Road Surface and Asphalt Off-Gassing (PAH Volatilization, Coal Tar Sealcoat, Benzo[a]pyrene, USGS Austin Study, Residential Proximity) — outdoor safety profile
Moderate riskRoad surfaces and parking lot sealcoats are significant sources of polycyclic aromatic hydrocarbon (PAH) exposure, with coal tar-based sealcoat representing the most concentrated source.
What is this product?
Road surfaces and parking lot sealcoats are significant sources of polycyclic aromatic hydrocarbon (PAH) exposure, with coal tar-based sealcoat representing the most concentrated source. Coal tar sealcoat contains 50,000-100,000 mg/kg total PAHs (including benzo[a]pyrene at 200-1,000 mg/kg), compared to 50-1,000 mg/kg PAH in asphalt emulsion sealcoat — a 50-1,000x difference. A landmark USGS study in Austin, Texas (Mahler et al., 2005, Environmental Science & Technology) identified coal tar sealcoat as the dominant PAH source in urban lake sediments, contributing an estimated 50-75% of total PAH loading to Lady Bird Lake. Subsequent USGS research (Van Metre et al., 2012) found that apartments with coal tar-sealed parking lots had indoor dust PAH concentrations 25x higher than apartments with asphalt-sealed or unsealed lots. Hot asphalt paving operations release volatile PAHs (naphthalene, phenanthrene, fluoranthene) and hydrogen sulfide gas during placement at 150-170C. NIOSH studies of highway workers found elevated urinary PAH metabolites (1-hydroxypyrene) during hot-mix asphalt paving operations. Residential proximity to newly paved or sealed surfaces increases PAH inhalation exposure — benzo[a]pyrene (IARC Group 1 human carcinogen) is the most potent PAH species, with an inhalation unit risk of 1.1 x 10-3 per ug/m3 (EPA IRIS). Multiple US cities and states have banned coal tar sealcoat, including Austin TX (2005), Washington DC (2009), Minnesota (2014), and New York state (2022).
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Carcinogenic Pah
Volatile Pah
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