Estimation of hydrocarbon biodegradation rates in marine environments: a critical review of the Q10 approach

An impact-based environmental risk assessment model toolbox for offshore produced water discharges

We present a novel approach to environmental risk assessment of produced water discharges based on explicit impact and probability, using a combination of transport, fate and toxicokinetic-toxicodynamic models within a super-individual framework, with a probabilistic element obtained from ensemble simulations. Our approach is motivated by a need for location and species specific tools which also accounts for the dynamic nature of exposure and uptake of produced water components in the sea. Our approach is based on the well-established fate model DREAM, and accounts for time-variable exposure, considers body burden and effects for specific species and stressors, and assesses the probability of impact. Using a produced water discharge in the Barents Sea, with early life stages of spawning haddock, we demonstrate that it is possible to conduct a model-based risk assessment that highlights the effect of natural variations in environmental conditions. The benefits, limitations and potential for further improvements are discussed.

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.

Scientific concepts and methods for moving persistence assessments into the 21st century

The evaluation of a chemical substance's persistence is key to understanding its environmental fate, exposure concentration, and, ultimately, environmental risk. Traditional biodegradation test methods were developed many years ago for soluble, nonvolatile, single-constituent test substances, which do not represent the wide range of manufactured chemical substances. In addition, the Organisation for Economic Co-operation and Development (OECD) screening and simulation test methods do not fully reflect the environmental conditions into which substances are released and, therefore, estimates of chemical degradation half-lives can be very uncertain and may misrepresent real environmental processes. In this paper, we address the challenges and limitations facing current test methods and the scientific advances that are helping to both understand and provide solutions to them. Some of these advancements include the following: (1) robust methods that provide a deeper understanding of microbial composition, diversity, and abundance to ensure consistency and/or interpret variability between tests; (2) benchmarking tools and reference substances that aid in persistence evaluations through comparison against substances with well-quantified degradation profiles; (3) analytical methods that allow quantification for parent and metabolites at environmentally relevant concentrations, and inform on test substance bioavailability, biochemical pathways, rates of primary versus overall degradation, and rates of metabolite formation and decay; (4) modeling tools that predict the likelihood of microbial biotransformation, as well as biochemical pathways; and (5) modeling approaches that allow for derivation of more generally applicable biotransformation rate constants, by accounting for physical and/or chemical processes and test system design when evaluating test data. We also identify that, while such advancements could improve the certainty and accuracy of persistence assessments, the mechanisms and processes by which they are translated into regulatory practice and development of new OECD test guidelines need improving and accelerating. Where uncertainty remains, holistic weight of evidence approaches may be required to accurately assess the persistence of chemicals. Integr Environ Assess Manag 2022;18:1454-1487. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Determining the Temperature Dependency of Biodegradation Kinetics for 34 Hydrocarbons while Avoiding Chemical and Microbial Confounding Factors

Biodegradation kinetics data are keystone for evaluating the environmental persistence and risk of chemicals. Biodegradation kinetics depend highly on the prevailing temperature, which influences microbial community structures, metabolic rates, and chemical availability. There is a lack of high-quality comparative biodegradation kinetics data that are determined at different test temperatures but with the same microbial inoculum and chemical availability. The present study was designed to determine the effect of test temperature on the biodegradation kinetics of hydrocarbons while avoiding confounding factors. We used inocula from a Northern river (2.7 °C) and a Central European river (12.5 °C). Aqueous stock solutions containing 45 individual hydrocarbons were generated by passive dosing and added to river water containing the native microorganisms. Compound-specific biodegradation kinetics were then determined at 2.7, 12, and 20 °C based on substrate depletion. Main findings comprise the following: (1) Degradation half-times (DegT₅₀) of 34 test chemicals were determined at different test temperatures and were largely consistent with the Arrhenius equation (activation energy, 65.4 kJ/mol). (2) Differences in biodegradation kinetics between tested isomers were rather limited. (3) The recent lowering of standard test temperature from 20 to 12 °C results typically in a doubling of DegT₅₀ values and can lead to a stricter persistency assessment.

