Parallel quantitation of salt dioctyl sodium sulfosuccinate (DOSS) and fingerprinting analysis of dispersed oil in aqueous samples.

In many jurisdictions, dispersants are included in contingency plans as a viable countermeasure that can help reduce the overall environmental impact of marine oil spills. When used, it is imperative to monitor the progression of dispersant and oil to assess their environmental fate and behaviour. Amphiphilic salt dioctyl sodium sulfosuccinate (DOSS) is the major effective component of the most commonly available dispersants, such as Corexit® EC9500A. Without proper sample preparation, dispersed oil in water samples could interfere with the accurate analysis of DOSS and easily contaminate the LC-MS system. In this work, solid phase extraction (SPE) weak anion exchange (WAX) cartridges were used to separate oil and DOSS in aqueous samples. DOSS was accurately determined by liquid chromatography coupled with a high resolution Orbitrap mass spectrometer (LC-HRMS). Oil fingerprinting analysis was conducted and total petroleum hydrocarbons (TPHs), polycyclic aromatic hydrocarbons (PAHs), and petroleum biomarkers were determined by gas chromatography-flame ionization detection (GC-FID) and mass spectrometry (GC-MS). This SPE-LC/GC-MS method was used for the analysis of oil-dispersant water samples containing a mixture of Corexit® EC9500A and a selection of crude oils and refined petroleum products. Nearly a 100% DOSS recovery was obtained for various oil-surfactant conditions. Parallel quantitation of oils with dispersants was achieved using this method. A portion of the TPH loss was possibly attributed to oil retained by the SPE column. Chemical fingerprints and diagnostic ratios of target compounds in recovered dispersed oil overall remain unchanged compared with those of all studied oils.

Application of gas chromatography-high resolution quadrupole time-of-flight mass spectrometry in fingerprinting analysis of polycyclic aromatic sulfur heterocycles.

Polycyclic aromatic sulfur heterocycles (PASHs), as a group of major sulfur-containing compounds, widely occur in crude oil and its refined products. Accurate analyses of these petrochemical components play an important role in monitoring oil quality, forensic source identification, and assessment of environmental impact of an oil spill. PASHs occur at relatively lower abundances in most crude oils and refined petroleum products than their corresponding aromatic hydrocarbons and are co-eluted together with some petroleum hydrocarbons in chromatographic analysis, resulting in high uncertainty for their quantitation. Capillary gas chromatography coupled with a quadrupole time-of-flight mass spectrometry (GC-QTOF-MS) provides high resolution and high mass accuracy, which facilitates discrimination of the delicate mass defects of isobaric compounds with the same nominal mass and external matrix material. In this work, GC-QTOF-MS was applied to analyze bicyclic to pentacyclic PASHs including benzothiophenes, dibenzothiophenes, benzonaphthothiophenes, dinaphthothiophenes and their C1- to C4- alkylated homologues in a number of crude oils, refined petroleum products, and environmental samples. GC-QTOF-MS analysis substantially improved the identification confidence and reduced quantitation uncertainty of PASHs and polycyclic aromatic hydrocarbons (PAHs) by eliminating the interferences presented in nominal mass chromatograms.

Enhanced marine monitoring and toxicity study of oil spill dispersants including Corexit EC9500A in the presence of diluted bitumen.

Observations made for the analysis of the oil spill dispersant tracer dioctyl sulfosuccinate (DOSS) during LC50 toxicity testing, highlighted a stability issue for this tracer compound in seawater. A liquid chromatography high-resolution quadrupole time-of-flight mass spectrometry (LC/QToF) was used to confirm monooctyl sulfosuccinate (MOSS) as the only significant DOSS breakdown product, and not the related isomer, 4-(2-ethylhexyl) 2-sulfobutanedioate. Combined analysis of DOSS and MOSS was shown to be applicable to monitoring of spill dispersants Corexit® EC9500A, Finasol OSR52, Slickgone NS, and Slickgone EW. The unassisted conversion of DOSS to MOSS occurred in all four oil spill dispersants solubilized in seawater, although differences were noted in the rate of MOSS formation. A marine microcosm study of Corexit EC9500A, the formulation most rapid to form MOSS, provided further evidence of the stoichiometric conversion of DOSS to MOSS under conditions relevant to real world dilbit spill. Results supported combined DOSS and MOSS analysis for the monitoring of spill dispersant in a marine environment, with a significant extension of sample collection time by 10 days or longer in cooler conditions. Implications of the unassisted formation of MOSS and combined DOSS:MOSS analysis are discussed in relation to improving dispersant LC50 toxicity studies.

