Learning with sparse reward in a gap junction network inspired by the insect mushroom body.

Animals can learn in real-life scenarios where rewards are often only available when a goal is achieved. This 'distal' or 'sparse' reward problem remains a challenge for conventional reinforcement learning algorithms. Here we investigate an algorithm for learning in such scenarios, inspired by the possibility that axo-axonal gap junction connections, observed in neural circuits with parallel fibres such as the insect mushroom body, could form a resistive network. In such a network, an active node represents the task state, connections between nodes represent state transitions and their connection to actions, and current flow to a target state can guide decision making. Building on evidence that gap junction weights are adaptive, we propose that experience of a task can modulate the connections to form a graph encoding the task structure. We demonstrate that the approach can be used for efficient reinforcement learning under sparse rewards, and discuss whether it is plausible as an account of the insect mushroom body.

Seasonal Formation of Low-Sorbing Methylthiolated Arsenates Induces Arsenic Mobilization in a Minerotrophic Peatland.

Peatlands are known sinks for arsenic (As). In the present study, seasonal As mobilization was observed in an acidic, minerotrophic peatland (called Lehstenbach) in late summer, accompanied by a peak in dissolved sulfide (S(-II)). Arsenic speciation revealed the lowest seasonal porewater concentrations of arsenite and arsenate, likely due to As(III)-S-bridging to natural organic matter. Arsenic mobilization was driven by the formation of arsenite-S(-II) colloids and formation of methylthiolated arsenates (up to 59% of the sum of As species) and to a minor extent also of inorganic thioarsenates (6%-30%) and oxymethylated arsenates (5%-24%). Sorption experiments using a purified model peat, the Lehstenbach peat, natural (to mimic winter conditions) and reacted with S(-II) (to mimic late summer conditions) at acidic and neutral pH confirmed low sorption of methylthiolated arsenates. At acidic pH and in the presence of S(-II), oxymethylated arsenates were completely thiolated. This methylthiolation decreased As sorption up to 10 and 20 times compared with oxymethylated arsenates and arsenite, respectively. At neutral pH, thiolation of monomethylated arsenates was incomplete, and As could be partially retained as oxymethylated arsenates. Dimethylated arsenate was still fully thiolated and highly mobile. Misidentification of methylthiolated arsenates as oxymethylated arsenates might explain previous contradictory reports of methylation decreasing or increasing As mobility.

Predictive Coding as a Neuromorphic Alternative to Backpropagation: A Critical Evaluation.

Backpropagation has rapidly become the workhorse credit assignment algorithm for modern deep learning methods. Recently, modified forms of predictive coding (PC), an algorithm with origins in computational neuroscience, have been shown to result in approximately or exactly equal parameter updates to those under backpropagation. Due to this connection, it has been suggested that PC can act as an alternative to backpropagation with desirable properties that may facilitate implementation in neuromorphic systems. Here, we explore these claims using the different contemporary PC variants proposed in the literature. We obtain time complexity bounds for these PC variants, which we show are lower bounded by backpropagation. We also present key properties of these variants that have implications for neurobiological plausibility and their interpretations, particularly from the perspective of standard PC as a variational Bayes algorithm for latent probabilistic models. Our findings shed new light on the connection between the two learning frameworks and suggest that in its current forms, PC may have more limited potential as a direct replacement of backpropagation than previously envisioned.

Mobilization of Colloid- and Nanoparticle-Bound Arsenic in Contaminated Paddy Soils during Reduction and Reoxidation.

The association of arsenic (As) with colloidal particles could facilitate its transport to adjacent water systems or alter its availability in soil-rice systems. However, little is known about the size distribution and composition of particle-bound As in paddy soils, particularly under changing redox conditions. Here, we incubated four As-contaminated paddy soils with distinctive geochemical properties to study the mobilization of particle-bound As during soil reduction and subsequent reoxidation. Using transmission electron microscopy-energy dispersive spectroscopy and asymmetric flow field-flow fractionation, we identified organic matter (OM)-stabilized colloidal Fe, most likely in the form of (oxy)hydroxide-clay composite, as the main arsenic carriers. Specifically, colloidal As was mainly associated with two size fractions of 0.3-40 and >130 kDa. Soil reduction facilitated the release of As from both fractions, whereas reoxidation caused their rapid sedimentation, coinciding with solution Fe variations. Further quantitative analysis demonstrated that As concentrations positively correlated with both Fe and OM concentrations at nanometric scales (0.3-40 kDa) in all studied soils during reduction and reoxidation, yet the correlations are pH-dependent. This study provides a quantitative and size-resolved understanding of particle-bound As in paddy soils, highlighting the importance of nanometric Fe-OM-As interactions in paddy As geochemical cycling.

