Response of Microbial Community Function to Fluctuating Geochemical Conditions within a Legacy Radioactive Waste Trench Environment

Abstract

During the 1960s, small quantities of radioactive materials were codisposed with chemical waste at the Little Forest Legacy Site (Sydney, Australia) in 3-meter-deep, unlined trenches. Chemical and microbial analyses, including functional and taxonomic information derived from shotgun metagenomics, were collected across a 6-week period immediately after a prolonged rainfall event to assess the impact of changing water levels upon the microbial ecology and contaminant mobility. Collectively, results demonstrated that oxygen-laden rainwater rapidly altered the redox balance in the trench water, strongly impacting microbial functioning as well as the radiochemistry. Two contaminants of concern, plutonium and americium, were shown to transition from solid-iron-associated species immediately after the initial rainwater pulse to progressively more soluble moieties as reducing conditions were enhanced. Functional metagenomics revealed the potentially important role that the taxonomically diverse microbial community played in this transition. In particular, aerobes dominated in the first day, followed by an increase of facultative anaerobes/denitrifiers at day 4. Toward the mid-end of the sampling period, the functional and taxonomic profiles depicted an anaerobic community distinguished by a higher representation of dissimilatory sulfate reduction and methanogenesis pathways. Our results have important implications to similar near-surface environmental systems in which redox cycling occurs. IMPORTANCEThe role of chemical and microbiological factors in mediating the biogeochemistry of groundwaters from trenches used to dispose of radioactive materials during the 1960s is examined in this study. Specifically, chemical and microbial analyses, including functional and taxonomic information derived from shotgun metagenomics, were collected across a 6-week period immediately after a prolonged rainfall event to assess how changing water levels influence microbial ecology and contaminant mobility. Results demonstrate that oxygen-laden rainwater rapidly altered the redox balance in the trench water, strongly impacting microbial functioning as well as the radiochemistry. Two contaminants of concern, plutonium and americium, were shown to transition from solid-iron-associated species immediately after the initial rainwater pulse to progressively more soluble moieties as reducing conditions were enhanced. Functional metagenomics revealed the important role that the taxonomically diverse microbial community played in this transition. Our results have important implications to similar near-surface environmental systems in which redox cycling occurs.

Long-term effects of straw return and straw-derived biochar amendment on bacterial communities in soil aggregates

“…Notably, the Venn diagram analysis showed that the phylum Omnitrophica was specifically enriched in both CB (0-40 cm) and CS (20-40 cm) (data not shown). Omnitrophica, belonging to the Planctomycetes-Verrucomicrobia-Chlamydiae (PVC) superphylum, was probably involved in the removal of recalcitrant substances in the contaminated sites 36 .…”

Genomic Insights Into the Archaea Inhabiting an Australian Radioactive Legacy Site

“…In order to better understand the archaeal contributions in LFLS groundwaters and their influence upon site biogeochemistry, raw sequencing reads from ENA project PRJEB14718 ( Vázquez-Campos et al, 2017 ) were reanalysed using genome-based metagenomic methodologies. Briefly, samples were collected in triplicate over a period of 47 days at four time-points, i.e., 0 (SAMEA4074280–2), 4 (SAMEA4074283–5), 21 (SAMEA4074286–8), and 47 (SAMEA4074289–91) days, after an intense rainfall event that filled the trench.…”

“…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 ).…”

Speciation of Uranium and Plutonium From Nuclear Legacy Sites to the Environment: A Mini Review

“…It was found that mobilization of Pu from the trenches is related to complex interactions between the influx of oxidizing groundwater during rainfall and the subsequent extended period of reducing conditions. The microbial activity influences the distributions of actinides and other redox-sensitive elements, such as iron and manganese (Vázquez-Campos et al, 2017 ). The study shows seasonal changes in redox conditions, which can significantly change the migration of redox-sensitive actinides, especially Pu.…”