Speciation and influencing factors of polycyclic aromatic hydrocarbons in soils of southwest China.

Purpose: Organic pollutants' transport, transformation, and biological effectiveness in soils depend mainly on their chemical forms. Therefore, in addition to studying the total content of pollutants, it is essential to understand the forms of organic pollutants in soils. In this study, we measured the speciations of polycyclic aromatic hydrocarbons (PAHs), including desorbing fraction, non-desorbing fraction, and bound residues, in soil samples from the Zhongliangshan karst terrain in Chongqing, southwest China. We also investigated the occurrence of PAHs in soils of the region. Moreover, we used principal component analysis (PCA) to analyze the relationship between soil properties and different speciations of PAHs in soils. The contents of ΣPAH16 ranged from 319.69–1215.64 ng/g, with a mean value of 615.02 ng/g. Desorbing fraction PAHs were significant, accounting for 34–81% of the total PAHs. The ratio of different speciations ordered as soluble > organic solvent extracted > bound residues. 2-3-ring were the major components of the total PAHs content in soils and desorbing fraction. PCA analysis determined that soil organic matter (SOM), total nitrogen (TN), and soil bulk density significantly affected the non-desorbing fraction, and pH and total organic carbon (TOC) had a significant positive correlation with the bound residues. The karst area is a complex and fragile ecosystem. The speciation of PAHs in soils is of great importance for assessing their risk and for remediation. However, most studies have focused on the concentration and distribution of PAHs in karst soils. Therefore, in this paper, we investigated the distribution of PAHs in soils in karst areas by investigating the distribution of different speciations of PAHs in soils. We also investigated the key factors influencing the distribution of different speciations. Materials and methods: Ten sites were selected in Zhongliangshan karst terrain, where 0–20 cm of soil was collected and the concentrations of 16 PAHs were measured. Three speciations of 16 PAHs in soils were extracted by sequential extraction. And the standard methods recommended by the Chinese Society of Soil Science were used to determine the basic soil properties. Result and discussion: In this study, we measured the speciation of PAHs in soil samples from the Zhongliangshan karst terrain in Chongqing, southwest China, including desorbing fraction, non-desorbing fraction, and bound residues. The total content of the 16 PAHs ranged from 319.69 to 1215.64 ng/g, with an average value of 615.02 ng/g. The desorbing fraction was significant, accounting for 34–81% of the total PAHs. The ratio of different speciations is ordered as desorbing fraction > non-desorbing fraction > bound residues. 2–3-ring were the major components of the total PAHs content in soils and each speciation. The PCA results show a significant effect of soil organic matter, TN, and soil bulk density on the non-desorbing fraction. pH and TOC had a relatively significant positive correlation with bound residues. Conclusions: This paper investigated the contamination status of PAHs in surface soils in the karst terrain of southwest China, and the speciation of PAHs. Under the special geological structure background in karst areas, studying the occurrence forms and influencing factors of PAHs pollutants in soils is of great significance for a deeper understanding of the occurrence forms of pollutants and effective control of their diffusion. [ABSTRACT FROM AUTHOR]