Comparative toxicity of three typical TiO2 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. TiO2 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. (C) 2017 Elsevier Ltd. All rights reserved.