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1.
Primary and placer gold mining sites in southern Ethiopia were studied to see the contribution of mining to the accumulation of metals in different environmental media. Sediment, water and plant samples were analyzed for Al, Mn, Fe, As, Ni, Cr, Cu, Co, Pb, W, Sb, Mo, Zn and V. Water parameters (pH, Eh, TDS, anions and cations) were also measured. The sediment analyses results show that the most abundant metals are Ni (average 224.7 mg/kg), Cr (199 mg/kg), Cu (174.2 mg/kg), V (167.3 mg/kg), Zn (105.5 mg/kg), Pb (61.5 mg/kg) and As (59.7 mg/kg) in the primary gold mining sites while the placer sites show high concentration of V (average 301.2 mg/kg), Cr (260.4 mg/kg), Zn (179 mg/kg), Ni (113.4 mg/kg), Cu (46.7 mg/kg), As (32.2 mg/kg) and Co (31 mg/kg). The metals Cu, Ni, W, Cr, As and Pb in primary and Sb, W, Cr, Ni, Zn, As and Mo in placer gold mining sites have geoaccumulation indexes (I geo) from one to four indicating considerable accumulation of these metals. Waters from both primary and placer mining sites are near neutral to alkaline. Arsenic (average 92.8 μg/l), Ni (276.6 μg/l), Pb (18.7 μg/l), Sb (10.7 μg/l), Mn (1 mg/l), Fe (8.3 mg/l) and Al (23.8 mg/l) exceeded the guideline value for drinking water. Plants show high concentration of Cr (average 174.5 mg/kg), Ni (163.5 mg/kg), Zn (96 mg/kg) and W (48 mg/kg). Zinc, W, Mo, Ni and Cr show the maximum biological absorption coefficient (BAC) ranging 0.4–1.7, 0.1–104.6, 1.1–2.6, 0.2–1.6 and 0.2–3.6, respectively, and the results suggest bioaccumulation of these elements in plants. The minerals especially sulfides in the ore aggregate are the ultimate source of the metals. The release of the metals into the environmental media is facilitated (in addition to normal geologic processes) by human activities related to gold mining.  相似文献   

2.
Environmental geochemistry of high arsenic groundwater at Hetao plain was studied on the basis of geochemical survey of the groundwater and a core sediment. Arsenic concentration in groundwater samples varies from 76 to 1093 μg/L. The high arsenic groundwater mostly appears to be weakly alkaline. The concentrations of NO3− and SO42− are relatively low, while the concentrations of DOC, NH4+, dissolved Fe and sulfide are relatively great. Analysis of arsenic speciation in 21 samples shows that arsenic is present in the solution predominantly as As(III), while particulate arsenic constitutes about 10% of the total arsenic. Methane is detected in five samples with the greatest content being 5107 μg/L. The shallow aquifer in Hangjinhouqi of western Hetao plain is of strongly reducing condition. The arsenic content in 23 core sediment samples varies from 7.7 to 34.6 mg/kg, with great value in clay and mild clay layer. The obvious positive relationship in content between Fe2O3, Mn, Sb, B, V and As indicates that the distribution of arsenic in the sediments may be related to Fe and Mn oxides, and the mobilization of Sb, B and V may be affected by similar geochemical processes as that of As.  相似文献   

