Stable isotopes (δ13C, δ15N, δ34S) of human skin during decomposition

In forensic investigations, estimation of the postmortem interval, or time since death, is essential to the legal process. The timeline of decomposition can be estimated through the use of various methods, however, these methods become less accurate or applicable in later stages. Previous stable isotope studies identify skin as a potentially useful substrate in the context of decomposition due to its durable nature, with some tissues exhibiting an increase in δ¹⁵N over time. In this study, stable isotope analysis was performed on human skin samples, collected from donors over several months within a "body farm" human decomposition facility. Changes in δ¹³C, δ¹⁵N, and δ³⁴S, and the impacts of sample pretreatments (chemical lipid extraction and protein solubilization) were examined in a 2 × 2 factorial design to determine the optimal sample pre-treatments to observe decomposition-associated changes. Through examination of interactions between decomposition byproducts and chemical pretreatments, our research was able to identify relationships between temperature, decay state, and isotopic changes. Our findings suggest that while changes occur in δ¹³C and δ¹⁵N in bulk skin during decomposition, the isolation of individual organic compounds may provide a better means of measuring and observing decomposition-driven isotopic changes relative to isotopic analysis of bulk skin and, therefore, represent a more promising avenue of research for estimating postmortem interval.