Interaction of Polar and Nonpolar Organic Pollutants with Soil Organic Matter: Sorption Experiments and Molecular Dynamics Simulation

摘要

The fate of organic pollutants in the environment is influenced by severalfactors including the type and strength of their interactions with soilcomponents especially SOM. However, a molecular level answer to the questionHow organic pollutants interact with SOM? is lacking. In order to exploremechanisms of this interaction, we have developed a new SOM model followed bycarrying out molecular dynamics (MD) simulations in parallel with sorptionexperiments. The new SOM model comprises free SOM functional groups (carboxylicacid and naphthalene) as well as SOM cavities (with two different sizes),representing the soil voids, containing the same SOM functional groups. Toexamine the effect of the hydrophobicity on the interaction, the organicpollutants hexachlorobenzene (HCB, non-polar) and sulfanilamide (SAA, polar)were considered. The experimental and the theoretical outcomes explored fourmajor points regarding sorption of SAA and HCB on soil. 1. The interactiondepends on the SOM chemical composition more than the SOM content. 2. Theinteraction causes a site-specific adsorption on the soil surfaces. 3. Sorptionhysteresis occurs, which can be explained by inclusion of these pollutantsinside soil voids. 4. It was observed that the hydrophobic HCB is adsorbed onsoil stronger than the hydrophilic SAA. Moreover, the theoretical resultsshowed that HCB forms stable complexes with all SOM models in the aqueoussolution while most of SAA complexes are accompanied by dissociation. TheSOM-cavity modeling showed a significant effect on binding of organicpollutants to SOM.