Solution speciation controls mercury isotope fractionation of Hg(II) sorption to goethite

The application of Hg isotope signatures as tracers for environmental Hg cycling requires the determination of isotope fractionation factors and mechanisms for individual processes. Here, we investigated Hg isotope fractionation of Hg(II) sorption to goethite in batch systems under different experimental conditions. We observed a mass-dependent enrichment of light Hg isotopes on the goethite surface relative to dissolved Hg (ε(202)Hg of -0.30‰ to -0.44‰) which was independent of the pH, chloride and sulfate concentration, type of surface complex, and equilibration time. Based on previous theoretical equilibrium fractionation factors, we propose that Hg isotope fractionation of Hg(II) sorption to goethite is controlled by an equilibrium isotope effect between Hg(II) solution species, expressed on the mineral surface by the adsorption of the cationic solution species. In contrast, the formation of outer-sphere complexes and subsequent conformation changes to different inner-sphere complexes appeared to have insignificant effects on the observed isotope fractionation. Our findings emphasize the importance of solution speciation in metal isotope sorption studies and suggest that the dissolved Hg(II) pool in soils and sediments, which is the most mobile and bioavailable, should be isotopically heavy, as light Hg isotopes are preferentially sequestered during binding to both mineral phases and natural organic matter

Source tracing of natural organic matter bound mercury in boreal forest runoff with mercury stable isotopes

Terrestrial runoff represents a major source of mercury (Hg) to aquatic ecosystems. In boreal forest catchments, such as the one in northern Sweden studied here, mercury bound to natural organic matter (NOM) represents a large fraction of mercury in the runoff. We present a method to measure Hg stable isotope signatures of colloidal Hg, mainly complexed by high molecular weight or colloidal natural organic matter (NOM) in natural waters based on pre-enrichment by ultrafiltration, followed by freeze-drying and combustion. We report that Hg associated with high molecular weight NOM in the boreal forest runoff has very similar Hg isotope signatures as compared to the organic soil horizons of the catchment area. The mass-independent fractionation (MIF) signatures (Δ; 199; Hg and Δ; 200; Hg) measured in soils and runoff were in agreement with typical values reported for atmospheric gaseous elemental mercury (Hg; 0; ) and distinctly different from reported Hg isotope signatures in precipitation. We therefore suggest that most Hg in the boreal terrestrial ecosystem originated from the deposition of Hg; 0; through foliar uptake rather than precipitation. Using a mixing model we calculated the contribution of soil horizons to the Hg in the runoff. At moderate to high flow runoff conditions, that prevailed during sampling, the uppermost part of the organic horizon (Oe/He) contributed 50-70% of the Hg in the runoff, while the underlying more humified organic Oa/Ha and the mineral soil horizons displayed a lower mobility of Hg. The good agreement of the Hg isotope results with other source tracing approaches using radiocarbon signatures and Hg : C ratios provides additional support for the strong coupling between Hg and NOM. The exploratory results from this study illustrate the potential of Hg stable isotopes to trace the source of Hg from atmospheric deposition through the terrestrial ecosystem to soil runoff, and provide a basis for more in-depth studies investigating the mobility of Hg in terrestrial ecosystems using Hg isotope signatures

Kinetics of Hg(II) exchange between organic ligands, goethite, and natural organic matter studied with an enriched stable isotope approach

The mobility and bioavailability of toxic Hg(II) in the environment strongly depends on its interactions with natural organic matter (NOM) and mineral surfaces. Using an enriched stable isotope approach, we investigated the exchange of Hg(II) between dissolved species (inorganically complexed or cysteine-, EDTA-, or NOM-bound) and solid-bound Hg(II) (carboxyl-/thiol-resin or goethite) over 30 days under constant conditions (pH, Hg and ligand concentrations). The Hg(II)-exchange was initially fast, followed by a slower phase, and depended on the properties of the dissolved ligands and sorbents. The results were described by a kinetic model allowing the simultaneous determination of adsorption and desorption rate coefficients. The time scales required to reach equilibrium with the carboxyl-resin varied greatly from 1.2 days for Hg(OH)2 to 16 days for Hg(II)-cysteine complexes and approximately 250 days for EDTA-bound Hg(II). Other experiments could not be described by an equilibrium model, suggesting that a significant fraction of total-bound Hg was present in a non-exchangeable form (thiol-resin and NOM: 53-58%; goethite: 22-29%). Based on the slow and incomplete exchange of Hg(II) described in this study, we suggest that kinetic effects must be considered to a greater extent in the assessment of the fate of Hg in the environment and the design of experimental studies, for example, for stability constant determination or metal isotope fractionation during sorption

Effect of small side games and runs on performance in sprints and agility in soccer players.

Title: Influence of small side games and runs on sprint performance and agility in football players. Purpose: The aim of the thesis is to find out the influence of selected movement interventions (small side games versus runs) on sprint performance and agility in elite football players in U14 category during the preseason period. Methods: The 30-meter Sprint was used to rate speed-strength performance. Players have executed 2 sprints at 30m. Sprint time was measured at 5, 10 and 30m. Agility tests included: test 505 and three-step test. Players also have executed 2 tries (one of each leg). A set of photocells (Alge Timing GmbH, Lustenau, Austria) was used to measure the time of all tests. Results: Both groups significantly improved in the three-step test (p 0.5). The SSG group, after a two-month intervention, significantly deteriorated in the sprint to 5, 10 and 30m (r = 0.38 - 0.69). The race group did not significantly improve in sprints at 5, 10 and 30m. In the agility test, we saw a significant improvement only in the Run groups and only on the left leg (r = 0.42). Based on the findings, we believe that the training units of the linear speed and speed with the change of direction maintain the level of player's speed during the season. Therefore, I recommend that they should appear in..

Vztah autoimunitnich tyreoidalnich chorob ke karcinomu prsu a nekterym vybranym celkovym chorobam.

The association of autoimmune thyroid diseases (AITD) with several autoimmune diseases such as diabetes mellitus type I or celiac disease (CD) is generally known. In contrast, the relationship between thyroid diseases and some nonautoimmune diseases, e.g. breast cancer, is not fully understood. Previous research has shown that AITD and subclinical or manifest hypothyroidism are frequently found in women with breast cancer. According to recent research, iodine intake and natrium-iodide symporter mediated iodine uptake have been supposed to play a potential role in the pathogenesis (PG) of both AITD and benign and malignant breast diseases. Several cytokines (CK) contribute to the PG of AITD. According to their role of PG of autoimmune diseases, CK could be divided into two groups.Th 1 CK play an important role in the cellular immune respons and contribute to the PG of Th 1 mediated autoimmune diseases and Th 2 CK which take part in the humoral immune response and contribute to the PG of Th 2 mediated autoimmune diseases. Changes in serum levels of some CK have been observed in patients with AITD. CD is a chronic illness of the small bowel caused by gliadin intolerance in genetically predisposed people with several features of autoimmunity. Some clinical studies have demonstrated a significant association between AITD and CD. If there exists a functional pathogenetic relationship between both illnesses or whether it is only a case of disposition to crossed autoimmune reactivity in persons with AITD, manifested in the positivity of various antibodies without any further clinical correlate, is not yet known.Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi

The impact of different forms of stretching for acute speed-strength performance for elite soccer players U16.

Sportovní hryFakulta tělesné výchovy a sportuFaculty of Physical Education and Spor

The impact of different forms of stretching for acute speed-strength performance for elite soccer players U16.

Sportovní hryFakulta tělesné výchovy a sportuFaculty of Physical Education and Spor