WHO Provisional Guideline Value Research Articles

Determination of a guidance value for the communication of individual-level biomonitoring data for urinary arsenic.

Available guidance values to interpret individual-level biomonitoring data (ILBD) for the sum of urinary inorganic-related arsenic species (SUIAS) are generally based on population statistical descriptors and not on a predetermined exposure level that should not be exceeded. The objective of this study was thus to propose a range of SUIAS concentrations, reflecting an exposure corresponding to WHO's provisional guideline value (PGV) for arsenic in drinking water (10μg/L), within which an exposure-based biomonitoring guidance value can be identified. METHOD A comprehensive literature review was carried out in order to identify studies that were relevant to the determination of a guidance value. Drinking water arsenic exposure and urinary biomonitoring concentrations obtained from selected studies were used to conduct a structural equation modeling meta-analysis, from which regression coefficients were obtained to derive an interpretative guidance range. RESULTS Individuals exposed to the arsenic background level comparable to North American and European countries and to a water source contaminated at the WHO's PGV, would have, on average, urinary SUIAS between 9 and 20μg/L, with the most probable value being 15μg/L. To address the associated uncertainty, the final guidance value selection within this range may be based on a targeted sensitivity and specificity towards detecting overexposed individuals. Indeed, spans of sensitivity of 60-82%, and of specificity of 58-85%, were estimated for the proposed range based on drinking water exposure raw data from the literature. CONCLUSION The range of guidance values obtained appears suitable for interpreting and communicating ILBD in any population biomonitoring studies in which background exposure is comparable to the North American and European context. Before selecting a single value within the proposed range, it will be important for Public Health officials to assess the possible consequences of this selection on the management and communication of the biomonitoring results.

Efficiency of Arsenic and Iron Removal Plants (AIRPs) for Groundwater Treatment in Rural Areas of Southwest Bangladesh

Arsenic (As) removal plants were installed in As-endemic areas of Bangladesh to remove As from well water. In many cases, these removal plants did not perform satisfactorily. This study evaluated the efficiency of 20 As and iron (Fe) removal plants (AIRPs) during pre- and post-monsoon conditions in rural Bangladesh. Results revealed that As removal efficiencies ranged from 67% to 98% and 74 to 93% during the pre- and post-monsoons periods, respectively. In the post-monsoon season As removal at individual AIRP sites was on average (4.01%) greater than in the pre-monsoon season. However, two removal plants were unable to remove As below 50 µg L−1 (Bangladesh drinking water standard) during pre-monsoon, while 11 samples out of 20 were unable to remove As below the WHO provisional guideline value of 10 µg L−1. During post-monsoon, none of the samples exceeded 50 µg L−1, but eight of them exceeded 10 µg L−1. The Fe removal efficiencies of AIRPs were evident in more than 80% samples. Although As removal efficiency was found to be substantial, a cancer risk assessment indicates that hazard quotient (HQ) and carcinogenic risk (CR) of As in treated water for adults and children are above the threshold limits. Thus, additional reductions of As concentrations in treated water are needed to further reduce the excess cancer risk due to As in drinking water. Since 55% and 40% of the AIRPs were unable to remove As < 10 µg L−1 during pre-monsoon and post-monsoon, further improvement including changes in AIRP design, regular cleaning of sludge, and periodic monitoring of water quality are suggested. Future research is needed to determine whether these modifications improve the performance of AIRPs.

Risk assessment of uranium in drinking water in Hisar district of Haryana, India

Abstract The present study highlights uranium concentrations, associated health risks and physico-chemical properties of groundwater samples collected from the Hisar district of Haryana State, India. We found that uranium concentrations in 21 out of 68 (30.9%) samples exceeded the WHO provisional guideline value of 30 μg L−1. The annual effective doses were estimated for different life stage groups. The highest dose was calculated for infants. From a radiological perspective, the mean cancer mortality risk and cancer morbidity risk were found to be 4.7 × 10−5 and 7.3 × 10−5, respectively, which are lower than the permissible limit of 1.67 × 10−4 as prescribed by the Atomic Energy Regulatory Board, India. The lifetime average daily dose (LADD) of uranium ranged from 0.03 to 7.83 μg kg−1 day−1. Approximately 23.5% of the samples showed significant chemical toxicity risk. A positive correlation between uranium and total dissolved solids (TDS) was observed.

Machine Learning Models of Groundwater Arsenic Spatial Distribution in Bangladesh: Influence of Holocene Sediment Depositional History.

