Search

Soil mercury (Hg) contamination is a serious threat to local ecology and public health. Exogenous selenium (Se) supplementation can effectively reduce the toxicity of Hg. However, the mechanisms affecting the changes in soil Hg speciation, soil properties and the microbial Hg-resistant system during the Se–Hg interaction after exogenous Se supplementation are not clear. Therefore, in this study, soil culture experiments were conducted to analyze the effects of different Se additions on the transformation of Hg speciation, soil properties and Hg-resistant microorganisms and resistant genes (mer operon). The results indicated that Se supplementation facilitated the transformation of soil Hg from bioavailable (exchangeable and carbonate-bound) to stable forms (organic material-bound and residual), significantly reducing Hg bioavailability. Se supplementation notably decreased the electrical conductivity of Hg-contaminated soil, but had no significant effect on the soil pH, organic matter content, cation exchange capacity or alkaline phosphatase and catalase activities. The maximum activity levels of soil sucrase and urease were observed when 1 mg kg−1 Se was added. Se significantly inhibited soil peroxidase and ascorbate oxidase activities, thereby alleviating the oxidative stress in the soil system caused by Hg. Additionally, Se significantly activated the Hg-resistant system in soil microorganisms by either decreasing or increasing the regulatory genes merD and merR, and it significantly upregulated the cytoplasmic protein gene merP and the membrane protein genes merC, merF and merT. This further increased the abundance of the organomercury lyase gene merB and the mercuric reductase gene merA, promoting the conversion of Hg species to Hg⁰. Furthermore, the abundance of mer operon-containing microorganisms, such as Thiobacillus ferrooxidants, Pseudomonas, Streptomyces and Cryptococcus, significantly increased with Se addition, explaining the role of soil microorganisms in mitigating soil Hg stress via Se supplementation. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ecology & Rural Environment is the property of Journal of Ecology & Rural Environment Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Soil mercury (Hg) contamination is a serious threat to local ecology and public health. Exogenous selenium (Se) supplementation can effectively reduce the toxicity of Hg. However, the mechanisms affecting the changes in soil Hg speciation, soil properties and the microbial Hg-resistant system during the Se–Hg interaction after exogenous Se supplementation are not clear. Therefore, in this study, soil culture experiments were conducted to analyze the effects of different Se additions on the transformation of Hg speciation, soil properties and Hg-resistant microorganisms and resistant genes (mer operon). The results indicated that Se supplementation facilitated the transformation of soil Hg from bioavailable (exchangeable and carbonate-bound) to stable forms (organic material-bound and residual), significantly reducing Hg bioavailability. Se supplementation notably decreased the electrical conductivity of Hg-contaminated soil, but had no significant effect on the soil pH, organic matter content, cation exchange capacity or alkaline phosphatase and catalase activities. The maximum activity levels of soil sucrase and urease were observed when 1 mg kg−1 Se was added. Se significantly inhibited soil peroxidase and ascorbate oxidase activities, thereby alleviating the oxidative stress in the soil system caused by Hg. Additionally, Se significantly activated the Hg-resistant system in soil microorganisms by either decreasing or increasing the regulatory genes merD and merR, and it significantly upregulated the cytoplasmic protein gene merP and the membrane protein genes merC, merF and merT. This further increased the abundance of the organomercury lyase gene merB and the mercuric reductase gene merA, promoting the conversion of Hg species to Hg⁰. Furthermore, the abundance of mer operon-containing microorganisms, such as Thiobacillus ferrooxidants, Pseudomonas, Streptomyces and Cryptococcus, significantly increased with Se addition, explaining the role of soil microorganisms in mitigating soil Hg stress via Se supplementation.

The partitioning of selenium in coal-fired flue gas and desulfurization wastewater is of great threat to the ecological environment and human health. However, the unclear understanding of interactions between selenium vapors and fly ash hinders the emission control of selenium from coal-fired power plants. To further illuminate the mechanism of selenium partitioning and transformation, this study carefully estimated selenium distribution characteristics in the coal combustion byproducts from several industrial power plants. The effective temperature range as well as the key ash components for selenium retention by fly ash was clarified by multiple-scale experiments and theoretical perspectives. The results showed that gaseous selenium tended to be captured by fly ash at a medium-to-low temperature range (i.e. below 650 °C). The limited residence time resulted in the incomplete capture of gaseous selenium by fly ash. Mullite, quartz, iron oxides, and anhydrite in fly ash were found to be the main trappers for gaseous selenium. Among these components, iron oxides showed excellent selenium adsorption performance at a wide temperature range of 150-700 °C, which was realized by the strong chemical adsorption. By contrast, as the dominant phases in fly ash for the physical adsorption of gaseous selenium, mullite and quartz mainly captured gaseous selenium below 300 °C. On the other hand, sulfur dioxides had priority over gaseous selenium to react with calcium-containing ash components by forming anhydrite in the high-temperature region. The formed anhydrite had a limited selenium adsorption capacity, which was confirmed to capture gaseous selenium through a combination of physical adsorption and weak chemical adsorption. For the in-depth control of selenium emitted into desulfurization system and atmosphere environment, these findings provided a comprehensive insight into the behavior of selenium partitioning and transformation into fly ash during coal combustion. [ABSTRACT FROM AUTHOR]

Arsenopyrite (FeAsS) is a typical gold-bearing sulfide mineral. It usually encapsulates the gold particles and seriously inhibits the leaching of gold, so oxidation pretreatment of arsenopyrite is prerequired for the effective leaching of gold. However, the oxidation of arsenopyrite is accompanied by arsenic mobility, potentially resulting in serious environmental issues. An eco-friendly oxidant, δ-MnO2, was herein used to effectively oxidize arsenopyrite and control the fate of arsenic under acidic conditions. Via characterization of the variation of leaching parameters, morphology change, and elemental speciation transformation on the mineral surface, it was found that adding δ-MnO2 significantly provoked the oxidation of Fe(II) and As(−I) to Fe(III) and As(V), and mediated the speciation transformation of Fe/As to FeAsO4. δ-MnO2 dosage remarkably controlled the oxidation efficiency of arsenopyrite and arsenic speciation transformation, efficiently regulating arsenic fate. These results suggest that δ-MnO2 could simultaneously promote the dissolution of arsenopyrite and the immobilization of arsenic, which could have implications for the oxidation pretreatment of refractory gold minerals and the source management of arsenic-contaminated environments. [ABSTRACT FROM AUTHOR]

