Responses of freshwater biofilm formation processes (from colonization to maturity) to anatase and rutile TiO2 nanoparticles: Effects of nanoparticles aging and transformation.

Abstract Most of the current studies on the toxicology of pristine nanoparticles (NPs) are environmentally irrelevant, because their ‘‘aging’’ process accompanied by the physicochemical transformation is inevitable in the environment. Considering aging phenomenon will gain a better understanding of the toxicity and fate of NPs in the environment. Here, we focused on the physicochemical transformation of anatase-NPs (TiO2-A) and rutile-NPs (TiO2-R) after 90 days of aging and investigated the responses of freshwater biofilm formation to the stress changes of naturally aged TiO2-NPs (aTiO2-NPs). We found that after aging, the TiO2-NPs underwent sophisticated physicochemical transformations in the original morphology and microstructure owing to organic and crystal salts inclusions, such as energy band changes and the formation of Ti3+ on the NPs surfaces. These comprehensive transformations increased the stability of NPs in the exposed suspension. However, the physicochemical transformations were crystal-forms-dependent, and aging did not change the crystal structure and crystallinity. Interestingly, compared to pristine NPs, aTiO2-NPs showed much lower cytotoxicity and had the weaker ability to promote or inhibit the biofilm formation (p   0.05). However, the toxicity of high-concentration aTiO2-NPs (10 mg/L) remained serious in a water environment. This study provides a better understanding for the water environmental risks evaluation and policy control of nanoparticles, that is, the effect of time aging has to be considered.