Applied Geochemistry (APPL GEOCHEM)

The Juan de Fuca Ridge is a hydrothermally active, sediment covered, spreading ridge situated a few hundred kilometres off the west coast of North America in the northeastern Pacific Ocean. Sediments from seven sites drilled during the Ocean Drilling Program (ODP) Legs 139 and 168 were analyzed for total hydrolyzable amino acids (THAA), individual amino acid distributions, total organic C (TOC) and total N (TN) contents. The aim was to evaluate the effects of hydrothermal stress on the decomposition and transformation of sedimentary amino acids. Hydrolyzable amino acids account for up to 3.3% of the total organic C content and up to 12% of the total N content of the upper sediments. The total amounts of amino acids decrease significantly with depth in all drilled holes. This trend is particularly pronounced in holes with a thermal gradient of around 0.6 degrees C/m or higher. The most abundant amino acids in shallow sediments are glycine, alanine, lysine, glutamic acid, valine and histidine. The changes in amino acid distributions in low temperature holes are characterized by increased relative abundances of non-protein beta-alanine and gamma-aminobutyric acid. In high temperature holes the amino acid compositions are characterized by high abundances of glycine, alanine, serine, ornithine and histidine at depth. D/L ratios of samples with amino acid distributions similar to those found in acid hydrolysates of kerogen, indicate that racemization rates of amino acids bound by condensation reactions may be diminished.

Cape Kalamba oil seeps occur at the south end of the Ubwari Peninsula, at the intersection of faults controlling the morphology of the northern basin of the Tanganyika Rift, East Africa. Oil samples collected at the surface of the lake 3-4 km offshore from Cape Kalamba have been studied. The aliphatic hydrocarbon and biomarker compositions, with the absence of the typical suite of polynuclear aromatic hydrocarbons, indicate an origin from hydrothermal alteration of immature microbial biomass in the sediments. These data show a similarity between a tar sample from the beach and the petroleum from the oil seeps, and confirm that the source of these oils is from organic matter consisting mainly of bacterial and degraded algal biomass, altered by hydrothermal activity. The compositions also demonstrate a < 200 degrees C temperature for formation/generation of this hydrothermal petroleum, similar to the fluid temperature identified for the Pemba hydrothermal site located 150 km north of Cape Kalamba. The 14C age of 25.6 ka B.P. obtained for the tar ball suggests that Pleistocene lake sediments could be the source rock. Hydrothermal generation may have occurred slightly before 25 ka B.P., during a dry climatic environment, when the lake level was lower than today. These results also suggest that the Cape Kalamba hydrothermal activity did not occur in connection with an increased flux of meteoric water, higher water tables and lake levels as demonstrated in the Kenya Rift and for the Pemba site. Hydrothermal petroleum formation is a facile process also in continental rift systems and should be considered in exploration for energy resources in such locales.

The transport of H2SO4 (at pH = 1.0, −1.0 and −3.0) through two mineralogically different compacted clays (Kc and Km) was examined using single-reservoir diffusion cells with constant source concentrations. At the end of the 216 day test period, geochemical analyses indicated increased depth of acid diffusion with increased reservoir acidity for both Kc and Km cells. Elevated Ca, Al, Fe and Si concentrations were associated with decreased pH values in all cells. XRD results showed that these elevated concentrations corresponded to the loss of carbonate and montmorillonite peaks and decreased peak intensities for illite and kaolinite in the Kc and Km pH −1.0 and −3.0 Km cells. Moreover, Si X-ray absorption near-edge structure (XANES) indicated dissolution of the phyllosilicate phases, a relative increase in the amount of quartz, and the potential formation of an amorphous silica phase. The results of this study showed that, despite the extreme pH values considered, movement of H2SO4 solutions with pH < 1.0 may be greatly retarded in the presence of a strongly neutralizing mineral phase, such as dolomite, within the clay.

Red Deer antler and bone collagen complexes, recent and 11 ka BP old, were solubilized in anhydrous formic acid, cleaving the α-chains to give arrays of large stable peptides. Calf-skin collagen was also compared. The antler and bone α-chains have survived substantially through this time-span as molecular entities, under bog conditions. These arrays reveal small but meaningful differences between the main collagen components of bone and antler and skin, which could be of post-translational origin. We report here an exploratory study of some problems of molecular survival in ancient collagenous material through 11 ka and also of antler growth as compared with bone growth in vivo.

A method for the in situ single spot δ11B characterisation of geological materials with laser ablation multicollector ICP mass spectrometry (LA-MC-ICPMS) has been developed. The mass spectrometer was equipped with both Faradays and multiple ion counters. Four samples with different B contents (12–31,400 ppm) and isotopic compositions (δ11B are between −8.71 and +13.6‰) were analysed. Samples include the B4 tourmaline and 3 MPI-DING glasses (StHs6/80-G, GOR132-G and GOR128-G).All sources of B isotopic fractionation during the analysis (mass bias, laser-induced isotopic fractionation and detector efficiency drift) have been evaluated and quantified. Instrumental mass bias is the major source of fractionation, altering the original isotopic ratio up to 13%. Fractionation related to laser sampling and transport to the ICP was found to be very low (less than 0.0015% s−1). Fractionation effects due to drift in ion counter efficiencies were found to be significant. Nevertheless, the “standard-sample-standard” bracketing approach could be used to correct for the above fractionation effects using NIST SRM 610 as external standard.With spot sizes of 60–80 μm in diameter, geologically meaningful results can be achieved on samples containing at least 10 ppm B, i.e., results with precisions that can discriminate between the different reservoirs on Earth. Data obtained with Faraday detectors on NIST SRM 610 and B4 tourmaline show high precision (down to 0.04‰, 1σ) and accuracy. Boron isotope ratios measured in the glass samples using multiple ion counting show significantly higher standard deviations (up to 2.5‰, 1σ), but they are very close to the values that can be expected from counting statistics. No significant variations with spot size or B contents were observed. Most of the values are within 1σ level of the reference values.The developed method was applied to a series of ashes from Mt. Etna erupted in 1995 having B contents between 14 and 20 ppm. The B isotope compositions of the ashes are between −4.8 and −10.7‰, with a weighted average value of −8.0 ± 1.9‰ (1σ).

The through- and out-diffusion of HTO, 36Cl− and 125I− in Opalinus Clay, an argillaceous rock from the northern part of Switzerland, was studied under different confining pressures between 4 and 15 MPa. The direction of diffusion and the confining pressure were perpendicular to the bedding. Confining pressure had only a small effect on diffusion. An increase in pressure from 4 to 15 MPa resulted in a decrease of the effective diffusion coefficient of ∼20%. Diffusion accessible porosities were not measurably affected. The values of the effective diffusion coefficients, De, ranged between (5.6±0.4)×10−12 and (6.7±0.4)×10−12 m2 s−1 for HTO, (7.1±0.5)×10−13 and (9.1±0.6)×10−13 m2 s−1 for 36Cl− and (4.5±0.3)×10−13 and (6.6±0.4)×10−13 m2 s−1 for 125I−. The rock capacity factors, α, measured were circa 0.14 for HTO, 0.040 for 36Cl− and 0.080 for 125I−. Because of anion exclusion effects, anions diffuse slower and exhibit smaller diffusion accessible porosities than the uncharged HTO. Unlike 36Cl−, 125I− sorbs weakly on Opalinus Clay resulting in a larger rock capacity factor. The sorption coefficient, Kd, for 125I− is of the order of 1–2×10−5 m3 kg−1. The effective diffusion coefficient for HTO is in good agreement with values measured in other sedimentary rocks and can be related to the porosity using Archie's Law with exponent m=2.5.

Data are presented here on the anthropogenic 129I inventory in regions that have been strongly affected by releases from European reprocessing facilities which, to the authors’ knowledge, presently account for >90% of the global isotope source in the Earth’s surface environment. The results show that >90% of the isotope inventory occurs in marine waters with the Nordic Seas and Eurasian basin of the Arctic Ocean containing most of the 129I. Within the terrestrial environment of Europe, soils contain the largest part of the isotope inventory. However, the inventory of the terrestrial system did not provide clues on the most plausible atmospheric source of 129I to Europe, thus supply from both gaseous and marine releases is proposed. The sum of the total inventory in both the marine and terrestrial environments did not match the estimated releases. This imbalance is likely to relate to unconstrained inventory estimates for marine basins (Irish Sea, English Channel and North Sea) close to the facilities, but also to the occurrence of 129I in the biosphere, and possible overestimated releases from the nuclear reprocessing facilities. There is no doubt that the available data on 129I distribution in the environment are far from representative and further research is urgently needed to construct a comprehensive picture.

