Oil-biodegradation; Dispersants; Ultra-high resolution mass spectrometry; Corexit; Gulf of Mexico
1. Introduction
Between April and July 2010, about 790 million liters of oil were released at a depth of 1500 m during the Deepwater Horizon (DWH) blowout in the northern Gulf of Mexico (hereafter Gulf) (McNutt et al., 2012). During the discharge, 7 million liters of chemical dispersants were used, mostly Corexit 9500A, of which ca. 3 million liters were applied directly to the discharging wellhead (National Response Team, 2011), and smaller amounts of Corexit 9527, which was mainly applied at the sea surface (Graham et al., 2011 and Kujawinski et al., 2011). The deep ocean application of dispersant was unprecedented. Many of the biological and physical factors that determine the distribution and degradation of chemically dispersed oil at sea remain poorly constrained (National Research Council, 2005). For example, there is insufficient knowledge about the rates at which dispersed oil binds to sediments, how quickly it is degraded in the ocean, whether and how it is taken up by organisms, and what (final) products are created during the degradation processes (National Research Council, 2005). The long-term fate of dispersant-derived products in the environment is a subject of ongoing research (White et al., 2014).
Chemical dispersants are applied after oil-spills to emulsify the AT9283 oil-derived molecules in water and to stimulate biodegradation (National Research Council, 2005). Their primary purpose is to prevent the formation of thick surface oil slicks by enhancing the solution of oil in water and microbial oil degradation by increasing the bioavailability of the oil in the water column. While dispersants are generally assumed to be less toxic than oil (National Research Council, 2005), the increased oil-in-water solubility could make chemically dispersed oil more toxic to aquatic organisms (George-Ares and Clark, 2000 and National Research Council, 2005), including algae (Lewis and Pryor, 2013), micro-zooplankton (Almeda et al., 2014) and fish (Ramachandran et al., 2004). Dispersants can also affect microbial degradation of oil-derived hydrocarbons (Lindstrom and Braddock, 2002). The commercially available dispersants Corexit 9500A and Corexit 9527 contain ca. 10% and 17% mass fraction (w/w%) of the anionic surfactant di-octyl sulfosuccinate (DOSS; Kujawinski et al., 2011), respectively, which has been shown to persist for more than four years after application in the deep ocean (Kujawinski et al., 2011 and White et al., 2014).
Quantifying the chemical composition of petroleum remains an analytical challenge (Marshall and Rodgers, 2008). Gas-chromatography (GC) is capable of resolving only a small fraction of oil-derived molecules and most of the molecules that remain at oil-contaminated sites after weathering fall outside the GC-amenable analytical window (Aeppli et al., 2012). Almost 60% of the total mass of organics in Macondo crude oil is not detectable by conventional GC analyses (McKenna et al., 2013). Ultra high-resolution mass spectrometry is an analytical method that is capable of determining the primary molecular composition of oil (Marshall and Rodgers, 2003 and Ruddy et al., 2014). The high mass accuracy of Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) allows the determination of thousands of molecular formulae in petroleum and dissolved organic matter (DOM; Marshall and Rodgers, 2008). While petroleum characterization via FT-ICR-MS has been the subject of several studies, the molecular characterization of the water-accommodated fraction (WAF) of oil or dispersant-derived compounds has received less attention, and previous studies on oil weathering and biodegradation focused mainly on oil-derived molecules from particulate organic matter (McKenna et al., 2013 and Ruddy et al., 2014).
The present study extends the work of Kleindienst et al. (2015b) who explored the effects of dispersants on the activity and composition of oil-degrading microorganisms in a laboratory experiment. In their study, Kleindienst et al. (2015b) found that the application of dispersant significantly changed the microbial community composition within a week and did not enhance rates of hydrocarbon degradation (determined by 14C-hydrocarbon tracer expe
1. Introduction
Between April and July 2010, about 790 million liters of oil were released at a depth of 1500 m during the Deepwater Horizon (DWH) blowout in the northern Gulf of Mexico (hereafter Gulf) (McNutt et al., 2012). During the discharge, 7 million liters of chemical dispersants were used, mostly Corexit 9500A, of which ca. 3 million liters were applied directly to the discharging wellhead (National Response Team, 2011), and smaller amounts of Corexit 9527, which was mainly applied at the sea surface (Graham et al., 2011 and Kujawinski et al., 2011). The deep ocean application of dispersant was unprecedented. Many of the biological and physical factors that determine the distribution and degradation of chemically dispersed oil at sea remain poorly constrained (National Research Council, 2005). For example, there is insufficient knowledge about the rates at which dispersed oil binds to sediments, how quickly it is degraded in the ocean, whether and how it is taken up by organisms, and what (final) products are created during the degradation processes (National Research Council, 2005). The long-term fate of dispersant-derived products in the environment is a subject of ongoing research (White et al., 2014).
Chemical dispersants are applied after oil-spills to emulsify the AT9283 oil-derived molecules in water and to stimulate biodegradation (National Research Council, 2005). Their primary purpose is to prevent the formation of thick surface oil slicks by enhancing the solution of oil in water and microbial oil degradation by increasing the bioavailability of the oil in the water column. While dispersants are generally assumed to be less toxic than oil (National Research Council, 2005), the increased oil-in-water solubility could make chemically dispersed oil more toxic to aquatic organisms (George-Ares and Clark, 2000 and National Research Council, 2005), including algae (Lewis and Pryor, 2013), micro-zooplankton (Almeda et al., 2014) and fish (Ramachandran et al., 2004). Dispersants can also affect microbial degradation of oil-derived hydrocarbons (Lindstrom and Braddock, 2002). The commercially available dispersants Corexit 9500A and Corexit 9527 contain ca. 10% and 17% mass fraction (w/w%) of the anionic surfactant di-octyl sulfosuccinate (DOSS; Kujawinski et al., 2011), respectively, which has been shown to persist for more than four years after application in the deep ocean (Kujawinski et al., 2011 and White et al., 2014).
Quantifying the chemical composition of petroleum remains an analytical challenge (Marshall and Rodgers, 2008). Gas-chromatography (GC) is capable of resolving only a small fraction of oil-derived molecules and most of the molecules that remain at oil-contaminated sites after weathering fall outside the GC-amenable analytical window (Aeppli et al., 2012). Almost 60% of the total mass of organics in Macondo crude oil is not detectable by conventional GC analyses (McKenna et al., 2013). Ultra high-resolution mass spectrometry is an analytical method that is capable of determining the primary molecular composition of oil (Marshall and Rodgers, 2003 and Ruddy et al., 2014). The high mass accuracy of Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) allows the determination of thousands of molecular formulae in petroleum and dissolved organic matter (DOM; Marshall and Rodgers, 2008). While petroleum characterization via FT-ICR-MS has been the subject of several studies, the molecular characterization of the water-accommodated fraction (WAF) of oil or dispersant-derived compounds has received less attention, and previous studies on oil weathering and biodegradation focused mainly on oil-derived molecules from particulate organic matter (McKenna et al., 2013 and Ruddy et al., 2014).
The present study extends the work of Kleindienst et al. (2015b) who explored the effects of dispersants on the activity and composition of oil-degrading microorganisms in a laboratory experiment. In their study, Kleindienst et al. (2015b) found that the application of dispersant significantly changed the microbial community composition within a week and did not enhance rates of hydrocarbon degradation (determined by 14C-hydrocarbon tracer expe