Environmental Radioactivity in the Marine Environment of Ha Long Bay, North Vietnam, and Biomagnification of Polonium

Environmental preservation of Ha Long Bay, a UNESCO World Heritage Site, is a national priority for Vietnam. Coal mining is growing in the region with interim coal stockpiling on the shore by the maritime harbour in Ha Long Bay. Due to the presence of radionuclides in coal, radioactivity analyses were carried out for the first time in coastal samples to assess the radionuclide levels in Ha Long Bay. Samples of coal, sediments, molluscs, shrimp, and fish were collected from the Bay site and analyzed for U, Th, 226 Ra, 210 Pb and 210 Po by alpha spectrometry, and for 40 K, 228 Ra and 137 Cs by gamma spectrometry. Radionuclide concentrations in sediments ranged from 21 to 43 Bq kg −1 dry weight (dw) for 238 U, from 14 to 35 Bq kg −1 dw for 226 Ra, and from 25 to 122 Bq kg −1 dw for 210 Pb and 210 Po. Radionuclide concentrations in marine biota were comparable to data reported for other coastal areas. It was concluded that despite discharges of the long-lasting coal mining industry in the area, no significant enhancement of radioactivity occurred in biota of Ha Long Bay. Although at naturally-occurring levels, 210 Po concentrations in biota were remarkably higher than concentrations of other radionuclides and showed a clear trend of biomagnification with increasing trophic levels, contrasting with the discrimination of U, Th and other radionuclides in the marine food chain. Radionuclides of artificial origin, namely 137 Cs, were present at very low level. Current radionuclide levels in marine biota do not represent a radiation hazard for sea food consumers. Highlights Coal mines discharges into the Bay enhanced U and Th levels in sediments Radioactivity in marine biota from the Bay was comparable to biota from other seas. Po was biomagnified in the marine food chain while U, Th, Ra, Pb were discriminated.