Applied Geochemistry (v.27, #1)

Acidification of Earth: An assessment across mechanisms and scales by Karen C. Rice; Janet S. Herman (1-14).
► Anthropogenic activities cause acidification of Earth’s air, waters, and soils. ► Coal combustion causes acid rain and elevated atmospheric carbon dioxide. ► Metal ore and coal extraction causes acid mine drainage; smelting causes acid rain. ► Acid rain acidifies soils and freshwaters; carbon dioxide acidifies the oceans. ► Over application of nitrogen fertilizer causes soil acidification.In this review article, anthropogenic activities that cause acidification of Earth’s air, waters, and soils are examined. Although there are many mechanisms of acidification, the focus is on the major ones, including emissions from combustion of fossil fuels and smelting of ores, mining of coal and metal ores, and application of nitrogen fertilizer to soils, by elucidating the underlying biogeochemical reactions as well as assessing the magnitude of the effects. These widespread activities have resulted in (1) increased CO2 concentration in the atmosphere that acidifies the oceans; (2) acidic atmospheric deposition that acidifies soils and bodies of freshwater; (3) acid mine drainage that acidifies bodies of freshwater and groundwaters; and (4) nitrification that acidifies soils. Although natural geochemical reactions of mineral weathering and ion exchange work to buffer acidification, the slow reaction rates or the limited abundance of reactant phases are overwhelmed by the onslaught of anthropogenic acid loading. Relatively recent modifications of resource extraction and usage in some regions of the world have begun to ameliorate local acidification, but expanding use of resources in other regions is causing environmental acidification in previously unnoticed places. World maps of coal consumption, Cu mining and smelting, and N fertilizer application are presented to demonstrate the complex spatial heterogeneity of resource consumption as well as the overlap in acidifying potential derived from distinctly different phenomena. Projected population increase by country over the next four decades indicates areas with the highest potential for acidification, so enabling anticipation and planning to offset or mitigate the deleterious environmental effects associated with these global shifts in the consumption of energy, mineral, and food resources.

► EDTA impact on hydroxyapatite Cd removal in pH range 4–9. ► XPS proof of the formation of Cd-enriched hydroxyapatite surface. ► The thermodynamic model of equilibrium of hydroxyapatite surface and Cd2+ in solution. ► More insoluble surface phase formation with the composition Ca8.4− x Cd x (HPO4)1.6(PO4)4.4(OH)0.4.The removal of Cd from aqueous solutions by hydroxyapatite (HAP) was investigated with and without EDTA being present. Batch experiments were carried out using synthetic hydroxyapatite with Ca/P 1.57 and a specific surface area of 37.5 m2/g in the pH range 4–9 (25 °C; 0.1 M KNO3). The surface composition of the solid phases were analysed by X-ray Photoelectron Spectroscopy (XPS). The surface layer of HAP was found to undergo a phase transformation with a (Ca + Cd)/P atomic ratio of 1.4 and the involvement of an ion exchange process (Ca2+  ↔ Cd2+). The amount of Cd removed from the solution increased with increasing pH, reaching ≈100% at pH 9. In the presence of EDTA Cd removal was reduced due to the formation of [CdEDTA]2− in solution. The solubility of HAP increases in the presence of EDTA at pH values above 5, mainly due to the formation of [CaEDTA]2−. In contrast to this, the solubility was found to decrease in the presence of Cd2+ and CdEDTA2−. Using XPS the formation of a Cd-enriched HAP surface was found, which was interpreted as the formation of a solid solution of the general composition: Ca 8.4 - x Cd x ( HPO 4 ) 1.6 ( PO 4 ) 4.4 ( OH ) 0.4 .The information from the chemical analyses and XPS data was used to design an equilibrium model that takes into account dissolution, solution and surface complexation, as well as possible phase transformations. The total concentration of Ca, phosphate, EDTA, and Cd in solution were used in the equilibrium analysis. In the calculations the computer code WinSGW, which is based on the SOLGASWATER algorithm, was used. The following equilibria and compositions of the solid solutions were found to give the best fit to experimental data: log K s ( Ca 7.6 Cd 0.8 ( HPO 4 ) 1.6 ( PO 4 ) 4.4 ( OH ) 0.4 ( s ) + 4.8 H + ⇋ 7.6 Ca 2 + + 0.8 Cd 2 + + 6 HPO 4 2 - + 0.4 H 2 O ) = - 28.03 ± 0.07 . The corresponding value for the composition Ca5.6Cd2.8(HPO4)1.6(PO4)4.4(OH)0.4(s) is −27.39 ± 0.06.The proposed model can be used to predict HAP dissolution and surface phase transformations in the presence of Cd and EDTA.

► Groundwater quality in the Belgian coastal plain is linked to Holocene geological evolution. ► Mixing, cation exchange, calcite dissolution and oxidation of organic matter are main reactions. ► Old samples (<10th century) show evidence of freshening as well of salinization. ► Old samples are testimonies of a dynamic geological environment. ► Younger samples are characterized by freshening of the aquifer due to impoldering.The Holocene geological evolution of the Belgian coastal plain is dominated by a transgression of the North Sea, silting up of the coastal plain and human intervention (impoldering). This has led to a typical pattern in groundwater quality which is discussed here for the central part of the coastal plain. Therefore, a database with available groundwater samples is composed. Water type according to the Stuyfzand classification is determined and different hydrosomes and their hydrochemical facies are identified. Based on this, the origin and evolution of the water types is explained using Piper plots and geochemical calculations with PHREEQC. Before the impoldering, salinising and freshening conditions alternated with a general salinisation of the aquifer after about 3400 BP. This results in a dominance of brackish and salt NaCl subtypes which are still found in the deeper part of the aquifer. The subsequent impoldering resulted in an major freshening of the aquifer leading to NaHCO3, MgHCO3 and CaHCO3 subtypes. Overall, mixing, cation exchange, carbonate mineral dissolution and oxidation of organic matter are identified as the major processes determining the general water quality. The close link between geological evolution, water quality and what is still observable today is illustrated with this example of the Belgian coastal plain.

► SGD-driven trace element fluxes were significant in seawater off a volcanic island. ► Concentrations of trace elements in seeping groundwater were highest in summer. ► Fe, Al, and Co fluxes through SGD showed the largest contributions to seawater. ► SGD-driven trace element fluxes are important for marine biogeochemistry.The concentrations of trace elements in groundwater and seawater were measured in a coastal embayment (Bangdu Bay) of a volcanic island (Jeju) off the southernmost coast of Korea in August and December of 2009. The concentrations of trace elements (Al, Mn, Fe, Co, Ni, and Cu) in the groundwater in summer were approximately 20-fold higher than those in winter, with good correlation to each other. Overall, the concentrations of most of the trace elements in the groundwater were 3- to 70-fold higher than those in the seawater of this Bay. Simple budget calculations showed that large fluxes of submarine groundwater discharge (SGD)-driven trace elements were responsible for the unusually enhanced concentrations of trace elements (particularly for Al, Fe and Co) in the summer seawater. The results imply that the temporal changes in SGD-driven trace element fluxes are large and may contribute considerably to the budget of trace elements in the coastal ocean, particularly off a highly permeable volcanic island.

Deciphering interaction of regional aquifers in Southern Tunisia using hydrochemistry and isotopic tools by Kamel Abid; Marek Dulinski; Friha Hadj Ammar; Kazimierz Rozanski; Kamel Zouari (44-55).
► We examine the origin and chemical evolution of groundwater in southern Tunisia. ► Contribution of water from the deep CI aquifer to Turonian formation was demonstrated. ► Influence of geogenic carbon dioxide in the studied groundwater system was shown. ► The work aids management strategies of scarce groundwater resources in Tunisia.Groundwater is the most important source of water supply in southern Tunisia. Previous hydrogeologic and isotopic studies carried out in this region revealed the existence of two major aquifer systems: the “Complex Terminal” (CT) and the “Continental Intercalaire” (CI). Turonian carbonates constitute one of the major aquifer levels of the CT multilayered aquifer. It extends over most of southern Tunisia, and its hydrodynamic regime is largely influenced by tectonics, lithology and recharge conditions. Forty-eight groundwater samples from the CI and Turonian aquifers were collected between January and April 2004 for chemical and isotopic analyses. Hydrochemistry and isotopic tools were combined to get an insight into the processes controlling chemical composition of groundwater and wide-scale interaction of these two aquifer systems. Analysis of the dissolved constituents revealed that several processes control the observed chemical composition: (i) incongruent dissolution of carbonate minerals, (ii) dissolution of evaporitic minerals, and (iii) cation exchange. Dissolution alone cannot account for the observed high supersaturation states of groundwater with respect to calcite and dolomite. The observed supersaturation is most probably linked to geogenic CO2 entering water-bearing horizons of the CT and CI aquifers via deep tectonic faults and discontinuities and subsequent degassing in the exploitation wells. Presence of geogenic CO2 in the investigated region was confirmed by C isotope data of the DIC reservoir. The radiocarbon content of the Turonian samples varied between 9.5 and 43 pmc. For CI samples generally lower values were recorded, between 3.8 and 22.5 pmc. Stable isotope composition of Turonian groundwater samples varied from −8.3 to −5.3‰ for δ 18O and from −60 to −25‰ for δ 2H. The corresponding ranges of δ values for the Continental Intercalaire samples were from −8.9‰ to −6.9‰ for δ 18O and from −68.2‰ to −45.7‰ for δ 2H. Stable isotope composition of groundwater representing CT and CI aquifers provide strong evidence for regional interaction between both systems.

