Applied Geochemistry (v.21, #6)

A conceptual model for the chemical evolution of near-field water chemistry in the proposed high-level nuclear waste repository at Yucca Mountain, Nevada is presented. This model considers the effects of differential solubility in flowing water that is subject to evaporation or condensation. The results of a simplified numerical implementation of the model are used to predict the aqueous chemistries produced from a variety of source waters under two bounding assumptions of separation. The model predicts that, under some conditions the most soluble ions will not always be present in solution. The more soluble ions may precipitate at different locations than ions of slightly less solubility leading to a highly complex system containing different brine compositions at different locations.

A geochemical assessment was performed on Lake Leopoldo, a tropical lake located on the Guayana Shield, Venezuela. The lake water was characterized (Ca2+, Mg2+, Na+, K+, Cl, NO 3 - , NO 2 - , SO 4 2 - , NH 4 + , Fe, and P), lacustrine setting the origin, transport and fate of sedimentary material in this highly unusual lacustrine setting. Lake sediments were analyzed for textural, mineralogical and chemical composition, including the rare earth element (REE) contents. In addition to %TOC, δ 13C, δ 15N and elemental C/N ratios, the molecular distributions of several biomarker compounds were determined and used to assess organic matter source and transport to the lake. Lake Leopoldo developed on a sequence of quartz arenites of the Precambrian Roraima Group. The area conforms to the definition of pseudo-karst morphology. The results show that the lake is oligotrophic where primary production seems to be limited by nutrients. In the sediments, organic matter shows an overwhelming higher plant-derived origin. Certain elements (K, V, Cu, Th, Ba, Hg, and LREE) displayed enrichments with organic matter, while others (Zr, Hf, Si, Sn, Pb, and Ta) displayed an association with the mineral fraction. The results obtained in this study suggest that the lake water characteristics and the affinities of trace elements for sediment organic fractions are controlled by biogeochemical processes within the surrounding forest soil environment, prior to the transport of the terrestrially-derived organic matter to the lake. The most significant geochemical finding is that organic matter can play an important role in the distribution of trace metals in such highly oligotrophic terrains of humid, tropical environments.

Geochemistry of surface and ground water in Guiyang, China: Water/rock interaction and pollution in a karst hydrological system by Yun-Chao Lang; Cong-Qiang Liu; Zhi-Qi Zhao; Si-Liang Li; Gui-Lin Han (887-903).
The chemical compositions of the surface/ground water of Guiyang, the capital city of Guizhou Province, China are dominated by Ca2+, Mg2+, HCO 3 - and SO 4 2 - , which have been derived largely from chemical weathering of carbonate rocks (limestone and dolomite). The production of SO 4 2 - has multiple origins, mainly from dissolution of sulfate evaporites, oxidation of sulfide minerals and organic S in the strata, and anthropogenic sources. Most ground water is exposed to soil CO2 and, therefore, the H2CO3 which attacks minerals contains much soil C. In addition, the H2SO4 produced as a result of the oxidation of sulfides in S-rich coal seams and/or organic S, is believed to be associated with the chemical weathering of rocks. The major anthropogenic components in the surface and ground water include K+, Na+, Cl, SO 4 2 - and NO 3 - , with Cl and NO 3 - being the main contributors to ground water pollution in Guiyang and its adjacent areas. The seasonal variations in concentrations of anthropogenic components demonstrate that the karst ground water system is liable to pollution by human activities. The higher content of NO 3 - in ground water compared to surface water during the summer and winter seasons, indicates that the karstic ground water system is not capable of denitrification and therefore does not easily recover once contaminated with nitrates.

