Hydrogeochemical characterization and evaluation of groundwater quality in Kangayam taluk, Tirupur district, Tamil Nadu, India, using GIS techniques

The main objective of the present study is to evaluate the hydrogeochemical characteristics of groundwater and its suitability for drinking water supply in Kangayam taluk, Tirupur district, Tamil Nadu, India. To achieve this objective, seventy-eight groundwater samples were collected from the wells spread over the study area during December 2016. The collected groundwater samples were tested in the laboratory for various hydrogeochemical parameters such as hydrogen ion concentration (pH), electrical conductivity, total dissolved solids, total hardness, calcium, magnesium, sodium, potassium, chloride, bicarbonate, carbonate, nitrate, sulphate and fluoride. The analytical results were compared with WHO drinking water standards to assess the suitability of groundwater for drinking purposes. To understand the spatial variation of hydrogeochemical parameters over the study area, choropleth (zonation) maps were prepared using geographical information system (GIS). Overall groundwater quality zones were demarcated by overlaying and integrating all the spatial plots using GIS. Three groundwater quality zones such as (1) most desirable, (2) maximum allowable and (3) not permissible were demarcated based on the limits prescribed by the WHO for drinking purposes. This study indicates that 49% of the study area does not possess potable groundwater. About 21% of the area represents "most desirable" category, and the remaining 30% area represents "maximum allowable" category for drinking purposes. The Piper's trilinear diagram indicates that groundwater of this region is Mixed CaMgCl type. As the groundwater quality is poor nearly 49% of the total area, it is necessary to go for treatment before drinking water supply. It is also essential to recharge the aquifer artificially to improve the quantity and quality of groundwater.

Groundwater flow velocities in a fractured carbonate aquifer-type: Implications for contaminant transport

Contaminants that are highly soluble in groundwater are rapidly transported via fractures in mechanically resistant sedimentary rock aquifers. Hence, a rigorous methodology is needed to estimate groundwater flow velocities in such fractured aquifers. Here, we propose an approach using borehole hydraulic testing to compute flow velocities in an un-faulted area of a fractured carbonate aquifer by applying the cubic law to a parallel plate model. The Cadeby Formation (Yorkshire, NE England) - a Permian dolostone aquifer present beneath the University of Leeds Farm - is the fractured aquifer selected for this hydraulic experiment. The bedding plane fractures of this dolostone aquifer, which are sub-horizontal, sub-parallel and laterally persistent, largely dominate the flow at shallow (<~40 mBGL) depths. These flowing bedding plane discontinuities are separated by a rock matrix which is relatively impermeable (K_well-test/K_core-plug~10⁴) as is common in fractured carbonate aquifers. In the workflow reported here, the number of flowing fractures - mainly bedding plane fractures - intersecting three open monitoring wells are found from temperature/fluid conductivity and acoustic/optical televiewer logging. Following well installation, average fracture hydraulic apertures for screened intervals are found from analysis of slug tests. For the case study aquifer, this workflow predicts hydraulic apertures ranging from 0.10 up to 0.54 mm. However, groundwater flow velocities range within two order of magnitude from 13 up to 242 m/day. Notably, fracture apertures and flow velocities rapidly reduce with increasing depth below the water table; the upper ~10 m shows relatively high values of hydraulic conductivity (0.30-2.85 m/day) and corresponding flow velocity (33-242 m/day). Permeability development around the water table in carbonate aquifer-types is common, and arises where high pCO₂ recharge water from the soil zone causes calcite/dolomite dissolution. Hence, agricultural contaminants entering the aquifer with recharge water are laterally transported rapidly within this upper part. Computation of groundwater flow velocities allows determination of the Reynolds number. Values of up ~1, indicating the lower limit of the transition from laminar to turbulent flow, are found at the studied site, which is situated away from major fault traces. Hence, turbulent flow is likely to arise in proximity to tectonic structures, such as normal faults, which localize flow and enhance karstification. The occurrence of turbulent flow in correspondence of such tectonic structures should be represented in regional groundwater flow simulations.

Experimental and numerical evaluation of Groundwater Circulation Wells as a remediation technology for persistent, low permeability contaminant source zones

Contaminants removal stoked inside low permeability zones of aquifers is one of the most important challenge of groundwater remediation process today. Low permeability layers can be considered persistent secondary sources of contamination because they release pollutants by molecular diffusion after primary source of contamination is reduced, causing long plum tails (Back-Diffusion). In this study, the Groundwater Circulation Well (GCW) system was investigated as an alternative remediation technology to the low efficient traditional pumping technologies to restore contaminated low permeability layers of aquifers. The GCW system creates vertical groundwater circulation cells by drawing groundwater through a screen of a multi-screen well and discharging it through another screen. The suitability of this technology to remediate contaminated low permeability zones was investigated by laboratory test and numerical simulations. The collected data were used to calibrate a model created to simulate the Back-Diffusion process and to evaluate the effect of different pumping technologies on the depletion time of that process. Results show that the efficiency of the GCW is dependent on the position and on the geometry of the low permeability zones, however the GCW system appears more suitable to restore contaminated low permeability layers of aquifers than the traditional pumping technology.

