Determining equilibrium partition coefficients between lipid/protein and polydimethylsiloxane for highly hydrophobic...

Bioaccumulation of hydrophobic organic contaminants is of great concern and understanding their partitioning to biological phases is crucial for estimating their bioaccumulation potential. The estimation, however, was of large uncertainty for highly hydrophobic organic contaminants (HHOCs) with log K_OW>9 due to the challenge of quantifying their water concentrations. In the present study, partition coefficients between polydimethylsiloxane (PDMS) and storage lipid (K_SL,PDMS), membrane lipid (K_ML,PDMS) and protein (K_pro,PDMS) were measured for 21 polychlorinated biphenyls (PCBs), 14 polybrominated diphenyl ethers (PBDEs), dechlorane plus (DP) and decabromodiphenyl ethane (DBDPE), covering log K_OW from 5.07 to 11.6, using a preloaded PDMS depletion method. The values of K_SL,PDMS, K_ML,PDMS and K_pro,PDMS were in the ranges of 5.36-52.5, 0.286-11.8 and 0.067-2.62g/g, respectively, being relatively constant although their K_OW values extend more than six orders of magnitude. The relative sorption capacity of the biological phases showed storage lipid was the dominant sorption phase in biota, followed by membrane lipid and protein was the lowest. The K_PDMS,pro values of the compounds with log K_OW<9 were similar (0.382-14.9g/g) regardless of the thickness of preloaded PDMS disks (58-209μm). For HHOCs, however, K_PDMS,pro values dropped when thinner PDMS disks were used, as a result of slow diffusion of HHOCs in PDMS. The K_PDMS,pro values of HHOCs measured by 58-μm PDMS disks ranged from 1.78 to 6.85g/g, which was consistent with compounds with log K_OW<9. This validated that partition coefficients between PDMS and biological phases were independent of chemical hydrophobicity, showing the advantage of using PDMS-based methods to directly estimate bioaccumulation potential of HHOCs.