Selenium Biotransformations in an Engineered Aquatic Ecosystem for Bioremediation of Agricultural Wastewater via Brine Shrimp Production

An engineered aquatic ecosystem was specifically designed to bioremediate selenium (Se), occurring as oxidized inorganic selenate from hypersalinized agricultural drainage water while producing brine shrimp enriched in organic Se and omega-3 and omega-6 fatty acids for use in value added nutraceutical food supplements. Selenate was successfully bioremediated by microalgal metabolism into organic Se (seleno-amino acids) and partially removed via gaseous volatile Se formation. Furthermore, filterfeeding brine shrimp that accumulated this organic Se were removed by net harvest. Thriving in this engineered pond system, brine shrimp (Artemia franciscana Kellogg) and brine fly (Ephydridae sp.) have major ecological relevance as important food sources for large populations of waterfowl, breeding, and migratory shore birds. This aquatic ecosystem was an ideal model for study because it mimics trophic interactions in a Se polluted wetland. Inorganic selenate in drainage water was metabolized differently in microalgae, bacteria, and diatoms where it was accumulated and reduced into various inorganic forms (selenite, selenide, or elemental Se) or partially incorporated into organic Se mainly as selenomethionine. Brine shrimp and brine fly larva then bioaccumulated Se from ingesting aquatic microorganisms and further metabolized Se predominately into organic Se forms. Importantly, adult brine flies, which hatched from aquatic larva, bioaccumulated the highest Se concentrations of all organisms tested

Probing Compositional Variation within Hybrid Nanostructures

We present a detailed analysis of the structural and magnetic properties of solution-grown PtCo-CdS hybrid structures in comparison to similar free-standing PtCo alloy nanoparticles. X-ray absorption spectroscopy is utilized as a sensitive probe for identifying subtle differences in the structure of the hybrid materials. We found that the growth of bimetallic tips on a CdS nanorod substrate leads to a more complex nanoparticle structure composed of a PtCo alloy core and thin CoO shell. The core-shell architecture is an unexpected consequence of the different nanoparticle growth mechanism on the nanorod tip, as compared to free growth in solution. Magnetic measurements indicate that the PtCo-CdS hybrid structures are superparamagnetic despite the presence of a CoO shell. The use of X-ray spectroscopic techniques to detect minute differences in atomic structure and bonding in complex nanosystems makes it possible to better understand and predict catalytic or magnetic properties for nanoscale bimetallic hybrid materials

Iron Speciation in PM2.5 from Urban, Agriculture, and Mixed Environments in Colorado, USA

Atmospheric iron solubility varies depending on whether the particles are collected in rural or urban areas, with urban areas showing increased iron solubility. In this study, we investigate if the iron species present in different environments affects its ultimate solubility. Field data are presented from the Platte River Air Pollution and Photochemistry Experiment (PRAPPE), aimed at understanding the interactions between organic carbon and trace elements in atmospheric particulate matter (PM). 24-hr PM2.5 samples were collected during the summer and winter (2016–2017), at three different sites on the Eastern Colorado plains: an urban, agricultural, and a mixed site. Downtown Denver had an average total and water-soluble iron air concentration of 181.2 and 7.7 ng m−3, respectively. Platteville, the mixed site, had an average of total iron of 76.1 ng m−3, with average water-soluble iron concentration of 9.1 ng m−3. Jackson State Park (rural/agricultural) had the lowest total iron average of 31.5 ng m−3 and the lowest water-soluble iron average, 1.3 ng m−3. The iron oxidation state and chemical speciation of 97 samples across all sites and seasons was probed by X-ray absorption near edge structure (XANES) spectroscopy. The most common iron phases observed were almandine (Fe₃Al₂Si₃O₁₂) (Denver 21%, Platteville 16%, Jackson 24%), magnetite (Fe3O4) (Denver 9%, Platteville 4%, Jackson 5%) and Fe (III)dextran (Denver 5%, Platteville 13%, Jackson 5%), a surrogate for Fe-organic complexes. Additionally, native iron [Fe(0)] was found in significant amounts at all sites. No correlation was observed between iron solubility and iron oxidation state or chemical speciation

