Applied Geochemistry (v.28, #C)

Editorial by Michael Kersten (1).

Arsenic in agricultural and grazing land soils of Europe by Timo Tarvainen; Stefano Albanese; Manfred Birke; Michal Poňavič; Clemens Reimann (2-10).
► Soil arsenic concentrations of European agricultural and grazing land are reported. ► The median As concentration was 5.7 mg/kg in agricultural soils (AR) and 5.8 mg/kg in grazing land (AR). ► Soil As concentrations are higher in southern than in northern Europe. ► Most of the As anomalies on geochemical maps can be directly linked to geology.Arsenic concentrations are reported for the <2 mm fraction of ca. 2200 soil samples each from agricultural (Ap horizon, 0–20 cm) and grazing land (Gr, 0–10 cm), covering western Europe at a sample density of 1 site/2500 km2. Median As concentrations in an aqua regia extraction determined by inductively coupled plasma emission mass spectrometer (ICP-MS) were 5.7 mg/kg for the Ap samples and 5.8 mg/kg for the Gr samples. The median for the total As concentration as determined by X-ray fluorescence spectrometry (XRF) was 7 mg/kg in both soil materials. Maps of the As distribution for both land-use types (Ap and Gr) show a very similar geographical distribution. The dominant feature in both maps is the southern margin of the former glacial cover seen in the form of a sharp boundary between northern and southern European As concentrations. In fact, the median As concentration in the agricultural soils of southern Europe was found to be more than 3-fold higher than in those of northern Europe (Ap: aqua regia: 2.5 vs. 8.0 mg/kg; total: 3 vs. 10 mg/kg). Most of the As anomalies on the maps can be directly linked to geology (ore occurrences, As-rich rock types). However, some features have an anthropogenic origin. The new data define the geochemical background of As in agricultural soils at the European scale.

Arsenic and iron speciation in uranium mine tailings using X-ray absorption spectroscopy by Joseph Essilfie-Dughan; M. Jim Hendry; Jeff Warner; Tom Kotzer (11-18).
► Bulk XAS study of As and Fe species in uranium mine tailings. ► Oxidation states of As and Fe in the mine tailings samples are predominantly +5 and +3 respectively. ► Fe exist predominantly in the tailings ferrihydrite. ► As present in tailings samples is adsorbed to the ferrihydrite though an inner-sphere bidentate linkage.In northern Saskatchewan, Canada, high-grade U ores and the resulting tailings can contain high levels of As. An environmental concern in the U mining industry is the long-term stability of As within tailings management facilities (TMFs) and its potential transfer to the surrounding groundwater. To mitigate this problem, U mill effluents are neutralized with lime to reduce the aqueous concentration of As. This results in the formation of predominantly Fe3+–As5+ secondary mineral phases, which act as solubility controls on the As in the tailings discharged to the TMF. Because the speciation of As in natural systems is critical for determining its long-term environmental fate, characterization of As-bearing mineral phases and complexes within the deposited tailings is required to evaluate its potential transformation, solubility, and long-term stability within the tailings mass. In this study, synchrotron-based bulk X-ray absorption spectroscopy (XAS) was used to study the speciation of As and Fe in mine tailings samples obtained from the Deilmann TMF at Key Lake, Saskatchewan. Comparisons of K-edge X-ray absorption spectra of tailings samples and reference compounds indicate the dominant oxidation states of As and Fe in the mine tailings samples are +5 and +3, respectively, largely reflecting their generation in a highly oxic mill process, deposition in an oxidized environment, and complexation within stable oxic phases. Linear combination fit analyses of the K-edges for the Fe X-ray absorption near edge spectra (XANES) to reference compounds suggest Fe is predominantly present as ferrihydrite with some amount of the primary minerals pyrite (8–15% in some samples) and chalcopyrite (5–15% in some samples). Extended X-ray absorption fine structure (EXAFS) analysis of As K-edge spectra indicates that As5+ (arsenate) present in tailings samples is adsorbed to the ferrihydrite though an inner-sphere bidentate linkage.

Groundwater recharge and evolution in the Dunhuang Basin, northwestern China by Jinzhu Ma; Jianhua He; Shi Qi; Gaofeng Zhu; Wei Zhao; W. Mike Edmunds; Yanping Zhao (19-31).
► The dominant geochemical processes of the aquifers of the groundwater in the Dunhuang Basin were determined. ► Multiple environmental tracers (chemicals and isotopes) were used. ► We identify the recharge sources, recharge environment and the residence time of the groundwater. ► The confined groundwater was recharged during the last glaciations under a cold climate and unrenewable.Groundwater recharge and evolution in the Quaternary aquifer beneath the Dunhuang Basin was investigated using chemical indicators, stable isotopes, and radiocarbon data to provide guidance for regional water management. The quality of groundwater and surface water is generally good with low salinity and it is unpolluted. The dissolution of halite and sylvite from fine-grained sediments controls concentrations of Na+ and K+ in the groundwater, but Na+/Cl molar ratios >1 in all samples are also indicative of weathering of feldspar contributing to excess Na+. The dissolution of carbonate minerals yields Ca2+ to the groundwater, thereby exerting a strong influence on groundwater salinity. The δ18O and δ2H values in unconfined groundwater are enriched along the groundwater flow path from SW to NE. In contrast, confined groundwater was depleted in heavy isotopes, with mean values of −10.4‰ δ18O and −74.4‰ δ2H. Compared with the precipitation values, all of the groundwater samples were strongly depleted in heavy isotopes, indicating that modern direct recharge to the groundwater aquifers in the plains area is quite limited. The unconfined water is generally young with radiocarbon values of 64.9–79.6 pmc. In the northern basin, radiocarbon content in the confined groundwater is less than 15 pmc and an uncorrected age of ∼15 ka, indicates that this groundwater was recharged during a humid climatic phases of the late Pleistocence or early Holocene. The results have important implications for inter-basin water allocation programmes and groundwater management in the Dunhuang Basin.

