Bicyclic naphthenic acids in oil sands process water: Identification by comprehensive multidimensional gas chromatography–mass spectrometry

Abstract

Although bicyclic acids have been reported to be the major naphthenic acids in oil sands process-affected water (OSPW) and a well-accepted screening assay indicated that some bicyclics were the most acutely toxic acids tested, none have yet been identified. Here we show by comprehensive multidimensional gas chromatography-mass spectrometry (GC×GC-MS), that >100 C8-15 bicyclic acids are typically present in OSPW. Synthesis or purchase allowed us to establish the GC×GC retention times of methyl esters of numerous of these and the mass spectra and published spectra of some additional types, allowed us to identify bicyclo[2.2.1]heptane, bicyclo[3.2.1]octane, bicyclo[4.3.0]nonane, bicyclo[3.3.1]nonane and bicyclo[4.4.0]decane acids in OSPW and a bicyclo[2.2.2]octane acid in a commercial acid mixture. The retention positions of authentic bicyclo[3.3.0]octane and bicyclo[4.2.0]octane carboxylic acid methyl esters and published retention indices, showed these were also possibilities, as were bicyclo[3.1.1]heptane acids. Bicyclo[5.3.0]decane and cyclopentylcyclopentane carboxylic acids were ruled out in the samples analysed, on the basis that the corresponding alkanes eluted well after bicyclo[4.4.0]decane (latest eluting acids). Bicyclo[4.2.1]nonane, bicyclo[3.2.2]nonane, bicyclo[3.3.2]decane, bicyclo[4.2.2]decane and spiro[4.5]decane carboxylic acids could not be ruled out or in, as no authentic compounds or literature data were available. Mass spectra of the methyl esters of the higher bicyclic C12-15 acids suggested that many were simply analogues of the acids identified above, with longer alkanoate chains and/or alkyl substituents. Our hypothesis is that these acids represent the biotransformation products of the initially somewhat more bio-resistant bicyclanes of petroleum. Although remediation studies suggest that many bicyclic acids can be relatively quickly removed from suitably treated OSPW, examination by GC×GC-MS may show which isomers are affected most. Knowledge of the structures will allow the toxicity of any residual isomers to be calculated and measured.

Diamondoids are not forever: microbial biotransformation of diamondoid carboxylic acids

“…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. Tricyclic (and bicyclic) diamondoid carboxylic acids are major components of OSPW, and unrefined oil sands bitumen are reported to contain 90% tricyclic acids (Rowland et al , ; Wilde et al , ). Both A1CA and 3EA exhibit chronic toxicity and specifically were found to disrupt human liver enzyme activity (Scarlett et al , ).…”

Overview of Existing Science to Inform Oil Sands Process Water Release: A Technical Workshop Summary

“…Some components of OSPW are well understood: trace elements including metals, semimetals, and metalloids (Nix and Martin ; Siwik et al ; Bicalho et al ; Donner et al ), salts and ammonia (COSIA ), and suspended solids (El‐Din et al ; COSIA ; McQueen, Hendrikse et al ). However, the complexity of the organics in OSPW creates a practical challenge for determining treatment methods (Headley et al ; Pereira et al 2013; Goff et al ; Brown and Ulrich ; Quinlan and Tam ; Wilde et al ; Ajaero et al ), in addition to estimating potential risks (West et al ; Huang et al ). The estimation of potential risk is further supported through an existing understanding of chemical properties such as the propensity for bioaccumulation (Zhang et al ; Morandi et al ).…”

Naphthenic acids in groundwater overlying undeveloped shale gas and tight oil reservoirs

“…Another possibility is that bicyclic acids were generated from in situ microbial alteration of shale organic matter (Saint-Édouard) and petroleum (Gaspé), as was inferred for the POT2 seep sample from the Haldimand region ( Figure 2). For instance, Wilde et al (2015)…”