Naphthenic Acid Fraction Compounds Research Articles

Low adsorption affinity of athabasca oil sands naphthenic acid fraction compounds to a peat-mineral mixture

Much of the toxicity in oil sands process-affected water in Athabasca oil sands tailings has been attributed to naphthenic acids (NAs) and associated naphthenic acid fraction compounds (NAFCs). Previous work has characterized the environmental behaviour and fate of these compounds, particularly in the context of constructed treatment wetlands. There is evidence that wetlands can attenuate NAFCs in natural and engineered contexts, but relative contributions of chemical, biotic, and physical adsorption with sequestration require deconvolution. In this work, the objective was to evaluate the extent to which prospective wetland substrate material may adsorb NAFCs using a peat-mineral mix (PMM) sourced from the Athabasca Oil Sands Region (AOSR). The PMM and NAFCs were first mixed and then equilibrated across a range of NAFC concentrations (5–500 mg/L) with moderate ionic strength and hardness (∼200 ppm combined Ca2+ and Mg2+) that approximate wetland water chemistry. Under these experimental conditions, low sorption of NAFCs to PMM was observed, where sorbed concentrations of NAFCs were approximately zero mg/kg at equilibrium. When NAFCs and PMM were mixed and equilibrated together at environmentally relevant concentrations, formula diversity increased more than could be explained by combining constituent spectra. The TOC present in this PMM was largely cellulose-derived, with low levels of thermally recalcitrant carbon (e.g., lignin, black carbon). The apparent enhancement of the concentration and diversity of components in PMM/NAFCs mixtures are likely related to aqueous solubility of some PMM-derived organic materials, as post-hoc combination of dissolved components from PMM and NAFCs cannot replicate enhanced complexity observed when the two components are agitated and equilibrated together.

Evaluations of Weathering of Polar and Nonpolar Petroleum Components in a Simulated Freshwater-Oil Spill by Orbitrap and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry.

The comprehensive chemical characterization of crude oil is important for the evaluation of the transformation and fate of components in the environment. Molecular-level speciation of naphthenic acid fraction compounds (NAFCs) was investigated in a mesoscale spill tank using both negative-ion electrospray ionization (ESI) Orbitrap mass spectrometry (MS) and positive-ion atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry (APPI-FT-ICR-MS). Both ionization techniques are coupled to high-resolution mass spectrometric detectors (ESI: Orbitrap MS; APPI: FT-ICR-MS at 9.4 T), enabling insight into the behavior and fate of petrogenic compounds during a simulated freshwater crude oil spill. Negative-ion ESI Orbitrap-MS reveals that oxygen-containing (Ox) classes are detected early in the spill, whereby species with more oxygen per molecule evolve later in the simulated spill. The O2-containing species gradually decreased in relative abundance, while O3 and O4 species increased in relative abundance throughout the simulated spill, which could correspond to a relative degree of oxygen incorporation. Nonpolar speciation by positive-ion APPI 9.4 T FT-ICR-MS allowed for the identification of water-soluble nonpolar and less polar acidic species. Molecular-level graphical representation of elemental compositions derived from simulated spill water-soluble and oil-soluble species suggest that biological activity is the primary degradation mechanism and that biodegradation was the dominant mechanism based on the negative-ion ESI Orbitrap-MS results.

Naphthenic acid fraction compounds, produced by the extraction of bitumen from oil sands, alter survival and behaviour of juvenile yellow perch (Perca flavescens)

