Persistence and biodegradation of oil at the ocean floor following Deepwater Horizon

Comparison of two field systems for determination of crude oil biodegradation in cold seawater

Marine oil spills have devastating environmental impacts and extrapolation of experimental fate and impact data from the lab to the field remains challenging due to the lack of comparable field data. In this work we compared two field systems used to study in situ oil depletion with emphasis on biodegradation and associated microbial communities. The systems were based on (i) oil impregnated clay beads and (ii) hydrophobic Fluortex adsorbents coated with thin oil films. The bacterial communities associated with the two systems displayed similar compositions of dominant bacterial taxa. Initial abundances of Oceanospirillales were observed in both systems with later emergences of Flavobacteriales, Alteromonadales and Rhodobacterales. Depletion of oil compounds was significantly faster in the Fluortex system and most likely related to the greater bioavailability of oil compounds as compared to the clay bead system.

Methylated cycloalkanes fuel a novel genus in the Porticoccaceae family (Ca. Reddybacter gen. nov)

Cycloalkanes are abundant and toxic compounds in subsurface petroleum reservoirs and their fate is important to ecosystems impacted by natural oil seeps and spills. This study focuses on the microbial metabolism of methylcyclohexane (MCH) and methylcyclopentane (MCP) in the deep Gulf of Mexico. MCH and MCP are often abundant cycloalkanes observed in petroleum and will dissolve into the water column when introduced at the seafloor via a spill or natural seep. We conducted incubations with deep Gulf of Mexico (GOM) seawater amended with MCH and MCP at four stations. Within incubations with active respiration of MCH and MCP, we found that a novel genus of bacteria belonging to the Porticoccaceae family (Candidatus Reddybacter) dominated the microbial community. Using metagenome-assembled genomes, we reconstructed the central metabolism of Candidatus Reddybacter, identifying a novel clade of the particulate hydrocarbon monooxygenase (pmo) that may play a central role in MCH and MCP metabolism. Through comparative analysis of 174 genomes, we parsed the taxonomy of the Porticoccaceae family and found evidence suggesting the acquisition of pmo and other genes related to the degradation of cyclic and branched hydrophobic compounds were likely key events in the ecology and evolution of this group of organisms.

Biodegradation of phenanthrene by piezotolerant Bacillus subtilis EB1 and genomic insights for bioremediation

A marine strain B. subtilis EB1, isolated from Equator water, showed excellent degradation towards a wide range of hydrocarbons. Degradation studies revealed dense growth with 93 % and 83 % removal of phenanthrene within 72 h at 0.1 and 20 MPa, respectively. The identification of phenanthrene degradation metabolites by GC-MS combined with its whole genome analysis provided the pathway involved in the degradation process. Whole genome sequencing indicated a genome size of 3,983,989 bp with 4331 annotated genes. The genome provided the genetic compartments, which includes monooxygenase, dioxygenase, dehydrogenase, biosurfactant synthesis catabolic genes for the biodegradation of aromatic compounds. Detailed COG and KEGG pathway analysis confirmed the genes involved in the oxygenation reaction of hydrocarbons, piezotolerance, siderophores, chemotaxis and transporter systems which were specific to adaptation for survival in extreme marine habitat. The results of this study will be a key to design an optimal bioremediation strategy for oil contaminated extreme marine environment.

Morphological and transcriptional effects of crude oil and dispersant exposure on the marine sponge Cinachyrella alloclada

Marine sponges play important roles in benthic ecosystems. More than providing shelter and food to other species, they help maintain water quality by regulating nitrogen and ammonium levels in the water, and bioaccumulate heavy metals. This system, however, is particularly sensitive to sudden environmental changes including catastrophic pollution event such as oil spills. Hundreds of oil platforms are currently actively extracting oil and gas in the Gulf of Mexico. To test the vulnerability of the benthic ecosystems to oil spills, we utilized the Caribbean reef sponge, Cinachyrella alloclada, as a novel experimental indicator. We have exposed organisms to crude oil and oil dispersant for up to 24 h and measured resultant gene expression changes. Our findings indicate that 1-hour exposure to water accommodated fractions (WAF) was enough to elicit massive shifts in gene expression in sponges and host bacterial communities (8052 differentially expressed transcripts) with the up-regulation of stress related pathways, cancer related pathways, and cell integrity pathways. Genes that were upregulated included heat shock proteins, apoptosis, oncogenes (Rab/Ras, Src, CMYC), and several E3 ubiquitin ligases. 24-hour exposure of chemically enhanced WAF (CE-WAF) had the greatest impact to benthic communities, resulting in mostly downregulation of gene expression (4248 differentially expressed transcripts). Gene deregulation from 1-hour treatments follow this decreasing trend of toxicity: WAF > CE-WAF > Dispersant, while the 24-hour treatment showed a shift to CE-WAF > Dispersant > WAF in our experiments. Thus, this study supports the development of Cinachyrella alloclada as a research model organism and bioindicator species for Florida reefs and underscores the importance of developing more efficient and safer ways to remove oil in the event of a spill catastrophe.

Chemical Weathering Patterns of Diluted Bitumen Spilled into Freshwater Limnocorrals

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

Influence of Extremely High Pressure and Oxygen on Hydrocarbon-Enriched Microbial Communities in Sediments from the Challenger Deep, Mariana Trench

Recent studies reported that highly abundant alkane content exists in the ~11,000 m sediment of the Mariana Trench, and a few key alkane-degrading bacteria were identified in the Mariana Trench. At present, most of the studies on microbes for degrading hydrocarbons were performed mainly at atmospheric pressure (0.1 MPa) and room temperature; little is known about which microbes could be enriched with the addition of n-alkanes under in-situ environmental pressure and temperature conditions in the hadal zone. In this study, we conducted microbial enrichments of sediment from the Mariana Trench with short-chain (SCAs, C7–C17) or long-chain (LCAs, C18–C36) n-alkanes and incubated them at 0.1 MPa/100 MPa and 4 °C under aerobic or anaerobic conditions for 150 days. Microbial diversity analysis showed that a higher microbial diversity was observed at 100 MPa than at 0.1 MPa, irrespective of whether SCAs or LCAs were added. Non-metric multidimensional scaling (nMDS) and hierarchical cluster analysis revealed that different microbial clusters were formed according to hydrostatic pressure and oxygen. Significantly different microbial communities were formed according to pressure or oxygen (p < 0.05). For example, Gammaproteobacteria (Thalassolituus) were the most abundant anaerobic n-alkanes-enriched microbes at 0.1 MPa, whereas the microbial communities shifted to dominance by Gammaproteobacteria (Idiomarina, Halomonas, and Methylophaga) and Bacteroidetes (Arenibacter) at 100 MPa. Compared to the anaerobic treatments, Actinobacteria (Microbacterium) and Alphaproteobacteria (Sulfitobacter and Phenylobacterium) were the most abundant groups with the addition of hydrocarbon under aerobic conditions at 100 MPa. Our results revealed that unique n-alkane-enriched microorganisms were present in the deepest sediment of the Mariana Trench, which may imply that extremely high hydrostatic pressure (100 MPa) and oxygen dramatically affected the processes of microbial-mediated alkane utilization.

