Metatranscriptomic response of deep ocean microbial populations to infusions of oil and/or synthetic chemical dispersant.

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.

Dispersant addition, but not nutrients, stimulated blooms of multiple hydrocarbonoclastic genera in nutrient-replete coastal marine surface waters.

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.

The dispersant Corexit 9500 and (dispersed) oil are lethal to coral endosymbionts.

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.

Intraspecific Variation in the Sublethal Effects of Physically and Chemically Dispersed Crude Oil on Early Life Stages of Atlantic Cod (Gadus morhua).

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.

Metagenomic and Metatranscriptomic Responses of Chemical Dispersant Application during a Marine Dilbit Spill.

The global increase in marine transportation of dilbit (diluted bitumen) can increase the risk of spills, and the application of chemical dispersants remains a common response practice in spill events. To reliably evaluate dispersant effects on dilbit biodegradation over time, we set large-scale (1,500 mL) microcosms without nutrient addition using a low dilbit concentration (30 ppm). Shotgun metagenomics and metatranscriptomics were deployed to investigate microbial community responses to naturally and chemically dispersed dilbit. We found that the large-scale microcosms could produce more reproducible community trajectories than small-scale (250 mL) ones based on the 16S rRNA gene amplicon sequencing. In the early-stage large-scale microcosms, multiple genera were involved in the biodegradation of dilbit, while dispersant addition enriched primarily Alteromonas and competed for the utilization of dilbit, causing depressed degradation of aromatics. The metatranscriptomic-based metagenome-assembled genomes (MAG) further elucidated early-stage microbial antioxidation mechanism, which showed that dispersant addition triggered the increased expression of the antioxidation process genes of Alteromonas species. Differently, in the late stage, the microbial communities showed high diversity and richness and similar compositions and metabolic functions regardless of dispersant addition, indicating that the biotransformation of remaining compounds can occur within the post-oil communities. These findings can guide future microcosm studies and the application of chemical dispersants for responding to a marine dilbit spill. IMPORTANCE In this study, we employed microcosms to study the effects of marine dilbit spill and dispersant application on microbial community dynamics over time. We evaluated the impacts of microcosm scale and found that increasing the scale is beneficial for reducing community stochasticity, especially in the late stage of biodegradation. We observed that dispersant application suppressed aromatics biodegradation in the early stage (6 days), whereas exerting insignificant effects in the late stage (50 days), from both substance removal and metagenomic/metatranscriptomic perspectives. We further found that Alteromonas species are vital for the early-stage chemically dispersed oil biodegradation and clarified their degradation and antioxidation mechanisms. These findings help us to better understand microcosm studies and microbial roles for biodegrading dilbit and chemically dispersed dilbit and suggest that dispersant evaluation in large-scale systems and even through field trails would be more realistic after marine oil spill response.

Machine learning-aided causal inference for unraveling chemical dispersant and salinity effects on crude oil biodegradation.

Chemical dispersants have been widely applied to tackle oil spills, but their effects on oil biodegradation in global aquatic systems with different salinities are not well understood. Here, both experiments and advanced machine learning-aided causal inference analysis were applied to evaluate related processes. A halotolerant oil-degrading and biosurfactant-producing species was selected and characterized within the salinity of 0-70 g/L NaCl. Notably, dispersant addition can relieve the biodegradation barriers caused by high salinities. To navigate the causal relationships behind the experimental data, a structural causal model to quantitatively estimate the strength of causal links among salinity, dispersant addition, cell abundance, biosurfactant productivity and oil biodegradation was built. The estimated causal effects were integrated into a weighted directed acyclic graph, which showed that overall positive effects of dispersant addition on oil biodegradation was mainly through the enrichment of cell abundance. These findings can benefit decision-making prior dispersant application under different saline environments.

Multi-domain probiotic consortium as an alternative to chemical remediation of oil spills at coral reefs and adjacent sites.

