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The World Health Organization has labeled the problem of arsenic contamination of groundwater in South Asia as “the largest mass poisoning in human history.” Various technical solutions to the problem fall into one of two broad categories: (i) cleaning contaminated water before human consumption and (ii) encouraging people to switch to less contaminated water sources. In this paper, we review research on the behavioral, social, political, and economic factors that determine the field-level effectiveness of the suite of technical solutions and the complexities that arise when scaling such solutions to reach large numbers of people. We highlight the conceptual links between arsenic-mitigation policy interventions and other development projects in Bangladesh and elsewhere, as analyzed by development economists, that can shed light on the key social and behavioral mechanisms at play. We conclude by identifying the most promising policy interventions to counter the arsenic crisis in Bangladesh. We support a national well-testing program combined with interventions that address the key market failures (affordability, coordination failures, and elite and political capture of public funds) that currently prevent more deep-well construction in Bangladesh.

Soils retain lead contamination from possible sources such as mining, smelting, battery recycling, waste incineration, leaded gasoline, and crumbling paint. Such contamination is often concentrated in toxic hot spots that need to be identified locally. To address this need, a simple field procedure was designed to screen soil for hazardous Pb for use by the general public. The procedure is a modification of the in vitrosoil Pb extraction described by Drexler and Brattin (Hum. Ecol. Risk Assess.2007, 13, 383) and EPA Method 1340, and uses a 0.4 M glycine solution at pH 1.5. A higher soil-to-solution ratio of 1:10 allows for classifying soil samples based on extractable Pb concentrations of <200 mg/kg (low), 200–400 mg/kg (medium), and >400 mg/kg (high) using sodium rhodizonate as a color indicator. The 1:10 soil-to-solution ratio also makes it possible to measure Pb concentrations in the glycine extract solutions on a continuous scale using a portable X-ray fluorescence analyzer. The procedure rather consistently extracts about one-third of the Pb extracted by the standard method across a wide range of Pb concentrations. Manufacturing the kit in larger quantities could reduce the cost of the materials well below the current $5/test.

About 20 million rural Bangladeshis continue to drink well water containing >50 μg/L arsenic (As). This analysis argues for reprioritizing interventions on the basis of a survey of wells serving a population of 380,000 conducted one decade after a previous round of testing overseen by the government. The available data indicate that testing alone reduced the exposed population in the area in the short term by about 130,000 by identifying the subset of low As wells that could be shared at a total cost of 150 m) wells and a single piped-water supply system by the government reduced exposure of little more than 7000 inhabitants at a cost of US$150 per person whose exposure was reduced. The findings make a strong case for long-term funding of free well testing on a massive scale with piped water or groundwater treatment only as a last resort.

Rice is the primary crop in Bangladesh, and rice yield is diminished due to the buildup of arsenic (As) in soil from irrigation with high-As groundwater. Implementing a soil inversion, where deeper low-As soil is exchanged with the surface high-As soil in contact with rice roots, may mitigate the negative impacts of As on yield. We compared soil As, soil nutrients, and rice yield in control plots with those in adjacent soil inversion plots. We also estimated the quantity of soil As deposited on a yearly basis via irrigation water, to explore the longevity of a soil inversion to reduce surface As. Soil As, organic carbon, nitrogen, and phosphorus concentrations decreased by about 40% in response to the inversion and remained lowered over four seasons of monitoring. Inversion plot yields increased above control plot yields by 15–30% after a one-season lag despite the recovering but still reduced nutrient levels. Farmers have started conducting soil inversions of their own volition, typically close to where irrigation water enters the field. However, the yield gain will be limited to a few decades at most due to deposition of As via well water, unless the field is irrigated with low-As river or pond water.

Rice was traditionally grown only during the summer (aman) monsoon in Bangladesh but more than half is now grown during the dry winter (boro) season and requires irrigation. A previous field study conducted in a small area irrigated by a single high-arsenic well has shown that the accumulation of arsenic (As) in soil from irrigating with high-As groundwater can reduce rice yield. We investigated the effect of soil As on rice yield under a range of field conditions by exchanging the top 15 cm of soil between 13 high-As and 13 low-As plots managed by 16 different farmers, and we explore the implications for mitigation. Soil As and rice yields were measured for soil replacement plots where the soil was exchanged and adjacent control plots where the soil was not exchanged. Differences in yield (ranging from +2 to −2 t/ha) were negatively correlated to the differences in soil As (ranging from −9 to +19 mg/kg) between adjacent replacement and control plots during two boro seasons. The relationship between soil As and yield suggests a boro rice yield loss over the entire country of 1.4–4.9 million tons annually, or 7–26% of the annual boro harvest, due to the accumulation of As in soil over the past 25 years.

