Considerations for Stable Isotope Analysis of Human Hair The Impact of Postmortem Environmental Exposure

Abstract

Stable isotope analysis of postmortem hair is performed in order to make inferences about an individual’s diet and geographic travel history prior to death. During analysis and interpretation, investigators assume that the hair collected from a postmortem environment has not been altered by exposure conditions and that the isotopic “signatures” of hair prior to exposure are preserved in postmortem samples. In order to confidently make inferences from postmortem hair samples, it is necessary to know whether their isotope ratios undergo postmortem changes. To address this question, post-exposure hair samples (n = 44) were collected from known body donors at the Anthropology Research Facility in Knoxville, Tennessee, USA, at various time points ranging from 22 to 1,140 days of exposure. These samples were analyzed for carbon (δ¹³C), nitrogen (δ¹⁵N), hydrogen (δ²H), and oxygen (δ¹⁸O) isotope ratios, and the results were compared with pre-exposure hair samples collected from the same donors. This study highlights considerations for the interpretation of isotope ratios obtained from postmortem hair samples in forensic contexts. The results indicate that δ¹³C, δ¹⁵N, and δ¹⁸O values from human hair remain relatively consistent over periods up to three years of outdoor exposure, while δ²H values changed significantly between pre-and post-exposure hair samples.