Marine ecosystem infested with arsenic

A doctoral research by Hanna Niemikoski, MSc, brings us new information on the impact on sea organisms of compounds leaking from munitions dumped in the Baltic Sea.

In her doctoral research, Hanna Niemikoski proves that phenylarsenic compounds used as chemical warfare agents (CWAs) are accumulating in sea organisms, e.g. fish, caught near the dumping sites. She used in vitro experiments in test tubes in the laboratory to find out how these compounds are transformed by metabolism, and proved their toxicity. Further, previously unreported compounds that have formed from CWAs containing arsenic were identified in the marine sediments collected from the dumping sites.

During the past 15 years, international multidisciplinary research projects have been able to identify munitions dumped in the sea after the world wars, pinpoint their exact locations, and specify their degree of corrosion.

However, the results presented in the thesis are unique, and no one has carried out comparable research before.

These results are important for the risk assessment related to chemical weapons when evaluating the environmental impact of munitions leaking at the bottom of the sea.

Based on the results presented in the thesis, it is important to monitor the presence of these compounds in marine organisms, and in future to also study the concentration levels of biotransformation products identified in the thesis in the sediments near the munitions, in order to know the total burden of chemical warfare agents on the marine ecosystem.

Samples from Bornholm, the Skagerrak Strait, and Måseskär

In her thesis, Niemikoski studied samples of marine organisms, mainly fishes, from three known dumping sites for chemical warfare agents.

In the largest study, muscle samples taken from 99 cods living in the vicinity of Bornholm dumping area, 14% of the analysed samples contained traces of phenylarsenic compounds. Similar results were reached with the samples from the Skagerrak and Måseskär dumping areas. The liver, gill and gall samples of fish were also analysed to gain information on bioaccumulation of studied chemicals after uptake by fish. In total, over 300 samples were analysed.

The study was able to analyse the metabolism of phenylarsenic compounds with in vitro models, as well as to study the toxicity of the main metabolic product is to fish cells.

–The metabolic product causes a toxic response in fish cells, so the metabolism may play an important role when it comes to the level of toxicity of the compounds. The identified compounds that form via metabolism can in future be used as target chemicals for determining the exposure of fish to phenylarsenic compounds, says Hanna Niemikoski.

Previously undescribed compounds found at the bottom of the sea

The thesis research also discovered new breakdown products consisting of phenylarsenic compounds in the marine sediments. The majority of the compounds had not been reported before, and none of them have been observed in marine sediments before.

The research did not specify how these compounds have formed, but the assumption is that they have formed as a result of microbial activities in the marine sediments.

Based on her research, Niemikoski claims that the level of phenylarsenic compounds formed as a result of these microbial activities in the marine sediments surrounding the munitions may be significant.

The thesis research was carried out at VERIFIN, the Finnish Institute for Verification of the Chemical Weapons Convention, a part of the Department of Chemistry at the University of Helsinki. Hanna Niemikoski is currently working as a chemist at the Finnish Environment Institute.

Master of Science Hanna Niemikoski will be defending her thesis at the University of Helsinki on Friday the 8th April 2022. The thesis is titled 'New approach in the assessment of impact of arsenic-based chemical warfare agents on marine environment.' Docent Raimo Ketola from the Finnish Institute for Health and Welfare will act as opponent and Professor Paula Vanninen from VERIFIN as custos. The dissertation will start at 12 noon on the Kumpula campus of the University of Helsinki, in auditorium Exactum CK112.

Contact details: Hanna Niemikoski,, phone +358 29 525 2173