Zinc Stable Isotope Research Articles

Applications of zinc stable isotope analysis in environmental and biological systems: a review

Zinc (Zn) is an essential trace element that is involved in both biotic and abiotic processes in Earth's surface environments. Over the last 20 years, advances in mass spectrometry instrumentation have enabled unprecedented high-precision Zn isotope abundance ratio determinations in natural and anthropogenic samples. Supported by a solid theoretical background inherited from the traditional non-metal stable isotopes (C, N, H, O, S), the understanding of the controlling factors of Zn isotope fractionation has rapidly evolved. In this article, we review the main applications and findings of Zn isotopes in a variety of scientific domains, including metal contamination, magmatic differentiation, plant uptake, weathering, global climate change, dietary and trophic chains, and biomedicine. The analytical aspects of Zn isotope determination in solid and water samples and the principles and mechanisms of Zn isotope fractionation are also reviewed. This work aims to provide a general yet in-depth panorama of Zn isotope chemistry and to demonstrate the versatility and potential of this isotope system for studying the biological, geological and chemical cycling of Zn.

Zinc isotope fractionation during the sorption of Zn to minerals and organic matter in sediment cores affected by anthropogenic pollution

Zinc stable isotopes (δ66Zn) serve as a widely fingerprinting tool for detecting anthropogenic Zn contamination. However, there is a limited understanding of δ66Zn behavior during the sorption of Zn to minerals and organic matter. In this study, we have determined the δ66Zn values in specific fractions to investigate their effectiveness in tracing anthropogenic Zn. The revised Community Bureau of Reference (BCR) extraction procedure was applied to a coastal marine core from Osaka Bay and from a lacustrine core from Lake Biwa, both with a history of anthropogenic metal pollution. The δ66Zn values varied from −0.14 ‰ to +1.00 ‰ across the four to five chemical fractions with up to 0.9 ‰ variation within a single horizon. The highest δ66Zn values in the acid-soluble fraction (up to +1.00 ‰) could be explained by the preferential sorption of 66Zn to carbonates and/or the preferential incorporation of 66Zn into calcite. The complex isotopic fractionation during the sorption of Zn to and co-precipitation with Fe–Mn oxyhydroxides likely resulted in an unclear pattern of the δ66Zn values of the reducible fraction. Low δ66Zn values in the oxidizable fraction (Osaka Bay) agree with the 64Zn enrichment in phytoplankton. Higher δ66Zn values of the reducible and oxidizable fractions of the Lake Biwa core indicate that environmental conditions (e.g. ionic strength) and for instance different phytoplankton species or dissolved and suspended particulate matter input drive the Zn isotope fractionation depending on the system (marine vs. lacustrine). The δ66Zn values of the acid-soluble fraction (Osaka Bay and Lake Biwa), of the reducible fraction (only Lake Biwa) and of oxidizable fraction (only Osaka Bay) better reflected the temporal changes in the Zn concentration than the bulk sediment, indicating that these fractions could be a sensitive fingerprinting tool for anthropogenic Zn contamination.

Zinc Stable Isotope Fractionation Mechanisms during Adsorption on and Substitution in Iron (Hydr)oxides.

The Zn isotope fingerprint is widely used as a proxy of various environmental geochemical processes, so it is crucial to determine which are the mechanisms responsible for isotopic fractionation. Iron (Fe) (hydr)oxides greatly control the cycling and fate and thus isotope fractionation factors of Zn in terrestrial environments. Here, Zn isotope fractionation and related mechanisms during adsorption on and substitution in three FeOOH polymorphs are explored. Results demonstrate that heavy Zn isotopes are preferentially enriched onto solids, with almost similar isotopic offsets (Δ66/64Znsolid-solution = 0.25-0.36‰) for goethite, lepidocrocite, and feroxyhyte. This is consistent with the same average Zn-O bond lengths for adsorbed Zn on these solids as revealed by Zn K-edge X-ray absorption fine structure spectroscopy. In contrast, at an initial Zn/Fe molar ratio of 0.02, incorporation of Zn into goethite and lepidocrocite by substituting for lattice Fe preferentially sequesters light Zn isotopes with Δ66/64Znsubstituted-stocksolution of -1.52 ± 0.09‰ and -1.18 ± 0.15‰, while Zn-substituted feroxyhyte (0.06 ± 0.11‰) indicates almost no isotope fractionation. This is closely related to the different crystal nucleation and growth rates during the Zn-doped FeOOH formation processes. These results provide direct experimental evidence of incorporation of isotopically light Zn into Fe (hydr)oxides and improve our understanding of Zn isotope fractionation mechanisms during mineral-solution interface processes.

