Polycyclic aromatic hydrocarbons (PAHs) are a group of recalcitrant organic contaminants which are potentially mutagenic or carcinogenic. Soil was viewed as a remarkable sink for PAHs from diverse sources such as direct emissions, aerosol dust deposition and wastewater irrigation. High level of PAHs in soils may pose severe health risks to the exposed human beings via food consumption, as crops grown on PAH-contaminated soils have been demonstrated to accumulate a certain amount of these contaminants. It is thus of great significance to examine the mechanisms on how these compounds are retained in soil and which soil compartment/fraction/constituent is their predominant sink. To elucidate the environmental fate of PAHs once released into soil, sixteen humic acids (HAs) and one humin (HM) fractions were sequentially extracted from a peat soil, and sixteen priority PAHs in these humic substances (HSs) were analyzed. It was found that the total concentration of 16 PAHs (∑16PAHs) increased evidently from HA1 to HA16, and then dramatically reached the highest value in HM. The trend of ∑16PAHs in HAs relates to surface carbon and C-H/C-C contents, the bulk aliphatic carbon content and aliphaticity, as well as the condensation enhancement of carbon domains, which were derived from elemental composition, XPS, 13C NMR, as well as thermal analyses. HM was identified to be the dominant sink of 16 PAHs retention in soil, due to its aliphatic carbon-rich chemical composition and the highly condensed physical makeup of its carbon domains. This study highlights the joint roles of the physical and chemical properties of HSs in retention of PAHs in soil and the associated mechanisms; the results improve understanding of the environmental fate of PAHs in soil, and provide theoretical and practical information for PAH-polluted soil risk assessment and remediation.

Association of 16 priority polycyclic aromatic hydrocarbons with humic acid and humin fractions in a peat soil and implications for their long-term retention

2019 Fall National Meeting

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