Applied Geochemistry (v.25, #12)

Modelling of bentonite–granite solutes transfer from an in situ full-scale experiment to simulate a deep geological repository (Grimsel Test Site, Switzerland) by B. Buil; P. Gómez; J. Peña; A. Garralón; M.J. Turrero; A. Escribano; L. Sánchez; J.M. Durán (1797-1804).
► The FEBEX experiment is a 1:1 simulation of a high level waste disposal facility in crystalline rock according to the Spanish radwaste disposal concept. ► Solute transfer processes occurrs at the bentonite–granite interface. ► An increase of Cl and Na is observed in granitic water of the surrounding of the experiment. ► Solute transfer does not affect the sealing and thermo-hydromechanical properties of the engineered barriers. ► A diffusive transport of Cl and Na simulated by 1D transport modeling with an effective diffusion coefficient of De  ≅ 5.0 E-11 m2/s.The FEBEX experiment is a 1:1 simulation of a high level waste disposal facility in crystalline rock according to the Spanish radwaste disposal concept. This experiment has been performed in a gallery drilled in the underground laboratory Grimsel Test Site (Switzerland). Two boreholes parallel to the FEBEX drift were drilled 20 and 60 cm away from the granite–bentonite interface to provide data on potential bentonite–granite solutes transfer. Periodic sampling and analysis of the major ions showed: (a) the existence of solutes transfer from the bentonite porewater towards the granite groundwater, explaining the Cl and Na+ contents of the latter; (b) that the concentration of the natural tracers coming into the granite groundwater from the bentonite porewater increased over time. This bentonite–granite solutes transfer was modelled in order to predict the increase in the Cl and Na+ concentrations of the granite groundwater. The modelled results seem to confirm that the mechanism of solute migration in this scenario is that of diffusive transport. An effective diffusion coefficient of De  = 5 × 10−11  m2/s was that which best fitted the data obtained.

Arsenic-enriched aquifers: Occurrences and mobilization of arsenic in groundwater of Ganges Delta Plain, Barasat, West Bengal, India by Sandeep Kar; Jyoti Prakash Maity; Jiin-Shuh Jean; Chia-Chuan Liu; Bibhash Nath; Huai-Jen Yang; Jochen Bundschuh (1805-1814).
► Groundwater is mostly Ca-HCO3 type and anoxic in Barasat, West Bengal, a part of Gangetic plain. ► High As (mostly As-III) present in the shallow aquifer depth (30–50 m). ► Presence of DOC in groundwater may actively drive the redox processes. ► A conceptual model shows arsenic release mechanism and mobilization process. ► Study supports microbially mediated reductive dissolution of Fe-oxyhydroxide for arsenic release to groundwater.Hydrogeochemical characteristics and elemental features of groundwater and core sediments have been studied to better understand the sources and mobilization process responsible for As-enrichment in part of the Gangetic plain (Barasat, West Bengal, India). Analysis of water samples from shallow tubewells (depth 24.3–48.5 m) and piezometer wells (depth 12.2–79.2 m) demonstrate that the groundwater is mostly the Ca-HCO3 type and anoxic in nature (mean EhSHE  = 34 mV). Arsenic concentrations ranged from <10–538 μg/L, with high concentrations only present in the shallow to medium depth (30–50 m) of the aquifer along with high Fe (0.07–9.8 mg/L) and relatively low Mn (0.15–3.38 mg/L) as also evidenced in core sediments. Most groundwater samples contained both As(III) and As(V) species in which the concentration of As(III) was generally higher than that of As(V), exhibiting the reducing condition. Results show lower concentrations of NO3, SO4 and NO2 along with higher values of DOC and HCO3, indicating the reducing nature of the aquifer with abundant organic matter that can promote the release of As from sediments into groundwater. Positive correlations of As with Fe and DOC were also observed. The presence of DOC may actively drive the redox processes. This study revealed that reduction processes of FeOOH was the dominant mechanism for the release of As into the groundwater in this part of the Ganges Delta plain.

