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(W/MF199) Using tissue residue and metallothionein concentration to assess metal bioavailability following a mine tailings spill. Gillis, Patricia1,2, Reynoldson, Trefor 2, Dixon, D. George 1, 1 2 ABSTRACT- Subcellular biological indicators such as tissue residue and metallothionein concentration can be used to determine the bioavailability of potential toxicants and predict their impact on natural populations. Metal tissue residue and the metal binding protein, metallothionein are useful tools in determining the bioavailability of trace metals in the sediment to benthic organisms. Earlier studies with the oligochaete Tubifex tubifex have found that metallothionein concentrations are responsive to sediment metal concentrations and correlate with effects at the organism level such as reproduction. Following the collapse of the Alancazar mine tailings impoundment, toxicity tests were performed on sediments from 5 sites in the Rio Guadimar in order to assess sediment quality in the area of tailings deposition. One of the tests was a 28 day survival and reproduction test using T. tubifex. Following exposure the worms were transferred to clean water for 24 hours for gut clearing and then analyzed for metal tissue residues and metallothionein. Metallothionein was measured using a mercury saturation assay. Nickel, Lead, Cadmium, Copper and Zinc were measured using graphite furnace atomic absorption spectrometry. Worms exposed to sediments from the impoundment site had significantly higher concentrations of Cd, Zn, Cu and Pb in their tissues than worms exposed to sediments from upstream of the spill. Tissue residues of Pb and Cu were also elevated at a site further downstream from the spill. Sediment characterization at this same downstream site showed a higher percent of fine material and the toxicity tests also found it to be the most toxic. The metallothionein concentration was not elevated at the impoundment site, however it peaked at the downstream site. The elevated concentration of metals in worms exposed to sediments from downstream of the spill confirms that the metals were bioavailable to benthic organisms and thus poised a threat to the fauna of the river. The large increase in metallothionein concentration corresponded with a decrease in reproduction in the worms. These data suggesting that metallothionein concentration is a useful indicator of metal toxicity to benthic animals. Key words: metallothionein, tissue residue, metal bioavailability, benthic invertebrates |
