Zn Stable Isotope Research Articles

Carbonate Transfer during the Onset of Slab Devolatilization: New Insights from Fe and Zn Stable Isotopes

Long-term carbon cycling is a subject of recent controversy as new mass balance calculations suggest that most carbon is transferred from the slab to the mantle wedge by fluids during subduction, limiting the efficiency of carbon recycling to the deep mantle. Here, we examine the large scale mobility of carbon during subduction using new isotopic tracers sensitive to H–C–O–S–Cl fluids, namely iron and zinc stable isotopes, in samples interpreted to represent residual slab (Queyras, Western Alps) and sub-arc mantle (Kohistan, Himalaya). We show that during subduction there are several stages of carbonate precipitation and dissolution at metasomatic interfaces between metasedimentary and ultramafic rocks in the slab. During the early stages of subduction, before the slab reaches the 300–400C isotherms, the infiltration of sediment-derived fluids into ultramafic lithologies enhances carbonate precipitation in antigorite-bearing serpentinites. Carbonate storage in serpentinites, therefore, acts as a temporary reservoir of carbon in subduction zones. This episode is accompanied by a decrease in serpentinite iron isotope composition (d56Fe), due to interaction with low-d56Fe sediment-derived fluids, and an increase in the concentrations of fluid-mobile elements (e.g. B, Li, As). At higher temperatures (>400C), carbonate is leached from the serpentinites by fluids. This is accompanied by a decrease in serpentinite zinc isotope composition (d66Zn) which we interpret as the release of a carbonate-bearing fluid with an isotopically heavy d66Zn signature. Thermodynamic modelling shows that the sudden change in fluid carbon mobility is due to a decrease in the aCO2 of the fluids released during slab prograde metamorphism, which shifts from sediment- to serpentinite-dominated dehydration. This demonstrates that slab fluids bearing oxidized carbon (e.g. CO2), associated with isotopically light Fe, heavy Zn and fluid-mobile elements, can be released before the slab reaches eclogite facies P-T conditions. These observations provide strong evidence for the mobility of carbon in fluids during the early stages of subduction. Moreover, the fluids released will act as a potential metasomatic agent for the fore-arc mantle (or slab/mantle interface). The observation of carbonate-bearing metamorphic veins in the Himalayan sub-arc mantle with complementary light d56Fe and heavy d66Zn signatures provides further support for the large scale transfer of both sulphate- and carbonate-bearing fluids during the early stages of subduction. This suggests that the fore-arc may have an important role in delivering water, sulfur and carbon to the source of arc-magmas.

Geochemistry and isotope composition (Sr, Pb, δ66Zn) of Vulcano fumaroles (Aeolian Islands, Italy)

We present and discuss temperatures, major and trace element gas geochemistry, radiogenic isotopes (Pb, Sr) and the first Zn isotope data of fumarole condensates and altered rocks from the Vulcano fumarolic field. The fumaroles of the La Fossa cone, sampled on 5th May 2015, have temperatures ranging between 233 and 427 °C. They plot compositionally on the mixing trend between the magmatic and hydrothermal end-members defined by previous studies, but are strongly displaced towards the hydrothermal component. Correlations of radiogenic (Sr, Pb) and stable isotopes of Zn with δ13CCO2 and several trace elements of the fumarolic acid condensates support mixing between the above mentioned distinct (magmatic and hydrothermal) fluids. The magmatic end-member has a less radiogenic Sr (87Sr/86Sr ~0.7045) and heavier Zn isotope composition (δ66Zn ~0.3‰). The hydrothermal fluid end-member has a more radiogenic 87Sr/86Sr signature (>0.7055), which could be due to leaching of radiogenic Sr from the crystalline basement rocks or reflect seawater Sr. It is also characterized by lighter Zn isotope composition (δ66Zn < −0.3), most likely reflecting equilibrium fractionation of Zn isotopes during precipitation of sphalerite (ZnS) from the hydrothermal fluid. Nonetheless, some scatter in the correlation trends suggests either the involvement of additional (subordinate) source(s) or temporal variations in isotopic and chemical compositions of the two above end-members.Pb isotope compositions of the fumaroles sampled in this study show a shift towards less radiogenic values compared to pre-2001 fumaroles. This could indicate either a change in the hydrothermal circulation pattern (leading to leaching of rocks with different isotopic compositions) or the involvement of a new, isotopically distinct, magmatic fluid.The alteration zones around the fumarole vents are also characterized by systematic correlations of Pb and Zn isotopes with major and trace elements. We interpret these as the result of the addition onto the substratum volcanic rock of Pb and Zn from the fumaroles. Zn isotope signatures of the alteration zones are significantly heavier than those of the corresponding fumaroles (δ66Zn = 0.3–1.6) probably due to equilibrium fractionation occurring during sphalerite precipitation at the vent discharge.

