Applied Geochemistry (v.22, #7)
Chemodynamics of an arsenic “hotspot” in a West Bengal aquifer: A field and reactive transport modeling study by Laurent Charlet; S. Chakraborty; C.A.J. Appelo; G. Roman-Ross; B. Nath; A.A. Ansari; M. Lanson; D. Chatterjee; S. Basu Mallik (1273-1292).
Extremely high As concentrations in drinking water of the Ganges Delta (West Bengal and Bangladesh) has emerged as an issue of great concern in the past decade because of its serious impact on the health of millions of people. The distribution pattern of As concentrations in the Ganges Delta region is patchy and there are numerous As “hotspots”. The present study is perhaps the first attempt in West Bengal to characterize such a hotspot by geophysical and geochemical methods, and to model the transport of the enrichment plume using a 1D reactive transport model (PHREEQC). The study site is located along the Hooghly River, 60 km north of Kolkota City, near the city of Chakdaha. Total As concentrations in the groundwater range from 0.5 to more than 6 μmol L−1; the WHO recommended maximum drinking water concentration is 0.13 μmol L−1 (i.e. 10 μg L−1). Results show groundwater is in chemical equilibrium with siderite and calcite, a mineral phase previously shown to be an efficient trap for As(III). Groundwater redox potential is controlled by the Fe(OH)3(am)/Fe2+ couple. The As(III) versus As(V) distribution (42% As(III) and 58% As(V), on average) is not at equilibrium with measured Eh values. No evidence of sulfide solid phases, such as As rich pyrite or arsenopyrite, was found. Although amorphous Fe dissolution is confirmed to play an important role in the release of As, selective dissolution extractions indicate that adsorption of As on carbonates and micas may also be an important component of As cycling in the sediment. Modelling results demonstrate the role of PO 4 3 - , HCO 3 - and Fe(II) in mobilizing the As plume, thereby increasing the threat to the 75,000 inhabitants of Chakdaha.
Cementation of kerogen-rich marls by alkaline fluids released during weathering of thermally metamorphosed marly sediments. Part I: Isotopic (C,O) study of the Khushaym Matruk natural analogue (central Jordan) by Serge Fourcade; Laurent Trotignon; Philippe Boulvais; Isabelle Techer; Marcel Elie; Didier Vandamme; Elias Salameh; Hani Khoury (1293-1310).
The Khushaym Matruk site in central Jordan may represent a natural analogue depicting the interaction of alkaline solutions with a clayey sedimentary formation or with clay-rich confining barriers at the interface with concrete structures in waste disposal sites. In this locality, past spontaneous combustion of organic matter in a clayey biomicritic formation produced a ca. 60 m-thick layer of cement-marble containing some of the high-temperature phases usually found in industrial cements (e.g., spurrite, brucite, and Ca-aluminate). A vertical cross-section of the underlying sediments was used in order to study the interaction between cement-marbles and neighbouring clayey limestones under weathering conditions. A thermodynamic approach of the alteration parageneses (calcite–jennite–afwillite–brucite and CSH phases) in the cement-marbles constrains the interacting solutions to have had pH-values between 10.5 and 12. Over 3 m, the sediments located beneath the metamorphic unit were compacted and underwent carbonation. They display large C and O isotopic variations with respect to “pristine” sediments from the bottom of the section. Low δ 13C-values down to −31.4‰/PDB show the contribution of CO2 derived from the oxidization of organic matter and from the atmosphere to the intense carbonation process affecting that particular sedimentary level. The size of the C isotopic anomalies, their geometrical extent and their coincidence with the variations of other markers like the Zn content, the structure of organic matter, the mineralogical composition, all argue that the carbonation process was induced by the percolation of high pH solutions which derived from the alteration of cement-marbles. The temperature of the carbonation process remains conjectural and some post-formation O isotopic reequilibration likely affected the newly-formed carbonate. Carbonation induced a considerable porosity reduction, both in fractures and matrixes. The Khushaym Matruk site may have some bearing to the early life of a repository site, when water saturation of the geological formations hosting the concrete structures is incomplete, enabling simultaneous diffusion of alkaline waters and gaseous CO2 in the near field.
Cementation of kerogen-rich marls by alkaline fluids released during weathering of thermally metamorphosed marly sediments. Part II: Organic matter evolution, magnetic susceptibility and metals (Ti, Cr, Fe) at the Khushaym Matruk natural analogue (Central Jordan) by Marcel Elie; Isabelle Techer; Laurent Trotignon; Hani Khoury; Elias Salameh; Didier Vandamme; Philippe Boulvais; Serge Fourcade (1311-1328).
