The clam boat whose crew dredged up canisters of mustard gas off Long Island earlier this month has been decontaminated and returned to the owner, the U.S. Coast Guard has announced.

The boat, the ESS Pursuit, was returned June 12, according to a statement released Saturday by the Coast Guard.

The final decontamination of the Massachusetts warehouse where the catch had been taken was completed June 22, the Coast Guard said. It said the decontamination of 180 clam cages seized from the Pursuit was completed Friday.

The clams were incinerated, the Coast Guard said.

The 145-foot clam dragger pulled up the World War I-era canisters on June 6 from an area of the Atlantic Ocean about 45 miles southwest of Fire Island, according to the Coast Guard. Doctors later said that tests revealed a fisherman on board who was sickened by the incident had been exposed to mustard gas. Four members of the boat were hospitalized.

Mustard gas was a battlefield weapon of choice during the trench warfare of World War I, dispersed as an aerosol to kill infantry troops confined to a maze of battle trenches.

Its mixture with other chemicals gave it a yellow-brown color and a distinctive smell, according to historians.

History suggests it was not an overly effective killing agent, though it gained a reputation for its incapacitating side effects and horrible burns.

The area where the canisters was found is a hot spot for commercial and recreational fishing, authorities said. However, the Coast Guard said nautical charts of the area note known dump sites that contain World War I and World War II-era ordinance. The site where the canisters were found is at least 60 feet deep, the Coast Guard said. The canisters were dumped overboard after the crew was exposed, officials said. It was unclear Monday if they had been recovered and examined or if they remained submerged on location.

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