Dumped chemical weapons

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After World War II, 28 ships were scuttled west of the island of Måseskär, in Skagerrak. Low levels of chemical warfare agents are still detectable in sediment and fish in the area, indicating that the ships’ cargoes contain chemical warfare material.

Low concentrations of chemical warfare agents are also measured in the Gotland Deep in connection to places where dumped chemical weapons are known.

The wrecks west of Måseskär

Low concentrations of mustard gas were measured in the marine sediments near Måseskär island in 1992. In addition, low concentrations of the chemical warfare agent Clark I were recently (2016-2017) found in Norway lobster, flatfish and North Sea shrimp from the area. An additional study in 2019 demonstrated the presence of degradation products of Clark I in locally caught hagfish.

The wrecks are located within an area of ​​five square kilometres. The area is marked on the map and is approximately 20 nautical miles west of the island of Måseskär. Thirteen wrecks have been found in the demarcated area and another fifteen nearby. The wrecks are located at a depth of between 140 and 280 meters.


Several different types of ships were scuttled, including naval ships in different sizes as well as passenger- and merchant ships, which were used for the transportation of materials. They were part of a large number of ships originally located in northern Germany and seized by the Allies after the war. Many of them were in poor condition or damaged. Most were scuttled in 1946-1947 after World War II, in scuttling operations carried out by the Allies. The ships were filled with conventional and/or chemical munitions and then towed or propelled by own machine to deep water areas in the Skagerrak where they were scuttled.

The information available on the amounts of warfare materials that were dumped during these operations is contradictory, but studies describe that at least 170,000 tonnes of chemical weapons were dumped in the Skagerrak during this time[1]. The majority were probably dumped at greater depths outside of Norway in the Arendal deep, but results from the studies carried out in the area west of Måseskär show that chemical weapons were dumped in this area as well. The wrecks are also believed to contain conventional ammunition and smaller amounts of oil.

The chemical weapons were mainly contained by various types of grenades or bombs, intended to be fired from artillery or dropped from aircraft. Prior to the dumping operations, the detonators in the chemical weapons were removed to avoid the risk of explosion. In some cases, the chemical weapons were also stored in other types of containers, such as oil drums.

You can read more about the wrecks west of Måseskär in the Swedish Maritime Administration’s report Environmental hazards with sunken shipwrecks II from 2015 (in Swedish).

In 2016 and 2017, a study was carried out in the dumping area near Måseskär on behalf of the Swedish Agency for Marine and Water Management (SwAM). The investigation involved exploratory fishing near the wrecks and analysis of the catch showed traces of degradation products from chemical warfare agents Clark I and/or Clark II. The results are presented in the report Examination of biota in connection to scuttled ships with chemical ammunition from (in Swedish).

In 2019, a new study was carried out on behalf of SwAM in dumping areas on both the Swedish west and east coast. The purpose was to investigate how widespread the environmental contamination from chemical ammunition is. Exploratory fishing took place in the eastern parts of the dumping area near Måseskär, and in the Gotland Deep close to locations with confirmed mustard gas bombs, which had been identified in previous studies using remotely operated vehicles (ROV).

On the west coast, Norway lobster, North Sea shrimp and hagfish were caught and analyzed. The analytical results of biota showed traces of degradation products from the chemical warfare agent Clark I. Degradation products were detected in a pooled sample from hagfish caught downstream from the wreck Bal141 on the west coast. Both Clark I and II contain arsenic compounds, which may explain observed high levels of arsenic in the sediments around and downstream of the wreck area.

The concentrations detected in the biota have been very low, detectable but below the analytical limit of quantification. How these concentrations of chemical warfare agents affect the fish and crustaceans in the area is unknown.

Warfare agents in the Gotland Deep

During the study in 2019, exploratory fishing was performed near positions of mustard gas bombs in the Gotland Deep. Cod and flounder were caught and analysed, alongside sediment samples.

Degradation products of chemical warfare agents were detected in two of the six pooled samples of cod caught in the area. The products found in cod were Clark I/II and Trifenylarsine, products often included in mustard gas.

All sediment samples contained products of chemical warfare agents, degradation products from Clark I/II, arsine oil and Adamsite. The quantities were measurable but below the limit of quantification. The results indicate that the area close to the dumped material is contaminated by the contents of the dumped warfare agents. Fish in the area do also, to a smaller extent, contain degradation products of chemical warfare agents.

The results are presented in the report Investigation of biota and sediment in connection with dumping areas of chemical ammunition on the west and east coast of Sweden, 2019 (in Swedish).

Risks with chemical warfare agents in biota and sediment

The risks of dispersal of the contents of the dumped chemical warfare material increase over time due to corrosion of the encapsulating casings. Natural current conditions lead to an increased risk downstream dumping areas. The risk of dispersal of the material can be further exacerbated by human sea-floor activities, such as bottom trawling.

The low levels of degradation products detected during the studies in 2016, 2017 and 2019 do not constitute an increased health risk from consumption according to the Swedish Food Agency. However, the presence of degradation products indicates that they may accumulate in the tissue of biota in the areas.

During 2021, another investigation is carried out on behalf of SwAM in the area west of Måseskär, to further investigate how widespread the contamination is. Exploratory fishing is carried out near wrecks, which were not previously examined. The results will add to the existing knowledge of the contamination in the area, which species of fish or other biota that is affected and to what extent. Furthermore, the results will be used as background material to investigate the possibility to limit fishing in the area, with the purpose to reduce the risk of further dispersal of the material.

Published: 2018-10-18
Updated: 2019-05-22