Bacterial responses to background organic pollutants in the northeast subarctic Pacific Ocean

Thousands of man-made synthetic chemicals are released to oceans and compose the anthropogenic dissolved organic carbon (ADOC). Little is known about the effects of this chronic pollution on marine microbiome activities. In this study, we measured the pollution level at three sites in the Northeast Subarctic Pacific Ocean (NESAP) and investigated how mixtures of three model families of ADOC at different environmentally relevant concentrations affected naturally occurring marine bacterioplankton communities' structure and metabolic functioning. The offshore northernmost site (North) had the lowest concentrations of hydrocarbons, as well as organophosphate ester plasticizers, contrasting with the two other continental shelf sites, the southern coastal site (South) being the most contaminated. At North, ADOC stimulated bacterial growth and promoted an increase in the contribution of some Gammaproteobacteria groups (e.g. Alteromonadales) to the 16 rRNA pool. These groups are described as fast responders after oil spills. In contrast, minor changes in South microbiome activities were observed. Gene expression profiles at Central showed the coexistence of ADOC degradation and stress-response strategies to cope with ADOC toxicities. These results show that marine microbial communities at three distinct domains in NESAP are influenced by background concentrations of ADOC, expanding previous assessments for polar and temperate waters.

Comparison of Hydrocarbon-Degrading Consortia from Surface and Deep Waters of the Eastern Mediterranean Sea: Characterization and Degradation Potential

The diversity and degradation capacity of hydrocarbon-degrading consortia from surface and deep waters of the Eastern Mediterranean Sea were studied in time-series experiments. Microcosms were set up in ONR7a medium at in situ temperatures of 25 °C and 14 °C for the Surface and Deep consortia, respectively, and crude oil as the sole source of carbon. The Deep consortium was additionally investigated at 25 °C to allow the direct comparison of the degradation rates to the Surface consortium. In total, ~50% of the alkanes and ~15% of the polycyclic aromatic hydrocarbons were degraded in all treatments by Day 24. Approximately ~95% of the total biodegradation by the Deep consortium took place within 6 days regardless of temperature, whereas comparable levels of degradation were reached on Day 12 by the Surface consortium. Both consortia were dominated by well-known hydrocarbon-degrading taxa. Temperature played a significant role in shaping the Deep consortia communities with Pseudomonas and Pseudoalteromonas dominating at 25 °C and Alcanivorax at 14 °C. Overall, the Deep consortium showed a higher efficiency for hydrocarbon degradation within the first week following contamination, which is critical in the case of oil spills, and thus merits further investigation for its exploitation in bioremediation technologies tailored to the Eastern Mediterranean Sea.

Modeling in-stream attenuation of N-nitrosodimethylamine and formaldehyde during urban river transportation based on seasonal and diurnal variation

Disinfection by-products (DBPs) discharged from sewage treatment plants (STPs) could harm downstream receiving waters and drinking water resources. In-stream attenuation of photo- and non-photodegradable DBPs during river transportation is currently not well understood. Here we sought to fill this knowledge gap by meta-data-analysis for modeling in-stream attenuation of DBPs. Data were collected along a treated-wastewater-dominated 1.6-km stretch of a river channel for 3 years and incorporated seasonal and diurnal patterns. Photo-irradiation and water temperature were the main factors responsible for in-stream attenuation of photodegradable N-nitrosodimethylamine (NDMA), and water temperature for that of non-photodegradable formaldehyde (FAH). The factors were incorporated into photo-dependent and -independent models to account for temporal variations in NDMA and FAH, respectively. Estimated mass recoveries of NDMA and FAH agreed well with observed values along the stretch. The models developed here offer a novel and useful tool for estimating levels of NDMA and FAH during river transportation.

