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Research advances made in the last decade and half in characterizing the mechanisms underlying the development of various forms of muscular dystrophy augurs well for optimism in managing and treating muscular dystrophy. Discovery of dystrophin and its molecular implications in Duchenne type and Becker muscular dystrophies are discussed.

Coastal cinnabar mining commenced in 2010 around Luhu on Seram (Ceram) Island, Indonesia. This study investigates the ore characteristics and environmental distribution and bioavailability of mercury in coastal sediments from eight sites adjacent to, and north and south of the mining area. Sediment and ore samples were digested using 1:3 HNO 3 :HCl for total extractable metal determination and separate samples were extracted with 1.0 HCl for bioavailable metals (Hg, Cu, Zn, Cr, Ni and Pb). Analysis was completed using inductively coupled plasma-mass spectrometry. Ore defined by miners as 'first class ore' was around 50 % cinnabar. Mercury concentrations were extremely elevated in near coastal sediments (up to 2796 mg/kg) with bioavailable concentrations exceeding 450 mg/kg. Marine sediments elevated in mercury extend to the north and south of the coastal mine site and cover in excess of 14 km. Total organic carbon in marine sediments was relatively low (predominately <0.6 %) suggesting mercury methylation will likely be slow, however, inorganic mercury is a known toxicant. Other metals of environmental concern (Cu, Zn, Cr, Ni and Pb) in sediments were not strongly associated with the mining operations, rather were elevated around coastal villages, but not at concentrations that raise immediate concerns. • Source cinnabar ores contain ~50 % mercury which is separated gravimetrically. • Coastal sediments near cinnabar mining contain up to 2796 mg/kg Hg. • Bioavailable Hg was 16–83 % of the total and up to 458 mg/kg. • Sediment elevated in Hg extend at least 14 km along the coastline. • Processed cinnabar to form liquid Hg enables small scale gold mining. [ABSTRACT FROM AUTHOR]

The Fe(II)-induced transformation of ferrihydrite, a potent scavenger for antimony (Sb), can considerably influence Sb mobility in reducing soils, sediments and groundwater systems. In these environments, humic acids (HA) are prevalent, yet their influence on Sb behaviour during ferrihydrite transformation is poorly understood. In this study, we investigated the effect of HA on (1) Sb partitioning between solid, colloidal and dissolved phases and (2) Sb redox speciation during the Fe(II)-induced transformation of Sb(V)-bearing ferrihydrite at pH 6.0 and 8.0 and Fe(II) concentrations of 0, 1 and 10 mM. The results show that, at pH 8.0 and in the presence of 10 mM Fe(II), ferrihydrite was replaced by goethite, lepidocrocite and magnetite across a wide range of HA concentrations. At pH 6.0 in the 10 mM Fe(II) treatments, ferrihydrite transformed to mainly lepidocrocite and goethite in both HA-free and low HA treatments. In contrast, high HA concentrations retarded the rate and extent of ferrihydrite transformation at both pH 6.0 and 8.0 in the 1 mM Fe(II) treatments. Antimony K-edge XANES spectroscopy revealed up to 60% reduction of solid-phase Sb(V) to Sb(III), which corresponded with an increase in the PO 4 3−-extractable fraction of solid-phase Sb in HA- and Fe(II)-rich conditions at pH 8.0. In contrast to the observations at pH 8.0, minimal reduction of solid-phase Sb(V) was observed in the pH 6.0 treatments with the highest HA content, yet some reduction of Sb(V) occurred (~30–40%) at intermediate HA concentrations. Humic acid-rich conditions were also found to promote the formation of substantial amounts of colloidal Sb in the <0.45 μm to 3 kDa size range at both pH 6.0 and 8.0. Our results demonstrate that HA can exert an important control on the partitioning, mobility and speciation of Sb during Fe(II)-induced transformation of ferrihydrite in sub-surface environments. Unlabelled Image • The effect of HA on Sb behaviour during Fe(II)-induced ferrihydrite transformation was investigated • Ferrihydrite underwent fast transformation in Fe(II)- and HA-rich treatments at pH 6.0 and 8.0. • In low Fe(II) or Fe(II)-free treatments HA hindered the transformation of ferrihydrite. • In HA-rich treatments transformation of Sb(V)-ferrihydrite generated substantial Sb(III). • HA promoted the formation of substantial amounts of colloidal Sb. [ABSTRACT FROM AUTHOR]

