Breakdown of 14 C‐chlorfenvinphos insecticide on crops

Abstract The breakdown of chlorfenvinphos has been studied by application of 14 C‐chlorfenvinphos, in the laboratory and in a glasshouse, to the foliage of potatoes, cabbage, and maize at initial dosage levels within the range 1‐30 ppm. On cabbage there was evidence for a possible conversion of some of the trans(β) isomer of chlorfenvinphos to the cis(α) isomer. The initial half‐life of chlorfenvinphos ( cis ‐ and trans ‐isomers together) was about 2‐3 days, and after this initial period the rate of loss decreased. Some of the chlorfenvinphos was lost, presumably by volatilisation, and most of the remainder was converted gradually to breakdown products. A major breakdown product was a sugar conjugate of 1‐(2′,4′‐dichlorophenyl)ethan‐1‐ol, and traces of desethyl‐chlorfenvinphos were also formed. There was no evidence of translocation of 14 C‐activity from treated to untreated leaves. At harvest 80‐112 days after application of chlorfenvinphos to foliage, no residues could be detected in the tubers of potatoes or in maize cobs, when the limit of detectability was 0.005 ppm. Residues (0.74 ppm‐2.1 ppm, as equivalent ppm of chlorfenvinphos) were present on the foliage of potatoes and maize and were mainly of the conjugate of the ethan‐1‐ol. This ethan‐1‐ol has a low mammalian toxicity. Cabbages at harvest 77 days after application contained 0.37 ppm of residues (expressed as chlorfenvinphos) which were mainly of the conjugated ethan‐1‐ol.