Photoaging mechanism of microplastics: a perspective on the effect of dissolved organic matter in natural water

Abstract

● Microplastics (MPs) undergo photoaging in natural water under light irradiation.

● ROS generation plays an important role in the photoaging pathway of MPs.

● Dissolved organic matter (DOM) ubiquitous in natural water affects MP photoaging.

● Future works are suggested to study the effect mechanism of DOM on MP photoaging.

Plastic products widespread in natural water can be broken into smaller-sized microplastics (MPs, < 5 mm) under light irradiation, thermal degradation and biodegradation, posing a serious threat to aquatic ecosystems and human health. This perspective concludes that MPs can generate reactive oxygen species (ROS) through initiation, propagation and termination steps, which can attack the polymer resulting in the photoaging and breakdown of C–C and C–H bonds under ultraviolet (UV) irradiation. Free radical generation and weathering degree of MPs depend on their physicochemical properties and environmental conditions. In general, UV irradiation and co-existed MPs can significantly accelerate MP photoaging. With plentiful chromophores (carbonyl, carboxyl and benzene rings, Dissolved organic matter (DOM) mainly absorbs photons (300–500 nm) and generates hydrated electrons, ³DOM* and ROS, which may affect MP photoaging. However, whether DOM may transfer the electron and energy to MPs under UV irradiation, affect ROS generation of MPs and their photoaging pathway are inadequately studied. More studies are needed to elucidate MP photoaging pathways and mechanisms, consider the influence of stabilization capacity, photosensitization and photoionization of DOM as well as their competitive light absorption with MPs, which provides valuable insights into the environmental behavior and ecological risk of MPs in natural water.

Graphical abstract

Keywords

Microplastics / Photoaging / Dissolved organic matter / ROS generation

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