Snow-Dependent Biogeochemical Cycling of Polycyclic Aromatic Hydrocarbons at Coastal Antarctica

The temporal trend of polycyclic aromatic hydrocarbons (PAHs) in coastal waters with highly dynamic sources and sinks is largely unknown, especially for polar regions. Here, we show the concurrent measurements of 73 individual PAHs and environmental data, including the composition of the bacterial community, during three austral summers at coastal Livingston (2015 and 2018) and Deception (2017) islands (Antarctica). The Livingston 2015 campaign was characterized by a larger snow melting input of PAHs and nutrients. The assessment of PAH diagnostic ratios, such as parent to alkyl-PAHs or LMW to HMW PAHs, showed that there was a larger biodegradation during the Livingston 2015 campaign than in the Deception 2017 and Livingston 2018 campaigns. The biogeochemical cycling, including microbial degradation, was thus yearly dependent on snow-derived inputs of matter, including PAHs, consistent with the microbial community significantly different between the different campaigns. The bivariate correlations between bacterial taxa and PAH concentrations showed that a decrease in PAH concentrations was concurrent with the higher abundance of some bacterial taxa, specifically the order Pseudomonadales in the class Gammaproteobacteria, known facultative hydrocarbonoclastic bacteria previously reported in degradation studies of oil spills. The work shows the potential for elucidation of biogeochemical processes by intensive field-derived time series, even in the harsh and highly variable Antarctic environment.

Microbiome enrichment from contaminated marine sediments unveils novel bacterial strains for petroleum hydrocarbon and heavy metal bioremediation

Petroleum hydrocarbons and heavy metals are some of the most widespread contaminants affecting marine ecosystems, urgently needing effective and sustainable remediation solutions. Microbial-based bioremediation is gaining increasing interest as an effective, economically and environmentally sustainable strategy. Here, we hypothesized that the heavily polluted coastal area facing the Sarno River mouth, which discharges >3 tons of polycyclic aromatic hydrocarbons (PAHs) and ∼15 tons of heavy metals (HMs) into the sea annually, hosts unique microbiomes including marine bacteria useful for PAHs and HMs bioremediation. We thus enriched the microbiome of marine sediments, contextually selecting for HM-resistant bacteria. The enriched mixed bacterial culture was subjected to whole-DNA sequencing, metagenome-assembled-genomes (MAGs) annotation, and further sub-culturing to obtain the major bacterial species as pure strains. We obtained two novel isolates corresponding to the two most abundant MAGs (Alcanivorax xenomutans strain-SRM1 and Halomonas alkaliantarctica strain-SRM2), and tested their ability to degrade PAHs and remove HMs. Both strains exhibited high PAHs degradation (60-100%) and HMs removal (21-100%) yield, and we described in detail >60 genes in their MAGs to unveil the possible genetic basis for such abilities. Most promising yields (∼100%) were obtained towards naphthalene, pyrene and lead. We propose these novel bacterial strains and related genetic repertoire to be further exploited for effective bioremediation of marine environments contaminated with both PAHs and HMs.

Environmental Hazard Screening of Heterocyclic Polyaromatic Hydrocarbons: Physicochemical Data and In Silico Models

Heterocyclic polyaromatic hydrocarbons (heterocyclic PAHs) are frequently found in the environment yet, compared to homocyclic PAHs, little attention has been paid to their environmental behavior and a comprehensive hazard assessment has not been undertaken. Surprisingly, the physicochemical data necessary to perform at least a screening-level assessment are also limited. To address this, we began by experimentally determining the physicochemical properties of heterocyclic PAHs, namely, water solubility (S_w), n-octanol-water partition coefficients (K_ow), and organic carbon-water partition coefficients (K_oc). The physicochemical data obtained in this study allowed for the development of clear structure-property relationships and evaluation of the predictive power of in silico models including conductor-like screening model for realistic solvation, the poly-parameter linear solvation energy relationship, and the quantitative structure-property relationship. Finally, heterocyclic and homocyclic PAHs were evaluated in terms of persistence, bioaccumulation, mobility, and toxicity to perform a screening-level comparative hazard assessment by integrating the data and evidence from multiple sources.

PAH depletion in weathered oil slicks estimated from modeled age-at-sea during the Deepwater Horizon oil spill

During time-periods oil slicks are in the marine environment (age-at-sea), weathering causes significant changes in composition and mass loss (depletion) of oil spill chemicals including the more toxic polycyclic aromatic hydrocarbons (PAHs). The goal of this study was to estimate the age-at-sea of weathered oil slicks using the oil spill module of the Connectivity Modeling System and to use this age to interpret PAH concentration measurements. Percent depletion (PD) for each measurement was computed as the percentage difference between the original and measured PAH concentration in the crude oil and weathered oil slicks, normalized upon the mass losses relative to hopane. Mean PD increased with estimated age-at-sea for all PAHs. Less PD was observed for alkylated than for parent PAHs, likely due to decreasing vapor pressure with increasing degree of alkylation. We conclude that estimated age-at-sea can be used to explain PAH depletion in weathered oil slicks. We propose PAH vapor pressure can be coupled with the model to expand capacity for predicting concentration distributions of individual parent and alkylated PAHs in weathered oil along the coastline. This new module will advance the science supporting oil spill response by providing more certain estimates of health risks from oil spills.

Shrimp-waste based dispersant as oil spill treating agent: Biodegradation of dispersant and dispersed oil

The emerging demand for the enhancement of biodegradation of persistent organic pollutants from marine oil spills using oil-treating agents to minimize the environmental impacts promotes the development of green dispersants. Shrimp waste is a potential raw material to generate green dispersants. The biodegradability of dispersed oil and dispersants themselves are key factors for the national consideration of the approval, stockpile, and usage of dispersants. However, it is unknown whether shrimp-waste-based dispersant (SWD) has high bioavailability or facilitates the biodegradation of dispersed oil. In this study, we tackled the biodegradation of oil dispersed by a purified SWD. Furthermore, the SWD biodegradability was evaluated by exploring the degradation genes via metagenomic sequencing, analyzing the enzymatic activities for dispersant biodegradation by molecular docking, and discussing the SWD toxicity. We discovered that the SWD facilitated the biodegradation of two crude oils (Alaska North Slope and Marine Fuel-No.6). The metagenomic analysis with molecular docking showed that fresh seawater had feasible enzymes to degrade the SWD to safety components. Additionally, the SWD was low toxic and high bioactive. The findings helped confirm that the purified SWD is an effective and eco-sustainable marine oil spill treating agent and tracked the biodegradation of dispersed oil and the SWD.

Recent advances in chemical and biological degradation of spilled oil: A review of dispersants application in the marine environment

Growing concerns over the risk of accidental releases of oil into the marine environment have emphasized our need to improve both oil spill preparedness and response strategies. Among the available spill response options, dispersants offer the advantages of breaking oil slicks into small oil droplets and promoting their dilution, dissolution, and biodegradation within the water column. Thus dispersants can reduce the probability of oil slicks at sea from reaching coastal regions and reduce their direct impact on mammals, sea birds and shoreline ecosystems. To facilitate marine oil spill response operations, especially addressing spill incidents in remote/Arctic offshore regions, an in-depth understanding of the transportation, fate and effects of naturally/chemically dispersed oil is of great importance. This review provides a synthesis of recent research results studies related to the application of dispersants at the surface and in the deep sea, the fate and transportation of naturally and chemically dispersed oil, and dispersant application in the Arctic and ice-covered waters. Future perspectives have been provided to identify the research gaps and help industries and spill response organizations develop science-based guidelines and protocols for the application of dispersants application.