The influence of the double spike proportion effect on stable isotope (Zn, Mo, Cd, and Sn) measurements by multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS)

This study investigates the double spike (DS) proportion effect on measurements of stable Zn, Mo, Cd, and Sn isotopes by multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS).

The influence of weathering and soil organic matter on Zn isotopes in soils

Zinc is an essential micronutrient that is ultimately released during mineral weathering. In soils, organic matter plays a key role in influencing Zn partitioning and therefore on Zn biogeochemical cycling. Soil organic matter is partitioned between carbon that is more readily available for decomposition by microorganisms, and more stable carbon transiently preserved from decomposition. The role of the stable pool of soil organic matter on Zn biogeochemical cycling remains poorly understood. The pool of stable carbon is controlled by combination with mineral constituents or is material that is intrinsically resistant to decomposition. The Zn stable isotopes are fractionated by interactions between Zn and soil mineral and organic constituents. This study reports the Zn isotope composition of five Icelandic soil profiles derived from the same parent basalt and characterized by contrasting degrees of weathering and organic matter content (δ66Zn=+0.10±0.05 to +0.35±0.02‰), the distribution of reactive mineral constituents available to form associations with soil organic matter, and the amount of stable organic carbon. Throughout these soils, the δ66Zn isotope variations are little influenced by mineral constituents, but rather by soil organic matter content. These data suggest that a combination of organic matter accumulation and Zn loss by leaching is required to explain the observed decrease in Zn concentration in soils and lighter soil δ66Zn with increasing organic carbon content. These results suggest that the presence of stable organic carbon in soils provides a pool of light Zn, attributed to the Zn isotope signature of organic matter partially preserved from decomposition. Crucially, this stable organic carbon pool may also contribute to the formation of the light Zn isotope sink reported in organic-rich marine sediments, a key output required to explain the oceanic mass balance of Zn isotopes.

Supplemental Zinc Decreases Fractional Zinc Absorption and Increases Lean Tissue Mass among Vietnamese Children with Tuberculosis

