Yasumasa Ogawa

Heavy metals contamination in water and sediments of an urban river in a developing country

Water and sediment samples were collected from 20 location of the Buriganga river of Bangladesh during Summer and Winter 2009 to determine the spatial distribution, seasonal and temporal variation of different heavy metal contents. Sequential extraction procedure was employed in sediment samples for the geochemical partitioning of the metals. Total trace metal content in water and sediment samples were analyzed and compared with different standard and reference values. Concentration of total chromium, lead, cadmium, zinc, copper, nickel, cobalt and arsenic in water samples were greatly exceeded the toxicity reference values in both season. Concentration of chromium, lead, copper and nickel in sediment samples were mostly higher than that of severe effect level values, at which the sediment is considered heavily polluted. On average 72 % chromium, 92 % lead, 88 % zinc, 73 % copper, 63 % nickel and 68 % of total cobalt were associated with the first three labile sequential extraction phases, which portion is readily bioavailable and might be associated with frequent negative biological effects. Enrichment factor values demonstrated that the lead, cadmium, zinc, chromium and copper in most of the sediment samples were enriched sever to very severely. The pollution load index value for the total area was as high as 21.1 in Summer and 24.6 in Winter season; while values above one indicates progressive deterioration of the sites and estuarine quality. The extent of heavy metals pollution in the Buriganga river system implies that the condition is much frightening and may severely affect the aquatic ecology of the river.

Seasonal and spatial distribution of trace elements in the water and sediments of the Tsurumi River in Japan

The Tsurumi, a class-one Japanese river, has a significant metal loading originating from urban environment. Water and sediment samples were collected from 20 sites in winter and summer, 2009 and were analyzed to determine and compare the extent of different trace element enrichment. A widely used five-step sequential extraction procedure was also employed for the fractionation of the trace elements. Concentrations of zinc, copper, lead, chromium, and cadmium were three to four times higher than that of reference values and downstream sediments are much more polluted than the upstream sites. Geochemical partitioning results suggest that the potential trace metal mobility in aquatic environment was in the order of: cadmium > zinc > lead > copper > cobalt > chromium > molybdenum > nickel. About 80.2% zinc, 77.9% molybdenum, 75.3% cobalt, 63.7% lead, 60.9% copper, 55.1% chromium, and 39.8% nickel in the sediment were contributed anthropogenically. According to intensity of pollution, Tsurumi river sediments are moderately to heavily contaminated by zinc, lead, and cobalt. Enrichment factor values demonstrated that zinc, lead, and molybdenum have minor enrichment in both the season. The pollution load index (PLI) has been used to access the pollution load of different sampling sites. The area load index and average PLI values of the river were 7.77 and 4.93 in winter and 7.72 and 4.89 in summer, respectively. If the magnitude of pollution with trace metal in the river system increases continuously, it may have a severe impact on the river’s aquatic ecology.

Novel stereocontrolled glycosidations of olivoses using montmorillonite K-10 as an environmentally benign catalyst

Novel stereocontrolled glycosidations of 3,4-di-O-protected olivoses and alcohols using a heterogeneous and environmentally benign solid acid, montmorillonite K-10, have been developed. The glycosidations of the 3-O-Ac-4-O-TBS-olivose (4) and various alcohols using montmorillonite K-10 in CH2Cl2 at 25 °C exclusively gave the corresponding α-olivosides in high yields. On the other hand, the corresponding β-olivosides were predominately obtained by the glycosidations of the 3-O-TBS-4-O-Ac-olivose (5) and various alcohols under similar conditions.

Rapid simultaneous multi-element determination of soils and environmental samples with polarizing energy dispersive X-ray fluorescence (EDXRF) spectrometry using pressed powder pellets.

