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1.
One of the most severe issues for water supply in Bangladesh is high arsenic concentrations. Widespread implementation of tubewells was determined to be highly problematic due to arsenic contamination in the groundwater. For substantial areas in Bangladesh, groundwater cannot be utilized for water supply without treatment to reduce arsenic levels. Thus, calculations for the incremental excess lifetime cancer risk are used to demonstrate that indeed, seeing elevated arsenicosis must be expected. By observing the correlations between arsenic and iron and the prevalence of arsenicosis patients, the relationships among the concentrations of arsenic and iron, and the percentage of contaminated wells are significant for determining the prevalence of arsenicosis. The results declare that high arsenic concentrations and high percentages of contaminated wells, as well as the lower iron concentrations, lead to a higher prevalence of arsenicosis patients. It demonstrates the validity of the risk calculation procedure and single arsenic concentrations cannot provide good prediction of arsenicosis risk. When the concentration of arsenic and iron are both high, the ratio of arsenic/iron will decrease, and the arsenicosis rates will lessen, as well. The findings indicate that co-precipitation of iron and arsenic can remove some of the arsenic before the groundwater is consumed.  相似文献   

2.
In natural waters arsenic concentrations up to a few milligrams per litre were measured. The natural content of arsenic found in soils varies between 0.01 mg/kg and a few hundred milligrams per kilogram. Anthropogenic sources of arsenic in the environment are the smelting of ores, the burning of coal, and the use of arsenic compounds in many products and production processes in the past. A lot of arsenic compounds are toxic and cause acute and chronic poisoning. In aqueous environment the inorganic arsenic species arsenite (As(III)) and arsenate (As(V)) are the most abundant species. The mobility of these species is influenced by the pH value, the redox potential, and the presence of adsorbents such as oxides and hydroxides of Fe(III), Al(III), Mn(III/IV), humic substances, and clay minerals.  相似文献   

3.
This paper deals with kinetics and equilibrium studies on the adsorption of arsenic species from simulated groundwater containing arsenic (As(III)/As(V), 1:1), Fe, and Mn in concentrations of 0.188, 2.8, and 0.6 mg/L, respectively, by Ca2+ impregnated granular activated charcoal (GAC‐Ca). Effects of agitation period and initial arsenic concentration on the removal of arsenic species have also been described. Although, most of the arsenic species are adsorbed within 10 h of agitation, equilibrium reaches after ～24 h. Amongst various kinetic models investigated, the pseudo second order model is more adequate to explain the adsorption kinetics and film diffusion is found to be the rate controlling step for the adsorption of arsenic species on GAC‐Ca. Freundlich isotherm is adequate to explain the adsorption equilibrium. However, empirical polynomial isotherm gives more accurate prediction on equilibrium specific uptakes of arsenic species. Maximum specific uptake (qmax) for the adsorption of As(T) as obtained from Langmuir isotherm is 135 µg/g.  相似文献   

4.
Concentrations of total arsenic and individual arsenic compounds were determined in livers of cetaceans (Dall's porpoise and short-finned pilot whale), pinnipeds (harp and ringed seals), sirenian (dugong), and sea turtles (green and loggerhead turtles) to characterize arsenic accumulation profiles in higher trophic marine animals. Hepatic arsenic concentrations in sea turtles were highest among the species examined. Chemical speciation of arsenic revealed that arsenobetaine was the major arsenic compound in almost all the species. In contrast, arsenobetaine was a minor constituent in dugong. Dimethylarsinic acid, methylarsonic acid, arsenocholine, tetramethylarsonium ion, arsenite, and an unidentified arsenic compound were also detected as minor constituents. However, the composition of arsenic compounds was different among these species. These results might reflect the differences in the metabolism of arsenic and/or the compositions of arsenic compounds in their preys. To our knowledge, this is the first report on the large variation in the composition of arsenic species in liver of marine mammals and sea turtles.  相似文献   

