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The efficient separation of metals from ores and secondary sources such as electronic waste is necessary to realising circularity in metal supply. Precipitation processes are increasingly popular and are reliant on designing and understanding chemical recognition to achieve selectivity. Here we show that a simple tertiary diamide precipitates gold selectively from aqueous acidic solutions, including from aqua regia solutions of electronic waste. The X-ray crystal structure of the precipitate displays an infinite chain of diamide cations interleaved with tetrachloridoaurate. Gold is released from the precipitate on contact with water, enabling ligand recycling. The diamide is highly selective, with its addition to 29 metals in 2 M HCl resulting in 70% gold uptake and minimal removal of other metals. At 6 M HCl, complete collection of gold, iron, tin, and platinum occurs, demonstrating that adaptable selective metal precipitation is controlled by just one variable. This discovery could be exploited in metal refining and recycling processes due to its tuneable selectivity under different leaching conditions, the avoidance of organic solvents inherent to biphasic extraction, and the straightforward recycling of the precipitant., The separation of metals from electronic waste is an enduring technological and societal challenge, and new metal extraction, refining and recycling solutions are needed. Here the authors report a recyclable and tuneable chemical reagent that separates valuable metals such as gold by direct and selective precipitation from various acidic, mixed-metal solutions of relevance to extraction and recycling industries.

Naturally occurring rare earth element (REE) bearing carbonate minerals contain different REEs, yet efforts to synthesize and understand their formation mechanisms have hitherto used single REE end-member experiments. In synthesising a mixed Lasingle bondNd carbonate, we document how the presence of two REEs affects the overall crystallisation process. We find that the mixed REE carbonate has a broadly similar crystallisation pathway as its end-members but with key differences. The process begins with the precipitation of amorphous spherical nanoparticles which mature into macrocrystals via an intermediary polymorphous phase. The resulting phase is identified as lanthanite, a naturally occurring REE carbonate mineral. The mixed carbonate has unit cell parameters and phase transition times in between that of its La and Nd end-members. Unlike the end-members, the crystallisation process of mixed REE carbonates has a consistent two-stage transition process between the nanoparticulate and the final phase. They also have a distinct and homogeneous morphology compared to their end-members. These results highlight the importance of considering multiple REEs simultaneously when studying the precipitation mechanisms of REE carbonates.

Subsurface storage of hydrogen, e.g. in depleted oil and gas fields (DOGF), is suggested as a means to overcome imbalances between supply and demand in the renewable energy sector. However, hydrogen is an electron donor for subsurface microbial processes, which may have important implications for hydrogen recovery, gas injectivity and corrosion. Here, we review the controls on the three major hydrogen consuming processes in the subsurface, methanogenesis, homoacetogenesis, and sulfate reduction, as a basis to estimate the risk for microbial growth in geological hydrogen storage. Evaluating our data on 42 DOGF showed that five of the fields may be considered sterile with respect to hydrogen-consuming microorganisms due to temperatures >122 °C. Only six DOGF can sustain all of the hydrogen consuming processes, due to either temperature, salinity or pressure constraints in the remaining fields. We calculated a potential microbial growth in the order of 1–17*107 cells ml−1 for DOGF with favorable conditions for microbial growth, reached after 0.1–19 days for growing cells and 0.2–6.6 years for resting cells. The associated hydrogen consumption is negligible to small (

Diversity, at every step along the scientific path, drives innovative research. Scientific societies, like the Geochemical Society (GS) and the European Association of Geochemistry (EAG), have a significant influence on which innovators are celebrated. Such choices have the consequence of shaping the future of research, and so are responsible for the evolution of our discipline and its relationship to the global community. These professional bodies are uniquely positioned to define and promote the success of all scientists, including those from under-represented groups, through proactive advocacy, inclusive mentorship, awards, and leadership. At present, the only data available to examine the distribution of under-represented groups between memberships, awardees leadership are those of gender. To assess gender diversity in the geochemistry and cosmochemistry community, we thus introspectively review available records of GS and EAG membership through Goldschmidt Conference attendees, awardees, leadership, and editorial boards. This work identifies areas for growth and begins a dialogue about how the society and its members can work together to better reflect and progress our community. Our examination of the record spanning the last decade demonstrates that leadership positions, awards, and honors have continued to be disproportionately given to white men, to the exclusion of women. The GS and EAG have recently taken positive steps towards becoming more inclusive; however, much more work is needed. In order for both communities to become diverse, equitable and inclusive, where all scientists flourish, we offer suggestions for swift steps that the GS and EAG and their members can pursue. The suggested structural improvements will require ongoing analysis and reforms, which must be shared by all of us, to create a sustainable legacy that we can be proud of.

An important gap in the management of land erosion in mining-affected areas is the understanding of the entire sediment routing system and the links between sources and storage at the catchment scale. In this study, we examine sediment delivery and its seasonality in the nickel mining-affected Santa Cruz and Pamalabawan catchments, in the Philippines. We monitored discharge, suspended sediment concentrations and suspended sediment loads across 13 sub-catchments with contrasting degrees of mining influence from June 2018 to July 2019. First, we show the importance of the size of the area that has been physically disturbed within our sub-catchments, with as little as 10-22% of relative disturbance area being enough to generate fourfold to eightfold increase in the sediment yield relative to less disturbed and pristine areas. We found that sub-catchments with >10% disturbance exhibit the highest sediment yields (15.5 ± 44.7 t km-2 d-1) compared with sub-catchments with

This study provides a novel insight into the degradation of sediment organic matter (SOM) regulated by algae-derived organic matter (AOM) based on priming effect. We tracked the dynamics of SOM mineralization products and pathways, together with priming effects (PE) using the compound-specific stable isotope (δ13C) technique following addition of low- and high-density algal debris in sediments. We found that algal debris increased the total carbon oxidation rate, and resulted in denitrification and methanogenesis-dominated SOM mineralization. While iron reduction and sulphate reduction played important roles in the early period of algal accumulation. Total carbon oxidation rate and anaerobic rates (Ranaerobic) were higher in the amended treatments compared with that in the control. Analysis indicated that algal debris had a positive PE on SOM mineralization, which caused an intensified mineralization in the initial phase with over 80% of dissolved inorganic carbon deriving from SOM degradation. Total carbon oxidation rate of SOM deduced from priming effect (RTCOR-PE) was similar to Ranaerobic, further indicating SOM mineralization was a critical source of the end products. These findings deviate the causal focus from the decomposition of AOM, and confirm the accumulation of AOM as the facilitator of SOM mineralization. Our study offers empirical evidences to advance the traditional view on the effect of AOM on SOM mineralization.

