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

The oral LD_50,s for 5 Organophosphate pesticides have been determined in CD-1 strain male and female mice. The values in mg/kg are: Triohlorfon, 800 and 800; Naled, 409 and 330; Dichlorvos, 139 and 133, GC6506, 23.4 and 17.8; Fospirate, 225 and 263 respectively. Toxicity was greater in males with Fospirate and greater in females with Naled and GC6506. The predicted LD₁'s and the extrapolated LD_0.1's have been determined for the 5 organophosphates from an unbalanced design, loaded heavily toward the lower end of the dose-response curve. It has been shown that the slopes of the curves obtained with 50, 100 and 660 animals are parallel for all compound except Fospirate in the 660 mouse experiments. This is probably related to excessive female deaths in the upper segment of the dose-response curve. Sex dependent lethality was observed with Trichlorfon, Dichlorvos and Fospirate with the males being more susceptible than the females except in the case of Fospirate where there was a reversal at the LD₅₀ with greater susceptibility in the females. The conditions for obtaining accurate results in such experiments have been established. The implications of human exposure to low levels of the environmental pollutants have been discussed.