PT-2016-NRL-TE-FASFC Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers

Transcription

1 CODA-CERVA Veterinary and Agrochemical Research Centre Belgian National Reference Laboratory for Trace Elements in Food and Feed PT-2016-NRL-TE-FASFC Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers Final report on the 2016 Proficiency Test organised by the National Reference Laboratory for Trace Elements in Food and Feed 29 September 2016 Dr ir Karlien Cheyns and Dr ir Nadia Waegeneers Central office Veterinary Operational Directions: Groeselenberg 99, B-1180 Brussels Tel. +32 (0) Fax +32 (0) (general) +32 (0) (director)) +32 (0) (dispatching) Agrochemical Operational Direction: Leuvensesteenweg 17 B-3080 Tervuren Tel. +32 (0) Fax +32 (0) Experimental centre Kerklaan 68 B-1830 Machelen Tel. +32 (0) Fax +32 (0) website :

2 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 2 Summary From the 1 st of January 2008, the laboratory for Trace Elements in the Veterinary and Agrochemical Research Centre (CODA-CERVA), Tervuren, operates as National Reference Laboratory for Trace Elements in Food and Feed (NRL-TE). One of its core tasks is to organise proficiency tests (PTs) among laboratories appointed by the Federal Agency for the Safety of the Food Chain. This report presents the results of the proficiency test organised by the NRL-TE which focused on the determination of trace elements rice wafers. The results from the PT were treated in CODA-CERVA, Tervuren. The 2016 PT was obligatory for all laboratories approved for the analysis of heavy metals in foodstuff by the Federal Agency for the Safety of the Food Chain (FASFC). Ten laboratories registered for and participated in the exercise. The test material used in this test was a rice wafer, bought in a local supermarket. The choice for this matrix was based on the implementation of maximum levels for inorganic arsenic in rice and rice products from the 1st of January 2016 (Commission Regulation (EC) No 2015/1006 [1]). The material was homogenized and used as such as PT material. Each participant received approximately 15 mg of homogenized test material. Participants were invited to report the mean value and measurement uncertainty on their results for arsenic (As), inorganic arsenic (As i ), cadmium (Cd), lead (Pb), copper (Cu) and zinc (Zn). The assigned values (x a ) and their uncertainty (u(x a )) were determined as the consensus of participant s results. Standard deviations for proficiency assessment were calculated using the modified Horwitz equation. Of the ten laboratories that registered for participation, ten submitted results for As, Cd, Cu and Zn; nine submitted results for Pb and four submitted results for As i. The laboratories performed excellent with only one z-score which was questionable. Only three of the calculated ζ-scores were unsatisfactory. It was a successful exercise and the laboratories have proven their competence to measure the concerned trace elements in the matrix.

3 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 3 Introduction Trace elements occur in varying amounts as natural elements in soils, plants and animals, and consequentially in food and feed. Concerning food and feed of plant origin, the characteristics of the soil on which the plants are grown have a considerable influence on the content of trace elements in the plant. The concentration of trace elements in plants is often correlated to the corresponding concentrations in the soil on which they were grown, but also soil texture, soil ph and soil organic matter content influence the trace element content in the plants. To ensure public health, maximum levels for trace elements in foodstuff have been laid down in the Commission Regulation (EC) N o 1881/2006 [2]. Scientific opinions of the European Food Safety Authority (EFSA) Panel on Contaminants in the Food Chain (CONTAM Panel) have led to developments of this commission regulation. The EFSA CONTAM Panel adopted an opinion on arsenic in food on 12 October The scientific opinion concluded that with the estimated dietary exposure to As i in Europe there was a possibility of a risk to some consumers. Rice waffles, rice wafers, rice crackers and rice cakes can contain high levels of inorganic arsenic and these commodities can make an important contribution to the dietary exposure of infants and young children. Therefore, a specific maximum level for these commodities should be envisaged (Figure 1, [1]). Figure 1 : Snapshot of maximum limits of As i (mg/kg) in foodstuff as published in [1]. An extra note was added by Commission Regulation (EC) No 333/2007[3] which states that Methods for analysis for total arsenic are appropriate for screening purpose for control on inorganic arsenic levels. If the total arsenic concentration is below the maximum level for inorganic arsenic, no further testing is required and the sample is considered to be compliant with the maximum level for inorganic arsenic. If the total arsenic concentration is at or above the maximum level for inorganic arsenic, follow-up testing shall be conducted to determine if the inorganic arsenic concentration is above the maximum level for inorganic arsenic. The EFSA CONTAM panel scientific opinion of 2009 concluded that the mean dietary exposures to cadmium in European countries are close to or slightly exceeding the Tolerable Weekly Intake (TWI) of 2,5 µg/kg body weight. Certain subgroups of the population may exceed the TWI by about 2 fold. The CONTAM Panel further concluded that, although adverse effects on kidney function are unlikely to occur for an individual exposed at this level, exposure to cadmium at the population level should be reduced. This opinion resulted in lower maximum limits for Cd in certain matrices [4]. The panel also concluded that processed cereal based foods and other baby foods for infants and young children are an important source of exposure to cadmium for infants and young children. A particular maximum level of cadmium (0.040 mg/kg) was therefore established for processed cereal based and

