Size effect of graphene oxide on vanadium cytotoxicity: From aggravation to mitigation

Vanadium-containing compounds and materials are widely used in industry, unavoidably leading to environmental contamination. Whether other pollutants released into the environment, e.g. the star material graphene oxide (GO), affect the threat that vanadium poses to human health is still unknown. This study investigated the combined toxicity of vanadium ions and GO of different sizes (S-GO: ∼229 nm; L-GO: ∼1082 nm) to A549 cells. Exposure to vanadium ions (0-400 μM) for 24 h caused a dose-dependent decrease in cell viability, where V(V) was more toxic than V(IV). The toxicity of vanadium was manifested as impaired proliferation and cell death. Vanadium toxicity was attributed to the overproduction of intracellular reactive oxygen species (ROS), the cell cycle arrest at the G2/M phase, mitochondrial dysfunction, decreased intracellular ATP and the apoptosis. Importantly, co-exposure to vanadium ions and different-sized GO (200 μg·mL^-1) resulted in distinct effects: S-GO and vanadium ions displayed the synergistic toxicity, whereas L-GO and vanadium ions exhibited an antagonistic effect. Co-exposure to vanadium ions and S-GO caused more severe cell damage, which was associated with a significant increase in vanadium uptake. In contrast, L-GO adhered to the cell surface and reduced vanadium uptake, alleviating vanadium toxicity. The results collectively indicated that vanadium pollutants might interact with other contaminants to alter the environmental safety.