Date: 01 Jan 2008

Effects of Cadmium Exposure on Embryogenesis of Stagnicola elodes (Mollusca, Gastropoda): Potential Consequences for Parasite Transmission

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Abstract

Experiments on the toxicity of cadmium (Cd2+) to the embryonic development of Stagnicola elodes (Mollusca, Gastropoda), obligatory first intermediate host of numerous trematodes of pathogenic importance, were carried out as part of a study on the effects of metal pollution on host-parasite relationships. Freshly laid snail eggs were exposed to Cd concentrations of 0, 0.02, 0.2, and 2.0 mg Cd2+/L, and survival and embryogenesis were examined for 30 days. Mean survival time (± SD) of the control group was 23.1 (± 5.3) days compared with 10.1 (± 3.2) at 0.02 mg Cd2+/L, 3.9 (± 0.7) at 0.2 mg Cd2+/L, and 1.1 (± 0.08) at 2.0 mg Cd2+/L. Mortality patterns of all test groups differed significantly from each other, demonstrating that the percentage of surviving individuals at any given time was inversely related to Cd concentration. Concentration-dependent effects of Cd exposure on snail embryogenesis were noted. While embryos of the control group developed properly and started hatching on day 16, eggs exposed to 0.02 mg Cd2+/L exhibited a prolonged gastrula period and failed to hatch. Eggs in the 0.2 mg Cd2+/L group were blocked in the gastrula stage on day 5, whereas individuals exposed to 2.0 mg Cd2+/L died in the morula stage on the second day. Data showed that Cd severely affects S. elodes embryogenesis. By implication, Cd contamination at concentrations ≥0.02 mg Cd2+/L will thus decrease transmission success of various trematodes by decreasing intermediate host snail abundance.