Coal-Tar Sealant and PAH Contamination
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Studies have identified coal-tar-base sealcoat – a product used to maintain and protect driveway and parking lot pavement – as a major source of polycyclic aromatic hydrocarbon (PAH) contamination in streams and lakes adjacent to where it is used. Before you sealcoat the driveway or parking lot of your home or business, consider the impact coal-tar sealcoating may have on water quality and human health.
What are PAHs? Polycyclic aromatic hydrocarbons, or PAHs, are chemicals that occur naturally in coal, crude oil, and gasoline, and are also present in products made from fossil fuels, such as coal-tar pitch, creosote, and asphalt. PAHs also come from the burning of carbon and are present in the smoke of forest and grass fires, volcanoes, vehicle exhaust, and cigarette smoke. |
Photo: USGS
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Relative amounts of PAHs
in sealcoat products Credit: Minnesota Pollution Control Agency |
What is Coal-Tar Sealant?
Pavement sealcoat—also called sealant or driveway sealer—is a black liquid sprayed onto the asphalt pavement of many residential driveways, parking lots, and even some playgrounds. It is marketed as protecting and beautifying the underlying pavement and is used commercially and by property owners across the country. Sealcoat comes in two basic varieties: coal-tar-based and asphalt-based. Sealcoat used in the central, southern, and eastern U.S. commonly contains coal-tar pitch, a byproduct of the manufacturing process, which is made up of at least 50% PAHs. Pavement sealants that contain coal-tar, therefore, have extremely high levels of PAHs compared to other PAH sources such as vehicle emissions, used motor oil, and tire particles. Coal-tar-based sealcoat typically contains from 50,000 to 100,000 milligrams per kilogram (or parts per million) PAHs, which is about 1,000 times higher than PAH concentrations in asphalt-based sealcoat products. Over time, sunlight and vehicle traffic wears down sealcoat and small particles of sealcoat are transported from parking lots and driveways to streams and lakes by stormwater runoff. Sealcoat wear is visible in high traffic areas within a few months after applications and manufacturers recommend reapplication every 2 to 4 years. |
Coal-tar-based pavement sealant is the largest source of polycyclic aromatic hydrocarbons (PAHs) found in 40 urban lakes studied by the U.S. Geological Survey (USGS). Asphalt-based sealcoat runoff can contain 10 times more PAHs than an uncoated driveway and the amount of PAHs in stormwater runoff in parking lots sealed with coal-tar sealants can be 65 times higher than stormwater from unsealed parking lots.
What Problems Are Caused By Using Coal-Tar Sealant?
While sealcoating makes parking lots and driveways look new, there are serious environmental and public health concerns with its use. Several PAHs are suspected human carcinogens and are toxic to fish and other aquatic life and their concentrations have been increasing in urban lakes in recent decades.
While sealcoating makes parking lots and driveways look new, there are serious environmental and public health concerns with its use. Several PAHs are suspected human carcinogens and are toxic to fish and other aquatic life and their concentrations have been increasing in urban lakes in recent decades.
Trends in Contaminates Since 1970
Credit: USGS (Van Metre et al., 2000, Environ. Sci. &Tech. Van Metre and Mahler, 2005, Environ. Sci. & Tech.)
Stormwater, snow melt, and water from hoses and sprinklers wash the PAHs and other pollutants along with the dirt off of driveways and into nearby streams and lakes. The PAHs in coal-tar stick to particles rather than remain dissolved in water and, therefore, will be found mostly in the sediments at the bottom of streams, ponds, and lakes. Although bacteria in waters or sunlight can break down some of these chemicals, others are quite persistent and will accumulate over time. Aquatic animals living in the sediments can take them up into their bodies and fish become exposed when they eat the PAH-contaminated prey.
Credit: USGS
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PAHs from coat-tar sealcoat are transported by different pathways. Once dry, the sealcoat product (A), is abraded into a powder and becomes part of the dust on the pavement (B). That dust, filled with a high concentration of PAHs, is transported to stormwater runoff (C) to stormwater management systems (D) or to streams and lakes (E). Parking lot dust also adheres to tires (F) that track it onto other surfaces, and wind and runoff transport the dust to nearby soils (G). Dust particles also are tracked by shoes into residences, where they become incorporated into house dust (H). Volatile PAHs in are also released into the air (I).
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When fish are exposed to PAHs, they exhibit chronic problems, including fin erosion, liver abnormalities, cataracts, skin tumors, and immune system impairments. When benthic macroinvertebrates, insects, and other organisms that live at the bottom of rivers and lakes are exposed to PAHs, they are susceptible to a number of detrimental effects, including inhibited reproduction, delayed emergence, and mortality. The health risk for humans is dependent upon the length and type of exposure to PAHs. House dust is a primary source of human exposure. USGS found that residences adjacent to parking lots with coal-tar sealants have PAH concentrations in house dust that are 25 times higher than those in house dust in residences adjacent to parking lots with other surface types.
