The Preservation and Persistence of Human DNA in Soil during Cadaver Decomposition

Recent decades have seen a marked increase in the amount of research concerning the impact of human cadaveric decomposition on the grave soil environment; however, despite such advances, the fate of important biological correlates in grave soil, including human DNA, have remained relatively understudied. This study redresses the current lack of knowledge regarding the preservation and persistence of human DNA in the soil during cadaveric decomposition, with the purpose of enhancing forensic identification efforts including the detection of primary burial sites. This study assessed the preservation (i.e., presence or absence) of human nuclear and mitochondrial DNA and evaluated the quantity and quality of recovered DNA from grave soil over the course of decomposition of four human cadavers placed at the University of Tennessee’s Anthropological Research Facility (ARF). End-point and real-time quantitative PCR were used to assess quality and quantity of human DNA extracted from the grave soil environment. The presence of human cadaveric DNA from soil samples was verified by aligning and comparing sequences from the human mitochondrial DNA control region (HVI and HVII) between cadaver blood samples taken prior to placement at the ARF and soil samples taken from below each cadaver following placement and the initiation of decomposition processes. Results indicate that human nuclear DNA from the cadavers was largely unrecoverable throughout decomposition. Conversely, cadaver mitochondrial DNA was detectable in the grave soil throughout all decomposition stages. Mitochondrial DNA copy number increased as decomposition progressed, peaked during the “Active Decay” stage of decomposition, and declined throughout the remainder of the decomposition process. The results of this study suggest that human mitochondrial DNA can be recovered from soil and is of a high enough quality to be used for exclusionary purposes during identification efforts. Therefore, the presence and persistence of this biomarker will prove useful in those forensic contexts in which DNA is not recoverable from a discovered set of remains or in the event that a cadaver is removed from its burial location