Kinetics of photodegradation of the fungicide fenarimol in natural waters and in various salt solutions: salinity effects and mechanistic considerations

Abstract

AbstractÐThe rate of photodegradation of the fungicide fenarimol (a-(2-chlorophenyl)-a-(4-chlorophenyl)-5-pyrimidine-methanol) by solar radiation has been studied in natural waters with dierent salinities. Photodegradation rates and quantum yields are found to decrease with increasing salinity.To explain this behaviour, experiments were performed with dierent salt solutions (NaCl, NaBr, BaCl 2 and ZnCl 2 ) using both solar irradiation and a photoreactor (l excit 313 nm). As with natural waters, marked eects of added salt were observed on the photolysis rate, which decreased signi®cantly from 0.67 h À1 in the absence of salt to 0.11 h À1 in the presence of BaCl 2 . In photoreactor studies, the observed order of quenching was BaCl 2 > ZnCl 2 and NaBr > NaCl. In contrast, neither the triplet state quencher sorbic acid nor oxygen had any eect on the photolysis, supporting the idea that photodegradation goes by the lowest excited singlet state of fenarimol.To understand the origin of the eect of added salts,¯uorescence quenching studies have been performed with various halide and nonhalide salts and the respective quenching constants determined. With NaCl and NaBr, the ratio of¯uorescence quenching constants is identical to the ratio of reciprocal quantum yields for photodegradation of fenarimol, indicating a common mechanism. The correlation of¯uorescence quenching rates with halide ion oxidation potentials strongly suggests that this involves an electron transfer mechanism. It is suggested that the eect may be used to stabilise the fungicide towards photodegradation. #

Influence of dissolved organic matter on the photodegradation and volatilization kinetics of chlorpyrifos in coastal waters

“…The half-life times (t 1/2 ) were 5 min in salt water and 6 min in natural saline water and unbuffered deionized water. In contrast with the behavior on photodegradation of the pesticide fenarimol, no stabilizing effect was observed on chlorpyrifos photolysis in saline waters [33].…”

Determination of the pesticides considered as endocrine‐disrupting compounds (EDCs) by solid‐phase extraction followed by gas chromatography with electron capture and mass spectrometric detection

“…This probably relates to the fact that they are insufficiently persistent. The low observed concentration of fenarimol, below the quantitation limit, may be due to photodegradation which was reported to be a major route of its dissipation in water [50] and occurs quickly in summer. Vinclozolin, which was detected in water samples from lake Pamvotis and the marine area of Igoumenitsa, was not detected in sediment samples and this indicates no accumulation in sediments.…”

Pesticides and Herbicides

“…2,4,6-Triphenylpyrylium ion encapsulated inside the supercages of Y zeolites was found to photocatalytically degrade methyl parathion in aqueous solution (Sanjuan et al, 2000). The rate of photodegradation of the fungicide fenarimol by solar radiation was studied in natural waters with different salinities (Mateus et al, 2000). Photodegradation rates and quantum yields were found to decrease with increasing salinity.…”