In this work, the photocatalytic conversion and mineralization of non-steroidal, anti-inflammatory drug diclofenac (DCF) was studied. UV-A irradiation at 3.37 x 10(-6) einstein/s photon flux was provided by a W lamp, while emphasis was given on the effect of catalyst type and loading (50-1600 mg/L), initial DCF concentration (5-20 mg/L) and the use of H2O2 (0.07-1.4 mM) as an additional oxidant on conversion and mineralization in various matrices (i.e. deionized water, groundwater and treated municipal effluent). Conversion was assessed by measuring sample absorbance at 276 nm, while mineralization by measuring total organic carbon. Of six commercially available TiO2 samples tested, Degussa P25 was found to be highly active for the DCF decomposition, whose extent was affected adversely by the complexity of the water matrix and at increased initial concentrations but it was maximized at optimal catalyst to DCF and H2O2 to DCF concentration ratios. DCF at 10 mg/L initial concentration was not toxic to freshwater species D. magna, unlike its photocatalytic degradation by-products that exhibited considerable toxicity. (C) 2010 Elsevier B.V. All rights reserved.