Distinct response of arsenic speciation and bioavailability to different exogenous organic matter in paddy soil.

Land application of organic waste has been increasingly encouraged since it could sequester carbon to mitigate climate change. Considering the susceptibility of arsenic (As) bioavailability in soils to organic matter, understanding the influence of different exogenous organic matter on As biogeochemical behavior in rice-soil system is crucial to reasonably recycle organic waste on soils and ensure the food safety. In this study, impacts of two typical organic matter amendments, rice straw and humic substance, on the As speciation and bioavailability in paddy soil were investigated. Results showed that addition of both rice straw and humic substance could increase the dissolved organic carbon (DOC) content in soil solution by 16.4%-34.4% and 21.7%-53.2%, respectively, but the response of As speciation and bioavailability was quite different, showing the decoupling between As release and DOC. Rice straw addition increased As release to porewater by 28.0%-28.4%, particularly at the initial 0-18 days after the soil was flooded, but humic substance presented the opposite effect, decreasing As release by 27.4%-43.1% which was mainly attributable to the AsIII immobilization. This study suggests that the organic matter with high contents of labile heteroaliphatic/aliphatic carbon, being easily to be biodegraded, should not be applied on As contaminated soils.

Twelve tips for developing and maintaining a successful peer mentoring program for junior faculty in academic medicine.

Effective mentorship is widely believed to be an important factor in career satisfaction and advancement. Adequate mentorship has been linked to perceived institutional support, research productivity, and protects against burnout. Despite these facts, less than half of junior faculty in academic medicine feel as if they have adequate mentorship. Given that the current landscape in academic medicine has a paucity of available mentors, both in rank and representation for true dyadic mentorship, junior faculty clinician educators may need mentorship and paths to sponsorship. The importance of peer networks has become increasingly recognized, and some institutions have begun to use peer mentoring as a means of addressing mentorship and sponsorship needs. This model can potentially circumvent some of the main barriers to mentorship by providing protected time, ameliorating power differentials, creating an environment where members have shared goals, and mitigating the need for senior faculty mentorship. The following are twelve tips to create and maintain a successful peer mentoring group for junior faculty clinician educators in academic medicine which can serve to complement the dyadic mentorship model.

A Novel In Situ Method for Simultaneously and Selectively Measuring AsIII, SbIII, and SeIV in Freshwater and Soils.

Anthropogenic and climatic perturbations redistribute arsenic (As), antimony (Sb), and selenium (Se) within the environment. The speciation characteristics of these elements determine their behavior and biogeochemical cycling, but these redox-sensitive species are challenging to capture, with few methods able to harmonize measurements across the whole plant-soil-ecosystem continuum. In this study, we developed a novel diffusive gradient in thin films (DGT) method based on aminopropyl and mercaptopropyl bi-functionalized mesoporous silica spheres (AMBS) to achieve in-situ, simultaneous, and selective quantification of AsIII, SbIII, and SeIV, three typical/toxic but difficult to measure inorganic species. When used for environmental monitoring within a river catchment, AMBS-DGT exhibited stable/accurate predictions of these species despite varying water chemistries (ionic strength 0.01-200 mmol L-1 NO3-, pH 5-9 for AsIII and SbIII, and pH 5-7.5 for SeIV). Furthermore, river deployments also showed that time-averaged species concentrations by AMBS-DGT were reproducible compared with high-frequency sampling and measurement by high performance liquid chromatography coupled with inductively coupled plasma mass spectroscopy. When AMBS-DGT was used for sub-mm scale chemical imaging of soil solute fluxes, the method resolved concomitant redox-constrained spatial patterns of AsIII, SbIII, and SeIV associated with root O2 penetration within anaerobic soil. Improved capabilities for measurement of compartment interfaces and microniche features are critical alongside the measurement of larger-scale hydrological processes that dictate the fine-scale effects, with the AMBS-DGT achieving this for AsIII, SbIII, and SeIV.

Enhanced mobilization of Cd from commercial pigments in the rhizosphere of flooded lowland rice.

