Increase In Arsenic Concentration Research Articles

Solubility of platinum-arsenide melt and sperrylite in synthetic basalt at 0.1 MPa and 1200 °C with implications for arsenic speciation and platinum sequestration in mafic igneous systems

To better understand the Pt-As association in natural magmas, experiments were done at 1200°C and 0.1MPa to measure the solubility of Pt and Pt-arsenide phases (melt and sperrylite, PtAs2), as well as to determine the oxidation state, and identify evidence for Pt-As complexing, in molten silicate. Samples consisting of synthetic basalt contained in chromite crucibles were subject to three experimental procedures. In the first, platinum solubility in the synthetic basalt was determined without added arsenic by equilibrating the sample with a platinum source (embedded wire or bead) in a gas-mixing furnace. In the second, the sample plus a Pt-arsenide source was equilibrated in a vacuum-sealed fused quartz tube containing a solid-oxide oxygen buffer. The third approach involved two steps: first equilibrating the sample in a gas-mixing furnace, then with added arsenide melt in a sealed quartz tube. Oxygen fugacity was estimated in the latter step using chromite/melt partitioning of vanadium.Method two experiments done at high initial arsenic activity (PtAs melt+PtAs2), showed significant loss of arsenic from the sample, the result of vapour transfer to newly-formed arsenide phases in the buffer. Method three experiments showed no loss of arsenic, yielding a uniform final distribution in the sample. Analyses of run-product glasses from experiments which did not show arsenic loss reveal significant increase in arsenic concentrations with fO2, varying from ∼10ppm (FMQ-3.25) to >10,000ppm (FMQ+5.5). Despite very high arsenic loadings (>1000ppm), the solubility of Pt is similar in arsenic-bearing and arsenic-free glasses. The variation in arsenic solubility with fO2 shows a linear relationship, that when corrected for the change in the activity of dissolved arsenic with the melt ferric/ferrous ratio, yields a solubility-fO2 relationship consistent with As3+ as the dissolved species. This result is confirmed by X-ray absorption near edge structure (XANES) determination on run-product glasses.Levels of arsenic required for Pt-arsenide saturation are 50–500ppm over the fO2 range of most terrestrial basalts (FMQ to FMQ-2), >100× higher than the arsenic concentrations typical of such magmas, indicating significant enrichment of arsenic is required if Pt-arsenide saturation is to occur. In contrast, the level of dissolved Pt required to saturate in sperrylite is >8× lower than for pure Pt, suggesting that arsenic enrichment could lead to Pt removal at concentrations much less than required for pure metal saturation.

Optimization of environmental conditions for the growth and bioaccumulation of As(III) and As(V) ions by growing Corynebacterium glutamicum MTCC 2745: inhibition kinetic study

The significant factors affecting simultaneously the growth and bioaccumulation of arsenic [As(III) and As(V)] ions by living cells of bacteria, Corynebacterium glutamicum MTCC 2745, were explored in growth media under various experimental environmental conditions such as pH, inoculum size, contact time, temperature, concentrations of peptone and arsenic [either As(III) or As(V)] ions. Three kinetic models namely competitive, noncompetitive and uncompetitive models were verified with the aim of deciding the toxic effects of arsenic on specific growth rate of C. glutamicum MTCC 2745. As(III) was observed to be more toxic than As(V). Competitive inhibition was found in either As(III) or As(V) systems which was suggested by almost same maximum specific growth rate (µm) value and an increase in the saturation constant (K′S,app) value that were evaluated from Lineweaver–Burk plots. A simultaneous reduction in the inhibition constant recommended that inhibitory effect increases with the increase in arsenic concentration.

