Growth inhibition in Raphidocelis subcapita – Evidence of nanospecific toxicity of silver nanoparticles

Abstract

Silver, known for its antibacterial properties and for its toxicity to aquatic organisms, is one of the most frequently used nanomaterials and silver nanoparticles can be found in a range of consumer products as well as medical applications. The present study investigated the toxicity of three different nanomaterials (Mesosilver, NM300K and NM302) and AgNO3, in the algae Raphidocelis subcapitata. Exposures in the low µg L-1 range were combined with characterization of exposure media to determine whether differences in toxicity could be linked to changes in Ag speciation. All tested Ag compounds, except the NM302 Ag rods, reduced growth in the following order AgNO3 ≥ M-Ag > NM300K > NM302 with 50 % effect concentrations of 7.09 (3.83-10.52), 9.7 (range not calculated) and 24.18 (15.66-98.16) µg L-1 , for AgNO3, Mesosilver and NM300K, respectively. Characterization of exposure media showed that both concentration and time influenced the speciation and stability of Ag in test media, regardless of Ag source, and also affected the toxicity to R. subcapitata. In both AgNO3 and Mesosilver exposure the toxicity was correlated with the presence of Ag(I) (< 10 kDa), however levels of Ag(I) were too low to account for the observed Mesosilver effects, indicating a nanospecific contribution. Nanospecific toxicity was also observed for NM300K after 24 h of exposure, however the algae population recovered over time probably due to changes in exposure caused by aggregation of the nanoparticles.