Fate of post-blast residue in soils from an armed conflict zone determined by magnetic, microbiological, and ecotoxicological assessments

Weapon detonations generate substantial quantities of post-blast residue (PBR), which contributes iron-rich particles to soils. After deposition, these residues undergo redox transformations that produce bioavailable iron compounds, potentially increasing phytotoxic risks to agricultural crops. In the present study, soil contamination by detonation of military weapons was simulated by adding 1% of < 1 mm PBR to soil, and iron mobilization under waterlogged conditions was subsequently monitored. Scanning electron microscopy revealed two components in PBR: iron-bearing spherules and metallic fragments composed of an iron core with an oxidized surface layer. Magnetic analyses confirmed that waterlogging had a limited impact on PBR, with no significant changes in explosion-derived iron spherules; however, a decrease was observed in hematite-like phases associated with surface-corroded iron fragments. This decrease was linked to the interaction of these phases with metabolically active soil microorganisms. Following the addition of a carbon and energy source (potato) to PBR-contaminated soil, the abiotic reaction of Fe0 oxidation to Fe2+ significantly accelerated due to microbial synthesis of organic acids and protons (H+) and iron mobilization by microbial activity. This markedly affected the soft magnetic material (fine pedogenic magnetite and iron core of PBR fragments) as well as highly coercive phases (oxidized coating of iron fragments and lithogenic hematite). Phytotoxic effects were evaluated by assessing seed germination, seedling, and root growth in representative species planted during the period of elevated soluble iron concentrations. Increased iron accumulation in stressed seedlings was a key indicator of PBR toxicity. These laboratory-simulation results improve our understanding of the potential environmental transformation of war-related iron residues and their implications for soil sustainability, which require validation under field conditions.