Abstract Mixed Cr(III)-Fe(III) (oxy)hydroxides are important Cr-bearing phases in natural, unpolluted soil. Fires frequently affect large areas of land around the world, causing the temporary development of elevated soil temperatures. This study examines the hypothesis that heating Cr(III)-Fe(III) (oxy)hydroxides at temperatures which occur in surface soils during fires can drive rapid oxidation of Cr(III) to hazardous Cr(VI). To test this, poorly-ordered Cr(III) x -Fe(III) 1- x (oxy)hydroxides, with x spanning 0.1 to 0.9, were heated at up to 800 °C for 2 h. Heating at 400–800 °C produced a highly crystalline hematite-eskolaite solid-solution (FeIII 2- n CrIII n O 3 , where n ranges from 0 to 2). Chromium K-edge X-ray absorption spectroscopy showed that during heating up to ∼40% of the initial Cr(III) was oxidized to Cr(VI), with the greatest extent of Cr(VI) formation occurring at 200–400 °C. At these temperatures, a substantial proportion (17%–70%) of the newly-formed Cr(VI) was exchangeable (i.e. extracted by a pH 7.2, 10 mM PO 4 3− solution). This suggests that much of the Cr(VI) formed by heating of Cr(III) x -Fe(III) 1- x (oxy)hydroxides at 200–400 °C is likely to be relatively mobile in fire-impacted soils. The results of this study provide new insights into a potentially-important pathway for the in-situ formation of Cr(VI) in soil. Graphical abstract Image 102 Highlights • Heating transforms Cr(III)-Fe(III)-(oxy)hydroxides to hematite/eskolaite. • During heating, up to 40% of solid-phase Cr(III) is rapidly oxidized to Cr(VI). • Cr(VI) formation depends on temperature and Cr(III)/Fe(III) substitution. • Much of the Cr(VI) formed at moderate temperature is readily mobile. [ABSTRACT FROM AUTHOR]

Abstract Iron oxides are important pedogenic Cr(III)-bearing phases which experience high-temperature alteration via fire-induced heating of surface soil. In this study, we examine if heating-induced alteration of Cr(III)-substituted Fe oxides can potentially facilitate rapid high-temperature oxidation of solid-phase Cr(III) to hazardous Cr(VI). Synthetic Cr(III)-substituted ferrihydrite, goethite and hematite were heated up to 800 °C for 2 h. Corresponding heating experiments were also conducted on an unpolluted Ferrosol-type soil, which had a total Cr content of 220 mg kg−1, initially undetectable Cr(VI) and Fe speciation comprising a mixture of hematite, goethite and ferrihydrite (according to Fe K-edge EXAFS spectroscopy). Up to ∼50% of the initial Cr(III) was oxidised to Cr(VI) during heating of Cr(III)-substituted ferrihydrite and hematite, with the greatest extent of Cr(VI) formation occurring at 200–400 °C. In contrast, heating of Cr(III)-substituted goethite resulted in up to ∼100% of Cr(III) oxidizing to Cr(VI) as the temperature approached 800 °C. In the Ferrosol-type soil, heating at ≥400 °C also resulted in large amounts of Cr(VI) formation, with a maximum total Cr(VI) concentration of 77 mg kg−1 forming at 600 °C (equating to oxidation of ∼35% of the soil's total Cr content). A relatively large portion (31–42%) of the total Cr(VI) which formed during heating of the soil was exchangeable, implying a high level of potential mobility and bioaccessibility. Overall, the results show that Cr(VI) forms rapidly via the oxidation of Fe oxide-bound Cr(III) at temperatures which occur in surface soils during fires. On this basis and given the frequency and extent of wild-fires around the world, we propose that fire-induced oxidation of Fe oxide-bound Cr(III) may represent a globally-significant pathway for the natural formation of hazardous Cr(VI) in surface soil. Graphical abstract Image 1 Highlights • Heating drives oxidation of Cr(III) substituted within Fe oxides to Cr(VI). • Fire-induced heating of unpolluted soil can drive hazardous Cr(VI) formation. • A large portion of newly-formed Cr(VI) is likely to be readily mobile. • Fire-induced Cr(III) oxidation may be an important pathway for Cr(VI) formation. Fire-induced oxidation of Fe oxide-bound Cr(III) may represent a largely unexplored, yet globally-significant pathway for the natural formation of hazardous Cr(VI) in soil. [ABSTRACT FROM AUTHOR]