Effect of source integration on the geochemical fluxes from springs by Marty D. Frisbee; Fred M. Phillips; Art F. White; Andrew R. Campbell; Fengjing Liu (32-54).
► Springflow generation is an integrative process similar to streamflow generation. ► No spring was consistently composed of 100% groundwater – ranged from 2% to 100%. ► Solute release from total springflow overestimates long-term solute release. ► Fractional springflow provides a better proxy for solute release from groundwater. ► Mass-balance approach does not retain information on residence time or dissolution rates.Geochemical fluxes from watersheds are typically defined using mass-balance methods that essentially lump all weathering processes operative in a watershed into a single flux of solute mass measured in streamflow at the watershed outlet. However, it is important that we understand how weathering processes in different hydrological zones of a watershed (i.e., surface, unsaturated, and saturated zones) contribute to the total geochemical flux from the watershed. This capability will improve understanding of how geochemical fluxes from these different zones may change in response to climate change. Here, the geochemical flux from weathering processes occurring solely in the saturated zone is investigated. This task, however, remains exceedingly difficult due to the sparsity of subsurface sampling points, especially in large, remote, and/or undeveloped watersheds. In such cases, springflow is often assumed to be a proxy for groundwater (defined as water residing in fully saturated geologic formations). However, springflow generation may integrate different sources of water including, but not limited to, groundwater. The authors’ hypothesis is that long-term estimates of geochemical fluxes from groundwater using springflow proxies will be too large due to the integrative nature of springflow generation. Two conceptual models of springflow generation are tested using endmember mixing analyses (EMMA) on observations of spring chemistries and stable isotopic compositions in a large alpine watershed in the San Juan Mountains of southwestern Colorado. In the “total springflow” conceptual model, springflow is assumed to be 100% groundwater. In the “fractional springflow” conceptual model, springflow is assumed to be an integration of different sources of water (e.g., groundwater, unsaturated flow, preferential flow in the soil, etc.) and groundwater is only a fractional component. The results indicate that groundwater contributions in springflow range from 2% to 100% overall and no springs are consistently composed of 100% groundwater; providing support for the fractional springflow conceptual model. Groundwater contributions are not strongly correlated with elevation, spring contributing area, spring discharge, or seasonality. This variability has a profound effect on long-term geochemical fluxes. The geochemical fluxes for total springflow overestimate long-term solute release by 22–48% as compared to fractional springflow. These findings illustrate that springflow generation, like streamflow generation, integrates many different sources of water reflecting solute concentrations obtained along many different geochemical weathering pathways. These data suggest that springs are not always ideal proxies for groundwater. Springs may be integrating very distinct portions of the groundwater flow field and these groundwater contributions may become mixed at the spring emergence with much younger sources of water that have never resided in the groundwater system.

Geochemical evaluation of flowback brine from Marcellus gas wells in Pennsylvania, USA by Lara O. Haluszczak; Arthur W. Rose; Lee R. Kump (55-61).
► Flowback brine from Marcellus gas wells is many times more saline than seawater. ► The high salinity brine is chemically similar to brine from sandstone reservoirs in the Paleozoic. ► The brines originated as seawater evaporated into the halite precipitation stage. ► The brines contain high concentrations of Ba and Ra.Large quantities of highly saline brine flow from gas wells in the Marcellus Formation after hydraulic stimulation (“fracking”). This study assesses the composition of these flowback waters from the Marcellus shale in Pennsylvania, USA. Concentrations of most inorganic components of flowback water (Cl, Br, Na, K, Ca, Mg, Sr, Ba, Ra, Fe, Mn, total dissolved solids, and others) increase with time from a well after hydraulic stimulation. Based on results in several datasets reported here, the greatest concentration of Cl in flowback water is 151,000 mg/L. For total Ra (combined 226Ra and 228Ra) in flowback, the highest level reported is 6540 pCi/L. Flowback waters from hydraulic fracturing of Marcellus wells resemble brines produced from conventional gas wells that tap into other Paleozoic formations in the region. The Br/Cl ratio and other parameters indicate that both types of brine formed by the evaporation of seawater followed by dolomitization, sulfate reduction and subsurface mixing with seawater and/or freshwater. Trends and relationships in brine composition indicate that (1) increased salt concentration in flowback is not mainly caused by dissolution of salt or other minerals in rock units, (2) the flowback waters represent a mixture of injection waters with highly concentrated in situ brines similar to those in the other formations, and (3) these waters contain concentrations of Ra and Ba that are commonly hundreds of times the US drinking water standards.

