On April 20, 2010, an explosion of an oil rig off the coast of Louisiana killed 11 workers. The world then watched helplessly as BP’s oil collapsed into the Gulf of Mexico for 87 days, killing countless millions of marine animals.
Dolphins who survived one of the worst environmental disasters ever seem to still be suffering the consequences more than a decade later.
Comparing bottlenose dolphin populations (Tursiops truncatus) of Barataria Bay in Louisiana living in the area of oil exposure to populations from Sarasota Bay, Florida, which have not been exposed to severe pollution, researchers have found there are still worrying health differences between them.
Previous studies have already revealed the short-term effects of the oil spill on the dolphins in Barataria Bay, including abnormal adrenal function, lung disease, reproductive impairment, immune system problems and reduced survival. Dolphins living in the spill area gave birth to live calves only 19 percent of the time.
Oiled dolphins swim in the northern Barataria Bay. (Louisiana Department of Wildlife and Fisheries)
Analyzing tissue samples from 34 dolphins in the Barataria Bay, veterinary scientist Sylvain De Guise and colleagues from the University of Connecticut discovered in 2018 a deterioration in the immune system comparable to that seen in the population in 2011. They then performed laboratory tests on dolphin cells and mice to confirm whether exposure to oil can cause these conditions.
“The parallel between findings in dolphins exposed after the Deepwater Horizon spill and laboratory mice experimentally exposed to oil was impressive and really helped build the weight of evidence between exposure to oil and specific effects on the immune system,” explains De Guise explains.
Both the mice exposed to oil and the dolphins had increased proliferation of T lymphocytes (white blood cells) and more cells that suppress the immune system – regulatory T cells. These cells usually prevent autoimmune diseases.
Although immunological changes have also been observed in dolphins exposed to other stresses, such as toxins for algal blooms, the pattern of changes was different from the dolphins in the Barataria Bay.
Studies in rodents have previously associated such changes in the immune system with an increased susceptibility to disease. De Guise’s team showed that these immune differences can also be transferred from rodents exposed to oil pollution to their young. And since the changes weren’t just in the older dolphins, the team is concerned that these limitations will be passed on to generations of 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 paper.
Samples from the Barataria Bay swamp sediments showed that oil concentrations were still 10 times higher than before the spill eight years later. Further research is needed to determine exactly what is happening.
Researchers are concerned that the long-term effects of oil spills are not 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 humans who have worked to clean up oil spills, suggesting that there is a common response to oil exposure in mammals.
“The long-term effects and the potential for multigenerational effects are of great concern about the recovery of dolphin populations after the spill,” said De Guise.
This research is published in Environmental Toxicology and Chemistry