Sea cucumber aquaculture is increasing in extent and importance throughout the Indo-Pacific region, supplying a luxury seafood market in Asia. In this context, the grow-out of hatchery-bred juveniles in community-farmed pens is proving to be a viable model, providing increased income security and alternative livelihood options to resource-limited communities. Here, we report a study of the impacts of such sea cucumber farming on the growth of seagrass (a favourable habitat for the animals) at a village-scale aquaculture site in southwest Madagascar. Using experiments, we found that the presence of the hatchery-bred sea cucumberHolothuria scabra(sandfish), at stocking densities of 300 g m-2(similar to the density used in the farmed pens, but relatively high for natural populations), resulted in a large (~30%), statistically significant increase in the leaf extension rate of the locally dominant seagrass speciesThalassia hemprichii. However, the other dominant seagrass species,Cymodocea serrulata, did not significantly change its leaf extension rate in the presence ofH. scabra. Since seagrass is a globally important coastal habitat, supporting high biodiversity, carbon sequestration, shoreline stability and nursery grounds for commercial and small-scale fisheries, the positive effect ofH. scabrafarming on the growth rate of at least one dominant seagrass species implies potential important ecological co-benefits. These co-benefits ofH. scabrafarming are likely to be relevant across the tropical Indo-Pacific coastlines, where this species is cultured.

The recycling of metals from end-of-life secondary sources such as electronic waste remains a significant environmental and technological challenge currently detrimental to the development of circular economies. The complex nature of electronic waste, containing a myriad of different elemental metals, means that sophisticated yet simple separation methods need to be developed in order to recycle these valuable and often critical metal resources. In this work simple primary, secondary, and tertiary amides are appraised as reagents that selectively transport gold from aqueous to organic phases in a solvent extraction experiment. While the strength of extraction of gold from single metal solutions is ordered 3o>2o>1o, the 3o and 2o amides are ineffective at gold transport from mixed-metal solutions of concentrations representative of smartphones due to the formation of a third, dense phase. Increasing the polarity of the organic phase can negate third phase formation but at the expense of selectivity. The identities of the species that reside in the organic and third phases have been studied by a combination of slope analysis, mass spectrometry, NMR spectroscopy, and computational methods. These techniques show that protonation of the amide L occurs at the oxygen atom, resulting in the protonated dimer HL2+ which acts as a receptor for AuCl4− to form dynamic supramolecular aggregates in the organic phase. The characterization of a tin complex in the third phase by X-ray crystallography supports these conclusions and furthermore, suggests the preference for the chelation of the proton by two amide molecules instead of the transport of hydronium into the organic phase and its subsequent use as structural template.

Zn isotope is a useful tool for tracing biogeochemical processes as zinc plays important roles in the biogeochemistry of natural systems. However, the Zn isotope composition in the lake ecosystems has not been well characterized. In order to resolve this problem, we investigate the Zn isotope compositions of suspended particulate matter (SPM) and biological samples collected from the Aha Lake and Hongfeng Lake, and their tributaries in summer and winter, aiming to explore the potential of this novel isotope system as a proxy for biogeochemical processes in aqueous environments. Concentration of dissolved Zn ranges from 0.65 to 5.06 μg/L and 0.74 to 12.04 μg/L for Aha Lake and Hongfeng Lake, respectively, while Zn (SPM) ranges from 0.18 to 0.70 mg/g and 0.24 to 0.75 mg/g for Aha Lake and Hongfeng Lake, respectively. The Zn isotope composition in SPM from Aha Lake and its main tributaries ranges from -0.18‰ to 0.27‰ and -0.17‰ to 0.46‰, respectively, and it varies from -0.29‰ to 0.26‰ and -0.04‰ to 0.48‰, respectively in Hongfeng Lake and its main tributaries, displaying a wider range in tributaries than lakes. These results imply that Zn isotope compositions are mainly affected by tributaries inputting into Aha Lake, while adsorption process by algae is the major factor for the Zn isotope composition in Hongfeng Lake, and ZnS precipitation leads to the light Zn isotope composition of SPM in summer. These data and results provide the basic information of the Zn isotope for the lake ecosystem, and promote the application of Zn isotope in biogeochemistry.

Cynara cardunculus L. is a multipurpose crop, characterized by high production of biomass suitable for energy purposes and green chemistry. Taking advantage of its already demonstrated ability to grow in polluted environments that characterize many world marginal lands, the aim of this work was to investigate the response of different cardoon genotypes to exposure to cadmium (Cd) and arsenic (As) pollution, in order to use this crop for rehabilitation of contaminated sites and its biomass for energy production. In this study, seeds of two wild cardoon accessions harvested in rural and industrial Sicilian areas and of a selected line of domestic cardoon were used, and the grown plants were spiked with As and Cd, alone or in combination, at two different concentrations (500 and 2000 μM) and monitored for 45 days. The growth parameters showed that all the plants survived until the end of experiment, with growth stimulation in the presence of low concentrations of As and Cd, relative to metal-free controls. Biomass production was mostly allocated in the roots in As treatment and in the shoots in Cd treatment. Cd EXAFS analysis showed that tolerance to high concentrations of both metals was likely linked to complexation of Cd with oxygen-containing ligands, possibly organic acids, in both root and leaf biomass with differences in behaviour among genotypes. Under As+Cd contamination, the ability of the plants to translocate As to aboveground system increased also showing that, for both metal(loid)s, there were significant differences between genotypes studied. Moreover, the results showed that Cynara cardunculus var. sylvestris collected in an industrial area is the genotype that, among those studied, had the best phytoextraction capability for each metal(loid).

Progressive reforms and community kindness are encouraged; terminology common among DEI discussions is explored here.

