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When I was a kid I daydreamed about seeing the bottom of the ocean and its secrets: strange fishes, giant squids, sunken pirate ships and their chests of filled with gold and gleaming jewels. Maybe you did too. Older now, I still daydream about those things, but the awareness I’ve gained about other things on the bottom---plastic, bottles, cans and other solid waste, sewage and sewage sludge, subway cars, wrecked or scuttled ships and countless barrels of industrial chemical or radioactive wastes---often intrude on the magical quality of those early musings.

Among the most troubling dream-wreckers are armaments and chemical warfare agents (CWA) now resting and deteriorating on the seafloor.  Beginning in World War I, continuing through World War II and the Vietnam War and probably into the 1990s, numerous countries dumped thousands of tons of bombs, ammunition, mines and steel drums containing some of the world’s most deadly chemicals into the ocean, just as they also did at many sites on land.  Useless except for warfare, the chemicals were designed to blister the skin of enemy soldiers (sulfur mustard, nitrogen mustard, Lewisite); irritate their nose and throat (Clark I, Clark II, Adamsite); blind them (tear gases, α-chloroacetophenone); prevent them breathing (phosgene, diphosgene); destroy their nervous systems (Tabun); or poison them (hydrogen cyanide). 

Countries dumped those chemicals to get rid of unused supplies at the end of their wars though some went to the bottom when ships carrying them sank during battle. Disposal usually occurred in deep and relatively inaccessible locations either by dumping or scuttling the entire ship, but sometimes disposal began shortly after a ship left harbor and continued until it reached the specified disposal site. That practice, as well as the wooden cases used to transport many munitions, which floated for a while after discharge from the ship, spread CWA over large areas. 

Deeply out of sight and mind, few thought about those sunken chemicals during the wars or their aftermath, though fishermen and beach goers sometimes received nasty reminders of their existence.  For example, in the Baltic Sea, where 50,000 tons of munitions were dumped, including 15,000 tons of CWA, fishermen brought up 115 CWA objects in their trawls between 1993 and 2012. Among incidents recounted in CHEMSEA, 7 fishermen on a Faroese trawler, F.V. Hildarstindür, hauled up an object containing mustard gas while trawling one night in 1984. Darkness prevented them from identifying it as unknown and dangerous. The men were severely injured and had to be evacuated to Copenhagen. In 1997, the Polish vessel F.V. WLA206 hauled up a 5-7 kg lump of mustard gas and dumped it in a rubbish container at port. The next day all 8 crewmembers suffered serious burns and lesions on their skin, and four had to be hospitalized for a few weeks, escaping death only because the incident took place in January when cold temperature stopped the gas from evaporating. In 2001, people and houses had to be evacuated when the Swedish trawler SG Delfin caught and brought to port an aircraft bomb containing mustard gas.  

As another example, the Japanese Ministry of the Environment reported 822 incidents between 1945 and 2004, including 400 injuries and 10 deaths, related to chemical weapons dumped in Japanese waters by Allied or Japanese forces at the end of World War II. 

Shores of the continental United States were also impacted, as documents reviewed by the Daily Press showed that between 1944 and 1970 the U.S. Army dumped 64 million pounds of nerve and mustard agents, 400,000 chemical-filled bombs, and more than 500 tons of radioactive waste into the waters spanning 11 states. 

The London Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter, enacted in 1972, made it illegal to dump weapons (or other waste) in the ocean, but enforcement is difficult to verify so illegal disposal may not have stopped immediately.  What’s more, not all countries have signed the Convention.

So the question remains of what to do with the legacy contamination from previous decades. Sonar and remotely operated vehicles can locate CWA in previously-designated dumping areas.  Locating  randomly discarded items is more difficult.  Finding, retrieving, disarming and detoxifying all sea-dumped CWA would be enormously expensive.

Some items might best be left alone, especially those in which the containers holding the toxic chemicals have rusted and degraded. Breakage during retrieval could spread the poisons and endanger recovery workers or others.  In some locations, sediments and detritus sinking out of the water column and settling on the bottom at rates of an inch or two per thousand years will slowly bury any materials left in place reducing their potential damage to people or the environment if they are left undisturbed.    

However, ridding the bottom of items that pose especially high risk and are sufficiently intact to be safely raised would advance ocean health, especially in places near coastlines or ongoing human activities and where burial by sediments does not occur.  For example, at the Hawaiian disposal site studied by HUMMA, currents scour the bottom and prevent burial of the munitions by sediments.

What are the risks of leaving CWA on the seafloor? CWA containers will continue to rust and degrade, potentially releasing more chemicals. Dangerous munitions may occasionally wash up on beaches or be caught by fishermen.  Coastal residents should know about CWA so that they can avoid and report suspect items. Special care will continually be needed by those fishing near disposal sites, as for example in the Baltic Sea where such boats must carry safety equipment to protect fishermen from hazardous substances.    

We probably won’t ever know the full extent of damage to marine life caused by CWA, though most is likely to be limited to habitats close to dumpsites. Fish don’t appear to contain CWA in their flesh, though some instances of damage to skin and organs have been found in catches near dump sites.  In the Baltic Sea any catches that contain a hauled up component must be discarded. 

It is worth emphasizing that dumped munitions containing CWA are by no means the only sources of ocean not the only sources of ocean pollution. Chemicals, excessive nutrients, pathogens and trash are carried and spread by rivers, runoff from land, water currents and winds. Achieving the cleanest ocean we can requires working to eliminate them while addressing  the legacy of dumped munitions.

Ocean disposal of CWA and other hazardous substances has been a sorry chapter in the long relationship between people and the sea. There is hope that the chapter is nearing its end. Groups actively addressing this general issue include the International Dialogue on Underwater Munitions (IDUM, also see). The Hawaii Undersea Military Munitions  Assessment (HUMMA), a project of the University of Hawaii at Manoa, conducts research to locate and assess the condition of munitions, their surroundings and nearby animals at a disposal site south of Pearl Harbor. An interactive global map of chemical munitions dumped at sea was prepared by the Monterey Institute of International Studies’ James Martin Center for Nonproliferation Studies 

Useful references:
CHEMSEA Findings: Results from the CHEMSEA Project – Chemical Munitions Search and Assessment.  Institute of Oceanology of the Polish Academy of Sciences.  http://underwatermunitions.org/pdf/CHEMSEA_Findings_24.01.pdf

HELCOM, 2013. Chemical Munitions Dumped in the Baltic Sea. Report of the ad hoc Expert Group to Update and Review the Existing Information on Dumped Chemical Munitions in the Baltic Sea (HELCOM MUNI). Baltic Sea Environment Proceeding (BSEP) No. 142. 128 pp. http://underwatermunitions.org/pdf/BSEP142.pdf