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BP Oil Disaster at One Year: Known Impacts to date (and the considerable unknowns)

Sarah Chasis

Posted April 20, 2011 in Moving Beyond Oil, Reviving the World's Oceans, Saving Wildlife and Wild Places

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The Deepwater Horizon incident released a complex mixture of hydrocarbons, the chemicals that make-up fossil fuels, into the Gulf of Mexico. Liquid oil comprised approximately 60% of the total hydrocarbons discharged (by weight) from the gusher on the ocean floor; the other 40% was released as gases.  In addition, an unprecedented volume of chemical dispersants were injected into the Gulf.  All of these are toxic - to varying degrees - and all had the potential to adversely impact the Gulf’s rich marine and coastal life. 

So what harm was done?

Below is a summary of the scientific knowledge to-date, as represented in the peer-review literature and a handful of government studies, which our staff scientists prepared for the one year anniversary.  A quick review reveals that so far only the ‘chemistry story’ is beginning to emerge.  Even within that scope, important pieces of the story remain missing. 

The biological and ecological impacts have, essentially, not yet been quantified or made publically available.  There are two principal reasons for this apparent delay.  First, many of the studies currently underway are part of the Natural Resources Damage Assessment.  Much of the results obtained for this effort are not being released by the government until the matter of ecological damages is settled or goes to court. 

Second, biological research takes time.  For example, ecologists are tasked with determining:  how many animals and plants were killed by the oil and dispersant during the spill (even the ones that died and sank out of sight), how the loss of reproductive adults has affected the size of the next year’s generation (i.e., how many babies are out there this spring?), how much non-fatal harm was done by the toxins (e.g., organ damage, disease), and how the non-fatal harm is affecting adult survivorship and reproduction, and the extent of habitat destruction above and below the waves.  In other words, ecology is a multi-generation and multi-year science. 

While it is tempting to turn the page on this disaster, the truth is, it is simply too soon to characterize the full scope of the environmental harm from the Gulf oil spill.  Biologists and ecologists have not even begun laying their puzzle pieces on the table.    

The Oil:

KNOWN

  • Approximately 170 million gallons (+/- 10%) of oil entered the Gulf of Mexico at 5000 feet of water.

Surface oil

  • A large, but undetermined, proportion of the oil traveled to the surface of the water and formed oil slicks.
  • Some, small undetermined fraction of this ‘oil’ dissolved as it traveled to the surface.1
  • Approximately 8% of the total oil was recovered via burning and skimming.2
  • An estimated 25% of the oil evaporated3 (a higher proportion of ‘evaporated oil’ was suggested by the results of de Gouw et al., 2011.  However, their estimate, 26% of total hydrocarbons evaporated,  included oil and gas together and this continuum of hydrocarbons are difficult to separate out in the analysis.4)
  • A portion of the oil went to land; 650 miles of coastline were ‘oiled’ (126 miles moderately to heavily).5
  • Some of the oil on the coast is beginning to get buried or sequestered.  For example, impervious rinds have formed on surfaces exposed to weather and wave action, slowing aeration and inhibiting microbial activity.6
  • A portion of the oil stuck to sediment and sunk to the shallow bottom.
  • A portion of the oil is floating as tar balls in the Gulf of Mexico.
  • A portion of the oil was consumed by bacteria (in the water and on land).
  • The proportions remain undetermined.

Sub-surface oil

  • Some smaller undetermined fraction of oil formed sub-surface plumes at between 2000 and 4000 feet and travelled horizontally mixing very slowly with deep water.7
  • A large portion of the subsurface oil was consumed by oil-eating bacteria.8,9
  • Some undetermined proportion of the subsurface oil was deposited onto the deep sea floor.

UNKNOWN

  • A refined oil budget has not been completed. These questions remain unanswered:

        - What proportion of oil remained subsurface?

        - What proportion of oil is on the bottom (in deep sea and shallow sub-tidal bottom)?

        - What proportion of oil made it to land?

        - What proportion of remained in the water?

  • The spatial distribution and concentration of oil on the bottom.
  • The spatial distribution and volume of buried oil in coastal zone.
  • Persistence of oil in the various environments. 

The Gases:

KNOWN

  • The Deepwater Horizon incident released a mixture of gases (e.g., methane, ethane, and propane) that comprised approximately 40% of the total hydrocarbons discharged (by weight).10,11,12
  • Most of this gas was methane which amounted to 200,000 metric tons.13,14
  • Essentially all of the gas was dissolved in the water following release.  It did not make it to the surface.15,16
  • The gas behaved similarly to the minute droplets of oil and formed horizontal hydrocarbon plumes between 2000 and 4000 feet of water.17,18,19
  • The bulk of the methane was consumed by methane-eating bacteria on a time scale of months.20,21
  • The stimulated bacterial populations depleted dissolved oxygen in the deep water plumes, though not below levels of ecological concern (a depletion of 3-6% on average and 20% at its measured maximum).22,23

UNKNOWN

  • If any of the gases continue to persist above background levels.
  • The ecological consequences of the enhanced bacterial growth in the deep water.

