Researchers studying an 80-year-old shipwreck in the North Sea have found that the ship, which was sunk by a bomb during World War II, is currently leaking toxic waste onto the ocean floor, influencing the microbiology and geochemistry of the ocean floor. This could be a reason for this ship, as well as other wrecks to be removed from the seabed, the researchers say.

The V-1302 John Mahn was a German fishing trawler that was later used by the Nazis used as a patrol boat. The British Royal Air Force bombed and sunk the ship in 1942. According to the new study, the ship has spent the large part of a century resting at 30 meters below sea level in the Belgian North Sea — and it’s been leaking toxic pollutants into the water.

A polluting shipwreck

The seabed of the North Sea is packed with thousands of ship and aircraft wrecks, warfare agents, and millions of tons of munition such as shells and bombs. Wrecks have hazardous substances such as petroleum and explosives that can harm the marine environment. However, there’s not much data on the actual location of the wrecks.

“The general public is often quite interested in shipwrecks because of their historical value, but the potential environmental impact of these wrecks is often overlooked,” Josefien Van Landuyt, study author, said in a statement. “They can be dangerous, human-made objects which were unintentionally introduced into a natural environment.”

Van Landuyt and her colleagues looked at how the V-1302 John is impacting the microbiome and geochemistry in its surrounding seabed. They took steel hull and sediment samples from and around the vessel, at an increasing distance from it and in different directions, and then analyzed the bio and geochemistry around the wreck.

They found different degrees of concentrations of toxic pollutants, including heavy metals (such as nickel and copper), polycyclic aromatic hydrocarbons (or PAH, chemicals that naturally occur in crude oil and gasoline), arsenic and explosive compounds. The highest metal concentrations were found in the sample closest to the ship’s coal bunker.

These concentrations have impacted the surrounding microbial life, the researchers said. They have found microbes such as Rhodobacteraceae and Chromatiaceae, known to degrade PAHs, in the samples that had the highest concentrations of pollutants. Sulfate-reducing bacteria (such as Desulfobulbia) were present in hull samples, most likely corroding the hull.

“Although we don’t see these old shipwrecks, and many of us don’t know where they are, they can still be polluting our marine ecosystem,” said Van Landuyt. “In fact, their advancing age might increase the environmental risk due to corrosion, which is opening up previously enclosed spaces. As such, their environmental impact is still evolving.”

The study is just the tip of the iceberg, Van Landuyt said. A larger number of shipwrecks in various locations would have to be sampled to better understand the total impact on the North Sea. For now, we know shipwrecks are more problematic than we would have probably thought and that the issue has to be further investigated.

The study was published in the journal Frontiers in Marine Science.