Biochar-derived dissolved organic matter (BDOM), is extensively involved in the recrystallization of minerals and the speciation alteration of associated toxic metals. This study investigates how BDOM extracted from tobacco petiole (TP) or tobacco stalk (TS) biochar influences the speciation repartitioning of Cr(VI) in environments impacted by acid mine drainage (AMD), focusing on interactions with secondary minerals during Schwertmannite (Sch) dissolution and recrystallization. TP-BDOM, rich in lignin-like substances, slowed down the Cr-Sch dissolution and Cr release under acidic conditions compared to TS-BDOM. TP-BDOM's higher O/C component exerts a delayed impact on Cr-Sch stability and Cr(VI) reduction. In-situ ATR-FTIR and 2D-COS analysis showed that carboxylic and aromatic N-OH groups in BDOM could interact with Cr-Sch surfaces, affecting sulfate and Cr(VI) release. It was also observed that slight recrystallization occurred from Cr-Sch to goethite, along with increased Cr incorporation into secondary minerals within TS-BDOM. This enhances our understanding of BDOM's role in Cr(VI) speciation changes in AMD-contaminated sites. [Display omitted] • Biochar-derived DOM with abundant lignin-like substances slowly induces Cr release. • Steric hindrance limits BDOM-induced Cr-Sch dissolution under acidic conditions. • Tannin-like and lignin-like substances are responsible for Cr(VI) reduction. • Carboxylic functional groups weaken Fe-O bond and drive structural sulfate release. • BDOM can slightly induce the transformation of metastable Cr-Sch into goethite. [ABSTRACT FROM AUTHOR]

Arsenopyrite (FeAsS) is a typical gold-bearing sulfide mineral. It usually encapsulates the gold particles and seriously inhibits the leaching of gold, so oxidation pretreatment of arsenopyrite is prerequired for the effective leaching of gold. However, the oxidation of arsenopyrite is accompanied by arsenic mobility, potentially resulting in serious environmental issues. An eco-friendly oxidant, δ-MnO2, was herein used to effectively oxidize arsenopyrite and control the fate of arsenic under acidic conditions. Via characterization of the variation of leaching parameters, morphology change, and elemental speciation transformation on the mineral surface, it was found that adding δ-MnO2 significantly provoked the oxidation of Fe(II) and As(−I) to Fe(III) and As(V), and mediated the speciation transformation of Fe/As to FeAsO4. δ-MnO2 dosage remarkably controlled the oxidation efficiency of arsenopyrite and arsenic speciation transformation, efficiently regulating arsenic fate. These results suggest that δ-MnO2 could simultaneously promote the dissolution of arsenopyrite and the immobilization of arsenic, which could have implications for the oxidation pretreatment of refractory gold minerals and the source management of arsenic-contaminated environments.

Heavy metal pollution at an abandoned smelter pose a significant risk to environmental health. However, remediation strategies are constrained by inadequate knowledge of the polymetallic distribution, speciation patterns, and transformation factors at these sites. This study investigates the influence of soil minerals, heavy metal occurrence forms, and environmental factors on heavy metal migration behaviors and speciation transformations. X-ray diffraction analysis revealed that the minerals associated with heavy metals are mainly hematite, franklinite, sphalerite, and galena. Sequential extraction results suggest that lead and zinc are primarily present in the organic-sulfide fractions (F4) and residual form (F5) in the soil, accounting for over 70% of the total heavy metal content. Zinc displayed greater instability in carbonate-bound (16%) and exchangeable (2%) forms. The migration and diffusion patterns of heavy metals in the subsurface environment were visualized through the simulation of labile state heavy metals, demonstrating high congruence with groundwater pollution distribution patterns. The key environmental factors influencing heavy metal stable states (F4 and F5) were assessed by integrating random forest models and redundancy analysis. Primary factors facilitating Pb transformation into stable states were available phosphorus, clay content, depth, and soil organic matter. For Zn, the principal drivers were Mn oxides, soil organic matter, clay content, and inorganic sulfur ions. These findings enhance understanding of the distribution and transformation of heavy metal speciation and can provide valuable insights into controlling heavy metal pollution at non-ferrous smelting sites. [Display omitted] • The samples from the site reveal considerable heavy metal contamination due to zinc iron spinel, galena, sphalerite, hematite. • Pb and Zn in the soil exist primarily in the stable form, with the labile state closely aligns with groundwater contamination. • The zinc content contributes to its excessive presence in groundwater due to temporal and spatial accumulation. • Available phosphorus, Mn oxides, clay, depth, and soil organic matter facilitate the transformation of heavy metals into stable states. [ABSTRACT FROM AUTHOR]

Ferric iron has a significant effect on the bioleaching of arsenopyrite, the most efficient way for pretreatment of arsenopyrite-bearing gold ores. Up to date, the differential effect of Fe(III) compounds on that process was rarely studied. Herein, FeCl3, Fe(NO3)3 and Fe2O3 were addressed to unravel their different promotion effects during arsenopyrite biooxidation by Sulfobacillus thermosulfidooxidans, in which the As/Fe/S speciation transformation were comprehensively analyzed mainly with synchrotron radiation-based X-ray diffraction (SR-XRD) and Fe L- and As/S K-edge X-ray absorption near edge structure (XANES) spectroscopy to detect the elimination of passivation, besides the changes in the morphology and the leaching parameters of the mineral. The results showed that, the bioleaching of arsenopyrite was efficiently promoted under addition of the Fe(III) compounds (0.6 g/L), for instance, the extraction rates of As were increased from 55% to 64–77%, the surface of arsenopyrite suffered more serious corrosion and covered with a loose and porous structure, the intermediates S0, thiosulfate and orpiment significantly decreased, and jarosites and schwertmannite increased, the remaining content of arsenopyrite was decreased from 31.5% to 21.7–5.3%. Those results indicated that, the iron/sulfur oxidation activity was enhanced and the transformation of those intermediates was accelerated by the Fe(III) compounds added. Such change intension accompanied with the promotion effect observes the order FeCl3 > Fe(NO3)3 > Fe2O3. These results reveale that the adding Fe(III) compounds, especially for FeCl3, can efficiently promote the biooxidation through removal of some intermediates from the surface of the arsenopyrite and thus optimize the pretreatment of arsenopyrite-bearing gold ores.

Lead (Pb) in soil may accumulate in crops and enter the human body. This study aimed to understand the speciation transformation and accumulation characteristics of exogenous Pb in calcareous soil with or without the application of soil amendments. Field experiments with continuous maize cultivation have been carried out for two years. The results showed that the contents of total Pb were slightly lower in 2016 than in 2015 for the same treatments; however, no significant difference between the years was observed. Soil Pb existed mainly in the residual fraction without exogenous Pb addition, and its proportion was more than 33% of the total soil Pb in the control and Ca treatments. When Pb was added to calcareous soil, Pb existed largely in the oxidizable and reducible fractions during the two-year experimental period, and those fractions made up over 83% of the total Pb. The proportion of the water-soluble Pb, regardless of the addition of Pb, was the lowest and was less than 0.0019% in all treatments, but the addition of Ca and chitosan amendments reduced the water-soluble and exchangeable Pb contents. The Pb content in different parts of maize followed the order root>leaf>stem>grain during the experimental period. Although maize had low transfer and enrichment factors in calcareous soil, which make the Pb content in the grain show no significant difference among the five treatments in the same year, adding Ca and chitosan to calcareous soil can reduce the Pb contents of maize, especially reduce the Pb contents of root, stem and leaf. Therefore, the addition of calcium and chitosan is an effective strategy for reducing Pb availability in calcareous soils.

