Isotope Studies of Karst Springs Included in the Water Supply System of the City of Rijeka (Croatia)

  • Diana Mance* Physics Department, University of Rijeka, Rijeka, Croatia; Stable Isotope Laboratory, Physics Department, Faculty of Medicine, University of Rijeka, Rijeka, Croatia
  • Danijela Lenac Water Supply Company, Rijeka, Croatia
  • Josip Rubinić Faculty of Civil Engineering, University of Rijeka, Croatia


Aim: To inform about the results of isotopic analyses of karstic springs, Rječina Spring and Zvir, that ensure potable water for more than 200,000 people in Rijeka County (Croatia).

Methods: Specific activities of selected radionuclides were determined by high resolution gamma spectrometric analysis and radiochemical separation method. Values of hydrogen and stable isotope contents were determined by water equilibration method on isotope ratio mass spectrometer in conjunction with dual inlet and equilibration peripheral unit.

Results: Anthropogenic radionuclides were detected in trace amounts. The results of the analysis show that the calculated yearly dose introduced to an adult human consuming 2 liters of water per day is approximately 20 mSv. Stable isotopes content of the spring waters indicate a dominant recharge of the analyzed hydrological system by winter precipitation. Different isotopic variations of spring water as a consequence of sudden precipitation inputs in summer and autumn indicate that water discharged at Rječina Spring mainly originates from a big water reservoir situated in the wide mountain region in the hinterland of the spring.

Conclusion: The examined water is potable and radiologically safe. Stable isotope variations of the spring water show a fast reaction to sudden precipitation inputs, confirming the ecological vulnerability of karstic springs. In light of recent heavy precipitation and flooding in different parts of Croatia, a more systematic research on isotopic water composition should be encouraged.

Keywords: drinking water, isotopes, radioisotopes