1.8 million tons of unexploded ordnance lies on the North Sea floor.

MAY 2, 2023

The explosives lie on the seafloor just beyond the Kiel harbor in the German North Sea, several kilometers from the beach, shallow enough to poke with a long fishing pole. Dumped by the Allies after World War II at a site known as Kolberger Heide, over an area the size of downtown Kiel, they formed an aqueous afterimage of the bombs that had recently leveled the city. The drowning of these weapons was in part a signal that Germany could move on from the war. Kiel began to rebuild. The munitions, soon forgotten, stayed where they were. “Today, any amateur diver could go there, take some TNT, bring it back, dry it out and make a bomb,” said Edmund Maser, one of the scientists spearheading North Sea Wrecks (NSW), a project investigating the ecological impacts of underwater ordnance. Then he paused for a moment and smiled. “Maybe don’t write that.”

Maser is the director of the Schleswig-Holstein University Clinic’s Institute of Toxicology, where he treats the occasional poisoning and studies how living organisms, including human beings, cope with toxic chemicals, like the ones leaching from world war-era dumpsites and shipwrecks around Europe. He’s punctilious and chatty, with a soft spot for mussels, water fleas and other uncuddly creatures, and a laissez-faire attitude toward personal risk — he rides a Harley-Davidson, likes his nightly beer and, contra clinic regulations, allowed us to go maskless in his office. There, he told me how he himself might have remained ignorant of the 1.8 million tons of submerged ordnance lying in German waters if he hadn’t been approached twelve years ago by Schleswig-Holstein’s Ministry of Agriculture, Environment and Rural Areas, which wanted his help in understanding if these munitions were poisoning the marine environment. Maser and his team began bringing mussels to Kolberger Heide and leaving them to stew around the corroding mines before collecting them again and assessing their health. The results, he said, were clear: “The mussels were suffering.”

Maser’s mussels were one symptom of a broad and amorphous problem decades in the making. At least 28,000 ships sank during the two world wars. When they went under, they took with them whatever chemicals were on board: the fuel in their tanks, the TNT in their unfired munitions, the mercury in their holds. At the time, the sea’s capacity for absorption seemed infinite: After World War II, Allied forces organized the large-scale dumping of Germany’s remaining arsenal of conventional and chemical munitions at designated sites like Kolberger Heide. It was a cheap and easy solution, one that militaries around the world continued to adopt for their own obsolete armaments until 1972, when most countries agreed to stop the practice at the U.N.-sponsored London Convention.

Maser’s favorite story recalls Giovanni Falcone, the incorruptible judge killed outside Palermo by the Mafia — to circumvent Falcone’s extensive security measures, the assassins blew up an entire section of highway under his motorcade, using 400 kilograms of explosives taken from a dredged-up naval mine.

These chemicals could remain sealed from the ecosystem for decades, trapped inside metal tanks and casings, and sealed by a secondary protective barrier of hydroids, anemones and moss animals that grew upon them. But over time, the metal has been corroded by salt water, agitated by currents and unsettled by shifting sediments. The containers have begun to crack. The first alarm bell sounded in 2001, when a fishing village in Micronesia, far removed from the global petroleum trade, awoke to find its turquoise lagoon blackened by oil. A typhoon had damaged the nearby wreck of a World War II-era U.S. Navy oil tanker, whose location, by a stroke of good luck, had been discovered by adventure divers just two months prior. In 2005, researchers calculated that old shipwrecks might still contain up to 6 billion gallons of oil among them, equal to 550 Exxon Valdez disasters.

