Transport pathways for arsenic and selenium: a minireview

Arsenic and selenium are metalloids found in the environment. Arsenic is considered to pose the most significant potential threat to human health based on frequency of occurrence, toxicity and human exposure. Selenium, on the other hand, ranks only 147th in toxicity but, in contrast to arsenic, is a required micronutrient. Whether a toxin or micronutrient, their metabolism requires that cells to accumulate these metalloids. In this review we discuss the membrane proteins that transport arsenic and selenium into cells, from bacteria to humans, as well as some of the efflux proteins involved in detoxification.     

Risk characterization and exposure assessment in arseniasis-endemic areas of Taiwan

This paper examines the age-specific human health risks exposed to inorganic arsenic through arsenic-contaminated farmed fish/shrimp and groundwater consumptions in arseniasis-endemic areas of blackfoot disease (BFD)-endemic area and Lanyang Plain in Taiwan, based on an probabilistic integrated risk assessment framework. We employ an age-dependent predictive physiologically-based pharmacokinetic model to account for arsenic concentrations in target organs. We reconstruct age-specific dose-response profiles for arsenicosis and arsenic-induced cancers by best fitting a pharmacodynamics-based three-parameter Hill equation model to published epidemiological data from West Bengal and Taiwan. The predicted median arsenic concentrations in age group-specific skin, lung, and bladder ranged from 2.24-5.70, 3.76-9.46, and 5.11-20.71 micro g g(-1) in BFD-endemic area, whereas 4.98-12.04, 8.23-19.92, and 11.07-43.45 micro g g(-1) in Lanyang Plain, respectively. Risk analysis indicates that consumption of arsenic-contaminated farmed fish/shrimp and groundwater in arseniasis-endemic areas may increase threat to prevalence of arsenicosis for all age groups, whereas adults may undergo potential risks of arsenic-induced skin, lung and bladder cancers. We show that peoples in Lanyang Plain are more readily associated with higher morbidities for arsenicosis and skin cancer as well as fatalities for lung and bladder cancers than that of peoples in BFD-endemic area. Here we report the first case in which theoretical human health risks for consuming As-contaminated farmed fish/shrimp and groundwater in the arseniasis-endemic areas are alarming under a conservative condition based on a probabilistic risk assessment framework.     

Arsenic geochemistry and health

Arsenic occurs naturally in the earth's crust and is widely distributed in the environment. Natural mineralization and activities of microorganisms enhance arsenic mobilization in the environment but human intervention has exacerbated arsenic contamination. Although arsenic is useful for industrial, agricultural, medicinal and other purposes, it exerts a toxic effect in a variety of organisms, including humans. Arsenic exposure may not only affect and disable organs of the body, especially the skin, but may also interfere with the proper functioning of the immune system. This paper, therefore, generally highlights the toxic effects of arsenic as well as its mobilization in the natural environment and possible controls. It also briefly attempts to outline the impact of arsenic on the immune system, whose alteration could lead to viral/bacterial infections.     

Aquatic arsenic: Toxicity,speciation, transformations,and remediation

This paper reviews the current knowledge on the toxicity, speciation and biogeochemistry of arsenic in aquatic environmental systems. The toxicity of arsenic is highly dependent on the chemical speciation. The effects of pH, E_h, adsorbing surfaces, biological mediation, organic matter, and key inorganic substances such as sulfide and phosphate combine in a complex and interwoven dynamic fashion to produce unique assemblages of arsenic species. The number of different arsenic species found in environmental samples and an understanding of the transformations between arsenic species has increased over the past few decades as a result of new and refined analytical methods. Changes in arsenic speciation and in total arsenic content of foods upon processing have suggested possible risks associated with processed and unprocessed food. Arsenic removal from water using adsorbents, chemical oxidation, photolysis and photocatalytic oxidation techniques is also reviewed.     

