Measurements of Octanol−Air Partition Coefficients (KOA) for Polybrominated Diphenyl Ethers (PBDEs):  Predicting Partitioning in the Environment

Octanol−air partition coefficients (KOA) are reported for 13 polybrominated diphenyl ethers (PBDEs) over the temperature range (15−45) °C. KOA exhibited a log−linear relationship with inverse absolute temperature, and values at 25 °C range from 9.3 (PBDE-17) to 12.0 (PBDE-126). These are approximately 1 to 2 orders of magnitude greater than those measured for the counterpart polychlorinated biphenyls (PCBs). PBDEs also showed a strong temperature dependence. The enthalpy of phase change from octanol to air, ΔHOA, was (≈70 to ≈120) kJ mol-1. This corresponds to a 20−100 times higher KOA value at 5 °C versus 35 °C. A method is presented for estimating KOA at any temperature for additional PBDEs using relative retention times. Log KOA values were compared against two sets of recently published subcooled liquid vapor pressures (poL) that show significant discrepancies. Activity coefficients in octanol (γO) for PBDEs ranged from 1 to 10 when one set of vapor pressures was used. This was consistent with other classes of SOCs and indicated near ideal solution behavior. When the second set of values was used, calculated activity coefficients were in the range 10−100, suggesting that these vapor pressure values were inaccurate. Application of KOA for describing partitioning of PBDEs to aerosols and soils was also examined. The predicted percentages (at 25 °C) on aerosols ranged from 1.2% for PBDE-17 to 85% for PBDE-183 and agreed well with measured data, confirming that surface−air partitioning is an important process for the distribution and fate of PBDEs in the environment. Results of illustrative calculations for air−soil partitioning suggest that, because of their high KOA values, PBDEs will exhibit similar background soil concentrations as the PCBs despite having much lower air concentrations.