Identification and Characterization of Sorption Domains in Soil Organic Matter Using Structurally Modified Humic Acids

Abstract

The sorption of phenanthrene was examined in humic acids (HAs) from different sources: a compost, a peat soil, and a mineral soil. Sub-samples of each HA were subjected to bleaching or hydrolysis to remove predetermined chemical groups from their structures. Bleaching successfully removed a large percentage of rigid, aromatic moieties, whereas hydrolysis removed the mobile, carbohydrate components. Phenanthrene sorption by all HAs was nonlinear (N < 1). However, the phenanthrene isotherms of the bleached HAs were more linear than those of the untreated HAs, whereas the removal of the carbohydrate components by hydrolysis produced more nonlinear isotherms. The introduction of pyrene to the phenanthrene sorption system yielded more linear isotherms for all the HAs, indicative of competitive sorption. Proton spin-spin (1H T2) relaxation determined by nuclear magnetic resonance (NMR) was used to identify separate rigid (condensed) and flexible (expanded) 1H populations and to determine their distribution. These 1H domains were highly sensitive to temperature and correlated well with reported glass transition temperatures for HAs. In combination with the chemical treatments, sorption, and spectroscopic data, we were able to observe some significant relationships among chemical groups, sorption behavior, and structural characteristics.

Effect of temperature on the sorption and desorption of perfluorooctane sulfonate on humic acid

“…The rigidity of a macromolecular structure was reflected by the glass transition temperature T g , which has been discovered for humic acids with differential scanning calorimetry analysis and ranged between 43 and 72°C (Schaumann and Antelmann, 2000;Katherine et al, 2000;LeBoef and Weber, 2000;Young and LeBoeuf, 2000). According to the temperature isotherms below the T g of humic acid in this study, the structure and properties of the humic acid should be unchanged (Gunasekara, 2003). It may be the reason for the similarity of TII values observed at 5, 25, and 35°C.…”

Role of extractable and residual organic matter fractions on sorption of phenanthrene in sediments

“…In contrast, pyrene displayed a strong nonlinear sorption isotherm on a degraded lignin (Chefetz et al, 2000). Gunasekara et al (2003) observed that Phen sorption isotherms were more linear on bleached humic acids that had lignin removed structurally than on the corresponding untreated humic acids. Hence the sorption mechanism of HOCs on lignin is still under discussion.…”

The Role of Organic Matter–Mineral Interactions in the Sorption of Organic Contaminants

“…3.1). Numerous studies have provided evidence for proportional relationships between the amount of contaminant sorption and OM aromaticity (Xing 2001;Gauthier et al 1987;Perminova et al 1999;Chefetz et al 2000;Chin et al 1997), specific OM domains (Salloum et al 2000;Gunasekara et al 2003;Simpson et al 2003;Mao et al 2002), and/or OM polarity (Xing et al 1994b;Gauthier et al 1987;Grathwohl 1990;Kopinke et al 2001). In addition to this, several reports suggest that the physical conformation (as illustrated in Fig.…”

“…Simpson et al (2003) also reported an increase in phenanthrene sorption to HA after the selective removal of carbohydrates and aromatic components. Gunasekara et al (2003) found that these chemical extractions resulted in a more A decrease in isotherm nonlinearity was also observed, suggesting that the removal of aromatic structures "opened up" mobile, liquid-like regions and rendered these domains more accessible to contaminants (Gunasekara et al 2003). A mass balance approach has also been used to test the role of OM conformation in contaminant sorption processes (Salloum et al 2001;Bonin and Simpson 2007a).…”