Mobilisation of arsenic and other trace elements in fluviolacustrine aquifers of the Huhhot Basin,Inner Mongolia     

《Applied Geochemistry》2003,18(9):1453-1477

Observed As concentrations in groundwater from boreholes and wells in the Huhhot Basin of Inner Mongolia, northern China, range between <1 μg l⁻¹ and 1480 μg l⁻¹. The aquifers are composed of Quaternary (largely Holocene) lacustrine and fluvial sediments. High concentrations are found in groundwater from both shallow and deep boreholes as well as from some dug wells (well depths ranging between <10 m and 400 m). Populations from the affected areas experience a number of As-related health problems, the most notable of which are skin lesions (keratosis, melanosis, skin cancer) but with internal cancers (lung and bladder cancer) also having been reported. In both the shallow and deep aquifers, groundwaters evolve down the flow gradient from oxidising conditions along the basin margins to reducing conditions in the low-lying central part of the basin. High As concentrations occur in anaerobic groundwaters from this low-lying area and are associated with moderately high dissolved Fe as well as high Mn, NH₄, dissolved organic C (DOC), HCO₃ and P concentrations. Many of the deep groundwaters have particularly enriched DOC concentrations (up to 30 mg l⁻¹) and are often brown as a result of the high concentrations of organic acid. In the reducing groundwaters, inorganic As(III) constitutes typically more than 60% of the total dissolved As. The highest As concentrations tend to be found in groundwater with low SO₄ concentrations and indicate that As mobilisation occurs under strongly reducing conditions, where SO₄ reduction has been an active process. High concentrations of Fe, Mn, NH₄, HCO₃ and P are a common feature of reducing high-As groundwater provinces (e.g. Bangladesh, West Bengal). High concentrations of organic acid (humic, fulvic acid) are not a universal feature of such aquifers, but have been found in groundwaters from Taiwan and Hungary for example. The observed range of total As concentrations in sediments is 3–29 mg kg⁻¹ (n=12) and the concentrations correlate positively with total Fe. Up to 30% of the As is oxalate-extractable and taken to be associated largely with Fe oxides. The release of As into solution under the reducing conditions is believed to be by desorption coupled with reductive dissolution of the Fe oxide minerals. The association of dissolved As with constituents such as HCO₃, DOC and P may be a coincidence related to the prevalent reducing conditions and slow groundwater flow, but they may also be directly involved because of their competition with As for binding sites on the Fe oxides. The Huhhot groundwaters also have some high concentrations of dissolved U (up to 53 μg l⁻¹) and F⁻ (up to 6.8 mg l⁻¹). In contrast to As, U occurs predominantly under the more oxidising conditions along the basin margins. Fluoride occurs dominantly in the shallow groundwaters which have Na and HCO₃ as the dominant ions. The combination of slow flow of groundwater and the young age of the aquifer sediments are also considered potentially important causes of the high dissolved As concentrations observed as the sediments are likely to contain newly-formed and reactive minerals and have not been well flushed since burial.  相似文献   

Hydrogeochemistry of arsenic and other inorganic constituents in groundwaters from La Pampa,Argentina     

《Applied Geochemistry》2002,17(3):259-284

Groundwaters from Quaternary loess aquifers in northern La Pampa Province of central Argentina have significant quality problems due to high concentrations of potentially harmful elements such as As, F, NO₃-N, B, Mo, Se and U and high salinity. The extent of the problems is not well-defined, but is believed to cover large parts of the Argentine Chaco-Pampean Plain, over an area of perhaps 10⁶ km². Groundwaters from La Pampa have a very large range of chemical compositions and spatial variability is considerable over distances of a few km. Dissolved As spans over 4 orders of magnitude (<4–5300 μg l⁻¹) and concentrations of F have a range of 0.03–29 mg l⁻¹, B of 0.5–14 mg l^−l, V of 0.02–5.4 mg l⁻¹, NO₃–N of <0.2–140 mg l⁻¹, Mo of 2.7–990 μg l⁻¹ and U of 6.2–250 μg l⁻¹. Of the groundwaters investigated, 95% exceed 10 μg As l⁻¹ (the WHO guideline value) and 73% exceed 50 μg As l⁻¹ (the Argentine national standard). In addition, 83% exceed the WHO guideline value for F (1.5 mg l⁻¹), 99% for B (0.5 mg l⁻¹), 47% for NO₃-N (11.3 mg l⁻¹), 39% for Mo (70 μg l⁻¹), 32% for Se (10 μg l⁻¹) and 100% for U (2 μg l⁻¹). Total dissolved solids range between 730 and 11400 mg l⁻¹, the high values resulting mainly from evaporation under ambient semi-arid climatic conditions. The groundwaters are universally oxidising with high dissolved-O₂ concentrations. Groundwater pHs are neutral to alkaline (7.0–8.7). Arsenic is present in solution predominantly as As(V). Groundwater As correlates positively with pH, alkalinity (HCO₃), F and V. Weaker correlations are also observed with B, Mo, U and Be. Desorption of these elements from metal oxides, especially Fe and Mn oxides under the high-pH conditions is considered an important control on their mobilisation. Mutual competition between these elements for sorption sites on oxide minerals may also have enhanced their mobility. Weathering of primary silicate minerals and accessory minerals such as apatite in the loess and incorporated volcanic ash may also have contributed a proportion of the dissolved As and other trace elements. Concentrations of As and other anions and oxyanions appear to be particularly high in groundwaters close to low-lying depressions which act as localised groundwater-discharge zones. Concentrations up to 7500 μg l⁻¹ were found in saturated-zone porewaters extracted from a cored borehole adjacent to one such depression. Concentrations are also relatively high where groundwater is abstracted from close to the water table, presumably because this zone is a location of more active weathering reactions. The development of groundwaters with high pH and alkalinity results from silicate and carbonate reactions, facilitated by the arid climatic conditions. These factors, together with the young age of the loess sediments and slow groundwater flow have enabled the accumulation of the high concentrations of As and other elements in solution without significant opportunity for flushing of the aquifer to enable their removal.  相似文献   

