Water Chemistry, Exposure Routes, and Metal Forms Determine the Bioaccumulation Dynamics of Silver (Ionic and Nanoparticulate) in Daphnia magna

Abstract Treatment wetlands utilize various physical and biological processes to reduce levels of organic contaminants, metals, bacteria, and suspended solids. Silver nanoparticles (AgNPs) are one type of contaminant that can enter treatment wetlands and impact the overall treatment efficacy. Grazing by filter-feeding zooplankton, such as Daphnia magna, is critical to treatment wetland functioning; but the effects of AgNPs on zooplankton are not fully understood, especially at environmentally relevant concentrations. We characterized the bioaccumulation kinetics of dissolved and nanoparticulate (citrate-coated) 109Ag in D. magna exposed to environmentally relevant 109Ag concentrations (i.e., 0.2–23 nmol L−1 Ag) using a stable isotope as a tracer of Ag. Both aqueous and nanoparticulate forms of 109Ag were bioavailable to D. magna after exposure. Water chemistry affected 109Ag influx from 109AgNP but not from 109AgNO3. Silver retention was greater for citrate-coated 109AgNP than dissolved 109Ag, indicating a greater potential for bioaccumulation from nanoparticulate Ag. Feeding inhibition was observed at higher dietary 109Ag concentrations, which could lead to reduced treatment wetland performance. Our results illustrate the importance of using environmentally relevant concentrations and media compositions when predicting Ag bioaccumulation and provide insight into potential effects on filter feeders critical to the function of treatment wetlands. Environ Toxicol Chem 2022;41:726–738. © 2021 SETAC Abstract Overview of experimental approach and key findings from development of biodynamic model comparing exposure of daphnids to dissolved and nanoparticulate silver (Ag). kuf = rate constant of dietborne 109Ag; AE = assimilation efficiency; IR = ingestion rate; ke = rate constant of 109Ag loss; kuw = influx rate constant of 109Ag.