From ingestion to aggregation: contrasting roles of prey and predator in microplastic processing by freshwater rotifers

Microplastics (MPs) are persistent contaminants of growing concern due to their widespread occurrence and potential ecological risks in aquatic environment. While biological interactions may influence the environmental fate of MP, their role in aggregation and removal remains poorly understood. This study investigated how exposure to carboxylate-modified polystyrene microplastics influences ingestion, trophic transfer, and particle processing in the freshwater rotifers Lecane inermis and Cephalodella gibba. Experimental results showed that MPs exposure did not significantly affect population growth of either species, indicating limited acute toxicity under the tested conditions. C. gibba ingested MP efficiently through both direct uptake from biofilms and trophic transfer via prey. L. inermis actively ingested MPs and promoted particle aggregation through fecal pellet production, indicating a biological processing pathway of MPs. Predation by C. gibba reduced aggregation efficiency, likely by altering feeding activity and population density of L. inermis and by disrupting fecal pellet formation. These findings demonstrate that trophic interactions regulate microplastic ingestion, trophic transfer, and aggregation in freshwater systems, highlighting the critical role of predator–prey relationships in determining the environmental fate of microplastics.