Applied Geochemistry (v.35, #C)

Arsenic immobilization in water and soil using acid mine drainage sludge by Myoung-Soo Ko; Ju-Yong Kim; Jin-Soo Lee; Ju-In Ko; Kyoung-Woong Kim (1-6).
Adsorption onto Fe-containing minerals is a well-known remediation method for As-contaminated water and soil. In this study, the use of acid mine drainage sludge (AMDS) to adsorb As was investigated. AMDS is composed of amorphous particles and so has a large surface area (251.2 m2  g−1). Here, adsorption of both arsenite and arsenate was found to be almost 100%, under various initial AMDS dosages, with the arsenate adsorption rate being faster. The optimum pH for As adsorption onto AMDS was pH 7.0 and the maximum adsorption capacities for arsenite and arsenate were 58.5 mg g−1 and 19.7 mg g−1 AMDS, respectively. In addition, experiments revealed that AMDS dosages decreased As release from contaminated soil. Therefore, the AMDS used in this study was confirmed to be a suitable candidate for immobilizing both arsenite and arsenate in contaminated soils.

The main aim of this study was to assess the natural and anthropogenic contributions of CO2 in the urban atmosphere of Wrocław City (SW Poland) using combined quantitative (CO2 concentrations) and qualitative analysis (δ13C of CO2). Between 21 January 2011 and 22 December 2011, 17 sampling campaigns were performed at 3-week intervals and in total 255 samples were collected. The mean CO2 concentration was 469 ± 71 ppm and the mean δ13C(CO2) was −10.8 ± 1‰.The measured δ13C(CO2) values of major end-members for two winter heating seasons (−25.7‰ in January–March of 2011 and −27.6 ‰ in October–December of 2011) and for one vegetative season (−20.4‰ in April–September of 2011) suggest soil respiration as a main source of atmospheric CO2 during the vegetative season, and a very significant impact of fossil fuel combustion during the winter heating seasons. There were significant increases of CO2 concentrations at many sampling locations after the opening of a new motorway on 31 August 2011. The authors hypothesise that the new motorway contributes to the increase of CO2 across the city.

The German Elbe River floodplains rank under the most polluted areas in Europe. A sudden concentration increase of potentially harmful elements (PHEs) is documented in sediment profiles of Elbe bayous. The increase is dated to the mid of the 20th century (137Cs) and indicates industrialization of the former German Democratic Republic (GDR) as the source of intense pollution. The collapse of the GDR and the industries in the 1990s is traced by a concentration decrease in young sediments. The contamination is restricted to an increase of unstable binding forms; the hydroxide binding form is predominant. The geogenic concentration portions are of normal level and remain stable throughout the profiles (0–2 m). The equilibrium of contradictory binding forms in the sediments makes it mandatory not to interfere with the thermodynamic conditions and to keep the Elbe floodplain as an undisturbed ecological system.

Americium sorption on smectite-rich natural clay from granitic ground water by S. Kumar; A.S. Pente; R.K. Bajpai; C.P. Kaushik; B.S. Tomar (28-34).
Because of their significant retention capability, clay minerals have been proposed as a potential engineered barrier in high level nuclear radioactive waste disposal repositories. Smectite-rich natural clay is being considered as a backfill and buffer material for the Indian repository program. In the present study the sorption of Am by the clay, from granitic ground water, has been investigated. To identify the minerals in the clay controlling the sorption process, the adsorption isotherm of Eu(III), a chemical analogue of Am(III), was determined on montmorillonite–kaolinite clay mixtures having 0–20 wt% kaolinite. The effect of experimental parameters, such as, pH, ionic strength, and the presence of cation and anions on Am(III) sorption was further investigated to develop a sorption model for the natural clay. Overlapping adsorption isotherms of Eu(III) obtained for different montmorillonite–kaolinite clay suspensions established montmorillonite as the main sorbent for Eu/Am(III) in the natural clay. Americium(III) sorption increases with pH in three distinct stages: at lower pH values (<4) the sorption is virtually insensitive to pH, then rises sharply (4–7) and subsequently attains a constant value at higher pH values (>8). Decreasing ionic strength increases the sorption at pH < 6 indicating the dominant role of ion exchange reactions at lower pH. A surface complexation model, developed for natural clay by including ion exchange site and amphoteric sites present at edges, simulates the sorption profiles at varying pH and ionic strength well and confirms the montmorillonite fraction as the sorbent controlling Am(III) sorption. The presence of Ca(II) as well as anions (Cl, NO 3 - ) does not affect Am(III) sorption on clay under granitic ground water pH and ionic strength conditions. However, the profile of Am(III) sorption to Ca(II)-equilibrated clay differs from that for Na-equilibrated clay corroborating weaker exchange of Ca(II)–Am(III) in comparison to Na(I)–Am(III). The presence of SO 4 2 - in the sorption system lowers Am(III) sorption at lower pH values. Modeling the sorption data indicated the participation of SO 4 2 - containing Am surface species. The thermodynamic model developed for sorption onto natural clay was checked for Eu(III) sorption from granitic ground water at pH 6.1. The model simulates the sorption at lower metal ion concentration while there is deviation at higher metal ion concentration. Inclusion of more types of surface sites and the effect of organic material need to be tested to correct the model for this deviation.

Redox-cycling of arsenic along the water pathways in sulfidic metasediment areas in northern Sweden by Gunnar Jacks; Zdenka Šlejkovec; Magnus Mörth; Prosun Bhattacharya (35-43).
Display OmittedArsenic has emerged as a problem element in groundwater. The most common mechanism of mobilising As from the solid phase into water is through the reductive dissolution of ferric oxyhydroxides. This investigation was made in northern Sweden where metasediments containing pyrite, pyrrhotite and arsenopyrite underlay about 4000 km2. The overlying till contains as much as up to 100 mg kg−1 As. Speciation of the dissolved As shows that arsenite dominates largely over arsenate. The Fe oxyhydroxides formed may contain up to 0.5% As. Sandy sediments may contain 100–500 mg kg−1. Arsenic and Fe are closely correlated. The cycling of As in water, flora and fauna in wetlands has been studied. Ferric reduction occurs in wetlands and groundwater rich in Fe, and As is found to be discharging into ditches, brooks and streams. Wetland trees and plants show a moderately elevated content of As with a few species showing above 2 mg kg−1, the permissible level in fodder for domestic animals. The only plants having a high content of As are Equisetum species showing up to 26 mg kg−1. These plants make up a small fraction of the food of wild, grazing and browsing animals, for example moose and reindeer, and does not seem to constitute an environmental risk. However, the animals could be exposed to considerable amounts of As by drinking water from springs in wetlands. In the fauna, an elevated As content has so far been found in a limited number of benthic macroinvertebrate samples (1.23–42.1 mg kg−1 dry weight), in which inorganic As species (arsenate) predominate in the extractable fraction (62–82%) with lower amounts of arsenite, mono- and dimethylarsenic acid. Some samples also contained arsenobetaine, trimethylarsine oxide and tetramethylarsonium ion. To the authors’ knowledge, this is the first report on As speciation in benthic macroinvertebrates. Fish species from polluted streams (pike and brown trout) had normal As levels (0.57–1.84 mg kg−1 dry weight), mainly present in a form of arsenobetaine (brown trout) or arsenobetaine and dimethylarsinic acid (pike). As both fish species also contained minor amounts of arsenite and arsenate, it is estimated that there is no serious health risk to potential consumers.

