2017 State-of the Science of Dispersants and Dispersed Oil (DDO) in U.S. Arctic Waters: Degradation and Fate

Chemical dispersants were employed on an unprecedented scale during the Deepwater Horizon oil spill in the Gulf of Mexico, and could be a response option should a large spill occur in Arctic waters. The use of dispersants in response to that spill raised concerns regarding the need for chemical dispersants, the fate of the oil and dispersants, and their potential impacts on human health and the environment. Concerns remain that would be more evident in the Arctic, where the remoteness and harsh environmental conditions would make a response to any oil spill very difficult. An outcome of a 2013 Arctic oil spill exercise for senior federal agency leadership identified the need for an evaluation of the state-of-the-science of dispersants and dispersed oil (DDO), and a clear delineation of the associated uncertainties that remain, particularly as they apply to Arctic waters. The National Oceanic and Atmospheric Administration (NOAA), in partnership with the Coastal Response Research Center (CRRC), and in consultation with the U.S. Environmental Protection Agency (EPA) embarked on a project to seek expert review and evaluation of the state-of-the-science and the uncertainties involving DDO. The project focused on five areas and how they might be affected by Arctic conditions: dispersant effectiveness, distribution and fate, transport and chemical behavior, environmental impacts, and public health and safety. This publication (1 of 5) addresses efficacy and effectiveness

Pentachlorophenol and spent engine oil degradation by Mucor ramosissimus

Pentachlorophenol (PCP) has been widely used for many years and belongs to the most toxic pollutants. Spent engine oils enter environment every day in many ways. Both of them cause great environmental concern. In the present work we focused on identifying metabolites of PCP biodegradation formed in the cultures of Mucor ramosissimus IM 6203 and optimizing medium composition to enhance PCP removal in the presence of engine oil acting as a carbon source. Pentachlorophenol (PCP) to tetrachlorohydroquinone (TCHQ) transformation was the most interesting transformation conducted by the tested strain. TCHQ was further transformed to 2,3,5,6-TCP and 2,3,4,6- TCP. Strain IM 6203 is also capable of PCP transformation to corresponding anisoles – pentachloromethoxybenzene (PCMB) and pentachloroethoxybenzene (PCEB). Characterization of enzymatic background involved in PCP to TCHQ transformation showed that TCHQ formation is catalyzed by inductive and cytochrome P-450 dependent enzymatic system. Experiments conducted on mineral medium allowed defining the optimal quantitative and qualitative medium make-up for PCP to TCHQ transformation. Biodegradation of PCP on the optimized synthetic medium X was more efficient than on rich Sabouraud medium. The tested strain is capable of growing in the presence of spent engine oil therefore we checked the ability of PCP transformation on optimized synthetic medium containing oil as a carbon source. The obtained results showed that PCP removal and TCHQ formation occurred were found to be the most efficient on the oil containing medium (OX medium). PCP removal and TCHQ formation after 240 h of culturing reached 1.19 mg/l and 0.89 mg/l, respectively. Additionally, 55.5% of oil introduced to the medium was removed during 10 days of the experiment. PCP biodegradation mechanisms used by Mucor species have not been sufficiently explained. The presented results point to the tested strain as an interesting model for the research on fungal PCP biodegradation in the areas highly contaminated with engine oil and for its future application in PCP and oils removal

