Spectroscopic techniques applied to discriminate soils for forensic purposes

Soils are a complex mixture with a variety of mineralogical, chemical, biological and physical properties, which can be explored within forensic case work. This study aimed to apply energy-dispersive X-ray fluorescence (EDXRF) and Fourier transform infrared (FTIR) spectroscopic techniques to discriminate soil samples collected in southern Brazil in a forensic context. Four replicates of soil were collected at four sites: two sites from the same parent material (claystone) and two other sites from limestone and granite/gneiss respectively. The physical and chemical (organic and mineral composition) and spectroscopic techniques (EDXRF and FTIR) produced 16 quantitative variables from only 2 g of sample. The main results from a forensic context were the separation of the soils collected from close neighbourhoods developed on the same parent material and the separation of soils collected in the A and B horizons of the same soil profile. The highest degree of similarity in the clustering of samples collected at the same site was 98.6% (B horizon in claystone domain). In addition to the parent material, the effect of organic matter on the chemical and mineralogical characteristics of the A horizon was important in the grouping dynamics of samples. This work demonstrated the potential of spectroscopic techniques in a forensic context.