► The microscopic distribution of CeIII/IV (as Pu analogue) was investigated in altered simulated nuclear waste glass. ► CeIV released from the glass was re-immobilized as CeIII spatially associated with secondary Mg-clay. ► Results suggest PuIV may also be immobilized reductively during dissolution of vitrified nuclear waste. ► However, a thermodynamic analysis showed that the Ce may not be a suitable chemical analogue of Pu.In the present study, the dissolution and mobilization of Ce introduced in a simulated nuclear waste glass (MW) as a surrogate of Pu was investigated after leaching in pure water over 12 a at 90 °C and pH ∼ 9.6. The microscopic distribution and oxidation state of Ce in the altered glass were studied using micro-X-ray fluorescence (micro-XRF) mapping techniques and micro-X-ray near-edge absorption spectroscopy (micro-XANES). Distribution maps of CeIII and CeIV were obtained by recording the L α fluorescence emission at two different incident X-ray energies, coinciding with the maximum contrast between CeIII and CeIV fluorescence intensities. The micro-XRF maps revealed that Ce was dominantly present as oxidized species (CeIV) in the original glass. After dissolution from the glass matrix, CeIV was partly reduced and re-immobilized as CeIII at grain boundaries or in the interstitial spaces between the glass particles. The concentration of CeIII was found to correlate with the spatial distribution of secondary Mg-clay formed during the aqueous corrosion as the main glass alteration product. Micro-XANES spectra collected at locations representative of both altered and non-altered glass domains confirmed the findings obtained by the redox mapping. Because redox-sensitive elements in the pristine MW glass (Fe, Cr, Se) occur almost exclusively as oxidized species, reduction of CeIV was probably mediated by an external source of reductants, such as Fe(0) from the steel reaction vessel.These results, in conjunction with an Eh–pH stability diagram of the CeIII/IV–O–H–CIV–P–SVI–Na–Cl system, indicate that the glass was leached at relatively low oxidation potentials (Eh < 0.2 V). However, the comparison with an equivalent Eh–pH diagram for Pu revealed that at comparable pH and water composition the reduction of PuIV to PuIII would require considerably more reducing conditions (Eh < −0.3 V). It is, therefore, concluded that Ce is not a good chemical analogue of Pu, in spite of its wide use as a surrogate in simulated radioactive waste.

Carbon export and HCO 3 - fate in carbonate catchments: A case study in the karst plateau of southwestern China by Shilu Wang; Kevin M. Yeager; Guojiang Wan; Congqiang Liu; Yuchun Wang; Yingchun Lü (64-72).
► Carbon mass balances were determined in a lake which is located in carbonate area. ► 80% of exported primary production from carbonate catchments is in the form of HCO 3 - . ► More carbon (39%) returns to the atmosphere as the consumed CO2 is conveyed. ► Only 13% of the CO2 is stored in lake sediments, which is much less than expected. ► The carbon sink of carbonate weathering may not be as significant as once thought.The consumption of CO2 due to carbonate weathering is thought to be an important terrestrial sink for atmospheric CO2. However, the reaction and fate of weathering products may significantly affect the magnitude of the sink. Carbon mass balances were determined in Hongfeng Lake, a small artificial lake located in the carbonate plateau of SW China. This was accomplished by measuring the concentrations of DIC (dissolved inorganic C), DOC (dissolved organic C), POC (particulate organic C), and CO2 partial pressure in lake waters, inflows and outflows, and in surrounding spring waters. Results show that maximum DIC (mainly HCO 3 - derived from carbonate weathering by CO2) to DOC ratios in the catchment export load reach ∼21, implying that as much as ∼80% of the exported primary production is in the form of HCO 3 - , and, therefore, the CO2 consumed by carbonate weathering and subsequent DIC export is a critical component of the C balance in this ecosystem. This exported HCO 3 - subsidizes C cycling of aquatic ecosystems in the catchment, and 32% (excluding carbonate-derived C) returns to the atmosphere as CO2 evasion through the fluvial and lacustrine water–air interface and 10% is stored in lake sediment. This lake has a small CO2 emission rate (13.2 ± 3.9 mmol m−2  d−1, or 0.097 mol m−2  a−1 relative to catchment area) compared to mean values for many reservoirs found in temperate and tropical climatic zones. This is likely due in part to low organic C loads supplied by the karst-dominated catchment, and low lake water DOC concentrations. The estimate indicates that more C (39%) returns to the atmosphere and much less (13%) is stored in sediments, implying that the C sink of carbonate weathering may not be as significant as once thought.

► Environmental isotopes enable the identification of seawater/groundwater interactions. ► Water isotope data show that groundwater is mostly replenished by winter precipitation. ► We identify salt water intrusion by using δ18O of dissolved groundwater sulfate. ► We characterize the sources and the chemical history of groundwater nitrate using δ18O and δ15N of nitrate. ► Using submarine groundwater discharge data the effect of Ireland’s water quality on the Atlantic coastal zone is discussed.The geochemistry and isotopic composition of a karstic coastal aquifer in western Ireland has shed light on the effect of sea-water/groundwater interactions on the water quality of Ireland’s Atlantic coastal zone. The use of stable isotope data from the IAEA precipitation station in Valentia, located in SW Ireland has facilitated the characterization of groundwater recharge conditions in the western part of Ireland and suggests that groundwater is mostly replenished by the isotopically light winter precipitation. The dissolved SO 4 2 - in the karstic groundwater that was collected during baseflow conditions with δ34S values between 4.6‰ and 18‰ may be composed of S stemming from three principal sources: SO 4 2 - derived from precipitation which is composed of both sea-spray S (δ34S: 20‰) and an isotopically light anthropogenic source (δ34S: 1–5‰), SO 4 2 - stemming from animal slurries (δ34S: ∼5‰), and intruding sea-water SO 4 2 - (δ34S: 20.2‰). The isotopic composition of δ18O in dissolved groundwater SO 4 2 - collected during baseflow conditions is interpreted as reflecting sea-water intrusion to the karstic coastal groundwater system. The highest δ18O values in dissolved groundwater SO 4 2 - were in samples collected near the coast (4.8 ± 0.4‰) and the lowest (2 ± 0.5‰) were collected further inland. The δ15N and δ18O values of groundwater NO 3 - were between 3.4‰ and 11.4‰ and approximately 7.7‰, respectively, and reflect geochemical conditions in the aquifer that do not promote attenuation of NO 3 - through denitrification. As a result N loading to Kinvara Bay that is controlled by submarine groundwater discharge (SGD) was calculated as 5 tons/day on average compared to an estimated N-input that derives from precipitation of approximately 2.5 tons/a. SGD into the bay may result in near coastal sea-water quality changes. These results represent one of the first studies addressing the effect of groundwater quality in Ireland on the European Atlantic coastal zone.