Arsenic load in rice ecosystem and its mitigation through deficit irrigation

Rice the staple food is a notable intake source of arsenic to the rural population of eastern India through food-chain. A field survey was carried out to study the variation of arsenic load in different parts of rice genotype Shatabdi (most popular genotype of the region) exposed to varying level of arsenic present in the irrigation water and soil. As irrigation is the primary source of arsenic contamination, a study was conducted to assess arsenic load in rice ecosystem under deficit irrigation practices like intermittent ponding (IP), saturation (SAT) and aerobic (AER) imposed during stress allowable stage (16–40 days after transplanting) of the crop (genotype Shatabdi). Present survey showed that arsenic content in water and soil influenced the arsenic load of rice grain. Variation in arsenic among different water and soil samples influenced grain arsenic load to the maximum extent followed by straw. Deviation in root arsenic load due to variation in water and soil arsenic content was lowest. Arsenic concentration of grain is strongly related to the arsenic content of both irrigation water and soil. However, water has 10% higher impact on grain arsenic load over soil. Translocation of arsenic from root to shoot decreased with the increase in arsenic content of water. Imposition of saturated and aerobic environment reduced both yield and grain arsenic load. In contrast under IP a marked decrease in grain arsenic content recorded with insignificant reduction in yield. Deficit irrigation resulted in significant reduction (17.6–25%) in arsenic content of polished rice and the values were lower than that of the toxic level (<0.2 mg kg−1). In contrast the decrease in yield was to the tune of 0.9% under IP regime over CP.

Study of arsenic accumulation in rice and evaluation of protective effects of Chorchorus olitorius leaves against arsenic contaminated rice induced toxicities in Wistar albino rats.

BackgroundIn the present study, we investigated the arsenic accumulation in different parts of rice irrigated with arsenic contaminated water. Besides, we also evaluated the protective effects of Corchorus olitorius leaves against arsenic contaminated rice induced toxicities in animal model.MethodsA pot experiment was conducted with arsenic amended irrigation water (0.0, 25.0, 50.0 and 75.0 mg/L As) to investigate the arsenic accumulation in different parts of rice. In order to evaluate the protective effects of Corchorus olitorius leaves, twenty Wistar albino rats were divided into four different groups. The control group (Group-I) was supplied with normal laboratory pellets while groups II, III, and IV received normal laboratory pellets supplemented with arsenic contaminated rice, C. olitorius leaf powder (4 %), arsenic contaminated rice plus C. olitorius leaf powder (4 %) respectively. Different haematological parameters and serum indices were analyzed to evaluate the protective effects of Corchorus olitorius leaves against arsenic intoxication. To gather more supportive evidences of Corchorus olitorius potentiality against arsenic intoxication, histopathological analysis of liver, kidney, spleen and heart tissues was also performed.ResultsFrom the pot experiment, we have found a significant (p ≤ 0.05) increase of arsenic accumulation in different parts of rice with the increase of arsenic concentrations in irrigation water and the trend of accumulation was found as root > straw > husk > grain. Another part of the experiment revealed that supplementation of C. olitorius leaves with arsenic contaminated rice significantly (p < 0.05) restored the altered haematological parameters and other serum indices towards the normal values. Arsenic deposition pattern on different organs and histological studies on the ultrastructural changes of liver, kidneys, spleen and heart also supported the protective roles of Corchorus olitorius leaves against arsenic contaminated rice induced toxicities.ConclusionArsenic accumulation in different parts of rice increased dose-dependently. Hence, for irrigation purpose arsenic contaminated water cannot be used. Furthermore, arsenic contaminated rice induced several toxicities in animal model, most of which could be minimized with the food supplementation of Corchorus olitorius leaves. Therefore, Corchorus olitorius can be used as a potential food supplement to the affected people of arsenic prone zone to ensure the food security.Electronic supplementary materialThe online version of this article (doi:10.1186/s40360-016-0091-8) contains supplementary material, which is available to authorized users.

