Effects of Competitor and Natural Organic Matter Characteristics on the Equilibrium Sorption of 1,2-Dichlorobenzene in Soil and Shale

Abstract

The competitive sorption behaviors of 1,2-DCB in binary solute systems in four natural sorbents having natural organic matter (NOM) matrixes of different physicochemical characters were investigated in batch reactors. Specifically, the study focused on investigating how the extent of 1,2-DCB competitive sorption depends on (i) the rigidity of NOM matrixes as assessed by the efficiency of chemical oxidation and (ii) the closeness of competitor structure to that of the primary solute. The chemical oxidation and elemental composition results suggest that the shale NOM is the most reduced and condensed, the peat was the most oxidized and amorphous, and two surface soils had intermediate NOM structures. Four chlorinated benzenes and phenanthrene were used as competing solutes. All five chemicals exhibited competition against 1,2-DCB in all sorbents, including the peat, but the extent of competition varied significantly. Little difference in the extent of competition with 1,2-DCB was observed for the various chlorinated benzenes even though some were liquids and some were solids at the experimental temperature. All of the chlorobenzenes were more effective competitors than phenanthrene. The shale showed markedly different competition features from the other sorbents, with a much smaller competitive effect at a given sorbed volume of competitor. However, normalizing sorbed competitor volumes by the capacity of the adsorption domain in the Polanyi-Manes single-solute partition-adsorption model (V0) produced qualitatively similar competitive behavior for each solute; displacement of 1,2-DCB increased with increasing sorbed competitor volumes up to V0, and little additional competition occurred beyond that point. The extent of competition was positively correlated with the maximum adsorption capacity and the fraction of "hard" and "soot" carbon contents as assessed by chemical and thermal oxidation methods. These findings indicate that competition is associated with voids in the NOM structure, that these voids are likely present within the condensed ("hard" plus "soot") carbon domain, and therefore that diagenetic alteration of NOM plays a central role in determining competitive sorption characteristics for hydrophobic contaminants.

Relationships between aging of PAHs and soil properties

“…During the diffusion processes, the PAHs were preferentially bound to the condensed OC domains and recalcitrant to mild extractants in soils (Tao et al, 2006). As a result, with the increase of hard OC in the soils, the slow diffusion rates were greatly limited by the strong affinity of PAHs in the condensed domain (Ju and Young, 2004) and exhibited a negative relationship with the hard OC in the soils (Fig. 4).…”

“…Hard OC was quantified after wet oxidation (with K 2 S 2 O 8 to OC at a ratio of 12:1) at 120 C for 4 h to remove the easily oxidized OC (Li and Werth, 2001;Ju and Young, 2004). Total OC (TOC) was measured after acid treatment (10% HCl) to remove inorganic carbon.…”

“…It was proposed that slow diffusion could be attributed to the diffusion through meso-and micropores (Pignatello and Xing, 1996;Nam and Alexander, 1998;Abu and Smith, 2006) and/or diffusion into the internal micropores of OCs or clay (Huang and Weber, 1997;Northcott and Jones, 2001;Bogan and Trbovic, 2003) in geomaterials. Condensed OC present can impact the distribution of hydrophobic micropores in soils (Ju and Young, 2004;Kwon and Pignatello, 2005). During the diffusion processes, the PAHs were preferentially bound to the condensed OC domains and recalcitrant to mild extractants in soils (Tao et al, 2006).…”

Concentration Effects on Competitive Sorption of Trichloroethylene and Tetrachloroethylene to the Roots of Typha latifolia: Implications for Phytomonitoring

“…Pignatello and Xing (1996) also found that total competitive effects strengthened as the concentration of competing compounds increased in the solid phase in their investigation of the competitive sorption of atrazine and other compounds to soil. In a separate study on the competitive sorption of 1,2-dichlorobenzene to four different types of soil, Ju and Young (2004) noticed that competition strengthened with increasing initial aqueous loading of the competitors. However, competitive effect became insignificant when the primary and competing compounds in the solute were beyond approximately 150-200% of the sorption capacity of the adsorbents (Ju and Young 2004).…”

“…Evidence is accumulating to suggest that competitive sorption is a common environmental phenomenon, and competitive sorption to sediments, nanotubes, wood materials, and chars has been reported (Xing and Pignatello 1997;Ju and Young 2004;Wang et al 2006;Yang et al 2006). The literature currently attributes nonlinear sorption behavior to one of the following three potential mechanisms: existence of two distinctively different sorption domains (glassy vs. rubbery) (Leboeuf and Weber 1997), high surface area carbonaceous materials (HSACM) in the composition of adsorbents (Chiou and Kile 1998), and pore filling (Xing and Pignatello 1997).…”