Spontaneous combustion, less than 1 Ma ago, affected a 60-m thick sediment pile of biomicrite at the Khushaym Matruck site (Jordan). The present study shows that three retrograde alteration stages occurred: weathering, thermal stress and oxidative alkaline perturbation. μ-FT-i.r. spectra of isolated kerogens and oxygen index of whole rocks indicate that oxidation of organic matter occurred down to ∼10 m beneath the metamorphosed zone at Khushaym Matruck. The occurrence of the oxidative weathering bacterially mediated, as suggested by the mass chromatograms of saturated hydrocarbons, can explain high Rock-Eval T max values and low petroliferous potential measured along the sedimentary pile. On the other hand, the thermal extent of combustion events was limited to the first 2 m from the contact. The mean reflectance of 0.20–0.24% and porosity of ca. 50% of the grey clayey biomicrites indicate that organic matter was very immature and sediments were unconsolidated at the time of the combustion event. Using mineralogy, microscopic analyses of vegetable debris and magnetic susceptibility, a suite of characteristic points corresponding to the thermal imprint can be assessed: (i) x = 0m, T ∼ 1000 °C, (ii) x = 1 m, T ∼ 350 °C, (iii) x = 2 m, T ∼ 150 °C and (iv) x > ∼ 8 m, T ∼ 30 °C. Paleocirculation of meteoric groundwater in the ‘cement-marbles’ generated high-pH fluids that have circulated via fractures and through the matrix porosity of the underlying biomicrites but have also induced alkaline hydrolysis and oxidative attack of the organic matter. The polysaccharide/lignin ratio derived from μ-FT-i.r. analyses shows that the delignification of vegetable debris and degradation of polysaccharides progressively decline in the indurated zone, which indicates a decrease in the pH of migrating solutions. The latter also severely oxidized organic matter at 2.10 and 3.05 m as revealed by the oxygen index and induced the generation of bitumen. The spatial correlation between the oxidation levels of organic matter and the metal contents (Fe, Ti and Cr) suggests that redox reactions were responsible for the immobilization of metals in the indurated biomicrites. The intensity of these reactions is attributed to changes in the fluid flow regime within the sedimentary column.
Diel variations in stream chemistry and isotopic composition of dissolved inorganic carbon, upper Clark Fork River, Montana, USA by Stephen R. Parker; Christopher H. Gammons; Simon R. Poulson; Michael D. DeGrandpre (1329-1343).
Many rivers undergo diel (24-h) concentration fluctuations of pH, dissolved gases, trace metals, nutrients, and other chemical species. A study conducted in 1994 documented such behavior in the upper Clark Fork River, Montana, a stream whose headwaters have been severely impacted by historic metal mining, milling, and smelting. The purpose of the present investigation was to expand on these earlier findings by conducting simultaneous diel samplings at two sites on the upper Clark Fork River separated by 2.5 h of stream travel time. By monitoring two stations, it was possible to more closely examine the processes that control temporal and spatial gradients in stream chemistry. Another objective was to examine diel changes in the δ13C composition of dissolved inorganic C (DIC) and their relationship to biological activity in the stream. The most important findings of this study include: (1) concentrations of dissolved and particulate heavy metals increased during the night and decreased during the day, in agreement with previous work; (2) these changes were positively correlated to diel changes in pH, dissolved O2, and water temperature; (3) dissolved NO 3 - concentrations increased during the night at the lower site, but showed the opposite behavior at the upper site; and (4) diel changes in δ13C-DIC were noted at both sites, although the timing and magnitudes of the cycles differed. Hypotheses to explain the first two observations include: cyclic co-precipitation of divalent metals with carbonate minerals; pH- and temperature-dependent sorption of metal cations onto the streambed and suspended particles; or photosynthetically enhanced oxidation and removal of Fe and Mn oxides at biofilm surfaces during the daytime. The latter model explains the majority of the field observations, including night-time increases in particulate forms of Fe and other elements.
The role of grain dissolution and diagenetic mineral precipitation in the cycling of metals and phosphorus: A study of a contaminated urban freshwater sediment by Kevin G. Taylor; Stephen Boult (1344-1358).