Zero carbon energy generation from renewable sources can reduce climate change by mitigating carbon emissions. A major challenge of renewable energy generation is the imbalance between supply and demand. Subsurface hydrogen storage in porous media is suggested as a large-scale and economic means to overcome these energy imbalances. However, hydrogen is an electron donor for many subsurface microbial processes which may have important implications for hydrogen recovery, gas injectivity and corrosion.We reviewed the state-of-the-art literature on the controls on the three major hydrogen-consuming processes in the subsurface: methanogenesis, homoacetogenesis, and sulphate reduction, as a basis to develop a hydrogen storage site selection tool. Sites with low temperature (Testing our tool on 42 depleted gas and oil fields of the British and Norwegian North Sea and the Irish Sea showed that seven of the fields may be considered sterile with respect to hydrogen-consuming microorganisms due to either temperatures >122 °C or salinities >5 M NaCl. Only three fields can sustain all of the major hydrogen-consuming processes, due to either temperature, salinity or pressure constraints in the remaining fields. We calculated a potential microbial growth in the order of 1-17*107 cells ml-1 for these fields. The associated hydrogen consumption is negligible to small (

The Black Lives Matter movement[1] and the global COVID-19 pandemic have highlighted inequalities in opportunities and vastly different lived experiences. This pandemic has exacerbated professional challenges among disproportionately affected and historically minoritized and marginalised people. Excellence in diversity, equity, and inclusion (DEI) is foundational for scientists to thrive and reach their full potential. Together, these factors have prompted the European Association of Geochemistry (EAG) to reflect on how to better DEI across all sectors, levels of employ, and positions of community leadership. It is with increased urgency that the EAG is acting to raise awareness of persisting challenges; creating new initiatives to reform practices that marginalise talented people, while building kind and understanding community cultures that are actively anti-racist and anti-discriminatory. In 2020, the EAG’s newly-constituted DEI Committee was charged with challenging the status quo and addressing system-wide barriers to participation in geochemistry and cosmochemistry[2]. Key to this committee’s work is the development of a DEI strategic plan and recommendations, informed by tangible data, for EAG Council. It is well documented that the wider geosciences continue to be gated, and is one of the least diverse STEM fields. Lack of diversity is detrimental for representation, but also critically limits scientific excellence[3]. This knowledge leads us to ask: does geochemistry and cosmochemistry - having particular field, laboratory, and instrument needs - foster less diverse communities relative to other fields within and beyond geosciences? If so, what are the procedural barriers and processes preventing underrepresented groups from thriving? We have prepared a survey to circulate among the membership (on an anonymous basis) after this Goldschmidt Conference to constrain the make up of our community. This survey will provide the first demographic data specific to our community, thereby benchmarking both our present mix and the condition of our culture. We appeal to the membership to engage and come together to help identify priority challenges and help us address them. 1Cooperdock et al., 2020. Black Lives Matter...Elements. http://elementsmagazine.org/2020/08/01/black-lives-matter-promoting-diversity-equity-and-inclusion-in-geochemistry/ 2Riches et al., 2021. Uniting to Advance Diversity, Equity, and Inclusion. https://blog.eag.eu.com/advance-dei-pandemic-post-pandemic/ 3Bernard and Cooperdock, 2018. No progress on diversity in 40 years. Nature Geosci. https://doi.org/10.1038/s41561-018-0116-6

The separation of gallium from iron by solvent extraction from chloride media is challenging because the anionic chloridometalates, FeCl4− and GaCl4−, display similar chemical properties. However, we report here that the selective separation of gallium from iron in HCl solution can be achieved using the dual-purpose ionic liquid methyltrioctylammonium iodide in a solvent extraction process. In this case, the reduction of Fe3+ to Fe2+ by the iodide counterion was found to inhibit Fe transport, facilitating quantitative Ga extraction by the ionic liquid with minimal Fe extraction from 2 M HCl.

The recycling of tantalum (Ta) is becoming increasingly important due to the criticality of its supply from a conflict mineral. It is used extensively in modern electronics, such as in capacitors, and so electronic waste is a potentially valuable secondary source of this metal. However, the recycling of Ta is difficult, not least because of the challenges of its leaching and subsequent separation from other metals. In this work, we show that Ta(V) halides, such as TaCl5 and TaF5, which can potentially be accessed from Ta metal upon acid halide leaching, can be recovered by solvent extraction using a simple primary amide reagent. The need for high halide concentrations in the aqueous phase implies the formation of the hexahalide salts [TaX6]&minus, (X = F, Cl) and that an anion-swing mechanism operates. While extraction of the fluorides is poor (up to 45%), excellent extraction under chloride conditions is found (&gt, 99%) and presents an alternative route to Ta recycling.

The chemical composition of soil from the Glasgow (UK) urban area was used to identify the controls on the availability of potentially harmful elements (PHEs) in soil to humans. Total and bioaccessible concentrations of arsenic (As), chromium (Cr) and lead (Pb) in 27 soil samples, collected from different land uses, were coupled to information on their solid-phase partitioning derived from sequential extraction data. The total element concentrations in the soils were in the range –1 for As; 65–3680mgkg–1 for Cr and 126–2160mgkg–1 for Pb, with bioaccessible concentrations averaging 27, 5 and 27% of the total values, respectively. Land use does not appear to be a predictor of contamination; however, the history of the contamination is critically important. The Chemometric Identification of Substrates and Element Distribution (CISED) sequential chemical extraction and associated self-modelling mixture resolution analysis identified three sample groupings and 16 geochemically distinct phases (substrates). These were related to iron (n=3), aluminium–silicon (Al–Si; n=2), calcium (n=3), phosphorus (n=1), magnesium (Mg; n=3), manganese (n=1) and easily extractable (n=3), which was predominantly made up of sodium and sulphur. As, Cr and Pb were respectively found in 9, 10 and 12 of the identified phases, with bioaccessible As predominantly associated with easily extractable phases, bioaccessible Cr with the Mg-dominated phases and bioaccessible Pb with both the Mg-dominated and Al–Si phases. Using a combination of the Unified Barge Method to measure the bioaccessibility of PHEs and CISED to identify the geochemical sources has allowed a much better understanding of the complexity of PHE mobility in the Glasgow urban environment. This approach can be applied to other urban environments and cases of soil contamination, and made part of land-use planning.