Evidence for nontraditional mcr-containing archaea contributing to biological methanogenesis in geothermal springs.

Recent discoveries of methyl-coenzyme M reductase-encoding genes (mcr) in uncultured archaea beyond traditional euryarchaeotal methanogens have reshaped our view of methanogenesis. However, whether any of these nontraditional archaea perform methanogenesis remains elusive. Here, we report field and microcosm experiments based on 13C-tracer labeling and genome-resolved metagenomics and metatranscriptomics, revealing that nontraditional archaea are predominant active methane producers in two geothermal springs. Archaeoglobales performed methanogenesis from methanol and may exhibit adaptability in using methylotrophic and hydrogenotrophic pathways based on temperature/substrate availability. A five-year field survey found Candidatus Nezhaarchaeota to be the predominant mcr-containing archaea inhabiting the springs; genomic inference and mcr expression under methanogenic conditions strongly suggested that this lineage mediated hydrogenotrophic methanogenesis in situ. Methanogenesis was temperature-sensitive , with a preference for methylotrophic over hydrogenotrophic pathways when incubation temperatures increased from 65° to 75°C. This study demonstrates an anoxic ecosystem wherein methanogenesis is primarily driven by archaea beyond known methanogens, highlighting diverse nontraditional mcr-containing archaea as previously unrecognized methane sources.

Methanogens-Driven Arsenic Methylation Preceding Formation of Methylated Thioarsenates in Sulfide-Rich Hot Springs.

Hot springs represent a major source of arsenic release into the environment. Speciation is typically reported to be dominated by arsenite, arsenate, and inorganic thiolated arsenates. Much less is known about the relevance and formation of methylated thioarsenates, a group with species of high mobility and toxicity. In hot spring samples taken from the Tengchong volcanic region in China, methylated thioarsenates contributed up to 13% to total arsenic. Enrichment cultures were obtained from the corresponding sediment samples and incubated to assess their capability to convert arsenite into methylated thioarsenates over time and in the presence of different microbial inhibitors. In contrast to observations in other environmental systems (e.g., paddy soils), there was no solid evidence, supporting that the sulfate-reducing bacteria contributed to the arsenic methylation. Methanosarcina, the sole genus of methanogens detected in the enrichment cultures, as well as Methanosarcina thermophila TM-1, a pure strain within the genus, did methylate arsenic. We propose that methylated thioarsenates in a typical sulfide-rich hot spring environment like Tengchong form via a combination of biotic arsenic methylation driven by thermophilic methanogens and arsenic thiolation with either geogenic sulfide or sulfide produced by sulfate-reducing bacteria.

Cr(VI) removal from contaminated waters using ultra-thin layered meixnerite.

Cr(VI) is of great concern to public health and environmental safety due to its high toxicity. Here, we report a low-cost yet highly efficient method to prepare a novel LDH, ultra-thin layered meixnerite, which performed superiorly in treatment of aqueous Cr(VI) with little secondary pollution being induced. The produced ultra-thin layered meixnerite was composed of nanoparticles with a thickness of around 7 nm, less than 9 times the thickness of a single LDH layer. The XRD patterns of the ultra-thin layered meixnerite, in which the characteristic diffraction peaks of a typical LDH were weakened or even disappeared, confirmed the successful delamination. This special morphology of the ultra-thin layered meixnerite was not only helpful to its full dispersion in the Cr(VI)-bearing solutions but also facilitated the formation of more active sorption sites on its external surface. As a result, the maximum sorption capacity of UTLM for Cr(VI) removal was 480.9 mg g-1, far higher than that of OM (196.9 mg g-1). In addition to electrostatic attraction and anion exchange, the ultra-thin layered meixnerite could also become restacked during removal of aqueous Cr(VI) to generate inner-sphere complexation, finally inducing an enhanced Cr(VI) uptake. Furthermore, XPS analysis characterized the promotion of the break of Al-OH bond with the increase in temperature, and the Cr-O peak increased correspondingly from 29.69% at 25 °C to 48.77% at 85 °C, resulting that the ultra-thin layered meixnerite could remove Cr(VI) more effectively at higher reaction temperatures. Therefore, ultra-thin layered meixnerite is very suitable for future application in treatment of industrial wastewaters with elevated temperatures.

