Arsenic in groundwater and the environment

Awareness of the problems associated with arsenic in drinking water and the environment has grown significantly over the last two decades or so and today an enormous literature exists documenting its occurrence, behaviour and impacts in many places across the globe. The mobilisation of arsenic in the environment occurs through a complex combination of natural biogeochemical reactions and human interactions. Most recognised problems are generated by mobilisation and transport under natural conditions, but mobilisation has also been caused, or exacerbated, by mining, fossil-fuel combustion and use of synthetic arsenical compounds (pesticides, herbicides, crop desiccants and arsenic-based additives in livestock feed). Arsenical pesticides and herbicides have been used much less over the last few decades, and more recent restrictions have been imposed on the use of arsenic in wood preservation (e.g. European Communities’ Directive 2003/2/EC), but the legacy of such sources may still pose a localised threat to the environment

Molybdenum in natural waters: a review of occurrence, distributions and controls

Molybdenum is an essential trace element for human, animal and plant health and has played an important part in the evolution of life on earth. Nonetheless, exposure to the element can be harmful and although the evidence for symptoms in humans is sparse, it has been linked with a number of health conditions in animal models. Molybdenum is present in trace quantities (1–10 mg/kg) in most rocks and soils and at concentrations less than, and often orders of magnitude less than, 10 μg/L in most freshwaters. It is the most abundant transition metal in open seawater (10 μg Mo/L) owing to the dominance, and low chemical reactivity, of the molybdate ion (MoO42-). The 2011 WHO Guidelines for Drinking-Water Quality (fourth edition) advised a health-based value of 70 μg/L for Mo but this is no longer promulgated as a formal guideline value as WHO consider such concentrations to be rarely found in drinking water. This is indeed usually the case, but there are instances where currently-used drinking waters do exceed 70 μg Mo/L. We therefore recommend more routine measurement of Mo in water, at least on a reconnaissance scale, in order to improve knowledge on occurrence in water used for potable supply. Where multi-element analytical procedures are already used (e.g. ICP-MS), the marginal cost of adding Mo to the list of elements to be analysed should not be great. We have reviewed nine areas in the world where high concentrations of Mo in freshwater, and in some cases drinking water, have been found: Argentina, Jordan, Qatar, Ethiopia, UK, USA (three) and Chile. These represent a range of geochemical environments. A common theme of the high-Mo occurrences is (i) oxic, alkaline conditions where, as for seawater, the Mo occurs as the stable molybdate ion; groundwater in oxic, alkaline conditions within volcanogenic sediments can have exceptionally high Mo concentrations (up to hundreds of μg/L) where felsic volcanic ash is present; (ii) anoxic, non-sulphidic waters where Mo can be released to solution by reductive dissolution of Mn and Fe oxides or by release from degradation of organic matter, notably within high-Mo organic-rich muds, black shales or oil shales; or (iii) surface waters or groundwater impacted by metal sulphide mining and/or mineralisation, in particular occurrences of porphyry deposits. Under such conditions, Mo concentrations can reach several tens to several hundreds of μg/L and while not all are otherwise suitable for drinking water, some are. Much of the basic geochemistry of Mo in oxic natural environments is now quite well understood. Critically, its behaviour is redox-sensitive like its near neighbours in the Periodic Table, W and V. At the near-neutral pH values characteristic of most natural waters, Mo is rather weakly sorbed and formation of Mo minerals is either not indicated or is extremely slow. Molybdenum becomes less mobile when converted to thiomolybdates under the strongly reducing conditions found in some present-day ocean basins (e.g. the Black Sea), fjords, stratified lakes and confined aquifers. This leads to concentrations of around 100 mg Mo/kg or more in black shales and other organic-rich mudstones. However, despite the many studies of these water bodies and the importance of Mo as a palaeoredox indicator, the mechanism of the highly-efficient and diagnostic scavenging of Mo in euxinic (H2S-rich) waters remains uncertain. Possibilities include the formation of an as yet unidentified Mo-Fe-S mineral or solid solution, or the scavenging by some pre-existing solid such as a sulphide or oxide mineral, or organic matter. The possible role of dispersed and reduced natural organic matter has become more prominent in recent years but this has proven difficult to quantify and the mechanism of binding is poorly understood. Molybdenum isotope studies now play an important role in constraining reaction pathways. At a more fundamental level, there is a lack of up-to-date thermodynamic and kinetic data for many of the reactions of importance for Mo in the natural environment and this limits the ability of current geochemical models to predict its fate and transport. This is particularly true for the strongly reducing conditions where Mo partitions to the solid phase, leading to the formation of the Mo-rich shales. Even the existence of reduced aqueous Mo species (e.g. in the Mo(V) and Mo(III) oxidation states) in natural waters is uncertain. These uncertainties will only be resolved with focused laboratory experiments using the benefits of modern instrumentation, combined where necessary with supporting molecular dynamics calculations. The mobility of Mo in aqueous systems has to date received far more attention in the marine than the freshwater setting. The value of Mo speciation as an indicator of redox conditions and of stable-isotopic variations as a tracer, can have more value in the arena of environment and health, and studies of the element's mobility in aqueous systems can be useful for themes varying from radioactive waste disposal, sustainability of unconventional hydrocarbon exploitation and wider surficial pollution

