GuLF Study Environmental Health Sciences (NIEHS), part of the National Institutes of Health, and aims to recruit 55,000 of the 150,000 workers who volunteered or were employed to help clean up the spill. It is led by Dale Sandler, head of the NIEHS's epidemiology branch. The "Deepwater Horizon" oil spill was the world's largest accidental marine oil spill. It began on 20 April 2010 after an explosion on the "Deepwater Horizon", a drilling rig leased by BP to drill an exploratory well. Between then and 15 July, when the well was capped, over four million barrels of oil (around 170 million US
Deepwater Horizon oil spill more than wide and deep. In a major study on the plume, experts were most concerned about the slow pace at which the oil was breaking down in the cold, water at depths of . In late 2012, a study from Georgia Tech and Universidad Autonoma de Aguascalientes in Environmental Pollution journal reported that Corexit used during the BP oil spill had increased the toxicity of the oil by 52 times. The scientists concluded that "Mixing oil with dispersant increased toxicity to ecosystems" and made the gulf oil spill worse." The three basic approaches for removing the oil from the