Abstract
SummaryOil sands process‐affected waters (OSPW) contain persistent, toxic naphthenic acids (NAs), including the abundant yet little‐studied diamondoid carboxylic acids. Therefore, we investigated the aerobic microbial biotransformation of two of the most abundant, chronically toxic and environmentally relevant diamondoid carboxylic acids: adamantane‐1‐carboxylic acid (A1CA) and 3‐ethyl adamantane carboxylic acid (3EA). We inoculated into minimal salts media with diamondoid carboxylic acids as sole carbon and energy source two samples: (i) a surface water sample (designated TPW) collected from a test pit from the Mildred Lake Settling Basin and (ii) a water sample (designated 2 m) collected at a water depth of 2 m from a tailings pond. By day 33, in TPW enrichments, 71% of A1CA and 50% of 3EA was transformed, with 50% reduction in EC20 toxicity. Similar results were found for 2 m enrichments. Biotransformation of A1CA and 3EA resulted in the production of two metabolites, tentatively identified as 2‐hydroxyadamantane‐1‐carboxylic acid and 3‐ethyladamantane‐2‐ol respectively. Accumulation of both metabolites was less than the loss of the parent compound, indicating that they would have continued to be transformed beyond 33 days and not accumulate as dead‐end metabolites. There were shifts in bacterial community composition during biotransformation, with Pseudomonas species, especially P. stutzeri, dominating enrichments irrespective of the diamondoid carboxylic acid. In conclusion, we demonstrated the microbial biotransformation of two diamondoid carboxylic acids, which has potential application for their removal and detoxification from vast OSPW that are a major environmental threat.
Highlights
The bacterial oxidation of petroleum hydrocarbons over geological time has resulted in the formation of vast oil sands deposits, such as those in northern Alberta, Canada, which contain approximately 270 9 109 m3 (1.6 9 1012 billion barrels) of bitumen (Chalaturnyk et al, 2002)
We investigated the aerobic biotransformation of two model diamondoid carboxylic acids, adamantane-1-carboxylic acid (A1CA) and 3-ethyl adamantane carboxylic acid (3EA), by microorganisms derived from oil sands process-affected water (OSPW), with a concomitant toxicity reduction
Our results showed that compared to the abiotic controls, the microbial community derived from an OSPW sample, transformed ~ 20% of A1CA by day 11 and 71% by day 33; whilst the microbial community derived from another OSPW sample transformed 15% of A1CA by day 11 and 64% by day 33 (Fig. 1B)
Summary
The bacterial oxidation of petroleum hydrocarbons over geological time has resulted in the formation of vast oil sands deposits, such as those in northern Alberta, Canada, which contain approximately 270 9 109 m3 (1.6 9 1012 billion barrels) of bitumen (Chalaturnyk et al, 2002). An extensive series of previously overlooked tri-, tetra- and pentacyclic naphthenic acids were identified as major components of oil sands and OSPW (Rowland et al, 2011a, 2012). These included the tricyclic diamondoid carboxylic acids, adamantane-1-carboxylic acid (A1CA) and 3-ethyl adamantane carboxylic acid (3EA), which were investigated in our study. Algae of the order Chlorellales and genus Acutodesmus dominated enrichments amended with A1CA, suggesting that microalgal-bacterial communities have the potential to degrade NAs in tailings ponds (Paulssen and Gieg, 2019) It is currently unknown whether other microorganisms can degrade diamondoid carboxylic acids found in OSPW. A1CA and 3EA were used as model diamondoid carboxylic acids to determine whether microorganisms derived from OSPW were capable of their biotransformation and to identify any metabolites produced, and the microorganisms potentially responsible
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