Changes In Chemical Speciation Research Articles

Fate of As(V) and Cr(VI) adsorbed on goethite in a mangrove‐microcosm experiment

AbstractMangroves provide fundamental ecosystem services; however, the growing impact of human activities has resulted in increased pollution pressure, such as chemical contaminants. The redox processes are major biogeochemical players in the fate of contaminants. We investigate the effects of the redox environment on As(V) and Cr(VI) adsorbed on goethite (i.e., Fe(III)‐oxide) over 40 days of incubation in columns containing mangrove soil subjected to seawater saturation cycles. Our spectroscopic data highlighted a less Fe(III)‐ordered arrangement on goethite over time; As(V) is strongly bound to goethite, which delayed until 20 days its remobilization and reduction to As(III). After 40 days, the goethite held ∼50% of the initial As, but it was 15% as As(III). On the other hand, Cr(VI) was desorbed almost completely in less than 10 days, and the residual Cr ions bound to goethite were almost totally converted to Cr(III). Our study stresses the importance of individual time‐dependence in evaluating chemical speciation changes among potential toxic elements in wetland systems, such as mangroves and artificial wetlands designed to water treatment or soil remediation.

Optimization of liquefaction process based on global meta-analysis and machine learning approach: Effect of process conditions and raw material selection on remaining ratio and bioavailability of heavy metals in biochar

<abstract> <p>Although liquefaction technology has been extensively applied, plenty of biomass remains tainted with heavy metals (HMs). A meta-analysis of literature published from 2010 to 2023 was conducted to investigate the effects of liquefaction conditions and biomass characteristics on the remaining ratio and chemical speciation of HMs in biochar, aiming to achieve harmless treatment of biomass contaminated with HMs. The results showed that a liquefaction time of 1–3 h led to the largest HMs remaining ratio in biochar, with the mean ranging from 84.09% to 92.76%, compared with liquefaction times of less than 1 h and more than 3 h. Organic and acidic solvents liquefied biochar exhibited the greatest and lowest HMs remaining ratio. The effect of liquefaction temperature on HMs remaining ratio was not significant. The C, H, O, volatile matter, and fixed carbon contents of biomass were negatively correlated with the HMs remaining ratio, and N, S, and ash were positively correlated. In addition, liquefaction significantly transformed the HMs in biochar from bioavailable fractions (F1 and F2) to stable fractions (F3) (<italic>P</italic> < 0.05) when the temperature was increased to 280–330 ℃, with a liquefaction time of 1–3 h, and organic solvent as the liquefaction solvent. N and ash in biomass were positively correlated with the residue state (F4) of HMs in biochar and negatively correlated with F1 or F2, while H, O, fixed carbon, and volatile matter were negatively correlated with F4 but positively correlated with F3. Machine learning results showed that the contribution of biomass characteristics to HMs remaining ratio was higher than that of liquefaction factor. The most prominent contribution to the chemical speciation changes of HMs was the characteristics of HMs themselves, followed by ash content in biomass, liquefaction time, and C content. The findings of this meta-analysis contribute to factor selection, modification, and application of liquefied biomass to reducing risks.</p> </abstract>

Changed mercury speciation in clouds driven by changing cloud water chemistry and impacts on photoreduction: Field evidence at Mt. Tai in eastern China

