Imperial College London

Professor Mark Rehkämper

Faculty of EngineeringDepartment of Earth Science & Engineering

Professor of Isotope Geochemistry
 
 
 
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Contact

 

+44 (0)20 7594 6391markrehk Website

 
 
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Location

 

450Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

189 results found

Packman H, Little SH, Baker AR, Bridgestock L, Chance RJ, Coles BJ, Kreissig K, Rehkämper M, van de Flierdt Tet al., 2022, Tracing natural and anthropogenic sources of aerosols to the Atlantic Ocean using Zn and Cu isotopes, Chemical Geology, ISSN: 0009-2541

Anthropogenic activities have significantly enhanced atmospheric metal inputs to the ocean, which has potentially important consequences for marine ecosystems. This study assesses the potential of Zn and Cu isotope compositions to distinguish between natural and anthropogenic atmospheric inputs of these metals to the surface ocean. To this end, the isotopic compositions of Zn and Cu in aerosols collected from the eastern tropical Atlantic Ocean on the GEOTRACES GA06 cruise are examined. Enrichment factors and fractional solubility measurements indicate the presence of a significant anthropogenic component in the aerosols collected furthest from the North African dust plume for both Zn and Cu. The mean δ65CuNIST SRM 976 for the fully digested aerosols is +0.07 ± 0.39 ‰ (n = 9, 2 SD), which is indistinguishable from the lithogenic value, and implies that Cu isotopes are not an effective tracer of aerosol sources in this region. The mean δ66ZnJMC-Lyon value for the aerosols that underwent a total digestion is +0.17 ± 0.22 ‰ (n = 11, 2 SD). The aerosols leached with ammonium acetate have similar Zn isotope compositions, with a mean of +0.15 ± 0.16 ‰ (n = 7, 2 SD). The aerosols were collected in a region with prevalent mineral dust but, despite this, exhibit isotopically lighter Zn than lithogenic Zn with δ66Zn ≈ +0.3 ‰. When coupled with the previously published Pb isotope data, the aerosols exhibit coupled Zn-Pb isotope systematics that are indicative of mixing between mineral dust (δ66Zn = +0.28 ‰ and 206Pb/207Pb = 1.205) and anthropogenic emissions (δ66Zn = −0.22 ‰ and 206Pb/207Pb = 1.129). This demonstrates the potential of Zn isotopes to trace atmospheric Zn inputs from anthropogenic sources to the surface ocean.

Journal article

Hunt AC, Theis KJ, Rehkamper M, Benedix GK, Andreasen R, Schonbachler Met al., 2022, THE DISSIPATION OF THE SOLAR NEBULA CONSTRAINED BY IMPACTS AND CORE COOLING IN PLANETESIMALS., 85th Annual Meeting of the Meteoritical-Society, Publisher: WILEY, ISSN: 1086-9379

Conference paper

Braukmueller N, Funk C, Abouchami W, Pickard HJ, Rehkaemper M, Bragagni A, Galer S, Muenker C, Becker H, Wombacher Fet al., 2022, Moderately volatile element fractionation in chondrites constrained by isotope dilution and Cd and Zn stable isotope data, 85th Annual Meeting of the Meteoritical Society (2022), Publisher: Wiley, ISSN: 1086-9379

Conference paper

Martins R, Kuthning S, Coles BJ, Kreissig K, Rehkaemper Met al., 2022, Nucleosynthetic Zn anomalies reveal the origin of Earth’s volatiles, 85th Annual Meeting of the Meteoritical Society (2022), Publisher: Wiley, ISSN: 1086-9379

Conference paper

Hunt AC, Theis KJ, Rehkamper M, Benedix GK, Andreasen R, Schönbächler Met al., 2022, The dissipation of the solar nebula constrained by impacts and core cooling in planetesimals, Nature Astronomy, Vol: 6, Pages: 812-818, ISSN: 2397-3366

Rapid cooling of planetesimal cores has been inferred for several iron meteorite parent bodies on the basis of metallographic cooling rates, and linked to the loss of their insulating mantles during impacts. However, the timing of these disruptive events is poorly constrained. Here, we used the short-lived 107Pd–107Ag decay system to date rapid core cooling by determining Pd–Ag ages for iron meteorites. We show that closure times for the iron meteorites equate to cooling in the time frame ~7.8–11.7 Myr after calcium–aluminium-rich inclusion formation, and that they indicate that an energetic inner Solar System persisted at this time. This probably results from the dissipation of gas in the protoplanetary disk, after which the damping effect of gas drag ceases. An early giant planet instability between 5 and 14 Myr after calcium–aluminium-rich inclusion formation could have reinforced this effect. This correlates well with the timing of impacts recorded by the Pd–Ag system for iron meteorites.

