Stanford University, researching the effect of the 2010 BP oil spill on tuna, has found crude oil "interrupts the ability of fish heart cells to beat effectively."
The study, done in conjunction with NOAA, is part of the Natural Resource Damage Assessment following the oil spill.
Scientists "discovered that crude oil interferes with fish heart cells," according to the report.
"The toxic consequence is a slowed heart rate, reduced cardiac contractility and irregular heartbeats that can lead to cardiac arrest and sudden cardiac death," according to a report on the study.
The research was released Thursday and published in an issue of the periodical Science.
The research team is led by Barbara Block, a Stanford professor of marine sciences who is considered one of the top tuna experts in the world.
The team discovered crude oil "interrupts a cellular pathway that allows fish heart cells to beat effectively," the report said. "The components of the pathway are present in the hearts of many animals, including humans."
The researchers' tests found "very low concentrations of crude oil" disrupt the process whereby molecules flow in and out of heart cells, the cells that handle contraction and relaxation in the heart muscle.
Although some aspects of crude oil were already known to be toxic to marine animals and "cardiotoxic" to young, growing fish, the report said the physiology behind the harmful effects was unclear until now.
The study also points up the risk to wildlife and humans from exposure to air pollution with the same heart-affecting chemicals that exist in crude oil.
The study was done taking advantage of captive populations of bluefin and yellowfin tuna, on which the research team "was able to directly observe the effects of crude oil samples collected from the Gulf of Mexico on living fish heart cells."
Researchers said they observed heart cells in vitro and were able to measure how they responded to crude oil.
In the company's response to the study, BP spokesman Jason Ryan said, "Bathing isolated heart cells with oil concentrations is simply not comparable to the real-world conditions and exposures that existed in the Gulf for whole fish."
He said the Stanford paper provides "no evidence" of an impact to the population of tuna or other fish in the Gulf.
"The paper provides no realistic exposure assessment, and it is scientifically inappropriate to take data from in vitro laboratory tests on isolated tuna heart cells and use it to make unsupported predictions about effects on a variety of live marine species or humans in the Gulf -- effects that no one has observed or measured in the field."
Science speaks for itself
Mississippi DEQ Director Trudy Fisher, in a statement Thursday after the study's release, said the science of the report speaks for itself.
The BP disaster spilled roughly 200 million gallons of crude oil into the Gulf over 87 days in spring and summer 2010, during the peak spawning time for the Atlantic bluefin tuna, raising the possibility eggs and larvae, which float near the surface waters, were exposed to oil, the report said.
The bluefin spawning population in the Gulf is 36 percent of what it was in the 1970s, the report said.
The Atlantic bluefin tuna are highly protected, especially in the Gulf. The yellowfin tuna are a valuable, popular fish, caught both commercially and recreationally in the Gulf.