ORGANOCHLORINE COMPOUNDS IN BED SEDIMENT AND FISH TISSUE IN THE SOUTHPLATTE RIVER BASIN, USA, 1992-1993

Bed-sediment and fish-tissue samples were collected in the South Platt e River Basin to determine the occurrence and distribution of organoch lorine compounds in the basin. During August-November 1992 and August 1993, bed sediment (23 sites) and fish tissue (subset of 19 sites) wer e sampled and analyzed for 32 organochlorine compounds in bed sediment and 27 compounds in fish tissue. More types of organochlorine compoun ds were detected in fish tissue than in bed sediment. Total DDT, p,p'- DDE, o,p'-DDE, p,p'-DDD, total PCB, Dac thal(R), dieldrin, cis-chlorda ne, cis-nonachlor, trans-nonachlor, and p,p'-DDT were detected in fish tissue at >25% of the sites; p,p'-DDE, total DDT, cis-chlordane, and trans-chlordane were detected in bed sediment at >25% of the sites. Or ganochlorine concentrations in bed sediment and fish tissue were relat ed to land-use settings. Few organochlorine compounds were detected at minimally impacted sites located in rangeland, forest, and built-up l and-use settings. Chlordane-related compounds and p,p'-methoxychlor in bed sediment and fish tissue, endrin in fish tissue, and endosulfan I in bed sediment were associated with urban and mixed (urban and agric ultural) sites. Dacthal(R) in bed sediment and fish tissue was associa ted with agricultural sites. The compounds HCB, gamma-HCH, PCA, and to xaphene were detected only at mixed land-use sites. Although DDT and D DT-metabolites, dieldrin, and total PCB were detected in urban, mixed, and agricultural land-use settings, highest mean concentrations were detected at mixed land-use sites. Mixed land-use sites had the greates t number of organochlorine compounds detected in fish tissue, whereas urban and mixed sites had the greatest number of organochlorine compou nds detected in bed sediment. Measuring concentrations of organochlori ne compounds in bed sediment and fish tissue at the same site offers a more complete picture of the persistence of organochlorine compounds in the environment and their relation to land-use settings.