The Pinhal do Souto mine exploited a quartz vein containing uranium minerals, mainly autunite and torbernite. This vein intersects a two-mica granite containing 10 ppm U and uraninite. The mine was exploited underground and produced 93,091 kg U 3 O 8 between 1978 and 1989 and was then closed down. Two dumps were left in the mine area and these are partially covered by natural vegetation. Groundwater and surface water have a similar slightly acid-to-alkaline pH. The UO 2 2+ is abundant and complexed with CO 3 2− , under neutral to alkaline pH. Metals and arsenic concentrations in the water increase during the dry season due to the evaporation. Uranium concentration in the water increases (up to 104.42 μg/l) in the wet season, because secondary uranium minerals are dissolved and uranium is released into the water. Soils tend to retain a higher concentration of several metals, including U (up to 336.79 mg/kg) than stream sediments (up to 35.68 mg/kg), because vermiculite from the former could adsorb it more easily than could kaolinite from the latter. The Fe-oxides precipitate retains the highest concentrations of several metals, including U and Th (up to 485.20 and 1053.12 mg/kg, respectively) and the metalloid As, because it is richer in oxyhydroxides and organic matter than stream sediments and soils. The median concentrations of Fe, As, Cd, Pb, Sb, Th, U, W and Zn in soils from this area are higher than in European soils of the FOREGS data. Waters from dry and wet seasons, stream sediments and soils are contaminated and must not be used. This area was compared with another Portuguese abandoned uranium mine area. The former mine caused a lower environmental impact attributable to it having lower sulphide concentration and mineral alteration than in the latter.

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The main purpose of this study is to assess arsenic and antimony availability in soils, as well as Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn availability in soils derived from the schist-metagraywacke complex close to old SbAu mines and in soils developed from Ordovician slates and close to an old As-Au mine in Portugal. The availability was determined using a European certified sequential extraction procedure (BCR). The results demonstrated that metalloids are not readily bioavailable, because they are mainly associated with the residual fraction. Arsenic and antimony proportions in exchangeable fractions are up to 3 and 1%, respectively. However, arsenic is up to 24% in oxy-hydroxide fractions, while antimony is up to 4% in them, demonstrating the highest bioavailability of arsenic compared to that of antimony, as metalloids are weakly bound to the soils in that fraction. Therefore, arsenic tends to be more toxic than antimony in all soils studied. However, the pseudo-total contents show that both metalloids are above the Italian and Dutch guidelines. Therefore, if physico-chemical changes occur arsenic and antimony will show higher potential environmental risk than evidenced by Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn.

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