The effects of different levels of dietary protein on the toxicity and metabolism of malathion and parathion and their oxygen analogues

Abstract

The toxicities of two widely used organophosphate insecticides, malathion and parathion, and their oxygen analogues were investigated in rats fed different levels of dietary protein. Male weanling rats were pair-fed either 5 or 20% casein diets for 10 days and control animals received a 20% casein diet ad libitum.

Toxicity studies showed that rats which received 5% casein diets were more susceptible to malathion and malaoxon (LD₅₀ = 151.1 mg/kg and 7.75 mg/kg) when compared with rats pair-fed 20% casein (LD₅₀ = 273.6 mg/kg and 14.33 mg/kg) or with rats fed 20% casein ad libitum (LD₅₀ = 418.6 mg/kg and 15.23 mg/kg). Rats which received 5% casein diets were similarly more susceptible to parathion and paraoxon (LD₅₀ = 1.24 mg/kg and 0.385 mg/kg) when compared with rats pair-fed 20% casein (LD₅₀ = 1.65 mg/kg and 0.537 mg/kg) or with rats fed 20% casein ad libitum (LD₅₀ = 2.04 mg/kg and 0.666 mg/kg). Toxicities of both the inactive parent co~pounds and their active analogues were affected by dietary protein intake.

Metabolism studies· based on excretion of p-nitrophenol, a metabolite of parathion and paraoxon, were largely inconclusive.

It is concluded from these studies that dietary protein intake is of major importance in determining the toxicities of malathion and parathion and their oxygen analogues and that the major effect of dietary protein is probably on the degradation and not the activation of the parent compounds.

It is further concluded that populations on low protein intake may be in greater danger than their well-fed counterparts when exposed to acute levels of these organophosphates and possibly other similar compounds.