Zinc Absorption Estimated by Fecal Monitoring of Zinc Stable Isotopes Validated by Comparison with Whole-Body Retention of Zinc Radioisotopes in Humans

Knowledge about zinc availability from human diets is limited due to methodological difficulties. Recently developed stable isotope techniques for estimating dietary zinc abosrption were compared with radioisotope techniques in five men and three women. Stable and radioactive zinc isotopes were simultaneously administered. Fecal excretion of the isotopes as well as whole-body retention of the radioactive zinc isotope was monitored. Concentration of stable zinc isotope label in fecal samples was determined by inductively coupled plasma mass spectrometry by fully quantitative measurements and from inductively coupled plasma mass spectrometry isotope ratios combined with analysis of total zinc content using atomic absorption spectrometry. Zinc absorption estimated from whole-body retention was 27 ± 6% (x̄ ± SD), estimated zinc absorption obtained by fecal monitoring of radioisotope was 26 ± 9%, and the two stable zinc measurements resulted in values of 29 ± 12 and 33 ± 12%, respectively. There was no signfiicant difference in zinc absorption estimated from whole-body retention and with the fecal monitoring methods. Recovered stable zinc isotope label was significantly lower than recovered radiolsotope. For individual fecal samples, systematic differences of 16% and 12%, respectively (P < 0.05), between the radioisotope recovery and the recovery of stable isotopes with the two methods for measurement was observed. The stable zinc isotope technique for measurement of zinc absorption resulted in mean results similar to those of the radioisotope technique, but with a larger variation in the measurements.

The geochemistry of zinc and copper stable isotopes in marine hydrothermal brine pools: Perspectives from metalliferous sediments of the Atlantis II Deep, Red Sea

This study provides a zinc and copper stable isotope characterization (δ66Zn, δ68Zn, and δ65Cu) of metalliferous seafloor sediments from the Atlantis II Deep, a hydrothermally influenced brine basin in the Red Sea. Samples collected from box cores that capture the entire stratigraphy in the Deep have δ66Zn and δ65Cu values of −0.31 to 0.34 ‰ (0.02 ‰ median) and − 1.81 to 1.02 ‰ (−0.34 ‰ median) relative to the JMC-Lyon and NIST SRM 976 standards, respectively. These results suggest enrichments of light stable isotopes in sediments compared to the hydrothermal inputs to the basin, which likely overlap the mantle-like isotopic signatures of basalts beneath the Deep. Such shifts to lower δ66Zn and δ65Cu values are consistent with widespread metal sulfide deposition from the brines because sulfide anions preferentially consume the light stable isotopes of zinc and copper. However, this interpretation contrasts with observations in the open ocean, where the fractionation of zinc and copper stable isotopes is strongly influenced by biological utilization and organic matter. Previous studies proposed that metal deposition in the Atlantis II Deep is also driven by adsorption onto iron oxides/hydroxides and their weakly crystalline (Si-)Fe-OOH precursor phases within the brines. However, because this process should accumulate heavy zinc and copper stable isotopes, its influence on isotopic fractionation is likely limited. Controls by metal sulfide precipitation are also indicated by spatial covariations between δ66Zn and concentrations of zinc and copper, that is, δ66Zn values increase whereas metal contents decrease with distance away from hydrothermal venting. Comparable trends are lacking for copper isotopes, perhaps because of additional influence by redox processes or, compared to zinc, a much stronger influence by adsorption onto (Si-)Fe-OOH phases, particularly in areas distal to hydrothermal venting where reduced sulfur could be scarce. Collectively, our results from the Atlantis II Deep indicate that zinc and copper stable isotopes could provide information about base and precious metals deposits from similar paleoenvironments. Firstly, zinc and copper stable isotopes shed light on metal sourcing and accumulation processes. Secondly, mineral precipitation in hydrothermally influenced brine pools produces zinc stable isotope patterns that, at least theoretically, could be of interest in mineral exploration at sub-basin and deposit scales.