► Efflorescent salts of Cu and Co precipitate at Kabwe site in Zambia during long-term dry period. ► They comprise an assemblage of Cu and Co minerals, some of them are very exotic in nature. ► Evaporation experiment in laboratory gave more hydrated forms of minerals found in the field. ► During rainy period, efflorescent salts dissolve with resulting high metals and acid pulse. ► During on-going climatic change, environmental impact may become more serious.Precipitated efflorescent salts in Cu–Co chemical leaching plant wastes in Kabwe, Zambia, have been studied using XRF analysis, powder X-ray diffraction, scanning electron microscopy (SEM), Raman spectroscopy, and evaporation experiments combined with geochemical modeling. Field samples of efflorescent salts contained up to 14.32 wt% Cu and 1.42 wt% Co. In the field, the principal minerals in the salts were gypsum (CaSO4·2H2O), moorhouseite (Co0.6Ni0.3 Mn 0.1 2 + (SO4)·6H2O), bloedite (Na2Mg(SO4)2·4H2O), starkeyite (MgSO4·4H2O), chalcanthite (CuSO4·5H2O) and kroehnkite (Na2Cu(SO4)2·2H2O). In the evaporation experiment, gypsum precipitated in the first and second evaporation steps, chalcanthite and bieberite (CoSO4·7H2O), started to precipitate in Step 3, after evaporation of 60% of water, and maximum amounts of Cu and Co sulfate salts accumulated in Step 4 after precipitation of 80% of water. Epsomite (MgSO4·7H2O), and hexahydrite (MgSO4·6H2O), precipitated only after evaporation of 97.5% of water in Step 5. Presence of chalcanthite, bloedite, and kroehnkite in precipitates of Step 4 was also confirmed by Raman spectroscopy. Magnesium and Na content in Cu and Co-sulfate phases gradually increased with evaporation progress, e.g. bieberite was replaced by Co-bloedite and chalcanthite was replaced by kroehnkite in later stages of evaporation. The precipitation order was consistent with results of geochemical modeling. The principal difference between field data and data obtained in the evaporation experiment was the presence of less hydrated sulfate phases in the field, which can be explained by different time scales available for evaporation and consecutive dehydration. Dissolution experiments using efflorescent salts collected in the field indicated fast dissolution with an instantaneous drop in pH to about 4.0 and a very fast increase of dissolved species concentrations. Such behavior may have a serious environmental impact at the beginning of the rainy period in November and December, when seepage through the impoundment dam was recorded. The wastes at the Kabwe site represent a long-term source of contamination, which may be especially significant as a consequence of on-going climatic change with increasing intensity of precipitation.

Nutrient availability correlates with bicarbonate accumulation in marine and freshwater sediments – Empirical evidence from pore water analyses by Tjisse van der Heide; Alfons J.P. Smolders; Leon P.M. Lamers; Marieke M. van Katwijk; Jan G.M. Roelofs (1825-1829).
► Bicarbonate correlates with ammonium and o-phosphate in pore waters of marine and freshwater sediments. ► Bicarbonate also correlates with sulfide levels in marine sediments. ► No relation was found with variables describing total nutrient content.In the last decades, eutrophication has become a major cause for concern in aquatic ecosystems worldwide. Apart from external nutrient loading, release of dissolved nutrients from sediment pore water into the water layer contributes importantly to eutrophication. Theory implies that pore water HCO 3 - and nutrient mobility are linked, because anaerobic organic matter breakdown stimulates release of HCO 3 - and nutrients, while HCO 3 - stimulates decay rates by increasing buffer capacity and pH. An investigation was performed on how HCO 3 - relates to commonly measured eutrophication-related variables in freshwater and marine sediments, by analyzing a database of 71 marine and 206 freshwater samples, using linear and non-linear regression. Results demonstrate that HCO 3 - is indeed strongly related with NH 4 + and PO 4 3 - in both freshwater and marine pore waters. Moreover, HCO 3 - also correlated with sulfide levels in marine sediments. Contrastingly, no relationship was found with variables describing total nutrient content (i.e. organic matter, total P and N), suggesting that these do not reveal information on nutrient availability in aquatic sediments.

