Comment on "New insights into the biomineralization of mercury selenide nanoparticles through stable isotope analysis in giant petrel tissues"

Some birds and cetaceans can demethylate the toxic methylmercury cysteinate (MeHgCys) complex into inert mercury sulfide (HgSe) through the formation of an intermediate tetrahedral selenolate complex with selenocysteine (Sec) residues (Hg(Sec)₄). The nucleation of the HgSe biominerals involves the substitution of the Se ligand for the Sec residues, which is considered to occur in the form of multinuclear Hg_x(Se,Sec)_y clusters mediated by proteins. Queipo-Abad et al. (2022) isolated HgSe nanoparticles from the biological tissues of giant petrels and measured the mass-dependent fractionation of the ²⁰²Hg isotope (δ²⁰²Hg). They concluded that the δ²⁰²Hg values of the HgSe nanoparticles from each tissue of individual petrels are specific to the HgSe species alone and that the Hg(Sec)₄ → HgSe reaction occurs without fractionation of the ²⁰²Hg isotope. We show (1) that the HgSe nanoparticles are likely mixtures of MeHgCys, Hg(Sec)₄, and HgSe, and therefore that the δ²⁰²Hg values are not species-specific, and (2) that the ²⁰²Hg isotope is actually fractionated during the Hg(Sec)₄ → HgSe reaction, and therefore that this isotope can be used to trace the Hg metabolic pathways between tissues in a single individual and in different animals.

Chemical Information in the L3 X-ray Absorption Spectra of Molybdenum Compounds by High-Energy-Resolution Detection and Density Functional Theory

X-ray spectroscopy using high-energy-resolution fluorescence detection (HERFD) has critically increased the information content in X-ray spectra. We extend this technique to the tender X-ray range and present a study at the L₃-edge of molybdenum. We show how information on the oxidation state, phase composition, and local environment in molybdenum-based compounds can be obtained by analyzing the HERFD L₃ X-ray absorption near-edge structure (XANES). We demonstrate that the chemical shift of the L₃-edge HERFD spectra follows a parabolic dependence on the oxidation state and show that a qualitative analysis of high-resolution spectra can help to estimate parameters such as distortion of a ligand environment and radial order of atoms around the absorber. In certain cases, the spectra allow disentangling the contributions from bond lengths and angles to the distortion of the ligand polyhedron. Comparison of the high-resolution spectra with theoretical simulations shows that the single-electron approximation is able to reproduce the spectral shape. The results of this work may be useful in every branch of physics, inorganic and organometallic chemistry, catalysis, materials science, biochemistry, and mineralogy where observed changes in performance or chemical properties of Mo-based compounds, accompanied by small changes in spectral shape, are to be related to the details of electronic structure and local atomic environment.

Mercury Isotope Fractionation by Internal Demethylation and Biomineralization Reactions in Seabirds: Implications for Environmental Mercury Science

A prerequisite for environmental and toxicological applications of mercury (Hg) stable isotopes in wildlife and humans is quantifying the isotopic fractionation of biological reactions. Here, we measured stable Hg isotope values of relevant tissues of giant petrels (Macronectes spp.). Isotopic data were interpreted with published HR-XANES spectroscopic data that document a stepwise transformation of methylmercury (MeHg) to Hg-tetraselenolate (Hg(Sec)₄) and mercury selenide (HgSe) (Sec = selenocysteine). By mathematical inversion of isotopic and spectroscopic data, identical δ²⁰²Hg values for MeHg (2.69 ± 0.04‰), Hg(Sec)₄ (-1.37 ± 0.06‰), and HgSe (0.18 ± 0.02‰) were determined in 23 tissues of eight birds from the Kerguelen Islands and Adélie Land (Antarctica). Isotopic differences in δ²⁰²Hg between MeHg and Hg(Sec)₄ (-4.1 ± 0.1‰) reflect mass-dependent fractionation from a kinetic isotope effect due to the MeHg → Hg(Sec)₄ demethylation reaction. Surprisingly, Hg(Sec)₄ and HgSe differed isotopically in δ²⁰²Hg (+1.6 ± 0.1‰) and mass-independent anomalies (i.e., changes in Δ¹⁹⁹Hg of ≤0.3‰), consistent with equilibrium isotope effects of mass-dependent and nuclear volume fractionation from Hg(Sec)₄ → HgSe biomineralization. The invariance of species-specific δ²⁰²Hg values across tissues and individual birds reflects the kinetic lability of Hg-ligand bonds and tissue-specific redistribution of MeHg and inorganic Hg, likely as Hg(Sec)₄. These observations provide fundamental information necessary to improve the interpretation of stable Hg isotope data and provoke a revisitation of processes governing isotopic fractionation in biota and toxicological risk assessment in wildlife.

Cellular remains in a ~3.42-billion-year-old subseafloor hydrothermal environment

Subsurface habitats on Earth host an extensive extant biosphere and likely provided one of Earth's earliest microbial habitats. Although the site of life's emergence continues to be debated, evidence of early life provides insights into its early evolution and metabolic affinity. Here, we present the discovery of exceptionally well-preserved, ~3.42-billion-year-old putative filamentous microfossils that inhabited a paleo-subseafloor hydrothermal vein system of the Barberton greenstone belt in South Africa. The filaments colonized the walls of conduits created by low-temperature hydrothermal fluid. Combined with their morphological and chemical characteristics as investigated over a range of scales, they can be considered the oldest methanogens and/or methanotrophs that thrived in an ultramafic volcanic substrate.

Acute Toxicity of Divalent Mercury to Bacteria Explained by the Formation of Dicysteinate and Tetracysteinate Complexes Bound to Proteins in Escherichia coli and Bacillus subtilis

Bacteria are the most abundant organisms on Earth and also the major life form affected by mercury (Hg) poisoning in aquatic and terrestrial food webs. In this study, we applied high energy-resolution X-ray absorption near edge structure (HR-XANES) spectroscopy to bacteria with intracellular concentrations of Hg as low as 0.7 ng/mg (ppm) for identifying the intracellular molecular forms and trafficking pathways of Hg in bacteria at environmentally relevant concentrations. Gram-positive Bacillus subtilis and Gram-negative Escherichia coli were exposed to three Hg species: HgCl₂, Hg-dicysteinate (Hg(Cys)₂), and Hg-dithioglycolate (Hg(TGA)₂). In all cases, Hg was transformed into new two- and four-coordinate cysteinate complexes, interpreted to be bound, respectively, to the consensus metal-binding CXXC motif and zinc finger domains of proteins, with glutathione acting as a transfer ligand. Replacement of zinc cofactors essential to gene regulatory proteins with Hg would inhibit vital functions such as DNA transcription and repair and is suggested to be a main cause of Hg genotoxicity.