4 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 4 other baby foods for infants and young children (Figure 2). This maximum level is thus applicable on rice wafers if they are intended and labeled for infants and young children. The maximum limit for cadmium in rice is 0.20 mg/kg. Figure 2 : Snapshot of maximum limits of Cd (mg/kg) in processed cereal-based foods and baby foods for infants and young children as published in [4]. The EFSA CONTAM panel scientific opinion of 2010 identified a need to reduce exposure of Pb due to concern over possible neurodevelopmental effects in young children. This resulted in a specific maximum limit for Pb in processed cereal-based foods and babyfoods for infants and young children. So when rice wafers are processed and labeled for infants and young children, a specific maximum limit is applicable according to Commission Regulation (EU) 2015/1005 [5], (Figure 3). The maximum limit for Pb in cereals is 0.20 mg/kg. Figure 3 : Snapshot of maximum limits of Pb (mg/kg) in processed cereal-based foods and baby foods for infants and young children as published in [5]. There is currently no European legislation regarding Cu or Zn in rice wafers. The scope of this PT was to test the competence of the participating laboratories to determine the total mass fraction of As, As i, Cd, Pb, Cu and Zn in rice wafers.

5 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 5 Time frame, test material and instructions to participants Invitation letters to this PT were sent to participants in April (Annex 1). The 2016 PT was obligatory for all laboratories approved for the analysis of heavy metals in foodstuff by the Federal Agency for the Safety of the Food Chain (FASFC). Ten laboratories, which were approved for these foodstuffs, registered for and participated in the exercise. The samples were dispatched to the participants by the end of May Reporting deadline was the 24th of June. This year the test material was a sample of rice wafers. The rice wafers were purchased in a local supermarket and were not specifically labeled for infants and young children. The material was milled and homogenized for 24 hours and divided in small portions of about 15 g. These portions were dry and dark stored at room temperature. The homogeneity of the test materials was tested following the recommended procedure according to IUPAC [6]. All the trace elements appeared to be homogeneously distributed in the samples (Annex 2). Each participant received the test material samples, an accompanying letter (Annex 3) with instructions on sample handling and reporting (Annex 4), a form that had to be sent after receipt of the samples to confirm their arrival (Annex 5) and a reporting form (Annex 6). Participants were instructed to store the materials in a dark and dry place until analysis. Before starting the analyses, the samples had to be re-homogenized by shaking for about 30 seconds. The procedure followed for the exercise, had to be as close as possible to the method used by the participant in routine sample analysis. Nevertheless participants were instructed to perform three independent measurements per parameter and to report measurement uncertainty. A questionnaire was attached to the reporting form. The questionnaire was intended to provide further information on the measurements and the laboratories. A copy of the questionnaire is presented in Annex 6. Laboratory codes were given randomly and communicated confidentially to the corresponding participant.

