The toxic legacy of 20th-century conflicts resurfaces from the North Sea: explosives and munitions threaten marine ecosystems.

The conflicts of the twentieth century have left us a legacy far more vivid than that sedimented between the pages of history books. Tens of meters deep, in the silence of the ocean, lie thousands of sunken ships and submarines during the two world wars. In the North Sea alone, there are estimated to be over three thousand of them.

Submerged submarines and cruisers, however, are revealing a much more insidious nature than we might associate with placid historical wrecks: the toxic substances contained in explosives and ammunition, in fact, are contaminating the marine environment, threatening ecosystems and the very food chain on which the heirs of the men who fought those wars depend.

A submerged legacy of armaments that threatens the oceans

When it sank on April 21, 1917, the German submarine SM UC-30 It had been in service for less than a year. It was a coastal minelayer U-boat of the UC II type, designed and built for the Imperial German Navy during the First World War. Almost 50 meters long and more than 5 meters wide, with a displacement of 400 tons on the surface and 480 tons submerged, the UC-30 carried 18 mines and 6 torpedoes when – due to engine problems – she abandoned her mission to Ireland to return to Germany. She was sailing in the waters near Rømø, on the west coast of Denmark, when she struck a British mine. The UC-30 sank. All 27 crew members lost their lives.

The wreck of the UC-30 remained lost on the ocean floor for nearly a century. It was discovered in 2016 by Danish diver Gert Normann Andersen. Today, thanks to the research project NorthSeaWrecks, we know a lot about that wreck. Katrine Juul Andresen, a lecturer at the Department of Geosciences at Aarhus University, contributed to the site investigations by collaborating with Navy divers:

Civilian diving on the wreck is not permitted, so we received valuable support from Navy divers. After receiving instructions, they dived to collect samples of sediment, water, and marine organisms from various points on the wreck and the surrounding seabed. They also filmed and took photographs, which we then used to assess the exposure of the mines and the condition of the wreck.

Andresen explained.

The results of these investigations, however, are decidedly worrying.

The UC-30 submarine releases TNT into the sea: the evidence is in mussels.

Explosives and munitions lost at sea during the two world wars are far from historical relics. Decades of exposure to the saline environment, in fact, have led to the corrosion of hulls and casings, with the result that today those wrecks actively release toxic substances in the oceans. As Andresen explains,

We have detected traces of TNT in marine organisms, in seabed sediments, and in the water column. Pollution is occurring. The question remains to be clarified regarding the extent of the impact and the distance from the wreck at which this pollution affects the marine environment. This is likely a relatively localized source of pollution, but the situation is likely to worsen as the wreck continues to deteriorate, exposing more explosive material contained in the mines.

To evaluate the biological risks associated with this form of pollution, the researchers sampled mussels (Mytilus edulis) at two specific locations in the North Sea and placed them inside cages which were then positioned in the vicinity of the wrecks identified for study (In addition to the UC-30, the Kolberg-class light cruiser was analyzed. SMS MAINZ and the fishing boat KW58 HENDERICUS, also lost in the North Sea loaded with ammunition).

They then studied the detoxification processes carried out by the mussels that had remained on the wrecks for several weeks, and discovered that only 3 mussels, out of 59 placed on the hull of the UC-30, did not present traces of TNT (or its metabolites)The German submarine sunk in 1917 is releasing TNT into the sea.

A phenomenon that could affect thousands of wrecks around the world

Today, environmental contamination is an explicit strategy of destruction in several conventional warfare scenarios. Yet it is increasingly clear that we have yet to understand and quantify the toxic legacy of the two world wars of the last century – which could be a much more cumbersome legacy than expected (or rather, than what was not foreseen).

As Dr. Andresen explains,

We have detected traces of TNT in marine organisms, in seabed sediments, and in the water column. Pollution is occurring. The question remains to be clarified regarding the extent of the impact and the distance from the wreck at which this pollution affects the marine environment. This is likely a relatively localized source of pollution, but the situation is likely to worsen as the wreck continues to deteriorate, exposing more explosive material contained in the mines.

And this applies to the UC-30, but potentially also to the wrecks of the over 10-15 thousand large vessels sunk between the First and Second World Wars, not to mention the thousands of smaller vessels, barges, and planes that have crashed into the sea. Some of these munitions-laden wrecks—who knows how many—could be releasing toxic substances into the sea even now, drowned out by the silence of the ocean depths and the indifferent march of history.

Scientists have just begun to reveal the outlines of thetoxic legacy of the wars of a hundred years ago (which, for a change, mainly concerns the ocean and its ecosystems), and to study some possible solutions.

Remediation, underwater drones and neutralization of dangerous explosive devices

Germany, explains Dr. Andresen, has already allocated significant funds for the recovery of some wrecks and ammunition dating back to World War II from the Baltic Sea:

"The Germans are ahead of us in Denmark on this front. Sometimes they recover explosives from the wrecks to neutralize them, but it's a very expensive operation."

Detonating explosives on siteFurthermore, it's not always the safest option: when the devices are detonated underwater, the shock wave can disperse contaminants into the surrounding environment. In some areas, this operation could worsen pollution rather than solve the problem.

"It depends on the area where the wreck and the devices are located. Currents and the morphology of the seabed play a fundamental role. In some cases, detonating them can cause more harm than good."

explains the doctor. An approach currently being tested involves theuse of robots Able to move across the seabed. These machines could precisely map the location of dangerous ordnance and help researchers more closely monitor deteriorating wrecks. In the future, these robots might be able to recover or neutralize these objects. After all, there's no need to "clean up" every excavation on the ocean floor:

Some wrecks are entirely or partially buried in the ocean floor. When they're covered with sand, the risk of polluting the surrounding sea is significantly lower. It's a matter of identifying where the environmental threat is greatest and then deciding whether to remove the ordnance from the wrecks.

concludes Andresen.

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