Competitive Exchange Research Articles

How does my country grow?: economic advice through story-telling

Written by a former World Bank economist, How Does My Country Grow? distils growth policy lessons from the author's first-hand experience in Poland, Kenya, India, and Russia, and his contributions to the economic policy debates that followed the emerging market crises of 1997 to 2001, extending up to the global financial crisis of 2008-09. Based on living and working in the field, the author argues that country economic analysis is in effect a separate, integrative branch of economics that draws upon but is distinct from academic economics. The country stories recounted, reinforced by the emerging market experience since the 1980s, point to a canonical growth policy package built around three interconnected elements: the intertemporal budget constraint of the government; the micropolicy trio of hard budgets, competition and competitive real exchange rates; and managing volatility from external, but especially domestic, sources. This package is underpinned by good governance, which finds its most immediate expression in the management of the public finances. While the discussion is tilted towards developing countries, the insights have considerable relevance for advanced economies, many of which today are in the throes of their own growth-cum-sovereign debt crises.

Seawater inundation of coastal floodplain sediments: Short-term changes in surface water and sediment geochemistry

Coastal floodplains are highly vulnerable to seawater inundation as a result of storm surge and sea-level rise due to their low elevation and proximity to the coastline. Intact soil cores from a levee, acid-sulfate soil scald and four backswamp sites on a coastal floodplain in eastern Australia were inundated with artificial seawater treatments (0%, 50% and 100%) for 14days to examine the short term consequences for surface water and floodplain sediment geochemistry. All sites displayed an initial decrease in surface water pH following inundation with 50% and 100% seawater. In addition, higher concentrations of trace metals (Al, Fe, Mn, Ni and Zn) were observed in most sites inundated with 50% or 100% seawater. This was generally attributed to competitive exchange and desorption of trace metals from sediments due to the higher ionic strength of the seawater solutions and upward diffusive flux of metals from the sediments to surface waters. At one backswamp site, reductive processes had established by day 7, which also resulted in elevated Fe2+ concentrations in the overlying surface waters. Transmission electron microscopy (TEM) identified the presence of poorly crystalline ferrihydrite and schwertmannite, and goethite and jarosite. These meta-stable Fe(III) minerals can act as a source of metals for desorption and can also be readily reduced and act as a source of Fe2+ to surface waters. Importantly, inundation with either 50% or 100% seawater resulted in a similar magnitude of acidity and trace metal mobilisation. The data suggest that an inundation event of ~0.2m depth with either 50% or 100% seawater could cause a pulse mobilisation of up to 64.8 and 9.1kgha−1 of Fe and Al, respectively — quantities of similar magnitude to previous estimates of annual drainage fluxes from similar backswamps. This study suggests that the short term inundation of coastal floodplain sediments by either brackish water or seawater will result in rapid declines in surface water quality as a result of increased liberation of acidity and trace metals.

Prices based on current cost or historical cost: How different are they?

In 1996, The Federal Communications Commission (FCC) prescribed total element long-run incremental cost (TELRIC) to determine rates incumbent local exchange carriers (ILECs) charge for most mandated wholesale services. TELRIC, which bases prices on a hypothetical incumbent that serves current volumes with completely new equipment, was a major departure from the predominant use of historical (or original) costs for regulated prices. The FCC made two exceptions: total service resale of local exchange services and rental of space by cable television providers and competitive local exchange carriers on poles and conduit owned by electric utilities and ILECs are based on original cost calculations. The FCC’s use of both current cost and historical cost methodologies recalls the fierce debates over whether regulated rates should be based on replacement (current) costs or original (historical costs) that preceded the US Supreme Court’s 1944 FPC v Hope decision. Parties advocating low rates favored replacement costs when equipment costs were expected to decrease, but original costs when such asset prices would be expected to increase. The Hope decision upheld the Federal Power Commission’s use of original costs, which subsequently were widely used by federal and state regulators. While rates based on current costs have, indeed, differed in the expected way from the corresponding rates based on historical costs, this paper demonstrates that (1) the large differences expected by conventional wisdom are the result of faulty application of the current cost methodology and (2) proper application substantially narrows the difference between the rates produced by the respective approaches.

