Keiichi Ohta

Natural denitrification in the Kakamigahara groundwater basin, Gifu prefecture, central Japan

Although nitrate is recognized as the most common groundwater contaminant due to growing anthropogenic sources, such as agriculture in particular, its adverse effects on human and animal health are debatable. The current issue, however, is to control and reduce nitrate contamination with regards to the long residence time of groundwater within aquifers. Denitrification has recently been recognized for its ability to reduce high nitrate concentrations in groundwater. The Kakamigahara groundwater basin, Gifu prefecture, Japan, witnessed rising levels of nitrate (>12 mg/l NO(3)-N) originating from agricultural sources. Chemical analyses for the determination of major constituents of groundwater and delta(15)N of residual nitrate were performed on representative groundwater samples in order to fulfill two main objectives. One is to investigate the current situation of nitrate groundwater pollution. The second objective is to determine whether the denitrification is a potential natural mechanism, which eliminates nitrate pollution in the Kakamigahara aquifer. Agricultural nitrate contamination of groundwater was obvious from characteristically high concentrations of Ca(2+), Mg(2+), NO(3)(-) and SO(4)(2-). High nitrate concentrations were found on the eastern side of the basin in association with vegetable cultivation fields, and decreased gradually towards the west of the basin along the direction of groundwater flow. The decrease of nitrate concentration was conveniently coupled with increase of HCO(3)(-) (the heterotrophic denitrification product), pH and delta(15)N of residual nitrate (due to isotopic fractionation) from east to west. Therefore, denitrification in situ is continuously removing nitrate from the Kakamigahara groundwater system.

Trends and factors governing polycyclic aromatic hydrocarbon levels in Tokyo Bay sediments

Abstract Polycyclic aromatic hydrocarbons (PAHs) in a dated sediment core from Tokyo Bay were determined by gas chromatography and GC/MS. These PAHs increase in concentration from the 1950s to the beginning of the 1970s and decrease after then. These changes, especially the decreasing trend, are discussed with respect to changes in the atmospheric paniculate concentration and fossil fuel consumption in Tokyo and districts. The results suggest that the increase in PAH concentrations was due to the increase in the fossil fuel consumption, and the decreasing trend was caused by the following factors: 1. 1) less fuel oil consumption; 2. 2) legal curbs on industrial and vehicular emissions of particulates and hydrocarbons; and 3. 3) other factors such as a gradual decrease in consumption of heavy oil and a temporary drop in the use of asphalt.

Isolation and characterization of low molecular weight carbohydrates dissolved in seawater

Chemical characterization and quantitative determination of dissolved low molecular weight carbohydrates in Mikawa Bay near Nagoya, Japan were conducted. The water samples were collected during the period of algal bloom of the dinoflagellate Prorocentrum minimum on 31 May 1980. Low molecular weight carbohydrates in seawater samples from depths of 1 and 6 m were first retained on a charcoal column and then eluted with aqueous ethanol. The carbohydrates obtained were permethylated and then isolated into each of the components by thin layer chromatography. The sugars isolated were characterized by gas chromatography (GC), combined gas chromatography and mass spectrometry (GC-MS), proton nuclear magnetic resonance spectroscopy (1H-NMR) and some chemical analyses. Laminaribiose, laminaritriose, sucrose, raffinose, 2-O-α-d-glucopyranosylglycerol, 1-O-β-d-galactopyranosylglycerol6-O-α-d-galactopyranosyl-1-O-β-d-galactopyranosylglycerol were fully characterized and quantified with ranges from 2.3 to 27.7 μg l−1 and from 0.5 to 17.8 μg l−1. These low molecular weight carbohydrates were also identified, with some difference in their relative abundance, in particulate matter consisting mainly of dinoflagellate cells collected on the same occasion from this bay. These results indicate that low molecular weight carbohydrates dissolved in seawater are directly derived from those of phytoplankton through extracellular release or cell lysis.

Sources of sulfate in winter aerosols over the Sea of Japan, as inferred from selenium composition

Abstract Aerosol samples were collected in winter at the Mikuni and Mihonoseki sites facing the Sea of Japan and analyzed for non-sea-salt sulfate (nss-SO42−), Se(IV) and Se(VI). Episodes of a high nss-SO42− concentration were observed 5 times during the observation period of 14 days. Based on the weather conditions as well as the Se/Snss-SO42− and Se(VI)/Se(IV) ratios, these episodes could be classified into three types, i.e., continental-coal, local-coal and local-petroleum types. The continental-coal type was characterized by the high Se/Snss-SO42− (5.0–7.6×10−4) and high Se(VI)/Se(IV) ratios (6.9–8.9). It was produced by a long-range transport of aerosols originating from coal-combustion sources in the Asian Continent. The local-coal type was due to aerosols from local coal-combustion sources around the observation sites together with high Se/Snss-SO42− (3.9×10−4) and low Se(VI)/Se(IV) ratios (0.2). The local-petroleum type was accompanied by low Se/Snss-SO42− (2.4×10−4) and low Se(VI)/Se(IV) ratios (3.3) and it was caused by aerosols from local petroleum-combustion sources. The boundary of the Se(VI)/Se(IV) ratio between continental and local types would be around 2.

