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

Abstract 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., 40 K, 238 U, 235 U, 234 U and 232 Th) and anthropogenic (e.g., 90 Sr, 137 Cs, 239 Pu and 240 Pu) radionuclides. Additionally, the 137 Cs activity in surface seawater was analysed. In soil, the decay series of 232 Th and 238 U are the highest contributors to the total radioactivity, while in sediments, 40 K is the main contributor to the total radioactivity. The massic activities of anthropogenic radionuclides in soil ( 90 Sr: 0.24–0.34 Bq kg −1 ; 137 Cs: < 0.3–0.65 Bq kg −1 ; 239+240 Pu: 0.002–0.057 Bq kg −1 ) and sediment ( 90 Sr: 0.15–0.17 Bq kg −1 ; 137 Cs: < 0.46–0.54 Bq kg −1 ; 239+240 Pu: 0.239–0.294 Bq kg −1 ), and the activity concentration of 137 Cs in seawater ( 137 Cs: 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 ( 240 Pu/ 239 Pu atom ratios: 0.17–0.19) is the global fallout from nuclear weapons testings (NWTs); in sediments ( 240 Pu/ 239 Pu 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.