Label-free electrochemical detection of prostate-specific antigen based on nucleic acid aptamer

We report a label-free aptasensor to make direct detection of prostate specific antigen (PSA, a biomarker of prostate cancer) using a quinone-containing conducting copolymer acting as redox transducer and grafting matrix for immobilization of the short aptamer strands. It is shown that capture of PSA generates a current decrease (signal-off) measured by Square Wave Voltammetry. This current decrease is specific for PSA above a limit of quantification in the ngmL−1 range. The change in current is used to determine the PSA–aptamer dissociation constant KD, of ca. 2.6nM. To consolidate the proof of concept, a heterogeneous competitive exchange with a complementary DNA strand which breaks PSA–aptamer interactions is studied. This double-check followed by a current increase provides full assurance of a perfectly specific recognition.

Iron-binding ligands and humic substances in the San Francisco Bay estuary and estuarine-influenced shelf regions of coastal California

Dissolved iron (dFe) and organic dFe-binding ligands were determined in San Francisco Bay, California by competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-ACSV) along a salinity gradient from the freshwater endmember of the Sacramento River (salinity <2) to the mouth of the estuary (salinity >26). A range of dFe-binding ligand classes was simultaneously determined using multiple analytical window analysis, involving titrations with multiple concentrations of the added ligand, salicylaldoxime. The highest dFe and ligand concentrations were determined in the low salinity end of the estuary, with dFe equal to 131.5nmolL−1 and strong ligand (log KFeL,Fe′cond≥12.0) concentrations equal to 139.5nmolL−1. The weakest ligands (log KFeL,Fe′cond<10.0) were always in excess of dFe in low salinity waters, but were rapidly flocculated within the estuary and were not detected at salinities greater than 7. The strongest ligands (log KFeL,Fe′cond>11.0) were tightly coupled to dFe throughout the estuary, with average excess ligand concentrations ([L]–[dFe]) equal to 0.5nmolL−1. Humic-like substances analyzed via both CLE-ACSV and proton nuclear magnetic resonance in several samples were found to be a significant portion of the dFe-binding ligand pool in San Francisco Bay, with concentrations ranging from 559.5μgL−1 to 67.5μgL−1 in the lowest and highest salinity samples, respectively. DFe-binding ligands and humic-like substances were also found in benthic boundary layer samples taken from the shelf near the mouths of San Francisco Bay and Eel River, suggesting estuaries are an important source of dFe-binding ligands to California coastal shelf waters.

ProMCC: An all-in-one tool for trace metal complexation studies

A new windows-based, user friendly program (ProMCC) for (i) the determination of metal complexation parameters (ligand concentration (L) and conditional stability constants (K′)) and for (ii) theoretical simulation of metal complexometric titration, assuming discrete ligand model, is developed. Although primarily intended for treatment of experimental data obtained either by anodic stripping voltammetry (ASV) or competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-AdCSV), it could manage titration-type data of other techniques (e.g. ISE, sorption isotherm). Currently, the program is capable to process (fit and/or simulate) titration data up to three discrete ligand classes. Procedure for adjustment of “true” analytical sensitivity incorporated in ProMCC was found to provide reasonably good estimates of sensitivity either for one-ligand or two-ligand system. The particular feature of ProMCC is that it incorporates two complementary fitting methodologies: (1) a non-linear fitting of conventional linearized transformations (e.g. Ružić/Van Den Berg, Langmuir/Gerringa) and (2) a “complete complexation model” — a matrix based optimization of mass balance equations. Comparison test of different non-linear fitting modes and titration types revealed that a slight underestimation of ligand concentration and overestimation of conditional stability constant may occur if titration is performed in logarithmic mode, mainly due to unfavorable noise distribution. An advantage of implemented “complete complexation model” fitting mode is that it allows simultaneous analysis of titrations obtained at multiple detection windows as unified dataset (multi-detection window approach), providing complexation parameters for up to three ligand classes. A new alternative “RAL-approach” in analyzing complexometric titrations obtained at multiple detection windows for copper–salicylaldoxime (Cu–SA) system is suggested. It assumes that the analytical sensitivity is changing along the titration curve respecting the true speciation of Cu–SA in sample. An adapted empirical equation for calculation of relative intensity (RAL) is proposed. Flexibility in adjusting parameters, immediate graphical feedback and visualizations make ProMCC handy for treatment of large set of experimental data, and a tool for research in refinement of the methods of metal complexing capacity determination which is continuously improving.

