Copper Isotope Fractionation Research Articles

Copper isotope fractionation during excretion from a phototrophic biofilm

The metal excretion and metal sorption are two important microbial processes in the regulation of intracellular metal concentration. However, the contribution of freshwater phototrophic biofilm to metal efflux in the environment and its related isotopic fractionation remain poorly known. In this study, Cu efflux from a mature phototrophic biofilm and related Cu isotopic fractionation between the biofilm and aqueous solution were studied over 4 days in closed batch and open drip-flow reactors (BR and DFR, respectively). The impact of a 48-h drying event on Cu efflux from the biofilm and its isotopic signature was quantified in the BR. Cu excretion from the biofilm depended on Cu concentration in the biomass and did not show a latent phase. For the wet biofilm, in DFR, the Cu efflux rate decreased over time whereas in BR, Cu efflux exhibited fluctuations with a net re-sorption phase.During short-term early excretion over the first 4 h (BR) and 24 h (DFR), the enrichment of solution in heavy isotopes with a Δ65Cu(sol–biofilm) of +0.7 ± 0.2‰ could be explained by a combination of i) desorption via competition between H+ and Cu2+ for surface sites and ii) release of isotopically heavy Cu(II)-organic complexes. In addition, there was a retention of isotopically light Cu (I) within the cells which is consistent with the biofilm ability to reduce Cu. With further exposure of the wet biofilm to the solution, a progressive decrease of Δ65Cu(sol–biofilm), down to 0 and −0.36‰ respectively in BR and DFR after 96 h, could be explained by an active efflux of Cu(I) and by a passive diffusion of Cu2+, both of these processes favoring light isotopes. The re-hydrated and wet biofilms showed distinctly different behavior during excretion, in terms of magnitude of the flux and direction of the fractionation for long term exposure. Indeed, the efflux from the re-hydrated biofilm was ten times higher than the one from the wet biofilm and the re-hydrated biofilm did not exhibit a decrease of Δ65Cu(sol–biofilm) after 24 h of reaction. This could be related to partial devitalization of the biofilm during drying, producing a release of isotopically heavy Cu and decreasing the intensity of Cu(I) active efflux of light isotopes. Taken together, the Cu isotopic signature in natural aquatic environments containing phototrophic biofilms varies up to 1‰ on a daily scale.

Copper isotopic fractionation during adsorption on manganese oxide: Effects of pH and desorption

Copper isotopic fractionation during adsorption on manganese oxide: Effects of pH and desorption

Small changes in Cu redox state and speciation generate large isotope fractionation during adsorption and incorporation of Cu by a phototrophic biofilm

Despite the importance of phototrophic biofilms in metal cycling in freshwater systems, metal isotope fractionation linked to metal adsorption and uptake by biofilm remains very poorly constrained. Here, copper isotope fractionation by a mature phototrophic biofilm during Cu surface adsorption and incorporation was studied in batch reactor (BR) and open drip flow reactor (DFR) systems at ambient conditions. X-ray Absorption Spectroscopy (both Near Edge Structure, XANES, and Extended Fine Structure, EXAFS) at Cu K-edge of the biofilm after its interaction with Cu in BR experiments allowed characterizing the molecular structure of assimilated Cu and quantifying the degree of CuII to CuI reduction linked to Cu assimilation. For both BR and DFR experiments, Cu adsorption caused enrichment in heavy isotope at the surface of the biofilm relative to the aqueous solution, with an apparent enrichment factor for the adsorption process, ε65Cuads, of +1.1±0.3‰. In contrast, the isotope enrichment factor during copper incorporation into the biofilm (ε65Cuinc) was highly variable, ranging from −0.6 to +0.8‰. This variability of the ε65Cuinc value was likely controlled by Cu cellular uptake via different transport pathways resulting in contrasting fractionation. Specifically, the CuII storage induced enrichment in heavy isotope, whereas the toxicity response of the biofilm to Cu exposure resulted in reduction of CuII to CuI, thus yielding the biofilm enrichment in light isotope. EXAFS analyses suggested that a major part of the Cu assimilated by the biofilm is bound to 5.1±0.3 oxygen or nitrogen atoms, with a small proportion of Cu linked to sulfur atoms (NS<0.6) of sulfhydryl groups. XANES analyses showed that the proportion of CuIIvs CuI, compared to the initial CuII/CuI ratio, decreased by 14% after the first hour of reaction and by 6% after 96h of reaction. The value of ε65Cuinc of the biofilm exhibited a similar trend over time of exposure. Our study demonstrates the complexity of biological processes associated with live phototrophic biofilms, which produce large and contrasting isotope fractionations following rather small Cu redox and speciation changes during uptake, storage or release of the metal, i.e., favoring heavy isotopes during complexation with carboxylate ligands and light isotopes during reduction of CuII-O/N to CuI-sulfhydryl moieties.

