Biodegradation of marine oil spills in the Arctic with a Greenland perspective

Evaluation of surfactant-aided polycyclic aromatic hydrocarbon biodegradation by molecular docking and molecular dynamic simulation in the marine environment

Marine oil spills directly cause polycyclic aromatic hydrocarbons (PAHs) pollution and affect marine organisms due to their toxic property. Chemical and bio-based dispersants composed of surfactants and solvents are considered effective oil spill-treating agents. Dispersants enhance oil biodegradation in the marine environment by rapidly increasing their solubility in the water column. However, the effect of dispersants, especially surfactants, on PAHs degradation by enzymes produced by microorganisms has not been studied at the molecular level. The role of the cytochrome P450 (CYP) enzyme in converting contaminants into reactive metabolites during the biodegradation process has been evidenced, but the activity in the presence of surfactants is still ambiguous. Thus, this study focused on the evaluation of the impact of chemical and bio-surfactants (i.e., Tween 80 (TWE) and Surfactin (SUC)) on the biodegradation of naphthalene (NAP), chrysene (CHR), and pyrene (PYR), the representative components of PAHs, with CYP enzyme from microalgae Parachlorella kessleri using molecular docking and molecular dynamics (MD) simulation. The molecular docking analysis revealed that PAHs bound to residues at the CYP active site through hydrophobic interactions for biodegradation. The MD simulation showed that the surfactant addition changed the enzyme conformation in the CYP-PAH complexes to provide more interactions between the enzyme and PAHs. This led to an increase in the enzyme's capability to degrade PAHs. Binding free energy (ΔG‌‌Bind) calculations confirmed that surfactant treatment could enhance PAHs degradation by the enzyme. The SUC gave a better result on NAP and PYR biodegradation based on ΔG‌‌Bind, while TWE facilitated the biodegradation of CHR. The research outputs could greatly facilitate evaluating the behaviors of oil spill-treating agents and oil spill response operations in the marine environment.

Autochthonous psychrophilic hydrocarbonoclastic bacteria and its ecological function in contaminated cold environments

Petroleum hydrocarbon (PH) pollution has mostly been caused by oil exploration, extraction, and transportation activities in colder regions, particularly in the Arctic and Antarctic regions, where it serves as a primary source of energy. Due to the resilience feature of nature, such polluted environments become the realized ecological niches for a wide community of psychrophilic hydrocarbonoclastic bacteria (PHcB). In contrast, to other psychrophilic species, PHcB is extremely cold-adapted and has unique characteristics that allow them to thrive in greater parts of the cold environment burdened with PHs. The stated group of bacteria in its ecological niche aids in the breakdown of litter, turnover of nutrients, cycling of carbon and nutrients, and bioremediation. Although such bacteria are the pioneers of harsh colder environments, their growth and distribution remain under the influence of various biotic and abiotic factors of the environment. The review discusses the prevalence of PHcB community in colder habitats, the metabolic processes involved in the biodegradation of PH, and the influence of biotic and abiotic stress factors. The existing understanding of the PH metabolism by PHcB offers confirmation of excellent enzymatic proficiency with high cold stability. The discovery of more flexible PH degrading strategies used by PHcB in colder environments could have a significant beneficial outcome on existing bioremediation technologies. Still, PHcB is least explored for other industrial and biotechnological applications as compared to non-PHcB psychrophiles. The present review highlights the pros and cons of the existing bioremediation technologies as well as the potential of different bioaugmentation processes for the effective removal of PH from the contaminated cold environment. Such research will not only serve to investigate the effects of pollution on the basic functional relationships that form the cold ecosystem but also to assess the efficacy of various remediation solutions for diverse settings and climatic conditions.

EOS - Environment & Oil Spill Response. An analytic tool for environmental assessments to support oil spill response planning: Framework, principles, and proof-of-concept by an Arctic example

The Environment & Oil Spill Response tool (EOS), supports oil spill response planning and decision making. This tool is developed on a research basis, and is an index based, generic and open-source analytic tool, which environmentally can optimise the choice of oil spill response methods for a given spill situation and for a given sea area with respect to environment and nature. The tool is not linked to a particular oil spill simulation model, although it is recommended using oil spill simulation models to have detailed data available for the analysis. The EOS tool consists of an Excel workbook with formulas for calculations and scores followed by screening through decision trees. As case for the EOS tool proof-of-concept, the area of Store Hellefiskebanke, West Greenland, is used. The tool can be downloaded from the Aarhus University home page as a free-of-charge application and is accompanied by a handbook for guidance.

