Precise measurement of Fe isotopes in marine and biological samples by pseudo-high-resolution multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS).

This paper introduces an enhanced technique for analyzing iron isotopes in complex marine and biological samples. A dedicated iron purification method for biological marine matrices, utilizing three ion exchange columns, is validated. The MC-ICPMS in pseudo-high-resolution mode determines precise iron isotopic ratios, with sensitivity improved through the DSN-100 desolvating nebulizer system and Apex-IR. Only 2 µg of iron on DSN versus 1 µg on Apex is needed for six replicates (30-60 times improvement) while 10 to 20 µg is required for a single measurement on a wet system considering the resolution power (Rp) is maintained at 11,000-13,000. The Ni-doping method with a Fe/Ni ratio of 1 yields more accurate isotopic ratios than standard-sample bracketing alone. Measurement reproducibility of triplicate samples from marine biological experiments on MC-ICPMS is ± 0.03‰ (2SD) for δ56Fe and ± 0.07‰ for δ57Fe (2SD). This study introduces a novel iron purification process specifically designed for marine and biological samples, enhancing sensitivity and enabling more reliable measurements with smaller sample sizes and reduced uncertainties. It proposes iron isotopic compositions for biological reference materials, offering a valuable reference dataset in diverse scientific disciplines.

Iron isotopic fractionation driven by low-temperature biogeochemical processes.

Iron is geologically important and biochemically crucial for all microorganisms, plants and animals due to its redox exchange, the involvement in electron transport and metabolic processes. Despite the abundance of iron in the earth crust, its bioavailability is very limited in nature due to its occurrence as ferrihydrite, goethite, and hematite where they are thermodynamically stable with low dissolution kinetics in neutral or alkaline environments. Organisms such as bacteria, fungi, and plants have evolved iron acquisition mechanisms to increase its bioavailability in such environments, thereby, contributing largely to the iron cycle in the environment. Biogeochemical cycling of metals including Fe in natural systems usually results in stable isotope fractionation; the extent of fractionation depends on processes involved. Our review suggests that significant fractionation of iron isotopes occurs in low-temperature environments, where the extent of fractionation is greatly governed by several biogeochemical processes such as redox reaction, alteration, complexation, adsorption, oxidation and reduction, with or without the influence of microorganisms. This paper includes relevant data sets on the theoretical calculations, experimental prediction, as well as laboratory studies on stable iron isotopes fractionation induced by different biogeochemical processes.

New Insights on End-Stage Renal Disease and Healthy Individual Gut Bacterial Translocation: Different Carbon Composition of Lipopolysaccharides and Different Impact on Monocyte Inflammatory Response.

Chronic kidney disease induces disruption of the intestinal epithelial barrier, leading to gut bacterial translocation. Here, we appreciated bacterial translocation by analyzing circulating lipopolysaccharides (LPS) using two methods, one measuring only active free LPS, and the other quantifying total LPS as well as LPS lipid A carbon chain length. This was done in end-stage renal disease (ESRD) patients and healthy volunteers (HV). We observed both higher LPS concentration in healthy volunteers and significant differences in composition of translocated LPS based on lipid A carbon chain length. Lower LPS activity to mass ratio and higher concentration of high-density lipoproteins were found in HV, suggesting a better plasma capacity to neutralize LPS activity. Higher serum concentrations of soluble CD14 and pro-inflammatory cytokines in ESRD patients confirmed this hypothesis. To further explore whether chronic inflammation in ESRD patients could be more related to LPS composition rather than its quantity, we tested the effect of HV and patient sera on cytokine secretion in monocyte cultures. Sera with predominance of 14-carbon chain lipid A-LPS induced higher secretion of pro-inflammatory cytokines than those with predominance of 18-carbon chain lipid A-LPS. TLR4 or LPS antagonists decreased LPS-induced cytokine production by monocytes, demonstrating an LPS-specific effect. Thereby, septic inflammation observed in ESRD patients may be not related to higher bacterial translocation, but to reduced LPS neutralization capacity and differences in translocated LPS subtypes.

