Testing the efficiency of soil recovery from clothing for analysis by SEM-EDS

Soil forensics is widely used to test associations between questioned samples and known locations. Improvements in analytical techniques mean that increasingly small amounts of soil can be analysed. This is particularly important as individual traces of soil relate to individual geographical locations and need to be analysed separately. However, improved analytical capability means that methods of soil recovery also need to improve. Three different methods of recovering soil from clothing for subsequent analysis by scanning electron microscopy with linked energy dispersive spectrometers (SEM-EDS) were tested. Three fabric types were analysed with duplicate samples being recovered by (a) dry brushing, (b) direct sticky tag lifting and (c) washing. The resultant soil samples were analysed using automated scanning electron microscopy with linked energy dispersive spectrometers. All three methods recovered a population of particles, the mineralogy of which corresponded with the control soil sample. However, the sticky tags recovered between 6 and 8× more particles than either the dry brushings or the washing samples. The direct lifting of trace soil evidence using sticky tags also has the advantage that the context of the analysed soil sample can be clearly imaged prior to recovery. Any soil evidence can be observed in context with the surface it is to be removed from, and as such, sampling can be targeted to specific areas or specific phases of soil deposition on a surface.