Aqueous–solid solution thermodynamic model of U(VI) uptake in C–S–H phases by Xavier Gaona; Dmitrii A. Kulik; Nathalie Macé; Erich Wieland (81-95).
Display Omitted► Uptake of U(VI) by C–S–H is explained with a multi-site solid solution thermodynamic model. ► Development of the model is based on wet chemistry data, spectroscopy and C–S–H structure. ► Model considers different types of C–S–H forming during cement hydration or degradation. ► Model correctly accounts for sorption trends of U(VI) on C–S–H and Hydrated Cement Paste. ► Different scenarios can be assessed with the model, e.g. U(VI) behaviour upon carbonate intrusion.Reliable thermodynamic models assessing the interaction of radionuclides with cementitious materials are important in connection with long-term predictions of the safe disposal of radioactive waste in cement-based repositories. In this study, a geochemical model of U(VI) interaction with calcium silicate hydrates (C–S–H phases), the main component of hardened cement paste (HCP), has been developed. Uranium(VI) sorption isotherms on C–S–H phases of different Ca:Si ratios (C:S) and structural data from spectroscopic studies provided the indispensable set of experimental data required for the model development. This information suggested that U(VI) is neither adsorbed nor incorporated in the Ca–O octahedral layers of the C–S–H structure, but rather is located in the interlayer, similar to Ca2+ and other cations. With a view to the high recrystallisation rates and the cryptocrystalline ‘gel-like’ structure of the C–S–H phases, these observations indicated a U(VI) uptake driven by the formation of a solid solution.The CSH3T-U model was further used to predict the effect of carbonate on the retention of U(VI) by cementitious materials. The presence of calcite (ubiquitous in conventional cement formulations) has no influence on the retention of U(VI) as the concentration of carbonate in solution is too low (<2 × 10−4  M) to influence U complexation under hyperalkaline conditions. However, the addition of free carbonate to the system accelerates the degradation of C–S–H by draining Ca2+ from the interlayer. At low C:S ratios, this effect can significantly reduce the retention of U by cementitious materials.

► We contribute the compared results of TSR simulation experiments of hydrocarbon with metal sulfates and sulfur in gold-tube confined system. ► The product yields of TSR including organic and inorganic gaseous and their stable carbon, hydrogen isotopes were reported. ► H2S was largely produced at very low temperature (250 °C) in sulfur treated rather than at high temperature (above 450 °C) in the MgSO4 treated.The yields and stable C and H isotopic composition of gaseous products from the reactions of pure n-C24 with (1) MgSO4; and (2) elemental S in sealed Au-tubes at a series of temperatures over the range 220–600 °C were monitored to better resolve the reaction mechanisms. Hydrogen sulfide formation from thermochemical sulfate reduction (TSR) of n-C24 with MgSO4 was initiated at 431 °C, coincident with the evolution of C2–C5 hydrocarbons. Whereas the yields of H2S increased progressively with pyrolysis temperature, the hydrocarbon yields decreased sharply above 490 °C due to subsequent S consumption. Ethane and propane were initially very 13C depleted, but became progressively heavier with pyrolysis temperature and were more 13C enriched than the values of a control treatment conducted on just n-C24 above 475 °C. TSR of MgSO4 also led to progressively higher concentrations of CO2 showing relatively low δ 13C values, possibly due to input of isotopically light CO2 derived from gaseous hydrocarbon oxidation (e.g., more depleted CH4).Sulfur reacted with n-C24 to produce H2S at the relatively low temperature of 250 °C, the H2S profile of the S treatment showed a consistent increase from 280 °C after a sharp increase at 250 °C, implicating S-hydrocarbon reactions as a potentially important source of subsurface H2S accumulations. Sulfur produced only low amounts of CO2 to 430 °C, indicating that abstraction of the H source for H2S occurred in the absence of C–C bond cleavages of the n-C24 reactant. Higher yields of 13C depleted CO2—S also showing a reactive preference for 12C bonds—and low MW hydrocarbons were evident from 431 °C, although a moderate reduction (i.e., not as rapid as MgSO4–TSR) of hydrocarbon levels and increase in δ 13C values above 490 °C was attributed to their direct S reaction. This demonstrates that S, as has previously been established for MgSO4–TSR, has a reactive preference for hydrocarbons of high MW. The reaction of low MW hydrocarbons with the S reactant (i.e., S) or the S produced by SO4 oxidation (i.e., MgSO4), may also account for the elemental S (S8, S7, S6 and S4) and organic S products detected in the solvent extracted residue of both treatments. Field translation and validation of the molecular and stable isotopic trends identified in this laboratory study should help to resolve the relative contributions of different sources and competing processes to subsurface accumulations of H2S.

Methylation of Hg downstream from the Bonanza Hg mine, Oregon by John E. Gray; Mark E. Hines; David P. Krabbenhoft; Bryn Thoms (106-114).
► Sediment downstream from the mine contains elevated Hg and methyl-Hg. ► Methyl-Hg concentrations in stream sediment correlate with total organic carbon. ► Isotopic-tracer methods indicate downstream sediment has high Hg methylation rates. ► Aquatic snails elevated in Hg indicate significant bioavailability and uptake of Hg. ► Hg methylation is enhanced by the temperate climate and high organic matter.Speciation of Hg and conversion to methyl-Hg were evaluated in stream sediment, stream water, and aquatic snails collected downstream from the Bonanza Hg mine, Oregon. Total production from the Bonanza mine was >1360 t of Hg, during mining from the late 1800s to 1960, ranking it as an intermediate sized Hg mine on an international scale. The primary objective of this study was to evaluate the distribution, transport, and methylation of Hg downstream from a Hg mine in a coastal temperate climatic zone. Data shown here for methyl-Hg, a neurotoxin hazardous to humans, are the first reported for sediment and water from this area. Stream sediment collected from Foster Creek flowing downstream from the Bonanza mine contained elevated Hg concentrations that ranged from 590 to 71,000 ng/g, all of which (except the most distal sample) exceeded the probable effect concentration (PEC) of 1060 ng/g, the Hg concentration above which harmful effects are likely to be observed in sediment-dwelling organisms. Concentrations of methyl-Hg in stream sediment collected from Foster Creek varied from 11 to 62 ng/g and were highly elevated compared to regional baseline concentrations (0.11–0.82 ng/g) established in this study. Methyl-Hg concentrations in stream sediment collected in this study showed a significant correlation with total organic C (TOC, R 2  = 0.62), generally indicating increased methyl-Hg formation with increasing TOC in sediment. Isotopic-tracer methods indicated that several samples of Foster Creek sediment exhibited high rates of Hg-methylation. Concentrations of Hg in water collected downstream from the mine varied from 17 to 270 ng/L and were also elevated compared to baselines, but all were below the 770 ng/L Hg standard recommended by the USEPA to protect against chronic effects to aquatic wildlife. Concentrations of methyl-Hg in the water collected from Foster Creek ranged from 0.17 to 1.8 ng/L, which were elevated compared to regional baseline sites upstream and downstream from the mine that varied from <0.02 to 0.22 ng/L. Aquatic snails collected downstream from the mine were elevated in Hg indicating significant bioavailability and uptake of Hg by these snails. Results for sediment and water indicated significant methyl-Hg formation in the ecosystem downstream from the Bonanza mine, which is enhanced by the temperate climate, high precipitation in the area, and high organic matter.

► Determination of VOCs in natural and anthropogenic fluids. ► Protocol for analytical and sampling techniques and materials. ► Consistency of the SPME and ST analytical results tested using a statistical approach. ► The SPME and ST techniques allow analysis of VOC from both gas vents and air.In the present study, two sampling and analytical methods for VOC determination in fumarolic exhalations related to hydrothermal-magmatic reservoirs in volcanic and geothermal areas and biogas released from waste landfills were compared: (a) Solid Traps (STs), consisting of three phase (Carboxen B, Carboxen C and Carbosieve S111) absorbent stainless steel tubes and (b) Solid Phase Micro Extraction (SPME) fibers, composed of DiVinylBenzene (DVB), Carboxen and PolyDimethylSiloxane. These techniques were applied to pre-concentrate VOCs discharged from: (i) low-to-high temperature fumaroles collected at Vulcano Island, Phlegrean Fields (Italy), and Nisyros Island (Greece), (ii) recovery wells in a solid waste disposal site located near Florence (Italy). A glass condensing system cooled with water was used to collect the dry fraction of the fumarolic gases, in order to allow more efficient VOC absorption avoiding any interference by water vapor and acidic gases, such as SO2, H2S, HF and HCl, typically present at relatively high concentrations in these fluids. Up to 37 organic species, in the range of 40–400  m/z, were determined by coupling gas chromatography to mass spectrometry (GC–MS). This study shows that the VOC compositions of fumaroles and biogas determined via SPME and ST are largely consistent and can be applied to the analysis of VOCs in gases released from different natural and anthropogenic environments. The SPME method is rapid and simple and more appropriate for volcanic and geothermal emissions, where VOCs are present at relatively high concentrations and prolonged gas sampling may be hazardous for the operator. The ST method, allowing the collection of large quantities of sample, is to be preferred to analyze the VOC composition of fluids from diffuse emissions and air, where these compounds are present at relatively low concentrations.

