Application of the Target Lipid Model and Passive Samplers to Characterize the Toxicity of Bioavailable Organics in Oil Sands Process-Affected Water

Comprehensive characterization of organics in oil sands process water in constructed mesocosms utilizing multiple analytical methods

This study aims to provide a thorough characterization of dissolved organics in oil sands process water (OSPW) in field-based aquatic mesocosms at both molecular and bulk measurement levels using multiple analytical methods. In a 3-year outdoor mesocosm experiment, the analysis of naphthenic acid (NA) species was conducted using ultra-performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOFMS). The results revealed the removal of both total NAs (38% and 35%) and classical NAs (O2-NAs, 58% and 49%) in undiluted and half-diluted OSPW, respectively. The increased ratios of oxidized NAs (O3-O6 NAs) to classical NAs suggested a transformation trend. The results also indicated that O2-NAs with higher carbon number and lower double bond equivalent (DBE) were more easily degraded in the mesocosm systems. Biomimetic extraction using solid-phase microextraction (BE-SPME) measurement displayed 26% (undiluted OSPW) and 30% (half-diluted OSPW) decrease in total bioavailable organics over 3 years. Naphthenic acids fraction compounds (NAFCs) obtained by liquid-liquid extraction (LLE) were also determined using Fourier transform infrared spectroscopy (FTIR). Reduction in acute toxicity for undiluted (43%) and half-diluted (26%) OSPW was observed over 3 years, which are well correlated with the decreases of NAs and BE-SPME concentrations. Moreover, BE-SPME values were found to be linearly correlated with total NAs concentrations (r = 0.96) and NAFCs (r = 0.96). Additionally, the linear relationships of individual O2-O6 NA species and BE-SPME concentrations unveiled the changes in the relative abundances of O2-O6 NA species in total bioavailable organics over time in the mesocosms. The present study has provided comprehensive insights by integrating various analytical methods, contributing valuable information for assessing the effectiveness of aquatic mesocosm systems in studying the temporal changes of organics in OSPW.

Exploring nature's filters: Peat-mineral mix for low and high-strength oilfield produced water reclamation

Nature-based solutions are encouraged for treating oilfield produced water from oil and gas extraction, a crucial undertaking that aligns with the Canadian oil sands industry's ambitious goal of zero waste, and the globally recognized Sustainable Development Goals (SDGs) pertaining to water conservation and ecosystem preservation. This study explored the use of peat-mineral mix (PMM), a leftover of inevitable oil sands mining, for treating low and high-strength wastewaters during biofiltration, which contained large molecular weight (44.3 kDa), which include alcohols, aliphatics, aromatics, and ketones, and can impart high toxicity to both fauna and flora (MicroTox: 99 %). The breakthrough curve indicated an effective initial adsorption phase driven by advection within the column dynamics. For complete organics removal and mechanistic insights, the wastewater was re-circulated in a continuous mode for up to 42 days. Here, we found that chemical oxygen demand was reduced from ∼85,000 mg/L to ∼965 mg/L). Kinetics investigations along with physicochemical characterization of PMM and wastewater suggested that chemisorption and anaerobic digestion contributed to the overall removal of contaminants. Chemisorption, led by hydrogen bonding and hydrophobic interactions, was the dominant mechanism, with a limited contribution from physical adsorption (surface area: 2.85 m2/g). The microbial community within the PMM bed was rich/diverse (Shannon > 6.0; Chao1 > 600), with ∼ 50 % unclassified phylotypes representing 'microbial dark matter'. High electric conductivity (332.1 μS cm-1) of PMM and the presence of Geobacter, syntrophs, and Methanosaeta suggest that direct interspecies electron transfer was likely occurring during anaerobic digestion. Both low and high-strength wastewaters showed effective removal of dissolved organics (e.g., naphthenic acids, acid extractable fraction, oil and grease content), nutrients, and potentially toxic metals. The successful use of PMM in treating oilfield produced water offers promising avenues for embracing nature-based remediation solutions at oil refining sites.

A Light Touch: Solar Photocatalysis Detoxifies Oil Sands Process-Affected Waters Prior to Significant Treatment of Naphthenic Acids

Environmental reclamation of Canada's oil sands tailings ponds is among the single largest water treatment challenges globally. The toxicity of oil sands process-affected water (OSPW) has been associated with its dissolved organics, a complex mixture of naphthenic acid fraction components (NAFCs). Here, we evaluated solar treatment with buoyant photocatalysts (BPCs) as a passive advanced oxidation process (P-AOP) for OSPW remediation. Photocatalysis fully degraded naphthenic acids (NAs) and acid extractable organics (AEO) in 3 different OSPW samples. However, classical NAs and AEO, traditionally considered among the principal toxicants in OSPW, were not correlated with OSPW toxicity herein. Instead, nontarget petroleomic analysis revealed that low-polarity organosulfur compounds, composing <10% of the total AEO, apparently accounted for the majority of waters' toxicity to fish, as described by a model of tissue partitioning. These findings have implications for OSPW release, for which a less extensive but more selective treatment may be required than previously expected.

