Applied Geochemistry (v.24, #10)

This work presents the results from evaluating the gases sorbed by coal samples extracted from the Paleocene Guasare Coalfield (Marcelina Formation, northwestern Venezuela), as well as by their distinct maceral concentrates. The aim of this work has been to obtain an initial experimental main value of the gas content per unit weight of high volatile bituminous A coal samples from the open-pit Paso Diablo mine. An additional goal was to study differences in the CH4 storage ability of the distinct maceral groups forming part of the coal matrix. Both the coal samples and the maceral concentrates were studied by thermogravimetric analysis (TGA) in order to determine the temperature to be used in subsequent experiments. On-line analyses of hydrocarbons (C1, C2, C3) and CO2 yielded gas concentrations, plus δ 13C values. Thermogenic gas is prevalent in the Guasare coals with vitrinite reflectance (%R o) values from 0.65% to 0.88%. The amount of gas retained in the coals and maceral concentrates was measured with a special device that allows determination of the volume of gas sorbed by a solid sample subjected to controlled thermal treatment. The average coalbed gas concentration obtained was 0.51 cm3/g. The following list of maceral concentrates shows the relative capacity for the volume of sorbed gas per unit weight: inertinite > low-density vitrinite > liptinite ≈ high-density vitrinite. It is concluded that the gas volumes retained in the distinct maceral concentrates are not controlled by porosity but rather by their microscopic morphology.

Iron(III) accumulations in inland saline waterways, Hunter Valley, Australia: Mineralogy, micromorphology and pore-water geochemistry by Lloyd S. Isaacson; Edward D. Burton; Richard T. Bush; David R.G. Mitchell; Scott G. Johnston; Bennett C.T. Macdonald; Leigh A. Sullivan; Ian White (1825-1834).
Discharge of Fe(II)-rich groundwaters into surface-waters results in the accumulation of Fe(III)-minerals in salinized sand-bed waterways of the Hunter Valley, Australia. The objective of this study was to characterise the mineralogy, micromorphology and pore-water geochemistry of these Fe(III) accumulations. Pore-waters had a circumneutral pH (6.2–7.2), were sub-oxic to oxic (Eh 59–453 mV), and had dissolved Fe(II) concentrations up to 81.6 mg L−1. X-ray diffraction (XRD) on natural and acid-ammonium-oxalate (AAO) extracted samples indicated a dominance of 2-line ferrihydrite in most samples, with lesser amounts of goethite, lepidocrocite, quartz, and alumino-silicate clays. The majority of Fe in the samples was bound in the AAO extractable fraction (FeOx) relative to the Na-dithionite extractable fraction (FeDi), with generally high FeOx:FeDi ratios (0.52–0.92). The presence of nano-crystalline 2-line ferrihydrite (Fe5HO3·4H2O) with lesser amounts of goethite (α-FeOOH) was confirmed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), and transmission electron microscopy (TEM) coupled with selected area electron diffraction (SAED). In addition, it was found that lepidocrocite (γ-FeOOH), which occurred as nanoparticles as little as ∼5 lattice spacings thick perpendicular to the (0 2 0) lattice plane, was also present in the studied Fe(III) deposits. Overall, the results highlight the complex variability in the crystallinity and particle-size of Fe(III)-minerals which form via oxidation of Fe(II)-rich groundwaters in sand-bed streams. This variability may be attributed to: (1) divergent precipitation conditions influencing the Fe(II) oxidation rate and the associated supply and hydrolysis of the Fe(III) ion, (2) the effect of interfering compounds, and (3) the influence of bacteria, especially Leptothrix ochracea.