Mercury in the tissues of five cephalopods species: First data on the nervous system

Mercury (Hg), one of the elements most toxic to biota, accumulates within organisms throughout their lifespan and biomagnifies along trophic chain. Due to their key role in marine systems, cephalopods constitute a major vector of Hg in predators. Further, they grow rapidly and display complex behaviours, which can be altered by neurotoxic Hg. This study investigated Hg concentrations within 81 cephalopod specimens sampled in the Bay of Biscay, which belonged to five species: Eledone cirrhosa, Sepia officinalis, Loligo vulgaris, Todaropsis eblanae and Illex coindetii. Hg concentrations were measured in the digestive gland, the mantle muscle and the optic lobes of the brain. The digestive gland and the mantle were tissues with the most concentrated Hg among all species considered (up to 1.50 μg.g^-1 dw), except E. cirrhosa. This benthic cephalopod had 1.3-fold higher Hg concentrations in the brain (up to 1.89 μg.g^-1 dw) than in the mantle, while other species had 2-fold lower concentrations of Hg in the brain than in the mantle. Brain-Hg concentrations can be predicted from muscle-Hg concentrations for a given species, which facilitates the assessment of Hg toxicokinetics in cephalopods. In the most contaminated E. cirrhosa individual, the chemical form of Hg in its digestive gland, mantle muscle and optic lobes, was determined using High energy-Resolution X-ray Absorption Near Edge Structure (HR XANES) spectroscopy. In the digestive gland, 33 ± 11% of total Hg was inorganic Hg speciated as a dicysteinate complex (Hg(Cys)₂), which suggested that the demethylation of dietary MeHg occurs in this organ. All Hg found in the mantle muscle and the optic lobes is methylated and bound to one cysteinyl group (MeHgCys complex), which implies that dietary MeHg is distributed to these tissues via the bloodstream. These results raised the questions regarding interspecific differences observed regarding Hg brain concentrations and the possible effect of Hg on cephalopod functional brain plasticity and behaviour.

In Vivo Formation of HgSe Nanoparticles and Hg-Tetraselenolate Complex from Methylmercury in Seabirds-Implications for the Hg-Se Antagonism

In vivo and in vitro evidence for detoxification of methylmercury (MeHg) as insoluble mercury selenide (HgSe) underlies the central paradigm that mercury exposure is not or little hazardous when tissue Se is in molar excess (Se:Hg > 1). However, this hypothesis overlooks the binding of Hg to selenoproteins, which lowers the amount of bioavailable Se that acts as a detoxification reservoir for MeHg, thereby underestimating the toxicity of mercury. This question was addressed by determining the chemical forms of Hg in various tissues of giant petrels Macronectes spp. using a combination of high energy-resolution X-ray absorption near edge structure and extended X-ray absorption fine structure spectroscopy, and transmission electron microscopy coupled to elemental mapping. Three main Hg species were identified, a MeHg-cysteinate complex, a four-coordinate selenocysteinate complex (Hg(Sec)₄), and a HgSe precipitate, together with a minor dicysteinate complex Hg(Cys)₂. The amount of HgSe decreases in the order liver > kidneys > brain = muscle, and the amount of Hg(Sec)₄ in the order muscle > kidneys > brain > liver. On the basis of biochemical considerations and structural modeling, we hypothesize that Hg(Sec)₄ is bound to the carboxy-terminus domain of selenoprotein P (SelP) which contains 12 Sec residues. Structural flexibility allows SelP to form multinuclear Hg_x(Se,Sec)_y complexes, which can be biomineralized to HgSe by protein self-assembly. Because Hg(Sec)₄ has a Se:Hg molar ratio of 4:1, this species severely depletes the stock of bioavailable Se for selenoprotein synthesis and activity to one μg Se/g dry wet in the muscle of several birds. This concentration is still relatively high because selenium is naturally abundant in seawater, therefore it probably does not fall below the metabolic need for essential selenium. However, this study shows that this may not be the case for terrestrial animals, and that muscle may be the first tissue potentially injured by Hg toxicity.

Demethylation of Methylmercury in Bird, Fish, and Earthworm

Toxicity of methylmercury (MeHg) to wildlife and humans results from its binding to cysteine residues of proteins, forming MeHg-cysteinate (MeHgCys) complexes that hinder biological functions. MeHgCys complexes can be detoxified in vivo, yet how this occurs is unknown. We report that MeHgCys complexes are transformed into selenocysteinate [Hg(Sec)₄] complexes in multiple animals from two phyla (a waterbird, freshwater fish, and earthworms) sampled in different geographical areas and contaminated by different Hg sources. In addition, high energy-resolution X-ray absorption spectroscopy (HR-XANES) and chromatography-inductively coupled plasma mass spectrometry of the waterbird liver support the binding of Hg(Sec)₄ to selenoprotein P and biomineralization of Hg(Sec)₄ to chemically inert nanoparticulate mercury selenide (HgSe). The results provide a foundation for understanding mercury detoxification in higher organisms and suggest that the identified MeHgCys to Hg(Sec)₄ demethylation pathway is common in nature.

The chemical species of mercury accumulated by Pseudomonas idrijaensis, a bacterium from a rock of the Idrija mercury mine, Slovenia

A mercury-resistant bacterial strain has been isolated from a rock of the Idrija mercury mine in Slovenia. The rock had 19 g carbon and 2952 mg mercury (Hg) per kg. Mass spectrometry and DNA sequencing showed that the bacterium belongs to the Pseudomonas genus. It is called Pseudomonas idrijaensis. This bacterial strain is sensitive to methylmercury (MeHg) like the reference P. aeruginosa strain PAO1, and is resistant to divalent mercury (Hg(II)) in contrast to PAO1. This difference could be attributed to the presence of the mer operon yet deprived of the merB gene encoding the organomercurial lyase, on the basis of whole genome sequencing. The P. idrijaensis mer operon displays the RTPCADE organization and is contained in the Tn5041 transposon. This transposon identified here occurs in other Gram-negative Hg-resistant strains isolated from mercury ores, aquatic systems and soils, including Pseudomonas strains from 15,000 to 40,000 years old Siberian permafrost. When P. idrijaensis was exposed to mercury chloride, two intracellular Hg species were identified by high energy-resolution XANES spectroscopy, a dithiolate Hg(SR)₂ and a tetrathiolate Hg(SR)₄ complex. P. idrijaensis had a much higher [Hg(SR)₂]/[Hg(SR)₄] molar ratio than bacteria lacking the mer operon when exposed to 4 μg Hg²⁺/L - resulting in an intracellular accumulation of 4.3 μg Hg/g dw. A higher amount of the Hg(SR)₂ complex provides a chemical signature for the expression of the dicysteinate Mer proteins in response to mercury toxicity.

