Adsorption behavior and co-pollutant interactions between representative polycyclic aromatic compounds and heavy metals mediated by soil organic matter and Fe oxides in soil aggregates

Purpose Polycyclic aromatic compounds (PACs) and heavy metals (HMs) frequently coexist in the soil of industrial areas, posing significant ecological risks. This study investigated the distribution and influencing factors of PACs and HMs in soil aggregates under co-contamination, as well as their interactive adsorption behavior and mechanisms with soil, with a focus on lead (Pb), phenanthrene (Phe), and 1-acenaphthenone (1-ACE). Methods Soil samples were collected from an industrial area and fractionated into four aggregate sizes. soil properties and the contents of PACs and HMs in different aggregates were determined. Single and co-adsorption behaviors of Pb, Phe, and 1-ACE were examined through batch adsorption experiments, with isotherms modeled using Freundlich, Langmuir, and Linear models. Adsorption mechanisms were further explored by X-ray photoelectron spectroscopy (XPS) analysis. Results Most PACs and HMs mainly accumulated in the < 0.002 mm aggregates, with HMs influenced by multiple soil properties and PACs primarily influenced by soil organic matter (SOM). The Freundlich parameters (K F and 1/n) indicated that Pb exhibited heterogeneous multilayer adsorption, while Phe and 1-ACE exhibited homogeneous adsorption. The presence of Phe inhibited Pb adsorption by 7.94–19.28%, whereas 1-ACE enhanced it by 3.28–12.65%. Conversely, Pb coexistence increased the adsorption of Phe (17.29–27.26%) and 1-ACE (40.10–60.03%). XPS revealed that Phe competed with Pb for C=O groups, weakening Pb’s complexation and ion exchange, while 1-ACE promoted Pb adsorption by increasing C=O proportions. Pb enhanced Phe adsorption via increased surface hydrophobicity and π-π interactions, while it promoted 1-ACE adsorption through strengthened complexation and iron oxides interactions. Conclusions The results demonstrated that the interaction between co-contaminants and soil can alter the adsorption behaviors of pollutants, thereby deepening our understanding of their environmental fates. These findings provide crucial insights for assessing environmental risks and developing remediation strategies for co-contaminated soils.