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