Hydrocalumite as well as the Formation of Scheelite Induced by Its Dissolution, Removing Aqueous Tungsten with Varying Concentrations.

As a toxic element, tungsten (W) in elevated concentrations, originating from human activities or geological sources, poses a severe threat to the environment. However, there has been a lack of robust remediation techniques focusing on aqueous tungsten contamination with varying initial concentrations, because only recently have the toxicity and the environmental threat of tungsten been fully realized. In this study, the removal of tungsten from an aqueous solution by hydrocalumite was investigated for the first time. Systematic removal experiments were carried out at designated contact time, temperature, and initial tungsten concentration. The results showed that hydrocalumite is capable of effectively removing tungsten under various conditions, especially at high initial tungsten concentrations, with the maximum uptake capacity being up to 1120.5 mg (tungsten)/g (hydrocalumite). The mechanisms of tungsten removal were studied based on the measured chemical compositions of the solution samples and their PHREEQC simulations as well as the solid sample characterization by XRD, SEM-EDX, and XPS. At low initial tungsten concentrations (below 1 mmol/L), anion exchange between the tungsten in solution and the Cl in the hydrocalumite interlayers played a critical role in tungsten removal. At high initial tungsten concentrations (higher than 5 mmol/L), the removal of W from the solution was solely caused by the precipitation of scheelite (CaWO4), facilitated by the substantial release of Ca2+ from hydrocalumite dissolution. At moderate tungsten concentrations (1-5 mmol/L), however, both mechanisms were responsible for the uptake of tungsten, with scheelite precipitation being more important. Hydrocalumite is promising for wide use in the treatment of high-tungsten natural waters or wastewaters.

Efficient and Fast Removal of Aqueous Tungstate by an Iron-Based LDH Delaminated in L-Asparagine.

High concentrations of tungstate in aqueous systems pose a severe threat to the environment and human health. This study explored the potential of iron-based LDHs to remove tungstate from water. To improve its tungstate uptake capacity, environment-friendly L-asparagine was used to delaminate iron-based LDH synthesized via a coprecipitation method. The successful delamination was proved by AFM, revealing that the thickness of the obtained nanoparticles was approximately 1-2 times that of a single LDH layer. XRD, TEM, and XPS analyses confirmed that the delaminated LDHs were amorphous and ultrathin and had surface defects within their nanosheets that acted as active sites, leading to a very fast tungstate sorption rate and superior tungstate uptake capacity. Notably, the original layered structure of the L-asparagine-treated LDH was recovered upon its reaction with tungstate-bearing solutions, and therefore, the high availability of aqueous tungstate to the interlayer regions during the structural restoration of the delaminated iron-based LDH contributed to its excellent capability of tungstate removal as well. In addition, the tungstate uptake by the delaminated iron-based LDH was not affected substantially by the presence of coexisting anions, implying that the strong inner-sphere complexation between the tungstate and LDH layers with defects (i.e., Fe-O bonds) was the primary mechanism responsible for the tungstate removal. The delamination process described in this paper was validated to be an effective way to enhance the immobilization of tungstate by iron-based LDHs without inducing secondary pollutions, and delaminated iron-based LDHs are promising to be used extensively in the practice of treating tungstate-rich waters.

Assessment of PM2.5-related health effects: A comparative study using multiple methods and multi-source data in China.

