Use of Dispersants in the Gulf Proves to Have Little Benefit

George Washington's picture


Dr. David Valentine - one of the world's leading experts on oil-eating bacteria - told me today:

We have found no Alcanivorax borkumensis in the deepwater plumes.

That may not seem like a very interesting or controversial sentence.

But it is actually a jaw-dropping statement, showing that the use of Corexit in the Gulf has failed by any measure.

To understand why, let's quickly run through the science of the oil spill.

Why Was Corexit Used in the Gulf?

many - including me - have accused BP of dumping millions of barrels of
Corexit in the Gulf in order to hide the oil, some scientists argued
that Corexit would make it easier for oil-eating microbes to break down
the oil.

As Scientific American pointed out in May:

last (and only) defense against the ongoing Deepwater Horizon oil
spill in the Gulf of Mexico is tiny—billions of hydrocarbon-chewing
microbes, such as Alcanivorax borkumensis.
In fact, the primary motive for using ... chemical dispersants on
the oil slick both above and below the surface of the sea is to break
the oil into smaller droplets that bacteria can more easily consume.

In fact, there is no clear science showing that dispersants help microbes break down oil. As Chemical and Engineering News noted in June:

those teams’ assumption lie murky data. The authors of the 2005
[National Research Council] dispersant report described the results of
three decades of research into dispersants’ effects on biodegradation
as “mixed” with studies showing evidence for “enhancement, inhibition,
and no effect.”

Nevertheless, tremendous quantities of Corexit have been sprayed some 5,000 feet underwater at the wellhead.

Does Corexit Interfere with the Microbes?

Valentine - a biogeochemist at the University of California, Santa
Barbara - received funding from the National Science Foundation to
characterize the microbial response to the Gulf oil spill. The National
Science Foundation has funded Dr. Valentine's research into how the
oil-eating microbes are dealing with the spill, and whether or not
Corexit is interfering with the microbes' ability to break down the oil.

As I wrote last month:

might be killing the oil-eating bacteria which would otherwise break
down the oil. University of Georgia scientist Samantha Joye notes that
scientists have no idea how the large quanties of dispersant will effect the Gulf's microbial communities (for more information, watch part 1, part 2, part 3, part 4 and part 5 of Dr. Joye's July 13th press conference).


Moreover, as MSNBC notes, oil-eating bacteria are less active in deepwater, where much of the oil sinks after treatment with dispersants:

note that little is known about the deepwater ecosystem — or how the
oil and dispersants will react under extremely high water pressure, very
low temperatures, limited oxygen and virtually no light.




conditions at the bottom of the Gulf also could affect the bacteria
that help break down the oil near the surface, as they are less active
in cold temperatures than in the warm surface waters, and they may be
less abundant in the deep.


“We know that the surface material
has been degrading,” says Ralph J. Portier, professor of environmental
studies at LSU. “But what about the microbial population at depth?”


As Scientific American points out:

colder, deeper waters inhibit microbial growth. "Metabolism slows by
about a factor of two or three for every 10 degree[s] Celsius you drop
in temperature," notes biogeochemist David Valentine of the University
of California, Santa Barbara, who just received funding from the
National Science Foundation to characterize the microbial response to
the ongoing oil spill. "The deeper stuff, that's going to happen very
slowly because the temperature is so low."


At the same
time, the addition of ... dispersants deep beneath the surface is having
uncertain effects; it may even end up killing the microbes it is meant
to help thanks to the fact that Corexit 9527A contains the solvent
2-butoxyethanol, which is a known human carcinogen and toxic to animals
and other life.

Mother Jones provides additional details:


Valentine ... warns the stuff may be riskier than just its toxicity.
Corexit may undermine the microbes that naturally eat oil.


Some of the most potent oil-eaters—Alcanivorax borkumensis —are relatively rare organisms that have evolved to eat hydrocarbons from naturally occurring oil seeps. Valentine tells Eli Kintisch at Science Insider that after spills, Alcanivorax
tend to be the dominant microbes found near the oil and that they
secrete their own surfactant molecules to break up the oil before
consuming the hydrocarbons. Other microbes don't make surfactants but
devour oil already broken into small enough globs—including those broken
down by Alcanivorax.


What we don't know is how the
surfactants in Corexit and its ilk might affect the ability of
Alcanivorax and other surfactant-makers to eat oil. Could Corexit
exclude Alcanivorax from binding to the oil? Could it affect the way
microbes makes their own surfactants? Could Corexit render natural
surfactants less effective?


The National Science Foundation has awarded Valentine a grant to study the problem.

borkumensis is the main microbe breaking down oil in the Gulf. For
the real science nerds, here are two illustrations of how breaks down
oil (click either image for full graphic):

No Microbes in Deepwater Plumes

I spoke with Dr. Valentine today, I asked him whether he has reached
any conclusion as to whether Corexit interferes with the ability of
Alcanivorax borkumensis to break down the crude.

