Influence of folic acid and vitamin B12 supplementation on arsenic methylation: A double-blinded, placebo-controlled trial in Bangladeshi children.

BACKGROUND: Inorganic arsenic is metabolized to monomethyl- (MMAs) and dimethyl- (DMAs) species via one-carbon metabolism (OCM); this facilitates urinary arsenic elimination. OCM is influenced by folate and vitamin B12 and previous randomized control trials (RCTs) showed that folic acid (FA) supplementation increases arsenic methylation in adults. This RCT investigated the effects of FA + B12 supplementation on arsenic methylation in children, a key developmental stage where OCM supports growth. METHODS: A total of 240 participants (8-11 years, 53 % female) drinking from wells with arsenic concentrations > 50 µg/L, were encouraged to switch to low arsenic wells and were randomized to receive 400 µg FA + 5 µg B12 or placebo daily for 12-weeks. Urine and blood samples were collected at baseline, week 1 (only urine) and week 12. Generalized estimated equation (GEE) models were used to assess treatment effects on arsenic species in blood and urine. RESULTS: At baseline, the mean ± SD total blood and urinary arsenic were 5.3 ± 2.9 µg/L and 91.2 ± 89.5 µg/L. Overall, total blood and urine arsenic decreased by 11.7% and 17.6%, respectively, at the end of follow up. Compared to placebo, the supplementation group experienced a significant increase in the concentration of blood DMAs by 14.0% (95% CI 5.0, 25.0) and blood secondary methylation index (DMAs/MMAs) by 0.19 (95% CI: 0.09, 0.35) at 12 weeks. Similarly, there was a 1.62% (95% CI: 0.43, 20.83) significantly higher urinary %DMAs and -1.10% (95% CI: -1.73, -0.48) significantly lower urinary %MMAs in the supplementatio group compared to the placebo group after 1 week. The direction of the changes in the urinary %iAs, %MMAs, and %DMAs at week 12 were consistent with those at week 1, though estimates were not significant. Treatment effects were stronger among participants with higher baseline blood arsenic concentrations. Results were consistent across males and females, and participants with higher and lower folate and B12 status at baseline. CONCLUSION: This RCT confirms that FA + B12 supplementation increases arsenic methylation in children as reflected by decreased MMAs and increased DMAs in blood and urine. Nutritional interventions may improve arsenic methylation and elimination in children, potentially reducing arsenic toxicity while also improving nutritional status.

Lead-based paint detection using perovskite fluorescence and X-ray fluorescence.

BACKGROUND: Ingestion of flakes of Pb-based paint by infants remains a global health hazard with life-long consequences. Pb-based paint was banned for residential use in the US and Western Europe decades ago but is still sold in many countries. This study evaluates the performance of a new kit for detecting exposed Pb-based paint relying on the formation of Pb-halide perovskite that fluoresces bright green under a UV flashlight after spraying a non-toxic reagent. RESULTS: Tests with the Lumetallix kit were conducted in parallel with X-fluorescence and inductively-coupled plasma atomic emission analysis upon acid digestion using paint currently sold in Côte d'Ivoire and samples of older US paint. Comparison of the three different methods indicates a detection limit for the Lumetallix kit of approximately 500 mg kg-1 (ppm) Pb in paint, with a sensitivity of 95 % and selectivity of 94 % relative to that threshold (n = 76). This detection limit is an order of magnitude below the US definition of Pb-based paint of 0.5 % (5,000 ppm) Pb by weight. SIGNIFICANCE: Because the kit is easy to use, exposed paint posing a risk could reliably be screened at scale by the general public. Any follow-up for confirmation and mitigation based on XRF measurements will need to consider that Pb-based paint covered with low-Pb paint will not respond to the kit but will be detected by XRF through the overpainted layer.

Elevated arsenic concentrations in groundwater of the Upper Indus Plain of Pakistan across a range of redox conditions.

