Fluorescence Elemental Mapping Research Articles

Morphology‐Dependent Magnetic Properties in Shallow‐Water Ferromanganese Concretions

AbstractFerromanganese concretions commonly occur in shallow‐water coastal regions worldwide. In the Baltic Sea, they can record information about past and present underwater environments and could be a potential source for critical raw materials. We report on their microstructural characteristics and magnetic properties and link them to their formation mechanisms and environmental significance. Microstructural investigations from nano‐ and micro‐computed tomography, electron microscopy, and micro‐X‐ray fluorescence elemental mapping reveal diverse growth patterns within concretions of different morphologies. Alternating Fe‐ and Mn‐rich growth bands indicate fluctuating redox conditions during formation. Bullet‐shaped magnetofossils, produced by magnetotactic bacteria, are present, which suggests the influence of bacterial activity on concretion formation. Spheroidal concretions, which occur in deeper and more tranquil environments, have enhanced microbial biomineralization and magnetofossil preservation. Conversely, crusts and discoidal concretions from shallower and more energetic environments contain fewer magnetofossils and have a greater detrital content. Our results provide insights into concretion formation mechanisms and highlight the importance of diagenetic processes, oxygen availability, and bacterial activity in the Baltic Sea.

Tourmaline growth in the border and wall zones of the Emmons pegmatite (Maine, U.S.A.): Evidence for disequilibrium crystallization and boundary layer formation

Abstract The anisotropic textures, including unidirectional solidification textures and graphic intergrowths, characteristic for pegmatites, are interpreted to result from disequilibrium crystallization at high degrees of undercooling. Experimental studies have revealed the existence of thin boundary layers surrounding the rapidly growing crystals. Here, tourmaline-bearing samples from the outer zones of the Emmons pegmatite (Maine, U.S.A.) are used to examine if a boundary layer can also occur in natural samples. Crystal morphology is linked with geochemistry to understand the evolution of pegmatite melts and to constrain disequilibrium conditions at large degrees of undercooling. Petrographic studies and semiquantitative micro-X-ray fluorescence element mapping were conducted to identify crystal morphology and zonation, complemented with electron microprobe analyses to determine major and minor element compositions and LA-ICP-MS analyses of selected trace elements. Three textural groups were identified: comb-like tourmaline, quartz-tourmaline intergrowths, and radiating tourmaline. The intergrowths are optically coherent and are split into three different morphologies: central, second tier, and skeletal tourmaline. Most tourmaline is schorl, but chemical variation occurs on three different scales: between textural groups, between different morphologies, and intracrystalline. The largest scale geochemical variation is caused by the progressive evolution of the melt as it crystallized from the borders inwards, while the intracrystalline variations are attributed to sector zoning. A model is suggested where the systematic variation of Mg, Mn, and Fe within individual intergrowths is proposed to be the result of crystallization from a boundary layer, rich in water and other fluxing elements (e.g., Li, P, B), formed around the rapidly growing central tourmaline. Here, we show the first examples of boundary layers in natural pegmatites. Furthermore, the results bring into question whether boundary layer tourmaline can be used as a bulk melt indicator in pegmatitic melts.

Nondestructive Observation of Multilayered Paintings on a Single Canvas by THz Time-Domain Imaging and X-ray Fluorescence Elemental Mapping

Nondestructive Observation of Multilayered Paintings on a Single Canvas by THz Time-Domain Imaging and X-ray Fluorescence Elemental Mapping

