Toxicity of synthetic naphthenic acids and mixtures of these to fish liver cells

A model naphthenic acid decouples oxidative phosphorylation through selective inhibition of mitochondrial complex activity

The naphthenic acid fraction compound (NAFC), 3,5-dimethyladamantane-1-acetic acid, was tested for its ability to uncouple mitochondrial oxidative phosphorylation. Mitochondria isolated from rainbow trout (Oncorhynchus mykiss) liver were exposed to 3,5-dimethyladamantane-1-acetic acid in state 3 and 4 respiration, and mitochondrial membrane potential were quantified. Electron transport chain (ETC) protein complexes were isolated using pharmacological agents and inhibitors, and their activities measured. The NAFC compound completely inhibited states 3 and 4 respiration with an IC50 of 0.77 and 1.01 mM, respectively. The NAFC compound partially uncoupled mitochondrial membrane potential in state 3 and 4 respiration with an IC50 of 2.19 and 1.73 mM, respectively. The NAFC impaired the activities of ETC protein complexes with a 9.5-fold range in sensitivity. The relative inhibitory effect of the ETC protein complexes to NAFC was CIV≥CI>CIII>CII. The impairment of mitochondrial oxidative phosphorylation by adamantane 3,5-dimethyladamantane-1-acetic acid is mediated via its inhibition of ETC protein complexes.

Electromembrane Extraction of Naphthenic Acids in Produced Water Followed by Ultra-High-Resolution Mass Spectrometry Analysis

Naphthenic acids comprise one of the most toxic compounds of the produced water released from offshore oil platforms. Therefore, developing and applying faster, simpler, and more efficient analytical methods for analyzing naphthenic acids are urgently needed. Electromembrane extraction (EME) uses the electrokinetic migration of target ions through a porous membrane. Herein, the EME method was applied to extract naphthenic acids from produced water. The EME method was optimized, and the optimal conditions encompassed decanol as the organic solvent, the sample with pH 10.0, 5 min of extraction at 200 V, and the ratio 4:1 (borate buffer/matrix, v/v). Electrochemical impedance spectroscopy confirmed charged species' migration from produced water through the EME. Subsequently, all extracts were analyzed by ultra-high-resolution mass spectrometry. The EME efficiency was assessed by comparing the extraction results to the liquid-liquid extraction (LLE) method results. Analytical results showed good linearity for both solvent and matrix curves (R² > 0.98). Low detection limits ranged from 0.10 to 0.13 μg mL^-1 and quantification limits from 0.36 to 0.45 μg mL^-1. Precision and accuracy values ranged from -13.3% to 16.5%. These values fit the proposed method, demonstrating that the EME was more efficient than LLE in naphthenic acid extraction. The EME method preferably extracted aromatic compounds with double-bond equivalence from 6 to 8. The EME coupled with ultra-high-resolution mass spectrometry was demonstrated as a promising analytical approach to naphthenic acid extraction as an efficient and more environmentally friendly alternative to conventional extraction methods.

Solar-activated zinc oxide photocatalytic treatment of real oil sands process water: Effect of treatment parameters on naphthenic acids, polyaromatic hydrocarbons and acute toxicity removal

Oil sands process water (OSPW) is an industrial process effluent that contains organic compounds such as naphthenic acids (NAs) and polyaromatic hydrocarbons (PAHs), as well as large quantities of inorganic compounds in its mixture. OSPW requires effective treatment for successful reclamation and water reuse. This study investigated the impact of solar-activated zinc oxide (ZnO) photocatalysis on the degradation and removal of NAs and PAHs in OSPW, as well as the elimination of its acute toxicity. With catalyst particles suspended in the effluent (at 1 g/L) under simulated solar radiation of steady irradiance of ~278 W/m², more than 99% removal of NAs was achieved after 4 h of treatment, while nearly all PAHs were simultaneously oxidized within the same reaction time. The photocatalytic treatment appeared to selectively convert classical NAs faster than oxidized NAs. Additionally, NAs with higher double-bond equivalents (DBEs) and higher carbon numbers seemed more susceptible to photocatalytic destruction than others. An overall pseudo first-order rate constant of 1.14 × 10^-2 min^-1, and a fluence-based rate constant of 6.81 × 10^-1 m²/MJ were recorded in apparently hydroxyl radicals (OH) and superoxide (O₂^-) radicals mediated NAs degradation mechanisms. Assessment of the toxicity levels in raw and treated OSPW samples by using Microtox® bioassay indicated that the photocatalytic treatment resulted in ~50% reduction in acute toxicity. Furthermore, we showed that by monitoring the expression levels of key proinflammatory genes using qPCR that treated OSPW significantly reduced the ability of raw OSPW to activate the inflammatory response of immune cells. This indicates that at acute sub-lethal exposure doses, photocatalytic treatment also reduces immunotoxicity. Overall, our results suggest that the ZnO-based photocatalytic degradation of these NAs and PAHs in OSPW could be a significant treatment process aimed at detoxifying OSPW.

