UDS and SCE in lymphocytes of persons occupationally exposed to low levels of ionizing radiation.

Unscheduled DNA synthesis induced by in vitro UV irradiation was investigated in lymphocytes of persons occupationally exposed to low doses of ionizing radiation (maximum registered radiation dose: 98 mrad/month). For radiation exposures greater than 14 mrad/month above background level, increased rates of UDS after in vitro UV irradiation of lymphocytes were found. The bromodeoxyuridine differential chromatid labeling technique was applied to the examination of spontaneous and Mitomycin C (MMC)-induced sister chromatid exchanges (SCE) in the same population. No statistically significant difference could be determined in spontaneously occurring SCEs, while MMC induced SCEs were significantly reduced in persons exposed to radiation doses greater than 14 mrad/month, thus indicating increased repair capability for DNA lesions inflicted by a second insult after protracted low-dose irradiation.