Fluid migration in subduction zones is one of the key phenomena to understand the global mass transfer system. While active volcanoes provide the most recognizable conduits for fluid flow in active margins, the existence of a large number of active fluid seepages demonstrates that other forms of fluid release are also important in subduction zone settings. The authors collected fluid samples from springs and wells across the forearc area in Kyushu, a southwestern island of Japan, covering hot spring activities associated with active volcanism and the Median Tectonic Line (MTL), a major fault system present in the southwestern part of Japan. In order to determine sources of these fluids, halogen concentrations as well as 129I/I and 36Cl/Cl ratios were measured in samples from several locations. While Cl concentrations of the forearc fluids in Kyushu range between seawater and meteoric water value, I concentrations are considerably higher than seawater value. Fluids in the Miyazaki area are much higher in I, and somewhat higher in Br, than waters in the Oita area, which is closely associated with the MTL. The differences between those two areas are also pronounced in 129I/I ratios, which range between 800 and 900 × 10−15 in the Oita area and between 100 and 360 × 10−15 in the Miyazaki area. The 129I/I ratios obtained from the Oita area are compatible with an I derivation from subducting marine sediments, similar to findings from an earlier investigation of fluids collected from Satsuma-Iwojima, an active volcano south of Kyushu Island. In the Miyazaki area, on the other hand, I ages are too old to be derived from currently subducting marine sediments and point to a derivation from old organic-rich materials in the upper plate of the forearc region. The results demonstrate the presence of very different fluid systems in the forearc area of Kyushu: old CH4-rich fluids dominate in the seaward side of the forearc, while fluids close to the MTL and the Quaternary Volcanic Front demonstrate derivations from subducting marine sediments. The latter fluids in the MTL area probably are transported through the fractures associated with the fault activities, suggesting that this fault system reaches the transition zone between upper and lower plates in this region.

This paper highlights an analytical method based on mass measurement that can be used to directly quantify 129I in groundwater samples at concentrations below the maximum contaminant level (MCL) without the need for sample pre-concentration or extraction. Samples were analyzed on a Perkin Elmer ELAN DRC II ICP-MS after minimal dilution using O2 as the reaction gas. Analysis of continuing calibration verification standards indicated that the dynamic reaction cell (DRC) mode could be used for quantitative analysis of 129I in samples below the MCL (0.0057 ng/mL or 1 pCi/L). The low analytical detection limit of 129I analysis in the DRC mode coupled with minimal sample dilution (1.02x) resulted in a final estimated quantification limit of 0.0051 ng/mL. Subsequent analysis of three groundwater samples containing 129I resulted in fully quantitative results in the DRC mode, and spike recovery analyses performed on all three samples confirmed that the groundwater matrix did not adversely impact the analysis of 129I in the DRC mode. This analytical approach has been proven to be a cost-effective, high-throughput technique for the direct, quantitative analysis of 129I in groundwater samples at environmentally relevant concentrations that reach below the current MCL.

The long-lived halogen radioisotopes 129I and 36Cl provide valuable information regarding the source of fluids in hydrocarbon systems and in localized areas where infiltration of younger meteoric water has occurred. Despite the utility of these two isotopes in providing time-signatures for fluid end-members, considerable uncertainty remains regarding the interpretation of “intermediate-age” waters in hydrologic systems. These waters are likely the result of the combination of two or more halogen sources at some time in the past, each with its own characteristic concentration and isotopic composition. In order to unravel the evolution of these “intermediate-age” waters, the effect that infiltration of meteoric water has on the isotopic composition of older formation waters is modeled. Also evaluated is the effect that the timing of dilution has on 129I and 36Cl signatures observed in the present, specifically, the hypothesis that halogen isotopic signatures imparted by the mixing of brine and meteoric waters early in the development of a sedimentary basin are quantitatively different from those imparted by the mixing of old brines with recent meteoric waters.

This study presents the characterization of Pu-bearing precipitates and the results from uptake studies of Np and Pu on inorganic colloidal particulates in J-13 water from the Yucca Mountain site. Plutonium solubilities determined experimentally at pH values of 6, 7, and 8.5 are about two orders of magnitude higher than those calculated using the existing thermodynamic database indicating the influence of colloidal Pu(IV) species. Solid phase characterization using X-ray diffraction revealed primarily Pu(IV) in all precipitates formed at pH 6, 7, and 8.5. The solubility controlling Pu-bearing solids precipitated at ambient temperature consisted of amorphous Pu(OH)4(s) with several Pu–O distances between 2.3 and 2.7 Å that are characteristic for Pu(IV) colloids. High temperature (90 °C) increased solid phase crystallinity and produced Pu(IV) solids that contained Pu oxidation state impurities. X-ray absorption spectroscopic studies revealed diminished Pu–O and Pu–Pu distances that were slightly different from those in crystalline PuO2(s). A Pu–O bond of 1.86 Å was identified that is consistent with the plutonyl(V) distance of 1.81 Å in PuO2+(aq). Hematite, montmorillonite, and silica colloids were used for uptake experiments with 239Pu(V) and 237Np(V). The capacity of hematite to sorb Pu significantly exceeded that of montmorillonite and silica. A low desorption rate was indicative of highly stable Pu-hematite colloids, which may facilitate Pu transport to the accessible environment. Neptunium uptake on all mineral phases was far less than Pu(V) uptake suggesting that a potential Pu(V)–Pu(IV) reductive sorption process was involved. The temperature effect on Pu solubility and pseudocolloid formation is also discussed.

Pleistocene vegetation history on the Chinese Loess Plateau has been traditionally investigated using palynological methods, and questions remain regarding whether an extensive broadleaf deciduous forest ever developed on the loess table under favorable climatic conditions. The authors have employed a C isotope approach to address this question by comparing δ13C values in soil organic matter from different loess ecological domains with known source vegetation to the C isotope values obtained from a paleosol section that can be dated back to 130 ka. The C isotopic compositions of modern soils from the loess table and the loess–desert transition gave δ13C values of −24.5‰ to −18.2‰ and −25.7‰ to −20.7‰, respectively. These C isotopic ratios are consistent with the standing modern vegetation that is dominated by a mixture of C3 and C4 plants and can be distinguished from that in the patchy forest areas where exclusive C3 trees yield a narrow δ13C value range from −26.9‰ to −25‰ (average −26.1‰). Obtained δ13C compositions from paleosols and loess sediments in the Lantian and the Luochuan profiles vary from −24‰ to −16.9‰, indicating a grass-dominated steppe with shifting C3 and C4 contributions controlled mainly by paleoclimatic changes during the late Pleistocene. The present results suggest no extensive forest coverage on the loess table during the past 130 ka even under the most suitable conditions for forest development. This conclusion supports the explanation of natural causes for the development of only patchy forests on the modern loess table and provides critical historical information toward the vegetation restoration project that is currently underway on the Chinese Loess Plateau.

Humic substances (HS) isolated from swamp water, surface soil, peat and brown coal were characterized using elemental composition, solid state 13C CP/MAS NMR and Py-GC/MS analysis. A substantial amount of information with regard to the source, maturity, depositional environment and degree of degradation of humic substances was obtained. The elemental composition, atomic ratio, 13C NMR spectra and Py-GC/MS results indicated that vascular plant matter is the main contributor to humic substances. Humic substances from swamp water and from soil in the surrounding area of the swamp were found to be identical, suggesting that the swamp humic substances are derived from surrounding soils. Humic substances from brown coal were characterized by a higher degree of humification, including loss of polysaccharides, degradation in lignin content and increase in aromaticity. Compared with humic substances from brown coal, the humic substances from peat showed a lower degree of humification and were considerably more aliphatic in nature.

