Biogeochemical Redox Processes and their Impact on Contaminant Dynamics

Abstract

Life and element cycling on Earth is directly related to electron transfer (or redox) reactions. An understanding of biogeochemical redox processes is crucial for predicting and protecting environmental health and can provide new opportunities for engineered remediation strategies. Energy can be released and stored by means of redox reactions via the oxidation of labile organic carbon or inorganic compounds (electron donors) by microorganisms coupled to the reduction of electron acceptors including humic substances, iron-bearing minerals, transition metals, metalloids, and actinides. Environmental redox processes play key roles in the formation and dissolution of mineral phases. Redox cycling of naturally occurring trace elements and their host minerals often controls the release or sequestration of inorganic contaminants. Redox processes control the chemical speciation, bioavailability, toxicity, and mobility of many major and trace elements including Fe, Mn, C, P, N, S, Cr, Cu, Co, As, Sb, Se, Hg, Tc, and U. Redox-active humic substances and mineral surfaces can catalyze the redox transformation and degradation of organic contaminants. In this review article, we highlight recent advances in our understanding of biogeochemical redox processes and their impact on contaminant fate and transport, including future research needs.

Environmental mobility of trace elements present in dusts emitted from Zn–Pb metallurgical processes

“…Arsenic in natural waters and soils is closely related to the presence of iron (hydr)oxides being arsenate and arsenite strongly sorbed onto the surfaces of Fe oxides, forming inner-sphere complexes. The simultaneous presence of high dissolved As and Fe(II) concentrations in anoxic groundwater has led to the conclusion that reductive dissolution of As rich Fe(III) (hydr)oxides mobilises geogenic As (Borch et al 2010, Voliante et al 2010 The plotted Eh and pH diagrams indicate that within the pH range of 4.5-7.5, which is characteristic of the soil and water environment of the area under study, the mobile forms of arsenic in this environment include HAsO 3-, HAsO 4 2-, H 2 AsO 4 -. Under these conditions tin occurs in the stable form of SnO 2 .…”

Review on iron availability in soil: interaction of Fe minerals, plants, and microbes

“…However, in cultivated soils, due to their redox fluctuation, most of soluble Fe is present in the Fe III form with the exception of poorly drained soils, where the quantity of its Fe II form could reach sufficient levels for plant uptake (Lindsay 1979(Lindsay , 1988. In fact, under waterlogged conditions, where the redox potential is low (Eh<0.4 V) and the pH is below 5, Fe III is easily reduced to Fe II by reducing bacteria, thus increasing consistently the micronutrient solubility (Borch et al 2010). Microbial sulfidogenesis can strongly affect Fe geochemistry through a variety of processes.…”

Effect of biogeochemical redox processes on the fate and transport of As and U at an abandoned uranium mine site: an X-ray absorption spectroscopy study

“…[10][11][12][13] Although U is less mobile in its reduced forms than in its oxidised forms, As is generally more mobile in its reduced form as As III . [14][15][16] Arsenic can adsorb to iron oxides under environmental pH as both As III (H 2 AsO 3 0 ) and As V (H 2 AsO 4 -). [17] Although As III has a greater sorption affinity to iron oxides than As V at pH 7, As V binds more strongly and is not as easily desorbed and released into surface waters.…”

“…However, U geochemistry has been studied extensively in Rifle, Colorado and other mill tailing sites. [1,14,38,39] At these sites, U immobilisation can occur with reduction to U IV or when U VI forms stable precipitates with, e.g. dissolved phosphate.…”