An oil dispersant is a mixture of emulsifiers and solvents that helps break oil into small droplets following an oil spill. Small droplets are easier to disperse throughout a water volume, and small droplets may be more readily biodegraded by microbes in the water. Dispersant use involves a trade-off between exposing coastal life to surface oil and exposing aquatic life to dispersed oil. While submerging the oil with dispersant may lessen exposure to marine life on the surface, it increases exposure for animals dwelling underwater, who may be harmed by toxicity of both dispersed oil and dispersant. Although dispersant reduces the amount of oil that lands ashore, it may allow faster, deeper penetration of oil into coastal terrain, where it is not easily biodegraded. History Torrey Canyon In 1967, the supertanker Torrey Canyon leaked oil onto the English coastline. Alkylphenol surfactants were primarily used to break up the oil, but proved very toxic in the marine environment; all types of marine life were killed. This led to a reformulation of dispersants to be more environmentally sensitive. After the Torrey Canyon spill, new boat-spraying systems were developed. Later reformulations allowed more dispersant to be contained (at a higher concentration) to be aerosolized. Exxon Valdez Alaska had fewer than 4,000 gallons of dispersants available at the time of the Exxon Valdez oil spill, and no aircraft with which to dispense them. The dispersants introduced were relatively ineffective due to insufficient wave action to mix the oil and water, and their use was shortly abandoned. A report by David Kirby for TakePart found that the main component of the Corexit 9527 formulation used during Exxon Valdez cleanup, 2-butoxyethanol, was identified as "one of the agents that caused liver, kidney, lung, nervous system, and blood disorders among cleanup crews in Alaska following the 1989 Exxon Valdez spill." Early use (by volume) Dispersants were applied to a number of oil spills between the years 1967 and 1989. Deepwater Horizon During the Deep water Horizon oil spill, an estimated 1.84 million gallons of Corexit was used in an attempt to increase the amount of surface oil and mitigate the damage to coastal habitat. BP purchased all of the world's supply of Corexit soon after the spill began. Nearly half (771,000 gallons) of the dispersants were applied directly at the wellhead. The primary dispersant used were Corexit 9527 and 9500, which were controversial due to toxicity. In