The evaluation to combined toxic effects of polypropylene microplastics and benzo[a]pyrene on macrophage cells

Microplastics (MPs) pollution has emerged as a significant concern for human health, and their toxicological mechanisms help to better understand their potential risks. Previous studies paid main attention on the toxicity of MPs themselves, but in recent years, there has been growing awareness of their combined effects with other environmental pollutants. This study investigated the toxic effects of polypropylene microplastics (PP MPs) prepared via nonsolvent induced phase separation method in conjunction with benzo[a]pyrene (BaP) stimulation in vitro to macrophagocytes based on toxicoproteomics. We observed that PP MPs alone exhibited no obvious toxicity to the cells at concentrations of 50-150 μg/mL, while individual BaP induced significant cytotoxicity. Moreover, the combined exposure of PP MPs and BaP caused enhanced toxicity compared to BaP alone, where their combined exposure significantly suppressed the proliferation of RAW264.7 cells, exacerbated cell membrane damage, and increased apoptosis, resulting in substantial cellular toxicity. The possible toxic mechanisms were explored by measuring oxidative stress levels. It was found that co-exposure to PP MPs and BaP markedly inhibited superoxide dismutase (SOD) and catalase activities (CAT), reduced glutathione (GSH) level, elevated malondialdehyde (MDA) level, and increased intracellular reactive oxygen species (ROS) level compared to individual BaP exposure. Furthermore, proteomic analysis suggested that combined stimulation could lead to more serious oxidative damage, and further trigger intense inflammatory responses, validated by significant alterations in SOD, CAT, GSH, MDA, ROS, and IL-6. Therefore, this study provides new insights into assessing the risks associated with combined exposure to MPs and polycyclic aromatic hydrocarbons.