Abstract
222Rn and 226Ra concentrations of less than a few to several thousands of Bq L−1 have been observed in several underground bodies of water around the world. Although regulations for these concentrations in water have been implemented internationally, there are currently no regulations in place in Japan. However, concentrations that exceed these internationally recognized regulatory values have also been observed in Japan. In this study, concentrations in spring water in the northern part of Japan were measured and the effective dose from intake of the water was evaluated. 222Rn concentrations were measured using a liquid scintillation counter, and 226Ra concentrations were measured using a high purity germanium detector after chemical preparation. The measured 222Rn concentrations (=12.7 ± 6.1 Bq L−1) and 226Ra concentrations (<0.019–0.022 Bq L−1) did not exceed the reference values set by international and European/American organizations. A conservative estimate of the annual effective ingestion dose of 8 μSv for 222Rn and 226Ra obtained in this study is much smaller than the estimated overall annual effective dose of 2.2 mSv from natural radiation to the Japanese population. However, this dosage accounts for 8% of the WHO individual dosing criteria of 0.1 mSv/year for drinking water.
Highlights
It is well known that 222 Rn, a decay product of 226 Ra, is the second leading cause of lung cancer after tobacco smoking [1]
226 Ra concentrations were below the minimum detectable concentrations (MDCs) at many sites
The conservative annual effective ingestion dose for 222 Rn and 226 Ra obtained in this study of 8 μSv is significantly smaller than the estimated overall annual effective dose of 2.2 mSv from natural radiation (=2.2 mSv) to the Japanese population [41]
Summary
It is well known that 222 Rn, a decay product of 226 Ra, is the second leading cause of lung cancer after tobacco smoking [1]. Since 226 Ra and 222 Rn are water soluble, groundwaters may contain 226 Ra and 222 Rn. The sources of 226 Ra to the groundwater-phase result from the decay of dissolved 230 Th, the dissolution of 226 Ra-containing rocks, α-recoil associated with the α-decay of 230 Th located in mineral surface layers, and the desorption.
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