Dissolved Fe(II) in a river-estuary system rich in dissolved organic matter

Reduced iron, Fe(II), accounts for a significant fraction of dissolved Fe across many natural surface waters despite its rapid oxidation under oxic conditions. Here we investigate the temporal and spatial variation in dissolved Fe redox state in a high dissolved organic matter (DOM) estuarine system, the River Beaulieu. We couple manual sample collection with the deployment of an autonomous in situ analyser, designed to simultaneously measure dissolved Fe(II) and total dissolved Fe, in order to investigate processes operating on the diurnal timescale and to evaluate the performance of the analyser in a high DOM environment.Concentrations of dissolved Fe available to the ligand ferrozine are elevated throughout the estuary (up to 21 μM in freshwater) and notably higher than those previously reported likely due to seasonal variation. Fe(II) is observed to account for a large, varying fraction of the dissolved Fe available to ferrozine (25.5 ± 12.5%) and this fraction decreases with increasing salinity. We demonstrate that the very high DOM concentration in this environment and association of this DOM with dissolved Fe, prevents the accurate measurement of dissolved Fe concentrations in situ using a sensor reliant on rapid competitive ligand exchange.

The relevance of ligand exchange kinetics in the measurement of iron speciation by CLE–AdCSV in seawater

CLE–AdCSV (competitive ligand exchange–adsorptive cathodic stripping voltammetry) has proved to be a decisive technique in recognising the key role that organic matter plays in modulating the biogeochemical cycle of iron in aquatic ecosystems. As the method requires equilibrium among all the constituents of the solution before measurements are taken, accurate knowledge of the kinetics of the undergoing ligand exchange is essential. The kinetics of the process has been most frequently described in terms of a dissociative (or Eigen–Wilkins) mechanism, with some authors even claiming that, under such approach, iron complexes would dissociate during CLE so slowly that the method would be invalidated. The complexity of the processes—largely exceeding the simple mechanistic description of the Eigen–Wilkins mechanism—is discussed on the basis of a broad overview of possible reaction routes. Evidence of the role of matrix components of natural waters is presented and the impossibility of exporting kinetic constants to systems characterised by different molecular mechanics, mostly ignored in previous studies, is highlighted. Experimental evidence obtained from various methodological approaches allows inferring the range of CLE equilibration times to be applied in CLE–AdCSV measurements and further proves that the Eigen–Wilkins mechanism is just one of the many reaction routes applicable in natural waters. Studying iron CLE mechanisms for proposed competing ligands before designing any experiment using CLE–AdCSV is recommended.

Mineral transformation controls speciation and pore-fluid transmission of contaminants in waste-weathered Hanford sediments

Portions of the Hanford Site (WA, USA) vadose zone were subjected to weathering by caustic solutions during documented releases of high level radioactive waste (containing Sr, Cs and I) from leaking underground storage tanks. Previous studies have shown that waste-sediment interactions can promote variable incorporation of contaminants into neo-formed mineral products (including feldspathoids and zeolites), but processes regulating the subsequent contaminant release from these phases into infiltrating background pore waters remain poorly known. In this paper, reactive transport experiments were conducted with Hanford sediments previously weathered for one year in simulated hyper-alkaline waste solutions containing high or low 88Sr, 127I, and 133Cs concentrations, with or without CO2(aq). These waste-weathered sediments were leached in flow-through column experiments with simulated background pore water (characteristic of meteoric recharge) to measure contaminant release from solids formed during waste-sediment interaction. Contaminant sorption–desorption kinetics and mineral transformation reactions were both monitored using continuous-flow and wet-dry cycling regimes for ca. 300 pore volumes. Less than 20% of contaminant 133Cs and 88Sr mass and less than 40% 127I mass were released over the course of the experiment. To elucidate molecular processes limiting contaminant release, reacted sediments were studied with micro- (TEM and XRD) and molecular- (Sr K-edge EXAFS) scale methods. Contaminant dynamics in column experiments were principally controlled by rapid dissolution of labile solids and competitive exchange reactions. In initially feldspathoidic systems, time-dependent changes in the local zeolitic bonding environment observed with X-ray diffraction and EXAFS are responsible for limiting contaminant release. Linear combination fits and shell-by-shell analysis of Sr K-edge EXAFS data revealed modification in Sr–Si/Al distances within the zeolite cage. Wet-dry cycling did not affect significantly molecular-scale transformations relative to continuous-flow controls. Results indicate that contaminants bound to the solid phase in distinct micro- and molecular-scale coordinative environments can generate similar macro-scale release behaviors, highlighting the need for multi-scale interrogations to constrain mechanisms of reactive transport. Data also indicate that weathering-induced change in ion exchange selectivity coefficients should be incorporated in simulations of contaminant release from caustic high-level radioactive waste impacted sediments.

