Applied Geochemistry (v.22, #11)
Groundwater resource degradation in coastal plains: The example of the Cecina area (Tuscany – Central Italy) by Sergio Grassi; Gianni Cortecci; Paolo Squarci (2273-2289).
The paper describes the degradation of the groundwater resources in the Cecina area, where seawater intrusion, B contamination and NO3 pollution are all affecting the heavily exploited Pleistocene aquifer. Over-pumping has brought water levels to about 0 m.a.s.l. as far as about 7 km from the shore line, thereby promoting the seawater intrusion. The intrusion, which is characterized by cation exchange phenomena and Ca–Cl type waters, enters the plain mostly through the shallower horizons. The saline front, which advanced from 0.5 to 1 km in 4 a, has by now reached the foot of the hills to the east of the town, where it is also affecting wells of the local aqueduct. Boron contamination, linked to past discharge of industrial waste transported downstream by the river, reached concentrations as high as 3.5 mg/L in the mid-1980s. Although a decreasing trend is now under way, B content is still close to 1 mg/L. The presence of high NO3, which, together with the seawater intrusion, represents a major issue for groundwater management in the area, is linked to the widespread utilization of fertilizers. Nitrate concentration, which reaches a maximum of about 300 mg/L in the shallow aquifer horizons and then decreases rather regularly with depth, is strongly influenced by precipitation. However, irrigation also contributes significantly to transporting the NO3 contamination to depth, as clearly shown by δ 18O data. The severe decline in the quality of the groundwater resource in the Cecina area is further compounded by an overall decrease in water availability in the region of Tuscany, as evidenced by long-term monitoring of precipitation and fluvial discharge.
Surface coatings on quartz grains in bentonites and their relevance to human health by Richard F. Wendlandt; Wendy J. Harrison; David J. Vaughan (2290-2306).
The cytotoxicity of quartz in the human lung is recognized to be dependent on both the inherent properties of the silica dust and external factors related to the history of the dust and including the presence of surface contamination. In this study, the physical and chemical surface properties of quartz grains in commercial bentonite deposits from the western (South Dakota) and southern (Alabama) USA were investigated. Measured quartz contents of bentonites range from 1.9 to 8.5 wt% with the <10 μm size fraction comprising 6–45% of this total. Trace element contents (Fe–Ti–Al) of quartz grains from any given bentonite are similar, indicating a single origin for the quartz with little if any contamination from other sources. Surface coatings are pervasive on all quartz grains and resist removal by repeated vigorous washings and reaction with HCl. Textural attributes and XPS and EDS analyses of these coatings are consistent with most being montmorillonite and, less frequently, mixtures of montmorillonite and opaline silica. Opaline silica (opal-A and opal-CT) occurs in two texturally distinct generations: an early massive grain-coating event and as later lepispheres. Montmorillonite coating thicknesses range from <1 μm to more than 10 μm thick. Surfaces of plagioclase, K-feldspar, and biotite grains are conspicuously devoid of montmorillonite coatings, but may show sparse distributions of opal-CT lepispheres. HRTEM has not confirmed a topotactic relationship or atomic structural concordance between montmorillonite coatings and underlying quartz grains. Alternatively, a precursor volcanic glass phase that coats the quartz surfaces during volcanic eruption and/or preferential early precipitation of opaline silica on quartz may provide substrates for development of montmorillonite coatings. Estimations of montmorillonite biodurability under pulmonary pH conditions suggest possible prolonged sequestration of respired bentonite quartz grains from contact with lung materials and modified cytotoxic reactivity.
Multi-isotopic (Li, B, Sr, Nd) approach for geothermal reservoir characterization in the Limagne Basin (Massif Central, France) by R. Millot; Ph. Négrel; E. Petelet-Giraud (2307-2325).