3.
Antimony (Sb) is strongly concentrated into hydrothermal mineral deposits, commonly with gold, in metasedimentary sequences around the Pacific Rim. These deposits represent potential point sources for Sb in the downstream environment, particularly when mines are developed. This study documents the magnitude and scale of Sb mobility near some mineral deposits in Australia and New Zealand. Two examples of New Zealand historic mining areas demonstrate that natural groundwater dissolution of Sb from mineral deposits dominates the Sb load in drainage waters, with Sb concentrations between 3 and 24 μg/L in major streams. Mine-related discharges can exceed 200 μg/L Sb, but volumes are small. Sb flux in principal stream waters is ca 1–14 mg/s, compared to mine tunnel fluxes of ca 0.001 mg/s. Dissolved Sb is strongly attenuated near some mine tunnels by adsorption on to iron oxyhydroxide precipitates. Similar Sb mobilisation and attenuation processes are occurring downstream of the historic/active Hillgrove antimony–gold mine of New South Wales, Australia, but historic discharges of Sb-bearing debris has resulted in elevated Sb levels in stream sediments (ca 10–100+ mg/kg) and riparian plants (up to 100 mg/kg) for ca 300 km downstream. Dissolution of Sb from these sediments ensures that river waters have elevated Sb (ca 10–1,000 μg/L) over that distance. Total Sb flux reaching the Pacific Ocean from the Hillgrove area is ca 8 tonnes/year, of which 7 tonnes/year is particulate and 1 tonne/year is dissolved.  相似文献   

4.
Twenty-six groundwater samples were collected from the Eastern Thessaly region and analysed by ICP-ES for these elements: Al, As, P, Pb, Zn, Mn, Fe, Cr, Sb, Cu, Na, Br, Cl, Si, Mg, Ag, Be, Bi, Dy, Er, Eu, Au, Ge, Ho, In, Ir, Os, Pt, Re, Rh, Ru, Lu, Hf, Hg, Tm, Zr and Nb. The objectives of the study were to assess the level of water contamination with respect to the EC and the USEPA health-based drinking water criteria. The geology of the studied area includes schists, amphibolites, marbles of Palaeozoic age, ophiolites, limestones of Triassic and Cretaceous age, Neogene and Quaternary deposits. The element ranges for groundwater samples are: Al 7–56 μg l−1, As 1–125 μg l−1, Br 6–60 μg l−1, Cl 500–25,000 μg l−1, Cr 1–6 μg l−1, Cu 1–15 μg l−1, Fe 10–352 μg l−1, Mg 2,940–40,100 μg l−1, Mn 0–8 μg l−1, Na 3,650–13,740 μg l−1, P 20–48 μg l−1, Pb 0–7 μg l−1, Sb 0–21 μg l−1, Si 3,310–13,240 μg l−1 and Zn 7–994 μg l−1. The results of groundwater analyses from the region of Eastern Thessaly showed elevated concentrations of As and Sb. Factor analysis explained 77.8% of the total variance of the data through five factors. Concentration of Br, Cl, Mg, Na and Si is directly related to the presence of saltwater in the aquifer, so grouping of these variables in factor 1 probably reflects the seawater intrusion. Al, As and Sb are known to form complexes in the environment, so grouping of these elements in factor 2 indicates their similar geochemical behaviour in the environment. The high negative loading of Mn in factor 2 indicates the presence of manganese oxides–hydroxides in the study area. Pb and Zn are associated together in sulphide mineralisation; so grouping of these elements in factor 3 reflects the sulphide mineralization paragenesis in the Melivoia area. P and Cu are associated together in phosphate fertilizers; so grouping of these variables in factor 4 could be related to agricultural practices. Cr, Fe, Mn and Mg are associated together in iron and manganese oxides–hydroxides and the weathering products of the olivine of the ultrabasic rocks; so grouping of these elements in factor 5 reflects the lithology of the area. There is a natural contamination of groundwaters with elevated concentrations of As and Sb due to the presence of the arsenopyrite and stibnite mineralisation in the Melivoia, Sotiritsa and Ano Polydendri areas. Contamination over the health-based drinking water guidelines given by EC and EPA has been investigated from nine sampling sites out of 26 of Eastern Thessaly region.  相似文献   

