Measurement of natural radioactive nuclide concentrations in various metal ores used as industrial raw materials in Japan and estimation of dose received by workers handling them

Natural resources such as ores and rocks contain natural radioactive nuclides at various concentrations. If these resources contain high concentrations of natural radioactive nuclides, workers handling them might be exposed to significant levels of radiation. Therefore, it is important to investigate the radioactive activity in these resources. In this study, concentrations of radioactive nuclides in Th, Zr, Ti, Mo, Mn, Al, W, Zn, V, and Cr ores used as industrial raw materials in Japan were investigated. The concentrations of ²³⁸U and ²³²Th were determined by inductively coupled plasma mass spectrometry (ICP-MS), while those of ²²⁶Ra, ²²⁸Ra, and ⁴⁰K were determined by gamma-ray spectrum. We found the concentrations of ²³⁸U series, ²³²Th series, and ⁴⁰K in Ti, Mo, Mn, Al, W, Zn, V, and Cr ores to be lower than the critical values defined by regulatory requirements as described in the International Atomic Energy Agency (IAEA) Safety Guide. The doses received by workers handling these materials were estimated by using methods for dose assessment given in a report by the European Commission. In transport, indoor storage, and outdoor storage scenarios, an effective dose due to the use of Th ore was above 4.3 × 10⁻² Sv y⁻¹, which was higher than that of the other ores. The maximum value of effective doses for other ores was estimated to be about 4.5 × 10⁻⁴ Sv y⁻¹, which was lower than intervention exemption levels (1.0 × 10⁻³ Sv y⁻¹) given in International Commission of Radiological Protection (ICRP) Publication 82.     

Assays of dioxins and dioxin-like compounds in actually contaminated soils using transgenic tobacco plants carrying a recombinant mouse aryl hydrocarbon receptor-mediated β-glucuronidase reporter gene expression system

The transgenic tobacco plant XD4V-26 carrying the recombinant mouse aryl hydrocarbon receptor XD4V-mediated β-glucuronidase (GUS) reporter gene expression system was used for assay of dioxins and dioxin-like compounds consisting of polychlorodibenzo-p-dioxins, polychlorinated dibenzofurans, and coplanar polychlorinated biphenyls (Co-PCBs) in actually contaminated soils. The transgenic tobacco plant XD4V-26 showed a significant dose-dependent induced GUS activity when cultured on MS medium containing PCB126 [toxic equivalency factor (TEF) = 0.1]. In contrast, PCB169 and PCB180, which have 0.03 of TEF and unassigned TEF values, respectively, did not significantly induce GUS activity under the same conditions as with PCB126. When the tobacco plants were cultivated for up to 5 weeks on actually contaminated soils with dioxins and dioxin-like compounds collected from the periphery of an incinerator used for disposal of life and industrial wastes, GUS activity in the leaves was dose-dependently increased. The plants clearly detected 360 pg-TEQ g(-1) of dioxins and dioxin-like compounds in this assay. There was a positive correlation between GUS activity and TEQ value of dioxins and dioxin-like compounds in the plants. This assay does not require any extraction and purification processes for the actually contaminated soil samples.     

Assays of dioxins and dioxin-like compounds in actually contaminated soils using transgenic tobacco plants carrying a recombinant mouse aryl hydrocarbon receptor-mediated β-glucuronidase reporter gene expression system

The transgenic tobacco plant XD4V-26 carrying the recombinant mouse aryl hydrocarbon receptor XD4V-mediated β-glucuronidase (GUS) reporter gene expression system was used for assay of dioxins and dioxin-like compounds consisting of polychlorinated dibenzeno-p-dioxins, polychlorinated dibenzofurans, and coplanar polychlorinated biphenyls (Co-PCBs) in actually contaminated soils. The transgenic tobacco plant XD4V-26 showed a significant dose-dependent induced GUS activity when cultured on MS medium containing PCB126 [toxic equivalency factor (TEF) = 0.1]. In contrast, PCB169 and PCB180, which have 0.03 of TEF and unassigned TEF values, respectively, did not significantly induce GUS activity under the same conditions as with PCB126. When the tobacco plants were cultivated for up to 5 weeks on actually contaminated soils with dioxins and dioxin-like compounds collected from the periphery of an incinerator used for disposal of residential and industrial wastes, GUS activity in the leaves was dose-dependently increased. The plants clearly detected 360 pg-TEQ g^?1 of dioxins and dioxin-like compounds in this assay. There was a positive correlation between GUS activity and TEQ value of dioxins and dioxin-like compounds in the plants. This assay does not require any extraction and purification processes for the actually contaminated soil samples.     

