Distribution of natural radionuclides and Cs-137 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. T he soil is also the main source of radon exposure to humans. Therefore it i s important to know the background levels of natural and anthropogenic radi oactivity in soils. In this study the radionuclides K-40, Ra-226, Th-232 an d (CS)-C-137 were measured in the soils of southwestern Ontario in order to determine the background levels and to understand the soil profile distrib ution. 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 o f these radionuclides is further influenced by pedogenic processes, particu larly 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 s oil animals such as earthworms and groundhogs, soil erosion and soil organi c matter cycling. Multiple regression analysis showed that clay content, sa nd content, percent CaCO3, pH and organic carbon content had variable influ ences on each of the radionuclide contents in the soil.