Contamination by arsenic and other trace elements of tube-well water along the Mekong River in Lao PDR

Structural and Functional Investigation of the Periplasmic Arsenate-Binding Protein ArrX from Chrysiogenes arsenatis

The anaerobic bacterium Chrysiogenes arsenatis respires using the oxyanion arsenate (AsO₄^3-) as the terminal electron acceptor, where it is reduced to arsenite (AsO₃^3-) while concomitantly oxidizing various organic (e.g., acetate) electron donors. This respiratory activity is catalyzed in the periplasm of the bacterium by the enzyme arsenate reductase (Arr), with expression of the enzyme controlled by a sensor histidine kinase (ArrS) and a periplasmic-binding protein (PBP), ArrX. Here, we report for the first time, the molecular structure of ArrX in the absence and presence of bound ligand arsenate. Comparison of the ligand-bound structure of ArrX with other PBPs shows a high level of conservation of critical residues for ligand binding by these proteins; however, this suite of PBPs shows different structural alterations upon ligand binding. For ArrX and its homologue AioX (from Rhizobium sp. str. NT-26), which specifically binds arsenite, the structures of the substrate-binding sites in the vicinity of a conserved and critical cysteine residue contribute to the discrimination of binding for these chemically similar ligands.

Prevalence of Anemia and Its Associate Factors among Women of Reproductive Age in Lao PDR: Evidence from a Nationally Representative Survey

Introduction

Anemia continues to be a major public health problem significant among women of reproductive age (WRA) in developing countries, including Lao People's Democratic Republic (Lao PDR), where the prevalence of anemia among women remains high. This study aimed to assess the prevalence of anemia and its associated factors among WRA 15–49 years in Lao PDR.

Methods

We conducted a cross-sectional study, using the Lao Social Indicator Survey II, 2017 dataset. A total of 12,519 WRA tested for anemia were included in this study, through multistage sampling approaches. Binary logistic regression was used to determine the associated factors of anemia.

Results

Of 12,519 women, 4,907 (39.2%) were anemic. Multivariate logistic regression revealed that living in central provinces (aOR: 2.16, 95% CI: 1.96–2.38), rural area (aOR: 1.1, 95% CI: 1.00–1.20), large family size with more than 6 persons (aOR: 1.14, 95% CI: 1.01–1.29), pregnancy (aOR: 1.46, 95% CI: 1.22–1.74), having any adverse pregnancy outcomes (aOR: 1.14, 95% CI: 1.03–1.25), poor drinking water (aOR: 1.24, 95% CI: 1.10–1.39), and poor sanitation facility (aOR: 1.15, 95% CI: 1.03–1.28) were significantly associated with an increased risk of anemia. Conversely, four factors were associated with anemia preventively, including being aged 25–34 years (aOR: 0.81, 95% CI: 0.74–0.90), postsecondary education (aOR: 0.76, 95% CI: 0.60–0.97), Hmong-Mien ethnicity (aOR: 0.48, 95% CI: 0.39–0.59), and watching television almost daily (aOR: 0.84, 95% CI: 0.75–0.95).

Conclusion

Anemia continues to be a major public health challenge in Lao PDR. Interventions should be considered on geographic variations, improving safe water and sanitation facility, promoting of iron supplements during pregnancy, and health education through mass media for women in rural areas.

High levels of boron promote anchorage-independent growth of nontumorigenic cells

WHO has presented a health-based guideline value for boron in drinking water. That fact indicates that a high level of boron is toxic for humans. However, there is no direct evidence of boron-mediated malignant transformation. In this study, human lung epithelial nontumorigenic BEAS-2B cells and tumorigenic A549 cells were used to investigate the tumorigenic toxicity of boron in vitro. Anchorage-independent growth, a hallmark of malignant transformation, was increased by boron at concentrations of 50, 250 and 500 μM in BEAS-2B cells, though the same concentrations of boron had no influence on anchorage-independent growth of A549 cells. Moreover, boron at concentrations of 250 and 500 μM activated the c-SRC/PI3K/AKT pathway of BEAS-2B cells. The results of our in vitro study suggest that exposure to high levels of boron promotes transforming activity of nontumorigenic cells.

