| 1. |
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| 2. |
- Bhattacharya, Prosun, 1962-, et al.
(författare)
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Arsenic in Groundwater of Bangladesh : Options for Safe Drinking Water
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The study was undertaken in order to find and scientifically validate the options for arsenic safewater in Bangladesh. The study has been carried out in a geological province where most of theshallow wells have arsenic above the allowable limit for drinking water according to Bangladeshstandard. The original study plan has been modified as newer information on arsenic mobilisationand mitigation was available. Accordingly the emphasis on dug well and arsenic removal filter hadbeen shifted to other options such as geologically targeted aquifers. Also at the same time therehas been collaboration with number of other projects been carried out in and around the studyarea. Eventually the main focus of the research was shifted to capacity development in order toenhance the local capability for finding safer sources drinking water in the study area and othersimilar environments in the country.
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| 3. |
- Bhattacharya, Prosun, 1962-, et al.
(författare)
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Arsenic in Swedish groundwater Mobility and risk for naturally elevated concentrations : Final Report
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Arsenic (As) in groundwater has become a serious global problem during the last few decades forseveral reasons. The chronic toxicity from drinking water has motivated the lowering of thehealth limit from 50 μg/L to 10 μg/L. Due to the rather complicated analytical chemistry of As ithas seldom been analysed in groundwater. Once the common occurrence of excess As ingroundwater has been discovered like in Bangladesh it has become evident that As in concentrationswell above the health limit can be easily mobilized from very moderate amounts in the aquifermaterial under specific conditions. There are essentially three mechanisms of mobilization: 1)oxidation of sulphides containing As; 2) reduction of ferric compounds releasing adsorbed Asand 3) high pH conditions leading to lowered adsorption capacity of ferric and aluminium compounds. This study has aimed at investigating the mobilization of As under the conditions existing in Precambrianrocks and the overlying tills in Sweden. As study area the north-eastern part of theVästerbotten county was chosen. The occurrence of sulphides both in mineralisations and insome of the country rocks may infer that the risk of elevated As concentrations in groundwatermay be a bit higher there than elsewhere in Sweden. The hypothesis was that the two firstmechanisms mentioned above would be responsible for any elevated groundwater As in groundwater,thus either oxidation of sulphides or reducing conditions leading the reduction of ferrichydroxides. Samples were collected from drilled wells, dug wells and springs. pH, Eh and temperature weremeasured in the field and the samples were filtered through 0.20 m filters in the field. As(II) wasseparated from As(V) in the field by ion-exchangers. As redox conditions are the determinantsfor the mobilization of As the groundwaters have been classified into five redox classes followinga classification developed by the Swedish Environmental Protection Agency. Dug wells with elevatedAs turned out to be in the oxidizing part of the classification while drilled wells were foundin all classes. This is reasonable as drilled wells often collect water from different environmentsthrough the different fracture systems the drilled wells contact. Wetland springs are found tohave moderately reducing water high in iron. While drilled wells and dug wells show a wide spectrumof As(III)/As(tot) ratios the As(III) is clearly dominant in wetland springs. Drilled wellsshowed the highest concentrations of As up to 300 μg/L and wells drilled in alkaline volcanicrocks had the highest median concentrations of As. Arsenic in wetland springs were strongly correlatedto iron. Another clear relationship was that groundwater with even low concentrations ofnitrate was low in As. Obviously the presence of nitrate indicates an oxidizing environmentwhere As is firmly adsorbed onto ferric hydroxides. There was no clear relationship with sulphateindicating that the drilled wells which made up the majority of the groundwaters often had waterof a mixed origin coming to the well via different fracture systems. The results indicate that As should in general be analysed in household wells as it is difficult topredict the presence of elevated concentrations from the major ion chemistry. High iron concentrationis a factor that indicates an elevated risk of As above the health limit. Nitrate on the otherhand indicates a low risk for elevated As concentration.
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| 4. |
- Bhattacharya, Prosun, et al.