Temporal variability of nitrate concentration in a schist aquifer and transfer to surface waters     

《Applied Geochemistry》2001,16(6):583-596

Nitrate concentrations monitored for 2.5 a in the stream water and groundwater of a small catchment, 86.5% of which is devoted to intensive agriculture, show temporal variations with a maximum during winter (as much as 200 mg l⁻¹ in groundwater and 100 mg l⁻¹ in stream water) and a minimum at the end of summer/beginning of autumn. Variations were also observed in the stream water and shallow groundwater after rainfall. The processes involved to explain these variations, determined mainly from NO₃⁻ Cl⁻, SO₄²⁻, piezometric and streamflow data, are: (a) variability of the relative contributions to stream water and shallow groundwater by upward fluxes of deeper groundwater which, as demonstrated previously, is denitrified mainly as a result of reaction with pyrite. (b) Denitrification of shallow groundwater during summer with organic matter acting as the electron donor. (c) Dilution by rain water. Nitrate concentrations in both stream water and shallow groundwater depend on the amount of precipitation, with an increased contribution from deep denitrified groundwater during dry periods. The temporal variations in NO₃⁻ concentration observed several metres below the water table are related to the preferential and rapid movement of NO₃⁻-polluted water through fractures and large fissures, which has been estimated at 1 m day⁻¹. Nitrate pollution in the catchment, because of the interaction with pyrite, also increases the net chemical weathering rate to values exceeding the world average.  相似文献   

Degradation of carbon disulphide (CS2) in soils and groundwater from a CS2-contaminated site     

Siobhan F. Cox  John D. McKinley  Andrew S. Ferguson  Gwen O’Sullivan  Robert M. Kalin 《Environmental Earth Sciences》2013,68(7):1935-1944

This study is the first investigation of biodegradation of carbon disulphide (CS₂) in soil that provides estimates of degradation rates and identifies intermediate degradation products and carbon isotope signatures of degradation. Microcosm studies were undertaken under anaerobic conditions using soil and groundwater recovered from CS₂-contaminated sites. Proposed degradation mechanisms were validated using equilibrium speciation modelling of concentrations and carbon isotope ratios. A first-order degradation rate constant of 1.25 × 10^?2 h^?1 was obtained for biological degradation with soil. Carbonyl sulphide (COS) and hydrogen sulphide (H₂S) were found to be intermediates of degradation, but did not accumulate in vials. A ¹³C/¹²C enrichment factor of ?7.5 ± 0.8 ‰ was obtained for degradation within microcosms with both soil and groundwater whereas a ¹³C/¹²C enrichment factor of ?23.0 ± 2.1 ‰ was obtained for degradation with site groundwater alone. It can be concluded that biological degradation of both CS₂-contaminated soil and groundwater is likely to occur in the field suggesting that natural attenuation may be an appropriate remedial tool at some sites. The presence of biodegradation by-products including COS and H₂S indicates that biodegradation of CS₂ is occurring and stable carbon isotopes are a promising tool to quantify CS₂ degradation.  相似文献   

Groundwater arsenic in the Chaco-Pampean Plain,Argentina: case study from Robles county,Santiago del Estero Province     

