This is a repository copy of Towards an understanding of thallium isotope fractionation during ad... more This is a repository copy of Towards an understanding of thallium isotope fractionation during adsorption to manganese oxides.
Stable 142Ce/140Ce isotope measurements of CeO2 nanoparticles and purified materials for the purp... more Stable 142Ce/140Ce isotope measurements of CeO2 nanoparticles and purified materials for the purpose of stable isotope tracing.
During isotopic analysis of Cd by MC-ICP-MS, organic resin residue can perturb instrumental mass ... more During isotopic analysis of Cd by MC-ICP-MS, organic resin residue can perturb instrumental mass fractionation. These organic compounds can be removed by a liquid–liquid extraction procedure using heptane.
During isotopic analysis of Cd by MC-ICP-MS, organic resin residue can perturb instrumental mass ... more During isotopic analysis of Cd by MC-ICP-MS, organic resin residue can perturb instrumental mass fractionation. These organic compounds can be removed by a liquid–liquid extraction procedure using heptane.
Biological reference materials with well-characterised stable isotope compositions are lacking in... more 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 δ(66/64)Zn (which denotes the deviation of the (66)Zn/(64)Zn 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 ...
Improving the geochemical database available for characterising potential natural and anthropogen... more 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 208 Pb/ 207 Pb vs.
Sixty five urine samples obtained during one or two non-consecutive days from 10 healthy individu... more 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.
Anthropogenic emissions completely overwhelmed natural marine lead (Pb) sources during the past c... more Anthropogenic emissions completely overwhelmed natural marine lead (Pb) sources during the past century, predominantly due to leaded petrol usage. Here, based on Pb isotope measurements, we reassess the importance of natural and anthropogenic Pb sources to the tropical North Atlantic following the nearly complete global cessation of leaded petrol use. Significant proportions of up to 30–50% of natural Pb, derived from mineral dust, are observed in Atlantic surface waters, reflecting the success of the global effort to reduce anthropogenic Pb emissions. The observation of mineral dust derived Pb in surface waters is governed by the elevated atmospheric mineral dust concentration of the North African dust plume and the dominance of dry deposition for the atmospheric aerosol flux to surface waters. Given these specific regional conditions, emissions from anthropogenic activities will remain the dominant global marine Pb source, even in the absence of leaded petrol combustion.
Stable isotope compositions can potentially be used to trace atmospheric Cd inputs to the surface... more Stable isotope compositions can potentially be used to trace atmospheric Cd inputs to the surface ocean and anthropogenic Cd emissions to the atmosphere. Both of these applications may provide valuable insights into the effects of anthropogenic activities on the cycling of Cd in the environment. However, a lack of constraints for the Cd isotope compositions of atmospheric aerosols is currently hindering such studies. Here we present stable Cd isotope data for aerosols collected over the Tropical Atlantic Ocean. The samples feature variable proportions of mineral dust-derived and anthropogenic Cd, yet exhibit similar isotope compositions, thus negating the distinction of these Cd sources by using isotopic signatures in this region. Isotopic variability between these two atmospheric Cd sources may be identified in other areas, and thus warrants further investigation. Regardless, these data provide important initial constraints on the isotope composition of atmospheric Cd inputs to the ocean.
A novel ion exchange chromatography was developed for the separation of Cu from biological sample... more A novel ion exchange chromatography was developed for the separation of Cu from biological samples prior to stable isotope analyses. In contrast to previous methods, the new technique makes use of the different distribution coefficients of Cu(I) and Cu(II) to anion exchange resin and this helps to significantly improve the purity of the Cu separates obtained from biological samples, whilst maintaining crucial quantitative yields. Careful method validation confirmed that the procedure yields sufficiently pure Cu fractions after a single pass through the anion exchange columns, with a recovery of 100 AE 2%. Subsequent isotopic analyses of the Cu by multi-collector inductively coupled plasma mass spectrometry, using admixed Ni for mass bias correction, produced accurate Cu stable isotope data with a reproducibility of AE0.04& for pure standard solutions and of AE0.15& for samples of biological origin.