The effect of hydrostatic pressure on the activity and community composition of hydrocarbon-degrading bacteria in Arctic seawater

IMPORTANCE

Increased ship traffic in the Arctic region raises the risk of oil spills. With an average sea depth of 1,000 m, there is a growing concern over the potential release of oil sinking in the form of marine oil snow into deep Arctic waters. At increasing depth, the oil-degrading community is exposed to increasing hydrostatic pressure, which can reduce microbial activity. However, microbes thriving in polar regions may adapt to low temperature by modulation of membrane fluidity, which is also a well-known adaptation to high hydrostatic pressure. At mild hydrostatic pressures up to 8-12 MPa, we did not observe an altered microbial activity or community composition, whereas comparable studies using deep-sea or sub-Arctic microbial communities with in situ temperatures of 4-5°C showed pressure-induced effects at 10-15 MPa. Our results suggest that the psychrophilic nature of the underwater microbial communities in the Arctic may be featured by specific traits that enhance their fitness at increasing hydrostatic pressure.

Does Caulerpa prolifera with Its Bacterial Coating Represent a Promising Association for Seawater Phytoremediation of Diesel Hydrocarbons?

Anthropic diesel-derived contamination of Mediterranean coastal waters is of great concern. Nature-based solutions such as phytoremediation are considered promising technologies to remove contaminants from marine environments. The aim of this work was to investigate the tolerance of the Mediterranean autochthonous seaweed Caulerpa prolifera (Forsskal) Lamouroux to diesel fuel and its hydrocarbon degradation potential. Changes in C. prolifera traits, including its associated bacterial community abundance and structure, were determined by fluorescence microscopy and next-generation sequencing techniques. Thalli of C. prolifera artificially exposed to increasing concentration of diesel fuel for 30 days and thalli collected from three natural sites with different levels of seawater diesel-derived hydrocarbons were analysed. Gas chromatography was applied to determine the seaweed hydrocarbon degradation potential. Overall, in controlled conditions the lower concentration of diesel (0.01%) did not affect C. prolifera survival and growth, whereas the higher concentration (1%) resulted in high mortality and blade damages. Similarly, only natural thalli, collected at the most polluted marine site (750 mg L^-1), were damaged. A higher abundance of epiphytic bacteria, with a higher relative abundance of Vibrio bacteria, was positively correlated to the health status of the seaweed as well as to its diesel-degradation ability. In conclusion, C. prolifera tolerated and degraded moderate concentrations of seawater diesel-derived compounds, especially changing the abundance and community structure of its bacterial coating. The protection and exploitation of this autochthonous natural seaweed-bacteria symbiosis represents a useful strategy to mitigate the hydrocarbon contamination in moderate polluted Mediterranean costal environments.

Green dispersants for oil spill response: A comprehensive review of recent advances

Green dispersants are so-called "green" because they are renewable (from bio-based sources), non-volatile (from ionic liquids), or are from naturally available solvents (vegetable oils). In this review, the effectiveness of different types of green dispersants, namely, protein isolates and hydrolysates from fish and marine wastes, biosurfactants from bacterial and fungal strains, vegetable-based oils such as soybean lecithin and castor oils, as well as green solvents like ionic liquids are reviewed. The challenges and opportunities offered by these green dispersants are also elucidated. The effectiveness of these dispersants varies widely and depends on oil type, dispersant hydrophilicity/hydrophobicity, and seawater conditions. However, their advantages lie in their relatively low toxicity and desirable physico-chemical properties, which make them potentially ecofriendly and effective dispersants for future oil spill response.

Response of microbial communities in North Saskatchewan River to diluted bitumen and conventional crude under freeze-thaw-refreeze cycle

