arsenic geochemistry of groundwater in southeast …2015/09/07 · offprint offprint review arsenic...

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REVIEW

Arsenic geochemistry of groundwater in Southeast Asia

Kyoung-Woong Kim (✉)1, Penradee Chanpiwat1, Hoang Thi Hanh1, Kongkea Phan1, Suthipong Sthiannopkao2

1School of Environmental Science & Engineering and International Environmental Analysis & Education Center (IEAEC), GwangjuInstitute of Science and Technology (GIST), Gwangju 500-712, South Korea; 2 Department of Environmental and Occupational Health,Medical College, National Cheng Kung University (NCKU), Tai Nan City 70403, Taiwan, China

© Higher Education Press and Springer-Verlag Berlin Heidelberg 2011

Abstract The occurrence of high concentrations of arsenic in the groundwater of the Southeast Asia region hasreceived much attention in the past decade. This study presents an overview of the arsenic contamination problemsin Vietnam, Cambodia, Lao People’s Democratic Republic and Thailand. Most groundwater used as a source ofdrinking water in rural areas has been found to be contaminated with arsenic exceeding the WHO drinking waterguideline of 10 μg$L–1. With the exception of Thailand, groundwater was found to be contaminated with naturallyoccurring arsenic in the region. Interestingly, high arsenic concentrations ( > 10 μg$L–1) were generally found inthe floodplain areas located along theMekong River. The source of elevated arsenic concentrations in groundwateris thought to be the release of arsenic from river sediments under highly reducing conditions. In Thailand, arsenichas never been found naturally in groundwater, but originates from tin mining activities. More than 10millionresidents in Southeast Asia are estimated to be at risk from consuming arsenic-contaminated groundwater. InSoutheast Asia, groundwater has been found to be a significant source of daily inorganic arsenic intake in humans.A positive correlation between groundwater arsenic concentration and arsenic concentration in human hair hasbeen observed in Cambodia and Vietnam. A substantial knowledge gap exists between the epidemiology ofarsenicosis and its impact on human health. More collaborative studies particularly on the scope of public healthand its epidemiology are needed to conduct to fulfill the knowledge gaps of As as well as to enhance the operationalresponses to As issue in Southeast Asian countries.

Keywords arsenic; groundwater; drinking water; arsenicosis; Mekong River; Southeast Asia

Introduction

Sustainable access to safe drinking water is one of the keyMillennium Development Goals (MDGs) proposed by theUnited Nations. In particular, accelerated and targeted effortsare needed to bring drinking water to all rural households.Groundwater resources, which constitute approximately 97percent of global freshwater [1], are an important source ofhousehold water consumption in many parts of the world,especially in rural areas. Groundwater is usually preferred as asource of drinking water due to its naturally stable state ofmicrobial quality [1,2]. However, in some cases, naturallyoccurring chemical constituents in groundwater have beenreported to pose significant risks to human health. The naturaloccurrence of arsenic in groundwater constitutes a setback in

the provision of safe drinking water to millions of people inAsia [3]. Arsenic (As) is a toxic element classified as a humancarcinogen that contributes to cancers of both skin andinternal organs (liver, bladder, kidney and intestinal) [4].Arsenic was detected in groundwater for the first time in theearly 1990s in Bangladesh and West Bengal of India. It hasnow also been detected in several parts of China, Nepal andPakistan and most Southeast Asian countries includingCambodia, Vietnam, Myanmar, Lao People’s DemocraticRepublic (Lao PDR), Thailand and Indonesia [3,5]. Accor-ding to an estimate by the World Bank, approximately 60million people in South and East Asia are at risk from highlevels of naturally occurring As in groundwater, with manypeople still drinking As-contaminated water on a daily basis[3]. Moreover, at least 700 000 people have been affected byarsenicosis, especially in rural areas. Even though a numberof review articles have been published on As-contaminatedgroundwater around the globe, there is still a significantdearth of knowledge relating to As contamination of

Received June 21, 2011; accepted September 8, 2011

Correspondence: [email protected]

Front. Med. 2011, 5(4): 420–433DOI 10.1007/s11684-011-0158-2

THE AUTHORS WARRANT THAT THEY WILL NOT POST THE E-OFFPRINT OF THE PAPER ON PUBLIC WEBSITES.

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groundwater in Southeast Asia (SEA). Therefore, the focus ofthis review is the current knowledge on As contamination ofgroundwater in the SEA region, especially the public healthaspects of groundwater protection as a component of anintegrated approach to drinking water safety management.Additionally, the most recent case studies on As contamina-tion of groundwater conducted by the International Environ-mental Analysis and Education Center (formerly known asthe International Environmental Research Center) overseveral areas of Vietnam, Cambodia, Lao PDR and Thailandare discussed.

Background of arsenic contamination ingroundwater and its health effects onhumans

Worldwide distribution of arsenic groundwatercontamination

The concentration of As in groundwater is typically below theWorld Health Organization (WHO) guideline for As indrinking water of 10 µg$L–1 [3,7]. However, a number oflarge aquifers with As naturally occurring at concentrationsgreater than 10 µg$L–1 or even significantly higher have beenidentified in several parts of the world [3,6]. Fig. 1 shows thedistribution of globally documented cases of naturally-occurring As groundwater contamination, which is particu-larly high in parts of Argentina, Bangladesh, Chile, China,

Hungary, India, Lao PDR, Mexico, Myanmar, Nepal,Pakistan, Romania and Vietnam as well as many south-western parts of the USA [3,5,6]. Some of the betterdocumented cases of naturally-occurring As groundwatercontamination have been reported by Smedley and Kinni-burgh [6] as well as Rahman et al. [5]. In contrast to theproblems associated with As from mining and geothermalactivities, which are generally localized, the occurrences ofAs in major aquifers usually occupy large areas [6]. Thus,such naturally-occuring As groundwater contamination maybe potentially much more serious than local As contaminationfrom mining or geothermal activities, since major aquiferstypically provide drinking water to large populations.Generally, As mobilization in groundwater can only existunder specific circumstances, which are mainly related to thegeochemical environment as well as the past and presenthydrogeological conditions in the area [3,6]. Moreover, a highconcentration of As in groundwater is not necessarily relatedto areas with high As concentration in source rocks [6].

Mechanisms of arsenic mobilization

As shows high sensitivity to mobilization at the pH valuestypically found in groundwater (pH 6.5 to 8.5), under bothreducing and oxidizing groundwater conditions [1] and canalso occur in both humid and arid climates [6]. Themobilization of As can also be favored by biotic and abioticprocesses [8].

Fig. 1 Distribution of globally documented naturally-occurring As groundwater contamination (Modified after References 2, 3, 5, 6)

Kyoung-Woong Kim et al. 421


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Reducing environmentsThe mobilization of As under reducing conditions is usuallyfound in recently-deposited fine-grained deltaic and alluvialsediments [3]. The aquifer sediments derived from riversystems are generally capped by a layer of clay or silt, whicheffectively restricts the entry of air to the aquifers [6]. In thepresence of degradable organic carbon (solid organic matter)deposited with sediments, highly reducing (anaerobic)conditions develop [3,6,8]. These highly reducing conditionsfavor desorption of As from the mineral sources in aquifersediments. The most important mineral sources in aquifers aremetal oxides (especially Fe oxides) and sulfide minerals(especially pyrite) [3]. The reduction of solid-phase As toAs(III), desorption of As from Fe oxides (As-bearing Fe(III)oxides), reductive dissolution of the oxides themselves andexpected changes in Fe-oxide structures as well as theirsurface properties follow the onset of the reducing conditions[3,6,8,9]. In such cases, anaerobic metal-reducing bacteriacan play a key role in the mobilization of As in sediments[6,10]. Therefore, the nature (type and availability) of organicmatter plays a key role in controlling the activity of themicrobial community and the subsequent rate of anygeochemical processes [6,10]. Moreover, it has been foundthat the capacity for the release of As is severely limited bythe availability of electron donors in the sediments [8].Several investigations have revealed that increased Ascontent in groundwater is well-correlated with several factorssuch as areal and vertical distributions of peat deposits, thedegradation of which is the major redox controller, the redoxdriver in the groundwater system, groundwater movement[9], pH, HCO3

–, Fe, Mn, and Al oxides and dissolved organiccarbon (DOC) concentrations of sediments [11] as well asgrain size [11,12]. As leaches out very strongly fromsediments rich in NaHCO3 and those with high pH [11].This type of As mobilization has generally been reported inQuaternary aquifers in South and East Asia [3,6].