Zinc oxide nanoparticles (ZnO NPs) are widely used in commercial products and knowledge of their ... more Zinc oxide nanoparticles (ZnO NPs) are widely used in commercial products and knowledge of their environmental fate is a priority for ecological protection. Here we synthesized model ZnO NPs that were made from and thus labeled with the stable isotope (68)Zn and this enables highly sensitive and selective detection of labeled components against high natural Zn background levels. We combine high precision stable isotope measurements and novel bioimaging techniques to characterize parallel water-borne exposures of the common mudshrimp Corophium volutator to (68)ZnO NPs, bulk (68)ZnO, and soluble (68)ZnCl(2) in the presence of sediment. C. volutator is an important component of coastal ecosystems where river-borne NPs will accumulate and is used on a routine basis for toxicity assessments. Our results demonstrate that ionic Zn from ZnO NPs is bioavailable to C. volutator and that Zn uptake is active. Bioavailability appears to be governed primarily by the dissolved Zn content of the water, whereby Zn uptake occurs via the aqueous phase and/or the ingestion of sediment particles with adsorbed Zn from dissolution of ZnO particles. The high sorption capacity of sediments for Zn thus enhances the potential for trophic transfer of Zn derived from readily soluble ZnO NPs. The uncertainties of our isotopic data are too large, however, to conclusively rule out any additional direct uptake route of ZnO NPs by C. volutator.
ABSTRACT Stable isotope labeling coupled with high precision isotope ratio measurements by multip... more ABSTRACT Stable isotope labeling coupled with high precision isotope ratio measurements by multiple collector-ICP-MS is effective for tracing zinc from zinc oxide nanoparticles (ZnO NPs) in complex media and against a high zinc background. Using this technique, a previous study detected a slightly enhanced uptake of Zn in the blood of human females following dermal exposure to a sunscreen containing ZnO NPs, relative to a sunscreen of the same formulation but with larger ZnO particles (‘bulk’ material). Until now, the results of these exposures and the accuracy of the analyses, which require the resolution of subtle differences in Zn isotope ratios, have not been independently confirmed. Here we compare data from the previous study with results obtained in new, independent analyses of the same and additional samples, that were performed using similar techniques and instrumentation but in a different laboratory. The data sets are in good agreement, with a Pearson correlation coefficient of r ≈ 0.98, thus establishing the usefulness of the methods for tracing engineered ZnO NPs (and other anthropogenic sources of Zn) in Zn-rich biological materials. Previously unanalyzed blood samples from the earlier study provide further evidence for the increased uptake of Zn from ZnO NPs relative to bulk ZnO and they confirm that uptake rates decrease once sunscreen application has ceased.
The environmental behaviour of ZnO nanoparticles (NPs), their availability to, uptake pathways by... more The environmental behaviour of ZnO nanoparticles (NPs), their availability to, uptake pathways by, and biokinetics in the earthworm Lumbricus rubellus were investigated using stable isotope labelling. Zinc isotopically enriched to 99.5% in (68)Zn ((68)Zn-E) was used to prepare (68)ZnO NPs and a dissolved phase of (68)Zn for comparison. These materials enabled tracing of environmentally relevant (below background) NP additions to soil of only 5 mg (68)Zn-E kg(-1). Uptake routes were isolated by introducing earthworms with sealed and unsealed mouthparts into test soils for up to 72 hours. The Zn isotope compositions of the soils, pore waters and earthworms were then determined using multiple collector inductively coupled plasma mass spectrometry. Detection and quantification of (68)Zn-E in earthworm tissue was possible after only 4 hours of dermal exposure, when the uptake of (68)Zn-E had increased the total Zn tissue concentration by 0.03‰. The results demonstrate that at these reali...
ABSTRACT Zinc isotope compositions (δ66Zn) and concentrations were determined for metal samples o... more ABSTRACT Zinc isotope compositions (δ66Zn) and concentrations were determined for metal samples of 15 iron meteorites across groups IAB, IIAB, and IIIAB. Also analyzed were troilite and other inclusions from the IAB iron Toluca. Furthermore, the first Zn isotope data are presented for metal-silicate partitioning experiments that were conducted at 1.5 GPa and 1650 K. Three partitioning experiments with run durations of between 10 and 60 min provide consistent Zn metal-silicate partition coefficients of ∼0.7 and indicate that Zn isotope fractionation between molten metal and silicate is either small (at less than about ) or absent. Metals from the different iron meteorite groups display distinct ranges in Zn contents, with concentrations of 0.08-0.24 μg/g for IIABs, 0.8-2.5 μg/g for IIIABs, and 12-40 μg/g for IABs. In contrast, all three groups show a similar range of δ66Zn values (reported relative to ‘JMC Lyon Zn’) from to , with no clear systematic differences between groups. However, distinct linear trends are defined by samples from each group in plots of δ66Zn vs. 1/Zn, and these correlations are supported by literature data. Based on the high Zn concentration and δ66Zn ≈ 0 determined for a chromite-rich inclusion of Toluca, modeling is employed to demonstrate that the Zn trends are best explained by segregation of chromite from the metal phase. This process can account for the observed Zn-δ66Zn-Cr systematics of iron meteorite metals, if Zn is highly compatible in chromite and Zn partitioning is accompanied by isotope fractionation with Δ66Znchr-met . Based on these findings, it is likely that the parent bodies of the IAB complex, IIAB and IIIAB iron meteorites featured δ66Zn values of about −1.0 to , similar to the Zn isotope composition inferred for the bulk silicate Earth and results obtained for chondritic meteorites. Together, this implies that most solar system bodies formed with similar bulk Zn isotope compositions despite large differences in Zn contents.