Caravaggio's copper

AbstractSt. John the Baptist in the Wilderness, commissioned for the private chapel of Genoese banker. Ottavio Costa in 1602/3 and now in the collection of the Nelson‐Atkins Museum of Art (#52‐25), provides an important opportunity to understand Caravaggio's use of materials from one of his best‐preserved paintings. macro‐X‐ray fluorescence (MA‐XRF) elemental mapping has now been used to build upon a 2016 stratigraphic study of the palette employing optical and UV fluorescence microscopies, scanning electron microscopy‐energy dispersive X‐ray spectrometry (SEM‐EDS), Raman spectroscopy, and polarized light microscopy. The combined results of these methods clarify aspects of the iconography that have previously been obscure and expand our understanding of the roles of the various pigments. The roles for copper‐based pigments are surprisingly diverse for a painting with few obvious green and blue passages, in which many greens are based on terraverte. Darkening of the foliage adjacent to the figure of St. John has long posed interpretive difficulties, due to poor legibility of the plants depicted there. The foliage has been clarified by the results of MA‐XRF mapping, which distinguish the plant species by the palette choices involved in their depiction. Copper pigments play a fundamental role in Caravaggio's work, shading and modulating complementary colors with the additional practical benefit of playing a siccative role in paints that would otherwise dry poorly. MA‐XRF mapping has also revealed a role for copper pigment used to lay out the composition that was not apparent through radiography or infrared imaging methods.

Synchrotron-Based X-ray Fluorescence Imaging Elucidates Uranium Toxicokinetics in Daphnia magna.

A combination of synchrotron-based elemental analysis and acute toxicity tests was used to investigate the biodistribution and adverse effects in Daphnia magna exposed to uranium nanoparticle (UNP, 3-5 nm) suspensions or to uranium reference (Uref) solutions. Speciation analysis revealed similar size distributions between exposures, and toxicity tests showed comparable acute effects (UNP LC50: 402 μg L-1 [336-484], Uref LC50: 268 μg L-1 [229-315]). However, the uranium body burden was 3- to 5-fold greater in UNP-exposed daphnids, and analysis of survival as a function of body burden revealed a ∼5-fold higher specific toxicity from the Uref exposure. High-resolution X-ray fluorescence elemental maps of intact, whole daphnids from sublethal, acute exposures of both treatments revealed high uranium accumulation onto the gills (epipodites) as well as within the hepatic ceca and the intestinal lumen. Uranium uptake into the hemolymph circulatory system was inferred from signals observed in organs such as the heart and the maxillary gland. The substantial uptake in the maxillary gland and the associated nephridium suggests that these organs play a role in uranium removal from the hemolymph and subsequent excretion. Uranium was also observed associated with the embryos and the remnants of the chorion, suggesting uptake in the offspring. The identification of target organs and tissues is of major importance to the understanding of uranium and UNP toxicity and exposure characterization that should ultimately contribute to reducing uncertainties in related environmental impact and risk assessments.

Carbonate Coprecipitation for Cd and Zn Treatment and Evaluation of Heavy Metal Stability Under Acidic Conditions.

Mining wastes or combustion ash are materials of high carbon sequestration potential but are also known for their toxicity in terms of heavy metal content. To utilize such waste materials for engineered carbon mineralization purposes, there is a need to investigate the fate and mobility of toxic metals. This is a study of the coprecipitation of metals with calcium carbonate for environmental heavy metal mitigation. The study also examines the stability of precipitated phases under environmentally relevant acid conditions. For a wide range of cadmium (Cd) and zinc (Zn) concentrations (10 to 5000 mg/L), induced coprecipitation led to greater than 99% uptake from water. The calcium carbonate phases were found to contain amounts as high as 9.9 wt % (Cd) and 17 wt % (Zn), as determined by novel synchrotron techniques, including X-ray fluorescence element mapping and three-dimensional (3D) nanotransmission X-ray microscopy (TXM). TXM imaging revealed first-of-a-kind observations of chemical gradients and internal nanoporosity within particles. These observations provided new insights into the mechanisms leading to the retention of coprecipitated heavy metals during the dissolution of calcite in acidic (pH 4) solutions. These observations highlight the feasibility of utilizing carbonate coprecipitation as an engineered approach to the durable sequestration of toxic metals.

Synchrotron XRF and Histological Analyses Identify Damage to Digestive Tract of Uranium NP-Exposed Daphnia magna.