Changes in arsenic exposure in Araihazar, Bangladesh from 2001 through 2015 following a blanket well testing and education campaign

BACKGROUND

Concentrations of arsenic (As) are elevated in a large proportion of wells in Bangladesh but are spatially variable even within a village. This heterogeneity can enable exposed households to switch to a nearby well lower in As in response to blanket (area-wide) well As testing.

OBJECTIVES

We document the evolution of As exposure in Araihazar, Bangladesh following a blanket well testing and education campaign, as well as the installation of a considerable number of low As community wells.

METHODS

We use well water and urinary As data collected between 2000 and 2008, along with household interviews extending through 2016, within a 25 km2 area of Araihazar upazila for nearly 12,000 participants enrolled in the Health Effects of Arsenic Longitudinal Study (HEALS). We observe changes in participants' well water and urinary As concentrations following interventions to lower their exposure and use logistic regression to determine the factors associated with participants' decisions to switch primary household wells.

RESULTS

Urinary As for participants drinking from wells with >100 μg/L As at baseline declined from a mean of 226 μg/L at baseline to 173 μg/L two years later, and further declined to 139 μg/L over 8 years. For comparison, urinary As concentrations for participants drinking from wells with ≤10 μg/L As remained close to 50 μg/L throughout. Whereas the interventions only partially reduced exposure, well status with respect to As was predictive of well-switching decisions for at least a decade after the initial testing. Participants with high-As wells were 7 times more likely to switch wells over the first two years and 1.4-1.8 times more likely to switch wells over the ensuing decade.

CONCLUSIONS

Arsenic exposure gradually declined following blanket well testing, an education campaign, and the installation of community wells but remained almost three times higher than for a subgroup of the participants drinking from wells with ≤10 μg/L. In addition, the number of participants with unknown As concentrations in their primary household wells increased substantially over time, indicating the importance of additional well testing as new wells continue to be installed, in addition to other means of reducing As exposure.

Deep tubewell microbial water quality and access in arsenic mitigation programs in rural Bangladesh

The objective of this paper is to determine whether deep tubewells installed through arsenic mitigation efforts in rural Bangladesh provide better drinking water microbial quality compared to shallow tubewells. We conducted a stratified random cross-sectional survey of 484 households to assess microbial contamination of deep tubewell water at source and at point of use (POU) compared to shallow tubewell water using the Compartment Bag Test. In addition, we measured storage time, distance, travel time and ownership status among both sets of users to assess deep tubewell efficacy and under what conditions they offer poorer or better water quality. Differences in tubewell characteristics were compared using non-parametric Mann-Whitney U tests and two-proportion Z-tests. Prevalence ratios of microbial contamination stratified by water quality, storage time and distance to tubewells and ownership were estimated using unadjusted Mantel-Haenszel tests. There was no significant difference in microbial contamination between shallow and deep tubewells at source. The presence of POU water microbial contamination in storage containers in deep tubewell households was 1.11 times the prevalence in shallow tubewell storage containers (95% CI = 0.97-1.27). Deep tubewell users stored water longer and walked significantly farther to obtain water compared to shallow tubewell users. Among deep tubewell households, those residing farther away from the source were 1.24 times as likely to drink contaminated water from storage containers compared to those located nearby (95% CI = 1.04-1.48). Our findings suggest that deep tubewells have comparable water quality to shallow tubewells at source, but increasing distance from the household exacerbates risk of microbial contamination at POU.

An alternative approach to control saltwater intrusion in coastal aquifers using a freshwater surface recharge canal

Aquifers are a major source of freshwater in many parts of the world. Saltwater intrusion from the sea or saline lakes into freshwater aquifers degrades the potable quality of these resources. Various methods have been introduced to mitigate saltwater intrusion, such as recharge wells and physical subsurface barriers. This paper presents an alternative approach to control saltwater intrusion in coastal aquifers using a surface water recharge canal. In this paper, the effectiveness of a recharge canal at mitigating saltwater intrusion is evaluated numerically using SEAWAT. The results indicate that the recharge canal leads to a reduction in the extent of the saltwater intrusion. Under a fixed hydraulic gradient, the extent of this reduction is dependent on the location of the recharge canal relative to the saltwater source. As the hydraulic gradient increases, with the optimum location of the recharge canal approaches the saltwater source location. The results also indicate that more effective saltwater repulsion is achieved when the recharge canal is located near the toe of the saltwater wedge. The results of a field scale case study indicate that a recharge canal with relatively small dimensions could have a significant effect on reduction in the extent of the saltwater intrusion.

