Adsorption Behavior of Nonylphenol on Polystyrene Microplastics and Their Cytotoxicity in Human Caco-2 Cells

As two environmental pollutants of great concern, polystyrene microplastics (PS-MPs) and nonylphenol (NP) often coexist in the environment and cause combined pollution. Batch adsorption experiments were carried out by varying parameters such as pH, the particle sizes of the PS-MPs, the initial concentration of NP, and metal ion content. The results showed that the particle size of the PS-MPs in the range tested (0.1, 1, 10, 50, and 100 μm) had a significant effect on their NP adsorption capacity. The NP adsorption process of the PS-MPs was best described by the pseudo-second-order kinetic model and the Langmuir isotherm model, while the intraparticle diffusion and Bangham models were also involved in determining the NP adsorption process of 0.1 μm PS-MPs. Both PS-MPs and NP significantly affected cell proliferation, which had been confirmed by reduced cell viability, a blocked cell cycle G1 phase, and elevated apoptosis by affecting the basic cell functions. Furthermore, the negative effects of 0.1 μm PS-MPs on cell proliferation and function were aggravated after the adsorption of NP. Further research on the potential health risks of PS-MPs combined with NP or other environmental contaminants is needed.