Diet-to-egg transfer kinetics of 28 polychlorinated biphenyl (PCB) congeners in laying hens: implications for controlling PCB residues in eggs

Polychlorinated biphenyls (PCBs) can enter the food chain via contaminated poultry feed and accumulate in eggs. Feed-to-egg transfer and elimination kinetics were quantified for 28 PCB congeners in laying hens fed a control diet or PCB-spiked diets for 21 days (mean dietary concentrations: 1.3 and 4.8 ng g⁻¹ dw), followed by depuration to Day 60 under contrasting low and high exposure scenarios. PCBs were quantified in egg yolk and hen tissues by GC-MS/MS. By Day 21, ΣPCBs in egg yolk reached 124.6 ng g⁻¹ lipid (low) and 487.5 ng g⁻¹ lipid (high). Congener-level elimination followed first-order kinetics; depuration rate constants were 0.026-0.089 d⁻¹ (low) and 0.041-0.110 d⁻¹ (high), corresponding to half-lives of 7.8-26.7 and 6.3-16.9 days. To account for yolk-formation delay and a post-cessation peak, sum-level depuration was referenced to Day 24 (C₂₄). For PCB sums (ΣPCBs and ΣICES-6), mono-exponential and biphasic models were evaluated by Akaike's information criterion (AIC) and favoured the biphasic form (ΔAIC = 2.7-8.3; wbi = 0.79-0.98), with a breakpoint at Day 45 and distinct α/β phases (t1/2,α = 11-14 days; t1/2,β = 16-24 days). Late-stage persistence was summarised as a residual fraction (RF = C₆₀/C₂₄), which was lower at high exposure than low exposure for ΣICES-6 (0.173 vs 0.238). These results support evidence-based withdrawal-period setting against the EU maximum level for ΣICES-6 in eggs (40 ng g⁻¹ fat).