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A new method for determining 236U/238U isotope ratios in environmental samples by means OF ICP-MS/MS

Year: 2020
Products: Apex systems
Authors: Diez-Fernández, S;Jaegler, H;Bresson, C;Chartier, F;Evrard, O;Hubert, A;Nonell, A;Pointurier, F;Isnard, H;
Journal: Talanta

The 236U/238U isotope ratio is a widely used tracer, which provides information on source identification for safeguard purposes, nuclear forensic studies and environmental monitoring. This paper describes an original approach to determine 236U/238U ratios, below 10-8, in environmental samples by combination of ICP-MS/MS for 236U/238U ratio and multiple collector ICPMS measurements for 235U/238U and 234U/235U isotope ratios. Since the hydride form of UO+ (UOH+) is less prone to occur than UH+, we were focused on the oxidised forms of uranium in order to reduce hydride based-interferences in ICP-MS/MS. Then, in-cell ion-molecule reactions with O2 and CO2 were assessed to detect the uranium isotopes in mass-shift mode (Q1: U+ → Q2: UO+). The performances in terms of UO+ sensitivity and minimisation of hydride form of UO+ were evaluated using five different desolvating systems. The best conditions, using an Apex Ω or an Aridus system, produced uranium oxide hydride rate (235U16O1H+/235U16O+) of about 10-7 with O2 in the collision cell. The method was validated through measurements of two certified IRMM standards with 236U/238U isotope ratio of 1.245 × 10-7 and 1.052 × 10-8, giving results in agreement with certified reference values. The relative standard deviations on seven independent measurements for each standard were respectively of 1.5% and 6.2%. Finally, environmental samples corresponding to sediments from the radioactive contamination plume emitted by the Fukushima Daiichi Nuclear Power Plant accident were analysed after a well-established uranium chemical separation procedure. 236U/238U atomic ratios between 1.5 × 10-8 and 7 × 10-9 were obtained with a level accuracy lower than 20%.

Tracing Dissolved Lead Sources in the Canadian Arctic: Insights from the Canadian GEOTRACES Program

Year: 2019
Products: low-flow PTFE nebulizer
Authors: Colombo, M;Rogalla, B;Myers, P;Allen, S;Orians, K;
Journal: ACS Earth Space Chem.

This study addresses an important knowledge gap in the distribution of lead (Pb) in the Arctic Ocean, by presenting dissolved Pb concentrations from samples collected during the GEOTRACES Canadian cruise in 2015. Dissolved Pb showed an increase in concentration from the Canada Basin toward Baffin Bay and the Labrador Sea. Canada Basin was the most isolated region from anthropogenic Pb inputs with low background concentrations (1.4−6.2 pmol kg−1 ) across most of the basin, although higher Pb features from the advection of Pacific-derived waters and sea ice meltwater were present. Likewise, high-Pb peaks (13.5−26.6 pmol kg−1 ) along narrow isopycnal surfaces (σθ, 27.4−27.6) in Baffin Bay were attributed to the advection of North Atlantic waters spreading a high-Pb signature into the bay, contrasting with the low values (2.5−7.4 pmol kg−1 ) present in the mixed layer, Arctic and Baffin Bay deep waters. The Labrador Sea, largely influenced by the recirculation of North Atlantic waters, had the highest Pb concentrations (∼17−34 pmol kg−1 ) measured in this study. The Canadian Arctic Archipelago (CAA) represents a transition environment influenced by Arctic waters imprinting a low-Pb signature in the western CAA and the southern side of Parry Channel, while Baffin Bay waters prevailed in the eastern CAA recirculating westward along the northern side of Parry Channel and progressively losing their relatively high Pb signature. Extremely low concentrations were measured in Canada Basin and CAA waters, which reflect the remoteness of this region from anthropogenic inputs as well as the old ventilation age of deep waters’ masses, providing a baseline for assessing future Pb studies. Finally, we successfully integrate modeling data with field observations demonstrating that dissolved lead, due to its distinctive anthropogenic signature in North Atlantic waters, can be a useful complementary tracer of water masses in the Canadian Arctic Ocean.

Copper speciation in different marine ecosystems around New Zealand

Year: 2019
Products: seaFAST
Authors: Zitoun, R;
Journal: Thesis

Copper (Cu) is an important bioactive trace metal in the marine environment, acting as an essential micronutrient for many marine species. However, it can also be harmful at elevated concentrations, triggering sub-lethal and toxic effects. During the last few decades, studies using electrochemical techniques have established that it is the particular chemical form of Cu, its so-called chemical speciation, and not its total concentration that controls the geochemical and biological behaviour and thus the bioavailability and toxicity of Cu in marine systems. The majority of dissolved Cu in the marine environment is strongly complexed by a heterogeneous mixture of Cu-binding organic ligands (L), reducing the free ionic Cu concentration ([Cu2+]) to femto- and picomolar levels. Free ionic Cu is generally considered the most bioavailable and thus the most beneficial or toxic form to marine organisms. Organic complexation reduces [Cu2+] in most marine systems to levels harmless, but above limitation, to many marine microorganisms. Measuring the inorganic, organic, and free Cu forms in the dissolved phase is critical to assess the fate (i.e., distribution, cycling, and reactivity) and the biological effects of Cu in the marine environment. However, the chemical speciation of Cu in natural saline waters is complex and is technically challenging to evaluate, resulting in cost-intensive and timeconsuming analyses. Consequently, despite the recognised importance, little data exists for Cu speciation and Cu-binding ligands in the marine environment, and ligand sources and chemical identities are generally understudied. Additionally, environmental processes and factors influencing and controlling Cu speciation in marine systems are still poorly understood. As a result, four different marine systems (i.e., estuarine, coastal and open ocean waters, as well as a shallow low-temperature hydrothermal vent system) were studied around New Zealand in an effort to advance the current understanding of Cu speciation processes and Cu-binding ligands in the marine environment. Total dissolved Cu concentrations were analysed using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), while Cu speciation was assessed with adsorptive cathodic stripping voltammetry (AdCSV) with salicylaldoxime (SA) as the competing ligand.