Copper isotope fractionation during sulfide-magma differentiation in the Tulaergen magmatic Ni–Cu deposit, NW China

Although it has been recently demonstrated that Cu isotope fractionation during mantle melting and basaltic magma differentiation is limited, the behavior of Cu isotopes during magmatic differentiation involving significant sulfide segregation remains unclear. Magmatic Ni–Cu deposits, which formed via sulfide segregation from basaltic or picritic magmas, are appropriate targets to address this issue. Here we report Cu isotope data for sulfides (chalcopyrite) from the Tulaergen Ni–Cu sulfide deposit in Xinjiang, NW China. Sulfides, including sparsely disseminated (hosted by hornblende gabbro), moderately disseminated (hosted by hornblende olivine websterite), densely disseminated (hosted by hornblende lherzolite) and massive sulfides (sandwiched between country rocks and mafic–ultramafic rocks), were collected from adits at 1050m, 1100m and 1150m levels. The sparsely and moderately disseminated sulfides on 1150m and 1050m levels have a restricted range of δ65Cu values from −0.38‰ to 0.15‰, whereas disseminated and massive sulfides on 1100m level have δ65Cu values ranging widely from −1.98‰ to −0.04‰ and from −1.08‰ to −0.52‰, respectively. The δ65Cu values of disseminated sulfides are negatively correlated with whole-rock S and Cu concentrations, and sulfides formed at later stages have heavier δ65Cu values. These observations suggest significant Cu isotope fractionation during sulfide-magma differentiation above 600°C. During the formation of the Tulaergen magmatic Ni–Cu deposit, sulfide segregation and crystallization of olivine and pyroxene caused the increase of Fe3+ contents in the residual magmas, which would move the redox reaction Cu++Fe3+=Fe2++Cu2+ toward larger amounts of Cu2+ in the melt. The presence of Cu2+ in melt allowed redox transformation to happen during sulfide segregation. The residual magmas are enriched in heavy Cu isotopes due to the removal of 65Cu-depleted sulfides, and sulfides formed at later stages will have heavier δ65Cu values, accounting for the large and systematic Cu isotopic variation as observed. Our results therefore demonstrate that Cu isotopes could be significantly fractionated during high temperature sulfide-magma differentiation (up to 2‰), and Cu isotopes may be used to trace the mineralization process of Ni–Cu (–PGE) deposits and indicate the movement direction of sulfide-enriched magmas.

Copper isotope fractionation during partial melting and melt percolation in the upper mantle: Evidence from massif peridotites in Ivrea-Verbano Zone, Italian Alps

