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Dispersant chemical found in beach oil patties four years after BP Deepwater Horizon oil spill, new study says
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Dispersant chemical found in beach oil patties four years after BP Deepwater Horizon oil spill, new study says

By Mark Schleifstein, | The Times-Picayune 

Traces of a chemical contained in dispersants used to break up oil during the 87-day BP Deepwater Horizon oil spill in 2010 were found in material deposited on deepwater corals six months after the spill, and in weathered oil patties on Gulf Coast beaches four years later, according to a scientific letter published online this week in Environmental Science & Technology, the peer-reviewed research journal of the American Chemical Society.

Researchers found tiny amounts of DOSS, an abbreviation of the chemical compound dioctyl sodium sulfosuccinate, in both the oil patties and deepwater sediment.

The research conducted by scientists with Haverford College in Pennsylvania and the Woods Hole Oceanographic Institution in Massachusetts raises new questions about the assumptions on how quickly two COREXIT brand dispersants disappeared after being used to break up oil into tiny droplets, said lead author Helen Kirsty White, an assistant professor of chemistry at Haverford.

"Now that we know the compound can exist for up to four years, it's important to understand whether the oil and dispersant mixture is toxic and the way it is exposed to life in the Gulf of Mexico," White said. "Those are important questions to be answered in order to understand the impact or damage it might be having on the environment."

The research described in the letter does not address the toxicity of the DOSS that was found in the samples, or its impacts on organisms in the Gulf or beach, she said.

Indeed, DOSS also is found in household products, such as dishwashing detergent. White said the researchers targeted DOSS because it's easier to find that other chemicals contained by the COREXIT dispersants that are believed to be more toxic.

The deepwater samples with DOSS were taken in December 2010 from an area containing corals located 8/10ths of a mile below the surface at an offshore oil lease area named Mississippi Canyon 294, about 6.8 miles southwest of BP's Macondo oil well. At that site, "coral colonies showed visible signs of stress and were covered in a brown, flocculent material ..., which contained weathered oil from a source consistent with the Macondo well," the letter said.

Samples also were taken from an area containing corals 1.1 miles below the surface at the Mississippi Canyon 388 lease area, about 13.7 miles east southeast of the Macondo well. At that site, the corals were not covered with the brown material.

The beach samples were collected between June 2012 and January 2014 in Louisiana, Florida, Alabama, and Mississippi.

"The weathered oil present in these types of samples has been found to be consistent with an origin from the (Deepwater Horizon) spill," the letter said.

The amount of DOSS found was truly tiny, White said. According to the research, the samples taken from the coral communities contained between 6 and 9,000 parts per billion of the chemical, while the amounts reaching the beaches were even smaller, between only 1 and 260 parts per billion in samples collected 26 to 45 months after the spill.

A spokesman for BP pointed to the low quantities of DOSS as proof that the study does not indicate an environmental problem in using the dispersants.

"The compounds cited in the Haverford College and Woods Hole Oceanographic Institution study were found in extremely low concentrations -- so small that they are not detectable with standard laboratory equipment -- and do not pose a risk to human health or aquatic life," said BP spokesman Jason Ryan. "In 2010, government agencies tested thousands of water and sediment samples for dispersant compounds in order to examine the potential persistence of dispersants in the environment. None of the samples tested exceeded the Environmental Protection Agency's dispersant benchmarks."

Ryan also questioned the researchers' conclusion that the DOSS in their samples came from the dispersants used in the spill, pointing to the use of DOSS in consumer products.

"Prior studies have noted that it is difficult to directly link DOSS traces in the environment to dispersants, given that these compounds can come from several sources," Ryan said.

However, the letter pointed out that the DOSS at deepwater locations was only found in a shallow layer of sediment, the same layer in which oil was found.

And for the material found on beaches, the letter said that a few samples that were found to contain weathered oil not associated with BP also contained no DOSS, while DOSS was found in the patties with oil believed to be from the Macondo well.

Other researchers are studying deep sea corals for potential impacts from both the oil and dispersants, and researchers also are studying similar impacts of weathered oil and associated dispersants that continue to wash up on Gulf Coast beaches, she said.

But until the tests of samples for DOSS described in the letter, there was no evidence that the constituents of the dispersants survived so long, White said.

Past laboratory studies have indicated that the dispersants used in the spill disappeared rather quickly, the result of their own surfactant properties that cause oil to break down quickly into tiny droplets that are more readily available as food for tiny organisms or to simply dissolve.

But some of the disappearance results from the chemicals being in warm water at the Gulf's surface and exposed to sunlight.

In nearly mile-deep water where the coral grows, the temperatures are much colder, and less light is available to assist in the chemical breakdown process.

White said she and her colleagues believe the DOSS found in the deepwater material actually came from the surface application of the dispersants, rather than when officials sprayed dispersant directly into the oil at the ocean floor as it was leaving the well. That's because it was found associated with the unevenly distributed flocculent material containing oil that also is believed to have begun its journey downward at the surface.

And the scientists believe DOSS is still being found in the oil patties on beaches because it became encapsulated inside the oil-sand-shell mix, "like a time capsule."

"We don't know that's true, but just the fact that we're seeing it after four years suggests it was captured and held pretty tightly," White said.

That may actually be helpful in terms of toxicity to wildlife, she said.

"It's not moving into the environment as long as wildlife is not eating the sand patties or is exposed to it," she said.

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