Recycling or reuse is in most instances environmentally preferable to disposal. Reuse of coal tar as an asphalt-pavement sealant for driveways and parking lots, however, has turned out to be an exception to this rule of thumb. See also: Asphalt and asphaltite; Pavement
A byproduct of the processing of coal to make coke, coal tar is a mixture of hundreds of organic chemicals. Fifty percent by weight or more of these organics can be polycyclic aromatic hydrocarbons (PAHs), which contain two or more fused benzene (aromatic) rings. Some PAHs are mutagens, teratogens, carcinogens, or endocrine disruptors. Because PAHs can potentially migrate out of coal tar products into the surrounding environment, their use in pavement sealants has been a point of concern. See also: Aromatic hydrocarbon; Coal chemicals; Coke; Environmental endocrine disruptors; Environmental toxicology; Mutagens and carcinogens; Polynuclear hydrocarbon
In 2003, the city of Austin, Texas concluded that the primary source of PAHs found in its waterway sediments had to be particles abraded from parking lots that had been sealed with coal-tar-based products. Storm water runoff would have carried these particles into local lakes and streams. Three years later, in 2006, Austin became the first city in the United States to ban the use of coal-tar sealants. A 2010 study of sediments from 40 U.S. lakes corroborated the hypothesis that coal-tar-based pavement sealants were major sources of PAH pollutants. See also: Water pollution
Evidence that the Austin ban had the desired effect emerged in a June 2014 report in the journal Environmental Science & Technology. Researchers from the U.S. Geological Survey found significantly declining concentrations of PAHs in sediment from the bottom of Lady Bird Lake, which receives the bulk of Austin’s runoff.
To date, 14 states (California, Illinois, Kansas, Maryland, Massachusetts, Michigan, Minnesota, Missouri, New York, North Carolina, South Carolina, Texas, Washington, and Wisconsin) and the District of Columbia have enacted restrictions on the use of coal-tar sealants. In addition, major retail stores across the United States have stopped selling coal-tar products for driveway sealing.