The Dispersants:

KNOWN

  • 1.8 million gallons of chemical dispersant (Corexit 9500 and 9527) were added to the environment (≈ 1.07 million gallons at sea surface and ≈ 771,000 gallons subsurface)
  • Chemical dispersants were quickly diluted to very low concentrations.24
  • One component of the dispersant (dioctyl sodium sulfosuccinate, DOSS) was sequestered in deepwater hydrocarbon plumes following subsurface application, and persisted for up to hundreds of km from the well, in a very dilute state.  This study offers evidence that the chemical dispersant may have interacted with the oil (a necessary step to being effective).25
  • In laboratory assays, Corexit 9500 had roughly the same level of toxicity to a Gulf mysid shrimp (Americamysis bahia) and the silverside fish (Menidia) as seven other chemical dispersants.26
  • In EPA laboratory assays, the oil-dispersant mixture (Corexit 9500) had higher toxicity than the dispersant alone to mysid shrimp and silverside fish.  However, the oil-dispersant mixture had similar toxicity as the oil itself (for mysid shrimp and the silverside fish.)
  • In EPA vitro assessments, found no evidence of any estrogenicity and androgenicity using in mammalian cell lines.
  • FDA tests for a component of the chemical dispersant, dioctyl sodium sulfosuccinate (DOSS), showed trace amounts of the chemical in 13 of the 1,735 samples of seafood, and all were well below the safety threshold of 100 parts per million for finfish and 500 parts per million for shrimp, crabs and oysters.  The data suggests that chemical dispersants are not building up in fish tissue. 

UNKNOWN

  • Were the dispersants effective (surface and subsurface)?  And if so, how  effective?*
  • Sensitivity of many Gulf organisms to chemical dispersants and dispersant/oil mixture, particularly deep sea organisms which may exhibit different sensitivities.
  • Impact of the dispersant on the bioavailability of the oil during this oil spill.
  • The effect that chemical dispersants had on the rate of bacterial degradation of the oil (enhanced, retarded, no effect?)
  • A rigorous analysis of the tradeoffs made with the use of chemical dispersants during the DWH oil spill.

The Wildlife:

KNOWN

  • Approximately 6000 dead birds were collected around the duration of the spill. 
  • Approximately 600 sea turtle carcasses were collected around the duration of the spill.   
  • Approximately100 marine mammal carcasses were collected around the duration of the spill.
  • Actual mortality of marine mammals during the spill could be 16 to more than 250 times higher than the carcass count indicates, since whales and dolphins tend to quickly sink when they die.27

UNKNOWN

  • Actual number of individual birds, turtles, and marine mammals killed by the oil spill (this includes a quantification of what proportion of known deaths resulted from the oil spill (which may be subtracted from the above carcass counts) as well as an estimate of the unaccounted for individual organisms that were killed by the oil (which will serve as a multiplier to oil-accounted deaths).

Fisheries:

UNKNOWN:

  • Little to nothing is known about fisheries impacts yet.  There are no published papers in the peer review literature.  Information being collected by NRDA is closed to the public.

Ecological Impacts to Gulf of Mexico Habitats:

KNOWN:

  • Oil-derived carbon quickly entered coastal planktonic food webs in the northern Gulf of Mexico.28

UNKNOWN:

  • Damage to various ecosystems has been observed (e.g., deep sea soft bottom, deep sea corals, mid-water, surface waters, floating Sargassum seaweed communities, estuarine muddy bottom, coastal marshes, sea grass beds, sandy beaches).  However, to date there is no quantitative information of scale of harm.  Similarly, there are little to no peer-review publications about population-level impacts for any species (aside from microbes).  Discussions regarding community-level or ecosystem-level impacts are also lacking. Information being collected by NRDA is closed to the public.

 


 

1. Kessler JD et al., A Persistent Oxygen Anomaly Reveals the Fate of Spilled Methane in the Deep Gulf of Mexico. Science 331: (6015): 312-315 JAN 21 2011.

2. Lehr B.P. et al,  2010.  Oil Budget Calculator: Deepwater Horizon.  A Report by: The Federal Interagency Solutions Group, Oil Budget Calculator Science and Engineering Team.

3. Lehr B.P. et al,  2010.  Oil Budget Calculator: Deepwater Horizon.  A Report by: The Federal Interagency Solutions Group, Oil Budget Calculator Science and Engineering Team.

