High-precision measurements of seawater Pb isotope compositions by double spike thermal ionization mass spectrometry

A new method for the determination of seawater Pb isotope compositions and concentrations was developed, which combines and optimizes previously published protocols for the separation and isotopic analysis of this element. For isotopic analysis, the procedure involves initial separation of Pb from 1 to 2 L of seawater by co-precipitation with Mg hydroxide and further purification by a two stage anion exchange procedure. The Pb isotope measurements are subsequently carried out by thermal ionization mass spectrometry using a Pb-207-Pb-204 double spike for correction of instrumental mass fractionation. These methods are associated with a total procedural Pb blank of 28 +/- 21 pg(1sd) and typical Pb recoveries of 40-60%. The Pb concentrations are determined by isotope dilution (ID) on 50 mL of seawater, using a simplified version of above methods. Analyses of multiple aliquots of six seawater samples yield a reproducibility of about +/- 1to +/- 10%(1sd) for Pb concentrations of between 7 and 50 pmol/kg, where precision was primarily limited by the uncertainty of the blank correction (12 +/- 4 pg; 1sd). For the Pb isotope analyses, typical reproducibilities (+/- 2sd) of 700-1500 ppm and 1000-2000ppm were achieved for Pb-207/Pb-206, Pb-208/Pb-206 and Pb-206/Pb-204, Pb-207/Pb-204, Pb-208/Pb-204, respectively. These results are superior to literature data that were obtained using plasma source mass spectrometry and they are at least a factor of five more precise for ratios involving the minor Pb-204 isotope. Both Pb concentration and isotope data, furthermore, show good agreement with published results for two seawater intercomparison samples of the GEOTRACES program. Finally, the new methods were applied to a seawater depth profile from the eastern South Atlantic. Both Pb contents and isotope compositions display a smooth evolution with depth, and no obvious outliers. Compared to previous Pb isotope data for seawater, the Pb-206/Pb-204 ratios are well correlated with Pb-207/Pb-206, underlining the significant improvement achieved in the measurement of the minor Pb-204 isotope

Investigation and application of thallium isotope fractionation

This contribution summarizes the current state of understanding and recent advances made in the field of stable thallium (Tl) isotope geochemistry. High precision measurements of Tl isotope compositions were developed in the late 1990s with the advent of multiple collector inductively coupled plasma mass spectrometry (MC-ICP MS) and subsequent studies revealed that Tl, despite the small relative mass difference of the two isotopes, exhibits substantial stable isotope fractionation, especially in the marine environment. The most fractionated reservoirs identified are ferromanganese sediments with ε205 Tl≈ +15 and low temperature altered oceanic crust with ε205 Tl≈–20. The total isotopic variability of more than 35 ε 205 Tl-units hence exceeds the current analytical reproducibility of the measurement technique by more than a factor of 70. This isotopic variation can be explained by invoking a combination of conventional mass dependent equilibrium isotope effects and nuclear field shift isotope fractionation, but the specific mechanisms are still largely unaccounted for. Thallium isotopes have been applied to investigate paleoceanographic processes in the Cenozoic and there is evidence to suggest that Tl isotopes may be utilized as a monitor of the marine manganese oxide burial flux over million year time scales. In addition, Tl isotopes can be used to calculate the magnitude of hydrothermal fluid circulation through ocean crust. It has also been shown that the subduction of marine ferromanganese sediments can be detected with Tl isotopes in lavas erupted in subduction zone settings as well as in ocean island basalts. Meteorite samples display Tl isotope variations that exceed the terrestrial range with a total variability of about 50 ε205 Tl. The large isotopic diversity, however, is generated by both stable Tl isotope fractionations, which reflect the highly volatile and labile cosmochemical nature of the element, and radiogenic decay of extinct 205 Pb to 205 Tl with a half-life of about 15 Ma. The difficulty of deconvolving these two sources of isotopic variability restricts the utility of both the 205 Pb-205 Tl chronometer and the Tl stable isotope system to inform on early solar system processes

Improvements in Cd stable isotope analysis achieved through use of liquid–liquid extraction to remove organic residues from Cd separates obtained by extraction chromatography