TEXS: in-vacuum tender X-ray emission spectrometer with 11 Johansson crystal analyzers

The design and first results of a large-solid-angle X-ray emission spectrometer that is optimized for energies between 1.5 keV and 5.5 keV are presented. The spectrometer is based on an array of 11 cylindrically bent Johansson crystal analyzers arranged in a non-dispersive Rowland circle geometry. The smallest achievable energy bandwidth is smaller than the core hole lifetime broadening of the absorption edges in this energy range. Energy scanning is achieved using an innovative design, maintaining the Rowland circle conditions for all crystals with only four motor motions. The entire spectrometer is encased in a high-vacuum chamber that allocates a liquid helium cryostat and provides sufficient space for in situ cells and operando catalysis reactors.

Divalent Mercury in Dissolved Organic Matter Is Bioavailable to Fish and Accumulates as Dithiolate and Tetrathiolate Complexes

The freshwater cyprinid Tanichthys albonubes was used to assess the bioavailability of divalent mercury (Hg(II)) complexed in dissolved organic matter (DOM) to fish. The fish acquired 0.3 to 2.2 μg Hg/g dry weight after 8 weeks in aquaria containing DOM from a Carex peat with complexed mercury at initial concentrations of 14 nM to 724 nM. Changes in the relative proportions of dithiolate Hg(SR)₂ and nanoparticulate β-HgS in the DOM, as quantified by high energy-resolution XANES (HR-XANES) spectroscopy, indicate that Hg(SR)₂ complexes either produced by microbially induced dissolution of nanoparticulate β-HgS in the DOM or present in the original DOM were the forms of mercury that entered the fish. In the fish with 2.2 μg Hg/g, 84 ± 8% of Hg(II) was bonded to two axial thiolate ligands and one or two equatorial N/O electron donors (Hg[(SR)₂+(N/O)_1-2] coordination), and 16% had a Hg(SR)₄ coordination, as determined by HR-XANES. For comparison, fish exposed to Hg²⁺ from 40 nM HgCl₂ contained 10.4 μg Hg/g in the forms of dithiolate (20 ± 10%) and tetrathiolate (23 ± 10%) complexes, and also Hg _xS _y clusters (57 ± 15%) having a β-HgS-type local structure and a dimension that exceeded the size of metallothionein clusters. There was no evidence of methylmercury in the fish or DOM within the 10% uncertainty of the HR-XANES. Together, the results indicate that inorganic Hg(II) bound to DOM is a source of mercury to biota with dithiolate Hg(SR)₂ complexes as the immediate species bioavailable to fish, and that these complexes transform in response to cellular processes.

Mercury(II) Binding to Metallothionein in Mytilus edulis revealed by High Energy-Resolution XANES Spectroscopy

Of all divalent metals, mercury (Hg^II) has the highest affinity for metallothioneins. Hg^II is considered to be enclosed in the α and β domains as tetrahedral α‐type Hg₄Cys_11‐12 and β‐type Hg₃Cys₉ clusters similar to Cd^II and Zn^II. However, neither the four‐fold coordination of Hg nor the existence of Hg–Hg atomic pairs have ever been demonstrated, and the Hg^II partitioning among the two protein domains is unknown. Using high energy‐resolution XANES spectroscopy, MP2 geometry optimization, and biochemical analysis, evidence for the coexistence of two‐coordinate Hg‐thiolate complex and four‐coordinate Hg‐thiolate cluster with a metacinnabar‐type (β‐HgS) structure in the α domain of separate metallothionein molecules from blue mussel under in vivo exposure is provided. The findings suggest that the CXXC claw setting of thiolate donors, which only exists in the α domain, acts as a nucleation center for the polynuclear complex and that the five CXC motifs from this domain serve as the cluster‐forming motifs. Oligomerization is driven by metallophilic Hg⋅⋅⋅Hg interactions. Our results provide clues as to why Hg has higher affinity for the α than the β domain. More generally, this work provides a foundation for understanding how metallothioneins mediate mercury detoxification in the cell under in vivo conditions.

Chemical Forms of Mercury in Pyrite: Implications for Predicting Mercury Releases in Acid Mine Drainage Settings

Pyrite (cubic FeS₂) is the most abundant metal sulfide in nature and also the main host mineral of toxic mercury (Hg). Release of mercury in acid mine drainage resulting from the oxidative dissolution of pyrite in coal and ore and rock resulting from mining, processing, waste management, reclamation, and large construction activities is an ongoing environmental challenge. The fate of mercury depends on its chemical forms at the point source, which in turn depends on how it occurs in pyrite. Here, we show that pyrite in coal, sedimentary rocks, and hydrothermal ore deposits can host varying structural forms of Hg which can be identified with high energy-resolution XANES (HR-XANES) spectroscopy. Nominally divalent Hg is incorporated at the Fe site in pyrite from coal and at a marcasite-type Fe site in pyrite from sedimentary rocks. Distinction of the two Hg bonding environments offers a mean to detect microscopic marcasite inclusions (orthorhombic FeS₂) in bulk pyrite. In epigenetic pyrite from Carlin-type Au deposit, up to 55 ± 6 at. % of the total Hg occurs as metacinnabar nanoparticles (β-HgS_NP), with the remainder being substitutional at the Fe site. Pyritic mercury from Idrija-type Hg deposit (α-HgS ore) is partly divalent and substitutional and partly reduced into elemental form (liquid). Divalent mercury ions, mercury sulfide nanoparticles, and elemental mercury released by the oxidation of pyrite in acid mine drainage settings would have different environmental pathways. Our results could find important applications for designing control strategies of mercury released to land and water in mine-impacted watersheds.

