Beyond Compliance: Which Congeners Drive Toxic Equivalency and PCB Burden in Raw Ruminant Milk?

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (DL-PCBs), and six indicator non-dioxin-like polychlorinated biphenyls (NDL-PCBs) were determined in 20 independent raw ruminant-milk samples (16 cow, 3 buffalo, and 1 goat) by gas chromatography–tandem mass spectrometry. Toxic equivalency (TEQ) was calculated using the World Health Organization 2005 toxic equivalency factors, and regulatory screening used upper-bound (UB) concentrations. All samples were below the applicable European Union maximum and action levels; the highest total UB TEQ was 0.877 pg/g fat, and the highest sum of six NDL-PCBs was 3.310 ng/g fat. PCB126 contributed 91.1% of DL-PCB UB TEQ and 48.5% of total UB TEQ, whereas PCB28 accounted for 44.8% of the NDL-PCB UB mass. The high apparent UB shares of 1,2,3,7,8-PeCDD and TCDD, quantified in 10% and 0% of samples, respectively, suggest substitution at the limit of quantification. Exploratory principal component analysis of 12 congeners quantified in at least 50% of samples explained 64.1% of variance in the first two components and identified distinct covariation patterns among higher-frequency congeners. The combined interpretation of regulatory totals, congener contributions, quantification frequency, and censoring therefore provides more informative food-control reporting than compliance totals alone.