Recent advances in machine learning methods offer the opportunity to improve risk assessment and to decipher factors influencing the spatial variability of groundwater arsenic ([As]gw). A systematic comparison reveals that boosted regression trees (BRT) and random forest (RF) outperform logistic regression. The probability of [As]gw exceeding 5 μg/L (approximate median value of Bangladesh [As]gw), 10 μg/L (WHO provisional guideline value), and 50 μg/L (Bangladesh drinking water standard) is modeled by BRT and RF methods for Bangladesh and its four subregions demarcated by major rivers. Of the 109 geo-environmental and hydrochemical predictor variables, phosphorus and iron emerge as the most important across spatial scales, consistent with known As mobilization mechanisms. Well depth is significant only when hydrochemical parameters are not considered, consistent with prior studies. A peak of probability of [As]gw exceedance at ∼30 m depth is evident in the partial dependence plots (PDPs) for spatial-parameter-only models but not in the equivalent all-parameter models, suggesting that sediment depositional history explains interdependent spatial patterns of groundwater As-P-Fe in Holocene aquifers. The South region exhibits a decrease of probability of [As]gw exceedance below 150 m depth in PDPs for spatial-parameter-only and all-parameter models, supporting that the deeper Pleistocene aquifer is a low-As water resource.

Positive Association of Cardiovascular Disease (CVD) with Chronic Exposure to Drinking Water Arsenic (As) at Concentrations below the WHO Provisional Guideline Value: A Systematic Review and Meta-Analysis.

To the best of our knowledge, a dose-response meta-analysis of the relationship between cardiovascular disease (CVD) and arsenic (As) exposure at drinking water As concentrations lower than the WHO provisional guideline value (10 µg/L) has not been published yet. We conducted a systematic review and meta-analyses to estimate the pooled association between the relative risk of each CVD endpoint and low-level As concentration in drinking water both linearly and non-linearly using a random effects dose-response model. In this study, a significant positive association was found between the risks of most CVD outcomes and drinking water As concentration for both linear and non-linear models (p-value for trend < 0.05). Using the preferred linear model, we found significant increased risks of coronary heart disease (CHD) mortality and CVD mortality as well as combined fatal and non-fatal CHD, CVD, carotid atherosclerosis disease and hypertension in those exposed to drinking water with an As concentration of 10 µg/L compared to the referent (drinking water As concentration of 1 µg/L) population. Notwithstanding limitations included, the observed significant increased risks of CVD endpoints arising from As concentrations in drinking water between 1 µg/L and the 10 µg/L suggests further lowering of this guideline value should be considered.

Factors controlling arsenic and selected potentially toxic elements in stream sediment–soil and groundwater–surface water systems of a hydrologically modified semi-closed basin (Uluova) in Elazığ Province, Eastern Turkey

The Uluova basin aquifer system (UBAS), comprised of fractured/karstic rock and multilayer basin-fill aquifers, provides water for both domestic and agricultural needs in the Elazığ province (Eastern Turkey). Although, the UBAS has been subject of large-scale hydrological modifications and controversial water management practices since late 1950s, thus far no studies have examined basinwide implications of such human perturbations in an integrated manner. In this study, GIS, geostatistics, R-mode factor analysis (R-mFA) and geochemical modeling techniques were employed to unravel the factors controlling the distribution and sources of arsenic (As) and selected potentially toxic elements (PTEs) in the stream sediment-soil and groundwater-surface water systems of the UBAS. As revealed by the results from R-mFA, three geogenic factors (F1: Clay minerals and Fe–Mn oxyhydroxides, F2: Weathering of parent materials, and F3: Sulfide oxidation in mineralized zones) govern the geochemical dynamics of the PTEs in the stream sediment/soil media. In stream sediment and soil samples, especially Ni, Cr, and Co presented significant enrichment relative to upper continental crust average composition, whereas As contents were relatively low, varying from 0.3 to 13 mg kg−1. Factors extracted from the combined water dataset (F1: Groundwater salinization and arsenic mobilization, F2: Clay minerals and Fe–Mn oxyhydroxides, F3: pH and redox conditions, and F4: Aquifer oxygenation and nitrate contamination) accounted for 72.59% of the total variance. Water-rock interaction (e.g. sulfide oxidation, carbonate dissolution, silicate hydrolysis, adsorption-desorption, ion exchange, and evaporite dissolution), dilution/mixing with fresh/saline water components, evapoconcentration, and human induced perturbations causing internal salinization and oxygenation of the UBAS were the key mechanisms controlling the chemistry of waters and mobilization of As. In the UBAS, majority of As-rich water samples are confined to central-northern half of the basin and typically display high levels of dissolved O2, inorganic oxyanions (HCO3−, SO42− and of Si, B, Mo, Sb and V) and alkaline pH. Oxidation of sulfides (e.g. pyrite and arsenopyrite) found within the highly fractured Elazığ magmatics in the upland areas at north and subsequent competitive adsorption-desorption processes occurring under alkaline, oxidizing and high ionic strength aquifer conditions along the downgradient groundwater flow path play a pivotal role in the As-enrichment in the UBAS. As concentrations ranged between 0.02 and 367.2 μg L−1 in groundwater, 0.13–4842 μg L−1 in spring water, and 0.04–31.1 μg L−1 in the stream water samples, of which 20.83% exceeded the WHO provisional guideline value. In the water samples, As occurs mainly as As(V) species (HAsO42− and H2AsO4−), indicated by the Eh-pH diagram and speciation calculations. The results of this study have shown that As enrichment in the UBAS can be attributed to both geogenic processes and anthropogenic activities that have modified the basin hydrology/hydrochemistry.

