Trophic transfer and egestion dynamics of microplastics in the Brachionus-Asplanchna rotifer system

Abstract Microplastics have become a pervasive contaminant in freshwater ecosystems worldwide, raising concerns about their impact on aquatic life, especially zooplankton, which play a pivotal role in freshwater food webs. Despite their ecological importance, knowledge on how microplastics move through predator–prey interactions in microscopic communities remains limited. We investigated this question using a classic freshwater system: the filter-feeding rotifer Brachionus caudatus and its predator, Asplanchna brightwellii . Specifically, we asked: How efficiently do these organisms ingest and eliminate microplastics, and to what extent are the particles transferred across trophic levels? We exposed B. caudatus to three concentrations of 1 µm fluorescent polystyrene microspheres (0.1, 0.5, and 1.0 µg ml −1 ) for 24 h, then fed this contaminated prey to A. brightwellii predators. Using fluorescence microscopy, we tracked the fate of the microplastics over 48 h in both species. Both rotifers readily consumed the microspheres, and they also eliminated them efficiently. Fluorescence intensity declined rapidly in both prey and predator, with minimal retention after 24–48 h. While predators initially accumulated more than twice the fluorescence of their prey (confirming trophic transfer), this accumulation was short-lived. The rapid clearance suggests that in this simple food chain, 1 µm polystyrene microspheres do not biomagnify. Our findings reveal that these microplastics behave more like transient contaminants than persistent pollutants in rotifer communities, offering new insights into how microplastics flow through freshwater food webs at the microscopic scale.