The role of nanominerals and mineral nanoparticles in the transport of toxic trace metals: Field-flow fractionation and analytical TEM analyses after nanoparticle isolation and density separation Kelly L. Plathe a,⇑ , Frank von der Kammer b , Martin Hassello ¨v c , Johnnie N. Moore d , Mitsuhiro Murayama e , Thilo Hofmann b , Michael F. Hochella Jr. a a Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA b Department of Environmental Geosciences, University of Vienna, 1090 Vienna, Austria c Department of Chemistry, University of Go ¨ teborg, Go ¨ teborg, Sweden d Department of Geology, University of Montana, Missoula, MT 59812, USA e Department of Materials Science and Engineering, Virginia Tech, Blacksburg, VA 24061, USA Received 29 July 2011; accepted in revised form 9 October 2012; Available online 24 October 2012 Abstract Nanominerals and mineral nanoparticles from a mining-contaminated river system were examined to determine their potential to co-transport toxic trace metals. A recent large-scale dam removal project on the Clark Fork River in western Montana (USA) has released reservoir and upstream sediments contaminated with toxic trace metals (Pb, As, Cu and Zn), which had accumulated there as a consequence of more than a century and a half of mining activity proximal to the river’s headwaters near the cities of Butte and Anaconda. To isolate the high-density nanoparticle fractions from riverbed and bank sediments, a density separation with sodium polytungstate (2.8 g/cm 3 ) was employed prior to a standard nanoparticle extraction procedure. The stable, dispersed nanoparticulate fraction was then analyzed by analytical transmission electron microscopy (aTEM) and flow field-flow fractionation (FlFFF) coupled to both multi-angle laser light scattering (MALLS) and high-resolution, inductively coupled plasma mass spectrometry (HR-ICPMS). FlFFF analysis revealed a size distribution in the nano range and that the elution profiles of the trace metals matched most closely to that for Fe and Ti. aTEM confirmed these results as the majority of the Fe and Ti oxides analyzed were associated with one or more of the trace metals of interest. The main mineral phases hosting trace metals are goethite, ferrihydrite and brookite. This demonstrates that they are likely playing a significant role in dictating the transport and distribution of trace metals in this river system, which could affect the bioavailability and toxicity of these metals. Ó 2012 Elsevier Ltd. All rights reserved. 1. INTRODUCTION Contamination of soils and sediments with trace metals is a worldwide problem stemming from many anthropo- genic activities, such as ore mining, ore processing (e.g. flo- tation and smelting of ores or preparation of nuclear fuels) and burning fossil fuels. Elevated concentrations of trace metals can also stem from natural sources (e.g. arsenic 0016-7037/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.gca.2012.10.029 ⇑ Corresponding author. Current address: EPFL ENAC IIE EML, CE 1 543 (Centre Est), Station 6, CH-1015 Lausanne, Switzerland. Tel.: +41 021 6936 396. E-mail address: kelly.plathe@epfl.ch (K.L. Plathe). www.elsevier.com/locate/gca Available online at www.sciencedirect.com Geochimica et Cosmochimica Acta 102 (2013) 213–225