Norio Ogura

Distribution and sources of polycyclic aromatic hydrocarbons (PAHs) in street dust from the Tokyo Metropolitan area

Molecular distributions of polycyclic aromatic hydrocarbons (PAHs) in street dust samples collected from the Tokyo Metropolitan area were determined by capillary gas chromatography following HPLC fractionation. Three- to six-ring PAHs and sulfur-heterocyclics were detected. PAHs in the dusts were dominated by three and four unsubstituted ring systems with significant amounts of their alkyl homologues. PAHs were widely distributed in the streets, with concentrations (sigma COMB) of a few microgram/g dust. Automobile exhaust, asphalt, gasoline fuel, diesel fuel, tyre particles, automobile crankcase oils, and atmospheric fallout were also analysed. The PAH profile, especially the relative abundance of alkyl-PAHs and sulfur-containing heterocyclics, indicated that PAHs in the street dusts from roads carrying heavy traffic are mainly derived from automobile exhausts; dusts from residential areas have a more significant contribution from atmospheric fallout.

Rapid removal of linear alkylbenzenesulfonates (LAS) by attached biofilm in an urban shallow stream

Field observations of linear alkylbenzenesulfonates (LAS) were conducted in the Nogawa river, a polluted shallow stream located in Tokyo, from 1987 to 1990. LAS concentrations decreased from ∼1 mg l−1 in the upper stream receiving untreated domestic wastewater to less than 0.05 mg l−1 at 6 km downstream. Within the upper portion of a 1.8 km concrete open channel (travelling time of water: 1–3 h), more than 80% of LAS were removed. The half-lives for LAS of ∼1 h were considerably shorter than those obtained from biodegradation experiments using only the river water (several tens of hours). Biodegradation experiments using biofilm collected from the stream bed indicated that LAS are much more rapidly degraded under the existence of biofilm. Measurement of LAS in the biofilm indicated negligible LAS accumulation in the stream bed. The field observations and laboratory experiments indicated that biodegradation by the stream bed biofilm is the predominant removal mechanism of LAS in the urban shallow stream.

Nitrogen stable isotope ratio of groundwater N2O

δ15N of N2O and NO3− were measured to determine the mechanisms producing N2O in nitrate contaminated groundwaters. These groundwaters contained N2O at concentrations between thirty to one hundred times higher than the atmospheric equilibrium. The N2O/NO3− molar ratios in groundwaters were from 0.2 × 10−3 to 4.4 × 10−3. The δ15N values of N2O, −5.8 to −21.3 permil, were much lower than those of coexistent NO3−, +3.6 to +7.3 permil. In the light of evidence that 15N in N2O from nitrification is highly depleted, the present findings suggest nitrification as a dominant mechanism for the production of N2O in the groundwaters. However, unlike other aquatic systems where nitrification is a major route of N2O production, no clear correlation was observed between ΔN2O and −ΔO2 in the groundwater. This poor correlation strongly suggests that N2O in the groundwater was predominantly produced in the soil column and/or unsaturated zone. Based on two-year observation of N2O flux from a spring, a possible charging rate of N2O to the aquifer was estimated as 1.2–2.3 mg N2O-N·m−2·y−1. The rate is much smaller than the reported soil emission rates, suggesting the groundwater N2O to be an insignificant source for atmospheric N2O. Large discrepancies in δ15N of N2O between the groundwaters and the surface airs support this view.

High molecular weight organic matter in seawater

Abstract The presence and nature of high molecular weight organic matter in seawater was critically reviewed and its biogeochemical cycle was discussed. Organic matter that passes through a filter of 0.5–1 μm pore size is called dissolved and that which does not pass through such a filter is defined as particulate. The size of colloidal particles ranges from 0.001 to 1 μm, and therefore, they are included in the dissolved fraction having high molecular weight. High molecular weight organic matter greater than 100,000 molecular weight was found in the seawater of Tokyo Bay. The values ranged from 0.1 to 1.5 mgC/l, and accounted for 8–45% of the total dissolved organic matter. Decomposition experiments on dissolved organic matter showed that macromolecular organic matter is refractory to bacterial attack. However, macromolecular organic materials tend to aggregate or adsorb on small particles to a sufficient size for precipitation. Organic aggregates thus formed sink to the bottom of the sea and bioelements included in them are removed from water column. High molecular weight organic materials are, therefore, considered to play an important role in transportation and distribution of matter in seawater. In order to elucidate the chemical and biological properties of macromolecular organic matter, concentration and isolation of this material are important, using methods such as adsorption on organic adsorbents or ultrafiltration.

Accumulation of nitrous oxide in aerobic groundwaters

Abstract N 2 O concentrations in the groundwaters collected in the Kanto District and Nagano Prefecture in Japan and five counties in New York State were determined. These N 2 O data were obtained from the water samples from wells, springs and seepages from soils in forests and cropping fields. The N 2 O concentrations in all samples greatly exceeded those of atmospheric equilibration. The average concentration of 690 nM N 2 O is one order of magnitude larger than that in deep ocean. All groundwaters of the present study were aerobic with a high level of NO 3 − , but with the absence of NO 2 − and NH 4 + , and with a very low level of dissolved organic carbon. These characteristics suggest that the nitrate respiration in the aquifers is of little significance for the production of N 2 O. ΔN 2 O/NO 3 − molar ratios in the groundwaters were between 10 −4 and 10 −2 (Δ indicates the excess gas over that which would be in equilibrium). This supports the above view since the observed N 2 O yield agrees with that reported for the production during an ammonia oxidation. If nitrification was indeed a major mechanism for the production of groundwater N 2 O, subsequent release of N 2 O from the aquifers that are polluted with nitrogen may deserve more close attention as a potential source of atmospheric N 2 O via diffusion and discharge.

