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Assessing the Impact of Drought on Arsenic Exposure from Private Domestic Wells in the Conterminous United States
- Melissa A. Lombard*Melissa A. Lombard*Email: [email protected]U.S. Geological Survey, New England Water Science Center, Pembroke, New Hampshire 03275, United StatesMore by Melissa A. Lombard
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- Johnni DanielJohnni DanielCenters for Disease Control and Prevention, 4770 Buford Highway, NE, Atlanta, Georgia 30341, United StatesMore by Johnni Daniel
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- Zuha JeddyZuha JeddyCenters for Disease Control and Prevention, 4770 Buford Highway, NE, Atlanta, Georgia 30341, United StatesMore by Zuha Jeddy
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- Lauren E. HayLauren E. HayFormerly U.S. Geological Survey, Water Mission Area, Lakewood, Colorado 80225, United StatesMore by Lauren E. Hay
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- Joseph D. AyotteJoseph D. AyotteU.S. Geological Survey, New England Water Science Center, Pembroke, New Hampshire 03275, United StatesMore by Joseph D. Ayotte
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Abstract
This study assesses the potential impact of drought on arsenic exposure from private domestic wells by using a previously developed statistical model that predicts the probability of elevated arsenic concentrations (>10 μg per liter) in water from domestic wells located in the conterminous United States (CONUS). The application of the model to simulate drought conditions used systematically reduced precipitation and recharge values. The drought conditions resulted in higher probabilities of elevated arsenic throughout most of the CONUS. While the increase in the probability of elevated arsenic was generally less than 10% at any one location, when considered over the entire CONUS, the increase has considerable public health implications. The population exposed to elevated arsenic from domestic wells was estimated to increase from approximately 2.7 million to 4.1 million people during drought. The model was also run using total annual precipitation and groundwater recharge values from the year 2012 when drought existed over a large extent of the CONUS. This simulation provided a method for comparing the duration of drought to changes in the predicted probability of high arsenic in domestic wells. These results suggest that the probability of exposure to arsenic concentrations greater than 10 μg per liter increases with increasing duration of drought. These findings indicate that drought has a potentially adverse impact on the arsenic hazard from domestic wells throughout the CONUS.
1. Introduction
ARTICLE SECTIONS
There is a recognized need for better understanding of potential drought impacts to public health in order to prepare public health officials, environmental health programs, and emergency preparedness/response managers with strategies for mitigation and interventions. (1−3) Unlike other climate-related health hazards such as flooding, hurricanes, and heat waves, drought typically occurs over extended time periods ranging from months to years, making it more difficult to assess its impacts on human health. (1) Drought can cause a variety of adverse health effects, including pulmonary inflammation from dry, dusty conditions; increased vector-borne diseases from changes in water levels resulting in pools of standing water; increased mental duress due to financial stress; and increased infectious diseases or gastrointestinal illnesses due to reduced water use for sanitation and hygiene. (1−3)
Less known are the effects of drought on the quality of water from drinking-water supply wells, and, more specifically, on the likelihood of human exposure to high concentrations of arsenic in private domestic wells; wells that typically serve a single household, hereafter referred to as domestic well(s). Arsenic is primarily a geogenic contaminant and commonly reported in drinking-water supply wells. The occurrence of geogenic arsenic in groundwater is due to a variety of complex geochemical interactions including desorption and/or reductive dissolution of arsenic from iron oxides, oxidation of sulfide minerals, which may cause arsenic to sorb to iron oxides and be re-released into groundwater through reductive dissolution, and evaporative concentration. (4,5) These desorption and dissolution reactions are highly dependent on pH and redox conditions of groundwater, which may vary with fluctuations in groundwater levels due to drought. Evaporative concentration may also result from drought. There are few existing studies that specifically assess the impact of drought on arsenic concentrations in groundwater and those that do report increases in arsenic concentrations from samples collected during drought. (6,7) Other studies report seasonal fluctuations in groundwater arsenic concentrations, which may be due to changes in groundwater levels as well as seasonal changes in groundwater flow paths. (8,9)
Chronic exposure to arsenic from drinking water is associated with an increased risk of several types of cancers including bladder, (10,11) lung, (11) prostate, (12) and skin. (13) Additional adverse health outcomes include developmental impairments, cardiovascular disease, adverse birth outcomes, and impacts on the immune and endocrine systems. (13) The U.S. Environmental Protection Agency (EPA) has established a maximum contaminant level (MCL) for arsenic of 10 μg per liter (μg/L) for public supply wells; however, the EPA is not authorized to regulate domestic wells. Because the onus is on the domestic well owner, water-quality testing occurs infrequently, thus increasing the likelihood of unrecognized exposure to drinking-water contaminants, including arsenic. (14) In 2010, an estimated 37.2–43.2 million people (15,16) in the conterminous United States (CONUS) used domestic wells for household water supply. There is evidence that concentrations of arsenic can vary seasonally in domestic and other wells, (8,9) suggesting that drought may be a driver for changing concentrations. (6,7) Chronic effects of drought to human health, such as changes in water quality, remain understudied. (3)
Droughts can have a broad range of impacts, subsequently different types of drought have been defined and include meteorological or climatological, agricultural, hydrological, and socioeconomic. (17,18) The common characteristic of all categories of drought is the lack of water. Several indices have been developed to quantify drought severity and the various impacts of drought. Commonly used drought indices in the United States (U.S.) include the Palmer Drought Severity Index, Palmer Hydrologic Drought Index, Palmer Z Index, Keetch-Byram Drought Index, Standardized Precipitation Index, and the U.S. Drought Monitor, among others. (18) The U.S. Drought Monitor began in 2000 and provides a nationally consistent indication of weekly conditions by county for the CONUS. To indicate the severity of drought, the U.S. Drought Monitor uses a classification scheme that ranges from abnormally dry (D0) to exceptional drought (D4). (19) These classifications take into consideration the Palmer Drought Severity Index, Climate Prediction Center Soil Moisture Model, the U.S. Geological Survey (USGS) weekly streamflow, the Standardized Precipitation Index, and objective drought indicators from regional representatives throughout the CONUS. (19) For this study, we use the U.S. Drought Monitor to identify and categorize drought because it provides a comprehensive method for drought classification and is available for the CONUS.
From 2010 to 2018, the U.S. experienced three droughts reaching historic proportions including the Southern Plains drought (2010–2011), a 2012 drought that impacted a large portion of the CONUS, and a persistent West Coast drought. The drought of 2012 in the U.S. was one of the worst droughts on record. On September 25, 2012, the drought encompassed 66% of the CONUS, the greatest areal extent recorded since the beginning of the U.S. Drought Monitor in 2000. (20) The onset of this drought occurred over an extended time period with areas of above average temperatures and below average precipitation during the winter and spring of 2012 that persisted throughout the summer. (20) In 2012, the spatial extent of the most severe drought (D3 and D4) was 24.1%, also the largest to date. (20) The regions of the CONUS that were hardest hit by the 2012 drought were the West, Great Plains, Midwest, and Southeast. Only New England and the Pacific Northwest regions did not experience drought during 2012. (20) When considering drought impacts to groundwater and drinking water, previous studies have focused largely on the reduced quantity of fresh water supplies. Few studies have assessed drought impacts to groundwater quality and those that did were primarily concerned with coastal aquifers and salt-water intrusion due to drawdown of fresh water supplies. (21−24) There is a recognized need for studies that assess the impact of drought on groundwater quality. (1,3,24,25)
A previously developed statistical model that predicts the probability of elevated arsenic (>10 μg/L) in domestic wells throughout the CONUS includes precipitation and groundwater recharge as important variables. (26) In that study, precipitation has an inverse relationship with the probability of elevated arsenic, suggesting that a decrease in precipitation would increase the probability of elevated arsenic. (26) Groundwater recharge, on the other hand, has a positive relationship with the model outcome, suggesting that a decrease in recharge would decrease the likelihood of elevated arsenic. The relationship of arsenic to precipitation was interpreted to represent climate regimes and the pattern of high arsenic concentrations in arid regions. (26) The relationship between recharge and elevated arsenic was interpreted as possibly representing the mechanism of reductive desorption and (or) dissolution of arsenic from iron oxides and/or alternatively representing a flushing of arsenic into the groundwater with increased recharge. (26) In areas with low precipitation and low recharge, increases in apparent recharge (albeit small) are associated with increased arsenic. (26) In the previous study, 30-year climate averages for total annual precipitation (1981–2010) and total annual estimated groundwater recharge (1951–1980) were used to develop the model and make predictions. Estimates of the population of domestic well users exposed to elevated arsenic were calculated based on the model results. In this paper, we apply the previously developed model to drought situations.
The objectives of the current study are (1) to assess the potential impact of drought on the probability of elevated arsenic concentrations (>10 μg/L) in domestic wells at the CONUS scale using an existing model that contains drought-related variables (precipitation and estimated groundwater recharge) and (2) to update estimates of the population of domestic well users exposed to high arsenic concentrations using new estimates of the population and location of domestic well users (15) and to estimate changes in the population of domestic well users exposed to elevated arsenic across the CONUS as a result of drought.
2. Methods
ARTICLE SECTIONS
In this study, we use a logistic regression model that predicts the likelihood of having high arsenic concentrations (>10 μg/L) in domestic wells, (26) hereafter referred to as the original model, as a tool for evaluating the potential impact of drought. Logistic regression is a useful technique for modeling environmental concentrations that are not normally distributed and contain samples with results below analytical detection limits. The original model predicts the probability of arsenic concentrations in domestic wells exceeding the MCL of 10 μg/L and consists of 42 predictor variables including geologic, geochemical, hydrologic, and land use information. The two predictor variables with the largest relative influence are average annual precipitation and average annual estimated groundwater recharge; however, these two variables have opposing relationships with the model outcome indicated by the different signs on the variable coefficients. Precipitation has an inverse relationship while recharge has a positive relationship with the probability of high arsenic in domestic wells according to the original model equation.
Here, we employ a two-prong approach for objective 1, estimating the impact of drought on arsenic concentrations in domestic wells (see Figure S1 for a schematic of methods). First, we ran the original model using systematically reduced precipitation and recharge values to simulate drought conditions to estimate the change in the probability of elevated arsenic if drought conditions existed across the entire CONUS. Second, we ran the original model using total annual precipitation and groundwater recharge values from the year 2012 when drought conditions existed over a large extent of the CONUS. (20,27) The second approach provided a method for comparing the duration of drought to changes in the predicted probability of high arsenic in domestic wells. Our second study objective, to estimate changes in the number of domestic well users exposed to high arsenic due to drought, was accomplished by using the results from a drought simulation and newly available spatial estimates of domestic well users. (15)
Our analysis does not account for human behavioral changes that could result from drought such as drilling deeper wells or changing water supplies, which might also alter the concentrations of arsenic in domestic well water. Similarly, increased irrigation due to drought could have locally important impacts on arsenic but is beyond the scope of this study.
Model predictions and statistical analyses were completed in the R computing environment. (28) Manipulation of model variables and mapping of model outputs were completed in ArcMap (release 10.5.1, Environmental Systems Research Institute, Redlands, CA). Details about the original model including the model equation, data, and raster files are available. (26,29) A data release is available that contains the model input and output files produced from this study. (30)
2.1. Drought Simulations
Values for the groundwater recharge and precipitation variables used in the original model were systematically reduced to simulate drought conditions and assess the impact on model predictions. The annual precipitation and groundwater recharge used in the original model were left the same or decreased by 25 or 50% for a total of eight different drought simulations (Table 1). Model predictions were made using the original model equation and adjusting the groundwater recharge and precipitation variables, while keeping all other model variables the same. These simulations applied the same reductions across the entire CONUS, for example in simulation 7 every grid cell in our model domain had a 25% reduction in precipitation and a 50% reduction in recharge. As described in Section 3.1, simulation 7 approximates the conditions experienced by the areas of drought in 2012. Additionally, 25 and 50% reductions in precipitation are recommended by the National Drought Mitigation Center for ranchers to consider in preparing for drought. (31)
Table 1. Various Scenarios Run in the Drought Simulation and the Dominant Change in Probability of High Arsenic Throughout the CONUS
| drought simulation run | precipitation | recharge | change in probability of high arsenic |
|---|---|---|---|
| 1 | decrease by 25% | unchanged | increase |
| 2 | decrease by 50% | unchanged | increase |
| 3 | unchanged | decrease by 25% | mixed |
| 4 | unchanged | decrease by 50% | mixed |
| 5 | decrease by 25% | decrease by 25% | increase |
| 6 | decrease by 50% | decrease by 50% | increase |
| 7a | decrease by 25% | decrease by 50% | mixed |
| 8 | decrease by 50% | decrease by 25% | increase |
a
Drought simulation that is similar to conditions experienced during the drought of 2012.
