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Copyright of Acta Petrologica et Mineralogica / Yanshi Kuangwuxue Zazhi is the property of Acta Petrologica et Mineralogica 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.)

The arsenic (As) release from litter decomposition of As-hyperaccumulator (Pteris vittata L.) in mine areas poses an ecological risk for metal dispersion into the soil. However, the effect of atmospheric nitrogen (N) deposition on the litter decomposition of As-hyperaccumulator in the tailing mine area remains poorly understood. In this study, we conducted a microcosm experiment to investigate the As release during the decomposition of P. vittata litter under four gradients of N addition (0, 5, 10, and 20 mg N g−1). The N10 treatment (10 mg N g−1) enhanced As release from P. vittata litter by 1.2–2.6 folds compared to control. Furthermore, Streptomyces, Pantoea, and Curtobacterium were found to primarily affect the As release during the litter decomposition process. Additionally, N addition decreased the soil pH, subsequently increased the microbial biomass, as well as hydrolase activities (NAG) which regulated N release. Thereby, N addition increased the As release from P. vittata litter and then transferred to the soil. Moreover, this process caused a transformation of non-labile As fractions into labile forms, resulting in an increase of available As concentration by 13.02–20.16% within the soil after a 90-day incubation period. Our findings provide valuable insights into assessing the ecological risk associated with As release from the decomposition of P. vittata litter towards the soil, particularly under elevated atmospheric N deposition.

Arsenopyrite dissolution is an important source of arsenic's environmental occurrence and is well-studied under oxidative conditions. However, little is known of anoxic leaching of arsenopyrite by water, though it is probably one of the dominant abiotic processes controlling arsenic mobility in oxygen-limited environments such as groundwaters and paddy fields. The present study attempts to probe the mechanism of arsenopyrite-water interaction in anoxic environment through examining the pH dependence of dissolution kinetics and stoichiometry, as well as speciation changes both on the surface and in solution. Batch and flow-through experiments were first carried out to measure dissolution rates and the results showed alkaline pH mildly encourages As release. Furthermore, the dissolution was found to be near stoichiometric with respect to As and S but not with Fe/As or Fe/S, and the non-stoichiometry exhibited a negative dependence on pH. Combining speciation analyses that revealed the presence of H 2 O 2 , SO 4 2− and S 2 O 3 2− in solutions and a positive correlation of surface species Fe(III)-O, S(-II), and As(I), As(III), As(V), and As(-III) to solution pH, we interpreted the anoxic dissolution behavior of arsenopyrite through a mechanism that combines surface complexation and interfacial redox reactions. The kinetic measurements came to be concerning as data indicates arsenopyrite dissolution in anoxic environment can lead to water having arsenic concentrations above the 10 ppb WHO guideline value in one day at the experimental conditions. The observed H 2 O 2 production indicated the dissolution is associated with or initiated by electron transfer despite the anoxic condition, further suggesting that a more comprehensive theory other than surface complexation model may be needed to better understand the geochemical behavior of As and possibly S in the context of sulfide mineral–water interactions. [ABSTRACT FROM AUTHOR]

Exposed and un-remediated metal(loid)-bearing mine tailings are susceptible to wind and water erosion that disperses toxic elements into the surrounding environment. Compost-assisted phytostabilization has been successfully applied to legacy tailings as an inexpensive, eco-friendly, and sustainable landscape rehabilitation that provides vegetative cover and subsurface scaffolding to inhibit offsite transport of contaminant laden particles. The possibility of augmented metal(loid) mobility from subsurface redox reactions driven by irrigation and organic amendments is known and arsenic (As) is of particular concern because of its high affinity for adsorption to reducible ferric (oxyhydr)oxide surface sites. However, the biogeochemical transformation of As in mine tailings during multiple redox oscillations has not yet been addressed. In the present study, a redox-stat reactor was used to control oscillations between 7 d oxic and 7 d anoxic half-cycles over a three-month period in mine tailings with and without amendment of compost-derived organic matter (OM) solution. Aqueous and solid phase analyses during and after redox oscillations by mass spectrometry and synchrotron X-ray absorption spectroscopy revealed that soluble OM addition stimulated pyrite oxidation, which resulted in accelerated acidification and increased aqueous sulfate activity. Soluble OM in the reactor solution significantly increased mobilization of As under anoxic half-cycles primarily through reductive dissolution of ferrihydrite. Microbially-mediated As reduction was also observed in compost treatments, which increased partitioning to the aqueous phase due to the lower affinity of As(III) for complexation on ferric surface sites, e.g. ferrihydrite. Oxic half-cycles showed As repartitioned to the solid phase concurrent with precipitation of ferrihydrite and jarosite. Multiple redox oscillations increased the crystallinity of Fe minerals in the Treatment reactors with compost solution due to the reductive dissolution of ferrihydrite and precipitation of jarosite. The release of As from tailings gradually decreased after repeated redox oscillations. The high sulfate, ferrous iron, and hydronium activity promoted the precipitation of jarosite, which sequestered arsenic. Our results indicated that redox oscillations under compost-assisted phytostabilization can promote As release that diminishes over time, which should inform remediation assessment and environmental risk assessment of mine site compost-assisted phytostabilization. [ABSTRACT FROM AUTHOR]

Coal is the primary energy source in China, and coal pyrolysis is considered an essential and efficient method for clean coal utilization. Three high arsenic coals collected from the southwestern Guizhou province of China were chosen in this study. Low-temperature ashing plus X-ray diffraction analysis (XRD) was used to identify the minerals in coals. The three coals were pyrolyzed in a tube furnace in an N2 atmosphere at 950 °C, 1200 °C, and 1400 °C, respectively. Environment scanning electron microscope (ESEM), XRD, X-ray fluorescence analysis (XRF), and inductively coupled plasma-mass spectrometry (ICP-MS) were adopted to determine the morphology, mineral compositions, and element compositions and arsenic contents of the coal pyrolysis ashes, respectively. It can be found that minerals in coal are mainly composed of quartz, pyrite, muscovite, and rutile. The minerals in the ashes generated from coal pyrolysis mainly contain quartz, dehydroxylated muscovite, iron oxide minerals, mullite, and silicon nitride. Oldhamite and gupeite exist at 950 °C and 1400 °C, respectively. The morphologies of oldhamite and gupeite at these temperatures are irregular block-shaped particles and irregular spherical particles, respectively. The mineralogical transformations in the process of coal pyrolysis affect coal utilization. The arsenic release rate is higher than 87% during pyrolysis at 1400 °C. The arsenic in organic matter is more able to be volatilized than mineral components. The retention time can slightly influence the arsenic release rate, and the influence of temperature is much more significant than the influence of retention time. The understanding of mineral evolution and arsenic environmental emission is helpful for the safety of high-arsenic coal pyrolysis. [ABSTRACT FROM AUTHOR]

