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Lithium cobalt oxide (LiCoO 2 ), an example of nanoscale transition metal oxide and a widely commercialized cathode material in lithium ion batteries, has been shown to induce oxidative stress and generate intracellular reactive oxygen species (ROS) in model organisms. In this study, we aimed to understand the time-dependent roles of abiotic ROS generation and Co ions released in aqueous medium by LiCoO 2 NPs, and examined the induced biological responses in model bacterium, B. subtilis upon exposure. We found that the redox-active LiCoO 2 NPs produced abiotic ROS primarily through H 2 O 2 generation when freshly suspended. Subsequently, the freshly-suspended LiCoO 2 NPs induced additional DNA breakage, and changes in expression of oxidative stress genes in B. subtilis that could not be accounted for by the released Co ions alone. Notably, in 48 hour old LiCoO 2 suspensions, H 2 O 2 generation subsided while higher concentrations of Co ions were released. The biological responses in DNA damage and gene expression to the aged LiCoO 2 NPs recapitulated those induced by the released Co ions. Our results demonstrated oxidative stress mechanisms for bacteria exposed to LiCoO 2 NPs were mediated by the generation of distinct biotic and abiotic ROS species, which depended on the aqueous transformation state of the NPs. This study revealed the interdependent and dynamic nature of NP transformation and their biological consequences where the state of NPs resulted in distinct NP-specific mechanisms of oxidative injury. Our work highlights the need to capture the dynamic transformation of NPs that may activate the multiple routes of oxidative stress responses in cells. 

The increasing use of nanoscale lithium nickel manganese cobalt oxide (Li x Ni y Mn z Co 1−y−z O 2 , NMC) as a cathode material in lithium-ion batteries poses risk to the environment. Learning toxicity mechanisms on molecular levels is critical to promote proactive risk assessment of these complex nanomaterials and inform their sustainable development. We focused on DNA damage as a toxicity mechanism and profiled in depth chemical and biological changes linked to DNA damage in two environmentally relevant bacteria upon nano-NMC exposure. DNA damage occurred in both bacteria, characterized by double-strand breakage and increased levels of many putative chemical modifications on bacterial DNA bases related to direct oxidative stress and lipid peroxidation, measured by cutting-edge DNA adductomic techniques. Chemical probes indicated elevated intracellular reactive oxygen species and transition metal ions, in agreement with DNA adductomics and gene expression analysis. By integrating multi-dimensional datasets from chemical and biological measurements, we present rich mechanistic insights on nano-NMC-induced DNA damage in bacteria, providing targets for biomarkers in the risk assessment of reactive materials that may be extrapolated to other nano–bio interactions. 

As lithium intercalating complex metal oxides become more widely used in energy storage devices, there is an increasing need to understand their environmental impact at the end of their life cycle due to the lack of recycling options. In this study, we examine the biological impact of a panel of nanoscale lithium nickel manganese cobalt oxides (LixNiyMnzCo1−y−zO2, 0 < x, y, z < 1, abbreviated as NMCs), to a model Gram-positive bacterium, Bacillus subtilis in terms of cellular respiration and growth. A highly sensitive single-cell gel electrophoresis method is also applied for the first time to understand the genotoxicity of this nanomaterial to bacterial cells. Results from these assays indicate that the free Ni and Co ions released from the incongruent dissolution of the NMC material in B. subtilis growth media induced both hindered growth and cellular respiration. More remarkably, the DNA damage induced by the combination of the two ions in solution is comparble to that induced by the NMC material, which suggests the free Ni and Co ions are responsible for the toxicity observed. A material redesign by enriching Mn is also presented. The combined approaches of evaluating impact on bacterial growth, respiration, DNA damage at a single-cell level, as well as other phenotypical changes allows us to probe the nanomaterial and bacterial cells from a mechanistic prospective, and provides a useful means to an understanding of bacterial response to new potential environmental stressors.