GEOCHEMICAL PARTITIONING AND BIOAVAILABILITY OF COPPER TO AQUATIC PLANTS IN AN ARTIFICIAL OXIDE-ORGANIC SEDIMENT

This study investigated the effects of competition between binding sub strates (organic matter and iron oxide) and between metals (cadmium an d copper), on the partitioning of sedimentary copper and its subsequen t bioavailability to an aquatic plant. Organic matter and a synthesize d iron oxide, ferrihydrite, were added singly and in combination to a series of sand sediments, which were then dosed with environmentally r ealistic concentrations of cadmuim and copper and planted with rice, O ryza sativa. Organic matter controlled copper partitioning and bioavai lability, whereas the synthetic ferrihydrite bound negligible amounts of either metal, even in the absence of organic matter. As organic mat ter concentrations increased, operationally-defined leachable copper d ecreased, organic-associated copper increased and the survival of rice plants improved in an approximately linear fashion. At a nominal star ting copper concentration of 5.8 mu g g dry wt(-1), plant survival aft er four weeks averaged 0-8% in sediments without organic matter, 25% i n a sediment containing 0.18% organic matter and 58% in a sediment con taining 0.36% organic matter. These results suggest that organic-assoc iated forms of copper are unavailable to plants, and that the operatio nal definition of 'leachable' copper (extracted with dilute ammonium a cetate) adequately represents the species of copper that is (are) avai lable to plants. Our study using a well-characterized artificial sedim ent supports the copper fractionation patterns and correlations betwee n copper partitioning and bioavailability reported from the heterogene ous, poorly characterized sediments of natural lake and river sediment s.