Mitigated toxicity of polystyrene nanoplastics in combination exposure with copper ions by transformation into copper (I) oxide: Inhibits the oxidative potential of nanoplastics.

The combined impact of trace metals and polystyrene (PS) microplastics is extremely concerning for human health because PS microplastics can serve as a vehicle for other contaminants. Herein, we investigated the combined effect of copper ions (Cu2+) on the toxicity of PS nanoplastics in vivo and in vitro. The pristine PS (PPS) and ultraviolet irradiated oxidized PS (OPS) nanoplastics with 50 nm-size were conjugated with Cu2+ (13-27 mg/g) for 4 days to get four types of samples: PPS, OPS, PPS/Cu, and OPS/Cu. The comparative toxic potentials of test samples were evaluated using a mouse pharyngeal aspiration model and relevant human cell lines (A549 and differentiated THP-1 cells). The results showed an antagonistic effect in vivo and in vitro by the presence of Cu ions: PPS > PPS/Cu; OPS > OPS/Cu. Furthermore, the OPS produced significantly increased toxic potentials compared to the corresponding PPS: OPS > PPS; OPS/Cu > PPS/Cu. The antagonistic effect of Cu2+ on the toxicity of PS was due to the transformation of Cu2+ and balanced the surface charge of the nanoplastics, which inhibited the oxidative potential of corresponding nanoplastics. These antagonistic effects may provide a better understanding of the combined effects of metals on the intrinsic toxic potential of microplastics under natural conditions.

Size- and oxidative potential-dependent toxicity of environmentally relevant expanded polystyrene styrofoam microplastics to macrophages.

Expanded polystyrene (EPS), also known as Styrofoam, is a widespread global pollutant, and its lightweight floating property increases its chances of weathering by abrasion and ultraviolet (UV) irradiation, resulting in microplastics. Herein, we investigated the effects of particle size ((1 µm versus 10 µm), UV irradiation (pristine versus UV oxidation), and origin (secondary versus primary) on the toxicity of Styrofoam microplastics. The target cells used in this study were selected based on human exposure-relevant cell lines: differentiated THP-1 cells for macrophages, Caco-2 for enterocytes, HepG2 for hepatocytes, and A549 for alveolar epithelial cells. In the differentiated THP-1 cells, the levels of cytotoxicity and inflammatory cytokines showed size- (1 µm > 10 µm), UV oxidation- (UV > pristine), and origin- (secondary > primary) dependency. Furthermore, the intrinsic oxidative potential of the test particles was positively correlated with cellular oxidative levels and toxicity endpoints, suggesting that the toxicity of Styrofoam microplastics also follows the oxidative stress paradigm. Additionally, all microplastics induced the activation of the pyrin domain-containing protein 3 (NLRP3) inflammasome and the release of interleukin-1ß (IL-1ß). These results imply that weathering process can aggravate the toxicity of Styrofoam microplastics due to the increased oxidative potential and decreased particle size.