The uptake of microplastics (MPs) and nano-plastics (NPs) in plants has been detected, especially accumulation in root hairs. MPs cannot enter into plant tissues directly as is expected because large size particles prevent them from entering into the plant cell walls, while NPs can directly enter into the plant cell walls. On the basis of pervious research, the polystyrene (PS) fluorescent microbeads were trapped in the cells outside the root cap mucilage usually obvious to the naked eye. (Noted in plants, the mucilage and exudates act as the first layer of protection, are negatively charged, and have been reported to inhibit positively charged metal uptake of NPs at the outer side of the cell wall). After entrance in the root tap, it may move to cell walls of cortical tissue of the roots and mainly observed in the vascular system, which showed that the beads passed through the intercellular channels, through apoplastic transport system.
Plastic particles enter the epidermal tissue of wheat’s primary and secondary roots and are stimulated through the pericycle and moved into the xylem. Inside the central cylinder, these particles may move to the aerial part of the plant through the xylem. Plastic particles transferred from root to shoot by the vascular system via the transpiration stream. MPs and NPs may travel in microscopic extracellular channels and reach the vasculature accountable for water transportation. Water transportation system supporting NPs quickly transfer to the stem, leaves, and possibly fruits.
Another pathway for plastic entry into the plant leaf is through the stomata dust on the leaves. Stomatal uptake is one possible pathway for NPs into the leaves and then moves to the vasculature. NP move from leaves to stems and later from stems to roots through vascular bundle. Similarly, PS NPs attach to the plant stomata, penetrate through phloem and reach the roots of plant and then ultimately enter into human food.
In conclusion, entrance of the plastic to food chain might create serious diseases in human beings. Thus, detailed investigations on various types of plastic types, size and their accumulation in plants are need of the time.
Reference
Azeem, I.; Adeel, M.; Ahmad, M.A.; Shakoor, N.; Jiangcuo, G.D.; Azeem, K.; Ishfaq, M.; Shakoor, A.; Ayaz, M.; Xu, M.; et al. Uptake and Accumulation of Nano/Microplastics in Plants: A Critical Review. Nanomaterials 2021, 11,2935. https://doi.org/10.3390/ nano11112935
