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Oil spills are a frequent perturbation to the marine environment that has rapid and significant impacts on the local microbiome. Previous studies have shown that exposure to synthetic dispersant alone did not enhance heterotrophic microbial activity or oxidation rates of specific hydrocarbon components but increased the abundance of some taxa (e.g., Colwellia). In contrast, exposure to oil, but not dispersants, increased the abundance of other taxa (e.g., Marinobacter) and stimulated hydrocarbon oxidation rates. Here, we advance these findings by interpreting metatranscriptomic data from this experiment to explore how and why specific components of the microbial community responded to distinct organic carbon exposure regimes. Dispersant alone was selected for a unique community and for dominant organisms that reflected treatment- and time-dependent responses. Dispersant amendment also led to diverging functional profiles among the different treatments. Similarly, oil alone was selected for a community that was distinct from treatments amended with dispersants. The presence of oil and dispersants with added nutrients led to substantial differences in microbial responses, likely suggesting increased fitness driven by the presence of additional inorganic nutrients. The oil-only additions led to a marked increase in the expression of phages, prophages, transposable elements, and plasmids (PPTEPs), suggesting that aspects of microbial community response to oil are driven by the mobilome, potentially through viral-associated regulation of metabolic pathways in ciliates and flagellates that would otherwise throttle the microbial community through grazing.IMPORTANCEMicrocosm experiments simulated the April 2010 Deepwater Horizon oil spill by applying oil and synthetic dispersants (Corexit EC9500A and EC9527A) to deep ocean water samples. The exposure regime revealed severe negative alterations in the treatments heterotrophic microbial activity and hydrocarbon oxidation rates. We expanded these findings by exploring metatranscriptomic signatures of the microbial communities during the chemical amendments in the microcosm experiments. Here we report how dominant organisms were uniquely associated with treatment- and time-dependent trajectories during the exposure regimes; nutrient availability was a significant factor in driving changes in metatranscriptomic responses. Remarkable signals associated with PPTEPs showed the potential role of mobilome and viral-associated survival responses. These insights underscore the time-dependent environmental perturbations of fragile marine environments under oil and anthropogenic stress.

Dispersants, a class of chemical spill-treating agents used to treat oil spills, are commonly used globally as an alternative response measure. Applying dispersants to an oil slick, shortly after the spill has occurred, can protect shoreline environments and sea surface-dwelling animals, such as some marine bird species, limiting individuals or local populations from the consequences of coming into contact with large quantities of oil. However, this benefit comes with the cost of increasing oil exposure risk to marine biota that spend time in the water column. It is generally believed that the benefits of dispersant use outweigh the costs under most circumstances. However, it is rarely acknowledged that the use of dispersants may have negative impacts on marine biota at the individual or local population level, including marine birds. In Canada, Corexit EC9500A, a regulated dispersant, is being proposed for expanded use beyond treating spills from an offshore oil and gas facility. To understand what the potential impacts from dispersant use are to marine birds, we conducted a literature review to identify the direct and indirect effects of their use. We also provide oil spill responders with a Pathway of Effects (POE) conceptual model, a tool for understanding the interactions between dispersants, marine birds, and their environment to support a holistic consideration as part of the oil spill response decision-making process. Fundamental uncertainties remain, however, and if left unaccounted for in the decision-making process, they may compromise the appropriateness of spill response approaches and outcomes. We recommend that oil spill responders incorporate the known benefits and costs of dispersant use on marine birds into a decision-making framework such as a Net Environmental Benefit Analysis (NEBA) and with consideration of the POE concept models provided. These recommendations are particularly relevant where a decision-making framework such as NEBA is becoming a more standardized component of the response process. Additionally, greater investment in lab and field-based research, and field observations through monitoring, is required to address existing decision-making uncertainties and provide information gap closure. [ABSTRACT FROM AUTHOR]

The offshore oil industry in Atlantic Canada necessitates a greater understanding of the potential impacts of oil exposure and spill response measures on cold‐water marine species. We used a standardized scoring index to characterize sublethal developmental impacts of physically and chemically dispersed crude oil in early life stages of Atlantic cod (Gadus morhua) and assessed intraspecific variation in the response among cod families. Cod (origin: Scotian Shelf, Canada) were laboratory‐crossed to produce embryos from five specific families, which were subsequently exposed prehatch to gradient dilutions of a water‐accommodated fraction (WAF) and a chemically enhanced WAF (CEWAF; prepared with Corexit 9500A) for 24 h. Postexposure, live embryos were transferred into filtered seawater and monitored to hatch; then, all live fish had sublethal endpoints assessed using the blue‐sac disease (BSD) severity index. In both WAF and CEWAF groups, increasing exposure concentrations (measured as total petroleum hydrocarbons) resulted in an increased incidence of BSD symptoms (impaired swimming ability, increased degree of spinal curvature, yolk‐sac edemas) in cod across all families. This positive concentration‐dependent increase in BSD was similar between physically (WAF) versus chemically (CEWAF) dispersed oil exposures, indicating that dispersant addition does not exacerbate the effect of crude oil on BSD incidence in cod. Sensitivity varied between families, with some families having less BSD than others with increasing exposure concentrations. To our knowledge, our study is the first to demonstrate the occurrence in fishes of intraspecific variation among families in sublethal responses to oil and dispersant exposure. Our results suggest that sublethal effects of crude oil exposure will not be uniformly observed across cod populations and that sensitivity depends on genetic background. Environ Toxicol Chem 2022;41:1967–1976. © 2022 SETAC [ABSTRACT FROM AUTHOR]

The range of impacts of chemical dispersants on indigenous marine microbial communities and their activity remains poorly constrained. We tested the response of nearshore surface waters chronically exposed to oil leakage from a downed platform and supplied with nutrients by the Mississippi River to Corexit dispersant and nutrient additions. As assessed using 14C-labeled tracers, hexadecane mineralization potential was orders of magnitude higher in all unamended samples than in previously assessed bathypelagic communities. Nutrient additions stimulated microbial mortality but did not affect community composition and had no generalizable effect on hydrocarbon mineralization potential. By contrast, Corexit amendments caused a rapid shift in community composition and a drawdown of inorganic nitrogen and orthophosphate though no generalizable effect on hydrocarbon mineralization potential. The hydrocarbonoclastic community's response to dispersants is largely driven by the relative availability of organic substrates and nutrients, underscoring the role of environmental conditions and multiple interacting stressors on hydrocarbon degradation potential. [Display omitted] • Examined nutrient-replete coastal microbial communities exposed to chronic oil leakage. • Hexadecane mineralization rates were orders of magnitude higher than in other studies. • Nutrients did not shift community composition or generally stimulate microbial activity. • Corexit amendments stimulated growth of numerous oil-degrading bacterial genera. • Corexit stimulated drawdown of dissolved inorganic nitrogen and orthophosphate. • Corexit did not stimulate or inhibit mineralization of naphthalene or hexadecane. [ABSTRACT FROM AUTHOR]