Climate-driven fluxes of organic-bound uranium to an alpine lake over the Holocene.

Uranium (U) isotopic signatures and concentration in sediments are widely used as paleo-redox proxies, as the behavior of U is often controlled by bottom water oxygenation. Here, we investigated the processes controlling U accumulation in the sediments of Lake Nègre (Mediterranean Alps, South-East France) over the past 9200 years. Exceptionally high natural U concentrations (350-1250 µg·g-1) allowed the measurement of U along with other elements by high-resolution X-Ray Fluorescence core-scanning. Weathering and erosion proxies (Ti content, Zr/Al and K/Ti ratios) indicate that sedimentary inputs were controlled by Holocene climatic variations. After a period of low erosion during the Holocene Climatic Optimum, a major regime shift was recorded at 4.2 kyr BP when terrigenous fluxes consistently increased until present with high sensitivity to centennial-scale climatic events. Sedimentary organic matter (OM) inputs were dominated by terrigenous OM from the catchment soils until 2.4 kyr BP, as attested by carbon to nitrogen (C/N) and bromine to organic carbon (Br/TOC) ratios. From 2.4 kyr BP to present, lake primary production and soils equally contributed to sedimentary OM. Uranium fluxes to the sediments were well correlated to terrigenous OM fluxes from 7 kyr BP to present, showing that U supply to the lake was controlled by U scavenging in the soils of the watershed followed by transport of U bound to detrital organic particles. Higher U/OM ratios before 7 kyr BP likely reflect the development of the upstream wetland. The fluctuations of U sedimentary inputs appear to be independent of bottom water oxygenation, as estimated from constant Fe/Mn ratios and δ238U isotopic signatures, and rather controlled by the production, erosion and sedimentation of terrigenous OM. This finding confirms that the use of U (and potentially other metals with high affinity to OM) concentrations alone should be used with caution for paleo-redox reconstructions.

Diagenetic formation of uranium-silica polymers in lake sediments over 3,300 years.

The long-term fate of uranium-contaminated sediments, especially downstream former mining areas, is a widespread environmental challenge. Essential for their management is the proper understanding of uranium (U) immobilization mechanisms in reducing environments. In particular, the long-term behavior of noncrystalline U(IV) species and their possible evolution to more stable phases in subsurface conditions is poorly documented, which limits our ability to predict U long-term geochemical reactivity. Here, we report direct evidence for the evolution of U speciation over 3,300 y in naturally highly U-enriched sediments (350-760 µg ⋅ g-1 U) from Lake Nègre (Mercantour Massif, Mediterranean Alps, France) by combining U isotopic data (δ238U and (234U/238U)) with U L3 -edge X-ray absorption fine structure spectroscopy. Constant isotopic ratios over the entire sediment core indicate stable U sources and accumulation modes, allowing for determination of the impact of aging on U speciation. We demonstrate that, after sediment deposition, mononuclear U(IV) species associated with organic matter transformed into authigenic polymeric U(IV)-silica species that might have partially converted to a nanocrystalline coffinite (UIVSiO4·nH2O)-like phase. This diagenetic transformation occurred in less than 700 y and is consistent with the high silica availability of sediments in which diatoms are abundant. It also yields consistency with laboratory studies that proposed the formation of colloidal polynuclear U(IV)-silica species, as precursors for coffinite formation. However, the incomplete transformation observed here only slightly reduces the potential lability of U, which could have important implications to evaluate the long-term management of U-contaminated sediments and, by extension, of U-bearing wastes in silica-rich subsurface environments.

Detection of nanoparticles by single-particle ICP-MS with complete transport efficiency through direct nebulization at few-microlitres-per-minute uptake rates.

