February 14, 2014
Fish Exposed To Crude Oil Suffer Host Of Heart Ailments
April Flowers for redOrbit.com - Your Universe Online
A new study from Stanford University and the National Oceanic and Atmospheric Administration (NOAA) has revealed that crude oil interferes with fish heart cells, resulting in a slowed heart rate, reduced cardiac contractility and irregular heartbeats that can lead to cardiac arrest and sudden cardiac death.The study is part of an ongoing Natural Resource Damage Assessment of the April 2010 Deepwater Horizon oil spill. The findings were published in a recent issue of Science.
Scientists have long known that crude oil is cardiotoxic to developing fish. However, the physiological mechanisms underlying its harmful effects have still been unclear. While studying the impact of the crude oil from the Deepwater Horizon spill on tuna, the Stanford and NOAA scientists discovered that the crude interrupts the ability of fish heart cells to beat effectively.
Some of the mixture of chemicals that make up crude oil are known to be toxic to marine animals. Prior studies have focused on "polycyclic aromatic hydrocarbons" (PAHs), in particular. PAHs can also be found in coal tar, creosote, air pollution and storm water runoff from land. PAHs can persist for many years in marine habitats after an oil spill, causing a variety of adverse environmental effects.
Oil interferes with cardiac cell excitability, contraction and relaxation, the researchers found. All of these processes are vital for normal beat-to-beat contraction and pacing of the heart. According to their tests, very low concentrations of crude oil disrupts the specialized ion channel pores—where molecules flow in and out of the heart cells—that control heart rate and contraction in the cardiac muscle cell.
In cells throughout the heart, this cyclical signaling pathway is what propels blood out of the pump on every beat. In the hearts of most animals, humans included, the protein components of the signaling pathway are highly conserved.
According to the findings, oil blocks the potassium channels distributed in heart cell membranes, which increases the time to restart the heart on every beat, prolonging the normal cardiac action potential and slowing the heartbeat. In tuna, the potassium ion channel impacted is responsible for restarting the heart muscle cell contraction cycle after every beat. This channel is highly conserved throughout vertebrates, which raises the possibility that animals as diverse as tuna, turtles and dolphins might be affected in similar ways by exposure to crude oil. The researchers also found that oil exposure resulted in arrhythmias in some ventricular cells.
"The ability of a heart cell to beat," explained Barbara Block, a professor of marine sciences at Stanford, "depends on its capacity to move essential ions like potassium and calcium into and out of the cells quickly. This dynamic process, which is common to all vertebrates, is called 'excitation-contraction coupling.' We have discovered that crude oil interferes with this vital signaling process essential for our heart cells to function properly."
"We've known from NOAA research over the past two decades that crude oil is toxic to the developing hearts of fish embryos and larvae, but haven't understood precisely why," said Nat Scholz, leader of the Ecotoxicology Program at NOAA's Northwest Fisheries Science Center in Seattle. "These new findings more clearly define petroleum-derived chemical threats to fish and other species in coastal and ocean habitats, with implications that extend beyond oil spills to other sources of pollution such as land-based urban stormwater runoff."
OTHER HAZARDS OF OIL SPILLS
The findings also bring new attention to a previously underappreciated risk to both humans and wildlife. This risk is from exposure to cardioactive PAHs that also exist at relatively enriched levels in air pollution.
"When we see these kinds of acute effects at the cardiac cell level," Block said, "it is not surprising that chronic exposure to oil from spills such as the Deepwater Horizon can lead to long-term problems in fish hearts, as our NOAA colleagues have observed in studies of larval fish development.
"The protein ion channels we observe in the tuna heart cells are similar to what we would find in any vertebrate heart and provide evidence as to how petroleum products may be negatively impacting cardiac function in a wide variety of animals," she said. "This raises the possibility that exposure to environmental PAHs in many animals – including humans – could lead to cardiac arrhythmias and bradycardia, or slowing of the heart."
The Deepwater Horizon disaster in April 2010 released over 4 million barrels of crude oil during the peak spawning time for the Atlantic bluefin tuna. Compiling electronic tagging and fisheries catch data, the team found that the Atlantic bluefin spawn in the area where the drilling rig collapsed. This raises the possibility that eggs and larvae, which float near the surface waters, were exposed to oil.
The spill took place in the major spawning ground of the western Atlantic population of bluefin tuna, located in the Gulf of Mexico. The estimated spawning population, taken in the most recent stock assessment of 2012, was only 36 percent of the 1970 baseline population. Many other pelagic fish species were also likely to have spawned in habitats corrupted with oil, including yellowfin tuna, blue marlin, and swordfish.
Prior studies by NOAA scientists revealed that exposure to crude oil-derived PAHs disrupts cardiac function and impairs development in larval fishes. Other studies, particularly in the aftermath of the Exxon Valdez spill in 1989, have shown a syndrome of embryonic heart failure, bradycardia, arrhythmias and edema in exposed fish embryos. In the aftermath of the Deepwater Horizon disaster, the potential for harmful effects on young fish is still being investigated. The current study was focused specifically on how oil impacts heart cells.
The team took advantage of captive populations of bluefin and yellowfin tuna at the Tuna Research and Conservation Center (a collaborative facility operated by Stanford and the Monterey Bay Aquarium) to directly observe the effects of crude oil samples collected from the Gulf of Mexico on living fish heart cells.
The Stanford researchers bathed isolated cardiac cells from the tuna in low dose crude oil concentrations similar to what fish in early life stages may have encountered in the surface waters where they were spawned after the April 2010 oil spill in the Gulf of Mexico.
The heart cells' response was measured using a combination of sophisticated electro-physiological techniques – including "patch clamping" and "confocal microscopy" – to record how ions flowed into and out of the heart cells, and to identify the specific proteins in the excitation-contraction pathway that were affected by crude oil chemical components.
"We can examine the function of healthy heart cells in vitro and actually measure in the microscope how they respond to the presence of crude oil in real time," said Fabien Brette, a research associate in Block's lab and lead author on the study.
"The normal sequence and synchronous contraction of the heart requires rapid activation in a coordinated way of the heart cells," Block said. "Like detectives, we dissected this process using laboratory physiological techniques to ask where oil was impacting this vital mechanism."