To investigate the behavior of Cu isotopes during partial melting and melt percolation in the mantle, we have analyzed Cu isotopic compositions of a suite of well-characterized Paleozoic peridotites from the Balmuccia and Baldissero massifs in the Ivrea-Verbano Zone (IVZ, Northern Italy). Our results show that fresh lherzolites and harzburgites have a large variation of δ65Cu ranging from −0.133 to 0.379‰, which are negatively correlated with Al2O3 contents as well as incompatible platinum-group (e.g., Pd) and chalcophile element (e.g., Cu, S, Se, and Te) contents. The high δ65Cu can be explained by Cu isotope fractionation during partial melting of a sulfide-bearing peridotite source, with the light isotope (63Cu) preferentially entering the melts. The low δ65Cu can be attributed to precipitation of sulfides enriched in 63Cu during sulfur-saturated melt percolation. Replacive dunites from the Balmuccia massif display high δ65Cu from 0.544 to 0.610‰ with lower Re, Pd, S, Se, and Te contents and lower Pd/Ir ratios relative to lherzolites, which may result from dissolution of sulfides during interactions between S-undersaturated melts and lherzolites at high melt/rock ratios. Thus, our results suggest that partial melting and melt percolation largely account for the Cu isotopic heterogeneity of the upper mantle.The correlation between δ65Cu and Cu contents of the lherzolites and harzburgites was used to model Cu isotope fractionation during partial melting of a sulfide-bearing peridotite, because Cu is predominantly hosted in sulfide. The modelling results indicate an isotope fractionation factor of αmelt-peridotite=0.99980–0.99965 (i.e., 103lnαmelt-peridotite=−0.20 to −0.35‰). In order to explain the Cu isotopic systematics of komatiites and mid-ocean ridge basalts reported previously, the estimated αmelt-peridotite was used to simulate Cu isotopic variations in melts generated by variable degrees of mantle melting. The results suggest that high degrees (>25%) of partial melting extracts nearly all source Cu and it cannot produce Cu isotope fractionation in komatiites relative to their mantle source, and that sulfide segregation during magma evolution have modified Cu isotopic compositions of mid-ocean ridge basalts.

Copper transporters are responsible for copper isotopic fractionation in eukaryotic cells

Copper isotopic composition is altered in cancerous compared to healthy tissues. However, the rationale for this difference is yet unknown. As a model of Cu isotopic fractionation, we monitored Cu uptake in Saccharomyces cerevisiae, whose Cu import is similar to human. Wild type cells are enriched in 63Cu relative to 65Cu. Likewise, 63Cu isotope enrichment in cells without high-affinity Cu transporters is of slightly lower magnitude. In cells with compromised Cu reductase activity, however, no isotope fractionation is observed and when Cu is provided solely in reduced form for this strain, copper is enriched in 63Cu like in the case of the wild type. Our results demonstrate that Cu isotope fractionation is generated by membrane importers and that its amplitude is modulated by Cu reduction. Based on ab initio calculations, we propose that the fractionation may be due to Cu binding with sulfur-rich amino acids: methionine and cysteine. In hepatocellular carcinoma (HCC), lower expression of the STEAP3 copper reductase and heavy Cu isotope enrichment have been reported for the tumor mass, relative to the surrounding tissue. Our study suggests that copper isotope fractionation observed in HCC could be due to lower reductase activity in the tumor.

Cu diffusion in a basaltic melt

Recent studies suggest a potential role of diffusive transport of metals (e.g., Cu, Au, PGE) in the formation of magmatic sulfide deposits and porphyry-type deposits. However, diffusivities of these metals are poorly determined in natural silicate melts. In this study, diffusivities of copper in an anhydrous basaltic melt ( 2 O) were measured at temperatures from 1298 to 1581 °C, and pressures of 0.5, 1, and 1.5 GPa. Copper diffusivities in anhydrous basaltic melt at 1 GPa can be described as: D Cu basalt = exp [ − ( 14 . 12 ± 0 . 50 ) − 11813 ± 838 T ] where D Cu basalt is the diffusivity in m 2 /s, T is the temperature in K, and errors are given at 1σ level. A fitting of all experimental data considering the pressure effect is: D Cu basalt = exp [ − ( 13 . 59 ± 0 . 81 ) − ( 12153 ± 1229 ) + ( 620 ± 241 ) P T ] where P is the pressure in GPa, which corresponds to a pre-exponential factor D 0 = (1.25 ×÷ 2.2)×10 −6 m 2 /s, an activation energy E a = 101 ± 10 kJ/mol at P = 0, and an activation volume V a = (5.2 ± 2.0)×10 −6 m 3 /mol. The diffusivity of copper in basaltic melt is high compared to most other cations, similar to that of Na. The high copper diffusivity is consistent with the occurrence of copper mostly as Cu + in silicate melts at or below NNO. Compared to the volatile species, copper diffusivity is generally smaller than water diffusivity, but about one order of magnitude higher than sulfur and chlorine diffusivities. Hence, Cu partitioning between a growing sulfide liquid drop and the surrounding silicate melt is roughly in equilibrium, whereas that between a growing fluid bubble and the surrounding melt can be out of equilibrium if the fluid is nearly pure H 2 O fluid. Our results are the first copper diffusion data in natural silicate melts, and can be applied to discuss natural processes such as copper transport and kinetic partitioning behavior in ore formation, as well as copper isotope fractionation caused by evaporation during tektite formation.

