Arsenic contamination in groundwater and its proposed remedial measures

Arsenic contamination occurs in groundwater of Bangladesh mainly from the alluvial and deltaic sediments. Arsenic contamination of groundwater in Bangladesh was first detected more than a decade ago and the ’shallow tubewells’ were reported as the main source of arsenic contaminated water. From the nutritional and metabolic points of view, arsenic is likely to adversely affect human health and nutrition. Up to now, several studies have been carried out on this context; however, inadequate knowledge on arsenic sources, mobilization and transport still remains as a constraint due to lack of data, information and technological advances. Thus, a review study has been undertaken on the sources of arsenic, its causes, mobilization, transport, effects on human health, arsenic test procedures and removal methods, in the context of groundwater contamination in Bangladesh, and finally sustainable remedial measures of arsenic have been proposed. This study suggests that laboratory facilities for testing of arsenic and effects of enhanced groundwater pumping, phosphate fertilizer etc., need to be updated, expanded and studied. This review work is significant to further knowledge improvement, as the topic is general and worldwide. It can be concluded that the integration of the proposed remedial measures with the national geographic information system interface database relating to arsenic for analysis, production of hazard maps, and dissemination on television show for the planners, engineers, managers, field supervisors and affected people, can reach at the sustainable solution for mitigating arsenic and associated problems successfully in Bangladesh.     

吉林西部地区高砷地下水砷的阈值分析及风险评价

高砷地下水导致的砷中毒是吉林西部地区近年来新发现的地方病。为评价饮用水中砷对人体健康产生的潜在危害,在野外调查、采样分析的基础上,开展了水砷安全阈值分析 ,确定了砷的总质量浓度0.05 mg/L为研究区的水砷安全阈值,建立了地下水健康风险评价模型,进行了地下水砷健康风险评价。结果表明:研究区地下水砷引起的个人年均风险度最高达2.11×10^-3 a^-1,其中高砷的第四系承压水中97.06%的采样点水砷对人体的个人年均致癌风险度,大于国际辐射防护委员会(ICRP)推荐的最大可接受值5.0×10^-5 a^-1;作为备用水源的第三系大安组、泰康组承压水69.57%采样点砷的致癌风险度也超过最大可接受风险水平。通过对风险度评价结果与砷中毒病情等资料的对比分析,风险评价结果与砷中毒病情基本一致,验证了评价结果的合理性。     

Characterization and assessment of groundwater resources using hydrogeochemical analysis,GIS, and field data in southern Wadi Qena,Egypt

An integrated approach using hydrogeochemical analysis, remote sensing, GIS, and field data was employed to characterize the groundwater resources in southern Wadi Qena, Egypt. Various thematic maps showing topography, lineaments, wadi deposits, slope, and stream networks were combined through GIS analysis to discriminate groundwater potential zones on the valley floor. The resulting map classifies the area into five groups of groundwater potentiality from very high to very low zones, supported by the groundwater level, well locations, and by the results of previous geophysical studies. Thirty-seven groundwater well data were tested from the Quaternary and Nubian Sandstone aquifers and analyzed for physio-chemical parameters. Results of hydrochemical analysis show that water quality varies widely through the aquifers, and groundwater in the Quaternary aquifer shows the highest salinity values and a predominance of Na and Cl in water chemical facies. Overlay GIS maps of alkalinity (SAR and RSC) and salinity hazards (EC and Cl) of the Quaternary aquifer were prepared. The resulting maps show that samples do not present an alkalinity hazard in most areas but are potentially salinity hazard. Therefore, the water is fit for agricultural use with certain restrictions, but is not suitable for direct human consumption because it is either very hard or too saline.     