Chemical evolution in the high arsenic groundwater of the Huhhot basin (Inner Mongolia, PR China) and its difference from the western Bengal basin (India) by Abhijit Mukherjee; Prosun Bhattacharya; Fei Shi; Alan E. Fryar; Arun B. Mukherjee; Zheng M. Xie; Gunnar Jacks; Jochen Bundschuh (1835-1851).
Elevated As concentrations in groundwater of the Huhhot basin (HB), Inner Mongolia, China, and the western Bengal basin (WBB), India, have been known for decades. However, few studies have been performed to comprehend the processes controlling overall groundwater chemistry in the HB. In this study, the controls on solute chemistry in the HB have been interpreted and compared with the well-studied WBB, which has a very different climate, physiography, lithology, and aquifer characteristics than the HB. In general, there are marked differences in solute chemistry between HB and WBB groundwaters. Stable isotopic signatures indicate meteoric recharge in the HB in a colder climate, distant from the source of moisture, in comparison to the warm, humid WBB. The major-ion composition of the moderately reducing HB groundwater is dominated by a mixed-ion (Ca–Na–HCO3–Cl) hydrochemical facies with an evolutionary trend along the regional hydraulic gradient. Molar ratios and thermodynamic calculations show that HB groundwater has not been affected by cation exchange, but is dominated by weathering of feldspars (allitization) and equilibrium with gibbsite and anorthite. Mineral weathering and mobilization of As could occur as recharging water flows through fractured, argillaceous, metamorphic or volcanic rocks in the adjoining mountain-front areas, and deposits solutes near the center of the basin. In contrast, WBB groundwater is Ca–HCO3-dominated, indicative of calcite weathering, with some cation exchange and silicate weathering (monosiallitization).

Modelling Zn(II) sorption onto clayey sediments using a multi-site ion-exchange model by E. Tertre; C. Beaucaire; N. Coreau; A. Juery (1852-1861).
In environmental studies, it is necessary to be able to predict the behaviour of contaminants in more or less complex physico-chemical contexts. The improvement of this prediction partly depends on establishing thermodynamic models that can describe the behaviour of these contaminants and, in particular, the sorption reactions on mineral surfaces. In this way, based on the mass action law, it is possible to use surface complexation models and ion exchange models. Therefore, the aim of this study is (i) to develop an ion-exchange model able to describe the sorption of transition metal onto pure clay minerals and (ii) to test the ability of this approach to predict the sorption of these elements onto natural materials containing clay minerals (i.e. soils/sediments) under various chemical conditions. This study is focused on the behaviour of Zn(II) in the presence of clayey sediments. Considering that clay minerals are cation exchangers containing multiple sorption sites, it is possible to interpret the sorption of Zn(II), as well as competitor cations, by ion-exchange equilibria with the clay minerals. This approach is applied with success to interpret the experimental data obtained previously in the Zn(II)–H+–Na+–montmorillonite system. The authors’ research team has already studied the behaviour of Na+, K+, Ca2+ and Mg2+ versus pH in terms of ion exchange onto pure montmorillonite, leading to the development of a thermodynamic database including the exchange site concentrations associated with montmorillonite and the selectivity coefficients of Na+, K+, Ca2+, Mg2+, and Zn2+ versus H+.In the present study, experimental isotherms of Zn(II) on two different sediments in batch reactors at different pH and ionic strengths, using NaCl and CaSO4 as electrolytes are reported. Assuming clay minerals are the main ion-exchanging phases, it is possible to predict Zn(II) sorption onto sediments under different experimental conditions, using the previously obtained data base on montmorillonite. Whatever the physico-chemical conditions tested, a relatively good agreement is observed between experimental results and the predicted sorption behaviour.

The influence of geology and land-use on inorganic stream water quality in the Oslo region, Norway by Clemens Reimann; Tor Erik Finne; Øystein Nordgulen; Ola Magne Sæther; Arnold Arnoldussen; David Banks (1862-1874).
Thirty-nine stream and river water samples were collected along a 120 km long transect through the Oslo Rift and the city of Oslo. All samples were analysed for 59 elements (Ca, Fe, K, Mg, Na, Si, Al, As, B, Be, Bi, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Gd, Ge, Hf, Ho, La, Li, Lu, Mn, Mo, Nb, Nd, Ni, P, Pb, Pr, Rb, Sb, Se, Sm, Sn, Sr, Tb, Th, Tl, Tm, U, V, W, Y, Yb, Zr, the anions Br, Cl - , F - , NO 2 - , NO 3 - , PO 4 3 - , SO 4 2 - ), and the additional parameters pH, alkalinity, colour, turbidity and electrical conductivity. The transect crosses four different lithologies, ranging from Precambrian gneisses, Cambro-Silurian sedimentary rocks (including black shales and limestones) to Permian syenites and granites. Parts of the transect are covered by glacial Drift or marine clays (especially in the south), others are Drift-free. Although varying forms of land-use occur throughout the transect, forestry is predominant in higher elevation, Drift-sparse areas, while agriculture and urban development are more characteristic of low lying areas with clayey Drift. Differences in stream water chemistry are likely to arise from the interrelationship between lithology, Drift cover, landscape, land-use and climate-related factors (different evaporation rates). It is possible to tentatively identify the impacts of marine influence, water–rock interaction, pH-related solubility and lithological influence (e.g. black shales). Even a city of the size of Oslo, which is a major diffuse source of contaminants in southern Norway, and intense agriculture have a limited influence on inorganic stream water quality. Nitrate, however, does appear to indicate human impacts, occurring in some streams in concentrations higher than can be explained by rainfall chemistry. Overall, “natural” element sources and processes dominate surface water chemistry at a short distance from any point source of contamination.

