THE RELATIONSHIP BETWEEN LAND-USE AND ORGANOCHLORINE COMPOUNDS IN STREAMBED SEDIMENT AND FISH IN THE CENTRAL COLUMBIA PLATEAU, WASHINGTON AND IDAHO, USA

We analyzed streambed sediment and fish in the Central Columbia Platea u in eastern Washington and Idaho for organochlorine pesticides and po lychlorinated biphenyls (Sigma PCB). Our objective was to assess the e ffects of land use on the occurrence and distribution of these compoun ds; land uses in the study area included forest, dryland and irrigated farming, and urban. We detected 16 organochlorine compounds in stream bed sediment and fish tissue; fish usually had more compounds and a gr eater frequency of detection. The most frequently detected compound wa s Sigma DDT (sum of six isomers), which was found in 52% of bed sedime nt samples and 94% of whole fish composite samples. The other commonly detected compounds were dimethyl tetrachloroterephthalate (DCPA), die ldrin, hexachlorobenzene, and Sigma chlordane (sum of cis-and trans-ch lordane, cis-and trans-nonachlor, oxychlordane, heptachlor, and heptac hlor epoxide). Forest was the only land use with no detections of orga nochlorine compounds in either fish or bed sediment. Hexachlorobenzene was the only organochlorine pesticide detected at concentrations that differed significantly among land uses: concentrations were higher in the dryland farming areas than in the irrigated farming or urban area s. In agricultural areas irrigated by surface water, Sigma DDT concent rations in both streambed sediment and fish tissue were related to the percentage of land irrigated by water delivered via furrows (gravity irrigation), although Sigma DDT was not detectable in bed sediments un til gravity irrigation exceeded 30%. Because of the relation between g ravity irrigation and soil erosion, our study supports the importance of controlling soil erosion in order to reduce the overall loading of organochlorine compounds to surface waters.