Internal U, Th and Rb concentrations of alkali-feldspar grains:Implications for luminescence dating

This study assesses whether internal U, Th and Rb concentrations of single grains of alkali-feldspar can impact upon luminescence dating. Internal alpha dose-rates determined for two sedimentary samples calculated from mean U and Th concentrations accounted for ∼10% of the total dose-rates, while internal beta dose-rates from mean Rb concentrations accounted for ∼2%. Depth profiles of measurements penetrating into each grain show that internal U and Th concentrations varied between grains, where some grains had effective internal alpha dose-rates up to 1.8 Gy/ka (32% of the total dose-rate). K concentrations inferred from Rb (KRb) for individual grains suggest that internal U and Th concentrations are related to the feldspar composition. Grains with KRb > 6% had low U and Th, and grains with KRb < 6% had higher U and Th concentrations. Internal alpha and beta dose-rates of the perthitic and Na-rich grains contaminating the density-separated K-feldspar fractions had a significant impact upon the single-grain De distributions, which was estimated to be equivalent to overdispersion values of ∼10 – 15%. The scatter in the De distributions arising from internal alpha and beta dose-rates for both samples could be reduced by selecting only the brightest 20% of grains for luminescence dating

Accounting for collaborative supply chain relationships : issues and strategies

The purpose of this discussion paper is to explore the contemporary business model that has arisen with the advent of B2B e-commerce systems in order to better understand the improvements needed in the financial reporting model. The contemporary business model has relegated the enterprise-centric view of corporate competition and the current financial reporting model to insignificance in many instances. Rather, today’s business environment is one dominated by competition between supply chains with an organization’s success ultimately hinging on the viability and success of its supply chain partners as much as, or more than, enterprise-centric policies and decisions. As a result, these highly integrative systems connect supply chain partners in a manner that is more tightly coupled than most consolidated entities. Still, the current financial reporting model fails to even minimally capture the complexity of this new reality. This discussion paper provides the foundation for elaborating on a detailed discussion of how this business model could be more accurately captured through an enhanced business reporting model.El objetivo de este documento de debate es explorar el modelo contemporáneo de negocios que ha surgido con la llegada del B2B – una situación en la que un negocio le hace una transferencia comercial a otro – a los sistemas de comercio electrónico, para así comprender mejor las mejoras necesarias en el modelo de información financiera. El modelo contemporáneo de negocios ha relegado la perspectiva de la empresa como centro de la competencia corporativa, y el actual modelo de información financiera a la insignificancia en ciertos momentos. Sin embargo, el entorno empresarial actual está dominado por la competición entre las cadenas de suministro con el éxito de una organización dependiendo de la viabilidad y el éxito de sus socios de dichas cadenas, tanto, o incluso más que, en las políticas y decisiones centradas en la empresa. Como resultado de ello, estos sistemas altamente integrantes conectan a sus socios de esas cadenas de manera que está más acoplada que la mayoría de las entidades consolidadas. Aún así, el modelo actual de información financiera falla en mínimamente capturar la complejidad de esta nueva realidad. Este documento proporciona la base para elaborar un debate detallado sobre cómo este modelo empresarial podría ser capturado de una forma más exacta, a través de un modelo de información empresarial mejorado

Luminescence dating of glacial advances at Lago Buenos Aires (∼46 °S), Patagonia

Understanding the timing of past glacial advances in Patagonia is of global climatic importance because of the insight this can provide into the influence on glacier behaviour of changes in temperature and precipitation related to the Southern Westerlies. In this paper we present new luminescence ages determined using single grains of K-feldspar from proglacial outwash sediments that were deposited by the Patagonian Ice Sheet around Lago Buenos Aires (∼46 °S), east of the contemporary Northern Patagonian Icefield. The new luminescence ages indicate that major outwash accumulations formed around ∼110 ± 20 ka to 140 ± 20 ka and that these correspond to the Moreno I and II moraine ridges, which were previously dated using cosmogenic isotope dating to 150 ± 30 ka. Luminescence dating at Lago Buenos Aires has also identified outwash sediments that were deposited during glacial advances ∼30.8 ± 5.7 ka and ∼34.0 ± 6.1 ka (MIS 3) that are not recorded in the moraine record. Younger outwash accumulations were then deposited between ∼14.7 ± 2.1 and 26.2 ± 1.6 ka which correspond to the Fenix I – V moraine ridges. The combined chronology suggests that glacial advances occurred ∼110 ± 20 ka to 150 ± 30 ka (MIS 6), ∼30.8 ± 5.7 ka to ∼34.0 ± 6.1 ka (MIS 3), and ∼14.7 ± 2.1 to 26.2 ± 1.6 ka (MIS 2) at Lago Buenos Aires. Overall luminescence dating using single grains of K-feldspar has excellent potential to contribute towards the ever-increasing geochronological dataset constraining the timings of glacial advances in Patagonia

Bleaching of the post-IR IRSL signal from individual grains of K-feldspar::implications for single-grain dating