In Silico Acute Aquatic Hazard Assessment and Prioritization Using a Grouped Target Site Model: A Case Study of Organic Substances Reported in Permian Basin Hydraulic Fracturing Operations

Hydraulic fracturing (HF) is commonly used to enhance onshore recovery of oil and gas during production. This process involves the use of a variety of chemicals to support the physical extraction of oil and gas, maintain appropriate conditions downhole (e.g., redox conditions, pH), and limit microbial growth. The diversity of chemicals used in HF presents a significant challenge for risk assessment. The objective of the present study is to establish a transparent, reproducible procedure for estimating 5th percentile acute aquatic hazard concentrations (e.g., acute hazard concentration 5th percentiles [HC5s]) for these substances and validating against existing toxicity data. A simplified, grouped target site model (gTSM) was developed using a database (n = 1696) of diverse compounds with known mode of action (MoA) information. Statistical significance testing was employed to reduce model complexity by combining 11 discrete MoAs into three general hazard groups. The new model was trained and validated using an 80:20 allocation of the experimental database. The gTSM predicts toxicity using a combination of target site water partition coefficients and hazard group-based critical target site concentrations. Model performance was comparable to the original TSM using 40% fewer parameters. Model predictions were judged to be sufficiently reliable and the gTSM was further used to prioritize a subset of reported Permian Basin HF substances for risk evaluation. The gTSM was applied to predict hazard groups, species acute toxicity, and acute HC5s for 186 organic compounds (neutral and ionic). Toxicity predictions and acute HC5 estimates were validated against measured acute toxicity data compiled for HF substances. This case study supports the gTSM as an efficient, cost-effective computational tool for rapid aquatic hazard assessment of diverse organic chemicals. Environ Toxicol Chem 2024;00:1-12. © 2024 ExxonMobil Petroleum and Chemical BV. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Sample preparation, analytical characterization, monitoring, risk assessment and treatment of naphthenic acids in industrial wastewater and surrounding water impacted by unconventional petroleum production

Industrial extraction of unconventional petroleum results in notable volumes of oil sands process water (OSPW), containing elevated concentrations of naphthenic acids (NAs). The presence of NAs represents an intricate amalgamation of dissolved organic constituents, thereby presenting a notable hurdle for the domain of environmental analytical chemistry. There is growing concern about monitoring the potential seepage of OSPW NAs into nearby groundwater and river water. This review summarizes recent studies on sample preparation, characterization, monitoring, risk assessment, and treatment of NAs in industrial wastewater and surrounding water. Sample preparation approaches, such as liquid-liquid extraction, solid phase microextraction, and solid phase extraction, are crucial in isolating chemical standards, performing molecular level analysis, assessing aquatic toxicity, monitoring, and treating OSPW. Instrument techniques for NAs analysis were reviewed to cover different injection modes, ionization sources, and mass analyzers. Recent studies of transfer and transformation of NAs provide insights to differentiate between anthropogenic and natural bitumen-derived sources of NAs. In addition, related risk assessment and treatment studies were also present for elucidation of environmental implication and reclamation strategies. The synthesis of the current state of scientific knowledge presented in this review targets government regulators, academic researchers, and industrial scientists with interests spanning analytical chemistry, toxicology, and wastewater management.

Modeling the Partitioning of Anionic Carboxylic and Perfluoroalkyl Carboxylic and Sulfonic Acids to Octanol and Membrane Lipid