5.
Historic antimony mining at Endeavour Inlet, New Zealand, was developed in a stibnite-rich mesothermal vein system hosted in a km scale shear zone in metasedimentary schist. The schist contains calcite, and all waters have pH between 7 and 8. Underground tunnels (adits) have largely collapsed, but two adits provided access to waters which have interacted chemically with mineralised rock. Natural groundwater entering an adit at the top of the mineralised catchment had 190 μg/l Sb and 10 μg/l As. The amount of arsenic increased along the adit as the water interacted with arsenopyrite-bearing rocks and debris (up to 2000 mg/kg As, 500 mg/kg Sb) on the adit floor. Sb(III) was below 14 μg/l, and there was no detectable As(III). Antimony content remained near constant in the adit but increased outside the adit because of interaction with stibnite-rich debris. Negligible attenuation of metalloids occurred via adsorption outside the adit, as iron oxyhydroxide is rare. Metalloid attenuation was by dilution in a nearby natural stream, which carried <30 μg/s Sb and <10 μg/s As away from the site. An adit 500 m downstream was developed in a lower, more arsenopyrite-rich portion of the mineralised system with debris containing up to 15,000 mg/kg As and 5000 mg/kg Sb. Water from this adit had up to 200 μg/l Sb and 1650 μg/l As. Arsenic was attenuated by adsorption outside this adit, and by dilution by the natural stream. Antimony was not attenuated by adsorption, nor by dilution as the natural stream contained up to 200 μg/l Sb. Metalloid flux away from this site was ca. 200 μg/s Sb and 40 μg/s As, and the adit contributed negligible amounts of metalloids to this flux. Total metalloid flux from the catchment is 14,000 μg/s antimony and 5000 μg/s arsenic, which is around three orders of magnitude greater than observed mine inputs to the catchment. Highest flux occurred in September as water tables rose in the winter. Nearly all the metalloid flux is derived by natural groundwater and surface water interaction with mineralised rock. This interaction between water and mineralised rock is enhanced in this area because the catchment runs subparallel to the shear zone which controls the mineralised veins.  相似文献   

6.
Systematic investigations on seasonal variations in arsenic (As) concentrations in groundwater in both space and time are scarce for most parts of West Bengal (India). Hence, this study has been undertaken to investigate the extent of As pollution and its temporal variability in parts of Murshidabad district (West Bengal, India). Water samples from 35 wells were collected during pre-monsoon, monsoon and post-monsoon seasons and analyzed for various elements. Based on the Indian permissible limit for As (50 μg/L) in the drinking water, water samples were classified into contaminated and uncontaminated category. 18 wells were reported as uncontaminated (on average 12 μg/L As) and 12 wells were found contaminated (129 μg/L As) throughout the year, while 5 wells could be classified as either contaminated or uncontaminated depending on when they were sampled. Although the number of wells that alternate between the contaminated and uncontaminated classification is relatively small (14%), distinct seasonal variation in As concentrations occur in all wells. This suggests that investigations conducted within the study area for the purpose of assessing the health risk posed by As in groundwater should not rely on a single round of water samples. In comparison to other areas, As is mainly released to the groundwater due to reductive dissolution of Fe-oxyhydroxides, a process, which is probably enhanced by anthropogenic input of organic carbon. The seasonal variation in As concentrations appear to be caused mainly by dilution effects during monsoon and post-monsoon. The relatively high concentrations of Mn (mean 0.9 mg/L), well above the WHO limit (0.4 mg/L), also cause great concern and necessitate further investigations.  相似文献   