Metal-reducing bacteria play a central and important role in the biogeochemical cycle of arsenic (As) and iron (Fe). Research on As/Fe migration from arsenic-containing iron minerals mediated by electronic shuttles is of significance to groundwater protection and human health. Further, the redox activity and bioavailability of goethite with differing occurrence and distribution of arsenic have not been studied clearly. In this study, the function of electron shuttle AQDS in Fe(III) bioreduction was determined. It was found that acidic conditions were conducive to the growth and reproduction of strain D2201, which was beneficial to the reduction of As(V)/Fe(III). The OD600nm value of the bacteria at pH 6 exceeded twice that at pH 8. Then, three types of goethite, namely pure goethite (Gt), coprecipitated As(V)-goethite (Gt-As), and adsorbed arsenic-goethite (Gt∗As), were compared for microbial reduction reactivity. X-ray photoelectron spectroscopy analysis illustrated the proportion of OH- content in Gt-As was much lower than that of Gt and Gt∗As, indicating Gt-As carried more surface defects and had higher bioavailability. The Fe(II) content released from AQDS-mediated bioreduction of Gt-As was two-fold higher than that of Gt and Gt∗As at pH 7. In addition, pH significantly affected goethite bioreduction efficiency and arsenic migration degree. The dissolved Fe(II) concentration for Gt-As was 0.98, 0.133, and 0.139 ​mM at pH 6, 7, and 8, respectively; corresponding to dissolved As(T) content of 3.51, 1.48, and 1.31 ​μM within 9 days of culture. This study highlights the significant influence of AQDS and mineral structure on the As/Fe biochemical cycle, which will help further develop the bioremediation of arsenic-contaminated sediments.

Arsenopyrite (FeAsS) and realgar (As4S4) are two common arsenic minerals that often cause serious environmental issues. Centralised treatment of arsenic-containing tailings can reduce land occupation and save management costs. The current work examined the remediation schemes of tailings from Hunan Province, China, where by different tailings containing arsenopyrite and realgar were blended with exogenous slag zero valence iron (ZVI). Introducing Fe-oxidising bacteria (Acidithiobacillus ferrooxidans) recreates a biologically oxidative environment. All bioleaching experiments were done over three stages, each for 7 days and the solid phase of all tests was characterised by scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and selective extraction analyses. The results showed that the mixture group reduced arsenic release by 72.9–74.7% compared with the control group. The addition of 0.2 g ZVI clearly decreased arsenic release, and the addition of 4.0 g ZVI led to the lowest arsenic release among all tests. The decrease of arsenic released from the tailings was due to the adsorption and uptake of arsenic by secondary iron-containing minerals and Fe–As(V) secondary mineralisation. The addition of large amounts of ZVI reduced the arsenic detected in the amorphous Fe precipitates. Therefore, a low cost and integrated strategy to reduce arsenic release from tailings is to mix two typical tailings and apply exogenous slag ZVI, which can apply to the in situ remediation of two kinds or more arsenic-containing tailings. [ABSTRACT FROM AUTHOR]

Periodic floods and ebb tides driven by seawater affect arsenic (As) behavior in coastal wetlands, which is not fully understood. In this study, we combined DGT, high-throughput sequencing, and real-time quantitative polymerase chain reaction (qPCR) techniques for the first time to investigate the effects of flood and ebb tide on As transformation and mobility in a typical coastal tidal flat wetland by laboratory experiments. In the flood-tide stage, more As was released into the water solution, and As(III) concentration in water solution was notably higher (51 μg/L) than in the ebb-tide stage, especially in SA (sodium acetate addition) treatment. As-methylation also occurred in this stage. The release of As was attributed to the reductive dissolution of amorphous and crystalline Fe oxides bound As induced by microbes. Fusibacter , Sva1033 , Bradyrhizobium , Ralstonia , and Desulfobacter were primarily involved in the reduction of As, Fe, and S. The copy numbers of arsC were 20–148 times higher than arrA , suggesting that the detoxification reduction pathway was the primary mechanism of direct As-reduction in the flood-tide stage. However, 2-D high-resolution DGT techniques revealed that the concentrations of As(III) and total As in pore water of sediments in the ebb-tide stage were higher than those in the flood-tide stage. The detected aioA gene indicated that As was oxidized in the sediment surface, resulting in As stabilization by crystalline iron minerals, whereas more As(III) were accumulated in pore water. The reduction pathway mediated by arrA may play a prominent role in the ebb-tide stage. This study provides new insights into As release processes in coastal wetlands in seawater environments, which further deepens our understanding of As biogeochemical cycling behavior in different natural environments. [Display omitted] • As Reduction and methylation occurred in coastal tidal flat sediments. • As(III) release in water solution was higher in the flood tide stage. • As Detoxification reduction was the primary mechanism in flood tide stage. • As(III) release in pore water of coastal sediments was higher in ebb tide stage. • As Reduction pathway mediated by arrA played a prominent role in the ebb tide stage. [ABSTRACT FROM AUTHOR]

