This report presents the results of a proficiency test exercise (PT) focussed on the determination of total cadmium, lead, arsenic, mercury and inorganic arsenic in mushrooms. The exercise was organised in support of the EU Regulation 1881:2006 which sets the maximum levels for certain contaminants in foodstuffs.
Thirty eight participants from twenty six countries registered to the exercise. Only one participant did not report results. The test item used was a blend of mushooms (of the variety Lentinula edodes). The assigned value was obtained as the average of results reported by five expert laboratories having demonstrated experience in the analysis of trace elements in different matrices. The associated uncertainties of the assigned values were computed according to the ISO/IEC Guide 98:2008 (GUM) and following ISO 13528:2005.
Participants were invited to report their measurement uncertainties. Laboratory results were rated with z- and zeta (ζ-) scores in accordance with ISO 13528:2005. The standard deviation for the proficiency assessment was based on the use of the modified Horwitz equation (for inorganic arsenic (19 % of Xref) and for the total mass fraction of lead, 20 % of Xref) while slightly lower percentages were decided, upon expert judgment of the advisory board of this PT exercise and based on previous participants' performance on similar measurands, for the total mass fractions of arsenic and mercury (15 % of Xref) and 10 % of Xref for the total mass fraction of cadmium.
The percentage of satisfactory z-scores ranged from 81 % (inorganic arsenic) to 97 % (total cadmium). Therefore, the outcome of the exercise shows an overall excellent performance for European National Reference Laboratories assuring compliance towards the European legislation related to the determination of the investigated food contaminants.