The recent proliferation of consumer products containing silver nanoparticles (elemental silver < 100nm) may be toxic to bacteria that carry out key ecosystem services, like denitrifying bacteria. Denitrification is the only means of permanently removing excess reactive nitrogen from aquatic ecosystems. Previous studies suggest that nanosilver causes severe oxidative stress and is lethal to bacteria in pure culture. It is unclear whether 1) antimicrobial properties exhibited by nanosilver in the laboratory persist in ecosystems and whether 2) nanosilver impacts are substantially different from ionic silver impacts.  To address this uncertainty, our study focuses on impacts of nanosilver and ionic silver on potential denitrification rates of denitrifier communities in natural stream sediments. We collected sediments from a forested stream in Durham, NC and pre-incubated them with a range of ionic silver or nanosilver concentrations for seven days before conducting DEA assays to measure potential denitrification rates.

Results/Conclusions

After the seven day pre-incubation, all urban stream sediments exposed to ionic silver exhibited an increase in potential denitrification rates averaging 52 percent greater than controls. In nanosilver amended sediments, however, there was an average decrease of 15 percent, relative to untreated controls. No clear dose response relationship, however, was observed with either ionic silver or nanosilver treatments. Our research suggests that 1) nanosilver released into the environment may continue to negatively affect microbial communities in natural ecosystems, though in an attenuated fashion and 2) the negative impact of nanosilver on the function of microbial communities (e.g., denitrification rates) may be greater than that of ionic silver. Changes in denitrifier community composition, as described by TRFLP data, may provide insight into the mechanism for observed differences in denitrification following treatment.