Paddy soil geochemistry, uptake of trace elements by rice grains (Oryza sativa) and resulting health risks in the Mekong River Delta, Vietnam

Soil geochemistry and phytoavailable trace elements were investigated in 80 paddy soil samples and corresponding rice grains from the Mekong River Delta in Vietnam. Soil parameters like Fe-, Al-, and Mn-phases, organic matter, and pH-value determine element concentrations in soil and affect their transfer into rice grains. Arsenic exceeded the allowed limit for Vietnamese agricultural soils in 11% of the samples, presumably caused by natural processes. Lead surpassed the limit in one soil sample. Other toxic elements were close to their natural concentrations and far below allowable limits for agricultural soil. There was no clear correlation of trace element concentrations in soils with those in corresponding grains, even if the different soil parameters and the large pH-range between 3.7 and 6.8 were considered. To assess health risks of critical elements in rice, the thresholds of tolerable upper intake level for total food and drinking water (UL) and of permissible maximum concentration (MC) for rice grains were evaluated. Surprisingly, rice grains grown on non- or low-polluted soils can surpass the upper limits. According to the UL concept, 12% of the grains exceeded the UL of As, 29% that of Cd, and 27% that of Pb for each gender. According to the MC concept, 5% of the rice grains exceeded the MC of inorganic As for adults and 38% that for young children. 24% of the grains surpassed the MC of Pb, while Cd in all grains was below the MC. The differing results of the UL and MC approaches show an urgent need for revision and harmonization concerning As, Cd, and Pb limits, especially regarding countries with high rice consumption.

Arsenic in a groundwater environment in Bangladesh: Occurrence and mobilization

Groundwater with an excessive level of Arsenic (As) is a threat to human health. In Bangladesh, out of 64 districts, the groundwater of 50 and 59 districts contains As exceeding the Bangladesh (50 μg/L) and WHO (10 μg/L) standards for potable water. This review focuses on the occurrence, origin, plausible sources, and mobilization mechanisms of As in the groundwater of Bangladesh to better understand its environmental as well as public health consequences. High As concentrations mainly was mainly occur from the natural origin of the Himalayan orogenic tract. Consequently, sedimentary processes transport the As-loaded sediments from the orogenic tract to the marginal foreland of Bangladesh, and under the favorable biogeochemical circumstances, As is discharged from the sediment to the groundwater. Rock weathering, regular floods, volcanic movement, deposition of hydrochemical ore, and leaching of geological formations in the Himalayan range cause As occurrence in the groundwater of Bangladesh. Redox and desorption processes along with microbe-related reduction are the key geochemical processes for As enrichment. Under reducing conditions, both reductive dissolution of Fe-oxides and desorption of As are the root causes of As mobilization. A medium alkaline and reductive environment, resulting from biochemical reactions, is the major factor mobilizing As in groundwater. An elevated pH value along with decoupling of As and HCO₃^- plays a vital role in mobilizing As. The As mobilization process is related to the reductive solution of metal oxides as well as hydroxides that exists in sporadic sediments in Bangladesh. Other mechanisms, such as pyrite oxidation, redox cycling, and competitive ion exchange processes, are also postulated as probable mechanisms of As mobilization. The reductive dissolution of MnOOH adds dissolved As and redox-sensitive components such as SO₄^2- and oxidized pyrite, which act as the major mechanisms to mobilize As. The reductive suspension of Mn(IV)-oxyhydroxides has also accelerated the As mobilization process in the groundwater of Bangladesh. Infiltration from the irrigation return flow and surface-wash water are also potential factors to remobilize As. Over-exploitation of groundwater and the competitive ion exchange process are also responsible for releasing As into the aquifers of Bangladesh.

Unraveling prevalence and public health risks of arsenic, uranium and co-occurring trace metals in groundwater along riverine ecosystem in Sindh and Punjab, Pakistan

The current study focuses on the understanding of contamination status, distribution, source apportionment and health perspectives of arsenic (As), uranium (U) and other co-occurring trace metals in the groundwater samples collected along the major rivers in Sindh and Punjab provinces, Pakistan. ICP-MS analysis revealed that the concentrations of As in the groundwater in Sindh and Punjab ranged from 0.2 to 81.1 µg/L (n = 38) and 1.1 to 501.1 µg/L (n = 110), respectively. Importantly, this study is the first evidence of U contamination in the groundwater samples in Pakistan, which revealed the concentrations of U at from 0.8 to 59.0 and 0.1 to 556.0 µg/L respectively, in Sindh and Punjab. Moreover, the concentrations of Sr and Mn exceeded the WHO limits in the current study area. Anthropogenic activities such as urbanization, direct dispose of industrial, agricultural waste into waterways and extensive use of pesticides and fertilizers might be the main sources of elevated levels of total dissolved solids and electrical conductivity, which increased the mobilization of As, U and Sr in the groundwater samples. Human health risk assessment parameters such as average daily dose, hazard quotient (HQ) and cancer risk indicated severe risks of As and U in the study area. The HQ values of As and U in Punjab were observed at 69.6 and 7.7, respectively, implying the severity of the health risks associated with consumption of contaminated groundwater for drinking purposes. In a nutshell, proactive control and rehabilitation measures are recommended to eradicate trace metals associated groundwater contamination in the targeted areas to avoid future worst scenarios.

