Exploring the long-term balance between radon mitigation systems and human behaviour in Romanian houses.

Radon is a naturally occurring radioactive gas that has high carcinogenic potential and may constitute a significant public health problem. The long-term effectiveness of radon mitigation systems is often assumed, yet rarely questioned beyond initial implementation. This study investigates the long-term performance of mitigation systems after installation, based on continuous monitoring conducted over several years. Ten Romanian dwellings served as case studies illustrating the interaction between technical remediation measures and various patterns of occupant behaviour. The remediation methods included sub-slab depressurization (SSD), heat recovery ventilation, both centralized (CHRV) and decentralized (DHRV), and the use of radon barriers. The results showed a variable efficiency of the remediation methods, with average radon concentration reduction values ranging from -8 % to 91 %, and an overall median of 59 %. The SSD-based remediation methods demonstrated superior performance and better stability over time, recording an average efficiency of 86 %, while the CHRV and DHRV systems showed much higher variability and a decline in efficiency over time. One of the most critical factors contributing to the success of the remediation was user behaviour, with intermittent use, disconnecting of systems, or lack of maintenance leading to increases in post-remediation radon concentration, in some cases even above pre-remediation levels. In contrast, the active involvement of the occupants, including constant monitoring and prompt reaction to malfunctions, ensured that low radon levels (below 50 Bq/m) were maintained. The findings suggest that maintaining low radon levels over time requires more than just technical interventions, highlighting the importance of a balanced interaction between automated systems and occupant engagement. These results highlight the need for public policies that combine engineering solutions with behavioural, educational, and ongoing support strategies to maintain the effectiveness of residential radon safeguards.