Groundwater of the Ravi River floodplain is particularly elevated in arsenic (As) on both sides of the Pakistan-India border. To understand this pattern, 14 sites were drilled to 12-30 m depth across floodplains and doabs of Pakistan after testing over 20,000 wells. Drill cuttings were collected at 1.5 m intervals, 132 of which were sand overlain by 77 intervals of clay and/or silt. Radiocarbon dating of clay indicates deposition of the aquifer sands tapped by wells 20-30 kyr ago. Most (85 %) of the sand samples were gray in color, indicating partial reduction to Fe(II) oxides, whereas most (92 %) of the clay and/or silt samples were orange. Associations between groundwater electrical conductivity, dissolved Fe, sulfate, and nitrate suggest that wells can be elevated (>10 µg/L) in As in the region due to either reductive dissolution of Fe oxides, evaporative concentration, or alkali desorption. In the Ravi floodplain, 47 % of 6445 wells tested contain >10 µg/L As compared to only 9 % of 14,165 tested wells in other floodplains and doabs. The As content of aquifer sands in the Ravi floodplain of Pakistan averages 4 ± 4 mg/kg (n = 66) and is higher than the average of 2 ± 2 mg/kg (n = 51) for aquifer sands outside the Ravi. Synchrotron spectroscopy and column-based speciation indicate predominance of As(V) over As(III) in both aquifer sands and groundwater. Whereas multiple processes may be responsible for elevated levels of As in groundwater across the region, spatial heterogeneity in groundwater As concentrations in the Ravi floodplain seems linked to variations in As concentrations in aquifer sands. Regulation by the solid phase may limit variations in groundwater As over time in response to natural and human-induced changes in hydrology. This means spatial heterogeneity could be taken advantage of to lower the exposure across the region with more testing and targeted drilling.

Widespread Pb contamination in urban backyard soils for >100 years identified in soil cores constrained by 210Pb and 137Cs.

Contaminated soil in urban residential areas is often overlooked as a source of childhood exposure to toxic levels of lead (Pb). We document mean Pb concentrations of 1200 ± 1000 mg/kg, three times the now outdated EPA soil hazard standard of 400 mg/kg, for 370 surface soils collected from 76 homes in the boroughs of Brooklyn and Manhattan of New York City. The mean Pb content of 250 ± 290 mg/kg Pb for 571 surface soils collected from tree pits and public parks was much lower. A subset of 22 surface samples analyzed by EPA Method 1340 extracted 86 ± 21 % (±1SD) of total soil Pb, indicating that it the Pb was highly bioavailable. To investigate the origin of backyard contamination, 49 cores were collected to an average depth of 30 cm from a subset of 27 homes. Twelve soil cores were analyzed for 210Pb and 137Cs to constrain processes that impact contaminant distribution and inventories (particle focusing, soil accumulation, loss, and mixing). Concentrations of Pb declined with depth in 60 % of the cores but usually did not reach background. Mean uncorrected Pb inventories of 340 ± 210 g/m2 Pb (mean ± 1SD, n = 12) were more than five times higher than the radionuclide corrected inventory of 57 g/m2 from Central Park soil cores. Average inventories of 210Pbxs (3.5 ± 0.9 kBq/m2) and 137Cs (0.9 ± 0.6 kBq/m2) corresponded to 71 ± 19 % and 50 ± 30 % of the predicted atmospheric inventories. Elevated Pb concentrations were found both in the fine (<1 mm) and coarse (>1 mm) fractions, the latter suggesting a local non-atmospheric source. This was confirmed by individual grains containing up to 6 % Pb and visible pieces of coal, bricks, and ash. Regardless of the source of contamination in backyard soils, systematic testing is needed to identify contaminated areas and reduce child exposure.

Anthropometric measures and arsenic methylation among pregnant women in rural northern Bangladesh.

