Interaction of gunshot residues (GSR) with natural and synthetic textiles having different structural features

This study relies on the ability of six different fabrics to retain gunshot residues on their surfaces, and their capability to let them pass through. The fabrics were cotton, linen, elastane, polyester, silk and viscose, each of them placed above a filter paper sheet. This last was used to retain residues passing through fabric. Microscopic structures of the chosen textiles were characterized by optical microscopy, and their surface morphology was characterized by stylus profilometry. A semi-automatic Sig Sauer P228 pistol, calibre 9 ×21 mm IMI, was exploited and two shooting distances were considered, 10 cm and 40 cm. Preliminary, inorganic residue (IGSR) deposition patterns were visualized by X-ray fluorescence spectroscopy. Scanning electron microscopy was also used to describe morphology and composition of IGSR generated by discharging the selected gun. Concentration of IGSR on targets was then quantitatively determined by inductively coupled plasma optical emission spectrometry, while nitrites and nitrates, originated by nitrocellulose content of smokeless powders, were identified by ion chromatography. As expected, the amount of metallic residues, nitrites and nitrates decreases inversely with the shooting distance. In addition, considering the same distance, concentration of these elements changes significantly depending on the analyzed cloth. Therefore, when evaluating shooting distance in a forensic case, the habit to use a cotton textile to construct a calibration curve, despite of the actual nature of the target, could not be quantitatively accurate. It was evidenced that a significant amount of GSR passed through target fabrics, making their identification possible even on underneath tissues.