Dimethylphosphorothioates. Reaction with malathion and effect on malathion toxicity

Area of Science:

• Agrochemicals
• Toxicology
• Organic Chemistry

Background:

• Dimethylphosphorothioates are organophosphorus compounds.
• Malathion is a widely used organophosphate insecticide.
• Understanding interactions between pesticides and other chemicals is crucial for safety.

Purpose of the Study:

• To evaluate the toxicity and malathion interaction of five dimethylphosphorothioates.
• To investigate the in vitro reaction of these compounds with malathion.
• To identify potential mechanisms of toxicity potentiation.

Main Methods:

• In vivo toxicity testing in rats.
• In vitro carboxylesterase inhibition assays.
• Incubation of dimethylphosphorothioates with malathion at varying temperatures.
• Analysis of reaction products using thin-layer chromatography (TLC), gas chromatography (GC), and mass spectrometry (MS).

Main Results:

• Dimethylphosphorothioates showed no inherent toxicity or potentiation of malathion toxicity in rats.
• S-acid diesters (II, III, IV) reacted with malathion to form toxic trimethylphosphorothioates.
• These S-acid diesters also promoted malathion isomerization to isomalathion, particularly diester IV.
• Formation of toxic products was confirmed by TLC, GC, MS, and carboxylesterase inhibition.

Conclusions:

• The S-acid diesters (II, III, IV) can transform malathion into more toxic forms.
• This transformation involves methylation to trimethylphosphorothioates and isomerization to isomalathion.
• These reactions highlight a potential safety concern for malathion use in the presence of specific organophosphorus impurities.