Adsorption Characteristics of Arsenite on Goethite by Flow Stirring Method

Adsorption characteristics of arsenite on goethite under the effects of the solution pH, concentration and temperature were investigated using a flow-stirring dynamic device. The results showed that the adsorption process of arsenic could be divided into rapid and slow reactions under different conditions.The maximum of arsenite adsorption fitted by the first order equation remarkably decreased with increase in the solution pH, for example, 246.9 mg·kg-1 at pH 3.0 and 99.8 mg·kg-1 at pH 7.0, respectively. The rate constant(k')of the apparent adsorption increased gradually along with the increase of solution pH, and so the half reaction time(t1/2)was smaller, and the equilibrium time of arsenic adsorption was shorter. At the same time, the b values of diffusion rate constant were reduced gradually. With the increase of arsenic concentration, the amounts of arsenic adsorption and the k' values increased gradually. The maximum amount of adsorption of arsenic was 96.5 mg·kg-1 and 249.1 mg·kg-1 when the arsenic concentration was 0.10 mg·L-1 and 1.00 mg·L-1, respectively. Adsorption constant(Kf)by the Freundlich equation decreased gradually with the extension of the reaction time and its ability of adsorption was gradually weakened. Distribution factor(RL)by Langmuir equation was between 0-1, and the adsorption of arsenic on goethite was accounted for the preferential adsorption. With the increase of temperature, the maximum amount of adsorption of arsenic was increased, for example, 241.1 mg·kg-1 at 298 K and 315.6 mg·kg-1 at 313 K, respectively. And the k' values of the apparent adsorption rate constant gradually rose in the meantime. The false thermodynamic constants were calculated using the b values of the diffusion rate by the parabolic diffusion equation. The reaction activation energy(Ea*)of Arsenic adsorption was 14.60 kJ·mol-1. The change of arsenic diffusion activation enthalpy(ΔHθ)decreased with the increase of temperature, and ΔHθ was positive in values and on behalf of the endothermic process. So the rising temperature was beneficial to the diffusion of arsenic. ΔGθ of activation free energy was increased as the temperatures rose, and helpful to accelerate the diffusion process. Entropy of activation(ΔSθ)was negative in all cases, suggesting that the system could improve its degree of order.

Arsenic record from a 3 m snow pit at Dome Argus, Antarctica

AbstractThis study presents an arsenic concentration time series from 1964–2009 at Dome Argus, Antarctica. The data show a very large increase in arsenic concentration from the mid-1980s to the late-1990s (by a factor of~22) compared with the values before the mid-1980s. This increase is likely to be related to the increased copper smelting in South America. Arsenic concentration then decreased in the late-1990s, most probably as a result of environmental regulations in South America. The sudden increase in arsenic concentration observed at Dome Argus coincides with similar increases observed at Dome Fuji and in Antarctica Ice Core-6 (IC-6) at the same time, suggesting that arsenic pollution during the period from the mid-1980s to the late-1990s was a regional phenomenon in Antarctica. Investigations of arsenic concentrations at these three Antarctic locations show that, during this time, regional arsenic distribution followed dust transport pathways associated with general climate models with South America as a major source region for the half of Antarctica facing the Atlantic and Indian oceans.

Health costs of arsenic contamination of drinking water in Assam, India

This paper estimates the health costs of arsenic contamination of drinking water in Assam, India, where nearly one million people are affected. Applying the Three Stage Least Square (3SLS) procedure to data collected through a primary survey of 355 households in 2013, it estimates three structural equations to determine health costs due to arsenic contamination. The estimates show that the average annual health cost of a 1 microgram increase in arsenic concentration per liter of drinking water is about INR4 per household. Furthermore, if the average level of arsenic concentration is reduced to the safe limit of 50 microgram per liter, the average annual welfare gain for a household is estimated to be INR 862 (USD 14). Projecting these figures to the entire arsenic-affected population of Assam, the annual health costs of a 1 microgram increase in arsenic concentration per liter are estimated to be about INR 0.76 million (USD 0.01 million) and the welfare gains from reducing the level of arsenic concentration to the safe limit are estimated to be INR 153 million (USD 2.49 million). The results also indicate that these health costs and welfare gains vary significantly across different levels of arsenic concentration and across districts. Finally, the paper draws policy implications for providing safe drinking water in Assam.