《Applied Geochemistry》2004,19(2):231-243

In large parts of rural Argentina people depend on groundwater whose As content exceeds the Argentine drinking water standards (0.05 mg l⁻¹). The most affected areas are located in the Chaco-Pampean Plain, where aquifers comprise Tertiary loess deposits (in the Pampean Plain) and Tertiary and Quaternary fluvial and aeolian sediments (in the Chaco Plain). Robles county is located in the alluvial cone of the Dulce River consisting of loess (aeolian), and gravel, silt, sand and clay (alluvial) deposits. In the shallow aquifers, more than 48% of the 63 studied wells show As at toxic levels (maximum 4.8 mg l⁻¹), while in the deep groundwater the concentration is below 0.05 mg l⁻¹. The pH of the shallow groundwaters range between 6.5 and 9 and generally have high electrical conductivity with mean values of 2072 and 1693 μS/cm⁻¹ in the years 1998 and 1999, respectively. Arsenic concentrations are high in the alkaline Na–HCO₃ type groundwaters, where As correlates positively with Na⁺ and HCO₃⁻. Moreover, As correlates positively with Mo, U, and V, while a negative correlation was observed with Ca²⁺ and Mg²⁺. The potential sources of groundwater As are: (i) layers of volcanic ash with 90% of rhyolitic glass; (ii) volcanic glass dispersed in the sediments; and (iii) clastic sediments of metamorphic and igneous origin. Great lateral variability in the concentration of groundwater As is caused by several hydrogeological and hydrogeochemical factors.  相似文献   

A review of the source,behaviour and distribution of arsenic in natural waters     

《Applied Geochemistry》2002,17(5):517-568

The range of As concentrations found in natural waters is large, ranging from less than 0.5 μg l⁻¹ to more than 5000 μg l⁻¹. Typical concentrations in freshwater are less than 10 μg l⁻¹ and frequently less than 1 μg l⁻¹. Rarely, much higher concentrations are found, particularly in groundwater. In such areas, more than 10% of wells may be ‘affected’ (defined as those exceeding 50 μg l⁻¹) and in the worst cases, this figure may exceed 90%. Well-known high-As groundwater areas have been found in Argentina, Chile, Mexico, China and Hungary, and more recently in West Bengal (India), Bangladesh and Vietnam. The scale of the problem in terms of population exposed to high As concentrations is greatest in the Bengal Basin with more than 40 million people drinking water containing ‘excessive’ As. These large-scale ‘natural’ As groundwater problem areas tend to be found in two types of environment: firstly, inland or closed basins in arid or semi-arid areas, and secondly, strongly reducing aquifers often derived from alluvium. Both environments tend to contain geologically young sediments and to be in flat, low-lying areas where groundwater flow is sluggish. Historically, these are poorly flushed aquifers and any As released from the sediments following burial has been able to accumulate in the groundwater. Arsenic-rich groundwaters are also found in geothermal areas and, on a more localised scale, in areas of mining activity and where oxidation of sulphide minerals has occurred. The As content of the aquifer materials in major problem aquifers does not appear to be exceptionally high, being normally in the range 1–20 mg kg⁻¹. There appear to be two distinct ‘triggers’ that can lead to the release of As on a large scale. The first is the development of high pH (>8.5) conditions in semi-arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates. This pH change leads either to the desorption of adsorbed As (especially As(V) species) and a range of other anion-forming elements (V, B, F, Mo, Se and U) from mineral oxides, especially Fe oxides, or it prevents them from being adsorbed. The second trigger is the development of strongly reducing conditions at near-neutral pH values, leading to the desorption of As from mineral oxides and to the reductive dissolution of Fe and Mn oxides, also leading to As release. Iron (II) and As(III) are relatively abundant in these groundwaters and SO₄ concentrations are small (typically 1 mg l⁻¹ or less). Large concentrations of phosphate, bicarbonate, silicate and possibly organic matter can enhance the desorption of As because of competition for adsorption sites. A characteristic feature of high groundwater As areas is the large degree of spatial variability in As concentrations in the groundwaters. This means that it may be difficult, or impossible, to predict reliably the likely concentration of As in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well. Arsenic-affected aquifers are restricted to certain environments and appear to be the exception rather than the rule. In most aquifers, the majority of wells are likely to be unaffected, even when, for example, they contain high concentrations of dissolved Fe.  相似文献   

