H2O2/UV-C and Photo-Fenton treatment of a nonylphenol polyethoxylate surfactant was investigated in synthetic freshwater. H2O2/UV-C treatment outperformed Photo-Fenton treatment in terms of mother pollutant abatement kinetics as well as overall organic carbon removal efficiencies. Short polyethoxy-chain nonylphenol polyethoxylates, polyethylene glycols, formic acid, acetic acid and formaldehyde were identified as the common degradation products of the nonionic surfactant. Monocarboxylated polyethylene glycols and oxalic acid were detected during H2O2/UV-C oxidation, whereas a degradation product resulting from the hydroxyl radical attack of the tertiary alkyl chain and the aromatic ring was detected during Photo-Fenton treatment. Based on the liquid chromatography-mass spectrometry results, it was suggested that the polyethoxy chain of the surfactant was more susceptible to degradation with the H2O2/UV-C treatment process, while the alkyl chain and aromatic ring were more prone to Photo-Fenton oxidation. Acute toxicity analysis employing the photobacteria Vibrio fischeri indicated that the inhibitory effect of the surfactant increased from 10% to 30% and 19% during the early stages of H2O2/UV-C and Photo-Fenton treatment, respectively. At the end of the treatment period, the inhibitory effect of the surfactant dropped back to less than 10%. According to the umu-genotoxicity test conducted with Salmonella typhimurium TA1535/pSK1002 strain, the genotoxic effect followed an increasing trend during the course of H2O2/UV-C treatment. A positive correlation was evident between the intensity of the nonylphenol monoethoxylate product ion and the genotoxic effect observed during H2O2/UV-C treatment. The genotoxic effect of Photo-Fenton-treated degradation products appeared to be relatively low as compared with those of H2O2/UV-C treatment. (C) 2013 Elsevier B.V. All rights reserved.