Dilute arsenate (As(V)) coprecipitation by ferrihydrite was investigated to determine if treatment of acid mine drainage containing dilute As(V) using coprecipitation is feasible. The sorption density obtained at pH 5 and 7 was nearly identical when As(V) was coprecipitated with ferrihydrite, while it was higher at pH 5 when As(V) was adsorbed on the ferrihydrite. The high sorption density of As(V) to ferrihydrite in coprecipitation with 1-h reaction time suggested that coprecipitation occurs via both adsorption and precipitation. Furthermore, the relationship between residual As(V) and sorption density revealed a BET-type isotherm, with a transition point from a low residual As(V) concentration to a high residual As(V) concentration being observed for all initial As(V) concentrations between 0.15 and 0.44 mmol/dm(3) when the initial molar ratio was 0.56 at pH 5 and 7. X-ray diffraction and the zeta potential revealed that the transition point from surface complexation to precipitation was obtained when the initial As/Fe ratio was 0.4 or 0.5. When dilute As(V) was coprecipitated with ferrihydrite at pH 5 and 7, it was primarily adsorbed as a surface complex when the initial molar ratio was As/Fe < 0.4, while a ferric arsenate and surface complex was formed when this ratio was >or= 0.4.

XRD/XAFS analysis were conducted to investigate the As(V) co-precipitation mechanism with ferrihydrite ( γ-FeOOH ). In As(V) co-precipitation with ferrihydrite, XRD results showed that As(V) complexation to the surface of ferrihydrite was dominant when the initial molar ratio of As/Fe was less than 0.25, whereas surface precipitation of amorphous ferric arsenate was formed when the initial molar ratio of As/Fe was more than 0.5.Both of XANES and EXAFS analysis on K-edge of As showed As(V) co-precipitates with ferrihydrite was the mixture of As(V) adsorbed ferrihydrite and amorphous ferric arsenate. Molar ratio of amorphous ferric arsenate in As(V) co-precipitates was estimated to be more than 0.5 when the initial molar ratio of As/Fe was more than 0.5. These results are in good agreement with the XRD results. EXAFS analysis assuming one surface complex for As-Fe bond showed the coordination number of As to Fe in As(V) co-precipitates increased with increasing the initial molar ratio of As/Fe. Moreover, EXAFS analysis assuming three kinds of surface complexes for As-Fe bond showed the coordination number for 2.85 Å of the atomic distance of As-Fe increased and it for 3.24 Å of the atomic distance of As-Fe decreased with increasing the initial As/Fe molar ratio. All experimental data obtained in this study showed As(V) co-precipitation mechanism shifted gradually from As(V) complexation to the surface of ferrihydrite toward amorphous ferric arsenate with increase in the initial molar ratio of As/Fe.

DNA-based transposable elements are ubiquitous constituents of eukaryotic genomes. Vertebrates are, however, exceptional in that most of their DNA-based elements appear to be inactivated. The Tol1 element of the medaka fish, Oryzias latipes, is one of the few elements for which copies containing an undamaged gene have been found. Spontaneous transposition of this element in somatic cells has previously been demonstrated, but there is only indirect evidence for its germline transposition. Here, we show direct evidence of spontaneous excision in the germline. Tyrosinase is the key enzyme in melanin biosynthesis. In an albino laboratory strain of medaka fish, which is homozygous for a mutant tyrosinase gene in which a Tol1 copy is inserted, we identified de novo reversion mutations related to melanin pigmentation. The gamete-based reversion rate was as high as 0.4%. The revertant fish carried the tyrosinase gene from which the Tol1 copy had been excised. We previously reported the germline transposition of Tol2, another DNA-based element that is thought to be a recent invader of the medaka fish genome. Tol1 is an ancient resident of the genome. Our results indicate that even an old element can contribute to genetic variation in the host genome as a natural mutator.

A method was devised for activity assay of the lipase [triacylglycerol acyl-hydrolase, EC 3.1.1.3] excreted from Chromobacterium viscosum into the culture medium; olive oil emulsified with the aid of Adekatol 45-S-8 (a non-ionic detergent, the ethoxylate of linear sec-alcohols having chain lengths of 10--16 carbon atoms) was used as the substrate. This method was specifically effective for Chromobacterium lipase acitvity assay, and was approximately twice as sensitive as the conventional method, in which polyvinyl alcohol is used for the emulsification of the substrate.

Spatial resolution of topographic information gives a great influence to distributed runoff analysis. The objective of this study is to evaluate the effects of spatial resolution of DEM (Digital Elevation Model) on flood analysis with main flow channel. Kinematic wave propagation is simulated through real and imaginary river channel data sets having various resolutions. This study reveals that (1) Low resolution of DEM shortens delayed time of peak discharge, because small horizontal curves of river channel are omitted and channel elements become shorter; (2) Vertical curves in channel profile have also significant influence to discharge. An accuracy of discharge analysis greatly depends on the correlation between spatial resolution and wavelength of topographic vertical curve; and (3) Sufficient resolution is about 1/50 of the wavelength.