No abstract

Between 1932 and 1968, industrial wastewater containing methylmercury (MeHg) and other mercury (Hg) compounds was discharged directly into Minamata Bay, Japan, seriously contaminating the fishery. Thousands of people who consumed tainted fish and shellfish developed a neurological disorder now known as Minamata disease. Concentrations of total mercury (THg) in recent fish and sediment samples from Minamata Bay remain higher than those in other Japanese coastal waters, and elevated concentrations of THg in sediments in the greater Yatsushiro Sea suggest that Hg has moved beyond the bay. We measured stable Hg isotope ratios in sediment cores from Minamata Bay and the southern Yatsushiro Sea and in archived fish from Minamata Bay dating from 1978 to 2013. Values of δ(202)Hg and Δ(199)Hg in Yatsushiro Sea surface sediments were indistinguishable from those in highly contaminated Minamata Bay sediments but distinct from and nonoverlapping with values in background (noncontaminated) sediments. We conclude that stable Hg isotope data can be used to track Minamata Bay Hg as it moves into the greater Yatsushiro Sea. In addition, our data suggest that MeHg is produced in bottom sediments and enters the food web without substantial prior photodegradation, possibly in sediment porewaters or near the sediment-water interface.

Carbon-supported Pt-Ru alloy (Pt-Ru/C) catalysts were prepared using the "polygonal barrel-sputtering method". From the preparation of a Pt-Ru alloy with Pt/Ru ) ca. 50:50 atom % on a glass plate as support, the optimum sputtering conditions were an Ar gas pressure of 0.9-0.7 Pa and room temperature. The amount of the sputtered Pt-Ru alloy was controlled by changing the ac power and the sputtering time. Subsequently, the Pt-Ru/C samples were prepared under the given optimum conditions. The Pt-Ru alloy was dispersed extensively in the form of nanoparticles on a carbon support. For the ac power levels of 130, 100, and 50 W, the size distributions were narrower when the ac power was lowered. The respective average particle sizes were 4.1 nm (130 W), 3.3 nm (100 W), and 2.2 nm (50 W). In the case of 30 W, however, the size distribution and the average particle size were almost identical to those for 50 W. In addition, when the Pt-Ru/C samples were prepared by changing the sputtering time, only the dispersion density of the alloy nanoparticles increased in the Pt and the Ru deposited without changing the particle size. The atomic ratios of Pt and Ru in individual Pt-Ru alloy nanoparticles for the prepared samples were similar to the sputtering ratio and homogeneous compared with those for the commercially available samples. With regard to the electrochemical properties for the prepared samples, the hydrodynamic voltammograms for H 2 oxidation were identical to that of the commercially available sample. However, for CO oxidation, the peak shapes and the peak potentials for the prepared samples were sharper and ca. 20 mV lower than those for the commercially available samples, due to the uniform Pt and Ru atomic ratios of the individual alloy particles for the prepared samples. The coulomb charges of the CO oxidation reaction per amount of Pt and Ru for the prepared samples increased linearly in the reversed average particle sizes, while on the other hand, the charges for the commercially available samples were not proportional to the reversed sizes. This shows that the Pt-Ru alloy for the prepared samples was more efficiently utilized for electrochemical reactions rather than were the commercial ones. In addition, the cell performances for the alloy loading of 0.08 or 0.02 mg/cm 2 using the prepared Pt-Ru/C samples were similar to those for 0.50 mg/cm 2 using the commercially available sample.

A new method for preparing SiO2-Al2O3 gels from aque ous solutions of tetraethoxysilane and aluminum chlo ride was investigated.Addition of propylene oxide to the solutions promoted gelation reaction, yielding translucent gels. It was found that the 4-coordinated Al incorporated in the framework of the gels was formed without heat treatment.Residual chloride ions were removed from the gels by heating. The gels ob tained had large surface areas and were presumed to be homogeneous.

No abstract