Oxidizing environmentsAs can also be released under oxidizing (aerobic) conditions,where the groundwater pH varies from acidic to basicconditions [3,6]. This tends to occur in arid and semi-arid

areas as a result of extensive mineral reactions andevaporation. Groundwater with high As concentration isfound in some arid inland basins in the western USA, Mexicoand Argentina [3,6]. Since the environment is arid in thoseareas, evaporation is the reason for the positive correlationbetween As concentration and high B, F, Mo, F, V, HCO3

–

levels, and salinity. Under arid conditions, silicate andcarbonate weathering reactions are pronounced and conse-quently, the groundwater often has high pH. Under oxidizingand high pH conditions, metal oxides in sediments (particu-larly Fe and Mn oxides and hydroxides) are expected to be themain source of As desorption under high pH conditions [6].

Metabolism of arsenic

Extensive biotransformation of As occurs after the ingestedinorganic As (both As(III) and As(V)) enters the cell [13].Metabolism of inorganic As occurs through a sequence ofreactions, as illustrated in Fig. 2 [13–16]. In brief, inorganicAs is enzymatically converted to methylated products, i.e.monomethyl arsenic (MMAs) and dimethyl arsenic (DMAs).Finally, biotransformation of inorganic As results in thepresence of inorganic, mono- and dimethylated arsenicals inurine [13]. The human body can absorb, process and excreteabout 40% to 70% of the total ingested inorganic As dosewithin 48 h [16].

As shown in Fig. 2, As usually occurs in two oxidationstates (III and V). Once absorbed, As(V) is reduced to As(III),mainly in the blood and liver [16]. The As(III) is then takenup by cells and oxidatively methylated from As(III) tomethylated As(V)-containing products. Thereafter, As in themethylated products is reduced from As(V) to As(III) beforethe next round of methylation. Thus, the coupling of oxidativemethylation and arsenate reduction in As metabolism has astriking effect on the distribution and clearance of thismetalloid [13]. The reduction of As(V) can be accomplishedby the concurrent chemical oxidation of a thiol-containingmolecule (such as glutathione) [14,15]. In addition, severalenzymes, including purine nucleoside phosphorylase,function as As(V) reductases [15]. S-adenosylmethionine-dependent methyltransferase (methyl donor) catalyzes the

Fig. 2 The metabolism of inorganic As (Modified after References 13–16).

422 Arsenic geochemistry of groundwater in Southeast Asia


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formation of MMAs and DMAs from As. Generally,arsenicals that contain As(III) are the preferred substratesfor enzymatically catalyzed methylation. Therefore,MMA(III) [15–17] and DMA(III) [18] are the intermediatesin the metabolic pathway and the obligatory substrates for thesecond and third methylation reactions that yield DMA andtrimethylarsine oxide (TMAO), respectively. TMAO is foundat very low concentrations in human urine. Rats are the onlyspecies that excrete significant amounts of TMAO [16].

(Bio)methylation of As has been generally considered aprimary detoxification mechanism [14,15,17]. However,trivalent methylated arsenicals (such as, MMA(III) andDMA(III)) have been detected in the urine of subjectschronically exposed to drinking water containing high levelsof inorganic As [14–16]. These trivalent arsenical intermedi-ates are highly reactive and more carcinogenic thanpentavalent arsenical intermediates [14]. Therefore, methyla-tion of As can also be considered an activation process.

Toxicity of As to humans

As has no known physiologic and biochemical function inany living organism, including humans [17]. The toxicity ofAs to humans largely depends on the chemical form andphysical state of the compound involved [7]. Even though Ascan occur in the environment in several oxidation states,inorganic oxyanion forms such as arsenite (As(III)) andarsenate (As(V)) are mostly found in natural waters [1]. As(III) is generally regarded as being more acutely toxic than As(V). Jomova et al. [14] have reported that the majority of Asthat enters the body is As(III) and it does so via a simplediffusion mechanism, while As(V) crosses cell membranesvia an energy-dependent transport system. Similar to othertoxic metals, the most potentially toxic forms of As areconverted to less toxic forms in the human body. Finally, As isthen excreted from the cell since it lacks biomagnificationproperties [17]. Dose [14] and host factors such as, individualsusceptibility to As [14], sex [15], age [14,15], nutritionalstatus [7,15,19], health status and lifestyle [13] of affectedindividuals are the major factors affecting the extent ofdamage caused by As poisoning.

Trivalent arsenic toxicityAs reported by Jomova et al. [14] and Hughes [18], theinhibition of numerous cellular enzymes caused by trivalentinorganic As (As(III)), such as pyruvate dehydrogenase,through thiol and vicinal sulfydryl group binding leads to theprohibition of the important biochemical processes and couldthen lead to toxicity; for example, the reduction in acetylcoenzyme A (CoA) and cellular ATP production as well as theactivity of the citric acid cycle. Moreover, trivalent inorganicAs can also inhibit the production of glutathione, whichprotects cells against oxidative damage [14].

Methylated trivalent arsenicals, such as MMA(III), are

potent inhibitors of glutathione (GSH) reductase andthioredoxin reductase. The inhibition of these enzymesresults in an altered cellular redox status and eventuallyleads to cytotoxicity. Both inorganic and organic trivalentarsenicals have also shown indirect genotoxicities in vitro[16]. Khan and Ho [20] reported that MMA(III) is the mostpotent inhibitor of DNA repair. The activities of methylatedtrivalent arsenicals are greater than those of trivalentinorganic As (As(III)), MMA(V), and DMA(V) [18].

Pentavalent arsenic toxicityThe toxicity of pentavalent inorganic As (As(V)) is due to itsconversion to trivalent As, from which the toxic effectsproceed as summarized earlier. More specifically, pentavalentinorganic As, which has a similar structure to that ofphosphate, can compete with inorganic phosphate and replacethe phosphate in the glycolytic and cellular respirationpathways [14,18].

It has been reported that long-term animal bioassays ofMMA(V) with doses higher than the maximum thresholdlevel of 400 ppm in the feed did not induce any tumors [16].However, DMA(V) was found to be a bladder carcinogenonly in rats and only when administered in the diet or drinkingwater at high doses [16]. The red blood cells of differentanimal species have different rates of uptake, reduction andmethylation of DMA(V). In most animal species, DMA(V)does not usually enter the cells and is excreted unchanged. Ina human study, approximately 70% of a single oral dose ofDMA(V) was found to be excreted in urine as unchangedDMA(V) within 4 days [16].

Arsenic and human disease: an overview

Non-carcinogenic health effectsSymptoms of acute As toxicity include severe projectilevomiting and watery diarrhea, muscular cramp, facial edemaas well as cardiac abnormalities [20].

Chronic effects of As exposure in humans have been well-reviewed and summarized by several research groups[14,18,21–25]. Human health effects caused by As havebeen found to be dependent on the magnitude of As exposure[14,24], source of As exposure [24], host factors [7,13–15,17–19] as well as the exposure duration [24] and exposureroute [20]. Many different body systems are affected bychronic exposure to As. However, the most affected organsare those involved in As absorption, accumulation andexcretion [22], including the gastrointestinal, cardiovascular,urinary, hepatic, dermal systems [22]. Some of these systemsand the signs of chronic effects are summarized in Table 1[14,18–20,22–24]. Of the symptoms caused by chroniceffects, dermal lesions are the most abundant, and have alsobeen known to occur within a period of about five years [23].However, the shortest exposure period that has been reportedfor the manifestation of As toxicity is about 8 months [20].



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The skin is known to localize and store As because of its highkeratin content, which contains several sulfydryl groups towhich As(III) may bind [23]. Moreover, verbal IQ and long-term memory can also be affected due to chronic As toxicity[24]. A strong relationship between chronic ingestion of Asand deleterious human health effects has been observed [24].Chronic effects of As exposure have been reported at variousAs concentrations ranging from < 10 µg$L–1 to severalthousand µg$L–1. Therefore, the US EPA has set the oralreference dose (RfD) of As at 3.0 � 10–4mg$kg–1 (body-weight)$day–1 as the threshold value for non-carcinogeniceffects of As [22]. Theoretically, the RfD is an estimate of adaily oral exposure to the human population, including thesensitive population that is likely to be without an appreciablerisk of deleterious effects during a lifetime. Thus, the non-carcinogenic effects of As are expected to be observed inindividuals who ingest more than the RfD of As on a dailybasis.

