Absorbed Dose Rate Due to Intake of NaturalRadionuclides by Tilapia Fish (Tilapia nilotica,Linnaeus, 1758) Estimated Near Uranium Miningat Caetite, Bahia, Brazil

摘要

The uranium mining at Caetite (Uranium Concentrate Unit - URA) is in its operational phase.Aiming to estimate the radiological environmental impact of the URA, a monitoring program isunderway. In order to preserve the biota of the deleterious effects from radiation and to act in a pro-activeway as expected from a licensing body, the present work aims to use an environmental protectionmethodology based on the calculation of absorbed dose rate in biota. Thus, selected target organism wasthe Tilapia fish (Tilapia nilotica, Linnaeus, 1758) and the radionuclides were: uranium (U-238), thorium(Th-232), radium (Ra-226 and Ra-228) and lead (Pb-210). As, in Brazil there are no radiation exposurelimits adopted for biota the value proposed by the Department of Energy (DOE) of the United States of3.5 x 10~3μGyy~(-1)has been used. The derived absorbed dose rate calculated for Tilapia was 2.51 x 10~0μGy y~(-1), that is less than 0.1 % of the dose limit established by DOE. The critical radionuclide was Ra-226, with 56 % of the absorbed dose rate, followed by U-238 with 34 % and Th-232 with 9 %. This valueof 0.1% of the limit allows to state that, in the operational conditions analyzed, natural radionuclides donot represent a radiological problem to biota.