Accumulation, Subcellular Distribution and Toxicity of Copper in Earthworm (Eisenia fetida) in the Presence of Ciprofloxacin

Land application of wastes from concentrated animal feeding operations results in accumulation of copper (Cu) and antimicrobials in terrestrial systems. Interaction between Cu and antimicrobials may change Cu speciation in soil solution, and affect Cu bioavailability and toxicity. In this study, earthworms were exposed to quartz sand percolated with different concentrations of Cu and ciprofloxacin (CIP). Copper uptake by earthworms, its subcellular partition, and toxicity were studied. An increase in the applied CIP decreased the free Cu ion concentration in external solution and mortalities of earthworm, while Cu contents in earthworms increased. Copper and CIP in earthworms were fractionated into five fractions: a granular fraction (D), a fraction consisting of tissue fragments, cell membranes, and intact cells (E), a microsomal fraction (F), a denatured proteins fraction (G), and a heat-stable proteins fraction (H). Most of the CIP in earthworms was in fraction H. Copper was redistributed from the metal-sensitive fraction E to fractions D, F, G, and H with increasing CIP concentration. These results challenge the free ion activity model and suggested that Cu may be partly taken up as Cu-CIP complexes in earthworms, changing the bioavailability, subcellular distribution, and toxicity of Cu to earthworms.

Structure and reactivity of the Ru(0 0 0 1) electrode towards fuel cell electrocatalysis

The reactivity of the Ru(0 0 0 1) electrode towards the adsorption and electrooxidation of CO and methanol has been studied by variable-temperature in situ FTIR spectroscopy in both perchloric acid and sodium hydroxide solution, and the results interpreted in terms of the surface chemistry of the Ru(0 0 0 1) electrode. Both linear (CO) and threefold hollow (CO) binding CO adsorbates (bands at 1970-2040 and 1770-1820 cm, respectively) were observed on the Ru(0 0 0 1) electrode in both 0.1 M HClO and 0.1 M NaOH solutions from the CO adsorption. In the acid solution, CO was detected as the main adsorbed species on Ru(0 0 0 1) surface over all the potential region studied. In contrast, in the alkaline solution, more CO than CO was detected at lower potentials, whilst increasing the potential resulted in the transformation of CO to CO. At higher potentials, the oxidation of the adsorbed CO took place via reaction with the active (1 × 1)-O oxide/hydroxide. It was found that no dissociative adsorption or electrooxidation of methanol took place at the Ru(0 0 0 1) at potentials below 900 mV vs Ag/AgCl in perchloric acid solution at both 20 and 55°C. However, in the alkaline solution, methanol did undergo dissociative adsorption, to form linearly adsorbed CO (CO) with little or no CO adsorbed at threefold hollow sites (CO) at both 20 and 55°C. Increasing the temperature from 20 to 55°C clearly facilitated the methanol dissociative adsorption to CO and also enhanced the electrooxidation of the CO. At the higher potentials, significant oxidation of methanol to CO and methyl formate in acid solution and to bicarbonate and formate in alkaline solution, was observed, which was attributed to the formation of an active RuO phase on the Ru(0 0 0 1) surface, in agreement with our previous studies. © 2003 Elsevier Ltd. All right reserved.

Arsenic removal from soil with high iron content using a natural surfactant and phosphate

An environment friendly arsenic removal technique from contaminated soil with high iron content has been studied. A natural surfactant extracted from soapnut fruit, phosphate solution and their mixture was used separately as extractants. The mixture was most effective in desorbing arsenic, attaining above 70 % efficiency in the pH range of 4–5. Desorption kinetics followed Elovich model. Micellar solubilization by soapnut and arsenic exchange mechanism by phosphate are the probable mechanisms behind arsenic desorption. Sequential extraction reveals that the mixed soapnut–phosphate system is effective in desorbing arsenic associated with amphoteric–Fe-oxide forms. No chemical change to the wash solutions was observed by Fourier transform-infrared spectra. Soil:solution ratio, surfactant and phosphate concentrations were found to affect the arsenic desorption process. Addition of phosphate boosted the performance of soapnut solution considerably. Response surface methodology approach predicted up to 80 % desorption of arsenic from soil when treated with a mixture of ≈1.5 % soapnut, ≈100 mM phosphate at a soil:solution ratio of 1:30.

