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Anthropogenic eutrophication of Lake Titicaca (Bolivia) revealed by carbon and nitrogen stable isotopes fingerprinting

Colin — Fri, 23 Aug 2024 13:14:24 +0000

Highlights

C and N stable isotopes were measured in four compartments of Lake Titicaca.
Anthropogenic discharge affects baseline C and N isotope signatures.
C recycling from soil, anthropogenic and lacustrine sources affect the δ¹³C signature.
δ¹⁵N signatures track anthropogenic contamination independently of plant type.
Decreased anthropogenic contribution in the bay assessed by isotope mixing model.

Abstract

Cultural eutrophication is the leading cause of water quality degradation worldwide. The traditional monitoring of eutrophication is time-consuming and not integrative in space and time. Here, we examined the use of carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopic composition to track the degree of eutrophication in a bay of Lake Titicaca impacted by anthropogenic (urban, industrial and agricultural wastewater) discharges. Our results show increasing δ¹³C and decreasing δ¹⁵N signatures in macrophytes and suspended particulate matter with distance to the wastewater source. In contrast to δ¹⁵N and δ¹³C signatures, in-between aquatic plants distributed along the slope were not only affected by anthropogenic discharges but also by the pathway of carbon uptake, i.e., atmospheric (emerged) vs aquatic (submerged). A binary mixing model elaborated from pristine and anthropogenic isotope end-members allowed the assessment of anthropogenically derived C and N incorporation in macrophytes with distance to the source. Higher anthropogenic contribution was observed during the wet season, attributed to enhanced wastewater discharges and leaching of agricultural areas. For both seasons, eutrophication was however found naturally attenuated within 6 to 8 km from the wastewater source. Here, we confirm that carbon and nitrogen stable isotopes are simple, integrative and time-saving tools to evaluate the degree of eutrophication (seasonally or annually) in anthropogenically impacted aquatic ecosystems.

Heredia, C., Guédron, S., Point, D., Perrot, V., Campillo, S., Verin, C., Espinoza, M.E., Fernandez, P., Duwig, C., Achá, D., 2022. Anthropogenic eutrophication of Lake Titicaca (Bolivia) revealed by carbon and nitrogen stable isotopes fingerprinting. Science of The Total Environment 845, 157286. https://doi.org/10.1016/j.scitotenv.2022.157286

The contribution of stable isotopes of antimony for tracing pollution sources and transfer processes in aquatic environments.

Colin — Sun, 11 Aug 2024 22:09:11 +0000

Abstract

Antimony (Sb) is an emerging priority pollutant in the environment and a potentially carcinogenic
element. The general objective of this thesis is to contribute to exploring the potential of stable
isotopes of antimony (121Sb/123Sb) to trace sources and processes in aquatic environments and especially downstream from mining sites. After development and validation of a new method for the separation and analysis of antimony isotopes, the isotopic fractionations associated to different biogeochemical processes were studied by a theoretical approach, an experimental approach, as well as a field study conducted on the hydrosystems downstream from the acid mine drainage of the San José mine in Oruro (Bolivia). The direction and amplitude of these fractionations have been characterized in order to interpret the δ123Sb signatures in the environment. Theoretical studies have highlighted the main processes fractionating antimony isotopes: the partial or total oxidation of Sb(III) in minerals (Δ123 Sb V-III from +0.4 to +1.2 ‰), the change of the nearest neighbor of antimony (Δ123SbSb-O – Sb-S ≈ +0.9 ‰), and finally, the distortion of the atomic polyhedron Sb – O and Sb – S (Δ123Sbdistordu-symmetrical ≈ -0.3 ‰). Experimental studies have shown a preferential adsorption of light isotopes on iron oxyhydroxides (Δ123Sbadsorbed-dissolved ≈ -0.3 ‰), an enrichment in light isotopes in Sb(V)aq (Δ123SbSb(V)-Sb(III) ≈ -0.2 ‰) during the microbiological oxidation of Sb(III)aq, and a lack of fractionation during chemical oxidation with H2O2. The field study showed a decrease in δ123Sb from +0.42 to +0.70 ‰ downstream from the AMD of San José, in relation with the natural attenuation of antimony by sorption on iron minerals, and highlighted seasonal variations of δ123 Sb in the waters of Lake Uru-Uru, from +0.28‰ to +0.55‰, attributed to a variable contribution of the AMD and the river draining the Vinto smelter.
Taken together, the results support the potential of antimony isotopes as tracers of sources and
processes in aquatic environments, particularly in mining and industrial areas, and suggest the need for further research in order to characterize other important processes and to better understand the origin of the observed fractionations.