Fiber coalescence treatment of oily wastewater: A new theory and application

Oil pollution from produced water in the offshore petroleum industry is one of the most serious marine pollutants worldwide, and efficient separation technology is crucial for the control of oil pollutant emission. Medium coalescence is an efficient oil-water separation technology, but its theory is lacking and the development is slow. In this work, the microscopic mechanism of fiber coalescence was revealed, and found that the effective collision positions were the three-phase contact line and the exposed fiber surface. Further, a theoretical model for calculating the separation performance of a fiber bed was established. For a given inlet droplet size distribution and bed geometric parameters, the outlet droplet size distribution and the total separation efficiency of the fiber bed can be predicted. Then, an Ω-shaped woven method composed of oil-wet fibers and oil-phobic fibers was designed and the separation performance of the fiber beds prepared by the method and the influence law of various parameters were clarified through macroscopic experiment. Finally, the novel technology achieved its first engineering application on an offshore platform, with the average oil content of the outlet was less than 25 mg/L, which could reform the current treatment process of produced water.

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 O_x-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.

Environmental effects of offshore produced water discharges: A review focused on the Norwegian continental shelf

Produced water (PW), a large byproduct of offshore oil and gas extraction, is reinjected to formations or discharged to the sea after treatment. The discharges contain dispersed crude oil, polycyclic aromatic hydrocarbons (PAHs), alkylphenols (APs), metals, and many other constituents of environmental relevance. Risk-based regulation, greener offshore chemicals and improved cleaning systems have reduced environmental risks of PW discharges, but PW is still the largest operational source of oil pollution to the sea from the offshore petroleum industry. Monitoring surveys find detectable exposures in caged mussel and fish several km downstream from PW outfalls, but biomarkers indicate only mild acute effects in these sentinels. On the other hand, increased concentrations of DNA adducts are found repeatedly in benthic fish populations, especially in haddock. It is uncertain whether increased adducts could be a long-term effect of sediment contamination due to ongoing PW discharges, or earlier discharges of oil-containing drilling waste. Another concern is uncertainty regarding the possible effect of PW discharges in the sub-Arctic Southern Barents Sea. So far, research suggests that sub-arctic species are largely comparable to temperate species in their sensitivity to PW exposure. Larval deformities and cardiac toxicity in fish early life stages are among the biomarkers and adverse outcome pathways that currently receive much attention in PW effect research. Herein, we summarize the accumulated ecotoxicological knowledge of offshore PW discharges and highlight some key remaining knowledge needs.

Caenorhabditis elegans As a Promising Alternative Model for Environmental Chemical Mixture Effect Assessment-A Comparative Study

A key challenge of mixture toxicity testing is that a multitude of substances with even more combinations need to be tested in a broad dose range. Consequently testing in rodent bioassays, the current gold standard of toxicity testing, is hardly feasible. High-throughput compatible cell culture systems, however, suffer from limitations with respect to toxicokinetics, tissue interactions, and compensatory mechanisms. Therefore, simple organisms like the nematode Caenorhabditis elegans, combining relevant advantages of complex in vivo and fast in vitro assays might prove highly valuable within a testing strategy for mixtures. To investigate the comparability between results obtained with C. elegans and traditional rodent assays, we used five azole fungicides as well investigated model substances. Our findings suggest that azoles act additively in C. elegans which is in line with previous results in rats. Additionally, we show that toxicokinetics are one important factor for the differences in the relative toxicity of the azoles in both species. Importantly, we also demonstrate that in contrast to most rodent in vivo studies, C. elegans assays provide well-defined concentration-response relationships which are a very good basis for the prediction of mixture effects. We conclude that C. elegans may be an appropriate model for mixture toxicity testing at least within a first step to identify and prioritize relevant mixtures for further testing.

Analysis of individual and combined estrogenic effects of bisphenol, nonylphenol and diethylstilbestrol in immature rats with mathematical models

BACKGROUND

Traditional toxicological studies focus on individual compounds. However, this single-compound approach neglects the fact that the mixture exposed to human may act additively or synergistically to induce greater toxicity than the single compounds exposure due to their similarities in the mode of action and targets. Mixture effects can occur even when all mixture components are present at levels that individually do not produce observable effects. So the individual chemical effect thresholds do not necessarily protect against combination effects, an understanding of the rules governing the interactive effects in mixtures is needed. The aim of the study was to test and analyze the individual and combined estrogenic effects of a mixture of three endocrine disrupting chemicals (EDCs), bisphenol A (BPA), nonylphenol (NP) and diethylstilbestrol (DES) in immature rats with mathematical models.

METHOD

In the present study, the data of individual estrogenic effects of BPA, NP and DES were obtained in uterotrophic bioassay respectively, the reference points for BPA, NP and DES were derived from the dose-response ralationship by using the traditional no observed adverse effect (NOAEL) or lowest observed adverse effect level (LOAEL) methods, and the benchmark dose (BMD) method. Then LOAEL values and the benchmark dose lower confidence limit (BMDL10) of single EDCs as the dose design basis for the study of the combined action pattern. Mixed prediction models, the 3 × 2 factorial design model and the concentration addition (CA) model, were employed to analyze the combined estrogenic effect of the three EDCs.

