Chromosome aberrations in radiation workers with internal deposits of plutonium

Chromosome analysis of G-banded peripheral blood lymphocytes was performed on two groups of plutonium workers with 20-50% and >50% maximum permissible body burdens (MPBB) of plutonium from the British Nuclear Fuels plc (BNFL) facility at Sellafield, UK, 10 years after an earlier study had reported increases in both symmetrical and asymmetrical aberrations. For each plutonium exposure group there was a significant difference in frequencies of symmetrical aberrations between plutonium workers, workers with similar histories of exposure to mainly external gamma radiation but with little or no intakes of plutonium, and controls with negligible exposure (<50 mSv). In contrast, no significant differences for asymmetrical aberrations were found, and since these are short-lived, this suggests that recent exposure of mature lymphocytes was minimal. Frequencies of symmetrical aberrations had increased significantly since the earlier sampling time. Additional external radiation exposure was negligible in the plutonium worker groups over this period. These results are consistent with the hypothesis that hemopoietic precursor cells are being irradiated by internally deposited plutonium with subsequent selection resulting in only cells with symmetrical aberrations reaching the peripheral lymphocyte pool. After removal of aberrations involving only chromosomes 7 and/or 14, which are thought to arise in vivo during immunological development, the breakpoints involved in the aberrations were distributed randomly among the chromosomes according to length in all three groups of workers. Within the chromosomes the distribution between terminal, interstitial and centromeric regions for the plutonium workers did not conform to that expected, there being an excess in the terminal regions and a deficit in the interstitial regions.