This paper describes the detrital mineralogy, early diagenetic reactions and authigenic mineral precipitates for freshwater contaminated sediments deposited in an urban water body (the Salford Quays of the Manchester Ship Canal, Greater Manchester, UK). These sediments contain a mix of natural and anthropogenic detrital grains. Detrital grains are dominated by quartz and clay grains, whilst anthropogenic grains are dominated by metal-rich glass grains, concentrated at a depth of 12–17 cm in the sediment as a result of historical inputs. Sediment porewaters contain significant concentrations of Fe, Mn, Zn and phosphate. Bacterial Fe(III) and Mn(IV) reduction are hypothesised to supply Fe2+ and Mn2+ to porewaters, with phosphate released from Fe oxide reduction or organic matter oxidation. Petrographic observations indicate that the metal-rich glass grains are undergoing chemical dissolution during early diagenesis, supplying Fe and Zn to porewaters.The most abundant authigenic mineral in the sediments is vivianite (Fe3(PO4)2 · 8H2O), containing a significant level of redlingite ( Mn 3 2 + ( PO 4 ) 2 · 8 H 2 O ) , with minor framboidal pyrite (FeS2). Electron microprobe analysis shows the vivianite to contain Zn, Cu and Pb, suggesting that vivianite acts as a long-term sink for these metals in this sediment. This implies that authigenic vivianite in freshwater sediments may act as a long-term sink for metals, in a similar manner to sulphides in marine sediments. This study highlights that the nature of detrital and diagenetic mineralogy, in addition to porewater and sediment chemistry, needs to be considered in assessing contaminated sediments.
50-year record and solid state speciation of mercury in natural and contaminated reservoir sediment by Sabine Castelle; Jörg Schäfer; Gérard Blanc; Stéphane Audry; Henri Etcheber; Jean-Pierre Lissalde (1359-1370).
Contaminated fluvial sediments represent both temporary sinks for river-borne pollutants and potential sources in case of natural and/or anthropogenic resuspension. Reservoir lakes play a very important role in sediment dynamics of watersheds and may offer great opportunities to study historical records of river-borne particles and associated elements transported in the past. The fate and potential environmental impact of Hg depends on its abundance, its carrier phases and its chemical speciation. Historical Hg records and solid state Hg speciation were compared in sediments from two contrasting reservoirs of the Lot River (France) upstream and downstream from a major polymetallic pollution (e.g. Cd, Zn) source. Natural (geochemical background) and anthropogenic Hg concentrations and their relationships with predominant carrier phases were determined. The results reveal important historical Hg contamination (up to 35 mg kg−1) of the downstream sediment, reflecting the historical evolution of industrial activity at the point source, i.e. former coal mining, Zn ore treatment and post-industrial remediation work. Single chemical extractions (ascorbate, H2O2, KOH) suggest that at both sites most (∼75%) of the Hg is bound to organic and/or reactive sulphide phases. Organo-chelated (KOH-extracted) Hg, representing an important fraction in the uncontaminated sediment, shows similar concentrations (∼0.02 mg kg−1) at both sites and may be mainly attributed to natural inputs and/or processes. Although, total Hg concentrations in recent surface sediments at both sites are still very different, similar mono-methylmercury concentrations (up to 4 μg kg−1) and vertical distributions were observed, suggesting comparable methylation-demethylation processes. High mono-methylmercury concentrations (4–15 μg kg−1) in 10–40 a-old, sulphide-rich, contaminated sediment suggest long-term persistence of mono-methylmercury. Beyond historical records of total concentrations, the studied reservoir sediments provided new insights in solid state speciation and carrier phases of natural and anthropogenic Hg. In case of sediment resuspension, the major part of the Hg historically stored in the Lot River sediments will be accessible to biogeochemical recycling in the downstream fluvial-estuarine environment.
The interaction of dissolved Boom Clay and Gorleben humic substances with selenium oxyanions (selenite and selenate) by C. Bruggeman; A. Maes; J. Vancluysen (1371-1379).
Batch experiments were performed in which the interaction of selenite ( Se + IV O 3 2 - ) and selenate ( Se + VI O 4 2 - ) with dissolved Boom Clay and Gorleben humic substances (HS) was followed as a function of time. Particulate HS (>25 nm) was first removed by centrifugation. The supernatant solutions were analyzed by a combination of Ion Chromatography, Gel Permeation Chromatography and Ultrafiltration to determine the Se solution speciation. A first experiment in which 1 × 10−6 M 75 SeO 4 2 - was in contact with 128 ppm Boom Clay HS or 160 ppm Gorleben HS in a synthetic clay H2O background electrolyte, showed that the total Se solution concentration and Se speciation remained unchanged, indicating that there was no interaction whatsoever between SeO 4 2 - and HS during the three months’ observation time. Upon contact of 1 × 10−6 M 75 SeO 4 2 - with the same HS-containing solution however, a decrease of ∼95% in total Se solution concentration after centrifugation was noted and final Se solution concentrations of 4.4 × 10−8 M (Boom Clay HS) and 1.3 × 10−7 M (Gorleben HS) were measured after six months observation. Together with the decrease in total solution concentration, a change in the Se solution speciation was observed. After one month, the solution speciation in both systems was dominated by a colloidal Se species that was associated with HS. The chemical nature of this Se species could not be determined. The SeO 3 2 - concentration decreased steadily to a final concentration of 1.9 × 10−8 M (Boom Clay HS) and 1.5 × 10−8 M (Gorleben HS). The detailed understanding of the mechanisms at work in these systems will necessitate spectroscopic measurements of the Se species present in the pellet and of Se associated with the humic substance fraction in solution.