High arsenic contamination and presence of other trace metals in drinking water of Kushtia district, Bangladesh

Drinking water with excessive concentration levels of arsenic (As) is a great threat to human health. A hydrochemical approach was employed in 50 drinking water samples (collected from Kushtia district, Bangladesh) to examine the occurrence of geogenic As and the presence of trace metals (TMs), as well as the factors controlling As release in aquifers. The results reveal that the drinking water of shallow aquifers is highly contaminated by As (6.05-590.7 μg/L); 82% of samples were found to exceed the WHO recommended limit (10 μg/L) for potable water, but the concentrations of Si, B, Mn, Sr, Se, Ba, Fe, Cd, Pb, F, U, Ni, Li, and Cr were within safe limits. The Ca-HCO₃-type drinking water was identified as having high contents of As, pH and HCO₃^-, a medium-high content EC, and low concentrations of NO₃^-, SO₄^2-, K⁺, and Cl^-. The significant correlation between As and NO₃^- indicates that NO₃^- might be attributed to the use of phosphate fertilizers and a factor responsible for enhancing As in aquifers. The study also reports that the occurrence of high As and the presence of TMs in drinking water may be a result of local anthropogenic activities, such as irrigation, intensive land use and the application of agrochemicals. The insignificant correlation between As and SO₄^2- demonstrated that As is released from SO₄^2- minerals under reducing conditions. An elevated pH value along with decoupling of As and HCO₃^- plays a vital role in mobilizing As to aquifer systems. Moreover, the positive relationship between As and Si indicated that As is transported in the biogeochemical environment. The reductive suspension of Mn(IV)-oxyhydroxides also accelerated the As mobilization process. Over exploitation of tube-well water and the competitive ion exchange process are also responsible for the release of As in aquifers.

Elucidating various geochemical mechanisms drive fluoride contamination in unconfined aquifers along the major rivers in Sindh and Punjab, Pakistan

The present study aims to investigate the spatial distribution and associated various geochemical mechanisms responsible for fluoride (F⁻) contamination in groundwater of unconfined aquifer system along major rivers in Sindh and Punjab, Pakistan. The concentration of F⁻ in groundwater samples ranged from 0.1 to 3.9 mg/L (mean = 1.0 mg/L) in Sindh and 0.1-10.3 mg/L (mean = 1.0 mg/L) in Punjab, respectively with 28.9% and 26.6% of samples exhibited F⁻ contamination beyond WHO permissible limit value (1.5 mg/L). The geochemical processes regulated F⁻ concentration in unconfined aquifer mainly in Sindh and Punjab were categorized as follows: 1) minerals weathering that observed as the key process to control groundwater chemistry in the study areas, 2) the strong correlation between F⁻ and alkaline pH, which provided favorable environmental conditions to promote F⁻ leaching through desperation or by ion exchange process, 3) the 72.6% of samples from Sindh and Punjab were dominated by Na⁺- Cl⁻ type of water, confirmed that the halite dissolution process was the major contributor for F⁻ enrichment in groundwater, 4) dolomite dissolution was main process frequently observed in Sindh, compared with Punjab, 5) the arid climatic conditions promote evaporation process or dissolution of evaporites or both were contributing to the formation of saline groundwater in the study area, 6) the positive correlation observed between elevated F⁻ and fluorite also suggested that the fluorite dissolution also played significant role for leaching of F⁻ in groundwater from sediments, and 7) calcite controlled Ca²⁺ level and enhanced the dissolution of F-bearing minerals and drive F⁻ concentration in groundwater. In a nut shell, this study revealed the worst scenarios of F⁻ contamination via various possible geochemical mechanisms in groundwater along major rivers in Sindh and Punjab, Pakistan, which need immediate attention of regulatory authorities to avoid future hazardous implications.