The biogeochemical cycle of arsenic (As) inherently associates with its species. Bacterially mediated redox reactions, such as those accomplished by dissimilatory iron-reducing bacteria (DFeRB) and sulfate-reducing bacteria (SRB), are regarded as the most important mechanisms affecting As species transformation and mobilization. The novelty of this study is that partial least squares (PLS) path model was used to explore the possible pathways of As species transformation mediated by DFeRB and SRB in sediments during an ice-bound period based on continuous As species monitoring of a sediment–water system. Results showed that the effects of DFeRB and SRB on the reduction of As(V) were 1.5 and 2.5 times those of the sterilized group, respectively. Additionally, the TAs and As(III) concentrations in the aqueous mediated by SRB were 1.4 and 1.5 times those of the DFeRB group on average, respectively. The discerned trends reveal that DFeRB and SRB retained their reduction capacity and efficiency during the ice-bound period, which influenced the As species transformation. The amount reduced from As(V) to As(III) and the endogenous release of As mediated by SRB was higher than that of DFeRB. DFeRB mediated the reduction and indirectly influenced the As species transformation through the reductive dissolution and re-distribution of Fe(III) oxyhydroxides and As-containing Fe(III) minerals, while SRB mediated the reduction process, the As in sediment-overlying water system was gradually transformed into a more stable sulfide binding state. This study provides information for redirecting the environmental effects of DFeRB and SRB in the biogeochemical cycle of As in lakes and soils located in cold regions. [ABSTRACT FROM AUTHOR]

Root exudate is a major source of soil organic matter and can significantly affect arsenic (As) migration and transformation in paddy soils. Citric acid is the main component of rice root exudate, however, the impacts and rules of citric acid on As bioavailability and rhizobacteria in different soils remains unclear. This study investigated the effects of citric acid on As transformation and microbial community in ten different paddy soils by flooded soil culture experiments. The results showed that citric acid addition increased total As and arsenate (As(V)) in the soil porewater by up to 41-fold and 65-fold, respectively, after 2-h incubation. As(V) was the main As species in soil porewater within 10 days with the addition of citric acid. Non-specifically sorbed As of soils, total Fe and total As were the main environmental factors affecting the soil microbial communities. High-throughput sequencing analysis demonstrated that citric acid addition significantly altered the soil microbial community structure, shifting the Proteobacteria-related reducing bacteria to Firmicutes-related reducing bacteria in different paddy soils. The relative abundance of Firmicutes was promoted by 174–196%. Clostridium -related bacteria belonging to Firmicutes became the dominant genera, which is believed to regulate As release through the reductive dissolution of iron oxides or the direct reduction of As(V) to arsenite (As(III)). However, citric acid addition significantly decreased the relative abundance of Geobacter and Anaeromyxobacter , which are also typical active As(V)- and ferric-reducing bacteria. Real-time quantitative polymerase chain reaction (qPCR) also revealed that the addition of citric acid significantly decreased the relative abundances of Geobacter in the different soils by 8–28 times while the relative abundances of Clostridium increased by 2–5 times. These results provide significant insight on As transformation in different types of rice rhizospheric soils and guidance for the application of rice varieties with low citric acid exuding to restrict As accumulation. [Display omitted] • Citric acid addition increased As(V) and total As in soil porewater in ten soils. • Different soil microbial communities were mainly affected by F1/Fe/As. • Citric acid shifted the main Fe(III)/As(V) reducing bacteria in different soils. • Citric acid decreased gene expression of Geobacter while increased Clostridium. • Citric acid addition increased the gene expression of arsC. [ABSTRACT FROM AUTHOR]

The oxidation of pyrite results in the formation of a solid film passivation layer on its surface. This layer effectively hinders the direct interaction between H 2 O, O 2 , and the pyrite surface, thereby impeding the oxidation dissolution of pyrite. There are few studies on whether alumina (Al 2 O 3), a common aluminum-containing oxide, affects the formation of a solid film passivation layer on the surface of pyrite and inhibits the oxidation dissolution of pyrite. This research investigates the impact of Al 2 O 3 incorporation on the speciation transformation of S, Fe, and Al on the surface of pyrite during oxygen pyrite process. The oxidation of pyrite followed the "polysulfide-thiosulfate" complex oxidation pathway. When <1.5 g/L Al 2 O 3 was introduced, it increase pyrite oxidation, whereas ≥1.5 g/L Al 2 O 3 prevented pyrite oxidation. The process of Al 2 O 3 dissolution results in the consumption of H+ and the subsequent release of Al3+. This, in turn, facilitates the hydrolysis of Fe3+ and Al3+ to generate a secondary mineral layer on the pyrite surface. As a result of the accumulation of S promotes the formation of polysulfide chemical (FeS n) or iron deficiency sulfide (Fe 1-x S), resulting in the formation of a solid film passivation layer composed of sulfur film and secondary mineral layer. The results demonstrated that Al 2 O 3 can promote the formation of a solid film passivation layer on the surface of pyrite, which has significant implications for controlling the oxidation dissolution process of pyrite and offers a new perspective for the source control of acid mine drainage. [Display omitted] • Morphological transformation of S, Fe and Al during pyrite oxidation were influenced by Al 2 O 3. • Al 2 O 3 was found to promote the development of a secondary mineral layer on the pyrite surface. • The secondary mineral layer facilitated the formation of a sulfur film on the pyrite surface. • The oxidation of pyrite followed the "polysulfide-thiosulfate" composite oxidation process. • The formation of solid film passivation inhibited the oxidative dissolution of pyrite. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[Display omitted] • Fractions and transformation of P together with key metals are researched. • P tends to transform into more stable P fractions during pyrolysis. • TP, IP, HCl-P and HCl-Ca/-Mg increases as pyrolysis temperature increases. • NaOH-P is the dominant fraction, enabling sludge biochars to act as a P fertilizer. Pyrolysis of sewage sludge (SS) to SS biochars (SBCs) is a promising method for maximizing the utilization of phosphorus (P) in SS. A comprehensive understanding of P distribution and transformation in SS and SBCs is fundamental for the recycling of P from these materials as a soil amendment. Most studies have focused on P itself in SS and SBCs, without examining the changes of closely related metals (e.g., Al, Ca, Fe and Mg) that are typically co-extracted with P. Thus, in this study, a series of investigations were performed in which an improved Hedley sequential extraction method of P was used together with advanced analytical techniques to determine the distribution and transformation of P in SS and SBCs. Increasing the pyrolysis temperature increased concentrations of total P and inorganic P in SS and SBCs. In addition, P and Al species in SS and SBCs were predominantly sodium hydroxide-soluble species—denoted NaOH-Al and NaOH-P—and increasing the pyrolysis temperature increased their concentrations in SBCs, especially for NaOH-Al, from 28.35 ± 2.56 mg/g to 38.18 ± 3.29 mg/g. Ca, Mg and Fe were predominantly extracted by HCl solution, showing that HCl-extracted P comprised not only Ca-P but also Fe-P, Mg-P and Al-P. Spectroscopic analyses revealed that the concentration of hydroxyapatite (HAp) in SS and SBCs increased with the pyrolysis temperature, and Al-P was the dominant species in both SS and SBCs. Thus the pyrolysis of SS affords SBCs that are a relatively stable pool of P for plants, enabling SBCs to serve as a slow-release P fertilizer in soil. These findings further contribute to fundamental knowledge on the recycling of P during integrated waste management. [ABSTRACT FROM AUTHOR]