2.2. Updated Data Sources
New and different data sets for annual estimated groundwater recharge and annual precipitation were used in this study to calculate the updated probabilities of high arsenic for a 30-year climate average and the year 2012. Comparisons between the 30-year climate average and individual years were not possible with the previous groundwater recharge estimates because values were not available for individual years. The precipitation data set was updated to be consistent with the precipitation values that were used in the updated groundwater recharge estimates. These updated values of groundwater recharge and precipitation were substituted into the original model. We ran the existing model with the updated data, and the model prediction results were quite similar; therefore a new model was not developed. Updated arsenic probability maps were made using the updated precipitation and groundwater recharge for a 30-year average and the year 2012. These maps allowed for comparisons between the change in predicted probability of high arsenic during 2012 and 30-year climate conditions and the duration of drought during 2012. New estimates of the quantity and location of domestic well users in the CONUS for the year 2010 were published since the original model. (15) We used these new domestic well population estimates to update the estimates of those exposed to high arsenic under average climate conditions and drought. Achieving our study objectives would not have been possible without using updated data sources.
2.2.1. Groundwater Recharge
Annual estimated groundwater recharge values used in the original model are means based on 30 years from 1951 to 1980; however, the values for individual years are not provided. (32) There are a limited number of estimates of total annual groundwater recharge values available at the CONUS scale on an annual basis. A data set of estimated total annual groundwater recharge values for the years 2000–2013 (33) was explored but was not used in this study because of its inclusion of irrigation, which was not in the original model; inclusion of irrigation may have complicated the interpretation of results because we are interested in naturally occurring changes due to drought. Also, the short time span of estimates does not allow for comparison with 30-year climate averages. Rather, the total annual groundwater recharge values used in this study are outputs from the Precipitation-Runoff Modeling System (PRMS) (34) as implemented in the National Hydrologic Model (NHM) infrastructure developed by the USGS (35,36) to support coordinated, comprehensive, and consistent hydrologic modeling at the watershed scale for the CONUS. These model recharge estimates take into account precipitation, snowmelt, evaporation and transpiration, plant canopy interception, Hortonian and Dunnian runoff, upslope runoff, and interflow in the soil zone, as well as gravity drainage and direct recharge from the capillary reservoir of the soil zone, among other processes. PRMS recharge estimates do not consider irrigation (i.e., natural recharge) and are available for the years 1981–2016. (37) The recharge estimates are from a calibrated version of the NHM-PRMS following methods documented elsewhere. (37,38) An updated 30-year climate average model prediction was made using the NHM-PRMS recharge estimates from 1981 to 2010, and drought conditions were modeled using values from 2012. This approach allowed for a comparison of the duration of drought during 2012 to changes in the predicted probability of high arsenic in domestic wells.
2.2.2. Precipitation
The original model used the 30-year normal annual precipitation for 1981 through 2010 from the PRISM (Parameter-elevation Regressions on Independent Slopes Model) Climate Group at Oregon State University (http://prism.oregonstate.edu). Total annual precipitation values are available from PRISM, and values for 2012 were tested in the model; however, these data were not used in our final analyses. The NHM-PRMS recharge is based on precipitation values from DaymetV3. (39) A comparison between the NHM-PRMS recharge values and PRISM precipitation values revealed that in some areas, the NHM-PRMS recharge values for 2012 were greater than the total precipitation from PRISM in 2012. Therefore, to maintain internal consistency between the groundwater recharge and precipitation values for 2012, the DaymetV3 precipitation values for 2012 were substituted into the model. DaymetV3 precipitation values from 1981 to 2010 were also used to calculate 30-year mean values and substituted into the original model to produce updated 30-year climate average predictions.
2.2.3. Private Domestic Well Users
The previous study that estimated the domestic well population exposed to high arsenic acknowledged that the estimates of the number of domestic well users have unknown levels of uncertainty. (26) We use new estimates of the domestic well population for 2010 (15) to update the original model estimate of those exposed to high arsenic and to compare the changes under drought simulation 7. The domestic well population estimated using the block group method (15) was used to calculate the updated values for the domestic well population exposed to high arsenic.
2.3. Calculations and Comparisons
The model prediction maps from the drought simulations were compared to the original model prediction map by subtracting the raster values in the original model from the raster values in the drought simulations to create new maps. Positive values in these maps represent an increase in the probability of high arsenic due to the drought simulation, conversely negative values indicate a decrease in the probability of high arsenic due to the drought simulation.
The 30-year model predictions and 2012 model predictions calculated using the updated groundwater recharge and precipitation data allow for a comparison of drought duration and change in the probability of high arsenic. The U.S. Drought Monitor determines a weekly drought status for each county in the CONUS. The Centers for Disease Control and Prevention (CDC) National Environmental Public Health Tracking Network has compiled these data and determined the number of weeks a county was categorized in moderate drought (D1) or worse on an annual basis. (40) The average change in probability by county was calculated and compared to the number of weeks that county experienced moderate drought or worse during 2012. The change in precipitation and recharge values for the year 2012 and the 30-year averages (1981–2010) was calculated to determine the reductions in precipitation and estimated groundwater recharge that are representative of drought–particularly the 2012 drought. The changes were averaged by county and compared to the number of weeks a county was at or above moderate drought in 2012.
Estimates of the population of domestic well users exposed to high arsenic were calculated based on the new estimates of domestic well users for 2010, arsenic probabilities from the original model including the upper and lower confidence intervals (CIs), and our drought simulation 7 that approximates conditions during the 2012 drought. The domestic well users exposed to high arsenic were calculated by multiplying the raster of the number of domestic well users by the raster of predicted arsenic probabilities of interest. The results were summed by county and state using the “zonal statistics as table” tool in ArcMap.
3. Results and Discussion
ARTICLE SECTIONS
3.1. Drought Simulation
To simulate drought conditions, reductions were made in the precipitation and recharge variables used in the original model either one variable at a time or in combination with each other, resulting in eight different drought simulation runs summarized in Table 1. These simulations assume equilibrium conditions and do not consider the potential time lag between a perturbation at the land surface such as drought and groundwater response.
Decreasing the precipitation values in the model while leaving the recharge values unchanged, which might occur if decreased precipitation occurs during winter seasons when evapotranspiration is minimal thereby leaving recharge unchanged (simulation runs 1 and 2), increases the probability of high arsenic. A 25% decrease in precipitation increases the probability of high arsenic by less than 10% in most locations. However, increases between 10 and 20% were predicted in southern Minnesota and northern Iowa, south Texas, Georgia, portions of Michigan, and the mid-Atlantic coast. Arsenic probabilities increase by more than 20% in portions of the Pacific Northwest, Illinois, Indiana, Ohio, and New England (Supporting Information Figure S2). A 50% decrease in precipitation values results in even greater increases in the probability of high arsenic (Supporting Information Figure S3), especially in the High Plains aquifer, along the Gulf Coast, in the Northeast, and upper Midwest.
Decreasing recharge values by 25% while leaving precipitation values unchanged (simulation run 3) decreases the probability of high arsenic by less than 10% throughout most of the CONUS (Supporting Information Figure S4). Reductions in recharge with a minimal change in precipitation could occur during warmer than normal and/or windier than normal conditions that would increase evapotranspiration and decrease recharge. Similar changes may also occur due to changes in land use where an increase in impervious surfaces results in a reduction in recharge. In a few locations, the predicted probabilities increase by up to 10% including portions of the states of Texas, New Mexico, Arizona, California, and Nevada. A 50% reduction in recharge (simulation run 4) results in greater changes to the predicted probabilities of high arsenic, especially in New England, the Pacific Northwest, and northern Idaho where probabilities decrease by more than 10% (Supporting Information Figure S5).
Decreasing both the precipitation and recharge values by 25% (simulation run 5) produces an increase in the probability of high arsenic across most of the CONUS (Supporting Information Figure S6). Areas with increases greater than 10% in predicted probabilities include New England, southern Minnesota, northern Iowa, and Florida. Decreasing the precipitation and recharge values by 50% (simulation run 6) results in even greater increases in the probability of high arsenic (Supporting Information Figure S7).
Model simulation run 7 with a 25% decrease in precipitation and 50% decrease in recharge results in an increase in the probability of high arsenic throughout most of the CONUS (Figure 1). Exceptions to this are in small areas of the West including parts of the Pacific Northwest, Idaho, Montana, Wyoming, and California. The reductions in precipitation and recharge in model simulation run 7 are most like those observed in 2012 for counties that experienced moderate drought or worse for more than 29 weeks of the year. The changes in precipitation and recharge values for the year 2012 and the 30-year averages (1981–2010) were averaged by county and compared to the number of weeks a county was at or above moderate drought in 2012 (Supporting Information Table S1). Counties that experienced extended periods of drought for 30–42 weeks and 43–52 weeks had median reductions in precipitation of 21 and 25%, respectively. The same counties had median reductions in recharge of 63 and 55%, respectively. Model simulation run 7 with a 25% reduction in recharge and 50% reduction in recharge approximates the reductions that occurred in counties experiencing extended periods of drought during 2012. To determine if the predicted probabilities from model simulation run 7 are within the upper 95% CI from the original model, the difference between the values was calculated and mapped (Supporting Information Figure S8). In most of the central and eastern portions of the CONUS, the drought simulation results are above the upper CI. However, in most of the western parts of the CONUS, the drought simulations are within the 95% CI of the original model. Predicted probabilities of high arsenic increase throughout the entire CONUS for model simulation run 8 (Supporting Information Figure S9).
Figure 1
Figure 1. Change in probability of high arsenic between the original model and drought simulation run 7. Positive values represent an increase in the probability for the drought simulation.
The changes in the probability of high arsenic resulting from the drought simulations align with expectations based on the original model equation. Precipitation has a negative coefficient in the model and decreasing the precipitation values increases the probabilities of elevated arsenic concentrations (Supporting Information Figures S2 and S3). Conversely, recharge has a positive model coefficient and decreasing recharge results in decreasing probabilities (Supporting Information Figures S4 and S5). Changes in the precipitation values have a larger influence on the model results compared to similar changes in the recharge values. This is illustrated by the results from drought simulation runs 5 and 6 (Supporting Information Figures S6 and S7) where the probabilities of high arsenic increase when both variables decrease by equal percentages. This was generally expected because in the model equation, precipitation has a standardized coefficient (−0.7063) with an absolute value greater than recharge (0.2909). (26) However, there are 40 additional variables in the model that also influence the outcome and as evidenced in the drought simulation results, not all areas of the CONUS respond similarly when the variables related to drought are perturbed. These regional differences, such as a decrease in the probability of high arsenic in the Pacific Northwest and New England during simulation run 4 (50% reduction in recharge), may indicate the varying geochemical mechanisms responsible for arsenic in groundwater in humid versus arid environments.
3.2. Drought of 2012
The location and duration of the drought in 2012 is depicted in Figure 2, which shows the number of weeks a county was classified at or above moderate drought (D1) by the U.S. Drought Monitor. The majority of Texas, the Southwest, California, Georgia, and portions of states in the northern Plains experienced moderate drought or worse for more than 44 weeks of the year. With the exceptions of the Pacific Northwest, northern New England, and the Appalachians, most of the country experienced drought in 2012.
Figure 2
Figure 2. Number of weeks in 2012 a county was classified as moderate drought or worse by the U.S. Drought Monitor.
Model predictions were made for the year 2012 using precipitation values from DaymetV3 and groundwater recharge from NHM-PRMS (Supporting Information Figure S10). In order to calculate a change in the probability of high arsenic during 2012 as compared to a 30-year climate average, model predictions were also made with mean annual precipitation values from DaymetV3 and groundwater recharge from NHM-PRMS for the 30-year time span from 1981–2010 (Supporting Information Figure S11). These model predictions were compared to the original model predictions and were found to be within 5% of each other for approximately 83% of the CONUS. These updated arsenic probabilities were considered sufficiently similar to the original probabilities to use in this analysis. The change in the probability of arsenic greater than 10 μg/L in domestic wells during 2012 was calculated by subtracting the 2012 values from the 30-year average values and is shown in Figure 3. Increases in the probability of high arsenic during drought conditions are evident in the Basin and Range aquifers located in Nevada, Arizona, Utah, southern California, and New Mexico. Increases are also evident in the High Plains aquifer located in Nebraska, Kansas, Oklahoma, and north Texas. South Texas and the Southeast also had increases in the probability of high arsenic. While interactions between all model variables are responsible for the model outcomes, these areas of increased probability are underlain by geologic units that are model variables. For example, the Pliocene continental geologic unit (Tpc, in the original model) underlies the High Plains region. Areas with increased arsenic probabilities had extended periods of drought in 2012 (Figure 2). Conversely, areas of the CONUS that did not experience extended periods of drought such as northern New England, the Pacific Northwest, and the Appalachians had a decrease in the probability of high arsenic.
Figure 3
Figure 3. Change in probability of high arsenic using recharge and precipitation from the year 2012 and the average from 1981–2010. Positive values indicate an increase in probability for 2012.
