A comprehensive biokinetic model for the dose to embryo and fetus due to radon intakes by the mother – Part I: the state of the art

RadoNorm is a European project that aims to support the European Union Member States, Associated Countries, and the European Commission to implement the Council Directive 2013/59/EURATOM regarding radon and NORM risk management, ensuring effective radiation protection based on most recent scientific studies and societal aspects. The Work Package 3 is focused on dosimetry and its subtask 3.3.1 targets on the design of a comprehensive model for the dose to embryo and fetus following radon intakes by the mother. The first part of the subtask consisted in gathering information on the state of the art on biokinetic models for embryo and fetus, and searching for animal and human data that could be useful to build a specific biokinetic model. This paper reports on the literature review on the identified data that are relevant to perform the task. Publications of the International Commission on Radiological Protection (ICRP), National Council on Radiation Protection and Measurements (NCRP), and the U.S. Nuclear Regulatory Commission were reviewed with regard to how doses from radon and radon progeny to the embryo and fetus have been calculated so far. Currently, a general approach for the calculation of the concentration of a radionuclide in embryonic and fetal tissues ( C F ) is based on the ratio to the concentration of that radionuclide in the mother's body ( C F ) as given in Publication 88 of the ICRP. However, no biokinetic model specific for radon and radon progeny is presented there. The challenging task of defining a specific biokinetic model for radon faces the lack of experimental data and the scarcity of recent works, especially regarding transfer of radionuclides through the placenta. Nevertheless, some results of animal studies on radon, radon progeny, and other noble gases can be used as a starting point to build the biokinetic model as well as some recent assumptions considering the concentration of radon in the fetus following intakes by the mother as being the same as in the mother's muscle, because fetal tissues do not contain much fat. Using the most recent adult model describing the biokinetics of radon in the mother and assuming the hypothesis of radon concentration in fetus being the same as in the mother's muscle are reasonable approaches to the biokinetic model. Animal studies provide useful information for a more realistic modelling of radon progeny biokinetics, with regard to lead and bismuth placental transfer and direct translocation of lead from maternal skeleton to fetal tissues.