BOSTON (AP) -- A fishing boat dredging for clams off New York's Long Island pulled up 10 canisters, including one that broke open and released an unidentified chemical that caused two crew members to blister and struggle to breathe, the U.S. Coast Guard said Monday.The ESS Pursuit took the sickened crew members back to its New Bedford, Mass., port, where emergency medical workers rushed them to St. Luke's Hospital on Monday morning.One was transferred to Massachusetts General Hospital for further treatment after his condition worsened, Fire Chief Brian Faria said. The other was released in the afternoon, St. Luke's Hospital spokeswoman Joyce Brennan said.The crew of six caught the canisters in their nets Sunday about 45 miles south of Long Island but dumped them back into the ocean when one crew member began developing blisters. It was several hours after he hadbeen exposed to the contents of the container that had broken open, Coast Guard spokesman Jeff Hall said.The vessel returned to New Bedford at about 4 a.m. Monday to drop off the sickened crew member for treatment before heading back to sea with the remaining five crew members, Faria said. But a second crew member reported feeling lightheaded, and the boat brought him back to the port at about 9:30 a.m. before going back out, he said.After learning of the incident, the Coast Guard issued a "captain of the port order," a rare command instructing the boat to return to port.The vessel was anchored south of New Bedford under quarantine Monday evening as members of the National Guard's hazardous material and a Rhode Island-based firefighting unit prepared to investigate and decontaminate it if necessary.The National Marine Fisheries Service and the Massachusetts Department of Food and Agriculture have been notified and are investigating whether the boat's catch, which was sold Monday in New Bedford, was contaminated, the Coast Guard said in a statement.Authorities were able to track down the catch and are holding it until the investigation is complete.It was not immediately clear what chemical was involved and experts were trying to determine its nature, Hall said.He declined to confirm comments he made earlier to the Standard Times of New Bedford that hospital workers and Emergency Medical Service technicians had reported that the crew may have been exposed to mustard agent, an oily liquid first used in World War I that can cause massive breakouts of blisters on contact and can be deadly if inhaled.Brennan of St. Luke's Hospital said the information did not come from its doctors and cautioned against relying on diagnosis by emergency medical technicians who may not have had enough time to study the patients and their symptoms.The Coast Guard plans to work with the National Oceanic and Atmospheric Administration to make sure the area where the hazardous containers were found is clearly marked, according to a statement.Officials are also trying to find the 10 discarded canisters.