In VitroAnticancer Activity of the Light Stable Zinc Isotope (64Zn) Compounds

Today, stable isotopes of zinc are actively used for diagnostic purposes in oncology. However, there is extremely limited data on the attempts to apply stable zinc isotopes in cancer therapy or about the molecular mechanisms of their effects on the biology of tumor cells. Therefore, in this in vitro research, we evaluated the cytotoxic activity of stable zinc isotope (64Zn) enriched compounds against malignant cells and determined the mechanisms of their action. Malignant and non-malignant cells of different histogenesis were used as objects of the study. The effect of the Zn64aspartate, Zn64glutamate, and Zn64sulfate on cell viability in a comparative aspect was evaluated. Compounds containing 64Zn stable isotope enriched to 99.2%. Western blot analysis was used to determine the expression level of apoptosis regulatory proteins. Salts of 64Zn with amino acids had the most significant cytotoxic effect on malignant cells. The studied tumor cells, and especially MB16 melanoma cells were the most sensitive to the cytotoxic effects of Zn64aspartate. Zn64aspartate showed more significant cytotoxic activity than Zn aspartate (with natural isotope distribution) in the studied cell models. Zn64aspartate induced caspase-dependent cell death in A-549 cells and the p53-mediated apoptosis in melanoma cells. Malignant cells were more sensitive to the cytotoxic effect of the Zn64aspartate than normal cells. An increase in the intracellular concentration of 64Zn, and hence isotope mass balance changes, may lead to the suppression of the viability and proliferation of malignant cells. These results can become the basis for developing a new generation of anticancer drugs.

Zinc isotopic evidence for enhanced continental weathering and organic carbon burial during the late Cambrian SPICE event

The globally recognized late Cambrian Steptoean Positive Carbon Isotope Excursion (SPICE; ca. 497–494 Ma) is one of the most prominent carbon isotope excursions during the Phanerozoic eon, yet its primary cause remains debatable. To provide new insights into this issue, here we investigate zinc stable isotopes (expressed as δ66Zn) on two coeval carbonate successions spanning the Miaolingian-Furongian transition in North China. Similar stratigraphic δ66Zn trends are observed in the two sections, indicating a widespread perturbation to the marine Zn cycling. An abrupt decline of δ66Zn values by up to 0.4‰ and a concomitant increase of Zn/Ca ratios are observed at the pre-SPICE to the early SPICE interval, which can be best explained by the enhanced influx of isotopically light Zn from continental weathering. Enhanced continental weathering increased the inputs of terrestrial-sourced nutrients to the oceans, promoting the primary productivity and burial fluxes of organically bound Zn. At the middle stage of the SPICE, the coupled positive shifts of δ66Zn and δ13Ccarb indicate a phase of marine Zn cycling fluctuations driven by massive organic matter burial. Enhanced sequestration of organic carbon caused a rise in atmospheric oxygen levels, favoring the remobilization of previously buried Zn at shallower marine settings. With the development of muted continental weathering during the falling limb of the SPICE, the return of δ66Zn to initial background values marks the reestablishment of the stable seawater chemistry condition. Our results constrain the important roles of enhanced continental weathering and organic matter burial in micronutrient fluctuations during the SPICE, which were most likely the primary trigger for the SPICE.

Metal contamination in a sediment core from Osaka Bay during the last 400 years

Osaka Bay adjacent to the Kyoto–Osaka–Kobe metropolitan area was affected by severe metal pollution during the twentieth century; yet little is known about the trace metal sources and pre-industrial human activities. We have determined the elemental concentrations and zinc stable isotope ratios (δ66Zn) in bulk sediments and the trace metal concentrations in chemical fractions of a 9-m-long sediment core from Osaka Bay. Our goals were (1) to reconstruct the historical trace metal contamination, and (2) to identify anthropogenic Zn sources and the solid phases of anthropogenic trace metals. The core provided a continuous environmental record of the last 2300 years based on radiocarbon dating of molluscan shells. Copper, Zn, and Pb showed an initial enrichment from the 1670s AD, which could be caused by human activities due to an increasing population. In agreement with previous findings, the trace metal concentrations slightly increased from the 1870s, strongly increased from the beginning of the twentieth century, and peaked around 1960 before environmental pollution control laws were enacted. Increasing trace metal concentrations in the acid-labile and reducible fractions obtained by the Community Bureau of Reference (BCR) sequential extraction procedure toward the surface indicate carbonates and Mn oxyhydroxides were the primary fractions for anthropogenic trace metals. The δ66Zn values (1) were constant until the 1940s, suggesting that the average δ66Zn of industrial sources was indistinguishable from that value of the natural background, (2) showed a slight decrease from the 1950s and remained constant until the present, and (3) fell in a binary mixing process between a lithogenic (~ + 0.27‰) and an anthropogenic endmember (~ + 0.17‰), the latter likely representing a mixture of various Zn sources such as road dust, tire wear, industrial effluents, and effluents from wastewater treatment plants. We conclude the combination of Zn stable isotopes together with chemical fractions obtained by the BCR method represents a promising approach to assess the trace metal sources and their potential mobility in sediment cores from anthropogenically affected coastal areas.