Disordered copper metabolism may be important in the aetiology of Parkinsonism, as caeruloplasmin... more Disordered copper metabolism may be important in the aetiology of Parkinsonism, as caeruloplasmin is a key enzyme in handling oxidative stress and is involved in the synthesis pathway of dopamine. The human Cu metabolism of ten Parkinsonism patients was compared to ten healthy controls with the aid of a stable 65 Cu isotope tracer. The analyses of blood serum 65 Cu/ 63 Cu ratios yielded individual isotopic profiles, which indicate that the Cu metabolism is less controlled in patients with Parkinsonism.
This contribution evaluates two possible routes of stable isotope tracing for ZnO nanomaterials. ... more This contribution evaluates two possible routes of stable isotope tracing for ZnO nanomaterials. For this we carried out the first high precision Zn isotope analyses of commercially available ZnO nanomaterials, to investigate whether such materials exhibit isotope fractionations that can be exploited for tracing purposes. These measurements revealed Zn isotopic compositions (of δ(66/64)Zn = +0.28 to -0.31‰ relative to JMC Lyon Zn) that are indistinguishable from "normal" natural and anthropogenic Zn in environmental samples. Stable isotope tracing therefore requires the application of purpose-made isotopically enriched ZnO nanoparticles. A detailed evaluation identified the most suitable and cost-effective labeling isotopes for different analytical requirements and techniques. It is shown that, using relatively inexpensive (68)Zn for labeling, ZnO nanoparticles can be reliably detected in natural samples with a Zn background of 100 μg/g at concentrations as low as about 5 ng/g, if the isotopic tracing analyses are carried out by high precision mass spectrometry. Stable isotope tracing may also be able to differentiate between the uptake by organisms of particulate ZnO and Zn(2+) ions from the dissolution of nanoparticles.
Zinc oxide nanoparticles (ZnO NPs) are among the most commercialized engineered nanomaterials. Th... more Zinc oxide nanoparticles (ZnO NPs) are among the most commercialized engineered nanomaterials. Their biological impact in aquatic organisms has been associated with dissolution, but there is also evidence of nanospecific effects. In this study the waterborne uptake and efflux kinetics of isotopically labeled (68)ZnO NPs (7.8 ± 1.2 nm), in comparison to aqueous (68)Zn and (68)ZnO bulk particles (up to 2 μm), were determined for the estuarine snail Peringia ulvae following a 7 d exposure (nominally 20 μg (68)Zn L(-1)) and 28 d depuration. Detection of the (68)Zn label was achieved by high precision multiple-collector ICP-MS (MC-ICP-MS). Previous characterization in artificial estuarine water revealed that the NPs underwent initial aggregation and solubilized up to 60% within 1-2 days. Bulk and aqueous forms were significantly more bioavailable than (68)ZnO NPs (p < 0.05), but after correcting for dissolution, aqueous (0.074 L(-1) g(-1) d(-1)) and NP (0.070 L(-1) g(-1) d(-1)) uptake rate constants were highly comparable. The rate constant of loss for (68)Zn aqueous (0.012 ± 0.005 d(-1)) and (68)ZnO NPs (0.012 ± 0.007 d(-1)) were identical. These results strongly suggest that in this exposure scenario the bioaccumulation of Zn from ZnO NPs is primarily dependent upon solubility.
Introduction: Sulphur is a common element in the solar system and, indeed, is the 6 th most abund... more Introduction: Sulphur is a common element in the solar system and, indeed, is the 6 th most abundant element on Earth. In meteorites, sulphur most often occurs in the form of Fe sulphides (troilite) and, more rarely when formed under very reducing conditions, as Ca (oldhamite), Mn (alabandite), and Mg (niningerite) sulphides. Troilite is uquitious in iron meteorites [1]. A recent study was undertaken to determine the initial solar system abundance of 205 Pb and 205 Tl, using the decay scheme 205 Pb⇒ 205 Tl (t ½ = 15My). To do this, Pb and Tl were measured in metal and sulphide in IAB iron meteorites. A correlation between 205 Tl composition and 204 Pb/ 203 Tl was found in the metal phase and interpreted as an isochron. However, this correlation was not found in sulphides from the same meteorites, which causes some concern in the interpretation of the metal phase isochron data. The explanation was that the Tl isotope system was disturbed by kinetic stable isotope fractionation in the sulphide. Similar observations were made for the Pd-Ag decay system [3]. In order to better understand sulphide chemistry we have undertaken a study to explore the trace element composition of sulphide in Toluca (IAB iron) to determine the level of chemical disturbance that might exist in these nodules.
