Tungsten is an emerging pollutant commonly assumed to occur as the simple oxyanion tungstate, yet it often condenses into a suite of polytungstates in polluted waters. Despite growing recognition that tungstate polymerization modulates tungsten's environmental fate, its effects on toxicity remain largely unexplored. Here, we tracked the (de)polymerization behavior of three representative (poly)tungstates and examined its associations with multiple measures of acute toxicity to Daphnia magna, including the median lethal concentration (LC50), toxicokinetics, reactive oxygen species (ROS) content, metabolomics, and histology. While tungstate remained stable, W12 metatungstate and phosphotungstate depolymerized to different extents, yielding three distinct polymerization regimes in the exposure media. Monomeric tungstate exhibited high LC50, rapid uptake and efficient excretion, weak ROS signals, and minimal disruption of intestinal integrity. Oligomeric tungstates displayed lower LC50 than tungstate, consistent with slow depuration that generated high internal burdens, ROS accumulation, and suppression-oriented metabolic responses. High-order polytungstates, despite limited uptake and low ROS levels, were associated with structural disruption including irreversible gut barrier damage and mitochondrial collapse and displayed the lowest LC50. Together, these results suggest that tungstate polymerization not only amplifies tungsten toxicity but also alters its mode of action, supporting mechanistic interpretation and prediction of its ecotoxicological dynamics.

Tungsten is an emerging pollutant commonly assumed to occur as the simple oxyanion tungstate, yet it often condenses into a suite of polytungstates in polluted waters. Despite growing recognition that tungstate polymerization modulates tungsten's environmental fate, its effects on toxicity remain largely unexplored. Here, we tracked the (de)polymerization behavior of three representative (poly)tungstates and examined its associations with multiple measures of acute toxicity to Daphnia magna, including the median lethal concentration (LC50), toxicokinetics, reactive oxygen species (ROS) content, metabolomics, and histology. While tungstate remained stable, W12 metatungstate and phosphotungstate depolymerized to different extents, yielding three distinct polymerization regimes in the exposure media. Monomeric tungstate exhibited high LC50, rapid uptake and efficient excretion, weak ROS signals, and minimal disruption of intestinal integrity. Oligomeric tungstates displayed lower LC50 than tungstate, consistent with slow depuration that generated high internal burdens, ROS accumulation, and suppression-oriented metabolic responses. High-order polytungstates, despite limited uptake and low ROS levels, were associated with structural disruption including irreversible gut barrier damage and mitochondrial collapse and displayed the lowest LC50. Together, these results suggest that tungstate polymerization not only amplifies tungsten toxicity but also alters its mode of action, supporting mechanistic interpretation and prediction of its ecotoxicological dynamics.

In the United States, private wells are not federally regulated, and many households do not test for Arsenic (As). Chronic exposure is linked with multiple health outcomes, and risk can change sharply over short distances and with well depth. Coarse maps or sparse sampling often miss exceedances. Most existing models operate at ∼1 km resolution and use groundwater chemistry or detailed geologic logs, which limits their use in undersampled areas where improved guidance is most needed. We overcome these limitations by developing a machine learning model for Minnesota, USA, that predicts As exposure risk using only surficial variables from remote sensing and global data sets. Variables related to surface water hydrology and geomorphology are selected based on mechanistic links that control redox conditions and As mobilization. Local training was essential, and surficial geology variables that are more sensitive to local conditions were needed to maximize model accuracy. The resulting complete model was sufficiently sensitive to generate accurate and detailed risk maps and depth profiles of As concentrations above the 10 μg/L maximum contaminant level. Accuracy depended on local training data density. We identified a training data density of 0.07 wells/km 2 as a practical target for stable county-level performance. Maps of exceedance probabilities highlight priority areas for testing that are particularly important in rural communities that have received less sampling. These results support public health action by guiding where to install wells and where to test them, how much new sampling is needed, and where treatment outreach is most urgent.

