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| 4. |
- Bhattacharya, Prosun, et al.
(författare)
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Distribution and mobility of arsenic in the Rio Dulce alluvial aquifers in Santiago del Estero Province, Argentina
- 2006
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 358:1-3, s. 97-120
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Tidskriftsartikel (refereegranskat)abstract
- Factors controlling arsenic (As) mobilization in the aquifers of the Rio Dulce alluvial cone were investigated. Groundwater analyses show severe As contamination (average concentration of 743 mu g/L) from geogenic sources, but spatial variability of As concentration is considerable. Sequential leaching of sediment samples from unsaturated zone using de-ionised water, bicarbonate, acetate, and oxalate extracted As to different extents. Sediment oxalate extraction showed that Al and Mn oxide and hydroxides are more abundant than Fe oxides and hydroxides, in spite of similar total Fe, Mn, and Al concentrations in the sediment. Speciation calculations performed for saturated zone samples indicated that Fe and Al oxides and hydroxides are stable in groundwater, suggesting that As adsorption processes may be to some extent controlled by the presence of Fe and Al mineral phases. Principal Component Analysis (PCA) showed that As is related to F, V, Mo, B, Si, most likely due to their common origin in volcanic ash. This suggests the volcanic ash as the probable source of groundwater As. Locally, elevated pH values linked to carbonate dissolution, cation exchange, and dissolution of silicates promote release of adsorbed As. Another factor contributing to the release of As locally may be the input of organic matter from excessive irrigation. The conceptual model of As release includes: i) As influx from dissolution of volcanic glass in volcanic ash, ii) adsorption of As on the surface of Fe and Al mineral phases in relatively low pH zones, and iii) high mobility of As in high pH zones. Future work should be focused on the determination of mineralogical forms of As in volcanic ash and on detailed investigation on factors controlling As mobility.
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| 5. |
- Bhattacharya, Prosun, et al.
(författare)
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Groundwater characteristics in the shallow aquifers of Huhhot region in Inner Mongolia, PR China : Implications on the mobilisation of arsenic
- 2006
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Ingår i: Natural Arsenic in Groundwaters of Latin America. ; , s. 11-12
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Elevated arsenic (As) concentration ingroundwater is becoming a worldwide problem. In Huhhot Alluvial Basin (HAB) in Inner Mongolia, People’s Republic ofChina, a population of over a million isexposed to severe health risk due to theconsumption of groundwater with high Asconcentration. In some arsenic seriouslyaffected areas, As concentration reach 1491µg L-1, 149 times over WHO’s drinkingwater guideline value for As and exceed theChinese drinking water standard by a factorof 30 times. Due to the acute shortage ofsafe water supply and inefficient watermanagement system, people are compelledto drink groundwater with high As concentration. Long period ingestion of water withhigh As concentration have lead to chronicarsenic poisoning among the residents ofthe region. This present work deals with thehydrogeochemical characterisation of thegroundwater of the shallow alluvial aquifers and their implications on the chemistryand its relation to the mechanism of Asmobilization in the HAB.Groundwater samples were collected during October 2003, from 29 sites in the village of Tie Men Jing, located about 100 kmfrom Inner Mongolia’s capital Huhhot. ThepH, redox potential (Eh), temperature andelectrical conductivity were measured atsites while major ions, trace elements including As total and As (III) were analyzedin laboratories at the Royal Institute ofTechnology and Stockholm University inSweden. Groundwater is generally neutralto alkaline and the pH varies from 6.67 to8.7. The redox potential (Eh) lies between74 and 669 mV. The electrical conductivity(EC) range varies from 581 to 5200 µS cm-1. Temperature ranges from 9.1 to 13.5 °C.Depths of wells are from 4 m to 75 m.Groundwater is mostly of Na-Mg-HCO3-Cl-type and dominated by HCO3-and Cl-asthe predominant anions. The concentrationsof SO42-range between 0.3 and 172.8 mg L-1and there is a trend of decreasing sulfateconcentrations with increase in well depth.The levels of NO3-were lower than theWHO´s guideline value of 50 mg L-1in 27wells. These high NO3-concentrations could have been caused by anthropogeniccontamination due to the sanitation practices.The PO43-concentration ranges between 0.04to 2.6 mg L-1.Total As concentration ranged from belowdetect limit (5.2 µg L-1) to 141 µg L-1. In 28of the investigated wells, As levels exceededWHO’s guideline value 10 µg L-1and 17wells exceeded Chinese standard 50 µg L-1.Among the 42 groundwater samples of theshallow aquifers only three complied withthe WHO drinking water guideline value forAs. The dominant species in the groundwaterwas As (III). In the 29 wells of Tie MenJing, the concentration of Fe and Mn –exceeded the WHO’s guideline value by afactor of 10.The aquifers are composed of Quaternary(mainly Holocene) fluvial and lacustrinesediments. High As occurring in anaerobicgroundwater in low-lying areas is associatedwith high concenrations of dissolved Fe andMn. Improved water supply system, employment new water and energy resources,poverty fighting and expertise cooperationare recommended to solve Huhhot basinrural area’s drinking water problem.
