Effects of Ionizing Radiation Combined with Other Stressors, on Non-Human Biota

Exposure of organisms in the environment to ionizing radiation is generally considered to be harmful, regardless of the dose. This assumption derives directly from the basic assumption used for human radiation protection, that harm is directly proportional to dose, without a threshold. The consequence of combined exposures is generally unknown, but is assumed to be either additive or multiplicative. We have examined the in vivo and in vitro responses of a variety of cells and organisms. We show that exposure to one stressor can influence the outcome of a subsequent exposure to the same or another stressor. In many cases, pre-exposure to one stressor appeared to induce an adaptive response that mitigated the harm from a second stressor. These observations challenge the basic assumptions used in environmental protection strategies, suggesting that new approaches are needed. Keywords: combined stressors; radiation; heat; chlorine; non-human biota