Deltamethrin degradation and effects on soil microbial activity

Deltamethrin [(S)-cyano-3-phenoxybenzyl-cis-(1R,3R)-2,2-dimethyl) cyclopropane carboxylate),1] labelled at gem-dimethyl groups of the cyclopropane ring was applied on two Egyptian soils at a level of 10mg/kg soil for a laboratory incubation experiment under aerobic and anaerobic conditions. A steady decrease of soil extractable(14)C-residues, accompanied by a corresponding increase of non- extractable bound C-14-residues was observed over a 90-day incubation period. The percentage of evolved (CO2)-C-14 increased with time under aerobic and anaerobic conditions in both soils. The effect of deltamethrin on soil microorganisms as well as the counter effect of microorganisms on the insecticide was also investigated. As the incubation period increased, the inhibitory effect of the insecticide on the microorganisms decreased and the evolution of carbon dioxide depended on the applied dose. The nature of soil methanol soluble residues was determined by chromatographic analysis which revealed the presence of the parent insecticide as the main product in addition to four metabolites: 3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane carboxylic acid (II); 3-phenoxybenzaldehyde (III); 3-phenoxybenzoic acid (IV); 3-phenoxybenzyl alcohol (V).