Arsenic (As) accumulation in rice poses a significant, worldwide threat to food safety. Arsenic uptake is highly sensitive to climate and environmental factors; however, a comprehensive understanding of how diverse climatic conditions influence As dynamics and subsequent grain accumulation remains elusive. To fill this gap, we investigated As in soil and rice grain across 243 floodplain paddy sites along a similar to 2000 km longitudinal transect in Vietnam (8 degrees N to 22 degrees N), which is part of the world's largest rice-growing belt in Asia. The median levels of As in soils ranged from 8.3 to 9.9 mg kg(-1), and the consequent median levels of As in straw and grain were 0.85 mg kg(-1) and 163.5 mu g kg(-1), respectively. Our findings reveal a clear tendency for rice grain As accumulation to vary with climate and cropping season. Particularly, data from contrasting seasons show that warmer temperatures promote higher As uptake in rice grains and enhance the accumulation of inorganic As species. These results underscore an urgent need to establish new, proactive mitigation strategies and sustainable land management practices in response to accelerating global warming to safeguard the global rice supply.

BACKGROUND:Lithium production and processing is rapidly expanding, potentially increasing its environmental release. However, population-level exposure is poorly characterized in most countries. OBJECTIVE:Our objective was to evaluate drinking water and urinary lithium levels in the Strong Heart Family Study, a longitudinal study conducted with tribal partners in Arizona, Oklahoma, and North Dakota and South Dakota. METHODS:Lithium was measured in household tap water samples collected in 2022-2024 (n = 673) and spot urine samples collected in 2006-2009 and 2022-2024 (n = 613 paired samples). We examined within-person changes in urinary lithium, correlations between water and urinary lithium, and used mixed-effects models to estimate geometric mean ratios (GMRs) of urinary lithium in relation to study phase, water lithium, water source, and participant characteristics. RESULTS:Median (interquartile range) water lithium was 35.6 (9.0, 54.1) µg/L. Water lithium exceeded the United States Geological Survey health-based screening level (10 µg/L) in 100% of Arizona, 93% of North Dakota/South Dakota, and 35% of Oklahoma samples. Median urinary lithium was 30.8 (17.4, 53.3) µg/g creatinine in 2006-2009 and 31.2 (18.0, 56.0) in 2022-2024. The GMR comparing urinary lithium in 2022-2024 to 2006-2009 was 1.08 (1.02-1.14). Water lithium correlated with urinary lithium in 2006-2009 (ρ = 0.61) and 2022-2024 (ρ = 0.59). Each doubling of water lithium was associated with 22% higher urinary lithium before and 9% higher after adjustment for study site; all models adjusted for participant characteristics and water source. Water lithium explained 29% of variation in urinary lithium levels. SIGNIFICANCE:Lithium in drinking water is a widespread and persistent source of human exposure across Tribal communities in the Western United States, with regional variation. Our findings also support the use of urinary lithium as a biomarker of environmental exposure. IMPACT:Our study provides novel evidence of high levels of lithium in household drinking water (2022-2024) in Native American communities. We found that drinking water lithium in Arizona, North Dakota and South Dakota often exceeded the United States Geological Survey health-based screening level, urinary lithium levels remained stable over 15-years of follow-up, and household drinking water lithium explained a substantial proportion of variability in urinary lithium. Our findings improve lithium exposure estimations among Strong Heart Family Study communities and support the need for further environmental monitoring and risk evaluation, particularly as lithium extraction and processing accelerate to meet energy demands.

