Activation of Polycyclic Aromatic Hydrocarbons in Soils by Root Exudate and Its Components
|School||Nanjing Agricultural College|
|Keywords||Soil Root exudates Polycyclic aromatic hydrocarbons (PAHs) Activation Sorption Desorption Availablity|
Organic pollutants entering into soils cause serious problems to ecological risk and to human health. How to remediate the contaminated soils and achieve the sustainable utilization of land resources has become the focus ring, is of worldwide concerns. Polycyclic aromatic hydrocarbons (PAHs) is readily fixed in soils, so understanding the activation of PAHs by the root exudates is paramount of determining the remediation strategies for soil contamination.In this research, the availability, sorption and desorption of phenanthrene and pyrene as representative PAHs in Typic Paleudalfs were studied on basic of present research situation of organic contaminated soil remediation. Main results are shown as follows:(1)The sorption of phenanthrene by Typic Paleudalfs was investigated in batch experiments designed to explore the effect of typical root exudates by addition of ARE, low-molecular-weight organic acids (LMWOA), amino acids and fructose. Phenanthrene sorption isotherms by Typic Paleudalfs could be well described by a linear sorption model irrespective of the addition of organic and amino acids. The addition of organic and amino acids significantly inhibited the sorption of phenanthrene by the soil, and adding larger amounts of these model root exudates to the soil resulted in stronger inhibition of phenanthrene sorption. With 65.1g·L-1 malic acid, Kd和Koc decreased from 998.3 L-kg-1 and 69909.0-kg-1 to 521.7L-kg-1 and 36534.0kg-1, was 47.7% of CK. Compared with amino acids and fructose, LMWOAs displayed stronger inhibition of phenanthrene sorption in soil. The inhibitory ability for phenanthrene sorption was in the order of LMWOA> amino acids> fructose. Experimental data suggest that concentrations of dissolved organic matter (DOM) increases slightly and concentrations of metal ions increase significantly in equilibrium solution of phenanthrene sorption with the addition of ARE, LMWOA, amino acids and fructose. The root exudates may disrupt humic-(metal ion)-mineral linkage, rise the degree of DOM, which may be the main reason that the RE inhibited the phenanthrene sorption in Typic Paleudalfs.(2)The effect of ARE, LMWOA, amino acids, fructose on desorption of PAHs was also investigated in Typic Paleudalfs. The data showed that the addition of ARE and its components remarkably enhanced the phenanthrene desorption. The desorption amounts of phenanthrene decrease with the increasing of the ageing time. Compared with amino acids and fructose, LMWOAs displayed stronger promote ability fo phenanthrene desorption in soil. For instance, the desorption amounts of phenanthrene increased from 10.7mg·kg-1 to 20.6,15.8,17.6,9.4,11.1,11.4 and 17.8mg·kg-1 with the addition of citric acid, malic acid, oxalic acid, serine, alanin, fructose and ARE concentration at 65.0·L-1. Based on the analyse, the mechanism of REs and its components’effect on the phenanthrene desorption was revealed.(3)The effect of ARE, LMWOA, amino acids,fructose on the availability of PAHs(phenanthrene and pyrene) was investigated. A butanol-extraction technique was used to evaluate the availability of phenanthrene and pyrene in Typic Paleudalfs. Soils spiked with phenanthrene and pyrene were aged for 30 days, and the extractable phenanthrene and pyrene were detected. With the addition of 20.0g·kg"1 citric acid, malic acid, oxalic acid, serine, alanin, fructose and ARE, the extractable phenanthrene were increased from 8.1 mg·kg-1 to 40.4,34.8,40.9,24.6,26.2,20.4 and 39.3mg-kg"’. Compared with other REs, LMWOAs had stronger effects on the availability of PAHs. Due to the larger numbers of benzene rings and higher molecular weight, pyrene was more recalcitrant to be degradated. The extractable phenanthrene increased by 386.0%(sterilized soil) and 310.8%(non-sterilized soil) with the ARE concentration at 20.6g·kg-1, while the value for pyrene was only 211.2%(sterilized soil) and 215.5%(non-sterilized soil) with the same concentration of ARE. Microbes also had evident influence on the availability of PAHs.