Silver Nanoparticles Inhibit Sodium Uptake in Juvenile Rainbow Trout (Oncorhynchus mykiss) Aaron G. Schultz, †,# Kimberly J. Ong, †,# Tyson MacCormack, ‡ Guibin Ma, § Jonathan G. C. Veinot, §,∥ and Greg G. Goss* ,†,∥ † Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6E4W1 ‡ Department of Chemistry and Biochemistry, Mount Allison University, Sackville, New Brunswick, Canada E4L1G8 § Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G2G2 ∥ Edmonton Research Facilities, National Institute for Nanotechnology, 11421 Saskatchewan Drive, Edmonton, Alberta, Canada T6G2M9 ABSTRACT: The silver ion (Ag + ) is well documented to be a potent inhibitor of sodium (Na + ) transport in fish. However, it has not been determined whether silver nanoparticles (Ag NPs) elicit this same effect and, if so, if the NP itself and/or the dissociation of ionic Ag + causes this effect. Citrate-capped Ag NPs were dialyzed in water to determine the dissolution rate of ionic Ag + from the NPs and the maximum concentration of free Ag + released from the NPs was used as a paired Ag + control to distinguish NP effects from ionic metal effects. The maximum concentration of ionic Ag + released from these NPs over 48 h was 0.02 μgl −1 . Juvenile rainbow trout were exposed to 1.0 mg l −1 citrate-capped Ag NPs and dialyzed citrate-capped Ag NPs or 10 μgl −1 and 0.02 μgl −1 ionic Ag + (as AgNO 3 ) as controls. Both nondialyzed and dialyzed Ag NPs and 10 μgl −1 ionic Ag + significantly inhibited unidirectional Na + influx by over 50% but had no effect on unidirectional Na + efflux. Na + ,K + -ATPase was significantly inhibited by the Ag NPs with no discernible effect on carbonic anhydrase activity. This study is the first to show that sodium regulation is disrupted by the presence of citrate-capped Ag NPs, and the results suggest that there are nanospecificeffects. ■ INTRODUCTION Nanotechnology is a multibillion dollar commercial industry that is rapidly expanding due to increased production efficiency and heightened development of nanomaterials (NMs). Nano- technology is defined as the design, synthesis, characterization, and use of small materials (at least 1−100 nm in one dimension) that have unique properties and functions resulting from their small size. 1,2 A large number of the NMs presently used in consumer products are metal-based nanoparticles (NPs), including Ag + , Cu + , Ti 2+ , Zn 2+ , and Au + . Silver (Ag) NPs are the most widely used due to their unique physicochemical properties and bactericidal function, as well as relatively low manufacturing cost. 4 The Woodrow Wilson database currently lists 315 consumer products that contain Ag NPs, including clothing, personal care products, wound dressings, teddy bears, washing machines, and air purifiers. 5 Increased production of Ag NP-containing products will result in greater release of these particles and resultant ionic Ag + into aquatic environments. Recent studies demonstrated ionic Ag + and Ag NP release into wastewater from socks, 6 washing machines, 7 fabrics, 8 facades, 9 athletic shirts, toothpaste, as well as shampoo and detergent. 10 Estimates indicate that one household could potentially release 470 μg of ionic Ag + into the sewer daily from Ag NP-containing products, 10 and, using SEM, these authors confirmed that Ag NPs are already present in wastewater. An expansive body of research has detailed the toxic effects and bioavailability of ionic Ag + on aquatic organisms. 11−14 Ag + may compete with Na + uptake across the apical membrane of the gills; 15 however, it is unlikely that this phenomena would occur with Ag NPs as the diameter of the channels would not permit NPs to enter. 3 A number of in vivo studies have demonstrated inhibition of Na + uptake and transporter activity in fish during exposure to ionic Ag +16,17 and it has been suggested this was attributable to inhibition of both carbonic anhydrase (CA) and Na + ,K + -ATPase 18 (NKA). In vitro studies have also confirmed acute ionic Ag + exposure in freshwater rainbow trout causes a reduction in Na + and Cl − uptake across the gills by inhibiting NKA and CA activity within mitochondrial-rich cells. 19,20 Received: May 3, 2012 Revised: August 14, 2012 Accepted: August 15, 2012 Published: August 15, 2012 Article pubs.acs.org/est © 2012 American Chemical Society 10295 dx.doi.org/10.1021/es3017717 | Environ. Sci. Technol. 2012, 46, 10295−10301