Iron-Rich Nanoparticles in Natural Aquatic Environments

Bjorn von der Heyden,Alakendra Roychoudhury,Satish Myneni

doi:10.3390/min9050287

Bjorn von der Heyden, Alakendra Roychoudhury + Show 1 more

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https://doi.org/10.3390/min9050287

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Journal: Minerals	Publication Date: May 11, 2019
Citations: 10	License type: CC BY 4.0

Affiliation: Stellenbosch University, Princeton University

Abstract

Naturally-occurring iron nanoparticles constitute a quantitatively-important and biogeochemically-active component of the broader Earth ecosystem. Yet detailed insights into their chemical speciation is sparse compared to the body of work conducted on engineered Fe nanoparticles. The present contribution briefly reviews the analytical approaches that can be used to characterize natural Fe nanoparticles, before detailing a dedicated synchrotron-based X-ray spectro-microscopic investigation into the speciation of suspended Fe nanoparticles collected from fluvial, marine, and lacustrine surface waters. Ferrous, ferric and magnetite classes of Fe nanoparticles (10–100 nm) were identified, and all three classes exhibited a high degree of heterogeneity in the local bonding environment around the Fe center. The heterogeneity is attributed to the possible presence of nanoparticle aggregates, and to the low degrees of crystallinity and ubiquitous presence of impurities (Al and organic moieties) in natural samples. This heterogeneity further precludes a spectroscopic distinction between the Fe nanoparticles and the larger sized Fe-rich particles that were evaluated. The presented results provide an important baseline for natural nanoparticle speciation in pristine aquatic systems, highlight the degree of inter-particle variability, which should be parameterized in future accurate biogeochemical models, and may inform predictions of the fate of released engineered Fe nanoparticles as they evolve and transform in natural systems.

Highlights

Iron (Fe) is the most abundant transition metal in the Earth’s crust, with important and biogeochemically-active repositories existing in all four of the Earth’s major subsystems
Given that the production of engineered Fe nanoparticles is expected to increase significantly in forthcoming years (2010 estimates at up to 42,000 t per year [61]), such a study focused on relatively pristine aquatic systems forms an important baseline from which to interpret future environmental change
The most common type of engineered Fe nanoparticle is the Fe0 class of nanoparticles, which are commonly used in environmental remediation efforts [7]

Summary

Introduction

Iron (Fe) is the most abundant transition metal in the Earth’s crust, with important and biogeochemically-active repositories existing in all four of the Earth’s major subsystems (viz. lithosphere, hydrosphere, atmosphere and biosphere). Despite their ubiquity and importance, natural Fe nanoparticles have received relatively limited scientific attention relative to the large body of work that focusses on the synthesis, behavior, stability, toxicity, and fate of engineered Fe nanoparticles (e.g., References [7,10,11]). A recent review presented by Sharma and coworkers [12] highlights that, relative to engineered nanoparticles, environmental inorganic nanoparticles may differ in both their biogeochemical behavior and their respective ecotoxicities. For this to be validated a greater body of work focused on identifying the speciation of natural Fe nanoparticles is required. Examples of previous work include Neubauer et al [13] who use Transmission Electron Microscopy (TEM) to investigate soil

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