An explosion of the oil rig off the coast of Louisiana killed eleven workers on April 20, 2010. The world then watched helplessly as BP oil came out into the Gulf of Mexico for 87 days, killing millions of marine animals.
Dolphins that survived one of the worst environmental disasters to date seem to be suffering the effects over a decade later.
Comparing common dolphin populations (Tursiops truncatus) from Louisiana’s Barataria Bay, who live in the area of oil exposure to populations in Florida’s Sarasota Bay, who have not been exposed to severe pollution, the researchers found that there are still worrying health differences between them.
Previous studies have already revealed the short-term impact of the oil spill on dolphins in the Gulf of Barataria, including abnormal adrenal function, lung disease, impaired reproduction, immune system problems and decreased survival. Dolphins living in the discharge area gave birth to live calves only 19% of the time.
Oil dolphin swimming in North Barataria Bay. (Louisiana Department of Wildlife and Fisheries)
Analyzing tissue samples from 34 dolphins in Barataria Bay, University of Connecticut veterinarian Sylvain De Guise and colleagues found immune system impairments in 2018 similar to those found in the population in 2011. They then performed tests. laboratory on dolphin cells and mice to confirm whether exposure to oil can trigger these conditions.
“The parallel between the findings in dolphins exposed to the Deepwater Horizon spill and laboratory mice experimentally exposed to oil was impressive and really helped build the burden of proof between oil exposure and specific effects on the immune system,” De Guise explained.
Both mice exposed to the oil and dolphins increased the proliferation of T lymphocytes (white blood cells) and more cells that suppress the immune system – regulatory T cells. These cells usually prevent autoimmune diseases.
While immunological changes were also observed in dolphins exposed to other stresses, such as algal bloom toxins, the pattern of changes was different from those observed in dolphins in the Gulf of Barataria.
Studies in rodents have previously linked such changes in the immune system to increased susceptibility to disease. De Guise’s team showed that these immune differences could also be transmitted by rodents that have been exposed to their children’s oil pollution. And because the changes have not only been 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 a continuous exposure to Deepwater Horizon oil that would not have been completely removed from the Gulf of Barataria ecosystem,” the team wrote in their paper.
Swamp sediment samples from Barataria Bay showed that oil concentrations were still 10 times higher than before the spill, eight years later. Further research will be 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 outcome of other long-lived species, such as turtles. Immune effects have also been reported in people who have worked to clean up oil leaks, suggesting that there is a common response to exposure to oil in mammals.
“The long-term effects and potential for multigenerational effects raise significant concerns for the recovery of dolphin populations from spills,” said De Guise.
This research was published in Toxicology and environmental chemistry.