Mercury Trithiolate Binding (HgS3) to a de Novo Designed Cyclic Decapeptide with Three Preoriented Cysteine Side Chains

Mercury(II) is an unphysiological soft ion with high binding affinity for thiolate ligands. Its toxicity lies in the interactions with low molecular weight thiols including glutathione and cysteine-containing proteins that disrupt the thiol balance and alter vital functions. However, mercury can also be detoxified via interactions with Hg(II)-responsive regulatory proteins such as MerR, which coordinates Hg(II) with three cysteine residues in a trigonal planar fashion (HgS₃ coordination). The model cyclodecapeptide P^3C, c(GCTCSGCSRP) was designed to promote Hg(II) chelation in a HgS₃ coordination environment through the parallel orientation of three cysteine side chains. The binding motif is derived from the dicysteine P^2C cyclodecapeptide validated previously as a model for d¹⁰ metal transporters containing the binding sequence CxxC. The formation of the mononuclear HgP^3C complex with a HgS₃ coordination is demonstrated using electrospray ionization mass spectrometry, UV absorption, and ¹⁹⁹Hg NMR. Hg L_III-edge extended X-ray absorption fine structure (EXAFS) spectroscopy indicates that the Hg(II) coordination environment is T-shaped with two short Hg-S distances at 2.45 Å and one longer distance at 2.60 Å. The solution structure of the HgP^3C complex was refined based on ¹H-¹H NMR constraints and EXAFS results. The cyclic peptide scaffold has a rectangular shape with the three binding cysteine side chains pointing toward Hg(II). The HgP^3CH complex has a p K_a of 4.3, indicating that the HgS₃ coordination mode is stable over a large range of pH. This low p K_a value suggests that the preorientation of the three cysteine groups is particularly well-achieved for Hg(II) trithiolate coordination in P^3C.

High energy-resolution x-ray spectroscopy at ultra-high dilution with spherically bent crystal analyzers of 0.5 m radius

We present the development, manufacturing, and performance of spherically bent crystal analyzers (SBCAs) of 100 mm diameter and 0.5 m bending radius. The elastic strain in the crystal wafer is partially released by a "strip-bent" method where the crystal wafer is cut into strips prior to the bending and the anodic bonding process. Compared to standard 1 m SBCAs, a gain in intensity is obtained without loss of energy resolution. The gain ranges between 2.5 and 4.5, depending on the experimental conditions and the width of the emission line measured. This reduces the acquisition times required to perform high energy-resolution x-ray absorption and emission spectroscopy on ultra-dilute species, accessing concentrations of the element of interest down to, or below, the ppm (ng/mg) level.

Chemical Forms of Mercury in Human Hair Reveal Sources of Exposure

Humans are contaminated by mercury in different forms from different sources. In practice, contamination by methylmercury from fish consumption is assessed by measuring hair mercury concentration, whereas exposure to elemental and inorganic mercury from other sources is tested by analysis of blood or urine. Here, we show that diverse sources of hair mercury at concentrations as low as 0.5 ppm can be individually identified by specific coordination to C, N, and S ligands with high energy-resolution X-ray absorption spectroscopy. Methylmercury from seafood, ethylmercury used as a bactericide, inorganic mercury from dental amalgams, and exogenously derived atmospheric mercury bind in distinctive intermolecular configurations to hair proteins, as supported by molecular modeling. A mercury spike located by X-ray nanofluorescence on one hair strand could even be dated to removal of a single dental amalgam. Chemical forms of other known or putative toxic metals in human tissues could be identified by this approach with potential broader applications to forensic, energy, and materials science.

Tumor heterogeneity of fibroblast growth factor receptor 3 (FGFR3) mutations in invasive bladder cancer: implications for perioperative anti-FGFR3 treatment

BACKGROUND

Fibroblast growth factor receptor 3 (FGFR3) is an actionable target in bladder cancer. Preclinical studies show that anti-FGFR3 treatment slows down tumor growth, suggesting that this tyrosine kinase receptor is a candidate for personalized bladder cancer treatment, particularly in patients with mutated FGFR3. We addressed tumor heterogeneity in a large multicenter, multi-laboratory study, as this may have significant impact on therapeutic response.

PATIENTS AND METHODS

We evaluated possible FGFR3 heterogeneity by the PCR-SNaPshot method in the superficial and deep compartments of tumors obtained by transurethral resection (TUR, n = 61) and in radical cystectomy (RC, n = 614) specimens and corresponding cancer-positive lymph nodes (LN+, n = 201).

RESULTS

We found FGFR3 mutations in 13/34 (38%) T1 and 8/27 (30%) ≥T2-TUR samples, with 100% concordance between superficial and deeper parts in T1-TUR samples. Of eight FGFR3 mutant ≥T2-TUR samples, only 4 (50%) displayed the mutation in the deeper part. We found 67/614 (11%) FGFR3 mutations in RC specimens. FGFR3 mutation was associated with pN0 (P < 0.001) at RC. In 10/201 (5%) LN+, an FGFR3 mutation was found, all concordant with the corresponding RC specimen. In the remaining 191 cases, RC and LN+ were both wild type.

CONCLUSIONS

FGFR3 mutation status seems promising to guide decision-making on adjuvant anti-FGFR3 therapy as it appeared homogeneous in RC and LN+. Based on the results of TUR, the deep part of the tumor needs to be assessed if neoadjuvant anti-FGFR3 treatment is considered. We conclude that studies on the heterogeneity of actionable molecular targets should precede clinical trials with these drugs in the perioperative setting.

Intramolecular Hg⋯π interactions of d-character with non-bridging atoms in mercury–aryl complexes

The late transition metal mercury, known for its propensity to not share 5d electrons, actually does so in short-range π-bonding and medium- to long-range π-interactions.

Formation of Mercury Sulfide from Hg(II)-Thiolate Complexes in Natural Organic Matter

Methylmercury is the environmental form of neurotoxic mercury that is biomagnified in the food chain. Methylation rates are reduced when the metal is sequestered in crystalline mercury sulfides or bound to thiol groups in macromolecular natural organic matter. Mercury sulfide minerals are known to nucleate in anoxic zones, by reaction of the thiol-bound mercury with biogenic sulfide, but not in oxic environments. We present experimental evidence that mercury sulfide forms from thiol-bound mercury alone in aqueous dark systems in contact with air. The maximum amount of nanoparticulate mercury sulfide relative to thiol-bound mercury obtained by reacting dissolved mercury and soil organic matter matches that detected in the organic horizon of a contaminated soil situated downstream from Oak Ridge, TN, in the United States. The nearly identical ratios of the two forms of mercury in field and experimental systems suggest a common reaction mechanism for nucleating the mineral. We identified a chemical reaction mechanism that is thermodynamically favorable in which thiol-bound mercury polymerizes to mercury-sulfur clusters. The clusters form by elimination of sulfur from the thiol complexes via breaking of mercury-sulfur bonds as in an alkylation reaction. Addition of sulfide is not required. This nucleation mechanism provides one explanation for how mercury may be immobilized, and eventually sequestered, in oxygenated surface environments.

