The 2010 BP oil spill in the Gulf of Mexico led to a record spike in bottlenose dolphin deaths that is still ongoing, a newly released federal study confirms.
Exposure to oil products has been clearly indicated by lesions on the lungs and adrenal glands of deceased dolphins recovered within the footprint of the massive Deepwater Horizon oil spill, researchers say.
Tests were conducted on dolphins found stranded along the Gulf coastline between June 2012 and December 2012 following the largest offshore spill of oil in U.S. history.
The study was conducted as part of the National Oceanic and Atmospheric Administration's Deepwater Horizon National Resource Damage Assessment.
Damaged adrenal glands are unable to produce vitally needed hormones that regulate metabolism, blood pressure and other body functions, which can result in fatal problems for dolphins, notes study author Kathleen Colegrove, a veterinary pathologist at the University of Illinois.
Adrenal glands in humans serve the same functions.
"This was an unusual abnormality to us that has not been previously documented in the literature," Colegrove says of both the adrenal and lung lesions. "That evidence is very striking and indicative that the adrenal lesions we are seeing is consistent with oil exposure."
Adrenal insufficiency in an animal makes it less equipped to cope with additional health stressors it encounters in its daily life, she explains.
Bacterial pneumonia was also found in many of the dead dolphins.
Dolphins must take deep breaths of air at the water's surface, where an oil spill and its fumes are strongest, and retain that air within their lungs for long periods of time during dives.
It follows that dolphins swimming into oil following the spill would be extremely susceptible to developing bacterial pneumonia, Venn-Watson says.
Scientists refer to a sudden spike in death in any species as an Unusual Mortality Event, or UME. So 5 years on from the BP spill, the dolphin die-off - the largest UME ever observed in the northern region of the Gulf of Mexico - is continuing, the researchers report.
Several times between the onset of the spill and now the death rate in dolphins has been as high as five times that considered normal in the Gulf waters involved in the spill, they say.
Deep Horizons well owner BP, for its part, has responded critically to the new study.
"The data we have seen thus far, including the new study from NOAA, do not show that oil from the Deepwater Horizon accident caused an increase in dolphin mortality," the company said in a statement.