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

Comparative toxicity of three typical TiO NPs (Anatase, Rutile, and Degussa P25, 50mg/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 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 PO (An+UV and P25+UV) and CO or COC (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.