The human lymphoblast cell line TK6 was exposed to the α-particle-emitting radon daughter212 Bi by adding DTPA-chelated212 Bi directly to the cell suspension. Cytotoxicity and mutagenicity at two genetic loci were measured, and the molecular nature of mutant clones was studied by Southern blot analysis. Induced mutant fractions were$2.5\times 10^{-5}/{\rm Gy}$ at the hprt locus and$3.75\times 10^{-5}/{\rm Gy}$ at the tk locus. Molecular analysis of HPRT- mutant DNAs showed a high frequency (69%) of clones with partial or full deletions of the hprt gene among radiation-induced mutants compared with spontaneous mutants (31%). Chi-squared analyses of mutational spectra show a significant difference (P ≤ 0.005) between spontaneous mutants and α-particle-induced mutants. Comparison with published studies of accelerator-produced heavy-ion exposures of TK6 cells indicates that the induction of mutations at the hprt locus, and perhaps a subset of mutations at the tk locus, is a simple linear function of particle fluence regardless of the ion species or its LET.

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