BACKGROUND: Beginning in the last century, coral reefs have suffered the consequences of anthropogenic activities, including oil contamination. Chemical remediation methods, such as dispersants, can cause substantial harm to corals and reduce their resilience to stressors. To evaluate the impacts of oil contamination and find potential alternative solutions to chemical dispersants, we conducted a mesocosm experiment with the fire coral Millepora alcicornis, which is sensitive to environmental changes. We exposed M. alcicornis to a realistic oil-spill scenario in which we applied an innovative multi-domain bioremediator consortium (bacteria, filamentous fungi, and yeast) and a chemical dispersant (Corexit® 9500, one of the most widely used dispersants), to assess the effects on host health and host-associated microbial communities. RESULTS: The selected multi-domain microbial consortium helped to mitigate the impacts of the oil, substantially degrading the polycyclic aromatic and n-alkane fractions and maintaining the physiological integrity of the corals. Exposure to Corexit 9500 negatively impacted the host physiology and altered the coral-associated microbial community. After exposure, the abundances of certain bacterial genera such as Rugeria and Roseovarius increased, as previously reported in stressed or diseased corals. We also identified several bioindicators of Corexit 9500 in the microbiome. The impact of Corexit 9500 on the coral health and microbial community was far greater than oil alone, killing corals after only 4 days of exposure in the flow-through system. In the treatments with Corexit 9500, the action of the bioremediator consortium could not be observed directly because of the extreme toxicity of the dispersant to M. alcicornis and its associated microbiome. CONCLUSIONS: Our results emphasize the importance of investigating the host-associated microbiome in order to detect and mitigate the effects of oil contamination on corals and the potential role of microbial mitigation and bioindicators as conservation tools. Chemical dispersants were far more damaging to corals and their associated microbiome than oil, and should not be used close to coral reefs. This study can aid in decision-making to minimize the negative effects of oil and dispersants on coral reefs. Video abstract.

Microfiltration of saline crude oil emulsions: Effects of dispersant and salinity.

Dispersants reduce oil-water interfacial tension making the separation of oil-water emulsions challenging. In this study, crude oil stabilized by the dispersant, Corexit EC9500A, was emulsified in synthetic sea water using a range of Corexit/crude oil concentration ratios (up to 10% by volume). With an interfacial tension of only 8.0 mJ/m2 at 0.5 mL(Corexit)/L, approximately 50% of the crude was dispersed into droplets <10 µm. Near complete rejection of oil in crossflow separation tests was accompanied by a precipitous flux decline attributable in part to dispersant- and salinity-induced decrease in membrane's oleophobicity (4.2 mJ/m2 decrease in surface energy). Screening of electrostatic interactions prompted oil coalescence that occurred at the membrane surface but not in the bulk of the emulsion. Real-time in situ visualization by Direct Observation Through Membrane gave direct evidence of surface coalescence pointing to both its detrimental effects (spread of contiguous films) and possible advantages (removal of large droplets by crossflow shear).

Effect of a chemical dispersant (Corexit 9500A) on the structure and ion transport function of blue crab (Callinectes sapidus) gills.

