Immersion of piglet carcasses in water--the applicability of microscopic analysis and limits of diatom testing on an animal model.

Investigation of bodies recovered in water comprises an important proportion of medico-legal cases, but is affected by relevant limits concerning the specific decomposition processes and the cause of death. Few indications are provided by literature concerning the post mortem modification of corpses in water, but for a general variability in decomposition degree, and only few experimental projects have been performed in order to verify the influence of water on the decomposition process. On the other hand, in order to reconstruct the cause of death, at present, the diatom test is considered as the "golden standard" for the diagnosis of drowning, although recent literature has pointed out its relative reliability and the frequent problems of contamination. This pilot study was performed to observe the changes of animal remains in aquatic environments. The following experimental system was set up: three piglet corpses, who died by natural causes independent from the study, were immerged in water rich in diatoms (Navicola, Order Pennales) in a tank exposed to the open air; macroscopic, histochemical and diatoms analysis were performed after 1, 2 and 3 months. Decomposition effects were fast: since the first month the skin appeared colliquated with exposure of the underlying bone surface, whereas at the second and third month the inner viscera were no longer recognizable; histology revealed that the skin was well preserved at 1 month, but morphology was completely altered at the second month, whereas at the third month epidermis was no longer visible. Diatom testing showed the presence of contamination both in the first and second piglet; the finding of a sea-diatom, on the other hand, was completely unexpected. This study performed for the first time histochemical testing on animal models submerged in water: although the results became negative after the second month, some microscopic structure could still be recognized at the end of the experimental project; on the other hand, the search for diatoms in the samples proved the high possibility of post mortem contamination.