5.
This study characterized the redox conditions in arsenic‐affected groundwater aquifers of the Lanyang plain, Taiwan. Discriminant analysis was adopted to delineate three redox zones (oxidative, transitional and reductive zones) in different aquifers and yielded 92·3% correctness on groundwater quality data. Arsenic is mainly distributed in the reductive zone, and arsenic distribution in the shallow aquifer is mainly affected by surface activities. According to PHREEQC modelling results, possible mechanisms for arsenic release to groundwater in Lanyang plain are explored. Arsenic released to groundwater in the oxidative zone (zone 1) is primarily caused by the oxidations of arsenic‐bearing pyrite minerals, and arsenate is the predominant species. While the reductive dissolution of Fe‐oxides are responsible for the high arsenic concentration found in the transitional and reductive zones (zones 2 and 3), arsenite is the predominant species. The reduction potential of groundwater rises as the depths and zones increase. Some sulphates may be reduced to form sulphide ions, which then react with arsenic to form arseno‐sulphide deposits (such as realgar, orpiment) and then slightly lower groundwater arsenic concentrations. A conceptual diagram which summarized the possible release processes of arsenic in different redox zones along groundwater flow in Lanyang plain is postulated. Arsenic‐bearing pyrite and arsenopyrite (FeAsS) are oxidized as they are exposed to the infiltrated oxygenated rainwater, releasing soluble arsenate Fe(II) and SO42? into zone 1. The dissolution of arsenic‐rich Fe‐oxides due to the onset of reducing conditions in zones 2 and 3 is responsible for the mobility of arsenic and likely to be the primary mechanism of arsenic release to groundwater in the Lanyang plain Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

6.
This study aims to investigate the control of arsenic distribution by biogeochemical processes in the Indian Sundarban mangrove ecosystem and the importance of this ecosystem as an arsenic source for surrounding coastal water. The As(V)/As(III) ratio was found to be significantly lower in both surface and pore waters compared to sea water, which could be attributed to biogeochemical interconversion of these arsenic forms. The biological uptake of arsenic due to primary and benthic production occurs during the post-monsoon season, and is followed by the release of arsenic during the biochemical degradation and dissolution of plankton in the pre-monsoon season. These results suggest that arsenic is immobilized during incorporation into the arsenic-bearing initial phase, and unlikely to be released into pore water until the complete microbial degradation of arsenic-bearing organic compounds.  相似文献   

7.
Inorganic arsenic is a carcinogen and consumption in low dose may lead to cancer. We estimated the cancer risk of the participants from arsenic endemic regions of West Bengal, India. The probable cancer risk was estimated following the assessment of daily inorganic arsenic intake through drinking water and diets of 20 participants for three consecutive years who had been using low arsenic water in the Indian context (median arsenic concentration in the study Years-I, II and III were 22, 16, 13 µg/l respectively). Probable cancer risk of the population was 2.80 × 10?4, 2.94 × 10?4, 3.12 × 10?4 in the three respective study years (Year-I, II and III); just higher than the US EPA risk level of concern. The arsenic species content of the paired raw, cooked rice and urine was estimated in the as is taken basis. The major diet component, rice contained 72–86% inorganic arsenic whereas urine contains 70% organic arsenic on an average. The cancer risk assessment has been proposed to be modified by inclusion of urine arsenic release, considering the fact of arsenic release through urine. The risk became 1.28 × 10?5, 1.13 × 10?5, 1.01 × 10?5 in the study Year-I, II and III respectively, considering urinary arsenic release, attributed the consideration of urine arsenic release into probable cancer risk estimation.  相似文献   

8.
Stability of arsenopyrite and As(III) in low-temperature acidic solutions   总被引：1，自引：0，他引：1  
Arsenopyrite is one of the most important pri-mary arsenic mineral. In the Eh-pH diagram of the As-O2-S-H2O system, if the total arsenic concentration (TAs) is taken to be 0.75 mg/L, the total sulfur con-centration, 32 mg/L, the temperature, 25℃and the pressure, one atmosphere pressure for the discrimina-tion of arsenic species, it may be found that under hy-pergene conditions, arsenopyrite is a moderately stable mineral. Only in the strongly alkaline and reducing environment can arsenopy…  相似文献   

9.
The maximum contaminant level for arsenic was reduced by the U.S. Environmental Protection Agency (U.S. E.P.A.) for Drinking Water Standards from 50 micrograms per liter (µg/L) to 10 µg/L, effective January 23, 2006. The subject site is a double-lined sanitary landfill facility located in the mid-Atlantic region of the United States. Arsenic was reported above the maximum contaminant level in a downgradient monitoring well (MW-18) in July 2005. Since July 2005, arsenic levels in MW-18 fluctuated above and below 10 µg/L. This research focuses on determining whether reducing conditions in groundwater, enhanced by subsurface landfill gas emissions, were causing naturally-occurring arsenic to mobilize from the native variably-saturated vadose zone soils into groundwater. The groundwater data collected from the impacted well (MW-18) were compared to an upgradient well (MW-8) to determine whether significant differences existed during the time period of April 2004 to April 2007. Linear regression analysis was also used to determine whether other parameters had a significant relationship with the arsenic concentrations detected in MW-18. The groundwater located in MW-18 was consistently more reduced than groundwater located in the upgradient/background well MW-8, and this was most likely attributed to the presence of subsurface landfill gas in the area. According to the U.S. E.P.A., oxidation-reduction potential (ORP) values in groundwater less than 50 millivolts (mv) suggest that a reducing environment may be present. The data presented in this study indicate that arsenic can mobilize into groundwater under moderately reducing conditions, with ORP measurements averaging 53 mv.  相似文献   