Many aquifers that are highly contaminated by arsenic in South and Southeast Asia are in the floodplains of large river networks. Under natural conditions, these aquifers would discharge into nearby rivers; however, large‐scale groundwater pumping has reversed the flow in some areas so that rivers now recharge aquifers. At a field site near Hanoi Vietnam, we find river water recharging the aquifer becomes high in arsenic, reaching concentrations above 1000 µg/L, within the upper meter of recently (< ∼10 years) deposited riverbed sediments as it is drawn into a heavily pumped aquifer along the Red River. Groundwater arsenic concentrations in aquifers adjacent to the river are largely controlled by river geomorphology. High (>50 µg/L) aqueous arsenic concentrations are found in aquifer regions adjacent to zones where the river has recently deposited sediment and low arsenic concentrations are found in aquifer regions adjacent to erosional zones. High arsenic concentrations are even found adjacent to a depositional river reach in a Pleistocene aquifer, a type of aquifer sediment which generally hosts low arsenic water. Using geochemical and isotopic data, we estimate the in situ rate of arsenic release from riverbed sediments to be up to 1000 times the rates calculated on inland aquifer sediments in Vietnam. Geochemical data for riverbed porewater conditions indicate that the reduction of reactive, poorly crystalline iron oxides controls arsenic release. We suggest that aquifers in these regions may be susceptible to further arsenic contamination where riverine recharge drawn into aquifers by extensive groundwater pumping flows through recently deposited river sediments before entering the aquifer. Rates of arsenic release from young riverbed sediments are up to 1000 times the release rates from aquifer sedimentRiver recharge induced by groundwater pumping may contaminate previously safe aquifers with arsenicRiverbank geomorphology can influence groundwater arsenic concentrations in aquifers adjacent to rivers

Oxidative stress and DNA methylation are metabolically linked through the relationship between one-carbon metabolism and the transsulfuration pathway, but possible modulating effects of oxidative stress on DNA methylation have not been extensively studied in humans. Enzymes involved in DNA methylation, including DNA methyltransferases and histone deacetylases, may show altered activity under oxidized cellular conditions. Additionally, in vitro studies suggest that glutathione (GSH) depletion leads to global DNA hypomethylation, possibly through the depletion of S-adenosylmethionine (SAM). We tested the hypothesis that a more oxidized blood GSH redox status is associated with decreased global peripheral blood mononuclear cell (PBMC) DNA methylation in a sample of Bangladeshi adults. Global PBMC DNA methylation and whole blood GSH, glutathione disulfide (GSSG), and SAM concentrations were measured in 320 adults. DNA methylation was measured by using the [3H]-methyl incorporation assay; values are inversely related to global DNA methylation. Whole blood GSH redox status (Eh) was calculated using the Nernst equation. We found that a more oxidized blood GSH Ehwas associated with decreased global DNA methylation (B ± SE, 271 ± 103, p = 0.009). Blood SAM and blood GSH were associated with global DNA methylation, but these relationships did not achieve statistical significance. Our findings support the hypothesis that a more oxidized blood GSH redox status is associated with decreased global methylation of PBMC DNA. Furthermore, blood SAM does not appear to mediate this association. Future research should explore mechanisms through which cellular redox might influence global DNA methylation.

Millions of people worldwide are chronically exposed to arsenic through drinking water, including 35–77 million people in Bangladesh. The association between arsenic exposure and mortality rate has not been prospectively investigated by use of individual-level data. We therefore prospectively assessed whether chronic and recent changes in arsenic exposure are associated with all-cause and chronic-disease mortalities in a Bangladeshi population.

The risk of skin lesions associated with arsenic exposure from drinking water in Bangladesh is considerably greater in men than in women.

