• • Inside the legacy production site, HBCD concentrations reached up to 1.18×10⁶ ng·g⁻¹ dw in surface soils, exceeding outside levels by orders of magnitude (outside range: ND–6.90×10² ng·g⁻¹ dw), indicating severe point-source contamination requiring immediate remediation.
• • Vertical profiling showed a sharp decline with depth: from 1.08×10⁴–1.18×10⁶ ng·g⁻¹ dw at the surface to 1.05–93.5 ng·g⁻¹ dw at ~4 m depth, suggesting limited vertical migration and potential containment feasibility.
• • Cumulative environmental burden analysis revealed that 23.7% of the total HBCD load is within 2 km, 40.1% within 2.81 km, 60.0% within 4 km, and 87.1% within 6 km, quantifying the spatial footprint and guiding risk-based management zones.
• • Health risk assessment identified oral ingestion as the dominant exposure pathway, with localized high-contamination areas inside the plant posing significant non-carcinogenic risks, while risks for children outside the plant remained acceptable, supporting differential remediation priorities.