Abstract The release of arsenic vapors (As3+) during high-arsenic coal combustion not only raises serious environmental concerns, but also causes catalyst deactivation in selective catalytic reduction (SCR) systems. To illuminate the mechanisms involved in the transformation of arsenic vapors towards less troublesome arsenates (As5+) during coal combustion, the accessory minerals in the high-arsenic coal were identified and the association relationship of these compounds with arsenic in fly ash was estimated. The results showed that Si/Al were the main inorganic elements in high-arsenic coal while the content of Ca was quite low. Ca was mostly transformed into sulfates during coal combustion and the effect of Ca on the arsenic transformation was limited. Al/Fe played a more significant role in arsenic speciation transformation and arsenic in the fly ash was predominantly bound with Al/Fe-oxides as arsenates. It was further confirmed that Al in kaolin/metakaolin showed good capacity on arsenic capture. In addition, few arsenic vapors were captured through the physical adsorption mechanism and the large fraction of As3+ in some fine particles was mostly attributed to the chemical reactions between arsenic vapors and Al-compounds. Meanwhile, a certain amount of arsenic vapors were converted into As 2 O 5 (s) under the influence of SCR catalyst and then carried by flue gas to participate in fly ash. Besides, part of arsenic distributed in the fly ash was through the stabilization of ash matrix in high temperature conditions. The transformation of arsenic from vapors towards particulate arsenic favored arsenic emission control by particulate matter control devices. [ABSTRACT FROM AUTHOR]

The interactions between low-molecular weight organic acids (LMWOAs) and selenium (Se) on mineral/water interfaces affect the release, immobilization and bioavailability of Se in nature. Herein, the effects of three environmentally relevant LMWOAs (i.e., oxalic (Oxa), succinic (Suc) and citric (Cit) acids) on Se(IV) adsorption to goethite under oxic conditions were investigated using batch experiments, speciation fractionation, and ATR-FTIR and XPS analyses. The LMWOAs exhibited a competitive-synergistic coupling effect on Se(IV) adsorption to goethite, which inhibited the adsorption rate of Se(IV) by 14.1, 13.3 and 8.0 times. However, immobilization of Se(IV) was simultaneously enhanced by 39.1%, 34.6% and 14.1% in the following order Oxa > Suc > Cit. The results obtained by fractionation of the adsorbed Se(IV) revealed that the enhancement was due to surface binding as well as speciation transformation from ligand-exchangeable Se(IV) into residual fractions, which increased by approximately 18% in the presence of the LMWOAs. The dissolution of goethite significantly improved due to the LMWOAs and decreased to different degrees as the concentration of Se(IV) increased. The monodentate mononuclear complexes (58.2%) and Lewis base sites bonded Se (41.8%) were the predominant surface species of Se(IV) in goethite-Se(IV) system. The ATR-FTIR and high-resolution XPS analyses demonstrated that the formation of ≡FeO(SeO)O-CO surface complexes (22.8–27.0%) occurred in the presence of LMWOAs, which could be closely correlated with the interface-mediated reduction of Se(IV). In addition, the predominant mechanism for the formation of residual Se is LMWOA specific, in which ferric selenite-like precipitation was dominant for Suc (10.6%) and Cit (11.6%) and reduction was dominant for Oxa (17.5%). Overall, LMWOAs play an important role in Se(IV) immobilization and speciation transformation and may facilitate understanding the Se bioavailability in rhizosphere soils under oxic conditions. Unlabelled Image • The effect of LMWOAs on Se(IV) speciation transformation was investigated under oxic conditions. • The fractionation and speciation of adsorbed Se(IV) were evaluated using ligand-exchange extraction, ATR-FTIR and XPS. • The LMWOAs significantly promote the transformation of surface Se(IV) into residual fractions. • Ferric selenite-like precipitates and reduced Se(0)/Se(-II) contribute to Se(IV) speciation transformation. • The underlying mechanism of Se(IV) speciation transformation is LMWOA specific. [ABSTRACT FROM AUTHOR]

• Migration and environmental risk of metals in thermal treatment of LCD panels were investigated. • Cr, Ni, In, Cu, Fe and Zn tends to migrate into gas/fly ash in the treating process. • Cr, Ni, Fe and In was partly transformed from stable fraction to unstable state. • Ecological risk of In and Cu in solid residue increased after thermal treatment. • Leaching toxicity of metals in solid residue decreased except that Cu and Ni increased. Thermal treatment has been proved to be an efficient and promising method for organics removal from LCD panels and for resource recycling. Considering with the toxic metals contained in LCD panels and their potential risk, it is necessary to study and evaluate the metals behavior and potential risk associated with the thermal treatment of LCD panels. In this study, the migration and transformation behavior of ten metals (Cr, As, Al, In, Ni, Cu, Zn, Cd, Fe, Sn) in LCD panels were investigated during thermal treatment, as well as their potential environmental risk and leaching toxicity in solid residue were evaluated. Results showed that Cr, Ni, In, Cu and Fe exhibit obvious migration behavior from solid into gas phase/fly ash during thermal treatment, with the maximum migration rate of 52.8%, 54.7%, 37.7%, 30.8%, and 34.9% respectively under the experimental condition. Speciation transformation for the metals of Cr, Ni, In, Cu, Fe and Zn was also observed in solid residue after thermal treatment, which leads to the ecological risk increase of Cu, In and contamination risk increase of Fe. Meanwhile, the leachable concentration and leaching toxicity of Cu and Ni in solid residue showed increasing trend after thermal treatment. The results indicate that attentions should be paid on the emission control of Cr, Ni, In, Cu, Fe during thermal treatment of LCD panel scraps. Environmental risk of Cu, In, Fe and the leaching toxicity of Ni in solid residue after thermal treatment should also be concerned. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Highlights: • Sewage sludge was hydrothermally treated to explore the phosphorus fate. • 70% of total phosphorus existed in the hydrothermal solid product. • NAIP gradually transformed into AP by the hydrothermal treatment. • Complete transformation of NAIP to AP was attained by the addition of CaO. Abstract Phosphorus is an essential resource for organism growth in nature. In order to recover phosphorus from sludge, the effects of temperature, time, pH and CaO on the migration and transformation of phosphorus during hydrothermal treatment were investigated. The results demonstrated that approximately 30% of total phosphorus (TP) existed in the hydrothermal supernatant in the temperature range of 200–260 °C. In the solid products, non-apatite inorganic phosphorus (NAIP) gradually transformed into apatite (AP) as the hydrothermal temperature increased. When the solution was adjusted to be acidic, both AP and NAIP were dissolved. However, only NAIP was dissolved in alkaline hydrothermal solution. Moreover, complete transformation of NAIP to AP was attained by the addition of CaO. The products Ca 3 (PO 4) 2 and Ca 7 Mg 2 (PO 4) 6 were detected by X-ray diffraction (XRD), which verified the speciation transformation of phosphorus in presence of CaO during the hydrothermal treatment process. These results had implications for the feasibility of directionally producing Ca-P with high bioavailability and reducing the dependence on limited phosphorus resource. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Although numerous studies on the stabilization of heavy metals in contaminated soil with iron-based materials have been conducted, the role of microorganisms in iron species and Cd speciation transformation has not been fully elucidated. Here, 2-line ferrihydrite (MGE) and goethite (GE) were prepared and used to stabilize Cd in contaminated soil. Based on the microbial community characteristics in the early, middle, and later stages, the role of microorganisms in Cd speciation transformation was explored. The exchangeable Cd decreased by 10.73 %–51.31 %, while the iron‑manganese oxide-bound speciation, and the residual speciation increased after MGE/GE application. The relative abundance of Proteobacteria , and Sphingomonas were obviously increased, and Trichoderma and Mortierella were decreased in the MGE group. The outcome in the GE group was the opposite. The complexity of the bacterial and fungal community network was increased in the MGE and GE groups. The lignin in MGE could stimulate the growth of iron-reducing bacteria (FeRB) and promote the reduction of iron minerals to Fe2+. The Fe2+ in the soil was oxidized and hydrolysed, which might lead to an increase in the soil pH. During the process of iron species transformation and iron redox mediated by FeRB, Cd was transformed to more stable speciation. [Display omitted] • Two iron-based materials promote Cd transformation to more stable speciation. • Microbial community structure and composition were obviously changed. • The complexity of the microbial community was increased. • The lignin in 2-line ferrihydrite stimulated the growth of iron-reducing bacteria. [ABSTRACT FROM AUTHOR]

