Proficiency test for heavy metals in compound feed

The here described proficiency test for heavy metals in compound feed was organised by RIKILT, Wageningen UR in accordance with ISO 17043. RIKILT Wageningen UR has an ISO/IEC 17043 accreditation for proficiency tests of residues in products of animal origin. However, this specific test is not part of the accreditation. The primary goal of this proficiency test was to give laboratories the opportunity to evaluate or demonstrate their competence for the analysis of heavy metals in compound feed. For this proficiency test, two test materials were dispatched. The heavy metal concentration in each material is given in mg/kg with a moisture content of 12%: • Chicken feed with a consensus value of 0.37 mg/kg cadmium and 5.2 mg/kg lead (A); • Chicken feed with a consensus value of 0.62 mg/kg cadmium and 3.0 mg/kg arsenic (B). The fortified materials were prepared by spiking a slurry of commercially obtained chicken compound feed, followed by extensive mixing and freeze-drying. Homogeneity assessment showed that all materials were sufficiently homogeneous for proficiency testing. The stability test demonstrated no statistically significant loss of cadmium, lead or arsenic from the materials during the timescale of the proficiency test. Twenty-one European laboratories participated in this proficiency test and submitted results in time. For test material A, twenty laboratories reported quantitative results and one laboratory reported a screening result for cadmium and for lead, twenty-one laboratories reported quantitative results. For test material B, twenty-one and nineteen laboratories reported quantitative results for respectively cadmium and arsenic. Two laboratories did not report quantitative results for arsenic due to the absence of the compound in their scope. Fifteen laboratories reported details of the applied extraction method. Twelve of the fifteen laboratories applied comparable digestion methods for sample preparation and in general used ICP-MS (six laboratories