Carcinogenic health effectsInorganic As is classified by the International Agency forResearch on Cancer [4,26] and the Integrated Risk Informa-tion System of the US EPA [22] as a known humancarcinogen. This classification is based on several epidemio-logical studies, which have shown a positive associationbetween exposure to As and development of cancer in manycountries [18,24]. There is epidemiological evidence for lung,bladder, liver, kidney, colon, prostate and skin cancers beingcaused by exposure to As [14,20–23,25,27]. A strongassociation between As exposure and risk of several internalcancers can be observed when As levels in drinking water arevery high ( > 150 µg$L–1) [28]. Exposure to arsenic even at alevel of 50 µg$L–1 could easily result in a combined cancerrisk in the order of 1 in 100 [29]. The lifetime risk of dyingfrom cancer from daily ingestion of 1 L of water containing50 µg$L–1 of As could be as high as 13 per 1000 peopleexposed [25]. Khan et al. [20] found that arsenical cancerssystematically appeared first on the skin followed by internalorgans [20]. It is believed that the mechanisms by which these

cancers originate may involve the promotion of oxidativestress by As compounds, in which the antioxidant capacity ofthe living organism is overwhelmed by reactive oxygenspecies (ROS), resulting in molecular damage to proteins,lipids and, most significantly, DNA [14].

Arsenic occurrence in groundwater inSoutheast Asia

VietnamSince the mid-1990s, the groundwater resources in the largealluvial deltas of the Red River in northern Vietnam, as wellas the Mekong River in southern Vietnam, have beenexploited for domestic use by private tube-wells [30]. Highlevels of As have been detected in the groundwater of the RedRiver delta and was first reported in 2001 (Table 2) [31], butthe contamination of groundwater with As in the MekongRiver delta was first reported in 2005 (Table 2) [32]. TheMekong River delta in Vietnam covers an area of 39 713 km2.Since 2007, comprehensive studies of As groundwatercontamination have been conducted in the Mekong Riverdelta region. A broad groundwater survey was first conductedfrom May to November 2007 in 4 provinces located in theMekong River delta, including An Giang, Dong Thap, KienGiang and Long An. Core samples were subsequentlycollected from An Giang and Dong Thap Provinces in May2008. Rice grain, drinking water and human hair sampleswere finally collected from two districts (An Phu and PhuTan) in An Giang Province in November 2009.

The results of groundwater analyses revealed that mostelemental concentrations other than those of As, Fe and Mn ingroundwater samples collected from 4 provinces in theMekong River delta during the rainy season were well belowthe WHO drinking water guidelines. Approximately half ofthe groundwater samples collected from An Giang and DongThap contained As concentrations higher than the WHO andnational guideline level of 10 μg$L–1 (Fig. 3). However, nosample from Kien Giang or Long An was found to exceed the

Table 1 Non-carcinogenic human health effects observed after chronic As exposure

Organ system Effects

Gastrointestinal Portal hypertension, gastrointestinal hemorrhage

Cardiovascular Peripheral vascular disorder- black foot disease, high blood pressure

Urinary Proximal tubule degeneration, papillary and cortical necrosis

Hepatic Hepatomegaly, portal fibrosis, cirrhosis, altered heme metabolism

Dermal Skin lesions (hyperpigmentation, hyperkeratosis, desquamation, loss of hair)

Nervous Peripheral neuropathy, encephalopathy

Hematological Bone marrow depression (anemia, leucopenia, thrombocytopenia)

Endocrine Diabetes, hormone regulation and hormone mediated gene transcription suppression

Respiratory and pulmonary Cough, bronchitis, chest sound, shortness of breath

Reproduction Fetal loss, necrosis, apoptosis, conception in the uterus, death of newborn, premature delivery, decreased birth weight of infants

From References 14, 18–20, 22–24.



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As guideline. The As concentrations in An Giang ground-water were found to be positively correlated with the totalorganic carbon (TOC) and Ba concentrations, but negativelycorrelated with the well depth, pH, and Mn, Ca, Mg, Na, Co,Ni and Si concentrations. However, positive correlations werefound between the As, TOC and Ba concentrations in thegroundwater of Dong Thap. Negative correlations were alsofound between the As level and distance from the well to theMekong River, pH and Si concentration in the groundwatercollected from the Dong Thap Province. The spatial influence

on the groundwater As concentration manifested in the co-variation of the As concentration with depth and distance ofthe well from the Mekong River. In the An Giang Province,sampling sites within 2 km from the Mekong River had meanAs concentrations nearly 10-fold higher than those atdistances beyond 2 km (P < 0.01). The observed variationin As concentration in groundwater with distance from theMekong River suggested that the Mekong River plays animportant role in contamination of the local aquifer.Depending on the intensity of interactions between riverwater and groundwater, more or less contamination may beexpected [33]. Shallow wells usually exhibited higher Asconcentrations, whereas deep wells appeared to be unaffected[33]. No spatial influence on the As concentration was foundfor groundwater in Kien Giang and Long An Provinces [33].

The highest concentrations of As in core samples collectedfrom An Giang and Dong Thap provinces were found atdepths of 46 and from 34.5 to 34.9 m, respectively. Relativelyhigh As concentrations were detected in the brown and black-to-brown clay layers with approximate pH values of 7.5,while the concentrations of As in yellow-to-brown clammyclay, and brown-to-gray and fine-to-medium grain sand werelower than 5 mg$kg–1. Moreover, the concentrations of Asand Fe in core samples were found to vary considerablydepending on the depth. In general, the levels of As and Fe incore samples were relatively high in subsurface zones, butgradually decreased with depth. A strong correlation wasfound between the total As and Fe concentrations in the coresamples (Pearson’s r = 0.4; P < 0.05). As in sediments wasmainly in the poorly crystalline iron oxide phase (37%–85%),which may explain the strong correlation observed betweenthe total As and Fe concentrations. Only very few coresamples contained As associated with the surface adsorbedphase or the manganese oxide phases. The organic matter andexchangeable phases contained small amounts of As. Thereason for the positive correlation between the As and Feconcentrations in core samples but not in the groundwatersamples may be that after being dissolved and released fromaquifer sediments to groundwater, As and Fe may be affectedby other processes, causing their concentrations to varyindependent of each other [33]. The total As concentration incore samples was found to be strongly correlated with the Aslevel in the poorly crystalline Fe oxide phase (Pearson’s r =

Table 2 Geodemographic data of naturally occurring As in groundwater in Southeast Asia

Country Population at risk Level of As (µg$L–1) Year of first discovery National standard of As indrinking water (µg$L–1)

References

Vietnam 10

- Red River delta 10 000 000 1–3 100 2001 3, 5, 31

- Mekong River delta 1 000 000 ND–1 351 2005 32, 33

Cambodia 100 000 Up to 3 500 1999 50 41

Lao PDR Unknown ND–278 2001 50 2, 3, 5

Thailand 15 000 1.3–5 114 1988 50 65, 66

Fig. 3 A map of arsenic groundwater contamination in South-east Asia.



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0.95; P < 0.01). The high proportion of As found in Feoxide-related phases in core samples provided convincingevidence that such phases were the principal source of Asreleased to groundwater. However, the reductive dissolutionsof the Fe and Mn phases were not necessarily dominantsources of As release to groundwater. Local hydro-biogeo-chemical conditions in the aquifer (including the presence ofsedimentary organic matter or other electron donors,indigenous microorganisms, groundwater oxidation-reduc-tion potential (ORP), pH, and the combined effects ofcoexisting ions in groundwater) may control the leaching ofAs from sediments to groundwater [33].

While contamination of groundwater with As in theMekong River delta of Vietnam has been well-addressed,information about As and other elements in rice is not readilyavailable.

The concentration of As in the polished rice grain samples(n = 39) collected from the target areas (An Phu and PhuTan districts, An Giang Province) ranged from 132 to471 µg$kg–1, with a mean value of 224 µg$kg–1 [35]. Thisresult was in good agreement with the range of 96 to465 µg$kg–1 (mean value of 215 µg$kg–1) of polished rice (n= 30) from the northern region of Vietnam reported by Tranet al. [34].

The amount of daily inorganic As intake through drinkingwater and rice consumption for all households in the MekongRiver delta region was estimated based on the assumption that100% and 80% of the total As was inorganic As contained ingroundwater and rice grains, respectively. According to thisassumption, groundwater contributed the most to the daily Asintake, while rice may only contribute negligible amounts.However, rice can sometimes account for as much as 99% ofthe daily inorganic As intake in households that have waterfilter columns and access to safe water [35]. Unfortunately,water filtration systems were not common in the study area.Vietnamese residents usually cook rice with only thenecessary amount of water that gets absorbed during thecooking process, so that no excess water is discarded. Thus,all of the As in the rice grains is preserved and readily entersthe human body [36,37]. However, since the local peopletypically use the same water source for drinking and cooking,the actual As intake from rice may be higher [38]. Dermalabsorption of As may be a significant route of exposure,particularly in those residents using As-contaminated ground-water for daily life activities, such as washing, cleaning andbathing.