Redox processes in the Oderbruch polder groundwater flow system in Germany     

《Applied Geochemistry》2004,19(6):863-886

Large scale redox processes were investigated in a river recharged aquifer in the Oderbruch polder alongside the river Oder in north-eastern Germany. Major hydraulic and hydrochemical processes were identified qualitatively. As a result of intensive drainage activities in the past 250 a, the groundwater level within the polder is situated below the river water level and a levee prevents flooding of the lowland. As a consequence, river water permanently infiltrates into the shallow confined aquifer. A sequence of redox reactions, driven by organic matter degradation, can be observed during infiltration of oxic river water into the groundwater. Up to 3 km from the river, reduction processes from O₂ respiration to SO²⁻₄ reduction dominate the groundwater chemistry. While reduction of Fe- and Mn(hydr)oxides is the source of the high amounts of dissolved Fe²⁺ and Mn²⁺, carbonate dissolution/precipitation reactions control the actual groundwater concentration of Mn²⁺. The first order rate constant for SO²⁻₄ reduction was found to be −0.0169 a⁻¹. Fe²⁺ is released into the groundwater at a rate of 0.0033 mmol l⁻¹ a⁻¹. The groundwater chemistry is strongly linked to the hydraulic conditions. Near the river, the groundwater is confined and recharged by bank-filtration only. In contrast, in the central polder the groundwater is unconfined and percolation of rainwater through the dried loam is possible because of texture changes such as shrinkage fissures. Geogenic pyrite present within the alluvial loam is oxidised and large amounts of SO²⁻₄ are released into the groundwater.  相似文献   

Infrared spectroscopic characterisation of arsenate (V) ion adsorption from mine waters,Macraes mine,New Zealand     

《Applied Geochemistry》2002,17(4):445-454

Processing waters contain up to 10 mg l⁻¹ dissolved As at the Macraes mine, New Zealand, and this is all removed by adsorption as the water percolates through a large earth dam. Laboratory experiments were set up to identify which mineral is the most effective substrate for this adsorption of As. The experiments were conducted using infrared (IR) spectroscopy of thin mineral films adhering to a ZnSe prism. Silicates, including kaolinite, adsorbed only small amounts of As which was readily washed off. Hydrated Fe oxides (HFO) were extremely effective at adsorbing As, particularly the natural amorphous HFO currently being deposited from dam discharge waters at the Macraes mine. An adsorption isotherm determined for this natural material has the adsorption constant, K_ads=(1.9±0.4)×10⁴ M⁻¹, and the substrate becomes saturated with adsorbed As when solution concentrations exceed about 50 mg l⁻¹. Saturation is not being reached at the Macraes mine. Arsenic adsorbed on to natural HFO has a distinctive IR spectrum with the absorption peak varying from 800 cm⁻¹ (alkaline solutions) to 820 cm⁻¹ (neutral to acid solutions). Much of this adsorbed As is strongly bound and difficult to wash off. Arsenate ions adsorb in a bidentate structure which may be a precursor for scorodite crystallisation.  相似文献   

Nature and practical implications of heterogeneities in the geochemistry of zinc-rich,alkaline mine waters in an underground F–Pb mine in the UK     

《Applied Geochemistry》2000,15(9):1383-1397

Water pollution arising from base metal sulphide mines is problematic in many countries, yet the hydrogeology of the subsurface contaminant sources is rarely well-characterized. Drainage water pumped from an active F–Pb mine in northern England has unusual chemistry (alkaline with up to 40 mg.l⁻¹ Zn) which profoundly impacts the ecology of the receiving watercourse. Detailed in-mine surveys of the quantity and quality of all ground water inflows to the mine were made. These revealed major, temporally persistent heterogeneities in ground water quality, with three broad types of water identified as being associated with distinct hydrostratigraphic units. Type I waters (associated with the Firestone Sill aquifer) are cool (<10°C), Ca–HCO₃–SO₄ waters, moderately mineralized (specific electrical conductance (SEC)≤410 μS.cm⁻¹) with <4 mg.l⁻¹ Zn. Type II waters (associated with the Great Limestone aquifer) are warmer (≈15°C), of Ca–SO₄ facies, highly mineralized (SEC≤1500 μS.cm⁻¹) with ≤40 mg.l⁻¹ Zn. Type III waters (in the deepest workings) are tepid (>18°C), of Ca–HCO₃–SO₄ facies, intermediately mineralized (SEC≤900 μS.cm⁻¹) with ≤13 mg.l⁻¹ Zn, and with significant Fe (≤12 mg.l⁻¹) and Pb (≤8 mg/l). Monotonic increases in temperature and Cl⁻ concentration with depth contrast with peaks in total mineralization, SO₄ and Zn at medium depth (in Type II waters). Sulphate, Pb and Zn are apparently sourced via oxidation of galena and sphalerite, which would release each metal in stoichiometric equality with SO₄. However, molal SO₄ concentrations typically exceed those of Pb and Zn by 2–3 orders of magnitude, which mineral equilibria suggest is due to precipitation of carbonate “sinks” for these metals. Contaminant loading budgets demonstrate that, although Type II waters amount to only 25% of the total ground water inflow to the mine, they account for almost 60% of the total Zn loading. This observation has important management implications for both the operational and post-abandonment phases of the mine life cycle.  相似文献   

