High arsenic groundwater: Mobilization,metabolism and mitigation – an overview in the Bengal Delta Plain

The widespread occurrence of high inorganic arsenic in natural waters is attributed to human carcinogen and is identified as a major global public health issue. The scale of the problem in terms of population exposure (36 million) and geographical area coverage (173 × 10³ Km²) to high arsenic contaminated groundwater (50–3200 gL^–1) compared to the National drinking water standard (50 gL^–1) and WHO recommended provisional limit (10 gL^–1) is greatest in the Holocene alluvium and deltaic aquifers of the Bengal Delta Plain (Bangladesh and West Bengal, India). This large-scale 'natural' high arsenic groundwater poses a great threat to human health via drinking water. Mobilization, metabolism and mitigation issues of high arsenic groundwater are complex and need holistic approach for sustainable development of the resource. Mobilization depends on the redox geo-chemistry of arsenic that plays a vital role in the release and subsequent transport of arsenic in groundwater. Metabolism narrates the biological response vis-à-vis clinical manifestations of arsenic due to various chemical and biological factors. Mitigation includes alternative source for safe drinking water supply. Drinking water quality regulatory standards as well as guidelines are yet to cover risk assessments for such metal toxicity. Lowering of the ingested inorganic arsenic level and introduction of newer treatment options (implementation of laterite, the natural material) to ensure safe water supply (arsenic free and/or low arsenic within permissible limit) are the urgent need to safe guard the mass arsenic poisoning and internal arsenic related health problems.     

Investigating the synergistic role of heavy metals in Arsenic-induced skin lesions in West Bengal,India

BackgroundArsenic toxicity is one of the major health issues throughout the world. Approximately 108 countries that account for more than 230 million people worldwide are at high risk of arsenic poisoning mainly through drinking water and diet. Chronic exposure to arsenic causes several pathophysiological end-points including skin lesions, peripheral neuropathy, cancer, etc. In India, the population living in the lower Gangetic basin possesses a great risk of arsenicosis and other diseases. Scientists are trying to understand the gene-environmental interactions behind arsenic toxicity revealing the potential role of genetic variants of individuals. Few pieces of the literature showed that the population is not exposed to a mixture of metals. Hence, in this study, an attempt has been made to explore whether some other metals play a synergistic role in As-induced toxicity.MethodsFor this, an assessment of the level of heavy metals using ED-XRF in soil, vegetables from As-exposed areas along with quantification of the heavy metal concentration in human blood and hair of the As-exposed population were conducted.ResultsResults show the concentration of urinary arsenic is very high signifying the magnitude of the exposure. In addition to this, the levels of iron (Fe), copper (Cu), chromium (Cr) were found to be very high in soil and Fe, manganese (Mn), lead (Pb) in vegetables were exceeding the WHO/FAO recommended permissible limit. However, Fe and zinc (Zn) were predominantly high in whole blood and hair of the arsenic-exposed population when compared with the control population.ConclusionIt can be confirmed that the population from Murshidabad is exposed to As and other heavy metals through drinking water as well as food. Particularly for this population, Fe, Zn and rubidium (Rb) may play a synergistic role in arsenic-induced toxicity. However, further studies on the large population-based investigation are required to establish the chemistry of the metal toxicity.     

Trace element concentration and arsenic speciation in the well water of a Taiwan area with endemic Blackfoot disease

Blackfoot disease is a peripheral vascular disease resulting in gangrene of the lower extremities. Although extensive epidemiological study has implicated high arsenic content in artesian well water in the endemic area, there is more to learn about the etiology of the disease. In this study, effort is paid on multielement determination and arsenic speciation in order to find out whether the trace element concentration pattern in well water in the Blackfoot disease endemic area is different from those of two control areas. Experimental results indicate that the concentrations of Fe, P, Na, and Ba in well water in the Blackfoot disease endemic area are found to be significantly higher than those of the controls, but they are still below the drinking water standard. The total arsenic in well water in the endemic area (671±149 ppb) is much higher than that of one normal control area of Hsin-Chu (<0.7 ppb), but is a similar level as that of other control areas of I-Lan (653±71 ppb) where no Blackfoot disease has ever been found. It was also found that the insoluble arsenic in the endemic area (21.9 ppb) is much higher than that in two control areas (≤1.8 ppb), and the concentration ratio between As(III) and As(V) species in the endemic area (2.6) is much lower than that in one of the control areas, where the total arsenic is also high (14.7). The possible connection of Blackfoot disease with trace elements, arsenic species, and possibly other as yet undefined environmental factors in the artesian well water, is discussed.     

