Chemical fingerprinting of naphthenic acids and oil sands process waters-A review of analytical methods for environmental samples

Advances in mass spectrometric characterization of naphthenic acids fraction compounds in oil sands environmental samples and crude oil--A review

There has been a recent surge in the development of mass spectrometric methods for detailed characterization of naphthenic acid fraction compounds (all C(c)H(h)N(n)O(o)S(s), species, including heteroatomic and aromatic components in the acid-extractable fraction) in environmental samples. This surge is driven by the increased activity in oil sands environmental monitoring programs in Canada, the exponential increase in research studies on the isolation and toxicity identification of components in oil sands process water (OSPW), and the analytical requirements for development of technologies for treatment of OSPW. There has been additional impetus due to the parallel studies to control corrosion from naphthenic acids during the mining and refining of heavy bitumen and crude oils. As a result, a range of new mass spectrometry tools have been introduced since our last major review of this topic in 2009. Of particular significance are the developments of combined mass spectrometric methods that incorporate technologies such as gas chromatography, liquid chromatography, and ion mobility. There has been additional progress with respect to improved visualization methods for petroleomics and oil sands environmental forensics. For comprehensive coverage and more reliable characterization of samples, an approach based on multiple-methods that employ two or more ionization modes is recommended. On-line or off-line fractionation of isolated extracts, with or without derivatization, might also be used prior to mass spectrometric analyses. Individual ionization methods have their associated strengths and weaknesses, including biases, and thus dependence upon a single ionization method is potentially misleading. There is also a growing trend to not rely solely on low-resolution mass spectrometric methods (<20,000 resolving power at m/z 200) for characterization of complex samples. Future research is anticipated to focus upon (i) structural elucidation of components to determine the correlation with toxicity or corrosion, (ii) verification of characterization studies based on authentic reference standards and reference materials, and (iii) integrated approaches based on multiple-methods and ionization methods for more-reliable oil sands environmental forensics.

Impact of temperature, pH, and salinity changes on the physico-chemical properties of model naphthenic acids

The effects of temperature, pH, and salinity change on naphthenic acids (NAs) present in oil-sands process wastewater were modeled for 55 representative NAs. COSMO-RS was used to estimate octanol-water (KOW) and octanol-air (KOA) partition ratios and Henry's law constants (H). Validation with experimental carboxylic acid data yielded log KOW and log H RMS errors of 0.45 and 0.55 respectively. Calculations of log KOW, (or log D, for pH-dependence), log KOA and log H (or log HD, for pH-dependence) were made for model NAs between -20 °C and 40 °C, pH between 0 and 14, and salinity between 0 and 3 g NaCl L(-1). Temperature increase by 60 °C resulted in 3-5 log unit increase in H and a similar magnitude decrease in KOA. pH increase above the NA pKa resulted in a dramatic decrease in both log D and log HD. Salinity increase over the 0-3 g NaCl L(-1) range resulted in a 0.3 log unit increase on average for KOW and H values. Log KOW values of the sodium salt and anion of the conjugate base were also estimated to examine their potential for contribution to the overall partitioning of NAs. Sodium salts and anions of naphthenic acids are predicted to have on average 4 log units and 6 log units lower log KOW values, respectively, with respect to the corresponding neutral NA. Partitioning properties are profoundly influenced by the by the relative prevailing pH and the substance's pKa at the relevant temperature.

