German WWI Submarine Wreck Still Leaks TNT Into North Sea, Study Finds

In April 1917, the German submarine UC-30 was returning to Germany after abandoning a mission to Ireland from engine problems. Carrying 18 mines and six torpedoes, it struck a British mine near Rømø and sank on April 19, killing all 27 crew members. The wreck lay undiscovered for nearly a century until Danish diver Gert Normann Andersen found it in 2016.

UC-30 has since been studied through the NorthSeaWrecks research project. Katrine Juul Andresen, a professor at Aarhus University's Department of Geoscience, worked with navy divers, since civilian diving on the wreck is banned, to collect sediment, water and wildlife samples, including starfish and mussels. The team found traces of TNT, a powerful explosive, in the wildlife, seabed and water column, showing that explosive material is entering the marine environment. Andresen said the pollution is likely localized but will worsen as the wreck deteriorates and exposes more explosives inside the mines.

During World War I, Germany and Britain relied heavily on naval mines to control the North Sea; an estimated 190,000 mines were placed there. The region was also the site of the Battle of Jutland, off Hanstholm, the largest naval clash in history, in which more than 25 ships were sunk and nearly 10,000 sailors died.

UC-30 is only one example. In a 2024 report for the Danish Environmental Protection Agency, commissioned to help Denmark meet the EU Water Framework Directive, Andresen found 10,127 wrecks in Danish waters, about 15 percent of them dating to the years around and during the two world wars.

Removing explosives from wrecks is costly and not always safe, since detonating munitions underwater can spread contaminants depending on local currents and seabed shape. Germany retrieves and neutralizes explosives from some wrecks in the Baltic Sea. Andresen is working with international researchers on the EU-funded REMARCO project, testing seabed robots that can map dangerous munitions, monitor wrecks, and in some cases retrieve and neutralize items.