Imperial College London


Faculty of EngineeringDepartment of Earth Science & Engineering

Professor of Environmental Geochemistry



+44 (0)20 7594 6383d.weiss




2.39Royal School of MinesSouth Kensington Campus





Publication Type

190 results found

Turney J, Muxworthy AR, Sims M, Weiss D, Fraser Aet al., 2024, Quantifying the characteristics of magnetic oil-water contacts in mature hydrocarbon reservoirs and their capacity for understanding hydrocarbon remigration, Geophysical Journal International, Vol: 237, Pages: 570-587, ISSN: 0956-540X

Increasing magnetization within mature hydrocarbon reservoirs provides a new technique in identifying oil–water contacts (OWCs) in cored wells with the potential to assess yield thereby reducing the need for further exploration. Authigenic precipitation of magnetic minerals at OWCs may also help locate palaeocontacts (PCs), where structural changes to the petroleum system have caused hydrocarbon remigration. This study determines the magnetic characteristics of magnetic enhancements at OWCs and possibly PCs in silliclastic and carbonate reservoirs at the Wytch Farm oil field, Wessex Basin, UK. Increases in saturation magnetization and susceptibility are observed at the OWC in 11 of the 12 analysed cored reservoirs owing to the increased presence of magnetite and vivianite. Geochemical analysis and shallow reservoirs suggest biogenic and inorganic mineral precipitation is extensive at the OWC depending on iron, sulphur and phosphorus availability. Similar magnetic characteristics have been observed in magnetic enhancements above the OWC in numerous wells which may represent OWCs before a basin-wide easterly tilt caused hydrocarbon remigration in the Cenozoic. Multiple magnetic enhancements above the OWC in westerly onshore wells, suggest this remigration may have occurred as numerous phases.

Journal article

Eikelboom M, Wang Y, Portlock G, Gourain A, Gardner J, Bullen J, Lewtas P, Carriere M, Alvarez A, Kumar A, O'Prey S, Tolgyes T, Omanovic D, Bhowmick S, Weiss D, Salaun Pet al., 2023, Voltammetric determination of inorganic arsenic in mildly acidified (pH 4.7) groundwaters from Mexico and India, Analytica Chimica Acta, Vol: 1276, ISSN: 0003-2670

Routine monitoring of inorganic arsenic in groundwater using sensitive, reliable, easy-to-use and affordable analytical methods is integral to identifying sources, and delivering appropriate remediation solutions, to the widespread global issue of arsenic pollution. Voltammetry has many advantages over other analytical techniques, but the low electroactivity of arsenic(V) requires the use of either reducing agents or relatively strong acidic conditions, which both complicate the analytical procedures, and require more complex material handling by skilled operators. Here, we present the voltammetric determination of total inorganic arsenic in conditions of near-neutral pH using a new commercially available 25 μm diameter gold microwire (called the Gold Wirebond), which is described here for the first time. The method is based on the addition of low concentrations of permanganate (10 μM MnO4−) which fulfils two roles: (1) to ensure that all inorganic arsenic is present as arsenate by chemically oxidising arsenite to arsenate and, (2) to provide a source of manganese allowing the sensitive detection of arsenate by anodic stripping voltammetry at a gold electrode. Tests were carried out in synthetic solutions of various pH (ranging from 4.7 to 9) in presence/absence of chloride. The best response was obtained in 0.25 M chloride-containing acetate buffer resulting in analytical parameters (limit of detection of 0.28 μg L−1 for 10 s deposition time, linear range up to 20 μg L−1 and a sensitivity of 63.5 nA ppb−1. s−1) better than those obtained in acidic conditions. We used this new method to measure arsenic concentrations in contrasting groundwaters: the reducing, arsenite-rich groundwaters of India (West Bengal and Bihar regions) and the oxidising, arsenate-rich groundwaters of Mexico (Guanajuato region). Very good agreement was obtained in all groundwaters with arsenic concentrations measured by inductively coupled plasma-mass

Journal article

Turney J, Weiss D, Muxworthy AR, Fraser Aet al., 2023, Greigite formation in aqueous solutions: critical constraints into the role of iron and sulphur ratios, pH and Eh, and temperature using reaction pathway modelling, Chemical Geology, Vol: 635, Pages: 1-16, ISSN: 0009-2541

Greigite forms as an intermediate phase along the pyrite reaction pathway. Despite being considered metastable, it is observed in numerous shallow natural systems, suggesting it could be a unique proxy for diagenetic and environmental conditions. We use thermodynamic reaction pathway modelling in PHREEQC software, to understand the role of iron and sulphur ratios, pH and Eh, and temperature on the formation and retention of greigite in aqueous solutions. With newly available experimental thermodynamic properties, this work identifies the chemical boundary conditions for greigite formation in aqueous solutions. Greigite precipitation is likely favourable in anoxic and alkaline aqueous solutions at or below 25 °C. Our numerical experiments show that greigite is closer to saturation in iron-rich solutions with minor sulphur input. Greigite precipitation in strongly alkaline solutions suggest polysulfides and ferric iron-bearing minerals may be favourable reactants for its formation. Greigite precipitates at iron and sulphur concentrations that are over two orders of magnitude greater than iron sulphide-hosted natural porewaters. This disparity between model and field observations suggest microenvironments within bulk solutions may be important for greigite formation and retention. These constraints suggest greigite is more likely to form alongside pyrite in shallow, non-steady state aqueous solutions.

