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How did USGS study parking lot runoff? USGS researchers sampled runoff at 13 parking lots in Austin. They also took scraping samples of parking lot surfaces to compare source materials to particles in the runoff. Scraping samples and the water and particles in the runoff samples were analyzed for a suite of PAHs, major elements, and trace elements. The researchers sprayed water on four different types of parking lot surfaces: lots sealed with coal -tar based sealcoat (top photo), lots sealed with asphalt -based sealcoat, unsealed asphalt lots, and unsealed concrete lots. The runoff was collected behind spill berms, pumped into containers (middle photo) and filtered through Teflon filters to collect the particulates for analysis (bottom photo). The particulates, the filtered water, and samples of sealcoat scraped from the parking lot surfaces were analyzed for PAHs at the USGS National Water Quality Laboratory in Denver, Colorado. Concentrations and yields (the amount of PAHs coming off a parking Iot per unit area) were used to determine levels of contamination in runoff from each type of parking lot and the impor- tance of sealed lots as a source of PAHs to urban streams. How does sealcoat get from parking lots into the environment? Vehicle tires abrade parking lot sealcoat into small particles. These small particles are washed off parking lots by precipitation and into storm sewers and streams. Sealcoat "wear and tear" is visible in high traffic areas within a few months after application. Sealcoat manu- facturers recommend reapplication every 2 to 3 years. What are potential environmental and human health concerns? PAHs are toxic to mammals (including humans), birds, fish, amphib- ians, invertebrates, and plants. Aquatic invertebrates, the insects and other small animals that live in streams and lakes, are particularly susceptible to PAH contami- nation, especially the bottom dwellers (benthic invertebrates) that live in the mud where PAHs tend to accumulate. They are an important part of the food chain and are often monitored as indica- tors of stream quality (analogous to the "canary in the coal mine" concept). Pos- sible effects of PAHs on aquatic inver- tebrates include inhibited reproduction, delayed emergence, sediment avoidance, and mortality, and possible adverse effects on fish include fin erosion, liver abnormalities, cataracts, and immune system impairments. PAHs tend to attach to sediment; the Probable Effect Concen- tration (PEC) —a widely used sediment quality guideline that is the concentra- tion of a contaminant in bed sediment expected to adversely affect benthic (or bottom dwelling) biota —is 22.8 mg/kg (milligrams per kilogram) for total PAHs. Studies by USGS and City of Austin did not evaluate human -health risk from exposure to sealcoat. Human -health risk from environmental contaminants is often evaluated in terms of exposure pathways. For example, people could potentially be exposed to PAHs in sealcoat through skin contact with abraded particles from parking lots, inhalation of wind -blown particles, and inhalation of fumes that volatilize from sealed parking lots. PAHs in streams and lakes rarely pose a human- health risk via drinking water because of their tendency to attach to sediment rather than dissolve in water. In addition, because PAHs do not readily bioaccu- mulate within the food chain, possible human health risks associated with con- sumption of fish are low. What are the concentrations of PAHs in runoff from sealed and unsealed parking Tots? Concentrations of PAHs in particles (including abraded sealcoat along with urban dust and other sediment) washed off from each of the different surface types including the unsealed park- ing lots -.were greater than the PEC of 22.8 mg/kg. The average concentration in particles washed off parking lots that were not sealcoated was 54 mg/kg. This is not surprising because runoff from parking lots is likely to contain PAHs from many sources, including leaking motor oil, tire particles, vehicle exhaust, and atmospheric deposition. Concentrations of PAHs were much higher in particles in runoff from parking lots sealed with coal-tar based sealcoat than from all other types of parking lot surfaces. Specifically, the average con- centration of PAHs from coal -tar sealed lots was 3,500 mg/kg, about 65 times higher than the average concentration in particles washed off unsealed parking lots. The average concentration in par- 100,1)00 E 0 10,000 Vl E 1,000 E y 0 1— 100 10 Type of parking lot Probable Effect Concentration o a \°o e� Q$ es c cs Q om cy •a any J SQr° t1) sa Concentrations of total PAHs in particles in runoff from sealed parking Lots greatly exceeded concentrations from unsealed parking Tots. The bar on each graph is the mean concentration. The y -axis is logarithmic.