INTRODUCTION: Arsenic methylation converts inorganic arsenic (iAs) to monomethyl (MMA) and dimethyl (DMA) arsenic compounds. Body mass index (BMI) has been positively associated with arsenic methylation efficiency (higher DMA%) in adults, but evidence in pregnancy is inconsistent. We estimated associations between anthropometric measures and arsenic methylation among pregnant women in rural northern Bangladesh. METHODS: We enrolled pregnant women (n = 784) (median [IQR] gestational week: 14 [13, 15]) in Gaibandha District, Bangladesh from 2018 to 2019. Anthropometric measures were BMI, subscapular and triceps skinfold thicknesses, and mid-upper arm circumference (MUAC), fat area (MUAFA), and muscle area (MUAMA). Arsenic methylation measures were urinary iAs, MMA, and DMA divided by their sum and multiplied by 100 (iAs%, MMA%, and DMA%), primary methylation index (MMA/iAs; PMI), and secondary methylation index (DMA/MMA; SMI). In complete cases (n = 765 [97.6%]), we fitted linear, beta, and Dirichlet regression models to estimate cross-sectional differences in iAs%, MMA%, DMA%, PMI, and SMI per IQR-unit difference in each anthropometric measure, adjusting for drinking water arsenic, age, gestational age, education, living standards index, and plasma folate, vitamin B12, and homocysteine. RESULTS: Median (IQR) BMI, subscapular skinfold thickness, triceps skinfold thickness, MUAC, MUAFA, and MUAMA were 21.5 (19.4, 23.8) kg/m2, 17.9 (13.2, 24.2) mm, 14.2 (10.2, 18.7) mm, 25.9 (23.8, 28.0) cm, 15.3 (10.5, 20.3) cm2, and 29.9 (25.6, 34.2) cm2, respectively. Median (IQR) iAs%, MMA%, DMA%, PMI, and SMI were 12.0 (9.3, 15.2)%, 6.6 (5.3, 8.3)%, 81.0 (77.1, 84.6)%, 0.6 (0.4, 0.7), and 12.2 (9.3, 15.7), respectively. In both unadjusted and adjusted linear models, all anthropometric measures were negatively associated with iAs%, MMA%, and PMI and positively associated with DMA% and SMI. For example, fully adjusted mean differences (95% CI) in DMA% per IQR-unit difference in BMI, subscapular skinfolds thickness, triceps skinfold thickness, MUAC, MUAFA, and MUAMA were 1.72 (1.16, 2.28), 1.58 (0.95, 2.21), 1.74 (1.11, 2.37), 1.45 (0.85, 2.06), 1.70 (1.08, 2.31), and 0.70 (0.13, 1.27) pp, respectively. CONCLUSIONS: Anthropometric measures were positively associated with arsenic methylation efficiency among pregnant women in the early second trimester.

Sulfate reduction accelerates groundwater arsenic contamination even in aquifers with abundant iron oxides.

Groundwater contamination by geogenic arsenic is a global problem affecting nearly 200 million people. In South and Southeast Asia, a cost-effective mitigation strategy is to use oxidized low-arsenic aquifers rather than reduced high-arsenic aquifers. Aquifers with abundant oxidized iron minerals are presumably safeguarded against immediate arsenic contamination, due to strong sorption of arsenic onto iron minerals. However, preferential pumping of low-arsenic aquifers can destabilize the boundaries between these aquifers, pulling high-arsenic water into low-arsenic aquifers. We investigate this scenario in a hybrid field-column experiment in Bangladesh where naturally high-arsenic groundwater is pumped through sediment cores from a low-arsenic aquifer, and detailed aqueous and solid-phase measurements are used to constrain reactive transport modelling. Here we show that elevated groundwater arsenic concentrations are induced by sulfate reduction and the predicted formation of highly mobile, poorly sorbing thioarsenic species. This process suggests that contamination of currently pristine aquifers with arsenic can occur up to over 1.5 times faster than previously thought, leading to a deterioration of urgently needed water resources.

The Pregnancy, Arsenic, and Immune Response (PAIR) Study in rural northern Bangladesh.

