Building an isoscape based on tooth enamel for human provenance estimation in Brazil

In this study, we present a correlation between δ¹⁸O_C values of carbonate in tooth enamel samples from the modern Brazilian population and the available δ¹⁸O_DW data for the meteoric water from the Global Network of Isotopes in Precipitation (GNIP). Tooth enamel from 119 Brazilian individuals from five different regions of the country were analyzed. The δ¹⁸O_C isoscape obtained is in good agreement with the isoscape based on regional meteoric and drinking water. The regression matrix obtained for the δ¹⁸O values of the carbonate tooth enamel and meteoric water was used to build an isoscape using the regression-kriging approach. Our data show that Brazil can be divided in two main regions with respect to the δ¹⁸O values of the carbonate tooth enamel: (1) the most easterly part of the northeast region, which is characterized by a warm and dry climate and (2) the remainder of the country, stretching from the Amazon rain forest to the more southernly regions. The data herein reported can be used for forensic purposes related to human identification.

Detection of bone particles in non-carbonate soils

A routine geologic test for the presence of carbonate minerals in soil is the application of dilute hydrochloric acid (HCl) and observation for an effervescent reaction. This study tests whether non-carbonate soils can exhibit effervescence in the presence of HCl if bone particles are present in the soil. Five bone fragments displaying various taphonomic alterations were ground and sieved to achieve uniform particle size fractions. A non-carbonate soil was mixed with each bone particle fraction, and 1 molar HCl solution was applied while observing the reaction using a stereo microscope. All tests resulted in the effervescence of bone particles, which could be easily located within the soil based on the presence of small bubbles surrounding the bone particle. These results show that a simple, quick, cost-effective test can be used to presumptively determine whether soil may contain bone particles, even if they are too small to be identified morphologically. Results also suggest that, since bone particles in soil can produce the same type of effervescence expected in carbonate soil, additional tests may be needed to determine the source of an effervescent reaction. These findings also highlight the insight that can be gained through interdisciplinary discussions and investigations.

A probabilistic approach towards source level inquiries for forensic soil examination based on mineral counts

Forensic soil examination has a well-established foundation in forensic science, this is in part due to the widely varied and complex nature of soil. Within this domain, mineral suite studies are a commonly utilized tool in soil examination. However, statistical or probabilistic approaches towards the interpretation of results from such analysis are lacking and this study aims to fill that gap. Soil samples from four different locations in the city of Lausanne, Switzerland were sampled and their mineral fractions, light and heavy of size between 90 and 180 µm, were studied utilizing microscopical methods. First, the light minerals were identified and counted by employing scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). Second, the heavy minerals were identified and counted manually under a polarized light microscope (PLM). The resulting count data were subjected to various multivariate statistical treatments such as principal components analysis (PCA), hierarchical clustering analysis (HCA), and linear discriminant analysis (LDA). These methods assist in identifying pertinent variables and subsequently in building various classification models. The validities of these models were then tested and evaluated using blind tests. Finally, these methods demonstrate how a probabilistic approach can be taken in the interpretation of the results to answer source level questions.

The forensic utility of reworked geological materials in soil

Geological materials such as rock fragments, microfossils and mineral grains are continuously being entrained (i.e. reworked) into soil during natural weathering processes. Distinctive reworked rock types in soil, and specific components of them such as palynomorphs (organic microfossils), can prove extremely useful in forensic investigations, i.e. to connect (match) people to places. If the outcrop area of a unique rock is small and well mapped, it potentially has substantial evidentiary value in soil forensic studies. Furthermore, clay minerals, geochemical data and minerals may support the presence of a suspect at a crime scene. Modern pollen and spores extracted from soil samples in forensic investigations can be invaluable in linking suspects to crime scenes. This is because the majority of localities, especially those with natural vegetation, have characteristic (often unique) floral character. Reworked (i.e. largely pre-Quaternary) palynomorphs and other microscopic fossils may co-occur with the in situ (indigenous) pollen and spores. If these reworked forms have relatively short geological ranges, they can indicate the age of the bedrock, thereby further helping to place a person at a location. However, stratigraphically recycled palynomorphs in the soil can be somewhat rare and sporadic, and many rock units are entirely or virtually devoid of palynomorphs. Furthermore, glacial sediments such as till can provide highly mixed reworked palynomorph associations due to their typically heterogenous nature. These diverse assemblages are frequently highly distinctive hence can potentially provide very powerful forensic evidence. The potential of geological materials derived from bedrock in soil for forensic investigations is absolutely clear. Hence, the use of reworked microfossils, minerals and rock should be considered in any major crime where the evidence includes soil.