Journal article

Poole GM, Stumpf R, Rehkämper M, 2022, New methods for determination of the mass-independent and mass-dependent platinum isotope compositions of iron meteorites by MC-ICP-MS, Journal of Analytical Atomic Spectrometry, Vol: 37, Pages: 783-794, ISSN: 0267-9477

Improved methods are presented for the separation of platinum from iron meteorites and subsequent analyses of both mass-independent and mass-dependent Pt isotope compositions of iron meteorites by multiple collector ICP-MS. The procedures are optimised for sample throughput and feature improvements in yield and the reduction of constituents that produce spectral interferences and matrix effects. The performance of the methods is demonstrated by replicate analyses of terrestrial reference materials and eight iron meteorites from the IC and IVB groups. The pilot iron meteorite analyses confirm previous work, which demonstrates that the Pt isotope compositions of iron meteorites are particularly sensitive to alteration by neutron capture reactions induced by exposure to galactic cosmic rays (GCR). It is shown that the mass-independent Pt isotope data obtained with the new methods are suitable for accurate correction of correlated cosmogenic isotope effects for other isotope systems in the same sample aliquots. The methods for the measurement of mass-dependent Pt isotope compositions (δ198Pt) employ a robust double spike approach. The accurate determination of δ198Pt values for iron meteorites requires, however, that possible cosmogenic isotope effects from GCR exposure are monitored and appropriately corrected on a sample aliquot specific basis. A robust approach for such corrections using the mass-independent Pt isotope data collected with the new methods is shown to provide accurate results for iron meteorites with variable compositions and GCR exposure histories. Initial results obtained for eight IC and IVB iron meteorites reveal both within- and between-group variations in δ198Pt values, which indicate that such analyses may provide novel constraints for studies of planetary processes.

Journal article

Gomez-Gonzalez MA, Rehkamper M, Han Z, Ryan MP, Laycock A, Porter AEet al., 2022, ZnO Nanomaterials and Ionic Zn Partition within Wastewater Sludge Investigated by Isotopic Labeling, Global Challenges, Vol: 6, ISSN: 2056-6646

The increasing commercial use of engineered zinc oxide nanomaterials necessitates a thorough understanding of their behavior following their release into wastewater. Herein, the fates of zinc oxide nanoparticles (ZnO NPs) and ionic Zn in a real primary sludge collected from a municipal wastewater system are studied via stable isotope tracing at an environmentally relevant spiking concentration of 15.2 µg g−1. Due to rapid dissolution, nanoparticulate ZnO does not impart particle-specific effects, and the Zn ions from NP dissolution and ionic Zn display indistinguishable behavior as they partition equally between the solid, liquid, and ultrafiltrate phases of the sludge over a 4-h incubation period. This work provides important constraints on the behavior of engineered ZnO nanomaterials in primary sludge—the first barrier in a wastewater treatment plant—at low, realistic concentrations. As the calculated solid–liquid partition coefficients are significantly lower than those reported in prior studies that employ unreasonably high spiking concentrations, this work highlights the importance of using low, environmentally relevant doses of engineered nanomaterials in experiments to obtain accurate risk assessments.

Journal article

Little SH, Wilson DJ, Rehkämper M, Adkins JF, Robinson LF, van de Flierdt Tet al., 2021, Cold-water corals as archives of seawater Zn and Cu isotopes, Chemical Geology, Vol: 578, Pages: 1-20, ISSN: 0009-2541

Traditional carbonate sedimentary archives have proven challenging to exploit for Zn and Cu isotopes, due to the high concentrations of trace metals in potential contaminants (e.g., Fe-Mn coatings) and their low concentrations in carbonate. Here, we present the first dataset of δ66ZnJMC-Lyon and δ65CuSRM 976 values for cold-water corals and address their potential as a seawater archive. Extensive cleaning experiments carried out on two corals with well-developed Fe-Mn rich coatings demonstrate that thorough physical and chemical cleaning can effectively remove detrital and authigenic contaminants. Next, we present metal/Ca ratios and δ66Zn and δ65Cu values for a geographically diverse sample set of Holocene age cold-water corals. Comparing cold-water coral δ66Zn values to estimated ambient seawater δ66Zn values (where Δ66Zncoral-sw = δ66Zncoral – δ66Znseawater), we find Δ66Zncoral-sw = +0.03 ± 0.17‰ (1SD, n = 20). Hence, to a first order, cold-water corals record seawater Zn isotope compositions without fractionation. The average Holocene coral Cu isotope composition is +0.59 ± 0.23‰ (1SD, n = 15), similar to the mean of published deep seawater δ65Cu values at +0.66 ± 0.09‰, but with considerable variability. Finally, δ66Zn and δ65Cu data are presented for a small subset of four glacial-age corals. These values overlap with the respective Holocene coral datasets, hinting at limited glacial-interglacial changes in oceanic Zn and Cu cycling.

Journal article

Sullivan KV, Moore RET, Capper MS, Schilling K, Goddard K, Ion C, Layton-Matthews D, Leybourne MI, Coles B, Kreissig K, Coombes RC, Larner F, Rehkamper Met al., 2021, Zinc stable isotope analysis reveals Zn dyshomeostasis in benign tumours, breast cancer, and adjacent histologically normal tissue, Matallomics, Vol: 13, Pages: 1-12, ISSN: 1756-591X

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.

Journal article

Schilling K, Moore RET, Sullivan KV, Capper M, Rehkamper M, Goddard K, Ion C, Coombes RC, Vesty-Edwards L, Lamb AD, Halliday AN, Larner Fet al., 2021, Zinc stable isotopes in urine as diagnostic for cancer of secretory organs, Metallomics: integrated biometal science, Vol: 13, Pages: 1-10, ISSN: 1756-5901

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 δ66Zn in 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 δ66Zn for 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 δ66Zn in 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 δ66Zn to healthy controls, implying that the expression of metalloproteins with sulfur-rich ligands is stronger in breast cancer tissues. In conclusion, urinary δ66Zn may 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.