The study of trace element emissions has become a new frontier field in coal combustion pollution. Especially some volatile elements or compounds which are discharged into the atmosphere become an important source of environmental pollution. The most volatile trace element arsenic has attracted wide attention. Qingshuigou char was selected for investigating the effect of steam on the release of arsenic in combustion at 800, 1 000 and 1 200 ℃ with 5% oxygen concentration in a customized isothermal combustion system. By changing the residence time, and further exploring the influence of steam on the arsenic release characteristics at different tem-peratures and particle sizes, the variation curve of arsenic release ratio with time during coal char combustion was obtained. The results show that the effect of steam on arsenic release from coal and coal char is synchronous, and the gasification reaction between steam and coke promotes arsenic release from coal char and then affects arsenic release from coal char. The presence of steam in the combustion atmosphere can promote the release of arsenic during the coal char combustion. The cause is that the steam reacted with coal char and accelerated the coal com-bustion. The promotion effect decreases with the increase of steam concentration. The promotion effect of steam on the release of arsenic at 1 000 ℃ is more obvious than that at 800 and 1 200 ℃. Under the same temperature and atmosphere, the smaller the particle size is, the greater the final release ratio of arsenic is. The temperature corre-sponding to the release peak of arsenic will move along the low temperature region with the decrease of particle size. The apparent activation energy and frequency factor of arsenic release with 20% steam are greater than those without steam. [ABSTRACT FROM AUTHOR]

Abstract The impact of seasonal fluctuations linked to monsoon and irrigation generates redox oscillations in the subsurface, influencing the release of arsenic (As) in aquifers. Here, the biogeochemical control on As mobility was investigated in batch experiments using redox cycling bioreactors and As- and SO 4 2−-amended sediment. Redox potential (E h) oscillations between anoxic (−300–0 mV) and oxic condition (0–500 mV) were implemented by automatically modulating an admixture of N 2 /CO 2 or compressed air. A carbon source (cellobiose, a monomer of cellulose) was added at the beginning of each reducing cycle to stimulate the metabolism of the native microbial community. Results show that successive redox cycles can decrease arsenic mobility by up to 92% during reducing conditions. Anoxic conditions drive mainly the conversion of soluble As(V) to As(III) in contrast to oxic conditions. Phylogenetic analyses of 16S rRNA amplified from the sediments revealed the presence of sulfate and iron – reducing bacteria, confirming that sulfate and iron reduction are key factors for As immobilization from the aqueous phase. As and S K-edge X-ray absorption spectroscopy suggested the association of Fe-(oxyhydr)oxides and the importance of pyrite (FeS 2(s)), rather than poorly ordered mackinawite (FeS (s)), for As sequestration under oxidizing and reducing conditions, respectively. Finally, these findings suggest a role for elemental sulfur in mediating aqueous thioarsenates formation in As-contaminated groundwater of the Mekong delta. Graphical abstract Unlabelled Image Highlights • Microbial sulfate reduction was found to contribute to arsenic (As) sequestration. • During anoxic conditions, the conversion of soluble As(V) to As(III) was observed. • The formation of pyrite, rather than mackinawite was observed in redox cycles. • Absorption/desorption of aqueous As on Fe-(oxyhydr)oxides and pyrite was observed. [ABSTRACT FROM AUTHOR]

Sulfate concentrations in eutrophic waters continue to increase; however, the transformations of arsenic (As) in sediments under these conditions are unclear. In this study, we constructed a series of microcosms to investigate the effect of algal degradation on As transformations in sediments with high sulfate concentrations. The results showed that both the elevated sulfate levels and algal degradation enhanced the release of As from sediments to the overlying water, and degradation of algal in the presence of elevated sulfate levels could further contribute to As release. Sulfate competed with arsenate for adsorption in the sediments, leading to As desorption, while algal degradation created a strongly anaerobic environment, leading to the loss of the redox layer in the surface sediments. With high sulfate, algal degradation enhanced sulfate reduction, and sulfur caused the formation of thioarsenates, which may cause re-dissolution of the arsenides, enhancing As mobility by changing the As speciation. The results of sedimentary As speciation analysis indicated that elevated sulfur levels and algal degradation led to a shift of As from Fe 2 O 3 /oxyhydroxide-bound state to specifically adsorbed state at the sediment water interface. This study indicated that algal degradation increases the risk of As pollution in sulfate-enriched eutrophic waters. [Display omitted] • Elevated sulfate in water promoted sedimentary As release under oxic condition. • Sulfate reduction and iron(Fe) speciation transformation together control As release. • Elevated sulfate and algal degradation reduced Fe 2 O 3 /oxyhydroxides-bound As. • Algal degradation under high sulfate enhanced the As release from sediments. [ABSTRACT FROM AUTHOR]

The arsenic (As) release from litter decomposition of As-hyperaccumulator (Pteris vittata L.) in mine areas poses an ecological risk for metal dispersion into the soil. However, the effect of atmospheric nitrogen (N) deposition on the litter decomposition of As-hyperaccumulator in the tailing mine area remains poorly understood. In this study, we conducted a microcosm experiment to investigate the As release during the decomposition of P. vittata litter under four gradients of N addition (0, 5, 10, and 20 mg N g−1). The N10 treatment (10 mg N g−1) enhanced As release from P. vittata litter by 1.2–2.6 folds compared to control. Furthermore, Streptomyces , Pantoea, and Curtobacterium were found to primarily affect the As release during the litter decomposition process. Additionally, N addition decreased the soil pH, subsequently increased the microbial biomass, as well as hydrolase activities (NAG) which regulated N release. Thereby, N addition increased the As release from P. vittata litter and then transferred to the soil. Moreover, this process caused a transformation of non-labile As fractions into labile forms, resulting in an increase of available As concentration by 13.02–20.16% within the soil after a 90-day incubation period. Our findings provide valuable insights into assessing the ecological risk associated with As release from the decomposition of P. vittata litter towards the soil, particularly under elevated atmospheric N deposition. [Display omitted] ● Pteris vittata litter acted as an As pollution source after decomposition. ● N addition promoted the As release from P. vittata litter. ● The litter C/N and G+ bacteria positively affected As release. ● Streptomyces , Pantoea, and Curtobacterium were dominant genus that regulated As release. ● Available As concentration in soil increased on the 90th day. [ABSTRACT FROM AUTHOR]

