Modeling of DR CALUX® bioassay response to screen PCDDs, PCDFs, and dioxin-like PCBs in farm milk from dairy herds

A recent issue in the EU legislation is the evaluation of the toxicologically-equivalent contribution of dioxin-like polychlorobiphenyls (DL-PCBs) in addition to that coming from polychlorodibenzodioxins (PCDDs) and polychlorodibenzofurans (PCDFs) as contaminants in foods for a total of 29 congeners. This fact is determining the need to revise analytical criteria both for confirmatory and screening analysis. In this work, a modeling was developed to check the reliability of the outcomes of the DR CALUX® bioassay when applied to farm milk samples characterized by large differences in congener patterns. To reproduce some field conditions where DL-PCB contributions up to 90% of total WHO-TEQs (HRGC-HRMS assessment) were recorded in dairy products, goat milk samples from a common bulk were fortified at different TEQ levels with mixtures containing either PCDDs and PCDFs or non-ortho substituted DL-PCBs. Fortification ranged approximately 4.5–15 pgWHO-TEQ/g fat. Based on the results, DR CALUX® relative potency value (REP) of DL-PCB 126 was estimated 0.061 against the canonical WHO-TEF of 0.1. The value of 0.061 together with the other DR CALUX® REPs from the literature for the remaining 28 congeners were used to model DR CALUX® response (C-TEQs) in milk samples with different congener patterns. The theoretical underestimation of DR CALUX® data could be mitigated by correcting the latter with the linear correlation experimentally obtained between C-TEQs and the WHO-TEQs. Under these conditions, the use as calibrants of reference samples with different analytical patterns could help those laboratories involved in a high throughput routine to set the most appropriate decision limits to optimize screening output.