CCQM-P39.1 was organized as a follow-up pilot study in parallel to the key comparison CCQM-K43 after the previous pilot study on tuna fish. CCQM-P39.1 was an activity of the Inorganic Analysis Working Group (IAWG) of CCQM and was coordinated by the Joint Research Centre–Institute for Reference Materials and Measurements (IRMM, Geel, Belgium) of the European Commission (EC). In CCQM-P39.1 the amount contents of As, Hg, Pb, Se and methylmercury (CH₃Hg) in salmon (muscle and skin) were the measurands under investigation. Besides the national metrology institutes (NMIs) also non-IAWG members, expert laboratories for mercury and methylmercury measurements, were invited to participate in this pilot study. Results were reported by six IAWG members and six expert laboratories. During the CCQM-IAWG autumn meeting in Berlin, October 2005, it was agreed that in CCQM-K43 the KCRV is calculated as the mixture model median (MM-median) of all reported results. Therefore in CCQM-P39.1 the reported results are presented graphically with the KCRV from CCQM-K43.

The reported results of the IAWG members fall within a range of ±4% for arsenic and lead relative to the CCQM-K43 KCRV. For mercury, the spread was ±2%, but one IAWG member reported a very large uncertainty on the measurement result. For selenium the spread of IAGW members is ±2% deviation from the CCQM-K43 KCRV. Including the reported results from the invited expert laboratories, the spread of results increased for arsenic, lead and mercury to ±8%. The reported results including the experts fall within a range of ±20% for selenium and ±30% for methylmercury.

The methods applied were isotope dilution mass spectrometry (IDMS) using sector field or quadrupole inductively coupled plasma-mass spectrometry (ICP-MS), external calibration or standard addition using ICP-MS, atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS), atomic emission detection (AED) and electron capture detection (ECD). Instrumental neutron activation analysis (INAA) and k₀-neutron activation analysis (k₀-NAA) were also used as analytical techniques. Each of the five analytes under investigation was measured with at least two of these analytical techniques.

IAEA reported two results for arsenic and lead. They were measured with ICP-MS and AAS, respectively. JSI reported two results for mercury, measured with NAA and AAS, and furthermore two results for methylmercury measured with GC-ECD and GC-CV-AFS.

This report presents the participants' results in CCQM-P39.1 for all analytes under investigation. In Annex 1, the results are displayed with the CCQM-K43 KCRV. In Annex 2, the different approaches for methlymercury measurements are presented in more detail. In Annex 3, the questionnaire data are presented. Annex 4 compiles all the CCQM-P39.1 information documents.

The key comparison CCQM-K43 was carried out in parallel to this pilot study for the same measurands in the same salmon material. Participation was meant for IAWG members, to support their CMCs in Appendix C.

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The final report has been peer-reviewed and approved for publication by the CCQM Working Group on Inorganic Analysis.