Iron, manganese and trace metal concentrations in seaweeds from the central west coast of the Gulf of California by Miguel Angel Huerta-Diaz; Francisco de León-Chavira; María Lucila Lares; Alfredo Chee-Barragán; Arturo Siqueiros-Valencia (1380-1392).
Concentrations of Co, Cu, Fe, Mn, Ni, Pb and Zn in four macroalgae species (Ulva lactuca, Chondracanthus squarrulosus, Sargassum sinicola and Gracilariopsis lemaneiformis) were obtained for the first time from the central part of the west coast of the Gulf of California. Generally, no differences in metal concentrations were found among the different seaweed species, although spatial differences were apparent. Iron, Mn and Cu exhibited higher concentrations at the stations located in front of Angel de la Guarda Island, probably because of high vertical mixing processes present in the zone. The results were compared with dissolved metal concentrations reported for the Gulf of California (Cd, Mn and Fe) and the North Pacific Ocean. The resulting linear regression of the results vs. North Pacific Ocean concentrations indicated that the levels of Cu, Ni and Zn measured in this study were within its 95% confidence level. Furthermore, this comparison was capable of detecting dissolved Fe and Mn enrichments in Gulf of California waters relative to the North Pacific Ocean concentrations. Calculations of total masses of metals associated with algal biomass on the west coast of the Gulf of California indicated that the lowest masses were represented by Cu (108 ± 25 kg) and Ni (184 ± 52 kg), whereas Pb (1.1 ± 0.6 ton) and Fe (10.9 ± 8.5 ton) were the elements with the highest associated masses.
Origin of petroliferous bitumen from the Büyük Menderes–Gediz geothermal graben system, Denizli – Sarayköy, western Turkey by Kadir Gürgey; Bernd R.T. Simoneit; Zühtü Batı; İsmail H. Karamanderesi; Baki Varol (1393-1415).
The KB-5 well is located at the intersection of the geothermally active Menderes and Gediz graben systems in western Turkey. Significant volumes of “petroleum-like material” (PLM) with its associated thermal water (120 °C) erupted onto the surface during drilling from a depth of 120–132 m (i.e., from the claystone and marl-rich Early to Middle Pliocene Kolonkoya formation). The purpose of this paper is: (1) to characterize this PLM, (2) to assess the source characteristics from which the PLM was likely generated, and (3) to recognize the generation mechanism considering the geothermal-gradual versus the hydrothermal-rapid processes. Analytical organic geochemistry using thin layer chromatographic separation followed by gas chromatography–mass spectrometry (GC–MS) was carried out.The PLM is composed primarily of polar NSO compounds + asphaltenes (77%). This feature is similar to hydrothermal petroleums (e.g., Calcite Springs, Yellowstone National Park, Wyoming). The PLM shows n-alkanes ranging from n-C19 to n-C38 (i.e., with a maximum at n-C30) but n-alkanes are depleted in <n-C19. An absence of acyclic isoprenoids (pristane and phytane) and considerably large UCM (unresolved complex mixture) indicate that the PLM has been subjected to a moderate degree of alteration possibly by the accompanying hot geothermal waters.The source specific biomarkers [i.e., low C29NH/C30H ratio; presence of gammacerane and 18α(H)-oleanane; high C35/C34 homohopane ratio and ββ-C29 sterane concentration; n-C28 < n-C27 < n-C29; C28 < C27 < C29αααR steranes; %C29αααR > %C27αααR] suggest that the PLM is a petroleum and was most likely generated from a Tertiary source rock with a carbonate-clay-rich lithology. The source organic matter was predominantly terrestrial and bacterial detritus deposited in relatively saline – anoxic environmental conditions. Maturity sensitive biomarker parameters (i.e., T m > T s; C29 sterane 20S/(20S + 20R) = 0.35; C32 hopane 22S/(22S + 22R) = 0.57; low diasterane/regular sterane ratio) correspond to a maturity level of approximately 0.50–0.60% R o. This level of maturation could not be reached by such a young (Upper Miocene–Lower Pliocene) and shallow sedimentary column (max. 600 m) in the absence of “instantaneous” hydrothermal activity. PAHs are not detectable, but series of alkylbenzenes, alkyltoluenes, alk-1-enes and triaromatic steranes are present. The lack of organic richness and maturity in the drilled section of the KB-5 well indicates that the petroleum was generated in the deeper sections of the formation. The temperature profile of the well and composition of the hydrocarbons in the petroleum suggest that the temperature of the hydrothermal activity during hydrocarbon generation was <180 °C.
