Photochemical transformation of acifluorfen under laboratory and natural conditions

Acifluorfen was irradiated in pure water at various excitation wavelengths and pH values. Numerous photoproducts were obtained which were identified b y [H-1]NMR and/or HPLC-MS/MS. The main reaction pathways were photo-decarbo xylation, photo-cleavage of the ether bonding with formation of phenolic co mpounds, photo-dechlorination and photo-Claisen type rearrangement. Decarbo xylation was observed in acidic and neutral media whereas cleavage of the e ther bonding dominated in basic media. The photo-Claisen type rearrangement only occurred on excitation at short wavelengths. The quantum yield of pho tolysis was significantly lower at 313 nm (6.1 x 10(-5)) than at 254 nm (2. 0 x 10(-3)). The photoreactivity of acifluorfen was then studied in conditi ons approaching environmental conditions. Acifluorfen was dissolved in pure water, in water containing humic substances or in a natural water, and exp osed to solar Light in June at Clermont-Ferrand (latitude 46 degreesN). In pure water, the half-life was estimated at 10 days and photo-decarboxylatio n accounted for 30% of the conversion. The presence of humic substances (10 mg litre(-1)) did not affect the rate of photo-transformation, However, th e half-life of acifluorfen dissolved in the natural water was only 6.8 days . (C) 2001 Society of Chemical Industry.