Journal article

Kenney JPL, Lezama-Pacheco J, Fendorf S, Alessi DS, Weiss DJet al., 2023, Uranium surface processes with sandstone and volcanic rocks in acidic and alkaline solutions, Journal of Colloid and Interface Science, Vol: 645, Pages: 715-723, ISSN: 0021-9797

Understanding the behaviour of uranium waste, for disposal purposes, is crucial due to the correlation between pH values and the disposal of distinct types of waste, with low level waste typically associated with acidic pH values, and higher and intermediate level waste commonly related to alkaline pH values. We studied the adsorption of U(VI) on sandstone and volcanic rock surfaces at pH 5.5 and 11.5 in aqueous solutions with and without bicarbonate (2 mM HCO3–) using XAS and FTIR. In the sandstone system, U(VI) adsorbs as a bidentate complex to Si at pH 5.5 without bicarbonate and as uranyl carbonate species with bicarbonate. At pH 11.5 without bicarbonate, U(VI) adsorbs as monodentate complexes to Si and precipitates as uranophane. With bicarbonate at pH 11.5, U(VI) precipitated as a Na-clarkeite mineral or remained as a uranyl carbonate surface species. In the volcanic rock system, U(VI) adsorbed to Si as an outer sphere complex at pH 5.5, regardless of the presence of bicarbonate. At pH 11.5 without bicarbonate, U(VI) adsorbed as a monodentate complex to one Si atom and precipitated as a Na-clarkeite mineral. With bicarbonate at pH 11.5, U(VI) sorbed as a bidentate carbonate complex to one Si atom. These results provide insight into the behaviour of U(VI) in heterogeneous, real-world systems related to the disposal of radioactive waste.

Journal article

Schleicher NJ, Weiss DJ, 2023, Identification of atmospheric particulate matter derived from coal and biomass burning and from non-exhaust traffic emissions using zinc isotope signatures, Environmental Pollution, Vol: 329, ISSN: 0269-7491

Improving urban air quality is a global challenge. To implement successful abatement measures that reduce atmospheric particulate matter (APM) and associated metal concentrations, precise source apportionment is needed. For this, apportioning contributions from coal and biomass burning and differentiating these from non-exhaust traffic emissions in urban APM is critical. Recent studies characterising the metal isotope composition of urban APM, and potential source materials suggested that non-traditional isotope systems could prove unique fingerprinting tools. Zinc isotopes should be able to separate APM derived from uncontrolled combustion (fly ash, isotopically heavy) from non-exhaust traffic sources (tyre and brake wear, intermediate) and from controlled industrial emissions (flue gas, light). To test this hypothesis, we determined zinc isotope ratios of APM (TSP, PM2.5, PM1) in Beijing (coal combustion for residential heating) and Varanasi (biomass burning in pre-monsoon periods). In Beijing, δ66ZnLyon values of PM2.5 ranged from −0.41 to +1.01‰ in 2015 (avg = +0.25 ± 0.50‰, n = 19). Aerosols (including TSP, PM2.5 and PM1 samples) from the heating period were significantly (t-test, p < 0.001) heavier (avg = +0.90 ± 0.12‰, n = 7) than those from the non-heating period (avg = +0.14 ± 0.36‰, n = 23). Average δ66ZnLyon values of PM2.5 in Varanasi in spring 2015 were +0.82 ± 0.11‰ (n = 4). Extent and direction of isotope fractionation is in line with that expected from theoretical models and the isotope signatures observed agree with previously determined ratios of source materials. Our study links for the first time comprehensively the heavy zinc isotope compositions in APM to coal and biomass burning and shows that zinc isotope compositions of aerosols can discriminate between non-exhaust traffic and combustion sources.

Journal article

Olivelli A, Murphy K, Bridgestock L, Wilson DJ, Rijkenberg M, Middag R, Weiss D, van de Flierdt T, Rehkamper Met al., 2023, Decline of anthropogenic lead in South Atlantic Ocean surface waters from 1990 to 2011: new constraints from concentration and isotope data, Marine Pollution Bulletin, Vol: 189, Pages: 1-14, ISSN: 0025-326X

Anthropogenic emissions have severely perturbed the marine biogeochemical cycle of lead (Pb). Here, we present new Pb concentration and isotope data for surface seawater from GEOTRACES section GA02, sampled in the western South Atlantic in 2011. The South Atlantic is divided into three hydrographic zones: equatorial (0–20°S), subtropical (20–40°S), and subantarctic (40–60°S). The equatorial zone is dominated by previously deposited Pb transported by surface currents. The subtropical zone largely reflects anthropogenic Pb emissions from South America, whilst the subantarctic zone presents a mixture of South American anthropogenic Pb and natural Pb from Patagonian dust. The mean Pb concentration of 16.7 ± 3.8 pmol/kg is 34 % lower than in the 1990s, mostly driven by changes in the subtropical zone, with the fraction of natural Pb increasing from 24 % to 36 % between 1996 and 2011. Although anthropogenic Pb remains predominant, these findings demonstrate the effectiveness of policies that banned leaded gasoline.