Abstract Acid sulfate systems commonly contain the metastable ferric oxyhydroxysulfate mineral schwertmannite, as well as phosphate (PO 4 3−) - a nutrient that causes eutrophication when present in excess. However, acid sulfate systems often experience reducing conditions that destabilize schwertmannite. Under such conditions, the long-term fate of both schwertmannite and PO 4 3− may be influenced by interactions during microbially-mediated Fe(III) and SO 4 2− reduction. This study investigates the influence of PO 4 3− on Fe(III) and SO 4 2− reduction and the subsequent mineralogical transformation(s) in schwertmannite-rich systems exposed to reducing conditions. To accomplish this, varied PO 4 3− loadings were established in microbially-inoculated schwertmannite suspensions that were incubated under anoxic conditions for 82 days. Increased PO 4 3− attenuated the onset of microbial Fe(III) reduction. This delayed consequent pH increases, which in turn had cascading effects on the initiation of SO 4 2− reduction and subsequent mineral species formed. Under zero PO 4 3− loading, goethite (αFeOOH) formed first, followed by mackinawite (FeS) and siderite (FeCO 3). In contrast, in higher PO 4 3− treatments, vivianite (Fe 3 (PO 4) 2) and/or sulfate green rust (FeII 4 FeIII 2 (OH) 12 SO 4) became increasingly important over time at the expense of goethite and mackinawite compared to PO 4 3−-free conditions. The findings imply that PO 4 3− loading alters the rates and onset of microbial Fe(III)- and SO 4 2−- reduction and the subsequent formation of secondary Fe-bearing phases. In addition, schwertmannite reduction and the associated mineralogical evolution under anoxic conditions appears to sequester large quantities of PO 4 3− in the form of green rusts and vivianite. Graphical abstract Unlabelled Image Highlights • PO 4 3− sorption attenuates onset of schwertmannite-Fe(III) and SO 4 2− reduction. • Phosphate is sequestered in green rust/vivianite in non-sulfidic conditions. • Mackinawite formation decreases with increased PO 4 3− loading. [ABSTRACT FROM AUTHOR]

Abstract Antimony is an environmental contaminant, whose mobility in soils, sediments and groundwater systems is strongly influenced by interactions with Fe(III) oxide minerals. When exposed to reducing conditions, these minerals can undergo reductive dissolution via the activity of Fe(III)-reducing microorganisms, thereby potentially liberating previously retained Sb. In addition, microbial Fe(III)-reduction and the consequent production of Fe(II) can induce the formation of secondary Fe(III)- and Fe(II)-bearing minerals, which may alter the speciation and partitioning of Sb. In this study, we examined Sb behaviour during (1) the microbially-mediated reduction and transformation of Sb(V)-bearing ferrihydrite by the dissimilatory Fe(III)-reducing bacterium, Shewanella putrefaciens (strain CN32), and (2) during the associated abiotic Fe(II)-catalyzed transformation of Sb(V)-bearing ferrihydrite. Antimony K-edge XANES spectroscopy showed negligible reduction of Sb(V) to Sb(III) in both experiments, reflecting the redox stability of Sb(V) under these conditions. X-ray diffraction and Fe K-edge EXAFS spectroscopy revealed that both microbially-mediated Fe(II) production as well as the experimental addition of aqueous Fe(II) under abiotic conditions triggered rapid transformation of the initial ferrihydrite to feroxyhyte (δ′-FeOOH) and goethite (α-FeOOH). Goethite has been widely observed as a product of the Fe(II)-catalyzed transformation of ferrihydrite. However, the present study is the first to document the formation of feroxyhyte via this pathway, with feroxyhyte formation appearing to be favored by the presence of Sb(V). The formation of these secondary Fe(III) oxides was associated with substantial decreases in aqueous Sb concentrations and in the amount of surface-bound Sb (as defined via extractions with 1 M PO 4 3−). This is consistent with the incorporation of Sb(V) into the newly formed feroxyhyte and goethite via substitution for Fe(III). The results of this study provide new perspectives on coupling between Sb geochemistry and Fe mineralogy by showing that microbial Fe(III)-reduction and associated secondary Fe(III)-oxide formation can help to immobilize Sb(V) in reducing environments. [ABSTRACT FROM AUTHOR]