Childhood tuberculosis (TB) is a major health concern in Vietnam. Dietary Zn absorption is greater in children recovering from TB, possibly due to increased demand of Zn for immune function. Zn supplementation, therefore, may improve the effectiveness of TB treatment. Our objective was to determine changes in Zn homeostasis in response to Zn supplements among children admitted for treatment of TB at the National Lung Hospital in Hanoi, Vietnam.After baseline, children matched by sex were randomized to 10 mg Zn/d (n=10) or placebo (n=11) for the first 2 mo of TB treatment. At baseline and after 2 mo, fractional Zn absorption (FZA) and exchangeable Zn pool size (EZP) were determined using Zn stable isotopes during an 8 d controlled‐diet metabolic study. After each of 3 meals on d 2, the child received 0.33 mg 67Zn orally and, 1 h following dinner, 0.1 mg 70Zn intravenously. FZA was determined from urinary Zn tracer‐tracee ratios (TTRs) in samples collected 5–7 d post isotope administration. EZP was estimated from the y‐intercept of the log‐transformed linear regression of urinary 70Zn TTRs. Height, weight, body mass index (BMI), mid‐upper arm circumference (MUAC), triceps skinfold thickness (TSK), and subscapular skinfold thickness (SSK) were determined. Mid‐upper arm muscle area (MUAM) and mid‐upper arm fat area (MUAF) were derived from MUAC and TSK.21 children 9 to 15 y, 11 male and 10 female, enrolled. 14 had pulmonary TB. Height‐ and BMI‐for‐age z‐scores were −1.2 (−1.9, −0.6) and −1.7 (−2.4, −1.0), respectively. After 2 mo, controlling for baseline values, FZA was significantly lower among Zn‐supplemented children vs. placebo: 25.8% (21.5, 30.1%) vs. 32% (27.7, 36.3%), p &lt; 0.05. EZP tended to be higher with Zn compared with placebo: 83.3 mg (69.2, 97.5 mg) vs. 70.1 mg (55.2, 85 mg), p = 0.19 (NS). No differences in weight, height, or BMI were observed. MUAC was higher among Zn supplemented, 21.1 cm (20.2, 22 cm), vs. placebo, 19.5 cm (18.7, 20.3 cm), p &lt; 0.05. MUAM was also higher among Zn supplemented, 19.6 cm2 (17.3, 22.2 cm2) vs. 15.7 cm2 (13.9, 17.6 cm2) placebo, p &lt; 0.05.In sum, 10 mg Zn/d led to a homeostatic response and improved lean tissue gain in Vietnamese children with TB, and thus should further be evaluated as part of their treatment. Given the sensitivity of MUAC and MUAM, these indicators should be included for monitoring the TB recovery process in future studies.Support or Funding InformationInternational Atomic Energy Agency, Contract 15859

Assessing the Dietary Bioavailability of Metals Associated with Natural Particles: Extending the Use of the Reverse Labeling Approach to Zinc.

We extend the use of a novel tracing technique to quantify the bioavailability of zinc (Zn) associated with natural particles using snails enriched with a less common Zn stable isotope. Lymnaea stagnalis is a model species that has relatively fast Zn uptake rates from the dissolved phase, enabling their rapid enrichment in 67Zn during the initial phase of labeling. Isotopically enriched snails were subsequently exposed to algae mixed with increasing amounts of metal-rich particles collected from two acid mine drainage impacted rivers. Zinc bioavailability from the natural particles was inferred from calculations of 66Zn assimilation into the snail's soft tissues. Zinc assimilation efficiency (AE) varied from 28% for the Animas River particles to 45% for the Snake River particles, indicating that particle-bound, or sorbed Zn, was bioavailable from acid mine drainage wastes. The relative binding strength of Zn sorption to the natural particles was inversely related to Zn bioavailability; a finding that would not have been possible without using the reverse labeling approach. Differences in the chemical composition of the particles suggest that their geochemical properties may influence the extent of Zn bioavailability.

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-characterised stable 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 (which denotes the deviation of the 66Zn/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 isotope analyses. This endorsement is reinforced by (i) the close agreement of our Zn isotope data for two of the samples (bovine 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.

Multi-Element Profiling Analyses of Symbiotic Zooxanthellae and Soft Tissues in a Giant Clam (Tridacna crocea) Living in the Coral Reefs and Their Intake Process of Zn and Cd

