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

Both subcooled liquid vapor pressure (P-L) and octanol-air partition coefficient (K-OA ) 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(L) and B-L for P-L (log P-L = A(L) + B-L / T) and A(O) and B-O for K-OA (log K-OA A(O) + B-O / T), where T is temperature in K. In this study, a simple equation to relate log K-OA and log P-L (log K-OA = -log P-L + 6.46) was derived, which also links the coefficients of A(L) & B-L and A(O) & B-O. Regression analysis of published data of internal energy Delta U-OA 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-OA at 25 degrees 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(O) & B-O and A(L) & B-L for all 209 PBDE congeners at the following steps. First, B-O was computed using the values of Delta U-OA. Next, we calculated the values of A(O) using the values of B-O and the values of log K-OA at 25 degrees C. Finally, the values of the parameter A(L) and B-L 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-L and K-OA 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. (C) 2018 Published by Elsevier B.V.