The University of Hawaii is investigating old mustard agent chemical weapons that were dumped 10 miles southeast of Pearl Harbor to see whether deterioration of the weaponry is having an effect on marine biology, water and sediment.

Investigators using UH manned submersibles and a towed-array camera identified what are believed to be more than 200 M-47 93-pound mustard aerial bombs that were part of a cache of 16,000 such bombs disposed of in the ocean, officials said.

UH officials and the Army announced the results Friday after a week’s worth of marine sampling near the weapons in 1,800 feet of water. The study will continue for several more days as part of an ongoing examination of the environmental impacts of the dumped munitions.

Another round of sampling using remotely operated vehicles will be conducted next year. Results from the studies are due out in 2015, officials said.

J.C. King, who is with the Army’s environment, safety and occupational health office, said the UH research effort has been “extremely successful.”

“We’re not trying to find every munition,” King said. “We’re trying to characterize the area as best we can, which means you get some idea of the kinds of munitions but primarily take samples — sediment samples, bio samples. So all of that together is very comprehensive.”

Margo Edwards, UH’s principal investigator for the effort, said the assessment is the most comprehensive deep-water munitions study in the United States.

UH is being paid about $7 million by the Army for past efforts and through next year’s search and sampling of the deep-water site.

A 2007 report to Congress said 2,558 tons of chemical agents, including lewisite, mustard, cyanogen chloride and cyanide, were dumped at three deep-water sites off Oahu.

Sulfur mustard, introduced in World War I, causes blistering of the skin and lungs on contact.

The excess munitions were dumped during and after World War II off Hawaii and other parts of the U.S. because it was felt that the depth and sheer volume of water would take care of the problem.

The practice was outlawed in 1972.

Edwards said the bombs that were discovered showed crushing from the water pressure, and the contents — presumably mustard — have spilled out in some cases.

The Army previously said chemical agents such as mustard are not water-soluble in the chilly depths and that the heavier-than-water mustard forms into nodules that develop a skin.

But three Defense Department contractors were burned in 1976 during a dredging operation after leaking mustard cylinders were inadvertently brought up.

Edwards said it’s “pretty unlikely” currents or tides would bring any of the mustard agent to shore.

“There’s a really steep cliff, a steep drop-off basically, once you get to between 150 to 300 meters water depth. It just sort of drops off, so gravity doesn’t want this stuff to go that way,” she said.

The mustard munitions were discovered by UH during a survey in late 2009 or early 2010 for a power cable from Molokai to Oahu, officials said. An earlier 2009 investigation seeking chemical weapons about five miles south of Pearl Harbor turned up more than 2,000 conventional munitions but no chemical counterparts.

UH sampled around the mustard bombs but did not retrieve any of the chemical. The Pentagon does not plan to remove the chemical weapons.