Congener-specific transfer modelling of dioxins and dioxin-like PCBs in free-ranging cattle grazing in the Dutch floodplains

Cattle grazing in the Dutch floodplains are exposed to polychlorinated dibenzo-p-dioxins and dibenzofurans (dioxins) and dioxin-like PCBs (dl-PCBs) through the consumption of grass and adhering soil. This can lead to elevated dioxin and dl-PCB levels in meat fat. To manage this contamination issue, the kinetics of these compounds in cattle need to be better understood. This study describes the development and application of a physiologically based kinetic (PBK) model to predict dioxin and dl-PCB levels in muscle fat of 'Rode Geus' cattle based on measured levels in grass and soil. Calibration of the model was performed separately for each congener, using measured dioxin and dl-PCB levels in various tissues of 14 animals. Model validation performed using dioxin and dl-PCB samples of 14 other cattle, showed that PBK model predictions were on average a factor 2.4 higher than the measured dioxin and dl-PCB TEQ levels in fat. Despite this difference, the model may still be particularly useful to better understand the relation between environmental dioxin and dl-PCB levels and those in cattle. The model is publicly available with a user-friendly interface on www.feedfoodtransfer.nl and may provide relevant insights for risk assessment and risk management.