Radon in Groundwater Public Supplies in the Metropolitan Area of Recife, Brazil

INTRODUCTION Man’s exposure to natural radiation accounts for around 70% of the total dose received by the population. Most of this exposure is due to Rn, a member of the U decay series, which is produced by the direct decay of Rn. Being a noble gas, radon produced in the rock or soil matrix can easily diffuse to the water trapped in the pore spaces and migrate to ground water, where it may be present in concentrations several orders of magnitude higher than those of its predecessor. Hydrological investigations concerning the presence of radionuclides in public and private drinking water supplies have been mainly related to groundwater sources, because the radon content of surface waters is typically low due to its desorption by aeration. In Brazil there are only a few studies concerning the presence of radionuclides in water (1,3). Recently, the Brazilian Ministry of Health issued new interim regulations concerning the quality of water for human consumption (4). As far as the levels of radioactive contaminants are concerned, it was stated that the gross alpha and beta activities should not exceed 0.1 Bq/L and 1 Bq/L, respectively. The regulation states that further analyses shall be carried out to identify the specific radionuclides present in the water, as well as their individual concentration, whenever the measured values are above limits those limits. In order to verify if the levels of radioactive contaminants in the water from public supplies are in compliance with the limits set by the Ministry of Health, a survey has been carried out in the metropolitan area of Recife, Brazil. This paper reports the results of this survey, as far as Rn is concerned.