Abstract Approximately 20 major-to-ultratrace elements in each organ (mantle, muscle, liver, kidney) of a giant clam, Tridacna crocea, and 16 elements in symbiotic zooxanthellae were determined by ICP-AES, ICP-MS, and CHN coder. The biogeochemical properties of T. crocea were then investigated using multi-element profiling analyses. The values for most elements were the highest in the kidney among all organs. However, the concentrations of Mn, Co, Ni, Zn, Se, Ag, Cd, and Pb in the mantle were higher than those in the muscle and liver. Therefore, these results indicate that most trace elements taken in by T. crocea through zooxanthellae may finally accumulate in the kidney. Moreover, 14 trace elements in zooxanthellae were present in the concentration range from 181 µg g−1 for Zn to 0.58 µg g−1 for U based on dry weight after isolating zooxanthellae from the mantle. The concentrations of some trace metals in zooxanthellae were relatively higher than those in other organs except for the kidney. These results suggest that zooxanthellae could play an important role in extracting trace metals from seawater and providing them to the soft tissues in giant clams. The concentrations of Mn, Co, Ni, Zn, As, Se, Ag, and Cd in zooxanthellae were almost equal to or higher than those reported in literature. In particular, Mn, Co, Zn, and Cd were present in concentrations higher than those in whole soft tissues of T. crocea by factors of at least 105. In addition, we investigated the intake route of Zn and Cd from seawater for T. crocea using enriched stable isotopes of Zn and Cd. These results suggest that zooxanthellae could play an important role for the intake of trace metals such as Zn and Cd from seawater and for providing them to soft tissues in the giant clam.

Zinc Homeostasis and isotopic fractionation in plants: a review

Recent advances in mass spectrometry have demonstrated that higher plants discriminate stable Zn isotopes during uptake and translocation depending on environmental conditions and physiological status of the plant. Stable Zn isotopes have emerged as a promising tool to characterize the plants response to inadequate Zn supply. The aim of this review is to build a comprehensive model linking Zn homeostasis and Zn isotopic fractionation in plants and advance our current view of Zn homeostasis and interaction with other micronutrients. The distribution of stable Zn isotopes in plants and the most likely causes of fractionation are reviewed, and the interactions with micronutrients Fe, Cu, and Ni are discussed. The main sources of Zn fractionation in plants are i) adsorption, ii) low- and high-affinity transport phenomena, iii) speciation, iv) compartmentalization, and v) diffusion. We propose a model for Zn fractionation during uptake and radial transport in the roots, root-to-shoot transport, and remobilization. Future work should concentrate on better understanding the molecular mechanisms underlying the fractionations as this will be the key to future development of this novel isotope system. A combination of stable isotopes and speciation analyses might prove a powerful tool for plant nutrition and homeostasis studies.

Zinc and lead isotope signatures of the Zhaxikang Pb[sbnd]Zn deposit, South Tibet: Implications for the source of the ore-forming metals

Stable Zn isotopes may be applied to trace the source of ore-forming metals in various types of PbZn deposits. To test this application, Zn and Pb isotope systematics for sulfides and associated basement rocks as well as FeMn carbonates (gangue) from the Zhaxikang PbZn deposit in South Tibet have been analyzed. The basement in this region includes metamorphosed mafic to felsic rocks (dolerite, quartz diorite, rhyolite porphyry, pyroclastics and porphyritic monzogranite). These rocks have similar δ66Zn values of 0.33 to 0.37‰, with an average value of 0.36±0.03‰ (2σ), except for the more evolved porphyritic monzogranite that has a heavier value of 0.49‰. FeMn carbonates are present as hydrothermal veins and were probably precipitated from magmatic fluids. They have an average δ66Zn value of 0.27±0.05‰, which is slightly lighter than the basement rocks, possibly representing δ66Zn isotopic compositions of the hydrothermal fluids. Sphalerite and galena have similar Zn isotopic compositions with δ66Zn ranging from 0.03 to 0.26‰ and 0.21 to 0.28‰, respectively. Considering the Zn isotope fractionation factor between sphalerite and fluids of −0.2‰ at ~300°C as reported in literature, hydrothermal fluids from which these sulfides precipitated will have δ66Zn values of ca. 0.39±0.10‰, which are consistent with the values of basement rocks and the FeMn carbonates. This similarity supports a magmatic-hydrothermal origin of the Zhaxikang PbZn deposit. Both Pb and S isotopes in these sphalerite and galena show large variations and are consistent with being derived from a mixture of basement and sedimentary rocks in various proportions. Zn isotopic compositions of the sulfides significantly extend the range of regional basement rocks, suggesting that sedimentary rocks (e.g., shales) are also a significant source of Zn. However, the Zn isotopic compositions of sphalerite and galena differ from those of marine carbonates and those of typical SEDEX-type deposits (e.g. Kelley et al., 2009), confirming a magmatic-hydrothermal model. Combined with regional geological observations and the age constraints of ~20Ma (Zheng et al., 2012, 2014), the results of our investigation indicate that the Zhaxikang PbZn deposit is most likely a magmatic-hydrothermal deposit.

