Fate of Ag-NPs in Sewage Sludge after Application on Agricultural Soils Ana E. Pradas del Real,* ,† Hiram Castillo-Michel, ‡ Ralf Kaegi, § Brian Sinnet, § Vale ́ rie Magnin, † Nathaniel Findling, † Julie Villanova, ∥ Marie Carrie ̀ re, ⊥,# Catherine Santaella, ¶ Alejandro Ferna ́ ndez-Martı ́ nez, † Cle ́ ment Levard, ∇ and Ge ́ raldine Sarret † † ISTerre (Institut des Sciences de la Terre), Universite ́ Grenoble Alpes and CNRS, 38041 Grenoble, France ‡ ID21, ESRF-The European Synchrotron, CS40220, 38043 Grenoble Cedex 9, France § Eawag, Particle Laboratory, Dü bendorf 8600, Switzerland ∥ ID16b, ESRF-The European Synchrotron, CS40220, 38043 Grenoble Cedex 9, France ⊥ Universite ́ Grenoble Alpes, INAC-SCIB, F-38000 Grenoble, France # CEA, INAC-SCIB, F-38000 Grenoble, France ¶ Lab Ecol Microb Rhizosphere & Environ Extrem, UMR 7265 CEA-CNRS-Aix Marseille Universite ́ , 13108 CEA Cadarache, Saint Paul Les Durance, France ∇ Aix-Marseille Universite ́ , CNRS, IRD, CEREGE UM34, 13545, Aix en Provence, France * S Supporting Information ABSTRACT: The objective of this work was to investigate the fate of silver nanoparticles (Ag-NPs) in a sludge-amended soil cultivated with monocot (Wheat) and dicot (Rape) crop species. A pot experiment was performed with sludges produced in a pilot wastewater treatment plant containing realistic Ag concentrations (18 and 400 mg kg −1 , 14 mg kg −1 for the control). Investigations focused on the highest dose treatment. X-ray absorption spectroscopy (XAS) showed that Ag 2 S was the main species in the sludge and amended soil before and after plant culture. The second most abundant species was an organic and/or amorphous AgS phase whose proportion slightly varied (from 24% to 36%) depending on the conditions. Micro and nano X-ray fluorescence (XRF) showed that Ag was preferentially associated with S-rich particles, including organic fragments, of the sludge and amended soils. Ag was distributed as heteroaggregates with soil components (size ranging from ≤0.5 to 1−3 μm) and as diffused zones likely corresponding to sorbed/complexed Ag species. Nano-XRF evidenced the presence of mixed metallic sulfides. Ag was weakly exchangeable and labile. However, micronutrient mobilization by plant roots and organic matter turnover may induce Ag species interconversion eventually leading to Ag release on longer time scales. Together, these data provide valuable information for risk assessment of sewage sludge application on agricultural soils. ■ INTRODUCTION Silver NPs (Ag-NPs) are one of the most prevalent metallic nanoparticles in consumer products due to their antimicrobial properties. 1 More than 244 consumer products containing Ag- NPs have been listed, including cosmetics, paints, fabrics, food containers, etc. (http://www.nanotechproject.org/). Ag-NPs are easily released from many of these products, for example from clothes during laundry, 2,3 from paints used in outdoor facades, 4 or from Ag containing commercial aerosols. 5 The majority of the released Ag-NPs is discharged into the municipal sewer system and transported to wastewater treatment plants (WWTPs). Therefore, WWTPs are considered as major hubs controlling the fluxes of NPs into surface waters. 6 WWTPs are very efficient at removing Ag-NPs from wastewater and concentrating Ag in the sewage sludge, with percentages of retention of Ag higher than 90%. 7−10 According to the European Environment Agency, about 50% of sewage sludge is used for agriculture and soil conditioning (data forecasted for 2005 11 ). Thus, sewage sludge is a major source of Ag for terrestrial ecosystems. 12 The current regulation imposes threshold values for some metals (not Ag) Received: September 17, 2015 Revised: January 5, 2016 Accepted: January 12, 2016 Published: January 12, 2016 Article pubs.acs.org/est © 2016 American Chemical Society 1759 DOI: 10.1021/acs.est.5b04550 Environ. Sci. Technol. 2016, 50, 1759−1768