Soil polycyclic aromatic hydrocarbons and their halogenated derivatives in a brominated flame retardant production area: Spatial and vertical variations, and influencing factors

Soils serve as major sinks for organic pollutants, yet the vertical distribution of polycyclic aromatic hydrocarbons (PAHs) and their halogenated derivatives (Cl-PAHs and Br-PAHs) in industrial environments remains poorly understood despite extensive research on surface contamination. This study investigated the spatial and vertical distribution of PAHs and Cl/Br-PAHs, as well as their influencing factors, by analyzing surface and soil core samples (0.10–5.00 m) from a brominated flame retardant production park and surrounding areas. The results revealed that surface soils within the park exhibited relatively lower concentrations (PAHs: 15.9 ng/g; Cl-PAHs: 1.08 ng/g; Br-PAHs: 5.38 ng/g) compared to historical reports, indicating effective emission control and reduced recent inputs. Vertical profiles showed distinct mid-depth concentration peaks. Maximum concentrations reached 171 ng/g for PAHs and 30.8 ng/g for Br-PAHs at a depth of 0.75 m, while Cl-PAHs peaked at 6.27 ng/g at 1.5 m. These patterns suggest the influence of legacy emissions and subsequent downward migration through the soil core profiles. Br-PAHs correlated strongly with soil organic matter ( p < 0.05), indicating high sorption affinity, whereas PAHs and Cl-PAHs showed weaker relationships. In contrast, clay content showed negligible effects on pollutant retention. These findings provide critical insights into the long-term fate, retention mechanisms, and vertical transport of PAHs and halogenated PAHs in deep, industrially impacted soils, underscoring the need for targeted monitoring and remediation strategies. • Spatial and vertical profiles of PAHs and Cl/Br-PAHs were characterized in soils. • The BFR park acted as a relatively lower contamination zone from cleaner production. • Mid-depth peaks were observed in vertical pollutant profiles. • Br-PAHs correlated strongly with SOM, unlike Cl-PAHs and parent PAHs. • Clay shows minimal retention of PAHs, Cl-PAHs, and most Br-PAHs.