Radioactive risk evaluation of mineral water in the Metropolitan Region of Recife, Northeastern Brazil

Abstract

The Metropolitan Region of Recife (MRR), Pernambuco State, Brazil, is well supplied in groundwater resources, mainly because of the water quality and exploitation capability of the Beberibe aquifer. The MRR is also located over uranium-bearing phosphate deposits of the coastal region of the Northeastern Brazil. Such sedimentary rocks present U3O8 content of 30–500 mg kg−1 (average of 150 mg kg−1), being considered one of the highest occurrences of this kind of deposit in the world. The mineral water recharging areas, when in contact with the uranium-phosphate rocks, may increase the radioactive contamination of water due to the leaching and transport of U and other radioactive chemical elements from the rocks to the groundwater. Taking into account the continuous increasing of production and preferential drinking of bottled mineral water in the region, notoriously in the last decade, this study encompassed the first results of gross alpha and beta activities in the bottled mineral water of the MRR. The determination of the alpha and beta activities was carried out in nine commercial mineral water brands from springs located in different regions over the Beberibe aquifer, using a low background gas flow proportional counter, model Canberra® S5-XLB. The methodology consisting of concomitant water evaporation steps in planchets was modified from the standard methods for the examination of water and wastewater. The levels of activities ranged from (35 ± 3) to (85 ± 5), and (200 ± 9) to (330 ± 8) mBq L−1 for the gross alpha and beta activities, respectively. A consistent spatial variation in the radioactivity levels in mineral water was observed for MRR springs, in which radiation decreased according to the increasing of distance from the MRR area. Since outcrops of phosphate rocks containing uranium have been already detected in the urban area, mineral water resources within the MRR might be in contact with uranium enriched rocks in the deeper geological layers. Even though, the risk of radioactive contamination was considered low because the gross alpha and beta activity concentrations were in accordance with the World Health Organization water potability standards of 500 and 1,000 mBq L−1, respectively.