Applied Geochemistry (v.18, #3)

Water inflows in 9 tunnels and galleries through the Alpine crystalline massifs have been analysed for their 3H activities and δ18O contents. Tritium provides information on water transit times and the dynamics of deep water circulation, whereas δ18O contributes to understanding the origin and flow paths of water in such mountainous regions. Owing to ambiguities arising from the irregularity of the historical 3H input function since 1945, a unequivocal and straightforward interpretation of water transit times in Alpine tunnels is not possible. Nevertheless, the ambiguity can be resolved by considering the 3H data in combination with (a) the generalized hydraulic conductivity of the massif obtained from discharge data, and (b) the Na and silica content of the water as an indication of the extent of rock-water interaction. When the data are resolved in this way, the waters that were sampled in the tunnels/galleries can be divided into 3 age groups, i.e. <15, 15–40 and >40 a. In general, water beneath a rock-cover thickness of <500 m is less than 15 a old, which confirms the active circulation of groundwater in a “decompressed zone” (i.e. a zone of unloading fractures that is expected to have a depth of this magnitude). Moreover, tunnel excavation can radically alter the hydrology, as is shown by the 3H content of a water inflow in the Gothard gallery. Oxygen-18 data primarily reflect the recharge altitude, which can be predicted a priori by considering the large-scale geological structures of each massif and the extent to which they control the subvertical paths followed by the groundwater. Anomalous δ18O data may reflect local or general departures from this interpretation. A general pattern is that downslope flow in the better jointed “decompressed zone”, which parallels the topography, may divert recharge from a higher to lower altitude before it follows the structural pathways into the tunnel. This results in a somewhat lower δ18O value than would be predicted from structure alone, but tends to confirm the existence and role of the “decompressed zone” indicated by the 3H. More local δ18O anomalies reflect recharge from rivers or lakes entering the tunnels, and are illustrated by examples in this paper. Results show that environmental isotopes contribute to a better understanding of the hydrogeology of mountain massifs and of the interactions between tunnels/galleries and groundwater. They provide information not given by other tracing methods and are thus a precious tool for tunnelling engineers and geologists.

Separate fractions of dentine and enamel of 12 individuals from the necropolis of Sion (Valais, Switzerland) have been analyzed for Pb and Sr isotope compositions. The individuals span a time period of more than 1 ka from ∼5.2 ka B.P. to ∼4.1 ka B.P. and include Middle Neolithic, Upper Neolithic, Bell Beaker and Old Bronze age civilizations. Individuals were buried either into or close to dolmens or into soil at 4 different sites on the alluvial fan of the Sionne stream, a tributary of the Rhone river. Isotopic composition of dentine and enamel pairs of the individuals indicate that teeth underwent post mortem contamination. Lead contamination is due to two different sources, petrol and natural Pb from soils. The preponderance of either petrol or natural Pb contamination in teeth depends on the burial sites. Differences in the content of Pb-retaining particles (organic matter, Fe-hydroxides, clay minerals), that depend largely on soil grain size, are suggested to be responsible for the differential Pb contamination at the investigated burial sites. Strontium contamination is stronger in individuals buried into or close to dolmens, which are made of calc-schist slabs. Despite post mortem contamination, both Pb and Sr isotopes have allowed the identification of an individual's enamel with isotopic compositions significantly different from those of the local substratum, suggesting his immigration to the Sion area from a geologically different region. This individual belongs to the Bell Beaker civilization, which is considered to have immigrated into Western Europe and the Mediterranean basin at the end of the Neolithic. Systematic differences between enamel and dentine isotopic compositions of all other individuals analyzed suggest that they assimilated in vivo Pb and Sr from an area nearby to that in which they were buried.

The Nambija Mineral District (NMD) is located in the southeastern part of Ecuador, east of Zamora (Zamora Chinchípe's country), Ecuadorian Amazon. In this district, Au occurrences have been know since colonial and pre-colonial times, but only after the early 1980s has intensive artisanal Au mining activity been developed. Currently, the different NMD Au occurrences continue to be exploited by artisanal operations and are difficult to control in the study area. The environmental impacts due to Au mining are a consequence of the illegal situation and deficiency in controlling the techniques of ore exploitation. The Au extraction is carried out by outdoor amalgamation, so the indiscriminate use of Hg by artisanal miners, associated with careless methods of tailings disposal, has caused occupational exposure and environmental degradation. The present study evaluated the geochemical dispersion and concentrations of local contamination of metallic Hg in soils, stream sediments and mine tailings in the NMD area. This article aims to contribute to the discussion of environmental changes caused by the artisanal Au mining in the Nambija district. A total of 82 samples (32 soil, 40 stream sediment and 10 mine tailings) were analyzed. The results were compared with the Hg levels in soil and stream sediments considered not to be contaminated in the Nambija mining area and in other areas where Hg is mined in the Amazon basin. In this work, mean total Hg (T-Hg) concentrations of 1.7 μg g−1 in soils and 2.7 μg g−1 in stream sediments have been found. Mercury values in the mine tailing samples revealed values ranging from 89 to 1555 μg g−1. The results found for Hg in the different analyzed materials pointed to contamination of the studied area by this metal, while soil erosion is responsible for an increase in stream sediment's T-Hg concentrations in the different aquatic ecosystems of the Nambija Creek and Nambija River.