10.
Arsenic is a well‐known groundwater contaminant that causes toxicological and carcinogenic effects in humans. Predicting the transport of arsenic in the subsurface is often problematic because of its complex sorption characteristics. Numerous researchers have reported that arsenic sorption on soil material is initially fast and then subsequently slow. A dual‐site numerical sorption model was previously developed to describe arsenic desorption from arsenic‐contaminated soils in batch experiments in terms of two different release mechanisms. Experiments involving synthetic acid rain leaching of four arsenic‐contaminated soil columns were performed to verify the dual‐site numerical sorption model in the context of one‐dimensional vertical transport. The fitted models successfully simulated the signature long tailings and the two‐stage arsenic leaching patterns for all four soil columns. The dual‐site sorption model was incorporated within the general solute transport simulation code Modular Three‐Dimensional Multispecies (MT3DMS), version 5.10. The resulting version was named MT3DDS and is available for public access. This experimental study has shown that MT3DDS is capable of simulating phase redistribution during transport, and thus provides a new numerical tool for simulating arsenic transport in the subsurface.  相似文献   

11.
Arsenic concentrations can be managed with a relatively simple strategy of grouting instead of completely destroying a selected interval of well. The strategy of selective grouting was investigated in Antelope Valley, California, where groundwater supplies most of the water demand. Naturally occurring arsenic typically exceeds concentrations of 10 µg/L in the water produced from these long-screened wells. The vertical distributions of arsenic concentrations in intervals of the aquifer contributing water to selected supply wells were characterized with depth-dependent water-quality sampling and flow logs. Arsenic primarily entered the lower half of the wells where lacustrine clay deposits and a deeper aquifer occurred. Five wells were modified by grouting from below the top of the lacustrine clay deposits to the bottom of the well, which reduced produced arsenic concentrations to less than 2 µg/L in four of the five wells. Long-term viability of well modification and reduction of specific capacity was assessed for well 4-54 with AnalyzeHOLE, which creates and uses axisymmetric, radial MODFLOW models. Two radial models were calibrated to observed borehole flows, drawdowns, and transmissivity by estimating hydraulic-conductivity values in the aquifer system and gravel packs of the original and modified wells. Lithology also constrained hydraulic-conductivity estimates as regularization observations. Well encrustations caused as much as 2 µg/L increase in simulated arsenic concentration by reducing the contribution of flow from the aquifer system above the lacustrine clay deposits. Simulated arsenic concentrations in the modified well remained less than 3 µg/L over a 20-year period.  相似文献   

12.
Concentrations of total arsenic and individual arsenic compounds were determined in liver, muscle, kidney and blubber of mother and fetus of Dall’s porpoises collected from off Sanriku, Japan, in the year 2000 to characterize the placental transfer of arsenic to fetus in cetaceans. Arsenic was detected in all the tissues of Dall’s porpoises. Total arsenic concentrations in liver, kidney, muscle and blubber were 0.76, 0.69, 0.35 and 0.55 μg/g wet wt, respectively, for mother and 0.28, 0.23, 0.26 and 0.07 μg/g wet wt, respectively, for fetus. In all the tissues, concentrations of total arsenic in mother Dall’s porpoise were higher than in fetus. Arsenic speciation revealed that arsenobetaine was the major arsenic compound in liver, kidney and muscle of both mother and fetus. The percentage of arsenobetaine to total arsenic ranged from 76.0 to 91.0% in the tissues. Dimethylarsinic acid, arsenocholine, methylarsonic acid and an unidentified arsenic compound were also detected in tissues of both mother and fetus as minor constituents, whereas tetramethylarsonium ion was not detected in tissues of the fetus. These results suggest that arsenobetaine, dimethylarsinic acid, arsenocholine and methylarsonic acid are transferable from mother to fetus in Dall’s porpoises. To our knowledge, this is the first report on placental transfer of arsenic compounds to fetus in marine mammals.  相似文献   