(författare)
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Groundwater chemistry and arsenic mobilization in the Holocene flood plains in south-central Bangladesh
- 2009
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Ingår i: Environmental Geochemistry and Health. - : Springer Science and Business Media LLC. - 0269-4042 .- 1573-2983. ; 31, s. 23-43
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Tidskriftsartikel (refereegranskat)abstract
- A comparative study of arsenic enrichment in the Bengal Delta (BD) was carried Out in three alluvial aquifers in south-central Bangladesh. Investigated sites included Sonargaon in Narayanganj, Chandina in Comilla and Sirajdikhan in Munshiganj districts. At all sites samples from different depths were collected, and water chemistry and redox status vs. depth trends were determined. The concentrations of DOC and HCO3- were highest at Sirajdikhan site, while at the Sonargaon and Chandina sites the concentrations were lower. On the contrary, the NH4+ concentration was high at the Chandina site as compared to the other sites. There was a good match between dissolved As and Fe at the Sirajdikhan and Sonargaon sites, but not at the Chandina site. The dissolved aqueous concentration of Mn was low at the Chandina site, which suggested that the Mn(IV) redox buffering step was missing. Speciation modeling indicated a possibility of siderite precipitation at all sites, but precipitation of rhodochrosite only at the Sonargaon and Sirajdikhan sites. At the Sirajdikhan site, the log P-CO2 values were very high (-1.37), which revealed the production Of CO2 in redox processes. Principal component analysis (PCA) indicated an impact of sea water and redox status of different samples. These results suggest that the dissolved As is de-coupled from dissolved Mn because when released, As is re-adsorbed onto the Fe(Ill) minerals in solid phase, as well as from dissolved Fe when precipitation of Fe(II) minerals controls the aqueous concentrations of Fe. In addition, several other concurrent redox processes may exert kinetic constraints depending on refractory characteristics of Fe(II) minerals.
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| 5. |
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| 6. |
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| 7. |
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| 8. |
- Bhattacharya, Prosun, et al.
(författare)
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Temporal and seasonal variability of arsenic in drinking water wells in Matlab, southeastern Bangladesh : A preliminary evaluation on the basis of a 4 year study
- 2011
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Ingår i: Journal of Environmental Science and Health. Part A. - : Informa UK Limited. - 1093-4529 .- 1532-4117. ; 46:11, s. 1177-1184
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Tidskriftsartikel (refereegranskat)abstract
- Temporal and seasonal variability of As concentrations in groundwater were evaluated in As-affected areas of Matlab, southeastern Bangladesh. Groundwater samples from 61 randomly selected tubewells were analyzed for As concentrations over a period of three years and four months (from July 2002 to November 2005) and monitored seasonally (three times a year). The mean As concentrations in the sampled tubewells decreased from 153 to 123 mu g/L during July 2002 to November 2005. Such changes were pronounced in tubewells with As concentration >50 mu g/L than those with As concentrations <50 mu g/L. Similarly, individual wells revealed temporal variability, for example some wells indicated a decreasing trend, while some other wells indicated stable As concentration during the monitoring period. The mean As concentrations were significantly higher in Matlab North compared with Matlab South. The spatial variations in the mean As concentrations may be due to the differences in local geological conditions and groundwater flow patterns. The variations in mean As concentrations were also observed in shallow (<40 m) and deep (>40 m) wells. However, to adequately evaluate temporal and seasonal variability of As concentration, it is imperative to monitor As concentrations in tubewells over a longer period of time. Such long-term monitoring will provide important information for the assessment of human health risk and the sustainability of safe drinking water supplies.
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| 9. |
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| 10. |
- Claudio, P., et al.
(författare)
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Geochemical modelling application for a 1-d arsenic reactive transport study in alluvial aquifers, Matlab Upazila, Bangladesh
- 2009
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Ingår i: Rendiconti Online della Società Geologica Italiana. - 2035-8008. ; 6, s. 364-365
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Tidskriftsartikel (refereegranskat)abstract
- Mechanistic modelling was used to investigate the hydrochemical evolution along a vertical column, should cross-contamination occur. 1-D reactive transport was carried out to assess sorption effects on aqueous/solid arsenic distribution in Matlab Upazila, Bangladesh. Thermodynamic relationships between aqueous ions and aquifer materials have been investigated: comparison between redox couples shows electrochemical disequilibrium; sorption mainly occurs on weak and strong Hydrous Ferric-Oxides, described by the Surface Complexation Mode. The basis for reactive transport calculations is given by a static model, that evaluates the competing ions net effect: they reduce by ca. 50% arsenic bounding. Desorption process alone can give unacceptable As (aq) concentrations, starting from only a few mg/kg As (sorb). Redox zonation was the starting point for the model conception, which allowed calculating the contamination evolution in an oxidising As-low aquifer. Groundwater analysis is worked out for a 20 cells column of aquifer material, whose top represents the upper reducing aquifer, the bottom the oxidising aquifer; contamination takes place through an As-rich solution percolating into the column. Results are a function of the flow velocity, that needs to be carefully defined before further modelling.
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| 11. |
- Hasan, Md. Aziz, 1960-, et al.
(författare)
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Arsenic in shallow groundwater of Bangladesh : investigations from three different physiographic settings
- 2007
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Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 15:8, s. 1507-1522
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Tidskriftsartikel (refereegranskat)abstract
- Occurrences of arsenic (As) in the Bengal Basin of Bangladesh show close relationships with depositional environments and sediment textures. Hydrochemical data from three sites with varying physiography and sedimentation history show marked variations in redox status and dissolved As concentrations. Arsenic concentration in groundwater of the Ganges Flood Plain (GFP) is characteristically low, where high Mn concentrations indicate redox buffering by reduction of Mn(IV)-oxyhydroxides. Low DOC, HCO3-, NH4+ and high NO3- and So(4)(2-) concentrations reflect an elevated redox status in GFP aquifers. In contrast, As concentration in the Ganges Delta Plain (GDP) is very high along with high Fe and low Mn. In the Meghna Flood Plain (MFP), moderate to high As and Fe concentrations and low Mn are detected. Degradation of organic matter probably drives redox reactions in the aquifers, particularly in MFP and GDP, thereby mobilising dissolved As. Speciation calculations indicate supersaturation with respect to siderite and vivianite in the groundwater samples at MFP and GDP, but groundwater in the GFP wells is generally supersaturated with respect to rhodochrosite. Values of log P-CO2 at MFP and GDP sites are generally higher than at the GFP site. This is consistent with Mn(IV)-redox buffering suggested at the GFP site compared to Fe(III)-redox buffering at MFP and GDP sites.
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| 12. |
- Hasan, Md. Aziz, 1960-, et al.
(författare)
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Geochemistry and mineralogy of shallow alluvial aquifers in Daudkandi upazila in the Meghna flood plain, Bangladesh
- 2009
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Ingår i: Environmental Geology. - : Springer Science and Business Media LLC. - 0943-0105 .- 1432-0495. ; 57:3, s. 499-511
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Tidskriftsartikel (refereegranskat)abstract
- The shallow alluvial aquifers of the delta plains and flood plains of Bangladesh, comprises about 70% of total land area are mostly affected by elevated concentrations of arsenic (As) in groundwater exposing a population of more than 35 million to As toxicity. Geochemical studies of shallow alluvial aquifer in the Meghna flood plain show that the uppermost yellowish grey sediment is low in As (1.03 mg/kg) compared to the lower dark grey to black sediment (5.24 mg/kg) rich in mica and organic matter. Sequential extraction data show that solid phase As bound to poorly crystalline and amorphous metal (Fe, Mn, Al)-oxyhydroxides is dominant in the grey to dark grey sediment and reaches its maximum level (3.05 mg/kg) in the mica rich layers. Amount of As bound to sulphides and organic matter also peaks in the dark grey to black sediment. Vertical distributions of major elements determined by X-ray fluorescence (XRF) show that iron (Fe2O3), aluminum (Al2O3) and manganese (MnO) follow the general trend of distribution of As in the sediments. Concentrations of As, Mn, Fe, HCO3 (-), SO4 (2-) and NO3 (-) in groundwater reflect the redox status of the aquifer and are consistent with solid phase geochemistry. Mineralogical analysis by X-ray diffraction (XRD) and scanning electron microscopy (SEM) fitted with energy dispersive X-ray spectrometer (EDS) revealed dominance of crystalline iron oxides and hydroxides like magnetite, hematite and goethite in the oxidised yellowish grey sediment. Amorphous Fe-oxyhydroxides identified as grain coating in the mica and organic matter rich sediment suggests weathering of biotite is playing a critical role as the source of Fe(III)-oxyhydroxides which in turn act as sink for As. Presence of authigenic pyrite in the dark grey sediment indicates active reduction in the aquifer.
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| 13. |
- Hasan, M. Aziz, et al.