Biochar, a carbon (C)-rich material obtained from the thermochemical conversion of biomass under oxygen-limited environments, has been proposed as one of the most promising materials for C sequestration and climate mitigation in soil. The C sequestration contribution of biochar hinges not only on its fused aromatic structure but also on its abiotic and biotic reactions with soil components across its entire life cycle in the environment. For instance, minerals and microorganisms can deeply participate in the mineralization or complexation of the labile (soluble and easily decomposable) and even recalcitrant fractions of biochar, thereby profoundly affecting C cycling and sequestration in soil. Here we identify five key issues closely related to the application of biochar for C sequestration in soil and review its outstanding advances. Specifically, the terms use of biochar, pyrochar, and hydrochar, the stability of biochar in soil, the effect of biochar on the flux and speciation changes of C in soil, the emission of nitrogen-containing greenhouse gases induced by biochar production and soil application, and the application barriers of biochar in soil are expounded. By elaborating on these critical issues, we discuss the challenges and knowledge gaps that hinder our understanding and application of biochar for C sequestration in soil and provide outlooks for future research directions. We suggest that combining the mechanistic understanding of biochar-to-soil interactions and long-term field studies, while considering the influence of multiple factors and processes, is essential to bridge these knowledge gaps. Further, the standards for biochar production and soil application should be widely implemented, and the threshold values of biochar application in soil should be urgently developed. Also needed are comprehensive and prospective life cycle assessments that are not restricted to soil C sequestration and account for the contributions of contamination remediation, soil quality improvement, and vegetation C sequestration to accurately reflect the total benefits of biochar on C sequestration in soil.

In soils, the speciation transformation of As were inherently related to the behaviors of iron (oxyhydr) oxides. It is poorly understood that the effects of the transformation of iron (oxyhydr) oxides coupled with As speciation transformation during dissimilatory Fe(III) reduction (DIR) involving with humic substances (HS) as electron donor or shuttle in soils with high arsenic geological background. In this study, the relationships between the transformation of iron (oxyhydr)oxides and As speciation transformation were investigated according to the response between continuously As speciation monitoring and iron (oxyhydr) oxides identification during DIR in the soils. The results showed that F4 (arsenic incorporated with amorphous iron (oxyhydr)oxides including ferrihydrite and schwertmannite) and F5 (arsenic incorporated with crystalline iron (oxyhydr)oxides including hematite and magnetite) were the main source and sink for As(III) Dissolved during DIR. During the incubation period, Fe(II) was the dominant driving force for the reduction of As(V) in the water-soil system. The XRD analysis indicated the changes of iron oxides such as ferrihydrite, schwertmannite, hematite and magnetite were closely related to the release and reduction of As, and those iron oxides could play governing roles for As speciation transformation during DIR in soils. Different from the known mechanism in low As concentrations, a limiting effect of As concentration on iron oxides transformation was found in our incubation experiments using soils with high As geological background (∼1000 mg/kg). This work provides new insights for Fe as governing role in As speciation transformation in soils with high arsenic geological background by firstly identifying the corresponding iron (oxyhydr)oxides in operationally defined arsenic speciation incorporated with iron oxides. [Display omitted] • Reduction and release of As was governed by iron (oxyhydr)oxides. • The minerals evidence of As speciation transformation was found out. • The potential pathway of As speciation transformation in DIR involved HS was explored. • As speciation transformation in soils with high arsenic geological background was investigated. [ABSTRACT FROM AUTHOR]

The release of arsenic (As) during municipal solid waste (MSW) incineration results in a new sources of anthropogenic arsenic contamination. Arsenic toxicity depends not only on the quantity but also on its speciation. At high temperatures, arsenic is predominantly present as vapors (As 2 O 3 (g)) and its speciation transformation is determined by the interactions between As 2 O 3 (g) and inorganic compounds. In this study, synchrotron X-ray absorption near-edge structure (XANES) was used to investigate the speciation transformation of arsenic during MSW combustion and flue gas cooling process. However, arsenates in various forms are hardly distinguished by using XANES alone. Considering that various arsenates are of different thermal stability, the thermal stability of arsenic in MSW incineration fly ash was examined to provide detailed information regarding arsenic speciation in the ash samples. To further understand the relationships between arsenic and inorganic compounds, the sequential extraction procedures of arsenic in the ash were conducted. The results show that the oxidation of As 2 O 3 (g) during MSW combustion is incomplete and is continuously performed in flue gas cooling process. The physical adsorption of As 2 O 3 (g) is favored at low temperature by ash particles, especially by the injection of CaO in the flue gas. Various kinds of arsenates are formed due to the interactions between As 2 O 3 (g) and Ca, Fe and/or Al compounds. Some of the arsenates are thermally unstable and are decomposed when the fly ash was heated at 1323 K. Part of arsenic is stabilized in the ash matrix including some un-oxidized As(III) which remained stable even when the ash was heated at 1323 K. [ABSTRACT FROM AUTHOR]

