This study aimed to understand how the physicochemical properties of silver nanoparticles (AgNPs) affected its toxicity in the aquatic environment. The morphologies of oleylamine-coated AgNPs (4 nm) under environmental and laboratory water conditions were studied under transmission electron microscopy, and the results showed oleylamine-coated AgNPs formed big aggregates in the environmental water samples after 12 h equilibration. Dynamic light scattering results also showed that oleylamine-coated AgNPs had larger hydrodynamic size in all water samples as compared to its primary size (4 nm). Exposure to oleylamine-coated AgNPs inhibited the growth of Bacillus subtilis (B. subtilis) and reduced its cell viability in Luria-Bertani (LB) broth and 0.85% NaCl, respectively. A dose-dependent toxicity of AgNPs in B. subtilis was observed in laboratorial medium conditions but not in environmental water condition. Low concentration of AgNPs exhibited lower toxicity in environmental water samples as compared to that in laboratorial medium conditions. Separating AgNPs from bacterial suspension through a dialysis membrane enhanced the cell viability of B. subtilis significantly. In the environmental water samples, the AgNPs-bacteria interaction would be reduced with the formation of big aggregates by AgNPs, which consequently decreased its toxicity in aquatic environment.

Keywords: Bacillus subtilis; aquatic toxicity; environmental water samples; laboratorial medium conditions; silver nanoparticles.