Image Courtesy: Kathrine Juul Andresen
A German submarine that sank in the North Sea during World War I is still releasing toxic explosive compounds into the surrounding marine environment more than a century later, researchers have found.
The UC-30 submarine was carrying 18 mines and six torpedoes when it struck a British mine on April 19, 1917, near the Danish island of Rømø. The explosion sank the vessel and killed all 27 crew members on board. Nearly a century later, Danish diver Gert Normann Andersen discovered the wreck in 2016, allowing scientists to investigate the environmental risks posed by its remaining munitions. Researchers collected water, sediment, starfish, and mussel samples from around the wreck.
The analysis found traces of TNT in marine wildlife, the surrounding seabed, and the water column. The findings suggest that explosive material remaining inside the submarine is already entering the local ecosystem.
Katrine Juul Andresen, a professor at Aarhus University’s Department of Geoscience, said the pollution appears to be occurring now, although researchers are still studying how far the contamination extends from the wreck.
The problem could worsen as the UC-30 continues to deteriorate. Corrosion and structural damage could expose more of the mines and other explosives that remain trapped inside the wreck.
The UC-30 is only one of thousands of historic shipwrecks scattered across Danish waters. A 2024 report prepared by Andresen for the Danish Environmental Protection Agency identified 10,127 wrecks, with approximately 15 percent dating from the periods surrounding the two world wars.
Many of those vessels contain fuel, ammunition, explosives, and other hazardous materials that have remained underwater for decades. Researchers are increasingly concerned that aging wrecks could become a growing source of localized marine pollution as their structures break down.
Removing the munitions, however, presents its own challenges. Germany has invested in recovering and neutralizing some historic explosives from the Baltic Sea, but such operations are expensive and potentially dangerous. Underwater detonations can also spread contaminants depending on local currents and seabed conditions.
Andresen and international researchers are now investigating safer methods of managing the threat through the EU-funded REMARCO project. Potential solutions include underwater robots capable of locating, monitoring, and potentially retrieving individual munitions.
Researchers say the priority will be identifying the wrecks that pose the greatest environmental risk. Some are partially or completely buried beneath sediment, which can significantly reduce the amount of contamination reaching the surrounding water.