砷污染与生态环境的关系

砷为广泛存在于自然界中的一种元素,在环境中表现出复杂的地球化学性质,不同形态的砷在大气、土壤及水体中的迁移和富集受许多物理化学因素的制约,并产生毒害程度不同的环境效应。总结砷的来源、其在不同环境介质中的存在状态及砷污染对生态环境的影响,提出应在了解不同介质环境中砷的赋存状态后,采用不同的治理方法有效地去除砷,以最大程度地降低砷对人体健康及生态环境造成的危害。     

Arsenic and fluoride removal from groundwater by reverse osmosis

The reverse osmosis process was evaluated for removal of naturally occurring arsenic and fluoride from groundwater. Arsenic removal was affected by the prevalent arsenic species present in the water. Arsenic concentrations were reduced by approximately 60%–90% from nearly 80 μg/L. Fluoride concentrations were reduced by approximately 60% from nearly 1.7 mg/L.     

Arsenic concentrations in rice, vegetables, and fish in Bangladesh: a preliminary study

Arsenic contaminating groundwater in Bangladesh is one of the largest environmental health hazards in the world. Because of the potential risk to human health through consumption of agricultural produce grown in fields irrigated with arsenic contaminated water, we have determined the level of contamination in 100 samples of crop, vegetables and fresh water fish collected from three different regions in Bangladesh. Arsenic concentrations were determined by hydride generation atomic absorption spectrophotometry. All 11 samples of water and 18 samples of soil exceeded the expected limits of arsenic. No samples of rice grain (Oryza sativa L.) had arsenic concentrations more than the recommended limit of 1.0 mg/kg. However, rice plants, especially the roots had a significantly higher concentration of arsenic (2.4 mg/kg) compared to stem (0.73 mg/kg) and rice grains (0.14 mg/kg). Arsenic contents of vegetables varied; those exceeding the food safety limits included Kachu sak (Colocasia antiquorum) (0.09-3.99 mg/kg, n=9), potatoes (Solanum tuberisum) (0.07-1.36 mg/kg, n=5), and Kalmi sak (Ipomoea reptoms) (0.1-1.53 mg/kg, n=6). Lata fish (Ophicephalus punctatus) did not contain unacceptable levels of arsenic. These results indicate that arsenic contaminates some food items in Bangladesh. Further studies with larger samples are needed to demonstrate the extent of arsenic contamination of food in Bangladesh.     

Assessment of arsenic level in the hair of the nonoccupational Egyptian population: pilot study.

Arsenic level of hair samples of apparently healthy Egyptian was measured by means of hydride atomic absorption spectrophotometery. It ranged between 0.04 and 1.04 mg As/kg hair, about 55% of the analysed hair samples were within the range of allowable values (0.08-0.25 mg As/kg hair), but 45% were not. There were no considerable sex-related differences (0.303 and 0.292 mg As/kg hair for males and females, respectively). Different educational levels did not influence it either, when the effect of the age had been excluded. Children and adolescents proved to be more susceptible to arsenic as their mean levels (0.353 microg/g), and were significantly higher than those in the adults (0.233 microg/g). Smoking and some dietary habits had an important role in the elevation of arsenic levels among the nonoccupational Egyptian population: 60% of smokers and 66.7% of indoor passive smokers had arsenic levels >0.25 mg As/kg hair. Arsenic levels were also dependent on the kind of smoking, as hair arsenic of the subject smoking molasses tobacco was found to be significantly higher than that of cigarette smokers (0.459 and 0.209 mg As/kg hair, respectively). The frequency of meat and fish consumption per week was also found to be positively, significantly correlated with arsenic levels. On the other hand, the frequency of consumption of fruits, fresh and cooked vegetables, milk and milk products per week beneficially influenced the arsenic level of the hair samples examined. Arsenic content of the consumed water in Egypt was 0.001 mg/l, which is below the maximum drinking water level allowed by World Health Organisation (WHO). Therefore, the arsenic content of domestic tap water hardly contributed to the arsenic exposure of the Egyptian population in the regions of the study. It is likely that exposure routes by smoking, fish and animal protein consumption are the principal cause of arsenic accumulation in the general Egyptian population.     

