Tracking explosive contaminants from dumped munition in the western Baltic Sea via urine and bile analysis of three flatfish species

Background Dumped munitions in German coastal waters, particularly the explosive 2,4,6-trinitrotoluene (TNT), may pose significant environmental risks. TNT and its metabolites, such as 2-amino-4,6-dinitrotoluene (2-ADNT) and 4-amino-2,6-dinitrotoluene (4-ADNT), contaminate marine organisms, including fish. These TNT metabolites bioaccumulate in fish tissues, serving as markers for environmental monitoring. Traditionally, fish bile has been a primary matrix to investigate TNT exposure; however, the present study is the first to explore the use of fish urine to detect TNT metabolites. Three flatfish species, common dab (Limanda limanda), European plaice (Pleuronectes platessa), and European flounder (Platichthys flesus) from three regions with munition dumping sites in the Western Baltic Sea were investigated. Results Differences in the levels of contamination at the dumping sites are reflected in the concentrations of explosives found in the urine and bile. Fish from the Kolberger Heide dumping site in Kiel Bight exhibited the highest concentrations of explosive contaminants. In individual dab, contamination with 2-ADNT was recorded up to 26.356 ng/ml in bile and 36.120 ng/ml in urine. Concentrations of 4-ADNT ranged up to 95.908 ng/ml in bile and 26.877 ng/ml in urine. The patterns of TNT metabolites in urine and bile varied, and the concentrations of these metabolites in urine and bile did not always correspond in individual fish. However, the different mean contamination levels in the three regions were reflected in both: urine and bile. Contamination levels of explosives in the three regions decreased in the order Kiel > Schlei > Lübeck. Conclusions TNT metabolites were detected in fish urine for the first time. Urine and bile can serve as useful matrices to assess environmental exposure of fish to TNT. Additionally, dab, plaice and flounder can be utilized in studies focusing on the analysis of explosives in bile or urine. The present study supports the development of fish urine usage for reliable and effective monitoring strategies for explosives.