Journal article

Codina AS, Huerta AT, Heiba HF, Bullen JC, Weiss DJ, Vilar Ret al., 2023, Functionalised polymeric materials for the removal of arsenate from contaminated water, Environmental Science: Water Research & Technology, Vol: 9, Pages: 772-780, ISSN: 2053-1419

Inorganic arsenic is a carcinogen and, in some regions, one of the biggest contaminants in drinking water. The World Health Organisation (WHO) has indicated that over 140 million people worldwide are drinking water with levels of arsenic above the recommended guideline value of 10 μg L−1. Therefore, there is a pressing need to find low-cost technologies for the removal of inorganic arsenic from water. As part of our efforts to tackle this problem, we previously developed an efficient sorbent material (ImpAs) based on a polymeric support (HypoGel) functionalised with a selective chemical receptor for arsenate (i.e. arsenic(V)). With the aim to lower the production cost of this material and improve its arsenate removal capacity, we have studied other polymeric materials as solid supports. Herein, we report the synthesis of new inexpensive sorbent materials by covalently attaching our previously reported arsenate receptor onto Merrifield and Purolite C106 polymer beads. We carried out batch and flow-through experiments with the new polymeric materials demonstrating that they have up to 60% higher arsenate removal capacities than the original functionalised HypoGel material. Furthermore, the new polymeric materials operate very well under flow-through conditions, removing over 99% of arsenate present in solutions containing low (15 μg L−1) and high (300 μg L−1) levels of arsenate. We also report on the lower production cost of the new Purolite-based material as compared to the original functionalised HypoGel polymer beads.

Journal article

Okell LC, Kwambai TK, Dhabangi A, Khairallah C, Nkosi-Gondwe T, Winskill P, Opoka R, Mousa A, Kühl M-J, Lucas TCD, Challenger JD, Idro R, Weiss DJ, Cairns M, Ter Kuile FO, Phiri K, Robberstad B, Mori ATet al., 2023, Projected health impact of post-discharge malaria chemoprevention among children with severe malarial anaemia in Africa, Nature Communications, Vol: 14, Pages: 1-10, ISSN: 2041-1723

Children recovering from severe malarial anaemia (SMA) remain at high risk of readmission and death after discharge from hospital. However, a recent trial found that post-discharge malaria chemoprevention (PDMC) with dihydroartemisinin-piperaquine reduces this risk. We developed a mathematical model describing the daily incidence of uncomplicated and severe malaria requiring readmission among 0–5-year old children after hospitalised SMA. We fitted the model to a multicentre clinical PDMC trial using Bayesian methods and modelled the potential impact of PDMC across malaria-endemic African countries. In the 20 highest-burden countries, we estimate that only 2–5 children need to be given PDMC to prevent one hospitalised malaria episode, and less than 100 to prevent one death. If all hospitalised SMA cases access PDMC in moderate-to-high transmission areas, 38,600 (range 16,900–88,400) malaria-associated readmissions could be prevented annually, depending on access to hospital care. We estimate that recurrent SMA post-discharge constitutes 19% of all SMA episodes in moderate-to-high transmission settings.

Journal article

Bullen JC, Landa-Cansigno O, Weiss DJ, 2023, Teaching Adsorption Chemistry by Constructing Surface Complexation Models (SCM) in PHREEQC, Journal of Chemical Education, ISSN: 0021-9584

Adsorption modeling is important to understand and predict both how water contamination occurs, and how it might be prevented or remediated. Surface complexation models (SCM) help us understand adsorption under changing environmental conditions. This computational class introduces undergraduate students to adsorption and surface complexation and provides a foundation in geochemical modeling using freely available PHREEQC software from USGS. Practical capabilities are developed by (1) performing aqueous speciation reactions, (2) determining the surface charge of suspended metal oxide/mineral powders using potentiometric titration data, (3) calculating pH adsorption edges and adsorption isotherms, (4) applying PHREEQC to answer possible water treatment scenarios, and (5) using Visual Basic coding with loops to generate large data sets. This class is contextualized around arsenic contaminated groundwater and its treatment using iron oxide minerals, with hundreds of millions at risk worldwide (e.g., India, Bangladesh, Mexico). Participants report increases in their understanding of adsorption chemistry and confidence in the application of geochemical models to perform predictive SCM calculations.

Journal article

Bullen JC, Lapinee C, Miller LA, Bullough F, Berry AJ, Najorka J, Cibin G, Vilar R, Weiss DJet al., 2022, Spectroscopic (XAS, FTIR) investigations into arsenic adsorption onto TiO2/Fe2O3 composites: evaluation of the surface complexes, speciation and precipitation predicted by modelling, Results in Surfaces and Interfaces, Vol: 9, ISSN: 2666-8459

Over 50 million people in South Asia are exposed to groundwater contaminated with carcinogenic arsenic(III). Photocatalyst-adsorbent composite materials are popularly developed for removing arsenic in a single-step water treatment. Here, As(III) is oxidised to As(V), which is subsequently removed via adsorption. We previously developed a component additive surface complexation model (CA-SCM) to predict the speciation of arsenic adsorbed onto TiO2/Fe2O3 under different environmental conditions, using surface complexes taken from studies of single-phase minerals. In this work, we critically evaluate this approach, using experimental observations of the surface structures of arsenic adsorbed onto TiO2/Fe2O3. Extended X-ray absorption fine structure spectroscopy (EXAFS) indicates significant As(III) surface precipitation, and the possible formation of tridentate 3C complexes. EXAFS was unable to identify As binding modes for TiO2 and Fe2O3 surface complexes simultaneously, highlighting the challenge of analysing composite surfaces. FTIR and zeta potential analysis indicate that As(III)-Fe2O3 surface complexes are protonated at neutral pH, whilst As(III)-TiO2, As(V)-Fe2O3 and As(V)-TiO2 surface complexes are negatively charged. Our study confirms the speciation predicted by CA-SCM, particularly As(III) surface precipitation, but also introduces the possibility of tridentate As(III) at acidic pH. This study highlights how experiment and modelling can be combined to assess surface complexation on composite surfaces.

