Do distributions of diamondoid hydrocarbons accumulated in oil-contaminated fish tissues help to identify the sources of oil?

Identifying the sources of environmental oil contamination can be challenging, especially for oil in motile organisms such as fish. Lipophilic hydrocarbons from oil can bioaccumulate in fish adipose tissue and potentially provide a forensic "fingerprint" of the original oil. Herein, diamondoid hydrocarbon distributions were employed to provide such fingerprints. Indices produced from diamondoids were used to compare extracts from fish adipose tissues and the crude and fuel oils to which the fish were exposed under laboratory conditions. A suite of 20 diamondoids was found to have bioaccumulated in the dietary-exposed fish. Cross-plots of indices between fish and exposure oils were close to the ideal 1:1 relationship. Comparisons with diamondoid distributions of non-exposure oils produced overall, but not exclusively, weaker correlations. Linear Discriminatory Analysis on a combined set of 15 diamondoid and bicyclane molecular ratios was able to identify the exposure oils, so a use of both compound classes is preferable.

Fish Fingerprinting: Identifying Crude Oil Pollutants using Bicyclic Sesquiterpanes (Bicyclanes) in the Tissues of Exposed Fish.

In the present study, we investigated the possibility of identifying the source oils of exposed fish using ratios of bicyclic sesquiterpane (bicyclane) chemical biomarkers. In the event of an oil spill, identification of source oil(s) for assessment, or for litigation purposes, typically uses diagnostic ratios of chemical biomarkers to produce characteristic oil "fingerprints." Although this has been applied in identifying oil residues in sediments, water, and sessile filtering organisms, so far as we are aware this has never been successfully demonstrated for oil-exposed fish. In a 35-day laboratory trial, juvenile Lates calcarifer (barramundi or Asian seabass) were exposed, via the diet (1% w/w), to either a heavy fuel oil or to Montara, an Australian medium crude oil. Two-dimensional gas chromatography with high-resolution mass spectrometry and gas chromatography-mass spectrometry were then used to measure selected ratios of the bicyclanes to examine whether the ratios were statistically reproducibly conserved in the fish tissues. Six diagnostic bicyclane ratios showed high correlation (r2 > 0.98) with those of each of the two source oils. A linear discriminatory analysis model showed that nine different petroleum products could be reproducibly discriminated using these bicyclane ratios. The model was then used to correctly identify the bicyclane profiles of each of the two exposure oils in the adipose tissue extracts of each of the 18 fish fed oil-enriched diets. From our initial study, bicyclane biomarkers appear to show good potential for providing reliable forensic fingerprints of the sources of oil contamination of exposed fish. Further research is needed to investigate the minimum exposure times required for bicyclane bioaccumulation to achieve detectable concentrations in fish adipose tissues and to determine bicyclane depuration rates once exposure to oil has ceased. Environ Toxicol Chem 2023;42:7-18. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Characterizations and comparison of low sulfur fuel oils compliant with 2020 global sulfur cap regulation for international shipping.

The International Marine Organization 2020 Global Sulfur Cap requires ships to burn fuels with <0.50% S and some countries require <0.10% S in certain Sulfur Emission Control Areas but little is known about these new types of fuels. Using both traditional GC-MS and more advanced chromatographic and mass spectrometry techniques, plus stable isotopic, δ13C and δ2H, analyses of pristane, phytane and n-alkanes, the organic components of a suite of three 0.50% S and three 0.10% S compliant fuels were characterized. Two oils were found to be near identical but all of the remaining oils could be forensically distinguished by comparison of their molecular biomarkers and by the profiles of the heterocyclic parent and alkylated homologues. Oils could also be differentiated by their δ13C and δ2H of n-alkanes and isoprenoids. This study provides important forensic data that may prove invaluable in the event of future oil spills.

MV Wakashio grounding incident in Mauritius 2020: The world's first major spillage of Very Low Sulfur Fuel Oil.