Journal article

Brett EKA, Prytulak J, Rehkämper M, Hammond SJ, Chauvel C, Stracke A, Willbold Met al., 2021, Thallium elemental and isotopic systematics in ocean island lavas, Geochimica et Cosmochimica Acta, Vol: 301, Pages: 187-210, ISSN: 0016-7037

The Earth’s mantle exhibits marked chemical heterogeneity. We provide an examination of thallium systematics in ocean island basalts (OIB): new high-precision trace element analyses, including Tl, and Tl isotopic compositions for 48 OIB spanning the entire range of observed Sr-Nd-Hf-Pb isotope ratios. All investigated OIB are characterised by ubiquitous Tl depletion requiring OIB mantle sources to have Tl concentrations as low as 0.2 ng/g, which is an order of magnitude lower than estimates for the primitive mantle and similar to Tl concentrations inferred for the depleted mantle. The low Tl concentrations inferred for OIB mantle sources are interpreted to reflect near quantitative removal of Tl during subduction and inefficient Tl recycling into the deeper mantle. If true, the Tl isotopic composition of surface materials may not be readily translated to the mantle sources of OIB.The new OIB dataset shows a >10 ε-unit range in primary isotopic variation, from ε205Tl = −6.4 to +6.6. However, the majority of samples (32 of 48) are within uncertainty of mantle values (ε205Tl = −2 ± 1), and show no co-variation with radiogenic isotopic composition. Notably, OIB with only minor Tl depletion (11 samples) have Tl isotopic compositions outside the mantle range. The Tl concentration contrast between the mantle and inputs such as sediments and altered basalt is so great that minor additions (<1% by mass) of high-Tl material will dominate the isotopic budget of a lava, with decoupling of Tl and radiogenic isotopic compositions as an expected result. Thallium isotopic compositions of OIB are therefore difficult to link directly to radiogenic isotope variations and the mantle components they may reflect. Indeed, if isotopically distinct Tl from altered oceanic crust and/or sediments were efficiently recycled into the mantle and sampled via OIB, more variation in the Tl isotopic composition of OIB would be expected than is ob

Journal article

Capper MS, Rehkämper M, Packman H, 2020, Rhenium-based complexes and in vivo testing: A brief history, ChemBioChem, Vol: 21, Pages: 2111-2115, ISSN: 1439-4227

The success of metal‐based anticancer therapeutics in the treatment of cancer is best exemplified by cisplatin. Currently used in 32 / 78 cancer regimens, the use for metal‐based therapeutics has a clear role in cancer therapy. Despite this, metal‐based therapeutics are not without drawbacks, with issues such as toxic side effects and the development of resistance mechanisms. This has led to investigations of other metal‐based therapeutics such as auranofin, a gold‐based drug candidate as well as ruthenium‐based candidates, NAMI‐A, NKP‐1339 and TLD‐1433. All are undergoing current clinical trials. Another class of complexes under study are rhenium‐based; such complexes have undergone extensive in vitro testing but only seven have displayed antitumor in vivo activity which is a necessary step before entering clinical trials. This present review will document, chronologically, the rhenium‐based drug candidates that have undergone in vivo testing and the outlook for such complexes.

Journal article

Griffiths A, Packman H, Leung YL, Coles BJ, Kreissig K, Little SH, van de Flierdt T, Rehkämper Met al., 2020, Evaluation of optimized procedures for high-precision Pb isotope analyses of seawater by MC-ICP-MS, Analytical Chemistry, Vol: 92, Pages: 11232-11241, ISSN: 0003-2700

The application of Pb isotopes to marine geochemistry is currently hindered by challenges associated with the analysis of Pb isotopes in seawater. The current study evaluates the performance of MC-ICP-MS measurements of seawater Pb isotope compositions following Pb separation by either solid-phase extraction with Nobias Chelate PA-1 resin or co-precipitation with Mg(OH)2, and using either a Pb double-spike or external normalization to Tl for mass bias correction. The four analytical combinations achieve results of similar quality when measuring 1–7 ng of seawater Pb, with reproducibilities (2SD) of 100–1200 ppm for 206Pb/207Pb, 208Pb/207Pb and 300–1700 ppm for ratios involving the minor 204Pb isotope. All four procedures enable significantly improved sample throughout compared to an established TIMS double-spike method and produce unbiased seawater Pb isotope compositions with similar or improved precision. Nobias extraction is preferable to co-precipitation due to its greater analytical throughput and suitability for analyses of large seawater samples with high Si(OH)4 contents. The most accurate Pb isotope data are produced following Nobias extraction and double-spike correction as such analyses are least susceptible to matrix effects. However, Nobias extraction with Tl-normalization constitutes an attractive alternative as, unlike the double-spike procedure, only a single mass spectrometric measurement is required, which improves analytical throughput and optimizes Pb consumption for analysis. Despite the advantages of solid-phase extraction, co-precipitation represents a useful Pb separation technique for samples with low to moderate Si contents as it is inexpensive, simple to implement and the data are only marginally less accurate, especially when combined with a Pb double-spike for mass bias correction.

Journal article

Sullivan K, Moore RET, Rehkämper M, Leybourne MI, Layton-Matthews D, Puxty J, Kyser Ket al., 2020, Postprandial zinc stable isotope response in human blood serum, Metallomics, ISSN: 1756-5901

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 concentration decrease by about 20%, depending on the size of meal, approximately 3 hours postprandially (i.e. after eating), before returning to baseline values if no meals are consumed over the following 4 to 5 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 peak 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.

