Mediation of arsenic mobility by organic matter in mining-impacted sediment from sub‐Arctic lakes: implications for environmental monitoring in a warming climate

Abstract

Arsenic (As) is commonly sequestered at the sediment–water interface (SWI) in mining-impacted lakes through adsorption and/or co-precipitation with authigenic iron (Fe)-(oxy)hydroxides or sulfides. The results of this study demonstrate that the accumulation of organic matter (OM) in near-surface sediments also influences the mobility and fate of As in sub-Arctic lakes. Sediment gravity cores, sediment grab samples, and porewaters were collected from three lakes downstream of the former Tundra gold mine, Northwest Territories, Canada. Analysis of sediment using combined micro-X-ray fluorescence/diffraction, K-edge X-ray Absorption Near-Edge Structure (XANES), and organic petrography shows that As is associated with both aquatic (benthic and planktonic alginate) and terrestrially derived OM (e.g., cutinite, funginite). Most As is hosted by fine-grained Fe-(oxy)hydroxides or sulfide minerals (e.g., goethite, orpiment, lepidocrocite, and mackinawite); however, grain-scale synchrotron-based analysis shows that As is also associated with amorphous OM. Mixed As oxidation states in porewater (median = 62% As (V), 18% As (III); n = 20) and sediment (median = 80% As (-I) and (III), 20% As (V); n = 9) indicate the presence of variable redox conditions in the near-surface sediment and suggest that post-depositional remobilization of As has occurred. Detailed characterization of As-bearing OM at and below the SWI suggests that OM plays an important role in stabilizing redox-sensitive authigenic minerals and associated As. Based on these findings, it is expected that increased concentrations of labile OM will drive post-depositional surface enrichment of As in mining-impacted lakes and may increase or decrease As flux from sediments to overlying surface waters.

Atomic spectrometry update: review of advances in elemental speciation

“…Arsenic is commonly sequestered at the sediment–water interface in mining-impacted lakes through adsorption and/or co-precipitation with authigenic Fe-(oxy)hydroxides or sulfides. A report by Miller et al 47 found that the accumulation of organic matter in near-surface sediments also influences the mobility and fate of As in sub-Arctic lakes. Sediment gravity cores, sediment grab samples, and porewater were collected from three lakes downstream of the former Tundra Au mine, Northwest Territories, Canada.…”

An analysis of arsenic toxicity's origins, manifestations, and remediation

“…In mining-impacted lakes, As is commonly sequestered at the sediment through adsorption and/or co sulphides (Miller et al, 2022). A mobile and toxic than As(III) under soil oxidizing conditions, because it is strongly adsorbed to Fe hydroxides of soil (Álvarez discharge and natural sources release heavy metals in soil and food crops for animal and human intake (Srivastava et al, 2017).…”

“…impacted lakes, As is commonly sequestered at the sediment-water interface through adsorption and/or co-precipitation with authigenic iron Fe-oxyhydroxides or sulphides (Miller et al, 2022). Arsenate [As(V)] is the predominant form of As and is less mobile and toxic than As(III) under soil oxidizing conditions, because it is strongly adsorbed to Fe hydroxides of soil (Álvarez-Robles et al, 2020).…”