Human exposure assessment of different arsenic species in household water sources in a high risk arsenic area.

Understanding arsenic speciation in water is important for managing the potential health risks associated with chronic arsenic exposure. Most arsenic monitoring studies to date have only measured total arsenic, with few looking at arsenic species. This study assessed 228 ground water sources in six unstudied villages in Pakistan for total, inorganic and organic arsenic species using ion chromatography inductively coupled plasma collision reaction cell mass spectrometry. The concentration levels approached 3090μgL-1 (95% CI, 130.31, 253.06) for total arsenic with a median of 57.55μgL-1, 3430μgL-1 (median=52) for arsenate (As+5) and 100μgL-1 (median=0.37) for arsenite (As+3). Exceedance of the WHO provisional guideline value for arsenic in drinking water (10μgL-1) occurred in 89% of water sources. Arsenic was present mainly as arsenate (As+5). Average daily intake of total arsenic for 398 residents living in the sampled houses was found up to 236.51μgkg-1day-1. This exposure estimate has indicated that 63% of rural residents exceeded the World Health Organization's provisional tolerable daily intake (PTDI) of 2.1μgkg-1day-1 body weight. Average daily intake of As+5 was found to be 15.63μgkg-1day-1 (95% CI, 5.53, 25.73) for children ≤16 and 15.07μgkg-1day-1 (95% CI, 10.33, 18.02) for adults. A mean daily intake of 0.09μgkg-1day-1 was determined for As+3 for children and 0.26μgkg-1day-1 for adults. Organic arsenic species such as monomethylarsonic acid (MMA), dimethylarsinic acid (DMA) and Arsenobetaine (AsB) were found to be below their method detection limits (MDLs).

Occurrence of cyanobacteria and microcystin toxins in raw and treated waters of the Nile River, Egypt: implication for water treatment and human health.

Monitoring of cyanobacteria and their associated toxins has intensified in raw water sources of drinking water treatment plants (WTPs) in most countries of the world. However, it is not explored yet for Egyptian WTPs. Therefore, this study was undertaken to investigate the occurrence of cyanobacteria and their microcystin (MC) toxins in the Nile River source water of Damietta WTP during warm months (April-September 2013) and to evaluate the removal efficiency of both cyanobacterial cells and MCs by conventional methods used in this plant as a representative of Egyptian drinking WTPs. The results showed that the source water at the intake of Damietta WTP contained dense cyanobacterial population (1.1-6.6 × 107 cells L(-1)) dominated by Microcystis aeruginosa. This bloom was found to produce MC-RR and MC-LR. Both cyanobacterial cell density and intracellular MCs in the intake source water increased with the increase in temperature and nutrients during the study period, with maximum values obtained in August. During treatment processes, cyanobacterial cells were incompletely removed by coagulation/flocculation/sedimentation (C/F/S; 91-96.8%) or sand filtration (93.3-98.9%). Coagulation/flocculation induced the release of MCs into the ambient water, and the toxins were not completely removed or degraded during further treatment stages (filtration and chlorination). MCs in outflow tank water were detected in high concentrations (1.1-3.6 μg L - 1), exceeding WHO provisional guideline value of 1 μg L - 1 for MC-LR in drinking water. Based on this study, regular monitoring of cyanobacteria and their cyanotoxins in the intake source water and at different stages at all WTPs is necessary to provide safe drinking water to consumers or to prevent exposure of consumers to hazardous cyanobacterial metabolites.

