Elucidating the Size-Dependency of In Vitro Digested Polystyrene Microplastics on Human Intestinal Cells Health and Function

The prevalence of microplastics (MPs) contamination in a broad spectrum of potable water sources has raised significant environmental and public health concerns. While evidence of ingested MPs bioaccumulation in the gastrointestinal tract (GIT) of aquatic and terrestrial organisms is mounting, the understanding of the effects of MPs on human gastrointestinal health remains scant. Herein, the potential deleterious biological effects of pristine and in vitro digested polystyrene (PS) MPs of varying sizes (i.e., 0.1, 1, and 10 µm) are systematically examined over a wide concentration range of 25–400 µg mL⁻¹ on two human intestinal cell lines, namely Caco-2 and NCM 460. Specifically, significant internalization of 0.1 and 1 µm PS -MPs have been observed in both cell types 24 h postexposure. However, multiparametric dose and time-dependent analysis encompassing cell viability, reactive oxygen species (ROS), and nutrient absorption/metabolism measurement revealed no significant adversarial outcomes. Interestingly, it is found that the 0.1 µm PS-MPs can perturb redox homeostasis in NCM460 but not in Caco-2 cells. Based on the in vitro experimental boundaries and findings, it is concluded that ingested PS-MPs pose little acute cytotoxic harm to human gastrointestinal health.