161 results found
Bullen J, Lapinee C, Salaün P, et al., 2020, On the application of photocatalyst-sorbent composite materials for arsenic(III) remediation: Insights from kinetic adsorption modelling, Journal of Environmental Chemical Engineering, Vol: 8, ISSN: 2213-3437
TiO2-Fe2O3 composites show great promise for the removal of arsenic(III) from drinking water: this single material combines the photocatalytic capabilities of TiO2 for the oxidation of arsenite (i.e. As(III)) with the high adsorption capacity of iron oxides towards the arsenate (i.e. As(V)) subsequently produced. To design an effective treatment, it is necessary to balance high sorbent concentrations, providing long filter lifetimes, with low photocatalyst concentrations, to achieve effective penetration of light into the system. In this work, we construct a predictive model using experimentally determined As(III) adsorption isotherms and kinetics to estimate arsenic treatment plant lifetimes. We considered sorbent loading, treatment time, and batch treatment versus continuous-flow. Our model indicated that batch treatment is more efficient than continuous-flow at low sorbent concentrations (<100 g L-1), and therefore more appropriate for the photocatalyst-sorbent system. However, with <100 g L-1 sorbent, media should be replaced several times per year to maintain effective treatment. In contrast, slurries of >100 g L-1 sorbent could operate for an entire year without media replacement. This work highlights the important implications of sorbent concentration when we consider the multifunctional photocatalysts-sorbent system, and highlights the need for further experimental work to design efficient arsenic treatment plants.
Bullen J, Kenney J, Fearn S, et al., 2020, Improved Accuracy in Multicomponent Surface Complexation Models Using Surface-Sensitive Analytical Techniques: Adsorption of Arsenic onto a TiO2/Fe2O3 Multifunctional Sorbent, Journal of Colloid and Interface Science, ISSN: 0021-9797
Many novel composite materials have been recently developed for water treatment applications, with the aim of achieving multifunctional behaviour, e.g. combining adsorption with light-driven remediation. The application of surface complexation models (SCM) is important to understand how adsorption changes as a function of pH, ionic strength and the presence of competitor ions. Component additive (CA) models describe composite sorbents using a combination of single-phase reference materials. However, predictive adsorption modelling using the CA-SCM approach remains unreliable, due to challenges in the quantitative determination of surface composition. In this study, we test the hypothesis that characterisation of the outermost surface using low energy ion scattering (LEIS) improves CA-SCM accuracy. We consider the TiO2/Fe2O3 photocatalyst-sorbents that are increasingly investigated for arsenic remediation. Due to an iron oxide surface coating that was not captured by bulk analysis, LEIS significantly improves the accuracy of our component additive predictions for monolayer surface processes: adsorption of arsenic(V) and surface acidity. We also demonstrate non-component additivity in multilayer arsenic(III) adsorption, due to changes in surface morphology/porosity. Our results demonstrate how surface-sensitive analytical techniques will improve adsorption modelling for the next generation of composite sorbents.
Liu F, Tan Q-G, Weiss D, et al., 2020, Unravelling metal speciation in the microenvironment surrounding phytoplankton cells to improve predictions of metal bioavailability., Environmental Science and Technology (Washington), ISSN: 0013-936X
A lack of knowledge on metal speciation in the microenvironment surrounding phytoplankton cells (i.e., the phycosphere) represents an impediment to accurately predicting metal bioavailability. Phycosphere pH and O2 concentrations from a diversity of algae species were compiled. For marine algae in the light, the average increases were 0.32 pH units and 0.17 mM O2 in the phycosphere, whereas in the dark the average decreases were 0.10 pH units and 0.03 mM O2, in comparison to bulk seawater. In freshwater algae, the phycosphere pH increased by 1.28 units, whereas O2 increased by 0.38 mM in the light. Equilibrium modeling showed that the pH alteration influenced the chemical species distribution (i.e., free ion, inorganic complexes, and organic complexes) of Al, Cd, Co, Cu, Fe, Hg, Mn, Ni, Pb, Sc, Sm, and Zn in the phycosphere, and the O2 fluctuation increased oxidation rates of Cu(I), Fe(II) and Mn(II) from 2 to 938-fold. The pH/O2-induced changes in phycosphere metal chemistry were larger for freshwater algae than for marine species. Reanalyses of algal metal uptake data in the literature showed that uptake of the trivalent metals (Sc, Sm and Fe), in addition to divalent metals, can be better predicted after considering the phycosphere chemistry.
Bullen JC, Torres-Huerta A, Salaün P, et al., 2020, Portable and rapid arsenic speciation in synthetic and natural waters by an As(V)-selective chemisorbent, validated against anodic stripping voltammetry, Water Research, Vol: 175, Pages: 1-11, ISSN: 0043-1354
Inorganic arsenic speciation, i.e. the differentiation between arsenite and arsenate, is an important step for any program aiming to address the global issue of arsenic contaminated groundwater, whether for monitoring purposes or the development of new water treatment regimes. Reliable speciation by easy-to-use, portable and cost-effective analytical techniques is still challenging for both synthetic and natural waters. Here we demonstrate the first application of an As(V)-selective chemisorbent material for simple and portable speciation of arsenic using handheld syringes, enabling high sample throughput with minimal set-up costs. We first show that ImpAs efficiently removes As(V) from a variety of synthetic groundwaters with a single treatment, whilst As(III) is not retained. We then exemplify the potential of ImpAs for simple and fast speciation by determining rate constants for the photooxidation of As(III) in presence of a TiO2 photocatalyst. Finally, we successfully speciate natural waters spiked with a mix of As(III) and As(V) in both Indian and UK groundwaters with less than 5 mg L−1 dissolved iron. Experimental results using ImpAs agreed with anodic stripping voltammetry (ASV), a benchmark portable technique, with analysis conditions optimised here for the groundwaters of South Asia. This new analytical tool is simple, portable and fast and should find applications within the overall multi-disciplinary remediation effort that is taking place to tackle this worldwide arsenic problem.