Volatile hydrocarbons inhibit methanogenic crude oil degradation

Methanogenic degradation of crude oil in subsurface sediments occurs slowly, but without the need for exogenous electron acceptors, is sustained for long periods and has enormous economic and environmental consequences. Here we show that volatile hydrocarbons are inhibitory to methanogenic oil biodegradation by comparing degradation of an artificially weathered crude oil with volatile hydrocarbons removed, with the same oil that was not weathered. Volatile hydrocarbons (nC5-nC10, methylcyclohexane, benzene, toluene, and xylenes) were quantified in the headspace of microcosms. Aliphatic (n-alkanes nC12-nC34) and aromatic hydrocarbons (4-methylbiphenyl, 3-methylbiphenyl, 2-methylnaphthalene, 1-methylnaphthalene) were quantified in the total hydrocarbon fraction extracted from the microcosms. 16S rRNA genes from key microorganisms known to play an important role in methanogenic alkane degradation (Smithella and Methanomicrobiales) were quantified by quantitative PCR. Methane production from degradation of weathered oil in microcosms was rapid (1.1 ± 0.1 μmol CH4/g sediment/day) with stoichiometric yields consistent with degradation of heavier n-alkanes (nC12-nC34). For non-weathered oil, degradation rates in microcosms were significantly lower (0.4 ± 0.3 μmol CH4/g sediment/day). This indicated that volatile hydrocarbons present in the non-weathered oil inhibit, but do not completely halt, methanogenic alkane biodegradation. These findings are significant with respect to rates of biodegradation of crude oils with abundant volatile hydrocarbons in anoxic, sulphate-depleted subsurface environments, such as contaminated marine sediments which have been entrained below the sulfate-reduction zone, as well as crude oil biodegradation in petroleum reservoirs and contaminated aquifers

Degradation of Dispersants and Dispersed Oil

Chemical oil dispersants are proprietary mixtures of surfactants and solvents which are directly applied to a spill in order to reduce the natural attractive forces of the oil. When oil treated with dispersants is exposed to mixing energy, typically from wind and wave action, it is broken up into small droplets which may then become entrained in the water column (Li et al., 2009a; Li et al., 2009b; Li, 2008; Lunel, 1995). Many of these droplets are small enough to be neutrally buoyant, and therefore, advection and diffusion forces dilute the plume and transport the droplets far from the site of the original spill. As compared to a surface oil slick or larger and more buoyant physically dispersed oil droplets, these chemically dispersed droplets are much easier for oil-degrading bacteria to colonize and break down (Venosa and Holder, 2007; Venosa and Zhu, 2003). In addition, small droplets enhance dissolution of soluble and semi-volatile compounds into surrounding waters, wherein biodegradation is carried out by aqueous phase microbes. Under these conditions, oil concentration are effectively reduced below toxicity threshold limits, and biodegradation becomes the most important process in reducing the total mass of petroleum hydrocarbons in the environment. By enabling rapid dispersion and biodegradation of surface oil slicks at sea, the use of chemical oil dispersants can be effective in preventing heavy oiling of sensitive coastal environments such as beaches and wetlands, and consequently mitigates risk associated with marine and terrestrial wildlife coming into direct contact with a slick

Kinetic parameters for nutrient enhanced crude oil biodegradation in intertidal marine sediments

