Corrosion, release and transformation of TNT from submerged munitions under simulated marine conditions

The corrosion of sea-dumped munitions represents a long-term source of explosive contamination in marine environments. However, the coupled processes governing corrosion, release and transformation remain poorly understood. This study presents a laboratory-scale munition analogue that simultaneously quantifies corrosion, TNT release, and transformation within a partially exposed corroding munition analogue under controlled marine conditions. Cast iron casings closed at one end and open at the other end (height = 4.2 cm, radius = 0.3 cm, and thickness = 0.045 cm) weighing 1.9 ± 0.15 g containing TNT cylinders of dimensions 3.9 cm height, 0.2 cm radius, and 1.1 g in weight were exposed to synthetic seawater for 90 days. Corrosion resulted in substantial material degradation, with a mass loss of 3.2% and a thickness reduction of 17.7%. The corrosion rate was 0.33 ± 0.05 mm year^-1 and the TNT release rate was found to be 1.61 × 10^-10 kg s^-1 (13.9 mg day^-1), which aligns with the measured aqueous concentrations using HPLC (<1 mg L^-1) in the 15 L system. However, the concentration profiles showed pronounced temporal variations, indicating non-steady release behaviour. A Buckingham Π-based analysis yielded a dimensionless coefficient (β ≈ 10^-8), indicating that release was strongly constrained by casing geometry and internal transport limitations. Additionally, corrosion-derived iron minerals may contribute to TNT transformation, as observed by the formation of ADNT. Collectively, the results demonstrate that TNT fate is governed by coupled interactions among structural degradation, transport-limited release, and corrosion-driven geochemical processes. The proposed mechanistic framework and Buckingham Π-based scaling approach provide a basis for improving predictive assessments of long-term contaminant release from sea-dumped munitions.