Copper and zinc isotope fractionation during deposition and weathering of highly metalliferous black shales in central China

Black shales represent one of the main reservoirs of metals released to hydrosphere via chemical weathering and play an important role in geochemical cycling of metals in the ocean. The stable isotope systematics of transitional metals (e.g., Cu and Zn) may be used as a proxy for evaluating their geochemical cycling. To investigate the behaviors of Cu and Zn isotopes during metal enrichment of black shales and the migration during weathering, in this study we reported Cu and Zn concentration and isotope data for unweathered and weathered metalliferous shales and siliceous interbeds from the Maokou Formation in central China. The unweathered shales and cherts have moderately enriched Cu and Zn concentrations with silicate-like δ65Cu (+0.14±0.09‰, 1σ) but heavy δ66Zn (0.51±0.11‰, 1σ). The elevated δ66Zn values reflect an important contribution from seawater via sulfide precipitation and/or organic matter (OM) adsorption. The Zn isotopic compositions of these metalliferous shales are different from those of the ‘normal’ shales, highlighting the potential of Zn isotopes as a tracer for metal enrichment in natural systems.The weathered shales and cherts have an extreme δ65Cu range from −6.42‰ to +19.73‰ and a modest δ66Zn range of +0.25‰ to +0.78‰. The strongly weathered samples have lower Cu and Zn concentrations and lighter isotopic compositions compared to the weakly weathered samples. The leaching of Cu- and Zn-rich sulfides in shallow depths and their downward transport and refixation by Fe-sulfide account for the Cu and Zn isotope fractionation, with the huge Cu isotope variation generated by multistage redox leaching. In general, δ66Zn values of the weathered shales shift towards light values compared to the unweathered protoliths, suggesting that shale weathering releases Zn which is isotopically heavier than igneous rocks and the global riverine average (+0.33‰). Our results therefore indicate that Cu isotopes can be extremely fractionated during weathering of Cu-rich shales and both heavy Cu and Zn isotopes are preferentially released into fluids during shale weathering. These results should be considered when evaluating geochemical cycling of Cu and Zn in the modern or past oceans.

Hypoxia induces copper stable isotope fractionation in hepatocellular carcinoma, in a HIF-independent manner.

Hepatocellular carcinoma (HCC) is the most frequent type of primary liver cancer, with increasing incidence worldwide. The unrestrained proliferation of tumour cells leads to tumour hypoxia which in turn promotes cancer aggressiveness. While changes in the concentration of copper (Cu) have long been observed upon cancerization, we have recently reported that the isotopic composition of copper is also altered in several types of cancer. In particular, we showed that in hepatocellular carcinoma, tumour tissue contains heavier copper compared to the surrounding parenchyma. However, the reasons behind such isotopic signature remained elusive. Here we show that hypoxia causes heavy copper enrichment in several human cell lines. We also demonstrate that this effect of hypoxia is pH, HIF-1 and -2 independent. Our data identify a previously unrecognized cellular process associated with hypoxia, and suggests that in vivo tumour hypoxia determines copper isotope fractionation in HCC and other solid cancers.

