Behaviour of carbon-14 containing low molecular weight organic compounds in contaminated groundwater under aerobic conditions.

Autor: Boylan AA; School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK., Stewart DI; School of Civil Engineering, University of Leeds, Leeds, LS2 9JT, UK., Graham JT; National Nuclear Laboratory, Sellafield, Cumbria, CA20 1PG, UK., Burke IT; School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK. Electronic address: I.T.Burke@leeds.ac.uk.
Jazyk: angličtina
Zdroj: Journal of environmental radioactivity [J Environ Radioact] 2018 Dec; Vol. 192, pp. 279-288. Date of Electronic Publication: 2018 Jul 07.
DOI: 10.1016/j.jenvrad.2018.06.016
Abstrakt: Short chain carbon-14 ( 14 C) containing organic compounds can be formed by abiotic oxidation of carbides and impurities within nuclear fuel cladding. During fuel reprocessing and subsequent waste storage there is potential for these organic compounds to enter shallow subsurface environments due to accidental discharges. Currently there is little data on the persistence of these compounds in such environments. Four 14 C-labelled compounds (acetate; formate; formaldehyde and methanol) were added to aerobic microcosm experiments that contained glacial outwash sediments and groundwater simulant representative of the Sellafield nuclear reprocessing site, UK. Two concentrations of each electron donor were used, low concentration (10 -5  M) to replicate predicted concentrations from an accidental release and high concentration (10 -2  M) to study the impact of the individual electron donor on the indigenous microbial community in the sediment. In the low concentration system only ∼5% of initial 14 C remained in solution at the end of experiments in contact with atmosphere (250-350 h). The production of 14 CO 2 (g) (measured after 48 h) suggests microbially mediated breakdown is the primary removal mechanism for these organic compounds, although methanol loss may have been partially by volatilisation. Highest retention of 14 C by the solid fractions was found in the acetate experiment, with 12% being associated with the inorganic fraction, suggesting modest precipitation as solid carbonate. In the high concentration systems only ∼5% of initial 14 C remains in solution at the end of the experiments for acetate, formate and methanol. In the formaldehyde experiment only limited loss from solution was observed (76% remained in solution). The microbial populations of unaltered sediment and those in the low concentration experiments were broadly similar, with highly diverse bacterial phyla present. Under high concentrations of the organic compounds the abundance of common operational taxonomic units was reduced by 66% and the community structure was dominated by Proteobacteria (particularly Betaproteobacteria) signifying a shift in community structure in response to the electron donor available. The results of this study suggest that many bacterial phyla that are ubiquitous in near surface soils are able to utilise a range of 14 C-containing low molecular weight organic substances very rapidly, and thus such substances are unlikely to persist in aerobic shallow subsurface environments.
(Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.)
Databáze: MEDLINE
Externí odkaz: