A multi proxy investigation into the effects of burial environments on nuclear DNA in bone over forensic and archaeological timescales

摘要

This research conducted a two-pronged approach to study the effects oftaphonomic processes by conducting analysis of experimental burials of porcinefemora and parallel analysis of ancient human archaeological remains fromgeologically distinct cemeteries. The aim of this study was to identify the majordegradative factors from depositional environments that affect the bonecomposition and the retention and retrieval of nucleic DNA from archaeologicalbone. Four different experimental burial environments of clay, compost, lime andsand were designed, displaying different properties of soil type, pH, water contentand organic content. Analysis of the burial mediums and bones were conducted atregular intervals over an 18 month period. Observations of changes in the burialmedium, comparisons of the rates and degree of soft tissue decomposition, bonediagenesis from compositional assessment, and bone colour change were madeand analysed in correspondence with the different environments. The analyticaldata collected on the diagenesis of the archaeological bone from both studies, wascompared to the DNA profiling success rates.The research and optimisation of sample preparation and DNA analysis enabledthe most cost-effective and appropriate methods to be identified and utilised inaccordance with the preservation state of the bone samples. This allowed theanalysis of ancient archaeological bone to be analysed in-line with forensicprotocols, to enable a uniform accessible approach to produce comparable resultsacross different laboratories.Drawing together the results from the various analytical techniques made itpossible to identify the variables that affect bone diagenesis and the survival ofnuclear DNA, and provide evidence that the rate of decomposition and bonedegradation is affected more significantly by the burial environment than durationof burial, as stated in the research hypothesis. The presence of water, sand and thelevel of organic content were found to be the most degradative variables within theexperimental burial conditions; causing changes in bone crystallinity, andinfiltration of contaminants into the bone. The presence of lime, chalk or limestone in an environment was found to have preserving properties in both the porcineand human burials, by retarding the rate and degree of soft tissue decomposition,and reducing the diagenetic changes in bone composition evident from the otherenvironments.Despite previous reports of success using analytical techniques as predictivemodels for DNA and bone preservation, no correlations with DNA survival could beestablished. However the use of a multi-disciplinary approach enabled thedetection and identification of soil contaminants affecting the bone structure andthe ability to amplify DNA, in relation to burial environments. This researchhighlighted the importance of utilising multiple analytical techniques, such ascolourimetry, ATR-FTIR, XRF and genetic analysis in order to avoidmisinterpretation and false reporting of the state of bone diagenesis orpreservation and the survival of DNA, due to environmental contaminants withinthe hard tissue.The research confirms the idea that in order to establish optimised sampling andDNA analysis of archaeological bone, it is imperative that certain protocols areadhered to. Precautions must be implemented from excavation through tolaboratory analysis to avoid contamination; and correct recording of burialenvironment is essential to enable consideration of extrinsic factors andcontaminants when reporting results.