Natural and anthropogenic radionuclides in selected environmental radioactivity monitoring sites in Singapore

This paper provides insights into the radioactivity levels in soils and marine sediments from selected monitoring sites in Singapore. The environmental samples were measured for naturally occurring (e.g., K-40, U-238, U-235, U-234 and Th-232) and anthropogenic (e.g., Sr-90, Cs-137, Pu-239 and Pu-240) radionuclides. Additionally, the Cs-137 activity in surface seawater was analysed. In soil, the decay series of Th-232 and U-238 are the highest contributors to the total radioactivity, while in sediments, K-40 is the main contributor to the total radioactivity. The massic activities of anthropogenic radionuclides in soil (Sr-90: 0.24-0.34 Bq kg(-1); Cs-137: < 0.3-0.65 Bq kg(-1); Pu239+240: 0.002-0.057 Bq kg(-1)) and sediment (Sr-90: 0.15-0.17 Bq kg(-1); Cs-137: < 0.46-0.54 Bq kg(-1); Pu239+240: 0.239-0.294 Bq kg(-1)), and the activity concentration of Cs-137 in seawater (Cs-137: 1.1 mBq kg(-1)), are low and comparable to the values reported for the region. The Pu isotope data demonstrates that the main source of anthropogenic radionuclides in soil (Pu-240/Pu-239 atom ratios: 0.17-0.19) is the global fallout from nuclear weapons testings (NWTs); in sediments (Pu-240/Pu-239 atom ratios: 0.24-0.26), contributions from the Pacific Proving Grounds (PPG) have also been identified. This study also highlights significant differences in radioactivity levels in soils between the northern and central regions of Singapore, which are attributed to soil disturbances in the northern region as a result of intensive anthropogenic activities carried out in the 1980s.