Estimation of the LD1 and extrapolation of the LD0.1 for five organothiophosphate pesticides.

The oral LD50's for five organothiophosphate pesticides have been determined in CD-1 strain male and female mice. The values in mg/kg are: parathion, 15.0 and 14.3; methyl parathion, 14.5 and 19.5; guthion, 7.15 and 6.35; imidan, 25.2 and 23.1; sumithion, 1,045 and 1,220 respectively. Toxicity was greater parathion but there was no difference in the males. The relationship between chemical structure and toxicity has been discussed. The addition of a methyl group in the meta position of the nitrophenyl group (sumithion) decreased toxicity 72 times compared to methyl parathion. The predicted LD1 and extrapolated LD0.1's have been determined for the five organothiophosphates and the conditions required for accurate results have been established. It has been shown that the slopes of the curves (males vs. females) obtained with 50, 100 and 660 animals are parallel for all compounds health implications of exposure to low levels of environmental pesticides have been discussed.