Distilled water was percolated for 38 days through Soultz granite (France) from the candidate site of the future Hot Dry Rock (HDR) geothermal exchanger at 180°C and 14 bars in a dynamic experimental system (plug-flow system with Ti reaction cell: I.D. 50 mm and L. 120 mm). The amplitude of dissolution and precipitation reactions was estimated after fluid analysis, and scanning electron microscope observations of the minerals were done following the percolation experiment. There were well developed etch pits on the surface of the feldspars. These were, therefore, the most reactive minerals. Dissolution and precipitation are distributed in zones along the flow path of the reacting fluid. Newly precipitated calcite is observed along the fluid flow path. Ferromagnesian saponite precipitates only at the outlet part of the system. The following mobility order was observed: SiO2 > HCO3 > F ∼ Na > Ca > Al > Li > Cs > Mg > Ba > Rb > B > Sr.By combining dissolution reaction kinetics, according to the law of the transition state theory, for the granite minerals, and the local chemical equilibrium approach for the precipitation of the secondary minerals and for the reactions of aqueous complexation, we were able to simulate the first reaction pathway of this experiment using the geochemical code EQ3/6 with the ‘fluid-centred flow-through' calculation mode.The experimental results (observations of minerals and chemial composition of theoutlet fluid) provided model constraints. Particular attention was paid to the effectively reactive surface of the minerals. The correction of the reactive surface in relation to the total measured surface was necessary so that calculated results would be in agreement, at least qualitatively, with observations. A good agreement is obtained only if the effective reactive surface of the minerals is taken to be from 0.03 to 3.2% of the total surface measured by the BET-N2 method.

Compositional data from published sources, environmental monitoring and new analyses demonstrate that for a wide range of water types (oilfield water, coal mine water, landfill leachate) NH4+ is present in amounts up to 2200 mg/L. Oilfield waters from Alberta, Canada contain 1–1000 mg/L NH4+, coal mine water (UK) surface discharges 1–45 mg/L NH4+, and landfill leachates (UK) up to 2200 mg/L NH4+. Ammonium contents generally show a positive correlation with K, and increase with increasing salinity. Geochemical modelling of sufficiently complete data using SOLMINEQ88 demonstrates that NH4+ activities vary systematically, and are consistent with a mineralogical control. Sodium–K exchange divides the entire sample suite into at least 4 groups, controlled by reaction temperature and reaction with either albite/K-feldspar or illitic clay minerals. In contrast, comparison of NH4+ and K divides the sample suite into 2 groups. On the basis of geological setting, these correspond to K–NH4+ exchange involving illitic (illite-muscovite) clays (and possibly feldspars) for samples from natural sources, and to exchange involving smectitic clays for samples from landfill sites. This study demonstrates the importance of NH4+ as a constituent of natural groundwaters, requiring that this reservoir of N is taken into account in detailed discussion of hydrological components of the N cycle.

Thirteen water-production wells in glacial sediments in and around Waterloo, Ontario, (Canada) were sampled for major ions, 3H, 13C, 14C and 18O in 1976 and again in 1988 to gauge the movement of bomb-spike tritium and 14C through the Waterloo aquifer and also to assess the reliability of a hydrogeochemical interpretation of the dynamic character of an aquifer based only on single sampling episode.The suite of samples collected in 1976 was not able to indicate how fast the tritium spike was moving or even if each well-screen was intercepting the front end or tail end of the bomb-spike peak corresponding to infiltration of mid-1960s precipitation. The second sampling event portrayed movement which, qualitatively at least, gave information relating to the more permeable zones of the aquifer and direction of water movement.Water from all but one of the 13 wells sampled in 1988 registered a drop in tritium relative to the 1976 sampling. A well is deemed to be intercepting the front end of the peak of the bomb-spike if its 1988 tritium activity (±2 TU analytical uncertainty) is greater than one half that of the tritium activity of well water measured in 1976 (±8 TU uncertainty). Only one well and two shallow piezometers met this criterion. Ten wells had TU1988/TU1976 ratios which could be interpreted as either greater than or less than 0.5, if the analytical uncertainties of both analyses in this ratio are rigorously applied. Screens of two wells intercept the tail end of the spike because both their uncertainty-adjusted TU1988/TU1976 ratios range from 0.29 to 0.41.Carbon-14 activity for individual wells varied by no more than 6 Per cent Modern Carbon (PMC) between 1976 and 1988. Bomb-spike 14C is not so easily detected as tritium in passage through aquifers because the thermonuclear input of 14C into the atmosphere was much less intense (relative to pre-bomb, background levels) than that for tritium. Also, incongruent dissolution of dolomite, coupled with differing dissolution kinetics between dolomite and calcite, precipitates 14C-bearing calcite in the saturated zone.Although the chemistry of an aquifer can be reasonably characterized by a single sampling episode, the recharge rate and groundwater flow paths are best delineated from a geochemical perspective by multiple samplings in which a persistent chemical and/or isotopic tracer is sought out and repeatedly analyzed. In the Waterloo aquifer, these are tritium and Cl. The sameness of 14C activity in waters sampled 12 a apart makes this a poor candidate to use in this scheme.

The detailed understanding of in situ biodegradation of petroleum hydrocarbons in porous aquifers requires knowledge on biogeochemical gradients, the distribution of individual redox species and microorganisms. The generally limited spatial resolution of conventional monitoring wells, however, hampers appropriate characterization of small-scale gradients and thus localization of the relevant processes. Groundwater sampling across a BTEX plume in a sandy aquifer by means of a novel high-resolution multi-level well (HR-MLW) is presented here. The presence of distinct and steep biogeochemical gradients is demonstrated in the centimeter and decimeter scale, which could not be resolved with a conventional multi-level well. The thin BTEX plume with a vertical extension of only 80 cm exhibited a decline of contaminant concentrations by two orders of magnitude within a few centimeters in the upper and lower fringe zone. The small-scale distribution of sulfate, sulfide and Fe(II) in relation to the contaminants and elevated δ34S and δ18O values of groundwater sulfate strongly indicated sulfate and iron reduction to be the dominant redox processes involved in biodegradation. High microbial activities and biomass especially at the plume fringes and the slope of chemical gradients supported the concept that the latter are regulated by microbial processes and transverse dispersion, i.e. vertical mixing of electron donors and acceptors. Transverse dispersion therefore was suggested to be a driving factor controlling biodegradation in porous aquifers, but not exclusively limiting natural attenuation processes at this site. Broad overlapping zones of electron donors and electron acceptors point towards additional factors limiting anaerobic biodegradation in situ. The identification of small-scale gradients substantially contributed to a better understanding of biodegradation processes and hence is a prerequisite for the development of reliable predictive mathematical models and future remediation strategies.

The potentially toxic elements Hg and As are found at high concentrations in surface/near-surface sediments from Arctic ocean cores collected from the Voronin Trough, Kara Sea, during 1965. The levels reach 2045 ppb for Hg and 270 ppm for As. Manganese high values (up to 1.27%) are also found in the cores’ surface/near-surface sections. Other heavy metals tracked by the Arctic Monitoring and Assessment Program (e.g., Cu, Ni, Pb, Sb, Ti, Zn) have baseline concentrations in the cores. The cores average >57% clay-size and >35% silt-size in their textural composition. The elevated contents may result from anthropogenic input for Hg and As with diagenesis adding to the As concentration. Possible sources for these elements are emissions and effluents from industry such as mining and smelting operations, and burning of fossil fuels in Siberia and the Urals. When discharged into the Kara Sea from Siberian catchments, the As and Hg likely attach to charged particulate surfaces of Fe oxy/hydroxides (for As) and particulate organic matter or clay minerals (for Hg). These are transported, entrained in ocean currents or adhered to pack ice, to the Voronin Trough where they deposit according to size and specific gravity.

A regional geochemical survey using soils, stream sediment and stream water sampling revealed multi-element geochemical anomalies, though of low environmental mobility, associated with Mesozoic sedimentary ironstones in Lincolnshire, UK. The most prominent of these anomalies were of As and V in soils and sediments, but elevated levels of elements such as Cr, La, Ce and Th were also observed. These were initially thought to be part of a residual resistate element or heavy-mineral suite, but careful examination suggests that these too may be primarily associated with the process of Fe oxide precipitation during the initial formation of the ironstones.

Atmospheric heavy metal deposition in Finland from 1985 to 1990 was monitored by the moss technique. The objectives were to examine the change in the heavy metal deposition with time and to produce information about the deposition and the emission sources.Samples were collected from the permanent sampling network systematically covering the country as a whole. The total number of samples was 4883 and the concentrations of Cd, Cr, Cu, Pb, Ni and V were determined.Some important emission sources cause local enhancements of the concentrations in moss. High metal concentrations were found around the Harjavalta smelters, around the Tornio steel mill and in the north-eastern parts of Lapland near the Finnish-Russian border close to heavy metal industry in the Kola Peninsula. Elevated levels were also found around the Raahe smeleter and around the oil refineries in Naantali and Porvoo. The effect of long-range transport from the Central and East Europe can be seen especially for Cd, Pb and V. Significant decrease in the concentrations of some elements was found from 1985 to 1990.