Very Low Sulfur Fuel Oils (VSLFO, <0.5% S) are a new class of marine fuel oils, introduced to meet recent International Maritime Organization regulations. The MV Wakashio was reported to have released 1000 t of VLSFO when it grounded on a reef in Mauritius on 25th July 2020. A field sample of oily residue contaminating the Mauritian coast was collected on 16th August 2020 and compared with the Wakashio fuel oil. Both oils were analyzed for organic and elemental content, and stable isotope ratios δ13C and δ2H measured. Comprehensive two-dimensional gas chromatography with high-resolution mass spectrometry was used to identify and compare biomarkers resistant to weathering. The aromatic content in the VLSFO was relatively low suggesting that the potential for ecosystem harm arising from exposure to toxic components may be less than with traditional fuel oil spills. The Wakashio oil spill is, to our knowledge, the first documented spill involving VLSFO.

Discriminating source of oil contamination in teleost fish, Lates calcarifer, using multivariate analysis of a suite of physiological and behavioral biomarkers.

The release of petroleum hydrocarbons into the environment from natural seeps, well blowouts, pipeline leaks, shipping accidents and deliberate tank washing poses an ongoing threat to marine ecosystems. Distinguishing the source of oil contamination in exposed biota can be relatively straightforward if samples of the oil are available but, in their absence, such discrimination in fish poses a major challenge. The use of physiological and behavioral biomarker analysis provides a useful tool to describe sub-lethal effects of toxicant exposure. In this study we describe the responses of 12 biomarkers in Lates calcarifer (Asian seabass) following a 33-day dietary exposure (1%w/w) to heavy fuel oil (HFO) and to Montara, a typical Australian medium crude oil (MCO). Principal components analysis was used to differentiate between fish exposed to HFO from those exposed to MCO. Inferences can be made about the composition of an oil from the biomarker profiles produced in exposed fish.

Advances in Distinguishing Groundwater Influenced by Oil Sands Process-Affected Water (OSPW) from Natural Bitumen-Influenced Groundwaters.

The objective of this study was to advance analytical methods for detecting oil sands process-affected water (OSPW) seepage from mining containments and discriminating any such seepage from the natural bitumen background in groundwaters influenced by the Alberta McMurray formation. Improved sampling methods and quantitative analyses of two groups of monoaromatic acids were employed to analyze OSPW and bitumen-affected natural background groundwaters for source discrimination. Both groups of monoaromatic acids showed significant enrichment in OSPW, while ratios of O2/O4 containing heteroatomic ion classes of acid extractable organics (AEOs) did not exhibit diagnostic differences. Evaluating the monoaromatic acids to track a known plume of OSPW-affected groundwater confirmed their diagnostic abilities. A secondary objective was to assess anthropogenically derived artificial sweeteners and per- and polyfluoroalkyl substances (PFAS) as potential tracers for OSPW. Despite the discovery of acesulfame and PFAS in most OSPW samples, trace levels in groundwaters influenced by general anthropogenic activities preclude them as individual robust tracers. However, their inclusion with the other metrics employed in this study served to augment the tiered, weight of evidence methodology developed. This methodology was then used to confirm earlier findings of OSPW migrations into groundwater reaching the Athabasca River system adjacent to the reclaimed pond at Tar Island Dyke.

Predicted and measured acute toxicity and developmental abnormalities in zebrafish embryos produced by exposure to individual aromatic acids.

Petroleum acids, often called 'Naphthenic Acids' (NA), enter the environment in complex mixtures from numerous sources. These include from Produced and Process-Affected waters discharged from some oil industry activities, and from the environmental weathering of spilled crude oil hydrocarbons. Here, we test the hypothesis that individual NA within the complex mixtures can induce developmental abnormalities in fish, by screening a range of individual acids, with known chemical structures. Sixteen aromatic NA were tested using a Thamnocephalus platyrus (beavertail fairyshrimp) assay, to establish acute toxicity. Toxicities ranged from 568 to 8 µM, with the methylbiphenyl acid, 4-(p-tolyl)benzoic acid, most toxic. Next, five of the most toxic monoacids and for comparison, a diacid, were assayed using Danio rerio (zebrafish) embryos to test for lethality and developmental abnormalities. The toxicities were also predicted using Admet predictor™ software. Exposure to the five monoacids produced deformities in zebrafish embryos in a dose-dependent manner. Thus, exposure to 4-(p-tolyl)benzoic acid produced abnormalities in >90% of the embryos at concentrations of <1 µM; exposure to dehydroabietic acid caused pericardial edema and stunted growth in 100% of the embryos at 6 µM and exposure to pyrene-1-carboxylic acid caused 80% of embryos to be affected at 3 µM. The findings of this preliminary study therefore suggest that some aromatic acids are targets for more detailed mechanistic studies of mode of action. The results should help to focus on those NA which may be important for monitoring in oil industry wastewaters and polluted environmental samples.

