Metal Levels and Intracellular Distributions in Benthic Insects Exposed to Mine Waste
D.J. Cain1, W.G. Wallace2, and S. Luoma11U.S. Geological Survey, MS 465, 345 Middlefield Rd., Menlo Park, CA 940252 Center for Environmental Science, The College of Staten Island/CUNY, 2800 Victory Blvd., 6S-310, Staten Island, NY 10314

Metal toxicity is affected by how organisms internally compartmentalize metals.  This study compared the concentrations and intracellular distributions of Cd and Cu among hydropsychid caddisflies, Hydropsyche spp. and Arctopsyche grandis, and mayflies, Baetis spp. and Serratella tibialis, from contaminated sites in the upper Clark Fork  river, Montana, and from an uncontaminated tributary (Blackfoot River).   Bioaccumulation patterns exhibited species and metal specificity.  Relative to uncontaminated samples, intracellular metal accumulation was greater in mayflies than in caddisflies.  For example, Cd concentrations in the cytosol (soluble cytoplasm) were 7 - 13 (g/g in Serratella and Baetis and 0.4 - 2 (g/g in Hydropsyche and Arctopsyche.  Cytosolic Cu concentrations were highest in Serratella (111 (g/g), and similar in Baetis, Hydropsyche and Arctopsyche (27 -  44 (g/g).  The cytosol was a major accumulation site for Cd.  Cadmium and Cu accumulation in the cytosol of Arctopsyche and Baetis was accompanied by a shift in the distribution of metal from “heat stable” (metal binding) to “heat denatured” (essential) proteins.  The relatively high intracellular metal concentrations in Serratella and Baetis are supportive evidence of the reported metal sensitivity of mayflies.  Species - specific toxicity may be further modified by how excess metal is partitioned among cytosolic ligands.