Effectiveness of a washing protocol for the removal of gunshot residue from forensically relevant Lucilia sericata larvae

Blowfly larvae (Diptera: Calliphoridae) have been suggested to have practical application as a toxicological target in forensic science. These larvae may be of use for gunshot residue analysis where traditional analytical targets such as the liver or entry wounds are absent and may allow an opportunity to identify toxins, drugs and gunshot residue from a corpse. A primary weakness of GSR identification in entomotoxicology is the lack of a standardised methodology for processing the larvae for accurate determination of GSR. In this study, Lucilia sericata (Meigen) larvae were exposed to pork mince that was shot 4 times at close range, the larvae were then sampled 12 hourly. A wash protocol for the larvae was developed and the concentrations of Ga, Ba, and Pb, key GSR markers were determined in Lucilia sericata larvae and the solution used to wash them to identify the effectiveness of the cleaning process. Both the whole larvae and each respective wash solution were analysed using inductively coupled plasma mass spectrometry (ICP-MS). Analysis of the wash solutions revealed that a minimum of two washes were required to remove external contaminants prior to ICP-MS analysis of the whole larvae. This work demonstrates the importance of implementing an effective wash protocol when measuring GSR of forensic interest within larvae, as contaminants on the surface of the larvae could lead to misinterpretation of data.