Using Stable Nitrogen Isotope Ratios from Human Skeletal Muscle Tissue for Postmortem Interval (PMI) Estimation (Part 1)

Abstract

Human skeletal muscle tissue was analyzed for stable nitrogen isotope analysis (δ¹⁵N) to test the applicability of changes in values (Δ¹⁵N) through the putrefaction process for postmortem interval (PMI) estimation. Seasonal differences in Δ¹⁵N values of decom-posing skeletal muscle tissue were analyzed from 20 human donors at the University of Tennessee Anthropology Research Facility. This study revealed that change in the δ¹⁵N ratios of decomposing muscle tissue has potential as a novel method for PMI estimation. In winter months, when identifiable muscle tissue can be retained on a body for months, the data indicate that there is a systematic increase in Δ¹⁵N values with increasing temperatures when putrefaction progresses faster with values shifting as much as 3.0‰. This initial study indicates there is value in further method development of this quantitative approach to PMI estimation for recently deceased individuals, but further work is needed. While the analysis only requires a small amount of tissue, has a user- friendly collection and analysis protocol, and is less subjective than visual methods, there is still significant research to be done prior to widespread applications as a PMI estimation method. Understanding variability in δ¹⁵N across decomposing muscle tissue groups, individual variation (i.e., muscle mass, disease, body chem-istry), and an accurate approximation for a perimortem δ¹⁵N value necessary to calculate Δ¹⁵N all need to be further researched prior to generation of a reliable regression formula and error rates.