North sea produced water PAH exposure and uptake in early life stages of Atlantic Cod

Produced water discharges from offshore oil and gas platforms represent a significant source of petroleum components such as polycyclic aromatic hydrocarbons (PAHs) released to the ocean. High molecular weight PAHs are persistent in the environment and have a potential for bioaccumulation, and the investigation of their fate and uptake pathways in marine life are relevant when assessing environmental risk of produced water discharges. To study the exposure and uptake of 2-5 ring PAHs in early life stages of Atlantic Cod in the North Sea, we run a coupled fate and individual-based numerical model that includes discharges from 26 platforms. We consider 26 different PAH components in produced water which biodegrade with primary degradation rates; intermediate degradation products are not included. Model simulations are run covering multiple years (2009-2012) to study annual exposure variability, while a one-day time slice of spawning products from the peak spawning season are followed. By covering multiple release points and large spatio-temporal scales, we show how individuals can be exposed to produced water from multiple regions in the North Sea. We find that a combination of oceanic fate processes and toxicokinetics lead to markedly different compositions in the predicted internal concentrations of PAHs compared to discharge concentrations; for instance, naphthalene makes up 30% of the total discharged PAHs, but contributes to at most 1% of internal concentrations. In all simulations we find the predicted total internal PAH concentration (26 components) to be below 1.2 nmol/g, a factor of 1000 less than concentrations commonly associated with acute narcotic effects.

Understanding the Dependence of Micropollutant Biotransformation Rates on Short-Term Temperature Shifts

Temperature is a key factor that influences chemical biotransformation potential and rates, on which exposure and fate models rely to predict the environmental (micro)pollutant fate. Arrhenius-based models are currently implemented in environmental exposure assessment to adapt biotransformation rates to actual temperatures, assuming validity in the 0-30 °C range. However, evidence on how temperature shifts affect the physicochemical and microbial features in biological systems is scarce, questioning the validity of the existing modeling approaches. In this work, laboratory-scale batch assays were designed to investigate how a mixed microbial community responds to short-term temperature shifts, and how this impacts its ability to biotransform a range of structurally diverse micropollutants. Our results revealed three distinct kinetic responses at temperatures above 20 °C, mostly deviating from the classic Arrhenius-type behavior. Micropollutants with similar temperature responses appeared to undergo mostly similar initial biotransformation reactions, with substitution-type reactions maintaining Arrhenius-type behavior up to higher temperatures than oxidation-type reactions. Above 20 °C, the microbial community also showed marked shifts in both composition and activity, which mostly correlated with the observed deviations from Arrhenius-type behavior, with compositional changes becoming a more relevant factor in biotransformations catalyzed by more specific enzymes (e.g., oxidation reactions). Our findings underline the need to re-examine and further develop current environmental fate models by integrating biological aspects, to improve accuracy in predicting the environmental fate of micropollutants.

Modelling biodegradation of crude oil components at low temperatures

For oil spilled at sea, the main weathering processes are evaporation, emulsification, photo-oxidation, dispersion and biodegradation. Of these, only biodegradation may completely remove hydrocarbons from the environment in the long term, as the other processes only serve to transform and dilute the oil components. As petroleum development is moving north, the probability of Arctic oil spills increases. Hence, it is imperative to develop methods for comprehensive risk assessment of oil spills in cold and ice-covered waters. Accurate biodegradation rates are an essential part of this, as they are required to predict the long-term effects of marine oil spills. In this paper, we present experimentally determined biodegradation rates for the component groups which are used to represent oil in the OSCAR oil spill model. The experiments have been carried out at seawater temperatures of -2^∘C, 0^∘C, 5^∘C, and 13^∘C. We show that for the lighter and more soluble oil components, the changes in degradation rates between 0^∘C and 13^∘C are well captured by a constant Q₁₀ scaling law. At lower temperatures, and for heavier and less soluble components, the rates are not well described by a constant Q₁₀, probably indicating that oil properties become important for the biodegradation rate.

Is the Arrhenius-correction of biodegradation rates, as recommended through REACH guidance, fit for environmentally relevant conditions? An example from petroleum biodegradation in environmental systems