Microorganisms dominated speciation of arsenic (As) play an important role in the biogeochemical cycling of As. In the study, species transformation of arsenite [As(III)] and As(III) influx and efflux across the cell membranes of Trichoderma asperellum SM-12F1, Penicillium janthinellum SM-12F4, and Fusarium oxysporum CZ-8F1 cells were studied using a cellular lysis plus chromatographic separation method and further the in-situ X-ray absorption near edge structure (XANES) analysis. The results indicated that As(III) can enter into fungal cells and that a portion of the As(III) can be exuded out of cells. For both As sequestrated into fungal cytoplasm and As adsorbtion onto cell walls, As(III) was found to be the dominated form of As. XANES analysis showed that As(III) accounted for 58.4%, 59.5%, and 73.0% of the total As in the cells of T . asperellum SM-12F1, P . janthinellum SM-12F4, and F . oxysporum CZ-8F1, respectively. Among these fungal strains, however, there were obvious differences in the relative proportions of arsenate [As(V)], monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA). For T . asperellum SM-12F1, the proportion (%) of MMA was 31.1%, and no As(V) or DMA was detected. For F . oxysporum CZ-8F1, the proportions of As(V) and MMA were 15.8% and 8.8%, respectively, but no DMA was observed. As(V), MMA, and DMA accounted for 4.2%, 29.5%, and 8.1%, respectively, of the P . janthinellum SM-12F4 cells. Some of the intracellular As(III) can be oxidated and methylated by these fungal strains and yield As(V), MMA, and DMA as products. [ABSTRACT FROM AUTHOR]

The biogeochemical cycle of sulfur can directly affect the speciation transformation of heavy metals in soils and their accumulation in plants. The toxicity of heavy metals in plants can be alleviated by their complexation with sulfur compounds like phytochelatins or metallothiones, consisting of the major mechanisms of phytodetoxification. Sulfur deficiency is becoming one of the limiting factors that influence Chinese agricultural production. Although the applications of sulfur fertilizer in soil have received much attention in recent years, the interaction mechanism of heavy metal with sulfur metabolism has not been studied extensively. In this paper, we reviewed current research advance on the impact of sulfur on the speciation transformation of soil heavy metals and their accumulation in plants, discussed the effect of sulfur on the detoxification mechanism of heavy metal in plants and provided further research prospective in this field. [ABSTRACT FROM AUTHOR]

Highlights: [•] Sb accumulation and its accompanied toxicities varied with plant species. [•] Many factors can affect the uptake and accumulation of Sb in plants. [•] Sb can disturb photosynthesis, and some substances’ uptake or assimilation. [•] Plants equip various mechanisms to alleviate Sb toxicity or reduce Sb uptake. [Copyright &y& Elsevier]

Abstract: Bioremediation of arsenic (As)-contaminated soil using microorganisms has been a focus of research because it is environment friendly and cost-effective. The As-resistant fungi Trichoderma asperellum SM-12F1, Penicillium janthinellum SM-12F4, and Fusarium oxysporum CZ-8F1 were exposed to 50mgl−1 of As(V), and the biotransformation of As and the concomitant variance of Eh and pH in the media were studied. Fresh weights of all three isolates increased and then decreased depended on cultivation period. After cultivation for 2 or 3days, the As(V) added to the media had been completely changed into As(III), whilst As(V) was predominate in fungal cells with concomitantly little As(III) during cultivation. After 15days, little monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) besides of As(V) and As(III) were found in the cells of T. asperellum SM-12F1, and the total As content was the highest in cells of P. janthinellum SM-12F4 (about 41.5μg) according to the quantitative analysis of As speciation in cultures. Moreover, when cultivation period reached 3days, the Eh and pH in the media of T. asperellum SM-12F1 (312.5mV and 4.8), P. janthinellum SM-12F4 (411.1mV and 4.2), and F. oxysporum CZ-8F1 (269.4mV and 4.8) might not responsible for the reduction of As(V) based on the previous study. Therefore, it is speculated that import/export, reduction, and methylation of As are conducted in fungal cells. Future studies investigating the biochemical behaviour of fungi responding to As are needed to gain a better understanding of bioremediation of As-contaminated soils. [Copyright &y& Elsevier]

This study assesses the level of contamination of Hg in farmland soils along the irrigating channel downstream from Guizhou Organic Chemical Factory (GOCF), where metallic mercury is used as a catalyst to produce acetic acid. The total input of mercury into the environment, as announced by GOCF, is 140 t in the past 30 years (1971–2000). Sampling sites were chosen based on the distance from the source of pollution—the chemical factory. A total of 39 samples were collected from the study area and analyzed for total mercury concentrations and methyl mercury concentrations. The characteristics of vertical and horizontal distributions of total mercury and methyl mercury in the study area (farmland) are described in this paper. Much attention was paid to the transformation of inorganic Hg into organic mercury species in soils as well. The results showed that the farmland has been heavily contaminated by Hg. Land cultivation activity, land utilization style and distance from the pollution source could be the dominant factors controlling the distribution of THg and MeHg. It is observed that active transformation of inorganic Hg into organic mercury species (MeHg) usually takes place in paddy soils. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sewage sludge addition modified potentially toxic element content and fractions. • Potentially toxic element content and ecological risks decreased over time. • Percentage of mobile fractions decreased and that of residual fractions increased. • Large-scale utilization of sewage sludge to forest soil is promising. Sewage sludge (SS) application on forest plantation soils as a fertilizer/soil amendment is increasingly becoming a forestry management measure. However, the potential risk of SS-derived potentially toxic elements (PTEs) is still a cause for concern. This research was carried out to evaluate PTEs behavior in SS applied as an amendment for forestland application purposes. Speciation and transformation perspectives on residual effects during a 3-year field experiment were evaluated. Sewage sludge was applied to soils under Eucalyptus urophylla S.T. Blake, Schima superba Gardn. et Champ, and Pinus elliottii Engelm plantations at 30 Mg·ha−1 (dry weight). We investigated the total concentrations of Cu, Zn, Pb, Cd, and Ni, as well as their concentrations of five fractions: exchangeable (F1), bound to carbonates (F2), Fe–Mn oxides (F3), organic matter (F4), and residual (F5) along with the 0–10 cm of a surface A horizon (topsoil) one day, one, two, and three years after SS application, respectively. Sewage sludge caused significant increase in PTEs total concentrations and proportion of fraction F1 or F2. The mobility index and potential ecological risk confirmed that the risk was linked to the presence of these PTEs, especially for Cd. The total concentration and corresponding ecological risks of PTEs in most cases decreased, suggesting a potential loss of PTEs from the topsoil system. The percentage of all PTEs in fractions F1–F4 decreased and that in F5 increased with time. These results illustrate that the residual and mobility of PTEs in the topsoil during SS utilization was lower than expected and more attention should be paid to the risk of PTEs transferring to other environments. [ABSTRACT FROM AUTHOR]

