Effects of Solution Chemistry on the Bactericidal Effects of Silver Nano Particles against Gordonia sp.

Silver nano particles (NPs) are the largest and fastest growing category of nanotechnology-based medicines and consumer products. Silver can be highly toxic to some aquatic organisms and as an antibiotic may also damage or alter the most abundant and vulnerable beneficial microbial communities in the environment, such as Gordonia sp. However, considering the complex chemical background of natural surface water, the silver NPs can have complicated processes with the background chemicals such as chloride, surfactants, and dissolved natural organic matters (NOM). The results show that the average particle size and dispersivity of silver NPs play an important role in the toxicity of silver NPs. Aggregation is signification for silver NPs in DI water. However, the presence of 3 mM sodium dodecyl sulfate (SDS) or 8 mg/L Suwannee river NOM reduced the aggregation of silver NPs apparently. Overall, the degree of aggregation increased in the order of 3 mM SDS < 8 mg/L NOM < DI water <10 mM NaCl <10 mM NaNO₃. When the silver NPs had an elevated concentration from 7.3 to 29.2 mg/L in DI water, the log inactivation of the Gordonia sp. increased from 0.16±0.04 to 0.45±0.13. However, the log inactivation rate increased to 1.40±0.26 and 0.87±0.12 in the presence of 3 mM SDS or 8 mg/L NOM, respectively with 29.2 mg/L silver NPs. On the other hand, 10 mMNaCl reduced the log inactivation rate to 0.07±0.07 due to causing moderate aggregation of silver NPs and forming likely less toxic silver chloride species.