WASHINGTON — Oil spilled during the 2010 Deepwater Horizon disaster caused severe defects in the developing hearts of tuna, according to a new study by government and academic scientists that hints at long-term damage from the accident.
The research, published Monday in Proceedings of the National Academy of Sciences, shows that the estimated 4.9 million barrels of crude that gushed out of BP’s failed Macondo well could have compromised tuna embryos and larvae, killing off some of the fish and shortening the lives of others.
The study — along with research published in the Feb. 14 issue of the journal Science — shows that polyaromatic hydrocarbons in crude harm heart development in bluefin tuna, amberjack and yellowfin tuna, by slowing the heart beat and disrupting its rhythm.
“Crude oil shuts down key cellular processes in fish heart valves,” said Barbara Block, a professor of marine science at Stanford University and a coauthor of the paper. “We can now say with certainty that oil causes cardiotoxic injuries in tuna, and we know the mechanism of exactly how this occurs.”
Tuna are a large predatory fish that spawn in the northern Gulf of Mexico during the spring and summer — right as BP’s well was sending oil into the water four years ago. Because the fish embryos float near the ocean surface, they were especially susceptible to floating crude.
The study published Monday does not document long-term damage to adult tuna, a long-lived species that cannot be commercially fished until they are eight years old.
But John Incardona, a research toxicologist with the National Oceanic and Atmospheric Administration, and the lead author of the paper, said the heart defects materializing in the young tuna could inhibit their swimming ability later on and lead to a “delayed mortality.”
Even when exposed to lower concentrations of oil, “fish that looked morphologically normal on the outside still had abnormal heart rhythms,” Incardona said. Those fish might survive “but would probably end up with a mild heart formation” and might die prematurely.
Researchers from the National Oceanic and Atmospheric Administration, Stanford and other universities, said the damage they documented to the young tuna in a Queensland, Australia laboratory is consistent with defects observed in Prince William Sound herring exposed to crude when the Exxon Valdez tanker ruptured 25 years ago.
The new study, which used actual crude collected from the Gulf of Mexico, was designed to emulate environmental conditions at the time of the disaster. Researchers exposed the transparent embryos to crude and used digital microscopes to capture video, revealing the fish’s heart rate and rhythm, the size of the heart chambers, the thickness of the muscle walls and other characteristics.
BP questioned the methodology of the study, saying that oil concentrations used in the lab experiments generally exceeded those in the Gulf during the 2010 spill.
“The paper provides no evidence to suggest a population-level impact on tuna, amberjack or other pelagic fish species in the Gulf of Mexico,” said Jason Ryan, a spokesman for the company. “The authors themselves note that it is nearly impossible to determine the early life impact to these species. To overcome this challenge, it would take more information than what’s presented in this paper.”
Scientists are still assessing how the 2010 oil spill affected marine life in the Gulf of Mexico, from tiny plankton and microscopic amoeba to big dolphins — a process that could take years.
It took eight years after the Exxon Valdez ran aground for Pacific herring to die off in Prince William Sound.
“The trickle-down impacts of this oil spill do take a long time to manifest among a population at a level one can see,” Block said.
The research could have much broader implications. Block noted that the scientific studies stemming from the 2010 spill are just now demonstrating “that one of the most common substances on the planet, petroleum, has a toxic cardiac impact to vertebrate hearts.”
Conservationists said the research — coming on the 25th anniversary of the Exxon Valdez disaster and as hundreds of first responders tackle a marine fuel spill in Galveston Bay — demonstrate the risks of oil development.
“Oil’s damage doesn’t disappear overnight, nor does it cease after the oil sheen goes away,” said Jacqueline Savitz, a vice president at the conservation group Oceana.
Oil’s toxicity extends from small fish “to the largest and most commercially valuable fish we know, tuna,” Savitz said. “For a species like Bluefin tuna, whose populations have crashed due to overfishing and are fighting to rebuild their former abundance, BP’s oil was a shot to the heart.”
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