Polonium-210 and Lead-210 in marine biota from a coastal region with high natural radioactivity

Coastal sediments and marine fish from a region with high natural radioactivity in Cox Bazar Bangladesh, were analyzed in order to investigate the levels of naturally occurring radionuclides. Sediment from the sea shore in high ambient radiation dose rate areas contained naturally occurring radionuclides at high concentrations. These sediments displayed ²²⁶Ra, ²³²Th and ²³⁵U activity concentrations of 2184 ± 88 Bq kg^-1 dry weight (d.w.), 3808 ± 200 Bq kg^-1 (d.w.) and 123 ± 15 Bq kg^-1 (d.w.), respectively. In contrast with these high values, radionuclide concentrations in sand from other areas of the Cox's Bazar coast were as low as 42 ± 3, 70 ± 4 and < 8 Bq kg^-1 (d.w.) for the same radionuclides, respectively, which are comparable to concentrations determined in many coastal areas elsewhere. The presence of sand deposits with high concentration of uranium series radionuclides could potentially originate high accumulation of alpha emitting radionuclides such as ²¹⁰Po in marine biota, and food chain transfer to man. ²¹⁰Po is a major contributor to the radiation dose both in marine organisms and sea food consumers. Determination of ²¹⁰Po in marine fish and shrimp from the area lead to concentration values ranging from 4.5±0.3 to 124±3 Bq kg^-1 (d.w.) in fish and 82.9±1.6 Bq kg^-1 (d.w.) in shrimp. Similar concentrations are commonly reported in marine biota from several regions. Therefore, in spite of the deposits of heavy mineral sands containing high concentrations of radionuclides such as ²¹⁰Pb and ²¹⁰Po no significant raise in the accumulation of these radionuclides in biota seems to occur, which suggests that radionuclides are tightly bound in sediment grains and are not significantly bioavailable. (author)