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

The definitive version is available at http://www.blackwell-synergy.com/loi/nphInternational audienceThe 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 F1 and F2 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 + Znaq) 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 + Znaq 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

Experimental Preservation of Muscle Tissue in Quartz Sand and Kaolinite

Siliciclastic sediments of the Ediacaran Period contain exceptionally preserved fossils of macroscopic organisms, including three-dimensional casts and molds commonly found in sandstones and siltstones and some two-dimensional compressions reported in shales. The sporadic and variable associations of these exceptionally preserved macroscopic fossils with pyrite, clay minerals, and microbial fossils and textures complicate our understanding of fossilization processes. This hinders inferences about the evolutionary histories, tissue types, original morphologies, and lifestyles of the enigmatic Ediacara biota. Here, we investigate the delayed decay of scallop muscles buried in quartz sand or kaolinite for 45 days. This process occurs in the presence of microbial activity in mixed redox environments, but in the absence of thick, sealing microbial mats. Microbial processes that mediate organic decay and release the highest concentrations of silica and Fe(II) into the pore fluids are associated with the most extensive tissue decay. Delayed decay and the preservation of thick muscles in sand are associated with less intense microbial iron reduction and the precipitation of iron oxides and iron sulfides that contain Fe(II) or Fe(III). In contrast, muscles buried in kaolinite are coated only by <10 μm-thick clay veneers composed of kaolinite grains and newly formed K- and Fe(II)-rich aluminosilicate phases. Muscles that undergo delayed decay in kaolinite lose more mass relative to the muscles buried in sand and undergo vertical collapse. These findings show that the composition of minerals that coat or precipitate within the tissues and the vertical dimension of the preserved features can depend on the type of sediment that buries the muscles. Similar processes in the zone of oscillating redox likely facilitated the formation of exceptionally preserved macrofossils in Ediacaran siliciclastic sediments

Mixing fraction of inner solar system material in comet 81P/Wild2

The presence of crystalline silicates in the comae of comets, inferred through infrared observations, has been a long-standing puzzle. Crystalline silicates are unexpectedif comets are composed of pristine interstellar material, since interstellar silicates are almost entirely amorphous. Heating to&gt; 1100 K can anneal silicates to crystallinity,but no protoplanetary heating sources have been identified that were sufficiently strong to heat materials in the outer nebula to such high temperatures. This conundrum led to the suggestion that large-scalemixing was important in theprotoplanetary disk. Reports of refractory calcium - aluminum-rich inclusion-like objects and large concentrations of noble gases in Stardust samples underscore the need for such mixing. However, the evidence from the Stardust samples until now has been largely anecdotal, and it has not been possible to place quantitative constraints on the mixing fraction. Here we report synchrotron-based X-ray microprobe measurements of the relative concentrations of the chemical state of iron in material from a known comet, the Jupiter-family comet 81P/Wild2. We find that the comet is rich in iron sulfides. The elemental S/Fe ratio based on the sulfide concentration, S/Fe&gt; 0.31(2 sigma), is higher than in most chondritic meteorites. We also found that Fe-bearing silicates are at least 50percent crystalline. Based on these measurements, we estimate the fraction psi of inner nebular material in 81P/Wild2. With the lower bound on the crystalline Fe-bearing silicate fraction, we find that psi&gt; 0.5. If the observed S depletion in the inner solar system predated or was contemporaneous with large-scale mixing, our lower bound on the S/Fe ratio gives an upper bound on psi of ~;; 0.65. This measurement may be used to test mixing models of the early solar system

Millisecond Kinetics of Nanocrystal Cation Exchange UsingMicrofluidic X-ray Absorption Spectroscopy

