Search

High As concentration in groundwater of Datong Basin has emerged as an issue of great concern in the past decade because of its serious impact on the health of many people. The present study is to our knowledge the first attempt model the transport of arsenic in this system using a 1D reactive transport model (PHREEQC). Based on published field data from Shanyin Field Site (Datong Basin), the importance of the (bio)geochemical processes for arsenic mobility is evaluated quantitatively using geochemical models of growing complexity. Arsenic mobility during the surface water and groundwater interactions can be explained by the reductive dissolution of iron oxyhydroxides, sulfate, nitrate and arsenate, and by surface sorption/de-sorption occurring in response to changes in geochemical conditions. Both the Fe(III) surface complexation model and the 1D reactive transport model were employed to depict the arsenic transport in shallow groundwater system during the surface water-groundwater interactions. The surface complexation model results showed that a total of 0.34 mmol and 0.56 mmol arsenic were sorbed onto Fe(III) oxyhydroxides for Well 1-2S and Well 2-2S, respectively, reflecting the important role of surface sorption process on arsenic transport. The 1D model results revealed that redox processes were also critical. The improved calibration of model simulations involving both of these components indicates that the combination of processes is critical to understanding and characterising the transport of arsenic in groundwater during groundwater surface water interaction, especially close to the surface water body. [ABSTRACT FROM AUTHOR]

In the southern part of the Cenozoic Duero Basin (Spain), naturally occurring arsenic and uranium in groundwater sometimes occur in concentrations exceeding the limits for potable water. Usually, concentrations of these elements are only slightly above the limit, but this is sufficient to invalidate its use as drinking water. Hydrogeotoxic risk or hydrogeotoxicity (HGT) is defined as the quotient between the observed concentration of an element and the limit set by health regulations (such as by the World Health Organization, WHO). Areas at risk of HGT from a given Potentially Toxic Geogenic Trace Element (PTGTE) are defined a quotient of > 1. Hydrogeotoxicity of arsenic and uranium (HGT As and HGT U ) were calculated for water samples and 34% returned HGT As above 1. For uranium, different HGT indexes were considered against a variety of thresholds for drinking water established by different countries and organizations (10 μg/L, Germany; 15 μg/L, WHO, 2004; 30 μg/L, WHO, 2011/US-EPA, 2011): 48% samples returned HGT U10 > 1; 29% samples, HGT U15 > 1 and 7% had HGT U30 > 1. In the water samples analyzed, the highest arsenic content were usually associated with the highest uranium concentrations. However sometimes these two hydrogeotoxicities do not coincide and the HGT As and HGT U10 distributions show different patterns. Hydrogeotoxicity due to more than one element (HGT As and HGT U10 ) was also considered; 17% samples showed a potentially hydrogeotoxic risk linked to both PTGTEs, leading to the delimitation of these zones as especially vulnerable to a combined hydrogeotoxic hazard. The linear distribution of HGT As seems to be related to the structure of the Cenozoic Duero Basin and to deep water inflows that are enriched in As and U, which are associated with its fissured basement. The HGT U can be partly linked to these deep flows with a significant hydrothermal component, but they are also linked to secondary processes occurring in the sedimentary basin, which could explain the scattered distribution of HGT U in some areas. As well as the HGT values, which are based on total concentrations, bioavailability of arsenic and uranium species was also considered in order to provide a comprehensive assessment of hydrogeotoxic risk over the study area. In all samples with HGT As > 1, arsenic was present as As(V) inorganic form. Likewise, in samples with HGT U10 > 1, uranium appears as U(VI). This hydrogeotoxic anomaly must be related to both the chemical and radiological hazards. [ABSTRACT FROM AUTHOR]