13.
A metal-contaminated overbank deposit in west-central South Dakota resulted from the discharge of a large volume of mine tailings into a river system between the late 1800s and 1977. The deposit along the Belle Fourche River is typically up to 2 m thick and extends about 90 m away from the channel along the insides of meander bends. The sediments contain above-background levels of copper, iron, manganese, zinc, and particularly arsenic, which is commonly two orders of magnitude above background level in the contaminated sediments. Carbonate minerals in the deposit limit the desorption of arsenic by preventing acid formation. Arsenic concentrations provide a measure of the dilution of mine tailings by uncontaminated sediment. The arsenic appears to have been transported and deposited as arsenopyrite, but is now at least partially associated with iron oxides and hydroxides. Within individual samples, arsenic concentration has an inverse relation with grain size that results from the more efficient accumulation of arsenic on the greater surface area of the smaller particles. Arsenic concentration is inversely related to the sample weight percent finer than 16 μm, however, as a consequence of the dilution of the contaminated sediments by uncontaminated sediment with a finer grain-size distribution. Dilution by uncontaminated sediment from tributaries cause arsenic concentrations to decrease by a factor of 3 along 100 km of floodplain. An influx at high streamflow of uncontaminated sediment from terraces and the premining floodplain as well as from tributaries causes arsenic concentrations in parts of the contaminated deposit that are farthest away from the channel to be two to three times less than arsenic concentrations in overbank sediment that is immediately adjacent to the channel.  相似文献   

14.
Concentrations of total arsenic and individual arsenic compounds were determined in liver, muscle, kidney and blubber of mother and fetus of Dall’s porpoises collected from off Sanriku, Japan, in the year 2000 to characterize the placental transfer of arsenic to fetus in cetaceans. Arsenic was detected in all the tissues of Dall’s porpoises. Total arsenic concentrations in liver, kidney, muscle and blubber were 0.76, 0.69, 0.35 and 0.55 μg/g wet wt, respectively, for mother and 0.28, 0.23, 0.26 and 0.07 μg/g wet wt, respectively, for fetus. In all the tissues, concentrations of total arsenic in mother Dall’s porpoise were higher than in fetus. Arsenic speciation revealed that arsenobetaine was the major arsenic compound in liver, kidney and muscle of both mother and fetus. The percentage of arsenobetaine to total arsenic ranged from 76.0 to 91.0% in the tissues. Dimethylarsinic acid, arsenocholine, methylarsonic acid and an unidentified arsenic compound were also detected in tissues of both mother and fetus as minor constituents, whereas tetramethylarsonium ion was not detected in tissues of the fetus. These results suggest that arsenobetaine, dimethylarsinic acid, arsenocholine and methylarsonic acid are transferable from mother to fetus in Dall’s porpoises. To our knowledge, this is the first report on placental transfer of arsenic compounds to fetus in marine mammals.  相似文献   

15.
Toxic and carcinogenic effects of arsenic in drinking water continue to impact people throughout the world and arsenic remains common in groundwater at cleanup sites and in areas with natural sources. Advances in groundwater remediation are needed to attain the low concentrations that are protective of human health and the environment. In this article, we present the successful use of a permeable reactive barrier (PRB) utilizing sulfate reduction coupled with zero‐valent iron (ZVI) to remediate the leading edge of a dissolved arsenic plume in a wetland area near Tacoma, Washington. A commercially available product (EHC‐M®, Adventus Americas Inc., Freeport, Illinois) that contains ZVI, organic carbon substrate, and sulfate was injected into a reducing, low‐seepage‐velocity aquifer elevated in dissolved arsenic and iron from a nearby, slag‐containing landfill. Removal effectiveness was strongly correlated with sulfate concentration, and was coincident with temporary redox potential (Eh) reductions, consistent with arsenic removal by iron sulfide precipitation. The PRB demonstrates that induced sulfate reduction and ZVI are capable of attaining a regulatory limit of 5 µg/L total arsenic, capturing of 97% of the arsenic entering the PRB, and sustaining decreased arsenic concentrations for approximately 2 years, suggesting that the technology is appropriate for consideration at other sites with similar hydrogeochemical conditions. The results indicate the importance of delivery and longevity of minimum sulfate concentrations and of maintaining sufficient dissolved organic carbon and/or microscale ZVI to precipitate FeS, a precursor phase to arsenic‐bearing pyrite that may provide a stable, long‐term sink for arsenic.  相似文献   

16.
含铁盐的高砷沉积物中,上覆水p H值和总磷浓度的变化对砷迁移的影响尚不明确.以含铁盐的高砷沉积物为研究对象,通过实验观测其暴露在不同p H值的上覆水及经过不同初始p H值、不同初始总磷浓度的溶液淋洗后,沉积物中砷的迁移规律.结果表明:当沉积物暴露在p H=10和11的上覆水时,分别在第11 d和第6 d后,沉积物中的砷溶出速度突然增大,说明当沉积物处于强碱性上覆水环境中,碱性越强,砷的溶出速度越快、溶出量越大.从室内实验条件的角度来看,上覆水的碱化有可能会增加沉积物中砷溶出的风险.而上覆水p H值在4~8之间时,上覆水的酸碱度对沉积物砷的迁移影响较小.此外,当上覆水总磷浓度不高于0.5 mg/L时,磷的竞争吸附对砷的迁移影响较小.  相似文献   