Abstract Arsenic (As) contamination was detected in paddy soils of Guangdong, China due to mining and weathering processes. Furthermore, As may be released into the soil and irrigation water during the application of phosphate (P). In this study, As behavior was assessed in three paddy soils (S6, S8 and TR) along the Hengshi river using batch and circular flow experiments with different phosphate application doses (0, 1, 5, 10, 50, 100 mg/L). The results indicate that pH variation (3–7) and higher phosphate concentrations in solution, can induce the release of As, with total As release ranked in the order: S6 > S8 > TR. In addition, AsV was the main state affected by phosphate in the circular soil solution. In particular, after 7 days of P 10 application, the highest As concentration in S6, S8 and TR soil solutions reached 2298.4, 829.9 and 153.9 μg/L respectively, with the AsV state accounting for 93%, 97% and 18% of As. Some minerals were found to be generated in the middle container, most of which were amorphous iron or aluminum oxides and hydroxides, as confirmed by XRD. With mineral generation, the As concentration in soil solutions decreased to 314.2, 98.1 and 34.1 μg/L. The SEM results indicate that the minerals became more fine (<100 nm) when more P was applied. In addition, XPS, SEM-eds and elemental analysis results also revealed that As distribution was closely associated with iron minerals. Along with soil depth, P influenced the state and distribution of iron minerals and As in the topsoil, while phosphate increased the available As and reduced the amorphous iron mineral content in the soil. Therefore, it is essential to evaluate As behavior in paddy soils, to monitor and avoid potential food security risks. Graphical abstract Unlabelled Image Highlights • The iron minerals generation were detected and minerals were collected. • Effect of P on As release from paddy soil in Dabaoshan mining area was identified. • The relationship among Fe, P and As in minerals and soils was discussed thoroughly. • As distribution characteristics in upstream and downstream paddy soils were revealed. [ABSTRACT FROM AUTHOR]

Irrigation water in rice cultivation significantly affects the arsenic (As) mobilization in the paddy field soil. This research assessed the effect of rainwater (RW) and groundwater (GW) on the dissolution dynamics of arsenic (As) in paddy field soil. Up-flow column flooding experiments were conducted continuously for 80 d with simulated RW and GW to evaluate As dissolution phenomena in actual field conditions. Arsenic dissolution from the soil was lower in GW (309 μg/kg) irrigation than in RW flooding conditions (1086 μg/kg). The redox potential (Eh) of the soil pore water decreased, and pH increased over-irrigation time in both flooding conditions. The dissolution of arsenic (As) and iron (Fe) in the soil pore increased, while the dissolution of manganese (Mn) decreased over flooding time. The release of As in the soil pore water was attributed to the dissolution of Fe–As and Mn–As minerals and microbial reduction of As. Fe–As dissolution ratios in the soil pore water were relatively low and estimated as 0.68 mol/mol and 4.9 mol/mol for RW and GW, respectively. The dissolution of As and Mn dominated in the initial phase (0–40 d) of flooding, while the dissolution of As and Fe dominated in the second phase (40–80 d). The release of As was much lower in GW flooding than in RW flooding conditions. The Presence of Ca, Mg, and Mn in the GW facilitated the reduction of As dissolution by precipitating Ca–As and Mg–As and the oxidizing dissolved Mn in the soil pore water. The findings of this study provide valuable insights into the mechanisms of As release during monsoon flooding and groundwater flooding to assess the potential risks of As contamination in rice grown in paddy field soils. [Display omitted] • As release from the soil in groundwater flooding was lower than rainwater flooding. • Redox potential (Eh) decreased with the flooding time. • Dissolution of As and Mn dominated in the first phase of the flooding. • Dissolution of As and Fe dominated in the second phase of the flooding. • As released decreased through Ca–As and Mg–As precipitation in GW irrigation. [ABSTRACT FROM AUTHOR]

The formation of arsenic-bearing acid mine drainage (AMD) via the oxidation of arsenopyrite refuse ore has attracted significant attention. Pyrite, as main a concomitant mineral, is a crucial factor that affects the (bio)dissolution of arsenopyrite, but there are still some points on the detailed action mechanism under normal environmental conditions that need further study. In this study, the effect mechanism of pyrite with a systematic pyrite content (0, 10, 25, 50, 75, 90, and 100 wt %) on arsenopyrite oxidation and arsenic release in the presence of Acidithiobacillus ferrooxidans was investigated. The X-ray diffraction (XRD), scanning election microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical analyses were also carried out. Results showed that the existence of pyrite and Acidithiobacillus ferrooxidans significantly accelerated the dissolution of arsenopyrite and the oxidation of As (Ⅲ) to As (Ⅴ), resulting from the galvanic effect, an increase in the Fe3+/Fe2+ ratio and the oxidation–reduction potential (Eh) value, and a decrease in pH level. As the detected main intermediate products, element sulphur was considered as the dominating obstructive factor during arsenopyrite oxidation, while the added pyrite could accelerate its oxidation. Moreover, a close relationship between different mineral proportions and the galvanic effect was also observed and discussed. Finally, suggestions on AMD governance and source control are proposed. [Display omitted] • (Bio)dissolution of pyrite/arsenopyrite in an AMD-like environment is revealed. • A systematic arsenopyrite/pyrite ratio (0, 10, 25, 50, 75, 90, 100 wt%) is used. • The effect of different mineral proportions on galvanic effect is proposed. • The oxidation of As (III) to As (V) with lower toxicity is facilitated by pyrite. • Some suggestions on AMD governance and source control are put forward. [ABSTRACT FROM AUTHOR]