Organic compounds released from resins that are commonly employed for trace element separations are known to have a detrimental impact on the quality of isotopic analyses by MC-ICP-MS. A recent study highlighted that such effects can be particularly problematic for Cd stable isotope measurements (M. Gault-Ringold and C. H. Stirling, J. Anal. At. Spectrom., 2012, 27, 449–459). In this case, the final stage of sample purification commonly applies extraction chromatography with Eichrom TRU resin, which employs particles coated with octylphenyl-N,N-di-isobutyl carbamoylphosphine oxide (CMPO) dissolved in tri-n-butyl phosphate (TBP). During chromatography, it appears that some of these compounds are eluted alongside Cd and cannot be removed by evaporation due to their high boiling points. When aliquots of the zero-ε reference material were processed through the purification procedure, refluxed in concentrated HNO(3) and analyzed at minimum dilution (in 1 ml 0.1 M HNO(3)), they yielded Cd isotopic compositions (ε(114/110)Cd = 4.6 ± 3.4, 2SD, n = 4) that differed significantly from the expected value, despite the use of a double spike technique to correct for instrumental mass fractionation. This result was accompanied by a 35% reduction in instrumental sensitivity for Cd. With increasing dilution of the organic resin residue, both of these effects are reduced and they are insignificant when the eluted Cd is dissolved in ≥3 ml 0.1 M HNO(3). Our results, furthermore, indicate that the isotopic artefacts are most likely related to anomalous mass bias behavior. Previous studies have shown that perchloric acid can be effective at avoiding such effects (Gault-Ringold and Stirling, 2012; K. C. Crocket, M. Lambelet, T. van de Flierdt, M. Rehkämper and L. F. Robinson, Chem. Geol., 2014, 374–375, 128–140), presumably by oxidizing the resin-derived organics, but there are numerous disadvantages to its use. Here we show that liquid–liquid extraction with n-heptane removes the organic compounds, dramatically improving quality of the Cd isotope data for samples that are analyzed at or close to minimum dilution factors. This technique is quick, simple and may be of use prior to analysis of other isotope systems where similar resins are employed

High precision zinc stable isotope measurement of certified biological reference materials using the double spike technique and multiple collector-ICP-MS

Biological reference materials with well-characterized s table isotope compositions are lacking in the field of ‘isotope biochemistry’, which seeks to understand bodily processes that rely on essential metals by determining metal stable isotope ratios. Here, we present Zn stable isotope data for six biological reference materials with certified trace metal concentrations, fish muscle, bovine muscle, pig kidney, human hair, human blood serum and human urine. Replicate analyses of multiple aliquots of each material achieved reproducibilities (2sd) of 0.04-0.13 ‰ for δ66/64Zn 22 (which denotes the deviation of the 66 Zn/64Zn ratio of a sample from a pure Zn reference material in parts per 1000). This implies only very minor isotopic heterogeneities within the samples, rendering them suitable as quality control materials for Zn isotopeanalyses. This endorsement is reinforced by (i) the close agreement of our Zn isotope data for two of the samples (bovine 2 muscle and human blood serum) to previously published results for different batches of the same material and (ii) the similarity of the isotopic data for the samples (δ66/64Zn≈ –0.8 to 0.0 ‰) to previously published Zn isotope results for similar biological materials. Further tests revealed that the applied Zn separation procedure is sufficiently effective to enable accurate data acquisition even at low mass resolving power (M/ΔM ≈ 400), as measurements and analyses conducted at much higher mass resolution (M/ΔM ≈ 8500) delivered essentially identical results

Nucleosynthetic and Mass-Dependent Molybdenum Isotope Anomalies in Iron Meteorites:Constraints on Solar Nebula Heterogeneities and Parent Body Processes

While iron meteorite parent bodies exhibit variable deficits in s-process Mo isotopes, they feature essentially identical stable Mo isotope compositions

The thallium isotope composition of carbonaceous chondrites - New evidence for live 205Pb in the early solar system

The extinct radionuclide 205Pb, which decays to 205Tl with a half-life of 15 Ma, is of considerable cosmochemical interest, as it is the only short-lived isotope that is produced exclusively by s-process nucleosynthesis. Evidence for the existence of 205Pb in the early solar system has only recently been obtained from analyses of IAB iron meteorites, but significant uncertainties remain about the initial 205Pb abundance and Tl isotope composition of the solar system. In an attempt to better constrain these values, a comprehensive 205Pb–205Tl isochron study was carried out on ten carbonaceous chondrites of groups CI, CM, CV, CO and CR. The Pb and Cd isotope compositions of the meteorites were also determined, to correct for terrestrial Pb contamination and eliminate samples that exhibit fractionated Tl isotope compositions from thermal processing.\ud The analyses revealed only limited variation in ε205Tl, with values of between − 4.0 and + 1.2, but nonetheless the Tl isotope compositions correlate with Pb/Tl ratios. This correlation is unlikely to be due to stable isotope fractionation from terrestrial weathering or early solar system processes, and is most readily explained by in situ decay of 205Pb to 205Tl. Previous 53Mn–53Cr and 107Pd–107Ag studies of bulk carbonaceous chondrites provide evidence that the Pb–Tl isochron records volatile fractionation in the solar nebula at close to 4567 Ma. The isochron thus yields the initial 205Pb abundance and Tl isotope composition of the solar system, with values of 205Pb/204PbSS,0 = (1.0 ± 0.4) × 10− 3 and ε205TlSS,0 = − 7.6 ± 2.1, respectively. These results confirm the previous Pb–Tl data for IAB iron meteorites, which provided the first clear evidence for the existence of live 205Pb in the early solar system.\ud The initial 205PbSS,0 abundance inferred from carbonaceous chondrites demonstrates that the 205Pb–205Tl decay system is well suited for chronological studies of early solar system processes that produce fractionations in Pb/Tl ratios, including core crystallization and the mobilization of volatiles during thermal processing. The 205PbSS,0 abundance is close to the upper limit of nucleosynthetic production estimates for AGB stars and thus in accord with contributions of such stars to the early solar system budget of freshly synthesized radioisotopes

