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Natural perchlorate (ClO4−) exists in many places on Earth, in lunar regolith, meteorites, and on the surface of Mars. Terrestrial natural ClO4− has widely variable Cl and O stable isotopic compositions (δ37Cl, δ18O, Δ17O). The δ18O and Δ17O values of ClO4− from the most hyper-arid locations co-vary. ClO4− from less arid areas has relatively little 17O excess and poor Δ17O-δ18O correlation. ClO4− from the Atacama Desert has unusually low δ37Cl (

Deicing salt is an important component of road safety during winter storms. Stormwater infiltration best management practices aim to prevent the salt from polluting streams and waterways, but this may shift pollutants to groundwater resources. In response to limited field studies investigating groundwater quality impacts caused by input of salt from stormwater infiltration best management practices, we monitored water levels and quality of groundwater at various depths in an unconfined aquifer around a stormwater infiltration basin using in situ sensors coupled with grab sampling. Our observations revealed differences in groundwater chemistry with depth in the aquifer and processes that were driven by the seasonal changes in the chemistry of stormwater (salt-impacted in winter and fresh in non-winter) recharging the aquifer. Water-matrix interactions in the vadose zone beneath the basin affected the transport of sodium (Na) into groundwater following non-winter recharge. Sodium movement through the aquifer was delayed relative to chloride (Cl), indicating a longer residence time of Na in the vadose zone. Radium (Ra) concentrations were correlated with Cl concentrations, suggesting salt-impacted recharge caused desorption of Ra into groundwater because of increased salinity. Stormwater-influenced groundwater followed a preferential flow path due to heterogeneity of the aquifer materials, and water chemistry varied with time and location along the flow path. These results highlight the importance of well screen length, placement and depth, and frequency of observations when designing a monitoring network.

The net change in the carbon inventory of arctic tundra remains uncertain as global warming leads to shifts in arctic water and carbon cycles. To better understand the response of arctic tundra carbon to changes in winter precipitation amount, we investigated soil depth profiles of carbon concentration and radionuclide activities (7Be, 137Cs, 210Pb, and 241Am) in the active layer of a twenty-two-year winter snow depth manipulation experiment in moist acidic tussock tundra at Toolik Lake, Alaska. Depth correlations of cumulative carbon dry mass (g cm−2) vs. unsupported 210Pb activity (mBq g−1) were examined using a modified constant rate of supply (CRS) model. Results were best fit by two-slope CRS models indicating an apparent step temporal increase in the accumulation rate of soil organic carbon. Most of the best-fit model chronologies indicated that the increase in carbon accumulation rate apparently began and persisted after snow fence construction in 1994. The inhomogeneous nature of permafrost soils and their relatively low net carbon accumulation rates make it challenging to establish robust chronologic records. Nonetheless, the data obtained in this study support a decadal-scale increase in net soil organic carbon accumulation rate in the active layer of arctic moist acidic tussock tundra under conditions of increased winter precipitation.

An integrated approach was developed to assess the sustainability, origin, age, evolution, and groundwater potential of large fossil aquifers using the Mega Aquifer System (MAS) (area: 2 × 106 km2) in the Arabian Peninsula as a test site. A two-step exercise was adopted, the sustainability of the MAS was first investigated through the analysis of GRACE data and land surface model (LSM) outputs. Then, integrated geochemical, remote sensing, and field studies were conducted to address the age, origin, hydrogeological setting, and evolution of the southern sections of the MAS (Rub Al Khali Aquifer System (RAKAS)), the area identified from the analysis of GRACE and LSMs as being the most suited for sustainable development. Analysis of GRACE and LSMs revealed: (1) the MAS central and northern sections are experiencing high groundwater extraction (6.6 km3/yr) and depletion rates (−2.8 ± 0.8 km3/yr) with minimum balancing potential through aquifer capture processes, yet sustainability could be achieved by reducing annual extraction by 2.8 km3, and (2) the MAS southern sections (Rub Al Khali Aquifer System (RAKAS)) are experiencing low groundwater depletion rates (eastern RAKAS: −1.8 ± 1.4 mm/yr) to steady-state conditions (western RAKAS: −0.73 ± 1.4 mm/yr). Geochemical, remote sensing, and field investigations over the RAKAS revealed: (1) the presence of west to east trending drainage networks and large-scale groundwater flow systems consistent with a meteoric source (precipitation over Red Sea Hills); (2) increasing 36Cl model ages along groundwater flow directions (up to 970,000 years), indicating aquifer recharge in wet Pleistocene periods; (3) progressive depletion in the O and H stable isotopic compositions of aquifers with increasing distance from the Red Sea Hills basement outcrops, indicating modest recharge during prevailing dry conditions; and (4) the presence of relatively fresh (TDS: 800–2800 mg/L) and non-radioactive (226Ra + 228Ra