Microchemical characterisation of natural gold and artefact gold as a tool for provenancing prehistoric gold artefacts: A case study in Ireland by R.J. Chapman; R.C. Leake; R.A. Warner; M.C. Cahill; N.R. Moles; C.A. Shell; J.J. Taylor (904-918).
The importance of Au to ancient societies has encouraged many archaeologists to search for the sources exploited in antiquity. These projects generally involve detailed studies of artefacts and comparison of their chemical characteristics with those reported for natural Au. However, descriptions of natural Au are frequently inadequate for provenancing studies, and the compositional variability of the material is not widely recognised. The present study describes a new approach to gold provenancing using the technique of microchemical characterisation in which populations of gold grains are classified according to the alloy compositions and the assemblages of microinclusions of other minerals. This technique, originally developed to identify sources of alluvial gold during Au exploration, has proved applicable to provenancing studies in four main areas. Firstly, microchemical characterisation of artefacts grouped according to archaeological criteria can indicate the number of sources exploited in relation to time and artefact taxonomy. Secondly, knowledge of the total variation in chemical characteristics of natural Au from a particular region provides an excellent database for provenancing and reduces the need for exhaustive sampling. Thirdly, it is possible to predict how Au alloys were modified during fabrication as a consequence of assimilation of mineral inclusions. Finally, identification of inclusion phases in artefact Au can provide information on metallurgical practices.These principles have been applied to the search for the source of Au used for the unique traditions of prehistoric Irish metalworking. Studies of 180 Irish Au artefacts belonging to four major metalworking traditions dating from the Early Bronze Age (2400 BC) to the Iron Age, (150 BC) show that each group exhibits distinctive Ag and Cu contents. Parallel studies of 2267 natural Au grains from 58 alluvial localities and four bedrock localities throughout Ireland reveal a broad pattern of alloy compositions consistent with style of mineralisation and host geology. The ranges of Ag contents of Early Bronze Age and Middle Bronze Age artefacts suggests that the Au source lies within Lower Palaeozoic sedimentary rocks of the Southern Uplands Terrane and significantly, that the same source (or sources) were used in both periods. A different source of relatively Ag-rich Au (most probably at Croagh Patrick, Co. Mayo), was exploited in the Late Bronze Age. Iron Age artefacts have Ag contents higher than natural Irish Au. Evidence for evolution of metallurgical practice during the Bronze Age is provided by the increasing Cu content of the gold alloys (to levels far in excess of natural gold) and the nature of inclusions in artefacts of different ages. Elevated Sn in Cu-rich alloys suggests deliberate or accidental alloying with bronze.This approach has provided the first clear indication that only a few individual indigenous Irish sources of Au were used during the Bronze Age and that their relative importance changed over time. Future archaeological investigations may adopt a geographical focus that was not previously possible.

Identification and emission factors of molecular tracers in organic aerosols from biomass burning: Part 3. Grasses by Daniel R. Oros; M. Radzi bin Abas; Nasr Yousef M.J. Omar; Noorsaadah A. Rahman; Bernd R.T. Simoneit (919-940).
Smoke particulate matter from grasses (Gramineae, temperate, tropical and arctic) subjected to controlled burning, both under smoldering and flaming conditions, was sampled by high volume air filtration on pre-cleaned quartz fiber filters. The filtered particles were extracted with dichloromethane/methanol and the crude extracts were methylated for separation by thin layer chromatography into hydrocarbon, carbonyl, carboxylic acid ester and polar fractions. Then, the total extract and individual fractions were analyzed by GC–MS. The major organic components directly emitted in grass smoke particles were the homologous series of n-alkanoic acids from plant lipids, n-alkanes from epicuticular wax, and sterols and triterpenols. The major natural products altered by combustion included pyrolysis products from cellulose and lignin biopolymers, and oxidation products from triterpenoids and sterols. Polycyclic aromatic hydrocarbons (PAH) were also present; however, only as minor components. Although the concentrations of organic compounds in smoke aerosols are highly variable and dependent on combustion temperature, the biomarkers and their combustion alteration products are in these cases source specific. The major components are adsorbed on or trapped in smoke particulate matter and thus may be utilized as molecular tracers in the atmosphere for determining fuel type and source contributions from grass burning.

