Factor analysis of organic soils for site discrimination in a forensic setting

Abstract

Organic soils are generally located in fluvial settings such as river floodplains that are commonly used for the disposal of bodies. Therefore, the aim of this study was to provide a protocol for the analysis of small amounts of organic soils for forensic purposes. The protocol was applied in five representative sites within the Curitiba metropolitan region (Brazil), with each site supplying four composite samples separated from one another by 3m. The soil samples were collected at a depth of 0 to 5cm. One gram of soil sample was used to determine the total elemental content and perform physical fractionation of the soil (>53μm and <53μm). For both soil size fractions, total C and N contents were determined, and the elements adsorbed to organic matter was determined only for the <53μm size fraction (Na-pyrophosphate extraction). Chemometric multivariate analyses were conducted for the total data set, where more than 77% of the variation was explained by the first three factors. It was determined that Ca, Ba, and Mg adsorbed to organic matter, and total Ba, Ca, K, Mg, Mo, and C contents were most important in sample groupings. As expected in forensic science, the five sites were efficiently distinguishable from each other and the four replicates collected at the same individual site were clearly grouped. This protocol for sampling, chemical analysis, and data treatment of organic soils can be used in real crime situations.