He replied that he doesn't yet have any findings on that issue.

However, he said, "We have found no Alcanivorax borkumensis in the deepwater plumes".

asked him whether that was because of the cold temperatures deep under
the surface of the ocean, and he replied "we don't know".

I had been worried that the microbes would break down the crude in the underwater oil plumes more slowly than normal ... but Valentine said there are no microbes at all down in the plumes.

Mongeese, Rats and Deepwater Oil Spills

The mongoose was introduced to Hawaii in order to control rats (the rats were eating the sugar cane used to make rum, and so were a real nuisance).

It didn't work out very well - mongeese are daylight-loving creatures while rats are nocturnal . So the mongeese didn't control the rats, and instead ran amok and trashed many native Hawaiian species.

scientists who assumed that Corexit would help the microbes break down
the oil from the Gulf spill haven't fared much better.

Remember, the US Minerals Management Service and a consortium of oil companies - including BP - found that as little as 2% of the oil which spills from deepwater wells ever makes it to the surface of the ocean. As Alexander Higgins noted in June:

[A] study called Project “Deep Spill”
... analyzed a wide range of controlled releases at different depths
below the sea surface of different types of oil found all over world
to help better understand the flow of hydrocarbons released from a
deepwater blowout.


One of the studies, called DeepBlow, released
10,000 barrels of oil per day at a depth of 800 meters which is less
than half of the depth of the Deepwater Horizon blowout.


The basic findings of that study has been recreated by scientists from the University of North Carolina.


In their research the scientists simulated of the formation of the underwater oil plumes that are created during deepwater blowouts.


Watch The University of North Caroline Simulation Shows How Oil Released Underwater Forms Plumes

the University of North Carolina simulation gives you a basic
understanding of how deepwater blowouts create oil plumes it does not
fully account for all the findings of Project “Deep Spill”.


In particular the final report of Project “Deep Spill” found:


1. Only 2% of the oil released in a deepwater blowout may actually make it to the surface.
That’s as little as 2% naturally without the use of dispersants. Add
dispersants into the equation and it could be less then one percent of
oil that makes it to the surface.




The buoyant parts of the oil released in a deepwater blowout split
from the main plume within the first 200 meters of release. Those
buoyant parts, which represent only a small portion of the total amount
of oil, turn into small droplets that float to the surface.

Here is a graph from the study showing this process.

Deepwater oil release - Buoyancy particle separation graph
Deepwater oil release – Buoyancy particle separation graph

Here is an image that captures the separation process

Deepwater oil release - Buoyancy particle separation simulation
Deepwater oil release – Buoyancy particle separation simulation

Deepwater oil plumes lose buoyancy within the first few couple hundred meters from release

Within the first 100 to 200 meters from the source of the release the
the majority of the oil loses its buoyancy and stops rising. This
majority of the oil remains submerged in an underwater plume that is
then carried away by subsurface currents.

As the University of California Santa Barbara notes, microbes like the lighter portions of the oil:

The microbes prefer the lighter compounds of oil, the gasoline part of the black goo ....

always seems to be a residue," Valentine said. "They (bacteria) hit a
wall. There seems to be stages in which they eat. There's the easy
stuff ––the steak. And then they work their way to the vegetables, and
then garnish, and then they stop eating after awhile. Just depends on
how hungry they are and what's fed to them."

Corexit: A Failed Science Experiment

So let's recap.

The overwhelming majority of oil from deepwater spills stays beneath the surface in plumes. See this and this.

Corexit helps oil to sink beneath the surface, so even more of the oil stays underwater. Oil-eating microbes like the lighter portions of oil.

Dr. Valentine found none of
the main oil-eating microbes in the deepwater plumes he tested. Whether
that is because the Corexit killed them, its too cold in the deep
ocean, they don't like the heavier portions of the oil that don't float
to the surface, or for some other reason, the result is a failure.

Scientists have already said that Corexit is dangerous to sealife and humans (see this and this),
and called the application of Corexit the largest science experiment
ever conducted. For example, Rob Kendall, director of Texas Tech’s
Institute of Environmental & Human Health, says:

is a catastrophe of enormous proportions. To me, this is the biggest
environmental toxicology experiment we’ve ever conducted.

And Kim Withers, a coastal ecologist at Texas A&M University in Corpus Christi notes:

It's like the biggest science experiment ever. Unfortunately, it's a completely uncontrolled experiment.

They were talking about the toxic effects of Corexit on sealife.

Dr. Valentine's findings lead me to conclude that the experiment on the
potential of Corexit to help the microbes break down the oil has failed
as well.