Boston » State and federal officials worked yesterday to decontaminate a clam boat anchored in isolation off Massachusetts after it dredged up old munitions containing mustard gas, severely sickening a crewman.

The Coast Guard was trying to locate the two military shells, which the crew tossed overboard in about 60 feet of water about 45 miles south of Long Island, said Coast Guard Petty Officer James Rhodes. He acknowledged finding the shells will be difficult.

The military used the ocean, including waters off Hawaii, as a dumping ground for munitions from after World War II through 1970. While the tons of old chemical weapons in offshore waters present a danger to fishermen, experts don’t believe they are a possible source of weapons for terrorists.

The Atlantic City, N.J.-based vessel was fishing Sunday in a charted munitions dumping zone, but the designation is just a warning and carries no fishing restrictions, Rhodes said.

The two shells—about a foot long and 3 inches in diameter—came aboard in a haul of clams. The Coast Guard suspects one of the shells cracked or otherwise leaked its contents.

Yesterday, a National Guard team boarded the vessel, the ESS Pursuit, to test for contamination, while the Coast Guard worked to secure the ship in waters off New Bedford so that it can be moored and decontaminated. The captain and first mate have declined to leave the 145-foot dragger, fearing it could run aground, the Coast Guard said.

The boat had returned to New Bedford early Monday after one of its six crewmen, Konstantin Burndshov, reported blistering and shortness of breath.

Hours later, another crewman was brought ashore after he reported feeling lightheaded. He was examined and released.

Burndshov had painful blisters about three-quarters of an inch high on an arm and a leg, said Dr. Edward Boyer, a toxicologist who is treating the man at UMass Memorial Medical Center in Worcester.

Boyer suspected exposure to mustard gas, used most frequently during World War I, given Burndshov’s telltale symptoms: blistering and the onset of his symptoms about 24 hours after exposure. On Monday night, blood and urine tests confirmed the diagnosis. Boyer said even though Burndshov was wearing protective clothing the mustard gas still penetrated to his skin.

"It literally pulls the top of the skin off the layer underneath it," Boyer said. The doctor said Burndshov was listed in good condition at UMass Memorial.

The military says it stopped dumping chemical and conventional munitions in the ocean in 1970, and two years later Congress banned waste disposal in oceans, including chemical weapons.

Officials say it’s impossible to know exactly how much and what type of weapons have been dumped in the ocean because of incomplete records. A 2001 Army report found 74 past instances of ocean disposal—32 off U.S. shores and 42 off foreign coasts.

Only some of the ocean dumps were mapped, and chemical munitions have been found in areas they weren’t supposed to have been dumped, such as just a few miles off Hawaii, said Craig Williams of the Chemical Weapons Working Group, a Kentucky-based organization.

In 1976, a fisherman in Hawaii was burned after bringing up a mortar round filled with mustard gas.

Mustard gas, also called sulphur mustard, is usually not a gas at all, but a thick, odorless and colorless liquid that turns solid in temperatures above 58 degrees. It looks brown when mixed with other chemicals and has a garliclike smell.

Mustard gas can be deadly if it’s used as an aerosol and inhaled, causing blisters and other problems in the lungs.