Temporal and Spatial Variation of Radon Concentrations in Environmental Water from Okinawa Island, Southwestern Part of Japan

Shunya Nakasone, Akinobu Ishimine, Shuhei Shiroma, Natsumi Masuda, Kaori Nakamura, Yoshitaka Shiroma, Sohei Ooka, Masahiro Tanaka, Akemi Kato, Masahiro Hosoda, Naofumi Akata, Yumi Yasuoka and Masahide Furukawa
Additional contact information
Shunya Nakasone: Graduate School of Engineering and Science, University of the Ryukyus, Nishihara, Okinawa 903–0213, Japan
Akinobu Ishimine: Department of Radioecology, Institute for Environmental Sciences, Rokkasho, Aomori 039–3212, Japan
Shuhei Shiroma: Faculty of Science, University of the Ryukyus, Nishihara, Okinawa 903–0213, Japan
Natsumi Masuda: Faculty of Science, University of the Ryukyus, Nishihara, Okinawa 903–0213, Japan
Kaori Nakamura: Graduate School of Engineering and Science, University of the Ryukyus, Nishihara, Okinawa 903–0213, Japan
Yoshitaka Shiroma: Faculty of Education, University of the Ryukyus, Nishihara, Okinawa 903–0213, Japan
Sohei Ooka: Nanto Co., Ltd., Naha, Okinawa 900–0013, Japan
Masahiro Tanaka: Department of Helical Plasma Research, National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Gifu 509–5292, Japan
Akemi Kato: Department of Engineering and Technical Services, National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Gifu 509–5292, Japan
Masahiro Hosoda: Department of Radiation Science, Hirosaki University Graduate School of Health Sciences, Hirosaki, Aomori 036–8564, Japan
Naofumi Akata: Department of Radiation Chemistry, Institute of Radiation Emergency Medicine, Hirosaki University, Hirosaki, Aomori 036–8564, Japan
Yumi Yasuoka: Radioisotope Research Center, Kobe Pharmaceutical University, Kobe, Hyogo 658–8558, Japan
Masahide Furukawa: Graduate School of Engineering and Science, University of the Ryukyus, Nishihara, Okinawa 903–0213, Japan

IJERPH, 2021, vol. 18, issue 3, 1-12

Abstract: In this study, to get a better understanding in characterizing groundwater and ensure its effective management, the radon concentrations in water samples were measured through Ryukyu limestone in southern Okinawa Island, Japan. Water samples were collected from a limestone cave (Gyokusendo cave, dropping water) and two springs (Ukinju and Komesu, spring water), and the radon concentrations were measured by liquid scintillation counters. The radon concentrations in the samples from the Gyokusendo cave, and Ukinju and Komesu springs were 10 ± 1.3 Bq L −1 , 3.2 ± 1.0 Bq L −1 , and 3.1 ± 1.1 Bq L −1 , respectively. The radon concentrations showed a gradually increasing trend from summer to autumn and decreased during winter. The variation of radon concentrations in the dripping water sample from the Gyokusendo cave showed a lagged response to precipitation changes by approximately 2–3 months. The estimated radon concentrations in the dripping water sample were calculated with the measured radon concentrations from the dripping water obtained during the study period. Based on our results, groundwater in the Gyokusendo cave system was estimated to percolate through the Ryukyu limestone in 7–10 days, and the residence time of groundwater in the soil above Gyokusendo cave was estimated to be approximately 50–80 days. This work makes a valuable contribution to the understanding of groundwater processes in limestone aquifers, which is essential for ensuring groundwater sustainability.

Keywords: radon concentration; groundwater; residence time; limestone aquifer; Okinawa Island (search for similar items in EconPapers)
JEL-codes: I I1 I3 Q Q5 (search for similar items in EconPapers)
Date: 2021
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