A congener-specific modelling approach for the transfer of polychlorinated dibenzo-p-dioxins and dibenzofurans and dioxin-like polychlorinated biphenyls from feed to eggs of laying hens

Calibration of a kinetic model for the transfer of PCDD/Fs and dl-PCBs from feed to the hen's body and eggs was thus far restricted to the total TEQ concentration, i.e. the summed concentrations of PCDD/Fs and dl-PCBs expressed in terms of equivalents of 2,3,7,8-TCDD. However, this approach may lead to over- or underestimation of the transfer if the mixture contains congeners with kinetic characteristics which differ considerably from those used in such a model. This paper extends a previous transfer model of PCDD/Fs and dl-PCBs from feed to egg yolk fat and abdominal fat of high production laying hens, based on the total TEQ approach, to the level of individual congeners. Both modelling approaches are compared and the new approach is presented as a webtool application. This congener-specific approach enabled the calibration of 25 of the 29 relevant PCDD/F and dl-PCB congeners with respect to their individual transfer characteristics to body fat and egg yolk fat and their clearance from the body. Limitations of the available experimental data prevented the calibration of 1,2,3,4,6,7,8-HpCDD, OCDD, OCDF and PCB 123. The fraction transferred to egg yolk fat after long-term daily intake of contaminated feed was found to be at least 0.78 for 2,3,7,8-TCDD, 0.75 for PeCDD, 0.42-0.61 for HxCDDs, 0.70 for 2,3,7,8-TCDF, 0.71 for PeCDF, 0.54-0.60 for HxCDFs, 0.18-0.24 for HpCDFs and 0.89-1.00 for dl-PCBs. Various experimental and feed incident mixtures were used to compare the total TEQ- model with the congener-specific approach. An overestimation of the transfer by the total TEQ method was shown in particular for mixtures with a substantial contribution of hexa-, hepta- and octa-PCDD/Fs to the total TEQ level.