Availability of inorganic nutrients, particularly nitrogen and phosphorous, is often a primary control on crude oil hydrocarbon degradation in marine systems. Many studies have empirically determined optimum levels of inorganic N and P for stimulation of hydrocarbon degradation. Nevertheless, there is a paucity of information on fundamental kinetic parameters for nutrient enhanced crude oil biodegradation that can be used to model the fate of crude oil in bioremediation programmes that use inorganic nutrient addition to stimulate oil biodegradation. Here we report fundamental kinetic parameters (Ks and qmax) for nitrate-and phosphate-stimulated crude oil biodegradation under nutrient limited conditions and with respect to crude oil, under conditions where N and P are not limiting. In the marine sediments studied, crude oil degradation was limited by both N and P availability. In sediments treated with 12.5 mg/g of oil but with no addition of N and P, hydrocarbon degradation rates, assessed on the basis of CO2 production, were 1.10 ± 0.03 μmol CO2/g wet sediment/day which were comparable to rates of CO2 production in sediments to which no oil was added (1.05 ± 0.27 μmol CO2/g wet sediment/day). When inorganic nitrogen was added alone maximum rates of CO2 production measured were 4.25 ± 0.91 μmol CO2/g wet sediment/day. However, when the same levels of inorganic nitrogen were added in the presence of 0.5% P w/w of oil (1.6 μmol P/g wet sediment) maximum rates of measured CO2 production increased more than four-fold to 18.40 ± 1.04 μmol CO2/g wet sediment/day. Ks and qmax estimates for inorganic N (in the form of sodium nitrate) when P was not limiting were 1.99 ± 0.86 μmol/g wet sediment and 16.16 ± 1.28 μmol CO2/g wet sediment/day respectively. The corresponding values for P were 63 ± 95 nmol/g wet sediment and 12.05 ± 1.31 μmol CO2/g wet sediment/day. The qmax values with respect to N and P were not significantly different (P < 0.05). When N and P were not limiting Ks and qmax for crude oil were 4.52 ± 1.51 mg oil/g wet sediment and 16.89 ± 1.25 μmol CO2/g wet sediment/day. At concentrations of inorganic N above 45 μmol/g wet sediment inhibition of CO2 production from hydrocarbon degradation was evident. Analysis of bacterial 16S rRNA genes indicated that Alcanivorax spp. were selected in these marine sediments with increasing inorganic nutrient concentration, whereas Cycloclasticus spp. were more prevalent at lower inorganic nutrient concentrations. These data suggest that simple empirical estimates of the proportion of nutrients added relative to crude oil concentrations may not be sufficient to guarantee successful crude oil bioremediation in oxic beach sediments. The data we present also help define the maximum rates and hence timescales required for bioremediation of beach sediments

Marine crude-oil biodegradation: a central role for interspecies interactions

The marine environment is highly susceptible to pollution by petroleum, and so it is important to understand how microorganisms degrade hydrocarbons, and thereby mitigate ecosystem damage. Our understanding about the ecology, physiology, biochemistry and genetics of oil-degrading bacteria and fungi has increased greatly in recent decades; however, individual populations of microbes do not function alone in nature. The diverse array of hydrocarbons present in crude oil requires resource partitioning by microbial populations, and microbial modification of oil components and the surrounding environment will lead to temporal succession. But even when just one type of hydrocarbon is present, a network of direct and indirect interactions within and between species is observed. In this review we consider competition for resources, but focus on some of the key cooperative interactions: consumption of metabolites, biosurfactant production, provision of oxygen and fixed nitrogen. The emphasis is largely on aerobic processes, and especially interactions between bacteria, fungi and microalgae. The self-construction of a functioning community is central to microbial success, and learning how such " microbial modules" interact will be pivotal to enhancing biotechnological processes, including the bioremediation of hydrocarbons. © 2012 McGenity et al.; licensee BioMed Central Ltd

Marine snow formation during oil spills: additional ecotoxicological consequences for the benthic ecosystem

