Natural radioactivity in the environment is a field gaining more attention in last decades. This work is focused on the study of natural radioactivity complemented with elementary characterization at former non-uraniferous mining areas in Sweden. This aim is addressed through the study of mining lakes, called pit lakes, which are water bodies generated after opencast mining. Environmental matrices (water, sediments and rocks) from 32 Swedish pit lakes, commonly used for recreational purposes were radiometrically characterized via alpha (238 U, 234 U, 232 Th, 230 Th, 210 Po isotopes) and gamma spectrometry (238 U and 232 Th series radionuclides). Additionally, ambient dose rate equivalent in the immediate surrounding of each pit lake was quantified. Physico-chemical parameters (pH, specific conductivity, dissolved oxygen, oxidation-reduction potential) and elemental composition (major and trace elements by ICP-MS) were analysed in water samples and elementary composition of sediments/rocks was measured by XRF and SEM-EDX in some specific cases. A non-negligible number of pit lakes (26%) with enhanced U levels in water was found. At some sites, rocks contained up to 4% of U in areas with high degree of interaction with local population. Concerning the elementary perspective, another popular site (due to its turquoise water) was found to have elevated dissolved heavy metal levels. Results obtained in this work prove that measurement of natural radioactivity is another component that should be included in routine analysis of characterization in mining areas, especially if restauration of post-mining sites is intended for human recreational. Mining activities in Sweden, the major metal mining country in the European Union, involving 63% of iron ore production, Zn (22%), Pb (20%) and Ag (17%) in 2014 1 , imply the generation of enormous quantities of mining wastes. Historically, more than 2,700 mines gather around 30,000 sites that have been minor mines and quarries according to the Geological Survey of Sweden (only 15 active mines in 2015) 2. Many of these sites were opencast mines to exploit sulfide, limestone, clay, etc. It is noteworthy that open-pit mining has increased substantially over the past two decades due to improvement of metallurgical techniques that enable metal extraction from low-grade ores 3. During exploitation by open-pit mining, the water table is suppressed to avoid the flooding of active mines. However, when mining activity ceases, the water table recovers its original position, flooding the open pits, and giving rise to mine pit lakes. The geochemistry of pit lake waters can vary enormously, depending on several factors such as local geology, hydrology or climate 4-7. A significant example is the case of sulfide mine pit lakes, where high/very high concentration of heavy metals in waters can be found due to the generation of acid mine drainage (AMD) processes 7. An important feature of AMD is that the sources of pollution can be active for years or even centuries after mine closure 8. However, ...