Endosymbionts (Symbiodiniaceae) play a vital role in the health of corals. Seawater pollution can harm these endosymbionts and dispersants used during oil spill cleanup can be extremely toxic to these organisms. Here, we examined the impact of oil and a specific dispersant, Corexit-9500, on two representative endosymbionts – Symbiodinium and Cladocopium – from the Southwestern endemic coral Mussismilia braziliensis. The survival and photosynthetic potential of the endosymbionts decreased dramatically after exposure to the dispersant and oil by ~25 % after 2 h and ~50 % after 7 days. Low concentrations of dispersant (0.005 ml/l) and dispersed oil (Polycyclic Aromatic Hydrocarbons, 1132 μg/l; Total Petroleum Hydrocarbons, 595 μg/l) proved highly toxic to both Symbiodinium and Cladocopium. These levels triggered a reduction in growth rate, cell size, and cell wall thickness. After a few hours of exposure, cellular organelles were damaged or destroyed. These acute toxic effects underline the fragile nature of coral endosymbionts. [Display omitted] • Dispersant and (dispersed) oil are lethal to endosymbionts. • Sharp decline in survival, photosynthetic potential, and cell size after 2 h. • Damage of organelles (e.g. nucleus and chloroplast). • Triacylglycerol accumulation to stress response after 7 days. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Following the explosion of the Deepwater Horizon MC252 oil rig in 2010, 319 live sea turtles exposed to crude oil and oil-dispersant (Corexit) combinations were admitted to rehabilitation centers for decontamination and treatment. Treatment of oiled sea turtles was guided by expected physiological and pathological effects of crude oil exposure extrapolated from studies in other species and from a single loggerhead sea turtle (Caretta caretta) study. While invaluable starting points, inherent limitations to extrapolation, and small sample size of the experimental exposure study, reduce their utility for clinical guidance and for assessing oil spill impacts. Effects of dispersants were not included in the previous experimental exposure study, and cannot be effectively isolated in the analysis of field data from actual spills. A terminal study of pivotal temperature of sex determination using eggs salvaged from doomed loggerhead nests provided an opportunity for an ancillary exposure study to investigate the acute effects of crude oil, dispersant, and a crude oil/dispersant combination in sea turtle hatchlings. Eggs were incubated at 27.2–30.8°C, and hatchlings were randomly assigned to control, oil, dispersant, and combined oil/dispersant exposures for 1 or 4 days. Contaminant exposures were started after a 3 day post-hatching period simulating nest emergence. Turtles were placed in individual glass bowls containing aged seawater and exposed to oil (Gulf Coast—Mixed Crude Oil Sweet, CAS #8002-05-9, 0.833 mL/L) and/or dispersant (Corexit 9500A, 0.083 mL/L), replicating concentrations encountered during oil spills and subsequent response. Statistically significant differences between treatments and non-exposed controls were detected for PCV, AST, uric acid, glucose, calcium, phosphorus, total protein, albumin, globulin, potassium, and sodium. The principal dyscrasias reflected acute osmolar, electrolyte and hydration challenges that were more numerous and greater in combined oil/dispersant exposures at 4 days. Clinicopathological findings were supported by a failure to gain weight (associated with normal hatchling hydration in seawater) in dispersant and combination exposed hatchlings. These findings can help guide clinical response for sea turtles exposed to crude oil and crude oil/dispersant combinations, and indicate potential impacts on wildlife to consider when deploying dispersants in an oil spill response.

Dispersants are used to reduce the impact of oil spills in marine environment. Experiments were conducted with natural materials which were contaminated by direct application of fresh Louisiana crude oil. The natural materials evaluated included sea sand (South Beach in Miami, Florida), red mangrove leaves (Rhizophora mangle), and sea shells (Donax variabili). Salt water at two different salinities (17 and 34 ppt) was used with two types of Corexit dispersant solutions (9500A and 9527A) in concentrations ranging from 100 to 3500 mg/L. Washing of the contaminated samples was conducted by a three-step mixing procedure (salt water only, then with the addition of the dispersant solution to the salt water, and salt water) to simulate oil-saltwater-dispersant interactions. In general, increasing dispersant concentration increased the percentage of oil dispersed into the aqueous phase up to dispersant solutions containing 400 mg/L for Corexit 9500A and 300 mg/L Corexit 9527A. Increasing the dispersant concentration above these levels also decreased the dispersion of oil from the surfaces. At very high concentrations of dispersant solutions (above 1500 mg/L), the percentage of oil dispersed into the solution from the contaminated surfaces was about one half what was observed at 400 mg/L with Corexit 9500A and 300 mg/L Corexit 9527A. Although dispersants were most effective for removing the fresh Louisiana crude oil from sand particles and dispersing into the solution due to large surface area of the particles per unit weight; the residual oil remaining on the sand particles was relatively high in comparison to mangrove leaves and sea shells due to clustering of sand particle with oil. There was some oil penetration into the porous structure of the sea shells (at the microscopic level) which could not be removed. Image 1 • A three step washing process was used to clean crude oil contaminated natural materials. • Two commonly used oil spill dispersants (Corexit 9500A and Corexit 9527A) were evaluated. • Contaminated sea sand, shells (Donax variabili), and r ed mangrove (Rhizophora mangle) leaves were evaluated. • Increasing dispersant concentration up to 400 mg/L increased the oil dispersed into the aqueous phase. • Higher residual oil remained on sand surfaces due to clustering of particles with oil. [ABSTRACT FROM AUTHOR]

Exposure to crude oil, its components, and oil dispersants during a major crude oil spill, such as the Deepwater Horizon Oil Spill, can elicit behavioral changes in animals and humans. However, the underlying mechanisms by which oil spill-related compounds alters behavior remains largely unknown. A major cause of behavioral changes generally is dysfunction of the blood-brain barrier (BBB). We investigated the impact of a crude oil high energy water accommodated fraction (HEWAF), benzo[a] pyrene (BaP; a major component of crude oil), and the oil dispersant COREXIT, on BBB function. BBB function was assessed by measuring transendothelial electrical resistance (TEER) of mouse brain microvascular endothelial cells (BMECs). Within 3 h after treatment, TEER was significantly reduced by exposure to high concentrations of all test compounds. TEER remained reduced in response to COREXIT after 48 h, but this effect waned in BMECs treated with HEWAF and BaP, with low-mid range concentrations inducing increased TEER compared to vehicle controls. At 48 h of treatment, BMEC viability was significantly reduced in response to 2% HEWAF, but was increased in response to BaP (25 and 50 μM). BMEC viability was increased with 80 ppm COREXIT, but was reduced with 160 ppm. Gene expression of tight junction-associated proteins (claudin-5 and tight junction protein-1), and cell adhesion receptor (vascular cell adhesion molecule-1) was reduced in response to HEWAF and COREXIT, but not BaP. Taken together, these data suggest that oil spill-related compounds markedly affect BBB function, and that these changes may underlie the observed behavioral changes due to crude oil exposure. Unlabelled Image • This paper is the first study to study the effects of DWH oil on blood brain barrier function in mammals. • HEWAF from DWH oil, benzo[a]pyrene, and COREXIT all disrupt blood brain barrier endothelial cell tight junctions. • The tested compounds to varying degrees all result in decreased expression of genes related to tight junction function. [ABSTRACT FROM AUTHOR]

