In a research report that happens to be fully available online at Van Metre, Peter C., Mahler, Barbara J., and Wilson, Jennifer T, “PAHs Underfoot: Contaminated Dust from Coal-Tar Sealcoated Pavement is Widespread in the United States” Environmental Science & Technology, January 2009, scientists from the United States Geological Survey out of Austin, Texas found a direct correlation between the use of coal-tar based sealants on parking lots and driveways and the presence of polycyclic aromatic hydrocarbons (PAHs) in nearby streams and lakes. The state of Texas alone sees 225 million liters of coal-tar based sealant applied annually. The chemicals examined include naphthalene, acenaphthylene, acenaphthene, 9H-fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[a]pyrene, and dibenzo[a,h]anthracene. The data support previous studies which indicate that coal tar based sealants may be the major source of PAH in stream sediment. The study suggests that coal-tar sealcoated driveways may also present a direct path of PAH for human ingestion.
The study used an interesting method by separating west-coast testing locations from central and east-coast testing locations. Coal-tar is primarily used east of the Rocky Mountains as it is sourced from waste materials generated by the steel industry, primarily located in the “rust belt.” By studying results from both areas, the study was able to find a very strong negative correlation between the use of asphalt-based sealcoats (West of Rockies) and coal-tar based sealcoats and the presence of PAH in nearby stream sediment. This leaves the strong suggestion that it is the presence of PAH in coal-tar based sealant that is the cause of the increase incidence of PAH in stream sediments near cities.
The study also presents the other variables that it examined and lays out the data in an easy to read format. The study is very compelling. Because PAHs are known carinogens it might not be surprising that these results were found. What is more surprising perhaps is that it took this long to develop such a compelling study protocol and that it was the USGS (instead of the EPA or one of several other federal agencies charged with environmental enforcement) that carried it out.