Assessment of water quality and trace metal contaminations in Mondolkiri province in the Northeastern part of Cambodia

The aim of the present study is to investigate water quality and potential trace metal contaminations in the Northeastern part of Cambodia. Tube well (n = 35), hand-dug well (n = 18), channel (n = 10) and lake/pond (n = 8) water samples were randomly collected from Mondolkiri province which is located in the Northeastern highland of Cambodia. A water sample was collected in two different bottles. One was filled in 30-mL polyethylene bottle after which was acidified to pH < 2 with concentrated HNO₃. Another was filled in 250-mL polyethylene bottle. The collected water sampled was stored in a cooler during fieldwork and transferred to a fridge where they are stored at 4 °C for analysis. The measurement of pH, ORP, dissolved oxygen (DO), turbidity, conductivity, total dissolved solids (TDS) and salinity was taken at laboratory following standard procedures. All chemical measurement of trace metals were taken by inductively coupled plasma mass spectrometry (ICP-MS). Analytical results reveal that tube well (47.1%), hand-dug well (77.8%) and channel water (20%) have pH < 6.5. Turbidity of tube well (32.4%), hand-dug well (5.6%), lake water (12.5%) and all channel water samples are exceeded Cambodia regulation of 5 NTU. Mean As, Cd, Cr, Cu, Ni, Pb and Zn concentrations in Mondolkiri's water sources are below Cambodian drinking water quality standard and WHO's drinking water quality guideline. However, the upper range of Pb in tube well and channel water and Zn in tube well are exceeding Cambodia regulation. Concurrently, the mean concentrations of Fe and Mn in tube well and channel water are exceeded Cambodian aesthetic guideline of 300 µg L^-1 and 100 µg L^-1, respectively. This study suggests that appropriate treatment technologies are necessary for residents in the Mondolkiri province to access to clean water and minimize their potential health risks.

Health risk assessment of arsenic and other potentially toxic elements in drinking water from an industrial zone of Gujrat, Pakistan: a case study

Present study aimed to provide a baseline data on arsenic (As) and other potentially toxic element (PTEs; Cd, Cr, Cu, Ni, and Pb) contamination in groundwater and soils (surface and sub-surface) from an industrial area of district Gujrat, Pakistan. Statistical parameters, principal component analysis-multiple linear regression (PCA-MLR), and health risk assessment model were used to elaborate the interrelations, source contributor, and associated health risks. This study revealed that the concentrations of Cd, Cr, Cu, and Pb in drinking water were within the permissible limits of the World Health Organization (WHO). However, As and Ni concentrations exceeded the WHO limits of 10 μg/L for As and 0.07 mg/L for Ni. In soils, the concentration of Cr was within permissible limits, whereas As, Cd, Cu, Ni, and Pb exceeded the prescribed values. Solid waste and industrial effluents from the area also contained high levels of As, Cd, Cr, Cu, Ni, and Pb. Calculated health index of As and other PTEs for industrial site and control area was less than 1 which indicated that the groundwater was assumed to be safe for drinking. High contamination of As (15 mg/kg) and other PTEs (Pb was 978, Cr 51, Cu 111, Cd 68, and Ni was 90 mg/kg, respectively) in upper soil could be due to the discharge of industrial effluent prior to the treatment, which signifies the industrial contribution towards As and heavy metal contamination. It can be concluded that critical examination of soil profile affinity to the respective, industrial waste pollutants can reduce the health risks to the local community. This trend not only reveals the geochemistry of the area but also useful for developing a link to access health risk and associated remediation processes.

Enhanced adsorption of arsenate and antimonate by calcined Mg/Al layered double hydroxide: Investigation of comparative adsorption mechanism by surface characterization