Kirby ME, Watson JS, Najorka J, et al., 2020, Experimental study of pH effect on uranium (UVI) particle formation and transport through quartz sand in alkaline 0.1 M sodium chloride solutions, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol: 592, Pages: 1-11, ISSN: 0927-7757
A thorough understanding of the aqueous uranium VI (UVI) chemistry in alkaline, sodium containing solutions is imperative to address a wide range of critical challenges in environmental engineering, including nuclear waste management. The aim of the present study was to characterise experimentally in more detail the control of pH on the removal of UVI from aqueous alkaline solutions through particle formation and on subsequent transport through porous media. We conducted first static batch experiments in the pH range between 10.5 and 12.5 containing 10 ppm UVI in 0.1 M NaCl solutions and examined the particles formed using filtration, dynamic light scattering, transition electron microscopy and X-ray powder diffraction. We found that at pH 10.5 and 11.5, between 75 and 96 % of UVI was removed from the solutions as clarkeite and studtite over a period of 48 h, forming particles with hydrodynamic diameters of 640 ± 111 nm and 837 ± 142 nm, respectively and representing aggregates of 10′s nm sized crystals randomly orientated. At pH 12.5, the formation of particles >0.2 μm became insignificant and no UVI was removed from solution. The mobility of UVI in these solutions was further studied using column experiments through quartz sand. We found that at pH 10.5 and 11.5, UVI containing particles were immobilised near the column inlet, likely due physical immobilisation of the particles (particle straining). At pH 12.5, however, UVI quantitatively eluted from the columns in the filter fraction <0.2 μm. The findings of our study reinforce a strong control of solution pH on particle size and U removal in alkaline solutions and subsequently on mobility of U through quartz porous media.
De Vleeschouwer F, Baron S, Cloy JM, et al., 2020, Comment on: "A novel approach to peatlands as archives of total cumulative spatial pollution loads from atmospheric deposition of airborne elements complementary to EMEP data: Priority pollutants (Pb, Cd, Hg)" by Ewa Miszczak, Sebastian Stefaniak, Adam Michczyński, Eiliv Steinnes and Irena Twardowska., Science of the Total Environment, ISSN: 0048-9697
A recent paper by Miszczak et al. (2020) examines metal contamination of mires in Poland and Norway. The authors conclude that lead (Pb) records in ombrotrophic peatlands cannot be used to reconstruct the chronological history of anthropogenic activities due to post-depositional mobility of the metal. We contest this general conclusion which stands in contrast with a significant body of literature demonstrating that Pb is largely immobile in the vast majority of ombrotrophic peatlands. Our aim is to reaffirm the crucial contribution that peat records have made to our knowledge of atmospheric Pb contamination. In addition, we reiterate the necessity of following established protocols to produce reliable records of anthropogenic Pb contamination in environmental archives.
Kirby ME, Sonnenberg JL, Simperler A, et al., 2020, Stability series for the complexation of six key siderophore functional Groups with uranyl using density functional theory, The Journal of Physical Chemistry A, Vol: 124, Pages: 2460-2472, ISSN: 1089-5639
Determining stability constants of uranyl complexes with the principal functional groups in siderophores and identifying stability series is of great importance to predict which siderophore classes preferentially bind to UVI and hence impact uranium speciation in the environment. It also helps to develop resins for scavenging UVI from aqueous solutions. Here, we apply a recently developed computational approach to calculate log β values for a set of geochemically relevant uranium organometallic complexes using Density Functional Theory (DFT). We determined the stability series for catecholate, hydroxamate, α-hydroxycarboxylate, α-aminocarboxylate, hydroxy-phenyloxazolonate, and α-hydroxyimidazole with the uranyl cation. In this work, the stability constants (log β110) of α-hydroxyimidazolate and hydroxy-phenyloxazolonate are calculated for the first time. Our approach employed the B3LYP density functional approximation, aug-cc-pVDZ basis set for ligand atoms, MDF60 ECP for UVI, and the IEFPCM solvation model. DFT calculated log β110 were corrected using a previously established fitting equation. We find that the siderophore functional groups stability decreases in the order: α-hydroxycarboxylate bound via the α-hydroxy and carboxylate groups (log β110 = 17.08), α-hydroxyimidazolate (log β110 = 16.55), catecholate (log β110 = 16.43), hydroxamate (log β110 = 9.00), hydroxy-phenyloxazolonate (log β110 = 8.43), α-hydroxycarboxylate bound via the carboxylate group (log β110 = 7.51) and α-aminocarboxylate (log β110 = 4.73). We confirm that the stability for the binding mode of the functional groups decrease in the order: bidentate, monodentate via ligand O atoms and monodentate via ligand N atoms. The stability series strongly suggests that α-hydroxyimidazolate is an important functional group that needs to be included when assessing uranyl mobility and removal fr
Zhang Y, Takahashi Y, Hong SP, et al., 2019, High-resolution label-free 3D mapping of extracellular pH of single living cells, Nature Communications, Vol: 10, ISSN: 2041-1723
Dynamic mapping of extracellular pH (pHe) at the single-cell level is critical for understanding the role of H+ in cellular and subcellular processes, with particular importance in cancer. While several pHe sensing techniques have been developed, accessing this information at the single-cell level requires improvement in sensitivity, spatial and temporal resolution. We report on a zwitterionic label-free pH nanoprobe that addresses these long-standing challenges. The probe has a sensitivity >0.01 units, 2 ms response time, and 50 nm spatial resolution. The technology was incorporated into a double-barrel nanoprobe integrating pH sensing with feedback-controlled distance sensing via Scanning Ion Conductance Microscopy. This allows for the simultaneous 3D topographical imaging and pHe monitoring of living cancer cells. These classes of nanoprobes were used for real-time high spatiotemporal resolution pHe mapping at the subcellular level and revealed tumour heterogeneity of the peri-cellular environments of melanoma and breast cancer cells.