PhD thesis

PhD thesis defended by Colin Ferrari on December 6th, 2022 in the University of Montpellier.

Download the full thesis on the button bellow.

Multi-isotope (Pb, Sb) approach to trace metallic contaminant sources at a historical mining and metallurgical site

Colin — Sat, 10 Aug 2024 20:13:47 +0000

Highlights

Soils are locally affected by extreme Pb and moderate Sb contamination.
Anthropogenic soil contamination is restricted to the surface horizons.
Antimony isotopes allowed to discriminate Sb from mining vs metallurgical sources.
Pb-Sb isotope coupling is a powerful tool to identify the anthropogenic sources.

Abstract

In mining and smelting sites, where diverse potentially toxic element-rich wastes (e.g., waste rocks and slags) are stored over a mineralized background, difficulties arise to decipher the influence of multiple sources in the contaminated compartments of the critical zone. This paper aimed at testing the coupling of Pb and Sb isotopes to distinguish the sources of an inherited anthropogenic contamination in a mining and smelting environment. To do so, a selection of contamination sources (ore-bearing rocks, n = 4; slags, n = 2; stack residues – matte, n = 2), mine dewatering gallery sediments (n = 3), river sediments (n = 3) and soil horizons (n = 31) were sampled at the Peisey-Nancroix mining and smelting site (PbAg, French Alps), which has been abandoned for >150 years. The contamination sources, the soils and some sediments display similar ²⁰⁶Pb/²⁰⁷Pb ratios (1.173 ± 0.003), but distinct Sb isotopic signature (δ¹²³Sb). Slags and stack residues have similar high δ¹²³Sb signature (+0.62 to +0.78 ‰), whereas the ore-bearing rocks display lower δ¹²³Sb signatures (−0.28 to +0.10 ‰). Such a result indicates Sb isotopes fractionation during smelting, suggesting Sb may be used to distinguish the contribution of metallurgic wastes from that of ore-bearing rocks to the environmental contamination. However, our results indicate that Sb isotopes alone cannot be used to discuss the degree of anthropogenic contamination, and must be coupled to another isotopic system. Coupling Pb and Sb isotopic systems, makes it possible to determine the degree of anthropogenic contamination (Pb isotopes) and the contribution of local ore vs slags (Sb isotopes) to it. This multi-isotope approach provides an added advantage to identify mining and metallurgical sources of contamination more accurately than using a single isotopic system.

Guillevic, F., Rossi, M., Resongles, E., Freydier, R., Ferrari, C., Quantin, C., Monvoisin, G., Poulenard, J., Arnaud, F., 2024. Multi-isotope (Pb, Sb) approach to trace metallic contaminant sources at a historical mining and metallurgical site. Chemical Geology 121958. https://doi.org/10.1016/j.chemgeo.2024.121958

Antimony isotope fractionation during Sb(V) and Sb(III) adsorption on secondary Fe-minerals (schwertmannite, ferrihydrite) typical of mine waters

Colin — Sat, 10 Aug 2024 20:08:10 +0000

Highlights

Experimental study of Sb isotope fractionation during its sorption on iron minerals.
Light isotope of Sb was preferentially adsorbed on schwertmannite and ferrihydrite.
Equilibrium fractionation factor (Δ¹²³Sb_{solid-solution}) between −0.36 ‰ and −0.25 ‰.

Abstract

The application of antimony (Sb) isotopes as tracers for Sb environmental cycling is currently limited. Indeed, there is a lack of knowledge of isotope fractionation factors associated with key (bio-) geochemical processes controlling its behaviour in surface environments. This study investigated the equilibrium isotope fractionation generated by Sb(V) and Sb(III) sorption on two iron minerals typical of acid mine drainage (AMD) impacted streams, ferrihydrite and schwertmannite, under controlled conditions of pH and solid to liquid ratio. Sorption behaviour and Sb isotope fractionation were similar for the different mineral phases and Sb oxidation degrees, with fractionation factors Δ¹²³Sb_{solid-solution} of −0.25 ± 0.08 ‰ for Sb(III) and −0.34 ± 0.08 ‰ for Sb(V) adsorbed on ferrihydrite and −0.36 ± 0.06 ‰ for Sb(III) and −0.27 ± 0.03 ‰ for Sb(V) adsorbed on schwertmannite. The pH and initial Fe:Sb ratio did not significantly affect the Δ¹²³Sb_{solid-solution} value under the experimental conditions. The light ¹²¹Sb isotope was preferentially adsorbed on the mineral phases, following an equilibrium closed system between dissolved and adsorbed Sb species. This fractionation may be related to the apparition of iron as the second closest neighbour which distorts the Sb(OH)₃ or Sb(OH)₆^– atomic polyhedron. This study confirms that Sb equilibrium isotope fractionation occurs during sorption of Sb(III) and Sb(V) onto secondary iron minerals and suggests that the pH and redox of Sb do not exert significant effect. pH and redox conditions are important parameters which control Sb mobility in AMD streams, therefore, the study provides data for interpreting Sb isotope signatures in mine waters.