A comprehensive petrochemical vulnerability index for marine fishes in the Gulf of Mexico

Oil and gas extraction activities occur across the globe, yet species-specific toxicological information on the biological and ecological impacts of exposure to petrochemicals is lacking for the vast majority of marine species. To help prioritize species for recovery, mitigation, and conservation in light of significant toxicological data gaps, a trait-based petrochemical vulnerability index was developed and applied to the more than 1700 marine fishes present across the entire Gulf of Mexico, including all known bony fishes, sharks, rays and chimaeras. Using life history and other traits related to likelihood of exposure, physiological sensitivity to exposure, and population resiliency, final calculated petrochemical vulnerability scores can be used to provide information on the relative sensitivity, or resilience, of marine fish populations across the Gulf of Mexico to oil and gas activities. Based on current knowledge of traits, marine fishes with the highest vulnerability scores primarily occur in areas of high petrochemical activity, are found at or near the surface, and have low reproductive turnover rates and/or highly specialized diet and habitat requirements. Relative population vulnerability scores for marine fishes can be improved with additional toxicokinetic studies, including those that account for the synergistic or additive effect of multiple stressors, as well as increased research on ecological and life history traits, especially for deep living species.

Natural attenuation of oil in marine environments: A review

Natural attenuation is an important process for oil spill management in marine environments. Natural attenuation affects the fate of oil by physical, chemical, and biological processes, which include evaporation, dispersion, dissolution, photo-oxidation, emulsification, oil particle aggregation, and biodegradation. This review examines the cumulative knowledge regarding these natural attenuation processes as well as their simulation and prediction using modelling approaches. An in-depth discussion is provided on how oil type, microbial community and environmental factors contribute to the biodegradation process. It describes how our understanding of the structure and function of indigenous oil degrading microbial communities in the marine environment has been advanced by the application of next generation sequencing tools. The synergetic and/or antagonist effects of oil spill countermeasures such as the application of chemical dispersants, in-situ burning and nutrient enrichment on natural attenuation were explored. Several knowledge gaps were identified regarding the synergetic and/or antagonistic effects of active response countermeasures on the natural attenuation/biodegradation process. This review highlighted the need for field data on both the effectiveness and potential detrimental effects of oil spill response options to support modelling and decision-making on their selection and application.

Bacteria, Fungi and Microalgae for the Bioremediation of Marine Sediments Contaminated by Petroleum Hydrocarbons in the Omics Era

Petroleum hydrocarbons (PHCs) are one of the most widespread and heterogeneous organic contaminants affecting marine ecosystems. The contamination of marine sediments or coastal areas by PHCs represents a major threat for the ecosystem and human health, calling for urgent, effective, and sustainable remediation solutions. Aside from some physical and chemical treatments that have been established over the years for marine sediment reclamation, bioremediation approaches based on the use of microorganisms are gaining increasing attention for their eco-compatibility, and lower costs. In this work, we review current knowledge concerning the bioremediation of PHCs in marine systems, presenting a synthesis of the most effective microbial taxa (i.e., bacteria, fungi, and microalgae) identified so far for hydrocarbon removal. We also discuss the challenges offered by innovative molecular approaches for the design of effective reclamation strategies based on these three microbial components of marine sediments contaminated by hydrocarbons.

Gill and liver transcriptomic responses of Achirus lineatus (Neopterygii: Achiridae) exposed to water-accommodated fraction (WAF) of light crude oil reveal an onset of hypoxia-like condition

Crude oil is one of the most widespread pollutants released into the marine environment, and native species have provided useful information about the effect of crude oil pollution in marine ecosystems. We consider that the lined sole Achirus lineatus can be a useful monitor of the effect of crude oil in the Gulf of Mexico (GoM) because this flounder species has a wide distribution along the GoM, and its response to oil components is relevant. The objective of this study was to compare the transcriptomic changes in liver and gill of adults lined sole fish (Achirus lineatus) exposed to a sublethal acute concentration of water-accommodated fraction (WAF) of light crude oil for 48 h. RNA-Seq was performed to assess the transcriptional changes in both organs. A total of 1073 differentially expressed genes (DEGs) were detected in gills; 662 (61.69%) were upregulated, and 411 (38.30%) were downregulated whereas in liver, 515 DEGs; 306 (59.42%) were upregulated, and 209 (40.58%) were downregulated. Xenobiotic metabolism and redox metabolism, along with DNA repair mechanisms, were activated. The induction of hypoxia-regulated genes and the generalized regulation of multiple signaling pathways support the hypothesis that WAF exposition causes a hypoxia-like condition.

Genetically engineered thermotolerant facultative anaerobes for high-efficient degradation of multiple hazardous nitroalkanes

Nitroalkanes are important industrial raw materials but also toxic pollutants, which are difficult to degrade once released into the environment. In this study, to significantly improve the degradation-efficiency of multiple nitroalkanes, a facultative anaerobe was genetically engineered, possible influencing factors and simulated application experiments of bioreactor were tested and evaluated. Among all engineered recombinants, the most effective strains NG-S1 (anaerobic) and NG-S2 (aerobic) displayed 2-fold and 2.8-fold final degradation rates higher than the wild type, respectively. Exogenous components, particularly those that enhance coenzyme synthesis, helped to increase the degradation rate, as the level of coenzymes affected full function of overexpressed nitroalkane oxidase. Importantly, simulated mixed-nitroalkane-wastewater bioreactor experiments proved excellent and sustainable degradation performance of the engineered strains for potential industrial applications. Collectively, these findings provide a promising thermophilic biological engineering platform and a new perspective for high-efficient and continuous environmental bioremediation of hazardous pollutants under aerobic and anaerobic conditions.

Physiological Responses of Fish to Oil Spills

Millions of tons of oil are spilled in aquatic environments every decade, and this oil has the potential to greatly impact fish populations. Here, we review available information on the physiological effects of oil and polycyclic aromatic hydrocarbons on fish. Oil toxicity affects multiple biological systems, including cardiac function, cholesterol biosynthesis, peripheral and central nervous system function, the stress response, and osmoregulatory and acid-base balance processes. We propose that cholesterol depletion may be a significant contributor to impacts on cardiac, neuronal, and synaptic function as well as reduced cortisol production and release. Furthermore, it is possible that intracellular calcium homeostasis-a part of cardiotoxic and neuronal function that is affected by oil exposure-may be related to cholesterol depletion. A detailed understanding of oil impacts and affected physiological processes is emerging, but knowledge of their combined effects on fish in natural habitats is largely lacking. We identify key areas deserving attention in future research.

Quantitative analysis of PAH compounds in DWH crude oil and their effects on Caenorhabditis elegans germ cell apoptosis, associated with CYP450s upregulation

The Deepwater Horizon (DWH) oil spill marked the largest environmental oil spill in human history, where it was estimated a large amount of the polycyclic aromatic hydrocarbons (PAHs) were released with crude oil into the environment. In this study, common PAH compounds were quantitatively determined in crude oil from the DWH spill by gas chromatography-mass spectroscopy (GC-MS). Twelve PAH compounds were identified and quantified from a 100× dilution of DWH crude oil: naphthalene (7800 ng/mL), acenaphthylene (590 ng/mL), acenaphtehen (540 ng/mL), fluorene (2550 ng/mL), phenanthrene (2910 ng/mL), anthracene (840 ng/mL), fluoranthene (490 ng/mL), pyrene (290 ng/mL), benzo(k) fluoranthene (1050 ng/mL), benzo(b)fluoranthene (1360 ng/mL), dibenz(a,h)anthracene (2560 ng/mL), and benzo(g, h, i) perylene (630 ng/mL). Toxicity assays using the nematode, Caenorhabditis elegans (C. elegans), indicated a single PAH compound naphthalene, exposure increased C. elegans germ cell apoptosis which may adversely affect progeny reproduction. The number of apoptotic germ cells significantly increased from 1.4 to 2.5 when worms were treated with 10 μg/mL of naphthalene and from 1.3 to 2.5 and 3.5 cells in presence of 1 μg/mL and 5 μg/mL of benzo(a)pyrene, respectively. Five CYP450 genes (CYP14A3, CYP35A1, CYP35A2, CYP35A5, and CYP35C1) were significantly upregulated following 500× dilution of dispersed crude oil exposure (p < 0.05). These results suggest that CYP450s may play a role in bioactivation of PAHs in crude oil, resulting in DNA damage related germ cell apoptosis.