Biodegradation is a major determinant of chemical persistence in the environment and an important consideration for PBT and environmental risk assessments. It is influenced by several environmental factors including temperature and microbial community structure. According to REACH guidance, a temperature correction based on the Arrhenius equation is recommended for chemical persistence data not performed at the recommended EU mean surface water temperature. Such corrections, however, can lead to overly conservative P/vP assessments. In this paper, the relevance of this temperature correction is assessed for petroleum hydrocarbons, using measured surface water (marine and freshwater) degradation half-time (DT50) and degradation half-life (HL) data compiled from relevant literature. Stringent screening criteria were used to specifically select data from biodegradation tests containing indigenous microbes and conducted at temperatures close to their ambient sampling temperature. As a result, ten independent studies were identified, with 993 data points covering 326 hydrocarbon constituents. These data were derived from tests conducted with natural seawater, or freshwater, at temperatures ranging from 5 to 21 °C. Regressions were performed on the full hydrocarbon dataset and on several individual hydrocarbons. The results were compared to the trend as predicted by the Arrhenius equation and using the activation energy (E_a) as recommend in the REACH Guidance. The comparison shows that the correction recommended in REACH Guidance over predicts the effect of temperature on hydrocarbon biodegradation. These results contrast with temperature manipulated inocula where the test temperature is different from the ambient sampling temperature. In these manipulated systems, the effect of temperature follows the Arrhenius equation more closely. In addition, a more striking effect of temperature on the lag phase was observed with longer lag phases more apparent at lower temperatures. This indicates that the effect of temperature may indeed be even lower when considering hydrocarbon biodegradation without the initial lag phase.

Modelling of oil thickness in the presence of an ice edge

Oil slick thickness is a key parameter for the behaviour of oil spilled at sea. It influences evaporation and entrainment, viable response options, and the risk to marine life at the surface. Determining this value is therefore of high relevance in oil spill modelling. In open water, oil can spread as thin films due to gravity alone, and may be further dispersed by horizontal diffusion and differential advection. In the presence of ice, however, a thin oil slick may become concentrated to higher thickness, if compressed against the ice edge. In the present study, we develop a simple model for the thickness of oil forced against a barrier by a current. We compare our theory to flume experiments, and obtain reasonable agreement. We describe an implementation in a Lagrangian oil spill model, and present some examples. We discuss the operational applicability, and suggest further research needs.

Changes in microbial community in the presence of oil and chemical dispersant and their effects on the corrosion of API 5L steel coupons in a marine-simulated microcosm

The influence of crude oil and chemical dispersant was evaluated over planktonic bacteria and biofilms grown on API 5L steel surfaces in microcosm systems. Three conditions were simulated, an untreated marine environment and a marine environment with the presence of crude oil and a containing crude oil and chemical dispersant. The results of coupon corrosion rates indicated that in the oil microcosm, there was a high corrosion rate when compared with the other two systems. Analysis of bacterial communities by 16S rRNA gene sequencing described a clear difference between the different treatments. In plankton communities, the Bacilli and Gammaproteobacteria classes were the most present in numbers of operational taxonomic unit (OTUs). The Vibrionales, Oceanospirillales, and Alteromonadales orders were predominant in the treatment with crude oil, whereas in the microcosm containing oil and chemical dispersant, mainly members of Bacillales order were detected. In the communities analyzed from biofilms attached to the coupons, the most preponderant class was Alphaproteobacteria, followed by Gammaproteobacteria. In the control microcosm, there was a prevalence of the orders Rhodobacterales, Aeromonadales, and Alteromonadales, whereas in the dispersed oil and oil systems, the members of the order Rhodobacterales were present in a larger number of OTUs. These results demonstrate how the presence of a chemical dispersant and oil influence the corrosion rate and bacterial community structures present in the water column and biofilms grown on API 5L steel surfaces in a marine environment. KEY POINTS: • Evaluation of the effects of oil and chemical surfactants on the corrosion of API 5L. • Changes in microbial communities do not present corrosive biofilm on API 5L coupons.

Hydrocarbon-Degrading Microbial Communities Are Site Specific, and Their Activity Is Limited by Synergies in Temperature and Nutrient Availability in Surface Ocean Waters

