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Inter-Compartment Comparison of Weathering Extent of Microplastics Using Carbonyl Index and Its Application in Source Identification
Summary
Researchers used carbonyl index measurements to quantify the weathering extent of microplastics collected from different environmental compartments—beach sand, river water, atmospheric deposition—and evaluated whether weathering extent can be used to identify plastic sources. Results showed that carbonyl index successfully distinguished microplastics from different exposure environments and could serve as a weathering fingerprint for source attribution.
The extent of aging in microplastics (MPs), widespread across the globe, is a critical factor in evaluating their adverse impacts and behavior. These synthetic particles undergo weathering during dispersion, primarily through photo-oxidation induced by ultraviolet (UV) light exposure, which leads to the formation of oxygen-containing functional groups and increases the potential for fragmentation into smaller-sized MPs. Time-relevant physicochemical changes of MPs can be quantified by the carbonyl index (CI), which serves not only an indicator for assessing the weathering (i.e., aging) extent of MPs, but also provides insights into the sources and/or transport pathways of MPs in different regions and compartments. In the present study, we compared the CI values of two prevalent MP polymers (PE and PP; ≥100 μm in cut-off size) transectionally collected from source regions (wastewater, river water, agricultural soils, and sand beach) to coastal region (inner- and outer-part of Incheon/Kyeonggi (I/K) bay at the Han River mouth), marginal seas (seawater of the Korean South Sea, the East China Sea, and the East Sea), the Northwestern Pacific, and the polar region (Arctic and Antarctic). Their CI values were also compared with those measured under accelerated UV light exposure in laboratory. Riverine and marine floating MPs were collected from the surface water using a manta-net, and all FT-IR spectra were obtained by the same instrument and procedure. PE in agricultural soils showed significantly higher CI values in outer soils than inner soils of greenhouse (0.32±0.16 vs. 0.25±0.16, respectively) (p0.05), indicating low UV exposure. Compared to the potential two sources, the PE in downstream water of the Han River exhibited much closer CIs (0.33±0.26) to those in neighboring soils than in wastewater, suggesting the importance diffuse source in riverine MPs. Floating PE particles in coastal seawater of I/K bay exhibited the significant separation of their CIs between the inner (0.32±0.17) and outer part (0.04±0.08) of the bay (p