The relationship of benthic community metrics to pyrethroids, metals, and sediment characteristics in Cache Slough, California

ABSTRACTA bioassessment multiple stressor study was conducted at 12 sites in Cache Slough, California during the Spring and Fall of 2012, 2013 and 2014. Specific study goals were to: (1) collect and identify benthic macroinvertebrates and develop a suite of benthic metrics; (2) measure total organic carbon (TOC), grain size, bulk metals, simultaneously extracted metals (SEM) and acid volatile sulfides (AVS), and 8 pyrethroids in sediment; (3) measure basic water quality parameters; and, (4) use univariate and stepwise multiple regressions and canonical correlation analysis to determine the relationship between various benthic metrics (i.e., taxa richness, abundance) and TOC, grain size, metals (bulk metals and SEM/AVS) and pyrethroids using the 3-year database. Five benthic metrics showed statistically significant relationships with environmental variables. Taxonomic Richness, a metric that decreases with stress, tended to be greater in less organic-rich, coarser sediments and the apparent relationships with toxicants such as pyrethroids or metals were diminished when these conditions are taken into account. The % Amphipod metric, which has a variable response to environmental stressors, showed a direct relationship with arsenic, an inverse relationship with chromium and an inverse relationship with % silt. The % Corbicula metric, which has a variable response to environmental stressors, was directly correlated with cypermethrin and nickel. Therefore, it appears that Corbicula tends to be associated with more contaminated sediments in Cache Slough. The metric % Collectors/Filterers & Collectors/Gatherers, a metric that increases in stressed environments, was reported to increase in sediments with higher arsenic concentrations. This relationship makes ecological sense because this metric should increase with an increase in arsenic concentrations. The benthic metric Abundance, a metric that decreases with stress, was reported to be inversely correlated with % TOC and % silt. The abundance of benthic communities increases in coarser, less organic rich sediments. In general, relatively few statistically significant relationships were observed between the various combinations of benthic metrics and environmental variables. Benthic communities in Cache Slough appear to be more closely associated with sediment characteristics and with metals concentrations than with the pyrethroid concentrations.

Transfer of Arsenic from Groundwater and Paddy Soil to Rice (Oryza sativa L.) Grain: A Micro Level Study in Chandina, Comilla

Rice (Oryza sativa L.) is one of the major food crops in many countries. As the cultivation of rice requires huge volume of water, long term use of Arsenic contaminated groundwater for irrigation may result in the increase of arsenic concentration in the agricultural soil and eventually accumulation in rice grains. A micro level study was conducted to investigate the transfer of arsenic from irrigation water and soil to rice plants in the arsenic affected 8 unions of Chandina upazilla, Comilla district. The level of arsenic in irrigation water (0.12±0.08 and 0.67±0.07 mg l-1) was much above the WHO permissible limit of 0.01 mg l-1 for drinking water and FAO permissible limit of 0.10 mg l-1 for irrigation water. The total soil arsenic concentrations ranged from 3.21±0.80 to 8.74±2.83 mg kg-1 dry weight of soil, which was below the maximum acceptable limit for agricultural soil of 20.0 mg kg-1 as recommended by the European Community. The accumulation of arsenic in the grain ranged from 0.12±0.04 to 0.58±0.06 mg kg-1 in Boro and 0.16±0.04 to 1.06±0.20 mg kg-1 in T. Aman. Except grain sample (T. Aman) of one union, the grains in both Boro and T. Aman of all unions did not exceed 1.0 mg kg-1 dry weight of arsenic (the permissible limit of arsenic in rice according to WHO recommendation). Thus, till now rice has remained harmless for consumption in the study area. The results clearly showed that the arsenic content in the grains of Boro rice is correlated to the intensity of arsenic contamination of irrigation water and soil. The Agriculturists 2014; 12(2) 74-82

