An oil rig explosion off the coast of Louisiana killed eleven workers on April 20, 2010. The world watched helplessly as BP oil spilled into the Gulf of Mexico for 87 days and killed millions of marine animals.
Dolphins that survived one of the worst environmental disasters in history still seem to suffer the effects more than a decade later.
Comparing populations of common bottlenose dolphins (Tursiops truncatus) from Barataria Bay, Louisiana, who live in the oil exposure zone of the populations of Sarasota Bay, Florida, who have not been exposed to severe pollution.
Previous studies have already revealed the short-term impacts of the oil spill on Barataria Bay dolphins, including abnormal adrenal function, lung disease, impaired reproduction, immune system problems, and decreased survival. Dolphins living in the spill area only gave birth to live calves 19 percent of the time.
Oilseed dolphins swimming in the northern bay of Barataria. (Louisiana Department of Wildlife and Fisheries)
Analyzing tissue samples from 34 dolphins in Barataria Bay, University of Connecticut veterinary scientist Sylvain De Guise and colleagues found immune system deficiencies in 2018 similar to those found in the population in 2011. Then they went perform laboratory tests on dolphin and mouse cells to confirm whether exposure to oil can trigger these conditions.
“The parallelism 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 testing between oil exposure and the specific effects on the immune system, “De Guise explained.
Both mice exposed to the oil and dolphins had a higher 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 immune changes have also been seen in dolphins exposed to other strains, such as algae flowering toxins, the pattern of changes was different from those seen in dolphins in Barataria Bay.
Studies in rodents have previously linked these changes in the immune system to an increase in susceptibility to the disease. De Guise’s team demonstrated that these immune differences could also be transmitted from rodents that had been exposed to oil contamination in their offspring. And because the changes were not only present in older dolphins, the team is concerned that these deficiencies are passed down through generations of dolphins.
However, there is another potential explanation for this.
“There may be continued exposure to Deepwater Horizon oil that may not have been completely removed from the Barataria Bay ecosystem,” the team wrote in its diary.
Samples from the sediments of the Barataria Bay swamp showed that oil concentrations were still 10 times higher than before the spill, eight years later. More research will be needed to determine exactly what is going on.
Researchers are concerned that the long-term effects of oil spills cannot be limited to dolphins. We still know little about the health outcome 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 among mammals.
“The long-term effects and potential for multigenerational effects raise important concerns for the recovery of dolphin populations after the spill,” De Guise said.
This research was published in Toxicology and Environmental Chemistry.