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| 7. |
- Bundschuh, J., et al.
(författare)
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Arsenic in Latin America : New findings on source, mobilization and mobility in human environments in 20 countries based on decadal research 2010-2020
- 2020
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Ingår i: Critical reviews in environmental science and technology. - : Taylor and Francis Inc.. - 1064-3389 .- 1547-6537. ; , s. 1-119
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Forskningsöversikt (refereegranskat)abstract
- Today (year 2020), the globally recognized problem of arsenic (As) contamination of water resources and other environments at toxic levels has been reported in all of the 20 Latin American countries. The present review indicates that As is prevalent in 200 areas across these countries. Arsenic is naturally released into the environment and mobilized from geogenic sources comprising: (i) volcanic rocks and emissions, the latter being transported over thousands of kilometers from the source, (ii) metallic mineral deposits, which get exposed to human beings and livestock through drinking water or food chain, and (iii) As-rich geothermal fluids ascending from deep geothermal reservoirs contaminate freshwater sources. The challenge for mitigation is increased manifold by mining and related activities, as As from mining sites is transported by rivers over long distances and even reaches and contaminates coastal environments. The recognition of the As problem by the authorities in several countries has led to various actions for remediation, but there is a lack of long-term strategies for such interventions. Often only total As concentration is reported, while data on As sources, mobilization, speciation, mobility and pathways are lacking which is imperative for assessing quality of any water source, i.e. public and private.
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| 8. |
- Bundschuh, Jochen, et al.
(författare)
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Hydrogeochemistry principles for geochemical modeling
- 2011
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Ingår i: Geochemical Modeling of Groundwater, Vadose and Geothermal Systems. - : CRC Press. - 9781439870532 - 9781138074446 ; , s. 3-26
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- A wide diversity of physical and chemical processes control the distribution of species in waters in the vadose zone above the water table, and in the saturated zone below. The mineralogical composition of rocks or sediments, chemical reactions between solid, aqueous and gas phases, and oxidation/reduction (redox) processes are principal factors that influence the chemical composition of vadose-zone, ground-and surface waters, and the concentrations and mobilities of individual species.
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| 10. |
- Mahanta, C., et al.
(författare)
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Hydrogeochemical controls on mobilization of arsenic in groundwater of a part of Brahmaputra river floodplain, India
- 2015
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Ingår i: Journal of Hydrology: Regional Studies. - : Elsevier BV. - 2214-5818.
