Accumulation Kinetics and Gut Microenvironment Responses to Environmentally Relevant Doses of Micro/Nanoplastics by Zooplankton Daphnia Magna

Microplastics are emerging pollutants that have been widely reported in aquatic ecosystems. Based on the analysis of environmentally relevant concentrations of microplastics in global freshwater systems, herein, we employed aggregated-induced emission (AIE) microplastic fluorogens and imaged and quantified the bioaccumulation of differentially charged micro- (20 μm)/nano- (200 nm) plastics (MNPs) in zooplankton Daphnia magna. We found that all particles of different sizes and charges were readily ingested, especially larger-sized and positively charged MNPs, with over 50% of the ingested particles accumulating in the gut. Bioaccumulation of MNPs reached 50% of steady-state condition within 1 h. The presence of algae inhibited the ingestion and depuration of MNPs. To further demonstrate the effects of such accumulation on gut health, we further applied the AIE probes for visualizing the pH and esterase in the digestive tract, as well as the gut inflammation. An accumulation of MNPs in D. magna significantly and rapidly induced the acidification of gut pH while inducing esterase activity. The NPs apparently induced gut inflammation in contrast to the MPs, demonstrating the size-dependent effects on oxidative stress. Our results highlighted that MNP exposure at environmentally relevant concentrations perturbed the microenvironments of zooplankton guts, which may significantly affect their digestion and assimilation of food materials as well as contaminant uptake.