Uptake and distribution of iodine in rice plants

Rice (Oryza sativa L.) plants were cultivated in an experimental field and separated at harvest into different components, including polished rice, rice bran, hull, straw, and root. The contents of iodine in these components and the soil were determined by inductively coupled plasma-mass spectrometry and radiochemical neutron activation analysis, respectively. Iodine content varied by more than three orders of magnitude among the plant components. Mean concentration of iodine in the entire plants was 20 mg kg(-1) dry weight, and the concentration of iodine in the surface soil (0-20 cm depth) was 48 mg kg(-1). The highest concentration of iodine (53 mg kg(-1) dry weight) was measured in root and the lowest concentration (0.034 mg kg(-1) dry weight) in polished rice. While the edible component (polished rice) accounted for 32% of the total dry weight, it contained only 0.055% of iodine found in the entire rice plants. Atmospheric gaseous iodine (5.9 ng m(-3)) was estimated to contribute <0.2% of the total iodine content in the biomass of rice plants; therefore nearly all of the iodine in the rice plants was a result of the uptake of iodine from the soil. The content of iodine in the aboveground part of rice plants was 16 mg kg(-1) dry weight and the percentage of iodine transferred per cropping from the soil into the aboveground biomass corresponded to 0.27% (20 mg m(-2)) of the upper soil layer content.     

Fate of radiocesium in sewage treatment process released by the nuclear accident at Fukushima

The nuclear accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) which occurred after the Great East Japan Earthquake on March 11, 2011 resulted in releases of radionuclides such as ¹³⁴Cs (half-life:T_1/2 = 2.06 yr), ¹³⁷Cs (T_1/2 = 30.04 yr) and ¹³¹I (T_1/2 = 8.05 d) to the environment. For this paper, we observed the monthly variations of radiocesium (¹³⁴Cs and ¹³⁷Cs) and stable Cs concentrations in influent, effluent, sewage sludge, and sludge ash collected from a sewage treatment plant 280 km north of the FDNPP from July to December, 2011. Using the stable Cs results, we concluded the mass balance of Cs in the sewage treatment plant showed that about 10% of the Cs entering the sewage treatment plant would be transferred to the sewage sludge, and then Cs in the sewage sludge was totally recovered in the sludge ash. The behavior of Cs was similar to that of Rb, but it was not similar to that of K in the sewage treatment process.     

Assays of dioxins and dioxin-like compounds in actually contaminated soils using transgenic tobacco plants carrying a recombinant mouse aryl hydrocarbon receptor-mediated β-glucuronidase reporter gene expression system

This article has been retracted.     

Sorption behavior of selenium on humic acid under increasing selenium concentration or increasing solid/liquid ratio

The sorption of selenium (Se) on humic acid (HA) was investigated in order to better understand the fate of stable and radioactive Se in soils and sediments. An ultrafiltration technique was used to determine size distributions of HA-sorbed-Se when increasing Se concentration and solid/liquid ratio. The results showed that the Se sorption onto HA followed the Freundlich isotherm. No solid/liquid ratio-dependence was observed especially when <3 kDa molecular size fraction was used from solid/liquid separation. The Freundlich isotherm parameters K(F) and n obtained using the <3 kDa molecular size fraction for solid/liquid separation were 3.7 x 10(2) and 0.82, respectively. In addition, since dissolved HA increased with decreased ionic strength in the HA suspension, ionic strength could promote aggregation of HA. The conformational change of HA could affect the sorption behavior of Se on HA.     

Metabolism and excretion of orally and intraperitoneally administered trimethylarsine oxide in the hamster

When trimethylarsine oxide (TMAO) was administered orally to hamsters once only, 86.9±11.1% of the administered dose of the compound was exreted in the urine during the following 24 hours: TMAO proved to be an arsenic compound eliminated extremely rapidly. The unchanged form of TMAO was the one and only trimethylarsenic compound (TMA) detected in the urine: in othe words, TMAO proved neither to be demethylated nor to be converted to arsenobetaine. It was shown, on the other hand, that TMAO is partly reduced in vivo and that only trimethylarsine was detected in expired air.