Study of Ni sorption onto Tio mine waste rock surfaces by B. Plante; M. Benzaazoua; B. Bussière; M.C. Biesinger; A.R. Pratt (1830-1844).
► The minerals composing the Tio mine waste rocks possess different sorption capacities. ► The plagioclase and ilmenite minerals are the major sorbing phases of the fresh waste rocks. ► Sequential extractions suggest that most sorption sites are associated with reducible fractions. ► XPS studies on sorbed surfaces suggest that Ni is sorbed as the hydroxide, Ni(OH)2. ► The semi-quantitative prediction of sorption capacities of simple mineral assemblages is feasible from the sorption capacities of the individual components.Sorption phenomena are known to play significant roles in metal mobility in mine drainage waters. The present study focuses on sorption phenomena controlling Ni concentrations in contaminated neutral drainage issued from the waste rock piles of the Tio mine, a hematite–ilmenite deposit near Havre-Saint-Pierre, Québec, Canada exploited by Rio Tinto Iron and Titanium. Batch sorption tests were conducted on waste rock samples of different composition and degree of alteration, as well as on the main mineral phases purified from the waste rocks. Sorbed phases were submitted to sequential extractions, XPS and DRIFT studies for further interpretation of sorption phenomena. The results from the present study confirm that sorption phenomena play a significant role in the Tio mine waste rocks, and that the main sorbent phases are the residual ilmenite ore in waste rocks, as well as plagioclase, the main gangue mineral. Sequential extractions suggest that most sorption sites are associated with reducible fractions, and XPS results indicate that Ni is sorbed as the hydroxide Ni(OH)2. The results from the present study provide useful information on sorption phenomena involved in the Tio mine waste rocks and enable further interpretation of Ni geochemistry in contaminated neutral drainage.

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 (1845-1859).
► 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.

The dynamics of central Main Ethiopian Rift waters: Evidence from δD, δ 18O and 87Sr/86Sr ratios by Tewodros Rango; Riccardo Petrini; Barbara Stenni; Gianluca Bianchini; Francesca Slejko; Luigi Beccaluva; Tenalem Ayenew (1860-1871).
► Chemical and isotope (δD, δ 18O and 87Sr/86Sr) techniques are applied to understand various hydrological processes in the Main Ethiopian Rift. ► Some of the studied groundwaters display a depleted δD–δ 18O composition when compared to the present-day average precipitation, thus suggesting that the rift floor aquifers also contains paleo-meteoric waters recharge associated with deep flow system. ► The pristine waters coming from the highlands display isotopic compositions characterized by less radiogenic 87Sr/86Sr (and more depleted δD, δ 18O). This isotopic signature subsequently evolves towards higher 87Sr/86Sr by an interaction with the more radiogenic rhyolites of the rift and their weathered and redeposited products.Water samples from cold and geothermal boreholes, hot springs, lakes and rivers were analyzed for δD, δ 18O and 87Sr/86Sr compositions in order to investigate lake water–groundwater mixing processes, water–rock interactions, and to evaluate groundwater flow paths in the central Main Ethiopian Rift (MER) of the Ziway–Shala basin. Different ranges of isotopic values were recorded for different water types: hot springs show δ 18O −3.36 to +3.69 and δD −15.85 to +24.23, deep Aluto-Langano geothermal wells show δ 18O −4.65 to −1.24 and δD −12.39 to −9.31, groundwater wells show δ 18O −3.99 to +5.14 and δD −19.69 to +32.27, whereas the lakes show δ 18O and δD in the range +3.98 to +7.92 and +26.19 to +45.71, respectively. The intersection of the Local Meteoric Water Line (LMWL: δD = 7 δ 18O + 11.2, R 2  = 0.94, n  = 42) and the Local Evaporation Line (LEL: δD = 5.63δ 18O + 8, n  = 14, R 2  = 0.82) was used to estimate the average isotopic composition of recharge water into the basin (δD = −5.15 and δ 18O = −2.34). These values are depleted if compared with the modern-day average precipitation, presumably indicating paleo-groundwater components recharged during previous humid climatic phases. The measured stable isotope values indicate that the geothermal wells, some of the hot springs and groundwater wells mainly consist of meteoric water. The Sr isotopic signatures in all waters are within the range of the Sr isotopic composition of the rift basalts and rhyolites. The variability of Sr isotopic data also pinpoints complex water–rock interaction and mixing processes in groundwater and surface water. The 87Sr/86Sr ratio ranges from 0.70445 to 0.70756 in the hot springs, from 0.70426 to 0.70537 in two deep geothermal wells, and from 0.70673 to 0.70721 in the rift lakes Ziway, Langano, Shala and Awasa. The radiogenic composition recorded by the lakes indicates that the input water was predominantly affected by progressive interaction with rhyolitic volcanics and lacustrine sediments.There is a change in MER water composition between the recharge-infiltration zone (surrounding highlands) and the discharge areas, from depleted δD, δ 18O and less radiogenic Sr isotope compositions to enriched δD, δ 18O and more radiogenic Sr isotope compositions. Isotope analyses are therefore useful in providing further understanding of the hydrologeological processes occurring within a productive aquifer and the surface water system.