Micro- and nanoscopic X-ray techniques were used to investigate the relationship between uranium (U) tissue distributions and adverse effects to the digestive tract of aquatic model organism Daphnia magna following uranium nanoparticle (UNP) exposure. X-ray absorption computed tomography measurements of intact daphnids exposed to sublethal concentrations of UNPs or a U reference solution (URef) showed adverse morphological changes to the midgut and the hepatic ceca. Histological analyses of exposed organisms revealed a high proportion of abnormal and irregularly shaped intestinal epithelial cells. Disruption of the hepatic ceca and midgut epithelial tissues implied digestive functions and intestinal barriers were compromised. Synchrotron-based micro X-ray fluorescence (XRF) elemental mapping identified U co-localized with morphological changes, with substantial accumulation of U in the lumen as well as in the epithelial tissues. Utilizing high-resolution nano-XRF, 400-1000 nm sized U particulates could be identified throughout the midgut and within hepatic ceca cells, coinciding with tissue damages. The results highlight disruption of intestinal function as an important mode of action of acute U toxicity in D. magna and that midgut epithelial cells as well as the hepatic ceca are key target organs.

A new beardfish (Teleostei, Polymixiiformes) from the Eocene Fur Formation, Denmark

ABSTRACT The earliest Eocene (Ypresian) Fur Formation (Denmark) is globally renowned for its exceptionally well-preserved fossils, including birds, sea turtles, insects, plants, and fishes. Fishes, albeit abundant and diverse, however, are only superficially known and very few detailed, taxonomic studies have been realized to date. A new polymixiiform fish, Polyspinatus fluere gen. et sp. nov., from the Fur Formation is described based on seven well-preserved, nearly complete specimens. All the specimens were studied by traditional stereomicroscopy, and by micro-X-ray fluorescence-element mapping. Digital 2D-element images of strontium-, phosphorus-, and calcium distributions of each specimen were directly applied for the taxonomic descriptions presented herein. Polyspinatus fluere gen. et sp. nov. is the first known Eocene record of the family Polymixiidae based on articulated skeletal remains. Polyspinatus gen. nov. exhibits a unique combination of characters that support its recognition as a new genus of the Polymixiidae. Its specialized hyoid apparatus with the first and second branchiostegal rays being sinuous and parallel to each other, and the third being wide and plate-like, followed by four saber-like elements, is strikingly similar to that of Polymixia, supporting a possible sister-group relationship with extant beardfishes.

The detrimental molten pool narrowing phenomenon in wire feed laser beam welding and its suppression by magnetohydrodynamic technique

Element transport in the wire feed laser beam welding (WFLBW) is directly determined by the molten pool shape and thermo-fluid flow therein. In this paper, an untypical molten pool profile, i.e., elongated at its top and bottom but narrowed at the middle, is found experimentally by real-time metal/glass observation and numerically by multi-physical modeling. Ex-situ X-ray fluorescence element mapping is used to characterize the element dilution status in the fusion zone. For the first time, the detrimental influence of the molten pool narrowing on the element transport is identified and discussed, combining the experimental and numerical results. A magnetohydrodynamic technique is utilized to suppress the narrowing, aiming at a more homogenous element distribution. It is found that due to the interaction of the two dominant circulations from the top and bottom regions of the molten pool, a low-temperature region is formed. It leads to an untypical growth of the mushy zone, narrowing the molten pool in the middle region. Its detrimental effect on material mixing is non-negligible considering the direct blocking effect on the downward flow and the premature solidification at the middle region. The Lorentz force from a transverse oscillating magnetic field can change the flow pattern into a single-circulation type. The downward transfer channel is widened, and its premature solidification is prevented because the low-temperature-gradient region is mitigated. This paper provides a supplementary reason regarding the common issue of insufficient material mixing during LBW, and a promising technique to optimize the process.

