Liposome and protein-water partitioning of polybrominated diphenyl ethers (PBDEs)

Bioaccumulation of polybrominated diphenyl ethers (PBDEs) in marine and terrestrial organisms is of great environmental concern. Understanding the partitioning of PBDEs to biological phases is crucial for elucidating their bioaccumulation behavior. In this study, partitioning coefficients of PBDEs from water to phospholipid liposomes (K(lipw)) and to bovine serum albumin (BSA) (K(BSAw)) were measured using a polymer depletion method. K(lipw) values measured in two laboratories are in an excellent agreement (within 0.14 log units), indicating a high method repeatability. The values of log K(lipw) and log K(BSAw) are in the range of 6.3-8.2 and 5.1-7.0, respectively, representing the highest of these partition coefficients measured to date. Log K(lipw) values for PBDEs are similar to the log of the octanol-water partition coefficients (K(ow)) (log K(lipw)-log K(ow)=-0.06±0.23; mean±SD of 7 congeners), consistent with the data of chlorobenzenes and polychlorinated biphenyls (PCBs) reported in the literature. No hydrophobicity cutoff was observed for partitioning to the liposome membrane. Log K(BSAw) values for PBDEs increase linearly with log K(ow) and do not follow the non-linear trend observed for polycyclic aromatic hydrocarbons (PAHs). This difference between PBDEs and PAHs suggests specific binding mechanisms to serum albumin even for hydrophobic compounds.