Pdf lessons from the 2010 deepwater horizon accident in the gulf

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Lessons from the 2010 Deepwater Horizon Accident in the Gulf of Mexico

Terry C. Hazen

Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 Lesson 1. Marine Oil Biodegradation Like All Politics Is Local and DWH Had Many Unique

Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3 Lesson 2. Oil in the Water Column and in Coastal Sediments Biodegraded Faster Than

Expected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 Lesson 3. Long-Term Adaption to Natural Seeps Played an Important Role in DWH Oil

Biodegradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5 Lesson 4. Jetting and Dispersants at the Well Head Increased Oil Biodegradation . . . . . . . 7 6 Lesson 5. Comparisons of DWH with Exxon Valdez Oil Spill for Oil Biodegradation Were Not

Appropriate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7 Lesson 6. Models for DWH Were Inappropriate at First . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 8 Lesson 7. Cometabolic Oil Biodegradation May Be Important in Deep Marine Basins . . 10 9 Lesson 8. Blooms of Oil Degraders in the Deep Led to a Temporal Succession of Other

Bacterial Communities with Unknown Effects on Trophic Levels . . . . . . . . . . . . . . . . . . . . . . . . 11 10 Lesson 9. Molecular Techniques Led to a More Thorough Understanding of DWH Oil

Biodegradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 11 Lesson 10. Hydrostatic Pressure Had Little Effect on DWH Oil Biodegradation . . . . . . . . . 12 12 Research Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

T. C. Hazen (*) Department of Civil and Environmental Engineering, Department of Earth and Planetary Sciences, Department of Microbiology, Institute for Secure and Sustainable Environment, Methane Center, University of Tennessee, Knoxville, TN, USA

Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA e-mail: tchazen@utk.edu

# Springer Nature Switzerland AG 2018

1

H. Wilkes (ed.), Hydrocarbons, Oils and Lipids: Diversity, Origin, Chemistry and Fate,

Handbook of Hydrocarbon and Lipid Microbiology,



2

T. C. Hazen

Abstract The 2010 Deepwater Horizon (DWH) accident in the Gulf of Mexico had many unique aspects to it not seen in previous marine spills. Indeed, research related to the DWH response phase, Natural Resource Damage Assessment, Gulf of Mexico Research Initiative (GoMRI), National Academy of Sciences, US agencies: NOAA, EPA, Fish & Wildlife, DOE, and Coast Guard have made this the most studied marine oil spill in the world. There are many oil biodegradation lessons learned from this experience and these will undoubtedly continue for many years.

1 Introduction

On April 20, 2010, the Deepwater Horizon (DWH) an ultra-deepwater, dynamically positioned, semi-submersible, mobile offshore drilling rig owned by Transocean caught fire while drilling at the Macondo prospect in the Mississippi Canyon Block 252 lease and exploded 77 km off the coast of Louisiana in the Gulf of Mexico with the loss of 11 lives. Several attempts to activate the blowout prevention device and the blind sheer ram failed. Two days later on April 22, 2010, the DWH sank to the seafloor at 1500 m, with the 53 cm riser pipe detaching from the rig it collapsed into a convoluted heap on the seafloor and began leaking oil in at least 3 sections. This caused the largest marine oil spill in United States history and the second largest marine oil spill in the world (Fig. 1). On June 3, 2010, the riser was cut off at the top of the blowout prevention device. After several attempts to stem the flow of oil failed, the well was successfully capped on July 15, 2010, and declared dead by the National Incident Commander on September 19, 2010. The government estimate of the amount of oil that came from the Macondo well directly into the environment was 4.1 million barrels with an additional 820,000 barrels captured via siphon tubes (Fig. 2) (FISG 2010). The cleanup effort was the largest ever in the world with more than 31,800 people involved (Fig. 2) (Deepwater Horizon Unified Command, 2010).

The DWH accident had many unique aspects to it not seen in previous marine spills. Indeed, research related to the DWH response phase, Natural Resource Damage Assessment, Gulf of Mexico Research Initiative (GoMRI), National Academy of Sciences, US agencies: NOAA, EPA, Fish & Wildlife, DOE, and Coast Guard have made this the most studied marine oil spill in the world. There are many oil biodegradation lessons learned from this experience and these will undoubtedly continue for many years.