Estimating the number of pure chemical components in a mixture by X-ray absorption spectroscopy

Principal component analysis (PCA) is a multivariate data analysis approach commonly used in X-ray absorption spectroscopy to estimate the number of pure compounds in multicomponent mixtures. This approach seeks to describe a large number of multicomponent spectra as weighted sums of a smaller number of component spectra. These component spectra are in turn considered to be linear combinations of the spectra from the actual species present in the system from which the experimental spectra were taken. The dimension of the experimental dataset is given by the number of meaningful abstract components, as estimated by the cascade or variance of the eigenvalues (EVs), the factor indicator function (IND), or the F-test on reduced EVs. It is shown on synthetic and real spectral mixtures that the performance of the IND and F-test critically depends on the amount of noise in the data, and may result in considerable underestimation or overestimation of the number of components even for a signal-to-noise (s/n) ratio of the order of 80 (σ = 20) in a XANES dataset. For a given s/n ratio, the accuracy of the component recovery from a random mixture depends on the size of the dataset and number of components, which is not known in advance, and deteriorates for larger datasets because the analysis picks up more noise components. The scree plot of the EVs for the components yields one or two values close to the significant number of components, but the result can be ambiguous and its uncertainty is unknown. A new estimator, NSS-stat, which includes the experimental error to XANES data analysis, is introduced and tested. It is shown that NSS-stat produces superior results compared with the three traditional forms of PCA-based component-number estimation. A graphical user-friendly interface for the calculation of EVs, IND, F-test and NSS-stat from a XANES dataset has been developed under LabVIEW for Windows and is supplied in the supporting information. Its possible application to EXAFS data is discussed, and several XANES and EXAFS datasets are also included for download.

Short-range and long-range order of phyllomanganate nanoparticles determined using high-energy X-ray scattering

High-energy X-ray scattering (HEXS) is used to explore the pH-dependent structure of randomly stacked manganese oxide nanosheets of nominal formula δ-MnO2. Data are simulated in real space by pair distribution function (PDF) analysis and in reciprocal space by both the Bragg-rod method and the Debye equation in order to maximize the information gained from the total scattering measurements. The essential new features of this triple-analysis approach are (1) the use of a two-dimensional supercell in PDF modeling to describe local distortions around Mn layer vacancies, (2) the implementation in Bragg-rod calculations of a lognormal crystal size distribution in the layer plane and an empirical function for the effect of strain, and (3) the incorporation into the model used with the Debye equation of an explicit elastic deformation of the two-dimensional nanocrystals. The PDF analysis reveals steady migration at acidic pH of the Mn atoms from layer to interlayer sites, either above or below the Mn layer vacancies, and important displacement of the remaining in-layer Mn atoms toward vacancies. The increased density of the vacancy–interlayer Mn pairs at low pH causes their mutual repulsion and results in short-range ordering. The layer microstructure, responsible for the long-range lateral disorder, is modeled with spherically and cylindrically bent crystallites having volume-averaged radii of 20–40 Å. Thebunit-cell parameter from the hexagonal layer has different values in PDF, Bragg-rod and Debye equation modeling, because of the use of different weighting contributions from long-range and short-range distances in each method. The PDFbparameter is in effect a measure of the average inlayer Mn...Mn distance and consistently deviates from the average structure value determined by the Bragg-rod method by 0.02 Å at low pH, as a result of the local relaxation induced by vacancies. The layer curvature increases the Bragg-rod value by 0.01–0.02 Å with the cylindrical model and as much as 0.04–0.05 Å with the spherical model. Therefore, in principle, the diffraction alone can unambiguously determine with good accuracy only a volume-averaged apparent layer dimension of the manganese oxide nanosheets. Thebparameter is model dependent and has no single straightforward interpretation, so comparison ofbbetween different samples only makes sense if done in the context of a single specified model.

Metallothionein-like multinuclear clusters of mercury(II) and sulfur in peat

Strong mercury(II)-sulfur (Hg-SR) bonds in natural organic matter, which influence mercury bioavailability, are difficult to characterize. We report evidence for two new Hg-SR structures using X-ray absorption spectroscopy in peats from the Florida Everglades with added Hg. The first, observed at a mole ratio of organic reduced S to Hg (S(red)/Hg) between 220 and 1140, is a Hg(4)S(x) type of cluster with each Hg atom bonded to two S atoms at 2.34 Å and one S at 2.53 Å, and all Hg atoms 4.12 Å apart. This model structure matches those of metal-thiolate clusters in metallothioneins, but not those of HgS minerals. The second, with one S atom at 2.34 Å and about six C atoms at 2.97 to 3.28 Å, occurred at S(red)/Hg between 0.80 and 4.3 and suggests Hg binding to a thiolated aromatic unit. The multinuclear Hg cluster indicates a strong binding environment to cysteinyl sulfur that might impede methylation. Along with a linear Hg(SR)(2) unit with Hg-S bond lengths of 2.34 Å at S(red)/Hg of about 10 to 20, the new structures support a continuum in Hg-SR binding strength in natural organic matter.

Natural attenuation of zinc pollution in smelter-affected soil

Previous synchrotron X-ray microprobe measurements of Zn speciation in contaminated and uncontaminated soils have identified phyllosilicate as the main sequestration phase. The emphasis now is focused on comparing the nature and properties of neoformed and geogenic phyllosilicate species to understand natural attenuation processes. Refined structural characterization of the two types of Zn-containing phyllosilicate in slightly basic smelter-affected agricultural soils were obtained using a so far unprecedented combination of X-ray microscopic techniques, including fluorescence (μ-XRF), absorption (μ-EXAFS), and diffraction (μ-XRD), and X-ray bulk-sensitive techniques, including powder and polarized EXAFS spectroscopy. The unpolluted and polluted species are both dioctahedral smectites, but the first which contains minor Zn (ca. 150 mg/kg) is aluminous and Fe-free, and the second, which contains several hundreds to a few thousands mg/kg Zn depending on the distance to the smelter and wind direction, is ferruginous with an average Fe/Al atomic ratio of 1.1 ± 0.5. The Zn(2+) and Fe(3+) in the neoformed smectite are derived from the weathering of ZnS, ZnO, FeS(2), and ZnFe(2)O(4) particles from the smelter. These cations diffuse away from their particulate mineral sources and coprecipitate with Al and Si in the soil clay matrix. Zinc sequestration in the octahedral sheet of dioctahedral smectite is potentially irreversible, because this type of phyllosilicate is stable over a large pH range, and the neoformed species is analogous to the native species which formed over time during pedogenesis.