Contamination of groundwater and risk assessment for arsenic exposure in Ha Nam province, Vietnam

The characteristics of arsenic-contaminated groundwater and the potential risks from the groundwater were investigated. Arsenic contamination in groundwater was found in four villages (Vinh Tru, Bo De, Hoa Hau, Nhan Dao) in Ha Nam province in northern Vietnam. Since the groundwater had been used as one of the main drinking water sources in these regions, groundwater and hair samples were collected in the villages. The concentrations of arsenic in the three villages (Vinh Tru, Bo De, Hoa Hau) significantly exceeded the Vietnamese drinking water standard for arsenic (10 microg/L) with average concentrations of 348, 211, and 325 microg/L, respectively. According to the results of the arsenic speciation testing, the predominant arsenic species in the groundwater existed as arsenite [As(III)]. Elevated concentrations of iron, manganese, and ammonium were also found in the groundwater. Although more than 90% of the arsenic was removed by sand filtration systems used in this region, arsenic concentrations of most treated groundwater were still higher than the drinking water standard. A significant positive correlation was found between the arsenic concentrations in the treated groundwater and in female human hair. The risk assessment for arsenic through drinking water pathways shows both potential chronic and carcinogenic risks to the local community. More than 40% of the people consuming treated groundwater are at chronic risk for arsenic exposure.     

Arsenic contamination of groundwater in the Terai region of Nepal: an overview of health concerns and treatment options

A review of published information on the arsenic contamination of groundwater in the Terai regions of Nepal showed that the source was mainly geogenic due to the dissolution of the arsenic-bearing minerals. Clinical observations of patients in the arsenic affected districts revealed chronic arsenic poisoning from drinking water. Half a million people inhabiting the region are believed to have been exposed to arsenic levels greater than 50 microg/L in their drinking water. Thirty-one percent of the population (3.5 million) in the region are estimated to have been exposed to arsenic levels between 10 and 50 microg/L. Iron assisted biosand filters currently distributed and in operation are a suitable alternative to mitigate the interim arsenic standard of 50 microg/L, as set by the Nepal Government. Arsenic biosand filters were also effective in removing bacteria and viruses from drinking water in laboratory and field tests. However, groundwater treatment targeting cluster communities in the Terai region is the sustainable way of mitigating the arsenic problem.     

Spatial distribution of arsenic in the intertidal sediments of River Scheldt, Belgium

A study was carried out to assess the spatial distribution of arsenic in the intertidal sediments of the River Scheldt in Belgium. Sediment samples were collected from different locations along the River Scheldt up to 100 cm depth and analysed for the major physicochemical properties. The study reveals that the arsenic contents in the sediment samples vary in a wide range, from 2.3 to 140.2 mg kg(-1) dry weight. Moreover, the arsenic concentrations are generally below the background concentrations and remediation thresholds of arsenic in Flanders, Belgium. The occurrence of arsenic is found closely related to some physicochemical properties of the sediments. Arsenic has a strong positive correlation with organic matter and clay contents. On the contrary, a negative correlation exists between arsenic, sand and pH. It is recommended to develop and use organic matter control practices for lowering further accumulation of arsenic within the sediments.     

Arsenic in North Carolina: public health implications

Arsenic is a known human carcinogen and relevant environmental contaminant in drinking water systems. We set out to comprehensively examine statewide arsenic trends and identify areas of public health concern. Specifically, arsenic trends in North Carolina private wells were evaluated over an eleven-year period using the North Carolina Department of Health and Human Services database for private domestic well waters. We geocoded over 63,000 domestic well measurements by applying a novel geocoding algorithm and error validation scheme. Arsenic measurements and geographical coordinates for database entries were mapped using Geographic Information System techniques. Furthermore, we employed a Bayesian Maximum Entropy (BME) geostatistical framework, which accounts for geocoding error to better estimate arsenic values across the state and identify trends for unmonitored locations. Of the approximately 63,000 monitored wells, 7712 showed detectable arsenic concentrations that ranged between 1 and 806 μg/L. Additionally, 1436 well samples exceeded the EPA drinking water standard. We reveal counties of concern and demonstrate a historical pattern of elevated arsenic in some counties, particularly those located along the Carolina terrane (Carolina slate belt). We analyzed these data in the context of populations using private well water and identify counties for targeted monitoring, such as Stanly and Union Counties. By spatiotemporally mapping these data, our BME estimate revealed arsenic trends at unmonitored locations within counties and better predicted well concentrations when compared to the classical kriging method. This study reveals relevant information on the location of arsenic-contaminated private domestic wells in North Carolina and indicates potential areas at increased risk for adverse health outcomes.     

