800-year pollution threat from WWII munitions detected in Baltic Sea

The southwestern Baltic Sea contains 3,000 kilograms of toxic chemicals leaking from unexploded ordnance (UXO), according to a GEOMAR Helmholtz Centre for Ocean Research Kiel study. Without intervention, contamination will increase as metal casings corrode, continuously releasing toxic compounds for an estimated 800 years.

Water samples taken in 2017 and 2018 showed contamination across the region, with high concentrations in the Bights of Kiel and Lübeck.

While current levels remain below immediate health risk thresholds, researchers warn that corrosion will accelerate contamination if UXO is not removed, said GEOMAR.

It is estimated that around 300,000 tons of UXO remain in the German Baltic Sea, mostly dumped after World War II. These sites are well documented, with ordnance mapped via underwater robots. However, toxic compounds are said to be spreading beyond dumping areas. Corrosion is steadily releasing chemicals, a process intensified by rising temperatures and stronger storms linked to climate change.

Water samples taken from the Bay of Kiel and the Bay of Lübeck in 2017 and 2018 revealed widespread contamination. Toxic substances from munitions – TNT (2,4,6-trinitrotoluene), RDX (1,3,5-trinitro-1,3,5-triazine), and DNB (1,3-dinitrobenzene) – were detected in nearly all samples. While concentrations remain below drinking water limits and toxicological thresholds for marine life, some levels approached critical values, GEOMAR noted.

“Unexploded ordnance contains toxic substances such as TNT (2,4,6-trinitrotoluene), RDX (1,3,5-trinitro-1,3,5-triazine), and DNB (1,3-dinitrobenzene), which are released into the seawater when the metal casings corrode,” said Lead Author Aaron Beck, Geochemist at GEOMAR.

“These compounds pose a threat to the marine environment and living organisms as they are toxic and carcinogenic.”

Contamination levels differ by region. High TNT concentrations were detected in the Bay of Kiel, while RDX and DNB levels were higher in the Bay of Lübeck. According to GEOMAR, most chemicals were found in dissolved form, rather than bound to sediments or suspended particles.

The study highlights UXO contamination as an international problem. Researchers urge the classification of dumped ordnance as “historical contaminants of emerging concern” and call for targeted remediation efforts.

“Unlike diffuse pollution sources, UXO exists in a concentrated, already packaged form. This means it can be physically removed from the environment,” Beck said. 

“With war relics, at least one environmental stressor can be permanently eliminated from the marine ecosystem.”

In August 2024, Germany allocated €2.4 million to a project led by north.io and GEOMAR Helmholtz Centre for Ocean Research Kiel, aimed at enhancing maritime security around critical subsea infrastructure using big data and artificial intelligence (AI).