Chemical speciation of mercury (Hg) in clouds largely determines the photochemistry of Hg in the atmosphere and consequently influences Hg deposition on the surface through precipitation. Cloud water chemistry has notably changed over the last decade in response to global changes, however, the effects on Hg speciation remain poorly understood. During summer 2021, we collected sixty cloud water samples at Mt. Tai in eastern China and compared the cloud chemistry and Hg speciation with our previous findings during summer 2015. The results showed that although there were no statistically significant differences in the concentrations of total Hg (THg), dissolved Hg (DHg), and particulate Hg (PHg), there was a distinct shift in DHg species from the predominated Hg-DOM (78.6% in 2015 campaign) to the more homogeneously distributed Hg(OH)2 (28.4% in 2021 campaign), HgBr2 (26.5%), Hg-DOM (17.3%) and HgBrOH (17.0%). Changes in cloud water chemistry, particularly the significant increase in pH values to 6.49 ± 0.27 and unexpectedly high levels of bromide ions (Br−, 0.19 ± 0.22 mg L−1), were found to drive the changing of Hg speciation by enhancing Hg(II) hydrolysis and binding by Br−. Elevated Br− originating primarily from the continent likely caused noticeable differences in the dominating DHg species between cloud water sourced from marine and continental regions. The changes in chemical speciation of DHg were estimated to result in a 2.6-fold decrease in Hg(II) photoreduction rate between 2015 and 2021 campaigns (0.178 ± 0.054 h−1 vs. 0.067 ± 0.027 h−1), implying a shortened lifetime of atmospheric Hg and increased ecological risks associated with Hg wet deposition.

The role of root carboxylate release on rare earth element (hyper)accumulation in plants – a biogeochemical perspective on rhizosphere chemistry

AbstractThe paper of van der Ent et al. (Plant Soil 485:247–257, 2023), published in the previous issue, reports the hyperaccumulation of rare earth elements (REE) in plant species from the Proteaceae for the first time. Indeed, the high REE accumulation in Proteaceae is not completely unexpected, given that the plants release large amounts of carboxylates to acquire phosphorus and micronutrients. However, it is somewhat questionable that the efficiency of element mobilization alone sufficiently explains the large variability in REE accumulation among different taxa of Proteaceae or other P-efficient species that typically show low concentrations of REE. Given that REE3+ share chemical similarities to Ca2+ but form stable complexes with ligands similar to Al3+, it is reasonable that uptake and accumulation of REE depend not solely on element mobility but also on the dynamics of element speciation governed by the formation, stability, and fate of carboxylate-REE-complexes in the rhizosheaths. The rationale behind this contention is that for elements with low mobility in soil, changes in chemical speciation may increase the availability only if the complex stabilities that depend on rhizosphere pH allow a breakdown during uptake. In this commentary, we explore the idea that REE accumulation depends on rhizosphere processes related to nutrient acquisition and element exclusion that overlap in time, space, and function depending on the composition of metal-chelating ligands released by plant roots in concert with rhizosphere pH. Based on data from greenhouse and field experiments, we propose a model where plants with a P-mining strategy (hyper)accumulate REE when rhizosphere pH is below a critical value shifting the REE speciation to available forms.

Chemical speciation changes of an all-solid-state lithium-ion battery caused by roasting determined by sequential acid leaching

All-solid-state lithium-ion batteries (ASS-LIBs) are expected to replace current liquid-based LIBs in the near future owing to their high energy density and improved safety. It would be preferable if ASS-LIBs could be recycled by the current recycling processes used for liquid-based LIBs, but this possibility remains to be determined. Here, we subjected an ASS-LIB test cell containing an argyrodite-type solid electrolyte (Li6PS5Cl) and nickel–manganese–cobalt-type active material (Li(Ni0.5Mn0.3Co0.2)O2) to roasting, a treatment process commonly used for recycling of the valuable metals from liquid-based LIBs, and investigated the changes in chemical speciation. Roasting was performed at various temperatures (350–900 °C), for various times (60–360 min), and under various oxygen fugacity (air or O2) conditions. The chemical speciation of each metal element after roasting was determined by sequential elemental leaching tests and X-ray diffraction analysis. Li formed sulfates or phosphates over a wide temperature range. Ni and Co followed very complicated reaction paths owing to coexistence of S, P, and C, and they formed sulfides, phosphates, and complex oxides. The optimum conditions for minimizing formation of insoluble compounds, such as complex oxides, were a roasting temperature of 450–500 °C and a roasting time of 120 min. The results indicated that although ASS-LIBs can be treated by the same roasting processes as those used for current liquid-based LIBs, the optimal roasting conditions have narrow ranges. Thus, careful process control will be needed to achieve high extraction percentages of the valuable metals from ASS-LIBs.

