Thousands of tonnes of ammunition rest at the bottom of the Baltic Sea, vestiges of the 20th century wars. Deliberately immersed after the Second World War, they gradually release toxic explosive substances in water. A study by Geomar Helmholtz Center for Ocean Research Kiel and Leibniz Institute for Baltic Sea Research, published in Chemosphere, reveals the extent of this contamination. The researchers detected traces of TNT, RDX and DNB in almost all the samples of water taken, with critical concentrations in certain areas.
Omnipresent toxic residues in the Baltic Sea
The analyzes, carried out in Kiel bay, reveal TNT levels of several thousand pmol/l. For their part, the RDX and the DNB dominate in the bays of Lübeck and Mecklenburg. There are respective peaks of 1,800 pmol/L and 15,000 pmol/l. Almost all of the 665 samples collected in 2017 and 2018 contained at least one of these compounds. Proof of generalized contamination. Unlike pollutants that attach to sediment, these explosive substances remain mainly in a solution in water. This unfortunately facilitates their diffusion on large areas. This dispersion increases the risk of exposure for marine organizations, including filter fish and invertebrates. They integrate these toxins into their metabolism. Some previous studies have already detected TNT residues in the tissues of certain fish species living near the spill sites.
© Beck et al., 2025
The study estimates that around 3,000 kg of dissolved explosive residues are currently circulating in the water column. In addition, this figure will continue to increase as long as the metallic envelopes of the ammunition is corroded. This progressive degradation leads to a constant release of toxins, evaluated between 3 and 10 kg of TNT per day! The extent of the contamination also depends on the nature and the location of ammunition deposits, often very concentrated in certain areas. In Kolberger Heide, thousands of mines and shells are dispersed on the seabed. According to oceanographic models, the dissolution of explosives could continue for more than 800 years. Although current concentrations remain below the treble toxicity thresholds for marine fauna, certain measured levels, especially for DNB, approach critical thresholds. Concerns appear concerning the chronic effects of prolonged exposure.
A threat amplified by climate change
The corrosion of submerged ammunition is a chemical process strongly influenced by environmental conditions. The rise in temperatures accelerates the oxidation of metal envelopes, thus facilitating the release of explosive compounds such as TNT, RDX and DNB in water. The increase in storms and marine currents also amplifies this dispersion by pretending to be contaminated particles. It also promotes contact between seawater and degraded shells. In Kolberger Heide, a particularly polluted area, the researchers observed that storms temporarily increased TNT in water. They suggest that extreme climatic episodes therefore contribute to the rapid mobilization of explosive residues. These phenomena complicate remediation strategies. Indeed, they make contamination more dynamic and unpredictable in time.
The study managed to integrate these factors into an oceanographic model to simulate the dispersion of explosive pollutants according to seasonal variations. The results show that TNT concentrations are significantly higher in summer. For what ? Because during this period the thermal stratification of water limits vertical brewing. She thus traps toxins in the deep layers. But in winter, cooling and storms promote a more effective mixture of the water column, partially diluting the contaminants. However, this dilution does not mean elimination …
A global problem requiring targeted actions, but not only in the Baltic Sea
The presence of submerged ammunition is a global problem, it far exceeds the borders of the Baltic Sea. According to the authors, the German seabed contains approximately 300,000 tonnes of explosive residues, but this situation is found elsewhere. European waters are home to more than 1.6 million tonnes of ammunition (Böttcher et al., 2011). Note also that historical deposits extend to the American and Asian ribs. This war waste gradually releases toxic substances that accumulate in the marine environment. They affect fauna and fishery resources.
Recall that these pollutants do not just dilute. They persist in the form of dissolved compounds and residues accumulated in sediments, extending their toxicity over centuries. Faced with this long -term contamination, researchers recommend classifying these ammunition as ” emerging historical contaminants ». They in fact require specific remediation measures adapted to the chemical and physical characteristics of explosives.
Germany is the first country to set up a large -scale depollution program for these submerged ammunition. In 2024, the federal government launched a pilot project for recovery and ecological destruction of explosives in the Baltic Sea. The budget amounts to 100 million euros. The operations started in Lübeck bay, identified as one of the main foci of contamination by the RDX and the DNB. The objective is twofold: withdraw the most degraded shells and mines to limit chemical pollution and test an innovative technological approach.
Germany is developing an autonomous submarine demining platform, capable of identifying, extracting and treating on-site ammunition by controlled incineration. This device, in the experimental phase, could be deployed on a larger scale if the results are conclusive.
Munitions lost at sea a bulky heritage that resurfaces
While Germany is engaged in a vast operation of depollution of immersed ammunition in the Baltic Sea, other countries still seem to have difficulty in trace of their explosives … In Australia, a simple walker discovered on a beach an lost training torpedo for several months after a military exercise. If the machine was harmless, the incident recalls that weapons, whether forgotten underwater for decades or lost by accident, always end up.
A reality which, between environmental issues and security challenges, can no longer be ignored. Perhaps it is time for the oceans to cease to be treated as military dumps, because sooner or later the sea always gives what it is entrusted to it.
Source: Aaron J. Beck et al, “Widespread Environmental Contamination from Relic Munitions in the Southwestern Baltic Sea”, Chemosphere (2025).
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