A multi-isotopic study of thermo-mineral waters from the Limagne Basin (French Massif Central) is reported. Lithium, B, Sr and Nd isotopic signatures in thermo-mineral waters and bedrocks were combined in order to determine the origin of these fluids from a reservoir point of view. Strontium and Nd isotopic systems showed that the thermo-mineral waters are mostly derived from a granitic reservoir type, with the exception of a few water samples having Sr and Nd isotopic signatures also reflecting a volcanic contribution (basalts). In a second step, Li and B isotopes were investigated, given that Li and B isotopic systematics are potentially affected by mass dependent fractionation during water/rock interaction and could provide some information on what takes place during this process. A great diversity of thermo-mineral waters within the Aigueperse area was clearly observed, which is directly related to the origin of these thermal waters in terms of reservoirs. These different geothermal reservoirs are characterized by different geological settings and intensity of water/rock interaction (i.e. depth and temperature).The combination of Li, B, Sr and Nd isotopic systems highlight the complexity of the study of these geothermal reservoirs and that the use of only one isotopic tool could lead to an incomplete interpretation of the origin of water. The new approach using Li isotopes shows a very interesting potential with additional information on the intensity of water/rock interaction.
Long-term neutralisation potential of red mud bauxite with brine amendment for the neutralisation of acidic mine tailings by M. Paradis; J. Duchesne; A. Lamontagne; D. Isabel (2326-2333).
Acid mine drainage is an environmental problem produced when sulphide in mine tailings dams comes in contact with O2, bacteria and water. Oxidation occurs and a succession of reactions is responsible for producing acid and metals in the environment. One solution proposed is to use red mud bauxite (RMB) that is very alkaline to neutralise acidic tailings. Previous experiments showed that RMB has a good neutralisation capacity for a short time, but the long-term neutralisation potential is uncertain. So brine was added to RMB to verify if it can improve long-term alkalinity retention of RMB. Some authors have presented results where seawater or other natural or artificial Ca- and Mg-rich brines were used with RMB to convert the basicity (mainly NaOH) and other soluble alkalinity into low solubility hydroxide, carbonate and hydroxycarbonate minerals. Results showed that neutral pH conditions were maintained over the entire test for RMB and a mixture of RMB with brine. Addition of brine to RMB slightly lowered the pH compared to RMB alone. RMB alone lost a lot of dissolved alkalinity at the beginning of the test. Most of the alkalinity was lost in water after a few flushes for RMB samples. The addition of brine helped to keep neutralisation potential over more cycles of leaching.
Tomographic radiotracer studies of the spatial distribution of heterogeneous geochemical transport processes by Marion Gründig; Michael Richter; Anita Seese; Osama Sabri (2334-2343).
Within the scope of the further development of geochemical transport models the consideration of the influence of the heterogeneous structures of the geological layers plays an important role. For the verification and parameter estimation of such models it is necessary to measure the heterogeneous transport and sorption processes inside the samples. Tomographic radiotracer methods (positron emission tomography (PET)) enable nondestructive spatially resolved observations of the transport processes in these layers. A special quantitative evaluation system for geoscientific PET studies was developed. Investigations of the water flow distribution in a drill core of a lignite mining dump and of the migration of Cu ions in a horizontal soil column illustrate the potential of this method. Spatial distribution functions of the flow velocity, the specific mass flow and the longitudinal dispersivity were determined on the basis of PET investigations.
Estimating the longevity of limestone drains in treating acid mine drainage containing high concentrations of iron by Silvana Santomartino; John A. Webb (2344-2361).
