Avaliação das características físico-químicas de ilhas de decomposição cadavérica no desenvolvimento de modelos de previsão do intervalo pós-morte em área de mata tropical

Abstract

The post mortem interval (PMI) consists in a fundamental parameter to be determined to clarify cases of homicide. However, most of the methods used to estimate it, are based on the way the cadaveric decomposition occurs in only one specific situation or are incapable to estimate long PMI with precision, wich are common when the victim’s body is hidden. Besides that, as the process of decomposition is strongly influenced by the environmental characteristics and the way of disposing the body, prevision technics of PMI based on other locations hardly can be utilized in Amazonas, due to climatic peculiarities of the region. Therefore, this project had as primary objective evaluate the modifications the decomposed carcass make in the physicochemical properties of the soil around it, in a forest region, for the development of a prevision model for long PMI applicable in regions of tropical climate, hot and wet, in cases where the victim had been positioned above or under the ground. The experiment took place in a primary forest (Adolpho Ducke Forest Reserve), utilizing 6 specimens of swine as carcass for analogy to human decomposition, which were positioned above and below ground for a period of 67 days, being periodically collected soil samples from under each of the swine carcass every 72 hours. Moreover, it was also collected soil samples from a distance of 10 meters from the carcass. Every sample collected was analyzed to determine the following characteristics: pH, moisture, granulometric class, percentage of ammonium and nitrate, concentration of carbon from the microbial biomass, rate of basal respiration, total concentration of carbon, total concentration of nitrogen, C/N ratio, concentration of macro (Al3+, Ca2+, Mg2+, Na+, K+, PO4 2-) and micronutrients (Cu2+, Fe3+, Zn2+, Mn2+). Among the analyzed parameters, only the micronutrients and moisture did not show variations in their concentration during the cadaveric decomposition that could be used in the development of a prevision model of PMI. Starting from the variation in the concentration of the rest of the studied parameters it was possible to observe the difference that each type of decomposing carcass (above and underneath ground) caused in the chemical composition of the soil, indicating the necessity of two distinct models, one for each case. The time of decomposition of the buried carcass was approximately 4 times longer than the carcass above ground, however, in both cases the rate of the decomposition process was slower than what appears in the literature. Those results provide initial information about the soil behavior when submitted to cadaveric decomposition in a tropical forest region, indicating the possibility of utilize soil characterization as an alternate way of development of a new prevision model of PMI, applicable in an interval of 67 days.