Radon and thoron in the ambient air of the caves in Bohol Island, Philippines

Radon and thoron concentrations in the ambient air were investigated in the caves of Bohol Island, Philippines. The study focused on Hinagdanan, Batungay, and Princess Manan-aw Caves to establish the baseline data on current radon and thoron levels and estimate the effective doses absorbed by tourists and workers during tour operations, specifically due to radon and its progeny. Radon and thoron were measured using a CR-39-based detector called the Raduet, which was placed along the cave pathways. Radon concentration inside the caves ranges from 127 to 1829 Bq m −3 , while thoron concentration varies from 28 to 1574 Bq m −3 . Results showed that radon levels in all three caves exceeded the recommended safety limit (300 Bq m −3 ), which may have been influenced by cave structures affecting natural ventilation. Despite the high radon concentrations in these caves, tourists are generally safe due to low exposure time. However, the estimated annual effective dose for cave guides was found to vary from 0.77 to 46.27 mSv y −1 . If uncontrolled, doses to occupationally exposed workers due to radon and thoron may exceed the country's national dose limit (20 mSv y −1 ) and may increase the risks of health effects.