The Deepwater Horizon oil rig explosion is shaping up to be one of the great disasters of our time. The equivalent of nearly 5 million barrels of crude oil has already been released into the Gulf of Mexico, endangering the local marine and coastal ecosystems. However, after months of false starts, it appears that the worst of the spill may finally be over.

Cleaning Up the Mess

In early August, BP began the “static kill” procedure: pumping heavy drilling mud into the top of the ruptured well to clog the top of the well and to prevent more oil from escaping. Engineers then sealed off the well in a layer of cement [1]. More work remains to ensure that there won’t be further leakage, but the critical mission of stopping the main leak is now complete.

Meanwhile, the federal government has undertaken the enormous task of dealing with the oil that has already been spilled. First, the oil on the surface is contained using giant booms that encircle the floating oil. This concentrates the oil into smaller areas and ideally blocks oil from reaching sensitive regions such as coastal wetlands. Oil was also actively removed from the Gulf by burning (much as lighting gasoline will consume it) and collection by surface skimmers and centrifuge-based machines that separate oil and water based on the liquids’ different densities [2]. To remove the oil products that have washed up on shore, teams of workers have been manually removing the “tar balls” from the sand, though more efficient mechanical sand shifters are now also in use [3].

Perhaps most controversially, oil was converted into tiny droplets through the use of chemical dispersants. For a given volume, oil droplets have considerably greater surface area compared to large swathes of oil, which allows oil-eating microbes to consume them more efficiently. These microbes naturally occur in the ocean, feeding upon the small bits of oil that routinely leak from the seabed. However, during a major spill, so much oil is released into the water that the microbes would take years to break it down if they had to eat an oil slick from the outside in. Dispersants act like a soap to reduce the surface tension keeping the oil and water separate, and so accelerate the breakdown process by giving the microbes better access to the oil.

However, there is concern that the dispersants themselves may be harmful. Corexit EC9500A and Corexit EC9527A, the primary dispersant chemicals used in the Gulf, are more toxic and less effective on Gulf crude oil than other commercially available dispersants [4]. In addition, never before in history have dispersants been used at the scale being applied now in the Gulf. More than 1,800,000 gallons of dispersants have been used to date. The long-term environmental and health effects of using dispersants in these quantities is unknown; but their use has been halted now that the well cap is in place.

The Environmental Impact

There are numerous ways by which the oil spill could affect the surrounding environment. Oil can be a deadly pollutant, and one particularly worrying hazard of this spill is methane toxicity, as the type of crude oil released in this spill is exceptionally high in methane [5]. Methane is a simple compound composed of hydrogen and carbon, or a hydrocarbon, that is utilized by oxygen-using microbes. High methane concentrations attract these microbes, which will begin to deplete local oxygen levels. This eventually leads to “dead zones” of low-oxygen water, in which marine life cannot survive. Although dead zones are reversible in the long term if the oxygen-depleting chemicals (in this case, oil) are removed, they can create irreparable damage in the short term as local species are wiped out from their traditional habitats.

This oil spill could have the same negative effects on local wildlife as previous major spills. The region impacted by the BP oil spill includes eight national parks [6], which contain habitats for numerous endangered animals, including dolphins, sperm whales, and several sea turtle species. The oil has access to the marine ecosystems of the Gulf as well as the coastal wetlands – all of which are important sources of biodiversity and crucial components of the local economy. Between April and July, more than 3600 dead animals were collected in the Gulf by volunteers and scientists. Alarmingly, crab larvae have already been found with microscopic oil deposits within their shells [7]. These larvae, along with other tiny plants and animals, form plankton – the nutrient rich “soup” of microscopic life which forms the foundation of the marine food chain. As you go up the food chain, toxins present in only minute amounts in plankton become increasingly concentrated as predators eats correspondingly more contaminated prey over longer periods of time.

Where Do We Go From Here?

The Deepwater Horizon disaster has dramatically altered our nation’s perspective of offshore drilling and environmental protection, and its long-term impact may not become clear for years to come. This spill is among the largest marine oil spills in history – only the spill in the Persian Gulf during the Gulf War outmatches it in volume of oil released into the ocean. A recently published study indicates that at least one major plume continues to leak oil into the Gulf. The same study shows that early estimates of the rate of oil metabolism by microbes may be overly optimistic due to the cold temperatures in the deeper parts of the Gulf [8]. The potential hazard of the dispersants themselves remains as yet unknown. Additional oil plumes may remain undetected. And of course, the remaining oil itself presents a pressing environmental concern.

Fortunately, the outlook is slowly improving. The well has been capped, and most of the oil has been removed, contained, or dispersed. The National Oceanic and Atmospheric Administration (NOAA) estimates that only about a quarter of the oil spilled remains at sea or on shore (although this excludes the 24% of oil volume that has been dispersed) [9]. This would be an impressive achievement, considering the huge amount of oil that had been streaming from the well over the past four months. Although the vast volumes of ocean being dealt with make precise analysis difficult – hence the ambiguous and sometimes outright-contradictory reports coming out of the Gulf – the great strength of science is that it continually improves itself. The knowledge we have already gained from this spill will undoubtedly lead to better responses to future spills.

The past few weeks have seen the doom and gloom of June and July replaced with a sense of cautious optimism. For Gulf Coast locals, perhaps the most encouraging sign to date is that a full one-third of the closed fishing area was re-opened at the end of July. In their report, the NOAA said that the newly re-opened area passed all “re-opening criteria”: the absence of surface sheen for at least 30 days, low risk of oil reintroduction to the region, and absence of hazardous chemicals in seafood samples [10]. Although it is far too soon to claim victory, the denizens of the Gulf, human and wildlife alike, can at last have hope that the corner has been turned.

Peter Yang

Harvard Medical School


[1] Krauss, Clifford. (2010, Aug 5) “BP done pumping cement into the well.” New York Times.

[2] Gabbatt, Adam. (2010, Jun 16) “BP oil spill: Kevin Costner’s oil-water separation machines help with clean-up.” The Guardian.

[3] Elliott, Debbie. (2010, August 16) “BP Shrinks Gulf Cleanup Crews, Tries New Tools.” NPR

[4] Quinlan, Paul. (2010 May 13) “Less toxic dispersants lose out in BP oil spill cleanup.” New York Times.

[5] Steenhuysen, Julie. (2010 Jun 22) “Methane in Gulf ‘astonishingly high’: US Scientist.” Reuters.

[6] National Parks Conservation Association. (2010) “National Parks Threatened by Gulf Oil Spill.”

[7] Stokstad, Eric. (2010 Jul 2) “Oil contamination of crab larvae could be widespread.” ScienceINSIDER.

[8] Gillis, Justin and Rudolf, John Collins. (2010 Aug 19) “Gulf oil plume is not breaking down fast, research says.” New York Times.

[9] Gillis, Justin. (2010 Aug 4) “U.S. finds most oil from spill poses little additional risk.” New York Times.

[10] Schwaab, Eric. (2010 Jul 20) Memorandum to Administrator Jane Lubchenco, NOAA with rationale for re-opening. National Oceanic and Atmospheric Administration.

Links of Interest:

American Association for the Advancement of Science (AAAS) “Science of the Oil Spill” Blog (Collected articles on the oil spill)

University of Georgia “Gulf Blog,” written and maintained Dr. Samatha Joye

New York Times Gulf oil spill articles

PopSci “How Do Oil Despersants Work?”

NOAA Report: “BP Deepwater Horizon Oil Budget: What Happened to the Oil?”

NOAA BP Oil Spill Emergency Response Factsheets

NOAA resource for data and current scientific missions underway in the Gulf

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