Ecological Toxicity
Corexit has been studied recently because of the many ecological effects that it may cause. Check out some of the possible organism specific effects below.
Daphnids
The acute toxicity of a new promising oil spill dispersant on Daphnia magna (shown in the picture below) was studied and compared to the toxicity of Corexit 9500. The toxicity of hyperbranchedpolyethyleneimine (HPEI) with various molecular weights and the toxicity of Corexit 9500 to Daphnia magna were determined according to US Environmental Protection Agency (EPA) Protocol 600/8–87/011. The LC50, (toxicant concentration at which death or immobilization would be observed in 50% of organisms) for each experiment was determined using Probit Analysis with a 95% confidence interval. Acute toxicity was found to be a function of HPEI polymer molecular weight. Greater HPEI polymer toxicity to daphnids was observed with increasing molecular weight (Mw). The LC50 of Corexit 9500 was found to be 0.14 ppm. Corexit 9500 was slightly more toxic than the 10,000 g/mol HPEI polymer (LC of 0.166 ppm). Six day old adult Daphnia magna were more resistant to Corexit 9500 compared to offspring daphnids (<24 hr old). Results of this study implied that both HPEI polymer and Corexit 9500 made the oil more toxic to the Daphnia magna, but toxicity was less for HPEI polymer (Mw:10,000 g/mole)than Corexit 9500.
Oysters
Oysters play an important role in many coastal economies, including in the Gulf of Mexico and toxicity of oil and dispersants can have impacts on the sustainability of natural oyster beds. A study performed by the FDA showed that one of the surfactants used in Corexit, commonly called DOSS, can accumulate in oysters while they are exposed to the substance. However, if the oyster is able to survive the exposure, it was shown that once they are no longer exposed to the chemical, it is naturally removed from their system. Additionally, in 2001 it was shown that the concentration of a Corexit and oil mixture at which 50% of the oysters would die was up to 6 times lower than Corexit concentration needed to obtain the same result.
A different study published in the journal Chemosphere found that concentrations of ANSC (Alaska North Slope crude oil) and dispersed oil (ANSC + Corexit 9500) higher than 30 ppm were required to show any significant toxic effects on the Crassostrea virginica (Eastern Oyster). This study also found that more than 83% of the tested species survived well after 24 hours of exposure to the different oil and oil-dispersant treatments. A similar article from the Marine Pollution Bulletin showed that when the Eastern oyster was exposed to oil and Corexit for 96 hours, adverse effects occurred during fertilization and early development. It was concluded that the presence of oil and dispersants during oyster spawning season may interfere with larval development and subsequent survival.
A different study published in the journal Chemosphere found that concentrations of ANSC (Alaska North Slope crude oil) and dispersed oil (ANSC + Corexit 9500) higher than 30 ppm were required to show any significant toxic effects on the Crassostrea virginica (Eastern Oyster). This study also found that more than 83% of the tested species survived well after 24 hours of exposure to the different oil and oil-dispersant treatments. A similar article from the Marine Pollution Bulletin showed that when the Eastern oyster was exposed to oil and Corexit for 96 hours, adverse effects occurred during fertilization and early development. It was concluded that the presence of oil and dispersants during oyster spawning season may interfere with larval development and subsequent survival.
Algae
Algae play an important role in marine ecosystems because they are form a considerable portion of the base of the food web. In a study published in the Bulletin of Environmental Contamination and Toxicology, Susan Laramore and her collaborators found that the growth and motility of two different species of microalgae, Isochrysis galbana and Chaetoceros sp., were negatively affected by the oil spill dispersants used in The Deep Water Horizon oil spill. However, since these are short lived species, long term consequences have yet to be seen.
Sargassum
The combination of Corexit 9500 and crude oil has been proven to have negative effects upon brown algae populations in the Gulf of Mexico. This toxic duo causes the brown algae to sink out of the Pelagic Zone (the zone generally considered to be the open ocean) and eventually die. This upsets the delicate ecosystem of the ocean. This affects not only the organisms living within the ecosystem, but also people living in the surrounding coasts who depend upon the fish in this region as a major source of income and sustenance. These trends found by SP Powers, can be seen in the bottom picture shown to the right. Treatment A and B are static conditions and treatment C and D are aerated conditions.