(författare)
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Geological controls on groundwater chemistry and arsenic mobilization : Hydrogeochemical study along an E-W transect in the Meghna basin, Bangladesh
- 2009
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 378:1-2, s. 105-118
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogeochemical investigations along an E-W transect in the middle Meghna basin show groundwater chemistry and redox condition vary considerably with the change in geology. Groundwater in the Holocene shallow (< 150 m bgl) alluvial aquifer in western part of the transect is affected by high arsenic concentration (As > 10 mu g/l) and salinity. On the other hand, groundwater from the Pliocene Dupi Tila sandy aquifer in the eastern part is fresh and low in As (< 10 mu g/l). The Holocene shallow aquifers are high in dissolved As. HCO3-, Fe and dissolved organic carbon (DOC), but generally low in SO2- and NO3-. High HCO3- concentrations (250-716 mg/l) together with high DOC concentrations (1.4-21.7 mg/l) in these aquifers reflect active sources of degradable natural organic matter that drives the biogeochemical process. There is generally de-coupling of As from other redox-sensitive elements. In contrast, the Pliocene aquifers are low in As, HCO3- and DOC. Molar ratio of HCO3-/H4SiO4 suggests that silicate weathering is dominant in the deeper Holocene aquifers and in the Pliocene aquifers. Molar ratios of Cl-/HCO3- and Na+/Cl- suggest mixing of relict seawater with the fresh water as the origin of groundwater salinity. Speciation calculations show that saturation indices for siderite and rhodochrosite vary significantly between the Holocene and Pliocene aquifers. Stable isotopes (delta H-2 and delta O-18) in groundwater indicate rapid infiltration without significant effects of evaporation. The isotopic data also indicates groundwater recharge from monsoonal precipitation with some impact of altitude effect at the base of the Tripura Hills in the east. The results of the study clearly indicate geological control (i.e. change in lithofacies) on groundwater chemistry and distribution of redox-sensitive elements such as As along the transect.
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| 14. |
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| 15. |
- Herbert, Roger, et al.
(författare)
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Mine waste stabilization with biosludge and Ca carbonate residues: Column experiments
- 2007
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Ingår i: Biohydrometallury. - : Trans Tech Publications Inc.. - 9780878494521 - 0878494529 ; , s. 291-294
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Konferensbidrag (refereegranskat)abstract
- Column experiments investigated the stabilization of waste rock from Ljusnarsberg mine in Kopparberg, Sweden. In order to inhibit the generation of acidic leachate from the waste rock, biosludge and a Ca carbonate – rich residue from the paper industry were mixed with the sulfidic mine waste. The results of the column experiments indicate that the stabilization of the waste rock with the reactive amendments succeeded in maintaining a near – neutral pH in the waste rock leachate, compared to a pH 3 leachate from untreated waste rock. Copper and Zn concentrations in leachate from the untreated waste exceeded 100 mg/L, while these metals were detected at concentrations less than 0.1 and 1 mg/L, respectively, in the leachate from the treated wastes. This study indicates that the stabilization of acid – generating waste rock with biosludge and Ca carbonate residues is effective in preventing the generation of acid mine drainage; the treatment is expected to continue until the reactive amendments are exhausted.
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| 16. |
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| 17. |
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| 18. |
- Hossain, M., et al.
(författare)
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Potentiality of intermediate depth aquifer as a source of arsenic and manganese safe tubewells in Bangladesh
- 2012
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Ingår i: Understanding the Geological and Medical Interface of Arsenic, As 2012 - 4th International Congress: Arsenic in the Environment. - : Taylor & Francis Group. - 9780415637633 ; , s. 71-73
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Konferensbidrag (refereegranskat)abstract
- Shallow tubewells excepting those installed in red/off-white sediments are mostly contaminated with high arsenic. Social survey conducted in 96 villages of Matlab, a worse-affected area of Bangladesh, reveals that only 18% of tubewells provide As-safe water. In such a condition, high Manganese in many wells is found to be an additional problem. Based on monitoring in depth-specific piezometers, drinking water wells were installed in intermediate depth aquifer around 120 m. Ninety percent of the wells installed in light grey medium sand, had arsenic concentrations below the Bangladesh standard of 50 ÎŒg/L and manganese was within the previous WHO guideline (0.4 mg/L). Availability of similar sand over this depth range could be targeted by local drillers to tap safe water at a reasonable cost. Replication trials and periodical monitoring are emphasized for validation and sustainability.
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| 19. |
- Hossain, Mohammed, et al.
