http://informahealthcare.com/nan ISSN: 1743-5390 (print), 1743-5404 (electronic) Nanotoxicology, Early Online: 1–10 ! 2014 Informa UK Ltd. DOI: 10.3109/17435390.2014.963724 ORIGINAL ARTICLE Uptake and elimination kinetics of silver nanoparticles and silver nitrate by Raphidocelis subcapitata: The influence of silver behaviour in solution Fabianne Ribeiro 1 , Julia ´n Alberto Gallego-Urrea 2 , Rhys M. Goodhead 3 , Cornelis A. M. Van Gestel 4 , Julian Moger 5 , Amadeu M. V. M. Soares 1 , and Susana Loureiro 1 1 Department of Biology & CESAM, University of Aveiro, Aveiro, Portugal, 2 Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden, 3 Department of Biosciences, Ecotoxicology and Aquatic Biology Research Group, College of Life and Environmental Sciences, University of Exeter, Devon, UK, 4 Department of Ecological Science, Faculty of Earth and Life Sciences, VU University. De Boelelaan, Amsterdam, The Netherlands, and 5 Department of Physics, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK Abstract Raphidocelis subcapitata is a freshwater algae species that constitutes the basis of many aquatic trophic chains. In this study, R. subcapitata was used as a model species to investigate the kinetics of uptake and elimination of silver nanoparticles (AgNP) in comparison to silver nitrate (AgNO 3 ) with particular focus on the Ag sized-fractions in solution. AgNP used in this study were provided in a suspension of 1 mg Ag/l, with an initial size of 3–8 nm and coated with an alkane material. Algae was exposed for 48 h to both AgNP and AgNO 3 and sampled at different time points to determine their internal Ag concentration over time. Samples were collected and separated into different sized fractions: total (Ag tot ), water column Ag (Ag water ), small particulate Ag (Ag small.part. ) and dissolved Ag (Ag dis ). At AgNO 3 exposures algae reached higher bioconcentration factor (BCF) and lower elimination rate constants than at AgNP exposures, meaning that Ag is more readily taken up by algae in its dissolved form than in its small particulate form, however slowly eliminated. When modelling the kinetics based on the Ag dis fraction, a higher BCF was found. This supports our hypothesis that Ag would be internalised by algae only in its dissolved form. In addition, algae images obtained by Coherent Anti-stokes Raman Scattering (CARS) microscopy demonstrated large aggregates of nanoparticles external to the algae cells with no evidence of its internalisation, thus providing a strong suggestion that these AgNP were not able to penetrate the cells and Ag accumulation happens through the uptake of Ag ions. Keywords Bioconcentration factor, Raphidocelis subcapitata, silver nanoparticles, toxicokinetics History Received 19 March 2014 Revised 12 August 2014 Accepted 25 August 2014 Published online 13 October 2014 Introduction Algae play a vital role in aquatic ecosystems, due to their major function as primary producers at the bottom of the trophic chain. Consequently, it is likely that any alteration of the algae community may be reflected at higher trophic levels and accordingly impact on the functioning of the ecosystem. For this reason, algae are often used as a model indicator species in the risk assessment of chemicals (Lewis, 1990; Pe ´rez et al., 2010, 2011). As the nanotechnology market expands, the production of nanomaterials and nanoparticles (NP) is rapidly increasing to supply the growing demand (Keller et al., 2013; Roco, 2011). Therefore, it is a natural assumption that nanoparticles and their transformation products, e.g. silver sulphide and silver chloride (Levard et al., 2012), will be present in the environment at some point, from production and application of nanoparticle-containing products to their final use and disposal (Benn & Westerhoff, 2008; Nowack et al., 2011). The entrance of silver nanoparticles (AgNP) into the environment is predicted to commonly occur as colloidal silver, i.e. in a size range between 1 and 1000 nm and eventually result in a suspension containing metallic silver particles and Ag ions (Bhatt & Tripathi, 2011). Moreover, silver nanoparticles will likely be transformed into silver sulphide (Ag 2 S) and silver chloride (AgCl) under environ- mental conditions (Levard et al., 2012; Wang et al., 2012). Today AgNP are among the most widely applied nanoparticles on the market due to their inherent antimicrobial properties (Kim et al., 2007; PEN – Project on Emerging Technologies, 2014). Before the advent of large-scale usage of nanotechnology, silver was already considered as one of the most toxic metals present in aquatic ecosystems, even at the low concentrations found in natural waters (Ratte, 1999; Seltenrich, 2013). These aspects have drawn attention to the toxicity of AgNP and Ag + to model species in aquatic ecotoxicology. There are many eco- toxicological studies demonstrating that AgNP induce negative effects in key species, such as algae (Oukarroum et al., 2012; Ribeiro et al., 2014), zooplankton (Wang et al., 2012; Zhao & Wang, 2010, 2011;) and fish (Choi et al., 2010; Farkas et al., 2011). The interaction of Ag with algae cells depends on the size of pores across the cell wall as well as the state of aggregation of Correspondence: Fabianne Ribeiro, Department of Biology & CESAM, University of Aveiro, Campus Universita ´rio de Santiago, 3810-093 Aveiro, Portugal. E-mail: ribeiro.f@ua.pt Susana Loureiro, Department of Biology & CESAM, University of Aveiro, Campus Universita ´rio de Santiago, 3810-093 Aveiro, Portugal. E- mail: sloureiro@ua.pt Nanotoxicology Downloaded from informahealthcare.com by Universidade de Aveiro on 10/13/14 For personal use only.