Changes in the sorption capacity of Coastal Plain sediments due to redox alteration of mineral surfaces     

《Applied Geochemistry》2002,17(4):387-398

Chemical characteristics of grain coatings in a Coastal Plain sandy aquifer on the Eastern Shore of Virginia were investigated where sediments have been exposed to distinct groundwater redox conditions. Dissolved O₂ was 5.0 to 10.6 mg L⁻¹ in the regionally extensive aerobic groundwater, whereas in a narrow leachate plume it was only <0.001 to 0.9 mg L⁻¹. The amount of dissolved Fe in the aerobic groundwater was only 0.005 to 0.01 mg L⁻¹, but it was 12 to 47 mg L⁻¹ in the anaerobic zone. The amount of extractable Fe was an order of magnitude higher for the aerobic sediments than for the anaerobic sediments indicating that reductive dissolution removed the oxide coatings. The capacity for anion sorption on the sediment surfaces, as indicated by the sorption of ³⁵SO₄^2-, was an order of magnitude higher in the aerobic vs. anaerobic sediments. The presence of anaerobic groundwater did not significantly alter the amount of extractable Al oxides on the surface of the sediments, and those coatings helped to maintain a high surface area. The removal of the Fe oxides from the grain surfaces under anaerobic conditions was solely responsible for the significant reduction of SO₄ sorption observed. This loss of capacity for anion sorption could lead to more extensive transport of negatively charged constituents such as some contaminant chemicals or bacteria that may be of concern in groundwater.  相似文献   

14C in bicarbonate and dissolved organics—a useful tracer?     

《Applied Geochemistry》1999,14(7):927-938

The tunnel excavation at the Äspö Hard Rock Laboratory opened several fracture zones at various depths in the crystalline bedrock. One of these zones is the `Redox zone', a vertical fracture zone penetrated at 70 m depth. Except for the tunnel intersection, several boreholes were drilled to intersect the zone at various depths (ranging from 5 to 70 m) and distances from the tunnel. The response in groundwater chemistry to the opening of the zone has been monitored in these boreholes during 3 a, starting in 1991 and for the boreholes at 70 m depth the monitoring is still ongoing. The water chemistry during this monitoring can be largely explained by mixing between fresh water and native saline groundwater (4900 ppm Cl⁻). An increase in HCO⁻₃ was recorded, which was interpreted as due to anaerobic respiration. This was supported by ¹⁴C-contents in dissolved organic Carbon and HCO⁻₃, indicating that recent organic C is transported into the zone and oxidised to CO₂. This study exemplifies the use of ¹⁴C-analyses of HCO⁻₃ in order to trace different C sources contributing to the HCO⁻₃ in the groundwater. Three sources were identified: (1) dissolved CO₂, dominantly soil-CO₂ possibly with some contribution of atmospheric CO₂; (2) dissolution of calcite, with low ¹⁴C content, which dominantly occurs in the near-surface recharge area; and (3) oxidation of organic material through anaerobic respiration. Corrections for ¹⁴C and HCO⁻₃ in the native saline water made it possible to determine 2 different fresh water components corresponding to different flow paths. The C isotope data are in accordance with the results from the tracer test and the groundwater flow model, and support that the extensive build up of HCO₃⁻ does not mainly takes place locally within the zone but is transported into the zone by dominantly lateral flow. The results from the monitoring showed that new hydrochemical stability is established, which also comprises the interaction between the organic and inorganic C cycles.  相似文献   

