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Supercritical-fluid extraction as a method for investigating the fate of the organic contaminants in soil.

Supercritical fluid extraction (SFE) has proven to be a method for the extraction of pollutants from the soil having serious difficulties to be standardized. A new possibility to use SFE for investigate the fate of pollutants in the soil structure is suggested. The recovery of the analyte from the soil matrix depends on the mass transfer. This includes the desorption of the analyte from the soil surface, its diffusion through the interior of the soil structure, and its transport within the bulk flow of supercritical fluid through the interstitial pores of the soil. The mass transfer can be expected to depend on both the different types of soil and the different location of the analyte in the soil structure. The analyte extraction is also controlled by thermodynamic factors such as the sorption/desorption equilibrium from the soil. On this basis, a mathematical model based on the supercritical fluid extraction conditions (viz, temperature, pressure, fluid flow, modifier,...), which are directly linked to the status of the analyte in the soil, is developed. The elaboration of the kinetical results using our model would permit to approximate the distribution of the contaminant to a non porous- or to a deep porous-soil structure model as a function of a fresh contamination or an aged contamination. These conditions can be described by spiked or native contaminant extraction time profiles, respectively.