Search

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.

Polycyclic aromatic hydrocarbons (PAHs) have been reported to absorb ultraviolet (UV) light, resulting in enhanced toxicity. Early developmental stages of bivalves may be particularly susceptible to photo-enhanced toxicity during oil spills. In the current study, toxicity tests were conducted with sperm and three larval ages of the eastern oyster ( Crassostrea virginica ) to evaluate the photo-enhanced toxicity of low-energy water-accommodated fractions (WAFs) of two weathered Macondo crude oils collected from the Deepwater Horizon incident. Larvae exposed to oil WAFs under UV-filtered light demonstrated consistently higher survival and normal development than larvae exposed to WAFs under UV light. The phototoxicity of weathered Macondo oil increased as a function of increasing UV light intensity and dose. Early developing oyster larvae were the most sensitive to photo-enhanced toxicity, whereas later shelled prodissoconch larvae were insensitive. Comparisons between two weathered crude oils demonstrated that toxicity was dependent on phototoxic PAH concentration and UV light intensity. [ABSTRACT FROM AUTHOR]

In order to characterize the state of oil spill research and describe how the field has changed since its inception in the 1960s and since the Deepwater Horizon spill in 2010, we examined approximately 10% of oil spill literature (1255 of over 11,000 publications) published from 1968 to 2015. We find that, despite its episodic nature, oil spill research is a rapidly expanding field with a growth rate faster than that of science as a whole. There is a massive post- Deepwater Horizon shift of research attention to the Gulf of Mexico, from 2% of studies in 2004–2008 to 61% in 2014–2015, thus ranking Deepwater Horizon as the most studied oil spill. There is, however, a longstanding gap in research in that only 1% of studies deal with the effects of oil spills on human health. These results provide a better understanding of the current trends and gaps within the field. [ABSTRACT FROM AUTHOR]

The effect of the Deepwater Horizon oil spill on benthic macrofauna in the deep-sea Gulf of Mexico was measured in September–October 2010. Macrofauna community diversity and abundance were lowest closest to the wellhead and increased with distance from the wellhead up to 10 km. The macrofauna loss was primarily in surface sediments, which could be due to the deposition of oil and other toxic chemicals. Crustacean taxa appeared to be sensitive to the deep-sea blowout. Polychaete taxa varied in their sensitivity, but Dorvilleidae which is often associated with organic enrichment, was responsible for the largest amount of dissimilarity between stations close and far from the wellhead. Several other taxa were classified as sensitive or tolerant to the deep-sea blowout by comparing their distributions among impacted and non-impacted zones. The macrobenthic communities in the deep Gulf of Mexico exhibit a toxic response to the blowout on the Deepwater Horizon well, and this is correlated with barium and petroleum hydrocarbons. [ABSTRACT FROM AUTHOR]

The present study examines the relationship between resilience, perceived meaning in life, and traumatic stress symptoms among coastal residents of Mississippi directly affected by the Deepwater Horizon oil spill (also known as the Gulf oil spill). The study was conducted as part of a larger project that assessed the spill's effect on the mental health of individuals seeking therapeutic services. Multiple regression analyses were conducted to determine if resilience and perceived meaning are significant predictors of scores from a measure of posttraumatic stress. Descriptive data, reliability coefficients, and correlations were also calculated. Higher levels of resilience and meaning together were predictive of fewer posttraumatic stress symptoms after controlling for the effect of the spill. Resilience and meaning appeared to be similar predictors of lower posttraumatic stress scores, and meaning appears to be an important facet of what makes a person resilient. [ABSTRACT FROM AUTHOR]