Molybdenum and zinc stable isotope variation in mining waste rock drainage and waste rock at the Antamina mine, Peru

The stable isotope composition of molybdenum (Mo) and zinc (Zn) in mine wastes at the Antamina Copper–Zn–Mo mine, Peru, was characterized to investigate whether isotopic variation of these elements indicated metal attenuation processes in mine drainage. Waste rock and ore minerals were analyzed to identify the isotopic composition of Mo and Zn sources, namely molybdenites (MoS2) and sphalerites (ZnS). Molybdenum and Zn stable isotope ratios are reported relative to the NIST-SRM-3134 and PCIGR-1 Zn standards, respectively. δ98Mo among molybdenites ranged from −0.6 to +0.6‰ (n=9) while sphalerites showed no δ66Zn variations (0.11±0.01‰, 2 SD, n=5). Mine drainage samples from field waste rock weathering experiments were also analyzed to examine the extent of isotopic variability in the dissolved phase. Variations spanned 2.2‰ in δ98Mo (−0.1 to +2.1‰) and 0.7‰ in δ66Zn (−0.4 to +0.3‰) in mine drainage over a wide pH range (pH2.2–8.6). Lighter δ66Zn signatures were observed in alkaline pH conditions, which was consistent with Zn adsorption and/or hydrozincite (Zn5(OH)6(CO3)2) formation. However, in acidic mine drainage Zn isotopic compositions reflected the value of sphalerites. In addition, molybdenum isotope compositions in mine drainage were shifted towards heavier values (0.89±1.25‰, 2 SD, n=16), with some overlap, in comparison to molybdenites and waste rock (0.13±0.82‰, 2 SD, n=9). The cause of heavy Mo isotopic signatures in mine drainage was more difficult to resolve due to isotopic heterogeneity among ore minerals and a variety of possible overlapping processes including dissolution, adsorption and secondary mineral precipitation. This study shows that variation in metal isotope ratios are promising indicators of metal attenuation. Future characterization of isotopic fractionation associated to key environmental reactions will improve the power of Mo and Zn isotope ratios to track the fate of these elements in mine drainage.

A node-localized transporter OsZIP3 is responsible for the preferential distribution of Zn to developing tissues in rice.

Developing tissues such as meristem with low transpiration require high Zn levels for their active growth, but the molecular mechanisms underlying the preferential distribution to these tissues are poorly understood. We found that a member of the ZIP (ZRT, IRT-like protein), OsZIP3, showed high expression in the nodes of rice (Oryza sativa). Immunostaining revealed that OsZIP3 was localized at the xylem intervening parenchyma cells and xylem transfer cells of the enlarged vascular bundle in both basal and upper nodes. Neither OsZIP3 gene expression nor encoded protein was affected by either deficiency or toxic levels of Zn. Knockdown of OsZIP3 resulted in significantly reduced Zn levels in the shoot basal region containing the shoot meristem and elongating zone, but increased Zn levels in the transpiration flow. A short-term experiment with the (67) Zn stable isotope showed that more Zn was distributed to the lower leaves, but less to the shoot elongating zone and nodes in the knockdown lines compared with the wild-type rice at both the vegetative and reproductive growth stages. Taken together, OsZIP3 located in the node is responsible for unloading Zn from the xylem of enlarged vascular bundles, which is the first step for preferential distribution of Zn to the developing tissues in rice.