Duerr-Auster T, Wiggenhauser M, Zeder C, et al., 2019, The use of Q-ICPMS to apply enriched Zinc stable isotope source tracing for organic fertilizers, Frontiers in Plant Science, Vol: 10, Pages: 1-12, ISSN: 1664-462X
Organic fertilizer applications can contribute to Zinc (Zn) biofortification of crops. An enriched stable isotope source tracing approach is a central tool to further determine the potential of this biofortification measure. Here, we assessed the use of the widely available quadrupole single-collector ICPMS (Q-ICPMS, analytical error = 1% relative standard deviation) and the less accessible but more precise multicollector ICPMS as reference instrument (MC-ICPMS, analytical error = 0.01% relative standard deviation) to measure enriched Zn stable isotope ratios in soil–fertilizer–plant systems. The isotope label was either applied to the fertilizer (direct method) or to the soil available Zn pool that was determined by isotope ratios measurements of the shoots that grew on labeled soils without fertilizer addition (indirect method). The latter approach is used to trace Zn that was added to soils with complex insoluble organic fertilizers that are difficult to label homogeneously. To reduce isobaric interferences during Zn isotope measurements, ion exchange chromatography was used to separate the Zn from the sample matrix. The 67Zn:66Zn isotope ratios altered from 0.148 at natural abundance to 1.561 in the fertilizer of the direct method and 0.218 to 0.305 in soil available Zn of the indirect method. Analysis of the difference (Bland–Altman) between the two analytical instruments revealed that the variation between 67Zn:66Zn isotope ratios measured with Q-ICPMS and MC-ICPMS were on average 0.08% [95% confidence interval (CI) = 0.68%]. The fractions of Zn derived from the fertilizer in the plant were on average 0.16% higher (CI = 0.49%) when analyzed with Q- compared to MC-ICPMS. The sample matrix had a larger impact on isotope measurements than the choice of analytical instrument, as non-purified samples resulted on average 5.79% (CI = 9.47%) higher isotope ratios than purified samples. Furthermore, the gain in analytical precision using MC-ICPMS inst
Kirby ME, Bullen JC, Hanif MD, et al., 2019, Determining the effect of pH on iron oxidation kinetics in aquatic environments: exploring a fundamental chemical reaction to grasp the significant ecosystem implications of iron bioavailability, Journal of Chemical Education, Vol: 97, Pages: 215-220, ISSN: 0021-9584
Understanding the controls of the oxidation rate of iron (Fe) in oxygenated aquatic systems is fundamental for students of the Earth and Environmental Sciences as it defines the bioavailability of Fe, a trace metal essential for life. The laboratory experiment presented here was successfully developed and used during a third-year undergraduate lab course at Imperial College London for several years. It employs ultraviolet–visible (UV–vis) spectroscopy calibrated externally with 0 to 50 μM Fe2+ standards created in a 492 μM ferrozine and 0.43 M acetate matrix. The students conducted the oxidation experiments in stirred batch reactors at equilibrium with atmospheric oxygen. The solution contained 40.5 μM initial Fe2+ concentration and a 5.1 mM imidazole buffer. The pH was adjusted to values between 7.22 and 7.77. The students observed a pseudo-first-order reaction with respect to Fe2+ concentration. Plotting the logarithms of the apparent rate constants (k′) at different pH values leads to a gradient of 2.2 ± 0.2 min–1 pH–1, indicating a second-order reaction with respect to OH– concentration, in agreement with published literature. The oxidation reaction occurred rapidly (tens of seconds to tens of minutes) indicating that in oxygenated aquatic systems, Fe3+ will be the dominant oxidation state, significantly reducing the bioavailability of Fe. The simple laboratory experiment presented here allows the students to learn about kinetic parameters for a fundamental chemical reaction. It allows the students to explore the significant implications this has for aquatic ecosystems.