It has been established that As levels in hair typically rangefrom 0.02 to 0.2 µg$g–1 for individuals without As exposureand from 3 to 10 µg$g–1 in persons exposed to groundwatercontaining increased levels of As [39]. In the study of Asconcentration in human hair in An Giang Province, about67% (n = 44), 42% (n = 28) and 15% (n = 10) of hair samplesfrom the target area contained As levels exceeding 1, 3 and10 µg$g–1, respectively. The highest As concentration(37.7 µg$g–1) was observed in a hair sample obtained from an

18-year-old female from the Phu Vinh, Cho Vam village inthe Phu Tan district of An Giang Province [35]. Interestingly,the hair sample of the subject’s 42-year-old mother alsocontained a high level of As (15.8 µg$g–1) and the hair sampleof the subject’s 41-year-old father contained the highest Aslevel (8.9 µg$g–1) among the 22 male participants. Thisfamily had been consuming groundwater containing336 µg$L–1 of As until 2008, when they transitioned to As-free tap water. The concentration of As in the rice consumedby the subjects was determined to be 225 µg$kg–1. Asconcentration in human hair from individuals living in thestudy location was significantly higher than that of indivi-duals in the control area (P = 0.011). A paired sample t-testdid not reveal any significant differences between the meanAs levels in female and male hair samples (P = 0.103),although female hair samples displayed a wider range andhigher average concentration of As than the male hairsamples. Positive correlations between daily inorganic Asintake and total As concentrations in female and male hairsamples were significant. Excessive levels of As wereobserved in the hair of residents even one year after theyhad last consumed As-contaminated groundwater. Thearsenic concentration in human hair may reduce as daily Asintake decreases. However, the minimum time required toobserve any change in the As levels of hair has not yet beendefined. Monitoring As levels in hair after a period ofexposure can improve our understanding of As detoxification.This field survey did not uncover any case of As poisoning oreven a symptom of skin lesion at an early stage. Therefore,the possibility of arsenicosis symptoms in the local commu-nity is still an issue of concern.

CambodiaIn Cambodia, unsafe concentrations of As in shallowgroundwater were first documented by the Japanese Interna-tional Cooperation Agency (JICA) in its initial unpublisheddraft report, named “The study on groundwater developmentin Southern Cambodia,” submitted to the Cambodia Ministryof Rural Development in 1999 [40]. Concurrently, theMinistry of Rural Development also conducted a nationaldrinking water quality assessment in 13 provinces ofCambodia with support from WHO. The assessmentindicated that 3 wells in Kandal Province had elevatedconcentrations of As [41]. In response to this discovery, Asfield test kits were used to test tube wells in a number ofprovinces to verify the magnitude of As hazards at ground-water access points. Additionally, the Royal Government ofCambodia established the Arsenic Inter-Ministerial Subcom-mittee in 2001 to formulate a government policy. An interimCambodia standard for As concentration in drinking water of50 µg $L-1 was adopted in 2003 as its first action (Table 2)[41]. Subsequently, numerous studies have documented Asbiogeochemistry and its health impacts in Cambodia. Severalinvestigations [30,42–47] have described the distribution of



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As concentrations in Cambodian shallow groundwater. Thechemical, biological and physical processes that controlheterogeneous As distribution in groundwater have also beenwidely studied [30,42–44,48–53]. Dangerous As concentra-tions have been observed in areas along the Mekong River(Fig. 3), particularly in Kratie, Prey Veng and KandalProvinces, where As(III) was predominantly found in thereducing groundwater [40,46,48,51]. However, As(V) hasmainly been observed in the oxidizing groundwater inKampong Cham Province [40]. There has been a generalagreement that the reductive dissolution of As-rich Fe (oxy)hydroxides may drive the release of As to groundwater [52].This mechanism was also observed to be true in the MekongRiver basin, Cambodia [48,51]. Using hydrologic andbiogeochemical measurements, Polizzotto et al. [52] showedthat As was released from the near-surface, river-derivedsediments within the Mekong River delta and transportedback to the river by groundwater flow through the underlyingaquifer on a centennial time scale.

Although many populations live alongside watersheds inCambodia, shallow groundwater is still the main source ofdrinking water [40]. This dependence on shallow ground-water is due to the lack of safe water supplies and watertreatment systems in rural areas and the long dry season(November to May), which causes poor rainwater catchment.Additionally, a cutting edge campaign of water and sanitationthat took place in the early 1990s promoted groundwater asmicrobiologically-clean and safe to use without any treat-ments. Consequently, many families were able to securesupposedly safe water through inexpensive and easily-drilledborehole tapping into the shallow aquifer groundwater [40].Arsenic treatment systems, modified from traditional sandfilters, have also been developed to enhance As removal fromgroundwater following the discovery of spatial and temporalvariations in the groundwater composition [55]. However, nosystematic and comprehensive field applications of Asremoval technologies have been performed in Cambodiadue to concerns associated with their operations, efficaciesand maintenance requirements [41]. The development ofvisual arsenicosis symptoms has generally been assumed tofollow a decade of consumption of As-rich groundwater.However, new cases discovered in Cambodia have followedexposure times as short as 3 years, due to the extremelyelevated As concentration in groundwater (3 500 µg$L–1),socioeconomic status, malnutrition, individual health statusand hygiene, as well as drinking water maintenance andstorage habits [40,41]. In fact, Mazumder et al. [56] found 70cases (n = 97) in Preak Russey village of Kandal Province thatshowed evidence of arsenical skin lesions with eitherpigmentation or keratosis, and clinical and laboratory testsconfirmed the lesions according to WHO’s diagnostic criteria.The largest number of cases was seen within the 31–45 yearsold group, and both genders were more or less equallyaffected. Evidence of both pigmentation and keratosis werefound in 60 cases, while only pigmentation and only keratosis

was observed in 6 and 4 cases, respectively. In addition,Mazumder et al. [56] revealed that 37.0% of children in theless than 16 years old group had skin lesions of arsenicosis.The youngest child with evidence of keratosis and pigmenta-tion was 8 years old, although the features of redness and mildthickening of the palms were observed even in children aged4–5 years old.

A recent cross-sectional health risk assessment of inorganicAs intake among Cambodian residents living in the MekongRiver basin through the groundwater drinking pathway usingthe US EPA model revealed that thousands of Cambodianswere at high risk of both toxic and carcinogenic effects of As.Approximately, 98.7% and 13.5% of the residents of theKandal and Kratie Provinces, respectively, were at risk of Astoxicity. Moreover, the cancer risk index indicated an averageof 5 in 1 000 exposure in the Kandal Province study area [40].

The cancer risk index indicated in the study was the cancerrisk caused specifically by As. The carcinogenic effects of Ascan be estimated as the incremental probability of anindividual developing cancer over a lifetime as a result ofexposure to a potential carcinogen. The cancer risk (CR)levels can be assessed as CR = 1 – exp( –CDI � SF), whereCDI is a chronic daily intake of As (mg$kg–1$d–1), SF is anoral cancer slope factor of As (1.5 mg$kg–1$d–1) [57]. Ingeneral, the US EPA considers the cancer risks that are belowabout 1 chance in 1 000 000 (1 � 10–6) to be so small as to benegligible and those of about 1 � 10–4 to be sufficiently largethat some kind of remediation is desirable. Therefore, cancerrisks ranging between 1 � 10–6 and 1 � 10–4 are generallyconsidered to be acceptable [58].

Although significant regional differences in both toxiceffects and cancer risks of As were observed, there were nosignificant differences in gender and age groups. Therefore,the health risk from As poisoning was more dependent ongroundwater As concentrations, the average daily dose andother factors related to groundwater consumption, such asexposure duration and ingestion rate, rather than anindividual’s status, such as gender or age [40]. The lateststage of As skin cancer was also reported in the MekongRiver basin of Cambodia. Cutaneous lesion characteristic ofchronic arsenicosis had manifested and squamous cellcarcinomas requiring amputation had developed in theindividual [59].