Dynamics of Zn in an urban wetland soil–plant system: Coupling isotopic and EXAFS approaches

Plants play a key role in the stabilization of metals in contaminated environments. Studies have been performed on Zn uptake and storage mechanisms, mainly for Zn hyperaccumulating plants, though less is known about Zn stabilization in the rhizosphere of non-accumulating plants. This study was focused on the dynamics of Zn in a whole soil–litter–plant system and the processes controlling Zn mobilization and stabilization. The site studied was an infiltration basin receiving urban stormwater, in which Phalaris arundinacea (reed canary grass) developed spontaneously. A combination of chemical extractions (CaCl2, DTPA), EXAFS spectroscopy and Zn stable isotope measurements was applied for the water inlet, soil, plant organs and decaying biomass. Zn speciation changed from the water inlet to the soil. In the soil, Zn was present as Zn-layered double hydroxide (Zn-LDH), tetrahedral and octahedral sorbed Zn species. The formation of Zn-LDH participates in Zn stabilization. Tetrahedral Zn species, which were partly DTPA exchangeable, were enriched in heavy isotopes, whereas octahedral Zn (Zn-LDH and sorbed species) were enriched in light isotopes. Based on a linear model between δ66Zn and Zn speciation, δ66Zn for pure tetrahedral and octahedral end-members were estimated at ca. 0.33‰ and 0.04‰, respectively. In the plant, a mixture of octahedral Zn (attributed to aqueous Zn-organic acid complexes present in the symplasm), and tetrahedral Zn (attributed to apoplasmic Zn-cell wall complexes) was observed in all organs. Large enrichment in light isotopes from the soil to the plant Δ66Zn (of ca. −0.6‰) was observed. The stem was enriched in light isotopes versus roots and, to a lesser extent, versus leaves. The results suggest that Zn was taken up via a low-affinity transport system and that Zn was sequestrated in the stem symplasm after transit through leaves. Finally, intense Zn exchanges were observed between the decaying biomass and the soil, with the sorption of heavy Zn from the soil to cell wall remains and release of light Zn to the soil. Overall, this study provides a complete overview of Zn cycling in an urban wetland soil–plant system, and describes several changes in Zn speciation with Zn isotopic fractionation processes in a complex system.

Tracing contamination sources in soils with Cu and Zn isotopic ratios

Copper (Cu) and zinc (Zn) are naturally present and ubiquitous in soils and are important micronutrients. Human activities contribute to the input of these metals to soils in different chemical forms, which can sometimes reach a toxic level for soil organisms and plants. Isotopic signatures could be used to trace sources of anthropogenic Cu and Zn pollution. The aim of this paper is to determine whether it is possible to identify (i) Cu and Zn contamination in soils and their sources, on the basis of their isotopic signatures, and (ii) situations that are a priori favorable or not for tracing Cu and Zn pollution using the isotopic approach. Therefore, we compiled data from the literature on Cu and Zn isotopes in soils, rocks and pollutants and added to this database the results of our own research. As only a few studies have dealt with agricultural contamination, we also studied a soil toposequence from Brittany, France, that experienced spreading of pig slurry for tens of years. In the surface horizons of the natural soils, the δ65Cu values vary from −0.15 to 0.44‰ and the δ66Zn from −0.03 to 0.43‰. Furthermore, vertical variations along soil profiles range from −0.95 to 0.44‰ for δ65Cu and from −0.53 to 0.64‰ for δ66Zn values. We concluded that pedogenetic processes can produce isotopic fractionation, yet, it is not always discernible and can be overprinted by an exogenous isotopic signature. Furthermore, some contaminants are enriched in heavy Cu or in light Zn compared to the rock or soil, but no generalization can be made. The anthropogenic inputs can be identified based on stable Cu and Zn isotope ratios if the isotope ratios of the sources are different from those of the soil, which needs to be tested for each individual case.

Impact of root-induced mobilization of zinc on stable Zn isotope variation in the soil-plant system.