The thallium isotope composition of carbonaceous chondrites - New evidence for live 205Pb in the early solar system

The extinct radionuclide 205Pb, which decays to 205Tl with a half-life of 15 Ma, is of considerable cosmochemical interest, as it is the only short-lived isotope that is produced exclusively by s-process nucleosynthesis. Evidence for the existence of 205Pb in the early solar system has only recently been obtained from analyses of IAB iron meteorites, but significant uncertainties remain about the initial 205Pb abundance and Tl isotope composition of the solar system. In an attempt to better constrain these values, a comprehensive 205Pb–205Tl isochron study was carried out on ten carbonaceous chondrites of groups CI, CM, CV, CO and CR. The Pb and Cd isotope compositions of the meteorites were also determined, to correct for terrestrial Pb contamination and eliminate samples that exhibit fractionated Tl isotope compositions from thermal processing. The analyses revealed only limited variation in ε205Tl, with values of between − 4.0 and + 1.2, but nonetheless the Tl isotope compositions correlate with Pb/Tl ratios. This correlation is unlikely to be due to stable isotope fractionation from terrestrial weathering or early solar system processes, and is most readily explained by in situ decay of 205Pb to 205Tl. Previous 53Mn–53Cr and 107Pd–107Ag studies of bulk carbonaceous chondrites provide evidence that the Pb–Tl isochron records volatile fractionation in the solar nebula at close to 4567 Ma. The isochron thus yields the initial 205Pb abundance and Tl isotope composition of the solar system, with values of 205Pb/204PbSS,0 = (1.0 ± 0.4) × 10− 3 and ε205TlSS,0 = − 7.6 ± 2.1, respectively. These results confirm the previous Pb–Tl data for IAB iron meteorites, which provided the first clear evidence for the existence of live 205Pb in the early solar system. The initial 205PbSS,0 abundance inferred from carbonaceous chondrites demonstrates that the 205Pb–205Tl decay system is well suited for chronological studies of early solar system processes that produce fractionations in Pb/Tl ratios, including core crystallization and the mobilization of volatiles during thermal processing. The 205PbSS,0 abundance is close to the upper limit of nucleosynthetic production estimates for AGB stars and thus in accord with contributions of such stars to the early solar system budget of freshly synthesized radioisotopes

Cadmium, copper and zinc stable isotopes as analytical tool to trace sources and processes in agricultural systems

In agriculture, mineral phosphate (P) fertilizer application leads to an unintended input of Cadmium (Cd) into agricultural systems. Cd is highly toxic and its incorporation into the food chain endangers human health. Copper (Cu) and zinc (Zn) are used as feed additives and pharmaceuticals and can accumulate with farmyard manure in agricultural soils. Although being micronutrients, high Cu and Zn concentrations are toxic. Former studies revealed Cd, Cu and Zn accumulations in Swiss agricultural soils in the past decades. However, these studies were not completely based on in-situ measured data. The aim of this study was to fill this gap and measure Cd, Cu and Zn fluxes at selected Swiss agricultural sites. Specifically, we aimed to trace the metals in the soil and to differentiate between anthropogenic and geogenic sources. Additionally, we further elucidated metal redistribution in Swiss agricultural systems, based on the measurements of stable metal isotope ratios of different system pools. For that purpose, metal balances of three arable (Cd) and three grassland (Cu & Zn) sites were determined by measuring the soil metal concentrations and all inputs (bulk deposition, mineral P fertilizers, manure & parent material) and outputs (seepage water, crop & grass harvest) during one hydrological year (May 2014 – May 2015). Furthermore, stable metal isotopes of the soil and all inputs and outputs were (Cd) and will be (Cu & Zn) determined. Cd mass balances showed losses for wheat cultivation (-0.01 to -0.35 g ha-1 y-1) and accumulations for barley cultivation (0.18 to 0.71 g ha-1 y-1). Isotopic ratios in wheat (∆114/110Cdstraw-grain = -0.34 to -0.38‰) and barley plants (-0.44 to -0.82‰) revealed that uptake and retranslocation of Cd in the plants is driven by physiological processes to reduce toxic Cd impacts. Cu and Zn mass balances showed that manure application is by far the most important Cu (146-340 g ha-1 y-1) and Zn (947-1’742 g ha-1 y-1) input. Inputs with bulk deposition and through parent material weathering were by 1-2 orders of magnitude smaller. Beside the Cu and Zn budgets, stable isotope data (not yet analysed) will be presented and discussed to assess the biogeochemical processes and redistribution of (anthropogenic) Cu and Zn in agricultural systems

