Oil Persists Eight Years After Deepwater Horizon

In 2011, Senior Research Scientist Christoph Aeppli spent weeks combing Gulf of Mexico beaches for evidence of something no one wanted to find there. He overturned rocks, dug in the sand, and crawled along jetties to collect samples of the sticky, smelly, greasy substance for chemical analysis.

The oil he was searching for came from the Deepwater Horizon spill, one of the largest accidental marine spills in history. Oil began seeping from the deep Macondo Well on April 20, 2010, and continued for 87 days.

Soon after, BP committed $500 million dollars toward independent research on the effects of the oil spill. Grants from the Gulf of Mexico Research Initiative funded Aeppli and Senior Research Scientist Beth Orcutt to study the fate and impact of Macondo Well oil in the environment.

“That first fieldwork trip was a bit of a treasure hunt,” Aeppli said. “I didn’t know where on beaches to look for samples, but I knew the oil was there.”

Today, eight years after the spill, both Aeppli and Orcutt have made substantial contributions to the nascent field of oil spill science. Aeppli’s work has focused on coastal areas and the processes that transform the complex chemical compounds of oil after it is released. Orcutt’s work has illuminated the fate of oil in the deep sea.

One of Aeppli’s most impactful findings is how new chemical compounds form after an oil spill. When oil is “weathered” through exposure to environmental forces like sunlight and microbes, the molecular composition changes. Aeppli found that sunlight is the most powerful force in oxidizing oil, and that this happens quickly – two-thirds of the oxidation measured between 2010 and 2016 occurred in the first ten days after the Deepwater Horizon spill.

“Oil weathering products persist for long time,” Aeppli said. “It’s surprising that we’re still finding these compounds after eight years.”

Deepwater Horizon oil can be found today on beaches in the form of “sand patties,” small clumps of oil and sand that wash ashore. On their most recent sampling trip in February 2018, Aeppli and his team found hundreds of sand patties in a single morning spent combing a beach in Alabama.

Most research and remediation efforts have focused on the ocean surface and nearby coastal habitats, but 15 percent of the spilled oil – about 30 million gallons – is estimated to have sunk to the seafloor. In the wake of the spill, many hoped that deep-sea microbes would consume the oil, effectively aiding clean-up efforts.

Orcutt designed experiments to track how microbes respond to small, contained oil spills on the Gulf of Mexico seafloor. Observing these experiments over four years showed that microbe populations, especially those that feed on sulfates, flourish soon after the addition of oil – but that the high productivity doesn’t last. As the microbes consume the oil, they deplete other essential nutrients that are spare in the stark seafloor environment, and the rate at which they break down the oil slows.

“They can’t really deal with the oil,” Orcutt said. “That layer of oil is going to sit there for quite a long time, until it gets buried by new layers of sediment.”

When new layers of mud eventually cover the patches of oil, organisms will be able to recolonize those regions of the seafloor. Orcutt believes it will be several decades before animals like shrimp return to areas that were covered in Macondo Well oil.

“There are microbes that can deal with the oil, but they can't eat it all in a timeframe that will remediate the sediment before it becomes buried,” Orcutt said.

What Aeppli and Orcutt have learned about the fate and impact of oil in the environment is essential to informing the response to future spills. Aeppli was recently awarded a grant by the Gulf Research Program that brings together research institutions and oil spill practitioners. This new effort will apply his findings to improve the accuracy of spill models and better inform long-term response efforts.

“The goal of this program is to bridge research and practice,” he said.

Oil spills have far-reaching impacts on local communities. Aeppli is studying toxic effects of oil in the environment, which can have broad repercussions for human health. He believes that natural scientists and social scientists should work together to better understand the human impacts of oil spills, which include physiological, mental, and economic effects.

“Just as polluted ecosystems impact humans, healthy ecosystems yield resilient communities,” Aeppli said. “Hopefully this work will ultimately help us understand the broader impact of spills on both human communities and the environment, and show why we need to be so careful with these ecosystems.”