Although the well-known antibiotic norfloxacin (NOR) is recognized as an important environmental pollutant, little is known about its impacts on ecological processes, particularly on species interactions. In this paper, we quantified Daphnia magna (Crustacea, Cladocera) responses in mortality rate at lethal NOR concentrations (0, 25, 50, 100, 200, 300 and 400 mg L⁻¹), and in heartbeat rate, swimming behavior and feeding rate (on the green alga Chlorella pyrenoidosa) at sublethal NOR concentrations (0, 25, 50 and 100 mg L⁻¹) to determine the effects of this antibiotic in plankton systems. In 96-h-long lethal experiment, mortality rates of D. magna increased significantly with increasing NOR concentration and exposure time. In sublethal experiments, heartbeat rate decreased, while time ratio of vertical to horizontal swimming (TVH) and the duration of quiescence increased in D. magna individuals exposed to increasing NOR concentrations after 4 and 12 h of exposure. These collectively led to decreases in both average swimming ability and feeding rate, consistent with the positive relationship between average swimming ability and feeding rate. Overall, results indicate that, by affecting zooplankton heartbeat rate and behavior, NOR decreased feeding efficiency of D. magna even at low doses, therefore, it might seriously compromise ecosystem health and function.

The widespread use of silver nanoparticles (AgNPs) is becoming a growing concern because of the risk they pose to the ecological environment and human health. Unfortunately, little is known about how AgNPs' toxicity affects the mechanisms of metabolite shift in aquatic organisms. The aim of this work is thus to study systematically the cellular metabolism of the cyanobacteria Microcystis aeruginosa upon exposure to AgNPs by using metabolomics based on non-targeted liquid chromatography and mass spectrometry. The results reveal that a total of 97 biochemical metabolites and 16 specific metabolic pathways are significantly altered by exposure to AgNPs, many of which are associated with cellular stress response. Importantly, a metabolic analysis identified some novel metabolic pathways that are specifically regulated by AgNPs, including arginine and proline metabolism, indole alkaloid biosynthesis, and phospholipid metabolism (phosphatidylinositol-4,5-bisphosphate). Further examination revealed that exposure to AgNPs elevates superoxide dismutase activity and malondialdehyde generation, damages the thylakoids, and interrupts the endocytosis process in algae cells. Together, the manifestation of differential metabolic profiles combined with the perturbation of physiological indicators upon AgNP exposure is taken as evidence of damage to photosynthesis and membranes. These results provide holistic information about complex disturbances in metabolite profiles of M. aeruginosa upon exposure to AgNPs and provide new insights into the mechanisms of AgNPs' toxicity in the aquatic environment.