Although yellow Cd pigments (Cd-YP), widely used in industrial colorants, are considered inert, increasing evidence suggests once released into the environment, photobleaching/weathering mobilizes Cd from these pigments posing a pollution threat. Although general redox conditions and biotic/microbial activity are known to be important factors in determining Cd release, how spatial trends and specific soil processes regulate the Cd-YP behavior are poorly understood. Using plant rhizotrons in controlled environmental conditions, this study investigated the behavior of Cd-YP amendments matched to levels (15 mg kg-1) representative of contaminated soils in Yixing, China. Using high-resolution two-dimensional diffusive-gradient-in-thin-films (HR-2D-DGT), planar-optode (PO) multilayer systems alongside targeted soil and porewater sampling for chemical analysis the biogeochemistry associated with Cd mobilization from Cd-YP rice rhizospheres were determined. The results showed that there was a significant release of Cd into soil porewaters (51.5 µg L-1), but this reduced by 90.9% and stabilized over time (after 6-days). HR-2D-DGT ion-maps revealed pronounced spatial variances. The flux-maxima for Cd, which located within aerobic-rhizosphere zones, was 9 to 19-fold higher than in associated anoxic bulk soil. In general, zones of radial O2 loss (ROL)/higher redox conditions and lower pH were associated with Cd release, with S2- to SO42- transitions marking the boundaries of high-flux areas. Some isolated colocalization of Fe and Cd hotspots were observed in lateral root regions, but on-the-whole Fe/Mn and Cd release were not linked. In addition, microniche development was also an important feature of Cd mobilization due to soil heterogeneity.

Combining Multiple High-Resolution In Situ Techniques to Understand Phosphorous Availability Around Rice Roots.

Resolving chemical/biological drivers of P behavior around lowland/flooded rice roots remains a challenge because of the heterogeneity of the plant-soil interactions, compounded by sampling and analytical constraints. High-spatial-resolution (sub-mm) visualization enables these processes to be isolated, characterized, and deciphered. Here, three advanced soil imaging systems, diffusive gradients in thin-film technique coupled with laser ablation-ICPMS (DGT-LA-ICPMS), O2 planar optode, and soil zymography, were integrated. This trio of approaches was then applied to a rice life cycle study to quantify solute-P supply, through two dimensions, in situ, and low-disturbance high-resolution (HR) chemical imaging. This allowed mechanisms of P release to be delineated by O2, Fe, and phosphatase activity mapping at the same scale. HR-DGT revealed P depletion around both living and dead rice roots but with highly spatially variable Fe/P ratios (∼0.2-12.0) which aligned with changing redox conditions and root activities. Partnering of HR-DGT and soil zymography revealed concurrent P depletion and phosphatase hotspots in the rhizosphere and detritusphere zones (Mantel: 0.610-0.810, p < 0.01). This close affinity between these responses (Pearson correlation: -0.265 to -0.660, p < 0.01) cross-validates the measurements and reaffirms that P depletion stimulates phosphatase activity and Porg mineralization. The µ-scale biogeochemical landscape of rice rhizospheres and detritusphere, as documented here, needs greater consideration when implementing interventions to improve sustainable P nutrition.

Development and application of diffusive gradients in thin-films for in situ sampling of the bitterest chemical - denatonium benzoate in waters.

Denatonium benzoate (DB), a commonly used bitter agent in numerous products, has recently been recognized as a waterborne contaminant due to concern about its potential persistence, mobility and toxicity (PMT). However, its occurrence, levels and fate in global aquatic environments are largely unknown. In this study, a new sampling method, based on diffusive gradients in thin films (DGT) with mixed-mode cation exchange (MCX) as the binding agent, was developed for measuring DB in waters. MCX shows a rapid adsorption and high capacity for DB. DB is linearly accumulated by MCX-DGT. pH (6-8), ionic strength (0.01-0.5 M), or DOM (0-10 M) do not show any significant effect on the MCX-DGT performance, confirming its reliability. The DGT measurements in a wastewater treatment plant (WWTP) are comparable to those by paralleled grab sampling. The field results suggest DB is persistent in WWTPs and could be a potential domestic wastewater indicator. Therefore, MCX-DGT is a promising technique for understanding the environmental occurrence, levels and fate of DB. This is a first report of using DGT for DB monitoring and of DB occurrence in Chinese environments. Further exploration of DGT as a reliable passive monitoring tool for a wide range of PMT substances in different applications is warranted.

