Assessing radioactive contaminants in Kathmandu soils: measurement and risk analysis

Soil samples from vegetable farmland in densely populated wards of Nepal were analyzed for natural radionuclide levels, employing a NaI(Tl) 3” \(\times \) $\times$ 3” gamma detector. The study aimed to evaluate the causes of radiation risk, attributing it to soil contamination resulting from the rapid urbanization and concretization that followed the earthquake in 2015. The activity concentration of radium-226, thorium-232, and potassium-40 and the ranges observed are 2.080±0.084–33.675±1.356 Bq kg \(^{-1}\) ${}^{-1}$ , 17.222±0.198–119.949±1.379 Bq kg \(^{-1}\) ${}^{-1}$ , and 11.203 ± 0.325–748.828±21.716 Bq kg \(^{-1}\) ${}^{-1}$ , respectively. The average values obtained for hazard indices are as follows: radium equivalent activity (82.779 Bq kg \(^{-1}\) ${}^{-1}$ ), absorbed dose rate (36.394 nGy h \(^{-1}\) ${}^{-1}$ ), annual effective dose equivalent (0.045 mSv yearr \(^{-1}\) ${}^{-1}$ ), gamma index (0.291), external hazard index (0.224), internal hazard index (0.253), excess lifetime cancer risk (0.159), annual gonadal dose equivalent (243.278 mSv year \(^{-1}\) ${}^{-1}$ ), alpha index (0.054), and activity utilization index (0.716). However, in most places, thorium-232 concentration is greater than those of the world average and recommended values. In specific locations such as Ward 4 in Baluwatar, the soil was found to have concentrations of Ra \(^{226}\) ${}^{226}$ and K \(^{40}\) ${}^{40}$ exceeding recommended limits. Despite this localized concern, the overall analysis of hazard indices across the studied areas revealed that most values were within permissible limits. This suggests that, on a broader scale, radiation exposure may not be a significant concern in the investigated regions. Nonetheless, the study recommends regular monitoring in additional locations to ensure a comprehensive and ongoing assessment of radiation levels.