Chemical transformations of UF4 under controlled temperature and relative humidity

• Chemical changes of UF 4 aged under controlled temperature and humidity were studied. • Aging at high relative humidity conditions caused hydration, forming UF 4 hydrates. • UF 4 exposed to high relative humidity formed UF 4 hydrates in as few as 90 days. • UF 4 exposed to moderate or low relative humidities was stable for up to 9 months. Uranium tetrafluoride (UF 4 ) is a critical compound in the nuclear fuel cycle , particularly as an intermediate in uranium hexafluoride (UF 6 ) and uranium metal production, and as a fuel for fluoride-based molten salt reactors . Changes to UF 4 in humid air were investigated by aging anhydrous UF 4 under various temperature and relative humidity (RH) conditions for up to 9 months. Powder X-ray diffraction (pXRD) and thermogravimetric analysis revealed UF 4 remained largely unchanged during the aging study for most of the conditions investigated (293 and 308 K, and ≤75% RH), consistent with the conventional consideration that UF 4 is stable under ambient conditions. However, aging under high RH conditions (>90%) resulted in chemical speciation changes and formation of UF 4 and UF 4 hydrate mixtures. Specifically, UF 4 ·2.5H 2 O was formed within 30 days for UF 4 aged at 293 K and 95% RH. Uranium tetrafluoride hydrates with less than 2.5 waters of hydration were formed within 180 days for UF 4 aged at 308 K and 91% RH. These findings represent the first report of UF 4 hydrates forming from the reaction of UF 4 with atmospheric water vapor at ambient temperatures. Investigation of the surface composition of unaged and aged UF 4 samples with X-ray photoelectron spectroscopy revealed degradation of the UF 4 surface, consistent with the degradation observed for the bulk UF 4 from the pXRD measurements. From a nuclear forensics perspective, these short timeline aging studies suggest that the presence of UF 4 hydrate in UF 4 materials may indicate it was stored under high humidity conditions.

Removal behavior and chemical speciation distributions of heavy metals in sewage sludge during bioleaching and combined bioleaching/Fenton-like processes

The removal and chemical speciation changes of heavy metals in the sewage sludge during the single bioleaching and combined bioleaching/Fenton-like processes were compared in this study. The improvement in the dewaterability of the treated sludge was also investigated. The single bioleaching led to a removal of Zn, Cu, Cd, Cr, Mn, Ni, As and Pb of 67.28%, 50.78%, 64.86%, 6.32%, 56.15%, 49.83%, 20.78% and 10.52% in 10 days, respectively. The chemical speciation analysis showed that the solubilization of heavy metals in mobile forms (exchangeable/acid soluble and reducible forms) and oxidizable form was the main reason for their removal. Subsequent Fenton-like treatment was carried out at different bioleaching stages when the bioleached sludge dropped to certain pH values (4.5, 4.0 and 3.0), by adding H2O2 at different dosages. The highest removal ratio of Zn, Cu, Cd, Cr, Mn and Ni could reach 75.53%, 52.17%, 71.91%, 11.63%, 66.29% and 65.19% after combined bioleaching/Fenton-like process, respectively, with appropriate pH and H2O2 dosages in less than 6 days. The solubilization efficiencies of these heavy metals in mobile forms were further improved by Fenton-like treatment. The removal efficiencies of As and Pb decreased due to their transformation into insoluble forms (mostly residual fraction) after Fenton treatment. The capillary suction times (CST) of the raw sludge (98.7 s) decreased by 79.43% after bioleaching and 87.44% after combined process, respectively.

A Method to Preserve Wetland Roots and Rhizospheres for Elemental Imaging.