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Tidskriftsartikel (refereegranskat)abstract
- Study region: Arsenic enriched groundwater regime within low-industrialized Brahmaputra floodplains in Assam, NE India. Study focus: We examined the origin, distribution and processes of As release by investigating the salient groundwater chemistry and subsurface sedimentological characteristics. Besides collection of groundwater samples from domestic and public water supply wells, sediment samples from boreholes were investigated for textural and colour linkages. New hydrological insights for the region: Arsenic concentrations above the WHO guideline value of 10. μg/L were present in 33 wells and above the previous Indian national drinking standard of 50. μg/L were present in 15 wells. The green-olive colour sediments were more likely to yield As-enriched groundwater. The supersaturation of groundwater with respect to Fe(II) minerals, such as siderite and vivianite, explained the poor correlation between dissolved As and Fe. The result reinforced the phenomenon of reductive dissolution of Fe(III) oxyhydroxides releasing As to groundwater. This study throws light on the processes and mechanisms involved with As release in groundwater. The homogenous floodplain terrain makes the hydrological As imprint unambiguous and the hydrogeological signatures untarnished. Considering the absence of anthropogenic sources in the study area, the conclusions on the nature and causes for As release to groundwater looked dependable although the final contamination at specific subsurface sites would be influenced by advection-dispersion of groundwater flow accompanied by retardation, ion exchange, surface complexation and possible biodegradation.
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| 11. |
- Ormachea Muñoz, Mauricio, et al.
(författare)
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Geogenic arsenic and other trace elements in the shallow hydrogeologic system of Southern Poopó Basin, Bolivian Altiplano
- 2013
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Ingår i: Journal of Hazardous Materials. - : Elsevier BV. - 0304-3894 .- 1873-3336. ; 262, s. 924-940
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Tidskriftsartikel (refereegranskat)abstract
- Environmental settings in the southern area of Lake Poopó in the Bolivian highlands, the Altiplano, have generated elevated amounts of arsenic (As) in the water. The area is characterised by a semiarid climate, slow hydrological flow and geologic formations of predominantly volcanic origin. The present study aimed at mapping the extent of the water contamination in the area and to investigate the geogenic sources and processes involved in the release of As to the groundwater.Ground- and surface-water samples were collected from 24 different sites, including drinking water wells and rivers, in the southern Poopó basin in two different field campaigns during the dry and rainy seasons. The results revealed variable levels of As in shallow drinking water wells and average concentration exceeding the WHO guidelines value. Arsenic concentrations range from below 5.2μg/L (the detection level) to 207μg/L and averages 72μg/L. Additionally, high boron (B) concentrations (average 1902μg/L), and high salinity are further serious concerns for deteriorating the groundwater quality and rendering it unsuitable for drinking. Groundwater is predominantly of the Na-Cl-HCO3 type or the Ca-Na-HCO3 type with neutral or slightly alkaline pH and oxidising character. While farmers are seriously concerned about the water scarcity, and on a few occasions about salinity, there are no concerns about As and B present at levels exceeding the WHO guidelines, and causing negative long term effects on human health.Sediment samples from two soil profiles and a river bed along with fourteen rock samples were also collected and analysed. Sequential extractions of the sediments together with the calculation of the mineral saturation indices indicate that iron oxides and hydroxides are the important secondary minerals phases which are important adsorbents for As. High pH values, and the competition of As with HCO3 and dissolved silica for the adsorption sites probably seems to be an important process for the mobilisation of As in the shallow groundwaters of the region. Continuous monitoring and expansion of monitoring systems are necessary prerequisites for better understanding of the pattern of As mobilisation in the Southern Poopó Basin.
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| 13. |
- Ramos Ramos, Oswaldo Eduardo, et al.
