World war shipwrecks are leaking pollutants into the world's oceans

Pollution from ships sunk during the First and Second World War are affecting undersea ecosystems.

Millions of tonnes of munitions, fuel and other chemicals were sunk during the conflicts, with much of the material still lying at the bottom of the world's oceans today. Many of these wrecks, deemed too costly or dangerous to clean up, have been leaking chemicals into the water for decades.

With areas such as the North Sea increasingly being developed for windfarms, fisheries and undersea farming, understanding these wrecks is more important than ever. A new study, published in the journal Frontiers in Marine Science, reveals that chemicals are influencing which microbes live around sunken vessels.

Ghent University PhD student Josefien Van Landuyt, who led the research, says, 'People often forget that below the ocean's surface, humanity has already made quite an impact on the local animals, microbes, and plants living there.'

'Wrecks, some of which we don't even remember are there, are leaching chemicals, fossil fuels and heavy metals into the water. As they get older, their environmental risk might increase due to corrosion opening up previously enclosed spaces. 

'As such, the environmental impact of these vessels is still evolving.' 

How do shipwrecks contaminate the environment?

Naval arms races in the nineteenth and twentieth centuries led to the development of increasingly powerful vessels, with ships increasingly made of metal and powered by oil and other fossil fuels.

Whereas their wooden predecessors decayed quickly and left little in the way of contamination, these newer ships left a variety of pollutants behind when they were sunk during skirmishes, battles and accidents.  

The scale of the problem is vast. During the Second World War alone, it is estimated that at least 20,000 ships were sunk around the world, with many more lost during other conflicts throughout this period. 

The most obvious causes of pollution are the contents of the ships themselves. As much as 20 million tonnes of oil and similar fuels were sunk during the First and Second World War, which can affect the growth, reproduction and survival of marine life.

Aside from fuel, the ships also contained millions of tonnes of ammunition, including chemical weapons. Even after the wars were over, significant amounts of ammunition was sunk intentionally as a quick method of disposal, a decision which still causes problems today.

The material of ships themselves can also pose a risk to the balance of marine ecosystems. A lack of iron is common in these environments and limits the growth of phytoplankton. Iron leaching from sunken ships can therefore contribute to algal blooms, which remove oxygen from the water and harm the growth of coral.

Despite the risks they pose, underwater shipwrecks have mostly been left in situ with only a few fully cleaned up. 

As part of an ongoing European project to document, assess and mitigate the risks of North Sea wrecks, researchers investigated a shipwreck off the coast of Belgium to see how 80 years of decay had affected the surrounding area.   

How are bacteria affected by shipwrecks?

The researchers took samples of the sediment and bacteria on and around the V-1302 John Mahn, a vessel under Nazi command which was sunk by RAF aircraft in 1942. A hole left by a bomb in the side of the hull opened the ship's interior to the elements.

The researchers found chemical traces of hydrocarbons emerging from the ship's coal bunker, while TNT and the products of its breakdown were found in the surrounding sediment. Heavy metal particles thought to be from the ship's paint and structure were also found in the nearby area.

Compared to other shipwrecks from this era, such as those powered by oil, the level of contamination is relatively low and within safe levels. 

Despite this, it still has a noticeable impact on the surrounding wildlife. Bacteria such as Rhodobacteraceae, which are known to break down certain compounds found in fossil fuels, were more dominant in contaminated sediments than the wider area.

'As far as we can see for this shipwreck, the changes in the microbial community of the sediment are due to the enrichment of aromatic hydrocarbon degraders, and do not seem to have a significant effect at a higher ecosystem level,' Josefien explains. 

'This is probably because current concentrations of pollutants are below toxic levels and the community is still very diverse.'

While for now the V-1302 is a relatively benign wreck, it may get worse as the ship continues to break down. 

This degradation will also be assisted by climate change, with higher ocean temperatures enhancing the ability of pollutants to dissolve into the water. This will potentially expose marine organisms, including commercial fish, to higher levels of toxic compounds.

As for other wrecks in the North Sea, only detailed examinations of each site will be able to reveal how the battles of the past form part of a continuing war on nature today.

'The impact of each shipwreck is unique, and depends on the age, contents and leakage of the ship,' Josefien says. 'To get a better overview of the total impact of shipwrecks on our North Sea, a large number of shipwrecks in various locations would have to be sampled.'

'This will help to decide which ship wrecks pose a risk to the environment, and by following up on these findings, we can do what needs to be done.'