Modulation of Phosphorylation of Tocopherol and Phosphatidylinositol by hTAP1/SEC14L2-Mediated Lipid Exchange

The vitamin E derivative, alpha-tocopheryl phosphate (αTP), is detectable in cultured cells, plasma and tissues in small amounts, suggesting the existence of enzyme(s) with α-tocopherol (αT) kinase activity. Here, we characterize the production of αTP from αT and [γ-32P]-ATP in primary human coronary artery smooth muscle cells (HCA-SMC) using separation by thin layer chromatography (TLC) and subsequent analysis by Ultra Performance Liquid Chromatography (UPLC). In addition to αT, although to a lower amount, also γT is phosphorylated. In THP-1 monocytes, γTP inhibits cell proliferation and reduces CD36 scavenger receptor expression more potently than αTP. Both αTP and γTP activate the promoter of the human vascular endothelial growth factor (VEGF) gene with similar potency, whereas αT and γT had no significant effect. The recombinant human tocopherol associated protein 1 (hTAP1, hSEC14L2) binds both αT and αTP and stimulates phosphorylation of αT possibly by facilitating its transport and presentation to a putative αT kinase. Recombinant hTAP1 reduces the in vitro activity of the phosphatidylinositol-3-kinase gamma (PI3Kγ) indicating the formation of a stalled/inactive hTAP1/PI3Kγ heterodimer. The addition of αT, βT, γT, δT or αTP differentially stimulates PI3Kγ, suggesting facilitated egress of sequestered PI from hTAP1 to the enzyme. It is suggested that the continuous competitive exchange of different lipophilic ligands in hTAPs with cell enzymes and membranes may be a way to make these lipophiles more accessible as substrates for enzymes and as components of specific membrane domains.

Flujos netos de capital, choques macroeconómicos y activos de reservas. El caso argentino (1994-2013)

Las reservas internacionales han sido empleadas como una fuente de protección contra la vulnerabilidad de la balanza de pagos, o alternativamente, para intentar mantener un tipo de cambio real competitivo y promover las exportaciones. En este trabajo se analiza la correlación existente entre los flujos netos de capital y las reservas y se evalúa el efecto de algunos choques macroeconómicos en dicha variable. Las estimaciones se realizan con modelos de VEC (modelo de corrección de errores) y datos trimestrales de la economía argentina, que cubren el período 1994-2013. Los resultados muestran una correlación negativa entre las reservas internacionales y los flujos netos de capital (acumulación de reservas a través de excedentes en la cuenta corriente). A su vez, las políticas fiscales expansivas y los aumentos persistentes y generalizados de precios afectarían negativamente a las reservas.

Dissolved copper speciation in the Tasman Sea, SW Pacific Ocean

The speciation of copper (Cu) in seawater is dominated by organic complexation but the sources, distribution and nature of these natural organic ligands remain unclear. The spatial distribution and character of organic copper binding ligands at two sites in the Tasman Sea were investigated using competitive ligand exchange adsorptive cathodic stripping voltammetry, utilising salicylaldoxime as the competing ligand. The first station was located in the oligotrophic north Tasman Sea and was contrasted with a second, mesotrophic, station in the south of the region where sampling coincided with a coccolithophore bloom. The northern P1 site (0–3000m) was characterised by detection of a single, strong, class of ligand with a uniformly distributed conditional stability constant (log K′CuL=12.97±0.26). At the two shallowest depths of the southern P3 site (13 and 28m), two ligands were detected. A single, stronger, ligand was detected at all other depths for this site. Below 120m, conditional stability constants at the southern P3 site (0–3500m) were uniformly distributed (log K′CuL=13.32±0.21). At both stations, ligand concentrations usually exceeded the total dissolved Cu concentration and mirrored the bio-intermediate Cu profile at depth. Dissolved Cu was more than 99% complexed by organic ligands at all depths except one, when dissolved Cu concentration exceeds the dissolve ligand concentration. The variability in ligand concentrations was greatest in the top 0–50m at the northern P1 site and 0–80m at the southern site. Based on a combination of phototrophic cell counts and biomarker pigment concentrations, the source of organic Cu-binding ligands in the north Tasman Sea is thought to be from cyanobacterial production, namely Synechococcus spp which dominates in the region. The detection of two organic Cu binding ligand classes at the southern P3 station indicates a more complex Cu-binding ligand pool in the surface waters. At this site, the ligands are likely sourced from cyanobacteria and eukaryotes, namely coccolithophores. At the northern P1 station only, a relationship between the proportion of unbound ligand available and the dissolved oxygen concentration was obtained. Given the simpler ligand pool dynamics of the northern station relative to the south, this relationship may reveal that complexation of organic Cu-binding ligands is important to prevent or slow ligand degradation in the deep sea.

