Plastics are materials that are commonly used in various industries, which include product packaging, agriculture, mechanical facilities, and medical application, and the global plastic production has increased exponentially from 2 million tons in 1950 to 460 million tons in 2019 (Ritchie and Roser, 2018). The range of global plastic production was estimated to be from 19 to 23 million metric tons in 2016, and the annual emissions of plastics were predicted to reach as high as 53 million metric tons, which even considered the ambitious global commitments in regards to reducing plastic emissions (Borrelle et al., 2020). The plastics that are mainly produced are non-biodegradable, such as polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), polyethylene terephthalate (PET), and polystyrene (PS), and the debris from these type of non-biodegradable plastics are steadily accumulating as opposed to decomposing in the environment (Geyer et al., 2017). Microplastics (MPs), which are plastic particles in the size range of 1 nm to 5 mm, are primarily categorized as being intentionally produced from industrial processes and secondary processes, which are formed by aging and degradation from items and waste containing plastics (Hartmann et al., 2019). The primary MPs are directly discharged into the environment, and they include plastic particles in cosmetics and resin particles that are used as raw material as well as also particles that are worn out during the processes of producing, using, and cleaning plastic products (Boucher and Friot, 2017; Gong and Xie, 2020). Secondary MPs are produced from the degradation of larger plastic objects by weathering, which include UV radiation, wave action, and wind (Efimova et al., 2018; MacLeod et al., 2021).

The pathways of MPs exposure to the human body are mostly through ingestion and inhalation (Domenech and Marcos, 2021). In addition, food containers are recognized as another source of MPs exposure to humans, because plastics are applied as food packaging as well as released from containers during storage (Jadhav et al., 2021). PS containers in particular readily release MPs in abundance, which is due to their loose structure and rough surface (Ajay et al., 2021; Du et al., 2020). It was discovered after an ingestion of MPs that the size and surface charge of MPs are critically influenced to pass the mucosal layer of the gastrointestinal tract (Hirt and Body-Malapel, 2020; Wright and Kelly, 2017). There are the potential pathways for the uptake of MPs via the intestinal tract, which include (1) endocytosis via enterocytes, (2) transcytosis via the microfold cells, (3) persorption via gaps at the tip of the villus, and (4) paracellur uptake across tight junctions between adjacent cells (Powell et al., 2010). MPs, which are uptaken via the gastrointestinal tract by ingestion, are mainly absorbed by Peyer's patches of ileum in the small intestine among these pathways. In addition, persorption is considered as another pathway to be the most capable for the MPs translocation, because a large range of particle sizes, which can be up to 130 μm in diameter, can be covered (Wright and Kelly, 2017). It was considered that junctional complexes may not allow microparticles to permeate, which is due to their selectively permeable barrier function. However, damaged tight junctions could allow very small sizes of MPs (Powell et al., 2010; Carr et al., 2012). The absorbed MPs could cause inflammation, genotoxicity, oxidative stress, apoptosis, and necrosis by its biopersistence (Wright and Kelly, 2017).

It was previously discovered that plant-derived tannic acid performed a high removal efficiency on PS by coagulation as well as reduced oxidative stress and inflammatory cytokines in rat intestine IEC18 cells, which is similar to the MPs-untreated group (Park et al., 2021). It was also indicated that green tea, which is in regard to another natural product that is rich in polyphenols, had inhibitory effects on a chemical pollutant that is likely to bind to MPs (Wright and Kelly, 2017; Baker and Bauer, 2015; Newsome et al., 2014; Wang et al., 2020; Zeng et al., 2019). The study revealed that green tea decreased bioaccessibilty of the HOCs, which included PAHs, whereas the nutrients, such as protein carbohydrates increased bioaccessibilty of the HOCs (Zeng et al., 2019). It was illustrated that green tea had an effect on decreasing the oxidative stress that was induced by PCB 126 via an in vivo study (Newsome et al., 2014). Epigallocatechin gallate (EGCG), which is the major catechin in green tea, inhibited PCB 102-induced proliferation of breast cancer cells (Baker and Bauer, 2015). The intestinal exposure and toxicology of MPs have been studied in the progress, but there are few studies about inhibition on the intestinal uptake of MPs with the intervention of a natural product. Hence, the current study investigated the intestinal metabolism of PS with different charges and sizes in a human epithelial cell model, which is the Caco-2 cell. In addition, the inhibitory effect of green tea extracts (GTEs) on intestinal absorption of MPs via intestinal epithelial membrane model was conducted.