The neodymium (Nd) isotopic composition of seawater is commonly used as a proxy to study past cha... more The neodymium (Nd) isotopic composition of seawater is commonly used as a proxy to study past changes in the thermohaline circulation. The modern database for such reconstructions is however poor and the understanding of the underlying processes is incomplete. Here we present new observational data for Nd isotopes and concentrations from twelve seawater depth profiles, which follow the flow path of North Atlantic Deep Water (NADW) from its formation region in the North Atlantic to the northern equatorial Atlantic. Samples were collected during two cruises constituting the northern part of the Dutch GEOTRACES transect GA02 in 2010. The results show that the different water masses in the subpolar North Atlantic Ocean, which ultimately constitute NADW, have the following Nd isotope characteristics: Upper Labrador Sea Water (ULSW), εNd = −14.2 ± 0.3; Labrador Sea Water (LSW), εNd = −13.7 ± 0.9; Northeast Atlantic Deep Water (NEADW), εNd = −12.5 ± 0.6; Northwest Atlantic Bottom Water (NWABW), εNd = −11.8 ± 1.4. In the subtropics, where these source water masses have mixed to form NADW, which is exported to the global ocean, upper-NADW is characterised by εNd values of −13.2 ± 1.0 (2sd) and lower-NADW exhibits values of εNd = −12.4 ± 0.4 (2sd). While both signatures overlap within error, the signature for lower-NADW is significantly more radiogenic than the traditionally used value for NADW (εNd = −13.5) due to the dominance of source waters from the Nordic Seas (NWABW and NEADW). Comparison between the concentration profiles and the corresponding Nd isotope profiles with other water mass properties such as salinity, silicate concentrations, neutral densities and chlorofluorocarbon (CFC) concentration provides novel insights into the geochemical cycle of Nd and reveals that different processes are necessary to account for the observed Nd characteristics in the subpolar and subtropical gyres and throughout the vertical water column. While our data set provides additional insights into the contribution of boundary exchange in areas of sediment resuspension, the results for open ocean seawater demonstrate, at an unprecedented level, the suitability of Nd isotopes to trace modern water masses in the strongly advecting western Atlantic Ocean.
The neodymium (Nd) isotopic composition of seawater is commonly used as a proxy to study past cha... more The neodymium (Nd) isotopic composition of seawater is commonly used as a proxy to study past changes in the thermo-haline circulation. The modern database for such reconstructions is however poor and the understanding of the underlying processes is incomplete. Here we present new observational data for Nd isotopes and concentrations from twelve seawater depth profiles, which follow the flow path of North Atlantic Deep Water (NADW) from its formation region in the North Atlantic to the northern equatorial Atlantic. Samples were collected during two cruises constituting the northern part of the Dutch GEOTRACES transect GA02 in 2010. The results show that the different water masses in the subpolar North Atlantic Ocean, which ultimately constitute NADW, have the following Nd isotope characteristics: Upper Labrador Sea Water (ULSW), e Nd = À14.2 ± 0.3; Labrador Sea Water (LSW), e Nd = À13.7 ± 0.9; Northeast Atlantic Deep Water (NEADW), e Nd = À12.5 ± 0.6; Northwest Atlantic Bottom Water (NWABW), e Nd = À11.8 ± 1.4. In the subtropics, where these source water masses have mixed to form NADW, which is exported to the global ocean, upper-NADW is characterised by e Nd values of À13.2 ± 1.0 (2sd) and lower-NADW exhibits values of e Nd = À12.4 ± 0.4 (2sd). While both signatures overlap within error, the signature for lower-NADW is significantly more radiogenic than the traditionally used value for NADW (e Nd = À13.5) due to the dominance of source waters from the Nordic Seas (NWABW and NEADW). Comparison between the concentration profiles and the corresponding Nd isotope profiles with other water mass properties such as salinity, silicate concentrations, neutral densities and chlorofluorocarbon (CFC) concentration provides novel insights into the geochemical cycle of Nd and reveals that different processes are necessary to account for the observed Nd characteristics in the subpolar and subtropical gyres and throughout the vertical water column. While our data set provides additional insights into the contribution of boundary exchange in areas of sediment resuspension, the results for open ocean seawater demonstrate, at an unprecedented level, the suitability of Nd isotopes to trace modern water masses in the strongly advecting western Atlantic Ocean.
