INVESTIGATION OF NATURAL RADIONUCLIDES IN DRINKING AND MINERAL WATERS IN BULGARIA AND RELATED DOSE ASSESSMENT

The activity of naturally occurring radionuclides in drinking and mineral waters in Bulgaria has been measured with high precision by means of nuclear and radiochemical methods. The survey is pointed at two radionuclides, which are most important from the point of view of public health in Bulgaria, because of their high toxicity and radiotoxicity in drinking water, namely radium-226 (Ra-226) and lead-210 (Pb-210). Twenty-four frequently used water sources were under investigation. The Ra-226 activity ranges from <= 2:3 mBq/L to 90 mBq/L in drinking water and from 13 mBq/L to 5020 mBq/L in mineral water, both currently available to the public. Activity of Pb-210 up to 17 mBq/L and 104 mBq/L was measured in drinking and mineral waters, respectively. Due to differences in the local geological structure of the aquifers, a large difference in values of the Ra-226 and Pb-210 activities was observed. The annual effective doses were calculated for all investigated waters for adult inhabitants assuming yearly consumption of 730 litres. Contributions to the annual effective doses from Ra-226 and Pb-210 varied from 2.56 mu Sv/y to 21 mu Sv/y and from 22 mu Sv/y to 1035 mu Sv/y for drinking and mineral waters, respectively. The results show that the annual effective dose of ingestion of these waters, excluding three mineral water samples, are below the individual dose criterion of 100 mu Sv/y according to the World Health Organization (WHO) recommendations. The data generated in this research may contribute to determine the base-line levels of natural radioactivity in drinking and mineral waters and help in the development of future guidelines for radiological protection of the Bulgarian population.