To detect the early warning stage of chronic arsenicosis, anappropriate biomarker of arsenic exposure should bepromptly validated. A biomarker (biological marker) isdefined as a substance, physiologic characteristic, or geneticstatus that indicates or may indicate the present of disease, aphysiologic abnormality or a physiologic condition [60]. Apositive correlation between groundwater As concentrationand As concentration in scalp hair was observed in theMekong River basin of Cambodia [40,54,61,62]. In addition,Gault et al. [61] assessed the use of total As concentration innail and hair as a biomarker of arsenic exposure from drinkingAs-rich groundwater, while Kubota et al. [54] utilized hair As



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and urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG) toverify As toxicity. Recently, Phan et al. [63] validated theuse of As concentration in scalp hair, fingernails and toenailsas biomarkers by studying exposure-biomarker relationships.It was found that As concentrations in scalp hair, fingernailsand toenails were positively associated with groundwater Asconcentration and an individual’s average daily dose ofarsenic, suggesting that As concentrations in scalp hair,fingernails and toenails can be used as biomarkers of chronicarsenic exposure from drinking As-rich groundwater. Of thethree biomarkers, As concentration in scalp hair is morefavorable due to the ease of sample processing andmeasurement. Interestingly, the study suggested that thethree biomarkers reflected different time windows ofexposure. As concentration in scalp hair might reflect pastexposure of 2–5 months prior to hair cutting; As concentra-tion in fingernails was more likely to indicate past exposure of6–12 months, while that in toenails might depict pastexposure as long as 12–18 months before clipping [63].Since arsenicosis continues to be a major public healthconcern in rural Cambodia, the application of biomarkers mayprove useful in detecting early stages of chronic As exposureand thus avoiding further harm. The onset of arsenicosissymptoms are generally assumed to manifest following adecade of suspected exposure to As. Nonetheless, simplerdiagnostic tools to detect and monitor chronic arsenicosisshould be encouraged, as testing for biomarkers is not alwaysfeasible in rural areas such as those in Cambodia [63].Furthermore, Sampson et al. [41] have suggested thatmanagement of groundwater in Cambodia with high levelsof As would be possible through identification of risk areas,comprehensive educational programs, and enforcement of thepolicy formulated by the Royal Government of Cambodia, tofacilitate the development of alternative water supplies andeducational programs.

Lao People’s Democratic RepublicUnlike other areas such as the Mekong valley in Cambodiaand Vietnam, where problems with groundwater As conta-mination have been well documented, little data are so faravailable in areas of Lao PDR. In 2001, the UNICEF carriedout preliminary testing of groundwater from wells in severalareas of Lao PDR, including Attapeu, Savannakhet, Cham-pasak, Saravane, Sekong, Khammuane and Bolikhamxai.Analysis of 200 samples indicated that some samples had Asconcentrations greater than 10 μg$L–1. Only one well in theAttapeu Province was found to contain water with an As level(112 μg$L–1) exceeding the national standard for As indrinking water of 50 μg$L–1 [64]. Even though the currentmaximum permissible concentration for As in drinking waterrecommended by WHO is 10 μg$L–1, Lao PDR still uses theformer WHO-recommended concentration of 50 μg$L–1 asthe national standard for As in drinking water due toeconomic considerations and lack of tools and techniques to

measure lower As concentrations accurately [3]. In 2004, theUNICEF, in collaboration with the government of Lao PDRand the Adventist Development and Relief Agency, testedapproximately 680 tube-well water samples taken from theHolocene aquifer in the Mekong valley areas, and reportedthat 21% of all samples had As concentrations exceeding theWHO guideline for drinking water (10 μg$L–1) while 1%exceeded the national standard (50 μg$L–1) [3].

During 2007 and 2008, Chanpiwat et al. [2] investigatedthe enrichment of As and As speciation in groundwatercollected from either household or community tube wellslocated along the Mekong River in Lao PDR (Vientiane,Bolikhamxai, Savannakhet, Saravane, Champasak, andAttapeu). It was found that about 55.7% of all 61 sampleshad As concentrations exceeding the WHO guideline fordrinking water (10 μg$L–1). The highest As concentration(278 μg$L–1) was found in the Champasak Province. Thepercentages of tube well samples in each province containingAs levels higher than the WHO guideline were 20% forAttapeu, 28.6% for Bolikhamxai, 76.9% for Champasak,54.6% for Saravane and 100% for Savannakhet (Fig. 3).Moreover, approximately 14.8% of all samples contained Asconcentration higher than the national standard for As(50 μg$L–1) in drinking water. Tube-well water samplescontaining As levels higher than 10 μg$L–1 were collectedmostly from the middle and southern parts of the country. Theareas along the Mekong River below the middle part aregenerally floodplains and are occupied by Quaternarysediments transported by the Mekong River. In addition, theresults of this recent study [2] clearly showed that tube-wellwater samples with pH less than 6.5 and low redox potentialgenerally had high As concentrations ( > 10 μg$L–1). There-fore, an acidic pH and reducing conditions were concluded tobe the major environmental factors enhancing the release ofAs from sediments. High As concentrations, such as thosefound in this study along the Mekong River in the central andsouthern Lao provinces, may thus have arisen under thereducing (anaerobic) conditions created in young (Quater-nary) alluvial and deltaic aquifers.

The As concentrations in tube wells in Lao PDR (ND–277.8 μg$L–1) were relatively lower than those found in theareas along the Mekong River of Cambodia and Vietnam(Table 2). The Mekong valleys of Cambodia and Vietnamhave lower topographic gradients than that of Laos.Consequently, both areas may contain larger amounts ofyoung alluvial soils. In addition, the As found in Champasak,Saravane and Attapeu may also be contributed in part byancient volcanic activities that occurred millions of years ago[2]. In metamorphic environments, As principally presents asarsenopyrite (sulfide minerals) precipitated from hydrother-mal fluids [1]. Fengthong et al. [64] also concluded based ontheir studies of surface and groundwater contamination anddrinking water quality in Lao PDR that the threat of naturallyoccurring As in groundwater was associated with certaingeological formations.



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In term of As speciation, 45.9% of all 61 tube-well sampleshad total As concentrations dominated by As(III) [2].Compared to As(V), another As inorganic species, As(III)is fairly soluble in water and generally regarded as being moreacutely toxic than As(V) [7]. After entering the human body,As(III) is readily absorbed from the GI tract into thebloodstream and then distributed widely among the internalorgans [7]. As has also been proposed to cause chromosomalabnormalities that lead to cancer, particularly skin cancer, andcancer of internal organs, such as lung, bladder, and kidney[7]. As(III) was the dominant As species in the tube-wellwater samples obtained from Bolikhamxai, Champasak,Saravane and Savannakhet. Concentrations of As(III) in thetube-well water samples varied from < 0.05 μg$L–1 (inBolikhamxai, Champasak, and Saravane) to274.95 μg$L–1 (in Champasak), with an average concentra-tion of 18.72 μg$L–1 [2]. However, the tube-well watercollected from Attapeu and Vientiane had mainly As(V) andparticulate As, respectively [2].

According to Chanpiwat et al. [2], the observed concentra-tions of total As as well as different As species clearlyrevealed that villagers living in the middle and southernregions of Lao PDR, especially in the Bolikhamxai,Savannakhet, Saravane and Champasak Provinces, havebeen subjected to detrimental health effects due to theconsumption of As-enriched groundwater. However, thehealth effects of As exposure and estimations of area andpopulation at risk should be further examined to ascertain thescale of the threat posed by As contamination.

ThailandIn Thailand, As has never been reported to naturally occur[65]. Groundwater As contamination in this country has beenreported to originate from both point sources (leachate fromore dressing plant wastes) and diffuse sources (undergroundplacer deposits) [65,66]. An area well-known to be affectedby As is the Ron Phibun District, Nakhon Si ThammaratProvince, on the southern peninsula of Thailand (Fig. 3). TheRon Phibun District lies within the Southeast (Main Range)Tin Belt of southern Thailand with respect to geology,metallogenesis and mining history [67]. The primary Sn-W-As mineralization and alluvial placer tin deposits were minedhere for over 100 years [68]. However, the mining sites wereclosed by the Department of Mineral Resources in 1990 [69].As a result of the mining operations, high-grade arsenopyrite,pyrite-rich waste piles, and waste from ore dressing plantsand panning were generated. High rainfall aided in theleaching out of toxic minerals such as As, leading tocontamination of soil, groundwater and surface water withAs over an area of 500 km2 within the district [67,69,70].Health problems linked to As in drinking water were firsthighlighted in the residents of the Ron Phibun District in 1987due to a case of arsenical skin cancer in a female resident[67,68,71]. In 1988, a preliminary survey on the extent,

distribution and epidemiology of arsenicosis in the provincewas established by the Ministry of Public Health. It wasreported that approximately 1 000 cases were diagnosed withAs-induced skin disorders, including keratosis and melanosis.In 1994, a collaborative study between the Thai and theBritish government authorities on the geochemical form of Asin aquifer systems in the affected area revealed that Ascontamination of shallow ground water ranged between 1.25and 5 114 μg$L–1 (Table 2). About 69.6% of the 23 shallowwells contained As concentrations exceeding the WHOguideline for drinking water (10 μg$L–1). Moreover, 39.1%of all collected samples had As levels above the nationalgroundwater quality standard of 50 μg$L–1 [67]. Furthermore,it was found that piped water in this area had an Asconcentration of 70 μg$L–1 [72]. At the time the problemswere first recognized, about 15 000 villagers were estimatedto be drinking water with more than 50 μg$L–1As [68](Table 2).