Manganese Accumulation and Tissue-level Distribution in the Australian Hyperaccumulator Gossia Bidwillii (Myrtaceae)

The manganese (Mn) hyperaccumulator Gossia bidwillii is a tree species native to subtropical eastern Australia where it occurs on Mn-rich soils. Here, we conducted the first Mn accumulation and tissue-level distribution study on wild and experimentally grown G. bidwillii. Gossia bidwillii plants were subjected to different levels of Mn (250 µg g−1, 500 µg g−1, 1000 µg g−1) soil dosing treatments, whereas the wild G. bidwillii was sampled from growing on highly Mn-enriched natural soils. We used laboratory-based micro-X-ray Fluorescence (µXRF) elemental mapping to elucidate in situ distribution patterns of Mn and other elements in hydrated wild and Mn-dosed G. bidwillii leaves. The data from wild G. bidwillii revealed that it can be strongly Mn-hyperaccumulating with foliar Mn concentrations of 39 000 µg g−1 and 24 000 µg g−1 in old and young leaves, respectively. In the Mn dosing trial, G. bidwillii accumulated 24 400 µg g−1 in old leaves and 17 100 µg g−1 in young leaves in the highest treatment level. The laboratory based µXRF data revealed that Mn is uniformly enriched throughout the laminae and petioles of both young and old leaves in wild G. bidwillii; while in Mn-dosed G. bidwillii, the foliar Mn distribution was primarily concentrated at the leaf-tip and lamina. The approach employed by combining data from the field and controlled experiments was especially meaningful for investigating Mn accumulation in this species and gaining added insight into the phenomenon of Mn hyperaccumulation.

Seasonal climate signals preserved in biochemical varves: insights from novel high-resolution sediment scanning techniques

Abstract. Varved lake sediments are exceptional archives of paleoclimatic information due to their precise chronological control and annual resolution. However, quantitative paleoclimate reconstructions based on the biogeochemical composition of biochemical varves are extremely rare, mainly because the climate–proxy relationships are complex and obtaining biogeochemical proxy data at very high (annual) resolution is difficult. Recent developments in high-resolution hyperspectral imaging (HSI) of sedimentary pigment biomarkers combined with micro X-ray fluorescence (µXRF) elemental mapping make it possible to measure the structure and composition of varves at unprecedented resolution. This provides opportunities to explore seasonal climate signals preserved in biochemical varves and, thus, assess the potential for annual-resolution climate reconstruction from biochemical varves. Here, we present a geochemical dataset including HSI-inferred sedimentary pigments and µXRF-inferred elements at very high spatial resolution (60 µm, i.e. > 100 data points per varve year) in varved sediments of Lake Żabińskie, Poland, over the period 1966–2019 CE. We compare these data with local meteorological observations to explore and quantify how changing seasonal meteorological conditions influenced sediment composition and varve formation processes. Based on the dissimilarity of within-varve multivariate geochemical time series, we classified varves into four types. Multivariate analysis of variance shows that these four varve types were formed in years with significantly different seasonal meteorological conditions. Generalized additive models (GAMs) were used to infer seasonal climate conditions based on sedimentary variables. Spring and summer (MAMJJA) temperatures were predicted using Ti and total C (Radj2=0.55; cross-validated root mean square error (CV-RMSE) = 0.7 ∘C, 14.4 %). Windy days from March to December (mean daily wind speed > 7 m s−1) were predicted using mass accumulation rate (MAR) and Si (Radj2=0.48; CV-RMSE = 19.0 %). This study demonstrates that high-resolution scanning techniques are promising tools to improve our understanding of varve formation processes and climate–proxy relationships in biochemical varves. This knowledge is the basis for quantitative high-resolution paleoclimate reconstructions, and here we provide examples of calibration and validation of annual-resolution seasonal weather inference from varve biogeochemical data.