In this study, we examined the removal of arsenite (As(III)) and arsenate (As(V)) by perilla leaf-derived biochars produced at 300 and 700 °C (referred as BC300 and BC700) in aqueous environments. Results revealed that the Langmuir isotherm model provided the best fit for As(III) and As(V) sorption, with the sorption affinity following the order: BC700-As(III) > BC700-As(V) > BC300-As(III) > BC300-As(V) ( Q L = 3.85–11.01 mg g −1 ). In general, As removal decreased (76–60%) with increasing pH from 7 to 10 except for the BC700-As(III) system, where notably higher As removal (88–90%) occurred at pH from 7 to 9. Surface functional moieties contributed to As sequestration by the biochars examined here. However, significantly higher surface area and aromaticity of BC700 favored a greater As removal compared to BC300, suggesting that surface complexation/precipitation dominated As removal by BC700. Arsenic K-edge X-ray absorption near edge structure (XANES) spectroscopy demonstrated that up to 64% of the added As(V) was reduced to As(III) in BC700- and BC300-As(V) sorption experiments, and in As(III) sorption experiments, partial oxidation of As(III) to As(V) occurred (37–39%). However, XANES spectroscopy was limited to precisely quantify As binding with sulfur species as As 2 S 3 -like phase. Both biochars efficiently removed As from natural As-contaminated groundwater (As: 23–190 μg L −1 ; n = 12) despite in the presence of co-occurring anions (e.g., CO 3 2− , PO 4 3− , SO 4 2− ) with the highest levels of As removal observed for BC700 (97–100%). Overall, this study highlights that perilla leaf biochars, notably BC700, possessed the greatest ability to remove As from solution and groundwater (drinking water). Significantly, the integrated spectroscopic techniques advanced our understanding to examine complex redox transformation of As(III)/As(V) with biochar, which are crucial to determine fate of As on biochar in aquatic environments. [ABSTRACT FROM AUTHOR]

The release of phosphorus (P) from benthic sediments can affect the P content, nutrient status and quality of overlying waters in coastal ecosystem. This study was carried out to investigate the influence of oxidation-reduction potential (ORP) and sulfide on P release from sediments in the coastal estuary of the Yuniao River, China. The results showed that ferric iron-bound P was the main P burial phase in the sediments. The P concentration in overlying water increased with ORP decrease and sulfide increase, displaying a significant linear correlation with the ORP and sulfide concentration. The results indicate that decreased ORP may elevate the zero equilibrium phosphorus concentration, enhancing the capability of P release. And increased sulfide may react or capture reactive iron in sediments, reducing the P adsorption capacity and accelerating P release. Therefore, the control of ORP and sulfide production is important in the sink/source conversion of P in coastal sediments. [ABSTRACT FROM AUTHOR]

