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

Both subcooled liquid vapor pressure (P) and octanol-air partition coefficient (K) 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 A and B for P (log P=A+B/T) and A and B for K (log K=A+B/T), where T is temperature in K. In this study, a simple equation to relate log K and log P (log K=-log P+6.46) was derived, which also links the coefficients of A &B and A &B. Regression analysis of published data of internal energy ΔU 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 K 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 A &B and A &B for all 209 PBDE congeners at the following steps. First, B was computed using the values of ΔU. Next, we calculated the values of A using the values of B and the values of log K at 25°C. Finally, the values of the parameter A and B 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 P and K 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.