Le Roux G, De Vleeschouwer F, Weiss D, et al., 2019, Learning from the past: fires, architecture, and environmental lead emissions, Environmental Science and Technology (Washington), Vol: 53, Pages: 8482-8484, ISSN: 0013-936X
Souto-Oliveira CE, Babinski M, Araujo DF, et al., 2019, Multi-isotope approach of Pb, Cu and Zn in urban aerosols and anthropogenic sources improves tracing of the atmospheric pollutant sources in megacities, ATMOSPHERIC ENVIRONMENT, Vol: 198, Pages: 427-437, ISSN: 1352-2310
Studies including multiple isotope systems in aerosols promises unparalleled insights into sources and pathways of metals in the atmosphere. However, such studies remain rare because of the challenges associated with small sample sizes and low analyte masses of the target elements. Here, we present the first study combining accurate and precise determination of Pb, Cu and Zn isotopic ratios in aerosols and anthropogenic materials collected in São Paulo, Brazil. We use a sequential ion chromatography procedure with two different resins for the separation and purification of the analytes. Multi collector mass spectrometry is used for the accurate and precise determination of the isotope ratios. Long term analytical reproducibilities are ±0.035 for 206Pb/204Pb, ± 0.13‰ for δ65CuNIST and ±0.1‰ for δ66ZnJMC (±2σ). Accuracy is assessed using certified reference materials (CRM NIST 2783 aerossol, BRP-1 and others). We analyzed 57 source samples (road dust, tires, cement, road tunnel aerosol) and 113 aerosol samples collected between 2013 and 2015. The results for São Paulo are critically compared with previously published data from studies conducted in São Paulo, London and Barcelona. The key findings are: 1. The isotope signatures for Zn in tires (δ66ZnJMC = 0.16 ± 0.14, 2σ, n = 9) and road dust (δ66ZnJMC = 0.17 ± 0.19, 2σ, n = 13) are similar in São Paulo and London suggesting that this isotope system can be used as element specific tracers for non-exhaust traffic. 2. 206Pb/207Pb vs δ66ZnJMC and δ66ZnJMC vs δ65CuNIST multi-isotopic diagrams successfully separate wear off from cars including tires and brakes, car exhaust, industrial emissions and cement sources and improves the discrimination of air pollutant sources. 3. The source identification based on isotope ratios agrees source apportionment based on emissions inventory from
Mondillo N, Wilkinson JJ, Boni M, et al., 2018, A global assessment of Zn isotope fractionation in secondary Zn minerals from sulfide and non-sulfide ore deposits and model for fractionation control, Chemical Geology, Vol: 500, Pages: 182-193, ISSN: 0009-2541
We investigated extent and direction of Zn isotope fractionation in secondary zinc minerals formed during low temperature hydrothermal and/or supergene oxidation of primary sulfide deposits. Zinc isotope data have been obtained from non-sulfide zinc mineral separates (willemite - Zn2SiO4, smithsonite - ZnCO3, hemimorphite - Zn4(Si2O7)(OH)2·H2O, hydrozincite - Zn5(CO3)2(OH)6, and sauconite - Na0.3Zn3(Si,Al)4O10(OH)2·4H2O) collected from several Zn deposits in Ireland, Belgium, Poland, Namibia, Peru, Yemen and Zambia. The data are compared with Zn isotope compositions measured on Zn sulfides collected in the same areas and/or derived from the existing literature, to establish the controls of direction and likely extent of any fractionations. We find that willemite has the greatest compositional variability, with measured δ66ZnJCM-Lyonvalues ranging from −0.42 to 1.39‰, spanning the entire range of terrestrial variation in Zn isotopes recorded to date. Overall, significant fractionations in positive and negative directions are recorded relative to the precursor phase (primary sphalerite or an earlier secondary phase), with primary sphalerite falling in a relatively narrow range of isotopic values (approximately −0.1 to +0.4‰). Most of the data observed on willemite, hemimorphite and hydrozincite can be explained with a model of isotopic fractionation, in which partial dissolution of primary sphalerite is followed by precipitation of an initial secondary phase that preferentially incorporates heavy Zn isotopes. Smithsonite, instead, preferentially incorporates light Zn isotopes. This reflects the variation in the Zn-x bond strengths of these secondary phases with respect to the original sulfides. We also observed that isotope compositions do not depend only on the difference between the fractionation factors of the involved phases but also on the amount of the secondary mineral precipitated after dissolution of primary sulfi
Kirby M, Simperler A, Krevor S, et al., 2018, Computational tools for calculating log β values of geochemically relevant uranium organometallic complexes, Journal of Physical Chemistry A, Vol: 122, Pages: 8007-8019, ISSN: 1089-5639
Uranium (UVI) interacts with organic ligands, subsequently controlling its aqueous chemistry. It is therefore imperative to assess the binding ability of natural organic molecules. We evidence that density functional theory (DFT) can be used as a practical protocol for predicting the stability of UVI organic ligand complexes, allowing for the development of a relative stability series for organic complexes with limited experimental data. Solvation methods and DFT settings were benchmarked to suggest a suitable off-the-shelf solution. The results indicate that the IEFPCM solvation method should be employed. A mixed solvation approach improves the accuracy of the calculated stability constant (log β); however, the calculated log β are approximately five times more favorable than experimental data. Different basis sets, functionals, and effective core potentials were tested to check that there were no major changes in molecular geometries and ΔrG. The recommended method employed is the B3LYP functional, aug-cc-pVDZ basis set for ligands, MDF60 ECP and basis set for UVI, and the IEFPCM solvation model. Using the fitting approach employed in the literature with these updated DFT settings allows fitting of 1:1 UVI complexes with root-mean-square deviation of 1.38 log β units. Fitting multiple bound carboxylate ligands indicates a second, separate fitting for 1:2 and 1:3 complexes.
Khondoker R, Weiss DJ, van de Flierdt T, et al., 2018, New constraints on elemental and Pb and Nd isotope compositions of South American and Southern African aerosol sources to the South Atlantic Ocean, Chemie der Erde / Geochemistry, Vol: 78, Pages: 372-384, ISSN: 0009-2819
Improving the geochemical database available for characterising potential natural and anthropogenic aerosol sources from South America and Southern Africa is a critical precondition for studies aimed at understanding trace metal controls on the marine biogeochemical cycles of the South Atlantic Ocean. We here present new elemental and isotopic data for a wide range of sample types from South America and Southern Africa that are potentially important aerosol sources. This includes road dust from Buenos Aires and lichen samples from Johannesburg, soil dust from Patagonia, volcanic ash from the Andean volcanic belt, and aerosol samples from São Paulo. All samples were investigated for major (Al, Ca, Fe, Mg, Na, K, Mn) and trace element (Cd, Co, Cr, Cu, Ni, Pb, REE, Sc, Th, Y, V, Zn) concentrations and Nd and Pb isotopic compositions. We show that diagrams of 208Pb/207Pb vs. εNd, 208Pb/207Pb vs. Pb/Al, 1/[Pb], Zn/Al, Cd/Al, Cu/Al, and εNd vs. Pb/Al, and 1/[Nd] are best suited to separate South American and South African source regions as well as natural and anthropogenic sources. A subset of samples from Patagonia and the Andes was additionally subjected to separation of a fine (<5 μm) fraction and compared to the composition of the bulk sample. We show that differences in the geochemical signature of bulk samples between individual regions and source types are significantly larger than between grain sizes. Jointly, these findings present an important step forward towards a quantitative assessment of aeolian trace metal inputs to the South Atlantic Ocean.
