Search

Iron-bound organic carbon (OC-Fe R ) is important for the stability of soil organic carbon (SOC) in salt marshes, and the Spartina alterniflora invasion reshaped local salt marshes and changed the SOC pool. To evaluate the effects of S. alterniflora invasion on the contribution of OC-Fe R to SOC, we determined the OC-Fe R content and soil characteristics in the 0-50 cm soil profile along the vegetation sequence, including mudflats (MF), S. alterniflora marshes established in 2003 (SA03) and 1989 (SA89), the ecotone of S. alterniflora and Phragmites australis (SE), S. salsa marsh (SS), and P. australis marsh (PA). The SOC content was 6.55-17.5 mg g -1 in the S. alterniflora marshes. Reactive iron oxides (Fe d , Fe o , Fe p ) accumulated significantly in the S. alterniflora and P. australis salt marshes. PA and S. alterniflora marshes had higher DOC contents of 0.28-0.77 mg g -1 . The OC-Fe R content in the 0-50 cm soil profile in these ecosystems ranged from 0.3 to 3.29 mg g -1 , with a contribution to the SOC content (f OC-FeR ) of approximately 11 %, which was highest in SA03 (16.3 % ~ 18.8 %), followed by SA89, SE, and PA. In addition, the molar ratios of OC-Fe R to Fe d were <1, indicating that the iron oxides were associated with SOC through sorption more than coprecipitation. According to the structural equation model, SOC, DOC and iron oxides were the direct driving factors of OC-Fe R formation, while the vegetation zone indirectly functioned by regulating organic C inputs, iron oxide formation, and pH. This study suggested that S. alterniflora invasion promotes iron-bound organic carbon accumulation by increasing organic C inputs and regulating iron oxide formation in salt marshes, but such promotion will degenerate with development duration., Competing Interests: Declaration of competing interest All the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Hematite tailings (HTs) are rich in silica and are used as replacements for fine aggregates in the preparation of construction materials. However, there is scope for a more effective utilization of the valuable elements present in HTs. In this paper, a process for preparing high-purity SiO 2 using HTs procured from Ansteel (China) is proposed. HTs were treated using the superconducting high-gradient magnetic separation (S-HGMS) technology, where the silica as part of the nonmagnetic fraction was obtained in the form of a high-silica concentrate, which was then subjected to mixed-acid leaching to dissolve impurities to achieve refined purification. The optimum process conditions for S-HGMS were determined, and the response surface methodology was applied to optimize the process parameters of the mixed-acid leaching process. The process indicators of the mixed-acid leaching step included the leaching time, leaching temperature, and molar ratio of the mixed acids. The optimum process conditions for S-HGMS were as follows: the magnetic strength-to-velocity ratio in the weak magnetic separation stage was set to 0.034 T·s/m whereas it was maintained at 0.076 T·s/m in the strong magnetic separation stage; the pulp concentration was 40 g/L, the pulp velocity was 500 mL/min, and the dispersant concentration was 1 mg/g. Under these conditions, the high-silica pulp was processed. The corresponding SiO 2 grade increased from 71.788 % to 95.260 %, and its recovery and yield reached 56.330 % and 42.450 %, respectively. The SiO 2 content in the sample increased from 95.260 % to 99.961 %. Further, the mechanisms of the S-HGMS and mixed-acid leaching were revealed. The proposed process is environmentally friendly and operationally inexpensive. It can reduce the amount of HTs by 42.450 %, and the obtained high-purity silica product has high economic value and good industrialization prospects., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Currently, atmospheric sulfate aerosols cannot be predicted reliably by numerical models because the pathways and kinetics of sulfate formation are unclear. Here, we systematically investigated the synergetic catalyzing role of transition-metal ions (TMIs, Fe 3+ /Mn 2+ ) in the oxidation of SO 2 by O 2 on aerosols using chamber experiments. Our results showed that the synergetic effect of TMIs is critically dependent on aerosol pH due to the solubility of Fe(III) species sensitive to the aqueous phase acidity, which is effective only under pH < 3 conditions. The sulfate formation rate on aerosols is 2 orders of magnitude larger than that in bulk solution and increases significantly on smaller aerosols, suggesting that such a synergetic-catalyzed oxidation occurs on the aerosol surface. The kinetic reaction rate can be described as R = k *[H + ] -2.95 [Mn(II)][Fe(III)][S(IV)] (pH ≤ 3.0). We found that TMI-synergetic-catalyzed oxidation is the dominant pathway of sulfate formation in Beijing when haze particles are very acidic, while heterogeneous oxidation of SO 2 by NO 2 is the most important pathway when haze particles are weakly acidic. Our work for the first time clarified the role and kinetics of TMI-synergetic-catalyzed oxidation of SO 2 by O 2 in haze periods, which can be parameterized into models for future studies of sulfate formation.

Clarifying the accumulation pattern of soil microbial residue carbon and its contribution to soil organic carbon (SOC) across stand age is helpful to understand the mechanism underlying soil carbon cycling. In this study, we analyzed the differences of amino sugar content, physicochemical properties and microbial composition in surface soil (0-10 cm) in young (6 a), middle-aged (13 a), near-mature (29 a), mature (38 a) and over-mature (57 a) Pinus massoniana plantations of subtropical China, quantified the microbial residue carbon content and its contribution to SOC, and discussed the mechanism. The results showed that SOC, total nitrogen, amorphous iron oxide and leucine aminopeptidase contents in the middle-aged plantation were significantly lower than those in the mature plantation. Soil pH and fungal/bacteria in young plantation were significantly higher than those in other age groups. Across the stand age gradient, the ranges of microbial, fungal and bacterial residue carbon were 7.52-14.63, 4.03-8.00 and 3.48-6.63 g·kg -1 , respectively. The contents of all the residue carbon were significantly higher in the mature plantation than that of the middle-aged plantation, which were positively affected by soil total nitrogen content. The contribution of microbial, fungal, and bacterial residue carbon to SOC was 59.7%-72.3%, 33.4%-45.6%, and 24.3%-30.8%, respectively. The contribution of fungal residue carbon to SOC in young plantation was significantly higher than that in other age groups, and the contribution of bacterial residue carbon to SOC in middle-aged plantation was significantly higher than that in young and near-mature plantations, both of which were affected by soil inorganic nitrogen. Fungal residue carbon content was 1.2-1.7 times as that of bacterial residue carbon content, and dominated for the accumulation of microbial residue carbon. Results of the partial least squares model showed that stand age, soil environmental factors (such as leucine aminopeptidase, amorphous iron oxide, pH, and total nitrogen), bacterial residue carbon, fungal residue carbon and the contribution of bacterial residue carbon to SOC had total effects on the contribution of fungal residue carbon to SOC (-0.37, -1.16, 0.90, 1.09, and 0.83, respectively). In conclusion, stand age promoted the accumulation of microbial residue carbon but did not increase its contribution to SOC.