Dissolved sulfide concentrations in the water column and in sediment pore waters were measured by square-wave voltammetry (nanomolar detection limit) during three cruises to the Santa Barbara Basin in February 1995, November–December 1995, and April 1997. In the water column, sulfide concentrations measured outside the basin averaged 3 ± 1 nM (n= 28) in the 0 to 600 m depth range. Inside the basin, dissolved sulfides increased to reach values of up to 15 nM at depths >400 m. A suite of box cores and multicores collected at four sites along the northeastern flank of the basin showed considerable range in surficial (<0.5 cm) pore-water sulfide concentrations: <0.008, 0.01, 0.02, to as much as 0.4 μM at the 340, 430, 550, and 590 m sites, respectively. At a core depth of 10 cm, however, pore–water sulfides exhibited an even wider range: 0.005, 0.05, 0.1, and 100 μM at the same sites, respectively. The sulfide flux into the deep basin, estimated from water-column profiles during three cruises, suggests a fairly consistent input of 100–300 nmole m−2h−1. In contrast, sulfide fluxes estimated from pore-water sulfide gradients at the sediment water interface were much more variable (−4 to 13,000 nmole m−2h−1). Dissolved silicate profiles show clear indications of irrigation at shallow sites (340 and 430 m) in comparison to deeper basin sites (550 and 590 m) with low (<10 μM) bottom-water dissolved-oxygen concentrations. Pore-water profiles indicate ammonia generation at all sites, but particularly at the deep-basin 590 m site with concentrations increasing with sediment depth to >400 μM at 10 cm. Decreases in water-column nitrate below the sill depth indicate nitrate consumption (−55 to −137 μmole m−2h−1) similar to nearby Santa Monica Basin. Peaks in pore-water iron concentrations were generally observed between 2 and 5 cm depth with shallowest peaks at the 590 m site. These observations, including observations of the benthic microfauna, suggest that the extent to which the sulfide flux, sustained by elevated pore-water concentrations, reaches the water column may be modulated by the abundance of sulfide-oxidizing bacteria in addition to iron redox and precipitation reactions.

The 1994 spring phytoplankton bloom in South San Francisco Bay caused substantial reductions in concentrations of dissolved Cd, Ni, and Zn, but not Cu. We estimate that the equivalent of ~60% of the total annual input of Cd, Ni, and Zn from local waste‐water treatment plants is cycled through the phytoplankton in South Bay. The results suggest that processes that affect phytoplankton bloom frequency or intensity in estuaries (e.g. nutrient enrichment) may also affect metal trapping. The bloom was characterized by hydrographic surveys conducted at weekly intervals for 9 weeks. Metal samples were collected from the water column on three occasions, timed to bracket the period when the bloom was predicted. Factors that might confound observations of biological influences, such as freshwater inputs, were relatively constant during the study. Before the bloom, concentrations of dissolved Cd were 0.81 ± 0.02 nmol kg−1, Zn concentrations were 19.8 ± 1.5 nmol kg−1, Ni were 42 ± 1.4 nmol kg−1, and Cu were 37 ± 1.4 nmol kg−1. These values are elevated relative to riverine and coastal end‐members, reflecting inputs from wastewater and(or) sediments. At the height of the bloom, dissolved Zn, Cd, and Ni were reduced to 19, 50, and 75% of their prebloom concentrations, respectively. Dissolved Cu concentrations increased 20%. The mass of Cd taken up by phytoplankton was similar to the mass of Cd removed from solution if particle settling was considered, and Cd concentrations estimated in phytoplankton were higher than concentrations in suspended particulate material (SPM). Particulate concentrations of Zn and Ni during the bloom appeared to be dominated by the influence of changes in resuspension of Zn and Ni‐rich sediments.

Surface waters of the Mediterranean Sea have higher trace-metal concentrations than open Atlantic surface waters1. This observation could be explained by sources within the basin, but recent data from the Alboran Sea2indicate that trace metals may already be enriched in Atlantic waters flowing into the Mediterranean through the Strait of Gibraltar. Here we present new data documenting the presence of trace-metal-enriched source waters west of the Strait, and present a mathematical analysis showing that Cu, Ni, Cd and Zn distributions in the Alboran Sea can be explained as linear mixtures of four well–defined sources: (1) Spanish coastal waters, (2) North Atlantic Central Water, (3) Atlantic surface water, and (4) Mediterranean Levantine Intermediate Water. In this analysis, salinity and trace metals are used for the first time to deconvolve mixing between water masses of different origins.