Inoculation of soil or seeds with plant growth promoting bacteria ameliorates metal toxicity to plants by changing metal speciation in plant tissues but the exact location of these changes remains unknown. Knowing where the changes occur is a critical first step to establish whether metal speciation changes are driven by microbial metabolism or by plant responses. Since bacteria concentrate in the rhizosphere, we hypothesised steep changes in metal speciation across the rhizosphere. We tested this by comparing speciation of zinc (Zn) in roots of Brassica juncea plants grown in soil contaminated with 600 mg kg−1 of Zn with that of bulk and rhizospheric soil using synchrotron X-ray absorption spectroscopy (XAS). Seeds were either uninoculated or inoculated with Rhizobium leguminosarum bv. trifolii and Zn was supplied in the form of sulfide (ZnS nanoparticles) and sulfate (ZnSO4). Consistent with previous studies, Zn toxicity, as assessed by plant growth parameters, was alleviated in B. juncea inoculated with Rhizobium leguminosarum. XAS results showed that in both ZnS and ZnSO4 treatments, the most significant changes in speciation occurred between the rhizosphere and the root, and involved an increase in the proportion of organic acids and thiol complexes. In ZnS treatments, Zn phytate and Zn citrate were the dominant organic acid complexes, whilst Zn histidine also appeared in roots exposed to ZnSO4. Inoculation with bacteria was associated with the appearance of Zn cysteine and Zn formate in roots, suggesting that these two forms are driven by bacterial metabolism. In contrast, Zn complexation with phytate, citrate and histidine is attributed to plant responses, perhaps in the form of exudates, some with long range influence into the bulk soil, leading to shallower speciation gradients.

The physical and chemical factors that can limit or prevent microbial growth in the deep subsurface are not well defined. Brines from an evaporite sequence were sampled in the Boulby Mine, United Kingdom between 800 and 1300 m depth. Ionic, hydrogen and oxygen isotopic composition were used to identify two brine sources, an aquifer situated in strata overlying the mine, and another ambiguous source distinct from the regional groundwater. The ability of the brines to support microbial replication was tested with culturing experiments using a diversity of inocula. The examined brines were found to be permissive for growth, except one. Testing this brine’s physicochemical properties showed it to have low water activity and to be chaotropic, which we attribute to the high concentration of magnesium and chloride ions. Metagenomic sequencing of the brines that supported growth showed their microbial communities to be similar to each other and comparable to those found in other hypersaline environments. These data show that solutions high in dissolved ions can shape the microbial diversity of the continental deep subsurface biosphere. Furthermore, under certain circumstances, complex brines can establish a hard limit to microbial replication in the deep biosphere, highlighting the potential for subsurface uninhabitable aqueous environments at depths far shallower than a geothermally-defined limit to life.

The traditional view of metal adsorption to bacterial surfaces is that it can act as a protective mechanism by externalizing the metal outside the cell. However, numerous studies focussing on the biodynamics of metal uptake using biotic ligand models consider metal adsorption to cell surfaces as an important first step in metal uptake and internalization. In order to resolve these conflicting views, we adsorbed two metals (copper and cadmium) with contrasting metal biotoxicity on E. coli JM109, and quantified the distribution of each metal amongst surface sites, periplasmic space and the cytoplasm. Distribution of each metal depended on biotoxicity and metal to biomass ratio. For both metals, low metal to biomass ratio led to most of the metal being associated with the periplasmic space, with less Cd being taken up by cells overall. At high metal to biomass ratios, most of the Cd was associated with surface sites, whereas Cu also increased in surface sites but remained below periplasmic concentrations. These observations are consistent with metal internalization being the dominant process at low metal to biomass ratios, whereas was active efflux when metal to biomass was high, leading to equilibrium between cytoplasm and surface concentrations. Significantly, efflux was more intense for high biotoxicity Cd, consistent with active enzymatic regulation of Cu internalization/homeastasis, which is essential at low concentrations. Moreover, metal internalization increases as surface-bound metal increases, the maximum being constrained by maximum adsorption consistent with Langmuir adsorption behaviour. Summarize of paper Bacterial metal internalization is a function of metal biotoxicity and metal loading.

The effects of zinc (Zn) speciation on plant growth in Zn-contaminated soil in the presence of bacteria are unknown but are critical to our understanding of metal biodynamics in the rhizosphere where bacteria are abundant. A 6-week pot experiment investigated the effects of two plant growth promoting bacteria (PGPB), Rhizobium leguminosarum and Pseudomonas brassicacearum, on Zn accumulation and speciation in Brassica juncea grown in soil amended with 600 mg kg-1 elemental Zn as three Zn species: soluble ZnSO4 and nanoparticles of ZnO and ZnS. Measures of plant growth were higher across all Zn treatments inoculated with PGPB compared to uninoculated controls, but Zn species effects were not significant. Transmission electron microscopy identified dense particles in the epidermis and intracellular spaces in roots, suggesting Zn uptake in both dissolved and particulate forms. X-ray absorption near-edge structure (XANES) analysis of roots revealed differences in Zn speciation between treatments. Uninoculated plants exposed to ZnSO4 contained Zn predominantly in the form of Zn phytate (35%) and Zn polygalacturonate (30%), whereas Zn cysteine (57%) and Zn polygalacturonate (37%) dominated in roots exposed to ZnO nanoparticles. Inoculation with PGPB increased (>50%) the proportion of Zn cysteine under all Zn treatments, suggesting Zn coordination with cysteine as the predominant mechanism of Zn toxicity reduction by PGPB. Using this approach, we show, for the first time, that although speciation is important, the presence of rhizospheric bacteria completely overrides speciation effects such that most of the Zn in plant tissue exists as complexes other than the original form.