Complexation of copper with polymeric silica in aqueous solution     

《Applied Geochemistry》1998,13(2):235-241

A series of experiments was conducted to study the uptake of Cu by colloidal SiO₂ in aqueous solution. Solutions consisting of 2400 mg l⁻¹ monomeric SiO₂ were allowed to polymerize for 24 h at pH values from 4 to 9, producing coexisting populations of monomer and polymer in each solution. These solutions were combined with aqueous CuCl₂ solutions in final Cu concentrations of 5–30 mg l⁻¹. After the solutions had equilibrated for 24 h, they were filtered through 0.1 μm Millipore filters and analyzed by ICP-AES and gel filtration chromatography (GFC).Experiments conducted at pH 7 with varying Cu concentrations yielded a critical coagulation concentration of 15±1 mg l⁻¹ Cu. GFC analyses of solutions in which coagulation occurred revealed no SiO₂ polymer in the filtrates, suggesting that coagulation is due to the coalescence of SiO₂ polymers by Cu. Experiments conducted with 20 mg l⁻¹ Cu exhibited a gradual increase in Cu uptake from pH 5 to 7, followed by a sharp decrease in Cu uptake from pH 7.25 to 7.50. The gradual increase in Cu uptake up to pH 7 may reflect the increasingly negative surface charge of SiO₂ polymer with increasing pH. The abrupt decrease in the adsorption of Cu to SiO₂ polymer at pH values > 7.25 may be attributed to the decrease in dissociated Cu²⁺ relative to Cu(OH)₂° at higher pH. Although it is traditionally held that the formation of Cu silicates, such as chrysocolla, occurs under acid conditions in supergene Cu deposits, this investigation suggests that Cu silicate formation may be favored in near-neutral solutions in nature.  相似文献   

Chemical and isotope compositions of shallow groundwater in areas impacted by hydraulic fracturing and surface mining in the Central Appalachian Basin,Eastern United States     

《Applied Geochemistry》2016

Hydraulic fracturing of shale deposits has greatly increased the productivity of the natural gas industry by allowing it to exploit previously inaccessible reservoirs. Previous research has demonstrated that this practice has the potential to contaminate shallow aquifers with methane (CH₄) from deeper formations. This study compares concentrations and isotopic compositions of CH₄ sampled from domestic groundwater wells in Letcher County, Eastern Kentucky in order to characterize its occurrence and origins in relation to both neighboring hydraulically fractured natural gas wells and surface coal mines. The studied groundwater showed concentrations of CH₄ ranging from 0.05 mg/L to 10 mg/L, thus, no immediate remediation is required. The δ¹³C values of CH₄ ranged from −66‰ to −16‰, and δ²H values ranged from −286‰ to −86‰, suggesting an immature thermogenic and mixed biogenic/thermogenic origin. The occurrence of CH₄ was not correlated with proximity to hydraulically fractured natural gas wells. Generally, CH₄ occurrence corresponded with groundwater abundant in Na⁺, Cl⁻, and HCO₃⁻, and with low concentrations of SO₄²⁻. The CH₄ and SO₄²⁻concentrations were best predicted by the oxidation/reduction potential of the studied groundwater. CH₄ was abundant in more reducing waters, and SO₄²⁻ was abundant in more oxidizing waters. Additionally, groundwater in greater proximity to surface mining was more likely to be oxidized. This, in turn, might have increased the likelihood of CH₄ oxidation in shallow groundwater.  相似文献   

Hydrochemical characterization,mechanism of mobilization,and natural background level evaluation of arsenic in the aquifers of upper Gangetic plain,India     

《Chemie der Erde / Geochemistry》2023,83(2):125952

Although arsenic (As) contamination has been extensively investigated in the aquifers of the lower and middle Gangetic plains, less attention has been given to the distribution and fate of As in the groundwater of the upper Gangetic plain, India. In the current study, groundwater samples (n = 40) were collected from Moradabad district in the upper Gangetic plain and analyzed for several physicochemical parameters to characterize the groundwater chemistry and evaluate various geogenic and anthropogenic factors controlling the occurrence, mobilization, and fate of As in the plain. Arsenic concentrations in groundwater ranged from 0.17 μg/L to 139 μg/L, with the majority of high-As groundwater associated with high Fe, Mn, and HCO₃⁻ and low NO₃⁻, SO₄²⁻, and negative Eh values, implying that As was released via reductive dissolution of Fe and Mn oxyhydroxides in reducing conditions under the influence of organic matter degradation. Interrelationships between various geochemical variables and the natural background level (NBL) quantification of As suggested the influence of anthropogenic processes on the mobility of As in groundwater. Piper and Gibbs diagrams and various bivariate plots revealed that the majority of groundwater was of the Ca²⁺ − Mg²⁺ − HCO₃⁻ type and that the major ions in groundwater were derived from carbonate and silicate weathering, cation exchange and reverse ion exchange processes, and anthropogenic activities. Moreover, the results of principal component analysis (PCA), and hierarchical cluster analysis (HCA) also suggested geogenic and anthropogenic sources for the ion concentration in groundwater. The health risk assessment showed a higher non-carcinogenic risk for children and a higher carcinogenic risk for adults, respectively, due to the daily intake of As contaminated groundwater. Overall, this study represents the first systematic investigation of the distribution, geochemical behavior, and release process of As in groundwater in the study area and provides a strong base for future research in the alluvial aquifers of the upper Gangetic plain.  相似文献   

