Embryotoxicity and teratogenicity of cadmium chloride in Xenopus laevis, assayed by the FETAX procedure

The embryotoxicity and teratogenicity of cadmium chloride (CdCl2) were tested by the FETAX (Frog Embryo Teratogenesis Assay: Xenopus) procedure in the South African frog, Xenopus laevis. In five assays, groups of Xenopus embryos were grown in media that contained CdCl2 at concentrations ranging from 0.75 to 56 mumol per L; control groups were incubated in the same medium without added CdCl2. The exposures to CdCl2 were begun at the blastula stage (five hours post-fertilization) and were terminated 96 hours later (101 hours post-fertilization). The embryos were counted, fixed in formalin, and examined by microscopy to score malformations and measure head-to-tail lengths. In control groups, greater than or equal to 95 percent of the embryos survived at 101 hours post-fertilization, and the incidence of malformations was less than or equal to 7 percent. In Cd(2+)-exposed groups, there was concentration-dependent mortality, and the embryos showed a concentration-related pattern of malformations, including gut malrotation, ocular anomalies, bent notochord, misshapen dorsal fin, facial dysplasia, cardiac deformities, and dermal blisters. Other abnormalities, not categorized as malformations, included stunted growth and hypopigmentation. The minimum concentration of CdCl2 that inhibited growth (MCIG) was 18 mumol per L. The median embryolethal concentration (LC50) of CdCl2 was 32 (SE +/- 4) mumol per L; the median teratogenic concentration (EC50) was 3.7 (SE +/- 1) mumol per L; the teratogenic index (TI = LC50/EC50) was 8.6. This study demonstrates that CdCl2 is teratogenic for Xenopus laevis and provides a standardized experimental model for studies of the molecular mechanisms of cadmium teratogenesis.