Estimating subcooled liquid vapor pressures and octanol-air partition coefficients of polybrominated diphenyl ethers and their temperature dependence

Abstract

Both subcooled liquid vapor pressure (PL) and octanol–air partition coefficient (KOA) are widely used as descriptors to predict gas-particle partitioning behavior of semi-volatile organic compounds (SVOCs), such as polybrominated diphenyl ethers (PBDEs). These two descriptors are functions of temperature, which are expressed as the Clausius-Clapeyron equations with the coefficients AL and BL for PL (log PL=AL+BL/T) and AO and BO for KOA (log KOA=AO+BO/T), where T is temperature in K. In this study, a simple equation to relate log KOA and log PL (log KOA=−log PL+6.46) was derived, which also links the coefficients of AL &BL and AO &BO. Regression analysis of published data of internal energy ΔUOA for 22 PBDE congeners with their mole mass was made, leading a regression equation to calculate the internal energy for all 209 PBDE congeners. Three datasets of log KOA at 25°C for all 209 PBDE congeners were evaluated; the one with the best match with experimentally measurements was selected. Using the datasets and equations described above, we calculated the values of Clausius-Clapeyron coefficients AO &BO and AL &BL for all 209 PBDE congeners at the following steps. First, BO was computed using the values of ΔUOA. Next, we calculated the values of AO using the values of BO and the values of log KOA at 25°C. Finally, the values of the parameter AL and BL were determined for all 209 PBDE congeners. Results are in consistent with data available in the literature and the accuracy of the data were also evaluated. With these Clausius-Clapeyron coefficients, the values of PL and KOA at any environmentally relevant temperature can be calculated for all 209 PBDE congeners, and thus provides a quick reference for environmental monitoring and modeling of PBDEs.