Arsenic speciation data showed high absolute As(III)concentrations ( > 50 μg$L–1) in several of the shallowgroundwater samples, although As(V) remained the dominantspecies throughout (As(III) = 2.4% to 6.1% of total As) [67].More recently, As concentrations in both shallow ground-water and shallow well pumps have been reported to exceedthe WHO guideline for drinking water ( > 700 μg$L–1 and10 μg$L–1, respectively) [69]. However, Tseng [71] con-cluded that wells deeper than 60 feet from the level oflimestone and slate were safe from As contamination.

Since the Chao Phraya River valley contains relativelyyoung sediments that could develop a combination ofgeochemical conditions, such as reducing or oxidizingconditions and high pH, that allow the release of As, thisarea may also suffer from contamination of groundwater withAs. A survey of groundwater As concentration was recentlyconducted in the groundwater sources located near a river incentral Thailand [65]. A total of 37 samples were collectedfrom shallow aquifers around a lower Chao Phraya Riverbasin area of Nakhonpathom Province. Arsenic concentra-tions in most of the shallow wells were about 5 μg$L–1 or less,with an average of 11 μg$L–1. Based on these results,Kohnhorst [65] concluded that As contamination of ground-water was not of public health significance in CentralThailand. In addition, most households have easy access tohigh-quality treated water making the possibility of arseni-cosis very low in this region [65].

Role of the Mekong River in arsenicgroundwater contamination

Countries in SEA generally have several common hydro-logical features, which have been recognized as the maincauses of naturally occurring As in groundwater, including:1) alluvial and low-lying flat topographies, 2) rapid Holocenesedimentation nourished by large rivers, 3) an abundance



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of degradable organic material, and 4) slow-movinggroundwater [1,5]. The Mekong delta is one of the floodplainswell-known for As-enriched groundwater in the region [73].Groundwater As problems along the Mekong valley, whichcovers parts of Lao PDR, Cambodia and Vietnam, have beenreported by numerous studies [2,5,30,32,33,40,46,47,73].The delta plain of the Mekong River delta spans a 62 520 km2

area in Vietnam (about 83%) and Cambodia [74]. This riverdelta is likely to play a significant role as an efficient trap forcollecting alluvial materials moved by the Mekong Riversystem due to Quaternary relative sea level changes [74,75].The decomposition of organic matter-rich sediments canenhance the reducing (low redox potential) conditions in theaquifer sediments [3,6,8]. As a result, As mobilization canoccur at acidic pH via the reductive dissolution of iron oxides.Metal oxides (particularly iron oxides) and sulfide minerals(particularly pyrite) are the most important mineral sources inaquifers [3]. Since a large amount of As is adsorbed onto ironoxides, once iron reducing conditions are established in theaquifer, As can be either desorbed from the surface of thedissolving Fe oxide or released from the mineral structureitself [3,44,76]. However, to initiate this process, a source ofdegradable organic carbon, such as those available in thealluvial sediments, as well as microbial activities, areessential [3,76]. So far few investigations have been carriedout in the Mekong valley as a whole. Most investigation todate appears to have been carried out in Cambodia andVietnam. It was found that high Fe and Mn concentrationsand anaerobic conditions are common features of thegroundwaters throughout the lowland areas of Cambodia.Areas of the great perceived risk with As concentrationsgreater than 50 µg$L–1 are those with Holocene sedimentsforming the main aquifer [5]. While As concentrations werefound to be mostly low for groundwaters from Holocencedeposits [5]. Different As concentrations for those ground-waters were found in the Middle and Upper Pleistocenedeposits ( < 1–32 µg$L–1), Lower Pleistocene deposits( < 1–7 µg$L–1), Pliocene deposits ( < 1–57 µg$L–1) [5].

Arsenic mitigation measures in SoutheastAsia

As reported by the World Bank [3], the operational responsesto As groundwater contamination in most SEA countries haveundertaken so far. Interestingly, Non-Governmental Organi-zations (NGOs) and international organizations seem to havebeen the main drivers, rather than government organizations.Indeed no country has taken major steps towards active andstrategic monitoring of Asian groundwater [3].

In response to As contamination of groundwater in SEA,several approaches have been implemented to mitigatethe levels of As in groundwater to an acceptable level( < 10 µg$L–1). Several membrane filtration units, supportedby the United Nations University, GIST, and WoongJin

Chemicals in South Korea, were installed in the ChampasakProvince of Lao PDR and the An Giang Province of Vietnamin December and May 2010, respectively. The installation ofmore filtration units are being processed in the Dong ThapProvince of Vietnam by Can Tho University in collaborationwith GIST.

After the discovery of As contamination of groundwater inCambodia in 1999 by JICA, the Royal Government ofCambodia formed an interior subcommittee to regulate Asconcentration in drinking water, with a permissible limit ofarsenic set at 50 µg$L–1, which is as low as it is in otherdeveloping countries. Testing of wells was conducted in anumber of provinces to identify the arsenic-affected areasusing arsenic field test kits. Concurrently, several NGOsdeveloped information, education and communication (IEC)materials to educate the affected communities about the risksof consuming arsenic-rich groundwater. Similarly, an educa-tional program for school children was developed andimplemented in a few schools in high-risk areas. Wellsfound to have arsenic concentrations higher than theCambodian national standard were painted red to indicatethat the water is not safe for drinking, as is the practice inBangladesh. This kind of educational effort was partlysuccessful in some communities [41]. However, the positiveimpact of this initiative was significantly reduced due tosuccessive installation of large numbers of new tube wells inareas at high risk of arsenic contamination without properarsenic testing. Arsenic removal units have recently beeninstalled by the Institute of Technology of Cambodia (ITC) inseveral affected communities in the Kandal and the Prey VengProvinces, with technical and financial support from LehighUniversity in the USA. Each of those units was expected toprovide arsenic-safe water for approximately 200 households.However, an educational program is needed to mobilizepeople to collect arsenic-safe water from the units.

Concluding remarks

Our review of published work revealed that the knowledge ofthe occurrence and distribution of As has improved greatlyover the last few years. As contamination of groundwater inthe SEA region is a serious problem, especially in thefloodplain areas along the Mekong River. Arsenic generallyoccurs and is enriched in aquifers through the reductivedissolution of river-derived sediments containing iron oxides.Young sediments in alluvial and deltaic plains are obvioustarget areas for further investigation. Groundwater containingAs concentration greater than the WHO guideline fordrinking water ( > 10 μg$L–1) is consumed by local peopleon a daily basis, especially in the form of drinking water. Dueto the carcinogenic nature of As, visual arsenicosis, such asarsenical skin lesions with pigmentation or keratosis, candevelop and can be observed in residents continuouslyexposed to As-contaminated groundwater, even for exposure



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times shorter than 10 years. However, there are stillknowledge gaps regarding As especially on the epidemiolo-gical side. The scope of public health concern on Ascontamination in medium and long terms is not yet clear.To ascertain the scale of the threat of As a systematicassessment of risk areas, As epidemiology, social and culturalconditions, as well as patient identification and treatmentshould be conducted. Appropriate technical solutions for Asmitigation that are practical to the local conditions in terms oftechnology, cost-benefit ratio and social considerationsshould be developed. Moreover, raising awareness througheducational programs as well as direct action and enforcementby governments should be immediately taken for sustainableAs mitigation.

Acknowledgements

This research was financially supported by the Woongjin ChemicalCo. and the Gwangju Institute of Science and Technology, South

Korea (Innovative Technology of Ecological Restoration).