► Bottled waters from the UK have major-ion compositions that broadly reflect the compositions of groundwaters abstracted directly from the corresponding host aquifers. ► Many trace elements differ in composition from in situ groundwaters due to post-abstraction modifying processes. ► All parameters analysed comply with European and national limits for drinking water and with WHO guideline values; elements that most closely approach the limits include U, Ba. ► Bottled water compositions clearly show the influence of contamination with Sb from PET bottles, although concentrations do not exceed drinking-water limits.The inorganic chemistry of 85 samples of bottled natural mineral waters and spring waters has been investigated from 67 sources across the British Isles (England, Wales, Scotland, Northern Ireland, Republic of Ireland). Sources include boreholes, springs and wells. Waters are from a diverse range of aquifer lithologies and are disproportionately derived from comparatively minor aquifers, the most represented being Lower Palaeozoic (10 sources), Devonian Sandstone (10 sources) and Carboniferous Limestone (9 sources). The waters show correspondingly variable major-ion compositions, ranging from Ca–HCO3, through mixed-cation–mixed-anion to Na–HCO3 types. Concentrations of total dissolved solids are mostly low to very low (range 58–800 mg/L). All samples analysed in the study had concentrations of inorganic constituents well within the limits for compliance with European and national standards for bottled waters. Concentrations of NO3–N reached up to half the limit of 11.3 mg/L, although 62% of samples had concentrations <1 mg/L. Concentrations of Ba were high (up to 1010 μg/L) in two spring water samples. Such concentrations would have been non-compliant had they been classed as natural mineral waters, although no limit exists for Ba in European bottled spring water. In addition, though no European limit exists for U in bottled water, should a limit commensurate with the current WHO provisional guideline value for U in drinking water (15 μg/L) be introduced in the future, a small number of groundwater sources would have concentrations close to this value. Two sources had groundwater U concentrations > 10 μg/L, both being from the Welsh Devonian Sandstone. The highest observed U concentration was 13.6 μg/L.Solute concentrations in waters contained in glass bottles compared with waters in PET showed slightly though significantly higher concentrations of Al, Ce, Cu, La, Nd, Mn, Sn, W, Zn and Zr (rank-sum testing, p  < 0.05). By contrast, Sb concentrations were significantly higher (p  < 0.001) in samples contained in PET bottles. This accords with other studies that have recognised Sb contamination in water from PET bottles. However, in no cases did the concentration of Sb exceed or approach the national and European limit for Sb in natural mineral water/spring water (5 μg/L), the highest observation being 1.35 μg/L.Bottled water compositions were mostly similar in their major-ion characteristics to raw groundwaters from the equivalent aquifers in Britain, although concentrations of several trace elements (Al, Cd, Cu, Fe, Mn, Pb and Zn) were appreciably lower, in some cases by one or two orders of magnitude. The most likely mechanism for the reduction is use of aeration, settling and filtration to remove unstable constituents before bottling. The comparatively low concentrations of Cd, Cu, Pb and Zn are likely to be due to co-precipitation with/adsorption to precipitated metal oxides, although choice of resilient pipework (e.g. stainless steel) in bottling plants may also be a factor. Although for the most part the major ions in the bottled waters appear representative of the groundwater in their host aquifers, the results suggest that many of the trace elements have been modified significantly from natural compositions in situ.