Development of novel methods to evaluate availability of zinc, selenium and manganese in Atlantic salmon (Salmo salar)

Year: 2019
Products: FAST
Authors: Silva, MS;
Journal: Thesis

During the recent years, the composition of salmonids diets has changed from the use of mainly marine-based ingredients (e.g. fish meal and fish oil) to an increased use of plant-based ingredients (e.g. soybean meal and vegetable oil). These changes in diet composition have an impact on the mineral concentration and mineral availability. For instance, zinc (Zn) is naturally present in both fish meal and plant-based ingredients, but in different concentrations. The Zn concentration is usually higher in fish meal than in plant-based ingredients so, with the increased use of plant-based ingredients the Zn concentration tends to decrease in the basal mixes. In addition, compounds from plantbased ingredients can reduce mineral availability. For instance, phytic acid, which is typically found in plant-based ingredients, can decrease mineral availability due to its high binding affinity for metal ions. Therefore, minerals such as Zn, selenium (Se) and manganese (Mn) are supplemented to diets to cover the nutritional requirement of farmed fish. These minerals may be added as organic or inorganic forms. Taken all of this information into consideration, there is a need to study mineral availability in the current salmon feed composition which is formulated mainly using plant-based ingredients. Further knowledge in this area will provide a better understanding regarding mineral availability and necessary strategies to increase mineral availability in Atlantic salmon. Increasing mineral availability will promote fish health and robustness, but also decrease the environmental load via faeces.

Palladiumin talteenotto yhdyskuntajätevesilietteestä

Year: 2019
Products: prepFAST
Authors: Dahl, O;
Journal: Thesis

Kriittiset raaka-aineet ovat alkuaineita, joilla on suuri taloudellinen merkitys, mutta niiden saatavuus aiheuttaa huolta. Tällaisia alkuaineita ovat mm. platinaryhmän metallit sekä harvinaiset maametallit. Kriittisillä raaka-aineilla on suuri merkitys suunniteltaessa kiertotaloutta, jolloin alkuaineita käytettäisiin ja kierrätettäisiin mahdollisimman tehokkaasti.1 Jätevesiliete on jätevedenpuhdistamolla muodostuvaa lietettä, jota muodostuu jätevesien käsittelyprosesseissa. Lietettä muodostuu niin kotitalouksien ja teollisuuden vesien kuin katujen hulevesien käsittelystä. Liete sisältää ravinteiden ja hyödyllisten orgaanisten aineiden lisäksi myös haitallisia raskasmetalleja ja patogeeneja.2 Lietteen on havaittu myös sisältävän arvokkaita jalometalleja sekä harvinaisia maametalleja. Etenkin jalometallien on havaittu rikastuneen lietteeseen, jolloin liete voisi olla potentiaalinen jalometallien sekundäärinen lähde.

Re-Evaluating the Age of Deep Biosphere Fossils in the Lockne Impact Structure

Year: 2019
Products: ArF excimer laser ablation system
Authors: Tillberg, M;Ivarsson, M;Drake, H;Whitehouse, M;Kooijman, E;Schmitt, M;
Journal: Geosciences

Impact-generated hydrothermal systems have been suggested as favourable environments for deep microbial ecosystems on Earth, and possibly beyond. Fossil evidence from a handful of impact craters worldwide have been used to support this notion. However, as always with mineralized remains of microorganisms in crystalline rock, certain time constraints with respect to the ecosystems and their subsequent fossilization are difficult to obtain. Here we re-evaluate previously described fungal fossils from the Lockne crater (458 Ma), Sweden. Based on in-situ Rb/Sr dating of secondary calcite-albite-feldspar (356.6 ± 6.7 Ma) we conclude that the fungal colonization took place at least 100 Myr after the impact event, thus long after the impact-induced hydrothermal activity ceased. We also present microscale stable isotope data of 13C-enriched calcite suggesting the presence of methanogens contemporary with the fungi. Thus, the Lockne fungi fossils are not, as previously thought, related to the impact event, but nevertheless have colonized fractures that may have been formed or were reactivated by the impact. Instead, the Lockne fossils show similar features as recent findings of ancient microbial remains elsewhere in the fractured Swedish Precambrian basement and may thus represent a more general feature in this scarcely explored habitat than previously known.

Pre-Columbian Fire Management Linked to Refractory Black Carbon Emissions in the Amazon

Year: 2019
Products: Apex-Q
Authors: Arienzo, M;Maezumi, S;Chellman, N;Iriarte, J;
Journal: Fire

Anthropogenic climate change—combined with increased human-caused ignitions—is leading to increased wildfire frequency, carbon dioxide emissions, and refractory black carbon (rBC) aerosol emissions. This is particularly evident in the Amazon rainforest, where fire activity has been complicated by the synchronicity of natural and anthropogenic drivers of ecological change, coupled with spatial and temporal heterogeneity in past and present land use. One approach to elucidating these factors is through long-term regional fire histories. Using a novel method for rBC determinations, we measured an approximately 3500-year sediment core record from Lake Caranã in the eastern Amazon for rBC influx, a proxy of biomass burning and fossil fuel combustion. Through comparisons with previously published records from Lake Caranã and regional evidence, we distinguished between local and regional rBC emission sources demonstrating increased local emissions of rBC from ~1250 to 500 calendar years before present (cal yr BP), coinciding with increased local-scale fire management during the apex of pre-Columbian activity. This was followed by a regional decline in biomass burning coincident with European contact, pre-Columbian population decline, and regional fire suppression associated with the rubber boom (1850–1910 CE), supporting the minimal influence of climate on regional burning at this time. During the past century, rBC influx has rapidly increased. Our results can serve to validate rBC modeling results, aiding with future predictions of rBC emissions and associated impacts to the climate system.

Inputs and processes affecting the distribution of particulate iron in the North Atlantic along the GEOVIDE (GEOTRACES GA01) section

Year: 2019
Products: quartz cyclonic spray chamber
Authors: Gourain, A;Planquette, H;Cheize, M;
Journal: ETH Zurich Research Collection

The aim of the GEOVIDE cruise (May–June 2014, R/V Pourquoi Pas?) was to provide a better understanding of trace metal biogeochemical cycles in the North Atlantic Ocean. As marine particles play a key role in the global biogeochemical cycle of trace elements in the ocean, we discuss the distribution of particulate iron (PFe), in relation to the distribution of particulate aluminium (PAl), manganese (PMn), and phosphorus (PP). Overall, 32 full vertical profiles were collected for trace metal analyses, representing more than 500 samples. This resolution provides a solid basis for assessing concentration distributions, elemental ratios, size fractionation, and adsorptive scavenging processes in key areas of the thermohaline overturning circulation. Total particulate iron concentrations ranged from as low as 9 pmol L−1 in surface waters of the Labrador Sea to 304 nmol L−1 near the Iberian margin, while median PFe concentrations of 1.15 nmol L−1 were measured over the sub-euphotic ocean interior. Within the Iberian Abyssal Plain, the ratio of PFe to PAl was identical to the continental crust molar ratio (0.21 mol mol−1 ), indicating the important influence of crustal particles in the water column. Overall, the lithogenic component explained more than 87% of PFe variance along the section. Within the Irminger and Labrador basins, the formation of biogenic particles led to an increase in the PFe/PAl ratio (up to 0.64 mol mol−1 ) compared to the continental crust ratio. Continental margins induce high concentrations of particulate trace elements within the surrounding water masses (up to 10 nmol L−1 of PFe). For example, horizontal advection of PFe was visible more than 250 km away from the Iberian margin. Additionally, several benthic nepheloid layers were observed more than 200 m above the seafloor along the transect, especially in the Icelandic, Irminger, and Labrador basins, suspending particles with high PFe content of up to 89 nmol L−1.

