title: Influence of liberated silver from silver nanoparticles on nitrification inhibition of Nitrosomonas europaea.
abstract: The ecotoxicity of silver nanoparticles (Ag-NPs) to wastewater biota, including ammonia oxidizing bacteria (AOB), is gaining increasing interest as the number of products containing Ag-NPs continues to rise exponentially and they are expected to accumulate in wastewater treatment plants. This research demonstrated that the addition order of Ag-NP and the media constituents had a profound influence on the stability of the Ag-NP suspension and the corresponding repeatability of results and sensitivity of Nitrosomonas europaea. N. europaea, a model AOB, was found to be extremely sensitive to ionic silver (Ag(+)) and two sizes of Ag-NPs (20 and 80 nm). Ag(+) exposures resulted in the highest level of toxicity with smaller Ag-NPs (20 nm) being more toxic than larger Ag-NPs (80 nm). The increased sensitivity of N. europaea to smaller Ag-NPs was caused by their higher rates of dissolved silver (dAg) release, via dissolution, due to a greater surface area to volume ratio. dAg was shown to be responsible for the vast majority of the observed Ag-NP toxicity, as determined by abiotic Ag-NP dissolution tests. For the sizes of Ag-NP studied (20 and 80 nm), there appears to be a negligible nanoparticle-specific toxicity. This was further supported by similarities in inhibition mechanisms between Ag(+) and Ag-NP, with both causing decreases in AMO activity and destabilization of the outer-membrane of N. europaea. Finally, equal concentrations of total silver were found to be tightly associated to both Ag(+) and Ag-NP-exposed cells despite Ag-NP concentrations being five times greater, by mass, than Ag(+) concentrations.
authors.affiliation: School of Chemical, Biological and Environmental Engineering, 102 Gleeson Hall, Oregon State University, Corvallis, OR 97331, USA. tyler.radniecki@oregonstate.edu
authors.forename: Tyler S
authors.initials: TS
authors.lastname: Radniecki
authors.forename: Dylan P
authors.initials: DP
authors.lastname: Stankus
authors.forename: Arianne
authors.initials: A
authors.lastname: Neigh
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Nason
authors.forename: Lewis
authors.initials: L
authors.lastname: Semprini
mesh_terms: D053758:Nanoparticles / Q000633:toxicity*; D058465:Nitrification; D043370:Nitrosomonas europaea / Q000378:metabolism*; D010316:Particle Size; D012834:Silver / Q000633:toxicity*
chemical_list: D012834:Silver