| This dissertation project utilizes an integrated approach to characterize waterborne silver toxicity; explore alternative avenues of silver exposure; define in situ animal sentinels used, to monitor detectable metals, including silver; and develop a reconstructed gill epithelium model to study the toxicological effects of silver.; Studies were conducted to determine the sensitivities of marine fish to silver and to characterize the influence of geochemical parameters on silver toxicity. These investigations concluded that silver is not an acute threat to marine fish. In addition, it was determined that increased concentrations of ammonia and reduced salinities enhanced silver toxicity, while sulfides were protective. Embryolarval stages of the summer flounder were extremely vulnerable to chronic silver exposure. Chronic values for the summer flounder were conservatively estimated to range from 0.8 to 2.8μg Ag/L.; The importance of oral (i.e., dietary) silver consumption also was studied. These studies tracked the effects of dietary silver from green algae, Selenastrum capricornutum, to the water flea, Ceriodaphnia dubia. Trophic transfer of silver inhibited reproductive output of C. dubia at all concentrations of dietary silver tested (i.e., >1 μg/g DW), while no effects on cladoceran survival were observed. The threshold dose for impaired reproductive output was ≤1.37ng Ag/daphnid/day.; Metal body burdens, hepatic metal residues, and hepatic metallothionein concentrations in the stoneroller minnow (i.e., animal sentinel) were used as predictive biomarkers of physiological alterations and ecological impact. Strong positive correlations (r > 0.95) were observed between hepatic metallothionein concentrations, metal body burden, and metal residues in tissues, and ecological impact in this species. In addition, metal concentrations in the minnow were used to develop metal multipliers that allowed for quantification of bioavailable metal from total recoverable metal concentrations.; Efforts also were taken to develop an appropriate in vitro model of the gill for use in toxicological evaluations of metals. Results of these investigations confirmed that reconstructed branchial epithelia could be cultured that closely mimic in vivo conditions. Toxicological characterization of the cultured epithelia with silver revealed that Na/K ATPase, which is a molecular target of silver, provided an endpoint that was extremely sensitive over a wide range of concentrations (0.1 to 20 μg Ag/L). |