In China, PM2.5 pollution has caused extensive death and economic loss. Thus, an accurate assessment of the spatial distribution of these losses is crucial for delineating priority areas for air pollution control in China. In this study, we assessed the PM2.5 exposure-related health effects according to the integrated exposure risk function and non-linear power law (NLP) function in 338 prefecture-level cities in China by utilizing online monitoring data and the PM2.5 Hindcast Database (PHD). Our results revealed no significant difference between the monitoring data and PHD (p value = 0.66 > 0.05). The number of deaths caused by PM2.5-related Stroke (cerebrovascular disease), ischemic heart disease, chronic obstructive pulmonary disease, and lung cancer at the national level estimated through the NLP function was 0.27 million (95% CI: 0.06-0.50), 0.23 million (95% CI: 0.08-0.38), 0.31 million (95% CI: 0.04-0.57), and 0.31 million (95% CI: 0.16-0.40), respectively. The total economic cost at the national level in 2016 was approximately US$80.25 billion (95% CI: 24.46-132.25). Based on a comparison of Z statistics, we propose that the evaluation results obtained using the NLP function and monitoring data are accurate. Additionally, according to scenario simulations, Beijing, Chongqing, Tianjin, and other cities should be priority areas for PM2.5 pollution control to achieve considerable health benefits. Our statistics can help improve the accuracy of PM2.5-related health effect assessments in China.

Effects of thiolation and methylation on arsenic sorption to geothermal sediments.

Arsenic (As) from deep crust is transported by geothermal waters to the earth surface and retained by sediment through adsorption, which depends significantly on the occurring As species. Adsorption of oxyarsenic species (i.e. arsenite [iAs(III)] and arsenate [iAs(V)]) on pure minerals was intensively investigated, yet studies with natural sediments and less known As species are scarce. To fill this gap, we investigated adsorption kinetics of nine different As species onto three typical geothermal sediments with different sedimentary organic matter (SOM) and iron (Fe) levels under anaerobic, sulfidic conditions (pH = 6). A multispecies pseudo-second-order (MPSO) model was applied to extract the adsorption rates of individual As species. Results showed that only the sediment with both high SOM and high Fe exhibited considerable As adsorption capacity. Air exposure or rise of either SOM or Fe levels in sediment favoured de-thiolation of aqueous thioarsenates, except for dimethylated thioarsenates. The overall adsorbed amount of the spiked As was affected by concurrent (de-)thiolation of the initial species, and the rates of their adsorption to the high SOM and high Fe sediment decreased in the order of tetrathioarsenate (TetraTA) > monothioarsenate (MTA) > iAs(V) > monomethyl arsenate (MMA) > dimethyl arsenate (DMA) > iAs(III) > monomethyl monothioarsenate (MMMTA) > dimethyl monothioarsenate (DMMTA) > dimethyl dithioarsenate (DMDTA). The fastest and slowest adsorption were suggested for inorganic thioarsenates and methylated thioarsenates, respectively. Therefore, under typical geothermal scenarios, thiolation of inorganic As would not necessarily increase its mobility, but the formation of methylated oxyarsenates and their further thiolation would endow geothermal As with strong migration ability.

Tungsten Accumulation in Hot Spring Sediments Resulting from Preferred Sorption of Aqueous Polytungstates to Goethite.

Geothermal waters usually have elevated tungsten concentrations, making geothermal systems important sources of tungsten in the environment. To study the transport of tungsten in hot springs to hot spring sediment, which is one of the key processes for the release of geothermally derived tungsten to the surface environment, geochemical investigations of the hot springs and their corresponding sediments in Rehai (a representative hydrothermal area in southwestern China) and systematic laboratory experiments of tungstate and polytungstate adsorption onto typical iron-bearing minerals in hot spring sediments (i.e., pyrite and goethite) were conducted. The results demonstrate that considerable tungsten concentrations (i.e., not much less than 10 µg/L), formation of polytungstates under acidic conditions, and enrichment of iron oxide minerals represented by goethite are the prerequisites for extreme enrichment of tungsten in hot spring sediments (e.g., 991 µg/g in the ZZQ spring outflow channel). The absence of any of these conditions would weaken the immobilization of aqueous tungsten and result in higher mobility of tungsten in the hot springs and its further transport downstream, possibly polluting the other natural waters in and around Rehai that serve as local drinking water sources. This study provides an insight for identifying the key geochemical processes controlling the transport and fate of undesirable elements (in this case, tungsten) in geothermal systems.