Roots extensively interact with their soil environment but visualizing such interactions between roots and the surrounding rhizosphere is challenging. The rhizosphere chemistry of wetland plants is particularly challenging to capture because of steep oxygen gradients from the roots to the bulk soil. Here a protocol is described that effectively preserves root structure and rhizosphere chemistry of wetland plants through slam-freezing and freeze drying. Slam-freezing, where the sample is frozen between copper blocks pre-cooled with liquid nitrogen, minimizes root damage and sample distortion that can occur with flash-freezing while still minimizing chemical speciation changes. While sample distortion is still possible, the ability to obtain multiple samples quickly and with minimal cost increases the potential to obtain satisfactory samples and optimizes imaging time. The data show that this method is successful in preserving reduced arsenic species in rice roots and rhizospheres associated with iron plaques. This method can be adopted for studies of plant-soil relationships in a wide variety of wetland environments that span concentration ranges from trace-element cycling to phytoremediation applications.

Influence of thermal hydrolysis treatment on chemical speciation and bioleaching behavior of heavy metals in the sewage sludge.

In this study, the transformation of chemical speciation of Cr, Mn, As and Cd in the sewage sludge before and after thermal hydrolysis treatment was investigated using modified BCR method. The effect of thermal hydrolysis treatment and chemical speciation change on the subsequent bioleaching behavior was also researched. The results showed that the concentrations of Cr, Mn, As and Cd in oxidizable fraction decreased in the sludge treated by thermal hydrolysis. Meanwhile, the proportions of Cr, Mn and As in the mobile fractions (acid-soluble/exchangeable and reducible fraction) all decreased, while Cd was concentrated in the sludge treated by thermal hydrolysis. The final pH value of bioleached sludge treated by thermal hydrolysis was lower than that in the bioleached raw sewage sludge. And faster increase of oxidation-reduction potential (ORP) was also found in the bioleaching process of the sludge treated by thermal hydrolysis. The removal percentage of Mn and Cd increased in the bioleached sludge treated by thermal hydrolysis. Thermal hydrolysis treatment can promote the bioleaching to some extent. Furthermore, the environmental risk of Cr, Mn, As and Cd in the bioleached sludge treated by thermal hydrolysis was all alleviated according to risk assessment analysis compared with the bioleached raw sewage sludge.

How does the microenvironment change during the stabilization of cadmium in exogenous remediation sediment?

The pollution degree of heavy metals is closely related to the sediment microenvironment. This study aims to give a comprehensive account of the changes of microenvironment in sediment during the stabilization of cadmium (Cd) by the sodium lignosulphonate (SLS) modified chlorapatites (SLS@nClAP). Chemical speciation change demonstrated that SLS@nClAP possessed better stabilizing capacity (65.84 %–76.66 %) for Cd than unmodified chlorapatites (ClAP) (45.88 %). It might be since that the surface of SLS@nClAP presented a more dispersive thin sheet structure with sulfonate groups compared with the aggregate block structure of ClAP. High-throughput sequencing results displayed that succession of microbial community occurred after remediation in sediment. Most importantly, the dominant genus changed from massilia to phosphate-solubilizing bacterium-pseudomonas which might be due to the remediation of chlorapatites and the stabilization of Cd. Moreover, enzyme activity changes showed that the activity of catalase and urease were highly influenced by the stability and bioavailability of Cd during the incubation. This study not only provided a novel remediation technology for Cd-polluted sediment but also confirmed that the change of microenvironment was closely related to the stability and bioavailability of Cd in sediment.

Study on the Treatment of Nickel-Contaminated Soil Using Calcium Oxide

Nickel-contaminated soil was treated by adding different amounts of calcium oxide in this study. The leaching concentration, pH, and bioavailability of the soil samples were investigated on the 3rd, 6th, 9th, 12th, and 15th days. The chemical speciation changes of the contaminated soil treated with calcium oxide were analyzed, and the soil phases were analyzed by X-ray diffraction (XRD). Results showed that the application of calcium oxide increased the pH of the soil, resulting in passivation of nickel ions in soil by forming a poorly soluble precipitate. It was identified that addition of 5% of calcium oxide showed the best result, with the leaching concentration on the third day reaching 0.35 mg/L, which is 99.21% lower than the untreated soil’s leaching concentration of 44.24 mg/L. On the 15th day, the bioavailability of nickel decreased from the untreated soil’s 93.82 to 36.73%. It was also observed that the pH of the soil increased at the beginning and decreased afterwards. The pH value was 7.94 on the 15th day. In addition, the water-soluble fraction of Ni decreased from 7.39 without treatment to 0.19%; the reducible fraction of Ni decreased from 35.14 to 25.79%, and the oxidizable fraction of Ni increased from 10.37 to 29.10%, respectively, on the 15th day after the treatment with calcium oxide. XRD analysis of soil samples showed the amorphous nickel hydroxide may be formed in the precipitation process.