Changes in the probability of high arsenic compared to the duration of drought in 2012 for each county are shown in Figure 4, which indicates that as the duration of drought increases, the probability of high arsenic increases. The maximum median change in the probability of high arsenic (0.024 or 2.4%) occurs in counties that experienced 30 to 42 weeks of drought during 2012. For counties that experienced zero to 7 weeks of drought during 2012, the probability of high arsenic slightly decreased (median change = −0.004) from the 30-year climate average; however, there is much more variability in the data compared with the other categories of drought duration.
Figure 4
Figure 4. Change in probability of high arsenic between 2012 and the 30-year climate average, averaged by county compared to the duration of drought during 2012. n equals the number of counties within each bin.
3.3. Results in the Context of Other Studies
Previous regional-scale studies that have compared arsenic concentrations in groundwater wells during drought and nondrought periods also report higher arsenic concentrations during drought. Wells near Perth, Australia, experienced increases in arsenic concentrations in areas where the water-table elevations decreased because of long-term drought and an increase in urban development. (6) Arsenic concentrations in the unconfined aquifer increased over a 28-year time span from below the detection limits of 10–20 μg/L to greater than 100 μg/L and up to 1000 μg/L. (6) The increase in arsenic concentrations was attributed to the lowering of the water table and subsequent oxidation and dissolution of arsenic-bearing sulfide minerals in the aquifer sediments. (6)
A study in the Salamanca province of Spain sampled groundwater wells during wet periods (spring 1998 and spring 1999) and drought periods (spring and summer 2005) and compared arsenic concentrations. (7) The sampled wells were not necessarily the same wells between the sampling periods. The distribution of arsenic concentrations in the same geologic zones was compared between the wet and dry periods. Higher arsenic concentrations were observed during the drought period and were attributed to a decrease in deep groundwater flow and a concentration effect.
In the San Joaquin Valley of California, increasing arsenic concentrations in groundwater have been attributed to land subsidence as a consequence of overpumping of the aquifer, in part due to drought. (41) The proposed mechanism responsible for the increase in arsenic is the release of clay pore water containing high arsenic concentrations because of the land subsidence, a phenomenon first observed and proposed in aquifers of the Mekong Delta of Vietnam. (42)
3.4. Estimates of the Domestic Well Population Exposed to High Arsenic and Changes Due to Drought
New estimates of the domestic well population exposed to elevated arsenic concentrations under normal conditions (i.e., 30-year climate average) are listed in Supporting Information Table S2 and are based on the original model predictions and updated estimates of the domestic well population in 2010. (15) Based on these new estimates, the population with arsenic concentrations greater than 10 μg/L is 2.7 million or 7.1% of domestic well users. Taking model uncertainty into account, the population estimates range from 2.0 to 3.6 million (5.3 to 9.7% of domestic well users, respectively). States with the largest estimated population using domestic well water with elevated arsenic concentrations are Ohio, Michigan, and Indiana (0.241, 0.226, and 0.161 million, respectively). States with the largest percentage of domestic well users using water with elevated arsenic concentrations are Nevada (25.9%), Maine (23.6%), and Arizona (20.2%).
The probability of high arsenic from drought model simulation 7 and the domestic well population for 2010 was used to estimate the change in population exposed to high arsenic during a drought scenario (Figure 5 and Supporting InformationTable S2). The model simulation was used rather than the 2012 conditions because decreases in precipitation and groundwater recharge were applied to all areas of the CONUS allowing for a general evaluation of the relative impact on the entire CONUS. Under these drought conditions, the overall high-arsenic domestic well population increased from 2.7 million (95% CI 2.0–3.6) to 4.1 million (95% CI 3.4–5.0) people, or a 54% increase. The states that have the largest estimated population increase in domestic well users exposed to elevated arsenic during simulated drought conditions are Ohio, Indiana, and Michigan with increases of 0.133, 0.105, and 0.094 million people, respectively. As a percentage of total domestic well users, the states with the largest increases in population exposed to elevated arsenic under the drought scenario are New Hampshire, Indiana, and Ohio (8.1, 7.5, and 7.3%, respectively). These results demonstrate how a small change in arsenic probability can have a large impact on states with a large population of private well users. Although the changes in the probability of high arsenic due to drought are generally less than 10% throughout most of the CONUS (Figure 1), when these changes are considered at the CONUS scale, the resulting increase in the population potentially exposed to high arsenic is large (1.4 million people). The increase in the population potentially exposed to high arsenic illustrates how a small change in a large population results in a large number. (43)
Figure 5
Figure 5. Increase in the population of domestic well users exposed to arsenic greater than 10 μg/L under drought simulation 7.
4. Limitations and Implications
ARTICLE SECTIONS
A statistical model was used in this study as a tool to assess the potential impact of drought on arsenic exposure from domestic wells in the CONUS. Climatic variables in the statistical model were changed to represent drought conditions. A limitation of this approach is that statistical models may not account for all interactions between the climate and arsenic concentrations in domestic well water. However, this method is widely used to understand the potential impact of climate change on the environment, especially at large spatial scales where climate is a dominate variable. (44−46) The statistical model approach assumes equilibrium conditions and does not account for the potential impact of groundwater age on water quality. The mean residence times and ages of groundwater from principal aquifers in the U.S. vary from less than 10 to greater than 15,000 years. (47,48) Recent and/or future droughts that occur on short timescales may not have an immediate influence on groundwater quality from aquifers containing old water. However, domestic wells in the U.S. are typically drilled at shallower depths than public supply wells; (48) consequently they may be more responsive to short-term climatic changes. Process-based or mechanistic models are an alternative to the statistical model approach but also have limitations. (49)
This national-scale study indicates that drought may increase the likelihood of having high concentrations of arsenic in domestic wells; however, it does not indicate how drought may impact arsenic concentrations at individual wells. For example, a detailed study of one domestic well located in New Hampshire found that the highest arsenic concentrations were related to spring recharge of the water table at the highest annual water table conditions. There was, however, a secondary peak of arsenic concentrations during periods of low water-table elevations that occurred in late summer or early fall. (9) Another study that included 1245 wells from various aquifers within the CONUS showed that arsenic concentrations increased slightly when water table conditions were low. (8) The changes were statistically significant only in wells from New England, indicating regional variability in mechanisms responsible for changes in arsenic concentrations. (8) The occurrence of arsenic in groundwater is complex and dependent on many local geochemical mechanisms, interactions, and hydrologic flow paths. The results from this study represent spatial averages and should not be substituted for (a) sampling and analysis of domestic wells to determine individual health hazards from arsenic in drinking water or (b) regional- to local-scale studies and findings because covariates associated with elevated arsenic in domestic wells throughout the CONUS differ at regional scales. (50) Frequent sampling of wells over long time spans that include droughts as well as normal and wetter than normal conditions would offer insights into the mechanisms responsible for the variations in arsenic concentrations.
Climate models predict increasing aridity in portions of North America during the 21st century. (51,52) Our findings suggest that as the duration of drought increases, the probability of exposure to arsenic concentrations greater than 10 μg/L also will increase. The median increase is approximately 2% but varies by up to 20% for areas that experienced drought for more than 20 weeks of the year during 2012 (Figure 4). We did not investigate the impact of drought duration beyond a single year; however, such a study might be relevant to preparing for future climate change scenarios. Our results also indicate that areas experiencing wetter than normal conditions may result in reduced concentrations of arsenic in domestic wells. While not an objective of this study, future studies may consider the impact of increased precipitation and/or more intense precipitation events on arsenic concentrations in drinking water.
Additional limitations to the development of this model include the spatial distribution of arsenic data for domestic wells and the availability and spatial resolution of predictor variable data sets. Some areas of the CONUS are well represented with many sampling locations whereas other areas are sparse. Predictor variables used in this model were limited to those that are available for the CONUS. Additional data sets may be relevant but only available on a regional or local scale and more accurate data sets may become available in the future. Quantifying groundwater recharge has inherent limitations and our study did not consider the potential impact of irrigation on groundwater recharge and arsenic concentrations, which may be regionally important and should be included in future studies. The location of domestic well users throughout the CONUS is estimated and presents another limitation to our study. This drought study could be refined as better estimates or actual data relevant to the location of domestic and public water supply users become available and new or updated CONUS-scale data sets become available. There are several limitations associated with our study, which might be addressed in future studies. The findings and their potential implications, however, are important to convey despite the limitations.
This study estimates potential changes across the CONUS in elevated arsenic concentrations in domestic wells due to drought. Our results are constrained by the limitations of the statistical model and estimates of the location and the number of domestic well users within the CONUS. As more accurate models are developed and/or better estimates or measures of domestic well users become available, these findings could be refined. The current findings suggest that drought has an adverse impact increasing the potential exposure to arsenic. This information may be useful for public health officials, environmental health managers and programs, well water safety programs, and emergency preparedness/response managers to help inform well owners, implement interventions, and build resiliency to drought.
Supporting Information
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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.9b05835.
Tables and figures; diagram of methods, maps of changes in probability of high arsenic from drought simulation runs, maps of predicted probabilities using updated data sources, change in precipitation and recharge compared to duration of drought for 2012 by county, and estimated domestic well population exposed to high arsenic during normal climate conditions and during drought conditions by state (PDF)
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Author Information
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- Melissa A. Lombard - U.S. Geological Survey, New England Water Science Center, Pembroke, New Hampshire 03275, United States;
http://orcid.org/0000-0001-5924-6556;
- Joseph D. Ayotte - U.S. Geological Survey, New England Water Science Center, Pembroke, New Hampshire 03275, United States;http://orcid.org/0000-0002-1892-2738
Acknowledgments
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The authors thank Leslie DeSimone, USGS; Paul Bradley, USGS; Bernard Nolan, retired USGS; Lorraine Backer, CDC; and Tegan Boehmer, CDC for helpful comments and reviews; Laura Hayes, USGS, for GIS assistance; and three anonymous reviewers for their comments and suggestions. This work was supported by the U.S. Centers for Disease Control and Prevention and the U.S. Geological Survey (Interagency agreement number 16FED1605626-0002-0000). Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.
References
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This article references 52 other publications.
- 1Centers for Disease Control and Prevention (CDC), U.S. Environmental Protection Agency, National Oceanic and Atmospheric Agency, and American Water Works Association. When Every Drop Counts: Protecting Public Health during Drought Conditions—a Guide for Public Health Professionals , 2010; p 56.Google ScholarThere is no corresponding record for this reference.
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- 4Smedley, P. L.; Kinniburgh, D.G. A review of the source, behaviour and distribution of arsenic in natural waters. Appl. Geochem. 2002, 17, 517– 568, DOI: 10.1016/s0883-2927(02)00018-5[Crossref], [CAS], Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XhvVSmur0%253D&md5=563c408bde5c60c44ec8d21ee1eeec28A review of the source, behaviour and distribution of arsenic in natural watersSmedley, P. L.; Kinniburgh, D. G.Applied Geochemistry (2002), 17 (5), 517-568CODEN: APPGEY; ISSN:0883-2927. (Elsevier Science Ltd.)A review. The range of As concns. found in natural waters is large, ranging from less than 0.5 μg l-1 to more than 5000 μg l-1. Typical concns. in freshwater are less than 10 μg l-1 and frequently less than 1 μg l-1. Rarely, much higher concns. are found, particularly in groundwater. In such areas, more than 10% of wells may be 'affected' (defined as those exceeding 50 μg l-1) and in the worst cases, this figure may exceed 90%. Well-known high-As groundwater areas have been found in Argentina, Chile, Mexico, China and Hungary, and more recently in West Bengal (India), Bangladesh and Vietnam. The scale of the problem in terms of population exposed to high As concns. is greatest in the Bengal Basin with more than 40 million people drinking water contg. 'excessive' As. These large-scale 'natural' As groundwater problem areas tend to be found in two types of environment: firstly, inland or closed basins in arid or semi-arid areas, and secondly, strongly reducing aquifers often derived from alluvium. Both environments tend to contain geol. young sediments and to be in flat, low-lying areas where groundwater flow is sluggish. Historically, these are poorly flushed aquifers and any As released from the sediments following burial has been able to accumulate in the groundwater. Arsenic-rich groundwaters are also found in geothermal areas and, on a more localized scale, in areas of mining activity and where oxidn. of sulfide minerals has occurred. The As content of the aquifer materials in major problem aquifers does not appear to be exceptionally high, being normally in the range 1-20 mg kg-1. There appear to be two distinct 'triggers' that can lead to the release of As on a large scale. The first is the development of high pH (>8.5) conditions in semi-arid or arid environments usually as a result of the combined effects of mineral weathering and high evapn. rates. This pH change leads either to the desorption of adsorbed As (esp. As(V) species) and a range of other anion-forming elements (V, B, F, Mo, Se and U) from mineral oxides, esp. Fe oxides, or it prevents them from being adsorbed. The second trigger is the development of strongly reducing conditions at near-neutral pH values, leading to the desorption of As from mineral oxides and to the reductive dissoln. of Fe and Mn oxides, also leading to As release. Iron (II) and As(III) are relatively abundant in these groundwaters and SO4 concns. are small (typically 1 mg l-1 or less). Large concns. of phosphate, bicarbonate, silicate and possibly org. matter can enhance the desorption of As because of competition for adsorption sites. A characteristic feature of high groundwater As areas is the large degree of spatial variability in As concns. in the groundwaters. This means that it may be difficult, or impossible, to predict reliably the likely concn. of As in a particular well from the results of neighboring wells and means that there is little alternative but to analyze each well. Arsenic-affected aquifers are restricted to certain environments and appear to be the exception rather than the rule. In most aquifers, the majority of wells are likely to be unaffected, even when, for example, they contain high concns. of dissolved Fe.
