Utility and Limitations of Portable X-Ray Fluorescence and Field Laboratory Conditions on the Geochemical Analysis of Soils and Floors at Areas of Known Human Activities

Portable x-ray fluorescence (pXRF) technology can be implemented in soil geochemical analysis for faster and more efficient testing of trace metals in soils. The level of soil phosphorus (P) is one of the major indicators of human activities related to food distribution, preparation, and waste disposal. Unfortunately, the low x-ray energy level of P and other light elements requires extensive sample preparation that may preclude pXRF as a field laboratory tool for P measurement. The high silicon content of soil causes serious interference in P analysis, yielding data of little value in midden prospection or activity area analysis. The Mehlich II or the Olsen bicarbonate extraction of soil samples can be conducted in a field laboratory providing excellent quality data. For pXRF analysis of soil samples in the field laboratory, it is recommended that soils are air-dry, and aggregates crushed, sieved (<2 mm), and mixed for better accuracy and reproducibility. Gridded soil samples from the central plaza of Telchaquillo, a contemporary village in Yucatan, were analyzed by the Mehlich II method for P and by pXRF and DTPA (diethylenetriaminepentaacetic acid) chelate extraction for trace metal concentrations. Areas of high P concentration were associated with an eatery and with two butchering posts. High DTPA extractable iron, copper, zinc, and manganese concentrations near the butchering posts were likely associated with the remnants of blood from butchered animals. The distributions and locations of elevated Fe concentrations were different for DTPA extractable Fe and pXRF total Fe and can be attributed to the different forms and solubility of crystalline iron in soil.