Using FlFFF and aTEM to determine trace metal–nanoparticle associations in riverbed sediment

Abstract

Environmental context. Determining associations between trace metals and nanoparticles in contaminated systems is important in order to make decisions regarding remediation. This study analysed contaminated sediment from the Clark Fork River Superfund Site and discovered that in the <1-µm fraction the trace metals were almost exclusively associated with nanoparticulate Fe and Ti oxides. This information is relevant because nanoparticles are often more reactive and show altered properties compared with their bulk equivalents, therefore affecting metal toxicity and bioavailability.Abstract. Analytical transmission electron microscopy (aTEM) and flow field flow fractionation (FlFFF) coupled to multi-angle laser light scattering (MALLS) and high-resolution inductively coupled plasma mass spectroscopy (HR-ICPMS) were utilised to elucidate relationships between trace metals and nanoparticles in contaminated sediment. Samples were obtained from the Clark Fork River (Montana, USA), where a large-scale dam removal project has released reservoir sediment contaminated with toxic trace metals (namely Pb, Zn, Cu and As) which had accumulated from a century of mining activities upstream. An aqueous extraction method was used to recover nanoparticles from the sediment for examination; FlFFF results indicate that the toxic metals are held in the nano-size fraction of the sediment and their peak shapes and size distributions correlate best with those for Fe and Ti. TEM data confirms this on a single nanoparticle scale; the toxic metals were found almost exclusively associated with nano-size oxide minerals, most commonly brookite, goethite and lepidocrocite.

Analysis of engineered nanomaterials in complex matrices (environment and biota): General considerations and conceptual case studies

“…For metal oxides such as TiO 2 or CeO 2 , the background concentrations are relatively high, as shown previously, and both actually appear as natural nanoparticles in sediments and soils (Plathe et al [64] and Fig. 1).…”

“…Attempts at quantification have been based on bulk water analyses and transforming these values into particle number concentrations from the combination of EM-determined particle size distributions and particle properties [62]. Natural Ti-bearing nanoparticles have been identified in river sediment [64], and at the investigated site they mainly appear in the brookite form.…”

“…1). These natural nanoparticles showed association with thorium in the EDS analysis [64]. The challenge to identify TiO 2 and CeO 2 ENPs as being of anthropogenic/engineered origin and to quantify further the amount of these ENPs arises from several complicating factors.…”

“…First, the abundance of ENPs is expected to be very low compared with the natural background concentrations of Ti and Ce. Second, these elements may occur in nanoparticulate form in nature [64], and the ionic forms of these elements tend to immediately adsorb to other natural surfaces. Finally, there is great variation in the natural background concentrations of these elements.…”

Stability of nTiO 2 particles and their attachment to sand: Effects of humic acid at different pH

“…Nanoparticles are toxic to mice, rats, aquatic organisms and human cells (HundRinke and Simon, 2006;Wiesner et al, 2006;Warheit et al, 2007;Battin et al, 2009;Brunet et al, 2009;Liu et al, 2009;Madl and Pinkerton, 2009), and their toxicity are much stronger than bulk materials due to their high surface areas. Besides, another major concern about nanoparticles is their ability to associate with other dissolved contaminants in groundwater, which might facilitate the transport of contaminants in sub-surface environment (Grolimund and Borkovec, 2005;Karathanasis et al, 2005;Sun et al, 2007;Zhang et al, 2007;Plathe et al, 2010;Wang et al, 2014;Wang et al, 2015). Therefore, our limited knowledge on their potential environmental and health effects has caused many public concerns.…”