This study aims to investigate adsorption mechanisms of As(V) and Sb(V) on calcined Mg/Al layered double hydroxide (LDH). The calcination process of Mg/Al LDH (CLDH) considerably enhanced the adsorption capacity of As(V) and Sb(V) via reconstruction and new formation of brandholzite-like compound, respectively. The maximum adsorption capacity for As(V) and Sb(V) by CLDH was 102.9 mg/g and 303.3 mg/g, respectively. The regeneration efficiency of As(V) by 0.5 M NaOH with 5 M NaCl mixed solution reached 72.3% during five regeneration cycles, while Sb(V) regeneration gradually decreased to 32.0% at the fifth regeneration cycles due to the irreversible surface complexation mechanism. Extended X-ray absorption fine structure (EXAFS) data displayed that Al plays a dominant role in the adsorption of As(V) on CLDH through bidentate-binuclear inner-sphere complex. On the other hand, XRD and EXAFS data revealed that Sb(V) formed a brandholzite-like structure Mg[Sb(OH)₆]₂·6H₂O which forms outer-sphere complex by the hydrogen bonding between hexagonal plates of magnesium and antimony hydroxide. Although the formation of brandholzite-like structure causes the partial transformation of original structure of Mg/Al LDH during reconstruction process with decreasing regeneration efficiency, it could be attributed to high binding affinity between Sb(V) and Mg/Al LDH.

Controls of paleochannels on groundwater arsenic distribution in shallow aquifers of alluvial plain in the Hetao Basin, China

Less is known about controls of sedimentary structures in groundwater As distributions in sedimentary aquifers, and quantitative description of relationship between sedimentary environment and high As groundwater (according to WHO, As>10μg/L) is a challenging issue. Three hundred and eighty-two hydrogeological borehole loggings (well depths of 50-300m) were collected and four hundred and ninety nine groundwater samples were taken to investigate controls of paleochannels on groundwater arsenic distribution in shallow aquifers of alluvial plain in the Hetao Basin. Results showed that the swing zone, formed by bursting, diversion and swing of ancient Yellow River course since the Late Pleistocene, has an obviously corresponding relationship with spatial variability of groundwater As in the Hetao Basin. "Swing Intensity Index" (S), which is firstly defined as the sum of clay-sand ratio (R) and the number of clay layers (N), can be used as the sedimentary facies symbol to establish the new recognition method for hosting high As groundwater. There is a positive correlation between the swing intensity index (S) of paleochannels and groundwater As concentrations. The swing zones of paleochannels with high S values represent hydrogeochemical characteristics of the strong reducing environment, serious evaporation, strong cation exchange, and the low infiltration recharge of surface water, which lead to enrichment of groundwater As in the shallow aquifers.

Bayesian modeling approach for characterizing groundwater arsenic contamination in the Mekong River basin

In the Mekong River basin, groundwater from tube-wells is a major drinking water source. However, arsenic (As) contamination in groundwater resources has become a critical issue in the watershed. In this study, As species such as total As (AsTOT), As(III), and As(V), were monitored across the watershed to investigate their characteristics and inter-relationships with water quality parameters, including pH and redox potential (Eh). The data illustrated a dramatic change in the relationship between AsTOT and Eh over a specific Eh range, suggesting the importance of Eh in predicting AsTOT. Thus, a Bayesian change-point model was developed to predict AsTOT concentrations based on Eh and pH, to determine changes in the AsTOT-Eh relationship. The model captured the Eh change-point (∼-100±15mV), which was compatible with the data. Importantly, the inclusion of this change-point in the model resulted in improved model fit and prediction accuracy; AsTOT concentrations were strongly negatively related to Eh values higher than the change-point. The process underlying this relationship was subsequently posited to be the reductive dissolution of mineral oxides and As release. Overall, AsTOT showed a weak positive relationship with Eh at a lower range, similar to those commonly observed in the Mekong River basin delta. It is expected that these results would serve as a guide for establishing public health strategies in the Mekong River Basin.

Enhanced Arsenate Removal Performance in Aqueous Solution by Yttrium-Based Adsorbents

Arsenic contamination in drinking water has become an increasingly important issue due to its high toxicity to humans. The present study focuses on the development of the yttrium-based adsorbents, with basic yttrium carbonate (BYC), Ti-loaded basic yttrium carbonate (Ti-loaded BYC) and yttrium hydroxide prepared using a co-precipitation method. The Langmuir isotherm results confirmed the maximum adsorption capacity of Ti-loaded BYC (348.5 mg/g) was 25% higher than either BYC (289.6 mg/g) or yttrium hydroxide (206.5 mg/g) due to its increased specific surface area (82 m²/g) and surface charge (PZC: 8.4). Pseudo first- and second-order kinetic models further confirmed that the arsenate removal rate of Ti-loaded BYC was faster than for BYC and yttrium hydroxide. It was subsequently posited that the dominant removal mechanism of BYC and Ti-loaded BYC was the carbonate-arsenate ion exchange process, whereas yttrium hydroxide was regarded to be a co-precipitation process. The Ti-loaded BYC also displayed the highest adsorption affinity for a wide pH range (3-11) and in the presence of coexisting anionic species such as phosphate, silicate, and bicarbonate. Therefore, it is expected that Ti-loaded BYC can be used as an effective and practical adsorbent for arsenate remediation in drinking water.