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- 6Appleyard, S. J.; Angeloni, J.; Watkins, R. Arsenic-rich groundwater in an urban area experiencing drought and increasing population density, Perth, Australia. Appl. Geochem. 2006, 21, 83– 97, DOI: 10.1016/j.apgeochem.2005.09.008[Crossref], [CAS], Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXhtlWqtL%252FP&md5=649967350f9c4337048b050ae5703e49Arsenic-rich groundwater in an urban area experiencing drought and increasing population density, Perth, AustraliaAppleyard, S. J.; Angeloni, J.; Watkins, R.Applied Geochemistry (2006), 21 (1), 83-97CODEN: APPGEY; ISSN:0883-2927. (Elsevier Ltd.)Groundwater in the Gwelup groundwater management area in Perth, Western Australia has been enriched in As due to the exposure of pyritic sediments caused by reduced rainfall, increased groundwater abstraction for irrigation and water supply, and prolonged dewatering carried out during urban construction activities. Groundwater near the watertable in a 25-60 m thick unconfined sandy aquifer has become acidic and has affected shallow wells used for garden irrigation. Arsenic concns. up to 7000 μg/L were measured in shallow groundwater, triggering concerns about possible health effects if residents were to use water from household wells as a drinking water source. Deep prodn. wells used for public water supply are not affected by acidity, but trends of progressively increasing concns. of Fe, SO4 and Ca over a 30-a period indicate that pyrite oxidn. products extend to the base of the unconfined aquifer. Falling Eh values are triggering the release of As from the redn. of Fe(III) oxyhydroxide minerals near the base of the unconfined aquifer, increasing the risk that groundwater used as a drinking water source will also become contaminated with high concns. of As.
- 7García-Prieto, J. C.; Cachaza, J. M.; Pérez-Galende, P.; Roig, M. G. Impact of drought on the ecological and chemical status of surface water and on the content of arsenic and fluoride pollutants of groundwater in the province of Salamanca (Western Spain). Chem. Ecol. 2012, 28, 545– 560, DOI: 10.1080/02757540.2012.686608[Crossref], [CAS], Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslamsLvP&md5=59b9ffe99ba7c6d8cb716490db2744a5Impact of drought on ecological and chemical status of surface water and on content of arsenic and fluoride pollutants of groundwaterGarcia-Prieto, Juan C.; Cachaza, Juan M.; Perez-Galende, Patricia; Roig, Manuel G.Chemistry and Ecology (2012), 28 (6), 545-560CODEN: CHECDY; ISSN:0275-7540. (Taylor & Francis Ltd.)The impact of drought on the ecol. and chem. status of surface and groundwaters of the River Tormes (River Duero basin, northwestern Iberian Peninsula) was studied to evaluate the evolution of the quality of the river during its passage through the city of Salamanca (Spain). The Water Quality Index (WQI) of the river revealed that the drought period of 2005 did not significantly affect water chem. quality. However, during the study period differences were found in surface water ecol. quality, using phytoplankton quality as AN indicator. These differences may be accentuated as a result of regulation of the River Tormes by the Santa Teresa reservoir. Arsenic and fluoride concns. were measured in water wells, finding higher arsenic concns. after the drought period and no correlation between the arsenic and fluoride contents. The results are useful for an overall understanding of potential impact of climate change on the ecol. and chem. status of water in regional systems.
- 8Ayotte, J. D.; Belaval, M.; Olson, S. A.; Burow, K. R.; Flanagan, S. M.; Hinkle, S. R.; Lindsey, B. D. Factors affecting temporal variability of arsenic in groundwater used for drinking water supply in the United States. Sci. Total Environ. 2015, 505, 1370– 1379, DOI: 10.1016/j.scitotenv.2014.02.057[Crossref], [PubMed], [CAS], Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXks1Wisb0%253D&md5=eebf2d6a0ce83afc0036f30f63234430Factors affecting temporal variability of arsenic in groundwater used for drinking water supply in the United StatesAyotte, Joseph D.; Belaval, Marcel; Olson, Scott A.; Burow, Karen R.; Flanagan, Sarah M.; Hinkle, Stephen R.; Lindsey, Bruce D.Science of the Total Environment (2015), 505 (), 1370-1379CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)The occurrence of As in groundwater is a recognized environmental hazard with worldwide importance and much effort has been focused on surveying and predicting where arsenic occurs. Temporal variability is one aspect of this environmental hazard that has until recently received less attention than other aspects. We analyzed 1245 wells with 2 samples/well. We suggest that temporal variability, often reported as affecting very few wells, is perhaps a larger issue than it appears and has been overshadowed by datasets with large nos. of non-detect data. Although there was only a slight difference in As concn. variability among samples from public and private wells (p =0.0452), the range of variability was larger for public than for private wells. We relate the variability we see to geochem. factors-primarily variability in redox-but also variability in major-ion chem. We also show that in New England there is a weak but statistically significant indication that seasonality may have an effect on concns., whereby concns. in the first two quarters of the year (Jan.-June) are significantly lower than in the 2nd 2 quarters (July-Dec.) (p <0.0001). In the Central Valley of California, the relation of As concn. to season was not statistically significant (p =0.4169). In New England, these changes appear to follow groundwater levels. It is possible that this difference in As concns. is related to groundwater level changes, pumping stresses, evapotranspiration effects, or perhaps mixing of more oxidizing, lower pH recharge water in wetter months. Focusing on the understanding the geochem. conditions in aquifers where As concns. are concerns and causes of geochem. changes in the groundwater environment may lead to a better understanding of where and by how much arsenic will vary over time.
- 9Levitt, J. P.; Degnan, J. R.; Flanagan, S. M.; Jurgens, B. C. Arsenic variability and groundwater age in three water supply wells in southeast New Hampshire. Geosci. Front. 2019, 10, 1669– 1683, DOI: 10.1016/j.gsf.2019.01.002[Crossref], [CAS], Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXis1SrurY%253D&md5=3d0d749756b7c87751db918eae7660a4Arsenic variability and groundwater age in three water supply wells in southeast New HampshireLevitt, J.; Degnan, J.; Flanagan, S.; Jurgens, B.Geoscience Frontiers (2019), 10 (5), 1669-1683CODEN: GFERA4; ISSN:1674-9871. (Elsevier B.V.)Three wells in New Hampshire were sampled bimonthly over three years to evaluate the temporal variability of arsenic concns. and groundwater age. All samples had measurable concns. of arsenic throughout the entire sampling period and concns. in individual wells had a mean variation of more than 7 μg/L. The time series data from this sampling effort showed that arsenic concns. ranged from a median of 4 μg/L in a glacial aquifer well (SGW-65) to medians of 19 μg/L and 37 μg/L in wells (SGW-93 and KFW-87) screened in the bedrock aquifer, resp. These high arsenic concns. were assocd. with the consistently high pH (median ≥ 8) and low dissolved oxygen (median <0.1 mg/L) in the bedrock aquifer wells, which is typical of fractured cryst. bedrock aquifers in New Hampshire. Groundwater from the glacial aquifer often has high dissolved oxygen, but in this case was consistently low. The pH also is generally acidic in the glacial aquifer but in this case was slightly alk. (median = 7.5). Also, sorption sites may be more abundant in glacial aquifer deposits than in fractured bedrock which may contribute to lower arsenic concns.Mean groundwater ages were less than 50 years old in all three wells and correlated with conservative tracer concns., such as chloride; however, mean age was not directly correlated with arsenic concns. Arsenic concns. at KFW-87 did correlate with water levels, in addn., there was a seasonal pattern, which suggests that either the timing of or multiple sampling efforts may be important to define the full range of arsenic concns. in domestic bedrock wells.Since geochem. reduced conditions and alk. pHs are common to both bedrock and glacial aquifer wells in this study, groundwater age correlates less strongly with arsenic concns. than geochem. conditions. There also is evidence of direct hydraulic connection between the glacial and bedrock aquifers, which can influence arsenic concns. Correlations between arsenic concns. and the age of the old fraction of water in SGW-65 and the age of the young fraction of water in SGW-93 suggest that water in the two aquifers may be mixing or at least some of the deeper, older water captured by the glacial aquifer well may be from a similar source as the shallow young groundwater from the bedrock aquifer. The contrast in arsenic concns. in the two aquifers may be because of increased adsorption capacity of glacio-fluvial sediments, which can limit contaminants more than fractured rock. In addn., this study illustrates that long residence times are not necessary to achieve more geochem. evolved conditions such as high pH and reduced conditions as is typically found with older water in other regions.
- 10Baris, D.; Waddell, R.; Beane Freeman, L. E.; Schwenn, M.; Colt, J. S.; Ayotte, J. D.; Ward, M. H.; Nuckols, J.; Schned, A.; Jackson, B.; Clerkin, C.; Rothman, N.; Moore, L. E.; Taylor, A.; Robinson, G.; Hosain, G. M.; Armenti, K. R.; McCoy, R.; Samanic, C.; Hoover, R. N.; Fraumeni, J. F., Jr.; Johnson, A.; Karagas, M. R.; Silverman, D. T. Elevated Bladder Cancer in Northern New England: The Role of Drinking Water and Arsenic. J. Natl. Cancer Inst. 2016, 108, djw099, DOI: 10.1093/jnci/djw099
- 11Mendez, W. M., Jr.; Eftim, S.; Cohen, J.; Warren, I.; Cowden, J.; Lee, J. S.; Sams, R. Relationships between arsenic concentrations in drinking water and lung and bladder cancer incidence in U.S. counties. J. Exposure Sci. Environ. Epidemiol. 2017, 27, 235– 243, DOI: 10.1038/jes.2016.58[Crossref], [PubMed], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVWqurfL&md5=0f00e8b458cf83275f1532b86aff698cRelationships between arsenic concentrations in drinking water and lung and bladder cancer incidence in U.S. countiesMendez, William M.; Eftim, Sorina; Cohen, Jonathan; Warren, Isaac; Cowden, John; Lee, Janice S.; Sams, ReederJournal of Exposure Science & Environmental Epidemiology (2017), 27 (3), 235-243CODEN: JESEBS; ISSN:1559-0631. (Nature Publishing Group)Increased risks of lung and bladder cancer have been obsd. in populations exposed to high levels of inorg. arsenic. However, studies at lower exposures (i.e., less than 100μg/l in water) have shown inconsistent results. We therefore conducted an ecol. anal. of the assocn. between historical drinking water arsenic concns. and lung and bladder cancer incidence in U. S. counties. We used drinking water arsenic concns. measured by the U. S. Geol. Survey and state agencies in the 1980s and 1990s as proxies for historical exposures in counties where public groundwater systems and private wells are important sources of drinking water. Relationships between arsenic levels and cancer incidence in 2006-2010 were explored by Poisson regression analyses, adjusted for groundwater dependence and important demog. covariates. The median and 95th percentile county mean arsenic concns. were 1.5 and 15.4μg/l, resp. Water arsenic concns. were significant and pos. assocd. with female and male bladder cancer, and with female lung cancer. Our findings support an assocn. between low water arsenic concns. and lung and bladder cancer incidence in the United States. However, the limitations of the ecol. study design suggest caution in interpreting these results.
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- 13Naujokas, M. F.; Anderson, B.; Ahsan, H.; Aposhian, H. V.; Graziano, J. H.; Thompson, C.; Suk, W. A. The broad scope of health effects from chronic arsenic exposure: update on a worldwide public health problem. Environ. Health Perspect. 2013, 121, 295– 302, DOI: 10.1289/ehp.1205875[Crossref], [PubMed], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3svjt1Ohtw%253D%253D&md5=77f941e606bf07120eedb3aead598aeeThe broad scope of health effects from chronic arsenic exposure: update on a worldwide public health problemNaujokas Marisa F; Anderson Beth; Ahsan Habibul; Aposhian H Vasken; Graziano Joseph H; Thompson Claudia; Suk William AEnvironmental health perspectives (2013), 121 (3), 295-302 ISSN:.BACKGROUND: Concerns for arsenic exposure are not limited to toxic waste sites and massive poisoning events. Chronic exposure continues to be a major public health problem worldwide, affecting hundreds of millions of persons. OBJECTIVES: We reviewed recent information on worldwide concerns for arsenic exposures and public health to heighten awareness of the current scope of arsenic exposure and health outcomes and the importance of reducing exposure, particularly during pregnancy and early life. METHODS: We synthesized the large body of current research pertaining to arsenic exposure and health outcomes with an emphasis on recent publications. DISCUSSION: Locations of high arsenic exposure via drinking water span from Bangladesh, Chile, and Taiwan to the United States. The U.S. Environmental Protection Agency maximum contaminant level (MCL) in drinking water is 10 μg/L; however, concentrations of > 3,000 μg/L have been found in wells in the United States. In addition, exposure through diet is of growing concern. Knowledge of the scope of arsenic-associated health effects has broadened; arsenic leaves essentially no bodily system untouched. Arsenic is a known carcinogen associated with skin, lung, bladder, kidney, and liver cancer. Dermatological, developmental, neurological, respiratory, cardiovascular, immunological, and endocrine effects are also evident. Most remarkably, early-life exposure may be related to increased risks for several types of cancer and other diseases during adulthood. CONCLUSIONS: These data call for heightened awareness of arsenic-related pathologies in broader contexts than previously perceived. Testing foods and drinking water for arsenic, including individual private wells, should be a top priority to reduce exposure, particularly for pregnant women and children, given the potential for life-long effects of developmental exposure.