Western Canada produces large amounts of bitumen, a heavy, highly weathered crude oil. Douglas Channel and Hecate Strait on the coast of British Columbia are two water bodies that may be impacted by a proposed pipeline and marine shipping route for diluted bitumen (dilbit). This study investigated the potential of microbial communities from these waters to mitigate the impacts of a potential dilbit spill. Microcosm experiments were set up with water samples representing different seasons, years, sampling stations, and dilbit blends. While the alkane fraction of the tested dilbit blends was almost completely degraded after 28 days, the majority of the polycyclic aromatic hydrocarbons (PAHs) remained. The addition of the dispersant Corexit 9500A most often had either no effect or an enhancing effect on dilbit degradation. Dilbit-degrading microbial communities were highly variable between seasons, years, and stations, with dilbit type having little impact on community trajectories. Potential oil-degrading genera showed a clear succession pattern and were for the most part recruited from the "rare biosphere." At the community level, dispersant appeared to stimulate an accelerated enrichment of genera typically associated with hydrocarbon degradation, even in dilbit-free controls. This suggests that dispersant-induced growth of hydrocarbon degraders (and not only increased bioavailability of oil-associated hydrocarbons) contributes to the degradation-enhancing effect previously reported for Corexit 9500A. IMPORTANCE Western Canada hosts large petroleum deposits, which ultimately enter the market in the form of dilbit. Tanker-based shipping represents the primary means to transport dilbit to international markets. With anticipated increases in production to meet global energy needs, the risk of a dilbit spill is expected to increase. This study investigated the potential of microbial communities naturally present in the waters of a potential dilbit shipping lane to mitigate the effects of a spill. Here we show that microbial degradation of dilbit was mostly limited to n-alkanes, while the overall concentration of polycyclic aromatic hydrocarbons, which represent the most toxic fraction of dilbit, decreased only slightly within the time frame of our experiments. We further investigated the effect of the oil dispersant Corexit 9500A on microbial dilbit degradation. Our results highlight the fact that dispersant-associated growth stimulation, and not only increased bioavailability of hydrocarbons and inhibition of specific genera, contributes to the overall effect of dispersant addition. [ABSTRACT FROM AUTHOR]

Abstract Spilled oil treated with Corexit dispersant can cause unintended impacts on marine environment systems including altering marine organic matter dynamics; however, impacts on microgels and marine oil snow (MOS) formation are still debated and remain to be fully understood. Extracellular polymeric substances (EPS) are a major source of marine organic carbon for MOS and microgel formation. EPS initial aggregation plays key roles in the oil degrading process and various biogeochemical reactions. Here we used four types of EPS with water accommodated fraction (WAF), chemically-enhanced WAF (CEWAF) and Corexit, to represent potential situations during oil spills and post-application of Corexit. We found that Corexit alone can inhibit EPS aggregation and disperse pre-existing microgels. CEWAF can enhance EPS aggregation with efficiency by up to 80%–100% and more aggregates accumulated within the air-water interface. Additionally, more hydrophobic EPS aggregates showed high resistance to Corexit dispersion while hydrophilic EPS were more sensitive. Effects of oil spills on marine gel particle formation are primarily determined by chemical characteristics (hydrophobicity and protein content) of the constituent EPS. This study offers unique insights for organic particle dynamics and identifies controlling factors for MOS or gel particles associated with oil spills and Corexit dispersant used. Graphical abstract Unlabelled Image Highlights • Corexit alone can inhibit EPS (extracellular polymeric substances) aggregation. • Pre-existing EPS microgels can be dispersed by Corexit. • Chemically-enhanced water accommodated fraction can enhance EPS aggregate formation. • Hydrophobic EPS aggregates showed more resistance to Corexit dispersion. • Hydrophobicity and protein content play key role in EPS behavior. [ABSTRACT FROM AUTHOR]

Highlights • Chemically-dispersed oil treatments resulted in lower photosynthetic rates and quantum yields. • Diatoms were the dominant eukaryote taxa in oil-only treatments, and the Euglenozoa dominated dispersed oil treatments. • More aggregation occurred in treatments that inhibited phytoplankton growth and photophysiology. Abstract During the 2010 Deepwater Horizon oil spill, the chemical dispersant Corexit was applied over vast areas of the Gulf of Mexico. Marine phytoplankton play a key role in aggregate formation through the production of extracellular polymeric materials (EPS), an important step in the biological carbon pump. This study examined the impacts of oil and dispersants on the composition and physiology of natural marine phytoplankton communities from the Gulf of Mexico during a 72-hour mesocosm experiment and consequences to carbon export. The communities were treated using the water accommodated fraction (WAF) of oil, which was produced by adding Macondo surrogate oil to natural seawater and mixed for 24 h in the dark. A chemically enhanced WAF (CEWAF) was made in a similar manner, but using a mixture of oil and the dispersant Corexit in a 20:1 ratio as well as a diluted CEWAF (DCEWAF). Phytoplankton communities exposed to WAF showed no significant changes in PSII quantum yield (F v /F m) or electron transfer rates (ETR max) compared to Control communities. In contrast, both F v /F m and ETR max declined rapidly in communities treated with either CEWAF or DCEWAF. Analysis of other photophysiological parameters showed that photosystem II (PSII) antenna size and PSII connectivity factor were not altered by exposure to DCEWAF, suggesting that processes downstream of PSII were affected. The eukaryote community composition in each experimental tank was characterized at the end of the 72 h exposure time using 18S rRNA sequencing. Diatoms dominated the communities in both the control and WAF treatments (52 and 56% relative abundance respectively), while in CEWAF and DCEWAF treatments were dominated by heterotrophic Euglenozoa (51 and 84% respectively). Diatoms made up the largest relative contribution to the autotrophic eukaryote community in all treatments. EPS concentration was four times higher in CEWAF tanks compared to other treatments. Changes in particle size distributions (a proxy for aggregates) over time indicated that a higher degree of particle aggregation occurred in both the CEWAF and DCEWAF treatments than the WAF or Controls. Our results demonstrate that chemically dispersed oil has more negative impacts on photophysiology, phytoplankton community structure and aggregation dynamics than oil alone, with potential implications for export processes that affect the distribution and turnover of carbon and oil in the water column. [ABSTRACT FROM AUTHOR]

