Tolerance and Resistance to Cadmium in White Suckers (Catostomus commersoni) Previously Exposed to Cadmium, Mercury, Zinc, or Selenium

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Abstract
White suckers' (Catostomus commersoni) tolerance of and resistance to Cd is increased as a consequence of previous metal exposure. The order of metal toxicity to white suckers was Hg > Cd > Zn >> Se. Toxicity curves clearly showed that white suckers exposed to sufficiently elevated Cd, Hg, or Zn levels subsequently survived longer than control suckers in Cd toxicity tests. The 96-h Cd LC50 increased by 61 or 127% following 1 wk exposure to.0.40 or 0.72, respectively, of the 96-h Cd LC50 (1.11 mg Cd/L) for control suckers. The 96-h Cd LC50 also increased by 260% following 1 wk exposure to 0.32 of the 96-h Hg LC50 (0.687 mg Hg/L). The 12- and 24-h Cd LC50 values were increased, but the 48-, 72-, and 96-h values were not, following 1 wk exposure to elevated Zn levels. Exposure to Se prior to toxicity testing had little or no effect on Cd toxicity. Mechanisms which might be responsible for the decreased Cd toxicity include decreased uptake, increased excretion, redistribution of metals to less-sensitive target sites, and/or induced synthesis of metallothionein. Possible consequences of increased tolerance to metals include compensatory adjustments which result in poor recruitment into the population, accumulation of potentially toxic metals, and increased survival in metal-impacted areas.Key words: tolerance, resistance, acclimation, cadmium, mercury, zinc, selenium, white sucker, Catostomus commersoni, toxicity
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