Return period of enhanced gamma ray dose rates: regional differences observed in Japan

We estimated the return period of an increased gamma ray dose rate (Delta gamma) derived from (222)Rn progeny deposited with precipitation. The approximate probability distribution for Delta gamma followed a Hazen plot, which is an empirical plotting equation, indicating that the distribution of Delta gamma was approximated by a nearly double-exponential. The distribution of Delta gamma was well represented by the Gumbel distribution, and the return period for Delta gamma was estimated theoretically. There was a notable regional difference in the return period between the coast of the Japan Sea and the inland or Pacific coast areas: the return period for a given Delta gamma at monitoring sites on the Sea of Japan coast was 1.5 to 2.5 times shorter than that in the inland or Pacific coast areas. This variation with locality suggests that the rate of wet-deposition of (222)Rn progeny is larger at sites on the Sea of Japan coast than inland or on the Pacific coast areas. The expected return period for the maximum Delta gamma at each site was about 10 years. This estimation of the return period of Delta gamma is a novel approach to the study of environmental science in fields such as radioactivity.     

Effect of different soil layers on porewater to remediate acidic surface environment at a close mine site

This paper describes the chemistry of porewater when constructing different soil layers on acidic weathered rock of a closed mine to remediate the surface environment. Three cases were set on a flat surface of the site, all under different layer systems. Case 1 was only composed of weathered rocks. A top neutralization layer was constructed on the weathered rocks in case 2, whereas both an upper low-permeable and middle neutralization layers were constructed on the weathered rocks in case 3. The low-permeable layer of 30?cm thick consists of clay, and the neutralization layer of 30?cm thick consists of the mixture of the weathered rock and calcium carbonate as a neutralizer. Porewater sampling systems and soil sensors to measure temperature, water content, and electrical conductivity were set at different depths. In case 1, steadily high concentrations of heavy metals were observed regardless of the depth, and the pH ranged from 2 to 4. In cases 2 and 3, a dramatic decrease in concentrations of heavy metals was observed, even below the neutralization layer. For both cases, pH values were circumneutral. There were no significant seasonable changes in heavy metals concentrations and pH of porewater by considering the temperature and precipitation. In addition, the water content of the layers in case 3 fluctuated more mildly than that in cases 1 and 2, indicating that the low-permeable layer reduced the rate of infiltration. Therefore, a significant reduction in the load of heavy metals released from the site can be achieved by both implementing neutralization and low-permeable layers.     

Two extreme types of mixing of dust with urban aerosols observed in Kosa particles: ‘After’ mixing and ‘on-the-way’ mixing

Besides well-known episodic Kosa during spring, high concentrations of Ca²⁺ in aerosols were observed early in summer as well as in the semi-continuous data of the aerosols at the summit of Mt. Fuji. We further analysed the data to study the chemical characteristics of the high calcium event during early summer. The back trajectory analyses of the event indicated that Ca was transported from arid and semi-arid regions (e.g. the Taklamakan desert) through the westerly-dominated troposphere higher than the height of the summit of Fuji. The amount of SO₄^2? was always equivalent to that of NH₄⁺ unlike the case of the normal Kosa period where SO₄^2? is in excess with respect to NH₄⁺. This shows the ‘after’ mixing of unreacted CaCO₃ of Kosa origin with (NH₄)₂SO₄, which was only realized by the downward injection of Kosa particles from higher altitudes to the air masses of different origin. In the case of normal Kosa, the air bearing Kosa particles passed through the polluted area to absorb unneutralized acids (‘on-the-way’ mixing), whereas in the case of the Kosa-like phenomena in summer, the acids from the polluted area have been neutralized by NH₄⁺ and become inactive before mixing with CaCO₃ (“after” mixing). We have simplified the chemistry of aerosols using their three major components, Ca²⁺, SO₄^2? and NH₄⁺, and introduced a new triangle diagram with the three assumed end-members of CaCO₃, CaSO₄ and (NH₄)₂SO₄ to quantify the contribution of the ‘after’ mixing to the aerosols (AMI; ‘after’ mixing index). Based on the back trajectories of some high AMI cases, CaCO₃ in Kosa particles was transported through the middle troposphere (5000–7000 m) and descended to meet another air mass where SO₄^2? had been already neutralized by NH₃.     

Determination of redox potential of sulfidic groundwater in unconsolidated sediments by long-term continuous in situ potentiometric measurements

This study was undertaken to investigate the redox potential (Eh) of sulfidic groundwater in unconsolidated sediments. The Eh was determined by long-term (several days to several weeks) continuous in situ potentiometric measurements using a platinum (Pt) electrode. The Eh values measured in two monitoring campaigns were ?259 and ?202 mV, respectively. Chemical analysis of groundwater showed that the redox species in the groundwater were sulfide (S^2???) and iron, respectively. The saturation indices calculated from the chemical analysis results indicated that FeS_(am) and mainly mackinawite were close to equilibrium in the analyzed waters. Comparison of the measured Eh values with those calculated using different redox couples revealed that the Eh values measured in the first monitoring campaign were nearly equal to those calculated using HS^???/SO $_{4}{^{2-}}$ , S^2???/SO $_{4}{^{2-}}$ , FeS $_{(\text{am})}$ /SO $_{4}{^{2-}}$ , and mackinawite/SO $_{4}{^{2-}}$ redox couples; on the other hand, the Eh values measured in the second monitoring campaign were almost consistent with those measured using the FeS₂/SO $_{4}{^{2-}}$ redox couple. The good fit between the measured Eh values and the theoretical calculated Eh values suggests that the sulfur system is related to the Eh value of sulfidic groundwater in unconsolidated sediments.     