The study of trace metal speciation has benefited from a great deal of interest leading to the development and the diversification of sequential extraction schemes (SES), which triggered the need for harmonization by the standard, measurements and testing programme (SM & T). However, some uncertainties still persist in the application of the harmonized 3-step protocol, because of the difficulty in conceptualizing a technique that can be applied to environmental samples irrespective of their nature. The alternative method proposed in this study is based on the solubility of the sample components progressively dissolved during the course of an acidimetric titration by 1 mol L−1 HCl. The major HCl-reactive mineralogical components are identified using mass balance calculation of H+ consumed by their dissolution together with the amount of major elements released into solution. The speciation of minor and trace elements is investigated by comparing their titrations to those of the major elements. This approach is much simpler than SES because it uses simple non-selective H+ at room temperature instead of a complex experimental design of so-called specific reagents. The different mineral components of the solid are no longer operationally defined and the problem of selectivity is irrelevant to the titration approach. The method was applied to several sediment samples from the Scheldt estuary and the particulate phase was further examined by Scanning Electron Microprobe and X-ray Diffraction techniques. The nearly complete consumption of H+ in the suspension is balanced by the total dissolution of carbonates and Fe-oxyhydroxides. In contrast to the speciation inferred from the Tessier SES, the acidimetric titration has demonstrated that the carbonate phase does not significantly contain trace metals with the exceptions of 40% of the Mn and 30% of the Co. In contrast, the Fe-oxyhydroxides seem to play a major role and account for 70% of Pb and 20% of Cr, in addition to 60% of P and additional amounts of 20% Co and 40% Mn. 70% of the Cu also occur in the oxyhydroxide phase, more likely coprecipitated with gibbsite. 90% of the Cd and 85% of Zn can be attributed to the Acid Volatile Sulfide (AVS) phase as evidenced from S titration. The acidimetric titration method not only provides information on the speciation of trace metals but also allows the quantification of their reactivity and mobility, if one considers that the titration roughly mimics pH changes that may occur as a result of chemical disequilibrium in the environment. The results demonstrate the potential of the acidimetric titration as an alternative to SES protocols in geochemical and environmental regulation studies. This method is applicable to a wide variety of environmental materials with little or minor adjustments.

Diagenetic and other highly mineralized waters in the Polish Carpathians by Andrzej Zuber; Józef Chowaniec (1889-1900).
Highly mineralized waters of different chemical types and origin occur in the flysch formations and their bedrocks in the western part of the Polish Carpathians. The marine sedimentation water of the flysch formations is not preserved, as the most mineralized and the heaviest isotopic values of flysch waters are characterized by δ 18O and δ 2H values in the ranges of 5–7‰ and −(20–30)‰, respectively. Their origin is related to the dehydration of clay minerals during burial diagenesis, with molecules of marine water completely removed by molecules of released bound water. They are relatively enriched in Na+ in respect to the marine water, supposedly due to the release of Na+ during the illitization of smectites and preferable incorporation of other cations from the primary brine into newly formed minerals. In some parts of younger formations, i.e. in the Badenian sediments, brines occur with isotopic composition close to SMOW and Cl contents greatly exceeding the typical marine value of about 19.6 g/L, supposedly due to ultrafiltration. Most probably, the marine water of the flysch formations was similarly enriched chemically in its initial burial stages. Final Cl contents in diagenetic waters depend on different Cl contents in the primary brines and on relationships between diagenetic and further ultrafiltration processes. In some areas, diagenetic waters migrate to the surface along fault zones and mix with young local meteoric waters becoming diluted, with the isotope composition scattering along typical mixing lines. In areas with independent CO2 flow from great depths, they form chloride CO2-rich waters. Common CO2-rich waters are formed in areas without near-surface occurrences of diagenetic waters. They change from the HCO3–Ca type for modern waters to HCO3–Mg–Ca, HCO3–Na–Ca and other types with elevated TDS, Mg2+ and/or Na contents for old waters reaching even those of glacial age. Bedrocks of the flysch are represented by Mesozoic and Paleozoic mudstones, sandstones and carbonates, and in some areas by Badenian sediments. Brines of the Mesozoic and Paleozoic bedrocks are usually significantly enriched in Ca2+ and Mg2+ in comparison with the Badenian brines. By analogy to the deepest brines in the adjacent Upper Silesian Coal Basin, they are supposed to originate from paleometeoric waters of a hot climate.