Multiple inorganic toxic substances contaminating the groundwater of Myingyan Township, Myanmar: arsenic, manganese, fluoride, iron, and uranium

In South Asia, the technological and societal shift from drinking surface water to groundwater has resulted in a great reduction of acute diseases due to water borne pathogens. However, arsenic and other naturally occurring inorganic toxic substances present in groundwater in the region have been linked to a variety of chronic diseases, including cancers, heart disease, and neurological problems. Due to the highly specific symptoms of chronic arsenic poisoning, arsenic was the first inorganic toxic substance to be noticed at unsafe levels in the groundwater of West Bengal, India and Bangladesh. Subsequently, other inorganic toxic substances, including manganese, uranium, and fluoride have been found at unsafe levels in groundwater in South Asia. While numerous drinking water wells throughout Myanmar have been tested for arsenic, relatively little is known about the concentrations of other inorganic toxic substances in Myanmar groundwater. In this study, we analyzed samples from 18 drinking water wells (12 in Myingyan City and 6 in nearby Tha Pyay Thar Village) and 2 locations in the Ayeyarwaddy River for arsenic, boron, barium, beryllium, cadmium, cobalt, chromium, copper, fluoride, iron, mercury, manganese, molybdenum, nickel, lead, antimony, selenium, thallium, uranium, vanadium, and zinc. Concentrations of arsenic, manganese, fluoride, iron, or uranium exceeded health-based reference values in most wells. In addition, any given well usually contained more than one toxic substance at unsafe concentrations. While water testing and well sharing could reduce health risks, none of the wells sampled provide water that is entirely safe with respect to inorganic toxic substances. It is imperative that users of these wells, and users of other wells that have not been tested for multiple inorganic toxic substances throughout the region, be informed of the need for drinking water testing and the health consequences of drinking water contaminated with inorganic toxic substances.

Human health risk assessment for ingestion exposure to groundwater contaminated by naturally occurring mixtures of toxic heavy metals in the Lao PDR

This study constitutes the first systematic risk assessment in the Lao PDR of the safety of groundwater for consumption. Groundwater and hair samples were collected from seven Lao provinces to determine the quantitative health impact of heavy metals through ingestion exposure. Contamination levels for arsenic (As; 46.0 %) and barium (Ba; 16.2 %) exceeded World Health Organization (WHO) guidelines, especially in Mekong River floodplains. A USEPA assessment model for health risks from daily groundwater ingestion, with adjustments for local water consumption values, was applied to estimate the size of the population at risk for noncarcinogenic and carcinogenic health problems. As was the only element contributing to noncarcinogenic health risks in all contaminated areas. The populations of Bolikhamxai, Savannakhet, Saravane, Champasak, and Attapeu, moreover, were at risks of cancer. In addition to the As groundwater concentration factor, noncarcinogenic and carcinogenic risks were positively correlated with the average daily dose of As, exposure duration, and subject body weight. The level of As in hair correlated with groundwater consumption and average daily dose of As. 25.5 % of the population (n = 228) showed As levels in hair above the toxicity level.

Review of remediation techniques for arsenic (As) contamination: a novel approach utilizing bio-organisms

Arsenic (As) contamination has recently become a worldwide problem, as it is found to be widespread not only in drinking water but also in various foodstuffs. Because of the high toxicity, As contamination poses a serious risk to human health and ecological system. To cope with this problem, a great deal of effort have been made to account for the mechanisms of As mineral formation and accumulation by some plants and aquatic organisms exposed to the high level of As. Hence, bio-remediation is now considered an effective and potent approach to breakdown As contamination. In this review, we provide up-to-date knowledge on how biological tools (such as plants for phytoremediation and to some extent microorganisms) can be used to help resolve the effects of As problems on the Earth's environment.