Determining the effect of oil sands process-affected water on grazing behaviour of Daphnia magna, long-term consequences, and mechanism

Oil sands process-affected water (OSPW) is a byproduct of the extraction of bitumen in the surface-mining oil sands industry and is currently stored in on-site tailings ponds. OSPW from three oil sands companies were studied to capture some of the variability associated with OSPW characteristics. To investigate the effect and mechanism(s) of effect of OSPW on feeding behaviour, Daphnia magna were exposed to low OSPW concentrations for 24 h and monitored for their feeding rate, olfactory response and swimming activity. The Al and Si content, which are indicators of suspended particulate matter in D. magna exposed to OSPW were investigated using energy-dispersive X-ray (EDX) spectroscopy. In long-term experiments, effects of exposure to OSPW for 21 days on feeding behaviour, growth, and reproduction of D. magna were evaluated. Feeding rates were similar among the three exposure populations, yielding a 24 h IC50 of 5.3% OSPW. Results of behavioural assays suggest that OSPW impairs the chemosensory function and reduces the total activity of D. magna. In EDX spectroscopy, Al and Si were detected in the body of the exposed D. magna, suggesting that D. magna filter clay particles from the OSPW solution. Results of the long-term exposure showed that OSPW significantly inhibits feeding behaviour, suppresses growth, and reduces reproductive output of D. magna. There were no differences in the toxicity of the three samples of OSPW, which was in agreement with the fact that there were no differences in the species of dissolved organic compounds in the OSPW samples.

Sensitivity of walleye (Sander vitreus) and fathead minnow (Pimephales promelas) early-life stages to naphthenic acid fraction components extracted from fresh oil sands process-affected waters

Unconventional oil production in Alberta's oil sands generates oil sands process-affected water (OSPW), which contains toxic constituents such as naphthenic acid fraction components (NAFCs). There have been few studies examining effects of NAFC exposure over long periods of early-life stage development in fish. Here we examined the effects of NAFCs extracted from OSPW to embryo-larval fathead minnow, exposed for 21 days. We compared the sensitivity of fathead minnow to walleye reared to 7 days post-hatch (18-20 days total). EC50s for hatch success, including deformities, and total survival were lower for walleye (10-11 mg/L) than fathead minnow (22-25 mg/L), with little post-hatch mortality observed in either species. NAFC exposure affected larval growth at concentrations below the EC50 in fathead minnow (total mass IC10 14-17 mg/L). These data contribute to an understanding of the developmental stages targeted by oil sands NAFCs, as well as their toxicity in a greater range of relevant taxa.

A novel solid-state fractionation of naphthenic acid fraction components from oil sands process-affected water

Various sorbent materials were evaluated for the fractionation of naphthenic acid fraction components (NAFCs) from oil sand process-affected water (OSPW). The solid phase materials include activated carbon (AC), cellulose, iron oxides (magnetite and goethite), polyaniline (PANI) and three types of biochar derived from biomass (BC-1; rice husks, BC-2; acacia low temperature and BC-3; acacia high temperature). NAFCs were semi-quantified using electrospray ionization high resolution Orbitrap mass spectrometry (ESI-MS) and the metals were assessed by inductively coupled plasma optical emission spectrometry (ICP-OES). The average removal efficacy of NAFCs by AC was 95%. The removal efficacy decreased in the following order: AC, BC-1>BC-2, BC-3, goethite>PANI>cellulose, magnetite. The removal of metals did not follow a clear trend; however, there was notable leaching of potassium by AC and biochar samples. The bound NAFCs by AC were desorbed efficiently with methanol. Methanol regeneration and recycling of AC revealed 88% removal on the fourth cycle; a 4.4% decrease from the first cycle. This fractionation method represents a rapid, cost-effective, efficient, and green strategy for NAFCs from OSPW, as compared with conventional solvent extraction.

Beyond Naphthenic Acids: Environmental Screening of Water from Natural Sources and the Athabasca Oil Sands Industry Using Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

There is a growing need for environmental screening of natural waters in the Athabasca region of Alberta, Canada, particularly in the differentiation between anthropogenic and naturally-derived organic compounds associated with weathered bitumen deposits. Previous research has focused primarily upon characterization of naphthenic acids in water samples by negative-ion electrospray ionization methods. Atmospheric pressure photoionization is a much less widely used ionization method, but one that affords the possibility of observing low polarity compounds that cannot be readily observed by electrospray ionization. This study describes the first usage of atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry (in both positive-ion and negative-ion modes) to characterize and compare extracts of oil sands process water, river water, and groundwater samples from areas associated with oil sands mining activities. When comparing mass spectra previously obtained by electrospray ionization and data acquired by atmospheric pressure photoionization, there can be a doubling of the number of components detected. In addition to polar compounds that have previously been observed, low-polarity, sulfur-containing compounds and hydrocarbons that do not incorporate a heteroatom were detected. These latter components, which are not amenable to electrospray ionization, have potential for screening efforts within monitoring programs of the oil sands.