The morphological evolution of micron-sized calcite crystals dissolved in static acidic solutions, with and without dissolved Pb2+ ions, was imaged using transmission X-ray microscopy (TXM). The ar...

Chlorine-36 abundances and stable chlorine isotope ratios ( 37 Cl/ 35 Cl) were analyzed to decipher sources of chloride and to estimate subsurface residence times of groundwaters from the Nubian Sandstone Aquifer System (NSAS), alluvial aquifers, and fractured basement aquifers in the Eastern Desert of Egypt. Chlorine-36 isotopic abundances ( 36 Cl/Cl) ranged from 5 × 10 −15 to 343 × 10 −15 . The range in δ 37 Cl values was −0.61 to +0.90‰. Groundwater solute compositions were dominated by Na, Ca, Cl, and SO 4 with total dissolved solids ranging from 445 to 13,700 mg/L. Chemical and isotopic data indicate that dry fallout of marine aerosols and evaporated vadose-zone residues from precipitation that recharged the aquifers may have been the main sources of groundwater solutes. Apparent groundwater 36 Cl model ages range from 0 (+/−40) to 1300 (+300/−180) kyr. Groundwater from the fractured basement aquifers in the southwestern part of the study area had the youngest apparent ages, while that from deep wells tapping the Nubian aquifer had the oldest apparent ages. Shallow alluvial aquifers having anomalously old apparent 36 Cl model ages indicate mixing of old Nubian aquifer water with modern recharge in alluvial aquifers. Stable isotope ratios of hydrogen and oxygen support this inferred mixing relationship and allowed quantitative estimation of old/young water mixing fractions.

The heterogeneous nucleation and growth of aluminum (oxy)hydroxide films in aqueous environments can be controlled by the speciation of dissolved Al species and the charge and structure of underlying mineral surfaces. The structure of gibbsite films nucleated at the interface between the muscovite (001) surface and 1 mM AlCl3 solutions was investigated as a function of pH using in situ X-ray reflectivity. The growth of well-ordered gibbsite films was observed at pH between 3 and 4, even when the solutions were undersaturated with respect to gibbsite. The ordering of these gibbsite films likely resulted from the structural similarity (i.e., epitaxy) between the basal planes of gibbsite and muscovite. The gibbsite films formed on the muscovite surface dissolved more than two orders of magnitude faster than bulk gibbsite in pH 4 HCl solution, indicating that they can be described as a metastable phase. In contrast, no film growth was observed at pH between 9 and 12 where the solutions were supersaturated wit...

Oxidation of magnetite (Fe3O4) has broad implications in geochemistry, environmental science and materials science. Spatially resolving strain fields and defect evolution during oxidation of magnetite provides further insight into its reaction mechanisms. Here we show that the morphology and internal strain distributions within individual nano-sized (~400 nm) magnetite crystals can be visualized using Bragg coherent diffractive imaging (BCDI). Oxidative dissolution in acidic solutions leads to increases in the magnitude and heterogeneity of internal strains. This heterogeneous strain likely results from lattice distortion caused by Fe(II) diffusion that leads to the observed domains of increasing compressive and tensile strains. In contrast, strain evolution is less pronounced during magnetite oxidation at elevated temperature in air. These results demonstrate that oxidative dissolution of magnetite can induce a rich array of strain and defect structures, which could be an important factor that contributes to the high reactivity observed on magnetite particles in aqueous environment., Oxidation of magnetite has broad implications in geochemistry and environmental science, but its reaction mechanisms are not fully understood yet. Here the authors use Bragg coherent diffractive imaging to show oxidative dissolution of magnetite inducing a rich array of strain and defect structures.

