Chronic human exposure to ionizing radiation: Individual variability of chromosomal aberration frequencies and G0 radiosensitivities.

Bio-monitoring of human radiation exposure is based, as a rule, on a single analysis of chromosomal aberrations. Factors such as radiosensitivity, adaptation, and the stability of cytogenetic indices are not taken into account. We studied frequency of chromosome aberrations (FCA) and G0 chromosome radiosensitivity following in vitro γ-exposure, over a 2.5-year period, for 129 residents of the Dolon settlement, part of the extreme radiation risk zone, Semipalatinsk nuclear test site region, Kazakhstan. Radiosensitivity was evaluated on the basis of FCA and dose assessment by physical dosimetry. FCA was 3-fold higher in Dolon inhabitants as in the control group (p ≤ 0.01). The average coefficient of variability of spontaneous FCA was 31 %. In 20 % of the subjects, it was very high (50-70 %). Individual dose estimation in a single study in such individuals may lead to significant errors. Individual G0-chromosomal radiosensitivity showed less variation (18.7 %). Chronic low-dose irradiation was an adaptive factor to the damaging dose (1 Gy). Three methods of individual radiosensitivity assessment were considered, based on: G0-chromosomal radiosensitivity under additional in vitro γ-radiation; FCA and average dose per year; FCA and total dose received during years of residence in a radiocontaminated settlement, according to physical dosimetry. There is a significant difference in response (FCA) between radiosensitive and radioresistant individuals. This should be taken into account in individual dosimetry and risk assessment of radiation exposure.