Hydration of α-UO3 following storage under controlled conditions of temperature and relative humidity.

Changes in chemical speciation of uranium oxides following storage under varied conditions of temperature and relative humidity are valuable for characterizing material provenance. In this study, subsamples of high purity α-UO3 were stored under four sets of controlled conditions of temperature and relative humidity over several years, and then measured periodically for chemical speciation. Powder X-ray diffraction (XRD) analysis and extended X-ray absorption fine structure spectroscopy confirm hydration of α-UO3 to a schoepite-like end product following storage under each of the varied storage conditions, but the species formed during exposure to the lower relative humidity and lower temperature condition follows different trends from those formed under the other three storage conditions (high relative humidity with high or low temperatures, and low relative humidity with a high temperature). Thermogravimetry coupled with XRD analysis was carried out to distinguish desorption pathways of water from the hydrated end products. Density functional theory calculations discern changes in the structure of α-UO3 following incorporation of 1, 2 or 3 H2O molecules or 1, 2 or 3 OH groups into the orthorhombic lattice, revealing differences in lattice constants, U-O bond lengths, and U-U distances. The collective results from this analysis are in contrast to analogous studies that report that U3O8 is oxidized and hydrated in air during storage under high relative humidity conditions.

Chemical transformation and surface functionalisation affect the potential to group nanoparticles for risk assessment

Pristine and transformed variant nanomaterials were assessed to identify whether chemical speciation changes and ecocorona association affected relatively toxicities and the potential for grouping.

Chemical Speciation Comparison of Drinking Water in North Central Province: An Affected Area of Chronic Kidney Disease of Unknown Etiology (CKDu) in Sri Lanka

Chronic Kidney Disease of Unknown Etiology (CKDu) is an increasing health issue in Sri Lanka. It is prominent in the North Central Province (NCP), Sri Lanka. This study mainly focuses on Chemical speciation modeling of drinking water in Padaviya, Madawachchiya, Kebethigollewa, Ruwanpura and Nuwaragampalatha central as affected areas in the NCP and Ampara as the reference area of CKDu. Chemical speciation is important for understanding bioavailability, chemical toxicity and environmental fate. Concentrations of major elements in water bodies were analysed and then how chemical speciation change according to the temperature, pH and ionic strength in water bodies were determined. Concentration of Ca2+, Mg2+, Fe2+, Cd2+, Cr3+, Cu2+, Mn2+, Ni2+, Zn2+, Pb2+, Al3+ and dissolved PO43-, SO42-, F-, CO32- and NO3- were used for chemical speciation modelling of drinking water in Ampara and affected areas. Visual MINTEQ version 3.0 software was used for the determination of the species distribution. Temperature varied from 25˚C to 32˚C and pH varied from 5.0 to 8.0. Among the metal ions considered above, only chemical species of Pb2+, Al3+, Cu2+ , Cr3+ and Cd2+ showed higher variations with pH and temperature change. AlF2+, AlF3 and AlF2+ species were formed only in affected areas. Ionic strength changed from 0.001 mol/kg to 0.01 mol/kg and the chemical species distribution of drinking water was also obtained from the software. The percentage of total concentration of Pb2+, Pb(OH)+, Al(OH)3, Al(OH)4- and Fe2+ changed slightly. According to the results obtained, there can be formation of some species Al3+, Cu2+, Cr3+ and Cd2+with the variations of the temperature and pH, which may have an effect on CKDu. Formations of different species were higher with the pH change than the temperature change. Different species which were formed mainly with F- ion in affected areas may also have some significant effect on CKDu. Keywords: Chronic kidney disease, Chemical speciation, Temperature, pH, Ionic strength

Cysteine Addition Promotes Sulfide Production and 4-Fold Hg(II)-S Coordination in Actively Metabolizing Escherichia coli.