Quantitative MRI susceptibility mapping reveals cortical signatures of changes in iron, calcium and zinc in malformations of cortical development in children with drug-resistant epilepsy

ObjectiveMalformations of cortical development (MCD), including focal cortical dysplasia (FCD), are the most common cause of drug-resistant focal epilepsy in children. Histopathological lesion characterisation demonstrates abnormal cell types and lamination, alterations in myelin (typically co-localised with iron), and sometimes calcification. Quantitative susceptibility mapping (QSM) is an emerging MRI technique that measures tissue magnetic susceptibility (χ) reflecting it's mineral composition.We used QSM to investigate abnormal tissue composition in a group of children with focal epilepsy with comparison to effective transverse relaxation rate (R2*) and Synchrotron radiation X-ray fluorescence (SRXRF) elemental maps. Our primary hypothesis was that reductions in χ would be found in FCD lesions, resulting from alterations in their iron and calcium content. We also evaluated deep grey matter nuclei for changes in χ with age. MethodsQSM and R2* maps were calculated for 40 paediatric patients with suspected MCD (18 histologically confirmed) and 17 age-matched controls.Patients’ sub-groups were defined based on concordant electro-clinical or histopathology data. Quantitative investigation of QSM and R2* was performed within lesions, using a surface-based approach with comparison to homologous regions, and within deep brain regions using a voxel-based approach with regional values modelled with age and epilepsy as covariates.Synchrotron radiation X-ray fluorescence (SRXRF) was performed on brain tissue resected from 4 patients to map changes in iron, calcium and zinc and relate them to MRI parameters. ResultsCompared to fluid‐attenuated inversion recovery (FLAIR) or T1‐weighted imaging, QSM improved lesion conspicuity in 5% of patients.In patients with well-localised lesions, quantitative profiling demonstrated decreased χ, but not R2*, across cortical depth with respect to the homologous regions. Contra-lateral homologous regions additionally exhibited increased χ at 2–3 mm cortical depth that was absent in lesions. The iron decrease measured by the SRXRF in FCDIIb lesions was in agreement with myelin reduction observed by Luxol Fast Blue histochemical staining.SRXRF analysis in two FCDIIb tissue samples showed increased zinc and calcium in one patient, and decreased iron in the brain region exhibiting low χ and high R2* in both patients. QSM revealed expected age-related changes in the striatum nuclei, substantia nigra, sub-thalamic and red nucleus. ConclusionQSM non-invasively revealed cortical/sub-cortical tissue alterations in MCD lesions and in particular that χ changes in FCDIIb lesions were consistent with reduced iron, co-localised with low myelin and increased calcium and zinc content. These findings suggest that measurements of cortical χ could be used to characterise tissue properties non-invasively in epilepsy lesions.

Spatial association between platinum minerals and magmatic sulfides imaged with the Maia Mapper and implications for the origin of the chromite-sulfide-PGE association

ABSTRACT The spatial association between Pt minerals, magmatic sulfides, and chromite has been investigated using microbeam X-ray fluorescence (XRF) element mapping and the Maia Mapper. This lab-based instrument combines the Maia parallel energy dispersive (ESD) detector array technology with a focused X-ray beam generated from a liquid metal source. It proves to be a powerful technique for imaging Pt distribution at low-ppm levels on minimally prepared cut rock surfaces over areas of tens to hundreds of square centimeters, an ideal scale for investigating these relationships. Images of a selection of samples from the Bushveld Complex and from the Norilsk-Talnakh ore deposits (Siberia) show strikingly close association of Pt hotspots, equated with the presence of Pt-rich mineral grains, with magmatic sulfide blebs in all cases, except for a taxitic low-S ore sample from Norilsk. In all of the Bushveld samples, at least 75% of Pt hotspots (by number) occur at or within a few hundred microns of the outer edges of sulfide blebs. In samples from the leader seams of the UG2 chromitite, sulfides and platinum hotspots are also very closely associated with the chromite seams and are almost completely absent from the intervening pyroxenite. In the Merensky Reef, the area ratio of Pt hotspots to sulfides is markedly higher in the chromite stringers than in the silicate-dominated lithologies over a few centimeters either side. We take these observations as confirmation that sulfide liquid is indeed the prime collector for Pt and, by inference, for the other platinum group elements (PGEs) in all these settings. We further propose a mechanism for the sulfide-PGE-chromite association in terms of in situ heterogeneous nucleation of all these phases coupled with transient sulfide saturation during chromite growth and subsequent sulfide loss by partial re-dissolution. In the case of the amygdular Norilsk taxite, the textural relationship and high PGE/S ratio is explained by extensive loss of S to an escaping aqueous vapor phase.

