LIFE-SPAN OF HUMAN-LYMPHOCYTES ESTIMATED DURING A 6 YEAR CYTOGENETIC FOLLOW-UP OF INDIVIDUALS ACCIDENTALLY EXPOSED IN THE 1987 RADIOLOGICAL ACCIDENT IN BRAZIL

Following the radiological accident which occurred in the city of Goiania (Brazil), in September 1987, a cytogenetic follow-up of 15 exposed patients was started, aiming to observe the mean lifetime of lymphocytes containing dicentric and ring aberrations. The results suggest that the disappearance rate of unstable aberrations follows a two-term exponential function. Up to 470 days after exposure, there is a rapid fall in the aberration frequency. After 470 days, the disappearance rate is very slow. These results may reflect different subpopulations of human lymphocytes, with different lifespans. The estimated average half-time of elimination of dicentrics and rings among the highly exposed group (doses above 1 Gy) was 110 days for the initial period after the exposure (up to 470 days). This value is significantly shorter than the usually accepted value of 3 years reported in the literature. Statistical analysis of possible correlations between the individual half-times and biological parameters, such as sex, age, leukopenia level shown during the critical period, absorbed dose (initial frequency of chromosomal aberrations) and the administration of the bone marrow stimulating factor (rHuGM-CSF) was performed. None of these parameters showed a correlation with the half-time of disappearance of chromosomal aberrations. For the individuals who had received less than 1 Gy the disappearance of aberrations was slower, with a half-time of 160 days during the period up to 470 days after exposure. Mean disappearance functions of unstable chromosome aberrations were inferred, to be applied in accident situations in which there is a blood sampling delay.