KWRRI Research Reports


Aquatic toxicity studies were performed on two natural populations of fathead minnows. One group of organisms was taken from a metal-contaminated flyash pond associated with a coal-fired power plant and the other group was collected from relatively uncontaminated hatchery ponds. Acute tests indicated that flyash pond fish were significantly more tolerant to cadmium and copper than were hatchery fish. At an exposure concentration of 6.0 mg Cd/L in moderately hard water, the median period of survival for flyash pond fish was 50.0 hr compared to 6.8 hr for hatchery fish. Both groups of organisms were about equally sensitive to zinc. The metal-induced tolerance observed with animals from the flyash pond was not a sustained response. Additional studies were undertaken to observe the responses of laboratory populations of fathead minnows to acutely toxic cadmium concentrations following acclimation to sublethal exposures of this metal. Based on 96-hr LC50 values, those animals which had received 35-days prior exposure to 10 and 50 μg Cd/L were 63 to 68% more tolerant to cadmium than were previously unexposed organisms. As with the natural population, tolerance to cadmium in the laboratory fish was not retained. After organisms which had been acclimated to 10 μg Cd/L were transferred to clean water, tolerance to cadmium decreased by three and one-half fold after only 7 days. Developing embryos of the fathead minnow and rainbow trout also acquired tolerance to cadmium. After eggs of the trout had been exposed to 0, 5, and 50 μg Cd/L for 24 days, subsequent acute toxicity tests conducted on the newly hatched larvae gave 7-day LC50 values of 0.70, 1.59, and 2.02 μg Cd/L, respectively.

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The work upon which this report is based was supported in part by funds provided by the United States Department of the Interior, Washington, D.C., as authorized by the Water Research and Development Act of 1978. Public Law 95-467.