Root responses to localised soil arsenic enrichment in the fern Pityrogramma calomelanos var. austroamericana grown in rhizoboxes

The terrestrial fern Pityrogramma calomelanos, a cosmopolitan tropical species, is one of the strongest known arsenic (As) hyperaccumulator plants. This study aimed to determine whether P. calomelanos preferentially forages for arsenite (As3+) or arsenate (As5+) in As-contaminated soils, and whether a positive root response to As enhances accumulation in P. calomelanos. Therefore, an experiment using rhizoboxes divided in two halves were constructed with a control soil (C) and As3+ or As5+ dosed soil at either 50 and 100 μg g−1 As. Micro-X-ray Fluorescence elemental mapping (μXRF) was employed to analyze the distribution of As in roots and fronds, and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS) was used to determine As distribution in the reproductive tissues of P. calomelanos. The results showed that Pityrogramma roots do not specifically forage for As-contaminated soil; the area based on pixel counts was similar across all the treatments with no statistical differences. However, frond biomass was slightly higher in the treatments C ǀ As3+ and C ǀ As5+, and the highest accumulation of As in fronds was in the As5+ ǀ As3+ (100 μg g−1) treatment, with 3418 and 2370 μg g−1 in old and young fronds respectively. Arsenic cycling across the roots was observed by the μXRF mapping; in C ǀ As5+ (100) the As was higher and evenly distributed in both sections, whilst in C ǀ As3+ (50), the As was higher in the As3+ side. The μXRF mapping showed a broader As distribution in older fronds, where As was highest in the rachis and extended into the pinnule through the midrib. Pityrogramma calomelanos does not specifically root forage for As-enriched zones in the soil and grows healthily without signs of toxicity at lower (50 μg g−1) and higher (100 μg g−1) concentrations of As3+ and As5+ in the soil.

Is the aquatic macrophyte Crassula helmsii a genuine copper hyperaccumulator?

The Australian native hemi-aquatic herb C. helmsii (Crassulaceae) is a copper (Cu) accumulator, tolerant to a wide range of climatic conditions and able to concentrate >9000 μg Cu g−1 in its living tissues. These characteristics suggest practical potential for decontamination of Cu-polluted mine waste waters using a phyto-extraction approach. The aim of this study was to investigate Cu uptake in C. helmsii at different Cu2+ concentrations in solution and to test for the effect of pH on the concentration of free Cu2+ and Cu accumulation in this species. Different solutions were tested in acid (pH 4.0) and mildly acidic (pH 5.8) conditions at five different Cu2+ concentrations (ranging from 0 to 5 mg Cu L−1). The concentration of free Cu2+ was evaluated using Geochem-EZ software. The distribution of Cu in C. helmsii tissues was examined with micro-X-ray Fluorescence (μXRF) elemental mapping and with Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS). The highest shoot Cu concentration in C. helmsii was 5870 μg Cu g−1 in the 5 mg Cu L−1 treatment. Copper bioaccumulation was positively correlated with the Cu2+ treatment in the different solutions. The μXRF and SEM-EDS analysis revealed that roots accumulated higher Cu concentrations than the shoots. The concentration of free Cu2+ was shown to be dependent upon the type of Fe-chelator (DTPA, EDDHA, HBED) used in the solution due to the displacement of Fe3+ and complexation of Cu2+. Crassula helmsii is highly tolerant to Cu2+ in solution at acidic and mildly acidic pH, and able to accumulate high Cu concentrations in its tissue. This confirms its potential for applications in Cu phyto-extraction of acidic mine effluent waters high in Cu2+.

Tracking Reactions of Asymmetric Organo-Osmium Transfer Hydrogenation Catalysts in Cancer Cells.