Lability and bioavailability of Co, Fe, Pb, U and Zn in a uranium mining restoration site using DGT and phytoscreening.

Mine restoration is a long and ongoing process, requiring careful management, which must be informed by site-specific, geochemical risk assessment. Paired topsoil and tree core samples from 4 sites within the uranium mining complex of INB Caldas in Minas Gerais (Brazil) were collected. Soil samples were analysed for their total content of Co, Fe, Pb, U and Zn by XRF, and subsequently, the potential environmental bioavailability of these metals were investigated by DGT and pore water analysis. In addition, results were compared with metal concentrations obtained by Tree Coring from the forest vegetation. In all sampling areas, mean total concentrations of U (Ctot. = 100.5 ± 66.5 to 129.6 ± 57.1 mg kg-1), Pb (Ctot. = 30.8 ± 12.7 to 90.8 ± 90.8 mg kg-1), Zn (Ctot. = 91.5 ± 24.7 to 99.6 ± 10.3 mg kg-1) and Co (Ctot. = 73.8 ± 25.5 to 119.7 ± 26.4 mg kg-1) in soils exceeded respective quality reference values. Study results suggest that AMD caused the increase of labile concentrations of Zn in affected soils. The high lability of the elements Pb (R = 62 ± 34 to 81 ± 29%), U (R = 57 ± 20 to 77 ± 28%) and Zn (R = 21 ± 25 to 34 ± 31%) in soils together with high bioconcentration factors found in wood samples for Pb (BCF = 0.0004 ± 0.0003 to 0.0026 ± 0.0033) and Zn (BCF = 0.012 ± 0.013 to 0.025 ± 0.021) indicated a high toxic potential of these elements to the biota in the soils of the study site. The combination of pore water and DGT analysis with Tree Coring showed to be a useful approach to specify the risk of metal polluted soils. However, the comparison of the results from DGT and Tree Coring could not predict the uptake of metals into the xylems of the sampled tree individuals.

Rapid classification of commercial teas according to their origin and type using elemental content with X-ray fluorescence (XRF) spectroscopy.

The authenticity of tea has become more important to the industry while the supply chains become complex. The quality and price of tea produced in different regions varies greatly. Currently, a rapid analytical method for testing the geographical origin of tea is missing. XRF is emerging as a screening technique for mineral and elemental analysis with applications in the traceability of foodstuffs, including tea. This study aims to develop a reliable multivariate classification model using XRF spectroscopy to obtain the mineral content. A total of 75 tea samples from tea producing countries throughout the world were analysed. After variable shortlisting, 18 elements were used to construct the multivariate models. Tea origin was determined by classifying the tea into 5 major geographical regions producing most of the global tea. PCA showed initial clustering in some regions, although the types of teas included in the study (black, green, white, herbal) showed no discrete cluster membership. The prediction power of each classification model developed was determined by using two multivariate classifiers, SIMCA and PLS-DA, against an independent validation set. The average overall correct classification rates of PLS-DA models were between 54-85% while the results of SIMCA models were between 70-84% resolving the poor clustering initially shown by PCA. This study demonstrated the potential of geographical origin of tea prediction using elemental contents of tea. Naturally, the classification can be linked not only to origin but to the type of tea as well. PRACTICAL APPLICATION: Wholesalers and retailers need a rapid and robust screening tool to confirm the origin and type of tea they sell to consumers. X-Ray fluorescence spectroscopy proved a good technique for achieving this in commercial teas sourced worldwide. Building on multivariate models, broad classification was accomplished both in terms of origin (Asian vs non-Asian) and in tea type with zero sample preparation and low cost of analysis.

