Lung and adrenal lesions found in dead bottlenose dolphins stranded along the Gulf of Mexico between June 2010 and December 2012 are consistent with the types of damage that marine mammals sustain from exposure to petroleum products after an oil spill, according to a new study published on Wednesday by researchers from the National Oceanic and Atmospheric Administration.
The findings are the latest results from the Deepwater Horizon National Resource Damage Assessment, an ongoing investigation by NOAA into the spill, the largest offshore oil spill in United States history. Combined with previous studies by the agency, this paper provides additional support to a link between the Deepwater Horizon oil spill in 2010 and mass dolphin deaths in Alabama, Louisiana and Mississippi.
“The evidence to date indicates that the Deepwater Horizon oil spill caused the adrenal and lung lesions that contributed to the deaths of this unusual mortality event,” said Stephanie Venn-Watson, a researcher with the National Marine Mammal Foundation who was the lead author of the report. “We reached that conclusion based on the accumulation of our studies including this paper,” she added.
The researchers analyzed tissue samples collected from 46 dolphins, shortly after they died, in the area affected by the spill. They then compared them with samples from 106 dolphins that had died at different times from the spill and in other regions, including in Florida, North Carolina, South Carolina and Texas.
They found more instances of adrenal and lung lesions in the dolphins that died near the Deepwater Horizon spill than in the other dolphins, the team reported in the journal PLOS ONE.
A third of the Gulf Coast dolphins had a thinned or damaged adrenal gland cortex compared with only 7 percent of the so-called reference dolphins, the researchers said.
Damaged adrenal glands cannot properly produce essential hormones, and can cause fatal problems in dolphins, according to Kathleen Colegrove, a veterinary pathologist at the University of Illinois and an author of the study. She said that there had been many reports of adrenal complications leading to death in mink after exposure to oil.
“This was an unusual abnormality to us that has not been previously documented in the literature,” Dr. Colegrove said of both the lung and adrenal lesions. “That evidence is very striking and indicative that the adrenal lesions we are seeing is consistent with oil exposure.”
The researchers also found that about a fifth of the Gulf Coast dolphins had lung lesions caused by bacterial pneumonia, and that 70 percent of that group died because of that condition. Only 2 percent of the reference dolphins had any trace of bacterial pneumonia.
The researchers said that the dolphins most likely inhaled the fumes from the petroleum products on the ocean surface. They added that exposure to oil fumes is one of the most common causes of chemical inhalation injury in other animals.
“These dolphins had some of the most severe lung lesions I have ever seen in wild dolphins throughout the United States,” Dr. Colegrove said.
The study was criticized by BP, which owned the well that blew out. It issued a statement saying that “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.”
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