Uniqueness of lead oral bioavailability in ammunition demolition soils: Role of high temperature-induced species assemblages.

Open burning /open detonation of ammunition causes severe soil lead contamination. However, risk assessments based solely on total Pb concentration may overestimate exposure risk, whereas bioavailability-based evaluations are more accurate. Yet systematic studies on Pb bioavailability in these soils remain scarce. This study focused on ammunition demolition sites, analyzing the relative bioavailability (RBA) and bioaccessibility (BAc) of soil Pb using an in vivo mouse model and two in vitro gastrointestinal simulation methods (SBRC and UBM). The mean Pb-RBA in soils from ammunition demolition sites was 53.8%, ranging from 30.2% to 80.8%. Notably, the site with the lowest total Pb concentration exhibited the highest Pb-RBA and gastric-phase Pb-BAc, demonstrating that total Pb alone was an unreliable predictor of exposure risk. High-temperature demolition processes induced unique Pb mineral phases, including nano- to submicron-sized metallic Pb particles, Pb oxide crystallites partially embedded in aggregated Fe oxyhydroxide matrices, and Pb associated with Fe oxyhydroxides. Although shooting ranges share an ammunition Pb source and incinerator waste sites share a high-temperature history, this multi-phase speciation was distinct from both, underscoring the site-specific nature of Pb bioavailability in demolition soils. The mean gastric-phase Pb-BAc values measured by SBRC and UBM were 52.0% and 26.5%, respectively. In vivo-in vitro correlation analysis revealed that the SBRC gastric-phase assay was suitable for predicting Pb-RBA in these soils, whereas the UBM method was limited by its higher solid-to-liquid ratio. Multiple statistical analyses revealed that pH, TOC, and total Pb concentration were negatively correlated with Pb-RBA and gastric-phase Pb-BAc, while Fe/Mn oxide-bound fraction showed a positive correlation, indicating that soil properties and chemical speciation govern the inter-site variability in Pb bioavailability. These findings improve the understanding of Pb bioavailability at ammunition demolition sites, support refined risk assessment, and help prevent unnecessary over-remediation.