Occurrence and phase distribution of polycyclic aromatic hydrocarbons in urban storm-water runoff

A total of 42 storm-water overland-flow samples were collected from four sampling sites (a highway off-ramp, a gas station, and a low- and high-traffic-volume parking lot). For each sample, the suspended-sediment and water phases were separated and analyzed for 16 polycyclic aromatic hydrocarbons (PAHs). The gas station site produced the highest total PAH loading (2.24 g/yr/m2), followed by the high-traffic-volume parking lot (5.56 X 10-2 g/yr/m2), the highway off-ramp (5.20 × 10-2 g/yr/m2), and the low-traffic-volume parking lot (3.23 × 10-2 g/yr/m2). In several samples, one or more PAHs were detected in the aqueous phase at concentrations above its aqueous solubility. This result suggests the presence of colloidal-size particles capable of sorbing PAHs to an appreciable extent, or the presence of an oil-and-grease microemulsion. Based on rainfall and PAH data from seven discrete storm events, PAH concentrations were usually highest during the “first flush” of storm-water runoff and tapered off rapidly as time progressed. It is apparent from these analyses that storm-water runoff from parking lots, highways, and gas stations is a significant source of PAHs to the environment. Because some of the PAHs are carcinogens or suspected carcinogens, best management practices such as oil/grit separators should be implemented at “hot spots” in urban areas to mitigate potential PAH pollution.