Evaluation of Soil Chemistry in Human Decomposition Sites
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Soil samples were analyzed from cadaver decomposition islands (CDI) of 63 human decomposition sites at the Forensic Anthropology Research Facility (FARF), Texas State University, in order to develop a method to estimate the postmortem interval (PMI) for each donation from these data. An additional 5 control site samples were also analyzed to establish a baseline record of undisturbed soils. Fifteen soil parameters were measured or calculated that included pH, electroconductivity, nitrate-N, ammonium-N, total dissolved nitrogen, dissolved organic nitrogen, orthophosphate-P, organic carbon, inorganic carbon, total carbon, sodium, potassium, magnesium, calcium and carbon/nitrogen ratio. Accumulated Degree Days (ADD) at a base temperature of 4°C (ADD_4) were also calculated for each donation. The data were analyzed using multiple regression with PMI and ADD_4 as the dependent variables and the soil parameters as independent variables. Regression formulae for 13 models were run that had R squared values ranging from 0.60 to 0.98 All of the models were statistically significant. The regression formulae results for ADD_4 were similar to PMI, indicating that ADD_4 may be used as a surrogate for estimating PMI. Measures of soil parameters derived from predator and microbial mediated decomposition of human remains show promise in estimating PMI accurately for a period up to nearly 5 years at FARF. This persistent change in soil chemistry extends the ability to estimate PMI in consort with the traditional methods of entomology and forensic anthropology in support of medical-legal investigations, humanitarian recovery efforts, and criminal and civil cases. This project has also recorded a baseline soil analysis for a new human decomposition research site.