Abstract A rapid simultaneous multi-element analysis method for soils and environmental samples has been established using polarizing energy dispersive X-ray fluorescence (EDXRF) spectrometry. The pressed powder pellet technique was adopted because it is simple and requires no specialized skills for sample preparation. The analytes examined were: Na2O, MgO, Al2O3, SiO2, P2O5, K2O, CaO, TiO2, MnO, Fe2O3, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Pb and Th. Twenty-six reference samples were used for the calibrations. Compton scatter radiation was used as an internal standard to compensate for variations in the sample matrix, particle size, packing density and operating characteristics of the instrument. The correlation coefficients of the linear regression lines were >0.98, with the exception of Na2O, MgO, Al2O3, SiO2, P2O5, Co, Pr and Nd. The values obtained using the proposed EDXRF spectrometry were compared with the values obtained using other methods. Out of the 31 analytes examined, the results for 12 compounds (CaO, K2O, TiO2, MnO, Fe2O3, Ni, Zn, Rb, Sr, Cs, Ba and Ce) obtained by the proposed EDXRF spectrometry compared favorably with those determined through conventional wet chemical methods. In contrast, the results for eight compounds (Na2O, MgO, Cr, Co, Zr, Sn, Sb and Pr) obtained by the proposed EDXRF spectrometry exhibited poor agreements with those obtained using chemical methods. Among these analytes, the poor agreements of Cr, Zr and Sn were attributable to incomplete dissolution and/or volatilization losses during the chemical treatments based on an acid attack. It can be concluded, therefore, that there is a high possibility of underestimating the concentrations of these elements if wet chemical methods are used. Although the results of the other 11 analytes were not as good as those of the first group, they still appeared to be of practical use, considering the time consuming and potentially hazardous wet chemical pretreatment.

Machine-learning techniques for geochemical discrimination of 2011 Tohoku tsunami deposits

Geochemical discrimination has recently been recognised as a potentially useful proxy for identifying tsunami deposits in addition to classical proxies such as sedimentological and micropalaeontological evidence. However, difficulties remain because it is unclear which elements best discriminate between tsunami and non-tsunami deposits. Herein, we propose a mathematical methodology for the geochemical discrimination of tsunami deposits using machine-learning techniques. The proposed method can determine the appropriate combinations of elements and the precise discrimination plane that best discerns tsunami deposits from non-tsunami deposits in high-dimensional compositional space through the use of data sets of bulk composition that have been categorised as tsunami or non-tsunami sediments. We applied this method to the 2011 Tohoku tsunami and to background marine sedimentary rocks. After an exhaustive search of all 262,144 (= 218) combinations of the 18 analysed elements, we observed several tens of combinations with discrimination rates higher than 99.0%. The analytical results show that elements such as Ca and several heavy-metal elements are important for discriminating tsunami deposits from marine sedimentary rocks. These elements are considered to reflect the formation mechanism and origin of the tsunami deposits. The proposed methodology has the potential to aid in the identification of past tsunamis by using other tsunami proxies.

The Global Climate Change over the Cenozoic Considered from the Carbon Cycle

The global carbon cycle controls the climate change in the Earths environment on a geological timescale and is mainly associated with greenhouse effects produced by atmospheric carbon dioxide (CO2) and methane (CH4). This paper reviews the relationship between the global carbon cycle and presumed climate events during the Cenozoic. The global carbon cycle is primarily regulated by the balance between weathering and metamorphism-volcanism. Moreover, the organic carbon subcycle involving oxidative weathering and burial is of secondary importance. The balance of these geochemical processes results in variations of atmospheric CO2. The past climate on a geological time scale is reconstructed by several geochemical and paleontological methods or proxies. For example, sea-surface and deep-water temperature are deduced from oxygen isotope ratio and Mg/Ca ratio of foraminiferal tests. Terrestrial atmospheric temperature is estimated from leaf fossil and paleovegetation. Atmospheric CO2 level is calculated from carbon isotope ratios of phytoplankton and soil carbonate, stomatal density of leaf fossil, boron isotope ratio of foraminiferal test, Ce anomaly, and global carbon cycle modeling. It is important to consider their advantages and disadvantages in order to evaluate the paleoclimate adequately. Next, we discuss climate change based on these proxies. As a general trend, the Cenozoic climate change is characterized by a transition from ice-free to ice-covered conditions across the Eocene/Oligocene boundary. The Earths surface environment was significantly warmed from the Paleocene to the Eocene by high levels of atmospheric CO2. Thereafter, it gradually cooled towards the present, which is possibly attributed to changes in ocean currents and other marine environments accompanying continental drift. This trend has been punctuated by several short-term climate events. The Paleocene-Eocene Thermal Maximum (PETM) was a remarkable warming event at the Paleocene/Eocene boundary, possibly attributed to the release of methane from hydrates into the atmosphere. Rapid cooling occurred at the Eocene/Oligocene boundary to form extensive continental ice sheets including the Antarctica, which seems to have been caused by atmospheric CO2 and change of oceanographic circulation and marine environment. After a moderate period from the late Oligocene to the early Miocene, there was a transient but significant warming in the middle Miocene. Since then, the Earths environment has gradually cooled towards the present accompanied by the evolution of glaciations and marine environmental changes but a causal link between cooling and global carbon cycle has recently been pointed out. Although the carbon cycle including atmospheric CO2 and CH4 cannot explain all of the global climate changes in Cenozoic, it has undoubtedly played a dominant role on the Earths climate.