Microorganisms are the first responder to oil spills and their response provides insight into the ecological effects of oils on aquatic ecosystems. Limited information is available about the impact of oil spills on freshwater ecosystems under seasonal river-ice regimes. This study aimed to investigate the microbial response of North Saskatchewan River water to diluted bitumen (DB) and conventional crude (CC) during the freeze-thaw-refreeze cycle. In two separate experiments, equivalent to 2 L of fresh DB and CC were spilled on the ice-covered river water within a mesoscale spill tank. The microbial response (changes in abundance and diversity) to oils under the freeze, thaw, and refreeze cycles were assessed for 10 days using 16S rRNA gene sequencing. The results showed that microbial communities exhibited different responses to the DB and CC oils. The effect of oils was more pronounced than that of the freeze or thaw cycles. The river microbial community rapidly responded to both spills, which coincided with a steady increase in the organic content of water throughout the freeze-thaw-refreeze cycle. Microbial diversity increased after the DB spill, but remain unchanged after the CC spill, regardless of the cycles. A higher number of new taxa emerged during the ice-covered period, while more microbial enrichment (increase in abundance) was observed during the thaw cycle. Flavobacterium (37 ± 5%) and Pseudomonas (36 ± 4%) remained the most predominant genera post-DB and CC spill, respectively. The results of this study suggest that ice coverage of 5 cm did not prevent the microbial communities from the effects of oils. Thus, a quick clean-up response to an oil spill on ice-covered water is equally critical to avoid the effects of oils on the underlying freshwater ecosystems.

Long-term patterns of hydrocarbon biodegradation and bacterial community composition in epipelagic and mesopelagic zones of an Arctic fjord

Oil spill attenuation in Arctic marine environments depends on oil-degrading bacteria. However, the seasonally harsh conditions in the Arctic such as nutrient limitations and sub-zero temperatures limit the activity even for bacteria capable of hydrocarbon metabolism at low temperatures. Here, we investigated whether the variance between epipelagic (seasonal temperature and inorganic nutrient variations) and mesopelagic zone (stable environmental conditions) could limit the growth of oil-degrading bacteria and lead to lower oil biodegradation rates in the epipelagic than in the mesopelagic zone. Therefore, we deployed absorbents coated with three oil types in a SW-Greenland fjord system at 10-20 m (epipelagic) and 615-650 m (mesopelagic) water depth for one year. During this period we monitored the development and succession of the bacterial biofilms colonizing the oil films by 16S rRNA gene amplicon quantification and sequencing, and the progression of oil biodegradation by gas chromatography - mass spectrometry oil fingerprinting analysis. The removal of hydrocarbons was significantly different, with several polycyclic aromatic hydrocarbons showing longer half-life times in the epipelagic than in the mesopelagic zone. Bacterial community composition and density (16S rRNA genes/ cm²) significantly differed between the two zones, with total bacteria reaching to log-fold higher densities (16S rRNA genes/cm²) in the mesopelagic than epipelagic oil-coated absorbents. Consequently, the environmental conditions in the epipelagic zone limited oil biodegradation performance by limiting bacterial growth.

The degradation and toxicity of commercially traded vegetable oils following spills in aquatic environment

The production of commodity and specialty vegetable oils is increasing every year to fulfill the ever-increasing demand where the trading of oils occurs primarily via sea shipping. Spills of vegetable oil into the aquatic environment may result in detrimental effects on aquatic ecosystems. Environmental degradation of vegetable oil spills occurs mainly via microbial activity, chemical oxidation, wave and wind actions. However, the polymerization of oils can hinder their ability to naturally degrade. Thus, human intervention in the form of both short- and long-term remediation, is desirable to reduce the effects of vegetable oil spills on aquatic ecosystems. Studies have been conducted to determine how the type and concentration of the vegetable oil contamination influence its toxicity on various organisms. Some studies show that the effect of vegetable oil spills is found to be relatively short-lived and to a certain extent increase the survivability of certain organisms. However, the integrated effect of vegetable oil spills on aquatic organisms and their environment is still being researched. This review summarizes the existing knowledge on the reported occurrences of vegetable oil spills, their degradation, and their toxicity towards the surrounding aquatic environment which would be helpful in the knowledge transfer of remediation of vegetable oils.

Petroleum spill bioremediation by an indigenous constructed bacterial consortium in marine environments