Elemental enrichment of sediments in an unprotected shallow groundwater of Lagos and Ogun States, Nigeria

Sediments quality is a good indicator of pollution in a water body where various elements were concentrated. Limited information is available on sediments from hand-dug wells. The present study evaluates sediment samples collected from groundwater of Lagos and Ogun States, Southwest Nigeria. Twenty sediment samples were collected from shallow groundwater, and ten rock samples were also collected from the vicinity of recently dug wells. Trace elements were determined in both the sediments and the rock samples using inductively coupled plasma-mass spectrometry. The enrichment factor was calculated for different elements using Fe, Ti, Mn and Cu as normalizing elements. The order of sediment contamination with each normalizing elements are Cu > Mn > Ti > Fe. The geo-accumulation (Igeo) indexes for Cr, Pb, Cu and Ni are 1.31, 1.05, 1.94 and 1.85, respectively. The Igeo for Lagos sediments is in the order Cr > Pb > Ni > Cu, while in Ogun sediments the order is Cu > Ni > Cr > Pb. The results were compared with Canadian Council of Ministers of Environment values of threshold effect level and probable effect level, which shows the sediments are not toxic. The pollution load index and ecological risk index values are 2.463 and 0.0014, respectively, which further indicates the sediments are not toxic in nature. The major source of most elements in sediments is the host rocks found in the vicinity of the groundwater while high level of some elements recorded in sediments are from the anthropogenic sources.

Redesigning and monitoring groundwater quality and quantity networks by using the entropy theory

This study aimed at redesigning and monitoring the groundwater network of Naqadeh plain in the southwest of Lake Urmia to examine the number and position of optimal wells for the salinity information transfer (EC) and survey of groundwater level at aquifer. In this regard, groundwater level data (35 wells) and electrical conductivity values (24 wells) were used during a 10-year period (2002-2012). In the first stage, simulation was conducted using the multivariate regression method and quantitative and qualitative values and the interaction of wells was observed. In the next stage, number of different classes was considered for clustering quantitative and quantitative values. The results of studying different classes of data clustering showed that the 12-class cluster had more accurate results based on the root mean square error and coefficient of determination. The root mean square error was improved by about 40, 21, and 15%, respectively, compared to the 3, 5, and 9-classe clusters. Finally, by choosing proper cluster of data, entropy indicators were investigated for quantitative and qualitative values at the aquifer level. The results of entropy indices at the aquifer showed that there was a severe shortage of information in terms of salinity in the Northwest of the aquifer, which necessitates drilling a new well in this area to accurately monitor the EC values. However, since more than 90% of the basin area is in surplus and approximately surplus conditions in terms of transferring information, the studied area has a good dispersion for qualitative monitoring. Information transfer index for the quantitative groundwater network monitoring showed that piezometers near Lake Urmia were faced with a lack of information, which according to piezometers ranking, is ranked last in terms of value of maintaining or keeping the network. Eastern areas of aquifer are also faced with shortage of piezometers accounting for about 3% of the total area. The results of survey of surplus wells in the aquifer showed that nine and six surplus wells are in the aquifer for the qualitative and quantitative network, respectively. There were also wells in which information transfer was not well done and their information could not be assured. Finally, based on the conditions, a new arrangement of wells and a new optimal network were proposed.

Arsenic contamination of rural community wells in Nicaragua: A review of two decades of experience

Several surveys have been conducted in Nicaragua between 1996 and 2015 confirming the presence of high levels of arsenic (>10 μg/L). In this paper, these peer-reviewed (n = 2) and non-peer reviewed sources (n = 14) have been combined to provide an extensive overview of the arsenic contamination of drinking water sources in Nicaragua. So far, arsenic contamination has been detected in over 80 rural communities located in 34 municipalities of the country and arsenic poisoning has been identified in at least six of those communities. The source of arsenic contamination in Nicaragua is probably volcanic in origin, both from volcanic rocks and geothermal fluids which are distributed across the country. Arsenic may have directly entered into the groundwater by geothermally-influenced water bodies, or indirectly by reductive dissolution or alkali desorption, depending on the local geochemical conditions.

