You do not see them, the danger - but it is there. "In the Bay of Kiel are located in sight of popular beaches torpedo head next explosive mine," says marine biologist Matthias Brenner of the Alfred Wegener Institute for Polar and Marine Research (AWI). Most of it dates back to World War II.
In Germany alone, 1.6 million tonnes of conventional weapons and 300,000 tonnes of chemical weapons are expected to be in the Baltic and North Seas. "That's huge," says Brenner.
On behalf of the Allies fishermen were to sink the ordnance far out at sea after the Second World War. According to the Fraunhofer Institute, a lot of ammunition was dumped outside the marked areas - possibly to save fuel.
Mines and bombs in places where they should never go
Due to ocean currents and bottom trawling, mines and bombs landed in places where they were never supposed to go. That makes it difficult to find them today. In the construction of new pipelines or offshore wind farms, companies often come across such weapons.
For almost 70 years, hardly anyone was interested in what is rotting in the oceans. "It's best not to touch it, it's going to decompose anyway," it said for a long time, "says Brenner. That this was wrong, you see today: Many bombs can still explode.
Over time, they become even more sensitive. A slight change in pressure or impact can cause it to explode. "The ammunition bodies are partly completely rotten, others are explosives," says Brenner. These toxic substances enter the sea unhindered.
Chemicals land in the Baltic Sea cod
AWI and Partners researched the impact of chemical weapons on the environment a few years ago in the Chemsea project. As marine biologist Brenner says, residues of chemical weapons in the filet could be detected in 10 to 13 percent of the Baltic Sea fish.
The amount is indeed low. "It may be that such a fish ends up on the plate," he says. To what extent these small amounts have an impact on the consumer has not yet been explored.
Now the successor project "Daimon" ("Decision Aid for Marine Ammunition") comes to an end. Researchers had studied the effect of conventional weapons on the environment. At the beginning of February the final conference took place in Bremerhaven. The Thünen Institute for Fishery Ecology has examined the flatfish dab, which lives on the seabed in the Kiel Bay. Around 35,000 tons of conventional ammunition are in the area, as Thomas Lang, deputy director of the institute, says.
In 25 percent of the copies, the researchers found liver tumors. In unencumbered areas, however, the rate is only 5 percent. "There are TNT clumps on the bottom that dissolve in the water, and the breakdown products enter the organism through water or food," says Lang. Laboratory tests have shown that the degradation products of TNT damage the DNA of fish, which is a possible explanation for the high tumor rate. However, the dumplings are not fished and marketed so that there is no danger for humans.
Sonar technology and magnetic probes help with detection
In addition to environmentalists, the economy has an interest in ridding the seabed of ammunition. "The ammunition is a risk to shipping and for the construction of wind turbines and the laying of submarine cables," says Lang. Divers are therefore constantly busy clearing fairways of mines that were actually considered unloaded.
An association of research institutes and companies is currently developing a system with the "Munitect" network to better locate and map old munitions. With sonar technology and magnetic probes, the war waste can already be detected quite well today. However, these methods are so expensive that they can only be used randomly and in previously defined areas, it says on the website of the network, which is coordinated by the Fraunhofer Institute for Computer Graphics (IGD).
These samples are also falsely traced to conventional scrap. "The precise identification of dangerous mines and ammunition bodies is very difficult and is very often carried out today by divers," explains Kristine Bauer, network coordinator at Fraunhofer IGD. "Munitect" has the goal to search larger areas more efficiently and accurately in the future.
Often the explosives found are brought ashore and professionally eliminated or - if they are no longer transportable - blown up. The problem: Then toxins can be distributed over a large area in the water. In addition, animals such as harbor porpoises and seals could cause noise damage.
Remote controlled robots with cameras
It is therefore demanded that emissions-free be recovered, so researchers Brenner. The Fraunhofer Institute and the University of Leipzig work together with partners from industry on exactly such a solution. Bomb-clearance services, such as Boskalis Hirdes, are already using cameras with remote-controlled underwater robots.
These machines release the weapons, experts inspect them and decide what to do with them. The aim is to remove people completely from the eviction, the company said.
In March, the company wants to present a concept for a robotic recovery and disposal process ("RoBEMM"). As Andreas Jeron of Boskalis Hirdes says, "RoBEMM" is supposed to evacuate non-transportable munitions that currently have to be blown up in the field. "With less negative impact on the environment."
