Forensic taphonomy: Characterization of the gravesoil chemistry using a multivariate approach combining chemical and volatile analyses.

Soil thanatochemistry, defined as the study of the chemical changes occurring during the decomposition of buried corpses, is a young and inadequately documented field of research. In this study, we aim to determine the effects of decomposition on soil physico-chemical properties by combining pedological, chemical, and volatile analyses of soils surrounding buried animals. We examined chemical and volatile changes over time occurring throughout the soil column in two common soil-texture types (sandy loam and loam). We buried dead rats and let them decompose for two months. During their excavations, we characterized the physico-chemical conditions of three soil layers above the rats and one layer below, including (1) pH, dry matter, and electrical conductivity, (2) organic carbon and total nitrogen, (3) bioavailable nutrients (K, Na, Mg, Ca, and P), and (4) volatile organic compounds. Multivariate analyses (permMANOVA) revealed that a decaying rat is associated with changes in soil chemical characteristics in both soil types. However, the observed changes were not homogenous throughout the soil columns. Conditions in soil layers nearest the cadavers changed most during decomposition. We generated a predictive model by combining chemical and volatile analyses (10 % error rate), allowing us to identify key gravesoil indicators that could be used to reveal the former existence of a buried corpse in loam and sandy loam (indicators in order of importance): organic carbon, calcium, pH, conductivity, dimethyl-disulfide, and nitrogen.