6 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 6 Assigned values The assigned values for the different trace elements in the rice wafer sample were determined as the consensus of participant s results [6]. The major advantages of consensus values are the straightforward calculation and the fact that none of the participants is accorded higher status. The disadvantages are that the consensus values are not independent of the participant s results and, especially in the current case with ten participants, that the uncertainty on the consensus (identified as the standard error) may be high and the information content of the z-scores will be correspondingly reduced. However, the IUPAC guide of 2010 on the selection and use of proficiency testing schemes for a limited number of participants [7] states that if the standard uncertainty of the assigned value u(x a ) is insignificant in comparison to the fit-for-intended-use target standard deviation σ p (u(x a ) 2 <0.1* σ p 2 ), then z-scores can be calculated in a small scheme in the same matter as recommended in IUPAC 2006 for a large scheme. A minimum of eight quantified results is accepted to calculate z- and ζ-scores (eight is the minimum number to create a Kernel density distribution). The robust statistic approach is a convenient modern method of handling results when they are expected to follow a near-normal distribution and it is suspected that they include a small proportion of outliers. There are many different robust estimators of mean and standard deviation [8]. The median and MAD (median absolute difference) were chosen here as robust estimators. The modified Horwitz equation was used to establish the standard deviation for proficiency testing (σ p ) [6][9]. It is an exponential relationship between the variability of chemical measurements and concentration. The Horwitz value is widely recognized as a fitness-for-purpose criterion in proficiency testing. a) Results that were identifiable invalid or extreme outliers were excluded. b) A visual presentation of the remaining results was examined. It was checked whether the distribution was apparently unimodal and roughly symmetric, possible outliers aside. If so c); else d). c) The robust mean ˆ rob and standard deviation ˆ rob of the n results were calculated as ˆ rob = median and ˆ rob = *MAD. If ˆ rob was less than about 1.2σ p, then ˆ rob was used as the assigned value x a and ˆ rob / n as its standard uncertainty u(x a ). d) A Kernel density estimate of the distribution was made using normal kernels with a bandwith h of 0.75σ p. If this resulted in a unimodal and roughly symmetric kernel density, and the mode and median were nearly coincident, then ˆ rob was used as the assigned value and ˆ rob / n as its standard uncertainty; else e). e) If the minor mode could be safely attributed to an outlying result, then ˆ rob was still used as the assigned value and could be derived. ˆ rob / n as its standard uncertainty; else no consensus value Scheme 1 : Scheme followed to calculate the assigned value according to [6]

7 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 7 The scheme that was followed to estimate the consensus and its uncertainty is outlined in Scheme 1. In the current case, steps (a) and (e) were not needed. Only for As, the visual presentation of the results appeared not to be unimodal (step b). In this case, the Kernel density plot (step d) was made and resulted in a unimodal and roughly symmetric kernel density. For As, Cd, Cu and Zn the assigned value was calculated as as ˆ rob = median and the standard deviation ˆ rob = *MAD. Because of the low number of data, only informal scores were given for As i and no scores were given for Pb. The consensus values, their standard uncertainty and some other statistical parameters are summarised in Table 1. Table 1 : Summary of statistical parameters for the test material. As As i Cd Pb Cu Zn mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg N Mean SD Robust mean (median) Robust SD ( ˆ ) rob Assigned value x a Standard uncertainty of the assigned value u(x a ) σ p Assigned value x a : median of the reported results; σ p : standard deviation for proficiency assessment.

8 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 8 Scores and evaluation criteria Individual laboratory performances are expressed in terms of z-scores and ζ-scores in accordance with ISO and the International Harmonised Protocol [6], [10]. z x lab x a u 2 p x ( x lab a x ) u a 2 ( x lab ) where: x lab is the mean of the individual measurement results as reported by the participant x a is the assigned value σ p is the standard deviation for proficiency assessment u(x a ) is the standard uncertainty for the assigned value u(x lab ) is the reported standard uncertainty on the reported value x lab. When no uncertainty was reported by the laboratory, it was set to zero. The z-score compares the participant's deviation from the reference value with the standard deviation accepted for the proficiency test, σ p. Should participants feel that these σ values are not fit for their purpose they can recalculate their scorings with a standard deviation matching their requirements. The z-score can be interpreted as: z 2 satisfactory result 2 < z 3 questionable result z > 3 unsatisfactory result The ζ-score states if the laboratory result agrees with the assigned value within the uncertainty claimed by this laboratory (taking due account of the uncertainty on the reference value itself). The interpretation of the ζ-score is similar to the interpretation of the z-score. ζ 2 satisfactory result 2 < ζ 3 questionable result ζ > 3 unsatisfactory result