Modeling the effect of stratification on cemented layer formation in sulfide-bearing mine tailings by Jeannet A. Meima; Torsten Graupner; Dieter Rammlmair (124-137).
► Stratification was found to play a crucial role in cemented layer formation. ► Mica-rich layer below iron-sulfide rich layer results in jarosite-rich cemented layer. ► Arsenopyrite-rich layer results in amorphous FeAsO4-rich cemented layer. ► Pore area becomes disconnected if porosity decreases below 15% => reduced O2 diffusion.Reactive transport simulations have been applied to investigate possible effects of stratification on the potential of sulfide-bearing mine tailings to form protective cemented layers. The simulations are based on characteristic strata found at a German tailings site, including sulfide-enriched heavy mineral layers, mica-enriched silt layers, and homogeneously mixed layers. The simulated secondary phases (jarosite, gypsum, amorphous ferric arsenate, amorphous Fe hydroxide, alunite, amorphous silica, and kaolinite) are similar to those observed in the field. Using scanning electron microscope analyses of cemented layers, it has been observed that the pore area becomes disconnected if the porosity is decreased to values below 15%, which would indicate a strong decrease in permeability. Stratification was found to play a crucial role in cemented layer formation. Cemented layers are absent or insignificant in systems with a homogeneous distribution of Fe-bearing sulfides. They are extensively developed in systems with (a) an arsenopyrite-rich layer or (b) a mica-enriched layer situated immediately below an Fe-sulfide enriched layer. The modeling results have clearly demonstrated that the key processes operating in scenario (a) are very different from the key processes in scenario (b). In scenario (a), the oxidation of arsenopyrite is followed by the precipitation of amorphous ferric arsenate, which can be solely responsible for significant pore reduction. In scenario (b), the presence of a large amount of reactive aluminosilicates (e.g. biotite and Ca-bearing plagioclase) immediately below the Fe-sulfide rich layer appears to be crucial. Key processes are extensive formation of Acid Rock Drainage (ARD) followed by enhanced (pH-driven) weathering of aluminosilicates, resulting in the accumulation of secondary phases directly below the Fe-sulfide rich layer. In both scenarios, a cemented layer is formed that effectively retards the further downward movement of the oxidation front. The presented details on the role of stratification in the formation of cemented layers could be considered in the construction of mining heaps as a possible measure to stimulate natural attenuation.

Top-/bottom-soil ratios and enrichment factors: What do they really show? by Julie Sucharovà; Ivan Suchara; Marie Hola; Sarka Marikova; Clemens Reimann; Rognvald Boyd; Peter Filzmoser; Peter Englmaier (138-145).
► Element concentrations are compared for soil O- and B-horizon samples collected at the scale of the Czech Republic. ► Top-/bottom soil ratios do not provide a valid tool to differentiate between anthropogenic and geogenic element sources. ► Enrichment factors do not provide a valid tool to differentiate between anthropogenic and geogenic element sources.High top-/bottom-soil ratios, or high values of “enrichment factors” (EFs), are used as a proof for major anthropogenic impact on the geochemistry of the Earth surface. The idea behind calculating such ratios is that soils taken at depth or “average crust” can provide the geochemical background for the soils collected at the Earth surface. However, a soil profile is not a closed system, element exchange between the different layers, depending on and varying with the chemical properties of the different elements, and their turnover in the biosphere is the essence of soil formation. High top-/bottom-soil ratios, or EFs, may thus highlight the geochemical de-coupling of the lithosphere from the biosphere rather than contamination. This is demonstrated by using regional data from 258 soil O- and B-horizon samples collected from the Czech Republic (76,800 km2). Results show no relationship between the ratios and the magnitude of anthropogenic emissions. The visible relationship between element concentrations and sources in a map of the spatial distribution of the elements is lost when maps for the top-/bottom-soil ratio or EFs are constructed. The value of the data lies in the spatial elemental distribution, and not in ratios calculated based on misconceptions.

PCB contamination from sampling equipment and packaging by Malin Andersson; Rolf Tore Ottesen; Morten Jartun; Ola Eggen; Ann-Christine Enqvist (146-150).
Work reported in this paper suggests that there are cases of contamination of soil and water samples by polychlorinated biphenyls (PCB) from paper and plastic packaging. Soil samples, which have been stored in paper bags for more than 20 years, share a similar congener distribution as the bags. Analyses showed a predominance of light congeners. PCB-analyses of water also indicate that water samples could be contaminated by plastic packaging. All analytical results of solid material packaging, as well as soil stored in the packaging, show a high relative amount of light weight PCB congeners. The paper bags that were analysed are made of strong paper and very popular among geochemists because of their watertight quality. These paper bags were manufactured more than 20 years ago. The plastic packaging that was analysed was produced in 1997 and 2008. The analyses of plastic and paper show that the raw material that has been used in the production at different times contains a wide concentration range of PCB. Re-sealable plastic bags, which contained the highest levels of PCB of the plastic material, are used by researchers world-wide as sampling bags for soils and sediments. This paper raises an important issue that packaging may potentially contaminate the samples that they hold.

Metallogeny and environmental impact of Hg in Zn deposits in China by Runsheng Yin; Xinbin Feng; Zhonggen Li; Qian Zhang; Xianwu Bi; Guanghui Li; Jinling Liu; Jingjing Zhu; Jianxu Wang (151-160).
► We investigated mercury distribution in 100 Zn ore deposits with four typical ore types in China. ► We found that Hg concentrations in Zn concentrates vary largely depending on the ore types and geneses. ► We explained the variation of Hg concentrations in Zn ores among different types. ► Based on Hg distribution data, we estimated annual Hg emission from Zn smelting in China.Zinc smelting is currently regarded as one of the most important atmospheric Hg emission sources in the world. In order to assess the potential environmental impacts of Hg from Zn smelting in China, the distribution of total Hg concentration (HgT) in Zn concentrates (ZCs) from 100 Zn deposits in China was investigated. It was found that HgT varies depending on the ore types and their geneses. Zinc concentrates from sedimentary-exhalative deposits (SEDEX, geometric mean = 48.2 μg/g) have the highest HgT. The possible explanation is that the sources of mineralizing solutions for SEDEX deposits are deep formational brines in contact with sedimentary rocks, and there are much higher background Hg contents in sedimentary rocks. Zinc concentrates from volcanic hosted massive sulfide deposits (VMS, geometric mean = 11.5 μg/g) and Mississippi Valley-Type (MVT, geometric mean = 10.1 μg/g) deposits have intermediate HgT. VMS may receive most of their Hg from fluid–rock interaction and/or by direct input of gaseous Hg from a mantle source. However, the source of metals within MVTs may be the low-temperature hydrothermal solution formed by diagenetic recrystallization of the carbonates. Intrusion related deposits (IRs) have the lowest HgT (Geomean = 2.4 μg/g), and the dispersion of Hg in the IRs seems to be influenced by the temperature of ore formation and/or the nature of wall–rock alteration. Finally, it was estimated that the annual Hg emission to the atmosphere from Zn smelting in China was about 107.7 tons in 2006.

► ANOVA indicates parent material classified urban soil mapping justified for geogenic elements. ► PM mapping more accurate than IDW grid mapping for As, Cr, Fe and K in Northampton urban area, UK. ► IDW grid mapping more accurate when anthropogenic input is principal spatial control.The purpose of the study reported here is to assess whether it may in some circumstances be useful and appropriate to use a parent material (PM) soil chemistry mapping method developed for national soil chemistry data to portray spatial variation in urban soil chemistry data in Great Britain. Analysis of variance (ANOVA) of the urban soil data suggests that spatial interpolation of soil ambient background concentrations (ABCs) using PM classified soil data may be justified for those elements with strong geogenic control. The PM soil chemistry mapping method for urban soil data is demonstrated using data from the Northampton urban area, in the English Midlands. Geometric mean (GM) and inverse distance weighting (IDW) interpolations based on the nearest four topsoil samples were evaluated. Independent validation indicated that for As, Cr, Fe and to a lesser extent K, which all exhibit relatively strong geogenic control in the Northampton urban area: (i) the PM soil chemistry mapping method is more accurate and effective than the conventional IDW grid mapping and (ii) PM soil chemistry mapping based on the average of the nearest four Lne element concentrations is more accurate than mapping based on IDW values calculated from the nearest four Lne element concentrations. The variation in effectiveness of the methods can be explained by the fact that PM exerts a significant control on As, Cr, Fe and K in the Northampton area whereas anthropogenic inputs appear to be the dominant control on the spatial variation of Pb, especially at high concentrations. The PM mapping method would be expected to work efficiently in other urban areas and for those elements where a significant proportion of the variation can be explained by PM.

