Effects of Low‐Molecular‐Weight Organic Acids on Sorption–Desorption of Phenanthrene in Soils

Abstract

The impact of low‐molecular‐weight organic acids (LMWOAs) on the sorption–desorption of phenanthrene, used as a representative of polycyclic aromatic hydrocarbons, was investigated with a laboratory batch technique. Experiments were conducted with three types of soil samples containing various organic components: citric, oxalic, and malic acids. The sorption of phenanthrene by soils could be well described by a linear‐type model irrespective of the addition of LMWOAs. The simulated distribution constant (Kd) and C‐normalized distribution constant (Koc) for phenanthrene sorption decreased significantly with the addition of LMWOAs to the soils (P < 0.05). In contrast, the desorption amounts of phenanthrene were clearly enhanced by the addition of LMWOAs, and the impact of citric acid on the sorption–desorption of phenanthrene was generally more significant than those of oxalic or malic acids, probably due to their chemical structures and properties. Compared with the baseline soil samples, the desorption amounts of phenanthrene in the presence of LMWOAs were significantly decreased in soils after 60 d of cultivation (P < 0.05), whereby the level of the fractional soil organic C content (foc, %) increased proportionally with the inhibition strength of phenanthrene desorption in the presence of LMWOAs. Based on these observations, we suggest that the availability of polycyclic aromatic hydrocarbons can be enhanced with suitable types and concentrations of LMWOAs.

Influences of artificial root exudate components on the behaviors of BDE-28 and BDE-47 in soils: desorption, availability, and biodegradation

“…Gao et al (2010b) and Sun et al (2012) also found that the effects of root exudates on the desorption of phenanthrene and pyrene from soils were dominantly due to the involvement of organic acids. Root exudate components are capable of increasing water solubilities of some organic contaminants, leading to their release from soils (Bais et al 2006).…”

Root Exudation: The Ecological Driver of Hydrocarbon Rhizoremediation

“…In contrast, over the past ten years many studies have demonstrated the beneficial impacts of biostimulation (amendment) with root exudates on hydrocarbon degradation [7,69,230,231,255,258,259,[263][264][265]298,299]. Furthermore, root exudates stimulate lateral gene transfer in the rhizosphere [283,289], including hydrocarbon degrading genes [228].…”

“…All these results suggest that the amendment of contaminated soils with LMWOAs can promote PAH desorption from soils, which might be used as a new approach to enhance bioavailability-and therefore bioremediation-of hydrophobic organic compounds in soils [7]. Organic acid anions exuded by roots may also enhance the desorption of hydrocarbons and/or compete for soil adsorption sites from the soil matrix, such as clay surfaces [6,255,266]. Moreover, some microorganisms are able to release biosurfactants, such as rhamnolipids, that can increase the solubility of certain organic contaminants and improve the ability of microbial cells to attach to oil droplets [267][268][269].…”

“…Root exudates can increase the solubility of hydrocarbons and alter their bioavailability [54, 254,255], making them more available for a future microbial attacks [256,257].Root exudates collected from plant roots [230,231,258] or artificial root exudate mixtures [229] can be amended to contaminated soils to enhance desorption and promote the success of rhizoremediation. For example, Gao et al [255] used artificial root exudates as amendments, and observed a considerable increase of desorption of phenanthrene and pyrene from soils. Similarly, LeFevre et al [259] showed that root exudates, both artificial and harvested from plants, enhanced naphthalene desorption from soils, providing an abiotic contribution to the "rhizosphere effect" for degradation of naphthalene.…”

“…Root exudates can increase the solubility of hydrocarbons and alter their bioavailability [54, 254,255], making them more available for a future microbial attacks [256,257]. Root exudates collected from plant roots [230,231,258] or artificial root exudate mixtures [229] can be amended to contaminated soils to enhance desorption and promote the success of rhizoremediation.…”