Gulf of Mexico Oil Spill Blog Oil Degradation

Oil Degradation

oil degradation

The Murky Picture Beneath the Surface

Reader Submission By Matthew Cimitile and Allie Wilkinson

When the final mud and cement was pumped into the damaged oil well to permanently seal the Deepwater Horizon leak, an estimated 5 million barrels of oil had gushed into the Gulf of Mexico.  Oil that would fill more than 280 Olympic-sized swimming pools spewed from the Macondo oil field to pollute beaches and wetlands, smother threatened and endangered species and disrupt Gulf tourism and fisheries.  According to the Census of Marine Life, the Gulf of Mexico holds the 5th greatest abundance of marine life.  Now after three months of apprehensively awaiting an end to the nation’s greatest environmental disaster, deciphering the true implications of the oil spill has begun.  This task is leading scientists to look far beneath the surface. 

There, the question that lingers like the oil plumes research vessels are hunting is how long will it remain?  The unprecedented volume of oil and other hydrocarbons determines the extent to which life – from the phytoplankton that feeds the sea to humans who feed from the sea – is being exposed.  That answer comes down to a variety of chemical properties like light, temperature and oxidation.  But maybe most importantly, the rate at which oil degrades will depend on a feeding, growing population of oil-consuming microbes.

Selected for Oil Degradation

oil degradation microbeAfter the well was capped and most surface oil had evaporated or was skimmed, burned or dispersed, microscopic droplets and possibly plumes of oil continue to exist below the surface.  How much is contested.  According to various government and academic reports, anywhere from 25 to 79 percent or 50 to 150 million gallons of oil and byproducts from the spill could still be in the Gulf. 

Oil is not a new element to the Gulf ecosystem.  Close to 500,000 barrels of oil seeps into its waters through the seafloor each year, according to Texas A&M and U.S. Geological Survey (USGS) researchers.  On a timescale of millions of years, this exposure has led to the natural selection of bacteria species that can efficiently digest and utilize the energy source.

“For that much oil to be naturally oozing out of the Gulf of Mexico on a yearly basis, and yet for beaches not to be touched regularly by oil, shows that the oil-eating bacteria are good at what they do,” said John Lisle, a USGS microbiologist in St. Petersburg, Fl.

Like humans, bacteria consume organic matter for energy and repair.  They do so by absorbing the carbon in oil through cell membranes and to the cell interior.  When the influx of oil from the Deepwater Horizon leak began, it is likely bacteria began consuming and reproducing rapidly, breaking down oil into byproducts such as carbon dioxide, water and other biomass. 

“You will undoubtedly get a stimulation of the growth in hydrocarbon degrading bacteria,” said Albert Venosa, Program Manager of Oil Spill Research Program at the EPA.  “Bacteria that are able to degrade hydrocarbons are ubiquitous on this planet; everywhere we look, they are there because hydrocarbons are everywhere on this planet.  The only thing that would limit their ability to degrade oil rapidly is the availability of nitrogen, phosphorus and oxygen.”

A study by scientists at the Lawrence Berkeley National Lab (LBNL) in California provides evidence that bacteria are eagerly doing just that.  Based on water samples taken in and around a giant oil plume in the Gulf, the study found twice as many bacterial cells per millimeter inside than outside the floating plume.  Genetic indicators showed that bacteria consuming the oil were coded with genes more effective in degrading oil than those outside the plume.  The team calculated that the amount of oil in the plume was being reduced in size by half every three days.

“Certain aspects of oil are relatively easy to chew away.  That light stuff is literally lighter than water, which is why oil floats,” said Ralph Portier, an environmental science professor and bioremediation expert at LSU, who is not affiliated with the study.  “This is an excellent piece of data, an example of how in the carbon cycle, bacteria can handle different components from a liquid to a gas to a solid.”

A Time Tested Method

The success of certain bacteria species in breaking down oil in water is also evident on land and has been used in recent decades to protect coastlines in Alaska to marshes in Louisiana from spills.  Bioremediation is a mitigating tool, where added nutrients – or the natural microbes themselves – are delivered to a contaminated environment to stimulate the acceleration of natural degradation.

“There are cisterns in Europe since the time of the Romans that you fill up with rain water and let microbes sitting at the bottom chew away at the organic matter to purify water.  We do the same thing with making wine and yogurt.  So in cleaning up the environment, we use the same tools of taking organisms that can degrade carbon and make sure they have sufficient amount of nutrients, optimum temperature and moisture and then let the microbes take over,” said Portier.