► Sand boil discharge had unique elemental chemistry signatures for deep and shallow seepage pathways beneath the levee. ► Deep pathways occurred where the levee was constructed on abandoned channel fill deposits. ► Differentiating deep and shallow seepage pathways offers an additional tool for site specific risk assessment of levee failure.Shortly after peak stage of the 2011 Mississippi River flood, water samples were collected from the river, from sand boils near the toe of the levee, and from actively flowing relief wells over a 55 km stretch north of Vicksburg, MS. Two distinct pathways for seepage under the levee were identified based on the elemental composition of water samples. Sand boil discharge was similar to water from relief wells only at a location where the levee sits on ancient channel fill deposits. Seepage at this site is forced along a deeper pathway beneath the fine-grained channel fill. Where the levee sits on sandy point bar deposits, shallow flow beneath the levee is unimpeded. The chemical composition of discharge from sand boils at these sites was clearly not just river water, nor a simple mixture of river and groundwater, but appears to reflect unique weathering or redox interactions occurring within the upper portion of the alluvial aquifer. Distinguishing shallow and deep seepage pathways may prove useful for evaluating site specific risk of levee failure.

Water chemistry in small lakes along a transect from boreal to arid ecoregions in European Russia: Effects of air pollution and climate change by T.I. Moiseenko; B.L. Skjelkvåle; N.A. Gashkina; A.D. Shalabodov; V.Yu. Khoroshavin (69-79).
Display Omitted► Features of the surface water geochemistry along a climatic ecoregions. ► The estimation of the main factors contributing to water chemistry formation. ► Zone distinctions and intrazone variations of water chemistry. ► Warming climate impact on surface water geochemistry.Water chemistry in 280 small lakes in European Russia along a climatic transect from the Kola Peninsula (in the tundra and taiga zones) to the Caspian Lowland (in the arid zone) was investigated from 2000 to 2005. Here the chemical compositions of lake waters in different climatic ecoregions are characterised. Variability in water chemistry within and between ecozones is documented and discussed. The results show that within the humid zone, there was little variability in water chemistry and anthropogenic, geological and morphometric characteristics of lakes and their catchments had a strong effect on the chemical composition of waters compared to lakes in the arid and semi-arid zones. An estimation of the potential effect of climate warming on water chemistry showed that a temperature rise of 0.5–1 °C is likely to have no effect on major ion concentrations, whereas a temperature increase of 2 °C may lead to an increase of approximately 25% in total ion concentrations in the southern regions. Total P may increase approximately 50% in lakes throughout the study area if the average daily temperature were to increase by 0.5 °C. This would have an important effect on the nutrient status of these lakes. In particular, these processes are expected to be most pronounced in the arid zones.

► Anthropogenic impact on reservoir sediments was assessed by chemical, mineralogical, and isotopic analysis. ► Most metals were bound to the reducible fraction, which is sensitive to environmental condition. ► Au–Ag and coal mines were identified as major pollutant sources using Pb isotope analysis.This study was conducted to assess the anthropogenic impact on metal concentrations in the bottom sediments of the Juam reservoir, Korea, and in stream sediments in its catchment, and to estimate the potential mobility of selected metals (Fe, Mn, Cu, Ni, Pb and Zn) using sequential extraction. A comparison of the metal concentrations in the stream sediments with mean background values in sediments collected from first- or second-order creeks shows that Pb, Cu and Ni are the most affected by anthropogenic inputs. The 206Pb/207Pb ratios of the bottom and core sediments (means: 1.2320 ± 0.0502 and 1.2212 ± 0.0040, respectively) suggest that Pb contamination is mainly due to the waste discharge of abandoned coal and metal mines rather than industrial and airborne sources. Considering the proportion of metals bound to the exchangeable, carbonate and reducible fractions, the comparative mobility of metals is suggested to decrease in the order Mn > Pb > Zn > Ni > Fe ≫ Cu.

► We assessed metal mobilization from lake sediments under oxidizing conditions. ► Low sulfur content of sediments; little apparent sulfide precipitation in most cases. ► With the exception of copper, oxidizing conditions did not lead to mobilization. ► Cu changed from insoluble CuS at low Eh, high pH to soluble CuO at high Eh, low pH. ► Most acid neutralized by bicarbonate.The sediments of City Park Lake (Baton Rouge, Louisiana, USA) are characterized by Pb concentrations that exceed the corresponding National Oceanic and Atmospheric Administration probable effect level by more than a factor of two and concentrations of As, Cd, Cu, Ni and Zn that exceed the corresponding threshold effect levels. The sediments of the lake are likely to be dredged because of concern over shoaling of the lake. There is concern that exposing these sediments to an oxidizing environment could mobilize toxic metal(loid)s that are effectively sequestered under reducing conditions. To address this concern, mixtures of sediments collected from seven locations in City Park Lake were incubated in microcosms under controlled oxidizing and reducing conditions. The slurries were sampled at time intervals over a period of nearly 750 h, and the dissolved Fe, Mn and trace metal concentrations determined. Eh and pH were negatively correlated, with Eh declining by 600 mV per unit increase in pH. Of the toxic metals, only the concentration of Cu was positively correlated with Eh, apparently because of the sequestration of Cu as a very insoluble sulfide precipitate under low Eh conditions. Precipitation of the other metals as sulfides was evidently insignificant because of the low S content of the sediments. Concentrations of the remaining potentially toxic metals were negatively correlated with Eh, apparently because of their sequestration as oxides and/or adsorption to Fe oxides or oxy-hydroxides. Concentrations of Ca, Mg, and Sr were positively correlated with Eh, presumably because of their sequestration in carbonate precipitates under low Eh/high pH conditions.

Sources and vertical distribution of 137Cs, 238Pu, 239+240Pu and 241Am in peat profiles from southwest Spitsbergen by E. Łokas; J.W. Mietelski; M.E. Ketterer; K. Kleszcz; P. Wachniew; S. Michalska; M. Miecznik (100-108).
► First comprehensive data on levels of transuranic elements and 137Cs in peats from Svalbard. ► Arctic peats can provide archives of atmospheric contamination. ► Global fallout from atmospheric nuclear weapons tests is a dominant source of transuranic elements and 137Cs in southwest Svalbard. ► ICP-MS measurements of 239Pu/240Pu ratios facilitate source identification.This paper presents a detailed survey of the activities of selected man-made radionuclides in peat deposits located in SW Spitsbergen. Peat cores from the High Arctic (SW Spitsbergen) were analyzed by gamma spectrometry (137Cs), alpha spectrometry (238Pu, 239,240Pu, 241Am activities) and by ICPMS (240Pu/239Pu atom ratios). Maximum activities evident in the peats correspond to the 1963/1964 global maximum fallout from atmospheric testing of nuclear weapons; some of the activity profiles have been altered post-deposition by water infiltration. Activity ratios of 238Pu/239+240Pu, 241Am/239+240Pu, 239+240Pu/137Cs and 240Pu/239Pu atom ratios indicate mixing between global (stratospheric) and regional (tropospheric) sources of these radionuclides in the Svalbard area. The 238Pu/239+240Pu activity ratios varied from 0.02 ± 0.01 to 0.09 ± 0.03, suggesting global fallout as the dominant source of Pu. The 239+240Pu/137Cs activity ratios varied from 0.01 ± 0.01 to 0.42 ± 0.11, which apparently arises from the post-depositional mobility of 137Cs. The 241Am/239+240Pu activity ratios ranged between 0.10 ± 0.02 and 1.5 ± 0.3 and exceed the published global fallout ratio for Svalbard of 0.37 due to the relatively higher geochemical mobility of Pu vs. Am and/or ingrowth of Am from the decay of 241Pu. The atom ratio 240Pu/239Pu ranged from 0.142 ± 0.006 to 0.241 ± 0.027; however, the vast majority of peat samples exhibited 240Pu/239Pu atom ratios similar to the stratospheric fallout (∼0.18).

Np(V/VI) redox chemistry in cementitious systems: XAFS investigations on the speciation under anoxic and oxidizing conditions by Xavier Gaona; Erich Wieland; Jan Tits; Andreas C. Scheinost; Rainer Dähn (109-118).
Display Omitted► Np(V) uptake by HCP is likely controlled by incorporation in the C―S―H structure. ► Np(VI) aqueous and sorbed species form under oxidizing hyperalkaline conditions. ► Two well-defined Np(VI) sorbed species prevail in C―S―H with C:S 0.75 and 1.65. ► EXAFS data confirm the formation of NpO 2 ( OH ) 4 2 - in oxidizing TMA-OH solutions.The use of cementitious materials is foreseen to immobilize long-lived intermediate level wastes that may contain significant amounts of 237Np. Predicting the release of Np from a cement-based repository requires an adequate understanding of its interaction with the main sorbing components of cement. Although Np(IV) will prevail under repository conditions after depletion of O2, Np(V) is expected to control the chemistry of Np in the early stage after repository closure as well as in the presence of oxidizing waste forms (i.e. high content of NO 3 - ). Moreover, little is known of the stability of Np(VI) under hyperalkaline conditions, resulting in a rather ill-defined Np(V/VI) redox chemistry in cementitious environments.XANES studies on Np(V)-doped calcium silicate hydrates (C―S―H phases) and hardened cement paste (HCP) samples prepared under anoxic and under oxidizing conditions (provided by 5 × 10−3  M NaClO) clearly showed the predominance of Np(V) and Np(VI), respectively. The presence of two different neptunyl moieties was confirmed by EXAFS, revealing significantly shorter Np―Oax and Np―Oeq distances obtained for the samples with NaClO (1.79–1.85 Å and 2.24–2.25 Å) compared to those prepared under anoxic conditions (1.88–1.89 Å and 2.39 Å). This indicates oxidation of Np(V) to Np(VI) in the presence of NaClO. The short Np–Oeq distances along with structural properties of the Si-shells (number of neighboring Si atoms, bond distances) suggest that an incorporation mechanism is responsible for Np(V/VI) uptake by C―S―H phases. The coordinative environments of both Np redox states in cement paste were found to be similar to those in C―S―H phases, indicating C―S―H as the uptake-controlling phase. In contrast to Np(V), the molecular environment of Np(VI) in C―S―H phases depends not only on the Ca:Si ratio of these phases but also on pH, presumably reflecting differences between the hydrolysis scheme of the two Np redox states under these pH conditions. EXAFS data further confirmed the predominance of aqueous Np(VI) species (as Np VI O 2 ( OH ) 4 2 - ) in hyperalkaline and oxidizing tetramethylammonium hydroxide (TMA-OH) solutions. Under anoxic conditions and in the presence of CO 3 2 - (as an impurity of TMA-OH), predominance of a mixed Np(V)―OH―CO3 species was indicated by EXAFS. These Np(V/VI) aqueous species are not considered in the current NEA thermodynamic selection and, therefore, deserve further attention.

