Desorption and bioaccessibility of high-molecular-weight PAHs in aged field soil and humin-like fraction from a coke plant

Abstract

The distribution of the sixteen priority polycyclic aromatic hydrocarbons (PAHs) in different components of field aged soil was investigated. Furthermore, the desorption and bioaccessibility of high molecular weight (HMW) PAHs with five and six aromatic rings were explored using XAD-2 resin-assisted desorption assay due to their high carcinogenicity, and Fourier Transform Infrared Spectroscopy (FTIR) was used to uncover the functional groups controlling PAHs bioaccessibility. It was revealed that nearly 99% PAHs were retained in mineral and humin-like fractions (HU), and the percentages reserved by HU fraction increase as aromatic ring increase. The accumulated HMW PAHs desorbed during the 120 d desorption experiment were 34 ~ 44% in soil with particle diameter less than 0.2 mm (referred as bulk soil hereafter) while 32 ~ 46% in HU. The desorption kinetics can be regressed well using the two-compartment model, and the fast desorption rates for bulk soil and HU were on the order of 10–2 d−1, an order of magnitude higher than the corresponding slow desorption rates. The FTIR spectra revealed that de-ashing the raw HU may expose PAHs combined with hydrophobic groups inside the mineral-organic complex to the desorption system, resulting in an overestimation of the bioaccessibility.