Beyond Thresholds: A Holistic Approach to Impact Assessment Is Needed to Enable Accurate Predictions of Environmental Risk from Oil Spills

The risk assessment for the environmental impact of oil spills in Australia is often conducted in part using a combination of spill mapping and toxicological thresholds derived from laboratory studies. While this process is useful in planning operational responses, such as where to position equipment stockpiles and whether to disperse oil, and can be used to identify areas near the spill site where impacts are likely to occur, it cannot accurately predict the environmental consequences of an oil spill or the ecosystem recovery times. Evidence of this disconnect between model predictions and observed impacts is the lack of a profound effect of the Deepwater Horizon wellhead blowout on recruitment to fisheries in the northern Gulf of Mexico, contrary to the predictions made in the Natural Resources Damage Assessment and despite the occurrence of impacts of the spill on marine mammals, marshes, and deep water ecosystems. The incongruity between predictions made with the current approach using threshold monitoring and impacts measured in the field results from some of the assumptions included in the oil spill models. The incorrect assumptions include that toxicity is acute, results from dissolved phase exposure, and would be readily reversible. The toxicity tests from which threshold models are derived use members of the ecosystem that are easily studied in the lab but may not represent the ecosystem as a whole. The test species are typically highly abundant plankton or planktonic life stages, and they have life histories that account for rapid changes in environmental conditions. As a consequence, these organisms recover quickly from an oil spill. The interdependence of ecosystem components, including the reliance of organisms on their microbiomes, is often overlooked. Additional research to assess these data gaps conducted using economically and ecologically relevant species, especially in Australia and other understudied areas of the world, and the use of population dynamic models, will improve the accuracy of environmental risk assessment for oil spills. Integr Environ Assess Manag 2020;16:813-830. © 2020 SETAC.

Oil leakage induces changes in microbiomes of deep-sea sediments of Campos Basin (Brazil)

The Campos Basin (100,000 km²) is located on the continental shelf of southeastern Brazil. Despite the significant oil and gas industrial activities underway in the Campos Basin, scarce information is available regarding the hydrocarbon contents and microbial communities in the deep-sea sediments. To gain new insights on these aspects, we first obtained deep-sea sediment samples with different degrees of oil exposure. We obtained samples from a seabed fissure (N = 28), surroundings (250 m to 500 m from the fissure; N = 24), and a control area (N = 4). We used shotgun metagenomics to characterize the taxonomic and metabolic diversity and analyzed biogeochemical parameters (metal and oil concentration) of all samples. The high levels of unresolved complex mixture of hydrocarbons in the fissure indicate a potentially recent petrogenic contribution in these sediments. The fissure area was found to have a higher abundance of hydrocarbonoclastic bacterial genera and hydrocarbon degradation genes. These bacteria may be used as biosensors of sediment contamination. The effects of oil contamination, mainly around the fissure, are less clear at 250 m and 500 m, suggesting that the surroundings may not have been heavily affected by the oil leakage. Our study demonstrates that metagenomics can disclose biosensors for environmental monitoring.

Formation and fate of oil-related aggregates (ORAs) in seawater at different temperatures

In this study, the formation and fate of oil-related aggregates (ORAs) from chemically dispersed oil in seawater (SW) were investigated at different temperatures (5 °C, 13 °C, 20 °C). Experiments in natural SW alone, and in SW amended with typical marine snow constituents (phytoplankton and mineral particles), showed that the presence of algae stimulated the formation of large ORAs, while high SW temperature resulted in faster aggregate formation. The ORAs formed at 5 °C and 13 °C required mineral particles for sinking, while the aggregates also sank in the absence of mineral particles at 20°. Early in the experimental periods, oil compound accumulation in ORAs was faster than biodegradation, particularly in aggregates with algae, followed by rapid biodegradation. High abundances of bacteria associated with hydrocarbon biodegradation were determined in the ORAs, together with algae-associated bacteria, while clustering analyses showed separation between bacterial communities in experiments with oil alone and oil with algae/mineral particles.

Bacterial motility enhances adhesion to oil droplets

Adhesion of bacteria to liquid-liquid interfaces can play a role in the biodegradation of dispersed hydrocarbons and in biochemical and bioprocess engineering. Whereas thermodynamic factors underpinning adhesion are well studied, the role of bacterial activity on adhesion is less explored. Here, we show that bacterial motility enhances adhesion to surfactant-decorated oil droplets dispersed in artificial sea water. Motile Halomonas titanicae adhered to hexadecane droplets stabilized with dioctyl sodium sulfosuccinate (DOSS) more rapidly and at greater surface densities compared to nonmotile H. titanicae, whose flagellar motion was arrested through addition of a proton uncoupler. Increasing the concentration of DOSS reduced the surface density of both motile and nonmotile bacteria as a result of the reduced interfacial tension.

Shell-by-Shell Functionalization of Inorganic Nanoparticles

The current state of the hierarchical chemical functionalization of inorganic nanoparticles (NPs) by shell-by-shell (SbS)-assembly of organic layers around the NP cores is summarized. This supramolecular functionalization concept is based on two steps: 1) the covalent grafting of a first ligand-shell consisting of, for example, long chain phosphonic acids and 2) the noncovalent interdigitation of amphiphiles forming the second ligand shell. The latter process is guaranteed predominantly by solvophobic interactions. These highly order organic-inorganic hybrid architectures are currently an emerging field at the interface of synthetic chemistry, nanotechnology, and materials science. The doubly functionalized NPs display tunable materials properties, such a controlled dispersibility and stability in various solvents, highly efficient trapping of guest molecules in between the ligand shells (water cleaning) as well as compartmentalization and modification of electronic interactions between photoactive components integrated in such complex nano-architectures. Such SbS-functionalized NPs have a high potential as water-cleaning materials and also some first prototype applications as biomedicinal therapeutics have been presented.

A data-driven framework for defining stages of oil weathering

Oil weathering is often described subjectively after a spill. Adjectives like "moderate" and "severe" help define the extent of oil loss but fail to communicate quantitatively and reproducibly the degree of weathering. The use of subjective weathering terms often leads to misperceptions about persistence and toxicity of oil residues in the environment. The weathering of MC252 oil from the Deepwater Horizon spill started immediately after release during the 1500-m ascent to the sea surface and continued as it was transported on the surface and reached the shoreline. Weathering processes included evaporation, dissolution, photo-degradation, and biodegradation, among others. With extensive sample collection and detailed chemistry and source fingerprinting analyses, the Deepwater Horizon data provide a unique opportunity to evaluate weathering processes semi-quantitatively. An objective method of defining the degree of oil weathering is developed based on the detailed chemical results for over 700 MC252 oil samples from the environment.

