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Crude oil spilled at sea is chemically altered through environmental processes such as dissolution, biodegradation, and photodegradation. Transformation of hydrocarbons to oxygenated species increases water-solubility. Metabolites and oxidation products largely remain uncharacterized by common analytical methods but may be more bioavailable to aquatic organisms. Studies have shown that unresolved (i.e. unidentified) polar compounds ('UPCs') may constitute > 90% of the water-accommodated fraction (WAF) of heavily weathered crude oils, but still there is a paucity of information characterizing their toxicological significance in relation to other oil-derived toxicants. In this study, low-energy WAFs (no droplets) were generated from two field-weathered oils (collected during the 2010 Deepwater Horizon incident) and their polar fractions were isolated through fractionation. To allow establishment of thresholds for acute toxicity (LC 50 ) of the dissolved and polar fraction of field collected oils, we concentrated both WAFs and polar fractions to beyond field-documented concentrations, and the acute toxicity of both to the marine copepod Acartia tonsa was measured and compared to the toxicity of the native WAF (non-concentrated). The difference in toxic units (TUs) between the total of the mixture and of identified compounds of known toxicity (polycyclic aromatic hydrocarbons [PAHs] and alkyl phenols) in both WAF and polar fractions was used to estimate the contribution of the UPC to overall toxicity. This approach identified that UPC had a similar contribution to toxicity as identified compounds within the WAFs of the field-weathered oils. This signifies the relative importance of polar compounds when assessing environmental impacts of spilled and weathered oil.

Photodegradation significantly influences marine oil spill behavior, yet its role remains underrepresented in current models, impairing predictive accuracy. Addressing this, our study rigorously examined oil properties and environmental determinants affecting marine oil spill photodegradation through laboratory simulations. We identified and quantified key factors and their interactions, noting particularly the positive influence of asphaltene and negative implications of oil density. We also discerned a negative correlation between n-alkane degradation and carbon numbers. Our findings underscored the pivotal roles of temperature and irradiance in photodegradation. All tested oils adhered to first-order kinetics, with rate constants ranging from 0.0348 to 0.0645 day -1 . Finally, we introduced a novel model incorporating temperature, irradiance and their interactions, ensuring reasonable simulations for marine oil spill photodegradation, fortifying marine oil spill management strategies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Due to the sudden nature of oil spills, few controlled studies have documented how oil weathers immediately following accidental release into a natural lake environment. Here, we evaluated the weathering patterns of Cold Lake Winter Blend, a diluted bitumen (dilbit) product, by performing a series of controlled spills into limnocorrals installed in a freshwater lake in Northern Ontario, Canada. Using a regression-based design, we added seven different dilbit volumes, ranging from 1.5 to 180 L, resulting in oil-to-water ratios between 1:71,000 (v/v) and 1:500 (v/v). We monitored changes in the composition of various petroleum hydrocarbons (PHCs), including n -alkanes, polycyclic aromatic hydrocarbons (PAHs), and oil biomarkers in dilbit over time, as it naturally weathered for 70 days. Depletion rate constants ( k D ) of n -alkanes and PAHs ranged from 0.0009 to 0.41 d -1 and 0.0008 to 0.38 d -1 , respectively. There was no significant relationship between k D and spill volume, suggesting that spill size did not influence the depletion of petroleum hydrocarbons from the slick. Diagnostic ratios calculated from concentrations of n -alkanes, isoprenoids, and PAHs indicated that evaporation and photooxidation were major processes contributing to dilbit weathering, whereas dissolution and biodegradation were less important. These results demonstrate the usefulness of large scale field studies carried out under realistic environmental conditions to elucidate the role of different weathering processes following a dilbit spill.

