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REPRODUCTIVE TOXICITY OF CHLORPYRIFOS, DIELDRIN, AND METHYL MERCURY MIXTURES TO THE AMPHIPOD, HYALELLA AZTECA
Citation:
Steevens, J. A., D. S. Block, AND W H. Benson. REPRODUCTIVE TOXICITY OF CHLORPYRIFOS, DIELDRIN, AND METHYL MERCURY MIXTURES TO THE AMPHIPOD, HYALELLA AZTECA. SETAC 20th Annual Meeting, Philadelphia, PA, 14-18 November 1999.
Description:
Toxicological interactions were assessed on the reproduction of the amphipod Hyalella azteca throughout a chronic exposure to methyl mercury (0.9, 4.7, 23.3 nM), chlorpyrifos (0.01, 0.05, 0.24), dieldrin (0.5, 2.3, 11.4 nM) and their binary mixtures. H. azteca were exposed to the model toxicants for four weeks followed by a three week period of recovery. Adult survival, cumulative offspring, and offspring fitness were assessed throughout the exposure and recovery periods. Fitness in offspring and adult organisms was assessed as a measure of the relative success of the organisms to survive and reproduce. At the end of the experiment, the fitness of adult organisms was assessed to determine the effects over four weeks exposure and three weeks of recovery. Chlorpyrifos and dieldrin did not have an effect on adult survival, while methyl mercury significantly decreased survival at a low concentration 23.3 nM (5.8 |g/L). Adverse reproductive effects were observed with all three chemicals at the medium and high concentrations. An hormetic response, increased reproduction, was observed at the lowest concentration for chlorpyrifos and dieldrin. However, the benefit of increased number of offspring was counteracted by a significant decrease in the fitness as compared to control organisms. No significant effects were observed on the fitness of adult organisms at the end of exposure period. In addition, mixtures of the model toxicants did not result in a significant deviation from the toxicity of the individual chemicals. These results suggest that the chemical mixture interactions may not be significant at low concentrations. In addition, the hormetic response observed with individual chemicals appeared to be abolished by the presence of the second chemical.