Transfer kinetics, tissue distribution, and maternal transfer of short- and medium-chain chlorinated paraffins in laying hens: A laboratory-to-field validation and dietary exposure assessment.

Chlorinated paraffins (CPs), particularly short- and medium-chain CPs (SCCPs and MCCPs), are emerging persistent organic pollutants with increasing concerns for the environment and food safety. However, the toxicokinetics of CP congener groups in food-producing animals remain poorly understood. Here, we conducted a 14-day exposure and subsequent 28-day depuration feeding study in laying hens to elucidate the kinetics, tissue distribution, and maternal transfer of SCCPs and MCCPs. The results showed that CPs accumulated rapidly in eggs, and clean feeding effectively reduced CP burdens with SCCP and MCCP apparent half-lives of 4.5 and 4.8 days, respectively. At the end of the exposure phase, the congener group profiles of SCCPs and MCCPs in eggs closely mirrored those in the contaminated feed, indicating that egg CP fingerprints can reliably reflect chicken dietary exposure sources. Tissue analysis identified the ovary as the primary accumulation site, where CPs peaked in the ovum, in contrast to the lower levels detected in liver and adipose tissue. Notably, bioaccumulation factors of CPs exhibited a polynomial relationship with their logKOW, revealing a threshold at logKOW 6.5-7.0, where accumulation behavior shifts from size-limited to lipophilicity-driven. The maternal transfer ratios of CPs also showed a polynomial regression trend with logKOW and were tissue-dependent, with MCCPs exhibiting higher transfer efficiencies than SCCPs. While the feed-to-egg transfer efficiencies determined under controlled conditions slightly underestimated the CP concentrations observed in paired field egg samples, the combined experimental and field data consistently demonstrated that the associated human exposure via egg consumption posed no health concern. This study provides critical scientific evidence for elucidating the fate of CPs in the poultry production chain and for informing risk assessment.