The objective of this study was to quantify the potential for hydrocarbon biodegradation in surface waters of three sites, representing geographic regions of major oil exploration (Beaufort Sea in the Arctic, northern Gulf of Mexico [GOM], and southern GOM), in a systematic experimental design that incorporated gradients in temperature and the availability of major nutrients. Surface seawater was amended in microcosms with Macondo surrogate oil to simulate an oil slick, and microcosms were incubated, with or without nutrient amendment, at temperatures ranging from 4 to 38^ºC. Using respiration rate as a proxy, distinct temperature responses were observed in surface seawater microcosms based on geographic origin; biodegradation was nearly always more rapid in the Arctic site samples than in the GOM samples. Nutrient amendment enhanced respiration rates by a factor of approximately 6, stimulated microbial growth, and generally elevated the taxonomic diversity of microbial communities within the optimal temperature range for activity at each site, while diversity remained the same or was lower at temperatures deviating from optimal conditions. Taken together, our results advance the understanding of how bacterioplankton communities from different geographic regions respond to oil perturbation. A pulsed disturbance of oil is proposed to favor copiotrophic r-strategists that are adapted to pointed seasonal inputs of phytoplankton carbon, displaying carbon and nutrient limitations, rather than oil exposure history. Further understanding of the ecological mechanisms underpinning the complex environmental controls of hydrocarbon degradation is required for improvement of predictive models of the fate and transport of spilled oil in marine environments.IMPORTANCE The risk of an oil spill accident in pristine regions of the world's oceans is increasing due to the development and transport of crude oil resources, especially in the Arctic region, as a result of the opening of ice-free transportation routes, and there is currently no consensus regarding the complex interplay among the environmental controls of petroleum hydrocarbon biodegradation for predictive modeling. We examined the hydrocarbon biodegradation potential of bacterioplankton from three representative geographic regions of oil exploration. Our results showed that rates of aerobic respiration coupled to hydrocarbon degradation in surface ocean waters are controlled to a large extent by effects of temperature and nutrient limitation; hydrocarbon exposure history did not appear to have a major impact. Further, the relationship between temperature and biodegradation rates is linked to microbial community structure, which is specific to the geographic origin.

Oil type and temperature dependent biodegradation dynamics - Combining chemical and microbial community data through multivariate analysis

BACKGROUND

This study investigates a comparative multivariate approach for studying the biodegradation of chemically dispersed oil. The rationale for this approach lies in the inherent complexity of the data and challenges associated with comparing multiple experiments with inconsistent sampling points, with respect to inferring correlations and visualizing multiple datasets with numerous variables. We aim to identify novel correlations among microbial community composition, the chemical change of individual petroleum hydrocarbons, oil type and temperature by creating modelled datasets from inconsistent sampling time points. Four different incubation experiments were conducted with freshly collected Norwegian seawater and either Grane and Troll oil dispersed with Corexit 9500. Incubations were conducted at two different temperatures (5 °C and 13 °C) over a period of 64 days.

RESULTS

PCA analysis of modelled chemical datasets and calculated half-lives revealed differences in the biodegradation of individual hydrocarbons among temperatures and oil types. At 5 °C, most n-alkanes biodegraded faster in heavy Grane oil compared to light Troll oil. PCA analysis of modelled microbial community datasets reveal differences between temperature and oil type, especially at low temperature. For both oils, Colwelliaceae and Oceanospirillaceae were more prominent in the colder incubation (5 °C) than the warmer (13 °C). Overall, Colwelliaceae, Oceanospirillaceae, Flavobacteriaceae, Rhodobacteraceae, Alteromonadaceae and Piscirickettsiaceae consistently dominated the microbial community at both temperatures and in both oil types. Other families known to include oil-degrading bacteria were also identified, such as Alcanivoracaceae, Methylophilaceae, Sphingomonadaceae and Erythrobacteraceae, but they were all present in dispersed oil incubations at a low abundance (< 1%).

CONCLUSIONS

In the current study, our goal was to introduce a comparative multivariate approach for studying the biodegradation of dispersed oil, including curve-fitted models of datasets for a greater data resolution and comparability. By applying these approaches, we have shown how different temperatures and oil types influence the biodegradation of oil in incubations with inconsistent sampling points. Clustering analysis revealed further how temperature and oil type influence single compound depletion and microbial community composition. Finally, correlation analysis of degraders community, with single compound data, revealed complexity beneath usual abundance cut-offs used for microbial community data in biodegradation studies.