Isotope geochemistry of drainage from an acid mine impaired watershed, Oakland, California by Thomas W. Butler (1416-1426).
Oxidation of sulfides at the Leona Heights Sulfur Mine has resulted in the liberation of acid, SO4 and metals to Leona Creek. Previous research at the site has indicated Fe(II) oxidation at rates faster than would be predicted by abiotic oxidation alone, particularly in the segment of stream between the Adit and Leona Street sample stations. In order to assess the mechanisms responsible for sulfide oxidation, samples were collected for isotopic analysis of water and SO4, the results of which were used to develop a stoichiometric isotope-balance model. This exercise indicated that the percentage of water-derived oxygen in SO4 increased spatially from between 56% and 64% at the Adit to between 71% and 72% at Leona Street, illustrating that increased sulfide oxidation via Fe(III) was occurring within, or as water flows over, the waste rock, relative to water emanating directly from the former mine. The incorporation of water-derived oxygen in SO4 during pyrite oxidation is a process controlled by Fe oxidizing bacteria such as A. ferrooxidans at low pH. The role of bacteria was further supported by estimates of the rate constant for Fe oxidation between sampling stations, yielding values that were approximately 106 faster than abiotic Fe oxidation alone. Stable isotopic analysis of water further indicates a close correlation of adit spring water to the local meteoric water line, while 3H data indicate a groundwater apparent age, or time of travel from its primary zone of recharge, of <5–18 a. Additionally, the δ34S data, in conjunction with reported albitized feldspars within the Leona Rhyolite host rock, indicate a magmatic origin of ore sulfur, contrary to previous interpretations at the site.
Groundwater chemistry of Al under Dutch sandy soils: Effects of land use and depth by Ellen P.M.J. Fest; Erwin J.M. Temminghoff; Jasper Griffioen; Bas Van Der Grift; Willem H. Van Riemsdijk (1427-1438).
Aluminium has received great attention in the second half of the 20th century, mainly in the context of the acid rain problem mostly in forest soils. In this research the effect of land use and depth of the groundwater on Al, pH and DOC concentration in groundwater under Dutch sandy soils has been studied. Both pH and DOC concentration play a major role in the speciation of Al in solution. Furthermore, the equilibrium with mineral phases like gibbsite, amorphous Al(OH)3 and imogolite, has been considered. Agricultural and natural land use were expected to have different effects on the pH and DOC concentration, which in turn could influence the total Al concentration and the speciation of Al in groundwater at different depths (phreatic, shallow and deep). An extensive dataset (n = 2181) from the national and some provincial monitoring networks on soil and groundwater quality was used. Land use type and groundwater depth did influence the pH, and Al and DOC concentrations in groundwater samples. The Al concentration ranged from <0.4 μmol L−1 at pH > 7 to 1941 μmol L−1 at pH < 4; highest Al concentrations were found for natural-phreatic groundwater. The DOC concentration decreased and the median pH increased with depth of the groundwater. Natural-phreatic groundwater showed lower pH than the agricultural-phreatic groundwater. Highest DOC concentrations were found for the agricultural-phreatic groundwater, induced by the application of organic fertilizers. Besides inorganic complexation, the NICA-Donnan model was used to calculate Al3+ concentrations for complexation with DOC. Below pH 4.5 groundwater samples were mainly in disequilibrium with a mineral phase. This disequilibrium is considered to be the result of kinetic constraints or equilibrium with organic matter. Log K values were derived by linear regression and were close to theoretical values for Al(OH)3 minerals (e.g. gibbsite or amorphous Al(OH)3), except for natural-phreatic groundwater for which lower log K values were found. Complexation of Al with DOC is shown to be an important factor for the Al concentrations, especially at high DOC concentrations as was found for agricultural-phreatic groundwater.
Ferrihydrite flocs, native copper nanocrystals and spontaneous remediation in the Fosso dei Noni stream, Tuscany, Italy by Alessandro Genovese; Marcello Mellini (1439-1450).