Further spectral and chromatographic studies of ambergris.

Jetsam ambergris, found washed ashore on beaches, is an environmentally modified form of a natural product of Sperm whales which sometimes develops a pleasant odour. Odorous samples have proved valuable in perfumery. Identification of jetsam ambergris by analysis of organic-soluble extracts by Fourier transform infra-red spectroscopy (FTIR) and of derivatised samples by gas chromatography-mass spectrometry (GC-MS) has already been shown. Here, we describe a different method, in which characteristic alkenic protons and carbon atoms of the major constituent ambrein, were identified in whole extracts using nuclear magnetic resonance spectroscopy (NMR). The advantages of employing NMR spectroscopy included rapidity, reduced losses of volatiles compared to GC-MS and detection of non-GC amenable constituents. However, the identities and quantities of co-occurring individual components (e.g. steroids) could not easily be assigned in the unfractionated extracts by NMR spectroscopy, whereas they were by GC-MS, so an approach combining FTIR, GC-MS and NMR spectroscopic methods is advocated.

Assessing spatial and temporal variability of acid-extractable organics in oil sands process-affected waters.

The acid-extractable organic compounds (AEOs), including naphthenic acids (NAs), present within oil sands process-affected water (OSPW) receive great attention due to their known toxicity. While recent progress in advanced separation and analytical methodologies for AEOs has improved our understanding of the composition of these mixtures, little is known regarding any variability (i.e., spatial, temporal) inherent within, or between, tailings ponds. In this study, 5 samples were collected from the same location of one tailings pond over a 2-week period. In addition, 5 samples were collected simultaneously from different locations within a tailings pond from a different mine site, as well as its associated recycling pond. In both cases, the AEOs were analyzed using SFS, ESI-MS, HRMS, GC×GC-ToF/MS, and GC- & LC-QToF/MS (GC analyses following conversion to methyl esters). Principal component analysis of HRMS data was able to distinguish the ponds from each other, while data from GC×GC-ToF/MS, and LC- and GC-QToF/MS were used to differentiate samples from within the temporal and spatial sample sets, with the greater variability associated with the latter. Spatial differences could be attributed to pond dynamics, including differences in inputs of tailings and surface run-off. Application of novel chemometric data analyses of unknown compounds detected by LC- and GC-QToF/MS allowed further differentiation of samples both within and between data sets, providing an innovative approach for future fingerprinting studies.

Diamondoid naphthenic acids cause in vivo genetic damage in gills and haemocytes of marine mussels.

Diamondoids are polycyclic saturated hydrocarbons that possess a cage-like carbon skeleton approaching that of diamond. These 'nano-diamonds' are used in a range of industries including nanotechnologies and biomedicine. Diamondoids were thought to be highly resistant to degradation, but their presumed degradation acid products have now been found in oil sands process-affected waters (OSPW) and numerous crude oils. Recently, a diamondoid-related structure, 3-noradamantane carboxylic acid, was reported to cause genetic damage in trout hepatocytes under in vitro conditions. This particular compound has never been reported in the environment but led us to hypothesise that other more environmentally relevant diamondoid acids could also be genotoxic. We carried out in vivo exposures (3 days, semi-static) of marine mussels to two environmentally relevant diamondoid acids, 1-adamantane carboxylic acid and 3,5-dimethyladamantane carboxylic acid plus 3-noradamantane carboxylic acid with genotoxic damage assessed using the Comet assay. An initial screening test confirmed that these acids displayed varying degrees of genotoxicity to haemocytes (increased DNA damage above that of controls) when exposed in vivo to a concentration of 30 µmol L(-1). In a further test focused on 1-adamantane carboxylic acid with varying concentrations (0.6, 6 and 30 µmol L(-1)), significant (P < 0.05%) DNA damage was observed in different target cells (viz. gills and haemocytes) at 0.6 µmol L(-1). Such a level of induced genetic damage was similar to that observed following exposure to a known genotoxin, benzo(a)pyrene (exposure concentration, 0.8 µmol L(-1)). These findings may have implications for a range of worldwide industries including oil extraction, nanotechnology and biomedicine.