Modeling groundwater nitrate exposure in private wells of North Carolina for the Agricultural Health Study

Unregulated private wells in the United States are susceptible to many groundwater contaminants. Ingestion of nitrate, the most common anthropogenic private well contaminant in the United States, can lead to the endogenous formation of N-nitroso-compounds, which are known human carcinogens. In this study, we expand upon previous efforts to model private well groundwater nitrate concentration in North Carolina by developing multiple machine learning models and testing against out-of-sample prediction. Our purpose was to develop exposure estimates in unmonitored areas for use in the Agricultural Health Study (AHS) cohort. Using approximately 22,000 private well nitrate measurements in North Carolina, we trained and tested continuous models including a censored maximum likelihood-based linear model, random forest, gradient boosted machine, support vector machine, neural networks, and kriging. Continuous nitrate models had low predictive performance (R2 < 0.33), so multiple random forest classification models were also trained and tested. The final classification approach predicted <1 mg/L, 1-5 mg/L, and ≥5 mg/L using a random forest model with 58 variables and maximizing the Cohen's kappa statistic. The final model had an overall accuracy of 0.75 and high specificity for the higher two categories and high sensitivity for the lowest category. The results will be used for the categorical prediction of private well nitrate for AHS cohort participants that reside in North Carolina.

Modeling Stream-Aquifer Interactions Under Seasonal Groundwater Pumping and Managed Aquifer Recharge

In South Korea, a significant amount of groundwater is used for the heating of water-curtain insulated greenhouses during the winter dry season, which had led to problems of groundwater depletion. A managed aquifer recharge (MAR) project is currently underway with the goal of preventing such groundwater depletion in a typical cultivation area, located on an alluvial aquifer near the Nam River. In the present study, FEFLOW, a three-dimensional finite element model, was used to evaluate different strategies for MAR of the cultivation areas. A conceptual model was developed to simulate the stream-aquifer dynamics under the influence of seasonal groundwater pumping and MAR. The optimal rates and duration of MAR were assessed by analyzing the recovery of the groundwater levels and the change in the groundwater temperature. The simulation results indicate that a MAR rate of 8000 m³ /d effectively restores the groundwater level when the injection wells are located inside the groundwater depletion area. It is also demonstrated that starting the MAR before the beginning of the seasonal pumping is more effective. Riverbank filtration is preferable for securing the injection water owing to plentiful source of induced recharge from the river. Locating the pumping wells adjacent to the river where there are thick permeable layers could be a good strategy for minimizing decreases in the groundwater level and temperature.

Effects of Intraborehole Flow on Purging and Sampling Long-Screened or Open Wells

Hydraulic head differences across the screened or open interval of a well significantly influence the sampled water mixture. Sample bias can occur due to an insufficient pumping rate and/or due to native groundwater displacement by intraborehole flow (IBF). Proper understanding of the sampled water mixture is crucial for accurate interpretation of environmental tracers and groundwater chemistry data, and hence groundwater characterization. This paper uses numerical modeling to quantify sample bias caused by IBF in an un-pumped high-yield well, and the influence of pumping rate and heterogeneity on the volume of pumpage required to purge an IBF plume. The results show that (1) the pumping rate must be at least an order of magnitude greater than the IBF rate to achieve permeability-weighted yield, (2) purge volume was 2.2 to 20.6 times larger than the IBF plume volume, with the ratio depending on plume location relative to hydraulic conductivity and head distributions, and (3) after an example 1000-day un-pumped period, purging required removal of at least three orders of magnitude more water than the common practice of three to five well volumes. These results highlight the importance of knowing the borehole flow regime to identify IBF inflow and outflow zones, estimate IBF rates, and to develop a strategic sampling approach.

Multi-Objective Optimization of Managed Aquifer Recharge

This study demonstrates the utilization of a multi-objective hybrid global/local optimization algorithm for solving managed aquifer recharge (MAR) design problems, in which the decision variables included spatial arrangement of water injection and abstraction wells and time-variant rates of pumping and injection. The objective of the optimization was to maximize the efficiency of the MAR scheme, which includes both quantitative and qualitative aspects. The case study used to demonstrate the capabilities of the proposed approach is based on a published report on designing a real MAR site with defined aquifer properties, chemical groundwater characteristics as well as quality and volumes of injected water. The demonstration problems include steady state and transient scenarios. The steady state scenario demonstrates optimization of spatial arrangement of multiple injection and recovery wells, whereas the transient scenario was developed with the purpose of finding optimal regimes of water injection and recovery at a single location. Both problems were defined as multi-objective problems. The scenarios were simulated by applying coupled numerical groundwater flow and solute transport models: MODFLOW-2005 and MT3D-USGS. The applied optimization method was a combination of global (the non-dominated sorting genetic algorithm [NSGA-2]) and local (the Nelder-Mead downhill simplex search algorithms). The analysis of the resulting Pareto optimal solutions led to the discovery of valuable patterns and dependencies between the decision variables, model properties, and problem objectives. Additionally, the performance of the traditional global and the hybrid optimization schemes were compared.

