Kinsela Andrew S, Payne Timothy E, Bligh Mark W, Vázquez-Campos Xabier, Wilkins Marc R, Comarmond M Josick, Rowling Brett, Waite T David
UNSW Water Research Centre and School of Civil and Environmental Engineering, The University of New South Wales, Sydney, Australia.
Environmental Research Theme, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.
Sci Total Environ. 2022 Dec 10;851(Pt 1):158241. doi: 10.1016/j.scitotenv.2022.158241. Epub 2022 Aug 23.
Numerous legacy near-surface radioactive waste sites dating from the mid 20th century have yet to be remediated and present a global contamination concern. Typically, there is insufficient understanding of contaminant release and redistribution, with invasive investigations often impractical due to the risk of disturbing the often significantly radiotoxic contaminants. Consequently, a replica waste trench (5.4 m), constructed adjacent to a legacy radioactive waste site (Little Forest Legacy Site, LFLS), was used to assist our understanding of the release and mixing processes of neodymium (Nd) - a chemical analogue for plutonium(III) and americium(III), two significant radionuclides in many contaminated environments. In order to clarify the behaviour of contaminants released from buried objects such as waste containers, a steel drum, representative of the hundreds of buried drums within the LFLS, was placed within the trench. Dissolved neodymium nitrate was introduced as a point-source contaminant to the base of the trench, outside the steel drum. Hydrologic conditions were manipulated to simulate natural rainfall intensities with dissolved lithium bromide added as a tracer. Neodymium was primarily retained both at its point of release at the bottom of the trench (>97 %) as well as at a steel container corrosion point, simulated through the emplacement of steel wool. However, over the 8-month field experiment, advective mixing initiated by surface water intrusions rapidly redistributed a small proportion of Nd to shallower waters (1.5-1.7 %), as well as throughout the buried steel drum. Suspended particulate forms of Nd (>0.2 μm) were measured at all depths in the suboxic trench and were persistent across the entire study. Analyses of the microbial communities showed that their relative abundances and metabolic functions were strongly influenced by the prevailing geochemical conditions as a result of fluctuating water depths associated with rainfall events. The site representing steel corrosion exhibited divergent biogeochemical results with anomalous changes (sharp decrease) observed in both dissolved contaminant concentration as well as microbial diversity and functionality. This research demonstrates that experimental trenches provide a safe and unique method for simulating the behaviour of subsurface radioactive contaminants with results demonstrating the initial retention, partial shallow water redistribution, and stability of particulate form(s) of this radioactive analogue. These results have relevance for appropriate management and remediation strategies for the adjacent legacy site as well as for similar sites across the globe.
许多可追溯到20世纪中叶的遗留近地表放射性废物场地尚未得到修复，这引发了全球范围内的污染担忧。通常情况下，人们对污染物的释放和再分布了解不足，由于存在扰动往往具有显著放射性毒性的污染物的风险，侵入性调查往往不切实际。因此，在一个遗留放射性废物场地（小森林遗留场地，LFLS）附近建造了一个复制的废物沟渠（约5.4米），以帮助我们了解钕（Nd）的释放和混合过程——钕是钚（III）和镅（III）的化学类似物，这两种是许多受污染环境中的重要放射性核素。为了阐明从诸如废物容器等埋藏物体中释放的污染物的行为，在沟渠内放置了一个代表LFLS内数百个埋藏钢桶的钢桶。将溶解的硝酸钕作为点源污染物引入沟渠底部，在钢桶外部。通过添加溶解的溴化锂作为示踪剂来控制水文条件，以模拟自然降雨强度。钕主要保留在其在沟渠底部的释放点（>97%）以及一个钢容器腐蚀点，通过放置钢丝棉来模拟该腐蚀点。然而，在为期8个月的现场实验中，由地表水入侵引发的平流混合迅速将一小部分钕重新分布到较浅的水域（约1.5 - 1.7%），以及整个埋藏的钢桶中。在亚oxic沟渠的所有深度都测量到了悬浮颗粒形式的钕（>0.2μm），并且在整个研究过程中都持续存在。对微生物群落的分析表明，由于与降雨事件相关的水深波动，其相对丰度和代谢功能受到主导地球化学条件的强烈影响。代表钢腐蚀的位点呈现出不同的生物地球化学结果，在溶解污染物浓度以及微生物多样性和功能方面都观察到了异常变化（急剧下降）。这项研究表明，实验沟渠为模拟地下放射性污染物的行为提供了一种安全且独特的方法，结果表明了这种放射性类似物的初始保留、部分向浅水的重新分布以及颗粒形式的稳定性。这些结果对于相邻遗留场地以及全球类似场地的适当管理和修复策略具有参考意义。