Clonal populations of the diatom Skeletonema costatum isolated from Lake Pontchartrain (Louisiana, USA) near the 2010 Deepwater Horizon oil release were exposed to uncontaminated f/2 medium or light slop oil emulsified (O-E; 25, 50, 75, 100 % of initial levels) in f/2 during short- (10 day) and long-term (21 day) incubations. During 10-day incubations, inhibition of logarithmic growth slopes occurred in the most severely contaminated populations (75, 100 % O-E f/2). Growth in oil-contaminated populations was reduced during 21-day incubations, and growth rates for all populations converged by ca. day 12. Additionally, total cell lipid contents for populations exposed to uncontaminated and contaminated media differed, and mean values for control populations were ca. 2-fold greater than populations maintained in 100 % O-E f/2 medium. Saturated and unsaturated cellular lipids in uncontaminated populations were greater than in petroleum-contaminated populations. Relative cellular fatty acids abundances and RuBisCO RNA transcript copy numbers, proxies for food storage and cellular stress, and mRNA transcript regulation influencing photosynthesis, respectively, were altered half-way through the long-term incubation; C16:0 and C16:1 fatty acids were greater and less, respectively, and RuBisCO transcript copy numbers were greater within severely contaminated populations (compared to uncontaminated populations). Yet, fatty acid abundances and RuBisCO copy numbers were equivalent among culture populations by the end of the incubation. Oil contaminants within the culture medium were measured; C-C hydrocarbons and arsenic coincided with (initial) growth inhibition and (later) altered cell physiologies, respectively. Relationships among assessed parameters were deemed useful determinants for evaluating phytoplankton inhibition in response to petroleum contamination. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are widespread in marine ecosystems and originate from natural sources and anthropogenic activities. PAHs enter the marine environment in two main ways, corresponding to chronic pollution or acute pollution by oil spills. The global PAH fluxes in marine environments are controlled by the microbial degradation and the biological pump, which plays a role in particle settling and in sequestration through bioaccumulation. Due to their low water solubility and hydrophobic nature, PAHs tightly adhere to sediments leading to accumulation in coastal and deep sediments. Microbial assemblages play an important role in determining the fate of PAHs in water and sediments, supporting the functioning of biogeochemical cycles and the microbial loop. This review summarises the knowledge recently acquired in terms of both chronic and acute PAH pollution. The importance of the microbial ecology in PAH-polluted marine ecosystems is highlighted as well as the importance of gaining further in-depth knowledge of the environmental services provided by microorganisms. [ABSTRACT FROM AUTHOR]

Exposure to polycyclic aromatic hydrocarbons (PAH) negatively impacts exercise performance in fish species but the physiological modifications that result in this phenotype are poorly understood. Prior studies have shown that embryonic and juvenile mahi–mahi ( Coryphaeus hippurus ) exposed to PAH exhibit morphological abnormalities, altered cardiac development and reduced swimming performance. It has been suggested that cardiovascular function inhibited by PAH exposure accounts for the compromised exercise performance in fish species. In this study we used in-situ techniques to measure hemodynamic responses of young adult mahi–mahi exposed to PAH for 24 h. The data indicate that stroke volume was reduced 44% in mahi–mahi exposed to 9.6 ± 2.7 μg l −1 geometric mean PAH (∑PAH) and resulted in a 39% reduction in cardiac output and a 52% reduction in stroke work. Maximal change in pressure over change in time was 28% lower in mahi–mahi exposed to this level of ∑PAH. Mean intraventricular pressures and heart rate were not significantly changed. This study suggests exposure to environmentally relevant PAH concentrations impairs aspects of cardiovascular function in mahi–mahi. [ABSTRACT FROM AUTHOR]

Adding clay to marine oil pollution represents a promising approach to enhance bacterial hydrocarbon degradation in nutrient poor waters. In this study, three types of regionally available clays (Ca-bentonite, Fuller's Earth and kaolin) were tested to stimulate the biodegradation of source and weathered oil collected from the Deepwater Horizon spill. The weathered oil showed little biodegradation prior to experimentation and was extensively degraded by bacteria in the laboratory in a similar way as the alkane-rich source oil. For both oils, the addition of natural clay-flakes showed minor enhancement of oil biodegradation compared to the non-clay bearing control, but the clay-oil films did limit evaporation. Only alkanes of a molecular weight (MW) > 420 showed significant reduction by enhanced biodegradation following natural clay treatment. In contrast, all fertilized clay flakes showed major bacterial degradation of the oil, with a 6–10 times reduction in alkane content, and an up to 8 fold increase in the rate of O 2 consumption. Compared to the control, such treatment showed particular reduction of longer chained alkanes (MW > 226). The application of natural and fertilized clay flakes also showed selective reduction of PAHs, mainly in the MW range of 200–300, but without significant change in the toxicity indices measured. These results imply that a large variety of clays may be used to boost oil biodegradation by aiding attachment of fertilizing nutrients to the oil. [ABSTRACT FROM AUTHOR]