OBJECTIVES:We examined the association of uranium in community water systems (CWS) and in urine with type 2 diabetes (T2D) incidence in the Strong Heart Family Study (SHFS), a prospective study of American Indian communities, and the Multi-Ethnic Study of Atherosclerosis (MESA), a prospective study of racially and ethnically diverse urban U.S. communities. METHODS:We evaluated participants from SHFS (N = 1609) and MESA (N = 3080) with CWS and urine uranium available, free of T2D at baseline (2001-2003 and 2000-2002, respectively). We used Cox mixed-effects models to account for clustering by residential ZIP Code and family (SHFS), and estimated hazard ratios (HRs) of incident T2D per log2-increase and across categories of CWS and urine uranium adjusted for T2D risk factors and arsenic levels. Urinary models accounted for kidney function. RESULTS:Incident T2D cases were 198 in SHFS (mean follow-up 5.6 years) and 525 in MESA (mean follow-up 13.8 years). In a meta-analysis across SHFS and MESA, the adjusted HR (95% CI) of incident T2D was 0.97 (0.89, 1.04) and 1.01 (0.97, 1.06) per log-doubling of CWS and urine uranium, respectively. We observed a stronger association between uranium exposure and T2D among participants with lower BMI compared to higher BMI in both cohorts, although this finding was limited by small case sizes in the lowest BMI subgroups. CONCLUSIONS:CWS and urine uranium were not statistically associated with T2D across U.S. cohorts with low uranium exposure (median <1.2 μg/L). Given the importance of uranium exposure, further evidence is needed at low-to moderate-exposure levels.

Hydraulic fracturing (fracking) of black shales such as the Marcellus has become a major method of natural gas extraction in the United States and globally. The process involves high-volume injection of hydraulic fracturing fluid (HFF) into deep rock formations, initiating a sequence of geochemical reactions that alter shale mineralogy and mobilize potentially hazardous trace elements over several timescales. The laboratory experiments reported herein explore how interactions between HFF and shale during stages of the fracking process-including the shut-in period, initial flowback, long-term gas production, and post-closure-affect the release and redistribution of a large suite of trace elements. Experimental results show that during shut-in, acid additions rapidly dissolve carbonates and sulfides, subsequently allowing sulfide oxidation; evidence of clay transformation, barite precipitation, and secondary iron mineral precipitation is seen. During the initial production phase, most elements are released via direct acid dissolution to flowback waters; oxoanion forming elements (P, As, Mo, Th) are mobilized somewhat later. These processes lead to the partial or complete loss of some trace elements (such as lanthanides, Zn and Sr) from the solid phase. Others such as As, Mo, and U are redistributed into more labile mineral forms, raising concerns about their long-term environmental mobility and potential for drinking water contamination, particularly as well networks expand and age.

Exposure to tungsten, an emerging pollutant, is linked to cancer incidence and causes immune dysfunction. Till date the impact of tungsten speciation on immunotoxicity remains unclear. Here, we contrasted the immunotoxic effects of monomeric tungstate (W1) and polytungstate, the main forms of tungsten in environmental waters, on adult zebrafish, following static short-term (14 days) exposure to 0-215 mg L-1 tungsten. In the W1- and phosphotungstate (PW12)-treated systems, W1 was the dominant species that accounted for > 92 % tungsten, whereas metatungstate (W12) mainly (>59 %) existed as polytungstates with 2, 4, and 6 tungsten atoms. W1 exposure caused 1 % mortality, with tungsten primarily accumulating in metabolically active organs, brain, and gill. Contrastingly, polytungstate exposure caused up to 75 % mortality and 16 times higher tungsten bioaccumulation. Furthermore, polytungstate predominantly accumulated in the immune organs, intestine, and spleen, leading to intestinal villi necrosis and splenic melano-macrophage accumulation. Based on intestinal and splenic transcriptome analysis, W1 exposure upregulated the cytosolic DNA-sensing pathway, whereas polytungstate exposure downregulated the nucleotide-binding oligomerization domain-like and C-type lectin receptor signaling pathways. Polytungstate exposure also disturbed inflammatory factor expression, consistent with severe immunosuppression and inflammatory damage. These findings demonstrate that tungsten speciation regulates its uptake and accumulation, as well as the immunosuppression and inflammatory responses. Future tungsten toxicity assessment should rigorously account for its speciation. ENVIRONMENTAL IMPLICATION: Tungsten forms tungstate and many polytungstate complexes in environmental waters. Here, we systematically evaluated how this diverse speciation would impact the immunotoxicity of tungsten to aquatic organisms and potentially humans, using the zebrafish model. Short-term polytungstate exposure caused markedly higher mortality, greater bioaccumulation particularly in the immune organs, more striking histopathological abnormalities, and more severe immunosuppression and inflammatory damage than tungstate exposure. These results highlight the need to quantitatively assess tungsten speciation for a holistic understanding of the health impacts of tungsten exposure and will support the management and risk assessment of tungsten contamination in aquatic environments.

