Photodegradation of the pyrethroid insecticide fenpropathrin in water, on soil and on plant foliage

摘要

AbstractThe photodegradation of fenpropathrin (RS)‐α‐cyano‐3‐phenoxybenzyl 2,2,3,3‐tetramethylcyclopropanecarboxylate (I), in water, on soil and on plant foliage, was investigated using14C‐preparations labelled separately at the cyano group, cyclopropyl‐C1or in the benzyl ring. On exposure to sunlight,Iwas photodecomposed with initial half‐lives of>6 weeks in distilled water, 6.0 weeks in humic acid aqueous solution, 2.7 weeks in river water, 1.6 weeks in sea water and 0.5 of a day in 2 aqueous acetone. A triplet photosensitiser, acetone, together with naturally occurring substances in river and sea water, including humic acid, enhanced the photodegradation ofI. On three kinds of soil,Iwas rapidly photodegraded with initial half‐lives of 1–5 days, whereas it was fairly photostable on a mandarin orange leaf. The photoreactions involved were: decarboxylation, hydration of the cyano group to carboxamide, cleavage of the ester or the diphenyl ether linkage, hydrolysis of the carboxamide group to carboxyl, and hydroxylation at either or both of thegemdimethyl groups. The predominant reactions in water were decarboxylation, ester bond cleavage and photo‐induced evolution of 14C carbon dioxide from the 14C cyano label; on soil, hydration or ester bond cleavage predominated. The hydration was also of importance in river and sea water. Decarboxylation did not occur on