The southern Gulf of Mexico: A baseline radiocarbon isoscape of surface sediments and isotopic excursions at depth

The southern Gulf of Mexico (sGoM) is home to an extensive oil recovery and development infrastructure. In addition, the basin harbors sites of submarine hydrocarbon seepage and receives terrestrial inputs from bordering rivers. We used stable carbon, nitrogen, and radiocarbon analyses of bulk sediment organic matter to define the current baseline isoscapes of surface sediments in the sGoM and determined which factors might influence them. These baseline surface isoscapes will be useful for accessing future environmental impacts. We also examined the region for influence of hydrocarbon deposition in the sedimentary record that might be associated with hydrocarbon recovery, spillage and seepage, as was found in the northern Gulf of Mexico (nGoM) following the Deepwater Horizon (DWH) oil spill in 2010. In 1979, the sGoM experienced a major oil spill, Ixtoc 1. Surface sediment δ13C values ranged from -22.4‰ to -19.9‰, while Δ14C values ranged from -337.1‰ to -69.2‰. Sediment δ15N values ranged from 2.8‰ to 7.2‰, while the %C on a carbonate-free basis ranged in value of 0.65% to 3.89% and %N ranged in value of 0.09% to 0.49%. Spatial trends for δ13C and Δ14C were driven by water depth and distance from the coastline, while spatial trends for δ15N were driven by location (latitude and longitude). Location and distance from the coastline were significantly correlated with %C and %N. At depth in two of twenty (10%) core profiles, we found negative δ13C and Δ14C excursions from baseline values in bulk sedimentary organic material, consistent with either oil-residue deposition or terrestrial inputs, but likely the latter. We then used 210Pb dating on those two profiles to determine the time in which the excursion-containing horizons were deposited. Despite the large spill in 1979, no evidence of hydrocarbon residue remained in the sediments from this specific time period.

Impacts of dibenzopyrenes on bacterial community isolated from Gulf of Mexico sediment

The presence of polycyclic aromatic hydrocarbons (PAHs) in marine environments as a result of contamination is an environmental concern, especially in regions where oil spills such as the Deepwater Horizon have occurred. While numerous PAHs have been studied for their effects on microbes, the family of dibenzopyrenes has yet to be investigated. In this preliminary study, the impacts of these molecules on the community structure of a bacterial consortium isolated from oil‐impacted Gulf of Mexico sediment were examined using high‐throughput sequencing, demonstrating intriguing negative impacts on species diversity and abundance. While no measurable degradation of the dibenzopyrenes was observed after 28‐day incubation, the abundance of known oil‐degrading bacteria from orders such as Oceanospirillales, Caulobacterales, Sphingomonadales, and Nitrosococcales were shown to be enhanced. Of the five isomers of dibenzopyrene studied, dibenzo[a,h]pyrene supported the fewer number of microbial species suggesting the isomer was more toxic compared to the other isomers.

Bacteria forming drag-increasing streamers on a drop implicates complementary fates of rising deep-sea oil droplets

Competing time scales involved in rapid rising micro-droplets in comparison to substantially slower biodegradation processes at oil-water interfaces highlights a perplexing question: how do biotic processes occur and alter the fates of oil micro-droplets (<500 μm) in the 400 m thick Deepwater Horizon deep-sea plume? For instance, a 200 μm droplet traverses the plume in ~48 h, while known biodegradation processes require weeks to complete. Using a microfluidic platform allowing microcosm observations of a droplet passing through a bacterial suspension at ecologically relevant length and time scales, we discover that within minutes bacteria attach onto an oil droplet and extrude polymeric streamers that rapidly bundle into an elongated aggregate, drastically increasing drag that consequently slows droplet rising velocity. Results provide a key mechanism bridging competing scales and establish a potential pathway to biodegradation and sedimentations as well as substantially alter physical transport of droplets during a deep-sea oil spill with dispersant.

Mesocosm experiments to better understand hydrocarbon half-lives for oil and oil dispersant mixtures

Concerns on the timing and processes associated with petroleum degradation were raised after the use of Corexit during the Deepwater Horizon oil spill. There is a lack of understanding of the removal of oil associated with flocculate materials to the sediment. Mesocosm studies employing coastal and open-ocean seawater from the Gulf of Mexico were undertaken to examine changes in oil concentration and composition with time. The water accommodated fractions (WAF) and chemically enhanced WAF (CEWAF) produced using Macondo surrogate oil and Corexit were followed over 3–4 days in controlled environmental conditions. Environmental half-lives of estimated oil equivalents (EOE), polycyclic aromatic hydrocarbons (PAH), n-alkanes (C10-C35), isoprenoids pristane and phytane, and total petroleum hydrocarbons (TPH) were determined. EOE and PAH concentrations decreased exponentially following first-order decay rate kinetics. WAF, CEWAF and DCEWAF (a 10X CEWAF dilution) treatments half-lives ranged from 0.9 to 3.2 days for EOE and 0.5 to 3.3 days for PAH, agreeing with estimates from previous mesocosm and field studies. The aliphatic half-lives for CEWAF and DECWAF treatments ranged from 0.8 to 2.0 days, but no half-life for WAF could be calculated as concentrations were below the detection limits. Biodegradation occurred in all treatments based on the temporal decrease of the nC₁₇/pristane and nC₁₈/phytane ratios. The heterogeneity observed in all treatments was likely due to the hydrophobicity of oil and weathering processes occurring at different rates and times. The presence of dispersant did not dramatically change the half-lives of oil. Comparing degradation of oil alone as well as with dispersant present is critical to determine the fate and transport of these materials in the ocean.

Assessment for oil spill chemicals: Current knowledge, data gaps, and uncertainties addressing human physical health risk

Limited models are available to estimate human physical health risks (e.g., probability of outcomes such as lung disease, cancer, skin disease) from exposure to chemicals resulting from oil spills that may occur offshore and later impact coastline spills. An approach is presented to assess physical health risks from oil spills that involves establishing a platform capable of assessing aggregate health risk (via inhalation, ingestion, and dermal exposure routes). Gaps include the need to develop models reflecting oil spill concentration distributions given the influence from environmental, physical, biological and chemical factors. Human activities need to be quantified for different populations including emergency response workers, fishermen, shellfish consumers, and children who play at beaches that may be impacted by oil spills. Work is also needed in developing comprehensive toxicological profiles for the majority of chemicals - including dispersants found in oil spills - and to estimate toxicity from mixtures.

Petroleum hydrocarbons in semipermeable membrane devices deployed in the Northern Gulf of Mexico and Florida keys following the Deepwater Horizon incident

The Deepwater Horizon (DWH) oil spill from April to July of 2010 contaminated Gulf of Mexico waters through release of an estimated 4.1 × 10⁶ barrels of oil. Beginning in June of 2010, semipermeable membrane devices (SPMDs) were deployed near areas with sensitive marine habitats (Alabama Alps and Western Shelf) potentially exposed to that oil. Elevated TPAH50 concentrations, flux rates and similarity of histograms and diagnostic ratios for polycyclic aromatic hydrocarbons (PAH) from SPMDs to weathered floating oil collected during the DWH spill indicates the Alabama Alps habitats were affected. While not affected by oil from the DWH spill, the temporal pattern of PAH contamination of SPMDs deployed near the Western Shelf between July 2010 and March 2011 could indicate prevailing currents affected contaminant transport to the Western Shelf Area (East and West Flower Garden, Sonnier, and Stetson Banks) from non-DWH sources, including oil and gas exploration, shipping, and Mississippi River effluent.

The interplay of extracellular polymeric substances and oil/Corexit to affect the petroleum incorporation into sinking marine oil snow in four mesocosms

Large amounts of oil containing mucous-like marine snow formed in surface waters adjacent to the Deepwater Horizon spill that was implicated in oil delivery to the seafloor. However, whether chemical dispersants that were used increased or decreased the oil incorporation and sedimentation efficiency, and how exopolymeric substances (EPS) are involved in this process remains unresolved. To investigate the microbial responses to oil and dispersants in different oceanic settings, indicated by EPS production, petro- and non-petro carbon sedimentation, four mesocosm (M) experiments were conducted: 1) nearshore seawater with a natural microbial consortia (M2); 2) offshore seawater with f/20 nutrients (M3); 3) coastal seawater with f/20 nutrients (M4); 4) nearshore seawater with a natural microbial consortia for a longer duration (M5). Four treatments were conducted in M2, M3 and M4 whereas only three in M5: 1) a water accommodated fraction of oil (WAF), 2) a chemically-enhanced WAF prepared with Corexit (CEWAF, not in M5), 3) a 10-fold diluted CEWAF (DCEWAF); and 4) controls. Overall, oil and dispersants input, nutrient and microbial biomass addition enhanced EPS production. Dispersant addition tended to induce the production of EPS with higher protein/carbohydrate (P/C) ratios, irrespective of oceanic regions. EPS produced in M4 was generally more hydrophobic than that produced in M3. The P/C ratio of EPS in both the aggregate and the colloidal fraction was a key factor that regulated oil contribution to sinking aggregates, based on the close correlation with %petro-carbon in these fractions. In the short term (4-5 days), both the petro and non-petro carbon sedimentation efficiencies showed decreasing trends when oil/dispersants were present. In comparison, in the longer-term (16 days), petro-carbon sedimentation efficiency was less influenced by dispersants, possibly due to biological and physicochemical changes of the components of the oil-EPS-mineral phase system, which cooperatively controlled the sinking velocities of the aggregates.

