(CN) — The immune systems of bottlenose dolphins in the northern Gulf of Mexico suffered long term damage following exposure to toxic oil spilled during the deadly Deepwater Horizon drilling explosion in 2010, according to a study released Wednesday.
British Petroleum’s Deepwater Horizon oil rig exploded and sank on April 20, 2010 in an oil field off the coast of Louisiana called the Macondo Prospect. The blowout-triggered release of oil into the ocean is considered the largest in history.
The explosion killed 11 workers and caused toxic gas and over 200 million gallons of crude oil to spill into the sea.
A conservation study published last year estimated that the blowout led to immense ecological damage and exposed nearby communities and wildlife to crude oil and the chemicals used to quell the blowout.
The populations of birds, whales, turtles and other wildlife in the Gulf plummeted in the years following the disaster, the report found, adding that 75% of pregnancies in the region’s dolphin population failed in the five years following the explosion.
To further understand the long term impacts of exposure to oil on marine mammals in the region, a team of U.S.-based researchers set their sights on examining the immune systems of bottlenose dolphins.
Between 2011 and 2018, the team collected samples from bottlenose dolphins near Barataria Bay, Louisiana, that were exposed to the 2010 spill as well as samples from bottlenose dolphins in Sarasota Bay, Florida, that were not exposed.
In the year following the blowout, researchers found that the Barataria Bay dolphins — scientific name tursiops truncatus — who experienced prolonged “oiling” displayed severe impairments to normal immune functions.
According to the study published Wednesday in the journal Environmental Toxicology and Chemistry, that damage was still present seven years later.
“Together, our findings present a pattern of immune changes in Barataria Bay in 2017 and 2018 similar to that observed in dolphins sampled in Barataria Bay a year after the Deepwater Horizon spill, which was reasonably attributed to the exposure to oil from the spill, different from patterns of immunotoxicity observed in association with other stressors, and in the absence of other compelling causes,” the study said. “Our results support a central role for Treg‐cell dysfunction as a key mechanism underlying those effects. Long‐term consequences of oil exposure on the highly sensitive immune system, with the potential for multigenerational effects, might have significant consequences on the potential for population recovery and raise concerns for other mammalian species.”
The team found that the negative impact of oiling on Barataria Bay dolphins’ immune systems was also seen in dolphins born years after the Deepwater Horizon spill.
Study author Sylvain De Guise of the University of Connecticut said in a statement released with the study that the team’s analysis led to robust evidence of the risks associated with mammals’ exposure to oil.
"The parallel between findings in dolphins exposed following the Deepwater Horizon spill and laboratory mice experimentally exposed to oil was impressive and really helped build the weight of evidence between oil exposure and specific effects on the immune system," De Guise said. "However, the long-term effects and potential for multigenerational effects raise significant concerns for the recovery of dolphin populations following the spill.”
Researchers believe the Barataria Bay dolphins may be facing ongoing exposure to oil that was not properly disposed of following the 2010 spill, according to the study.
“In fact, oil in Barataria Bay marsh sediments 8 yr after the Deepwater Horizon spill was still 10 times above prespill concentrations, with [a separate study] suggesting ‘a long‐term contamination by oil or oil residues that will remain for decades,’” the study said. “Of interest is a particular ongoing feeding behavior observed in Barataria Bay dolphins, whereby they appear to ‘drill into the sediments’ with the potential to inadvertently ingest and/or resuspend oil constituents and continue their exposure.”
As part of the study, scientists also exposed female mice to crude oil in order to assess chemicals’ impact on other mammals.
After six weeks, the mice were euthanized and their blood was examined for T‐lymphocyte cell levels and concentrations of plasma cytokines to assess damage to immune functions.
The study found that mice born to non-control group mice after the study showed signs of immune impairment.
“Mice experimentally exposed to Louisiana sweet crude oil by gavage (needle) for 6 wk showed no significant changes in splenocyte T‐lymphocyte proliferation compared to control mice gavaged with mineral oil,” the study said. “However, the unexposed progeny of exposed mice had significantly (15–33%) higher ConA‐ and PHA‐ induced T‐lymphocyte proliferation compared to the progeny of control mice.”
Researchers did not immediately respond to requests for further comment on the study.
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