It was shown that the apparent absorption of PCBs and PCDD/Fs was reduced when cows were exposed via the grass silage-soil mixture compared to grass silage alone. Physicochemical compound properties, such as a higher chlorinated degree and concomitantly higher lipophilicity (octanol:water partition coefficient, KOW), were negatively correlated with the AR. Animal physiology affected the rate further with higher ARs in primi- vs. multiparous cows, presumably resulting from a higher lipid digestibility in the former. Accordingly, suckling calves showed the highest ARs via the ingestion of a highly digestible lipid-rich diet (milk) compared to cows, even without the reducing effect of the PCB chlorination degree, resulting in a transgenerational bioaccumulation. Calf blood serum and subcutaneous adipose tissue PCB and PCDD/F concentrations were therefore twice as high as in cows until DIM164. Transfer rates to milk and decontamination half-lives in milk were also affected by the physicochemical compound properties and the cow reproductive parity (encompasses differences in DM intake, body lipid mobilization and accretion dynamics, and milk yield). Increasing PCB chlorination resulted in a higher TR, with an inverse relationship for PCDD/F. Transfer rates were lower with decreasing milk yield (i.e., in primiparous cows), resulting further into longer half-lives in milk.
To quantify the PCB and PCDD/F fraction not transferred to milk, a transgenerational input-output mass balance was performed. The estimated metabolized fraction was negative correlated with the chlorinated degree, whereas young calves (3 months old) had a reduced estimated metabolism efficiency. Calves excreted only a small fraction via the feces, so that the main part ingested was accumulated within the body, especially for highly chlorinated PCBs. Still, calves were more efficient in reducing their PCB and PCDD/F body concentrations compared to cows, presumably due to a higher increase in body lipid mass over the course of lactation. In both cow and calf, a liver-specific PCB and PCDD/F enrichment was identified, with an additional enhanced accumulation in kidney and muscles for some congeners, especially lower chlorinated ones.
This study is so far, to the best of our knowledge, the largest and most comprehensive one about the fate of PCBs and PCDD/Fs in suckling cow husbandries. It delivered detailed insights into the transgenerational fate of PCBs and PCDD/Fs from grass silage and soil into suckling cow and calf. It was clearly shown that transfer assessment should consider the complex interplay between physicochemical compound properties and ruminant physiology on absorption, distribution, metabolism and excretion. Furthermore, it was shown that adipose tissue concentrations might underestimate up to 2-fold the levels in most consumed beef-tissues (i.e., muscle), which is important to take into account for monitoring purpose. In conclusion, these results help to implement new recommendations for agricultural practices to further reduce beef cattle PCB and PCDD/F exposure and accumulation, and subsequently improve bovine meat safety.
Besides, the project also encompassed other aspects, such as in silico applications to support risk assessment and specific practice oriented recommendations, which were detailed in previous annual reports and publications listed below.