Methodenentwicklung und Validierung von neuen Verfahren zur Charakterisierung und Quantifizierung von anthropogenen Nanopartikeln in der aquatischen Umwelt

Year: 2019
Products: Autosampler
Authors: Dutschke, F;
Journal: Thesis

Manufactured titanium dioxide (TiO2) nanoparticles (TiO2 NPs) are nowadays widely present in products that are accessible to the mass market, such as paints, cosmetics, or sunscreens. Despite the significant increase in their use, the potential effects of these nanoparticles on the environment and biological systems have not been sufficiently studied until now; therefore, reliable analytical methods are required to better characterize these emerging materials. This work uses the hyphenation of inductively coupled plasma-mass spectrometry (ICP-MS) with a separation technique, such as sedimentation field-flow fractionation (SdFFF), to obtain information related to the size and state of agglomeration of the nanoparticles investigated. Initial experiments related to the online coupling of SdFFF with inductively coupled plasmatandem mass spectrometry (ICP-MS/MS) were conducted, allowing the detection and separation of TiO2 NPs. The first step involved the application of the ICP-MS/MS technology using an Ammonia (NH3) mass shift mode, which allows the removal of the different molecular and isobaric interferences that complicate the reliable detection and quantification of titanium (Ti). Under optimized conditions, the achievable instrumental detection limits in matrix solutions were found to be below 10 ng L-1 of Ti. The separation parameters of the SdFFF system were then optimized using NIST SRM 1898, a TiO2 NPs reference material, with nominal sizes of 25 nm. This material is characterized by a hydrodynamic diameter and the state of aggregation; it also uses a multi-angle light scattering (MALS) analysis detector. Moreover, a transmission electron microscopy (TEM) technique was applied to confirm the sizes and shapes of the TiO2 NPs as well as the presence of aggregates.

Links between the phytoplankton community composition and trace metal distribution in summer surface waters of the Atlantic Southern Ocean

Year: 2019
Products: seaFAST-pico SC-4 DX module
Authors: Viljoen, JJ;Weir, I;Fietz, S;Cloete, R;Loock, J;Philibert, R;
Journal: Thesis

This study assessed changes in the phytoplankton community related to macronutrient and bioactive trace metal distribution in surface waters of the Atlantic sector of the Southern Ocean, between Cape Town and Antarctica along the GEOTRACES GIPY_05 (mainly along prime meridian) transect in summer 2014–2015. Several general community structure features were reaffirmed, such as the restriction of cyanobacteria to the northern Subtropical Zone, while haptophytes, such as Phaeocystis, along with diatoms, dominate the community north of the Polar Front, and diatoms clearly dominate south of the Polar Front. These community structure changes were often linked with macro- and micro-nutrient composition changes. For example, the concentration of diatoms increased southwards with the availability of silica whereas the cyanobacterial contribution in the northern Subtropical Zone appeared to be linked with labile cobalt depletion. However, these links were not consistent along the entire transect, i.e., no individual nutrient, such as silica or iron, was linked to community composition changes across all water masses. Each station showed a rather unique combination of nutrient and community compositions. Our findings also indicated impacts on the phytoplankton community through trace metal distributions that could be related to a deep mixing event at ∼54◦S and to ice melt at ∼65 and 68◦S. The timing of sampling after such trace metal fluxes proved to be an important consideration, particularly where iron appeared to be preferentially depleted to near-limiting concentrations, possibly driving utilization of other metals. The study highlights the importance of considering a suite of trace metals when assessing controls of phytoplankton variability in the open ocean and emphasizes the need for higher resolution trace metal sampling and multi-element incubation studies to further study the complex relationships between phytoplankton and nutrients.

Accumulation and Spatial Distribution of Lead and Other Trace Elements in Keratinized Tissues: Investigations Based on Analytical Atomic Spectrometry

Year: 2019
Products: Autosampler
Authors: Tehrani, MW;
Journal: Thesis

Human biomonitoring for toxic metals such as lead (Pb) provides information about absorbed dose from all exposure routes, and is critical for identifying exposed individuals and assessing health risks. Blood Pb and bone Pb are the primary validated biomarkers for assessing short-term and historical Pb exposures, respectively, while non-traditional matrices, including keratinized tissues, can provide complementary exposure information. Hard keratinized tissues – including hair, nails, hooves, and horns – grow incrementally, potentially preserving chemical exposure histories over a span of days to years. Analytical limitations and poor interlaboratory reproducibility, however, have led to debate around the use of human nails and hair in biomonitoring, particularly for Pb. This dissertation addressed several knowledge gaps and analytical challenges relevant to the study of trace element accumulation and distribution in keratinized tissues, with a special focus on Pb. Lead and 16 other elements were measured by atomic mass spectrometry in caprine horns obtained post-mortem from 11 Pb-dosed animals, following cleaning, homogenization, and aciddigestion of each horn. Results for horn Pb displayed a potentially non-linear association with cumulative administered Pb dose, and a significant correlation with absorbed Pb dose as represented by bone Pb measurements. Elemental imaging studies conducted using micro X-ray fluorescence found that Pb is excreted into horns of dosed goats in discrete accumulations or “rings.” While the pattern of these Pb rings did not fully match the dosing history, the data suggested that Pb is eventually excreted into the horn in a manner that reflects the complex recycling of Pb between body compartments after multiple doses.

Deconstructed Microfluidic Bone Marrow On-A-Chip to Study Normal and Malignant Hemopoietic Cell-Niche Interactions

Year: 2019
Products: four‐channel precision micro peristaltic pump
Authors: Aleman, J;George, SK;Herberg, S;Devarasetty, M;Porada, CD;Skardal, A;Almeida-Porada, G;
Journal: Small

Human hematopoietic niches are complex specialized microenvironments that maintain and regulate hematopoietic stem and progenitor cells (HSPC). Thus far, most of the studies performed investigating alterations of HSPC-niche dynamic interactions are conducted in animal models. Herein, organ microengineering with microfluidics is combined to develop a human bone marrow (BM)-on-a-chip with an integrated recirculating perfusion system that consolidates a variety of important parameters such as 3D architecture, cell-cell/cell-matrix interactions, and circulation, allowing a better mimicry of in vivo conditions. The complex BM environment is deconvoluted to 4 major distinct, but integrated, tissue-engineered 3D niche constructs housed within a single, closed, recirculating microfluidic device system, and equipped with cell tracking technology. It is shown that this technology successfully enables the identification and quantification of preferential interactions-homing and retention-of circulating normal and malignant HSPC with distinct niches.