(författare)
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Sediment color tool for targeting arsenic-safe aquifers for the installation of shallow drinking water tubewells
- 2014
-
Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 493, s. 615-625
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Tidskriftsartikel (refereegranskat)abstract
- In rural Bangladesh, drinking water supply mostly comes from shallow hand tubewells installed manually by the local drillers, the main driving force in tubewell installation. This study was aimed at developing a sediment color tool on the basis of local driller's perception of sediment color, arsenic (As) concentration of tubewell waters and respective color of aquifer sediments. Laboratory analysis of 521 groundwater samples collected from 144 wells during 2009 to 2011 indicate that As concentrations in groundwater were generally higher in the black colored sediments with an average of 239 mu g/L. All 39 wells producing water from red sediments provide safe water following the Bangladesh drinking water standard for As (50 mu g/L) where mean and median values were less than the WHO guideline value of 10 mu g/L. Observations for off-white sediments were also quite similar. White sediments were rare and seemed to be less important for well installations at shallow depths. A total of 2240 sediment samples were collected at intervals of 1.5 m down to depths of 100 m at 15 locations spread over a 410 km(2) area in Matlab, Bangladesh and compared with the Munsell Color Chart with the purpose of direct comparison of sediment color in a consistent manner. All samples were assigned with Munsell Color and Munsell Code, which eventually led to identify 60 color shade varieties which were narrowed to four colors (black, white, off-white and red) as perceived and used by the local drillers. During the process of color grouping, participatory approach was considered taking the opinions of local drillers, technicians, and geologists into account. This simplified sediment color tool can be used conveniently during shallow tubewell installation and thus shows the potential for educating local drillers to target safe aquifers on the basis of the color characteristics of the sediments.
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| 20. |
- Hossain, Mohammad, et al.
(författare)
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Strategic approach for up-scaling safe water access considering hydrogeological suitability and social mapping in Matlab, southeastern Bangladesh
- 2013
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Konferensbidrag (refereegranskat)abstract
- In recent years, there has been a significant progress in understanding the source and mobilization process, sediment-water interactions, and distributions of arsenic in groundwater environment in Bangladesh. However, the impacts of arsenic mitigation are still very limited. A social survey conducted during 2009-2011 in 96 villages in Matlab revealed that only 18% of total tubewells provide As-safe water. The safe water access also varied between 0 and 90 percent in the region due to lack of knowledge about the local geology and unplanned tubewell development. SASMIT, an initiative of KTH-International Groundwater Arsenic Research Group has developed a method for safe tubewell installation considering hydrogeological suitability, safe water access and other relevant social and demographic information into account.Piezometers installed at 15 locations over an area of 410 km2, using local boring techniques allowed to delineate the hydrostratigraphy, characterize the aquifers in terms of sediment characteristics, water chemistry and hydraulic head distribution, which ultimately led to the identification of the suitable aquifers for tapping safe water. The piezometer locations with safe drinking water quality were then targeted for safe well installation based on the determination of safe buffer distances in a cluster of a few villages (mouzas). Social mapping of all the villages within the mauzas were done using GIS to evaluate the availability of safe water options for a cluster of households (bari). For safe well installations, priority was given to regions with safe water access, greater number of beneficiaries especially in poor households, and easy access to the site from a cluster of households. Through this approach, it was thus possible to make 95% of the newly installed wells As-safe thus scaled up the safe water access upto 40% in some mauzas. Thus the as a strategy to improve safe water access, the SASMIT study recommends investigating the hydrogeological suitability through installation of few piezometers with a minimum effort and based on the results the implementation plan can be made using GIS based social mappings for relatively uniform distribution and to maximize the safe water access.
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| 21. |
- Jacks, Gunnar, et al.
(författare)
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Arsenic and its bioavailability in surface waters in a black schist area in northern Sweden
- 2012
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Ingår i: Understanding the Geological and Medical Interface of Arsenic, As 2012 - 4th International Congress: Arsenic in the Environment. - : Taylor & Francis Group. - 9780415637633 ; , s. 249-250
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Konferensbidrag (refereegranskat)abstract
- The Västerbotten county in northern Sweden is largely underlain by Precambrian bedrock. There are numerous sulfide ore bodies and gold deposits accompanied by arsenic. However, more black schists with a sulfur content of about 1% are a more widespread source of arsenic (As). The arsenic is accumulated in the B-horizon of tills but also remobilized in wetlands and released into surface water. Sandy sediments in brooks and streams may contain up to 500 mg/kg As adsorbed onto ferric (Fe) oxyhydroxides. Lakes may contain up to 19 ÎŒg/LAs. Speciation of As has been investigated in lake water by filtration and dialysis. Four lakes have been investigated varying from a clear-water lake to lakes high in Fe and DOC (dissolved organic carbon). The As is closely correlated to Fe in the different fractions. The fraction < 1 kDa is low in As indicating that the As has low bioavailability. Fishing is important in the area both for local people as well as for tourists. The low bioavailability of As is verified by a few analysis of fish, pike and trout, in which the As content is relatively low and consisting of predominantly organic species like MMA, DMA and arsenobetaine. Thus in spite of elevated As contents in sediments and in water the As does not seem to pose a health risk for fish consumers.