Biogeochemical gradients above a coal tar DNAPL.

Naturally occurring distribution and attenuation processes can keep hydrocarbon emissions from dense non aqueous phase liquids (DNAPL) into the adjacent groundwater at a minimum. In a historically coal tar DNAPL-impacted site, the de facto absence of a plume sparked investigations regarding the character of natural attenuation and DNAPL resolubilization processes at the site. Steep vertical gradients of polycyclic aromatic hydrocarbons, microbial community composition, secondary water quality and redox-parameters were found to occur between the DNAPL-proximal and shallow waters. While methanogenic and mixed-electron acceptor conditions prevailed close to the DNAPL, aerobic conditions and very low dissolved contaminant concentrations were identified in three meters vertical distance from the phase. Comprehensive two-dimensional gas chromatography-mass spectrometry (GC×GC-MS) proved to be an efficient tool to characterize the behavior of the present complex contaminant mixture. Medium to low bioavailability of ferric iron and manganese oxides of aquifer samples was detected via incubation with Shewanella alga and evidence for iron and manganese reduction was collected. In contrast, 16S rDNA phylogenetic analysis revealed the absence of common iron reducing bacteria. Aerobic hydrocarbon degraders were abundant in shallow horizons, while nitrate reducers were dominating in deeper aquifer regions, in addition to a low relative abundance of methanogenic archaea. Partial Least Squares - Canonical Correspondence Analysis (PLS-CCA) suggested that nitrate and oxygen concentrations had the greatest impact on aquifer community structure in on- and offsite wells, which had a similarly high biodiversity (H' and Chao1). Overall, slow hydrocarbon dissolution from the DNAPL appears to dominate natural attenuation processes. This site may serve as a model for developing legal and technical strategies for the treatment of DNAPL-impacted sites where contaminant plumes are absent or shrinking.

Synergistic androgenic effect of a petroleum product caused by the joint action of at least three different types of compounds.

In a previous study, we found a dose-dependent synergistic effect in recombinant yeast stably transfected with the human androgen receptor (AR), in response to co-exposure to testosterone and a commercially-available lubricant (engine) oil for cars. As there is relatively little knowledge on synergistic toxic effects and causative compounds, particularly for the androgenic system, the objective of the present study was to investigate this oil in more detail. The oil was fractionated into SARA fractions (so-called 'saturates', 'aromatics', 'resins', and 'asphaltenes') by open column chromatography. Surprisingly, when exposing the recombinant AR yeast to testosterone in combination with the separate SARA fractions, the synergistic effect could not be reproduced fully. After pooling the fractions again however, the full synergism returned. From subsequent exposures to combinations of two or three SARA fractions, it appeared that both the 'saturates' and the 'resins' fraction were required for obtaining the synergistic response with testosterone. This clearly demonstrates a synergistic effect related to the androgenic system caused by the joint action of at least three chemically-distinct compounds, or groups of compounds (i.e. testosterone, 'resins' and 'saturates'). Although detailed chemical analyses could not reveal the identity of the causative compounds and the in vivo relevance of the present results remains unclear, the results do add to the growing body of evidence on the potentially extremely complex character of mixture effects.

Do stressful conditions make adaptation difficult? Guppies in the oil-polluted environments of southern Trinidad.

