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In order to control the quality of rare earth determinations in environmental matrices, the Standards, Measurements and Testing Programme (formerly Community Bureau of Reference, BCR) of the European Commission has started a project, the final aim of which is to certify four types of matrices (tuna muscle, mussel tissue, aquatic plant and estuarine sediment) for their contents of a range of rare earth elements (Sc, Y and the lanthanides: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu). The elements U and Th were added to the study. The first part of this project consisted of an interlaboratory study which aimed to test the feasibility of preparation of environmental reference materials and to detect and remove most of the pitfalls observed in rare earth determinations. This paper presents the preparation of the four matrices for the intercomparison study and for the candidate reference material. The main results are presented of the interlaboratory study that was carried out prior to the certification campaign. This collaborative trial is the first attempt ever carried out at this scale to evaluate the state-of-the-art of rare earth determinations in the environment. Its impact on the improvement of chemical measurements will have positive effects on the comparability of data necessary for environmental monitoring.

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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