Perfluoroalkyl carboxylic and sulfonic acids (PFCAs and PFSAs, respectively) have low acid dissociation constant values and are, therefore, deprotonated under most experimental and environmental conditions. Hence, the anionic species dominate their partitioning between water and organic phases, including octanol and phospholipid bilayers which are often used as model systems for environmental and biological matrices. However, data for solvent-water (SW) and membrane-water partition coefficients of the anion species are only available for a few per- and polyfluoroalkyl substances (PFAS). In the present study, an equation is derived using a Born-Haber cycle that relates the partition coefficients of the anions to those of the corresponding neutral species. It is shown via a thermodynamic analysis that for carboxylic acids (CAs), PFCAs, and PFSAs, the log of the solvent-water partition coefficient of the anion, log KSW (A- ), is linearly related to the log of the solvent-water partition coefficient of the neutral acid, log KSW (HA), with a unity slope and a solvent-dependent but solute-independent intercept within a PFAS (or CA) family. This finding provides a method for estimating the partition coefficients of PFCAs and PFSAs anions using the partition coefficients of the neutral species, which can be reliably predicted using quantum chemical methods. In addition, we have found that the neutral octanol-water partition coefficient, log KOW , is linearly correlated to the neutral membrane-water partition coefficient, log KMW ; therefore, log KOW , being a much easier property to estimate and/or measure, can be used to predict the neutral log KMW . Application of this approach to KOW and KMW for PFCAs and PFSAs demonstrates the utility of this methodology for evaluating reported experimental data and extending anion property data for chain lengths that are unavailable. Environ Toxicol Chem 2023;42:2317-2328. © 2023 SETAC.

Abiotic and biotic constituents of oil sands process-affected waters

The oil sands in Northern Alberta are the largest oil sands in the world, providing an important economic resource for the Canadian energy industry. The extraction of petroleum in the oil sands begins with the addition of hot water to the bituminous sediment, generating oil sands process-affected water (OSPW), which is acutely toxic to organisms. Trillions of litres of OSPW are stored on oil sands mining leased sites in man-made reservoirs called tailings ponds. As the volume of OSPW increases, concerns arise regarding the reclamation and eventual release of this water back into the environment. OSPW is composed of a complex and heterogeneous mix of components that vary based on factors such as company extraction techniques, age of the water, location, and bitumen ore quality. Therefore, the effective remediation of OSPW requires the consideration of abiotic and biotic constituents within it to understand short and long term effects of treatments used. This review summarizes selected chemicals and organisms in these waters and their interactions to provide a holistic perspective on the physiochemical and microbial dynamics underpinning OSPW .

Recommendations for advancing test protocols examining the photo-induced toxicity of petroleum and polycyclic aromatic compounds

Photo-induced toxicity of petroleum products and polycyclic aromatic compounds (PACs) is the enhanced toxicity caused by their interaction with ultraviolet radiation and occurs by two distinct mechanisms: photosensitization and photomodification. Laboratory approaches for designing, conducting, and reporting of photo-induced toxicity studies are reviewed and recommended to enhance the original Chemical Response to Oil Spills: Ecological Research Forum (CROSERF) protocols which did not address photo-induced toxicity. Guidance is provided on conducting photo-induced toxicity tests, including test species, endpoints, experimental design and dosing, light sources, irradiance measurement, chemical characterization, and data reporting. Because of distinct mechanisms, aspects of photosensitization (change in compound energy state) and photomodification (change in compound structure) are addressed separately, and practical applications in laboratory and field studies and advances in predictive modeling are discussed. One goal for developing standardized testing protocols is to support lab-to-field extrapolations, which in the case of petroleum substances often requires a modeling framework to account for differential physicochemical properties of the constituents. Recommendations are provided to promote greater standardization of laboratory studies on photo-induced toxicity, thus facilitating comparisons across studies and generating data needed to improve models used in oil spill science.

Bridging the lab to field divide: Advancing oil spill biological effects models requires revisiting aquatic toxicity testing

Oil fate and exposure modeling addresses the complexities of oil composition, weathering, partitioning in the environment, and the distributions and behaviors of aquatic biota to estimate exposure histories, i.e., oil component concentrations and environmental conditions experienced over time. Several approaches with increasing levels of complexity (i.e., aquatic toxicity model tiers, corresponding to varying purposes and applications) have been and continue to be developed to predict adverse effects resulting from these exposures. At Tiers 1 and 2, toxicity-based screening thresholds for assumed representative oil component compositions are used to inform spill response and risk evaluations, requiring limited toxicity data, analytical oil characterizations, and computer resources. Concentration-response relationships are employed in Tier 3 to quantify effects of assumed oil component mixture compositions. Oil spill modeling capabilities presently allow predictions of spatial and temporal compositional changes during exposure, which support mixture-based modeling frameworks. Such approaches rely on summed effects of components using toxic units to enable more realistic analyses (Tier 4). This review provides guidance for toxicological studies to inform the development of, provide input to, and validate Tier 4 aquatic toxicity models for assessing oil spill effects on aquatic biota. Evaluation of organisms' exposure histories using a toxic unit model reflects the current state-of the-science and provides an improved approach for quantifying effects of oil constituents on aquatic organisms. Since the mixture compositions in toxicity tests are not representative of field exposures, modelers rely on studies using single compounds to build toxicity models accounting for the additive effects of dynamic mixture exposures that occur after spills. Single compound toxicity data are needed to quantify the influence of exposure duration and modifying environmental factors (e.g., temperature, light) on observed effects for advancing use of this framework. Well-characterized whole oil bioassay data should be used to validate and refine these models.