Mechanical oil recovery (i.e., booming and skimming) is the most common tool for oil spill response. The recovered fluid generated from skimming processes may contain a considerable proportion of water (10 % ~ 70 %). As a result of regulatory prohibition on the discharge of contaminated waters at sea, vessels and/or storage barges must make frequent trips to shore for oil-water waste disposal. This practice can be time- consuming thus reduces the overall efficiency and capacity of oil recovery. One potential solution is on-site oil-water separation and disposal of water fraction at sea. However, currently available decanting processes may have limited oil/water separation capabilities, especially in the presence of oil-water emulsion, which is inevitable in mechanical oil recovery. The decanted water may not meet the discharge standards and cause severe ecotoxicological impacts. This paper therefore comprehensively reviews the principles and progress in oil/water separation, demulsification, and on-site treatment technologies, investigates their applicability on decanting at sea, and discusses the ecotoxicity of decanted water in the marine environment. The outputs provide the fundamental and practical knowledge on decanting and help enhance response effectiveness and consequently reducing the environmental impacts of oil spills., (Copyright © 2022 Elsevier B.V. All rights reserved.)

In the GuLF Study, a study investigating possible adverse health effects associated with work on the oil spill response and clean-up (OSRC) following the Deepwater Horizon disaster in the Gulf of Mexico, we used a job-exposure matrix (JEM) approach to estimate exposures. The JEM linked interview responses of study participants to measurement data through exposure groups (EGs). Here we describe a systematic process used to develop transparent and precise EGs that allowed characterization of exposure levels among the large number of OSRC activities performed across the Gulf of Mexico over time and space. EGs were identified by exposure determinants available to us in our measurement database, from a substantial body of other spill-related information, and from responses provided by study participants in a detailed interview. These determinants included: job/activity/task, vessel and type of vessel, weathering of the released oil, area of the Gulf of Mexico, Gulf coast state, and time period. Over 3000 EGs were developed for inhalation exposure and applied to each of 6 JEMs of oil-related substances (total hydrocarbons, benzene, toluene, ethylbenzene, total xylene, and n-hexane). Subsets of those EGs were used for characterization of exposures to dispersants, particulate matter, and oil mist. The EGs allowed assignment to study participants of exposure estimates developed from measurement data or from estimation models through linkage in the JEM for the investigation of exposure-response relationships., (© The Author(s) 2022. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.)

Following accidental release into marine environments, crude oil progressively weathers, influencing composition, fate, and toxicity. However, published studies draw conflicting conclusions on the effects of oil weathering on ecotoxicity. Using the PETROTOX model, this study characterized the effect of weathering on acute oil toxicity for four aquatic species. Results indicated that predicted acute toxicity decreased with increased oil weathering, due to reductions in overall concentrations and bioavailability of hydrocarbon constituents., (Copyright © 2020. Published by Elsevier Ltd.)

The Deepwater Horizon oil spill was the largest, longest-lasting, and deepest oil accident to date in US waters. As oil and natural gas jetted from release points at 1,500-m depth in the northern Gulf of Mexico, entrainment of the surrounding ocean water into a buoyant plume, rich in soluble hydrocarbons and dispersed microdroplets of oil, created a deep (1,000-m) intrusion layer. Larger droplets of liquid oil rose to the surface, forming a slick of mostly insoluble, hydrocarbon-type compounds. A variety of physical, chemical, and biological mechanisms helped to transform, remove, and redisperse the oil and gas that was released. Biodegradation removed up to 60% of the oil in the intrusion layer but was less efficient in the surface slick, due to nutrient limitation. Photochemical processes altered up to 50% (by mass) of the floating oil. The surface oil expression changed daily due to wind and currents, whereas the intrusion layer flowed southwestward. A portion of the weathered surface oil stranded along shorelines. Oil from both surface and intrusion layers were deposited onto the seafloor via sinking marine oil snow. The biodegradation rates of stranded or sedimented oil were low, with resuspension and redistribution transiently increasing biodegradation. The subsequent research efforts increased our understanding of the fate of spilled oil immensely, with novel insights focusing on the importance of photooxidation, the microbial communities driving biodegradation, and the formation of marine oil snow that transports oil to the seafloor.

Oil weathering is often described subjectively after a spill. Adjectives like "moderate" and "severe" help define the extent of oil loss but fail to communicate quantitatively and reproducibly the degree of weathering. The use of subjective weathering terms often leads to misperceptions about persistence and toxicity of oil residues in the environment. The weathering of MC252 oil from the Deepwater Horizon spill started immediately after release during the 1500-m ascent to the sea surface and continued as it was transported on the surface and reached the shoreline. Weathering processes included evaporation, dissolution, photo-degradation, and biodegradation, among others. With extensive sample collection and detailed chemistry and source fingerprinting analyses, the Deepwater Horizon data provide a unique opportunity to evaluate weathering processes semi-quantitatively. An objective method of defining the degree of oil weathering is developed based on the detailed chemical results for over 700 MC252 oil samples from the environment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Declaration of competing interest None., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

There has been increasing urgency to develop methods for detecting oil in sea ice owing to the effects of climate change in the Arctic. A multidisciplinary study of crude oil behavior in a sea ice environment was conducted at the University of Manitoba during the winter of 2016. In the experiment, medium-light crude oil was injected underneath young sea ice in a mesocosm. The physical and thermodynamic properties of the oil-infiltrated sea ice were monitored over a three-week time span, with concomitant analysis of the oil composition using analytical instrumentation. A resonant perturbation technique was used to measure the oil dielectric properties, and the contaminated sea ice dielectric properties were modeled using a mixture model approach. Results showed that the interactions between the oil and sea ice altered their physical and thermodynamic properties. These changes led to an overall decrease in sea ice dielectrics, potentially detectable by remote sensing systems., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Paper spray ionization mass spectrometry (PSI-MS) was applied for the first time to study temporal change of photo-oxidized and weathered oils subjected to degradation. PSI is chosen in this study because it is an optimal ionization technique for the analysis of degraded oils with limited sample quantity and prone to salt and particulate contamination. With PSI-MS, quantitative analysis of oils can be successfully performed with as little as 2 μg of oil sample. In addition, oil solutions containing up to 0.05% sodium chloride were successfully analyzed with PSI-MS. In the PSI-MS spectra of photo-degraded oils, the relative abundance of compounds having double equivalence value (DBE) ≥ 5 increased but those with DBE < 5 decreased in number. The summed abundance ratio of compounds having DBE < 5 and DBE ≥ 5 showed a negative exponential correlation with the duration of UV exposure in laboratory experiments. The same trend was observed from spilled oils obtained from the environment. Therefore, this ratio serves as an effective means to estimate the degree of weathering in spilled oils., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Oil degradation by surface-level atmospheric ozone has been largely ignored in the field. To address this knowledge gap, this study investigated the ozonation rate and extent of typical petroleum compounds by simulated surface-level ozone, including total petroleum hydrocarbons (TPHs), n-alkanes, and polycyclic aromatic hydrocarbons (PAHs). Moreover, the work explored the effect of a prototype oil dispersant, Corexit EC9500A, on the ozonation rate. Rapid oxidation of TPHs, n-alkanes and PAHs was observed at various gaseous ozone concentrations (i.e. 86, 200 and 300 ppbv). Generally, the presence of the oil dispersant enhanced ozonation of the oil compounds. The addition of humic acid inhibited the reaction, while increasing salinity accelerated the degradation. Both direct ozonation by molecular ozone and indirect oxidation by ozone-induced radicals play important roles in the degradation process. The findings indicate that ozonation should be taken into account in assessing environmental fate