A new ecology-on-a-chip microfluidic platform to study interactions of microbes with a rising oil droplet

Advances in microfluidics technology has enabled many discoveries on microbial mechanisms and phenotypes owing to its exquisite controls over biological and chemical environments. However, emulating accurate ecologically relevant flow environments (e.g. microbes around a rising oil droplet) in microfluidics remains challenging. Here, we present a microfluidic platform, i.e. ecology-on-a-chip (eChip), that simulates environmental conditions around an oil droplet rising through ocean water as commonly occurred during a deep-sea oil spill or a natural seep, and enables detailed observations of microbe-oil interactions at scales relevant to marine ecology (i.e. spatial scales of individual bacterium in a dense suspension and temporal scales from milliseconds to weeks or months). Owing to the unique capabilities, we present unprecedented observations of polymeric microbial aggregates formed on rising oil droplets and their associated hydrodynamic impacts including flow fields and momentum budgets. Using the platform with Pseudomonas, Marinobacter, and Alcarnivorax, we have shown that polymeric aggregates formed by them present significant differences in morphology, growth rates, and hydrodynamic impacts. This platform enables us to investigate unexplored array of microbial interactions with oil drops.

Modulation of microbial growth and enzymatic activities in the marine environment due to exposure to organic contaminants of emerging concern and hydrocarbons

Organic pollutants are continuously being introduced in seawater with uncharacterized impacts on the engines of the marine biogeochemical cycles, the microorganisms. The effects on marine microbial communities were assessed for perfluoroalkyl substances, organophosphate esters flame retardants and plasticizers, polycyclic aromatic hydrocarbons, and n-alkanes. Dose-response experiments were performed at three stations and at three depths in the NW Mediterranean with contrasted nutrient and pollutant concentrations. In these experiments, the microbial growth rates, the abundances of the main bacterial groups, measured by Catalyzed Reporter Deposition Fluorescence In Situ Hybridization (CARD-FISH), and extracellular enzymatic activities, were quantified. Increasing concentrations of organic pollutants (OPs) promoted different responses in the communities that were compound, organism and nutrient availability (trophic status). The largest differences between OP treatments and controls in the growth rates of both heterotrophic and phototrophic microbial groups were observed in seawater from the deep chlorophyll maxima. Furthermore, there was a compound specific stimulation of different extracellular enzymatic activities after the exposure to OPs. Our results revealed that marine microbial communities reacted not only to hydrocarbons, known to be used as a carbon source, but also to low concentrations of organic pollutants of emerging concern in a complex manner, reflecting the variability of various environmental variables. Multiple linear regressions suggested that organic pollutants modulated the bacterial growth and extracellular enzymatic activities, but this modulation was of lower magnitude than the observed pronounced response of the microbial community to nutrient availability.

Snow Amplification of Persistent Organic Pollutants at Coastal Antarctica

Many legacy and emerging persistent organic pollutants (POPs) have been reported in polar regions, and act as sentinels of global pollution. Maritime Antarctica is recipient of abundant snow precipitation. Snow scavenges air pollutants, and after snow melting, it can induce an unquantified and poorly understood amplification of concentrations of POPs. Air, snow, the fugacity in soils and snow, seawater and plankton were sampled concurrently from late spring to late summer at Livingston Island (Antarctica). Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) concentrations in snow and air were close to equilibrium. POPs in soils showed concentrations close to soil-air equilibrium or net volatilization depending on chemical volatility. Seawater-air fugacity ratios were highly correlated with the product of the snow-air partition coefficient and the Henry's law constant (K_SA H'), a measure of snow amplification of fugacity. Therefore, coastal seawater mirrored the PCB congener profile and increased concentrations in snowmelt due to snowpack releasing POPs to seawater. The influence of snowpack and glacier inputs was further evidenced by the correlation between net volatilization fluxes of PCBs and seawater salinity. A meta-analysis of K_SA, estimated as the ratio of POP concentrations in snow and air from previously reported simultaneous field measurements, showed that snow amplification is relevant for diverse families of POPs, independent of their volatility. We claim that the potential impact of atmospheric pollution on aquatic ecosystems has been under-predicted by only considering air-water partitioning, as snow amplification influences, and may even control, the POP occurrence in cold environments.

Effect of spatial origin and hydrocarbon composition on bacterial consortia community structure and hydrocarbon biodegradation rates

Oil reserves in deep-sea sediments are currently subject to intense exploration, with associated risks of oil spills. Previous research suggests that microbial communities from deep-sea sediment (>1000m) can degrade hydrocarbons (HCs), but have a lower degradation ability than shallow (<200m) communities, probably due to in situ temperature. This study aimed to assess the effect of marine origin on microbial HC degradation potential while separating the influence of temperature, and to characterise associated HC-degrading bacterial communities. Microbial communities from 135 and 1000 m deep sediments were selectively enriched on crude oil at in situ temperatures and both consortia were subsequently incubated for 42 days at 20°C with two HC mixtures: diesel fuel or model oil. Significant HC biodegradation occurred rapidly in the presence of both consortia, especially of low molecular weight HCs and was concomitant with microbial community changes. Further, oil degradation was higher with the shallow consortium than with the deep one. Dominant HC-degrading bacteria differed based on both spatial origin of the consortia and supplemented HC types. This study provides evidence for influence of sediment spatial origin and HC composition on the selection and activity of marine HC-degrading bacterial communities and is relevant for future bioremediationdevelopments.

Metagenomics sheds light on the metabolic repertoire of oil-biodegrading microbes of the South Atlantic Ocean

Unplanned oil spills during offshore oil production are a serious problem for the industry and the marine environment. Here we assess the biodegradation potential of marine microorganisms from three water depths in the Campos Basin (South Atlantic Ocean): (i) 5 m (surface), (ii) ∼80 m (chlorophyll maximum layer), and (iii) ∼1200 m (near the bottom). After incubating seawater samples with or without crude oil for 52 days, we used metagenomics and classic microbiology techniques to analyze microbial abundance and diversity, and measured physical-chemical parameters to better understand biodegradation processes. We observed increased microbial abundance and concomitant decreases in dissolved oxygen and hydrocarbon concentrations, indicating oil biodegradation in the three water depths treatments within approximately 27 days. An increase in metagenomic sequences of oil-degrading archaea, fungi, and bacteria (Alcanivorax, Alteromonas, Colwellia, Marinobacter, and Pseudomonas) accompanied by a significant increase in metagenomic sequences involved in the degradation of aromatic compounds indicate that crude oil promotes the growth of microorganisms with oil degradation potential. The abundance of genes involved in biodegrading benzene, toluene, ethylbenzene, xylene, alkanes, and poly-aromatic hydrocarbons peaked approximately 3 days after oil addition. All 12 novel metagenome-assembled genomes contained genes involved in hydrocarbon degradation, indicating the oil-degrading potential of planktonic microbes in the Campos Basin.

