Potentiation of Toxicity of Malathion by Triorthotolyl Phosphate. ∗

Abstract

Summary

Toxicity of malathion to male rats was markedly increased after treatment of animals with TOTP. At 24 hours after dermal application or intraperitoneal administration of 110 mg/kg of TOTP the LD₅₀ of malathion was reduced from normal value of 1100 mg/kg to 12.5 and 8.2 mg/kg respectively. The increased susceptibility of rats to malathion persisted for as long as 14 days after treatment with TOTP. When TOTP was given 24 hours after malathion no potentiation was observed. TOTP inhibited enzymatic detoxification of malathion thus providing an explanation for its potentiating action. These findings indicate that the problem of potentiation of toxicity of organic phosphate insecticides extends beyond those agents commonly used for insecticidal purposes.