The bacterial uptake of mercury(II), Hg(II), is believed to be energy-dependent and is enhanced by cysteine in diverse species of bacteria under aerobic and anaerobic conditions. To gain insight into this Hg(II) biouptake pathway, we have employed X-ray absorption spectroscopy (XAS) to investigate the relationship between exogenous cysteine, cellular metabolism, cellular localization, and Hg(II) coordination in aerobically respiring Escherichia coli (E. coli). We show that cells harvested in exponential growth phase consistently display mixtures of 2-fold and 4-fold Hg(II) coordination to sulfur (Hg-S2 and Hg-S4), with added cysteine enhancing Hg-S4 formation. In contrast, cells in stationary growth phase or cells treated with a protonophore causing a decrease in cellular ATP predominantly contain Hg-S2, regardless of cysteine addition. Our XAS results favor metacinnabar (β-HgS) as the Hg-S4 species, which we show is associated with both the cell envelope and cytoplasm. Additionally, we observe that added cysteine abiotically oxidizes to cystine and exponentially growing E. coli degrade high cysteine concentrations (100-1000 μM) into sulfide. Thermodynamic calculations confirm that cysteine-induced sulfide biosynthesis can promote the formation of dissolved and particulate Hg(II)-sulfide species. This report reveals new complexities arising in Hg(II) bioassays with cysteine and emphasizes the need for considering changes in chemical speciation as well as growth stage.

An Investigation of Harned’s Rule for Predicting the Activity Coefficients of Strong Aqueous Electrolyte Solution Mixtures at 25 °C

From a critical evaluation of the relevant literature, Harned coefficients at 25 °C and their corresponding trace activity coefficients are reported for 72 mixtures of strong aqueous electrolytes with a common ion. The work confirms the generality of Harned’s rule in its simplest form, that is, with only one (linear) term. Uncertainties in predicted mean activity coefficients are typically less than 0.01, comparable with the experimental reproducibility. Unless there are good grounds to suggest that significant changes in chemical speciation are occurring, experimental measurements that do not conform to the rule should be regarded with suspicion. We find that the estimates of errors made by authors of single potentiometric investigations are often as much as an order of magnitude too optimistic. Even the work of Harned and colleagues, which was typically of high quality, is sometimes much worse than is claimed or implied in the literature. The unfortunately common practice of introducing a quadratic term...

Effect of carbonation on leachability, strength and microstructural characteristics of KMP binder stabilized Zn and Pb contaminated soils

This study presents a systematic investigation of effects of carbonation on the contaminant leachability and unconfined compressive strength of KMP stabilized contaminated soils. A field soil spiked with Zn and Pb individually and together is stabilized using a new KMP additive under standard curing conditions and also with carbonation. The KMP additive is composed of oxalic acid-activated phosphate rock, monopotassium phosphate and reactive magnesia. The stabilized soils are tested for acid neutralization capacity, toxic characteristics leaching characteristics, contaminant speciation and unconfined compression strength. X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy analyses are performed to assess reaction products. The results demonstrate that carbonation increases both acid buffer capacity index and unconfined compressive strength, but decreases leachability of KMP stabilized soils. These results are interpreted based on the changes in chemical speciation of Zn and Pb and also stability and solubility of the reaction products (metal phosphates and carbonates) formed in the soils. Overall, this study demonstrates that carbonation has positive effects on leachability and strength of the KMP stabilized soils.