and weathering of spilled oil., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The primary aim of this research was to identify the physicochemical properties of the oil and water-in-oil (W/O) emulsions used during a NOFO Oil-on-Water field trials that reduced the performance of the skimmers recovery efficacy during the trials. Extensive studies were performed at SINTEF laboratories with the residues of oil topped (i.e. evaporative loss of crude oil components by distillation process at large scale) for the field trial and compared it with different residues of oil topped by bench scale laboratory procedures. In order to obtain a sufficient stable W/O emulsion for the field trial, bunker fuel oil (IFO380) and various concentrations of an emulsifier (Paramul®) were also added to the residues of oil topped on large scale and investigated through interfacial tension, contact angle, droplet adhesion and "dip and withdraw" tests. The investigations revealed that the addition of an emulsifier lowered the interfacial tension of oil residues, which consequently reduced the adherence properties of the oil and emulsions to the surface of the skimmer material. Too high concentration of an emulsifier (>0,5%) also had a negative effect on the stability of W/O emulsion., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The 2010 Deepwater Horizon (DwH) oil spill contaminated ~1,773km of the Gulf of Mexico shorelines. Yet, few field data are available on the long-term fate and persistency of sediment-retained oil. While an unprecedented amount of oil dispersants was applied, the effects of oil dispersants on desorption of field aged oil remain unknown. This study aimed to investigate the abundance, distributions and physico-chemical availability of the oil retained in Bay Jimmy sediment, Louisiana, five years after the DwH oil spill, and to determine the effects of two model oil dispersants on the desorption potential of the residual oil. Total petroleum hydrocarbons (TPHs), n-alkanes and polycyclic aromatic hydrocarbons (PAHs) in the sediment were analyzed and compared with those in the crude oil and the pre-DwH levels, and batch desorption kinetic tests were carried out to quantify the dispersant effects on the desorption rate and extent. The biomarker hopanes profile and diagnostic ratio were analyzed, which confirmed the origin and persistence of the sediment-retained oil. After five-year natural weathering, the oil level in the sediment remained orders of magnitude higher than the pre-spill level. Nearly all low-molecular-weight n-alkanes and 2-ring PAHs had been degraded. Oil dispersants, SPC 1000 and Corexit EC9500A, were able to enhance solubilization of the sediment-retained oil upon resuspension of the sediment. Successive desorption experiments indicated that 71.6% of TPHs, 74.8% of n-alkanes, and 91.9% of PAHs in the sediment remained highly stable and hardly desorbable by seawater; yet, addition of 18mg/L of SPC 1000 enhanced the desorption and lowered these fractions to 57.3%, 68.1%, and 81.4%, respectively. The findings are important for understanding the natural weathering rate and persistence of oil residual and the effects of dispersants on the physical and biological availabilities of aged oil in coastal sediments., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The fate and behavior of diluted bitumen spilled in marine conditions has recently become a topic of much interest, yet, only limited knowledge is available. One of the major issues of a diluted bitumen spill on water is whether the product will sink, especially when suspended sediment is present in the water column. This study demonstrated how weathering processes influenced the key spill-related properties of a diluted bitumen product (Cold Lake Blend-Winter), and how interaction of diluted bitumen with sediment affected its tendency to float or sink in water. This study showed that the weathering states of the oils as well as the size of sediment are important factors influencing oil-sediment interactions and the tendency of the formed oil-particulate aggregates for buoyancy. When mixing with fine- and medium-sized sediments, the fresh to moderately weathered oils formed oil-particulate aggregates and sank in saltwater, while the very heavily-weathered oil formed discrete free-floating tarballs., (Copyright © 2017. Published by Elsevier Ltd.)