Occurrence of uranium in Swiss drinking water

The results of a nationwide survey of uranium in Swiss drinking water are reported. Elevated concentrations of uranium in groundwater are found mainly in the alpine regions and can be traced back to the geology of the bedrock. Water sources were systematically surveyed and analysed for the presence of Li, B, Si, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Cd, Sn, Sb, Ba, Tl, Pb and U and the results were analysed to determine if any correlation with uranium concentration was apparent. No correlation was found. The results are interpreted in relation to the current WHO guideline and those of other countries with a view to determining which areas would be affected if a maximum value were to be adopted and which areas require further investigation. Uranium content varied considerably, from below the limit of detection to almost 100 μg L −1. Of the 5548 data samples, 98% are below the 2004 WHO provisional guideline value of 15 μg L −1 and 99.7% below the revised (2011) value of 30 μg L −1.

Arsenic in drinking water wells on the Bolivian high plain: Field monitoring and effect of salinity on removal efficiency of iron-oxides-containing filters

In the rural areas around Oruro (Bolivia), untreated groundwater is used directly as drinking water. This research aimed to evaluate the general drinking water quality, with focus on arsenic (As) concentrations, based on analysis of 67 samples from about 16 communities of the Oruro district. Subsequently a filter using Iron Oxide Coated Sand (IOCS) and a filter using a Composite Iron Matrix (CIM) were tested for their arsenic removal capacity using synthetic water mimicking real groundwater. Heavy metal concentrations in the sampled drinking water barely exceeded WHO guidelines. Arsenic concentrations reached values up to 964 μ g L−1 and exceeded the current WHO provisional guideline value of 10 μ g L−1 in more than 50% of the sampled wells. The WHO guideline of 250 mg L−1 for chloride and sulphate was also exceeded in more than a third of the samples, indicating high salinity in the drinking waters. Synthetic drinking water could be treated effectively by the IOCS- and CIM-based filters reducing As to concentrations lower than 10 μ g L−1. High levels of chloride and sulphate did not influence As removal efficiency. However, phosphate concentrations in the range from 4 to 24 mg L−1 drastically decreased removal efficiency of the IOCS-based filter but had no effects on removal efficiency of the CIM-based filter. Results of this study can be used as a base for further testing and practical implementation of drinking water purification in the Oruro region.

Analysis of dissolved microcystins in surface water samples from Kovada Lake, Turkey

Dissolved (extracellular) microcystin (MC) concentrations were determined at 3 sampling stations on Lake Kovada, Turkey. The dominant species of cyanobacteria found in August and September of 2006 were Microcystis aeruginosa, Synechococcus sp., Phormidium limosum, Phormidium formosa and Planktothrix limnetica. MC concentrations in water were measured by ELISA and MC variants were examined by HPLC-PDA. Quantitative analysis by HPLC indicated that five MC variants (MC–LR, –RR, –LA, –LW, –LF) were identified in water samples from Kovada Lake. The maximum concentration of dissolved MC–LW was 98.9 µg l − 1 in October. MC–LR was only detected in May at a concentration of 0.5 µg l − 1 . The cross reactivity of the antibody (MC10E7) to variants such as MC–LA MC–LW & MC–LF was low. Hence the results determined by ELISA were lower than those determined by HPLC in September and October samples due to differences in the specificity of the antibody to MC variants. Total extraceullar MCs was quantified by ELISA and ranged from 0.73 to 48.5 µg MC–LR equivalents l − 1 , which in some cases exceeded the WHO provisional Guideline Value for MC–LR in drinking water. This study confirms that the lakes of Turkey should be monitored for toxic cyanobacteria and for MCs to avoid or reduce the potential exposure of people to these health hazards.

Presence of arsenic, iron and manganese in groundwater within the gold-belt zone of Ghana

About 45% of the total drinking water in Ghana is produced from groundwater. The presence of arsenic and manganese in groundwater above the recommended WHO drinking- water guidelines pose a threat to consumers’ health. To provide additional information on groundwater quality in the gold-belt zone of Ghana, nearly 290 well water samples from three regions namely Ashanti, Western and Brong-Ahafo, were analyzed for the presence of arsenic, iron and manganese. It was found that 5–12% of sampled wells had arsenic levels exceeding the 10 μg l −1 —WHO provisional guideline value. Communities within the studied area with high arsenic presence in their groundwater are located within the Birimian and Tarkwaian geological formations. Most of these arsenic contaminated wells (70%) have been in use for more than 15 years. Brong-Ahafo, Ashanti and Western regions had 5%, 25% and 50% of wells, respectively with iron levels above 0.3 mg l −1 , the drinking-water guideline value commonly accepted for iron. Thirteen percent of wells in Ashanti and 29% in the Western region exceeded 0.4 mg l −1 —the WHO health-based guideline value for manganese.

