Thermal persistence and physicochemical modification of inorganic gunshot residue (IGSR)

In the medicolegal context, GSR analysis plays a key role in clarifying the dynamics of firearm-related deaths, including lesion identification and firing distance determination. However, postmortem alterations of the body, such as thermal exposure, may influence the analysis of lesions and complicate interpretation. This study aimed to evaluate the persistence and modifications of GSR under different firing distances and thermal treatments using Scanning Electron Microscopy equipped with Energy-Dispersive X-ray Spectroscopy (SEM-EDS) and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Ballistic tests were conducted on calcium-magnesium silicate substrates using a self-reloading 9 × 21 mm pistol at five barrel-to-target distances (5-100 cm). To simulate fire exposure, a subset of the targets was heat-treated in a muffle furnace for 30 min at 250, 750, and 1000°C. SEM-EDS and ICP-OES analyses were then performed, focusing on morphology and chemical composition. GSR remained detectable under all experimental conditions. Both firing distance and thermal exposure affected gunshot residues, leading to changes in morphology, particle size, and elemental composition. An antagonistic interaction between these variables on GSR composition was identified, indicating that, depending on the temperature exposure, metal concentrations may vary with firing distance. Among the metallic elements, lead showed the strongest response, as explained by its low melting point. Notably, at 1000°C, no particles fulfilled the ASTM E1588-25 criterion for characteristic GSR (Pb, Ba, and Sb), rendering the trimetallic population undetectable. These results highlight changes in GSR characteristics compared to standard criteria, suggesting the need to adapt GSR protocols in cases of burned remains.