Bone decomposition in aquatic environments

Abstract

Numerous studies have been undertaken on decomposing human remains in different terrestrial contexts. Determining postmortem interval and bone decomposition rate in cases where remains have been located in aquatic contexts, however, has been problematic due to numerous variables in the aquatic environment. These include but are not limited to water temperature, chemistry, bacteria, scavengers and current or tidal activity. Hence, research in this field has occurred in a somewhat limited capacity, with studies mainly focusing on the effects of water temperature and microorganisms on the decomposition of remains. This study used a controlled animal model experiment over 12 months between January 2019 and December 2019 in the Gold Coast region of Australia. Forty-eight de-fleshed pig femora were placed in tanks replicating differing types of aquatic environments, including riverine, oceanic, estuarine and dam, with a further four femora situated terrestrially to act as controls. Twelve femora were placed in each water type, with three removed at intervals of three, six, nine and twelve months, and four femora on a gravel surface (terrestrial control) surrounded by a cage, with one removed at the previously mentioned intervals. All femora were recorded before and during the fieldwork to examine the effects of taphonomic variables such as individual environment, water chemistry, marine scavenger activity and weathering. Following the removal and collection of the femora at the three-, six---, nine--- and twelve- month intervals, additional analysis was undertaken on the remains, including macro and microscopic quantification of bone surface modifications. This analysis, including measuring any increase in porosity to the surface of the bones, assessing changes in the weight of the bone from commencement to completion of the study, measuring the staining to the interior surface of the bone once cut into a thick section, and histologically inspecting and measuring any inclusions and infiltrations to the thin sections of bone, was used to determine the potential use of each in estimating bone decomposition rate in aquatic environments. The results demonstrated that water chemistry in differing locations plays a large part in the way in which remains decompose. For example, bones subject to the replicated ocean and estuarine environments were slower to decompose due to the scale-forming nature of the water, whereas bones subjected to the more corrosive environments of the riverine and weir environments were more rapidly degraded. It was found that it is indeed possible to measure and quantify bone diagenesis in differing aquatic environments and formulate methods to determine how long remains potentially may have been exposed to water, a bone decomposition, rate using both macroscopic and microscopic techniques. The implications are that in forensic cases where an isolated bone is located in an aquatic environment, researchers may be able to better determine how long this bone had been exposed to water in situ using the techniques developed with this research. Show more