In vivo biocompatibility and immunogenicity of metal–phenolic gelation

Year: 2019
Products: ESI-SC FAST autosampler
Authors: Björnmalm, M;Wong, L;Wojciechowski, J;Penders, J;Horgan, C;Booth, M;Martin, N;Sattler, S;Stevens, M;
Journal: Chem. Sci.

In vivo forming hydrogels are of interest for diverse biomedical applications due to their ease-of-use and minimal invasiveness and therefore high translational potential. Supramolecular hydrogels that can be assembled using metal–phenolic coordination of naturally occurring polyphenols and group IV metal ions (e.g. TiIV or ZrIV) provide a versatile and robust platform for engineering such materials. However, the in situ formation and in vivo response to this new class of materials has not yet been reported. Here, we demonstrate that metal–phenolic supramolecular gelation occurs successfully in vivo and we investigate the host response to the material over 14 weeks. The TiIV–tannic acid materials form stable gels that are well-tolerated following subcutaneous injection. Histology reveals a mild foreign body reaction, and titanium biodistribution studies show low accumulation in distal tissues. Compared to poloxamer-based hydrogels (commonly used for in vivo gelation), TiIV–tannic acid materials show a substantially improved in vitro drug release profile for the corticosteroid dexamethasone (from <1 day to >10 days). These results provide essential in vivo characterization for this new class of metal–phenolic hydrogels, and highlight their potential suitability for biomedical applications in areas such as drug delivery and regenerative medicine.

In vitro and in vivo evaluation of degradation, toxicity, biodistribution, and clearance of silica nanoparticles as a function of size, porosity, density, and composition

Year: 2019
Products: syringe-FAST introduction system
Authors: Hadipour Moghaddam, SP;Mohammadpour, R;Ghandehari, H;
Journal: J Control Release

Silica nanoparticles (SiO2 NPs) have potential utility in controlled release. Despite significant research in this area, there is a gap in the understanding of the correlation between SiO2 NP physicochemical properties on the one hand and their degradation in solutions, in cells, and in vivo on the other. Here, we fabricated SiO2 NPs with variations in size, porosity, density, and composition: 100 nm Stöber, 100 and 500 nm mesoporous, 100 nm disulfide-based mesoporous, and 100 nm disulfide-based hollow mesoporous. Degradation profiles over 28 days were investigated in simulated biological fluids and deionized water. Results show Meso 100, and 500 nanoparticles degraded faster at higher pH values. Results from macrophages indicate Meso 100 nanoparticles showed the highest degradation amount (~3.8%). Cytotoxicity evaluation of the particles in Human Aortal Endothelial Cells (HAECs) shows concentration-dependent toxicity for the particles. Results from CD-1 mice show ~53% of Meso 100 nanoparticles (25 mg kg-1) degraded and were detected in urine after seven days. It was shown nanoparticle porosity and composition as well as pH and ionic strength of the medium play the predominant roles for degradation of SiO2 NPs. Based on histological evaluations, at the injected doses investigated, the particles did not show toxicity.

Silver-functionalized silica aerogels and their application in the removal of iodine from aqueous environments

Year: 2019
Products: SC2 DX FAST auto-sampler interface
Authors: Asmussen, RM;Matyáš, J;Qafoku, NP;Kruger, AA;
Journal: J. Hazard. Mater.

One of the key challenges for radioactive waste management is the efficient capture and immobilization of radioiodine, because of its radiotoxicity, high mobility in the environment, and long half-life (t1/2 = 1.57 × 107 years). Silver-functionalized silica aerogel (AgAero) represents a strong candidate for safe sequestration of radioiodine from various nuclear waste streams and subsurface environments. Batch sorption experiments up to 10 days long were carried out in oxic and anoxic conditions in both deionized water (DIW) and various Hanford Site Waste Treatment Plant (WTP) off-gas condensate simulants containing from 5 to 10 ppm of iodide (I-) or iodate (IO3-). Also tested was the selectivity of AgAero towards I- in the presence of other halide anions. AgAero exhibited fast and complete removal of I- from DIW, slower but complete removal of I- from WTP off-gas simulants, preferred removal of I- over Br- and Cl-, and it demonstrated ability to remove IO3- through reduction to I-.

Lowering the size detection limits of Ag and TiO2 nanoparticles by Single Particle ICP-MS

Year: 2019
Products: Apex Omega
Authors: Hadioui, M;Knapp, G;Azimzada, A;Jreije, I;Frechette-Viens, L;Wilkinson, KJ;
Journal: Anal. Chem.

As the production and use of engineered nanomaterials increase, there is an urgent need to develop analytical techniques that are sufficiently sensitive to be able to measure the very small nanoparticles (NP) at very low concentrations. Although single particle ICP-MS (SP-ICP-MS) is emerging as one of the best techniques for detecting NP, it is limited by relatively high size detection limits for several NP, including many of the oxides. The use of a high sensitivity sector field ICP-MS (ICP-SF-MS), microsecond dwell times, and dry aerosol sample introduction systems were examined with the goal of lowering the size detection limits of the technique. For samples injected as a wet aerosol, size detection limits as low as 4.9 nm for Ag NP and 19.2 nm for TiO2 NP were determined. By using a dry aerosol, a significant gain in ion extraction from the plasma was obtained, which resulted in a noticeable decrease of the size detection limits to 3.5 nm for the Ag NP and 12.1 nm for the TiO2 NP. These substantial improvements were applied to the detection of TiO2 NP in sunscreen lotions, rainwaters, and swimming pool waters. Concentrations of Ti-containing NP between 27 and 193 μL–1 were found in rain samples. Similar NP concentrations were detected in public swimming pools, although much higher particle number concentrations (6046 ± 290 μL–1) were measured in a paddling pool, which was attributed to a high concentration of sunscreen lotions in a small recirculated water volume. High losses of TiO2 NP through adsorption or agglomeration resulted in recoveries ranging from 14–34%.

Ultratrace Metal Speciation Analysis by Coupling of Sector-Field ICP-MS to High-Resolution Size Exclusion and Reversed-Phase Liquid Chromatography

Year: 2019
Products: Apex Q
Authors: Küpper, H;Bokhari, SNH;Jaime-Pérez, N;Lyubenova, L;Ashraf, N;Andresen, E;
Journal: Anal. Chem.