The aim of this study was to seek the origin of a B peak found in two sediment profiles from a small lake close to a small-sized town in Finland. The peak was found by chance when an environmental multielement study was performed. Altogether 51 chemical elements were determined with ICP-MS, after aqua regia digestion. None of the other determined elements were enriched or depleted in the B rich layer, including elements derived from sea-salt inclusions (Na and Sr) and anthropogenic sources (Pb, Cu, Cd, Hg, etc.). Boron stable isotopes, dating of the sediment cores, and the B concentrations found in possible source materials suggest that the B rich layer is the result of leaching of wood ash produced in a fire that destroyed half of the nearby wooden town in the early 19th century. The results imply that the concentrations and isotopic signatures of B in lacustrine environments (sediments) can be used to detect historic fires.

In the central part of the Pannonian Basin, factors controlling the distribution of As in sediments and groundwater of the upper 500 m were studied. In core samples, the amounts of As, Fe and Mn extractable with hydroxylamine hydrochloride (NH2OH · HCl) in 25% acetic acid, the proportion of the <0.063 mm size fraction, and the sediment organic C (Corg) contents were measured. In the groundwaters concentrations of As, humic substances, and selected major chemical components were determined. In most core samples extractable Fe, as FeOOH, and Corg are correlated, but some samples have excess Fe, or organic matter. In cases where either excess Fe or excess organic matter is found, the amount of As is also elevated. The spatial distribution of As in the groundwater and the lack of a consistent correlation of As with a single component indicate that there is no single factor controlling the concentration of dissolved As over the entire study area. The only consistent feature is enrichment of As relative to Fe in the groundwater, compared to the sediments. This suggests that the dissolution of Fe minerals, which primarily adsorb As, is not congruent. In reducing conditions Fe(III) oxyhydroxides together with adsorbed As dissolve, and siderite with little or no As precipitates. When sub-regions are separated and studied individually, it can be shown that hydrogeological features of the sediments, the proportions of Fe minerals and sedimentary organic matter, and the concentration of dissolved humic materials, all influence the accumulation and mobilization of As. The significance of the different mobilizing processes, however, and the mean concentration of As, is different in the recharge, through-flow and discharge areas.

Investigation of bacterial hopanoid inputs to soils from Western Canada by Chubashini Shunthirasingham; Myrna J. Simpson (964-976).
Hopanoids have been widely used as characteristic biomarkers to study inputs of bacterial biomass to sediments because they are preserved in the geologic record. A limited number of studies have been performed on hopanoid biomarkers in soils. The present study examined the distribution and potential preservation of hopanoids in soils that are developed under different climatic conditions and varying vegetative inputs. Solvent extraction and sequential chemical degradation methods were employed to extract both “free” and “bound” hopanoids, from three grassland soils, a grassland–forest transition soil, and a forest soil from Western Canada. Identification and quantification of hopanoids in the soil samples were carried out by gas chromatography–mass spectrometry. Methylbishomohopanol, bishomohopanol and bishomohopanoic acid were detected in all solvent extracts. The base hydrolysis and ruthenium tetroxide extracts contained only bishomohopanoic acid at a concentration range of 0.8–8.8 μg/gC and 2.2–28.3 μg/gC, respectively. The acid hydrolysis procedure did not release detectable amounts of hopanoids. The solvent extraction yielded the greatest amounts of “free” hopanoids in two of the grassland soils (Dark Brown and Black Chernozems) and in the forest soil (Gray Luvisol). In contrast, the chemical degradation methods resulted in higher amounts of “bound” hopanoids in the third grassland soil (Brown Chernozem) and the transition soil (Dark Gray Chernozem), indicating that more hopanoids exist in the “bound” form in these soils. Overall, the forest and the transition soils contained more hopanoids than the grassland soils. This is hypothesized to be due to the greater degradation of hopanoids in the grassland soils and or sorption to clay minerals, as compared to the forest and transition soils.