Convergence-optimized procedure for applying the NICA-Donnan model to potentiometric titrations of humic substances

Despite the high success of the NICA-Donnan (N-D) model to describe the interaction of protons and metal ions with natural organic matter, the large number of fit parameters is a major hindrance to its capacity to provide unique numerical solutions. This well-known difficulty is reflected in the unusually low value of the generic proton binding constant for carboxylic-type groups of fulvic acid (pK(H1) = 2.34), and to some extent of humic acid (2.93), and by the considerable covariance of the other generic N-D parameters. In some studies, the number of parameters obtained by regression is reduced by estimating some values independently with other techniques. Alternatively, the applicability of the model can be improved by devising a rigorous simulation procedure, which constrains the model-fit to converge toward chemically and physically realistic values. A procedure based on three successive iterations is proposed, and the solution is shown to be stable and invariant with the initial set of parameter values. The new generic parameters, in particular pK(H1)(FA) = 3.54 and pK(H1)(HA) = 3.87, derived from the same data set as the previous generic parameters, are in better agreement with literature data.

Number of independent parameters in the potentiometric titration of humic substances

With the advent of high-precision automatic titrators operating in pH stat mode, measuring the mass balance of protons in solid-solution mixtures against the pH of natural and synthetic polyelectrolytes is now routine. However, titration curves of complex molecules typically lack obvious inflection points, which complicates their analysis despite the high-precision measurements. The calculation of site densities and median proton affinity constants (pK) from such data can lead to considerable covariance between fit parameters. Knowing the number of independent parameters that can be freely varied during the least-squares minimization of a model fit to titration data is necessary to improve the model's applicability. This number was calculated for natural organic matter by applying principal component analysis (PCA) to a reference data set of 47 independent titration curves from fulvic and humic acids measured at I = 0.1 M. The complete data set was reconstructed statistically from pH 3.5 to 9.8 with only six parameters, compared to seven or eight generally adjusted with common semi-empirical speciation models for organic matter, and explains correlations that occur with the higher number of parameters. Existing proton-binding models are not necessarily overparametrized, but instead titration data lack the sensitivity needed to quantify the full set of binding properties of humic materials. Model-independent conditional pK values can be obtained directly from the derivative of titration data, and this approach is the most conservative. The apparent proton-binding constants of the 23 fulvic acids (FA) and 24 humic acids (HA) derived from a high-quality polynomial parametrization of the data set are pK(H,COOH)(FA) = 4.18 +/- 0.21, pK(H,Ph-OH)(FA) = 9.29 +/- 0.33, pK(H,COOH)(HA) = 4.49 +/- 0.18, and pK(H,Ph-OH)(HA) = 9.29 +/- 0.38. Their values at other ionic strengths are more reliably calculated with the empirical Davies equation than any existing model fit.

Zinc distribution and speciation in Arabidopsis halleri x Arabidopsis lyrata progenies presenting various zinc accumulation capacities

The purpose of this study was to investigate the relationship between the chemical form and localization of zinc (Zn) in plant leaves and their Zn accumulation capacity. An interspecific cross between Arabidopsis halleri sp. halleri and Arabidopsis lyrata sp. petrea segregating for Zn accumulation was used. Zinc (Zn) speciation and Zn distribution in the leaves of the parent plants and of selected F(1) and F(2) progenies were investigated by spectroscopic and microscopic techniques and chemical analyses. A correlation was observed between the proportion of Zn being in octahedral coordination complexed to organic acids and free in solution (Zn-OAs + Zn(aq)) and Zn content in the leaves. This pool varied between 40% and 80% of total leaf Zn depending on the plant studied. Elemental mapping of the leaves revealed different Zn partitioning between the veins and the leaf tissue. The vein : tissue fluorescence ratio was negatively correlated with Zn accumulation. The higher proportion of Zn-OAs + Zn(aq) and the depletion of the veins in the stronger accumulators are attributed to a higher xylem unloading and vacuolar sequestration in the leaf cells. Elemental distributions in the trichomes were also investigated, and results support the role of carboxyl and/or hydroxyl groups as major Zn ligands in these cells.

High-resolution spectroscopy on an X-ray absorption beamline

A bent-crystal spectrometer based on the Rowland circle geometry has been installed and tested on the BM30b/FAME beamline at the European Synchrotron Radiation Facility to improve its performances. The energy resolution of the spectrometer allows different kinds of measurements to be performed, including X-ray absorption spectroscopy, resonant inelastic X-ray scattering and X-ray Raman scattering experiments. The simplicity of the experimental device makes it easily implemented on a classical X-ray absorption beamline. This improvement in the fluorescence detection is of particular importance when the probed element is embedded in a complex and/or heavy matrix, for example in environmental sciences.

[Childhood septic temporomandibular arthritis]

OBJECTIVE

To report a clinical case of acute otitis media in a child, complicated by septic temporomandibular arthritis and to present a review of the literature.

PATIENT AND METHODS

We report a case of a 7-year-old boy who presented an altered general condition, major hyperthermia, associated with a left temporozygomatic mass in a context of recurrent bilateral acute otitis media lasting for 2 months. Emergency computed tomodensitometry (CT scan) showed left temporomandibular joint arthritis. Treatment consisted of a parenteral double antibiotic therapy and prevention of temporomandibula (TM) ankylosis.

RESULTS

After 20 months of follow-up, the child showed a normal ORL examination with no maxillofacial sequelae.

CONCLUSION

All temporozygomatic masses presenting in a septic context should suggest the diagnosis of TM arthritis; computed tomodensitometry should be done immediately.