The temperature sensitivity of soil carbon mineralization ( Q 10 ) is an important index to evaluate the responses of ecosystem carbon cycling to climate change. We examined the effects of three electron acceptors [SO 4 2- , NO 3 - and Fe(Ⅲ)] addition on the Q 10 value of anaerobic carbon mineralization of Phragmites australis community soil (0-10 cm) in the Yellow River Estuary wetland with the closed culture-gas chromatography method. The results showed that the three electron acceptors addition inhibited the production of CO 2 and CH 4 during the 48-day culture period, with a decrease of 17.3%-20.8% for CO 2 and 29.2%-36.2% for CH 4 . Generally, the CO 2 production differed with the concentrations of electron acceptors, while CH 4 production differed with the type of electron acceptors. The CO 2 :CH 4 ratios were significantly different with temperature, indicating an obvious temperature dependence for the anaerobic carbon mineralization pathway. The Q 10 values of CO 2 and CH 4 production under three electron acceptor additions ranged from 1.08 to 1.11 and from 1.19 to 1.37, respectively, showing an increasing trend compared with the control. The type and concentration of electron acceptors affected the temperature dependence of CO 2 production, while electron acceptors affected that of CH 4 production. It is suggested that the input of reducing salts would retard the mineralization loss of organic carbon in estuary freshwater wetlands under the background of climate change, but enhance the sensitivity of carbon mineralization to increasing temperature.

Porewater arsenic mobility above the groundwater table has been recognized as a potential cause of arsenic-rich groundwater, but the processing pathways of dissolved organic matter (DOM) in that hyporheic zone and their effect on porewater arsenic release remain poorly understood. To address these issues, two porewater profiles were sampled in a surface water-groundwater interaction zone from the Hetao Basin, China, to monitor the porewater geochemistry and DOM molecular characteristics. The results show that the porewater arsenic, Fe(II), and DOC concentrations were all significantly higher than those of the intruding pond water, and were located above the conservative mixing model lines. This indicates a net release of these solutes from the sediment. By comparing the porewater with pond water DOM, we found that the carboxyl-rich alicyclic molecules (CRAM) were selectively preserved, carbohydrates and aliphatics/proteins were preferentially consumed, and low O/C-ratio compounds with high bioproduction index (I&#95;bioprod) and terrestrial index (I&#95;terr) were produced. The transformation of CHO to CHOS compounds also represented a pathway of recalcitrant DOM production. The produced recalcitrant organic compounds mostly contributed to the elevated porewater DOC concentrations, but their contribution decreased along the filtration path. The consumption of labile DOM compounds would be responsible for Fe(III) hydroxide reduction and arsenic release. The generated recalcitrant DOM may also be a driver of porewater arsenic mobility by acting as electron shuttles. This study highlights the importance of the hyporheic zone in shaping shallow groundwater DOM composition and the potential contribution to arsenic enrichment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Algal blooms can aggravate arsenic (As) release from sediments and thus pose a pollution risk in the marine environment. However, the driving mechanism of algal blooms on sedimentary As cycling remains unclear. This study undertakes the first comprehensive examination of As release mechanisms under algal bloom conditions based on the evidence provided by temporal and depth profile changes of As species in the overlying water column, porewater and sediment, as well as As-related functional genes over the course of a 30-day incubation experiment using algal addition. The higher rate of increase of dissolved total As (dTAs) concentrations in a high biomass algal group (HAG) than an experimental control group (CG) suggested that algal degradation promoted the release of sedimentary As. The solid phase in all experimental groups remained rich in As(V), while in porewater As(III) and As(V) were the dominant As species during the initial rapid and subsequent slow degradation phases of organic matter, respectively, indicating that microbial reduction of As(V) and Fe(III) controlled the release of As during these two periods. A pronounced increase in arrA gene copies, and not a corresponding increase in the Geobacter copies, in HAG relative to CG supported the notion that algal blooms promoted microbial As(V) reduction. Additionally, the lower concentration of dissolved As(III) and cumulative dTAs flux in the sterilized-HAG treatment than in the sterilized-CG one further suggested that geochemically-mediated processes were not the main pathways of As release. Finally, it is estimated that summer algal blooms in the Changjiang Estuary can cause the release of 1440 kg of sedimentary As into the overlying water., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Although the environmental and health risks of chlorinated organophosphate esters (OPEs-Cl) have drawn much attention, its environmental behaviors have been insufficiently characterized. As a notable sink of this emerging contaminant, non-sanitary landfills, which may decompose/accumulate OPEs-Cl, is of particular concern. In the present study, the dynamic processes of the typical OPEs-Cl, tris(2-chloroethyl) phosphate (TCEP), in non-sanitary landfill soils were analyzed under anaerobic condition, and the microbial taxa involved in these processes were explored. Our results showed that TCEP could be simultaneously reduced by abiotic and biotic processes, as it was reduced by 73.9% and 65.5% over the 120-day experiment in landfill humus and subsoil, respectively. Notably, the degradation of TCEP was significantly (p < 0.05) enhanced under the stress of a high TCEP concentration (10 μg g -1 ), while its ecological consequences were found insignificant regarding the microbial diversity and community structure and the typical soil redox processes, including Fe(III)/SO 4 2- reduction and methanogenesis, in both soils. The microbial diversity of subsoil was significantly lower, and acetate was an important factor in changing microbial communities in landfill soils. The microbes in the family Nocardioidaceae and genus Pseudomonas might contribute to in the degradation of TCEP in landfill humus and subsoil, respectively. The metabolism related to sulfur and sulfate respiration were significantly (p < 0.05) correlated with TCEP reduction, and Desulfosporosinus were found as a potentially functional microbial taxon in TCEP degradation in both soils. The results could advance our understanding of the environmental behavior of OPEs-Cl in landfill-like complex environments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier Ltd.)

Phthalate esters (PAEs) have been extensively used as additives in plastics and wallcovering, causing severe environmental contamination and increasing public health concerns. Here, we find that hematite nanoparticles with specific facet-control can efficiently catalyze PAEs hydrolysis under ambient humidity conditions, with the hydrolysis rates 2 orders of magnitude higher than that in water saturated condition. The catalytic performance of hematite shows a significant facet-dependence with the reactivity in the order {012} > {104} ≫ {001}, related to the atomic array of surface undercoordinated Fe. The {012} and {104} facets with the proper neighboring Fe-Fe distance of 0.34-0.39 nm can bidentately coordinate with PAEs, and thus induce much stronger Lewis-acid catalysis. Our study may inspire the development of nanomaterials with appropriate surface atomic arrays, improves our understanding for the natural transformation of PAEs under low humidity environment, and provides a promising approach to remediate/purify the ambient air contaminated by PAEs., (© 2022. The Author(s).)

