Uptake and Translocation of Fragmented Plastics
Individuals working in textile or other industries capable of producing microplastics are supposed to be at an occupational health risk. Common issues reported by such individuals are respiratory irritation , dyspnea, coughing and reduced lung capacity [26,27]. Histopathological studies of lung biopsies of workers of textile industries showed granulomatous lesions and interstitial fibrosis due to fragmented textile dust. The symptoms were similar to that of allergic alveolitis . It has been reported that malignant and non-neoplastic lung tissue contains both plastic and cellulose microfibers . Size and shape of the fibers play a key role in toxicity. Small and thin fibers are capable of passing through the respiratory tract and cause toxicity to pulmonary cells . Nylon fibers of less than 2 pm diameter can be respired.
Uptake in Respiratory Tract by Endocytosis
Microplastics may enter the respiratory epithelium via diffusion. However, active cellular uptake has also been reported to transport micro- and nanofragments . Energy- dependent endocytosis and phagocytosis also assist in the active uptake of micro- and nanoparticles . Particles of 1-3 pm are cleared from alveoli through phagocytosis .
Uptake in Gastrointestinal Tract by Endocytosis
The ileum, specifically the Peyer’s patches, are the regions of small intestine and the major sites for uptake and translocation of fragmented particles [33,34]. Other non- biodegradable microelements like titanium dioxide and aluminosilicates are retained over the phagocytic cells of ileum . This region acts as a compartment where microplastics accumulate and can take the endogenous route, thus compromising local immunity.
Uptake by the Persorption Method
The persorption method is the process where mechanical kneading of microparticles occurs and they are eventually taken up by the gaps in the epithelial cells into the circulatory system [35,36]. It was observed that micro PVC particles of 5-110 pm tend to pass between the enterocytes in the villi . Persorption has also been reported in humans. Granules have been reported in bile, urine, cerebrospinal fluid, breast milk and peritoneal fluid .