Yoshishige Kawabe

Distribution of dissolved and particulate radiocesium concentrations along rivers and the relations between radiocesium concentration and deposition after the nuclear power plant accident in Fukushima

This study involved measurement of concentrations of dissolved and particulate radiocesium ((134)Cs and (137)Cs) in river water, and determination of the quantitative relations between the amount of deposited (137)Cs and (137)Cs concentrations in river waters after the Fukushima Daiichi nuclear power plant accident. First, the current concentrations of dissolved and particulate (134)Cs·(137)Cs were determined in a river watershed from 20 sampling locations in four contaminated rivers (Abukuma, Kuchibuto, Shakado, and Ota). Distribution characteristics of different (137)Cs forms varied with rivers. Moreover, a higher dissolved (137)Cs concentration was observed at the sampling location where the (137)Cs deposition occurred much more heavily. In contrast, particulate (137)Cs concentration along the river was quite irregular, because fluctuations in suspended solids concentrations occur easily from disturbance and heavy precipitation. A similar tendency with dissolved (137)Cs distribution was observed for the (137)Cs concentration per unit weight of suspended solids. Regression analysis between deposited (137)Cs and dissolved/particulate (137)Cs concentrations was performed for the four rivers. The results showed a strong correlation between deposited (137)Cs and dissolved (137)Cs, and a relatively weak correlation between deposited (137)Cs and particulate (137)Cs concentration for each river. However, if the particulate (137)Cs concentration was converted to (137)Cs concentration per unit weight of suspended solid, the values showed a strong correlation with deposited (137)Cs.

Rapid measurement of radiocesium in water using a Prussian blue impregnated nonwoven fabric

We developed a rapid method for concentrating and measuring radiocesium (134Cs and 137Cs) dissolved in fresh water using nonwoven fabric impregnated with Prussian blue (PB) as a radiocesium absorber in combination with gamma-ray spectrometry using a germanium (Ge) detector. Utilizing this method, dissolved radiocesium in a 20–100 L freshwater sample could be concentrated within a period of 20–60 min by passing the sample through 10–12 columns, connected in series, that had been fitted with nonwoven fabric disks impregnated with PB. Laboratory tests using water samples containing known amounts of radiocesium confirmed that the overall recovery rate of the isotope was 100%–108%, and that the first six columns recovered 84%–97% of the isotope. The detection limit of this method was determined to be 0.002 Bq/L with a sample of 100 L and measurement time of 43,200 s. In comparison with traditional methods using ion-exchange resin, co-precipitation with ammonium phosphomolybdate, etc., our method has the advantages of reduced cost and a significantly shorter concentration time. Since water samples can be treated in short periods of time, it is now possible to conduct radiocesium pre-concentration in situ, thus eliminating the need to transport large-volume water samples to laboratories.

Comparative study of microbial dechlorination of chlorinated ethenes in an aquifer and a clayey aquitard.

In order to determine whether natural attenuation of chlorinated ethenes by microbial activity occurs in aquitards, sediments at a site contaminated with tetrachloroethene were vertically studied by drilling. The distribution of microbes (Dehalococcoides group and anaerobic hydrogen producers) and the ability of the sediments to sustain microbial dechlorination were determined in an aquitard as well as in an aquifer. Close-spaced sampling revealed the existence of large populations of Dehalococcoides and H(2)-producing bacteria, especially in the organic-rich clayey aquitard rather than in the aquifer. The vinyl chloride reductase gene was also detected in the clay layer. Furthermore, incubation experiments indicated that the clay sediment could sustain transformations of tetrachloroethene at least to vinyl chloride. In contrast, no significant transformation was observed in the aquifer sand. Our results indicate that dechlorination of tetrachloroethene by bacteria can take place in an organic-rich clayey aquitard, and that organic-rich clay may also be important in the natural attenuation in an adjacent aquifer, possibly supplying a carbon source or an electron donor.

Extraction of heavy metals characteristics of the 2011 Tohoku tsunami deposits using multiple classification analysis.

Tsunami deposits accumulated on the Tohoku coastal area in Japan due to the impact of the Tohoku-oki earthquake. In the study reported in this paper, we applied principal component analysis (PCA) and cluster analysis (CA) to determine the concentrations of heavy metals in tsunami deposits that had been diluted with water or digested using 1 M HCl. The results suggest that the environmental risk is relatively low, evidenced by the following geometric mean concentrations: Pb, 16 mg kg(-1) and 0.003 ml L(-1); As, 1.8 mg kg(-1) and 0.004 ml L(-1); and Cd, 0.17 mg kg(-1) and 0.0001 ml L(-1). CA was performed after outliers were excluded using PCA. The analysis grouped the concentrations of heavy metals for leaching in water and acid. For the acid case, the first cluster contained Ni, Fe, Cd, Cu, Al, Cr, Zn, and Mn; while the second contained Pb, Sb, As, and Mo. For water, the first cluster contained Ni, Fe, Al, and Cr; and the second cluster contained Mo, Sb, As, Cu, Zn, Pb, and Mn. Statistical analysis revealed that the typical toxic elements, As, Pb, and Cd have steady correlations for acid leaching but are relatively sparse for water leaching. Pb and As from the tsunami deposits seemed to reveal a kind of redox elution mechanism using 1 M HCl.

Evaluation of Natural Degradation of Persistent Organic Chemicals in Acid Sulfate Soils Distributed in a Coastal Area

Abstract—Coastal acid sulfate soils are naturally generated sediments, mainly containing iron sulfides. This study investigated the natural distribution of acid sulfate soils at the mouth of a river, and their remediation ability of persistent organic chemicals. These soils were distributed on a small scale in southern Japan; Iriomote Island was used as the study site. Coastal acid sulfate soils were found to be restricted to the surface in the downstream portions but distribution depth increased upstream. The shallow, surficial portion of acid sulfate soils in upstream areas had already oxidized and leached sulfuric acid. The degradation ability of sampled acid sulfate soils for dieldrin was confirmed in laboratory experiments and the degradation ability was found to increase with iron sulfide content. These reactions were controlled by the chemical reactivity of iron sulfides in natural systems but independent of microbial activity.

Risk Evaluation of Toxic Chemicals in the Geo‐environment by Site‐Specific Risk Assessment Model

A risk assessment model which can be evaluated risk levels of toxic chemicals for human beings living in contaminated both onsite and offsite have been developed. The case studies of the risk assessment by using this model were carried out and the exposure rates, the distribution of exposure paths and the risk level of toxic chemicals in the geo‐environment were estimated. The main exposure pathways of trichloroethylene (TCE) at the onsite were inhalation air, groundwater intake and crops intake, which indicates that TCE easily volatilize into the air and migrate into the pore water from the soil. The exposure rate of the inhalation air at the offsite was not so high, because the concentration of TCE in the air at the offsite was decreased by the fresh air. However, the exposure rate of the groundwater intake at the offsite had a high risk when no degradation and no adsorption of TCE occurred in the groundwater environment. Considering the adsorption or the degradation of TCE, the risk level from the groundwater intake at the offsite was not so high. To raise the precision of the evaluation, it is very important to obtain these site‐specific parameters.