The effect of a milk diet on the retention of 74As labelled arsenic in mice

The effect of 3 diets with different proportion of milk proteins on retention of arsenic was studied in mice. Arsenic was administered via drinking water in concentration 50 mg As [III] per litre labelled with 74As in amount 2.96 MBq per 100 ml. After 2, 4, 8, 16 and 32 days of exposure the mice in groups of 6 each from all 3 experimental cohorts were decapitated and the content of 74As was determined in whole body, blood, liver, kidneys, spleen, lungs and heart by measuring of the activity in Gamma Scintillation Counter Tesla. From the intake of drinking water and amount of arsenic found in the experimental animals was calculated retention of arsenic in mice at different exposure intervals in all three diets. The values of arsenic found at the exposure intervals in examined materials of all three experimental cohorts were compared. The results obtained indicate that a milk diet has no adverse effect at exposure to arsenic in the sense of enhancing of its retention in mice at given experimental conditions. The found data seemed to suggest that the milk protein rich diet caused retardation of the increase of arsenic concentrations in blood, liver and kidneys that might lead at a lower exposure rate to a decrease in arsenic content in tissues of exposed animals.     

A subgroup of plant aquaporins facilitate the bi-directional diffusion of As(OH)<Subscript>3</Subscript> and Sb(OH)<Subscript>3</Subscript>across membranes

Background  

Arsenic is a toxic and highly abundant metalloid that endangers human health through drinking water and the food chain. The most common forms of arsenic in the environment are arsenate (As(V)) and arsenite (As(III)). As(V) is a non-functional phosphate analog that enters the food chain via plant phosphate transporters. Inside cells, As(V) becomes reduced to As(III) for subsequent extrusion or compartmentation. Although much is known about As(III) transport and handling in microbes and mammals, the transport systems for As(III) have not yet been characterized in plants.     

Genes involved in arsenic transformation and resistance associated with different levels of arsenic-contaminated soils

Background  

Arsenic is known as a toxic metalloid, which primarily exists in inorganic form [As(III) and As(V)] and can be transformed by microbial redox processes in the natural environment. As(III) is much more toxic and mobile than As(V), hence microbial arsenic redox transformation has a major impact on arsenic toxiCity and mobility which can greatly influence the human health. Our main purpose was to investigate the distribution and diversity of microbial arsenite-resistant species in three different arsenic-contaminated soils, and further study the As(III) resistance levels and related functional genes of these species.     

An integrated health risk assessment of indigenous children exposed to arsenic in Sonora,Mexico

Exposure to inorganic arsenic (InAs) through drinking water, even at low to moderate concentrations, is a global public health problem. The objectives of this study were to estimate the risk ratio (HQ), cancer risk (R), and DNA damage (comet assay) of children from three indigenous Yaqui populations located in southern Sonora, Mexico, who were exposed to InAs through drinking water. A cross-sectional study was employed, and analysis of InAs in water and urine was performed via HPLC/ICP-MS. InAs levels in drinking water from Pótam, Vícam, and Cócorit were 108.2, 36.0, and 6.2 μg/L^?1 respectively. Children from Pótam had arsenic concentrations in urine of 107.1 μg As L^?1 compared with 40.3 μg As L^?1 for the children of Cócorit. The HQ values for the children of Pótam, Vícam, and Cócorit were 16.64, 6.02, and 0.94, while the R values were 9.4E-04, 3.5E-04, and 5.7E-05, respectively. Children with the highest arsenic exposure had significantly increased DNA damage (OTM = 14.4 vs. 4.3) [p < 0.0005] which positively correlated with urinary arsenic levels (r = 0.56, p < 0.0001). In conclusion, children of Pótam and Vícam are at significant risk of developing chronic diseases and cancers associated with chronic exposure to this metalloid.     

