The BP Deepwater Horizon oil spill began in the Gulf of Mexico on April 20, 2010. Following the event through 2012, more than a thousand dolphins washed up dead along the Gulf, in three major strandings. That’s four to five times higher than the region’s usual rate of dolphin deaths.

“We found that dolphins dying after the oil spill had distinct adrenal gland and lung lesions that were not present in the stranded dolphins from other areas.”

Kathleen Colegrove of the University of Illinois was the lead veterinary pathologist of the latest in a series of studies analyzing the die-off. She and her study co-authors took part in a telephone press conference on May 20th.

“Now, surprisingly, one in three dolphins that stranded in Louisiana, Mississippi and Alabama had a thin adrenal gland cortex. And when looking at just the Barataria Bay dolphins, half of them had this lesion.”

Barataria Bay got an especially high dose of oil.

“This prevalence was significantly higher than in the reference population, in which less than one in 10 had this lesion. Now, this thinning of the adrenal gland cortex was a very unusual abnormality for us, that has not been previously reported in dolphins in the literature…now, aside from chemical exposure, conditions that can cause the adrenal gland to become thin include things like cancer, autoimmune disease, fungal infections and tuberculosis. And we did not find any evidence of these alternative causes in the dolphins.

“Now, in addition many dolphins dying after the oil spill again in Louisiana, Mississippi and Alabama had evidence of significant lung disease…in fact, these dolphins had some of the most severe lung lesions I have ever seen in wild dolphins from throughout the U.S.”

The study is in the journal PLoS ONE. [Stephanie Venn-Watson et al, Adrenal Gland and Lung Lesions in Gulf of Mexico Common Bottlenose Dolphins (Tursiops truncatus) Found Dead following the Deepwater Horizon Oil Spill]

BP disputes the link between the dolphins and the oil spill. But the study’s lead author, Stephanie Venn-Watson of the National Marine Mammal Foundation contends:

“The evidence to date indicates that the Deepwater Horizon oil spill and associated compounds caused the adrenal and lung lesions which contributed to the increased deaths as part of this unusual mortality event.”

—Steve Mirsky

[The above text is a transcript of this podcast.]