Posted by Rick Civelli | 12.12.2012 | Marine Science

Oil + Corexit = Concentrated Chemical Cocktail

Unsurprising news out of the Gulf of Mexico this month: the oil that spewed from the Deep Water Horizon well and the subsequently used clean-up dispersants apparently make for a toxic combination. Few will be astonished by this news, but what is startling is the synergistic toxicity of these two substances – the combination of oil and Corexit result in a substance 52 times more toxic.

Images of the BP Deep Water Horizon spill are permanently seared into our memories. An estimated 4.9 million barrels – enough to fill over 3 Olympic size swimming pools each day of the spill– plumed up from the ocean depths. Then there was the Corexit dispersant application – another estimated 1,000,000 gallons added to the mix. All these ingredients combined to create a toxic soup that was exceptionally hazardous to both marine life and human.

To test the synergistic effect, researchers from Georgia Institute of Technology and Universidad Autonoma de Aguascalientes mixed oil from the spill with Corexit (2 different types were used: Corexit 9527A and 9500.) They then used rotifers, an aquatic invertebrate found in both freshwater and marine systems, to test the toxicity. Not only did this chemical cocktail cause rotifer mortality, but as little as 2.6% of the mixture would result in a loss of 50% of rotifer egg hatching.

Rotifers are a type of microscopic zooplankton that comprise their own phylum Rotifera (Latin for wheel bearer – a reflection of the wheel-like organ used for movement and feeding.) Rotifers are frequently used as a marine “canary in the coal mine” as they have a quick response time. Successful rotifer hatching are vital for the entire aquatic environment. These small, vase-shaped animals are a primary food source. In the ocean they provide sustenance for copepods, juvenile fish, crabs, shrimp, and many more.

We knew that the oil engulfing the Gulf was toxic. We long suspected that the Corexit used to clean the mess, was toxic. But together the two chemicals pack at toxic punch that is 52-fold stronger than it counterparts. While rotifers are small, and therefore seemingly easy to dismiss, they are the bearers of some big news that has the potential to ripple through clean-up efforts around the world.