Temporal chemical composition changes in water below a crude oil slick irradiated with natural sunlight

Photooxidation can alter the environmental fate and effects of spilled oil. To better understand this process, oil slicks were generated on seawater mesocosms and exposed to sunlight for 8 days. The molecular composition of seawater under irradiated and non-irradiated oil slicks was characterized using ion mobility spectrometry-mass spectrometry and polyaromatic hydrocarbons analyses. Biomimetic extraction was performed to quantify neutral and ionized constituents. Results show that seawater underneath irradiated oil showed significantly higher amounts of hydrocarbons with oxygen- and sulfur-containing by-products peaking by day 4-6; however, concentrations of dissolved organic carbon were similar. Biomimetic extraction indicated toxic units in irradiated mesocosms increased, mainly due to ionized components, but remained <1, suggesting limited potential for ecotoxicity. Because the experimental design mimicked important aspects of natural conditions (freshly collected seawater, natural sunlight, and relevant oil thickness and concentrations), this study improves our understanding of the effects of photooxidation during a marine oil spill.

Treatment of naphthenic acids in oil sands process-affected waters with a surface flow treatment wetland: mass removal, half-life, and toxicity-reduction

This study is the first to investigate the removal of naphthenic acids in a full-scale constructed wetland within the Alberta Oil Sands region. The average mass-removal efficiency for all O₂-naphthenic acids measured in three separate deployments in the wetland ranged from 7.5% to 68.9% and appeared sensitive to physicochemical properties of the naphthenic acids, environmental conditions, and water quality. Treatment efficiency of individual naphthenic acids was found to increase with increasing carbon number and decreasing number of double bond equivalents in the molecule. Treatment efficiency was also found to increase with both higher initial turbidity in OSPW entering the wetland, and warmer average OSPW temperatures during wetland operation. Half-life times of naphthenic acids in the treatment wetland ranged between 8.9 and 39 days and were substantially lower than those in tailings ponds (i.e., 12.9-13.6 years) and laboratory studies focussed on bench-scale aerobic microbial biodegradation (i.e., 44-315 days). Using published dose-response data, biomimetic extraction measurements using solid phase microextraction fibers indicate that 14 days of wetland treatment resulted in a reduction in (4 d) deformity of Danio rerio from 50 to 16%, while exhibiting less than 1% toxic response for less sensitive toxic endpoints. The study concludes that wetland treatment is a feasible and productive treatment method for naphthenic acids in oil sands process-affected water due to a combination of sorption and biodegradation.

Interlaboratory Comparison of a Biomimetic Extraction Method Applied to Oil Sands Process-Affected Waters

Biomimetic extraction using solid-phase microextraction is a passive sampling analytical method that can predict the aquatic toxicity of complex petroleum substances. The method provides a nonanimal alternative to traditional bioassays with the potential to reduce both vertebrate and invertebrate aquatic toxicity testing. The technique uses commercially available polydimethylsiloxane-coated fibers that, following nondepletive extraction of water samples, are injected into a gas chromatograph with flame ionization detection. As the predictive nature of the method is operationally defined, it is critical that its application be harmonized with regard to extraction, analysis, and standardization parameters. Results are presented from a round robin program comparing the results from 10 laboratories analyzing four different sample sets of dissolved organics in water. Samples included two incurred oil sands process-affected waters and a cracked gas oil water accommodated fraction. A fourth sample of cracked gas oil blended in an oil sands process-affected water was analyzed to demonstrate the method's ability to differentiate between neutral and ionizable dissolved hydrocarbons. Six of the 10 laboratories applied an automated version of the method using a robotic autosampler where the critical extraction steps are precisely controlled and which permits batch screening of water samples for aquatic toxicity potential. The remaining four laboratories performed the solid-phase microextraction manually. The automated method demonstrated good reproducibility with between-laboratory variability across the six laboratories and four samples yielding a mean relative standard deviation of 14%. The corresponding between-laboratory variability across the four laboratories applying the manual extraction was 53%, demonstrating the importance of precisely controlling the extraction procedure. Environ Toxicol Chem 2022;41:1613-1622. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Changes in Chemical Composition and Copepod Toxicity during Petroleum Photo-oxidation

