Average transfer factors are not enough: The influence of growing cattle physiology on the transfer rate of polychlorinated biphenyls from feed to adipose.

Food of animal origin accounts for >90% of the overall human exposure to polychlorinated biphenyls (PCBs). Food regulatory maximum levels help to control this exposure, but bovine meat has been found to be prone to exceed those occasionally. In order to ensure the chemical safety of bovine meat, the aim was to explore the dependency of the bioconcentration (BCF) and biotransfer (BTF) factor, and assimilation efficiency (AE) of PCBs on carcass lipid proportion and growth rate of beef cattle. Eleven bulls were fattened for 293 days with three different diets (7.0, 7.4, 7.5 MJ net energy for growth kg-1 dry matter) at PCB background levels, until slaughter at 530 or 600 kg body weight. Feed and perirenal adipose tissue were sampled for PCB analyses via GC/HRMS and carcass lipid proportion was estimated by the 11th rib dissection technique. For all tested PCBs, BCF (ranging from 0.7 to 18.4) and BTF (ranging from 0.1 to 2.7) decreased at least 1.5 up to 10.6-fold when the carcass lipid proportion increased by 4%, resulting from a typical dilution process. For a faster growth rate of 0.18 kg d-1 however, only a non-significant increasing trend in transfer factors (1.1 to 2.1-fold) was seen. Besides, the transfer factors increased with PCB chlorination degree, non-ortho substitution and lipophilicity. These results underpin the complex interaction between animal physiology and PCB physicochemical properties, making it challenging to interpret average transfer factors to support chemical risk assessment and management.