Measurement of nanoparticle (NP) concentration and size by single-particle inductively coupled plasma mass spectrometry (spICP-MS) usually requires the use of a NP reference material to determine the loss of NPs and/or ions during their transport from the sample solution to the detection system. The determination of this loss, qualified as nebulization efficiency (ηNebulization) and/or transport efficiency (ηTransport), is time-consuming, costly and lacks reliability. Nebulization of the NPs directly into the plasma (without a spray chamber) results in ηNebulization = 100% and is thus a promising strategy to avoid these calibration steps. In this work, we used the µ-dDIHEN introduction system: a demountable direct injection high-efficiency nebulizer (dDIHEN) hyphenated to a flow-injection valve and a gas displacement pump. For the first time with a continuous flow nebulizer, complete transport efficiency was reached (i.e. ηTransport = 100%). Operated at a very low uptake rate (as low as 8 µL min-1), the µ-dDIHEN accurately and reproducibly determined average diameters of Au-, Ag- and Pt-NPs, in full agreement with their reference values. It was also successfully tested for Au-NPs in complex matrices, such as surface waters. spICP-MS analyses with the µ-dDIHEN sample introduction system only require a dissolved standard calibration to determine NP average diameter (dNPs in nm) and number concentration (NNPs) from the simplified set of equations: [Formula: see text] and [Formula: see text]Graphical abstract.

End-Stage Renal Disease-Associated Gut Bacterial Translocation: Evolution and Impact on Chronic Inflammation and Acute Rejection After Renal Transplantation.

Chronic inflammation in end-stage renal disease (ESRD) is partly attributed to gut bacterial translocation (GBT) due to loss of intestinal epithelium integrity. Increased levels of circulating lipopolysaccharide (LPS) -a surrogate marker of GBT- contribute to maintain a chronic inflammatory state. However, circulating LPS can be neutralized by lipoproteins and transported to the liver for elimination. While ESRD-associated GBT has been widely described, less is known about its changes and impact on clinical outcome after kidney transplantation (KT). One hundred and forty-six renal transplant recipients with serum samples obtained immediately before and 1 year after transplantation (1-Year post KT) were included. Intestinal epithelium integrity (iFABP), total LPS (by measuring 3-hydroxymyristate), LPS activity (biologically active LPS measured by the LAL assay), inflammatory biomarkers (sCD14 and cytokines), lipoproteins and LPS-binding proteins (LBP and phospholipid transfer protein [PLTP] activity) were simultaneously measured. At 1-Year post KT, iFABP decreased but remained higher than in normal volunteers. Total LPS concentration remained stable while LPS activity decreased. Inflammation biomarkers decreased 1-Year post KT. We concomitantly observed an increase in lipoproteins. Higher sCD14 levels before transplantation was associated with lower incidence of acute rejection. Although GBT remained stable after KT, the contemporary increase in lipoproteins could bind circulating LPS and contribute concomitantly to neutralization of LPS activity, as well as improvement in ESRD-associated chronic inflammation. Chronic exposure to LPS in ESRD could promote endotoxin tolerance and explain why patients with higher pre-transplant sCD14 are less prompt to develop acute rejection after transplantation.

Earthquake-induced structural deformations enhance long-term solute fluxes from active volcanic systems.

Evidence for relationships between seismotectonic activity and dissolved weathering fluxes remains limited. Motivated by the occurrence of new springs emerging after the 2016 Kumamoto earthquake and supported by historical groundwater data, this study focuses on the long-term effect of near-surface structural deformation on the contribution of deep, highly saline fluids to the solute fluxes from the Aso caldera, Kyushu, Japan. Available hydrologic and structural data suggest that concentrated, over-pressured groundwaters migrate to the surface when new hydraulic pathways open during seismic deformation. These new springs have a hydrochemical fingerprint (including δDH2O, δ18OH2O, δ7Li, δ11B, δ18OSO4, and δ34SSO4) indistinguishable from long-established confined groundwater that likely reflects a mixture of infiltrated meteoric water with high-sulfate hydrothermal fluids. A comparison of historical hydrochemistry data and patterns of past seismicity suggests that discharge of deep fluids is associated with similar deformation structures to those observed during the Kumamoto earthquake, and that seismic activity plays an important role over historic timescales in delivering the majority of the solutes to the caldera outlet, sustaining fluxes that are amongst the world's highest. This upwelling mechanism might be relevant for other systems too, and could contribute to the over-proportional share of active volcanic areas in global weathering fluxes.