Ferrari, C., Resongles, E., Freydier, R., Casiot, C., 2024. Antimony isotope fractionation during Sb(V) and Sb(III) adsorption on secondary Fe-minerals (schwertmannite, ferrihydrite) typical of mine waters. Applied Geochemistry 163, 105935. https://doi.org/10.1016/j.apgeochem.2024.105935

Antimony isotopic fractionation during Sb(III) oxidation to Sb(V): Biotic and abiotic processes

Colin — Sat, 10 Aug 2024 19:55:36 +0000

Highlights

Antimony isotope fractionation during oxidation documented for the first time.
Biotic and chemical oxidation fractionated Sb isotopes in opposite direction.
Multi-step reactions underlie the fractionation process.

Abstract

Oxidation of antimonite (Sb(III)) to antimonate (Sb(V)) plays an important role in the control of Sb mobility in aquatic systems. Fractionation of Sb isotopes (¹²³Sb/¹²¹Sb) during Sb(III) oxidation has been investigated in the present study at concentrations relevant to mining environments. The isotopic composition (δ¹²³Sb) of dissolved Sb(III) and Sb(V) species was analysed during biotic oxidation of Sb(III) at pH 6 and ∼ 0.1 mM Sb. Biotic experiments used a aioA gene carrier bacterial strain of the genus Ensifer isolated from Sb-rich river sediments. Chemical oxidation experiments with H₂O₂ were also conducted either in NaNO₃ or HCl medium. During biotic oxidation, the Sb(V) produced was enriched in the light isotope compared to Sb(III), with an apparent fractionation factor Δ¹²³Sb_{Sb(V)-Sb(III)} of −0.20 ± 0.07 ‰. The Δ¹²³Sb value was independent of the oxidation kinetics within the range 0.03 to 0.05 μmol.L⁻¹.min⁻¹; the fractionation observed was rather attributed to kinetic effect that weakens over time in the experiments, although this hypothesis would require further investigation. During abiotic experiments in NaNO₃ medium, the Sb(V) produced was not isotopically fractionated relatively to Sb(III), while in HCl medium, the Sb(V) produced was enriched with the heavier isotope relatively to Sb(III), with a Rayleigh fractionation factor ε¹²³Sb of +0.30 ± 0.05 ‰. These differences were attributed to different reaction pathways involving multi-step reactions and either hydroxy- or chloride-Sb species. Altogether, these results showed a low fractionation of Sb isotopes during Sb(III) oxidation, although significant variability occurred according to experimental conditions. Further experimental research and confrontation with natural systems is necessary before applying Sb isotopes as process tracer in water.

Ferrari, C., Resongles, E., Héry, M., Désoeuvre, A., Freydier, R., Delpoux, S., Bruneel, O., Casiot, C., 2023. Antimony isotopic fractionation during Sb(III) oxidation to Sb(V): Biotic and abiotic processes. Chemical Geology 121788. https://doi.org/10.1016/j.chemgeo.2023.121788

Equilibrium mass-dependent isotope fractionation of antimony between stibnite and Sb secondary minerals: A first-principles study

Colin — Sat, 10 Aug 2024 19:45:15 +0000

Highlights

First estimation of equilibrium Sb isotope fractionation factors among Sb minerals.
PBEsol pseudopotential best reproduces Sb mineral lattices and Raman frequencies.
Factors affecting Sb isotope fractionation: Sb oxidation > change in Sb first-neighbour > polyhedral SbO distortion.
Theoretical Sb isotope fractionation extends over 2.3 ‰ at 22°C, similar to the observed range of natural variations.
Secondary Sb minerals are isotopically heavier than stibnite, the main Sb ore.