Alteration of As-bearing phases in a small watershed located on a high grade arsenic-geochemical anomaly (French Massif Central) by A. Bossy; C. Grosbois; S. Beauchemin; A. Courtin-Nomade; W. Hendershot; H. Bril (1889-1901).
► Characterization of As-carriers at a microscale by in-situ techniques in a soil profile. ► Decrease of As content from the saprolite to the surface horizon during pedogenesis. ► As was initially associated to Ba-rich pharmacosiderite in the saprolite. ► As was then in goethite, hematite, ferrihydrite-type and aluminosilicates .At a watershed scale, sediments and soil weathering exerts a control on solid and dissolved transport of trace elements in surface waters and it can be considered as a source of pollution. The studied subwatershed (1.5 km2) was located on an As-geochemical anomaly. The studied soil profile showed a significant decrease of As content from 1500 mg kg−1 in the 135–165 cm deepest soil layer to 385 mg kg−1 in the upper 0–5 cm soil layer. Directly in the stream, suspended matter and the <63 μm fraction of bed sediments had As concentrations greater than 400 mg kg−1. In all these solid fractions, the main representative As-bearing phases were determined at two different observation scales: bulk analyses using X-ray absorption structure spectroscopy (XAS) and microanalyses using scanning electron microscope (SEM) and associated electron probe microanalyses (EPMA), as well as micro-Raman spectroscopy and synchrotron-based micro-scanning X-ray diffraction (μSXRD) characterization. Three main As-bearing phases were identified: (i) arsenates (mostly pharmacosiderite), the most concentrated phases As in both the coherent weathered bedrock and the 135–165 cm soil layer but not observed in the river solid fraction, (ii) Fe-oxyhydroxides with in situ As content up to 15.4 wt.% in the deepest soil layer, and (iii) aluminosilicates, the least concentrated As carriers. The mineralogical evolution of As-bearing phases in the soil profile, coupled with the decrease of bulk As content, may be related to pedogenesis processes, suggesting an evolution of arsenates into As-rich Fe-oxyhydroxides. Therefore, weathering and mineralogical evolution of these As-rich phases may release As to surface waters.

Effect of changes in water level on sediment pore water redox geochemistry at a reservoir shoreline by Richard A. Wildman; Nathan W. Chan; Nathan F. Dalleska; Mark Anderson; Janet G. Hering (1902-1911).
► Initially, reducing conditions existed in pore water of submerged shoreline sediment. ► Exposure of sediment to air by falling water level appears to have oxidized the sediment. ► Re-submergence of sediment led to reducing conditions in pore water after <5 days in one location. ► Pore water manganese and uranium generally show opposite trends in response to redox conditions.Pore water samplers with high vertical resolution were used to evaluate the response of sediment redox geochemistry during transient hydrologic conditions at Lake Powell, a large reservoir in Utah and Arizona, USA. Samplers were deployed at two different yet proximal shoreline locations, White and Farley Canyons, before and after exposure of sediment to air and subsequent resubmersion, which resulted from fluctuations in the water level of the reservoir. Before exposure to air, an observed increase in dissolved Mn concentrations and, at Farley Canyon, an observed decrease in dissolved U concentrations across and immediately below the sediment–water interface indicated reducing conditions in the sub-surface. After exposure and resubmersion of the sediment, pore water profiles at each site differed distinctly from those observed before the fluctuation in water level. At White Canyon, an increase in U concentrations and a decrease in Mn concentrations in pore water after exposure and subsequent resubmersion are suggestive of oxidative processes occurring during the period of sediment exposure. Data from Farley Canyon suggest that the same processes may be occurring, but to a lesser extent. Depth profiles of As and Pb were also examined, but were relatively featureless compared to those of Mn and U. At both sites, sediment evaluated for pore water chemistry in the second sampling was only fully resubmerged for 2–5 days prior to the second sampling event, yet reducing conditions were clearly evident in the Mn pore water profiles. This suggests that the dynamics of the biogeochemical processes occurring in surface sediment at Lake Powell are responsive on the timescale defined by the fluctuating water levels in the reservoir.

