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Dispersant makes oil from spills 52 times more toxic
As in 2010 Gulf of Mexico disaster, it makes petroleum less visible, but much more harmful
By Douglas Main
LiveScience
For microscopic animals living in the Gulf of Mexico, even worse than the toxic oil released during the 2010 Deepwater Horizon disaster may be the very oil dispersants used to clean it up, a new study finds.
More than 2 million gallons (7.5 million liters) of oil dispersants called Corexit 9527A and 9500A were dumped into the gulf in an effort to prevent oil from reaching shore and to help it degrade more quickly.
However, when oil and Corexit are combined, the mixture becomes up to 52 times more toxic than oil alone, according to a study* published online this week in the journal Environmental Pollution.
"There is a synergistic interaction between crude oil and the dispersant that makes it more toxic," said Terry Snell, a study co-author and biologist at Georgia Tech. Using dispersants breaks up the oil into small droplets and makes it less visible, but, "on the other hand, makes it more toxic to the planktonic food chain," Snell told LiveScience.
Toxic mixture
That mixture of dispersant and oil in the gulf would've wreaked havoc on rotifers, which form the base of the marine food web, and their eggs in seafloor sediments, Snell said.
In the study, Snell and colleagues tested ratios of oil and dispersant found in the gulf in 2010, using actual oil from the well that leaked in the Deepwater Horizon oil spill and the dispersant. The mixture was similarly toxic at the various ratios tested, the study found. His group exposed several varieties of rotifers to concentrations of the oil-dispersant mixture likely seen over a large area of the gulf.
"The levels in the gulf were toxic, and seriously toxic," Snell said. "That probably put a big dent in the planktonic food web for some extended period of time, but nobody really made the measurements to figure out the impact."
The dispersant makes the oil more deadly by decreasing the size of the droplets, making it more "bio-available" to small organisms, said Ian MacDonald, a researcher at Florida State University. "The effect is specifically a toxic synergy — the sum is worse than the parts," said MacDonald, who was not involved in the research.
A cautionary tale
This is one of the first studies to look at the impact of the oil-dispersant mixture on plankton. A decline in populations of plankton could impact larger animals all the way up to whales, he said. In general, plankton can rebound quickly, although the toxicity to larvae in sediments is concerning, since it reduces the size of the next generation. This ocean-bottom oil slurry could also have impacted other species that spend part of their life cycles here like algae and crustaceans.
"This is an important study that adds badly needed data to help us better understand the effects of oil spills and oil spill remediation strategies, such as the use of dispersants," said Stephen Klaine, an environmental toxicologist at Clemson University who wasn't involved in the research. "Species' differences in the sensitivity to any toxic compounds, including the ones in this discussion, can be huge."
The results contrast with those released by the Environmental Protection Agency in August 2010. That study found that a mixture of oil and Corexit isn't more toxic than oil alone to both a species of shrimp and species of fish. However, several studies have found the mixture is more toxic than oil to the embryos of several fish species. The EPA could not immediately be reached for comment.
"To date, EPA has done nothing but congratulate itself on how Corexit was used and avow they would do it the same way again," MacDonald said.
However, Snell said the dispersant should not be used. It would be better to let the oil disperse on its own to minimize ecological damage, he said.
"This is a cautionary tale that we need to do the science before the emergency happens so we can make decisions that are fully informed," Snell said. "In this case, the Corexit is simply there to make the oil disperse and go out of sight. But out of sight doesn't mean it's safe in regard to the food web."
"It's hard to sit by and not do something," Snell said. "But in this case, doing something actually made it more toxic."
Reach Douglas Main at dmain@techmedianetwork.com. Follow him on Twitter @Douglas_Main. Follow LiveScience on Twitter @livescience.
*
As in 2010 Gulf of Mexico disaster, it makes petroleum less visible, but much more harmful
By Douglas Main
LiveScience
For microscopic animals living in the Gulf of Mexico, even worse than the toxic oil released during the 2010 Deepwater Horizon disaster may be the very oil dispersants used to clean it up, a new study finds.
More than 2 million gallons (7.5 million liters) of oil dispersants called Corexit 9527A and 9500A were dumped into the gulf in an effort to prevent oil from reaching shore and to help it degrade more quickly.
