Internal radiation dose to the herring gull embryo due to ⁹⁰Sr in the egg

Birds are bioindicators of anthropogenic environmental stress, including the changes caused by radioactive contamination of ecosystems. Any radiation-induced biological effects can be the consequence of exposure both after hatching and during the embryonic period. Therefore, it is necessary to quantify radiation doses to the embryo when interpreting observed radiobiological effects in birds. This is especially true for areas contaminated with Ca-like ⁹⁰Sr. The levels of radionuclide accumulation in the eggshell can be extremely high, which leads to chronic embryo exposure. Consequently, the objective of the present study was to develop a method to calculate the dose to a herring gull embryo exposed to ⁹⁰Sr distributed in egg compartments (shell, embryo body, albumen and yolk). To achieve this, the time-dependent Sr distribution in the egg compartments was modeled. Additionally, dosimetric modeling was carried out to obtain dose factors that convert the radionuclide activity in different compartments of an egg to embryo dose at various stages of embryogenesis. It has been shown that the accumulated dose to the herring gull embryo can be calculated based on ⁹⁰Sr total activity in the egg using a dose conversion factor of 0.44 μGy Bq^-1. Since the eggshell contains more than 90% of total ⁹⁰Sr activity, the conversion from eggshell activity to embryo dose would be practically the same as that from the total egg activity - 0.46 μGy Bq^-1. The main dose fraction (~ 99%) accumulates at the last stage of embryogenesis (from 13 to 26 days). The proposed method allows for an estimation of individual radiation doses to embryos based on eggshell radiometry. This creates a new opportunity to study how dangerous any radiation exposure of birds could be during the embryonic period.