What underlies the recent growth comeback in developing economies?

We find that the frequency of growth takeoffs in developing economies has risen markedly in the past two decades, with recent takeoffs lasting longer than those prior to the 1990s. Also, unlike takeoffs prior to the 1990s, developing economies in recent takeoffs experienced an improvement in economic policies, with lower post-takeoff debt and inflation; more competitive real exchange rates; and stronger structural reforms and institutions. These conditions have tended to be associated in the literature as conducive to sustaining strong growth. We also find that the chances of starting a takeoff in the 2000s was triple that before the 1990s, with domestic conditions accounting for most of the increase. Thus, if developing economies improve their economic policies and sustain them forward, they are more likely to jumpstart takeoffs and avoid the reversals in economic fortunes that affected many developing economies in the past.

Local Telephony Rates: Has Deregulation Lead to Higher Competition and Lower Rates?

Since the mid 2000’s, sixteen states have deregulated local telephony rates under the assumption that increasing competition among cable digital phone, over-the-top VoIP, competitive local exchange carriers (CLECs), wireless telephony, and incumbent local exchange carriers (ILECs) is sufficient to discipline rates and therefore regulation would no longer be necessary. Using a cross sectional time/series panel of states to analyze how local telephony rates have changed as a function of state regulatory policy, we found that rates have risen more rapidly in states that have deregulated in comparison to states that have not. Moreover, the increase in residential local rates is not due to rate rebalancing between small-business and residential rates, nor to the loss of ILEC market share which in turn might increase average ILEC costs per remaining customer. Thus, results suggest that ILECs still have sufficient market power to increase local rates despite the presence of competition.

Tuning of the methylimidazolium/imidazole balance in polycations for gene carrier

The chemical structure of methylated poly(1-vinylimidazole) (PVIm-Me) has been tuned for gene carrier properties, which are cell viability, the stability of its DNA polyion complexes, and gene expression. The resulting PVIm-Me with lower methylation degree (6 and 20 mol%) exhibited no significant cytotoxicity, as compared with 40 mol% PVIm-Me, in spite of the same concentration and chemical structure of positive charges. The DNA complex with 20 mol% PVIm-Me stably retained the DNA, as compared with 6 or 40 mol% PVIm-Me, which was examined by competitive exchange with dextran sulfate. As a result, the DNA complex with 20 mol% PVIm-Me mediated most efficient gene delivery, where the resulting transfection activity was higher than that mediated by a positive control, poly(ethylenimine). These results suggest that the optimization of the balance of the methylimidazolium and the imidazole groups of PVIm-Me is essential for gene carrier design. Copyright © 2014 John Wiley & Sons, Ltd.

Distinct pools of dissolved iron‐binding ligands in the surface and benthic boundary layer of the California Current

Organic dissolved iron (dFe)—binding ligands were measured by competitive ligand exchange—adsorptive cathodic stripping voltammetry (CLE‐ACSV) at multiple analytical windows (side reaction coefficient of salicylaldoxime, αFe(SA)2 = 30, 60 and 100) in surface and benthic boundary layer (BBL) samples along the central California coast during spring and summer. The weakest ligands were detected in the BBL at the lowest analytical window with average log KcondFeL,Fe' = 10.2 ± 0.4 in the summer and 10.8 ± 0.2 in the spring. Between 3% and 18% of the dFe complexation in the BBL was accounted for by HS, which were measured separately in samples by ACSV and may indicate a source of dFe‐binding ligands from San Francisco Bay. The strongest ligands were found in nearshore spring surface waters at the highest analytical window with average log KcondFeL,Fe' = 11.9 ± 0.3, and the concentrations of these ligands declined rapidly offshore. The ligand pools in the surface and BBL waters were distinct from each other based on principal components analysis, with variances in the BBL ligand pool explained by sample location, and variance in surface waters explained by water mass. The use of multiple analytical window analysis elucidated several distinct iron‐binding ligand pools, each with unique distributions in the central California Current system.