BACKGROUND: Arsenic exposure and micronutrient deficiencies may alter immune reactivity to influenza vaccination in pregnant women, transplacental transfer of maternal antibodies to the foetus, and maternal and infant acute morbidity. OBJECTIVES: The Pregnancy, Arsenic, and Immune Response (PAIR) Study was designed to assess whether arsenic exposure and micronutrient deficiencies alter maternal and newborn immunity and acute morbidity following maternal seasonal influenza vaccination during pregnancy. POPULATION: The PAIR Study recruited pregnant women across a large rural study area in Gaibandha District, northern Bangladesh, 2018-2019. DESIGN: Prospective, longitudinal pregnancy and birth cohort. METHODS: We conducted home visits to enrol pregnant women in the late first or early second trimester (11-17 weeks of gestational age). Women received a quadrivalent seasonal inactivated influenza vaccine at enrolment. Follow-up included up to 13 visits between enrolment and 3 months postpartum. Arsenic was measured in drinking water and maternal urine. Micronutrient deficiencies were assessed using plasma biomarkers. Vaccine-specific antibody titres were measured in maternal and infant serum. Weekly telephone surveillance ascertained acute morbidity symptoms in women and infants. PRELIMINARY RESULTS: We enrolled 784 pregnant women between October 2018 and March 2019. Of 784 women who enrolled, 736 (93.9%) delivered live births and 551 (70.3%) completed follow-up visits to 3 months postpartum. Arsenic was detected (≥0.02 µg/L) in 99.7% of water specimens collected from participants at enrolment. The medians (interquartile ranges) of water and urinary arsenic at enrolment were 5.1 (0.5, 25.1) µg/L and 33.1 (19.6, 56.5) µg/L, respectively. Water and urinary arsenic were strongly correlated (Spearman's ⍴ = 0.72) among women with water arsenic ≥ median but weakly correlated (⍴ = 0.17) among women with water arsenic < median. CONCLUSIONS: The PAIR Study is well positioned to examine the effects of low-moderate arsenic exposure and micronutrient deficiencies on immune outcomes in women and infants. REGISTRATION: NCT03930017.

Mass fluxes of dissolved arsenic discharging to the Meghna River are sufficient to account for the mass of arsenic in riverbank sediments.

Shallow (<30 m) reducing groundwater commonly contains abundant dissolved arsenic (As) in Bangladesh. We hypothesize that dissolved As in iron (Fe)-rich groundwater discharging to rivers is trapped onto Fe(III)-oxyhydroxides which precipitate in shallow riverbank sediments under the influence of tidal fluctuations. Therefore, the goal of this study is to compare the calculated mass of sediment-bound As that would be sequestered from dissolved groundwater As that discharges through riverbanks of the Meghna River to the observed mass of As trapped within riverbank sediments. To calculate groundwater discharge, a Boussinesq aquifer analytical groundwater flow model was developed and constrained by cyclical seasonal fluctuations in hydraulic heads and river stages observed at three sites along a 13 km reach in central Bangladesh. At all sites, groundwater discharges to the river year-round but most of it passes through an intertidal zone created by ocean tides propagating upstream from the Bay of Bengal in the dry season. The annualized groundwater discharge per unit width at the three sites ranges from 173 to 891 m2/yr (average 540 m2/yr). Assuming that riverbanks have been stable since the Brahmaputra River avulsed far away from this area 200 years ago and dissolved As is completely trapped within riverbank sediments, the mass of accumulated sediment As can be calculated by multiplying groundwater discharge by ambient aquifer As concentrations measured in 1969 wells. Across all sites, the range of calculated sediment As concentrations in the riverbank is 78-849 mg/kg, which is higher than the observed concentrations (17-599 mg/kg). This discovery supports the hypothesis that the dissolved As in groundwater discharge to the river is sufficient to account for the observed buried deposits of As along riverbanks.

A mass-balance approach to evaluate arsenic intake and excretion in different populations.