Toxicity of naphthenic acid fraction components extracted from fresh and aged oil sands process-affected waters, and commercial naphthenic acid mixtures, to fathead minnow (Pimephales promelas) embryos

Naphthenic acids (NAs) are constituents of oil sands process-affected water (OSPW). These compounds can be both toxic and persistent and thus are a primary concern for the ultimate remediation of tailings ponds in northern Alberta's oil sands regions. Recent research has focused on the toxicity of NAs to the highly vulnerable early life-stages of fish. Here we examined fathead minnow embryonic survival, growth and deformities after exposure to extracted NA fraction components (NAFCs), from fresh and aged oil sands process-affected water (OSPW), as well as commercially available NA mixtures. Commercial NA mixtures were dominated by acyclic O2 species, while NAFCs from OSPW were dominated by bi- and tricyclic O2 species. Fathead minnow embryos less than 24h old were reared in tissue culture plates terminating at hatch. Both NAFC and commercial NA mixtures reduced hatch success, although NAFCs from OSPW were less toxic (EC50=5-12mg/L, nominal concentrations) than commercial NAs (2mg/L, nominal concentrations). The toxicities of NAFCs from aged and fresh OSPW were similar. Embryonic heart rates at 2 days post-fertilization (dpf) declined with increasing NAFC exposure, paralleling patterns of hatch success and rates of cardiovascular abnormalities (e.g., pericardial edemas) at hatch. Finfold deformities increased in exposures to commercial NA mixtures, not NAFCs. Thus, commercial NA mixtures are not appropriate surrogates for NAFC toxicity. Further work clarifying the mechanisms of action of NAFCs in OSPW, as well as comparisons with additional aged sources of OSPW, is merited.

Characterization of organic composition in snow and surface waters in the Athabasca Oil Sands Region, using ultrahigh resolution Fourier transform mass spectrometry

This study was conducted to characterize the composition of dissolved organic compounds present in snow and surface waters in the Athabasca Oil Sands Region (AOSR) with the goal of identifying whether atmospherically-derived organic compounds present in snow are a significant contributor to the compounds detected in surface waters (i.e., rivers and lakes). We used electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR MS) to characterize the dissolved organic compound compositions of snow and surface water samples. The organic profiles obtained for the snow samples show compositional differences between samples from near-field sites (<5 km from oil sands activities) and those from more distant locations (i.e., far-field sites). There are also significant compositional differences between samples collected in near-field sites and surface water samples in the AOSR. The composition of dissolved organic compounds at the upstream Athabasca River site (i.e., Athabasca River at Athabasca) is found to be different from samples obtained from downstream sites in the vicinity of oil sands operations (i.e., Athabasca River at Fort McMurray and Athabasca River at Firebag confluence). The upstream Athabasca River sites tended to share some compositional similarities with far-field snow deposition, while the downstream Athabasca River sites are more similar to local lakes and tributaries. This contrast likely indicates the relative role of regional snowmelt contributions to the Athabasca River vs inputs from local catchments in the reach downstream of Fort McMurray.