The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the previous IDP2014. For the first time, the IDP2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope (TEI) sources. The TEI data in the IDP2017 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at crossover stations. The IDP2017 consists of two parts: (1) a compilation of digital data for more than 450 TEIs as well as standard hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing an on-line atlas that includes more than 590 section plots and 130 animated 3D scenes. The digital data are provided in several formats, including ASCII, Excel spreadsheet, netCDF, and Ocean Data View collection. Users can download the full data packages or make their own custom selections with a new on-line data extraction service. In addition to the actual data values, the IDP2017 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering and for statistical analysis. Metadata about data originators, analytical methods and original publications related to the data are linked in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2017 as section plots and rotating 3D scenes. The basin-wide 3D scenes combine data from many cruises and provide quick overviews of large-scale tracer distributions. These 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or alo
Sonnenberg J, Kirby M, Simperler A, et al., 2018, Towards stability constant prediction in uranium siderophore complexes, 256th National Meeting and Exposition of the American-Chemical-Society (ACS) - Nanoscience, Nanotechnology and Beyond, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Araujo DF, Machado W, Weiss D, et al., 2018, Zinc isotopes as tracers of anthropogenic sources and biogeochemical processes in contaminated mangroves, Applied Geochemistry, Vol: 95, Pages: 25-32, ISSN: 0883-2927
Recent work has shown that variations in zinc (Zn) isotope ratios enable us to identify contamination sources in the terrestrial environment and uptake processes in higher plants. Here in this study, we demonstrate that this also holds true for mangrove forests, which play an important role in the biogeochemical cycling of metals in tropical coastal ecosystems and that are seriously threatened by anthropogenic pollution. To this end, we determined zinc concentration and isotope composition (expressed using the δ66Zn notation relative to the JMC 3-0749-L standard) in sediments and tree leaves collected from a mangrove close to Rio de Janeiro in Brazil. The δ66ZnJMC values of sediments vary between +0.36 and + 0.84‰ and fall on a mixing line between detrital terrestrial sources (characterized with δ66ZnJMC = +0.28 ± 0.12‰, 2σ) and metallurgical ore sources (δ66ZnJMC = +0.86‰ ±0.15‰, 2σ). Leaves of Laguncularia racemose, in contrast, showed δ66ZnJMC values ranging between +0.08 and + 0.23‰, suggesting that processes including uptake, translocation and bioavailability in the rhizosphere control the isotope composition of zinc in the mangrove plant.
Kenney JPL, Ellis T, Nicol FS, et al., 2018, The effect of bacterial growth phase and culture concentration on U(VI) removal from aqueous solution, Chemical Geology, Vol: 482, Pages: 61-71, ISSN: 0009-2541
Bacteria play a key role in controlling the mobility of contaminants, such as uranium (U), in the environment. Uranium could be sourced from disposed radioactive waste, derived either from surface disposal trenches for Low Level Waste (LLW) that, because of the waste type and disposal concept, would typically present acidic conditions or from the geological disposal of LLW or Intermediate Level Waste (ILW) that, because of the waste type and the disposal concept, would typically present alkaline conditions. In disposed radioactive waste, there could be variable amounts of cellulosic material. Bacterial cells may be living in a range of different growth phases, depending on the growth conditions and nutrients available at the time any waste-derived U migrated to the cells. A key knowledge gap to date has been the lack of a mechanistic understanding of how bacterial growth phases (exponential, stationary, and death phase) affect the ability of bacteria to remove U(VI) from solution. To address this, we first characterised the cells using potentiometric titrations to detect any differences in proton binding to proton active sites on Pseudomonas putida cells at each growth phase under aerobic conditions, or under anaerobic conditions favourable to U(IV) reoxidation. We then conducted batch U(VI) removal experiments with bacteria at each phase suspended in 1 and 10 ppm U aqueous solutions with the pH adjusted from 2 to 12 as well as with culture concentrations from 0.01 to 10 g/L, to identify the minimal concentration of bacteria in solution necessary to affect U removal. We found that, in death phase, P. putida cells exhibited double the concentration of proton active sites than bacteria grown to exponential and stationary phase. However, we did not see a difference in the extent of U(VI) removal, from a 10 ppm U solution, between the different growth phases as a function of pH (2 to 12). Culture concentration affected U removal between pH 2–8, where U removal dec
Martín A, Caldelas C, Weiss D, et al., 2018, Assessment of metal immission in urban environments using elemental concentrations and zinc isotope signatures in leaves of Nerium oleander, Environmental Science and Technology, Vol: 52, Pages: 2071-2080, ISSN: 0013-936X
A thorough understanding of spatial and temporal emission and immission patterns of air pollutants in urban areas is challenged by the low number of air-quality monitoring stations available. Plants are promising low-cost biomonitoring tools. However, source identification of the trace metals incorporated in plant tissues (i.e., natural vs anthropogenic) and the identification of the best plant to use remain fundamental challenges. To this end, Nerium oleander L. collected in the city of Zaragoza (NE Spain) has been investigated as a biomonitoring tool for assessing the spatial immission patterns of airborne metals (Pb, Cu, Cr, Ni, Ce, and Zn). N. oleander leaves were sampled at 118 locations across the city, including the city center, industrial hotspots, ring-roads, and outskirts. Metal concentrations were generally higher within a 4 km radius around the city center. Calculated enrichment factors relative to upper continental crust suggest an anthropogenic origin for Cr, Cu, Ni, Pb, and Zn. Zinc isotopes showed significant variability that likely reflects different pollution sources. Plants closer to industrial hotspots showed heavier isotopic compositions (δ66ZnLyonup to +0.70‰), indicating significant contributions of fly ash particles, while those far away were isotopically light (up to -0.95‰), indicating significant contributions from exhaust emissions and flue gas. We suggest that this information is applied for improving the environmental and human risk assessment related to the exposure to air pollution in urban areas.
