Predicting volatile organic vapor sorption from soil specific surface areaand texture

Vapor sorption of a volatile organic chemical (VOC) to soil minerals at low water contents can increase the total VOC sorption capacity of the soil by several orders of magnitude. Vapor sorption can subsequently cause high VO C fluxes out of the soil during periods with fluctuating low soil water con tents. Models for predicting VOC sorption, including vapor sorption, as a f unction of soil water content are therefore valuable for evaluating contami nant volatilization and exposure risk at polluted sites. A model for estima ting trichloroethylene (TCE) sorption parameters at low relative vapor pres sure from ethylene glycol monoethyl ether (EGME)-measured soil specific sur face area (SA) and soil clay and organic carbon content was developed based on TCE sorption data from 26 different porous media, Significant improveme nt in prediction accuracy compared with a previous model was achieved. Base d on data for 13 soils, an organic carbon partitioning coefficient of K-oc = 0.60 f(oc) cm(3) g(-1) (R-2 = 0.97) for TCE is recommended for use in the new TCE sorption model. In case SA is not available, an expression for pre dicting SA from soil clay content is proposed. The clay-based TCE sorption model was tested against independent data for two Japanese soils (a sand an d a clay loam) measured in this study by a gas chromatography-based soil mi crocolumn method. The sorption model accurately predicted TCE retardation ( sorption) as a function of soil water content for both soils, Model calibra tion to sorption data for three different VOC's (benzene, TCE, and toluene) implies that the sorption model may also be applied to chemicals other tha n TCE, However, sorption measurements for more chemicals and soils at varyi ng water contents are necessary to further generalize the VOC sorption mode l.