The ability of populations to rapidly adapt to new environments will determine their future in an increasingly human-modified world. Although meta-analyses do frequently uncover signatures of local adaptation, they also reveal many exceptions. We suggest that particular constraints on local adaptation might arise when organisms are exposed to novel stressors, such as anthropogenic pollution. To inform this possibility, we studied the extent to which guppies (Poecilia reticulata) show local adaptation to oil pollution in southern Trinidad. Neutral genetic markers revealed that paired populations in oil-polluted versus not-polluted habitats diverged independently in two different watersheds. Morphometrics revealed some divergence (particularly in head shape) between these environments, some of which was parallel between rivers. Reciprocal transplant experiments in nature, however, found little evidence of local adaptation based on survival and growth. Moreover, subsequent laboratory experiments showed that the two populations from oil-polluted sites showed only weak local adaptation even when compared to guppies from oil-free northern Trinidad. We conclude that guppies show little local adaptation to oil pollution, which might result from the challenges associated with adaptation to particularly stressful environments. It might also reflect genetic drift owing to small population sizes and/or high gene flow between environments.

Use of the distributions of adamantane acids to profile short-term temporal and pond-scale spatial variations in the composition of oil sands process-affected waters.

Oil industry produced waters, such as the oils sands process-affected waters (OSPW) of Alberta, Canada, represent a challenge in terms of risk assessment and reclamation due to their extreme complexity, particularly of the organic chemical constituents, including the naphthenic acids (NA). The identification of numerous NA in single samples has raised promise for the use of NA distributions for profiling OSPW. However, monitoring of the success of containment is still difficult, due to the lack of knowledge of the homogeneity (or otherwise) of OSPW composition within, and between, different industry containments. Here we used GC×GC-MS to compare the NA of five OSPW samples from each of two different industries. Short-term temporal and pond-scale spatial variations in the distributions of known adamantane acids and diacids and other unknown tricyclic acids were examined and a statistical appraisal of the replicate data made. The presence/absence of individual acids easily distinguished the OSPW NA of one industry from those of the other. The proportions of tricyclic acids with different carbon numbers also varied significantly between the OSPW of the two industries. The pond-scale spatial variation in NA in OSPW samples was higher than the short-term (2 weeks) temporal variations. An OSPW sample from an aged pond was exceptionally high in the proportion of C15,16,17 compounds, possibly due to increased biotransformation. Such techniques could possibly also help to distinguish different sources of NA in the environment.

Bicyclic naphthenic acids in oil sands process water: identification by comprehensive multidimensional gas chromatography-mass spectrometry.

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.

Aquatic hazard assessment of a commercial sample of naphthenic acids.

This paper presents chemical composition and aquatic toxicity characteristics of a commercial sample of naphthenic acids (NAs). Naphthenic acids are derived from the refining of petroleum middle distillates and can contribute to refinery effluent toxicity. NAs are also present in oil sands process-affected water (OSPW), but differences in the NAs compositions from these sources precludes using a common aquatic toxicity dataset to represent the aquatic hazards of NAs from both origins. Our chemical characterization of a commercial sample of NAs showed it to contain in order of abundance, 1-ring>2-ring>acyclic>3-ring acids (∼84%). Also present were monoaromatic acids (7%) and non-acids (9%, polyaromatic hydrocarbons and sulfur heterocyclic compounds). While the acyclic acids were only the third most abundant group, the five most abundant individual compounds were identified as C(10-14) n-acids (n-decanoic acid to n-tetradecanoic acid). Aquatic toxicity testing of fish (Pimephales promelas), invertebrate (Daphnia magna), algae (Pseudokirchneriella subcapitata), and bacteria (Vibrio fischeri) showed P. promelas to be the most sensitive species with 96-h LL50=9.0 mg L(-1) (LC50=5.6 mg L(-1)). Acute EL50 values for the other species ranged 24-46 mg L(-1) (EC50 values ranged 20-30 mg L(-1)). Biomimetic extraction via solid-phase-microextraction (BE-SPME) suggested a nonpolar narcosis mode of toxic action for D. magna, P. subcapitata, and V. fischeri. The BE analysis under-predicted fish toxicity, which indicates that a specific mode of action, besides narcosis, may be a factor for fishes.

Can two-dimensional gas chromatography/mass spectrometric identification of bicyclic aromatic acids in petroleum fractions help to reveal further details of aromatic hydrocarbon biotransformation pathways?