The release of trace metals caused by industrial effluents and anthropogenic activities has been recorded in the Xixi River estuary, southern China. However, a thorough understanding of the behavior of trace heavy metals in Xixi River sediments is lacking. A total of 12 sediment cores were collected in June and December in the upper estuary section and mouth of the estuary. Here, an in situ high-resolution sampling technique, namely, diffusive gradients in thin films (DGT), was employed to acquire profiles of trace element concentrations and the release of bioavailable metals from sediments in different seasons. A three-step Community Bureau of Reference (BCR) sequential extraction method was used to explore the chemical speciation of trace metals in different seasons and to thereby assess the release potential of trace elements in sediments. The BCR sequential extraction results showed that the trace metals Fe, Mn, Co and Pb were mainly in the residual fraction, which rarely influences living organisms. The total mobile fractions (F1 + F2 + F3) of all trace metals were higher in winter than in summer, suggesting that accumulation occurred from summer to winter. DGT measurements showed that the intensity of sulfate reduction was higher in summer than in winter because of the high temperatures and high organic matter in summer. The intensity of sulfate and Mn(III/IV) reduction increased from the upper estuary section to the lower estuary. Fe(III) reduction decreased in summer but increased slowly in winter. The Pearson correlation results showed that the release of DGT-labile Co in pore water was related to Mn(III/IV) reduction, while the release of DGT-labile Pb was basically not controlled by the Fe-Mn-S redox transition. Abnormally high DGT-labile Pb concentrations were observed at the sampling station (XR3) closest to the estuary in winter, which might have been caused by the high Pb content in the local micro-sediments., Competing Interests: Declaration of Competing Interest None., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Fiddler crabs, found in coastal wetlands worldwide, function as ecosystem engineers. Their burrowing activity can significantly alter biogeochemistry at the local scale, however, the mobility of heavy metals (HMs) in burrow sediments remains unclear. Here, we used diffusive gradients in thin-film probes to obtain bioavailable Fe and HMs (Cu, Zn, Ni, Cd, Pb, Co, and Mo) in crab burrows from coastal wetlands (mudflats, salt marshes, and mangroves). The depth-profile results showed that most HMs were enriched at shallow and deep depths but deficient at middle depths. We highlighted that bioturbation improved oxic conditions, enhanced HM concentrations, and favored dissolved HM retention in burrow sediments, which served as a sink for overlying water HMs via burrow flushing but a potential source of particle HMs via enhanced resuspension. In deep anoxic layers, Fe(III) reduction drove the remobilization of HMs, except Cu and Mo, leading to the co-release of HMs with Fe. This Fe-HM coupling/decoupling was verified using enhanced two-dimensional high-resolution imaging, which revealed highly spatial heterogeneity of multiple HMs. Moreover, the hydrological conditions regulating bioturbation effects on HM behavior varied across different coastal wetlands. With coastal environmental changes, the key role of ubiquitous bioturbation in HM migration and bioavailability should be reconsidered., (Copyright © 2022 Elsevier B.V. All rights reserved.)

This study quantified the rate and relative contribution of each sedimentary organic carbon (OC) mineralization pathway in the Yantai coastal area. The results showed that scallop farming activities with raft-breeding facilities led to increased accumulation of OC and reactive Fe(III), which in turn promoted OC aerobic mineralization, Fe reduction, and competitively inhibited sulfate reduction. In the scallop farming area (SFA), O 2 reduction, dissimilatory Fe reduction, and sulfate reduction contributed 32.17 %, 27.77 %, and 30.18 % of the total OC mineralization, 1.6 times, 1.2 times, and 0.6 times those of the non-farming area, respectively. Nevertheless, scallop harvesting and resuspension by water currents will increase the short-term risk of dissolved inorganic carbon accumulation in the water column. The OC budget showed that the Yantai coastal area exhibited more OC mineralization than storage, with only 5.0-7.2 % of the net settled OC being permanently buried in the sediment., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The clay layer is a source to facilitate arsenic (As) enrichment in the aquifer. However, little is known about microbial processes in the clay layer and their roles in As mobilization in the underlying aquifer. In this study, high-throughput sequencing of full-length 16S rRNA gene and metagenomics were used to characterize the microbial composition and functional potential in a sediment borehole across the clay and sand layers in Hetao Basin, Inner Mongolia, China. Results showed the significant differences between the clay layer and underlying sand layer in the geochemistry, microbial composition and functional potential. Fermentation, Fe(III) reduction, As(V) reduction, sulfate reduction, thiosulfate disproportionation, reductive tricarboxylic acid and Wood-Ljungdahl pathway identified in sediments from the clay layer were positively correlated to the observed high levels of TOC, soluble ammonium, H 3 PO 4 -extractable As(III) and As(V) and HCl-extractable Fe(II). Although the microbial compositions of the clay and sand layers were different, the microbial functional potential at the interface between the clay and sand layers was similar with the characteristics of fermentation, ammonification and As(V) reduction. The similarity of microbial functional potential at the interface may be attributable to the interaction between the sand and adjacent clay layer with the fluctuation of groundwater level. These metabolic products from the microbial processes in the clay layers and interface would migrate into the underlying groundwater during groundwater overpumping, which facilitates As enrichment in groundwater., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

An anaerobic, alkaliphilic, halotolerant, Gram-stain-positive and rod-shaped bacterium, designated Q10-2 T , was isolated from mangrove sediment sampled at the Jiulong river estuary, PR China. The cells of strain Q10-2 T were motile and 0.5×2-4 µm in size. Strain Q10-2 T grew at 8-45 °C (optimum, 32 °C), at pH 7.0-10.5 (optimum, pH 8.5) and in the presence of 0-6 % (w/v) NaCl (optimum, 3 %). It could use complex organic compounds and carbohydrates including d-fructose, d-galactose, d-glucose, d-mannitol, d-xylose, trehalose, lactose, maltose, sucrose and starch as carbon sources and electron donors. It could reduce sulphate, thiosulphate and elemental sulphur to sulphide, but not sulphite. Fe (Ⅲ) citrate, ferrihydrite, haematite and goethite in the presence of glucose as the electron donor were also reduced. Acetate, butyrate, ethanol, CO 2 and H 2 were end products of glucose fermentation. The predominant cellular fatty acids were composed of C 14 : 0 , C 16 : 0 and summed features containing C 16 : 1  ω7 c and/or iso-C 15 : 0 2-OH and iso-C 17 : 1 and/or anteiso-C 17 : 1 B. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the novel strain was most closely related to Fusibacter paucivorans DSM 12116 T (95.5 % sequence similarity). The genome size of strain Q10-2 T was 5.0 Mb, with a G+C content of 37.4 mol%. The average nucleotide identity and digital DNA-DNA hybridization values between strain Q10-2 T and F. paucivorans DSM 12116 T were 69.1 and 21.8 %, respectively. The combined genotypic and phenotypic data showed that strain Q10-2 T represents a novel species of the genus Fusibacter , for which the name Fusibacter ferrireducens sp. nov. is proposed. The type strain is Q10-2 T (=MCCC 1A16257 T =KCTC 15906 T ).