RESULTS

From the dose-response relationship of estrogenic effects of BPA, NP and DES in the model of the prepuberty rats, the BMDL10(NOAEL) of the estrogenic effects of BPA, NP and DES were 90(120) mg/kg body weight, 6 mg/kg body weight and 0.10(0.25) μg/kg body weight, and the LOAEL of the the estrogenic effects of three EDCs were 240 mg/kg body weight, 15 mg/kg body weight and 0.50 μg/kg body weight, respectively. At BMDL10 doses based on the CA concept and the factorial analysis, the mode of combined effects of the three EDCs were dose addition. Mixtures in LOAEL doses, NP and DES combined effects on rat uterine/body weight ratio indicates antagonistic based on the CA concept but additive based on the factorial analysis. Combined effects of other mixtures are all additive by using the two models.

CONCLUSION

Our results showed that CA model provide more accurate results than the factorial analysis, the mode of combined effects of the three EDCs were dose addition, except mixtures in LOAEL doses, NP and DES combined effects indicates antagonistic effects based on the CA model but additive based on the factorial analysis. In particular, BPA and NP produced combination effects that are larger than the effect of each mixture component applied separately at BMDL doses, which show that additivity is important in the assessment of chemicals with estrogenic effects. The use of BMDL as point of departure in risk assessment may lead to underestimation of risk, and a more balanced approach should be considered in risk assessment.

Assessment of ozonation reactivity of aromatic and oxidized naphthenic acids species separated using a silver-ion solid phase extraction method

Owing to the complexity of naphthenic acids (NAs) in oil sands process water (OSPW), previous ozone-treatment studies mainly investigated the removal of classical NAs (aliphatic O₂-NAs) and the understanding of ozonation reactivity of other NA species has been limited. This work utilized a silver-ion solid phase extraction (SPE) approach to separate individual NA species into 20 fractions before subsequent ozone treatment. The ozonation reactivity of aromatic and oxidized NA species in isolated fractions was studied for the first time. Untreated and ozone-treated SPE fractions were characterized using ultra performance liquid chromatography ion mobility time-of-flight mass spectrometry. The removals of aliphatic O₂-NAs (Fraction 3), aromatic O₂-NAs (Fraction 8), O₃-NAs (Fraction 11), and O₄-NAs (Fraction 17) with an applied ozone dosage of 16.8 mg L^-1 were 97.2%, 94.7%, 59.4% and 44.7%, respectively. The results showed that aromatic and oxidized NAs with larger carbon number were favorably removed during ozonation treatment. Comparison of the ozone utilization efficiency for different NA species indicated that the degradation of oxidized NAs consumed more ozone in molar ratio than the degradation of classical and aromatic NAs. The reactivity of oxidized NAs was lower than that of classical NAs because the former consumed more ozone in molar ratio during reactions. Knowing the reactivity of different NA species is crucial for the design of ozonation systems targeting species with high toxicity. Moreover, the utilization of silver-ion SPE pre-separation approach has been demonstrated for future studies investigating the degradation mechanism of distinct NA species under other treatment conditions.

Exposure to naphthenic acids and the acid extractable organic fraction from oil sands process-affected water alters the subcellular structure and dynamics of plant cells

Oil sands surface mining generates vast quantities of oil sands process-affected water (OSPW) as a by-product of bitumen extraction. The acid extractable organic (AEO) fraction of OSPW contains several contaminants, including naphthenic acids (NAs). While responses of living organisms to NA and AEO exposure have been described at the developmental, physiological, metabolic and gene expression levels, the effects of these compounds at the cellular and subcellular level are limited. Using live cell fluorescence microscopy and a suite of fluorescent marker proteins, we studied the intracellular responses of the plant cell cytoskeleton and several membrane-bound organelles to NA and AEO treatments. A rapid disassembly of cortical microtubules and a decrease in dynamics associated with actin filaments was observed in response to these treatments. Concomitantly, the integrity and dynamics of mitochondria, peroxisomes, Golgi stacks, and endoplasmic reticulum were also altered. AEO treatments were the most toxic to cells and resulted in the accumulation reactive oxygen species. This study provides foundational evidence for intracellular responses to NA and AEO exposure using two evolutionarily diverse model plant cell types. This cellular assay could be used to identify the most toxic components of AEO sub-fractions, and assist in determining the effectiveness of OSPW remediation efforts.