Simultaneous removal of harmful anions from geothermal waters using OH- intercalated Mg-Fe-LDH: batch and field column studies.

Unlike collectively treatable industrial wastewaters where only one or a few pollutants have concentrations much higher than the relevant standards, geothermal waters, in which multiple harmful constituents coexist, are usually discharged dispersedly, provoking a big challenge for their effective treatment. Here, a Mg/Fe layered double hydroxide with OH- intercalated (Mg-Fe-OH-LDH) was synthesized in a mechanochemical way and then applied in the treatment of various types of high-temperature geothermal waters in western Yunnan (China) containing a variety of harmful anions (As, Sb, W, and F) and inducing local environmental pollution. Due to the endothermic nature of removal of aqueous As, Sb, W, and F by Mg-Fe-OH-LDH, the original high temperatures of the geothermal waters could promote their sorption effectively. Batch sorption experiments demonstrated that over 94% and 80% of the As and W removal amounts could be reached within the first 10 and 20 min, respectively. On-site column experiments confirmed that the sorbent could remove the targeted harmful constituents from the investigated geothermal waters efficiently. In fact, the performance of the sorbent in the column studies was even better than that in the batch experiments, which can be ascribed to the continuous impetus for sorption caused by the concentration gradient in the flowing sorption system. Specifically, Mg-Fe-OH-LDH displayed the best sorption performance for As(V) among various harmful constituents, and the sorption of As along with W and F was little affected by the coexisting common anions in the geothermal waters, including Cl-, SO42-, and HCO3-/CO32-. In contrast, the removal of Sb(V) from geothermal waters may be impeded to a certain extent by SO42- and CO32-, which possessed stronger electronegativity or smaller ionic radii. This study is the first attempt to apply Mg-Fe-LDH in treatment of geothermal waters with multiple harmful constituents and sheds a light on providing a practical approach for field treatment of geothermal water-derived pollution.

[Estimation of the Urban Heat Island Intensity Change and Its Relationships with Driving Factors Across China Based on the Human Settlement Scale].

Considering a background of global warming, the effect of urban heat island (UHI) has become a serious ecological and environmental problem that is commonly faced by modern cities worldwide, posing challenges to the physical and mental health of residents in urban areas, air quality, and the healthy growth of surface vegetation. Using time series MODIS land surface temperature data products from 2001 to 2018, we evaluated the urban heat island intensity (UHII) and its spatiotemporal patterns in 1232 major urban human settlement patches (area>10 km2) across China based on the consistency method. A random forest regression model (RF) was also used to reveal the driving mechanism of urban heat island intensity in China due to human activities, urban morphology, vegetation, topography, and meteorological factors. The results show that more than 90% of cities and towns in China have exhibited significant diurnal heat island phenomena on the scale of human settlements. The diurnal UHII reaches up to (0.75±0.6)℃ and (0.81±0.53)℃, respectively. The daytime UHII in summer was significantly higher than that in winter, while there was little difference in nighttime UHII between summer and winter. During the past 18 years, the daytime UHII in China has shown a slight downward trend, while the nighttime UHII has increased significantly, with no significant change in summer and on mean annual scales. In terms of spatial distribution, the eastern coastal provinces have higher daytime UHII than those of the western or plateau provinces, while the nighttime UHII shows the opposite pattern. The RF regression results show that the average annual rainfall and latitudinal position of cities and towns are the two most important factors controlling the daytime and nighttime UHII in China. Narrowing the differences in vegetation growth between urban and rural environments will have a mitigating effect on the daytime UHII, and controlling the expansion of small and medium-sized towns will also play a positive role in the continuously rising nighttime UHII.

Evaluating Cultural Ecosystem Services of Urban Residential Green Spaces From the Perspective of Residents' Satisfaction With Green Space.

