Can Micro/Nanoplastics Influence PM2.5 Characteristics: An Ex Situ Investigation by Physicochemical Indicators of PM2.5 and Their Bacterial Model Toxicity

Exposure to PM2.5 and its associated micropollutants, including micro- and nanoplastics, has been strongly linked to adverse health effects in humans. The risk posed by micro/nanoplastics can be attributed to the particles themselves and their ability to leach into the surrounding environment. However, the impact of micro/nanoplastics on the surrounding environment through leaching is still underestimated. In this study, we conducted ex situ experiments involving micro/nanoplastics and PM2.5 at various particulate matter mass concentrations and exposure times (1–336 h). The micro/nanoplastics were then removed from the PM2.5 media, and the aromaticity, light absorption, zeta potential, and oxidative potential of the PM2.5 were measured. Furthermore, the toxicity of the PM2.5 was investigated using a bacterial model by Staphylococcus aureus. Changes in the aromaticity, light absorption, zeta potential, and oxidative potential of PM2.5 indicated the impact of the micro/nanoplastics on the PM2.5. For example, PM2.5 exhibited higher aromaticity in the initial exposure stages (2–4% and 9–11%), whereas its light absorption (0.5–6-fold) increased with prolonged exposure to micro/nanoplastics. Overall, more negative zeta potentials and higher oxidative inputs (~6–40%) were obtained in PM2.5 after micro/nanoplastic treatment. The bacterial model revealed that the viability and biofilm formation of bacteria were affected by PM2.5 exposed to micro/nanoplastics, compared to PM2.5 not exposed to micro/nanoplastics, for example, 0.5–2-fold higher bacterial activity with longer MNP exposure and 4–39% higher biofilm formation. Furthermore, the oxidative stress-related bacterial indicators were primarily influenced by the aromaticity, zeta potential, and oxidative potential of PM2.5. The results of this study suggest that the bacterium Staphylococcus aureus can adapt to PM2.5 contaminated with micro/nanoplastics. Therefore, this study highlights the potential impact of micro/nanoplastics on bacterial adaptation to environmental contaminants and antibiotic resistance via PM2.5.