Direct UV photolysis of aerated aqueous solutions of propoxur leads to an almost complete disappearance of the starting material and the formation of the photo-Fries rearrangement products. The degree of mineralization estimated by the difference between the initial and the combined final moles is, however, small. Laser flash photolysis techniques established that the key intermediate in the direct aqueous photolysis is 2-isopropoxyphenoxyl radical. Photocatalyzed mineralizations using 2,4,6-triphenylpyrylium ion encapsulated inside the supercages of Zeolite Y under irradiation conditions in which propoxur is not directly altered, produces a degree of mineralization comparable to that achieved using TiO2. Formation of minor amounts of 2-isopropoxyphenol, 1,2-dihydroxybenzene and isopropoxy-dihydroxybenzene was observed in photocatalyzed degradations. Laser flash photolysis established that a mechanism involving an initial electron transfer between excited TP+ and propoxur is possible. (C) 2000 Elsevier Science B.V. All rights reserved.