Lake eutrophication and algal blooms may result in the mortality of macrozoobenthos. However, it is still not clear how macrozoobenthos decomposition affect phosphorus (P) mobility in sediments. High-resolution dialysis (HR-Peeper) and the diffusive gradients in thin films (DGT) technique were used in this study to assess the dissolved organic matter (DOM), dissolved/DGT-labile iron (Fe), P, and sulfur (S(-II)) profiles at a millimeter resolution. The decomposition of Bellamya aeruginosa significantly increased the internal loading of sediments P. The Fe(III) and sulfate were reduced under anaerobic conditions and promoted P desorption from sediments. This was supported by the significant increase in DGT-labile S(-II) and dissolved/DGT-labile P, Fe(II) and the significant positive correlation between Fe and P on day 8. The simultaneous increase in DOM and soluble reactive phosphorus (SRP) and the significant positive relationship between these factors were observed during the decomposition of B. aeruginosa. This suggested that complexation of DOM with metals may promotes the release of P from sediments., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Organic matter (OM) has been accepted as an important trigger fueling Fe(III) oxide reduction and arsenic release in the late Pleistocene-Holocene anoxic aquifers, whereas its fates and roles on arsenic mobility in the Pliocene aquifer are unclear. To fill this gap, groundwaters from a confined Pliocene aquifer (CG) and an unconfined Holocene aquifer (UG) were sampled in the Guide Basin, China, to monitor evolutions of groundwater geochemistry and OM molecular signatures along the groundwater flow path. The outcomes showed that groundwater pH, temperature, and arsenic concentrations in the CG samples generally increased along the groundwater flow path, which were much higher than those in the UG samples. The numbers and intensities of recalcitrant molecules (polycyclic aromatics and polyphenols) in the CG samples remarkably increased along the path, but relatively labile molecules (highly unsaturated and phenolic compounds and aliphatic compounds) showed the opposite trends. The arsenic-poor (<10 μg/L) UG samples contained more labile molecules than the arsenic-rich CG samples. High groundwater pH, temperature, and sediment age in the confined aquifers may be responsible for the selective mobilization of the unique polycyclic aromatics and polyphenols. The mobilized recalcitrant organic molecules may enhance arsenic release via electron shuttling, complexation, and competition. Furthermore, high temperature and pH may also facilitate arsenic desorption. The study provides molecular-scale evidences that the mobilization of recalcitrant organic molecules and arsenic were concurrent in the geothermal confined groundwater., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Abstract: High-intensity focused ultrasound (HIFU) is effective for the ablation of uterine fibroids. However, no research has indicated whether HIFU ablation of uterine fibroids might be improved by application of contrast-enhanced ultrasonography (CEUS) with Sonazoid as a contrast agent. This study aimed to assess the clinical significance of Sonazoid-based CEUS 30 minute before HIFU ablation of uterine fibroids.This retrospective cohort study included Asian patients with solitary uterine fibroids who were treated with HIFU at Seoul HICARE Clinic (South Korea; n = 34) and the Second Affiliated Hospital of Chongqing Medical University (China; n = 30) between August 1, 2017, and October 31, 2017. The patients in Seoul underwent Sonazoid-based CEUS 30 minute before HIFU. All the patients received contrast-enhanced magnetic resonance imaging to diagnose uterine fibroids. The ablation results were evaluated 1 day after HIFU by contrast-enhanced magnetic resonance imaging or Sonazoid-based CEUS.All the patients were successfully treated with HIFU. The CEUS+HIFU group had lower values for sonication power, treatment time, sonication time, total energy applied, and energy efficiency factor compared with HIFU alone group (P < .001). There were no major adverse events after ablation therapy in either group. The incidence of post-procedure sacrococcygeal pain was lower in the CEUS+HIFU group than that in the HIFU alone group (P = .045), while the incidences of all other intraoperative and postoperative adverse events were similar between the 2 groups.Our findings suggest that Sonazoid-based CEUS before HIFU may enhance the ablation of uterine fibroids., Competing Interests: The authors have no conflicts of interest to disclose., (Copyright © 2021 the Author(s). Published by Wolters Kluwer Health, Inc.)

Lanmuchang mercury-thallium mine, a typical polymetallic mine is located in southwestern Guizhou, China, is the most serious and typical area resulted from multi-metal contamination (Tl, Hg, As, and Sb). After the mercury-thallium mining, a large area of surrounding rocks such as argillaceous sandstone with high contents of Tl, Hg, As, and Sb is exposed to air. Weathering caused the argillaceous sandstone to form different weathering layers, including the grey-black external layer, the brown-yellow middle layer and the gray-white inner layer, and the external layer was enriched with higher heavy metals. However, the reason of heavy metal migration and transformation in argillaceous sandstone caused by weathering is unclear. The objective of this paper was to investigate the migration, transformation and release characteristics of Tl, Hg, As, and Sb in argillaceous sandstone during the weathering. The results indicated that weathering not only promoted an acidic oxidation environment in argillaceous sandstone, but also increased its specific surface area, pore volume and hydrophilicity, which are beneficial to the permeability of oxygen and etching liquids during the process of weathering and leaching. Meanwhile, weathering led to the transformation or decomposition of hydrophilic groups, such as -OH and -C˭O in the grey-black external layer of argillaceous sandstone, resulting in the further release of heavy metals bound to these groups. The concentration of Tl, Hg, As, and Sb in the leaching solution of argillaceous sandstone represented a positive correlation with that of Fe, Ca, Mg at different levels, indicating that Tl, Hg, As, and Sb were released with the dissolution of Fe, Ca and Mg during weathering and leaching. In summary, these results indicated that weathering caused the dissolution and migration of heavy metals in the argillaceous sandstone. Tl, Hg, As, and Sb migrated from the grey-white inner layer to the grey-black external layer and partially adsorbed by free alumina (Al d ), jarosite and Ca-bearing minerals, showing enrichment phenomena, partially released into the environment, causing environmental pollution., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Mining activities of antimony (Sb) and arsenic (As) typically result in severe environmental contamination. These contaminants accumulate in rice and thus threaten the health of local residents, who consume Sb- and As-enriched rice grains. Microorganisms play a critical role in the transformation and transportation of Sb and As in paddy soil. Thus, an understanding of the microbiology of contaminated sites would promote the production of safe agricultural products. In this study, six Sb- and As-contaminated rice fields near an active Sb-mining area were investigated. The Sb and As concentrations of all samples were elevated compared to the background level in China. Nitrate, total As, total Sb, and Fe(III) were the major determinants of the microbial community structure. Seven bacterial taxa (i.e. Bradyrhizobium, Bryobacter, Candidatus Solibacter, Geobacter, Gemmatimonas, Halingium, and Sphingomonas) were identified as the core microbiome. These taxa were strongly correlated with the As and Sb contaminant fractions and likely to metabolize As and Sb. Results imply that many soil microbes can survival in the Sb/As contaminated sites., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Cadmium (Cd) contamination in the agricultural soils of China is a serious and growing environmental problem that urgently needs to be controlled and completely remediated. The biogeochemical cycles of nitrogen (N), sulfur (S), and iron (Fe), and the coupled cycles of Fe-N and Fe-S have been reported to control Cd transportation in the soil-rice system. Exploring practical remediation strategies for Cd from the perspective of the application of nutrients such as N, S, and Fe for rice growth is expected to obtain farm-specific and state-of-the-art technologies and products to reduce the accumulation of Cd in rice grains. Using our earlier study as a basis, the rhizosphere bag-pot experiment with ferrous sulfate (FeSO 4 ) and ferric nitrate[Fe(NO 3 ) 3 ] treatments was conducted to investigate Cd bioavailability in rhizosphere soil and Cd translocation in rice plants, and to highlight some possible factors and mechanisms controlling Cd accumulation in rice grains. The results showed that both FeSO 4 and Fe(NO 3 ) 3 treatments reduced the bioavailable Cd (NH 4 Ac-Cd) content in rhizosphere soil, with the decreasing extent being significantly lower in the former (55.6%) than in the latter (76.0%). Both FeSO 4 and Fe(NO 3 ) 3 treatments changed the distribution characteristics of Cd in rice tissues, and the FeSO 4 treatment increased the Cd content in brown rice (0.6 mg·kg -1 ), but the Fe(NO 3 ) 3 treatment decreased the Cd content in brown rice (0.1 mg·kg -1 ). Adsorption or co-precipitation of Cd by iron plaque, increased accumulations of Cd in root, stem, and leaf, and enhanced translocations of Cd from root, stem, and nodule to brown rice occurred with the increased Cd content in brown rice of the FeSO 4 treatment. However, the decreased Cd content in brown rice with the Fe(NO 3 ) 3 treatment was ascribed to adsorption or co-precipitation of Cd by poorly crystalline Fe oxides and solid Fe sulfides, decreased accumulations of Cd in stem and nodule, and weakened translocations of Cd from root, leaf, and nodule to brown rice. These findings provide a scientific basis for the exploration and application of nutritive soil amendment, and will have significance in regards to the remediation of Cd-contaminated agricultural soils in China.

