Influence of particle size and feeding conditions on microplastic ingestion and depuration in Daphnia magna

Microplastic (MP) uptake and retention in freshwater invertebrates are shaped by both particle characteristics and feeding conditions, yet the specific influence of diet composition remains poorly understood. This study examined the concentration- and time-dependent ingestion, as well as depuration, of 45-53, 63-75, and 90-106 μm polyethylene MPs in adult Daphnia magna acclimated to three diets, with exposure assays conducted under either fed or unfed conditions. Concentration-dependent accumulation experiments were conducted at 4, 8, 40, 80, 400, and 800 mg/L for 48-h. Time-dependent accumulation was assessed at 60 mg/mL for 60h. Depuration was measured for 6h following a 48h exposure to 60 mg/L. The experimental diets consisted of live Chlorella vulgaris, a dried spirulina and yeast mixture, or a combination of both. Concentration-dependent uptake followed Michaelis-Menten kinetics, with the smallest MPs retained in the highest numbers and food deprivation resulting in greater particle retention across all diets. Time-dependent uptake showed a sigmoidal trend shaped by MP size, diet type, and food availability. Depuration exhibited a reverse sigmoidal pattern, and D. magna acclimated to the live algae diet generally displayed more rapid MP clearance, indicating that prior dietary history influenced elimination. Together, these results indicate that MP ingestion and depuration in adult D. magna depend on both MP size and feeding conditions, and that diet composition plays a critical role in short-term MP fate. In conclusion, the present study suggests that feeding history and diet composition influence MP ingestion and depuration under controlled conditions and should be considered when designing and interpreting laboratory exposure studies.