Sediments in Lake Qinghai archive important information about past environmental changes. In order to faithfully interpret the sediment records and constrain the elemental cycles, it is critical to trace various sources of sediments in the lake. The results show that the elemental input–output budgets are imbalanced for most major elements between riverine fluxes and mass accumulation rate (MAR) of Lake Qinghai sediments. A realistic model must include contributions of dry/wet atmospheric deposition that allow the major element mass balance for the lake to be defined. The budget estimation is based on mass balances of Si and Al, which are relatively immobile and carried to the lake via particulate forms. Estimated annual budget of dry atmospheric deposition is ∼1.3 ± 0.3 × 103  kt/a (accounting for ∼65% of the total inputs) to the lake sediments, assuming local loess within the catchment as a candidate for dry atmospheric deposition to the lake. The resultant flux of 300 ± 45 g/m2/a falls within the flux average of the desert area (400 g/m2/a) and the loess plateau (250 g/m2/a), consistent with the geographical setting of Lake Qinghai. The role of atmospheric deposition would be more significant if wet deposition via rainfall and snow were taken into account. This highlights the potential importance of dust as a significant source for sediment preservation flux for other catchments worldwide. The results also indicate that nearly all Ca input was preserved in the lake sediments under modern conditions, consistent with Ca2+ supersaturation of the lake water.

Acid mine drainage, downstream transport of metal-rich water and sediment runoff adversely effect the environment surrounding the Halıköy Hg mine. This study focuses on the environmental effects of the Halıköy Hg mine on soil, stream sediment and water because the area is used for agricultural purposes. Stream sediment and farming soil have been polluted by contaminants derived from the mine. The effects of Hg mining and the distribution of contaminants in soil and stream sediment were evaluated by calculation of enrichment factors (EFs) which indicated enrichments for As, Hg, Sb and Pb. Other metals Cd, Co, Cr, Cu, Fe and Zn show moderate enrichment in soil close to the mine. EFs indicate soil contamination in the order of: Hg > As > Sb > Ni > Co > Cu > Fe > Zn > Cr > Pb > Cd. The greatest contamination was found near mine wastes, decreasing with increasing distance from the mine site. Concentrations of As, Cd, Cu, Ni, Pb and Zn are enriched in mine water. Acidic mine water samples have low pH (2.5–3.0) and high dissolved solids with electrical conductivity (EC) of about 3800 μS/cm. Low pH in the groundwater (as low as 3.7) was also observed close to the stream draining of the mine. The source of acidity is the oxidation Fe-sulfides (dominantly pyrite) which release Fe, SO 4 2 - and H+ forming acid in mine water runoff. Concentrations of Hg are elevated (0.04–1.2 μg/L) in acidic mine water and groundwater exceeding the US Environmental Protection Agency (USEPA) aquatic life Hg standard of 12 ng/L by as much as 100 times.

Fifty soil samples collected from agricultural land in four regions of Poland with different anthropopressure were analysed for their content of 16PAHs by GC/MS. The regions correspond to Polish administrative units (voievodeships): Podlaskie and Lubelskie are situated in the rural East part of the country and more industrialised Slaskie and Dolnoslaskie voievodeships – in the South-West part. Basic physicochemical properties as well as the content of selected potentially harmful metals (Pb and Zn) were included in the soil analysis. Overall accumulation of Σ16PAHs in the upper soil layer was within the range 73–1800 μg kg−1 with a geometric mean (GM) of 252 μg kg−1, while the mean benzo(a)pyrene (BaP) load was 20 μg kg−1. This corresponds with data for other European countries. Carcinogenic compounds contributed nearly in 50% to the total PAHs loads. In uncontaminated rural regions the mean Σ16PAHs and BaP contents were 113–159 μg kg−1 and 11–13 μg kg−1, respectively. Regional conditions strongly influenced the accumulation of PAHs ⩾4-rings, which were highly dependent (over 95%) on local anthropopressure expressed as dust and 4PAHs emission indexes. Soil acidity was the main soil parameter related to the accumulation of higher molecular weight PAHs in soils. In more contaminated regions a significant link between soil OM and PAH loads was noted. The same regions were characterised by associations between PAHs and potentially harmful metals implying common sources of pollution. Those relationships were not observed in the uncontaminated part of the country. The lower molecular weight PAHs contributed to a smaller extent (about 20%) to the total PAHs content in soils, and were less affected by anthropogenic factors.