Analysis of excitation functions of (p,n) reactions for the stable isotopes of zinc and copper up to 40 MeV

Analysis of excitation functions of (p,n) reactions for the stable isotopes of zinc and copper up to 40 MeV

Cu and Zn stable isotopes in suspended particulate matter sub-fractions from the northern Bay of Biscay help identify biogenic and geogenic particle pools

Marine suspended particulate matter (SPM) plays a pivotal role in the marine biogeochemical cycling of trace elements. This study investigates metal distributions and copper (Cu) and zinc (Zn) stable isotope ratios in different size fractions of SPM from two sampling stations on the inner continental shelf of northern Bay of Biscay (NE Atlantic), a zone highly influenced by the macrotidal Loire estuary, the outlet of a major European river. The objective of this study is to test stable isotopes as tools to infer the origins of particles and their formation processes, and to infer relevant Cu and Zn biogenic pools involved in marine trophic transfers of these metals. SPM samples were nearly quantitatively mineralized (i.e., without HF) to determine metals and Cu and Zn isotopes in their more labile and reactive phases. Their δ65CuSRM-976 values ranged from −0.45 to +0.51‰, with higher Cu concentrations accompanying particle size decreasing. The δ66ZnJMC-Lyon values in SPM sub-fractions varied from +0.14 to +0.76‰, and were uncorrelated to both Zn concentrations and particle size. Compared to larger size fractions, increased Al and Fe levels (proxies for terrigenous materials) and enrichments in lighter Cu and Zn isotopes observed in the smaller size SPM sub-fractions suggest that a major proportion of SPM Cu and Zn is associated with geogenic particles. Conversely, the relative enrichment of heavy isotopes in coarser particles is attributable to an increase of Cu and Zn metabolically incorporated into biogenic organic particles (e.g., plankton), and by surface adsorption onto organic detrital particles. The higher δ-values attributed to biogenic particles likely represents the isotope composition of the local marine organic matter available to primary consumers like filter-feeders (oysters). Thus, this study shows that targeting particles of specific size classes allows to identify relative dominances of biogenic and geogenic carrier phases. Identifying these pools and their isotopic composition may help to track Cu and Zn transfers through marine food-web in future studies.

Zinc in soil reflecting the intensive coal mining activities: Evidence from stable zinc isotopes analysis

In the mining area affected by coal mining activities for a long time, heavy metal Zn pollution poses a serious threat to soil quality and human health, and direct evidence showing the relationship between Zn accumulation mechanism in soils and mining activities is lacking. In this study, the Zn content and isotopes composition (δ66Zn) from soil and environmental samples around mining area were determined and analyzed to clarify the Zn characteristics in soil. Moreover, the distribution and source of Zn content in soil of mining area were analyzed by mathematical statistics, correlation analysis and isotope mass mixing model. The results showed that: (1) the Zn content in soil ranged from 95 to 327 mg·kg−1 (mean: 233 mg·kg−1), exceeding the control point and the soil background value of Anhui Province; (2) the results of Zn isotope analysis showed that Zn in soil mainly derived from the wind dispersion input of fine particles in gangue and fly ash, followed by the natural weathering of parent material; (3) isotopic mass mixing model can be used to distinguish the contribution of anthropogenic and natural Zn sources. Mining input was the main contribution source of Zn in soil (mean: 67%), followed by natural background (mean: 33%). The employment of Zn isotopes can effectively evaluate the impact of anthropogenic and natural long-term processes on Zn in the soil of the mining area, and provide important information for the formulation of soil metal pollution control measures.