Copper and zinc isotope fractionation during deposition and weathering of highly metalliferous black shales in central China

Copper and zinc isotope fractionation during deposition and weathering of highly metalliferous black shales in central China

Copper isotope fractionation during adsorption onto kaolinite: Experimental approach and applications

Abstract The adsorption of copper and other heavy metals onto clay minerals is an important process that controls the distribution of trace metals in natural environments. Copper isotopes are a potentially useful tool to track the source of contaminated metals in soils formed in natural systems, but Cu isotope fractionation during adsorption onto clay minerals, the major component in soils, has not been thoroughly studied. In this study, we carried out for the first time a series of experiments to investigate the isotope fractionation of Cu during adsorption onto kaolinite for a wide range of conditions, including the contact time (t = 10–360 min), temperature (T = 1–50 °C), initial Cu concentration of the starting solution (C 0 = 2–100 μg/g), pH value (4.0–6.0) and ionic strength (NaNO 3 ; I = 0–0.1 mol/L). Our results indicate that Cu isotopes are significantly fractionated with preferential adsorption of the light isotope ( 63 Cu) onto the mineral surface. The fractionation factors (Δ 65 Cu adsorbed-solution = δ 65 Cu adsorbed − δ 65 Cu solution ) weakly depend on the pH and temperature with a constant value of approximately − 0.27‰ at C 0 = 20 μg/g and in the absence of NaNO 3 . Addition of NaNO 3 into the starting solution has a dramatic negative influence on the Δ 65 Cu adsorbed-solution values that range from − 1.46‰ to − 0.29‰. Such results are useful for interpreting Cu isotopic variations observed in sediments, soils and water from estuarine settings or industrial sewage pollution areas. The Δ 65 Cu adsorbed-solution values significantly increase with increasing initial Cu concentration of the starting solutions at C 0 0 > 30 μg/g. The results imply that the isotopic compositions of the Cu adsorbed onto natural soils may vary greatly at relatively low Cu concentrations of the soil solutions. Furthermore, the pore waters after draining kaolinite-bearing rocks would become isotopically heavier due to the preferential adsorption of 63 Cu onto kaolinite. Given that no redox change occurred in all experiments, we propose that the most likely mechanism responsible for such Cu isotope fractionation is the different adsorption capacities of isotopically different species in aqueous solutions and the formation of outer-sphere surface Cu(II) complexes. Our study represents one important step for future studies to use Cu isotopes to trace the source of metal contaminants in natural soils.

Copper Isotope Fractionation during Porphyry and Skarn‐type Metallogeny: A Case Study of Tongling District in the Middle‐Lower Yangtze Valley

Acta Geologica Sinica - English EditionVolume 88, Issue s2 p. 1578-1579 Meeting Abstracts Copper Isotope Fractionation during Porphyry and Skarn-type Metallogeny: A Case Study of Tongling District in the Middle-Lower Yangtze Valley Yue WANG, Yue WANG Laboratory of Isotope Geology, MLR, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037Search for more papers by this authorXiangkun ZHU, Corresponding Author Xiangkun ZHU Laboratory of Isotope Geology, MLR, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037Corresponding author. E-mail: xiangkun@cags.ac.cnSearch for more papers by this author Yue WANG, Yue WANG Laboratory of Isotope Geology, MLR, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037Search for more papers by this authorXiangkun ZHU, Corresponding Author Xiangkun ZHU Laboratory of Isotope Geology, MLR, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037Corresponding author. E-mail: xiangkun@cags.ac.cnSearch for more papers by this author First published: 29 December 2014 https://doi.org/10.1111/1755-6724.12384_14Citations: 1Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume88, Issues2Special Issue: Meeting Abstracts: The 14th Quadrennial International Association on the Genesis of Ore Deposits Symposium. August 19–22, 2014, Kunming, ChinaDecember 2014Pages 1578-1579 RelatedInformation

Tracing low-temperature aqueous metal migration in mineralized watersheds with Cu isotope fractionation