Biosphere Sr isotope composition data from Iceland and Scotland suggest that terrestrially feeding birds from these two countries will have significantly different 87Sr/86Sr isotope composition in their tissues. The aim of this study is to test if these differences can be measured within the bone and feather of migratory wading birds, who feed terrestrially as juveniles, thus providing a provenance tool for these birds.The study shows that birds can be distinguished on the basis of the Sr isotope composition of their bone. The field for Icelandic birds is defined by data from juvenile common redshank (Tringa totanus) and whimbrel (Numenius phaeopus) which give 0.7056 ± 0.0012, (2σ, n  = 7). The majority of Scottish birds in this study are from coastal regions and have a signature close to that of seawater of 0.7095 ± 0.0006 (2σ, n  = 9). The Sr ratios in the body tissue of these two populations of all Icelandic and Scottish adult and juvenile birds analysed are significantly different (p  < 0.001, at 95% confidence limits). Scottish birds from inland areas such as a common snipe (Gallinago gallinago) record 87Sr/86Sr values as high as 0.7194 which reflect their non-marine diet. Icelandic redshank (Tringa totanus robusta) that have flown to Scotland and returned to Iceland show the effect of the Scottish contribution to their diet with elevated values of 0.7086 ± 0.0004, (2σ, n  = 6). Redshank found in Scotland that cannot be classified on the basis biometric analysis are shown to be of Icelandic origin and analysis of the primary feathers from two birds demonstrates that isotope variation between feathers could be used to track changes in diet related to the timing of individual feather growth.

The concentration and composition of lignin-derived phenols, which are often used as biomarkers for terrigenous organic matter (OM) inputs, were examined in North Atlantic Ocean sediments from IODP core U1302A (50°9.985′N, 45°38.271′W, 3568 m water depth), Orphan Knoll, 650 km NE of St. John’s, Newfoundland, Canada for the period of ca. 1100–810 ka BP. Lignin-derived phenols were extracted from sediments using CuO oxidation which yielded eight characteristic phenols. The majority of sediments have low syringyl phenol to vanillyl phenol (S/V) ratios and high cinnamyl phenol to vanillyl phenol (C/V) ratios, suggesting predominant concentrations of gymnosperm-derived organic matter inputs from adjacent continents (most likely eastern Canada and possibly southern Greenland). The S/V values were lower for the period of ca. 958–840 ka BP relative to ca. 1090–1078, 1042–958 and 840–818 ka BP, indicating fluctuations in the proportion of angiosperm- and gymnosperm-derived lignin delivery to the ocean. The greater fraction of gymnosperms for the period of 958–840 ka BP likely reflects the response of vegetation in source regions to climate cooling in the early part of the mid-Pleistocene. Lignin-derived phenol concentrations also displayed high variability during the investigated period, which did not show positive correlations with magnetic susceptibility or Gamma Ray Attenuation density. Considering that a fundamental climate change (41–100 ka cyclicity) occurred within the mid-Pleistocene, large variations in abundance and composition of lignin-derived phenols in core U1302A is likely indicative of dynamic environmental conditions, reflected by the variability in both concentrations and types of vegetation on adjacent continents and/or different mechanisms to transport terrigenous organic matter to the deep ocean.