Exchangeable Zinc Pool Size Reflects Form of Zinc Supplementation in Young Children and Is Not Associated with Markers of Inflammation.

A sensitive and reliable biomarker of zinc status has yet to be identified, but observational research suggests that the exchangeable zinc pool (EZP) size may be a possible biomarker. This randomized, placebo-controlled trial aimed to compare the change in EZP size from baseline to endline in 174 children who were preventatively supplemented with 10 mg of zinc as part of a multiple micronutrient power (MNP) or as a standalone dispersible tablet for 24 weeks versus a placebo powder. The effects of systemic inflammation on EZP size were also evaluated. Zinc stable isotopes were administered intravenously to children at baseline and endline, and the EZP was measured by the urine extrapolation method. A total of 156 children completed the study with the zinc dispersible tablet group having the greatest increase in EZP (14.1 mg) over 24 weeks when compared with the MNP group (6.8 mg) (p < 0.01) or placebo group (2.0 mg) (p < 0.001). Median EZP size was not different between children with normal or elevated serum inflammatory markers. EZP size was responsive to longitudinal zinc supplementation and reflected the expected difference in bioavailability for two forms of supplementation. The apparent absence of an effect of inflammation on EZP size may offer an advantage for use as a biomarker for group comparisons between different interventions.

The Use of Stable Zinc Isotope Soil Labeling to Assess the Contribution of Complex Organic Fertilizers to the Zinc Nutrition of Ryegrass.

Manure and sewage sludge are known to add significant amounts of zinc (Zn) and other metals to soils. However, there is a paucity of information on the fate of Zn that derives from complex organic fertilizers in soil–plant systems and the contribution of these fertilizers to the Zn nutrition of crops. To answer these questions, we grew Italian ryegrass in the presence of ZnSO4, sewage sludge, and cattle and poultry manure in an acidic soil from Heitenried, Switzerland, and an alkaline soil from Strickhof, Switzerland, where the isotopically exchangeable Zn had been labeled with 67Zn. This allowed us to calculate the fraction of Zn in the shoots that was derived from fertilizer, soil, and seed over 4 successive cuts. In addition, we measured the 67Zn:66Zn isotope ratio with the diffusive gradients in thin films technique (DGT) on soils labeled with 67Zn and incubated with the same fertilizers. After 48 days of growth, the largest fraction of Zn in the ryegrass shoots was derived from the soil (79–88%), followed by the Zn-containing fertilizer (11–20%); the least (<2.3%) came from the seed. Only a minor fraction of the Zn applied with the fertilizer was transferred to the shoots (4.7–12%), which indicates that most of the freshly added Zn remained in the soil after one crop cycle and may thereby contribute to a residual Zn pool in the soil. The 67Zn:66Zn isotope ratios in the DGT extracts and the shoots measured at cut 4 were identical, suggesting that the DGT and plant took up Zn from the same pool. The proportion of Zn derived from the fertilizers in the DGT extracts was also identical to that measured in ryegrass shoots at cut 4. In conclusion, this work shows that stable Zn isotope labeling of the soil available Zn can be used to precisely quantify the impact of complex organic fertilizers on the Zn nutrition of crops. It also demonstrates that DGT extractions on labeled soils could be used to estimate the contribution of Zn fertilizers to plant nutrition.

Trace metal geochemical and Zn stable isotope data as tracers for anthropogenic metal contributions in a sediment core from Lake Biwa, Japan