The environmental impact of oil spills is immediate and telegenic. The effects of munitions, which dissolve into the water slowly and invisibly, have received much less attention. White phosphorus has been collected by unwitting beachcombers who mistake it for amber, only to have it catch fire in their pockets. Unexploded bombs have hampered the Nord Stream sabotage investigation, cost offshore wind farm operators hundreds of millions of dollars in cleanup costs and nixed a bridge connecting Scotland and Northern Ireland. In Beaufort’s Dyke — the trench through which this bridge would have passed, and where the British conducted extensive postwar dumping — random underwater explosions big enough to trigger seismograph readings occur every three months; the resulting shockwaves can deafen whales a mile away. Maser’s favorite story recalls Giovanni Falcone, the incorruptible judge killed outside Palermo by the Mafia — to circumvent Falcone’s extensive security measures, the assassins blew up an entire section of highway under his motorcade, using 400 kilograms of explosives taken from a dredged-up naval mine.

But what most interests Maser as a scientist is the warfare unfolding on a molecular scale. In his lab, that begins with examining fish and mussel samples, which are kept frozen in zip-close bags labeled according to the shipwrecks from which they were taken, like the “John Mahn” or the “SMS Ariadne.” When he showed me the freezer, I joked that the grad students might think to raid it after the cafeteria closed.

“That’s what everyone wants to know,” Maser answered, thoughtful. “Can you still eat the seafood?”

TNT is a chemical compound that looks like pale yellow-brown toffee. Highly explosive, it is also toxic in its natural state, absorbing easily into the human bloodstream through the lungs, the digestive system and even the skin. World war-era munitions workers, mostly women, were known as “canary girls” because handling TNT stained their hair and skin bright yellow. Later in life, many of them developed health problems ranging from liver disease to anemia.

To measure whether fish contain dangerous levels of TNT, samples must first be ground up into particles fine enough to dissolve in a solution, which is then homogenized into thimble-size samples of clear liquid that can be run through a mass spectrometer, a machine that counts how many of each molecule make up the fish. At a nearby computer, Maser pointed to the sharp blue peak that appeared in a graph on the screen: “That’s the TNT. 1.6 nanograms per gram.”

Is that bad? After I asked him the question, I sensed an annoyed formality creeping into his voice. Commercial fishing is a 300 million euro industry in Germany. In a different conversation, he recalled how back when he first began speaking about this issue to the press, he had stated that seafood may be dangerously contaminated. Local fishers heard about his remarks and began complaining about the toxicologist set on destroying their business. “They left the subjunctive out of my verdict,” Maser said. “I was saying, ‘It may be,’ but they just said, ‘It is.’ Afterwards I started to be a little more careful.” When I talked to Sven Bergmann, NSW’s project coordinator, he put it more succinctly: “If they quote you as saying, ‘You cannot eat the fish,’ then your project is dead.”

Nonetheless, Maser assured me that the current TNT levels in seafood are negligible to human health. Then came the “buts.” First was the environmental damage. “Maybe we can eat the fish and the mussels, but what good is that if in 20 years there are no more fish to eat?”

For the animals, living in a TNT bath is what for us would be like living inside a smoke-filled bar. Every sampled mussel, Maser told me, showed signs of oxidative stress, a marker of an organism overwhelmed by more cellular damage than it can repair. More than half of the fish caught around North Sea wrecks exhibited extreme liver tumors. As Maser walked me through the statistics, it was at times difficult, in the gleaming, sterile lab environment, to keep a picture of the living creatures in mind. At one point my eyes gravitated to some beakers in whose liquid I could make out the fluid, aleatoric movements of organic life. “Those are our daphnia,” Maser said, as I looked closer at the pellucid, midge-size swimmers. “We use them as a quick TNT check. If you put a few drops of water in the beaker, and the water has TNT in it, the daphnia will stop moving.”

Unlike other chemicals, which, once they are in the water, can be neutralized only by the entropic cleansing of time, munitions can still be picked up and taken out of the sea.

The levels of toxic contamination are also liable to grow. The metal casings of these munitions are corroding. Someday they will be gone. “And we know from Kolberger Heide that when the TNT is fully exposed to the water, its concentrations in mussels can go up to 50 times higher compared to what we’re seeing at the North Sea wreck sites,” Maser said. “And those levels can pose a threat to human health.” The disappearance of the casings would also complicate the process of discovering the many potentially dangerous wrecks and dumpsites whose locations are still unknown, a process that relies on metal detectors.

