Uptake, depuration, and radiation dose estimation in zebrafish exposed to radionuclides via aqueous or dietary routes

Abstract

Understanding uptake and depuration of radionuclides in organisms is necessary to relate exposure to radiation dose and ultimately to biological effects. We investigated uptake and depuration of a mixture of radionuclides to link bioaccumulation with radiation dose in zebrafish, Danio rerio. Adult zebrafish were exposed to radionuclides (54Mn, 60Co, 65Zn, 75Se, 109Cd, 110mAg, 134Cs and 241Am) at tracer levels (greater than 200 Bq g−1) for 14 d, either via water or diet. Radioactivity concentrations were measured in whole body and excised gonads of exposed fish during uptake (14 d) and depuration phases (47 d and 42 d for aqueous and dietary exposures respectively), and dose rates were modelled from activity concentrations in whole body and exposure medium (water or diet). After 14-day aqueous exposure, radionuclides were detected in decreasing activity concentrations: 75Se greater than 65Zn greater than 109Cd greater than 110mAg greater than 54Mn greater than 60Co greater than 241Am greater than 134Cs (range: 175–8 Bq g1). After dietary exposure the order of radionuclide activity concentration in tissues (Bq g−1) was: 65Zn greater than 60Co greater than 75Se greater than 109Cd greater than 110mAg greater than 241Am greater than 54Mn greater than 134Cs (range: 91–1 Bq g−1). Aqueous exposure resulted in higher whole body activity concentrations for all radionuclides except 60Co. Route of exposure did not appear to influence activity concentrations in gonads, except for 54Mn, 65Zn, and 75Se, which had higher activity concentrations in gonads following aqueous exposure. Highest gonad activity concentrations (Bq g−1) were for 75Se (211), 109Cd (142), and 65Zn (117), and highest dose rates (μGy h−1) were from 241Am (aqueous, 1050; diet 242). This study links radionuclide bioaccumulation data obtained in laboratory experiments with radiation dose determined by application of a dosimetry modelling tool, an approach that will enable better linkages to be made between exposure, dose, and effects of radionuclides in organisms.