Preliminary data of potentially hazardous radon concentrations in Modrič Cave (Croatia)

Authors

Robert Lončarić, Department of Geography, University of Zadar, CroatiaFollow
Vanja Radolić, Department of Physics, J. J. Strossmayer University of Osijek, CroatiaFollow
Maša Surić, Department of Geography, University of Zadar, CroatiaFollow
Igor Miklavčić, Department of Physics, J. J. Strossmayer University of Osijek, CroatiaFollow
Matea Šatalić, Speleological section Liburnija, Mountaineering Association Paklenica, Zadar, CroatiaFollow
Dalibor Paar, Department of Physics, University of Zagreb, CroatiaFollow
Lukrecija Obšivač, Speleological section Liburnija, Mountaineering Association Paklenica, Zadar, CroatiaFollow

Highlights

• Variations of radon concentrations are investigated in Modrič Cave (Croatia)
• Biogenic CO₂ as a carrier gas governs seasonal radon variations
• Morphology of two main passages controls spatial variations of radon
• The left, touristic passage is safe year round
• Maximal radon concentrations in the right passage can be considered a health hazard

Abstract

Instigated by relatively high cave-air CO₂ concentrations in Modrič Cave (Croatia) recorded for the purpose of speleothem-based paleoclimate research, we established preliminary monitoring of radon (²²²Rn) concentrations within the cave for a 4.5-year period (2018–2022). As radioactive geogenic gas, radon, which often correlates with cave-air CO₂ concentrations, presents a potential health hazard in cases of longer exposure time in high concentration conditions. Since the Modrič Cave is open to tourists and long-term scientific research has been performed within, a safety assessment for radon concentrations was essential. The integrated measurements of radon concentrations were performed by passive LR115 detectors that were exposed from three to six months at eight sites within the cave. Preliminary results showed seasonal variations of radon concentrations (0.08–13.6 kBq/m³) governed by the cave ventilation patterns, but superimposed on this, cave morphology and bedrock architecture control the radon variations on finer spatial scale. The 3-months average ²²²Rn concentration of up to 13.6 kBq/m³ during summer in one of the cave passages is among the highest measured seasonal averaged radon concentrations in Croatian caves, but maximum concentrations were even higher. Based on obtained results and calculations, potential negative health effects of radon exposure for cave visitors, guides and scientists were assessed and the results showed values of exposure to be below recommended levels. Calculated worst-case scenario for cave guides (most affected by radon and its progeny) revealed that they would receive dose slightly below the occupational dose limit of 20 mSv/y (19.0 ± 5.2 mSv/y) in the touristic part of the cave and significantly higher doses (34.1 ± 9.2 mSv/y) in the non-touristic part of the cave. To detect precise spatio-temporal radon concentration variations (up to diurnal scale) we recently established continuous radon measurements. This will enable detection of possibly health threatening short-term peaks in radon concentration and consequently further improve cave management.

DOI

https://doi.org/10.5038/1827-806X.52.1.2469

Creative Commons License

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.

Recommended Citation

Lončarić, R., Radolić, V., Surić, M., Miklavčić, I., Šatalić M., Paar, D., Obšivač, L., 2023. Preliminary data of potentially hazardous radon concentrations in Modrič Cave (Croatia). International Journal of Speleology, 52(1), 65-74. https://doi.org/10.5038/1827-806X.52.1.2469