This is a repository copy of Towards an understanding of thallium isotope fractionation during ad... more This is a repository copy of Towards an understanding of thallium isotope fractionation during adsorption to manganese oxides.
Stable 142Ce/140Ce isotope measurements of CeO2 nanoparticles and purified materials for the purp... more Stable 142Ce/140Ce isotope measurements of CeO2 nanoparticles and purified materials for the purpose of stable isotope tracing.
During isotopic analysis of Cd by MC-ICP-MS, organic resin residue can perturb instrumental mass ... more During isotopic analysis of Cd by MC-ICP-MS, organic resin residue can perturb instrumental mass fractionation. These organic compounds can be removed by a liquid–liquid extraction procedure using heptane.
During isotopic analysis of Cd by MC-ICP-MS, organic resin residue can perturb instrumental mass ... more During isotopic analysis of Cd by MC-ICP-MS, organic resin residue can perturb instrumental mass fractionation. These organic compounds can be removed by a liquid–liquid extraction procedure using heptane.
Biological reference materials with well-characterised stable isotope compositions are lacking in... more 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 δ(66/64)Zn (which denotes the deviation of the (66)Zn/(64)Zn 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 ...
Improving the geochemical database available for characterising potential natural and anthropogen... more 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 208 Pb/ 207 Pb vs.
Sixty five urine samples obtained during one or two non-consecutive days from 10 healthy individu... more 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.
Anthropogenic emissions completely overwhelmed natural marine lead (Pb) sources during the past c... more Anthropogenic emissions completely overwhelmed natural marine lead (Pb) sources during the past century, predominantly due to leaded petrol usage. Here, based on Pb isotope measurements, we reassess the importance of natural and anthropogenic Pb sources to the tropical North Atlantic following the nearly complete global cessation of leaded petrol use. Significant proportions of up to 30–50% of natural Pb, derived from mineral dust, are observed in Atlantic surface waters, reflecting the success of the global effort to reduce anthropogenic Pb emissions. The observation of mineral dust derived Pb in surface waters is governed by the elevated atmospheric mineral dust concentration of the North African dust plume and the dominance of dry deposition for the atmospheric aerosol flux to surface waters. Given these specific regional conditions, emissions from anthropogenic activities will remain the dominant global marine Pb source, even in the absence of leaded petrol combustion.
Stable isotope compositions can potentially be used to trace atmospheric Cd inputs to the surface... more Stable isotope compositions can potentially be used to trace atmospheric Cd inputs to the surface ocean and anthropogenic Cd emissions to the atmosphere. Both of these applications may provide valuable insights into the effects of anthropogenic activities on the cycling of Cd in the environment. However, a lack of constraints for the Cd isotope compositions of atmospheric aerosols is currently hindering such studies. Here we present stable Cd isotope data for aerosols collected over the Tropical Atlantic Ocean. The samples feature variable proportions of mineral dust-derived and anthropogenic Cd, yet exhibit similar isotope compositions, thus negating the distinction of these Cd sources by using isotopic signatures in this region. Isotopic variability between these two atmospheric Cd sources may be identified in other areas, and thus warrants further investigation. Regardless, these data provide important initial constraints on the isotope composition of atmospheric Cd inputs to the ocean.
A novel ion exchange chromatography was developed for the separation of Cu from biological sample... more A novel ion exchange chromatography was developed for the separation of Cu from biological samples prior to stable isotope analyses. In contrast to previous methods, the new technique makes use of the different distribution coefficients of Cu(I) and Cu(II) to anion exchange resin and this helps to significantly improve the purity of the Cu separates obtained from biological samples, whilst maintaining crucial quantitative yields. Careful method validation confirmed that the procedure yields sufficiently pure Cu fractions after a single pass through the anion exchange columns, with a recovery of 100 AE 2%. Subsequent isotopic analyses of the Cu by multi-collector inductively coupled plasma mass spectrometry, using admixed Ni for mass bias correction, produced accurate Cu stable isotope data with a reproducibility of AE0.04& for pure standard solutions and of AE0.15& for samples of biological origin.