7.
The study area covers an about 100 km2 of the middle Ganga plain in Uttar Pradesh, experiencing intensive groundwater extraction. In order to recognize the arsenic contamination zones of the Varanasi environs, sixty eight groundwater samples have been collected and analyzed for major ions, iron and arsenic. Twenty one sediment samples in the four boreholes were also collected to deduce the source of arsenic in the groundwater. The preliminary survey reports for the first time indicates that part of rural and urban population of Varanasi environs are drinking and using for irrigation arsenic contaminated water mostly from hand tube wells (<70 m). The study area is a part of middle Ganga plain which comprises of Quaternary alluvium consists of an alternating succession of clay, clayey silt and sand deposits. The high arsenic content in groundwater samples of the study area indicates that 14% of the samples are exceeding the 10 μg/l and 5% of the samples are exceeding 50 μg/l. The high arsenic concentration is found in the villages such as Bahadurpur, Madhiya, Bhojpur, Ratanpur, Semra, Jalilpur, Kateswar, Bhakhara and Kodupur (eastern side of Ganga River in Varanasi), situated within the newer alluvium deposited during middle Holocene to Recent. The older alluvial aquifers situated in the western side of the Ganga River are arsenic safe (maximum As concentration of 9 μg/l) though the borehole sediments shows high arsenic (mean 5.2 mg/kg) and iron content (529 mg/kg) in shallow and medium depths. This may be due to lack of reducing conditions (i.e organic content) for releasing arsenic into the groundwater. Rainfall infiltration, organic matter from recently accumulated biomass from flood prone belt in the newer alluvium plays a critical role in releasing arsenic and iron present in sediments. The main mechanism for the release of As into groundwater in the Holocene sandy aquifer sediments of Varanasi environs may be due to the reductive dissolution of Fe oxyhydroxide present as coatings on sand grains as well as altered mica content. The high societal problems of this study will help to mitigate the severity of arsenic contamination by providing alternate drinking water resources to the people in middle Ganga plain and to arrange permanent arsenic safe drinking water source by the authorities.  相似文献   

8.
The Guadalupe Valley aquifer is the only water source for one of the most important wine industries in Mexico, and also the main public water supply for the nearby city of Ensenada. This groundwater is monitored for major ion, N-NO3, P-PO4, Fe, As, Se, Mo, Cd, Cu, Pb, Zn and Sb concentrations, as well as TDS, pH, dissolved oxygen and temperature. High concentrations of N-NO3 (26 mg l−1), Se (70 μg l−1), Mo (18 μg l−1) and Cu (4.3 μg l−1) suggest that groundwater is being polluted by the use of fertilizers only in the western section of the aquifer, known as El Porvenir graben. Unlike the sites located near the main recharge area to the East of the aquifer, the water in El Porvenir graben has low tritium concentrations (<1.9 TU), indicating a pre-modern age, and thus longer water residence time. No significant variations in water quality (generally <10%) were detected throughout 2001–2002 in the aquifer, suggesting that reduced rainfall and recharge during this dry period did not significantly affect water quality. However, the wells nearest to the main recharge area in the Eastern aquifer show a slight but constant increase in TDS with time, probably as a result of the high (∼200 L S−1) uninterrupted extraction of water at this specific recharge site. Relatively high As concentrations for the aquifer (10.5 μg l−1) are only found near the northern limit of the basin associated with a geological fault.  相似文献   

9.
Environmental contamination with As and Sb caused by past mining activities at Sb mines is a significant problem in Slovakia. This study is focused on the environmental effects of the 5 abandoned Sb mines on water, stream sediment and soil since the mines are situated in the close vicinity of residential areas. Samples of mine wastes, various types of waters, stream sediments, soils, and leachates of the mine wastes, stream sediments and selected soils were analyzed for As and Sb to evaluate their geochemical dispersion from the mines. Mine wastes collected at the mine sites contained up to 5166 mg/kg As and 9861 mg/kg Sb. Arsenic in mine wastes was associated mostly with Fe oxides, whereas Sb was present frequently in the form of individual Sb, Sb(Fe) and Fe(Sb) oxides. Waters of different types such as groundwater, surface waters and mine waters, all contained elevated concentrations of As and Sb, reaching up to 2150 μg/L As and 9300 μg/L Sb, and had circum-neutral pH values because of the buffering capacity of abundant Ca- and Mg-carbonates. The concentrations of Sb in several household wells are a cause for concern, exceeding the Sb drinking water limit of 5 μg/L by as much as 25 times. Some attenuation of the As and Sb concentrations in mine and impoundment waters was expected because of the deposition of metalloids onto hydrous ferric oxides built up below adit entrances and impoundment discharges. These HFOs contained >20 wt.% As and 1.5 wt.% Sb. Stream sediments and soils have also been contaminated by As and Sb with the peak concentrations generally found near open adits and mine wastes. In addition to the discharged waters from open adits, the significant source of As and Sb contamination are waste-rock dumps and tailings impoundments. Leachates from mine wastes contained as much as 8400 μg/L As and 4060 μg/L Sb, suggesting that the mine wastes would have a great potential to contaminate the downstream environment. Moreover, the results of water leaching tests showed that Sb was released from the solids more efficiently than As under oxidizing conditions. This might partly explain the predominance of Sb over As in most water samples.  相似文献   