Assessment of arsenic and fluoride pollution in groundwater in Dawukou area,Northwest China,and the associated health risk for inhabitants

Exposure to arsenic and fluoride through contaminated drinking water can cause serious health effects. In this study, the sources and occurrence of arsenic and fluoride contaminants in groundwater are analyzed in Dawukou area, northwest China, where inhabitants rely on groundwater as the source of drinking water. The triangular fuzzy numbers approach is adopted to assess health risk. The fuzzy risk assessment model incorporates the uncertainties that are caused by data gaps and variability in the degree of exposure to contaminants. The results showed that arsenic and fluoride in groundwater were mainly controlled by the dissolution–precipitation of Ca-arsenate and fluorite under weakly alkaline conditions. The arsenic and fluoride concentrations were higher in the shallow groundwater. The most probable risk values for arsenic and fluoride were 4.57 × 10^?4 and 0.4 in the shallow groundwater, and 1.58 × 10^?4 and 0.3 in the deep groundwater. Although the risks of fluoride were almost within the acceptable limit (<1.0), the risk values of arsenic were all beyond the acceptable levels of 10^?6 for drinking water. Further, the local administration should pay more attention to the potential health risk through dietary intake and to the safety of deep water by ensuring it is not contaminated under prolonged pumping conditions. The fuzzy risk model treats the uncertainties associated with a quantitative approach and provides valuable information for decision makers when uncertainties are explicitly acknowledged, particularly for the variability in contaminants. This study can provide a new insight for solving data uncertainties in risk management.     

Groundwater arsenic contamination in Ganga–Meghna–Brahmaputra plain, its health effects and an approach for mitigation

The authors’ survey of the Ganga–Meghna–Brahmaputra (GMB) plain (area 569,749 km²; population >500 million) over the past 20 years and analysis of more than 220,000 hand tube-well water samples revealed groundwater arsenic contamination in the floodplains of the Ganga–Brahmaputra river (Uttar Pradesh, Bihar, Jharkhand, West Bengal, and Assam) in India and the Padma–Meghna–Brahmaputra river in Bangladesh. On average, 50 % of the water samples contain arsenic above the World Health Organization guideline value of 10 μg/L in India and Bangladesh. More than 100 million people in the GMB plain are potentially at risk. The authors’ medical team screened around 155,000 people from the affected villages and registered 16,000 patients with different types of arsenical skin lesions. Arsenic neuropathy and adverse pregnancy outcomes have been recorded. Infants and children drinking arsenic-contaminated water are believed to be at high risk. About 45,000 biological samples analyzed from arsenic-affected villages of the GMB plain revealed an elevated level of arsenic present in patients as well as non-patients, indicating that many are sub-clinically affected. In West Bengal and Bangladesh, there are huge surface water in rivers, wetlands, and flooded river basins. In the arsenic-affected GMB plain, the crisis is not over water scarcity but about managing the available water resources.     

Slow arsenic poisoning of the contaminated groundwater users

This paper gives impact of Arsenic contaminated water on human health as well as overview of the extent and severity of groundwater arsenic contamination in Bangladesh. Scalp hair is the most important part of the human body to monitor the accumulation of this type of poison. Therefore, an experiment has been carried out by Neutron Activation Analysis (NAA) at Atomic Energy Research Establishment (AERE), Savar, Dhaka, Bangladesh on human hair of corresponding tube well water users of these areas to determine the total accumulation of arsenic to their body. Hair samples collected from the region where the groundwater was found highly contaminated with arsenic. The obtained results of arsenic concentration in the lower age (Hb) categories of users (below 12 years of age users) is in the range of 0.33 to 3.29 /gmg/g (ppm) and that in the Hu categories (upper 12 years of age users) is 0.47 to 6.64 μg/g (ppm). Where as maximum permissible range is 1 ppm certified from WHO. Results show that the peoples are highly affected where the groundwater is highly contaminated with arsenic and acts as the primary source of arsenic poisoning among the peoples of those areas. The results indicate that human population is affected with arsenic locally using the contaminated water for a long time.     