► Lead isotope ratios in mussels from Magela more uranogenic than from Sandy catchment. ► Additional input of Broken Hill type lead further downstream of mine site. ► Lead isotope ratios in mussels ideal for source apportionment of lead into waterways.Concentrations of Fe, Mn, Cu, Zn, U and Pb, and stable Pb isotopes 206Pb, 207Pb and 208Pb were measured via inductively coupled plasma mass spectrometry in sediments, water and freshwater mussels (Velesunio angasi) from two catchments in the Alligator Rivers Region, Australia. Sediment U and Pb concentrations were higher in Magela Creek downstream than upstream of the Ranger U mine due to the mineralised nature of the catchment and potential local input of sediment from the mine site. Water metal concentrations were highest in Georgetown Creek, which is a tributary of Magela Creek and part drains the Ranger mine site, but there was little difference in concentrations between the Magela Creek upstream and downstream sites. Metal concentrations in mussels collected immediately upstream and downstream of the mine site also showed little difference, whereas Pb isotope ratios displayed a very distinct pattern. The 206Pb/207Pb and 208Pb/207Pb isotope ratios were more uranogenic downstream than upstream of the site and also more uranogenic than ratios measured in Sandy Billabong, a reference billabong in a catchment not influenced by U mineralisation. Isotope ratios were also more uranogenic in younger mussels, potentially due to the increasing footprint of the mine site over the past decade. The most uranogenic ratios were found in mussels from Georgetown Creek and at a site approximately 2 km downstream. At Mudginberri Billabong, approximately 12 km downstream of the Ranger mine, the relative contribution of uranogenic Pb to the total Pb concentration in mussels was small and overwhelmed by the input of industrial Pb with a Broken Hill type Pb signature. Whereas metal uptake by and thus concentrations in mussel flesh are influenced by water chemistry, mussel condition and metabolic rates, Pb isotope ratios are independent of these factors and provide a powerful means of source apportionment of contaminants in mussels and waterways, in particular in an U mining environment.

► Measured S oxidation rates in a nutrient solution were 9.9 × 10−4 (6°C) to 6.2 × 10−3 (32°C) μg S0 cm-2 d-1 (Q10  ≈ 1.6-1.9). ► Measured S oxidation rates in a DI water solution were (3.8-4.9 × 10−4 μg S0 cm−2 d−1) and did not increase with temperature. ► Based on in situ hybridization analyses, > 95% of total SO4 2- generated is attributed to autotrophic microbial activity. ► Essentially all oxygen incorporated into generated SO4 2- during oxidation originates from water.Globally escalating excess supplies of elemental S (S0) are often stored in large outdoor S0 blocks that are exposed over time to the environment. Here S0 oxidation experiments were conducted under ambient conditions to investigate (i) the rate of S0 oxidation at a range of ambient temperatures (6–32 °C) in the presence and absence of Acidithiobacillus thiooxidans and (ii) the O- and S-isotope fractionation during oxidation to identify sources of O incorporated into the resulting SO 4 2 - . Experiments were conducted using four different δ18OH2O values in a nutrient and nutrient free solution. Results showed that >95% of total SO 4 2 - generated could be attributed to autotrophic microbial activity. Experiments conducted in the nutrient solution showed oxidation rates increased with temperature (Q 10  ≈ 1.7–1.9); while experiments conducted in a nutrient-free solution showed no increase in oxidation rate with temperatures between 12 and 32 °C. The contribution of water-derived O to SO 4 2 - by S0 oxidation ranged from 84% to 97% for all treatments. The final δ18O(SO4) value indicated nearly all SO 4 2 - oxygen originates from water, and the ε 18OSO4–H2O was estimated to be between −0.9‰ and −6.2‰ with a mean of −3.6 ± 2.7‰ for the nutrient tests and +1.1‰ to −3.4‰ with a mean of −1.5 ± 2.4‰ for nutrient free tests. A relationship between the proportions of water O incorporated from O2 or water into the SO 4 2 - and temperature was not observed. The δ34S data showed that the oxidation of S0 produces SO 4 2 - with a δ34S value that is nearly indistinguishable from the parent S0. The findings suggest that SO 4 2 - accumulation in S0 block effluent would be minimized by limiting H2O influx and preventing microbial inhabitation of the block.

In 2001 a surface geochemical survey was carried out in the Carpathian Foredeep, in the area between Jarosław and Radymno (SE Poland) where multihorizon gas deposits were discovered. These deposits accumulate microbial CH4 with small amounts of N2 and higher molecular weight gaseous hydrocarbons. Soil–gas composition in the hydrocarbon fields in the study area is relatively different from the original composition of natural gas occurring in the subsurface reservoir. In 449 analyzed soil gas samples collected from 1.2 m depth relatively low concentrations were found for CH4 (median value 2.2 ppm) and its homologues (median value of total alkanes C2–C4 – 0.02 ppm). Alkenes were encountered in 36.3% of the analyzed samples (mean value of total alkenes C2–C4 – 0.015 ppm) together with distinctly higher concentrations of H2 (maximum value – 544 ppm, mean value – 42 ppm) and CO2 (maximum value – 10.26 vol.%, mean value – 2.27 vol.%). Individual, very high concentrations of CH4 (up to about 35 vol.%) resulted from sub-surface biochemical reactions whereas higher alkanes detected in soil gases (up to about 68 ppm) originated from deep gas accumulations. Both the H2 and alkenes may be indirect indicators of deep hydrocarbon accumulations. Carbon dioxide may also be useful for hydrocarbon exploration, revealing increased concentrations in those sampling sites where CH4 concentrations are strongly depleted, presumably due to bacterial oxidation. These relationships are valid only for the study area and should not be extended as an universal principle.The interpreted zones of cumulative anomalies of CH4, higher molecular weight gaseous hydrocarbons, H2 and CO2 related to the results of geological and geophysical studies directly or indirectly point to the presence of undiscovered, deep gas accumulations and suggest larger sizes for known deposits. The character of the anomalies along with the relationships between the components of soil gases support the opinion that gas accumulations occur at various depths. Moreover, the results indicate that the surface geochemical pattern is significantly influenced by tectonic discontinuities.

► Travertine deposition at Huanglong decreased greatly compared to early 1990s. ► The decrease in deposition may result from the phosphate inhibition of calcite. ► It was the tourism activities that introduced more phosphate into water. ► Water-temperature and dilution showed also controls on travertine deposition.Huanglong, well known for its unique natural travertine landscape, was listed by UNESCO as an entry in the World’s Nature Heritage in 1992, and attracts more than one million of tourists from all over the world each year. However, the landscape has undergone significant degradation (notably, serious decay of travertine) during the past two decades as the tourist numbers have increased remarkably. To understand the variations of travertine deposition rates and their controlling factors, especially the impact of tourism activities, paired water and modern travertine samples deposited on plexiglass substrates were taken along the Huanglong stream at regular intervals from early May to early November in 2010 (i.e., in the wet season). The travertine deposition rates have declined significantly compared to those in early 90s in all four subsystems in the Huanglong Ravine. The largest decrease (89.5%) occurred at the lowest sampling site. The reduction in travertine deposition most likely resulted from the phosphate pollution caused by the tourism activities. In spite of an increase in concentrations of Ca, calcite saturation, and water temperature, which facilitate calcite precipitation, deposition rates decreased because of inhibition by PO 4 3 - ions. Seasonally, three control patterns of travertine deposition rates were distinguished along the Ravine. They are control by water-temperature, control by dilution of rainwater and snow-melting water and control by PO4-inhibition of calcite precipitation.

