Chemical Property Estimation Techniques for Environmental Modeling

Mathematical modeling of chemical fate provides an excellent framework for sorting out massive quantities of environmental data in an organized way. Parameters in a model may be varied to gain an understanding as to what processes are most important in determining the environmental behavior of a chemical. One of the most useful modeling approaches integrates data on physical-chemical properties of the compound in question with hydrodynamic or aerodynamic transport models. The approach employs the results of such laboratory measurements as aqueous solubility, saturation vapor pressure, liquid and vapor molecular diffusivity, Henry\´s law constant, UV-adsorption spectra, octanol-water partition coefficient, photolysis rate, microbial degradation rate, etc. These data are then incorporated into various steady-state or time dependent fate models. In recent applications of these models to simulate the environmental behavior of PCBs, PCDDs, PCDFs, and other chlorinated aromatic hydrocarbons (CAHs) in the Great Lakes, it quickly became obvious that much of the aforementioned data are lacking. While property estimation techniques have been used extensively in the fields of chemical engineering and pharmacology, the data base for the CAHs has not been of sufficient quality and quantity to test these procedures. However, recent work has produced high quality and self consistent data on aqueous solubilities, saturation vapor pressures, and octanol-water partition coefficients for the CAHs. In this paper we present a summary of some of the more useful estimation techniques for aqueous solubilities and vapor pressures. This is followed by an examination as to how well these techniques work for compounds whose aqueous solubilities and saturation vapor pressures range down to M and atm.