Aerobic granular sludge and naphthenic acids treatment by varying initial concentrations and supplemental carbon concentrations

Aerobic granular sludge (AGS) has previously been utilized in the treatment of toxic compounds due to its diverse and dense microbial structure. The present study subjected mature AGS to model naphthenic acids (NAs) representative of the Canadian oil sands. To this effect, three NA concentrations (10, 50 and 100 mg/L) and three supplemental carbon source concentrations (600, 1200 and 2500 mg/L) were studied in batch reactors for 5 days. The responding variables were chemical oxygen demand (COD), NA concentrations and nutrients. Cyclohexane carboxylic acid (CHCA), cyclohexane acetic acid (CHAA) and 1-adamantane carboxylic acid (ACA) were chosen to study structure-based degradation kinetics. The optimal COD according to the runs was 1200 mg/L. CHCA was removed completely with biodegradation rate constants increasing with lower NA concentrations and lower COD concentrations. CHAA was also removed completely, however, an optimal rate constant of 1.9 d^-1 was achieved at NA and COD concentrations of 50 mg/L and 1200 mg/L, respectively. ACA removal trends did not follow statistically significant regressions; however, degradation and sorption helped remove ACA up to 19.9%. Pseudomonas, Acinetobacter, Hyphomonas and Brevundimonas spp. increased over time, indicating increased AGS adaptability to NAs.

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

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

Deciphering the Combined Effects of Environmental Stressors on Gene Transcription: A Conceptual Approach

The use of classical mixture toxicity models to predict the combined effects of environmental stressors based on toxicogenomics (OMICS) data is still in its infancy. Although several studies have made attempts to implement mixture modeling in OMICS analysis to understand the low-dose interactions of stressors, it is not clear how interactions occur at the molecular level and how results generated from such approaches can be better used to inform future studies and cumulative hazard assessment of multiple stressors. The present work was therefore conducted to propose a conceptual approach for combined effect assessment using global gene expression data, as illustrated by a case study on assessment of combined effects of gamma radiation and depleted uranium (DU) on Atlantic salmon ( Salmo salar). Implementation of the independent action (IA) model in reanalysis of a previously published microarray gene expression dataset was performed to describe gene expression patterns of combined effects and identify key gene sets and pathways that were relevant for understanding the interactive effects of these stressors. By using this approach, 3120 differentially expressed genes (DEGs) were found to display additive effects, whereas 279 (273 synergistic, 6 antagonistic) were found to deviate from additivity. Functional analysis further revealed that multiple toxicity pathways, such as oxidative stress responses, cell cycle regulation, lipid metabolism, and immune responses were enriched by DEGs showing synergistic gene expression. A key toxicity pathway of DNA damage leading to enhanced tumorigenesis signaling is highlighted and discussed in detail as an example of how to take advantage of the approach. Furthermore, a conceptual workflow describing the integration of combined effect modeling, OMICS analysis, and bioinformatics is proposed. The present study presents a conceptual framework for utilizing OMICS data in combined effect assessment and may provide novel strategies for dealing with data analysis and interpretation of molecular responses of multiple stressors.

Characterization and determination of naphthenic acids species in oil sands process-affected water and groundwater from oil sands development area of Alberta, Canada

This work reports the monitoring and assessment of naphthenic acids (NAs) in oil sands process-affected water (OSPW), Pleistocene channel aquifer groundwater (PLCA), and oil sands basal aquifer groundwater (OSBA) from an active oil sands development in Alberta, Canada, using ultra performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOF-MS) analysis with internal standard (ISTD) and external standard (ESTD) calibration methods and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) for compositional analysis. PLCA was collected at 45-51 m depth and OSBA was collected at 67-144 m depth. Results of O_x-NA concentrations follow an order as OSPW > OSBA > PLCA, indicating that occurrences of NAs in OSBA were likely related to natural bitumen deposits instead of OSPW. Liquid-liquid extraction (LLE) was applied to avoid the matrix effect for the ESTD method. Reduced LLE efficiency accounted for the divergence of the ISTD and ESTD calibrated results for oxidized NAs. Principle component analysis results of O₂ and O₄ species could be employed for differentiation of water types, while classical NAs with C13-15 and Z (-4)-(-6) and aromatic O₂-NAs with C16-18 and Z (-14)-(-16) could be measured as marker compounds to characterize water sources and potential temporal variations of samples, respectively. FTICR-MS results revealed that compositions of NA species varied greatly among OSPW, PLCA, and OSBA, because of NA transfer and transformation processes. This work contributed to the understanding of the concentration and composition of NAs in various types of water, and provided a useful combination of analytical and statistical tools for monitoring studies, in support of future safe discharge of treated OSPW.

Fate and abundance of classical and heteroatomic naphthenic acid species after advanced oxidation processes: Insights and indicators of transformation and degradation

