Carvalho Fernando P, Oliveira João M, Lopes Irene, Batista Aleluia
Instituto Tecnológico e Nuclear, Departamento de Protecção Radiológica e Segurança Nuclear, E.N. 10, 2686-953 Sacavém, Portugal.
J Environ Radioact. 2007;98(3):298-314. doi: 10.1016/j.jenvrad.2007.05.007. Epub 2007 Jul 12.
During several decades and until a few years ago, uranium mines were exploited in the Centre of Portugal and wastewaters from uranium ore milling facilities were discharged into river basins. To investigate enhancement of radioactivity in freshwater ecosystems, radionuclides of uranium and thorium series were measured in water, sediments, suspended matter, and fish samples from the rivers Vouga, Dão, Távora and Mondego. The results show that these rivers carry sediments with relatively high naturally occurring radioactivity, and display relatively high concentrations of radon dissolved in water, which is typical of a uranium rich region. Riverbed sediments show enhanced concentrations of radionuclides in the mid-section of the Mondego River, a sign of past wastewater discharges from mining and milling works at Urgeiriça confirmed by the enhanced values of (238)U/(232)Th radionuclide ratios in sediments. Radionuclide concentrations in water, suspended matter and freshwater fish from that section of Mondego are also enhanced in comparison with concentrations measured in other rivers. Based on current radionuclide concentrations in fish, regular consumption of freshwater species by local populations would add 0.032 mSv a(-1) of dose equivalent (1%) to the average background radiation dose. Therefore, it is concluded that current levels of enhanced radioactivity do not pose a significant radiological risk either to aquatic fauna or to freshwater fish consumers.
在几十年间，直至几年前，葡萄牙中部一直在开采铀矿，铀矿石研磨设施产生的废水被排放到流域中。为了调查淡水生态系统中放射性的增强情况，对沃加河、道河、塔沃拉河和蒙德戈河的水、沉积物、悬浮物和鱼类样本中的铀和钍系列放射性核素进行了测量。结果表明，这些河流携带的沉积物具有相对较高的天然放射性，并且水中溶解的氡浓度相对较高，这是富含铀地区的典型特征。蒙德戈河中游河床沉积物中的放射性核素浓度有所增加，这表明过去在乌尔热里萨的采矿和研磨作业排放的废水，沉积物中(238)U/(232)Th放射性核素比值的增加证实了这一点。与其他河流测量的浓度相比，蒙德戈河该河段的水、悬浮物和淡水鱼中的放射性核素浓度也有所增加。根据目前鱼类中的放射性核素浓度，当地居民经常食用淡水物种将使平均背景辐射剂量增加0.032毫希沃特每年（1%）。因此，得出的结论是，目前放射性增强的水平对水生动物或淡水鱼消费者都不会构成重大的辐射风险。
