The Evaluation of the Freshwater Western Pearl Mussel, Margaritifera falcata (Gould, 1850), as a Bioindicator Through the Analysis of Metal Partitioning and Bioaccumulation

Abstract

We assessed the effectiveness of the western pearl mussel (Margaritifera falcata, Gould, 1850) as a bioindicator of aquatic system health. Fifty-years ago a large dredge mining operation for columbite-tantalite ores [(Fe,Mn)(Nb,Ta)2O6] disturbed a substantial portion of the Middle Fork of the Salmon River headwaters in Idaho. The disturbance likely increased concentrations of dissolved metals at the time. To evaluate the potential long-term impacts, if any, concentrations of Fe, Mg, Mn, and Zn in shell and soft tissues of western pearl mussels, collected from five reaches in Bear Valley Creek, were analyzed. We quantified the partitioning and bioaccumulation with respect to age of the four metals in the shell, gills and mantle, and remaining soft tissue of the western pearl mussel. Overall, gills and mantle had higher concentrations of Fe, Mg, Mn, and Zn than the remaining soft tissue and shell. Bioaccumulation with respect to age was not uniform among elements or mussel material. We did not detect significant metal accumulation along an upstream gradient approaching the historic dredge site. Metal accumulation downstream did not appear to be in response to the physical disturbance or potential enhancement of dissolved metals during dredging activities in the mid-1950s. However, no mussels were located within the historic dredging zone. Possible reasons for no mussels in the dredging zone are discussed, but not reconciled. We conclude that using freshwater mussels and a water quality assessment might provide a useful approach to biological monitoring of past and current exposures to essential and non-essential elements.