Hydrogeological and geochemical approaches were combined to investigate the impact of a short-term artificial flooding event on arsenic and associated hydrogeochemisty at a field monitoring site of high arsenic aquifers in Datong Basin, northern China. The groundwater levels fluctuated in response to the flooding (the surface water level and groundwater level fluctuated with time in a range of over 80 cm and 30 cm, respectively), indicating groundwater–surface water interaction. Redox indices, major ions, trace element concentrations, O, H and Sr isotope compositions for surface water and groundwater were determined before and after the flooding. δ 2 H and δ 18 O values for all water samples plot close to the global meteoric water line (GMWL); a subset of the samples (shallow wells) averagely increased from − 11.78 to − 11.26 for δ 18 O and from − 86.59 to − 83.49 for δ 2 H, commensurate with mixing with ~ 10% surface water. The relationship between compositions of strontium isotope 87 Sr/ 86 Sr ratios and Mg concentration also clearly indicates the effect of mixing between groundwater and surface water. Before and after the flooding, there were obvious variations in water chemistry, including arsenic concentrations. Increases and positive correlations between Cl − and Na + , Mg 2 + , Ca 2 + and SO 4 2 − following flooding revealed surface water infiltration into groundwater, plus additional input from dissolution of evaporate minerals and/or evaporated pore-water. Organic matter and oxygen are carried into groundwater together with surface water; oxidation of organic matter leads to exhaustion of oxygen and consumption of terminal electron acceptors (e.g. ferric iron, sulfate, nitrate) inducing a more reducing groundwater environment (indicated by decreased ORP values). Consequently, reductive dissolution of iron oxides/hydroxides resulted in an observed elevation of HS, NH 4 -N, Fe(II), with the concentrations increasing from 5 μg/L to 10 μg/L, from 0.19 mg/L to 0.68 mg/L and from 0.06 mg/L to 1.86 mg/L, respectively. This may explain that the As concentrations were enhanced after surface water flooding (from mean value of 22.6 μg/L to 31 μg/L). However, a positive correlation was observed between enhance values of As and Cl in the groundwater after flooding is interpreted as reflecting re-dissolution of evaporate crusts and/or saline pore water during infiltration, and this may alone explain the increase in As observed in the groundwater. Surface water As concentration increased to a minor degree following flooding also (from 14 μg/L to 15.1 μg/L), possibly reflecting return flow of the high As groundwater during a temporary switch to gaining conditions. [ABSTRACT FROM AUTHOR]

Arsenic concentrations were analysed for 328 water samples collected in the Vicano–Cimino Volcanic District (VCVD), an area where severe contamination of groundwater has become a serious problem following the recent application of the EU Directive on the maximum allowable concentration level for As in drinking waters. In addition, uranium and vanadium concentrations were also analysed in light of the enhanced interest on their environmental toxicity. Waters were collected from springs and wells fed by cold and shallow volcanic–sedimentary aquifers, which locally represent the main drinking water source. Thermal springs (≤ 63 °C) related to an active hydrothermal reservoir and waters associated with a CO 2 -rich gas phase of deep provenance were also analysed. The collected data showed that the As concentrations in the shallow aquifers varied in a wide range (0.05–300 μg/L) and were primarily controlled by water–rock interaction processes. High As concentrations (up to 300 μg/L) were measured in springs and wells discharging from the volcanic products, and about 66% exceeded the limit of 10 μg/L for drinking waters, whereas waters circulating within the sedimentary formations displayed much lower values (0.05–13 μg/L; ~ 4% exceeding the threshold limit). Thermal waters showed the highest As concentrations (up to 610 μg/L) as the result of the enhanced solubility of As-rich volcanic rocks during water–rock interaction processes at high temperatures. Where the local structural setting favoured the rise of fluids from the deep hydrothermal reservoir and their interaction with the shallow volcanic aquifer, relatively higher concentrations were found. Moreover, well overexploitation likely caused the lateral inflow of As-rich waters towards not contaminated areas. Uranium and vanadium concentrations of waters circulating in the volcanic rocks ranged from 0.01 to 85 μg/L and 0.05 to 62 μg/L, respectively. Less than 2% of analysed samples exceeded the World Health Organization's provisional guidelines for U (30 μg/L), while none of them was above the Italian limit value of V in drinking water (120 μg/L). Lower U (0.07–22 μg/L and 0.02–13 μg/L, respectively) and V concentrations (0.05–24 μg/L and 0.18–17 μg/L, respectively) were measured in the water samples from the sedimentary aquifer and thermal waters. Local lithology appeared as the main factor affecting the U and V contents in the shallow aquifers, due to the high concentrations of these two elements in the volcanic formations when compared to the sedimentary units. In addition, high U concentrations were found in correspondence with U mineralization occurring within the VCVD, from which U is released in solution mainly through supergene oxidative alteration. Redox conditions seem to play a major role in controlling the concentrations of U and V in waters. Oxidizing conditions characterizing the cold waters favour the formation of soluble U- and V-species, whereas thermal waters under anoxic conditions are dominated by relatively insoluble species. Geostatistical techniques were used to draw contour maps by using variogram models and kriging estimation aimed to define the areas of potential health risk characterized by As, U and V-rich waters, thus providing a useful tool for water management in a naturally contaminated area to local Authorities. [ABSTRACT FROM AUTHOR]