Arsenic mobilisation in a new well field for drinking water production along the Red River, Nam Du, Hanoi

Arsenic enrichment of groundwater in the Red River (Song Hong) delta in Vietnam was discovered in 1998. Several studies performed in this area found concentrations of As exceeding the WHO-guideline of 10 μg/L. This study focuses on an area south of Hanoi city, Nam Du, where a new well field came into operation in 2004. The new well field is situated on the bank along the Red River in order to facilitate induced infiltration. The Nam Du area receives surface water with a high load of nutrients and organic matter from the Hanoi sewage system, and is subject to recently increased groundwater extraction from the Pleistocene aquifer system. The objective of the study was (1) to assess the situation in the Nam Du area by mapping the distribution of As, (2) to identify possible sources of As in the groundwater and (3) to investigate the mobilisation processes releasing As into the groundwater. Two main field campaigns were carried out, in 2006 and 2007, both during the dry season. Groundwater and surface water levels were measured and water- and sediment samples were collected. The water in the Pleistocene aquifer shows the same water-level variations as the Red River at a distance of 2.5 km from the riverbank, while the Holocene aquifer heads are recharged by surface water ponds and show less seasonal variation. The concentration of As in the groundwater in Nam Du exceeded the WHO provisional guideline value at all sampled locations. The main conclusions are summarised as (i) the distribution of As is highly variable but the zones with the highest concentrations of As are near the Red River in the Holocene aquifer and just down gradient from this in the Pleistocene aquifer, (ii) the sediments within the aquifers are considered to be the source of the As, where the Holocene aquifer is believed to act as the main source of As into the Pleistocene aquifer as reduced groundwater containing As from the Holocene aquifer is flowing downwards due to the downward gradient, and (iii) two different processes appear to take part in the mobilisation process. In the Holocene aquifer, reductive dissolution of FeOOH and the release of adsorbed As appear to be the main mobilisation processes. In the Pleistocene, however, mobilisation of adsorbed As due to competition from HCO3- ions for surface sites on FeOOH may be a major mechanism of As mobilisation. It is suggested that the drinking water supplier undertakes the following actions to ensure acceptable levels of As in the treated drinking water: (a) to implement a long-term monitoring program, (b) implement alternative treatment technologies; and (c) to possibly consider an alternative drinking water source.

Toxic cyanobacteria and cyanotoxins in public hot springs in Saudi Arabia

Toxic cyanobacteria are well reported in rivers, lakes and even marine environments, but the toxin production of cyanobacteria in hot springs is largely unexplored. Therefore, the present study investigated the presence of toxic cyanobacteria and cyanotoxins in public hot springs in Saudi Arabia. The results of an enzyme-linked immunosorbent assay (ELISA) revealed that Saudi spring cyanobacterial mats contained microcystins (MCYSTs) at concentrations ranging from 468 to 512.5 μg g −1. The Limulus amebocyte lystae (LAL) assay detected lipopolysaccharide (LPS) endotoxins in these mats at concentrations ranging from 433.3 to 506.8 EU g −1. MCYSTs and endotoxins were also detected in spring waters at levels of 5.7 μg l −1 and 640 EU ml −1, respectively, exceeding WHO's provisional guideline value for MCYST-LR in drinking-water. High-performance liquid chromatography (HPLC) analysis revealed that only Oscillatoria limosa and Synechococcus lividus can produce MCYSTs with a profile consisting of MCYST-RR and -LR. Based on the LAL assay, 12 out of 17 cyanobacterial species contained LPS at concentrations ranging from 0.93 to 21.06 EU g −1. However, not all LPS of these species were toxic to mice. This study suggests that the hot springs in the world including Saudi Arabia should be screened for toxic cyanobacteria to avoid the exposure of people recreating and bathing in spring waters to cyanobacterial toxins.