Sustainable Yield of a Hydrothermal Area: From Theoretical Concepts to the Practical Approach

Sustainable use of groundwater in the hydrothermal area of Viterbo (Central Italy) was analyzed. In this area, multipurposes utilization of groundwater coexists: several thermal springs and wells supply spas and public pools, cold and fresh water is used for irrigation and drinking-water. Starting from theoretical concepts, a management plan has been developed to ensure groundwater sustainability in response to the increased demand of withdrawal from thermal wells, by integrating previous hydrogeological studies, new investigations and a new finite-difference model. The most stringent constraints considered are: to maintain the quality of thermal and fresh waters, to limit the effects on the hydraulic equilibrium existing between overlapping aquifers, to ensure a significant flow to the natural thermal springs and the quality and flow rate of the spring used for drinking purposes. The practical approach included identification of the maximum pumping rate from the wells of the spas, analysis of the response time of the system under development and drafting of a safeguard and monitoring plan. The case examined takes into account the complexity of the task in defining practical measures for groundwater management on the basis of theoretical concepts of its sustainable use. A participative approach among the different water decision-makers and adaptive management in the use of groundwater resources with different quality represent the key points to overcome conflicts between different users, with the awareness of the ineludible uncertainties of the hydrogeological model.

Field testing of over 30,000 wells for arsenic across 400 villages of the Punjab plains of Pakistan and India: Implications for prioritizing mitigation

Most of the rural population of 90 million in Punjab province in Pakistan and Punjab state in India drinks, and cooks with, untreated water drawn from shallow wells. Limited laboratory testing has shown that groundwater in the region can contain toxic levels of arsenic. To refine this assessment, a total of 30,567 wells from 383 villages were tested with a field kit in northern Punjab province of Pakistan and western Punjab state of India. A subset of 431 samples also tested in the laboratory show that 85% of wells were correctly classified by the kit relative to the World Health Organization guideline of 10 μg/L for arsenic in drinking water. The kit data show that 23% of the tested wells did not meet the WHO guideline for arsenic but also that 87% of households with a well high in arsenic live within 100 m of a well that meets the WHO guideline. The implication is that many households could rapidly lower their exposure if the subset of safe wells could be shared. In a follow-up conducted one year later in five villages where 59% of wells were elevated in arsenic, two-thirds of households indicated that they had switched to a neighboring well in response to the testing. The blanket testing of millions of wells for arsenic in the region should therefore be prioritized over much costlier water treatment and piped water supply projects that will take much longer to have a comparable impact.

Radon concentrations in the community groundwater system of South Korea

Groundwater samples were collected from 3818 wells used for the community groundwater system (CGS) in the remote rural areas of South Korea and analyzed to determine radon concentrations. Radon concentrations varied with rock type, ranging from 0.1 to 2393.5 Bq/L with an average of 86.6 Bq/L and a median of 46.4 Bq/L. Among 10 geological units, the median CGS radon concentration was highest (59.6-103.0 Bq/L) in granite, and lower in sedimentary rocks (16.9-21.1 Bq/L) and porous volcanic rocks (17.6 Bq/L), respectively. Of the 3818 samples, 26.1% exceeded the World Health Organization (WHO) radon level limit of 100 Bq/L. The application of the natural radon reduction rate (26.5%) recently suggested by Yun et al. Applied Radiation and Isotopes, 126(1), 23-25 (2017) to the CGS water tank appeared to decrease exceedance of the WHO radon level limit to 20.2%. Because of the high radon concentrations in CGS groundwater in South Korea, the establishment of a radon level limit for drinking water is strongly recommended to ensure the health and safety of the people using CGS water.

Characterizing Flaring from Unconventional Oil and Gas Operations in South Texas Using Satellite Observations

Over the past decade, increases in high-volume hydraulic fracturing for oil and gas extraction in the United States have raised concerns with residents living near wells. Flaring, or the combustion of petroleum products into the open atmosphere, is a common practice associated with oil and gas exploration and production, and has been under-examined as a potential source of exposure. We leveraged data from the Visible Infrared Imaging Spectroradiometer (VIIRS) Nightfire satellite product to characterize the extent of flaring in the Eagle Ford Shale region of south Texas, one of the most productive in the nation. Spatiotemporal hierarchical clustering identified flaring sources, and a regression-based approach combining VIIRS information with reported estimates of vented and flared gas from the Railroad Commission of Texas enabled estimation of flared gas volume at each flare. We identified 43887 distinct oil and gas flares in the study region from 2012 to 2016, with a peak in activity in 2014 and an estimated 4.5 billion cubic meters of total gas volume flared over the study period. A comparison with well permit data indicated the majority of flares were associated with oil-producing (82%) and horizontally drilled (92%) wells. Of the 49 counties in the region, 5 accounted for 71% of the total flaring. Our results suggest flaring may be a significant environmental exposure in parts of this region.

