Up to 100,000 tons of Nazi chemical weapons dating to the end of World War II may be lying at the bottom of the Baltic Sea, according to a report warning of the toxic dangers of the aging weapons.

Polish daily Gazeta Wyborcza said that it was difficult to get an exact estimate of the number of bombs, barrels and mines on the bottom of the Baltic. But they said the best guess is approximately 40,000 to 100,000 tons.

The long forgotten chemical weapons are likely mostly barrels of mustard gas, aerial bombs, and chemical warfare agent containing mines. The mines would likely be full of mustard gas and arsenic.

The danger is that each bomb full of mustard gas could pollute up to 230 square feet of water, destroying animals and plants, the Polish Academy of Sciences said in a study.

In the years after World War II, unused Nazi weapons were buried in the Baltic Sea by a tripartite commission made up of the United States, the United Kingdom and the USSR.