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 metal s to these invertebrates, bioaccumulation of As, Cd, Cu, Pb, and Zn fr om sediment was evaluated by exposing the amphipod Hyalella azteca for 28 d in the laboratory to samples of sediment collected from depositi onal areas of the Clark Fork River. Benthic invertebrates collected fr om riffles adjacent to the depositional areas were also analyzed for m etals. The pattern of metal accumulation between laboratory-exposed an d 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 met als to invertebrates in the Clark Fork River. Additional studies shoul d be conducted to determine threshold concentrations for effects of di etary metals on fish. Long-term monitoring of the river should include sampling benthic invertebrates for metal accumulation.