2 Lesson 1. Marine Oil Biodegradation Like All Politics Is Local and DWH Had Many Unique Aspects

Marine oil biodegradation is affected by a large number of parameters, e.g., oil type, currents, weather, temperature, pressure, limiting nutrients, water depth, input of oil (leak, spill, failure of blowout prevention device), season, risk receptors, and ability

Lessons from the 2010 Deepwater Horizon Accident in the Gulf of Mexico

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Fig. 1 Graphic depiction of Deepwater Horizon spill and cleanup, showing oil droplets rising to the surface and small droplet forming a deepwater cloud, oil sheens, and slicks the surface, with burning skimming, weathering, and blowout prevention (BOP) device that failed and injection of dispersant in the deep and at the surface. (After Atlas and Hazen (2011))

to apply remediation (dispersants, siphon tubes, booms, skimmers, burns). Many of these can work synergistically to impact oil biodegradation: (1) chemical dispersants + mineral fines can enhance formation and transfer of oil from the surface into the water column (Li et al. 2007), (2) autoinoculation from gyres + "memory response" of oil degraders leads to an increase in microbial abundance and accelerated oil biodegradation (Valentine et al. 2012), (3) oil droplet size + dispersion + biodegradation rates + dissolution enhances biodegradation, dissolution and dispersion rated oil hydrocarbons (Brakstad et al. 2015a), (4) cometabolic biodegradation + dispersion + secondary electron donors enhances biodegradation, dissolution, and dispersion rates of oil hydrocarbons even when the oil itself cannot be a suitable electron donor (Hazen et al. 2016), and (5) biosurfactants from multiple microorganisms can enhance bioavailability of poorly soluble hydrocarbons in the oil (Singh et al. 2007; McGenity et al. 2012).

DWH had many unique aspects, it was the deepest oil well blowout that has ever occurred, and it was the first time that dispersants were applied at the well head. It was not controlled for 84 days. It had deep water temperatures of 4 C and simultaneous surface water temperatures of over 30 C (Hazen et al. 2010).

4

Number of barrels and % breakdown*

Skimmed

160,000 3%

Burned

4.9m

total oil leaked

260,000 5%

Chemically dispersed

770,000 16%

Naturally dispersed

630,000 13%

13% 17%

Captured

820,000 17%

23%

Evaporated/dissolved

1.2M 23%

Remaining oil

1.1M 23%

23%

The cleanup effort to date

31,800

personnel involved in protecting and cleaning the shoreline and wildlife

1.84m

gallons of dispersant used

T. C. Hazen

3,447km 441

containment and absorbent

controlled burns

boom deployed

conducted

* Based on Flow Rate Techical Group's estimate

Sources: Deepwater Horizon Unified Command. NOAA

Fig. 2 Where the oil went? The Federal Interagency Solutions Group, Oil Budget Calculator Science and Engineering Team (November, 2010)

It occurred during the hurricane season, but only two major storms occurred during the period. There was a deepwater gyre at 1100 m that went from the Macondo well head out 15 km to the SW before turning back (Valentine et al. 2012). Deep water plumes occurred at four depths: 25, 265, 865, 1175 m, oil at the surface was moving to the North East while oil in the 1100 m plume was moving to the South West, the other three water column plumes moved to the SE, and NW (Spier et al. 2013). The Gulf of Mexico has more natural seeps than any other deepwater basin being considered for deepwater oil production (NAS 2003). Macondo oil is a very light crude, the Macondo well was jetting oil at high temperature (200 C) and high pressure (676 bars) at the well head (pressure of the ocean at 1500 m was 152 bars).

Lessons from the 2010 Deepwater Horizon Accident in the Gulf of Mexico

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The Macondo well was also one of the deepest wells; thus, the hydrostatic pressure may have had an effect on oil degraders like we have not seen before (Marietou et al. 2018). The Macondo oil had a high proportion of methane (Kessler et al. 2011). Nutrients from the Mississippi River made the overall nutrients higher near the spill (Hazen et al. 2010), and many hydrocarbons found in the Macondo oil and in the CORREXIT dispersant used were also found in Mississippi River and drainage into the Gulf of Mexico from non DWH sources (Kujawinski et al. 2011; King et al. 2014a).

3 Lesson 2. Oil in the Water Column and in Coastal Sediments Biodegraded Faster Than Expected

One of the first studies on oil biodegradation reported that the Macondo oil average half-life of alkanes in the deep water (1100) plume was 1.2?6.1 days (Table 1) (Hazen et al. 2010). The deepwater plume contained more than 80% alkanes, and four different techniques were used to make these calculations using microcosms with water and fresh Macondo oil at 5 C, mixed consortia (Venosa and Holder 2007) incubations with fresh Macondo oil at 5 C, and changes in alkane concentration from in the plume from the source to 10 km down gradient with split sample analyses done by two different labs and considering whether it took 2 days or 5 days to traverse that 10 km gradient (Hazen et al. 2010; Valentine et al. 2012). This surprised a lot of people. Rapid biodegradation also occurred initially of propane and ethane (Valentine et al. 2010). A more recent study again verified these findings (Thessen and North 2017). Considering that below 700 m the temperature in the Gulf of Mexico is always 5 C or less and it has been that way for millions of years, it should not be surprising that there are true psychrophiles that can degrade oil faster at 5 C then at 20 C and given there potentially long period of adaption degrade it faster than in previous studies at the surface (Baelum et al. 2012; Chakraborty et al. 2012; Dubinsky et al. 2013; Brakstad et al. 2015a; Hazen et al. 2016).