Stable Zn isotopes are increasingly used to trace the source of metal pollution in the environment and to gain a better understanding of the biogeochemical cycle of Zn. In this work, we investigated the effect of plants on Zn isotope fractionation in the soil-plant system of the surface horizon of two Zn-rich Technosols (pH 6.73-7.51, total Zn concentration = 9470-56600 mg kg(-1)). In a column experiment, the presence of Agrostis capillaris L. significantly increased the mobilization of Zn from soil to leachate, predominantly as a result of root-induced soil acidification. The zinc isotope compositions of plants and leachates indicated that the Zn uptake by A. capillaris did not fractionate Zn isotopes as compared to the leachates. Within the plant, heavier Zn isotopes were preferentially retained in roots (Δ66Znroot - shoot=+0.24 to +0.40 ‰). More importantly, the Zn released in leachates due to root-induced mobilization was isotopically heavier than the Zn released in the absence of plants (Δ66Zn=+0.16 to +0.18 ‰). This indicates that the rhizosphere activity of A. capillaris mobilized Zn from another pool than the one that spontaneously releases Zn upon contact with the percolating solution. Mobilization of Zn by the roots might thus exert a stronger influence on the Zn isotope composition in the soil solution than the Zn uptake by the plant. This study highlights the key role of the rhizosphere activity in Zn release in soil and demonstrates that stable Zn isotopes provide a useful proxy for the detection of Zn mobilization in soil-plant systems.

Isotopic fractionation of Zn in tomato plants suggests the role of root exudates on Zn uptake

Aims Phytosiderophore-chelated Zn can be absorbed in grasses. Root exudates of dicotyledonous plants can mobilize soil Zn but it is unclear how this affects Zn bioavailability. Stable Zn isotope shifts can indicate exudate-facilitated Zn uptake, since complexation of Zn2+ by organic ligands in solution yields a small, but detectable, enrichment of the heavy Zn isotope due to thermodynamic fractionation.

Isotopes Trace Biogeochemistry and Sources of Cu and Zn in an intertidal soil

River floodplain soils are sinks and potential sources for toxic trace metals like Cu and Zn. We hypothesize that stable Cu and Zn isotope ratios reflect both the mobilization and the sources of metals. We determined the soil properties, the concentrations and partitioning of Cu and Zn, and variations in δ65Cu and δ66Zn values in a core obtained from an Aquic Udifluvent developed on a freshwater intertidal mudflat of the River Elbe, Germany. The core was sampled at 2 cm intervals to a depth of 34 cm, which corresponds to approximately 9 yr of sedimentation. Elevated concentrations of Cu (up to 320 μg g−1) and Zn (up to 2080 μg g−1) indicated anthropogenic pollution. At the time of sampling the redox conditions changed from oxic (Eh 200 to 400 mV, above 22 cm deep) to strongly anoxic conditions (-100 to -200 mV, below 22 cm deep). The δ65Cu values varied systematically with depth (from -0.02 to 0.16‰) and were correlated with the Fe, C, and N concentrations. Although pre-depositional variations cannot be ruled out, the systematic variation with depth suggests post-sedimentation fractionation of δ65Cu in response to seasonally variable organic matter deposition and redox conditions. In contrast, the δ66ZnIRMM values were uniform (from -0.07 to 0.01‰) throughout the core, indicating that the Zn isotopes did not significantly fractionate after deposition and that the Zn sources were homogeneous throughout the sedimentation.

Toxicological applications of cryogenic laser ablation inductively coupled plasma time of flight mass spectrometry (CLA-ICP-TOF-MS)

