Ion‐release kinetics and ecotoxicity effects of silver nanoparticles

Abstract The environmental toxicity associated with silver nanoparticles (AgNPs) has been a major focus in nanotoxicology. The Ag + released from AgNPs may affect ecotoxicity, although whether the major toxic effect is governed by Ag + ions or by AgNPs themselves is unclear. In the present study, we have examined the ecotoxicity of AgNPs in aquatic organisms, silver ion‐release kinetics of AgNPs, and their relationship. The 48‐h median effective concentration (EC50) values for Daphnia magna of powder‐type AgNP suspensions were 0.75 µg/L (95% confidence interval [CI] = 0.71–0.78) total Ag and 0.37 µg/L (95% CI = 0.36–0.38) dissolved Ag. For sol‐type AgNP suspension, the 48‐h EC50 values for D. magna were 7.98 µg/L (95% CI = 7.04–9.03) total Ag and 0.88 µg/L (95% CI = 0.80–0.97) dissolved Ag. The EC50 values for the dissolved Ag of powder‐type and sol‐type AgNPs for D. magna showed similar results (0.37 µg/L and 0.88 µg/L) despite their differences of EC50 values in total Ag. We observed that the first‐order rate constant ( k ) of Ag + ions released from AgNPs was 0.0734/h at 0.05 mg/L total Ag at 22°C within 6 h. The kinetic experiments and the toxicity test showed that 36% and 11% of sol‐type AgNPs were converted to the Ag + ion form under oxidation conditions, respectively. Powder‐type AgNPs showed 49% conversion rate of Ag + ion from AgNPs. We also confirmed that Ag + ion concentration in AgNP suspension reaches an equilibrium concentration after 48 h, which is an exposure time of the acute aquatic toxicity test. Environ. Toxicol. Chem. 2012;31:155–159. © 2011 SETAC