RATIONALE: The identification of key acid metabolites ('signature' metabolites) has allowed significant improvements to be made in our understanding of the biodegradation of petroleum hydrocarbons, in reservoir and in contaminated natural systems, such as aquifers and seawater. On this basis, anaerobic oxidation is now more widely accepted as one viable mechanism, for instance. However, identification of metabolites in the complex acid mixtures from petroleum degradation is challenging and would benefit from use of more highly resolving analytical methods. METHODS: Comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GCxGC/TOFMS) with both nominal mass and accurate mass measurement was used to study the complex mixtures of aromatic acids (as methyl esters) in petroleum fractions. RESULTS: Numerous mono- and di-aromatic acid isomers were identified in a commercial naphthenic acids fraction from petroleum and in an acids fraction from a biodegraded petroleum. In many instances, compounds were identified by comparison of mass spectral and retention time data with those of authentic compounds. CONCLUSIONS: The identification of a variety of alkyl naphthalene carboxylic and alkanoic and alkyl tetralin carboxylic and alkanoic acids, plus identifications of a range of alkyl indane acids, provides further evidence for 'signature' metabolites of biodegradation of aromatic petroleum hydrocarbons. Identifications such as these now offer the prospect of better differentiation of metabolites of bacterial processes (e.g. aerobic, methanogenic, sulphate-reducing) in polar petroleum fractions.

Profiling oil sands mixtures from industrial developments and natural groundwaters for source identification.

The objective of this study was to identify chemical components that could distinguish chemical mixtures in oil sands process-affected water (OSPW) that had potentially migrated to groundwater in the oil sands development area of northern Alberta, Canada. In the first part of the study, OSPW samples from two different tailings ponds and a broad range of natural groundwater samples were assessed with historically employed techniques as Level-1 analyses, including geochemistry, total concentrations of naphthenic acids (NAs) and synchronous fluorescence spectroscopy (SFS). While these analyses did not allow for reliable source differentiation, they did identify samples containing significant concentrations of oil sands acid-extractable organics (AEOs). In applying Level-2 profiling analyses using electrospray ionization high resolution mass spectrometry (ESI-HRMS) and comprehensive multidimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOF/MS) to samples containing appreciable AEO concentrations, differentiation of natural from OSPW sources was apparent through measurements of O2:O4 ion class ratios (ESI-HRMS) and diagnostic ions for two families of suspected monoaromatic acids (GC × GC-TOF/MS). The resemblance between the AEO profiles from OSPW and from 6 groundwater samples adjacent to two tailings ponds implies a common source, supporting the use of these complimentary analyses for source identification. These samples included two of upward flowing groundwater collected <1 m beneath the Athabasca River, suggesting OSPW-affected groundwater is reaching the river system.

Diaromatic sulphur-containing 'naphthenic' acids in process waters.

Polar organic compounds found in industrial process waters, particularly those originating from biodegraded petroleum residues, include 'naphthenic acids' (NA). Some NA have been shown to have acute toxicity to fish and also to produce sub-lethal effects. Whilst some of these toxic effects are produced by identifiable carboxylic acids, acids such as sulphur-containing acids, which have been detected, but not yet identified, may produce others. Therefore, in the present study, the sulphur-containing acids in oil sands process water were studied. A fraction (ca 12% by weight of the total NA containing ca 1.5% weight sulphur) was obtained by elution of methylated NA through an argentation solid phase extraction column with diethyl ether. This was examined by multidimensional comprehensive gas chromatography-mass spectrometry (GCxGC-MS) in both nominal and high resolution mass accuracy modes and by GCxGC-sulphur chemiluminescence detection (GCxGC-SCD). Interpretation of the mass spectra and retention behaviour of methyl esters of several synthesised sulphur acids and the unknowns allowed delimitation of the structures, but not complete identification. Diaromatic sulphur-containing alkanoic acids were suggested. Computer modelling of the toxicities of some of the possible acids suggested they would have similar toxicities to one another and to dehydroabietic acid. However, the sulphur-rich fraction was not toxic or estrogenic to trout hepatocytes, suggesting the concentrations of sulphur acids in this sample were too low to produce any such effects in vitro. Further samples should probably be examined for these compounds.