title: Interaction of polar and nonpolar organic pollutants with soil organic matter: sorption experiments and molecular dynamics simulation.
abstract: The fate of organic pollutants in the environment is influenced by several factors including the type and strength of their interactions with soil components especially SOM. However, a molecular level answer to the question "How organic pollutants interact with SOM?" is still lacking. In order to explore mechanisms of this interaction, we have developed a new SOM model and carried out molecular dynamics (MD) simulations in parallel with sorption experiments. The new SOM model comprises free SOM functional groups (carboxylic acid and naphthalene) as well as SOM cavities (with two different sizes), simulating the soil voids, containing the same SOM functional groups. To examine the effect of the hydrophobicity on the interaction, the organic pollutants hexachlorobenzene (HCB, non-polar) and sulfanilamide (SAA, polar) were considered. The experimental and theoretical investigations explored four major points regarding sorption of SAA and HCB on soil, yielding the following results. 1--The interaction depends on the SOM chemical composition more than the SOM content. 2--The interaction causes a site-specific adsorption on the soil surfaces. 3--Sorption hysteresis occurs, which can be explained by inclusion of these pollutants inside soil voids. 4--The hydrophobic HCB is adsorbed on soil stronger than the hydrophilic SAA. Moreover, the theoretical results showed that HCB forms stable complexes with all SOM models in the aqueous solution, while most of SAA-SOM complexes are accompanied by dissociation into SAA and the free SOM models. The SOM-cavity modeling had a significant effect on binding of organic pollutants to SOM. Both HCB and SAA bind to the SOM models in the order of models with a small cavity>a large cavity>no cavity. Although HCB binds to all SOM models stronger than SAA, the latter is more affected by the presence of the cavity. Finally, HCB and SAA bind to the hydrophobic functional group (naphthalene) stronger than to the hydrophilic one (carboxylic acid) for all SOM models containing a cavity. For models without a cavity, SAA binds to carboxylic acid stronger than to naphthalene.
authors.affiliation: University of Rostock, Institute of Physics, D-18051 Rostock, Germany; University of Cairo, Faculty of Science, Department of Chemistry, 12613 Giza, Egypt. Electronic address: ashour.ahmed@uni-rostock.de.
authors.forename: Ashour A
authors.initials: AA
authors.lastname: Ahmed
authors.affiliation: University of Trier, Soil Science, D-54286 Trier, Germany. Electronic address: thiele@uni-trier.de.
authors.forename: Sören
authors.initials: S
authors.lastname: Thiele-Bruhn
authors.affiliation: King Abdulaziz University, Faculty of Science, Department of Chemistry, Jeddah 21589, Saudi Arabia. Electronic address: saziz@kau.edu.sa.
authors.forename: Saadullah G
authors.initials: SG
authors.lastname: Aziz
authors.affiliation: University of Cairo, Faculty of Science, Department of Chemistry, 12613 Giza, Egypt; King Abdulaziz University, Faculty of Science, Department of Chemistry, Jeddah 21589, Saudi Arabia. Electronic address: rhilal@kau.edu.sa.
authors.forename: Rifaat H
authors.initials: RH
authors.lastname: Hilal
authors.affiliation: King Abdulaziz University, Faculty of Science, Department of Chemistry, Jeddah 21589, Saudi Arabia; University of Beni-Suef, Faculty of Science, Department of Chemistry, Beni-Suef, Egypt. Electronic address: skamel@kau.edu.sa.
authors.forename: Shaaban A
authors.initials: SA
authors.lastname: Elroby
authors.affiliation: King Abdulaziz University, Faculty of Science, Department of Chemistry, Jeddah 21589, Saudi Arabia. Electronic address: aalyoubi@kau.edu.sa.
authors.forename: Abdulrahman O
authors.initials: AO
authors.lastname: Al-Youbi
authors.affiliation: University of Rostock, Soil Science, D-18051 Rostock, Germany. Electronic address: peter.leinweber@uni-rostock.de.
authors.forename: Peter
authors.initials: P
authors.lastname: Leinweber
authors.affiliation: University of Rostock, Institute of Physics, D-18051 Rostock, Germany. Electronic address: oliver.kuehn@uni-rostock.de.
authors.forename: Oliver
authors.initials: O
authors.lastname: Kühn
mesh_terms: D000327:Adsorption; D006581:Hexachlorobenzene / Q000737:chemistry; D056004:Molecular Dynamics Simulation; D009281:Naphthalenes / Q000737:chemistry; D009930:Organic Chemicals / Q000737:chemistry*; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000737:chemistry*
chemical_list: D009281:Naphthalenes; D009930:Organic Chemicals; D012987:Soil; D012989:Soil Pollutants; C031721:naphthalene; D006581:Hexachlorobenzene
keywords: Hexachlorobenzene (HCB); Molecular dynamics simulation; Molecular modeling; Organic pollutants; Soil organic matter (SOM); Sorption isotherms; Sulfanilamide (SAA)