Effect of Moisture Content and UV Irradiation on Degradation of Fenpropathrin on Soil Surfaces

Abstract

The effect of a moisture content and UV irradiation on the degradation of the pyrethroid insecticide fenpropathrin (I) [(RS)-a-cyano-3-phenoxybenzy12,2,3,3-tetramethylcyclopropanecarboxylate] on soil surfaces was examined using a xenon lamp (A>290 nm). I was rapidly degraded at a lower moisture content of soil via hydration of the a-cyano group and UV irradiation was found to slightly facilitate the degradation.As with an increase of moisture, the degradation pathways previously reported in aerobic and anaerobic soil metabolism became predominant on the soil surfaces. The marked change of a surface acidity of clay with a moisture content was likely to account for the moisture dependency of the degradation.

Theoretical and organic chemical approaches to environmental behavior and metabolism of pesticides

“…When fenpropathrin was incubated in darkness by varying the water content of three Japanese upland soils from the oven-or air-dried condition to 10-100% of MWHC, the formation rate of the α-amide derivative increased markedly in the dried soils by a factor of 10-100 over the moistened ones, with no correlation of the soil organic matter content. 44) Its final yield was 67-84% in the air-died clay (kaolinite) prepared from the Ushiku soil, comparable to that in the air-dried soil. It is known that the surface acidity of kaolinite is a function of water content, and it corresponds to that of concentrated H 2 SO 4 under the oven-dried condition.…”

Clay-Catalyzed Nitration of a Carbamate Fungicide Diethofencarb

“…The catalytic behavior of clays is well-known and has been utilized for many types of organic syntheses (7,14). In relation to soil metabolism of pesticides, the involvement of catalytic reactions on clay surface has been reported for hydrolysis of organophosphorus pesticides (15,16) and carbamates (17,18) and hydration of cyano group of fenpropathrin (19), where the Bro ¨nsted acidity on the clay surface originating from the proton dissociation of bound water around the exchangeable metal cations had a great role in the reactions. The lesser water content of clays is known to make a water molecule coordinated to a counter metal cation more reactive for nucleophilic attack (20) and to extremely increase the surface acidity nearly up to 90% H 2 SO 4 (12) under the dry conditions.…”