Composition:
- OGSR: Primarily composed of organic compounds. These include partially burned or unburned propellant chemicals, stabilisers, plasticisers, and other additives used in the gunpowder.
- IGSR: Consists of metallic particles, primarily from the primer and the bullet casing. Typically, lead (Pb), barium (Ba), and antimony (Sb) compose these particles.
Source:
- OGSR: These residues originate from the propellant in the cartridge. The combustion of gunpowder during a firearm discharge forms them.
- IGSR: Inorganic residues originate from the primer, which the firing pin strikes to ignite the propellant, as well as from the bullet and casing materials.
Persistence and Transfer:
- OGSR: Organic residues tend to degrade or dissipate more quickly than inorganic particles. Environmental factors such as heat, humidity, and contact with surfaces (e.g., wiping hands or washing) can significantly affect their persistence.
- IGSR: Inorganic residues are generally more stable and persist longer on surfaces such as skin, clothing, or objects. Environmental conditions affect them less, but physical actions like handwashing or friction can still transfer or remove them.
Research evaluated the quantities of OGSR and IGSR on the right and left hands, forearms, face, and nostrils of four shooters.
Specimens were collected immediately before discharge (blank specimens) and shortly after (30 minutes) using carbon adhesive stubs.
The organic compounds were first extracted from the collection device and analysed using ultra-high-performance liquid chromatography tandem mass spectrometry.
Following this, IGSR particles were detected on the same stubs using scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM/EDS).
The analysis of the blank specimens revealed background contamination of both OGSR and IGSR in the shooters’ environment, largely due to the presence of an indoor shooting range. However, the background levels were generally lower than those found in the specimens collected 30 minutes after discharge. At the 30-minute mark, investigators typically detected higher quantities of GSR on the shooters’ hands compared to other areas for both residue types.
Forearms and face also emerged as important collection sites, particularly in cases where the person of interest may have washed their hands after discharge. In contrast, the researchers found very low levels of GSR in the nostrils.
The results further indicated that OGSR and IGSR exhibit different patterns of transfer and persistence, emphasising the need for specific knowledge in handling these residues during firearm-related investigations.