Groundwater uranium (U) contamination poses a significant health risk, particularly in Native American communities reliant on private wells. This study examines groundwater U cycling in a tribal region in South Dakota that participates in the Strong Heart Water Study based on samples from 140 private wells. We measured U concentrations, δ238U, (234U/238U), and redox-sensitive elements, including iron (Fe), manganese (Mn), nitrate (NO3-), selenium (Se), and vanadium (V). Uranium concentrations range from 0.4 to 48.2 μg/L, with 5% exceeding the U.S. EPA maximum contaminant level of 30 μg/L. Spatial patterns in δ238U and (234U/238U) delineate distinct redox regimes: oxidizing zones in the northeast show higher U (median = 18 μg/L) and positive δ238U values (from 0.08 to 0.30‰), while reducing zones in the southwest display lower U (median = 10 μg/L) and large negative δ238U values (from -0.61 to -0.30‰). The (234U/238U) values (from 1.53 to 3.07, median of 2.03) serve as a tracer of source proximity, with lower values (1.53-1.80) indicating shorter travel distance relative to the U source and higher values (1.80-2.50) reflecting U transported farther along flow paths. Cluster and uniform manifold approximation and projection (UMAP) analyses identify three geochemical environments consistent with oxidizing, reducing, and intermediate redox conditions. Constructing the first δ238U and (234U/238U) isoscapes for a sandstone aquifer, we show that U is released by oxidative dissolution in the northeast and removed under reducing conditions in the southwest and that the northeastern zone may require continuous monitoring and intervention for exposure reduction.

A high specific surface area (SSA) typically signifies a superior adsorption capacity. Nevertheless, minerals with high SSAs tend to possess tiny pores that may not be accessible to relatively large (poly)oxyanionic metals. Herein, we assessed the adsorption of (poly)oxyanionic metals on 2-line and 6-line ferrihydrite and goethite with distinct SSAs and pore geometries. SSA was estimated by BET isotherm using N-2, while pore geometry was measured by N-2 adsorption isotherms and positron annihilation lifetime spectroscopy. Tungstate and its polymers were chosen as representative (poly)oxyanions. Adsorption experiments were performed with constant mineral surface area, but different contact time, pH, and tungsten concentrations. Unexpectedly, the Langmuir adsorption capacities per unit surface area on 6-line ferrihydrite and goethite were 2-6 and 3-11 times as high as those on 2-line ferrihydrite, respectively. Adsorption on 2-line ferrihydrite was also severely kinetically limited. The varying rates and magnitudes of adsorption were attributed to distinct mineral pore widths: (poly)tungstates could hardly fit within the abundant tiny pores in 2-line ferrihydrite formed by voids between the primary particles/aggregates, but could enter the larger pores in 6-line ferrihydrite and goethite. Consequently, significant decreases of mineral microporosity (<2 nm) were observed following (poly)tungstate adsorption. Tungstate and polytungstate with different hydrated ion radii exhibited similar adsorption behavior, most likely due to the formation of adsorbed polytungstate directly on mineral surface. Our data demonstrate that mineral pore geometry controls the solid-solution partitioning of (poly)oxyanionic metals, which is crucial to comprehend their environmental fate and to mitigate their contamination.

Pleistocene aquifers are key for lowering the chronic exposure of the rural population to arsenic. Too little is known, however, about the sources of reactive carbon that maintain reducing conditions in these low-arsenic aquifers. This matters as enhanced supply of reactive carbon due to perturbations in groundwater flow could potentially release arsenic to groundwater. To shed light on this process, our team measures the radiocarbon content of labile microbial matter (RNA) and compares it to the radiocarbon content of potential sources of reactive carbon. Results to date suggest that recent recharge supplies reactive carbon in the dissolved form rather than the sediment, possibly in part in the form of methane. This dynamic situation suggests arsenic concentration could vary of time and should be monitored in vulnerable areas.