For the past six years, Maser has been delivering these warnings in meetings with politicians, scientists and the media on an almost monthly basis; the day before our meeting, Maser presented on this issue at the Baltic Sea Parliamentary Conference. He is often met with skepticism at these talks. Are munitions really as harmful as other ocean pollutants, like pesticides or pharmaceuticals? He is quick to point out that munitions are fundamentally different in one key aspect: Unlike other chemicals, which, once they are in the water, can be neutralized only by the entropic cleansing of time, munitions can still be picked up and taken out of the sea.

At least, theoretically.

Sven Van Haelst remembers the moment he realized that shipwrecks might pose a threat to man and nature rather than the other way around. In the ’90s, long before he became a scientist, he was part of the small community of hardcore divers who plumbed the rough and turbid North Sea in search of sunken ships. At the time, he worried more about powerful currents beating these fragile relics and “pirate” divers plundering souvenirs. Then, on one outing, while a buddy was jimmying a rusted porthole, he saw something unexpected. When the porthole opened, a large chocolate-colored bubble billowed through the opening, followed by another, and another, until an opaque plume was shooting up from the ship and rising through the water like a ghost unleashed. It was oil, Van Haelst realized, and in seconds it had reached the surface, where it spread out like an iridescent blanket, seeming to weigh down the sea, killing even the waves. “That was the first time I thought there might be problem,” he said.

An underwater archaeologist and scientific diver, Van Haelst helped develop the plan for which shipwrecks NSW would sample, and how. In his native Belgium, information about the locations and identities of war wrecks is publicly available (unlike in other countries, like the Netherlands, where it remains restricted to deter sightseers). His experience is crucial for assessing which wrecks are both feasible and useful to study. Some might be covered with several feet of sediment or toppled in a way that makes exploration too hazardous. Others might lie in shipping lanes, making research access impractical. Still others might have already used up the bulk of their arsenals before they sank, a possibility that NSW’s researchers try to assess by reconstructing the duration and intensity of each ship’s battles using sailors’ diaries and captains’ logs.

Because the currents in the North Sea are so strong, dives can take place only during a few precious hours on the two days of neap tide each month. Weather adds further complications: Half of dives are canceled, either because of fog or because the waves are too high to safely retrieve divers. Even if a dive goes forward, the visibility underwater can be so low that divers can’t see beyond their own fingertips.

“The first time you dive at the North Sea, you have the impression that you’re diving in a scrap metal yard,” Van Haelst explained. “Unless you really know your ship anatomy, that’s all you’ll see.” In videos he showed me, the descent begins as a movement through pure, undulating color, an aquamarine blindness. Closer to the seafloor, thick streams of organic matter rush along with the current. Finally, a shadow appears, a few lines, the telltale colonies of wan anemones, and then clearer shapes: polygons and tubes, barrels and pipes, but nothing that resembles a ship. The munitions may be scattered anywhere amid the wreckage, their once-sharp, gleaming lineaments blurred out by mossy gunk.

Treasure hunters remove munitions by hand, but outside of ideal conditions, this is considered too dangerous for full-scale remediation efforts.

During their recent excursions to the John Mahn, a German warship in the Belgian North Sea and a major focus of the group’s research, NSW’s divers were unable to visually confirm any anti-aircraft shells, which archival data suggested should have been plentiful. They don’t know whether that’s because the shells had been moved by the current and covered with sediment, or because they were all taken by treasure hunters. Hobby divers regularly scour wreck sites, taking everything from gold coins and brass instruments to porthole casings and false teeth. In Great Britain, the Maritime and Coastguard Agency found that 40 former warships had been stripped bare in the last decade.

