Negligible effects of TiO2 nanoparticles at environmentally relevant concentrations on the translocation and accumulation of perfluorooctanoic acid and perfluorooctanesulfonate in hydroponically grown pumpkin seedlings (Cucurbita maxima × C. moschata)

Abstract

Titanium dioxide nanoparticles (TiO2-NPs) are widely distributed in the environment. It has been demonstrated that TiO2-NPs could modify the environmental fate and bioavailability of organic pollutants, which affects ecological risks of TiO2-NPs and organic pollutants. In this study, the uptake, translocation and accumulation of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) in pumpkin plants was investigated in the presence of TiO2-NPs. We reported for the first time the negligible effects of TiO2-NPs at environmentally relevant concentrations (0.05–5 mg/L) on the uptake and accumulation of PFOA and PFOS in hydroponically grown pumpkin seedlings regardless of root, stem and leaf. This phenomenon was independent of the initial concentrations of PFOA/PFOS and TiO2-NPs in the exposure solution. Also, seedling mass and contents of chlorophyll and anthocyanin were not affected by the co-exposure. Adsorption tests demonstrated the negligible adsorption of PFOA/PFOS on TiO2-NPs in the exposure solution. Moreover, uptake of PFOA/PFOS was insensitive to aquaporin inhibitor AgNO3 but significantly inhibited by niflumic acid (anion channel blocker) and 2,4-dinitrophenol (metabolic inhibitor) whereas Ti concentration in root was not affected by niflumic acid and 2,4-dinitrophenol but significantly decreased by AgNO3, indicating that transport of PFOA/PFOS and TiO2-NPs were via different routes into the pumpkin seedling. It was proposed that different pathways by which TiO2-NPs and PFOA/PFOS transported into the pumpkin seedling and negligible adsorption of PFOA/PFOS on TiO2-NPs contributed to the negligible effects of TiO2-NPs on the uptake, translocation and accumulation of PFOA/PFOS in pumpkin seedlings. In total, this work would improve our understanding of the ecological risks of TiO2-NPs in the environment.