Background. Many people in Taiwan have been living in buildings constructed with cobalt-60-contaminated steel rods. To study the biological effects of chronic low-dose ionising radiation on the residents of one such building, micronucleus formation in these individuals was compared with that in controls. Methods. The 73 residents had 77 age-and-sex-matched controls: 31 had 31 close relatives as controls (group A controls); eight of the 31 had a second set of close relatives; and the other controls were 38 residents in neighbouring buildings. Two micronucleus assays were used--a cytochalasin B (CBMN) assay and another involving incubation with cytarabine (CBMNA). Assay results are given as 'frequency', or the number of binucleate cells containing one micronucleus per 1000 randomly examined binucleate cells. Findings. The CBMN and CBMNA mean (SD) frequencies for 31 exposed individuals (0·016 [0·009] and 0·025 [0·013] respectively) were greater than those for their group A controls (0·009 [0·004] and 0·016 [0·009], respectively) (p = 0·0006 and 0·0002, respectively). The mean CBMN and CBMNA frequencies for all the exposed individuals (0·017 [0·011] and 0·030 [0·014], respectively) were significantly greater than those for all controls [0·011 [0·008] and 0·019 [0·01]; p = 0·0001 for both comparisons). The ranges of the differences in CBMN or CBMNA frequencies between 31 exposed individuals and their group A controls were 0·003 to 0·020 and 0·001 to 0·032, respectively. After adjustment for age, sex, and cigarette smoking, the adjusted relative risks of micronucleus formation from radiation exposure in all 73 residents was 1·56 (95% Cl 1·42-1·71; p = 0·0001) by the CBMN assay and 1·64 (1·53-1·77; p = 0·0001) by the CBMNA assay. Interpretation. These findings suggest that chronic low-dose and low-dose-rate γ-ray environmental exposure may induce cytogenetic damage in human beings.
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