Nanoparticulate mackinawite (FeS) can be an important host-phase for arsenic (As) in sulfidic, subsurface environments. Although not previously investigated, phosphate (PO 4 3− ) may compete with As for available sorption sites on FeS, thereby enhancing As mobility in FeS-bearing soils, sediments and groundwater systems. In this study, we examine the effect of PO 4 3− on sorption of arsenate (As(V)) and arsenite (As(III)) to nanoparticulate FeS at pH 6, 7 and 9. Results show that PO 4 3− (at 0.01–1.0 mM P) did not significantly affect sorption of either As(V) or As(III) to nanoparticulate FeS at initial aqueous As concentrations ranging from 0.01 to 1.0 mM. At pH 9 and 7, sorption of both As(III) and As(V) to nanoparticulate FeS was similar, with distribution coefficient (K d ) values spanning 0.76–15 L g −1 (which corresponds to removal of 87–98% of initial aqueous As(III) and As(V) concentrations). Conversely, at pH 6, the sorption of As(III) was characterized by substantially higher K d values (6.3–93.4 L g −1 ) than those for As(V) (K d = 0.21–0.96 L g −1 ). Arsenic K-edge X-ray absorption near edge structure (XANES) spectroscopy indicated that up to 52% of the added As(V) was reduced to As(III) in As(V) sorption experiments, as well as the formation of minor amounts of an As 2 S 3 -like species. In As(III) sorption experiments, XANES spectroscopy also demonstrated the formation of an As 2 S 3 -like species and the partial oxidation of As(III) to As(V) (despite the strictly O 2 -free experimental conditions). Overall, the XANES data indicate that As sorption to nanoparticulate FeS involves several redox transformations and various sorbed species, which display a complex dependency on pH and As loading but that are not influenced by the co-occurrence of PO 4 3− . This study shows that nanoparticulate FeS can help to immobilize As(III) and As(V) in sulfidic subsurface environments where As co-exists with PO 4 3− . [ABSTRACT FROM AUTHOR]

Titratable actual acidity (TAA) is a technique commonly used to estimate the existing pool of exchangeable H + in acid sulfate soils (ASS). A widely adopted version of the TAA method involves titrating a 1M KCl suspension of oven-dry soil (1:40) with NaOH to a known pH endpoint. However, when ASS are subject to long term re-flooding during wetland remediation, former sulfuric horizons can develop substantial quantities of porewater Fe 2+ , non-sulfidic solid-phase Fe(II) and a variety of reduced inorganic sulfur (RIS) species (e.g. pyrite, mackinawite, greigite and elemental sulfur). For these sediments, an oven-drying approach may induce oxidation of the abundant Fe(II) and/or reactive RIS species, thereby generating H + and leading to overestimation of existing in situ exchangeable H + . In this study, we compare TAA via the standard approach (1M KCl; 1:40; oven-dry soil, 4 hr extract; TAA D ) with an identical O 2 -free extraction approach using wet-sediment (TAA W ). We apply both methods to former sulfuric horizon sediments from freshwater re-flooded ASS wetlands. There are significant ( α = 0.01) differences (up to 12×) between TAA measured by the two methods, with the oven-dried standard approach overestimating TAA relative to the wet, O 2 -free approach in 85% of cases. Despite the fact that all AVS-S and some S(0) was oxidised during the oven-drying process, the increases in TAA (TAA D –TAA W ) show very weak correlation(s) with corresponding losses in RIS species or increases in water soluble sulfate and KCl extractable sulfate. However, oven-drying caused substantial loss of 1M KCl exchangeable Fe(II) and 1 M HCl-extractable Fe(II) and led to large increases in 1 M HCl-extractable Fe(III). These changes in Fe fractions displayed strong positive linear correlation ( α = 0.01) with increases in TAA. Although this is not evidence of causality, it suggests that oxidation of Fe(II) species are playing an important role in the development of additional exchangeable H + and may be largely responsible for the contrasting TAA derived by the two methods. The differences in TAA between the two methods are greatest in organic-rich surface sediments and are significantly positively correlated with total organic carbon content. These findings have major implications for accurately assessing TAA in re-flooded ASS wetlands. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates iron (Fe) and sulfur (S) cycling in sediments from the eutrophic Peel–Harvey Estuary in Western Australia, which is subject to localized accumulation of strongly reducing, organic- and sulfide-rich sediments. Sedimentary iron was mostly present in highly reactive form (on average 73% of total Fe) and showed extensive sulfidization even in surface sediments, despite being overlain by a well-mixed oxygenated water column. This indicates that, under eutrophic marine conditions, Fe sulfidization may be driven by reductive processes in the sediment without requiring oxygen depletion in the overlying waters. Strong enrichments in iron monosulfide (FeS>300μmolg−1) were observed in fine-grained sediment intervals up to 45cm depth. This metastable Fe sulfide is commonly restricted to thin subsurface sediment intervals, below which pyrite (FeS2) dominates. Our findings suggest inhibition of the dissolution–precipitation processes that replace FeS with FeS2 in sediments. Rates of pyrite formation based on the FeS2 profiles were much lower than those predicted by applying commonly used kinetic equations for pyrite formation. Dissolved H2S was present at millimolar levels throughout the investigated sediment profiles. This may indicate that (i) pyrite formation via reaction between dissolved Fe (including Fe clusters) and H2S was limited by low availability of dissolved Fe or (ii) reaction kinetics of pyrite formation via the H2S pathway may be relatively slow in natural reducing sediments. We propose that rapid burial of the FeS under anoxic conditions in these organic-rich reducing sediments minimizes the potential for pyrite formation, possibly by preventing dissolution of FeS or by limiting the availability of oxidized sulfur species that are required for pyrite formation via the polysulfide pathway. [Copyright &y& Elsevier]

