Dependence of the Translocation Frequency in Blood Lymphocytes on the Dose and Age at the Onset of Exposure in Residents of the Techa Riverside Settlements

Abstract

Evaluation of age effect on the frequency of radiation-induced translocations, registered using FISH in circulating T-lymphocytes in the long-term period after exposure, is both of theoretical and practical interest for the purposes of biodosimetry. The objective of our study was to analyze the dose dependence of the translocation frequency in the peripheral blood T-lymphocytes in donors of different age who were exposed in the Techa Riverside settlements (n = 197). In cytogenetic studies, whole chromosome painting probes were used to stain three pairs of chromosomes. A total of 104,721 genome equivalents (GE) were calculated and 2,540 translocations were found. For each donor, the individual absorbed doses in organs and tissues at the time of blood sampling were calculated using the Techa River Dosimetry System. In addition, doses to T-lymphocytes and their progenitors were calculated using the innovative modelling approach with due account of age related-dynamics of T-lymphocytes. The age dependence of the translocation frequency was associated particularly with these doses. The main sources of donor exposure were 89,90Sr, accumulating in bones and irradiating the bone marrow almost locally. To assess the parameters of the dose-effect relationship, linear regression model was used. After taking into account background values, the lowest frequency of translocations per 1000 GE per Gy was found in donors aged 0–5 years at the time of exposure (9.3 ± 1.3), which is statistically significantly lower than in children aged 6–18 years (15.3 ± 1.5), but not in adults (11.9 ± 2.9). The value for adults (18 years) was characterized by the maximum scatter, but was close to the values obtained in an international study of nuclear enterprise personnel after external exposure (11.6 ± 1.6). The values of the background translocation frequencies registered in various age groups correspond to the published data obtained in a joint international study on unexposed donors. We have also confirmed the absence of sex-effect on the frequency of translocations.