The effect of oxygen concentration on the X-ray induction of chromosome aberrations in human lymphocytes

In vitro dose--response curves, for unstable chromosome aberration induction in human lymphocytes under conditions of full oxygenation or of anoxia, have been obtained using 250 kVp X-rays. Dicentric yields have been fitted to the quadratic function Y = alpha D + beta D2. An Oxygen Enhancement Ratio (OER) ranging from 7.2 to 2.7 was calculated from the coefficients of these curves possibly indicating that the data do not fit to the dose-modifying model of the oxygen effect although the differences are not statistically significant. A similar analysis of total aberration data yields an OER of 3.6 to 2.7 fitting much more satisfactorily to the dose-modifying model. Variations in dicentric yield induced by 3.0 Gy and 0.75 Gy of X-rays with increasing oxygen concentration were plotted and for each dose a constant dicentric yield was observed at oxygen levels of 2 and 250 ppm. Above 250 ppm yields increased steeply up to about 1% oxygen and then more gradually to a maximum at 100% oxygen.