(författare)
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Sources and behavior of arsenic and trace elements in groundwater and surface water in the Poopó Lake Basin, Bolivian Altiplano
- 2012
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Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 66:3, s. 793-807
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Tidskriftsartikel (refereegranskat)abstract
- Water management in semiarid and arid catchments such as the Poopó Lake Basin requires improved understanding of the complex behavior of the various contaminants, which affect the drinking water quality and considered as crucial for sustainable development of the region. Mechanisms of arsenic (As) release in the surface and groundwater were studied. Hydrochemical data for surface water (4 samples) and groundwater (28 samples) were collected in a small watershed in the Poopó catchment at the highland of the Bolivian Andes (Altiplano). All of them show high electrical conductivity values and moderately oxidizing conditions. The surface water contains high concentration of sulfate and the trace elements As, Zn and Pb in the zone affected by acid mine drainage. There is a large variability of the concentration of As and of the trace elements in the groundwater in the five different regions within the Poopó catchment. The metal concentrations sensitive to changes of redox state and results of speciation modeling suggest that As (V) is a predominant aqueous species, which conforms to the prevailing oxidizing conditions in the shallow groundwater environment. Two generalized trends for As distribution were identified in groundwater: (a) high concentrations are found in the arid zone (100-250 Όg/L) in the southern (region III) and in the northwestern (region V) regions, and (b) low concentrations (< 50 Όg/L) are found in the remaining part of the basin (region I, II and IV). However, the spatial distribution within these regions needs to be investigated further. A conclusion from the present study is that there are multiple sources of As as well as other trace elements (such as Cd, Mn and Zn) in the Poopó Lake Basin. Among the sources and the processes which led to the mobility of As and other trace metals in the region are: (a) weathering of sulfide minerals, (b) oxidation of pyrite and/or arsenopyrite in mineralized areas and (c) desorption from hydrous ferric oxide (HFO) surfaces. In non-mining areas, volcanic ash is suggested to be a significant source of As.
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| 14. |
- Sengupta, S., et al.
(författare)
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Spatial variation of groundwater arsenic distribution in the Chianan Plain, SW Taiwan : Role of local hydrogeological factors and geothermal sources
- 2014
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 518, s. 393-409
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Tidskriftsartikel (refereegranskat)abstract
- We present here major ion, trace element, stable and radioisotope data based on forty-six groundwater samples collected from various locations along few selected profiles across the Chianan Plain, southwestern Taiwan including the area affected by well known Blackfoot disease manifested by peripheral vascular gangrene. The objective of the study was to understand the role of local hydrogeology in terms of spatial variation of arsenic concentration in groundwater wells of the entire Chianan Plain and the foothill belt of the Central Mountain Range. An attempt has also been made to assess the contribution of nearby geothermal sources to the arsenic budget in groundwater of the Chianan Plain. Our study shows a gradual increase in all major and trace ion concentrations including total arsenic from foothill belt (arsenic: median = 4 mu g/L, range = 0-667.6 mu g/L, sample number n = 16) to coastal zones (arsenic: median = 42.74 mu g/L, range = 0.14-348.6 mu g/L, n = 15) of the plain. Inverse geochemical modeling shows that Ca may be exchanged on clays, and that the degree of the exchange increases from the foothill to the coastal zones. Inverse geochemical modeling further suggests that the oxidation of organic matter (CH2O) required in various east-west profiles across the plain to balance the total bicarbonate concentration and CO2 input from organic matters significantly increases from the foothill to the coastal zones with transfer coefficients ranging from 1.55 x 10(-2) to 1.69 x 10(-5) mol/L. High concentrations of tritium (mean = 1.33 +/- 0.11 TU; n = 4) in foothill groundwater and low concentration of tritium in groundwater of central zone suggest gradually increasing water-rock interaction from the foothill to the coastal part. Few elevated arsenic (median = 171.8 mu g/L,maximum = 667.60 mu g/L, minimum = 24 mu g/L; n = 6) hotspots are identified in the foothill belt. Available lithologs and aquifer test data suggest that the presence of impermeable clay around those pockets possibly inhibits vertical and lateral flushing of the aquifer and aids strong water-rock interactions subsequently leading to release of arsenic into groundwater. Using oxygen isotope and chloride mass balance method, we estimated that geothermal sources can recharge a maximum of 4% of groundwater in proximal aquifers and contribute <2% of average As concentration in the groundwater of Chianan Plain. Our preliminary observations thus show some arsenic enrichment in foothill aquifers, providing a necessity of detailed study of the aquifer systems in these understudied regions. Moreover, our research indicates that the contribution of arsenic from geothermal sources is insignificant, which stands in contrast to earlier studies suggesting that mud volcanoes and thermal springs in the Western Foothill Belt of the Central Mountain Range were potential sources of groundwater arsenic in the Chianan Plain aquifers.