The Deepwater Horizon (DWH) oil spill in the Gulf of Mexico in 2010 was one of the largest oil spills in history. For three months, oil leaked from the Macondo well at 1,500 m depth into the Gulf. As one of the spill responses, an unprecedented amount of dispersants were applied, both at the sea surface and, for the first time ever, directly injected into the wellhead. During the spill, unusually large amounts of marine snow, including Extracellular Polymeric Substances (EPS), were formed. Oil-contaminated marine snow aggregates were formed by aggregation of EPS with suspended solids, phytoplankton cells due to the spring bloom, and the dispersed oil droplets. The marine snow sank through the water column and settled on the ocean floor. This process was named MOSSFA: Marine Oil Snow Sedimentation and Flocculent Accumulation. MOSSFA was an important pathway of transferring oil to the deep-sea, and 14-21% of the total discharged oil is estimated to have settled on the sediment, where it impacted the benthic ecosystem. This thesis focused first on the mechanism of EPS snow formation, and then more in depth on the additional ecotoxicological consequences of marine snow formation during oil spills for the benthic ecosystem. Chapter 2 describes the role of chemical dispersants in the presence of phytoplankton in the formation of EPS, one of the main ingredients of marine snow. Results show that phytoplankton-associated bacteria were responsible for the EPS formation, and the symbiosis between the phytoplankton and its associated bacterial community provided the bacteria with energy to produce the EPS. The microcosm experiment in Chapter 3 investigated the effect of marine snow on oil biodegradation in microcosms without benthic macroinvertebrates. Results showed that marine snow hampers oil biodegradation: the presence of marine snow reduced the depletion of oil alkanes by 40%, most likely due to the high biodegradability of marine snow organics compared to the oil. Biodegradation of marine snow resulted in anaerobic conditions in the top of the sediment layer. This reduced the oil biodegradation. Marine snow thus prolongs the residence time of oil in the benthic ecosystem. The next microcosm experiment, described in Chapter 4, investigated the effects of oil-contaminated marine snow on benthic macroinvertebrates, and the effect of macroinvertebrates on oil biodegradation. Bioturbation by the invertebrates increased the oxygenated top layer of the sediment and partly counterbalanced the inhibition of oil biodegradation due to oxygen consumption by marine snow. Survival of three benthic invertebrate species was reduced by (oil-contaminated) marine snow. Oxygen depletion near the sediment surface seemed to be the main reason for the observed adverse effects of the marine snow. In addition, indications were found that some species used the marine snow as food source, even when it was oil-contaminated. In the last microcosm experiment, described in Chapter 5, two benthic invertebrate species were monitored over a period of 42 days after which new animals were introduced and observed for an additional period of 22 days. Marine snow degradation again resulted in lower dissolved oxygen concentrations in the water column, which inhibited oil biodegradation on the sediment compared to oil in combination with clay. The oxygenated top layer of the sediment disappeared, and recovered after ~20 days. At the end of the experiment, mudsnails from the treatments with oiled marine snow had higher PAH concentrations in their tissues than the animals from the treatments with the same amount of oil in clay only, confirming the use of marine snow as food source. Overall, oil-contaminated marine snow on the ocean sediment can negatively affect benthic ecosystems, and can hamper oil biodegradation and ecosystem recovery. The additional consequences of MOSSFA during oil spills and spill responses should be taken into account in oil spill response planning.</p

Influence of salinity and fungal prevalence on bioremediation of crude oil polluted soil

The effect of NaCI salt on bioremediation of crude oil polluted soil was studied. Salt&#183; treatments included NaCI amendments to adjust the soil solution electrical conductivities to 50, 130, 210 dsm-1. Oil biodegradation was estimated from quantities of CO2 evolved. Salt concentration at 210 dsm-1 in oil polluted soil resulted in a significant decrease (p &lt;0.05) in oil biodegradation. A salt concentration of 50 dsm-1 reduced bioremediation by about 12%. The physico-chemical properties of the soil samples examined showed that the total hydrocarbon (THC) content increased with the oil pollution but significantly decreased (p &lt; 0.05) with NaCI addition. The prevalence of fungal species in the soil samples during each sampling intervals showed that the oil contaminated soil and the uncontaminated soil supported fungal growth while addition of NaCI reduced the fungalpopulation in the soi

Gas Chromatographic Investigation of Oil Biodegradation Degree

The research of the degree of oil biodegradation by gas chromatography and individual classes of hydrocarbons by various strains of hydrocarbon-oxidizing microorganisms isolated from indigenous microflora of oil fields was carried out. It has been shown that some of the investigated strains of hydrocarbon-oxidizing microorganisms are 100% capable to biotransform naphthenes and olefins, showing high activity in the destruction of paraffins and isoparaffins. There are no signs of biodegradation of aromatic compounds due to the large duration of the process. All investigated strains of hydrocarbon-oxidizing microorganisms are largely able to reduce the total number of individual components of oil. The obtained data can be used to develop new biologics of the purpose