Are boron isotopes a reliable tracer of anthropogenic inputs to rivers over time?

This study aims at determining how the boron signal of the Seine River evolved in terms of concentration and isotopic signatures over eighteen years (1994-95 and 2006-12) and if boron isotopes can reliably trace anthropogenic inputs over time. In the anthropised Seine River watershed, boron is widely released by human activities, and even if boron concentrations ([B]) are below the potability limit, our study confirms the potential of boron isotopes (δ11B) to trace urban anthropogenic contaminations. Between 1994 and 2012, [B] have decreased across the anthropised part of the Seine River basin (and by a factor of two in Paris) while δ11B has increased. This means either that urban inputs have been reduced or that the boron signature of urban inputs has changed over time. Both hypotheses are in agreement with the decrease of perborate consumption in Europe over 15years and are not mutually exclusive. Results of a thorough analysis of urban effluents from the sewage network of Paris conurbation that are in fine released to the Seine River suggest a shift of the urban δ11B from -10‰ in 1994 to 1.5±2.0‰ in 2012, in agreement with our second hypothesis. We attribute this change to the removal of perborates from detergents rather than to the modernisation of wastewater treatment network, because it does not significantly impact the wastewater boron signatures. Eighteen years after the first assessment and despite the decreased use of perborates, geochemical and isotopic mass budgets confirm, that boron in the Seine River basin is mainly released from urban activities (60-100%), especially in Paris and the downstream part of the basin. Contrastingly, in headwaters and/or tributaries with low urbanisation, the relative boron input to river from agricultural practices and rains increased, up to 10% and by 10 to 30%, respectively.

Trace metals dynamics under contrasted land uses: contribution of statistical, isotopic, and EXAFS approaches.

Three sub-basins of the Seine River (France) under contrasted land uses (i.e., forested, agricultural, and urban) have been investigated in order to assess the origin and seasonal variation of trace metals, and evaluate their geochemical background and dynamics. Our results highlight a high anthropogenic impact on all elements for both the dissolved and particulate fractions. The main source for each element in the dissolved phase was determined and shows that transition and post-transition metals mainly originate from forested areas, while alkali and alkaline earth elements, metalloids, and halogens rather originate from agricultural land use. Conversely, for the particulate phase, most of the elements cannot be associated with a specific land use. Seasonal variation of elements was assessed according to the forested and agricultural land uses, and geochemical backgrounds were determined using average export rates, highlighting that the geochemical background for the forested land use is higher than the agricultural one for most of the elements. Finally, to confirm those results, Zn dynamics in the three characteristic sub-basins and between the different land uses was investigated using a combination of Zn speciation, Zn isotopic ratio, and Zn export rates.

Legacy of contaminant N sources to the NO3- signature in rivers: a combined isotopic (δ15N-NO3-, δ18O-NO3-, δ11B) and microbiological investigation.

Nitrate content of surface waters results from complex mixing of multiple sources, whose signatures can be modified through N reactions occurring within the different compartments of the whole catchment. Despite this complexity, the determination of nitrate origin is the first and crucial step for water resource preservation. Here, for the first time, we combined at the catchment scale stable isotopic tracers (δ15N and δ18O of nitrate and δ11B) and fecal indicators to trace nitrate sources and pathways to the stream. We tested this approach on two rivers in an agricultural region of SW France. Boron isotopic ratios evidenced inflow from anthropogenic waters, microbiological markers revealed organic contaminations from both human and animal wastes. Nitrate δ15N and δ18O traced inputs from the surface leaching during high flow events and from the subsurface drainage in base flow regime. They also showed that denitrification occurred within the soils before reaching the rivers. Furthermore, this study highlighted the determinant role of the soil compartment in nitrate formation and recycling with important spatial heterogeneity and temporal variability.

