The influence of taphonomy on histological and isotopic analyses of treated and untreated buried modern human bone

The chemical (e.g., preservation/embalming) treatment of skeletal remains can reduce overall DNA quality and quantity. The histological and stable isotope examination of treated and untreated human remains improves our understanding of how chemical preservatives impact bone diagenesis and will determine if chemical treatment adversely affects stable isotope ratio analysis of collagen. Fidelity in the application(s) of stable isotope interpretations requires that the isotope delta (δ) values have not been altered postmortem. Re-associated antimeres and refits of chemically treated and untreated rib and long bones from eight casualties [thin-sectioned human bone (n = 43) and collagen extraction/stable isotope analysis (n = 42)] from the World War II Battle of Tarawa were examined to compare skeletal elements from the same individual that had different taphonomic histories. Histological analyses included scoring upon the Oxford Histological Index (OHI) and Birefringence scale, recording microbial invasion, and general observations. The collected data were analyzed via simple descriptive statistics and paired samples t-tests. Treated remains scored higher on the OHI and for Birefringence, indicating that bone quality was good to excellent. The untreated samples scored lower on the OHI and Birefringence scales suggesting poorer preservation than the treated remains. Histology results were supported by the isotope sample preparation results: the collagen % yield was higher for treated bone than untreated bone. Additionally, chemical preservation had no meaningful impact on isotope δ values of treated and untreated remains from the same element or pair-matched elements. Overall, treated remains exhibited good preservation while untreated remains exhibit poorer preservation with significant microfocal destruction to the extent that little histological analyses can be applied. Stable isotope ratio analysis is viable for both treated and untreated remains indicating this testing modality likely can be used for most treated remains, regardless of origin