17.
Coal samples from high arsenic coal areas have been analyzed by electron micropbe analyzer (EMPA), scanning electron microscopy with an energy dispersive X-ray analyzer (SEM-EDX), X-ray diffinction analysis (XRD), low temperature ashing (LTA), transmission electron microscopy (TEM), X-ray absorption fine structure (XAFS), instnunent neutron activation analysis (INAA) and wet chemical analysis. Although some As-bearing minerals such as pyrite, arsenopyrite, realgar (?), As-bearing sulfate, and As-bearing clays are found in the high arsenic coals, their contents do not account for the abundance of arsenic in the some coals. Analysis of the coal indicates that arsenic exists mainly in the form of As 5+ and As 3+, combined with compounds in the organic matrix. The occurrence of such exceptionally high arsenic contents in coal and the fact that the arsenic is dominantly organically associated are unique observations. The modes of occurrence of arsenic in high As-coals are discussed.  相似文献   

18.
A study was conducted to evaluate monitored natural attenuation (MNA) as a remedy for arsenic in groundwater at a former phosphate mining and manufacturing facility. The mineralogy, speciation, and lability of arsenic in phosphatic wastes present in soils were characterized using sequential extraction procedures, leaching experiments, batch adsorption tests, and microchemical speciation analysis. A PHREEQC-based reactive transport model was also parameterized using these laboratory results, and it was used to evaluate the importance of identified attenuation mechanisms on arsenic concentrations along a vertical flow path from a shallow, alluvial aquifer to the underlying Floridan aquifer. Arsenic was found to occur in several chemical forms in phosphatic wastes, including unstable sulfide minerals, adsorbed surface complexes, and relatively insoluble phosphate and oxide minerals. Most arsenic was associated with stable minerals. The reactive transport model predicted that historical leaching of solid-phase waste materials in soils would not have generated enough arsenic to explain the concentrations observed in downgradient groundwater; instead, the source of arsenic to groundwater was likely acidic and saline process water that infiltrated though unlined ponds and ditches during historical manufacturing operations. A key factor affecting the long-term effectiveness of natural attenuation of arsenic in groundwater is the occurrence and stability of iron oxyhydroxides in aquifer sediments. According to laboratory and reactive transport model results, sufficient levels were found to be present at the site to effectively limit arsenic migration at concentrations exceeding drinking water standards in the future in the Floridan aquifer. This study presents the geochemical evaluations that are needed to satisfy EPA guidelines on determining whether or not MNA is an acceptable remedy for a site. It specifically details the characterization and modeling that were used to demonstrate effectiveness at a site where MNA was ultimately selected as the remedy for arsenic in groundwater.  相似文献   

19.
Arsenic distribution in sediments of the Mirim-Patos lagoonal system is investigated. Deposits of fresh water Mirim Lagoon and those of the fresh water part of the Patos Lagoon contain 2.5 and 7.7 mg kg(-1), respectively, on average of total arsenic. In contrast, estuarine sediments of the Patos Lagoon are evidently contaminated by arsenic in high concentrations (up to 50 mg kg(-1)), and about 80% of the arsenic there is found in a bioavailable form. Analytical data coupled with direct, visual observations of estuarine water contamination by raw phosphorites and fertilizers suggest that the major source of arsenic in the estuarine sediments originated from the fertilizer industry.  相似文献   

20.
The area east of Varanasi is one of numerous places along the watershed of the Ganges River with groundwater concentrations of arsenic surpassing the maximum value of 10 parts per billion (ppb) recommended by the World Health Organization in drinking water. Here we apply geostatistics and compositional data analysis for the mapping of arsenic and iron to help in understanding the conditions leading to the occurrence of elevated level of arsenic in groundwater. The methodology allows for displaying concentrations of arsenic and iron as maps consistent with the limited information from 95 water wells across an area of approximately 210 km2; visualization of the uncertainty associated with the sampling; and summary of the findings in the form of probability maps. For thousands of years, Varanasi has been on the erosional side in a meander of the river that is free of arsenic values above 10 ppb. Maps reveal two anomalies of high arsenic concentrations on the depositional side of the valley, which has started seeing urban development. The methodology using geostatistics combined with compositional data analysis is completely general, so this study could be used as a prototype for hydrochemistry mapping in other areas.  相似文献   

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