Limestone drains are often implemented in the treatment of acid mine drainage (AMD), but when the AMD contains high levels of dissolved Fe their lifetime is dependent on the rate of precipitation of Fe hydroxide on the limestone surface. This study used a small-scale laboratory experiment to define the longevity of a limestone drain by determining the thickness of the Fe coating encapsulating the limestone particles when the system lost its maximum neutralising potential. Synthetic AMD (100 mg/L Fe, pH 4–4.8) was pumped through a column containing limestone particles for 1110 h, when the effluent pH had dropped from a maximum of 6.45–4.9. The decline in neutralisation during the experiment was due to the formation of Fe hydroxide coatings on the limestone grains. These coatings are composed of lepidocrocite/goethite in three distinct layers: an initial thick porous orange layer, overlain by a dense dark brown crust, succeeded by a layer of loosely-bound, porous orange globules. After 744 h, a marked increase in the rate of pH decline occurred, and the system was regarded as having effectively failed. At this time the Fe hydroxide crust effectively encapsulated the limestone grains, forming a diffusion barrier that slowed down limestone dissolution. Between the coating and the limestone substrate was a 60 μm wide void, so that agitation of the limestone sample would readily remove the coating from the limestone surface.In the experimental system, the time for sufficient Fe hydroxide to precipitate on the limestone to cause a distinct decline in the rate of neutralisation was defined by: t ( years ) = surface area ( m 2 ) × 4.4 fraction Fe retained in system × [ Fe 2 + ] ( mg / L ) × flowrate ( L / h ) . At this time the limestone in the drain would need to be replaced or mechanically agitated to remove the Fe hydroxide coating, to allow the system to continue functioning at its maximum potential. Application of this formula to the field situation shows that even when the influent Fe concentrations are moderately high, limestone drains will continue to function well for one to several years. Thus, passive limestone systems can be used in AMD treatment when the influent Fe concentration is considerably greater than 1 mg/L, the currently recommended limit, particularly given that the Fe precipitates armouring the limestone grains may be loosely bound and relatively easily dislodged. Therefore, limestone drains are more widely applicable than presently realised.
Transportation and evolution of trace element bearing phases in stream sediments in a mining – Influenced basin (Upper Isle River, France) by C. Grosbois; A. Courtin-Nomade; F. Martin; H. Bril (2362-2374).
Arsenic-bearing stream sediments enter the Upper Isle River, an Au mining-influenced basin (France), by the discharge of mining sites, tailings runoff and weathering of mineralized veins in granites and gneiss. Some fresh ochreous As-rich deposits on the river banks and in floodplains are identified as additional As-rich point sources (As between 0.07 and 6.5 wt.%). The <63 μm fraction of stream sediments contains elevated As bulk concentrations, ranging from 160 to 890 mg/kg, compared to the geochemical background (70 mg/kg on average). It is also enriched in Cd, Hg and W. Spatial variations of these trace elements show 3 significant increases corresponding to the 3 drained mining districts. They decrease down river but are still enriched 30 km downstream of the mining districts due to downstream transportation. Three types of trace element-bearing phases have been identified as: (i) detrital primary sulfides, with high in situ As percentages (up to 43.7 wt.%). They also carry significant amounts of W according to the differences in chemical compositions of the total and light <63 μm fractions. These sulfide particles do not show any sign of alteration in the oxygenated stream sediments; (ii) Secondary Fe–Mn oxyhydroxides,some with very high in situ As2O5 concentrations (up to 59.8 wt.%) and with about 40% of the total Cd composition. They occur as fresh precipitates in the river banks and floodplains and as discrete particles in stream sediments and (iii) Al–Si fine-grained phases. Their major element composition is highly variable with in situ As2O5 concentrations ranging between 430 and 5020 mg/kg. This type of solid phase is also the major carrier of Hg.
Sorption of cadmium, nickel, and zinc in mono- and multimetal systems by V. Antoniadis; C.D. Tsadilas (2375-2380).
The sorption behaviour of Cd, Ni, and Zn was studied in monometal, as well as in multimetal competitive systems (binary and ternary). Metal sorption was described using the SRS equation, a multicomponent Freundlich-type isotherm curve fit model. It was found that Zn was more strongly bound than Cd and Ni, with the order of reduced sorption being Zn > Ni > Cd. Specific sorption onto clay lattice edges, as determined by the first hydrolysis product of the metals, seems to have been the mechanism that explained metal retention. It was also found that competition suppressed the sorption of all three metals. However, Zn was affected much less than Cd and Ni, probably because it was the most strongly retained metal of the three. The SRS equation successfully predicted the competitive sorption of the metals, as the observed experimental data were correlated satisfactorily with the predicted data (R 2 = 0.95).
Long term redox evolution in granitic rocks: Modelling the redox front propagation in the rock matrix by M. Sidborn; I. Neretnieks (2381-2396).
