Deepwater Horizon oil spill: 5 years later

April 20th 2015 marks the 5 year anniversary of the Deepwater Horizon oil rig explosion that lead to what is considered the world’s largest accidental oil spill since the petroleum industry began.  An explosion and subsequent fire onboard the Deepwater Horizon (DWH) oil rig resulted in a sea-floor oil gusher flowing for 87 days straight, discharging an estimated total of 4.9 million barrels (210 million US gal) of oil into the Gulf of Mexico 1.

A massive response ensued immediately following the spill to protect beaches, wetlands and estuaries from the spreading oil, utilising skimmer ships, floating booms, controlled burns and 1.84 million US gallons of Corexit oil dispersant, however due to the extended period over which the leak lasted, extensive damage to marine and wildlife habitats was reported 2.

The fire and subsequent oil leak of the DWH

The fire and subsequent oil leak of the DWH

Now 5 years later, several studies have been conducted by researchers from Florida Atlantic University’s Harbor Branch Oceanographic Institute which attempted to determine the impacts of the DWH on marine organisms such as oysters, conch, shrimp, corals as well as marine plankton (microalgae or phytoplankton, rotifers or zooplankton), which provide the basis of coastal and oceanic food webs.

Oil releases may affect marine organisms in a number of ways including physically, through toxic effects known to produce carcinogenic and mutagenic effects by modifying behaviour, or through modifications in their natural habitats,” said Susan Laramore, Ph.D., an author in both of the publications, assistant research professor, and a marine and molecular biologist who studies aquatic animal health issues at FAU’s Harbor Branch Aquatic Animal Health Laboratory. The Deepwater Horizon oil spill happened to coincide with the spring spawning season for a number of aquatic organisms, including shrimp and the eastern oyster.”

In the study published in the Journal of Shellfish Research, Laramore and her collaborators conducted studies to assess fertilisation success, development, survival, and swimming behaviour as well as sub-lethal exposure laboratory experiments to assess the impacts of brief exposures on the growth and survival of oysters (average lifespan of two years in the Gulf of Mexico). Findings from this study show that the DWH oil and dispersed oil impacted all of the factors listed above, although the extent of the impact varied depending on oyster life stage, amount of exposure and oil concentration. Fishermen report that the population of oysters have not come back to pre-spill levels. Diminished populations of oysters also affect marine coastal food webs and associated ecosystems.

In the second published study, Laramore and her collaborators examined two species of algae, used to feed molluscs, crustaceans and fish. These two species served as “models” for phytoplankton species in the Gulf of Mexico that were exposed to crude oil and weathered oil, dispersant and dispersed oil during the DWH oil spill. Results from this study revealed that the dispersant and dispersed oil affected the growth and motility of the algae, which may have had negative impacts on the food chain.

Marine animals coated in oil following the DWH spill

Marine animals coated in oil following the DWH spill

Many such studies are still being published to this day regarding the environmental impacts of the DWH spill, as gaining information on the long term ecological effects of mass oil spills could prove extremely valuable in the event of future spills. A 2014 paper conducted by researchers at Stanford University and the National Oceanic and Atmospheric Administration 3 found that toxins released by the oil spill killed fish by causing cardiac arrest. The study found that even very low concentrations of crude oil can slow the pace of fish heartbeats. It focused on tuna partly because the spill occurred in an area where Atlantic bluefin tuna were spawning. The effects were considered especially problematic for fish embryos and early developing fish, because the heartbeat changes could affect the development of other organs, including the lungs and liver. The study was conducted as part of the federal Natural Resource Damage Assessment process required by the Oil Pollution Act and published in the journal Science. 

Another peer-reviewed study, released in March 2014 and conducted by 17 scientists from the United States and Australia and published in the Proceedings of the National Academy of Sciences, found that tuna and amberjack that were exposed to oil from the spill developed deformities of the heart and other organs.

A large concern regarding the emergency response efforts in the aftermath of the spill was the use of Corexit 9500A oil dispersant. Chemical dispersants are a mixture of surfactants and solvents that help break oil into small droplets following an oil spill, so the oil is more readily dispersed throughout a volume of water. In essence, chemical dispersants do not remove oil from water, but merely accelerate its natural dispersion. Although the use of dispersants decreased the impact of oil to shorelines and surface-dwelling organisms (such as birds), dispersants allowed the oil to be more easily taken up by organisms that live in the water column. Rather than disappearing, the dispersed oil ended up in bottom sediments, where it remains, posing future threats to pelagic and benthic organisms. One recent study even went as far as to claim that when oil and Corexit are combined, the mixture becomes up to 52 times more toxic than oil alone 4.