Recent advances in the bioremediation of arsenic-contaminated groundwater

The biological treatment of groundwater is used primarily to remove electron donors from water sources, providing (biologically) stable drinking water, which preclude bacterial regrowth during subsequent water distribution. To the electron donors belong also the dissolved metal cations of ferrous iron and manganese, which are common contaminants found in most (anaerobic) groundwater. The removal of iron and manganese is usually accomplished by the application of chemical oxidation and filtration. However, biological oxidation has recently gained increased importance and application due to the existence of certain advantages, over the conventional physicochemical treatment. The oxidation of iron and manganese is accelerated by the presence of certain indigenous bacteria, the so-called "iron and manganese oxidizing bacteria." In the present paper, selected long-term experimental results will be presented, regarding the bioremediation of natural groundwater, containing elevated concentrations of iron and arsenic. Arsenic is considered as a primary pollutant in drinking water due to its high toxicity. Therefore, its efficient removal from natural waters intended for drinking water is considered of great importance. The application of biological processes for the oxidation and removal of dissolved iron was found to be an efficient treatment technique for the simultaneous removal of arsenic, from initial concentrations between 60 and 80 microg/l to residual (effluent) arsenic concentrations lower than the limit of 10 microg/l. The paper was focused on the removal of As(III) as the most common species in anaerobic groundwater and generally is removed less efficiently than the oxidized form of As(V). To obtain information for the mechanism of As(III) removal, X-ray photoelectron spectroscopy (XPS) analyses were applied and it was found that As(III) was partially oxidized to As(V), which enabled the high arsenic removal efficiency over a treatment period of 10 months.     

Assessment of arsenic and heavy metal concentrations in water and sediments of the Rio Grande at El Paso-Juarez metroplex region

The Rio Grande located along the US-Mexico border is affected by anthropogenic activities along its geographical course. Runoff and wind deposition of smelting residues may contribute to the pollution of the Rio Grande in the El Paso-Ciudad Juarez area. Few studies have addressed the presence or impacts of heavy metals or arsenic in this ecosystem. This study reports a survey of heavy metals (Cr, Cu, Cd, Ni, Pb, and Zn) and arsenic (As) in water and sediments of the Rio Grande collected from seven sites in the El Paso-Juarez region. Since water quality influences metal content in water, physical (temperature, flow and conductivity), and chemical (pH, dissolved oxygen, nitrates, alkalinity, and water hardness) parameters were measured at each site. Arsenic and heavy metal levels were determined using Inductively Couple Plasma (ICP) emission spectroscopy following EPA procedures. Zinc and lead were found as both total and dissolved metals in most of the samples, with concentrations of total recoverable metals reaching up to 105 and 70 microg/l, respectively. Most metals were found in sediment samples collected from four of seven sites. The highest Cu concentration (35 mg/l) was found at the American Dam site. Concentrations of metals found through this survey will be used as a reference for future studies in monitoring arsenic, heavy metals, and their impacts in the Rio Grande.     

Arsenic poisoning in groundwater: health risk and geochemical sources in Bangladesh

Of the 2508 water samples analyzed in 10 districts of Bangladesh, 51%, on an average, contained arsenic levels of 0.05 to 2.50 mg/l. 95% of nail, 96% of hair, and 94% of urine samples contained arsenic above the normal level. Approximately 3.58 million people out of a total of 17.92 million who are drinking water containing arsenic levels >0.20 mg/l are potentially exposed to high risk of health hazard. Eight thousand and five hundred arsenic patients are identified; they are suffering from various skin lesions, gangrene in leg, skin, lung, bladder, liver, and renal cancer. A big portion of the total population is highly vulnerable to various internal cancers. Lowest arsenic concentration in drinking water producing dermatological disease is found to be 0.103 mg/l. However, the exposure time to develop arsenicosis varies from case to case reflecting its dependence on arsenic level in drinking water and food, nutritional status, genetic variant of human being, and compounding factors. This study has determined the high intensity of fluorescent humic substances in drinking water containing elevated concentrations of arsenic and very low concentrations of heavy metals. The synergistic/antagonistic effect of fluorescent compounds present in drinking water may aggravate the toxicity of arsenic. Geochemical study suggests that arsenic may be released from both reductive dissolution of Fe and Mn (oxy)hydroxide and microbial oxidation of organic matter.     