Uniform fabrication of Ge nanocrystals embedded into SiO2 film via neutron transmutation doping

Nanocrystalline 74Ge embedded SiO2 films were prepared by employing ion implantation and neutron transmutation doping methods. Transmission electron microscopy, energy dispersive x-ray spectroscopy, and photoluminescence of the obtained samples were measured. The existence of As dopants transmuted from 74Ge is significant to guarantee the uniformity and higher volume density of Ge nanocrystals by tuning the system׳s crystallinity and activating mass transfer process. It was observed that the photoluminescence intensity of Ge nanocrystals increased first then decreased with the increase of arsenic concentration. The optimized fluence of neutron transmutation doping was found to be 5.5×1017cm−2 to achieve maximum photoluminescence emission in Ge embedded SiO2 film. This work opens a route in the three-dimensional nanofabrication of uniform Ge nanocrystals.

Metal stoichiometry of isolated and arsenic substituted metallothionein: PIXE and ESI-MS study

The stoichiometric analysis of the metal induced Metallothionein (MT) is pertinent for understanding the metal-MT interactions. Despite innumerable publications on MT, the literature addressing these aspects is limited. To bridge this gap, PIXE and ESI-MS analysis of the commercial rabbit liver MT1 (an isoform of MT), zinc induced isolated rat liver MT1, apo and Arsenic substituted rabbit liver MT1 have been carried out. These techniques in combination provide information about number and the signature of all the metal ions bound to MT. By using ESI-MS in the rabbit MT1, ions of Zn n MT1 (n = 0, 1, 4, 5, 6, 7) whereas, in rat MT1, the Zn1MT1 and Zn5MT1 ions are observed. PIXE analysis shows that some copper along with zinc is also present in the rabbit as well as rat MT1 which could not be assessed with ESI-MS. During As metallation reaction with rabbit MT1, with increase in arsenic concentration, the amount of arsenic bound to MT1 also increases, though not proportionally. The presence of both Zn and Cu in MT1 on Zn supplementation can be related to the role of MT in Zn and Cu homeostasis. Further, the presence of partially metallated MT1 suggests that MT1 may donate fractional amount of metal from it's fully metallated form to other proteins where Zn acts as a cofactor.

English

The effect of different levels (2, 4, 6, 8 and 10 mg/L) of arsenic (as sodium arsenate and sodium arsenite) on germination percentage, mean germination time, days to 50% germination, plumule and radicle length and seedling vigour index of four sunflower cultivars (FH-331, FH-385, FH-405 and FH-415) was determined under laboratory conditions. Germination percentage was gradually decreased with the increase in arsenic concentration in case of all sunflower cultivars. Low concentrations (2 and 4 mg/L arsenic) increased while higher concentrations (6, 8 and 10 mg/L arsenic) posed stress and caused reduction in plumule and radicle length (mm) of seedlings as compared to control. Out of all the four sunflower cultivars, H1 (FH-331) proved the most sensitive one by giving least values for plumule length, radicle length and seedling vigour index as observed during the course of this experiment.&nbsp;&nbsp; &nbsp; Key words:&nbsp;Sodium arsenate, sodium arsenite, sunflower, seed germination, seedling growth.