Behaviour of chromium(VI) in stormwater soil infiltration systems by Karin Cederkvist; Simon T. Ingvertsen; Marina B. Jensen; Peter E. Holm (44-50).
The ability of stormwater infiltration systems to retain Cr(VI) was tested by applying a synthetic stormwater runoff solution with a neutral pH and high Cr(VI) concentrations to four intact soil columns excavated from two roadside infiltration swales in Germany. Inlet flow rates mimicked normal (10 mm in 2 h) and extreme (100 mm in 3 h) rain events. The objectives were to understand the behaviour of the anionic and toxic Cr(VI) in soil at neutral pH and to asses treatment efficiency towards Cr(VI). During normal rain events Cr(VI) was largely retained (more than 50%), even though pH was neutral, while under extreme rain events approximately 20% of Cr(VI) was retained. In both cases effluent concentrations of Cr(VI) would exceed the threshold value of 3.4 μg/L if the infiltrated water were introduced to freshwater environments. More knowledge on the composition of the stormwater runoff, and especially the occurrence of Cr(VI), is needed.

This study investigated modern loess weathering and its control on the chemistry of surface water and sediment within the Daihai Lake catchment. The mineral types and the abundances of major and trace elements in loess, sediments and bedrocks were determined to ascertain the provenance of river sediment. The major cation compositions and Sr isotopic ratios of surface and subsurface waters were measured to distinguish the contributions of dissolved loads from various parent materials. The data show that mineralogical characteristics and elemental abundances of the river sediments are almost identical with those of the loess, but are different from the bedrocks, indicating that river sediments are predominantly derived from loess. River waters feeding Daihai Lake show a similar range in 87Sr/86Sr ratios as those of HOAc-soluble carbonate minerals in loess from the Chinese Loess Plateau. The slightly lower 87Sr/86Sr of river waters in the southern catchment relative to other rivers reflect potential weathering of large areas of outcropping basalt. These results imply that (1) surface processes are dominated by weathering of loess which only accounts for 18% of the total catchment area, and (2) loess weathering but not basalt controls the river Sr isotopic signature, although the latter covers a larger catchment area. For groundwater, 87Sr/86Sr ratios indicate that subsurface processes might be controlled by interactions with ambient lithology and hydrological flowpaths.Comparing the rivers draining the Chinese Loess Plateau with global rivers, both Mg/Ca and 87Sr/86Sr in the Daihai surprisingly agree well with those in the upper and downstream Huanghe (Yellow River), as well as HOAc-soluble loess, but differ significantly from other global rivers. This result reinforces the argument that loess weathering plays the most important role in controlling the sediment and water chemistry in the loess-covered areas, whereas the influence of bedrock weathering is minor. This study on modern processes might provide baselines to decipher down core records for paleoclimate reconstructions, especially for lake/river sediments in (semi-)arid areas.

The co-adsorption of Cu(II) and arsenate onto the surface of goethite has been studied by performing adsorption experiments and potentiometric titrations, and a surface complexation model has been developed to describe the experimental results. Models for the binary systems, Cu–goethite and arsenate–goethite, were acquired separately and the model parameters were then included in the ternary system, together with the solubility products of solid Cu(II) arsenates reported in the literature. The adsorption of Cu(II) was described applying a model in which Cu(II) forms bidentate bridging mono- and binuclear surface complexes. According to recent interpretations of ATR-FTIR and EXAFS data the arsenate ions are assumed to be coordinated in a monodentate fashion to singly coordinated hydroxyl groups at the surface, and hydrogen-bonded to neighbouring triply coordinated surface oxide sites. In the case of co-adsorption of Cu(II) and arsenate, the adsorption could not be predicted by applying the combined model from the two binary systems. Two ternary Cu(II)–arsenate–goethite surface complexes must be included, one complex in which an arsenate ion is coordinating to surface Fe(III) (FeOAsO3Cu0.5−) and one complex in which arsenate is bound to the surface by coordinating to an adsorbed Cu(II) ion ( ( Fe 3 OFeOH ) Cu 2 ( OH ) 2 HAsO 4 1 - ) . No solid Cu(II) arsenate phases were formed under the experimental conditions in the present study. From constructed predominance area diagrams, the significance of adsorption and precipitation processes are discussed. Furthermore, calculated solubility of Cu(II) and As(V) is used to indicate optimum conditions for the cleaning of contaminated natural waters.

Redox buffering is one important factor to be considered when assessing the barrier function of potential host rocks for a deep geological repository for long-lived radioactive waste. If such a repository is to be sited in fractured crystalline host rock it must be demonstrated that waste will be emplaced deeper than the maximum depth to which oxidizing waters can penetrate from the earth’s surface via fractures, during the assessment timeframe (typically 1 Ma). An analogue for penetration of such oxidizing water occurs in the Cretaceous Toki Granite of central Japan. Here, a deep redox front is developed along water-conducting fractures at a depth of 210 m below the ground surface. Detailed petrographical studies and geochemical analyses were carried out on drill core specimens of this redox front. The aim was to determine the buffering processes and behavior of major and minor elements, including rare earth elements (REEs), during redox front development. The results are compared with analytical data from an oxidized zone found along shallow fractures (up to 20 m from the surface) in the same granitic rock, in order to understand differences in elemental migration according to the depth below the ground surface of redox-front formation. Geochemical analyses by XRF and ICP-MS of the oxidized zone at 210 m depth reveal clear changes in Fe(III)/Fe(II) ratios and Ca depletion across the front, while Fe concentrations vary little. In contrast, the redox front identified along shallow fractures shows strong enrichments of Fe, Mn and trace elements in the oxidized zone compared with the fresh rock matrix. The difference can be ascribed to the changing Eh and pH of groundwater as it flows downwards in the granite, due to reactions with rock forming minerals, in particular feldspar dissolution. These observations give important insights into the processes that control the rates of redox front penetration in fractured crystalline rock. The findings of the study can be used to help build confidence among stakeholders that radioactive waste would be emplaced in such rocks at greater depth than that to which oxidizing water is likely to penetrate in future.

