20th-century shipwrecks are poisoning our oceans—but underwater microbes are fighting back

Here’s what you’ll learn when you read this story:

• Shipwrecks, especially those from World War I and World War II, are leaking dangerous contents into the world’s oceans.
• A new study analyzes marine sediments from the minewells of a sunken German UC-30 submarine from WWI and found an increase in certain microbes capable of breaking down hydrocarbons and surviving extreme chemical stress.
• The study is an example of how nature can be a powerful, bioremediation tool for tackling some of the dangerous chemicals that still lurk in the deep.

The world’s oceans are littered with shipwrecks, with some estimates placing the number at around 3 million. Unfortunately for the aquatic environments in which they rest, most of these come from the modern area (the 18^th, 19^th, and 20^th centuries), when the presence of hazardous materials of dangerous ordnance onboard was not only possible, but likely. Of the three million, roughly 15,000 can date to the years during which World War I and World War II were fought, and a vast majority of those ships are slowly poisoning their surrounding environments. There are 87 “potentially polluting wrecks” in U.S. waters alone—a country that, famously, wasn’t a major theater in either war.

The big problem with relatively modern shipwrecks is that corrosion is beginning to do its deadly work. The hulls of these ships are slowly releasing their deadly contents into the sea. One wreck of particular concern is a German UC-30 submarine located 66 nautical miles west of Nymindegab, Denmark. Lying 23 meters below the surface on a shallow, sandy reef of glacial deposits in the North Sea, this UC-30 submarine specialized in minelaying intended to wreak havoc on enemy harbors and shipping lanes. A necessary part of that job was carrying lots of 2,4,6-trinitrotoluene, more commonly known as TNT, which was housed in 18 onboard sea mines.

Because these submarines have been subjected to the salty waters of the North Sea for more than a century—in this particular case, the submarine sank in 1917—scientists are becoming worried that an unexpected rupture could imperil the area. But it turns out they might have a microscopic ally on their side.

In a new study published in the journal Communications Earth & Environment, a team of researchers from Germany, Belgium, and Denmark analyzed sediments from the submarine’s minewells—six vertical shafts built into the pressure hull that carried three mines each—to understand the make-up of the microbiome at work. The minewells present a unique microcosm for study, as they provide a consistent, localized contamination source that can be studied.

“Anthropogenic chemical pollutants are increasingly infiltrating marine environments, posing significant threats to ecosystem integrity and biological functioning,” the authors wrote. “The current situation creates an opportunity to explore the inherent capacity of indigenous marine microbiomes to detect, transform, and degrade environmental contaminants.”

In samples taken from the wreck, scientists found distinct taxonomic shifts within the minewells of the wreck—specifically, a drastic increase of Proteobacteria like Haliaceae and Rhodobacteraceae, both of which are microbes that can break down hydrocarbons and survive extreme chemical stress. The microbes do this by leveraging survival enzymes like Glutathione transferases (a major family of detoxification enzymes) and oxidoreductases (an enzyme that catalyzes electrons from one molecule to another).

To test this effect further, the team exposed marine sediments similar to conditions under lab cultures for 12 weeks. They found significant overlap between the microbial communities in-situ and in laboratory conditions, and observed that the molecules possessed enzymatic pathways capable of neutralizing TNT into reduced intermediates.

“These results indicate that contaminated minewell environments exert selective pressures that shape microbial assemblages toward enhanced stress tolerance and potential transformation capacity,” the researchers wrote. “By demonstrating this effect for TNT, our findings provide a framework that can be extended to investigate microbial adaptation, metabolic versatility, and natural attenuation processes across a wider range of contaminated marine sediments.”