source: "Pollution Prevention and Management Strategies for Polycyclic Aromatic Hydrocarbons in the New York/New Jersey Harbor" by the New York Academy of Sciences
An interesting debate has arisen over an emerging contaminant of concern, PolyAromatic Hydrocarbons, or PAHs. These compounds are produced whenever organic materials are heated in the absence of oxygen and water. This can occur whenever combustion is incomplete, such as smoky campfires, flickering candles, incense sticks, cigarettes, poorly functioning gasoline and diesel combustion engines, forest fires, and charcoal and tar production. PAHs form a large and diverse family of compounds, some of which are known to be potent genotoxic carcinogens.
Regulators are cracking down, but they don't know where to turn first, because these compounds are ubiquitous in modern, industrialized, civilization. Washington State and Washington DC have become two of the first areas in the US to begin taking action by banning coal-tar sealants. These sealants are typically applied to parking lots and driveways to make them black and pretty, and they also contain high levels of PAHs.
But are driveway sealants really the culprit? The coal-tar sealant industry points out that some shampoo bottles contain as much PAH as 100 acres of sealed parking lot. Indeed, a basic understanding of aromatic chemistry indicates that these compounds should be extremely water insoluble; they are most hazardous when they are volatilized in fires and the soot is inhaled. So the debate continues, with both industry, government, and citizen action groups trying to make sense of the science.