Associations between DOM characteristics and microplastic size distributions in the Three Gorges Reservoir.

Abstract

Reservoirs are regarded as crucial sinks for terrestrial microplastics (MPs). Here, the occurrence, size distribution, and morphological features of MPs in the surface waters of tributaries of the Three Gorges Reservoir (TGR), the world's largest hydropower project, were comprehensively investigated. The results showed the ubiquitous presence of MPs in the tributaries of the TGR (1,132 to 13,316 items/m3) and a small-MPs (SMPs, < 300 μm)-dominated distribution pattern, with low-density polyethylene (PE) MPs as the predominant contributors. Interestingly, the proportion of SMPs was significantly negatively correlated with DOM concentration. Furthermore, correlation analysis based on excitation-emission matrix spectroscopy coupled with parallel factor analysis (EEM-PARAFAC) results indicated that the proportion of SMPs was also negatively correlated with the relative contributions of the humic-like and fulvic-like components. The laboratory accelerated-irradiation experiment showed that PE MPs exhibited attenuated surface damage and oxidation in the presence of model dissolved organic matter (i.e., humic acid (HA) and fulvic acid (FA)), with HA exerting a relatively higher inhibitory effect, as evidenced by reduced surface deterioration and lower O/C ratios. The findings of this study indicate that MP size distributions in reservoir surface waters are associated with both DOM concentration and composition, thereby deepening our understanding of the environmental fate of MPs and providing scientific insights into the development of management strategies for MPs in reservoirs.

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