Journal article

Moore R, Ullah I, de Oliveira VH, Hammond SJ, Strekopytov S, Tibbett M, Dunwell JM, Rehkamper Met al., 2020, Cadmium isotope fractionation reveals genetic variation in Cd uptake and translocation by Theobroma cacao and role of natural resistance-associated macrophage protein 5 and heavy metal ATPase-family transporters, Horticulture Research, Vol: 7, ISSN: 2052-7276

In response to new European Union regulations, studies are underway to mitigate accumulation of toxic cadmium (Cd) in cacao (Theobroma cacao, Tc). This study advances such research with Cd isotope analyses of 19 genetically diverse cacao clones and yeast transformed to express cacao natural resistance-associated macrophage protein (NRAMP5) and heavy metal ATPases (HMAs). The plants were enriched in light Cd isotopes relative to the hydroponic solution with Δ114/110Cdtot-sol = −0.22 ± 0.08‰. Leaves show a systematic enrichment of isotopically heavy Cd relative to total plants, in accord with closed-system isotope fractionation of Δ114/110Cdseq-mob = −0.13‰, by sequestering isotopically light Cd in roots/stems and mobilisation of remaining Cd to leaves. The findings demonstrate that (i) transfer of Cd between roots and leaves is primarily unidirectional; (ii) different clones utilise similar pathways for Cd sequestration, which differ from those of other studied plants; (iii) clones differ in their efficiency of Cd sequestration. Transgenic yeast that expresses TcNRAMP5 (T. cacao natural resistance-associated macrophage gene) had isotopically lighter Cd than did cacao. This suggests that NRAMP5 transporters constitute an important pathway for uptake of Cd by cacao. Cd isotope signatures of transgenic yeast expressing HMA-family proteins suggest that they may contribute to Cd sequestration. The data are the first to record isotope fractionation induced by transporter proteins in vivo.

Journal article

Barraza F, Moore R, Rehkamper M, Schreck E, Lefeuvre G, Kreissig K, Coles B, Maurice Let al., 2019, Cadmium isotope fractionation in soil-cacao systems of Ecuador: a pilot field study, RSC Advances: an international journal to further the chemical sciences, Vol: 9, Pages: 34011-34022, ISSN: 2046-2069

The often high Cd concentrations of cacao beans are a serious concern for producers in Latin America due to the implementation of stricter Cd limits for cocoa products by the European Union in 2019. This is the first investigation to employ coupled Cd isotope and concentration measurements to study soil – cacao systems. Analyses were carried out for 29 samples of soils, soil amendments and cacao tree organs from organic farms in Ecuador that harvest three distinct cacao cultivars. The majority of soils from 0–80 cm depth have very similar δ114/110Cd of about −0.1‰ to 0‰. Two 0–5 cm topsoils, however, have high Cd concentrations coupled with heavy Cd isotope compositions of δ114/110Cd ≈ 0.2%, possibly indicating Cd additions from the tree litter used as organic fertilizer. Whilst cacao leaves, pods and beans are ubiquitously enriched in Cd relative to soils there are distinct Cd isotope signatures. The leaves and pods are isotopically heavier than the soils, with similar Δ114/110Cdleaf–soil values of 0.22 ± 0.07‰ to 0.41 ± 0.09‰. In contrast, the data reveal differences in Δ114/110Cdbean–leaf that may be linked to distinct cacao cultivars. In detail, Δ114/110Cdbean–leaf values of −0.34‰ to −0.40‰ were obtained for Nacional cacao from two farms, whilst CCN-51 hybrid cacao from a third farm showed no fractionation within error (−0.08 ± 0.13‰). As such, further work to investigate whether Cd isotopes are indeed useful for tracing sources of Cd enrichments in soils and to inform genetic efforts to reduce the Cd burden of cocoa is indicated.

Journal article

Xie RC, Rehkamper M, Grasse P, van de Flierdt T, Frank M, Xue Zet al., 2019, Isotopic evidence for complex biogeochemical cycling of Cd in the eastern tropical South Pacific (vol 512, 134, 2019), EARTH AND PLANETARY SCIENCE LETTERS, Vol: 524, ISSN: 0012-821X

Journal article

Zhang P, Misra S, Guo Z, Rehkamper M, Valsami-Jones Eet al., 2019, Stable isotope labelling of metal/metal oxide nanomaterials for environmental and biological tracing, Nature Protocols, Vol: 14, Pages: 2878-2899, ISSN: 1750-2799

Engineered nanomaterials are often compositionally indistinguishable from their natural counterparts and thus their tracking in the environment or within biota requires the development of appropriate labelling tools. Stable isotope labelling has become a well-established such tool, developed to assign “ownership” or “source” to engineered nanomaterial enabling their tracing and quantification, especially in complex environments. A particular methodological challenge for the stable isotope labelling is to ensure the label is traceable in a range of environmental scenarios but without inducing modification of the properties of the nanoamaterial and without loss of signal from the label, thus retaining realism and relevance. This protocol describes the strategy for stable isotope labelling of several widely used metal and metal oxide nanomaterials, namely ZnO, CuO, Ag, and TiO2, using isotopically enriched precursors, namely 67Zn or 68Zn metal, 65CuCl2, 107Ag or 109Ag metal, and 47 TiO2 powder. A complete synthesis requires 1 to 8 days depending on the type of nanomaterial, the precursors used and the synthesis methods adopted. The physicochemical properties of the labeled particles are determined by optical, diffraction and spectroscopic techniques for quality control. The procedures for tracing the labels in aquatic (snail and mussel) and terrestrial (earthworm) organisms and monitoring the environmental transformation of labelled silver nanomaterials are also described. We anticipate this labelling strategy can be adopted by industry to facilitate applications such as nanosafety assessments before nanomaterials enter the market and environment as well as product authentication and tracking.