Chemical dispersants are commercially available mixtures of surfactants and solvents that have become important tools in the remediation of spilled oil. Given the importance of oil to the world economy, the recurring nature of spills, and the prevalence of dispersant use in remediation, there is a critical need to understand potential toxic impacts of dispersants on invertebrate and vertebrate animals. Blue crabs (Callinectes sapidus) play ecologically important roles in the environments they inhabit and support economically important fisheries along the Atlantic Coast and in the Gulf of Mexico. In studies reported here, we assessed the impact of a chemical dispersant, Corexit 9500A, on the structure and ion transport function of blue crab gills. Exposure of blue crabs to Corexit 9500A for 24 h (0-300 ppm in artificial seawater under static conditions) revealed a 24-h lethal concentration 50 (LC50) estimate of 210 ppm. A histological analysis of gills from crabs exposed for 24 h to a sub-lethal concentration of Corexit 9500A (125 ppm) revealed evidence of loss or disruption of cuticle, and an increase in stained amorphous material in the hemolymph spaces of gill lamellae. Quantitative image analysis of stained gill sections revealed the area/length ratio of gill lamellae in crabs exposed to Corexit 9500A (24 h, 125 ppm), was greater than that in gill lamellae from control crabs; the results are consistent with the presence of edematous swelling in gill lamellae from dispersant-exposed crabs. Quantitative PCR was used to measure the relative abundance of transcripts encoding three ion transport proteins (Na+/K+ ATPase, plasma membrane Ca2+ ATPase (PMCA), and sarcoplasmic reticulum/endoplasmic reticulum Ca2+ ATPase (SERCA)) in gills from Corexit-exposed and control crabs. In general, the abundance of transcripts encoding each ion transport protein was lower in gills from dispersant-exposed crabs than in gills from control crabs. The combined results are consistent with the hypothesis that 24-h exposure of blue crabs to a sublethal concentration of Corexit 9500A impacts both the structure and ion transport function of gills.

Sensitivity to oil dispersants: Effects on the valve movements of the blue mussel Mytilus edulis and the giant scallop Placopecten magellanicus, in sub-arctic conditions.

In response to accidental oil spills at sea, chemical oil dispersants are utilized to limit negative impacts on nearby littoral zones. However, current evidence suggests that such dispersants may be toxic to aquatic organisms. Blue mussels (Mytilus edulis) and giant scallops (Placopecten magellanicus) were exposed to different environmentally relevant concentrations of oil dispersant and their behavioural responses were closely monitored using high frequency (10Hz) valvometry. Behavioural valve responses included rapid closures when oil dispersant was added to the experimental tanks. At higher concentrations, the mussels remained closed throughout the exposure period. The giant scallop displayed escape behaviours (clapping) prior to mortality, suggesting toxicity of the oil dispersant. Relationships between different behavioural indicators and oil dispersant concentrations were observed for both species, but with different trends. While scallops demonstrated positive correlations between gaping behaviours and dispersant concentration, mussels exhibited a concentration threshold beyond which the gaping behaviour was characteristic of longer closure periods. This study highlights behavioural response differences consistent with bivalve-specific biological traits: the continuous valve closure of an intertidal species, M. edulis, firmly attached to the substrate, and the escapement behaviours of a semi-mobile subtidal species, P. magellanicus. From these observations, it appears that valvometry could be used as a tool for environmental assessments.

The Complexity of Spills: The Fate of the Deepwater Horizon Oil.

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.

Comparative Proteomics of Marinobacter sp. TT1 Reveals Corexit Impacts on Hydrocarbon Metabolism, Chemotactic Motility, and Biofilm Formation.

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.

The Interactive Effects of Crude Oil and Corexit 9500 on Their Biodegradation in Arctic Seawater.

