A dark legacy of warfare still sits on the bottom of the world’s bodies of water, including millions of pounds of unexploded bombs and other explosive devices. In the Gulf of Mexico, that tally could even include containers of the chemical weapon mustard gas. Some of them are in areas marked for resource exploitation, including fishing and undersea oil drilling, heightening fears they could cause a manmade disaster.

After World War II, the U.S. military began dumping surplus munitions into the oceans as a way to get rid of them. According to William Bryant and Neil Slowey, oceanographers at Texas A&M University, at least 31,000,000 pounds of bombs were disposed in the Gulf of Mexico and in the shores off 16 states, including New Jersey and Hawaii. The dumping started in 1946 and ended in 1970.

The munitions, says Texas A&M Today, include 250-, 500-, and 1,000-lb. aircraft bombs, as well as items such as land mines. Many are weapons captured from Germany at the end of World War II. “Several types” of chemical weapons were dumped, including containers of mustard gas. A chemical agent that affects the respiratory system, mustard gas was widely used during World War I. It was stockpiled by many countries during World War II but never used.

Nobody—not even the military—really knows how many bombs are out there, or where they are located. Oceanographers believe some of the bombs are in areas marked for oil drilling, raising concerns that they are a danger to the 30,000 oil workers working in the Gulf of Mexico at any one time. Shrimpers have hauled up mustard gas barrels and other munitions in their nets.

More information can be found in the original article published on the Popular Mechanics website here