The Effect of Moisture and Soil Texture on the Adsorption of Organic Vapors

Abstract

The fate of volatile organic compounds (VOCs) moving as vapors in the subsurface is dependent on their interaction with the soil. Adsorption of VOC vapors is greatly influenced by soil texture and soil‐water content. The effects of differences in texture and soil‐water content on vapor partition coefficients for trichloroethylene (TCE) were examined. Batch experiments were conducted for a variety of soils and at different soil‐water contents, w, to determine the relationship between the vapor/solid partition coefficient, KD′, and w. In dry soils, KD′ was nonlinearly related to soil‐water content because, in that range, water molecules compete with VOC molecules for adsorption sites on the soil surface. Under wet conditions, KD′ became linearly related to water content according to Henry's law, indicating that adsorbed water molecules were acting as a solvent for VOC molecules. In general, KD′ under oven‐dry conditions did not relate well to total specific surface area of soils, most likely because VOC molecules adsorb only on the outside surfaces of soil particles (due to their nonpolarity), rather than the total surface area present. In the dry range, adsorption was dominated by soils with high specific areas (i.e., high clay content), while soils with higher organic carbon content manifested higher adsorption amounts in the wet moisture range. A one‐parameter, exponential model well described the log KD′‐w curve in the nonlinear region. The model parameter, a, was found to be highly dependent on the specific surface area of the soil. The proposed KD′‐(w) model incorporated in conventional VOC transport models seems promising for analyzing the effects of VOC vapor adsorption on VOC subsurface transport.

Substrate-induced volatile organic compound emissions from compost-amended soils

“…In contrast to this and despite microbial VOC production, plain soil (without plant roots) is reported to be a VOC sink, strongly dependent on soil temperature and moisture (Asensio et al 2007a). Volatile organic compound sorption to clay minerals (Petersen et al 1995;Chen and Wu 1998;Ruiz et al 1998;Poulsen et al 1998;Serrano and Gallego 2006), solubilisation in the soil aqueous phase (Asensio et al 2007a) or degradation by other microorganisms (Cleveland and Yavitt 1998;Smolander et al 2006;Owen et al 2007;Insam and Seewald 2010) may explain any soil net VOC uptake or variations between replicates (Leff and Fierer 2008). Microbial VOCs may derive from many different metabolic sources, such as primary metabolism like end products of fermentative pathways such as ethanol (ethanol fermentation), butyric acid and acetone (butyric acid fermentation) and as volatile intermediates of aerobic or anaerobic detritus decomposition (Castaldelli et al 2003;Karl et al 2003).…”

A new mechanistic framework to predict OCS fluxes from soils

“…For organic vapours it has been shown that K sw is highly correlated with soil characteristics such as C content (Petersen et al, 1995), specific surface area or clay content (Yamaguchi et al, 1999), and that K sg is usually significant at soil water contents corresponding to less than five molecular layers of water coverage (Petersen et al, 1995). In this range of soil moisture, direct chemical adsorption onto dry mineral surfaces dominates and can increase the adsorption capacity of soils by several orders of magnitude.…”

“…In this range of soil moisture, direct chemical adsorption onto dry mineral surfaces dominates and can increase the adsorption capacity of soils by several orders of magnitude. For these organic vapours the relationship of K sg with soil moisture can be related to soil specific surface area (Petersen et al, 1995) or clay content (Yamaguchi et al, 1999). However these relationships obtained for organic vapours are unlikely to be applicable for OCS because the adsorption mechanisms may be completely different.…”

Soil Infrastructure, Interfaces & Translocation Processes in Inner Space ("Soil-it-is"): towards a road map for the constraints and crossroads of soil architecture and biophysical processes

“…Other important interface processes that are intimately linked to soil architecture (matrix and pore systems) and soil OM quality and quantity in combination with organo-clay complexing are sorption of organic vapors (Amali et al, 1994;Petersen et al, 1994Petersen et al, , 1995 as well as dissolved chemicals (de Jonge et al, 2000. Taking a closer look at gaseous phase sorption in soils can lead to a renewed understanding of soil interface phenomena.…”