Energy-dispersive X-ray fluorescence methods for environmental characterization of soils

With recent requirements for rapid, field-based methods for environmental characterization, we have evaluated energy-dispersive X-ray fluorescence (EDXRF) techniques for elemental analyses of soils at Los Alamos using laboratory, transportable, and portable instruments. Fundamental parameters provide reasonably accurate standardization, and spectral interferences are generally absent. Detection limits are below screening action levels or background soil abundances for all elements of concern except As and Be. Results for certified materials indicate that accuracy is typically better than +/-10%, although some elements have few or no suitable reference materials to evaluate accuracy. Portable and fixed-base instruments typically give consistent results. However, large positive biases (2-78x) are generally found between EDXRF and standard EPA nitric acid digestion methods. This reflects the fact that EDXRF measures total amounts of the analyte, whereas EPA methods measure only the components labile in nitric acid and not the matrix. Consequently, EDXRF and EPA methods are not directly comparable for pristine soils, whereas contaminated soils should give more comparable results for the two techniques. Our data indicate that EDXRF can vastly exceed analytical requirements for field screening, and that this simple and fast technique can yield fully quantitative elemental analyses for soils in environmental studies.