Assessment of indoor Radon concentration in monumental mosque minarets of Muğla Province, Türkiye: Geological correlations, building materials, and public health implications

Radon-222 (²²²Rn) is a radioactive, inert noble gas and a known carcinogen that is imperceptible to human senses. Due to its health risks and undetectable nature, understanding its indoor accumulation is critical for public safety. This study investigates indoor radon concentrations (IRCs) in 840 monumental mosque minarets (MMs) across 13 districts of Muğla Province, southwestern Türkiye, and examines their relationship with soil radon concentrations (SRCs), geological formations, building materials, and active fault lines. IRC and SRC were measured using RadonEye and Markus 10 devices, respectively, between 2018 and 2020, and spatial analyses were conducted using ArcGIS software. The highest IRC (2809 Bq/m³) was recorded in Marmaris in a minaret constructed from uranium-rich volcanic rocks, while the highest SRC (120 000 Bq/m³) was observed in Bodrum in alluvium derived from similar lithologies near active faults. Conversely, the lowest SRC (1000 Bq/m³) was found in Datça in peridotite-derived alluvium. Approximately 10 % of MMs exceeded the European Indoor Radon Reference Value (EIRRV) of 200 Bq/m³, with 30 % and 40 % surpassing 300 and 400 Bq/m³, respectively. These findings highlight the urgent need for systematic radon monitoring and mitigation in buildings, particularly in geologically susceptible regions, to reduce long-term public health risks.