4. de Gouw J.A. et al., 2001.  Organic aerosol formation downwind from the Deepwater Horizon Oil Spill.  Science 11: 1295-1299.

5. Owens et al., 2011. The Deepwater Horizon-Macondo 2010 shoreline cleanup assessment technique (SCAT) program. Geological Society of America Abstracts with Programs, Vol. 43, No. 3, p. 11.

6. Deocampo et al., 2011. Biodegradation of Deepwater Horizon petroleum hydrocarbons in Barataria Bay marshes: geomicrobiology and clay mineral enhancement. Geological Society of America Abstracts with Programs, Vol. 43, No. 3, p. 12.

7. Camilli R. et al., 2010. Tracking hydrocarbon plume transport and biodegradation at Deepwater Horizon. Science 330: 201-204.

8. Hazen T.C. et al., 2010. Deep-sea oil plume enriches indigenous oil-degrading bacteria. Science 330: 204-208.

9. Valentine D.L. et al., 2010.Propane respiration jump-starts microbial response to a deep oil spill. Science 330: 208-211.

10. Kessler et al., 2011. A Persistent Oxygen Anomaly Reveals the Fate of Spilled Methane in the Deep Gulf of Mexico.  Science 331:  312-315

11. Joye S.B. et al., 2011. Magnitude and oxidation potential of hydrocarbon gases released from the BP oil well blowout. Nature Geoscience. DOI: 10.1038/NGEO1067.

12. Ryerson T.B.  et al.,  2011. Atmospheric emissions from the Deepwater Horizon spill constrain air-water partitioning, hydrocarbon fate, and leak rate.  Geophysical Research Letters Vol. 38, L07803, 6 PP. doi:10.1029/2011GL046726.

13. Kessler et al., 2011. A Persistent Oxygen Anomaly Reveals the Fate of Spilled Methane in the Deep Gulf of Mexico.  Science 331:  312-315

14. Joye S.B. et al., 2011. Magnitude and oxidation potential of hydrocarbon gases released from the BP oil well blowout. Nature Geoscience. DOI: 10.1038/NGEO1067.

15. Yvon-Lewis S.A., et al.  2011. Methane flux to the atmosphere from the Deepwater Horizon oil disaster. Geophysical Research Letters, 38: Art. No. L01602.

16. Ryerson T.B.  et al.,  2011. Atmospheric emissions from the Deepwater Horizon spill constrain air-water partitioning, hydrocarbon fate, and leak rate.  Geophysical Research Letters Vol. 38, L07803, 6 PP. doi:10.1029/2011GL046726.

17. Kessler et al., 2011. A Persistent Oxygen Anomaly Reveals the Fate of Spilled Methane in the Deep Gulf of Mexico.  Science 331:  312-315

18. Joye S.B. et al., 2011. Magnitude and oxidation potential of hydrocarbon gases released from the BP oil well blowout. Nature Geoscience. DOI: 10.1038/NGEO1067

19. Valentine D.L. et al., 2010.Propane respiration jump-starts microbial response to a deep oil spill. Science 330: 208-211.

20. Hazen T.C. et al., 2010. Deep-sea oil plume enriches indigenous oil-degrading bacteria. Science 330: 204-208.

21. Valentine D.L. et al., 2010.Propane respiration jump-starts microbial response to a deep oil spill. Science 330: 208-211.

22. Kessler et al., 2011. A Persistent Oxygen Anomaly Reveals the Fate of Spilled Methane in the Deep Gulf of Mexico.  Science 331:  312-315

23. Valentine D.L. et al., 2010.Propane respiration jump-starts microbial response to a deep oil spill. Science 330: 208-211.

24. Kujawinski E.B.et al., 2011.  Fate of dispersants associated with the Deepwater Horizon oil spill. Environmental Science & Technology 45: 1298-1306. 

25. Ibid

26. Judson RS et al., 2010.  Analysis of Eight Oil Spill Dispersants Using Rapid, In Vitro Tests for Endocrine and Other Biological Activity.  Environmental Science and Technology: 44(15): 5979-5985

27. Williams R. et al., 2011. Underestimating the damage: interpreting cetacean carcass recoveries in the context of the Deepwater Horizon/BP incident. Conservation Letters: 0 (2011) 1–6.

28. Graham M. et al., 2010. Oil carbon entered the coastal planktonic food web during the Deepwater Horizon oil spill. Environmental Research Letters DOI:10.1088/1748-9326/5/4/045301.

 


 

* The Federal Oil Budget estimated that 16% of the total volume of oil, nearly 33 million gallons, was chemically dispersed.  However, this ‘estimate’ is not regarded as reliable given disagreement among experts advising the federal working group and the lack of critical information, such as the size of oil droplets pre- and post-application.

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