Mangeret Arnaud, Reyss Jean-Louis, Seder-Colomina Marina, Stetten Lucie, Morin Guillaume, Thouvenot Antoine, Souhaut Marc, van Beek Pieter
Institut de Radioprotection et de Sureté Nucléaire (IRSN), PSE-ENV. BP 17, Fontenay-aux-Roses, 92262, France.
Laboratoire des Sciences du Climat et de l'Environnement (LSCE/IPSL), CEA-CNRS-UVSQ, Université Paris-Saclay, 91198, Gif-sur-Yvette, France.
J Environ Radioact. 2020 Oct;222:106324. doi: 10.1016/j.jenvrad.2020.106324. Epub 2020 Jul 7.
Radium is a naturally occurring radioactive element commonly found at low levels in natural systems such as lacustrine or marine sediments. Anthropogenic activities including former uranium mining activities can lead to the dissemination of radium isotopes having high radiological toxicities, which potentially threaten the safety of nearby environments. Although radium mobility in oxidized environments is known to be largely governed by sorption/desorption onto Fe and Mn oxyhydroxides and coprecipitation with sulfate minerals (e.g. barite), little is known regarding its behavior under reducing conditions, which are the conditions typically encountered in organic-rich systems such as wetlands and lake sediments. The present study aims at understanding the behavior of long-lived radium isotopes (Ra and Ra), during early diagenesis of lake sediments contaminated by former uranium mining activities. Solid and pore water concentrations of Ra and Ra were determined using ultra low background gamma spectrometry, which allowed improvement of detection limits and measurement accuracy. This study shows that the downcore distribution of radium isotopes is closely related to the reductive dissolution of iron and manganese oxyhydroxides below the sediment-water interface. The resulting diffusive fluxes of Ra and Ra (4.1 10 and 4.7 10 mol cm.s) are however significantly lower than other radium-impacted environments, such as uranium mill tailings pond and phosphate industry-impacted sediments, and are similar to those reported for natural marine environments. Hence, in the reduced lake sediments of Saint-Clement, the major fraction of radium is trapped by the solid phase, while early diagenesis only induces a slight mobility of this radioelement.
镭是一种天然存在的放射性元素，通常在湖泊或海洋沉积物等自然系统中以低含量形式存在。包括以前的铀矿开采活动在内的人为活动会导致具有高放射性毒性的镭同位素扩散，这可能威胁到附近环境的安全。尽管已知镭在氧化环境中的迁移主要受其在铁和锰的羟基氧化物上的吸附/解吸以及与硫酸盐矿物（如重晶石）的共沉淀控制，但对于其在还原条件下的行为却知之甚少，而还原条件是在富含有机物的系统（如湿地和湖泊沉积物）中通常会遇到的条件。本研究旨在了解受以前铀矿开采活动污染的湖泊沉积物早期成岩过程中长寿命镭同位素（镭-226和镭-228）的行为。使用超低本底伽马能谱法测定了镭-226和镭-228的固相和孔隙水浓度，这提高了检测限和测量精度。本研究表明，镭同位素的垂向分布与沉积物-水界面以下铁和锰的羟基氧化物的还原溶解密切相关。然而，由此产生的镭-226和镭-228的扩散通量（分别为4.1×10⁻⁹和4.7×⁻⁹摩尔·厘米⁻²·秒⁻¹）明显低于其他受镭影响的环境，如铀矿尾矿池和受磷矿工业影响的沉积物，并且与天然海洋环境中报道的通量相似。因此，在圣克莱门特的还原湖泊沉积物中，大部分镭被固相捕获，而成岩作用仅导致这种放射性元素有轻微的迁移。
