SUITMA 2005 Cairo - Characteristic properties of soil organic matter with technogenic input and their impact on sorption of organic pollutants
SUITMA 2005 Cairo
| This abstract is about one of the papers of the Properties of unconventional soils theme of the SUITMA 2005 symposium. |
| Kerstin Abelmann,i | Heike Knicker,i |
| Kai Uwe Totsche,i | Ingrid Kögel-Knabner.i |
- i - Lehrstuhl für Bodenkunde - Technische Universität München (TUM), Freising-Weihenstephan, Germany.
Industrial and mining processes led to an enrichment of technogenic organic material in soils of industrialized areas. Those inputs alter composition and structural properties of the soil organic matter (SOM), which also affects sorption of hydrophobic organic compounds (HOC). In the present study several natural SOM, soils with technogenic input and carbonaceous organic material such as soot, coal residues and their combustion remains were characterized by solid state 13C NMR spectroscopy. The structural properties were related to Freundlich sorption isotherms of five HOCs (benzene, tetrachloroethylene, 1,2-dichlorobenzene, 1,4-dichlorobenzene and phenanthrene). The Freundlich sorption coefficients were normalized to the organic carbon content (KOC°-values).
The aromaticity increased with a decreasing proportion of polar compounds. Some soils with technogenic input showed low polarity but high aromaticity. Here, the polarity was calculated from the proportion of polar (aryl C, alkyl C) to non-polar C (carboxyl C, O/N-alkyl C, O-aryl C) C groups. Within the coals and the soils with technogenic input increasing aromatic C was accompanied by decreasing alkyl C. The determination of structural parameters by the NMR technique allowed to verify the presence of carbonaceous material and thus to differentiate between natural mineral and soils with technogenic input by solely analytical means. A distinct positive correlation between KOC°-values and aromaticity was found. The highest sorption capacities were observed for samples with a high proportion of carbonaceous material as detected by NMR. A negative correlation between Freundlich exponent (1/n) and aromaticity was obtained. Large amounts of carbonaceous OM and high aromaticity caused dominating adsorption, whereas partitioning determines the HOC sorption of SOM containing a high proportion of polar compounds.
Advanced NMR techniques such as dipolar dephasing and variable contact time measurements indicated a slight increase of the portion of bridged aryl C from the natural mineral soils to the coals, concurrently with an increase in aromaticity. The size of the basic aromatic structure was found to be limited to benzene- up to naphtacene-like units or to clusters with a size of maximal six rings, both with at most four substituents. For the soils with technogenic input, the content of bridged aromatic C varied independently of the aromatic carbons, emphasizing that the structural alterations are dependent upon the kind of carbonaceous OM. A significant relationship between sorption capacity and the proportions of bridged and protonated domains within the total organic matter were obtained, showing, that both aromatic domains are important sorption sites. However, for the sorption behavior of the protonated domains a higher sensitivity with respect to the origin of the technogenic input was observed. This clearly demonstrates that beside the parameters aromaticity or polarity of SOM, structural properties of its aromatic portion have to be considered for a more precise description of the sorption behavior of HOCs.