We evaluated whether naphthenic acid fraction compounds (NAFCs) extracted from oil sand tailings adversely affect fish survival and behaviour. Following a before–after-control-impact design, we housed wild-caught juvenile yellow perch ( Perca flavescens) in outdoor mesocosms to assess survival and behaviour under baseline conditions, then exposed fish to one of three treatments: negative control, 2 mg/L NAFC, or 15 mg/L NAFC. We performed behavioural assays (no-stimulus activity, food stimulus, and predator stimulus using a model bird) and assessed a comprehensive suite of endpoints (equilibrium losses, activity, shoaling, burst swimming, freezing, and space use). We found that exposure to 15 mg/L NAFCs substantially reduced fish survival and impaired fish equilibrium in all three behavioural tests. Furthermore, exposure to NAFCs impaired anti-predator behaviour: while the activity of control fish increased by two-fold in response to a predator stimulus, fish exposed to 2 or 15 mg/L NAFC did not change their activity levels after stimulation. No significant changes were observed in other behavioural endpoints. Overall, our findings suggest that a week-long exposure to NAFCs at concentrations commonly found in tailings ponds, constructed wetlands, and other mining-impacted waters may affect multiple facets of fish behaviour that could ultimately lead to reduced fitness in fish populations.

Pros and Cons of Separation, Fractionation and Cleanup for Enhancement of the Quantitative Analysis of Bitumen-Derived Organics in Process-Affected Waters—A Review

Oil sands process-affected water (OSPW) contains a diverse mixture of inorganic and organic compounds. Naphthenic acids (NAs) are a subset of the organic naphthenic acid fraction compounds (NAFCs) and are a major contributor of toxicity to aquatic species. Thousands of unique chemical formulae are measured in OSPW by accurate mass spectrometry and high-resolution mass spectrometry (MS) analysis of NAFCs. As no commercial reference standard is available to cover the range of compounds present in NAFCs, quantitation may best be referred to as “semi-quantitative” and is based on the responses of one or more model compounds. Negative mode electrospray ionization (ESI-) is often used for NAFC measurement but is prone to ion suppression in complex matrices. This review discusses aspects of off-line sample preparation techniques and liquid chromatography (LC) separations to help reduce ion suppression effects and improve the comparability of both inter-laboratory and intra-laboratory results. Alternative approaches to the analytical parameters discussed include extraction solvents, salt content of samples, extraction pH, off-line sample cleanup, on-line LC chromatography, calibration standards, MS ionization modes, NAFC compound classes, MS mass resolution, and the use of internal standards.

Evaluating the attenuation of naphthenic acids in constructed wetland mesocosms planted with Carex aquatilis

Surface oil sands mining and extraction in northern Alberta’s Athabasca oil sands region produce large volumes of oil sands process–affected water (OSPW). OSPW is a complex mixture containing major contaminant classes including trace metals, polycyclic aromatic hydrocarbons, and naphthenic acid fraction compounds (NAFCs). Naphthenic acids (NAs) are the primary organic toxicants in OSPW, and reducing their concentrations is a priority for oil sands companies. Previous evidence has shown that constructed wetland treatment systems (CWTSs) are capable of reducing the concentration of NAs and the toxicity of OSPW through bioremediation. In this study, we constructed greenhouse mesocosms with OSPW or lab process water (LPW) (i.e., water designed to mimic OSPW minus the NAFC content) with three treatments: (1) OSPW planted with Carex aquatilis; (2) OSPW, no plants; and (3) LPW, no plants. The OSPW–C. aquatilis treatment saw a significant reduction in NAFC concentrations in comparison to OSPW, no plant treatments, but both changed the distribution of the NAFCs in similar ways. Upon completion of the study, treatments with OSPW saw fewer high-molecular-weight NAs and an increase in the abundance of O3- and O4-containing formulae. Results from this study provide invaluable information on how constructed wetlands can be used in future remediation of OSPW in a way that previous studies were unable to achieve due to uncontrollable environmental factors in field experiments and the active, high-energy processes used in CWTSs pilot studies.

