Toxicological Properties of the Organophosphorus Insecticide Dimethoate

Abstract

The results are presented of extensive toxicological studies on the systemic organophosphate insecticide dimethoate, and compared with published results from other laboratories. It behaves as a typical indirect anticholinesterase, by conversion in the liver to at least four short-lived active metabolites, whose hydrolysis products are rapidly excreted, mainly in the urine. The acute oral toxicity of dimethoate is low in mammals but higher in avians. Dermal absorption is notably slow and dermal toxicity correspondingly low. Cumulative dosing of rats and guinea-pigs gave no cholinesterase inhibition at 0 7 and 4 mg./kg./day respectively. Dietary feeding to growing rats caused no cholinesterase inhibition at 0-5 mg./kg./day and no other effect at 10 times this dose. The main plant metabolite is identical with one formed in the liver, and comparative feeding tests with normal dimethoate and that partly metabolized in vegetation showed that residue analysis determined total hazard. Tests on humans, some with 32P-labelled material, confirmed that metabolism and urinary excretion are very rapid, that skin absorption is very slow, and that at least 2-5 mg., and probably up to 18 mg., could be ingested daily for at least three weeks without cholinesterase inhibition or other effects. Vapour hazards proved negligible. Oral toxicity was not potentiated by any of 17 other insecticides. The earliest detectable effect of dimethoate poisoning was always erythrocyte cholinesterase inhibition. Symptoms of poisoning could be effectively treated by atropine but not by oxime therapy. No known cases of occupational poisoning have occurred during five years' commercial usage of dimethoate.

Simultaneous Geno- and Immunotoxicological Investigations for Early Detection of Organophosphate Toxicity in Rats

“…It has been described that repeated oral exposure of rats by a similar dose range of DM decreases body weight gain (Sanderson and Edson 1964); a larger (150 mg/kg) repeated DM dose induced severe hematological changes (Reena et al, 1989). Repeated low doses of MPT (0.036}1.479 mg/kg) had no evaluable e!ect on the body weight gain and (except for the relative spleen weight) on the organ weights of rabbits (Street and Sharma, 1975).…”

Acetylcholinesterase inhibition and altered locomotor behavior in the carabid beetle Pterostichus cupreus. A linkage between biomarkers at two levels of biological complexity

“…In its habitat, P. cupreus is exposed to direct pesticide spraying as well as residual and oral uptake. Dimethoate, a widely used organophosphorous insecticide in arable land and in orchards, was selected because of its known AChE inhibition [27,28] and effects on locomotor behavior in arthropods [22,29].…”

“…A vehicle control group of 20 males and 20 females received ethanol only. Hereafter, the animals were returned to the tracking room for further 24 h at 18°C in their individual tracking arenas allowing dimethoate to be metabolized and to exert its anticholinesterase effect [27,28].…”

Genotoxicity associated with oxidative damage in the liver and kidney of mice exposed to dimethoate subchronic intoxication

“…DM at doses of 1, 5, 10, 15, and 30 mg/kg body weight, respectively, for 30 consecutive days. These doses correspond respectively to 2%, 10%, 20%, 30%, and 60% of the LD 50 (Sanderson and Edson 1964). Group 1, receiving equivalent amount of vehicle alone, served as the control.…”