Driveways and other asphalt-paved areas must be maintained in order to ensure their usefulness over time.  Often, this involves applying sealing agents made with coal tar (CT) that contain a complex mixture of chemicals including polycyclic aromatic hydrocarbons (PAHs).  These compounds have been shown to cause DNA damage and are known to enter the environment in the form of, water runoff, vapor and  dust. Many studies have demonstrated that these are common routes by which human exposure occurs.
 
To investigate this exposure, researchers at Health Canada performed a 28-day oral exposure study of CT-based sealant extracts in the transgenic Muta™Mouse. Both DNA adducts and lacZ gene mutations were identified in multiple tissues including lung, liver, glandular stomach and small intestine. Notably, the pattern of damage observed in this study matched the sites of cancer formation in a previous study looking at the long-term effects of CT. Researchers also used In Vivo MicroFlow BASIC kits to examine peripheral blood micronucleus formation. Results showed a more than 2-fold increase in micronuclei. This indicates some of the active agents in the CT-based sealants had an impact beyond the main contact sites for oral exposures.
 
Overall the experiments demonstrated “conclusive identification of in vivo mammalian genotoxic hazard from oral exposure to a PAH extract from coal tar-based driveway sealcoat”. These results suggest that humans exposed to CT-based products could be at risk for experiencing similar genotoxic hazards and resulting biological effects.