A mass balance of tri- to hexa-brominated diphenyl ethers in lactating cows.

Beef and dairy products can be important vectors of human exposure to polybrominated diphenylethers (BDEs), and hence an understanding of BDE transfer from feed to cows’ milk and tissue is important for BDE exposure assessment. The fate of tri- to hexaBDEs in lactating cows exposed to a naturally contaminated diet was studied by analyzing feed, feces, and milk samples from a mass balance study. Tissue distribution was studied in one cow slaughtered after the experiment. The carryover rates from feed to milk ranged from 0.15 to 0.35 for the major congeners. Lower values were observed for several of the tetrabrominated congeners, and this was attributed to metabolism. The dietary absorption efficiency decreased with increasing octanol−water partition coefficient of the BDE congener. The absorption behavior was consistent with a model based on chemical lipophilicity, but agreed less well with a model based on effective molecular diameter, and it violated Lipinski’s “rule of 5”. The lipid normalized concentrations were similar in all tissues analyzed including liver and milk, suggesting that tissue distribution is governed by partitioning into lipids. Overall, the behavior of the tri- to hexaBDEs was consistent with that observed for other classes of halogenated aromatic contaminants such as PCBs and PCDD/Fs, but it differed markedly from the behavior of the hepta- decaBDEs