Exploring methods for PMSI estimation on clothed and unclothed submerged remains, in a lentic, sequestered volume of freshwater

There is a current lack of established forensic techniques for estimating the time interval a set of remains has been submerged, a consequence of the limited research in aquatic decomposition. This preliminary research aimed to determine potential methods to estimate a post-mortem submersion interval (PMSI) for bare and clothed remains in fresh water. A combined approach, utilising field trials and controlled laboratory experiments was developed to explore multiple methods of PMSI estimation including microbial analysis, pathological changes, water parameters and insect activity. As part of field investigations, remains were submerged bare, dressed in natural cotton, or dressed in synthetic nylon, and were assessed using decomposition stages, insect activity, algal identification, bacterial community analysis (16S rRNA gene next generation sequencing) and water parameter measurements (conductivity, total dissolved solids (TDS), salinity, pH, and dissolved oxygen (DO)). Additionally, bare and dressed pork pieces (in cotton or synthetic) were submerged in freshwater, inoculated with water samples from the field trials, to assess the contribution of materials on the formation of bacterial biofilms, under controlled conditions. This research found the rate of decomposition for remains dressed in a synthetic fibre was slowed due to the preservation of soft tissues. Insect activity was minimal due to the cool weather and did not present in a predictable, informative pattern. Water parameters exhibited similar trends independent of the clothing condition of remains. Algal colonisation was not affected by clothing presence or fibre type and developed successionally over time. Biofilm analysis found the bacterial diversity to change over time and were specific to the presence and type of clothing. Further investigation into algal and bacterial development over time could identify markers that complement different stages of decomposition, highlighting the usability of microbes to infer PMSIs.