Assessing the current state of the Gironde Estuary by mapping priority contaminant distribution and risk potential in surface sediment by Aurélie Larrose; Alexandra Coynel; Jörg Schäfer; Gérard Blanc; Laurent Massé; Eric Maneux (1912-1923).
► First distribution maps for the eight trace elements in the Gironde Estuary sediment. ► Surface-weighted average trace element concentrations are relatively low. ► Successful sediment management should focus on limiting fluvial metal fluxes. ► First spatially resolved risk assessment of the trace element cocktail. ► ∼95% of the sediment are ‘Low–Medium’-priority zones.Based on high spatial resolution monitoring, the first spatial distribution maps for the eight trace elements identified as priority contaminants in aquatic systems (i.e. As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) in surface sediments of the Gironde Estuary (SW France) are presented. This large European fluvial–estuarine system is known for important historical multi-element (mainly Cd, Zn, Cu and Pb) pollution by former mining and mineral processing activation in the Riou-Mort watershed located 350 km upstream the estuary. As a consequence, oyster production in the estuary is prohibited, and Cd concentrations in oysters from the Marennes-Oléron area are close to consumption thresholds. Surface sediment samples were analysed for grain size, particulate organic C and trace element concentrations. Determination of trace elements was carried out by ICP-MS for As, Cd, Cr, Cu, Ni, Pb, Th and Zn, and by CV-AAS for Hg. Total and potentially released trace element stocks in the surface sediment were evaluated by using concentrations in the estuary and in selected sediment core. Assuming that sediment resuspension affects mainly the uppermost sediment layer, the total trace element stocks in the studied 0–10 cm depth range may represent the equivalent of one (Cd) to eight (As, Cr) times the annual fluvial trace element inputs into the estuary. Comparing total trace element concentrations in surface sediment with: (i) data on the regional geochemical baseline to evaluate the potentially remobilised fraction and (ii) the potentially bioavailable fraction aimed at establishing a first spatially resolved risk assessment of the trace element “cocktail” present in these sediments at the estuary scale. After correction for grain size effects by Th normalisation, potentially highly toxic metals such as Cd and Hg showed the highest enrichment factors. From ecotoxicological indices, areas were identified and quantified where trace element levels and mobility may bear a risk to benthic organisms. The GIS-based spatial distribution of ecotoxicological indices for the trace element “cocktail” suggests that ∼95% of the surface sediment are ‘Low–Medium’-priority zones, highlighting the need for further impact studies. The produced maps of trace element distributions and associated risk potentials are likely to be a useful tool to authorities in charge of sustainable estuarine management, e.g. for the optimisation of dredging activities or development of the estuarine infrastructure.

► Groundwater is mostly Ca-HCO3 type in the Shuicheng Basin, Southwest China. ► Groundwater quality was seriously affected by anthropogenic activities. ► Cl and Na+ were derived mostly from domestic sewage containing table salt. ► High NO 3 - concentrations could be a result of domestic sewage and nitrogen fertilizers. ► SO 4 2 - ion was derived mostly from domestic wastewater, rainwater, and sulfide oxidation.Rapidly increasing populations, and associated intensification of agriculture, urbanization and industrialization, place increased demands on water resources and increased likelihood of pollution in many areas of the world. The Shuicheng Basin, southwestern China, is one such area and in order to understand water–rock interactions (carbonate dissolution) and anthropogenic impacts on groundwater quality in this karstic landform-dominated area, chemical as well as C, Sr and S isotopic compositions of groundwater (spring and well) and surface water (river) were measured during and following rainy seasons. The concentrations of various ions in groundwater were characterized by the dominant cations (Ca2+, Mg2+) and anions ( HCO 3 - , SO 4 2 - ), which account for more than 80% of the total ion concentration. Strontium isotope ratios (87Sr/86Sr, 0.70760–0.70918, mean 0.70831) and δ 13CDIC (−14.2‰ to −8.4‰, mean −10.7‰) indicate that the weathering dissolution of limestone controls Ca2+ and HCO 3 - . The decrease in δ 13CDIC values with increasing concentrations of anthropogenic species (Cl, NO 3 - and Na+) shows that the C isotopic composition of DIC can be a useful tracer of contaminants. Chemical compositions, hydrogeological conditions and δ 34S analyses showed increasing SO 4 2 - concentration, resulting from domestic wastewater, fertilizer applications, atmospheric inputs through coal combustion, and oxidation of sulfide minerals, which typically are abundant in coal formations in the basin. Groundwater from the old downtown, industrial and agricultural areas exhibited high concentrations of Cl, NO 3 - , SO 4 2 - and Na+, suggesting the groundwater is impacted by significant levels of contamination from human activities.

