The levels of radioactive gas in three well-known caves in Bohol are higher than international safety standards

09 Jul 2026

Caves are popular tourist spots in the Philippines, especially in places like Bohol Island. But while they attract visitors with their natural beauty, they may also expose people to something invisible and dangerous—radioactive gases like radon and thoron. Our research is the first in the Philippines to measure the levels of these gases inside caves. We focused on three well-known caves in Bohol: Hinagdanan, Batungay, and Princess Manan-aw.

Using a scientific device called a CR-39 detector, we found that radon levels in all three caves were higher than international safety limits, especially in deeper parts where air doesn’t circulate well. Tourists are generally safe because they don’t stay in the caves very long. However, cave guides who work inside these caves regularly may receive radiation doses that could be harmful to their health over time. This is especially true in Batungay Cave, where some estimated doses may even exceed the allowable limit for occupational exposure, with estimated doses for workers surpassing the national occupational exposure limit of 20 mSv/y.

We also discovered that radon levels vary depending on the cave’s structure, airflow, and rock type. But since our data was only gathered during one season, we caution that these results might not reflect the whole year. This study highlights the need for further monitoring and safety measures, especially for workers. It also supports future efforts to protect both people and the environment in tourist caves. In short, our research aims to make cave tourism safer—not to discourage it, but to improve how we manage it.

This study presents the first comprehensive assessment of radon and thoron concentrations in cave environments in the Philippines. The results underscore the potential health risks in cave tourism and the need for improved radiation protection measures. The study contributes novel data from a tropical setting, offering insights into radon and thoron behavior in warm, humid climates where seasonal variability is less pronounced. It highlights the influence of cave structure, geology, and ventilation on gas distribution. Beyond advancing local scientific knowledge, the study supports national efforts to strengthen environmental monitoring, cave management, and occupational safety. It also provides a foundation for regulatory updates and future research on radon exposure in natural tourist sites across the Philippines.

Authors: Angelo A. Panlaqui (Environmental Engineering Program, College of Engineering, University of the Philippines Diliman | Department of Science and Technology, Philippine Nuclear Research Institute), Florencio C. Ballesteros Jr. (Environmental Engineering Program, College of Engineering, University of the Philippines Diliman), Kristine Marie R. Dean (Department of Science and Technology, Philippine Nuclear Research Institute), Chutima Kranrod (Institute of Radiation Emergency Medicine, Hirosaki University), and Shinji Tokonami (Institute of Radiation Emergency Medicine, Hirosaki University)

Read the full paper: http://doi.org/10.1016/j.net.2025.103702

The levels of radioactive gas in three well-known caves in Bohol are higher than international safety standards

Caves are popular tourist spots in the Philippines, especially in places like Bohol Island. But while they attract visitors with their natural beauty, they may also expose people to something invisible and dangerous—radioactive gases like radon and thoron. Our research is the first in the Philippines to measure the levels of these gases inside caves. We focused on three well-known caves in Bohol: Hinagdanan, Batungay, and Princess Manan-aw.

Using a scientific device called a CR-39 detector, we found that radon levels in all three caves were higher than international safety limits, especially in deeper parts where air doesn’t circulate well. Tourists are generally safe because they don’t stay in the caves very long. However, cave guides who work inside these caves regularly may receive radiation doses that could be harmful to their health over time. This is especially true in Batungay Cave, where some estimated doses may even exceed the allowable limit for occupational exposure, with estimated doses for workers surpassing the national occupational exposure limit of 20 mSv/y.

We also discovered that radon levels vary depending on the cave’s structure, airflow, and rock type. But since our data was only gathered during one season, we caution that these results might not reflect the whole year. This study highlights the need for further monitoring and safety measures, especially for workers. It also supports future efforts to protect both people and the environment in tourist caves. In short, our research aims to make cave tourism safer—not to discourage it, but to improve how we manage it.

This study presents the first comprehensive assessment of radon and thoron concentrations in cave environments in the Philippines. The results underscore the potential health risks in cave tourism and the need for improved radiation protection measures. The study contributes novel data from a tropical setting, offering insights into radon and thoron behavior in warm, humid climates where seasonal variability is less pronounced. It highlights the influence of cave structure, geology, and ventilation on gas distribution. Beyond advancing local scientific knowledge, the study supports national efforts to strengthen environmental monitoring, cave management, and occupational safety. It also provides a foundation for regulatory updates and future research on radon exposure in natural tourist sites across the Philippines.

Authors: Angelo A. Panlaqui (Environmental Engineering Program, College of Engineering, University of the Philippines Diliman | Department of Science and Technology, Philippine Nuclear Research Institute), Florencio C. Ballesteros Jr. (Environmental Engineering Program, College of Engineering, University of the Philippines Diliman), Kristine Marie R. Dean (Department of Science and Technology, Philippine Nuclear Research Institute), Chutima Kranrod (Institute of Radiation Emergency Medicine, Hirosaki University), and Shinji Tokonami (Institute of Radiation Emergency Medicine, Hirosaki University)

Read the full paper: http://doi.org/10.1016/j.net.2025.103702