Low-molecular-weight organic acids enhance the release of bound PAH residues in soils

Abstract

Understanding the release and availability of bound residues of polycyclic aromatic hydrocarbons (PAHs) in the rhizosphere is essential when assessing their fate and risk in the soil environment. However, limited information is available regarding the impact of root-secreted low-molecular-weight organic acids (LMWOAs) on the release of bound PAH residues in soils. The aim of this study was to investigate the LMWOA-influenced release of soil bound PAH residues. An n-butanol extraction procedure was used to evaluate the release of soil bound PAH residues. LMWOAs can dramatically promote the release of bound PAH residues and enhance the extractability and availability of PAHs in soil. The addition of LMWOAs significantly increased the extractable concentrations of ΣPAH and each individual PAH in soils containing bound PAH residues in a LMWOA-concentration dependent manner. Compared with control treatments without addition of LMWOA, the concentrations of butanol-extractable ΣPAH and each PAH in soils following the addition of 10–100mmol/kg LMWOAs were 54–745% and 58–605% larger after 40 and 80 days, respectively. Citric acid always generated the largest PAH release from soil bound PAH residues, while malic acid generated the lowest release among the three LMWOAs tested. The results of this work provide important information regarding the fate of bound PAH residues in the soil environment, and will be useful for the risk assessment of PAH-contaminated soils and the development of remedial strategies for contaminated sites.