Unless a toxicant builds up in a deep compartment, intake by the human body must on average balance the amount that is lost. We apply this idea to assess arsenic (As) exposure misclassification in three previously studied populations in rural Bangladesh (n = 11,224), Navajo Nation in the Southwestern United States (n = 619), and northern Chile (n = 630), under varying assumptions about As sources. Relationships between As intake and excretion were simulated by taking into account additional sources, as well as variability in urine dilution inferred from urinary creatinine. The simulations bring As intake closer to As excretion but also indicate that some exposure misclassification remains. In rural Bangladesh, accounting for intake from more than one well and rice improved the alignment of intake and excretion, especially at low exposure. In Navajo Nation, comparing intake and excretion revealed home dust as an important source. Finally, in northern Chile, while food-frequency questionnaires and urinary As speciation indicate fish and shellfish sources, persistent imbalance of intake and excretion suggests imprecise measures of drinking water arsenic as a major cause of exposure misclassification. The mass-balance approach could prove to be useful for evaluating sources of exposure to toxicants in other settings.

A mass-balance model to assess arsenic exposure from multiple wells in Bangladesh.

BACKGROUND: Water arsenic (As) sources beyond a rural household's primary well may be a significant source for certain individuals, including schoolchildren and men working elsewhere. OBJECTIVE: To improve exposure assessment by estimating the fraction of drinking water that comes from wells other than the household's primary well in a densely populated area. METHODS: We use well water and urinary As data collected in 2000-2001 within a 25 km2 area of Araihazar upazila, Bangladesh, for 11,197 participants in the Health Effects of Arsenic Longitudinal Study (HEALS). We estimate the fraction of water that participants drink from different wells by imposing a long-term mass-balance constraint for both As and water. RESULTS: The mass-balance model suggest that, on average, HEALS participants obtain 60-75% of their drinking water from their primary household wells and 25-40% from other wells, in addition to water from food and cellular respiration. Because of this newly quantified contribution from other wells, As in drinking water rather than rice was identified as the largest source of As exposure at baseline for HEALS participants with a primary household well containing ≤50 µg/L As. SIGNIFICANCE: Dose-response relationships for As based on water As should take into account other wells. The mass-balance approach could be applied to study other toxicants.

Groundwater fluoride across the Punjab plains of Pakistan and India: Distribution and underlying mechanisms.

Chronic exposure from drinking well-water with naturally high concentrations of fluoride (F-) has serious health consequences in several regions across the world including South Asia, where the rural population is particularly dependent on untreated groundwater pumped from private wells. An extensive campaign to test 28,648 wells was conducted across the Punjab plains of Pakistan and India by relying primarily on field kits to document the scale of the problem and shed light on the underlying mechanisms. Groundwater samples were collected from a subset of 712 wells for laboratory analysis of F- and other constituents. A handful of sites showing contrasting levels of F- in groundwater were also drilled to determine if the composition of aquifer sediment differed between these sites. The laboratory data show that the field kits correctly classified 91% of the samples relative to the World Health Organization guideline for drinking water of 1.5 mg/L F-. The kit data indicate that 9% of wells across a region extending from the Indus to the Sutlej rivers were elevated in F- relative to this guideline. Field data indicate an association between the proportion of well-water samples with F- > 1.5 mg/L and electric conductivity (EC) > 1.5 mS/cm across six floodplains and six intervening doabs. Low Ca2+ concentrations and elevated bicarbonate (HCO3- > 500 mg/L) and sodium (Na+ > 200 mg/L) in high F- groundwater suggest regulation by fluorite. This could be through either the lack of precipitation or the dissolution of fluorite regulated by the loss of Ca2+ from groundwater due to precipitation of calcite and/or ion exchange with clay minerals. Widespread salinization of Punjab aquifers attributed to irrigation may have contributed to higher F- levels in groundwater of the region. Historical conductivity data suggest salinization has yet to be reversed in spite of changes in water resources management.