The effectiveness of plant growth promoting bacteria (PGPB) in improving metal phytoremediation is still limited by stunted plant growth under high soil metal concentrations. Meanwhile, mixed planting with leguminous plants is known to improve yield in nutrient deficient soils but the use of a metal tolerant legume to enhance metal tolerance of a phytoremediator has not been explored. We compared the use of Pseudomonas brassicacearum, Rhizobium leguminosarum, and the metal tolerant leguminous plant Vicia sativa to promote the growth of Brassica juncea in soil contaminated with 400 mg Zn kg–1, and used synchrotron based microfocus X-ray absorption spectroscopy to probe Zn speciation in plant roots. B. juncea grew better when planted with V. sativa than when inoculated with PGPB. By combining PGPB with mixed planting, B. juncea recovered full growth while also achieving soil remediation efficiency of >75%, the maximum ever demonstrated for B. juncea. μXANES analysis of V. sativa suggested possible root exudation of the Zn chelates histidine and cysteine were responsible for reducing Zn toxicity. We propose the exploration of a legume-assisted-phytoremediation system as a more effective alternative to PGPB for Zn bioremediation.

A mechanistic understanding of processes controlling the transport and viability of bacteria in porous media is critical for designing in situ bioremediation and microbiological water decontamination programs. We investigated the combined influence of coating sand with iron oxide and silver nanoparticles on the transport and viability of Escherichia coli cells under saturated conditions. Results showed that iron oxide coatings increase cell deposition which was generally reversed by silver nanoparticle coatings in the early stages of injection. These observations are consistent with short-term, particle surface charge controls on bacteria transport, where a negatively charged surface induced by silver nanoparticles reverses the positive charge due to iron oxide coatings, but columns eventually recovered irreversible cell deposition. Silver nanoparticle coatings significantly increased cell inactivation during transit through the columns. However, when viability data is normalized to volume throughput, only a small improvement in cell inactivation is observed for silver nanoparticle coated sands relative to iron oxide coating alone. This counterintuitive result underscores the importance of net surface charge in controlling cell transport and inactivation, and implies that the extra cost for implementing silver nanoparticle coatings on porous beds coated with iron oxides may not be justified in designing point of use water filters in low income countries.

The mechanism of antibacterial action of silver nanoparticles (AgNp) was investigated by employing a combination of microbiology and geochemical approaches to contribute to the realistic assessment of nanotoxicity. Our studies showed that suspending AgNp in media with different levels of chloride relevant to environmental conditions produced low levels of ionic silver thereby suggesting that dissolution of silver ions from nanoparticulate surface could not be the sole mechanism of toxicity. An Escherichia coli based bioreporter strain responsive to silver ions together with mutant strains of E. coli lacking specific protective systems were tested against AgNp. Deletion mutants lacking silver ion efflux systems and resistance mechanisms against oxidative stress showed an increased sensitivity to AgNp. However, the bioreporter did not respond to silver nanoparticles. Our results suggest that oxidative stress is a major toxicity mechanism and that this is at least partially associated with ionic silver, but that bulk dissolution of silver into the medium is not sufficient to account for the observed effects. Chloride ions do not appear to offer significant protection, indicating that chloride in receiving waters will not necessarily protect environmental bacteria from the toxic effects of nanoparticles in effluents.

The growth and metal-extraction efficiency of plants exposed to toxic metals has been reported to be enhanced by inoculating plants with certain bacteria but the mechanisms behind this process remain unclear. We report results from glasshouse experiments on Brassica juncea plants exposed to 400 mg Zn kg −1 that investigated the abilities of Pseudomonas brassicacearum and Rhizobium leguminosarum to promote growth, coupled with synchrotron based μXANES analysis to probe Zn speciation in the plant roots. P. brassicacearum exhibited the poorest plant growth promoting ability, while R. leguminosarum alone and in combination with P. brassicacearum enhanced plant growth and Zn phytoextraction. Reduced growth in un-inoculated plants was attributed to accumulation of Zn oxalate and Zn sulfate in roots. In plants inoculated with P. brassicacearum the high concentration of Zn polygalacturonic acid in the root may be responsible for the stunted growth and reduced Zn phytoextraction. The improved growth and increased metal accumulation observed in plants inoculated with R. leguminosarum and in combination with P. brassicacearum was attributed to the storage of Zn in the form of Zn phytate and Zn cysteine in the root. When combined with the observation that both bacteria do not statistically improve B. juncea growth in the absence of Zn, this work suggests that bacteria-induced metal chelation is the key mechanism of plant growth promoting bacteria in toxicity attenuation and microbial-assisted phytoremediation.

The last two decades have seen geomicrobiology evolve into a broad field encompassing a wide range of environmentally significant processes such as proton and metal adsorption onto cell surfaces, and the effect of microbes on mineralisation, redox cycling, and contaminant transport. Within this sphere, research groups have conducted studies using bacteria, fungi, diatoms and sludges, all of which can play a part in geochemical processes. Here, we review research on the role played by microbial extracellular polymeric substances (EPS), focussing on bacterial and cyanobacterial EPS. We conclude by outlining future research directions in order to investigate unresolved questions in the field. The effect of EPS on metal adsorption is complex; whereas some studies report an increase in metal adsorption when cells contain EPS, some report no differences; yet others report a decrease. These discrepancies may reflect differences in molecular and functional group composition of the EPS. EPS provides a template for adsorption of metal cations to which carbonate ions are attracted to induce local mineral supersaturation. This may be behind observed changes in both crystal polymorphism favouring formation of less stable polymorphs, and crystal morphology where the presence of EPS promotes the formation of rounded, smoothed crystals or spheroids. The role of EPS in mineral dissolution, bioleaching and corrosion is equivocal. EPS alone appears to have little effect on mineral dissolution, bioleaching or biocorrosion. Instead, it appears that EPS increases rates of mineral weathering and leaching by forming complexes with metallic ions released by the mineral surface, which may themselves catalyse bioleaching in the case of sulphides. EPS in biofilms forms effective barriers to the transport of particulate phases, and exerts important controls on the transport and deposition of natural and engineered nanoparticles. Much less is known about the role of EPS in the cycling of redox-sensitive trace metals. Intuitively, and as observed in microbial mats with sulphate reducing bacteria, EPS is a labile electron donor for microbial metabolism that could affect metal biogeochemistry but this remains to be conclusively demonstrated in laboratory experiments. Hence, in this and other areas, further studies are required to develop a mechanistic basis for including the effects of EPS in biogeochemical models.