Previous studies have shown that biochar enhances microbial reduction of iron (Fe) oxyhydroxide under anaerobic incubation. However, there is a lack of data on its influence on arsenic (As) release from As-contaminated paddy soils. In this study, paddy soil slurries (120 mg As kg −1 ) were incubated under anaerobic conditions for 60 days with and without the addition of biochar (3%, w/w) prepared from rice straw at 500 °C. Arsenic release, Fe reduction, and As fractionation were determined at 1, 10, 20, 30, and 60 d, while Illumina sequencing and real-time PCR were used to characterize changes in soil microbial community structure and As transformation function genes. During the first month of incubation, As released into soil solution increased sharply from 27.9 and 55.9 to 486 and 630 μg kg −1 in unamended and biochar amended slurries, with inorganic trivalent As (As III ) being the dominant specie (52.7–91.0% of total As). Compared to unamended slurries, biochar addition increased As and ferrous ion (Fe 2+ ) concentrations in soil solution but decreased soil As concentration in the amorphous Fe/Al oxide fraction (F3). Difference in released As between biochar and unamended treatments ( Δ As) increased with incubation time, showing strong linear relationships (R 2 = 0.23–0.33) with Δ Fe 2+ and Δ F3, confirming increased As release due to enhanced Fe reduction. Biochar addition increased the abundance of Fe reducing bacteria such as Clostridum (27.3% vs. 22.7%), Bacillus (3.34% vs. 2.39%), and Caloramator (4.46% vs. 3.88%). In addition, copy numbers in biochar amended slurries of respiratory As reducing ( arrA ) and detoxifying reducing genes ( arsC ) increased 19.0 and 1.70 fold, suggesting microbial reduction of pentavalent As (As V ) adsorbed on Fe oxides to As III , further contributing to increased As release. [ABSTRACT FROM AUTHOR]

The mineral tooeleite (Fe6(AsO3)4SO4(OH)4·4H2O) is a secondary mineral containing-As(III) in acid mine drainage, and is proposed as a candidate for arsenic immobilization technology. The dissolution interaction of tooeleite withAcidithiobacillus ferrooxidanswas investigated by batch experiments. The arsenic released from tooeleite decreases with pH increase due to the adsorption of arsenic on iron hydroxide. The amount of arsenic released from tooeleite at pH 2 is increased by 3.2 times as compared to the dissolution under only culture medium, which reaches 345 mg/L. The bacterial activity has a strong effect on the arsenic amount released from tooeleite. The incongruent dissolution was observed for tooeleite when pH is >3. The infrared spectroscopy and XRD both identified the alteration product of tooeleite as jarosite. This information is useful for immobilizing arsenic and is proposed as a suitable mechanism for trapping arsenic. [ABSTRACT FROM PUBLISHER]

To understand the mechanisms of arsenic release from the sediment of the Seino Basins, Nobi Plain, Japan, the present study investigated the characteristics of arsenic dissolution and arsenic phases in the sediments of the G1 and G2 aquifers and their upper layers. No significant, direct positive relationship between the total and water-soluble arsenic was found. The results of sequential extraction showed that the main sources of water-soluble arsenic were the non-specifically and weakly bound arsenic phases. In addition, a small portion of the arsenic specifically sorbed on the surface of the sediment was dissolved by water extraction. Multiple regression analyses demonstrated that high pH, total arsenic content, and water-soluble organic carbon (WSOC) content strongly contributed to the enhancement of arsenic release from the specifically bound arsenic fraction. These results suggest that high levels of total and non-specifically bound arsenic are responsible for higher levels of arsenic release. In addition, high pH and WSOC content facilitate arsenic release. [ABSTRACT FROM AUTHOR]

Mining activities release arsenopyrite into calcareous soils where it undergoes weathering generating toxic compounds. The research evaluates the environmental impacts of these processes under semi-alkaline carbonated conditions. Electrochemical (cyclic voltammetry, chronoamperometry, EIS), spectroscopic (Raman, XPS), and microscopic (SEM, AFM, TEM) techniques are combined along with chemical analyses of leachates collected from simulated arsenopyrite weathering to comprehensively examine the interfacial mechanisms. Early oxidation stages enhance mineral reactivity through the formation of surface sulfur phases (e.g., S/S) with semiconductor properties, leading to oscillatory mineral reactivity. Subsequent steps entail the generation of intermediate siderite (FeCO)-like, followed by the formation of low-compact mass sub-micro ferric oxyhydroxides (α, γ-FeOOH) with adsorbed arsenic (mainly As(III), and lower amounts of As(V)). In addition, weathering reactions can be influenced by accessible arsenic resulting in the formation of a symplesite (Fe(AsO))-like compound which is dependent on the amount of accessible arsenic in the system. It is proposed that arsenic release occurs via diffusion across secondary α, γ-FeOOH structures during arsenopyrite weathering. We suggest weathering mechanisms of arsenopyrite in calcareous soil and environmental implications based on experimental data. [ABSTRACT FROM AUTHOR]

This is the response to “Commentary on ‘Arsenic mobility in the arsenic-contaminated Yangzonghai Lake in China’ by Changliang Yang et al. [Ecotoxicology and Environmental Safety, 107(2014)321-327]” (by Jing Chen et al.). To doubts and questions raised by Chen et al., we give further explanations and provide more relevant evidences. The water temperature stratification existed in Lake Yangzonghai in summer, and affected by which arsenic concentration with water depth was uneven and peaked in the bottom layer in summer. In the case of adding carbon source (glucose) and maintaining anerobic state, enhanced microbial activity promoted the release of arsenic from sediment to water which was observed in the laboratory experiments. Errors might exist in sampling, determination and calculation, but they would not change the main conclusions of the article. [ABSTRACT FROM AUTHOR]

Reductive dissolution of iron oxides in flooded paddy soils is the most important cause of arsenic (As) release into soil aqueous solution and thus entry into rice. From the perspective of soil cleanup, however, As release under flooded condition could facilitate labile As removal. In this study, a porous column pre-loaded with ferrihydrite (Fh) was constructed, and its efficiency of soil As extraction was investigated using a purpose-designed mesocosm coupled with diffusive gradients in thin films (DGT) for in situ visualization. With Fh-column deployed in aqueous solution, >90% removal of As(III) was achieved within 5 days at initial As (100 mg L−1) of two orders of magnitude higher than in most paddy soil solutions (1–1538 μg L−1). By applying Fh-column in a seriously contaminated paddy soil (102 mg As kg−1), porewater As showed stepwise decreases from 2727 μg L−1 to 129–1455 μg L−1 at a distance-dependent manner over four intermittent extractions during 91 days. Soil DGT-As exhibited similar spatiotemporal changes to porewater As. After four extractions, 17.8% of total soil As was removed by Fh-column in a 10 cm radius range on average and ∼1/3 of As bound to amorphous and crystalline Fe/Al oxides was depleted, which accounted for 88.7% of decline in total soil As. With the post-extracted soil, a 48% lower As accumulation in rice seedlings and a 65% decline in bulk soil DGT-As were attained. This study provides a conceptual foundation for rapid removal of high soluble As by Fh-columns from flooded soils, improving seriously As-contaminated paddies to sustainable resources for safe food production. [Display omitted] • Fh-column can serve rapid removal of high labile As from flooded soils. • Porewater As decreased by 47–95% after four extractions during 91 days of flooding. • 17.8% of total soil As was removed by Fh-column in a 10 cm radius range. • 89% of decline in soil total As was associated with Fe/Al oxides. • Soluble As removal by Fh-column caused significantly decreased As bioavailability. [ABSTRACT FROM AUTHOR]

Release of arsenic (As) from sedimentary rocks has resulted in contamination of groundwater in aquifers of the New Jersey Piedmont Physiographic Province, USA; the contamination also may affect the quality of the region's streamwater to which groundwater discharges. Biogeochemical mechanisms involved in the release process were investigated in the streambeds of Six Mile Run and Pike Run, tributaries to the Millstone River in the Piedmont. At Six Mile Run, streambed pore water and shallow groundwater were low or depleted in oxygen, and contained As at concentrations greater than 20 μg/L. At Pike Run, oxidizing conditions were present in the streambed, and the As concentration in pore water was 2.1 μg/L. The 16S rRNA gene and the As(V) respiratory reductase gene, arrA , were amplified from DNA extracted from streambed pore water at both sites and analyzed, revealing that distinct bacterial communities that corresponded to the redox conditions were present at each site. Anaerobic enrichment cultures were inoculated with pore water from gaining reaches of the streams with acetate and As(V). As(V) was reduced by microbes to As(III) in enrichments with Six Mile Run pore water and groundwater, whereas no reduction occurred in enrichments with Pike Run pore water. Cloning and sequencing of the arrA gene indicated 8 unique operational taxonomic units (OTUs) at Six Mile Run and 11 unique OTUs at Pike Run, which may be representative of the arsenite oxidase gene arxA . Low-oxygen conditions at Six Mile Run have favored microbial As reduction and release, whereas release was inhibited by oxidizing conditions at Pike Run. [ABSTRACT FROM AUTHOR]

Arsenic (As) was known as human carcinogen. It was therefore of great importance to better understanding the release behavior of arsenic in soils for managing and controlling the potential risks of smelter contaminated sites. The present work evaluated arsenic bioavailability and bioaccessibility, in combination with geochemical fractionation and valence analysis by X–ray photoelectron spectroscopy (XPS), and also investigated the release patterns of bioavailable and bioaccessible arsenic in soils. The present results showed that there was a significant variation in the bioavailable and bioaccessible fractions of arsenic, due to the great difference in soil properties, extractants types, and in vitro assays. Moreover, it was found that KH 2 PO 4 presented the relatively higher arsenic bioavailability with wide range of 9.89–25.5 %, which might better predict the arsenic bioavailability in soils than the other extractants. In addition, the relatively higher arsenic bioaccesibility was found in Solubility Bioaccessibility Research Consortium (SBRC) assay, ranging from 5.50 to 67.4 % for gastric phase (GP) and 3.85–18.8 % for gastrointestinal phase (GIP), respectively. In addition, the time–dependent release of bioavailable arsenic was controlled by the competitive desorption between phosphate and As (V) ions, while the time–dependent release of bioaccessible arsenic was dominated by the stable complexation of organic ligands and the strong affinity of Al, Mn and Fe–(hydr) oxides. According to the study results, a new insight into the arsenic behavior was provided to more scientifically evaluate its contamination risks. [Display omitted] • The updated knowledge was provided for arsenic geochemical behavior in smelter soils. • KH 2 PO 4 was identified as the best extractant to assess the arsenic bioavailability. • SBRC showed the relatively higher arsenic bioaccessibility than PBET and IVG. • Arsenic desorption reaction was better explained by the pseudo second order model. [ABSTRACT FROM AUTHOR]

High arsenic groundwater has been widely found in two kinds of regions (including arid inland basin and humid river delta) in China, which seriously affects resident health, Hetao Basin, Huhhot Basin, Yinchuan Basin and Datong Basin were selected as the arid inland basins, and Pearl River Delta and Jianghan Plain as the humid river deltas. Chemical characteristics and hydrogeochemical processes of high arsenic groundwater in different regions of China were analyzed. The type of high arsenic groundwater is HCO3-Ca in Jianghan Plain, HCO3-Na in Datong Basin, Hetao Basin and Yinchuan Basin, and CI-Na in Pearl River Delta. Oxidation-reduction potential in high arsenic groundwater is low, indicating reduction environment. In these environments mass concentrations of SO2-4 and NO-3 are generally low. Mass concentration of SO2-4 in Jianghan Plain is the lowest among all the six regions, while that of NO-3 in Hetao Basin is the lowest. There is no significant correlation between mass concentrations of As and Fe. Mass concentrations of Fe and Mn are the highest, but As is relatively lower in Pearl River Delta, and mass concentrations of Fe and Mn are the lowest, but As is relatively higher in Datong Basin. Weathering, cation-exchange adsorption and reduction occur in high arsenic groundwater system. Pyrile precipitation may be an important process for controlling mass concentrations of Fe and As in addition to reductive dissolution of Fe/Mn oxides in Hetao Basin and Huhhot Basin. However-reductive dissolution of Fe/Mn oxides and Fe( II ) re-adsorption are the major hydrogeochemical processes in Jianghan Plain. Desorption of adsorbed arsenic also contributes to arsenic enrichment in groundwater of arid inland basins with weak alkaline environment. [ABSTRACT FROM AUTHOR]

Highlights: [•] Is organic matter a source for arsenic release in groundwater? [•] Organic matter can be both a source and redox driver for As release in groundwater. [•] Association of arsenic with organic matter in aquifer sediments. [•] DOC derived from sedimentary OM, surface organic matter and petroleum. [Copyright &y& Elsevier]