Journal article

Peers De Nieuwburgh C, Watson J, Weiss D, Sephton MAet al., 2022, Environmental screening of water associated with shale gas extraction by fluorescence excitation emission matrix, Environmental Science: Water Research & Technology, Vol: 8, Pages: 2196-2206, ISSN: 2053-1400

The shale revolution has involved the production of oil and gas from shale reservoirs enabled by modern techniques such as horizontal drilling and hydraulic fracturing. Large volumes of water-based fluids are required for hydraulic fracturing, some of which return to the surface as produced water. The recycling and effective disposal of produced water reduces water demand and avoids environmental impacts, respectively. Yet risks of water quality degradation surrounding shale oil and gas extraction operations remain highest during produced water treatment and disposal. Risk assessments related to produced water use are difficult to generate due to a lack of standard monitoring methods to characterise produced water and a lack of baseline monitoring data of surrounding water resources. We have performed a study on laboratory shale leachates using fluorescence Excitation Emission Matrix (EEM) spectra and have demonstrated the utility of this spectroscopic technique as a standard method for environmental screening in which the chemical constitution of produced water is monitored. EEM spectra recorded in this work show that dissolved organic matter (DOM) in laboratory shale leachates contains chromophores such as humic acid-like and soluble microbial-like material. Short emission wavelengths (<380 nm) EEM spectra may indicate anthropogenic contamination incidents in future operations, especially as they correspond to fluorescence signatures of some injection fluid additives. Our simple fluorescence method requires little sample preparation and could be coupled with remote sensors for real time, in-situ monitoring of contamination incidents.

Journal article

Liu F, Gledhill M, Tan Q-G, Zhu K, Zhang Q, Salaun P, Tagliabue A, Zhang Y, Weiss D, Achterberg EP, Korchev Yet al., 2022, Phycosphere pH of unicellular nano- and micro- phytoplankton cells and consequences for iron speciation, The ISME Journal: multidisciplinary journal of microbial ecology, Vol: 16, Pages: 2329-2336, ISSN: 1751-7362

Surface ocean pH is declining due to anthropogenic atmospheric CO2 uptake with a global decline of ~0.3 possible by 2100. Extracellular pH influences a range of biological processes, including nutrient uptake, calcification and silicification. However, there are poor constraints on how pH levels in the extracellular microenvironment surrounding phytoplankton cells (the phycosphere) differ from bulk seawater. This adds uncertainty to biological impacts of environmental change. Furthermore, previous modelling work suggests that phycosphere pH of small cells is close to bulk seawater, and this has not been experimentally verified. Here we observe under 140 μmol photons·m−2·s−1 the phycosphere pH of Chlamydomonas concordia (5 µm diameter), Emiliania huxleyi (5 µm), Coscinodiscus radiatus (50 µm) and C. wailesii (100 µm) are 0.11 ± 0.07, 0.20 ± 0.09, 0.41 ± 0.04 and 0.15 ± 0.20 (mean ± SD) higher than bulk seawater (pH 8.00), respectively. Thickness of the pH boundary layer of C. wailesii increases from 18 ± 4 to 122 ± 17 µm when bulk seawater pH decreases from 8.00 to 7.78. Phycosphere pH is regulated by photosynthesis and extracellular enzymatic transformation of bicarbonate, as well as being influenced by light intensity and seawater pH and buffering capacity. The pH change alters Fe speciation in the phycosphere, and hence Fe availability to phytoplankton is likely better predicted by the phycosphere, rather than bulk seawater. Overall, the precise quantification of chemical conditions in the phycosphere is crucial for assessing the sensitivity of marine phytoplankton to ongoing ocean acidification and Fe limitation in surface oceans.

Journal article

Barreira J, Araujo DF, Soares R, Sanders CJ, Weiss DJ, Machado Wet al., 2022, Didactic Strategy for the Teaching of Isotope Mixing Models for Stable Isotopes Relevant to Biogeochemistry Based on the Analogy with Color Composition, JOURNAL OF CHEMICAL EDUCATION, ISSN: 0021-9584

Journal article

Northover G, Mao Y, Blasco S, Vilar R, Garcia-Espana E, Rocco C, Hanif M, Weiss Det al., 2022, Synergistic use of siderophores and weak organic ligands during zinc transport in the rhizosphere controlled by pH and ion strength gradients, Scientific Reports, Vol: 12, ISSN: 2045-2322

Citrate (Cit) and Deferoxamine B (DFOB) are two important organic ligands coexisting in soils with distinct different affinities for metal ions. It has been theorized that siderophores and weak organic ligands play a synergistic role during the transport of micronutrients in the rhizosphere, but the geochemical controls of this process remain unknown. Here we test the hypothesis that gradients in pH and ion strength regulate and enable the cooperation. To this end, first we use potentiometric titrations to identify the dominant Zn(II)–Cit and Zn(II)–DFOB complexes and to determine their ionic strength dependent stability constants between 0 and 1 mol dm−3. We parametrise the Extended Debye-Hückel (EDH) equation and determine accurate intrinsic association constants (logβ0) for the formation of the complexes present. The speciation model developed confirms the presence of [Zn(Cit)]−, [Zn(HCit)], [Zn2(Cit)2(OH)2]4−, and [Zn(Cit)2]4−, with [Zn(Cit)]− and [Zn2(Cit)2(OH)2]4− the dominant species in the pH range relevant to rhizosphere. We propose the existence of a new [Zn(Cit)(OH)3]4− complex above pH 10. We also verify the existence of two hexadentate Zn(II)–DFOB species, i.e., [Zn(DFOB)]− and [Zn(HDFOB)], and of one tetradentate species [Zn(H2DFOB)]+. Second, we identify the pH and ionic strength dependent ligand exchange points (LEP) of Zn with citrate and DFOB and the stability windows for Zn(II)–Cit and Zn(II)–DFOB complexes in NaCl and rice soil solutions. We find that the LEPs fall within the pH and ionic strength gradients expected in rhizospheres and that the stability windows for Zn(II)–citrate and Zn(II)–DFOB, i.e., low and high affinity ligands, can be distinctly set off. This suggests that pH and ion strength gradients allow for Zn(II) complexes with citrate and DFOB to dominate in different parts of the rhizosphere and this explains why mixtures of low and h