Surface heat flow and CO2 emissions within the Ohaaki hydrothermal field, Taupo Volcanic Zone, New Zealand by Clinton Rissmann; Bruce Christenson; Cynthia Werner; Matthew Leybourne; Jim Cole; Darren Gravley (223-239).
► Surface heat flow and CO2 emissions were measured after 20 years of production. ► Thermal feature response is dependent on feature type and reservoir permeability. ► Despite production, CO2 flux and heat flow reflect reservoir geochemical models. ► Stable isotopes of soil gas define gas transport and CO2 source.Carbon dioxide emissions and heat flow have been determined from the Ohaaki hydrothermal field, Taupo Volcanic Zone (TVZ), New Zealand following 20 a of production (116 MWe). Soil CO2 degassing was quantified with 2663 CO2 flux measurements using the accumulation chamber method, and 2563 soil temperatures were measured and converted to equivalent heat flow (W m−2) using published soil temperature heat flow functions. Both CO2 flux and heat flow were analysed statistically and then modelled using 500 sequential Gaussian simulations. Forty subsoil CO2 gas samples were also analysed for stable C isotopes. Following 20 a of production, current CO2 emissions equated to 111 ± 6.7 T/d. Observed heat flow was 70 ± 6.4 MW, compared with a pre-production value of 122 MW. This 52 MW reduction in surface heat flow is due to production-induced drying up of all alkali–Cl outflows (61.5 MW) and steam-heated pools (8.6 MW) within the Ohaaki West thermal area (OHW). The drying up of all alkali–Cl outflows at Ohaaki means that the soil zone is now the major natural pathway of heat release from the high-temperature reservoir. On the other hand, a net gain in thermal ground heat flow of 18 MW (from 25 MW to 43.3 ± 5 MW) at OHW is associated with permeability increases resulting from surface unit fracturing by production-induced ground subsidence. The Ohaaki East (OHE) thermal area showed no change in distribution of shallow and deep soil temperature contours despite 20 a of production, with an observed heat flow of 26.7 ± 3 MW and a CO2 emission rate of 39 ± 3 T/d. The negligible change in the thermal status of the OHE thermal area is attributed to the low permeability of the reservoir beneath this area, which has limited production (mass extraction) and sheltered the area from the pressure decline within the main reservoir. Chemistry suggests that although alkali–Cl outflows once contributed significantly to the natural surface heat flow (∼50%) they contributed little (<1%) to pre-production CO2 emissions due to the loss of >99% of the original CO2 content due to depressurisation and boiling as the fluids ascended to the surface. Consequently, the soil has persisted as the major (99%) pathway of CO2 release to the atmosphere from the high temperature reservoir at Ohaaki. The CO2 flux and heat flow surveys indicate that despite 20 a of production the variability in location, spatial extent and magnitude of CO2 flux remains consistent with established geochemical and geophysical models of the Ohaaki Field. At both OHW and OHE carbon isotopic analyses of soil gas indicate a two-stage fractionation process for moderate-flux (>60 g m−2  d−1) sites; boiling during fluid ascent within the underlying reservoir and isotopic enrichment as CO2 diffuses through porous media of the soil zone. For high-flux sites (>300 g m−2  d−1), the δ 13CO2 signature (−7.4 ± 0.3‰ OHW and −6.5 ± 0.6‰ OHE) is unaffected by near-surface (soil zone) fractionation processes and reflects the composition of the boiled magmatic CO2 source for each respective upflow. Flux thresholds of <30 g m−2  d−1 for purely diffusive gas transport, between 30 and 300 g m−2  d−1 for combined diffusive–advective transport, and ⩾300 g m−2  d−1 for purely advective gas transport at Ohaaki were assigned. δ 13CO2 values and cumulative probability plots of CO2 flux data both identified a threshold of ∼15 g m−2  d−1 by which background (atmospheric and soil respired) CO2 may be differentiated from hydrothermal CO2.

► We present a graphical and statistical tool to assess geochemical background levels. ► Confidence intervals provide a useful measure of uncertainty of median values. ► We demonstrate the procedure on data from the Talvivaara Ni–Cu–Co–Zn–Mn deposit. ► Acid rock drainage was evident under pre-mining conditions at Talvivaara. ► Chemical concentrations of 544 organic and 102 minerogenic stream sediment samples.Geochemical background levels and pre-mining conditions can be defined and quantified in several ways with different outcomes. Numerous authors have attacked the background assessment problem by generating various statistical procedures for estimating the level or threshold for concentrations assumed to represent the background. None of the methods have been generally accepted as a de facto standard. Some methods assume a normal distribution, leading to trimming or normalization procedures and some are based on more generally applicable non-parametric methods. The uncertainties always present in geochemical data are rarely reported with background levels. In this study the geochemical background is considered as the range of levels anchored at the time of sampling under pre-mining conditions. A statistical description of a distribution assumed to represent such a background is suggested including the non-parametric median, confidence interval of the median and a modified beanplot, which illustrate the variation and uncertainty of the data. The procedure is demonstrated on data from the vicinity of the Talvivaara black shale -hosted Ni–Cu–Co–Zn–Mn mine in eastern Finland, and the differences in levels between the mineralized and non-mineralized subareas in stream sediments and stream water are presented. The sampled materials are well-decomposed organic stream sediments (259 samples), poorly decomposed organic stream sediments (285 samples), minerogenic stream sediments (102 samples), and stream water (149 samples). The median values for Cu, Fe, Ni, Pb and Zn are significantly higher in mineralized subareas than in non-mineralized subareas in organic stream sediments and minerogenic stream sediments. In stream waters Cu, Ni and Zn behave similarly showing a significant difference. The results show that the average geochemical background in stream sediments and stream water can vary significantly across lithologies, and that medians with confidence intervals together with diagrams depicting the distributions in detail, such as beanplots, are useful tools for assessing and illustrating the background levels.

Diffusion, degradation or on-site stabilisation – Identifying causes of kinetic processes involved in metal–humate complexation by Holger Lippold; Sascha Eidner; Michael U. Kumke; Johanna Lippmann-Pipke (250-256).
► Stabilisation processes for metal–humate complexes occur on different time scales. ► In-diffusion of metals to strong internal sites can be ruled out as an explanation. ► Polynuclear metal species in touch with humic colloids are not generally metastable. ► Structural changes around humic-bound metals were spectroscopically detected.The applicability of equilibrium models for humic-bound transport of toxic or radioactive metals is affected by kinetic processes leading to an increasing inertness of metal–humic complexes. The chemical background is not yet understood. It is widely believed that bound metals undergo an in-diffusion process within the humic colloids, changing from weaker to stronger binding sites. This work is focussed on the competition effect of Al(III) on complexation of Tb(III) or Eu(III) as analogues of trivalent actinides. By using ion exchange and spectroscopic methods, their bound fractions were determined for solutions of Al and humic acid that had been pre-equilibrated for different periods of time. Whilst the amount of bound Al remained unchanged, its blocking effect was found to increase over a time frame of 2 days, which corresponds to the kinetics of the increase in complex inertness reported in most pertinent studies. Thus, the derived “diffusion theory” turned out to be inapplicable, since it cannot explain an increase in competition for the “initial” sites. A delayed degradation of polynuclear species (as found for Fe) does not occur. Consequently, the temporal changes must be based on structural rearrangements in the vicinity of bound Al, complicating the exchange or access. Time-dependent studies by laser fluorescence spectroscopy (steady-state and time-resolved) yielded evidence of substantial alterations, which were, however, immediately induced and did not show any significant trend on the time scale of interest, suggesting that the stabilisation process is based on comparatively moderate changes.

Semi-automatic determination of the carbon and oxygen stable isotope compositions of calcite and dolomite in natural mixtures by M. Baudrand; G. Aloisi; C. Lécuyer; F. Martineau; F. Fourel; G. Escarguel; M.-M. Blanc-Valleron; J.-M. Rouchy; V. Grossi (257-265).
► This method allows the determination of δ 13C and δ 18O of dolomite and calcite mixtures. ► It combines XRD measurements and automated isotopic measurements. ► It is designed for a MultiPrep™ system online with a Dual-Inlet Isoprime™ IRMS. ► The measurements are fast and repeatable for sample size as low as 300 μg. ► Errors are evaluated with a Monte-Carlo procedure of error propagation.A semi-automatic, on-line method was developed to determine the δ 13C and δ 18O values of coexisting calcite and dolomite. An isotopic mass balance is used to calculate the compositions of dolomite after having measured that of calcite and of the “bulk” sample. The limit of validity of this method is established by performing isotopic measurements of artificial mixtures made of precisely weighted and isotopically-characterised dolomite and calcite. The accuracy and repeatability of the calculation of dolomite δ 13C and δ 18O are statistically determined with a Monte-Carlo procedure of error propagation. Stable isotope ratios are determined by using an automated MultiPrep™ system on-line with an isotope-ratio mass-spectrometer (IRMS). The reaction time and the temperature of reaction were optimised by comparing the results with the isotopic composition of known mixtures. The best results were obtained by phosphoric acid digestion after 20 min at 40 °C for calcite and 45 min at 90 °C for dolomite. This procedure allows an accurate determination of the isotopic ratios from small samples (300 μg). Application of this protocol to natural mixtures of calcite and dolomite requires the accurate determination of the relative abundance of calcite and dolomite by combining Mélières manocalcimetry (MMC) and X-ray diffractometry (XRD).