References

1. Schmoll O, Howard G, Chilton J, Chorus I. Protecting groundwaterfor health: Managing the quality of drinking-water resources. WorldHealth Organization. London: IWA publishing, 2006

2. Chanpiwat P, Sthiannopkao S, Cho KH, Kim KW, San V,Suvanthong B, Vongthavady C. Contamination by arsenic and

other trace elements of tube-well water along the Mekong River inLao PDR. Environ Pollut 2011; 159(2): 567–576

3. The World Bank, the Water Sanitation Program. World Bank policyreport: towards a more effective operational response. Arseniccontamination of groundwater in South and East Asian Countries.Massachusetts:The International Bank for Reconstruction andDevelopment, 2005

4. International Agency for Research on Cancer (IARC). IARCmonographs on the evaluation of carcinogenic risks to humans,Supplement 7: Overall evaluations of carcinogenicity: An updatingof IARC monographs volumes 1 to 42. http://monographs.iarc.fr/ENG/Monographs/suppl17-19.pdf (Access on June 26, 2011)

5. Rahman MM, Naidu R, Bhattacharya P. Arsenic contamination ingroundwater in the Southeast Asia region. Environ Geochem Health

2009; 31(Suppl 1): 9–21

6. Smedley PL, Kinniburgh DG. A review of the source, behavior anddistribution of arsenic in natural waters. Appl Geochem 2002; 17(5):517–568

7. Adriano DC. Trace elements in terrestrial environments: biogeo-chemistry, bioavailability, and risk of metal. 2nd ed. Springer-

Verlag, NY, USA, 2001

8. Islam FS, Gault AG, Boothman C, Polya DA, Charnock JM,Chatterjee D, Lloyd JR. Role of metal-reducing bacteria in arsenicrelease from Bengal delta sediments. Nature 2004; 430(6995): 68–71

9. Stüben D, Berner Z, Chandrasekharam D, Karmakar J. Arsenic

enrichment in groundwater of West Bengal, India: geochemicalevidence for mobilization of As under reducing conditions. ApplGeochem 2003; 18(9): 1417–1434

10. Rowland HAL, Polya DA, Lloyd JR, Pancost RD. Characterisationof organic matter in a shallow, reducing, arsenic-rich aquifer, WestBengal. Org Geochem 2006; 37(9): 1101–1114

11. Anawar HM, Akai J, Komaki K, Terao H, Yoshioka T, Ishizuka T,

Safiullah S, Kato K. Geochemical occurrence of arsenic ingroundwater of Bangladesh L sources and mobilization processes.J Geochem Explor 2003; 77(2–3): 109–131

12. Routh J, Hjelmquist O. Distribution of arsenic and its mobility inshallow aquifer sediments from Ambikanagar, West Bengal, India.Appl Geochem 2011; 26(4): 505–515

13. Thomas DJ. Arsenolysis and thiol-dependent arsenate reduction.Toxicol Sci 2010; 117(2): 249–252

14. Jomova K, Jenisova Z, Feszterova M, Baros S, Liska J, HudecovaD, Rhodes CJ, Valko M. Arsenic: toxicity, oxidative stress andhuman disease. J Appl Toxicol 2011; 31(2): 95–107

15. Abernathy CO, Thomas DJ, Calderon RL. Health effects and risk

assessment of arsenic. J Nutr 2003; 133(5 Suppl 1): 1536S–1538S

16. Cohen SM, Arnold LL, Eldan M, Lewis AS, Beck BD. Methylatedarsenicals: the implications of metabolism and carcinogenicitystudies in rodents to human risk assessment. Crit Rev Toxicol 2006;36(2): 99–133

17. Roy P, Saha A. Metabolism and toxicity of arsenic: a human

carcinogen. Curr Sci 2002; 82(1): 38–45

18. Hughes MF. Arsenic toxicity and potential mechanisms of action.Toxicol Lett 2002; 133(1): 1–16

19. Masotti A, Sacco LD, Bottazzo GF, Sturchio E. Risk assessment ofinorganic arsenic pollution on human health. Environ Pollut 2009;157(6): 1771–1772

20. Khan MM, Sakauchi F, Sonoda T, Washio M, Mori M. Magnitudeof arsenic toxicity in tube-well drinking water in Bangladesh and itsadverse effects on human health including cancer: evidence from areview of the literature. Asian Pac J Cancer Prev 2003; 4(1): 7–14

21. Khan MA, Ho YS. Arsenic in drinking water: a review ontoxicological effects, mechanism of accumulation and remediation.

Asian Journal of Chemistry 2011; 23(5): 1899–1901

22. Integrated Risk Information System (IRIS). http://www.epa.gov/IRIS/ (Access on July 27, 2011)

23. Duker AA, Carranza EJM, Hale M. Arsenic geochemistry andhealth. Environ Int 2005; 31(5): 631–641

24. Kapaj S, Peterson H, Liber K, Bhattacharya P. Human health effectsfrom chronic arsenic poisoning—a review. J Environ Sci Health ATox Hazard Subst Environ Eng 2006; 41(10): 2399–2428

25. Rahman MM, Ng JC, Naidu R. Chronic exposure of arsenic via

drinking water and its adverse health impacts on humans. EnvironGeochem Health 2009; 31(Suppl 1): 189–200

26. International Agency for Research on Cancer (IARC). Arsenic indrinking water 1. Exposure data — IARC monographs. http://monographs.iarc.fr/ENG/Monographs/vol84/mono84-6A.pdf(Access on August 18, 2011)

27. Benbrahim-Tallaa L, Waalkes MP. Inorganic arsenic and humanprostate cancer. Environ Health Perspect 2008; 116(2): 158–164

28. Cantor KP, Lubin JH. Arsenic, internal cancers, and issues ininference from studies of low-level exposures in human populations.Toxicol Appl Pharmacol 2007; 222(3): 252–257



offprint

offprint

29. Bonior DE. Public exposure to arsenic in drinking water inMichigan. http://oversight-archive.waxman.house.gov/documents/20040607132512-45841.pdf (Access on August 19, 2011)

30. Berg M, Stengel C, Trang P P, Hungviet M, Sampson M, Leng S,Samreth D, Fredericks. Magnitude of arsenic pollution in theMekong and Red River Deltas—Cambodia and Vietnam. Sci TotalEnviron 2007; 372(2–3): 413–425

31. Berg M, Tran HC, Nguyen TC, Pham HV, Schertenleib R, Giger W.Arsenic contamination of groundwater and drinking water inVietnam: a human health threat. Environ Sci Technol 2001; 35(13): 2621–2626

32. Stanger G, Truong TV, Ngoc KS, Luyen TV, Thanh TT. Arsenic ingroundwaters of the lower Mekong. Environ Geochem Health 2005;

27(4): 341–357

33. Hoang TH, Bang S, Kim KW, Nguyen MH, Dang DM. Arsenic ingroundwater and sediment in the Mekong River delta, Vietnam.Environ Pollut 2010; 158(8): 2648–2658

34. Phuong TD, Kokot S, Chuong PV, Tong Khiem D. Elementalcontent of Vietnamese rice. Part 1: sampling, analysis, and

comparison with previous studies. Analyst (Lond) 1999; 124(4):553–560

35. Hoang TH, Bang S, Kim KW, Nguyen MH. Community exposureto arsenic in the Mekong River delta, southern Vietnam. J EnvironMonit 2011; 13: 2025–2032

36. Sengupta MK, Hossain MA, Mukherjee A, Ahamed S, Das B,

Nayak B, Pal A, Chakraborti D. Arsenic burden of cooked rice:traditional and modern methods. Food Chem Toxicol 2006; 44(11):1823–1829

37. Signes A, Mitra K, Burló F, Carbonell-Barrachina AA. Contributionof water and cooked rice to an estimation of the dietary intake ofinorganic arsenic in a rural village of West Bengal, India. FoodAddit Contam Part A Chem Anal Control Expo Risk Assess 2008;25(1): 41–50

38. Ohno K, Yanase T, Matsuo Y, Kimura T, Hamidur Rahman M,Magara Y, Matsui Y. Arsenic intake via water and food by apopulation living in an arsenic-affected area of Bangladesh. SciTotal Environ 2007; 381(1–3): 68–76

39. Cleland B, Tsuchiya A, Kalman DA, Dills R, Burbacher TM, WhiteJW, Faustman EM, Mariën K. Arsenic exposure within the Koreancommunity (United States) based on dietary behavior and arsenic

levels in hair, urine, air, and water. Environ Health Perspect 2009;117(4): 632–638

40. Phan K, Sthiannopkao S, Kim KW, Wong MH, Sao V, Hashim JH,Mohamed Yasin MS, Aljunid SM. Health risk assessment ofinorganic arsenic intake of Cambodia residents through groundwaterdrinking pathway. Water Res 2010; 44(19): 5777–5788

41. Sampson ML, Bostick B, Chiew H, Hangan JM, Shantz A.Arsenicosis in Cambodia: case studies and policy response. ApplGeochem 2008; 23(11): 2976–2985

