Mechanisms for facet-dependent biological effects and environmental risks of engineered nanoparticles: A review

Engineered nanoparticles (NPs) have revolutionized multiple disciplines due to their unique physicochemical properties, which is significantly influenced by the specific crystal facets exposed on the surfaces of NPs. This review critically examined underlying mechanisms by which crystal facets impacted biological effects and environmental risks of NPs. We illustrated facet-dependent interactions between NPs and macromolecules like natural organic matter, extracellular polymeric substances, and proteins, wherein the interactions modulated biological effects of NPs. Also, facet-dependent transformation, bioavailability, and risk of NPs were discussed based on the fate of NPs during their environmental processes, documenting that the exposed facets inevitably influenced environmental risk of NPs. We elaborated on potential mechanisms for the facet-dependent generation or quenching of reactive oxygen species that were highly associated with biological effects or environmental risk through oxidative stress. By systematically elucidating the facet-dependent mechanisms for biological effects and environmental risks of NPs, this review provided an insight into environmental health of NPs that was attributable to differences in the atom-level arrangement on the surface of NPs.