Eh/pH diagram based on the in situ conditions measured on the archaeological site of Glinet (France, 16th century).Display Omitted► Long-term corrosion behaviour of ferrous archaeological artefacts in anoxic media. ► Use of thermodynamic modelling to correlate the corrosion products to the environmental data. ► Thermodynamic data for carbonate phases from the rosasite group (chukanovite).This article is part of an ongoing study on the long-term corrosion behaviour of ferrous archaeological artefacts. The aim of this study is to correlate the corrosion products formed on ancient artefacts in an anoxic medium to the environmental data using thermodynamic modelling. For this purpose, measurement campaigns have been conducted on the archaeological site of Glinet (16th century, High Normandy (Seine-Maritime), France) where the evolution of the pore water chemistry has been recorded for a period of one year. Three evolution steps have been distinguished after the oxidizing perturbation which was induced by the piezometers installation. The first step was related to an oxidizing environment in which pore water was in equilibrium with a Fe(III) precipitated phase: ferrihydrite (FeOOH·0.4 H2O). The second step was considered as an intermediate step and Fe speciation had evolved; equilibrium was achieved between ferrihydrite and a Fe(II) carbonate phase: siderite (Fe(II)CO3). The last step of the evolution was related to a reducing stage where pore water was in equilibrium with magnetite ( Fe 3 ( II,III ) O4) and with chukanovite ( Fe 2 ( II ) (OH)2CO3). As these phases were present in the corrosion layers formed on the archaeological samples, it is possible to conclude that the thermodynamic approach was helpful in developing a better understanding of the effect of geochemical conditions on the composition and mineralogy of the corrosion products formed on archaeological artefacts. This work could be used as a reference for further corrosion studies, especially on long-term corrosion processes applied to nuclear waste disposal.

An updated insight into the natural attenuation of As concentrations in Reigous Creek (southern France) by Marion Egal; Corinne Casiot; Guillaume Morin; Françoise Elbaz-Poulichet; Marie-Ange Cordier; Odile Bruneel (1949-1957).
► Coprecipitation of Fe and As with a constant percentage of As removed close to 30%. ► Tooeleite precipitate in the AMD in stromatolite-like structures. ► Diel cycles of dissolved concentrations of As and Fe concentrations are a potential source of pollution due to the photoreduction of iron oxides.The removal of metals and metalloids occurring in acid mine drainage has been studied on different scales (years, days). Dissolved and particulate concentrations of Fe and As were monitored over a 4-a period along Reigous Creek, an acid mine drainage from a former Pb–Zn mine in southern France. Dissolved concentrations of Fe (12–25 mmol L−1), As (0.9–3.5 mmol L−1) and SO 4 2 - (10–70 mmol L−1) exhibited seasonal variations related to rainfall, with an increase during the driest months. About 30% of the As initially present in solution as As(III) was coprecipitated with Fe oxides in the first 40 m of Reigous Creek. The corresponding As removal rate was 3.58 × 10−7  mol L−1  s−1. The mineralogy of resultant precipitates varied spatially and seasonally. Over the first 40 m, amorphous As(V)–Fe(III) phases and tooeleite, were formed. Sediments deposited in the bed of the creek close to the spring contained both types of solid phases. Laminated concretions, which consist of precipitates around bacterial structures, were mainly constituted of tooeleite. Further downstream, these Fe-oxide phases were replaced by schwertmannite and ferrihydrite. On a daily basis, concentrations of dissolved Fe and As have been shown to vary up to 10% during the day as a result of photoreduction of Fe-oxide phases.