Forensic Taphonomy: Copper and Aluminum Staining on Skeletal Material

Abstract

In forensic investigations, when an unknown decedent is found, the postmortem interval is a critical data point in establishing identification as well as reconstructing circumstances surrounding the death event. When the body reaches the fourth stage of decomposition, advanced decay, the soft tissues have been completely broken down. The decomposition of soft tissues leads to skeletonization, where only the hard skeletal tissues remain. These materials are then subject to diagenetic processes, including discoloration. The most commonly encountered stains on bones are from soil, organic materials, or metals. Staining on bone from metal compounds can be caused by numerous circumstances wherein various types of metal from clothing, projectiles, or other personal artifacts comes in contact with the remains. Because several factors influence the rate of decomposition, the postmortem interval between death and skeletonization can vary widely. Furthermore, the methods for determining the time between skeletonization and discovery are limited.

The following study explored the potential for estimating the postmortem interval via copper and aluminum staining patterns on skeletal remains. The specific goal of this research was to determine whether the discolorations can assist in estimating time since skeletonization and reconstructing the depositional environment. Additionally, the two types of metals were compared to establish any distinct staining pattern or discoloration on bone that is unique and can be presumed as belonging to either copper or aluminum. In the experiment, seven deer tibias were buried in a temperature-controlled environment. Pieces of copper and aluminum were affixed to each tibia. Once a week, for 20 weeks, each bone was examined for signs of discoloration from the metals. Munsell soil color charts were used to quantify the observed skeletal color changes, and a qualitative scoring system was used to measure the degree of staining each week. The staining on bone caused by copper was predominantly green with some yellow and grey variation and became more pronounced over time. Aluminum staining was largely white and exhibited a lesser extent of color change. The data analysis suggested both types of staining possess a rate of color change whose variability is correlated with time. The results of this study will contribute to the identification and assessment of discolorations on skeletal remains, which can potentially help reconstruct the depositional scene and estimate the time since skeletonization.