Biodegradation of Crude Oil and Corexit 9500 in Arctic Seawater

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

Biodegradation-mediated alterations in acute toxicity of water-accommodated fraction and single crude oil components in cold seawater

Hydrocarbon biodegradation may be slower in cold Arctic than in temperate seawater, and this will affect the toxicity time window of the hydrocarbons. In this study, the acute toxicities of water-soluble phases of 1,3-dimethylnaphthalene, phenanthrene, fluoranthene, and low energy water-accommodated fractions (LE-WAFs) of an evaporated (200 °C+) crude oil, were screened by a Microtox bioassay during biodegradation in cold seawater (4-5 °C). The water-solubility of fluoranthene was too low to provoke a toxic response at any time, whereas the toxicity of 1,3-dimethylnaphthalene and phenanthrene decreased over time in relation to biotransformation of these compounds. In LE-WAFs, the Microtox EC₅₀ was associated with biodegradation of the predominant hydrocarbons (naphthalenes, 2- to 3-ring PAH), as well as with phenol degradation products. The acute toxicities of single hydrocarbons and LE-WAFs persisted for a longer period in the cold seawater than previously shown at higher seawater temperatures. These results suggest implications for fate and effects assessment of hydrocarbons after oil spills in cold environments, like the Arctic. However, further biodegradation studies using Arctic seawater and relevant species for toxicity testing are needed for confirmation.

Bacterial community succession and degradation patterns of hydrocarbons in seawater at low temperature

The risk of oil spills in cold marine environments is expected to increase in response to trans-Arctic shipping and as Arctic oil reserves get exploited. Marine hydrocarbon-degrading microbes can reduce the impact of spilled hydrocarbons, but their degradation capabilities at low temperature are yet to be uncovered. We combined DNA amplicon sequencing and chemometrics to investigate the effect of decreasing temperature (0-15 °C) on the succession and function of hydrocarbon-degrading bacteria in seawater. The bacterial community and degradation patterns were investigated at time points when a similar amount of hydrocarbons was mineralised at the different temperatures. This allowed decomposing the effect of temperature into a main component related to the reduced microbial activity at low temperature and a secondary effect. The reduced microbial activity at low temperature delayed the microbial community succession and degradation rates. The secondary effect of temperature was most pronounced at 0 °C, where (1) degradation of the least water-soluble n-alkanes (>C12) was suppressed in contrast to a relative stronger degradation of the most water-soluble n-alkanes (<C12) and polycyclic aromatic hydrocarbons; and (2) bacterial taxa which we identified as psychrosensitive were inhibited, whereas taxa identified as psychrophilic flourished.

Integrating Dispersants in Oil Spill Response in Arctic and Other Icy Environments

Future oil exploration and marine navigation may well extend into the Arctic Ocean, and government agencies and responders need to plan for accidental oil spills. We argue that dispersants should play an important role in these plans, since they have substantial logistical benefits, work effectively under Arctic conditions, and stimulate the rapid biodegradation of spilled oil. They also minimize the risk of surface slicks to birds and mammals, the stranding of oil on fragile shorelines and minimize the need for large work crews to be exposed to Arctic conditions.

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

New economic developments in the Arctic, such as shipping and oil exploitation, bring along unprecedented risks of marine oil spills. Microorganisms have played a central role in degrading and reducing the impact of the spilled oil during past oil disasters. However, in the Arctic, and in particular in its pristine areas, the self-cleaning capacity and biodegradation potential of the natural microbial communities have yet to be uncovered. This review compiles and investigates the current knowledge with respect to environmental parameters and biochemical constraints that control oil biodegradation in the Arctic. Hereby, seawaters off Greenland are considered as a case study. Key factors for biodegradation include the bioavailability of hydrocarbons, the presence of hydrocarbon-degrading bacteria and the availability of nutrients. We show how these key factors may be influenced by the physical oceanographic conditions in seawaters off Greenland and other environmental parameters including low temperature, sea ice, sunlight regime, suspended sediment plumes and phytoplankton blooms that characterize the Arctic. Based on the acquired insights, a first qualitative assessment of the biodegradation potential in seawaters off Greenland is presented. In addition to the most apparent Arctic characteristics, such as low temperature and sea ice, the impact of typical Arctic features such as the oligotrophic environment, poor microbial adaptation to hydrocarbon degradation, mixing of stratified water masses, and massive phytoplankton blooms and suspended sediment plumes merit to be topics of future investigation.

