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

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 (<200Bqg ^-1) for 14d, either via water or diet. Radioactivity concentrations were measured in whole body and excised gonads of exposed fish during uptake (14d) and depuration phases (47d and 42d 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> ⁶⁵Zn> ¹⁰⁹Cd> ^110mAg> ⁵⁴Mn> ⁶⁰Co> ²⁴¹Am> ¹³⁴Cs (range: 175-8Bqg ¹). After dietary exposure the order of radionuclide activity concentration in tissues (Bqg ^-1) was: ⁶⁵Zn> ⁶⁰Co> ⁷⁵Se> ¹⁰⁹Cd> ^110mAg> ²⁴¹Am> ⁵⁴Mn> ¹³⁴Cs (range: 91-1Bqg ^-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 (Bqg ^-1) were for ⁷⁵Se (211), ¹⁰⁹Cd (142), and ⁶⁵Zn (117), and highest dose rates (-Gyh ^-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.