Sources and sinks of sulphate dissolved in lake water of a dam reservoir: S and O isotopic approach by Dominika Lewicka-Szczebak; Adriana Trojanowska; Wojciech Drzewicki; Maciej Górka; Mariusz-Orion Jędrysek; Piotr Jezierski; Marta Kurasiewicz; Janusz Krajniak (1941-1950).
Understanding the cycling of biophilic elements is crucial for successful management of water quality in lowland dam reservoirs. This study aimed to determine the sources and sinks of SO 4 2 - in lakewater using S and O stable isotope analysis. Water samples were collected from 5 sampling points along the Sulejów Reservoir (central Poland) on 5 separate sampling campaigns (spring 2005, summer 2005, winter 2006, spring 2006 and summer 2006) applying a diel sampling strategy. Pronounced spatial, seasonal and diurnal variations were found in SO 4 2 - concentration (from 10.3 to 36.2 mg L−1) and in their S (δ 34S from 2.1‰ to 5.4‰) and O isotopic composition (δ 18O from 2.8‰ to 10.6‰). Sulphate isotopic signature has been applied to define the fluxes of SO 4 2 - by means of the isotopic mass balance and thus identify “missing” fluxes. A significant seasonal input of SO 4 2 - from the direct catchment was found during the spring, whereas this input appeared to be fairly negligible in summer. Moreover, an additional SO 4 2 - flux from mobilisation of reduced S compounds stored in the sediments was identified, especially during periods of elongated water retention time. Pronounced diurnal variation was observed for δ 18O( SO 4 2 - ) (up to 4‰) in all seasons except winter, which is probably caused by dynamic biochemical red-ox reactions and intensive mixing processes of SO 4 2 - originating from different sources.

Gasoline range hydrocarbons (C5–C12) are usually associated with petroleum generation, yet few surface geochemical surveys have attempted to evaluate the gasoline range hydrocarbons in near-surface marine sediments. This is due to the difficulty in capturing and analyzing this volatile range of hydrocarbons with minimum loss and evaporative fractionation. In this study, a Headspace Solid Phase Microextraction (HSPME) method was developed and evaluated for the purpose of capturing the gasoline range of hydrocarbons within unconsolidated sediment using a solventless protocol.The sediment SPME extraction method is based on the condition that phase/composition equilibrium is reached between sediment/water mix, container headspace, and SPME fiber coated with sorbent. In the experiments, the effectiveness of SPME to detect and measure low concentrations of migrated crude oil in marine sediments was evaluated. The following optimum laboratory procedure for SPME gasoline monitoring was established: collect the sample in sealed disrupter chamber (sealed sediment storage container which breaks apart sediment and releases interstitial volatile hydrocarbons), use a water bath to keep a stable laboratory temperature, use an NaCl saturated solution to help aromatic compounds move out of the solution to vapor phase, and wait a sufficient time to reach equilibrium. The results show that HSPME is very sensitive with sub ppm detection limits. SPME proved to be suitable to reveal the natural background and micro-seepage level of gasoline hydrocarbons in marine sediments.

Metal sources of black smoker chimneys, Endeavour Segment, Juan de Fuca Ridge: Pb isotope constraints by Hui-Qiang Yao; Huai-Yang Zhou; Xiao-Tong Peng; Shen-Xu Bao; Zi-Jun Wu; Jiang-Tao Li; Zhi-Lei Sun; Zhi-Qiang Chen; Ji-Wei Li; Guang-Qian Chen (1971-1977).
Hydrothermal chimney sulfides, vent cap chimney samples, Fe-oxide and basalts from sediment-starving Juan de Fuca Ridge, in the Endeavour segment, exhibit a range of Pb isotope ratios (206Pb/204Pb = 18.658–18.769; 207Pb/204Pb = 15.457–15.566; 208Pb/204Pb = 37.810–38.276). The data array is not parallel to the northern hemisphere mantle reservoirs indicating a possible sediment component within the sulfides. By assuming that the potential end-member sediment component has a 207Pb/204Pb (15.70) similar to Middle Valley sediment, it is suggested the potential end-member sediment component may have 206Pb/204Pb = 18.90; 208Pb/204Pb = 38.82. Basalt-derived Pb for the Endeavour segment hydrothermal system involves about 50/50 leaching of E-MORB and T2-MORB. Detailed observations show the Mothra field derives more Pb from T2-MORB than the Main Endeavour field does. According to the binary mixing model, the results show little Pb (<1.5%) or no Pb derivation from sedimentary sources. However, the high NH 4 + , CH4 and Br/Cl ratios in hydrothermal fluids are consistent with a sediment component within the segment. Reconciling the Pb isotope data with the chemistry data of hydrothermal fluids, it is suggested that the sediment component may be located in a lower temperature recharge zone where Pb could not be mobilized from the sediment.

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.