Well-Switching to Reduce Arsenic Exposure in Bangladesh: Making the Most of Inaccurate Field Kit Measurements.

Well-switching programs in Bangladesh have successfully lowered arsenic exposure. In these programs, households switch from wells that are labeled "unsafe" to nearby wells labeled "safe," but these designations are usually based on inherently inaccurate field kit measurements. Here, we (a) compare the efficacy of field-kit measurements to accurate laboratory measurements for well switching, (b) investigate the potential impact on well switching of the chosen "safe" threshold, and (c) consider the possible benefits of providing more detailed concentration information than just "safe" and "unsafe." We explore different hypothetical mitigation scenarios by combining two extensive data sets from Araihazar Bangladesh: a blanket survey of 6595 wells over 25 km2 based on laboratory measurements and 943 paired kit and laboratory measurements from the same area. The results indicate that the decline in average arsenic exposure from relying on kit rather than laboratory data is modest in relation to the logistical and financial challenge of delivering exclusively laboratory data. The analysis further indicates that the 50 µg/L threshold used in Bangladesh to distinguish safe and unsafe wells, rather than the WHO guideline of 10 µg/L, is close to optimal in terms of average exposure reduction. We also show that providing kit data at the maximum possible resolution rather than merely classifying wells as unsafe or safe would be even better. These findings are relevant as the government of Bangladesh is about to launch a new blanket testing campaign of millions of wells using field kits.

Testing Homes for Potential Sources of Lead Exposure as a High-School Science Project.

High-school students tested soil, paint, and water for lead (Pb) in a total of 80 houses in their town of Pelham, New York, where blood-Pb data indicate relatively high levels of child exposure. All the samples were tested in the laboratory using established procedures but this was preceded by testing of soil and paint in the field with a kit by the students. The total Pb concentration in 32 of the 159 soil samples that were collected exceeded 400 ppm, the EPA standard for bare soil in residential areas where children play. Only 4 of the 118 tap water samples that were collected contained over 15 ppb Pb, with the data showing that flushing for 2 min clearly lowered Pb concentration further across the board. The highest risk of child exposure may be posed by old Pb-based paint, however, which was detected in 9 of the 48 samples that were tested. Residents were also the least willing to let the students test or sample their paint. High-school students could help reduce exposure in the many towns where child blood-Pb levels remain high today by identifying sources and, while doing so, learn about environmental science and measurement from this hands-on experience.

Assessment of Excess Mortality and Household Income in Rural Bangladesh During the COVID-19 Pandemic in 2020.

Importance: A slow or incomplete civil registry makes it impossible to determine excess mortality due to COVID-19 and difficult to inform policy. Objective: To quantify the association of the COVID-19 pandemic with excess mortality and household income in rural Bangladesh in 2020. Design, Setting, and Participants: This repeated survey study is based on an in-person census followed by 2 rounds of telephone calls. Data were collected from a sample of 135 villages within a densely populated 350-km2 rural area of Bangladesh. Household data were obtained first in person and subsequently over the telephone. For the analysis, mortality data were stratified by month, age, sex, and household education. Mortality rates were modeled by bayesian multilevel regression, and the strata were aggregated to the population by poststratification. Data analysis was performed from February to April 2021. Exposures: Date and cause of any changes in household composition, as well as changes in income and food availability. Main Outcomes and Measures: Mortality rates were compared for 2019 and 2020, both without adjustment and after adjustment for nonresponse and differences in demographic variables between surveys. Income and food availability reported for January, May, and November 2020 were also compared. Results: Enumerators collected data from an initial 16 054 households in January 2020; 14 551 households (91%) responded when contacted again by telephone in May 2020, and 11 933 households (74%)responded when reached again over the telephone in November 2020, for a total of 58 806 individuals (29 726 female participants [50.5%]; mean [SD] age, 26.4 [19.8] years). A total of 276 deaths were reported between February and the end of October 2020 for the subset of the population that could be contacted twice over the telephone, slightly below the 289 deaths reported for the same population over the same period in 2019. After adjustment for survey nonresponse and poststratification, 2020 mortality changed by -8% (95% CI, -21% to 7%) compared with an annualized mortality of 6.1 deaths per 1000 individuals in 2019. However, in May 2020, salaried primary income earners reported a 40% decrease in monthly income (from 17 485 to 10 835 Bangladeshi Taka), and self-employed earners reported a 60% decrease in monthly income (23 083 to 8521 Bangladeshi Taka), with only a small recovery observed by November 2020. Conclusions and Relevance: In this study of households in rural Bangladesh, all-cause mortality was lower in 2020 compared with 2019. Restrictions imposed by the government may have limited the scale of the COVID-19 pandemic in rural areas, although economic data suggest that these restrictions need to be accompanied by expanded welfare programs.

