Microplastic pollution: Phytotoxicity, environmental risks, and phytoremediation strategies

Microplastics (MPs) are emerging contaminants that adversely affect environmental health. In this review, we discuss the uptake of MPs by plants via endocytosis and crack-entry pathways in the roots and stomata of leaves; the translocation of MPs via xylem and phloem; and the toxicity of MPs to diverse plant species through oxidative stress, inhibition of photosynthesis, cytotoxicity, and genotoxicity. It's difficult to assess the health risks of MPs because they directly cause toxicity and also change soil properties and the bioavailability of coexisting pollutants, such as plastic additives, in the plant rhizosphere, and bioaccumulate along the food chain. Moreover, compared to the uptake behavior and phytotoxicity effects of MPs in laboratory and hydroponic studies, MPs of various shapes, sizes, and types are likely to cause different effects on plants in complex natural environments. This review proposes potential phytoremediation strategies, including phytoextraction, immobilization, and rhizoremediation, for MP pollutants and provides guidelines for the bioremediation of MP-contaminated environments to enhance environmental sustainability. In the phytoremediation of MP pollution, the selection and disposal of plants used for phytoremediation and the optimization of functional microbes in the rhizosphere remain challenging. Future studies should address knowledge gaps in (i) methods for determining environmentally-relevant concentrations of MPs, (ii) the assessment of the ecological and human health risks of MPs in the natural environment, and (iii) the development of effective strategies for the phytoremediation of MP pollution.