Influence of Dissolved and Colloidal Phase Humic Substances on the Transport of Hydrophobic Organic Contaminants in Soils

Dissolved and colloidal size organic matter (DOM) controls the mobility of hydrophobic organic chemicals (HOC) in soils by affecting the sorptive interaction between the soil matrix and the solution phase. The association between HOC and DOM in the soil solution leads to an increase in the water solubility of HOC. DOM is a reactive component of the soil solution with respect to the immobile solid phase. Therefore the overall mobility of HOC in soils is enhanced due to co-transport with DOM as the mobile carrier or reduced due to co-sorption or cumulative sorption. The specific processes relevant to the DOM-mediated fate of HOC in natural and contaminated soils are discussed, with special consideration to the effect of (i) soil physico-chemical parameters (ionic strength, composition, pH), (ii) DOM of different origin, and (iii) aging of a contamination on HOC release.