Parking-lot pollution

Coal-tar based sealcoat - the black, shiny emulsion painted or sprayed on asphalt pavement such as parking lots - can affect the quality of downstream water resources, according to a recent joint study in

by the

National Water-Quality Assessment (NAWQA) Program and the City of

.

That’s because the sealcoat has extremely elevated concentrations of polycyclic aromatic hydrocarbons (PAHs), an environmental concern because they are toxic to aquatic life and because several are suspected human carcinogens.

Small particles of sealcoat flake off as they are abraded by vehicle tyres, and can wash into urban streams with rain and runoff.

The study found that particles in runoff from coal-tar based sealcoated parking lots have PAH concentrations that are about 65 times higher than in particles washed off parking lots that have not been sealcoated.

Particles in runoff from parking lots sealed with asphalt-based sealcoat, the other major product on the market, have PAH concentrations about 10 times higher than those from unsealed lots.