Further studies of the degradation of the pyrethroid insecticide cypermethrin in soils

Studies of the degradation of the pyrethroid insecticide cypermethrin (NRDC 149) and its cis‐ and trans‐isomers (NRDC 160 and NRDC 159, respectively), have been extended. In soils stored in the laboratory for up to 52 weeks, cypermethrin continued to be degraded by hydrolysis and oxidation. A previously unidentified product has now been identified as the dicarboxylic acid 3‐(2, 2‐dichlorovinyl)‐1‐methylcyclopropane‐1, 2‐dicarboxylic acid. Comparative experiments carried out under indoor and outdoor conditions showed that essentially the same products were formed under these different conditions. However, α‐carboxy‐3‐phenoxybenzyl 3‐(2, 2‐dichlorovinyl)‐2, 2‐dimethyl‐cyclopropanecarboxylate was one minor product detected only under outdoor conditions. Evidence is presented for the further degradation of bound residues arising in soil from cypermethrin treatments. There was limited uptake of the radiolabel into wheat grown in soil containing radiolabelled bound residues.