Photodegradation of the Pyrethroid Insecticide Cypermethrin in Water and on Soil Surface

Abstract

Photodegradation of (1R, cis, ceRS)-and (1R, traps, ceRS)-isomers of Cypermethrin [(RS)-a-cyano-3-phenoxybenzyl(1RS)-cis, traps-3-(2, 2-dichlorovinyl)-2, 2-dimethylcyclopropanecarboxylate] in water and on soil surface was studied, using 14C preparations labeled separately at the cyclopropyl C-1, cyano or benzyl ring. The cis-isomer was photodecomposed 1. 4-1. 7 times faster in sunlight than the traps-isomer in water. The half-life of the cis-isomer was 2. 3-2. 6 days in distilled water and 1 ppm humic acid aqueous solution, and 0. 6-0. 7 day in natural river and sea water, and <0. 5 day in 2% aqueous acetone. A triplet photosensitizer acetone together with the naturally occurring substances in river and sea water enhanced the photodegradation of both isomers. On three kinds of soil surface, both isomers were rapidly photodegraded with the initial half-life of 0. 6-1. 9 days. The photoreactions involved were: 1R/1S and cis/trans isomerization of the cyclopropane ring, cleavage of the ester or diphenyl ether linkage, oxidation of the CHO group to the COOH group, hydration of the CN group to the CONH2 group, hydrolysis of the CONH2 group to the COOH group, oxidative cleavage of the halogenated side chain, dehalogenation, intramolecular cyclization to form y-or 8-lactone, and photomineralization of the cyclopropyl C-1, cyano and benzyl ring to 14CO2.

Photodegradation of Selected Herbicides in Various Natural Waters and Soils under Environmental Conditions

“…Mean indirect photolysis depths were reported to be greater than 0.7 mm for outdoor experiments. Several studies (Takahashi et al, 1985; Lartiges and Carrigues, 1995; Zepp et al, 1985; Zafiriou et al, 1984; Jensen‐Korte et al, 1987; Vaughan and Blough, 1998) have indicated that humic acids are capable of acting as sensitizers for the production of reactive intermediates such as singlet oxygen ( 1 O 2 ), hydroxyl radicals (·OH), superoxide anion (·O 2 − ), hydrogen peroxide (H 2 O 2 ), and peroxy radicals (ROO·). For example, sediment‐sorbed DDE photolyzes faster than when it is dissolved, and the product mixture differs in a way that suggests an environment rich in H‐donors, probably organic matter (Zafiriou et al, 1984; Miller and Zepp, 1979).…”

“…There is relatively little information in the open literature on the phototransformation of pesticides under natural environmental conditions (Takahashi et al, 1985; Kochany and Maguire, 1994; Lartiges and Carrigues, 1995; Hebert and Miller, 1990). The present work tries to approximate appropriate environmental conditions using natural sunlight and natural water and soil samples.…”

Behavior of cyphenothrin in aquatic environment

“…38) The photoproduct distribution is also similar between cis and trans isomers through the photolysis of permethrin 37) and cypermethrin 38) in water and that of resmethrin on a silica gel surface. 34) Therefore, the experimental results for trans-1 can be reasonably translated to 1.…”

Isomerization of chiral pesticides in the environment

“…Although the clear demonstration of photo-induced racemization or enantiomerization by using individual stereoisomer(s) is limited, not only (1R)/(1S) but also trans/cis isomerization was found to proceed in aqueous photolysis of (1R)-trans-and (1R)-cis-isomers of cypermethrin (14). 51) More rapid isomerization of cis-isomers over trans-isomers was observed in water, but the isomerization on soil surfaces was of minor importance. In addition to the (αS) (αR) epimerization at the α-cyanobenzyl carbon, the photo-induced isomerization of deltamethrin (15) proceeded in the cyclopropyl moiety, producing the (1S)-and trans-isomers with the predominance of the (1S)-cis-(αS)-isomer.…”