Environmental impacts of aquifer thermal energy storage investigated by field and laboratory experiments

Aquifer thermal energy storage (ATES) uses groundwater to store energy for heating or cooling purposes in the built environment. This paper presents field and laboratory results aiming to elucidate the effects that ATES operation may have on chemical groundwater quality. Field data from an ATES site in the south of the Netherlands show that ATES results in chemical quality perturbations due to homogenisation of the initially present vertical water quality gradient. We tested this hypothesis by numerical modelling of groundwater flow and coupled SO4 transport during extraction and injection of groundwater by the ATES system. The modelling results confirm that extracting groundwater from an aquifer with a natural quality stratification, mixing this water in the ATES system, and subsequent injection in the second ATES well can adequately describe the observation data. This mixing effect masks any potential temperature effects in typical low temperature ATES systems (&amp;lt;25 °C) which was the reason to complement the field investigations with laboratory experiments focusing on temperature effects. The laboratory experiments indicated that temperature effects until 25 °C are limited; most interestingly was an increase in arsenic concentration. At 60 °C, carbonate precipitation, mobilisation of dissolved oxygen concentration, K and Li, and desorption of trace metals like As can occur.

Determination of the optical constants of amorphous As xS 100− x films using effective-medium approximation and OJL model

The transmission spectra were used to obtain an efficient parameterization of the spectral dependences of the optical constants of amorphous As–S thin films by applying a suitable dielectric function model. For studying the compositional dependence of the optical constants, different compositions of As x S 100− x ( x = 10, 15, 20, 25, 30 and 40 at%) thin films were deposited by thermal evaporation technique in a base pressure of 7.5 × 10 −6 Torr at room temperature. The transmission spectra (measured in the wavelength range of 0.2–0.9 μm) were analyzed by applying O’Leary, Johnson, and Lim (OJL) model based on the joint density of states (JDOS) functions. However, the best fit of the optical data was obtained by considering the two-layer configuration film; the top layer was assumed to be consisted of a bulk AsS material embedded in voids (air). Therefore, OJL model along with Bruggeman effective-medium approximation (BEMA) model was used to determine the effective optical constants of the As–S thin films. The photon energy dependence of the dielectric function, ɛ = ɛ r − iɛ i of the investigated As–S films was presented. The film thickness, absorption coefficient α, refractive index n, extinction coefficient k, static refractive index n(0) and optical band gap E g have been deduced. It was found that with the increase in arsenic content up to the stoichiometric As 40S 60, the indirect optical energy gap decreases, while the refractive index increases.

Association Between Low-Level Environmental Arsenic Exposure and QT Interval Duration in a General Population Study

High-level arsenic exposure is consistently associated with QT prolongation, a risk factor for arrhythmia and sudden cardiac death. Arsenic may act on QT by increasing cardiac calcium currents. The authors hypothesized that low-level arsenic exposure would be associated with QT duration and that this effect would be stronger among persons not using calcium channel blockers. They performed a cross-sectional analysis in elderly men from the Normative Aging Study to analyze associations between toenail arsenic and QT and heart rate-corrected QT (QTc) durations and to examine effect modification by calcium channel blocker use, using linear regression and adjusting for potential confounders. Participants were examined in Boston, Massachusetts, between 2000 and 2002 or in 2006. An interquartile range increase in arsenic concentration was associated with a 3.8-millisecond increase in QT (95% confidence interval: 0.82, 6.8) and a 2.5-millisecond increase in QTc (95% confidence interval: 0.11, 4.9). There was no evidence of effect modification by medication use for either QT (P = 0.93) or QTc (P = 0.58). The authors observed positive associations between a biomarker of arsenic exposure and QT duration but found no evidence of effect modification by calcium channel blocker use, possibly because of modest power.

Geochemistry of redox-sensitive elements and sulfur isotopes in the high arsenic groundwater system of Datong Basin, China