Heavy metal contamination and health risk assessment for children near a large Cu-smelter in central China

Nonferrous metallurgy is causing significant concerns due to its emissions of heavy metals into environment, degrading environmental quality, and consequently posing high risks to human health. In this study, the concentration levels of Cadmium (Cd), Copper (Cu), Lead (Pb), and Arsenic (As) were investigated in soil, crop, well water, and fish samples collected around the Daye Copper Smelter in Hubei province, China, and the potential health risks were assessed for local children. The results showed that soils near the smelter were heavily polluted by Cd, Cu, Pb, and As, with the mean concentrations of 4.87, 195.26, 92.65, and 35.84 mg/kg, respectively, which were significantly higher than the values of soil Cd (0.18 mg/kg), Cu (32.84 mg/kg), Pb (28.46 mg/kg), and As (13.65 mg/kg) in the reference area (p < 0.001). The concentrations of Cd and As in vegetable samples collected from smelter-affected area exceeded the maximum permissible level (MPL) for food in China by 82% and 39%, respectively. The concentrations of Cd and Pb in rice grain harvested from smelter-affected area were 9.35 and 1.35 times higher than the corresponding MPL, respectively. The concentrations of Cd, As, and Cu in fish muscle from smelter-affected area exceeded the national MPL by 72%, 41%, and 24% of analyzed samples, respectively. The concentrations of Cd (p < 0.05) and As (p < 0.01) in well water were significantly higher in the smelter-affected area than those in the reference area, respectively. The health risks to local children in the smelter-affected area were 30.25 times higher than the acceptable level of 1, and most of the risks were resulted from Cd (46%), As (27%) and Pb (20%). The intake of crops was a major source (78%) to health risks for local children.

Characteristics, sources, water quality and health risk assessment of trace elements in river water and well water in the Chinese Loess Plateau

Water resources and water quality are restrictive factors in the Chinese Loess Plateau (CLP), a unique area with most severe soil erosion, fragile ecology and water shortage. River and well water samples were firstly analyzed, and multiple methods and indexes, including principal component analysis (PCA), correlation analysis (CA), sodium adsorption ratio (SAR), water quality index (WQI), hazard quotient (HQ), and hazard index (HI), were used to investigate characteristics, water quality and health risk assessment of trace elements in CLP. The average trace elements concentrations were higher than the world average with a slightly alkaline characteristic. PCA and CA showed that Al, Fe, Li, B, As, and F had natural origins from loess weathering and leaching; Cr, Pb, Cd, Cu, Ag, and Tl were mainly from anthropogenic input; Co, Ni, and Mn were dominated by both anthropogenic and natural sources. The poor river water quality was mainly related with high sodium (alkalinity) and salinity hazard. The poor well water quality samples with high WQI values, especially for As, Cr, and B, were distributed in the northwest and the Fenhe River sub-basin. The pollution level of trace elements in rivers in CLP was in medium level compared with other rivers worldwide. Arsenic pollution was the worst in well water and was the potential pollutant in river water especially for children. Arid climate together with anthropogenic input and special water characteristics (high Na, pH, and low Ca) aggravated As pollution. More work should be done to monitor the secular variation and remove As in the high As areas. The results of this study can provide the basic data for efficient water management and human health protection in CLP.

Prospective Biopsy-Based Study of CKD of Unknown Etiology in Sri Lanka

BACKGROUND AND OBJECTIVES

A kidney disease of unknown cause is common in Sri Lanka's lowland (dry) region. Detailed clinical characterizations of patients with biopsy-proven disease are limited, and there is no current consensus on criteria for a noninvasive diagnosis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We designed a prospective study in a major Sri Lankan hospital servicing endemic areas to ascertain pathologic and clinical characteristics of and assess risk factors for primary tubulointerstitial kidney disease. We used logistic regression to determine whether common clinical characteristics could be used to predict the presence of primary tubulointerstitial kidney disease on kidney biopsy.