Affholder M-C, Weiss DJ, Wissuwa M, et al., 2017, Soil CO2 venting as one of the mechanisms for tolerance of Zn deficiency by rice in flooded soils., Plant, Cell and Environment, Vol: 40, Pages: 3018-3030, ISSN: 0140-7791
We sought to explain rice (Oryza sativa) genotype differences in tolerance of zinc (Zn) deficiency in flooded paddy soils and the counter-intuitive observation, made in earlier field experiments, that Zn uptake per plant increases with increasing planting density. We grew tolerant and intolerant genotypes in a Zn-deficient flooded soil at high and low planting densities, and found (a) plant Zn concentrations and growth increased with planting density and more so in the tolerant genotype, whereas the concentrations of other nutrients decreased, indicating a specific effect on Zn uptake; (b) the effects of planting density and genotype on Zn uptake could only be explained if the plants induced changes in the soil to make Zn more soluble; and (c) the genotype and planting density effects were both associated with decreases in dissolved CO2 in the rhizosphere soil solution and resulting increases in pH. We suggest the increases in pH caused solubilisation of soil Zn by dissolution of alkali-soluble, Zn-complexing organic ligands from soil organic matter. We conclude that differences in venting of soil CO2 through root aerenchyma were responsible for the genotype and planting density effects.
Araujo D, Machado W, Weiss D, et al., 2017, A critical examination of the possible application of zinc stable isotope ratios in bivalve mollusks and suspended particulate matter to trace zinc pollution in a tropical estuary, Environmental Pollution, Vol: 226, Pages: 41-47, ISSN: 0269-7491
The application of zinc (Zn) isotopes in bivalve tissues to identify zinc sources in estuaries was critically assessed. We determined the zinc isotope composition of mollusks (Crassostrea brasiliana and Perna perna) and suspended particulate matter (SPM) in a tropical estuary (Sepetiba Bay, Brazil) historically impacted by metallurgical activities. The zinc isotope systematics of the SPM was in line with mixing of zinc derived from fluvial material and from metallurgical activities. In contrast, source mixing alone cannot account for the isotope ratios observed in the bivalves, which are significantly lighter in the contaminated metallurgical zone (δ66ZnJMC = +0.49 ± 0.06‰, 2σ, n = 3) compared to sampling locations outside (δ66ZnJMC = +0.83 ± 0.10‰, 2σ, n = 22). This observation suggests that additional factors such as speciation, bioavailability and bioaccumulation pathways (via solution or particulate matter) influence the zinc isotope composition of bivalves.
Kenney J, Kirby, Cuadros J, et al., 2017, A conceptual model to predict uranium removal from aqueous solutions in water–rock systems associated with low- and intermediate-level radioactive waste disposal, RSC Advances, Vol: 7, Pages: 7876-7884, ISSN: 2046-2069
Global stores of radioactive waste are housed in surface stores where actinides are susceptible to environmental release. It is imperative that waste disposal facilities are built to safely contain this waste. However, to do this we must ensure that the engineered and natural barriers are sufficient to prevent the buried materials from migrating through to the surface. Solutions migrating from repositories (ILW and LLW) will have a wide range of chemical compositions and conceptual models constraining the key mineral-water interactions with realistic lithologies are urgently needed. To this end, we conducted experiments to study U removal from solution via mineral-surface interactions with quartz, sandstone, and volcanic rock over a pH range of 2-12, with varying concentrations of U (10 ppb, 0.1 ppm, 1 ppm, and 10 ppm) and with and without bicarbonate added (2 mM) with 0.1 M NaCl electrolyte. We observed that the U concentration in solution had little effect on the extent of U removal from solution as a function of pH or bicarbonate concentration 2with quartz and sandstone but was important for volcanic rocks, where removal ofU, due to adsorption, decreased with increasing U concentration between pH 4 and 8. When bicarbonate was added to solution then the quartz, sandstone, and volcanicrock geomaterials acted similarly in their abilities to immobilize uranium, with an adsorption envelope from pH 4-8 followed by an increase in U removal, likely via precipitation, at high pH. When bicarbonate was not added,the removal of U from solution was more controlled by the geomaterial. Bicarbonate addition at pH 6 -10 lowered adsorption. However, the addition of bicarbonate in experiments with 10 ppm U at pH 10 -12 allowed for precipitation of U at the rock surface, making bicarbonate
Dong S, Ochoa Gonzalez R, Harrison RM, et al., 2017, Isotopic signatures in atmospheric particulate matter suggest important contributions from recycled gasoline for lead and non-exhaust traffic sources for copper and zinc in aerosols in London, United Kingdom, ATMOSPHERIC ENVIRONMENT, ISSN: 1352-2310