Chemical analysis of sediment cores collected up to 8 km from the Macondo well in 2010/2011 demonstrates the extent of weathering of the Macondo oil deposited in deep-sea sediments following the Deepwater Horizon disaster. On average, dissolution and biodegradation of the oil on the seafloor increased with distance from the well indicating that weathering occurred rapidly and overwhelmingly during the oil's transport as dispersed oil droplets within the deep-sea plume. Beyond about 5 km from the well, the oil deposited on the seafloor had lost most mass below C 25 , was relatively enriched in n -C 25 + n -alkanes and C 3 – and C 4 -alkylated benz[ a ]anthracenes/chrysenes, the latter owing to 95% depletion of total PAHs. Biodegradation of C 28 and C 29 tricyclic terpanes, C 34 and C 35 17α(H),21β(H)-homohopanes, C 27 13β(H),17α(H)-dia and C 27 14β(H),17β(H)-steranes and dissolution of C 26 to C 28 triaromatic steroids occurred. The results provide a means to distinguish Macondo oil in deep-sea sediments from naturally-occurring seep oils and pervasive ambient background hydrocarbons. [ABSTRACT FROM AUTHOR]

Following the Deepwater Horizon oil spill, the spilled Macondo oil was severely weathered during its transport within the deep-sea plume as discrete particles, which were subsequently deposited on the seafloor. The Macondo oil deposited in deep-sea sediments was distinguished from ambient (background) hydrocarbons and naturally-seeped and genetically-similar oils in the Mississippi Canyon region using a forensic method based upon a systematic, multi-year study of 724 deep-sea sediment cores collected in late 2010 and 2011. The method relied upon: (1) chemical fingerprinting of the distinct features of the wax-rich, severely-weathered Macondo oil; (2) hydrocarbon concentrations, considering a core's proximity to the Macondo well or to known or apparent natural oil seeps, and also vertically within a core; and (3) results from proximal cores and flocculent material from core supernatants and slurp gun filters. The results presented herein establish the geographic extent of “fingerprintable” Macondo oil recognized on the seafloor in 2010/2011. [ABSTRACT FROM AUTHOR]

The marine alphaproteobacterium strain O3.65 was isolated from an enrichment culture of surface seawater contaminated with weathered oil (slicks) from the Deepwater Horizon (DWH) oil spill and belongs to the ubiquitous, diverse and ecological relevant Roseobacter group within the Rhodobacteraceae. Here, we present a preliminary set of physiological features of strain O3.65 and a description and annotation of its draft genome sequence. Based on our data we suggest potential ecological roles of the isolate in the degradation of crude oil within the network of the oil-enriched microbial community. The draft genome comprises 4,852,484 bp with 4,591 protein-coding genes and 63 RNA genes. Strain O3.65 utilizes pentoses, hexoses, disaccharides and amino acids as carbon and energy source and is able to grow on several hydroxylated and substituted aromatic compounds. Based on 16S rRNA gene comparison the closest described and validated strain is Phaeobacter inhibens DSM 17395, however, strain O3.65 is lacking several phenotypic and genomic characteristics specific for the genus Phaeobacter. Phylogenomic analyses based on the whole genome support extensive genetic exchange of strain O3.65 with members of the genus Ruegeria, potentially by using the secretion system type IV. Our physiological observations are consistent with the genomic and phylogenomic analyses and support that strain O3.65 is a novel species of a new genus within the Rhodobacteraceae. [ABSTRACT FROM AUTHOR]

The temporal and geographic attributes of the Deepwater Horizon incident in 2010 likely exposed pelagic game fish species, such as mahi-mahi, to crude oil. Although much of the research assessing the effects of the spill has focused on early life stages of fish, studies examining whole-animal physiological responses of adult marine fish species are lacking. Using swim chamber respirometry, the present study demonstrates that acute exposure to a sublethal concentration of the water accommodated fraction of Deepwater Horizon crude oil results in significant swim performance impacts on young adult mahi-mahi, representing the first report of acute sublethal toxicity on adult pelagic fish in the Gulf of Mexico following the spill. At an exposure concentration of 8.4 ± 0.6 µg L−1 sum of 50 selected polycyclic aromatic hydrocarbons (PAHs; mean of geometric means ± standard error of the mean), significant decreases in the critical and optimal swimming speeds of 14% and 10%, respectively ( p < 0.05), were observed. In addition, a 20% reduction in the maximum metabolic rate and a 29% reduction in aerobic scope resulted from exposure to this level of ΣPAHs. Using environmentally relevant crude oil exposure concentrations and a commercially and ecologically valuable Gulf of Mexico fish species, the present results provide insight into the effects of the Deepwater Horizon oil spill on adult pelagic fish. Environ Toxicol Chem 2016;35:2613-2622. © 2016 SETAC [ABSTRACT FROM AUTHOR]

