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Evaluating in situ biodegradation of 13C-labelled naphthenic acids in groundwater near oil sands tailings ponds.

Ahad, Jason M. E.; Pakdel, Hooshang; Gammon, Paul R.; Siddique, Tariq; Kuznetsova, Alsu; Savard, Martine M. (2018). Evaluating in situ biodegradation of 13C-labelled naphthenic acids in groundwater near oil sands tailings ponds. Science of The Total Environment , vol. 643 . p. 392-399. DOI: 10.1016/j.scitotenv.2018.06.159.

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Résumé

Potential seepage of naphthenic acids (NAs) from tailings ponds into surface water and groundwater is one of the main environmental concerns associated with the Canadian Athabasca oil sands mining operations. Here we report the application of ¹³C-labelled NA surrogate compounds to evaluate intrinsic biodegradation along groundwater flow-paths originating from oil sands tailings ponds at two different sites: a glacio-fluvial aquifer (Site 1) and a low-lying wetland (Site 2). Microcosms containing the carboxyl group labelled (99%) NA surrogates (cyclohexanecarboxylic acid, CHCA; 1,2-cyclohexanedicarboxylic acid, CHDCA; 1-adamantanecarboxylic acid, ACA) were lowered into monitoring wells for several months to allow sufficient time for substrate degradation and formation of a biofilm in conditions characteristic of the local aquifer. Phospholipid fatty acids (PLFAs), biomarkers for the active microbial population, were extracted from the biofilms for stable carbon isotope (δ13C) analysis. At Site 1, highly ¹³C-enriched δ¹³C values (up to ~+7100‰) confirmed the in situ microbial breakdown of CHCA and CHDCA. At Site 2, δ¹³C-PLFA values from −60.6 to −24.5‰ indicated uptake of a ¹³C-depleted substrate such as biogenic methane and not ¹³C-labelled ACA. Determination of the microbial community using 16s RNA sequencing confirmed the presence of methane-oxidizing bacteria in the subsurface at Site 2. The in situ biodegradation of NAs at Site 1 demonstrates that the indigenous microbial population in the shallow subsurface near tailings ponds can readily break down some of these compounds prior to surface water discharge. The lack of evidence for microbial uptake of ¹³C-labelled ACA at Site 2 demonstrates that other NAs, in particular tricyclic diamondoid acids, may persist in the environment following seepage from tailings ponds or natural sources.

Type de document: Article
Mots-clés libres: naphthenic acids; groundwater; stable isotope probing; phospholipid fatty; acids; 16s RNA; tailings ponds
Centre: Centre Eau Terre Environnement
Date de dépôt: 25 oct. 2018 19:20
Dernière modification: 25 oct. 2018 19:20
URI: http://espace.inrs.ca/id/eprint/7715

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