Crude oil that is inadvertently spilled in the marine environment can interact with suspended sediment to form oil-mineral aggregates (OMA). Researchers have identified OMA formation as a natural method of oil dispersion, and have sought ways to enhance this process for oil spill remediation. Currently there is a lack of understanding of how the weathering of oil will affect the formation of OMA due to a lack of published data on this relationship. Based on literature, we identified two conflicting hypotheses: OMA formation 1) increases with weathering as a result of increased asphaltene and polar compound content; or 2) decreases with weathering as a result of increased viscosity. While it is indeed true that the viscosity and the relative amount of polar compounds will increase with weathering, their net effects on OMA formation is unclear. Controlled laboratory experiments were carried out to systematically test these two conflicting hypotheses. Experimental results using light, intermediate, and heavy crude oils, each at five weathering stages, show a decrease in OMA formation as oil weathers., (Copyright © 2017 Elsevier B.V. All rights reserved.)

This work investigated effects of a popular oil dispersant (Corexit EC9500A) on oxidation of phenanthrene and pyrene (two model polycyclic aromatic hydrocarbons) in Gulf coast seawater under simulated atmospheric ozone. The degradation data followed a two-stage pseudo-first order kinetics, a slower initial reaction rate followed by a much faster rate in longer time. The ozonation rate for pyrene was faster than that for phenanthrene. The presence of 18 and 180 mg/L of the dispersant inhibited the first-order degradation rate by 32-80% for phenanthrene, and 51-85% for pyrene. In the presence of 18 mg/L of the dispersant, the pyrene degradation rate increased with increasing ozone concentration, but decreased with increasing solution pH and temperature, while remained independent of ionic strength. For the first time, the results indicate that atmospheric ozone may play a significant role in the weathering of dispersed persistent oil components in natural and engineered systems., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

In case of oil spills due to disasters, one of the environmental concerns is the oil trajectories and spatial distribution. To meet these new challenges, spill response plans need to be upgraded. An important component of such a plan would be models able to simulate the behaviour of oil in terms of trajectories and spatial distribution, if accidentally released, in deep water. All these models need to be calibrated with independent observations. The aim of the present paper is to demonstrate that significant support to oil slick monitoring can be obtained by the synergistic use of oil drift models and remote sensing observations. Based on transport properties and weathering processes, oil drift models can indeed predict the fate of spilled oil under the action of water current velocity and wind in terms of oil position, concentration and thickness distribution. The oil spill event that occurred on 31 May 2003 in the Baltic Sea offshore the Swedish and Danish coasts is considered a case study with the aim of producing three-dimensional models of sea circulation and oil contaminant transport. The High-Resolution Limited Area Model (HIRLAM) is used for atmospheric forcing. The results of the numerical modelling of current speed and water surface elevation data are validated by measurements carried out in Kalmarsund, Simrishamn and Kungsholmsfort stations over a period of 18 days and 17 h. The oil spill model uses the current field obtained from a circulation model. Near-infrared (NIR) satellite images were compared with numerical simulations. The simulation was able to predict both the oil spill trajectories of the observed slick and thickness distribution. Therefore, this work shows how oil drift modelling and remotely sensed data can provide the right synergy to reproduce the timing and transport of the oil and to get reliable estimates of thicknesses of spilled oil to prepare an emergency plan and to assess the magnitude of risk involved in case of oil spills due to disaster.

This study investigated the effects of 3 model oil dispersants (Corexit EC9500A, Corexit EC9527A and SPC 1000) on photodegradation of pyrene under simulated sunlight. Both Corexit dispersants enhanced photodegradation of pyrene, while SPC1000 slightly inhibited the reaction. Span 80 and Tween 85 were the key ingredients causing the effects, though the underlying mechanisms differed. Span 80 enriches pyrene in the upper layer of water column, whereas Tween 85 induces a photosensitization process. Two reactive oxygen species, 1 O 2 and O 2 - , were found responsible for pyrene photodegradation, though the presence of EC9500A suppressed the 1 O 2 pathway. In terms of photodegradation products, EC9500A enhanced generation of polyaromatic intermediates, i.e., phenaleno[1,9-cd][1,2]dioxine, 1-hydroxypyrene, and 1,8-pyrenequinone, but did not alter the classical photodegradation pathway. The Corexit dispersants were more prone to photochemical decomposition, with multiple by-products detected. The information aids in our understanding of the effects of dispersants on photochemical weathering of oil compositions., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Zooplankton are suggested to be biotic contributors to the transport and weathering of oil in marine environments due to their ingestion of oil. In the present experiment, feeding activity and microbial communities in feces from Calanus finmarchicus feeding in oil dispersions were characterized. Feeding activity was significantly reduced in oil dispersions. The microbial communities in clean and oil-containing copepod feces were dominated by Rhodobacteraceae family bacteria (Lesingera, Phaeobacter, Rugeria, and Sulfitobacter), which were suggested to be indigenous to copepod feces. The results also indicated that these bacteria were metabolizing oil compounds, as a significant increase in the concentrations of viable oil degrading microorganisms was observed in oil-containing feces. This study shows that bacteria in feces from copepods feeding in dilute oil dispersions have capacity for degradation of oil. Zooplankton may therefore contribute to weathering of oil by excreting feces with microbial communities already adapted to degradation of oil., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