The aim of this study was to improve our understanding of what controls the isotope composition of Cu, Zn and Pb in particulate matter (PM) in the urban environment and to develop these isotope systems as possible source tracers. To this end, isotope ratios (Cu, Zn and Pb) and trace element concentrations (Fe, Al, Cu, Zn, Sb, Ba, Pb, Cr, Ni and V) were determined in PM10 collected at two road sites with contrasting traffic densities in central London, UK, during two weeks in summer 2010, and in potential sources, including non-combustion traffic emissions (tires and brakes), road furniture (road paint, manhole cover and road tarmac surface) and road dust. The isotope signatures of other important sources (gasoline and exhaust emissions) were taken from previous published data. Iron, Ba and Sb were used as proxies for emissions derived from brake pads, and Ni, and V for emissions derived from fossil fuel oil. The isotopic composition of Pb (expressed using 206Pb/207Pb) ranged between 1.1137 and 1.1364. The isotope ratios of Cu and Zn expressed as δ65CuNIST976 and δ66ZnLyon ranged between -0.01‰ and +0.51‰ and between -0.21‰ and +0.33‰, respectively. We did not find significant differences in the isotope signatures in PM10 over the two weeks sampling period and between the two sites, suggesting similar sources for each metal at both sites despite their different traffic densities. The stable isotope composition of Pb suggests significant contribution from road dust resuspension and from recycled leaded gasoline. The Cu and Zn isotope signatures of tires, brakes and road dust overlap with those of PM10. The correlation between the enrichments of Sb, Cu, Ba and Fe in PM10 support the previously established hypothesis that Cu isotope ratios are controlled by non-exhaust traffic emission sources in urban environments (Ochoa Gonzalez et al., 2016). Analysis of the Zn isotope signatures in PM10 and possible sources at the two sites su
Caldelas C, Weiss DJ, 2016, Zinc Homeostasis and isotopic fractionation in plants: a review, Plant and Soil, Vol: 411, Pages: 17-46, ISSN: 0032-079X
AimsRecent advances in mass spectrometry have demonstrated that higher plants discriminate stable Zn isotopes during uptake and translocation depending on environmental conditions and physiological status of the plant. Stable Zn isotopes have emerged as a promising tool to characterize the plants response to inadequate Zn supply. The aim of this review is to build a comprehensive model linking Zn homeostasis and Zn isotopic fractionation in plants and advance our current view of Zn homeostasis and interaction with other micronutrients.MethodsThe distribution of stable Zn isotopes in plants and the most likely causes of fractionation are reviewed, and the interactions with micronutrients Fe, Cu, and Ni are discussed.ResultsThe main sources of Zn fractionation in plants are i) adsorption, ii) low- and high-affinity transport phenomena, iii) speciation, iv) compartmentalization, and v) diffusion. We propose a model for Zn fractionation during uptake and radial transport in the roots, root-to-shoot transport, and remobilization.ConclusionsFuture work should concentrate on better understanding the molecular mechanisms underlying the fractionations as this will be the key to future development of this novel isotope system. A combination of stable isotopes and speciation analyses might prove a powerful tool for plant nutrition and homeostasis studies.
Zafar R, Watson JS, Weiss DJ, et al., 2016, Organic compound-mineral interactions: using flash pyrolysis to monitor the adsorption of fatty acids on calcite, Journal of Analytical and Applied Pyrolysis, Vol: 123, Pages: 184-193, ISSN: 1873-250X
Fatty acids are near ubiquitous organic compounds in living organisms in the Earth’s biosphere. Following death of an organism in the marine environment its fatty acids may survive descent to the sea bed where they can be juxtaposed with minerals. The aim of this study was to investigate the interaction of fatty acids with the common marine mineral calcite. Adsorption of tetradecanoic acid (C14) on calcite results in a sigmoidal or “s” isotherm. Flash pyrolysis experiments were conducted on samples of fatty acid adsorbed onto calcite and were compared with similar experiments on pure fatty acid and on salts of a fatty acid. Flash pyrolysis of pure tetradecanoic acid generated unsaturated and saturated hydrocarbons and a series of unsaturated and saturated low molecular weight fatty acids. Flash pyrolysis of free tetradecanoic acid salt produced saturated and unsaturated hydrocarbons, an aldehyde and a homologous series of saturated and unsaturated ketones, one of which was a symmetrical mid chain ketone (14-heptacosanone). Flash pyrolysis data from adsorbed tetradecanoic acid samples suggested that adsorption is analogous to the formation of the calcium salt of tetradecanoic acid. A key characteristic of the flash pyrolysis products of adsorbed fatty acids and fatty acid salts was the production of ketones with higher molecular weights than the starting fatty acids. Ketonisation was not observed from the flash pyrolysis of pure acid which implied the catalytic significance of the calcite mineral surface. The abundance of hydrocarbons relative to ketones in the pyrolysates negatively correlated with the proportion of fatty acids adsorbed to the surface of calcite. The ability to use flash pyrolysis to diagnose the nature of fatty acid interactions with mineral surfaces provides a valuable tool for monitoring the fate of these important lipids at the Earth’s surface as they pass into the geosphere and are subjected to diagenetic processes.