To improve understanding of spatial, seasonal, and inter-annual variations in nitrate sources and in-stream processes in the Illinois River system, nitrate concentrations and isotopic compositions were measured in 445 water samples collected over a four-year period (2004–2008) from the Upper Illinois River Basin (UIRB). Samples included surface water in the river and major tributaries, effluent samples from Chicago’s largest wastewater treatment plant (WTP), and representative groundwater from shallow wells in agricultural land. Two principal nitrate endmember sources within the UIRB had distinctive isotopic compositions: WTP effluent with δ15N = 8.6 ± 1.7‰ and δ18O = 0.8 ± 1.4‰ and agricultural groundwater with δ15N-NO3 = 3.4 ± 0.6‰ and δ18O = 3.7 ± 0.5‰ (when minimally affected by nitrate reduction). Isotopic data indicated that the large pulse of nitrate exported from the river basin during the spring was mostly derived from agricultural land drainage, while nitrate from large WTP effluent point sources was predominant in the upper reaches of the river near Chicago. During low base-flow conditions in late-summer and fall, the agricultural nitrate source was greatly diminished and the headwater WTP source was predominant in the river basin export. Our results indicated biogeochemical nitrate reduction and isotopic fractionation occurred within the river network, affecting both agricultural and urban sources during surface-water transport. In addition, diminished agricultural nitrate export was attributable to preferential discharge of biogeochemically reduced groundwater during low base flow. Isotopic indicators of spatial and seasonal variations in the relative importance of different nitrate sources, and their relative susceptibility to natural attenuation, might be useful for guiding monitoring and management practices to reduce nitrate export from complex watersheds with mixed land uses.

Thin films grown on mineral surfaces can immobilize toxic metals in natural systems, but the effects of epitaxy and film thickness on dissolution rates of the overgrowth are typically unknown. To explore these effects, otavite (CdCO3) films were grown on dolomite (104) surfaces from aqueous solutions containing [Cd] = [Ca] = [CO3] = 0.2 mM for 1–48 h and then dissolved in deionized water. Films of various thicknesses and strain states were obtained by varying the growth reaction time. Growth for up to 3 h produced strained thin films with Cd coverages of

Compound-specific isotope analysis (CSIA), position-specific isotope analysis (PSIA), and computational modeling (e.g., quantum mechanical models; reactive-transport models) are increasingly being used to monitor and predict biotic and abiotic transformations of organic contaminants in the field. However, identifying the isotope effect(s) associated with a specific transformation remains challenging in many cases. Here, we describe and interpret the position-specific isotope effects of C and N associated with a S

