Soils

Abstract

Forensic soil science, as a developing discipline of soil science, has matured to the extent that well-defined questions and crime scene investigations are being addressed in increasingly refined ways to assist both law enforcement and environmental agencies. Natural soil and human-made soil materials (e.g., bricks) are being used in forensic investigations to associate a soil sample taken from an item, such as clothing with a specific location. Soil forensic investigation usually involves collection of one or more soil samples followed by soil characterization. Collected samples are categorized as (1) questioned soil samples whose origin is unknown or disputed (suspect or victim), (2) control samples whose origin is known (crime scene), and (3) alibi samples whose origin is known and that provide a measure of the uniqueness of the questioned and control samples. Soil characterization often requires the following four-stage approach, which combines descriptive, analytical, and spatial information: (1) Initial characterization for screening of samples involving morphological descriptions. (2) Semi-detailed characterization involving semi-quantification of minerals and organic matter following sample selection and size fractionation (<50μm). (3) Detailed characterization and quantification of minerals and organic matter using advanced analytical methods. (4) Integration and extrapolation of soil information from one scale to next, to build a coherent model of soil information from microscopic observations to the landscape scale, which often involves soil/geological maps and geophysics. Progression of a soil forensic examination through each of the four stages will depend on the amount of sample available and the results from the early stages of the examination. The significance and relevance of established concepts and standard terminologies used in soil science and geology with practical relevance to forensic science are emphasized.