Selective ingestion and response by Daphnia magna to environmental challenges of microplastics

Our current understandings of the effects of microplastics and nanoplastics (MNPs) on aquatic animals are predominantly based on the single types of plastic particles. In the present study, we employed the highly fluorescent MNPs that incorporated aggregation-induced emission fluorogens and investigated the selective ingestion and response of Daphnia exposed to different types of plastics at environmentally relevant concentrations simultaneously. When daphnids were exposed to a single MNP, D. magna ingested them instantly in significant amounts. However, even low concentrations of algae had a significant negative impact on the MNP uptake. Specifically, algae caused the MPs to pass through the gut faster, reduced acidification and esterase activity, and changed the distribution of MPs in the gut. In addition, we also quantified the influences of size and surface charge on the selectivity of D. magna. The daphnids selectively ingested larger and positively charged plastics. MPs effectively reduced the uptake of NP and increased its gut passage time. Aggregation of positively and negatively charged MNPs also influenced the gut distribution and increased the gut passage time. The positively charged MPs accumulated in the middle and posterior gut, while aggregation of MNPs also increased acidification and esterase activity. These findings provided fundamental knowledge on the selectivity of MNPs and the microenvironmental responses of zooplankton guts.