► Groundwater mixing in travertine aquifer has been enhanced by groundwater extraction. ► Chemical and isotope tracers distinguish different sources and groundwater flowpaths. ► Geochemical modeling results confirm a conceptual model inferred from collected data. ► Previous equal contribution from different sources is changing now in a 1:2 proportion. ► Geochemical changes along flowpaths evidence that the aquifer is a dynamic system.In the Tivoli Plain (Rome, Central Italy) the interaction between shallow and deep groundwater flow systems enhanced by groundwater extraction has been investigated using isotopic and chemical tracers. A conceptual model of the groundwater flowpaths has been developed and verified by geochemical modeling. A combined hydrogeochemical and isotopic investigation using ion relationships such as DIC/Cl, Ca/(Ca + Mg)/SO4/(SO4  + HCO3), and environmental isotopes (δ 18O, δ 2H, 87Sr/86Sr, δ 34S and δ 13C) was carried out in order to determine the sources of recharge of the aquifer, the origin of solutes and the mixing processes in groundwater of Tivoli Plain. Multivariate statistical methods such as principal component analysis and Cluster analyses have confirmed the existence of different geochemical facies and the role of mixing in the chemical composition of the groundwater.Results indicate that the hydrochemistry of groundwater is characterized by mixing between end-members coming directly from carbonate recharge areas and to groundwater circulating in a deeply buried Meso-Cenozoic carbonate sequence. The travertine aquifer is fed by both flow systems, but a local contribution by direct input in the Plain has also been recognized. The stable isotope data (18O, 2H, 13C and 34S) supports the flow system conceptual model inferred from the geochemical data and represents key data to quantify the geochemical mixing in the different groundwaters of the Plain. The results of numerical modeling (PHREEQC) are consistent with the flowpaths derived from the hydrogeochemical conceptual model. The inverse models performed generated the main geochemical processes occurring in the groundwater flow system, which also included mixing. Geochemical and isotope modeling demonstrate an increasing influence of groundwater from the deeply buried aquifer in the travertine aquifer, enhanced by lowering of the travertine aquifer water table due to quarry pumping.

► At circumneutral pH As and Sb oxidation was catalyzed by microbes. ► At acid pH As and Sb are oxidized abiotically by Fe(III). ► At acid pH Fe(III) was formed by microbial oxidation. ► In abiotic Fe(III)-solutions, Sb oxidizes slightly faster than As. ► Oxidation rates increased by increasing As, Sb, Fe(III), and Cl with light.Arsenic and Sb are common mine-water pollutants and their toxicity and fate are strongly influenced by redox processes. In this study, simultaneous Fe(II), As(III) and Sb(III) oxidation experiments were conducted to obtain rates under laboratory conditions similar to those found in the field for mine waters of both low and circumneutral pH. Additional experiments were performed under abiotic sterile conditions to determine the biotic and abiotic contributions to the oxidation processes. The results showed that under abiotic conditions in aerated Fe(III)–H2SO4 solutions, Sb(III) oxidizes slightly faster than As(III). The oxidation rates of both elements were accelerated by increasing As(III), Sb(III), Fe(III), and Cl concentrations in the presence of light. For unfiltered circumneutral water from the Giant Mine (Yellowknife, NWT, Canada), As(III) oxidized at 15–78 μmol/L/h whereas Sb(III) oxidized at 0.03–0.05 μmol/L/h during microbial exponential growth. In contrast, As(III) and Sb(III) oxidation rates of 0.01–0.03 and 0.01–0.02 μmol/L/h, respectively, were obtained in experiments performed with acid unfiltered mine waters from the Iberian Pyritic Belt (SW Spain). These results suggest that the Fe(III) formed from microbial oxidation abiotically oxidized As(III) and Sb(III). After sterile filtration of both mine water samples, neither As(III), Sb(III), nor Fe(II) oxidation was observed. Hence, under the experimental conditions, bacteria were catalyzing As and Sb oxidation in the Giant Mine waters and Fe oxidation in the acid waters of the Iberian Pyrite Belt.

Dissolved organic carbon from the traditional jute processing technique and its potential influence on arsenic enrichment in the Bengal Delta by S.H. Farooq; D. Chandrasekharam; G. Abbt-Braun; Z. Berner; S. Norra; D. Stüben (292-303).
► Paper highlights the excessive production of DOC on the surface of Bengal Delta. ► We examined the interaction of DOC derived from jute processing with sub surface sediments. ► Paper experimentally proves the potential of DOC in mobilizing arsenic from sediments to groundwater. ► Study also shows the threat to groundwater resources if DOC production on surface continues.Dissolved organic C (DOC) plays an important role in the mobilization of As from sediments. In West Bengal, the widely used technique for obtaining jute fiber involves retting of the jute plant in ponds (hereafter such ponds are termed jute decomposing ponds) for several weeks, which produces significant amounts of DOC in the ponds. These ponds thus act as point sources of DOC and supply huge quantities of organic C to the Bengal Delta sediments. This study has been carried out to investigate the role of such DOC in enriching the groundwater with As in the Bengal Delta. Data clearly show that due to the effect of DOC, As is mobilized from the upper 2.6 m of the sediment profile, and is fixed between 2.6 and 6.1 m, while the lower part (6.1–9 m) largely remains unaffected. The reducing conditions mainly developed due to the decay of the percolating DOC seem to help the mobilization and transportation of As and other redox sensitive elements (Fe, Mn), as well as elements (Cu, Zn) attached to oxy-hydroxides of those redox-sensitive elements. Experiments also indicate that if the DOC production at the surface continues for a longer period of time, the zone of As fixation (2.6–6.1 m) may get shifted further downwards and ultimately intercept the water table resulting in As enrichment of groundwater.

Arsenic exists in a variety of chemical forms, and microbial metabolism results in the occurrence of thermodynamically unstable arsenite (AsIII) and methylarsenic compounds in freshwaters (rivers and lakes). The inorganic forms (AsV and AsIII) and the methylated forms (methylarsonic acid; MMAAV and dimethylarsinic acid; DMAAV) are the main species of As in freshwaters while the bulk of the total dissolved As is inorganic species. Although the predominant forms of methylarsenic compounds are consistently DMAAV followed by MMAAV, the DMAAIII and MMAAIII species have also been found in freshwaters. Several observations have revealed that phytoplankton activities are responsible for the seasonal variations of methylarsenic compounds in freshwaters. Although it was unclear if the occurrences of methylarsenic compounds were from the breakdown of larger molecules or the end-products of phytoplankton biosynthesis, recent studies have revealed that less toxic As–glutathione complexes are intermediates in the biosynthesis of organoarsenic compounds by phytoplankton. Recent studies have also revealed that eutrophication plays an important role in the production, distribution, and cycling of methylarsenic compounds in freshwaters. In this review, the recent reports on the influence of eutrophication on distribution, speciation, and bioaccumulation in freshwaters are discussed.

Characterisation of organic matter and microbial communities in contrasting arsenic-rich Holocene and arsenic-poor Pleistocene aquifers, Red River Delta, Vietnam by Wafa M. Al Lawati; Athanasios Rizoulis; Elisabeth Eiche; Christopher Boothman; David A. Polya; Jonathan R. Lloyd; Michael Berg; Patricio Vasquez-Aguilar; Bart E. van Dongen (315-325).
► First lipid analysis of Pleistocene aquifer sediments from a groundwater As-prone region. ► No difference in lipids between (As-rich) Holocene and (As-poor) Pleistocene aquifers. ► Lack of in situ microbially mediated As mobilisation in any of the sediments. ► Groundwater As at depth controlled by As mobilisation processes elsewhere.High concentrations of geogenic As in the groundwaters of south and SE Asia, which are used as drinking waters, are causing severe health impacts to the exposed human populations. It is widely accepted that As mobilisation from sediments into these shallow reducing groundwaters requires active metal-reducing microbes and electron donors such as organic matter (OM). Although OM in such Holocene aquifers has been characterised, there is a dearth of data on Pleistocene aquifers from the same areas. Reported here are preliminary studies of OM and microbial communities present in two aquifers, one of Pleistocene and one of Holocene age, with contrasting concentrations of As (viz. Pleistocene: low As <10 μg/L; Holocene: high As up to 600 μg/L) from Van Phuc village in the Red River Delta, Vietnam. Results revealed OM inputs from multiple sources, including potential contributions from naturally occurring petroleum seeping into the shallow aquifer sediments from deeper thermally mature source rocks. Although concentrations vary, no noticeable systematic differences in biomarker distribution patterns within the OM were observed between the two sites. Microbial analyses did not show a presence of microbial communities previously associated with As mobilisation. All clone libraries were dominated by α-, β-, and γ-Proteobacteria not known to be able to reduce Fe(III) or sorbed As(V). Furthermore, representatives of the Fe(III)-reducing genus Geobacter could only be detected at very low abundance by PCR, using highly selective 16S rRNA gene primers, supporting the hypothesis that metal reduction is not a dominant in situ process in these sediments. No correlation between As concentration in groundwater and OM composition nor microbial community in the host sediments was found. This suggests that either (i) As is not being significantly mobilised in situ in these sediments, instead As appears to be mobilised elsewhere and transported by groundwater flow to the sites or (ii) sorption/desorption processes, as implicated by geochemical data from the cores, play a critical role in controlling As concentrations at these sites.