Mobilization of arsenic (As) in groundwater has become a focus of attention in recent years. A few years back, groundwater As is found as a geogenic contaminant in the upper stream Ganges River basin immediately adjoining to the Himalayan foothills (the Terai Region of Nepal). The source is said to be leached due to weathering of As-bearing minerals. In this study, geologic, hydrogeologic, and geochemical data were used to characterize the As source and the geochemical process controlling As-mobilization in the groundwater aquifers of Terai Region. The findings suggest that the reductive dissolution of iron-oxyhydroxide is the main mechanism of As-mobilization in Terai aquifers. This mechanism is supported by a number of evidences including, 1) presence of arsenolite and scorodite As-bearing minerals; 2) presence of high concentration of As, Fe and low concentration of SO 4 2 − and NO 3 − ; 3) presence of strong linkage between As and HCO 3 − and negative correlation between As and oxidation reduction potential; 4) presence of abundant percentage of Fe and Mn-oxides in the sediment samples; 5) presence of similar depth profile trend of As with those of Fe and Mn-oxides; 6) presence of Fe, O and Mn confirmed by energy dispersive X-ray spectroscopy analysis; and 6) presence of predominant form of As adsorbed on organic matter and Fe-oxyhydroxide phases of sequential leaching. [ABSTRACT FROM AUTHOR]

Abstract: Temporal variations in groundwater As concentration are crucial for understanding the mechanisms of As cycling and developing effective strategies for sustainable usage of low As groundwater in As-affected areas. Little is known about temporal variations in As concentration of shallow groundwater from the Hetao basin. Groundwater samples were taken once each year in July/August from 2006 to 2010. Another sampling campaign was carried out in November 2006. Groundwater tables were monitored as well. Results showed that water levels were higher during December–April than during May–September in the front of the alluvial fans where irrigation relied mainly on groundwater. In contrast, the highest water levels were observed in May–June and in November in the flat plain region where the diverted Yellow River water was utilized for irrigation. Concentrations of Na+, Cl−, and HCO3 − were relatively constant over 4years, although most wells showed slight decreasing trends in concentrations of Ca2+ and Mg2+. Although concentrations of As in most wells were lower in 2006 than in 2007, there were no significant changes in As concentration between 2006 and 2010 at p =0.05. Shallow groundwaters sampled in November from the flat plain region with surface water irrigation showed generally higher As concentrations than in July. This was caused by more reducing conditions due to less oxygen dispersing into the aquifers when irrigation water flooded the soil and perhaps the un-saturated zone, as evidenced by the lower redox potential of shallow groundwater in November. Results of μ-XRF showed that As contents were well correlated with Fe contents in the sediment samples from the shallow aquifers. The most plausible explanation for the decoupling between temporal variation in As concentration and in Fe concentration was expected to be the reductive desorption of As(V), due to the analogical variation trends between As(III) and total As. [Copyright &y& Elsevier]

