Explosion can occur due to the munitions detonating even long after the end of the conflict that caused them to be dumped at sea.
This was the case of the weather ship Laplace, which was blown up by an underwater mine in 1950, east of Cap Fréhel in Brittany.
However, the explosion may occur on the deck of a dredger or fishing boat, when the ammunition is brought to the surface in a bucket or trawl net.
In 1952, ammunition exploded on the dredger Pas-de-Calais 2 in the port of Boulogne, killing 4 people and leaving 7 people unaccounted for. A blast onboard the Marteen Jacob in the Baltic Sea killed 3 people.
In the case of phosphorous bombs, auto-ignition in free air can also occur, involving the projection of ignited matter but no explosion.
Whether a risk of explosion or ignition, this problem is cause for great concern. A researcher, Ezio Amato, reported that 5 people had been killed and 252 injured due to dumped munitions since the Second World War among Italian fishermen in the Adriatic Sea.
Release of toxic substances
Toxic substances can be released, due to the corrosion of ammunition, when such devices are brought to the surface by a trawler, or on the seafloor. Studies have shown that the level of corrosion resulting in a leak can be reached after 10 to 400 years, according to the type of ammunition and the conditions in which it was dumped.
In the event of a leak on the seafloor, the risk depends on the substance’s solubility in water and its effect on the surrounding flora and fauna.
There are many possible contaminants: lead, arsenic, antimony, methylmercury, lead nitrate, lead azide, trinitrotoluene, phosgene, hydrogen cyanide, cyanogen chloride, chloropicrin, mustard gas, etc.
Very little is known of the fate of these contaminants in water and their effect on species. If impact studies have been conducted, a point that is not clearly demonstrated, any such studies remain partial and confidential.
In the case of a leak onboard a fishing boat, the risk is generated by the vapour’s toxicity for humans. Accounts of fishermen with blistered hands, suffering intolerable pain, who have had to have skin grafts, can easily be found.
A specific case is that of the German submarine U-864, sunk on 9 February 1945 near Bergen with 65 tonnes of mercury onboard, bound for the Pacific to support the Japanese war effort. In the face of the environmental risk generated by this mercury, stored in sealed metal drums, the Norwegian Government decided to refloat the wreck and its cargo in 2007.