Identification of sources and processes in a low-level radioactive waste site adjacent to landfills: groundwater hydrogeochemistry and isotopes

Cendón, Dioni I.; Hughes, Catherine E.; Harrison, Jennifer; Hankin, Stuart; Johansen, Mathew P.; Payne, Timothy E.; Wong, Henri; Rowling, Brett; Vine, Marilyn F.; Wilsher, Kerry L.; Guinea, Ander; Thiruvoth, Sangeeth

doi:10.1080/08120099.2015.975155

Cited by 36 publications

(32 citation statements)

References 37 publications

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“…Similar maximum relative abundances, about 1.4·10 -4 , of 5-methyltetrahydrosarcinapterin:corrinoid/iron-sulfur protein Co -methyltransferase (RXN-12908, EC:2.1.1.245, Figure 5D) and coenzyme F 420 -dependent hydrogenase (COENZYME-F420-HYDROGENASE-RXN, EC:1.12.98.1, Figure S4), which are specific RXNs for the methanogenesis from acetate and H 2 and CO 2 , were observed at day 47. The presence of methanogenesis-specific RXNs is supported by previous isotopic measurements, showing δ 2 H enrichment, relative to δ 18 O, in the vicinity of the trenches (11). Concurrently, the taxonomy revealed the presence of the ANME-2d division contributing up to 13.8% of all Archaea at day 47 (1.5% of the community).…”

Section: Resultssupporting

confidence: 75%

“…The ten-fold reduction in the sulfur concentration is thought to result from the loss of dissolved sulfate via reduction to sulfide and subsequent precipitation of insoluble heavy metal sulfides, particularly FeS. This interpretation is supported by the lack of measurable sulfides in the trench water (see Chemical analyses of trench waters), along with previous reports showing sulfate reduction based on isotopic fractionation and severe (10 to 100-fold) depletion in sulfate concentrations in trench waters relative to surrounding wells (11). The potential contribution of sulfate- and nitrite-dependent anaerobic methane oxidation (S-DAMO and N-DAMO respectively) was discounted due to the near complete absence of ANME taxa ( Archaea ) aside from ANME-2d, and NC10 ( Bacteria ) (see Nitrogen cycling) (44, 59, 64, 65).…”

Section: Resultsmentioning

confidence: 71%

“…Of the cations and anions analysed (Figure 2), iron displayed one of the greatest variations in concentration, increasing from 0.42 mM at day 0, to 1.00 mM by day 47. The elevated concentrations of iron are unsurprising, given that the LLRW at LFLS was disposed of in-part within ~760 steel drums (36), and buried within a highly weathered shale geological matrix (11). The continuous presence of Fe(II), even at day 0, confers reducing conditions in excess of E h values recorded, casting uncertainty over the absolute values supplied by the E h probe.…”

Section: Resultsmentioning

confidence: 99%

“…The exception, noted at day 4, can be explained by the proliferation of Burkholderiales . The constant abundance of cellulose is unsurprising given the historical records which indicate a range of organic (particularly cellulose-based) compounds were co-disposed of in the LFLS trenches (11). This hypothesis accords with previous stable isotope measurements, which identified the degradation of legacy organic matter as being responsible for enriched δ 13 C (inorganic) values measured near the trench (11).…”

Section: Resultsmentioning

confidence: 99%

“…The LFLS trenches were excavated within undisturbed geological matrices of red-brown and grey clay (primarily kaolinite and illite/smectite) derived from the underlying weathered shale, interspersed with minor phases of hematite and goethite (11, 13). The site was chosen in part due to the low hydraulic conductivities of these materials (~ 9 to 66 mm/day) in order to isolate the LLRW from waters associated with the local hydrology cycle (10–12).…”

Section: Introductionmentioning

confidence: 99%

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Response of microbial community function to fluctuating geochemical conditions within a legacy radioactive waste trench environment

Vázquez-Campos

Kinsela

Bligh

et al. 2017

Preprint

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During the 1960s, small quantities of radioactive materials were co-disposed with chemical waste at the Little Forest Legacy Site (Sydney, Australia) in three-metre-deep, unlined trenches. Chemical and microbial analyses, including functional and taxonomic information derived from shotgun metagenomics, were collected across a six-week period immediately after a prolonged rainfall event to assess how changing water levels impact 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 four. Towards 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 six-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 solidiron-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.

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Section: Resultssupporting

confidence: 75%