Reactivity of the cement–bentonite interface with alkaline solutions using transport cells by Raúl Fernández; Jaime Cuevas; Laura Sánchez; Raquel Vigil de la Villa; Santiago Leguey (977-992).
Clayey formations are considered as suitable host rocks to develop a Deep Geological Repository (DGR) for nuclear wastes. A concrete ring, located between the clayey formation and the bentonite barrier, is needed as structural support for the galleries. This material will act as a source of alkaline fluids when the formation’s pore water saturates the system. This investigation evaluates the performance of the concrete-bentonite system by means of both geochemical codes and experimental results.A column made of compacted bentonite from La Serrata (Almería, Spain) (1.4 g/cm3, dry density) was held in contact with an ordinary Portland cement (OPC) mortar. Two alkaline solutions (Ca(OH)2 saturated and NaOH 0.25 M) were injected from the mortar’s side at 25, 60 and 120 °C. The permeability of the system and the effluent fluid composition were determined periodically. Finally, the solid phase was sampled and analyzed after 1 year of treatment.Ca(OH)2 saturated fluids does not alter the mineralogy over the experiment time scale. NaOH fluids produced minor changes at 60–25 °C but at 120 °C a thin tobermorite layer of 1.5 mm precipitates in the clay aggregate surfaces at the interface. After this layer, analcime nucleates in heterogeneous patches affecting the whole compacted bentonite probe (2 cm thickness). The use of the PHREEQC code thermodynamic approach predicts the mineralogical transformations. However, it is necessary to introduce kinetic laws and to consider the existence of stagnant zones in the model in order to simulate the heterogeneous spatial alteration observed.

Spectroscopic investigation on the chemical forms of Cu during the synthesis of zeolite X at low temperature by Roberto Terzano; Matteo Spagnuolo; Luca Medici; Fabio Tateo; Bart Vekemans; Koen Janssens; Pacifico Ruggiero (993-1005).
The direct synthesis of zeolites in polluted soils has proved to be a promising process for the stabilization of metals inside these minerals. Nevertheless, more detailed information about this process is still needed in order to better foresee the fate of metals in treated soils. In this work, zeolite X has been synthesized under alkaline conditions in an aqueous solution containing 2500 mg kg−1 of Cu, starting from Na silicate and Al hydroxide at 60 °C. Aluminium, Si and Cu concentrations in the aqueous phase, during zeolite synthesis, were measured over a period of 160 h. The solid products have been characterized over time by XRD, SEM-EDX, ESR, FT-IR, and synchrotron radiation X-ray microbeam absorption near edge structure (μ-XANES) and extended X-ray absorption fine structure (μ-EXAFS) spectroscopy. It appears that the marked reduction of Cu concentration in solution is not only due to a simple precipitation effect, but also to processes connected with the formation of zeolite X which could entrap, inside its porous structure, nano- or micro-occlusions of precipitated Cu hydroxides and/or oxides. In addition, EXAFS observations strengthen the hypothesis of the presence of different Cu phases even at a short-range molecular level and suggest that some of these occlusions could be even bound to the zeolite framework. The results suggest that zeolite formation could be used to reduce the availability of metals in polluted soils.

