RP-HPLC measurement and quantitative structure - property relationship analysis of the n-octanol - water partitioning coefficients of selected metabolites of polybrominated diphenyl ethers

Abstract

Environmental context. Polybrominated diphenyl ethers (PBDEs) are ubiquitous environmental contaminants and numerous studies have demonstrated a marked increase in the levels of PBDEs in human biological tissues and fluids, especially breast milk. How PBDEs are transported through the environment, taken up by biota, transported across membranes, and metabolised depends strongly on such fundamental properties as lipophilicity (log KOW). However, very little data on log KOW exist for PBDEs. In the present paper, the authors determine PBDE metabolites’ log KOW using reversed-phase high performance liquid chromatography, as recommended by the Organisation for Economic Co-operation and Development and US Environmental Protection Agency, along with quantitative structure–property relationships. Abstract. n-Octanol–water partitioning coefficient (log KOW) values of selected hydroxylated and methoxylated polybrominated diphenyl ether metabolites were measured for the first time by reversed-phase high performance liquid chromatography (RP-HPLC) using a C18 stationary phase with a water/methanol mixture as a mobile phase. The retention parameters, log kw (extrapolated retention indices) and k′ (gradient retention indices) were calibrated to log KOW by a set of calibration standards. For the PBDE metabolites investigated, extrapolated retention indices from isocratic elution seem to be more reliable and their RP-HPLC-derived log KOW values were found to range from 4.63 to 7.67. Some commonly available software, including ClogP, KowWin, AclogP, MlogP, AlogP, MilogP, and XlogP, was used to estimate the log KOW values of the analytes. Significant correlations were obtained between the RP-HPLC-derived log KOW and the software-computed log KOW, with squared correlation coefficients (R2) ranging from 0.793 to 0.922, but the difference between them was also significant. Then a quantitative structure–property relationship model based on topological descriptors was established and showed good reliability and predictive power for the estimation of RP-HPLC-derived log KOW values of PBDE metabolites. It was applied to estimate the log KOW values of some PBDE metabolites that are commercially available or have appeared in the literature. Lastly, factor analysis was carried out using the theoretical linear salvation/free-energy relationships, which indicated the average polarisability (α) and the most negative atomic partial Mulliken charge in the molecule (q–) were the most important parameters affecting their partition between n-octanol and water, supporting the factorisation of log KOW in bulk and electronic terms.