Poisons, pragmatic governance and deliberative democracy: The arsenic crisis in Bangladesh

The paper applies some of the principles of pragmatism to the environmental health crisis of arsenic pollution in the groundwater of Bangladesh. This hazard affects between 28 and 57 million people and it has been called “the largest mass poisoning of a population in history”. Such hyperbole aside, the authors consider the dysfunctional nature of central and local government in Bangladesh, which at all levels can be said to have failed water consumers. This leads to a discussion of the nature of governance generally, particularly with regard to two principles derived from the pragmatism of John Dewey: first, an orientation to political action through local, community-based experimentation; and, second, a conviction that participatory democracy draws its strength from the beliefs and attitudes distributed in social networks. The paper then assesses a number of interventions, for instance the World Bank’s large-scale Bangladesh Arsenic Mitigation Water Supply Project which has faced administrative problems since its inception in 1997 and was very slow to find its feet. NGOs with a stake in arsenic mitigation are also highlighted, particularly for their role in the so-called franchise state. It is argued that a number of conditions of inertia and resistance explain the sluggish response to the arsenic hazard. Indeterminacy about the science and technology of arsenic is one factor, and another is the distribution of power at the local level. The paper argues that future policies and projects would do well to consider deliberative democracy in guises appropriate to rural Bangladesh. This must include better information availability and opportunities for participation at the village level, for instance in civic science. The overall conclusion is that pragmatic principles are helpful in promoting community-focused mitigation measures but that accountability is essential if policies are to avoid problems of local power, patronage and clientelism.     

Human Health Risk Assessment Model of Organic Pollution in Groundwater: Shijiazhuang Industrial Zone

In this study, a risk-based management model is developed and applied to an industrial zone. The models proposed by the United States Environmental Protection Agency and Han Bing have been improved by adding a residual ratio of volatile organic compounds (VOC) after boiling and deleting the related parameters in half-life. Using this improved model, an integrated process was used to assess human health risk level in the study area. Compared with water quality analysis, the results highlight the importance of applying an integrated approach for decision making on risk levels and water protection. The results of this study demonstrated that: (1) Compared with these permissible level standards in China (GB 3838-2002) and National Primary Drinking Water Regulations of the United States, the residents’ daily life had not been affected by the groundwater in this area (except for relative bad water quality of HB3-4 and HB3-6); (2) The typical detected organic contaminants of all groundwater samples were chloroform, carbon tetrachloride, trichloroethylene and tetrachloroethene, and the pollution sources were mainly industrial sources by preliminary investigations; (3) As for groundwater, the non-carcinogenic risk values of all samples do not exceed the permissible level of 1.0 and the carcinogenic risk values are relatively lower than the permissible level of 1.00E-06 to 1.00E-04; (4) Drinking water pathway of trichloroethylene and tetrachloroethylene mainly contribute to increasing the health risk of residents’ in study areas; (5) In terms of non-carcinogenic risk and carcinogenic risk, the health risk order for drinking water pathway and dermal contact pathway was: drinking water pathway > dermal contact pathway.     

Using geographical information systems to assess groundwater contamination from arsenic and related diseases based on survey data in Lahore,Pakistan

The present study was aimed at assessing the groundwater contamination from arsenic (As) and its impact on health from survey data in Lahore, Pakistan. OK (ordinary kriging) technique was used to create As and pH surfaces for samples from 380 groundwater wells at different locations and depths in the study area. Geographic information systems (GIS) was applied to delineate areas for safe, risk, and dangerous zones of As in drinking water from groundwater wells at 640 to 850 ft depths. To analyze effects of high As on public health, GIS-based field surveys were conducted to link health data along location of respondents to As contamination levels in the delineated safe, risk, and dangerous zones. Moreover, various pH levels and their effectiveness were studied to suggest cost-effective As treatment in the study area. Our results show that As contaminated strata varies with depth of groundwater wells, i.e., 44.50% areas comprising safe zone of drinking water from deep wells at 850 ft depth compared to 26% areas of shallow water at 640 ft depth. About 35% area with pH range (7 to 7.5) is marked in the risk and danger zones of As that can be initially targeted for treatment. Surveys confirm that people living in the risk and danger zones have some kind of As-related diseases.     

Hydrochemical assessment of groundwater from shallow aquifers in parts of Wadi Al Hamad,Madinah, Saudi Arabia

The present study was carried out in the Mulaylih area which forms a part of Wadi Al Hamad in the Madinah Province of Saudi Arabia. Thirty groundwater samples from agricultural farms were collected and analyzed for various physio-chemical parameters including trace elements. The area is occupied by the Quaternary alluvium deposits which form shallow unconfined aquifers. Evaporation and ion exchange are the major processes which control the major ion chemistry of the area. The extreme aridity has results in high total dissolved solid values (average of 9793.47 mg/l). Trace element concentrations are low and are mainly attributed to geogenic sources (silicate weathering). Na-Cl groundwater type is the main hydrochemical facies found in the area. The waters are found to be oversaturated with calcite/aragonite and dolomite. The average nitrate concentration was found to be 134.10 mg/l and is much higher than the WHO recommended limit of 50 mg/l in drinking water. Their high values are mainly associated with the application of N-fertilizers on the agricultural farms. The average fluoride concentration in the study was found to be 1.54 mg/l. The relation between F and Cl and Cl and Na reveals that the fluoride concentrations are mainly attributed to geogenic sources. A comparison of the groundwater quality with the Saudi drinking water standards shows that the water is unfit for drinking. The high salinity and sodicity of the groundwater make it unfit for irrigation. Principal component analysis resulted in extraction of four principal components accounting for 79.5% of the total data variability and supports the fact that the natural hydrochemical processes (evaporation and ion exchange) control the overall groundwater chemistry.     

Arsenic contamination of ground and pond water and water purification system using pond water in Bangladesh

This paper, firstly, shows the distribution of arsenic-contaminated groundwater in Samta village. This village, which is in Jessore district in Bangladesh, was chosen as a model village for investigating the mechanism of groundwater contamination. 90% of the tube wells in this village had arsenic concentrations above the Bangladesh standard of 0.05 mg/l. Tube wells with arsenic concentrations of over 0.50 mg/l were distributed in the southern part of the village with a belt-like shape from east to west. Secondly, groundwater distribution is discussed with respect to its flow and the high arsenic zone (As≥0.50 mg/l) agrees well with the drifting zone of the groundwater. Furthermore, arsenic-free water supply systems suitable for a small area in the village have been developed. A pond sand filter (PSF) system which purifies pond water is discussed in this paper. Prior to the construction of the PSF, the water quality in ponds was examined for arsenic levels. The inflow of drainage from the tube wells was found to be the major cause of arsenic contamination of pond water. The PSF installed in Samta is working very well and produces a good quality of treated water.     

鄱阳湖平原地下水重金属含量特征与健康风险评估

鄱阳湖平原作为长江中下游平原的重要组成部分,随着城镇化进程的快速推进,由于工矿业污染物、农村生活污水和农业生产废水向地下水的过量排放,农村地下水污染程度和范围不断扩大,为了解鄱阳湖平原地下水重金属污染状况,本研究在大量的水文地质调查和水化学样品测试基础上,分析该区地下水中重金属Cu、As、Cr、Hg、Pb、Cd含量特征,利用美国环境保护署(USEPA)的健康风险评价模型对鄱阳湖平原地下水重金属进行健康风险评价。研究区171个地下水样品中Cd、Cu、Hg、As、Pb、Cr等6种重金属元素含量变化幅度大,其中Hg、Cd和As平均值超过《地下水环境质量标准》(GB/T14848—2017)Ⅲ类标准,结果表明鄱阳湖平原地下水水质受人为影响大,局部地下水存在严重的污染。致癌物健康风险评价结果显示,Cr、As和Cd的平均个人年健康风险值均大于可接受风险值,Cr的健康风险值最大,是主要的致癌因子,As次之,Cd最低;非致癌物质健康风险结果显示,Hg、Pb和Cu的健康风险水平表现为Hg>Pb>Cu,属于可忽略风险。区域饮水途径上的健康风险主要来自致癌物质,总体上男性健康风险大于女性的健康风险。鄱阳湖平原地下水水质污染状况研究及治理监管工作提供理论依据,为其他区域地下水重金属的监测和质量控制提供参考和借鉴。     

