Open access publications in the SLU publication database

Abstract

To make proper risk assessments of sites with contaminated soil it’s important to understand the biogeochemical processes determining transport and sequestration of the contaminants in soil. Soil organic matter (SOM) is the most important component in soil for adsorption of hydrophobic organic compounds (HOC) and the organic carbon normalized partitioning constant (KOC) is used to model partitioning of HOCs between the aqueous phase and SOM. The aqueous solubility of HOCs is low and association to dissolved organic matter (DOM) in soil solution is therefore important for the mobility of HOCs. Similarly, association to the solid phase of SOM, in this thesis denoted particulate organic matter (POM), controls the retention of HOCs in organic rich soils. Few data are reported on the partitioning of HOCs to DOM (KDOC) and to POM (KPOC) determined in the same equilibrium system. In short-term adsorption experiments with controlled equilibrium systems, adsorption to DOM and POM was best described by linear isotherms for chlorophenols (CPs) and nitrobenzene (NB), indicative of a hydrophobic partitioning mechanism. Adsorption of aniline was best described by the Langmuir isotherm, indicative of a specific interaction to functional groups of DOM and POM. Trinitrotoluene (TNT) adsorption data revealed specific interactions of degradation products to DOM and hydrophobic partitioning of TNT to POM. As a complement to the short-term adsorption experiments, soils with aged contaminants were investigated. Chlorophenols (CP), phenoxy phenols (PCPP), diphenyl ethers (PCDE), dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) associated to DOM and POM and the free analyte in the aqueous phase were determined. In both the adsorption experiments and the soils with aged contaminants, POM showed a higher binding affinity towards HOCs than DOM, when normalized to organic carbon content. The partitioning towards POM, relative to DOM, increased with increasing hydrophobicity of the classes of compound studied in the order CP<PCDE<PCDF<PCDD. No major differences in carbon chemistry were revealed between DOM and POM (using 13C-NMR, XPS and elemental analysis), thus it is suggested that some other property is responsible for the difference in binding to POM and DOM. The physical size of hydrophobic structures could be such an important property.