Deciphering the effects of CeO2 nanoparticles on Escherichia coli in the presence of ferrous and sulfide ions: Physicochemical transformation-induced toxicity and detoxification mechanisms

The physicochemical transformations as well as the redox reaction-induced toxicity changes of ceria nanoparticles (CeO2 NPs) in reducing conditions is extremely lacking. Herein, the behaviors, chemical modifications and toxicity of CeO2 NPs in the presence of reduction-active ions (namely Fe2+ and S2-) were investigated, with a particular emphasis on the cytotoxicity mechanism associated with their physicochemical transformations. The presence of Fe2+ and S2- differently altered the surface properties and toxicity of CeO2 NPs. Redox reactions with Fe2+ led to form small aggregates, boosted the reduction of CeIVO2 and enhanced dissolved Ce3+ concentration. Moreover, CeO2 NPs possessed a high affinity for Escherichia coli (E. coli) and induced the generation of ?OH abiotically after reaction with Fe2+, provoking serious disruption of cell membranes and causing high toxicity to E. coli. In contrast, the amending of S2- protected E. coli from direct contact with CeO2 NPs by creating new Ce2S3 precipitated on the surface, accelerating the aggregation of NPs and reducing the concentration of dissolved Ce3+. This study suggested that the chemical interactions between the reactive surfaces of CeO2 and reductionactive ions highly determined the stability and cytotoxicity of CeO2 NPs, which provides fundamental insights into the environmental risks of CeO2 NPs.

Automated summary

The presence of Fe2+ and S2- had different effects on the surface properties and toxicity of CeO2 NPs. The redox reactions with Fe2+ resulted in the formation of small aggregates, boosted the reduction of CeIVO2, and increased the concentration of dissolved Ce3+.