Formation of metallic copper nanoparticles at the soil-root interface

Copper is an essential element in the cellular electron-transport chain, but as a free ion it can catalyze production of damaging radicals. Thus, all life forms attempt to prevent copper toxicity. Plants diminish excess copper in two structural regions: rare hyperaccumulators bind cationic copper to organic ligands in subaerial tissues, whereas widespread metal-tolerant plants segregate copper dominantly in roots by mechanisms thought to be analogous. Here we show using synchrotron microanalyses that common wetlands plants Phragmites australis and Iris pseudoacorus can transform copper into metallic nanoparticles in and near roots with evidence of assistance by endomycorrhizal fungi when grown in contaminated soil in the natural environment. Biomolecular responses to oxidative stress, similar to reactions used to abiotically synthesize Cu0 nanostructures of controlled size and shape, likely cause the transformation. This newly identified mode of copper biomineralization by plant roots under copper stress may be common in oxygenated environments.

Chemical forms of calcium in Ca,Zn- and Ca,Cd-containing grains excreted by tobacco trichomes

Tobacco (Nicotiana tabacum L. cv. Xanthi) plants exposed to toxic levels of zinc and cadmium excrete metals through their leaf trichomes (epidermal hairs) as Zn,Ca- and Cd,Ca-containing grains. Little is known about the nature and formation mechanism of these precipitates. The chemical, crystalline, and noncrystalline compositions of individual grains produced by tobacco were studied by scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM-EDX), micro-X-ray diffraction (µXRD), and calcium K-edge micro X-ray absorption near edge structure (µXANES) spectroscopy. Zinc is predominantly incorporated in calcite and cadmium in calcite and vaterite. Aragonite, which occurs occasionally, does not seem to contain trace metals. In addition to being precipitated in its three possible polymorphic forms, calcite, aragonite, and vaterite, calcium is also speciated as amorphous CaCO3 and possibly organic Ca in some grains. Most often, a particular grain consists of two or more crystalline and noncrystalline phases. The observed variability of intra- and inter-grain elemental and phase composition suggests that this biomineralization process is not constrained by biological factors but instead results from thermodynamically and kinetically controlled reactions. This study illustrates the potential of laterally resolved X-ray synchrotron radiation techniques (µXRD and µXANES) to study biomineralization and metal immobilization processes in plants.Key words: biomineralization, detoxification, micro-XANES, micro-XRD.

Zn incorporation in hydroxy-Al- and keggin Al13-intercalated montmorillonite: a powder and polarized EXAFS study

The sorption mechanism of Zn on gibbsite and mont-morillonite exchanged with Al3+ (Al-mont) or Keggin Al13 polymer (Al13-mont) was probed by powder and polarized EXAFS spectroscopy as a function of pH (5.85-7), reaction time (1-65 days), and sorbate to sorbent ratio (50-Zn is octahedrally coordinated to oxygens at approximately 2.08(2) A, and surrounded in-plane by six Al atoms at 3.02-3.06(2) A, and another six at 6 A. No out-of plane Si neighbors are detected. These results are interpreted as Zn incorporation in vacant octahedral sites of gibbsite-like layers at the basal and/or interlayer surface of montmorillonite particles. Zinc sorbed on the edges of gibbsite layers would give a split first oxygen shell with bond distances of 2.00(2) and 2.16(3) A, and 2.1(8) nearest Al at 3.02 A with no second-nearest Al, none of which were observed in Al-mont. The binding environment of Zn on Al13-mont after 1 day is similar to that on the edges of gibbsite, and is interpreted as Zn complexation at the surface of Al polymers. After 28 days, the Zn environment resembles that of Zn-sorbed Al-mont, indicating the progressive buildup of Zn-containing gibbsite-like layers parallel to montmorillonite layers. The results of this work clarify the incorporation mechanism of Zn in hydroxy-Al interlayered phyllosilicate and provide insight on the formation mechanism of this common Zn species in soil.

Trichomes of tobacco excrete zinc as zinc-substituted calcium carbonate and other zinc-containing compounds

Tobacco (Nicotiana tabacum L. cv Xanthi) plants were exposed to toxic levels of zinc (Zn). Zn exposure resulted in toxicity signs in plants, and these damages were partly reduced by a calcium (Ca) supplement. Confocal imaging of intracellular Zn using Zinquin showed that Zn was preferentially accumulated in trichomes. Exposure to Zn and Zn + Ca increased the trichome density and induced the production of Ca/Zn mineral grains on the head cells of trichomes. These grains were aggregates of submicrometer-sized crystals and poorly crystalline material and contained Ca as major element, along with subordinate amounts of Zn, manganese, potassium, chlorine, phosphorus, silicon, and magnesium. Micro x-ray diffraction revealed that the large majority of the grains were composed essentially of metal-substituted calcite (CaCO3). CaCO3 polymorphs (aragonite and vaterite) and CaC2O4 (Ca oxalate) mono- and dihydrate also were identified, either as an admixture to calcite or in separate grains. Some grains did not diffract, although they contained Ca, suggesting the presence of amorphous form of Ca. The presence of Zn-substituted calcite was confirmed by Zn K-edge micro-extended x-ray absorption fine structure spectroscopy. Zn bound to organic compounds and Zn-containing silica and phosphate were also identified by this technique. The proportion of Zn-substituted calcite relative to the other species increased with Ca exposure. The production of Zn-containing biogenic calcite and other Zn compounds through the trichomes is a novel mechanism involved in Zn detoxification. This study illustrates the potential of laterally resolved x-ray synchrotron radiation techniques to study biomineralization and metal homeostasis processes in plants.

Zinc sorption by a bacterial biofilm

Microbial biofilms are present in soils, sediments, and natural waters. They contain bioorganic metal-complexing functional groups and are thought to play an important role in metal cycling in natural and contaminated environments. In this study, the metal-complexing functional groups present within a suspension of bacterial cell aggregates embedded in extracellular polymeric substances (EPS) were identified in Zn adsorption experiments conducted at pH 6.9 with the freshwater and soil bacterium Pseudomonas putida. The adsorption data were fit with the van Bemmelen-Freundlich model. The molecular speciation of Zn within the biofilm was examined with Zn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The Zn EXAFS data were analyzed by shell-by-shell fitting and linear least-squares fitting with reference spectra. Zinc sorption to the biofilm was attributed to predominantly Zn--phosphoryl (85 +/- 10 mol %) complexes, with a smaller contribution to sorption from carboxyl-type complexes (23 +/- 10 mol %). The results of this study spectroscopically confirm the importance of phosphoryl functional groups in Zn sorption by a bacterial biofilm at neutral pH.

