Toxicity of Guthion super( registered ) and Guthion super( registered ) 2S to Xenopus laevis Embryos

Embryos of the African clawed frog were exposed to various concentrations of technical grade Guthion and a commercial formulation, Guthion 2S in either 10- or 100-ml exposure volumes of the pesticide. Greater mortality, deformations, smaller sizes, and lower LC sub(50)s were noted in the lower volume exposure groups. Up to 89% of the embryos exposed to 3 mg Guthion/l in the 10-ml volume were deformed, compared to less than 2% in the 100-ml volume exposure group. The commercial formulation was more toxic than the technical grade, having an LC sub(50) of 1.6 mg/l in the 100-ml volume. Concentrations of 0.48 to 7.96 mg/l were the no-observed-adverse-effect-levels for the compounds, and these concentrations were well above 0.01 mu g/l-the upper limit of current acceptable water concentrations.