Abstract

Antimony (Sb) isotopes are gaining increasing interest for their potential as geochemical tracers in geological, environmental and archaeological studies. However, little is known about the parameters controlling Sb isotope fractionation, which is essential to interpret variations of isotopic signature in natural systems. In this study, equilibrium mass-dependent isotope fractionation factors (β-factor) were calculated between different Sb-bearing minerals commonly found in mining environments including primary Sb sulphide (stibnite Sb₂S₃) and its oxidation products (valentinite Sb₂O₃, senarmontite Sb₂O₃, cervantite Sb₂O₄) and synthetic antimony pentoxide Sb₂O₅. First-principles calculations within the Density Functional Theory (DFT) were performed with different functionals to test the robustness of the method. Among the studied minerals, stibnite has the lowest β-factor (ln(β) = 0.71 ‰ at 22°C), then β-factors progressively increase from valentinite (ln(β) = 1.64 ‰ at 22°C), to senarmontite (ln(β) = 1.80 ‰ at 22°C), cervantite (ln(β) = 2.20 ‰ at 22°C) and antimony pentoxide (ln(β) = 3.03 ‰ at 22°C). The factors that most fractionate Sb isotopes are found to be i) the change of Sb oxidation state (Sb isotope ratio in Sb(V)-bearing minerals is higher than in Sb(III)-bearing minerals), ii) the change of first neighbour of Sb (Sb isotope ratio in SbO bonds is higher than in SbS bonds) and iii) distortion of the atomic SbO polyhedrons. The negligible differences in the β-factors obtained with different functionals showed the robustness of the approach for the calculation of β-factors, despite differences in the calculated mineral lattice and Raman frequencies. The results of this study provide a theoretical basis to interpret natural Sb isotope variations. The results suggest that a significant enrichment in the heavy isotope could occur during oxidative dissolution of stibnite and subsequent precipitation of Sb(III) and Sb(V) oxides in sulphide environments. More generally, this work strongly supports that Sb isotopes may be a useful tracer of Sb transformation processes in nature.

Ferrari, C., Méheut, M., Resongles, E., Freydier, R., Casiot, C., 2022. Equilibrium mass-dependent isotope fractionation of antimony between stibnite and Sb secondary minerals: A first-principles study. Chemical Geology 121115. https://doi.org/10.1016/j.chemgeo.2022.121115

A single-step purification method for the precise determination of antimony isotopic composition

Colin — Sat, 10 Aug 2024 19:29:29 +0000

Abstract

Antimony isotopes have been recently used as geochemical tracers for archeological or environmental purposes. The purification of antimony in samples with a low Sb concentration and a complex matrix is a critical step to measure the ¹²³Sb/¹²¹Sb ratio by hydride generation coupled to a multi-collector inductively coupled plasma mass spectrometer (HG-MC-ICP-MS). A single-step purification method based on the use of thiol-functionalized mesoporous silica powder (TSP) was developed to separate antimony from other elements. A low amount of Sb (40–100 ng) is required thanks to low procedural blanks (<1 ng Sb) and an efficient removal (98.7% on average) of potential interfering elements (including As, Cd, Co, Cr, Cu, Fe, Ni, Pb, Se, and Sn). The method was validated on fourteen Certified Reference Materials (CRMs) including environmental materials (sediments and soils), biological materials (plants, human blood and urine), rocks and anthropogenic materials (fly ash, road dust and polyethylene). Antimony was recovered at 100 ± 7% and no isotopic fractionation occurred during the procedure. The isotopic composition of Sb (δ¹²³Sb) in the CRMs ranged between −0.52 ± 0.06‰ (2 sd) and 0.40 ± 0.03‰ (2 sd) relative to an in-house isotopic standard solution (SPEX). The external reproducibility was evaluated at 0.05‰ (2 sd) for δ¹²³Sb, based on replicated measurements of independently digested and purified CRMs. CRMs GSD-3, SDO-1 and BCR-176R exhibited δ¹²³Sb values similar to previous measurements by Rouxel et al. (2003). In addition, three pure standard solutions of Sb were measured against the in-house isotopic standard solution. Two of them were isotopically similar (δ¹²³Sb = 0.00 ± 0.05‰, Sb Fisher Scientific® and PlasmaCAL-1, SCP Science®), while a δ¹²³Sb value of 0.62 ± 0.02‰ was measured for the third one (PlasmaCAL-2, SCP Science®). This raises the importance of choosing a common isotopic standard solution to compare already published and future Sb isotope data.

Ferrari, C., Resongles, E., Freydier, R., Casiot, C., 2021. A single-step purification method for the precise determination of antimony isotopic composition of environmental, geological and biological samples by HG-MC-ICP-MS. Journal of Analytical Atomic Spectrometry 36, 776–785. https://doi.org/10.1039/D0JA00452A