At present, the terms Environmental Geochemistry and Applied Geochemistry are poorly defined in English. In fact they usually mean just what a particular geochemist, or geochemist(s), wishes them to mean.There is a less common term, Landscape Geochemistry, which describes a holistic scientific discipline aimed at the geochemistry of the environment. Although little known outside the U.S.S.R., the basics of landscape geochemistry were first described more than 60 a ago. Since then, landscape geochemistry has had a history pertinent to all scientists who participate in environmental geochemistry today.This review traces the evolution of landscape geochemistry, and related disciplines, over the past 90 a and shows how they all relate to the development of modern environmental geochemistry worldwide.In landscape geochemistry, the term “landscape” refers to both the horizontal stratification of land (e.g. into terrestial, bog and aquatic ecosystems which co-exist in an area of country) and to the vertical stratification within these units (e. g. into vegetation, soils etc.). In these respects landscape geochemistry resembles Landscape Ecology, which is currently a discipline of growing importance in environmental science.Landscape geochemistry differs from landscape ecology because it focuses attention on all aspects of the behaviour of chemical entities (e. g. isotopes, elements and ions), in both living and dead matter in landscapes of all kinds.From the viewpoint of general geochemistry, landscape geochemistry focusess on the interaction of the lithosphere with the hydrosphere, atmosphere and biosphere. This holistic approach provides a common theoretical background for both “pure” and “applied” environmental geochemistry worldwide.An important aspect of landscape geochemistry, particularly pertinent to environmental geochemistry in the non-Soviet world today, is that the subject provides a link between modern exploration geochemistry and modern environmental science, including geochemistry.Historically, landscape geochemistry stems from the Russian school of “Landscape Science”. This developed from the ideas of V. V. Dokuchaev (1846–1903) around the turn of the century. Concepts unique to landscape geochemistry were first described in the 1920s by one of Dokuchaev's students, B. B. Polynov (1867–1952). A. I. Perel'man (1909- ), a student of Polynov, began to teach landscape geochemistry at Moscow University in 1952. Since then, the subject has become firmly established as the focus for fundamental and applied environmental geochemistry in the U.S.S.R.This review traces the development of landscape geochemistry from its origins around 1920 until 1990. The volume of literature pertinent to the review is voluminous. For this reason, attention is usually focused on the basic concepts and principles of landscape geochemistry and related scientific disciplines. Readers who require more detailed information on subjects covered in this review should consult the references cited.The review is organized in four parts. The first three trace the historical development of landscape geochemistry, and related disciplines, in three time periods. These are: (1) pre-1950; (2) between 1950 and 1980; and (3) 1980–1990. Part 4 uses paradigms to summarize the historical evolution of landscape geochemistry and indicates how a Global Landscape Geochemistry might develop in the future.

The foundations of geochemistry and health are associated with work in Canada, U.S.A., C.I.S. and U.K. in the 1960s and parallel studies in geomedicine in Scandinavia. The development of geochemical mapping techniques and compilation of geochemical atlases have led to innovative multidis-ciplinary research into their applications in the areas of agriculture and land use, fresh water quality for irrigation and potable supplies, estuarine and coastal waters and fisheries, medicine and public health, and environmental pollution. Recent developments have concerned the influence of geochemistry in wildlife nutrition. Research in urban geochemistry has been applied to the modification of the chemical environment in towns and cities arising from urban and industrial development.The paper illustrates this research with some specific case histories and presents the author's opinion as to those priority areas that will require both national and international input in the present decade and beyond.

Despite the widespread occurrence of chlorophenols as groundwater contaminants, the aqueous solubilities of the chlorophenols are not well-characterized. In this study, the authors report the solubility of 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP) based on experiments conducted as a function of pH, ionic strength and temperature, and a speciation-based model for estimating the solubilities of other chlorophenols is derived.Narrow constraints on the aqueous solubility of both chlorophenols were made possible by conducting experiments in pure water and in 0.1 NaCl at 25°C and 55°C, from both under- and over-saturation. The solubility of the chlorophenols is pH-independent under low pH conditions, but at higher pH values it increases with increasing pH. The concentration of the protonated chlorophenol species determines the low pH solubility and, at 25°C, the log molality of the protonated species of 2,4,6-TCP is −2.8±0.1, whereas for PCP the value is −5.1±0.3. Two other properties were used to model the solubility as a function of pH: the acidity constant (Ka) and the stability constant for a Na-chlorophenolate complex. The pKa and Na-chlorophenolate log stability constant values that best fit the solubility data for 2,4,6-TCP are 6.1±0.3 and 1.0±0.5, respectively; the values for PCP are 4.5±0.3 and 1.0±0.5, respectively. At 55°C, the log molality of protonated PCP increases to −4.7±0.2 and the pKa and log stability constant value are 4.1±0.3 and 0.9±0.5, respectively. The log stability constant for NaPCP° at 55°C is equal to 0.9±0.5.The experimental solubility measurements are used to construct a theoretical model which defines the solubility of a chlorophenol in terms of its acidity constant and its low pH minimum solubility. This approach enables estimations of the aqueous solubility of other chlorophenol molecules as a function of pH, ionic strength and temperature. In order to facilitate application of this model to other chlorophenol molecules, the authors compile and critically review the solubility data for 20 chlorophenols from the literature. The results of the experiments and review enable estimations of chlorophenol solubilities under a wide range of conditions of environmental interest.

Many water-supply systems in South America utilize the waters of the Guarani aquifer at least as part of their networks. However, there is little present knowledge in Brazil of the factors affecting Rn presence in the water supplied for end-users, despite the economic importance of Guarani aquifer. 222Rn analyzes of 162 water samples were performed at 8 municipalities in São Paulo State, Brazil, with the aim of investigating the major factors affecting its presence in solution. The 222Rn activity concentration ranged from 0.04 up to 204.9 Bq/L, with three samples exceeding the World Health Organization maximum limit of 100 Bq/L. Aeration was confirmed as the most important factor for Rn release, as expected due to its gaseous nature. Accumulation in pipes and stratification in the water column were other significant factors explaining the data obtained in some circumstances. The Rn daughters 214Pb and 214Bi were also determined in a set of selected samples and their presence was directly related to the occurrence of Rn dissolved in water.

Laboratory time-scale experiments were conducted on Carboniferous Limestone gravels from the Mendip Hills area, England, with the purpose of evaluating the release of222Rn to the water phase. The specific surface areas of the samples were 4.14 and 1.69 cm2 g−1 , which provided, respectively, values of 50.6 and 12.7 pCi for the released Rn. These results allowed the calculation of the emanation coefficient of this rock matrix with respect to the release of Rn, where completely different values corresponding to 23% and 6% were found, suggesting that the extent to which grain boundaries or imperfections in aggregates of micro-crystals of calcite intersect the particle surface certainly affects the Rn release. They also permitted the evaluation of models for the generation of Rn in rocks and transfer to water, in order to interpret the radioactivity due to this gas in groundwaters from the karstic aquifer of the Mendip Hills area, where the calculated activities in groundwater based on the values of 23% and 6% for the emanation coefficient were about 51 and 15 times higher than actually measured in groundwater. Therefore, the emanation coefficient in nature is considerably smaller than in the lab experiment, and another factork (0 < k < 1) may be introduced into the equations related to the modelling, with the aim of adjusting the theoretical-practical results.

Water draining from abandoned open-pit coal mines in southeastern Ohio typically has a low pH and high concentrations of Fe, Al and Mn, as well as of trace metals (Pb, Cu, Zn, Ni, Co, etc.) and of the rare earth elements (REEs). The cations of different elements are sorbed selectively by Fe and Al hydroxide precipitates which form with increasing pH. As a result, the trace elements are separated from each other when the hydroxide precipitates are deposited in the channel of a flowing stream. Therefore, the low-energy environment of a stream contaminated by mine effluent is a favorable site for the chemical fractionation of the REEs and of other groups of elements with similar chemical properties. The interpretation of chemical analyses of water collected along a 30-km-stretch of Rush Creek near the town of New Lexington, Perry County, Ohio, indicates that the abundances of the REEs in the water appear to change downstream when they are normalized to the REE concentrations of the mine effluent. In addition, the Ce/La ratios (and those of all REEs) in the water decrease consistently downstream. The evidence indicates that the REEs which remain in solution are enriched La and Ce because the other REEs are sorbed more efficiently. The solid Fe(OH)3 precipitates in the channel of Rush Creek upstream of New Lexington also contain radioactive 226Ra that was sorbed from the water. This isotope of Ra is a decay product of 238U which occurs in the Middle Pennsylvanian (Upper Carboniferous) coal and in the associated shale of southeastern Ohio. The activity of 226Ra of the Fe(OH)3 precipitates increases with rising pH, but then declines farther downstream as the concentration of Ra remaining in the water decreases.

