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., 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.