The catchment of Lake Biwa, the largest freshwater lake in Japan, has experienced rapid urbanization and industrialization in the second half of the 20th century; yet little is known about the historical trend of metal pollution. We analyzed the elemental concentrations and zinc stable isotope ratios (δ66Zn) in a sediment core from the Northern basin of the lake. The goals were 1) to reconstruct the historical trend of trace metals in the lake and 2) to understand whether the range of Zn concentrations was derived from natural or anthropogenic sources. The first increase in Cu and Zn concentrations from the late 1910s until approximately 1940 could be due to human-induced higher contributions from the surrounding mafic igneous rocks. A second increase in the Zn concentrations accompanied by a slight decrease in the δ66Zn values from the late 1950s coincided with the period of the industrialization and urbanization. The δ66Zn values fell in a binary mixing process between a lithogenic (∼+0.28‰) and an anthropogenic endmember (∼+0.14‰). Although industrial effluents were strictly regulated by law from the late 1960s, constant Zn concentrations throughout the 1980s indicated contributions from domestic wastewaters and diffusive sources such as runoff from paddy fields, roads, and industrial areas. Zinc, Ni, and Co were still enriched in recent surface sediment compared to the pre-industrial times. The metal fractions obtained by the BCR sequential extraction procedure showed that Pb was mainly hosted in the reducible fraction, and Cu and Zn were mainly hosted in the residual fraction. The increasing trace metal concentrations in the acid-labile and reducible fractions towards the surface indicate these fractions were the primary host for anthropogenic trace metals. We conclude it is unlikely that the natural condition of the lake sediment will be recovered owing to the continuing urbanization around Lake Biwa.

Zinc stable isotope analysis reveals Zn dyshomeostasis in benign tumours, breast cancer, and adjacent histologically normal tissue.

The disruption of Zn homeostasis has been linked with breast cancer development and progression. To enhance our understanding of changes in Zn homeostasis both inside and around the tumour microenvironment, Zn concentrations and isotopic compositions (δ66Zn) were determined in benign (BT) and malignant (MT) tumours, healthy tissue from reduction mammoplasty (HT), and histologically normal tissue adjacent to benign (NAT(BT)) and malignant tumours (NAT(MT)). Mean Zn concentrations in NAT(BT) are 5.5 µg g-1 greater than in NAT(MT) (p=0.00056) and 5.1 µg g-1 greater than in HT (p=0.0026). Zinc concentrations in MT are 12.9 µg g-1 greater than in HT (p=0.00012) and 13.3 µg g-1 greater than in NAT(MT) (p <0.0001), whereas δ66Zn is 0.17‰ lower in MT than HT (p=0.017). Benign tumour Zn concentrations are also elevated compared to HT (p=0.00013), but are not significantly elevated compared to NAT(BT) (p=0.32). The δ66Zn of BT is 0.15‰ lower than in NAT(BT) (p=0.045). The similar light δ66Zn of BT and MT compared to HT and NAT may be related to the isotopic compensation of increased metallothionein (64Zn-rich) expression by activated matrix metalloproteinase (66Zn-rich) in MT, and indicates a resultant 66Zn-rich reservoir may exist in patients with breast tumours. Zinc isotopic compositions thus show promise as a potential diagnostic tool for the detection of breast tumours. The revealed differences of Zn accumulation in healthy and tumour-adjacent tissues require additional investigation.

Zinc stable isotopes in urine as diagnostic for cancer of secretory organs.

Breast, prostate, and pancreatic cancers alter the zinc (Zn) metabolism. Combined analyses of urinary Zn concentrations [Zn] and Zn stable isotope compositions (δ66Zn)may provide a non-invasive approach for tracing malignancy-induced Zn dyshomeostasis. In this study, we measured [Zn] and δ66Znin urine from prostate (n=22), breast (n=16), and from women with benign breast disease (n=14) and compared those with age-matched healthy controls (22-49 years or 50+ years) and published data for pancreatic cancer (n=17). Our results show that cancer-induced changes are reflected in higher urinary [Zn] and lower urinary δ66Znfor pancreatic and prostate cancer and benign breast disease when compared with healthy controls. For prostate cancer, the progression of low [Zn] and high δ66Zn for patients of low-risk disease toward high [Zn] and low δ66Zn for the higher risk patients demonstrates that [Zn] and δ66Znin urine could serve as a reliable prognostic tool. Urinary excretion of isotopically light Zn by patients with prostatic and pancreatic cancer is probably the result of increased reactive oxygen species in cancerous cells, which limits the scavenging of hydroxyl radicals and thus facilitates the oxidation of metalloproteins with sulfur-rich ligands. Urine from breast cancer patients shows undistinguishable δ66Znto healthy controls, implying that the expression of metalloproteins with sulfur-rich ligands is stronger in breast cancer tissues. In conclusion, urinary δ66Znmay provide a non-invasive diagnostic tool for pancreatic cancer and support disease prognosis for prostate cancer. These findings should translate to comprehensive transverse and longitudinal cohort studies in future.

