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Polydimethylsiloxane (PDMS) is a polymer material with high absorptive properties increasingly used as a passive environmental sampler for persistent organic compounds. However, the partitioning behavior of hydrophobic chemicals to PDMS remains largely unknown. Organochlorines (OCs) and polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants of great concern due to their persistence and potential toxic effects on humans and animals. In this study, the affinity of 20 OCs and 25 PAHs for commercially available PDMS pellets was determined to assess their effectiveness as passive samplers. Experiments were conducted to estimate the absorption rates (k) and equilibrium concentrations, demonstrating that 16 OCs and 21 PAHs were efficiently absorbed by PDMS, while others remained dissolved in water. A model has been proposed to predict dissolved concentrations in water based on the Kow of the compound, suggesting that PDMS is a suitable passive sampler for these compounds. [ABSTRACT FROM AUTHOR]

Using theoretical models, retention mechanisms of amlodipine besilate and its impurities D, E, and F were tested, as well as bisoprolol fumarate and its impurities A, C, K, and L. Appropriate theoretical retention models for tested compounds were used, which enabled the determination of retention mechanisms responsible for the separation of tested compounds on three different HILIC column: silica, amino, and diol. In order to describe the effect of ratio of aqueous and organic portion of the mobile phase on the retention behavior of tested compounds, as well as the consideration of shares of partition and adsorption processes in HILIC retention mechanism in all three columns, partitioning and adsorption retention theoretical models were calculated. For this purpose, the water content was varied in the range from 4% to 29%, corresponding to the HILIC region of mobile phase composition. During the experiment, values of other factors of mobile phase were maintained at a constant level. Regression coefficients of partition and adsorption retention models and the corresponding determination coefficients were determined (R2). Partitioning models for all tested compounds on amino column had higher R2 values, while adsorption models for all compounds tested on silica and diol column had higher R2 value. [ABSTRACT FROM AUTHOR]

A CALPHAD-type thermodynamic assessment of the Al-C-Mn system was carried out in the present work. Special attention was paid to the ternary κ-phase with the aid of ab initio calculations. The enthalpies of formation at 0 K of all end-members of the κ phase were derived from the ab initio calculations and utilized in the present optimization. The κ phase was modeled as an ordered form of the fcc structure for the substitutional sub-lattices, employing the following formula within the framework of compound energy formalism: (Al,Mn) 0.25 (Al,Mn) 0.25 (Al,Mn) 0.25 (Al,Mn) 0.25 (C,Va) 0.25 . With the present optimized model parameters, the wide homogeneity range of the κ phase was reproduced satisfactorily. Comparison between the predicted and measured phase equilibria as well as the ab initio calculation results validates the present optimized model parameters. [ABSTRACT FROM AUTHOR]

The Al-C-Fe system was assessed in the framework of the CALPHAD approach. Through the critical review of thermochemical properties of liquid Al-Fe alloys, the binary Al-Fe description was revised to agree better with the experimental data. The partitioning model based on the Compound Energy Formalism (CEF) was utilized to describe the disordered and ordered bcc, fcc and κ phases. Moreover, ab initio calculations were performed to determine the enthalpies of formation of the ordered structures based on the bcc and fcc lattices in the binary Al-Fe and for the end-members of the κ phase in the ternary Al-C-Fe system. In order to simplify the database, the present work also employed a two-sublattice model to describe the B2 ordered phase in the Al-Fe system, which can be applied easily to diffusion simulations. Comprehensive comparison between the model-predicted and experimental data confirms that the present evaluation describe the Al-C-Fe system satisfactorily, especially the κ phase. [ABSTRACT FROM AUTHOR]

A model was developed to assess the impact of adding acids and bases to processed municipal sewage sludge (MSS) to mobilize contaminants, facilitating their removal from sludge by flushing prior to land application. Among 312 organic contaminants documented to occur in U.S. MSS, 71 or 23% were identified as ionizable organic contaminants (IOCs), contributing a disproportionately large fraction of 82% of the total mass of sludge-borne contaminants. Detected IOCs included 57 pharmaceuticals and personal care products, 12 perfluorinated compounds, one surfactant and one pesticide. Annually, about 2000 t of IOCs were estimated to be released to U.S. soils via land-application of MSS. A partitioning model developed to assess the impact of pH on hydrophobic sorption revealed that between 36 and 85% of the mass of individual classes of IOCs potentially could be desorbed from MSS via pH adjustment and flushing. Thus, modeling results suggest that a sequential pH treatment [acidic (~ pH 2) followed by basic (~ pH 12) treatment] has the potential to reduce the burden of harmful IOCs in MSS applied on U.S. land by up to 40 ± 16 t annually. This approach may serve as a cost-effective treatment process that can be implemented easily in existing sludge treatment infrastructure in the U.S. and worldwide, serving to significantly improve the quality of MSS destined for land application. [ABSTRACT FROM AUTHOR]