Journal article

Kirby M, Weiss DJ, 2022, A pilot study on the effect of desferrioxamine B on uranium VI precipitation and dissolution in pH 11.5, 0.1 M NaCl solutions, Journal of Radioanalytical and Nuclear Chemistry: an International Journal dealing with all Aspects�and Applications of Nuclear Chemistry, Vol: 331, Pages: 1779-1784, ISSN: 0236-5731

A pilot study investigating the possible role of desferrioxamine B (DFOB) to prevent UVI precipitation in alkaline NaCl solutions was carried out. Desferrioxamine B is a hydroxamate siderophore occurring naturally in the environment. The siderophore can possibly mobilize UVI from a wide range of sources such as mine tailings, contaminated land and radioactive waste storage and disposal facilities. The results from a series of batch experiments covering a wide range of naturally occurring concentrations over relevant time scales (3 days and 2 months) show that DFOB can quantitatively prevent UVI precipitation as ≥ 0.2 μm precipitates when 130 µM and 420 µM of the DFOB is present in solution. The impact is minimized as its concentration decrease to below 10 µM, suggesting these ligands will have a less mobilizing effect on uranium from a geological disposal facility if present in its VI oxidation state.

Journal article

Bullen JC, Heiba HF, Kafizas A, Weiss DJet al., 2022, Parasitic light absorption, rate laws and heterojunctions in the photocatalytic oxidation of arsenic(III) using composite TiO2/Fe2O3, Chemistry: A European Journal, Vol: 28, ISSN: 0947-6539

Composite photocatalyst-adsorbents such as TiO2/Fe2O3 are promising materials for the one-step treatment of arsenite contaminated water. However, no previous study has investigated how coupling TiO2 with Fe2O3 influences the photocatalytic oxidation of arsenic(III). Herein, we develop new hybrid experiment/modelling approaches to study light absorption, charge carrier behaviour and changes in the rate law of the TiO2/Fe2O3 system, using UV-Vis spectroscopy, transient absorption spectroscopy (TAS), and kinetic analysis. Whilst coupling TiO2 with Fe2O3 improves total arsenic removal by adsorption, oxidation rates significantly decrease (up to a factor of 60), primarily due to the parasitic absorption of light by Fe2O3 (88% of photons at 368 nm) and secondly due to changes in the rate law from disguised zero-order kinetics to first-order kinetics. Charge transfer across this TiO2-Fe2O3 heterojunction is not observed. Our study demonstrates the first application of a multi-adsorbate surface complexation model (SCM) towards describing As(III) oxidation kinetics which, unlike Langmuir-Hinshelwood kinetics, includes the competitive adsorption of As(V), and we further highlight the importance of parasitic light absorption and catalyst fouling when designing heterogeneous photocatalysts for As(III) remediation.

Journal article

Heiba HF, Bullen JC, Kafizas A, Petit C, Skinner SJ, Weiss Det al., 2022, The determination of oxidation rates and quantum yields during the photocatalytic oxidation of As(III) over TiO2, Journal of Photochemistry and Photobiology A: Chemistry, Vol: 424, Pages: 113628-113628, ISSN: 1010-6030

The determination of reaction rates for the photocatalytic oxidation (PCO) of arsenite (As(III)) using TiO2 under UV radiation is challenging due to the numerous experimental processes. This includes chemical processes running simultaneously with PCO (e.g. adsorption of arsenic species, direct UV photolysis of As(III)) and the analytical approach used (e.g. whether As(III) or As(V) are measured and used in the calculation of the PCO rate). The various experimental approaches used to date have led to oxidation rates and rate constants which vary by orders of magnitude and contradicting information on rate laws. Here we present the results of a critical examination of possible controls affecting the experimental determination of PCO rates. First, we demonstrate that the choice of analytical technique is not critical, provided that the rate constants are calculated based on the depletion of As(III) after correction of the directly adsorbed As(III). Second, we show the correction of the directly adsorbed As(III) at each time interval is best done by running two parallel experiments (one under UV and the other in dark) instead of running sequential experiment (i.e. running the experiment in the dark then turning on the UV lamp). These findings are supported by XPS analysis of the oxidation state of TiO2-sorbed As. Third, we demonstrate that photolysis by the light source itself, as well as the chemical composition of the solution (i.e. the effect of HEPES and the ionic strength), can significantly increase As(III) oxidation rates and need to be corrected. Finally, to determine the quantum yield of As(III) oxidation, we measured the photon absorption by the TiO2 photocatalyst. Our results showed that the quantum yield (Ø) for this oxidation reaction was low, and in the region of 0.1 to 0.2 %.