Assessing arsenic intake from groundwater and rice by residents in Prey Veng province, Cambodia

We investigated total daily intake of As by residents in Prey Veng province in the Mekong River basin of Cambodia. Groundwater (n = 11), rice (n = 11) and fingernail (n = 23) samples were randomly collected from the households and analyzed for total As by inductively coupled plasma mass spectrometry. Calculation indicated that daily dose of inorganic As was greater than the lower limits on the benchmark dose for a 0.5% increased incidence of lung cancer (BMDL0.5 equals to 3.0 μg d(-1) kg(-1)body wt.). Moreover, positive correlation between As in fingernail and daily dose of As from groundwater and rice and total daily dose of As were found. These results suggest that the Prey Veng residents are exposed to As in groundwater. As in rice is an additional source which is attributable to high As accumulation in human bodies in the Mekong River basin of Cambodia.

Arsenic contamination in the food chain and its risk assessment of populations residing in the Mekong River basin of Cambodia

In the present study, we investigated the potential arsenic exposure of Cambodian residents from their daily food consumption. Environmental and ecological samples such as paddy soils, paddy rice (unhusked), staple rice (uncooked and cooked), fish and vegetables were collected from Kandal, Kratie and Kampong Cham provinces in the Mekong River basin of Cambodia. After acid-digestion, digestates were chemically analyzed by inductively coupled plasma mass spectrometry. Results revealed that the means of total arsenic concentration ([As]tot) in paddy soils and paddy rice from Kandal were significantly higher than those from Kampong Cham province (t-test, p<0.05). Moreover, a significant positive correlation between the [As]tot in paddy soils and paddy rice was found (r(14) = 0.826, p<0.01). Calculations of arsenic intake from food consumption indicated that the upper end of the range of the daily dose of inorganic arsenic for Kandal residents (0.089-8.386 μg d(-1) kg(-1) body wt.) was greater than the lower limits on the benchmark dose for a 0.5% increased incidence of lung cancer (BMDL0.5 is equal to 3.0 μg d(-1) kg(-1) body wt.). The present study suggests that the residents in Kandal are at risk of arsenic intake from their daily food consumption. However, the residents in Kratie and Kampong Cham provinces are less likely to be exposed to arsenic through their daily dietary intake. To the best of our knowledge, this is the first report estimating the daily intake and daily dose of inorganic arsenic from food consumption in the Mekong River basin of Cambodia.

Assessing mixed trace elements in groundwater and their health risk of residents living in the Mekong River basin of Cambodia

We investigated the potential contamination of trace elements in shallow Cambodian groundwater. Groundwater and hair samples were collected from three provinces in the Mekong River basin of Cambodia and analyzed by ICP-MS. Groundwater from Kandal (n = 46) and Kraite (n = 12) were enriched in As, Mn, Ba and Fe whereas none of tube wells in Kampong Cham (n = 18) had trace elements higher than Cambodian permissible limits. Risk computations indicated that 98.7% and 12.4% of residents in the study areas of Kandal (n = 297) and Kratie (n = 89) were at risk of non-carcinogenic effects from exposure to multiple elements, yet none were at risk in Kampong Cham (n = 184). Arsenic contributed 99.5%, 60.3% and 84.2% of the aggregate risk in Kandal, Kratie and Kampong Cham, respectively. Sustainable and appropriate treatment technologies must therefore be implemented in order for Cambodian groundwater to be used as potable water.

World Health Organization discontinues its drinking-water guideline for manganese

BACKGROUND

The World Health Organization (WHO) released the fourth edition of Guidelines for Drinking-Water Quality in July 2011. In this edition, the 400-µg/L drinking-water guideline for manganese (Mn) was discontinued with the assertion that because "this health-based value is well above concentrations of manganese normally found in drinking water, it is not considered necessary to derive a formal guideline value."

OBJECTIVE

In this commentary, we review the WHO guideline for Mn in drinking water--from its introduction in 1958 through its discontinuation in 2011.

METHODS

For the primary references, we used the WHO publications that documented the Mn guidelines. We used peer-reviewed journal articles, government reports, published conference proceedings, and theses to identify countries with drinking water or potential drinking-water supplies exceeding 400 µg/L Mn and peer-reviewed journal articles to summarize the health effects of Mn.

DISCUSSION

Drinking water or potential drinking-water supplies with Mn concentrations > 400 µg/L are found in a substantial number of countries worldwide. The drinking water of many tens of millions of people has Mn concentrations > 400 µg/L. Recent research on the health effects of Mn suggests that the earlier WHO guideline of 400 µg/L may have been too high to adequately protect public health.

