Xenopus laevis embryos and tadpoles as models for testing for pollution by zinc, copper, lead and cadmium
The toxicity of bio available Zn, Cu, Pb, and Cd on the life stages of Xenopus laevis embryos and tadpoles was investigated. Cu and Cd were found to affect the hatching success of the embryos, with a strong negative relationship existing between the increase in Cu concentrations and the hatching of the embryos. Only concentrations above 0.6 ppm Cd affected the hatching of the embryos. All metals affected the survival of tadpoles over the seven days of exposure, with Zn and Cu showing a steady linear toxicity and Pb and Cd a threshold toxicity effect. Metals affected the growth of the tadpoles by reducing body length with increasing concentrations. An increase in the concentration of each metal resulted in an increase in the frequency and severity of malformations among the tadpoles. The percentage of malformed tadpoles was dependent on the metal and concentration to which they were exposed. Our data describe the relationships among hatching success, survival, growth rate and the frequency of malforma tions of tadpoles in relation to different concentrations of the four metals. Xenopus laevis embryos and tadpoles can be used successfully in bioassays to biologically quantify the severity of Zn, Cu, Pb and Cd pollution.
Key words: tadpoles, metals, survival, growth, malformations.