Online Membrane Sampling for the Mass Spectrometric Analysis of Oil Sands Process Affected Water-Derived Naphthenic Acids in Real-World Samples

Large volumes of oil sands process-affected waters (OSPW) result from heavy oil extraction in Alberta, Canada. Currently, a toxic legacy of ca. 500 Mm3 is stored in tailings ponds under a zero-discharge policy. OSPW is a complex mixture of suspended and dissolved materials including a wide range of inorganic and organic contaminants. Classically defined naphthenic acids (NAs; CnH2n+ZO2) are one of the primary toxic fractions in OSPW and have therefore been the subject of considerable research interest. Most studies employ considerable sample cleanup followed by liquid chromatography and/or high-resolution mass spectrometry (HRMS) for the characterization of these complex mixtures. However, these strategies can be time- and cost-intensive, limiting the scope of research and adoption for regulatory purposes. Condensed phase membrane introduction mass spectrometry (CP-MIMS) is emerging as a “fit-for-purpose” approach for the analysis of NAs. This technique directly interfaces the mass spectrometer with an aqueous sample using a hydrophobic semi-permeable membrane, requiring only pH adjustment to convert NAs to a membrane-permeable form. Here, we examine the perm-selectivity of classical NAs (O2) relative to their more oxidized counterparts (O3–O7) and heteroatomic (N, S) species collectively termed naphthenic acid fraction compounds (NAFCs). The investigation of 14 model compounds revealed that classically defined NAs are greater than 50-fold more membrane permeable than their oxidized/heteroatomic analogs. HRMS analysis of real OSPW extracts with and without membrane clean-up further supported selectivity towards the toxic O2 class of NAs, with >85% of the overall signal intensity attributable to O2 NAs in the membrane permeate despite as little as 34.7 ± 0.6% O2 NAs observed in the directly infused mixture. The information collected with HRMS is leveraged to refine our method for analysis of NAs at unit mass resolution. This new method is applied to 28 archived real-world samples containing NAs/NAFCs from constructed wetlands, OSPW, and environmental monitoring campaigns. Concentrations ranged from 0–25 mg/L O2 NAs and the results measured by CP-MIMS (unit mass) and SPE-HRMS (Orbitrap) showed good agreement (slope = 0.80; R2 = 0.76).

Chemical communication in wood frog (Rana sylvatica) tadpoles is influenced by early-life exposure to naphthenic acid fraction compounds

Environmental pollutants can disrupt chemical communication between aquatic organisms by interfering with the production, transmission, and/or detection of, as well as responses to, chemical cues. Here, we test the hypothesis that early-life exposure to naphthenic acid fraction compounds (NAFCs) from oil sands tailings disrupts antipredator-associated chemical communication in larval amphibians. Wild adult wood frogs (Rana sylvatica) captured during their natural breeding period were combined (1 female:2 males) in six replicate mesocosms filled with either uncontaminated lakewater or with NAFCs isolated from an active tailings pond in Alberta, Canada, at nominal 5 mg/L concentrations. Egg clutches were incubated and tadpoles maintained in their respective mesocosms for ∼40 days post-hatch. Tadpoles (Gosner stage 25-31) were then transferred individually to trial arenas filled with uncontaminated water and exposed to one of six chemical alarm cue (AC) stimuli solutions following a 3 × 2 × 2 design (3 AC types × 2 stimulus carriers × 2 rearing exposure groups). Relative to control tadpoles, NAFC-exposed tadpoles demonstrated higher baseline activity levels (line crosses and direction changes) when introduced to uncontaminated water. Antipredator responses differed in graded fashion with AC type, with control ACs eliciting the greatest latency to resume activity, water the least, and NAFC-exposed ACs intermediate. Pre- to post-stimulus difference scores were non-significant in control tadpoles, while NAFC-exposed tadpoles demonstrated significantly greater variation. While this suggests that exposure to NAFCs from fertilization through hatching may have interfered with AC production, it is unclear whether the quality or quantity of cues was affected. There was also no clear evidence that NAFC carrier water interfered with ACs or the alarm response in unexposed control tadpoles. These results emphasize the importance of understanding how behavioral and physiological effects of early-life NAFC exposure on critical antipredator responses may persist across life history stages.

