Evaluation of surveillance methods for dumped chemical munitions in Skagerrak

This report describes a visual inspection of the condition of three scuttled wrecks in Skagerrak. Landers with blue mussels, European giant file clam, and passive samplers were deployed at one wreck to establish the best monitoring methods for pollution from chemical munitions around the wrecks. In addition, we analysed samples from the annual shrimp survey conducted by the Norwegian Institute of Marine Research. Our goal was not to map the pollution in the area. For that, the number of sampling positions would have been too small. To visually inspect the condition of the wrecks, we used a remotely operated underwater vehicle. We looked for changes in their condition since the last inspection in 2002 and observed whether marine life around the wrecks was normal. Our findings indicate that the wrecks in Skagerrak have not started to collapse, but certain light constructions are on the verge of breaking due to corrosion. The ammunition does not seem to affect marine life in the area. Two of the landers were retrieved after 10-week deployment, while the last one was retrieved after 51 weeks at the sea bottom. We found traces of 4-nitrotoluene, 2,4- and 2,6-dinitrotoluene associated with explosives and decomposition products from chemical warfare agents containing sulphur mustard and arsenic in the analysed samples. The levels do not give rise to concern but show that these compounds are spread over a large area on the sea bottom. Passive samplers of SPMD-EWL type were well suited for collecting chemical warfare agents and related compounds and could be a good alternative to bivalves. A histological examination of the bivalves showed that the blue mussels had passive and partially degraded digestive tissues and severe degradative changes in several tissues. The observed changes indicate that the blue mussels will not be suitable as an indicator organism for long periods under these conditions. The file clam had only moderate tissue alterations, indicating that they had less food available, compared to the reference position at shallow water. The file clam is therefore a suitable surveillance organism for deep water. The concentration of metals in the shellfish were at the same level as elsewhere along the Norwegian coastline and the content of organoarsenic compounds were low. The heavy metal content in shellfish and passive samplers are therefore probably due to metal parts from the wrecks or other sources in the area. Twelve recommendations for further investigations of the wrecks have been set up. The condition of more wrecks with different degree of deterioration should be investigated and the remaining hull thickness measured. Samples of sediments, pore water, and passive samplers from several locations should be analysed to measure how far from the wreck the pollution stretch out, how it is dispersed and how much is available for uptake in biota. The use of blue mussels as indicator for periods up to one month and the usefulness of sponges and other types of passive samples should be evaluated for more efficient sampling. Several of the suggested recommendations should be carried out at the same time and in cooperation with other actors to save money.