Mixed messages from benthic microbial communities exposed to nanoparticulate and ionic silver: 3D structure picks up nano-specific effects, while EPS and traditional endpoints indicate a concentration-dependent impact of silver ions

Abstract

Silver nanoparticles (AgNP) are currently defined as emerging pollutants in surface water ecosystems. Whether the toxic effects of AgNP towards freshwater organisms are fully explainable by the release of ionic silver (Ag+) has not been conclusively elucidated. Long-term effects to benthic microbial communities (periphyton) that provide essential functions in stream ecosystems are unknown. The effects of exposure of periphyton to 2 and 20 μg/L Ag+ (AgNO3) and AgNP (polyvinylpyrrolidone stabilised) were investigated in artificial indoor streams. The extracellular polymeric substances (EPS) and 3D biofilm structure, biomass, algae species, Ag concentrations in the water phase and bioassociated Ag were analysed. A strong decrease in total Ag was observed within 4 days. Bioassociated Ag was proportional to dissolved Ag indicating a rate limitation by diffusion across the diffusive boundary layer. Two micrograms per liter of AgNO3 or AgNP did not induce significant effects despite detectable bioassociation of Ag. The 20-μg/L AgNO3 affected green algae and diatom communities, biomass and the ratio of polysaccharides to proteins in EPS. The 20-μg/L AgNO3 and AgNP decreased biofilm volume to about 50 %, while the decrease of biomass was lower in 20 μg/L AgNP samples than the 20-μg/L AgNO3 indicating a compaction of the NP-exposed biofilms. Roughness coefficients were lower in 20 μg/L AgNP-treated samples. The more traditional endpoints (biomass and diversity) indicated silver ion concentration-dependent effects, while the newly introduced parameters (3D structure and EPS) indicated both silver ion concentration-dependent effects and effects related to the silver species applied.Electronic supplementary materialThe online version of this article (doi:10.1007/s11356-015-4887-7) contains supplementary material, which is available to authorized users.

Effects of low dose silver nanoparticle treatment on the structure and community composition of bacterial freshwater biofilms

“…Although natural organic matter (NOM) leads to colloidal stabilization of AgNPs at low cation concentrations, NOM can induce the formation of bridging determined aggregates at high cation concentrations [ 7 ]. Consequently, the aggregation of AgNPs can finally result in their sedimentation accompanied by accumulation in microbial biofilms [ 8 ], which serve as a sink for organic and inorganic pollutants. Due to their metabolic and genetic diversity, bacterial biofilm communities play a key role in the production and degradation of NOM; cycling of nitrogen, phosphorous, sulfur and metals [ 9 ]; and transformation and/or degradation of pollutants.…”

“…Pertaining to the effects of AgNPs on bacteria in aquatic environments, a range of habitats, such as marine biofilms [ 14 – 15 ], activated sludge [ 16 – 17 ], surface stream water [ 18 ], and freshwater biofilms [ 8 , 19 ], have been investigated. A reduction in biomass [ 8 , 14 ], alterations in bacterial community composition [ 14 , 17 – 18 ] and reduced metabolic activities [ 18 – 19 ] as a consequence of AgNP exposure have been reported. Contradictory effects have been shown for wastewater biofilms which were highly tolerant to AgNP treatment [ 16 ] and for marine biofilms which were only negligibly affected [ 15 ].…”

Aging reduces the toxicity of pristine but not sulphidised silver nanoparticles to soil bacteria

“…Aging was carried out over 24 h hours to mirror ENP changes under the test conditions and to gain an understanding whether the starting or final particle properties have a greater contribution to their toxicity. Finally, aliquots of the aged total were taken after the 24 h aging period and centrifuged for 3 hours at 20800 g following a method by Kroll et all 2016 36 . Centrifugation at this speed predicts settling of particles > 3 nm according to Stoke's law.…”

Addition of silver nanoparticles has no long‐term effects on natural phytoplankton community dynamics in a boreal lake

“…We analyzed frozen samples on filters to determine the concentration and relative ratios of pigments indicative of different algal groups (Leavitt and Hodgson 2001). We extracted pigment from filters for 24 h in an 80% acetone and 20% methanol solution, then removed filters and dried the samples in the dark with N 2 gas, before resuspension in injection fluid consisting of 70% acetone, 25% ion pairing reagent, and 5% methanol.…”