title: Effects of cadmium exposure on embryogenesis of Stagnicola elodes (Mollusca, Gastropoda): potential consequences for parasite transmission.
abstract: Experiments on the toxicity of cadmium (Cd(2+)) 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 Cd(2+)/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 Cd(2+)/L, 3.9 (+/- 0.7) at 0.2 mg Cd(2+)/L, and 1.1 (+/- 0.08) at 2.0 mg Cd(2+)/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 Cd(2+)/L exhibited a prolonged gastrula period and failed to hatch. Eggs in the 0.2 mg Cd(2+)/L group were blocked in the gastrula stage on day 5, whereas individuals exposed to 2.0 mg Cd(2+)/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 >or=0.02 mg Cd(2+)/L will thus decrease transmission success of various trematodes by decreasing intermediate host snail abundance.
authors.affiliation: Fluvial Ecosystem Research Section, Aquatic Ecosystem Protection Research Division, Water Science and Technology Directorate, Science and Technology Branch, Environment Canada, St. Lawrence Centre, Montreal, QC, Canada. michael.pietrock@usask.ca
authors.forename: M
authors.initials: M
authors.lastname: Pietrock
authors.forename: T
authors.initials: T
authors.lastname: Meinelt
authors.forename: D J
authors.initials: DJ
authors.lastname: Marcogliese
mesh_terms: D000818:Animals; D002104:Cadmium / Q000633:toxicity*; D004625:Embryo, Nonmammalian / Q000187:drug effects; D047108:Embryonic Development / Q000187:drug effects*; D049851:Gastropoda / Q000187:drug effects* / Q000254:growth & development / Q000469:parasitology; D006790:Host-Parasite Interactions; D007928:Lethal Dose 50; D014200:Trematoda / Q000502:physiology
chemical_list: D002104:Cadmium