Naphthenic acid fraction compounds reduce the reproductive success of wood frogs (Rana sylvatica) by affecting offspring viability

Understanding the toxicity of organic compounds in oil sands process-affected water (OSPW) is necessary to inform the development of environmental guidelines related to wastewater management in Canada's oil sands region. In the present study, we investigated the effects of naphthenic acid fraction compounds (NAFCs), one of the most toxic components of OSPW, on mating behaviour, fertility, and offspring viability in the wood frog (Rana sylvatica). Wild adult wood frogs were exposed separately from the opposite sex to 0, 5, or 10 mg/L of OSPW-derived NAFCs for 24 h and then combined in outdoor lake water mesocosms containing the same NAFC concentrations (n = 2 males and 1 female per mesocosm, n = 3 mesocosms per treatment). Mating events were recorded for 48 h and egg masses were measured to determine adult fertility. NAFC exposure had no significant effect on mating behaviour (probability of amplexus and oviposition, amplexus and oviposition latency, total duration of amplexus and number of amplectic events) or fertility (fertilization success and clutch size). Tadpoles (50 individuals per mesocosm at hatching, and 15 individuals per mesocosm from 42 d post-hatch) were reared in the same mesocosms under chronic NAFC exposure until metamorphic climax (61–85 d after hatching). Offspring exposed to 10 mg/L NAFCs during development were less likely to survive and complete metamorphosis, grew at a reduced rate, and displayed more frequent morphological abnormalities. These abnormalities included limb anomalies at metamorphosis, described for the first time after NAFC exposure. The results of this study suggest that NAFCs reduce wood frog reproductive success through declines in offspring viability and therefore raise the concern that exposure to NAFCs during reproduction and development may affect the recruitment of native amphibian populations in the oil sands region.

Naphthenic Acid Fraction Compounds Reduce the Reproductive Success of Wood Frogs (Rana Sylvatica)

Naphthenic Acid Fraction Compounds Reduce the Reproductive Success of Wood Frogs (Rana Sylvatica)

Transcriptome Analysis of Environmental Pseudomonas Isolates Reveals Mechanisms of Biodegradation of Naphthenic Acid Fraction Compounds (NAFCs) in Oil Sands Tailings.

Naphthenic acid fraction compounds (NAFCs) are highly recalcitrant constituents of oil sands tailings. Although some microorganisms in the tailings can individually and synergistically metabolize NAFCs, the biochemical mechanisms that underpin these processes are hitherto unknown. To this end, we isolated two microorganisms, Pseudomonas protegens and Pseudomonas putida, from oils sands tailings and analyzed their transcriptomes to shed light on the metabolic processes employed by them to degrade and detoxify NAFCs. We identified 1048, 521 and 1434 genes that are upregulated in P. protegens, P. putida and a 1:1 co-culture of the strains, respectively. We subsequently enumerated the biochemical activities of enriched genes and gene products to reveal the identities of the enzymes that are associated with NAFC degradation. Separately, we analyzed the NAFCs that are degraded by the two pseudomonads and their 1:1 co-culture and determined the composition of the molecules using mass spectrometry. We then compared these molecular formulas to those of the cognate substrates of the enriched enzymes to chart the metabolic network and understand the mechanisms of degradation that are employed by the microbial cultures. Not only does the consortium behave differently than the pure cultures, but our analysis also revealed the mechanisms responsible for accelerated rate of degradation of NAFCs by the co-culture. Our findings provide new directions for engineering or evolving microorganisms and their consortia for degrading NAFCs more stably and aggressively.

Transformation of bitumen-derived naphthenic acid fraction compounds across surface waters of wetlands in the Athabasca Oil Sands region