Single-pass flow-through test elucidation of weathering behavior and evaluation of contaminant release models for Hanford tank residual radioactive waste by Kirk J. Cantrell; Kenneth C. Carroll; Edgar C. Buck; Doinita Neiner; Keith N. Geiszler (119-127).
► Release models were developed for several Hanford tank residual wastes. ► Ca rich precipitates were found to inhibit dissolution of uranium phases. ► Technetium release was modeled using an equilibrium Kd model. ► Chromium release was described using a constant concentration model.Contaminant release models are required to evaluate and predict long-term environmental impacts of residual amounts of high-level radioactive waste after cleanup and closure of radioactively contaminated sites such as the DOE’s Hanford Site. More realistic and representative models have been developed for release of U, Tc and Cr from Hanford Site tanks C-202, C-203, and C-103 residual wastes using data collected with a single-pass flow-through test (SPFT) method. These revised models indicate that contaminant release concentrations from these residual wastes will be considerably lower than previous estimates based on batch experiments. For U, a thermodynamic solubility model provides an effective description of U release, which can account for differences in pore fluid chemistry contacting the waste that could occur through time and as a result of different closure scenarios. Under certain circumstances in the SPFT experiments various Ca-rich precipitates (Ca phosphates and calcite) form on the surfaces of the waste particles, inhibiting dissolution of the underlying U phases in the waste. This behavior was not observed in previous batch experiments. For both Tc and Cr, empirical release models were developed. In the case of Tc, release from all three wastes was modeled using an equilibrium Kd model. For Cr release, a constant concentration model was applied for all three wastes.

Input of seabird-derived nitrogen into rice-paddy fields near a breeding/roosting colony of the Great Cormorant (Phalacrocorax carbo), and its effects on wild grass by Kentaro Kazama; Hirotatsu Murano; Kazuhide Tsuzuki; Hidenori Fujii; Yasuaki Niizuma; Chitoshi Mizota (128-134).
► Marine-derived N was input into rice-fields as cormorant feces from a nearby colony. ► δ15N values of soils indicate that cormorant-N was transported via irrigation water. ► Vegetation in soils with larger amount of cormorant-N had luxurious growth.Terrestrial ecosystems near breeding/roosting colonies of piscivorous seabirds can receive a large amount of marine-derived N in the form of bird feces. It has been well demonstrated that N input from seabirds strongly affects plant communities in forests or coastal grasslands. The effects of nutrient input on plant communities in agricultural ecosystems near seabird colonies, however, have rarely been evaluated. This relationship was examined in rice-paddy fields irrigated by a pond system located near a colony of the Great Cormorant Phalacrocorax carbo in Aichi, central Japan. In the present study, spatial variations in N content (N %) and N stable isotope composition (δ15N) of soils and wild grass species together with the growth height of plants in paddy fields in early spring (fallow period) were examined. Soils had a higher N % and δ15N values in fields associated with an irrigation pond that had N input from cormorants. The δ15N values tended to be higher around the inlet of irrigation waters, relative to the outlet. These results indicate that cormorant-derived N was input into the paddy fields via the irrigation systems. Plants growing in soil with higher δ15N had higher δ15N in the above-ground part of the plants and had luxurious growth. A positive correlation in plant height and δ15N of NO3–N was observed in soil plough horizons.

Enhancing microbial iron reduction in hyperalkaline, chromium contaminated sediments by pH amendment by R.A. Whittleston; D.I. Stewart; R.J.G. Mortimer; I.T. Burke (135-144).
► The observation of microbial metabolism using soil organic matter at pH 12. ► Novel approach to bio-stimulation of iron reducing alkaliphiles through pH amendment. ► A potential bioremediation strategy for COPR contaminated environments.Soil collected from beneath a chromite ore processing residue (COPR) disposal site contained a diverse population of anaerobic alkaliphiles, despite receiving a continuous influx of a Cr(VI) contaminated, hyperalkaline leachate (pH 12.2). Chromium was found to have accumulated in this soil as a result of an abiotic reaction of Cr(VI) with Fe(II) present in the soil. This sediment associated Fe(II) was, therefore, acting as a natural reactive zone beneath the COPR and thereby preventing the spread of Cr(VI). In anaerobic microcosm experiments soil microorganisms were able to reduce NO 3 - at pH 11.2 coupled to the oxidation of electron donors derived from the original soil organic matter, but progressive anoxia did not develop to the point of Fe reduction over a period of 9 months. It is not clear, therefore, if Fe(II) can be actively replenished by microbial processes occurring within the soil at in situ conditions. Sodium bicarbonate was added to this soil to investigate whether bioreduction of Fe in hyperalkaline Cr contaminated soils could be enhanced by reducing the pH to a value optimal for many alkaliphilic bacteria. The addition of NaHCO3 produced a well buffered system with a pH of ∼9.3 and Fe reducing conditions developed within 1 month once complete denitrification had occurred. Fe(III) reduction was associated with an increase in the proportion of genetic clone libraries that were from the phylum Firmicutes, suggesting that these species are responsible for the Fe(III) reduction observed. Amendment of the pH using bicarbonate may provide a suitable strategy for stimulating the bioreduction of Fe(III) in COPR leachate contaminated soils or other environments where microbial reduction is inhibited by elevated pH.