Iron and zinc stable isotope evidence for open-system high-pressure dehydration of antigorite serpentinite in subduction zones

Subducted serpentinites have the potential to control the exchange of volatile and redox sensitive elements (e.g., Fe, S, C, N) between the slab, the mantle wedge and the deep mantle. Here we examine the mobility of iron and zinc in serpentinite-derived fluids by using their stable isotopes (δ56Fe and δ66Zn) in high-pressure subducted meta-serpentinites from the Cerro del Almirez massif (Spain). This massif preserves a metamorphic front between antigorite (Atg-serpentinite) and antigorite-olivine-orthopyroxene (transitional lithologies) -bearing serpentinites, and chlorite-bearing harzburgite (Chl-harzburgite), displaying granofels, spinifex and fine-grained recrystallized textures. Those rocks were formed at eclogite facies conditions (1.6–1.9 GPa and 680–710 °C). The mean δ56Fe of all the Cerro del Almirez meta-serpentinites (+0.05 ± 0.01‰) is identical within an error to that of primitive mantle (+0.03 ± 0.03‰). A positive correlation between δ56Fe and indices of peridotite protolith fertility (e.g., Al2O3/SiO2) suggests that the δ56Fe values of Cerro del Almirez samples predominantly reflect protolith compositional variations, likely produced by prior episodes of melt extraction. In contrast, the Zn concentrations ([Zn] = 34–67 ppm) and isotope signatures (δ66Zn = +0.18 – +0.55‰) of the Cerro del Almirez samples show a broad range of values, distinct to those of the primitive mantle ([Zn] = 54 ppm; δ66Zn = +0.16 ± 0.06‰). The Atg-serpentinites ([Zn] = 34–46 ppm; δ66Zn = +0.23 ± 0.06‰) display similar [Zn] and δ66Zn values to those of slab serpentinites from other high-pressure meta-ophiolites. Both [Zn] and δ66Zn increase in transitional lithologies ([Zn] = 45–67 ppm; δ66Zn = +0.30 ± 0.06‰) and Chl-harzburgites with granofels ([Zn] = 38–59 ppm; δ66Zn = +0.33 ± 0.04‰) or spinifex ([Zn] = 48–66 ppm; δ66Zn = +0.43 ± 0.09‰) textures. Importantly, Cerro del Almirez transitional lithologies and Chl-harzburgites display abnormally high [Zn] relative to abyssal peridotites and serpentinites (29–45 ppm) and a positive correlation exists between [Zn] and δ66Zn. This correlation is interpreted to reflect the mobilization of Zn by subduction zone fluids at high pressures and temperatures coupled with significant Zn stable isotope fractionation. An increase in [Zn] and δ66Zn from Atg-serpentinite to Chl-harzburgite is associated with an increase in U/Yb, Sr/Y, Ba/Ce and Rb/Ce, suggesting that both [Zn] and δ66Zn record the interaction of the transitional lithologies and the Chl-harzburgites with fluids that had equilibrated with metasedimentary rocks. Quantitative models show that metasediment derived fluids can have isotopically heavy Zn as a consequence of sediment carbonate dissolution and subsequent Zn complexation with carbonate species in the released fluids (e.g., [ZnHCO3(H2O)5+] or [ZnCO3(H2O)3]). Our models further demonstrate that Zn complexation with reduced carbon species cannot produce fluids with heavy δ66Zn signature and hence explain the δ66Zn variations observed in the Chl-harzburgites. The most straightforward explanation for the heavy δ66Zn of the Cerro del Almirez samples is thus serpentinite dehydration accompanied by the open system infiltration of the massif by oxidized, carbonate-rich sediment-derived fluids released during prograde subduction-related metamorphism.

