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Issues of The Environment: The Dangers Of Coal Tar Sealants

Driveway sealant
Wikimedia Commons

Awareness of a serious environmental and health threat is beginning to come to the fore. Serious damage is possible when we use Coal Tar Sealants on our driveways and parking lots. That's the focus of this week's edition of Issues of the Environment.


  • Studies suggest a common sealant using coal tar contains hazardous chemicals that elevate lifetime cancer risk. So some cities and states are banning its use.
  • Michigan has introduced legislation that would ban the use of coal tar sealants entirely and it would be the second state to do so.
  • Laura Rubin, Executive Director of the Huron River Watershed Council, says that coal tar sealants our concern to our waterways and a ban will protect our local watershed.

Coal Tar Sealant Hazards
Coal-Tar Sealant - What is coal-tar and what is its danger? Applying sealcoat to asphalt is a common practice. In Michigan, coal tar-based sealcoat is applied widely on driveways, parking lots, and even playgrounds. Sealcoat applicators and their customers say the product enhances the look of weathered asphalt surfaces and prolongs product life.
However, coal tar sealcoats are incredibly high in polycyclic aromatic hydrocarbons, or PAHs. PAHs are of concern because many of these compounds have been identified as toxic, mutagenic, teratogenic (causing birth defects) and/or probable human carcinogens. Coal tar sealants contain 1000 times more PAHs than asphalt-based sealants (a readily available alternative) and are the number one source of PAHs in lake sediments. In fact, studies show up to 50-75% of all PAHs found in sediments within the Great Lakes region comes from coal tar sealcoat.
PAHs from coal tar sealcoat are released into the environment in several ways. When applied, these compounds volatilize into the air, affecting air quality. As the sealcoat weathers, dust from the pavement makes its way into homes on shoes and clothing. When it rains, loose particles move into soils, stormwater catch basins, lakes, and rivers.
Aquatic health impacts - In rivers and lakes, PAHs are found primarily in the sediments. Organisms that spend part or all of their life cycle in contact with these sediments can experience adverse effects due to exposure to elevated concentrations of PAHs. Affected organisms include mammals, birds, fish, amphibians and plants. Studies have linked PAH exposure in aquatic animals to stunted growth, reduced reproduction, difficulty swimming, liver problems, altered development, immune system impairment and death.
Human health impacts - For someone who spends their lifetime living adjacent to coal tar sealcoated pavement, the average excess cancer risk is estimated to be 38 times higher than the urban background exposure. Much of the increased risk occurs during early childhood. Children play on and near these surfaces and are, therefore, more likely to inhale or ingest PAHs associated with coal tar sealcoat.
What you can do - Homeowners and those who manage grounds for private entities such as churches, daycares or businesses can: Eliminate sealcoating as a maintenance practice for asphalt surfaces
If sealcoating cannot be eliminated, use asphalt-based sealcoat rather than coal tar sealcoat. There are contractors who will apply asphalt-based sealcoat, and this alternative is also available at most hardware stores. (The big hardware store chains have already banned coal tar sealcoat from their shelves.)

  • If you represent a company that will offer alternatives to coal-tar and service the Washtenaw/Wayne/Oakland/Livingston County area and would like to be listed here, please contact psteen@hrwc.org.

Cities and other municipalities can: Pass an ordinance banning the use of coal tar sealant within the municipality. [They could also,] adopt a resolution committing to the reduction or elimination of the use of coal tar sealant on city property.
Universities and schools can: Commit to phase out the use of coal tar sealcoat on their properties. The University of Michigan, for example, does not use sealcoats of any variety.

Contact David: dfair@emich.edu