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| 15. |
- Sracek, O., et al.
(författare)
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Behavior of arsenic and geochemical modeling of arsenic enrichment in aqueous environments
- 2004
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Ingår i: Applied Geochemistry. - : Elsevier BV. - 0883-2927 .- 1872-9134. ; 19:2, s. 169-180
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Tidskriftsartikel (refereegranskat)abstract
- Arsenic is present in aqueous environments in +III and +V oxidation states. In oxidizing environments, the principle attenuation mechanism of As migration is its adsorption on Fe(III) oxide and hydroxides. The adsorption affinity is higher for As(V) under lower pH conditions and for As(III) under higher pH conditions. Ferric oxide and hydroxides can dissolve under low Eh and pH conditions releasing adsorbed As. Oxidation-reduction processes often involve high organic matter content in sediments and also contamination by organics such as BTEX. Arsenic may desorb under high pH conditions. Changes of pH can be related to some redox reactions, cation exchange reactions driving dissolution of carbonates, and dissolution of silicates. In very reducing environments, where SO4 reduction takes place, secondary sulfide minerals like As-bearing pyrite and orpiment, As2S3, can incorporate As. Geochemical modeling can be divided into two principal categories: (a) forward modeling and (b) inverse modeling. Forward modeling is used to predict water chemistry after completion of predetermined reactions. Inverse modeling is used to suggest which processes take place along a flowpath. Complex coupled transport and geochemistry programs, which allow for simulation of As adsorption, are becoming available. A common modeling approach is based on forward modeling with surface complexation modeling (SCM) of As adsorption, which can incorporate the effect of different adsorbent/As ratios, adsorption sites density, area available for adsorption, pH changes and competition of As for adsorption sites with other dissolved species such as phosphate. The adsorption modeling can be performed in both batch and transport modes in codes such as PHREEQC. Inverse modeling is generally used to verify hypotheses on the origin of As. Basic prerequisites of inverse modeling are the knowledge of flow pattern (sampling points used in model have to be hydraulically connected) and information about mineralogy including As mineral phases. Case studies of geochemical modeling including modeling of As adsorption are presented.
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| 18. |
- von Brömssen, Mattias, et al.
(författare)
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Targeting low-arsenic aquifers in Matlab Upazila, Southeastern Bangladesh
- 2007
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 375:2-3, s. 121-132
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Tidskriftsartikel (refereegranskat)abstract
- Groundwater with high concentration of geogenic arsenic (As) occurs extensively in the Holocene alluvial aquifers of Bangladesh. Local drillers in Matlab Upazilla are constructing deeper tubewells than in the recent past, primarily because of low concentrations of dissolved Fe and As. Locally a thick layer of black to grey sediments overlies an oxidised unit of yellowish-grey to reddish-brown sediments. The correlation between the colour of both units and the groundwater redox conditions was investigated to provide an easy tool for targeting low-arsenic groundwater. Based on the sediment colour at the screen depths described by local drillers, 40 domestic shallow tubewells were selected for water sampling. Four colours were used to describe the sediments: black, white, off-white (buff) and red. Generally, the groundwater was anoxic and the As concentrations ranged from less than 5.2 to 355 mu g/L. Water derived from the black sediment is characterized by relatively higher concentrations of dissolved NH4+, DOC, Fe, P, As and by low Mn and SO42- concentrations. The off-white and red sediments had high concentration of Mn and low NH4+, DOC, Fe, P and As concentrations. The water abstracted from the black sediments indicated the most reducing environment, followed by white, off-white and red respectively. Three boreholes verified the driller's perception of the subsurface lithologic conditions. Discrepancies between the driller's and the research team description of the sediment colours were insignificant. This study shows that sediment colour is a reliable indicator of high and low-As concentrations and can be used by local drillers to target low-arsenic groundwater.
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