Biodegradable and Traditional Microplastics Affect sediment DOM: Chemical properties, keystone microbes, functional genes

Microplastics (MPs) are emerging contaminants and accumulate in river sediments, which pose great threaten to the self-purification capacity of rivers by affecting the fate of dissolved organic matter (DOM). Although the impact of MPs on sediment DOM has already been confirmed, it remains unclear how differences in MP characteristics affect the chemical properties of DOM. Thus, this study selects 2 traditional MPs (polystyrene, PS; polypropylene, PP) and 1 biodegradable MPs (polylactic acid, PLA) to construct microcosm incubation system. We found a 3.17-fold increase in DOM concentrations within biodegradable MPs, while traditional MPs exhibited a marked reduction of 76%-97% in DOM humification. FTIR analysis indicated biodegradable MPs enhance degradation of carboxylic acids in DOM. Microbial analysis showed that MPs pollution significantly changed the composition and community of keystone microbes in sediment. Compared to PS (6) and PP (4), PLA (11) enriched more tolerant microbes in sediments and significantly reduced the abundance of functional genes associated with methanotrophy (23%) and hydrocarbon_degradation (25%). Our results further revealed that MPs affected DOM fractions by changing the composition and abundance of keystone microbes, thereby increasing the sediment DOM concentration. This study provided a new insight into the ecological risks of MPs in river ecosystems.