Soil samples, forensic comparisons

The major question posed now is how can soils be used to make accurate forensic comparisons when we know that soils are highly complex and that there are thousands of different soil types in existence For example, according to the USDA, which collects soil data at many different scales, there are more than 50,000 different varieties of soil in the United States alone. Parent material, climate, organisms, and the amount of time it takes for these properties to interact will vary worldwide. First of all, soil samples must be carefully collected and handled at the crime scene and then compared by a soil scientist with forensic science experience to ensure that the soil samples can be useful during an investigation. 

The lead contents of 206 soil samples determined by AAS indicated that such determination provides a useful parameter for soil comparison and discrimination in forensic science (Chaperlin 1981). Soil investigations near a former smelter in Colorado revealed that historic use of arsenical pesticides has contributed significantly to anthropogenic background concentrations of arsenic on certain residential properties. A variety of forensic techniques including spatial analysis, arsenic speciation and calculation of metal ratios were successful in the separation of smelter impacts from pesticide impacts (Folkes, Kuehster, and Litle 2001). 

Pye, K., Blott, S. J., Croft D. J., and Carter, J. F. (2006). Forensic comparison of soil samples Assessment of small-scale spatial variability in elemental composition, carbon and nitrogen isotope ratios, colour, and particle size distribution. Forensic Sci. Int. 163, 59-80. 

The systematic development of spot test methods of analysis occupied Fritz Feigl in Vienna and Rio de Janeiro for half a century up to 1970. Although in the past few decades chemical analysis has undergone a formidable process of sophistication with the development of advanced instrumental tools, there has been at the same time a contrary trend toward simplification in selected areas in the form of simple, rapid, and inexpensive spot and screening tests. Commercial companies are selling large numbers of compact spot test systems for the rapid establishment of the presence or absence of particular substances in clinical, food, water, soil, and forensic samples. The tests are essentially qualitative, but often can be semiquantitative if procedures as simple as visual comparison of color intensity are used. 

Practising analytical chemists face both qualitative and quantitative problems. As an example of the former, the presence of boron in distilled water is very damaging in the manufacture of microelectronic components - Does this distilled water sample contain any boron . Again, the comparison of soil samples is a common problem in forensic science - Could these two soil samples have come from the same site . In other cases the problems posed are quantitative. How much albumin is there in this sampie of biood serum , How much lead in this sample of tap-water , This steei sampie contains smaii quantities of chromium, tungsten and manganese - how much of each these are typicai exampies of single-component or multiple-component quantitative anaiyses. 

The Munsell color system is conceptually similar to the QELAB system, but with some significant differences. The Munsell system was conceived by the American painter Albert H. MunseU in 1905 with subsequent revisions and variations. The three variables used to describe colors in the system are hue, brightness (similar to lightness in QELAB), and saturation (similar to chroma also called value). As shown in Figure 11.14, the color space is cylindrical. The hue is divided into 100 equal spaces around the circle that forms the cross section of the cylinder, while the y direction is the brightness, scaled from 0 to 18. The x-axis is the saturation, scaled from 10 to 18. Munsell charts and collections are used in the forensic analysis of paints and soils. Because books and samples of color are used for color comparison, the Munsell color space is sometimes referred to as a catalog system. An example application is in soil analysis in which soil particles can be seived, sorted, and grouped by their Munsell color. 

---