Zn speciation in the organic horizon of a contaminated soil by micro-X-ray fluorescence, micro- and powder-EXAFS spectroscopy, and isotopic dilution

Soils that have been acutely contaminated by heavy metals show distinct characteristics, such as colonization by metal-tolerant plant species and topsoil enrichment in weakly degraded plant debris, because biodegradation processes are strongly inhibited by contamination. Such an organic topsoil, located downwind of an active zinc smelter and extremely rich in Zn (approximately 2%, dry weight), was investigated by X-ray diffraction, synchrotron-based X-ray microfluorescence, and powder- and micro-extended X-ray absorption fine structure (EXAFS) spectroscopy for Zn speciation and by isotopic dilution for Zn lability. EXAFS spectra recorded on size fractions and on selected spots of thin sections were analyzed by principal component analysis and linear combination fits. Although Zn primary minerals (franklinite, sphalerite, and willemite) are still present (approximately 15% of total Zn) in the bulk soil, Zn was found to be predominantly speciated as Zn-organic matter complexes (approximately 45%), outer-sphere complexes (approximately 20%), Zn-sorbed phosphate (approximately 10%), and Zn-sorbed iron oxyhydroxides (approximately 10%). The bioaccumulated Zn fraction is likely complexed to soil organic matter after the plants' death. The proportion of labile Zn ranges from 54 to 92%, depending on the soil fraction, in agreement with the high proportion of organically bound Zn. Despite its marked lability, Zn seems to be retained in the topsoil thanks to the huge content of organic matter, which confers to this horizon a high sorption capacity. The speciation of Zn in this organic soil horizon is compared with that found in other types of soils.

Beamline 10.3.2 at ALS: a hard X-ray microprobe for environmental and materials sciences

Beamline 10.3.2 at the ALS is a bend-magnet line designed mostly for work on environmental problems involving heavy-metal speciation and location. It offers a unique combination of X-ray fluorescence mapping, X-ray microspectroscopy and micro-X-ray diffraction. The optics allow the user to trade spot size for flux in a size range of 5-17 microm in an energy range of 3-17 keV. The focusing uses a Kirkpatrick-Baez mirror pair to image a variable-size virtual source onto the sample. Thus, the user can reduce the effective size of the source, thereby reducing the spot size on the sample, at the cost of flux. This decoupling from the actual source also allows for some independence from source motion. The X-ray fluorescence mapping is performed with a continuously scanning stage which avoids the time overhead incurred by step-and-repeat mapping schemes. The special features of this beamline are described, and some scientific results shown.

Hydrous ferric oxide: evaluation of Cd-HFO surface complexation models combining Cd(K) EXAFS data, potentiometric titration results, and surface site structures identified from mineralogical knowledge

The surface properties of ferrihydrite were studied by combining wet chemical data, Cd(K) EXAFS data, and a surface structure and protonation model of the ferrihydrite surface. Acid-base titration experiments and Cd(II)-ferrihydrite sorption experiments were performed within 3<-log[H(+)]<10.5 and 0.5<[Cd(t)]<12 mM in 0.3 M NaClO(4) at 25 degrees C, where [Cd(t)] refers to total Cd concentration. Measurements at -5.5<or=log[Cd(t)]<or=-1.4 at fixed pH completed the wet chemical data set. The acid-base titration data could be adequately modeled by triple bond Fe- OH(2)(+1/2)-H(+)<-->triple bond Fe-OH(-1/2),logk((int))=-8.29, assuming the existence of a unique intrinsic microscopic constant, logk((int)), and consequently the existence of a single significant type of acid-base reactive functional groups. The surface structure model indicates that these groups are terminal water groups. The Cd(II) data were modeled assuming the existence of a single reactive site. The model fits the data set at low Cd(II) concentration and up to 50% surface coverage. At high coverage more Cd(II) ions than predicted are adsorbed, which is indicative of the existence of a second type of site of lower affinity. This agrees with the surface structure and protonation model developed, which indicates comparable concentrations of high- and low-affinity sites. The model further shows that for each class of low- and high-affinity sites there exists a variety of corresponding Cd surface complex structure, depending on the model crystal faces on which the complexes develop. Generally, high-affinity surface structures have surface coordinations of 3 and 4, as compared to 1 and 2 for low-affinity surface structures.

[Infectious complications after surgery for hypopharyngeal and laryngeal carcinomas]

OBJECTIVE

The objective of this study was to analyze the infectious complications of procedures for carcinoma of the hypopharynx and the larynx to optimize the prevention of septic risks.

MATERIAL AND METHODS

This retrospective study included 608 patients who underwent total (n=270) or partial (n=338) laryngectomy between 1984 and 1999. The procedures were performed under rigorous conditions of surgical asepsis and with prolonged antibiotic chemotherapy depending on the type of laryngectomy and past history of external radiotherapy. Twenty factors were studied. Univariate analysis, including 9 factors, and multivariate analysis were performed.

RESULTS

The global rate of infectious complications was 11.1%. The percentages of salivary leaks, other wound infections and non-wound infections were respectively 11.9%; 1.5%; 1.5% for total laryngectomy and 1.8%; 2.4%; 3.8% for partial laryngectomy. Statistically significant factors were tumor stage, postoperative hematoma, postoperative lymphorrhea and, to a lesser degree, pharyngeal localization.

CONCLUSION

Our rate of infectious complications in oncologic pharyngeal and laryngeal surgery, which is low compared with data in the literature, emphasizes the importance of strict measures of surgical asepsis and prolonged antibiotic chemotherapy as is recommended for so-called contaminated surgery.

Molecular-scale speciation of Zn and Ni in soil ferromanganese nodules from loess soils of the Mississippi Basin

Determining how environmentally important trace metals are sequestered in soils at the molecular scale is critical to developing a solid scientific basis for maintaining soil quality and formulating effective remediation strategies. The speciation of Zn and Ni in ferromanganese nodules from loess soils of the Mississippi Basin was determined by a synergistic use of three noninvasive synchrotron-based techniques: X-ray microfluorescence (microXRF), X-ray microdiffraction (microXRD), and extended X-ray absorption fine structure spectroscopy (EXAFS). We show that Ni is distributed between goethite (alpha-FeOOH) and the manganese oxide lithiophorite, whereas Zn is bound to goethite, lithiophorite, phyllosilicates, and the manganese oxide birnessite. The selective association of Ni with only iron and manganese oxides is an explanation for its higher partitioning in nodules over the soil clay matrix reported from soils worldwide. This could also explain the observed enrichment of Ni in oceanic manganese nodules. The combination of these three techniques provides a new method for determining trace metal speciation in both natural and contaminated environmental materials.