Urban sprawl leaves its PAH signature

The increasing vehicle traffic associated with urban sprawl in the United S tates is frequently linked to degradation of air quality, but its effect on aquatic sediment is less well-recognized. This study evaluates trends in P AHs, a group of contaminants with multiple urban sources, in sediment cores from 10 reservoirs and lakes in six U.S. metropolitan areas. The watershed s chosen represent a range in degree and age of urbanization. Concentration s of PAHs in all 10 reservoirs and fakes increased during the past 20-40 ye ars. PAH contamination of the most recently deposited sediment at all sites exceeded sediment-quality guidelines established by Environment Canada, in some cases by several orders of magnitude. These results add a new chapter to the story told by previous coring studies that reported decreasing conc entrations of PAHs after reaching highs in the 1950s. Concurrent with the i ncrease in concentrations is a change in the assemblage of PAHs that indica tes the increasing trends are driven by combustion sources. The increase in PAH concentrations tracks closely with increases in automobile use, even i n watersheds that have not undergone substantial changes in urban land-use levels since the 1970s.