The toxicological effects from all components in oil sands process-affected water (OSPW) are not known. Alternatively, monitoring the variations and abundance of different classes and compounds after treatments might be a useful approach in OSPW remediation. In this study, the variations in the compositions of classical and heteroatomic naphthenic acids (NAs) after treatment using advanced oxidation processes (AOPs), mainly ozone and peroxone, and two different mass spectrometry methods; ultra-performance liquid chromatography time-of-flight (UPLC-TOFMS) and Fourier transform ion cyclotron resonance (FTICR-MS), were examined. Two markers (O₂S:O₃S:O₄S and O₂:O₄ ratios) were used to reveal changes and similarities of the treated water characteristics with those in natural waters. Both ratios decreased after all treatments, from 2.7:4.8:2.1 and 3.59 in raw OSPW to 0:1.4:0.5 and 0.7, respectively, in peroxone (1:2), becoming close to the reported ratios in natural waters. Toxicity toward Vibrio fischeri showed residual toxic effects after AOPs, suggesting that part of OSPW toxicity may be caused by specific compounds of NAs (i.e., similar reduction (50%) was achieved in both toxicity and abundance in O₂ species with carbon 15-26) and/or generated by-products (e.g., O₃S classes at double bond equivalent (DBE) = 4 and C₉H₁₂O₂ at DBE = 4). Although by-products were generated, the best biodegradability enhancement and chemical oxygen demand reduction were achieved in peroxone (1:2) compared to ozone, suggesting the possibility of using combined OSPW remediation approaches (i.e., peroxone coupled with biological process). The recommended indicators can assist in evaluating the treatments' performance and in examining the best removal levels to accomplish significant toxicity reduction.

Naphthenic acids removal from high TDS produced water by persulfate mediated iron oxide functionalized catalytic membrane, and by nanofiltration

Oil industries generate large amounts of produced water containing organic contaminants, such as naphthenic acids (NA) and very high concentrations of inorganic salts. Recovery of potable water from produced water can be highly energy intensive is some cases due to its high salt concentration, and safe discharge is more suitable. Here, we explored catalytic properties of iron oxide (FexOy nanoparticles) functionalized membranes in oxidizing NA from water containing high concentrations of total dissolved solids (TDS) using persulfate as an oxidizing agent. Catalytic decomposition of persulfate by FexOy functionalized membranes followed pseudo-first order kinetics with an apparent activation energy of 18 Kcal/mol. FexOy functionalized membranes were capable of lowering the NA concentrations to less than discharge limits of 10 ppm at 40 °C. Oxidation state of iron during reaction was quantified. Membrane performance was investigated for extended period of time. A coupled process of advanced oxidation catalyzed by membrane and nanofiltration was also evaluated. Commercially available nanofiltration membranes were found capable of retaining NA from water containing high concentrations of dissolved salts. Commercial NF membranes, Dow NF270 (Dow), and NF8 (Nanostone) had NA rejection of 79% and 82%, respectively. Retentate for the nanofiltration was further treated with advanced oxidation catalyzed by FexOy functionalized membrane for removal of NA.

Toxicity of organic compounds from unresolved complex mixtures (UCMs) to primary fish hepatocytes

Many environmental matrices contaminated with organic pollutants derived from crude oil or degraded petroleum contain mixtures so complex that they are typically unresolved by conventional analytical techniques such as gas chromatography. The resulting chromatographic features have become known as 'humps' or unresolved complex mixtures (UCMs). These UCMs often dominate the organic contaminants of polluted environmental samples: for example, in oil sands produced water up to 150mgL^-1 of 'naphthenic acids' appear as UCMs when examined by gas chromatography as the esters. In oil-contaminated mussels, aromatic hydrocarbon UCMs may comprise almost all of the total toxic hydrocarbons, with over 7000μgg^-1 dry weight reported in some samples. Over the last 25 years, efforts to resolve and thus identify, or at least to produce average structures, for some UCM components, have proved fruitful. Numerous non-polar UCM hydrocarbons and more polar UCM acids have been identified, then synthesised or purchased from commercial suppliers. As UCMs have been proposed to represent a risk to aquatic organisms, the need for assessment of the ecotoxicological effects and characterisation of the mode of action (MoA) of these environmental pollutants has arisen. In the present study, several chemicals with structures typical of those found in some UCMs, were assessed for their potential to disrupt membrane integrity, inhibit metabolic activity, activate the aryl hydrocarbon receptor (AhR), and activate the estrogen receptor (ER) in primary rainbow trout hepatocytes (Oncorhynchus mykiss). These endpoints were determined in order to screen for common toxic modes of action (MoA) in this diverse group of chemicals. The results from the in vitro screening indicated that of the endpoints tested, the predominant toxic MoA was cytotoxicity. EC₅₀ values for cytotoxicity were obtained for 16 compounds and ranged from 77μM-24mM, whereof aliphatic monocyclic acids, monoaromatic acids, polycyclic monoaromatic acids and alkylnaphthalenes were the most toxic. The observed cytotoxicity of the chemicals correlated well with the hydrophobicity (LogK_OW) suggesting that the toxicity was predominantly due to a non-specific MoA. Interestingly, two compounds induced the ER-mediated production of vitellogenin (Vtg) and six compounds induced the AhR-mediated Ethoxyresorufin-O-deethylase (EROD) enzymatic activity to >20% of the positive control; by doing so suggesting that they may act as ER or AhR agonists in fish. The heterogeneous group of 'UCM compounds' tested exhibited multiple MoA that may potentially cause adverse effects in fish. Additional studies to determine if these compounds may cause adverse effects in vivo at environmentally relevant concentrations, are warranted to identify if such compounds are indeed of potential environmental concern.