Fish micronucleus assay to assess genotoxic potential of arsenic at its guideline exposure in aquatic environment

The exposure to arsenic, a potential genotoxic carcinogen in humans, via drinking water is a serious worldwide health hazard. The arsenic content of 10 μg L^?1 in drinking water, however, has been established as its guideline standard (maximum contaminant limit) that has been estimated to pose minimum risk to cancer. Since micronucleus induction in the erythrocytes of fish is a sensitive indicator of genotoxic agents in water, the piscine micronucleus assay was used in the present experiment to assess the genotoxic potential of arsenic at its various exposure levels including the guideline value for drinking water. The experiments were conducted in two different species of fishes, the pond murrel (Channa punctatus) and the goldfish (Carassius auratus). Significant increases in the frequency of micronucleated erythrocytes were documented in a dose-dependent manner in both Channa and Carassius. The fishes, however, exhibited variations in inter-specific sensitivity to micronucleus induction following arsenic exposure. The exposure level of arsenic at its guideline value for drinking water, therefore, exhibited marked genotoxicity in fishes.     

Arsenic in Drinking Water and Mortality for Cancer and Chronic Diseases in Central Italy, 1990-2010

Background

In several volcanic areas of Italy, arsenic levels exceed European regulatory limits (10 μg/L in drinking water). There is still uncertainty about health risks from arsenic at low-medium doses (<100 μg/L).

Objectives

A large population-based study using an administrative cohort of residents in the Viterbo province (Central Italy), chronically exposed to low-medium arsenic levels via drinking water, was investigated to evaluate the effects of a lifetime exposure to arsenic on mortality from cancers and chronic diseases.

Methods

The study population consisted of 165,609 residents of 17 municipalities, followed from 1990 until 2010. Average individual arsenic exposure at the first residence (As_I) was estimated through a space-time modeling approach using residential history and arsenic concentrations from water supply. A time-dependent Cumulative Arsenic dose Indicator (CAI) was calculated, accounting for daily water intake and exposure duration. Mortality Hazard Ratios (HR) were estimated by gender for different diseases using Cox proportional models, adjusting for individual and area-level confounders. A flexible non-parametric approach was used to investigate dose-response relationships.

Results

Mean As_I exposure was 19.3 μg/L, and average exposure duration was 39.5 years. Associations of As_I and CAI indicators with several diseases were found, with greatest risks found for lung cancer in both sexes (HR = 2.61 males; HR = 2.09 females), myocardial infarction, peripheral arterial disease and COPD in males (HR = 2.94; HR = 2.44; HR = 2.54 respectively) and diabetes in females (HR = 2.56). For lung cancer and cardiovascular diseases dose-response relationship is modelled by piecewise linear functions revealing effects even for doses lower than 10 μg/L, and no threshold dose value was identified as safe for health.

Conclusions

Results provide new evidence for risk assessment of low-medium concentrations of arsenic and contribute to the ongoing debate about the threshold-dose of effect, suggesting that even concentrations below 10 μg/L carry a mortality risk. Policy actions are urgently needed in areas exposed to arsenic like in the Viterbo province, to comply with current EU regulations.     

Sediment Core Sectioning and Extraction of Pore Waters under Anoxic Conditions

We demonstrate a method for sectioning sediment cores and extracting pore waters while maintaining oxygen-free conditions. A simple, inexpensive system is built and can be transported to a temporary work space close to field sampling site(s) to facilitate rapid analysis. Cores are extruded into a portable glove bag, where they are sectioned and each 1-3 cm thick section (depending on core diameter) is sealed into 50 ml centrifuge tubes. Pore waters are separated with centrifugation outside of the glove bag and then returned to the glove bag for separation from the sediment. These extracted pore water samples can be analyzed immediately. Immediate analyses of redox sensitive species, such as sulfide, iron speciation, and arsenic speciation indicate that oxidation of pore waters is minimal; some samples show approximately 100% of the reduced species, e.g. 100% Fe(II) with no detectable Fe(III). Both sediment and pore water samples can be preserved to maintain chemical species for further analysis upon return to the laboratory.     