Bitumen is extracted from oil sands in the Athabasca Oil Sands region (AOSR) of Alberta, Canada. Much of the bitumen-derived toxicity in mine waste is attributable to naphthenic acid fraction compounds (NAFCs). Mines in the AOSR are required to be returned to a natural state after closure; thus, cost-effective strategies are needed to reduce toxicity from NAFCs. Previous studies have demonstrated the capability of constructed wetlands to attenuate NAFCs. However, the capacity of wetlands in the natural environment to degrade and transform NAFCs to less toxic components is poorly understood. To better understand the spatial distribution and fate of NAFCs in natural wetlands, samples were collected across the surfaces of two mature opportunistic wetlands near active oil sands mines. The first wetland has a well-defined surface flow pathway and inflows affected by overburden containing lean bitumen ore. The second wetland, in contrast, is a stagnant water body with raw bitumen visible along its edges. For the wetland with a well defined flow path, NAFCs decreased in concentration down gradient, while oxidized NAFCs constituted a greater proportion of NAFCs with increase in flow path. Likewise there was a decrease in the molecular weights of NAFCs, similar to trends observed in constructed wetland treatment systems. In comparison, NAFCs were more uniformly distributed across the relatively stagnant wetland. Overall, these data provide new evidence that mature opportunistic wetlands in the AOSR can promote the degradation and oxidation of bitumen-derived naphthenic acids into less toxic compounds.

Characterization of naphthenic acid fraction compounds in water from Athabasca oil sands wetlands by Orbitrap high-resolution mass spectrometry.

Classical naphthenic acids (NAs) are known to be primary aquatic toxicants of concern in the Athabasca oil sands region (AOSR), and are a component of naphthenic acid fraction compounds (NAFCs). Recent studies conducted in the AOSR have examined metals and polycyclic aromatic hydrocarbons in regional wetlands. However, few studies have described NAs and/or NAFCs in AOSR wetlands. To address this gap, we examined NAFC profiles in the water of different wetlands in the AOSR, including naturalized borrow pits (i.e., abandoned pits created by excavation of road-building materials), and opportunistically-formed wetlands associated with reclamation activities. For comparison, NAFC profiles from these wetlands were compared to an opportunistic wetland formed from tailings pond dyke seepage. Samples were prepared using solid-phase extraction and analyzed using negative-ion high-resolution Orbitrap mass spectrometry. Principal component analyses (PCA) revealed patterns to the NAFC profiles in the wetlands. The first distinct grouping of wetlands included water bodies associated with reclamation activities that are located on and/or adjacent to mining overburden. One other wetland, HATS5w, separated from all other wetlands during PCA, and had a unique NAFC profile; detailed examination of NAFCs revealed HATS5w contained the heaviest (i.e., high m/z components) and most unsaturated NAFCs among study locations, demonstrating the usefulness of high-resolution mass spectrometry for characterizing individual wetlands. The NAFCs of HATS5w are also substantially different from bitumen-derived inputs in overburden-adjacent opportunistic wetlands. Collectively, the NAFC profiles presented provide new information on background levels of polar bitumen-derived organics in AOSR wetlands.

Molecular profiles of naphthenic acid fraction compounds from mine lease wetlands in the Athabasca Oil Sands Region

Naphthenic acid fraction compounds (NAFCs) are a toxicologically relevant component of oil sands process-affected materials (OSPM). For the first time, we report on differences in the concentrations and distribution of NAFCs from wetlands on an Athabasca oil sands mine site with varied histories of solid and liquid OSPM input. Sampling locations included natural and naturalized reference wetlands, a reclaimed tailings pond, wetlands supplemented with OSPM, opportunistic wetlands, and tailings ponds. Samples were prepared using solid-phase extraction, and analyzed by high-resolution Orbitrap mass spectrometry; NAFC concentrations and characteristics were evaluated for all locations. The NAFCs from tailings ponds were dominated by O3-NAFCs and classical naphthenic acids (NAs; i.e., O2 species) with double bond equivalences of 3 and 4. Reference wetlands had no dominant species, and relatively little NAFC content. The heteroatomic species in opportunistic wetlands were dominated by highly-oxidized NAFC species, where Σ [O3:O6] species constituted 55–75% of the assignable spectrum and 3–4% NAs; in tailings ponds NAs constituted 47–51%. A relatively young (4-year-old) wetland built on a former tailings pond had NAFC concentrations between 65 and 80 mg/L, and NAs constituted 47% of the assignable spectrum. There was thus little apparent oxidation of NAFCs at this young wetland. The composition of NAFCs from one wetland (≥15 years old) supplemented with OSPM contained a greater proportion of oxidized species than tailings, suggesting NAFC transformation therein. These data suggest that while NAFCs are persistent in some wetlands, there is preliminary evidence for oxidation in mature wetlands.