Macondo oil was also deposited in the sediments especially around the well head and in some other parts closer to shore as marine snow etc. (Rahsepar et al. 2017). Numerous studies also found that the sediment microbial community was degrading the Macondo oil faster than initially expected (Kimes et al. 2013, 2014; King et al. 2014a; Mason et al. 2014). Studies showed that a very active microbial community in the sediment was enriched in anaerobes (Deltaproteobacteria) in the deeper sediment and aerobes (Gammaproteobacteria) at the sediment surface that was very actively degrading a variety of Macondo well hydrocarbons including aromatic hydrocarbons (Kimes et al. 2013; Mason et al. 2014). Key hydrocarbon degradation pathways were determined by 14C-labeled substrates in order: propylene, glycol, dodecane, toluene, and phenanthrene (Mason et al. 2014).

Many studies along the coast where emulsified and weathered Macondo oil washed ashore also found that degradation rates of the Macondo oil were faster than previous studies at other sites around the world had shown (King et al. 2012, 2014a, b). Beach samples collected during the response phase and after showed a

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T. C. Hazen

Table 1 MC-252 alkane half-life (days) from field and laboratory with currents of 2?5 days to move 10 km from source. (After Hazen et al. (2010))

Mixed

Plume Plume BP BP Consortia samples samples data data 5C

Average 2.4

6.1

1.2 2.9 3.5

n-Tridecane C13alk 1.6

4.0

1.4 3.5 3.1

n-Tetradecane C14alk 1.5

3.8

1.4 3.4 3.5

Pentadecane C15alk 1.5

3.8

1.0 2.4 3.6

n-hexadecane C16alk 1.6

4.0

2.0 5.0 3.6

n-heptadecane C17alk 1.7

4.3

1.1 2.8 3.6

Pristane

C19teralk 1.6

4.1

1.3 3.2 3.0

n-octadecane C18alk 2.1

5.2

1.0 2.6 4.2

Phytane

C20teralk 1.8

4.6

1.4 3.4 3.6

n-Nonadecane C19alk 2.1

5.4

1.0 2.6 3.6

eicosane

C20alk 3.2

7.9

1.0 2.5 3.7

Heneicosane C21alk 3.7

9.3

1.9 4.7 3.5

n-Docosane C22alk 3.8

9.5

1.0 2.5 3.7

Tricosane

C23alk 3.7

9.2

1.0 2.5 3.6

tetracosane

C24alk 3.2

8.0

0.9 2.2 3.5

n-Pentacosane C25alk 2.8

7.0

0.8 1.9 3.6

n-hexacosane C26alk 3.1

7.8

0.6 1.6 3.1

Microcosm water, 5C 2.2 2.1 2.3 2.1 2.2 2.3 2.3 2.3 2.3 2.3 2.3 2.6 2.2 2.2 2.3 2.0 1.7

dominance of Alphaproteobacteria and Gammaproteobacteria (Kostka et al. 2011; Lamendella et al. 2014). Taxonomic diversity decreased in the sands for first few months but rebounded 1 year after the oil came ashore and much of the oil had been degraded (King et al. 2014a). Initially Pensacola Beach sands oil-degraders increased two orders of magnitude within the first week, while diversity decreased 50% (Huettel et al. 2018). Half-lives of the aliphatic and aromatic hydrocarbons were less than 25 days. Aerobic oil degradation was significantly promoted by tidal pumping. In the coastal salt marsh (Mobile Bay), the oil degrading community increased in richness and abundance especially among the Proteobacteria, Bacteroidetes, and Actinobacteria (Beazley et al. 2012). This study also suggested that marsh rhizosphere microbial communities could be contributing to the hydrocarbon degradation since there was a greater decrease in Macondo oil in marsh grass sediments than in inlet sediments that lacked marsh grass (King et al. 2014a). Studies in marshes in Barataria Bay, Louisiana, also showed increases in the bacteria Rhodobacterales and Sphingomonadales and the fungi Dothideomycetes (Mahmoudi et al. 2013). Another study that included 11 sites in southern Louisiana found that all studied marshes had increased abundance in Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria during the first 4 months, but after 2 years with barely detectable hydrocarbon levels the bacteria communities were more diverse and dominated by Alphaproteobacteria (Rhizobiales), Chloroflexi (Dehalococcoidia), and Planctomycetes (Engel et al. 2017).

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