Measurement of Henry's law constants of seven polybrominated diphenyl ether (PBDE) congeners as a function of temperature

Abstract

Polybrominated diphenyl ethers (PBDEs) are emerging as a significant class of semivolatile environmental pollutants. The Henry's law constant (H) is an important parameter in predicting the transport, behavior and fate of semivolatile organic compounds (SOCs) in the environment and it is required to model the chemical transfer between air and water. Henry's law constants for 7 PBDE congeners (BDE 28, 47, 99, 100, 153, 154, and 209) that have been frequently detected in the environment were experimentally determined between 5 and 40 °C using a gas-stripping technique. The Henry's law constants ranged between 0.04±0.01 Pa m3 mol−1 (BDE 209) and 4.83±0.67 Pa m3 mol−1 (BDE 28) at 25 °C. Dimensionless Henry's law constants (H′) of PBDEs increase with temperature more than 15 times (15.3 times for BDE 100 and 34.1 times for BDE 99) over the studied temperature range. The enthalpies of phase change (ΔHH) ranged between 54.1 kJ mol−1 (BDE 154) and 70.8 kJ mol−1 (BDE 99) and they were within the ranges previously reported for other organic compounds. The gas phase overall mass transfer coefficients (Kg) for 7 PBDE congeners calculated for a moderate wind speed (3 m s−1) and a temperature of 25 °C ranged between 0.17 and 0.27 cm s−1. Calculated resistances indicated that only the mass transfer of BDE 28 that has a relatively higher H value is controlled by both air- and water-side resistances. However, for the remaining congeners the mass transfer is controlled by air-side resistance.