'Invisible and Toxic' Oil From Deepwater Horizon Spill May Have Made Disaster Much Worse Than Previously Thought

The catastrophic Deepwater Horizon (DWH) oil spill, which occurred in 2010, may have been significantly worse than previously thought due to "invisible and toxic" oil, research suggests.

The spill was the largest in marine history, releasing around 795 million liters (210 million gallons) of oil into the Gulf of Mexico with slicks covering an estimated area of 57,500 square miles. The disaster caused extensive environmental damage and forced the closure of vast stretches of the Gulf to fishing operations.

Normally, scientists primarily use satellites to track major oil spills such as these, however, this technique does not necessarily reveal the full extent of the environmental problem.

According to a study published in the journal Science Advances, the "toxic extent" of the spill could have been up to 30 percent greater than what previous satellite data has suggested, leaving a footprint which stretched from Florida's Gulf Coast, to the shores of Texas and the Florida Keys.

"While the Deepwater Horizon oil spill has been extensively studied, several fundamental questions remained unanswered: What was the full extent of the DWH oil spill? Does the satellite footprint account for the entire oil spill extent? And is there a part of the spill that extends beyond the satellite footprint but is still toxic to marine animals?" the authors of the study Igal Berenshtein and Claire Paris from the University of Miami, told Newsweek.

"These fundamental questions are highly important for our understanding of the Deepwater Horizon oil spill in particular, and marine oil spills in general," they said.

For the study, the scientists examined previously published on-site measurements taken by other teams at the spill site, in addition to satellite imagery and models of oil movement in the Gulf.

Their analysis revealed that large areas of the Gulf or Mexico beyond the assumed boundary of the spill area determined by satellites were exposed to "invisible" oil that was toxic to marine organisms.

"We found that the oil spill extended beyond the satellite footprint, reaching areas which were considered non-contaminated such as the West Florida shelf and Texas shores. A part of the invisible portion that extended beyond the satellite footprint was toxic to marine life," the authors said.

According to the study, toxic chemicals known as polycyclic aromatic hydrocarbons may still be present in water for days or even weeks after satellites can no longer detect an oil slick.

Deepwater Horizon oil spill
Support ships are seen near the Deepwater Horizon spill site on July 3, 2010 in the Gulf of Mexico off the coast of Louisiana. Joe Raedle/Getty Images

"Thanks to this study we now know that toxic concentrations of oil can extend beyond the satellite footprint, and can persist in the water after the spill is no longer visible," the authors said.

"We provide a quantitative framework to compute these oil concentrations and their extent in time and space, to better account for the impact of oil spills on the marine ecosystem. We show that the environmental damage extends substantially beyond what was previously estimated both in space and time."

The researchers say that the analysis they used in the study could be applied to future oil spills in order to better assess their impacts.

"We recommend this method as complementary to satellite estimates," Berenshtein Paris said in a statement. "Currently, satellites provide the most rapid and accurate indication of the locations of the oil slicks. But the oil spill also extends in the water column where currents are decoupled from the upper circulation."

The authors say the latest findings could have significant implications given that activities related to petroleum production are increasing around the world.

"Oil spills are highly frequent events worldwide. In the general, the conception regarding oil spills is that oil is hazardous where it is visible," the authors told Newsweek. "There is nearly no accounting for the portions of the oil that are invisible but are still toxic. We bring forward and quantify the concept of the DWH toxic and invisible oil, and stress that this portion should be accounted for when assessing damage and/or risk of future oil spills."

The Deepwater spill was caused by an explosion on the BP-operated Deepwater Horizon oil drilling rig—located around 41 miles off the Louisiana coast—on April 20, 2010, which resulted in the deaths of 11 workers.

The rig subsequently sank and more than four million barrels of oil gushed out of the damaged Macondo well over the course of 87 days until the leak was finally capped, according to the Environmental Protection Agency.

The spill was one of the worst environmental disasters in American history, severely damaging the Gulf of Mexico ecosystem and the regional economy, while also harming the health of many residents in the region.

In 2014, a U.S. federal judge ruled that BP had displayed gross negligence in its operation of the rig and was primarily responsible for the spill. A year later, the British company agreed to pay fines worth around $18.7 billion to the U.S. government and five states. This is the largest corporate settlement in American history, Reuters reported.