Experimental and Theoretical Determination of Henry's Law Constant for Polychlorinated Biphenyls: Its Dependence on Solubility and Degree of Chlorination.

The fate of a pollutant in the environment depends on its interaction with the surroundings. Henry's law constant (HLC) is one of the important properties useful for assessment of environmental risk and estimation of mass transfer of the pollutant between water and air. Estimation of HLC is relatively a difficult task for many of the organic pollutants due to their very low aqueous solubility. People have attempted the measurement of HLC for persistent organic pollutants, such as polychlorinated biphenyls (PCBs), but due to the difficulty in estimation, there is a variation of approximately 2-3 orders of magnitude in reported values of HLC for PCBs in the literature. A study was performed for estimation of HLC for PCBs using the static method with a modification that eliminates any disturbance in equilibrium due to sampling and also avoids removal or addition of material in or out of the system unlike the conventional methods. The results were consistent with the literature values. The experimental values of HLC ranged from 0.004 to 0.08 for different congeners. All of the experimental values were in agreement with the literature values. The experimental data was further used for deriving a correlation equation for theoretical estimation of the HLC from aqueous solubility and chlorination number. The equation gave a very good estimation of HLC values for all the PCBs congeners except single- and double-chlorinated congeners. The theoretically predicted values were also found to be in close agreement with the reported HLC values.