Preparation and surface modification of submicron YAl2 particles by mixed milling with magnesium for fabricating YAl2p/MgLiAl composites

A new process for the preparation and surface modification of submicron YAl2 intermetallic particles was proposed to control the agglomeration of ultrafine YAl2 particles and interface in the fabrication of YAl2p/MgLiAl composites. The morphological and structural evolution during mechanical milling of YAl2 powders (< 30 μm) with magnesium particles (~ 100 μm) has been characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results show that YAl2 particles are refined to submicron scale and separately cladded in magnesium coatings after mixed milling with magnesium particles for 20 h. Mechanical and metallurgical bonds have been found in YAl2/Mg interfaces without any interface reactions. Both the refining and mechanical activation efficiencies for YAl2 particles are enhanced, which may be related to the addition of magnesium particles leading to atomic solid solution and playing a role as “dispersion stabilizer”.

T- and L-type Ca2+ currents in freshly dispersed smooth muscle cells from the human proximal urethra

The purpose of the present study was to characterise Ca2+ currents in smooth muscle cells isolated from biopsy samples taken from the proximal urethra of patients undergoing surgery for bladder or prostate cancer. Cells were studied at 37 degreesC using the amphotericin B perforated-patch configuration of the patch-clamp technique. Currents were recorded using Cs+-rich pipette solutions to block K+ currents. Two components of current, with electrophysiological and pharmacological properties typical of T- and L-type Ca2+ currents, were present in these cells. When steady-state inactivation curves for the L current were fitted with a Boltzmann equation, this yielded a V-1/2 of -45 +/- 5 mV. In contrast, the T current inactivated with a V-1/2 of -80 +/- 3 mV. The L currents were reduced in a concentration-dependent manner by nifedipine (ED50 = 159 +/- 54 nm) and Ni2+ (ED50 = 65 +/- 16 muM) but were enhanced when external Ca2+ was substituted with Ba2+. The T current was little affected by TTX, reduction in external Na+, application of nifedipine at concentrations below 300 nm or substitution of external Ca2+ with Ba2+, but was reduced by Ni2+ with an ED50 of 6 +/- 1 mum. When cells were stepped from -100 to -30 mV in Ca2+-free conditions, small inward currents could be detected. These were enhanced 40-fold in divalent-cation-free solution and blocked in a concentration-dependent manner by Mg2+ with an ED50 of 32 +/- 16 mum. These data support the idea that human urethral myocytes possess currents with electrophysiological and pharmacological properties typical of T- and L-type Ca2+ currents.

Crack propagation in non-homogenous materials: Evaluation of mixed-mode SIFs, T-stress and kinking angle using a variant EFG method

A new variant of the Element-Free Galerkin (EFG) method, that combines the diffraction method, to characterize the crack tip solution, and the Heaviside enrichment function for representing discontinuity due to a crack, has been used to model crack propagation through non-homogenous materials. In the case of interface crack propagation, the kink angle is predicted by applying the maximum tangential principal stress (MTPS) criterion in conjunction with consideration of the energy release rate (ERR). The MTPS criterion is applied to the crack tip stress field described by both the stress intensity factor (SIF) and the T-stress, which are extracted using the interaction integral method. The proposed EFG method has been developed and applied for 2D case studies involving a crack in an orthotropic material, crack along an interface and a crack terminating at a bi-material interface, under mechanical or thermal loading; this is done to demonstrate the advantages and efficiency of the proposed methodology. The computed SIFs, T-stress and the predicted interface crack kink angles are compared with existing results in the literature and are found to be in good agreement. An example of crack growth through a particle-reinforced composite materials, which may involve crack meandering around the particle, is reported.

Reversibility Iteration Method to Understand Reaction Networks and to Solve Micro-Kinetics in Heterogeneous Catalysis

Solving microkinetics of catalytic systems, which bridges microscopic processes and macroscopic reaction rates, is currently vital for understanding catalysis in silico. However, traditional microkinetic solvers possess several drawbacks that make the process slow and unreliable for complicated catalytic systems. In this paper, a new approach, the so-called reversibility iteration method (RIM), is developed to solve microkinetics for catalytic systems. Using the chemical potential notation we previously proposed to simplify the kinetic framework, the catalytic systems can be analytically illustrated to be logically equivalent to the electric circuit, and the reaction rate and coverage can be calculated by updating the values of reversibilities. Compared to the traditional modified Newton iteration method (NIM), our method is not sensitive to the initial guess of the solution and typically requires fewer iteration steps. Moreover, the method does not require arbitrary-precision arithmetic and has a higher probability of successfully solving the system. These features make it ∼1000 times faster than the modified Newton iteration method for the systems we tested. Moreover, the derived concept and the mathematical framework presented in this work may provide new insight into catalytic reaction networks.