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| 22. |
- Jakariya, Md., et al.
(författare)
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Searching for sustainable arsenic mitigation strategy in Bangladesh : experience from two upazilas
- 2007
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Ingår i: International Journal of Environment and Pollution. - 0957-4352 .- 1741-5101. ; 31:3-4, s. 415-430
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Tidskriftsartikel (refereegranskat)abstract
- Arsenic concentrations of tubewell water that exceed the Bangladesh Drinking Water Standard pose a serious health problem for millions of people in Bangladesh. Groundwater is the source of drinking water for 98% of the population. The main object of the study was to review the status of the provided options, which were distributed during 1999-2001 in two upazilas. It was observed that acceptability of the distributed options was not encouraging; less than 2% of the provided options were found to be in operation. However, two new approaches emerged from people's initiatives, which are making rapid and positive contributions to safe water coverage.
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| 23. |
- Jonasson, Sven, et al.
(författare)
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Modeller för transport och spridning av föroreningar fas 2
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Grundvattenmodeller kan vara mycket kraftfulla verktyg för att beräkna och visualisera grundvattenflöde och föroreningstransport. I rätt sammanhang och rätt använda är grundvattenmodeller viktiga och kostnadseffektiva verktyg för att ta fram beslutsunderlag för riskbedömningar, åtgärdsförslag, projektering av efterbehandlingsåtgärder, etc. Föreliggande handledning syftar till att underlätta användning av modellverktyg för beskrivning av föroreningstransport med grundvatten, samt medverka till att höja kunskapsnivån så att dessa verktyg används på ett lämpligt sätt. Handledningen är programoberoende och har tagits fram för att ge handfasta råd för upprättande av modeller för simulering av föroreningstransport. Handledningen omfattar hela modelleringsprocessen, från de förberedande arbetena, själva upprättandet av modellen till avrapporteringen. Modelleringsprocessen tar sin början i problemformuleringen. Sedan följer upprättandet en konceptuell hydrogeologisk modell över det aktuella området. Den konceptuella modellen används som underlag vid skapande av den numeriska modellen. För detta arbete krävs en god förståelse geologiska förhållanden, anläggningar som ändrar de naturliga grundvattenflödena, områdets vattenbalans, grundvattennivåer, grundvattenflöden och vattenstånd i vattendrag och grundvattenkemisk karaktärisering. Numeriska beräkningsmodeller för beräkning av föroreningstransport kan göras på många olika sätt alltifrån relativt enkla till mycket komplexa modeller. Den numeriska flödesmodellen upprättas sedan i en programvara/-kod. Modellen lagerindelas på lämpligt sätt utifrån de geologiska förutsättningarna och avgränsas geografiskt utifrån de hydrauliska förutsättningarna genom ansättande av s k randvillkor. Baserat på vilken flödesmodell som utnyttjas kan sedan olika moduler kopplas på för att beräkna masstransporten av föroreningar som tar hänsyn till diffusion och dispersion, nedbrytning, kemiska reaktioner, avångning, sorptionsprocesser etc. Det är viktigt att modellen inte blir mer komplex än att den ger de svar som vi är ute efter. För att modellera och simulera ämnestransport i grundvatten krävs ett antal nödvändiga indata och kvalitet. Mängd och typ styr hur komplex modellen kan vara samt vilka resultat som kan förväntas från modelleringsarbetet. När modellen har upprättats skall den kalibreras och valideras. Kalibrering i egentlig betydelse innebär att man på ett objektivt sätt justerar modellen till dess att överensstämmelse mellan konstaterade förhållanden och av modellen predikterade förhållanden erhålls. För att värdera hur bra modellen är kalibrerad och överensstämmer med verkligheten bör den testas mot oberoende data. Det kan t ex vara från en annan tidsperiod eller från uppmätta nivåer eller flöden som ej använts för kalibreringen. Detta kallas validering. När väl detta är genomfört kan modellen användas för att beräkna föroreningstransport för olika scenarion och som beslutsunderlag för att miljökonsekvenser, åtgärdsförslag, kontrollprogram, etc.
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| 24. |
- Kibria, M. G., et al.