10.
High arsenic (As) groundwater is widely distributed in northwestern Hetao Plain, an arid region with sluggish groundwater flow. Observed As concentration in groundwater from wells ranges from 76 to 1,093 μg/l. Most water samples have high total dissolved solids, with Cl and HCO3 as the dominant anions and Na as the dominant cation. The major hydrochemical types of most saline groundwaters are Na–Mg–Cl–HCO3 and Na–Mg–Cl. By contrast, fresh groundwaters generally belong to the Na–Mg–HCO3 type. High concentrations of arsenic in shallow aquifers are associated with strongly reducing conditions, as evidenced by high concentrations of dissolved organic carbon, ammonium, as well as dissolved sulfide and Fe, dominance of arsenite, relatively low concentrations of nitrate and sulfate, and occasionally high content of dissolved methane (CH4). High As groundwaters from different places at Hetao Plain experienced different redox processes. Fluoride is also present in high As groundwater, ranging between 0.40 and 3.36 mg/l. Although fluorosis poses an additional health problem in the region, it does not correlate well with As in spatial distribution. Geochemical analysis indicates that evapotranspiration is an important process controlling the enrichment of Na and Cl, as well as trace elements such as As, B, and Br in groundwater. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

11.
Mineralogical and geochemical studies were undertaken in the volcanic area of Biancavilla (Catania, Italy) with the aim of explaining the nature of the high As and F contents of the area’s rocks. As and F contents in soils and groundwater were also investigated. The metasomatised benmoreite lavas show fluorine and arsenic concentrations up to about 3,000 and 1,000 mg/kg, respectively. Mineralogical analyses show that fluorine occurs mostly in fluoro-edenite and apatite-(CaF) crystals, both abundantly present in the altered rocks, while As is exclusively attributed to the apatite-(CaF) crystals. Specifically, arsenic was observed only at the borders of these apatite crystals. Leaching tests and sequential extraction procedures were carried out to evaluate the potential remobilisation of As and F by the mineral phases and the eventual risks induced by their spreading. The results of the leaching tests suggest that As is almost totally associated with the ‘easily reducible’ fraction and that it is released by the preferential dissolution of the arsenic enriched rims of apatite-(CaF) crystals. In soils, As concentration is relatively low (about 15 mg/kg, on average), while F ranges from 236 to 683 mg/kg. The underground waters supplying the town of Biancavilla show As and F contents lower than the allowed limits for drinking water, (As:10 μg/L, F:1–1.5 mg/L). The limited distribution of these rocks and the relatively limited mobilisation by the minerals both contribute to maintain low As and F values, in soils and groundwaters, despite the high values in metasomatised lava samples.  相似文献   

12.
Groundwater arsenic distribution in South-western Uruguay   总被引：1，自引：0，他引：1  
This is the first specific information regarding arsenic distribution of groundwater in SW Uruguay. Twenty-eight wells were sampled on the aquifers of Mercedes, Raigón and Chuy in five localities. The pH, specific conductivity and temperature were determined in the field. The hydrochemical characterization (major and trace elements) was carried out by both inductively coupled plasma-optical emission spectrometry and inductively coupled plasma-mass spectrometry. The occurring arsenic concentrations exceed the recommended threshold for drinking water of the World Health Organization (10 μg/l of As) in 22 samples, with more than 50 μg/l of As in two cases. The median, minimum and maximum concentrations were 0.1, 16.9 and 58.0 μg/l of As, respectively. The studied aquifers present a horizontal and a vertical variation of the concentrations as a whole as well as individually. The highest values were observed in the Mercedes Aquifer in the areas near the Uruguay River.  相似文献   