Rice Rhizospheric Effects on the Bioavailability of Toxic Trace Elements during Land Application of Biochar.

Land application of biochar, the product of organic waste carbonization, can improve soil fertility as well as sequester carbon to mitigate climate change. In addition, biochar can greatly influence the bioavailability of toxic trace elements (TTEs) in soils resulting from its large internal surface areas, abundance in organic carbon, and ability to modify soil pH. Most research to date employs batch leaching tests to predict how biochar addition impacts TTE bioavailability, but these ex situ tests rarely considered the rhizospheric effect which might offset or intensify the changes induced by organic residue addition. This is especially so in rice rhizospheres because of strong clines in localized redox conditions. In this study, we adopted in situ high-resolution (HR) diffusive gradients in thin films (DGT) as well as rhizo-bag porewater sampling experiments to depict an overall picture of the difference in TTE (As, Cd, Cu, Ni, and Pb) bioavailability between the rice rhizosphere and bulk soils during land application of biochar. Porewater sampling experiments revealed that biochar additions stimulated TTE release due to the increase of dissolved organic carbon (DOC) and H+ concentrations. In the rhizosphere, although biochar still promoted As, Cd, and Ni release into porewaters, the rhizospheric effect was one of dampening/reduction compared with the bulk soil. When we focused on the localized changes of TTE bioavailability in the rhizosphere using an in situ HR-DGT approach, on the contrary, flux maxima of Cd, Cu, and Ni occurred near/on the root surface, and hot spots of As can be observed at peripheries of the rooting zone, which demonstrated the high heterogeneity and complexity of the rhizosphere's influence on TTE bioavailability.

Who is Responsible for Discharge Education of Patients? A Multi-Institutional Survey of Internal Medicine Residents.

BACKGROUND: Safely and effectively discharging a patient from the hospital requires working within a multidisciplinary team. However, little is known about how perceptions of responsibility among the team impact discharge communication practices. OBJECTIVE: Our study attempts to understand residents' perceptions of who is primarily responsible for discharge education, how these perceptions affect their own reported communication with patients, and how residents envision improving multidisciplinary communication around discharges. DESIGN: A multi-institutional cross-sectional survey. PARTICIPANTS: Internal medicine (IM) residents from seven US residency programs at academic medical centers were invited to participate between March and May 2019, via email of an electronic link to the survey. MAIN MEASURES: Data collected included resident perception of who on the multidisciplinary team is primarily responsible for discharge communication, their own reported discharge communication practices, and open-ended comments on ways discharge multidisciplinary team communication could be improved. KEY RESULTS: Of the 613 resident responses (63% response rate), 35% reported they were unsure which member of the multidisciplinary team is primarily responsible for discharge education. Residents who believed it was either the intern's or the resident's primary responsibility had 4.28 (95% CI, 2.51-7.30) and 3.01 (95% CI, 1.66-5.71) times the odds, respectively, of reporting doing discharge communication practices frequently compared to those who were not sure who was primarily responsible. To improve multidisciplinary discharge communication, residents called for the following among team members: (1) clarifying roles and responsibilities for communication with patients, (2) setting expectations for communication among multidisciplinary team members, and (3) redefining culture around discharges. CONCLUSIONS: Residents report a lack of understanding of who is responsible for discharge education. This diffusion of ownership impacts how much residents invest in patient education, with more perceived responsibility associated with more frequent discharge communication.

COVID-19, Social Media, and the Role of the Public Physician.

The COVID-19 pandemic has resulted in an avalanche of information, much of it false or misleading. Social media posts with misleading or dangerous opinions and analyses are often amplified by celebrities and social media influencers; these posts have contributed substantially to this avalanche of information. An emerging force in this information infodemic is public physicians, doctors who view a public presence as a large segment of their mission. These physicians bring authority and real-world experience to the COVID-19 discussion. To investigate the role of public physicians, we interviewed a convenience cohort of physicians who have played a role in the infodemic. We asked the physicians about how their roles have changed, how their audience has changed, what role politics plays, and how they address misinformation. The physicians noted increased audience size with an increased focus on the pandemic. Most avoided confronting politics, but others found it unavoidable or that even if they tried to avoide it, it would be brought up by their audience. The physicians felt that confronting and correcting misinformation was a core part of their mission. Public physicians on social media are a new occurrence and are an important part of fighting online misinformation.