Treatment of oil sands process affected waters by constructed wetlands: Evaluation of designs and plant types

Constructed wetland treatment systems (CWTS)s can be used to treat various wastewaters. The main constituent in oil sands process-affected water (OSPW) with uncertain treatment by CWTS are naphthenic acid fraction compounds (NAFC)s. The NAFCs are also among the primary contributors of toxicity to aquatic organisms. While there is preliminary evidence that some CWTSs are capable of treating OSPW for future potential discharge, there is little information comparing the effectiveness and efficiencies of different CWTS designs.Obtaining large volumes of OSPW for testing can be difficult, and while it is known that synthetic NAFCs are simpler and have different toxicity than OSPW-NAFCs, it is unknown whether they could serve as a proxy for optimization of CWTS design and operation. This study presents a comprehensive comparison of CWTS performance operated with both synthetic OSPW and OSPW for four CWTS designs differing in plant type, aeration, flow path, water depth, and substrate type. This study evaluated the potential biodegradation of NAFCs including: (1) decrease in total NAFC concentration, (2) shifts in Ox-NAFC fractions from O2- to O3-, O4-, and O5-NAFC, (3) decrease in carbon number, (4) decrease of the double bond equivalencies (DBE), and (5) change in toxicity of the waters to test organisms.CWTS planted with Sedge achieved the greatest extent of NAFC treatment and detoxification regardless of design. Although CWTSs planted with Cattail and Bulrush also degraded NAFCs and decreased toxicity, a greater hydraulic retention time was required, and the total extent of treatment was less than the CWTSs planted with Sedge. While synthetic OSPW was more toxic and experienced faster degradation rates, it showed similar trends to OSPW in terms of CWTS design efficiencies and function. Although synthetic OSPW would not be appropriate for modelling or scaling of CWTSs, it can be useful for testing designs and operating conditions.

Developments in Molecular Level Characterization of Naphthenic Acid Fraction Compounds Degradation in a Constructed Wetland Treatment System

The reclamation of oil sands process-affected water (OSPW) is a matter of environmental importance because of the aquatic toxicity to biota. This study describes refinements in advanced analytical methods to assess the performance of biological treatment systems for OSPW, such as constructed wetland treatment systems (CWTSs). Assessment of treatment efficiency by measurement of the degradation of naphthenic acid fraction compounds (NAFCs) in OSPW is challenging in CWTS due to potentially interfering constituents such as humic acids, organic acids, salts, and hydrocarbons. Here we have applied a previous weak anion exchange (WAX) solid-phase extraction (SPE) method and high-resolution Orbitrap-mass spectrometry (MS) to remove major interferences from the NAFC analysis. The refinements in data processing employing principal component analysis (PCA) indicates that the relative abundance of NAFCs decreased with time in the treated OSPW relative to the untreated OSPW. The most saturated NAFCs with higher carbon numbers were relatively more degraded as compared to unsaturated NAFCs. The use of Kendrick plots and van Krevelen plots for assessment of the performance of the CWTS is shown to be well-suited to detailed monitoring of the complex composition of NAFCs as a function of degradation. The developments and application of analytical methods such as the WAX SPE method and high-resolution Orbitrap-MS are demonstrated as tools enabling the advancement of CWTS design and optimization, enabling passive or semi-passive water treatment systems to be a viable opportunity for OSPW treatment.