The temperature dependence of the self-diffusion of HTO, 22Na+ and 36Cl− in Opalinus Clay (OPA) was studied using a through-diffusion technique, in which the temperature was gradually increased in the steady state phase of the diffusion. The measurements were done on samples from two different geological locations. The dependence of the effective diffusion coefficient on temperature was found to be of an Arrhenius type in the temperature range between 0 and 70 °C. A slight difference between the two locations could be observed. The average value of the activation energy of the self-diffusion of HTO in OPA was 21.1 ± 1.6 kJ mol−1, and 21.0 ± 3.5 and 19.4 ± 1.5 kJ mol−1 for 22Na+ and 36Cl−, respectively. The measured values for HTO are slightly higher than the values found for the bulk liquid water (HTO: 18.8 ± 0.4 kJ mol−1). This indicates that the structure of the confined water in OPA might be slightly different from that of bulk liquid water. Also for Na+ and Cl−, slightly higher values than in bulk liquid water (Na+: 18.4 kJ mol−1; Cl−: 17.4 kJ mol−1) were observed.The Stokes–Einstein relationship, based on the temperature dependency of the viscosity of bulk water, could not be used to describe the temperature dependence of the diffusion of HTO in OPA. This additionally indicates the slightly different structure of the pore water in OPA.

The isotope activity ratios ²³⁴U/²³⁸U and ²³⁰Th/²³⁴U have been investigated in drill core samples up to 1300 m depth in three granitoids from Australia to identify the nature of possible recent (<1 Ma) radionuclide mobilisation. Most whole-rock samples from the Coles Bay Granite, Tasmania, display secular equilibrium between ²³⁴U and ²³⁸U (²³⁴U/²³⁸U∼ 1.0) and preferential ²³⁴U loss occurring in one highly fractured sample. Significant ²³⁰Th/²³⁴U disequilibrium throughout most of the drill core is attributed to a depletion in bulk U and production of excess ²³⁰Th. Radioactive disequilibrium which occurs between ²³⁸U, ²³⁴U and ²³⁰Th in drill core samples from the Kambalda Granodiorite, Western Australia indicates U gain as a result of interaction with ground waters enriched in ²³⁴U. Near-surface samples are weathered and display preferential loss of ²³⁴U through further surface water interaction. Significant radioactive disequilibrium in the Roxby Downs Granite, South Australia suggests that a number of interactive U accumulation and removal events have occurred. Initial U deposition from enriched ground water is indicated in samples to 530 m depth and has been followed by selective removal of ²³⁴U (²³⁸U/²³⁴U∼ 1.0 and ²³⁰Th/²³⁴U> 1.0) which has generated excess ²³⁰Th. These enriched ground waters do not appear to have penetrated below 530 m depth, and ²³⁰Th excess indicates bulk loss of U.

It is difficult to measure accurately the natural long-term corrosion rates of highly durable nuclear waste glasses. Care should be taken when using data from high temperature experiments to predict corrosion rates under ambient repository conditions as there are many factors (such as the precipitation of secondary compounds, the chemistry of the water in contact with the glass, or circulation of this water through the repository) that can influence the temperature dependence of aqueous reactions. In this study, some standard leach tests using pure water, in continuous flow and direct sampling autoclaves, were performed on a synthetic medieval glass. Archaeological glass samples of a similar composition and which had suffered several centuries of corrosion in damp soil had been the subject of previous studies. The corrosion of the archaeological samples in damp soil was well understood and the aim was to determine how well standard leach tests would predict the observed corrosion.

Natural and constructed clay liners are routinely used to contain waste and wastewater. The impact of acidic solutions on the geochemistry and mineralogy of clays has been widely investigated in relation to acid mine drainage systems at pH > 1.0. The impact of H2SO4 leachate characterized by pH < 1.0 and potentially negative pH values on the geochemistry and mineralogy of clays is, however, not clear. Thus, laboratory batch experiments were conducted on three natural clay samples with different mass ratios of smectite, illite and kaolinite to investigate the impact of H2SO4 on the geochemistry and mineralogy of aluminosilicates from pH 5.0 to −3.0. Batch testing was conducted at seven pH treatments (5.0, 3.0, 1.0, 0.0, −1.0, −2.0 and −3.0) using standardized H2SO4 solutions for four exposure periods (14, 90, 180, and 365 d). Aqueous geochemical and XRD analyses showed: increased dissolution of aluminosilicates with decreasing pH and increasing exposure period, that smectite was more susceptible to dissolution than illite and kaolinite, precipitation of an amorphous silica phase occurred at pH ⩽ 0.0, and anhydrite precipitated in Ca-rich clays at pH ⩽ −1.0. In addition, global dissolution rates were calculated for the clays and showed good agreement to literature smectite, illite and kaolinite dissolution rates, which suggests global dissolution rates for complex clays could be determined from monomineralic studies. A stepwise conceptual model of the impact of H2SO4 on aluminosilicate geochemistry and mineralogy between pH 5.0 and −3.0 is proposed.

The authors report here halogen concentrations in pore waters and sediments collected from the Mallik 5L-38 gas hydrate production research well, a permafrost location in the Mackenzie Delta, Northwest Territories, Canada. Iodine and Br are commonly enriched in waters associated with CH4, reflecting the close association between these halogens and source organic materials. Pore waters collected from the Mallik well show I enrichment, by one order of magnitude above that of seawater, particularly in sandy layers below the gas hydrate stability zone (GHSZ). Although Cl and Br concentrations increase with depth similar to the I profile, they remain below seawater values. The increase in I concentrations observed below the GHSZ suggests that I-rich fluids responsible for the accumulation of CH4 in gas hydrates are preferentially transported through the sandy permeable layers below the GHSZ. The Br and I concentrations and I/Br ratios in Mallik are considerably lower than those in marine gas hydrate locations, demonstrating a terrestrial nature for the organic materials responsible for the CH4 at the Mallik site. Halogen systematics in Mallik suggest that they are the result of mixing between seawater, freshwater and an I-rich source fluid. The comparison between I/Br ratios in pore waters and sediments speaks against the origin of the source fluids within the host formations of gas hydrates, a finding compatible with the results from a limited set of 129I/I ratios determined in pore waters, which gives a minimum age of 29 Ma for the source material, i.e. at the lower end of the age range of the host formations. The likely scenario for the gas hydrate formation in Mallik is the derivation of CH4 together with I from the terrestrial source materials in formations other than the host layers through sandy permeable layers into the present gas hydrate zones.

Phosphonic acids are commonly used as scale and corrosion inhibitors, but little is known about their solubility and stoichiometry. Hence, questions concerning the retention mechanisms of phosphonates in reservoir systems remain unanswered. A method is described in this paper to measure the solubility and stoichiometry of the phosphonates and is applied to diethylenetriaminepenta (methylene phosphonic acid) (DTPMP). The experiments reported herein were performed in 2.0 M brine solutions at 70°C for varying Ca and DTPMP concentrations at 4.7 and 5.0 pH.The conditional equilibrium constants of the Ca-DTPMP salts formed under the conditions of the experiment are 4.34 × 10−4 and 3.04 × 10−4 at pH values of 4.7 and 5.0, respectively. The stoichiometry of the solid phase precipitated in the experiments and the dominant solution complex are Ca3.5H3PHN·3H2O and Ca3H3PHN1− where PHN refers to the deprotonated DTPMP ligand. These results suggest that retention mechanisms involved in an inhibitor squeeze are either adsorption or precipitation/coprecipitation with cations other than Ca and/or other ligands.