The application of chemical dispersants during marine oil spills can affect the community composition and activity of marine microorganisms. Several studies have indicated that certain marine hydrocarbon-degrading bacteria, such as Marinobacter spp., can be inhibited by chemical dispersants, resulting in lower abundances and/or reduced biodegradation rates. However, a major knowledge gap exists regarding the mechanisms underlying these physiological effects. Here, we performed comparative proteomics of the Deepwater Horizon isolate Marinobacter sp. TT1 grown under different conditions. Strain TT1 received different carbon sources (pyruvate vs. n-hexadecane) with and without added dispersant (Corexit EC9500A). Additional treatments contained crude oil in the form of a water-accommodated fraction (WAF) or chemically-enhanced WAF (CEWAF; with Corexit). For the first time, we identified the proteins associated with alkane metabolism and alginate biosynthesis in strain TT1, report on its potential for aromatic hydrocarbon biodegradation and present a protein-based proposed metabolism of Corexit components as carbon substrates. Our findings revealed that Corexit exposure affects hydrocarbon metabolism, chemotactic motility, biofilm formation, and induces solvent tolerance mechanisms, like efflux pumps, in strain TT1. This study provides novel insights into dispersant impacts on microbial hydrocarbon degraders that should be taken into consideration for future oil spill response actions.

During marine oil spills, chemical dispersants are used routinely to disperse surface slicks, transferring the hydrocarbon constituents of oil into the aqueous phase. Nonetheless, a comprehensive understanding of how dispersants affect natural populations of hydrocarbon-degrading bacteria, particularly under environmentally relevant conditions, is lacking. We investigated the impacts of the dispersant Corexit EC9500A on the marine hydrocarbon degrader Marinobacter sp. TT1 when pre-adapted to either low n-hexadecane concentrations (starved culture) or high n-hexadecane concentrations (well-fed culture). The growth of previously starved cells was inhibited when exposed to the dispersant, as evidenced by 55% lower cell numbers and 30% lower n-hexadecane biodegradation efficiency compared to cells grown on n-hexadecane alone. Cultures that were well-fed did not exhibit dispersant-induced inhibition of growth or n-hexadecane degradation. In addition, fluorescence microscopy revealed amorphous cell aggregate structures when the starved culture was exposed to dispersants, suggesting that Corexit affected the biofilm formation behavior of starved cells. Our findings indicate that (previous) substrate limitation, resembling oligotrophic open ocean conditions, can impact the response and hydrocarbon-degrading activities of oil-degrading organisms when exposed to Corexit, and highlight the need for further work to better understand the implications of environmental stressors on oil biodegradation and microbial community dynamics.

The eastern oyster Crassostrea virginica is an ecologically and economically important species that is vulnerable to oil pollution. We assessed sublethal effects of soluble fractions of crude oil alone (WAF) and crude oil in combination with Corexit 9500 dispersant (CEWAF) on oysters at three life history stages. Veliger swimming, pediveliger settlement, and adult clearance rates were quantified after 24 h exposures to the contaminants. Veliger swimming speeds were not significantly impacted by 24 h exposures to WAF or CEWAF. A larger proportion of veligers were inactive following WAF and CEWAF exposure as compared to the control, but the effect was greater for pediveligers, and pediveliger settlement in the highest concentration CEWAF treatment decreased by 50% compared to controls. Thus, pediveligers may be particularly vulnerable to oil exposure. In the adults, we found significant clearance rates reductions that persisted 33 days after acute exposure to CEWAF. Knowledge of sublethal effects of oil and dispersant at multiple life history stages aids understanding of how this important species will respond to an oil spill.

The need to understand the biodegradation of oil and chemical dispersants in Arctic marine environments is increasing alongside growth in oil exploration and transport in the region. We chemically quantified biodegradation and abiotic losses of crude oil and Corexit 9500, when present separately, in incubations of Arctic seawater and identified microorganisms potentially involved in biodegradation of these substrates based on shifts in bacterial community structure (16S rRNA genes) and abundance of biodegradation genes (GeoChip 5.0 microarray). Incubations were performed over 28-day time courses using surface seawater collected from near-shore and offshore locations in the Chukchi Sea. Within 28 days, the indigenous microbial community biodegraded 36% (k = 0.010 day-1) and 41% (k = 0.014 day-1) of oil and biodegraded 77% and 33% (k = 0.015 day-1) of the Corexit 9500 component dioctyl sodium sulfosuccinate (DOSS) in respective near-shore and offshore incubations. Non-ionic surfactants (Span 80, Tween 80, and Tween 85) present in Corexit 9500 were non-detectable by 28 days due to a combination of abiotic losses and biodegradation. Microorganisms utilized oil and Corexit 9500 as growth substrates during the incubation, with the Corexit 9500 stimulating more extensive growth than oil within 28 days. Taxa known to include oil-degrading bacteria (e.g., Oleispira, Polaribacter, and Colwellia) and some oil biodegradation genes (e.g., alkB, nagG, and pchCF) increased in relative abundance in response to both oil and Corexit 9500. These results increase our understanding of oil and dispersant biodegradation in the Arctic and suggest that some bacteria may be capable of biodegrading both oil and Corexit 9500.

Extracellular enzymes and extracellular polymeric substances (EPS) play a key role in overall microbial activity, growth and survival in the ocean. EPS, being amphiphilic in nature, can act as biological surfactant in an oil spill situation. Extracellular enzymes help microbes to digest and utilize fractions of organic matter, including EPS, which can stimulate growth and enhance microbial activity. These natural processes might have been altered during the 2010 Deepwater Horizon oil spill due to the presence of hydrocarbon and dispersant. This study aims to investigate the role of bacterial extracellular enzymes during exposure to hydrocarbons and dispersant. Mesocosm studies were conducted using a water accommodated fraction of oil mixed with the chemical dispersant, Corexit (CEWAF) in seawater collected from two different locations in the Gulf of Mexico and corresponding controls (no additions). Activities of five extracellular enzymes typically found in the EPS secreted by the microbial community – α- and β-glucosidase, lipase, alkaline phosphatase, leucine amino-peptidase – were measured using fluorogenic substrates in three different layers of the mesocosm tanks (surface, water column and bottom). Enhanced EPS production and extracellular enzyme activities were observed in the CEWAF treatment compared to the Control. Higher bacterial and micro-aggregate counts were also observed in the CEWAF treatment compared to Controls. Bacterial genera in the order Alteromonadaceae were the most abundant bacterial 16S rRNA amplicons recovered. Genomes of Alteromonadaceae commonly have alkaline phosphatase and leucine aminopeptidase, therefore they may contribute significantly to the measured enzyme activities. Only Alteromonadaceae and Pseudomonadaceae among bacteria detected here have higher percentage of genes for lipase. Piscirickettsiaceae was abundant; genomes from this order commonly have genes for leucine aminopeptidase. Overall, this study provides insights into the alteration to the microbial processes such as EPS and extracellular enzyme production, and to the microbial community, when exposed to the mixture of oil and dispersant.

