Abstract
Most cases involving soil in criminal investigations in Brazil have focused on the chemical and mineralogical analyses of soil fractions without including the organic matter. The organic fraction contains plant-wax markers which may be useful to “fingerprint” forensic soils due to their chemical diversity, relative longevity and resistant nature. The aim of this study was to test the long- (kilometre), medium- (metre) and short- (centimetre) scale variability of plant-wax biomarkers in a forensic context in anthropised urban soils and soils developed under subtropical conditions. Two areas from the Curitiba municipality and two areas from the Colombo municipality, Paraná State, South Brazil, were selected. Soil colour analysis was carried out to obtain reflectance data over the 360–740 nm wavelength range. Furthermore, plant-wax marker compounds (n-alkanes and fatty-alcohols) were assessed by extraction and separation into different classes and an analysis of the compounds by gas chromatography (GC/MS). The compositions of the wax-marker profiles were different in samples collected side-by-side, showing sensitivity to local variations under subtropical conditions and in areas under intense human urban disturbance. Under these conditions, biomarkers may be used in real crime scenes, even on a micrometric scale of variation.
Highlights
In forensic science, soil is an important form of trace evidence and can be used to test for potential links between soil on a questioned item and a potential source location
This material can be used successfully in forensic studies, as organic matter is an inherent part of the soil, that is, for a given material to be considered as soil, it must have a minimum level of organic material, in addition to containing the inorganic mineral fractions in different proportions
As the concentration of organic matter varies with the soil concentration, dilutions of the organic matter content depend on the amount of soil sampled at the crime scene, such as the amount found on the sole of shoes and on the vehicle tires [3,4,12,13]
Summary
In forensic science, soil is an important form of trace evidence and can be used to test for potential links between soil on a questioned item and a potential source location. Many soils have less than 5% (w/w) of organic matter content, tropical and subtropical soils, and this has expressive effects on the biological, chemical and physical characteristics of the soil, even if it is present at reduced contents. This material can be used successfully in forensic studies, as organic matter is an inherent part of the soil, that is, for a given material to be considered as soil, it must have a minimum level of organic material, in addition to containing the inorganic mineral fractions (sand, silt and clay) in different proportions. As the concentration of organic matter varies with the soil concentration, dilutions of the organic matter content depend on the amount of soil sampled at the crime scene, such as the amount found on the sole of shoes and on the vehicle tires [3,4,12,13]
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