The applicability of accelerated solvent extraction (ASE) to extract lipid biomarkers from soils by Boris Jansen; Klaas G.J. Nierop; Marcel C. Kotte; Pim de Voogt; Jacobus M. Verstraten (1006-1015).
We investigated the ability of accelerated solvent extraction (ASE) to extract selected lipid biomarkers (C19–C34 n-alkanes, n-alcohols and n-fatty acids as well as dehydroabietic acid and β-sitosterol) from a sandy soil profile under Corsican pine. Two organic layers (moss and F1) as well as two mineral soil horizons (EA and C1) were sampled and extracted with DCM/MeOH (93:7 v/v) by ASE at 75 °C and a pressure of 6.9 × 106  Pa or 17 × 106  Pa. Soxhlet extractions were used as the established reference method. After clean-up and derivatization with BSTFA, the extracts were analyzed on GC/MS.Using Soxhlet as a reference, we found ASE to extract all compounds adequately. The n-alkanes, especially, were found to be extracted very efficiently from all horizons studied. Only the n-fatty acids and β-sitosterol from the organic layers seemed to be extracted at a slightly lower efficiency by ASE. In all but two instances the relative abundance of extracted lipids within a component class was the same regardless of the extraction method used.Using a higher pressure in the ASE extractions significantly increased the extraction efficiency for all component classes in the moss layer, except β-sitosterol. The effect was most pronounced for the n-alkanes. In the EA horizon, a higher pressure slightly reduced the extraction efficiency for dehydroabietic acid. The observed differences between ASE and Soxhlet extractions as well as the pressure effect can be explained by a decrease in polarity of the extractant due to the elevated pressure and temperature applied during ASE extractions as compared to Soxhlet extractions. This would mainly increase the extraction efficiency of the least polar biomarkers: the n-alkanes as was observed. In addition, a better penetration of still partially water-filled micro pores under elevated pressure and temperature may have played a role.

Sources of groundwater nitrate revealed using residence time and isotope methods by Keara B. Moore; Brenda Ekwurzel; Bradley K. Esser; G. Bryant Hudson; Jean E. Moran (1016-1029).
Nitrate concentrations approaching and greater than the maximum contaminant level are impairing the viability of many groundwater basins as drinking water sources. Nitrate isotope data are effective in determining contaminant sources, especially when combined with other isotopic tracers such as stable isotopes of water and 3H–He ages to give insight into the routes and timing of NO3 inputs to the flow system. This combination of techniques is demonstrated in Livermore, CA, where it is determined that low NO3 reclaimed wastewater predominates in the NW, while two flowpaths with distinct NO3 sources originate in the SE. Along the eastern flowpath, δ 15N values greater than 10‰ indicate that animal waste is the primary source. Diminishing concentrations over time suggest that contamination results from historical land use practices. The other flowpath begins in an area where rapid recharge, primarily of low-NO3 imported water (identified by stable isotopes of water and a 3H–He residence time of <1 year), mobilizes a significant local NO3 source, bringing groundwater concentrations up to 53 mg NO3  L−1. In this area, artificial recharge of imported water via local arroyos increases the flux of NO3 to the regional aquifer. The low δ 15N value (3.1‰) in this location implicates synthetic fertilizer. In addition to these anthropogenic sources, natural NO3 background levels between 15 and 20 mg NO3  L−1 are found in deep wells with residence times greater than 50 a.

Transport of Cd, Cu and Pb in an acid soil amended with phosphogypsum, sugar foam and phosphoric rock by C.G. Campbell; F. Garrido; V. Illera; M.T. García-González (1030-1043).
Metal pollution in soils is a world-wide problem requiring new tools for environmental management. This study investigated the transport processes of metals (Cd, Cu and Pb) in undisturbed soil columns of an acid soil amended with phosphogypsum, sugar foam, and phosphoric rock (PG, SF and PR). Sorption mechanisms have been examined in a companion paper using sequential extraction methods. This investigation focused on how these sorption mechanisms relate to transport parameters estimated from metal breakthrough curves using temporal moment analysis. The application of the 3 soil amendments significantly reduced the total metal mass leached from all the columns. Metal travel times were also longer with the addition of the amendments, although retardation values were much lower than those reported in batch studies. Retardation (R) values for Cd, Cu and Pb averaged 1.6, 1.8 and 1.7, respectively, for all treated columns. These R values for the control columns were 1.2, 1.3 and 1.4 for Cd, Cu and Pb, respectively. Additional observations of Al, Ca and SO 4 2 - leaching from the columns revealed the existence of fast exchange and precipitation–dissolution reactions included in the transport of metals through the soil. Under the conditions of this study, it is estimated that the mass of Cd, Cu and Pb leached from the soil would be reduced by more than 60–99% with the addition of the amendments. Therefore, all 3 amendments (PG, SF, and PR) appear to have reasonable potential to be applied to reduce metal leaching in polluted agricultural soils.