Mass-dependent and -independent signature of Fe isotopes in magnetotactic bacteria.

Magnetotactic bacteria perform biomineralization of intracellular magnetite (Fe3O4) nanoparticles. Although they may be among the earliest microorganisms capable of biomineralization on Earth, identifying their activity in ancient sedimentary rocks remains challenging because of the lack of a reliable biosignature. We determined Fe isotope fractionations by the magnetotactic bacterium Magnetospirillum magneticum AMB-1. The AMB-1 strain produced magnetite strongly depleted in heavy Fe isotopes, by 1.5 to 2.5 per mil relative to the initial growth medium. Moreover, we observed mass-independent isotope fractionations in (57)Fe during magnetite biomineralization but not in even Fe isotopes ((54)Fe, (56)Fe, and (58)Fe), highlighting a magnetic isotope effect. This Fe isotope anomaly provides a potential biosignature for the identification of magnetite produced by magnetotactic bacteria in the geological record.

Determination of Bromine Stable Isotope Ratios from Saline Solutions by "Wet Plasma" MC-ICPMS Including a Comparison between High- and Low-Resolution Modes, and Three Introduction Systems.

We describe a novel method for measuring stable bromine isotope compositions in saline solutions such as seawater, brines, and formation waters. Bromine is extracted from the samples by ion exchange chromatography on anion exchange resin AG 1-X4 with NH4NO3 and measured by MC-ICP-MS in wet plasma conditions. Sample introduction through a small spray chamber provided good sensitivity and stability of the Br signal compared to direct injection (d-DIHEN) and desolvation (APEX). NH4NO3 media allowed fast (<3 min) washing of the system. Despite Ar2H(+) spectral interference on (81)Br(+), for the first time low-resolution mode (with appropriate tuning of Ar2H(+)/(81)Br(+) sensitivity) gave higher precision (81)Br/(79)Br measurements than high-resolution (HR), due to the narrowness of the (81)Br(+) plateau in HR mode and to slight mass drifting with time. Additionally, 1 µg Br is the lower amount needed for a triplicate determination of δ(81)Br by MC-ICP-MS, with reproducibility often < ± 0.1‰ (2 SD). Four HBr solutions were prepared by evaporation/condensation in order to obtain in-house reference solutions with 3‰ variations in δ(81)Br and to assess the reproducibility and accuracy of the method. Long-term (>3 years) reproducibility between ± 0.11 and ± 0.27‰ (2 SD) was obtained for the four HBr solutions, the international standard reference material NIST SRM 977 (δ(81)BrSMOB = -0.65 ± 1.1‰, 1 SD), and seawaters (synthetic and natural). The accuracy of the MC-ICP-MS method was validated by comparing the δ(81)Br obtained for these solutions with dual-inlet IRMS measurements on CH3Br gas. Finally, the method was successfully applied to 22 natural samples.

Zn Isotope Fractionation during Sorption onto Kaolinite.

In this study, we quantify zinc isotope fractionation during its sorption onto kaolinite, by performing experiments under various pH, ionic strength, and total Zn concentrations. A systematic enrichment in heavy Zn isotopes on the surface of kaolinite was measured, with Δ(66)Znadsorbed-solution ranging from 0.11‰ at low pH and low ionic strength to 0.49‰ at high pH and high ionic strength. Both the measured Zn concentration and its isotopic ratio are correctly described using a thermodynamic sorption model that considers two binding sites: external basal surfaces and edge sites. Based on this modeling approach, two distinct Zn isotopic fractionation factors were calculated: Δ(66)Znadsorbed-solution = 0.18 ± 0.06‰ for ion exchange onto basal sites, and Δ(66)Znadsorbed-solution = 0.49 ± 0.06‰ for specific complexation onto edge sites. These two distinct factors indicate that Zn isotope fractionation is dominantly controlled by the chemical composition of the solution (pH, ionic strength).

