Oil Dispersants Used During Gulf Spill Degrade Slowly In Cold Water | Chemical & Engineering News
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Web Date: February 13, 2013

Oil Dispersants Used During Gulf Spill Degrade Slowly In Cold Water

Oil Spill Response: Persistence of Corexit 9500 at deep-sea and Arctic temperatures suggests more research is needed on the chemicals’ toxicity, researchers say
Department: Science & Technology | Collection: Disaster in Gulf
News Channels: Environmental SCENE
Keywords: dispersants, Corexit 9500, oil spill, Deepwater Horizon, biodegradation
In May, 2010, ships assemble at the site of the Deepwater Horizon spill.
Credit: Mark Schrope
Aerial photograph of clean up ships near site of Deepwater Horizon spill.
In May, 2010, ships assemble at the site of the Deepwater Horizon spill.
Credit: Mark Schrope

During the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, clean up crews applied millions of liters of oil dispersants both at the ocean surface and in the deep sea. At the time, the public and some scientists worried about the environmental effects of the chemicals, in particular how long they would last in the deep sea. According to a new Environmental Protection Agency study, the key active ingredient in the dispersants degrades very rapidly under conditions similar to those found at the Gulf surface during the spill. Meanwhile, in the much colder temperatures found in the deep sea, the breakdown is quite slow (Environ. Sci. Technol., DOI: 10.1021/es303881h).

Dispersants break up oil into tiny droplets so bacteria and chemical processes can degrade it more quickly. To try to lessen the harm caused by the oil released into the Gulf, oil spill responders initiated what would turn out to be the second largest application of dispersants in history. Also, for the first time, the crews pumped dispersants 5,000 feet below the ocean surface—into the Deepwater Horizon’s blown wellhead to break up oil as it gushed into the Gulf.

EPA oil spill expert Albert D. Venosa, working with academic researchers, wanted to better understand the degradation of Corexit 9500, the main dispersant used during the spill. They ran tests on artificial seawater at 5 ºC, about the temperature at the wellhead, and at 25 ºC, roughly the temperature of the surface waters during the hot summer of the spill.

One key round of experiments involved adding an oil and dispersant mix to flasks of water that the scientists had inoculated with bacterial communities. For the cold water flasks, the team used bacteria isolated from the deep Gulf, and for the warm water, they used microbes from shallow water.

Using liquid chromatography tandem mass spectrometry, the team tracked levels of dioctyl sodium sulfosuccinate (DOSS), Corexit 9500’s main surfactant. In the warm water, when mixed with oil, DOSS broke down quickly, with most of the compound gone in eight days.

In the cold water tests, however, the team didn’t observe significant dispersant breakdown for almost a month, and some DOSS persisted at the end of the 42-day experiment. The reason, the authors say, is likely that at low temperatures the microbes slowly produce the enzymes needed to chew up DOSS.

The results fit well with previous observations in the Gulf: Months after the spill ended, teams still detected DOSS at very low concentrations in the deep sea (Environ. Sci. Technol., DOI: 10.1021/es103838p).

In the paper, the authors conclude that their results on DOSS’ persistence at cold temperatures suggest more research is needed to understand the chemical’s toxicity and that of its breakdown products in colder environments. Cold water conditions are a concern not only for deep sea oil spills, they write, but also for spills in Arctic waters.

David L. Valentine, a microbiologist at the University of California, Santa Barbara, was part of the group that measured deep-sea DOSS levels during the spill. He says the EPA work gives researchers an improved understanding of dispersant fate in different environments and the mechanisms driving the breakdown of the compounds. However, he suggests caution when applying the results directly to actual spills because other key factors, such as levels of nutrients bacteria need, may differ from the laboratory conditions.

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Bill Reeder (June 12, 2013 10:49 AM)
The one thing you can be assured of is if Al Venosa is part of a test it is to provide cover for some problem. Al's laboratory test does not reflect what actually happens in the environment which suggests the experiment was manipulated. DOSS does not breakdown in 8 days it persists for years as was seen in the Ixtoc, Valdez and now the BP spill. There are scientists who have conducted sampling in the Gulf that show years after applying Corexit 9527 and Corexit 9500 the oil still persists in the water due to the fact that DOSS and 2 butoxyethanol act as biocides preventing microbes from being able to form pathways to digest the oil. The Ixtoc spill was still adversely effecting the Gulf 20 years after applying Corexit 9527 and the Valdez spill is still on the Alaskan seabed over 20 years since Corexit and Inipol EAP 22 ( which is basically Corexit with nutirents). The EPA mislead the public when they stated Corewxit 9500 did not contain 2 butoxy ethanol when the EPA NCP notebook in 1999 clearly showed Corexit 9500 was basically the same product as Corexit 9527 except it had about 30% less 2 butoxy ethanol. These are horrifically toxic Dispersant chemicals that have no nplace in any environment, and the US EPA has misused public funds for over 23 years promoting Exoon's products even though they end up costing oil companies more money to use over non toxic first response bioremediation product such as Oil Spill Eater II. Almost all the deleterious effects seen in oil spills are from the use of Exxon's toxic dispersants and yet they continue to have the EPA push these products to the detriment of their own bottom line profits. Al Venoisa in 2000 published a fact sheet in regards to bioremediation that only discussed microbial and fertilizer/nutrient type bioremediation products which have very little application in the open environment, and within the same month of publishing this incomplete report he was made aware of the fact category EA/OSE II was a first response product and had proven so with the millions spent by the EPA during the EPA/NETAC testing, and even after being made aware of what he should have already known he misguided the RRT's on purpose to make sure bioremediation would not get used. This misguidance has cost responsible parties and states millions if not billions in natural resource damages. The OSEI Corporation has now made known to the RRT's that they were all duped by Al Venosa, so when his name appears on any writings you can bet he is trying to misguide, since this is his track record for 23 years.
John Reid (June 29, 2013 11:04 AM)
I really appreciate this post. very informative. It would be great if you can comment further on why the MSDS sheet provided from Nalco for COREXIT 9500 does not list 2 butoxy ethanol as an ingredient, nor the warning of bioaccumulation, nor the warning of known carcinogens.

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