Journal article

Weiss D, Northover G, Hanif M, García-España E, Vilar R, Arnold T, Markovic T, Wissuwa M, Delgado Eet al., 2021, Isotope fractionation of zinc in the paddy rice soil-water environment and the role of 2’deoxymugineic acid (DMA) as zincophore under Zn limiting conditions, Chemical Geology, Vol: 577, Pages: 1-21, ISSN: 0009-2541

Non-traditional stable isotope systems are increasingly used to study micronutrient cycling and acquisition in terrestrial ecosystems. We previously proposed for zinc (Zn) a conceptual model linking observed isotope signatures and fractionations to biogeochemical processes occurring in the rice soil environment and we suggested that 2’deoxymugineic acid (DMA) could play an important role for rice during the acquisition of Zn when grown under Zn limiting conditions. This proposition was sustained by the extent and direction of isotope fractionation observed during the complexation of Zn with DMA synthesised in our laboratory. Here we report a new set of experimental data from field and laboratory studies designed to further elucidate the mechanisms controlling Zn isotope fractionation in the rice rhizosphere and the role of DMA. First, we present acidity (pKa) and complexation (logK) constants for DMA with H+ and Zn2+, respectively, using synthetic 2’deoxymugineic acid and show that they are significantly different from previously published data using isolates from plants. Our new set of thermodynamic data allows for a more accurate calculation of the formation of ZnDMA complexes over pH ranges typically found in the rhizosphere of flooded lowland rice soils and in rice plant compartments (xylem, phloem). We show that at pH > 6.5, Zn is fully complexed by DMA and at pH <4.5 fully dissociated. This has important implications, i.e. that in alkaline paddy soils, DMA can strip Zn from soil solids (organic and inorganic) and that ZnDMA complexes are stable at the root interface if the pH is alkaline and in the phloem and xylem of the rice shoot. Second, we present a new set of Zn isotope data in rice grown in alkaline soils with low Zn availability with and without Zn addition. We used two genotypes not tested to date, i.e. A69–1, tolerant to low Zn supply, and IR26, sensitive to low Zn supply. We confirm previous findings that, in contrast to obse

Journal article

Northover G, Mao Y, Ahmed H, Blasco S, Vilar R, Garcia-Espana E, Weiss Det al., 2021, Effect of salinity on the zinc(II) binding efficiency of siderophore functional groups and implications for salinity tolerance mechanisms in barley, Scientific Reports, Vol: 11, Pages: 1-12, ISSN: 2045-2322

Bacteria, fungi and grasses use siderophores to access micronutrients. Hence, the metal binding efficiency of siderophores is directly related to ecosystem productivity. Salinization of natural solutions, linked to climate change induced sea level rise and changing precipitation patterns, is a serious ecological threat. In this study, we investigate the impact of salinization on the zinc(II) binding efficiency of the major siderophore functional groups, namely the catecholate (for bacterial siderophores), α-hydroxycarboxylate (for plant siderophores; phytosiderophores) and hydroxamate (for fungal siderophores) bidentate motifs. Our analysis suggests that the order of increasing susceptibility of siderophore classes to salinity in terms of their zinc(II) chelating ability is: hydroxamate < catecholate < α-hydroxycarboxylate. Based on this ordering, we predict that plant productivity is more sensitive to salinization than either bacterial or fungal productivity. Finally, we show that previously observed increases in phytosiderophore release by barley plants grown under salt stress in a medium without initial micronutrient deficiencies (i.e., no micronutrient limitations prior to salinization), are in line with the reduced zinc(II) binding efficiency of the α-hydroxycarboxylate ligand and hence important for the salinity tolerance of whole-plant zinc(II) status.

Journal article

Weiss D, Resongle E, harrison R, Dietze V, Green D, Tremper A, Ochoa Ret al., 2021, Strong evidence for the continued contribution of lead deposited during the 20th century to the atmospheric environment of today, Proceedings of the National Academy of Sciences of USA, Vol: 118, ISSN: 0027-8424

Although leaded gasoline was banned at the end of the last century, lead (Pb) remains significantly enriched in airborne particles in large cities. The remobilization of historical Pb deposited in soils from atmospheric removal has been suggested as an important source providing evidence for the hypothetical long-term persistency of lead, and possibly other pollutants, in the urban environment. Here, we present data on Pb isotopic composition in airborne particles collected in London (2014 to 2018), which provide strong support that lead deposited via gasoline combustion still contributes significantly to the lead burden in present-day London. Lead concentration and isotopic signature of airborne particles collected at a heavily trafficked site did not vary significantly over the last decade, suggesting that sources remained unchanged. Lead isotopic composition of airborne particles matches that of road dust and topsoils and can only be explained with a significant contribution (estimate of 32 ± 10 to 43 ± 9% based on a binary mixing model) of Pb from leaded gasoline. The lead isotopes furthermore suggest significant contributions from nonexhaust traffic emissions, even though isotopic signatures of anthropogenic sources are increasingly overlapping. Lead isotopic composition of airborne particles collected at building height shows a similar signature to that collected at street level, suggesting effective mixing of lead within the urban street canyon. Our results have important implications on the persistence of Pb in urban environments and suggest that atmospheric Pb reached a baseline in London that is difficult to decrease further with present policy measures.

