Microplastics are important environmental pollutants due to their persistence and widespread occurrence in aquatic systems and sediments. Under natural conditions, they are exposed to biotic aging processes, which alter their physicochemical properties and affect particle transport and retention in sediments. To investigate these processes, this study examined the transport of polyethylene (PE) and polylactic acid (PLA) microplastics through sediment and assessed the influence of biotic aging on their mobility. Experiments were conducted in a horizontal column simulating river sediment conditions. We compared unaged and biotically aged microplastics, analysed biofilm formation, particle density, and its retention along the sediment column. The results showed that biofilm significantly affected the transport of both polymers. PE was retained more strongly in the initial sediment segments, while aging further reduced its mobility possibly due to the presence of extracellular polymeric substances with adhesive properties. In contrast, aged PLA microplastics travelled further, which could be associated with decreased density after aging. These findings contribute to a better understanding of the impact of biotic aging on microplastics transport in natural sediments.
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