Abstract Large-scale exopolymeric substances (EPS) formation was observed in contaminated surface waters of the Gulf of Mexico, after the Deepwater Horizon oil spill. The conditions under which EPS are produced can cause variations in their physico-chemical properties, affecting the fate of the oil through either emulsification or coagulation with particles, followed by aggregation and marine oil snow (MOS) sedimentation. Here, we report results from a four-day mesocosm experiment that examined EPS production, the change in the bulk chemical composition (mainly polysaccharides and proteins), as well as the partitioning into different size fractions (suspended particulate matter (SPM), colloidal fraction, and sinking MOS). The treatments included 1) natural coastal seawater (Control), 2) a water accommodated fraction of oil (WAF), 3) a chemically-enhanced WAF with addition of oil dispersant Corexit (CEWAF), and 4) a diluted CEWAF (DCEWAF). Generally, the presence of WAF stimulated more extracellular polysaccharide production, whereas the addition of Corexit promoted more protein production. Moreover, marine aggregates changed from a terrestrial signature (higher aromaticity, lower EPS content and more uniform monosaccharide distribution) in the early stages of the experiment, to a fresher autochthonous signature (less aromatic, higher EPS content and glucose-dominated monosaccharide distribution) in the later stage of the mesocosm experiment. Corexit promoted the association between oil and proteins, assisting to emulsify the oil in colloids and SPM and delay the settling of EPS and oil (MOS) for the duration of the mesocosm. Furthermore, when oil, especially Corexit-dispersed oil, was present, extracellular polysaccharides were preferentially incorporated into sinking MOS relative to proteins, as evidenced from a lower protein-C/carbohydrate-C ratio of the sinking MOS than those of SPM and colloidal fraction in WAF, CEWAF and DCEWAF, respectively. This is in contrast to a higher protein-C/carbohydrate-C ratio in the sinking marine snow than those of SPM and colloidal fraction in the control. Likely, microbially-mediated extracellular polysaccharides are the key component that anchors the mineral ballast until the aggregates become dense enough and overcome the buoyancy added to the aggregates as a result of their association with oil/Corexit. We conclude that interactions between Corexit and EPS components regulate petroleum hydrocarbon distribution between the water column and sinking MOS. Graphical abstract Unlabelled Image Highlights • WAF stimulated polysaccharide production over protein, while CEWAF did the opposite • MOS from a more degraded terrestrial signature to a fresher autochthonous signature • Corexit promoted the interactions between oil and EPS via interaction with protein • When oil present, MOS selectively incorporate exopolysaccharides over protein • Extracellular polysaccharide as the key component in anchoring mineral ballast [ABSTRACT FROM AUTHOR]

Abstract Amphiphilic substances can interact with oil in the water to form emulsions and aggregates; dispersants are designed to form emulsions to prevent oil droplets from coalescing and stabilize them in a suspension. Amphiphilic extracellular polymeric substances (EPS) concentrated at the air-water interface where surface tension was measured to determine their propensity for formation of emulsions and/or aggregates. Here we investigated mechanisms governing the self-assembly and phase separation for protein-polysaccharide-oil-dispersant interactions through measurements of surface tension, chemical composition, and confocal microscopy. EPS colloid fractions from treatments of WAF (water accommodated fraction of oil), CEWAF (chemically enhanced WAF using the dispersant Corexit), and a control mesocosm were examined. In analyzing the size fractions of water column samples, it was found that treatments with oil and/or Corexit showed EPS with enhanced protein:polysaccharide carbon-based ratios and lower surface tension (SFT), suggesting the effective bioemulsifying effects of proteins. In addition, EPS model constituents of protein slightly increased SFT at low concentrations of less than a few mg/L, but decreased it at higher concentrations of 8 mg/L or more. These model molecules appear to be more efficient than Corexit in inducing the self-assembly of micelles in the seawater even when only very low concentrations of these constituents are present. Our results suggest that EPS are more efficient than Corexit at forming micelles. Results from this study provides mechanistic insights into the fate and distribution of oil in the surface ocean. Highlights • The presence of oil and/or Corexit can lead to higher protein:polysaccharide ratios of EPS • Higher protein:polysaccharide ratios of EPS correlate to lower surface tension (SFT) in the EPS colloidal fraction • Microscopy techniques (i.e., CLSM and SEM) revealed different aggregate sizes and their dispersion • CLSM and SEM showed the importance of aggregate formation through Ca2+ "bridging" between anionic EPS component moieties • Small changes in SFT with increasing protein that coincide with changes in pH (tenths of a unit) can lead to self-assembly • Protein slightly increased SFT at low concentrations, but decreased SFT at concentrations of 8 mg/L or greater [ABSTRACT FROM AUTHOR]

The need to understand the biodegradation of oil and chemical dispersants in Arctic marine environments is increasing alongside growth in oil exploration and transport in the region. We chemically quantified biodegradation and abiotic losses of crude oil and Corexit 9500, when present separately, in incubations of Arctic seawater and identified microorganisms potentially involved in biodegradation of these substrates based on shifts in bacterial community structure (16S rRNA genes) and abundance of biodegradation genes (GeoChip 5.0 microarray). Incubations were performed over 28-day time courses using surface seawater collected from near-shore and offshore locations in the Chukchi Sea. Within 28 days, the indigenous microbial community biodegraded 36% (k = 0.010 day-1) and 41% (k = 0.014 day-1) of oil and biodegraded 77% and 33% (k = 0.015 day-1) of the Corexit 9500 component dioctyl sodium sulfosuccinate (DOSS) in respective near-shore and offshore incubations. Non-ionic surfactants (Span 80, Tween 80, and Tween 85) present in Corexit 9500 were non-detectable by 28 days due to a combination of abiotic losses and biodegradation. Microorganisms utilized oil and Corexit 9500 as growth substrates during the incubation, with the Corexit 9500 stimulating more extensive growth than oil within 28 days. Taxa known to include oil-degrading bacteria (e.g., Oleispira , Polaribacter , and Colwellia) and some oil biodegradation genes (e.g., alkB , nagG , and pchCF) increased in relative abundance in response to both oil and Corexit 9500. These results increase our understanding of oil and dispersant biodegradation in the Arctic and suggest that some bacteria may be capable of biodegrading both oil and Corexit 9500. [ABSTRACT FROM AUTHOR]