Journal article

Wang L, Jin Y, Weiss DJ, Schleicher NJ, Wilcke W, Wu L, Guo Q, Chen J, O'Connor D, Hou Det al., 2021, Possible application of stable isotope compositions for the identification of metal sources in soil, Journal of Hazardous Materials, Vol: 407, ISSN: 0304-3894

Metals in soil are potentially harmful to humans and ecosystems. Stable isotope measurement may provide "fingerprint" information on the sources of metals. In light of the rapid progress in this emerging field, we present a state-of-the-art overview of how useful stable isotopes are in soil metal source identification. Distinct isotope signals in different sources are the key prerequisites for source apportionment. In this context, Zn and Cd isotopes are particularly helpful for the identification of combustion-related industrial sources, since high-temperature evaporation-condensation would largely fractionate the isotopes of both elements. The mass-independent fractionation of Hg isotopes during photochemical reactions allows for the identification of atmospheric sources. However, compared with traditionally used Sr and Pb isotopes for source tracking whose variations are due to the radiogenic processes, the biogeochemical low-temperature fractionation of Cr, Cu, Zn, Cd, Hg and Tl isotopes renders much uncertainty, since large intra-source variations may overlap the distinct signatures of inter-source variations (i.e., blur the source signals). Stable isotope signatures of non-metallic elements can also aid in source identification in an indirect way. In fact, the soils are often contaminated with different elements. In this case, a combination of stable isotope analysis with mineralogical or statistical approaches would provide more accurate results. Furthermore, isotope-based source identification will also be helpful for comprehending the temporal changes of metal accumulation in soil systems.

Journal article

Bullen JC, Saleesongsom S, Gallagher K, Weiss DJet al., 2021, A revised pseudo-second-order kinetic model for adsorption, sensitive to changes in adsorbate and adsorbent concentrations, Langmuir: the ACS journal of surfaces and colloids, Vol: 37, Pages: 3189-3201, ISSN: 0743-7463

The development of new adsorbent materials for the removal of toxic contaminants from drinking water is crucial toward achieving the United Nations Sustainable Development Goal 6 (clean water and sanitation). The characterization of these materials includes fitting models of adsorption kinetics to experimental data, most commonly the pseudo-second-order (PSO) model. The PSO model, however, is not sensitive to parameters such as adsorbate and adsorbent concentrations (C0 and Cs) and consequently is not able to predict changes in performance as a function of operating conditions. Furthermore, the experimental conditionality of the PSO rate constant, k2, can lead to erroneous conclusions when comparing literature results. In this study, we analyze 103 kinetic experiments from 47 literature sources to develop a relatively simple modification of the PSO rate equation, yielding . Unlike the original PSO model, this revised rate equation (rPSO) provides the first-order and zero-order dependencies upon C0 and Cs that we observe empirically. Our new model reduces the residual sum of squares by 66% when using a single rate constant to model multiple adsorption experiments with varying initial conditions. Furthermore, we demonstrate how the rPSO rate constant k’ is more appropriate for comparing literature studies, highlighting faster kinetics in the adsorption of arsenic onto alumina versus iron oxides. This revised rate equation should find applications in engineering studies, especially since the rPSO rate constant k’ does not show a counter-intuitive inverse relationship with increasing reaction rates when C0 is increased, unlike the PSO rate constant k2.

Journal article

Northover GHR, Garcia-España E, Weiss DJ, 2021, Unravelling the modus operandi of phytosiderophores during zinc uptake in rice: the importance of geochemical gradients and accurate stability constants, Journal of Experimental Botany, Vol: 72, Pages: 1517-1526, ISSN: 0022-0957

Micronutrient deficiencies threaten global food production. Attempts to biofortify crops rely on a clear understanding of micronutrient uptake processes. Zinc deficiency in rice is a serious problem. One of the pathways proposed for the transfer of zinc from soils into rice plants involves deoxymugineic acid (DMA), a phytosiderophore. The idea that phytosiderophores play a wider role in nutrition of Poaceae beyond iron is well established. However, key mechanistic details of the DMA-assisted zinc uptake pathway in rice remain uncertain. In particular, questions surround the form in which zinc from DMA is taken up [i.e. as free aqueous Zn(II) or as Zn(II)-DMA complexes] and the role of competitive behaviour of other metals with DMA. We propose that an accurate description of the effect of changes in pH, ligand concentration, and ionic strength on the stability of Zn(II)-DMA complexes in the presence of other metals in the microenvironment around root cells is critical for understanding the modus operandi of DMA during zinc uptake. To that end, we reveal the importance of geochemical changes in the microenvironment around root cells and demonstrate the effect of inaccurate stability constants on speciation models.

Journal article

Araujo DF, Ponzevera E, Weiss DJ, Knoery J, Briant N, Yepez S, Bruzac S, Sireau T, Brach-Papa Cet al., 2021, Application of Zn isotope compositions in oysters to monitor and quantify anthropogenic Zn bioaccumulation in marine environments over four decades: A "Mussel Watch Program" upgrade, ACS ES&T Water, Vol: 1, Pages: 1035-1046, ISSN: 2690-0637

The application of zinc (Zn) isotope compositions in bivalve organisms to quantify anthropogenic Zn bioaccumulation in marine biota is of great interest to environmental marine management programs such as the “Mussel Watch Program”. Field studies, however, are urgently needed to test its practical value. To this end, we investigated Zn isotope variations in the oyster Crassostrea gigas collected over four decades near the Loire estuary (France), where previous geochemical studies provided evidence for a regionally uniform but temporally variable metal contamination. We show that the Zn temporal isotope profile of oysters matches that of the sedimentary records with an isotope offset of approximately +0.5–0.7‰, tentatively attributed to compromised estuarine processes and trophic transfer. A Zn isotope model for quantifying anthropogenic Zn bioaccumulation suggests an overall decrease in anthropogenic estuarine Zn levels over the past 40 years. This first successful application of Zn isotope ratios in a bivalve species to quantify anthropogenic Zn bioaccumulation confirms their utility for supporting environmental management strategies in marine biomonitoring programs.