Demand for Information on Environmental Health Risk, Mode of Delivery, and Behavioral Change: Evidence from Sonargaon, Bangladesh.

Millions of villagers in Bangladesh are exposed to arsenic by drinking contaminated water from private wells. Testing for arsenic can encourage switching from unsafe wells to safer sources. This study describes results from a cluster randomized controlled trial conducted in 112 villages in Bangladesh to evaluate the effectiveness of different test selling schemes at inducing switching from unsafe wells. At a price of about US0.60, only one in four households purchased a test. Sales were not increased by informal inter-household agreements to share water from wells found to be safe, or by visual reminders of well status in the form of metal placards mounted on the well pump. However, switching away from unsafe wells almost doubled in response to agreements or placards relative to the one in three proportion of households that switched away from an unsafe well with simple individual sales.

Recommended Sampling Intervals for Arsenic in Private Wells.

Geogenic arsenic in drinking water is a worldwide problem. For private well owners, testing (e.g., private or government laboratory) is the main method to determine arsenic concentration. However, the temporal variability of arsenic concentrations is not well characterized and it is not clear how often private wells should be tested. To answer this question, three datasets, two new and one publicly available, with temporal arsenic data were utilized: 6370 private wells from New Jersey tested at least twice since 2002, 2174 wells from the USGS NAWQA database, and 391 private wells sampled 14 years apart from Bangladesh. Two arsenic drinking water standards are used for the analysis: 10 µg/L, the WHO guideline and EPA standard or maximum contaminant level (MCL) and 5 µg/L, the New Jersey MCL. A rate of change was determined for each well and these rates were used to predict the temporal change in arsenic for a range of initial arsenic concentrations below an MCL. For each MCL and initial concentration, the probability of exceeding an MCL over time was predicted. Results show that to limit a person to below a 5% chance of drinking water above an MCL, wells that are ½ an MCL and above should be tested every year and wells below ½ an MCL should be tested every 5 years. These results indicate that one test result below an MCL is inadequate to ensure long-term compliance. Future recommendations should account for temporal variability when creating drinking water standards and guidance for private well owners.

Evaluation of a field kit for testing arsenic in paddy soil contaminated by irrigation water.

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. Soil testing with an inexpensive kit could help farmers target high-As soil for mitigation or decide to switch to a different crop that is less sensitive to As in soil. A total of 3,240 field kit measurements of As in 0.5 g of fresh soil added to 50 mL of water were compared with total soil As concentrations measured on oven-dried homogenized soil by X-ray fluorescence (XRF). For sets of 12 soil samples collected within a series of rice fields, the average of kit As measurements was a linear function of the average of XRF measurements (r2=0.69). Taking into account that the kit overestimates water As concentrations by about a factor of two, the relationship suggests that about a quarter of the As in paddy soil is released in the kit's reaction vessel. Using the relationship and considering XRF measurements as the reference, the 12-sample average determined correctly whether soil As was above or below a 30 mg/kg threshold in 86% of cases where soil As was above the threshold and in 79% of cases where soil As was below the threshold. We also used a Bayesian approach using 12 kit measurements to estimate the probability that soil As was above a given threshold indicated by XRF measurements. The Bayesian approach is theoretically optimal but was only slightly more accurate than the linear regression. These results show that rice farmers can identify high-As portions of their fields for mitigation using a dozen field kit measurements on fresh soil and base their decisions on this information.