Oil sands naphthenic acids: a review of properties, measurement, and treatment

The Alberta oil sands contain one of the world's largest reserves of oil - over 169 billion barrels of bitumen are economically recoverable with current extraction technologies. Surface mining and subsequent hot water extraction of bitumen from the ore generates about nine cubic meters of raw tailings per cubic meter of oil. Oil sands facilities are required to operate under a policy of zero water discharge, resulting in ponds containing more than one billion cubic meters of tailings, a mixture of sand, fines and process-affected water. Process-affected water contains numerous organic compounds, including naphthenic acids (NAs), which have been identified as the primary source of acute toxicity of process-affected water. Developments in analytical techniques, aerobic biodegradability, and treatment via chemical oxidation (ozone) of NAs are reviewed. The field continues to be challenged by the lack of a cost-effective, accurate analytical technique for NAs or an understanding of all the organic constituents in process-affected water that may be contributing to observed toxicity and thus requiring treatment.

Removal and toxicity reduction of naphthenic acids by ozonation and combined ozonation-aerobic biodegradation

A commercial naphthenic acids (NAs) mixture (TCI Chemicals) and five model NA compounds were ozonated in a semibatch mode. Ozonation of 25 and 35 mg/L NA mixture followed pseudo first-order kinetics (k(obs)=0.11±0.008 min(-1); r(2)=0.989) with a residual NAs concentration of about 5 mg/L. Ozone reacted preferentially with NAs of higher cyclicity and molecular weight and decreased both cyclicity and the acute Microtox® toxicity by 3.3-fold. The ozone reactivity with acyclic and monocyclic model NAs varied and depended on other structural features, such as branching and the presence of tertiary or quaternary carbons. Batch aerobic degradation of unozonated NA mixture using a NA-enriched culture resulted in 83% NA removal and a 6.7-fold decrease in toxicity, whereas a combination of ozonation-biodegradation resulted in 89% NA removal and a 15-fold decrease in toxicity. Thus, ozonation of NA-bearing waste streams coupled with biodegradation are effective treatment processes.

Identification of estrogenic compounds in oil sands process waters by effect directed analysis

Using effect directed analysis, the presence of estrogenic components in untreated and biologically treated oil sands process water (OSPW) was detected with the yeast estrogenic screening assay after fractionation with solid phase extraction followed by reversed phase high performance liquid chromatography. Comparison of the composition, as determined by electrospray ionization combined with high-resolution linear trap quadropole (LTQ)-Orbitrap Velos Pro hybrid mass spectrometry (negative ion) of selected estrogenic and nonestrogenic fractions identified compounds that were uniquely present in the estrogenic samples, biologically treated and untreated. Of the 30 most abundant compounds, there were 14 possible nonaromatic structures and 16 possible aromatic structures. Based on the published literature, the latter are the most likely to cause estrogenicity and were O2, O3 and O4 C17 to C20 compounds with double bond equivalents between 6 and 10 and chemical formulas similar to estrone- and estradiol-like compounds. This study shows exact formulas and masses of possible estrogenic compounds in OSPW. These findings will help to focus study on the most environmentally significant components in OSPW.

Interfacial sciences in unconventional petroleum production: from fundamentals to applications

With the ever increasing demand for energy to meet the needs of growth in population and improvement in the living standards, in particular in developing countries, the abundant unconventional oil reserves (about 70% of total world oil), such as heavy oil, oil/tar sands and shale oil, are playing an increasingly important role in securing global energy supply.

Mass spectral characterisation of a polar, esterified fraction of an organic extract of an oil sands process water

RATIONALE

Characterising complex mixtures of organic compounds in polar fractions of heavy petroleum is challenging, but is important for pollution studies and for exploration and production geochemistry. Oil sands process-affected water (OSPW) stored in large tailings ponds by Canadian oil sands industries contains such mixtures.

METHODS

A polar OSPW fraction was obtained by silver ion solid-phase extraction with methanol elution. This was examined by numerous methods, including electrospray ionisation (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) and ultra-high-pressure liquid chromatography (uHPLC)/Orbitrap MS, in multiple ionisation and MS/MS modes. Compounds were also synthesised for comparison.