Most metallodrugs are prodrugs that can undergo ligand exchange and redox reactions in biological media. Here we have investigated the cellular stability of the anticancer complex [OsII[(η6‐p‐cymene)(RR/SS‐MePh‐DPEN)] [1] (MePh‐DPEN=tosyl‐diphenylethylenediamine) which catalyses the enantioselective reduction of pyruvate to lactate in cells. The introduction of a bromide tag at an unreactive site on a phenyl substituent of Ph‐DPEN allowed us to probe the fate of this ligand and Os in human cancer cells by a combination of X‐ray fluorescence (XRF) elemental mapping and inductively coupled plasma‐mass spectrometry (ICP‐MS). The BrPh‐DPEN ligand is readily displaced by reaction with endogenous thiols and translocated to the nucleus, whereas the Os fragment is exported from the cells. These data explain why the efficiency of catalysis is low, and suggests that it could be optimised by developing thiol resistant analogues. Moreover, this work also provides a new way for the delivery of ligands which are inactive when administered on their own.

Tracking Reactions of Asymmetric Organo‐Osmium Transfer Hydrogenation Catalysts in Cancer Cells

AbstractMost metallodrugs are prodrugs that can undergo ligand exchange and redox reactions in biological media. Here we have investigated the cellular stability of the anticancer complex [OsII[(η6‐p‐cymene)(RR/SS‐MePh‐DPEN)] [1] (MePh‐DPEN=tosyl‐diphenylethylenediamine) which catalyses the enantioselective reduction of pyruvate to lactate in cells. The introduction of a bromide tag at an unreactive site on a phenyl substituent of Ph‐DPEN allowed us to probe the fate of this ligand and Os in human cancer cells by a combination of X‐ray fluorescence (XRF) elemental mapping and inductively coupled plasma‐mass spectrometry (ICP‐MS). The BrPh‐DPEN ligand is readily displaced by reaction with endogenous thiols and translocated to the nucleus, whereas the Os fragment is exported from the cells. These data explain why the efficiency of catalysis is low, and suggests that it could be optimised by developing thiol resistant analogues. Moreover, this work also provides a new way for the delivery of ligands which are inactive when administered on their own.

Compositional Heterogeneity of Impact Melt Rocks at the Haughton Impact Structure, Canada: Implications for Planetary Processes and Remote Sensing

AbstractConnecting the surface expression of impact crater‐related lithologies to planetary or regional subsurface compositions requires an understanding of material transport during crater formation. Here, we use imaging spectroscopy of six clast‐rich impact melt rock outcrops within the well‐preserved 23.5‐Ma, 23‐km diameter Haughton impact structure, Canada, to determine melt rock composition and spatial heterogeneity. We compare results from outcrop to outcrop, using clasts, groundmass, and integrated clast‐groundmass compositions as tracers of transport during crater‐fill melt rock formation and cooling. Supporting laboratory imaging spectroscopy analyses of 91 melt‐bearing breccia and clast samples and microscopic X‐ray fluorescence elemental mapping of cut samples paired with spectroscopy of identical surfaces validate outcrop‐scale lithological determinations. Results show different clast‐rich impact melt rock compositions at three sites kilometers apart and an inverse correlation between silica‐rich (sandstone, gneiss, and phyllosilicate‐rich shales) and gypsum‐rich rocks that suggests differences in source depth with location. In the target stratigraphy, gypsum is primarily sourced from ~1‐km depth, while gneiss is from >1.8‐km depth, sandstone from >1.3 km, and shales from ~1.6–1.7 km. Observed heterogeneities likely result from different excavation depths coupled with rapid quenching of the melt due to high content of cool clasts. Results provide quantitative constraints for numerical models of impact structure formation and give new details on melt rock heterogeneity important in interpreting mission data and planning sample return of impactites, particularly for bodies with impacts into sedimentary and volatile‐bearing targets, e.g., Mars and Ceres.