13.
The geochemical study of groundwaters and core sediments from the Old Brahmaputra plain of Bangladesh was conducted to investigate the distribution of arsenic and related trace elements. Groundwaters from tube wells are characterized by pH of 6.4–7.4, dissolved oxygen (DO) of 0.8–1.8 mg/l, Ca contents of 5–50 mg/l, and Fe contents of 0.2–12.9 mg/l. Arsenic concentrations ranged from 8 to 251 μg/l, with an average value of 63 μg/l. A strong positive correlation exists between As and Fe (r 2 = 0.802; p = 0.001) concentrations in groundwater. The stratigraphic sequences in the cores consist of yellowish silty clays at top, passing downward into grayish to yellowish clays and sands. The uppermost 3 m and lower parts (from 13 to 31 m) of the core sediments are oxidized (average oxidation reduction potential (ORP) +170 and +220 mV, respectively), and the ORP values gradually become negative from 3 to 13 m depths (−35 to −180 mV), indicating that anoxic conditions prevail in the shallow aquifers of the Brahmaputra plain. Age determinations suggest that clay horizons at ~10 m depth were deposited at around 2,000 and 5,000 years BP (14C ages) during the transgressive phase of sea-level change. Elevated concentrations of As, Pb, Zn, Cu, Ni, Cr, and V are present in the silts and clays, probably due to adsorption onto clay particles. Significant concentrations of As occur in black peat and peaty sediments at depths between 9 and 13 m. A strong positive correlation between As and Fe was found in the sediments, indicating As may be adsorbed onto Fe oxides in aquifer sediments.  相似文献   

14.
Hydrochemical study had been carried out on the groundwater resources of Potharlanka Island, Krishna delta, India. Groundwater samples were collected and analyzed at 42 sites in December 2001 and October 2006. A comparative study of hydrochemical data indicates: groundwater is mildly alkaline with a pH of 7.0–8.2; electrical conductivity (EC) varies from 605 to 5,770 μS/cm in December 2001, and 652–5,310 μS/cm in October 2006. More than 62% of the groundwater samples in 2006 have TDS value <2,000 mg/l, which is within permissible limit of potable water, but 57% of the samples in 2001, are higher than the maximum permissible limit. Extremely low HCO3/Cl and variable high Mg/Ca (molar ratios) had been indicated the transformation of the fresh groundwater aquifer systems to saline in 2001. Groundwater of this Island is mainly classified as Na–Cl and mixed types. A high percentage of Na–Cl type of these waters indicates the possibility of seawater ingression/intrusion process during 2001 and comparatively mixed water type indicates the dilution activities of groundwater. Excessive withdrawal of groundwater has caused the increase of saline water intrusion. Improvement of groundwater quality in this Island due to artificial recharge structures made by NGRI under RGNDWM project and affects of the flood due to heavy rainfall of the months of September–October 2005 are discussed in this paper.  相似文献   

15.
Two boreholes and ten piezometers in the Ganges flood plain were drilled and installed for collecting As-rich sediments and groundwater. Groundwater samples from the Ganges flood plain were collected for the analysis of cations (Ca2+, Mg2+, K+, Na+), anions (Cl−, NO3 −, SO4 2−), total organic carbon (TOC), and trace elements (As, Mn, Fe, Sr, Se, Ni, Co, Cu, Mo, Sb, Pb). X-ray powder diffraction was performed to characterize the major mineral contents of aquifer sediments and X-ray fluorescence (XRF) to analyze the major chemical composition of alluvial sediments. Results of XRF analysis clearly show that fine-grained sediments contain higher amounts of trace element because of their high surface area for adsorption. Relative fluorescence index (15–38 QSU) of humic substance in groundwater was measured using spectrofluorometer, the results revealed that groundwater in the Ganges flood plain contains less organic matter (OM). Arsenic concentration in water ranges from 2.8 to 170 μg/L (mean 50 μg/L) in the Ganges flood plain. Arsenic content in sediments ranges from 2.1 to 14 mg/kg (mean 4.58 mg/kg) in the flood plains. TOC ranges from 0.49 to 3.53 g/kg (mean 1.64 g/kg) in the Ganges flood plain. Arsenic is positively correlated with TOC (R 2 = 0.55) in sediments of this plain. Humic substances were extracted from the sediments from the Ganges flood plain. Fourier transform infrared analysis of the sediments revealed that the plain contains less humic substances. The source of organic carbon was assigned from δ13C values obtained using elemental analysis-isotope ratio mass spectrometry (EA-IRMS); the values (−10 to −29.44‰) strongly support the hypothesis that the OM of the Ganges flood plain is of terrestrial origin.  相似文献   