In the process of marine oil spill remediation, adding highly efficient oil degrading microorganisms can effectively promote oil degradation. However, in practice, the effect is far less than expected due to the inadaptability of microorganisms to the environment and their disadvantage in the competition with indigenous bacteria for nutrients. In this article, four strains of oil degrading bacteria were isolated from seawater in Jiaozhou Bay, China, where a crude oil pipeline explosion occurred seven years ago. Results of high-throughput sequencing, diesel degradation tests and surface activity tests indicated that Peseudomonas aeruginosa ZS1 was a highly efficient petroleum degrading bacterium with the ability to produce surface active substances. A diesel oil-degrading bacterial consortium (named SA) was constructed by ZS1 and another oil degrading bacteria by diesel degradation test. Degradation products analysis indicated that SA has a good ability to degrade short chain alkanes, especially n-alkanes (C₁₀-C₁₈). Community structure analysis showed that OTUs of Alcanivorax, Peseudomona, Ruegeria, Pseudophaeobacter, Hyphomonas and Thalassospira on genus level increased after the oil spill and remained stable throughout the recovery period. Most of these enriched microorganisms were related to known alkane and hydrocarbon degraders by the previous study. However, it is the first time to report that Pseudophaeobacter was enriched by using diesel as the sole carbon source. The results also indicated that ZS1 may have a dominant position in competition with indigenous bacteria. Oil pollution has an obvious selective effect on marine microorganisms. Although the oil degradation was promoted after SA injection, the recovery of microbial community structure took a longer time.

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.

Effects of chronic crude oil exposure on the fitness of polar cod (Boreogadus saida) through changes in growth, energy reserves and survival

Climate models predict extended periods with sea-ice free Arctic waters during the next decade, which will allow more shipping activity and easier access to petroleum resources. Increased industrial activities raise concerns about the biological effects of accidental petroleum release on key species of the Arctic marine ecosystem, such as the polar cod (Boreogadus saida). This study examines effects on physiological traits related to the fitness of adult polar cod, such as growth, survival, and lipid parameters. Fish were exposed to environmentally-relevant crude oil doses through their diet over an 8-month period, concurrent with reproductive development. In liver tissue, lipid class composition differed between treatments while in gonad tissue, lipid class composition varied between sexes, but not treatments. Crude oil did not affect growth and survival, which indicated that polar cod were relatively robust to dietary crude oil exposure at doses tested (0.11-1.14 μg crude oil/g fish/day) in this study.

Impacts of Frazil Ice on the Effectiveness of Oil Dispersion and Migration of Dispersed Oil

Oil spills in the Arctic have drawn dramatic attention in recent years. Frazil ice, as the essential formation of sea ice, may affect the effectiveness of dispersants during oil spill response and the associated behaviors of dispersed oil. However, these impacts remain poorly understood, limiting the appropriate usage of dispersants in ice-covered regions. Herein this work explored the effects of frazil ice on the dispersion effectiveness of two dispersants (Corexit 9500A and hydrolyzed shrimp waste) and the migration of dispersed oil within frazil ice. We discovered that frazil ice inhibited dispersion effectiveness by attenuating water velocity. Permeable frazil ice encapsulated 11-30% of dispersed oil, implying a lower oil bioavailability. We thus proposed and verified a microscopic mechanism to unravel the migration of dispersed oil toward permeable constrictions in frazil ice. We predicted the concentration of dispersed oil encapsulated in frazil ice using bed filtration theory and verified the prediction through experiments. Furthermore, the presence of frazil ice can lead to the breakup and coalescence of dispersed oil. Overall, our findings would facilitate the appropriate planning and decision-making of dispersant-based oil spill response and a better understanding of the fate of dispersed oil in the frazil ice-infested ocean.

Biodegradation of water-accommodated aromatic oil compounds in Arctic seawater at 0 °C

Oil spills in Arctic marine environments are expected to increase concurrently with the expansion of shipping routes and petroleum exploitation into previously inaccessible ice-dominated regions. Most research on oil biodegradation focusses on the bulk oil, but the fate of the water-accommodated fraction (WAF), mainly composed of toxic aromatic compounds, is largely underexplored. To evaluate the bacterial degradation capacity of such dissolved aromatics in Greenlandic seawater, microcosms consisting of 0 °C seawater polluted with WAF were investigated over a 3-month period. With a half-life (t_1/2) of 26 days, m-xylene was the fastest degraded compound, as measured by gas chromatography - mass spectrometry. Substantial slower degradation was observed for ethylbenzene, naphthalenes, phenanthrene, acenaphthylene, acenaphthene and fluorenes with t_1/2 of 40-105 days. Colwellia, identified by 16S rRNA gene sequencing, was the main potential degrader of m-xylene. This genus occupied up to 47 % of the bacterial community until day 10 in the microcosms. Cycloclasticus and Zhongshania aliphaticivorans, potentially utilizing one-to three-ringed aromatics, replaced Colwellia between day 10 and 96 and occupied up to 6 % and 23 % of the community, respectively. Although most of the WAF can ultimately be eliminated in microcosms, our results suggest that the restoration of an oil-impacted Arctic environment may be slow as most analysed compounds had t_1/2 of over 2-3 months and the detrimental effects of a spill towards the marine ecosystem likely persist during this time.

