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

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.

Radon Levels and Risk Assessment due to its Ingestion and Inhalation from Groundwater of Lapai, North-Central Nigeria

“…However, the obtained concentration levels are relatively low in contrast to some of the values in the range of 2.1 ± 0.7 BqL -1 to 27.9 ± 2.5 BqL -1 and 2.8 ± 1.1 BqL -1 to 39.5 ± 1.5 BqL -1 that was obtained respectively for open well and borehole groundwater samples of the Bosso community, North-Central Nigeria (Kolo et al, 2023). The two communities share the same geology; hence, the disparity in values could be attributed to the seasonal difference since the measurements for the groundwater of Bosso were made during the rainy season when concentration levels are usually at their peak (Nakasone et al, 2021) as opposed to the present research where the samples were collected in the dry season when the concentration of Radon is likely low.…”

“…Radon ( 222 Rn) is a colorless, odorless, and inert alphaemitting gas soluble in water and absorbed by underground water when released from surrounding soil and rocks. Its concentration in underground water depends on factors such as temperature, type of surrounding rock formation, and environmental pollution (Nagaraja et al, 2019;Nakasone et al, 2021;Yong et al, 2021). In addition, the radon concentration in groundwater is subject to seasonal variations, with concentration levels becoming high in summer, highest in autumn, and lowest in winter (Nakasone et al, 2021).…”

“…Its concentration in underground water depends on factors such as temperature, type of surrounding rock formation, and environmental pollution (Nagaraja et al, 2019;Nakasone et al, 2021;Yong et al, 2021). In addition, the radon concentration in groundwater is subject to seasonal variations, with concentration levels becoming high in summer, highest in autumn, and lowest in winter (Nakasone et al, 2021). The ingestion of Radon dissolved in water and its inhalation when released from water constitute dose contributions to the stomach and lungs, respectively.…”

A Preliminary Study of Radon Equilibrium Factor at a Tourist Cave in Okinawa, Japan

“…It is now a part of the tourist attraction called "Okinawa World" and is visited by one million people a year. Gyokusen-do Cave is a limestone cave situated in a 120-m-thick body of Ryukyu limestone; its total length reaches 5000 m, of which approximately 900 m is open for tourism [24,25].…”