The vertical distribution of selected trace metals and organic compounds in bottom materials of the proposed lower Columbia River export channel, Oregon, 1984

Abstract

A proposal to deepen the lower Columbia River navigation channel prompted a study of the vertical distribution of selected trace metals and organic compounds in bottom materials, to evaluate the effects of dredging and disposal operations. Bottom-material core samples and native-mixing water samples were collected during September and October 1984. Bottom materials were cored to 6 meters, to coincide with proposed channel depths. Attempts to use lead-210 isotopic techniques to chronologically relate trace-metal concentrations to different core depths were severely hampered by a lack of fine grain-sized sediments. Instead, a deposition rate between 0.8 and 1.3 centimeters per year was estimated by using cesium-137 isotopic data. Elutriation testing of bottom material indicated chemical concentrations as large as 900 /ig/L (micrograms per liter) for barium (from the midddle interval of the Skipanon River core), 6,500 //g/L for manganese (from the upper interval of the Cathlamet Bay core), and 14 /zg/L for nickel (from the lower interval of the Skipanon River core). The amount of oxygen present during elutriation testing of reduced bottom material (middle interval of the Skipanon River core) was shown to have a negligible effect on manganese elutriate-test concentrations, but did affect barium and iron concentrations; barium concentrations were larger under reducing test conditions (900 /ug/L) than under oxic test conditions (500 /ug/L) , and, conversely, iron concentrations were smaller under reducing test conditions (440 /zg/L) than under oxic test conditions (800 /zg/L) . Sediment-associated organochlorine compounds detected in Skipanon River (SR-S2)and Cathlamet Bay (CB-S6) core samples were as large as 0.1 /ng/kg (micrograms per kilogram) for aldrin, 2.0 /zg/kg for chlordane, 27 /ug/kg for DDD (dichloro diphenyl dichloroethane), 5.0 A*g/kg for DDE (dichloro diphenyl dichloroethylene), 0.2 /zg/kg for DOT (dichloro diphenyl trichloroethane) , 0.2 A*g/kg for dieldrin, 37 A*g/kg for PCB's (polychlorinated biphenyls), 0.1 /zg/kg for PCN's (polychlorinated naphthalenes), and 0.1 /zg/kg for heptachlor epoxide. Mathematical normalization of the data to grain size shows that organochlorine compounds are preferentially sorbed to fine,-grained sediments rich in organic carbon. Small concentrations of phthalate esters (7 to 20 /ng/kg) were detected in Skipanon River core samples and larger concentrations of polycyclic aromatics (8 to 278 /zg/kg) were detected in Cathlamet Bay core samples. Concentrations of cadmium, lead, and zinc in selected cores were found to exceed those of local basalt rocks. In the Columbia River core sample collected near Astoria, concentrations of cadmium as large as 3.6 /ng/g were found in a portion of the core. In the Skipanon River core sample, concentrations of lead and zinc were as large as 26 /ug/g and 210 A*g/g, respectively, throughout the core. In the Cathlamet Bay core sample, concentrations of cadmium, chromium, copper, iron, and zinc associated with the less-than-100micrometer size fraction are larger than those associated with the greater-than-100-micrometer fraction. Within upper core depths of the same core, large concentrations of cadmium, mercury, and zinc correspond to a time when naval vessels were being maintained in the Cathlamet Bay area. Results of differential extraction techniques indicate that much cadmium and lead is sorbed to particle surfaces in upper core intervals from Skipanon River, Cathlamet Bay, and the Columbia River near Hammond. Because cadmium is associated with large concentrations of total organic carbon, it is unlikely to adversely affect benthic organisms. Lead, however, may bioaccumulate in benthic organisms, although concentrations of lead in clam tissue from the study area are estimated to be slightly less than World Health Food Standards.