Techniques for metal speciation analysis with subnanomolar (ppt) detection limits in complex matrices, with simultaneous quantification of matrix elements, have become a necessity for investigating targets of trace metal binding to macromolecules and pigments at environmentally relevant concentrations. In this work we optimized the analysis of such metal binding in a custom-built HPLC-ICP-MS system. Key elements of the optimization were the choice of components for the metal-free HPLC-DAD system and sector-field ICP-MS detection (ICF-sfMS) with desolvating injection and optimization of sample handling. Protein analysis was done using ammonium bicarbonate buffer and size exclusion chromatography (SEC-ICP-sfMS), with possible addition of anion exchange chromatography. Detection of metal exchange in pigments (chlorophylls and bacteriochlorophylls) was based on reversed-phase chromatography with a methanol-acetone gradient and coupling to the ICP-sfMS via a dedicated organic matrix interface (RPC-ICP-sfMS). The resulting HPLC-DAD-ICP-sfMS system has detection limits in the picomolar range in protein buffer, limited by the maximal achievable purity of buffers/solvents and not by system sensitivity. Tests for method optimization showed that sonication, meant to increase protein solubilization, leads to artifacts of metal loss from metalloproteins. Examples for Cd binding to soybean proteins and chlorophyll, Cr binding to Arabidopsis thaliana proteins, La binding to Desmodesmus quadricauda proteins, and Cu binding to Rhodospirillum rubrum proteins and pigments are shown. These application examples demonstrate that the system is sensitive enough to detect binding of metals to proteins and pigments at background concentration levels of typical nutrient solutions made from analytical grade chemicals, equivalent to ultratrace metal concentrations in nonpolluted environments.

Investigating the Uptake of Arsenate by Chlamydomonas reinhardtii Cells and its Effect on their Lipid Profile using Single Cell ICP-MS and Easy Ambient Sonic-Spray Ionization-MS

Year: 2019
Products: PFA nebulizer
Authors: Mavrakis, E;Mavroudakis, L;Lydakis-Simantiris, N;Pergantis, SA;
Journal: Anal. Chem.

The complementary use of single cell atomic mass spectrometry (MS) and ambient molecular MS allowed for the in-depth study of arsenate uptake by Chlamydomonas reinhardtii cells and of the effect this toxic metalloid species has on their lipid profile. Compared to conventional inductively coupled plasma mass spectrometry (ICP-MS) analysis, in which case hundreds of thousands of cells are digested and then analyzed, it is demonstrated that single cell (SC) ICP-MS provides uptake data that are potentially of greater biological relevance. This includes the arsenic mass distribution within the cell population, which fits to a log-normal probability function, the most frequently contained arsenic mass within the cells (1.5-1.8 fg As per cell), and the mean arsenic uptake value (ranging from 2.7 to 4.1 fg As per cell for the three arsenate incubation concentrations, that is, 15, 22.5, and 30 μg As per mL) derived from the log-normal arsenic mass distribution within the cell population. The SC approach also allows for differentiating the arsenic present in and/or adsorbed on the cells, from the arsenic present in the extracellular solution, in a single analysis. In a similar fashion, ambient molecular MS in the form of desorption easy ambient sonic spray ionization (EASI) -MS was used to rapidly profile cell membrane lipids from cells spotted directly on a glass slide. EASI-MS analysis revealed that cells grown in the presence of increasing concentrations of arsenate exhibited changes in the degree of saturation of their membrane lipids, as was observed by the increasing intensity ratio of lipids with less unsaturated acyl chains to the same type of lipids with more unsaturated fatty acid chains. Thus, indicating "homeoviscous adaptation" of extraplastidial and thylakoid cell membranes, induced by the presence of arsenate.

Living near an active U.S. military base in Iraq is associated with significantly higher hair thorium and increased likelihood of congenital anomalies in infants and children

Year: 2019
Products: autosampler 4DX
Authors: Savabieasfahani, M;Basher Ahamadani, F;Mahdavi Damghani, A;
Journal: Environmental Pollution

In Iraq, war contamination is the result of dispensed bombs, bullets, detonation of chemical and conventional weapons, and burn-pit emissions by US bases. Increases in congenital anomalies were reported from Iraqi cities post-2003. These cities were heavily bombed and encircled by US bases with burn-pits. The Institute of Medicine has acknowledged that people exposed to burn-pit emissions can suffer from health consequences. A US base with an active burn-pit (Camp Taji) is located near Nasiriyah. Thorium is a radioactive compound and a direct depleted-uranium decay-product. Radioactive materials, including depleted uranium, are routinely stored in US bases and they have been shown to leak into the environment. We conducted a case-control study to investigate associations between proximity to Camp Taji and congenital anomalies, and associations between levels of toxic metals in hair and congenital anomalies. Data was analyzed by logistic regression mixed effect models (mean metal levels as the outcome variable and distance to the US base as a predictor variable, controlling for child's age, sex and father's education. We found significance with distance predictor for the random effect model with village as a random effect (p = 0.0437). Adding thorium to the model we found significance with the distance predictor at p = 0.0339 for the random effect model with village as a random effect. Mediation analysis was used to test if uranium/thorium exposure is mediating the association between proximity to Camp Taji and congenital anomalies, adjusting for child's age, sex, and father's education. This analysis suggests that higher levels of hair thorium effect congenital anomalies. A standard deviation increase in the hair thorium levels was association with a 65% (odds ratio: 1.65, 95% CIs: 1.01, 2.69) increase in the risk of congenital anomalies. Studies are necessary to understand the scope of war contamination and its impact on congenital anomalies in Iraq.

Deposition of ionic species and black carbon to the Arctic snowpack: combining snow pit observations with modeling

Year: 2019
Products: APEX-Q
Authors: Jacobi, H;Obleitner, F;Da Costa, S;Ginot, P;Eleftheriadis, K;Aas, W;Zanatta, M;
Journal: Atmos. Chem. Phys.

Although aerosols in the Arctic have multiple and complex impacts on the regional climate, their removal due to deposition is still not well quantified. We combined meteorological, aerosol, precipitation, and snowpack observations with simulations to derive information about the deposition of sea salt components and black carbon (BC) from November 2011 to April 2012 to the Arctic snowpack at two locations close to Ny-Ålesund, Svalbard. The dominating role of sea salt and the contribution of dust for the composition of atmospheric aerosols were reflected in the seasonal composition of the snowpack. The strong alignment of the concentrations of the major sea salt components in the aerosols, the precipitation, and the snowpack is linked to the importance of wet deposition for transfer from the atmosphere to the snowpack. This agreement was less strong for monthly snow budgets and deposition, indicating important relocation of the impurities inside the snowpack after deposition. Wet deposition was less important for the transfer of nitrate, non-sea-salt sulfate, and BC to the snow during the winter period. The average BC concentration in the snowpack remains small, with a limited impact on snow albedo and melting. Nevertheless, the observations also indicate an important redistribution of BC in the snowpack, leading to layers with enhanced concentrations. The complex behavior of bromide due to modifications during sea salt aerosol formation and remobilization in the atmosphere and in the snow were not resolved because of the lack of bromide measurements in aerosols and precipitation.