Two major oil crises in United States history, the 1989 Exxon-Valdez oil spill in Alaska and the 2010 Deepwater Horizon Oil Rig explosion in the Gulf of Mexico, drew attention to the need for toxicological experiments on oil and chemically dispersed oil. We are still learning the effects these spills had on wildlife. However, little data is known about the toxicity of these substances in marine mammals. The objective of this study is to determine the toxicity of Alaskan oil, as well as chemically dispersed oil. Oil experiments were performed using the water accommodated fraction of Alaskan oil (WAF) and the chemically enhanced water accommodated fraction of Alaskan oil (CEWAF). The Alaskan WAF is not cytotoxic to sperm whale skin cells though it did induce chromosome damage; S9-mediated metabolism did not affect the cytotoxicity of WAF but did increase the levels of chromosome damage. Alaskan CEWAF is more cytotoxic and genotoxic than the WAF; S9 mediated metabolism increased both cytotoxicity and genotoxicity of CEWAF. Analysis of the PAH content of Alaskan WAF and CEWAF revealed a forty-fold increase in the total levels of PAHs in CEWAF compared to WAF. These findings show that chemically dispersed oil leads to higher levels of PAH exposure which are more toxic and likely to lead to longer and more persistent health effects. [ABSTRACT FROM AUTHOR]

Extracellular enzymes and extracellular polymeric substances (EPS) play a key role in overall microbial activity, growth and survival in the ocean. EPS, being amphiphilic in nature, can act as biological surfactant in an oil spill situation. Extracellular enzymes help microbes to digest and utilize fractions of organic matter, including EPS, which can stimulate growth and enhance microbial activity. These natural processes might have been altered during the 2010 Deepwater Horizon oil spill due to the presence of hydrocarbon and dispersant. This study aims to investigate the role of bacterial extracellular enzymes during exposure to hydrocarbons and dispersant. Mesocosm studies were conducted using a water accommodated fraction of oil mixed with the chemical dispersant, Corexit (CEWAF) in seawater collected from two different locations in the Gulf of Mexico and corresponding controls (no additions). Activities of five extracellular enzymes typically found in the EPS secreted by the microbial community - a- and b-glucosidase, lipase, alkaline phosphatase, leucine amino-peptidase - were measured using fluorogenic substrates in three different layers of the mesocosm tanks (surface, water column and bottom). Enhanced EPS production and extracellular enzyme activities were observed in the CEWAF treatment compared to the Control. Higher bacterial and micro-aggregate counts were also observed in the CEWAF treatment compared to Controls. Bacterial genera in the order Alteromonadaceae were the most abundant bacterial 16S rRNA amplicons recovered. Genomes of Alteromonadaceae commonly have alkaline phosphatase and leucine aminopeptidase, therefore they may contribute significantly to the measured enzyme activities. Only Alteromonadaceae and Pseudomonadaceae among bacteria detected here have higher percentage of genes for lipase. Piscirickettsiaceae was abundant; genomes from this order commonly have genes for leucine aminopeptidase. Overall, this study provides insights into the alteration to the microbial processes such as EPS and extracellular enzyme production, and to the microbial community, when exposed to the mixture of oil and dispersant. [ABSTRACT FROM AUTHOR]

The 2010 Deepwater Horizon (DWH) oil spill is the largest marine oil spill in US history. In the aftermath of the spill, the response efforts used a chemical dispersant, Corexit, to disperse the oil spill. The health impacts of crude oil and Corexit mixture to humans, mammals, fishes, and birds are mostly unknown. The purpose of this study is to investigate the in vivo effects of DWH oil, Corexit, and oil-Corexit mixture on the general behavior, hematological markers, and liver and kidney functions of rodents. C57 Bl6 mice were treated with DWH oil (80 mg/kg) and/or Corexit (95 mg/kg), and several hematological markers, lipid profile, liver and kidney functions were monitored. The results show that both DWH oil and Corexit altered the white blood cells and platelet counts. Moreover, they also impacted the lipid profile and induced toxic effects on the liver and kidney functions. The impacts were more pronounced when the mice were treated with a mixture of DWH-oil and Corexit. This study provides preliminary data to elucidate the potential toxicological effects of DWH oil, Corexit, and their mixtures on mammalian health. Residues from the DWH spill continue to remain trapped along various Gulf Coast beaches and therefore further studies are needed to fully understand their long-term impacts on coastal ecosystems. [ABSTRACT FROM AUTHOR]

During the Deepwater Horizon (DwH) oil spill, interactions between oil, clay particles and marine snow lead to the formation of aggregates. Interactions between these components play an important, but yet not well understood, role in biodegradation of oil in the ocean water. The aim of this study is to explore the effect of these interactions on biodegradation of oil in the water. Laboratory experiments were performed, analyzing respiration and n- alkane and BTEX biodegradation in multiple conditions containing Corexit, alginate particles as marine snow, and kaolin clay. Two oil degrading bacterial pure cultures were added, Pseudomonas putida F1 and Rhodococcus qingshengii TUHH-12. Results show that the presence of alginate particles enhances oil biodegradation. The presence of Corexit alone or in combination with alginate particles and/or kaolin clay, hampers oil biodegradation. Kaolin clay and Corexit have a synergistic effect in increasing BTEX concentrations in the water and cause delay in oil biodegradation. [ABSTRACT FROM AUTHOR]

Benthic surveys of mesophotic reefs in the Gulf of Mexico post Deepwater Horizon (DWH) showed that Swiftia exserta octocorals exhibited significantly more injury than in years before the spill. To determine the vulnerability of S. exserta to oil and dispersants, 96 h toxicity assays of surrogate DWH oil water-accommodated fractions (WAF), Corexit® 9500 dispersant, and the combination of both (CEWAF) were conducted in the laboratory. Fragment mortality occurred within 48 h for some fragments in the dispersant-alone and oil-dispersant treatments, while the WAF group remained relatively unaffected. The 96 h LC 50 values were 70.27 mg/L for Corexit-alone and 41.04 mg/L for Corexit in CEWAF. This study provides new information on octocoral sensitivity to toxins, and indicates that combinations of oil and dispersants are more toxic to octocorals than exposure to oil alone. These results have important implications for the assessment of effects of the DWH spill on deep-water organisms. [ABSTRACT FROM AUTHOR]

