The weighting of absorbed dose in environmental risk assessments

Practical applications of using absorbed dose for radiation protection purposes forces consideration of the biological effectiveness of different types of radiation. For human radiation protection this is taken into account by applying dimensionless radiation weighting factors. Similarly, environmental dosimetry requires weighting factors, based on experimentally obtained RBE values, relevant for biota. The expected doses and dose rates in contaminated environments are low and the dose distribution is assumed to be highly heterogeneous. The identification of relevant RBE values for biota implies the recognition of critical end-points leading to reproductive disturbances. Concurrently, a mechanistic understanding of these end-points, whether they are of stochastic (single track) or deterministic origin, has to be elucidated. In a risk assessment framework it seems necessary to postulate the criteria for selecting appropriate RBE values, and to indicate a span for weighting factors applicable to different exposure situations and ecosystems. (author)