Decomposition of partially submerged remains: a study on the reliability of insect colonisation for PMI/PMSI estimation.

The terrestrial decomposition of remains and associated insect colonisation have been highly researched, and recently studies have expanded to investigate the aquatic decomposition of remains. However, there are instances where remains may experience both terrestrial and aquatic conditions simultaneously due to partial submersion in tidal areas, or influx or efflux of water caused by flood or drought. Decomposition and post-mortem interval (PMI) research to date has focused on remains wholly exposed to either terrestrial or aquatic environments, with limited consideration of dual simultaneous exposure. This study was conducted in artificial lentic environments to ascertain how simultaneous zones of terrestrial and aquatic environments on a single body may impact decomposition. Three trials were completed over a period of 12 months, with each trial consisting of 12 stillborn piglets; three partially submerged head exposed, three partially submerged abdomen exposed, three fully submerged aquatic controls and three terrestrial controls. Decomposition stage and rate were inferred from physical characteristics and insect activity. The decomposition rate of the exposed region of each piglet was significantly faster than the submerged region. The exposed zone of each was colonised by insects and reached skeletonization, whereas the submerged zone without orifice exposure had no insect activity and had a significantly slower decomposition rate. This indicated the ability to utilise terrestrial entomological approaches to estimate a minimum PMI for the exposed portion of the remains. However, without the ability to determine the amount of time the remains may have been submerged for, this estimation represents only a minimum PMSI, with the possibility the remains were submerged for a period of time without insect access and colonisation.