Assessment and mapping of the high background radiation anomaly associated with laterite utilization in the south coastal region of Kenya

Laterite is commonly used in Kenya and other tropical countries as an aggregate material for road paving. However, the use and relocation of laterite and other geological materials from high background radiation areas (HBRA) may increase exposure to ionizing radiation in areas that were originally at background radiation levels. We present the results of an in-situ radiometric survey conducted at sites associated with laterite utilization around the Mrima Hill HBRA and adjoining environs along a section of the main road in south coastal region of Kenya. The goal of this study was to determine the levels of primordial radionuclides, as well as to assess and map the associated radiation exposure due to the modified radiation field resulting from the use of laterite in the region. It was found that air absorbed gamma dose-rates on parts of the road and side road intersections (median values are 326 ± 52 and 987 ± 138 nGy h−1, respectively) range 4–14 times higher than the adjoining areas. This anomaly was attributed to elevated levels of 238U and 232Th (activity concentrations range 202–1452 Bq kg−1 and 315–1579 Bq kg−1, respectively) measured adjacent to the laterite roadbeds. In addition, results from the energy dispersive X-ray fluorescence analysis of lateritic soils showed that Th correlates positively with monazite constituent elements namely P, La, Ce and Nd suggesting that the laterite used for road paving in parts of the region was sourced from Mrima Hill.