High arsenic groundwater in the Quaternary aquifers of Datong Basin, northern China contain As up to 1820 µg/L and the high concentration plume is located in the slow flowing central parts of the basin. In this study we used hydrochemical data and sulfur isotope ratios of sulfate to better understand the conditions that are likely to control arsenic mobilization. Groundwater and spring samples were collected along two flow paths from the west and east margins of the basin and a third set along the basin flow path. Arsenic concentrations range from 68 to 670 µg/L in the basin and from 3.1 to 44 µg/L in the western and eastern margins. The margins have relatively oxidized waters with low contents of arsenic, relatively high proportions of As(V) among As species, and high contents of sulfate and uranium. By contrast, the central parts of the basin are reducing with high contents of arsenic in groundwater, commonly with high proportions of As(III) among As species, and low contents of sulfate and uranium. No statistical correlations were observed between arsenic and Eh, sulfate, Fe, Mn, Mo and U. While the mobility of sulfate, uranium and molybdenum is possibly controlled by the change in redox conditions as the groundwater flows towards central parts of the basin, the reducing conditions alone cannot account for the occurrence of high arsenic groundwater in the basin but it does explain the characteristics of arsenic speciation. With one exception, all the groundwaters with As(III) as the major As species have low Eh and those with As(V) have high Eh. Reductive dissolution of Fe-oxyhydroxides or reduction of As(V) are consistent with the observations, however no increase in dissolved Fe concentration was noted. Furthermore, water from the well with the highest arsenic was relatively oxidizing and contained mostly As(V). From previous work Fe-oxyhydroxides are speculated to exist as coatings rather than primary minerals. The wide range of δ 34S [SO4] values (from − 2.5 to + 36.1‰) in the basin relative to the margins (from + 8‰ to + 15‰) indicate that sulfur is undergoing redox cycling. The highly enriched values point to sulfate reduction that was probably mediated by bacteria. The presence of monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) is also evidence of microbial reactions. The depleted signatures indicate that some oxidation of depleted sulfide occurred in the basin. It must be noted that the samples with depleted sulfur isotope values have very low sulfate concentrations and therefore even a small amount of sulfide oxidation will bias the ratio. No significant correlation was observed between δ 34S [SO4] values and total arsenic contents when all the samples were considered. However, the wells in the central basin do appear to become enriched in δ 34S [SO4] as arsenic concentration increases. Although there is evidence for sulfate reduction, it is clear that sulfate reduction does not co-precipitate or sequester arsenic. The one sample with high arsenic that is oxidizing cannot be explained by oxidation of pyrite and is likely an indication that there are multiple redox zones that control arsenic speciation but not necessarily its mobilization and contradict the possibility that Fe-oxyhydroxides sorb appreciable amounts of arsenic in this study area. It is evident that this basin like other two young sedimentary basins (Huhhot and Hetao in Inner Mongolia) of northern China with high arsenic groundwater is transporting arsenic at a very slow rate. The data are consistent with the possibility that the traditional models of arsenic mobilization, namely reductive dissolution of Fe-oxyhydroxides, reduction of As(V) to more mobile As(III), and bacteria mediated reactions, are active to varying degrees. It is also likely that different processes control arsenic mobilization at different locations of the basin and more detailed studies along major flow paths upgradient of the high arsenic aquifers will shed more light on the mechanisms.

Effects of Fulvic and Humic Acids on Arsenate Adsorption to Goethite: Experiments and Modeling

Data for interactions between arsenate (AsO4(3-) and fulvic acids (FA) or humic acids (HA) at the surface of goethite are presented (pH 3-7, ionic strength 2 mM and 10 mM). Adsorption of FA and HA leads to desorption of arsenate and a correspondingly strong increase of arsenic concentration in solution. Adsorption of both FA and HA is mutually decreased by the competition with arsenate. The competition between FA and arsenate is much stronger than that between HA and arsenate. Using an advanced model, the LCD model (Ligand and Charge Distribution), arsenate adsorption to goethite in the presence of both adsorbed FA and HA can be predicted reasonably well. The stronger effects of FA on arsenate adsorption are caused, according to the model, by its spatial location which is closer to the oxide surface, and as a consequence, the electrostatic interactions between adsorbed FA particles and arsenate ions are much stronger than those for HA particles. The results show that site and electrostatic competition are the major mechanisms explaining the effects of natural organic matter on the arsenic speciation, whereas other possible mechanisms, such as a chemical reduction of arsenate to arsenite and formation of ternary organic arsenic complexes, are of minor significance.

