Arsenic in drinking water and incidence of urinary cancers

To investigate the effects of a new nonNMDA antagonist on the trisynaptic pathways in the hippocampus, the author examined kainate(KA)-induced generalized seizures in rats. A novel nonNMDA antagonist, YM90K, showed the blockade of the Schaffer collaterals in 2-deoxyglucose study (2-DG) and that the CA1-2 pyramidal cells of the hippocampus were preserved seven days after the KA injections. On the other hand, the control and MK-801 (NMDA-antagonist) treated rats did not depress the Schaffer collaterals and showed persistent hypermetabolism of glucose in the CA1 pyramidal cell layer, where neurons were not preserved seven days later. 2-DG was useful to reveal the effects of nonNMDA antagonist on the KA-induced generalized seizures. This suggests that YM90K is a potent nonNMDA antagonist and that it has a neuroprotective effect in rats.     

Chlorate Formation in Chlorine Dioxide Delignification—An Analysis via Elementary Kinetic Modeling

Abstract

Elementary kinetic modeling was used to study the mechanism of chlorate formation in chlorine dioxide delignification. Reaction conditions reflecting typical industrial processes (T = 50°C, pH 1.5–4) were examined. Fe mediated Cl(III) decomposition and a reaction between hypochlorous acid and chlorous acid (or their equilibrium counterparts) were found to be the major reaction routes responsible for chlorate formation at pH < 3. The latter route accounts for chlorate formation at pH ≥ 3. The rate of chlorous acid (HClO₂) self-decomposition was too slow either to compete against the other routes (pH < 3) or to yield notable amounts of chlorate within the given time frame (pH ≥ 3). The results suggest that chlorate formation could be suppressed, without adverse effects on chlorine dioxide regeneration, by aiming for end pH 3–3.5, ensuring a moderate chloride ion concentration and by favoring concentrated solutions/suspensions.     

A Model for Chlorine Dioxide Delignification of Chemical Pulp

Abstract

A phenomenon based model for chlorine dioxide delignification of chemical pulp is introduced. The pulp suspension environment is modeled using the concept of two liquid phases, one inside and the other external to the fiber wall. Physico-chemical processes taking place during delignification are implemented with thermodynamic, mass transfer and reaction kinetic models. A broad library of chemical reactions is introduced. Inclusion of each reaction is justified. The model response is tested against experimental laboratory delignification results (o-delignified birch pulp). The experimental data consists of kappa number, hexenuronic acid, inorganic oxy-chlorine compound, and organochlorine (AOX, OX) measurements at several time points during five delignification experiments. The model predictions are mainly in good agreement with the experimental results. The predictions regarding hypochlorous acid driven processes (HexA removal, organochlorine formation, chlorite and chlorate concentration) are somewhat incoherent, indicating that knowledge regarding the intermediately formed hypochlorous acid is presently insufficient.     

Resonant ultrasound spectroscopy: applications, current status and limitations

Over the last 10 years, resonant ultrasound spectroscopy (RUS) has become a versatile laboratory technique for measuring second-order elastic constants and ultrasonic attenuation in solids. The technique is based on measuring the spectrum of mechanical resonances for a sample of known shape (usually a parallelepiped). This spectrum cannot be deconvoluted to deduce the elastic constants. Instead, an approximate spectrum is calculated from the known sample dimensions, its mass, and a set of ‘guessed’ elastic constants. A multidimensional minimization of the error between the measured and calculated spectra enables deducing all the elastic constants of the solid from a single frequency scan. Currently, the technique can be applied to crystals of orthorhombic symmetry (9 elastic constants) or higher using desktop computers and software developed for this purpose.     

A COMPARISON OF HPLC WITH FLUORESCENCE DETECTION AND FIXED WAVELENGTH FLUORESCENCE METHODS FOR THE DETERMINATION OF POLYCYCLIC AROMATIC HYDROCARBON METABOLITES IN FISH BILE

Fish exposed to polycyclic aromatic hydrocarbons (PAHs) accumulate only a small amount of PAH in their tissues. Hydrophobic PAHs are readily transformed into hydrophilic metabolites and excreted in bile. Bile samples of five fish species were collected from the Baltic Sea and analyzed using two methods: high-performance liquid chromatography (HPLC) with fluorescence detection and a fixed wavelength fluorescence method. With the HPLC method PAH compounds were quantitated after hydrolysis, and with the fluorescence method without enzyme-assisted hydrolysis. In HPLC analysis the major metabolite in all fish species, 1-hydroxypyrene, was the only metabolite detected in perch and salmon samples. 1-Hydroxyphenanthrene was detected in a few flounder and in most eelpouts. The correlation between the two methods for pyrene-type metabolites was good (r² = 0.773).     

Retrotransposable elements R1 and R2 in the rDNA units of Drosophila mercatorum: abnormal abdomen revisited

R1 and R2 retrotransposable elements are stable components of the 28S rRNA genes of arthropods. While each retrotransposition event leads to incremental losses of rDNA unit expression, little is known about the selective consequences of these elements on the host genome. Previous reports suggested that in the abnormal abdomen (aa) phenotype of Drosophila mercatorum, high levels of rDNA insertions (R1) in conjunction with the under-replication locus (ur), enable the utilization of different ecological conditions via a population level shift to younger age. We have sequenced the R1 and R2 elements of D. mercatorum and show that the levels of R1- and R2-inserted rDNA units were inaccurately scored in the original studies of aa, leading to several misinterpretations. In particular, contrary to earlier reports, aa flies differentially underreplicate R1- and R2-inserted rDNA units, like other species of Drosophila. However, aa flies do not undergo the lower level of underreplication of their functional rDNA units (general underreplication) that is seen in wild-type strains. The lack of general underreplication is expected to confer a selective advantage and, thus, can be interpreted as an adaptation to overcome high levels of R1 and R2 insertions. These results allow us to reconcile some of the apparently contradictory effects of aa and the bobbed phenotype found in other species of Drosophila.