Biological effects of munition left on war wrecks on the health of caged blue mussels (Mytilus edulis, L.) in the southern North Sea

The North Sea was the scene of many naval battles during both World Wars. As a result, military ships, civilian merchants, and cargo vessels sank. Today, the German Maritime Museum in Bremerhaven, Germany, suspects approx. 240 wrecks in Danish, at least 100 in Belgian and about 120 military wrecks including airplanes in the German EEZ and territorial waters. Many of these wrecks were partially or fully loaded with munition at the time of the sinking. However, based on archive information, visible inspections or survey reports only rough estimates about remaining quantities of munition on or in the vicinity of these wrecks can be made. After 75-100 years in the marine environment munition shells are corroding and start leaking chemicals of their explosive cargo into the marine environment. They main component of munition is 2,4,6 trinitrotoluene (TNT). Next to its ability to explode, TNT is also known for its toxicity and for being carcinogenic and mutagenic. In order to test for leaked explosives in the surrounding waters, sediments and biota field studies were conducted on wrecks sites in Belgium, Germany and Denmark. The measured concentration of explosive were subsequently correlated with potential health impairments, using blue mussels (Mytilus edulis) deriving from munition free site. These mussels were exposed for several weeks in steel cages on or near three wrecks sites. In Belgian waters the KW 58 Hendricus a transport vessel loaded with several tons of landmines sunken during WW II was selected for this investigations. In German waters the light cruiser SMS Mainz laying approx. 40sm west of the island of Heligoland was chosen and in Danish waters a German mine laying submarine (UC30) situated a few miles west of Esbjerg was investigated using caged blue mussels. Three to four cages filled with blue mussels were placed at different locations on each of the three wrecks. At the end of the exposure time mussels were retrieved and first examined for mortality, subsequently dissected and analysed in the lab for biomarker responses according to a multi-biomarker approach. First results show very different water concentrations around the wreck sites ranging from low ng/L of dissolved TNT up to the µg/L and mg/L level. Further, also the uptake of TNT by mussels could be proven resulting in measurable biomarker responses of the exposed blue mussels.