In this study we describe the mobility and fractionation of REEs in two deep (up to 30 m) tropical weathering profiles developed on two granites from the Kuala Lumpur pluton, Malaysia, sampled at Cheras and Rawang. On the basis of Na2O and K2O both are S-type granites, but Rawang has higher CaO, MgO and FeO than Cheras and lower SiO2. With respect to Al-saturation Rawang is I-type and Cheras is S-type. We compared the two profiles in terms of total REEs, magnitude and changes in Ce and Eu anomalies, REE mobility and LREE/HREE fractionation. Rawang profiles have higher REE contents, display lower mobility for most except the heaviest REEs and show higher LREE/HREE fractionation than those from Cheras. These differences can be linked to differences in primary mineralogy and degree of weathering, the latter controlling the type and volume of secondary minerals. Specifically, bowl-shaped parent-rock-normalised patterns in the Cheras saprolites appear to be a result of apatite dissolution. Moreover, moderate weathering evident in lower Mineralogical Indices of Alteration (MIA) at Cheras has conserved parent rock REE patterns and fractionation factors in the saprolites. By contrast, more intense weathering observed in Rawang profiles has produced abundant kaolinite group minerals that have preferentially retained LREE, which consequently display high LREE/HREE fractionation. This study provides important insights into the factors controlling REE mobility during tropical weathering, and its potential as an indicator of weathering intensity.

The ability to predict the impact of metal–microbe interactions on biofilm stability, hydrodynamics and contaminant transport is a key goal in hydrogeology, membrane bioreactors and geomicrobiology. Yet, we have not been able to find experimental studies reporting the coupling of these three elements in a systematic way. In this study sand column experiments were carried out to investigate the coupled effects of aqueous zinc (Zn2 +) on biofilm stability and of biofilm on Zn2 + transport in saturated sand columns. A series of aqueous Zn concentrations ranging from 0 to 100 ppm were pumped through biofilm-colonised columns and a set of related parameters (hydraulic conductivity, cell numbers, EPS, metal breakthrough curve and metal distribution) was measured. Our results show that biofilm formation prior to introduction of Zn resulted in a significant decrease of hydraulic conductivities. After 10 days of metal exposure, Zn showed concentration-dependent toxicity on bacterial cells in the biofilm. However different Zn concentrations produced distinct non-linear effects on EPS production, which resulted in either recovery or further decrease of hydraulic conductivity in the porous matrix. This non-linear response of biofilm to metal concentration could lead to different metal transport patterns in the long term. The concentration of metal contaminants plays a critical role in regulating the effect of metal–biofilm interaction. Our phenomenological study establishes linkages between chemical, microbial and physical processes of metal–biofilm interaction, and is an essential precursor to the development of models for this complex system. Specifically, these interactions are shown to be unpredictable, suggesting that more work needs to be done to constrain flow and transport parameters in biofilm-colonised porous media.

We investigated the possibility of bacterial symbiosis in Globigerina bulloides, a palaeoceanographically important, planktonic foraminifer. This marine protist is commonly used in investigations of climatically sensitive subpolar and temperate water masses and wind driven upwelling regions of the world’s oceans. G. bulloides is unusual because it lacks the protist algal symbionts that are often found in other spinose species and has an atypical geochemical shell signature. This is suggestive of a divergent ecology, making it a good candidate for investigating the potential for bacterial symbiosis as a contributory factor in shell calcification. Such ecological information is essential to evaluate fully the potential response of G. bulloides to ocean acidification and climate change. To investigate the ecological interactions between G. bulloides and bacterial populations in the water column, 18S rRNA gene sequencing, fluorescence microscopy, 16S rRNA gene metabarcoding and transmission electron microscopy (TEM) were performed on individual specimens of G. bulloides (Type IId) collected from two locations in the California Current. Intracellular DNA extracted from five G. bulloides specimens was subjected to 16S rRNA gene metabarcoding and, remarkably, 37–87 % of all 16S rRNA gene sequences recovered were assigned to operational taxonomic units (OTUs) of the picocyanobacterium, Synechococcus. This finding was supported by TEM observations of intact Synechococcus cells in both the cytoplasm and vacuoles of G. bulloides. Concentrations were up to four orders of magnitude greater inside the foraminifera than those reported for the Californian Current water column and approximately 5 % of the intracellular Synechococcus cells observed were dividing. This suggests that Synechococcus is an endobiont of G. bulloides Type IId, which is the first report of a bacterial endobiont in the planktonic foraminifera. We consider the potential roles of Synechococcus and G. bulloides within the relationship and the need to determine how widespread the possible symbiotic association is within the widely distributed G. bulloides morphospecies. The possible influence of Synechococcus respiration on G. bulloides shell geochemistry is also discussed.

The increasing production and use of engineered nanoparticles, coupled with their demonstrated toxicity to different organisms, demands the development of a systematic understanding of how nanoparticle toxicity depends on important environmental parameters as well as surface properties of both cells and nanomaterials. We demonstrate that production of the extracellular polymeric substance (EPS), colanic acid by engineered Escherichia coli protects the bacteria against silver nanoparticle toxicity. Moreover, exogenous addition of EPS to a control strain results in an increase in cell viability, as does the addition of commercial EPS polymer analogue xanthan. Furthermore, we have found that an EPS producing strain of Sinorhizobium meliloti shows higher survival upon exposure to silver nanoparticles than the parent strain. Transmission electron microscopy (TEM) observations showed that EPS traps the nanoparticles outside the cells and reduces the exposed surface area of cells to incoming nanoparticles by inducing cell aggregation. Nanoparticle size characterization in the presence of EPS and xanthan indicated a marked tendency towards aggregation. Both are likely effective mechanisms for reducing nanoparticle toxicity in the natural environment.