Journal article

Bullen J, Kenney J, Fearn S, Kafizas A, Skinner S, Weiss Det 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, Vol: 580, Pages: 834-849, 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.

Journal article

Bullen J, Lapinee C, Salaün P, Vilar R, Weiss Det 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.

Journal article

Kirby M, Sonnenberg JL, Watson JS, Weiss Det al., 2020, Prevention of UVI precipitation in alkaline aqueous solutions by the siderophore desferrioxamine B, Publisher: American Chemical Society (ACS)

In alkaline and saline solutions, uranium VI (UVI) forms uranyl salts, limiting its mobility in leachates released from nuclear waste repositories into groundwater. However, recent experimental and computational work suggested that natural organic molecules widely present in groundwater such as siderophores could potentially prevent solid precipitation because of the formation of stable UVI-siderophore complexes. It is important we assess the impact of siderophores on aqueous UVI chemistry as they could mobilise UVI from contaminated land and radioactive waste storage and disposal sites. Here we test this hypothesis by combining for the first time experimental studies on uranium precipitation in alkaline pH in the presence of desferrioxamine B (DFOB) and electron structure method calculation of uranyl – hydroxamate complexes to assess their stability. Stirred batch experiments containing 0 to 420 µM DFOB, 42 µM UVI and 0.1 M NaCl were conducted at pH 11.5. DFT was employed to explore the relative stability of different UVI-hydroxamate complexes, representative of the local binding mode of DFOB. During the stirred batch experiments, 5%, 11-12%, 41-53%, 95-96% and 100% of UVI passes through the filter membranes (0.2-1 µm pore diameter) after 24 hours when 0, 4.2, 42, 130 and 420 µM DFOB was added to solution. The DFT results suggest one hydroxamate functional group is most likely to complex with UVI with ∆rG calculated as +3 kJ/mol and -9 kJ/mol for [UO2(OH)3(Lmono)]2- and [UO2(OH)2(L)]- respectively. Conversion of the experimentally derived log β (-1.2 ± 0.3) through the equation ∆rG = -2.303RTlogβ provides ∆rG of +7 kJ/mol, similar to the ∆rG of these two complexes. The results of our study confirm that UVI precipitation could be hindered by the formation of a DFOB complex with UVI complexation through a single hydroxamate functional group as a likely mechanism. These results highlight the mobilising effect siderophores

Working paper

De Vleeschouwer F, Baron S, Cloy JM, Enrico M, Ettler V, Fagel N, Kempter H, Kylander M, Li C, Longman J, Martinez-Cortizas A, Marx S, Mattielli N, Mighall T, Nieminen TM, Piotrowska N, Pontevedra-Pombal X, Pratte S, Renson V, Shotyk W, Shuttleworth E, Sikorski J, Stromsoe N, Talbot J, von Scheffer C, Weiss D, Zaccone C, Le Roux Get 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, Vol: 737, 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.

Journal article

Liu F, Tan Q-G, Weiss D, Crémazy A, Fortin C, Campbell PGCet al., 2020, Unravelling metal speciation in the microenvironment surrounding phytoplankton cells to improve predictions of metal bioavailability., Environmental Science and Technology (Washington), Vol: 54, Pages: 8177-8185, 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.

Journal article

Schleicher NJ, Dong S, Packman H, Little SH, Ochoa Gonzalez R, Najorka J, Sun Y, Weiss DJet al., 2020, A global assessment of copper, zinc, and lead isotopes in mineral dust sources and aerosols, Frontiers in Earth Science, Vol: 8, Pages: 1-20, ISSN: 2296-6463

The stable isotope compositions of Cu and Zn in major geochemical reservoirs are increasingly studied with the aim to develop these isotope systems as tools to investigate the global biogeochemical cycles of these trace metals. The objectives of the present study were (i) to expand the range of Cu, Zn, and Pb isotope compositions of mineral dust by analyzing samples from major mineral dust sources in Asia and Africa (Chinese Loess Plateau, Chinese deserts, Thar desert, Sahel region) and (ii) to assess the potential impact of human activities on the isotope composition of aerosols by synthesizing published Cu and Zn isotope compositions in aerosols and natural and anthropogenic sources. For the newly analyzed mineral dust areas in Asia and Africa, δ65CuNIST−976 values range from −0.54 to +0.52‰, δ66ZnJMC−Lyon values from −0.07 to +0.57‰, and 206Pb/204Pb values from 18.522 to 19.696. We find a significant geographic control with samples from the Thar Desert having the heaviest isotopic compositions (δ65CuNIST−976 = +0.48 ± 0.06‰, δ66ZnJMC−Lyon = +0.49 ± 0.11‰) and samples from the Sahel and the Badain Jaran desert having the lightest Zn isotope composition (δ66ZnJMC−Lyon = +0.19 ± 0.15‰ and +0.07 ± 0.07‰, respectively). We find important variations in the isotope signatures between particle size fractions with heavier isotopic compositions in the smallest and largest particle size fractions and lighter isotopic compositions in the mid particle size fractions. Associations with the mineralogical composition are less clear. Newly analyzed aerosol samples for Beijing and Xi'an show δ65CuNIST−976 values of +0.29 ± 0.19‰ and +0.16 ± 0.04‰, δ66ZnJMC−Lyon values of −0.36 ± 0.04‰ and +0.02 ± 0.06‰, and 206Pb/204Pb values of 18.129 ± 0.003 and 18

Journal article

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