EFFECT OF METAL MIXTURE (Cu, Zn, Pb, and Ni) ON CADMIUM PARTITIONING IN LITTORAL SEDIMENTS AND ITS ACCUMULATION BY THE FRESHWATER

The effect of a metal mixture (Cu, Zn, Pb, and Ni) on Cd fractionation in sediment and its accumulation by the freshwater macrophyte Eriocaùlon septangulàre was examined in an in situ experiment in the littoral zone at the Experimental Lakes Area, northwestern Ontario, Canada. Fresh sediment was spiked with Cd alone and together with the metal mixture at three concentration levels. Macrophytes were planted in the spiked sediment and placed at a water depth of 0.5 m. The distribution of Cd among sediment fractions (easily reducible [ER], reducible [R-ER], and organic [ORG]), pore water, and macrophytes was determined every 2 weeks for 10 weeks. Small differences among treatment levels in the recovery of Cd from the geochemical fractions were observed after 2 and 8 weeks but not after 10 weeks. At the highest concentration of the metal mixture, Cd repartitioned from the ER fraction onto the R-ER fraction after 2 weeks in situ. After 10 weeks, Cd was accumulated by the shoots (,2.6 mg/g dry weight) and roots (,45 mg/g dry weight) of E. septangulàre and had not reached steady state. Significantly higher Cd concentrations were found in the shoots of plants in the treatment with Cd alone and the treatment with the highest concentration of the metal mixture than in treatments with intermediate levels of the mixture. Partitioning of Cd among geochemical fractions in sediment alone did not explain differences in tissue Cd concentrations related to treatment level. Keywords—Cadmium Mixtures Freshwater macrophyte Simultaneous extraction Bioaccumulation