Arsenic resistance in fungi conferred by extracellular bonding and vacuole-septa compartmentalization.

Microbes play a crucial role in arsenic (As) biogeochemical cycling and show great potential for environmental detoxification and bioremediation. Efflux, transformation, and compartmentalization are key processes in microbial As resistance. However, organelle specific As detoxification and fate during intracellular transfer and compartmentalization is not well understood. We conducted a time course experiment (2-5 days) of the organelle separation for fungal strains to explore subcellular As distributions. After exposure to 10 mg L-1 of arsenate (As(V)), the As accumulation among fungal organelles was generally in the order of extracellular (65 %) > cell wall (15 %) > vacuole (10 %) > other organelles (8 %). The vacuole As accounted for 55 % of the protoplast As. Extracellular bonding and vacuole compartmentalization were the main mechanisms of As resistance in the fungal strains tested. Glutathione (GSH) increases in fungal protoplast in response to As toxicity, acting as a reasonable indicator of As tolerance. Fourier transform infrared (FT-IR) spectroscopy indicated that carboxyl and amines groups within fungal cell walls potentially bind with As preventing As influx. Further analysis using scanning transmission X-ray microscopy (STXM) identified that fungal septa besides vacuole could also immobilize As.

Functionalized Mesoporous Silicon Nanomaterials in Inorganic Soil Pollution Research: Opportunities for Soil Protection and Advanced Chemical Imaging.

"Innovative actions towards a pollution free-planet" is a goal of the United Nations Environment Assembly (UNEA). Aided by both the Food and Agricultural Organisation (FAO) and its Global Soil Partnership under the 3rd UNEA resolution, a consensus from > 170 countries have agreed a need for accelerated action and collaboration to combat soil pollution. This initiative has been tasked to find new and improved solutions to prevent and reduce soil pollution, and it is in this context that this review provides an updated perspective on an emerging technology platform that has already provided demonstrable utility for measurement, mapping, and monitoring of toxic trace elements (TTEs) in soils, in addition to the entrapment, removal, and remediation of pollutant sources. In this article, the development and characteristics of functionalized mesoporous silica nanomaterials (FMSN) will be discussed and compared with other common metal scavenging materials. The chemistries of the common functionalizations will be reviewed, in addition to providing an outlook on some of the future directions/applications of FMSN. The use of FMSN in soil will be considered with some specific case studies focusing on Hg and As. Finally, the advantages and developments of FMSN in the widely used diffusive gradients-in-thin films (DGT) technique will be discussed, in particular, its advantages as a DGT substrate for integration with oxygen planar optodes in multilayer systems that provide 2D mapping of metal pollutant fluxes at submillimeter resolution, which can be used to measure detailed sediment-water fluxes as well as soil-root interactions, to predict plant uptake and bioavailability.

Localized Intensification of Arsenic Release within the Emergent Rice Rhizosphere.

Behavior of trace elements in flooded/lowland rice soils is controlled by root-zone iron oxidation. Insoluble iron species bind/capture toxic elements, i.e., arsenic. However, it was recently observed that within this territory of arsenic immobilization lies a zone of prolific iron release, accompanied by a significant flux of arsenic in close proximity to rice root apices. Questions still remain on how common this phenomenon is and whether the chemical imaging approaches or soils/cultivars used influence this event. Here, three types of ultrathin/high-resolution diffusive gradient in thin films (DGT) substrates were integrated with oxygen planar optodes in a multilayer system, providing two-dimensional mapping of solute fluxes. The three DGT approaches revealed a consistent/overlapping spatial distribution with localized flux maxima for arsenic, which occurred in all experiments, concomitant with iron mobilization. Soil/porewater microsampling within the rhizosphere revealed no significant elevation in the solid phase's total iron and arsenic concentrations between aerobic and anaerobic zones. Contrary to arsenic, phosphorus bioavailability was shown to decrease in the arsenic/iron flux maxima. Rice roots, in addition to their role in nutrient acquisition, also perform a key sensory function. Flux maxima represent a significant departure from the chemical conditions of the bulk/field environment, but our observations of a complete rhizosphere reveal a mixed mode of root-soil interactions.

