Fish-tissue and bed-sediment samples were
collected from 20 sites in the upper Snake River
Basin in Idaho and western Wyoming as part of the
National Water-Quality Assessment Program to
determine the occurrence and distribution of organochlorine compounds. During 1992-94, 41 samples were analyzed for 28 different organochlorine
compounds in whole-fish tissue and 32 compounds
in bed sediment. Sites sampled were third- through
seventh-order streams that represented three environmental settings: reference conditions, agricultural land use, and mixed (agricultural and urban)
land use. Fourteen organochlorine compounds
were detected in fish tissue and nine in bed sediment. All compounds detected in bed sediment also
were detected in fish tissue. Fish-tissue and bed-
sediment samples from agricultural and mixed
land-use sites contained one or more organochlorine compounds. The most frequently detected
compound at all sites was p,p'DDE, which was
present in 80 percent of the fish-tissue and 30 percent of the bed-sediment samples. A maximum of
three compounds were detected, all in fish-tissue
samples from reference (forest and rangeland)
sites. The highest number of compounds was
detected in fish-tissue (nine) and bed-sediment
(eight) samples from mixed land-use sites. No clear
relation was apparent between the occurrence of
external anomalies and fish-tissue contaminant
concentrations or land use.
The distribution of organochlorine compounds in the basin was related to land use. Total
DDT was detected at sites in all land uses; total
PCB was detected at only agricultural and mixed
land-use sites. Total chlordane was detected in fish-
tissue samples from primarily mixed land-use sites;
samples from six of the eight sites contained
detectable concentrations. Median concentrations
of p,p'DDE in fish-tissue samples from mixed land-
use sites were significantly higher (p