Chemical forms of cadmium in a calcareous soil treated with different levels of phosphorus-containing acidifying agents

Calcareous soils with high background cadmium (Cd) levels are widely distributed in south-west China and soil acidity is a major environmental problem. However, little effort has been made to study the changes in chemical speciation as affected by soil acidification other than by acidic rain. In the present study, we investigated the impact of mono-ammonium phosphate (MAP) and phosphoric acid on soil pH and chemical transformation of Cd in calcareous soils. Calcareous soils collected from south-west China were treated with three concentrations (0.1, 0.2 and 0.4 mol kg–1 soil) of MAP and phosphoric acid, and without the addition of acidifying agent, before being incubated at 25 ± 2°C near field capacity moisture content for 60 days. The chemical forms of Cd in the soils were determined by the Tessier sequential extraction scheme. The concentration of Cd in the form bound to iron and manganese oxides (CdFeOx+MnOy) decreased significantly with increasing levels of the two acidifying agents, but the concentration of exchangeable Cd (CdEx) exhibited a significant increase, indicating that the two acidifying agents can effectively promote the transformation of CdFeOx+MnOy to CdEx. MAP may promote the same amount of CdFeOx+MnOy to CdEx as phosphoric acid at the same rate of addition, but the soil pH clearly differed, implying that an increase in water-soluble P with addition of acidifying agent may be one major factor affecting the chemical transformation of Cd. MAP and phosphoric acid should be used carefully as sources of water-soluble phosphorus for calcareous soils with high background concentrations of Cd.

Batch and column sorption of arsenic onto iron-impregnated biochar synthesized through hydrolysis

Iron (Fe)-impregnated biochar, prepared through a novel method that directly hydrolyzes iron salt onto hickory biochar, was investigated for its performance as a low-cost arsenic (As) sorbent. Although iron impregnation decreased the specific surface areas of the biochar, the impregnated biochar showed much better sorption of aqueous As (maximum sorption capacity of 2.16 mg g−1) than the pristine biochar (no/little As sorption capacity). Scanning electron microscope equipped with an energy dispersive spectrometer and X-ray diffraction analysis indicated the presence of crystalline Fe hydroxide in the impregnated biochar but no crystal forms of arsenic were found in the post-sorption biochar samples. However, large shifts in the binding energy of Fe2p, As3d, O1s and C1s region on the following As sorption indicated a change in chemical speciation from As(V) to As(III) and Fe(II) to Fe(III) and strong As interaction with oxygen-containing function groups of the Fe-impregnated biochar. These findings suggest that the As sorption on the Fe-impregnated biochar is mainly controlled by the chemisorption mechanism. Columns packed with Fe-impregnated biochar showed good As retention, and was regenerated with 0.05 mol L−1 NaHCO3 solution. These findings indicate that Fe-impregnated biochar can be used as a low-cost filter material to remove arsenic from aqueous solutions.

Foliar uptake and metal(loid) bioaccessibility in vegetables exposed to particulate matter.

At the global scale, high concentrations of particulate matter (PM) enriched with metal(loid)s are currently observed in the atmosphere of urban areas. Foliar lead uptake was demonstrated for vegetables exposed to airborne PM. Our main objective here was to highlight the health risk associated with the consumption of vegetables exposed to foliar deposits of PM enriched with the various metal(loid)s frequently observed in the atmosphere of urban areas (Cd, Sb, Zn and Pb). Leaves of mature cabbage and spinach were exposed to manufactured mono-metallic oxide particles (CdO, Sb2O3 and ZnO) or to complex process PM mainly enriched with lead. Total and bioaccessible metal(loid) concentrations were then measured for polluted vegetables and the various PM used as sources. Finally, scanning electronic microscopy coupled with energy dispersive X-ray microanalysis was used to study PM-phyllosphere interactions. High quantities of Cd, Sb, Zn and Pb were taken up by the plant leaves. These levels depended on both the plant species and nature of the PM, highlighting the interest of acquiring data for different plants and sources of exposure in order to better identify and manage health risks. A maximum of 2% of the leaf surfaces were covered with the PM. However, particles appeared to be enriched in stomatal openings, with up to 12% of their area occupied. Metal(loid) bioaccessibility was significantly higher for vegetables compared to PM sources, certainly due to chemical speciation changes. Taken together, these results confirm the importance of taking atmospheric PM into account when assessing the health risks associated with ingestion of vegetables grown in urban vegetable crops or kitchen gardens.