Metallurgical industries have created numerous wastelands where large quantities of wastes have been stocked. The presence of micropollutants is not as much of a problem as the fact that this pollution is mobile and could thereby affect human health. Strong reductive conditions present in several natural or anthropogenic situations could influence metal release to the environment. Two waste samples (difference in age: ca. 20 a) from the Mortagne-du-Nord (France) wasteland were studied to evaluate the behaviour of their metal ions under reductive conditions: a recent sample mainly composed of sulphides and an older solid composed of oxidised phases. Under reductive conditions, release of metals increased in the old sample, but no modifications were observed in the recent solid. As shown by a weathering experiment, alteration of the older solid (initially consisting of sulphides) induced the creation of Fe oxyhydroxides, which adsorbed or coprecipitated the other metals. Under reductive conditions, these oxyhydroxides were dissolved, and the metallic content of the sample was released into the aqueous medium.

Arsenic in iron cements developed within tailings of a former metalliferous mine—Enguialès, Aveyron, France by Alexandra Courtin-Nomade; Hubert Bril; Catherine Neel; Jean-François Lenain (395-408).
Arsenopyrite-rich waste from a former metalliferous mine were spread out over the sloping side of a deep valley after processing. Over the past 30 a, they have been subjected to rainfall and acid water originating from the abandoned mine galleries. This intensive leaching has led to the formation of thin layers of As–Fe crusts on the tailings surface acting as a cement. X-ray diffraction and SEM coupled with EDS determined that jarosite was present in all mineral samples and could contain a small amount of As (∼5.7 wt.%). In addition EMPA and Raman microspectroscopy characterised the presence of amorphous As(V) Fe hydrates as well as rare arsenate minerals (e.g. scorodite). Raman microspectroscopy in particular identified a preponderance of goethite or hematite within the mineral framework of the tailings materials that is likely to sorb recalcitrant As species. The characterisation of the components of the tailings enable the identification of their evolution, shows the progressive decrease of their As-content and emphasises the consequences of the temporary trapping of As in the very acidic and oxidising conditions prevailing in such environments. Resinous amorphous material was identified as the richest in As with As ∼17.1 wt.%. This material evolved toward more crystallised phases (e.g. goethite, jarosite) which contained less As (3.2 wt.%<As <5.7 wt.%). Paragenesis showed the progressive release of As with the crystallisation evolution of the As-trapping material.

Heavy metal partitioning in river sediments severely polluted by acid mine drainage in the Iberian Pyrite Belt by E Galán; J.L Gómez-Ariza; I González; J.C Fernández-Caliani; E Morales; I Giráldez (409-421).
This study provides a geochemical partitioning pattern of Fe, Mn and potentially toxic trace elements (As, Cd, Cr, Cu, Ni, Pb, Zn) in sediments historically contaminated with acid mine drainage, as determined by using a 4-step sequential extraction scheme. At the upperstream, the sediments occur as ochreous precipitates consisting of amorphous or poorly crystalline oxy-hydroxides of Fe, and locally jarosite, whereas the estuarine sediments are composed mainly of detrital quartz, illite, kaolinite, feldspars, carbonates and heavy minerals, with minor authigenic phases (gypsum, vivianite, halite, pyrite). The sediments are severely contaminated with As, Cd, Cu, Pb and Zn, especially in the vicinity of the mining pollution sources and some sites of the estuary, where the metal concentrations are several orders of magnitude above background levels. Although a significant proportion of Zn, Cd and Cu is present in a readily soluble form, the majority of heavy metals are bonded to reducible phases, suggesting that Fe oxy-hydroxides have a dominant role in the metal accumulation. In the estuary, the sediments are potentially less reactive than in the riverine environment, because relevant concentrations of heavy metals are immobilised in the crystalline structure of minerals.

Subsurface codisposal of toxic metals and radionuclides with organic chelating agents has created vast areas of contaminated soils and groundwater. The fate of the metal/ radionuclide and ligand are inexorably linked in their interaction with soil minerals and aquifer solids. The present study was conducted to investigate the geochemical reactions (sorption, dissolution, dissociation, oxidation) that govern the fate of CoIINTA complexes in contact with natural subsurface materials that are typical of materials underlying some waste disposal areas. Equilibrium measurements indicated that at low pH (4) and in the presence of abundant surface exchangeable Al, the adsorption of Co and NTA was independent of the presence of the other component. By contrast, at higher pH (6 and 7.4) the sorption of both Co and NTA decreased in the presence of the other moiety. Solution phase analyses indicated that the decrease in sorption was driven by the formation of stable aqueous complexes of Co(II) and Co(III) with NTA. The time-dependent loss of CoIINTA from solution was accounted for by sorption, complex dissociation, and the oxidation of Co(II) to Co(III). Biodegradation of NTA was not an important process over the 21-day incubation period. Formation of Co(III) complexes has broad implications in these systems as these species are kinetically and thermodynamically stable, exhibit lower adsorption onto solids, and are resistant to biodegradation. Thus, with the exception of relatively extreme conditions (low pH, abundant readily available Al), NTA decreased Co partitioning to surfaces through the formation of stable aqueous complexes. This behavior may contribute to the undesirable transport of 60Co through the subsurface.