"Candidatus Macondimonas diazotrophica", a novel gammaproteobacterial genus dominating crude-oil-contaminated coastal sediments

Modeling crude-oil biodegradation in sediments remains a challenge due in part to the lack of appropriate model organisms. Here we report the metagenome-guided isolation of a novel organism that represents a phylogenetically narrow (>97% 16S rRNA gene identity) group of previously uncharacterized, crude-oil degraders. Analysis of available sequence data showed that these organisms are highly abundant in oiled sediments of coastal marine ecosystems across the world, often comprising ~30% of the total community, and virtually absent in pristine sediments or seawater. The isolate genome encodes functional nitrogen fixation and hydrocarbon degradation genes together with putative genes for biosurfactant production that apparently facilitate growth in the typically nitrogen-limited, oiled environment. Comparisons to available genomes revealed that this isolate represents a novel genus within the Gammaproteobacteria, for which we propose the provisional name "Candidatus Macondimonas diazotrophica" gen. nov., sp. nov. "Ca. M. diazotrophica" appears to play a key ecological role in the response to oil spills around the globe and could be a promising model organism for studying ecophysiological responses to oil spills.

Petrocarbon evolution: Ramped pyrolysis/oxidation and isotopic studies of contaminated oil sediments from the Deepwater Horizon oil spill in the Gulf of Mexico

Hydrocarbons released during the Deepwater Horizon (DWH) oil spill weathered due to exposure to oxygen, light, and microbes. During weathering, the hydrocarbons' reactivity and lability was altered, but it remained identifiable as "petrocarbon" due to its retention of the distinctive isotope signatures (14C and 13C) of petroleum. Relative to the initial estimates of the quantity of oil-residue deposited in Gulf sediments based on 2010-2011 data, the overall coverage and quantity of the fossil carbon on the seafloor has been attenuated. To analyze recovery of oil contaminated deep-sea sediments in the northern Gulf of Mexico we tracked the carbon isotopic composition (13C and 14C, radiocarbon) of bulk sedimentary organic carbon through time at 4 sites. Using ramped pyrolysis/oxidation, we determined the thermochemical stability of sediment organic matter at 5 sites, two of these in time series. There were clear differences between crude oil (which decomposed at a lower temperature during ramped oxidation), natural hydrocarbon seep sediment (decomposing at a higher temperature; Δ14C = -912‰) and our control site (decomposing at a moderate temperature; Δ14C = -189‰), in both the stability (ability to withstand ramped temperatures in oxic conditions) and carbon isotope signatures. We observed recovery toward our control site bulk Δ14C composition at sites further from the wellhead in ~4 years, whereas sites in closer proximity had longer recovery times. The thermographs also indicated temporal changes in the composition of contaminated sediment, with shifts towards higher temperature CO2 evolution over time at a site near the wellhead, and loss of higher temperature CO2 peaks at a more distant site.

Inorganic nutrients have a significant, but minimal, impact on a coastal microbial community's response to fresh diluted bitumen

Microbes capable of degrading hydrocarbons in oil are present in low abundances in coastal waters, but quickly respond to oil following a spill. When estimating potential biodegradation rates in the laboratory, high concentrations of inorganic nutrients are often added to prevent nutrient limitation. In this study, we tested the short term response of coastal microbes to fresh diluted bitumen under varying nutrient conditions in a cold water regime. Total hydrocarbon concentrations changed minimally over five days; however, oil composition changed over time and the abundance of microbes increased in all treatments. Addition of phosphate, with or without nitrogen, resulted in rapid changes in community composition, but after three days treatments no longer differed. Nutrients were never depleted in any treatment suggesting that, even at low inorganic nutrient concentrations, microbial communities can quickly respond to hydrocarbons following a spill.

Petroleum hydrocarbon release behavior study in oil-sediment aggregates: turbulence intensity and chemical dispersion effect

This study investigated the effects of turbulence and oil dispersants on release of petroleum hydrocarbons in oil-sediment aggregates. A kinetic study showed that the static oil release process could be fitted to the first-order kinetics model. The oil concentration increased with increasing temperature and salinity, while remaining independent of pH. The dispersant desorption ability of petroleum hydrocarbons followed the sequence of: Tween 80 > Tween 85 > Span 80 > DOSS. In the presence of turbulence, the maximum release ratio was 40.28%. However, the combination of dispersants and turbulence had a smaller effect than turbulence alone. Furthermore, residual n-alkanes and PAHs in the sediments were analyzed. The results showed higher proportions of C₁₅–C₃₅ and 2–3 ring PAHs in residual oil. These results can help assess the fate and distribution of oil spills in marine environments.

This study investigated the effects of turbulence and oil dispersants on release of petroleum hydrocarbons in oil-sediment aggregates.

Reduced TCA cycle rates at high hydrostatic pressure hinder hydrocarbon degradation and obligate oil degraders in natural, deep-sea microbial communities

Petroleum hydrocarbons reach the deep-sea following natural and anthropogenic factors. The process by which they enter deep-sea microbial food webs and impact the biogeochemical cycling of carbon and other elements is unclear. Hydrostatic pressure (HP) is a distinctive parameter of the deep sea, although rarely investigated. Whether HP alone affects the assembly and activity of oil-degrading communities remains to be resolved. Here we have demonstrated that hydrocarbon degradation in deep-sea microbial communities is lower at native HP (10 MPa, about 1000 m below sea surface level) than at ambient pressure. In long-term enrichments, increased HP selectively inhibited obligate hydrocarbon-degraders and downregulated the expression of beta-oxidation-related proteins (i.e., the main hydrocarbon-degradation pathway) resulting in low cell growth and CO₂ production. Short-term experiments with HP-adapted synthetic communities confirmed this data, revealing a HP-dependent accumulation of citrate and dihydroxyacetone. Citrate accumulation suggests rates of aerobic oxidation of fatty acids in the TCA cycle were reduced. Dihydroxyacetone is connected to citrate through glycerol metabolism and glycolysis, both upregulated with increased HP. High degradation rates by obligate hydrocarbon-degraders may thus be unfavourable at increased HP, explaining their selective suppression. Through lab-scale cultivation, the present study is the first to highlight a link between impaired cell metabolism and microbial community assembly in hydrocarbon degradation at high HP. Overall, this data indicate that hydrocarbons fate differs substantially in surface waters as compared to deep-sea environments, with in situ low temperature and limited nutrients availability expected to further prolong hydrocarbons persistence at deep sea.

Salt marsh denitrification is impacted by oiling intensity six years after the Deepwater Horizon oil spill

Coastal salt marshes provide the valuable ecosystem service of removing anthropogenic nitrogen (N) via microbially-mediated denitrification. During the 2010 Deepwater Horizon (DWH) spill, oil exposure killed marsh plants in some regions and contributed to rapid compositional shifts in sediment microbial communities, which can impact ecosystem denitrification capacity. Within 3-5 years of the spill, plant biomass and microbial communities in some impacted marshes can recover to a new stable state. The objective of this study was to determine whether marsh recovery 6 years after the DWH oil spill results in subsequent recovery of denitrification capacity. We measured denitrification capacity (isotope pairing technique), microbial 16S rRNA gene composition, and denitrifier abundance (quantitative PCR) at sites subjected to light, moderate, and heavy oiling during the spill that were not targeted by any clean-up efforts. There were no differences in plant belowground biomass, sediment extractable NH₄⁺, inorganic nitrogen flux, 16S rRNA composition, 16S rRNA diversity, or denitrifier functional gene (nirS, norB, and nosZ) abundances associated with oiling status, indicating that certain drivers of ecosystem denitrification capacity have recovered or achieved a new stable state six years after the spill. However, on average, denitrification capacities at the moderately and heavily oiled sites were less than 49% of that of the lightly oiled site (27.7 ± 14.7 and 37.2 ± 24.5 vs 71.8 ± 33.8 μmol N m^-2 h^-1, respectively). The presence of heavily weathered oiled residue (matched and non-matched for MC252) had no effect on process rates or microbial composition. The loss of function at the moderately and heavily oiled sites compared to the lightly oiled site despite the comparable microbial and environmental factors suggests that oiling intensity plays a role in the long-term recovery of marsh ecosystem services.