Oil sands process affected water sourced Trichoderma harzianum demonstrates capacity for mycoremediation of naphthenic acid fraction compounds

Development of Alberta’s oil sands requires large volumes of water, leading to the abundance of oil sands process affected water (OSPW) that must be remediated prior to discharge or reuse. OSPW contains a variety of dissolved organic compounds, however naphthenic acids (NAs) have been found to contribute significantly to the toxicity of OSPW. A fungus, Trichoderma harzianum, isolated directly from OSPW, has previously demonstrated a high tolerance and capacity for growth in the presence of commercial NAs. This study conducted microcosm experiments to elucidate and characterize the capacity of T. harzianum to degrade labile commercial NAs (Merichem), and OSPW-sourced naphthenic acid fraction compounds (NAFCs). Additionally, two model NA compounds, the simple single ring cyclohexane carboxylic acid (CHCA) and complex diamondoid 1-adamanatane carboxylic acid (ADA), were utilized to determine the influence of NA structure on degradation. T. harzianum degraded 14% of CHCA, 13% of ADA, and 23–47% of Merichem NAs. Additionally, Orbitrap mass spectrometry revealed a large change in Z-series within NAFCs. This removal and shift in composition correlated to a 59% and 52% drop in toxicity as per Microtox, for Merichem NAs and NAFCs respectively. This proof of concept experiment confirms that the fungal species T. harzianum can contribute to the biodegradation of complex dissolved organics found in OSPW, including cyclic and diamondoid structures.

Fourier transform infrared spectroscopy as a surrogate tool for the quantification of naphthenic acids in oil sands process water and groundwater

Naphthenic acid fraction compounds (NAFCs), defined herein as the polar organic compounds extracted from the acidified oil sands process water (OSPW) samples using dichloromethane, are becoming the research hotspot due to their presence in large amount in OSPW and along with other potentially NA-contaminated water streams from the mining site. Fourier transform infrared spectroscopy (FTIR) method is commonly used to quantify NAFCs and assumes that the total NA concentration is measured as the sum of the responses for all carboxylic acid functional groups. In this study, the NAFCs in various OSPW and groundwater (GW) samples from an active oil sands mining site were analyzed using FTIR. All water samples were pretreated using either solid-phase extraction (SPE) or liquid-liquid extraction (LLE) methods before analysis. The results showed that SPE produced higher recoveries of NAFCs than LLE for most water samples under current experimental conditions. For the quantification of NAFCs, commercial Fluka NA mixture and a pre-calibrated OSPW extract were employed as the calibration standards. The NAFCs calibrated with Fluka NA mixture and OSPW extract had clear linear relationships. The concentrations of NAFCs obtained using OSPW extract standard curve were 2.5 times the NAFC concentrations obtained using the Fluka NA mixture standard curve. Additionally, good linear correlations were observed between the total NAs and O2-O6 NA species determined by ultra-performance liquid chromatography coupled with time-of-flight mass spectrometry (UPLC-TOFMS) and the NAFCs measured by FTIR. According to these correlations, the NA compositions in NAFCs were developed, and the relative abundances of O2-O6 NA species in NAFCs were similar for SPE and LLE pretreated samples. The findings of this study demonstrated that FTIR could be used as a promising tool to monitor total NA species and to estimate the NA profile in different environmental water samples.

Characterization of naphthenic acids in crude oils and refined petroleum products

Naphthenic acids (NAs) or naphthenic acid fraction compounds (NAFCs) are generally recognized as a family of cycloaliphatic carboxylic acids naturally occurring in petroleum. These acid extractable organics (AEOs) from petroleum industry activities including oil sands produced waters (OSPW) have led to increasing environmental concern in recent years due to their potential release into the environment. This study presents a characterization of naphthenic acids in a number of crude oils and refined petroleum products from various sources. NAs with unsaturated degree of z −2 to z −24 and carbon number ranging from 6 to 60 were determined by liquid chromatography-high resolution Orbitrap mass spectrometry (LC-HRMS). NA profiles generally vary from oil to oil. Conventional light crude oils generally contain low concentrations of NAs, while heavier crudes and oil sands bitumen contain significant levels of NAs. NAs in Federated and Alaska North Slope crude oils are relatively low with O2-NA concentrations of 139 µg/g and 419 µg/g, respectively, while their abundances are as high as 7994 µg/g in Venezuelan Orinoco bitumen. The ratio of even to odd (E/O) carbon number NAs in all petroleum oils studied is close to 1.0 for z −2 to z −24 NAs. NA series z 0 to z −12 in bitumen account for about 90% of the total determined NAs, and z −14 to z −24 NAs make up the remaining ∼10%. Moreover, z −2∼−6 (1- to 3-ring) NAs are the most predominant in all oil samples. In terms of distribution according to carbon number, C6 to C21 NAs (α-group) make up about 44.2% of the total NAs in an Alberta oil sands bitumen. Caustic extraction of oil sands bitumen mostly transports the more toxic low-molecular weight portion of NAs into OSPW, in which α-group NAs constitute about 90% of the total NAs. Evaporation (up to 23.6% by weight) weathering slightly enriched the NAs but likely did not affect the distribution profile of NAs in a diluted bitumen (dilbit).