(författare)
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Hydrogeochemistry and microbial geochemistry on different depth aquifer sediments from Matlab, Bangladesh
- 2014
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Ingår i: One Century of the Discovery of Arsenicosis in Latin America (1914-2014). - : CRC Press. - 9781138001411 ; , s. 101-103
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Konferensbidrag (refereegranskat)abstract
- Arsenic (As) poses the greatest hazard towards drinking water quality in Bangladesh. Tubewell drinking water is one of the main sources for household based water options in rural Bangladesh. Our study area is in Matlab Upazila, in Bangladesh. The overall objective of this research and the SASMIT project is to develop a community based initiative for sustainable As mitigation by developing a sediment color based tool for the local drillers prioritizing on the hydrogeological and biogeochemical investigations. For this purpose we analyzed different depth colored sediments and water for find out the sustainable low Arsenic contaminated aquifer.
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| 25. |
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| 26. |
- 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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| 27. |
- von Brömssen, Mattias, et al.
(författare)
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Geochemical characterisation of shallow aquifer sediments of Matlab Upazila, Southeastern Bangladesh - Implications for targeting low-As aquifers
- 2008
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Ingår i: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 99:1-4, s. 137-149
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Tidskriftsartikel (refereegranskat)abstract
- High arsenic (As) concentrations in groundwater pose a serious threat to the health of millions of people in Bangladesh. Reductive dissolution of Fe(Ill)-oxyhydroxides and release of its adsorbed As is considered to be the principal mechanism responsible for mobilisation ofAs. The distribution ofAs is extremely heterogeneous both laterally and vertically. Groundwater abstracted from oxidised reddish sediments, in contrast to greyish reducing sediments, contains significantly lower amount of dissolved arsenic and can be a source of safe water. In order to study the sustainability of that mitigation option, this study describes the lithofacies and genesis of the sediments within 60 m depth and establishes a relationship between aqueous and solid phase geochemistry. Oxalate extractable Fe and Mn contents are higher in the reduced unit than in the oxidised unit, where Fe and Mn are present in more crystalline mineral phases. Equilibrium modelling of saturation indices suggest that the concentrations of dissolved Fe, Mn and PO43--tot in groundwater is influenced by 4 secondary mineral phases in addition to redox processes. Simulating As-[I] adsorption on hydroferric oxides using the Diffuse Layer Model and analytical data gave realistic concentrations of dissolved and adsorbed As-[I] for the reducing aquifer and we speculate that the presence of high PO43--tot in combination with reductive dissolution results in the high-As groundwater. The study confirms high mobility of As in reducing aquifers with typically dark colour of sediments found in previous studies and thus validates the approach for location of wells used by local drillers based on sediment colour. A more systematic and standardised colour description and similar studies at more locations are necessary for wider application of the approach.
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| 28. |
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| 29. |
- von Brömssen, Mattias
(författare)
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Hydrogeological and geochemical assessment of aquifer systems with geogenic arsenic in Southeastern Bangladesh : Targeting low arsenic aquifers for safe drinking water supplies in Matlab
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Naturally occurring arsenic (As) in Holocene aquifers in Bangladesh have undermined a long success of supplying the population with safe drinking water. Arsenic is mobilised in reducing environments through reductive dissolution of Fe(III)-oxyhydroxides. Several studies have shown that many of the tested mitigation options have not been well accepted by the people. Instead, local drillers target presumed safe groundwater on the basis of the colour of the sediments. The overall objective of the study has thus been focussed on assessing the potential for local drillers to target As safe groundwater. The specific objectives have been to validate the correlation between aquifer sediment colours and groundwater chemical composition, characterize aqueous and solid phase geochemistry and dynamics of As mobility and to assess the risk for cross-contamination of As between aquifers in Daudkandi and Matlab Upazilas in SE-Bangladesh. In Matlab, drillings to a depth of 60 m revealed two distinct hydrostratigraphic units, a strongly reducing aquifer unit with black to grey sediments overlies a patchy sequence of weathered and oxidised white, yellowish-grey to reddish-brown sediment. The aquifers are separated by an impervious clay unit. The reducing aquifer is characterized by high concentrations of dissolved As, DOC, Fe and PO43--tot. On the other hand, the off-white and red sediments contain relatively higher concentrations of Mn and SO42- and low As. Groundwater chemistry correlates well with the colours of the aquifer sediments. Geochemical investigations indicate that secondary mineral phases control dissolved concentrations of Mn, Fe and PO43--tot. Dissolved As is influenced by the amount of Hfo, pH and PO43--tot as a competing ion. Laboratory studies suggest that oxidised sediments have a higher capacity to absorb As. Monitored hydraulic heads and groundwater modelling illustrate a complex aquifer system with three aquifers to a depth of 250 m. Groundwater modelling illustrate two groundwater flowsystems: i) a deeper regional predominantly horizontal flow system, and ii) a number of shallow local flow systems. It was confirmed that groundwater irrigation, locally, affects the hydraulic heads at deeper depths. The aquifer system is however fully recharged during the monsoon. Groundwater abstraction for drinking water purposes in rural areas poses little threat for cross-contamination. Installing irrigation- or high capacity drinking water supply wells at deeper depths is however strongly discouraged and assessing sustainability of targeted low-As aquifers remain a main concern. The knowledge gained here can be used for developing guidelines for installing safe wells at similar environments in other areas of Bangladesh.
