Sorption behavior of anthropogenic humic matter

Abstract

Humic organic matter is a catchall term for persistent biopolymers occurring in soil, sediments, and water. It is known to influence the transport, the bioavailability, and the toxicity of organic and inorganic pollutants profoundly. In addition to natural pathways, humic organic matter may also be formed on the basis of organic compounds arising from human activities. Typical examples include dumps and dump-site leaching water. Our interest is focused on a pond for wastewater from a carbonization plant in the German state of Saxony-Anhalt [1]. The coal wastewaters were originally pink, and turned dark brown as a result of autooxidation processes of organic pollutants including phenols, aromatic nitrogen bases, and PAHs. We designated these dark polymers as anthropogenic humic matter. The anthropogenic humic and fulvic acids are deposited in the sediments at the bottom of the pond and are dissolved colloidally in the water. In contrast to the knowledge about natural organic matter, which was frequently been the subject of interest (see [2, 3] and literature cited therein), the knowledge relating to both the structure and the complexing behavior of anthropogenic humic matter is rather poor. Beyond basic scientific interest, the investigation of the complexing behavior of such anthropogenic humic matter with regard to pollutants may be helpful in developing remediation strategies for contaminated sites. Therefore, our investigations aim to characterize the structure of the humic matter by combining several chromatographic (HPLC, GPC, pyrolysis-GC/MS) and spectroscopic (FTIR, 1H-NMR, ICPMS, thermogravimetry-MS) methods. Furthermore, we ~ire interested in their sorption behavior towards selected organic pollutants in water [4]. Surprisingly, anthropogenic and natural humic materials do not differ significantly in their sorption behavior towards nonpolar hydrocarbons (cf. Fig. 1). Until now, the description of sorption phenomena by physicochemical parameters has been considered impractical. However, by modifying the Flory-Huggins theory we succeeded in obtaining a mathematical expression describing the connection between the lipophilicity of a solute i, expressed by its octanol/water partition coefficient Kow, and its sorption coefficient on organic matter KoM: