Susceptibility of early life stages of Xenopus laevis to cadmium

The susceptibility of Xenopus laevis to cadmium during different stages of development was evaluated by exposing embryos to cadmium concentrations ranging from 0.1 to 10 mg Cd2+/L for 24, 48, and 72 h and assessing lethality and malformations. Susceptibility increased from the two blastomeres stage (stage 2) to stage 40, in which the 24-h LC100 was 1.13 mg Cd2+/L, and resistence increased from this stage onward. Malformations occurred at all developmental stages evaluated, the most common being reduced size, incurvated axis, underdeveloped or abnormally developed An, microcephaly, and microphtalmy. Scanning electron microscopy revealed changes in the ectodermal surface ranging from slightly vaulted cells to a severe reduction in the number of ciliated cells as the concentration of cadmium increased. The intraspecific variation evaluated in embryos (from four sets of parents) at seven developmental stages, expressed as the coefficient of variation of the LC100, ranged from 10 to 112% and reflects the capacity of Xenopus laevis to adapt to changing environmental conditions at different embryonic stages.