Taeko Koga

Mortality and Cancer Incidence in Misasa, Japan, a Spa Area with Elevated Radon Levels

A historical cohort study was conducted in Misasa town, Tottori prefecture, Japan, where radon spas have been operating for a long time. Misasa town was divided into an elevated radon level area and a control area, with mean indoor radon levels of about 60 and 20 Bq/m3, respectively. In total, 3,083 subjects in the elevated radon level area and 1,248 in the control area, all aged 40 or older on January 1, 1976, were followed up until December 31, 1993, for a mean period of 14 years. The mortality rates from all causes exhibited no difference between the elevated radon level area and the control area for both sexes. No difference was observed in the incidence of all‐site cancers (age, period‐adjusted rate ratios by Poisson regression, RR=1.06, 95% confidence interval (CI) 0.79–1.42 for males, RR=0.90, 95% CI 0.65–1.24 for females), while stomach cancer incidence seemed to decrease for both sexes (RR=0.70, 95% CI 0.44–1.11 for male, RR=0.58, 95% CI 0.34–1.00 for female) and lung cancer incidence for males only seemed to increase (RR=1.65, 95% CI 0.83–3.30 for male, RR=1.07, 95% CI 0.28–4.14 for female) in the elevated radon level area. Caution is needed in the interpretation of these findings, however, since the individual exposure level was not measured and major confounding factors, such as smoking and diet, could not be controlled in this study.

Effect of spring water on the radon concentration in the air at Masutomi spa in Yamanashi Prefecture, Japan

The concentrations of 222Rn existing in air have been studied by using a convenient and highly sensitive Pico-rad detector system at Masutomi spa in Yamanashi Prefecture, Japan. The measurements in air were carried out indoors and outdoors during the winter of 2000 and the summers of 1999 and 2005. The concentrations of 222Rn in spring water in this region were measured by the liquid scintillation method. The concentrations of natural radionuclides contained in soils surrounding spa areas were also examined by means of the γ-ray energy spectrometry technique using a Ge diode detector to investigate the correlation between the radionuclides contents and 222Rn concentrations in air at each point of interest. The atmospheric 222Rn concentrations in these areas were high, ranging from 5 Bq/m3 to 2676 Bq/m3. The radon concentration at each hotel was high in the order of the bath room, the dressing room, the lobby, and the outdoor area near the hotel, with averages and standard deviations of the concentration of 441 ± 79 Bq/m3, 351 ± 283 Bq/m3, 121 ± 5 Bq/m3, and 23 ± 1 Bq/m3, respectively. The source of 222Rn in the air in the bath room is more likely to be the spring water than the soil. The spring water plays carries the radon to the atmosphere. Our measurements indicated that the 222Rn concentration in the air was affected by the 222Rn concentration in spring water rather than that in soil.

STUDIES ON THE RELEASE OF RADIOACTIVITIES FROM THE ION EXCHANGE RESINS INTO THE SEA WATER

Abstract For the purpose of estimating the release of radioactivities from ion exchange resins disposed into sea water, we have conducted a series of experiments in a water bath containing natural sea water, using such radioactive nuclides as 51Cr, 55Fe, 60Co, 89Sr and fission products by changing the weight ratio of ion exchange resin to the sea water and the amount of nuclide initially adsorbed on the ion exchange resin under static and turbulent conditions. The results are summarized as follows: 1 The radioactivities were rapidly released from the ion exchange resin particles (Dowex 50 and Dowex 1, 50–100 mesh) on contact with the sea water. However, some differences were observed in the degree of release depending on the different nuclides. Such nuclides as 60Co and 89Sr were easily released, while 51Cr and 55Fe not so easily. 2 The released activity was observed to increase with the decreasing weight ratio of the ion exchange resin to the sea water, but with the weight ratio below 10–4 of the ion exchange resin to the sea water no remarkable difference was observed. 3 The results of fractionation of suspended matter in sea water containing 55Fe, 60Co and 89Sr will be discussed also.