Abstract
Chronological changes of chromosome aberration rates along with accumulated doses in specific pathogen free (SPF) mice continuously exposed to low-dose- rates (LDR) gamma- rays were studied by centromere FISH and M-FISH methods. Chromosome aberrations in mouse splenocytes were serially observed following irradiation for about 400 days (total dose of 8,000 mGy) at 20 mGy/22hr/day and for about 615 days (total dose of 615 mGy) at 1 mGy/22hr/day. For comparison, high-dose-rate (0.89 Gy/min) gamma-irradiation was also performed. Both dicentrics and translocations increased almost linearly up to 8,000 mGy at 20 mGy/22hr/day, accompanied by complex aberrations and clonal aberrations. Incidences of dicentrics at 1 mGy/22hr/day were lower than 20 mGy/22hr/day and increased up to 412.5 mGy. The incidences of dicentrics and translocations slightly increased with age. The dose and dose-rate effectiveness factor (DDREF) for dicentric chromosomes was estimated from the ratio of slope in fitting regression lines of acute and low-dose rate irradiation data. The most fitting lines were obtained in each different dose-range. DDREF changed from 1.9 to 3.6 in each dose-range at 200 mGy after irradiation at 20 mGy/22hr/day, which indicates variable DDREF depending on dose-range and dose-rates. These results are important to evaluate biological effects of chronic exposure to low-dose radiation. This study was supported by a grant from Aomori Prefecture, Japan.