Estimation of Multimedia Inorganic Arsenic Intake in the U.S. Population

Arsenic is widely distributed in the environment by natural and human means. The potential for adverse health effects from inorganic arsenic depends on the level and route of exposure. To estimate potential health risks of inorganic arsenic, the apportionment of exposure among sources of inorganic arsenic is critical. In this study, daily inorganic arsenic intake of U.S. adults from food, water, and soil ingestion and from airborne particle inhalation was estimated. To account for variations in exposure across the U.S., a Monte Carlo approach was taken using simulations for 100,000 individuals representing the age, gender, and county of residence of the U.S. population based on census data. Our analysis found that food is the greatest source of inorganic arsenic intake and that drinking water is the next highest contributor. Inhalation of airborne arsenic-containing particles and ingestion of arsenic-containing soils were negligible contributors. The exposure is best represented by the ranges of inorganic arsenic intake (at the 10^th and 90^th percentiles), which were 1.8 to 11.4 µg/day for males and 1.3 to 9.4 µg/day for females. Regional differences in inorganic arsenic exposure were due mostly to consumption of drinking water containing differing inorganic arsenic content rather than to food preferences.     

Arsenic exposure levels of petrochemical workers in three workplace settings in Rayong Province,Thailand

Background: Crude oil and natural gas are often contaminated with arsenic. As a carcinogen, arsenic contamination in the workplace is of concern, particularly when urinary arsenic levels are higher than the standard. The aim of this study was to identify exposure sources of arsenic among petrochemical workers. Methods: A total of 188 operators and 30 office workers participated in the study. Ninety-three workplace air samples, three main meals in five consecutive days, and drinking water were collected from each participant. Urine was collected at the end of the day after the last food sample was collected from each subject. Urine samples where arsenic concentration exceeded 100 mg/L were further analyzed to identify species. Results: The average arsenic concentrations in operators' and office workers' food and urine were 0.55 ± 1.00 and 0.49 ± 0.67 mg/kg; and 76.43 ± 107.36 and 149.92 ± 200.28 mg/L, respectively. The arsenic concentrations in air and water were well below their standards. The urinary arsenic correlated well with arsenic in the food but not in the air and water. Conclusion: Occupational exposure to arsenic among operators and office workers was lower than 1% TLV (Threshold limit value) and did not differ significantly. The major source of arsenic exposure Q2 was food.     

Acclimation of arsenic-resistant Fe(II)-oxidizing bacteria in aqueous environment

This study investigated the potential of the Fe(II)-oxidizing bacteria in removing arsenic in aqueous environment. The bacteria were isolated from the batch of tap water and rusty iron wires, and were acclimated to culture media amended with arsenic concentrations, gradually increasing from 100 μg L⁻¹ to 100 mg L⁻¹. Acclimated bacteria with enhanced arsenic tolerance were used to remove arsenic from the aqueous solution. These bacteria belonged to Pseudomonas species according to 16S rRNA gene sequences. Extracellular enzymes produced by these bacteria played important roles in microbial Fe(II) oxidization and Fe oxide precipitation. Moreover, these bacteria survived and propagated in high arsenic condition (100 mg L⁻¹ As). However, after As(III/V) acclimation, morphological characteristics of the bacteria showed some changes, e.g., shrinking of long bacillus. XRD (X-ray diffraction) patterns indicated that Fe oxide precipitations by Fe(II)-oxidizing bacteria in Fe-rich culture medium were poorly-crystallized ferrihydrites. Adsorption on the biogenic ferrihydrites greatly contributed to high arsenic removal efficiency of Fe(II)-oxidizing bacteria.     