The same experiment proved that the addition of the oil-dispersant combination can rapidly deplete the dissolved oxygen concentration in the water. When winds are calm and the Sargassum exists in mats, which are formed when individual plants clump together to form a single mass, this rapid depletion of the oxygen within the water column can be problematic. This will create an effect where pockets of anoxic/hypoxic water exist in the ocean.
For more information about the methods and results of this research, the entire paper can be found here.
The same experiment proved that the addition of the oil-dispersant combination can rapidly deplete the dissolved oxygen concentration in the water. When winds are calm and the Sargassum exists in mats, which are formed when individual plants clump together to form a single mass, this rapid depletion of the oxygen within the water column can be problematic. This will create an effect where pockets of anoxic/hypoxic water exist in the ocean.
For more information about the methods and results of this research, the entire paper can be found here.
References
Benner, R. a, El Said, K. R., Jester, E., Flurer, R. a, & Boyd, B. L. (2010). Investigation of Corexit 9500 dispersant in Gulf of Mexico Seafood Species. Gulf Coast
Seafood Laboratory, (4), 1–22.
Garr, A. L., Laramore, S., & Krebs, W. (2014). Toxic effects of oil and dispersant on marine microalgae. Bulletin of Environmental Contamination and Toxicology,
93(6), 654–9. http://doi.org/10.1007/s00128-014-1395-2
Liu, B., Romaire, R. P., Delaune, R. D., & Lindau, C. W. (2006). Field investigation on the toxicity of Alaska North Slope crude oil (ANSC) and dispersed ANSC
crude to Gulf killifish, Eastern oyster and white shrimp. Chemosphere, 62(4), 520–526. http://doi.org/10.1016/j.chemosphere.2005.06.054
Powers, S. P., Hernandez, F. J., Condon, R. H., Drymon, J. M., & Free, C. M. (2013). Novel pathways for injury from offshore oil spills: direct, sublethal and indirect
effects of the Deepwater Horizon oil spill on pelagic Sargassum communities. PloS One, 8(9), e74802. http://doi.org/10.1371/journal.pone.0074802
Vignier, J., Donaghy, L., Soudant, P., Chu, F. L. E., Morris, J. M., Carney, M. W., … Volety, a. K. (2015). Impacts of Deepwater Horizon oil and associated dispersant
on early development of the Eastern oyster Crassostrea virginica. Marine Pollution Bulletin. http://doi.org/10.1016/j.marpolbul.2015.08.011
Seafood Laboratory, (4), 1–22.
Garr, A. L., Laramore, S., & Krebs, W. (2014). Toxic effects of oil and dispersant on marine microalgae. Bulletin of Environmental Contamination and Toxicology,
93(6), 654–9. http://doi.org/10.1007/s00128-014-1395-2
Liu, B., Romaire, R. P., Delaune, R. D., & Lindau, C. W. (2006). Field investigation on the toxicity of Alaska North Slope crude oil (ANSC) and dispersed ANSC
crude to Gulf killifish, Eastern oyster and white shrimp. Chemosphere, 62(4), 520–526. http://doi.org/10.1016/j.chemosphere.2005.06.054
Powers, S. P., Hernandez, F. J., Condon, R. H., Drymon, J. M., & Free, C. M. (2013). Novel pathways for injury from offshore oil spills: direct, sublethal and indirect
effects of the Deepwater Horizon oil spill on pelagic Sargassum communities. PloS One, 8(9), e74802. http://doi.org/10.1371/journal.pone.0074802
Vignier, J., Donaghy, L., Soudant, P., Chu, F. L. E., Morris, J. M., Carney, M. W., … Volety, a. K. (2015). Impacts of Deepwater Horizon oil and associated dispersant
on early development of the Eastern oyster Crassostrea virginica. Marine Pollution Bulletin. http://doi.org/10.1016/j.marpolbul.2015.08.011