Determinations of pollutants in various matrices are routinely performed by a number of organizations for monitoring contamination levels of the marine environment. Projects for improving the quality of determinations of trace metals in seawater have been successfully concluded within the scope of the BCR-Programme (now renamed Standards, Measurements and Testing Programme) of the European Commission; however, the determination of total mercury could not be considered at this stage both because of the poor analytical performances observed and the unsuitability of the containers (polyethylene) used for the seawater certified reference material (CRM 579). A specific project has therefore been organized to improve the state of the art of Hg determination in seawater and to investigate the best way of storing a candidate CRM. Two interlaboratory studies have been concluded and a certification campaign has now started. The materials have been collected in the Southern Bight of the North Sea, carefully prepared (filtered and acidified) and their homogeneity and stability were verified. This paper presents the results of the two interlaboratory studies.

A wide range of certified reference materials is needed for the quality control of analyses performed in the frame of marine environmental programmes. As a response to this need, the Measurements and Testing Programme (formerly BCR) has conducted an interlaboratory project to certify the total mercury content of a sea-water reference material. This paper describes the preparation of the reference material, its homogeneity and stability studies and the analytical work performed for the certification of total mercury (1.85 ± 0.20 ng kg 21 ).

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