Green spaces in residential areas provide multiple cultural ecosystem services (CES), which can contribute to human health by increasing the frequency of residents' visits. We evaluated the CES of residential green spaces by assessing residents' satisfaction with these spaces in the city of Zhengzhou, China. The data reveal the supply capacity of CES in residential green spaces: the results suggest that the level of recreational services is low, whereas the residents' satisfaction with the sense of place and neighborhood relations is high. The lower the frequency of residents who visit a park outside the residential area, the higher the satisfaction with the CES. This suggests that residential green spaces can effectively compensate for the lack of nearby parks owing to their proximity to residents' living quarters. The CES in residential communities increased as vegetation coverage increased, indicating that natural vegetation is a source of CES. In addition, the results showed that residents' perceptions of plant decoration, landscape patterns, and management and infrastructure in particular can effectively improve the level of CES, and this could compensate for CES that have shrunk owing to low green space coverage. This study has practical significance and value for the planning and design of residential green spaces, offering suggestions for urban landscape planners and decision makers. Future research should combine the residents' perception of demand and supply of CES and should clarify the gap and trade-off between them.

Speciation of antimony in representative sulfidic hot springs in the YST Geothermal Province (China) and its immobilization by spring sediments.

As a well-known toxic element, antimony occurred in a wide range of concentrations in the geothermal waters discharging from Rehai and Daggyai, two representative hydrothermal areas in the Yunnan-Sichuan-Tibet Geothermal Province of China. Antimony speciation in different types of the hot springs in Rehai and Daggyai varied greatly as well, and tri- and tetrathioantimonate were detected in most neutral to alkaline Rehai hot springs. Neutral to alkaline pH, high sulfide concentrations, and high sulfide to antimony ratios were the critical factors promoting the formation of thioantimonates. The fact that no thioantimonates were detected in neutral to alkaline Daggyai hot springs is attributed to high concentrations of coexistent arsenic capable of inhibiting the thiolation of oxyantimony anions, because thioantimonates are kinetically more labile than thioarsenates. Upon discharge of the hot springs, both total aqueous antimony and arsenic decreased rapidly and substantially via immobilization to the sediments in the spring vents and their outflow channels. Some of the common iron-bearing minerals in the spring sediments, like pyrite and goethite, are known sinks for antimony and arsenic. Yet, an interesting difference was observed with antimony and iron contents in the sediment samples showing a significant correlation that was lacking for arsenic and iron contents. The explanation might be that for arsenic, sorption affinities are known to vary significantly with aqueous arsenic speciation and mineral phases. Typically, thiolation increases, and oxidation decreases arsenic mobility. Sorption experiments for antimony conducted in the present study, in contrast, showed that different antimony species were comparably sorbed to pyrite over a wide range of initial antimony concentrations and to goethite at relatively low initial antimony concentrations (but still covering the concentration range of antimony in common natural waters), so neither thiolation nor oxidation contributed significantly to the mobility of antimony in the hot springs investigated in this study.

[A critical review of progresses and perspectives on ecosystem services from 1997 to 2018]. / 1997­2018å¹´ç”Ÿæ€ç³»ç»ŸæœåŠ¡ç ”ç©¶çƒ­ç‚¹å˜åŒ–ä¸ŽåŠ¨å‘.

Ecosystem services (ESs) are the research highlight and hot topic in ecology, geography and environmental economics. Based on the literature database on ecosystem services from Web of Science, Citespace, Carrot 2 and textual analysis were used to review the progresses of ESs research during 1997-2018. The results showed that ESs research institutions and its publications increased quickly in the latest 20 years. The main leading countries on ecosystem services research were the United States, UK, Germany, China and Australia, with the United States being the first in terms of literature volume and the influence. Although the research of ESs in China started relatively late, its development was rapid and the scientific research output increased significantly. Meanwhile, there was a huge gap to the international level, the quality and influence of literature should be improved, and the international cooperation and exchange need to be enhanced too. The hotspots and frontiers of ecosystem services mainly included evaluation methods and models, climate change, biodiversity, land use change, trade-off and synergy, scientific research for decision-making and management. The further research and practice trends include the mechanism of ESs, the indicators and methods for ESs evaluation, the spatiotemporal dynamics of ESs trade-offs and synergies and influencing factors, the coupling relationship between ecosystem services and human well-being, and the scientific research and social needs for sustainable development for decision-making and management.