► Water residence time indirectly affects the release of As by controlling the pH. ► Ca2+ ions greater than ca. 50 mg/L retard the mobility of As. ► Mechanisms of As release include dissolution, pyrite oxidation and adsorption. ► As[V] is the dominant As species released from the altered rock. ► Speciation of As is controlled by the pH dependent adsorption of As species.This paper describes the mobilization and speciation of As found in hydrothermally altered rock under oxic column conditions. The altered rock sample was obtained from a tunnel project located in the Nakakoshi area of Hokkaido, Japan, whose geology is represented by slate, shale and sandstone. This area has undergone silicification, pyritization and argillic alteration resulting in As-enrichment of the rock. Results of the column experiments show that the infiltration rate, bulk density and rock bed thickness affected the duration of water residence, which in turn influenced the pH of the rock–water system. Coexisting ions most notably Ca2+ at amounts greater than ca. 50 mg/L retarded the mobilization of As. Mobilization of As from the rock with time occurred in two stages: stage 1 (weeks 1–20) with higher As leaching and stage 2 (weeks 20–76) characterized by nearly constant As release. In addition, pore water As concentrations revealed that the columns developed into two regions: the top half where most of the leaching occurred and the bottom part dominated by adsorption. Thus, the mechanism controlling the mobilization of As from the rock is a combination of one or more of the following processes: dissolution of soluble As-bearing fractions, pyrite oxidation and adsorption reactions. Arsenite (As[III]) was the dominant species in the effluent at the start of the experiment in columns with shorter water residence time and lower pH conditions (<8). On the other hand, arsenate (As[V]) was the major inorganic species released from the rock at higher pH (8–9.5) and when the system was close to equilibrium. Speciation of As with depth also indicated that As[III] disappeared around the bottom half of the columns, probably as a result of adsorption and/or oxidation. Arsenic speciation is partially controlled by the pH dependent adsorption of As species. The important adsorbent phases in the rock included Fe–Al oxides/oxyhydroxides, clay minerals and organic matter, which permitted the columns to attenuate additional As loadings including As[III]. Implications of these results on the design of a novel disposal method for these altered rocks include the enhancement of As adsorption through the addition of natural or artificial adsorbents and the utilization of a covering soil with low permeability to minimize rainwater infiltration into the rock.

The distribution of total mercury and methyl mercury in a shallow hypereutrophic lake (Lake Taihu) in two seasons by Shaofeng Wang; Denghua Xing; Yonfeng Jia; Biao Li; Kuanling Wang (343-351).
► We investigated Hg speciation and distribution in a large-shallow hypereutrophic lake. ► Total Hg in lake water was significantly elevated, nor did methyl Hg. ► Hg diffusion from sediment contributed greatly to the elevation of THg in lake water. ► Elevated organic material loading in sediments did not enhance net rate of Hg methylation.To understand the geochemical cycle of Hg in hypereutrophic freshwater lake, two sampling campaigns were conducted in Lake Taihu in China during May and September of 2009. The concentrations of unfiltered total Hg (unfTHg) were in the range of 6.8–83 ng L−1 (28 ± 18 ng L−1) in the lake water and total Hg in the sediment was 12–470 ng g−1, both of which are higher than in other background lakes. The concentration of unfTHg in ∼11% of the lake water samples exceeded the second class of the Chinese environmental standards for surface water of 50 ng L−1 (GB 3838-2002), indicating that a high ecological risk is posed by the Hg in Lake Taihu. However, the concentrations of unfiltered total MeHg (unfMeHg) were relatively low in the lake water (0.14 ± 0.05 ng L−1, excluding two samples with 0.81 and 1.0 ng L−1). Lake sediment MeHg varied from 0.2–0.96 ng g−1, with generally low ratios of MeHg/THg of <1%. The low concentrations of TMeHg in the lake water may have resulted from a strong uptake by the high primary productivity and the demethylation of MeHg in oxic conditions. In addition, contrary to the results of previous research conducted in deep-water lakes and reservoirs, the low concentrations of MeHg and low ratio of MeHg/THg in the lake sediment indicates that the net methylation of Hg was not accelerated by the elevated organic matter load created by the eutrophication of Lake Taihu. The results also showed that sediments were a source of THg and MeHg in the water. Higher diffusion fluxes of THg and MeHg may be partly responsible for the higher concentrations of THg in the lake water in May, 2009.

Recent paleorecords document rising mercury contamination in Lake Tanganyika by Christopher H. Conaway; Peter W. Swarzenski; Andrew S. Cohen (352-359).
► We studied Hg accumulation in lake sediment from Lake Tanganyika. ► Sediment Hg accumulation relates to changes in sedimentation and atmospheric Hg flux. ► Mercury in Lake Tanganyika has increased from the 19th century to the present.Recent Lake Tanganyika Hg deposition records were derived using 14C and excess 210Pb geochronometers in sediment cores collected from two contrasting depositional environments: the Kalya Platform, located mid-lake and more removed from watershed impacts, and the Nyasanga/Kahama River delta region, located close to the lake’s shoreline north of Kigoma. At the Kalya Platform area, pre-industrial Hg concentrations are 23 ± 0.2 ng/g, increasing to 74 ng/g in modern surface sediment, and the Hg accumulation rate has increased from 1.0 to 7.2 μg/m2/a from pre-industrial to present, which overall represents a 6-fold increase in Hg concentration and accumulation. At the Nyasanga/Kahama delta region, pre-industrial Hg concentrations are 20 ± 3 ng/g, increasing to 46 ng/g in surface sediment. Mercury accumulation rate has increased from 30 to 70 μg/m2/a at this site, representing a 2–3-fold increase in Hg concentration and accumulation. There is a lack of correlation between charcoal abundance and Hg accumulation rate in the sediment cores, demonstrating that local biomass burning has little relationship with the observed Hg concentration or Hg accumulation rates. Examined using a sediment focusing-corrected mass accumulation rate approach, the cores have similar anthropogenic atmospheric Hg deposition profiles, suggesting that after accounting for background sediment concentrations the source of accumulating Hg is predominantly atmospheric in origin. In summary, the data document an increase of Hg flux to the Lake Tanganyika ecosystem that is consistent with increasing watershed sediment delivery with background-level Hg contamination, and regional as well as global increases in atmospheric Hg deposition.

Carbon and hydrogen isotopic evidence for the origin of combustible gases in water-supply wells in north-central Pennsylvania by Kinga M. Révész; Kevin J. Breen; Alfred J. Baldassare; Robert C. Burruss (361-375).
► Stray gas origin. ► Methane. ► Isotope. ► Water wells.The origin of the combustible gases in groundwater from glacial-outwash and fractured-bedrock aquifers was investigated in northern Tioga County, Pennsylvania. Thermogenic methane (CH4) and ethane (C2H6) and microbial CH4 were found. Microbial CH4 is from natural in situ processes in the shale bedrock and occurs chiefly in the bedrock aquifer. The δ 13C values of CH4 and C2H6 for the majority of thermogenic gases from water wells either matched or were between values for the samples of non-native storage-field gas from injection wells and the samples of gas from storage-field observation wells. Traces of C2H6 with microbial CH4 and a range of C and H isotopic compositions of CH4 indicate gases of different origins are mixing in sub-surface pathways; gas mixtures are present in groundwater. Pathways for gas migration and a specific source of the gases were not identified. Processes responsible for the presence of microbial gases in groundwater could be elucidated with further geochemical study.