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Developing a materials perspective of how to control the degradation and negative impact of complex metal oxides requires an integrated understanding of how these nanomaterials transform in the environment and interact with biological systems. Doping with aluminum is known to stabilize oxide materials, but has not been assessed cohesively from synthesis to environmental fate and biological impact. In the present study, the influence of aluminum doping on metal ion release from transition metal oxides was investigated by comparing aqueous transformations of lithium nickel cobalt aluminum oxide (LiNi0.82Co0.15Al0.03O2; NCA) and lithium nickel cobalt oxide (LiNi0.80Co0.20O2; NC) nanoparticles and by calculating the energetics of metal release using a density functional theory (DFT) and thermodynamics method. Two model environmental organisms were used to assess biological impact, and metal ion release was compared for NCA and NC nanoparticles incubated in their respective growth media: moderately hard reconstituted water (MHRW) for the freshwater invertebrate Daphnia magna (D. magna) and minimal growth medium for the Gram-negative bacterium Shewanella oneidensis MR-1 (S. oneidensis). The amount of metal ions released was reduced for NCA compared to NC in MHRW, which correlated to changes in the modeled energetics of release upon Al substitution in the lattice. In minimal medium, metal ion release was approximately an order of magnitude higher compared to MHRW and was similar to the stoichiometry of the bulk nanoparticles for both NCA and NC. Interpretation of the release profiles and modeling indicated that the increase in total metal ion release and the reduced influence of Al doping arises from lactate complexation of metal ions in solution. The relative biological impacts of NC and NCA exposure for both S. oneidensis and D. magna were consistent with the metal release trends observed for minimal medium and MHRW, respectively. Together, these results demonstrate how a combined experimental and computational approach provides valuable insight into the aqueous transformations and biological impacts of complex metal oxide nanoparticles. 

Lithium intercalation compounds, such as the complex metal oxide, lithium nickel manganese cobalt oxide (LiNi x Mn y Co 1−x−y O 2 , herein referred to as NMC), have demonstrated their utility as energy storage materials. In response to recent concerns about the global supply of cobalt, industrially synthesized NMCs are shifting toward using NMC compositions with enriched nickel content. However, nickel is one of the more toxic components of NMC materials, meriting investigation of the toxicity of these materials on environmentally relevant organisms. Herein, the toxicity of both nanoscale and microscale Ni-enriched NMCs to the bacterium, Shewanella oneidensis MR-1, and the zooplankton, Daphnia magna , was assessed. Unexpectedly, for the bacteria, all NMC materials exhibited similar toxicity when used at equal surface area-based doses, despite the different nickel content in each. Material dissolution to toxic species, namely nickel and cobalt ions, was therefore modelled using a combined density functional theory and thermodynamics approach, which showed an increase in material stability due to the Ni-enriched material containing nickel with an oxidation state >2. The increased stability of this material means that similar dissolution is expected between Ni-enriched NMC and equistoichiometric NMC, which is what was found in experiments. For S. oneidensis , the toxicity of the released ions recapitulated toxicity of NMC nanoparticles. For D. magna , nickel enrichment increased the observed toxicity of NMC, but this toxicity was not due to ion release. Association of the NMC was observed with both S. oneidensis and D. magna. This work demonstrates that for organisms where the major mode of toxicity is based on ion release, including more nickel in NMC does not impact toxicity due to increased particle stability; however, for organisms where the core composition dictates the toxicity, including more nickel in the redesign strategy may lead to greater toxicity due to nanoparticle-specific impacts on the organism. 

We aim to establish the effect of environmental diversity in evaluating nanotoxicity to bacteria. We assessed the toxicity of 4 nm polyallylamine hydrochloride-wrapped gold nanoparticles (PAH AuNPs) to a panel of bacteria from diverse environmental niches. The bacteria experienced a range of toxicities as evidenced by the different minimum bactericidal concentrations determined; the sensitivities of the bacteria was A. vinelandii = P. aeruginosa > S. oneidensis MR-4 > A. baylyi > S. oneidensis MR-1. Interactions between gold nanoparticles and molecular components of the cell wall were investigated by TEM, flow cytometry, and computational modeling. Binding results showed a general trend that bacteria with smooth lipopolysaccharides (LPS) bind more PAH AuNPs than bacteria with rough LPS. Computational models reveal that PAH migrates to phosphate groups in the core of the LPS structure. Overall, our results demonstrate that simple interactions between nanoparticles and the bacterial cell wall cannot fully account for observed trends in toxicity, which points to the importance of establishing more comprehensive approaches for modeling environmental nanotoxicity.