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- 24Green, T. R.; Taniguchi, M.; Kooi, H.; Gurdak, J. J.; Allen, D. M.; Hiscock, K. M.; Treidel, H.; Aureli, A. Beneath the surface of global change: Impacts of climate change on groundwater. J. Hydrol. 2011, 405, 532– 560, DOI: 10.1016/j.jhydrol.2011.05.002
- 25Murti, M.; Yard, E.; Kramer, R.; Haselow, D.; Mettler, M.; McElvany, R.; Martin, C. Impact of the 2012 extreme drought conditions on private well owners in the United States, a qualitative analysis. BMC Public Health 2016, 16, 430, DOI: 10.1186/s12889-016-3039-4[Crossref], [PubMed], [CAS], Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2s%252FjtlOnsw%253D%253D&md5=6611d4ebc27fcf998c0e910d65cc3b0fImpact of the 2012 extreme drought conditions on private well owners in the United States, a qualitative analysisMurti Michelle; Yard Ellen; Martin Colleen; Kramer Rachel; Haselow Dirk; Mettler Mike; McElvany RockyBMC public health (2016), 16 (), 430 ISSN:.BACKGROUND: Extreme hot and dry weather during summer 2012 resulted in some of the most devastating drought conditions in the last half-century in the United States (U.S.). While public drinking water systems have contingency plans and access to alternative resources to maintain supply for their customers during drought, little is known about the impacts of drought on private well owners, who are responsible for maintaining their own water supply. The purpose of this investigation was to explore the public health impacts of the 2012 drought on private well owners' water quality and quantity, identify their needs for planning and preparing for drought, and to explore their knowledge, attitudes, and well maintenance behaviors during drought. METHODS: In the spring of 2013, we conducted six focus group discussions with private well owners in Arkansas, Indiana, and Oklahoma. RESULTS: There were a total of 41 participants, two-thirds of whom were men aged 55 years or older. While participants agreed that 2012 was the worst drought in memory, few experienced direct impacts on their water quantity or quality. However, all groups had heard of areas or individuals whose wells had run dry. Participants conserved water by reducing their indoor and outdoor consumption, but they had few suggestions on additional ways to conserve, and they raised concerns about limiting water use too much. Participants wanted information on how to test their well and any water quality issues in their area. CONCLUSIONS: This investigation identified information needs regarding drought preparedness and well management for well owners.
- 26Ayotte, J. D.; Medalie, L.; Qi, S. L.; Backer, L. C.; Nolan, B. T. Estimating the High-Arsenic Domestic-Well Population in the Conterminous United States. Environ. Sci. Technol. 2017, 51, 12443– 12454, DOI: 10.1021/acs.est.7b02881[ACS Full Text
], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1Kgu77M&md5=fb41fe08154c95ab6a5729277c4af85eEstimating the High-Arsenic Domestic-Well Population in the Conterminous United StatesAyotte, Joseph D.; Medalie, Laura; Qi, Sharon L.; Backer, Lorraine C.; Nolan, Bernard T.Environmental Science & Technology (2017), 51 (21), 12443-12454CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Arsenic concns. from 20450 domestic wells in the U.S. were used to develop a logistic regression model of the probability of having arsenic >10 μg/L ("high arsenic"), which is presented at the county, state, and national scales. Variables representing geol. sources, geochem., hydrol., and phys. features were among the significant predictors of high arsenic. For U.S. Census blocks, the mean probability of arsenic >10 μg/L was multiplied by the population using domestic wells to est. the potential high-arsenic domestic-well population. Approx. 44.1 M people in the U.S. use water from domestic wells. The population in the conterminous U.S. using water from domestic wells with predicted arsenic concn. >10 μg/L is 2.1 M people (95% CI is 1.5 to 2.9 M). Although areas of the U.S. were underrepresented with arsenic data, predictive variables available in national data sets were used to est. high arsenic in unsampled areas. Addnl., by predicting to all of the conterminous U.S., we identify areas of high and low potential exposure in areas of limited arsenic data. These areas may be viewed as potential areas to investigate further or to compare to more detailed local information. Linking predictive modeling to private well use information nationally, despite the uncertainty, is beneficial for broad screening of the population at risk from elevated arsenic in drinking water from private wells. - 27Mallya, G.; Zhao, L.; Song, X. C.; Niyogi, D.; Govindaraju, R. S. 2012 Midwest Drought in the United States. J. Hydrol. Eng. 2013, 18, 737– 745, DOI: 10.1061/(asce)he.1943-5584.0000786
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- 35Regan, R. S.; Markstrom, S. L.; Hay, L. E.; Viger, R. J.; Norton, P. A.; Driscoll, J. M.; LaFontaine, J. H. Description of the National Hydrologic Model for use with the Precipitation-Runoff Modeling System (PRMS); U.S. Geological Survey Techniques and Methods, Reston, VA., Book 6, Chap B9, 38 p. https://doi.org/10.3133/tm6B9.Google ScholarThere is no corresponding record for this reference.
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- 41Smith, R.; Knight, R.; Fendorf, S. Overpumping leads to California groundwater arsenic threat. Nat. Commun. 2018, 9, 2089, DOI: 10.1038/s41467-018-04475-3[Crossref], [PubMed], [CAS], Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1Mbkt1yqtA%253D%253D&md5=6aeca9f69daed5347745c4cc7e25a459Overpumping leads to California groundwater arsenic threatSmith Ryan; Knight Rosemary; Fendorf ScottNature communications (2018), 9 (1), 2089 ISSN:.Water resources are being challenged to meet domestic, agricultural, and industrial needs. To complement finite surface water supplies that are being stressed by changes in precipitation and increased demand, groundwater is increasingly being used. Sustaining groundwater use requires considering both water quantity and quality. A unique challenge for groundwater use, as compared with surface water, is the presence of naturally occurring contaminants within aquifer sediments, which can enter the water supply. Here we find that recent groundwater pumping, observed through land subsidence, results in an increase in aquifer arsenic concentrations in the San Joaquin Valley of California. By comparison, historic groundwater pumping shows no link to current groundwater arsenic concentrations. Our results support the premise that arsenic can reside within pore water of clay strata within aquifers and is released due to overpumping. We provide a quantitative model for using subsidence as an indicator of arsenic concentrations correlated with groundwater pumping.
- 42Erban, L. E.; Gorelick, S. M.; Zebker, H. A.; Fendorf, S. Release of arsenic to deep groundwater in the Mekong Delta, Vietnam, linked to pumping-induced land subsidence. Proc. Natl. Acad. Sci. U.S.A. 2013, 110, 13751– 13756, DOI: 10.1073/pnas.1300503110[Crossref], [PubMed], [CAS], Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtlKqu7rL&md5=59c3b05851cc85be8d0698c3857a27cfRelease of arsenic to deep groundwater in the Mekong Delta, Vietnam, linked to pumping-induced land subsidenceErban, Laura E.; Gorelick, Steven M.; Zebker, Howard A.; Fendorf, ScottProceedings of the National Academy of Sciences of the United States of America (2013), 110 (34), 13751-13756,S13751/1-S13751/6CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Deep aquifers in South and Southeast Asia are increasingly exploited as presumed sources of pathogen- and arsenic-free water, although little is known of the processes that may compromise their long-term viability. We analyze a large area (>1,000 km2) of the Mekong Delta, Vietnam, in which arsenic is found pervasively in deep, Pliocene-Miocene-age aquifers, where nearly 900 wells at depths of 200-500 m are contaminated. There, intensive groundwater extn. is causing land subsidence of up to 3 cm/y as measured using satellite-based radar images from 2007 to 2010 and consistent with transient 3D aquifer simulations showing similar subsidence rates and total subsidence of up to 27 cm since 1988. We propose a previously unrecognized mechanism in which deep groundwater extn. is causing interbedded clays to compact and expel water contg. dissolved arsenic or arsenic-mobilizing solutes (e.g., dissolved org. carbon and competing ions) to deep aquifers over decades. The implication for the broader Mekong Delta region, and potentially others like it across Asia, is that deep, untreated groundwater will not necessarily remain a safe source of drinking water.
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- 50Frederick, L.; VanDerslice, J.; Taddie, M.; Malecki, K.; Gregg, J.; Faust, N.; Johnson, W. P. Contrasting regional and national mechanisms for predicting elevated arsenic in private wells across the United States using classification and regression trees. Water Res. 2016, 91, 295– 304, DOI: 10.1016/j.watres.2016.01.023[Crossref], [PubMed], [CAS], Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1Gjsrs%253D&md5=ca346a76150c07dab267a0303aae135dContrasting regional and national mechanisms for predicting elevated arsenic in private wells across the United States using classification and regression treesFrederick, Logan; VanDerslice, James; Taddie, Marissa; Malecki, Kristen; Gregg, Josh; Faust, Nicholas; Johnson, William P.Water Research (2016), 91 (), 295-304CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)Arsenic contamination in groundwater is a public health and environmental concern in the United States (U.S.) particularly where monitoring is not required under the Safe Water Drinking Act. Previous studies suggest the influence of regional mechanisms for arsenic mobilization into groundwater; however, no study has examd. how influencing parameters change at a continental scale spanning multiple regions. We herein examine covariates for groundwater in the western, central and eastern U. S. regions representing mechanisms assocd. with arsenic concns. exceeding the U. S. Environmental Protection Agency max. contamination level (MCL) of 10 ppb (ppb). Statistically significant covariates were identified via classification and regression tree (CART) anal., and included hydrometeorol. and groundwater chem. parameters. The CART analyses were performed at two scales: national and regional; for which three physiog. regions located in the western (Payette Section and the Snake River Plain), central (Osage Plains of the Central Lowlands), and eastern (Embayed Section of the Coastal Plains) U. S. were examd. Validity of each of the three regional CART models was indicated by values >85% for the area under the receiver-operating characteristic curve. Aridity (pptn. minus potential evapotranspiration) was identified as the primary covariate assocd. with elevated arsenic at the national scale. At the regional scale, aridity and pH were the major covariates in the arid to semi-arid (western) region; whereas dissolved iron (taken to represent chem. reducing conditions) and pH were major covariates in the temperate (eastern) region, although addnl. important covariates emerged, including elevated phosphate. Anal. in the central U. S. region indicated that elevated arsenic concns. were driven by a mixt. of those obsd. in the western and eastern regions.
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- Bennett Siphiwe Dintsi, Mokgehle Refiloe Letsoalo, Abayneh Ataro Ambushe. Bioaccumulation and Human Health Risk Assessment of Arsenic and Chromium Species in Water–Soil–Vegetables System in Lephalale, Limpopo Province, South Africa. Minerals 2023, 13 (7) , 930. https://doi.org/10.3390/min13070930
- Donglin Li, Hucai Zhang, Fengqin Chang, Lizeng Duan, Yang Zhang. Environmental arsenic (As) and its potential relationship with endemic disease in southwestern China. Journal of Environmental Sciences 2023, 36 https://doi.org/10.1016/j.jes.2023.05.005
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Abstract
Figure 1
Figure 1. Change in probability of high arsenic between the original model and drought simulation run 7. Positive values represent an increase in the probability for the drought simulation.
Figure 2
Figure 2. Number of weeks in 2012 a county was classified as moderate drought or worse by the U.S. Drought Monitor.
Figure 3
Figure 3. Change in probability of high arsenic using recharge and precipitation from the year 2012 and the average from 1981–2010. Positive values indicate an increase in probability for 2012.
Figure 4
Figure 4. Change in probability of high arsenic between 2012 and the 30-year climate average, averaged by county compared to the duration of drought during 2012. n equals the number of counties within each bin.
Figure 5
Figure 5. Increase in the population of domestic well users exposed to arsenic greater than 10 μg/L under drought simulation 7.
References
ARTICLE SECTIONSThis article references 52 other publications.
- 1Centers for Disease Control and Prevention (CDC), U.S. Environmental Protection Agency, National Oceanic and Atmospheric Agency, and American Water Works Association. When Every Drop Counts: Protecting Public Health during Drought Conditions—a Guide for Public Health Professionals , 2010; p 56.Google ScholarThere is no corresponding record for this reference.