16.
Understanding the mechanism of arsenic mobilization from sediments to groundwater is important for water quality management in areas of endemic arsenic poisoning, such as the Hetao Basin in Inner Mongolia, northern China. Aquifer geochemistry was characterized at three field sites (SH, HF, TYS) in Hangjinhouqi County of northwestern Hetao Basin. The results of bulk geochemistry analysis of sediment samples indicated that total As concentrations have a range of 6.8–58.5 mg/kg, with a median of 14.4 mg/kg. The highest As concentrations were found at 15–25 m depth. In the meanwhile, the range of As concentration in the sediments from background borehole is 3–21.8 mg/kg, with a median value of 9 mg/kg. The As sediments concentrations with depth from the SH borehole were correlated with the contents of Fe, Sb, B, V, total C and total S. Generally, the abundance of elements varied with grain size, with higher concentrations in finer fractions of the sediments. Distinct lithology profile and different geochemical characteristics of aquifer sediments indicate the sediments are associated with different sources and diverse sedimentary environments. Up to one third of arsenic in the sediments could be extracted by ammonium oxalate, suggesting that Fe oxyhydroxides may be the major sink of As in the aquifer. Sequential extraction results indicate that arsenic occurs as strongly adsorbed on and/or co-precipitated with amorphous Fe oxyhydroxides in sediments accounting for 35 and 20%, respectively, of the total contents of arsenic. The release of As into groundwater may occur by desorption from the mineral surface driven by reductive dissolution of the Fe oxide minerals. Furthermore, small proportions of As associated with iron sulfides occur in the reductive sediments.  相似文献   

17.
Arsenic and fluoride in a loess aquifer in the central area of Argentina   总被引：3，自引：0，他引：3  
The objective of this study is to analyze the geochemical conditions associated with the presence of arsenic (As) and fluoride (F) in the phreatic aquifer of Coronel Moldes, in the central sector of the Argentine Chacopampean plain. The studied aquifer is composed of silty sand sediments of aeolian origin, typically loess-like sediments. The geochemical composition of water varies from sodium bicarbonate to sodium sulfate-chloride water. As contents range from low concentrations, below detection level, to 250 μg/l. High values of F (up to 12 mg/l) were recorded. A high As–F correlation was found (R 2 = 0.84). The pH varied from 7.31 to 8.85 and the nitrates reached concentrations up to 200 mg/l, indicating an oxidant environment. The highest values of As and F agreed with sodium bicarbonate waters as well as with the highest values of pH recorded. There was a high correlation between As and F− as well as between As and the Na/Ca ratio. The composition and texture of loess, low permeability and hydraulic gradients together with the geochemical features of sodium bicarbonate waters are proper conditions for the mobilization of As and F in groundwater in the central area of Argentina.  相似文献   

