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ticles washed off parking lots sealed with asphalt -based sealcoat was 620 mg/kg, about 10 times higher than the average concentration from unsealed parking lots and 6 times less than the average concen- tration from coal-tar sealed lots. The Large differences between concentrations associated with sealed and unsealed parking lots indicate that abraded sealcoat is a major and previ- ously unrecognized contributor to PAH contamination. How do PAHs from sealcoat affect the quality and biology of streams? Studies by USGS scientists dem- onstrated possible connections between PAHs in particles washed off sealed parking lots and PAHs in suspended sedi- ment in four streams in Austin and Fort Worth, Texas. The total mass of PAHs (or "load expected to wash off seated parking lots was compared to the load of PAHs measured in suspended sediment in the four streams after rainstorms. The load of PAHs estimated to come from the sealed parking lots was comparable to the measured load in the streams, indicating that runoff from sealed parking lots could account for the majority of PAHs in these streams. Findings also showed that PAHs in suspended sediment in the streams were chemically similar to those in par- ticles washed off parking lots sealed with coal-tar based sealcoat. What would be the effect on PAH loading to the streams if parking lots were not sealed? Estimates -5 E 61 go C 3 0 0 E 5 h 0 uyi 10 0 X 15 20 0 500 1,00D 1,500 2,000 Change in total PAHs, in micrograms per gram organic carbon (upstream to downstream) How did City of Austin scientists conduct biological studies? City of Austin biologists conducted laboratory and field studies to evaluate the effects of sealcoated parking lots on aquatic communities in area streams. These studies included toxicity testing in controlled laboratory experiments that exposed organisms to sediment spiked with coal -tar and asphalt -based sealcoat (left photo); controlled experiments that used aquariums with diverse natural biological communities to which sealcoat was added (middle photo); and field assessments of aquatic communities in streams upstream and downstream from inflows of runoff from sealcoated parking lots (right photo). from the USGS study indicate that total loads of PAHs coming from parking lots in the studied watersheds would be reduced to about one -tenth of their cur- rent levels if all of the parking lots were unsealed. Studies by City of Austin biologists showed that PAHs in sediment con- taminated with abraded sealcoat could be adversely affecting aquatic communities. Specifically, toxicity testing of organisms in the laboratory showed large increases in mortality as sealcoat amounts and PAH concentrations were increased, and that sediment contaminated with coal -tar sealcoat was toxic to aquatic life at PAH concentrations observed in Austin water- 2,500 a E t 50 0 E 100 N C t0 o 150 0 E z 200 0 ways. Controlled experiments that used aquariums with diverse natural biological communities showed significant biologi- cal degradation in response to the addi- tion of sealcoat particles. Finally, field assessments in selected Austin streams showed loss of species and decreases in the number of aquatic organisms down- stream from inflows of runoff from coal tar sealcoated parking lots. These effects coincided with increases in concentra- tions of PAHs in stream sediment below sealcoated parking lots. Overall, City of Austin scientists have reported PAH contamination at levels predicted to be toxic to benthic invertebrates in about 13 percent of sampled Austin creeks. 500 1,000 1,500 2,000 Change in total PAHs, in :micrograms per gram organic carbon (upstream to downstream) Field assessments in five selected Austin streams showed Toss of species (taxa) and decreases in the number of aquatic organisms downstream of coal -tar sealcoated parking Tots that can be, in large part, explained by increases in total PAHs. 2,500