Pollution par les nitrates des nappes phréatiques sous environnement semi-urbain non assaini: example de la nappe de Yeumbeul, Sénégal     

A.A Tandia  E.S Diop  C.B Gaye 《Journal of African Earth Sciences》1999,29(4):582

High nitrate concentrations, above the WHO guideline of 50 mg l⁻¹, were observed in samples of shallow wells reaching the Yeumbeul suburb (Senegal) area groundwater. This groundwater is exploited by 7000 houses and therefore there are health implications. Correlations between parameters such as nitrate content (NO₃⁻) in the groundwater and soil water, the distance between shallow wells and family latrines, and soil water chloride (Cl⁻) and colon bacillus content led to two possible sources of groundwater pollution: first, contamination by non impervious and shallow latrines; and second, the leaching of soil NO₃⁻ from waste organic matter carried in groundwater.  相似文献   

Evaluation of the origin and fate of nitrate in the Abbotsford Aquifer using the isotopes of15N and18O in NO3−     

《Applied Geochemistry》1995,10(4):391-405

Extensive NO₃⁻ contamination of groundwater in the Abbotsford aquifer to levels above drinking water limits is a major problem in the Fraser Lowlands of southwestern British Columbia, Canada. Nitrate concentrations in the aquifer ranged from 0 to 151 mg/l NO₃⁻, with a median concentration of 46 mg/l NO₃⁻. Of 117 wells sampled, 54% had NO₃⁻ concentrations exceeding the drinking water limit of 45 mg/1. Approximately 80% of the study area had groundwater NO₃⁻ concentrations exceeding 40 mg/1 NO₃⁻. Potential NO₃⁻ source materials were poultry manure N and synthetic NH₄ based fertilizers. Theδ¹⁵N of solid poultry manure samples ranged between + 7.9 and + 8.6‰ (AIR). Four brands of synthetic fertilizers commonly used hadδ¹⁵N values between −1.5 and −0.6‰. Ammonia volatilization caused theδ¹⁵N of groundwater NO₃⁻ produced from poultry manure N to range between +8 and +16‰. Theδ¹⁸O values of groundwater NO₃⁻, by contrast, mostly ranged between +2 and +5‰ (SMOW). This narrow range ofδ¹⁸O values fell within the expected range of NO₃⁻ produced by nitrification of reduced N forms such as poultry manure N and NH₄ fertilizers, and had a similar range ofδ¹⁸O values as NO₃⁻ in the upper part of the unsaturated zone below raspberry fields and beneath former manure piles. Theδ¹⁵N-NO₃⁻ andδ¹⁸O-NO₃⁻ data confirmed that NO₃⁻ in the aquifer was predominantly derived from poultry manure and to a lesser extent from synthetic fertilizers. Theδ¹⁸O-NO₃⁻ data further suggested the nitrification process occurred mainly in the summer months, with the soil NO₃⁻ produced subsequently flushed into the aquifer during fall recharge. Theδ¹⁵N-NO₃⁻andδ¹⁸O-NO₃⁻ data conclusively indicated that no significant bacterial denitrification is taking place in the Abbotsford aquifer.  相似文献   

Origins of high nitrate in groundwater in Tanzania   总被引：3，自引：0，他引：3  

H. Nkotagu 《Journal of African Earth Sciences》1996,22(4):471-478

Dodoma is located in a semi-arid climate (mean annual rainfall 550 mm) in an area of crystalline basement rock. The groundwater contains high nitrate with NO₃⁻ concentrations averaging 150 mg l⁻¹ and total mineralization between 1000–3000 mg l⁻¹. Factor analysis has been used for the identification of factors that bring about the chemical character of groundwater. Three rotated factors, explaining 77.2% of the total data variance, were extracted. The first factor accounts for 51.0% of the variance and shows high positive correlation with Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl⁻, SO₄²⁻, HCO₃⁻ and SEC and is attributed to the leaching of surface and soil salts together with mineral dissolution. The second factor accounts for 14.1% of the variance and is positively correlated with NO₃⁻ and negatively correlated with pH; this is explained by the nitrification process taking place on the sewage effluents. The third factor is highly positively correlated with ¹⁸O and ²H, accounting for 12.1% of the variance and is a consequence of evaporation processes. Nitrate concentrations greater than 100 mg l⁻¹ are commonly found in both deep and shallow groundwaters. It is concluded that the high nitrate concentrations have originated from the sewage effluents that are advecting and dispersing through macropores under bypass flow mechanisms.  相似文献   

