Residential and occupational exposure to indoor radon and associated human health risk in Nigeria buildings assessed by multiple monitoring techniques.

Indoor radon exposure is a significant public health concern, as it is the second leading cause of lung cancer globally. This systematic review evaluated radon concentrations and associated health risks in Nigerian buildings, including homes, schools, and workplaces, through various monitoring techniques such as CR-39 detectors and RAD7 monitors. A total of 47 eligible studies were included following PRISMA guidelines that covered the spatial variations of radon exposure across Nigeria, revealed a weighted mean indoor radon concentration of 104 Bq/m, exceeding the WHO reference level of 100 Bq/m but below the USEPA action level of 148 Bq/m. Certain locations such as Odo-Ona, Ibadan, recorded 531.85 Bq/m, corresponding to an annual effective dose of 13.42 mSv/yr, an excess lifetime cancer risk of 51.66 × 10, and an estimated lung cancer burden of 242 cases/year per million people. Other regions, including Sokoto Metropolis and Oke-Ogun, also exceeded safety limits, while coastal areas like Lagos showed the lowest concentrations (7.52 Bq/m). Geographic disparities were evident, with southwestern Nigeria showing the highest risk and accounting for 63 % of studies, while northern and southeastern regions remain underrepresented. Comparative analysis revealed that Nigerian hotspots surpass radon levels reported in several radon-prone countries, including Bulgaria and Northwest Spain, highlighting a significant health risk. This review presents Nigeria's first indoor radon exposure map in residential and occupational settings nationwide that clearly identified critical hotspots and emphasizing the urgent need for targeted interventions. Awareness of the presence of radon and its potential health effects is very low in Nigeria. Radon mitigation should integrate geological assessments with radon-resistant construction materials, proper ventilation, and sealed entry points, especially in uranium-rich and permeable soils. Public awareness, routine monitoring, and regulatory policies are essential, while future research should focus on underrepresented regions and uncover long-term exposure patterns.