The use of Sporosarcina pasteurii to precipitate calcium carbonate in the anoxic subsurface via ureolysis has been proposed for reducing porosity and sealing fractures in rocks. Here we show that S. pasteurii is unable to grow anaerobically and that the ureolytic activity previously shown under anoxic conditions is a consequence of the urease enzyme already present in the cells of the aerobically grown inoculum. The implications are discussed, suggesting that de novo synthesis of urease under anoxic conditions is not possible and that ureolysis may decline over time without repeated injection of S. pasteurii as the urease enzyme degrades and/or becomes inhibited. Augmentation with a different ureolytic species that is able to grow anaerobically or stimulation of natural communities may be preferable for carbonate precipitation over the long term.

In order to understand the contribution of geogenic phosphorus to lake eutrophication, we have investigated the rate and extent of fluorapatite dissolution in the presence of two common soil bacteria ( Pantoea agglomerans and Bacillus megaterium ) at T = 25 °C for 26 days. The release of calcium (Ca), phosphorus (P), and rare earth elements (REE) under biotic and abiotic conditions was compared to investigate the effect of microorganism on apatite dissolution. The release of Ca and P was enhanced under the influence of bacteria. Apatite dissolution rates obtained from solution Ca concentration in the biotic reactors increased above error compared with abiotic controls. Chemical analysis of biomass showed that bacteria scavenged Ca, P, and REE during their growth, which lowered their fluid concentrations, leading to apparent lower release rates. The temporal evolution of pH in the reactors reflected the balance of apatite weathering, solution reactions, bacterial metabolism, and potentially secondary precipitation, which was implied in the variety of REE patterns in the biotic and abiotic reactors. Light rare earth elements (LREE) were preferentially adsorbed to cell surfaces, whereas heavy rare earth elements (HREE) were retained in the fluid phase. Decoupling of LREE and HREE could possibly be due to preferential release of HREE from apatite or selective secondary precipitation of LREE enriched phosphates, especially in the presence of bacteria. When corrected for intracellular concentrations, both biotic reactors showed high P and REE release compared with the abiotic control. We speculate that lack of this correction explains the conflicting findings about the role of bacteria in mineral weathering rates. The observation that bacteria enhance the release rates of P and REE from apatite could account for some of the phosphorus burden and metal pollution in aquatic environments.

Groundwater is increasingly being used for public and private water supplies in Scotland, but there is growing evidence that manganese (Mn) concentrations in many groundwater supplies exceed the national drinking water limit of 0.05 mg l(-1). This study examines the extent and magnitude of high Mn concentrations in groundwater in Scotland and investigates the factors controlling Mn concentrations. A dataset containing 475 high quality groundwater samples was compiled using new data from Baseline Scotland supplemented with additional high quality data where available. Concentrations ranged up to 1.9 mg l(-1); median Mn concentration was 0.013 mg l(-1) with 25th and 75th percentiles 0.0014 and 0.072 mg l(-1) respectively. The Scottish drinking water limit (0.05 mg l(-1)) was exceeded for 30% of samples and the WHO health guideline (0.4 mg l(-1)) by 9%; concentrations were highest in the Carboniferous sedimentary aquifer in central Scotland, the Devonian sedimentary aquifer of Morayshire, and superficial aquifers. Further analysis using 137 samples from the Devonian aquifers indicated strong redox and pH controls (pH, Eh and dissolved oxygen accounted for 58% of variance in Mn concentrations). In addition, an independent relationship between Fe and Mn was observed, suggesting that Fe behaviour in groundwater may affect Mn solubility. Given the redox status and pH of Scottish groundwaters the most likely explanation is sorption of Mn to Fe oxides, which are released into solution when Fe is reduced. Since the occurrence of elevated Mn concentrations is widespread in groundwaters from all aquifer types, consideration should be given to monitoring Mn more widely in both public and private groundwater supplies in Scotland and by implication elsewhere.

Biosorption has emerged as an alternative sustainable strategy for cleaning up water contaminated through industrial activities and/or natural processes. Since biomaterials contain discrete reactive sites to which adsorption takes place, the biosorption process is amenable to thermodynamic treatment using surface complexation theory, enabling the development of predictive models for complex natural or industrial mixtures. In this paper, we present such a surface complexation formalism as it relates to bacterial surfaces, which is verified using proton and single metal biosorption data plotted as a function of pH. The parameters extracted from these verification experiments are then used to predict biosorption in mixtures of metals, with excellent success. The model should be applicable to other biomaterials, such as algae, fungi and higher plants.

This study investigated Zn adsorption to an extracellular polymeric substance (EPS)-producing bacterial strain, Bacillus licheniformis S-86. Batch metal adsorption experiments and spectroscopic (EXAFS) analysis were conducted using both native (EPS-covered) cells and EPS-free cells in order to assess the contribution made by EPS to metal adsorption by this strain. Thermodynamic modelling of the macroscopic adsorption data indicated that Zn complexation to both native and EPS-free cells was predominantly to carboxyl (pK(a)5.3-5.4) and phosphate (pK(a)7.4-7.5) functional groups, but with some adsorption to phosphodiester (pK(a)3.3-3.4) groups also evident. EXAFS analysis shows Zn-carboxyl complexation, but possibly with a significant contribution from a second, phosphate functional group. Apparently, EPS removal does not affect the metal adsorption capacity at the metal: biomass ratios used here. As the concentration of carboxyl and phosphate functional groups is only slightly affected by EPS extraction, complexation to these functional groups explains why EPS removal does not reduce the amount of Zn adsorbed by the cells. It was also observed that EPS production induces aggregation of cells in suspension. This may reduce the cell surface area available for metal adsorption, thus counteracting any greater availability of metal-complexing ligands in the EPS layer compared to an EPS-free cell surface. Furthermore, the EPS layer appears to be the major source of dissolved organic carbon (DOC) released to solution during the metal adsorption experiments. This DOC may reduce metal binding to the cell surfaces by acting as a competing complexing ligand. These observations have implications for industrial application of biofilms and suggest that over-production of EPS in bio-reactors may reduce the metal removal efficiency of the biomass.

