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.

Long-term study (1987-2023) on the distribution of 137Cs in soil following the Chernobyl nuclear accident: a comparison of temporal migration measurements and compartment model predictions.

After the Chernobyl accident, a designated area of ~1000 m2 within the University farm of Aristotle University of Thessaloniki in Northern Greece was utilized as a test ground for radioecological measurements. The profile of 137Cs in the soil was monitored from 1987 to 2023, with soil samples collected in 5-cm-thick slices (layers) down to a depth of 30 cm. The mean total deposition of 137Cs in the area, backdated to the time of the Chernobyl accident, was determined to be 18.6 ± 1.8 kBq m-2 based on four follow-up profile measurements of 137Cs in the soil for the years 2022 and 2023. It is noteworthy that this value is similar the total deposition at the site, which was independently measured to be about 20 kBq m-2 during the first year after the Chernobyl accident. The fractional contribution of each soil layer (e.g., 0-5 cm, 5-10 cm, 10-15 cm, etc.) to the total deposition of 137Cs (0-30 cm) is presented and analyzed. A compartment model was utilized to forecast the temporal evolution of fractional contributions of the different soil layers to the total deposition of 137Cs (0-30 cm). In this model, each soil layer is represented as a separate compartment. The model assumes that the transfer rates between adjacent compartments are equal. The agreement between the measured fractional contributions and the model predictions suggests that the compartment model with equal transfer rates can capture the broad patterns of 137Cs migration within the soil layers over the long period of 1987-2023. However, the use of a second compartment model with increasing transfer rates between consecutive soil layers did not align with the observed outcomes. This indicates that diffusion may not be the primary migration mechanism over the 36-y period covered by our study.

In-depth study of radon in water in a Greek village with enhanced radon concentrations.

This study focused on the radon transfer from the water to the air and the subsequent impact of waterborne radon indoors, taking advantage of the enhanced and decreasing from year to year radon-in-water concentrations observed in the Arnea village in Northern Greece. Some other essential aspects and observations regarding radon-in-water were also discussed. Concerning radon transfer from water to the air, the transfer efficiencies for showering and the use of the bathroom tap were estimated by measuring the radon-in-water and the waterborne radon-in-air concentrations in sealed bathrooms of two apartments in Arnea. The transfer efficiency for the bathroom tap use ranged from 22 to 28.9% for water flow rates of 2.7-7 L min-1. For showering, the transfer efficiency ranged from 45 to 48.3% for water flow rates of 6 L min-1 and 8 L min-1, respectively. As for the impact of waterborne radon indoors, each year's two-week monitoring of radon-in-water and radon-in-air concentrations in a house in Arnea from 2018 to 2022 revealed rapid and sharp increases in the bathroom air related to waterborne radon. Following the results obtained in the house's bathroom in Arnea, showering is the most significant exposure of humans to waterborne radon due to the person's proximity to waterborne radon, the enclosed space, the high transfer efficiency of showering, and the significant amount of water consumed. Each year's two-week average indoor radon concentrations measured in the examined house in Arnea showed that waterborne radon's contribution is less important than the other parameters affecting indoor radon, such as ventilation rates and radon emanation from the soil beneath the house's structure. Time variation (2018-2022) of radon activity concentration measured in a borehole supplying Arnea with water showed a relatively low standard deviation (10.2%) at a coverage factor of k = 1. A disequilibrium was observed between radon and its progenies immediately after pumping water from a borehole. This disequilibrium was observed for 1.3 years and seems to be continuous. Regarding radon removal from water, the diffused bubble aeration System constructed in Arnea reduces the radon-in-water activity concentration by more than 90% when using an air-to-water ratio of 10:1 and a detention time of 60 min. The System does not affect the adjacent outer space radon-in-air concentrations.