RESULTS

From 600 new patients presenting to a tertiary nephrology clinic over the course of 1 year, 87 underwent kidney biopsy, and 43 (49%) had a biopsy diagnosis of primary tubulointerstitial kidney disease. On detailed biopsy review, 13 (30%) had evidence of moderate to severe active kidney disease, and six (15%) had evidence of moderate to severe chronic tubulointerstitial kidney disease. Patients with tubulointerstitial kidney disease were exclusively born in endemic provinces; 91% spent a majority of their lifespan there. They were more likely men and farmers (risk ratio, 2.0; 95% confidence interval, 1.2 to 2.9), and they were more likely to have used tobacco (risk ratio, 1.7; 95% confidence interval, 1.0 to 2.3) and well water (risk ratio, 1.5; 95% confidence interval, 1.1 to 2.0). Three clinical characteristics-age, urine dipstick for protein, and serum albumin-could predict likelihood of tubulointerstitial kidney disease on biopsy (model sensitivity of 79% and specificity of 84%). Patients referred for kidney biopsy despite comorbid diabetes or hypertension did not experience lower odds of tubulointerstitial kidney disease.

CONCLUSIONS

A primary tubulointerstitial kidney disease occurs commonly in specific regions of Sri Lanka with characteristic environmental and lifestyle exposures.

Modeling fate and transport of hydraulic fracturing fluid in the presence of abandoned wells

Hydraulic fracturing in shale/tight gas reservoirs creates fracture network systems that can intersect pre-existing subsurface flow pathways, e.g. fractures, faults or abandoned wells. This way, hydraulic fracturing operations could pose environmental risks to shallow groundwater systems. This paper explores the long-term (> 30 years) flow and transport of fracturing fluids into overburden layers and groundwater aquifers through a leaky abandoned well, using the geological setting of North German Basin as a case study. A three-dimensional model consisting of 15 sedimentary layers with three hydrostratigraphic units representing the hydrocarbon reservoir, overburden, and the aquifer is built. The model considers one perforation location at the first section of the horizontal part of the well, and a discrete hydraulic fracture intersecting an abandoned well. A sensitivity analysis is carried out to quantify and understand the influence of a broad spectrum of field possibilities (reservoir properties, overburden properties, abandoned well properties and its proximity to hydraulic fractures) on the flow of fracturing fluid to shallower permeable strata. The model results suggest the spatial properties of the abandoned well as well as its distance from the hydraulic fracture are the most important factors influencing the vertical flow of fracturing fluid. It is observed that even for various field set-tings, only a limited amount of fracturing fluid can reach the aquifer in a long-term period.

Arsenic exposure and young adult's mortality risk: A 13-year follow-up study in Matlab, Bangladesh

BACKGROUND

Widespread arsenic contamination in underground water is a well-documented public health concern that threatens millions of lives worldwide. We investigated the risk of young-adult mortality due to high chronic exposure to arsenic through years of drinking arsenic contaminated water.

METHODS

A prospective cohort study of 58,406 individuals was enrolled who were 4-18 years at baseline. Since Matlab HDSS (Health and Demographic Surveillance System) has an active surveillance system, all individuals were included in the follow up. Each individual's arsenic exposure was calculated at (1) baseline As level as current exposure (2) time-weighted lifetime (average or lifetime average) and (3) cumulative arsenic exposure. Age, sex, educational attainment and SES were adjusted during the analysis. In this 13 years closed-cohort study (2003-2015), all young-adult deaths were captured through verbal autopsy (VA) using International Classification of Diseases (ICD-10) to define the causes.

RESULTS

Although, girls had higher values of cumulative arsenic exposure via tube well water than boys (median: 1858.5 μg/year/L vs. 1798.8 μg/year/L) but higher mortality due to cancers and due to cerebro-vascular disease, cardio-vascular disease, and respiratory disease (7.0 vs. 5.7 per 100,000 person-years and 6.4 vs. 4.2 per 100,000 person-years respectively). Higher risk of deaths among young adults (Adjusted HR: 2.7, 1.3-5.8) due to all cancers among those who were exposed to As > 138.7 compared to As ≤ 1.1 μg/L. For cerebro-vascular disease, cardio-vascular disease, and respiratory disease deaths, average arsenic in well water (>223.1 μg/L vs. ≤90.9 μg/L) and cumulative arsenic in well water (>2711.0 μg/year/L vs. ≤1013.3 μg/year/L) had 4.8 (1.8-12.8) and 5.1 (1.7-15.1) times higher risks of mortality than to those lowest exposed.

CONCLUSION

Higher concentration of, and chronic exposure to arsenic in drinking water, increases the mortality risk among the young adults, regardless of gender.

The role of gut microbiome and its interaction with arsenic exposure in carotid intima-media thickness in a Bangladesh population

BACKGROUND

Emerging data suggest that inorganic arsenic exposure and gut microbiome are associated with the risk of cardiovascular disease. The gut microbiome may modify disease risk associated with arsenic exposure. Our aim was to examine the inter-relationships between arsenic exposure, the gut microbiome, and carotid intima-media thickness (IMT)-a surrogate marker for atherosclerosis.