Assessments of large-scale disasters, such as the Deepwater Horizon oil spill, are problematic because while measurements of post-disturbance conditions are common, measurements of pre-disturbance baselines are only rarely available. Without adequate observations of pre-disaster organismal and environmental conditions, it is impossible to assess the impact of such catastrophes on animal populations and ecological communities. Here, we use long-term biological tissue records to provide pre-disaster data for a vulnerable marine organism. Keratin samples from the carapace of loggerhead sea turtles record the foraging history for up to 18 years, allowing us to evaluate the effect of the oil spill on sea turtle foraging patterns. Samples were collected from 76 satellite-tracked adult loggerheads in 2011 and 2012, approximately one to two years after the spill. Of the 10 individuals that foraged in areas exposed to surface oil, none demonstrated significant changes in foraging patterns post spill. The observed long-term fidelity to foraging sites indicates that loggerheads in the northern Gulf of Mexico likely remained in established foraging sites, regardless of the introduction of oil and chemical dispersants. More research is needed to address potential long-term health consequences to turtles in this region. Mobile marine organisms present challenges for researchers to monitor effects of environmental disasters, both spatially and temporally. We demonstrate that biological tissues can reveal long-term histories of animal behavior and provide critical pre-disaster baselines following an anthropogenic disturbance or natural disaster. [ABSTRACT FROM AUTHOR]

Knowledge of the spatial distribution of oil thickness patterns within an on-water spill is of obvious importance for immediate spill response activities as well as for subsequent evaluation of the spill impacts. For long-lasting continuous spills like the 2010 3-month Deepwater Horizon (DWH) event in the Gulf of Mexico, it is also important to identify changes in the dominant oil features through time. This study utilized very high resolution (≤ 5 m) aerial and satellite imagery acquired during the DWH spill to evaluate the shape, size and thickness of surface oil features that dominated the DWH slick. Results indicate that outside of the immediate spill source region, oil distributions did not encompass a broad, varied range of thicknesses. Instead, the oil separated into four primary, distinct characterizations: 1) invisible surface films detectable only with Synthetic Aperture Radar imaging because of the decreased surface backscatter, 2) thicker sheen & rainbow areas (< 0.005 mm), 3) large regional areas of relatively thin, “metallic appearance” films (0.005–0.08 mm), and 4) strands of thick, emulsified oil (> 1 mm) that were consistently hundreds of meters long but most commonly only 10–50 m wide. Where present within the slick footprint, each of the three distinct visible oil thickness classes maintained its shape characteristics both spatially (at different distances from the source and in different portions of the slick), and temporally (from mid-May through July 2010). The region over the source site tended to contain a more continuous range of oil thicknesses, however, our results indicate that the continuous injection of subsurface dispersants starting in late May significantly altered (lowered) that range. In addition to characterizing the oil thickness distribution patterns through the timeline of one of the world's largest oil spills, this paper also details the extension of using high resolution aerial imagery to calibrate medium resolution satellite data sources such as USA's Thematic Mapper (30 m) to provide larger-scale spatial views of major spills, and discusses implications for utilizing such data for oil spill characterizations and spill response. [ABSTRACT FROM AUTHOR]

