Background Pesticides are listed among the main environmental stressors directly correlated with severe impacts on ecosystems and human health. Here, the potential of TiO2-mediated photocatalytic oxidation of the insecticide thiacloprid, in aqueous media, is investigated thoroughly. Results Degradation was investigated under various operational conditions, including the initial concentration of the pesticide, the type and amount of catalyst, pH and the presence of electron acceptors. The prevalence of TiO2 P25 in comparison to the other titania employed, is obvious both in the case of decomposition and carbon mineralization. Twenty-seven transformation products generated during the photocatalytic decomposition of thiacloprid under UV-A irradiation were elucidated by high-resolution liquid chromatography mass spectrometry analysis, enabling the proposition of potential fragmentation pathways. The initial ecotoxicity of the insecticide determined by measurements of the bioluminescence of marine bacteria Vibrio fischeri was eliminated within 240 min of UV-A irradiation in the presence of TiO2 P25. A phytotoxicity evaluation based on three eukaryotic plant species led to similar conclusions, resulting in the complete removal of phytotoxicity within 240 min of UV-A illumination in the presence of TiO2 P25. Conclusions These findings suggest that TiO2-mediated photocatalytic oxidation has the potential to efficiently detoxify water containing neonicotinoid pesticides. (c) 2019 Society of Chemical Industry