Air concentrations of polychlorinated biphenyls (PCBs) in both gas and particle phases were measured in an urban site (BUTAL-Merinos) of the city of Bursa, Turkey between August 2004 and May 2005. The mean of total (particle+gas) PCB concentrations was about 491.8±189.4pg/m3. The main contributors for PCBs in the sampling site were the local sources and long-range atmospheric transport supported by back trajectory analysis. Lower molecular weight PCB congeners generally dominated in the samples. The particle phase of the measured PCBs accounted for 15% of the total PCB concentrations. Gas/particle distribution was investigated using different approaches such as log K P −log P L o, log K P −log K OA and the Junge–Pankow model. Regression analysis among log K P, log P L o and log K OA exhibited significant correlation at p <0.05. Correlation between PCB homologs and meteorological parameters was formed to investigate the possible relationships. [Copyright &y& Elsevier]

Abstract Background Rates of molecular evolution are known to vary across taxa and among genes, and this requires rate calibration for each specific dataset based on external information. Calibration is sensitive to evolutionary model parameters, partitioning schemes and clock model. However, the way in which these and other analytical aspects affect both the rates and the resulting clade ages from calibrated phylogenies are not yet well understood. To investigate these aspects we have conducted calibration analyses for the genus Carabus (Coleoptera, Carabidae) on five mitochondrial and four nuclear DNA fragments with 7888 nt total length, testing different clock models and partitioning schemes to select the most suitable using Bayes Factors comparisons. Results We used these data to investigate the effect of ambiguous character and outgroup inclusion on both the rates of molecular evolution and the TMRCA of Carabus. We found considerable variation in rates of molecular evolution depending on the fragment studied (ranging from 5.02% in cob to 0.26% divergence/My in LSU-A), but also on analytical conditions. Alternative choices of clock model, partitioning scheme, treatment of ambiguous characters, and outgroup inclusion resulted in rate increments ranging from 28% (HUWE1) to 1000% (LSU-B and ITS2) and increments in the TMRCA of Carabus ranging from 8.4% (cox1-A) to 540% (ITS2). Results support an origin of the genus Carabus during the Oligocene in the Eurasian continent followed by a Miocene differentiation that originated all main extant lineages. Conclusions The combination of several genes is proposed as the best strategy to minimise both the idiosyncratic behaviors of individual markers and the effect of analytical aspects in rate and age estimations. Our results highlight the importance of estimating rates of molecular evolution for each specific dataset, selecting for optimal clock and partitioning models as well as other methodological issues potentially affecting rate estimation.

In vitro extraction of contaminated sediments using the digestive fluid of a deposit-feeding polychaete has recently been proposed to study contaminant bioaccumulation mechanisms and perhaps to better quantify the bioavailable contaminant fraction. This approach was evaluated using digestive fluid from the polychaete Arenicola brasiliensis and six marine sediments containing both spiked radiolabeled polycyclicaromatic hydrocarbons (PAHs) and in situ-contaminated unlabeled PAHs. The proportion of total contaminant extracted by digestive fluid from each sediment varied from 22 to 71% and 13 to 52%, for phenanthrene and benzo[a]pyrene, respectively. The proportions of contaminant solubilized were inversely correlated with the sediments' organic carbon content. The extent of PAH solubilization among sediments by A. brasiliensis digestive fluid was highly correlated with that of digestive fluid from the echiuran Urechis caupo and appears to be a consequence of surfactant properties of the fluids rather than of their enzymatic activity. The proportion of PAHs solubilized in vitro was similarto in vivo measurements of solubilization for contaminant exposures lasting about 24 h. However, with continued exposure, in vivo PAH concentrations in the digestive fluid increased fivefold, suggesting that digestive fluid is retained in the gut longer than sediment and thus accumulates PAHs through sequential digestion of many gut volumes. This phenomenon may enhance contaminant fugacity in the gut and increase the potential for bioaccumulation or toxicity. [ABSTRACT FROM AUTHOR]