In all, 53 elements were analyzed in 1406 coastal sea sediment samples collected from an area off Hokkaido and the Tohoku region of Japan during a nationwide marine geochemical mapping project. The spatial distribution patterns of the elemental concentrations in coastal seas along with the existing geochemical maps in terrestrial areas were used to define natural geochemical background variation and mass transport processes. The terrestrial area is covered by mafic volcanic rocks and accretionary complexes associated with ophiolite, which has small amounts of felsic volcanic rocks and granite. The spatial distribution patterns of elements enriched in mafic lithologies such as Fe (Total Fe2O3) and Sc in marine environments are influenced by adjoining terrestrial materials. The spatial distribution patterns of Cr and Ni concentrations, which are highly abundant in ultramafic rocks on land, are used to evaluate the mass transport from land to the sea and the dispersive processes caused by oceanic currents. The scale of mass transport by oceanic currents occurs up to a distance of 100–200 km from the coast along the coastal areas. The regional differences of elements rich in felsic lithologies such as K (K2O), Nb and La in marine sediments are determined mainly by the relative proportion of minerals and lithic fragments enriching felsic materials to those associated with mafic materials. The spatial distribution of elemental concentration is not always continuous between the land areas and coastal sea areas. That difference is interpreted as resulting from (1) transportation of marine sediments by oceanic currents and storm waves, (2) contribution of volcanic materials such as tephra, (3) occurrence of shell fragments and foraminifera tests and (4) distribution of relict sediments of the last glacial age and early transgression age. Contamination with Cu, Zn, Cd, As, Mo, Sn, Sb, Hg, Pb and Bi was not observed in marine environments because the study area has little anthropogenic activity. Terrestrial materials are the dominant source for these metals. The Mo, Cd, Sn, Sb, Hg, Pb and Bi are abundant in silty and clayey sediments locally because of early diagenetic processes, authigenic precipitation and organic substances associated with these elements. The spatial distribution of As concentration shows exceptions: it is concentrated in some coarse and fine sands on the shelf. The enrichment is explained by adsorption of As, sourced from a coal field, to Fe hydroxide.

Many countries are considering options for long-term management of nuclear waste. One common aspect among deep geological disposal options in granitic host rock is the use of clay-based buffer materials to limit radionuclide migration in case of container failure. The isothermal test (ITT) involved placing ∼2.4 m3 of clay-based buffer in a borehole at the 240 m level of AECL's Underground Research Laboratory to study the response of buffer to resaturation by groundwater over a 6.5-year period. Results are reported here on measurements taken at the end of the test for microbial, redox and organic characterization of the buffer. Results from enumerations and biomass determinations suggested that the viable population of cells in the buffer was several orders of magnitude larger than could be cultured. It is postulated that, due to the constrictive and nutrient-poor buffer environment, viable and active cells became stressed during burial and lost activity and culturability but not viability. Culturable microbial populations at interfaces in the ITT were about an order of magnitude larger than in comparable bulk buffer samples, suggesting that interfaces may be preferred sites for microbial activity and transport. The presence of culturable SO4-reducing bacteria and an increase in solid sulphide concentrations in the buffer suggested SO4 reduction, which appeared to be very variable locally. Only about 0.02–0.5% of SO4 was converted to sulphide, suggesting that SO4 reduction was not (yet) a dominant process. No methanogens could be enumerated from the ITT, and phospholipid fatty acid (PLFA) profiles did not suggest their presence. Gas analysis of samples recovered from the ITT suggested some reduction in O2 near the top of the experiment, but deeper samples did not show a significant decrease in O2 and had only a small increase in CH4 and H2 levels. This suggested that microbial processes were depressed in the buffer but may have been more active near the concrete/buffer interface. The suggestion of low microbial activity in the buffer was corroborated by the results from the PLFA analysis, which indicated low biomass turnover rates and starvation biomarkers. The combination of enumerations, PLFA and gas analysis results suggested that no significant evolution towards reducing conditions occurred during the duration of the ITT. Fulvic acids made up the largest fraction of water-leachable humic substances but accounted for only about 2% of the total C inventory of the buffer material. The complexing capacity of these humic substances, based on carboxylic functional groups, ranged from 24 to 32 meq/g dissolved organic C. This may provide buffer porewater with considerable complexing capacity for radionuclides.

Many water-supply systems in South America utilize the waters of the Guarani aquifer at least as part of their networks. However, there is little present knowledge in Brazil of the factors affecting Rn presence in the water supplied for end-users, despite the economic importance of Guarani aquifer. 222Rn analyzes of 162 water samples were performed at 8 municipalities in São Paulo State, Brazil, with the aim of investigating the major factors affecting its presence in solution. The 222Rn activity concentration ranged from 0.04 up to 204.9 Bq/L, with three samples exceeding the World Health Organization maximum limit of 100 Bq/L. Aeration was confirmed as the most important factor for Rn release, as expected due to its gaseous nature. Accumulation in pipes and stratification in the water column were other significant factors explaining the data obtained in some circumstances. The Rn daughters 214Pb and 214Bi were also determined in a set of selected samples and their presence was directly related to the occurrence of Rn dissolved in water.

Laboratory time-scale experiments were conducted on Carboniferous Limestone gravels from the Mendip Hills area, England, with the purpose of evaluating the release of222Rn to the water phase. The specific surface areas of the samples were 4.14 and 1.69 cm2 g−1 , which provided, respectively, values of 50.6 and 12.7 pCi for the released Rn. These results allowed the calculation of the emanation coefficient of this rock matrix with respect to the release of Rn, where completely different values corresponding to 23% and 6% were found, suggesting that the extent to which grain boundaries or imperfections in aggregates of micro-crystals of calcite intersect the particle surface certainly affects the Rn release. They also permitted the evaluation of models for the generation of Rn in rocks and transfer to water, in order to interpret the radioactivity due to this gas in groundwaters from the karstic aquifer of the Mendip Hills area, where the calculated activities in groundwater based on the values of 23% and 6% for the emanation coefficient were about 51 and 15 times higher than actually measured in groundwater. Therefore, the emanation coefficient in nature is considerably smaller than in the lab experiment, and another factork (0 < k < 1) may be introduced into the equations related to the modelling, with the aim of adjusting the theoretical-practical results.

Water draining from abandoned open-pit coal mines in southeastern Ohio typically has a low pH and high concentrations of Fe, Al and Mn, as well as of trace metals (Pb, Cu, Zn, Ni, Co, etc.) and of the rare earth elements (REEs). The cations of different elements are sorbed selectively by Fe and Al hydroxide precipitates which form with increasing pH. As a result, the trace elements are separated from each other when the hydroxide precipitates are deposited in the channel of a flowing stream. Therefore, the low-energy environment of a stream contaminated by mine effluent is a favorable site for the chemical fractionation of the REEs and of other groups of elements with similar chemical properties. The interpretation of chemical analyses of water collected along a 30-km-stretch of Rush Creek near the town of New Lexington, Perry County, Ohio, indicates that the abundances of the REEs in the water appear to change downstream when they are normalized to the REE concentrations of the mine effluent. In addition, the Ce/La ratios (and those of all REEs) in the water decrease consistently downstream. The evidence indicates that the REEs which remain in solution are enriched La and Ce because the other REEs are sorbed more efficiently. The solid Fe(OH)3 precipitates in the channel of Rush Creek upstream of New Lexington also contain radioactive 226Ra that was sorbed from the water. This isotope of Ra is a decay product of 238U which occurs in the Middle Pennsylvanian (Upper Carboniferous) coal and in the associated shale of southeastern Ohio. The activity of 226Ra of the Fe(OH)3 precipitates increases with rising pH, but then declines farther downstream as the concentration of Ra remaining in the water decreases.

The temperature dependence of the self-diffusion of HTO, 22Na+ and 36Cl− in Opalinus Clay (OPA) was studied using a through-diffusion technique, in which the temperature was gradually increased in the steady state phase of the diffusion. The measurements were done on samples from two different geological locations. The dependence of the effective diffusion coefficient on temperature was found to be of an Arrhenius type in the temperature range between 0 and 70 °C. A slight difference between the two locations could be observed. The average value of the activation energy of the self-diffusion of HTO in OPA was 21.1 ± 1.6 kJ mol−1, and 21.0 ± 3.5 and 19.4 ± 1.5 kJ mol−1 for 22Na+ and 36Cl−, respectively. The measured values for HTO are slightly higher than the values found for the bulk liquid water (HTO: 18.8 ± 0.4 kJ mol−1). This indicates that the structure of the confined water in OPA might be slightly different from that of bulk liquid water. Also for Na+ and Cl−, slightly higher values than in bulk liquid water (Na+: 18.4 kJ mol−1; Cl−: 17.4 kJ mol−1) were observed.The Stokes–Einstein relationship, based on the temperature dependency of the viscosity of bulk water, could not be used to describe the temperature dependence of the diffusion of HTO in OPA. This additionally indicates the slightly different structure of the pore water in OPA.

