The Influence of Alkaline or Acid Liquids on Cut Marks and on the Structure of Bone: An Experimental Study on Porcine Ribs

After attending this presentation, attendees will be aware of the macroscopic and microscopic effects of acid and basic solutions when used with the purpose of destroying a corpse and thus hindering discovery and identification. This presentation will impact the forensic science community by highlighting the effects of acid and basic solutions on bone and the importance in correctly assessing their effectiveness in the destruction of tissues and in the modification of signs of trauma. Among the different methods that are seldom used with the goal of destroying a corpse and thus preventing discovery or at least identification, the use of highly acidic or basic solutions is something forensic pathologists sometimes have to deal with, especially in criminal scenarios. Moreover, determining whether a bone (or even a single fragment) was in contact with an acidic/basic solution could be a crucial question posed to the anthropologist. Of all taphonomical modifications during decomposition processes, little is known about the action of high or low pH to human tissues and bones. The main question is, are these solutions able to make a cadaver completely “disappear” and, when human tissues come in contact with these substances, what kind of changes do they undergo? How are they recognizable? Only a few studies have focused on this issue and have referred only to macroscopic surveys. In this study, a total of 60 samples of porcine bone (Sus scrofa) were completely skeletonized manually, without any chemical or other artificial treatment. Furthermore, on each sample, a cut mark was produced with a scalpel in order to evaluate the modifications that these signs can undergo in such conditions. Specimens were then divided in groups of ten each and put in six different liquid solutions with different pH (1, 3, 5, 9, 12, 14) prepared by adding sulfuric and acetic acids and sodium hydroxide to water. A neutral control solution (pH 7) was also prepared. Specimens were analyzed every five days over a period of 70 days. The appearance of the outer cortical layer of the bone and the aspect of the cut marks were investigated first macroscopically and then microscopically with a Wild Heerbrug® M650 stereomicroscope and Scanning Electron Microscopy (SEM). Finally, thin undecalcified sections were prepared and analyzed with a transmitted light microscope in order to evaluate the changes of the osteonic structures and the appearance of characteristic patterns. Regarding the macroscopic observation, minimal lytic modifications became evident in all the samples, but only those exposed to a pH 14 for a long time showed evident alterations of the cortical bone, such as large erosions and cracking. Cut marks showed alterations in 50% of the cases, especially when exposed to basic solutions, detectable as enlargements, distortions, or detachment of bone flakes. The most interesting results arose from light microscopy of thin sections: if further significant elements were not gained with stereomicroscopy, scanning electron microscopy and light microscopy provided the most interesting results. The first enabled the observation of significant alterations on the surface of the cortical bone, with evident deposits of organic and inorganic matter as the pH became more acidic and as contact time increased. This layer of matter gives an important contribution to the macroscopic alterations of cut marks on bone which may, as in the case of pH 1 and 14, no longer be even recognizable. Moreover, the study showed for the first time that, even without detectable macroscopic alterations, the osteon structure visible in light microscopy is severely deteriorated by acids and bases, frequently with peculiar patterns, like radial or multidirectional cracking. The information gained from the present study can be of great help in the detection of an exposure of human tissues to high or low environmental pH and in understanding the effects that these solutions can exert on human bones. Extreme pH can significantly alter the structure of human bone and make signs of traumas undetectable, but the contact between solutions and bone can be detected if thoroughly analyzed, especially through light microscopy.