Distribution of natural radionuclides and 137Cs in soils of southwestern Ontario

In Canada and the United States approximately 82% of the annual total dose of radiation to any person comes from terrestrial and cosmogenic sources. The soil is also the main source of radon exposure to humans. Therefore it is important to know the background levels of natural and anthropogenic radioactivity in soils. In this study the radionuclides K-40, Ra-226, Th-232 and (CS)-C-137 were measured in the soils of southwestern Ontario in order to determine the background levels and to understand the soil profile distribution. Clay content is the most important variable affecting the background levels of K-40, Ra-226, and Th-232 in the soil. The profile distribution of these radionuclides is further influenced by pedogenic processes, particularly carbonate leaching from the solum and clay illuviation from the Ae to the Bt horizons. The lateral and vertical distribution of bomb-fallout Cs-137 is influenced by soil management such as tillage, biopedoturbation by soil animals such as earthworms and groundhogs, soil erosion and soil organic matter cycling. Multiple regression analysis showed that clay content, sand content, percent CaCO3, pH and organic carbon content had variable influences on each of the radionuclide contents in the soil.