Photoaging mechanism of microplastics: a perspective on the effect of dissolved organic matter in natural water
Ying Yu1,2, Xinna Liu3, Yong Liu1(), Jia Liu4, Yang Li2()
1. College of Arts and Sciences, Northeast Agricultural University, Harbin 150030, China 2. Key Laboratory of Water and Sediment Sciences of Ministry of Education, State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China 3. Institutional Center for Shared Technologies and Facilities, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, 100101 China 4. Institute of Analysis and Testing, Beijing Academy of Science and Technology, Beijing Center for Physical & Chemical Analysis, Beijing 100089, China
● 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.
Ying Yu,Xinna Liu,Yong Liu, et al. Photoaging mechanism of microplastics: a perspective on the effect of dissolved organic matter in natural water[J]. Front. Environ. Sci. Eng.,
2023, 17(11): 143.
Fig.1 (a) Photooxidation reactions of PVC, (b) PET (Gardette and Lemaire, 1991; Fechine et al., 2004), and (c) photo-fries rearrangement reactions of PC (Diepens and Gijsman, 2007).
Artificial seawaterSalinity of 20%;312 mmol/L Cl?;0.312 mmol/L Br?
1. UV irradiation can promote the organotin compounds (OTCs) release from PVC MPs and their photodegradation compared with visible light.2. 3DOM* can react with Br? and Cl? to decrease ?OH consumption, which results in OTCs release from PVC MPs.
Chen et al. (2019)
PS/PP
20.1 ± 5.68μm, 2 g/L
UV irradiation(318/370 nm)
NA
Ultrapure water
1. PS MPs significantly accelerates the photoaging of co-existing PP MPs.2. DOM can be released from PS MPs and generate 1O2 and ?OH to attack MPs in the later stage of MP aging.
Liu et al. (2022b)
PS
50/75/150 μm, 25 g/L
Sunlight irradiation(200?1100 nm)
DOM = 20.8 mg/L
Mixed solution (sediment to water = 1:3)
1. DOM undergoes photooxidation to produce O2?? and oxidizes the pristine MPs to excited state MPs.2. O2?? can promote the generation ?OH and attack the co-excited MPs.
1. HA can promote photooxidation of MPs.2. HA decreases the photoaging dehydrochlorination of PVC MPs.
He et al. (2023)
PP/PET
1?2 mm,2.5 g/L
UV irradiation(254 nm)
DOM = 15/30 mg C/L
Ultrapure water
1. DOM can be released from MP photoaging and adsorb on plastic particle surfaces.2. DOM undergoes the photosensitization due to its unique fermentative and aromatic structure, which can generate more ROS and promote MP photoaging.
1. FA can absorb UV light and produce reactive species (the triplet excited state, ?OH and 1O2) to attack PS MPs, enhancing PS MP photoaging.2. FA plays more important role in photooxidation of PS MPs than other constituents (Cl?, CO32?and NO3?) in wastewater.
Liu et al. (2022a)
PS
100 nm/71.8?106.7 μm, 1 g/L
UV irradiation(365 nm)
DOM = 20 mg/L
Ultrapure water
1. HA/FA can promote photoaging of aliphatic polymers, but inhibit or have little effect on aromatic NPs/MPs photoaging.
Cao et al. (2022)
PP
42.1?107.2μm, 1 g/L
2. ?OH generated by photolysis of DOM can attack PP MPs via a hydrogen extraction reaction and C–C bond cleavage reaction.
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