WHOI scientist Judith McDowell said that acute toxicity levels of BTEX are in the range of 5 to 50 milligrams per liter for aquatic organisms--100 to 1,000 times greater than that observed in the plume.
Sublethal effects, including neurological impairment, are observed at lower levels, she said.
"In most instances the BTEX compounds are volatilized very quickly, such that exposure duration is very short," McDowell said. "The persistence of BTEX at depth poses an interesting question as to the potential effects of these compounds on mid-water organisms."
A critical component of the study was a one-of-a-kind fluid sample the team collected directly from the broken riser at the Macondo well.
To accomplish this, the team used an isobaric gas-tight sampler, a unique piece of equipment developed by WHOI geochemist Jeff Seewald and his colleagues, and intended for use collecting fluids from deep-sea hydrothermal vents.
With the gas-tight sampler and other necessary equipment, the lead scientists were shuttled from their active research vessel to a smaller boat and brought to the Ocean Intervention III, operating above the Macondo well.
They were then given 12 hours--working with many unknowns--to do something never done before.
Using an oil industry remotely operated vehicle, they maneuvered the gas-tight sampler to the source of the spill to capture an "end-member" sample of fluid as it exited the riser pipe.
No other such sample exists.
By analyzing this sample, the scientists were able to determine what was in fluid spewing from the Macondo well before nature had a chance to weather it and the exact ratio of gas and oil in the fluid.
"Getting this sample was probably the most dramatic and thrilling thing I have done in my life," Reddy said.
Using petroleum industry terms, they found a gas-to-oil ratio (GOR) of 1,
|Contact: Cheryl Dybas|
National Science Foundation