Concentrations and source variations of n-alkanes in a 21 m ice core and snow samples at Belukha glacier, Russian Altai mountains

Abstract Ice-core and snow samples collected on Belukha glacier, Russian Altai mountains, were analyzed for n-alkanes by gas chromatography. On the basis of the total concentrations (T-HCs), carbon preference index (CPI) values and the plant wax contributions (WaxC n ), it is suggested that mountain glaciers on the Asian continent received higher loading of n-alkanes from natural and anthropogenic sources than the Greenland ice sheet. It appears that the loading and variation of n-alkanes on glaciers in the Altai are approximately the same as those of the mountain in general, because the concentrations, CPI values and WaxC n percentages of n-alkanes in Sofiyskiy glacier, also in the Russian Altai, are at the same levels as or slightly greater than those in ice-core and snow samples from Belukha glacier. It seems that the n-alkanes on Belukha glacier are derived mainly from higher plant wax and petroleum exhaust other than from diesel engines. Vertical profiles of T-HCs and CPI values of n-alkanes show that the non-WaxC n portions and T-HCs have recently increased with a decrease in CPI values on Belukha glacier. A similar trend of n-alkanes was reported for Sofiyskiy glacier, indicating that the influence of human activities has gradually increased around the Altai.

Photochemical Degradation of Dissolved Organic Carbon to Carbon Monoxide in Coastal Seawater

Carbon Monoxide concentrations in the Seto Inland Sea (Stns. 3 and 6) and Ise Bay (Sugashima) were measured by the headspace method during the 95-1 cruise of the R/V Toyoshio Maru (Hiroshima University) and at the Sugashima Marine Laboratory (Nagoya University), respectively.

Organic components in size-separated aerosols from the western North Pacific.

Marine aerosols in the western North Pacific were collected using a cascade impactor. Size-separated aerosols were analyzed for organic carbon, alkanes and polycyclic aromatic hydrocarbons (PAH). The results showed that the rate of decrease of the atmospheric concentrations of these organic components with increase in distance from Japan as well as from the coast of the Eurasian Continent was in the order PAH≫alkanes>organic carbon. The bulk of all these organic components occurred in the smallest size fraction of particles (<1Μm). Analysis of the alkanes and PAH indicated that the hydrocarbons in aerosols in Japanese coastal marine areas are primarily derived from terrestrial anthropogenic sources which also contribute to a lesser extent to aerosols in marine areas about 1,000 km off the coast of Japan. In remote marine areas the hydrocarbons on small particles (<1Μm) have principally a natural terrestrial origin while those on larger particles are marine in origin.

Binding interactions of 1-naphthol with dissolved organic matter of Lake Biwa and treated sewage wastewater: The role of microbial fulvic acid†

The binding interactions of 1-naphthol with effluent and whole natural dissolved organic matter (DOM) samples were analyzed by using a fluorescence quenching technique. Nonfractionated DOM samples from Lake Biwa (Japan), creek water, treated sewage effluents, and an extracted Lake Biwa fulvic acid (LBFA) standard were used as quenchers and compared at the same 1-naphthol with DOM organic carbon ratios found for low natural dissolved organic carbon (DOC) levels (∼4.5 mg/L). Natural and effluent DOM (eDOM) samples were characterized by the DOC level, relative hydrophobicity (RH%), ultraviolet (UV)-visible absorbance and fluorescence excitation emission spectroscopy. These parameters were compared with those of the reference LBFA standard. Concave-up Stern-Volmer plots accounted for both the partitioning and the adsorptive binding in the eDOM-polycyclic aromatic hydrocarbons (PAH) system as compared with the nonspecific partitioning in the natural DOM-PAH system. Strong linear regressions (r(2)  > 0.80) between the log K(DOC) values, the RH%, the UV absorbances, and the Fl(340-435) -UV(340) indices for the structural composition and molecular weights of the DOM samples were obtained. These results suggest that low molecular weight microbial fulvic acid (<800 Da) is dominant in the eDOM-PAH binding interactions, as well as in the distinct molecular structure of the eDOM samples, which resulted in fivefold to sixfold higher binding magnitude for 1-naphthol than for the other samples.

Vertical distribution of iron(II) and its relation to organic substances in Lake Biwa, Japan

Iron speciation in freshwater is largely regulated by pH, dissolved oxygen and characteristics of dissolved organic compounds that coexist in the water. Solubility of iron(III) is very low in neutral pH, but some organic compounds serve as chelators with iron(III) to form dissolved stable complexes. In Lake Biwa, Japan, dissolved iron concentration is very high (mean 84 nmol L -l, median 28 nmol L -l in the north basin; Mrro et al. 2004). However, when taking into account iron complexation, the labile iron concentration is very low and may serve as a co-limiting factor of primary production, as seen in the eutrophic Lake Kasumigaura, Japan (NAGAI et al. 2006). Iron(II) is a minor component in oxic circumneutral freshwater because it is immediately oxidized to iron(III) species., It has high potential bioavailability for primary production, however, because of its high solubility and low complexation compared with iron(III) that sometimes form a stable organic complex unavailable to phytoplankton (IMAI et al. 1999). According to SIVAN et al. (1998), iron(II) exists in the epilimnion ofthe oxic freshwater Lake Kinneret in the order oftens o f nmol L -• While iron(II) is oxidized by Oz, 0 2·and H20 2 in water, colored dissolved organic matter (CDOM), such as humic substances, serves as a mediator o f photoreduction o f iron(III) to iron(II) at the lake surface (EMMENEGGER et al. 200 l). We analyzed the vertical profiles of iron(II) in summer and autumn in Lake Biwa. Because the concentration of iron(II) is estimated to be low, solid phase extraction of iron(II)ferrozine complex was investigated using a modified method ofYI et al. (1992). To verify the photoreductive formation of iron(II) at the lake surface, the water of Lake Biwa was irradiated by sunlight.

Studies on the Piscicidal Components of Justicia Hayatai var. decumbens :Part I. Isolation and Piscicidal Activities of Justicidin A and B

Justicidin A, C22H18O7, mp 263°C and B, C21H16O6, mp 240°C were isolated as fish-killing components from Justicia Hayatai var. decumbens. The piscicidal activities of both compounds were demonstrated to be as strong as rotenone and about ten times stronger than that of pentachlorophenol.