Isotopic Taphonomy of Human Remains

As submitted by the proposer: Isotope abundance ratios in human remains can record diet, birthplace and travel history - valuable information for identifying unknown remains. However, these ratios may vary among tissues and can alter during decomposition and burial. Therefore, we propose to measure changes in isotope ratios of carbon, nitrogen, oxygen, hydrogen, strontium, and lead in various human tissues emplaced in forensically relevant settings to determine conditions that preserve identifying information. We also propose to compare the isotope ratios of human tissues from known places of residence and/or birthplace to expectations from published isotopic landscapes ("isoscapes"). However, human remains have not been systematically compared to the isoscape models. Complications include diet and travel history. Therefore, our aim is to answer these questions: 1) Are pre-mortem isotopic compositions in different tissues retained during decomposition? 2) How reliable are the correlations between isotope ratios of remains and geography that underlie the use of isoscapes? Samples from ten human donors will be emplaced, six at ARF (Tennessee) and four at FARF (Texas). Donor histories will provide pre-mortem travel and geographic life histories. Subjects will be evenly divided between the sexes, and include maximum race/ethnic diversity permitted by donor availability. Samples, including hair, tooth enamel, and skeletal elements, will be collected at donor arrival, and after decomposition in either surficial or shallow burial conditions. Samples will be buried for 2000 Accumulated Degree Hours to encompass the major stages of decomposition. Analyses will include IRMS (carbon, nitrogen, oxygen, hydrogen), MC-ICP-MS (strontium and lead), and Q-ICP-MS for supporting analyses. We hypothesize that: a) tooth enamel will be robust under all conditions; b) hair will be the most easily altered; and c) donors in the Tennessee climate will alter more than those in Texas. This study will facilitate application of isotope analyses in forensics. There are 9,578 open cases of US unidentified human remains. Identification using osteological characteristics or DNA requires reference samples or known osteological/dental characteristics, and rarely provides information about birthplace or travel history. European case studies of isotopes in unknown decedents illustrate the value of isotopic analyses for US law enforcement. Research dissemination will include peer-reviewed publications and a website documenting best practices for sampling, storage, and isotopic analysis of human remains. Associated tutorials for law enforcement and medical examiners will discuss isotopic variations, analysis, and limitations. ca/ncf