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- 4Smedley, P. L.; Kinniburgh, D.G. A review of the source, behaviour and distribution of arsenic in natural waters. Appl. Geochem. 2002, 17, 517– 568, DOI: 10.1016/s0883-2927(02)00018-5[Crossref], [CAS], Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XhvVSmur0%253D&md5=563c408bde5c60c44ec8d21ee1eeec28A review of the source, behaviour and distribution of arsenic in natural watersSmedley, P. L.; Kinniburgh, D. G.Applied Geochemistry (2002), 17 (5), 517-568CODEN: APPGEY; ISSN:0883-2927. (Elsevier Science Ltd.)A review. The range of As concns. found in natural waters is large, ranging from less than 0.5 μg l-1 to more than 5000 μg l-1. Typical concns. in freshwater are less than 10 μg l-1 and frequently less than 1 μg l-1. Rarely, much higher concns. are found, particularly in groundwater. In such areas, more than 10% of wells may be 'affected' (defined as those exceeding 50 μg l-1) and in the worst cases, this figure may exceed 90%. Well-known high-As groundwater areas have been found in Argentina, Chile, Mexico, China and Hungary, and more recently in West Bengal (India), Bangladesh and Vietnam. The scale of the problem in terms of population exposed to high As concns. is greatest in the Bengal Basin with more than 40 million people drinking water contg. 'excessive' As. These large-scale 'natural' As groundwater problem areas tend to be found in two types of environment: firstly, inland or closed basins in arid or semi-arid areas, and secondly, strongly reducing aquifers often derived from alluvium. Both environments tend to contain geol. young sediments and to be in flat, low-lying areas where groundwater flow is sluggish. Historically, these are poorly flushed aquifers and any As released from the sediments following burial has been able to accumulate in the groundwater. Arsenic-rich groundwaters are also found in geothermal areas and, on a more localized scale, in areas of mining activity and where oxidn. of sulfide minerals has occurred. The As content of the aquifer materials in major problem aquifers does not appear to be exceptionally high, being normally in the range 1-20 mg kg-1. There appear to be two distinct 'triggers' that can lead to the release of As on a large scale. The first is the development of high pH (>8.5) conditions in semi-arid or arid environments usually as a result of the combined effects of mineral weathering and high evapn. rates. This pH change leads either to the desorption of adsorbed As (esp. As(V) species) and a range of other anion-forming elements (V, B, F, Mo, Se and U) from mineral oxides, esp. Fe oxides, or it prevents them from being adsorbed. The second trigger is the development of strongly reducing conditions at near-neutral pH values, leading to the desorption of As from mineral oxides and to the reductive dissoln. of Fe and Mn oxides, also leading to As release. Iron (II) and As(III) are relatively abundant in these groundwaters and SO4 concns. are small (typically 1 mg l-1 or less). Large concns. of phosphate, bicarbonate, silicate and possibly org. matter can enhance the desorption of As because of competition for adsorption sites. A characteristic feature of high groundwater As areas is the large degree of spatial variability in As concns. in the groundwaters. This means that it may be difficult, or impossible, to predict reliably the likely concn. of As in a particular well from the results of neighboring wells and means that there is little alternative but to analyze each well. Arsenic-affected aquifers are restricted to certain environments and appear to be the exception rather than the rule. In most aquifers, the majority of wells are likely to be unaffected, even when, for example, they contain high concns. of dissolved Fe.
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- 6Appleyard, S. J.; Angeloni, J.; Watkins, R. Arsenic-rich groundwater in an urban area experiencing drought and increasing population density, Perth, Australia. Appl. Geochem. 2006, 21, 83– 97, DOI: 10.1016/j.apgeochem.2005.09.008[Crossref], [CAS], Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXhtlWqtL%252FP&md5=649967350f9c4337048b050ae5703e49Arsenic-rich groundwater in an urban area experiencing drought and increasing population density, Perth, AustraliaAppleyard, S. J.; Angeloni, J.; Watkins, R.Applied Geochemistry (2006), 21 (1), 83-97CODEN: APPGEY; ISSN:0883-2927. (Elsevier Ltd.)Groundwater in the Gwelup groundwater management area in Perth, Western Australia has been enriched in As due to the exposure of pyritic sediments caused by reduced rainfall, increased groundwater abstraction for irrigation and water supply, and prolonged dewatering carried out during urban construction activities. Groundwater near the watertable in a 25-60 m thick unconfined sandy aquifer has become acidic and has affected shallow wells used for garden irrigation. Arsenic concns. up to 7000 μg/L were measured in shallow groundwater, triggering concerns about possible health effects if residents were to use water from household wells as a drinking water source. Deep prodn. wells used for public water supply are not affected by acidity, but trends of progressively increasing concns. of Fe, SO4 and Ca over a 30-a period indicate that pyrite oxidn. products extend to the base of the unconfined aquifer. Falling Eh values are triggering the release of As from the redn. of Fe(III) oxyhydroxide minerals near the base of the unconfined aquifer, increasing the risk that groundwater used as a drinking water source will also become contaminated with high concns. of As.
- 7García-Prieto, J. C.; Cachaza, J. M.; Pérez-Galende, P.; Roig, M. G. Impact of drought on the ecological and chemical status of surface water and on the content of arsenic and fluoride pollutants of groundwater in the province of Salamanca (Western Spain). Chem. Ecol. 2012, 28, 545– 560, DOI: 10.1080/02757540.2012.686608[Crossref], [CAS], Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslamsLvP&md5=59b9ffe99ba7c6d8cb716490db2744a5Impact of drought on ecological and chemical status of surface water and on content of arsenic and fluoride pollutants of groundwaterGarcia-Prieto, Juan C.; Cachaza, Juan M.; Perez-Galende, Patricia; Roig, Manuel G.Chemistry and Ecology (2012), 28 (6), 545-560CODEN: CHECDY; ISSN:0275-7540. (Taylor & Francis Ltd.)The impact of drought on the ecol. and chem. status of surface and groundwaters of the River Tormes (River Duero basin, northwestern Iberian Peninsula) was studied to evaluate the evolution of the quality of the river during its passage through the city of Salamanca (Spain). The Water Quality Index (WQI) of the river revealed that the drought period of 2005 did not significantly affect water chem. quality. However, during the study period differences were found in surface water ecol. quality, using phytoplankton quality as AN indicator. These differences may be accentuated as a result of regulation of the River Tormes by the Santa Teresa reservoir. Arsenic and fluoride concns. were measured in water wells, finding higher arsenic concns. after the drought period and no correlation between the arsenic and fluoride contents. The results are useful for an overall understanding of potential impact of climate change on the ecol. and chem. status of water in regional systems.
- 8Ayotte, J. D.; Belaval, M.; Olson, S. A.; Burow, K. R.; Flanagan, S. M.; Hinkle, S. R.; Lindsey, B. D. Factors affecting temporal variability of arsenic in groundwater used for drinking water supply in the United States. Sci. Total Environ. 2015, 505, 1370– 1379, DOI: 10.1016/j.scitotenv.2014.02.057[Crossref], [PubMed], [CAS], Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXks1Wisb0%253D&md5=eebf2d6a0ce83afc0036f30f63234430Factors affecting temporal variability of arsenic in groundwater used for drinking water supply in the United StatesAyotte, Joseph D.; Belaval, Marcel; Olson, Scott A.; Burow, Karen R.; Flanagan, Sarah M.; Hinkle, Stephen R.; Lindsey, Bruce D.Science of the Total Environment (2015), 505 (), 1370-1379CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)The occurrence of As in groundwater is a recognized environmental hazard with worldwide importance and much effort has been focused on surveying and predicting where arsenic occurs. Temporal variability is one aspect of this environmental hazard that has until recently received less attention than other aspects. We analyzed 1245 wells with 2 samples/well. We suggest that temporal variability, often reported as affecting very few wells, is perhaps a larger issue than it appears and has been overshadowed by datasets with large nos. of non-detect data. Although there was only a slight difference in As concn. variability among samples from public and private wells (p =0.0452), the range of variability was larger for public than for private wells. We relate the variability we see to geochem. factors-primarily variability in redox-but also variability in major-ion chem. We also show that in New England there is a weak but statistically significant indication that seasonality may have an effect on concns., whereby concns. in the first two quarters of the year (Jan.-June) are significantly lower than in the 2nd 2 quarters (July-Dec.) (p <0.0001). In the Central Valley of California, the relation of As concn. to season was not statistically significant (p =0.4169). In New England, these changes appear to follow groundwater levels. It is possible that this difference in As concns. is related to groundwater level changes, pumping stresses, evapotranspiration effects, or perhaps mixing of more oxidizing, lower pH recharge water in wetter months. Focusing on the understanding the geochem. conditions in aquifers where As concns. are concerns and causes of geochem. changes in the groundwater environment may lead to a better understanding of where and by how much arsenic will vary over time.
- 9Levitt, J. P.; Degnan, J. R.; Flanagan, S. M.; Jurgens, B. C. Arsenic variability and groundwater age in three water supply wells in southeast New Hampshire. Geosci. Front. 2019, 10, 1669– 1683, DOI: 10.1016/j.gsf.2019.01.002[Crossref], [CAS], Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXis1SrurY%253D&md5=3d0d749756b7c87751db918eae7660a4Arsenic variability and groundwater age in three water supply wells in southeast New HampshireLevitt, J.; Degnan, J.; Flanagan, S.; Jurgens, B.Geoscience Frontiers (2019), 10 (5), 1669-1683CODEN: GFERA4; ISSN:1674-9871. (Elsevier B.V.)Three wells in New Hampshire were sampled bimonthly over three years to evaluate the temporal variability of arsenic concns. and groundwater age. All samples had measurable concns. of arsenic throughout the entire sampling period and concns. in individual wells had a mean variation of more than 7 μg/L. The time series data from this sampling effort showed that arsenic concns. ranged from a median of 4 μg/L in a glacial aquifer well (SGW-65) to medians of 19 μg/L and 37 μg/L in wells (SGW-93 and KFW-87) screened in the bedrock aquifer, resp. These high arsenic concns. were assocd. with the consistently high pH (median ≥ 8) and low dissolved oxygen (median <0.1 mg/L) in the bedrock aquifer wells, which is typical of fractured cryst. bedrock aquifers in New Hampshire. Groundwater from the glacial aquifer often has high dissolved oxygen, but in this case was consistently low. The pH also is generally acidic in the glacial aquifer but in this case was slightly alk. (median = 7.5). Also, sorption sites may be more abundant in glacial aquifer deposits than in fractured bedrock which may contribute to lower arsenic concns.Mean groundwater ages were less than 50 years old in all three wells and correlated with conservative tracer concns., such as chloride; however, mean age was not directly correlated with arsenic concns. Arsenic concns. at KFW-87 did correlate with water levels, in addn., there was a seasonal pattern, which suggests that either the timing of or multiple sampling efforts may be important to define the full range of arsenic concns. in domestic bedrock wells.Since geochem. reduced conditions and alk. pHs are common to both bedrock and glacial aquifer wells in this study, groundwater age correlates less strongly with arsenic concns. than geochem. conditions. There also is evidence of direct hydraulic connection between the glacial and bedrock aquifers, which can influence arsenic concns. Correlations between arsenic concns. and the age of the old fraction of water in SGW-65 and the age of the young fraction of water in SGW-93 suggest that water in the two aquifers may be mixing or at least some of the deeper, older water captured by the glacial aquifer well may be from a similar source as the shallow young groundwater from the bedrock aquifer. The contrast in arsenic concns. in the two aquifers may be because of increased adsorption capacity of glacio-fluvial sediments, which can limit contaminants more than fractured rock. In addn., this study illustrates that long residence times are not necessary to achieve more geochem. evolved conditions such as high pH and reduced conditions as is typically found with older water in other regions.
