Natural radioactivity of thermal springs in Croatia

The objective of this paper was to estimate total natural radioactivity (226Ra, 228Ra decay) in thermal and mineral waters used for bathing and drinking for the purpose of rehabilitation and medical therapy as well as sports and recreation from the several spas in Croatia. The study was also designated to estimate dose contribution from thermomineral waters of Croatia to total exposure from the natural radiation. The dose from ingestion of thermomineral water has been considered. Over the past few years, thermal and mineral water samples were repeatedly taken at selected springs in the Republic of Croatia, mostly spas and health resorts. The collected water samples were gamma spectrometrically analysed in the laboratory using Ge(Li) Ortec detector (resolution 1.78 keV on 1.33 MeV 60Co, relative efficiency 16.8%) with a 4.096 channel analyser and a personal computer. All samples were measured in Marinelli beaker, volume 1L. Measurement time was 80.000 sec. The activity concentrations of 226Ra and 228Ra were determined in all thermal and mineral water samples. In several springs, the waters of which are used for bathing purposes, 226Ra activities were found to exceed the maximal permissible level of 1000 Bqm-3 for drinking water. From the obtained data the 226Ra and 228Ra activity ratio was calculated for each investigated spa. The estimated dose of 226Ra and 228Ra incorporated through a drinking cure was calculated according to the ICRP recommendations assuming that during a 4-week-drinking cure a patient consumes 1 litre of mineral water a day (in consideration were taken only the samples from the spas where therapy involved drinking cure). According to our results, effective dose received from ingestion of 226Ra and 224Ra in a medical drinking cure over a 4-week period was as much as two times higher than the dose received from drinking public system tap water over a year. Considering the popularity of the spas and the habits of our population to use the beneficial effects of thermal and mineral water springs it is of interest to estimate the radiation dose that might be received by patients or tourists likely to visit or stay in spas more frequently. Since natural radioactivity in some spas exceeds the maximum permissible level for 226Ra in drinking water, the practice of using these waters should be controlled and water radioactivity regularly monitored in order to avoid any possible health effects. (author)