Degradation of organic contaminants in marine sediments by peroxymonosulfate over LaFeO3 nanoparticles supported on water caltrop shell-derived biochar and the associated microbial community responses

Sediment is an important final repository of persistent organic pollutants such as polycyclic aromatic hydrocarbons (PAHs). Herein, a novel catalyst of LaFeO₃ nanoparticles supported on biochar was synthesized from water caltrop shell by chemical precipitation. The composite (LFBC) was used as peroxymonosulfate (PMS) activator to oxidize PAHs in real marine sediments. Systematic surface characterization confirmed the immobilization of well crystalline nano LaFeO₃ particles onto the biochar surface. Under optimal conditions, i.e., [PMS] = 3 × 10^-4 M, [LFBC] = 0.75 g/L, pH 6.0, and seawater, the total PAH degradation efficiency was 90%, while that of 2-, 3-, 4-, 5-, and 6-ring PAHs was 52%, 61%, 66%, 56%, and 29%, respectively, in 24 h. The Langmuir-Hinshelwood equation better predicted the PAHs degradation kinetics over LFBC by PMS. Interactions between surface oxygen species at LaFeO₃ defective sites and the graphitized biochar network facilitated the PAHs degradation. Furthermore, changes in the bacterial community during the LFBC/PMS treatment were highlighted to assess the sustainable development of the sediment ecosystem. The LFBC/PMS process enhanced the biological richness and diversity of sediment eco-systems. The major phylum was Proteobacteria initially, while Hyphomonas was the genera after LFBC/PMS treatment of the sediment.

Large Enrichment of Anthropogenic Organic Matter Degrading Bacteria in the Sea-Surface Microlayer at Coastal Livingston Island (Antarctica)

The composition of bacteria inhabiting the sea-surface microlayer (SML) is poorly characterized globally and yet undescribed for the Southern Ocean, despite their relevance for the biogeochemistry of the surface ocean. We report the abundances and diversity of bacteria inhabiting the SML and the subsurface waters (SSL) determined from a unique sample set from a polar coastal ecosystem (Livingston Island, Antarctica). From early to late austral summer (January–March 2018), we consistently found a higher abundance of bacteria in the SML than in the SSL. The SML was enriched in some Gammaproteobacteria genus such as Pseudoalteromonas, Pseudomonas, and Colwellia, known to degrade a wide range of semivolatile, hydrophobic, and surfactant-like organic pollutants. Hydrocarbons and other synthetic chemicals including surfactants, such as perfluoroalkyl substances (PFAS), reach remote marine environments by atmospheric transport and deposition and by oceanic currents, and are known to accumulate in the SML. Relative abundances of specific SML-enriched bacterial groups were significantly correlated to concentrations of PFASs, taken as a proxy of hydrophobic anthropogenic pollutants present in the SML and its stability. Our observations provide evidence for an important pollutant-bacteria interaction in the marine SML. Given that pollutant emissions have increased during the Anthropocene, our results point to the need to assess chemical pollution as a factor modulating marine microbiomes in the contemporaneous and future oceans.

Biophysical methods to quantify bacterial behaviors at oil-water interfaces

Motivated by the need for improved understanding of physical processes involved in bacterial biodegradation of catastrophic oil spills, we review biophysical methods to probe bacterial motility and adhesion at oil-water interfaces. This review summarizes methods that probe bulk, average behaviors as well as local, microscopic behaviors, and highlights opportunities for future work to bridge the gap between biodegradation and biophysics.

The crucial role of bacterial laccases in the bioremediation of petroleum hydrocarbons

Laccases (EC 1.10.3.2) are a class of metallo-oxidases found in a variety of fungi, plants, and bacteria as well as in certain insects. They can oxidize a wide variety of organic compounds and can be widely applied in many fields, especially in the field of biodegradation and detoxification of environmental pollutants. The practical efficacy of laccases depends on their ability to capture the target substance as well as their catalytic activity, which is related to their catalytic center, substrate selectivity, and substrate tolerance. Over the past few decades, many laccases have been identified in plants and fungi. Concurrently, bacterial laccases have received increasing attention because of their high thermostability and high tolerance to organic compounds. The aim of this review is to summarize the role of bacterial laccases in the bioremediation of petroleum hydrocarbons and to outline the correlation between the molecular structure of the mononuclear T1 Cu center of bacterial laccases and their substrate preference.