Photoproducts can be formed rapidly in the initial phase of a marine oil spill. However, their toxicity is not well understood. In this study, oil was irradiated, chemically characterized, and tested for toxicity in three copepod species (Acartia tonsa, Temora longicornis, and Calanus finmarchicus). Irradiation led to a depletion of polycyclic aromatic hydrocarbons (PAHs) and n-alkanes in oil residues, along with an enrichment in aromatic and aliphatic oil photoproducts. Target lipid model-based calculations of PAH toxicity units predicted that PAH toxicities were lower in water-accommodated fractions (WAFs) of irradiated oil residues ("irradiated WAFs") than in WAFs of dark-control samples ("dark WAFs"). In contrast, biomimetic extraction (BE) measurements showed increased bioaccumulation potential of dissolved constituents of irradiated WAFs compared to dark WAFs, mainly driven by photoproducts present in irradiated oil. In line with the BE results, copepod mortality increased in irradiated WAFs compared to dark WAFs. However, low copepod toxicities were observed for WAFs produced with photo-oxidized oil slicks collected during the Deepwater Horizon oil spill. The results of this study suggest that while oil photoproducts have the potential to be a significant source of copepod toxicity, dilution and dispersion of these higher solubility products appear to help mitigate their toxicity at sea.

A critical review of the ecological status of lakes and rivers from Canada's oil sands region

We synthesize the information available from the peer-reviewed literature on the ecological status of lakes and rivers in the oil sands region (OSR) of Canada. The majority of the research from the OSR has been performed in or near the minable region and examines the concentrations, flux, or enrichment of contaminants of concern (CoCs). Proximity to oil sands facilities and the beginning of commercial activities tend to be associated with greater estimates of CoCs across studies. Research suggests the higher measurements of CoCs are typically associated with wind-blown dust, but other sources also contribute. Exploratory analyses further suggest relationships with facility production and fuel use data. Exceedances of environmental quality guidelines for CoCs are also reported in lake sediments, but there are no indications of toxicity including those within the areas of the greatest atmospheric deposition. Instead, primary production has increased in most lakes over time. Spatial differences are observed in streams, but causal relationships with industrial activity are often confounded by substantial natural influences. Despite this, there may be signals associated with site preparation for new mines, potential persistent differences, and a potential effect of petroleum coke used as fuel on some indices of health in fish captured in the Steepbank River. There is also evidence of improvements in the ecological condition of some rivers. Despite the volume of material available, much of the work remains temporally, spatially, or technically isolated. Overcoming the isolation of studies would enhance the utility of information available for the region, but additional recommendations for improving monitoring can be made, such as a shift to site-specific analyses in streams and further use of industry-reported data. Integr Environ Assess Manag 2022;18:361-387. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Assessment of oil refinery wastewater and effluent integrating bioassays, mechanistic modelling and bioavailability evaluation

Water is used in petroleum oil refineries in significant volumes for cooling, steam generation and processing of raw materials. Effective water management is required at refineries to ensure their efficient and responsible operation with respect to the water environment. However, ascertaining the potential environmental risks associated with discharge of refinery effluents to receiving waters is challenging because of their compositional complexity. Recent European research and regulatory initiatives propose a more holistic approach including biological effect methods to assess complex effluents and surface water quality. The study presented here investigated potential effects of effluent composition, particularly hydrocarbons, on aquatic toxicity and was a component of a larger study assessing contaminant removal during refinery wastewater treatment (Hjort et al 2021). The evaluation of effects utilised a novel combination of mechanistic toxicity modelling based on the exposure composition, measured bioavailable hydrocarbons using biomimetic solid phase microextraction (BE-SPME), and bioassays. The results indicate that in the refinery effluent assessments measured bioavailable hydrocarbons using BE-SPME was correlated with the responses in standard bioassays. It confirms that bioassays are providing relevant data and that BE-SPME measurement, combined with knowledge of other known non-hydrocarbon toxic constituents, provide key tools for toxicity identification. Overall, the results indicate that oil refinery effluents treated in accordance to the EU Industrial Emissions Directive requirements have low to negligible toxicity to aquatic organisms and their receiving environments. Low-cost, animal-free BE-SPME represents a compelling tool for rapid effluent characterization.