9 Lab code Result 1 (mg kg -1 ) Result 2 (mg kg -1 ) Result 3 (mg kg -1 ) Mean (mg kg -1 ) Extended uncertainty (k = 2) z-scores ζ-scores PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 9 Results Arsenic (As) x a = 0.18 ± 0.01 mg/kg (k = 2) All ten laboratories submitted results for total As concentrations. Nine laboratories obtained satisfactory z-scores for As against the standard deviation accepted for the proficiency test (Table 2, Figure 4). The z-score of L10 was questionable. Nine laboratories obtained satisfactory ζ-scores against their stated measurement uncertainty. The ζ-score of L10 was unsatisfactory. Table 2 : values reported for As (mg/kg) by the participants and scores calculated by the organizer (ulab; mg kg -1 )

10 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 10 (A) (B) Figure 4 : (a) Results with expanded uncertainty for As, as reported by the participants (dashed lines: x a ± 2 u(x a ), dotted lines: x a ± 2 σ p and (b) z (blue bars) and ζ-scores (orange bars)

11 Lab code Result 1 (mg kg -1 ) Result 2 (mg kg -1 ) Result 3 (mg kg -1 ) Mean (mg kg -1 ) Extended uncertainty (k = 2) PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 11 Inorganic arsenic (Asi) x a = ± 0.02 mg/kg (k = 2) Only four laboratories submitted results for As i concentrations. The relative standard deviation of the values of the results was less than 15%. Therefore, the median of these four results was used as informal consensus value. The four laboratories obtained satisfactory informal z-scores for As i against the standard deviation accepted for the proficiency test (Table 3, Figure 5). These laboratories did also obtain good informal ζ-scores against their stated measurement uncertainty. Table 3 : values reported for As i (mg/kg) by the participants and scores calculated by the organizer. (ulab; mg kg -1 ) Informal z-scores Informal ζ-scores

12 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 12 (A) (B) Figure 5 : (a) Results with expanded uncertainty for As i, as reported by the participants (dashed lines: x a ± 2 u(x a ), dotted lines: x a ± 2 σ p and (b) informal z (blue bars) and ζ-scores (orange bars)

13 Lab code Result 1 (mg kg -1 ) Result 2 (mg kg -1 ) Result 3 (mg kg -1 ) Mean (mg kg -1 ) Extended uncertainty (k = 2) z-scores ζ-scores PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 13 Cadmium (Cd) x a = 0.12 ± 0.01 mg/kg (k = 2) Ten laboratories submitted results for Cd concentrations. One laboratory could not produce results above their limit of quantification. The median of the nine results was used as assigned value. All nine laboratories obtained satisfactory z-scores for Cd against the standard deviation accepted for the proficiency test (Table 4, Figure 6). The laboratories did also obtain good ζ-scores against their stated measurement uncertainty. The quantification limits of L02 was not lower than the corresponding x a -3 u(x a ) value, so the statements is satisfactory. Table 4 : values reported for Cd (mg/kg) by the participants and scores calculated by the organizer <0.6 <0.4 <0.6 < (ulab; mg kg -1 )

14 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 14 (A) (B) Figure 6 : (a) Results with expanded uncertainty for Cd, as reported by the participants (dashed lines: x a ± 2 u(x a ), dotted lines: x a ± 2 σ p, red bars represent the limits of quantification of the corresponding labs with the y-axis cut-off at 0.2 mg/kg) and (b) z (blue bars) and ζ-scores (orange bars)

15 Lab code Result 1 (mg kg -1 ) Result 2 (mg kg -1 ) Result 3 (mg kg -1 ) Mean (mg kg -1 ) Extended uncertainty (k = 2) PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 15 Lead (Pb) Nine laboratories submitted results for Pb concentrations. Only three laboratories could produce results above their limit of quantification. It was not possible to calculate an assigned value from these results. The median value was mg/kg. Table 5 : values reported for Pb (mg/kg) in by the participants 1 < < < < < <0.040 (ulab; mg kg -1 )