Tungsten from typical magmatic hydrothermal systems in China and its environmental transport.

Tungsten is of extraordinarily high concentrations in the geothermal waters discharging from several representative Tibetan magmatic hydrothermal systems (up to 1103 µg/L), which are also characterized by exceptionally high W/Mo molar ratios (up to 1182). The geochemical origins of the tungsten in these geothermal waters were investigated, with a comparison to those from Rehai, the sole magmatic hydrothermal system in Yunnan, which is another major part of the Yunnan-Sichuan-Tibet Geothermal Province of China. The results show that the lithology of reservoir host rocks is the primary factor controlling the tungsten concentrations of the geothermal waters, although the contribution of magmatic fluid input cannot be ruled out. In this study, the geothermal waters are generally rich in sulfide, and therefore the molybdenum in the reservoir fluids has been substantially precipitated as the form of molybdenite; in contrast, the reservoir fluids are well undersaturated with respect to tungstenite which is much more soluble than molybdenite. Thus the neutral/alkaline hot springs, i.e. the evolved reservoir fluids, have high W/Mo molar ratios as well. In the hot spring sediments, the distribution pattern of tungsten is quite different. The concentrations of tungsten are the highest in the sediments with high iron concentrations collected from the acid hot spring vents and outflow channels. The adsorption of aqueous tungsten onto iron-bearing minerals, like goethite or pyrite, is favorable at acid pH values and thereby responsible for the very high tungsten concentrations of these acid hot spring sediments. The proportions of thiotungstates in total tungsten are quite low for all the hot springs, as indicated by thermodynamic calculations, suggesting that thiolation of tungstate has little impacts on the environmental transport and fate of geothermal tungsten in the investigated hydrothermal areas. This is the first study to report the tungsten geochemistry of hot springs in mainland China.

Tungstate removal from aqueous solution by nanocrystalline iowaite: An iron-bearing layered double hydroxide.

Tungstate enrichment in aquatic systems may cause negative environmental and health effects. This study addresses tungstate removal from aqueous solution by nanocrystalline iowaite, an iron-bearing layered double hydroxide, which has not been used for treatment of tungstate-rich waters so far. Tungstate sorption experiments were conducted with various contact times, temperatures, initial tungstate concentrations (0.001-2 mM), and solution pH values (2-13), the results indicating that iowaite sorbed aqueous tungstate effectively and quickly, and the sorption maximum can be up to 71.9 mg/g. Moreover, the tungsten sorption capacity keeps nearly constant at a wide pH range from 3 to 11. Duo to its pH buffering effect, the alkaline conditions were generated by the addition of iowaite, which are favorable for the removal of aqueous tungstate because the polymerization of tungstate can be prohibited at alkaline pH values. Zeta potential, XRD and XPS analyses were employed to clarify the sorption mechanisms, and it was concluded that tungstate was sorbed via its exchange with the chloride originally intercalated into iowaite interlayers as well as its stronger inner-sphere complexation with the Fe atoms located in iowaite layers. Nanocrystalline iowaite is suitable for treating both tungstate-bearing natural waters with moderately high tungstate concentrations and industrial wastewaters extremely rich in tungstate.

Method Development for Direct Multielement Quantification by LA-ICP-MS in Food Samples.

A novel calibration strategy for the accurate determination of essential and toxic elements in both plant-based and animal-based foods was developed by synthesizing spiked agarose gels as matrix-matched external standards and carbon as the internal standard (IS). Aqueous solutions of agarose (4%, m/v) with defined amounts of the analytes were cast on a mold and then dried to form the agarose-gel standards. The spatial distributions of the analytes in the gel were examined using surface- and depth-mapping laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) protocols, and the gel homogeneity was found to be excellent (i.e., relative standard derivation <10%). Recovery of the 19 spiked elements in the gel standards was in the range of 86.9-94.7%. The limits of detection (LODs) ranged from 0.0005 (Rb) to 33.7 µg g-1 (S). Analysis results were in good agreement with certified values for various certified reference materials (CRMs). Furthermore, a porous rubber sample supporter was developed to improve the analysis throughput by about 3-fold.