Role of nanoparticle surface charge in their toxicity

Dust often contains chemical airborne pollutants that might negatively affect human health. Polystyrene is one of the most widely used types of plastic. Bulk polystyrene exhibits no short-term cytotoxicity. However, during degradation of polystyrene, small nanoparticles are formed. Due to specific properties, such as the large surface to volume ratio, toxicity of nanoparticles might be different to that of the bulk material. Hence, particularly the surface chemistry is crucial for nanoparticle behaviour in biological environment. For this study, carboxyl(PS-COOH) and amino-functionalized (PS-NH2) nanoparticles were prepared by free-radical copolymerization in a direct (oil in water) miniemulsion system. We show that surface functionalization of polystyrene nanoparticles with amino groups (PS-NH2), but not with carboxyl groups (PS-COOH), induced inhibition of proliferation in a monocytic cell line and induce a specific cell death, apoptosis. In PS-NH2–treated cells, acidic vesicular organelles exhibited elevated pH and impaired processing of a lysosomal enzyme. Moreover, solely in PS-NH2-treated cells, but not in PS-COOHtreated cells, this was followed by permeabilization of acidic vesicular organelles and induction of cell death. These data indicate that surface charge of nanoplastics defines their effects on biological systems and can be used to predict environmental toxicity of nanoplastics.