Groundwater in sedimentary deposits in China, Southern, and Southeast Asia down gradient from the Tibetan plateau contains elevated As concentrations on a regional scale. To ascertain the possibility of source region As enrichment, samples of water (n=86), stream sediment (n=77) and soil (n=73) were collected from the Singe Tsangpo (upstream of the Indus River), Yarlung Tsangpo (upstream of the Brahmaputra River) and other drainage basins in Tibet in June of 2008. The average arsenic concentration in stream waters, sediments and soils was 58±70μg/L (n=39, range 2–252μg/L), 42±40mg/kg (n=37, range 12–227mg/kg), and 44±27mg/kg (n=28, range 12–84mg/kg) respectively for the Singe Tsangpo and was 11±17μg/L (n=30, range 2–83μg/L), 28±11mg/kg (n=28, range 2–61mg/kg), and 30±34mg/kg (n=21, range 6–173mg/kg) respectively for the Yarlung Tsangpo. A dug well contained 195μg/L of As. In addition to elevated As levels in surface and shallow groundwater of Tibet, hot spring and alkaline salt lake waters displayed very high As levels, reaching a maximum value of 5,985μg/L and 10,626μg/L As, respectively. The positive correlation between [As] and [Na]+[K] in stream waters indicates that these surface water arsenic enrichments are linked to the hot springs and/or salt lakes. Further, 24% of As in stream sediment is reductively leachable, with bulk As displaying a positive correlation with stream water As, suggesting sorption from stream water. In contrast, the fraction of reductively leachable As is negligible for soils and several rock samples, suggesting that As in them is associated with un-weathered minerals. Whether the pronounced As anomaly found in Tibet affects the sedimentary As content in deltas downstream or not requires further study. [ABSTRACT FROM AUTHOR]

Abstract: Effects of phosphate and bicarbonate concentration on mobilization of arsenic in aquifer sediments have not been extensively studied in flow-through experiments, where the dynamic-release behavior of elements can be monitored. In this work, these effects were investigated both through batch and column experiments, using a high-arsenic sediment sample from the Datong Basin, northern China. A solution of 1.0mM Ca(NO3)2 was first applied to a water-saturated column packed with the sediment; this was followed by leaching with either 0.10mM Na2HPO4 or 8.2mM NaHCO3 solutions. When the sediment was initially leached with 1.0mM Ca(NO3)2 solution, a rapid spike of As, Fe, Mn, and major cations was observed in the first 20 column pore volumes, reflecting the initial equilibration of the sediment to the influent Ca(NO3)2 in response to cation exchange (for cations) and sorption equilibrium (for Mn, Fe, As).After the Ca(NO3)2 solution was replaced with either the Na2HPO4 or NaHCO3 solution, a rapid increase in As concentration in the effluent was observed, consistent with the batch test results. Induced desorption of As from oxyhydroxide sorbents by Na2HPO4 suggests that phosphate competition was the major factor responsible for the observed increase of As, as indicated by a coinciding increase of K+ replaced in the exchange process. In the column leached with 8.2mM NaHCO3, high concentrations of sodium result in greater clay dispersion, and the transport of Fe/Mn oxyhydroxides with adsorbed arsenic may account for the enhanced arsenic concentration in the effluent, as suggested by the concurrently observed increase in Fe and Mn concentrations in the effluent. [Copyright &y& Elsevier]

Groundwater is a strategic resource in Yinchuan Plain, with deep groundwater increasingly used for drinking water supply to reduce arsenic exposure of rural villagers who have relied on shallow tube wells for drinking. To understand the sources and mobilization processes for arsenic enrichment in groundwater, a well water and sediment geochemistry study was carried out. Considerable spatial variability of groundwater arsenic exists. Arsenic concentration in deeper groundwater (40–250m) was generally less than 10μg/L (n =26) except for seven wells, with a mean of 7.0μg/L (n =33). For shallower depths (4–40m), As concentration increased from <1μg/L in the alluvial plain at higher elevation to 177μg/L near the center of alluvial lacustrine plain at lower elevation. Two clusters of high arsenic, shallow groundwater run nearly parallel to the Yellow River present day and ancient courses as two narrow strips where groundwater flow is sluggish. Arsenic content in sediments ranged from 3.7μg/g to 49.8μg/g with an average of 9.2μg/g, and was positively correlated with concentrations of sediment Cu, Fe2O3, Mn, Ba, Zn, F and organic C. Concentrations of arsenic between Dec. 2007 to Aug. 2011 in groundwater samples collected monthly vary more for the shallower depths (8m: 76±29μg/L; 12m: 116±27μg/L; 15m: 88±26μg/L; 20m: 164±14μg/L) than for the deeper depths (30m: 35±4μg/L; 80m: 33±5μg/L). Temporal variability of As concentrations in shallow groundwater correlates with water levels, driven by irrigation to a large extent. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates how spatial distributions of groundwater arsenic (As) concentration and speciation are related to and are dependent on regional hydraulic gradients in a shallow aquifer containing elevated groundwater As in the Hetao Plain of Northern China. Groundwater samples (n=165) were collected along three representative transects in the western, central and eastern parts of the Hetao Plain, spanning a wide range of total As concentration (0.36–916.7μg/l), arsenite concentration (0.2–719.4μg/l) and hydraulic gradients (0.11–23.31‰). The hydrodynamic conditions of the aquifer generally fall into the following four categories from the north to the south: Piedmont and discharge areas with high hydraulic gradient, runoff areas with weak or strong hydraulic gradient, and areas influenced by recharge from the Yellow River. Along all three transects, high groundwater As usually corresponds to low hydraulic gradients except for the discharge areas. In the runoff area in central Hetao Plain and the recharge area in southern Hetao Plain, the concentration of arsenic is more than 10μg/l when the hydraulic gradient is less than 0.8‰. An empirical relationship between groundwater As concentration and groundwater hydraulic gradient can be established for the runoff area. The systematic changes in As concentrations and speciation along the groundwater flow path in the shallow groundwater support the notion that low hydraulic gradient of the groundwater is important in promoting As enrichment in groundwater. [Copyright &y& Elsevier]