Improved oil spill dispersant monitoring in seawater using dual tracers: Dioctyl and monoctyl sulfosuccinates sourced from corexit EC9500A.

A high resolution mass spectrometry method was developed for the environmental impact monitoring of oil spill dispersants. Previously reported instability of dioctyl sulfosuccinate (DOSS) dispersant tracer was addressed by the new procedure. The method monitors both DOSS and its degradation product, monooctyl sulfosuccinate (MOSS), by liquid chromatography time-of-flight mass spectrometry. The related isomer, 4-(2-ethylhexyl) 2-sulfobutanedioate, was chromatographically resolved from MOSS but was not a product of DOSS degradation. Using this direct injection method (10 µL), the practical lower limit of quantitation was 0.5 nM for each analyte, a concentration equivalent to 0.22 ng mL-1, or 0.30 ng mL-1 including initial dilution factor with acetonitrile. The method was shown applicable to analysis of the dispersants Corexit® EC9500 A, Finasol OSR 52, Slickgone NS, and Slickgone EW for which DOSS is an active ingredient. A marine microcosm study of Corexit EC9500A, together with diluted bitumen (dilbit), at 15 ± 1 °C, provided evidence of the stoichiometric conversion of DOSS to MOSS under conditions reflecting a western Canadian marine environment. The advantage of the developed method is in its ability to extend environmental seawater sample collection time from 4 days for DOSS alone, to 14 days when both DOSS and MOSS are simultaneously analysed and results combined. The collection time is likely extended beyond the 14 day period with cooler temperatures. Preservation of collected seawater samples using sodium hydroxide, converting DOSS into MOSS in situ, was rejected due to stability issues. Addition of disodium ethylenediaminetetraacetic acid did not improve hold times, thus eliminating the theory of cation induced micelle effects causing DOSS loss.

Acute toxicity of Corexit EC9500A and assessment of dioctyl sulfosuccinate as an indicator for monitoring four oil dispersants applied to diluted bitumen.

The present study investigated oil dispersant toxicity to fish species typical of the cooler regions of Canada, together with less well-documented issues pertaining to oil dispersant monitoring. The oil dispersant toxicity of Corexit EC9500A was assessed for the freshwater fish species rainbow trout and the seawater species coho, chinook, and chum, with a final median lethal concentration (LC50) acute lethality range between 35.3 and 59.8 mg/L. The LC50 range was calculated using confirmed 0-h dispersant concentrations that were justified by fish mortality within the first 24 h of exposure and by variability of the dispersant indicator dioctyl sulfosuccinate (DOSS) used to monitor concentrations at later time points. To investigate DOSS as an oil dispersant indicator in the environment, microcosm systems were prepared containing Corexit EC9500A, Finasol OSR52, Slickgone NS, and Slickgone EW dispersants together with diluted bitumen. The DOSS indicator recovery was found to be stable for up to 13 d at 5 °C, 8 d at 10 °C, but significantly less than 8 d at ≥15 °C. After 3 d at temperatures ≥15 °C, the DOSS indicator recovery became less accurate and was dependent on multiple environmental factors including temperature, microbial activity, and aeration, with potential for loss of solvents and stabilizers. A final assessment determined DOSS to be a discrepant indicator for long-term monitoring of oil dispersant in seawater. Environ Toxicol Chem 2018;37:1309-1319. © 2018 SETAC.

Characterization of chemical fingerprints of unconventional Bakken crude oil.