无机砷在植物体内的吸收和代谢机制

砷污染已成为全球非常突出且急需解决的环境问题,严重威胁人类健康和环境安全.在自然环境和土壤系统中,砷的存在形态相当复杂,但植物砷毒害主要源于As（V）和As（Ⅲ）暴露.As（V）通过Pi的吸收通道被植物根系吸收,并在还原酶（AR）作用下被快速还原为As（Ⅲ）.As（Ⅲ）通过NIP蛋白通道进入植物体内,在砷甲基转移酶(ArsM)的作用下转化为甲基化砷或与谷胱甘肽（GSH）、植物螯合肽（PC）等多肽的巯基螯合封存在根部液泡或转运到地上部分,从而起到砷解毒的作用.同时,植物吸收的一部分砷也可外排到外部介质.本文以农作物尤其是水稻为主线,详述了As（V）和As（Ⅲ）吸收、外排及As（V）还原、As（Ⅲ）甲基化、螯合作用的最新研究进展,并提出了今后的研究重点.     

Carcinogenic and Non-carcinogenic Risk Assessment of Heavy Metals in Groundwater Wells in Neyshabur Plain,Iran

The present work reports the As, Cr, Cu, Pb, Zn, and Fe concentrations of drinking water samples in Neyshabur Plain, Iran. This study aimed also to ascertain the potential consumers’ health risk of heavy metal intake. Heavy metal concentrations were analyzed by inductively coupled plasma optical emission spectrometry. The highest and lowest average values in the analyzed water samples were observed for Fe (9.78 ± 5.61 μg/L) and As (1.30 ± 2.99 μg/L), respectively. These values were well below the limits recommended by the World Health Organization and the Iranian national standard. Heavy metal pollution index and heavy metal evaluation index were used to evaluate drinking water quality. The risk index was calculated by chronic daily intake and hazard quotient according to the United States Environmental Protection Agency approach. Heavy metal pollution index in all the samples was less than 100, indicating that it is a low-level heavy metal. The total risk of all heavy metals in the urban environment varied from 40.164 × 10⁻⁷ to 174.8 × 10⁻⁷. In this research, the maximum average of risk belonged to lead and copper with the respective values of 60.10 × 10⁻⁷and 33.99 × 10⁻⁷ from the selected wells. However, considering the toxic effect of some elements, including Pb and As, in the chronic exposure of consumers, we suggest a continuous evaluation and monitoring of drinking water resources.

     

Biogeochemical transformations of arsenic in circumneutral freshwater sediments

Arsenic is a wide-spread contaminant of soils and sediments, andmany watersheds worldwide regularly experience severe arsenic loading. While the toxicityof arsenic to plants and animals is well recognized, the geochemical and biological transformationsthat alter its bioavailability in the environment are multifaceted and remain poorly understood.This communication provides a brief overview of our current understanding of the biogeochemistryof arsenic in circumneutral freshwater sediments, placing special emphasis on microbialtransformations. Arsenic can reside in a number of oxidation states and complex ions. The commoninorganic aqueous species at circumneutral pH are the negatively charged arsenates(H₂As^VO₄ ^- and Has^VO₄ ^2-) and zero-charged arsenite(H₃As^IIIO₃ ⁰). Arsenic undergoes diagenesis in response to both physicaland biogeochemical processes. It accumulates in oxic sediments by adsorption on and/orco-precipitation with hydrous iron and manganese oxides. Burial of such sediments in anoxic/suboxicenvironments favors their reduction, releasing Fe(II), Mn(II) and associatedadsorbed/coprecipitated As. Upward advection can translocate these cations and As into theoverlying oxic zone where they may reprecipitate. Alternatively, As may be repartitioned tothe sulfidic phase, forming precipitates such as arsenopyrite and orpiment. Soluble and adsorbedAs species undergo biotic transformations. As(V) can serve as the terminal electronacceptor in the biological oxidation of organic matter, and the limited number of microbes capableof this transformations are diverse in their phylogeny and physiology. Fe(III)-respiring bacteriacan mobilize both As(V) and As(III) bound to ferric oxides by the reductive dissolution ofiron-arsenate minerals. SO₄ ^2--reducing bacteria canpromote deposition of As(III) as sulfide minerals via their production of sulfide. A limited number of As(III)-oxidizing bacteriahave been identified, some of which couple this reaction to growth. Lastly, prokaryotic andeukaryotic microbes can alter arsenic toxicity either by coupling cellular export to its reductionor by converting inorganic As to organo-arsenical compounds. The degree to which each ofthese metabolic transformations influences As mobilization or sequestration in differentsedimentary matrices remains to be established.     

