The University of Hawaii will be examining dumped chemical weapons in deep water off the south coast of Oahu for the last time to see what effects they have on seawater, marine life and sediment.

The UH research vessel Kilo Moana will leave port Wednesday and deploy the Woods Hole Oceanographic Institution’s Jason II remotely operated vehicle in the military dump site known as HI-05, 5 to 10 miles south of Pearl Harbor, officials said.

As many as 16,000 M47 aerial mustard bombs with 73 pounds each of the chemical agent mustard were believed to have been rolled off ships in the area during or after World War II.

Since 2007, UH has been awarded approximately $7.5 million by the Army to conduct the Hawaii Undersea Military Munitions Assessment. This week’s trip is the final phase.

Four previous field programs "imaged" thousands of conventional and suspected chemical munitions, UH’s School of Ocean and Earth Science and Technology said.

Analyses of sediment samples collected less than 6 feet from suspected chemical munitions revealed mustard agent and its degradation products at levels of less than 5 parts per million — which UH said is very low.

Shrimp scavenging nearby and sea stars living directly on top of suspected chemical munitions exhibited no adverse impact from munitions constituents, the university said.

"The problem that we’re kind of bumping up against is that right now I’ve looked very closely at six munitions (bombs). And we can say that on the basis of looking at those six munitions, we don’t see any kind of poisons being absorbed into the animals that are in direct contact with them," said Margo Edwards, UH principal investigator for the project.

"But six is a pretty small number compared to what it is that we’re trying to look for," Edwards added. "So our hope is that with Jason we can go and increase the number of samples that we’ve collected."

The 7,300-pound Jason II, which will be out at sea for about a week, has high-resolution video gear and a mass spectrometer chemical "sniffer" that will test the water around the munitions for mustard down to parts per million.

A prototype of the Jason II — Jason Jr. — was used to explore the wreck of the Titanic in 1986.

According to one military count, 181 tons of lewisite, 2,184 tons of mustard, 204 tons of cyanogen chloride and 2 tons of cyanide were dumped in at least four deep-water sites off Oahu.

The Defense Department said it disposed of approximately 30,000 tons of chemical warfare material in deep waters in the Atlantic, Pacific and Gulf of Mexico between 1919 and 1970.

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

In 2012, UH manned submersibles discovered what were believed to be more than 200 mustard bombs in 1,800 feet of water.

The Army previously said mustard is not water-soluble in the chilly depths and that the heavier-than-water chemical agent was known to form into nodules.

Edwards said those factors have been found in the Baltic Sea but haven’t been found in the past near Oahu, "and that’s an interesting question."

"In fact, we’ve now been to the point where we’ve seen the noses falling off these munitions and we see what’s on the inside — and it doesn’t look anything like those nodules. So the question is, How come?" Edwards said.

When the thin-walled munitions were disposed of, they contained pockets of air, and Edwards’ theory is that pressure caused the bombs to implode as they descended, "and that implosion exposes seawater to the constituents inside and there is a chemical reaction," she said.

Decades later there are trace amounts of mustard — parts per million and parts per billion, she said.

"Everything that I see right now says those chemical reactions happened 70 years ago as those things were going through the water column," she said.

The finned bombs, identified by two green bands, also have deteriorated to the point that when a submersible’s arm nudged one on a past dive, it disintegrated into a cloud of dust, Edwards said.

Three defense contractors were injured in 1976 aboard a commercial vessel after dredging up cylinders containing mustard. Edwards said the munitions might act differently at different water depths.

"Most of the munitions that I’ve sampled now are at 550 meters (1,804 feet), so if I went to a munition that was at 400 meters (1,312 feet) water depth, maybe it didn’t implode," Edwards said.

Edwards said the goal is to take samples around mustard bombs in less than 1,800 feet of water.