Characteristics and Biodegradation of Nonextractable Residues of Polycyclic Aromatic Hydrocarbons in Historically Polluted Soils

Polycyclic aromatic hydrocarbons (PAHs) can form nonextractable residues in soil, significantly impacting their environmental behavior and fate. Although considerable research has been conducted on the formation of nonextractable residues of PAHs in soil through spiked experiments using representative PAH compounds, limited research has been given to the nonextractable residues of 16 priority PAHs in historically polluted soils. This study aimed to investigate the concentrations and compositions of the nonextractable residues for parent PAHs in five historically polluted soils and their biodegradation in three soils. The results indicated that the average contents of total nonextractable residues ranged from 183–2922 μg∙kg−1 in the five soils, with 4-ring PAHs (42.1 ± 4.2