Dioxins and furans in bed sediment and fish tissue of the Willamette Basin, Oregon, 1992-1995

Dioxins and furans were found in bed sediment and fish tissue throughout the Willamette Basin, including samples from the most remote sites. The highest concentrations in bed sediment were found at sites where industrial or urban inputs were most likely; potential toxicity at these sites (as measured by toxicity equivalents concentration) was high enough to be associated with increased risk to sensitive mammalian wildlife. From 30 to 60 percent of the toxicity equivalents concentration in bed sediment was due to hepta- and octa- congeners, not 2,3,7,8-TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), which was detected at only 6 of 22 sites. Compared to bed sediment from the same site, fish tissue usually had lower total concentrations of dioxins and furans, but contained a higher proportion of the most toxic congeners, such as 2,3,7,8-TCDD and 2,3,7,8-TCDF (2,3,7,8-tetrachlorodibenzofuran). Concentrations of dioxins and furans in bed sediment at most sites in agricultural and forested are