The isotope activity ratios ²³⁴U/²³⁸U and ²³⁰Th/²³⁴U have been investigated in drill core samples up to 1300 m depth in three granitoids from Australia to identify the nature of possible recent (<1 Ma) radionuclide mobilisation. Most whole-rock samples from the Coles Bay Granite, Tasmania, display secular equilibrium between ²³⁴U and ²³⁸U (²³⁴U/²³⁸U∼ 1.0) and preferential ²³⁴U loss occurring in one highly fractured sample. Significant ²³⁰Th/²³⁴U disequilibrium throughout most of the drill core is attributed to a depletion in bulk U and production of excess ²³⁰Th. Radioactive disequilibrium which occurs between ²³⁸U, ²³⁴U and ²³⁰Th in drill core samples from the Kambalda Granodiorite, Western Australia indicates U gain as a result of interaction with ground waters enriched in ²³⁴U. Near-surface samples are weathered and display preferential loss of ²³⁴U through further surface water interaction. Significant radioactive disequilibrium in the Roxby Downs Granite, South Australia suggests that a number of interactive U accumulation and removal events have occurred. Initial U deposition from enriched ground water is indicated in samples to 530 m depth and has been followed by selective removal of ²³⁴U (²³⁸U/²³⁴U∼ 1.0 and ²³⁰Th/²³⁴U> 1.0) which has generated excess ²³⁰Th. These enriched ground waters do not appear to have penetrated below 530 m depth, and ²³⁰Th excess indicates bulk loss of U.

It is difficult to measure accurately the natural long-term corrosion rates of highly durable nuclear waste glasses. Care should be taken when using data from high temperature experiments to predict corrosion rates under ambient repository conditions as there are many factors (such as the precipitation of secondary compounds, the chemistry of the water in contact with the glass, or circulation of this water through the repository) that can influence the temperature dependence of aqueous reactions. In this study, some standard leach tests using pure water, in continuous flow and direct sampling autoclaves, were performed on a synthetic medieval glass. Archaeological glass samples of a similar composition and which had suffered several centuries of corrosion in damp soil had been the subject of previous studies. The corrosion of the archaeological samples in damp soil was well understood and the aim was to determine how well standard leach tests would predict the observed corrosion.

Natural and constructed clay liners are routinely used to contain waste and wastewater. The impact of acidic solutions on the geochemistry and mineralogy of clays has been widely investigated in relation to acid mine drainage systems at pH > 1.0. The impact of H2SO4 leachate characterized by pH < 1.0 and potentially negative pH values on the geochemistry and mineralogy of clays is, however, not clear. Thus, laboratory batch experiments were conducted on three natural clay samples with different mass ratios of smectite, illite and kaolinite to investigate the impact of H2SO4 on the geochemistry and mineralogy of aluminosilicates from pH 5.0 to −3.0. Batch testing was conducted at seven pH treatments (5.0, 3.0, 1.0, 0.0, −1.0, −2.0 and −3.0) using standardized H2SO4 solutions for four exposure periods (14, 90, 180, and 365 d). Aqueous geochemical and XRD analyses showed: increased dissolution of aluminosilicates with decreasing pH and increasing exposure period, that smectite was more susceptible to dissolution than illite and kaolinite, precipitation of an amorphous silica phase occurred at pH ⩽ 0.0, and anhydrite precipitated in Ca-rich clays at pH ⩽ −1.0. In addition, global dissolution rates were calculated for the clays and showed good agreement to literature smectite, illite and kaolinite dissolution rates, which suggests global dissolution rates for complex clays could be determined from monomineralic studies. A stepwise conceptual model of the impact of H2SO4 on aluminosilicate geochemistry and mineralogy between pH 5.0 and −3.0 is proposed.

The authors report here halogen concentrations in pore waters and sediments collected from the Mallik 5L-38 gas hydrate production research well, a permafrost location in the Mackenzie Delta, Northwest Territories, Canada. Iodine and Br are commonly enriched in waters associated with CH4, reflecting the close association between these halogens and source organic materials. Pore waters collected from the Mallik well show I enrichment, by one order of magnitude above that of seawater, particularly in sandy layers below the gas hydrate stability zone (GHSZ). Although Cl and Br concentrations increase with depth similar to the I profile, they remain below seawater values. The increase in I concentrations observed below the GHSZ suggests that I-rich fluids responsible for the accumulation of CH4 in gas hydrates are preferentially transported through the sandy permeable layers below the GHSZ. The Br and I concentrations and I/Br ratios in Mallik are considerably lower than those in marine gas hydrate locations, demonstrating a terrestrial nature for the organic materials responsible for the CH4 at the Mallik site. Halogen systematics in Mallik suggest that they are the result of mixing between seawater, freshwater and an I-rich source fluid. The comparison between I/Br ratios in pore waters and sediments speaks against the origin of the source fluids within the host formations of gas hydrates, a finding compatible with the results from a limited set of 129I/I ratios determined in pore waters, which gives a minimum age of 29 Ma for the source material, i.e. at the lower end of the age range of the host formations. The likely scenario for the gas hydrate formation in Mallik is the derivation of CH4 together with I from the terrestrial source materials in formations other than the host layers through sandy permeable layers into the present gas hydrate zones.

Phosphonic acids are commonly used as scale and corrosion inhibitors, but little is known about their solubility and stoichiometry. Hence, questions concerning the retention mechanisms of phosphonates in reservoir systems remain unanswered. A method is described in this paper to measure the solubility and stoichiometry of the phosphonates and is applied to diethylenetriaminepenta (methylene phosphonic acid) (DTPMP). The experiments reported herein were performed in 2.0 M brine solutions at 70°C for varying Ca and DTPMP concentrations at 4.7 and 5.0 pH.The conditional equilibrium constants of the Ca-DTPMP salts formed under the conditions of the experiment are 4.34 × 10−4 and 3.04 × 10−4 at pH values of 4.7 and 5.0, respectively. The stoichiometry of the solid phase precipitated in the experiments and the dominant solution complex are Ca3.5H3PHN·3H2O and Ca3H3PHN1− where PHN refers to the deprotonated DTPMP ligand. These results suggest that retention mechanisms involved in an inhibitor squeeze are either adsorption or precipitation/coprecipitation with cations other than Ca and/or other ligands.

In all, 53 elements were analyzed in 1406 coastal sea sediment samples collected from an area off Hokkaido and the Tohoku region of Japan during a nationwide marine geochemical mapping project. The spatial distribution patterns of the elemental concentrations in coastal seas along with the existing geochemical maps in terrestrial areas were used to define natural geochemical background variation and mass transport processes. The terrestrial area is covered by mafic volcanic rocks and accretionary complexes associated with ophiolite, which has small amounts of felsic volcanic rocks and granite. The spatial distribution patterns of elements enriched in mafic lithologies such as Fe (Total Fe2O3) and Sc in marine environments are influenced by adjoining terrestrial materials. The spatial distribution patterns of Cr and Ni concentrations, which are highly abundant in ultramafic rocks on land, are used to evaluate the mass transport from land to the sea and the dispersive processes caused by oceanic currents. The scale of mass transport by oceanic currents occurs up to a distance of 100–200 km from the coast along the coastal areas. The regional differences of elements rich in felsic lithologies such as K (K2O), Nb and La in marine sediments are determined mainly by the relative proportion of minerals and lithic fragments enriching felsic materials to those associated with mafic materials. The spatial distribution of elemental concentration is not always continuous between the land areas and coastal sea areas. That difference is interpreted as resulting from (1) transportation of marine sediments by oceanic currents and storm waves, (2) contribution of volcanic materials such as tephra, (3) occurrence of shell fragments and foraminifera tests and (4) distribution of relict sediments of the last glacial age and early transgression age. Contamination with Cu, Zn, Cd, As, Mo, Sn, Sb, Hg, Pb and Bi was not observed in marine environments because the study area has little anthropogenic activity. Terrestrial materials are the dominant source for these metals. The Mo, Cd, Sn, Sb, Hg, Pb and Bi are abundant in silty and clayey sediments locally because of early diagenetic processes, authigenic precipitation and organic substances associated with these elements. The spatial distribution of As concentration shows exceptions: it is concentrated in some coarse and fine sands on the shelf. The enrichment is explained by adsorption of As, sourced from a coal field, to Fe hydroxide.