- 10Baris, D.; Waddell, R.; Beane Freeman, L. E.; Schwenn, M.; Colt, J. S.; Ayotte, J. D.; Ward, M. H.; Nuckols, J.; Schned, A.; Jackson, B.; Clerkin, C.; Rothman, N.; Moore, L. E.; Taylor, A.; Robinson, G.; Hosain, G. M.; Armenti, K. R.; McCoy, R.; Samanic, C.; Hoover, R. N.; Fraumeni, J. F., Jr.; Johnson, A.; Karagas, M. R.; Silverman, D. T. Elevated Bladder Cancer in Northern New England: The Role of Drinking Water and Arsenic. J. Natl. Cancer Inst. 2016, 108, djw099, DOI: 10.1093/jnci/djw099
- 11Mendez, W. M., Jr.; Eftim, S.; Cohen, J.; Warren, I.; Cowden, J.; Lee, J. S.; Sams, R. Relationships between arsenic concentrations in drinking water and lung and bladder cancer incidence in U.S. counties. J. Exposure Sci. Environ. Epidemiol. 2017, 27, 235– 243, DOI: 10.1038/jes.2016.58[Crossref], [PubMed], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVWqurfL&md5=0f00e8b458cf83275f1532b86aff698cRelationships between arsenic concentrations in drinking water and lung and bladder cancer incidence in U.S. countiesMendez, William M.; Eftim, Sorina; Cohen, Jonathan; Warren, Isaac; Cowden, John; Lee, Janice S.; Sams, ReederJournal of Exposure Science & Environmental Epidemiology (2017), 27 (3), 235-243CODEN: JESEBS; ISSN:1559-0631. (Nature Publishing Group)Increased risks of lung and bladder cancer have been obsd. in populations exposed to high levels of inorg. arsenic. However, studies at lower exposures (i.e., less than 100μg/l in water) have shown inconsistent results. We therefore conducted an ecol. anal. of the assocn. between historical drinking water arsenic concns. and lung and bladder cancer incidence in U. S. counties. We used drinking water arsenic concns. measured by the U. S. Geol. Survey and state agencies in the 1980s and 1990s as proxies for historical exposures in counties where public groundwater systems and private wells are important sources of drinking water. Relationships between arsenic levels and cancer incidence in 2006-2010 were explored by Poisson regression analyses, adjusted for groundwater dependence and important demog. covariates. The median and 95th percentile county mean arsenic concns. were 1.5 and 15.4μg/l, resp. Water arsenic concns. were significant and pos. assocd. with female and male bladder cancer, and with female lung cancer. Our findings support an assocn. between low water arsenic concns. and lung and bladder cancer incidence in the United States. However, the limitations of the ecol. study design suggest caution in interpreting these results.
- 12Bulka, C. M.; Jones, R. M.; Turyk, M. E.; Stayner, L. T.; Argos, M. Arsenic in drinking water and prostate cancer in Illinois counties: An ecologic study. Environ. Res. 2016, 148, 450– 456, DOI: 10.1016/j.envres.2016.04.030[Crossref], [PubMed], [CAS], Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XntFCku7o%253D&md5=9faa18a5f2f86c037382b1dac963d676Arsenic in drinking water and prostate cancer in Illinois counties: An ecologic studyBulka, Catherine M.; Jones, Rachael M.; Turyk, Mary E.; Stayner, Leslie T.; Argos, MariaEnvironmental Research (2016), 148 (), 450-456CODEN: ENVRAL; ISSN:0013-9351. (Elsevier)Inorg. arsenic is a lung, bladder, and skin carcinogen. One of the major sources of exposure to arsenic is through naturally contaminated drinking water. While pos. assocns. have been obsd. between arsenic in drinking water and prostate cancer, few studies have explored this assocn. in the United States. To evaluate the assocn. between inorg. arsenic concns. in community water systems and prostate cancer incidence in Illinois using an ecol. study design. Illinois Environmental Protection Agency data on arsenic concns. in drinking water from community water systems throughout the state were linked with county-level prostate cancer incidence data from 2007 to 2011 from the Illinois State Cancer Registry. Incidence rates were indirectly standardized by age to calc. standardized incidence ratios (SIRs) for each county. A Poisson regression model was used to model the assocn. between county-level SIRs and mean arsenic tertile (0.33-0.72, 0.73-1.60, and 1.61-16.23 ppb), adjusting for potential confounders. For counties with mean arsenic levels in the second tertile, the SIR was 1.05 (95% CI: 0.96-1.16). For counties with mean arsenic levels in the third tertile, the SIR was 1.10 (95% CI: 1.03-1.19). There was a significant linear dose-response relationship obsd. between mean arsenic levels and prostate cancer incidence (p for trend=0.003). In this ecol. study, counties with higher mean arsenic levels in community water systems had significantly higher prostate cancer incidence. Individual-level studies of prostate cancer incidence and low-level arsenic exposure are needed.
- 13Naujokas, M. F.; Anderson, B.; Ahsan, H.; Aposhian, H. V.; Graziano, J. H.; Thompson, C.; Suk, W. A. The broad scope of health effects from chronic arsenic exposure: update on a worldwide public health problem. Environ. Health Perspect. 2013, 121, 295– 302, DOI: 10.1289/ehp.1205875[Crossref], [PubMed], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3svjt1Ohtw%253D%253D&md5=77f941e606bf07120eedb3aead598aeeThe broad scope of health effects from chronic arsenic exposure: update on a worldwide public health problemNaujokas Marisa F; Anderson Beth; Ahsan Habibul; Aposhian H Vasken; Graziano Joseph H; Thompson Claudia; Suk William AEnvironmental health perspectives (2013), 121 (3), 295-302 ISSN:.BACKGROUND: Concerns for arsenic exposure are not limited to toxic waste sites and massive poisoning events. Chronic exposure continues to be a major public health problem worldwide, affecting hundreds of millions of persons. OBJECTIVES: We reviewed recent information on worldwide concerns for arsenic exposures and public health to heighten awareness of the current scope of arsenic exposure and health outcomes and the importance of reducing exposure, particularly during pregnancy and early life. METHODS: We synthesized the large body of current research pertaining to arsenic exposure and health outcomes with an emphasis on recent publications. DISCUSSION: Locations of high arsenic exposure via drinking water span from Bangladesh, Chile, and Taiwan to the United States. The U.S. Environmental Protection Agency maximum contaminant level (MCL) in drinking water is 10 μg/L; however, concentrations of > 3,000 μg/L have been found in wells in the United States. In addition, exposure through diet is of growing concern. Knowledge of the scope of arsenic-associated health effects has broadened; arsenic leaves essentially no bodily system untouched. Arsenic is a known carcinogen associated with skin, lung, bladder, kidney, and liver cancer. Dermatological, developmental, neurological, respiratory, cardiovascular, immunological, and endocrine effects are also evident. Most remarkably, early-life exposure may be related to increased risks for several types of cancer and other diseases during adulthood. CONCLUSIONS: These data call for heightened awareness of arsenic-related pathologies in broader contexts than previously perceived. Testing foods and drinking water for arsenic, including individual private wells, should be a top priority to reduce exposure, particularly for pregnant women and children, given the potential for life-long effects of developmental exposure.
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- 15Johnson, T. D.; Belitz, K.; Lombard, M. A. Estimating domestic well locations and populations served in the contiguous U.S. for years 2000 and 2010. Sci. Total Environ. 2019, 687, 1261– 1273, DOI: 10.1016/j.scitotenv.2019.06.036[Crossref], [PubMed], [CAS], Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXht1ekt77F&md5=759004dd17b81213f54cfaf9dba615b5Estimating domestic well locations and populations served in the contiguous U.S. for years 2000 and 2010Johnson, Tyler D.; Belitz, Kenneth; Lombard, Melissa A.Science of the Total Environment (2019), 687 (), 1261-1273CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)Domestic wells provide drinking water supply for approx. 40 million people in the United States. Knowing the location of these wells, and the populations they serve, is important for identifying heavily used aquifers, locations susceptible to contamination, and populations potentially impacted by poor-quality groundwater. The 1990 census was the last nationally consistent survey of a home's source of water, and has not been surveyed since. This paper presents a method for projecting the population dependent on domestic wells for years after 1990, using information from the 1990 census along with population data from subsequent censuses. The method is based on the "domestic ratio" at the census block-group level, defined here as the no. of households dependent on domestic wells divided by the total population. Anal. of 1990 data (>220,000 block-groups) indicates that the domestic ratio is a function of the household d. As household d. increases, the domestic ratio decreases, once a household d. threshold is met. The 1990 data were used to develop a relationship between household d. and the domestic ratio. The fitted model, along with household d. data from 2000 and 2010, was used to est. domestic ratios for each decadal year. In turn, the no. of households dependent on domestic wells was estd. at the block-group level for 2000 and 2010. High-resoln. census-block population data were used to refine the spatial distribution of domestic-well usage and to convert the data into population nos. The results are presented in two downloadable raster datasets for each decadal year. It is estd. that the total population using domestic-well water in the contiguous U. S. increased 1.5% from 1990 to 2000 to a total of 37.25 million people and increased slightly from 2000 to 2010 to 37.29 million people.
- 16Maupin, M. A., Kenny, J.F., Hutson, S.S., Lovelace, J.K., Barber, N.L., Linsey, K.S. Estimated Use of Water in the United States in 2010; U.S. Geological Survey Circular 1405, 2014 https://doi.org/10.3133/cir1405.
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- 22Khan, S. J.; Deere, D.; Leusch, F. D. L.; Humpage, A.; Jenkins, M.; Cunliffe, D. Extreme weather events: Should drinking water quality management systems adapt to changing risk profiles?. Water Res. 2015, 85, 124– 136, DOI: 10.1016/j.watres.2015.08.018[Crossref], [PubMed], [CAS], Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVaju7vE&md5=7d8eac0f039dc98a18d61be7692b02ecExtreme weather events: Should drinking water quality management systems adapt to changing risk profiles?Khan, Stuart J.; Deere, Daniel; Leusch, Frederic D. L.; Humpage, Andrew; Jenkins, Madeleine; Cunliffe, DavidWater Research (2015), 85 (), 124-136CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)Among the most widely predicted and accepted consequences of global climate change are increases in both the frequency and severity of a variety of extreme weather events. Such weather events include heavy rainfall and floods, cyclones, droughts, heatwaves, extreme cold, and wildfires, each of which can potentially impact drinking water quality by affecting water catchments, storage reservoirs, the performance of water treatment processes or the integrity of distribution systems. Drinking water guidelines, such as the Australian Drinking Water Guidelines and the World Health Organization Guidelines for Drinking-water Quality, provide guidance for the safe management of drinking water. These documents present principles and strategies for managing risks that may be posed to drinking water quality. While these principles and strategies are applicable to all types of water quality risks, very little specific attention has been paid to the management of extreme weather events. We present a review of recent literature on water quality impacts of extreme weather events and consider practical opportunities for improved guidance for water managers. We conclude that there is a case for an enhanced focus on the management of water quality impacts from extreme weather events in future revisions of water quality guidance documents.
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- 24Green, T. R.; Taniguchi, M.; Kooi, H.; Gurdak, J. J.; Allen, D. M.; Hiscock, K. M.; Treidel, H.; Aureli, A. Beneath the surface of global change: Impacts of climate change on groundwater. J. Hydrol. 2011, 405, 532– 560, DOI: 10.1016/j.jhydrol.2011.05.002
- 25Murti, M.; Yard, E.; Kramer, R.; Haselow, D.; Mettler, M.; McElvany, R.; Martin, C. Impact of the 2012 extreme drought conditions on private well owners in the United States, a qualitative analysis. BMC Public Health 2016, 16, 430, DOI: 10.1186/s12889-016-3039-4[Crossref], [PubMed], [CAS], Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2s%252FjtlOnsw%253D%253D&md5=6611d4ebc27fcf998c0e910d65cc3b0fImpact of the 2012 extreme drought conditions on private well owners in the United States, a qualitative analysisMurti Michelle; Yard Ellen; Martin Colleen; Kramer Rachel; Haselow Dirk; Mettler Mike; McElvany RockyBMC public health (2016), 16 (), 430 ISSN:.BACKGROUND: Extreme hot and dry weather during summer 2012 resulted in some of the most devastating drought conditions in the last half-century in the United States (U.S.). While public drinking water systems have contingency plans and access to alternative resources to maintain supply for their customers during drought, little is known about the impacts of drought on private well owners, who are responsible for maintaining their own water supply. The purpose of this investigation was to explore the public health impacts of the 2012 drought on private well owners' water quality and quantity, identify their needs for planning and preparing for drought, and to explore their knowledge, attitudes, and well maintenance behaviors during drought. METHODS: In the spring of 2013, we conducted six focus group discussions with private well owners in Arkansas, Indiana, and Oklahoma. RESULTS: There were a total of 41 participants, two-thirds of whom were men aged 55 years or older. While participants agreed that 2012 was the worst drought in memory, few experienced direct impacts on their water quantity or quality. However, all groups had heard of areas or individuals whose wells had run dry. Participants conserved water by reducing their indoor and outdoor consumption, but they had few suggestions on additional ways to conserve, and they raised concerns about limiting water use too much. Participants wanted information on how to test their well and any water quality issues in their area. CONCLUSIONS: This investigation identified information needs regarding drought preparedness and well management for well owners.