Here we report on a set of six apatite reference materials (chlorapatites MGMH#133648, TUBAF#38 and fluorapatites MGMH#128441A, TUBAF#37, 40, 50) which we have characterised for their chlorine isotope ratios; these RMs span a range of Cl mass fractions within the apatite Ca10(PO4)6(F,Cl,OH)2 solid solution series. Numerous apatite specimens, obtained from mineralogical collections, were initially screened for 37Cl/35Cl homogeneity using SIMS followed by δ37Cl characterisation by gas source mass spectrometry using both dual‐inlet and continuous‐flow modes. We also report major and key trace element compositions as determined by EPMA. The repeatability of our SIMS results was better than ± 0.10% (1s) for the five samples with > 0.5% m/m Cl and ± 0.19% (1s) for the low Cl abundance material (0.27% m/m). We also observed a small, but significant crystal orientation effect of 0.38% between the mean 37Cl/35Cl ratios measured on three oriented apatite fragments. Furthermore, the results of GS‐IRMS analyses show small but systematic offset of δ37ClSMOC values between the three laboratories. Nonetheless, all studied samples have comparable chlorine isotope compositions, with mean 103δ37ClSMOC values between +0.09 and +0.42 and in all cases with 1s ≤ ± 0.25., Key Points: Six apatite reference materials having various Cl mass fractions were characterised for chlorine isotope ratios by SIMS and three GS‐IRMS laboratories. A small, but significant, crystal orientation effect was recorded by SIMS analyses. Correlation of instrumental mass fractionation factor with Cl mass fraction is visible along the apatite solid solution series., Narodowe Centrum Nauki, Deutscher Akademischer Austauschdienst, Helmholtz Recruiting Initiative, Institute of Geological Sciences, Polish Academy of Sciences

Natural chlorate (ClO

This study integrates observations from field and remote sensing data, along with geochemical and isotopic analyses, to assess the environmental impacts of cyanidation and mining activities in the Sukari gold mine (SGM), Eastern Desert, Egypt, in particular, and the orogenic gold deposits of the Arabian-Nubian Shield (ANS) in general. Our findings indicate: (1) groundwater flows south to north in the highly fractured basement aquifer related to the brittle deformation associated with the Najd Fault System; (2) massive gabbroic bodies separate the fractured basement aquifer into east and west conduits; (3) the tailings storage facility (TSF) pond and leach pad were constructed over the west conduit; and (4) cyanide-rich wastewater has leaked downward through tears and cuts in the lining of the TSF pond into the fractured aquifer and cyanide contaminants have migrated northward along the west conduit. Evidence for the latter includes: (1) toxic concentrations of cyanide (total: 0.018–9.4 mg/L; free weak-acid dissociable: 0.003–0.7 mg/L) were observed in groundwater samples north of the TSF pond; (2) similarities in electrical conductivity (EC) values and chloride/bromide (Cl−/Br−) ratios between groundwater north of the pond (EC: 88.8 mS/cm; Cl−/Br−: 346 to 363) and those of the TSF pond water (mean EC: 99 mS/cm; Cl−/Br−: 242 to 383) were observed; (3) the geochemical (e.g., sodium [Na+], Cl−) and isotopic compositions (δ18O and δ2H values) of groundwater are consistent with mixing of groundwater upgradient from the SGM with isotopically enriched pond water; and (4) cyanide contamination could not have resulted from an overflow of the TSF pond during flash flood events, given that rainfall is negligible and effective flood control systems are in place. Our findings show that the international codes/regulations do not fully address site-specific characteristics and highlight the importance of considering these parameters in mining of orogenic gold deposits in the ANS.

Made available in DSpace on 2020-12-12T01:17:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-06-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação para o Desenvolvimento da UNESP (FUNDUNESP) International Atomic Energy Agency National Center for Atmospheric Research Universidade Estadual Paulista World Meteorological Organization The stable isotope ratios of oxygen and hydrogen in shallow groundwater reflect the long-term amount-weighted mean isotopic composition of precipitation. Here, we report the isotopic composition of more than 1000 shallow groundwater samples (age < ∼5,000 yr) across continental Brazil. Recent studies of global precipitation have shown a strong negative correlation between the isotopic compositions (e.g., δ18O values) and stratiform fractions of Brazilian precipitation, with geospatial correspondence to the South Atlantic convergence zone pattern. This isotope-precipitation type geospatial correlation is also reflected in the isotopic compositions of shallow groundwaters, and speleothem records from the region show small variations in δ18O values, implying general climatic stability in this region during the past few millennia. We propose that shallow groundwater isotopic compositions reflect bulk proportions of convective and stratiform fractions in precipitation and could thus be useful in conjunction with groundwater dating as proxy archives to characterize past changes in the proportions of convective and stratiform precipitation in tropical and subtropical latitudes. This groundwater isotope-precipitation type relationship could also have broader implications when considered for paleoclimatic interpretation of oxygen isotope records in dated speleothems from other locations. São Paulo State University UNESP Dept. of Applied Geology and Basin Studies Laboratory (LEBAC) São Paulo State University UNESP Environmental Studies Center (CEA) and Basin Studies Laboratory (LEBAC) Isotope Hydrology Section International Atomic Energy Agency University of Delaware Dept. of Earth Sciences Earth Observing Laboratory National Center for Atmospheric Research São Paulo State University UNESP Dept. of Applied Geology and Basin Studies Laboratory (LEBAC) São Paulo State University UNESP Environmental Studies Center (CEA) and Basin Studies Laboratory (LEBAC)