Fluoride and arsenic hydrogeochemistry of groundwater at Yuncheng basin,Northern China

High fluoride and arsenic concentrations in groundwater have led to serious health problems to local inhabitants at Yuncheng basin, Northern China. In this study, groundwater with high fluoride and arsenic concentration at Yuncheng basin was investigated. A majority of the samples (over 60%) belong to HCO₃ type water. The predominant water type for the shallow groundwater collected from southern and eastern mountain areas was Ca/Mg-Ca-HCO₃ types. For the shallow groundwater from flow through and discharge area it is Na-HCO₃/SO₄-Cl/SO₄/Cl type. The predominant water type for the intermediate and deep groundwater is of Na/Ca/Mg-Ca-HCO₃ type. According to our field investigation, fluoride concentration in groundwater ranges between 0.31 and 14.2 mg/L, and arsenic concentration ranges between 0.243 and 153.7 μg/L. Out of seventy collected groundwater samples, there are 31 samples that exceed the World Health Organization (WHO) standard of 1.5 mg/L for fluoride, and 15 samples exceeds the WHO standard of 10 μg/L for arsenic. Over 40% of high fluoride and arsenic groundwater are related to the Na-HCO₃ type water, and the other fifty percent associated with Na-SO₄-Cl/HCO₃-SO₄-Cl type water; little relation was found in calcium bicarbonate type water. A moderate positive correlation between fluoride and arsenic with pH were found in this study. It is due to the pH-dependent adsorption characteristics of F and As onto the oxide surfaces in the sediments. The observed negative correlation between fluoride and calcium could stem from the dissolution equilibrium of fluorite. The high concentration of bicarbonate in groundwater can serve as a powerful competitor and lead to the enrichment of fluoride and arsenic in groundwater. Most of the groundwater with high fluoride or arsenic content has nitrate content about or over 10 mg/L which, together with the observed positive correlations between nitrate and fluoride/arsenic, are indicative of common source of manmade pollution and of prevailing condition of leaching in the study area.     

Lake and reservoir water quality affected by metals leaching from tropical soils, Bangladesh

 The release of metals during weathering has been studied in order to assess its geochemical controls and possible effects on environmental health in Bangladesh. A total of 27 soil samples and 7 surface water samples were collected from four locations covering three major regions in the country. Results show that weathering effects are a strong function of climatic conditions. Surface waters are typically enriched in Al, Mg, Ca, Na, K, As, Ba, Cr, Cu, Ni, Pb and Zn. The solubility of metal ions, organometallic complexes, co-precipitation or co-existence with the colloidal clay fraction are the main processes that lead to metal enrichment in lake and reservoir water. Aluminium concentrations exceed World Health Organization (WHO) drinking-water standards in all samples, and in two regions, arsenic concentrations also significantly exceed WHO standards. The elevated levels of As indicate that arsenic contamination of water supplies in Bangladesh is not confined to groundwater. Received: 4 June 1999 · Accepted: 17 August 1999     

Arsenic movement and traces in the groundwater from the Hetao area, Inner Mongolia

In the Hetao area of Inner Mongolia, Quaternary alluvial aquifers used for the water supply are contaminated by naturally occurring arsenic, which heavily affects the health of 200,000 local residents. This study on the isotopes of strontium and relevant elements contained in the groundwater as well as the arsenic in the groundwater and residents’ hair indicates that the arsenic originally derives from the upper reaches of this area where arsenic levels are high in groundwater, rock, and soil. Over, respectively, 44 km (work-line AA′) and 36 km (work-line BB′) away from there, the levels of arsenic in the water, corresponding to the trend of the residents’ arseniasis, decrease along the direction of the flow from 0.251 to 0.05 mg/L and 0.232 to 0.036 mg/L. The result of this research suggests that long-term strategies to deal with this arseniasis should involve finding hydrous terrains uncontaminated by water from the upper reaches and developing routes to prevent water from taking arsenic.     

