RESUMO
The effects of continuous treatment with cadmium on Bufo arenarum embryos from the 2-cell stage onwards, were evaluated by light and scanning electron microscopy. Damages were concentration-dependent (between 0.03 and 4.00 mg Cd++/L in 10% Holtfreter's solution) and ranged between teratogenic effects and lethality. In the 0.50-4.00 mg Cd++/L range high mortality, delayed development and significant alterations in the gastrulation and neurulation processes were observed. In embryos maintained at concentrations between 0.03 and 0.25 mg Cd++/L, lethality was considerably lower and development proceeded to more advanced stages. In this group of embryos the toxicity signs were: retarded growth rate, reduced body size, behavioral disorders and a variety of malformations such as microcephaly, underdevelopment of gills and abnormal fins. The ectodermal tissue exhibited predominance of ciliated cells and/or atypical distribution of them. These findings were compared with the effect of cadmium and other heavy metals on embryos, larvae and adults of several amphibian, fish and mammalian species. The findings were interpreted on the basis of known biochemical effects of cadmium.