Exploring the upper particle size limit for field flow fractionation online with ICP-MS to address the challenges of water samples from the Taihu Lake

Year: 2019
Products: APEX IR system
Authors: Yang, J;Tan, P;Huang, T;Nischwitz, V;
Journal: Analytica Chimica Acta

Regular algal blooms are occurring in Taihu lake, which may be triggered by resuspension of sediments containing relevant amounts of phosphorus. Therefore, our study aims at quantification of phosphorus concentrations bound to suspended particulate matter in Taihu water samples to investigate this hypothesis. A field flow fractionation (FFF) method online with ICP-MS detection was developed to achieve an overview on particulate fractions of phosphorus and related elements including Fe, Al and C from the low nanometer to the low micrometer size range. Mass balance of dissolved and particulate elemental contents was established for quality control purpose and indicated low recovery of Fe, Al and P. Complementary determination of volume based particle size distribution by dynamic imaging analysis showed a majority of particle volume and thus mass in particles with size >5 μm. In order to address this challenge, the upper particle size limit of FFF online with ICP-MS was for the first time investigated in detail using well characterised monodisperse latex particles as model for organic matter in the low micrometer size range including microalgae. The effect of pre-filtration of the sample as well as the contribution of sample introduction via three different interfaces including micromist nebuliser/spray chamber, direct injection nebulisation and APEX with heated spray chamber and solvent removal by condensation on the particulate carbon recovery was studied by ICP-MS detection. The same instrumental setup was also applied for the characterisation of particulate elemental contents in the Taihu water samples as far as possible. Significant improvement of the detected particulate fraction in Taihu water samples was achieved by increasing the membrane pore size for pre-filtration and by using the APEX for introduction of the eluate from FFF into ICP-MS.

Provenance and fate of trace and rare earth elements in the sediment-aquifers systems of Majuli River Island, India

Year: 2019
Products: PFA nebulizer
Authors: Kumar, M;Goswami, R;Awasthi, N;Das, R;
Journal: Chemosphere

In this work we present a completely new dataset of Rare Earth Element (REE) distribution and fractionation in the groundwater and sediments of the world's largest populated river island-Majuli, located in the Brahmaputra River, India. Groundwater (n = 9) and borehole sediments (n = 23) of different depths were collected randomly and analyzed for REEs using inductively coupled plasma mass spectrometry (ICP-MS). Multivariate statistical techniques were applied to determine interrelationships among different REEs. Both water and sediments exhibit a higher content of light rare earth elements (LREEs) than heavy rare earth elements (HREEs), implying that source rock composition primarily controls the REE signatures of these river sediments, largely owing to variations in levels of chlorite and monazite, which are more abundant in bottom river sediments of the Brahmaputra. However, lower LREE/HREE ratios in groundwater samples (8.42-14.48) compared to sediments (8.9-52.6) suggest less dissolved phase mobilization of LREE during weathering and transport. Hierarchical cluster analysis showed more consistent clustering in sediment compared to water and clear demarcations of MREE, HREE and LREE were observed in the sediments. The primitive mantle-normalized REE patterns of borehole sediments were similar to the upper continental crust (UCC) and the compositions of average Himalayan rocks. LREE enrichment compared to HREE suggest dominance of a felsic source. However, a La/V versus Th/Yb plot suggests a small contribution from the mafic source component. The sediments show high Th/Sc (>1 of UCC) and high Zr/Sc. A Eu/Eu* verses GdN/YbN plot suggests that the dominant source with Upper crustal composition has undergone multiple recycling.

Early life and adolescent arsenic exposure from drinking water and blood pressure in adolescence

Year: 2019
Products: Elemental Scientific SC-4 DX autosampler
Authors: Chen, Y;Wu, F;Liu, X;Parvez, F;LoIacono, NJ;Gibson, EA;Kioumourtzoglou, MA;Levy, D;Shahriar, H;Uddin, MN;Islam, T;Lomax, A;Saxena, R;Sanchez, T;Santiago, D;Ellis, T;Ahsan, H;Wasserman, GA;Graziano, JH;
Journal: Environ. Res.

Evidence of the association between inorganic arsenic (As) exposure, especially early-life exposure, and blood pressure (BP) in adolescence is limited. We examined the association of As exposure during early childhood, childhood, and adolescence with BP in adolescence. We conducted a cross-sectional study of 726 adolescents aged 14-17 (mean 14.75) years whose mothers were participants in the Bangladesh Health Effects of Arsenic Longitudinal Study (HEALS). Adolescents' BP was measured at the time of their recruitment between December 2012 and December 2016. We considered maternal urinary As (UAs), repeatedly measured during childhood, as proxy measures of early childhood (<5 years old, A1) and childhood (5-12 years old, A2) exposure. Adolescents' current UAs was collected at the time of recruitment (14-17 years of age, A3). Every doubling of UAs at A3 and maternal UAs at A1 was positively associated with a difference of 0.7-mmHg (95% confidence interval [CI]: 0.1, 1.3) and a 0.7-mmHg (95% CI: 0.05, 1.4) in SBP, respectively. These associations were stronger in adolescents with a BMI above the median (17.7 kg/m2) than those with a BMI below the median (P for interaction = 0.03 and 0.03, respectively). There was no significant association between any of the exposure measures and DBP. The Weighted Quantile Sum (WQS) regression confirmed that adolescents' UAs at A3 and maternal UAs at A1 contributed the most to the overall effect of As exposure at three life stages on SBP. Mixture analyses using Bayesian Kernel Machine Regression identified UAs at A3 as a significant contributor to SBP and DBP independent of other concurrent blood levels of cadmium, lead, manganese, and selenium. Our findings suggest an association of current exposure and early childhood exposure to As with higher BP in adolescents, which may be exacerbated by higher BMI at adolescence.

High-resolution Cd isotope systematics in multiple zones of the Southern Ocean from the Antarctic Circumnavigation Expedition

Year: 2019
Products: seaFAST system
Authors: Sieber, M;Conway, T;de Souza, G;Hassler, C;Ellwood, M;Vance, D;
Journal: Earth and Planetary Science Letters

The Southern Ocean plays a major role in determining the global distribution of trace metals such as cadmium (Cd). Here, we present 17 high-depth-resolution profiles of dissolved Cd and its stable isotope composition (δ114Cd) over the top 1000 m of the Pacific and Atlantic sectors of the Southern Ocean, collected during the Antarctic Circumnavigation Expedition. Our dataset reinforces the view that Cd and its isotopes are dominated by shallow biological cycling in this region. A close examination of variations in Cd cycling across the different zones of the Southern Ocean reveals how the interplay between uptake and regeneration, seasonal mixing, and upwelling controls both Cd and δ114Cd in this region. The only deviations from these systematics are due to the influence of local processes such as continental influence or Fe-fertilization, close to the Mertz Glacier and the Balleny Islands, respectively. Deep convection during winter incorporates the Southern Ocean Cd isotope signatures into Subantarctic Mode Water and Antarctic Intermediate Water during water mass formation. Incorporating published data, we present the first complete picture of how Cd is cycled through the entire Pacific Ocean, revealing the manner in which the Southern Ocean controls the global cycling of Cd and δ114Cd; analogous to Si or Zn, we propose that Southern Ocean processes, in combination with global ocean circulation, cause a division into two separate Cd regimes, a Cd-depleted surface ocean above a Cd-rich deep ocean loop. Therefore, the relationship between Cd and PO4 on a global scale is largely a result of these processes in the Southern Ocean, rather than a local correlation between the two elements.

