Predictive Capability of Transport and Fate Processes

Predictive Capability. Estimation of Ksc from solubility would suffice as a screening test for making decisions for further detailed measurements. Mill (1980) developed a regression equation  

A regression line has been plotted using and the aqueous solubility of a variety of chemicals (accurately measured). One can estimate K c within a power of ten for most nonpolar chemicals, which is sufficiently accurate for screening most chemicals. 

Hydrolysis of organic compounds usually results in the substitution of a group by a hydroxyl group. In water, the reaction is catalyzed by H, OH, and ions. In moist soils, labile complexes of calcium and copper act as catalysts. Sorption tends to increase a chemical s reactivity to or OH radicals. Mabey and Mill (1978) reviewed the kinetic data for hydrolysis of a variety of organic chemicals in aquatic systems and the chemical characteristics of most fresh-water systems. These data could be used to calculate the persistence (half-life for hydrolysis) of chemicals under natural environmental conditions. 

Predictive Capability. Screening and detailed test methods to calculate various hydrolytic kinetic parameters and their temperature dependence are available (Mill etal., 1978). A significant data base on semiempirical structure-activity relationships for most kinds of hydrolytic reactions are available in literature (Wells, 1963 Taft, 1956). The data base is large enough to predict a rate constant within a factor of 2 or 3 for a specific chemical within a family of structurally related chemicals. 

Volatilizational loss of chemicals from water to air is an important fate process for chemicals with low aqueous solubility and low polarity. Many chemicals, despite their low vapor pressure, can volatilize rapidly owing to their high activity coefficients in solution. Volatilizational loss from surfaces is a significant transport process. Volatilization of organic chemicals from the soil surface is complicated by other variables. There is no simple laboratory 

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