Indoor Radon Concentrations and Associated Health Effects: A Review

This paper presents a review of research on indoor radon concentrations in 27 countries worldwide, focusing on residential buildings, workplaces, schools, and kindergartens, as well as the health effects of long-term radon exposure. The analysis included radon measurements and epidemiological studies on the association between radon exposure and the risk of lung cancer. The results show significant regional variability in radon concentrations, influenced by geological characteristics, building age, construction materials, ventilation, and climatic factors. Concentrations ranged from <20 Bq/m3 to 56,000 Bq/m3. The highest values were recorded in Sweden, Norway, the Czech Republic, Serbia, Montenegro, Poland, Albania, Croatia, Hungary, and Slovenia, while lower concentrations were generally observed in some countries in Africa and Asia. Particularly elevated concentrations were recorded in schools and kindergartens, highlighting the need for systematic monitoring, especially among children. Epidemiological and cohort studies provide significant evidence of an association between radon and an increased risk of lung cancer. Meta-analyses indicate an increase in risk of approximately 5–15% for every 100 Bq/m3 increase in radon concentration, while estimates suggest that radon may be responsible for approximately 3–20% of lung cancer mortality and a significant proportion of cases among never-smokers. The synergistic effect of radon and smoking is particularly significant. Biological mechanisms include alpha radiation from radon progeny, DNA damage, oxidative stress, chronic inflammation, and genetic changes associated with carcinogenesis. Most epidemiological evidence supports a linear no-threshold relationship between radon and lung cancer risk, although some studies at concentrations <200–250 Bq/m3 have not demonstrated a statistically significant increase in risk. Debate regarding the effects of low concentrations continues, including the linear no-threshold model and the hypothesis of ionizing radiation-induced hormesis. Despite substantial evidence, gaps remain in knowledge and risk management. Epidemiological studies show heterogeneity in study design, measurement methodology, exposure assessment, and control of confounding factors, while radon potential maps and comprehensive monitoring are unavailable in many countries. In countries with elevated concentrations, risk management systems are often insufficiently developed. Standardized measurement procedures, continuous monitoring, improved mapping, harmonized exposure assessment, and more reliable epidemiological models are needed, together with strengthened national action plans and integrated strategies to reduce exposure and the associated health burden.