POLLUTION STATUS OF NORTH-SEA SEDIMENTS - AN INTERNATIONAL INTEGRATIVE STUDY

This paper describes the pollution status of North Sea sediments, and is based on results of sediment testing conducted during the Bremerhaven Workshop designed to test various methods (chemical and biological) for assessing the status of North Sea waters, sediments and biota. Testing comprised 2 transects, one down current from an abandoned drilling site, and the other across the German Bight from the mouth of the Elbe northwest. Sediment methods focused on toxicity testing, chemical analyses, and measures of in situ benthic community structure. Together these 3 methods comprise the Sediment Quality Triad. Using the Triad in a burden-of-evidence approach, it was determined that sediments nearest the Elbe are moderately polluted (pollution is defined as contamination, toxicity and benthic community alteration), and that sediments offshore and at Dogger Bank are unpolluted. Sediments nearest the drilling site show evidence of relatively low level toxicity and benthic community alteration. Limited chemical measurements did not indicate contamination. Observed laboratory toxicity and alterations in benthic infauna community structure may be due to unmeasured toxic chemicals. Anticipated effects due to drilling were not observed and appear to have been ameliorated by natural deposition of clean sediment. North Sea sediments away from point sources of pollution (e.g. coastal areas, drilling platforms) are expected to be unpolluted. Lesions in bottom fish in such offshore areas (e.g. the Dogger Bank) cannot be attributed to sediment pollution in these areas, but if they are truly indicative of anthropogenic pollution, could be due to other factor(s) such as exposure of planktonic larvae to sea surface microlayer chemical contamination and toxicity. Integrative assessments such as the Triad are essential for adequately assessing the status of European marine ecosystems. Although relatively expensive, such complete studies determine and prioritise problem areas such that managers, regulators and the public have access to the best possible information for decision-making and resource allocation.