Use of Electronic Noses in Seawater Quality Monitoring: A Systematic Review

Electronic nose (eNose) systems are particularly appreciated for their portability, usability, relative low cost, and real-time or near real-time response. Their application finds space in several domains, including environmental monitoring. Within this field, marine monitoring is of particular scientific relevance due to the fragility of this specific environment, daily threatened by human activities that can potentially bring to catastrophic and irreversible consequences on marine wildlife. Under such considerations, a systematic review, complying with the PRISMA guidelines, was conducted covering the period up to 15 October 2018, in PubMed, ScienceDirect, and Google Scholar. Despite the relatively low number of articles published on this specific topic and the heterogeneity of the technological approaches employed, the results obtained by the various groups highlight the positive contribution eNose has given and can provide in near future for the monitoring and safeguarding of this delicate environment.

Assessment of Shorebird Migratory Fueling Physiology and Departure Timing in Relation to Polycyclic Aromatic Hydrocarbon Contamination in the Gulf of Mexico

Shorebirds depend on staging sites in the Gulf of Mexico that are frequently subject to pollution by oil and its toxic constituents, polycyclic aromatic hydrocarbons (PAHs). It was hypothesized that PAH contamination lowers staging site quality for migratory shorebirds, with consequences for fueling and departure timing. Sediment total PAH concentrations were measured at six staging sites along the Texas and Louisiana Gulf Coast. Sites in Louisiana were expected to have higher total PAH concentrations as they were more heavily impacted by the Deepwater Horizon oil spill. From 2015 to 2017, 165 Sanderling ( Calidris alba) and 55 Red knots ( C. canutus) were captured at these same sites during their northward migration (late April to mid May). Mass, body morphometrics, and plasma metabolite measurements were taken to determine fuel loads and fueling rates, and a subset of birds (120 Sanderling and 39 Red knots) received a coded radio tag to determine departure dates using the Motus telemetry array. Compared to Texas sites, sediment in Louisiana had higher total PAH concentrations, dominated by heavier 6 ring indeno[1,2,3- cd]pyrene (48%). Plasma metabolite profiles suggested that fueling rates for Sanderling, but not Red knots, tended to be lower in Louisiana, and both species departed later than the study average from Louisiana. However, multiple factors, including migration patterns, food supply, and other contaminants, also likely influenced fueling and departures. PAH contamination in the Gulf of Mexico remains an ongoing issue that may be impacting the staging site quality and migration timing of long-distance migratory birds.

Adhesion of Marinobacter hydrocarbonoclasticus to Surfactant-Decorated Dodecane Droplets

We investigate the effect of interfacial properties on the adhesion of bacteria at oil/water interfaces using confocal microscopy. Surfactant-decorated dodecane droplets of diameter 20-60 μm are generated using a coflow microfluidic device, introduced into an aqueous saline suspension of Marinobacter hydrocarbonoclasticus bacteria, and imaged in 3-D over time. Using image analysis algorithms, we determine the number of bacteria adhering at oil/water interfaces over time in the presence of dioctyl sodium succinate (DOSS), a component of the dispersant used in oil-spill recovery. The adsorption of bacteria at the oil/water interface follows Langmuir first-order kinetics for all droplet sizes, with the greatest areal number density of bacteria adhered to the smallest droplets. We vary the surfactant type [DOSS, dicyclohexyl sodium sulfosuccinate, dibutyl sodium sulfosuccinate, cetyltrimethylammonium bromide, and Tween 20] and concentration and examine the effects on long-time adhesion of bacteria. For a fixed droplet size, the areal density of bacteria at the interface decreases with increasing surfactant concentration because of a reduction in oil/water interfacial tension that increases the free energy of adhesion of the bacterium.

A critical review of marine snow in the context of oil spills and oil spill dispersant treatment with focus on the Deepwater Horizon oil spill

Natural marine snow (NMS) is defined as the "shower" of particle aggregates formed by processes that occur in the world's oceans, consisting of macroscopic aggregates of detritus, living organisms and inorganic matter. Recent studies from the Deepwater Horizon oil spill suggest that marine snow is also formed in association with oil spills and was an important factor for the transport of oil to the seabed. This review summarizes the research and literature on MS, mainly from the DWH oil spill, with a focus on the relation between the use of oil spill dispersants and the formation and fate of oil-related marine snow (ORMS). Studies are still required to determine ORMS processes at oil concentrations as relevant as possible for chemically dispersed oil.

Degradation of the recalcitrant oil spill components anthracene and pyrene by a microbially driven Fenton reaction

Oil spill components include a range of toxic saturated, aromatic and polar hydrocarbons, including pyrene and anthracene. Such contaminants harm natural ecosystems, adversely affect human health and negatively impact tourism and the fishing industries. Current physical, chemical and biological remediation technologies are often unable to completely remove recalcitrant oil spill components, which accumulate at levels greater than regulatory limits set by the Environmental Protection Agency. In the present study, a microbially driven Fenton reaction, previously shown to produce hydroxyl (HO • ) radicals that degrade chlorinated solvents and associated solvent stabilizers, was also found to degrade source zone concentrations of the oil spill components, pyrene (10 μM) and anthracene (1 μM), at initial rates of 0.82 and 0.20 μM h -1 , respectively. The pyrene- and anthracene-degrading Fenton reaction was driven by the metal-reducing facultative anaerobe Shewanella oneidensis exposed to alternating aerobic and anaerobic conditions in the presence of Fe(III). Similar to the chlorinated solvent degradation system, the pyrene and anthracene degradation systems required neither the continual supply of exogenous H 2 O 2 nor UV-induced Fe(III) reduction to regenerate Fe(II). The microbially driven Fenton reaction provides the foundation for the development of alternate ex situ and in situ oil and gas spill remediation technologies.

An Electronic Nose Based Method for the Discrimination of Weathered Petroleum-Derived Products

In recent years pollution due to hydrocarbon spills has increased markedly as a result of the numerous advances in technologies and industrial processes. Anthropogenic activities (accidental or illegal) are responsible for most of these incidents. In some cases, the spills are not detected at the moment they occur and the contaminants are subjected to different degradation phenomena that may change the chemical composition of the hydrocarbon over time. An incorrect or ineffective identification of the spill could lead to significant consequences, bearing in mind that most spills are hazardous to the environment. In the present work the capacity of the analytical technique based on the Electronic Nose (eNose) combined with chemometrics in the identification and discrimination of different weathered petroleum-derived products (PDPs) was studied. Different volumes (40 &mu;L and 80 &mu;L) of PDPs (gasoline, diesel, and paraffin) were poured onto different supports (wood, cork, paper, and cotton sheet) and subjected to a natural weathering process by evaporation for one month. The porosity of the support was also studied. The application of linear discriminant analysis allowed the full discrimination of the samples according to the presence/absence of PDP and a 97.7% of correct discrimination of the different PDPs regardless of the weathering time, support or volume used. The results show that the system is capable of detecting and discriminating the presence of petroleum-derived products in any of the situations studied.