Caesium-137 in Southeast Asia: Is there enough left for soil erosion and sediment redistribution studies?

Low reference inventories of the fallout radionuclide Cs-137 in low latitudes may limit its present and future application for studies of soil erosion and sediment redistribution in Southeast Asia. Cs-137 reference inventories and concentrations in surface materials measured in nine and five areas, respectively, across Southeast Asia are here reported and reviewed. The compiled reference inventories decrease from north to south. Three global estimates of Cs-137 total fallout are also reviewed and compared to the measured data while taking into account factors that affect the fallout estimates and the reference inventory. The results are presented as a schematic regional distribution map of Cs-137 reference inventories for the year 2012. A relationship between a reference inventory and topsoil concentration is also provided. The measured Cs-137 concentrations suggest that a minimum detectable activity (MDA) less than 0.5 Bq/kg is required for detection of Cs-137 activity in topsoils in the lowest reference inventory areas. This sensitivity should allow, at present, Cs-137 to be a useful tool for analysis of soil erosion in Southeast Asia, should also be a useful chronometer, and will be a useful tracer at least where the reference inventory is more than 500-600 Bq/m(2). This level of MDA has been demonstrated in previous studies to be achievable by gamma-ray spectrometry using non-destructive sample treatment. As the nuclide decays, sufficient will remain to be useful until the middle of this century in most areas in Peninsular Malaysia and southern maritime Southeast Asia, and a few decades more in the rest of the region. (C) 2013 Elsevier Ltd. All rights reserved.