16 Lab code Result 1 (mg kg -1 ) Result 1 (mg kg -1 ) Result 1 (mg kg -1 ) Mean (mg kg -1 ) Extended uncertainty (k=2) z-scores ζ-scores PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 16 Copper (Cu) x a = 3.28 ± 0.12 µg/kg (k = 2) Ten laboratories submitted results for Cu concentrations. The median of these ten results was used as assigned value. All ten laboratories obtained satisfactory z-scores for Cu against the standard deviation accepted for the proficiency test (Table 6, Figure 7). And all of these laboratories did also obtain good ζ-scores against their stated measurement uncertainty. Table 6 : values reported for Cu (mg/kg) by the participants and scores calculated by the organizer (ulab; mg kg -1 )

17 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 17 (A) (B) Figure 7 : (a) Results with expanded uncertainty for Cu, as reported by the participants (dashed lines: x a ± 2 u(x a ), dotted lines: x a ± 2 σ p, and (b) z (blue bars) and ζ-scores (orange bars)

18 Lab code Result 1 (mg kg -1 ) Result 1 (mg kg -1 ) Result 1 (mg kg -1 ) Mean (mg kg -1 ) Extended uncertainty (k = 2) z-scores ζ-scores PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 18 Zinc (Zn) x a = 21.3 ± 0.3 mg/kg (k = 2) Ten laboratories submitted results for Zn concentrations. The median of the ten results was used as assigned value. All laboratories obtained satisfactory z-scores for Zn against the standard deviation accepted for the proficiency test (Table 7, Figure 8). Eight laboratories did obtain also satisfactory ζ- scores against their stated measurement uncertainty. Two laboratories (L09 and L10) obtained unsatisfactory ζ-scores of which one laboratory (L10) did not report a measurement uncertainty value. Table 7 : values reported for Zn (mg/kg) by the participants and scores calculated by the organizer (ulab; mg kg -1 )

19 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 19 (A) (B) Figure 8 : (a) Results with expanded uncertainty for Zn, as reported by the participants (dashed lines: x a ± 2 u(x a ), dotted lines: x a ± 2 σ p, and (b) z (blue bars) and ζ-scores (orange bars)

20 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 20 Discussion and conclusion The most commonly used technique for the analysis of As, Cd, Pb, Cu and Zn was ICP-MS (Inductively Coupled Plasma-Mass Spectrometry). Only one exception was noticed by a lab which uses INAA (Instrumental Neutral Activation Analysis). For Cu and/or Zn some laboratories used ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometry). As for inorganic As, the samples were all analysed by ICP-MS. Three laboratories used HPLC (High Performance Liquid Chromatography), coupled to the ICP-MS as separation method and one laboratory used SPE (Solid Phase Extraction). The measurement results seem to be similar for both approaches, although the results with SPE method were slightly lower compared with the HPLC-ICP- MS method. Already four laboratories participated successfully for As i in this PT. The laboratories were asked to state if the samples are compliant according to the current legislation. In Commission Regulation (EC) 333/2007 [3] it is described when a sample is accepted: The lot or sublot is accepted if the analytical result of the laboratory sample does not exceed the respective maximum level as laid down in Regulation (EC) No 1881/2006 taking into account the expanded measurement uncertainty and correction of the result for recovery if an extraction step has been applied in the analytical method used. The lot or sublot is rejected if the analytical result of the laboratory sample exceeds beyond reasonable doubt the respective maximum level as laid down in Regulation (EC) No 1881/2006 taking into account the expanded measurement uncertainty and correction of the result for recovery if an extraction step has been applied in the analytical method used. For the concerned matrix there are clear maximum limits for As i (0.30 mg/kg). The organizers gave no information as would the wafers be intended for infants and young children, but if this was the case the maximum limit for Cd and Pb in this matrix is and mg/kg, respectively. Table 8 : Compliant statements of the participating laboratories (no(n) or yes(y)) compared with the measured values minus the expanded measurement uncertainty (x a -U(x a )) for As, As i, Cd and Pb. As* As i Cd Pb x lab -U(x lab ) (mg/kg) stated by lab L <0.020 Y L <0.5 - L <0.020 Y L Y L <0.05 Y/N** L <0.05 Y L Y L <0.016 Y L L <0.04 Y ML ** 0.050** *as screening method **only if matrix is intended for infants and young children