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| 30. |
- von Brömssen, Mattias, et al.
(författare)
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Modeller för transport och spridning av föroreningar – fas 1 : Förstudie – Användning av numeriska beräkningsmodeller för beskrivning av transport och spridning av föroreningar i grundvatten
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- rundvattenmodeller kan vara mycket kraftfulla verktyg att beräkna och visualisera grundvattenflöde och föroreningstransport, speciellt vid akvifärer med komplicerad geometri. I rätt sammanhang och rätt använda är grundvattenmodeller viktiga och kostnadseffektiva verktyg för att ta fram beslutsunderlag beträffande olika grundvatten- och föroreningsfrågor. Detta gäller särskilt där skyddsobjekten är stora, tydliga och värdefulla. Idag saknas emellertid kunskap och indata för att allmänt i Sverige med hjälp av befintliga numeriska beräkningsmodeller, med precision kvantifiera och prediktera transport av föroreningar i grundvatten. Föreliggande rapport syftar till att beskriva den erfarenhet och kunskap om sådan modellering, för svenska förhållanden, som finns i ”branschen” och vid universiteten. Dessutom föreslås en metodik för användningen av dessa modeller i samband med miljöriskbedömningar för förorenade områden samt så redovisas ett protokoll för hur osäkerheter kan beskrivas. Vidare föreslås ett antal rekommendationer för fortsatta arbeten inom ämnesområdet i Sverige. För att få en bild av statusläget i Sverige utfördes intervjuer med ca 25 nyckelpersoner med direkt erfarenhet i ämnet. Ett mindre antal aktörer i Danmark, Finland och Norge kontaktades även för att erhålla underlag för en syntes av statusen i respektive land. Utöver detta genomfördes en litteratursökning av svenska erfarenheter av modellering av föroreningsspridning med grundvatten under svenska förhållanden.Sammanfattningsvis kan sägas att många aktörer använder grundvattenmodeller vid projekt med anknytning till förorenad mark. Detta sker dock oftast på ett kraftigt förenklat sätt. Det är vanligt att använda enbart en flödesmodell, samt partikelspårning. Masstransportmodeller används i princip bara i FoU-projekt och för hypotetiska scenarion (där man inte behöver eller kan kalibrera) eller alternativt mycket stora projekt. Oftast tvingas man bortse från heterogeniteter i förenklade modeller. Osäkerheter hanteras sällan systematiskt men ofta genom en förenklad känslighetsanalys. Sveriges geologi med tämligen små avrinningsområden och akvifärer, begränsad användning av grundvatten för kommunalt dricksvatten, liksom svårigheter att kommunicera mervärden med uppdragsgivare synes vara orsaker till en begränsad användning av grundvattenmodeller i Sverige. Olika mervärden är förknippade med grundvattenmodeller såsom att man kan pröva hypoteser samt att man tvingas skapa en vattenbalans för systemet. Oväntade simuleringsresultat erhålls relativt frekvent. Detta torde vara ett mervärde då detta tyder på att utan användning av modellen skulle relevant information ha förbigåtts. Modeller anses även vara mycket pedagogiska för redovisning av resultat. I andra länder (t.ex. Danmark) har nyttan av modeller varit mer uppenbar och därför har modeller kommit mer till användning. Erfarenhetsvärden på de olika parametrar som behövs vid masstransportmodellering efterfrågas av många aktörer. Även baskunskaper om dessa processer samt hantering av heterogeniteter och parameterisering efterfrågas. Det finns även ett stort behov av erfarenhetsspridning och – återföring beträffande grundvattenmodellering i allmänhet och transportmodellering i synnerhet. Vidare saknas lättanvänt kalibreringsverktyg eller protokoll. Protokollet bör innehålla information om vad man behöver för typ av information i relation till olika osäkerheter. Det bedöms inte nödvändigt att utveckla (särskild) generell programkod i Sverige för de vanliga tillämpningarna i branschen.
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| 31. |
- 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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