Environmentally persistent free radicals on micro- and nano-plastics: a double-edged sword to environmental and biological safety

Environmentally persistent free radicals (EPFRs) are a new kind of pollutant that are stable and persistent in the environment and are mainly produced on particles or organics under heating or light irradiation. Aged micro- and nano-plastics (MNPs) are important sources of EPFRs. Existing reviews have focused particularly on the environmental and biological hazards of aged MNPs themselves. Few reviews have focused on the role of EPFRs on aged MNPs, let alone their fate in the environment and their positive applications. This review summarizes the factors that influence the occurrence and formation of EPFRs from aged MNPs, their types and decay periods in the environment, and their conversion into reactive species (RS). This article also discusses the environmental effects of EPFRs on microbial community structure, the cycles of elements (C, N, Cl, S, and P), and the survival of microorganisms, plants, and animals in soil and water. Moreover, the biological effects of EPFRs from aged MNPs are discussed, including oxidative stress, neurotoxicity, reproductive toxicity, respiratory toxicity, and their impact on aging. Meanwhile, the high reactivity of EPFRs can be harnessed to transform them into environmental protection warriors. Hence, the applications of EPFRs in improving environmental pollution are also reviewed, including their use in fixing metals, degrading organic pollutants (including antibiotics and MNPs), and sterilization. Finally, this text provides insights for future research on the dual nature of EPFRs on aged MNPs. This review aims to mitigate the environmental and biological risks of EPFRs and provide a reference for their optimal application.