Mechanism of arsenic release to groundwater,Bangladesh and West Bengal     

《Applied Geochemistry》2000,15(4):403-413

In some areas of Bangladesh and West Bengal, concentrations of As in groundwater exceed guide concentrations, set internationally and nationally at 10 to 50 μg l⁻¹ and may reach levels in the mg l⁻¹ range. The As derives from reductive dissolution of Fe oxyhydroxide and release of its sorbed As. The Fe oxyhydroxide exists in the aquifer as dispersed phases, such as coatings on sedimentary grains. Recalculated to pure FeOOH, As concentrations in this phase reach 517 ppm. Reduction of the Fe is driven by microbial metabolism of sedimentary organic matter, which is present in concentrations as high as 6% C. Arsenic released by oxidation of pyrite, as water levels are drawn down and air enters the aquifer, contributes negligibly to the problem of As pollution. Identification of the mechanism of As release to groundwater helps to provide a framework to guide the placement of new water wells so that they will have acceptable concentrations of As.  相似文献   

Groundwater transport of arsenic and chromium at a historical tannery,Woburn, Massachusetts,U.S.A.     

《Applied Geochemistry》1994,9(5):569-582

The geochemical environment in hide piles at a historical tanning and rendering site (Woburn, Massachusetts, U.S.A.) is strongly reducing, as reflected by the presence of H₂S and CH₃HS in the pile offgas. The presence of a reducing environment in the Subjacent groundwater, along with DOC (≥ 100mg/l) from hide breakdown, results in reduction of As(V) to As(III), and subsequent methylation to monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA). The reducing conditions also result in precipitation of FeS_(am), while hydrophilic organic acids have increased Cr(III) solubility. Three spatially sequential geochemical redox facies were recognized in groundwater downgradient from the hide piles. Typically, a reduced core zone was present adjacent to the hide piles, characterized by S²⁻ ≥ 1mg/l, Fe²⁺ <5mg/l,NH₃ ≥ 200mg/l and the presence of MMAA in conjunction with DOC (−30mg/l). This facies transitions through an intermediate zone, represented by Fe²⁺ > 20mg/l, NH₃ (5–200 mg/l) and the sporadic presence of measurable S²⁻ (1–2 mg/l), to an oxidizing peripheral zone characterized by conditions representative of background (i.e. DO> 1mg/l, Eh> 0mV, Fe²⁺ < 20mg/l, S²⁻ < 1mg/l,NH₃ < 5mg/l and NO₃⁻ >NH₃), accompanied by precipitation of amorphous ferric hydroxide, sorption of As and co-precipitation-sorption of Cu, Pb and Zn. Electron microprobe analysis of hide-pile materials demonstrated authigenic precipitation of amorphous ferric hydroxide and gypsum, in agreement with the results of geochemical modeling.  相似文献   

Cobalt sorption–desorption behavior of calcareous soils from some Iranian soils     

《Chemie der Erde / Geochemistry》2016,76(1):95-102

Little research has been done to study the role of soil parameters in cobalt (Co) retention, release and the processes involved in calcareous soils of arid and semi-arid regions. We studied the Co sorption and desorption capacity of various calcareous soils using batch technique. The sorption and desorption behavior of Co varied greatly among the studied soils. The sorbed fraction ranged from 92.3% to 97.2% and from 51.0% to 71.8%, when 5 and 200 mg Co l⁻¹, was added to the soil samples, respectively. Cobalt sorption curves were well fitted with Langmuir, Freundlich, and linear equations. The values of the distribution coefficients obtained from linear equation ranged from 9.5 l kg⁻¹ to 23.4 l kg⁻¹. Desorption experiments resulted in a Co recovery ranged from 3.6% to 11.4%, indicating a low desorption of Co from soils. The results of the geochemical modeling indicated that under low Co addition, the solutions were undersaturated with respect to Co(OH)_2(am), Co(OH)_2(c), Co₃(PO₄)_2(s), CoCl_2(s), CoHPO_4(s), CoCl₂·6H₂O_(s), and CoO_(s), whereas under higher Co addition, the solutions were undersaturated with respect to Co(OH)_2(am), CoCl_2(s), CoCl₂·6H₂O_(s), CoO_(s), CoHPO_4(s), and saturated with respect to Co₃(PO₄)_2(s), and CoCO_3(s). The hysteresis indices indicated that desorption of freshly sorbed Co with 0.01 M CaCl₂ was hysteretic in all soils and low mobility and leaching potential of freshly sorbed Co can be expected from these calcareous soils. Statistical correlations revealed that Co sorption and desorption onto the soils were influenced by the presence of CaCO₃ in soils. These findings suggested that calcareous soils are able to retain strongly Co in which the movement of Co in the soil profile would be negligible. Thus, little risk of groundwater contamination can be expected with Co in these calcareous soils.  相似文献