Derivatization for Nontargeted Screening of Acids in Oilfield Refinery Wastewater: Identification and Behaviors of Recalcitrant Chlorinated Naphthenic Acids.

The nontargeted scanning chemical profiling approach has shown great potential to identify unknown pollutants or novel biological markers; however, the structure identification of unknown compounds is a challenge. In this study, a carboxyl-specific derivatization reagent, N-(4-aminomethylphenyl) pyridinium (AMPP), was coupled with QTOF-MSE-MS scanning to establish a high-throughput nontargeted scanning method for acid compounds. The scanning method can isolate the precursor by data-independent acquisition and can select all of the acid compounds based on the characteristic fragment generated from the derivatization reagent. The method was applied to scan naphthenic acid fraction compounds in petroleum refinery wastewater and identify 70-126 NAs, 30-68 oxy-NAs, 54-60 NAs containing nitrogen, and 66-75 NAs containing both nitrogen and oxygen. Chlorinated NAs (Cl-NAs) including monochlorinated NAs (Cl-NAs), monochlorinated hydroxylated NAs (Cl-OH-NAs), and dichlorinated dihydroxylated NAs (Cl2-(OH)2-NAs) were first identified with the aid of chlorine isotopic patterns. The Cl-NAs might be naturally presented in crude oil together with NAs. Occurrences and mass balances of Cl-NAs were further assessed in the wastewater treatment plant in north China. The total concentrations of ∑Cl-NAs were estimated to be 12 ± 7.8-18 ± 17 μg/L and 8.5 ± 2.0-68 ± 35 μg/g in the wastewater and solid samples, respectively. The removal efficiencies of Cl-NAs (-29.9 to 34.3%) were much lower than those of NAs, suggesting the high recalcitrance of chlorinated compounds during the treatment processes. The estimated mass loss fractions due to degradation for Cl-NAs were 26.5-53.4% of initial loadings, and relatively high fractions (32.1-56.8%) were observed in the effluent directly discharged to the environment. Advanced treatment techniques are needed to effectively reduce the persistent Cl-NAs in the wastewater.

Fate and behavior of oil sands naphthenic acids in a pilot-scale treatment wetland as characterized by negative-ion electrospray ionization Orbitrap mass spectrometry

Large volumes of oil sands process-affected water (OSPW) are generated during the extraction of bitumen from oil sands in the Athabasca region of northeastern Alberta, Canada. As part of the development of treatment technologies, molecular characterization of naphthenic acids (NAs) and naphthenic acid fraction compounds (NAFC) in wetlands is a topic of research to better understand their fate and behavior in aquatic environments. Reported here is the application of high-resolution negative-ion electrospray Orbitrap-mass spectrometry for molecular characterization of NAs and NAFCs in a non-aerated constructed treatment wetland. The effectiveness of the wetlands to remove OSPW-NAs and NAFCs was evaluated by monitoring the changes in distributions of NAFC compounds in the untreated sample and non-aerated treatment system. After correction for measured evapotranspiration, the removal rate of the classical NAs followed approximately first-order kinetics, with higher rates observed for structures with relatively higher number of carbon atoms. These findings indicate that constructed wetland treatment is a viable method for removal of classical NAs in OSPW. Work is underway to evaluate the effects of wetland design on water quality improvement, preferential removal of different NAFC species, and reduction in toxicity.