The Oxygen Effect

Abstract

The term “oxygen effect” refers to the observation that the radiation sensitivity of macromolecules and biological systems irradiated in the presence of oxygen or air is generally higher than when they are irradiated under vacuum or in an inert atmosphere. This only applies, however, with ionizing radiations; in UV irradiation experiments, an oxygen effect is only rarely observed. As with the temperature effect, justice is not done to the oxygen effect by treating it merely as a troublesome side-effect of radiation action. It is actually a phenomenon of great heuristic importance for the elucidation of the molecular nature of radiation damage. It is a pity that here, as in many other aspects of radiation biology, relevant experiments are scarce and the many facets of the oxygen effect tend in general to produce confusion rather than understanding. It is therefore not surprising that there is no satisfactory interpretation of the oxygen effect as yet. Nevertheless, an attempt will be made to describe the oxygen effect quantitatively, with the aid of known physico-chemical data and taking specific aspects of the inactivation of microorganisms into account. The chemical mechanisms underlying the oxygen effect will be studied, in the light of experiments on the radiation inactivation of biological macromolecules.