The risk of petroleum spills coupled with the potential application of chemical dispersants as a spill response strategy necessitates further understanding of the fate of oil and dispersants and their interactive effects during biodegradation. Using Arctic seawater mesocosms amended with either crude oil, Corexit 9500, or both together, we quantified the chemical losses of crude oil and Corexit 9500 and identified microbial taxa implicated in their biodegradation based on shifts in the microbial community structure over a 30-day time course. Chemical analyses included total petroleum hydrocarbons (TPH), n-alkanes, branched alkanes, and polycyclic aromatic hydrocarbons (PAHs) for oil loss and the surfactant components dioctyl sodium sulfosuccinate (DOSS), Span 80, Tween 80, Tween 85, and the DOSS metabolite ethylhexyl sulfosuccinate (EHSS) for Corexit loss. Changes to the microbial communities and identification of key taxa were determined by 16S rRNA gene amplicon sequencing. The nonionic surfactants of Corexit 9500 (Span 80 and Tweens 80 and 85) biodegraded rapidly, dropping to below the limits of detection within 5 days and prior to any detectable initiation of oil biodegradation. This resulted in no observable suppression of petroleum biodegradation in the presence of Corexit compared to that of oil alone. In contrast, biodegradation of DOSS was delayed in the presence of oil, based on the prolonged presence of DOSS and accumulation of the degradation intermediate EHSS that did not occur in the absence of oil. Microbial analyses revealed that oil and Corexit enriched different overall microbial communities, with the presence of both resulting in a community composition that shifted from one more similar to that of Corexit only to one reflecting the oil-only community over time, in parallel with the degradation of predominantly Corexit and then oil components. Some microbial taxa (Oleispira, Pseudofulvibacter, and Roseobacter) responded to either oil or Corexit, suggesting that some organisms may be capable of utilizing both substrates. Together, these findings reveal interactive effects of crude oil and Corexit 9500 on chemical losses and microbial communities as they biodegrade, providing further insight into their fate when copresent in the environment.IMPORTANCE Chemical dispersants such as Corexit 9500 are commonly used in oil spill response and are currently under consideration for use in the Arctic, where their fate and effects have not been well studied. This research was performed to determine the interactive effects of the copresence of crude oil and Corexit 9500 on the degradation of components from each mixture and the associated microbial community structure over time in Arctic seawater. These findings will help yield a better understanding of the biodegradability of dispersant components applied to an oil spill, the temporal microbial community response to dispersed oil, and the fundamental microbial ecology of organic contaminant biodegradation processes in the Arctic marine environment.

The Impact of the Deepwater Horizon Oil Spill upon Lung Health-Mouse Model-Based RNA-Seq Analyses.

We used a transcriptomic approach to interrogate the effects of a saline-accommodated fraction from the Macondo 252 well (MC252) oil and Corexit dispersants on lung tissue. Wild-type C57BL/6 male and female mice were exposed on days 0, 7 and 13 by oropharyngeal aspiration to saline accommodated fractions (SAF) of crude oil from the Macondo (MC252) well, Corexit 9500, Corexit 9527, 9500+oil and 9527+oil or a saline solution as the vehicle control. These treatments did not cause overt toxicity, with the exception of the Corexit exposures which caused brief weight loss after the first exposure. On day 14, total RNA was isolated from the left lung for RNA-seq analyses. KEGG-pathway-based differential expression revealed that Corexit 9527 elicited the strongest changes involving the upregulation of 19 KEGG pathways (FDR < 0.10), followed by Corexit 9500 with the upregulation of seven pathways (FDR < 0.10). As an important signature, pathways related to a response to DNA damage (e.g., p53 signaling and mismatch repair) dominate those upregulated by Corexit 9527 and Corexit 9500. In addition, pro-inflammatory pathways (e.g., cytokine-cytokine receptor interaction, IL-17 signaling pathway and TNF signaling pathways) were upregulated selectively in oil-treated male mice. Surprisingly, oil + dispersant combinations caused lesser effects than the individual treatments at the transcriptomic level. Overall, these findings support potential genotoxicity, inflammation and cell death due to dispersant or oil exposures. Similar exposures to lung tumor bearing K-RasLA1 mice provided evidence for tumor promotion by oil and Corexit dispersant treatments. Our mouse RNA-seq analyses may be relevant to the pulmonary health hazards of MC252 oil and dispersants experienced in exposed populations.

Impact of dispersant on crude oil content of airborne fine particulate matter emitted from seawater after an oil spill.

