Plutonium: A novel soil erosion tracer in Eastern Africa

Soil erosion presents a significant risk to land degradation globally, with developing countries facing the greatest risk due to rapid expansion of agriculture, sometimes onto marginal land in response to rapid increases in population as well as the limited availability of land suitable for agriculture. In this study, the usability of plutonium (Pu) to determine soil redistribution rates within the Winam gulf catchment of western Kenya was investigated at sites with differing land use and clearance scale. Fallout Radionuclide inventories (unsupported 210Pb, 137Cs and 239+240Pu) were determined across seven suitable reference sites by gamma spectroscopy and ICP-MS/MS to test the applicability of Pu as a tracer of soil erosion. The lowest variability across the reference sites was found for 239+240Pu which can be attributed to increased sensitivity in detection by ICP-MS/MS compared to gamma spectroscopy. Subsequently 239+240Pu was used as a tracer at four study sites representing different land management approaches and history of land clearance of tropical rainforest. Plutonium showed interesting spatial characteristics for land management techniques highlighting the differences between top-down mitigation strategies and bottom-up (farmer led) mitigation strategies. In short, 239+240Pu presents a valuable tool for the determination of soil erosion rates in tropical Africa to increase understanding of land degradation. Therefore, providing reliable data to help decision making in the planning of appropriate mitigation strategies. This work demonstrates the potential for interdisciplinary benefits of research to be derived from novel analytical methodology to better inform land management.