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An original approach is proposed to investigate inorganic (iHg) and methylmercury (MeHg) trophic transfer and fate in a model fish, Danio rerio, by combining natural isotopic fractionation and speciation. Animals were exposed to three different dietary conditions: (1) 50 ng Hg g(-1), 80% as MeHg; (2) diet enriched in MeHg 10,000 ng Hg g(-1), 95% as MeHg, and (3) diet enriched in iHg 10,000 ng Hg g(-1), 99% as iHg. Harvesting was carried out after 0, 7, 25, and 62 days. Time-dependent Hg species distribution and isotopic fractionation in fish organs (muscle, brain, liver) and feces, exhibited different patterns, as a consequence of their dissimilar metabolization. The rapid isotopic re-equilibration to the new MeHg-food source reflects its high bioaccumulation rate. Relevant aspects related to Hg excretion are also described. This study confirms Hg isotopic fractionation as a powerful tool to investigate biological processes, although its deconvolution and fully understanding is still a challenge.

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Ta-doped Ti1−xTaxCoSb (0⩽x⩽0.08) half-Heusler compounds were synthesized by melting and annealing process. Their thermoelectric properties were studied in the temperature range of 300–900K. The Ti1−xTaxCoSb compounds exhibit negative Seebeck coefficients with considerably large absolute values. With increasing Ta substitution, the electrical conductivity was greatly increased, but the thermal conductivity was reduced. Because of the combined effects of increased electrical conductivity and reduced thermal conductivity, the thermoelectric performance of Ti1−xTaxCoSb alloys was apparently improved by doping Ta. The dimensionless figure of merit of 0.3 was obtained for Ti0.92Ta0.08CoSb compound at 900K. This value is about ten times larger than that of the undoped TiCoSb compound.

The crystallographic properties and defects of hydrothat hydrothermal BaTiO 3 powders show structural peculiarities that are closely connected with a considerable content of water. thermally grown barium titanate crystallites are reported. When a precursor with a Ba:Ti molar ratio of 1.0 was used, On annealing the powders to 500ЊC, the water is gradually released and the normal structural properties of BaTiO 3 recur. cubic barium titanate crystallites were formed. However, when the precursor Ba:Ti molar ratio was 3.0, the product In this paper, systematic measurements of hydrothermal BaTiO 3 crystallites are presented. The formation of defects, the relationwas tetragonal. The defect concentration (including OH defects and barium vacancies) was higher in cubic crystalliship between defect content, the reaction conditions, and the crystallographic properties of the crystallites are discussed. tes than in tetragonal crystallites. Because of the defects in the crystallites, the displacement of Ba 2؉ cations and the deformation of the Ti-O 6 octahedrons was suppressed;II. Experimental Procedure thus, no phase transition from cubic to tetragonal occurred at the Curie point. When the defects were eliminated by (1) Hydrothermal Synthesis of BaTiO 3 Crystallites thermal treatment, the normal crystallographic propertiesThe hydrothermal experiments were performed in a platinumwere obtained. A high reaction temperature and a high lined tube-type autoclave with an internal diameter of 30 mm Ba:Ti molar ratio in the precursor were beneficial to limand a length of 450 mm. Many types of precursors were utiiting defect dormation in the crystallites; thus, tetragonal lized, including commercial TiO 2 (CP, Shanghai Institute of crystallites were obtained.Fine Chemicals) and Ba(OH) 2 и8H 2 O (AR, Shanghai Institute of Fine Ceramics) powders; hydrolysis product of tetrabutyl I. Introduction titanate and Ba(OH) 2 и8H 2 O powders; newly prepared barium titanium acetate gel 11 and barium titanium peroxide gel. 12 The N UMEROUS ceramic powders can be conveniently synthe-fill parameter of the hydrothermal reaction system was selected sized by the hydrothermal method. Hydrothermal synthesis in a range from 80% to 90%, the reaction temperature in a range makes it possible to prepare phase-pure products from inexpenfrom 75Њ to 400ЊC, and the reaction time (the time at the sive and easily accessible precursors in a single step. Also, reaction temperature) in a range from 4 to 72 h. The heating the synthesis can be performed at moderate temperature and rate for all experiments was fixed at 7ЊC/min. pressure using a simple autoclave. The conditions of hydrothermal reactions can be optimized by varying the chemical process(2) Characterization of the Crystallites variables, such as reagent concentrations, temperature, presAfter they were washed with distilled water and absolute sure, and pH. Traditionally, the process variables, with few ethanol several times, the hydrothermal products were dried in exceptions, 1,2 are adjusted empirically in a t...

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Methylmercury (MeHg), a neurotoxic compound biomagnifying in aquatic food webs, can be a threat to human health via fish consumption. However, the composition and distribution of the microbial communities mediating the methylation of mercury (Hg) to MeHg in marine systems remain largely unknown. In order to fill this knowledge gap, we used the Baltic Sea Reference Metagenome (BARM) dataset to study the abundance and distribution of the genes involved in Hg methylation (the hgcAB gene cluster). We determined the relative abundance of the hgcAB genes and their taxonomic identity in 81 brackish metagenomes that cover spatial, seasonal and redox variability in the Baltic Sea water column. The hgcAB genes were predominantly detected in anoxic water, but some hgcAB genes were also detected in hypoxic and normoxic waters. Phylogenetic analysis identified putative Hg methylators within Deltaproteobacteria, in oxygen-deficient water layers, but also Spirochaetes-like and Kiritimatiellaeota-like bacteria. Higher relative quantities of hgcAB genes were found in metagenomes from marine particles compared to free-living communities in anoxic water, suggesting that such particles are hotspot habitats for Hg methylators in oxygen-depleted seawater. Altogether, our work unveils the diversity of the microorganisms with the potential to mediate MeHg production in the Baltic Sea and pinpoint the important ecological niches for these microorganisms within the marine water column.