Degradation of monocrotophos in soils

The degradation of a widely used organophosphorus insecticide, monocrotophos (dimethyl (E)-1-methyl-2-methylcarbamoyl vinyl phosphate) in two Indian agricultural soils at two concentration levels, 10 and 100 μg g−1 soil under aerobic conditions at 60% water-holding capacity at 28 ± 4 °C was studied in a laboratory. The degradation of monocrotophos at both concentrations in black vertisol and red alfinsol soils was rapid accounting for 96–98% of the applied quantity and followed the first-order kinetics with rate constants (k) of 0.0753 and 0.0606 day−1 and half-lives (t1/2) of 9.2 and 11.4 days, respectively. Degradation of monocrotophos in soils proceeded by hydrolysis with formation of N-methylacetoacetamide. Even three additions of monocrotophos at 10 μg g−1 soil did not result in its enhanced degradation. However, there was cumulative accumulation of N-methylacetoacetamide in soils pretreated with monocrotophos to the tune of 7–15 μg g−1 soil. Both biotic and abiotic factors were involved in degradation of monocrotophos in soils.