The ability to characterize the composition of emerging unconventional Bakken tight oil is essential to better prepare for potential spills and to assess associated environmental concerns. The present work measured and compared the physical and chemical properties of Bakken crudes with conventional crude oils from various regions and different types of refined petroleum products. The physicochemical properties of Bakken crude are overall similar to those of conventional light crudes. The Bakken crude consists of high concentrations of monoaromatic hydrocarbons and alkylated PAHs with a clear dominance of the alkylated naphthalene homologues followed by the phenanthrene series. Its pyrogenic index (PI) values are considerably lower than typical conventional crude oils. The Bakken crude oils in this study exhibit a low abundance of petroleum biomarker such as terpanes, steranes and diamondoids and bicyclic sesquiterpanes. Since tight oil from the Bakken region is produced from low-permeability formations, variations in abundance and diagnostic ratios of common target petroleum hydrocarbons were found among these oils.

Studies on water-in-oil products from crude oils and petroleum products.

Water-in-oil mixtures such as emulsions, often form and complicate oil spill countermeasures. The formation of water-in-oil mixtures was studied using more than 300 crude oils and petroleum products. Water-in-oil types were characterized by resolution of water at 1 and 7 days, and some after 1 year. Rheology measurements were carried out at the same intervals. The objective of this laboratory study was to characterize the formed water-in-oil products and relate these properties to starting oil properties. Analysis of the starting oil properties of these water-in-oil types shows that the existence of each type relates to the starting oil viscosity and its asphaltene and resin contents. This confirms that water-in-oil emulsification is a result of physical stabilization by oil viscosity and chemical stabilization by asphaltenes and resins. This stabilization is illustrated using simple graphical techniques. Four water-in-oil types exist: stable, unstable, meso-stable and entrained. Each of these has distinct physical properties.

Formation of water-in-oil emulsions and application to oil spill modelling.

Water-in-oil mixtures were grouped into four states or classes: stable, mesostable, unstable, and entrained water. Of these, only stable and mesostable states can be characterized as emulsions. These states were established according to lifetime, visual appearance, complex modulus, and differences in viscosity. Water content at formation was not an important factor. Water-in-oil emulsions made from crude oils have different classes of stability as a result of the asphaltene and resin contents, as well as differences in the viscosity of the starting oil. The different types of water-in-oil classes are readily distinguished simply by appearance, as well as by rheological properties. A review of past modelling efforts to predict emulsion formation showed that these older schemes were based on first-order rate equations that were developed before extensive work on emulsion physics took place. These results do not correspond to either laboratory or field results. The present authors suggest that both the formation and characteristics of emulsions could be predicted using empirical data. If the same oil type as already studied is to be modelled, the laboratory data on the state and properties can be used directly. In this paper, a new numerical modelling scheme is proposed and is based on empirical data and the corresponding physical knowledge of emulsion formation. The density, viscosity, saturate, asphaltene and resin contents are used to compute a class index which yields either an unstable or entrained water-in-oil state or a mesostable or stable emulsion. A prediction scheme is given to estimate the water content and viscosity of the resulting water-in-oil state and the time to formation with input of wave height.

Studies of the formation process of water-in-oil emulsions.

This paper summarizes studies to determine the formation process of water-in-oil emulsions and the stability of such emulsions formed in the laboratory and in a large test tank. These studies have confirmed that water-in-oil mixtures can be grouped into four states: stable emulsions, unstable water-in-oil mixtures, mesostable emulsions, and entrained water. These states are differentiated by rheological properties as well as by differences in visual appearance. The viscosity of a stable emulsion at a shear rate of one reciprocal second is about three orders of magnitude greater than that of the starting oil. An unstable emulsion usually has a viscosity no more than about 20 times greater than that of the starting oil. A stable emulsion has a significant elasticity, whereas an unstable emulsion does not. A mesostable emulsion has properties between stable and unstable, but breaks down within a few days of standing. The usual situation is that emulsions are either obviously stable, mesostable, or unstable. Entrained water, water suspended in oil by viscous forces alone, is also evident. Very few emulsions have questionable stability. Analytical techniques were developed to test these observations. The type of emulsion produced is determined primarily by the properties of the starting oil. The most important of these properties are the asphaltene and resin content and the viscosity of the oil. The composition and property ranges of the starting oil that would be required to form each of the water-in-oil states are discussed in this paper.