Magnesium and zinc stable isotopes as a new tool to understand Mg and Zn sources in stream food webs

AbstractNon‐traditional stable isotopes of metals were recently shown as new dietary tracers in terrestrial and marine mammals. Whether these metal stable isotopes can be used to understand feeding habits in stream food webs is not known yet. In this study, we explored the potential of stable isotopes of essential Mg (δ26Mg) and Zn (δ66Zn) as a new tool in stream ecology. For this purpose, we determined δ26Mg and δ66Zn values of stream organisms and their potential metal sources in upper and lower reaches of two streams in the Lake Biwa catchment, Central Japan. Our goals were (1) to explore variations in δ26Mg and δ66Zn across organisms of different feeding habits and (2) to understand Mg and Zn sources to stream organisms. Overall, δ26Mg and δ66Zn values of organisms were neither related to each other, nor to δ13C and δ15N values, indicating different elemental sources and factors controlling isotopic fractionation depending on element and taxa. Low δ26Mg values in filter‐feeding caddisfly larvae and small gobies indicated aqueous Mg uptake. Higher δ26Mg values in leaf‐shredding crane fly and grazing mayfly larvae suggested Mg isotopic fractionation during Mg uptake from the diet. While the δ26Mg values of stonefly nymphs reflected those of caddisfly larvae as a potential prey, the highest δ26Mg values found in dobsonfly nymphs can be explained by 26Mg enrichment during maturing. δ66Zn values of caddisfly and mayfly larvae indicated Zn was a mixture of aqueous and dietary available Zn, while higher δ66Zn values in crane fly larvae pointed to Zn isotopic fractionation during Zn uptake from plant litter. δ66Zn values in stonefly and dobsonfly nymphs were often in the range of those of caddisfly larvae as their prey, while dragonfly nymphs and small goby were depleted in 66Zn relative to their dietary Zn sources. We conclude that δ26Mg is a promising indicator to assess Mg sources in stream ecology depending on taxa, while the use of δ66Zn is limited due to the complexity in Zn sources.

High‐Precision Zinc Isotopic Measurement of Certified Reference Materials Relevant to the Environmental, Earth, Planetary and Biomedical Sciences

The zinc (Zn) stable isotope system has emerged as a powerful tool for investigating natural and anthropogenic processes of interest to disciplines ranging from the Earth and planetary sciences to biomedical research. In nature, Zn isotopes typically fractionate (66Zn/64Zn) within the range of −1 and +1 permil (‰), and however, analytical limitations restrict the application of the Zn isotope system. Specifically, there is a lack of well‐characterised matrix‐matched reference materials covering most Zn isotope applications that are essential for validating laboratory performance, particularly given the contamination prone nature of Zn. Furthermore, the increasing demand for analysis of size‐limited materials and sample types displaying small, sub‐permil level Zn isotope variations requires improvements in measurement procedures. To address these limitations, the δ66Zn values of two pure Zn solutions and eighteen reference materials including the previously uncharacterised RGM‐2, BCR‐279, DOLT‐4, DOLT‐5, NASS‐7, SBC‐1, SGR‐1b, MESS‐3 and HISS‐1, and the understudied QLO‐1, SDC‐1, BCR‐414, NASS‐6 and COQ‐1 materials are reported. Furthermore, a 70Zn‐67Zn double‐spike design has been implemented that routinely achieves intermediate measurement precision better than ± 0.02‰. This represents at least a two‐fold improvement when compared with other double‐spike designs, providing a robust platform of δ66Zn values required for quality control procedures.

Postprandial zinc stable isotope response in human blood serum.

In recent years, considerable advances have been made in the field of medical isotope metallomics, but numerous fundamental physiological processes remain to be investigated. Past studies report that blood serum Zn concentrations decrease by between about 10 and 25%, depending on the size of meal, approximately three hours postprandially (i.e. after eating), before returning to baseline values if no meals are consumed over the following four to five hours. Nine participants were recruited for this study to investigate whether this postprandial Zn concentration decrease is accompanied by a stable isotope response. A baseline serum sample was collected from participants in the morning after overnight fasting. A 576 kcal meal was then provided and additional serum samples were taken 90 and 180 minutes post-meal to coincide with the postprandial response. Serum Zn concentrations decreased postprandially by an average of 21 ± 9% (1SD), but this was not accompanied by a change in stable Zn isotope composition (mean Δ66Zn180-minute-baseline = 0.01 ± 0.09‰, 2SD). We propose that hemodilution and the rapid, efficient postprandial transfer of albumin-bound Zn from serum to the liver and pancreas is responsible for the lack of postprandial serum Zn isotopic response. These results indicate that studies examining solely the distribution of Zn isotopes in serum may obtain samples without considering timing of the most recent meal. However, future studies seeking to compare serum Zn concentrations with δ66Zn values should draw blood samples in the morning after overnight fasting.