Arsenic exposure through groundwater in the middle Ganga plain in the Varanasi environs,India: A future threat

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.     

Naturally occurring arsenic in groundwater and identification of the geochemical sources in the Duero Cenozoic Basin, Spain

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.     

长江中游河湖平原浅层地下水中砷空间异质性的同位素指示

近年来陆续有报道发现长江中游河湖平原广泛分布着高砷地下水,鄱阳湖平原与江北平原（古彭蠡泽）作为长江中游南北两岸典型的河湖平原,其地下水资源丰富,但砷的空间分布规律尚不清楚,区域供水安全存在风险.本研究在两个区域系统采集98个浅层地下水（< 40 m）样品和8个地表水样品,通过水化学、氢氧稳定同位素分析,查明地下水中砷的空间分布异质性及其影响因素.研究发现江北平原浅层地下水砷含量为0.65~956.72 μg/L（平均值210.78 μg/L）,高砷地下水集中分布于长江古河道;鄱阳湖平原浅层地下水砷含量为0.09~267.45 μg/L（平均值11.85 μg/L）,高砷地下水仅分布于赣江三角洲局部地区.江北平原地下水δD与δ18O值相对鄱阳湖平原更偏负,且与地表水的差异更大.地下水化学及主成分分析结果表明物源和含水层结构差异是影响鄱阳湖平原和江北平原砷空间分布异质性的关键因素,来自长江物源的古彭蠡泽区域沉积物为高砷含水层的形成提供了物质来源,湖相含水层中含砷铁氧化物的还原性溶解是地下水砷富集的主要过程.地下水氢氧稳定同位素指示江北平原较鄱阳湖平原地下水赋存环境更封闭,地下水循环交替速度缓慢,有利于砷的富集.      

Comprehensive evaluation of shallow groundwater quality in Central and Southern Jiangsu Province,China

Evaluation of the shallow groundwater quality in Central and Southern Jiangsu Province (CSJ) in China is important not only to public health but also to sustainable development and utilization of groundwater resources. In this work, 968 groundwater samples were collected by field surveys during 2006 to 2010 to investigate spatial distribution and extent of pollution. The single factor pollution standard index method, considering the values of both the natural groundwater background and the standard of safe drinking water, was used to assess the groundwater quality in the study area. Results showed that the shallow groundwater was severely polluted with Grade V and VI (i.e., severe and extremely severe pollution) groundwater covered about 1/3 and 1/4 of the study area, respectively. The main groundwater contaminants that cause the severe and extremely severe pollutions were manganese, iron, arsenic, and nitrogen. Findings from this work showed that natural hydrogeochemical processes were the main causes of the iron and manganese pollution, however, human activities (e.g., industrial, agricultural, and domestic pollutions) mainly contributed to the nitrogen pollution in the study area.     

Hydrogeochemistry and arsenic contamination of groundwater in the Rayen area, southeastern Iran

High As contents in groundwater were found in Rayen area and chosen for a detailed hydrogeochemical study. A total of 121 groundwater samples were collected from existing tube wells in the study areas in January 2012 and analyzed. Hydrogeochemical data of samples suggested that the groundwater is mostly Na–Cl type; also nearly 25.62 % of samples have arsenic concentrations above WHO permissible value (10 μg/l) for drinking waters with maximum concentration of aqueous arsenic up to 25,000 μg/l. The reducing conditions prevailing in the area and high arsenic concentration correlated with high bicarbonate and pH. Results show that arsenic is released into groundwater by two major phenomena: (1) through reduction of arsenic-bearing iron oxides/oxyhydroxides and Fe may be precipitated as iron sulfide when anoxic conditions prevail in the aquifer sediments and (2) transferring of As into the water system during water–acidic volcanic rock interactions.