Permissible dose limit based on the analysis of stable chromosome aberrations in the lymphocytes.

Permissible dose limit for the public is one of the most important subjects in the regulation of radiation. We have analyzed chromosome translocations in the peripheral lymphocytes of people who live in normal living circumstances. The number of cells analyzed was over 7000 cells per child and over 4000 cells per adult. The results are reported by Wang et al. at this congress (ICRR 2007). Average genomic frequencies of translocations in 1,000 cells in 20 residents (61.2 year-old on average) in a large city and in 16 residents (64.4 year-old on average) in a remote village and in 8 children (12.3 year-old on average) in the remote village were 9.6, 8.4, and 3.2, respectively. Their standard deviations were 5.0, 3.1 and 2.0. Since exposed dose can be estimated by the frequency of chromosome aberrations, we converted those frequencies of translocations shown above to radiation doses. Lloyd et al. (1983) reported that the induction rate of dicentrics by chronic low dose gamma irradiation is about 2.5 in 10,000 cells per cSv. Since translocations and dicentrics are induced by radiation in about equal frequency (Zhang and Hayata, 2004), the induction rate of translocation is considered as 2.5 in 10,000 cells per cSv. In case of acute exposure the frequency follows the dose response shown as: Y = 2.31 x 10-4D + 6.33 x 10-6 D2 (Sasaki et al., 2000), where Y is the frequency of dicentrics per 1,000 cells, and D is the dose in cSv. If we assume all the translocations observed in our study mentioned above are induced by chronic irradiation, the calculated doses for 9.6 (adult in a large city), 8.4 (adult in a remote village) and 3.2 (child in a remote village) in 1000 cells become 384 mSv, 336 mSv, and 128 mSv. In case of acute irradiation the calculated doses for them become 248 mSv, 225 mSv, and 107 mSv. Standard deviations were 200 mSv, 124 mSv and 80 mSv in chronic exposures, and 153 mSv, 104 mSv and 72 mSv in acute exposures. It is not possible to distinguish the cohort if the difference is within the standard deviation of the control. Therefore, our findings suggest that it is not possible to detect any effects of radiation to be caused on the human body at least up to124 mSv in adult and up to 80 mSv in child in chronic exposures, and up to 107 mSv in adult and up to 72 mSv in child in acute exposures. Permissible dose limit for the public will be discussed.197613th International Congress of Radiation Researc