The Navy says sailors need these training exercises to learn how to fire real weapons and sink enemy warships, but opponents say the U.S. Navy Ship Sinking Exercise - or "SINKEX" - should be scrapped.

Colby Self, director of the Basal Action Networks' green ship recycling campaign, said the Navy had to find a cheaper way to dismantle old ships, so it escalated the sinking program. Basal and the Sierra Club plan to submit a petition to the Environmental Protection Agency today demanding that it revoke the Navy's SINKEX permit.

Polychlorinated biphenyls - PCBs - were once common in everything from paint to electric motors. Their toxicity, with links to everything from skin rashes to low birth weight and cancer, led them to be banned by Congress in 1979.

Old U.S. warships are filled with PCBs and other toxins, and now, so are U.S. waters, environmentalists say.

Following an outcry over lax environmental and worker safety regulations at ship-breaking yards in India, the Navy agreed in 1999 to only send its decommissioned ships to U.S. scrappers.

But that same year, the EPA issued the Navy a letter of agreement that allowed it to sink ships as long as it studied the environmental impacts, stayed a certain depth and distance from the coastline, removed most of the toxins, and estimated the amount of PCBs that remained on the ship.

Hawaii has become the most popular graveyard for decommissioned ships. Fifty-three ships weighing an estimated 286,000 tons and containing an estimated 501 pounds of PCBs have been sunk in the deep waters surrounding the islands from 2000 to 2010, according to the Navy.

Another 32 ships weighing an estimated 281,000 tons were sunk in the Atlantic Ocean off the coast of the Carolinas. Those ships contained an estimated 700 pounds of PCBs, the bulk of which were on the supercarrier USS America.

In May, the Navy won approval to start sinking two decommissioned ships each year into the Gulf of Alaska. The pristine waters are home to several endangered species and one of the nation's largest fisheries for Alaskan pollack, a white fish commonly used in frozen food, fast food and imitation crabmeat.

In all, the number of decommissioned ships used in sinking exercises leaped from 32 ships between 1990 and 1999 - the year tougher ship-scrapping regulations were passed - to 110 ships between 2000 and 2010, according to documents obtained by The Daily.

The Navy's annual reports estimated that most of its ships had little to no PCBs onboard when they were sunk. But experts interviewed by The Daily said that it would be impossible to remove all hazardous materials, which also include asbestos, chromates, mercury and other heavy metals, without completely tearing apart the ship.

"If you break it up, it's decontaminated down to the last nut and bolt. But if you don't break it up, there's no way you can completely decontaminate it," said Robert Berry, vice president of International Ship Breaking, which decontaminates and scraps ships for the Navy.

Thomas Dydek, a toxicology expert at Dydek Toxicology Consulting, also said a lot of toxins are inside a ship's hull. He said the harmful effect to humans depends on how quickly they get into the food chain.

"That would be the concern, that if it's disbursed into the water, then it could get into the food chain and eventually get into a fish that a person would eat," said Dydek.