BIOACCUMULATION OF METALS BY HYALELLA-AZTECA EXPOSED TO CONTAMINATED SEDIMENTS FROM THE UPPER CLARK-FORK RIVER, MONTANA

Macroinvertebrates contaminated with metals in the Clark Fork River of Montana have been demonstrated to be a potentially toxic component in the diet of trout. Because sediment was the suspected source of metals to these invertebrates, bioaccumulation of As, Cd, Cu, Pb, and Zn from sediment was evaluated by exposing the amphipod Hyalella azteca for 28 d in the laboratory to samples of sediment collected from depositional areas of the Clark Fork River. Benthic invertebrates collected from riffles adjacent to the depositional areas were also analyzed for metals. The pattern of metal accumulation between laboratory-exposed and field-collected animals was similar; however, The concentrations of metals in laboratory-exposed amphipods were often 50 to 75% less than were the concentrations of metals in the field-collected invertebrates. These findings indicate that sediment is a significant source of metals to invertebrates in the Clark Fork River. Additional studies should be conducted to determine threshold concentrations for effects of dietary metals on fish. Long-term monitoring of the river should include sampling benthic invertebrates for metal accumulation.