The Deepwater Horizon oil spill in the Gulf of Mexico, known as the BP spill, is the largest oil spill in human history. But animal agribusiness has a well-hidden secret- that animal waste runoff is responsible for an ecological dead zone that scientists have called just as problematic as BP’s disaster!

Polluted water drains into the Gulf of Mexico, and will flow into the Gulf dead zone. (Photo: Omar Torres/AFP/Getty)

A “dead zone” is an area in a body of water that has become hypoxic (oxygen depleted), and is thus unable to support any marine life- plant or animal. Nitrogen and phosphorus are the two main culprits of hypoxic zones and thus, fertilizer and waste runoff from farms and ranches are primary contributors. The graphic below describes the process from the point at which the nitrogen and phosphorus enter the water and begins to deplete the area of life-supporting oxygen.

The Gulf of Mexico's "dead" or hypoxic zone is only one of over 400 dead zones worldwide. It is the 2nd largest dead zone worldwide, following the Baltic Sea dead zone which is roughly the size of Denmark.

Hypoxic zones occur annually, starting in the spring and ending in the fall, and tend to occur in coastal regions, devastating all forms of sea life in the area. Despite efforts to reduce the size and occurrence of dead zones, in a recent National Oceanic and Atmospheric Administration (NOAA) report with the White House commission, researchers reported a 30-fold increase in U.S. hypoxic zones since 1960. At least half of the 647 U.S. waterways included in the study were considered "stressful" or hypoxic. There has also been an increase, globally, in the number of dead zones, up from 146 in 2004 to 405 in 2008. Scientists estimate that the number of dead zones will double every 10 years. The size of the Gulf of Mexico's dead zone has also continued to rise each year. The locations of dead zones worldwide are also depicted in the image below.

The Gulf of Mexico dead zone is the second largest in the world, spanning between 8,722 square miles (size of New Jersey) and 10,555 square miles (size of Massachusetts). The variance in size estimates is due to the fact that inclement weather prematurely ended measuring efforts by scientists this year.

Although dead zones do occur as a result of natural phenomena such as wind and current patters, today they are primarily the result of human activities. The primary cause of the dead zone is excessive nutrient runoff (i.e. fertilizer for corn and soy, and nitrogen, i.e. from animal waste) flowing down the Mississippi River from farms upstream. The Mississippi River drains over 40% of the land in the contiguous U.S. states. A 2009 US Geological Survey found that the watersheds most responsible for polluting the Gulf of Mexico were in the corn belt of Indiana and Illinois. In fact, the survey revealed that 70% of the pollution came from the following nine states: Illinois, Iowa, Indiana, Missouri,Arkansas, Kentucky, Tennesse, Ohio, and Mississippi.

It is important to note that more than half of the corn and soy grown in the U.S. is used to feed livestock.

Your Food's "Dead-Zone Footprint"

As reported in the Journal of Environmental Science & Technology, two environmental scientists at the University of Pittsburgh assessed the nitrogen footprint or "eutrophication" potential of various foods and compared those figures to the carbon footprint of the same foods. The researchers studied the foods from farm to table, assessing the nitrogen footprint through the farming, processing, packaging, transportation phases.

The "winner" for both nitrogen and carbon footprints? Red meat. Red meat had the greatest impact on global warming and the highest dead zone footprint. Eating a pound of beef creates 22 lbs of greenhouse gases and approximately 2.5 ozs of nitrogen pollution. Cereals and carbohydrates had the smallest footprints with a pound of food creating 3 lbs of greenhouse gases and almost no nitrogen pollution.

Don't be fooled by dairy! Dairy products scored 2nd to red meat in terms of nitrogen pollution with 1.1 oz per pound. But dairy's nitrogen pollution adds up. In a Chemical & Engineering News article reviewing the above study, Emily Gertz explains that as the averge Amercian consumes 10 times more dairy products than beef each year, that equates to 42 pounds of nitrogen pollution per year for dairy compared to 9 lbs for beef. And although dairy products score low in terms of greenhouse gases (along with cereals), the average American's consumption of dairy and beef amounts to equal emissions of greenhouse gases.

Other environmental researchers suggest that a complete assessment of a food's nitrogen footprint needs to include the food's resulting human waste, since treated sewage deposits nutrients into the ecosystem.

The Gulf of Meixco dead zone and many others like it, are environmental disasters that are scarcely talked about outside of scientific communities, perhaps because it is not the fault of any one vilified company. Like all environmental disasters that result from animal agriculture, it is up to each person who eats animal products to end their role in this devastation. Learn more about the harm done to the environment by farming animals and see how you can get involved.