Abstract: Arsenicosis and fluorosis, two endemic diseases known to result from exposure to their elevated concentrations in groundwater of north China used by many rural households for drinking, have been major public health concerns for several decades. Over the last decade, a large number of investigations have been carried out to delineate the spatial distribution and to characterize the chemical compositions of high As and F groundwaters with a focus on several inland basins in north China. Findings from these studies, including improved understanding of the hydrogeological and geochemical factors resulting in their enrichments, have been applied to guide development of clean and safe groundwater in these endemic disease areas. Survey efforts have led to the recognition of iodine in groundwater as an emerging public health concern. This paper reviews the new understandings gained through these studies, including those published in this special issue, and points out the direction for future research that will shed light on safe guarding a long-term supply of low As and F groundwater in these water scarce semi-arid and arid inland basins of north China. [Copyright &y& Elsevier]

Abstract: Sediments from two boreholes drilled in the Drava and Sava depressions were analyzed to determine the origin of the elevated arsenic (As) concentrations in groundwaters in eastern Croatia. The composition of the sediments was investigated by total chemical analysis and sequential extraction. In addition, groundwater samples were taken from eight producing wells, and hydrochemical and trace element and As speciation analyses were performed. The concentrations of As in the sediment were high (up to 471 and 65.1mg/kg, in the <0.065mm fraction in the boreholes in the Drava and Sava depression respectively) supporting the hypothesis proposed in a previous hydrochemical study that the Middle and Upper Pleistocene sediments are the main source of As in eastern Croatian groundwaters. Mineralogical and chemical analyses showed that sediments from the Drava and the Sava boreholes differed, supporting different origins of the sediments in the boreholes concerned: the provenance of PVc-3 sediments being the Alps, and of G1 sediments, the Bosnian mountains. In both boreholes, the large amount of As was bound to amorphous Fe and Mn (hydr)oxides (on average 32% and 60% in boreholes PVc-3 and G1 respectively). Sediment and groundwater analyses indicate that reductive dissolution of iron (hydr)oxides and concomitant release of sorbed or co-precipitated As into the groundwater is ready to occur. Since the groundwaters in eastern Croatia are generally anoxic and reducing conditions, in which S2− and Fe2+ are stable, prevail the concentration of As released by reductive dissolution of iron (hydr)oxides may be controlled by the secondary formed sulfides which could act as a sink rather than as a source of As in the groundwater. Depending on local geomorphological and hydrogeochemical conditions, in the zones with a longer groundwater retention time, pH dependant As desorption from iron (hydr)oxides can occur and other trace elements such as Mo may become mobile. [Copyright &y& Elsevier]