The components and concentrations of metals in street dust are indictors of environmental pollution. To explore the pollution levels of Cd, Cr, Cu, Mn, Ni and Pb in street dust and their spatial distribution characteristics, 220 dust samples were collected in a grid pattern from urban street surfaces in Beijing. Multivariate statistics and spatial analyses were adopted to investigate the associations between metals and to identify their pollution patterns. In comparison with the soil background values, elevated metal concentrations were found, except those for Mn and Ni. The results of the geo-accumulation index (Igeo ) and the potential ecological risk index (Eri ) of the metals revealed the following orders: Cd > Cu > Cr > Pb > Ni > Mn and Cd > Cu > Pb > Cr > Ni. Levels of Igeo ranging from 0 to 5 were found and about 80% of the samples were below the moderately polluted level. The Eri values of single elements were within the low ecological risk level in most sampling sites. Most of the metals in the street dust of Beijing were statistically significantly correlated. It is hard to clearly identify the sources of each metal in the street dust since local environments are very complex. Cadmium, Cu, Cr, Mn and Pb showed medium spatial autocorrelations within the sampling region. Similar spatial distribution patterns were observed for Cu, Cr and Pb, and these metals had relatively high spatial variabilities and were enriched in the center of the city with several peaks scattered in the suburbs. Metal pollution anomalies were identified by using cluster and outlier analyses. Locations identified as clusters with high values indicated non-point source pollution, while locations identified as outliers with high values indicated point source pollution. Traffic, construction, and other human activities influenced these high values. In addition, the locations identified as outliers with low values in urban areas might benefit from less transportation and better management.

The Heihe River is one of the largest and most intensely exploited inland rivers of arid northwestern China, which is currently threatened by water shortage and ecological problems driven by climate change and human activity. To constrain SO 4 2 - sources to the river and evaluate the influence of hydrological processes on SO 4 2 - sources and transport in the large river basin, chemical and isotopic measurements of surface and groundwater samples were carried out in the Heihe River basin. The river water had SO 4 2 - concentrations in a range of 117–316 mg/L with an average of 199 mg/L, characterized by δ34SSO4 values ranging from +2.5‰ to +5.4‰ and δ18OSO4 values ranging from −1.8‰ to +10.2‰. The shallow groundwater had SO 4 2 - concentrations in a range of 54–1222 mg/L with an average of 383 mg/L, characterized by δ34SSO4 values ranging from 0‰ to +7.4‰ and δ18OSO4 values ranging from −2.6‰ to +10.9‰. A significant correlation was found between δ34SSO4 and δ18OSO4 values of the river water. A gradual downstream shift from lower δ34SSO4 and δ18OSO4 values to higher δ34SSO4 and δ18OSO4 values was observed for both the riverine and groundwater SO 4 2 - , which corresponds to a change in the SO 4 2 - sources, governed by the geology, from oxidation of sulfides in the upstream part to dissolution of evaporite and/or soil sulfate in the downstream part of the Heihe River basin. Sulfate input dominated by sulfide oxidation via mountain groundwater discharge at the Yingluo Valley is a major contributor to river SO 4 2 - in the upper reaches. Admixture of groundwater SO 4 2 - enhanced by intensive agricultural activities is responsible for increasing river SO 4 2 - concentration in the middle reaches. Evapotranspiration effects in the lower reaches result in indirect mixture of groundwater SO 4 2 - via dissolution of soil sulfate that has cycled through the soil organic matter pool. This study implies that mixing of groundwater SO 4 2 - with surface water is the dominant process affecting SO 4 2 - sources and S cycling of the Heihe River, which is controlled by the regional hydrological processes affected by natural and anthropogenic factors.

Nitrate pollution of groundwater is an increasingly serious anthropogenic problem. In this study, the hydrogeochemistry of major ions and stable isotope ratios of NO 3 - in groundwater were determined to identify the contamination sources and chemical transformation processes occurring in the shallow groundwater of Xi’an, the capital of Shaanxi province, NW China. Of a total of 32 groundwater samples, 31% had NO 3 - – N concentrations exceeding the accepted drinking water limit of 10 mg-N L−1. Most of these samples were from the urban center of the study area, while samples with <10 mg-N L−1 were mainly from suburban areas. Combined with information on NO 3 - and Cl, the variation in isotopes of NO 3 - in the groundwater suggest a mixing of multiple NO 3 - sources in areas on the urban/suburban border. By determining rainwater and river water NO 3 - isotopic values, the groundwater recharge mode can be deduced for Xi’an city. Chemical fertilizers and nitrification of N-containing organic materials contribute NO 3 - to suburban groundwater, while sewage effluent and nitrification dominate NO 3 - distribution in urban groundwater. Nitrification from organic soil N, manure and sewage was significant in some sampling areas, and NO 3 - isotopic values from groundwater in Xi’an indicated that the effects of denitrification were not an obvious contributor. Thus, the δ 15 N – NO 3 - enrichment process is mainly caused by the intense anthropogenic activity in the city center. From the urban center to suburban areas, the mean δ 15 N – NO 3 - values varied from +16.4‰ to +5.4‰, and the mean NO 3 - – N concentrations varied from 28.0 mg L−1 to 4.0 mg L−1. In particular, the δ 15 N – NO 3 - value (r  = −0.75, p  < 0.01) correlated more significantly with distance from the urban center than did the NO 3 - – N concentration data (r  = −0.49, p  < 0.01), which suggests that NO 3 - isotopic values are an effective indicator of contamination sources. In addition, the δ 15 N – NO 3 - values and population density show a significant logarithmic correlation in Xi’an city.

Citrate adsorption can decrease soluble phosphate concentration in soils: Results of theoretical modeling by Marek Duputel; Nicolas Devau; Michel Brossard; Benoît Jaillard; Davey L. Jones; Philippe Hinsinger; Frédéric Gérard (120-131).
A major problem for 21st century agriculture is the prospect of P scarcity. Adsorption of PO4 on the soil’s solid phase is the primary mechanism regulating P availability. Release of citrate by roots is generally thought to increase the availability of P, which in turn improves P acquisition by plants. However, the interaction between citrate and PO4 remains poorly understood in soils and conflicting results are found in the literature. Here modeling is used to investigate the effects of citrate adsorption on P availability in a chromic cambisol, a luvisol and two ferralsols over a range of soil pH values. The effect of different levels of exchangeable Ca, soil organic C (SOC), dissolved organic C (DOC) and PO4 fertilization were also tested in order to cover a wider range of environmental conditions.Results showed that the competition of citrate for PO4 binding sites was not the only mechanism regulating P availability. Citrate adsorption can also increase PO4 adsorption through electrostatic interactions with adsorbed Ca2+ ions and actively reduce P availability. More precisely, it was found that the addition of 10 μmol citrate kg−1 soil decreased P availability in both chromic cambisol and luvisol. The same trend was predicted by the model with 100 μmol of citrate kg−1 soil in the chromic cambisol, whereas available P was found to increase in the luvisol. In contrast, the addition of citrate at these two concentrations always increased P availability in the two ferralsols. Increasing exchangeable Ca further decreased P availability in the chromic cambisol and luvisol, while it further increased available P in ferralsols. Additional sensitivity tests showed that DOC concentration had little influence on these results. In contrast, increasing SOC concentration massively counteracted the deleterious influence of citrate in chromic cambisol, while the effect was amplified in luvisol. In ferralsols, it was mainly observed that the increase of SOC further promoted P availability.To conclude, it was found that citrate can either increase or decrease P availability in soil, depending mainly on the occurrence of 2:1 clay minerals and on the concentrations of citrate, adsorbed Ca, and soil organic C. Special attention should, therefore, be given to possible adverse effects of rhizosphere management for improved P nutrition.

