UNH research adds to mounting evidence against popular pavement seal coat

The research, detailed in a recent feature article in the journal Environmental Science & Technology, has found that one type of pavement sealcoat, common on driveways and parking lots throughout the nation, has significant health and ecosystem implications. Alison Watts, research assistant professor of civil engineering at UNH, is a co-author of the article "Coal-Tar-Based Pavement Sealcoat and PAHs: Implications for the Environment, Human Health, and Stormwater Management."

Sealcoat, a black surface applied over asphalt pavements that is marketed as improving appearance and enhancing pavement longevity, is made of either an asphalt emulsion or a refined coal-tar pitch emulsion. Although the two sealcoats are similar in appearance and cost, concentrations of PAHs (polycyclic aromatic hydrocarbons), a group of organic compounds known to be detrimental to human and ecosystem health, are about 1,000 times higher in coal-tar-based sealcoats than those based in asphalt.

Conducting side-by-side studies of coal-tar-based sealcoated and nonsealcoated parking lots at UNH's West Edge lot, Watts, a researcher with the UNH Stormwater Center, found that the soil at the edge of the sealcoated lot contained "orders of magnitude higher concentrations" – several hundred parts per million (ppm) from the sealcoated lot versus less than 10 ppm from the lot without sealcoating -- of PAHs. What's more, soil samples taken three years after the initial application of sealcoat remained high in PAHs. Read More