Abstract: Groundwater contaminated with arsenic (As), when extensively used for irrigation, causes potentially long term detrimental effects to surface soils. Such contamination can also directly affect human health when irrigated crops, such as rice, vegetable and fruits, are used for human consumption. Therefore, an understanding of the sorption and desorption behavior of As in surface soils is of high importance, because these processes regulate the bioavailability of As in the soil environment. In this study, we have collected soils from guava orchards of Baruipur, West Bengal, and characterized soil chemistry and batch sorption and desorption behavior in the laboratory. The sorption and desorption behavior of As in the soils were examined using the Langmuir and Freundlich sorption equation. Regression analysis of the soil chemical characteristics and sorption equation parameters were also performed. The results suggest that the sorption behavior of arsenate is highly dependent on soil characteristics, specifically organic carbon, clay and Al2O3 content of the soils. Whereas desorption behavior is critically influenced by the presence of high concentrations of amorphous and/or crystalline Fe2O3 in the soils. Retention of the significant portion of As in the soils (~84% of the total) suggests that As in the orchard soils may not be highly bioavailable to plants for uptake. However, more detailed studies will be required to ascertain the role of individual soil components on the As sorption and desorption processes. [Copyright &y& Elsevier]

Abstract: Groundwater with high geogenic arsenic (As) is extensively present in the Holocene alluvial aquifers of Ghazipur District in the middle Gangetic Plain, India. A shift in the climatic conditions, weathering of carbonate and silicate minerals, surface water interactions, ion exchange, redox processes, and anthropogenic activities are responsible for high concentrations of cations, anions and As in the groundwater. The spatial and temporal variations for As concentrations were greater in the pre-monsoon (6.4–259.5μg/L) when compared to the post-monsoon period (5.1–205.5µg/L). The As enrichment was encountered in the sampling sites that were close to the Ganges River (i.e. south and southeast part of Ghazipur district). The depth profile of As revealed that low concentrations of NO3 − are associated with high concentration of As and that As depleted with increasing depth. The poor relationship between As and Fe indicates the As release into the groundwater, depends on several processes such as mineral weathering, O2 consumption, and NO3 − reduction and is de-coupled from Fe cycling. Correlation matrix and factor analysis were used to identify various factors influencing the gradual As enrichment in the middle Gangetic Plain. Groundwater is generally supersaturated with respect to calcite and dolomite in post-monsoon period, but not in pre-monsoon period. Saturation in both periods is reached for crystalline Fe phases such as goethite, but not with respect to poorly crystalline Fe phases and any As-bearing phase. The results indicate release of arsenic in redox processes in dry period and dilution of arsenic concentration by recharge during monsoon. Increased concentrations of bicarbonate after monsoon are caused by intense flushing of unsaturated zone, where CO2 is formed by decomposition of organic matter and reactions with carbonate minerals in solid phase. The present study is vital considering the fact that groundwater is an exclusive source of drinking water in the region which not only makes situation alarming but also calls for the immediate attention. [Copyright &y& Elsevier]

Abstract: Arsenic contaminated waters are not uncommon; indeed from naturally occurring contaminated waters through to those that are a direct consequence of human activities such as mining, all are affecting the quality of water resources worldwide. The ever increasing demands on natural water resources mean that the effective control of this toxic contaminant is paramount and this is reflected in the ever increasing global legislation. There are currently three mechanisms by which arsenic is commercially treated in effluents. These are physical separation processes such as reverse osmosis, precipitation/adsorption processes, some of which are bacterially assisted, and a whole variety of ion exchange processes, again with some bacterial enhancement. The choice of treatment is not only driven by cost but by the chemistry of the water and the water quality standard to be met. In this study a very high arsenic enriched groundwater, containing in excess of 25,000 µg/L arsenic, was treated by a typical treatment method through a continuously operated pilot plant. In the treatment, iron III salts were added to the influent in order to form precipitates with the arsenic and to form an adsorptive surface that would assist with treatment of the enriched water. This addition of iron III salts for the removal of arsenic is common practice in the water treatment industry as the resulting iron III arsenates are highly stable. However, results from the pilot plant show that the process was further enhanced by the addition of small amounts of hydrogen peroxide. Hydrogen peroxide is a powerful oxidising reagent and assists in ensuring the complete conversion of any arsenic III to arsenic V that was then effectively removed in the pilot plant. After treatment residual arsenic levels of 10 µg/L were obtained compared to 68 µg/L without oxidation reagent addition. [Copyright &y& Elsevier]