Objective: We examined the association of arsenic in federally regulated community water systems (CWS) and unregulated private wells with type 2 diabetes (T2D) incidence in the Strong Heart Family Study (SHFS), a prospective study of American Indian communities, and the Multi-Ethnic Study of Atherosclerosis (MESA), a prospective study of racially/ethnically diverse urban U.S. communities. Research Design and Methods: We evaluated N=1,791 participants from SHFS and N=5,777 participants from MESA with water arsenic estimates available and free of T2D at baseline (2001-2003 and 2000-2002, respectively). Participants were followed for incident T2D until 2010 (SHFS) or 2019 (MESA). We used Cox proportional hazards mixed-effects models to account for clustering by family and residential zip code, with adjustment for sex, baseline age, body mass index (BMI), smoking status, and education. Results: T2D incidence was 24.4 cases per 1,000 person-years (mean follow-up 5.6 years) in SHFS and 11.2 per 1,000 person-years (mean follow-up 6.0 years) in MESA. In a meta-analysis across SHFS and MESA, the hazard ratio (95% confidence interval) per doubling in CWS arsenic was 1.10 (95%CI 1.02, 1.18). The corresponding hazard ratio was 1.09 (0.95, 1.26) in SHFS and 1.10 (1.01, 1.20) in MESA. The corresponding hazard ratio (95%CI) for arsenic in private wells and incident T2D in SHFS was 1.05 (0.95, 1.16). We observed statistical interaction and larger magnitude hazard ratios for participants with BMI <25 kg/m2 and female participants. Conclusions: Low to moderate water arsenic levels (<10 µg/L) were associated with T2D incidence in the SHFS and MESA.

A multitude of geochemical processes control the aqueous concentration and transport properties of trace metal contaminants such as arsenic (As) in groundwater environments. Effective As remediation, especially under reducing conditions, has remained a significant challenge. Fe(II) nitrate treatments are a promising option for As immobilization but require optimization to be most effective. Here, we develop a process-based numerical modeling framework to provide an in-depth understanding of the geochemical mechanisms controlling the response of As-contaminated sediments to Fe(II) nitrate treatment. The analyzed data sets included time series from two batch experiments (control vs treatment) and effluent concentrations from a flow-through column experiment. The reaction network incorporates a mixture of homogeneous and heterogeneous reactions affecting Fe redox chemistry. Modeling revealed that the precipitation of the Fe treatment caused a rapid pH decline, which then triggered multiple heterogeneous buffering processes. The model quantifies key processes for effective remediation, including the transfer of aqueous As to adsorbed As and the transformation of Fe minerals, which act as sorption hosts, from amorphous to more stable phases. The developed model provides the basis for predictions of the remedial benefits of Fe(II) nitrate treatments under varying geochemical and hydrogeological conditions, particularly in high-As coastal environments.

Chronic exposure to inorganic arsenic (As) and uranium (U) in the United States (US) occurs from unregulated private wells and federally regulated community water systems (CWSs). The contribution of water to total exposure is assumed to be low when water As and U concentrations are low. We examined the contribution of water As and U to urinary biomarkers in the Strong Heart Family Study (SHFS), a prospective study of American Indian communities, and the Multi-Ethnic Study of Atherosclerosis (MESA), a prospective study of racially/ethnically diverse urban U.S. communities. We assigned residential zip code-level estimates in CWSs (µg/L) and private wells (90th percentile probability of As >10 µg/L) to up to 1485 and 6722 participants with dietary information and urinary biomarkers in the SHFS (2001–2003) and MESA (2000–2002; 2010–2011), respectively. Urine As was estimated as the sum of inorganic and methylated species, and urine U was total uranium. We used linear mixed-effects models to account for participant clustering and removed the effect of dietary sources via regression adjustment. The median (interquartile range) urine As was 5.32 (3.29, 8.53) and 6.32 (3.34, 12.48) µg/L for SHFS and MESA, respectively, and urine U was 0.037 (0.014, 0.071) and 0.007 (0.003, 0.018) µg/L. In a meta-analysis across both studies, urine As was 11% (95% CI: 3, 20%) higher and urine U was 35% (5, 73%) higher per twofold higher CWS As and U, respectively. In the SHFS, zip-code level factors such as private well and CWS As contributed 46% of variation in urine As, while in MESA, zip-code level factors, e.g., CWS As and U, contribute 30 and 49% of variation in urine As and U, respectively. We found that water from unregulated private wells and regulated CWSs is a major contributor to urinary As and U (an estimated measure of internal dose) in both rural, American Indian populations and urban, racially/ethnically diverse populations nationwide, even at levels below the current regulatory standard. Our findings indicate that additional drinking water interventions, regulations, and policies can have a major impact on reducing total exposures to As and U, which are linked to adverse health effects even at low levels.

