The present work refers to the study of the topsoil layer for forensic application through
non-destructive in situ and in the laboratory analyses using portable equipment of
magnetic susceptibility, spectrophotometry and X-ray fluorescence in order to evaluate
the viability and reproducibility of the results obtained by different techniques in situ and
in the samples, collected on site and analyzed in the laboratory, before and after drying.
Two locations were studied, Arroteia in Leça do Balio, and Contumil in the proximity of
Estádio do Dragão, Porto. The work included two phases of collection and analyses, in
two seasons, Winter and Summer, in order to understand whether the season, in which
the investigation is carried out, has an influence on the results.. The aspect of transfer
and persistence of soil was also evaluated, since the residue of soil retained on the boots
used during the in situ analysis was studied.
With this study it was possible to verify that the methods used are viable and easy to
use. The results obtained are reproducible, although there are always some differences,
especially in the in situ analysis, since the analysis is punctual, with the sampled point
being variable and the soil without homogenization. In this case, the analyzes carried out
in the laboratory (on dry samples / wet samples) correlate better with each other than
the analyzes carried out in situ compared to those carried out in the laboratory.
Among the techniques used, we can conclude that magnetic susceptibility is the most
reliable analysis, because it has a higher correlation between samples analyzed in the
laboratory and in situ, compared to the other techniques.
The elaboration of this work allowed us to conclude that the season in which the
investigation is carried out may affect results since it was found that the data obtained in
the laboratory analysis with the wet sample is similar to the data obtained in the in situ
analysis carried out in the Winter, with higher humidity, and that the data obtained in the
laboratory analysis with the dry sample is similar to the data obtained in the in situ
analysis carried out in the summer.
The study of the soil retained on the boots allow its correlation with its source área.
The clusters analysis allowed to discriminate the two studied sites and also zones within
the sites.
This work will be added to a soil database of the FCUP and the Scientific Police
Laboratory of the Judicial Police, which may in the future be used in sample identification
work in situations where a crime has occurred