Evidence for a Pathophysiological Role of Keratinocyte-Derived Type III Interferon (IFNλ) in Cutaneous Lupus Erythematosus

Type I IFNs (IFNα/β) have been shown to have a central role in the pathophysiology of lupus erythematosus (LE). The recently discovered type III IFNs (IFNλ1/IL29, IFNλ2/IL28a, IFNλ3/IL28b) share several functional similarities with type I IFNs, particularly in antiviral immunity. As IFNλs act primarily on epithelial cells, we investigated whether type III IFNs might also have a role in the pathogenesis of cutaneous LE (CLE). Our investigations demonstrate that IFNλ and the IFNλ receptor were strongly expressed in the epidermis of CLE skin lesions and related autoimmune diseases (lichen planus and dermatomyositis). Significantly enhanced IFNλ1 could be measured in the serum of CLE patients with active skin lesions. Functional analyses revealed that human keratinocytes are able to produce high levels of IFNλ1 but only low amounts of IFNα/β/γ in response to immunostimulatory nuclear acids, suggesting that IFNλ is a major IFN produced by these cells. Exposure of human keratinocytes to IFNλ1 induced the expression of several proinflammatory cytokines, including CXCL9 (CXC-motiv ligand 9), which drive the recruitment of immune cells and are associated with the formation of CLE skin lesions. Our results provide evidence for a role of type III IFNs in not only antiviral immunity but also autoimmune diseases of the skin

Cadmium isotope fractionation during metal-silicate partitioning – Results and implications for Earth's volatile accretion

Metal-silicate partitioning experiments were carried out at 1.5 GPa and 1508 to 1843 K to constrain Cd partitioning and isotope fractionation during core formation. At the studied conditions, there was no significant stable isotope fractionation during Cd partitioning between metal and silicate phases with a mean ∆114Cdmet-sil = −0.02 ± 0.09‰ (2SD, n = 7). Two experiments that investigated sulphide-silicate partitioning of Cd yielded fractionation factors of −0.04 ± 0.06‰ and − 0.23 ± 0.07‰ (2SE), whereby the latter result was obtained for a short run that may not represent full equilibrium. In summary, the findings suggest that Cd isotope fractionation during segregation of Earth's core was either absent or very minor. The Cd partitioning data of this and previous investigations were combined in multiple linear regression analyses to better constrain Cd metal-silicate partitioning during core formation. In accord with earlier work, the analyses reveal that Cd metal-silicate partitioning is not significantly impacted by temperature and pressure but affected by the S content of the metal phase. In addition, it is shown that the presence of C and Si in the metal reduce the siderophile character of Cd. Based on estimates for the composition of Earth's core, the data suggest a metal-silicate partition coefficient DCd of about 0.4 for a single-stage core formation event. However, given uncertainties about the light element composition of Earth's core, DCd values larger than 1 cannot be ruled out at present for core formation. The results of this study and data on the composition of the bulk silicate Earth and chondritic meteorites were applied in mass balance calculations to constrain the Cd signature of Earth's main stage accretion material prior to delivery of the late veneer. The modelling indicates Earth's main stage of accretion involved material with an average Cd isotope composition that was lighter than that of known carbonaceous and enstatite chondrites. Most likely, this reflects either poor characterisation of these meteorites by the few precise data currently available or that a significant fraction of the terrestrial volatile inventory was acquired from material not directly related to carbonaceous and enstatite chondrites. Furthermore, terrestrial accretion most likely did not encompass the addition of a volatile-rich late veneer exceeding 2% of Earth's mass, in accord with accretion models, which invoke that volatile delivery occurred primarily during main stage accretion, alongside core formation