RESULTS

The major ESI ionisable compounds detected (+ion mode) were C15-28 SO3 species with 3-7 double bond equivalents (DBE) and C27-28 SO5 species with 5 DBE. ESI-MS/MS collision-induced losses were due to water, methanol, water plus methanol and water plus methyl formate, typical of methyl esters of hydroxy acids. Once the fraction was re-saponified, species originally detected by positive ion MS, could be detected only by negative ion MS, consistent with their assignment as sulphur-containing hydroxy carboxylic acids. The free acid of a keto dibenzothiophene alkanoic acid was added to an unesterified acid extract of OSPW in known concentrations as a putative internal standard, but attempted quantification in this way proved unreliable.

CONCLUSIONS

The results suggest the more polar acidic organic SO3 constituents of OSPW include C15-28  S-containing, alicyclic and aromatic hydroxy carboxylic acids. SO5 species are possibly sulphone analogues of these. The origin of such compounds is probably via further biotransformation (hydroxylation) of the related S-containing carboxylic acids identified previously in a less polar OSPW fraction. The environmental risks, corrosivity and oil flow assurance effects should be easier to assess, given that partial structures are now known, although further identification is still needed.

Rapid characterization of naphthenic acids using differential mobility spectrometry and mass spectrometry

To analyze the naphthenic acid content of environmental waters quickly and efficiently, we have developed a method that employs differential mobility spectrometry (DMS) coupled to mass spectrometry (MS). This technique combines the benefits of infusion-based MS experiments (parallel, on-demand access to individual components) with DMS's ability to provide liquid chromatography-like separations of isobaric and isomeric compounds in a fraction of the time. In this study, we have applied a DMS-MS workflow to the rapid gas-phase separation of naphthenic acids (NAs) within a technical standard and a real-world oil sands process-affected water (OSPW) extract. Among the findings provided by this workflow are the rapid characterization of isomeric NAs (i.e., same molecular formulas) in a complex OSPW sample, the ability to use DMS to isolate individual NA components (including isomeric NAs) for in-depth structural analyses, and a method by which NA analytes, background ions, and dimer species can be characterized by their distinct behaviors in DMS. Overall, the profiles of the NA content of the technical and OSPW samples were consistent with published values for similar samples, such that the benefits of DMS technology do not detract from the workflow's accuracy or quality.

Evaluation of biologically mediated changes in oil sands naphthenic acid composition by Chlamydomonas reinhardtii using negative-ion electrospray orbitrap mass spectrometry

Industrial activity associated with oil-sands extraction in Canada's Athabasca region produces a variety of contaminants of concern, including naphthenic acid fraction components (NAFCs). NAFCs are a complex mixture of organic compounds that are poorly understood both in terms of their chemical composition and effects on the environment. NAFC toxicity in the unicellular green algae Chlamydomonas reinhardtii P.A.Dangeard was correlated with the presence of the algal cell wall. It was suggested that the toxicity of NAFCs in C. reinhardtii was due to surfactant effects. Surfactant-cell wall interactions are specific and governed by the compound class and structure, and by the nature of the biological material. Here, we investigate the effects of wildtype (WT) C. reinhardtii and two cell-wall mutants on specific classes of NAFCs when growing cultures were treated with a 100 mg · L(-1) solution of NAFCs. Changes in the NAFC composition in the media were examined using high resolution mass spectrometry over a period of 4 d. Algal mediated changes in the NAFCs were limited to specific classes of NAFCs. In particular, the removal of large, classical naphthenic acids, with a double bond equivalent of 8, was observed in WT C. reinhardtii cultures. The observed algal mediated changes in NAFC composition would have been masked by low resolution mass spectrometry and highlight the importance of this tool in examining bioremediation of complex mixtures of NAFCs.

