Gamma radioactivity in podzolic soils of Northern Ontario, Canada

Abstract

Naturally occurring gamma radionuclides 226Ra, 232Th, 40K and anthropogenic 137Cs were measured in podzolic soils derived from calcareous gravel storm ridges in the Hudson and James Bay Lowlands of northern Ontario. The soils were sampled by genetic horizon so as to investigate the relationship between pedogenesis and the radionuclide distribution. The mean concentration of 40K was comparable to levels in other soils. However 226Ra and 232Th had means considerably lower than the world-wide average. This was likely a function of the coarse nature of the storm ridge parent materials. 137Cs decreased exponentially with soil depth. The organic surface layers of the soils retained the 137Cs, although the 137Cs did appear to extend to greater depths in the organic surfaces relative to the mineral portions of the soil profiles. Generally, the concentrations of 226Ra, 232Th, and 40K increase in the solum with the progressive dissolution of carbonates with time. However, there is evidence that 232Th and 226Ra are weathering out of primary mineral grains in the Ae horizon and are transported to the B horizon through the podzolization process. Preliminary data suggest that the background radioactivity in these soils is correlated with finer particle sizes. 137Cs correlated with total precipitation in the area, with the exception of Akimiski Island where the greatest amount of 137Cs was deposited.