Redox evolution in groundwaters in granitic rocks is considered to be largely due to reactions between dissolved species in the groundwater and minerals that line the walls of fractures in the bedrock. In a long term perspective, however, the reducing fracture minerals eventually become depleted. In this situation, O2 diffuses out from the fractures and reacts with reducing species present in the porous rock matrix. The rock matrix contains the main reservoir of reducing capacity in the form of reducing minerals such as biotite. The aim of this work is to emphasize the coupled transport and reaction processes deemed important for the redox evolution in recharge groundwaters over long times, i.e. thousands of years. Results indicate that matrix diffusion of O2 becomes limiting for the redox reactions rapidly after the reducing capacity of the fractures is depleted. The numerical model results are verified by simplified cases solved analytically. From the analytical solutions insights also are gained into when different mechanisms dominate the overall reaction, which is more difficult if only numerical results are available.
Effect of organic complexation on the toxicity of Cu to the earthworm Eisenia fetida by R.E. Arnold; M.E. Hodson; S. Comber (2397-2405).
The relationship between Cu speciation in solution and mortality and tissue Cu concentrations in Eisenia fetida was investigated. E. fetida were exposed to solutions containing 0.009, 0.049 and 0.125 mg Cu L−1and 0, 0.15, 0.35 and 50 mg EDTA L−1. Mortalities of 100, 60, 50 and 25% were recorded in the 0.125 mg Cu L−1 solutions containing 0, 0.15, 0.35 and 50 mg EDTA L−1, respectively. Similarly tissue body burden decreased with increasing EDTA concentration. Complexation capacity of the solution increased with EDTA concentration. In the 0.125 mg Cu L−1 solution labile Cu concentration decreased with increasing EDTA concentration. These trends are attributed to complexation of free Cu ions with EDTA molecules, and the non-bioavailable nature of the resultant Cu–EDTA complex.
A sequential extraction to determine the distribution of apatite in granitoid soil mineral pools with application to weathering at the Hubbard Brook Experimental Forest, NH, USA by Carmen A. Nezat; Joel D. Blum; Ruth D. Yanai; Steven P. Hamburg (2406-2421).
Mineral weathering in soils is an important source of many nutrients to forest ecosystems. Apatite, a Ca phosphate mineral, occurs in trace amounts in virtually all igneous and metamorphic rocks and is often found as small mineral inclusions in more weathering-resistant silicate minerals. To better understand the distribution of apatite in soils and its exposure to soil solutions, a sequential extraction method was developed to selectively dissolve minerals from soils so that the amount of apatite in contact with soil solutions versus that armored by silicate minerals could be quantified. The use of three molarities of HNO3 (0.01, 0.1 and 1 M) at three temperatures (0, 10, or 20 °C) was explored and it was found that apatite congruently dissolved in 1 M HNO3 at all three temperatures, but did not completely dissolve in weaker HNO3 solutions. Soil horizons, glacial till (i.e., soil parent material), and individual minerals separated from till collected from the Hubbard Brook Experimental Forest (HBEF), NH, were subjected to a 4-step sequential extraction. Chemical analyses of the extracts indicate that 1 M NH4Cl (pH 7; 20 °C) removes exchangeable ions, 1 M HNO3 at 20 °C primarily dissolves apatite in contact with solutions, 1 M HNO3 at 200 °C primarily dissolves biotite and chlorite (and apatite armored by them), and a mixture of concentrated HNO3, HCl, and HF at 200 °C dissolves the more refractory minerals including muscovite, alkali feldspar, plagioclase feldspar and quartz (and apatite armored by these minerals). This extraction method was applied to soil profiles from HBEF to demonstrate that it could be used to interpret the abundance of apatite and other minerals as a function of depth. Approximately 70% of the apatite in the HBEF soil parent material is exposed to soil solutions; the remaining 30% is armored in more weathering-resistant micas and feldspars. In the upper soil horizons, the only apatite that has not been weathered from the soil occurs as inclusions in micas and feldspars and thus the rate of dissolution of apatite in weathered soil horizons is controlled by silicate mineral dissolution.
The effect of organic materials on the mobility and toxicity of metals in contaminated soils by René van Herwijnen; Tim Laverye; Jane Poole; Mark E. Hodson; Tony R. Hutchings (2422-2434).