CONCLUSIONS

The toxic effects and geographic distribution of Mn in drinking-water supplies justify a reevaluation by the WHO of its decision to discontinue its drinking-water guideline for Mn.

Arsenic geochemistry of groundwater in Southeast Asia

The occurrence of high concentrations of arsenic in the groundwater of the Southeast Asia region has received much attention in the past decade. This study presents an overview of the arsenic contamination problems in Vietnam, Cambodia, Lao People's Democratic Republic and Thailand. Most groundwater used as a source of drinking water in rural areas has been found to be contaminated with arsenic exceeding the WHO drinking water guideline of 10 μg·L(-1). With the exception of Thailand, groundwater was found to be contaminated with naturally occurring arsenic in the region. Interestingly, high arsenic concentrations (> 10 μg·L(-1)) were generally found in the floodplain areas located along the Mekong River. The source of elevated arsenic concentrations in groundwater is thought to be the release of arsenic from river sediments under highly reducing conditions. In Thailand, arsenic has never been found naturally in groundwater, but originates from tin mining activities. More than 10 million residents in Southeast Asia are estimated to be at risk from consuming arsenic-contaminated groundwater. In Southeast 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 has been observed in Cambodia and Vietnam. A substantial knowledge gap exists between the epidemiology of arsenicosis and its impact on human health. More collaborative studies particularly on the scope of public health and its epidemiology are needed to conduct to fulfill the knowledge gaps of As as well as to enhance the operational responses to As issue in Southeast Asian countries.

Prediction of contamination potential of groundwater arsenic in Cambodia, Laos, and Thailand using artificial neural network

The arsenic (As) contamination of groundwater has increasingly been recognized as a major global issue of concern. As groundwater resources are one of most important freshwater sources for water supplies in Southeast Asian countries, it is important to investigate the spatial distribution of As contamination and evaluate the health risk of As for these countries. The detection of As contamination in groundwater resources, however, can create a substantial labor and cost burden for Southeast Asian countries. Therefore, modeling approaches for As concentration using conventional on-site measurement data can be an alternative to quantify the As contamination. The objective of this study is to evaluate the predictive performance of four different models; specifically, multiple linear regression (MLR), principal component regression (PCR), artificial neural network (ANN), and the combination of principal components and an artificial neural network (PC-ANN) in the prediction of As concentration, and to provide assessment tools for Southeast Asian countries including Cambodia, Laos, and Thailand. The modeling results show that the prediction accuracy of PC-ANN (Nash-Sutcliffe model efficiency coefficients: 0.98 (traning step) and 0.71 (validation step)) is superior among the four different models. This finding can be explained by the fact that the PC-ANN not only solves the problem of collinearity of input variables, but also reflects the presence of high variability in observed As concentrations. We expect that the model developed in this work can be used to predict As concentrations using conventional water quality data obtained from on-site measurements, and can further provide reliable and predictive information for public health management policies.

Barium promotes anchorage-independent growth and invasion of human HaCaT keratinocytes via activation of c-SRC kinase

Explosive increases in skin cancers have been reported in more than 36 million patients with arsenicosis caused by drinking arsenic-polluted well water. This study and previous studies showed high levels of barium as well as arsenic in the well water. However, there have been no reports showing a correlation between barium and cancer. In this study, we examined whether barium (BaCl₂) may independently have cancer-related effects on human precancerous keratinocytes (HaCaT). Barium (5–50 µM) biologically promoted anchorage-independent growth and invasion of HaCaT cells in vitro. Barium (5 µM) biochemically enhanced activities of c-SRC, FAK, ERK and MT1-MMP molecules, which regulate anchorage-independent growth and/or invasion. A SRC kinase specific inhibitor, protein phosphatase 2 (PP2), blocked barium-mediated promotion of anchorage-independent growth and invasion with decreased c-SRC kinase activity. Barium (2.5–5 µM) also promoted anchorage-independent growth and invasion of fibroblasts (NIH3T3) and immortalized nontumorigenic melanocytes (melan-a), but not transformed cutaneous squamous cell carcinoma (HSC5 and A431) and malignant melanoma (Mel-ret) cells, with activation of c-SRC kinase. Taken together, our biological and biochemical findings newly suggest that the levels of barium shown in drinking well water independently has the cancer-promoting effects on precancerous keratinocytes, fibroblast and melanocytes in vitro.