Similar retardation of arsenic in gray Holocene and orange Pleistocene sediments: Evidence from field-based column experiments in Bangladesh.

Groundwater flow has the potential to introduce arsenic (As) in previously uncontaminated aquifers. The extent to which As transport is retarded by adsorption is particularly relevant in Bangladesh where low-As wells offer the best chance of reducing chronic exposure to As of a large rural population dependent on groundwater. In this study, column experiments were conducted with intact cores in the field to measure As retardation. Freshly collected cores of reduced iron (Fe-II) dominated gray sediment of Holocene age as well as oxidized Fe (III)-coated orange sediment of Pleistocene age were eluted at pore-water velocities of 40-230 cm/day with anoxic groundwater pumped directly from a well and containing 320 µg/L As. Up to 100 µg/L As was immediately released from gray sand but the main As breakthrough for both gray and orange sand occurred between 30 and 70 pore volumes, depending on flow rate. The early release of As from gray sand is attributed to the presence of a weakly bound pool of As. The sorption of As was kinetically limited in both gray and orange sand columns. We used a reversible multi-reaction transport model to simulate As breakthrough curves while keeping the model parameters as constant as possible. Contrary to the notion that dissolved As is sorbed more strongly to orange sands, we show that As was similarly retarded in both gray and orange sands in the field.

Arsenic contamination of Bangladesh aquifers exacerbated by clay layers.

Confining clay layers typically protect groundwater aquifers against downward intrusion of contaminants. In the context of groundwater arsenic in Bangladesh, we challenge this notion here by showing that organic carbon drawn from a clay layer into a low-arsenic pre-Holocene (>12 kyr-old) aquifer promotes the reductive dissolution of iron oxides and the release of arsenic. The finding explains a steady rise in arsenic concentrations in a pre-Holocene aquifer below such a clay layer and the repeated failure of a structurally sound community well. Tritium measurements indicate that groundwater from the affected depth interval (40-50 m) was recharged >60 years ago. Deeper (55-65 m) groundwater in the same pre-Holocene aquifer was recharged only 10-50 years ago but is still low in arsenic. Proximity to a confining clay layer that expels organic carbon as an indirect response to groundwater pumping, rather than directly accelerated recharge, caused arsenic contamination of this pre-Holocene aquifer.

New Approaches to Identifying and Reducing the Global Burden of Disease From Pollution.

Pollution from multiple sources causes significant disease and death worldwide. Some sources are legacy, such as heavy metals accumulated in soils, and some are current, such as particulate matter. Because the global burden of disease from pollution is so high, it is important to identify legacy and current sources and to develop and implement effective techniques to reduce human exposure. But many limitations exist in our understanding of the distribution and transport processes of pollutants themselves, as well as the complicated overprint of human behavior and susceptibility. New approaches are being developed to identify and eliminate pollution in multiple environments. Community-scale detection of geogenic arsenic and fluoride in Bangladesh is helping to map the distribution of these harmful elements in drinking water. Biosensors such as bees and their honey are being used to measure heavy metal contamination in cities such as Vancouver and Sydney. Drone-based remote sensors are being used to map metal hot spots in soils from former mining regions in Zambia and Mozambique. The explosion of low-cost air monitors has allowed researchers to build dense air quality sensing networks to capture ephemeral and local releases of harmful materials, building on other developments in personal exposure sensing. And citizen science is helping communities without adequate resources measure their own environments and in this way gain agency in controlling local pollution exposure sources and/or alerting authorities to environmental hazards. The future of GeoHealth will depend on building on these developments and others to protect a growing population from multiple pollution exposure risks.