Microbial communities in seawater from an Arctic and a temperate Norwegian fjord and their potentials for biodegradation of chemically dispersed oil at low seawater temperatures

Biodegradation of chemically dispersed oil at low temperature (0-2 °C) was compared in natural seawater from Arctic (Svalbard) and a temperate (Norway) fjords. The oil was premixed with a dispersant (Corexit 9500) and small-droplet oil dispersions prepared. Faster biotransformation of n-alkanes in the Arctic than in the temperate seawater were associated with the initially higher abundance of the alkane-degrading genus Oleispira in the Arctic than the temperate seawater. Comparable transformation of aromatic hydrocarbons was further associated with the late emergences Cycloclasticus in both seawater sources. The results showed that chemically dispersed oil may be rapidly biodegraded by microbial communities in Arctic seawater. Compared to oil biodegradation studies at higher seawater temperatures, longer lag-periods were experienced here, and may be attributed to both microbial and oil properties at these low seawater temperatures.

Bioremediation of hydrocarbon-contaminated soils in cold regions: Development of a pre-optimized biostimulation biopile-scale field assay in Antarctica

Bioremediation proved to be an effective approach to deal with soil contamination, especially in isolated, cold environments such as Antarctica. Biostimulation, involving the addition of macronutrients -mainly nitrogen and phosphorous- is considered the simplest and cheapest bioremediation process. Optimizing the levels of these nutrients is a key step prior to the application of a biostimulation strategy. In this work, N and P levels, optimized by Response Surface Methodology (RSM) at lab-scale, were applied to an Antarctic hydrocarbon contaminated soil. The process was performed on-site, using high density polyethylene geomembranes (800μm) to isolate treated soil from the surroundings and under environmental conditions at Carlini station (Antarctica) during 50days. Two 0.5ton biopiles were used as experimental units; a control biopile (CC), and a biostimulated system (BS), amended with N and P. At the end of the assay, hydrocarbon removal was significantly higher in BS system compared to CC (75.79% and 49.54% respectively), showing that the applied strategy was effective enough to perform a field-assay in Antarctica that significantly reduce soil contamination levels; and proving that RSM represents a fundamental tool for the optimization of nutrient levels to apply during bioremediation of fuel contaminated cold soils.

Corexit 9500 Enhances Oil Biodegradation and Changes Active Bacterial Community Structure of Oil-Enriched Microcosms

To better understand the impacts of Corexit 9500 on the structure and activity levels of hydrocarbon-degrading microbial communities, we analyzed next-generation 16S rRNA gene sequencing libraries of hydrocarbon enrichments grown at 5 and 25°C using both DNA and RNA extracts as the sequencing templates. Oil biodegradation patterns in both 5 and 25°C enrichments were consistent with those reported in the literature (i.e., aliphatics were degraded faster than aromatics). Slight increases in biodegradation were observed in the presence of Corexit at both temperatures. Differences in community structure were observed between treatment conditions in the DNA-based libraries. The 25°C consortia were dominated by Vibrio, Idiomarina, Marinobacter, Alcanivorax, and Thalassospira species, while the 5°C consortia were dominated by several species of the genera Flavobacterium, Alcanivorax, and Oleispira Most of these genera have been linked to hydrocarbon degradation and have been observed after oil spills. Colwellia and Cycloclasticus, known aromatic degraders, were also found in these enrichments. The addition of Corexit did not have an effect on the active bacterial community structure of the 5°C consortia, while at 25°C, a decrease in the relative abundance of Marinobacter was observed. At 25°C, Thalassospira, Marinobacter, and Idiomarina were present at higher relative abundances in the RNA than DNA libraries, suggesting that they were active in degradation. Similarly, Oleispira was greatly stimulated by the addition of oil at 5°C.IMPORTANCE While dispersants such as Corexit 9500 can be used to treat oil spills, there is still debate on the effectiveness on enhancing oil biodegradation and its potential toxic effect on oil-degrading microbial communities. The results of this study provide some insights on the microbial dynamics of hydrocarbon-degrading bacterial populations in the presence of Corexit 9500. Operational taxonomic unit (OTU) analyses indicated that several OTUs were inhibited by the addition of Corexit. Conversely, a number of OTUs were stimulated by the addition of the dispersant, many of which were identified as known hydrocarbon-degrading bacteria. The results highlight the value of using RNA-based methods to further understand the impact of dispersant on the overall activity of different hydrocarbon-degrading bacterial groups.