Araújo DF, Boaventura GR, Machado W, et al., 2016, Tracing of anthropogenic zinc sources in coastal environments using stable isotope composition, Chemical Geology, Vol: 449, Pages: 226-235, ISSN: 1872-6836
The use of zinc isotopes to trace anthropogenic sources in coastal areas has been tested in this study. We determined the stable isotopic composition of zinc in sediment cores, suspended particulate matter (SPM) and rocks collected at the Sepetiba Bay (southeastern Brazil), an estuarine lagoon heavily impacted by metallurgic activities. These isotopic signatures were compared with those from willemite ore, which represent the main mineral refined by the major industrial source of zinc. The aim was to test if this tracer system enables to identify sources and sinks of anthropogenic zinc and to reconstruct the temporal and spatial evolution of zinc contamination. The zinc isotopic compositions (expressed using the δ66Zn notation relative to the JMC 3-0749-L solution) showed significant variations in the sediment cores, the SPM, and willemite ore minerals, ranging between − 0.01 and + 1.15‰. Spatial and temporal analysis of sediments samples fit well in a model of mixing involving three main end-members: i) Terrestrial background (δ66ZnJMC = + 0.28 ± 0.12‰, 2σ); ii) marine detrital material (δ66ZnJMC = + 0.45 ± 0.03‰, 2σ); and iii) a major anthropogenic source associated with electroplating wastes released into the bay (δ66ZnJMC = + 0.86 ± 0.15‰, 2σ). Sediment cores collected in the mud flats showed high correlation between δ66Zn and zinc enrichment factors, suggesting good preservation of the isotopic records of natural and anthropogenic sources. The sediment core sampled from a mangrove wetland located in a zone impacted by the metallurgy presented levels of zinc up to 4% (sediment dry weight) and preserved the isotopic signatures of electroplating wastes, despite evidences that post depositional processes slightly changed the isotopic signatures in some layers from this core toward heavier δ66ZnJMC values (above + 1.0‰). A two component mixing model su
Gioia SMCL, Babinski M, Weiss DJ, et al., 2016, An isotopic study of atmospheric lead in a megacity after phasing out of leaded gasoline, Atmospheric Environment, Vol: 149, Pages: 70-83, ISSN: 1352-2310
Atmospheric lead (Pb) concentrations in São Paulo city, Brazil, remain significant, despite the fact that leaded gasoline was phased out. The use of its isotope signature allows tracing emissions to the increasing number of cars, urban construction, and industrial emissions in this densely populated area. High-precision and accurate stable isotope ratio determinations using isotope dilution thermal ionization mass spectrometry (ID-TIMS) combined with particle induced X-ray emission (PIXE) and multivariate analysis were used to identify the main sources of lead present in São Paulo atmospheric particulates. Throughout a period of sixty days, aerosol samples were collected every 12 h during the summer of 2005 at the University of São Paulo (USP) and simultaneously during one week in an industrial area (Cubatão) and in two more remote areas (São Lourenço da Serra and Juquitiba). The data suggests that aerosols from São Paulo are mainly derived from vehicular exhaust (mostly gasoline) and traffic dust resuspension, with the admixture of industrial emissions, including cement. Lead isotopic compositions (expressed as 206Pb/207Pb ratios) measured in São Paulo aerosols range from 1.1491 to 1.2527 and are similar to those determined from tunnel dust, fuels, and vehicular exhaust; therefore, those are likely to be the main lead sources in the atmosphere of São Paulo. Vehicular traffic (fuel combustion, dust from vehicular components, and road dust) remains an important source of lead in the atmosphere. The maximum concentration occurring during the summer was 0.055 μg m−3 in fine particles, which is detrimental for human health and may lead to exceedances of the Air Quality Standard for lead of 0.15 μg m−3 (3-month average) during other seasons when the dispersion of pollutants is less favourable.
Markovic T, Manzoor S, Humphreys-Williams E, et al., 2016, Experimental determination of zinc isotope fractionation in complexes with the phytosiderophore 2’-deoxymugeneic acid (DMA) and its structural analogues, and implications for plant uptake mechanisms, Environmental Science & Technology, Vol: 51, Pages: 98-107, ISSN: 0013-936X
The stable isotope signatures of zinc are increasingly used to study plant and soil processes. Complexation with phytosiderophores is a key process and understanding the controls of isotope fractionation is central to such studies. Here, we investigated isotope fractionation during complexation of Zn2+ with the phytosiderophore 2’-deoxymugeneic acid (DMA) - which we synthesised - and with three commercially-available structural analogues of DMA: EDTA, TmDTA and CyDTA. We used ion exchange chromatography to separate free and complexed zinc, and identified appropriate cation exchange resins for the individual systems. These were Chelex-100 for EDTA and CyDTA, Amberlite CG50 for TmDTA and Amberlite IR120 for DMA. With all the ligands we found preferential partitioning of isotopically heavy zinc in the complexed form, and the extent of fractionation was independent of the Zn:ligand ratio used, indicating isotopic equilibrium and that the results were not significantly affected by artefacts during separation. The fractionations (in ‰) were +0.33 ± 0.07 (1, n=3), +0.45 ± 0.02 (1, n=2), +0.62 ± 0.05 (1, n=3) and +0.30 ± 0.07 (1, n=4) for EDTA, TmDTA, CyDTA and DMA, respectively. Despite the similarity in Zn-coordinating donor groups, the fractionation factors are significantly different and extent of fractionation seems proportional to the complexation stability constant. The extent of fractionation with DMA agreed with observed fractionations in zinc uptake by paddy rice in field experiments, supporting the possible involvement of DMA in zinc uptake by rice.
Cheng A, Tyne R, Kwok YT, et al., 2016, Investigating arsenic contents in surface and drinking water by voltammetry and the method of standard additions, Journal of Chemical Education, Vol: 93, Pages: 1945-1950, ISSN: 1938-1328
Testing water samples for arsenic (As) contamination has become an important water quality issue worldwide. Arsenic usually occurs in very small concentrations and a sensitive analytical method is needed. We present here a 1-day laboratory module developed to introduce Earth Sciences and/or Chemistry student undergraduates to key aspects of this topical issue. In this practical session, students were first introduced to the worldwide problems of arsenic contamination in groundwaters as a motivation of the experimental work. This latter consisted in the quantification of As levels in surface and drinking water at the trace level (nM - ppb) using the electroanalytical technique of anodic stripping voltammetry and the method of standard addition. Results were then discussed with respect to water quality guidelines and geology. The complexity of data interpretation in this exercise can be tailored to a range of abilities and subject areas suited to the students and the course.
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