Towards a good environmental status: a 4-year monitoring study on the contamination of the Bay of Luebeck with energetic compounds prior to munitions remediation

In the Bay of Luebeck, two out of several munition dumping areas in the German Baltic Sea are located, where approximately 65,000 t of munitions were dumped in the post-World War II period. The explosives used in these munitions, such as the nitroaromatic compound 2,4,6-trinitrotoluene (TNT) and its metabolic transformation products 4-amino-2,6-dinitrotoluene (4-ADNT) and 2-amino-4,6-dinitrotoluene, (2-ADNT) are considered mutagenic and carcinogenic and pose a potential threat to marine ecology and human health when they leak from corroding shells into the surrounding water. A 4-year pilot monitoring program, conducted in collaboration with the Ministry of the Environment of Schleswig-Holstein, aimed to assess the current contamination level of the Bay of Luebeck's waters with various energetic compounds (EC) from dumped munitions and to evaluate the feasibility of integrating these investigations into the monthly routine sampling program of Schleswig-Holstein's coastal waters. This routine water sampling was expanded by direct monitoring of specific munition dumping sites in the Bay of Luebeck. Beyond repeated water samples, these specific dumping areas were long term monitored by using blue mussels and passive sampler systems which both are ideal approaches to infer whether these compounds are entering marine ecosystems such as in the Bay of Luebeck. In all water samples from the routine program collected monthly at four locations from the seabed and surface, TNT and six other EC were detected. However, only 1,3-dinitrobenzene (1,3-DNB), 2,4-dinitrotoluene (2,4-DNT), and 1,3,5-trinitro-1,3,5-triazine (RDX) were measured at average concentrations exceeding 1 ng/L. As expected, TNT water concentrations at the specific dumping arears were slightly higher (by a factor of 2-4) compared to the routine monitoring sites. At the same locations, EC were detected in a few individual blue mussel samples, with all concentrations remaining below 0.6 ng/g dry weight. EC concentrations in the passive samplers were in the one or two-digit nanogram range per passive sampler, except for 1,3-DNB which reached up to 105 ng per passive sampler. As a conclusion, over the course of the last 3 years, it became apparent that EC are ubiquitous distributed in the Bay of Luebeck, but their concentrations are still relatively low, even in both specific dumping areas.