A survey of explosive traces in public places

Abstract

Interpretation and evaluation of trace explosives evidence requires practitioner understanding of factors including transfer, persistence, and environmental prevalence. This study builds on previous work and studies the contemporary prevalence of organic high explosives and inorganic ions of explosives significance in public places. 450 swab and vacuum samples were collected from across Great Britain. Analysis was conducted using liquid chromatography–high resolution mass spectrometry and ion chromatography–mass spectrometry to screen for a wider number of explosives analytes with a higher degree of selectivity and with lower limits of detection than previous studies. Analytes screened for included military high explosives, organic peroxide explosives, and inorganic ions of explosives significance. Only eight low nanogram level traces of organic explosives (HMX, NG, PETN, and RDX) were detected. The results indicate that high explosives traces remain uncommon in the public environment and transport network. Due to the low prevalence, these results strengthen the association between the detection of a trace and explosives activity, and assist the practitioner in assigning significance. Many inorganic ions (ammonium, calcium, chloride, magnesium, nitrate, nitrite, potassium, sodium, and sulfate) were detected at milligram or sub-milligram quantities. They are common in the environment, naturally occurring, and used commercially. Interpreting the general significance when detecting traces of common inorganic species is challenging. Barium, chlorate, perchlorate, strontium, and thiocyanate were not detected and are therefore more uncommon, strengthening the association between detection and explosives activity.