Inhalation of PM2.5, particles with an aerodynamic diameter <2.5 µm, from sea spray after crude oil spills could present serious health concerns. The addition of dispersants to effectively spread the crude oil throughout the water column has been practiced in recent years. Here, we investigated the possibility of an increase in the toxic content of fine PM after adding dispersant. A laboratory setup consisted of a vertical tank filled with seawater, 31.5 L airspace for aerosol sampling, and a bubble generating nozzle that aerosolized the oily droplets. Four different cases were studied: no slick, 0.5-mm-thick slick of pure crude oil (MC252 surrogate), dispersant (Corexit 9500A) mixed with crude oil at dispersant to oil ratio (DOR) 1:25, and DOR 1:100. The resulting airborne droplets were sampled for gravimetric and chemical analyses through development of a gas chromatography and mass spectrometry technique. Also, PM2.5 particles were size-fractioned into 13 size bins covering <60 nm to 12.1 µm using a low-pressure cascade impactor. The highest PM2.5 concentration (20.83 ± 5.21 µg/m3) was released from a slick of DOR 1:25, 8.83× greater than the case with pure crude oil. The average ratio of crude oil content from the slick of DOR 1:25 to the case with pure crude oil was 2.37 (1.83 vs 0.77 µg/m3) that decreased to 1.17 (0.90 vs 0.77 µg/m3) at DOR 1:100. For particles <220 nm, the resultant crude oil concentrations were 0.64 and 0.29 µg/m3 at DOR 1:25 and 1:100, both higher than 0.11 µg/m3 from the slick of pure crude oil.

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

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

A ribosomal sequence-based oil sensitivity index for phytoplankton groups.

Species-level variability has made it difficult to determine the relative sensitivity of phytoplankton to oil and mixtures of oil and dispersant. Here we develop a phytoplankton group sensitivity index using ribosome sequence data that we apply to a mesocosm experiment in which a natural microbial community was exposed to oil and two oil-dispersant mixtures. The relative sensitivity of four phytoplankton taxonomic groups, diatoms, dinoflagellates, green algae, and Chrysophytes, was computed using the log of the ratio of the number of species that increase to the number that decrease in relative abundance in the treatment relative to the control. The index indicates that dinoflagellates are the most sensitive group to oil and oil-dispersant treatments while the Chrysophytes benefit under oil exposure compared to the other groups examined. The phytoplankton group sensitivity index can be generally applied to quantify and rank the relative sensitivity of diverse microbial groups to environmental conditions and pollutants.

Oil dispersant Corexit 9500 is weakly estrogenic, but does not skew the sex ratio in Alligator mississippiensis.

During the Deepwater Horizon oil spill, vast quantities of a chemical dispersant Corexit 9500 were applied in remediation efforts. In addition to the acute toxicity, it is essential to evaluate Corexit further with a broader scope of long-term sublethal endocrine endpoints. The American alligator (Alligator mississippiensis) is an excellent organism for such an endeavor. It exhibits temperature-dependent sex determination, in which egg incubation temperatures during a thermosensitive period (TSP) in embryonic development determine the sex of embryos. Estrogen signals play a critical role in this process. For example, a single exposure to exogenous estrogen during the TSP overrides the effects of temperature and leads to skewed sex ratios. At a concentration of 100 ppm, Corexit significantly induced transcriptional activity of both alligator nuclear estrogen receptors 1 and 2 in vitro in reporter gene assays. To investigate the estrogenic effects of Corexit on gonadal development, alligator eggs were exposed to Corexit at environmentally relevant concentrations (0.25, 2.5 and 25 ppm) before the TSP in ovo. Exposure to Corexit at 0.25 and 25 ppm significantly delayed hatching and growth. Corexit exposure at any treatment level did not affect sex ratios or testicular mRNA abundance as measured at 1-week post-hatching, suggesting that the combination of Corexit components did not synergize enough to induce ovarian development in ovo. These results point to a need for further investigations on individual and combined components of Corexit to understand better their long-term effects on the development and reproductive health of alligators and other coastal aquatic wildlife.

Crude Oil and Dispersant Cause Acute Clinicopathological Abnormalities in Hatchling Loggerhead Sea Turtles (Caretta caretta).

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.

Removal of crude oil from highly contaminated natural surfaces with corexit dispersants.

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.