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application. It has been estimated that about 5% of sealcoat wears off the driving areas of parking lots each year (Scoggins, 2009). Sealcoat manufacturers recommend reapplication every 2 to 4 years. The East -West divide Product use translates to PAH concentrations In one USGS study, dust was swept from sealcoated and unsealcoated parking lots in nine cities across the U.S. and analyzed for PAHs. For six cities in the central and eastern U.S., the median PAH concentration in dust from sealcoated parking lots was 2,200 milligrams per kilogram (mg /kg), about 1,000 times higher than in dust from sealcoated parking lots in the western U.S. (median concentration 0.8 mg /kg). This agrees well with reports that the coal tar -based sealcoat product is used predominantly east of the Continental Divide and the asphalt -based product is used predominantly west of the Continental Divide, and with PAH concentrations in the products themselves (about 90,000 mg /kg in coal- tar -based products and 50 mg /kg in asphalt -based products (City of Austin, 2005). What are the concerns for our environment and for us? PAHs are toxic to mammals (including humans), birds, fish, amphibians, invertebrates, and plants. Aquatic invertebrates, the insects and other small animals that live in streams and lakes, are particularly susceptible to PAH contamination, 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 indicators of stream quality (analogous to the "canary in the coal mine" concept). Possible effects of PAHs on aquatic invertebrates 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 Concentration (PEC) —a widely used sediment quality guideline that is the concentration 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. Human health risk from environmental contaminants usually is evaluated in terms of exposure pathways. For example, people could potentially be exposed to PAHs in sealcoat through skin contact with abraded particles from driveways or parking Tots either by direct touching of touching of toys or other items that have been in contact with the pavement, 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.