After World War I and World War II, officials decided to dump hundreds of thousands of metric tons of munitions into the oceans around Europe, which at the time appeared to be the most easily accessible disposal ground. Some of those weapons — including mines containing mustard gas — were simply dropped into the Baltic and North seas in the heart of Europe rather than being taken to faraway dump sites near the Arctic Circle.

But the hidden legacy of those world wars may come to haunt the continent for decades to come.

This week, the Belgian newspaper Het Laatste Nieuws reported that officials have grown concerned that one of those dump sites — close to the Belgian coastal municipality of Knokke-Heist — has started to leak. At the site, two out of 23 probed locations showed signs of contamination, the paper said. The revelation followed months of official inquiries into what authorities fear could be a mounting public safety threat.

Used as a potentially deadly chemical agent during World War I, mustard gas can burn victims’ skin, respiratory tract and eyes.

If confirmed, the leaks would hardly come as a surprise to other officials around Europe. They see themselves in a race against time to prevent the leaking of deadly gases and other hazardous substances, but they have struggled to have their concerns heard.