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Photoinduced Degradation of the Herbicide Clomazone Model Reactions for Natural and Technical Systems
Author(s) -
David Gara Pedro M.,
Bosio Gabriela N.,
Arce Valeria B.,
Poulsen Lars,
Ogilby Peter R.,
Giudici Reinaldo,
Gonzalez Mónica C.,
Mártire Daniel O.
Publication year - 2009
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.2008.00467.x
Subject(s) - clomazone , degradation (telecommunications) , natural (archaeology) , chemistry , biochemical engineering , biological system , environmental science , photochemistry , computer science , engineering , agronomy , biology , telecommunications , weed control , paleontology
The photodegradation of the herbicide clomazone in the presence of S 2 O 8 2− or of humic substances of different origin was investigated. A value of (9.4 ± 0.4) × 10 8 m −1 s −1 was measured for the bimolecular rate constant for the reaction of sulfate radicals with clomazone in flash‐photolysis experiments. Steady state photolysis of peroxydisulfate, leading to the formation of the sulfate radicals, in the presence of clomazone was shown to be an efficient photodegradation method of the herbicide. This is a relevant result regarding the in situ chemical oxidation procedures involving peroxydisulfate as the oxidant. The main reaction products are 2‐chlorobenzylalcohol and 2‐chlorobenzaldehyde. The degradation kinetics of clomazone was also studied under steady state conditions induced by photolysis of Aldrich humic acid or a vermicompost extract (VCE). The results indicate that singlet oxygen is the main species responsible for clomazone degradation. The quantum yield of O 2 (a 1 Δ g ) generation (λ = 400 nm) for the VCE in D 2 O, Φ Δ = (1.3 ± 0.1) × 10 −3 , was determined by measuring the O 2 (a 1 Δ g ) phosphorescence at 1270 nm. The value of the overall quenching constant of O 2 (a 1 Δ g ) by clomazone was found to be (5.7 ± 0.3) × 10 7 m −1 s −1 in D 2 O. The bimolecular rate constant for the reaction of clomazone with singlet oxygen was k r = (5.4 ± 0.1) × 10 7 m −1 s −1 , which means that the quenching process is mainly reactive.