BP oil spill 7-year anniversary: A look at Corexit's deadly effects on the Gulf of Mexico

Throughout the recovery of the Gulf of Mexico, scientists have been generally slow to pinpoint the specific blight dispersants have had on the toxicity in the water column. Yet, from the very beginning almost, scientists were telling reporters to wait til their papers were published, til others' papers were published.

A purported 1.84 million U.S. gallons of the dispersant called Corexit were used in the Gulf, much of it airdropped in areas like Barataria Bay, Louisiana, and around parts of Mississippi and Alabama most impacted by the spill that began April 20, 2010. The Macondo well was finally sealed July 15 of that year.

Well, several papers explaining the toxicity of Corexit, in particular, have been published, and they draw direct links to how its use is far more deadly than oil alone. For example, in July, 2014, in a study called "Dispersant, UV Radiation Increase Oil Spill Impacts on Zooplankton but Food Web Interactions may Reduce Them", investigators from the University of Texas Marine Science Institute, including students from California and China, assessed impacts of crude oil, dispersant, and natural phenomena on zooplankton from the Gulf.

Zooplankton is a form of plankton popular in the Gulf of Mexico, renowned for the arrow worm or chaetognath. This type of zooplankton essentially feeds on its own kind; and there are 24 types in the Gulf. Zooplankton, like other plankton, is a vital food source for fish in the Gulf and in the sea generally.

So when researchers found that oil plus dispersants were very toxic to zooplankton, it was a big deal. As they said themselves, zooplankton are vulnerable to pollutants - and pollutants were found aplenty in the Gulf following the spill. First oil, then Corexit.

Researchers wrote that "at the oil-dispersant ratio commonly used to treat spills, dispersant and dispersant-treated oil were over twice as toxic as crude oil alone and that UVB radiation further increased crude oil toxicity to zooplankton."

Investigators also found "bioaccumulation of selected polycyclic aromatic hydrocarbons (PAHs) in zooplankton; however, the presence of marine protozoans reduced PAH bioaccumulation in copepods and may mitigate harmful impacts and subsequent transfer to the food chain."

Further, researchers said: "Zooplankton also play a role in influencing the fate of toxins by absorbing, transforming, and eliminating contaminates. These complex interactions may potentially impact the larger marine environment. For this study, researchers focused on natural mesozooplankton assemblages and on the copepod Acartia tonsa, a widespread and dominant planktonic species in the Gulf of Mexico. The team used Light Louisiana sweet crude oil, considered to have similar chemical composition and toxicity to Deepwater Horizon oil, and Corexit 9500A in experiments to better understand the interactions between these pollutants and zooplankton."

Zooplankton samples were collected from surface waters in the northern Gulf and in the Aransas Ship Channel, at Port Aransas, Texas.” Presumably, zooplankton studied off the Texas coast would have been used as a point of comparison to the plankton in waters closer to the spill, such as around Louisiana and the northern gulf.

Researchers say the impacts from oil spills on planktonic communities “depends on many physical, chemical and biological factors,” and effects would “vary depending on the circumstances of each spill.” They want “further experiments that mimic the natural environment” to accurately evaluate the toxic effects and PAH bioaccumulation in zooplankton, because their findings suggest that zooplankton are “highly sensitive” to Corexit 9500A.

The study’s authors were Rodrigo Almeda, Zoe Wambaugh, Zucheng Wang, Cammie Hyatt, Zhanfei Liu, and Edward J. Buskey (PLOS ONE, 2013 8(6): e67212).

This research was made possible in part by a grant from theGulf of Mexico Research Initiative (GoMRI), a program established through a $500 million financial commitment from BP. For more information, visit http://gulfresearchinitiative.org/.

PHOTO: Sign protesting use of toxic "Corexit" chemical dispersant in the BP Gulf of Mexico oil disaster, at the Bastille Day Tumble, French Quarter, New Orleans; Infrogmation of New Orleans - by Infrogmation of New Orleans, courtesy of Wikimedia Commons Images.