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Coal Tar Sealants Runoff Packed with Fast-Acting Toxins And Slow-Release Carcinogens Months After Application

Sorry Kelly Clarkson, unfortunately "what doesn't kill you, only makes you stronger" doesn't apply to coal tar pavement sealers.  New research from the United States Geological Survey (USGS) leaves one wondering when it is safe to apply coal tar pavement sealants.  The report, Concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) and Azaarenes in Runoff from Coal-tar- and Asphalt-Sealcoated Pavement, details the washoff of chemicals following the application of pavement sealcoat on a paved asphalt parking lot.  They found concentrations of chemicals that have a fast-acting (acute) toxicity in high concentrations soon after the application of sealer and eventually the runoff water is dominated by concentrations of chemicals which can form mutations and cancer. Typically the industry calls for a 24 hour waiting period for curing, but these tests show that the discharge of pollutants continue well after this curing time.
Photo from the USGS.
Photos from the USGS.
As you can see from the below graph (labelled Figure 2), the sum of the PAH concentrations really don't go down over time. But in the graph labelled Figure b, the light-weight PAHs (generally toxic) go down over time, but the heavyweight PAHs (generally carcinogenic) go up.




Are these concentrations of concern?  Here's what the report says:

  • the concentration of one PAH would kill 50% of rainbow trout if exposed to runoff up to 7 days after application.  Could this really happen?  Yes...check out this video.
  • another PAH chemical concentration that is known to cause "gross anomalies" in rainbow trout was exceeded by a factor of 10 to 100 up to 111 days after application.
  • Don't have trout?  Even the common bluegill would be negatively affected by runoff of any samples on the first 7 days after application.
But What About People?

The report also explores for the first time in coal tar sealer research the runoff of a near-PAH chemical family called "azaarenes," which are chemicals similar in structure to PAHs but containing a nitrogen atom in the place of a carbon atom.  Canadian research first called one of these chemicals, quinoline, into question back in 2012, where we covered it in an article entitled "Canadians Find Overlooked Chemical in Coal Tar Sealants "May Constitute a Danger.. to Human Life or Health".  One of their findings was:
Based on the information presented in this draft screening assessment (of coal-tar based sealers), it is proposed that quinoline is entering or may be entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity. On the basis of the carcinogenicity of quinoline, for which there may be a probability of harm at any level of exposure, it is proposed that quinoline may be entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health.
Other findings from the study:

  • PAHs are an environmental health concern because they are toxic to fish and other aquatic life. A 2012 human health-risk analysis found that people living near pavement sealed with coal-tar-based products have an elevated risk of cancer.
  • Concentrations of PAHs and azaarenes in runoff from the coal-tar-sealcoated pavement were about 20 times higher than in runoff from the asphalt-sealcoated pavement, and about 40 times higher than in runoff from unsealed asphalt. 
  • Concentrations and assemblages of PAHs indicated that the asphalt-based sealcoat might have contained a small amount (5-10%) of coal-tar-based sealcoat.
  • This study is the first to investigate concentrations of azaarenes associated with sealcoat runoff. Sources of azaarenes include coal-tar and oil-shale processing, wood preserving, and chemical manufacturing. In samples of runoff collected just hours after sealcoat application, concentrations of the azaarene carbazole exceeded those of any other PAH or azaarene measured. Azaarenes have a large range of ecotoxicological effects, including acute toxicity, but have been less well studied than PAHs.

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