In the national and international guidelines for drinking water quality, it is recommended that arsenic (As) and selenium (Se) concentrations in drinking water do not exceed 0.01 mg L-1 (10 μg L-1) . Since As and Se concentrations are thought to be lower than 1/10 of the recommended values in>90% of surface river waters, it is difficult to describe nationwide As and Se concentration levels in Japan. The recently developed octapole reaction system for inductively coupled plasma mass spectrometry (ORS-ICP-MS) could achieve low detection limits for As and Se compared to atomic absorption spectrometry and ICP optical emission spectrometry. In this study, direct measurement of trace levels of As and Se in river water for 25 major rivers, 10 samplings per river, were carried out using ORS-ICP-MS. In order to determine As and Se, He gas and H2gas, respectively, were introduced into the ORS as reaction gas. The concentrations of As and Se were determined in more than 95% of the samples, and the cumulative probability distributions of these elements were on log-normal lines. Their respective geometric mean concentrations were calculated as 0.68μg L-1and 0.062μg L-1, and the values were lower than the recommended ones. The concentration ranges of these elements in ten samples collected from the upper stream to the river mouth were usually narrow. Possibly, the observed concentrations originated from weathering of bedrock.
The dual tracer autoradiography using18F-FDG and14C-FDG was applied to the estimation of changes in the metabolic trapping rate in rat brain. Rats were infused with kainic acid (1μg/μL) into the right striatum 3 hours prior to the tracer experiment. 18F-FDG was intravenously injected into the rats, and14C-FDG was injected 44 minutes after18F-FDG injection. The rats were decapitated at 1 minute post-injection of14C-FDG, and frozen brain sections were prepared. The slices were exposed on imaging plate for 1 hour, and18F-FDG images (45 minutes) were obtained. After the decay of18F, the same slices were contacted with imaging plate for 1 week, and14C-FDG images (1 minute) were obtained. Radioactivity concentrations in cerebral cortex at 1 minute and 45 minutes after18F-FDG injection were determined by the dissection method, the values were used to normalize18F-FDG and14C-FDG image. The subtraction image was made by subtracting the normalized14C-FDG image from the18F-FDG image. In the results, intrastriatal infusion of kainic acid significantly enhanced the metabolic trapping process of FDG. The dual tracer autoradiography with18F-FDG and14C-FDG seems to be useful to assess the metabolic trapping rate of FDG in brain injury.
Concentration of222Rn in well water at Meiji University, Kawasaki, Japan, was observed from 2000 to 2001. The222Rn concentration in the groundwater ranged from 3 to 5 Bq/L. The variation pattern of monthly averaged concentration of222Rn in the groundwater was similar to that of precipitation: the monthly averaged concentration in groundwater tended to increase in summer and autumn with large amount of precipitation and to decrease in winter and spring with small amount of precipitation. The variation pattern suggested that the precipitation may give rise to the mixing of groundwaters of different origins.
The radon measurement with a gas-filled ionization chamber is generally performed at many laboratories in Japan as a standard method. In this paper, the characteristics of the method have been examined as follows. The wall effects against the different filled gases, nitrogen and dry air, have been evaluated with Monte Carlo simulation. The columnar recombination has been also evaluated from two different ways; one is the common evaluation from the relationship between inverse of ionization current and inverse of applied voltage; another is the evaluation from the relationship between the ionization current in the different gas pressure and the wall effect expected in each pressure.Both results have been agreed with each other. As the total, the efficiencies of ionization chamber, volume of which is 1.5 L, are estimated to be 0.02706 Bq.fA-1for nitrogen gas of 93.3 kPa and 0.02701 Bq.fA-1for air of 101.3 kPa, and the values are very close to the conversion factor on the literatures within 3% of difference. Furthermore the effect by humidity has been preliminarily estimated, and the effect is almost -3% per 1 % of absolute humidity but it can be easily removed by the suitable dryer. These examinations have proven the method with a gas filled ionization chamber has high accuracy for radon measurement. An241Am disk source was used with same methods to confirm the results above mentioned.