Chemical and ecotoxicological characterization of Columbia River sediments below the Hanford site (USA).

Columbia River sediments were characterized (metals, organics, porewater toxicity) with samples (n=12) from four dams below the Hanford site. Analyses were supplemented with colocated radionuclide data, along with comparable data from the Priest Rapids dam, immediately upriver from Hanford. Although not statistically significant (Bonferroni P>0.05), metals were generally highest at Priest Rapids, relative to downriver dams. Semivolatiles, Aroclors, and organochlorine pesticides were below method reporting limits. Radionuclide differences across locations were minor (Bonferroni P>0.05). Whereas Microtox showed little toxicity, Daphnia IQ tests exhibited measurable toxicity at all locations (EC50 = 22 - 78% porewater). Ecotoxicological benchmarks for metals were exceeded at several locations, most notably at Priest Rapids. Except for K-40, radionuclides were below benchmarks. Overall, chemistry and ecotoxicity results suggested that sediments may pose a risk to benthic biota, likely due to metals (derived largely from upriver mining) or factors associated with a reducing environment (e.g., low oxygen, high ammonia).