Transfer of alkaline earth elements in mothers' milk and doses from ⁴⁵Ca, ⁹⁰Sr and ²²⁶Ra

An international programme of work is currently under way to develop methods for calculating doses to infants from ingestion of radionuclides present in mothers' milk. This paper considers the special case of the alkaline earth elements. Models have been developed for ⁴⁵Ca, ⁹⁰Sr and ²²⁶Ra and the sensitivity of results to various changes in parameter values is discussed. A complication when calculating doses from intakes of radium is that the International Commission on Radiological Protection has previously recommended that doses from decay products of radium should be calculated using element-specific biokinetic models (so-called independent biokinetics). An extension of this method to the models for breastfeeding is proposed. Preliminary estimates of the doses received by the infant for a number of maternal intake scenarios show that doses to the infant can exceed the corresponding adult dose, such as for ⁴⁵Ca (ratio= 3.1) while, in other cases such as ⁹⁰Sr, the infant dose can be a significant fraction of the adult dose.