The photocatalytic degradation of fenamiphos in leaching water has been studied using zinc oxide (ZnO), different mixed-phase titanium dioxide (TiO2), tungsten(VI) oxide (WO3), and tin(IV) oxide (SnO2) at pilot plant scale under natural sunlight. Photocatalytic experiments showed that the addition of semiconductors in tandem with the oxidant (Na2S2O8) strongly enhances the degradation rate of fenamiphos in comparisons carried out with photolytic tests. The primary degradation of fenamiphos followed a pseudo-first order kinetics. The time required for 50% degradation was in the range 1-3 min for ZnO and TiO2. The main photocatalytic intermediates (fenamiphos-sulfoxide and fenamiphos sulfone) detected during the degradation of fenamiphos were identified. Comparison of catalysts showed that ZnO is the most efficient for catalyzing the removal of fenamiphos and their metabolites. Thus, complete disappearance of all the compounds studied achieved after 240 min of illumination in the ZnO/Na2S2O8 system. (C) 2011 Elsevier B.V. All rights reserved.