Calcium–phosphate treatment of contaminated soil for arsenic immobilization by Ghanashyam Neupane; Rona J. Donahoe (145-154).
► As concentration in soil was 278 ppm after >5 decades of As-herbicide application. ► Phosphate treatments were tested for in situ fixation of arsenic in soil. ► Phosphate only treatment was not able to immobilize arsenic in soil. ► Phosphate–calcium treatment helped immobilize arsenic in soil at pH > 7. ► Arsenic immobilization occurred by precipitation of As-phosphate phases.The application of As-based herbicides at several industrial sites has resulted in numerous localized areas of As-contaminated soil. In this study, an As-contaminated soil (As = 278 mg/kg) collected from an industrial site located in the southeastern USA was subjected to inorganic phosphate (Pi) treatments. Although Pi treatments have been previously used for flushing As from contaminated soils, in this study, contaminated soil was amended with Pi to study the possible immobilization of As through a co-precipitation mechanism. Specifically, the Pi amendment was aimed at simultaneous flushing of As from the soil with orthophosphoric acid and co-precipitating it as Ca–phosphate–arsenate phases. Bench-scale Pi treatment experiments were performed at different pH conditions, with and without the addition of Ca. Sorption of Pi on BH soil in the presence or absence of additional Ca was determined, along with the associated mobilization of As from the soil. A significant amount of the HNO3-digestible As (up to 55% at pH 4, 10–15% at pH 8, and ∼30% at pH 11) was released from the contaminated soil during the Pi sorption experiments. This increased mobility of As after the addition of Pi resulted from the competitive desorption of As from the soil. Although Pi sorption at high pH (>8) was largely controlled by precipitation, As did not co-precipitate with Pi. Aqueous geochemical modeling indicated that the lack of As co-precipitation during Pi-only treatment primarily resulted from the deficiency of Ca in the system. When additional Ca (16.9 mmol) was supplied along with Pi (3.38 mmol), the mobility of As decreased significantly at circum-neutral to high solution pH. Geochemical modeling suggested that the leachable As in the soil was potentially precipitated as As-bearing Ca–Pi phases. X-ray diffraction analysis of precipitates separated from the treated soil and from the synthetic leachate confirmed that the formation of a poorly crystalline carbonate apatite phase occurred as a consequence of the treatment. The results of this study support the potential application of Ca–Pi treatment for remediation of As-contaminated soil at environmentally relevant pH conditions.

Display Omitted► We evaluate the consequences of carbon steels on the reduction of aqueous nitrate in the presence of hydrogen. ► Carbon steel constitutes an electron donor by itself but hydrogen can enhance the reaction rate under certain conditions. ► Magnetite is the main corrosion by-product and it is also a catalyst by itself. ► Hydrogen alone is not sufficient by itself to reduce nitrate in the 90–200 °C temperature range.Reducing conditions induced by steel canister corrosion and associated H2 generation are expected in nuclear waste repositories. Aqueous NO 3 - present in the aquifers will become thermodynamically unstable and may potentially be converted to N2 and/or NH 4 + . However, NO 3 - reduction by H2, in the absence of bio-mediators, is generally thought to be kinetically hindered at low temperature, although the reaction may be promoted by the concomitant oxidation of Fe. In this study the reduction rate of aqueous NO 3 - is quantified in the presence of H2 and carbon steel surfaces from waste canisters and construction materials, as well as magnetite as their possible corrosion by-products. A parametric study (0 <  P(H2) < 10 bar, 0.1 < [ NO 3 - ] < 10 mM, 90 <  T° < 180 °C, 4 < pH in situ  < 9) reveals that even at 90 °C the reaction can occur within hours or days and leads to the formation of NH 4 + and pH increase. Different mechanisms may be potentially involved. It is shown that NO 3 - reduction in the presence of carbon steel does not require H2, since steel constitutes an electron donor by itself, as does metallic Fe. The reaction rate is strongly pH-dependent. Activation energy in the 90–180 °C range is found to be 45 kJ/mol. Magnetite is the main corrosion by-product and specific experimental runs demonstrate that it can serve as a catalyst for the NO 3 - – H 2 reaction. Hydrogen alone, without the presence of steel, is not sufficient to reduce NO 3 - under the temperature and pressure conditions used in this study.

