U.S. Geological Survey U.S. Geological Survey Polychlorinated dibenzo-p-dioxins and dibenzofurans were found in bed sediment at 14 Willamette River Basin sites that were representative of agricultural, urban, industrial and pristine environments. The octachlorodibenzo-p-dioxin congener (OCDD) was found at all sites; concentrations ranged from 57 ng/kg at a pristine site located in old-growth forest to 32,000 ng/kg at an urban/industrial site. Despite the wide concentration range, the same pattern of congener concentrations was evident at all sites but one. OCDD was the most abundant and the heptachlorodioxin congener class was next in abundance--- about one-fourth that of OCDD. The octa- and heptachlorodibenzofuran classes followed and were roughly equal to one another in abundance. Tetrachlorodibenzo-p-dioxin (TCDD) was the most infrequently detected congener class and was found at only 4 of the 14 sites. The 2,3,7,8-TCDD isomer was detected at one site. In addition to bed sediment, whole fish were sampled at 6 of the 14 sites. The congener concentrations in fish did not resemble those in bed sediment. OCDD was detected in only one fish sample. The 2,3,7,8-TCDD isomer was detected in whole fish at two sites, but was not detected in bed sediment at the same sites.