Factors Controlling the Fractionation and Seasonal Mobility Variations of Ga and In in Systems Impacted by Acidic Thermal Waters: Effects of Thermodynamics and Bacterial Activity

This work assessed both the fractionation and the seasonal mobility variations of Ga and In in systems impacted by acidic thermal waters. This was accomplished by performing thermodynamic calculations using the PHREEQC algorithm and by assessing the activity of acidophilic iron-oxidizing bacteria. The pH of the Kusatsu thermal waters in Gunma Prefecture, central Japan, is rapidly increased following the addition of a lime suspension. After an abrupt pH increase, under which conditions free ions of Ga and In and their complexes with Cl− and SO42− exist only in negligible quantities, the majority of dissolved Ga and In is removed by sorption onto suspended hydrous ferric oxides (HFOs). These HFOs are then transported to an artificial lake without significant sedimentation along the river. Subsequently, the suspended HFOs settle out and are added to sediments without significant fractionation between Ga and In. The Tamagawa thermal waters in Akita Prefecture, northeast Japan, are also treated with lime. However, complete neutralization requires mixing with some tributary streams, leading to a gradual downstream increase in pH. Dissolved Ga is, in general, sorbed by HFOs in upstream areas, leading to wide dispersal of Ga across the entire watershed. In comparison, In is transported to the lake inlet predominantly as a Cl− complex species without significant removal along the river, with the majority being precipitated in an artificial lake, where Cl− concentrations are too low to form stable complex species with In, and thus, dissolved In is sorbed by HFOs. As a result, In is effectively concentrated within downstream lakebed sediments, whereas Ga is dispersed along the river. Seasonal variations in Ga mobility within the Tamagawa field between snowmelt and low-flow seasons are primarily controlled by pH, because hydrolysis reactions of these metals, which are related to sorption reactions, tend to occur in the upstream regions in the snowmelt season. However, under warmer conditions, HFO formation preferably occurs due to the activity of acidophilic iron-oxidizing bacteria. Thus, under similar pH variations, dissolved Ga is more effectively removed by HFOs during warmer seasons. On the contrary, because HFOs are abundantly formed in low-flow season, even under colder conditions, before In hydrolysis reaction starts to occur, In mobility is less affected by water temperature and then bacterial activity.

The Influences Of Grain Sizes And Chemical Weathering Level On Extractability Of Elements From Sedimentary Rock

The extractability of elements (Cu, Rb, Sr, La and Pb) from sedimentary rock (black slate) was investigated for establishing reliable extraction method. At first, the influence of the grain sizes on the extractability was examined by using non‐weathered sample. Cu, Sr, La and Pb were abundantly extracted from roughly crushed black slate, whereas Rb extraction from powdered one was more effective. Especially, the dissolutions of heavy metals from well‐ground slate were drastically lowered maybe due to re‐adsorption artifacts. The extraction experiments using the black slate with different weathering levels were also performed for the purpose of investigations of chemical weathering on the dissolution behavior of above elements. The extracted solutions were successively filtered through 0.45 μm, 0.20 μm and 100 kDa. The almost of all elements were extracted from non‐weathered as truly dissolved species. On the other hand, the elements extracted from weathered slates were almost completely removed by the ult...

REE Behavior During Anhydrite and Gypsum Formations of the Kuroko Type Massive Sulfide‐Sulfate Deposits

The Sr and rare earth elements (REEs) concentrations and Sr isotopic composition (87Sr/86Sr) of anhydrite and gypsum have been determined for samples from the Matsumine, Shakanai and Hanaoka Kuroko‐type massive sulfide‐sulfate deposits in the Hokuroku District in Akita Pref. in northern Japan. The anhydrite samples exhibit two styles of chondrite‐normalized REE patterns; one with a decrease from light to heavy REEs (Type I), and another with a light REE‐depleted pattern with peak in Sm (Type II). The Sr content of Type I anhydrite is higher than that of Type II. The 87Sr/86Sr ratios of all anhydrite samples are intermediate between that of middle Miocene seawater and that of country rocks. 87Sr/86Sr of Type I anhydrite is closer to Miocene seawater, and that of Type II is closer to the country rocks. Based on the Sr data obtained by this study and previous reports on geochemical data on the Kuroko mineralization, geochemical environment of anhydrite formation was investigated. However, from that investiga...