The consumption of agricultural products grown on paddy soils contaminated with toxic element has a detrimental effect on human health. However, the processes and mechanisms of iron (Fe) mineral-associated arsenic (As) availability and As reactivity in different paddy soil profiles are not well understood. In this study, the fractions, immobilization, and release risk of As in eleven soil profiles from the Changzhutan urban agglomeration in China were investigated; these studied soils were markedly contaminated with As. Sequential extraction experiments were used to analyze fractions of As and Fe oxide minerals, and kinetic experiments were used to characterize the reactivity of Fe oxide minerals. The results showed that concentrations of total As and As fractions had a downward trend with depth, but the average proportions of As fractions only showed relatively small changes, which implied that the decrease in the total As concentrations influenced the changes in fraction concentrations along the sampling depth. Moreover, we found that easily reducible Fe (Fe ox1 ) mainly controlled the reductive dissolution of the Fe oxides, which suggest that the reductive dissolution process could potentially release As during the flooded period of rice production. In addition, a high proportion of As was specifically absorbed As (As-F2) (average 20.4%) in paddy soils, higher than that in other soils. The total organic carbon (TOC) content had a positive correlation with the amount of non-specifically bound As (As-F1) (R = 0.56), which means that TOC was one factor that affected the As extractability in the As-F1. Consequently, high inputs of organic fertilizers may elevate the release of As and accelerate the diffusion of As. Graphical abstract.

As a recently discovered process of nitrogen cycling, anaerobic ammonium oxidation coupled to ferric iron reduction (Feammox) has attracted more attentions. This study investigated the spatial variation of Feammox in the sediment of different zones of a shallow freshwater lake and the effect of organic matter derived from algae and macrophyte on Feammox process. The potential Feammox rates showed significant differences among sediments from algae-dominated area (ADA), transitional area in the center of the lake (TDA), and macrophyte-dominated area (MDA), and in a descending order, ADA, MDA, and TDA. The potential Feammox rate ranged from 0.14 to 0.34 mg N kg -1 day -1 in the freshwater lake sediment. The potential Feammox rates of the sediment with algae or macrophyte amendment were 12.29% and 15.31% higher than the control test without algae and macrophyte amendment. The addition of algae or macrophyte to the sediment from TDA could improve the amount of HCl-extractable total Fe, Fe(III) reduction rate, and the abundance of FeRB. These results demonstrated that organic matter is one of the key regulators of Feammox process.

Oxidation of surface sediments is an important means for altering phosphorus (P) exchanges across sediment-water interface (SWI) in shallow lakes. In this study, the potential and composition of regenerated oxidation capacity (OC) of surface sediments were evaluated in three large shallow lakes (Tai Lake, Chao Lake, and Dianchi Lake) in China; the transformation of sedimentary P was quantified through P fractionation scheme. The composition of the regenerated OC differed among these three lakes, with Fe(III) and SO 4 2- dominant in Dianchi Lake, Mn(IV) and Fe(III) in Chao Lake and Tai Lake. Oxidation of sediments enhanced the transformation of sedimentary P and altered P exchanges across the SWI. In Chao Lake, the HCl-P was transformed to BD-P; in Tai Lake, the NaOH-P was involved too, and transformed to BD-P; whereas in Dianchi Lake, an increase in NH 4 Cl-P was also observed except for the transformation from HCl-P to BD-P. The sediment-to-water flux of P was enhanced with 0.17 mg/g DW in Dianchi Lake and 0.08 mg/g DW in Chao Lake, while a contrary water-to-sediment flux of P was observed in Tai Lake, reaching 0.01 mg/g DW. This study advances our knowledge on the impacts of sediment oxidation on P cycles in lakes, which will be beneficial to eutrophication control.

Molecular characteristics of natural organic matter (NOM) and their potential connections to arsenic enrichment processes remain poorly understood. Here, we examine dissolved organic matter (DOM) in groundwater and water-soluble organic matter (WSOM) in aquifer sediments being depth-matched with groundwater samples from a typical arid-semiarid basin (Hetao Basin, China) hosting high arsenic groundwater. We used Fourier transform ion cyclotron resonance mass spectrometry to determine molecular characteristics of DOM and WSOM and evaluate potential roles of biodegradable compounds in microbially mediated arsenic mobility at the molecular level. High-arsenic groundwater DOM was generally enriched in recalcitrant molecules (including lignins and aromatic structures). Although potential contribution of recalcitrant compounds to arsenic enrichment cannot be ruled out, preferential degradation of the labile molecules coupled with reduction of Fe(III) (oxyhydr)oxides seemed to dominate arsenic mobilization. Both the number and the intensity of biodegradable compounds (including aliphatic/proteins and carbohydrates) were higher in WSOM than those in DOM in depth-matched high-arsenic groundwater (arsenic >0.67 μmol/L or 50 μg/L). Groundwater arsenic concentration generally increased with the increase in the number and the intensity of unique biodegradable compounds (especially N-containing compounds) in WSOM at matched depths. Anoxic incubations of sediments and deionized water show that more arsenic and Fe(II) were released from aquifer sediments with greater numbers and intensities of consumed biodegradable compounds in WSOM (especially N-containing compounds), with a higher proportion of microbially derived compounds produced. These observations indicate that the biodegradation of aliphatic/proteins and carbohydrates (especially CHON formulas) in WSOM fueling the reductive dissolution of Fe(III) (oxyhydr)oxides predominantly promotes arsenic release from aquifer solids. Our unique data present a better understanding of arsenic mobilization shaped by microbial degradation of labile organic compounds in anoxic aquifers at the molecular level.