Organic materials such as compost are often proposed as suitable materials for the remediation of contaminated brownfield sites intended for soft end-use. In addition to vitalising the soil, they are also believed to immobilise metals thereby breaking contaminant-receptor pathways and reducing the ecotoxicity of the contaminants. However, some research has demonstrated contradictory effects between composts on metal immobilisation. In the present study, four different composts and a liming product containing organic matter (LimeX70) were tested to examine both their metal retention and toxicity reduction capabilities on three different metal contaminated soils. Leaching tests, a plant growth test with Greek cress (Lepidium sativum), an earthworm (Eisenia fetida) survival and condition test and a bacterial toxicity test using Vibrio fischeri were carried out. The leaching test results showed that spent mushroom compost caused an increase in metal concentration in the leachates, while LimeX70 caused a decrease. The variation in behaviour between different amendments for each soil was high, so a generic conclusion could not be drawn. Toxicity tests showed significant reduction of metal bioavailability and toxicity for Greek cress, earthworms and bacteria. The results also suggest that more research should be undertaken to understand the mechanisms involved in metal complexation using different types of organic matter, in order to optimise the use of organic materials like compost for soil remediation.
Characterization of urban NOM in a municipal area with disused toxic waste sites by U. Gottschalch; M. Birke; H. Kupsch; H.-J. Stärk; H. Lippold (2435-2455).
Natural organic matter (NOM) formed under urban conditions exhibits characteristic features reflecting the diversity of anthropogenically influenced soils. These NOM species indicate the state of the urban soil in respect of humification as well as contaminant loads and transport. Humic and fulvic acids isolated at two dump sites in the municipal area of Staßfurt (Germany) are characterized by a high oxygen functionality and a predominance of aliphatic structures. Permanent metal loads of soil humic acids mainly consist of Mg, Al, K and Fe. Soil fulvic acids are additionally loaded with Ca and Zn. The main feature of all humic and fulvic acids from the investigated area is an enrichment of chalcophile elements relative to the elemental distribution in the upper continental crust. Based on the permanent loads and other characteristics of the site-specific humic substances, an input of organic material from a waste dump into the aquifer could be demonstrated. Aquatic fulvic acids are charged along the ground water flow path, correlating with the elemental content of the dumped materials. A long-term observation of the seepage water path is recommended in order to assess the spreading behaviour of organically bound contaminant metals when humification proceeds.
Compositions, sources and depositional environments of organic matter from the Middle Jurassic clays of Poland by Leszek Marynowski; Michał Zatoń; Bernd R.T. Simoneit; Angelika Otto; Mariusz O. Jędrysek; Cezary Grelowski; Slawomir Kurkiewicz (2456-2485).
The comprehensive biomarker characteristics from previously undescribed Middle Jurassic clays of Poland are presented. The molecular composition of the organic matter (OM) derived from clays of Aalenian to Callovian age has not changed significantly through time. High relative concentrations of many biomarkers typical for terrestrial material suggest a distinct dominance of OM derived from land plants. Increasing concentrations of C29-diaster-13(17)-enes towards the northern part of the basin indicate an increase in terrestrial input. This terrestrial material would have originated from the enhanced transport of organic matter from land situated at the northern bank of the basin, i.e., the Fennoscandian Shield. The organic matter was deposited in an oxic to suboxic environment, as indicated by relatively low concentrations of C33–C35 homohopanes, moderate to high Pr/Ph ratio values, an absence of compounds characteristic for anoxia and water column stratification, such as isorenieratane, aryl isoprenoids and gammacerane, as well as common benthic fauna and burrows. δ 18O measurements from calcitic rostra of belemnites suggest that the mean value of the Middle Jurassic sea-water temperature of the Polish Basin was 13.1 °C. It is suggested that this mirrored the temperature of the lower water column because belemnites are considered here to be necto-benthic. The organic matter from the Middle Jurassic basin of Poland is immature. This is clearly indicated by a large concentration of biomarkers with the biogenic configurations, such as ββ-hopanes, hop-13(18)-enes, hop-17(21)-enes, diasterenes and sterenes. The identification of preserved, unaltered biomolecules like ferruginol, 6,7-dehydroferruginol and sugiol in Protopodocarpoxylon wood samples from these sediments present particularly strong evidence for the presence of immature OM in the Middle Jurassic sediments. Moreover, the occurrence of these polar diterpenoids is important due to the fact that they are definitely the oldest known natural products detected in geological samples.
