Impact of Fe and Ag Nanoparticles on Seed Germination and Differences in Bioavailability During Exposure in Aqueous Suspension and Soil Yehia Sayed El-Temsah, Erik J. Joner Bioforsk Soil and Environment, Frederik A. Dahls vei 20, N-1432 A ˚ s, Norway Received 1 October 2009; revised 9 March 2010; accepted 13 March 2010 ABSTRACT: The potential environmental toxicity of zero-valent iron nanoparticles (nZVI) and three types of nanosilver differing in average particle size from 1 to 20 nm was evaluated using seed germination tests with ryegrass, barley, and flax exposed to 0–5000 mg L 21 nZVI or 0–100 mg L 21 Ag. For nZVI, germination tests were conducted both in water and in two contrasting soils to test the impact of assumed differences in bioavailability of nanoparticles. Inhibitory effects were observed in aqueous suspensions at 250 mg L 21 for nZVI and 10 mg L 21 for Ag. Reduction in shoot growth was a more sensitive endpoint than germination percentage. Complete inhibition of germination was observed at 1000–2000 mg L 21 for nZVI. For Ag, complete inhibition was not achieved. The presence of soil had a modest influence on toxicity, and inhibi- tory effects were observed at 300 mg nZVI L 21 water in soil (equivalent to 1000 mg nZVI kg 21 soil). Com- plete inhibition was observed at 750 and 1500 mg L 21 in sandy soil for flax and ryegrass, respectively, while for barley 13% germination still occurred at 1500 mg L 21 . In clay soil, inhibition was less pro- nounced. Our results indicate that nZVI at low concentrations can be used without detrimental effects on plants and thus be suitable for combined remediation where plants are involved. Silver nanoparticles inhibited seed germination at lower concentrations, but showed no clear size-dependant effects, and never completely impeded germination. Thus, seed germination tests seem less suited for estimation of environmental impact of Ag. # 2010 Wiley Periodicals, Inc. Environ Toxicol 27: 42–49, 2012. Keywords: bioavailability; ecotoxicity; nanoparticles; silver; zero-valent iron INTRODUCTION Within nanotechnology, iron nanoparticles can be used for a range of different applications, including catalysts for car- bon nanotube production (Wong et al., 2005), magnetic flu- ids (Wu et al., 1999), magnetic resonance imaging (MRI) contrast agents (Mornet et al., 2004; Jun et al., 2005), core materials in Ni-Fe batteries, and catalysts and sorbents for environmental remediation (Li et al., 2003; Zhang, 2003). All these applications are in some ways exploiting the altered properties of nanosized iron particles with respect to enhanced surface area and high surface reactivity compared to otherwise identical larger particles. In the case of reme- diation, zero-valent iron (nZVI) is the most relevant type of nanoiron, as its high reduction potential has proven valua- ble for degradation of several organic pollutants, included chlorinated compounds like TCE and atrazine (Liu et al., 2007; Satapanajaru et al., 2008). Silver-based materials have been widely used over the last decades within medicine, electronics, photography, etc. (Ratte, 1999). Even after the widespread replacement of photographic films with numeric cameras, the annual release of silver into the environment from industrial wastes and other emissions has been high. In the US, amounts in the order of 2500 tons year 21 have been reported, out of which 150 tons ended up in sewage sludge and 80 tons have been released into surface waters (Khaydarov et al., Correspondence to: E. J. Joner; e-mail: Erik.Joner@bioforsk.no Contract grant sponsor: The Research Council of Norway Published online 26 May 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/tox.20610  C 2010 Wiley Periodicals, Inc. 42