The Effect of Water Conditions on Decomposition Rate: A Comparative Study of the Estimation of Post-mortem Submersion Interval

Abstract

Many factors affect aquatic decomposition and the accuracy of Post-mortem Submersion Interval (PMSI) estimations but have not been researched thoroughly. The extent of decomposition in bodies recovered from water is measured using visual decomposition scoring systems (DSS). The applicability of the Heaton, van Daalen and Reh DSS is limited because they were developed with predominantly pale-skinned individuals in temperate climates. This PhD aimed to (1) determine the effect of water temperature, hardness, salinity, and current on decomposition rate in human analogues, (2) compare the effectiveness and suitability of these DSS for assessing decomposition changes in human analogues/human remains and estimating PMSI in dark-skinned individuals.

Laboratory studies, where 660 mice decomposed for 35 days, were conducted to investigate the effect of salinity, hardness and current on decomposition rate. To augment the laboratory results with larger human analogues, 35 pigs were decomposed for 70 days in water of varied salinity. To evaluate the accuracy of the DSS in PMSI estimation of human cases, the Heaton, van Daalen and Reh DSS to assess the extent of decomposition visible in pictures of drowning victims from the Netherlands, U.K., and South Africa and compared with known PMSI. A ‘drowning database’ of data from global drowning cases cited in scientific literature and media was collated to understand worldwide drowning demographics.

This research demonstrated that temperature, salinity, hardness, and current significantly affected the decomposition rate of human analogues (p<0.05) and has shown for the first time that discolouration changes can be misleading in dark skin-toned individuals when using the DSS, and these DSS are inaccurate for estimating the PMSI of dark and pale-skinned bodies in advanced decomposition states or recovered in winter. Recommendations for applying the DSS to dark-skinned individuals have been made to improve the estimation of PMSI. Therefore, temperature, salinity, current, and hardness levels should be considered when estimating the PMSI of bodies recovered from marine environments, and more global studies should be conducted to improve the suitability of these DSS in assessing decomposition and estimating PMSI in darker-skin-toned individuals.