The role of birds in dissemination of human waterborne enteropathogens

Cryptosporidiosis, giardiasis and microsporidiosis are serious human diseases of waterborne origin; their etiologic agents and a substantial fecal coliform load can enter surface, drinking and recreational water resources from aquatic birds. The aim of this article is to present interactions between waterfowl and these waters that imply a negative public health impact, reinforcing the need for either better water-quality indicators or for water monitoring specifically for Cryptosporidium, Giardia and microsporidia. Where justifiable, the presence of waterfowl should be supported; however, management of drinking and recreational water resources needs to be improved by incorporating effective protection measures for pathogens linked to these birds.     

A Dietary Risk Assessment for Indigenous Consumption of Natural Salt Deposits in the Darhad Valley,Northern Mongolia

The nomadic herding population of the Darhad Valley, in northern Mongolia, collects and utilizes a salt precipitate, called hujir, which develops at the saline system, Tohi. This culturally important indigenous dietary supplement is consumed daily as an ingredient in a salty milk-tea and because of its essential micro- and macronutrients it is a beneficial and necessary part of their daily diet. Despite its benefits, there are increasing health concerns among the Darhad people as a result of consuming hujir. Therefore, we conducted a dietary risk assessment. Consumption rates were obtained from interviews with nomadic herders of the valley and a chronic exposure assessment was completed using chemical analyses on hujir samples. A combination of chronic toxicity threshold values, dietary reference intake recommendations, and drinking water guidelines were used to estimate dietary risks related to hujir consumption. Exposures to arsenic, fluoride, and nitrate were as high as 33, 1.2, and 1.3 times the chronic oral reference dose, respectively. Exposures to antimony, arsenic, and lead were 1.7, 19, and 14 times the drinking water guidelines, respectively. Given these results, additional studies are needed to better understand possible health effects associated with hujir consumption in the Darhad population, especially for arsenic.     

Arsenic Compromises Conducting Airway Epithelial Barrier Properties in Primary Mouse and Immortalized Human Cell Cultures

Arsenic is a lung toxicant that can lead to respiratory illness through inhalation and ingestion, although the most common exposure is through contaminated drinking water. Lung effects reported from arsenic exposure include lung cancer and obstructive lung disease, as well as reductions in lung function and immune response. As part of their role in innate immune function, airway epithelial cells provide a barrier that protects underlying tissue from inhaled particulates, pathogens, and toxicants frequently found in inspired air. We evaluated the effects of a five-day exposure to environmentally relevant levels of arsenic {<4μM [~300 μg/L (ppb)] as NaAsO₂} on airway epithelial barrier function and structure. In a primary mouse tracheal epithelial (MTE) cell model we found that both micromolar (3.9 μM) and submicromolar (0.8 μM) arsenic concentrations reduced transepithelial resistance, a measure of barrier function. Immunofluorescent staining of arsenic-treated MTE cells showed altered patterns of localization of the transmembrane tight junction proteins claudin (Cl) Cl-1, Cl-4, Cl-7 and occludin at cell-cell contacts when compared with untreated controls. To better quantify arsenic-induced changes in tight junction transmembrane proteins we conducted arsenic exposure experiments with an immortalized human bronchial epithelial cell line (16HBE14o-). We found that arsenic exposure significantly increased the protein expression of Cl-4 and occludin as well as the mRNA levels of Cl-4 and Cl-7 in these cells. Additionally, arsenic exposure resulted in altered phosphorylation of occludin. In summary, exposure to environmentally relevant levels of arsenic can alter both the function and structure of airway epithelial barrier constituents. These changes likely contribute to the observed arsenic-induced loss in basic innate immune defense and increased infection in the airway.