Many ships were sunk during World War II. So the wrecks have been lying on the seabed for decades. Researchers are now taking a closer look at one and are finding numerous questionable substances with equally questionable values.
80 years after its sinking, a German warship is still endangering the seabed off the Belgian coast. Bacteria that break down substances from coal and oil thrive in its environment. And in the sediment of the sea floor there are traces of heavy metals and the explosive trinitrotoluene (TNT) and its decomposition products. In addition, sulphur-reducing or sulphur-oxidizing bacteria increasingly corrode the ship’s steel hull – which could lead to a further hazard. This is reported by a group led by Josefien van Landuyt from the University of Ghent in the journal “Frontiers in Marine Science”.
On February 12, 1942, the British Air Force sank the German Navy’s picket boat V-1302 in the North Sea. V-1302 was originally a fishing boat converted for war purposes. Coal bunkers, petroleum products, explosives and explosive ordnance went down with the ship and are gradually being leached out by the sea water.
Samples from the seabed around the shipwreck show changes in the content of heavy metals, among other things: “From bow to stern, we observe higher concentrations as we approach the ship,” write the researchers. The levels of nickel, copper and arsenic were particularly high near the bunker that contained the coal for the steam boiler at the rear of the ship.
Younger sediments behind the stern contained particularly large amounts of metal. Van Landuyt and colleagues suspect that this may be due to the deposition of metal flakes that detached from the wreck along with sediment particles.
The team also examined the seabed for polycyclic aromatic hydrocarbons (PAHs), which are found in coal and petroleum and are believed to be harmful to health. Their concentrations increased on the port and bow sides the closer they got to the wreck. On the stern and on the starboard side, on the other hand, freshly deposited sediment reduced the PAH values. In zones with a higher PAH content, the scientists found a particularly large number of bacteria from the Rhodobacteraceae and Chromatiaceae families that break down PAHs.
The researchers also identified a number of bacterial strains that process sulfur in the biofilm on the ship’s hull. Acid is formed during these processes, which intensifies the corrosion that is already occurring. In fact, increasing corrosion can increase the environmental risk and open previously closed rooms, van Landuyt is quoted in a statement from the specialist magazine. “Therefore, the impact on the environment is still evolving.”
The explosive TNT and its decomposition products were found around the wreck in concentrations of up to 45 nanograms per kilogram of dried sediment. An exception was a spot about 15 meters from the stern: The concentration there was even 120 nanograms.
“We only examined one ship at a certain depth in a certain place,” says van Landuyt. In order to get a better overview of the ecological consequences of shipwrecks on the North Sea, a large number of shipwrecks should be sampled at different locations, the researcher emphasizes.
