Natural Gamma Radiation and Uranium Distribution in Soils and Waters in the Agueda River Basin (Spain-Portugal)

Gamma dose equivalent (0.18 ìSv/h) is higher than background of Salamanca province, Guarda district and worldwide average.The concentration of water-soluble U (or bioavailable) in soils regionally distributed with no influence of mining works, ranges from 1 to 137 μg/L with a median of 9 μg/l.The U content in shallow well waters ranges 0.1 – 79.5 μg/L with a median of 0.4 μg/l. In river and stream samples the concentration are lower (median < 0.1 μg/L). The association of U, As and pH in water samples indicates an increase of U and As solubility with increasing pH linked to the formation of uranyl-carbonate and uranyl-arsenate complexes.