Tungsten is an emerging environmental pollutant. However, a proved robust method for preserving and determining the concentrations of tungsten in environmental media is still lacking. This study examined and compared the suitability of classic methods and previously reported tungsten-oriented methods on preserving dissolved tungsten and recovering tungsten from soil/sediment matrix. Tungsten concentrations in the water samples and digestates were then determined by inductively coupled plasma mass spectrometry. Our data showed that the tungsten-oriented HF and alkaline preservatives indeed successfully maintained the stability of dissolved tungsten. Even when preserved using HNO3 or HCl, dissolved tungsten concentrations did not notably change in most of our water samples over the course of ∼4 months. Using glass containers for storing water samples also did not produce much difference from using high-density polyethylene containers. Our data further suggested that the addition of HF in digestion was important for tungsten solubilization from soil/sediment matrix. The digestion methods with HNO3/HCl/HF and HNO3/HF/NH4OH/EDTA both yielded quantitative recoveries of tungsten from certified reference materials and known synthetic samples, while the other tested methods had limited recoveries. The methods validated by this study could be used to accurately determine tungsten concentrations in environmental media and thereby to assess the fate and potential risks of tungsten.

Millions of people worldwide are exposed to arsenic (As) contaminated groundwater. Despite decades of research and evidence of As mobilisation in anoxic aquifers being caused by reductive dissolution of iron minerals, the mechanisms behind the local scale variability of dissolved As remains unclear. Therefore, the trans-disciplinary AdvectAs project investigates the environmental behaviour and spatial heterogeneity of dissolved As in groundwater in the Red River delta, Vietnam. Here we present the results from hydrochemical and water isotope investigations. In particular, we will show how the large As variability (0.1–510 µg/L) is related to consecutive As (im)mobilisation steps, depending on site hydrology, geology and the interplay of Fe, Mn, S and organic matter cycles. Such complexity of (im)mobilisation processes can be simplified in 5 major hydro(geo)chemical zones, providing a conceptual tool with potential for application at other sites in Asia affected by geogenic As contamination of groundwater.