In Situ Selective Measurement Based on Diffusive Gradients in Thin Films Technique with Mercapto-Functionalized Mesoporous Silica for High-Resolution Imaging of SbIII in Soil.

In situ monitoring of Sb speciation improves the understanding of Sb biogeochemistry and toxicity in ecosystems. Precise measurement of Sb is a challenge due to its instability of oxidation and ultratrace concentration. The development of simple and reliable methods specific to SbIII measurement is not only appealing but essential for implementing regulations. Here, we present an in situ speciation analysis method for SbIII, using the diffusive gradients in thin films (DGT) technique, combined with mercapto-functionalized SBA-15 mesoporous silica nanoparticles (MSBA). Laboratory performance tests confirmed MSBA-DGT uptake was independent of pH (4-9) and ionic strength (0.1-200 mmol L-1). DGT devices equipped with MSBA-based binding gels showed a theoretically linear accumulation of SbIII and exhibited a high capacity for SbIII at 65 µg/gel disc, with negligible accumulation of SbV over a 72 h deployment. Compared with commercial 3-mercaptopropyl-functionalized silica (MFS), the nanosized MSBA facilitate its even distribution in the binding gels. Furthermore, the good selectivity and high homogeneity of the MSBA gel enabled it to be applied in a rice rhizosphere in conjunction with AgI gel to investigate the effects of sulfur application on the SbIII solubility. In summary, the newly developed MSBA-DGT provides a selective measurement of SbIII, showing potential for environmental monitoring and further application in understanding the biogeochemical process of Sb.

Residual biomass of coffee as a binding agent in diffusive gradients in thin-films technique for Cd, Cu, Ni, Pb and Zn measurement in waters.

Spent coffee grounds (SCG) immobilized in agarose gel are proposed as a novel binding agent for application in the Diffusive Gradients in Thin films (DGT) technique for the determination of Cd, Cu, Ni, Pb and Zn in waters. The SCG-agarose gel was characterized by Scanning Electron Microscopy, Energy Dispersive X-ray Spectrometry and Porosimetry by nitrogen adsorption. Elution of analytes from the binding agent was effectively performed with 2 mol L-1 HCl. The effects of key DGT parameters (e.g. immersion time, ionic strength and pH) were evaluated with a deployment of DGT devices (DGT-SCG) in synthetic solutions with ionic strengths between 0.005 mol L-1 and 0.1 mol L-1 and within a pH range of 3.5-8.0. The results were in excellent agreement with the predicted theoretical curve for mass uptake. Consistent results were found for solutions with ionic strengths between 0.005 mol L-1 and 0.1 mol L-1 and within a pH range of 3.5-8.0. The DGT-SCG performance was also evaluated in two spiked river water samples (Corumbataí and Piracicaba river) with satisfactory uptake values (CDGT-SCG/Csol) between 0.74 and 1.53. The proposed DGT-SCG opens opportunities for using residual biomass as binding phase in the DGT technique, showing low costs in production and complying with "green" technology approaches.

Maritime Deposition of Organic and Inorganic Arsenic.

The speciation of arsenic in wet and dry deposition are ambiguously described in current literature. Presented here is a 2 year study quantifying arsenic species in atmospheric deposition collected daily from an E. Atlantic coastal, semirural site, with comparative urban locations. Inorganic arsenic (Asi) was the principal form of arsenic in wet deposition, with a mean concentration of 0.54 µmol/m3. Trimethylarsine oxide (TMAO) was found to be the dominant form of organic arsenic, determined as above the LoD in 33% of wet deposition samples with a mean concentration of 0.12 µmol/m3. Comparison with codeposited trace elements and prevailing weather trajectories indicated that both anthropogenic and marine sources contribute to atmospheric deposition. Analysis of dry deposition revealed it to be a less significant input to the land-surface for Asi, contributing 32% of that deposited by wet deposition. Dry deposition had a larger proportion of Asi than that found in wet deposition, with TMAO making up only 12% of the sum of species. In comparison, urban sites showed large spatial and temporal variations in organic arsenic deposition, indicating that local sources of methylated species may be likely and that further understanding of biogenic arsine evolution and degradation are required to adequately assess the atmospheric arsenic burden and subsequent contribution to terrestrial ecosystems.