The Deepwater Horizon oil spill was one of the worst environmental disasters on record in the United States. Response efforts to reduce the magnitude of the oil slick included the use of thousands of gallons of the chemical dispersant Corexit™ in surface and deep-water environments. The immunotoxicity of Louisiana sweet crude oil and the chemical dispersant Corexit was examined using lymphocyte proliferation (LP) and natural killer cell (NK) assays as measures of impact on the adaptive (LP) and innate (NK) immune response in bottlenose dolphins. Study results show that both high-energy media-accommodated fractions (MAF) and chemically enhanced MAF (CEMAF) mixtures modulate immune function. Following exposure to Louisiana sweet crude, both B- and T-cell proliferation of white blood cells was increased for all exposure concentrations, compared to control; however, this increase was only significant for the 50% and 100% treatments. In contrast, exposure of white blood cells to the CEMAF mixture significantly decreased both T- and B-cell proliferation in the 25%, 50% and 100% treatments. NK cell activity was enhanced significantly by CEMAF mixtures for the 50% and 100% treatments. The immunosuppression of LP at environmentally relevant concentrations of oil and dispersant suggests that marine mammals may be unable to mount an adequate defense against xenobiotic threats following exposure to oil and dispersant, leaving them more susceptible to disease. In contrast, NK cell activity was significantly enhanced, which may increase an organism's tumor or viral surveillance ability by mounting an enhanced immune response. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

At the onset of the 2010 Gulf oil spill, analytical methods for the quantification of the surfactants in Corexit did not exist in the peer-reviewed literature. To date, only a single study reports the presence of bis-(2-ethylhexyl) sodium sulfosuccinate (DOSS) in deep-sea Gulf sediment collected in 2010 from a single location. There are no data on the occurrence of DOSS in association with settling solids (i.e., sediment-trap solids). To address this data gap, DOSS was initially quantified by liquid chromatography tandem quadrupole mass spectrometry (LC-MS/MS) in sediment and sediment-trap solids collected from multiple sites in the Gulf between 2010 and 2013. However, interferences confounded analyses using only a quadrupole (MS/MS) system; therefore, a LC-high mass accuracy quadruple time of flight mass spectrometry (LC-QTOF-MS) method was developed. The LC-QTOF method was validated and applied to eight representative samples of sediment and of sediment-trap solids. The presented method quantifies DOSS in solids of marine origin at concentrations above the limit of quantification of 0.23 μg kg with recoveries of 97 ± 20 % (mean ± 95 CI). Gulf sediment and sediment-trap solids gave DOSS concentrations of

Massive oil spills leading to 'Black Tides' have been sad features of the last half century, although fortunately of generally decreasing frequency. Such spills often led to massive bird mortality and enormous public pressure for mitigation. One unfortunately misunderstood response has been the development of chemical dispersants designed to move floating slicks into the water column as tiny droplets. These droplets become entrained in the water and dilute to levels below those of acute toxic concern within hours; equally importantly, they naturally biodegrade within weeks, and do not impact shorelines. Initial dispersants were not especially effective, but a deeper understanding of what controls the lowering of interfacial tension between oil and water has led to very effective modern products, exemplified by Corexit 9500 used in the Deepwater Horizon response. By getting oil off the sea surface, dispersants protect birds and animals from potentially lethal oiling and the likely fouling of shorelines with its attendant problems of human exposure to oil residues as shorelines are physically cleaned. And by increasing the surface area of the spilled oil they promote indigenous microbial biodegradation, which can consume oil droplets with a half-life of 1–3 weeks without the need for any additional intervention. Dispersants thus provide the most environmentally-beneficial bioremediation option for ameliorating potentially environmentally devastating oil spills (when they work), and it is disappointing that they are not always tried on a significant (not test) scale. • Dispersants offer the ultimate bioremediation option for large marine oil spills. • Birds and animals are protected by getting oil off the water surface. • Dispersed oil does not stick on shorelines. • Effectively dispersed oil dilutes below levels of acute toxic concern in hours. • Effectively dispersed oil becomes so dilute that biodegradation is not usually nutrient limited. [ABSTRACT FROM AUTHOR]

Following the Deepwater Horizon (DWH) spill in 2010, an enormous amount of oil was observed in the deep and surface waters of the northern Gulf of Mexico. Surface waters are characterized by intense sunlight and high temperature during summer. While the oil-degrading bacterial communities in the deep-sea plume have been widely investigated, the effect of natural sunlight on those in oil polluted surface waters remains unexplored to date. In this study, we incubated surface water from the DWH site with amendments of crude oil, Corexit dispersant, or both for 36 d under natural sunlight in the northern Gulf of Mexico. The bacterial community was analyzed over time for total abundance, density of alkane and polycyclic aromatic hydrocarbon degraders, and community composition via pyrosequencing. Our results showed that, for treatments with oil and/or Corexit, sunlight significantly reduced bacterial diversity and evenness and was a key driver of shifts in bacterial community structure. In samples containing oil or dispersant, sunlight greatly reduced abundance of the Cyanobacterium Synechococcus but increased the relative abundances of Alteromonas, Marinobacter, Labrenzia, Sandarakinotalea, Bartonella, and Halomonas. Dark samples with oil were represented by members of Thalassobius, Winogradskyella, Alcanivorax, Formosa, Pseudomonas, Eubacterium, Erythrobacter, Natronocella, and Coxiella. Both oil and Corexit inhibited the Candidatus Pelagibacter with or without sunlight exposure. For the first time, we demonstrated the effects of light in structuring microbial communities in water with oil and/or Corexit. Overall, our findings improve understanding of oil pollution in surface water, and provide unequivocal evidence that sunlight is a key factor in determining bacterial community composition and dynamics in oil polluted marine waters.

We examined lethality and behavioral effects of Corexit EC 9500A (C-9500A) exposure on the model marine zooplankton Brachionus plicatilis singularly and in combination with abiotic and biotic factors. C-9500A exposure at standard husbandry conditions (17.5 ppt, 24 °C, 200 rotifer*mL − 1 density) identified the 24 h median lethal concentration, by Probit analysis, to be 107 ppm for cultured B . plicatilis . Rotifers surviving exposure to higher concentrations (100 and 150 ppm) exhibited a decreased swimming velocity and a reduced net to gross movement ratio. Significant interaction between C-9500A exposure and temperature or salinity was observed. Upper thermal range was reduced and maximal salinity stress was seen as ca. 25 ppt. Increased or decreased nutritional availability over the exposure period did not significantly alter mortality of B . plicatilis populations at the concentrations tested. Results from this study may be useful for predicting possible outcomes on marine zooplankton following dispersant application under diverse natural conditions. [ABSTRACT FROM AUTHOR]