Journal article

Rehkamper M, Moore R, Maret W, Larner Fet al., 2019, Assessment of coupled Zn concentration and natural stable isotope analyses of urine as a novel probe of Zn status, Metallomics, Vol: 11, Pages: 1506-1517, ISSN: 1756-5901

Zinc is a common trace metal in the human body, present in about 10% of proteins. Despite numerous roles of Zn in health and disease, there is still a need for a robust biomarker of Zn status. Many parameters have been proposed, with varying levels of success, with plasma Zn often favoured. This study investigates if Zn status can be assessed from the natural stable Zn isotope composition of urine. To this end, 60 urine samples were analysed from ten healthy participants. Remarkably, samples with lower Zn concentrations are systematically enriched in heavy Zn isotopes. Most of the low-Zn urine originated from individuals who omitted dairy, meat or both from their diets. When data for blood serum from age-matched, healthy individuals are compared with the urine results, the former plot at the extension of the urine trend at higher Zn concentrations and lighter isotope compositions. The observed co-variation of Zn isotope compositions with concentrations is indicative of an isotope fractionation system where both properties are controlled by the same processes. It is interpreted as arising from filtration and/or reabsorption processes within the kidney, which are associated with absorbed dietary Zn. The data suggest that the Zn in blood serum that is bound to low molecular weight molecules has an isotope composition distinct from total serum, due to the different affinities of molecular Zn-binding residues to heavy and light Zn isotopes. This technique provides additional information into an individual's Zn status compared to urine or plasma Zn levels alone.

Journal article

Junk T, Rehkamper M, Laycock A, 2019, High-sensitivity tracing of stable isotope labeled Ag nanoparticles in environmental samples using MC-ICP-MS, Journal of Analytical Atomic Spectrometry, Vol: 34, Pages: 1173-1183, ISSN: 1364-5544

Silver nanoparticles (Ag NPs) are among the most widely used engineered nanomaterials and this warrants further investigation of their behaviour and fate in the environment. To support such work, we developed new techniques for efficient tracing of Ag NPs that are produced from, and hence labelled with, enriched 109 28 Ag (Ag-En). The methods encompass a one-step anion exchange separation of Ag from the sample matrix and precise determination of 109Ag/107Ag ratios and 109Ag abundances by multiple-collector ICP-MS. The sample preparation procedure has an Ag yield of 104 ± 13% (1 SD) and a procedural Ag blank of less than 7 pg, enabling analysis of samples with only trace Ag contents.Analyses of Ag solutions and realistic samples show that careful correction of memory effects is paramount for ensuring data quality. Using appropriate procedures, the 109Ag/107Ag ratios of samples containing Ag-En can be determined to a precision and trueness of better than about 0.5%, when more than 0.5 ng Ag are available for analysis. Even if Ag is only present at 50 pg or less, the Ag isotope ratios and Ag-En concentrations of samples can be measured to better than 5 to 10%. The methods are therefore able to resolve the presence of 1 pg of Ag-En in samples that contain as little as 10 pg and to up to 1 ng of natural Ag. As such, the techniques allow robust detection and quantification of Ag-En in environmental samples even when highly variable quantities of Ag-En and natural Ag are present. The new methodology thus enables the use of stable isotope tracing to investigate the fate of Ag NPs in complex environmental systems at dosing concentrations similar to the predicted environmental concentrations and for very small samples, whilst also providing high sample throughput.

Journal article

Xie RC, Rehkamper M, Grasse P, van de Flierdt T, Frank M, Xue Zet al., 2019, Isotopic evidence for complex biogeochemical cycling of Cd in the eastern tropical South Pacific, Earth and Planetary Science Letters, Vol: 512, Pages: 134-146, ISSN: 0012-821X

Over the past decades, observations have confirmed decreasing oxygen levels and shoaling of oxygen minimum zones (OMZs) in the tropical oceans. Such changes impact the biogeochemical cycling of micronutrients such as Cd, but the potential consequences are only poorly constrained. Here, we present seawater Cd concentrations and isotope compositions for 12 depth profiles at coastal, nearshore and offshore stations from 4ºS to 14ºS in the eastern tropical South Pacific, where one of the world’s strongest OMZs prevails.The depth profiles of Cd isotopes display high δ114/110 Cd at the surface and decreasing δ114/110 Cd with increasing water depth, consistent with preferential utilization of lighter Cd isotopes during biological uptake in the euphotic zone and subsequent remineralization of the sinking biomass. In the surface and subsurface ocean, seawater displays similar δ114/110 Cd signatures of 0.47 ±0.23‰ to 0.82±0.05‰ across the entire eastern tropical South Pacific despite highly variable Cd concentrations between 0.01 and 0.84 nmol/kg. This observation, best explained by an open system steady-state fractionation model, contrasts with previous studies of the South Atlantic and South Pacific Oceans, where only Cd-deficient waters have a relatively constant Cd isotope signature. For the subsurface to about 500 m depth, the variability of seawater Cd isotope compositions can be modeled by mixing of remineralized Cd with subsurface water from the base of the mixed layer. In the intermediate and deep eastern tropical South Pacific (>500 m), seawater [Cd] and δ114/110 Cd appear to follow the distribution and mixing of major water masses. We identified modified AAIW of the ETSP to be more enriched in [Cd] than AAIW from the source region, whilst both water masses have similar δ114/110 Cd. A mass balance estimate thus constrains a δ114/110 Cd of between 0.38‰ and 0.56‰ for the

