Biogeochemical Mobility of Contaminants from a Replica Radioactive Waste Trench in Response to Rainfall-Induced Redox Oscillations

Abstract

Results of investigations into factors influencing contaminant mobility in a replica trench located adjacent to a legacy radioactive waste site are presented in this study. The trench was filled with nonhazardous iron- and organic matter (OM)-rich components, as well as three contaminant analogues strontium, cesium, and neodymium to examine contaminant behavior. Imposed redox/water-level oscillations, where oxygen-laden rainwater was added to the anoxic trench, resulted in marked biogeochemical changes including the removal of aqueous Fe­(II) and circulation of dissolved carbon, along with shifts to microbial communities involved in cycling iron (Gallionella, Sideroxydans) and methane generation (Methylomonas, Methylococcaceae). Contaminant mobility depended upon element speciation and rainfall event intensity. Strontium remained mobile, being readily translocated under hydrological perturbations. Strong ion-exchange reactions and structural incorporation into double-layer clay minerals were likely responsible for greater retention of Cs, which, along with Sr, was unaffected by redox oscillations. Neodymium was initially immobilized within the anoxic trenches, due to either secondary mineral (phosphate) precipitation or via the chemisorption of organic– and carbonate–Nd complexes onto variably charged solid phases. Oxic rainwater intrusions altered Nd mobility via competing effects. Oxidation of Fe­(II) led to partial retention of Nd within highly sorbing Fe­(III)/OM phases, whereas pH decreases associated with rainwater influxes resulted in a release of adsorbed Nd to solution with both pH and OM presumed to be the key factors controlling Nd attenuation. Collectively, the behavior of simulated contaminants within this replica trench provided unique insights into trench water biogeochemistry and contaminant cycling in a redox oscillatory environment.

REE Concentrations in Secondary Uranium Minerals from the Izera Metamorphic Complex (SW Poland)

“…These minerals are characterized by specific YREE and Nb signatures produced by hydrothermal processes [24]. These signatures may also be inherited by secondary uranium minerals, which are formed from their decomposition [24][25][26]. However, our results show that the YREE signatures in the secondary minerals studied differ from those of the primary phases.…”

“…Similar behavior of Sm is also noted, but not in metatorbernite and torbernite. The formation of a negative anomaly may be related to the presence of REE anionic complexes, which are highly stable and mobile in water solutions [25], and also to the changing redox potential of pore fluids, as a result of which some REEs, i.e., La and Ce, are sensitive to the oxidative properties of fluids [30,31]. Another possible cause of the observed anomaly may be YREE sorption onto iron hydroxides and oxyhydroxides [26].…”

Oxalate promoted iron dissolution of hematite via proton coupled electron transfer

“…Iron is the most abundant transition metal element in the Earth's crust, mainly in the form of iron (oxyhydr)oxide minerals, and its global biogeochemical cycling is coupled to various processes in natural environments. 1–5 Due to the low solubility and slow dissolution kinetics of iron (oxyhydr)oxides, their iron dissolution is the rate limiting step for iron participation in global biogeochemical cycling. 6–9 In the natural world, iron dissolution is usually promoted by plants and microorganisms through the release of natural ligands, such as siderophores and low-molecular-weight organic acids with a carboxyl group ( e.g.…”

Genomic Insights Into the Archaea Inhabiting an Australian Radioactive Legacy Site

“…An unintended consequence of this, is that surface water infiltrates into the more porous trench waste form at a greater rate when compared to the surrounding geology, and during intense and prolonged rainfall events the contaminated water levels in trenches fill up, akin to a ‘bathtub’ ( Payne et al, 2013 , 2020 ). Aside from providing a mechanism enabling the export of contaminants, occurring when trench waters (infrequently) overflow out of the ‘bathtub’ to the surrounding environment ( Payne et al, 2013 ), the periodic influx of oxic waters into these natural reducing zones results in transitory microbial population shifts associated with pronounced elemental cycling ( Vázquez-Campos et al, 2017 ; Kinsela et al, 2021 ). Our previous research showed that the archaeal community in the LFLS waste trenches, while constituting a minor portion of the whole microbial community, included a number of potentially interesting members, either in terms of phylogeny and/or functionality ( Vázquez-Campos et al, 2017 ).…”