Copper isotope signatures in waters emanating from mineralized watersheds provide evidence for the source aqueous copper in solution. Low-temperature aqueous oxidation of Cu sulfide minerals produces significant copper isotopic fractionation between solutions and residues. Abiotic experimental data of fractionation (defined as Δliquid–solid ‰=δ65Culiquid−δ65Cusolid) are on the order of 1–3‰ and are unique for copper rich-sulfide minerals. Data presented here from ores and waters within defined boundaries of porphyry copper, massive sulfide, skarn, and epithermal ore deposits mimic abiotic experiments. Thus, the oxidation of sulfide minerals appears to cause the signatures in the waters although significant biological, temperature, and pH variations exist in the fluids. Regardless of the deposit type, water type, concentration of Cu in solution, or location, the data provide a means to trace sources of metals in solutions. This relationship allows for tracking sources and degree of metal migration in low temperature aqueous systems and has direct application to exploration geology and environmental geochemistry.

Copper and iron isotope fractionation during weathering and pedogenesis: Insights from saprolite profiles

Iron and copper isotopes are useful tools to track redox transformation and biogeochemical cycling in natural environment. To study the relationships of stable Fe and Cu isotopic variations with redox regime and biological processes during weathering and pedogenesis, we carried out Fe and Cu isotope analyses for two sets of basalt weathering profiles (South Carolina, USA and Hainan Island, China), which formed under different climatic conditions (subtropical vs. tropical). Unaltered parent rocks from both profiles have uniform δ56Fe and δ65Cu values close to the average of global basalts. In the South Carolina profile, δ56Fe values of saprolites vary from −0.01‰ to 0.92‰ in the lower (reduced) part and positively correlate with Fe3+/ΣFe (R2=0.90), whereas δ65Cu values are almost constant. By contrast, δ56Fe values are less variable and negatively correlate with Fe3+/ΣFe (R2=0.88) in the upper (oxidized) part, where large (4.85‰) δ65Cu variation is observed with most samples enriched in heavy isotopes. In the Hainan profile formed by extreme weathering under oxidized condition, δ56Fe values vary little (0.05–0.14‰), whereas δ65Cu values successively decrease from 0.32‰ to −0.12‰ with depth below 3m and increase from −0.17‰ to 0.02‰ with depth above 3m. Throughout the whole profile, δ65Cu positively correlate with Cu concentration and negatively correlate with the content of total organic carbon (TOC). Overall, the contrasting Fe isotopic patterns under different redox conditions suggest redox states play the key controls on Fe mobility and isotope fractionation. The negative correlation between δ56Fe and Fe3+/ΣFe in the oxidized part of the South Carolina profile may reflect addition of isotopically light Fe. This is demonstrated by leaching experiments, which show that Fe mineral pools extracted by 0.5N HCl, representing poorly-crystalline Fe (hydr)-oxides, are enriched in light Fe isotopes. The systematic Cu isotopic variation in the Hainan profile reflects desorption and downward transport of isotopically heavy Cu, leaving the organically-bound Cu enriched in light isotope as supported by the negative correlation of δ65Cu with TOC (R2=0.88). The contrasting (mostly positive vs. negative) Cu isotopic signatures in the upper parts of these two profiles can be attributed to the different climatic conditions, e.g., high rainfall at a tropical climate in Hainan favors desorption and the development of organism, whereas relatively dry climate in South Carolina favors Cu re-precipitation from soil solutions and adsorption onto Fe (hydr)-oxides. Our results highlight the potential applications of Fe and Cu isotopes as great tracers of redox condition, ancient climate and biological cycling during chemical weathering and pedogenic translocation.

Copper isotope fractionation during equilibration with natural and synthetic ligands.