Quantitative evaluation of in-situ bioremediation of compound pollution of oil and heavy metal in sediments from the Bohai Sea, China

Owing to the semi-enclosed environment of the Bohai Sea, the ecological effects caused by an oil spill would be significant. A typical in- situ bioremediation engineering project for of oil-spilled marine sediments was performed in the Bohai Sea and a quantitative assessment of the ecological restoration was performed. The bioremediation efficiencies of n-alkane and PAHs in the sediment are 32.84 ± 21.66% and 50.42 ± 17.49% after 70 days of bioremediation, and 60.99 ± 10.14% and 68.01 ± 18.60% after 210 days, respectively. After 210 days of bioremediation, the degradation rates of two- to three ring PAHs and four-ring PAHs are 84.44 ± 23.03% and 26.62 ± 43.76%, respectively. In addition, the concentrations of the heavy metals first increased by 6.00% due to oil spill degradation and release, and then decreased by 72.60% with the degradation of oil caused by bioremediation or vertical migration. According to the continuous tracking monitoring, the composition of the microbial community in the restored area was similar to that in the control area and the clean area in Bohai Sea after 210 days of bioremediation. These results may provide some theoretical and scientific data to understand the degradation mechanism and assessing the ecological remediation efficiency for oil spills in open sea areas.

Biodegradation, Photo-oxidation, and Dissolution of Petroleum Compounds in an Arctic Fjord during Summer

Increased economic activity in the Arctic may increase the risk of oil spills. Yet, little is known about the degradation of oil spills by solar radiation and the impact of nutrient limitation on oil biodegradation under Arctic conditions. We deployed adsorbents coated with thin oil films for up to 4 months in a fjord in SW Greenland to simulate and investigate in situ biodegradation and photo-oxidation of dispersed oil droplets. Oil compound depletion by dissolution, biodegradation, and photo-oxidation was untangled by gas chromatography-mass spectrometry-based oil fingerprinting. Biodegradation was limited by low nutrient concentrations, reaching 97% removal of nC_13-26-alkanes only after 112 days. Sequencing of bacterial DNA showed the slow development of a bacterial biofilm on the oil films predominated by the known oil degrading bacteria Oleispira, Alkanindiges and Cycloclasticus. These taxa could be related to biodegradation of shorter-chain (≤C₂₆) alkanes, longer-chain (≥C₁₆) and branched alkanes, and polycyclic aromatic compounds (PACs), respectively. The combination of biodegradation, dissolution, and photo-oxidation depleted most PACs at substantially faster rates than the biodegradation of alkanes. In Arctic fjords during summer, nutrient limitation may severely delay oil biodegradation, but in the photic zone, photolytic transformation of PACs may play an important role.

Tolerance of Fucus vesiculosus exposed to diesel water-accommodated fraction (WAF) and degradation of hydrocarbons by the associated bacteria

The viability and physiological state of brown macroalgae Fucus vesiculosus and its associated epiphytic bacteria exposed to diesel water-accommodated fraction (WAF), as well as the capacity of this association to deplete petroleum hydrocarbons (HCs) were experimentally tested. After a 6-day exposure treatment, the algal-surface associated bacteria were identified as primarily hydrocarbon-oxidising bacteria (HOB), and the algal-HOB association was able to deplete petroleum hydrocarbons from the diesel WAF by 80%. The HOB density on the algal surface exposed to diesel WAF was 350% higher compared to the control (i.e. HOB density on the algal surface exposed to ambient seawater), which suggest that they actively proliferated in the presence of hydrocarbons and most likely consumed hydrocarbons as their primary organic substrate. Exposure to diesel WAF did not affect the metabolic activity of F. vesiculosus. Higher lipid peroxidation was observed in F. vesiculosus exposed to diesel WAF while catalase concentration decreased only during the first day of exposure. Results suggest F. vesiculosus is tolerant to oil pollution and the algal-HOB association can efficiently deplete petroleum hydrocarbons in oil-contaminated seas.