Accidental crude oil releases, such as the Deepwater Horizon ( DWH ) accident, are always a potential threat to pristine marine ecosystems. Since the toxicity of crude oil heavily depends on its variable composition, the comprehensive characterization of crude oil compounds as a function of weathering is an important area of research. Traditional gas chromatography-based characterization presents significant limitations, and the use of ultrahigh-resolution mass spectrometric (UHRMS) techniques (that allow for the assignment of molecular formulae) has been shown to be better equipped to address the complex nature of crude oils. This study used an Orbitrap Q Exactive mass spectrometer operated at a resolving power of 140,000 FWHM with both electrospray ionization (ESI) and atmospheric pressure photoionization (APPI) sources, in order to characterize a crude oil weathering series of the Macondo oil released during the DWH incident (the source oil, two differently weathered surface slicks, and a beached residue). Preliminary gas chromatography mass spectrometry (GC–MS) and gas chromatography flame ionization detection (GC–FID) results suggested that the four oils comprised a true weathering series (including biodegradation and photodegradation in addition to other well-known processes such as dissolution and evaporation). UHRMS results showed a clear increase in oxygenated compounds with weathering, and further suggested a significant gain of acidic compounds, as well as the transformation of phenols to ketonic and quinonic compounds with weathering. A complementary study on a weathered oil sample amended with selected model compounds contributed additional insight into the functional group types that are accessible in each ionization technique. [ABSTRACT FROM AUTHOR]

The April 2010 Deepwater Horizon (DWH) oil spill was the largest coastal spill in U.S. history. Monitoring subsequent change in marsh plant community distributions is critical to assess ecosystem impacts and to establish future coastal management priorities. Strategically deployed airborne imaging spectrometers, like the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS), offer the spectral and spatial resolution needed to differentiate plant species. However, obtaining satisfactory and consistent classification accuracies over time is a major challenge, particularly in dynamic intertidal landscapes. Here, we develop and evaluate an image classification system for a time series of AVIRIS data for mapping dominant species in a heavily oiled salt marsh ecosystem. Using field-referenced image endmembers and canonical discriminant analysis (CDA), we classified 21 AVIRIS images acquired during the fall of 2010, 2011 and 2012. Classification results were evaluated using ground surveys that were conducted contemporaneously to AVIRIS collection dates. We analyzed changes in dominant species cover from 2010 to 2012 for oiled and non-oiled shorelines. CDA discriminated dominant species with a high level of accuracy (overall accuracy = 82%, kappa = 0.78) and consistency over three imaging dates (overall 2010 = 82%, overall 2011 = 82%, overall 2012 = 88%). Marshes dominated by Spartina alterniflora were the most spatially abundant in shoreline zones (≤ 28 m from shore) for all three dates (2010 = 79%, 2011 = 61%, 2012 = 63%), followed by Juncus roemerianus (2010 = 11%, 2011 = 19%, 2012 = 17%) and Distichlis spicata (2010 = 4%, 2011 = 10%, 2012 = 7%). Marshes that were heavily contaminated with oil exhibited variable responses from 2010 to 2012. Marsh vegetation classes converted to a subtidal, open water class along oiled and non-oiled shorelines that were similarly situated in the landscape. However, marsh loss along oil-contaminated shorelines doubled that of non-oiled shorelines. Only S. alterniflora dominated marshes were extensively degraded, losing 15% (354,604 m 2 ) cover in oiled shoreline zones, suggesting that S. alterniflora marshes may be more vulnerable to shoreline erosion following hydrocarbon stress, due to their landscape position. [ABSTRACT FROM AUTHOR]

Evaluating long-term contaminant effects on wildlife populations depends on spatial information about habitat quality, heterogeneity in contaminant exposure, and sensitivities and distributions of species integrated into a systems modeling approach. Rarely is this information readily available, making it difficult to determine the applicability of realistic models to quantify population-level risks. To evaluate the trade-offs between data demands and increased specificity of spatially explicit models for population-level risk assessments, we developed a model for a standard toxicity test species, the sheepshead minnow ( Cyprinodon variegatus), exposed to oil contamination following the Deepwater Horizon oil spill and compared the output with various levels of model complexity to a standard risk quotient approach. The model uses habitat and fish occupancy data collected over five sampling periods throughout 2008-2010 in Pensacola and Choctawhatchee Bays, Florida, USA, to predict species distribution, field-collected and publically available data on oil distribution and concentration, and chronic toxicity data from laboratory assays applied to a matrix population model. The habitat suitability model established distribution of fish within Barataria Bay, Louisiana, USA, and the population model projected the dynamics of the species in the study area over a 5-yr period (October 2009-September 2014). Vital rates were modified according to estimated contaminant concentrations to simulate oil exposure effects. To evaluate the differences in levels of model complexity, simulations varied from temporally and spatially explicit, including seasonal variation and location-specific oiling, to simple interpretations of a risk quotient derived for the study area. The results of this study indicate that species distribution, as well as spatially and temporally variable contaminant concentrations, can provide a more ecologically relevant evaluation of species recovery from catastrophic environmental impacts but might not be cost-effective or efficient for rapid assessment needs. [ABSTRACT FROM AUTHOR]

Crude oil released from the Deepwater Horizon disaster into the Gulf of Mexico posed potential impacts to infaunal invertebrates inhabiting near shore habitats. The effects of sediment-associated weathered slick oil on the amphipod Leptocheirus plumulosus was assessed using 28-d exposures to total PAH sediment concentrations ranging from 0.3 to 24 mg/kg (sum of 50 PAHs or tPAH50). Survival and growth rate were significantly decreased in the 2.6, 11.4 and 24.2 mg/kg treatments, but only growth in 5.5 mg/kg. Offspring production was dramatically decreased but was variable and significantly different only for 24.2 mg/kg. The concentrations associated with 20% decreases relative to reference were 1.05 (95% CI = 0–2.89) mg/kg tPAH50 for growth rate and 0.632 (95% CI = 0.11–2.15) mg/kg tPAH50 for offspring production. The concentrations of PAHs affecting amphipods are within the range of concentrations measured in marsh areas reportedly impacted by DWH oil after its release. [ABSTRACT FROM AUTHOR]

The present study examined the effects of chronic exposure of eastern oyster ( Crassostrea virginica) larvae to the water-accommodated fractions of fresh and weathered oils collected from the Deepwater Horizon incident, with and without additions of the dispersant Corexit 9500A, as well as to solutions of Corexit alone. Both shell growth of larvae exposed to test materials for a period of 10 d and larval settlement after 28 d of exposure were the most sensitive endpoints, with the 10-d growth endpoint being less variable among replicates. Growth and settlement endpoints were more sensitive than larval survival and normal development after 10 d and 28 d. Acute-to-chronic ratios calculated in the present study suggest that acute toxicities of oils and dispersant for oysters are not predictive of chronic effect levels for growth and settlement; therefore, chronic bioassays are necessary to assess these sublethal effects, in addition to standard 48-h acute toxicity tests. Comparison of 10% effective concentration (EC10) values for chronic 10-d growth and 28-d settlement endpoints with concentrations of total polycyclic aromatic hydrocarbons and dipropylene glycol n-butyl ether (a marker for Corexit) in seawater samples, collected during and after the Deepwater Horizon incident, indicated it was unlikely that elevated concentrations of water-soluble fractions of oil and dispersant in the nearshore environment had significant adverse effects on the growth and settlement of eastern oyster larvae. Environ Toxicol Chem 2016;35:2029-2040. © 2016 SETAC [ABSTRACT FROM AUTHOR]

Acute toxicity tests (48-96-h duration) were conducted with larvae of 2 echinoderm species ( Strongylocentrotus purpuratus and Dendraster excentricus) and 4 bivalve mollusk species ( Crassostrea virginica, Crassostrea gigas, Mytilus galloprovincialis, and Mercenaria mercenaria). Developing larvae were exposed to water-accommodated fractions (WAFs) and chemically enhanced water-accommodated fractions (CEWAFs) of fresh and weathered oils collected from the Gulf of Mexico during the Deepwater Horizon incident. The WAFs (oils alone), CEWAFs (oils plus Corexit 9500A dispersant), and WAFs of Corexit alone were prepared using low-energy mixing. The WAFs of weathered oils had no effect on survival and development of echinoderm and bivalve larvae, whereas WAFs of fresh oils showed adverse effects on larval development. Similar toxicities were observed for weathered oil CEWAFs and WAFs prepared with Corexit alone for oyster ( C. gigas and C. virginica) larvae, which were the most sensitive of the tested invertebrate species to Corexit. Mean 10% effective concentration values for total polycyclic aromatic hydrocarbons and dipropylene glycol n-butyl ether (a marker for Corexit) in the present study were higher than all concentrations reported in nearshore field samples collected during and after the Deepwater Horizon incident. The results suggest that water-soluble fractions of weathered oils and Corexit dispersant associated with the Deepwater Horizon incident had limited, if any, acute impacts on nearshore larvae of eastern oysters and clams, as well as other organisms with similar sensitivities to those of test species in the present study; however, exposure to sediments and long-term effects were not evaluated. Environ Toxicol Chem 2016;35:2016-2028. © 2016 SETAC [ABSTRACT FROM AUTHOR]

