title: Photochemistry and photoinduced toxicity of acifluorfen, a diphenyl-ether herbicide.
abstract: Photochemistry studies can be helpful in assessing the environmental fate of chemicals. Photochemical reactions lead to the formation of by-products that can exhibit different toxicological properties from the original compound. For this reason the photochemical behavior of the herbicide acifluorfen (5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid) in the presence of different solvents was studied. Photochemical reactions were carried out using a high-pressure mercury arc and a solar simulator. Kinetic parameters and quantum yields were determined. The identification of photoproducts was performed by mass spectrometry and [1H] nuclear magnetic resonance (NMR). Nitrofluorfen, hydroxy-nitrofluorfen, 2-chloro-4-(trifluoromethyl)phenol, 5-trifluoromethyl-5'-nitrodibenzofuran, and other derivatives were identified. The photochemical reactions were also carried out in the presence of either a singlet or a triplet quencher, and in the presence of either a radical initiator or a radical inhibitor. Substances used as inhibitors of the excited levels T1 and S1 showed that photodegradation of acifluorfen begins from a singlet state S1 through a pi,pi* transition. The role of free radicals in the photodegradation of acifluorfen was determined and a radical mechanism was proposed. Toxicity tests against Daphnia magna Strauss showed that acifluorfen was not toxic at a concentration of 0.1 mM; however, photoproducts formed after 36 h of UV exposure of the herbicide induced a remarkable toxicity to the test organism.
authors.affiliation: Dipartimento di Produzione Vegetale, Università della Basilicata, Potenza, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Scrano
authors.forename: Sabino A
authors.initials: SA
authors.lastname: Bufo
authors.forename: Maurizio
authors.initials: M
authors.lastname: D'Auria
authors.forename: Pierre
authors.initials: P
authors.lastname: Meallier
authors.forename: Akbar
authors.initials: A
authors.lastname: Behechti
authors.forename: Karl Werner
authors.initials: KW
authors.lastname: Shramm
mesh_terms: D000818:Animals; D003621:Daphnia; D006540:Herbicides / Q000737:chemistry* / Q000633:toxicity*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D009579:Nitrobenzoates / Q000737:chemistry* / Q000633:toxicity*; D010777:Photochemistry; D018675:Toxicity Tests; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D006540:Herbicides; D009579:Nitrobenzoates; D014874:Water Pollutants, Chemical; C018425:acifluorfen