In flooded paddy soils, some metal reducers are also capable of nitrogen (N) fixation, which is essential in ensuring a reliable N-supply for rice growth. Microbial iron [Fe(III)] reduction is an important biogeochemical process that can be stimulated by ferrihydrite amendment to paddy soil. Therefore, this study aimed to investigate the abundance and succession of the N 2 -fixing bacterial community in ferrihydrite enriched paddy soils collected from Hunan (HN) and Sichuan (SC) provinces, China. The relationship between the N 2 -fixing bacterial community and Fe(III) reduction was also assessed. When compared with the control treatment, ferrihydrite enrichment significantly enhanced nitrogenase (nifH) gene abundance by 8.05 × 10 5 to 4.45 × 10 6  copies g -1 soil during the 40-day flooding of HN soil, while nifH gene abundance in SC soil was remarkably increased by 5.90 × 10 7 to 9.56 × 10 7  copies g -1 soil during day 1 to 5 in response to ferrihydrite amendment. The relative abundance of N 2 -fixing bacteria peaked on day 5 (21.5% in HN soil and 5.4% in SC soil) and gradually decreased to a stable abundance after day 20. Remarkable increases in relative abundance of N 2 -fixing bacteria during the first 10 days of flooding were detected in both soils with ferrihydrite enrichment, whereas little difference was found after day 10 of flooding. During the early stage of flooding, the Shannon and Simpson indexes of N 2 -fixing bacteria with ferrihydrite enrichment were significantly decreased, and the community structure changed greatly. Most N 2 -fixing bacteria in ferrihydrite enriched paddy soils were phylogenetically related to the order Clostridiales, with some of those potentially capable of Fe(III) reduction. The community succession of N 2 -fixing bacteria closely correlated with Fe(III) reduction. Thus, improving N 2 -fixation via stimulation of Fe(III) reduction might aid in the reduction of N-fertilizer application to paddy field., Competing Interests: Declaration of competing interest We certify that no conflict of interest exits in this manuscript. The manuscript has not been submitted elsewhere for publication. The submission is approval by all authors and institutional authorities immediately involved. The authors agree with Inter-Research terms of publication., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Oxygen can enter into reductive aquifer through natural and artificial processes. However, the joint response of groundwater chemistry and functional microbial communities to oxygenation is not well understood due to the gap between taxonomic and functional microbial composition. Here, two wells named CZK15 and CZK22 at the second confined aquifer in Central China were in situ aerated, and the chemical parameters of groundwater and microbial communities in bio-trapping sand sediment were analysed during aeration. The microbial metabolic functions related to C, N, S, Fe transformation were predicted by Functional Annotation of Prokaryotic Taxa (FAPROTAX) approach and some key functional genes, such as phe, nah, narG, and soxB were verified by the real-time quantitative Polymerase Chain Reaction (qPCR) method. The biomass was promoted, microbial diversity fluctuated, and microbial composition changed remarkably with aeration mainly constrained by reduction-oxidation (redox) variation and SO 4 2- concentration. Among functional microbes, aerobic chemoheterotrophs including aromatic compound degraders (also especially for relative abundance of phe and some nah gene) and methylotrophs are dramatically enriched interpreting dissolved oxygen (DO) consumption and total organic carbon (TOC) decomposing in sediment. Whilst fermenters and methanogen expectedly decreased during aeration. Denitrifying microbes and narG gene relative abundance increased corresponding to the NO 3 - increase after aeration, while microbes for N 2 fixation, ammonification, and nitrification decreased relating to the source of NH 4 + . The sulfide oxidation causing increased SO 4 2- was reflected by the blooming of sulfur-oxidizing microbes and soxB gene. Some sulfate reducers persisted in sediment after aeration due to sufficient SO 4 2- as substrate. Fe(II) was mainly chemically oxidized as iron-oxidizing microbes were of low abundance and tended to decrease with aeration. The iron-reducing bacteria Geobacteraceae increased with aeration corresponding to the increased Fe(III) oxides formation. The findings of this study could have important implications in understanding the biogeochemical behaviours with cyclic redox conditions., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Bauxite residue is the by-product of the aluminium industry with an annual output of more than 200 million metric tons in China. Its treatment is still a big problem because more than 96% of that is stockpiled on land causing environmental pollution and threatening the human health. This study used bauxite residue to remove Cr (Ⅲ) from aqueous solution and analyzed the removal mechanism. The removal time was dependent on the initial concentrations of Cr (Ⅲ) and different active components acted on different reaction period. Reaction time increased from <5 min to >2 h with an increase of Cr (Ⅲ) concentration from 5 to 100 and 170 mg/L. The existing forms of adsorbed-Cr were iron oxide-bound Cr (40.80%-87.85%), sulfide-bound Cr (4.04%-20.28%) and residue (6.60%-33.72%). All the components started to react as soon as bauxite residue was added. Cr did not precipitate in the presence of high alkalinity bauxite residue due to the slow release of alkalinity maintaining pH < 6, thus producing Cr(OH) 2+ , Cr 2 (OH) 2 4+ and Cr 3 (OH) 4 5+ by hydrolysis without precipitation. Fe 2 O 3 and Al-containing components were the main active phases for Cr (Ⅲ) removal, with the reaction time lasting more than 2 h and producing Ca 6 Al 4 Cr 2 O 15 , AlCr 2 , (Si, Al) 2 O 4 , Fe(Cr, Al) 2 O 4 , FeCr 2 Si 3 O 12 , MgCr 0·1 Fe 1·9 O 4 and MgCr 0·4 Fe 1·6 O 4 . Finally, bauxite residue was granulated and used for column tests. Cr (Ⅲ) wastewater (1 and 50 mg/L) was treated and the effluent can meet the first level of the Shanghai standard (0.1 mg/L) defined by Integrated Wastewater Discharge Standard (DB 31/199-2009)., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Large areas of the paddy fields in South China are contaminated with arsenic (As), which causes serious problems, including high As concentrations in brown rice. Three As-resistant iron-oxidizing bacteria (FeOB) namely, Bacillus sp. T2, Pseudomonas sp. Yangling I4 and Bacillus sp. TF1-3, were isolated and applied to rice grown in different As-contaminated environments to study the effects of FeOB on the As accumulation in rice and clarify the possible mechanisms involved. The results showed that FeOB inoculation significantly decreased the inorganic As concentrations in brown rice grown in pots and paddy fields by 3.7-13.3% and 4.6-12.1%, respectively. FeOB inoculation enhanced the formation of Fe plaque, which sequestered more As on the root surface. Moreover, a significantly lower level of As(III) influx was observed in the rice cultivated with FeOB than in the control. FeOB inoculation also decreased the As concentrations in pore water and the Fe(II)/Fe(III) ratio in rhizosphere soil. The present results suggest that FeOB inoculation decreased the inorganic As concentrations in brown rice by affecting the formation of Fe plaque, As(III) uptake kinetics and rhizosphere soil properties. Based on our results, FeOB inoculation could be considered a useful method to decrease inorganic As concentrations in brown rice grown in As-contaminated paddy fields., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Arsenic (As) release and mobility in groundwater is coupled to the iron (Fe) cycling and the associated transformation of Fe-oxides present in sediments. Recent in situ experiments have provided observations on arsenic mobilization and co-occurring reductive mineral transformation when placing As-loaded ferrihydrite-coated sand for 80 days in wells of an As-contaminated aquifer of Northern China. However, the complex temporal change in solid-associated arsenic and the multiple geochemical processes occurring when the flowing groundwater contacts the As-loaded ferrihydrite-coated sand hamper a detailed evaluation of the experimental data set. In this study, we develop a modeling approach that allows a quantitative interpretation of arsenic release and ferrihydrite transformation observed during the in situ experiments. The model accounts for the interplay of abiotic and biotic geochemical processes (i.e., surface complexation, reductive dissolution, formation of secondary iron minerals, and arsenic sequestration into the newly formed minerals) involved in the transformation of Fe-oxides and controlling arsenic mobility. The results show the capability of the proposed approach to reproduce the temporal trends of solid arsenic and ferrihydrite concentrations, as well as the spatial variability of mineral transformation, observed in different wells using a common set of surface complexation parameters and kinetic rate constants. The simulation outcomes allowed us to disentangle the specific contribution of the different mechanisms controlling the release of arsenic. It was possible to identify an initial rapid but minor release of As (13-23% of the initial surface concentration) due to desorption from ferrihydrite, as well as the reduction of adsorbed As(V) to As(III) upon contact with the flowing anoxic groundwater. Successively, reductive dissolution of ferrihydrite caused the decrease of the amount of the Fe mineral phase and led to a major depletion of solid-associated arsenic. The produced Fe(II) catalyzed the ferrihydrite conversion into more crystalline Fe(III) oxides (i.e., lepidocrocite and goethite) through Ostwald ripening, and resulted in the formation of siderite and mackinawite upon reaction with carbonates and sulfides naturally present in the groundwater. The model results also showed that, whereas the decrease in surface sites during reductive dissolution of ferrihydrite promoted arsenic mobilization, the mineral transformation limited As release through its sequestration into the newly formed secondary mineral phases.

