Indoor Radon Exposure and Age-Dependent Lung Retention Modelling in Murang’a County, Kenya
Abstract
Indoor radon (²²²Rn), from the ²³⁸U decay chain via ²²⁶Ra is a major natural radiation source and a recognized lung carcinogen through inhalation of its short-lived alpha-emitting progeny, particularly ²¹⁸Po and ²¹⁴Po. This study quantified indoor radon concentrations in Murang’a County, Kenya, and modelled age-dependent respiratory deposition, retention (lung inventories), and annual effective doses using the International Commission on Radiological Protection (ICRP) Human Respiratory Tract Model (HRTM). Radon concentrations were measured in 30 residential houses using a RAD7 detector, with values ranging from 9.74 to 54.23 Bq m⁻³. The verified dataset was used consistently for the concentration, inventory, and dose analyses. The revised computational model incorporated the 11-compartment HRTM structure of ICRP Publication 130, with the age-dependent dosimetric framework and homeradon dose coefficients of ICRP Publication 158. The three study groups were mapped to the ICRP reference ages of 3 months, 10 years, and adult. An equilibrium factor of 0.4 and agespecific mean home breathing rates of 0.12, 0.56, and 0.78 m³ h⁻¹ for infants, children, and adults, respectively, were applied. The model explicitly tracked the decay chain ²¹⁸Po → ²¹⁴Pb → ²¹⁴Bi → ²¹⁴Po and was solved numerically in Python using the BDF method. Lung inventories increased with indoor radon concentration and approached quasi-steady conditions within the simulated exposure period. Adults exhibited the highest retained physical lung inventories, whereas infants had the highest modelled annual effective doses. Mean progenyonly annual effective doses were 1.060, 0.830, and 0.811 mSv y⁻¹ for infants, children, and adults, respectively. The highest estimated infant dose occurred in House 8, which had the highest measured radon concentration of 54.23 Bq m⁻³. All radon concentration measurements obtained were lower than the reference values established by WHO and ICRP. These data show age-related variations in respiratory retention and radiation dose modelling and represent a quantitative basis for indoor radon exposure assessment in Murang’a County.