# Spatial Mobility of U and Th in a U-enriched Area (Central Portugal)
## 1 Introduction  
The metal uranium (U) is toxic due to its chemical and radioactivity. However, its chemical toxicity is harmful to human health, while thorium (Th) is considered only radiotoxic. The biochemical toxicity of U has a higher danger than that resulting from its radioactivity, by six orders of magnitude [1]. The uranium mines, with associated open-pits and dumps, promote the leaching of uranium to streams, sediments, and soils. This uranium mobility causes relevant pollution to surface and groundwater, sediments, soils, and humans. Different areas of closed U-bearing mines are potentially dangerous to the environment and human health due to high uranium concentrations. Uranium can be mobilized from mine dumps to water (surface and groundwater), sediments, and soils.  
Uranium is a toxic metal that causes kidney disease and increases the risk associated with reproductive cancers and human fertility problems [2]. In areas with uranium-contaminated sites, this metal could enter the human food chain by water (surface and groundwater) and/or from soil to plants, and consequently to animals. In mining areas, some metals, like uranium, being transferred from mine dumps to sediments and soils, by water drainage and atmospheric deposition processes, constitute a major issue concerning soil pollution [3].  
The human health hazards associated with the radionuclides depend on their ability to accumulate in human tissues [4].  
In Europe, uranium mines overtook the maximum exploitation rate, particularly during the period 1960-1990, and consequently a U depletion of the deposits occurred and the mines ceased their activities [5]. As a result, in the European Union, there are about 150 uranium mines, particularly concentrated in the eastern region of Europe [6; 7]. These uranium mines present several millions of tons of tailings and associated mine wastes [8]. However, the effect of naturally occurring radioactive material (NORM) and the impact of solid waste on human health are not understood [9]. There are abandoned mines in France [10], Poland [11], Portugal [12], the United Kingdom [13], and Spain [14], where workers and citizens are exposed to human health risks. In Portugal, more than 60 uranium mines were developed, including underground and/or open-pit mines. These mines were included in a national program, and were strongly associated with the collaboration with the United Kingdom Atomic Energy Authority, to provide uranium materials for nuclear armament support during the Cold War in the late 1940s [15]. There are uranium deposits from Portugal that were also used in the nuclear industry in the United States [16].  
Risk assessments of soil contamination with NORM are very important, particularly for young children, due to soil ingestion whether purposefully or inadvertently [17].  
The abandoned uranium mine of Canto do Lagar is located in the center region of Portugal. The mine area includes two dumps with deposited rejected materials and an open pit filled with rainwater. The main subject of this paper is the evaluation of U and Th mobility, and associated trace elements, through the mine dump's materials, stream sediments, and soils. The obtained results allow for the assessment of mobility processes from different solid reservoirs and the potential contamination associated with the old mine and background enrichment from the region.