DIFFERENTIATING SOILS IN WESTERN NEW YORK USING XRF AND XRD TO BUILD A DATABASE

A common application of forensic geoscience involves analysis of soil deposits on tires, shoes, etc. and direct comparison with materials found at the crime scene. In an on-going intrusive analysis project, 100g soil samples from selected urban, suburban and rural areas are being collected in order to test our ability to distinguish their points of origin. The samples are oven dried, examined under a stereomicroscope, and sorted by grain size. The fines are analyzed using XRD and FPXRF. A long-term goal of this research is to compile a database of soil characteristics for western New York that can be used to help identify potential source areas for soil trace evidence. At the present time we are still quite far from that goal. This talk will present some results gathered thus far.

In the first example, samples were taken along the rivers in the Buffalo River watershed. The Buffalo River is located in the City of Buffalo, flows from the east through the city discharging into Lake Erie. Three samples were collected in the Buffalo River, two in the Cayuga Creek watershed, two in the Buffalo Creek watershed and three in the Cazenovia Creek watershed. The hope was that each of these areas would show distinct characteristics. Instead, the XRD diffractograms were virtually identical, demonstrating strong similarity of the mineral composition. Also, elemental composition shows no consistent patterns. The highest Pb, Mn and Zn levels were in the Buffalo River nearest the mouth, but the next highest were in the middle of Cazenovia Creek. Three samples, one from the Buffalo River and two from Cazenovia Creek, had moderate levels of Sb, Sn and Ag, but again there was no pattern relative to the flow of the river system. Local anthropogenic signals may dominate here.

Another example involves FPXRF sampling of public playgrounds. Thus far, all of the urban samples show significantly higher levels of Pb (150 - 370 ppm), Fe (~28,350 ppm) and Zn (230 ppm). These levels drop notably as you move into the suburbs: Pb ~ 35ppm, Fe ~ 20,000ppm and Zn ~ 100ppm. However, based on the data set so far, no reliable patterns for identification of source area have emerged. FPXRF can readily be used as a screening tool to differentiate soils from significantly different areas, though its utility to distinguish samples taken from relatively close proximity has yet to be established.