Abstract: Schwertmannite is an important Fe(III) mineral in acid–sulfate soil and acid–mine drainage environments because it is both widespread and highly reactive towards trace elements, such as As. Transformation of schwertmannite to more crystalline phases, such as goethite, may strongly influence As mobility. However, previous research suggests that the rate and extent of schwertmannite transformation can be strongly retarded by the presence of Si – a ubiquitous species in natural waters. The present study examines the impact of Si on reductive transformation of schwertmannite and the associated behavior of Fe and coprecipitated As. Synthetic As(V)-coprecipitated schwertmannite (Fe8O8(OH)4.2(SO4)1.9(AsO4)0.0005) was subjected to microbially-mediated reducing conditions for 126days in the presence of three environmentally-relevant Si concentrations (0, 1.9 and 9.5mM Si). In addition, complementary sorption experiments and short-term abiotic mineral transformation experiments were conducted to examine the interactive impacts of Si and Fe2+ on schwertmannite stability. Sorption experiments revealed negligible Si sorption to schwertmannite under acidic conditions, with Si sorption only being important towards near-neutral pH. In the 126day biotic incubations, the onset of reducing conditions in the initially acidic schwertmannite suspensions stimulated dissimilatory Fe(III) reduction, producing Fe2+ and simultaneously causing pH to increase to ∼6.5. Sorption of Si to the schwertmannite surface at this near-neutral pH partially retarded the rate of Fe2+-catalyzed transformation of schwertmannite to goethite. However, the effect of Si was minor under microbially-reducing conditions, with Fe2+ catalyzing rapid schwertmannite transformation even in the presence of abundant Si. Our short-term abiotic experiments demonstrate that the limited effect of Si is a consequence of Fe2+ being produced concurrently with increases in pH. This allows Fe2+-schwertmannite interactions to proceed prior to the formation of surface-passivating Si species. The Fe2+ catalyzed transformation of As(V)-coprecipitated schwertmannite to goethite caused a major increase in -extractable As, but had little effect on aqueous As concentrations. The reduction of Fe(III) and the subsequent onset of dissimilatory reduction led to formation of siderite (FeCO3) and mackinawite (FeS), respectively. The reduction of As(V) to As(III) was associated with the Si-dependent mobilization of As into the aqueous-phase. There was a concurrent decrease over time in the concentrations of -extractable As, which occurred independent of Si concentrations and appeared to be related to formation of siderite and mackinawite. The findings from this study provide new insights into the evolution of iron mineralogy and associated arsenic mobility following the establishment of reducing conditions in schwertmannite- and Si-rich environments. [Copyright &y& Elsevier]