Influence of a summer storm event on the flux and composition of dissolved organic matter in a subtropical river, China by Liyang Yang; Weidong Guo; Nengwang Chen; Huasheng Hong; Jinliang Huang; Jing Xu; Shuiying Huang (164-171).
► Dynamics of DOM in a storm event were studied in a subtropical river. ► The flux of DOM increased greatly in the storm flow. ► The aromaticity and molecular weight of DOM increased during the storm event. ► The fraction of a humic-like fluorescent component (C3) increased in the event. ► Changes in DOM composition lagged behind those in DOM flux.Dissolved organic matter (DOM) has not been studied fully for tropical and subtropical rivers, in particular during storm events. DOM dynamics during a summer storm event in June, 2011 were examined in a subtropical river (the North Jiulong River, China). Stormwater runoff was sampled for measurement of dissolved organic C (DOC), absorption spectroscopy and fluorescence excitation emission matrix spectroscopy (EEMs). Three different fluorescent components were identified using parallel factor analysis (PARAFAC), including humic-like C1 and C3, and C2 as a combination of humic-like and protein-like fluorophores. The flux of DOC increased fivefold from 0.4 kg s−1 at baseflow to 2.0 kg s−1 at peak flow. Chromophoric DOM (CDOM) and fluorescent components also showed large increases with stormflow. The flux of DOC was similar during the rising and falling hydrographs at equal water discharge, while those of CDOM and fluorescent components were much higher during the falling-hydrograph. Carbon specific CDOM absorption coefficient at UV (SUVA254) and the fraction of C3 which fluoresced at long emission wavelength correlated positively to each other but negatively to absorption spectral slope ratio (S R) and C2%. They showed notable temporal variations indicative of increases in aromaticity, C3% and average molecular weight of DOM during the storm event. Changes in DOM composition lagged behind those in DOM flux. Changes in the flux and quality of DOM during the storm event, which were monitored effectively by absorption spectroscopy and EEMs–PARAFAC, could affect biogeochemical processes in the river and receiving coastal waters.

Extent and limits of biodegradation by in situ methanogenic consortia in shale and formation fluids by Melissa E. Schlegel; Jennifer C. McIntosh; Steven T. Petsch; William H. Orem; Elizabeth J.P. Jones; Anna M. Martini (172-184).
► Labile organic compounds in New Albany Shale fluids suggest limited biodegradation. ► Low biodegradation indices in core samples also indicate limited biodegradation. ► The New Albany Shale is less biodegraded than similar microbial methane reservoirs. ► Enhancing CH4 production may entail stimulating microbial consortia and methanogens.Consortia of microbes degrade recalcitrant organic-matter in deep subsurface reservoirs, such as shales and coals, under anaerobic conditions into simple C molecules such as CO2 and acetate. These substrates are subsequently metabolized by methanogens into economic quantities of natural gas in sedimentary basins world-wide. This study explores organic matter in the Devonian New Albany Shale (Illinois Basin, USA) and associated fluids to investigate the extent of organic matter biodegradation, and evaluate the potential for stimulating in situ gas production. Identification of labile compound classes such as n-alkanes, fatty acids, and phenols in produced waters of the New Albany Shale, and low biodegradation indices in the shale core samples indicate limited biodegradation. Together with detectable acetate concentrations (up to 225.1 μM), these observations suggest that both the supporting microbial consortia and methanogens are limited in extent and activity. By comparison, the New Albany Shale is much less biodegraded than the microbial CH4-producing Michigan Basin Antrim Shale, Powder River Basin coals, or San Juan Basin coals. In the New Albany Shale, the extent of biodegradation generally becomes more varied with higher salinities, suggesting diverse microbial adaptations to degrade OM at high salinities. Enhancement of in situ CH4 production may be most effective if targeted at stimulating production of the supporting microbial consortia as well as methanogens.

Adsorption of selenate onto ferrihydrite, goethite, and lepidocrocite under neutral pH conditions by Soumya Das; M. Jim Hendry; Joseph Essilfie-Dughan (185-193).
► Ferrihydrite is the best adsorbent for Se(VI) at pH ∼ 7 at any solid concentrations. ► For goethite and lepidocrocite, adsorption attained a maxima at ∼60–70%. ► Se(VI) tends to form strong inner-sphere complexes on all of these synthetic solids. ► Ferrihydrite can be used as a potential adsorbent for Se(VI).This study evaluates the adsorption of dissolved Se(VI) onto three synthetic Fe oxy-hydroxides (i.e., 2-line ferrihydrite, goethite and lepidocrocite). Selenate adsorption was measured as a function of sorbent concentration (0.01–50 g L−1) at near neutral pH (∼7) and room temperature (25 °C) via batch experiments. Inductively coupled plasma-mass spectrometry (ICP-MS) analyses on the aqueous samples showed that 2-line ferrihydrite is by far the strongest adsorbent for Se(VI) when compared to goethite and lepidocrocite at all sorbate:sorbent ratios tested. Goethite has a slightly greater affinity for Se(VI) than lepidocrocite, irrespective of a lower specific surface area under similar experimental conditions (pH, solids concentration). Selenium(VI) surface complexes on the solids were not observed in Raman spectra or attenuated total reflectance-infrared (ATR-IR) spectra of selenate adsorbed phases, likely due to low surface coverage. However, X-ray absorption spectroscopy (XAS) showed that all three Fe oxy-hydroxides adsorbed Se(VI) via inner-sphere surface complexation irrespective of their dissimilar affinities for selenate at pH ∼ 7. Similarly, sorption data for the three synthetic solids was modeled using the Langmuir isotherm. Overall, 2-line ferrihydrite appears to efficiently and effectively adsorb Se(VI) under near neutral conditions and, as such, should be considered a potential sink for Se(VI) in a transient system.