Formation of sequences of cemented layers and hardpans within sulfide-bearing mine tailings (mine district Freiberg, Germany) by Torsten Graupner; Andrea Kassahun; Dieter Rammlmair; Jeannet A. Meima; Dagmar Kock; Markus Furche; Adrian Fiege; Axel Schippers; Frank Melcher (2486-2508).
The roles of mineral dissolution, precipitation, transformation and mass transport processes related to formation of characteristic cemented layer–hardpan sequences were studied in low sulfide and low carbonate Freiberg polymetallic mine tailings. Using high resolution profiling, combined geochemical, geomicrobiological and geophysical methods allowed description of the process of weathering of reactive mineral phases and the position of the oxidation front in detail, as well as revealing the mechanisms of cementation of tailings predominantly by the formation of gels/poorly crystalline phases. Autochthonous and allochthonous gels reduced the porosity of cemented layers to values ⩽1%, whereas secondary crystalline phases were less efficient in filling the pore space. Electron microprobe analysis of cemented tailings showed that common jarosite-group minerals contained up to about 8 wt.% PbO and 0.2–1.9 wt.% As2O5. Iron–As–Si gels reached contents of up to ∼44 wt.% As2O5 in gel-rich cemented layers. Zinc was below the detection limit in the studied secondary phases. Sequential extraction of cemented and related oxidized brown silt layers confirmed that the bulk of As was bound to amorphous/poorly crystalline hydrous oxides of Fe, whereas Pb was often bound to jarosite. Zinc was found preferentially in the water-soluble and the exchangeable fractions. In the grey silt and the sand directly underlying the oxidized layers, As, Pb and Zn occurred as sulfide minerals. The main effects of the cemented layer–hardpan sequences at the studied site are (1) a temporary natural attenuation of the toxic compounds, (2) a restriction of the downward movement of the oxidation front, and (3) a reduction of the extent of the erosion of the surface of the tailings impoundment by wind and water. The potential of a heap to form cemented layers and hardpans is greatly increased by a heterogeneous distribution of grain sizes and reactive materials in the topmost zone, as well as by the occurrence of sulfide-rich tailings on top of layers with low permeability.
Comparative distributions of size fractionated metals in pore waters sampled by in situ dialysis and whole-core sediment squeezing: Implications for diffusive flux calculations by Miguel Angel Huerta-Diaz; Ignacio Rivera-Duarte; Sergio A. Sañudo-Wilhelmy; A. Russell Flegal (2509-2525).
Trace elements (Ag, Cd, Co, Cr, Cu, Fe, Mn, Pb, V, Zn) and ammonia were measured in pore waters extracted from sediments collected in Green Sands Beach (Mare Island, San Francisco, CA) using peepers and whole-core squeezers. Samples were size-fractionated, either by using 0.45 and 0.1 μm polycarbonate filters (whole-core squeezers), or by passive filtration using peepers with 0.45 μm and 3000 MWCO (3 kDa) membranes. Results indicate that the distribution profiles of pore water constituents in the traditionally defined total dissolved fraction (C TD = <0.45 μm) reflect different diagenetic processes, as well as anthropogenic inputs from the former Mare Island Naval Shipyard. Metal concentrations and profiles in the truly dissolved phase (C D = <3 kDa) for Mn, Co, Cr, V and NH 4 + were similar to the ones obtained for C TD. Profiles for the small-sized dissolved fraction (C SSD = <0.1 μm) and in the C TD pool were almost identical for all of the analysed metals. Absolute values of the ratios between the diffusive fluxes of the different size fractions relative to the total dissolved fluxes ranged from 0.012 to 41. Of these, 37% were lower than 0.50 and 12% showed values in excess of 2.0. However, in 22% of the cases, the fluxes were in directions opposite to the metal fluxes calculated using C TD gradients. Hence, gradients of total dissolved trace metals, which are the only ones normally measured in pore waters, may not necessarily reflect the mass flow of dissolved constituents across the sediment column.