Microbial responses to anthropogenic dissolved organic carbon in the Arctic and Antarctic coastal seawaters

Thousands of semi-volatile hydrophobic organic pollutants (OPs) reach open oceans through atmospheric deposition, causing a chronic and ubiquitous pollution by anthropogenic dissolved organic carbon (ADOC). Hydrophobic ADOC accumulates in cellular lipids, inducing harmful effects on marine biota, and can be partially prone to microbial degradation. Unfortunately, their possible effects on microorganisms, key drivers of global biogeochemical cycles, remain unknown. We challenged coastal microbial communities from Ny-Ålesund (Arctic) and Livingston Island (Antarctica) with ADOC concentrations within the range of oceanic concentrations in 24 h. ADOC addition elicited clear transcriptional responses in multiple microbial heterotrophic metabolisms in ubiquitous groups such as Flavobacteriia, Gammaproteobacteria and SAR11. Importantly, a suite of cellular adaptations and detoxifying mechanisms, including remodelling of membrane lipids and transporters, was detected. ADOC exposure also changed the composition of microbial communities, through stimulation of rare biosphere taxa. Many of these taxa belong to recognized OPs degraders. This work shows that ADOC at environmentally relevant concentrations substantially influences marine microbial communities. Given that emissions of organic pollutants are growing during the Anthropocene, the results shown here suggest an increasing influence of ADOC on the structure of microbial communities and the biogeochemical cycles regulated by marine microbes.

On-board saline black water treatment by bioaugmentation original marine bacteria with Pseudoalteromonas sp. SCSE709-6 and the associated microbial community

To reduce fresh water load on ships, seawater can be used for toilet flushing on-board. And saline black water was treated on-site by bioaugmentation original marine bacteria with Pseudoalteromonas sp. SCSE709-6 (P. sp. SCSE709-6) to prevent marine pollution. In the batch experiments, P. sp. SCSE709-6 was effective in nutrient removal, which was not closely related to the amount of inoculation. In the on-board continuous experiments, the systems inoculated with P. sp. SCSE709-6 possessed excellent TP removal ability (removal rate: 80.93% for T3 and 88.39% for T4). The inoculum of P. sp. SCSE709-6 changed the microbial community structure and increased the similarity of microbial communities. P. sp. SCSE709-6 had a significant influence on the performance and microbial community of the systems. This study strongly proposes that the P. sp. SCSE709-6 is a promising alternative in saline black water treatment, which has great significance to the practice of on-board seawater flushing toilet.

Acute oil exposure reduces physiological process rates in Arctic phyto- and zooplankton

Arctic shipping and oil exploration are expected to increase, as sea ice extent is reduced. This enhances the risk for accidental oil spills throughout the Arctic, which emphasises the need to quantify potential consequences to the marine ecosystem and to evaluate risk and choose appropriate remediation methods. This study investigated the sensitivity of Arctic marine plankton to the water accommodated fraction (WAF) of heavy fuel oil. Arctic marine phytoplankton and copepods (Calanus finmarchicus) were exposed to three WAF concentrations corresponding to total hydrocarbon contents of 0.07 mg l^-1, 0.28 mg l^-1 and 0.55 mg l^-1. Additionally, the potential phototoxic effects of exposing the WAF to sunlight, including the UV spectrum, were tested. The study determined sub-lethal effects of WAF exposure on rates of key ecosystem processes: primary production of phytoplankton and grazing (faecal pellet production) of copepods. Both phytoplankton and copepods responded negatively to WAF exposure. Biomass specific primary production was reduced by 6, 52 and 73% and faecal pellet production by 18, 51 and 86% with increasing WAF concentrations compared to controls. The phototoxic effect reduced primary production in the two highest WAF concentration treatments by 71 and 91%, respectively. This experiment contributes to the limited knowledge of acute sub-lethal effects of potential oil spills to the Arctic pelagic food web.

In situ biodegradation, photooxidation and dissolution of petroleum compounds in Arctic seawater and sea ice