The Deepwater Horizon disaster caused a shift in microbial communities in Gulf of Mexico seawater, but less is known about the baseline for microbial communities in the underlying sediments. We compared 16S rRNA and functional gene sequences deriving from DNA and RNA with geochemical profiles (sulfate and methane concentrations, δ 13 C of methane and carbon dioxide, and chloride concentrations) of a sediment gravity core from the upper continental slope of the northwestern Gulf of Mexico (MC118) in 2008, 15 km from the spill site. The highest number of archaeal sequences were ANME-1 and ANME-2 archaea in the sulfate-reducing upper core segments (12 and 42 cmbsf), ANME-1 and Methanomicrobiales in the middle methanogenic depths (200 and 235 cmbsf), and ANME-1 at the deepest depths (309, 400, and 424 cmbsf). The presence of mcrA gene transcripts showed that members of the ANME-1 group are active throughout the core and transcribe the mcrA gene, a key gene of methanogenesis and anaerobic methane oxidation. The bacterial community consists mostly of members of the Deltaproteobacteria , Chloroflexi , Cytophaga , Epsilonproteobacteria , and the Japan Sea Group 1 throughout the core. The commonly detected genera of gammaproteobacterial hydrocarbon-degrading bacteria in the water column are not found in this sediment survey, indicating that the benthic sediment is an unlikely reservoir for these aerobes. However, the sediments contain members of the sulfate-reducing families Desulfobulbaceae and Desulfobacteraceae , some members of which degrade and completely oxidize aromatic hydrocarbons and alkanes, and the Desulfobacterium anilini lineage of obligately aromatics-degrading sulfate reducers. Thus, the benthic sediments are the most likely reservoir for the active deltaproteobacterial populations that were observed repeatedly after the Deepwater Horizon spill in the fall of 2010. [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]

Within months of the BP Macondo Wellhead blowout, elevated methane concentrations within the water column revealed a significant retention of light hydrocarbons in deep waters plus corresponding dissolved oxygen (DO) deficits. However, chemical plume tracking efforts were hindered by a lack of in situ monitoring capabilities. Here, we describe results from in situ time-series, lander-based investigations of physical and biogeochemical processes controlling dissolved oxygen, and methane at Mississippi Canyon lease block 118 (~18 km from the oil spill) conducted shortly after the blowout through April 2012. Multiple sensor arrays plus open-cylinder flux chambers (“chimneys”) deployed from a benthic lander collected oxygen, methane, pressure, and current speed and direction data within one meter of the seafloor. The ROVARD lander system was deployed for an initial 21-day test experiment (9/13/2010–10/04/2010) at 882 m depth before a longer 160-day deployment (10/24/2011–4/01/2012) at 884 m depth. Temporal variability in current directions and velocities and water temperatures revealed strong influences of bathymetrically steered currents and overlying along-shelf flows on local and regional water transport processes. DO concentrations and temperature were inversely correlated as a result of water mass mixing processes. Flux chamber measurements during the 160-day deployment revealed total oxygen utilization (TOU) averaging 11.6 mmol/m 2 day. Chimney DO concentrations measured during the 21-day deployment exhibited quasi-daily variations apparently resulting from an interaction between near inertial waves and the steep topography of an elevated scarp immediately adjacent to the 21-day deployment site that modulated currents at the top of the chimney. Variability in dissolved methane concentrations suggested significant temporal variability in gas release from nearby hydrocarbon seeps and/or delivery by local water transport processes. Free-vehicle (lander) monitoring over time scales of months to years utilizing in situ sensors can provide an understanding of processes controlling water transport, respiration and the fate and impacts of accidental and natural gas and oil releases. [ABSTRACT FROM AUTHOR]

