title: 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.
authors.affiliation: Environmental Toxicology, Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600, Dübendorf, Switzerland. alexandra.kroll@eawag.ch.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Kroll
authors.affiliation: Ecotoxicology, Acremann Section, NERC Centre for Ecology and Hydrology, Maclean Building, Benson Lane, Crowmarsh Gifford, Wallingford, OX10 8BB, UK.
authors.forename: Marianne
authors.initials: M
authors.lastname: Matzke
authors.affiliation: Faculty Environmental Sciences, Institute for Hydrobiology, Technical University of Dresden, Zellescher Weg 40, 01217, Dresden, Germany.
authors.forename: Marcus
authors.initials: M
authors.lastname: Rybicki
authors.affiliation: Faculty Environmental Sciences, Institute for Hydrobiology, Technical University of Dresden, Zellescher Weg 40, 01217, Dresden, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Obert-Rauser
authors.affiliation: Faculty Environmental Sciences, Institute for Hydrobiology, Technical University of Dresden, Zellescher Weg 40, 01217, Dresden, Germany.
authors.forename: Corinna
authors.initials: C
authors.lastname: Burkart
authors.affiliation: Department of Materials, Oxford University, Begbroke Science Park, Begbroke Hill, Yarnton, Oxford, OX5 1PF, UK.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Jurkschat
authors.affiliation: Department of Animal Ecology, Faculty of Earth and Life Sciences, Institute of Ecological Science, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV, Amsterdam, The Netherlands.
authors.forename: Rudo
authors.initials: R
authors.lastname: Verweij
authors.affiliation: Environmental Toxicology, Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600, Dübendorf, Switzerland.
authors.forename: Linn
authors.initials: L
authors.lastname: Sgier
authors.affiliation: Faculty Environmental Sciences, Institute for Hydrobiology, Technical University of Dresden, Zellescher Weg 40, 01217, Dresden, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Jungmann
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Carl Skottsbergs Gata 22 B, 40530, Gothenburg, Sweden.
authors.forename: Thomas
authors.initials: T
authors.lastname: Backhaus
authors.affiliation: Ecotoxicology, Acremann Section, NERC Centre for Ecology and Hydrology, Maclean Building, Benson Lane, Crowmarsh Gifford, Wallingford, OX10 8BB, UK.
authors.forename: Claus
authors.initials: C
authors.lastname: Svendsen
mesh_terms: D018441:Biofilms / Q000254:growth & development; D018533:Biomass; D001704:Biopolymers / Q000032:analysis*; D000460:Chlorophyta / Q000187:drug effects; D017377:Diatoms / Q000187:drug effects; D017753:Ecosystem; D007477:Ions; D053768:Metal Nanoparticles / Q000633:toxicity*; D059013:Microbial Consortia / Q000187:drug effects*; D012834:Silver / Q000633:toxicity*; D012835:Silver Nitrate / Q000633:toxicity; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D001704:Biopolymers; D007477:Ions; D014874:Water Pollutants, Chemical; D012834:Silver; D012835:Silver Nitrate
keywords: 3D structure; Biofilms; Community ecotoxicology; Extracellular polymeric substances (EPS); Periphyton; Silver nanoparticles