ENERGY-DISPERSIVE X-RAY-FLUORESCENCE METHODS FOR ENVIRONMENTAL CHARACTERIZATION OF SOILS

With recent requirements for rapid, field-based methods for environmen tal characterization, we have evaluated energy-dispersive X-ray fluore scence (EDXRF) techniques for elemental analyses of soils at Los Alamo s using laboratory, transportable, and portable instruments. Fundament al parameters provide reasonably accurate standardization, and spectra l interferences are generally absent. Detection limits are below scree ning action levels or background soil abundances for all elements of c oncern 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 tha t EDXRF measures total amounts of the analyte, whereas EPA methods mea sure only the components labile in nitric acid and not the matrix. Con sequently, EDXRF and EPA methods are not directly comparable for prist ine soils, whereas contaminated soils should give more comparable resu lts for the two techniques. Our data indicate that EDXRF can vastly ex ceed analytical requirements for field screening, and that this simple and fast technique can yield fully quantitative elemental analyses fo r soils in environmental studies.