Perspectives and challenges of micro/nano plastics induced toxicity with special reference to phytotoxicity.

Plastics pollution has become a global concern for ecosystem health and biodiversity conservation. Concentrations of plastics are manifold higher in terrestrial system than the aquatic one. Micro/nano plastics have the ability to alter soil enzymatic system, soil properties and also affect soil borne microorganisms and earthworms. Despite, almost all works targeting ecotoxicological potential of micro/nano plastics are based on aquatic system and reports on their phytotoxic potentials are limited. The presence of cell wall that could restrict micro/nano plastics invasion into plant roots might be the putative cause of this limitation. Micro/nano plastics inhibit plant growth, seed germination and gene expression; and they also induce cytogenotoxicity by aggravating ROS (Reactive Oxygen Species) generation. Dynamic behaviour of cell wall; the pores formed either by cell wall degrading enzymes or by plant-pathogen interactions or by mechanical injury might facilitate the micro/nano plastics entry into roots. This review also provides the possible mechanism of large sized microplastics induced phytotoxicity especially for those that cannot pass through cell wall pores. As micro/nano plastics affect soil microbial community and soil parameters, it is hypothesized they could have the potential to affect N2 fixation and research works should be conducted in this direction. Reports on micro/nano plastics induced toxicity mainly focused only on one polymer type (polystyrene) in spite of the toxicological relevancies of other polymer types like- polyethylene, polypropylene etc. So, the assessment of ecotoxicological potential of micro/nano plastics should be done using other plastic polymers in real environment as they are known to interact with other environmental stressors such as heavy metals and pesticides and could modify effects of each other.