快速木质纤维素分解菌复合系MC1对秸秆的分解能力及稳定性

以天然水稻秸秆为材料研究了快速降解木质纤维素的细菌复合系MC1对木质纤维素的分解能力;并在不同条件保藏、高温处理以及利用变性梯度胶电泳(DGGE)技术研究了复合系的稳定性.结果表明,复合系MC1在50℃液体静止培养条件下8～10d,把培养液2%干重的水稻秸秆完全分解溶化;经过9d的培养,水稻秸秆的总干重减少81%,其中纤维素减少99%,半纤维素减少74%,木质素减少51%.连续继代培养4a、常温干燥保存4a、-20℃冷冻藏4a、培养液直接在室温和4℃保存1a、90℃处理30min仍具旺盛的分解能力并稳定传代.平板培养基培养证明MC1全部由细菌组成,16SrDNA变性梯度胶电泳(DGGE)检测结果,在6个月内主要条带几乎没有变化,说明MC1的菌种组成相当稳定.MC1对纤维素的分解利用具重要前景.     

Temporal variation of Cs and Pu in the sea of Japan

Concentrations of the anthropogenic ¹³⁷Cs and ^239,240Pu in surface water of the Sea of Japan were in the ranges of 2·7–3·8 mBq l^-1 and 1·3–8·0 μBq l^-1, respectively, in 1993–1994, which are in the same order of magnitude as those in the North Pacific. The time-series data indicated a marked increase of surface ¹³⁷Cs in 1986 and 1987 after the major radioactive dumping and the Chernobyl fallout in 1986 and then rapidly decreased thereafter. The apparent half-residence time of ¹³⁷Cs in the surface water was estimated to be about 3 years for excess ¹³⁷Cs and 16 years for a rather long time-scale transport, respectively. For ^239,240Pu in the surface water, no systematic temporal variation was observed over the past two decades, which may reflect rapid recycling of deeper Pu. The results revealed that most of the recent radioactivity in water columns of the Sea of Japan was of global fallout origin from atmospheric nuclear testing and partly the Chernobyl fallout. No clear signal about the effect of radioactivity from Russian dumping was observed.     

Long Range Transport of Asian Dust from Dust Storms and its Impact on Japan

We simulated the long range transport of dust emitted from dust storms that occurred in China by using a global three-dimensional chemical transport model. A modified dust emission flux scheme and a nonlocal diffusion scheme for determining the atmospheric eddy diffusivity in the atmospheric boundary layer were implemented to improve the chemical transport model. We examined the dust transport by comparing the model results with TOMS satellite images. The model calculated monthly total deposition of dust masses were used for comparison with the measurements collected at sampling stations in Japan, and good agreement was found. The model generally reproduced the temporal and spatial variations of dust reasonably well.     

Converting waste polystyrene into a polymer flocculant for wastewater treatment

We have succeeded in converting waste polystyrene from electrical appliances into a polymer flocculant for treating some kinds of wastewater after chemical modification. Waste polystyrene, such as polystyrene foam and additive-containing TV cabinets, was converted into a water-soluble polymer, polystyrene sulfate (PSS), and PSS of various degrees of aqueous viscosity was obtained by introducing sulfone bridges during sulfonation. We examined the relationship between the degree of flocculation of wastewater and the aqueous viscosity of the PSS, and found that PSS with medium viscosity is most suitable for flocculating inorganic wastewater from a factory, and PSS with high viscosity is most suitable for dewatering organic domestic wastewater. We report how PSS containing sulfone bridges works as a polymer flocculant for treating wastewater. Received: July 19, 2000 / Accepted: September 21, 2000     

Depositional behaviors of plutonium and thorium isotopes at Tsukuba and Mt. Haruna in Japan indicate the sources of atmospheric dust

Monthly plutonium and thorium depositions at Tsukuba (28 m asl) and Mt. Haruna (1370 m asl) were measured during 2006 and 2007 (Jan 2006-Dec 2007 at Tsukuba, Nov 2006-Dec 2007 at Mt. Haruna). The monthly ^239,240Pu depositions ranged from 0.044 to 2.67 mBq m⁻² at Tsukuba and from 0.05 to 0.9 mBq m⁻² at Mt. Haruna during the measurement periods. Monthly ^239,240Pu deposition did not differ markedly between the two sites except in April 2007. Seasonal pattern of monthly ^239,240Pu depositions at both sites showed high in spring and low in summer, and typical of seasonal variations in northeastern Asia. Thorium deposition at Tsukuba was higher than that at Mt. Haruna except in May and June 2007. ²³⁰Th/²³²Th activity ratios were used to partition deposition samples into locally and remotely derived fractions. The results revealed that a major proportion of total ^239,240Pu and Th deposits are derived from remote sources, especially in spring.     

一组高效稳定纤维素分解菌复合系MC1的筛选及功能

从4种堆肥样品中分别筛选出纤维素分解能力较强的4组混合菌,再以酸碱反应互补的原则重新优化组合并驯化成1组纤维素分解能力非常强而稳定的纤维素分解菌复合系MC1.100mL培养物在50℃静止培养72h,分别可分解0.48g滤纸、0.49g脱脂棉、0.19g麦秆和0.08g锯末.分解滤纸时,第24h CMC糖化力最高,为122.3U·mL^-在初始pH4～10的不同培养基上接种,均能把pH调到中性,最后稳定在8.0～8.5之间.在连续投放滤纸情况下纤维素分解能力稳定保持20d以上,其发酵液的pH在有滤纸时稳定在6.0～6.5之间,没有滤纸时稳定在8.0～8.5之间.