What should be done with chemical weapons found on the bottom of the Baltic Sea? Research efforts continue under the DAIMON 2 project

After the Second World War, chemical weapons produced during World Wars, were captured by the Allies and disposed of by sea-dumping. The intentions may have been good, but the problem was not eliminated. In fact, the opposite is true.

Soon it was noticed that the dumped weapons and the parts of the containers ended up in fishers’ nets or drifted to the shores. Decades later, it was realized that toxic chemical warfare agents are leaking into the surrounding marine environment. The rate of leakage increase as the barrels rust, most likely affecting the entire marine ecosystem.

An enormous task to tackle

Gathering the documentation on the dumping sites already began in the 1990s. Despite the surveying commencing at the same time, only the major dumping sites located in the Baltic Sea area are currently known.

Recently, offshore constructions involving utilization of the sea floor, such as gas pipelines and wind power stations have raised the interest of   companies and governments in this problem dealing with dumped munitions. The offshore investments cannot be safely constructed if there are dumped chemical munitions in the same area on the seabed.

The first sediment samples collected from dumping site were already analysed 15 years ago at VERIFIN, the Finnish Institute for the Verification of the Chemical Weapons Convention operating under the Department of Chemistry, University of Helsinki.

“At the time, it was already confirmed that mustard gas and phenylarsenic compounds were leaking into the surrounding marine ecosystem,” says Professor Paula Vanninen, director of VERIFIN.

Studies carried out in recent years at VERIFIN have demonstrated that Clark compounds and other chemical warfare agent-related phenylarsenic compounds are leaking into sediment are also uptake by marine biota. The primary degradation products of phenylarsenic chemical warfare agents have been found in marine biota samples (e.g. fish and lobsters) collected from three different known dumping areas in the Baltic Sea area.

The most recent study revealed that 14% of the cod samples taken from the Bornholm dumping area contained traces of phenylarsenic compounds originating from dumped chemical weapons.

A doctoral thesis by Hanna Niemikoski, to be preliminarily examined in autumn 2020, describes the identification of new degradation products formedfrom phenylarsenic compounds used as warfare agents, in seafloor sediments. The compounds are most likely the result of microbial activity, and there is no research-based knowledge on their behaviour and impact on the marine ecosystem. The thesis also investigates the metabolism of the compounds using in vitro models. In addition to the primary degradation products, some of the identified metabolites have been found in fish caught from the dumpsites.

DAIMON produces research-based knowledge in support of decision-making

Governments and authorities have to constantly weigh up the situation and assess the risks related to dumped munitions. Is salvaging badly damaged barrels riskier than leaving them at the dumping sites for now? There are no simple solutions.

VERIFIN has participated in EU-funded joint projects carried out by the countries bordering the Baltic Sea, finding the best solutions to this problem. In the DAIMON 2 project, an online software, Decision Support System (DSS), has been developed to support decision-making. In DAIMON 2, the tool will be developed further to serve as guidelines in various circumstances.

“We are analysing sediment samples on behalf of our clients, in addition to which we will continue the development of relevant techniques. Our aim is to recruit a new doctoral student in autumn 2020 after Hanna Niemikoski has defended her doctoral thesis in either autumn 2020 or spring 2021,” says Vanninen.

Further information:

Paula Vanninen, research director
Email: paula.vanninen@helsinki.fi
Phone: +358 40 5502204

Published studies and links to research project websites:



Höher, N., Turja, R., Brenner, M., Nyholm, J. R., Östin, A., Leffler, P., Butrimavičienė, L., Baršienė, J., Halme, M., Karjalainen, M., Niemikoski, H., Vanninen, P., Broeg, K., Lehtonen, K. K., & Berglind, R. (2019). Toxic effects of chemical warfare agent mixtures on the mussel Mytilus trossulus in the Baltic Sea: A laboratory exposure study. Marine Environmental Research, 145, 112–122. https://doi.org/10.1016/j.marenvres.2019.02.001

Lastumäki, A., Turja, R., Brenner, M., Vanninen, P., Niemikoski, H., Butrimavičienė, L., Stankevičiūtė, M., & Lehtonen, K. K. (2020). Biological effects of dumped chemical weapons in the Baltic Sea: a multi-biomarker study using caged mussels at the Bornholm main dumping site. Marine Environmental Research.

Niemikoski, H., Söderström, M., & Vanninen, P. (2017). Detection of Chemical Warfare Agent-Related Phenylarsenic Compounds in Marine Biota Samples by LC-HESI/MS/MS. Analytical Chemistry, 89(20). https://doi.org/10.1021/acs.analchem.7b03429

Niemikoski, Hanna, Koske, D., Kammann, U., Lang, T., & Vanninen, P. (2020). Studying the metabolism of toxic chemical warfare agent-related phenylarsenic chemicals in vitro in cod liver. Journal of Hazardous Materials, 122221.

Niemikoski, Hanna, Soderstrom, M., Kiljunen, H., Östin, A., & Vanninen, P. (2020). Identification of novel degradation products of sea-dumped chemical warfare agent-related phenylarsenic chemicals in marine sediment. Analytical Chemistry.

Niemikoski, Hanna, Straumer, K., Ahvo, A., Turja, R., Brenner, M., Rautanen, T., Lang, T., Lehtonen, K. K., & Vanninen, P. (2020). Detection of chemical warfare agent related phenylarsenic compounds and multi-biomarker responses in cod (Gadus morhua) from munition dumpsites. Marine Environmental Research.

Vanninen, P., Östin, A., Bełdowski, J., Pedersen, E.A., Söderström, M.,Szubska, M., Grabowski, Mił., Siedlewicz, G., Czub, Michał., Popiel, Stanisł., Nawała, J., Dziedzic, D.,Jakacki, J., Pączek, Bartł. (2020). Exposure status of sea-dumped chemical warfare agents in the Baltic Sea, Marine Environmental Research (2020), doi: https://doi.org/10.1016/j.marenvres.2020.105