Assessment of Availability of Phenanthrene and Pyrene in Aging Soil

The availability of polycyclic aromatic hydrocarbons (PAHs) in aging soils has not been well elucidated. In this study, sequential extraction was utilized to evaluate the availability of phenanthrene and pyrene as representative PAHs in four typical zonal Chinese soils with aging period for 16 weeks. The tested PAHs were fractionated into two groups: the extractable fractions and bound residues. The former, including desorbing and non-desorbing fractions, is the available fractions in soil that can be taken up by plants and/or soil-inhabiting animals. Both the desorbing and non-desorbing fractions were observed to generally decrease over time, primarily due to microbial biodegradation of the available residues, the desorbing fractions were more readily biodegradable (>91.4% and >71.2% for phenanthrene and pyrene, respectively) than the non-desorbing fractions. Attenuation of the desorbing fraction accounted for more than 92.1% and 76.8% of the observed reduction of the available residues of phenanthrene and pyrene, respectively. The observed concentrations of bound PAH residues were much lower than those of the available residues. In comparison with microbial biodegradation, the transformation of available fractions to bound residues accounted for only a negligible reduction of the available residues of the PAHs tested. These results are useful for risk assessments of PAHs related to human health and environmental contamination.