Occurrence and potential adverse effects of semivolatile organic compoundsin streambed sediment, United States, 1992-1995

The occurrence and potential adverse effects of select semivolatile organic compounds (SVOCs) in streambed sediment were assessed at 536 sites in 20 m ajor river basins across the United States from 1992 to 1995. Fifty-six SVO Cs were detected at one or more sites, and one or more SVOCs were detected at 71% of sites. The northeastern and Great Lakes regions and large metropo litan areas have the highest SVOC concentrations. Polycyclic aromatic hydro carbons (PAHs) were detected most frequently and at the highest concentrati ons. Concentrations of PAHs and phthalates were about 10 times higher at si tes influenced by urban activities than at sites in other land-use areas. S emivolatile organic compounds were significantly (alpha = 0.05) correlated with land use and population density, and PAHs also correlated with physica l/chemical properties. On the basis of sediment-quality guidelines, adverse effects are probable at 7.5% and possible at 16.2% of the sites. Most of t he potential for adverse effects is due to PAHs. The median percentage of u rban land use was 8% at sites with possible adverse effects and 16% at site s with probable adverse effects. Urbanization profoundly affects sediment q uality, even though it comprised a small percentage of most drainage basins .