Carvalho Fernando P, Oliveira João M, Faria Isabel
Departamento de Protecção Radiológica e Segurança Nuclear, Instituto Tecnológico e Nuclear, 2686-953 Sacavém, Portugal.
Bull Environ Contam Toxicol. 2009 Nov;83(5):668-73. doi: 10.1007/s00128-009-9808-3. Epub 2009 Jul 10.
Two large uranium mines, Quinta do Bispo and Cunha Baixa, district of Viseu, North of Portugal, were exploited until 1991. Sulfuric acid was used for in situ uranium leaching in Cunha Baixa mine and for heap leaching of low grade ores at both mines. Large amounts of mining and milling residues were accumulated nearby. Since closure of mines, the treatment of acid mine waters has been maintained and treated water is released into surface water lines. Analysis of radionuclides in the soluble phase and in the suspended matter of water samples from the uranium mines, from the creeks receiving the discharges of mine effluents, from the rivers and from wells in this area, show an enhancement of radioactivity levels. For example, downstream the discharge of mine effluents into Castelo Stream, the concentrations of dissolved uranium isotopes and uranium daughters were up to 14 times the concentrations measured upstream; (238)U concentration in suspended particulate matter of Castelo Stream reached 72 kBq kg(-1), which is about 170 times higher than background concentrations in Mondego River. Nevertheless, radionuclide concentrations decreased rapidly to near background values within a distance of about 7 kilometers from the discharge point. Enhancement of radioactivity in underground waters was positively correlated with a decrease in water pH and with an increase of sulfate ion concentration, pointing out to Cunha Baixa mine as the source of groundwater contamination. The radiotoxic exposure risk arising from using these well waters as drinking water and as irrigation water is discussed and implementation of environmental remediation measures is advised.
葡萄牙北部维塞乌区的两个大型铀矿，即昆塔·多·比斯波矿和库尼亚·baix a矿，一直开采到1991年。库尼亚·baix a矿采用硫酸进行原地铀浸出，两个矿均采用硫酸对低品位矿石进行堆浸。大量采矿和选矿残渣堆积在附近。自矿山关闭以来，酸性矿井水的处理一直在进行，处理后的水排入地表水管道。对该地区铀矿、接纳矿井废水排放的小溪、河流和水井的水样中可溶相和悬浮物中的放射性核素进行分析，结果表明放射性水平有所提高。例如，在矿井废水排入卡斯特洛溪的下游，溶解铀同位素和铀子体的浓度比上游测得的浓度高出14倍；卡斯特洛溪悬浮颗粒物中的（238）U浓度达到72 kBq kg（-1），约为蒙德戈河背景浓度的170倍。然而，放射性核素浓度在距排放点约7公里的距离内迅速降至接近背景值。地下水中放射性的增强与水pH值的降低和硫酸根离子浓度的增加呈正相关，表明库尼亚·baix a矿是地下水污染的源头。讨论了将这些井水用作饮用水和灌溉水所产生的辐射毒性暴露风险，并建议实施环境修复措施。
