Toxic effects of three crystalline phases of TiO2 nanoparticles on extracellular polymeric substances in freshwater biofilms

Comparative toxicity of three typical TiO 2 NPs (Anatase, Rutile, and Degussa P25, 50   mg/L respectively) under UVC irradiation (An   +   UV, Ru   +   UV, and P25   +   UV) on production and chemical characteristics of EPS in freshwater biofilms were investigated. Rutile was more stable in lake water, yet P25 and anatase were endowed with better photo-oxidation capacity. TiO 2 NPs   +   UV enhanced total EPS, manifesting as LB-EPS increased by 98.16% (An   +   UV), 143.03% (Ru   +   UV), and 48.21% (P25   +   UV), while TB-EPS increased to 1.51 (An   +   UV), 1.36 (Ru   +   UV), and 1.61 (P25   +   UV) times greater than control without NPs and UVC, being mainly attributed to increase of polysaccharide and proteins. Three-dimensional fluorescence spectrum revealed tyrosine (An   +   UV and P25   +   UV) and tryptophan (P25   +   UV) protein-like substances vanished in LB-EPS. Fourier transform infrared spectroscopy indicated P O (An   +   UV and P25   +   UV) and C O or C O C (P25   +   UV) disappeared in EPS. P25   +   UV and An   +   UV caused more lactate dehydrogenase release, while Ru   +   UV induced more reactive oxygen species and malondialdehyde production, consistent with decreased in cells viability.