Risk assessment from radon in domestic water for the Greek population

This study focused on assessing the risk from the exposure to radon contained in domestic water for a significant part (~20%) of the Greek population. Also, the variation of radon in domestic water was monitored from 2017 to 2023 in certain villages that showed relatively high radon levels and relied on boreholes for their water supply. The radon in domestic water activity concentrations measured in the investigated Greek places ranged from lower than the minimum detection limit (2 Bq L-1) levels up to 187 Bq L-1 with an average value of 9.1 Bq L-1. Overall, higher radon in domestic water activity concentrations were observed in places supplied from boreholes located inside granitic and metamorphic rock areas. Only one out of the 487 examined places, which accounts for 0.015% of the examined Greek population, showed an average radon-in-water activity concentration higher than the parametric value of 100 Bq L-1 adopted by Greece following the EURATOM Directive (2013/51/EURATOM). Therefore, radon-in-water does not pose a health concern (risk) for the investigated Greek population. The total (inhalation and ingestion) annual effective doses to adults, corresponding to the measured radon-in-water activity concentrations, ranged from nearly 0 to 1.20 mSv y-1 with an average value of 0.059 mSv y-1, while for children, they ranged from almost 0 to 1.26 mSv y-1 with an average value of 0.061 mSv y-1. Regarding the variation of radon in domestic water monitoring, places supplied with water from one borehole showed no significant fluctuations from their average radon-in-water activity concentration, with standard deviations of ~20% at a coverage factor of k = 1. Even though some places supplied from three to four boreholes showed no significant fluctuations (standard deviation <= 30% at k = 1) from their average radon level, special attention is needed for places supplied from many boreholes when one measurement over the year is to be performed for the annual effective dose assessment. This is because the prevailing during-year borehole combination may not exist on the measurement day, resulting in an underestimated or overestimated dose assessment. Radon removal from domestic water supplies in the Arnea village (due to elevated radon-in-water activity concentrations) did not affect the inhalation risk for the residents of an examined house in Arnea. However, radon removal from the water supply was essential to reduce the ingestion risk for the house occupants. There is a possibility of radiation overexposure (>20 mSv y-1) for the workers in a thermal spa on Ikaria Island, and further investigation needs to be conducted with extended measurement periods.