Abstract: Soil surveys have demonstrated arsenic (As) contents of up to 1600mgkg−1 in surface horizons of degraded fens in the Bavarian Molasse basin, Germany. Ground water from the Tertiary aquifer seems to be the primary source of As. Yet, the cause of its accumulation in the topsoil is unclear. Focussing the influence of redox processes on As redistribution, we conducted soil column experiments with the A (716mg Askg−1), Ag (293mg Askg−1) and 2Ag (37mg Askg−1) horizons of a Mollic Gleysol (pH 7.2). The fixed beds were equipped with redox electrodes and suction cups and subjected to a saturation–drainage–saturation cycle. Water table fluctuations were simulated by defined pressure heads applied to the lower column boundaries via a digitally controlled vacuum system. After water saturation, the redox potential (EH) dropped to minimum values of around 0mV in the A/Ag and−400mV in the 2Ag horizon. Soil drainage resulted in a quick return to oxidising conditions. Both in the A and Ag horizons total aqueous As concentrations were low (up to 20μgl−1) and not related to EH. In contrast, aqueous As concentrations of the 2Ag horizon were between 5 and 140μgl−1 and increased as the EH decreased. However, the As species distribution showed no clear trend with EH since both As(III) and As(V) were detected under reducing conditions. High release of As in the 2Ag horizon is consistent with low contents in Fe (hydr)oxides. In the A and Ag horizons, pedogenetic enrichment of sesquioxides contributes to a comparably lower sensitivity of EH to water saturation and favours As retention. Thereby, As released under saturated conditions in the 2Ag horizon may be stabilised in the topsoil following capillary rise. Thus, surface horizons may act both as historic and as recent sinks for geogenic As at the site. [Copyright &y& Elsevier]

Arsenic (As), ammonium-nitrogen (N), nitrate-N concentrations, and oxidation-reduction potential (ORP) in the water samples from the river, pond, dug well, and shallow and deep tube wells (TW) were investigated in a farming village of southwestern Bangladesh. Concentrations of As and ammonium-N were the highest, whereas ORP was the lowest in the shallow TW water among the water sources. The ammonium-N concentration correlated positively with the As concentration and negatively with ORP for all samples, irrespective of the water sources. A rise in the ammonium-N concentration was hypothesized to enhance microbial activity, which in turn would lower ORP, and then As was released from sediments to the surrounding water in a reducing condition. The source of ammonium-N in the shallow TW water was identified as N fertilizer, based on the δ15N analysis. Thus, the influence of N fertilizer application on As contamination in groundwater was suggested. [ABSTRACT FROM AUTHOR]

Previous work has shown that arsenic can accumulate in drinking water distribution system (DWDS) solids (Lytle et~al., 2004) when arsenic is present in the water. The release of arsenic back into the water through particulate transport and/or chemical release (e.g. desorption, dissolution) could result in elevated arsenic levels at the consumers' tap. The primary objective of this work was to examine the impact of pH and orthophosphate on the chemical release (i.e. desorption) of arsenic from nine DWDS solids collected from utilities located in the Midwest. Arsenic release comparisons were based on the examination of arsenic and other water quality parameters in leach water after contact with the solids over the course of 168~hours. Results showed that arsenic was released from solids and suggested that arsenic release was a result of desorption rather than dissolution. Arsenic release generally increased with increasing initial arsenic concentration in the solid and increasing pH levels (in the test range of 7 to 9). Finally, orthophosphate (3 and 5 mg PO4/L) increased arsenic release at all pH values examined. Based on the study results, utilities with measurable levels of arsenic present in their water should be aware that some water quality changes can cause arsenic release in the DWDS potentially resulting in elevated levels at the consumer's tap. [ABSTRACT FROM AUTHOR]

Sea-level rise (SLR) has a vital influence on coastal hydrogeological systems, biogeochemical processes, and the fate of coastal contaminants. However, the effects of SLR-induced perturbations on the mobilization of coastal pollutants are not fully understood. In this study, the impact of SLR-induced flooding on the concentration and speciation of arsenic and selected hazardous chemicals is investigated using exceedingly contaminated sediments (5–6% As) collected from an urban coastal site in Wilmington, DE, USA. The release of contaminants from sediments was monitored before, during, and after flooding with different intensities (bottom shear stresses) through laboratory-based erosion chamber experiments. Significantly increased release of As (up to 150%) and NO 3 (up to 50%) from sediments at shear stress levels typically measured in estuaries were found. The release of toxic chemicals from contaminated coastal sediments is thus not restricted to extreme flooding events but can occur throughout the year. The results also suggest that the dissolved concentrations of pollutants continue to be considerably high even after the flooding. SLR-induced flooding can hence increase the release of contaminants not only during erosion events but over longer timescales. The release mechanism proposed here contributes to improving the risk assessment of coastal water pollution as climate change and SLR continue to occur. [Display omitted] • Low intensity flooding events pose significant threats to metal release. • Substantial release due to sediment resuspension does not require large storms. • Flooding increases dissolved arsenic and nitrate by 150% and 50%. • Dissolved As(III) increases due to flooding. • Sediment resuspension plays an important role in releasing arsenic to the water. [ABSTRACT FROM AUTHOR]

