Oil from the Deepwater Horizon disaster is still causing dolphin deaths five years after the spill, with sea mammals in the Gulf of Mexico showing clear signs of petroleum exposure, according to study results published Wednesday by the National Oceanographic and Atmospheric Administration (NOAA).
Researchers conducting the study said they found that bottlenose dolphins were succumbing to the effects of lesions on their lungs and adrenal glands. The severity of the normally rare lesions shocked scientists studying dolphin corpses from the Gulf in the years since the 2010 disaster.
On April 20 of that year, the Deepwater Horizon, an offshore oil platform owned by BP, was drilling a well that blew out, leading to an explosion on the platform, which collapsed in the ensuing fire. Eleven workers died, and 200 million gallons of oil spilled into the Gulf over almost three months. The spill had devastating consequences for wildlife and the fishing industry in the region.
Repair crews plugged the well in July 2010. BP faces billions of dollars of civil claims and fines.
In the NOAA study, published in the academic journal PLOS One, researchers said they could not find any apparent cause of death other than the lesions for about half the dolphins suffering from them.
“These dolphins had some of the most severe lung lesions I have seen in the over 13 years that I have been examining dead dolphin tissues from throughout the United States,” said Kathleen Colegrove, a veterinarian who worked on the study.
More than 1,000 sick dolphins died from 2010 to 2015, the NOAA said, most often from lesions linked to oil exposure.
“The timing, location and nature of the detected lesions support that contaminants from the Deepwater Horizon oil spill caused these lesions and contributed to the high numbers of dolphin deaths within this oil spill’s footprint,” the NOAA said in a release.
The damage to the adrenal glands, crucial hormone-producing organs, was particularly harmful to many dolphins. “Animals with adrenal insufficiency are less able to cope with additional stressors in their everyday lives, and when those stressors occur, they are more likely to die,” Stephanie Venn-Watson, a veterinarian at the National Marine Mammal Foundation and the lead author of the study, said in a statement. The NOAA helped write the report, along with BP, state agencies and other federal agencies.
The scientists also found that about a third of the dolphins that died in the oil spill footprint suffered from respiratory illness, identifying “increased susceptibility to primary bacterial pneumonia, possibly due to lung injury or alterations in immune function ... Many of these cases were unusual in severity and caused or contributed to death,” the report read.
Exposure to water polluted with oil isn’t healthy for any animals, but dolphins “are particularly susceptible to inhalation effects due to their large lungs, deep breaths and extended breath hold times,” the NOAA study report said.
“These studies have increasingly pointed to the presence of petroleum hydrocarbons as being the most significant cause of the illnesses and deaths plaguing the Gulf’s dolphin population,” said Teri Rowles, a veterinarian who took part in the study and works with the NOAA’s marine mammal health and stranding response program.
The Deepwater Horizon disaster is causing the longest known unusual mortality event, or UME, in the Gulf of Mexico. The second-longest UME was in 2005 and 2006, lasting 17 months. The UME with the second-largest dolphin death toll took place in 1990, with at least 344 cetacean deaths. That die-off was traced to bacterial infection, a National Marine Fisheries Service study found.