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The Iberian Pyrite Belt (IPB) is a part of the South Zone of the Hercynian Iberian Massif (SW of Iberian Peninsula),being pyrite (FeS2) the main mineral associated to this Volcano-Sedimentary Complex.The intensive mining activities in the area,which started in the Roman Empire,have generated mine pits where underground and/or rainwater has been stored.The stored waters have produced oxidation of pyrite and,consequently,the pH of pit water has become acid (pH around 2),causing the dissolution of metals and natural radionuclides.The main objective of this work is to show and discuss the levels found for different natural radionuclides (mainly uranium isotopes via α/γ spectrometry) in water samples and sediments collected from several mine pit lakes located in the South-West of Spain.The sampling collection was carried out in summer of 2012,and simultaneously several physical and chemical parameters have been measured to be used in the result discussion.The waters of the studied pit lakes can interact with the environment,and a fraction can be transferred to surrounding aquifers and even to the main river of the zone (the Odiel river).The waters of this river,when cross the mining area,show low pH values and high concentrations of U-isotopes due to acid mining drainage.Through the analysis of several isotope activity ratios,the presence of natural radionuclides in these pit lakes and its influence in the surrounding area and Odiel river will be additionally evaluated.