The National Oceanic and Atmospheric Administration has been conducting an on-going damage assessment following the April 20, 2010 Deepwater Horizon oil spill. A recent paper titled Deepwater Horizon crude oil impacts the developing hearts of large predatory pelagic fish reports the findings of research conducted by NOAA and other scientists on the effects of crude oil exposure on the embryos and larvae of tuna. Not surprisingly, the study finds that exposure to crude oil is bad for fish.
The Coast Guard’s Sept. 2011 report on the Deepwater Horizon spill operation contained the following estimates:
- 27,000 barrels of oil recovered
- 250,000 barrels of oil burned
- 4.9 million barrels of oil leaked
The study is flawed in a number of ways.
The study did not collect any specimens from the Gulf of Mexico. They collected no embryos and larvae, either damaged or undamaged. The testing was conducted on embryos and larvae at two tuna hatcheries, marine research facilities in Australia and Panama. There, the spawn of bluefin tuna and yellowfin tuna were exposed to crude oil collected from the riser at the Deepwater Horizon oil spill.
The study was looking at the effects that oil-derived polycyclic aromatic hydrocarbons (PAHs) had on the development of the heart in tuna exposed to it in crude oil. Additionally, the researchers were looking for other fatal or non-fatal abnormalities.
Developmental abnormalities were evident in bluefin and yellowfin tunas at very low concentrations, in the range of approximately one to 15 parts per billion total PAHs. These levels are below the measured PAH concentrations in many samples collected from the upper water column of the northern Gulf during the active Deepwater Horizon spill phase.
There are several issues in that quote. PAH levels, according to the quote, were lower than the 15 ppb damage threshold in some Deepwater samples. The upper water column, in addition, was the subject of a number of remedial actions including the injection of oil dispersants which would have changed the chemical mix. The oil within the column, upon reaching the surface, dispersed into a slick and then to a sheen which again changed the mix.
Do tuna raised in Australia or Panama have identical reactions to chemical exposures as the tuna in the northern Gulf of Mexico? The answer matters in assessing the validity of the study’s findings. What effects do oil dispersants have on bluefin and yellowfin tunas, embryos and larvae? Again, given the massive use of these chemicals during the spill, the answer points to an alternative theory for any damage.
The study also ignores the issue of oil seeps throughout the gulf and in the area of the Deepwater Horizon. There are hundreds of these seeps, leaking crude oil into the gulf, all naturally occurring. In 2000, one researcher estimated that 500,000 barrels of oil seep into the Gulf each year. How do you measure the effects of a 2010 exposure to the Deepwater spill versus exposure to natural spills year after year?
The NOAA study in the headlines raises more questions than it answers. No one believes that crude oil exposure is safe for all living things. But the lack of Gulf data on damage and the poisoning of tuna thousands of miles from the Deepwater spill certainly do not contribute to the advancement of science on crude oil toxicity.