Sea-dumped ammunition as a possible source of mercury to the Baltic Sea sediments

After World War II, as a move toward Germany demilitarization, up to 385,000 t of munitions were sunk in the Baltic Sea. Munition containing various harmful substances, including chemical warfare agents (CWA) and explosives, that can affect marine biota were dumped on the seafloor. Some of those objects contained mercury, either as elemental mercury or mercury compounds (e.g., mercury fulminate, a common explosive primer), and thus could act as a specific local source of mercury in the dumping areas. Unfortunately, there is a lack of information on how dumped munitions impact the mercury concentrations in the Baltic Sea sediments. This report aims to answer the question how much sedimentary mercury in the dumping areas originates from munitions and to determine to what extent the mercury present in those areas originates from mercury fulminate. Concentrations of total sedimentary mercury- Hg_TOT in samples collected from conventional (Kolberger Heide) and chemical (Bornholm Deep) munitions dumping sites are characterized by high variability. However, an increase in Hg_TOT concentrations was observed with a decreasing distance to particular munition objects at both study sites. Moreover, mercury speciation in sediments from Kolberger Heide proves that the mercury there can be traced back directly to mercury fulminate. Results of our study confirm that munitions dumpsites are a local point sources of mercury. Due to the ecosystem constrains, varying transport modes and pathways, and both unknown and varying decomposition rates, these sea-bed mercury concentrations are hard to evaluate quantitatively. Therefore we recommend that further detailed studies should be conducted to assess sedimentary mercury provenience in munitions dumpsites more accurately.