Ion adsorption at solid-water interfaces is commonly described by interactions between specific surface sites and adsorbed ions in classical models. However, energetic contributions from non-site-specific ion-ion interactions have been less well understood. Here, we report nonclassical behaviors observed during competitive adsorption between Sr

Identifying shallow (near-surface) groundwater in arid and hyper-arid areas has significant societal benefits, yet it is a costly operation when traditional methods (geophysics and drilling) are applied over large domains. In this study, we developed and successfully applied methodologies that rely heavily on readily available temporal, visible, and near-infrared radar and thermal remote sensing data sets and field data, as well as statistical approaches to map the distribution of shallow (1–5 m deep) groundwater occurrences in Al Qunfudah Province, Saudi Arabia, and to identify the factors controlling their development. A four-fold approach was adopted: (1) constructing a digital database to host relevant geologic, hydrogeologic, topographic, land use, climatic, and remote sensing data sets, (2) identifying the distribution of areas characterized by shallow groundwater levels, (3) developing conceptual and statistical models to map the distribution of shallow groundwater occurrences, and (4) constructing an artificial neural network (ANN) and multivariate regression (MR) models to map the distribution of shallow groundwater, test the models over areas of known depth to groundwater (area of Al Qunfudah city and surroundings: 294 km2), and apply the better of the two models to map the shallow groundwater occurrences across the entire Al Qunfudah Province (area: 4680 km2). Findings include: (1) high performance for the ANN (92%) and MR (88%) models in predicting the distribution of shallow groundwater using temporal-derived remote sensing products (e.g., normalized difference vegetation index (NDVI), radar backscatter coefficient, precipitation, and brightness temperature) and field data (depth to water table), (2) areas witnessing shallow groundwater levels show high NDVI (mean and standard deviation (STD)), radar backscatter coefficient values (mean and STD), and low brightness temperature (mean and STD) compared to their surroundings, (3) correlations of temporal groundwater levels and satellite-based precipitation suggest that the observed (2017–2019) rise in groundwater levels is related to an increase in precipitation in these years compared to the previous three years (2014–2016), and (4) the adopted methodologies are reliable, cost-effective, and could potentially be applied to identify shallow groundwater along the Red Sea Hills and in similar settings worldwide.

The environmental fate of insensitive munitions compounds, such as 2,4-dinitroanisole (DNAN), has drawn increasing attention because of their growing use in military activities. One of the main attenuation mechanisms of DNAN degradation in aqueous environments is alkaline hydrolysis. We investigated the pathway for alkaline hydrolysis of DNAN at pH 12 by a combined approach of experiment and theory. An experiment using