Calcium carbonate scaling poses highly challenging tasks for its prediction and preventative action. Here an elemental, isotopic and modelling approach was used to decipher the evolution of alkaline tunnel drainage solutions and sinter formation mechanisms for 3 sites in Austria. Drainage solutions originate from local groundwater and form their characteristic chemical composition by interaction with shotcrete/concrete. This interaction is indicated by a positive correlation of dissolved K+ and pH (up to 12.3), and a decrease of aqueous Mg2+ by the formation of brucite (pH > 10.5). Variability in Ca2+ and DIC is strongly attributed to portlandite dissolution, calcite precipitation and CO2 exchange with the atmosphere, where the 13C/ 12C and 18O/ 16O signatures of calcite can be traced back to the source of carbonate. The internal PCO2 value is a reliable proxy to evaluate whether uptake of CO2 results in an increase or decrease of the degree of calcite saturation with a threshold value of 10−6.15  atm at 25 °C (pH ≈ 11). Precipitation rates of calcite are highest at pH ≈ 10. Mixing of groundwater-like solutions with strong alkaline drainage solutions has to be considered as a crucial factor for evaluating apparent composition of drainage solutions and calcite precipitation capacities.

Diffuse soil emission of hydrothermal gases (CO2, CH4, and C6H6) at Solfatara crater (Campi Flegrei, southern Italy) by F. Tassi; B. Nisi; C. Cardellini; F. Capecchiacci; M. Donnini; O. Vaselli; R. Avino; G. Chiodini (142-153).
Measurements of soil fluxes of hydrothermal gases, with special emphasis on C6H6, as well as chemical composition of mono-aromatic compounds in fumaroles and air, were carried out in April 2012 at the Solfatara crater (Campi Flegrei, Southern Italy) to investigate the distribution and behavior of these species as they migrate through the soil from their deep source to the atmosphere. Soil fluxes of CO2, CH4 and C6H6 exhibit good spatial correlation, suggesting that diffuse degassing is mainly controlled by local fractures. The calculated total output of diffuse C6H6 from Solfatara is 0.10 kg day−1, whereas fluxes of CO2 and CH4 are 79 × 103 and 1.04 kg day−1, respectively. A comparison between soil gas fluxes and fumarole composition reveals that within the crater soil CH4 is significantly affected by oxidation processes, which are more efficient for low gas fluxes, being dependent on the residence time of the uprising hydrothermal gases at shallow depth. Benzene degradation, mainly proceeding through oxidation via benzoate, seems to be strongly controlled by the presence of a shallow SO 4 2 - -rich aquifer located in the central and southwestern sectors of the crater, suggesting that the process is particularly efficient when SO 4 2 - acts as terminal electron acceptor (SO4 reduction). Relatively high C6H6/C7H8 ratios, typical of hydrothermal fluids, were measured in air close to the main fumarolic field of Solfatara crater. Here, C6H6 concentrations, whose detection limit is ∼0.1 μg m−3, are more than one order of magnitude higher than the limit value for ambient air (5 μg m−3). This suggests that hydrothermal fluids have a strong impact on air quality in the immediate surroundings of the fumarolic vents. Significant concentrations of endogenous mono-aromatics were also detected in air samples collected from the northern and western sides of the crater, where these gas compounds are mostly fed by diffuse degassing through the crater bottom soil.

Arsenic attenuation in geothermal streamwater coupled with biogenic arsenic(III) oxidation by Satoshi Mitsunobu; Natsuko Hamanura; Takafumi Kataoka; Fumito Shiraishi (154-160).
In the present study, we investigated As behavior in a high-As hot spring (Sambe hot spring, Shimane, Japan) by coupling direct chemical speciation by synchrotron-based XAFS and HPLC–ICP-MS with microbial As-redox transformation gene analysis. The concentration of soluble As in the spring streamwater decreased immediately along the flow in correlation with Fe behavior, indicating that As in the streamwater was naturally attenuated in the streamwater. Iron XAFS analysis suggested deposition of Fe(III) oxyhydroxides along the flow. Thus, considering the strong affinity of As to Fe oxyhydroxides, the observed attenuation in As was possibly caused by sorption (or incorporation) of As on Fe(III) oxyhydroxides. Both dissolved As(III) and As(V) were present in the aqueous phase, and As(III) was rapidly oxidized to As(V) (<30 s) along the flow. The oxidation kinetics indicated the occurrence of biotic As(III) oxidation, because obtained As(III) oxidation rate (6.7–7.8 μM min−1) was much faster than the reported abiotic oxidation rates. Furthermore, the bacterial arsenite oxidase gene (aioA) was detected in DNA extracted from all samples (average of 2.0 × 105  copies dry g−1), which also supported potential attributes of biological As(III) oxidation in situ. In solid phase samples from sampling points analyzed by XAFS, most of the As existed as oxidized pentavalent form, As(V). This result indicated that this form was preferentially partitioned to the solid phase because of the much higher affinity of As(V) than of As(III) to Fe(III) oxyhydroxides. Considering the kinetic and microbiological findings, it is indicated that biotic process was predominantly responsible for As(III) oxidation at the present site, and this biotic As(III) oxidation to As(V) controlled the observed attenuation of As, because oxidized As(V) was removed from the aqueous phase by Fe(III) oxyhydroxides more efficiently.

Hydrated Portland cement was reacted with CO2 in supercritical, gaseous and aqueous phases to understand the potential cement alteration processes along the length of a wellbore, extending from a deep CO2 storage reservoir to the shallow subsurface during geologic carbon sequestration. The 3-D X-ray microtomography (XMT) images showed that the cement alteration was significantly more extensive with CO2-saturated synthetic groundwater than dry or wet supercritical CO2 at high P (10 MPa)-T (50 °C) conditions. Scanning electron microscopy with energy dispersive spectroscopy (SEM–EDS) analysis also exhibited a systematic Ca depletion and C enrichment in cement matrix exposed to CO2-saturated groundwater. Integrated XMT, XRD and SEM–EDS analyses identified the formation of an extensive carbonated zone filled with CaCO3(s), as well as a porous degradation front and an outermost silica-rich zone in cement after exposure to CO2-saturated groundwater. Cement alteration by CO2-saturated groundwater for 2–8 months overall decreased the porosity from 31% to 22% and the permeability by an order of magnitude. Cement alteration by dry or wet supercritical CO2 was slow and minor compared to CO2-saturated groundwater. A thin single carbonation zone was formed in cement after exposure to wet supercritical CO2 for 8 months or dry supercritical CO2 for 15 months. An extensive calcite coating was formed on the outside surface of a cement sample after exposure to wet gaseous CO2 for 1–3 months. The chemical–physical characterization of hydrated Portland cement after exposure to various phases of CO2 indicates that the extent of cement carbonation can be significantly heterogeneous depending on the CO2 phase present in the wellbore environment. Both experimental and geochemical modeling results suggest that wellbore cement exposure to supercritical, gaseous and aqueous phases of CO2 during geologic C sequestration is unlikely to damage the wellbore integrity because cement alteration by all phases of CO2 is dominated by carbonation reactions. This is consistent with previous field studies of wellbore cement with extensive carbonation after exposure to CO2 for three decades. However, XMT imaging indicates that preferential cement alteration by supercritical CO2 or CO2-saturated groundwater can occur along the cement–steel or cement–rock interfaces. This highlights the importance of further investigation of cement degradation along the interfaces of wellbore materials to ensure permanent geologic carbon storage.

