Germany's rusting sea munitions are a toxic time bomb

The legacy of two world wars

Beneath the seas off Germany's northern coast, vast quantities of bombs and other weapons are slowly rusting away. They are part of an estimated 1.6 million metric tons of conventional munitions in the North Sea and Baltic Sea, a legacy of two world wars and the mass disposal of weapons after 1945.

For decades, the material was largely left alone unless it posed an explosive danger. But as metal casings corrode, a different problem is emerging. Some weapons are remnants of fighting: mines, unexploded bombs and ammunition lost at sea. But huge quantities were deliberately dumped after Nazi Germany surrendered in 1945, as the Allies disposed of the country's vast arsenal.

What was once regarded as an explosive hazard has now become an environmental one. "It's clear that due to corrosion of these items, compounds enter the marine ecosystem and enter marine life," Kiel University toxicologist Edmund Maser told DW. "It turned out that these compounds are toxic and carcinogenic, both for human life and also for marine life," he said.

The UC-30 submarine and its toxic cargo

One example of the problem is the German Type UC II minelaying submarine UC-30, which sank in 1917 after hitting a British mine near the island of Rømø off Denmark's coast. The U-boat carried 18 mines, six torpedoes, and a crew of 27. For almost a century, it lay undiscovered. Then a team led by Aarhus University geoscientist Katrine Juul Andresen mapped the wreck. Their study, published in the journal Marine Pollution Bulletin, used blue mussels (Mytilus edulis) as bioindicators and found TNT in the wildlife, the seabed, and the water column.

The most common chemical explosives in the decaying munitions are TNT, RDX, and DNB. TNT was found in seawater around UC-30 at 72.6 nanograms per liter (parts per trillion). Test mussels showed disrupted metabolisms, reduced glycogen in digestive tissue, and trouble detoxifying. Similar tests were conducted near the SMS Mainz and KW 58 Hendricus wrecks.

Andresen noted that pollution from the wreck is "likely a relatively localized source of pollution, but it will worsen as the wreck continues to deteriorate and expose more of the explosive material inside the mines."

Contamination in marine life

Researchers have documented the effects of these leaks on marine organisms. Jörn Scharsack of Germany's Thünen Institute of Fisheries Ecology looked for evidence of TNT in dab fish. "We find TNT in the fish, or let's say, metabolization, degradation products of TNT," he told DW. The quantities are tiny — measured in nanograms — and not every fish contains detectable levels. But researchers repeatedly find the compounds around old munitions hotspots. "It's low. But it's there."

So far, the contamination does not appear to be making fish acutely sick. "The fish look healthy when we take them out. They do not have more diseases in terms of viral, b" (the quote is cut off in the original). But liver tumors are a recurring finding. Maser's team, working with the Alfred Wegener Institute, found liver abnormalities in more than 50% of fish around munitions dumping grounds compared to 1-2% normally. Mussels showed biochemical signs of oxidative stress, which can lead to cancer. TNT-related compounds were also detected in tissue samples from two stranded whales.

For humans, eating seafood is currently not dangerous according to scientists. Scharsack said, "I'm still eating fish." But the situation may change. Maser examined archived mussels from 1985 and found contamination increasing steadily from around 2000 to 2022. He expects concentrations could harm human seafood consumers in coming decades.

The Baltic Sea problem appears worse due to weaker currents. And as corrosion continues, contamination may worsen. "If we wait maybe 40 years, then all these metal cases are corroded and we have no chance to get these munition compounds out of the water," Maser said.

The challenge of cleanup

Germany has begun pilot projects for systematic clearance to prevent environmental harm. The plan includes floating treatment platforms (pontoons) for burning munitions at sea. But the scale of the task is daunting. Maser estimates a pontoon might process 700 to 1,000 tons annually, so removing all munitions would take decades.

Andresen noted that Germany has devoted resources to retrieving sunken munitions in the Baltic Sea, but solutions are costly. She also suggested that some wrecks buried in sand pose lower pollution risk, and that removal may not be necessary in all cases.

Maser is also researching bacteria and fungi to break down residues, but that work is still at laboratory stage. As the metal cases continue to corrode, the window for action may be closing.