Barium in deep-sea bamboo corals: Phase associations, barium stable isotopes, & prospects for paleoceanography

Year: 2019
Products: New Wave
Authors: Geyman, B;Ptacek, J;LaVigne, M;Horner, T;
Journal: Earth and Planetary Science Letters

Reconstruction of past seawater δ138/134BaNIST (barium-isotopic compositions) can augment existing proxies of water mass provenance and deep-ocean circulation. Deep-sea bamboo corals are uniquely poised to record Ba-isotopic variations, given their widespread oceanographic distribution and incorporation of ambient Ba in approximate proportion to that in surrounding seawater. However, the utility of such records requires knowing: the phases hosting Ba in deep-sea coral skeletons, that specimens faithfully capture modern Ba-isotopic chemistry, and that internal skeletal variability relates principally to historical variations in the composition of ambient seawater. We investigated each of these requirements using a stepped cleaning experiment, a ‘core-top’ comparison of eight live-collected specimens from the California margin (870–2,055 m) against ambient seawater, and through examination of historical variability in skeletal Ba chemistry, respectively. First, we report that non-carbonate phases minimally contribute to bamboo coral Ba/Ca, obviating the need for chemical cleaning of live-collected specimens. Second, using newly-obtained profiles of northeast Pacific Ba-isotopic chemistry, we observe that bamboo corals faithfully reflect ambient seawater with a taxonomically- and environmentally-invariant Ba-isotopic offset, Δ138/134Bacoral–SW, of −0.37±0.03‰ (±2 SD, n=8). The partition coefficient for Ba, KDBa, is similarly insensitive to taxonomy, but linearly decreases with depth. The driving mechanism is unresolved. Third, we find minimal Ba/Ca and Ba-isotopic variability in historical growth representing the past century. We interpret this invariance as evidencing the overall fidelity of deep-sea bamboo corals for ambient Ba chemistry over their long lifespans. The insensitivity of Δ138/134Bacoral–SW to environmental gradients indicates that the Ba-isotopic composition of bamboo corals can be solely interpreted in terms of seawater composition, which should find myriad applications to the study of past ocean circulation over a range of timescales.

Testing the Canyon Hypothesis: Evaluating light and nutrient controls of phytoplankton growth in penguin foraging hotspots along the West Antarctic Peninsula

Year: 2019
Products: SeaFAST pico system
Authors: Carvalho, F;Fitzsimmons, J;Couto, N;Waite, N;Gorbunov, M;Kohut, J;Oliver, M;Sherrell, R;Schofield, O;
Journal: Limnol Oceanogr

Major penguin breeding colonies around Anvers, Avian, and Charcot Islands are associated with cross‐shelf submarine canyon systems where increased chlorophyll has been recorded throughout the spring/summer season (Prézelin et al. 2000; Ducklow et al. 2012; Oliver et al. 2013; Kavanaugh et al. 2015; Kim et al. 2018). These canyons act as conduits for warm, nutrient‐enriched deep mUCDW to penetrate to the nearshore regions (Prézelin et al. 2004; Martinson et al. 2008). Relatively high sea surface temperatures resulting from the intrusion of mUCDW have been hypothesized to result in earlier sea ice retreat, increased melting, shallower MLD, and increased chlorophyll (Kavanaugh et al. 2015). The hypothesis that recurrent pulses of mUCDW replenish surface waters with abundant macro‐ and micronutrients required to fuel primary production (Prézelin et al. 2000, 2004) is plausible, yet the results from this and other recent studies (Carvalho et al. 2016; Annett et al. 2017; Bown et al. 2017; Sherrell et al. 2018) do not support this hypothesis. Our analysis reveals that neither mixing deep water with surface water (simulating upwelling of mUCDW) nor iron enrichment stimulated phytoplankton growth, as nutrients were already abundant in the nearshore surface layers. While we recognize that only one set of experiments were reported at each location, comparison of the physical and biogeochemical dynamics at these timepoints and locations with the 25‐yr time series collected for the PAL‐LTER project in the WAP, show that the physical setting observed this year was not statistically different from the previous ones (Supporting Information Fig. S1). Also, high‐resolution autonomous underwater glider‐based surveys at the head of PD showed that although intrusion and mixing of mUCDW to the euphotic zone does occur near Anvers Island (Carvalho et al. 2016), the timing of these events is important, as winter water is present throughout the duration of the spring and summer phytoplankton blooms. Though this water mass was eroded slowly both from above and below, it acted as a physical barrier preventing the warm, deep (and nutrient enriched) water from mixing with surface waters during the bloom season. A recent study at PD has shown that local supply of iron to the upper ocean in the canyon is derived primarily from shallow sediment resuspension (Sherrell et al. 2018), further supporting the notion that mUCDW does not play a key role in nutrient input throughout the growth season. Additionally, the lack of a response to micronutrient additions in all of the treatments suggests that surface waters were indeed iron‐replete.

Potassium isotopic compositions of howardite-eucrite-diogenite meteorites

Year: 2019
Products: Elemental Scientific APEX
Authors: Tian, Z;Chen, H;Fegley, B;Lodders, K;Barrat, J;Day, J;Wang, K;
Journal: Geochimica et Cosmochimica Acta

We report new high-precision stable K isotope data for three martian meteorites, one lunar meteorite, one ordinary chondrite, four terrestrial igneous United States Geological Survey (USGS) reference materials, and twenty howardite–eucrite–diogenite [HED] meteorites. The three martian meteorites define a relatively narrow δ41K range with an average of −0.36 ± 0.12‰ (2 SD) that is slightly heavier than the Bulk Silicate Earth (BSE) K isotopic composition (−0.48 ± 0.03‰). Except for the four Northwest Africa samples which were terrestrially contaminated, all HED meteorites reveal substantial 41K enrichment compared to BSE, lunar samples, martian meteorites, and chondrites. We propose that the average δ41K (+0.36 ± 0.16‰) obtained from HED meteorites is representative of Bulk Silicate 4-Vesta. The coupled volatile depletion and heavy K isotope enrichment in 4-Vesta could be attributed to both nebula-scale processes and parent-body events. The asteroid 4-Vesta is likely to have accreted from planetary feedstocks that have been significantly volatile-depleted prior to the major phases of planetary accretion in the early Solar System, with secondary effects of K loss during accretionary growth and magma ocean degassing.