We describe the use of a flow-focusing microfluidic reactorto measure the kinetics of theCdSe-to-Ag2Se nanocrystal cation exchangereaction using micro-X-ray absorption spectroscopy (mu XAS). The smallmicroreactor dimensions facilitate the millisecond mixing of CdSenanocrystal and Ag+ reactant solutions, and the transposition of thereaction time onto spatial coordinates enables the in situ observation ofthe millisecond reaction with mu XAS. XAS spectra show the progression ofCdSe nanocrystals to Ag2Se over the course of 100 ms without the presenceof long-lived intermediates. These results, along with supporting stoppedflow absorption experiments, suggest that this nanocrystal cationexchange reaction is highly efficient and provide insight into how thereaction progresses in individual particles. This experiment illustratesthe value and potential of in situ microfluidic X-ray synchrotrontechniques for detailed studies of the millisecond structuraltransformations of nanoparticles and other solution-phase reactions inwhich diffusive mixing initiates changes in local bond structures oroxidation states

Getting to the Root of Selenium Hyperaccumulation—Localization and Speciation of Root Selenium and Its Effects on Nematodes

Elemental hyperaccumulation protects plants from many aboveground herbivores. Little is known about effects of hyperaccumulation on belowground herbivores or their ecological interactions. To examine effects of plant selenium (Se) hyperaccumulation on nematode root herbivory, we investigated spatial distribution and speciation of Se in hyperaccumulator roots using X-ray microprobe analysis, and effects of root Se concentration on root-associated nematode communities. Perennial hyperaccumulators Stanleya pinnata and Astragalus bisulcatus, collected from a natural seleniferous grassland contained 100–1500 mg Se kg−1 root dry weight (DW). Selenium was concentrated in the cortex and epidermis of hyperaccumulator roots, with lower levels in the stele. The accumulated Se consisted of organic (C-Se-C) compounds, indistinguishable from methyl-selenocysteine. The field-collected roots yielded 5–400 nematodes g−1 DW in Baermann funnel extraction, with no correlation between root Se concentration and nematode densities. Even roots containing \u3e 1000 mg Se kg−1 DW yielded herbivorous nematodes. However, greenhouse-grown S. pinnata plants treated with Se had fewer total nematodes than those without Se. Thus, while root Se hyperaccumulation may protect plants from non-specialist herbivorous nematodes, Se-resistant nematode taxa appear to associate with hyperaccumulators in seleniferous habitats, and may utilize high-Se hyperaccumulator roots as food source. These findings give new insight into the ecological implications of plant Se (hyper)accumulation

Selenium tolerance, accumulation, localization and speciation in a Cardamine hyperaccumulator and a non-hyperaccumulator

Cardamine violifolia (family Brassicaceae) is the first discovered selenium hyperaccumulator from the genus Cardamine with unique properties in terms of selenium accumulation, i.e., high abundance of selenolanthionine. In our study, a fully comprehensive experiment was conducted with the comparison of a non-hyperaccumulator Cardamine species, Cardamine pratensis, covering growth characteristics, chlorophyll fluorescence, spatial selenium/sulfur distribution patterns through elemental analyses (synchrotron-based X-Ray Fluorescence and ICP-OES) and speciation data through selenium K-edge micro X-ray absorption near-edge structure analysis (μXANES) and strong cation exchange (SCX)-ICP-MS. The results revealed remarkable differences in contrast to other selenium hyperaccumulators as neither Cardamine species showed evidence of growth stimulation by selenium. Also, selenite uptake was not inhibited by phosphate for either of the Cardamine species. Sulfate inhibited selenate uptake, but the two Cardamine species did not show any difference in this respect. However, μXRF derived speciation maps and selenium/sulfur uptake characteristics provided results that are similar to other formerly reported hyperaccumulator and non-hyperaccumulator Brassicaceae species. μXANES showed organic selenium, "C-Se-C", in seedlings of both species and also in mature C. violifolia plants. In contrast, selenate-supplied mature C. pratensis contained approximately half "C-Se-C" and half selenate. SCX-ICP-MS data showed evidence of the lack of selenocystine in any of the Cardamine plant extracts. Thus, C. violifolia shows clear selenium-related physiological and biochemical differences compared to C. pratensis and other selenium hyperaccumulators