Eleven workers were killed in an explosion off the coast of Louisiana on April 20, 2010. The world then watched helplessly as BP’s oil spilled over the Gulf of Mexico for 87 days, killing millions of marine animals.
Dolphins that survived one of the worst environmental disasters ever, it seems to have another decade later.
Compare populations of common bottlenose dolphins (Tursiops truncatus) from Barataria Bay in Louisiana living in the area of oil exposure to populations of Sarasota Bay in Florida that have not been exposed to serious pollution, researchers have found that there are still worrying health disparities between them.
Previous studies have already revealed the short-term effects of the oil spill on the Baratari Bay dolphins, including abnormal adrenal glands, lung diseases, impaired reproduction, immune system problems and reduced survival. Dolphins that live within the fall area have only 19 percent of their lives born to live calves.
Oiled dolphins swimming in Northern Barataria Bay. (Louisiana Department of Wildlife and Fisheries)
The tissue samples from 34 Barataria Bay dolphins were analyzed, and veterinary scientist Sylvain De Guise, University of Connecticut, and colleagues found in 2018 immune system disorders similar to those found in the 2011 population. They performed laboratory tests on dolphin cells and mice to confirm whether it was oil exposure. can cause these conditions.
“The parallel between findings in dolphins exposed after the dump of Deepwater Horizon and laboratory mice experimentally exposed to oil was impressive and helped build the weight of evidence between oil exposure and specific effects on the immune system,” explains De Guise.
Both the oil-exposed mice and the dolphins have the proliferation of T lymphocytes (white blood cells) and more cells that suppress the immune system – T-regulatory cells. These cells usually prevent autoimmune diseases.
While immunological changes were also seen in dolphins exposed to other stresses, such as algae flower toxins, the pattern of changes was different than in the Barataria Bay dolphins.
Studies in rodents have previously linked such changes in the immune system to increased susceptibility to disease. The team at De Guise has shown that the immune differences can also be transmitted to rodents exposed to oil pollution. And since the changes were not just present in the older dolphins, the team is concerned that these disabilities are being passed on by the slaughtered dolphins.
However, there is another possible explanation for this.
“It is possible that there is ongoing exposure to the Deepwater Horizon oil that may not have been completely removed from the Barataria Bay ecosystem,” the team wrote in their newspaper.
Samples of the Barataria Bay marsh deposits showed that the oil concentration was still ten times higher eight years later than before the spill. Further research is needed to determine exactly what is happening.
Researchers are concerned that the long-term effects of oil spills may not be limited to dolphins. We still know little about the health outcomes of other long-lived species such as turtles. Immune effects have also been reported in people who have worked to clear up oil spills, suggesting that there is a common response to oil exposure in mammals.
“The long-term effects and potential for multigenerational effects raise significant concerns about the recovery of dolphin populations after the spill,” De Guise said.
This research was published in Environmental toxicology and chemistry.