Comparative migration behaviour of 90Sr, 239+240Pu and 241Am in mineral and organic soils of France by N. Solovitch-Vella; L. Pourcelot; V.T. Chen; P. Froidevaux; F. Gauthier-Lafaye; P. Stille; D. Aubert (2526-2535).
The vertical migration of 90Sr, 239+240Pu and 241Am has been studied in two types of soils in France (acid forest soil in the Vosges Mountains and organic-rich alkaline wetland in the Mercantour area). In order to interpret the different migration behaviour of radionuclides, the combination of two approaches are proposed – a statistical study of the evolution of radionuclide ratios (241Am/239+240Pu, 90Sr/239+240Pu) with depth and a calculation of the radionuclide migration rates. Migration behaviour of 90Sr, 239+240Pu and 241Am is significantly different in the Vosges and Mercantour soils. In the Mercantour soil 241Am was found to be less mobile than 239+240Pu. In both profiles 90Sr is more mobile than 239+240Pu. The high sand content (55–60%) and weathering processes of cations in the Vosges soil are thought to be responsible for the larger migration rates of radionuclides in depth, while the high organic matter content (>70%) of Mercantour soil is thought to be responsible for the stronger retention of 241Am in the first 10 cm of the soil.
Anion exclusion effects in compacted bentonites: Towards a better understanding of anion diffusion by Luc R. Van Loon; Martin A. Glaus; Werner Müller (2536-2552).
Diffusion of 36Cl− in compacted bentonite was studied using through-diffusion, out-diffusion and profile analysis techniques. Both the bulk dry density of the bentonite and the composition of the external solution were varied. Increasing the bulk dry density of the bentonite resulted in a decrease of both the effective diffusion coefficient and the Cl-accessible porosity. Increasing the ionic strength of the external solutions resulted in an increase of both the effective diffusion coefficient and the Cl-accessible porosity. This can be explained by anion exclusion effects (Donnan exclusion). At high ionic strength values (I ⩾ 1 M NaCl) the Cl-accessible porosity approaches the interparticle porosity. This interparticle porosity is the difference between the total and interlayer porosity of the bentonite. The interlayer porosity was found to depend on the degree of compaction. Up to a bulk dry density of 1300 kg m−3 the interlayer is built up of 3 water layers. Between 1300 and 1800 kg m−3 the interlayer water is reduced from 3 to 2 layers of water. Above 1800 kg m−3 evidence for a further decrease to 1 layer of water was found. These findings are in agreement with X-ray data found in the literature showing a decrease of the basal spacing of montmorillonite (the main clay mineral in bentonite) with increasing degree of compaction. The relationship between the effective diffusion coefficient of Cl− and the diffusion-accessible porosity can be described by an empirical relationship analogous to Archie’s law. To predict the effective diffusion coefficient of Cl− in compacted bentonite, the diffusion coefficient of Cl− in water, the bulk dry density and the ionic strength of the pore water have to be known.
Compound-specific C- and H-isotope compositions of enclosed organic matter in carbonate rocks: Implications for source identification of sedimentary organic matter and paleoenvironmental reconstruction by Yongqiang Xiong; Yanmei Wang; Yongquan Wang; Shiping Xu (2553-2565).
The Bohai Bay Basin is one of the most important oil-producing provinces in China. Molecular organic geochemical characteristics of Lower Paleozoic source rocks in this area have been investigated by analyzing chemical and isotopic compositions of solvent extracts and acid-released organic matter from the Lower Paleozoic carbonate rocks in the Jiyang Sub-basin of the Bohai Bay Basin. The results indicate that enclosed organic matter in carbonate rocks has not been recognizably altered by post-depositional processes. Two end-member compositions are suggested for early organic matter trapped in the Lower Paleozoic carbonate rocks: (1) a source dominated by aquatic organisms and deposited in a relatively deep marine environment and (2) a relatively high saline, evaporative marine depositional environment. In contrast, chemical and isotopic compositions of solvent extracts from these Lower Paleozoic carbonate rocks are relatively complicated, not only inheriting original characteristics of their precursors, but also overprinted by various post-depositional alterations, such as thermal maturation, biodegradation and mixing. Therefore, the integration of both organic matter characteristics can provide more useful information on the origin of organic matter present in carbonate rocks and the environments of their deposition.