Mitigating arsenic accumulation in rice (Oryza sativa L.) from typical arsenic contaminated paddy soil of southern China using nanostructured α-MnO2: Pot experiment and field application.

Manganese oxides are naturally occurring powerful oxidants and scavengers, which can control the mobility and bioavailability of arsenic (As). However, the effect of synthetic nanostructured manganese oxides on the mobilization and transportation of As at actual paddy soils are poorly understood, especially in soils with low or medium background Mn concentration. In the present study, a novel nano manganese oxide with superior reactivity and surface area has been synthesized. A 90-d soil incubation experiment combined with pot and field rice cultivation trials were designed to evaluate the effectiveness of exogenous α-MnO2 nanorods on the mobilization and transportation of As in soil-rice systems. Our results proved that the addition of α-MnO2 nanorods can effectively control the soil-to-solution partitioning of As under anaerobic conditions. After treatment with different amounts of α-MnO2 nanorods, the content of effective As decreased, offset by an increase in residual As and insoluble binding As (Ca-As and Fe-As). Enhancing the oxidation of As(III) into As(V), the α-MnO2 nanorods increased the adsorption of As onto indigenous iron (hydr)oxides which greatly reduced the soil porewater As content. In addition, pot experiments and field applications revealed that the influx of As into the aerial parts of rice plants (stems, husk and leaves) was strictly prohibited after treatments with different amount of α-MnO2 nanorods; more interestingly, significantly negative correlations have been observed between As and Mn in rice, which indicated that as Mn is increased in soil, As in brown rice decreases. Our results demonstrated that the use of α-MnO2 nanorods in As polluted paddy soil containing low levels of background Mn oxides can be a promising remediation strategy.

In Situ Measurement of Thallium in Natural Waters by a Technique Based on Diffusive Gradients in Thin Films Containing a δ-MnO2 Gel Layer.

Thallium (Tl) has been identified as a priority contaminant because of its severe toxic effects. Exact measurement of Tl is a challenge because it is difficult to avoid altering the element's chemical speciation during sampling, transport, and storage. In situ measurement may be a good choice. Based on the in situ technique of diffusive gradients in thin films (DGT), new DGT devices equipped with novel laboratory-synthesized manganese oxide (δ-MnO2) binding gels were developed and systematically validated for the measurement of Tl, including Tl(I) and Tl(III) species, in water. Comparison between Chelex binding gel and δ-MnO2 gel on the uptake kinetics of Tl demonstrated that δ-MnO2 binding gels could adsorb Tl rapidly and effectively. Removal of Tl from the δ-MnO2 gels was achieved by use of 1 mol·L-1 oxalic acid, yielding elution efficiencies of 1.0 for Tl(I) and 0.86 for TI(III). Theoretical responses from DGT devices loaded with δ-MnO2 gel (δ-MnO2-DGT) were obtained irrespective of pH (4-9) and ionic strength (0.1-200 mmol·L-1 NaNO3). δ-MnO2-DGT showed good potential for long-term monitoring of Tl due to its high adsorption capacity of 27.1 µg·cm-2 and the stable performance of δ-MnO2 binding gel kept in solution, containing only 10 mmol·L-1 NaNO3, for at least 117 days. Field deployment trials confirmed that δ-MnO2-DGT can accurately measure the time-averaged concentrations of Tl in fluvial watercourses. In summary, the newly developed δ-MnO2-DGT technique shows potential for environmental monitoring and biogeochemical investigation of Tl in waters.