Application of the Target Lipid Model to Assess Toxicity of Heterocyclic Aromatic Compounds to Aquatic Organisms

Heterocyclic aromatic compounds can be found in crude oil and coal and often co-exist in environmental samples with their homocyclic aromatic counterparts. The target lipid model (TLM) is a modeling framework that relates aquatic toxicity to the octanol-water partition coefficient (K_OW ) that has been calibrated and validated for hydrocarbons. A systematic analysis of the applicability of the TLM to heterocyclic aromatic compounds has not been performed. The objective of the present study was to compile reliable toxicity data for heterocycles and determine whether observed toxicity could be successfully described by the TLM. Results indicated that the TLM could be applied to this compound class by adopting an empirically derived coefficient that accounts for partitioning between water and lipid. This coefficient was larger than previously reported for aromatic hydrocarbons, indicating that these heterocyclic compounds exhibit higher affinity to target lipid and toxicity. A mechanistic evaluation confirmed that the hydrogen bonding accepting moieties of the heteroatoms helped explain differences in partitioning behavior. Given the TLM chemical class coefficient reported in the present study, heterocyclic aromatics can now be explicitly incorporated in TLM-based risk assessments of petroleum substances, other products, or environmental media containing these compounds. Environ Toxicol Chem 2021;40:3000-3009. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Novel polar AhR-active chemicals detected in sediments of an industrial area using effect-directed analysis based on in vitro bioassays with full-scan high resolution mass spectrometric screening

Studies investigating aryl hydrocarbon receptor (AhR)-active compounds in the environment typically focus on non- and mid-polar substances, such as PAHs; while, information on polar AhR agonists remains limited. Here, we identified polar AhR agonists in sediments collected from the inland creeks of an industrialized area (Lake Sihwa, Korea) using effect-directed analysis combined with full-scan screening analysis (FSA; using LC-QTOFMS). Strong AhR-mediated potencies were observed for the polar and latter fractions of RP-HPLC (F3.5-F3.8) from sediment organic extracts in the H4IIE-luc in vitro bioassays. FSA was performed on the corresponding fractions. Twenty-eight tentative AhR agonists were chosen using a five-step process. Toxicological confirmation using bioassay revealed that canrenone, rutaecarpine, ciprofloxacin, mepanipyrim, genistein, protopine, hydrocortisone, and medroxyprogesterone were significantly active. The relative potencies of these AhR-active compounds compared to that of benzo[a]pyrene ranged from 0.00002 to 2.0. Potency balance analysis showed that polar AhR agonists explained, on average, ~6% of total AhR-mediated potencies in samples. Some novel polar AhR agonists also exhibited endocrine-disrupting potentials capable of binding to estrogen and glucocorticoid receptors, as identified by QSAR modeling. In conclusion, the focused studies on distributions, sources, fate, and ecotoxicological effects of novel polar AhR agonists in the environment are necessary.

Characterization of raw and ozonated oil sands process water utilizing atmospheric pressure gas chromatography time-of-flight mass spectrometry combined with solid phase microextractionun

This work describes a novel application of atmospheric pressure gas chromatography time-of-flight mass spectrometry (APGC-TOF-MS) combined with solid-phase microextraction (SPME) for the simultaneous analysis of hydrocarbons and naphthenic acids (NAs) species in raw and ozone-treated oil sands process water (OSPW). SPME method using polydimethylsiloxane (PDMS)-coated fibers was validated using gas chromatography with flame ionization detector (GC-FID) to ensure the SPME extractions were operated appropriately. The ionization pathways of the hydrocarbon species in OSPW in the APGC source were verified by analyzing a mixture of eight polyaromatic hydrocarbons which were ionized primarily via charge transfer to produce [M⁺] while NAs in OSPW were found to be ionized through protonation to generate [MH⁺] in the wet APGC source. SPME/APGC-TOF-MS analysis demonstrated a different composition profile in OSPW #1, with 74.5% of hydrocarbon species, 23.4% of O₂-NAs, and 2.1% of the oxidized NA species at extraction pH 2.0 compared with that obtained by UPLC-TOF-MS analysis (36.9% of O₂-NAs, 26.8% of O₃-NAs, 24.9% of O₄-NAs, 9.1% of O₅-NAs, 2.3% of O₆-NAs). Moreover, the peak areas of the total NAs and the total peak areas of NAs + hydrocarbons measured by SPME/APGC-TOF-MS correlated excellently with the total NA concentration determined by UPLC-TOF-MS (R² = 0.90) and the concentrations of the total acid-extractable organics determined by SPME/GC-FID (R² = 0.98), respectively. APGC-TOF-MS integrated with the SPME techniques could extend the range of target compounds and be a promising alternative to evaluate and characterize NAs and hydrocarbon in different water types.