Zinc oxide nanoparticles (ZnO NPs) are widely used in commercial products and knowledge of their ... more Zinc oxide nanoparticles (ZnO NPs) are widely used in commercial products and knowledge of their environmental fate is a priority for ecological protection. Here we synthesized model ZnO NPs that were made from and thus labeled with the stable isotope (68)Zn and this enables highly sensitive and selective detection of labeled components against high natural Zn background levels. We combine high precision stable isotope measurements and novel bioimaging techniques to characterize parallel water-borne exposures of the common mudshrimp Corophium volutator to (68)ZnO NPs, bulk (68)ZnO, and soluble (68)ZnCl(2) in the presence of sediment. C. volutator is an important component of coastal ecosystems where river-borne NPs will accumulate and is used on a routine basis for toxicity assessments. Our results demonstrate that ionic Zn from ZnO NPs is bioavailable to C. volutator and that Zn uptake is active. Bioavailability appears to be governed primarily by the dissolved Zn content of the water, whereby Zn uptake occurs via the aqueous phase and/or the ingestion of sediment particles with adsorbed Zn from dissolution of ZnO particles. The high sorption capacity of sediments for Zn thus enhances the potential for trophic transfer of Zn derived from readily soluble ZnO NPs. The uncertainties of our isotopic data are too large, however, to conclusively rule out any additional direct uptake route of ZnO NPs by C. volutator.
ABSTRACT Stable isotope labeling coupled with high precision isotope ratio measurements by multip... more ABSTRACT Stable isotope labeling coupled with high precision isotope ratio measurements by multiple collector-ICP-MS is effective for tracing zinc from zinc oxide nanoparticles (ZnO NPs) in complex media and against a high zinc background. Using this technique, a previous study detected a slightly enhanced uptake of Zn in the blood of human females following dermal exposure to a sunscreen containing ZnO NPs, relative to a sunscreen of the same formulation but with larger ZnO particles (‘bulk’ material). Until now, the results of these exposures and the accuracy of the analyses, which require the resolution of subtle differences in Zn isotope ratios, have not been independently confirmed. Here we compare data from the previous study with results obtained in new, independent analyses of the same and additional samples, that were performed using similar techniques and instrumentation but in a different laboratory. The data sets are in good agreement, with a Pearson correlation coefficient of r ≈ 0.98, thus establishing the usefulness of the methods for tracing engineered ZnO NPs (and other anthropogenic sources of Zn) in Zn-rich biological materials. Previously unanalyzed blood samples from the earlier study provide further evidence for the increased uptake of Zn from ZnO NPs relative to bulk ZnO and they confirm that uptake rates decrease once sunscreen application has ceased.
The environmental behaviour of ZnO nanoparticles (NPs), their availability to, uptake pathways by... more The environmental behaviour of ZnO nanoparticles (NPs), their availability to, uptake pathways by, and biokinetics in the earthworm Lumbricus rubellus were investigated using stable isotope labelling. Zinc isotopically enriched to 99.5% in (68)Zn ((68)Zn-E) was used to prepare (68)ZnO NPs and a dissolved phase of (68)Zn for comparison. These materials enabled tracing of environmentally relevant (below background) NP additions to soil of only 5 mg (68)Zn-E kg(-1). Uptake routes were isolated by introducing earthworms with sealed and unsealed mouthparts into test soils for up to 72 hours. The Zn isotope compositions of the soils, pore waters and earthworms were then determined using multiple collector inductively coupled plasma mass spectrometry. Detection and quantification of (68)Zn-E in earthworm tissue was possible after only 4 hours of dermal exposure, when the uptake of (68)Zn-E had increased the total Zn tissue concentration by 0.03‰. The results demonstrate that at these reali...
ABSTRACT Zinc isotope compositions (δ66Zn) and concentrations were determined for metal samples o... more ABSTRACT Zinc isotope compositions (δ66Zn) and concentrations were determined for metal samples of 15 iron meteorites across groups IAB, IIAB, and IIIAB. Also analyzed were troilite and other inclusions from the IAB iron Toluca. Furthermore, the first Zn isotope data are presented for metal-silicate partitioning experiments that were conducted at 1.5 GPa and 1650 K. Three partitioning experiments with run durations of between 10 and 60 min provide consistent Zn metal-silicate partition coefficients of ∼0.7 and indicate that Zn isotope fractionation between molten metal and silicate is either small (at less than about ) or absent. Metals from the different iron meteorite groups display distinct ranges in Zn contents, with concentrations of 0.08-0.24 μg/g for IIABs, 0.8-2.5 μg/g for IIIABs, and 12-40 μg/g for IABs. In contrast, all three groups show a similar range of δ66Zn values (reported relative to ‘JMC Lyon Zn’) from to , with no clear systematic differences between groups. However, distinct linear trends are defined by samples from each group in plots of δ66Zn vs. 1/Zn, and these correlations are supported by literature data. Based on the high Zn concentration and δ66Zn ≈ 0 determined for a chromite-rich inclusion of Toluca, modeling is employed to demonstrate that the Zn trends are best explained by segregation of chromite from the metal phase. This process can account for the observed Zn-δ66Zn-Cr systematics of iron meteorite metals, if Zn is highly compatible in chromite and Zn partitioning is accompanied by isotope fractionation with Δ66Znchr-met . Based on these findings, it is likely that the parent bodies of the IAB complex, IIAB and IIIAB iron meteorites featured δ66Zn values of about −1.0 to , similar to the Zn isotope composition inferred for the bulk silicate Earth and results obtained for chondritic meteorites. Together, this implies that most solar system bodies formed with similar bulk Zn isotope compositions despite large differences in Zn contents.
