DR-CALUX((R)) screening of food samples: evaluation of the quantitative approach to measure dioxin, furans and dioxin-like PCBs

European legislation laid down maximum tolerable levels of dioxin in feed and food as well as analytical method requirements. In order to face with large monitoring programs, it was foreseen in the EU strategy to integrate screening methods, using either a qualitative (screening) approach, or a quantitative approach. In this study, dioxin results obtained using the Dioxin Responsive Chemical-Activated LUciferase gene eXpression (DR-CALUX^®) cell-based assay (quantitative approach), were compared with gas chromatography–high resolution mass spectrometry (GC–HRMS) analyses data. Instead of using World Health Organization–toxic equivalent factor (WHO–TEF), the comparison was based on the assessment of relative effective potencies (REPs) for each congener of the 17 toxic 2,3,7,8-polychlorodibenzo-p-dioxins/furans (PCDD/Fs) and 12 dioxin-like polychlorobiphenyls (DL-PCBs). According to published data, DR-CALUX^®-REP evaluated here appear similar to WHO–TEF for PCDD/Fs while lower values were observed for DL-PCBs.

We analyzed two “home made” contaminated fat samples, displaying both the same WHO–toxic equivalent quantities (WHO–TEQ) concentration (12 pg WHO–TEQ g⁻¹). They were spiked with either a low or a high amount of DL-PCBs. In both cases, the DR-CALUX^® measured concentration (picogram 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) eq. g⁻¹) corresponded to the PCDD/Fs WHO–TEQ concentration only. A good agreement was nevertheless found between the DR-CALUX^® measurements and the recalculated DR-CALUX^®-TEQ contents (using DR-CALUX^®-REP instead of WHO–TEF), demonstrating that the observed response was due, in both cases, to the addition of the responses of the standards added to the fat. By contrast, in real contaminated samples (feed or cod liver samples), DR-CALUX^® measured concentrations were similar to WHO–TEQ GC–HRMS measured concentrations. But, depending on the PCDD/Fs and DL-PCBs congener content, the DR-CALUX^® measured concentrations were either lower or higher than calculated DR-CALUX^®-TEQ contents, demonstrating that possible co-extracted contaminants contributed to the CALUX response.

Owing to these divergences, the quantitative determination of dioxin-like content in food and feed using CALUX as screening method is questionable, except for samples displaying constant congener patterns, in which cases, correction factors could be applied.