Several different pesticides (alachlor, atrazine, chlorfenvinphos, diuron, isoproturon and pentachlorophenol) considered PS (priority substances) by the European Commission and dissolved in water at 50 mg/L (or at maximum water solubility) have been degraded at pilot-plant scale using photo-Fenton and TiO2photocatalysis driven by solar energy. Two different iron concentrations (2 and 55 mg/L) and TiO2at 200 mg/L have been tested and discussed, using mainly TOC mineralisation for comparison of treatment effectiveness. Vibrio fischeri (Microtox®) toxicity assays were also employed for evaluating the photocatalytic treatments, and comparison between these results and parent compound disappearance, TOC evolution and anion (or ammonia) release were discussed. Almost complete mineralisation and total detoxification were always attained. It has been demonstrated that evolution of chloride could be a key-parameter for predicting toxicity of chlorinated compounds. © 2005 Elsevier B.V. All rights reserved.