Radiation risks in the context of multiple stressors in the environment-issues for consideration

The field of multiple stressors is highly complex. Agents can interact in an additive, antagonist or synergistic manner. The outcome following low dose multiple stressor exposure also is impacted by the context in which the stressors are received or perceived by the organism or tissue. Modem biology has given us very sensitive tools to access change following stressor interaction with biological systems at several levels of organization but the effect-harm-risk relationship remains difficult to resolve. This paper reviews some of the issues, using low dose ionizing radiation as a common stressor and chemicals known to act through similar mechanisms, as examples Since multiple stressor exposure is the norm in the environment, it is essential to move away from single stressor based protection and to develop tools, including legal instruments, which will enable us to use response-based risk assessment. The problem of radiation protection in the context of multiple stressors includes consideration of humans and non-humans as separate groups requiring separate assessment frameworks. This is because for humans, individual survival and prevention of cancer are paramount but for animals, it is considered sufficient to protect populations and cancer is not of concern. The need to revisit this position is discussed not only from the environmental perspective but because the importance of pollution as a cause of non-cancer disease is increasingly being recognized. Finally a way forward involving experimental assessment of biomarker performance coupled with modeling is discussed.