Fundamental Research for Forensic Characterization of Soil Samples by Using Instrumental Analysis

Abstract

Soil can be one of the most important physical evidence in a criminal investigation which contributes to prove a linkage between the suspect and the crime scene. In this work, the validity of multiple instrumental analytical techniques for forensic soil identiˆcation was studied using 148 soil samples collected from the Tokyo metropolitan area. The samples were characterized by X-ray diŠraction (XRD) analysis, X-ray ‰uorescence (XRF) analysis, magnetic susceptibility determination, scanning electron microscopy with an energy dispersive X-ray spectrometer (SEM-EDS) and high-energy synchrotron radiation X-ray ‰uorescence (SR-XRF) analysis. It was found that soil samples collected from railway stations and roadside dust showed higher magnetic susceptibilities (≧0.5×10-4 m 3 kg-1 for 25 of the samples collected) than those of soil samples collected from rivers, ponds, and lakes (＜0.1×10-4 m 3 kg-1 for 40 of the samples colleted). Microscopic examination of the soil samples revealed three kinds of characteristic spherules: i.e., transparent, white, and black particles. The SEM-EDS analyses of the spherule samples showed the following compositional characteristics. The transparent spherules exhibited two compositional types: Na Ca Si O and Ba Ti Si O types. On the other hand, black ones were either Fe O or Si Mg O types and white ones were either Al O or Sr Al O types. It was concluded that these six types of spherules were found at characteristic points and consequently, they can be used as forensic soil identiˆcation.