To unveil behavior and fate of uranium (U) in the Quaternary aquifer system of Datong basin (China), we analyzed sediment and groundwater samples, and performed geochemical modeling. The analyses for sediments were implemented by a sequential extraction procedure and measurements including X-ray power diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Concentrations of main elements and U, and 234 U/ 238 U activity ratios for groundwater were determined. Results show that sediment U contents range from 1.93 to 8.80 (average 3.00 ± 1.69) mg/kg. In relation to the total U, average fractions of residual U (probably as betafite) and U(VI) bound to carbonates and FeMn oxides are 74.4 ± 18.7%, 17.2 ± 13.3%, and 4.3 ± 2.9%, respectively. Lower average fractions were determined for both organic matter- and sulfide-bound U (mainly as U(IV), e.g., brannerite) (2.0 ± 0.7%) and exchangeable U(VI) (2.0 ± 2.8%). For the groundwater (pH 7.36-8.86), Ca 2 UO 2 (CO 3 ) 3 0 , CaUO 2 (CO 3 ) 3 2- , and UO 2 (CO 3 ) 3 4- constitute >99.5% of the total dissolved U; and elevated U concentrations occur mainly in shallow aquifers (3-40 m deep below land surface) of the west flow-through and discharge areas, with 50% of the sampled points exceeding 30 μg/L. We argue that betafite and carbonate weathering and U(VI) desorption from ferrihydrite are the primary geochemical processes responsible for U mobilization, with a minor contrition from U(IV) oxidation. Abiotic U(IV) oxidation may be induced mainly by dissolved oxygen under oxic/suboxic conditions (e.g., in the recharge and flow-through areas), but significantly linked to amorphous ferrihydrite under Fe(III)- and sulfate-reducing conditions. Abiotic U(VI) reduction could be caused principally by siderite and mackinawite. Under alkaline conditions, higher HCO 3 - concentrations and lower Ca 2+ /HCO 3 - molar ratios (<~0.2) cause formation of CaUO 2 (CO 3 ) 3 2- and UO 2 (CO 3 ) 3 4- , and U(VI) desorption. With increases in concentrations of Ca 2+ and Ca 2+ /HCO 3 - ratios (>~0.2), these anionic forms may shift to neutral Ca 2 UO 2 (CO 3 ) 3 0 , which can facilitate further desorption of U(VI). Our results improve the understanding of U environmental geochemistry and are important for groundwater resources management in this and similar other Quaternary aquifer systems., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Coal gangue has become one of the largest industrial solid waste in China, but it is also a kind of reserve resources. Representative coal gangue samples from different coal mines (mainly in Permo-Carboniferous and Jurassic) in Weibei area in Shaanxi Province are collected, and potentially useful elements (Al, Fe, Ga, Ge, U) in coal gangue are analyzed. The results show that the reserves of Al and Fe in Chinese coal gangue are 262 million tons and 196 million tons, respectively, based on the geometric mean values of Al 2 O 3 (15.18%, weight percent) and Fe 2 O 3 (6.24%, weight percent). Meanwhile, the crude reserves estimation of Ga, Ge, and U are 55,282, 6867, and 32,981 tons, respectively, based on the weighted mean contents of Ga, Ge, and U in coal gangue at 17.55, 2.18, and 10.47 mg/kg, respectively. Furthermore, Ga and Al contents in quite a large number of coal gangue mines exceed the cutoff value, which has a prospect of development and utilization from coal gangue. The policy implications from this study may include that (1) recycling of useful elements in Chinese coal gangue should be treated as an integral part of sustainable development with professional legislations and (2) establishing a basic database of coal gangue and authoritative system with relevant departments for solid waste management may effectively improve comprehensive utilization of coal gangue in the future.

