The photocatalytic degradation of triazophos in aqueous TiO2 suspension has been studied in a photoreactor operating with simulated solar radiation. The decrease in triazophos concentration followed first-order kinetics with a half-life of 4.76 +/- 0.42 h at a TiO2 suspension concentration of 10 mg/L. Seventeen degradation products were identified using HPLC-UV, HPLC/MS/MS, GC/MS/MS and IC, and by comparing retention times and spectra with commercially available authentic standards. On the basis of the observed transformation products, two routes were proposed, one based on the initial oxidative cleavage of P = S bond to P = 0 bond, and the other on initial cleavage of the ester P-O bonds. Photocatalysis holds promise for the solar treatment of pesticide-contaminated waters. (C) 2006 Elsevier B.V. All rights reserved.