Transient signal isotope analysis: validation of the method for isotope signal synchronization with the determination of amplifier first-order time constants.

RATIONALE: During transient signal acquisition by Multi-Collection Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS), an isotope ratio increase or decrease (isotopic drift hereafter) is often observed which is related to the different time responses of the amplifiers involved in multi-collection. This isotopic drift affects the quality of the isotopic data and, in a recent study, a method of internal amplifier signal synchronization for isotope drift correction was proposed. In this work the determination of the amplifier time constants was investigated in order to validate the method of internal amplifier signal synchronization for isotope ratio drift correction. METHODS: Two different MC-ICPMS instruments, the Neptune and the Neptune Plus, were used, and both the lead transient signals and the signal decay curves of the amplifiers were investigated. RESULTS: Our results show that the first part of the amplifier signal decay curve is characterized by a pure exponential decay. This part of the signal decay was used for the effective calculation of the amplifier first-order time constants. The small differences between these time constants were compared with time lag values obtained from the method of isotope signal synchronization and were found to be in good agreement. CONCLUSIONS: This work proposes a way of determining amplifier first-order time constants. We show that isotopic drift is directly related to the amplifier first-order time constants and the method of internal amplifier signal synchronization for isotope ratio drift correction is validated.

Persistence of lymphocyte function perturbations after granulocyte-colony-stimulating factor mobilization and cytapheresis in normal peripheral blood stem cell donors.

BACKGROUND: The short-term effects of granulocyte-colony-stimulating factor (G-CSF) have been extensively studied, but recent reports of G-CSF-induced genetic perturbations raised concerns regarding its long-term safety. In this respect, duration of G-CSF-induced perturbations has been less studied than short-term effects and needs to be evaluated. STUDY DESIGN AND METHODS: G-CSF mobilization-induced immunologic alterations were prospectively analyzed in a cohort of 24 healthy donors. Blood samples were taken before G-CSF administration; at the time of administration; and at 1, 3, 6, and 12 months and analyzed for blood cell counts and in vitro cytokines (interleukin [IL]-2, -8, and -10) and immunoglobulin production, quantified in the culture supernatant of peripheral blood mononuclear cells (PBMNCs) after, respectively, phytohemagglutinin and pokeweed mitogen stimulation. RESULTS: Platelet, granulocyte, monocyte, B, and dendritic blood cell counts as well as the IL-2, -8, and -10 secretion by PBMNCs, perturbed at the time of G-CSF mobilization, returned to baseline values at 1 month, with T-cell and natural killer cell counts recovering at 3 months. In vitro immunoglobulin production was increased up to 6 months after mobilization. CONCLUSION: Although assessment of the potential long-term risk of G-CSF administration will require prolonged observation of larger cohorts, our data show that the duration of immunologic perturbations may be more persistent than previously anticipated, especially for B-cell functional alterations. Most perturbations remain, however, transient with a return to baseline values within 1 year.

Zinc isotopic fractionation: why organic matters.