An added dimension: GC atmospheric pressure chemical ionization FTICR MS and the Athabasca oil sands

The Athabasca oil sands industry, an alternative source of petroleum, uses large quantities of water during processing of the oil sands. In keeping with Canadian environmental policy, the processed water cannot be released to natural waters and is thus retained on-site in large tailings ponds. There is an increasing need for further development of analytical methods for environmental monitoring. The following details the first example of the application of gas chromatography atmospheric pressure chemical ionization Fourier transform ion cyclotron resonance mass spectrometry (GC-APCI-FTICR MS) for the study of environmental samples from the Athabasca region of Canada. APCI offers the advantages of reduced fragmentation compared to other ionization methods and is also more amenable to compounds that are inaccessible by electrospray ionization. The combination of GC with ultrahigh resolution mass spectrometry can improve the characterization of complex mixtures where components cannot be resolved by GC alone. This, in turn, affords the ability to monitor extracted ion chromatograms for components of the same nominal mass and isomers in the complex mixtures. The proof of concept work described here is based upon the characterization of one oil sands process water sample and two groundwater samples in the area of oil sands activity. Using the new method, the Ox and OxS compound classes predominated, with OxS classes being particularly relevant to the oil sands industry. The potential to resolve retention times for individual components within the complex mixture, highlighting contributions from isomers, and to characterize retention time profiles for homologous series is shown, in addition to the ability to follow profiles of double bond equivalents and carbon number for a compound class as a function of retention time. The method is shown to be well-suited for environmental forensics.

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.

Uptake and speciation of vanadium in the benthic invertebrate Hyalella azteca

Vanadium has the potential to leach into the environment from petroleum coke, an oil sands byproduct. To determine uptake of vanadium species in the biota, we exposed the benthic invertebrate Hyalella azteca with increasing concentrations of two different vanadium species, V(IV) and V(V), for seven days. The concentrations of vanadium in the H. azteca tissue increased with the concentration of vanadium in the exposure water. Speciation analysis revealed that V(IV) in the exposure water was oxidized to V(V) between renewal periods, and therefore the animals were mostly exposed to V(V). Speciation analysis of the H. azteca tissue showed the presence of V(V), V(IV), and an unidentified vanadium species. These results indicate the uptake and metabolism of vanadium by H. azteca. Because H. azteca are widely distributed in freshwater systems and are an important food supply for many fish, determining the uptake and metabolism of vanadium allows for a better understanding of the potential environmental effects on invertebrates.

Diamondoid diacids ('O4' species) in oil sands process-affected water

RATIONALE

As a by-product of oil sands extraction, large volumes of oil sands process water (OSPW) are generated, which are contaminated with a large range of water-soluble organic compounds. The acids are thought to be derived from hydrocarbons via natural biodegradation pathways such as α- and β-oxidation of alkyl substituents, which could produce mono- and diacids, for example. However, while several monoacids ('O2' species) have been identified, the presence of diacids (i.e. 'O4' species) has only been deduced from results obtained via Fourier transform infrared (FTIR) spectroscopy, Fourier transform ion cyclotron resonance high-resolution mass spectrometry (FTICR-HRMS) and nuclear magnetic resonance ((1)H-NMR) spectroscopy and the structures have never been confirmed.

METHODS

An extract of an OSPW from a Canadian tailings pond was analysed and the retention times and the electron ionization mass spectra of some analytes were compared with those of bis-methyl esters of authentic diacids by gas chromatography × gas chromatography/time-of-flight mass spectrometry (GCxGC/TOFMS) in nominal and accurate mass configurations.

RESULTS

Two diamondoid diacids (3-carboxymethyladamantane-1-carboxylic acid and adamantane-1,3-dicarboxylic acid) were firmly identified as their bis-methyl esters by retention time and mass spectral matching and several other structural isomers were more tentatively assigned. Diacids have substantially increased polarity over the hydrocarbon and monoacid species from which they probably derive: as late members of biodegradation processes they may be useful indicators of weathering and ageing, not only of OSPW, but potentially of crude oil residues more generally.

CONCLUSIONS

Structures of O4 species in OSPW have been identified. This confirms pathways of microbial biodegradation, which were only postulated previously, and may be a further indication that remediation of OSPW toxicity can occur by natural microbial action. The presence and abundance of these diacids might therefore be useful as a measure of biodegradation and weathering.