The effects of various geochemical processes on arsenic enrichment in a high-arsenic aquifer at Jianghan Plain in Central China were investigated using multivariate models developed from combined adaptive neuro-fuzzy inference system (ANFIS) and multiple linear regression (MLR). The results indicated that the optimum variable group for the AFNIS model consisted of bicarbonate, ammonium, phosphorus, iron, manganese, fluorescence index, pH, and siderite saturation. These data suggest that reductive dissolution of iron/manganese oxides, phosphate-competitive adsorption, pH-dependent desorption, and siderite precipitation could integrally affect arsenic concentration. Analysis of the MLR models indicated that reductive dissolution of iron(III) was primarily responsible for arsenic mobilization in groundwaters with low arsenic concentration. By contrast, for groundwaters with high arsenic concentration (i.e., > 170 μg/L), reductive dissolution of iron oxides approached a dynamic equilibrium. The desorption effects from phosphate-competitive adsorption and the increase in pH exhibited arsenic enrichment superior to that caused by iron(III) reductive dissolution as the groundwater chemistry evolved. The inhibition effect of siderite precipitation on arsenic mobilization was expected to exist in groundwater that was highly saturated with siderite. The results suggest an evolutionary dominance of specific geochemical process over other factors controlling arsenic concentration, which presented a heterogeneous distribution in aquifers. Supplemental materials are available for this article. Go to the publisher's online edition of the Journal of Environmental Science and Health, Part A, to view the supplemental file.

The role of bacteria in the occasional emergence of red water, which has been documented worldwide, has yet to be determined. To better understand the mechanisms that drive occurrences of red water, the bacterial community composition and the relative abundance of several functional bacterial groups in a water distribution system of Beijing during a large-scale red water event were determined using several molecular methods. Individual clone libraries of the 16S rRNA gene were constructed for three red water samples and one sample of normal water. Beta-, Alpha-, and Gammaproteobacteria comprised the major bacterial communities in both red water and normal water samples, in agreement with previous reports. A high percentage of red water clones (25.2 to 57.1%) were affiliated with or closely related to a diverse array of iron-oxidizing bacteria, including the neutrophilic microaerobic genera Gallionella and Sideroxydans, the acidophilic species Acidothiobacillus ferrooxidans, and the anaerobic denitrifying Thermomonas bacteria. The genus Gallionella comprised 18.7 to 28.6% of all clones in the three red water libraries. Quantitative real-time PCR analysis showed that the 16S rRNA gene copy concentration of Gallionella spp. was between (4.1 ± 0.9) × 10⁷ (mean ± standard deviation) and (1.6 ± 0.3) × 10⁸ per liter in red water, accounting for 13.1% ± 2.9% to 17.2% ± 3.6% of the total Bacteria spp. in these samples. By comparison, the percentages of Gallionella spp. in the normal water samples were 0.1% or lower (below the limit of detection), suggesting an important role of Gallionella spp. in the formation of red water.

Stream sediments play an important role in the transport and storage of phosphorus in the stream ecosystems. This research investigated the sorption and fraction of P in the sediments of a long-term seriously contaminated river, the Daliao river system, using isotherm sorption and selective sequentially extraction tests. Results indicated that the total content of P in the sediments was 479-1202 mg kg(-1), depending on iron content in the sediments. The content of potential bioavailable P, including soluble and loosely bound P, Al bound P, Fe bound P, and reductant soluble P was only 10-20% of total P in the sediments of the Hun river and Taizi river, while it was 40-55% in the sediments of the Daliao river, the downstream of the river system. Equilibrium phosphorus concentration without net P sorption (EPC(0)) was from 0.05 to 0.54 mg L(-1), with an increasing trend from upstream to downstream, indicating increasingly release potential. On the other hand, the upstream sediment generally sorbed more P than the downstream sediment for each river at the same equilibrium P concentration. The binding energy constant of P on the strong sites of the sediments generally decreased from 2.24 to 2.65 L mg(-1) at upstream to 0.41 L mg(-1) at downstream or estuary, suggesting that the strong binding sites have been occupied and partly saturated by the phosphate added by point and diffuse sources along the river. On the other hand, molar ratio of Fe to TP contents in the sediments showed sorption capacity of the sediments to P might be under-saturated. The added or sorbed P by the isotherm test was primarily bound to Fe oxides and secondly to Al oxides. Long-term pollution of the river lead to the decrease of P sorption capacity of the river sediment and the increase of P release potential.

Magnetic fractions (MFs) in fly ashes from eight coal-burning power plants were extracted by magnetic separation procedure. Their mineralogy and potential leachability of heavy metals were analyzed using rock magnetism, X-ray diffraction (XRD), scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM/EDX) and leaching procedures (toxicity characteristics leaching procedure by the United States Environmental Protection Agency, TCLP, and gastric juice simulation test, GJST). Results show that the MFs in the fly ashes range between 2.2 and 16.3wt%, and are generally composed of magnetite, hematite, quartz and mullite. Thermomagnetic analysis and SEM/EDX indicate that the main magnetic carrier magnetite is substituted with small amounts of impure ions, and its structures are featured by rough, dendritic and granular iron spherules. The MFs are found to be rich in Fe, Mn, Cr, Cu, Cd and Pb. Compared with the non-magnetic fractions (NMFs), the MFs have about 5 times higher iron, and 1.6 times higher Mn, Cr, Cu and Cd concentrations. The TCLP test shows that the TCLP-extractable Cr, Cu, and Pb concentrations in the MFs are higher than those in the NMFs, while the TCLP-extractable Cd concentration in the MFs and NMFs is below the detection limit (<0.1mg/L). The GJST-extractable Cd, Cr, Cu, and Pb concentrations in the MFs are higher those in the NMFs. No significant difference in the leachability ratio of Cr, Cu and Pb with TCLP and GJST is found in the MFs and NMFs. However, the GJST test showed that Pb has higher leachability in MFs than that in NMFs. The leachability ratio of heavy metals has an order of Cu>Cr>Pb>Cd. The heavy metals of fly ashes have a great potential to be released into the environment under acid environment.

Enhanced concentrations of phosphorus entering the aquatic systems have been linked with eutrophication and its associated problems. Jar tests were applied to a secondary effluent in order to determine optimal conditions for coagulation. The coagulants studied were ferric sulfate [Fe2(SO4)3], aluminum sulfate [Al2(SO4)3.18H2O] and polyaluminum chloride (PAC). The experiments were carried out using simplex research technique to determine the optimum conditions of these coagulants for phosphorus removal. For each coagulant examined, 18-25 experiments were carried out until a maximum removal was observed through the experimental procession. Increases of greater than 30% were found for the removal efficiencies of these three coagulants over the course of the experiments. Good removal efficiencies averaging at least 87.25% were obtained through the simplex procession. The orthophosphate removal efficiency was higher than that of total phosphorus for each coagulant. The maximum removal efficiency of total phosphorus obtained from the optimization procedures for ferric sulfate, aluminum sulfate and polyaluminum chloride was 87.3, 95.6 and 94.0%, respectively, and the minimum total phosphorus residual was 0.35, 0.12 and 0.16 mg/L, respectively.