Joint toxicity of cadmium and SDBS on Daphnia magna and Danio rerio

Information on joint toxicity is limited. To clarify the joint toxicity and the interactions among toxicants on different aquatic organisms, we investigated the acute toxicity of cadmium and sodium dodecyl benzene sulfonate, two chemicals with high concerns in Chinese waters, on the immobilization of Daphnia magna (D. magna) and the swimming behavior of Danio rerio (D. rerio). Our results illustrated that cadmium and sodium dodecyl benzene sulfonate expressed a synergistic effect on the immobilization of D. magna; and an antagonistic effect on the swimming speed D. rerio, but a synergistic effect on its vertical position in the water column. Based on the observed data, we found the independent action model was more appropriate than the concentration addition model in the prediction of their joint toxicity. Our results gave an example of the joint toxicity investigation, and aided to comprehensive the toxicity action mode of chemical mixtures.

Silver-Ion Solid Phase Extraction Separation of Classical, Aromatic, Oxidized, and Heteroatomic Naphthenic Acids from Oil Sands Process-Affected Water

The separation of classical, aromatic, oxidized, and heteroatomic (sulfur-containing) naphthenic acid (NA) species from unprocessed and ozone-treated oil sands process-affected water (OSPW) was performed using silver-ion (Ag-ion) solid phase extraction (SPE) without the requirement of pre-methylation for NAs. OSPW samples before SPE and SPE fractions were characterized using ultra performance liquid chromatography ion mobility time-of-flight mass spectrometry (UPLC-IM-TOFMS) to corroborate the separation of distinct NA species. The mass spectrum identification applied a mass tolerance of ±1.5 mDa due to the mass errors of NAs were measured within this range, allowing the identification of O2S-NAs from O2-NAs. Moreover, separated NA species facilitated the tandem mass spectrometry (MS/MS) characterization of NA compounds due to the removal of matrix and a simplified composition. MS/MS results showed that classical, aromatic, oxidized, and sulfur-containing NA compounds were eluted into individual SPE fractions. Overall results indicated that the separation of NA species using Ag-ion SPE is a valuable method for extracting individual NA species that are of great interest for environmental toxicology and wastewater treatment research, to conduct species-specific studies. Furthermore, the separated NA species on the milligram level could be widely used as the standard materials for environmental monitoring of NAs from various contamination sites.

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.

Effect of ozonation on the naphthenic acids' speciation and toxicity of pH-dependent organic extracts of oil sands process-affected water

The presence of naphthenic acids (NAs) and other organic constituents in oil sands process-affected water (OSPW) stored in tailings ponds, poses a serious environmental threat due to their potential toxicity to aquatic organisms and wild life. In this work, four fractions of OSPW, extracted by dichloromethane at different pHs, were ozonated to determine the ozone impact on NAs degradation. Extracts distributions showed that high carbon number NAs (14-22) were associated with higher pH fractions (pH>7) and smaller carbon number NAs (7-13) with lower pH fractions (pH≤7). Extracts showed similar hydrogen deficiency (Z-number) patterns centered on Z=6. Analysis of the speciation of NAs and oxidized NAs in the four fractions showed that ozonation degraded most NAs (55% to 98%). Despite the high degradation levels, there was still significant toxicity of the fractions toward goldfish macrophages and measurable toxicity toward Vibrio fischeri. The toxicity of such a complex matrix as OSPW may be attributed to other organic compounds and degradation by-products not currently detected. Thus, there is a need to elucidate which compounds are responsible for the remaining OSPW toxicity and to determine if combined processes, such as ozonation followed by biological treatment, are able to completely detoxify OSPW. This work is taking the first steps into this direction, narrowing down the range of compounds which might be responsible for the toxicity.

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.

Fractionation of carboxylate anions from aqueous solution using chitosan cross-linked sorbent materials

The sorptive uptake properties are reported for chitosan and cross-linked chitosan–glutaraldehyde (CG) polymers with single component and mixtures of carboxylic acids (surrogates; Si, i = 1–4).

Quantitative structure-toxicity relationship of the aquatic toxicity for various narcotic pollutants using the norm indexes

The aquatic toxicity value of hazardous contaminants plays an important role in the risk assessments of aquatic ecosystems. The following study presents a stable and accurate structure-toxicity relationship model based on the norm indexes for the prediction of toxicity value (log(LC50)) for 190 diverse narcotic pollutants (96 h LC50 data for Poecilia reticulata). Research indicates that this new model is very efficient and provides satisfactory results. The suggested prediction model is evidenced by R(2) (square correlation coefficient) and ARD (average relative difference) values of 0.9376 and 10.45%, respectively, for the training set, and 0.9264 and 13.90% for the testing set. Comparison results with reference models demonstrate that this new method, based on the norm indexes proposed in this work, results in significant improvements, both in accuracy and stability for predicting aquatic toxicity values of narcotic pollutants.

