Over the last few years, the research into the problem of coal tar sealants (CTSs) has covered a variety of specific areas including CTS wash off, wear off, parking lot dust, household dust, biological effects and lake cores (deposits that end up in lake sediments). All of these studies have increased our understanding of the sealants and the challenge they present in the environment. Until now it has been a little tough for the less scientific among us to track all of these studies.
Coal tar is the byproduct of making coke from coal in the production of steel. For years, coal tar has been the main ingredient in pavement sealants on parking lots, driveways and playgrounds. Research has shown these sealants are a potent source of what the Environmental Protection Agency calls a "persistent, bioaccumulative toxin," part of the group of chemicals called "polycyclic aromatic hydrocarbons" or PAHs.
Now a new publication summarizes much of the work done to date by the U.S. Geological Survey (USGS) and others in an easy to read format with a lot less technical jargon. This document would be great for anyone wanting to go into more detail about the subject without wading too deeply into the science and statistics of a technical journal article.
Here are some key ideas from the document:
- Residences adjacent to parking lots with coal-tar-based sealcoat have PAH concentrations in house dust that are 25 times higher than those in house dust in residences adjacent to parking lots without coal-tar-based sealcoat. While the U.S. doesn't have a dust standard for these chemicals, a German guideline to avoid adverse health effects was frequently exceeded.
- Dust from pavement with coal-tar-based sealcoat has greatly elevated PAHs compared to dust from unsealed pavement.
- Coal-tar-based sealcoat is the largest source of PAH contamination to 40 urban lakes studied, accounting for one-half of all PAH inputs.
- Coal-tar-based sealcoat use is the primary cause of upward trends in PAHs, since the 1960s, in urban lake sediment.
- PAHs move from a sealcoated surface into our environment by many mechanisms: storm runoff, adhesion to tires, wind, foot traffic, and volatilization.
And some additional factoids:
- LEED for Healthcare (2009) gives credit for facilities that do not use coal tar sealants.
- Coal-tar pitch is 50 percent or more PAHs by weight and is known to cause cancer in humans (International Agency for Research on Cancer, 1980).
- Coal-tar-based sealcoat products typically are 20 to 35 percent coal-tar pitch.
- Product analyses indicate that coal-tar-based sealcoat products contain about 1,000 times more PAHs than sealcoat products with an asphalt base (more than 50,000 milligrams per kilogram [mg/kg] in coal-tar-based products and 50 mg/kg in asphalt-based products - City of Austin, 2005).
- Concentrations of PAHs in dust swept from sealed parking lots in central and eastern U.S. cities, where coal-tar-based-sealcoat use dominates, were about 1,000 times higher than in western U.S. cities.
- Additional effects from PAHs include DNA damage to male sperm, IQ deficits in children, and asthma.
What can you do if you suspect CTS might be on your paved surface?
- First, test your parking lot sealant to see what kind it is. A simple test with supplies that can be purchased from a hardware store can give a good indication. A free, detailed description of how to do this is at: http://coaltarfreeamerica.blogspot.com/2010/12/field-test-for-coal-tar-sealant.html. For about $200 to $300, a certified laboratory can give a more definitive test.
- Improve cleaning of the parking lot. Frequently sweep the surface (with a dedicated tool), and collect the sweepings to minimize the accumulation of debris.
- Provide plenty of entrance matting, and encourage those entering the facility to wipe their feet.
- Encourage occupants to increase hand washing after being on the parking lot surface.
- Consider completely removing the sealant or at least putting a non-coal tar pavement sealant over the top of the contaminated surface. Pictures and video of this being done can be found at: http://coaltarfreeamerica.blogspot.com/2011/01/chicago-tribune-what-if-cts-is-on-my.html
