Genomic instability, bystander effects and radiation risks: implications for development of protection strategies for man and the environment.

The last few years has seen what people are now referring to as a "shifting Paradigm" in our way of thinking about radiation effects on biological systems. The concept of the central role of DNA damage due to double strand breaks induced by a radiation "hit" has been itself hit by many studies showing persistent effects in the distant progeny of radiation exposed cells. This phenomenon is known as radiation induced genomic instability. More recently evidence has been accumulating that not even the parent cell need be exposed to radiation (the bystander effect). The new paradigm suggests that cellular stress responses or damage signalling through a range of signal transduction pathways are involved and that cell-cell contact or secretion of damage signalling molecules can induce responses in undamaged and unirradiated cells. Are these new effects relevant to risk assessment, or does it matter HOW radiation affects cells if we have good epidemiological evidence of which to base our risk estimates? The aim of this paper is to introduce the new concepts and to consider reasons why they might alter our methods of risk estimation. The paper also considers the impact of the new concepts on environmental protection and discusses the need for research in the field of comparative radiobiology if we are to develop policies which can adequately protect biodiversity.