Perchlorate (ClO4−) in groundwater can be from synthetic or natural sources. Natural sources include ClO4− associated with historical application of imported natural nitrate fertilizer from the Atacama Desert of Chile, and indigenous ClO4− that accumulates locally in arid regions from atmospheric deposition. The Rialto-Colton groundwater subbasin, 80 km east of Los Angeles, California, includes two mapped ClO4− plumes from known military/industrial sources. Larger areas downgradient from those plumes, and in the Chino subbasin to the southwest, also contain ClO4−. Perchlorate from wells was analyzed for chlorine and oxygen stable isotope ratios (δ37Cl, δ18O, Δ17O) and radioactive chlorine-36 (36Cl) isotopic abundance, along with other geochemical, isotopic, and hydrogeologic data. Isotopic data show that synthetic ClO4− was the dominant source within the mapped plumes. Downgradient from the mapped plumes, and in the Chino subbasin, the dominant source of ClO4− was related to past agricultural use of Chilean (Atacama) nitrate fertilizer. The 36Cl and δ18O data indicate that wells having predominantly synthetic or Atacama ClO4− also contained small fractions of indigenous ClO4−. Little or no differences were observed in isotopic composition or ClO4− source with depth in depth-dependent data from selected wells. Indigenous ClO4− was most evident in upgradient wells having ClO4− concentrations

Sediment cores from 41 sites were collected from the Laurentian Great Lakes during 2010–2014, sectioned into 0.5–2.0 cm intervals, and the activities of 210Pb, 137Cs, and 226Ra were measured in the upper 25 to 40 cm of the sediment column by gamma spectrometry. Sediment mass accumulation rates (dry mass) calculated from 210Pb profiles range from 0.006 ± 0.001 to 0.59 ± 0.06 g cm−2 yr −1 and are similar to those reported in previous Great Lakes sediment studies. Sediment mass accumulation rates decreased with increasing water depth. 210Pb-based models in cores exhibiting favorable characteristics (i.e., those having the highest unsupported-210Pb activity at the sediment-water interface, exponential decrease of unsupported-210Pb with increasing depth in sediment cores, and a clear peak in 137Cs activity at some depth below the sediment-water interface) give calendar date profiles that are largely concordant with the maximum 137Cs peak activity at 1963. Sediment focusing factors derived from unsupported-210Pb inventories range from 0.09 to >5.34, and are well correlated with those derived from 137Cs inventories that range from 0.07 to 4.04, demonstrating the ubiquitous occurrence of horizontal sediment transport processes within the lakes. This more recent survey provides a Great Lakes-wide chronological framework for comparing the depositional histories and inventories of a wide variety of persistent, bioaccumulative and toxic pollutants that have been measured in the same sediment cores. This information will be useful for resolving scientific and practical issues pertaining to the environmental quality and management of contaminated sediments in the Laurentian Great Lakes ecosystem.

Inorganic carbon (IC), total organic carbon (OC), and black carbon (BC) were analyzed in eight sediment cores obtained from deep water (>30 m) sediments in the Chippewa and south Chippewa basins, as well as Green Bay in Lake Michigan. These cores were segmented at high resolution and radio-dated to reconstruct a detailed history of deposition to the lake both spatially and temporally since ca. 1850 CE. To help interpret the depositional record, cores were also characterized for stable isotopes (13C and 15N), as well as particle size distribution, density, organic matter (OM), and other parameters. Fine (silt and clay) sediment particles contained OM of primarily lacustrine algal biomass origin. Sedimentation fluxes showed large increases in OM and OC fluxes through much of the lake during the onset of industrialization and the period of rapid industrialization to onset of Great Lakes environmental legislation. In contrast, fluxes and loading of BC increased dramatically in the southern basin until the 1930's, then decreased substantially after the 1940's. This observation was due largely to results from site M009 nearest the steel mills and industrial zones of Chicago and northern Indiana. Together, whole lake loadings of OM and BC provide evidence that changing industrial activity and legislation intended to curb air pollution in the Great Lakes region have had a fairly rapid and dramatic impact. In contrast, legislation intended to decrease eutrophication through reductions in nutrient loading to the lake have not had a similar impact on sedimentation of OM in the lake.