Organoarsenicals in poultry litter: Detection,fate, and toxicity

Arsenic contamination in groundwater has endangered the health and safety of millions of people around the world. One less studied mechanism for arsenic introduction into the environment is the use of organoarsenicals in animal feed. Four organoarsenicals are commonly employed as feed additives: arsanilic acid, carbarsone, nitarsone, and roxarsone. Organoarsenicals are composed of a phenylarsonic acid molecule with substituted functional groups. This review documents the use of organoarsenicals in the poultry industry, reports analytical methods available for quantifying organic arsenic, discusses the fate and transport of organoarsenicals in environmental systems, and identifies toxicological concerns associated with these chemicals. In reviewing the literature on organoarsenicals, several research needs were highlighted: advanced analytical instrumentation that allows for identification and quantification of organoarsenical degradation products; a greater research emphasis on arsanilic acid, carbarsone, and nitarsone; identification of degradation pathways, products, and kinetics; and testing/development of agricultural wastewater and solid treatment technologies for organoarsenical-laden waste.     

Omics and biotechnology of arsenic stress and detoxification in plants: Current updates and prospective

Arsenic (As), a naturally occurring metallic element, is a dreadful health hazard to millions of people across the globe. Arsenic is present in low amount in the environment and originates from anthropogenic impact and geogenic sources. The presence of As in groundwater used for irrigation is a worldwide problem as it affects crop productivity, accumulates to different tissues and contaminates food chain. The consumption of As contaminated water or food products leads to several diseases and even death. Recently, studies have been carried out to explore the biochemical and molecular mechanisms which contribute to As toxicity, accumulation, detoxification and tolerance acquisition in plants. This information has led to the development of the biotechnological tools for developing plants with modulated As tolerance and detoxification to safeguard cellular and genetic integrity as well as to minimize food chain contamination. This review aims to provide current updates about the biochemical and molecular networks involved in As uptake by plants and the recent developments in the area of functional genomics in terms of developing As tolerant and low As accumulating plants.     

Delivering Arsenic-free Drinking Water-Made Practically Possible: Continuous Scale Electrochemical Arsenic Remediation Process Furnished,based on Experimental Studies and ANN Simulation

Environment, Development and Sustainability - Arsenic (As) in groundwater has become a worldwide concern due to its high toxicity as it is classified as a potent carcinogen, when exposed to...     

Risk assessment and pathway study of arsenic in industrially contaminated sites of Hyderabad: a case study

Different areas in the industrial region of Patancheru near Hyderabad, Andhra Pradesh (A.P), India are contaminated with high concentration of arsenic, which is attributed to industrial source like veterinary chemicals, pharmaceuticals, pesticide industries, etc. Fourteen villages of this area of Patancheru were assessed for arsenic contamination by collecting samples of water (surface and ground), soil, fodder, milk, and vegetables. The total arsenic content in the whole blood, urine, hair, and nails of the residents showing arsenical skin lesions and other clinical manifestations were also studied. To understand the bioavailability of arsenic in this environment and its possible entry into human food chain, speciation studies of arsenic was carried out and the results are presented in this paper.     

Arsenic in groundwater: A threat to sustainable agriculture in South and South-east Asia

The problem of arsenic pollution of groundwater used for domestic water supplies is now well recognised in Bangladesh, India and some other countries of South and South-east Asia. However, it has recently become apparent that arsenic-polluted water used for irrigation is adding sufficient arsenic to soils and rice to pose serious threats to sustainable agricultural production in those countries and to the health and livelihoods of affected people. This paper reviews the nature of those threats, taking into account the natural sources of arsenic pollution, areas affected, factors influencing arsenic uptake by soils and plants, toxicity levels and the dietary risk to people consuming arsenic-contaminated rice.