Treasure hunters remove munitions by hand, but outside of ideal conditions, this is considered too dangerous for full-scale remediation efforts. Van Haelst is currently working with the Belgian navy to develop a plan for manually removing a cargo of anti-tank mines from a German transport vessel, but these mines were shipped without detonators, so there’s no risk of explosion. In most other cases, cleanup operations rest on the shoulders of underwater drones. These can be effective when dealing with munitions lying directly on the seafloor, less so when navigating the crevices of a wreck. Maarten De Rijcke, another of NSW’s scientific divers, said that the organization had considered using drones to collect samples but decided against it. “Maritime robots are the future, but working with a remotely operated vehicle near a shipwreck, where there’s a large risk of entanglement, is hard to do in a way that’s safe around explosives,” De Rijcke said.

Some private companies offer munitions removal services, albeit at prices (around 60,000 euros for a single mine) that make sense only for large infrastructure projects. Part of the cost is the disposal of explosive materials once they are brought to shore. In Germany, only one facility, run by the Chemical Agents and Legacy Munitions Disposal Company (GEKA), is certified to destroy salvaged munitions, and its capacity is limited to 100 tons per year, enough to handle stray munitions that wash up on the beach or float into a wind farm but not enough to deal with the 1.8 million tons of weapons lying in Germany’s waters. Building more plants would represent a political headache. As Maser said, “Who wants to have a factory on their coastline burning all these mines and grenades?”

“When you’re down there and you see exactly where the bomb hit the ship,” De Rijcke told me, “and you know how it sank in 30 seconds, and you think about the people who lost their lives in 30 seconds, about why they were there when they shouldn’t have been there — when you see their personal belongings, it’s a very human experience.”

To date, governments have preferred low-tech solutions, like blast-in-place operations, which remove detonation risks but accelerate environmental damage by damaging metal casings. Nonetheless, the German government, perhaps motivated by the need to build offshore natural gas platforms in response to Russia’s gas embargo, recently earmarked 102 million euros to prototype an autonomous floating platform that could detect, retrieve and incinerate munitions systematically, at scale and, crucially, at sea. But even this platform could destroy only 1,000 tons of munitions per year. Solving the problem would require at least 100 platforms, according to ThyssenKrupp, the company that won the bid (an ironically appropriate victor, given that its parent companies produced much of the steel and TNT now lying underwater). At the current price tag, such a fleet would represent a fifth of Germany’s entire defense budget.

When I spoke with Maser and NSW’s other land-based researchers, they all emphasized the need to remove munitions from the sea as quickly as possible. Van Haelst and De Rijcke, on the other hand, were less strident. They argued that the shipwrecks they’d studied should be monitored, but that at present the concentrations of TNT in the water at all but one of these sites are well below established toxic levels. They were also quick to bring up other reasons for protecting the wrecks, whether as biodiversity hotspots, war graves or cultural heritage sites.

“When you’re down there and you see exactly where the bomb hit the ship,” De Rijcke told me, “and you know how it sank in 30 seconds, and you think about the people who lost their lives in 30 seconds, about why they were there when they shouldn’t have been there — when you see their personal belongings, it’s a very human experience.”

After my interviews in Kiel, I took a walk through the town, down to the harbor. Unlike many German cities, Kiel wears its postwar rebuild like a laundry day outfit. Its old town is aggressively ersatz, a warning about the perils of moving on too quickly. I bought a baked fish sandwich at the Christmas market and sat down along the quay, where I watched tiny ripples moiling distractingly upon the dove-gray surface of the water. There were probably grenades somewhere under the waves. There was probably TNT in my fish. There were probably toxic chemicals in the sea spray; several researchers had told me that this was going to become a hot field of study. I tried to keep all this in my mind at one time, but I was cold and hungry, and the sea kept burbling nonsense. I ate my sandwich, breathed the air and made my way back to the train station. This would have to do for my human experience, maybe the most common one shared by the people in this city, on this continent: ignoring the past until it found some way to kill me.