A suite of trace metals was analyzed in water and sediment samples from the Blesbokspruit, a Ramsar certified riparian wetland, to assess the impact of mining on the sediment quality and the fate of trace metals in the environment. Limited mobility of trace metals was observed primarily because of their high partition coefficient in alkaline waters. Nickel was most mobile with a mean K d of 103.28  L kg−1 whereas Zr was least mobile with a mean K d of 105.47  L kg−1. The overall trace metal mobility sequence, derived for the Blesbokspruit, in increasing order, is: Zr < Cr < Pb < Ba < V < Cu < Zn < Sr < Mn < U < Mo < Co < Ni. Once removed from the solution, most trace metals were preferentially associated with the carbonate and Fe–Mn oxide fraction followed by the exchangeable fraction of the sediments. Organic C played a limited role in trace metal uptake. Only Cu was primarily associated with the organic fraction whereas Ti and Zr were mostly found in the residual fraction. Compared to their regional background, Au and Ag were most enriched, at times by a factor of 20–400, in the sediments. Significant enrichment of U, Hg, V, Cr, Co, Cu and Zn was also observed in the sediments.The calculated geoaccumulation indices suggest that the sediments are very lightly to lightly polluted with respect to most trace metals and highly polluted with respect to Au and Ag. The metal pollution index (MPI) for the 20 sampled sites varied between 2.9 and 45.7. The highest MPI values were found at sites that were close to tailings dams. Sediment eco-toxicity was quantified by calculating the sediment quality guideline index (SQG-I). The calculated SQG-I values (0.09–0.69) suggest that the sediments at the study area have low to moderate potential for eco-toxicity.

Evidence of precursor phenomena in the Kobe earthquake obtained from atmospheric radon concentration by Yumi Yasuoka; George Igarashi; Testuo Ishikawa; Shinji Tokonami; Masaki Shinogi (1064-1072).
Atmospheric 222Rn concentrations were determined over a 10a period, which included the date of the Kobe, Japan earthquake, on January 17th 1995. It was found that the seismically related 222Rn anomaly was higher than the 99% confidence limits for the residual value of atmospheric 222Rn which had been observed 2 months before. The residual 222Rn concentration, in which residual values of the daily minimum are the difference between each normal 222Rn concentration (calculated from January 1984 to December 1993) and the daily minimum 222Rn concentration (January 1994 to January 1995), was calculated by applying the exponential smoothing method to the residual values for each day. It was found that the fluctuations of the residual values can be fitted very well to a log-periodic oscillation model. The real residual values stopped increasing at 1994.999 (December 31st 1994), which corresponds with the critical point (t c) of best fit model. This anomalous 222Rn variation can be seen as the result of local stresses, not primary stresses which directly lead to the Kobe earthquake. On the other hand, when the critical exponent (z) and the radial frequency (ω) of the model were simultaneously fixed 0.2 ⩽  z  ⩽ 0.6 and 6 ⩽  ω  ⩽ 12, t c (critical point) was between January 13th 1995 and January 27th 1995. The Kobe earthquake occurrence date (January 17th 1995) is within this range. Therefore this anomalous 222Rn variation can also be seen as the result of primary stresses which possibly led to the Kobe earthquake. There is a distinct possibility that similar statistical oscillations will be detected in other measurements such as microseismicity, tectonic strain, fluctuation in the ground level, or changes in groundwater elevations and composition.

In the lower part of the River Saale, Germany, U shows concentrations of up to 4 μg/L. Former mining activities and their still existing dewatering systems in the drainage basin of the River Saale are responsible for the high salt and trace metal concentrations in the water of some tributaries. An old adit from the Mansfeld mining district flowing into the Schlenze Stream with mean U concentrations of about 60 μg/L increases the U concentration of the River Saale by 0.5 μg/L. The U concentrations in the running waters of the study area can be explained by mixing processes. Uranium from the adit and the Schlenze is mainly transported in the <0.45 μm fraction as a carbonate complex.