The Fosso dei Noni stream drains the abandoned mixed-sulfide mining area of Fenice Capanne in Italy. Water pollution mostly derives from two tributaries, one of which adds Cu and the other Zn. Downstream, water pollution is progressively remediated through the spontaneous precipitation of abundant, deeply-colored flocs. Within 1 km, flocs change from yellow–red to whitish and green, as the pH increases from 4.59 to 7.70 and the Eh decreases from +311 to +165 mV. Flocs are initially amorphous; with a near-neutral pH, their X-ray diffraction properties suggest the presence of two-line ferrihydrite. Transmission electron microscopy reveals major nanotextural modifications in flocs along the entire stream. Upstream, flocs consist of globular particles with a radius of 25–50 nm. Downstream, they change to globular particles with elongated features. Lastly, further downstream, flocs consist of elongated features interconnected by continuous films. Nanochemical data are consistent with Al and Fe hydroxides (largely contaminated by S, Si, Ca, Cu and Zn); the Cu content increases progressively downstream to a maximum of 18 at. %. The increasing Cu content is paralleled by the appearance of isolated Cu nanocrystals adsorbed on floc surfaces. Spontaneous processes in the Fosso dei Noni stream (water neutralization, formation of ferrihydrite-like flocs and crystallization of native Cu) allow the temporary storage of Cu, providing hints on how to optimize remediation processes and Cu recovery.
Gaseous elemental mercury exchange with low mercury containing soils: Investigation of controlling factors by Mei Xin; Mae Sexauer Gustin (1451-1466).
Deposition of atmospheric elemental Hg (Hg0) to soils may be an important pathway for the transfer of Hg0 to terrestrial ecosystems. In this study a laboratory method was applied to investigate the role of soils with natural background Hg concentrations (<0.1 μg/g) as a source or sink for atmospheric Hg0 and to identify factors influencing Hg0 exchange between these soils and air. Air–soil Hg0 exchange was measured for a variety of dry substrates (8 pure soil constituents and 35 soils) under controlled experimental conditions. Fluxes measured using the pure soil constituents indicated that the mineralogical nature of the soil particles may play an important role in the sorption of atmospheric Hg0. In individual tests for 26 of the 35 natural soils, statistically significant linear correlations were found between Hg0 flux and air Hg0 concentration. Mercury flux under light conditions was typically higher than that in the dark, and soil air compensation points (CP, the air Hg0 concentrations at which there is no net Hg0 exchange) were significantly higher under light exposure. When all soil data were combined, at low air concentrations (2.8 ± 0.8 ng/m3) soils emitted Hg0 to the air in light conditions (mean flux: 1.3 ± 1.0 ng/m2 h) and adsorbed Hg0 in dark conditions (mean flux: −1.1 ± 1.2 ng/m2 h); while at elevated air Hg0 concentration (5.8 ± 1.0 ng/m3) deposition was the dominant flux (mean flux of −2.1 ± 1.6 and −4.6 ± 1.25 ng/m2 h in the light and dark, respectively). At air Hg0 concentrations similar to the ambient air (<5 ng/m3; 1.7 ± 1.6 ng/m3), Hg0 concentration in the air, light, and soil Hg concentration were significantly correlated with air–soil Hg0 exchange, while at higher air Hg0 concentrations (⩾5 ng/m3; 8.2 ± 2.2 ng/m3) that might be found in urban areas, soil Hg concentration, pH, and organic matter were the primary factors correlated with Hg0 flux. This study indicates that natural background soil may be a source or sink of atmospheric Hg0 depending on environmental parameters and soil physical and chemical properties.
Formation of mixed Al–Fe colloidal sorbent and dissolved-colloidal partitioning of Cu and Zn in the Cement Creek – Animas River Confluence, Silverton, Colorado by Laurence E. Schemel; Briant A. Kimball; Robert L. Runkel; Marisa H. Cox (1467-1484).
Transport and chemical transformations of dissolved and colloidal Al, Fe, Cu and Zn were studied by detailed sampling in the mixing zone downstream from the confluence of Cement Creek (pH 4.1) with the Animas River (pH 7.6). Complete mixing resulted in circumneutral pH in the downstream reach of the 1300 m study area. All four metals were transported through this mixing zone without significant losses to the streambed, and they exhibited transformations from dissolved to colloidal forms to varying degrees during the mixing process. Nearly all of the Al formed colloidal hydrous Al oxides (HAO) as pH increased (4.8–6.5), whereas colloidal hydrous Fe oxides (HFO) were supplied by Cement Creek as well as formed in the mixing zone primarily at higher pH (>6.5). The short travel time through the mixing zone (approx. 40 min) and pH limited the formation of HFO from dissolved Fe2+ supplied by Cement Creek. Although the proportions of HAO and HFO varied as the streams mixed, the colloidal sorbent typically was enriched in HAO relative to HFO by a factor of 1.5–2.1 (by mole) in the pH range where dissolved-to-colloidal partitioning of Cu and Zn was observed. Model simulations of sorption by HFO (alone) greatly underestimated the dissolved-to-colloidal partitioning of Zn. Previous studies have shown that HAO–HFO mixtures can sorb greater amounts of Zn than HFO alone, but the high Zn-to-sorbent ratio in this mixing zone could also account for greater partitioning. In contrast to Zn, comparisons with model simulations did not show that Cu sorption was greater than that for HFO alone, and also indicated that sorption was possibly less than what would be expected for a non-interactive mixture of these two sorbents. These field results for Cu, however, might be influenced by (organic) complexation or other factors in this natural system. Laboratory mixing experiments using natural source waters (upstream of the confluence) showed that the presence of HFO in the mixed sorbent resulted in greater Cu partitioning than for HAO alone, and that the effect was greater with increasing (mole fraction) HFO. This was consistent with field results that showed greater Cu sorption when additional HFO was formed in the downstream reach of the mixing zone. Further research is needed to identify the significance of surface-related mechanisms specific to HAO–HFO mixtures that could affect the partitioning of Cu in natural systems.