Significant amounts of oil accumulated at the sea surface and in a subsurface plume during the Deepwater Horizon (DwH) spill in the Gulf of Mexico (GoM) in 2010. A substantial fraction of this oil was removed from the marine environment by mechanical recovery or burning, or it reached shorelines, whereas another fraction remained within the marine environment, where it dispersed (chemically or naturally), emulsified or sedimented. After the DwH accident the sedimentation of hydrocarbons to the seafloor via rapidly sinking, oil-associated marine snow has become a focus of attention, and it has been hypothesized that marine snow formation significantly impacted the distribution of the oil from the DwH spill. Here, roller table experiments are presented that investigated the conditions inducing the formation of oil-associated marine snow, focusing especially on the effects of oil type, photochemical aging of oil, and the presence of phytoplankton or dispersant. Large, mucus-rich marine snow, termed microbial marine snow, formed in treatments incubated with the oil that had accumulated at the sea surface. This bacteria-mediated formation of up to cm-sized marine snow in the absence of particles >1 µm, represents a unique formation pathway different from that of the physical coagulation of particles. Microbial marine snow, albeit smaller, also formed in the presence of crude oil that had been aged for ≥3 weeks in sunlight, but no particles formed in the presence of unaltered crude. The dispersant Corexit 9500A (Corexit:oil ratio=1:100) impeded the formation of microbial marine snow, requiring a re-evaluation of the benefits and detriments of Corexit 9500A as a mediating measure. Phytoplankton aggregates also incorporated fossil carbon, providing an alternate pathway for the formation of oil-associated marine snow. The ubiquitous formation and rapid sedimentation of oil-rich marine snow can explain the high accumulation rate of flocculent material at the seafloor and on corals observed after the DwH spill. These results may raise awareness that oil spill response and assessment need to include sedimentation of hydrocarbons via marine snow as a significant distribution mechanism and may guide future modeling efforts and budget calculations. [ABSTRACT FROM AUTHOR]

After the April 2010 explosion on the Deepwater Horizon oil rig, and subsequent release of millions of barrels of oil, two Corexit oil dispersant formulations were used in unprecedented quantities both on the surface and sub-surface of the Gulf of Mexico. Although the dispersant formulations contain four classes of surfactants, current studies to date focus on the anionic surfactant, bis-(2-ethylhexyl) sulfosuccinate (DOSS). Factors affecting the integrity of environmental and laboratory samples for Corexit analysis have not been systematically investigated. For this reason, a quantitative analytical method was developed for the detection of all four classes of surfactants, as well as the hydrolysis products of DOSS, the enantiomeric mixture of α- and β-ethylhexyl sulfosuccinate (α-/β-EHSS). The analytical method was then used to evaluate which practices for sample collection, storage, and analysis resulted in high quality data. Large volume, direct injection of seawater followed by liquid chromatography tandem mass spectrometry (LC–MS/MS) minimized analytical artifacts, analysis time, and both chemical and solid waste. Concentrations of DOSS in the seawater samples ranged from 71 to 13,000 ng/L, while the nonionic surfactants including Span 80, Tween 80, Tween 85 were detected infrequently (26% of samples) at concentrations from 840 to 9100 ng/L. The enantiomers α-/β-EHSS were detected in seawater, at concentrations from 200 to 1900 ng/L, and in both Corexit dispersant formulations, indicating α-/β-EHSS were applied to the oil spill and may be not unambiguous indicator of DOSS degradation. Best practices are provided to ensure sample integrity and data quality for environmental monitoring studies and laboratory that require the detection and quantification of Corexit-based surfactants in seawater. [ABSTRACT FROM AUTHOR]

During the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, three million liters of chemical dispersants (Corexit 9500 and 9527) were directly applied at the discharging wellhead at 1500 m water depth. Such a deep-water large-scale application was unprecedented and the effect of dispersants on oil biodegradation is not yet completely understood. The present study explores the biodegradation of oil, dispersant, dispersed oil or dispersed oil and nutrients at the molecular level using ultra-high resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR–MS) following a laboratory experiment with Gulf deep water. Oil-derived molecular formulae exhibited a specific molecular fingerprint and were mainly observed in the mass range <300 Da. The relative abundance of heteroatom-containing (N, S, and P) compounds decreased over time in the oil-only treatments, indicating that they may have served as nutrients when oil-derived hydrocarbons were metabolized. Relative changes over time in the molecular composition were less pronounced in the dispersed oil treatments compared to the oil-only treatments, suggesting that dispersants affected the metabolic pathways of organic matter biodegradation. In particular, dispersant addition led to an increase of S-containing organic molecular formulae, likely derived from the surfactant di-octyl sulfosuccinate (DOSS). DOSS and several dispersant-derived metabolites (with and without S) were still detectable after six weeks of incubation, underscoring that they were not rapidly biodegraded under the experimental conditions. FT-ICR–MS fragmentation studies allowed tentatively assigning structures to several of these molecules, and we propose that they are degradation products of DOSS and other dispersant components. The present study suggests preferential degradation, transformation and enrichment of distinct dispersant molecules, highlighting the need to include these compounds when tracking Corexit-derived compounds in the environment. [ABSTRACT FROM AUTHOR]

Cold-water corals serve as important foundation species by building complex habitat within deep-sea benthic communities. Little is known about the stress response of these foundation species yet they are increasingly exposed to anthropogenic disturbance as human industrial presence expands further into the deep sea. A recent prominent example is the Deepwater Horizon oil-spill disaster and ensuing clean-up efforts that employed chemical dispersants. This study examined the effects of bulk oil–water mixtures, water-accommodated oil fractions, the dispersant Corexit 9500A ® , and the combination of hydrocarbons and dispersants on three species of corals living near the spill site in the Gulf of Mexico between 500 and 1100 m depths: Paramuricea type B3, Callogorgia delta and Leiopathes glaberrima . Following short-term toxicological assays (0–96 h), all three coral species examined showed more severe health declines in response to dispersant alone (2.3–3.4 fold) and the oil–dispersant mixtures (1.1–4.4 fold) than in the oil-only treatments. Higher concentrations of dispersant alone and the oil–dispersant mixtures resulted in more severe health declines. C. delta exhibited somewhat less severe health declines than the other two species in response to oil and oil/dispersant mixture treatments, likely related to its increased abundance near natural hydrocarbon seeps. These experiments provide direct evidence for the toxicity of both oil and dispersant on deep-water corals, which should be taken into consideration in the development of strategies for intervention in future oil spills. [ABSTRACT FROM AUTHOR]

The grounding of the MVRenahas highlighted the lack of information concerning the effects of oil-related compounds on New Zealand marine life. Yellowtail kingfish (YTK),Seriola lalandi, embryos were exposed in static incubations to the water-accommodated fraction (WAF) ofRenaheavy fuel oil as well as a similar preparation treated with the commercial dispersant Corexit 9500. Mortality in WAF treatments generally increased in association with total polycyclic aromatic hydrocarbon (tPAH) concentration over a 24-h period. Physical abnormalities were observed in some of the larvae exposed to WAF for 48 h. There was no survival in dispersed oil treatments after 24 h of exposure. These treatments had greater tPAH concentrations (2–53 µgL−1) than equivalent WAF dilutions (0.2–1.5 µgL−1 tPAH). Indications are that significant morbidity is induced in YTK at ecologically relevant tPAH concentrations. This highlights the need for further research into oil and dispersant toxicity in New Zealand marine species. [ABSTRACT FROM AUTHOR]