This reactive transport modeling study presents a follow up to the mass balance-based identification and quantification of the main hydrogeochemical processes that occurred during an aquifer storage and recovery (ASR) trial in an anoxic sandy aquifer (Herten, the Netherlands). Kinetic rate expressions were used to simulate oxidation of pyrite, soil organic matter (SOM), and ferrous iron, and dissolution of calcite and Mn-siderite. Cation exchange, precipitation of Fe- and Mn-(hydr)oxides, and surface complexation were treated as equilibrium processes. The PHREEQC model was automatically calibrated with PEST to observations from the first ASR cycle, and was then allowed to run for all 14 cycles to evaluate its long term performance. A sensitivity analysis was conducted to find the most controlling model parameters. Pyrite was ranked as the most important reductant, followed by SOM, whereas Fe(II) was least important. Moreover, the pH and oxygen gradients were found to enhance the rate of pyrite over SOM oxidation with distance away from the ASR well. The increasing sorption capacity of precipitating Fe-hydroxides was reflected by the decreasing Fe(II) concentrations with subsequent cycles whereas Mn(II) showed a tendency to mobilize during recovery and remain above standards. Oxidation and dissolution rates were found to depend on travel time and injection rate as well as on the presence or absence of flow. Oxygen enrichment of the injection water increased oxidation rates and therefore accelerated the aquifer’s leaching from its reactive species. We specifically focused on impeding the release of Mn(II) to the groundwater, a process that acted as a restraining factor for the feasibility of ASR application at this site. The undesirable side-effects of oxygen enrichment as well as the Mn(II) issues were found to be partly suppressed by enriching the source water with pH buffers according to scenario simulations.

The effectiveness of carbon capture and geologic storage depends on many factors, including and especially the permeability of the reservoir’s caprock. While caprock integrity is generally assumed if petroleum has been preserved, it is poorly constrained in reservoirs containing only saline waters, and CO2 leakage poses a potential risk to shallow aquifers. Naturally-occurring He accumulates in pore waters over time with the concentration being strongly dependent on the long term flux of fluid through the caprock. Furthermore, a small fraction of pore-water He diffuses into quartz and this may be used as a proxy for He concentrations in pore water, where dissolved gas samples are difficult to obtain, such as in deep sedimentary basins. In this paper He contained in quartz grains is measured and compared to previously measured pore water concentrations. Quartz was purified from core samples from the San Juan Basin, New Mexico and the Great Artesian Basin, South Australia. Quartz separates were heated at 290 °C to release He from the quartz. The quartz from the San Juan Basin and high purity quartz from the Spruce Pine Intrusion, North Carolina was repeatedly impregnated at varying pressures using pure He, heated and analyzed to build He sorption isotherms. The isotherms appear linear but vary between samples, possibly due to fluid inclusions within the quartz grains as high purity quartz samples partition only 1.5% of He that partitions into San Juan Basin samples. Concentrations of He in the pore water were calculated using the He-accessible volume of the quartz and the air–water He solubility. The mean San Juan Basin He pore water concentration was 2 × 10–5  cc STP He/g water, ∼400 times greater than atmospheric solubility. Great Artesian Basin samples contain a mean He concentration of 3 × 10–6  cc STP He/g water or 65 times greater than atmospheric solubility. However, pore water He concentrations in both the San Juan and Great Artesian Basins differ by up to an order of magnitude compared to samples collected with an alternate method. The reason for the offset is attributable to either partial saturation of the pore volume or a lack of He equilibrium between quartz and pore water. Coating of clay or other mineral phases on quartz grains, which tends to reduce the effective diffusion coefficient, may cause the latter. This technique of assessing permeability is promising due to the abundance of existing core samples from numerous basins where carbon sequestration may ultimately occur.

Metal contamination and retention of the former mining site Schwarzwand (Salzburg, Austria) by W. Adlassnig; S. Sassmann; T. Lendl; S. Wernitznig; F. Hofhansl; I. Lang; I.K. Lichtscheidl (196-206).
The Schwarzwand is a unique hygric, Cu-contaminated habitat formed by mining activities from the 16th to 18th century. Today, a large spoil heap and several creeks fed by Cu-rich mine drainage are present. The vegetation of the Schwarzwand differs clearly from the surrounding subalpine forests. It is by no means impoverished but rather a hotspot of biodiversity. Interestingly, most of the Cu precipitates within the Schwarzwand and the creeks leave the Schwarzwand virtually clean. This study maps the distribution of Cu within the Schwarzwand and within selected vascular plants, moss and microorganisms and correlates them with water and soil chemistry in order to identify the sinks of Cu and to elucidate the remarkable capability of the Schwarzwand for natural attenuation.Two types of water could be distinguished, one acidic precipitating limonite with a constant Cu content of about 0.6 mg L−1, and one circumneutral, which decreases far more rapidly in Cu content than would be expected due to chemical considerations. A dense microbial mat covering most of the bed of the circumneutral creeks could be identified as the main sink. It consists of the cyanobacterium Phormidium sp. and retains Cu both by adsorption to mucilaginous sheaths and by precipitation as secondary minerals such as sampleite. Layers of dead biofilm can be found covered by a few centimetres of soil at the banks of the circumneutral creeks; the extremely high concentration and the low solubility of Cu in this soil indicates permanent immobilisation of the metals. High concentrations of Cu were also found in mosses of the family Bryaceae which, however, play a negligible role for the metal retention of the habitat due to their low biomass.The retention of Cu within the Schwarzwand is a remarkable example of the sustainable self-cleaning of a contaminated habitat which takes place without any human intervention. The artificial establishment of microbial communities similar to the Schwarzwand could result in cheap and sustainable strategies for the remediation of suitable metal-contaminated waters.

