抄録
In this paper, in order to provide a useful piece of information about inter-laboratory calibration study using in vitro bioassay in Japan and its evaluation method, outline and results of inter-laboratory calibration study for dioxins in food/feedstuff using DR-CALUX (Dioxin-Responsive Chemical-Activated LUciferase gene eXpression) assay with 21 participants were reported. The interlaboratory calibration study was divided into three phases. In Phase I, pure chemical mixtures consisted of PCDDs/PCDFs and Co-PCBs were analyzed. The TeCDD equivalents calculated using DR-CALUX assay (CALUX-TEQs) were equivalent to the theoretical CALUX-TEQs calculated chemically using concentrations of PCDDs/PCDFs and Co-PCBs and CALUX relative potencies to 2,3,7,8-TeCDD for these samples. Although lowest concentration sample indicated about 0.3 pM CALUX-TEQs per well, its reproducibility was comparatively good. During Phase II, cleaned sediment and food/feedstuff extracts prepared by organizer were analyzed. Decreases of interlaboratory reproducibility were observed with decrease of CALUX-TEQs in samples. In Phase II, samples indicating wide dispersion had low concentrations which were almost less than 0.3 pM CALUX-TEQs per well. In consideration of results for Phase I, although the limit of quantification for DR-CALUX assay was about 1 pM in general, 0.3 pM CALUX-TEQs per well might be the real limit of quantification. In Phase I and II, dispersion of data wasn't depending on a type of sample or dilution effect. In Phase III, whole fish oils and feedstuffs were extracted, cleaned, and analyzed by each participant according to protocol delivered by the organizer. The CALUX-TEQs were almost equivalent to the WHO-TEQs for these samples. Interlaboratory reproducibility tended to be higher than those during phase I and II. Increases of it were also observed with decrease of concentration in samples. The results demonstrated that the extraction and cleanup processes cause a major variation. From this study, it was indicated that Z-score provides useful information for identifying the cause of dispersion of data for each phase.
