Phototransformation of phosphite induced by zinc oxide nanoparticles (ZnO NPs) in aquatic environments

•ZnO NPs could mediate the phototransformation of phosphite to phosphate at different pH.•ROS generated by the irradiated ZnO NPs were responsible for phosphite phototransformation.•NO3− accelerated the phosphite phototransformation in eutrophic water.•Produced phosphate probably suppresses the toxicity of Zn2+.•The mechanism of phototransformation of phosphite induced by ZnO NPs was firstly proposed. Phosphite, an essential component in the biogeochemical phosphorus cycle, may make significant contributions to the bioavailable phosphorus pool as well as water eutrophication. However, to date, the potential impacts of coexisting photochemically active substances on the environmental fate and transformation of phosphite in aquatic environments have been sparsely elucidated. In the present study, the effect of zinc oxide nanoparticles (ZnO NPs), a widely distributed photocatalyst in aquatic environments, on phosphite phototransformation under simulated solar irradiation was systematically investigated. The physicochemical characteristics of the pristine and reacted ZnO NPs were thoroughly characterized. The results showed that the presence of ZnO NPs induced the indirect phototransformation of phosphite to phosphate, and the reaction rate increased with increasing ZnO NPs concentration. Through experiments with quenching and trapping free radicals, it was proved that photogenerated reactive oxygen species (ROS), such as hydroxyl radical (•OH), superoxide anion (O2•−), and singlet oxygen (1O2), made substantial contributions to phosphite phototransformation. In addition, the influencing factors such as initial phosphite concentration, pH, water matrixes (Cl−, F−, Br−, SO42−, NO3−, NO2−, HCO3−, humic acid (HA) and citric acid (CA)) were investigated. The component of generated precipitates after the phosphite phototransformation induced by ZnO NPs was still dominated by ZnO NPs, while the presence of amorphous Zn3(PO4)2 was identified. This work explored ZnO NPs-mediated phosphite phototransformation processes, indicating that nanophotocatalysts released into aquatic environments such as ZnO NPs may function as photosensitizers to play a beneficial role in the transformation of phosphite to phosphate, thereby potentially mitigating the toxicity of phosphite to aquatic organisms while exacerbating eutrophication. The findings of this study provide a novel insight into the comprehensive assessment of the environmental fate, potential ecological risk, and biogeoc