This study was designed to combine surface complexation modelling of macroscopic adsorption data with X-ray Absorption Spectroscopic (XAS) measurements to identify lanthanide sorption sites on the bacterial surface. The adsorption of selected representatives for light (La and Nd), middle (Sm and Gd) and heavy (Er and Yb) lanthanides was measured as a function of pH, and biomass samples exposed to 4 mg/L lanthanide at pH 3.5 and 6 were analysed using XAS. Surface complexation modelling was consistent with the light lanthanides adsorbing to phosphate sites, whereas the adsorption of middle and heavy lanthanides could be modelled equally well by carboxyl and phosphate sites. The existence of such mixed mode coordination was confirmed by Extended X-ray Absorption Fine Structure (EXAFS) analysis, which was also consistent with adsorption to phosphate sites at low pH, with secondary involvement of carboxyl sites at high adsorption density (high pH). Thus, the two approaches yield broadly consistent information with regard to surface site identity and lanthanide coordination environment. Furthermore, spectroscopic analysis suggests that coordination to phosphate sites is monodentate at the metal/biomass ratios used. Based on the best-fitting pKa site, we infer that the phosphate sites are located on N-acetylglucosamine phosphate, the most likely polymer on gram-negative cells with potential phosphate sites that deprotonate around neutral pH.

The effect of bacterial extracellular polymers (EPS) on calcium carbonate morphology and polymorphism was investigated by means of free-drift mineralisation experiments, conducted using cells of the EPS-producing thermotolerant Bacillus licheniformis S-86. The cells either had the EPS layer intact (native cells) or had the EPS layer removed (EPS-free cells). Experiments were also undertaken in the absence of cells, but with the addition of the extracted EPS solution. It was found that the abiotic control and EPS-free cell experiments contained vaterite and calcite when sampled after 12 h and 48 h, whereas the native cell and EPS-solution experiments contained only calcite. These results suggest that the presence of EPS inhibits vaterite precipitation. It is proposed that dissolved organic carbon (DOC) released from the EPS complexes Ca2+ ions in solution, reducing the calcium carbonate saturation and favouring calcite precipitation over vaterite. After 7 days, all experiments contained only calcite. However, distinct morphological differences between the calcite crystals precipitated in the four experiments were preserved after a period of 7 days, suggesting that crystal morphology may indicate the biological conditions under which calcite precipitated.

The correlation between permeability and petrographical parameters in cored samples can be used by extrapolations to predict permeability in uncored intervals. The core analysis described here is concerned with the study of fluid-rock interactions in rock samples from three sandstone reservoirs, in particular the effect of petrographical parameters on flow behavior. A positive correlation between liquid permeability and the volume fraction of silica is clearly demonstrated. Liquid permeability was correlated using multivariate regressions to one to five petrographical parameters, the results of which have useful application in the estimation of reservoir permeability where samples are not available for experimental testing.

This paper is based on detailed mineralogical, structural, petrophysical, and geochemical studies of sandstone core samples, using routine core analysis methods. These include X-ray computer tomography (CT) scanning, magnetic resonance imaging (MRI), particle size analysis, point counting based on petrographic thin sections, environmental scanning microscopy (ESEM), X-ray diffraction (XRD), and X-ray fluorescence (XRF). In this study, we demonstrate the feasibility of combing these complementary methods in the characterization of reservoir properties of sandstone cores. Four types of sandstones (Slick Rock Aeolian, Fife, Locharbriggs, and Berea sandstones) that differ in grain size, porosity, and mineralogy have been characterized. The results of the different methods used were found to be consistent with each other, but the combination of a variety of methods has allowed a fuller characterization of the rock samples than each method used on its own, bringing out subtle variations in petrographic characteristics that add significant value towards a better description of reservoir properties. For example, it becomes apparent that some types of rocks like Berea sandstones thought to be homogeneous are in fact heterogeneous. The recognition that rock heterogeneity at the sub-centimeter scale may have a significant effect on hydrocarbon recovery requires that field-scale reservoir models take account of these small-scale effects in order to lay claim to reasonable accuracy in production forecasts.

This study investigated proton adsorption to an extracellular polymeric substance (EPS) producing bacterial strain, Bacillus licheniformis S-86, in order to characterise and quantify the contribution made by EPS to cell surface reactivity. Potentiometric titrations were conducted using both untreated cells and cells from which the EPS layer had been extracted. Surface-complexation modelling indicated the presence of four different functional groups in both untreated and EPS-free cells. These sites are assigned to phosphodiester, (p K a 3.3–3.4), carboxylic (p K a 5.3–5.4), phosphoryl/ (p K a 7.4–7.5) and hydroxyl/amine (p K a 9.9–10.1) type groups. The p K a values for the four groups were very similar for untreated and EPS-free cells, indicating no qualitative difference in composition, but site concentrations in the untreated cells were statistically found to be significantly higher than those in the EPS-free cells for the p K a 3.3–3.4 and p K a 9.9–10.1 sites. Infrared analysis provided supporting evidence that site 2 is carboxylic in nature but did not reveal any difference in IR absorption between the native and EPS-free cells. Dissolved organic carbon (DOC) analysis conducted during this study indicated that DOC release by cells is significant, and that the EPS layer is the major contributor.

We report the first measurements of hydrodynamic dispersion in a microfractured granite using a combination of novel techniques. A fracture network was induced in a cylindrical plug of Ailsa Craig micro-granite by thermal stressing, to produce an isotropic network of fractures with an average aperture of ∼0.3 μm, a density of approximately 4×10 4 fractures/mm 3 and a permeability of 5.5×10 −17 m 2 . After saturating the cores with 0.01 M NaCl solution a step in the concentration profile to 1 M was advected into the plug at flow rates of 0.07 to 2.13 cm 3 h −1 . The longitudinal electrical impedance of the plug was measured continuously as the solute front advected through its length until the plug was saturated with the concentrated electrolyte. Analysis of the impedance versus time relationships allows the derivation of the longitudinal dispersion coefficient, DL, and hydrodynamic retardation, RH. The Peclet number–dispersion relationship for the micro-fracture network is very similar to that predicted for other, radically different, fracture networks. Thus dispersion may be more dependent on fracture connectivity and length than fracture density and display a relationship similar to that shown by particle beds and clastic sandstones. The high retardation values observed (2.2–4.9) reflect flow behaviour within a fracture network with a proportion of ‘blind’ sections, and demonstrates how such networks can slow the advance of conservative solute components. © 2007 Elsevier B.V. All rights reserved.