Methylmercury (MeHg) is known to be extremely toxic, which is of particular concern since this compound is widespread in the environment. The lack of knowledge of toxical impact of MeHg in sediment (e.g. on filter-feeding organisms) and the need to better understand the environmental pathways justifies the monitoring of this compound in various matrices (biota, water and sediment). Legislation on MeHg within the European Union, e.g. in food (national regulations) or water (EC Directives), requires that the determinations are of proven quality which justifies the preparation of representative certified reference materials.

The project aimed to evaluate the state-of-the-art of methylmercury determination in sediment through an interlaboratory study involving 15 expert EU laboratories and to subsequently certify a sediment reference material for its total Hg and MeHg contents (CRM 580).
The project successfully demonstrated the feasibility of preparation of a sediment reference material containing stable content of MeHg and showed that the state-of-the-art was good enough to contemplate certification. The certification was concluded in 1996 and the sediment CRM was certified for its total Hg and MeHg contents as planned in the work programme. The material is now available at the IRMM (Report EUR 17658 EN, 1997).
The project consisted in (1) a feasibility study for stabilising a reference material containing MeHg (using gamma-irradiation), (2) an interlaboratory study, (3) the preparation of a large batch of candidate sediment reference material, (4) the organisation of a certification campaign, and (5) the technical and statistical evaluation of the results.