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article imageDeepwater Horizon oil spill aftermath: Deadly toxins still remain

By Karen Graham     Aug 5, 2014 in Environment
On April 20, 2010, the petroleum industry experienced its largest marine oil spill ever with the explosion and sinking of the Deepwater Horizon oil rig. The oil gusher flowed for 87 days before being capped, releasing 4.9 million barrels of oil.
Clean-up efforts were primarily focused on the surface, and it was an extraordinarily large area. Covering almost 30,000 sq. miles, the oil slick was the size of the state of South Carolina. The slick was broken up with the use of 1.8 million gallons of a dispersant called Corexit. This solution emulsifies the oil by changing the chemical and physical properties of the oil, making it easier for bacteria to eat. They do not reduce the amount of oil entering into the environment.
An article in Scientific American on May 25, 2010 pointed out that the only solution to cleaning up the oil spill in the Gulf of Mexico, on the surface and below, was utilizing the specialized bacteria and other microbes found in the ocean. In fact, they suggested the only reason for the use of dispersants was so that these specialized bacterias could consume the oil droplets. So what are these microbes?
Deepwater Horizon oil spill imagined in true color on May 17 by the MODIS instrument aboard NASA s T...
Deepwater Horizon oil spill imagined in true color on May 17 by the MODIS instrument aboard NASA's TERRA satellite.
NASA Goddard / Rob Gutro
Alcanivorax borkumensis
One of them, Alcanivorax borkumensis is a rod-shaped bacteria that relies on oil for its energy sources. It is found in all the world's oceans, but is relatively rare, unless there is an oil spill. Scientists discovered how the genetic makeup of this organism made it able to digest oil. The bacterium has specialized genes that break down alkanes in oil to use as food. The organism is also able to utilize hydrocarbons and organic and inorganic nitrogen.
Scientists claimed that the sequencing of the genome of the Alcanivorax bacterium would help scientists to harness its power in cleaning up future oil spills. They said: "The genome data and their functional analysis provides us with an invaluable knowledge base essential to design, develop, test and optimize rational strategies to mitigate the ecological damage caused by oil spills in marine systems."
Even with the clean up, deadly toxins remain
The extent of the Deepwater Horizon oil spill may never be known, but it is far more damaging than previously thought. Two studies have recently been released, one on the extent of coral colony degradation, and the other on highly toxic contaminants still remaining on the sea floor.
Charles Fisher, a Pennsylvania State University biology professor led a study published in the online Early Edition of Proceedings of the National Academy of Sciences. In his paper, he reports the discovery of five previously unknown coral communities near the wellhead, two of which show signs of damage resulting from the spill.
Previously it had been thought that only one coral community had been impacted by the oil spill. This coral group was eight miles from the well-head. But the new study found five new coral communities, one almost 14 miles from the well-head and in water twice as deep as the one that was discovered first. These findings further expand the impact area of the oil spill as well as impacting the biodiversity and reproductive activities of the marine organisms of the area.
Assistant Professor Olivia Mason, a Florida State University researcher, published the results of two studies in the journal Frontiers in Microbiology recently. In her studies, a species of bacteria called Colwellia was found to have likely consumed the gaseous hydrocarbons as well as the benzene, toluene, ethylbenzene and xylene compounds from the oil spill.
The most important finding was what the bacteria did not consume. There was an extremely toxic contaminant in the water column and on the seabed. These toxic contaminants are called polycyclic aromatic hydrocarbons or PAHs. PAHs are a group of organic compounds found in crude oil and are capable of causing long-term health problems, including cancer.
Remember the caution several years ago about eating meat cooked over a charcoal grill? This was because PAHs were discovered to be present in high levels in meat cooked at high temperatures over an open flame. Because of the number and potency of negative effects from PAHs, they are considered a pollutant. Because they mix more easily with oil than water, they are considered to be lipophilic. Following the Deepwater Horizon oil spill, PAH levels were found to be 40 times higher than before the spill.
"Those PAHs could persist for a long time, particularly if they are buried in the ocean floor where lack of oxygen would slow PAH degradation by microorganisms," Mason said. "They're going to persist in the environment and have deleterious effects on whatever is living in the sediment." Because some of the oil from the spill has never been accounted for, there is no way of predicting the environmental and health consequences to come.
Mason and her research partners investigated oil deposits around the well-head, taking 64 different samples from the ocean floor. Microbial DNA sequencing was done on 14 samples to see how the microorganisms performed in degrading the oil. Of the 14 samples tested, seven were so contaminated with PAHs they exceeded the EPA's acceptable water quality standards for marine life.
More about Deepwater horizon oil spill, hydrocarboneating microbes, Oxygen depletion, polycyclic aromatic hydrocarbons, most toxic
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