Evaluating the potential of Dissolved Organic Matter (DOM) analysis and characterization for the investigation of clandestine graves

The presence of a decomposing body being victim of concealment by clandestine burial represents a localized disturbance in the complex equilibrium that characterizes the turnover of organic matter in the soil. However, although intuitively a biogeochemical analysis of the soil matrix affected by the concealment should provide clear evidence of the presence of a decomposing body, the relevant literature has shown that this is not the case, particularly with regard to the observation of TOC (Total Organic Carbon). In fact, its ubiquitous nature by definition makes the abnormal concentration of organic matter a difficult proxy to identify, but one that is urgently needed for complete crime scene profiling: the ability to distinguish the natural organic matter present in a soil from that derived from the nutrient input caused by the cadaver decomposition processes would represent the operational key to guide investigators towards a more complete and informative analysis of the case. In particular, an anomaly in the concentration and distribution of organic matter within the soil may provide information regarding the Post Burial Interval (PBI) of a concealment victim, as well as be suggestive of a possible previous burial site. For this reason, at the Forensic Taphonomy Facility of the University of Milan (Ticino-LEAFs), a simulation of clandestine burials in a natural environment was carried out using cadavers of piglets that had died of natural causes as a model for human decomposition research. At pre-determined intervals, the piglets, which had undergone various treatments prior to burial (namely being covered in quicklime, wrapped in cotton clothes, and harmed post-mortem), were exhumed and soil samples were taken at different depths to monitor changes in the concentration of the organic matter with increasing exposure of the body to the environment. For this purpose, an analysis of dissolved organic matter (DOM), both natural and affected by the presence of the body, was carried out, combined with complementary spectroscopic techniques (FT-IR). This analysis revealed anomalies in the concentration of dissolved organic matter in the soil horizons containing and immediately underlying the body, also showing the presence of organic compounds otherwise absent in the undisturbed soil. However, some variability attributable to the treatments the bodies underwent prior to burial was also observed, namely the presence of quicklime, which seems to be able to further disrupt the hypogeal environment. The rapidity of the analysis, its relative inexpensiveness, and the small amount of soil sample required could make this technique an innovative tool to be incorporated into forensic casework to help estimate the post-burial interval in the investigation of clandestine burials.