Understanding the long-range transport of polybrominated diphenyl ethers

Polybrominated diphenyl ethers (PBDEs) are a class of emerging environmental pollutants. Their structural similarities to polychlorinated biphenyls (PCBs) and pervasive use in consumer products as flame retardants have lead to widespread contamination. High indoor concentrations have led to serious concerns on human exposure. Although these compounds have been used since the late 1970s, most published reports on environmental detection have been available only in recent years. Information on their physical-chemical properties is particularly scarce which leads to poor understanding and prediction of fate and transport characteristics. The Henry's Law constant was the major focus of this study because it describes the partitioning process between key environmental phases of air and water. Until three years ago, no published data existed for this property.; Henry's Law constants of PBDEs and PCBs were experimentally determined using the standard gas-stripping method and two of its variations---modified gas-stripping and integrated gas-stripping methods (developed in this study). The assumptions of the standard method were evaluated by the development of a mass balance approach which was systematically implemented for the first time. The mass balance results showed that the highly brominated PBDEs exhibited extensive adsorption/desorption with solid surfaces, which affected the accuracy of the aqueous concentration. The sorption characteristic also implied a lower mobility in the environment and potential for long-range transport.; The temperature dependence of Henry's Law constants were also measured since they are sensitive to temperature change, which are compound-specific. The increase in Henry's Law constants with temperature for PBDEs were not as great as the PCBs which further implied lower volatility and therefore mobility within this temperature range. The highly brominated PBDE congeners would not undergo extensive long-range transport and remain close to the area of emission while the less brominated congeners would have a much higher potential in traveling long distances. Finally, three different estimation methods---bond contribution method, group contribution method and polarizable continuum model---were used to predict Henry's Law constants of the same compounds. Unfortunately, predicted values contained substantial errors.