• Speciation and fate of as during FeAsS bio-oxidation with RM added is studied. • RM can significantly affect FeAsS dissolution and as fate. • Small amount of RM (≤ 4 g/L) favors for FeAsS dissolution and as precipitation. • SiO 2 @ (As, Fe, Al, Si) spherical nanoparticles (SNs) substantially immobilize as. • The formation of SiO 2 -based SNs is defined by Fe3+ concentration and solution pH. Red mud (RM) as waste of industrial aluminum production is piling up in huge ponds. RM could be a cost-effective adsorbent for heavy metals, but adsorption is vulnerable to pH changes, metal ions speciation and the occurrence of iron bearing minerals. In this study, the precipitation and elemental speciation transformation relevant to arsenic fate in responding to the addition of RM during arsenopyrite bio-oxidation by Sulfobacillus thermosulfidooxidan s was investigated. The results show that the addition of RM significantly changed the arsenic precipitation and the solution chemistry and thus affected the arsenopyrite bio-oxidation and arsenic fate. An addition of a small amount (≤ 4 g/L) of RM substantially promoted arsenopyrite bio-oxidation with formation of SiO 2 @ (As, Fe, Al, Si) spherical nanoparticles that can enhance the stability of the immobilized arsenic. The SiO 2 -based spherical nanoparticles precipitate was mainly composed of jarosites, amorphous ferric arsenate and crystalline scorodite, and its formation were controlled by Fe3+ concentration and solution pH. An addition of increased amount of RM (≥ 6 g/L) resulted in a significant increase of the solution pH and a decrease in the Fe2+ bio-oxidation activity, and spherical nanoparticles were not formed. Consequently, the dissolution of arsenopyrite was inhibited and the release of arsenic was blocked. This study suggests the applicability of RM in mitigation of arsenic pollution from bio-oxidation of As-bearing sulfide minerals. [Display omitted] [ABSTRACT FROM AUTHOR]

• HA affects FeAsS weathering from electrochemical view was first studied. • HA promoted FeAsS erosion, As transfer and inhibited H+ release to a certain degree • The weathering rate of FeAsS and temperature/acidity had a linear relationship. • Charge transfer surface reaction controlled FeAsS weathering at E a of 24.1 KJ•mol−1. • As-HA/As-Fe-HA formation via -COOH/-OH ligand exchange decreased As bioavailability. Arsenopyrite is a common metal sulfide mineral and weathers readily in the open environment, releases As, and pollutes the surrounding environment. Humic acid (HA) is ubiquitous in soils, sediments and waters, and contains various functional groups and complex with arsenic, iron and other metal ions that affect the weathering behavior of arsenopyrite. Because As, iron, and HA are redox-active compounds, electrochemical techniques, including polarization curves, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), were used to fundamentally investigate the weathering process and mechanism of arsenopyrite over a wide range of environmental relevant conditions. Polarization curves showed higher HA concentrations (0-1000 mg•L−1), higher temperatures (5-35°C) or acidities (pH 1.0-7.0) promoted arsenopyrite weathering; there was a linear relationship between the corrosion current density (i corr), temperature (T) and acidity (pH): i corr = -3691.2/ T + 13.942 and i corr = -0.2445pH + 2.2125, respectively. Arsenopyrite weathering readily occurred in the presence of HA as confirmed by its activation energy of 24.1 kJ•mol−1, and EIS measurements confirmed that the kinetics were controlled by surface reaction as confirmed by decreased double layer resistance. CV and surface characterization (FTIR and XPS) showed that arsenopyrite initially oxidized to S0, As(III) and Fe2+, then S0 and Fe2+ were ultimately converted into SO 4 2− and Fe3+, while As(III) oxidized to As(V). Furthermore, the carboxyl (–COOH) and phenolic (–OH) of HA could bind with As(III)/(V) and Fe3+ via a ligand exchange mechanism forming As(III)/(V)-HA and As(III)/(V)-Fe-HA complexes that hinders the formation of FeAsO 4 and decreases the bioavailability of As. Findings gained from this study are valuable for the understanding of the fate and transport of As in acidic conditions, and have powerful implications for the remediation and management of As-bearing sites affected by mining activities. [Display omitted] [ABSTRACT FROM AUTHOR]

Landfill refuse is a mixture of inorganic minerals and organic matter that is capable of undergoing complexation and redox reactions due to its active functional groups. Organic matter often combines with minerals in landfill refuse and it remains unclear whether this combination involves electron transfer. Therefore, the effects of landfill refuse composition on reductive dechlorination and speciation transformation of heavy metals were investigated in this study. Results show that landfill refuse comprises protein- and humic-like substances, aliphatic structures, and a large number of hydroxyl, carboxyl, quinoid and other active functional group. The electron donating capacity (0.09–0.26 μmol/g(C)) of landfill refuse was found to be higher than its electron accepting capacity (0.03–0.23 μmol/g(C)), indicating that electron donating groups (hydroxyl) were the main redox-active moieties, facilitating the reductive dechlorination of pentachlorophenol (PCP) by microorganism. Fe 2 O 3 , FeO and SiO 2 were the main inorganic minerals affecting PCP dechlorination. The speciation distribution of heavy metals in landfill refuse was determined by the BCR sequential extraction method. Results showed that Zn and Ni have high potential migration capacity, poor stability and the highest bioavailability, while Cr, Cu and Pb are relatively stable and have weak migration potential. The oxygen- and nitrogen-containing functional groups, aliphatic structures and aromatic carbon in landfill refuse can promote the transformation of Ni and Cr from an unstable to stable state. Protein-like substances exhibit a strong Cu binding ability, allowing Cu to combine with organic matter more easily than other assessed heavy metals. Both Fe 2 O 3 and FeO affected the stability of Cu. FeO promoted the stabilization of Zn, whereas Fe 2 O 3 and SiO 2 promoted Cu instability. These results could provide some references for the treatment of organic chlorides and the stabilization of heavy metals in landfill refuse in China. Unlabelled Image • The EDC of landfill refuse was higher than the EAC. • Fe 2 O 3 , FeO and SiO 2 were the main inorganic minerals affecting PCP dechlorination. • Zn and Ni have high migration potential, while Cr, Cu and Pb have the opposite. [ABSTRACT FROM AUTHOR]

• Se is higher in the rear ESP ash than in front hopper due to Se enrichment in PM 2.5. • Se (IV) was the dominant chemical species (＞90%) including SeO 2 (s) and selenites. • Fe may lead to the Se (VI) formation in coarse fly ash. • Fabric filter (FF) can relatively capture more selenium (＞60%) through physical condensation at lower temperature. Selenium (Se) mostly evaporates during coal combustion and the transformation of gaseous Se towards particulate forms favors its emission control by dust purification devices. For better control of Se emission, the present study explored the relationship between Se retention and fine particles removal during coal burning. The distribution of Se within the dust collection system followed a non-linear increasing trends i.e., the concentration of Se peaked in the last ESP hoppers and was significantly enriched in PM 2.5. Further study demonstrated that the conversion pathway of SeO 2 (g) to the particulate Se is related to the types of ash collection devices (ESP vs FF). More Se (g) condensed to SeO 2 in FF ash (greater than 60%) whereas the chemisorption dominated the formation of Se-enriched ESP ash (greater than 65%). With selenites (IV) being the dominant chemical forms in fly ashes, selenate (VI) was found to be enriched in the coarse ESP ash which may be formed through the capture and oxidation by Fe-oxides. Compared with arsenic from the same power plants, more gaseous selenium penetrated the ash collection devices. Se tended to be more enriched in fine particles and can be more captured by fly ash through physisorption relative to As. The results suggested that the contribution of each ash collection devices for Se removal should consider not only the unique enrichment behavior of Se towards the rear ESP hoppers and fine particles (PM 2.5), but also using fabric filter or other techniques for strengthening the process of condensation of SeO 2 (g). [ABSTRACT FROM AUTHOR]