Post-IR IRSL (pIRIR) signals from K-feldspar grains measured at elevated temperatures are increasingly being used for dating sediments. Unfortunately the pIRIR signal from K-feldspars bleaches more slowly than other signals (e.g. OSL from quartz) upon exposure to daylight, leading to concerns about residual signals remaining at deposition. However, earlier studies have not assessed whether the pIRIR signal bleaches at the same rate in all feldspar grains. In this study laboratory bleaching experiments have been conducted and for the first time the results show that the rate at which the pIRIR signal from individual K-feldspar grains bleach varies. To determine whether grain-to-grain variability in bleaching rate has a dominant control on equivalent dose (De) distributions determined using single grains, analysis was undertaken on three samples with independent age control from different depositional environments (two aeolian and one glaciofluvial). The De value determined from each grain was compared with the rate at which the pIRIR225 signal from the grain bleaches. The bleaching rate of each grain was assessed by giving a 52 Gy dose and measuring the residual De after bleaching for an hour in a solar simulator. There is no clear relationship between the rate at which the pIRIR225 signal of an individual grain bleaches and the magnitude of its De. It is concluded that variability in the bleaching rate of the pIRIR225 signal from one grain to another does not appear to be a dominant control on single grain De distributions

Empirical assessment of beta dose heterogeneity in sediments:Implications for luminescence dating

Optically stimulated luminescence (OSL) dating of single grains is often required to determine an accurate age for partially-bleached sediment by identifying those grains with OSL signals that were well bleached prior to burial. However, single-grain De distributions are typically characterised by greater amounts of scatter in comparison to multiple grains. Here we investigate the scatter in single-grain De distributions of quartz from 56 proglacial samples associated with the retreat of the last British-Irish Ice Sheet. Our findings provide the first empirical dataset showing that beta-dose heterogeneity can impact the extrinsic scatter in single-grain De distributions, in addition to partial bleaching in nature. The additional scatter in single-grain De distributions caused by beta-dose heterogeneity suggests that it is inappropriate to apply a fixed threshold to determine between well-bleached and partially-bleached De distributions, but the skewness of the De distributions could alternatively be used. Autoradiography and QEMSCAN analyses show that there was a negative relationship between the relative standard deviation (RSD) of the beta-dose heterogeneity and the beta dose-rate. This relationship offers the opportunity to infer the RSD of the beta-dose heterogeneity for each sample using just the beta dose-rate, instead of acquiring empirical data for every sample. For this large suite of sedimentary samples, we observe a minimum OD of 20 % arising from the effects of beta-dose heterogeneity (Fig. 3e), which should be added (in quadrature) to the intrinsic OD to determine σb for the minimum age model (MAM) to calculate accurate OSL ages and prevent underestimation of the burial age

Arsenite sorption and co-precipitation with calcite

Sorption of As(III) by calcite was investigated as a function of As(III) concentration, time and pH. The sorption isotherm, i.e. the log As(III) vs. log [As(OH)3 degrees / Assat] plot is S-shaped and has been modelled on an extended version of the surface precipitation model. At low concentrations, As(OH)3 degrees is adsorbed by complexation to surface Ca surface sites, as previously described by the X-ray standing wave technique. The inflexion point of the isotherm, where As(OH)3 degrees is limited by the amount of surface sites (ST), yields 6 sites nm-2 in good agreement with crystallographic data. Beyond this value, the amount of sorbed arsenic increases linearly with solution concentration, up to the saturation of arsenic with respect to the precipitation of CaHAsO3(s). The solid solutions formed in this concentration range were examined by X-ray and neutron diffraction. The doped calcite lattice parameters increase with arsenic content while c/a ratio remains constant. Our results made on bulk calcite on the atomic displacement of As atoms along [0001] direction extend those published by Cheng et al., (1999) on calcite surface. This study provides a molecular-level explanation for why As(III) is trapped by calcite in industrial treatments.Comment: 9 page

High-throughput Agrobacterium-mediated barley transformation

<p>Abstract</p> <p>Background</p> <p>Plant transformation is an invaluable tool for basic plant research, as well as a useful technique for the direct improvement of commercial crops. Barley (<it>Hordeum vulgare</it>) is the fourth most abundant cereal crop in the world. It also provides a useful model for the study of wheat, which has a larger and more complex genome. Most existing barley transformation methodologies are either complex or have low (<10%) transformation efficiencies.</p> <p>Results</p> <p>A robust, simple and reproducible barley transformation protocol has been developed that yields average transformation efficiencies of 25%. This protocol is based on the infection of immature barley embryos with <it>Agrobacterium </it>strain AGL1, carrying vectors from the pBract series that contain the <it>hpt </it>gene (conferring hygromycin resistance) as a selectable marker. Results of large scale experiments utilising the <it>luc </it>(firefly luciferase) gene as a reporter are described. The method presented here has been used to produce hundreds of independent, transgenic plant lines and we show that a large proportion of these lines contain single copies of the <it>luc </it>gene.</p> <p>Conclusion</p> <p>This protocol demonstrates significant improvements in both efficiency and ease of use over existing barley transformation methods. This opens up opportunities for the development of functional genomics resources in barley.</p