Electron exchange capacity of pyrogenic dissolved organic matter (pyDOM): complementarity of square-wave voltammetry in DMSO and mediated chronoamperometry in water.

Pyrogenic dissolved organic matter (pyDOM) is derived from black carbon, which is important in the global carbon cycle and other biogeochemical redox processes. The electron-exchange capacity (EEC) of pyDOM has been characterized in water using mediated chronoamperometry (MCA), which gives precise results under specific operational conditions, but the broader significance of these EECs is less clear. In this study, we described a novel but complementary electrochemical approach to quantify EECs of pyDOM without mediation using square-wave voltammetry (SWV) in dimethyl sulfoxide (DMSO).

Influence of Organic Ligands on the Redox Properties of Fe(II) as Determined by Mediated Electrochemical Oxidation.

Fe(II) has been extensively studied due to its importance as a reductant in biogeochemical processes and contaminant attenuation. Previous studies have shown that ligands can alter aqueous Fe(II) redox reactivity but their data interpretation is constrained by the use of probe compounds. Here, we employed mediated electrochemical oxidation (MEO) as an approach to directly quantify the extent of Fe(II) oxidation in the absence and presence of three model organic ligands (citrate, nitrilotriacetic acid, and ferrozine) across a range of potentials () and pH, thereby manipulating oxidation over a broad range of fixed thermodynamic conditions.

Spatial distribution and biogeochemistry of redox active species in arctic sedimentary porewaters and seeps.

Redox active species in Arctic lacustrine sediments play an important, regulatory role in the carbon cycle, yet there is little information on their spatial distribution, abundance, and oxidation states. Here, we use voltammetric microelectrodes to quantify the concentrations of redox-active species at high vertical resolution (mm to cm) in the benthic porewaters of an oligotrophic Arctic lake (Toolik Lake, AK, USA). Mn(II), Fe(II), O, and Fe(III)-organic complexes were detected as the major redox-active species in these porewaters, indicating both Fe(II) oxidation and reductive dissolution of Fe(III) and Mn(IV) minerals.

A durable and inexpensive pump profiler to monitor stratified water columns with high vertical resolution.

A pump profiling system for real time sample collection has been constructed for a cost of <$1000 (USD) and mated with a ship's rosette that has conductivity, temperature, depth (CTD) and other sensors. The system permits the collection of ~15 L of water in one minute without exposure to O from air for discrete sampling of chemical, microbial and other constituents as well as for real time analyses using sensors. We also coupled a shipboard voltammetry system with solid-state microelectrodes to detect dissolved O and HS.

Achieving synergy between chemical oxidation and stabilization in a contaminated soil.

Eight in situ solidification/stabilization (ISS) amendments were tested to promote in situ chemical oxidation (ISCO) with activated persulfate (PS) in a contaminated soil. A 3% (by weight) dose of all ISS amendments selected for this study completely activated a 1.5% dose of PS within 3 h by raising temperatures above 30 °C (heat activation) and/or increasing pH above 10.