Persistence of methidathion in soils

Summary

The organophosphorus insecticide, methidathion, degraded rapidly in a sandy loam, silt loam, clay loam and organic soil. Fifty percent of the initial applications decomposed in less than 2 weeks and more than 90% of the insecticide disappeared within 16 weeks. When soils were treated with methidathion containing¹⁴C in the ring or methyl side chain 40 to 66% of the radioactivity was expired as¹⁴CO₂ after 16 weeks. Over half of the remaining radioactivity could not be extracted from the soils while lesser amounts were recovered as the parent compound or as water-soluble degradation products.

In fumigated soils 50% of the initial insecticide applications still remained after 16 weeks and less than 3% of the radioactivity was expired as¹⁴CO₂ which suggests that microorganisms are primarily responsible for the degradation of methidathion in soil.