Genotoxic potential of several naphthenic acids and a synthetic oil sands process-affected water in rainbow trout (Oncorhynchus mykiss)

The exploitation of oil sands has raised major environmental concerns, particularly regarding the presence of high concentration in contaminants such as polycyclic aromatic hydrocarbons (PAHs) and naphthenic acids (NAs) in oil sands process-affected water (OSPW). The purpose of this study was, first to evaluate the genotoxic impact of OSPW-related compounds such as NAs and PAHs in a salmonid species and secondly to assess if OSPW exposure leads to genotoxicity. For this purpose, rainbow trout hepatocytes were exposed in vitro to environmentally relevant concentrations of synthetic NAs, naphtalene, benzo(a)pyrene, and extracts of synthetic OSPW (generated by a laboratory bitumen extraction) and of oil sands leaching water (OSLW, mimicking leaching of oil sands in river water). Primary DNA damage was assessed by the formamidopyrimidine-DNA glycolyase (Fpg)-modified comet assay. Genotoxicity was observed in hepatocytes exposed to several NAs, mixture of them, OSPW and OSLW extracts. The chemical structure of NAs influences the genotoxicity potential: among the NAs tested, the most cyclic NA was the most genotoxic. It also appears that genotoxicity was more marked for OSPW than for OSLW. Because exposure to OSPW led to oxidative DNA damage, while after exposure to several NAs, these types of DNA damage were limited, the NAs tested in this study could not be qualified as the only major contaminants responsible for OSPW genotoxicity. Notwithstanding, it should be noteworthy that exposure to NAs resulted in genotoxic impact at concentrations lower than those documented by literature for fresh OSPW. Further research is needed to explore the relationships between the chemical structure of NAs and their genotoxicity in the light of the distribution of NAs in fresh OSPW samples as well as in surface waters.

Environmental risk assessment of combined effects in aquatic ecotoxicology: a discussion paper

Environmental regulatory edicts within the EU, such as the regulatory framework for chemicals REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals), the Water Framework Directive (WFD), and the Marine Strategy Framework Directive (MSFD) focus mainly on toxicity assessment of individual chemicals although the effect of contaminant mixtures is a matter of increasing concern. This discussion paper provides an overview of the field of combined effects in aquatic ecotoxicology and addresses some of the major challenges related to assessment of combined effects in connection with environmental risk assessment (ERA) and regulation. Potentials and obstacles related to different experimental, modelling and predictive ERA approaches are described. On-going ERA guideline and manual developments in Europe aiming to incorporate combined effects of contaminants, the use of different experimental approaches for providing combined effect data, the involvement of biomarkers to characterize Mode of Action and toxicity pathways and efforts to identify relevant risk scenarios related to combined effects are discussed.

Diaromatic sulphur-containing 'naphthenic' acids in process waters

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

Development of a screening system for the detection of chemically induced DNA methylation alterations in a zebrafish liver cell line

Early molecular events with correlation to disease, such as aberrant DNA methylation, emphasize the importance of DNA methylation as a potential environmental biomarker. Currently, little is known regarding how various environmental contaminants and mixtures alter DNA methylation in aquatic organisms, and testing is both time- and labor-consuming. Therefore, the potential of an in vitro screening method was evaluated by exposing zebrafish liver cells (ZF-L) for 96 h to the nonmutagenic model substance 5'-azacytidine (AZA), as well as a selection of environmental pollutants such as sodium arsenite (NAS), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 17α-ethinylestradiol (EE2), and diethylstilbestrol (DES). Six single genes with reported and anticipated importance in cancer were selected for analysis. Methylation of gene promoter areas was monitored by bisulfite conversion and high-resolution melt (HRM) analysis after exposure to sublethal concentrations of the test compounds. Subsequently, results were validated with direct bisulfite sequencing. Exposure of ZF-L cells to 0.5 μM AZA for 96 h led to hypomethylation of genes with both low and high basal methylation indicating similarity to mechanism of action in mammals. Further, NAS, EE2, and DES were shown to induce significant alterations in methylation, whereas TCDD did not. It was concluded that cell line exposure in combination with HRM may provide an initial contaminant screening assay by quantifying DNA methylation alterations with high throughput capacity. In addition, the rapid determination of effects following contaminant exposure with this in vitro system points to the possibility for new in vivo applications to be useful for environmental monitoring.

