Persistent and toxic chemical pollutants in fish consumed by Asians in Chicago, United States.

Consumption of seafood brings health benefits but may increase the ingestion of contaminants. Compared with other ethnic groups in the U.S.

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 , yet how this occurs is unknown. We report that MeHgCys complexes are transformed into selenocysteinate [Hg(Sec)] complexes in multiple animals from two phyla (a waterbird, freshwater fish, and earthworms) sampled in different geographical areas and contaminated by different Hg sources.

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.

Real-time observation of cation exchange kinetics and dynamics at the muscovite-water interface.

Ion exchange at charged solid-liquid interfaces is central to a broad range of chemical and transport phenomena. Real-time observations of adsorption/desorption at the molecular-scale elucidate exchange reaction pathways. Here we report temporal variation in the distribution of Rb species at the muscovite (001)-water interface during exchange with Na.

Spatial Dependence of Reduced Sulfur in Everglades Dissolved Organic Matter Controlled by Sulfate Enrichment.

Sulfate inputs to the Florida Everglades stimulate sulfidic conditions in freshwater wetland sediments that affect ecological and biogeochemical processes. An unexplored implication of sulfate enrichment is alteration of the content and speciation of sulfur in dissolved organic matter (DOM), which influences the reactivity of DOM with trace metals. Here, we describe the vertical and lateral spatial dependence of sulfur chemistry in the hydrophobic organic acid fraction of DOM from unimpacted and sulfate-impacted Everglades wetlands using X-ray absorption spectroscopy and ultrahigh-resolution mass spectrometry.

Nucleation of mercury sulfide by dealkylation.

Metal sulfide minerals are assumed to form naturally at ambient conditions via reaction of a metallic element with (poly)sulfide ions, usually produced by microbes in oxygen-depleted environments. Recently, the formation of mercury sulfide (β-HgS) directly from linear Hg(II)-thiolate complexes (Hg(SR)) in natural organic matter and in cysteine solutions was demonstrated under aerated conditions. Here, a detailed description of this non-sulfidic reaction is provided by computations at a high level of molecular-orbital theory.

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.

Structural Characterization of Aluminum (Oxy)hydroxide Films at the Muscovite (001)-Water Interface.

The formation of Al (oxy)hydroxide on the basal surface of muscovite mica was investigated to understand how the structure of the substrate controls the nucleation and growth of secondary phases. Atomic force microscopy images showed that solid phases nucleated on the surface initially as two-dimensional islands that were ≤10 Å in height and ≤200 Å in diameter after 16-50 h of reaction in a 100 μM AlCl3 solution at pH 4.2 at room temperature.

Structure, Bonding, and Stability of Mercury Complexes with Thiolate and Thioether Ligands from High-Resolution XANES Spectroscopy and First-Principles Calculations.

We present results obtained from high energy-resolution L3-edge XANES spectroscopy and first-principles calculations for the structure, bonding, and stability of mercury(II) complexes with thiolate and thioether ligands in crystalline compounds, aqueous solution, and macromolecular natural organic matter (NOM). Core-to-valence XANES features that vary in intensity differentiate with unprecedented sensitivity the number and identity of Hg ligands and the geometry of the ligand environment. Post-Hartree-Fock XANES calculations, coupled with natural population analysis, performed on MP2-optimized Hg[(SR)2···(RSR)n] complexes show that the shape, position, and number of electronic transitions observed at high energy-resolution are directly correlated to the Hg and S (l,m)-projected empty densities of states and occupations of the hybridized Hg 6s and 5d valence orbitals.

Fish Consumption and Hair Mercury Among Asians in Chicago.

Objectives: The aim of the study was to characterize the risk for elevated mercury (Hg) from fish consumption among Asians in Chicago. Consumption of fish contaminated with methyl Hg (MeHg) can affect the neurodevelopment in children and cardiovascular disease risk in adults.

Methods: We collected fish consumption information and hair samples for Hg at two health fairs.

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.

Incorporation of Pb at the calcite (104)-water interface.

Lead (Pb) is a common environmental pollutant, and its transport in surface waters and groundwater is controlled in part by sorption and precipitation reactions at mineral surfaces. Using in situ specular and resonant anomalous X-ray reflectivity measurements, we investigated the interaction of the calcite (104) surface with a dilute Pb- and EDTA-bearing solution that is slightly undersaturated with respect to calcite. The X-ray results reveal Pb coherently substituting for Ca in the near-surface layers of strained calcite with Pb/(Pb + Ca) atom fractions as high as 0.

Thlaspi arvense binds Cu(II) as a bis-(L-histidinato) complex on root cell walls in an urban ecosystem.