The application of Corexit 9500A has been criticised due to it's toxicity

The application of Corexit 9500A has been criticised due to it’s toxicity

In 2014, a team led by Charles Fisher, professor of biology at Penn State University, made a discovery of two additional coral communities showing signs of damage from the Deepwater Horizon oil spill 5.  “The footprint of the impact of the spill on coral communities is both deeper and wider than previous data indicated,” said Fisher. “This study very clearly shows that multiple coral communities, up to 22 kilometers from the spill site and at depths over 1800 meters, were impacted by the spill.”  This study and those like it offer evidence that expands the impact footprint of the 2010 spill.

At the 2013 “Gulf of Mexico Oil Spill and Ecosystem Science Conference”, oceanographer David Hollander presented data that showed as much as one-third of the oil released during the spill may still be in the gulf. Researchers described a phenomenon called “dirty blizzard”: oil caused deep ocean sediments to clumped together, falling to the ocean floor at ten times the normal rate in an “underwater rain of oily particles”. The result could have long-term effects on both humans and marine life. With commercially fished species feeding on marine organisms in the sediment, the oil from the Deepwater Horizon spill could remain in the food chain for generations.

Photos of the DHW inferno were captured by the crew of nearby ships

Photos of the DHW inferno were captured by the crews of nearby ships

Cynthia Sarthou, executive director of Gulf Restoration Network says that after five years, there are more questions than answers about what the lingering impact of the spill means. “Dolphin deaths continue, oil is still on the bottom of the ocean, tar balls keep coming up,” she says. “And nobody really is able to say what we may find in five years, 10 years. It’s really distressing to me.

Sarthou says there’s no certainty the spill won’t be a problem for generations to come.

“It’s not publicly seen but it is out there. It’s in the marine environment,” she says. “And so whether we see it or not the potential impacts of its presence may plague us for decades.

But BP senior vice president Geoff Morrell says the signs are good for a healthy Gulf.

“There is nothing to suggest other than that the Gulf is a resilient body of water that has bounced back strongly,” he says. “The Gulf has not been damaged anywhere near the degree some people feared it would have in the midst of the spill.”

Morrell says BP has already spent $28 billion on response and cleanup and to pay economic claims to oil spill victims. Under federal law, BP will have to pay to restore the damage to natural resources caused by its spill — a scientific assessment that is ongoing and could take years to resolve. BP also faces a court judgment that could top $13 billion in an ongoing liability case. A New Orleans federal judge has ruled that BP’s gross negligence and willful misconduct are to blame for the disaster.

– JK

Article Reference:
  1. Susan Laramore, William Krebs, Amber Garr. Effects of Macondo Canyon 252 Oil (Naturally and Chemically Dispersed) on LarvalCrassostrea virginica(Gmelin, 1791). Journal of Shellfish Research, 2014; 33 (3): 709 DOI:10.2983/035.033.0305
  2. Amber L. Garr, Susan Laramore, William Krebs. Toxic Effects of Oil and Dispersant on Marine Microalgae. Bulletin of Environmental Contamination and Toxicology, 2014; 93 (6): 654 DOI: 10.1007/s00128-014-1395-2

Photo Header Credit: 

DWH oil slick as seen from space – NASA

Additonal References

1. On Scene Coordinator Report on Deepwater Horizon Oil Spill (PDF) (Report). September 2011. Retrieved22 February 2013.

2. Juhasz, Antonia (18 April 2012). “Investigation: Two Years After the BP Spill, A Hidden Health Crisis Festers”.The Nation. Re

3. Wines, Michael (24 March 2014). “Fish Embryos Exposed to Oil From BP Spill Develop Deformities, a Study Finds”. The New York Times. Retrieved 25 March2014.

4. Roberto Rico-Martínez, Terry W. Snell, Tonya L. Shearer. Synergistic toxicity of Macondo crude oil and dispersant Corexit 9500A® to the Brachionus plicatilis species complex (Rotifera). Environmental Pollution.


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