ABSTRACTLong-term exposure to trace levels of arsenic (As) in shallow groundwater used for drinking and irrigation puts millions of people at risk of chronic disease. Although microbial processes are implicated in mobilizing arsenic from aquifer sediments into groundwater, the precise mechanism remains ambiguous. The goal of this work was to target, for the first time, a comprehensive suite of state-of-the-art molecular techniques in order to better constrain the relationship between indigenous microbial communities and the iron and arsenic mineral phases present in sediments at two well-characterized arsenic-impacted aquifers in Bangladesh. At both sites, arsenate [As(V)] was the major species of As present in sediments at depths with low aqueous As concentrations, while most sediment As was arsenite [As(III)] at depths with elevated aqueous As concentrations. This is consistent with a role for the microbial As(V) reduction in mobilizing arsenic. 16S rRNA gene analysis indicates that the arsenic-rich sediments were colonized by diverse bacterial communities implicated in both dissimilatory Fe(III) and As(V) reduction, while the correlation analyses involved phylogenetic groups not normally associated with As mobilization. Findings suggest that direct As redox transformations are central to arsenic fate and transport and that there is a residual reactive pool of both As(V) and Fe(III) in deeper sediments that could be released by microbial respiration in response to hydrologic perturbation, such as increased groundwater pumping that introduces reactive organic carbon to depth.IMPORTANCEThe consumption of arsenic in waters collected from tube wells threatens the lives of millions worldwide and is particularly acute in the floodplains and deltas of southern Asia. The cause of arsenic mobilization from natural sediments within these aquifers to groundwater is complex, with recent studies suggesting that sediment-dwelling microorganisms may be the cause. In the absence of oxygen at depth, specialist bacteria are thought able to use metals within the sediments to support their metabolism. Via these processes, arsenic-contaminated iron minerals are transformed, resulting in the release of arsenic into the aquifer waters. Focusing on a field site in Bangladesh, a comprehensive, multidisciplinary study using state-of-the-art geological and microbiological techniques has helped better understand the microbes that are present naturally in a high-arsenic aquifer and how they may transform the chemistry of the sediment to potentially lethal effect.

OBJECTIVE: To evaluate the association between arsenic exposure and mortality from cardiovascular disease and to assess whether cigarette smoking influences the association. Design Prospective cohort study with arsenic exposure measured in drinking water from wells and urine. Setting General population in Araihazar, Bangladesh. Participants 11 746 men and women who provided urine samples in 2000 and were followed up for an average of 6.6 years. MAIN OUTCOME MEASURE: Death from cardiovascular disease. RESULTS: 198 people died from diseases of circulatory system, accounting for 43% of total mortality in the population. The mortality rate for cardiovascular disease was 214.3 per 100 000 person years in people drinking water containing <12.0 µg/L arsenic, compared with 271.1 per 100 000 person years in people drinking water with ≥12.0 µg/L arsenic. There was a dose-response relation between exposure to arsenic in well water assessed at baseline and mortality from ischaemic heart disease and other heart disease; the hazard ratios in increasing quarters of arsenic concentration in well water (0.1-12.0, 12.1-62.0, 62.1-148.0, and 148.1-864.0 µg/L) were 1.00 (reference), 1.22 (0.65 to 2.32), 1.35 (0.71 to 2.57), and 1.92 (1.07 to 3.43) (P=0.0019 for trend), respectively, after adjustment for potential confounders including age, sex, smoking status, educational attainment, body mass index (BMI), and changes in urinary arsenic concentration since baseline. Similar associations were observed when baseline total urinary arsenic was used as the exposure variable and for mortality from ischaemic heart disease specifically. The data indicate a significant synergistic interaction between arsenic exposure and cigarette smoking in mortality from ischaemic heart disease and other heart disease. In particular, the hazard ratio for the joint effect of a moderate level of arsenic exposure (middle third of well arsenic concentration 25.3-114.0 µg/L, mean 63.5 µg/L) and cigarette smoking on mortality from heart disease was greater than the sum of the hazard ratios associated with their individual effect (relative excess risk for interaction 1.56, 0.05 to 3.14; P=0.010). CONCLUSIONS: Exposure to arsenic in drinking water is adversely associated with mortality from heart disease, especially among smokers.