Effects of fenitrothion and carbaryl on Xenopus laevis development.

When Xenopus laevis embryos were treated with fenitrothion, a substantial proportion failed to survive to hatching only when the concentration approached saturation. However, after exposure to 10 ppm of fenitrothion, most were abnormal and did not survive past feeding stage. Different embryonic stages were not equally sensitive to fenitrothion and the greatest sensitivity was observed at gastrulation. The most common visible abnormalities were altered body shape, including microcephaly, and edema. Internally, abnormalities of the heart, spinal cord and notochord were common. Though carbaryl was toxic at somewhat lower concentrations, carbaryl-induced abnormalities were less severe. In particular, cardiac malformations were less extreme. Recently hatched tadpoles were less sensitive to carbaryl than were the embryos, but were more sensitive to fenitrothion. However, with both compounds, the effects were seen only at concentrations higher than would normally be expected in the environment after spraying.