On April 20, 2010, BP's deepwater Macondo well ruptured and continued to discharge oil into the Gulf of Mexico for 86 days. Also referred to as the Deepwater Horizon oil spill, the BP oil spill was a major environmental disaster that released an estimated 250 million gallons of oil into the water. Oil spills are a type of “point source” pollution—the contaminants are discharged from a fixed point—but once the oil is in the water, it can spread and have impacts far from its origin. The oil affects organisms and ecosystems, in the water and on the coast, both directly and indirectly. In addition, the chemicals used to help clean up the spill can also have damaging effects.

A dispersant is a detergent-like substance that is used to help break up the oil into fine droplets. As small droplets, the oil is more easily broken down by nature and less likely to stick to marine animals, shoreline rocks, and plants. Dispersants are supposed to be less harmful to the environment than crude oil; however, their effectiveness and impact on the environment are controversial. In an effort to mitigate the potential damage from the BP oil spill, it is estimated that 1.8 million gallons of the dispersant Corexit were used on the surface and underwater.

In addition to the ecological damage, there are health concerns for the people who were exposed to the oil and dispersants. The BP oil spill was unusual in both the amount of oil released and its duration. Some chemical components of crude oil are known to be toxic—for example, benzene is irritating to the skin, eyes, and respiratory tract and is also considered a human carcinogen. The two different formulas of Corexit that were used also contained chemicals that are considered hazardous: one formula contained 2-butoxyethanol, which may cause respiratory, liver, kidney, and blood problems.

In addition to the acute toxic effects from exposure to the volatile organic compounds in the oil and the chemicals in the dispersants, there may also be long-term human health risks. The magnitude of the spill and its cleanup effort was unprecedented. Nobody really knows the toxicity associated with the use of such large amounts of dispersant or the effects of the combination of crude oil and chemical dispersant. People have reported symptoms such as fatigue, sleep disorders, headaches, and respiratory and gastrointestinal problems. However, many symptoms could also be due to anxiety, depression, or post-traumatic stress disorder related to the trauma and the economic insecurity caused by the spill. A 10-year study is underway to monitor the health of 55,000 cleanup workers and others who had direct exposure to the crude oil and dispersant.

One year after the spill, the long-term impacts on human health and the environment were still unclear. Unknown numbers of crustaceans, fish, birds, turtles, and dolphins died from the spill, and scientists found patches of seafloor devoid of their usual deep-sea life. Marsh area had been lost, affecting marine nurseries and feeding grounds. Animals were found with oil on them, but most of the oil appeared to be gone from the water. However, some consequences may not yet be evident. For example, subtle changes in ecosystem components and damage at the base of the food web may not have had visible effects in the first year. It may be years before the full impact of the spill becomes apparent.

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