The analysis of acid digested bulk tissue samples by ICP-MS is a primary method for toxicologists when trying to characterize the uptake and storage of a trace metal by an organism. This approach is sensitive, reliable and reproducible but requires the homogenization of the tissue for analysis. This procedure does not provide any information on the distribution of the analyte of interest within the tissue sample. Sub-sampling is a possible alternative method for preserving distribution data but in many cases sub-sampling on the scale necessary for useful information is not an option due to sample size limitations. By coupling a laser ablation system equipped with a cryogenic cell to an Inductively Coupled Plasma Mass Spectrometer (CLA-ICP-MS), it is possible to achieve high-resolution trace metal distribution data on toxicological tissue samples. A cryo-cell is critical for proper ablation of soft tissue samples by LA-ICP-MS. The system used for the work presented is a commercially available cryo cell from GeoMed Analytical capable of temperatures as low as −30 °C, coupled to a GBC Scientific ICP-Time of Flight-MS (ICP-TOF-MS). The speed of the TOF system is an ideal platform for the analysis of the transient signal produced by laser ablation and has detection limits that are comparable to traditional ICP-MS (i.e. low ppb range). This system is suitable for the ablation of a range of tissues with a spatial resolution of 25 microns for most elements. Results will be presented that identify the optimal ablation settings for obtaining accurate and precise Zn and Cu isotope ratios in tissue samples. A demonstration of the potential toxicological application of the CLA-ICP-TOF-MS system using a Zn stable isotope tracer in the earthworm Lumbricus terrestris will also be presented.

Low-blank chemistry for Zn stable isotope ratio determination using extraction chromatographic resin and double spike-multiple collector-ICP-MS

A new low-blank Zn separation method employing an extraction chromatographic resin using Aliquat 336 (commercially available as TEVA resin) has been developed for Zn isotope composition determination by double spike-multiple collector-ICP-MS. The silicate sample solution containing 0.1 μg Zn in 0.5 mol L−1 HBr containing 0.15% ascorbic acid (AA) is passed through a 1 mL column with 0.33 mL TEVA resin. While Zn is absorbed, major elements are eluted with 0.5 mol L−1 HBr with AA. Afterwards, Zn was recovered with 2 mol L−1 HNO3. Recovery yield using silicate samples was 96.7 ± 6.8% (n = 10) and total blank was 0.05 ng (n = 6). The blank level is from 1/300 to 1/20 of previous studies, meaning 0.1 μg of Zn is sufficient for analysis. The 67Zn–70Zn double spike method was used in MC-ICP-MS. δ66Zn of three USGS standard silicate reference materials (BHVO-1, AGV-1 and PCC-1) and seven GSJ silicate reference materials (JB-1, -2, -3, JA-1, -2, -3 and JP-1) were determined. Reproducibility of δ66Zn of the total silicates was 0.19‰ (2SD). δ66Zn of three carbonaceous chondrites (Orgueil, Murchison and Allende) were also determined and compared with those of references.

Fractionation of Stable Zinc Isotopes in the Field-Grown Zinc Hyperaccumulator Noccaea caerulescens and the Zinc-Tolerant Plant Silene vulgaris

Stable Zn isotope signatures offer a potential tool for tracing Zn uptake and transfer mechanisms within plant-soil systems. Zinc isotopic compositions were determined in the Zn hyperaccumulator Noccaea caerulescens collected at a Zn-contaminated site (Viviez), a serpentine site (Vosges), and a noncontaminated site (Sainte Eulalie) in France. Meanwhile, a Zn-tolerant plant ( Silene vulgaris ) was also collected at Viviez for comparison. While δ(66)Zn was substantially differentiated among N. caerulescens from the three localities, they all exhibited an enrichment in heavy Zn isotopes of 0.40-0.72‰ from soil to root, followed by a depletion in heavy Zn from root to shoot (-0.10 to -0.50‰). The enrichment of heavy Zn in roots is ascribed to the transport systems responsible for Zn absorption into root symplast and root-to-shoot translocation, while the depletion in heavy Zn in shoots is likely to be mediated by a diffusive process and an efficient translocation driven by energy-required transporters (e.g., NcHMA4). The mass balance yielded a bulk Zn isotopic composition between plant and soil (Δ(66)Zn(plant-soil)) of -0.01‰ to 0.63‰ in N. caerulescens , indicative of high- and/or low-affinity transport systems operating in the three ecotypes. In S. vulgaris , however, there was no significant isotope fractionation between whole plant and rhizosphere soil and between root and shoot, suggesting that this species appears to have a particular Zn homeostasis. We confirm that quantifying stable Zn isotopes is useful for understanding Zn accumulation mechanisms in plants.