METHODS

We recruited 250 participants from the Health Effects of Arsenic Longitudinal Study in Bangladesh, measured IMT and collected fecal samples in year 2015-2016. 16S rRNA gene sequencing was conducted on microbial DNA extracted from the fecal samples. Arsenic exposure was measured using data on arsenic concentration in drinking water wells over time to derive a time-weighted water arsenic index. Multivariable linear regression models were used to test the inter-relationships between arsenic exposure, relative abundance of selected bacterial taxa from phylum to genus levels, and IMT.

RESULTS

We identified nominally significant associations between arsenic exposure, measured using either time-weighted water arsenic or urinary arsenic, and the relative abundances of several bacterial taxa from the phylum Tenericutes, Proteobacteria, and Firmicutes. However, none of the associations retained significance after correction for multiple testing. The relative abundances of the family Aeromonadaceae and genus Citrobacter were significantly associated with IMT after correction for multiple testing (P-value = 0.02 and 0.03, respectively). Every 1% increase in the relative abundance of Aeromonadaceae and Citrobacter was related to an 18.2-μm (95% CI: 7.8, 28.5) and 97.3-μm (95% CI: 42.3, 152.3) difference in IMT, respectively. These two taxa were also the only selected family and genus using the LASSO variable selection method. There was a significant interaction between Citrobacter and time-weighted water arsenic in IMT (P for interaction = 0.04).

CONCLUSIONS

Our findings suggest a role of Citrobacter in the development of atherosclerosis, especially among individuals with higher levels of arsenic exposure.

Maternal swimming pool exposure during pregnancy in relation to birth outcomes and cord blood DNA methylation among private well users

Swimming in pools during pregnancy may expose the fetus to water disinfection by-products (DBP). As yet, our understanding of the impacts on DBPs on the fetus is uncertain. Individuals with public water systems are typically exposed to DBPs through drinking, showering and bathing, whereas among those on private water systems, swimming in pools may be the primary exposure source. We analyzed the effects of maternal swimming on birth outcomes and cord blood epigenetic changes in the New Hampshire Birth Cohort Study, a cohort of pregnant women with households on private water systems. Information about swimming in pools during pregnancy was obtained from 1033 women via questionnaires. Swimming pool use and duration were modeled using linear regression with newborn weight, length, and head circumference (z-scores) and genome wide cord blood DNA methylation as the outcomes and with adjustment for potential confounders. Overall 19.7% of women reported swimming in a pool during pregnancy. Among swimmers, duration of swimming was inversely related to head circumference (-0.02 z-score per 10% increase in duration, P = 0.004). No associations were observed with birth weight, length or DNA methylation modifications. Our findings suggest swimming pool exposure may impact the developing fetus although longer-term studies are needed.

Enhanced distribution of humic acid-modified nanoscale magnesia for in situ reactive zone removal of Cd from simulated groundwater

Efficient injection and distribution of nanoparticles in porous media are considered a formidable technical hurdle for injection-based in situ remediation. One approach to enhance the mobility of nanoparticles in an aquifer is to use surface modifiers. In this study, nanoscale magnesia (NMgOs), an innovative and effective remedial material for cadmium (Cd) removal from groundwater, was modified with the negatively charged and eco-friendly humic acid to enhance its mobility in aquifers. A two-dimensional reactor (60 × 50 × 10 cm), with 2 injection wells and 30 monitoring wells was designed, constructed, and sand-packed in the laboratory to simulate a saturated aquifer. The simulated aquifer was pre-contaminated with Cd to simulate a plume in groundwater. The distribution of injected unmodified NMgOs and humic acid-modified NMgOs slurry were evaluated in the reactor. The radius of influence (ROI) of humic acid-modified NMgOs was estimated to be approximately 5 cm based on visual observation, while no ROI was apparent for the unmodified NMgOs because of their aggregation at the bottom of the injection wells. The concentrations of Cd and magnesium (Mg) were monitored in all 30 monitoring wells at different time intervals to evaluate the effectiveness of Cd removal. The breakthrough curve analysis revealed that humic acid enhances the transport of NMgOs in the saturated porous media. Furthermore, the results of scanning electron microscopy-energy dispersive x-ray (SEM-EDX) characterization of silica sand before and after injection of NMgOs verified the presence of 5.78% of Mg from humic acid-modified NMgOs and 0.19% from unmodified NMgOs at 35 cm downgradient of the injection wells, which are consistent with the conclusion drawn from the breakthrough curves.