Review: The Detection of Gunshot Residues in the Nasal Mucus of Suspected Shooters

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Emily C. Lennert

 

Category

Chemistry

Keywords

gunshot residue, GSR, suspected shooter, sampling, nasal, mucus, antimony, Sb, barium, Ba, instrumental neutron activation analysis, INAA

Article Reviewed

  1. Merli, D.; Brandone, A.; Amadasi, A.; Cattaneo, C.; Profumo, A. The detection of gunshot residues in the nasal mucus of suspected shooters. International Journal of Legal Medicine. 2016, 130, 1045-1052.

Disclaimer

The opinions expressed in this review are an interpretation of the research presented in the article. These opinions are those of the summation author and do not necessarily represent the position of the University of Central Florida or of the authors of the original article.

Summary

Gunshot residue (GSR) is formed in a plume that is expelled when a weapon is discharged. This plume contains gasses and solid particulates that cool rapidly to produce GSR particles. The particles contain chemical residues originating from the ammunition primer and propellant, as well as metallic components from the ammunition and firearm. Lead, barium, and antimony are typically considered to be metals that are indicative of GSR. GSR may be used to indicate whether an individual has recently fired a weapon. Currently, sampling methods include swabs, glue lifts, and tape lifts from hands, which are then analyzed by a number of techniques: scanning electron microscopy with energy dispersive x-ray (SEM-EDX), neutron activation analysis (NAA), electrothermal atomic absorption spectroscopy (ET-AAS), and more. However, previous research cited by the author has indicated the possibility that GSR particles may become lodged in the nasal passages, within nasal mucus, after a weapon has been discharged. Despite this indication, little research has been done to investigate the utility of nasal mucus as an alternative sample for use in GSR detection.

Barium and antimony were selected as GSR indicators in this study. Lead was excluded due to its common presence in the environment. Samples were collected using paper tissues. While wearing gloves, the subject blew their nose into the tissue, which was then transferred into an individual plastic container. Samples were directly analyzed by Instrumental Neutron Activation Analysis (INAA). INAA is an instrument that is used to determine the concentration of elements in a sample. This instrument operates similarly to an SEM-EDX which is commonly used in GSR analysis. Both instrument measure the x-rays of the element in the sample to determine the types of elements present.
Prior to experimental sampling, preliminary tests were conducted to determine whether barium and antimony quantities were different between shooters and non-shooters. A total of 29 blank samples were obtained, i.e. subjects had not fired weapons. Shooter samples were obtained from 17 subjects. Two weapons, a pistol and a revolver, were used, and the number of shots fired varied between subjects, ranging 1-50 shots fired. In the blank samples, 21 samples had barium and antimony levels below the instrumental quantification limit: 0.002 μg for barium and 0.005 μg for antimony. Only 8 blank samples contained quantifiable amounts of barium and antimony, with barium ranging 0.003-0.054 μg and antimony ranging 0.006-0.066 μg per sample. Shooter samples contained considerably higher levels of barium and antimony, with all but one sample containing quantifiable levels of barium and antimony. Barium ranged 0.009 μg in a sample obtained from a subject that fired 1 shot from a revolver to 2.011 μg in a sample obtained from a subject that fired 31 shots from a pistol. Antimony ranged from <0.005 μg, i.e. below the limit of quantification, in a sample from a subject that fired 1 shot from a revolver to 1.09 μg in a sample from a subject that fired 31 shots from a pistol. Based on preliminary results, the authors stated that the barium and antimony levels in shooters were approximately 2 orders of magnitude greater than those in non-shooters.

The authors then proceeded to experimental firings. A pistol and a revolver were used for the firings, and 21 subjects were included in the study. Subjects fired their given weapon between 1 and 100 times, and samples were acquired immediately after the end of the firing session. The individual’s nose status was also recorded as either free or closed. Although “free” and “closed” are not clearly defined, the definitions may be related to congestion of the nasal passages, based on context. Samples were then analyzed, and shooter results are summarized in table 2 within the study. All shooter samples showed significantly higher levels of barium and antimony when compared to non-shooters, regardless of the number of shots, weapon type, or whether the individual’s nose was free or closed.

Additional firings were then conducted, with samples taken at larger time intervals following the firing: 30 and 60 minutes. Results of these trials are summarized in table 4 within the study and show a general decrease in GSR over time, however the amounts of barium and antimony remain significantly higher than those in non-shooter samples. Furthermore, the ratio of antimony to barium remains generally constant during this period, approximately 1.21:1. This indicates that the ratio of antimony to barium may be of importance in using this method for forensic purposes. Other shooters were then sampled, e.g. shooters 22-34, 2 and 3 hours after firing a pistol; these results are summarized in tables 5 and 6 and indicate that GSR remains present in the nasal passages, showing varying levels of GSR.

Simulated forensic case samples were also prepared, and the results are reported in tables within the supplementary materials associated with the article. Samples were taken at 0, 1, 3, 12 and 24 hours. According to the authors, samples taken at less than 3 h were highly probative for the firing event, while samples taken at 12 h were reliable only if the subject had fired several times, and samples taken at 24 h were deemed inconclusive for the presence of GSR.

Scientific Highlights

  • A simple sampling procedure, blowing the nose in a tissue, was presented that allowed for analysis of barium and antimony in nasal mucus by INAA.
  • The amount of GSR varied based on the number of shots fired and time between firing and sampling. Highest concentrations of GSR were found if sampling occurred between 0 and 3 h after firing. After 24 h, no GSR was detectable.
  • The ratio of antimony to barium was indicative of the presence of GSR. While antimony and barium may be present in the environment, the 1.21:1 ratio appears indicative of GSR.
  • Sampling of nasal mucus, rather than hands, may result in samples that are less contaminated by environment. Additionally, GSR may persist longer in nasal mucus than on hands.

Relevance

GSR detection may be used to establish whether an individual has recently fired a weapon, which may help to link a suspect to a crime. This sampling method provides an alternative to traditional sampling of the hands.

Potential Conclusions

  • Nasal mucus sampling may be a viable alternative for sampling of GSR in suspected shooters.