Many countries are considering options for long-term management of nuclear waste. One common aspect among deep geological disposal options in granitic host rock is the use of clay-based buffer materials to limit radionuclide migration in case of container failure. The isothermal test (ITT) involved placing ∼2.4 m3 of clay-based buffer in a borehole at the 240 m level of AECL's Underground Research Laboratory to study the response of buffer to resaturation by groundwater over a 6.5-year period. Results are reported here on measurements taken at the end of the test for microbial, redox and organic characterization of the buffer. Results from enumerations and biomass determinations suggested that the viable population of cells in the buffer was several orders of magnitude larger than could be cultured. It is postulated that, due to the constrictive and nutrient-poor buffer environment, viable and active cells became stressed during burial and lost activity and culturability but not viability. Culturable microbial populations at interfaces in the ITT were about an order of magnitude larger than in comparable bulk buffer samples, suggesting that interfaces may be preferred sites for microbial activity and transport. The presence of culturable SO4-reducing bacteria and an increase in solid sulphide concentrations in the buffer suggested SO4 reduction, which appeared to be very variable locally. Only about 0.02–0.5% of SO4 was converted to sulphide, suggesting that SO4 reduction was not (yet) a dominant process. No methanogens could be enumerated from the ITT, and phospholipid fatty acid (PLFA) profiles did not suggest their presence. Gas analysis of samples recovered from the ITT suggested some reduction in O2 near the top of the experiment, but deeper samples did not show a significant decrease in O2 and had only a small increase in CH4 and H2 levels. This suggested that microbial processes were depressed in the buffer but may have been more active near the concrete/buffer interface. The suggestion of low microbial activity in the buffer was corroborated by the results from the PLFA analysis, which indicated low biomass turnover rates and starvation biomarkers. The combination of enumerations, PLFA and gas analysis results suggested that no significant evolution towards reducing conditions occurred during the duration of the ITT. Fulvic acids made up the largest fraction of water-leachable humic substances but accounted for only about 2% of the total C inventory of the buffer material. The complexing capacity of these humic substances, based on carboxylic functional groups, ranged from 24 to 32 meq/g dissolved organic C. This may provide buffer porewater with considerable complexing capacity for radionuclides.

The effect of malonate on the dissolution rate of the reservoir minerals: albite, quartz, and microcline has been examined. The effect of pH on rate has been decoupled from the effect of the ligand by controlling pH using dilute buffer solutions at values of pH 4 through pH 10 at 70°C. Any effect of the buffer ligands (acetate and borate) or alkali cation (Na) on rate was accounted for by comparing the measured dissolution rates in buffer solutions with and without malonate. Flowing reactors were used and malonate concentration was varied from 1 to 100 mmolal.As malonate anion concentration is increased, the dissolution rate of these minerals also increases. At moderately acidic to near neutral pH in the solutions containing the highest malonate concentration, malonate most significantly increases the dissolution rate of the silicates over that expected due to simple hydrolysis. At alkaline pH the effect of malonate on the dissolution rate of these silicates is not significant, compared to the dissolution rate due to simple hydrolysis alone.

Almost invariably the compositions of porewaters given for highly compacted bentonite are calculated values because reliable water samples from compacted material are virtually impossible to obtain, even by squeezing under very high pressures. Assumptions and simplifications are made in the geochemical models used to perform such calculations and the predictions are seldom if ever tested. One of the main hypotheses in a recently proposed model for calculating the porewater in compacted bentonite was that the initial pH is determined by the state of the amphoteric surface hydroxyl groups, SOH type sites, on the montmorillonite component. The calculations indicated that the initial pH of the porewater is a value close to 8. The aims of the work reported here are to check the predictions of the model in terms of the pH, which is one of the most important parameters for any porewater, and the strong buffering effect of the SOH type sites. The concept behind the tests was to take a powdered bentonite and a background electrolyte (0.2 M CaCl2) containing known quantities of acid or base (pH values between 1.5 and 12), mix them together at a high solid to liquid ratio (312 g L−1) and then allow them to react in the absence of air in a closed system. If the model concepts and parameter values are valid, then the model should be able to predict the pH measured in such experiments. The model calculations agreed well with the measured pH values and confirmed that it is highly likely that the SOH type sites determine the initial pH of the porewater in compacted bentonite systems. Further, these amphoteric surface hydroxyl groups at the edges of montmorillonite provide an extremely high buffer capacity in the compacted system for maintaining the bentonite porewater pH at a value of ∼8.

The Sr isotope composition of formation waters is a sensitive indicator of diagenetic processes in the host sediments, mixing processes between different bodies of water, and the connectivity of hydrological systems. The87Sr/86Sr ratio of present seawater is constant worldwife, while formation waters in hydrocarbon reservoirs have various values, depending on the aforementioned effects, in most cases different from modern seawater. This forms the basis of anatural tracer technique for seawater injection projects, involving characterization of the87Sr/86Sr ratios and Sr contents of formation waters in the reservoir before injection commences, followed by monitoring of these parameters in the produced water as injection proceeds. This method is best suited to reservoirs in which the formation waters have low Sr concentrations and87Sr/86Sr ratios much higher or lower than seawater. Available data for reservoir formation waters suggest that breakthrough recognition could be expected at <10% seawater in many sandstone reservoirs, while the method would be less sensitive in carbonate reservoir or situations where the formation waters had interacted with evaporites, as the associated waters tend to have high Sr contents. In heterogeneous but well-mapped reservoirs, it may be possible to obtain information about flow paths/mechanismsbefore breakthrough. Combination with other chemical and isotopic tracers creates a very powerful tool, the Sr method acting as a safeguard should the batch of water containing the conventional tracers be overtaken by subsequently injected seawater. The Sr method could also be used for injection projects that were begun without the addition of tracers. A natural analogue of a water injection process is found in the Jurassic Lincolnshire Limestone aquifer in England, where rapidly moving fresh meteoric water mixes progressively with an older saline formation water. The87Sr/86Sr data enable quantitative modelling of this mixing process. The infiltrating fresh water becomes progressively modified by dissolution of detrital carbonate and calcite cement in the limestone, with depth becoming increasingly dominated by Sr derived from the more soluble detrital components. The saline formation water contains water molecules of meteoric origin and an87Sr/86Sr ratio much higher than Jurassic seawater or marine carbonate; the solute content has been influence by interaction of the water with non-carbonate phases.

Acid mine drainage from the abandoned Spenceville Cu mine contributes toxic levels of metals to nearby streams. The majority of metal contamination, however, is removed from the system over a short spatial distance. The primary mechanism responsible for this geochemical scavenging is adsorption onto Fe, Mn and Al-hydroxide precipitates that are clearly visible in the streambed. A 5-step sequential extraction procedure was performed on the streambed sediments in order to characterize solid phase speciation of metals in this area. Two fractions (carbonate and amorphous Fe-Mn hydroxide) were considered to be bioavailable, with the possibility of the metals in these phases being remobilized under changing ambient conditions. Copper and Zn were found to have the highest bioavailability, followed by Cd, Pb and Al. Although most metal in the acid mine drainage was rapidly removed from the system, aqueous concentrations of Cu and Zn exceeded California water quality criteria 0.5 km downstream of the mine site.

Wales, with its long history of metalliferous mining, has many abandonded mines and ore-rich spoil tips, several of which are very extensive. Most of the ore minerals are sulphides, Zn occurring as sphalerite in which Cd is ubiquitous. Soils in the vicinity of the tips contain up to 1000 ppm Cd. Analyses of the ZnS reveal Cd values up to 0.52% with Zn/Cd ratios ranging from 120 to 665, mean 306. Fine spoil from the area contains up to 1050 ppm Cd, the mean Zn/Cd ratio of the most metal-rich samples being 75. Surface samples of tip contain high levels of water-soluble Cd but Zn/Cd ratios are much higher than those for the whole tip material, suggesting that Zn is preferentially leached out.Adit and spoil drainage waters have Cd levels up to 2.5 mg/1 while ground waters from the tips contain up to 2.7 mg/1. The Zn/Cd ratios of these waters are very variable ranging from ~20 to >1000. The Zn/Cd ratio in the ground waters is generally <100, while surface and adit drainage waters are mostly in the range 100–250. The differing ratios in surface and subsurface waters probably reflect variable Eh and pH conditions. In addition, it has been found that adit and tip waters which are rich in Fe and tend to precipitate ochre have relatively high Zn/Cd ratios, typically between 300 and 800, while the ochreous precipitates have ratios between 140 and 250. It is suggested that the Cd content of these waters is controlled by oxidation with consequent precipitation of Fe which scavenges Cd. The Cd content of tip drainage waters shows marked seasonal variation with highest values recorded in winter and after summer droughts. However, the Zn/Cd ratio of individual streams shows remarkable temporal constancy.