Interlaboratory comparison on dioxins in food 2007. Eight round of an international study
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In 2007, the eight round of the Interlaboratory Comparison on Dioxins in Food was conducted on the determination of the 2,3,7,8-chlorinated dibenzo-pdioxins (PCDDs) and dibenzofurans (PCDFs) as well as dioxin-like non-ortho and mono-ortho chlorinated biphenyls (PCBs) in three different food items. In addition laboratories could voluntarily determine and report six Indicator PCBs, polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD). The objectives of this interlaboratory comparison study were a) to offer a quality assurance instrument for the participating laboratories, b) to assess the between laboratory reproducibility and c) to assess the readiness of expert laboratories world-wide to determine levels of chlorinated and brominated persistent organic pollutants in regular foodstuffs. The 2007 study was performed on sample homogenates of salmon filet, chicken meat and butter. In addition, six standard solutions were provided containing known concentrations of a) PCDDs/ PCDFs, b) nonortho PCBs, c) mono-ortho PCBs, d) PBDEs, e) Indicator PCBs and f) α-HBCD. The testing materials were sent to 105 laboratories in January 2007, and results were returned from 100 laboratories in 27 different countries by the deadline in April. Most laboratories analyzed all the three food items. A draft report was made available on the web in August and was discussed among the participants at the Waters Users’ Meeting during the DIOXIN2007 Symposium in Tokyo, Japan. This report presents the reported results for: all seventeen 2,3,7,8-substituted PCDDs/PCDFs, the non-ortho substituted PCBs #77, 81, 126 and 169 and the eight mono-ortho substituted PCBs #105, 114, 118, 123, 156, 157, 167, 189 in the three food items on a fresh weight and lipid weight basis. In addition, the results for eight PBDE congeners BDE #28, 47, 99, 100, 153, 154, 183 and 209, six Indicator PCBs #28, 52, 101, 138, 153 and 180, and total HBCD as well as the α-, β- and γ-isomers were reported from those laboratories that voluntarily determined their concentrations. Non-detected congeners were assigned a concen tration corresponding to the reported detection limit except for PBDEs, Indicator PCBs and HBCD where non-detects were removed from the data set. The consensus concentration (assigned value) for each analyte in the three food samples was determined as follows: The median of all reported concentrations for each analyte was calculated. All values above two times the median were removed from the calculation. The consensus median and consensus mean plus standard deviation (SD) were calculated from the remaining data. Toxic equivalents (TEQs) were calculated from the consensus values of individual congeners using the toxic equivalency factors derived by WHO in 1998 and 2006. Z-scores for PCDD/PCDF TEQs were calculated for each laboratory using ± 20% of the consensus TEQs as a value for target standard deviation (σ). Further, Z-scores were calculated for the non-ortho PCB TEQ, the mono-ortho PCB TEQ, the total TEQ, the sum of six Indicator PCBs, the sum of eight PBDEs, total HBCD, and the three isomers of HBCD and for each single congener in all three matrices. The consensus values for the standard solutions were calculated as mentioned above except that values outside ± 50% of the median of all values were removed prior to the final calculation of the consensus median and mean. The consensus values for the lipid content were calculated by first excluding results deviating more than two SD from the mean of all values and then re-calculating the median, mean and SD. For the determination of total TEQs, Z-scores within ± 1 were obtained by 64-75% of the laboratories. The majority of the laboratories (83-89%) reported results for total TEQ with a trueness of ± 40% for all food samples (Z-score ± 2). The relative standard deviation (RSD) calculated for the total TEQ after removal of outliers is quite low (8-15%). It is therefore concluded that the performance of laboratories world-wide in determining dioxin-like compounds is generally good for the food samples included in this study. Between 54 to 62 laboratories reported results for the six Indicator PCBs, 34-42 laboratories reported concentrations for the seven tetra- to hepta-BDEs and 23-28 laboratories reported concentrations for BDE-209. The concentrations of the sum of seven PBDEs ranged from 78 pg/g fresh weight in chicken meat to 516 pg/g fresh weight in salmon filet. The RSD for PBDE concentrations on fresh weight basis was on average 33, 42 and 44% for salmon filet, butter and chicken meat respectively. The consensus concentrations for BDE-209 were 38, 47 and 53 pg/g fresh weight in salmon filet, chicken meat and butter respectively. The corresponding RSD on fresh weight basis was 74, 95 and 45%. The consensus concentrations calculated for HBCD are just indicative values as few laboratories reported these congeners. The sum of concentrations for six Indicator PCBs ranged from 3.7 ng/g fresh weight in butter to 21.4 ng/g fresh weight in chicken meat. The average RSDs were 32, 34 and 38% for salmon filet, chicken meat and butter respectively.