Seasonal Temperature Oscillations Drive Contrasting Arsenic and Antimony Mobilization in a Mining‐Impacted River System

Abstract

Arsenic (As) and antimony (Sb) speciation and mobility in river systems can be influenced by the redox conditions of benthic and hyporheic zone sediments. However, our understanding of how temperature fluctuations influence riverine As and Sb mobility over diel and seasonal time frames, via moderation of sediment redox conditions, is poorly constrained. Here we compare diel and seasonal water quality data from a river system contaminated with As and Sb with results from sediment-water incubations conducted at temperatures spanning 8°C to 32°C under low-dissolved oxygen conditions. Higher incubation temperatures caused faster microbial respiration, lower redox potential, and greater As aq concentrations, coincident with reduction of As(V), Mn (III/IV), Fe (III), and SO 4 2−. Initial rates of As 3+ aq formation increased exponentially with temperature (Q 10 = 3.3 ± 0.5) and were positively correlated with microbial respiration (r 2 = 0.99, P < 0.01). In contrast, Sb aq displayed an initially negative and comparatively weak overall temperature dependence during incubations. In river waters, diel mobilization of reduced species (As 3+ aq and Fe 2+ aq) and contrasting attenuation of Sb was coincident with lower redox potential during nightly respiration cycles. Distinct seasonal oscillations in river water As aq were exponentially correlated with temperature (r 2 = 0.68, P < 0.01), whereas Sb aq was not. These characteristics reflect the fundamental role of anaerobic metabolism (as influenced by temperature) within benthic and hyporheic zone sediments as a key driver of contrasting riverine As and Sb mobility. The findings imply that riverine As mobility may be enhanced, while Sb mobility possibly attenuated, by eutrophication or by elevated stream temperatures due to a warming climate.

Arsenic-Imposed Effects on Schwertmannite and Jarosite Formation in Acid Mine Drainage and Coupled Impacts on Arsenic Mobility

“…Arsenic XANES data were collected using the XAS beamline at the Australian Synchrotron, as described previously. 21 Fluorescence data (on samples diluted with cellulose to 0.1% As) were collected at 4 °K by a 100 element array Ge solidstate detector. The X-ray energy for each sample was calibrated against the first inflection point of the absorption edge of Au(0).…”

“…The relative abundance of As(III) and As(V) in selected solid-phase samples was quantified by linear combination fitting of XANES spectra against As(V) and As(III) reference standards. 21…”

“…Microbially mediated oxidation of soluble Fe­(II) in AMD into less soluble Fe­(III) leads to oversaturation with respect to Fe­(III) minerals. Initially, high levels of oversaturation kinetically favor the formation of poorly ordered Fe­(III) phases, such as schwertmannite [Fe 8 O 8 (OH) 6 SO 4 ]. − Poorly ordered hydrous Fe­(III)–As­(V) oxides or hydroxysulfates may also form from waters with high As­(V)/Fe­(III) ratios. − Over time, crystalline Fe­(III) minerals such as goethite (αFeOOH), jarosite [KFe 3 (SO 4 ) 2 (OH) 6 ], and scorodite (FeAsO 4 ·2H 2 O) may replace the initial poorly ordered phases. ,− These minerals can be important host phases for As under acidic-oxidizing conditions, yet may act as As sources under reducing conditions (e.g., as a result of burial in the presence of labile organic matter) and/or higher pH conditions (e.g., as a result of AMD neutralization). − …”

Morphology, Mineralogy, and Chemistry of Ocherous Precipitate Aggregates Downstream of an Abandoned Mine Site

“…Based on both the decrease in Sb concentration in the stream waters and low Sb contents in the aggregate, other solid phases may be controlling Sb uptake. A possible candidate for Sb uptaker is organic matter in the stream, as inferred from Johnston [4] and Ratié [8]. In addition, the Fe-oxyhydroxysulfate mineral schwertmannite [7] and amorphous iron and manganese oxides [2] can adsorb Sb, whereas the ferrihydrite in this study area cannot.…”

“…Precipitates formed by the dissolution and oxidation of iron and aluminum-containing minerals often occur downstream of abandoned and/or uncontrolled mine sites. Precipitates occur on river sediments [1][2][3][4], below and/or on the sides of the dam water outflow [5][6][7], on riverbanks [8], and in cemented layers, such as hardpans [9]. The precipitates effectively adsorb heavy metal ions, such as As and Sb, and inhibit the outflow of these ions downstream.…”