Emerging Frameworks for Regulation of Over-the-Top Services on Mobile Networks: An International Comparison

This paper is a comparative analysis of national regulations proposed for Over-The-Top (OTT) services provided over mobile networks. Specifically, the paper will examine the terms of access, interconnection and pricing for OTT services, where they are delivered to end-customers over unaffiliated mobile networks. The objective would be to evaluate alternative national regulations for the degree to which they offer fair compensation to mobile network operators while ensuring competitive neutrality between platforms and providers, and thus suggest best practices for OTT regulation. OTT services such as Skype, WeChat, KakaoTalk and WhatsApp have dramatically proliferated in the past two years, and are increasingly drawing voice and SMS traffic away from mobile operators. Mobile revenues have stagnated or declined in many major markets, leading many mobile operators to propose to slow or block OTT traffic, or deploy their own OTT services in competition with the third-party providers, or ask for regulatory relief in the form of termination charges for OTT traffic. These attempts raise troubling questions about access, interconnection, and discrimination. Such debates have previously occurred regarding access for video content providers over ISPs, or for interconnection of competitive local exchange carriers with incumbents’ networks.In this paper, we will compare regulations in different national jurisdictions dealing with OTT services on mobile networks. These proposals have ranged from an outright ban on OTT services in Vietnam, to the European Telecommunications Network Operators’ (ETNO) proposal in 2012 to request payment for termination of OTT traffic, to the unrestricted markets currently obtaining in most countries. Specifically, we compare the provisions relevant to OTT-mobile network interconnection in selected national regulations: (1) the Korea Communications Commission’s 2011 Guidelines for Network Neutrality and Internet Traffic Management; (2) the Chinese Ministry of Industry and Information Technology’s 2013 proposal to require WeChat to pay mobile carriers for the use of their facilities; and (3) the European Commission’s 2009 regulatory framework on net neutrality. Comparative analysis suggests that asking OTTs to pay for having their content delivered to consumers – as WeChat was asked to do in China – may be a form of “double dipping” since consumers already pay for their subscriptions. Jurisdictions have taken specific steps to prevent the use of pricing as a form of barrier to entry against competing OTTs, by ISPs that provide substitute services. Also, regulations have generally avoided restrictions or asymmetric pricing only on some OTTs as impractical since OTT service markets have low barriers to entry and consumers can switch easily to “free” OTT services. Finally, regulations have considered OTT-mobile network access generally in the context of legal requirements for net neutrality, though no jurisdiction currently has an unequivocal stand for or against net neutrality. Though interconnection and pricing issues for OTT services on mobile networks have not been satisfactorily resolved in any jurisdiction, comparative analysis identifies the contours of emerging “best practices” in terms of access, interconnection and pricing for OTT services. However, a sustainable pricing plan has to be competitively neutral between competing OTTs; cannot be used to favor of the ISP’s own vertically integrated services; has to be reflective of the mobile networks’ costs of providing access and network services; and cannot “double dip” – that is, collect payments for the same traffic from content provider and consumer. Potentially, only a pricing model based on usage based pricing, in which consumers are subject to a two-part tariff, inclusive of a basic access fee and a usage charge indexed to user’s data usage, might fulfill all these requirements.

Elevated arsenic and manganese in groundwaters of Murshidabad, West Bengal, India