- 26Ayotte, J. D.; Medalie, L.; Qi, S. L.; Backer, L. C.; Nolan, B. T. Estimating the High-Arsenic Domestic-Well Population in the Conterminous United States. Environ. Sci. Technol. 2017, 51, 12443– 12454, DOI: 10.1021/acs.est.7b02881[ACS Full Text], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1Kgu77M&md5=fb41fe08154c95ab6a5729277c4af85eEstimating the High-Arsenic Domestic-Well Population in the Conterminous United StatesAyotte, Joseph D.; Medalie, Laura; Qi, Sharon L.; Backer, Lorraine C.; Nolan, Bernard T.Environmental Science & Technology (2017), 51 (21), 12443-12454CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)Arsenic concns. from 20450 domestic wells in the U.S. were used to develop a logistic regression model of the probability of having arsenic >10 μg/L ("high arsenic"), which is presented at the county, state, and national scales. Variables representing geol. sources, geochem., hydrol., and phys. features were among the significant predictors of high arsenic. For U.S. Census blocks, the mean probability of arsenic >10 μg/L was multiplied by the population using domestic wells to est. the potential high-arsenic domestic-well population. Approx. 44.1 M people in the U.S. use water from domestic wells. The population in the conterminous U.S. using water from domestic wells with predicted arsenic concn. >10 μg/L is 2.1 M people (95% CI is 1.5 to 2.9 M). Although areas of the U.S. were underrepresented with arsenic data, predictive variables available in national data sets were used to est. high arsenic in unsampled areas. Addnl., by predicting to all of the conterminous U.S., we identify areas of high and low potential exposure in areas of limited arsenic data. These areas may be viewed as potential areas to investigate further or to compare to more detailed local information. Linking predictive modeling to private well use information nationally, despite the uncertainty, is beneficial for broad screening of the population at risk from elevated arsenic in drinking water from private wells.
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- 30Lombard, M. A. Datasets for assessing the impact of drought on arsenic exposure from private domestic wells in the conterminous United States; U.S. Geological Survey data release, 2021. https://doi.org/10.5066/P9TU0R2T.Google ScholarThere is no corresponding record for this reference.
- 31National Drought Mitigation Center. Average Precipitation and Drought Severity. https://drought.unl.edu/ranchplan/InventoryandMonitor/Precipitation/AveragePrecipitationandDroughtSeverity.aspx.Google ScholarThere is no corresponding record for this reference.
- 32Wolock, D. M. Estimated Mean Annual Natural Ground-Water Recharge in the Conterminous United States; U.S. Geological Survey Open-File Report 2003-311, http://pubs.er.usgs.gov/publication/ofr03311, 2003.
- 33Reitz, M.; Sanford, W. E.; Senay, G. B.; Cazenas, J. Annual Estimates of Recharge, Quick-Flow Runoff, and Evapotranspiration for the Contiguous U.S. Using Empirical Regression Equations. J. Am. Water Resour. Assoc. 2017, 53, 961– 983, DOI: 10.1111/1752-1688.12546
- 34Markstrom, S. L., Regan, R.S., Hay, L.E., Viger, R.J., Webb, R. M., Payn, R.A., LaFontaine, J.H. PRMS-IV, the precipitation-runoff modeling system, version 4. U.S. Geological Survey Techniques and Methods, book 6; U.S. Geological Survey, 2015, Chapter B7, p 158.
- 35Regan, R. S.; Markstrom, S. L.; Hay, L. E.; Viger, R. J.; Norton, P. A.; Driscoll, J. M.; LaFontaine, J. H. Description of the National Hydrologic Model for use with the Precipitation-Runoff Modeling System (PRMS); U.S. Geological Survey Techniques and Methods, Reston, VA., Book 6, Chap B9, 38 p. https://doi.org/10.3133/tm6B9.Google ScholarThere is no corresponding record for this reference.
- 36Regan, R. S.; Juracek, K. E.; Hay, L. E.; Markstrom, S. L.; Viger, R. J.; Driscoll, J. M.; LaFontaine, J. H.; Norton, P. A. The U. S. Geological Survey National Hydrologic Model infrastructure: Rationale, description, and application of a watershed-scale model for the conterminous United States. Environ. Model. Software 2019, 111, 192– 203, DOI: 10.1016/j.envsoft.2018.09.023
- 37Hay, L. E. Application of the National Hydrologic Model Infrastructure with the Precipitation-Runoff Modeling System (NHM-PRMS), by HRU Calibrated Version: U.S. Geological Survey data release; U.S. Geological Survey data release, 2019. https://doi.org/10.5066/P9NM8K8WGoogle ScholarThere is no corresponding record for this reference.
- 38LaFontaine, J. H.; Hart, R. M.; Hay, L. E.; Farmer, W. H.; Bock, A. R.; Viger, R. J.; Markstrom, S. L.; Regan, R. S.; Driscoll, J. M. Simulation of Water Availability in the Southeastern United States for Historical and Potential Future Climate and Land-Cover Conditions; U.S. Geological Survey Scientific Investigations Report 2019-5039; Reston, VA, 2019.
- 39Thornton, P. E.; Thornton, M. M.; Mayer, B. W.; Wei, Y.; Devarakonda, R.; Vose, R. S.; Cook, R. B. Daymet: Daily Surface Weather Data on a 1-km Grid for North America, Version 3;ORNL Distributed Active Archive Center, 2018.Google ScholarThere is no corresponding record for this reference.
- 40Centers for Disease Control and Prevention. National Environmental Public Health Tracking Network. https://ephtracking.cdc.gov/showDroughtIndicators (accessed Nov 2, 2018).Google ScholarThere is no corresponding record for this reference.
- 41Smith, R.; Knight, R.; Fendorf, S. Overpumping leads to California groundwater arsenic threat. Nat. Commun. 2018, 9, 2089, DOI: 10.1038/s41467-018-04475-3[Crossref], [PubMed], [CAS], Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1Mbkt1yqtA%253D%253D&md5=6aeca9f69daed5347745c4cc7e25a459Overpumping leads to California groundwater arsenic threatSmith Ryan; Knight Rosemary; Fendorf ScottNature communications (2018), 9 (1), 2089 ISSN:.Water resources are being challenged to meet domestic, agricultural, and industrial needs. To complement finite surface water supplies that are being stressed by changes in precipitation and increased demand, groundwater is increasingly being used. Sustaining groundwater use requires considering both water quantity and quality. A unique challenge for groundwater use, as compared with surface water, is the presence of naturally occurring contaminants within aquifer sediments, which can enter the water supply. Here we find that recent groundwater pumping, observed through land subsidence, results in an increase in aquifer arsenic concentrations in the San Joaquin Valley of California. By comparison, historic groundwater pumping shows no link to current groundwater arsenic concentrations. Our results support the premise that arsenic can reside within pore water of clay strata within aquifers and is released due to overpumping. We provide a quantitative model for using subsidence as an indicator of arsenic concentrations correlated with groundwater pumping.
- 42Erban, L. E.; Gorelick, S. M.; Zebker, H. A.; Fendorf, S. Release of arsenic to deep groundwater in the Mekong Delta, Vietnam, linked to pumping-induced land subsidence. Proc. Natl. Acad. Sci. U.S.A. 2013, 110, 13751– 13756, DOI: 10.1073/pnas.1300503110[Crossref], [PubMed], [CAS], Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtlKqu7rL&md5=59c3b05851cc85be8d0698c3857a27cfRelease of arsenic to deep groundwater in the Mekong Delta, Vietnam, linked to pumping-induced land subsidenceErban, Laura E.; Gorelick, Steven M.; Zebker, Howard A.; Fendorf, ScottProceedings of the National Academy of Sciences of the United States of America (2013), 110 (34), 13751-13756,S13751/1-S13751/6CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Deep aquifers in South and Southeast Asia are increasingly exploited as presumed sources of pathogen- and arsenic-free water, although little is known of the processes that may compromise their long-term viability. We analyze a large area (>1,000 km2) of the Mekong Delta, Vietnam, in which arsenic is found pervasively in deep, Pliocene-Miocene-age aquifers, where nearly 900 wells at depths of 200-500 m are contaminated. There, intensive groundwater extn. is causing land subsidence of up to 3 cm/y as measured using satellite-based radar images from 2007 to 2010 and consistent with transient 3D aquifer simulations showing similar subsidence rates and total subsidence of up to 27 cm since 1988. We propose a previously unrecognized mechanism in which deep groundwater extn. is causing interbedded clays to compact and expel water contg. dissolved arsenic or arsenic-mobilizing solutes (e.g., dissolved org. carbon and competing ions) to deep aquifers over decades. The implication for the broader Mekong Delta region, and potentially others like it across Asia, is that deep, untreated groundwater will not necessarily remain a safe source of drinking water.
- 43Oreskes, N. How Small is Small?. Sci. Am. 2020, 322 (6), 77, DOI: 10.1038/scientificamerican0620-77
- 44Lawler, J. J.; Shafer, S. L.; White, D.; Kareiva, P.; Maurer, E. P.; Blaustein, A. R.; Bartlein, P. J., Projected climate-induced faunal change in the Western Hemisphere. Ecology 2009, 90, 588- 597, DOI: 10.1890/08-0823.1 .[Crossref], [PubMed], [CAS], Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD1M3lsV2ltg%253D%253D&md5=28a1a519ac2bcb8f87b2759f8b4a2fc3Projected climate-induced faunal change in the Western HemisphereLawler Joshua J; Shafer Sarah L; White Denis; Kareiva Peter; Maurer Edwin P; Blaustein Andrew R; Bartlein Patrick JEcology (2009), 90 (3), 588-97 ISSN:0012-9658.Climate change is predicted to be one of the greatest drivers of ecological change in the coming century. Increases in temperature over the last century have clearly been linked to shifts in species distributions. Given the magnitude of projected future climatic changes, we can expect even larger range shifts in the coming century. These changes will, in turn, alter ecological communities and the functioning of ecosystems. Despite the seriousness of predicted climate change, the uncertainty in climate-change projections makes it difficult for conservation managers and planners to proactively respond to climate stresses. To address one aspect of this uncertainty, we identified predictions of faunal change for which a high level of consensus was exhibited by different climate models. Specifically, we assessed the potential effects of 30 coupled atmosphere-ocean general circulation model (AOGCM) future-climate simulations on the geographic ranges of 2954 species of birds, mammals, and amphibians in the Western Hemisphere. Eighty percent of the climate projections based on a relatively low greenhouse-gas emissions scenario result in the local loss of at least 10% of the vertebrate fauna over much of North and South America. The largest changes in fauna are predicted for the tundra, Central America, and the Andes Mountains where, assuming no dispersal constraints, specific areas are likely to experience over 90% turnover, so that faunal distributions in the future will bear little resemblance to those of today.
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- 50Frederick, L.; VanDerslice, J.; Taddie, M.; Malecki, K.; Gregg, J.; Faust, N.; Johnson, W. P. Contrasting regional and national mechanisms for predicting elevated arsenic in private wells across the United States using classification and regression trees. Water Res. 2016, 91, 295– 304, DOI: 10.1016/j.watres.2016.01.023[Crossref], [PubMed], [CAS], Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1Gjsrs%253D&md5=ca346a76150c07dab267a0303aae135dContrasting regional and national mechanisms for predicting elevated arsenic in private wells across the United States using classification and regression treesFrederick, Logan; VanDerslice, James; Taddie, Marissa; Malecki, Kristen; Gregg, Josh; Faust, Nicholas; Johnson, William P.Water Research (2016), 91 (), 295-304CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)Arsenic contamination in groundwater is a public health and environmental concern in the United States (U.S.) particularly where monitoring is not required under the Safe Water Drinking Act. Previous studies suggest the influence of regional mechanisms for arsenic mobilization into groundwater; however, no study has examd. how influencing parameters change at a continental scale spanning multiple regions. We herein examine covariates for groundwater in the western, central and eastern U. S. regions representing mechanisms assocd. with arsenic concns. exceeding the U. S. Environmental Protection Agency max. contamination level (MCL) of 10 ppb (ppb). Statistically significant covariates were identified via classification and regression tree (CART) anal., and included hydrometeorol. and groundwater chem. parameters. The CART analyses were performed at two scales: national and regional; for which three physiog. regions located in the western (Payette Section and the Snake River Plain), central (Osage Plains of the Central Lowlands), and eastern (Embayed Section of the Coastal Plains) U. S. were examd. Validity of each of the three regional CART models was indicated by values >85% for the area under the receiver-operating characteristic curve. Aridity (pptn. minus potential evapotranspiration) was identified as the primary covariate assocd. with elevated arsenic at the national scale. At the regional scale, aridity and pH were the major covariates in the arid to semi-arid (western) region; whereas dissolved iron (taken to represent chem. reducing conditions) and pH were major covariates in the temperate (eastern) region, although addnl. important covariates emerged, including elevated phosphate. Anal. in the central U. S. region indicated that elevated arsenic concns. were driven by a mixt. of those obsd. in the western and eastern regions.
- 51Dai, A. Drought under global warming: a review. Wiley Interdiscip. Rev. Clim. Change 2011, 2, 45– 65, DOI: 10.1002/wcc.81
- 52Zhou, S.; Zhang, Y.; Park Williams, A.; Gentine, P. Projected increases in intensity, frequency, and terrestrial carbon costs of compound drought and aridity events. Sci. Adv. 2019, 5, eaau5740 DOI: 10.1126/sciadv.aau5740
Supporting Information
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ARTICLE SECTIONSThe Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.9b05835.
Tables and figures; diagram of methods, maps of changes in probability of high arsenic from drought simulation runs, maps of predicted probabilities using updated data sources, change in precipitation and recharge compared to duration of drought for 2012 by county, and estimated domestic well population exposed to high arsenic during normal climate conditions and during drought conditions by state (PDF)
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