Chemicals commonly found in parking lot sealants have been found to degrade aquatic ecosystems and are suspected to be human carcinogens, according to recent studies. Polycyclic aromatic hydrocarbons (PAHs) are organic contaminants typically formed during the incomplete burning of coal, gasoline, garbage, and other organic substances and are found in coal tar, crude oil, auto exhaust, and roofing tar. Studies by the U.S. Geological Survey (USGS) and City of Austin concluded that coal tar-based parking lot sealants are a major, previously unrecognized source of PAH contamination.

Coal tar is a byproduct from the coking of coal, and coal tar-based sealants are typically 20 to 35 percent coal-tar pitch – the residue that remains after the distillation of coal tar. Used in an effort to protect and beautify asphalt, coal tar-based sealants have been identified with average PAH concentrations 1,000 times higher than asphalt-based sealants.

Natural wear and tear by vehicles on parking lots and driveways crushes sealcoats into small particles. People can potentially be exposed to these contaminants through skin contact of sealant particles or inhalation of particles and fumes. Findings by USGS have shown that residences next to coal tar-sealed parking lots have house dust with PAH concentrations 25 times higher than residences adjacent to parking lots without coal tar-based sealcoats. Although the health effects of dust with high PAH concentrations from coal tar sealants have not been studied extensively, a 2008 Columbia University study in China found that babies in utero exposed to PAHs emitted by a coal plant had delayed cognitive development compared to babies that were in utero after the coal plant was closed.

Coal tar sealcoat particles are also washed into streams, lakes, and reservoirs, where they are toxic to aquatic bottom dwellers (benthic invertebrates) – solid indicators of stream health and an important part of the food chain – and jeopardize the health of fish, with potential effects such as liver abnormalities, fin erosion, and immune-deficiencies. PAHs have not been proven to present threats to drinking water, because they do not easily dissolve in water, but rather stick to solid particles and settle in the bottoms of lakes and streams.

With recommended reapplications of 2-3 years, parking lot sealants can have major impacts on local watersheds. The City of Austin, Texas estimates about 600,000 gallons of sealant are used within its jurisdiction every year. USGS scientists found that loads of PAHs in the studied watersheds could be reduced to one-tenth of their current levels if all parking lots were unsealed.

Several local governments are taking action to address these risks. Effective in January 2006, the sale and use of coal tar-based sealants were banned from the City of Austin and surrounding territories. Washington, D.C. banned the sale and use of coal tar pavement products in 2009 to protect the Anacostia and Potomac Rivers and Chesapeake Bay. Director of the D.C. Department of the Environment, George S. Hawkins, said, “It’s rare that we have a chance to knock out this kind of pollution in one fell swoop. Now that we’ve discovered what’s in coal tar and what it does, we have a rare opportunity to protect our waterways relatively easily.” Dane County, Wisconsin and a few suburbs in Minneapolis, Minnesota have also banned the use of coal tar sealants. A bill calling for the statewide ban of coal tar sealants has made its way to the Washington state Senate this month after passing the House 67-30. There are many alternatives to coal tar-based sealants – all of which are asphalt-based – which can be used to significantly reduce PAH pollution.

On the federal level, Rep. Lloyd Doggett (D-TX) has called for a nationwide ban of coal-tar sealants and wrote a letter to the Environmental Protection Agency requesting an investigation, suggesting the “study should identify gaps in our scientific understanding and regulatory control of coal-tar sealants.”

To help federal policymakers more fully understand the latest scientific research on coal-tar sealants and PAHs, the Environmental and Energy Study Institute, Water Environment Foundation, and the Office of Rep. Doggett will bring Barbara Mahler, a USGS scientist, to Capitol Hill for a briefing on April 14, 2011 . This briefing is open to the public and video will be posted at after the event.