Green ammunition’s organic residues

Firing a gun releases a burst of gases and microparticles that deposit on people and surfaces. Forensic scientists analyze this gunshot residue to investigate crimes. Today, this analysis relies mostly on heavy-metal particles used in ammunition, but the push to replace these metals with greener materials has recently led forensic scientists to study organic gunshot residues.

Researchers have now used both human skin and synthetic skin membranes to evaluate how long organic gunshot residues persist on skin and other surfaces and how they get transferred or lost (Forensic Chem. 2023, DOI: 10.1016/j.forc.2023.100498). “Very little is known about organics, which behave completely differently from heavy metals,” says Tatiana Trejos, a forensic chemist at West Virginia University.

Trejos, chemist Luis Arroyo, and colleagues developed a liquid chromatography/​mass spectrometry (LC/MS) method to detect residues of organic compounds such as diphenylamine and nitroglycerine found in bullets. LC/MS requires large molecules, so the team used complexing agents that encapsulate the microparticles to form larger complexes for analysis.

The researchers used over 650 samples to study gunshot residues on human skin and synthetic skin, as well as on fabric onto which residue is transferred. They ran tests hours after firing and after tasks such as washing hands and running.

Organic residues persisted for a shorter time on fabric and skin than inorganic ones, the team found, but they were more likely to remain in their original location after washing or shaking hands.

The team has also developed a portable technology based on laser-induced breakdown spectroscopy and electrochemical sensors that detects inorganic gunshot residues with nearly 98% accuracy. While typical lab tests take hours, Trejos says, “this takes only 5 min and can be brought to the crime scene.”