Uptake and impact of silver nanoparticles on the growth of an estuarine dinoflagellate, Prorocentrum minimum

Abstract

Silver nanoparticles (AgNPs) are widely used and have been shown to have relatively high inherent toxicity to a range of living organisms including fish, annelids, daphnia and algae. AgNPs capped with either citrate (cit-AgNPs) or polyvinylpyrrolidone (PVP; PVP-AgNPs) were exposed to the estuarine dinoflagellate Prorocentrum minimum at a range of concentrations (1–1000 μg L−1). Transformations of the AgNPs (e.g. dissolution), along with their uptake and biological effects were measured. DLS and TEM measurements indicated a particle diameter of 15 nm for both particle types. A multi-method approach showed that both particle types underwent rapid and concentration-dependent dissolution and agglomeration. The effects were most apparent for the cit-AgNPs. With a larger total Ag addition, a larger percentage and mass of Ag was operationally defined as internalized in or strongly bound to cells, regardless of capping agent. Exposure to AgNP concentrations of 50–100 μg L−1 significantly decreased cellular growth after 72 h resulting in EC50 values of 60.5 μg L−1 (cit-AgNP), 67.1 μg L−1 (PVP-AgNP), and 30.3 μg L−1 (AgNO3(aq) control). The calculated no observed effect concentrations (NOEC) were 24.0, 19.0, 0.2 μg L−1 for cit-AgNP, PVP-AgNP and AgNO3 respectively. Using a predicted exposure concentration (PEC) of 0.116 ng L−1 for nano-Ag in the environment and predicted no effect concentrations (PNEC) of 0.02, 0.02, 0.002 μg L−1 (respectively), PEC/PNEC risk assessment ratios of <1 were determined for all treatments. This indicated no immediate concern for AgNPs toxicity to P. minimum.