The cytotoxic and mutagenic effects of radon and its progeny were compared in murine lymphoblast L5178Y-R16 cells after exposure at three institutions. The cells were exposed to222 Rn at Case Western Reserve University (CWRU) and Pacific Northwest Laboratories (PNL) and to212 Bi, a decay product of220 Rn, at the University of Chicago (UC). The dose to the cell nucleus was calculated using a dosimetric model which addressed both the contribution of the dose from the radioactivity in the medium and that associated with the cells. The dose-response curves for cell survival showed$D_{0}\text{'}{\rm s}$ of 0.30 Gy at CWRU, 0.20 Gy at PNL, 0.37 Gy for chelated212 Bi, and 0.13 Gy for unchelated212 Bi. Induced mutant frequencies at the thymidine kinase locus at the 37% survival level were$1470\times 10^{-6}$ at CWRU, 1518 at PNL, and$2414\times 10^{-6}$ at UC using combined results for chelated and unchelated212 Bi. The variation between institutions was greater than obtained in a previous interlaboratory comparison of the effects of radon on CHO cells. Since less radioactivity was associated with CHO cells than L5178Y cells, we have concluded that the variation between institutions in the case of L5178Y cells is caused by the differences in cell-associated radioactivity and errors related to the measurement of this parameter.

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