18.
Sediment and groundwater profiles were compared in two villages of Bangladesh to understand the geochemical and hydrogeological factors that regulate dissolved As concentrations in groundwater. In both villages, fine-grained sediment layers separate shallow aquifers (< 28 m) high in As from deeper aquifers (40-90 m) containing < 10 μg/L As. In one village (Dari), radiocarbon dating indicates deposition of the deeper aquifer sediments > 50 ka ago and a groundwater age of thousands of years. In the other village (Bay), the sediment is < 20 ka old down to 90 m and the deeper aquifer groundwater is younger, on the order of hundreds of years. The shallow aquifers in both villages that are high in As contain bomb-3H and bomb-14C, indicating recent recharge. The major and minor ion compositions of the shallow and deeper aquifers also differ significantly. Deeper aquifer water is of the Na+-HCO3- type, with relatively little dissolved NH4+ (76 ± 192 μmol/L), Fe (27 ± 43 μmol/L) and Mn (3 ± 2 μmol/L). In contrast, shallow aquifer water is of the Ca2+-Mg2+-HCO3- type, with elevated concentrations of dissolved NH4+ (306 ± 355 μmol/L), Fe (191 ± 73 μmol/L), and Mn (27 ± 43 μmol/L). In both villages, the quantity of As extractable from deeper aquifer sands with a 1 mol/L phosphate solution (0.2 ± 0.3 mg/kg, n = 12; 0.1 ± 0.1 mg/kg, n = 5) is 1 order of magnitude lower than P-extractable As from shallow deposits (1.7 ± 1.2 mg/kg, n = 9; 1.4 ± 2.0 mg/kg, n = 11). The differences suggest that the concentration of P-extractable As in the sediment is a factor controlling the concentration of As in groundwater. Low P-extractable As levels are observed in both deeper aquifers that are low in As, even though there is a large difference in the time of deposition of these aquifers in the two villages. The geochemical data and hydrographs presented in this study suggest that both Holocene and Pleistocene deeper aquifers that are low in As should be a viable source of drinking water as long as withdrawals do not exceed recharge rates of ∼1 cm/yr.  相似文献   

19.
Arsenic concentrations surpassing potability limit of 10 μg/L in the groundwater supplies of an extensive area in the Duero Cenozoic Basin (central Spain) have been detected and the main sources of arsenic identified. Arsenic in 514 samples of groundwater, having mean values of 40.8 μg/L, is natural in origin. Geochemical analysis of 553 rock samples, assaying arsenic mean values of 23 mg/kg, was performed. Spatial coincidence between the arsenic anomaly in groundwater and the arsenic lithogeochemical distribution recorded in the Middle Miocene clayey organic-rich Zaratan facies illustrates that the rocks of this unit are the main source of arsenic in groundwater. The ferricretes associated to the Late Cretaceous–Middle Miocene siliciclastics also constitute a potential arsenic source. Mineralogical study has identified the presence of arsenic in iron oxides, authigenic pyrite, manganese oxides, inherited titanium–iron oxides, phyllosilicates and organomineral compounds. Arsenic mobilization to groundwater corresponds to arsenic desorption from iron and manganese oxides and from organic matter.  相似文献   

20.
The 1000 km long Ok Tedi/Fly River system receives about 66 Mt/year of mining waste from the Ok Tedi copper-gold porphyry mine. Mine input has increased the suspended sediment load of the Middle Fly River about 5–10 times over the natural background. A significant yet unknown amount of copper-rich material deposits unevenly in the extensive tropical lowland floodplain. Recent alluvial sediments of the Fly River floodplain have copper contents of 620 mg/kg (±1σ: 430–900), whereas the regional background is 40 mg/kg (±σ: 25–60). This pattern is mirrored and enhanced by the gold dispersal pattern with a 7 ppb Au background versus a 140–275 ppb population in mine-derived material. Very high deposition rates (around 4 cm/y) of mine-derived sediment were determined in locations close to the creeks and channels which link the Fly River with the outer floodplain. A thin layer of 1–5 cm of copper-rich material (400–900 mg/kg Cu) was usually found on the bottom of drowned (tributary) valley lakes. Average dissolved copper content in waters of the inner floodplain is around 9 μg/l (±1σ: 5–14) as compared to unpolluted water from the outer floodplain with < 2 μg/l Cu. The present Fly River water, about 600 km downstream of the mine site, has concentrations of 17 ± 3 μg/l dissolved Cu. Received: 30 June 1996 / Accepted: 9 January 1997  相似文献   

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