COMPARATIVE RISK ASSESSMENT FOR HOMOGENEOUS AND NONHOMOGENEOUS MAMMALIAN POPULATIONS EXPOSED TO LOW LEVEL RADIATION

摘要

We have developed mathematical models that describe radiation-induced mortality dynamics for homogeneous and nonhomogeneous (in radiosensitivity) mammalian populations. These models relate statistical biometric functions with statistical and dynamic characteristics of a critical body system in specimens belonging to these populations. The model of mortality for the nonhomogeneous population involves two types of distributions, the normal and the log-normal, for its specimens with respect to the index of radiosensitivity for critical system cells. The mortality model for the homogeneous population quantitatively reproduces the mortality rate of laboratory mice chronically irradiated at low dose rates when the hematopoietic system (specifically, the thrombocytopoiesis) is the critical one. Comparison of the results obtained within the framework of the mortality models for homogeneous and nonhomogeneous populations show that the mortality model for the nonhomogeneous population predicts a higher mortality rate and a lower survival than would have been predicted from the averaged values of the radiosensitivity index of the critical system cells. The level of chronic dose rates presenting a hazard to nonhomogeneous mammalian populations becomes lower as the variance of their radiosensitivity indices become greater. For individuals possessing hyperradiosensitive critical system cells, even low-level irradiation can lead to mortality. These modeling results demonstrate the importance of taking into account the variability of individual radiosensitivity when predicting the mortality of mammals exposed to low-level irradiation. These models of radiation-induced mortality, as well as the approaches suggested in the course of their elaboration, outline new pathways in the development of radiation risk assessment methodology. Additionally, the same methodology produces other useful information: a criterion is established that elucidates the groups of radiation risk among population residing in areas with elevated radiation background and among persons subjected to occupational irradiation. (Only routine blood sampling is necessary.) Applying the complete set of preventive and protective measures to persons revealed enables one to reduce the radiation risk both for the individuals and for the population as a whole.