However, when oil and Corexit are combined, the mixture becomes up to 52 times more toxic than oil alone, according to a study* published online this week in the journal Environmental Pollution.
"There is a synergistic interaction between crude oil and the dispersant that makes it more toxic," said Terry Snell, a study co-author and biologist at Georgia Tech. Using dispersants breaks up the oil into small droplets and makes it less visible, but, "on the other hand, makes it more toxic to the planktonic food chain," Snell told LiveScience.
Toxic mixture
That mixture of dispersant and oil in the gulf would've wreaked havoc on rotifers, which form the base of the marine food web, and their eggs in seafloor sediments, Snell said.
In the study, Snell and colleagues tested ratios of oil and dispersant found in the gulf in 2010, using actual oil from the well that leaked in the Deepwater Horizon oil spill and the dispersant. The mixture was similarly toxic at the various ratios tested, the study found. His group exposed several varieties of rotifers to concentrations of the oil-dispersant mixture likely seen over a large area of the gulf.
"The levels in the gulf were toxic, and seriously toxic," Snell said. "That probably put a big dent in the planktonic food web for some extended period of time, but nobody really made the measurements to figure out the impact."
The dispersant makes the oil more deadly by decreasing the size of the droplets, making it more "bio-available" to small organisms, said Ian MacDonald, a researcher at Florida State University. "The effect is specifically a toxic synergy — the sum is worse than the parts," said MacDonald, who was not involved in the research.
A cautionary tale
This is one of the first studies to look at the impact of the oil-dispersant mixture on plankton. A decline in populations of plankton could impact larger animals all the way up to whales, he said. In general, plankton can rebound quickly, although the toxicity to larvae in sediments is concerning, since it reduces the size of the next generation. This ocean-bottom oil slurry could also have impacted other species that spend part of their life cycles here like algae and crustaceans.
"This is an important study that adds badly needed data to help us better understand the effects of oil spills and oil spill remediation strategies, such as the use of dispersants," said Stephen Klaine, an environmental toxicologist at Clemson University who wasn't involved in the research. "Species' differences in the sensitivity to any toxic compounds, including the ones in this discussion, can be huge."
The results contrast with those released by the Environmental Protection Agency in August 2010. That study found that a mixture of oil and Corexit isn't more toxic than oil alone to both a species of shrimp and species of fish. However, several studies have found the mixture is more toxic than oil to the embryos of several fish species. The EPA could not immediately be reached for comment.
"To date, EPA has done nothing but congratulate itself on how Corexit was used and avow they would do it the same way again," MacDonald said.
However, Snell said the dispersant should not be used. It would be better to let the oil disperse on its own to minimize ecological damage, he said.
"This is a cautionary tale that we need to do the science before the emergency happens so we can make decisions that are fully informed," Snell said. "In this case, the Corexit is simply there to make the oil disperse and go out of sight. But out of sight doesn't mean it's safe in regard to the food web."
"It's hard to sit by and not do something," Snell said. "But in this case, doing something actually made it more toxic."
Reach Douglas Main at dmain@techmedianetwork.com. Follow him on Twitter @Douglas_Main. Follow LiveScience on Twitter @livescience.
*
https://www.sciencedirect.com/science/article/pii/S0269749112004344Abstract
Using the marine rotifer Brachionus plicatilis acute toxicity tests, we estimated the toxicity of Corexit 9500A®, propylene glycol, and Macondo oil. Ratios of 1:10, 1:50 and 1:130 for Corexit 9500A®:Macondo oil mixture represent: maximum exposure concentrations, recommended ratios for deploying Corexit (1:10–1:50), 1:130 the actual dispersantil ratio used in the Deep Water Horizon spill. Corexit 9500A® and oil are similar in their toxicity. However, when Corexit 9500A® and oil are mixed, toxicity to B. manjavacas increases up to 52-fold. Extrapolating these results to the oil released by the Macondo well, suggests underestimation of increased toxicity from Corexit application. We found small differences in sensitivity among species of the B. plicatilis species complex, likely reflecting phylogenetic similarity. Just 2.6% of the water-accommodated fraction of oil inhibited rotifer cyst hatching by 50%, an ecologically significant result because rotifer cyst in sediments are critical resources for the recolonization of populations each Spring.
