Natural radionuclides measurements in drinking water by liquid scintillation counting methods and results

Abstract

Concern about total radionuclides content in water intended for human consumption has been brought to public attention by the recent Council Directive 98/83/EC, subsequently enforced through an Italian law. Parameter values have been fixed for Tritium content (100 mBq/l) and total indicative dose (0,1 mSv/year): the Directive points out that the total indicative dose must be evaluated excluding Tritium, K, C, Radon and its decay products, but including all other natural series radionuclides. Maximum concentration values for Radon are separately proposed in Commission Recommendation 2001/928/Euratom. Tritium determination follows a well established procedure, standardized by International Standard Organization. On the contrary, total indicative dose evaluation requires more specific and cumbersome procedures for the measurement of radioactivity content, with special regard to natural series radionuclides. The large number of possibly involved radionuclides and the good sensitivities required make the application of traditional analytical techniques unsuitable in view of a large scale monitoring program. World Health Organization guidelines for drinking water suggest performing an indirect evaluation of committed dose by measuring alpha and beta gross radioactivity and checking compliance to derived limit values; the proposed limit values are 0,1 Bq/l for gross alpha and 1 Bq/l for gross beta radioactivity. Nevertheless, it is desirable to identify single radionuclides contribution to alpha and beta activity in order to perform more accurate measurements of committed dose. Ultra-low level liquid scintillation counting coupled to extractive techniques and alphabeta discrimination allows rapid and simple determination of all radiometric parameters relevant to dose evaluation, namely gross alpha and beta activity, uranium and radium isotopes content. For tritium and radon determination well established procedures, based on LSC, can also be used. These techniques were applied to a preliminary monitoring program of tap waters in Lombardia; up to now, total alpha and beta activity and uranium isotope concentration have been measured. A Quantulus-Wallac scintillation counter has been used in this work. Some brands of bottled water were examined too, both for testing methods and because of the widespread use of mineral water by the Italian population. Mineral water brands are not reported here. 2 METHODS AND RESULTS