DNA damage induced in human diploid cells by decay of incorporated radionuclides

Alkaline and neutral elution techniques were used to characterize the production of single- and double-strand DNA breaks in human diploid fibroblasts by incorporated radionuclides. 125I was incorporated in DNA as [125I]iododeoxyuridine, 3H as [3H]-thymidine, and 14C as [14C]thymidine. Under frozen conditions, 125I was 3 times as efficient as 3H per decay in inducing single-strand breaks and 6 times as efficient as 14C. For double-strand break production, however, 125I was 6 times as efficient per decay as 3H. It was calculated that, on the average, each 125I decay produces about one double-strand break in the frozen state. Under nonfrozen conditions, 125I and external X-rays were roughly 5-fold and 3H about 3-fold more efficient in double-strand break induction than under frozen conditions.