Root cell walls accumulate metal cations both during acquisition from the environment and removal from the protoplast to avoid toxicity, but molecular forms of the metals under field conditions remain elusive. We have identified how copper is bound to cell walls of intact roots of native Thlaspi arvense by combining synchrotron X-ray fluorescence and absorption techniques (XANES and EXAFS) at the nano-, micro-, and bulk scales. The plants grew naturally in sediment in a stormwater runoff basin at copper concentrations typical of urban ecosystems.

Monovalent ion adsorption at the muscovite (001)-solution interface: relationships among ion coverage and speciation, interfacial water structure, and substrate relaxation.

The interfacial structure between the muscovite (001) surface and aqueous solutions containing monovalent cations (3 × 10(-3) m Li(+), Na(+), H(3)O(+), K(+), Rb(+), or Cs(+), or 3 × 10(-2) m Li(+) or Na(+)) was measured using in situ specular X-ray reflectivity. The element-specific distribution of Rb(+) was also obtained with resonant anomalous X-ray reflectivity. The results demonstrate complex interdependencies among adsorbed cation coverage and speciation, interfacial hydration structure, and muscovite surface relaxation.

Heavy metal sorption at the muscovite (001)-fulvic acid interface.

The role of fulvic acid (FA) in modifying the adsorption mode and sorption capacity of divalent metal cations on the muscovite (001) surface was evaluated by measuring the uptake of Cu(2+), Zn(2+), and Pb(2+) from 0.01 m solutions at pH 3.7 with FA using in situ resonant anomalous X-ray reflectivity.

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.

Hydrated cation speciation at the muscovite (001)-water interface.

Charged materials in aqueous systems interact according to their interfacial properties, typically described by the electrical double layer (EDL). Distributions of divalent metal cations at the muscovite (001)-solution interface observed using resonant anomalous X-ray reflectivity demonstrate an unexpected complexity with respect to the EDL structure. Three forms of adsorbed cations can coexist: the classical inner-sphere and outer-sphere complexes and a third "extended" outer-sphere complex located farther from the surface.

Enhanced uptake and modified distribution of mercury(II) by fulvic acid on the muscovite (001) surface.

Evidence is increasing for the mobility and bioavailability of aqueous mercury(II) species being related to the interactions of mercury with dissolved organic matter (DOM). Here, we assess the relative roles of the mineral surface and DOM in controlling mercury(II) uptake at the muscovite (001)-solution interface using interface-specific X-ray reflectivity combined with element-specific resonant anomalous X-ray reflectivity. Experiments were performed with single crystals of muscovite and solutions of 100 mg/kg Elliott Soil Fulvic Acid II and 0.

Thermodynamics, interfacial structure, and pH hysteresis of Rb+ and Sr2+ adsorption at the muscovite (001)-solution interface.

The coverage and average height of adsorbed Rb+ and Sr2+ at the muscovite (001)-solution interface were measured with resonant anomalous X-ray reflectivity (RAXR) as a function of cation concentration (10-8 < [Sr2+] < 10(-1) m, 10-6 < [Rb+] < 10(-1) m at pH 5.5 and 3.5) and pH (1.

Fulvic acid sorption on muscovite mica as a function of pH and time using in situ X-ray reflectivity.

Interfacial structures of the basal surface of muscovite mica in 100 mg kg (-1) Elliott Soil Fulvic Acid II solutions were investigated using in situ X-ray reflectivity. Molecular-scale variations in the thickness and internal structure of the fulvic acid (FA) film were observed and quantified as a function of pH (2-12) and reaction time (3-500 h at pH 3.7).

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.

Relationships between Hg(II)-S bond distance and Hg(II) coordination in thiolates.

Extended X-ray absorption fine structure (EXAFS) spectroscopy is a sensitive structural probe of the coordination environments of Hg(II) with thiol (sulfhydryl) groups, and is equally applicable to solid and aqueous organic or inorganic matter. Information on the number and geometric arrangement of S ligands can be derived from metal-ligand distances because the distances vary with Hg stereochemistry and can be accurately measured by the EXAFS technique. To improve the reliability of determining coordination structures of Hg with thiol groups, correlations among Hg-S bond distance, Hg coordination, and S-Hg-S angle in homoleptic Hg(II)-thiolates were calculated from analysis of the structures of the 162 Hg(SR)n motifs (n = 2, 3, 4) contained in the Cambridge Structural Database v.

Hydration and distribution of ions at the mica-water interface.

Molecular-scale structures of mica surfaces in electrolyte solutions reveal how ion and interfacial hydration control cation adsorption. Key differences are obtained for Rb+and Sr2+ using resonant anomalous x-ray reflectivity: Rb+ adsorbs in a partially hydrated state and incompletely compensates the surface charge, but Sr2+ adsorbs in both fully and partially hydrated states while achieving full charge compensation. These differences are driven by balancing the energy cost of disrupting ion and interface hydration with the electrostatic attraction between the cation and charged surface.