Assessment of three approaches of bioremediation (Natural Attenuation, Landfarming and Bioagumentation - Assistited Landfarming) for a petroleum hydrocarbons contaminated soil

Contamination with total petroleum hydrocarbons (TPH) subsequent to refining activities, is currently one of the major environmental problems. Among the biological remediation approaches, landfarming and in situ bioremediation strategies are of great interest. Purpose of this study was to verify the feasibility of a remediation process wholly based on biological degradation applied to contaminated soils from a decommissioned refinery. This study evaluated through a pot experiment three bioremediation strategies: a) Natural Attenuation (NA), b) Landfarming (L), c) Bioaugmentation-assisted Landfarming (LB) for the treatment of a contaminated soil with petroleum hydrocarbons (TPHs). After a 90-days trial, Bioagumentation - assistited Landfarming approach produced the best results and the greatest evident effect was shown with the most polluted samples reaching a reduction of about 86% of total petroleum hydrocarbons (TPH), followed by Landfarming (70%), and Natural Attenuation (57%). The results of this study demonstrated that the combined use of bioremediation strategies was the most advantageous option for the treatment of contaminated soil with petroleum hydrocarbons, as compared to natural attenuation, bioaugmentation or landfarming applied alone. Besides, our results indicate that incubation with an autochthonous bacterial consortium may be a promising method for bioremediation of TPH-contaminated soils.

Bioconcentration, biotransformation and elimination of pyrene in the arctic crustacean Gammarus setosus (Amphipoda) at two temperatures

The influence of temperature on the bioaccumulation, toxicokinetics, biotransformation and depuration of pyrene was studied in the arctic marine amphipod Gammarus setosus. A two-compartment model was used to fit experimental values of total body burden, total metabolites and parent pyrene concentrations and to calculate toxicokinetic variables derived for two experimental treatments (2 and 8 °C). No statistically significant differences were observed with temperature for these toxicokinetic variables or bioconcentration factors. Contrarily, the Q10 values suggested that the toxicokinetic variables ke and km were temperature-dependent. This may be explained by the high standard deviation of the Q10 values. Q10 is the variation in the rate of a metabolic reaction with a 10 °C increase in temperature. Depuration rate constants were calculated from linear best fit equations applied to measured pyrene concentrations over time during the depuration phase of the experiment. During depuration, the parent pyrene was eliminated in two stages with faster elimination observed at 8 °C compared to 2 °C. This finding was also indicated by the Q10. No changes in total body burdens of metabolite concentrations were observed during the monitoring of depuration over a period of 96 h. The biotransformation pathway of pyrene in G. setosus was also investigated in this study with two main phase II biotransformation products discovered by liquid chromatography. These products are conditionally identified as the sulphate and glucose conjugates of 1-hydroxy-pyrene. Overall, the study contributes new knowledge to the understanding of the fate of PAHs in arctic biota. In particular, the study provides valuable insight into the bioaccumulation and biotransformation of an important PAH and its metabolites in a species that serves as both a predator and prey in the arctic ecosystem.

Hydrocarbon biodegradation in intertidal wetland sediments

Intertidal wetlands, primarily salt marsh, mangrove and mudflats, which provide many essential ecosystem services, are under threat on numerous fronts; a situation that is made worse by crude-oil pollution. Microbes are the main vehicle for remediation of such sediments, and new discoveries, such as novel biodegradation pathways, means of accessing oil, multi-species interactions, and community-level responses to oil addition, are helping us to understand, predict and monitor the fate of oil. Despite this, there are many challenges, not least because of the heterogeneity of these ecosystems and the complexity of crude oil. For example, there is growing awareness about the toxicity of the oxygenated products that result from crude-oil weathering, which are difficult to degrade. This review highlights how developments in areas as diverse as systems biology, microbiology, ecology, biogeochemistry and analytical chemistry are enhancing our understanding of hydrocarbon biodegradation and thus bioremediation of oil-polluted intertidal wetlands.