Fe2+ Alleviated the Toxicity of ZnO Nanoparticles to Pseudomonas tolaasii Y-11 by Changing Nanoparticles Behavior in Solution

The negative effect of ZnO nanoparticles (ZnO-NPs) on the biological removal of nitrate (NO₃^-) has received extensive attention, but the underlying mechanism is controversial. Additionally, there is no research on Fe²⁺ used to alleviate the cytotoxicity of NPs. In this paper, the effects of different doses of ZnO-NPs on the growth and NO₃^- removal of <i>Pseudomonas tolaasii</i> Y-11 were studied with or without Fe²⁺. The results showed that ZnO-NPs had a dose-dependent inhibition on the growth and NO₃^- removal of <i>Pseudomonas tolaasii</i> Y-11 and achieved cytotoxic effects through both the NPs themselves and the released Zn²⁺. The addition of Fe²⁺ changed the behavior of ZnO-NPs in an aqueous solution (inhibiting the release of toxic Zn²⁺ and promoting the aggregation of ZnO-NPs), thereby alleviating the poisonous effect of ZnO-NPs on the growth and nitrogen removal of <i>P. tolaasii</i> Y-11. This study provides a theoretical method for exploring the mitigation of the acute toxicity of ZnO-NPs to denitrifying microorganisms.