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Environmental Processes
CHARACTERISTICS AND STABILITY OF INCIDENTAL IRON OXIDE NANOPARTICLES DURING REMEDIATION OF A MINING-IMPACTED STREAM Logan N Rand, and James F. Ranville Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.9b03036 • Publication Date (Web): 26 Aug 2019 Downloaded from pubs.acs.org on August 28, 2019
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Environmental Science & Technology
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CHARACTERISTICS AND STABILITY OF
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INCIDENTAL IRON OXIDE NANOPARTICLES
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DURING REMEDIATION OF A MINING-
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IMPACTED STREAM
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Logan N. Rand; James F. Ranville*
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Department of Chemistry, Colorado School of Mines, 1500 Illinois St., Golden, CO
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80401
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ABSTRACT: Acid mine drainage (AMD) produces nanoparticulate Fe-oxides and sorbed
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toxic metals, such as Cu and Zn. As an indirect product of human activity, these Fe-oxides
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can be classified as incidental nanoparticles (INPs) and their colloidal aggregates.
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Research in nanoparticle fate and transport has advanced with the development of single
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particle inductively coupled plasma-mass spectrometry (spICP-MS), but AMD INPs have
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received little attention. We examined the characteristics and abundance of Fe-oxide
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INPs in an AMD impacted stream over the first six months of remediation. Fe and Cu INP
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concentrations were approximately 107 and 105 particles mL-1, before and after treatment
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respectively. Overall, ~4 Cu-containing INPs were counted for every 100 Fe-containing
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INPs. We also studied surface chemistry changes during the treatment period using
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hematite, a model Fe INP, suspended in filtered field waters. Changes in zeta potential
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and INP size, measured by dynamic light scattering, support that the contaminated
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stream chemistry (low pH, high ionic strength) promoted rapid aggregation while
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improved water quality favored stability. However, the water chemistry and INP stability
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during snowmelt were additionally impacted by electrolyte dilution, the addition of
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dissolved organic matter, and physical scouring. By linking field measurements to
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laboratory experiments, this work explores the effects of surface chemistry on AMD-
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generated INP behavior before and during remediation in a hydrologically-dynamic alpine
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stream. To our knowledge, this is the first investigation of remediation effects on AMD
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INPs and the first use of spICP-MS as a technique to measure them.
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INTRODUCTION
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Acid mine drainage (AMD) generates elevated metal concentrations that can pose
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long-term ecotoxicological and public health risks.1–9 This study provides insights into
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the processes of stream recovery that follow the remediation of AMD inputs. Fe- and Al-
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oxides, formed by AMD, are commonly nanoparticulate (