We have compiled and mapped available carbon isotope data from sedimentary organic material sampled from the Gulf of Mexico prior to 2010. These data provide a baseline to which any changes in the Gulf of Mexico after the 2010 Deepwater Horizon oil spill can be compared. The mean (±1 σ ) δ 13 C values, relative to PDB, are −21.4±1.9‰ (entire Gulf of Mexico), −21.7±1.2‰ (shelf sediments), −20.4±1.6‰ (deepwater sediments), and −25.2±4.1‰ (seep-affected sediments). We compare pre-spill mean δ 13 C values to carbon isotope measurements of sedimentary organic material from coretop samples collected after the 2010 Deepwater Horizon oil spill. The differences between the mean compiled δ 13 C values and the post-spill δ 13 C values are corroborated by qualitative relationships with the concentration of polycyclic aromatic hydrocarbons (PAHs), a proxy for oil contamination, in the sediment. The relationships between δ 13 C of the sedimentary organic material and PAH concentrations allow estimation of background levels of PAHs on the shelf and in the deep Gulf of Mexico. Higher background levels of PAH on the shelf likely relate to Mississippi River outflow and its deposition of petrogenic PAH in riverine sediments. [ABSTRACT FROM AUTHOR]

Pathologies in over 400 octocoral and antipatharian colonies were quantified in the aftermath of the DWH oil discharge. Observations were made in September 2011 at water depths of 65–75 m in the Pinnacle Reef trend area offshore from Mississippi and Alabama, Gulf of Mexico, using a digital macro camera deployed from an ROV to examine the coral populations for injury at two principal sites: Alabama Alps Reef (AAR) and Roughtongue Reef (RTR). Taxa observed to exhibit injury included gorgonian octocorals Hypnogorgia pendula , Bebryce spp., Thesea nivea , and Swiftia exserta , the antipatharian Antipathes atlantica, and the sea whips Stichopathes sp., and Ellisella barbadensis . The most common type of injury was a biofilm with a clumped or flake-like appearance covering sea-fan branches. Extreme injuries were characterized by bare skeletons, broken and missing branches. Comparing the 2011 results to previous photo surveys of the same study sites between 1997 and 1999, we found significantly more occurrences of injury in 2011 among taxa with growth forms >0.5 m. We hypothesize that Tropical Storm Bonnie facilitated and accelerated the mixing process of dispersant-treated hydrocarbons into the water column, resulting in harmful contact with coral colonies at mesophotic depths. Analysis of total polycyclic aromatic hydrocarbon (tPAH) concentrations in sediments at AAR and RTR found levels elevated above pre-discharge values, but orders of magnitude below toxicity thresholds established for fauna in estuarine sediments. The tPAH concentrations measured in octocoral and echinoderm tissue samples from AAR and RTR were detectable (mean values ranged from 51 to 345 ppb); however, bioeffect thresholds do not currently exist with which to evaluate the potential harm these levels may cause. Our findings indicate that coral injuries observed in 2011 may have resulted from an acute, isolated event rather than ongoing natural processes. [ABSTRACT FROM AUTHOR]

The relative effects of hydrodynamic, thermodynamic, and geochemical factors on the fate and transport of oil in the subsea are not well understood to date. This glaring lack of knowledge in deep-sea spill studies precludes the parameterization of blowout far-field models. Here we use observations from the Macondo blowout to evaluate the importance of input variables in a numerical model of oil transport and fate. We adapt a multi-hydrocarbon fraction module to oil dissolution and run sensitivity analyses under various parameterization scenarios. We find that the inclusion of oil droplet atomization, variable flow rates (VFR), high-pressure biodegradation (HPB), and vertical currents׳ velocities (VV) affects significantly the subsea oil mass distribution in the water column as well as the evolution of deep plumes. In particular, droplets up to 50 μm are neutrally buoyant and moved by deep currents predominantly driven by the topography, while the depth of the deep plume is very sensitive to the VV of the hydrodynamic model. We find good agreement between CTD cast observations and modeled mean depth of the oil mass, whereby HPB provide increased accuracy of predictions with time. The model suggests that VFR and HPB are mechanisms for the persistence of the southwestern deep plume observed at 1100 m by increasing the residence time of the oil in the water column. Modeled oil concentrations range from 5 to 500 ppb and present the highest values in the western and deepest locations of the subsea plume, which corroborate with field observations. We hypothesize that a substantial amount of subsea oil mass might have interacted with the bottom of the Mississippi Canyon. [ABSTRACT FROM AUTHOR]