Arsenic distribution and bioaccessibility across particle fractions in historically contaminated soils

Incidental soil ingestion is a common contaminant exposure pathway for humans, notably children. It is widely accepted that the inclusion of total soil metal concentrations greatly overestimates the risk through soil ingestion for people due to contaminant bioavailability constraints. The assumption also assumes that the contaminant distribution and the bioaccessible fraction is consistent across all particle sizes. In this study, we investigated the distribution of arsenic across five particle size fractions as well as arsenic bioaccessibility in the <250-, <100-, <10- and 2.5-microm soil particle fractions in 50 contaminated soils. The distribution of arsenic was generally uniform across the larger particle size fractions but increased markedly in the <2.5-microm soil particle fraction. The marked increase in arsenic concentration in the <2.5-microm fraction was associated with a marked increase in the iron content. Arsenic bioaccessibility, in contrast, increased with decreasing particle size. The mean arsenic bioaccessibility increased from 25 +/- 16% in the <250-microm soil particle fraction to 42 +/- 23% in the <10-microm soil particle fraction. These results indicate that the assumption of static arsenic bioaccessibility values across particle size fractions should be reconsidered if the ingested material is enriched with small particle fractions such as those found in household dust.

Chronic exposure to low concentration of arsenic is immunotoxic to fish: Role of head kidney macrophages as biomarkers of arsenic toxicity to Clarias batrachus

The present study was aimed at elucidating the effect of chronic low-level arsenic exposure on the head kidney (HK) of Clarias batrachus and at determining the changes in head kidney macrophage (HKM) activity in response to arsenic exposure. Chronic exposure (30 days) to arsenic (As 2O 3, 0.50 μM) led to significant increase in arsenic content in the HK accompanied by reduction in both HKM number and head kidney somatic index (HKSI). Arsenic induced HK hypertrophy, reduction in melano-macrophage population and increased hemosiderin accumulation. Transmission electron microscopy of 30 days exposed HKM revealed prominent endoplasmic reticulum, chromatin condensation and loss in structural integrity of nuclear membrane. Head kidney macrophages from exposed fish demonstrated significant levels of superoxide anions but on infection with Aeromonas hydrophila were unable to clear the intracellular bacteria and died. Exposure–challenge experiments with A. hydrophila revealed that chronic exposure to micromolar concentration of arsenic interfered with the phagocytic potential of HKM, helped in intracellular survival of the ingested bacteria inside the HKM inducing significant HKM cytotoxicity. The immunosuppressive effect of arsenic was further evident from the ability of A. hydrophila to colonize and disseminate efficiently in exposed fish. Enzyme linked immunosorbent assay indicated that chronic exposure to arsenic suppressed the production of pro-inflammatory ‘IL-1β like’ factors from HKM. It is concluded that arsenic even at very low concentration is immunotoxic to fish and the changes observed in HKM may provide a useful early biomarker of low-level xenobiotic exposure.

Effects of arsenic mole fraction x on the gain characteristics of type-II InP/GaAsxSb1−x DHBTs

The static gain characteristics of N–p–N InP/GaAsxSb1−x/InP double heterojunction bipolar transistors (DHBTs) were studied as a function of the base arsenic (As) mole fraction x. Compared to the devices with a lattice-matched base (x=0.51), a current gain improvement largely arising from a base current reduction is observed in DHBTs with higher As base mole fractions (and consequently a reduced type-II conduction band discontinuity ΔEC at the emitter-base heterojunction). Both the surface periphery and the intrinsic recombination currents decrease markedly as the base arsenic concentration increases. The present work therefore unambiguously demonstrates that the emitter type-II conduction band discontinuity between the InP emitter and the GaAsxSb1−x base enhances the undesirable emitter size effects (ESEs) and increases intrinsic recombination currents directly under the emitter contact.