• The effect of humic acid (HA) on bio-oxidation of FeAsS was first studied. • HA simultaneously promotes FeAsS dissolution and As immobilization. • The flocculent porous structure favors to FeAsS dissolution in the presence of HA. • A new way was provided for As immobilization in FeAsS bio-treatment. The bio-oxidative dissolution of arsenopyrite, the most severe arsenic contamination source, can be mediated by organic substances, but pertinent studies on this subject are scarce. In this study, the bio-oxidative dissolution of arsenopyrite by Sulfobacillus thermosulfidooxidans and arsenic immobilization were evaluated in the presence of humic acid (HA). The mineral dissolution was monitored through analyses of the parameters in solution, phase and element speciation transformations on the mineral surface, and arsenic immobilization on the surfaces of cells and jarosites-HA. The results show that the presence of HA enhances the dissolution of arsenopyrite, e.g., 7.1% of arsenopyrite was in the residue after 12 d of bio-oxidation compared to 19.3% in the absence of HA. Meanwhile, the presence of HA led to changes of the fates of As and Fe and no accumulation of elemental sulfur (S0) or ferric arsenate on the mineral surface. Moreover, a flocculent porous structure was formed on the surfaces of both microbial cells and jarosites, on which a large amount of arsenic was adsorbed. These results clearly indicate that HA can simultaneously promote the dissolution of arsenopyrite and arsenic immobilization, which may be significant for bioleaching of arsenopyrite-bearing contaminated sites. [ABSTRACT FROM AUTHOR]

We constructed consortia of Chlorella salina and Bacillus subtilis with various alga-bacterium ratios (1:0, 1:1, 1:2, 1:3, 1:4). After being treated with arsenate [As(Ⅴ)] for 7 d, we measured the growth, As accumulation, adsorption and absorption, and As speciation transformation of consortia. Results showed that the chlorophyll content, dry weight, and specific growth rate of the symbiont increased significantly with increasing B. subtilis ratio after the As(Ⅴ) treatment, being 1.81 mg·L -1 , 125.0 mg, and 0.28 mg·L -1 ·d -1 under the condition of the alga-bacterium ratio being 1∶4 and As(Ⅴ) being 750 μg·L -1 , respectively. The accumulation and absorption of As by the consortia decreased with the bacterial proportion increasing from 1:0 to 1:4. As accumulation changed with the As concentration, with a dominance of absorption under 75-150 μg·L -1 As(Ⅴ) and a dominance of adsorption under 300-750 μg·L -1 As(V). There were As(Ⅴ) and As(Ⅲ) in the consortia. When the proportion of bacteria increased, the rate of As(Ⅴ) reduction enhanced (up to 12.6%). Our results indicated that the increases of B. subtilis improved As(Ⅴ) tolerance and reduction, but decreased the As(Ⅴ) accumulation by the symbiont.

The mobility of plutonium (Pu) in groundwater is dependent of its speciation distribution and transformation. The speciation and transformation kinetics of Pu(IV) and its colloids in highly saline groundwater have, however, been rarely studied. In the present study, groundwater (Ionic strength 1 M) from Dunhuang region, NW China, was collected for investigating the speciation, transformation kinetics and fate of spiked Pu (IV) with aging time. The results showed that ~99% of the spiked Pu (IV) (over initial concentration c 0 range 2.5 × 10−10–7.8 × 10−7 mol·L−1) was easily associated with the natural colloids and transformed into relatively unstable Pu pseudo-colloids in 1 day, which then gradually deposited and/or adsorbed on the container walls with aging. The suspended Pu pseudo-colloids decreased in similar exponential models, with rate equations r(t) = −3.1 × 10−10e– t /4 and −1.3 × 10−8e–/3 for c 0 = 1.25 × 10−9 mol·L−1and 4.17 × 10−8 mol·L−1, respectively. The chemical speciation of the suspended colloidal Pu was dominated by "Fe/Mn Oxides" at the early time, while "Carbonates" with slower depositing rate ( r(t) = −6.9 × 10−12e– 0.149 t ) dominated it (~82%) at equilibrium state. Whatever the c 0 was, the concentration of dissolved Pu (i.e., the apparent solubility of Pu) kept at 0.7 × 10−11 mol·L−1 over aging. The valence of dissolved Pu was dominated by Pu(IV) at early time, while Pu(V + VI) would become dominant (~95%) at equilibrium state with transformation rate of r(t) = −92.9e– t/ 16. 6 + 96.9. The equilibrium times of Pu deposition (and/or adsorption), speciation transformation of the suspended colloidal Pu, and valence change of the dissolved Pu were 30 d, 80 d and 120 d, respectively. The kinetic process for each Pu species could be well fitted with exponential model. These results suggest that the majority of released Pu(IV) into highly saline groundwater will be easily associated with natural aquatic colloids and then become immobile in short time due to deposition (and/or adsorption) onto the environmental medium, but potential migration risk caused by stable suspended Pu colloids cannot be ignored. Unlabelled Image • We investigated the speciation transformation kinetics and fate of spiked Pu (IV) in highly saline groundwater from Dunhuang region, NW china for the first time. • We found that ~99% of the spiked Pu (IV) was easily associated with the natural aquatic colloids and transformed into relatively unstable Pu pseudo-colloids in 1 day, which then gradually deposited. • The suspended Pu pseudo-colloids decreased in exponential mode with the rate equations of r(t) = –3.1×10-10e– t /4 and r(t) = –1.3×10-8e– t /3 for c 0 of 1.25×10-9 mol·L-1and 4.17×10-8 mol·L-1, respectively • The equilibrium times of the deposition and the speciation transformation of the colloidal Pu and the speciation transformation of the dissolved Pu are 30 d, 80 d and 120 d, respectively • The relative lower apparent solubility of Pu in the groundwater was obtained to be 0.7 × 10-11 mol·L-1. [ABSTRACT FROM AUTHOR]

The application of sewage and manure in protected vegetable cultivation can induce the occurrence of heavy metals contamination. The present research studied the transformation of heavy metals (Cd, Cu, Pb and Zn) by incubating contaminated protected soil with maize straw and then leaching. The results showed that soil pH was significantly decreased, being more evident in maize straw treatment; soil Eh dropped quickly below -280 mV. Maize straw treatment promoted the activation of Cd, Cu, Pb and Zn from soil, and the total percent of oxidizable fraction and residual fraction of Cd, Cu, Pb and Zn declined at 9 th day; the amount of Cd, Cu, Pb and Zn in soil reduced 18.1%, 19.0%, 16.1% and 15.7% at 15 th day, respectively. Compared to control, maize straw treatment could increase the concentrations of dissolved Cd and Zn, but Cu decreased. The concentration of colloidal-bound Cd and Pb increased, Cu decreased and no significant change occurred in Zn in maize straw treatment. Strong reductive approach could activate heavy metals in protected vegetable soil, increase the risk of heavy metals accumulation in vegetables, and possibly cause water pollution accompanied with soil water mobilization.