The technique is being considered for the Gulf’s fragile marshes that have been oiled and could face more in the coming weeks and months.  Application poses its own set of challenges.  For one, fertilizer application could be inefficient as it doesn’t target specific organisms.  Or as the Gulf area knows, it could be too efficient, causing bacteria to rampantly respire and consume too much oxygen and harm other life. 

Bioremediation tools are currently being weighed for use in marshes by BP and the U.S. Coast Guard.  Portier and other groups like Osprey Biotechnics in Sarasota are hoping a decision is made quickly because oil is there now and options for removing or breaking down the oil to less harmful compounds are limited.

“Marshes are sensitive to mechanical manipulation and what typically happens is that marshes are either left alone or managers may wait for the growing season to be finished and then do a burn, which may get rid of surface oil but presents other issues,” said Victoria Finley of Osprey Biotechnics, an industrial microbiology company that develops an oil-eating bacteria product.  “But an alternative and the least invasive one at that, is using proven oil degrading microbes.”

The Oily Chain of Events

Because crude oil is a mixture of thousands of compounds, some aspects are much more readily degradable than others.  According to NOAA, the sweet Louisiana crude that penetrated the Gulf is easier to degrade than other crude oils because it is high in alkanes, single-bonded carbon chains that microorganisms can easily feed on.  It also is low in much sturdier components of oil like asphaltic fractions that is used to make asphalt, said Portier

“This spill is a light oil.  We were fortunate in that the oil was native, if it was Venezuelan oil it would have been a very different story,” said Portier.

Regardless of how light, all crude oil still contains a toxic cocktail of volatile organic compounds such as benzene that are lethal to fish eggs and acutely toxic to humans through inhalation.  While heavier components like asphaltic fractions (tar balls) can sink to the seafloor and harm benthic habitats.  These toxins and heavy oil compounds floating throughout the water column, not including the 1.8 million gallons of dispersants BP has claimed to use, will take months to years and possibly decades to degrade under the most rapid scenarios. 

And the very process of degrading oil can pose serious challenges to the ecosystem.  Oxygen depletion is indicative of bacterial respiration.  With the tremendous amount of bacterial activity around the oil, substantial lowered oxygen levels should be taking place – potentially to the degree that many marine scientists fear.

“The majority of these organisms need oxygen in order to degrade the oil and because there is so much carbon in the oil, they will need more and more oxygen to utilize it,” said Lisle.  “Bacteria do not work on a conservation method.  They have no clues or meters out there saying we need to slow down because we are going to consume all the oxygen.  They just keep degrading the oil until the oxygen is gone.”

Each year a dead zone the size of New Jersey forms at the mouth of the Mississippi River due to excess nutrient runoff from watersheds throughout the central U.S.  Deprived of oxygen, these deadly waters move around the northern Gulf of Mexico in response to wind and current patterns, claiming the lives of organisms that cannot move away fast enough.  Researchers fear the microbial activity around great oil masses may result in other similar zones. 

Several academic and government reports have found either very little depletion or up to 20 percent drops in oxygen levels.  All levels measured so far are not enough to form dead zones.  It is also becoming increasingly unlikely any will form, since oil is no longer escaping into the deep sea, and oil that remains is either diluted or dispersed, said Venosa. 

Low rates of oxygen depletion are a good sign, but it also provides clues that bacterial degradation around some oil plumes and pockets could be happening at a much slower pace.  As a Woods Hole Oceanographic study that analyzed thousands of chemical samples around a giant plume reported the small drop in oxygen levels measured is indicative that ‘microbes were degrading the plume relatively slowly’.   

Making Sense of the Uncertain

Marine microbial research has always been an inadequately funded field.   That may change with the recent disaster.  The urgency to understand the interaction between bacteria and oil in the Gulf has led the National Science Foundation to award rapid-response grants to study how the abundance and virulence of bacteria species are changing in response to the spill.  Other federal and state agencies and academic institutions are chartering vessels to further decipher what is taking place below the surface.

“Very little is known about the deep sea, and at 5,000 feet below the surface we have hardly any experience with dispersing oil or monitoring micro biodegradation,” said Venosa.  “This type of spill is new to us, and we need to start understanding the microbiology of the deep sea in relation to oil spills such as blowouts like this.”

The varying data on oil degradation and oxygen depletion rates is in many ways similar to the debate over how much oil remains and how much oil was released from the wellhead since the beginning of the spill.  They are all infused with a degree of uncertainty, a murkiness too well associated with Gulf waters, which will take time and resources to sort out. 

source: The Murky Picture Beneath the Surface – Science News – redOrbit

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