These highly dangerous chemicals are expected to cause cancer in people.

PAHs form if oil, coal, wood and petroleum do not burn completely. Sources include vehicles, factories, power plants and pavement sealcoats. Of the many sources of PAHs in the environment, it is not known how much of it comes from sealcoated pavements.

As the black, shiny sealcoats wear away over time, small, dusty particles form. The specks can contain PAHs and other chemicals found in the sealants.

Wind and water disperse the particles into the surrounding environment. Wind carries the contaminated dust almost everywhere — into the water, onto other pavements or onto land used for gardens or crops. Potentially, the dust, if very fine, could be breathed in by animals and people.

The dust is also washed off the surfaces into local lakes, streams and other waterways by rain and snow melt. The stormwater runoff can contain high levels of PAHs. Some researchers suggest that coal-tar based sealcoats are a major source of PAH pollution in streams. Often, high levels of PAHs are found in the sediments of the lakes and streams accepting the stormwater runoff.

This pollution poses an environmental health risk for the organisms that live in the waterways, including fish that may be eaten by humans. A study of sealcoats in runoff in Austin, Texas, has linked adverse effects in local amphibians to sealcoat dust runoff (Bryer et al. 2006).

Van Metre, PC, BJ Mahler and JT Wilson. PAHs underfoot: Contaminated dust from coal-tar sealcoated pavement is widespread in the United States. Environmental Science and Technology doi: 10.1021/es802119h.

Link to full report at Environmental Health News

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Postscript

05/08/09

I received an email this morning from an author of some of the reports mentioned in this post:

Hello Susie,

I was most interested to read about coal-tar sealcoat in the Canary Report. As an author of some of the reports, I’d like to clarify that sealcoat is used on asphalt pavement (e.g., parking lots and driveways) but generally not on roads.

Sincerely,
Barbara Mahler
Research Hydrologist
USGS

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Tags: Air, Cancer, Chemicals, Children's Health, Environment, Food, Health, Pollution, Toxic