Kinetic studies on arsenic (As) release from soils are commonly performed using soils spiked or artificially contaminated with As at soil to solution ratios of 1:10 to 1:50 by mass, which make the conditions of study very different from the prevailing field situations. In this study, the kinetics of As release were investigated using different extractants including 1 M K 2 HPO 4 , 0.5 M Na 3 C 6 H 5 O 7 , 1 M NaOH , 1 M NH 4 F , and 1 M (NH 4) 2 SO 4 in five naturally As-contaminated soils (80–1680 mg total As/kg) at half saturation moisture over a long period of time (15 min–60 d). Six kinetic models were employed to fit the data. Results indicated that the trend of As release was initially rapid followed by a slow release with K 2 HPO 4 , (NH 4) 2 SO 4 and Na 3 C 6 H 5 O 7 solutions, whereas with NaOH and NH 4 F an increasing As release was followed by a decreasing trend at longer times, and a considerable amount of the released As was re-adsorbed or precipitated. The order of the cumulative amounts of As released by extractants was K 2 HPO 4 > Na 3 C 6 H 5 O 7 > NaOH > NH 4 F > (NH 4) 2 SO 4. The percentage of total As released during the reaction time was less than 3% for all extractants except K 2 HPO 4 , which was between 4.0 and 8.5% in different soils. Therefore, much lower extractability of As occurred in the naturally As-contaminated soils at half saturation moisture than has previously been reported for soils spiked or artificially contaminated with As at lower soil to solution ratios (1:10 to 1:50) suggests that caution should be exercised in extending or applying the results of As release studies on artificially contaminated soils to naturally contaminated soils for remediation purposes. Finally among six kinetic models, only the power function and the simplified Elovich models described the release data satisfactorily. • Arsenic release from naturally enriched soils at half saturation moisture was low. • Kinetics of As release were initially rapid followed by a slow release. • An increasing As release with NaOH and NH 4 F was followed by a decreasing trend. • The order of the As release efficiency was K 2 HPO 4 > Na 3 C 6 H 5 O 7 > NaOH > NH 4 F > (NH 4) 2 SO 4. • The power function equation best described the As release data. [ABSTRACT FROM AUTHOR]

• Biomass inhibit the arsenic release in co-combustion except rice straw. • Mineral metals inhibit the arsenic release, but Si promote the release of arsenic. • Heat from combustion of volatiles accelerate arsenic release. • Co-combustion of biomass and coal reduce the risk of arsenic leaching. After the co-combustion of tobacco stem/black bean straw/wheat straw/millet straw/corn stalk/rice straw and coal, it was found that all tested biomass in this study could inhibit arsenic release, but only rice straw promoted arsenic release. When the acid washed biomass was mixed with coal during combustion, the release of arsenic increased. When mineral metals (Na, K, Mg, Ca, Al and Fe) and Si elements were added to the coal, the mineral metals inhibited arsenic release. However, the release of arsenic was increased when the silicon content in biomass was high. The volatiles in the biomass also promoted the release of arsenic during co-combustion. The arsenic in the ash generated from co-combustion was mainly in the sulphide-bound state. Co-combustion of biomass and coal reduced the occurrence of an exchangeable state in the ash, and also significantly reduce the possibility of leaching. [ABSTRACT FROM AUTHOR]

High arsenic concentration in groundwater is influenced by redox reactions in As-bearing iron (oxy)hydroxide minerals and elevated total organic carbon, resulting in arsenic contamination and enrichment in groundwater after introduction of seawater into an aquifer. In this study, hydrochemical and isotopic (S, O and C) techniques were used to relate arsenic contamination and seawater flooding/intrusion in groundwater aquifers in the Chianan Plain, southwestern Taiwan. Thirty-three samples (30 from groundwater and 3 from river water) were collected from April–June of 2014. Most of the groundwater samples collected from the Chianan Plain were dominated by As(III), indicating that reducing conditions prevailed within the aquifers. The δ18O-δD plots of most of the groundwater samples from the Chianan Plain are generally lined on the global meteoric water line (GMWL), but the δ18O and δD isotopic compositions of the river water samples show enriched signals. Salinity and sulfate concentrations of river water and shallow groundwater have been found to increase after seawater flooding/intrusion. The δ18O and δD isotopic compositions of the river water showed a gradual trend toward those of seawater. The trend in the isotopic compositions of the river and groundwater samples indicated a mixing of seawater and meteoric water. Up to the present, the groundwater levels in the coastal areas of the Chianan Plain have dropped to zero meters in elevation parallel to sea level due to excessive groundwater withdrawal, resulting in seawater intrusion into the aquifers in Budai, Yichu, and Beimen in the Plain. Moreover, high salinity (48.1‰) occurred only in the Beimen 2B shallow groundwater at a depth of 60 m is a result of seawater flooding infiltration from the nearby salinized Pachang River. The δ34S [SO 4 ] /δ18O [SO 4 ] isotopic ratios (2.63–2.82) of low-As (concentration < 50 μg/L) river water samples were similar to those of marine sulfate minerals dissolved in seawater, but were variable (0 − 2.93) among the high-As (concentration ≧ 50 μg/L) groundwater samples from the Chianan Plain. Sulfates in seawater were introduced into the coastal aquifers of the Chianan Plain under the Holocene marine transgression, wherein the mixing of paleo- and modern-sulfates due to seawater intrusion might have occurred or are occurring. The release of sulfur and arsenic (mostly arsenite) in the Chianan Plain groundwater under reducing environments indicating redox reactions in sulfates and iron (oxy)hydroxide minerals may change the isotopic (S and O in sulfate) compositions in groundwater, resulting in enrichment of δ34S [SO 4 ] and δ18O [SO 4 ]. Salinity can promote arsenic release in groundwater and thus enrich the δ34S [SO 4 ] and δ18O [SO 4 ] isotopic compositions, in which 6.0–22.8‰ δ34S [SO 4 ] and 9.3–15.5‰ δ18O [SO 4 ] occur in shallow fresh groundwater (depth < 60 m) but up to 27.7‰ δ34S [SO 4 ] and 20.4‰ δ18O [SO 4 ] occur in shallow saline groundwater, in comparison to 0‰ δ34S [SO 4 ] and 5.4–6.5‰ δ18O [SO 4 ] in deep fresh groundwater (depth between 60 and 318 m) and up to 38.5‰ δ34S [SO 4 ] and 18.7‰ δ18O [SO 4 ] in deep brackish groundwater. This study provides insights suggesting that the As-containing iron(II) minerals are oxidized to iron(III) minerals and then re-reduced to iron(II) which leads to As release. Unlabelled Image • A rsenic enrichment in groundwater occurred after introduction of seawater. • The trend of δD [H 2 O] /δ18O [H 2 O] indicated a mixing of seawater and meteoric water. • Enriched δ34S [SO 4 ] and δ18O [SO 4 ] in groundwater occurred under reducing conditions. • As-contained Fe-oxide/hydroxide minerals are major aqueous As source in groundwater. • Redox reactions can change the isotopic composition of dissolved sulfate. [ABSTRACT FROM AUTHOR]