Legacy, organic pollutants, including polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), naphthalenes (PCNs), and diphenyl ethers (PCDEs) were quantified in sediments of the Laurentian Great Lakes of North American. A total of 40 cores (939 core segments) and 198 Ponar surface grab samples were collected from the five Great Lakes between 2010 and 2014. Median concentrations in Ponar grab samples were 8.4, 0.27, 0.05, 0.19 and 0.01 ng/g dry weight (dw) for total-PCBs, ∑7PCDDs, ∑10PCDFs, ∑12PCNs, and ∑7PCDEs, respectively. By using Geographic Information Systems Analysis with the inverse distance weight (IDW) interpretation of the spatial distribution of the chemical inventory at coring sites, total mass loads in the five lakes combined were estimated to be 511, 15.3, 5.3, 20.7 and 2.9 t for total-PCBs, ∑7PCDDs, ∑10PCDFs, ∑12PCNs, and ∑7PCDEs, respectively. Patterns of spatial distributions revealed pollution hotspots and provided evidence for historical local sources. Concentrations of residues in Ponar grabs and inventories at coring sites, when normalized to concentrations of organic carbon, exhibited statistically significantly correlations with latitude and longitude of the sampling sites for all five chemical groups. At most coring sites, concentrations have been decreasing towards the sediment surface. At locations relatively close to known or suspected sources, estimated half-times for all classes of chemicals were approximately 20 years. The declining trends of PCDDs and PCDFs were unclear at some locations, suggesting the presence of currently active emission sources.

Radionuclides have been recognized as a limiting factor of groundwater quality in the Middle East and Northeastern Africa. High levels of naturally occurring radioactivity, mostly from radium and radon isotopes, have been reported in waters from the Nubian Sandstone Aquifer System (NSAS) in several countries in the Middle East including the Sinai Peninsula of Egypt. This study aims at extending the existing data coverage by investigating radionuclide concentrations and their potential geological and hydrogeochemical controls in groundwater of the NSAS and the overlying alluvial aquifers in the Eastern Desert of Egypt. Radium isotope activities (226Ra and 228Ra) and uranium concentrations were analyzed in 39 groundwater samples from these aquifers. The shallow Nubian aquifer has 226Ra and 228Ra activities ranging from 0.016 to 0.750 and 0.018–1.421 Bq/L, respectively. The deep Nubian aquifer has 226Ra and 228Ra activities ranging from 0.019 to 0.051 and 0.014–0.248 Bq/L, respectively. The shallow alluvial aquifers have 226Ra and 228Ra activities ranging from 0.008 to 0.086 and 0.006–0.081 Bq/L, respectively. Groundwater in the Nubian aquifer may have Ra activities substantially in excess of the drinking water MCL values of the US Environmental Protection Agency (EPA), the European Union (EU), and the World Health Organization (WHO). The concentration of U varies from 0.06 to 33.06 μg/L, 0.06–15.46 μg/L, and 0.01–13.19 μg/L for the shallow Nubian aquifer, the deep Nubian aquifer, and the shallow alluvial aquifers, respectively. U concentrations exceed the EPA and WHO MCL values in some wells, mostly from the shallow Nubian aquifer.

Current and historical concentrations of 22 poly- and perfluorinated compounds (PFASs) in sediment collected from Lake Superior and northern Lake Michigan in 2011 and Lake Huron in 2012 are reported. The sampling was performed in two ways, Ponar grabs of surface sediments for current spatial distribution across the lake and dated cores for multi-decadal temporal trends. Mean concentrations of the sum of PFASs (∑PFASs) were 1.5, 4.6 and 3.1 ng g−1 dry mas (dm) in surface sediments for Lakes Superior, Michigan and Huron, respectively. Of the five Laurentian Lakes, the watersheds of Superior and Huron are the less densely populated by humans, and concentrations observed were typically less and from more diffuse sources, due to lesser urbanization and industrialization. However, some regions of greater concentrations were observed and might indicate more local, point sources. In core samples concentrations ranged from 7 that include perfluoro-n-octane sulfonate (PFOS) bind more strongly to sediment, which resulted in more accurate analyses of temporal trends. Shorter-chain PFASs, such as perfluoro-n-butanoic acid which is the primary replacement for C8 PFASs that have been phased out, are more soluble and were identified in some core layers at depths corresponding to pre-production periods. Thus, analyses of temporal trends of these more soluble compounds in cores of sediments were less accurate. Total elemental fluorine (TF) and extractable organic fluorine (EOF) indicated that identified PFASs were not a significant fraction of fluorine containing compounds in sediment (