Zinc isotopic fractionation during adsorption onto a purified humic acid (PHA), an analogue of organic matter (OM), has been investigated experimentally as a function of pH. The Donnan Membrane device (DM) was used to separate Zn bound to the PHA from free Zn2+ ions in solution and allowed us to measure the isotopic ratios of free Zn2+. Below pH 6, adsorption of Zn on the PHA resulted in no measurable isotopic fractionation, while at higher pH, Zn bound to PHA was heavier than free Zn2+ (delta66Zn(PHA-FreeZn2+) = +0.24 per thousand +/- 0.06 2sigma, n = 4). This can be explained by changes in Zn speciation with pH, with higher complexation constants and shorter bond lengths for Zn-PHA complex compared to the free Zn2+. Complexation of Zn with PHA occurred mostly through binding to high affinity sites (HAS) and low affinity sites (LAS). Fractionation factors for 66Zn/64Zn ratios determined by mass balance calculations were equal to 1.0004 for HAS (alpha(HAS-solution)) and 1.000 for LAS (alpha(LAS-soultion)). delta66Zn(OM-FreeZn2+) should then vary according to the heterogeneous nature of the OM, because of the variable relative proportions of these two types of sites. The NICA-Donnan model, along with these fractionation factors and measured delta66Zn(TotalDissolved), was used to simulate the corresponding isotopic composition of free Zn2+ in the Seine River, France: delta66Zn(TotalDissolved-FreeZn2+) varied from +0.02 per thousand to +0.18 per thousand, depending on the HAS/LAS ratio assumed for the OM. This study allows a better understanding of Zn isotope fractionation mechanisms associated with organic mater binding.

Zinc isotopes in the Seine River waters, France: a probe of anthropogenic contamination.

The use of zinc (Zn) isotope ratios as a tracer of anthropogenic contamination has been assessed using an extensive collection of river water samples from the Seine River basin (France) collected between 2004 and 2007. The 66Zn/64Zn ratios (expressed as delta66Zn) of dissolved Zn have been measured by MC-ICP-MS after chemical separation of Zn using an improved technique adapted to large volumes of water. Significant isotopic variations (0.07-0.58 per thousand) occur along a transect from pristine areas of the Seine basin to the estuary and with time in Paris, and are coherent with the Zn enrichment factor. Dissolved Zn in the Seine River displays conservative behavior, making Zn isotopes a good tracer of the different sources of contamination. Dissolved Zn in the Seine River is essentially of anthropogenic origin (> 90%) compared to natural sources (< 7%). Roof leaching from Paris conurbation is a major source of Zn, characterized by low delta66Zn values that are distinct from other natural and anthropogenic sources of Zn. Our study highlights the absence of distinctive delta66Zn signatures of fertilizer, compost or rain in river waters of rural areas, and therefore suggests the strong retention of Zn in the soils of the Basin. Our study demonstrates that Zn isotope ratios will be a powerful new tool to trace pathways of anthropogenic Zn in the environment.

Studies of strontium biokinetics in humans. Part 2: uptake of strontium from aqueous solutions and labelled foodstuffs.

The accidental release of radioactive isotopes of strontium, mainly (90)Sr, into the environment and its transfer into the biosphere results in an internal radiation exposure of the affected population. In order to obtain reliable estimates of the committed dose due to an intake of Sr radionuclides, reliable information on its metabolic behaviour inside the human body is needed, i.e. biokinetic data on fractional uptake from contaminated foodstuffs, distribution to and retention in different organs and tissues of the human body. Such information can be obtained by tracer kinetic investigations. The committed effective dose is dependent on the fractional intestinal absorption of the ingested activity (f(1) value). The International Commission on Radiological Protection in its publication ICRP 67 adopted an f(1) value of 0.3 for adults. This study is aimed at investigating if the value corresponds with the actual uptake from contaminated foodstuffs. Aqueous solutions and contaminated vegetables, i.e. cress and salad (lettuce) were used as test materials. For this purpose, the methodology for intrinsic labelling of foodstuffs described in part 1 was applied. For aqueous solutions, a mean f(1) value of 0.63+/-0.14 (mean +/- SD) was obtained by administering 1 mg of strontium. The uptake of Sr from cress intrinsically labelled with about 1 mg Sr almost corresponds to that from aqueous solutions (f(1)=0.62+/-0.10), but from lettuce it is reduced by a factor of 2 (f(1)=0.27+/-0.08).