Journal article

Wiggenhauser M, Bigalke M, Imseng M, Keller A, Rehkämper M, Wilcke W, Frossard Eet al., 2019, Using isotopes to trace freshly applied cadmium through mineral phosphorus fertilization in soil-fertilizer-plant systems, Science of the Total Environment, Vol: 648, Pages: 779-786, ISSN: 0048-9697

Applications of mineral phosphorus (P) fertilizer can lead to cadmium (Cd) accumulation in soils and can increase Cd concentrations in edible crop parts. To determine the fate of freshly applied Cd, a Cd source tracing experiment was conducted in three soil-fertilizer-wheat systems by using a mineral P fertilizer labeled with the radio isotope 109Cd and by exploiting natural differences in Cd stable isotope compositions (δ114/110Cd). Source tracing with stable isotopes overestimated the proportion of Cd in plants derived from the P fertilizer, because the isotope ratios of the sources were not sufficiently distinct from those of the soils. Despite indistinguishable extractable Cd pools between control and treatments, the addition of P fertilizer resulted in a more negative apparent isotope fractionation between soil and wheat. Overall, the radio isotope approach provided more robust results and revealed that 6.5 to 15% of the Cd in the shoot derived from the fertilizer. From the introduced Cd, a maximum of 2.2% reached the wheat shoots, whilst 97.8% remained in the roots and soils. The low recoveries of the fertilizer derived Cd suggest that continuous P fertilizer application in the past decades can lead to a build-up of a residual Cd pool in soils.

Journal article

Kocher S, Wilkinson JJ, Armstrong RN, McDonald L, Rehkaemper M, Creaser RA, Lode JNet al., 2019, Trace element chemistry, polytypes, isotopic composition and Re-Os dates of molybdenite from the Bingham Canyon Cu-Au-Mo porphyry deposit, Utah, 15th SGA Biennial Meeting on Life with Ore Deposits on Earth, Publisher: SOC GEOLOGY APPLIED MINERAL DEPOSITS-SGA, Pages: 1120-1123

Conference paper

Imseng M, Wiggenhauser M, Keller A, Müller M, Rehkamper M, Murphy K, Kreissig K, Frossard E, Wilcke W, Bigalke Met al., 2019, Towards an understanding of the Cd isotope fractionation during transfer from the soil to the cereal grain, Environmental Pollution, Vol: 244, Pages: 834-844, ISSN: 0269-7491

Cd in soils might be taken up by plants, enter the food chain and endanger human health. This study investigates the isotopic fractionation of major processes during the Cd transfer from soils to cereal grains. Thereto, soil, soil solution, wheat and barley plants (roots, straw and grains) were sampled in the field at three study sites during two vegetation periods. Cd concentrations and δ114/110Cd values were determined in all samples. The composition of the soil solution was analyzed and the speciation of the dissolved Cd was modelled. Isotopic fractionation between soils and soil solutions (Δ114/110Cd20-50cm-soil solution = −0.61 to −0.68‰) was nearly constant among the three soils. Cd isotope compositions in plants were heavier than in soils (Δ114/110Cd0-20cm-plants = −0.55 to −0.31‰) but lighter than in soil solutions (Δ114/110Cdsoil solution-plants = 0.06–0.36‰) and these differences correlated with Cd plant-uptake rates. In a conceptual model, desorption from soil, soil solution speciation, adsorption on root surfaces, diffusion, and plant uptake were identified as the responsible processes for the Cd isotope fractionation between soil, soil solution and plants whereas the first two processes dominated over the last three processes. Within plants, compartments with lower Cd concentrations were enriched in light isotopes which might be a consequence of Cd retention mechanisms, following a Rayleigh fractionation, in which barley cultivars were more efficient than wheat cultivars.

Journal article

Moore R, Rehkamper M, Kreissig K, Strekopytov S, Larner Fet al., 2018, Determination of major and trace element variability in healthy human urine by ICP-QMS and specific gravity normalisation, RSC Advances, Vol: 8, Pages: 38022-38035, ISSN: 2046-2069