Distribution of rare earth elements in seaweed: implication of two different sources of rare earth elements and silicon in seaweed

Rare earth elements (REEs) and Si in five species of seaweed, ambient surface seawaters, and suspended solid particles in the seawaters were determined separately. Inductively coupled plasma mass spectrometry (ICP‐MS) was used for REEs and inductively coupled plasma emission spectrometry (ICP‐ES) was used for Si in order to evaluate REEs as a tracer in seaweeds and to understand the source of inorganic elements, especially Si, in seaweeds. Two different REE patterns, one similar to that of the seawater solution and another resembling that of suspended particles, were observed in seaweeds, and the variation of REE patterns seems to show a clear dependence on the abundance of Si. The REE pattern and Si concentration seem to vary depending on the division: green and red algae showed REE patterns similar to that of suspended particles, but brown algae showed patterns closer to that of seawater solutions and relatively lower Si concentration. The possibility of contamination from silicate particles on the surface of seaweeds was ruled out for several reasons. Silicate particles, not dissolved silicate, have been identified as the direct source of REEs and Si in plants ( Fu et al. 1998 ), and seaweeds are no exception. We have to consider that seaweeds can take up Si from suspended particles through their blade or branches. From the appearance of tetrad‐effect‐like variation of REEs, Si is assumed to enter a dissolved state just before the particles are taken up. From the results of a sonication experiment, REEs, once taken up as silicate particles, seem to be separated from Si in the thallus.

Removal of linear alkylbenzenesulfonates (LAS) in the Tamagawa Estuary

Abstract To examine the processes for removal of organic micropollutants in an estuary, the anionic surfactants linear alkylbenzenesulfonates (LAS) were measured in the Tamagawa Estuary (Japan). Six surveys were conducted along axial transects from zero salinity to the river-mouth. The distributions of LAS in dissolved and suspended phases in the estuarine water were determined by high-performance liquid chromatography (HPLC). Mixing diagrams demonstrated that LAS are removed from the estuarine water throughout the salinity range (0.1–29ℵ.). In summer, LAS were completely removed, but in winter, 80% of LAS input from freshwater was removed in the estuary and the remaining 20% was discharged to Tokyo Bay. It is estimated that a few hundred kilograms of LAS per day are removed in the estuary. The isomeric compositions of LAS suggest that LAS were biodegraded in the estuary. LAS concentrations in the estuarine sediments also show a seaward decrease. Laboratory incubation experiments and mixing experiments as well as the above surveys indicate that LAS removal in the estuary is mainly caused by microbial degradation.

The Concentrations and Sources of Fluoride in Atmospheric Depositions in Beijing, China

This study was carried out from June 1995 to December 1998 to explore the current status of fluoride pollution, fluoride deposition, and sources of fluoride in Beijing. The mean fluorideconcentration of ambient aerosols in Beijing was 0.61 μg m-3, with a range of 0.08 to 1.61 μg m-3. The highest concentration (1.61 μg m-3) occurred in winterand was 20 times higher than in summer. This maximum concentration is to compare with annual volume-weighted averagefluoride concentration in Chongqing, Sichuan Province, an areaseriously polluted with fluoride. Fluoride pollution occurred inwinter in Beijing, because of the increased consumption of coal for heating, which resulted also in the highest dry deposition during winter and lowest in summer. The seasonal variations intotal fluoride were different from those of dry deposition. Thehighest total deposition was observed in summer, when 75% of theannual precipitation falls. Soil dust and coal combustion wereconsidered the main sources of fluoride in Beijing.

Chemical composition of precipitation in a forest area of Chongqing, Southwest China

Experiments were carried.out in Chongging-a city seriously damaged by acid precipitation in southwest China — to explore chemical compositions of open bulk precipitation, throughfall and stemflow in a Masson pine (Pinus massoniana) forest. The results showed that annual mean pH values of and annual ion depositions in the three types of rain water were 4.47 and 50.6 g m−2, 3.82 and 69.7 g m−2, and 2.92 and 0.215 g m−2 respectively. pH values demonstrated an obvious seasonal variation; they were lower in winter than in the rest of the year. Ca2+ and NHinf4sup+together made up more than 80% of the total cation, while SOin4sup2−alone contributed over 90% to the total anion. This high level of SOin4sup2−in rain water in Chongqing, which outran those found in other cities in China, was closely related to the combustion of locally produced coal that contains 3 to 5% sulphur. Thus, acid precipitation in Chongqing is of a typical sulphuric-acid type.

Determination of 2-(4-Morpholinyl)benzothiazole in Environmental Samples by a Gas Chromatograph Equipped with a Flame Photometric Detector.

2-(4-Morpholinyl)benzothiazole (24MoBT) exists in automobile tire rubber as an impurity of a vulcanization accelerator and has been proposed as a potential molecular marker of street runoff (Spies, R. B.; Andresen, B. D.; Rice, D. W., Jr. Nature 1987, 327, 697-699). The present paper describes an analytical method for 24MoBT in environmental samples (e.g., street dusts and river sediments) by gas chromatography. The method relies upon extraction with a 6:4 (v/v) mixture of benzene and methanol, purification by acid extraction, and adsorption column chromatography, followed by determination using capillary GC equipped with a sulfur-selective detector (i.e., FPD). The recovery of 24MoBT for the entire procedure was 85%, and the relative standard deviation for four replicated analyses was 1.5%. The detection limit was 0.08 ng injected 24MoBT, corresponding to 0.20 ng/g of dry sample. The selectivity and sensitivity of the present method permit the determination of 24MoBT at the trace levels (e.g., ∼ng/g) encountered in environmental samples. 24MoBT concentrations in various environmental samples are also reported.