A Critical Review of Analytical Methods for Comprehensive Characterization of Produced Water

Produced water is the largest waste stream associated with oil and gas production. It has a complex matrix composed of native constituents from geologic formation, chemical additives from fracturing fluids, and ubiquitous bacteria. Characterization of produced water is critical to monitor field operation, control processes, evaluate appropriate management practices and treatment effectiveness, and assess potential risks to public health and environment during the use of treated water. There is a limited understanding of produced water composition due to the inherent complexity and lack of reliable and standardized analytical methods. A comprehensive description of current analytical techniques for produced water characterization, including both standard and research methods, is discussed in this review. Multi-tiered analytical procedures are proposed, including field sampling; sample preservation; pretreatment techniques; basic water quality measurements; organic, inorganic, and radioactive materials analysis; and biological characterization. The challenges, knowledge gaps, and research needs for developing advanced analytical methods for produced water characterization, including target and nontarget analyses of unknown chemicals, are discussed.

Treatment of Polycyclic Aromatic Hydrocarbons in Oil Sands Process-Affected Water with a Surface Flow Treatment Wetland

This study applied a passive sampling approach using low-density polyethylene passive samplers to determine the treatment efficiency of the Kearl surface flow treatment wetland for polycyclic aromatic hydrocarbons (PAHs) in Oil Sands Process-affected Waters (OSPW). Treatment efficiency was measured as concentration-reduction and mass-removal from the OSPW. The results show that the wetland’s ability to remove individual PAHs from the influent varied substantially among the PAHs investigated. Treatment efficiencies of individual PAHs ranged between essentially 0% for certain methylated PAHs (e.g., 2,6-dimethylnaphthalene) to 95% for fluoranthene. Treatment in the Kearl wetland reduced the combined total mass of all detected PAHs by 54 to 83%. This corresponded to a reduction in the concentration of total PAHs in OSPW of 56 to 82% with inflow concentrations of total PAHs ranging from 7.5 to 19.4 ng/L. The concentration of pyrene in water fell below water quality targets in the Muskeg River Interim Management Framework as a result of wetland treatment. The application of the passive samplers for toxicity assessment showed that in this study PAHs in both the influent and effluent were not expected to cause acute toxicity. Passive sampling appeared to be a useful and cost-effective method for monitoring contaminants and for determining the treatment efficiency of contaminants in the treatment wetland.

Mechanisms of pH-Dependent Uptake of Ionizable Organic Chemicals by Fish from Oil Sands Process-Affected Water (OSPW)

Uptake and effects of ionizable organic chemicals (IOCs) that are weak acids in aqueous solution by fish can differ as a function of pH. While the pH-dependent behavior of select IOCs is well-understood, complex mixtures of IOCs, e.g., from oil sands process-affected water (OSPW), have not yet been studied systematically. Here, we established an in vitro screening method using the rainbow trout gill cell line, RTgill-W1, to investigate pH-dependent cytotoxicity and permeation of IOCs across cultured epithelia using ultra-high-performance liquid chromatography with high-resolution mass spectrometry (UPLC-HRMS). The assay was benchmarked using model chemicals and technical mixtures, and then used to characterize fractions and reconstituted extracts of field-collected OSPW. Significant pH-dependent cytotoxicity of individual IOCs, acidic fractions, and reconstituted extracts of OSPW was observed. In vitro data were in good agreement with data from a 96 h in vivo exposure experiment with juvenile rainbow trout. Permeation of some IOCs from OSPW was mediated by active transport, as revealed by studies in which inhibitors of these active transport mechanisms were applied. We conclude that the RTgill-W1 in vitro assay is useful for the screening of pH-dependent uptake of IOCs in fish, and has applications for in vitro-in vivo extrapolation, and prioritization of chemicals in nontarget screenings.

Recommendations for Improving Methods and Models for Aquatic Hazard Assessment of Ionizable Organic Chemicals

Ionizable organic chemicals (IOCs) such as organic acids and bases are an important substance class requiring aquatic hazard evaluation. Although the aquatic toxicity of IOCs is highly dependent on the water pH, many toxicity studies in the literature cannot be interpreted because pH was not reported or not kept constant during the experiment, calling for an adaptation and improvement of testing guidelines. The modulating influence of pH on toxicity is mainly caused by pH-dependent uptake and bioaccumulation of IOCs, which can be described by ion-trapping and toxicokinetic models. The internal effect concentrations of IOCs were found to be independent of the external pH because of organisms' and cells' ability to maintain a stable internal pH milieu. If the external pH is close to the internal pH, existing quantitative structure-activity relationships (QSARs) for neutral organics can be adapted by substituting the octanol-water partition coefficient by the ionization-corrected liposome-water distribution ratio as the hydrophobicity descriptor, demonstrated by modification of the target lipid model. Charged, zwitterionic and neutral species of an IOC can all contribute to observed toxicity, either through concentration-additive mixture effects or by interaction of different species, as is the case for uncoupling of mitochondrial respiration. For specifically acting IOCs, we recommend a 2-step screening procedure with ion-trapping/QSAR models used to predict the baseline toxicity, followed by adjustment using the toxic ratio derived from in vitro systems. Receptor- or plasma-binding models also show promise for elucidating IOC toxicity. The present review is intended to help demystify the ecotoxicity of IOCs and provide recommendations for their hazard and risk assessment. Environ Toxicol Chem 2020;39:269-286. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Persistent and transgenerational effects of raw and ozonated oil sands process-affected water exposure on a model vertebrate, the zebrafish

