Exposure to PAHs disrupts basic cellular function of heart muscles
By Summit Voice
FRISCO — When BP’s failed Deepwater Horizon drill rig spewed millions of gallons of oil into the Gulf of Mexico, scientists immediately began documenting impacts to natural resources, finding dead corals on the seafloor, sick dolphins in Barataria Bay and remnant oil in the splash zone along Florida beaches.
Even low levels of oil pollution can damage the developing hearts of fish embryos and larvae, reducing the likelihood that those fish will survive. Scientists have known of this effect for some time, but the underlying mechanism has remained elusive.
But recent research by scientists with NOAA and Stanford University, shows how oil-derived chemicals disrupt the normal functioning of the heart muscle cells of fish. The findings, published in the Feb. 14 issue of Science, describe how toxic oil-based chemicals disrupt cardiac function in young bluefin and yellowfin tuna by blocking ion channels in their heart muscle cells.
The findings are part of the Natural Resource Damage Assessment conducted by NOAA and other federal and state trustee agencies following the 2010 Deepwater Horizon oil spill in the Gulf of Mexico. That spill occurred across a large region where the Western stock of Atlantic bluefin tuna spawn, raising the possibility that the eggs and larvae of this valuable species were exposed to crude oil. Natural Resource Damage Assessments are used to determine liabilities after a spill and to help develop restoration plans.
“We’ve known that oil causes problems with the hearts of developing fish based on research following the Exxon Valdez oil spill,” said Nat Scholz, one of the authors of the paper and the leader of the Ecotoxicology Program at NOAA’s Northwest Fisheries Science Center in Seattle. “Now that we better understand the precise mechanism, we can develop more subtle and sensitive indicators of cardiac stress in fish embryos and larvae and more accurately assess the impact of pollution on our natural resources,” Scholz said.
“We typically hear about people having broken hearts on Valentine’s Day, but this year the heartbreak story is about tuna,” said Oceana’s vice president for U.S. oceans Jacqueline Savitz. “The heart is a critical organ … if their hearts don’t function properly, fish don’t have much chance for survival,” Savitz said.
“For many Bluefin tuna, which are economically important but severely depleted, broken or poorly functioning hearts may have been the end of their story. We need to rebuild our economically important fisheries, like the Bluefin tuna fishery, rather than subjecting them to the effects of offshore drilling. Breaking our addiction to oil and moving to clean energy provides many benefits while also being better for fish,” she added
To demonstrate the effect of PAHs on the cardiac cells of tuna, scientists had to measure the flow of electrical current across the membranes of individual cells.
This experimental capacity was provided by the Tuna Research and Conservation Center, jointly operated by Stanford University and the Monterey Bay Aquarium. Scientists there measured the electrical properties of individual heart muscle cells using a “patch clamp” technique, which involves micron-scale glass electrodes.
The Stanford scientists provided expertise in tuna husbandry, cardiac physiology, single-cell electrophysiology, and optical imaging. NOAA’s Ecotoxicology Program provided expertise in designing oil exposure studies, and in understanding the effects of oil on whole fish embryos and larvae. The NOAA group also developed new methods for preparing environmentally realistic oil mixtures for use in the lab.
This will lead to new tools for assessing the impact of pollution on natural resources. For instance, scientists might assess the baseline level of those biomarkers, then test for them again if an oil spill occurs to measure the impact on fish. Such a technique might be particularly useful in the Arctic, where retreating ice cover is opening new areas to oil development. Because the ecosystem there is still relatively pristine, now is the ideal time to collect baseline measures of ecosystem function, before oil development takes place.
PAHs are also present in urban stormwater runoff to coastal areas and watersheds that fish use as spawning grounds. Many municipalities are working to improve water quality using pervious pavements, green roofs, and other surfaces that absorb stormwater. With new diagnostic techniques based on biomarkers, scientists will be better able to evaluate the effectiveness of these pollution control measures.
The authors will present their findings at the 2014 annual meeting of the American Academy for the Advancement of Science in Chicago.