As copper (Cu) stable isotopes emerge as a tool for tracing Cu biogeochemical cycling, an understanding of how Cu isotopes fractionate during complexation with soluble organic ligands in natural waters and soil solutions is required. A Donnan dialysis technique was employed to assess the isotopic fractionation of Cu during complexation with the soluble synthetic ligands ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA) and desferrioxamine B (DFOB), as well as with Suwannee River fulvic acid (SRFA). The results indicated enrichment of the heavy isotope ((65)Cu) in the complexes, with Δ(65)Cu complex-free values ranging from +0.14 to +0.84‰. A strong linear correlation was found between the logarithms of the stability constants of the Cu complexes and the magnitudes of isotopic fractionation. These results show that complexation of Cu by organic ligands can affect the isotopic signature of the free Cu ion. This free Cu is considered the most bioavailable species, and hence, our results highlight the importance of understanding fractionation processes in the uptake medium when using Cu isotopes to study the uptake mechanisms of organisms. These data contribute a vital piece to the emerging picture of Cu isotope cycling in the natural environment, as organic complexation plays a key role in the Cu cycle.

The role of bacterial consortium and organic amendment in Cu and Fe isotope fractionation in plants on a polluted mine site

Copper and iron isotope fractionation by plant uptake and translocation is a matter of current research. As a way to apply the use of Cu and Fe stable isotopes in the phytoremediation of contaminated sites, the effects of organic amendment and microbial addition in a mine-spoiled soil seeded with Helianthus annuus in pot experiments and field trials were studied. Results show that the addition of a microbial consortium of ten bacterial strains has an influence on Cu and Fe isotope fractionation by the uptake and translocation in pot experiments, with an increase in average of 0.99 ‰ for the δ(65)Cu values from soil to roots. In the field trial, the amendment with the addition of bacteria and mycorrhiza as single and double inoculation enriches the leaves in (65)Cu compared to the soil. As a result of the same trial, the δ(56)Fe values in the leaves are lower than those from the bulk soil, although some differences are seen according to the amendment used. Siderophores, possibly released by the bacterial consortium, can be responsible for this change in the Cu and Fe fractionation. The overall isotopic fractionation trend for Cu and Fe does not vary for pot and field experiments with or without bacteria. However, variations in specific metabolic pathways related to metal-organic complexation and weathering can modify particular isotopic signatures.

Copper speciation and isotopic fractionation in plants: uptake and translocation mechanisms

The fractionation of stable copper (Cu) isotopes during uptake into plant roots and translocation to shoots can provide information on Cu acquisition mechanisms. Isotope fractionation ((65) Cu/(63) Cu) and intact tissue speciation techniques (X-ray absorption spectroscopy, XAS) were used to examine the uptake, translocation and speciation of Cu in strategy I (tomato-Solanum lycopersicum) and strategy II (oat-Avena sativa) plant species. Plants were grown in controlled solution cultures, under varied iron (Fe) conditions, to test whether the stimulation of Fe-acquiring mechanisms can affect Cu uptake in plants. Isotopically light Cu was preferentially incorporated into tomatoes (Δ(65) Cu(whole plant-solution ) = c. -1‰), whereas oats showed minimal isotopic fractionation, with no effect of Fe supply in either species. The heavier isotope was preferentially translocated to shoots in tomato, whereas oat plants showed no significant fractionation during translocation. The majority of Cu in the roots and leaves of both species existed as sulfur-coordinated Cu(I) species resembling glutathione/cysteine-rich proteins. The presence of isotopically light Cu in tomatoes is attributed to a reductive uptake mechanism, and the isotopic shifts within various tissues are attributed to redox cycling during translocation. The lack of isotopic discrimination in oat plants suggests that Cu uptake and translocation are not redox selective.

Copper isotope fractionation between aqueous compounds relevant to low temperature geochemistry and biology

