Degradation of the pyrethroid insecticide WL 41706, (±)‐α‐cyano‐3‐phenoxybenzyl 2,2,3,3‐tetramethylcyclopropanecarboxylate, in soils

Abstract

AbstractThe degradation of the insecticide WL 41706, (±)‐α‐cyano‐3‐phenoxybenzyl 2,2,3,3‐tetramethylcyclopropanecarboxylate, (I), in two soils from Spain and one from the UK has been studied in the laboratory. Samples of (I) labelled separately with 14C in the benzyl ring (uniform labelling) and at C(1) of the cyclopropyl ring were used. The insecticide underwent degradation by hydrolysis at the cyano group to form the amide and carboxylic acid analogues. However, the major degradative route was hydrolysis at the ester linkage leading initially to the formation of 3‐phenoxy‐benzoic acid and 2,2,3,3‐tetramethylcyclopropanecarboxylic acid. When a sandy clay soil was treated with [benzyl−14C]‐WL 41706 under balance conditions, 14CO2 was evolved at a steady rate and 16 % of the applied radiolabel was detected as 14CO2 over a 26 week period. The rate of degradation of I was most rapid on a moist sandy clay (loss of 50 % initial quantity in 4 weeks) but it was considerably slower on dry sandy clay and moist clay soils (> 16 weeks). Under flooded, anaerobic conditions the rate of hydrolysis of the insecticide was slower than under aerobic conditions and the 3‐phenoxybenzoic acid and 2,2,3,3‐tetramethylcyclopropanecarboxylic acid were found to accumulate over the 24 weeks of the experiment.