Abstract: Sulfur biogeochemical cycling and associated Fe–S mineralization processes exert a major influence over acidity dynamics, electron flow and contaminant mobility in wetlands, benthic sediments and groundwater systems. While S biogeochemical cycling has been studied intensively in many environmental settings, relatively little direct information exists on S cycling in formerly drained wetlands that have been remediated via tidal re-flooding. This study focuses on a tidal wetland that was drained in the 1970s (causing severe soil and water acidification), and subsequently remediated by controlled re-flooding in 2002. We examine reduction rates and Fe–S mineralization at the tidal fringe, 7years after the commencement of re-flooding. The initial drainage of the wetland examined here caused in-situ pyrite (FeS2) oxidation, resulting in the drained soil layers being highly acidic and rich in -bearing Fe(III) minerals, including jarosite (KFe3(SO4)2(OH)6). Tidal re-flooding has neutralized much of the previous acidity, with the pore-water pH now mostly spanning pH 5–7. The fastest rates of in-situ reduction (up to ∼300nmolcm−3 day−1) occur within the inter-tidal zone in the near-surface soil layers (to ∼60cm below ground surface). The reduction rates correlate with pore-water dissolved organic C concentrations, thereby suggesting that electron donor supply was the predominant rate determining factor. Elemental S was a major short-term product of reduction, comprising up to 69% of reduced inorganic S in the near-surface soil layers. This enrichment in elemental S can be partly attributed to interactions between biogenic H2S and jarosite – a process that also contributed to enrichment in pore-water Fe2+ (up to 55mM) and (up to 50mM). The iron sulfide thiospinel, greigite (Fe3S4), was abundant in near-surface soil layers within the inter- to sub-tidal zone where tidal water level fluctuations created oscillatory redox conditions. There was evidence for relatively rapid pyrite re-formation within the re-flooded soil layers. However, the results indicate that pyrite re-formation has occurred mainly in the lower formerly drained soil layers, whereas the accumulation of elemental S and greigite has been confined towards the soil surface. The discovery that pyrite formation was spatially decoupled from that of elemental S and greigite challenges the concept that greigite is an essential precursor required for sedimentary pyrite formation. In fact, the results suggest that greigite and pyrite may represent distinct end-points of divergent Fe–S mineralization pathways. Overall, this study highlights novel aspects of Fe–S mineralization within tidal wetlands that have been drained and re-flooded, in contrast to normal, undisturbed tidal wetlands. As such, the long-term biogeochemical trajectory of drained and acidified wetlands that are remediated by tidal re-flooding cannot be predicted from the well-studied behaviour of normal tidal wetlands. [Copyright &y& Elsevier]

Abstract: Microbial sulfidogenesis plays a potentially important role in Fe and As biogeochemistry within wetland soils, sediments and aquifers. This study investigates the specific effects of microbial sulfidogenesis on Fe mineralogy and associated As mobility in mildly acidic (pH 6) and mildly basic (pH 8) advective-flow environments. A series of experiments were conducted using advective-flow columns, with an initial solid-phase comprising As(III)-bearing ferrihydrite-coated quartz sand. Columns for each pH treatment were inoculated with the sulfate-reducing bacteria Desulfovibrio vulgaris, and were compared to additional abiotic control columns. Over a period of 28days, microbial sulfidogenesis (as coupled to the incomplete oxidation of lactate) caused major changes in Fe mineralogy, including replacement of ferrihydrite by mackinawite and magnetite at the in-flow end of the inoculated columns. At pH 8, the Fe2+ produced by electron transfer between sulfide and ferrihydrite was mainly retained near its zone of formation. In contrast, at pH 6, much of the produced Fe2+ was transported with advecting groundwater, facilitating the downstream Fe2+-catalyzed transformation of ferrihydrite to goethite. At both pH 6 and pH 8, the sulfide-driven reductive dissolution of ferrihydrite and its replacement by mackinawite at the in-flow end of the inoculated columns resulted in substantial mobilization of As into the pore-water. At pH 8, this caused the downstream As concentrations within the inoculated columns to be greater than the corresponding abiotic column. However, the opposite occurred under pH 6 conditions, with the Fe2+-catalyzed transformation of ferrihydrite to goethite in the inoculated columns causing a decrease in downstream As concentrations compared to the abiotic column. Although thermodynamically favorable at intermediate times and depth intervals within the inoculated columns, solid As sulfide phases were undetectable by As XANES spectroscopy. Our findings show that microbial sulfidogenesis can trigger significant As mobilization in subsurface environments with advective groundwater flow. The results also demonstrate that formation of mackinawite by sulfidization of ferric (hydr)oxides is not effective for the immobilization of As, whereas the Fe2+-catalyzed transformation of ferrihydrite to goethite under mildly acidic conditions may mitigate As mobility. [Copyright &y& Elsevier]