In vivo endocrine effects of naphthenic acids in fish

Oil pollution from various sources, including exploration, production and transportation, is a growing global concern. The highest toxicity of hydrocarbon pollutants is associated with the water-soluble phase compounds, including naphthenic acids, a known component found in all hydrocarbon deposits. Recently, naphthenic acids (NAs) have shown estrogenic and anti-androgenic effects in vitro. For this reason we investigated the potential effects of two commercial mixtures of naphthenic acids on fish in vivo, using the three-spined stickleback (Gasterosteus aculeatus) as a model species. Anti-androgenic and estrogenic properties of tested compounds were evaluated using the androgenized female stickleback screen (AFSS) and a variant of the 21-d fish screen (TG230) respectively. One-dimensional gas chromatography-mass spectrometry (GC-MS) showed that the complex commercial NAs mixtures were dominated by acyclic carboxylic acids. In one experiment (freshwater) we found a clear effect of NA exposure on spiggin levels; this was contrary to our hypothesis since NAs enhanced the androgenic potency of DHT (when co-administered) without inducing spiggin when tested in the absence of DHT. Exposure to NAs did not have a statistically significant effect on vitellogenin (Vtg) production in male stickleback, although the Vtg responses were increasing with increasing exposure concentrations. This study shows that in contrast to previous in vitro data, NAs did not exhibit either estrogenic or anti-androgenic properties in vivo, at the concentrations tested. On the contrary, at least in freshwater, NAs appear to have an overall androgenic effect that is not mediated via the androgen receptor involved in spiggin synthesis. Possible reasons for this discrepancy between in vitro and in vivo results as well as between our studies are discussed.

Metal and pharmaceutical mixtures: is ion loss the mechanism underlying acute toxicity and widespread additive toxicity in zebrafish?

The acute toxicities and mechanisms of action of a variety of environmental contaminants were examined using zebrafish larvae (Danio rerio; 4-8 days post fertilization). Toxic interactions were observed between metals. For example, the addition of a sublethal level of nickel (15% of the LC50, one third of the LC01) to all copper treatments decreased the copper 96 h LC50 by 58%, while sublethal copper exposure (6% of the copper LC50, 13% of the LC01) decreased the cadmium 96 h LC50 by 47%. Two predictive models were assessed, the concentration addition (CA) model, which assumes similar mechanisms of action, and the independent action (IA) model, which assumes different mechanisms of action. Quantitative comparisons indicated the CA model performed better than the IA model; the latter tended to underestimate combined toxicity to a greater extent. The effects of mixtures with nickel or ammonia were typically additive, while mixtures with copper or cadmium were typically greater than additive. Larvae exposed to cadmium, copper or nickel experienced whole body ion loss. Decreases were greatest for Na(+) followed by K(+) (as high as 19% and 9%, respectively, in 24h). Additive toxicity between copper and other pharmaceutical compounds such as fluoxetine (Prozac™), β-naphthoflavone, estrogen and 17α-ethinylestradiol were also observed. Similar to metals, acutely toxic concentrations of fluoxetine, β-naphthoflavone and ammonia all decreased whole body Na(+) and K(+). Overall, whole body Na(+) loss showed the greatest correlation with mortality across a variety of toxicants. We theorize that a disruption of ion homeostasis may be a common mechanism underlying the acute additive toxicity of many contaminants in fish.

Acute toxicity of aromatic and non-aromatic fractions of naphthenic acids extracted from oil sands process-affected water to larval zebrafish

The toxicity of oil sands process-affected water (OSPW) has regularly been attributed to naphthenic acids, which exist in complex mixtures. If on remediation treatment (e.g., ozonation) or on entering the environment, the mixtures of these acids all behave in the same way, then they can be studied as a whole. If, however, some acids are resistant to change, whilst others are not, or are less resistant, it is important to establish which sub-classes of acids are the most toxic. In the present study we therefore assayed the acute toxicity to larval fish, of a whole acidified OSPW extract and an esterifiable naphthenic acids fraction, de-esterified with alkali: both fractions were toxic (LC50 ∼5-8mgL(-1)). We then fractionated the acids by argentation solid phase extraction of the esters and examined the acute toxicity of two fractions: a de-esterified alicyclic acids fraction, which contained, for example, adamantane and diamantane carboxylic acids, and an aromatic acids fraction. The alicyclic acids were toxic (LC50 13mgL(-1)) but the higher molecular weight aromatic acids fraction was somewhat more toxic, at least on a weight per volume basis (LC50 8mgL(-1); P<0.05) (for comparison, the monoaromatic dehydroabietic acid had a LC50 of ∼1mgL(-1)). These results show how toxic naphthenic acids of OSPW are to these larval fish and that on a weight per volume basis, the aromatic acids are at least as toxic as the 'classical' alicyclic acids. The environmental fates and other toxic effects, if any, of the fractions remain to be established.

Effects of naphthenic acid exposure on development and liver metabolic processes in anuran tadpoles

Naphthenic acids (NA) are used in a variety of commercial and industrial applications, and are primary toxic components of oil sands wastewater. We investigated developmental and metabolic responses of tadpoles exposed to sub-lethal concentrations of a commercial NA blend throughout development. We exposed Lithobates pipiens tadpoles to 1 and 2 mg/L NA for 75 days and monitored growth and development, condition factor, gonad and liver sizes, and levels of liver glucose, glycogen, lipids and cholesterol following exposure. NA decreased growth and development, significantly reduced glycogen stores and increased triglycerides, indicating disruption to processes associated with energy metabolism and hepatic glycolysis. Effects on liver function may explain reduced growth and delayed development observed in this and previous studies. Our data highlight the need for greater understanding of the mechanisms leading to hepatotoxicity in NA-exposed organisms, and indicate that strict guidelines may be needed for the release of NA into aquatic environments.