Together with elements like cadmium, lead, mercury and arsenic, the element chromium appears very frequently in lists of toxic substances of national regulations (water, sewage sludge etc.) and EC directives. In most cases the knowledge of the total chromium content is sufficient for impact studies as well as for the evaluation of long term trends and biochemical pathways. The increasing awareness for quality assurance in analytical laboratories will enhance the demand for reference materials certified for chromium. This need, combined with the difficulties arising in the determination of this element, justified the production of additional reference matrices certified for their chromium content.

The aim of the project was to certify the chromium content in five reference materials, namely rye grass (CRM 281), beech leaves (CRM 100), aquatic plant Trapa natans (CRM 596), fly ash (CRM 038) and sewage sludge (CRM 597).
The five CRMs have been certified in 1996 and are now available at the IRMM (Report EUR 16840 EN, 1996).
The programme consisted in the preparation of two new reference materials (CRMs 596 and 597) and the verification of their homogeneity, the organisation of a certification campaign involving 9 EU laboratories, and the technical and statistical evaluation of the results.