42. Polya DA, Lythgoe PR, Abou-Shakra F, Gault AG, Brydie JR,Webster JG, Brown KL, Nimfopoulos MK, Michailidis KM. IC-ICP-MS and IC-ICP-HEX-MS determination of arsenic speciationin surface and groundwaters: preservation and analytical issues.Mineral Mag 2003; 67(2): 247–261

43. Polya DA, Gault AG, Diebe N, Feldman P, Rosenboom JW,Gilligan E, Fredericks D, Milton AH, Sampson M, Rowland HAL,Lythgoe PR, Jones JC, Middleton C, Cooke DA. Arsenic hazard in

shallow Cambodian groundwaters. Mineral Mag 2005; 69(5): 807–823

44. Buschmann J, Berg M, Stengel C, Winkel L, Sampson ML, TrangPT, Viet PH. Contamination of drinking water resources in theMekong delta floodplains: arsenic and other trace metals poseserious health risks to population. Environ Int 2008; 34(6): 756–764

45. Quicksall AN, Bostick BC, Sampson ML. Linking organic matter

deposition and iron mineral transformations to groundwater arseniclevels in the Mekong delta, Cambodia. Appl Geochem 2008; 23(11):3088–3098

46. Sthiannopkao S, Kim KW, Sotham S, Choup S. Arsenic andmanganese in tube well waters of Prey Veng and Kandal Provinces,Cambodia. Appl Geochem 2008; 23(5): 1086–1093

47. Luu TT, Sthiannopkao S, Kim KW. Arsenic and other traceelements contamination in groundwater and a risk assessment studyfor the residents in the Kandal Province of Cambodia. Environ Int2009; 35(3): 455–460

48. Rowland HAL, Gault AG, Lythgoe P, Polya DA. Geochemistry ofaquifer sediments and arsenic-rich groundwaters from KandalProvince, Cambodia. Appl Geochem 2008; 23(11): 3029–3046

49. Lear G, Song B, Gault AG, Polya DA, Lloyd JR. Molecular analysisof arsenate-reducing bacteria within Cambodian sediments follow-ing amendment with acetate. Appl Environ Microbiol 2007; 73(4):1041–1048

50. Benner SG, Polizzotto ML, Kocar BD, Ganguly S, Phan K, Ouch K,

Sampson M, Fendorf S. Groundwater flow in an arsenic-contaminated aquifer, Mekong Delta, Cambodia. Appl Geochem

2008; 23(11): 3072–3087

51. Kocar BD, Polizzotto ML, Benner SG, Ying SC, Ung M, Ouch K,Samreth S, Suy B, Phan K, Sampson M. Integrated biogeochemicaland hydrologic processes driving arsenic release from shallowsediments to groundwaters of the Mekong delta. Appl Geochem2008; 23(11): 3059–3071

52. Polizzotto ML, Kocar BD, Benner SG, Sampson M, Fendorf S.Near-surface wetland sediments as a source of arsenic release toground water in Asia. Nature 2008; 454(7203): 505–508

53. Robinson DA, Lebron I, Kocar B, Phan K, Sampson M, Crook N.Time-lapse geophysical imaging of soil moisture dynamics intropical deltaic soils: As aid to interpreting hydrological andgeochemical processes. Water Resour Res 2009; 45:W00D342.

54. Kubota R, Kunito T, Agusa T, Fujihara J, Monirith I, Iwata H,Subramanian A, Seang Tana T, Tanabe S. Urinary 8-hydroxy-2′-deoxyguanosine in inhabitants chronically exposed to arsenic ingroundwater in Cambodia. J Environ Monit 2006; 8(2): 293–299

55. Chiew H, Sampson ML, Huch S, Ken S, Bostick BC. Effect ofgroundwater iron and phosphate on the efficacy of arsenic removalby iron-amended BioSand filters. Environ Sci Technol 2009; 43(16):6295–6300

56. Mazumder DN, Majumdar KK, Santra SC, Kol H, Vicheth C.Occurrence of arsenicosis in a rural village of Cambodia. J EnvironSci Health A Tox Hazard Subst Environ Eng 2009; 44(5): 480–487

57. Office of Emergency and Remedial Response, U.S. EnvironmentalProtection Agency. Risk Interim final, EPA/540/1–89/002, 1989

58. Environmental Protection Agency. HH: Risk characterization. http://www.epa.gov/region8/r8risk/hh_risk.html (Access on July 27,2011)

59. James GG, Adam CG, Colinda H, Erin MK, Kayla J, Say BV.



offprint

offprint

Arsenic and amputations in Cambodia. Asian Biomed 2010; 4(3):469–474

60. Youngson RM. Collis dictionary of medicine. 4th ed. London:Harper Collins, 2007

61. Gault AG, Rowland HAL, Charnock JM, Wogelius RA, Gomez-Morilla I, Vong S, Leng M, Samreth S, Sampson ML, Polya DA.Arsenic in hair and nails of individuals exposed to arsenic-rich

groundwaters in Kandal Province, Cambodia. Sci Total Environ2008; 393(1): 168–176

62. Sthiannopkao S, Kim KW, Cho KH, Wantala K, Sotham S,Sokuntheara C, Kim JH. Arsenic levels in human hair, KandalProvince, Cambodia: the influences of groundwater arsenic,consumption period, age and gender. Appl Geochem 2010; 25(1):81–90

63. Phan K, Sthiannopkao S, Kim KW. Surveillance on chronic arsenicexposure in the Mekong River basin of Cambodia using differentbiomarkers. Int J Hyg Environ Health 2011 Aug 4. [Epub ahead ofprint]

64. Fengthong T, Dethoudom S, Keosavanh O. Drinking water qualityin the Lao People’s Democratic Republic. Seminar on theenvironmental and public health risks due to contamination of

soils, crops, surface and groundwater from urban, industrial, andnatural sources in South East Asia, Hanoi, Vietnam. December2002, UN-ESCAP

65. Kohnhorst R, Kunito T, Agusa T, Fujihara J, Monirith I, Iwata H.Arsenic in groundwater in selected countries in South and SoutheastAsia: a review. J Trop Med Parasitol 2005; 28: 73–82

66. Caussy D. Epidemiological methods for mitigating health impactsof arsenic in South East Asia region of the World HealthOrganization. http://www.bvsde.ops-oms.org/bvsacd/arsenico/Arsenic2004/theme1/paper1.2.pdf

67. Williams M, Fordyee F, Paijitprapapon A, Charoenchaisri P.Arsenic contamination in surface drainage and groundwater inpart of the Southeast Asian tin belt, Nakhon Si Thammarat Province,

southern Thailand. Environmental Geology 1996; 27(1): 16–33

68. Smedley PL. Sources and distribution of arsenic in groundwater andaquifers. In: Appelo T. Arsenic in groundwater — a world problem.Proceedings of seminar Utrecht 29 November 2006. http://www.iah.org/downloads/occupub/arsenic_gw.pdf

69. Jindal R, Ratanamalaya P. Investigations on the status of arseniccontamination in southern Thailand. In: International Water

Association (IWA). Southeast Asian Water Environment 1. London:IWA Publishing, 2006: 223–229

70. Ruangwises S, Saipan P. Dietary intake of total and inorganicarsenic by adults in arsenic-contaminated area of Ron Phibundistrict, Thailand. Bull Environ Contam Toxicol 2010; 84(3): 274–277

71. Tseng CH. Chronic arsenic intoxication in Asia: current perspec-tives. www.tsim.org.tw/journal/jour10-6/P10_224.PDF

72. Kadushkin A, Siddiqui Z, Shipin O. Groundwater quality assess-ment and management in selected countries of East and SoutheastAsia. 2004. http://www.bvsde.paho.org/bvsacd/cd63/groundwater-quality.pdf

73. The World Bank, the Water Sanitation Program. World Bank policyreport: volume II technical report. Arsenic contamination ofgroundwater in South and East Asian Countries. Massachusetts:the International Bank for Reconstruction and Development, 2005

74. .Lap Nguyen V, Oanh TK, Tateishi M. Late Holocene depositionalenvironments and coastal evolution of the Mekong River Delta,Southern Vietnam. J Southeast Asian Earth Sci 2000; 18(4): 427–439

75. Lu XX, Siew RY. Water discharge and sediment flux changes in theLower Mekong River. Hydrol Earth Syst Discuss 2005; 2(6): 2287–2325

76. Winkel L, Berg M, Stengel C, Rosenberg T. Hydrogeologicalsurvey assessing arsenic and other groundwater contaminants in thelowlands of Sumatra, Indonesia. Appl Geochem 2008; 23(11):

3019–3028



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