Disordered copper metabolism may be important in the aetiology of Parkinsonism, as caeruloplasmin... more Disordered copper metabolism may be important in the aetiology of Parkinsonism, as caeruloplasmin is a key enzyme in handling oxidative stress and is involved in the synthesis pathway of dopamine. The human Cu metabolism of ten Parkinsonism patients was compared to ten healthy controls with the aid of a stable 65 Cu isotope tracer. The analyses of blood serum 65 Cu/ 63 Cu ratios yielded individual isotopic profiles, which indicate that the Cu metabolism is less controlled in patients with Parkinsonism.
This contribution evaluates two possible routes of stable isotope tracing for ZnO nanomaterials. ... more This contribution evaluates two possible routes of stable isotope tracing for ZnO nanomaterials. For this we carried out the first high precision Zn isotope analyses of commercially available ZnO nanomaterials, to investigate whether such materials exhibit isotope fractionations that can be exploited for tracing purposes. These measurements revealed Zn isotopic compositions (of δ(66/64)Zn = +0.28 to -0.31‰ relative to JMC Lyon Zn) that are indistinguishable from "normal" natural and anthropogenic Zn in environmental samples. Stable isotope tracing therefore requires the application of purpose-made isotopically enriched ZnO nanoparticles. A detailed evaluation identified the most suitable and cost-effective labeling isotopes for different analytical requirements and techniques. It is shown that, using relatively inexpensive (68)Zn for labeling, ZnO nanoparticles can be reliably detected in natural samples with a Zn background of 100 μg/g at concentrations as low as about 5 ng/g, if the isotopic tracing analyses are carried out by high precision mass spectrometry. Stable isotope tracing may also be able to differentiate between the uptake by organisms of particulate ZnO and Zn(2+) ions from the dissolution of nanoparticles.
Zinc oxide nanoparticles (ZnO NPs) are among the most commercialized engineered nanomaterials. Th... more Zinc oxide nanoparticles (ZnO NPs) are among the most commercialized engineered nanomaterials. Their biological impact in aquatic organisms has been associated with dissolution, but there is also evidence of nanospecific effects. In this study the waterborne uptake and efflux kinetics of isotopically labeled (68)ZnO NPs (7.8 ± 1.2 nm), in comparison to aqueous (68)Zn and (68)ZnO bulk particles (up to 2 μm), were determined for the estuarine snail Peringia ulvae following a 7 d exposure (nominally 20 μg (68)Zn L(-1)) and 28 d depuration. Detection of the (68)Zn label was achieved by high precision multiple-collector ICP-MS (MC-ICP-MS). Previous characterization in artificial estuarine water revealed that the NPs underwent initial aggregation and solubilized up to 60% within 1-2 days. Bulk and aqueous forms were significantly more bioavailable than (68)ZnO NPs (p < 0.05), but after correcting for dissolution, aqueous (0.074 L(-1) g(-1) d(-1)) and NP (0.070 L(-1) g(-1) d(-1)) uptake rate constants were highly comparable. The rate constant of loss for (68)Zn aqueous (0.012 ± 0.005 d(-1)) and (68)ZnO NPs (0.012 ± 0.007 d(-1)) were identical. These results strongly suggest that in this exposure scenario the bioaccumulation of Zn from ZnO NPs is primarily dependent upon solubility.
Introduction: Sulphur is a common element in the solar system and, indeed, is the 6 th most abund... more Introduction: Sulphur is a common element in the solar system and, indeed, is the 6 th most abundant element on Earth. In meteorites, sulphur most often occurs in the form of Fe sulphides (troilite) and, more rarely when formed under very reducing conditions, as Ca (oldhamite), Mn (alabandite), and Mg (niningerite) sulphides. Troilite is uquitious in iron meteorites [1]. A recent study was undertaken to determine the initial solar system abundance of 205 Pb and 205 Tl, using the decay scheme 205 Pb⇒ 205 Tl (t ½ = 15My). To do this, Pb and Tl were measured in metal and sulphide in IAB iron meteorites. A correlation between 205 Tl composition and 204 Pb/ 203 Tl was found in the metal phase and interpreted as an isochron. However, this correlation was not found in sulphides from the same meteorites, which causes some concern in the interpretation of the metal phase isochron data. The explanation was that the Tl isotope system was disturbed by kinetic stable isotope fractionation in the sulphide. Similar observations were made for the Pd-Ag decay system [3]. In order to better understand sulphide chemistry we have undertaken a study to explore the trace element composition of sulphide in Toluca (IAB iron) to determine the level of chemical disturbance that might exist in these nodules.