21 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 21 So the measured concentration should be compared with these MLs, taking into account the expanded measurement uncertainty. This means that a sample is non-compliant if x lab -U(x lab )>ML. Table 8 shows this exercise for the participants. All laboratories stated this sample as compliant and this was right in case the wafers were not intended especially for infants and young children (note: information about the intended use was not given by the organizers). No calculated x lab -U(x lab ) exceeded the ML for As i. This conclusion could also be drawn when only As was measured as the total concentration did also not exceed the ML. However, when the wafers should be intended for infants and young children, the sample would be non-compliant regarding the Cd concentration; there was only one laboratory that noticed this nuance. To conclude, this was a very successful exercise. Of the ten laboratories that registered for participation, ten submitted results for As, Cd, Cu and Zn; nine submitted results for Pb and four submitted results for As i. The laboratories performed excellent with only one z-score which was questionable. The laboratories have thus proven their competence to measure the concerned trace elements in the matrix.

22 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 22 Bibliography [1] European Commission, Commission Regulation (EU) 2015/1006 of 25 June 2015 amending Regulation (EC) No 1881/2006 as regards maximum levels of inorganic arsenic in foodstuffs, Off. J. Eur. Union, vol. L161, no. 14, pp , [2] European Commission, Commission Regulation (EC) No 1881/2006 of 19 December 2006 setting maximum levels for certain contaminants in foodstuffs, Off. J. Eur. Union, vol. L364, no. 78, pp. 5 24, [3] European Commission, Commission Regulation (EC) No 333/2007 of 28 March 2007 laying down the methods of sampling and analysis for the official control of the levels of lead, cadmium, mercury, inorganic tin, 3-MCPD and benzo(a)pyrene in foodstuffs, Off. J. Eur. Union, vol. L88, no. 333, pp , [4] European Commission, Commission Regulation (EU) No 488/2014 of 12 May 2014 amending Regulation (EC) No 1881/2006 as regards maximum levels of cadmium in foodstuffs, Off. J. Eur. Union, vol. L138, no. 75, pp , [5] European Commission, Commission Regulation (EU) 2015/1005 of 25 June 2015 amending Regulation (EC) No 1881/2006 as regards maximum levels of lead in certain foodstuffs, Off. J. Eur. Union, vol. 161, no. 9, pp. 8 12, [6] M. Thompson, S. L. R. Ellison, and R. Wood, The International Harmonized Protocol for the proficiency testing of analytical chemistry laboratories (IUPAC Technical Report), Pure Appl. Chem., vol. 78, no. 1, pp , [7] I. Kuselman and A. Fajgelj, IUPAC/CITAC Guide: Selection and use of proficiency testing schemes for a limited number of participants chemical analytical laboratories (IUPAC Technical Report), Pure Appl. Chem., vol. 82, no. 5, pp , [8] AMC, Robust statistics: a method of coping with outliers, AMC Tech. Br., no. 6, [9] M. Thompson, The amazing Horwitz function, AMC Tech. Br., no. 17, [10] ISO 13528, Statistical methods for use in proficiency testing by interlaboratory comparison, vol

23 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 23 Annexes Annex 1: Invitation letter to laboratories

24 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 24 Annex 2: Results of the homogeneity studies As Cd Pb Cu Zn Cochran test for variance outliers Cochran test statistic Critical (99%) Cochran < critical use complete dataset use complete dataset use complete dataset Remove outlier use complete dataset Cochran test statistic (9 samples) Critical (99%) (9 samples) Test for sufficient homogeneity S an ² S sam ² σ all ² F F Critical S sam ² < critical? accept accept accept accept accept

25 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 25 Annex 3: Letter accompanying the sample

26 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 26 Annex 4: Instructions to participants

27 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 27 Annex 5: Materials receipt form

28 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 28 Annex 6: Reporting form and questionnaire

29 PT-2016-NRL-TE-FASFC: Determination of As, Asi, Cd, Pb, Cu and Zn in rice wafers 29