Lead and its isotopes in the sediment of three sites on the Lebanese coast: Identification of contamination sources and mobility by C. Abi-Ghanem; J.F. Chiffoleau; A. Bermond; K. Nakhlé; G. Khalaf; D. Borschneck; D. Cossa (1990-1999).
Lead concentrations and isotopic composition of sediment samples collected from three sites within the Lebanese coastal zones were measured: at Akkar, Dora and Selaata. Akkar is located far from any direct source of contamination, while Dora and Selaata receive urban and industrial wastes, respectively. Low Pb concentrations (6–16 μg g−1) were detected in the Akkar sediments, and high concentrations of Pb (70–101 μg g−1) were detected in the Dora sediments. Measuring stable isotope ratios of Pb makes it possible to identify the principal sources of Pb in the Akkar sediments as Pb emitted from gasoline combustion and Pb originating from natural sources. On the other hand, Pb stable isotopic ratios in Dora sediments indicate that they are more highly influenced by anthropogenic sources. Isotopic Pb ratios in the Selaata deposits, where Pb concentrations range between 5 and 35 μg g−1, have an exceptional radiogenic signature for marine sediments 1.25 <  206Pb/207Pb < 1.6 and 0.5 <  206Pb/208Pb < 0.67, which shows the impact of the phosphogypsum discharged by Selaata’s chemical plant. Isotopic Pb analysis applied to EDTA extracts, to test the mobility of Pb, shows that that this mobility is high (>60%) after 24 h of extraction, and that the extracted Pb is less radiogenic than the residual Pb.

Samples of Opalinus Clays from Mont Terri Underground Research Laboratory in the Swiss Jura were analyzed repetitively relative to the duration of their exposure to atmosphere. The objective was the evaluation of such a progressive exposure on the chemical composition of whole-rock samples, and on the chemical and Sr isotopic compositions of leachates obtained by leaching the rock powders with dilute acetic acid. This chemical study was complemented by scanning electron microscope observations to identify the related mineral alterations. The chemical data for the rock powders remained quite constant whatever the duration of the storage, whereas significant changes were observed for the leachates. Similar changes were observed in the leachates of samples collected progressively closer to the walls of a previously excavated niche. When storage time or distance to gallery wall increases, the main variations are: (1) a progressive decrease of the element contents and of the 87Sr/86Sr ratio in the leachates, (2) an alteration of pyrite followed by precipitation of Ca-sulfate in the rocks, both observed by SEM, and (3) a probable precipitation of new mineral phases in the rocks, such as Fe-oxyhydroxides and/or jarosite that could not be visualized by electron microscopic observation because of their very limited amount and very small grain size. The modifications call for an oxidation of pyrite that probably induced also an oxidation of the organic matter. It could also be shown that the reactions were enhanced by temperature increase, and that they were less pronounced in the samples behind the gallery wall than in the cores stored in laboratory conditions.Of importance for the waste-disposal assessment is the fact that the chemical characteristics, and therefore the mineral assemblages, of the studied argillaceous rocks are reactive to changing oxidation/reduction conditions monitored by dehydration. The resulting mineral reorganization seems to contribute to a sealing of the rocks, as the amounts of elements released into the leachates decrease progressively with storage time. This tendency is detectable after several months for the core samples stored under vacuum in Al-foil at room temperature but with periodic exposure to atmosphere, and after several years for the in situ samples collected behind an excavation wall.

The environmental behaviour of colloidal clay in aquatic systems is linked to the properties of their aggregates. Earlier investigations of clay colloids were performed with electron microscope techniques which caused de-hydration of the particles. Information on the structure of colloid aggregates is needed for understanding their sedimentation behaviour, as well as colloid contaminant transport properties in natural systems. Scanning transmission X-ray microspectroscopy successfully produced images of montmorillonite colloid aggregates in a pseudo-equilibrium state in 1 mM NaCl suspensions equilibrated for more than a year. These clay aggregates were revealed at photon energies below the O absorption edges of clay and water. They were spherical or ellipsoidal with diameters of the order of 100–800 nm. The aggregates are porous and gel like with lower densities than the clay mineral. These investigations are important for modelling the occurrence of clay aggregates in aqueous environments.

Reply to the comment on “Geochemical gradients in soil O-horizon samples from southern Norway: Natural or anthropogenic?” by Eiliv Steinnes by Clemens Reimann; Peter Englmaier; Belinda Flem; Larry Gough; Paul Lamothe; Øystein Nordgulen; David Smith (2023-2025).