Water chemistry, exposure routes and metal forms determine the bioaccumulation dynamics of silver (ionic and nanoparticulate) in Daphnia magna

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.