Measuring changes in toxicity of oil spills over time
When the Deepwater Horizon offshore drilling rig exploded and sank in the Gulf of Mexico in 2010, it caused the largest offshore oil spill in U.S. history. The main toxic component of this crude oil was a class of compounds called polycyclic aromatic hydrocarbons (PAH); exposure to PAHs can cause significant ecological and human health issues.
Over time, crude oil becomes “weathered”, meaning parts of it dissolve, evaporate or get eaten by bacteria. NC State University scientist Damian Shea is working with the UNC SRP to determine how this weathering affects PAH levels and their toxicity to fish and shellfish in the impacted areas, and how to effectively measure the changes in the months and years after a spill.
In his lab, Shea and his team set up a series of aquariums filled with water and oil samples from the Gulf at various stages of weathering. Each tank is home to oysters and blue crabs, as well as passive sampling devices (PSDs) developed by Shea to mimic the gill membranes of sea life and measure an organism’s long-term exposure to chemicals. (See the Summer 2012 Superfund Scoop for more on these devices.) The researchers regularly measure how much PAH is accumulating in the organisms and on the devices.
“We’ve found that the PAHs decrease significantly in concentration as the oil weathers, and those that remain are less likely to be released to the aquatic organisms,” Shea reported. “We’ve also found that our PSDs can accurately predict the amount of PAH that enters the marine animals. That is good news, because the devices could be used at future spill sites to estimate exposure without having to use actual organisms.”
Shea’s next step is to determine what is happening at the molecular level during the weathering process to make PAHs less available to harm marine organisms and, ultimately, the entire food chain.