Geochemical and isotopic variations in shallow groundwater in areas of the Fayetteville Shale development, north-central Arkansas by Nathaniel R. Warner; Timothy M. Kresse; Phillip D. Hays; Adrian Down; Jonathan D. Karr; Robert B. Jackson; Avner Vengosh (207-220).
Display OmittedExploration of unconventional natural gas reservoirs such as impermeable shale basins through the use of horizontal drilling and hydraulic fracturing has changed the energy landscape in the USA providing a vast new energy source. The accelerated production of natural gas has triggered a debate concerning the safety and possible environmental impacts of these operations. This study investigates one of the critical aspects of the environmental effects; the possible degradation of water quality in shallow aquifers overlying producing shale formations. The geochemistry of domestic groundwater wells was investigated in aquifers overlying the Fayetteville Shale in north-central Arkansas, where approximately 4000 wells have been drilled since 2004 to extract unconventional natural gas. Monitoring was performed on 127 drinking water wells and the geochemistry of major ions, trace metals, CH4 gas content and its C isotopes (δ13CCH4), and select isotope tracers (δ11B, 87Sr/86Sr, δ2H, δ18O, δ13CDIC) compared to the composition of flowback-water samples directly from Fayetteville Shale gas wells. Dissolved CH4 was detected in 63% of the drinking-water wells (32 of 51 samples), but only six wells exceeded concentrations of 0.5 mg CH4/L. The δ13CCH4 of dissolved CH4 ranged from −42.3‰ to −74.7‰, with the most negative values characteristic of a biogenic source also associated with the highest observed CH4 concentrations, with a possible minor contribution of trace amounts of thermogenic CH4. The majority of these values are distinct from the reported thermogenic composition of the Fayetteville Shale gas (δ13CCH4  = −35.4‰ to −41.9‰). Based on major element chemistry, four shallow groundwater types were identified: (1) low (<100 mg/L) total dissolved solids (TDS), (2) TDS > 100 mg/L and Ca–HCO3 dominated, (3) TDS > 100 mg/L and Na–HCO3 dominated, and (4) slightly saline groundwater with TDS > 100 mg/L and Cl > 20 mg/L with elevated Br/Cl ratios (>0.001). The Sr (87Sr/86Sr = 0.7097–0.7166), C (δ13CDIC  = −21.3‰ to −4.7‰), and B (δ11B = 3.9–32.9‰) isotopes clearly reflect water–rock interactions within the aquifer rocks, while the stable O and H isotopic composition mimics the local meteoric water composition. Overall, there was a geochemical gradient from low-mineralized recharge water to more evolved Ca–HCO3, and higher-mineralized Na–HCO3 composition generated by a combination of carbonate dissolution, silicate weathering, and reverse base-exchange reactions. The chemical and isotopic compositions of the bulk shallow groundwater samples were distinct from the Na–Cl type Fayetteville flowback/produced waters (TDS ∼10,000–20,000 mg/L). Yet, the high Br/Cl variations in a small subset of saline shallow groundwater suggest that they were derived from dilution of saline water similar to the brine in the Fayetteville Shale. Nonetheless, no spatial relationship was found between CH4 and salinity occurrences in shallow drinking water wells with proximity to shale-gas drilling sites. The integration of multiple geochemical and isotopic proxies shows no direct evidence of contamination in shallow drinking-water aquifers associated with natural gas extraction from the Fayetteville Shale.

Modelling of pH and inorganic aluminium after termination of liming in 3000 Swedish lakes by Carin Sjöstedt; Cecilia Andrén; Jens Fölster; Jon Petter Gustafsson (221-229).
Significant resources are spent on counteracting the effects of acidification, mainly by liming. Due to lower S and N deposition in Europe and North America, authorities are changing directives and strategies for remediation and reducing liming. However, as the acid–base buffer capacity differs in different water bodies, the desirable reduction of the lime dose is variable. In this study, a geochemical model is used to predict pH and inorganic monomeric Al (Ali) when liming is reduced and finally terminated in the 3000 Swedish lakes currently treated with lime. To estimate Ca and Mg concentrations not affected by liming for use in the model, the Ca/Mg ratio in nearby unlimed reference lakes was used. For the modelling of pH and inorganic Al the Visual MINTEQ program including the Stockholm Humic Model recently calibrated for Swedish fresh water was used. The predictions were validated with modelling results from six monitored lakes, in which liming had been terminated. The use of geochemical modelling appeared to be a promising tool for the calculation of accurate lime requirements in acid waters. For simulations in which liming was completely terminated, the pH value decreased by, on average, 1 pH unit to pH 5.7, whereas Ali increased by 17 μg L−1 to 32 μg L−1. If liming was reduced by half, the pH would drop only 0.3 pH units and Ali would increase by 2 μg L−1. Lakes in the south-western part of Sweden were predicted to reach a lower pH and higher Ali, which would be expected due to their greater historical S deposition. The results indicate that liming can be terminated in certain areas and in other areas be reduced without increases in the lake acidity.

Using δ15N and δ18O values to identify sources of nitrate in karstic springs in the Paris basin (France) by Fatima-Zahra J. El Gaouzi; Mathieu Sebilo; Pierre Ribstein; Valérie Plagnes; Pascal Boeckx; Dongmei Xue; Sylvie Derenne; Manon Zakeossian (230-243).
In many parts of the world, groundwater quality deterioration is occurring often due to changes in land use along with overexploitation of some aquifers. Some of the drinking water distributed in Paris (France) is collected from a karstic Cretaceous chalk aquifer at two groups of springs located 80 km south of Paris, in the Lunain catchment. Although geographically close to each other, these springs (Sp1 and Sp2) have quite different hydrogeochemical characteristics. In Sp1, an increase in the NO 3 - concentrations of 18 mg L−1 (from 16 mg L−1 in 1965 to 34 mg L−1 in 2009) has been observed and in Sp2, NO 3 - concentrations have increased by 26 mg L−1 (from 20 mg L−1 in 1965 to 46 mg L−1 in 2009). The origin of the NO 3 - was, however, unclear. The stable isotopic composition of NO 3 - was used to identify the sources causing the increase of NO 3 - concentrations and to assess seasonal variations. The isotopic composition of two potential sources including agricultural effluents and wastewater was determined. Likewise, two additional NO 3 - sources, the chalk groundwater and the Lunain River water, were considered, following the hydrogeological context of the Lunain catchment. Determination the concentrations and the δ15N and δ18O values of spring water NO 3 - and the use of a Bayesian isotopic mixing model SIAR (Stable Isotope Analyses in R) allowed determination of the proportional contribution of respective NO 3 - sources in the springs. In spring Sp1, all the potential NO 3 - sources (4) contributed almost equally during the low flow period, but higher NO 3 - contributions from the agricultural source and the chalk groundwater were observed during the high flow period. For the Sp2 group of springs, elevated contributions of NO 3 - from the agricultural source and from the chalk aquifer were observed during the high flow period as well as during the low flow period. Knowledge of NO 3 - sources contributing to these springs is important for the implementation of remediation measures to protect the water resource and avoid further water quality deterioration.