Isotope fractionation between the common Cu species present in solution (Cu+, Cu2+, hydroxide, chloride, sulfide, carbonate, oxalate, and ascorbate) has been investigated using both ab initio methods and experimental solvent extraction techniques. In order to establish unambiguously the existence of equilibrium isotope fractionation (as opposed to kinetic isotope fractionation), we first performed laboratory-scale liquid–liquid distribution experiments. Upon exchange between HCl medium and a macrocyclic complex, the 65Cu/63Cu ratio fractionated by −1.06‰ to −0.39‰. The acidity dependence of the fractionation was appropriately explained by ligand exchange reactions between hydrated H2O and Cl− via intramolecular vibrations. The magnitude of the Cu isotope fractionation among important Cu ligands was also estimated by ab initio methods. The magnitude of the nuclear field shift effect to the Cu isotope fractionation represents only ∼3% of the mass-dependent fractionation. The theoretical estimation was expanded to chlorides, hydroxides, sulfides, sulfates, and carbonates under different conditions of pH. Copper isotope fractionation of up to 2‰ is expected for different forms of Cu present in seawater and for different sediments (carbonates, hydroxides, and sulfides). We found that Cu in dissolved carbonates and sulfates is isotopically much heavier (+0.6‰) than free Cu. Isotope fractionation of Cu in hydroxide is minimal. The relevance of these new results to the understanding of metabolic processes was also discussed. Copper is an essential element used by a large number of proteins for electron transfer. Further theoretical estimates of δ65Cu in hydrated Cu(I) and Cu(II) ions, Cu(II) ascorbates, and Cu(II) oxalate predict Cu isotope fractionation during the breakdown of ascorbate into oxalate and account for the isotopically heavy Cu found in animal kidneys.

Is aging recorded in blood Cu and Zn isotope compositions?

Recent isotopic observations of animal samples indicate body accumulation of heavy zinc and light copper throughout life. This hypothesis has never been tested for humans, but the existence of a relationship between blood isotopic composition and age could be promising for age assessment methodologies. Dietary habits can also influence the blood zinc isotope composition, being an additional source of isotopic variation. In order to reduce this putative source of variation, we selected a population living in an isolated area (Sakha Republic, Russia) where diverse foods are of limited availability. We sampled blood from 8 male and 31 female Yakut volunteers between the ages of 18 and 74. Zinc, iron and copper were purified by liquid chromatography on ion exchange resin and their stable isotope ratios were measured using multiple-collector inductively coupled plasma mass spectrometry. According to observations of animal samples, the (66)Zn/(64)Zn ratio increases with age. We also observe that the (65)Cu/(63)Cu ratio decreases with age, whereas iron isotopic compositions are unrelated to age. The copper and zinc isotope compositions of the Yakut's blood are significantly lighter and heavier, respectively, than in samples of European and Japanese populations. The Yakut is a circumpolar population in which individuals have an elevated basal metabolic rate in response to cold stress. This elevated basal metabolic rate could enhance copper and zinc isotopic fractionation by accelerating the turnover of the copper and zinc stores.

Copper and iron isotope fractionation in mine tailings at the Laver and Kristineberg mines, northern Sweden

Previous research has shown that Cu and Fe isotopes are fractionated by dissolution and precipitation reactions driven by changing redox conditions. In this study, Cu isotope composition (65Cu/63Cu ratios) was studied in profiles through sulphide-bearing tailings at the former Cu mine at Laver and in a pilot-scale test cell at the Kristineberg mine, both in northern Sweden. The profile at Kristineberg was also analysed for Fe isotope composition (56Fe/54Fe ratios). At both sites sulphide oxidation resulted in an enrichment of the lighter Cu isotope in the oxidised zone of the tailings compared to the original isotope ratio, probably due to preferential losses of the heavier Cu isotope into the liquid phase during oxidation of sulphides. In a zone with secondary enrichment of Cu, located just below the oxidation front at Laver, δ65Cu (compared to ERM-AE633) was as low as −4.35±0.02‰, which can be compared to the original value of 1.31±0.03‰ in the unoxidised tailings. Precipitation of covellite in the secondary Cu enrichment zone explains this fractionation. The Fe isotopic composition in the Kristineberg profile is similar in the oxidised zone and in the unoxidised zone, with average δ56Fe values (relative to the IRMM-014) of −0.58±0.06‰ and −0.49±0.05‰, respectively. At the well-defined oxidation front, δ56Fe was less negative, −0.24±0.01‰. Processes such as Fe(II)–Fe(III) equilibrium and precipitation of Fe-(oxy)hydroxides at the oxidation front are assumed to cause this Fe isotope fractionation. This field study provides additional support for the importance of redox processes for the isotopic composition of Cu and Fe in natural systems.