Titanium isotope signatures of calcium-aluminum-rich inclusions from CV and CK chondrites: Implications for early Solar System reservoirs and mixing

Year: 2019
Products: Apex-Q desolvating system
Authors: Torrano, Z;Brennecka, G;Williams, C;Romaniello, S;Rai, V;Hines, R;Wadhwa, M;
Journal: Geochimica et Cosmochimica Acta

Calcium-aluminum-rich inclusions (CAIs) are the first solids to form in the early Solar System, and they exhibit nucleosynthetic anomalies in many isotope systems. The overwhelming majority of isotopic data for CAIs is limited to inclusions from the CV chondrite Allende and a few other CV, CO, CM, and ordinary chondrites. It is therefore important to ascertain whether previously reported values for CAIs are representative of the broader CAI-forming region and to make a more rigorous assessment of the extent and implications of isotopic heterogeneity in the early Solar System. Here, we report the mass-independent Ti isotopic compositions of a suite of 23 CAIs of diverse petrologic and geochemical types, including 11 from Allende and 12 from 7 other CV3 and CK3 chondrites; the data for CAIs from CK chondrites are the first reported measurements of Ti isotopic compositions of CAIs from this meteorite class. The resolved variation in the mass-independent Ti isotopic compositions of these CAIs indicates that the CAI-forming region of the early Solar System preserved isotopic variability. Nevertheless, the range of Ti isotopic compositions reported here for CAIs from CV and CK chondrites falls within the range observed in previously analyzed CAIs from CV, CO, CM, and ordinary chondrites. This implies that CAIs from CV, CK, CO, CM, and ordinary chondrites originated from a common nebular source reservoir characterized by mass-independent isotopic variability in Ti (and certain other elements). We further interpret these data to indicate that the Ti isotopic anomalies in CAIs represent the isotopic signatures of supernova components in presolar grains that were incorporated into the Solar System in an initially poorly mixed reservoir that was progressively homogenized over time. We conclude that the differing degrees of isotopic variability observed for different elements in normal CAIs are the result of distinct carrier phases and that these CAIs were likely formed towards the final stages of homogenization of the large-scale isotopic heterogeneity that initially existed in the solar nebula.

Iron isotope fractionation during sulfide liquid segregation and crystallization at the Lengshuiqing Ni-Cu magmatic sulfide deposit, SW China

Year: 2019
Products: PFA MicroFlow PTFE nebulize
Authors: Ding, X;Ripley, E;Wang, W;Li, C;Huang, F;
Journal: Geochimica et Cosmochimica Acta

We report the first measurements of Fe isotope fractionation between coexisting pyrrhotite and chalcopyrite from the Lengshuiqing Ni-Cu magmatic sulfide deposit, Southwest China. The δ56Fe values of chalcopyrite (Cp) range from 0.24‰ to 1.25‰, much higher than those in the coexisting pyrrhotite (Po, −1.25‰ to −0.13‰). The δ56Fe values of pyroxene separates from the Lengshuiqing intrusions are in a range from −0.03‰ to 0.18‰. Pyrrhotite in sulfide-mineralized rocks with greater than ∼2 wt.% S has δ56Fe values of −0.3 ± 0.2‰, indicating Δ56FePo-sil (pyrrhotite – silicate melt) in the range of −0.4 ± 0.2‰ with parental silicate magma δ56Fe of 0.1‰ as calculated from the least evolved pyroxene δ56Fe value. This fractionation is similar to that experimentally determined by Schuessler et al. (2007) for pyrrhotite and a rhyolitic melt, suggesting that Δ56FePo-sil of approximately −0.4‰ represents a near-equilibrium value for sulfide-rich mineralization in the Lengshuiqing intrusions. Pyrrhotite-dominated sulfide separates in samples with less than ∼2 wt.% S show δ56Fe values as low as −1.25‰. The low δ56Fe values can be modeled by a non-equilibrium process, where the fractionation between immiscible sulfide liquid and silicate magma decreases from −0.4 to −1.4‰ as the R-factor (mass ratio of silicate melt to coexisting sulfide liquid) increases from 1 to 1000. We suggest that the relative proportion of externally introduced Fe from sulfidic sedimentary country rocks may be higher in low-S samples, controlling the low δ56Fe values of the sulfide assemblage in the mineralized rocks.

Multiple negative molybdenum isotope excursions in the Doushantuo Formation (South China) fingerprint complex redox-related processes in the Ediacaran Nanhua Basin

Year: 2019
Products: Apex inlet system
Authors: Ostrander, C;Sahoo, S;Kendall, B;Jiang, G;Planavsky, N;Lyons, T;Nielsen, S;Owens, J;Gordon, G;Romaniello, S;Anbar, A;
Journal: Geochimica et Cosmochimica Acta

The Ediacaran Doushantuo Formation offers one of the most complete and extensively studied records of end-Neoproterozoic biotic and environmental change. Here, we report multiple coeval negative molybdenum (Mo) isotope excursions (to as low as δ98MoNIST+0.25 = −2.24 ± 0.10‰; 2SD) in shales from four separate sites in South China (Rongxi, Taoying, Wuhe, and Yuanjia) that preserve the Doushantuo Formation. The negative δ98Mo excursions appear coincident with previously discovered and seemingly peculiar redox-sensitive element (RSE) patterns in the same sedimentary rocks. We propose that these geochemical trends can be explained by some combination of (a) enhanced local marine oxygenation in the sedimentary basin where the Doushantuo Formation was originally deposited (the Nanhua Basin) and (b) changes in the degree of connectivity between this paleo basin and the open ocean. Enhanced local marine oxygenation, by exposing more sediments in the Nanhua basin to H2S-poor conditions, could have hindered quantitative tetrathiomolybdate formation within these sediments. Local marine oxygenation could have also stimulated the operation of a Mn oxide shuttle. Today, both of these processes are shown to promote the retention of lighter-mass Mo isotopes in sediments and also govern RSE enrichment patterns. Alternatively, or in addition, the Nanhua Basin may not have maintained an uninterrupted connection with the open ocean during the entirety of the Ediacaran Period. The negative δ98Mo excursions occur coincident with sea level highstands that could have also exposed more sediments in the basin to H2S poor conditions and/or catalyzed the operation of a local Mn oxide shuttle. When trying to infer temporal changes in ancient global ocean redox, it is important to consider the influence of sea level changes and associated variations in local depositional conditions on stratigraphic trends in RSE enrichments and isotope compositions.


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