Sixty five urine samples obtained during one or two non-consecutive days from 10 healthy individuals were analysed for major (Na, Mg, K, Ca) and trace (Co, Cu, Zn, As, Rb, Sr, Mo and Pb) element concentrations. Following microwave digestion, the analyses were carried out using ICP-QMS (inductively coupled plasma quadrupole mass spectrometry) incorporating a collision/reaction cell. Repeat analyses of quality control samples show that the procedure produces unbiased results and is well suited for routine urinalysis of the investigated elements. Concentrations were normalised using specific gravity (SG) and the resultant decrease in variability supports previous conclusions that SG-normalisation appropriately corrects for differences in urine dilution. The elemental concentrations of the individual urine samples show large differences in dispersion. Most variable are As, Co and Zn, with CVs (coefficients of variation) of >75%. The major elements as well as Rb, Sr and Mo display intermediate variability, whilst Cu and Pb have the least elemental dispersion with CV values of about 30%. A detailed assessment shows that the overall elemental variability is governed both by differences between individuals and variations for a single individual over time. Spot urine samples exhibit elemental concentrations that, on average, resemble the daily mean values to within about 30% for all elements except K and Rb. Diet-related changes in urinary element concentration are most prominent for Mg, K, Co, Rb and Pb. The concentrations of Co, As and Rb appear to vary systematically with gender but this may primarily reflect co-variance with specific diets.

Journal article

Brett A, Prytulak J, Hammond SJ, Rehkamper Met al., 2018, Thallium mass fraction and stable isotope ratios of sixteen geological reference materials, Geostandards and Geoanalytical Research, Vol: 42, Pages: 339-360, ISSN: 1639-4488

Thallium stable isotope ratio and mass fraction measurements were performed on sixteen geological reference materials spanning three orders of magnitude in thallium mass fraction, including both whole-rock and partially-separated mineral powders. For stable isotope ratio measurements, a minimum of three independent digestions of each reference material were obtained. High-precision trace element measurements (including Tl) were also performed for the majority of these RMs. The range of Tl mass fractions represented is 10 ng g-1 to 16 μg g-1, and Tl stable isotope ratios (reported for historical reasons as ε205Tl relative to NIST SRM 997) span the range -4 to +2. With the exception – attributed to between-bottle heterogeneity – of G-2, the majority of data are in good agreement with published or certified values, where available. The precision of mean of independent measurement results between independent dissolutions suggests that, for the majority of materials analysed, a minimum digested mass of 100 mg is recommended tomitigate the impact of small-scale powder heterogeneity. Of the sixteen materials analysed, we therefore recommend for use as Tl reference materials the USGS materials BCR-2, COQ-1, GSP-2, and STM-1; CRPG materials AL-I, AN-G, FK-N, ISH-G, MDO-G, Mica-Fe, Mica-Mg, and UB-N; NIST SRM 607; and OREAS14P.

Journal article

Khondoker R, Weiss DJ, van de Flierdt T, Rehkamper M, Kreissig K, Coles BJ, Strekopytov S, Humphreys-Williams E, Dong S, Bory A, Bout-Roumazeilles V, Smichowski P, Cid-Agüero P, Babinski M, Losno R, Monna Fet al., 2018, New constraints on elemental and Pb and Nd isotope compositions of South American and Southern African aerosol sources to the South Atlantic Ocean, Chemie der Erde / Geochemistry, Vol: 78, Pages: 372-384, ISSN: 0009-2819

Improving the geochemical database available for characterising potential natural and anthropogenic aerosol sources from South America and Southern Africa is a critical precondition for studies aimed at understanding trace metal controls on the marine biogeochemical cycles of the South Atlantic Ocean. We here present new elemental and isotopic data for a wide range of sample types from South America and Southern Africa that are potentially important aerosol sources. This includes road dust from Buenos Aires and lichen samples from Johannesburg, soil dust from Patagonia, volcanic ash from the Andean volcanic belt, and aerosol samples from São Paulo. All samples were investigated for major (Al, Ca, Fe, Mg, Na, K, Mn) and trace element (Cd, Co, Cr, Cu, Ni, Pb, REE, Sc, Th, Y, V, Zn) concentrations and Nd and Pb isotopic compositions. We show that diagrams of 208Pb/207Pb vs. εNd, 208Pb/207Pb vs. Pb/Al, 1/[Pb], Zn/Al, Cd/Al, Cu/Al, and εNd vs. Pb/Al, and 1/[Nd] are best suited to separate South American and South African source regions as well as natural and anthropogenic sources. A subset of samples from Patagonia and the Andes was additionally subjected to separation of a fine (<5 μm) fraction and compared to the composition of the bulk sample. We show that differences in the geochemical signature of bulk samples between individual regions and source types are significantly larger than between grain sizes. Jointly, these findings present an important step forward towards a quantitative assessment of aeolian trace metal inputs to the South Atlantic Ocean.

Journal article

Schlitzer R, Anderson RF, Dodas EM, Lohan M, Geibert W, Tagliabue A, Bowie A, Jeandel C, Maldonado MT, Landing WM, Cockwell D, Abadie C, Abouchami W, Achterberg EP, Agather A, Aguliar-Islas A, van Aken HM, Andersen M, Archer C, Auro M, de Baar HJ, Baars O, Baker AR, Bakker K, Basak C, Baskaran M, Bates NR, Bauch D, van Beek P, Behrens MK, Black E, Bluhm K, Bopp L, Bouman H, Bowman K, Bown J, Boyd P, Boye M, Boyle EA, Branellec P, Bridgestock L, Brissebrat G, Browning T, Bruland KW, Brumsack HJ, Brzezinski M, Buck CS, Buck KN, Buesseler K, Bull A, Butler E, Cai P, Mor PC, Cardinal D, Carlson C, Carrasco G, Casacuberta N, Casciotti KL, Castrillejo M, Chamizo E, Chance R, Charette MA, Chaves JE, Cheng H, Chever F, Christl M, Church TM, Closset I, Colman A, Conway TM, Cossa D, Croot P, Cullen JT, Cutter GA, Daniels C, Dehairs F, Deng F, Dieu HT, Duggan B, Dulaquais G, Dumousseaud C, Echegoyen-Sanz Y, Edwards RL, Ellwood M, Fahrbach E, Fitzsimmons JNet al., 2018, The GEOTRACES Intermediate Data Product 2017, Chemical Geology, Vol: 493, Pages: 210-223, ISSN: 0009-2541