Arsenic and Other Metal Contamination of Groundwaters in the Industrial Area of Thessaloniki, Northern Greece

In groundwater, used for drinking water supply in the greater industrial area of Thessaloniki, in Northern Greece, concentrations of total arsenic exceeded the WHO provisional guideline value and the EU maximum contaminant level (MCL) of 10 microg/L. The concentration of total arsenic was in the range between 4-130 microg/L, whereas the median value was 36 microg/L and the average concentration 46 microg/L. Nine out of the eleven wells contained total arsenic at concentration higher than 10 microg/L and it should be stressed that 6 of them contain arsenic at concentrations between 10 (new MCL) and 50 microg/L (previous MCL). The examined groundwaters were found to contain elevated concentrations of manganese and phosphate. Arsenic had a positive correlation with the pH, indicating the possible effect of pH on arsenic mobilisation. These findings emerge the problem of contamination from arsenic, since, according to the EU directive 98/83, all drinking water sources within the European Union should have achieved compliance with the new limits by 12/2003, implying that the situation requires urgent remedial action.

Removal of Arsenic by Bead Cellulose Loaded with Iron Oxyhydroxide from Groundwater

A new adsorbent, bead cellulose loaded with iron oxyhydroxide (BCF), was prepared and applied for the adsorption and removal of arsenate and arsenite from aqueous systems. The continuing loading process of Fe in the cellulose beads was realized through hydrolization of ferric salts when alkaline solution was added dropwise. Spherical BCF had excellent mechanical and hydraulic properties. Akaganeite (beta-FeOOH), the reactive center of BCF that was stably loaded into the cellulose, had a high sensitivity to arsenite as well as arsenate. The maximum content of Fe in BCF reached 50% (w/w). In this study we investigated the adsorption behavior of arsenite and arsenate on BCF, including adsorption isotherms, adsorption kinetics, the influence of pH and competing anions on adsorption, and column experiments. The adsorption data accorded with both Freundlich and Langmuir isotherms. The adsorption capacity for arsenite and arsenate was 99.6 and 33.2 mg/g BCF at pH 7.0 with an Fe content of 220 mg/ mL. Kinetic data fitted well to the pseudo-second-order reaction model. Arsenate elimination was favored at acidic pH, whereas the adsorption of arsenite by BCF was found to be effective in a wide pH range of 5-11. Under the experimental conditions, the addition of sulfate had no effect on arsenic adsorption, whereas phosphate greatly influenced the elimination of both arsenite and aresenate. Silicate moderately decreased the adsorption of arsenite, but not arsenate. Both batch experiments and column experiments indicated that BCF had higher removal efficiency for arsenite than for arsenate. While the influent contaminant concentration was 500 microg/L in groundwater and the empty-bed contact time (EBCT) for arsenite and arsenate was 4.2 and 5.9 min, breakthrough empty-bed volumes at the WHO provisional guideline value of 10 microg/L were 2200 and 5000, respectively. BCF can be effectively regenerated when elution is done with 2 M NaOH solution. The column experiments for four cycles showed that stable and high removal efficiency of arsenic was sustained by BCF after regeneration.

Ineffectiveness and Poor Reliability of Arsenic Removal Plants in West Bengal, India

In the recent past, arsenic contamination in groundwater has emerged as an epidemic in different Asian countries, such as Bangladesh, India, and China. Arsenic removal plants (ARP) are one possible option to provide arsenic-safe drinking water. This paper evaluates the efficiency of ARP projects in removing arsenic and iron from raw groundwater, on the basis of our 2-year-long study covering 18 ARPs from 11 manufacturers, both from home and abroad, installed in an arsenic affected area of West Bengal, India, known as the Technology Park Project (TP project). Immediately after installation of ARPs on August 29, 2001, the villagers began using filtered water for drinking and cooking, even though our first analysis on September 13, 2001 found that 10 of 13 ARPs failed to remove arsenic below the WHO provisional guideline value (10 microg/L), while six plants could not achieve the Indian Standard value (50 microg/L). The highest concentration of arsenic in filtered water was observed to be 364 microg/L. Our 2-year study showed that none of the ARPs could maintain arsenic in filtered water below the WHO provisional guideline value and only two could meet the Indian standard value (50 microg/L) throughout. Standard statistical techniques showed that ARPs from the same manufacturers were not equally efficient. Efficiency of the ARPs was evaluated on the basis of point and interval estimates of the proportion of failure. During the study period almost all the ARPs have undergone minor or major modifications to improve their performance, and after our study, 15 (78%) out of 18 ARPs were no longer in use. In this study, we also analyzed urine samples from villagers in the TP project area and found that 82% of the samples contained arsenic above the normal limit.