Exposure to oil sands process-affected water (OSPW), a by-product of Canadian oil sands mining operations, can cause both acute and chronic adverse effects in aquatic life. Ozonation effectively degrades naphthenic acids in OSPW, mitigating some of the toxicological effects of exposure. In this study we examined the effect of developmental exposure to raw and ozonated OSPW had on the breeding success, prey capture, and alarm cue response in fish months/years after exposure and the transgenerational effect exposure had on gene expression, global DNA methylation, and larval basal activity. Exposure to raw and ozonated OSPW had no effect on breeding success, and global DNA methylation. Exposure altered the expression of vtg and nkx2.5 in the unexposed F1 generation. Exposure to both raw and ozonated OSPW had a transgenerational impact on larval activity levels, anxiety behaviors, and maximum swim speed compared to the control population. Prey capture success was unaffected, however, the variability in the behavioral responses to the introduction of prey was decreased. Fish developmentally exposed to either treatment were less active before exposure and did not have an anxiety response to the alarm cue hypoxanthine-3-n-oxide. Though ozonation was able to mitigate some of the effects of OSPW exposure, further studies are needed to understand the transgenerational effects and the implications of exposure on complex fish behaviors.

Current knowledge of seepage from oil sands tailings ponds and its environmental influence in northeastern Alberta

Seepage of oil sand process-affected waters (OSPW) from tailings ponds into surface waters is a common concern in the minable oil sands region of northeast Alberta. Research on seepage has been extensive, but few comprehensive treatments evaluating all aspects relevant to the phenomenon are available. In this work, the current information relevant for understanding the state of seepage from tailings ponds was reviewed. The information suggests the infiltration of OSPW into groundwater occurs near some ponds. OSPW may also be present in sediments beneath the Athabasca River adjacent to one pond, but there are no clear observations of OSPW in the river water. Similarly, most water samples from tributaries also show no evidence of OSPW, but these observations are limited by the lack of systematic, systemic, and repeated surveys, missing baseline data, standard analytical approaches, and reference materials. Waters naturally influenced by bitumen, discharge of saline groundwaters, and dilution also potentially affect the consolidation of information and certainty of any conclusions. Despite these challenges, some data suggest OSPW may be present in two tributaries of the Athabasca River adjacent to tailings ponds: McLean Creek and Lower Beaver River. Irrespective of the possible source(s), constituents of OSPW often affect organisms exposed in laboratories, but research in all but one study suggests the concentrations of organics in the surface water bodies assessed are below the standard toxicological effect thresholds for these compounds. In contrast, many samples of groundwater, irrespective of source, likely affect biota. Biomonitoring of surface waters suggests generic responses to stressors, but the influence of natural phenomena and occasionally nutrient enrichment are often suggested by data. In summary, valuable research has been done on seepage. The data suggest infiltration into groundwater is common, seepage into surface waters is not, and anthropogenic biological impacts are not likely.

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

The extraction of oil sands from mining operations in the Athabasca Oil Sands Region uses an alkaline hot water extraction process. The oil sands process water (OSPW) is recycled to facilitate material transport (e.g., ore and tailings), process cooling, and is also reused in the extraction process. The industry has expanded since commercial mining began in 1967 and companies have been accumulating increasing inventories of OSPW. Short- and long-term sustainable water management practices require the ability to return treated water to the environment. The safe release of OSPW needs to be based on sound science and engineering practices to ensure downstream protection of ecological and human health. A significant body of research has contributed to the understanding of the chemistry and toxicity of OSPW. A multistakeholder science workshop was held in September 2017 to summarize the state of science on the toxicity and chemistry of OSPW. The goal of the workshop was to review completed research in the areas of toxicology, chemical analysis, and monitoring to support the release of treated oil sands water. A key outcome from the workshop was identifying research needs to inform future water management practices required to support OSPW return. Another key outcome of the workshop was the recognition that methods are sufficiently developed to characterize chemical and toxicological characteristics of OSPW to address and close knowledge gaps. Industry, government, and local indigenous stakeholders have proceeded to utilize these insights in reviewing policy and regulations. Integr Environ Assess Manag 2019;15:519-527. © 2019 SETAC.