Platinum-group elements (Ir, Pd, Pt and Rh) in road-deposited sediments in two urban watersheds, Hawaii by Ross A. Sutherland; D. Graham Pearson; Chris J. Ottley (1485-1501).
This study represents the first detailed investigation of platinum-group elements (PGEs) in road-deposited sediment (RDS) in Hawaii, USA. Thirty-three sample locations, in two urban watersheds in Honolulu, Oahu, Hawaii were sampled. The <63 μm fraction of RDS was digested with aqua regia, followed by matrix separation with Dowex AG50-X8 cation exchange resin. PGEs were analyzed with inductively coupled plasma-mass spectrometry (ICP-MS) equipped with a desolvating nebulizer. Concentrations of Rh, Pd and Pt in residential streets reached 64, 105 and 506 ng/g, respectively. Maximum enrichment ratios, computed as RDS concentrations relative to baseline values, exceeded 400, indicating a significant anthropogenic signal with the sequence Rh > Pt > Pd. Iridium concentrations were uniformly low <1 ng/g, and enrichment ratios support a geogenic source. Significant interelement PGE correlations (Pd–Pt–Rh), combined with the magnitude of PGE pair-wise ratios (Pt/Pd, Pt/Rh and Pd/Rh), and relative percentages comparable to European RDS and roadside soil in Indiana, USA all suggest an automobile source. Attrition of PGE-loaded automobile catalytic converters and subsequent loss to the environment by exhaust emissions explains the significant environmental signal of PGEs in road environments of Hawaii. Further PGE work is required to quantify urban transport paths as PGEs are known to bioaccumulate, cause cellular damage and may have detrimental human health effects.
Resolving archaeological populations with Sr-isotope mixing models by Janet Montgomery; Jane A. Evans; Rachel E. Cooper (1502-1514).
Strontium isotope analysis of tooth enamel is a useful provenancing technique to investigate the childhood origins and residential mobility of ancient people. However, where different geographical target regions have similar biosphere 87Sr/86Sr it is often difficult to resolve the 87Sr/86Sr ranges of two different groups of people and establish what constitutes the local range at each site. Here a multi-period study is presented from the Outer Hebrides, Scotland and an investigation of Neolithic and Early Bronze Age populations from the Yorkshire Wolds, NE England. The aim is to demonstrate that, despite complex human dietary strategies, simple mixing systems with only two end-members do occur in archaeological human populations in certain geological provinces and, despite overlapping 87Sr/86Sr ranges, it is possible to separate two populations based on the structure within the data set.
Effects of industrial by-product amendments on As, Cd and Tl retention/release in an element-spiked acidic soil by Javier Aguilar-Carrillo; Laura Barrios; Fernando Garrido; María Teresa García-González (1515-1529).
To asses the efficiency of two by-products (phosphogypsum (PG) and sugar foam (SF), rich in gypsum and calcium carbonate, respectively) in the immobilization of three toxic elements (As, Cd and Tl) in an acidic soil, batch-scale sorption and desorption experiments were conducted after 18 months of in situ amendment application. The Langmuir isotherms applied for sorption studies showed that the estimated maximum sorption capacity of the elements was highest in the SF-treated samples. The amount of element retained and the percentage of extraction after TCLP tests indicated that those samples amended with sugar foam (SF and PG + SF) had the potential to immobilize As, Cd and Tl in an acidic soil with low sorptive capacity. In addition to sorption and desorption experiments, scanning electron microscopy in back-scattered electron mode (SEM-BSE) showed the formation of Al-hydroxy polymers which provides the soil with additional sorption capacity. The three target elements were associated with the Al-hydroxy polymers, probably through direct coordination or the formation of ternary complexes. By means of statistical analysis it has been found that sorption processes of As, Cd and Tl in this soil mainly depend on the treatment, whereas desorption is an element-dependent process.
37Cl, 15N, 13C isotopic analysis of common agro-chemicals for identifying non-point source agricultural contaminants by W.K. Annable; S.K. Frape; O. Shouakar-Stash; T. Shanoff; R.J. Drimmie; F.E. Harvey (1530-1536).
