From human to environmental radioprotection: Some crucial issues worth considering.
F. Bréchignac & J.C. Barescut
3rd International Symposium on the Protection of the Environment from Ionising Radiation -22/26 juillet 2002 -Darwin (Australia).
The need to establish a system capable of ensuring adequate protection of the environment from the harmful effects of ionising radiation is at present particularly challenged. This comes both from a restrictive consideration of the environment in the so far existing system for human radioprotection, and the planetary-wide growing concerns about man’s technogenic influence on his environment which have yielded “sustainability” and “precaution” as guiding principles for environmental protection. Whilst the issue of environmental radioprotection is not starting from scratch, it is however important to scrupulously identify where are the current limits of our knowledge, what is the relevance of this later to the goals pursued, and not to ignore the most advanced concepts which emerge from the efforts to deriving improved approaches to Environmental Risk Assessment.
This paper will identify and discuss some crucial issues worth considering in this context. For the sake of protection, the environment is traditionally addressed through its biota since these are the sensitive components of ecosystems. Similarities between man and biotas root from the ubiquitous mechanistic effects of radiation on life which disrupt molecules. However, important differences also arise in a number of perspectives, from the large spectrum of different biotas species to their hierarchical self-organisation as interacting populations within ecosystems. Altogether, these aspects are prone to promote complex arrays of different responses to stress which lie beyond the scope of human radioprotection due to its focus on individuals of one single species. Illustrations will be discussed along the current challenges faced in proper identification of measurable effect endpoints (stochastic/deterministic, individual/population- or ecosystem-relevant), dose limits in chronic exposure (or levels of concern), and their ponderation according to radiation types (RBE) and concommitance of other contaminants (synergies/antagonisms) which call for filling critical gaps in knowledge.
It is to be noted that the system of human radioprotection has conceptually been targetted at limiting the occurrence of cancer induction (stochastic) in human individuals, whereas the current approach in radioprotection of biota targets at reproductive success (deterministic) and cytogenetic effects, thought to have the highest significance at population and ecosystem levels. The focus on individuals in a bottom-up approach, due to its easier amenability to quantification, has prompted the development of current ecotoxicological methods as a scientific fundation to regulating environmental protection. Exclusive basement of risk assessment on this reductionist approach, however, is currently questioned by the most recent ecological theories which, by emphasising on complex systems as a key to modern ecological understanding, call for additional consideration of more holistic, top-down, approaches. The crucial point here is that dose-effect relationships of the subsystem components often lose their predictive ability at system level.