Chrysotile dissolution rates: Implications for carbon sequestration by James G.M. Thom; Gregory M. Dipple; Ian M. Power; Anna L. Harrison (244-254).
Display OmittedSerpentine minerals (e.g., chrysotile) are a potentially important medium for sequestration of CO2 via carbonation reactions. The goals of this study are to report a steady-state, far from equilibrium chrysotile dissolution rate law and to better define what role serpentine dissolution kinetics will have in constraining rates of carbon sequestration via serpentine carbonation. The steady-state dissolution rate of chrysotile in 0.1  m NaCl solutions was measured at 22 °C and pH ranging from 2 to 8. Dissolution experiments were performed in a continuously stirred flow-through reactor with the input solutions pre-equilibrated with atmospheric CO2. Both Mg and Si steady-state fluxes from the chrysotile surface, and the overall chrysotile flux were regressed and the following empirical relationships were obtained: F Mg = - 0.22 pH - 10.02 ; F Si = - 0.19 pH - 10.37 ; F chrysotile = - 0.21 pH - 10.57 where F Mg, F Si, and F chrysotile are the log10 Mg, Si, and molar chrysotile fluxes in mol/m2/s, respectively. Element fluxes were used in reaction-path calculations to constrain the rate of CO2 sequestration in two geological environments that have been proposed as potential sinks for anthropogenic CO2. Carbon sequestration in chrysotile tailings at 10 °C is approximately an order of magnitude faster than carbon sequestration in a serpentinite-hosted aquifer at 60 °C on a per kilogram of water basis. A serpentinite-hosted aquifer, however, provides a larger sequestration capacity. The chrysotile dissolution rate law determined in this study has important implications for constraining potential rates of sequestration in serpentinite-hosted aquifers and under accelerated sequestration scenarios in mine tailings.

Experiments were conducted under static batch and dynamic flow conditions to evaluate the sorption of FeII onto three goethites (G1, G2 and G3) having different crystal habits, morphologies and surface properties. Results reveal that G1 exhibited the highest FeII sorption extent and lowest kinetic rate constant, which may result from higher surface site density, surface roughness and edge surface faces. Surface complexation modeling parameters derived from batch experiments were combined with hydrodynamic parameters to simulate breakthrough curves in goethite-coated sand packed columns. The total sorbed amount of FeII at complete breakthrough was in agreement with that expected from the batch experiments, except for G1. Sorption breakthrough predictions that make use of surface complexation parameters accurately predicted FeII mobility in G2 and G3 columns, but poorly in G1 column. Experiments at various flow rates in G1 columns represented different amounts of FeII sorbed at complete breakthrough, thereby underscoring the impact of kinetic sorption. Moreover, Fe dissolution/re-precipitation or FeII-induced transformation of goethite was suspected at the lowest flow rate in the G1 column. The influence of goethite phase specific reactivity on FeII sorption under batch versus advective–dispersive flow is herein demonstrated. These findings have strong implications to assess transport of FeII and environmental contaminants both in natural and engineered systems.

The standard thermodynamic properties of vermiculites and prediction of their occurrence during water–rock interaction by Carmine Apollaro; Luigi Marini; Teresa Critelli; Rosanna De Rosa (264-278).
The standard thermodynamic properties ( Δ G f ° , Δ H f ° , S°, and V°), at 298.15 K, 1 bar, of 16 vermiculites and their heat-capacity coefficients were computed in this research following the approach of Wolery and Jove-Colon (2007). In this way, data consistent with those of other sheet silicates contained in the thermodynamic database data0.ymp.R5 of the EQ3/6 software package were obtained.Although the uncertainty of these data is too high to investigate exchange reactions involving vermiculites, they can be profitably used to predict the conditions of vermiculite formation during weathering. The shallow groundwaters interacting with granitoid and gneissic rocks and overlying soils, from an area of the Sila Massif (Calabria Region, Italy), were taken into account for an example of application. Results of speciation–saturation calculations for these waters show that: (i) in general, production of vermiculites hosting Mg2+ and Ca2+ ions in the interlayer sites is favoured with respect to generation of vermiculites whose interlayer sites are occupied by Na+ and K+ ions; (ii) the possibly forming solid phases (all metastable with respect to Mg–Fe–vermiculite) are kaolinite, Mg–Al–vermiculite, and Mg–Mg–Fe–vermiculite, in order of increasing pH values. In detail, kaolinite/Mg–Al–vermiculite coexistence occurs at pH close to 6.7, whereas Mg–Al–vermiculite/Mg–Mg–Fe–vermiculite coexistence occurs at pH close to 7.3.

Display OmittedThe reduction of NO 3 - in natural waters is commonly promoted by biological activity. In the context of deep geological nuclear waste repositories with potentially high H2 pressure, abiotic redox reactions may be envisaged. Here, the catalytic effect of “inert” metallic surfaces, in part used for nuclear waste canisters, on NO 3 - reduction under H2 pressure is evaluated. The study is focused on stainless steels by testing the 316L and Hastelloy C276 steels. A parametric kinetic study (0 <  P(H2) < 10 bar, 0.1 < [ NO 3 - ] < 10 mM, 90 <  T° < 150 °C, 4 < pH in situ< 9) reveals that NO 3 - reduction, in the presence of stainless steel 316L and Hastelloy C276, proceeds via a pH-independent reaction requiring H2 as an electron donor. No corrosion of these steels is observed indicating a true catalytic process. The reaction is inhibited in the presence of PO 4 3 - . Activation energies assuming a first-order reaction in the 90–150 °C temperature range are found to be 46 kJ/mol for stainless steel 316L and 186 kJ/mol for Hastelloy C276, making the reaction efficient at lower temperature and on a human time scale.Nitrate sorption at the metallic surface being thought to be the limiting step, sorption and competitive sorption isotherms of several oxyanions were performed at 90 °C on 316L. Nitrate and PO 4 3 - are more strongly sorbed than SO 4 2 - , likely as inner sphere complexes, and in a large pH range, from acidic to pH 9. The Langmuir–Hinshelwood formalism best fits the kinetic data. The nature of the surface complex, and the competition for sorption between NO 3 - and PO 4 3 - account for the macroscopic features of NO 3 - reduction by H2 observed at the steel surface. It should be stressed that some engineered materials such as stainless steels should be considered both as geological material and as geocatalysts as they could remain in the environment over an extremely long period of time.

