Evaluation of gas-stripping methods for the determination of Henry's law constants for polybrominated diphenyl ethers and polychlorinated biphenyls

The objective of this research was to determine the Henry's law constants for a series of PBDE and PCB congeners using three different gas-stripping methods and to assess which method was the most accurate. A mass balance approach was applied to test the assumptions of the standard gas-stripping methodology and to quantitatively determine the fate of the chemical. The mass balance calculations showed that PCBs behaved differently in the gas-stripping systems as compared to PBDEs. The PCBs and mono- to tri-brominated PBDEs behaved ideally in the gas-stripping system while the tetra- and penta-brominated PBDEs showed extensive adsorption that invalidated the standard gas-stripping method. Also, as the number of PBDE bromine substitution increased, differences between the two classes of compounds increased. Henry's law constants for PCBs were effectively independent of the degree of chlorination, although there was a slight increase in Henry's law constants with increasing chlorination. In contrast, the PBDEs showed declining Henry's law constants with increasing bromination, from 20 Pa·m ³/mol for mono-PBDEs to 1.6 Pa·m ³/mol for penta-PBDEs.