Sorption and Desorption of Naphthalene by Soil Organic Matter

Abstract

Nonlinear isotherm behavior has been reported for the sorption of hydrophobic organic compounds (HOCs) in soil organic matter (SOM), but the exact mechanisms are unknown. Our objective was to provide insight into the sorption mechanism of HOCs in SOM by studying the sorption-desorption processes of naphthalene in a mineral soil, its humic fractions, and lignin. Additionally, humin and lignin were used for studying the effects of temperature and cosolvent on HOC sorption. All isotherms were nonlinear. The humin and lignin isotherms became more linear at elevated temperatures and with the addition of methanol indicating a condensed to expanded structural phase transition. Isotherm nonlinearity and hysteresis increased in the following order: soil humic acid (HA) < soil < soil humin. Of the samples, aliphatic-rich humin exhibited the largest degree of nonlinearity and had the highest sorption capacity for naphthalene. High nonlinearity and hysteresis in humin were most likely caused by its condensed structure. A novel aliphatic, amorphous condensed conformation is proposed. This conformation can account for both high sorption capacities and increased nonlinearity observed for aliphatic-rich samples and can explain many sorption disparities discussed in the literature. This study clearly illustrates the importance of both aliphatic and aromatic moieties for HOC sorption in SOM.

Sorption of 2,4,6-Trichlorophenol in Model Humic Acid−Clay Systems

“…Previous reports demonstrated that some organic matters, such as Canada peat, exhibited no measurable desorption hysteresis. However, mature organic matters and kerogen exhibited appreciable desorption hysteresis (34). In our desorption experiments, humic acids with different origins showed obvious desorption hysteresis, which was evidenced by lower N d /N s values (HI values).…”

“…The domains are characterized as expanded and condensed, analogous to rubbery and glassy synthetic polymers, respectively. The sorption of organic pollutants to the expanded "rubbery-like" domain generates linear isotherms due to partitioning while nonlinear isotherms are observed for the condensed "glassy-like" domain (34). On the basis of the component of humic acid and the nonlinearity of sorption isotherm, HA 1 appeared to have a relatively more rigid structure (rich in glassy or condensed phase).…”

Determinação do coeficiente de distribuição (Kd) de benzo(a)pireno em solo por isotermas de sorção

“…Um levantamento mais detalhado da literatura mostrou que vários pesquisadores também observaram isotermas de sorção do tipo-S para compostos orgânicos não polares [15][16][17] . Mas até hoje, ainda não foi estabelecido um conceito claro para explicar o comportamento de interação de compostos orgânicos não polares com o solo.…”

Impact of Biochar on Organic Contaminants in Soil: A Tool for Mitigating Risk?

“…However, increases in soil-chemical contact time result in decreases in desorbing fractions and also produce a non-bioavailable, highly sequestered (non-extractable) fractions in soils (Figure 1) [24,25]. The concentration of the chemical and properties of soil also determines how much could be sorbed within the soil [46,47]. The chemical activity of a contaminant is closely related to fugacity and freely dissolved concentrations; it quantifies the energetic state of the chemical and determines the potential for diffusion, sorption and partitioning [48].…”