AbstractThis chapter assesses human health risks of inorganic arsenic (As) from drinking well water and consumption of rice irrigated by high-As groundwater in the Mekong River Delta. Geogenic inorganic As (iAs) occurring at elevated levels in groundwater has been detected in more than 70 countries. Among mostly rural residents relying on groundwater for drinking, this exposure has resulted in negative health consequences including visible skin lesions, multiple internal organ cancers, numerous invisible non-cancer health effects such as cardiovascular diseases, and premature deaths. In the Mekong River Delta (MRD, defined by elevation <10 m above sea level in this book), As issues in groundwater have been documented as early as 1999 in Cambodia, with literature reporting its occurrence in Vietnam since 2005. Since the early 2000s, efforts have been made to test for As in about 100,000 wells from Cambodia, Laos, Vietnam and Thailand. Here, a combined dataset with a total of 94,768 unique As tests was analyzed to illustrate the spatial patterns and to assess the health risks of drinking well water As in Cambodia and in southern Vietnam. Although knowledge is far more limited, an attempt was also made to examine the potential health risks associated with iAs exposure from rice, a major staple for the MRD. Here, irrigation using highly As enriched groundwater for rice cultivation has expanded this environmental health problem from the hydrosphere (water) to the geosphere (soil) and, in turn, the biosphere (rice, and ultimately humans). Of 41,928 tests in Cambodia, 35.8% exceeded 10 μg/L, the WHO guideline value for drinking water As, while 21.5% exceeded 50 μg/L, the Cambodian drinking water standard. Of 52,858 tests in Vietnam, the exceedance rate for 10 μg/L, which is also the Vietnamese drinking water standard, is 10.0%. High As wells, regardless of whether it is relative to 10 or 50 μg/L, are located in proximity to the main course of the Mekong-Bassac Rivers, especially within a 5 km distance. The vast majority (>98%) of high-As wells are located in low-lying areas, i.e. <25 m elevation in Cambodia and <10 m elevation in Vietnam. High-As wells occur frequently at shallow depths (<70 m) across the MRD but also at deeper depths (300–500 m) in Vietnam. Due to the clustering of high As wells along the Mekong-Bassac Rivers, extreme human health tolls are identified in 11 districts of Cambodia and 3 districts of Vietnam with a population attributable fraction exceeding 0.1, meaning that >1 in every 10 adult deaths is solely due to drinking water As exposure. The annual excess deaths attributable to arsenic exposure alone is 1204 in Cambodia and 1486 in Vietnam, or 1 in every 27 adult deaths and 1 in every 78 adult deaths, respectively. In addition to uncertainties in bioavailability and toxicity of iAs in rice grains, soil and rice As data, especially rice As speciation data needed for risk assessment, are still limited in the MRD.

We have measured the absolute doubly differential angular sputtering yield for 20 keV Kr+ impacting a polycrystalline Cu slab at an incidence angle of θi = 45° relative to the surface normal. Sputtered Cu atoms were captured using collectors mounted on a half dome above the sample, and the sputtering distribution was measured as a function of the sputtering polar, θs, and azimuthal, ϕs, angles. Absolute results of the sputtering yield were determined from the mass gain of each collector, the ion dose, and the solid angle subtended, after irradiation to a total fluence of ∼1 × 1018 ions/cm2. Our approach overcomes shortcomings of commonly used methods that only provide relative yields as a function of θs in the incidence plane (defined by the ion velocity and the surface normal). Our experimental results display an azimuthal variation that increases with increasing θs and is clearly discrepant with simulations using binary collision theory. We attribute the observed azimuthal anisotropy to ion-induced formation of micro- and nano-scale surface features that suppress the sputtering yield through shadowing and redeposition effects, neither of which are accounted for in the simulations. Our experimental results demonstrate the importance of doubly differential angular sputtering studies to probe ion sputtering processes at a fundamental level and to explore the effect of ion-beam-generated surface roughness.

Geogenic arsenic (As) in groundwater is widespread, affecting drinking water and irrigation supplies globally, with food security and safety concerns on the rise. Here, we present push-pull tests that demonstrate field-scale As immobilization through the injection of small amounts of ferrous iron (Fe) and nitrate, two readily available agricultural fertilizers. Such injections into an aquifer with As-rich (200 +/- 52 mu g/L) reducing groundwater led to the formation of a regenerable As reactive filter in situ, producing 15 m(3) of groundwater meeting the irrigation water quality standard of 50 mu g/L. Concurrently, sediment magnetic properties were markedly enhanced around the well screen, pointing to neo-formed magnetite-like minerals. A reactive transport modeling approach was used to quantitatively evaluate the experimental observations and assess potential strategies for larger-scale implementation. The modeling results demonstrate that As removal was primarily achieved by adsorption onto neo-formed minerals and that an increased adsorption site density coincides with the finer-grained textures of the target aquifer. Up-scaled model simulations with 80-fold more Fe-nitrate reactants suggest that enough As-safe water can be produced to irrigate 1000 m(2) of arid land for one season of water-intense rice cultivation at a low cost without causing undue contamination in surface soils that threatens agricultural sustainability.