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Uranium and thorium are toxic in different environments. The exploitation of uranium mines and associated mine drainage leaching towards streams, sediments, and soils cause relevant pollution. The U-mine areas present high concentrations of potentially toxic elements with several consequences to ecosystems and human health. Physicochemical and potentially toxic elements of mine dumps, stream sediments, and soils from the Canto Lagar uranium mine area (Central Portugal) were analyzed. Stream sediments, soils, and mine dumps show a large range in the concentration values of Fe, U, As, Cu, Zn, Pb, and Th, suggesting geological and mine contributions. Most of the selected potential toxic elements from sediments present a low to moderate contamination degree, except for As, W, and U, which vary between high and very high contamination index. The soils must not be used in agricultural or residential activities due to contamination in As and U. This abandoned mine represents an environmental risk due to the spatial mobility and dispersion of potentially toxic elements from the dumps to the sediments and soils, as well as by surface runoff and wind.

The Picoto mining area is in the village of Vilar Seco (Viseu), central Portugal. Mineralization occurs mainly in quartz veins with meta-torbernite and uranophane and some U-bearing minerals, cutting a Variscan granite. Exploitation took place in two phases, between 1917 and 1953, and since the closure, the area has never been remediated. Water–rock interaction processes, including the mobility of potentially toxic elements through soil and water (surface and groundwater), were identified with the determination in situ of physicochemical parameters and selected anions and cations, by ICP-OES. The soils are contaminated with As (>44 mg/kg), Cu (>23 mg/kg), and U (>40 mg/kg) and cannot be used for agricultural or domestic purposes. The waters are generally weakly mineralized and have pH values ranging from acidic to neutral. However, some of them are contaminated with NO2 (up to 2.3 mg/L), Fe (up to 1849 mg/L), Mn (up to 777 mg/L), Cu (up to 5.4 g/L), As (up to 14.7 g/L), and U (up to 66.2 g/L) and cannot be used for human consumption or agricultural activities. The soil and water contamination are mainly related to the old mine activities and the subsequent human activities that have developed in the area.

Acid mine drainage represents an extreme environment with high concentrations of potentially toxic elements and low pH values. These aquatic habitats are characterised by harsh conditions for biota, being dominated by acidophilic organisms. The study site, São Domingos mine, located in one of the largest metallogenetic provinces in the world, the Iberian Pyrite Belt, was closed without preventive measures. To identify the algae species and understand the relationships with abiotic parameters of the ecosystem, water and biological material were collected and analysed. Digital terrain models were obtained with an unmanned aerial vehicle for geomorphological and hydrologic characterisation of the mine degraded landscape. The results show two types of algal colours that seem to represent different degrees of photosynthetic activity. Optical and scanning electron microscopy revealed 14 taxa at the genus level, divided into eight classes. The genus Mougeotia is the most abundant multicellular algae. With respect to unicellular algae, diatoms are ubiquitous and abundant. Abiotic analyses expose typical features of acid mine drainage and support an inverse relationship between chemical contamination and biological diversity. Factorial correspondence analysis indicates three groups of attributes and samples by their relationship with specific toxic elements. This analysis also suggests a close association between Spirogyra and Pb, together composing a structurally simple ecosystem. The highest contamination in the river system is related to the hydrologic patterns obtained from photogrammetric products, such as the digital surface model and flow map accumulation, indicating the input of leachates from the section having the finest sulfide-rich wastes. Information about the algae community and their association with flow patterns of toxic elements is a relevant tool from a biomonitoring perspective.