title: Transformation of AgCl nanoparticles in a sewer system--A field study.
abstract: Silver nanoparticles (Ag-NP) are increasingly used in consumer products and their release during the use phase may negatively affect aquatic ecosystems. Research efforts, so far, have mainly addressed the application and use of metallic Ag(0)-NP. However, as shown by recent studies on the release of Ag from textiles, other forms of Ag, especially silver chloride (AgCl), are released in much larger quantities than metallic Ag(0). In this field study, we report the release of AgCl-NP from a point source (industrial laundry that applied AgCl-NP during a piloting phase over a period of several months to protect textiles from bacterial regrowth) to the public sewer system and investigate the transformation of Ag during its transport in the sewer system and in the municipal wastewater treatment plant (WWTP). During the study period, the laundry discharged ~85 g of Ag per day, which dominated the Ag loads in the sewer system from the respective catchment (72-95%) and the Ag in the digested WWTP sludge (67%). Combined results from electron microscopy and X-ray absorption spectroscopy revealed that the Ag discharged from the laundry to the sewer consisted of about one third AgCl and two thirds Ag2S, both forms primarily occurring as nanoparticles with diameters<100 nm. During the 800 m transport in the sewer channel to the nearby WWTP, corresponding to a travel time of ~30 min, the remaining AgCl was transformed into nanoparticulate Ag2S. Ag2S-NP also dominated the Ag speciation in the digested sludge. In line with results from earlier studies, the very low Ag concentrations measured in the effluent of the WWTP (<0.5 μg L(-1)) confirmed the very high removal efficiency of Ag from the wastewater stream (>95%).
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, 8600 Dübendorf, Switzerland. Electronic address: ralf.kaegi@eawag.ch.
authors.forename: Ralf
authors.initials: R
authors.lastname: Kaegi
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, 8600 Dübendorf, Switzerland.
authors.forename: Andreas
authors.initials: A
authors.lastname: Voegelin
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, 8600 Dübendorf, Switzerland.
authors.forename: Brian
authors.initials: B
authors.lastname: Sinnet
authors.affiliation: KUSTER+HAGER Group, Oberstrasse 222, 9014 St. Gallen, Switzerland.
authors.forename: Steffen
authors.initials: S
authors.lastname: Zuleeg
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, 8600 Dübendorf, Switzerland.
authors.forename: Hansruedi
authors.initials: H
authors.lastname: Siegrist
authors.affiliation: HSR University of Applied Sciences, Institute of Environmental and Process Engineering (UMTEC), Oberseestrasse 10, 8640 Rapperswil, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Burkhardt
mesh_terms: D004784:Environmental Monitoring; D008956:Models, Chemical; D053758:Nanoparticles / Q000032:analysis* / Q000737:chemistry; D012722:Sewage; D018030:Silver Compounds / Q000032:analysis* / Q000737:chemistry; D062065:Wastewater / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry
chemical_list: D012722:Sewage; D018030:Silver Compounds; D062065:Wastewater; D014874:Water Pollutants, Chemical; C037548:silver chloride
keywords: Sewer; Silver chloride; Silver nanoparticles; Silver sulfide; Speciation; Transformation; Waste water