What is Being Done to Address PAHs? Several states and cities have taken action to address PAHs from coat-tar sealant by banning the sale and use of pavement sealants containing coal-tar. Several other states, including Michigan, Illinois, and New York, are also considering bans. As well, major retailers such as Home Depot, Lowe's, Ace, and United Hardware have stopped selling coal-tar sealants. |
Credit A.E. Pinkney.
Tumors in brown bullhead catfish from the Anacostia River, Washington, D.C. are believed to be related to elevated PAH concentrations.
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Credit: Justin McInnis, U.S. Geological Survey
A professional applicator applies a coal-tar-based sealant to a test plot used to measure emission of polycyclic aromatic carbons (PAHs) into the air in Austin at the University of Texas.
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How Can You Help Prevent Further PAH Contamination in our Lakes?
Support a ban in your community or a statewide ban in Michigan and make sure you are not using any coal-tar sealants. There are other pavement options such as pervious concrete, permeable asphalt, and paver systems that do not require sealants. These types of pavements also allow for stormwater to naturally infiltrate, resulting in decreased runoff. If you do choose to use a sealcoat, choose alternatives to coal-tar-based sealants, such as asphalt-based sealants or latex sealants. How Can You Tell if a Product Contains Coal-Tar? You can determine whether a product contains coal-tar by reading the label and product information. If you are hiring a contractor to perform the job, make sure you specify a product without coal-tar and ask to see the ingredient list of the product they are using. If you are doing the work yourself, look for the Chemical Abstracts Service (CAS) number 65996-93-2 on the product Material Safety Data Sheet (MSDS). The words “coal-tar,” “refined coal-tar,” “refined tar,” “refined coal-tar pitch,” or other similar terms may be listed on the container or MSDS. |
Additional Resources
Coal-Tar-Based Pavement Sealcoat—Potential Concerns for Human Health and Aquatic Life
USGS Fact Sheet (April 2016) https://pubs.er.usgs.gov/publication/fs20163017
USGS webpages on PAHs and coat-tar based sealcoat
http://water.usgs.gov/nawqa/asphalt_sealers.html
http://tx.usgs.gov/sealcoat.html
EPA's Stormwater Pollution Prevention Webinar Series: Stormwater,
Coal-Tar Sealcoat, and Polycyclic Aromatic Hydrocarbons (PAHs)
http://water.epa.gov/polwaste/npdes/stormwater/EPAs-Stormwater-Pollution-Prevention-Webinar-Series-Stormwater-Coal-Tar-Sealcoat-and-Polycyclic-Aromatic-Hydrocarbons-PAHs.cfm
Freshwater Future Coal-Tar Sealants webpage
http://freshwaterfuture.org/ourissues/coal-tar-sealants/
Great Lakes Coal-Tar Sealcoat PAH Reduction Project (Minnesota Pollution Control Agency)
http://www.pca.state.mn.us/index.php/water/water-types-and-programs/stormwater/stormwater-management/great-lakes-coal-tar-sealcoat-pah-reduction-project/index.html
(Above data adapted from the U.S. Environmental Protection Agency and USGS.)
Coal-Tar-Based Pavement Sealcoat—Potential Concerns for Human Health and Aquatic Life
USGS Fact Sheet (April 2016) https://pubs.er.usgs.gov/publication/fs20163017
USGS webpages on PAHs and coat-tar based sealcoat
http://water.usgs.gov/nawqa/asphalt_sealers.html
http://tx.usgs.gov/sealcoat.html
EPA's Stormwater Pollution Prevention Webinar Series: Stormwater,
Coal-Tar Sealcoat, and Polycyclic Aromatic Hydrocarbons (PAHs)
http://water.epa.gov/polwaste/npdes/stormwater/EPAs-Stormwater-Pollution-Prevention-Webinar-Series-Stormwater-Coal-Tar-Sealcoat-and-Polycyclic-Aromatic-Hydrocarbons-PAHs.cfm
Freshwater Future Coal-Tar Sealants webpage
http://freshwaterfuture.org/ourissues/coal-tar-sealants/
Great Lakes Coal-Tar Sealcoat PAH Reduction Project (Minnesota Pollution Control Agency)
http://www.pca.state.mn.us/index.php/water/water-types-and-programs/stormwater/stormwater-management/great-lakes-coal-tar-sealcoat-pah-reduction-project/index.html
(Above data adapted from the U.S. Environmental Protection Agency and USGS.)
