Octanol/air partitioning of polychlorinated biphenyls

The partitioning of 16 polychlorinated biphenyls (PCBs) between air and 1-octanol was investigated using a fugacity meter. The measurements were conducted over an environmentally relevant temperature range (10–43°C). For a given congener the measured 1-octanol/air partition coefficient KOA was exponentially proportional to the reciprocal temperature. The enthalpy of phase change (octanol to air) ΔHOA ranged from 71 to 93 kJ/mol. Up to log KOA values of 9.37 (corresponding to 2,2′,3,4′,5′,6-hexachlorobiphenyl), the enthalpy of phase change was similar to the enthalpy of vaporization of the subcooled liquid PCB. For the less volatile congeners (log KOA > 9.37), the enthalpies of vaporization exceeded the enthalpies of phase change, the difference increasing with increasing log KOA. Solubilities of the PCBs in 1-octanol were calculated from the data, and the results were in excellent agreement with octanol solubilities calculated using the OCTASOL fragment method. A very good correlation between the measured octanol/air partition coefficients and values calculated from octanol/water and air/water partition coefficients was obtained. This yielded a method to estimate reliably the octanol/air partitioning of all PCB congeners.