Polycyclic aromatic hydrocarbons (PAHs) are a class of more than 100 chemicals that occur naturally in coal, crude oil, and gasoline, and are also present in products made from fossil fuels, such as coal-tar pitch, creosote, and asphalt. They also come from burning carbon, forest and grass fires, vehicle exhaust, and even char-broiled foods. Some PAHs, either individually or combined, can cause adverse health effects, including cancer.
PAHs build up in stormwater ponds, man-hole sumps, catch basins, rain gardens, ditches, underground treatment systems, street sweepings, and other parts of stormwater collection and conveyance systems where sediment accumulates. They are also accumulating in the sediments of natural lakes, streams, rivers, and wetlands that receive untreated stormwater runoff.
PAHs are part of the contamination caused by petroleum leaks and spills and by industrial activities. They are found at a number of contaminated sites in Minnesota.
Coal-tar sealants, a type of asphalt sealant banned in Minnesota since 2014, have been a significant source of PAHs in stormwater runoff in the state.
Human health and environmental concerns
Some PAHs, either individually or combined, can cause adverse health effects, including cancer. Inhaling high levels of PAHs has caused respiratory effects and suppressed immune system in humans. Benzo(a)pyrene, a PAH that has been studied extensively, is considered a potent carcinogen, meaning low doses may cause cancer.