In Vivo Toxicity of Silver Nanoparticles in the Marine Rotifer Brachionus plicatilis: Integrating Metabolic Activity and Generation of Reactive Oxygen Species

Silver nanoparticles (AgNPs) have been widely employed across various industrial, medical, and consumer applications due to their unique biocidal properties, raising concerns about their potential impact on biota such as planktonic microinvertebrates, which, in turn, necessitates the rapid development of in vivo nanotoxicological bioassays. Here, we combined physicochemical particle characterization with organismal responses to assess the in vivo nanotoxicity of chemically synthesized AgNPs in the marine rotifer Brachionus plicatilis (Ploimida, Brachionidae). Particles were fully characterized by dynamic light scattering (hydrodynamic diameter and polydispersity), zeta potential, transmission electron microscopy, and UV–Vis spectroscopy in both stock and exposure media. Rotifers were exposed to low AgNP concentrations: 0 (control), 2, and 20 µg/L. After a 24 h exposure, in vivo metabolic activity was quantified via resazurin reduction. Reactive oxygen species (ROS) were measured using the fluorescent probe H2DCF-DA (excitation 485 nm, emission 530 nm), quantified by fluorimeter and fluorescence microscopy. Results showed that AgNP exposure decreased ROS levels at both tested concentrations, a finding that can be linked to reduced aerobic metabolic activity in the rotifers. These findings demonstrate that B. plicatilis provides a rapid and sensitive in vivo toxicity assessment that integrates metabolic and ROS endpoints for nano-ecotoxicity evaluations.