The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the previous IDP2014. For the first time, the IDP2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope (TEI) sources. The TEI data in the IDP2017 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at crossover stations. The IDP2017 consists of two parts: (1) a compilation of digital data for more than 450 TEIs as well as standard hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing an on-line atlas that includes more than 590 section plots and 130 animated 3D scenes. The digital data are provided in several formats, including ASCII, Excel spreadsheet, netCDF, and Ocean Data View collection. Users can download the full data packages or make their own custom selections with a new on-line data extraction service. In addition to the actual data values, the IDP2017 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering and for statistical analysis. Metadata about data originators, analytical methods and original publications related to the data are linked in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2017 as section plots and rotating 3D scenes. The basin-wide 3D scenes combine data from many cruises and provide quick overviews of large-scale tracer distributions. These 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or alo

Journal article

Bridgestock L, Rehkamper M, van de Flierdt T, Paul M, Milne A, Lohan MC, Achterberg EPet al., 2018, The distribution of lead concentrations and isotope compositions in the eastern Tropical Atlantic Ocean, Geochimica et Cosmochimica Acta, Vol: 225, Pages: 36-51, ISSN: 0016-7037

Anthropogenic emissions have dominated marine Pb sources during the past century. Here we present Pb concentrations and isotope compositions for ocean depth profiles collected in the eastern Tropical Atlantic Ocean (GEOTRACES section GA06), to trace the transfer of anthropogenic Pb into the ocean interior. Variations in Pb concentration and isotope composition were associated with changes in hydrography. Water masses ventilated in the southern hemisphere generally featured lower 206Pb/207Pb and 208Pb/207Pb ratios than those ventilated in the northern hemisphere, in accordance with Pb isotope data of historic anthropogenic Pb emissions. The distributions of Pb concentrations and isotope compositions in northern sourced waters were consistent with differences in their ventilation timescales. For example, a Pb concentration maximum at intermediate depth (600–900 m, 35 pmol kg−1) in waters sourced from the Irminger/Labrador Seas, is associated with Pb isotope compositions (206Pb/207Pb = 1.1818–1.1824, 208Pb/207Pb = 2.4472–2.4483) indicative of northern hemispheric emissions during the 1950s and 1960s close to peak leaded petrol usage, and a transit time of ∼50–60 years. In contrast, North Atlantic Deep Water (2000–4000 m water depth) featured lower Pb concentrations and isotope compositions (206Pb/207Pb = 1.1762–1.184, 208Pb/207Pb = 2.4482–2.4545) indicative of northern hemispheric emissions during the 1910s and 1930s and a transit time of ∼80–100 years. This supports the notion that transient anthropogenic Pb inputs are predominantly transferred into the ocean interior by water mass transport. However, the interpretation of Pb concentration and isotope composition distributions in terms of ventilation timescales and pathways is complicated by (1) the chemical reactivity of Pb in the ocean, and (2) mixing of waters ventilated during different time periods. The complex effects of water mass mixing on Pb distri

Journal article

Imseng M, Wiggenhauser M, Keller A, Müller M, Rehkamper M, Murphy K, Kreissig K, Frossard E, Wilcke W, Bigalke Met al., 2018, Fate of Cd in agricultural soils: a stable isotope approach to anthropogenic impact, soil formation and soil-plant cycling, Environmental Science and Technology, Vol: 52, Pages: 1919-1928, ISSN: 0013-936X

The application of mineral phosphate (P) fertilizers leads to an unintended Cd input into agricultural systems, which might affect soil fertility and quality of crops. The Cd fluxes at three arable sites in Switzerland were determined by a detailed analysis of all inputs (atmospheric deposition, mineral P fertilizers, manure, and weathering) and outputs (seepage water, wheat and barley harvest) during one hydrological year. The most important inputs were mineral P fertilizers (0.49 to 0.57 g Cd ha–1 yr–1) and manure (0.20 to 0.91 g Cd ha–1 yr–1). Mass balances revealed net Cd losses for cultivation of wheat (−0.01 to −0.49 g Cd ha–1 yr–1) but net accumulations for that of barley (+0.18 to +0.71 g Cd ha–1 yr–1). To trace Cd sources and redistribution processes in the soils, we used natural variations in the Cd stable isotope compositions. Cadmium in seepage water (δ114/110Cd = 0.39 to 0.79‰) and plant harvest (0.27 to 0.94‰) was isotopically heavier than in soil (−0.21 to 0.14‰). Consequently, parent material weathering shifted bulk soil isotope compositions to lighter signals following a Rayleigh fractionation process (ε ≈ 0.16). Furthermore, soil-plant cycling extracted isotopically heavy Cd from the subsoil and moved it to the topsoil. These long-term processes and not anthropogenic inputs determined the Cd distribution in our soils.

Journal article

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