Oil from BP’s Macondo well has again been linked to heart defects in embryonic and newborn bluefin and yellowfin tuna and in amberjack, key commercial, open water fish that were spawning in the Gulf of Mexico at the time of the catastrophic blowout, according to a peer-reviewed lab study released Monday by the National Oceanic and Atmospheric Administration.
"We can now say with certainty that oil causes cardiotoxicity in fish," said Stanford University fisheries biologist Barbara Block, who studies bluefin tuna in the Gulf, during a Monday (March 24) news conference about the study. Block is one of the authors of the study, which was published in latest edition of the Proceedings of the National Academy of Sciences.
Photographs and videos released with the study show deformed hearts and hearts that are not beating properly in recently hatched larvae of the three fish species that were tested at hatcheries in Australia and Panama.
The findings by the team of scientists with NOAA and several universities in the United States and Australia, were announced on the 25th anniversary of the Exxon Valdez oil spill.
In the paper, the researchers point out that Atlantic bluefin tuna population based in the Gulf is at a historically low level, and is being considered for listing as threatened or endangered under the federal Endangered Species Act.
“We know from the 1989 Exxon Valdez spill in Prince William Sound that recently spawned fish are especially vulnerable to crude oil toxicity,” said Nat Scholz, a marine biologist and leader of the ecotoxicology program at NOAA's Northwest Fisheries Science Center in Seattle, in a news release announcing the study. “That spill taught us to pay close attention to the formation and function of the heart.”
“The timing and location of the spill raised immediate concerns for bluefin tuna,” Block said. “This spill occurred in prime bluefin spawning habitats, and the new evidence indicates a compromising effect of oil on the physiology and morphology of bluefin embryos and larvae.”
BP immediately released a statement questioning the results of the new study.
“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 the statement. "The oil concentrations used in these lab experiments were rarely seen in the Gulf during or after the Deepwater Horizon accident. In addition, 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.”
BP's contention that the concentrations used in the experiments were rarely seen in the Gulf is at odds with the comments of NOAA toxicologists during Monday's news conference, who said the amounts were similar to those seen in water samples taken from the Gulf.
The three fish species tested during the study produce embryos that float near the surface of the ocean. Compounds contained in the BP oil called polycyclic aromatic hydrocarbons have been linked by the new study to a slowing of the heartbeat or an uncoordinated heart rhythm in embryos and young larvae that can lead to heart failure. The chemicals also caused visible heart malformations
The study concludes that “environmentally realistic exposures” of the BP oil containing PAHs in amounts as small as 1 to 15 parts per billion were possible in the spawning area in the Gulf near the well.
“A considerable portion of Gulf water samples collected during the spill had PAH concentrations exceeding toxicity thresholds observed here, indicating the potential for looses of pelagic fish larvae,” the study concluded.
In the paper, the scientists recommended that researchers developing vulnerability assessments for future oil spills, including in the Arctic, “should focus on the developing heart of resident fish species as an exceptionally sensitive and consistent indicator of crude oil impacts.”
The research also is part of the federal Natural Resource Damage Assessment process required by the Oil Pollution Act in the aftermath of the spill. The assessment's findings will be used by federal and state officials, working with BP, to determine the damage caused by the spill to natural resources, and how those damages should be mitigated.
An earlier study published Feb. 14 in the journal Science outlined how scientists believe the chemical compound actually do their damage. That study found that PAHs interfere with fish heart muscle cells by disrupting how calcium ions trigger heartbeats, slowing heart rates.
In the news conference, Block said the two scientific studies for the first time outline key concerns about crude oil.
"In the 21st Century, we have only now realized that one of the most common substances on earth, petroleum, has a toxic impact on the cardiopulmonary system," she said.
In the new study, scientists used samples of crude oil that were collected from BP’s damaged riser pipe in the aftermath of the blowout and from oil skimmed at the surface during the spill.
The researchers then took the samples to a bluefin tuna hatchery in Australia and a yellowfin tuna hatchery in Panama, where embryos were exposed to tiny amounts of the oil.
Hatchery eggs and larvae were used because of the difficulty of collecting larvae and eggs in the ocean, in which nets would be used, which were likely to place damaging stress on the organisms.
The researchers used a commercial blender to mimic the effects of oil released a mile below the surface from the Macondo well at pressure, which turned it into similar tiny droplets distributed in sea water, which was used to expose the embryos.
Digital video microscopy was then used to track the effects of the oil over time, during which the scientists found changes in normal heart rates and rhythms, differences in the development of heart chambers, and in muscle walls.
"At higher levels of exposure, the embryos were severely malformed, said Dr. John Incardona, a cardiologist and toxicologist who heads the ecotoxicology program at NOAA's Northwest Fisheries Science Center in Seattle, Wash.
At lower exposure rates, fish had abnormal heart rhythms and other irregularities, he said. Those fish were likely to survive immediate exposure to the toxic compounds, but the malformations would reduce their aerobic performance as they grew towards maturity, increasing the chances they wouldn't survive to produce more fish, he said.
Block said the concern for larger "pelagic" fish -- fish that live in the open ocean and are at the top of the food chain -- is that the immediate death of eggs and larvae and the longer-term heart deformities will reduce the number of fish in a species already in trouble.
Bluefin tuna take between 8 and 14 years to reach maturity, which could make it difficult to determine the long-term effects of the oil. But Block said additional studies being conducted by university scienntists and NOAA are underway to estimate the extent of contamination of BP oil on the area used by tuna and other species in the Gulf.
Scholz said that environmental modeling using that information, the results of water samples taken during the spill, and the results of the toxicity research will be used to determine likely losses from the spill.
A spokesman for Pew Charitable Trusts recommended that NOAA take actions to close the Gulf of Mexico to surface long line fishing to protect spawning bluefin, and enforcing an annual limit on incidental catch from the entire surface longline fleet."To keep fishermen on the water when bluefin are in the Gulf, restoration monies provided by BP and other companies responsible for the Deepwater Horizon oil spill could help pay for fishermen to transition from surface longlining to more selective fishing methods," said Pew spokesman Tom Wheatley. "This could protect spawning bluefin and other non-target ocean wildlife, while maintaining access by commercial fishermen to their target catch."
The environmental group Oceana pointed out that the effects described in the new research might be happening again this spring, thanks to a new, large spill of oil off the Texas coast, the result of a collision Saturday (March 22) between an oil tanker barge and a cargo ship.
Oceana added: "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. Many larval tuna exposed to this oil likely perished. Besides being bad news for the fish, it also hurts fishermen, coastal economies, consumers and ocean ecosystems.
"Rather than rushing to let BP and its competitors go back to drilling into our oceans, the Obama administration should be devising a smarter energy strategy, charting a course to break our oil addiction by building a clean energy driven future."
(An earlier version of this story incorrectly said the study concluded that texposures of between 1 and 15 parts per million of BP oil were possible in the area where spawning was occurring. The paper actually said the exposures were between 1 and 15 parts per billion.)