Formation of secondary mineral coatings and the persistence of reduced metal-bearing phases in soils developing on historic coal mine spoil

Acid mine drainage (AMD) from historic and abandoned coal mine spoil represents a potential long-term source of contaminants to surface and groundwater. Determining the risk associated within AMD generation and metal(loid) transport from coal mine spoil is complicated by the heterogeneous natural of spoil heaps and mineralogical and hydro(bio)geochemical factors that may limit or promote metal(loid) transport. The current work aims to determine if primary, reduced phases such as pyrite continue to persist in abandoned and historic coal mine spoil. This objective was accomplished through characterization soils undergoing active weathering while developing on coal mine spoil in Appalachian Ohio to determine the factors that might limit oxidative dissolution. Soils in the Huff Run Watershed (Ohio, USA) were sampled at 0–10 cm, 30–40 cm, 70–80 cm, and 110–120 cm depth. X-ray Diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS), and synchrotron-based X-ray Microprobe (XMP) analyses were used to determine the speciation and distribution of metal(loid)s and the minerals they are associated with. The XMP analyses included micro-focused XRD (μ-XRD), X-ray Fluorescence (μ-XRF) element and redox state mapping, and X-ray absorption Near Edge Structure (μ-XANES) Spectroscopy. Soil mineralogy was dominated by quartz, muscovite, kaolinite, and feldspar, with minor amounts of chlorite and other phases including pyrite, arsenopyrite, realgar, orpiment, hematite, and goethite. Soils from all depths contained metal(loid)-sulfide particles with secondary mineral surface coatings, often in physically complex and heterogeneous aggregates that were composed of clay minerals and secondary Fe(III)-(oxy)hydroxides. These assemblages were typically 10–20 μm in diameter, with an individual pyrite particle core grain size ranging from 0.5 to 10 μm, and secondary mineral surface coatings ranging in thickness from undetectable to 1 μm. Within these aggregates, S and As were present as: (1) small (<20 μm) phases that were spatially correlated with Fe and other trace metal(loids) (Cu, Se, and Zn) and identified as metal(loid)-sulfide minerals; and (2) As(III), As(VI), and S(VI) associated with secondary Fe(III)-(oxy)hydroxides. Intermediate S oxidation state was also observed to be associated with remnant coal and organic matter. These results indicate that pyrite and other metal(loid) sulfides are present in soils developing on historic coal mine spoil after several decades since waste emplacement. The persistence of the μm-scale pyrite grains is likely the result of the formation of the secondary mineral surface coatings which can limit complete oxidative dissolution. These phases also play a role in re-sequestration of metal(loid)s release from sulfide mineral weathering. This work highlights the importance for considering AMD generation from non-point sources, and the potential for long-term ecosystem impairment.

Visualizing mineralization processes and fossil anatomy using synchronous synchrotron X-ray fluorescence and X-ray diffraction mapping

Fossils, including those that occasionally preserve decay-prone soft tissues, are mostly made of minerals. Accessing their chemical composition provides unique insight into their past biology and/or the mechanisms by which they preserve, leading to a series of developments in chemical and elemental imaging. However, the mineral composition of fossils, particularly where soft tissues are preserved, is often only inferred indirectly from elemental data, while X-ray diffraction that specifically provides phase identification received little attention. Here, we show the use of synchrotron radiation to generate not only X-ray fluorescence elemental maps of a fossil, but also mineralogical maps in transmission geometry using a two-dimensional area detector placed behind the fossil. This innovative approach was applied to millimetre-thick cross-sections prepared through three-dimensionally preserved fossils, as well as to compressed fossils. It identifies and maps mineral phases and their distribution at the microscale over centimetre-sized areas, benefitting from the elemental information collected synchronously, and further informs on texture (preferential orientation), crystallite size and local strain. Probing such crystallographic information is instrumental in defining mineralization sequences, reconstructing the fossilization environment and constraining preservation biases. Similarly, this approach could potentially provide new knowledge on other (bio)mineralization processes in environmental sciences. We also illustrate that mineralogical contrasts between fossil tissues and/or the encasing sedimentary matrix can be used to visualize hidden anatomies in fossils.