While they are relatively unknown to the public, PAHs—a class of chemical contaminants - have been shown to cause high rates of lesions and tumors on bottom-dwelling fish in at least two Bay tributaries: the Anacostia and Elizabeth rivers.
PAHs, or polynuclear aromatic hydrocarbons, are formed when coal, gasoline and fuel oil are burned. They are also a major component of tar and coal-tar based products. Specific sources of PAHs include:
In particular, coal-tar based driveway and parking lot sealants are a significant source of PAHs to the environment.
According to a study by the U.S. Geological Survey (USGS) in Austin, Texas, the average yield of PAHs from sealed parking lots was 50 times greater than that from unsealed lots. Estimates from this study indicate that total loads of PAHs coming from parking lots in the watersheds studied would be reduced to about one-tenth of their current loads if all of the parking lots were unsealed.
PAHs enter water bodies through run off from roads, driveways and parking lots into the closest storm water drain. Like PCBs, PAHs attach to sediment in water, where they are known to be toxic to plankton and bottom-dwelling organisms such as oysters and some fish.
Population growth and development are recognized as specific causes of PAH contamination of sediments. The USGS National Water Quality Assessment Program found that the most rapid increases of PAH collection in sediments were found in areas undergoing urban sprawl and increases in motor vehicle traffic.
Tumors and lesions found on fish in two Bay tributaries have been linked to high PAH concentrations.
In a study by the U.S. Fish and Wildlife Service (USFWS), between 50 and 60 percent of fish collected from the Anacostia River had liver tumors. These rates are alarming, as scientists consider an area with a liver tumor rate of more than 5 percent to be highly contaminated. Tests on fish tissues and bottom sediments suggest that exposure to PAHs is likely responsible for the tumors.
A related study examined the effects of PAH-contaminated sediments on mummichogs in Virginia's Elizabeth River. The study showed a strong correlation between tumors and liver lesions in mummichogs and PAH concentrations in the river.
Scientists are also taking a close look at the South River, located in Anne Arundel County, Maryland. In a 2005 study by the USFWS, 53 percent of brown bullheads had visible skin tumors and 20 percent had liver tumors. However, monitoring data for the South River do not show high PAH concentrations in bottom sediments.
Since the USGS study that found coal-tar sealants are a major source of PAHs, the city of Austin, Texas, has banned these sealants from use on parking lots. While there are no federal regulations against coal tar use in products, consumers can instead choose for their own driveways asphalt-based sealants, which contain significantly less PAHs.