► XRD, RS, and SEM revealed that hematite were stable at 75 °C and pH 10 for 7 day. ► No change in crystal morphology or reduction in surface area was evident. ► Hematite with adsorbed Mo was similar in size/shape to pure hematite. ► ICP-MS analyses indicate that hematite retains adsorbed Mo after aging.Hematite is a common primary/secondary mineral in mine drainage and mine waste settings that can adsorb dissolved metals and metalloids. This study explored the ability of synthetic hematite to retain one such contaminant, molybdate, on its surfaces under highly alkaline (pH = ∼10) conditions. X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), and specific surface area (BET) analyses show that synthetic hematite particles are stable and able to adsorb molybdate. Raman spectra show that the hematite efficiently adsorbs molybdate and retains it on its surfaces via strong inner-sphere surface complexation. Inductively coupled plasma-mass spectrometry (ICP-MS) data indicate that hematite aged (7 and 9 days) at high and room temperatures (75 and 25 °C) retains adsorbed molybdate and that molybdate sorption increases with aging. SEM images show that aged hematite particles with adsorbed molybdate are similar in size and shape to pure hematite and exhibit no significant reduction in surface area. These findings are valuable for understanding the fate of Mo in mine wastes and mill tailings environments where the 2-line ferrihydrite to which it is adsorbed can transform to hematite.

► Geochemical data should be opened prior to analysis. ► Geochemical pattern is a superimposition of multi-processes and should be decomposed. ► The S–A fractal model is a powerful tool to decompose a mixed geochemical pattern.Geochemical data are typical compositional data which should be opened prior to univariate and multivariate data analysis. In this study, a frequency-based method (robust principal component analysis, RPCA) and a frequency-space-based method (spectrum–area fractal model, S–A) are applied to explore the effects of the data closure problem and to study the integrated geochemical anomalies associated with polymetallic Cu mineralization using a stream sediment geochemical dataset collected from the Zhongteng district, Fujian Province (China). The results show that: (1) geochemical data should be opened prior to RPCA to avoid spurious correlation between variables; (2) geochemical pattern is a superimposition of multi-processes and should be decomposed; and (3) the S–A fractal model is a powerful tool for decomposing the mixed geochemical pattern.

Anthropogenic PAHs in mangrove sediments of the Calabar River, SE Niger Delta, Nigeria by Orok E. Oyo-Ita; John O. Offem; Bassey O. Ekpo; Peter A. Adie (212-219).
Polycyclic aromatic hydrocarbons (PAHs) in some coastal and mangrove sediments from the Calabar River were determined using GC–MS to assess the degree of contamination. The sediments exhibited significant spatial variations in concentrations of individual and total PAHs (TPAHs) as reflected in the wide range of the values (1670–20,100 ng/g dw) and a mean with a large standard deviation (9370 ± 579), suggesting that the contamination was localized. Mangrove area samples showed much higher TPAH contents, capable of posing a serious health threat to resident flora/fauna, than the coastal samples. A set of seven molecular ratios were calculated to evaluate different PAH sources and their relative importance. The results show that the river was predominated by petroleum-derived PAHs. However, Pyr/Pery and *Pery/PAHpenta profiles indicated the importance of a pyrolytic origin for perylene in relation to its diagenetic production. Factor analysis data confirmed this pattern and explained about 70.8% of the total variance.

Lead isotopic analysis within a multiproxy approach to trace pottery sources. The example of White Slip II sherds from Late Bronze Age sites in Cyprus and Syria by V. Renson; A. Martínez-Cortizas; N. Mattielli; J. Coenaerts; C. Sauvage; F. De Vleeschouwer; C. Lorre; F. Vanhaecke; R. Bindler; M. Rautman; K. Nys; Ph. Claeys (220-234).
► The use of lead isotopes in multiproxy approach to trace pottery provenance is tested. ► Pottery fragments and potential clay sources from Cyprus are analyzed. ► Various origins are proposed for the pottery fragments. ► A link is established between the pottery fragments and some clay sources. ► Clay processing prior to pottery making is attested.Lead isotope analyses were carried out on fragments of White Slip II ware, a Late Bronze Age Cypriote pottery ware, and on raw materials possibly used for their production. Sherds originate from three Late Bronze Age sites (Hala Sultan Tekke and Sanidha in Cyprus and Minet el-Beida in Syria) and clays come from the surroundings of Sanidha, a production site for White Slip ware. X-ray fluorescence (XRF) and a Principal Component Analysis (PCA) are combined with Pb isotope analyses to further investigate the effectiveness of the latter method within a multiproxy approach for pottery provenance study. The pottery sherds from the three sites are compared between themselves and with potential raw material. Additional X-ray diffraction (XRD) and analyses using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray detection (EDX) facility were performed on selected sherds and clays. This work confirms that the clay source used for pottery production in Sanidha derives from local weathered gabbro. It also shows that different origins can be proposed for White Slip II ware sherds from Hala Sultan Tekke and Minet el-Beida and that clays were prepared prior to White Slip II ware production. It finally confirms the effectiveness of Pb isotopes in tracing pottery provenance not only by comparing sherd assemblages but also by comparing sherds to potential raw materials.