Batch sorption isotherms of two nonpolar compounds (1,3-dichlorobenzene and 1,3,5-trichlorobenzene) and two polar compounds (1,3-dinitrobenzene and 1,3,5-trinitrobenzene) to heated (at 375 °C for 24 h) and unheated coals (lignite and anthracite) were compared with those to a soil humic acid and a maize stalk derived biochar. For all test compounds, unheated lignite and anthracite exhibited much stronger sorption than humic substances (the organic carbon-normalized distribution coefficient was up to 2–3 orders of magnitude larger), but lower sorption than biochar. This sorption trend is consistent with the degree of sorbent condensation (biochar > coal > humic acid). The results indicate that sorption of the test sorbates (regardless of the difference in polarity) to soils would be dominated by carbonaceous geosorbents. Notably, the organic carbon contents of the coals were pronouncedly lowered by the heat treatment, from 47.4% to 7.3% for lignite, and from 80.1% to 58.1% for anthracite. Moreover, the heat treatment markedly decreased organic carbon-normalized distribution coefficient to coals (up to one order of magnitude), attributable to the decreased hydrophobicity of sorbents due to increased O-containing groups from oxidation. An important implication is that heat treatment, which is commonly used to quantify the content of carbonaceous geosorbents in soil and sediment, may cause significant underestimation of sorption contribution of carbonaceous geosorbents due to the combined effect of reduced organic carbon content and decreased hydrophobicity of less graphitized carbonaceous geosorbents (coals). This was illustrated using a widely adopted dual-component model that combines linear partition to humic substances (represented by humic acid) and nonlinear adsorption on condensed geosorbents (represented by biochar and coal).

Modeling of the impact of dolomite and biotite dissolution on vermiculite composition in a gneissic shallow aquifer of the Sila Massif (Calabria, Italy) by Carmine Apollaro; Luigi Marini; Teresa Critelli; Rosanna De Rosa; Andrea Bloise; Domenico Miriello; Manuela Catalano; Vincenza Armano (297-311).
Reaction path modeling of water–rock interaction in a gneissic shallow aquifer of the Sila Massif was performed in kinetic (time) mode, under conditions of closed-system with secondary minerals and closed-system with CO2, to investigate the influence of both dolomite dissolution and biotite dissolution on the chemical characteristics of secondary vermiculites. Magnesium–Al- and calcium–Al-vermiculites are the major components of the vermiculite solid solution precipitated in the early stages of the process, which is dominated by dolomite dissolution. In contrast, Mg–Mg–Fe- and Ca–Mg–Fe vermiculites are important components of the vermiculite solid solution produced in the late stages of the process, where biotite dissolution prevails. Outcomes of this reaction-path-modeling exercise on vermiculite chemistry are fully consistent with the results obtained by Apollaro et al. (in press) through speciation–saturation calculations. In particular, Apollaro et al. (in press) showed that the pH of Mg–Al-vermiculite/Mg–Mg–Fe-vermiculite coexistence is 7.3. This value is virtually equal to the pH of Mg–Al-vermiculite/Mg–Mg–Fe-vermiculite iso-activity, 7.35, which is obtained from the results of reaction-path-modeling runs 3 and 4 carried out in this work.

Dissolved Rn was determined in 192 samples collected from cold shallow volcanic and sedimentary aquifers, deep thermal aquifers and from waters associated with bubbling gases in the western sector of the Sabatini Volcanic District and the Tolfa Mountains (central Italy). Shallow aquifers hosted in the Quaternary volcanic complexes show values ranging from 1.0 to 352 Bq/L (median value 55 and inter-quartile distance 62 Bq/L), while waters circulating within the permeable horizons of the sandy-to-clayey sediments of the Tolfa flysch have values from 1.0 to 44 Bq/L (median value 6.9 and inter-quartile distance 8.1 Bq/L). Thermal waters are hosted in the Mesozoic carbonate formations and move towards the surface along faults. Here, dissolved Rn values range from 0 to 37 Bq/L (median value 3.0 and inter-quartile distance 9.5 Bq/L). Waters associated with bubbling gases show dissolved Rn contents ranging from 2.0 to 48 Bq/L (median value 6.2 and inter-quartile distance 23 Bq/L). Those results suggest that lithology is the main factor affecting the Rn contents in shallow aquifers, due to the high levels of Rn progenitors U and Ra in the volcanic rocks relative to sedimentary units. The influence of other factors such as the presence of a fracture network, seasonal flow variations, type of discharge (from well or spring) was also investigated. Radon contents of thermal waters result from mixing with shallow waters (from both volcanic and sedimentary rock aquifers) and decrease of Rn solubility with temperature, while for bubbling pools the effects of strong degassing were also considered.In terms of health hazard from direct ingestion of Rn-rich waters, 20.8% of those circulating within the volcanic aquifer show values higher than the recommended value of 100 Bq/L, while none of those circulating within the sedimentary aquifers exceed the threshold value. Geostatistical techniques were used for the elaboration of contour maps by using variogram models and kriging estimation aimed at defining the areas where a potential health hazard due to the direct ingestion of Rn-rich waters and to inhalation of air following degassing of Rn from waters may be expected.

Immobilization of P by oxidation of Fe(II) ions leading to nanoparticle formation and aggregation by Xavier Châtellier; Malgorzata Grybos; Mustapha Abdelmoula; Kenneth M. Kemner; Gary G. Leppard; Christian Mustin; M. Marcia West; Dogan Paktunc (325-339).
Ferrous iron was oxidized at pH 6.0 in the presence of dissolved oxygen and increasing concentrations of phosphate. The resulting precipitates were characterized by TEM, SEM, XRD, IR spectroscopy, Mössbauer spectroscopy, EXAFS spectroscopy, and chemical analyses. The kinetics and the stoichiometry of oxidation were also determined. Chemical analyses revealed that all the P introduced was immobilized up to an introduced P/Fe molar ratio of 0.6–0.7. In the presence of excess phosphate, the maximum P/Fe ratio of the precipitates was found to be equal to about 0.86. Incorporation of phosphate hindered the sorption of dissolved carbonates, but favored the immobilization of monovalent cations such as Na or K. The number of OH ions per Fe atom introduced during the reaction decreased from 2 in the absence of P to about 1.5 ± 0.1 in the presence of excess phosphate. In all cases, no residual Fe(II) could be detected. In the absence of phosphate, the samples were composed of poorly crystallized ferrihydrite, lepidocrocite and goethite nanoparticles. Even just a small amount of phosphate (P/Fe = 0.02) was sufficient to effectively restrict the formation of goethite. In contrast, the formation of lepidocrocite was detected by XRD for P/Fe ratios as high as 0.1. At higher P/Fe ratios, only non-crystalline particles were detected. For 0.1 < P/Fe < 0.5, the characteristic size of all particles was smaller than 10 nm. For P/Fe > 0.5, a new category of particles with characteristic length scales larger than 10 nm appeared and became prominent as P/Fe increased. The transition was accompanied by a change in color of the suspension, from dark red to light yellow. For an introduced P/Fe ratio larger than 1, only the larger particles remained. As the introduced P/Fe ratio increased further, the incorporated P/Fe ratio increased only slightly. In contrast the size of the particles increased significantly, reaching a size larger than 50 nm in the presence of a large excess of PO 4 3 - . The kinetics of oxidation and hydrolysis were shown to obey a typical autocatalytic process in the presence as well as in the absence of PO 4 3 - .