We examined the degree of DNA damage caused by three fractions (F1, aliphatic hydrocarbons; F2, aromatic hydrocarbons; and F3, polar compounds) of the organic extract of sediments taken from Taean, Korea, following the Hebei Spirit oil spill. DNA damage was measured using the comet assay with blood cells of the striped beakfish (Oplegnathus fasciatus). DNA damage was also examined for fractions of crude oil (Iranian Heavy Crude Oil, IHC), weathered oil and six subfractions (F2.1-F2.6). The greatest DNA damage was found from the Sinduri dune region and DNA damage decreased to 40% weathered oil in F2 fraction compared with crude oil. The DNA damage of the sum of fractions was found higher than the organic extracts of sediments, suggesting antagonistic interactions between the genotoxic compounds. This study confirmed the persistence of potential genotoxicity in sediments of the severely affected regions as long as 5 years after the oil spill., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

This work investigated effects of a popular oil dispersant (Corexit EC9500A) on UV- or sunlight-mediated photodegradation of pyrene (a model polycyclic aromatic hydrocarbon) in seawater. The presence of 18 and 180mg/L of the dispersant increased the first-order photodegradation rate by 5.5% and 16.7%, respectively, and reduced or ceased pyrene volatilization. By combining individual first-order rate laws for volatilization and photodegradation, we proposed an integrated kinetic model that can adequately predict the overall dissipation of pyrene from seawater. Mechanistic studies indicated that superoxide radicals played a predominant role in pyrene photodegradation, and the dispersant enhanced formation of superoxide radicals. 1-Hydroxypyrene was the main intermediate regardless of the dispersant, suggesting that electrons were transferred from excited pyrene to oxygen. In the presence of 18mg/L of the dispersant, the photodegradation rate increased with increasing ionic strength and temperature, but decreased with increasing HA concentration, and remained independent of solution pH. The results are important in understanding roles of oil dispersants on environmental fate of persistent oil components in natural and engineered systems., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The major AhR-active PAHs were identified in crude oil and oil-contaminated sediments by use of effect-directed analysis. As part of the study, an enhanced potency balance analysis was conducted by establishing the novel relative potency values of (alkyl)-PAHs from the H4IIE-luc bioassay. Silica gel column fractionation of crude oil resulted in greater AhR-mediated potencies in fractions of aromatics (F2) and resins (F3), and such trend was also observed for field collected sediment samples. AhR-mediated potencies of six F2 sub-fractions from HPLC indicated that the majority of F2 responses were attributable to 3-4 ring aromatics. Target PAHs including C4-phenanthrene, C1-chrysene, and C3-chrysene in sediments explained ∼ 18% of the bioassay-derived TCDD-EQs, however, the unknown AhR agonists and potential mixture effects remain in question. Overall, the AhR-potency and antagonistic potential of residual oil in sediment tended to decrease over time, thus monitoring of weathering process would be key for the post management of oil-contaminated sites., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Ecotoxicological monitoring of intertidal sediments was performed for 5 years after the Hebei Spirit oil spill in Taean, Korea. Sediment toxicity was observed on most of the beaches 4 months after the spill and later decreased rapidly to nontoxic levels 8 months after the spill. The concentrations of total polycyclic aromatic hydrocarbons (TPAHs) in the sediments ranged from 2 to 530,000 ng/g during the monitoring. More than half of the samples exhibited significant toxicity 5 years after the Hebei Spirit oil spill. Using a logistic regression model, the median lethal concentration of TPAHs to amphipod Monocorophium uenoi was estimated to be 36,000 ng/g. From the 63 chemistry and toxicity data, the effect range-low, effect range median, threshold effect level, and probable effect level were derived to be 3190, 54,100, 2480, and 29,000 ng/g, respectively. The relative compositions of the PAH groups indicated that the weathering process is still ongoing., (Copyright © 2013 Elsevier Ltd. All rights reserved.)