Activity concentration levels of natural radionuclides in soils of Anambra State, South-east Nigeria

Much focus has not been paid to mapping of radionuclides in sedimentary formation in Nigeria. Thus, the relevance of this study which measured (mapped) the activity levels of radionuclides in the soils of Anambra State, Nigeria. Anambra State underlain by a younger sedimentary formation was chosen, as radionuclides levels in soils of older, consolidated sedimentary rocks and Basement complex rocks in Nigeria have been studied. To contribute to radionuclide mapping in Nigeria, the study measured radionuclides in soils of a predominantly sedimentary geologic formations much under-studied in Nigeria, and assessed how seasonal changes influences natural radionuclides levels in soil. The study was conducted for the year 2022 dry and wet seasons of 2022. The study area was stratified into two geological formations, and twenty sampling points used. The major study objective is to determine the activity level of the radionuclides (U-238, Th-232, K-40, Ra-226)in the soil and; determine whether there is variation between the seasons (dry and wet). Our results show that there were variations in the levels of radionuclides (U-238, Th-232, K-40, Ra-226) between the dry and wet seasons in the four locations of the study area based on the geologic formation. The levels of the radionuclides are generally higher in dry season than the wet season (U-238, Th-232, K-40, Ra-226). This was attributed to lack of moisture, which dampens gamma radiation. The study also showed that the levels of U-238 and Th-232 were significantly higher than their respective UNSCEAR (2000) population weighted averages in Ayamelum (Imo Shale), while they were significantly lower in the other locations- Orumba North (Imo Shale), Anambra East and Aguata (Nanka Shale),. The levels of Ra-226 levels were significantly higher than UNSCEAR (2000) population weighted averages in all the locations. However, the levels of K-40 in all the locations were significantly lower than the population weighted averages. The study results also showed that statistically, the levels of U-238, Th-232 and Ra-226 in the soils varied between the two seasons (wet and dry). However, there was no statistically significant difference in the level of K-40 between the two seasons. The result finding therefore implies that season influences the levels of U-238, Th-232 and Ra-226 in the soils of Anambra State. Many other factors such as environmental, may be influencing the significant variations in radionuclides levels (U-238 and Th-232) in soils at different locations in the study area underlain by the same geologic formation.