Isotopic investigations of carbonate growth on concrete structures by R.V. Krishnamurthy; D. Schmitt; E.A. Atekwana; M. Baskaran (435-444).
Stable C and O isotope ratios were measured in carbonate minerals, growing under concrete structures from two locations in the United States. These locations were under a bridge in Michigan and under an overpass in New York. The δ13C of the carbonate samples ranged from −21.6 to −31.4‰ (with respect to V-PDB) and clearly indicated precipitation under non-equilibrium conditions. Indeed, the values in some cases were more negative than could be accounted for by existing models that invoke 4 stages of kinetic fractionation. There have been suggestions that microbial activity involving C from gasoline and other fossil fuel sources might be responsible for the relatively low C isotope ratios measured in these carbonates. To explore this possibility, 14C measurements were made in some of the samples. All samples measured for 14C contained bomb C. The range of 14C concentrations suggested a non-uniform growth rate, although possible fossil fuel-derived carbon in the system needs future investigation. The δ18O values of the carbonates analyzed from Michigan range from 12.5 to 15.7‰ (with respect to V-SMOW), with a mean value of 13.7‰. The δ18O values of the NY samples range from 11.8 to 15.2‰, with a mean value of 13.1‰. The nearly identical mean values at both locations favors incorporation of O from atmospheric CO2 in carbonate precipitation. Additionally, the 210Pb radiometric technique was also attempted to explore the applicability of this technique in dating concrete derived carbonates as well as recent carbonates forming in a wide variety of environments. The results gave ages between 64 and 3.8 a and are consistent when compared with the date the bridge was constructed.

Since the Shu103 well was successfully drilled in 1995, the Buried Hill reservoir is receiving a new exploration emphasis in the Liaohe Basin, China. The Buried Hill oils can be divided into 3 main types in the Shuguang-Huangxiling area based on their chemical and isotopic compositions. The first type is collected mostly from the Shuguang area. The similarity to the Es4 oils and the Es4 source rock extracts indicates that they were mainly expelled from the fourth member of the Shahejie formation (Es4) in the Chenjia Sag and/or Panshan Sag, deposited in a stratified paleolake system. The second is charactized by a relative high Pr/Ph ratio, low gammacerane content and depletion of 12C in individual n-alkanes. These characteristics represent a typical origin from dominantly freshwater paralic lacustrine sediments. Various biomarker indices of the other Buried Hill oils fall between the former two types. The authors infer that these oils may be derived from the adjacent Qingshui Sag and/or Panshan Sag, and were likely generated from transitional sedimentary facies between well-circulated freshwater paralic lacustrine and relatively closed saline lacustrine.

Metal partitioning depends on the physical–chemical conditions of a system and can be affected by anthropogenic inputs. In this study, the authors report the results of trace metal partitioning between particulate (>1.2 μm), colloidal (1.2 μm–1 kDa) and truly dissolved (<1 kDa) fractions in the polluted section of the Upper Vistula River compared with the non-polluted headwaters. It was found that the salt input in the Vistula River induced a decrease of colloid concentration and the increase of suspended particulate matter. Compared with upstream from the polluted section, the metal concentrations (Co, Cu, Cr, Mn and Zn) in the colloidal fraction were lower. It was mainly due to the rapid colloid coagulation at increased salinity, the competition with ligands and major ions (Ca and Mg) and the weak mobility of metals associated with particles at the pollution sources.

Characterization and diagenesis of strong-acid carboxyl groups in humic substances by J.A Leenheer; R.L Wershaw; G.K Brown; M.M Reddy (471-482).
A small fraction of carboxylic acid functional groups in humic substances are exceptionally acidic with pK a values as low as 0.5. A review of acid-group theory eliminated most models and explanations for these exceptionally acidic carboxyl groups. These acidic carboxyl groups in Suwannee River fulvic acid were enriched by a 2-stage fractionation process and the fractions were characterized by elemental, molecular-weight, and titrimetric analyses, and by infrared and 13C- and 1H-nuclear magnetic resonance spectrometry. An average structural model of the most acidic fraction derived from the characterization data indicated a high density of carboxyl groups clustered on oxygen-heterocycle alicyclic rings. Intramolecular H-bonding between adjacent carboxyl groups in these ring structures enhanced stabilization of the carboxylate anion which results in low pK a1 values. The standard, tetrahydrofuran tetracarboxylic acid, was shown to have similar acidity characteristics to the highly acidic fulvic acid fraction. The end products of 3 known diagenetic pathways for the formation of humic substances were shown to result in carboxyl groups clustered on oxygen-heterocycle alicyclic rings.