High levels of geogenic arsenic (As) and manganese (Mn) in drinking water has led to widespread health problems for the population of West Bengal, India. Here we delineate the extent of occurrences of As and Mn in Murshidabad, where the contaminated aquifers occur at shallow depths between 35 and 40m and where access to safe drinking water is a critical issue for the local population.A total of 78 well-water samples were taken in 4 blocks on either side of the river Bhagirathi: Nabagram and Kandi (west, Pleistocene sediments), Hariharpara and Beldanga (east, Holocene sediments). High As, total iron (FeT) and low Mn concentrations were found in waters from the Holocene gray sediment aquifers east of the river Bhagirathi, while the opposite was found in the Pleistocene reddish-brown aquifer west of the river Bhagirathi in Murshidabad. Speciation of As in water samples from Holocene sediments revealed the dominant species to be As(III), with ratios of As(III):AsT ranging from 0.55 to 0.98 (average 0.74). There were indications from saturation index estimations that Mn solubility is limited by the precipitation of MnCO3. Tubewells from high As areas in proximity to anthropogenic waste influx sources showing high molar Cl/Br ratios, low SO42− and low NO3− demonstrate relatively lower As concentrations, thereby reducing As pollution in those wells.Analyses of core samples (2 in each of the blocks) drilled to a depth of 45m indicate that there is no significant variation in bulk As (5–20mg/kg) between the Holocene and Pleistocene sediments, indicating that favorable subsurface redox conditions conducive to mobilization are responsible for the release of As. The same applies to Mn, but concentrations vary more widely (20–2000mg/kg). Sequential extraction of Holocene sediments showed As to be associated with ‘specifically sorbed-phosphate-extractable’ phases (10–15%) and with ‘amorphous and well crystalline Fe-oxyhydroxide’ phases (around 37%) at As-contaminated well depths, suggesting that the main As release mechanisms could be either competitive ion exchange with PO43−, or the dissolution of Fe oxyhydroxides. In the Pleistocene sediments Mn is predominantly found in the easily exchangeable fraction.

Diffusion and sorption of Cs+, Na+, I− and HTO in compacted sodium montmorillonite as a function of porewater salinity: Integrated sorption and diffusion model

Montmorillonite clay is an important component of barrier materials such as bentonites and argillaceous rocks for the safe geological disposal of radioactive waste. The diffusion and sorption behaviors of cationic Cs+ and Na+, anionic I− and neutral tritiated water (HTO) tracers in compacted montmorillonite were investigated as a function of porewater salinity by experimental and modeling approaches. The effective diffusivities of these tracers were measured by the through-diffusion method coupled with multiple curve analysis including depth profiles, and typical salinity-dependent cation excess and anion exclusion effects were shown. The distribution coefficients for Cs+ and Na+ obtained by through-diffusion tests were sensitive to salinity because of competitive ion exchange and were in good agreement with those obtained by batch sorption tests. However, trends in the apparent diffusivities of Cs+ and Na+ were mostly independent of salinity.A diffusion model based on a simplified pore structure and electrical double layer theory, describing the change of ionic concentration and viscoelectric effects caused by the electrostatic interaction with negatively charged clay surfaces, could quantitatively account for the cation excess and anion exclusion behaviors and their salinity dependence. The trends in the distribution coefficients predicted by the ion exchange sorption model show good agreement with the measured values as a function of salinity. Salinity-independent apparent diffusivities could be interpreted as results of the coupled effects of the drastic dependence of diffusion and sorption on salinity. The difference in the diffusion and sorption behaviors between Cs+ and Na+ can be explained by the difference in the sorption mechanism (inner- and outer-sphere) and their representation in the diffusion model (cation excess diffusion). This integrated sorption and diffusion model was further demonstrated as being applicable to the diffusion data of these monovalent cations and anions in compacted bentonites over a wide range of compaction.

Speciation study of aluminium in beverages by Competitive Ligand Exchange–Adsorptive Stripping Voltammetry

Competitive Ligand Exchange-Adsorptive Stripping Voltammetry (CLE-AdSV) was used for determining the speciation of aluminium in commonly consumed beverages (water, tea, infusion, coffee, orange juice, tomato juice, beer and red wine). Aluminium determination involves the adsorption of Al-complexes with the ligand cupferron onto a hanging mercury drop electrode. All samples were studied at pH 6.5 with an accumulation step at -0.60 V (all potential values in the paper are given versus the Ag/AgCl, [KCl]=3 M reference electrode) during 60 s, and a final cupferron concentration of 4 × 10(-4)M. These conditions were used to establish (i) the concentration of electro-labile aluminium, (ii) the range of ligand concentrations and (iii) the conditional stability constants of beverage samples using titration procedures. The results based on Ruzic plots were compared to computer simulation with Visual MINTEQ. This comparison suggests that labile monomeric Al-forms and soluble organic complexes of low molecular weight can be quantified by the CLE-AdSV procedure. Overall the relative uncertainties on the determination of the electro-active Al fraction and the complexing parameters, i.e., concentration and conditional stability constant of natural ligands in the samples, are less than 15%. Thanks to these results, information on Al bioavailability in beverages was collected and discussed. This study also illustrates the value of computer simulations when complex, time-consuming voltammetric techniques are applied.