HYDROPHOBIC COMPOUNDS IN THE ENVIRONMENT - ADSORPTION EQUILIBRIUM AT THE AIR-WATER-INTERFACE

Thermodynamic parameters such as free energy, enthalpy and entropy of transfer from the bulk aqueous phase to the air-water interface at 25 degrees C for 41 hydrophobic compounds of environmental interest are c alculated from literature data on adsorption. The compounds considered are neutral, non-polar or slightly polar in nature. They comprise ali phatic hydrocarbons, halocarbons, formates, esters, branched alkanes, alcohols, acids and aromatic hydrocarbons and halocarbons. The trends in values among various homologous series of compounds are ascertained . A simple adsorption model based on interfacial energy changes predic ts the values satisfactorily; however, the prediction is sensitive to the orientation of the molecule at the air-water interface. The free e nergy changes are linearly related to other water to solvent (octanol) partition constants. The significance of air-water interfacial adsorp tion parameters in high surface area environmental systems is discusse d with special relevance to several important examples.