The neodymium (Nd) isotopic composition of seawater is commonly used as a proxy to study past cha... more The neodymium (Nd) isotopic composition of seawater is commonly used as a proxy to study past changes in the thermohaline circulation. The modern database for such reconstructions is however poor and the understanding of the underlying processes is incomplete. Here we present new observational data for Nd isotopes and concentrations from twelve seawater depth profiles, which follow the flow path of North Atlantic Deep Water (NADW) from its formation region in the North Atlantic to the northern equatorial Atlantic. Samples were collected during two cruises constituting the northern part of the Dutch GEOTRACES transect GA02 in 2010. The results show that the different water masses in the subpolar North Atlantic Ocean, which ultimately constitute NADW, have the following Nd isotope characteristics: Upper Labrador Sea Water (ULSW), εNd = −14.2 ± 0.3; Labrador Sea Water (LSW), εNd = −13.7 ± 0.9; Northeast Atlantic Deep Water (NEADW), εNd = −12.5 ± 0.6; Northwest Atlantic Bottom Water (NWABW), εNd = −11.8 ± 1.4. In the subtropics, where these source water masses have mixed to form NADW, which is exported to the global ocean, upper-NADW is characterised by εNd values of −13.2 ± 1.0 (2sd) and lower-NADW exhibits values of εNd = −12.4 ± 0.4 (2sd). While both signatures overlap within error, the signature for lower-NADW is significantly more radiogenic than the traditionally used value for NADW (εNd = −13.5) due to the dominance of source waters from the Nordic Seas (NWABW and NEADW). Comparison between the concentration profiles and the corresponding Nd isotope profiles with other water mass properties such as salinity, silicate concentrations, neutral densities and chlorofluorocarbon (CFC) concentration provides novel insights into the geochemical cycle of Nd and reveals that different processes are necessary to account for the observed Nd characteristics in the subpolar and subtropical gyres and throughout the vertical water column. While our data set provides additional insights into the contribution of boundary exchange in areas of sediment resuspension, the results for open ocean seawater demonstrate, at an unprecedented level, the suitability of Nd isotopes to trace modern water masses in the strongly advecting western Atlantic Ocean.
The neodymium (Nd) isotopic composition of seawater is commonly used as a proxy to study past cha... more The neodymium (Nd) isotopic composition of seawater is commonly used as a proxy to study past changes in the thermo-haline circulation. The modern database for such reconstructions is however poor and the understanding of the underlying processes is incomplete. Here we present new observational data for Nd isotopes and concentrations from twelve seawater depth profiles, which follow the flow path of North Atlantic Deep Water (NADW) from its formation region in the North Atlantic to the northern equatorial Atlantic. Samples were collected during two cruises constituting the northern part of the Dutch GEOTRACES transect GA02 in 2010. The results show that the different water masses in the subpolar North Atlantic Ocean, which ultimately constitute NADW, have the following Nd isotope characteristics: Upper Labrador Sea Water (ULSW), e Nd = À14.2 ± 0.3; Labrador Sea Water (LSW), e Nd = À13.7 ± 0.9; Northeast Atlantic Deep Water (NEADW), e Nd = À12.5 ± 0.6; Northwest Atlantic Bottom Water (NWABW), e Nd = À11.8 ± 1.4. In the subtropics, where these source water masses have mixed to form NADW, which is exported to the global ocean, upper-NADW is characterised by e Nd values of À13.2 ± 1.0 (2sd) and lower-NADW exhibits values of e Nd = À12.4 ± 0.4 (2sd). While both signatures overlap within error, the signature for lower-NADW is significantly more radiogenic than the traditionally used value for NADW (e Nd = À13.5) due to the dominance of source waters from the Nordic Seas (NWABW and NEADW). Comparison between the concentration profiles and the corresponding Nd isotope profiles with other water mass properties such as salinity, silicate concentrations, neutral densities and chlorofluorocarbon (CFC) concentration provides novel insights into the geochemical cycle of Nd and reveals that different processes are necessary to account for the observed Nd characteristics in the subpolar and subtropical gyres and throughout the vertical water column. While our data set provides additional insights into the contribution of boundary exchange in areas of sediment resuspension, the results for open ocean seawater demonstrate, at an unprecedented level, the suitability of Nd isotopes to trace modern water masses in the strongly advecting western Atlantic Ocean.
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Papers by Mark Rehkämper