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Concentration-dependent uptake by Daphnia pulex
Summary
Tiny water fleas called Daphnia—a key food source for fish—actually eat microplastic particles at pollution levels found in real lakes and rivers, not just in extreme lab conditions. This matters because it shows plastic pollution can enter the food web at a very basic level, meaning those particles could work their way up to the fish that end up on our plates. More research is needed to know exactly how much plastic makes it that far and what it means for our health, but this study confirms an early, important link in that chain.
Microplastics are widespread contaminants in aquatic environments that may be ingested by zooplankton, raising concerns about their ecological impacts in freshwater ecosystems. Although microplastic uptake in Daphnia has been well documented under laboratory conditions, it remains unclear whether ingestion occurs at environmentally relevant (ER) concentrations. This study evaluated microplastic uptake in Daphnia pulex across a range of exposure concentrations from 1,000-50,000 particles/L to determine whether ingestion occurred within reported ER levels. Individuals were exposed to polyvinyl chloride (PVC) microplastics for 20 minutes and visually assessed for the presence or absence of particles in the digestive tract. Uptake increased with concentration, with no ingestion observed at the 1,000 particles/L and consistent uptake concentrations >10,000 particles/L, indicating a concentration dependent response with a threshold between 1,000 and 2,000 particles/L. Rapid gut clearance suggests that uptake may be underestimated at lower concentrations. These findings demonstrate that Daphnia ingest microplastics at concentrations within or near environmentally relevant ranges, highlighting their potential role in microplastic transfer through freshwater food webs.