The evolution and accommodation of lattice strain in an epitaxial mineral film grown on an isostructural substrate were observed as a function of film thickness. Cadmium carbonate films (approximately CdCO3 (otavite) in composition) were grown on the (104) surface of CaMg(CO3)2 (dolomite) from aqueous solutions that were supersaturated with respect to both pure otavite and Cd-rich (Cd1–xCax)CO3. Specular and nonspecular X-ray reflectivity (XR) revealed that the structure and strain of the otavite overgrowths evolved in a manner that is fully consistent with a Stranski-Krastanov growth mode. Otavite films initially grew as coherently strained films, up to an average thickness of ∼15 A, with lateral compressive strains and an expansion of the vertical film lattice spacing resulting in a unit cell volume consistent with pure otavite. Thicker films (>15 A) became incommensurate with the substrate, having lattice parameters that are indistinguishable from pure otavite. These results indicate that the evolution...

Radium isotopes ( 226 Ra and 228 Ra) were analyzed in 18 groundwater samples from the Nubian Sandstone Aquifer System (NSAS) and the shallow alluvial aquifers overlying the basement complex of the Sinai Peninsula, Egypt. Groundwater samples from deep Nubian aquifer wells (total depths 747 to 1250 m) have 226 Ra and 228 Ra activities ranging from 0.168 to 0.802 and 0.056 to 1.032 Bq/L, respectively. The shallower Nubian aquifer wells (63 to 366 m) have 226 Ra and 228 Ra activities ranging from 0.033 to 0.191 and 0.029 to 0.312 Bq/L, respectively. The basement shallow alluvial aquifers have 226 Ra and 228 Ra activities ranging from 0.014 to 0.038 and 0.007 to 0.051 Bq/L, respectively. Combined Ra activities in most wells were generally in excess of the US Environmental Protection Agency (EPA), the European Union (EU), and the World Health Organization (WHO) maximum contaminant levels (MCL) for drinking water. Radium in groundwater is produced mainly by decay of parent nuclides in the aquifer solids, and observed activities of dissolved Ra isotopes result from a combination of alpha-recoil, adsorption/desorption, co-precipitation/dissolution processes. The observed correlation between Ra activities and salinity indicates that adsorption/desorption processes may be the dominant factor controlling Ra mobility in Sinai groundwater. Radium activities in central and northern Sinai are generally higher than those in southern Sinai, consistent with a gradual increase in salinity and water-rock interaction with increasing groundwater age. Barite is approximately saturated in the groundwater and may limit maximum dissolved Ra concentration. The results of this study indicate that Sinai groundwater should be used with caution, possibly requiring Ra removal from water produced for domestic and agricultural consumption.

The growth of lepidocrocite (γ-FeOOH) has been observed through oxidation of Fe(II) on calcite (CaCO3). Here, we seek to understand the structural relation between lepidocrocite and the calcite substrate and its growth mechanism. The formation of iron oxyhydroxide layers having distinct morphologies was observed during the dissolution of calcite in acidic Fe(II)-rich solutions. A pseudomorphic lepidocrocite shell together with multiple iron oxyhydroxide layers encapsulated within the shell was imaged by optical and transmission X-ray microscopies. The presence of a several-nanometer-thick ordered lepidocrocite film was observed by X-ray reflectivity, with the lepidocrocite (100) plane oriented parallel to the calcite (104) surface. Lath-shaped lepidocrocite aggregates formed during the initial precipitation, which eventually grew into clusters of parallel platy crystals. The formation of a nanometer-thick well-ordered lepidocrocite film on a pristine calcite surface appears critical for the subsequent pse...