The isotopic compositions of commercially available herbicides were analyzed to determine their respective 15N, 13C and 37Cl signatures for the purposes of developing a discrete tool for tracing and identifying non-point source contaminants in agricultural watersheds. Findings demonstrate that of the agrochemicals evaluated, chlorine stable isotopes signatures range between δ37Cl = −4.55‰ and +3.40‰, whereas most naturally occurring chlorine stable isotopes signatures, including those of road salt, sewage sludge and fertilizers, vary in a narrow range about the Standard Mean Ocean Chloride (SMOC) between −2.00‰ and +1.00‰. Nitrogen stable isotope values varied widely from δ15N = −10.86‰ to +1.44‰ and carbon stable isotope analysis gave an observed range between δ13C = −37.13‰ and −21.35‰ for the entire suite of agro-chemicals analyzed. When nitrogen, carbon and chlorine stable isotope analyses were compared in a cross-correlation analysis, statistically independent isotopic signatures exist suggesting a new potential tracer tool for identifying herbicides in the environment.
Isolation and characterization of dissolved organic matter from the Callovo–Oxfordian formation by Amandine Courdouan; Iso Christl; Sébastien Meylan; Paul Wersin; Ruben Kretzschmar (1537-1548).
Characterizing dissolved organic matter (DOM) in the pore water of the Callovo–Oxfordian formation, a potential host rock for the disposal of radioactive waste, is important to estimate its potential influence on the mobility of radionuclides in the rock. To isolate DOM, crushed rock material was extracted under anoxic conditions with deionized water, 0.1 M NaOH and synthetic pore water (SPW, water containing all major ions at pore water concentrations but no organic matter), respectively. The effects of extraction parameters on the extracted DOM including the solid-to-liquid ratio, extraction time, exposure to O2 and acid pretreatment of the rock material prior to the anoxic extraction were evaluated. In addition, DOM in one of the first pore water samples collected in the underground rock laboratory at Bure (France) was characterized for comparison. The size distribution and the low molecular weight organic acid contents of the extracts and pore water DOM were determined by liquid chromatography coupled with an organic C detector (LC-OCD) and by ion chromatography. The results revealed that only a fraction of less than 1.2% of the total organic C present in the rock was extractable. Maximum dissolved organic C (DOC) concentrations in the anoxic extracts ranged from 5.5 ± 0.3 mg/L for SPW extracts to 14.2 ± 1.1 mg/L for 0.1 M NaOH extracts. The major portion of the DOC in the anoxic extracts consisted of hydrophilic compounds (48–78%) having a molecular weight of less than 500 Da. Up to 21% of DOC in the anoxic extracts was identified as acetate, formate, lactate and malate. The short-term exposure of rock material to O2 during rock crushing strongly increased DOC concentrations and led to a shift towards smaller molecular weight compounds and to a higher low molecular weight organic acid (LMWOA) content as compared to the strictly anoxic extraction. The pore water sampled from a packed-off borehole exhibited a higher DOC concentration (56.7 mg/L) than the rock extracts. The pore water DOM was almost exclusively composed of acetate and propionate (88% of the DOC). The predominance of LMWOA in the pore water compared to the anoxic extracts may arise from the heterogeneity of the rock material, a more effective DOM filtration by the rock formation compared to laboratory extractions, or possibly, bacterial activity in the pore water induced by the borehole disturbance.
Element contents in mountain birch leaves, bark and wood under different anthropogenic and geogenic conditions by Clemens Reimann; Arnold Arnoldussen; Tor Erik Finne; Friedrich Koller; Øystein Nordgulen; Peter Englmaier (1549-1566).
Forty samples each of leaves, bark and wood of mountain birch (Betula pubescens EHRH.) were collected along a 120 km long south–north transect running through Norway’s largest city, Oslo. Concentrations of 26 chemical elements (Ag, As, Au, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, La, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Sr, Ti and Zn) as well as loss on ignition for the three sample materials are reported. By far the highest concentrations of most elements appear in the leaves. Prominent exceptions are Au and Pb, both of which are enriched in wood, indicating the importance of root-uptake, and As which is enriched in bark. Bedrock lithology, ore occurrences, soil pH and urban contamination all have a visible influence on the element concentrations in mountain birch leaves, bark and wood. It is often impossible to differentiate between all the factors that can influence element concentrations in the three sample materials. Mountain birch bark shows the strongest anthropogenic impact of the city of Oslo for dust-related elements (Fe, La, Ti) and Sb. Even in mountain birch bark the influence of the city on element concentrations is no longer discernible from the background variation at a distance of less than 20 km from Oslo centre. Compared to terrestrial moss, mountain birch appears to be of little value as a biomonitor for urban contamination.