Recent advances in the adverse effects and toxicity of nanomaterials: A review

Nanotechnology is one of the most innovative technologies that entered the 21 st century. It showed great promise in energy production, environmental remediation, and disease diagnostics. However, the very same physicochemical properties that make nanomaterials (NMs) functional also threaten to adversely affect human health and the environment. NMs toxicity is increasingly recognized to be context dependent: carbon nanotubes induce T-cell mediated inflammation; some carbon nanoparticles (NPs) can migrate across the blood-brain barrier; ZnO NPs cause immunotoxicity; metal-based NPs induce genotoxicity in plants. Size is another relevant factor that can lead to NM toxicity, as decreased NP size (< 20 nm) has enhanced biological activity and uptake: smaller sized (20 nm) Ag NPs showed significantly higher deposition in the respiratory tract than larger particles. Modes of action for metal oxides like TiO 2 and ZnO primarily cause toxicity through reactive oxygen species production while carbon-based NMs are mostly affected by surface functionalization. Predicted environmental concentrations of several widely produced NMs are relatively low across most compartments (e.g., TiO 2 : 0.1–5 μg/L surface waters; Ag NPs: 0.01–1 μg/L soil and wastewater; ZnO: 0.5–10 μg/L surface water/aquatic and groundwater; carbon nanotubes: 0.001–0.1 μg/kg soil/sediment). However, there are some hotspots where concentrations may be higher such as wastewater effluents and sludge-amended soils. As with all types of toxicity, NM toxicity is dictated by many factors (dose, exposure time, size and shape, surface chemistry, model organism, etc.). The present review focusses on findings from 2015–2025 that analyses the environmental fate, modulating properties, mechanistic pathways, and biological outcomes of metal, metal oxide, and carbon-based NMs, considering their unique properties. Furthermore, the review examines the mechanisms of toxicity disruption, including genotoxicity, inflammation, and the generation of reactive oxygen species. Unlike other studies that describe NM toxicity in general terms, this review focuses on specific variables. By providing more detailed insights into each component, this study aims to guide nanotechnology toward a more sustainable direction.