Uncertainty in committed effective doses caused by assuming a single intake pathway in the interpretation of bioassay results

Intakes of radionuclides through both inhalation and ingestion pathways may occur during an incident involving unsealed radionuclides. If one assumes only one intake pathway in this case, which is usual in a routine monitoring, a significant error in the evaluated committed effective dose (E₅₀) may result. In order to quantify this potential error, variations of resultant committed effective doses were analyzed for different fractions of the inhaled activities to the total intake of some selected radionuclides: ^57,58,60Co, ^134,137Cs, ^89,90Sr and ³²P. Simulated bioassay measurements for the whole body, urine and feces at 1 day after the intakes were generated based on the biokinetic models and data of the radionuclides. For the inhalation intake, AMAD of 5 μm was assumed and the different absorption Types were considered. Given that the intake happened via both pathways, the ratio of E₅₀ with assumption of a single intake pathway to the true E₅₀ were in the range of 0.01 - 72.59 for ⁹⁰Sr (Type S) and of 0.06 - 16.70 for ⁶⁰Co (Type S), which are unacceptably wide ranges. Generally larger errors are expected when the feces assay and Type S are applied. A strategy which employs two methods of bioassay or two successive measurements is proposed to reduce the potential error caused by a misjudgment of the intake pathway. (author)