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Polystyrene nanoplastics alone and in mixture with caffeine induced increased swimming behavior of adult Daphnia magna
Summary
Scientists exposed tiny water fleas (a key food source for fish) to nanoplastics and caffeine—both common pollutants in wastewater—and found the plastics made the fleas swim more erratically, likely because plastic particles stuck to their bodies and guts. While this study looked at aquatic life rather than humans directly, it's a reminder that plastic pollution is building up in waterways and affecting the small creatures at the bottom of the food chain that fish (and eventually we) rely on. More research is needed to know if these same nanoplastics, which are increasingly found in tap water and food, could similarly disrupt human biology
Due to the abundant and increasing anthropogenic release of nanoplastics (NPs) and pharmaceutically active compounds (PhACs) into wastewater, it is critical to fully characterize the potential synergistic effects of mixtures of these emerging pollutants on freshwater organisms. In this study, we evaluated the behavioral and physiological responses of Daphnia magna exposed to NPs and an overlooked PhAC, caffeine (CAF). Namely, pregnant adult D. magna were exposed over 48 h to 50 mg/L synthesized polystyrene nanoplastics (PSNPs, 300 nm), 100 µg/L CAF, and CAF + NP mixtures. Then, the following variables were evaluated: (1) the total number of offspring produced, (2) swimming behavior, quantified as average speed (mm/s), average acceleration (mm/s), mobility rate (%), exploration rate (%), and total distance traveled (mm) during one minute, and (3) heart rate, appendage curling rate, and post-abdominal claw movement counted during one minute. We determined significantly elevated swimming behavior for NPs and CAF + NPs treatment groups compared to the controls. The observed responses are hypothesized to be somehow related to the adherence of NPs on the carapace and digestive tract of the daphnids, verified by scanning electron microscope (SEM) imaging. Although not conclusive, the number of offspring exposed to NPs was decreased compared to the control, but not in the CAF + NPs treatment indicating an antagonistic effect of the mixture that requires further testing. This study contributes important information towards the understanding of sublethal impacts of CAF-NP mixtures on freshwater invertebrates and the corresponding ecological consequences of behavior changes.