In pristine sea ice-covered Arctic waters the potential of natural attenuation of oil spills has yet to be uncovered, but increasing shipping and oil exploitation may bring along unprecedented risks of oil spills. We deployed adsorbents coated with thin oil films for up to 2.5 month in ice-covered seawater and sea ice in Godthaab Fjord, SW Greenland, to simulate and investigate in situ biodegradation and photooxidation of dispersed oil. GC-MS-based chemometric methods for oil fingerprinting were used to identify characteristic signatures for dissolution, biodegradation and photooxidation. In sub-zero temperature seawater, fast degradation of n-alkanes was observed with estimated half-life times of ∼7 days. PCR amplicon sequencing and qPCR quantification of bacterial genes showed that a biofilm with a diverse microbial community colonised the oil films, yet a population related to the psychrophilic hydrocarbonoclastic gammaproteobacterium Oleispira antarctica seemed to play a key role in n-alkane degradation. Although Oleispira populations were also present in sea ice, we found that biofilms in sea ice had 25 to 100 times lower bacterial densities than in seawater, which explained the non-detectable n-alkane degradation in sea ice. Fingerprinting revealed that photooxidation, but not biodegradation, transformed polycyclic aromatic compounds through 50 cm-thick sea ice and in the upper water column with removal rates up to ∼1% per day. Overall, our results showed a fast biodegradation of n-alkanes in sea ice-covered seawater, but suggested that oils spills will expose the Arctic ecosystem to bio-recalcitrant PACs over prolonged periods of time.

Pivotal Role of Snow Deposition and Melting Driving Fluxes of Polycyclic Aromatic Hydrocarbons at Coastal Livingston Island (Antarctica)

The atmosphere-land-ocean dynamics of semivolatile organic compounds in polar regions is poorly understood, also for the abundant and ubiquitous polycyclic aromatic hydrocarbons (PAHs). We report the concentrations and fluxes of PAHs in a polar coastal ecosystem (Livingston Island, Antarctica). From late spring (December 2014) to late summer (February 2015), we sampled air, snow, coastal seawater, plankton, and the fugacity in soils and snow. The concentrations of PAHs in seawater were low but increased during the austral summer. The PAH concentrations in snow were significantly higher than in coastal seawater. Soil-air fugacity ratios showed a net volatilization of PAH when soils were covered with lichens, and close to air-soil equilibrium for bare soils. Concentrations in surface snow were also close to equilibrium with atmospheric PAHs. Conversely, there was a net diffusive deposition of PAHs to coastal seawater during late spring, but a net volatilization from seawater during late summer. Volatilization fluxes were correlated with seawater temperature and salinity, consistent with a key role of snowmelt to the fluxes and dissolved phase concentrations during the austral summer. The comprehensive assessment provided here shows that the fugacity amplification in snow is transferred to soils and coastal seawater supporting PAH concentrations and fluxes.

Petroleum hydrocarbon and microbial community structure successions in marine oil-related aggregates associated with diatoms relevant for Arctic conditions

Oil-related aggregates (ORAs) may contribute to the fate of oil spilled offshore. However, our understanding about the impact of diatoms and associated bacteria involved in the formation of ORAs and the fate of oil compounds in these aggregates is still limited. We investigated these processes in microcosm experiments with defined oil dispersions in seawater at 5 °C, employing the Arctic diatom Fragilariopsis cylindrus and its associated bacterial assemblage to promote ORA formation. Accumulation of oil compounds, as well as biodegradation of naphthalenes in ORAs and corresponding water phases, was enhanced in the presence of diatoms. Interestingly, the genus Nonlabens was predominating the bacterial communities in diatom-supplemented microcosms, while this genus was not abundant in other samples. This work elucidates the relevance of diatom biomass for the formation of ORAs, microbial community structures and biodegradation processes in chemically dispersed oil at low temperatures relevant for Arctic conditions.

Impact of Pyrene Exposure during Overwintering of the Arctic Copepod Calanus glacialis

While ongoing warming and sea ice decline threaten unique Arctic ecosystems, they improve the prospect of exploiting fossil fuels in the seafloor. Arctic Calanus copepods can accumulate oil compounds in the large lipid reserves that enable them to cope with highly seasonal food availability characteristic of the Arctic. While spending a significant part of their lives overwintering at depth, their vulnerability to oil contamination during winter remains unknown. We investigated effects of the hazardous crude oil component pyrene on overwintering Calanus glacialis, a key species in Arctic shelf areas. Females were exposed from December to March and then transferred to clean water and fed until April. We showed that long-term exposure during overwintering reduced survival and lipid mobilization in a dose-dependent manner at concentrations previously considered sublethal. After exposure, strong delayed effects were observed in lipid recovery, fecal pellet, and egg production. We showed that 50% lethal threshold concentrations were at least 300 times lower than expected, and that 50% effect thresholds for pellet and egg production were at least 10 times lower than previously documented. Our study provides novel insights to the effects of oil contamination during winter, which is essential to evaluate ecological impacts of Arctic oil pollution.