Application of Synchrotron Radiation X-Ray Fluorescence (μ-SRXF) and X-Ray Microanalysis (SEM/EDX) for the Quantitative and Qualitative Evaluation of Trace Element Accumulation in Woody Plants

Different analytical techniques were applied to describe the localization of lead and chromium in the tissues of walnut (Juglans regia) and maple (Acer saccharinum) plants exposed to soils that had been artificially contaminated with heavy metals. Two X-ray-based techniques, synchrotron radiation X-ray fluorescence (μ-SRXF) and X-ray microanalysis (SEM/EDX), were utilized in association with induced coupled plasma optical emission spectrometry (ICP-OES). These techniques allowed the definition of maps showing a preferential accumulation of lead in the root periderm of both plants and a limited translocation of the metal to the stems. Accordingly, estimation of the lead concentration with ICP-OES showed that roots contained, on a dry weight basis, 20 to 40 times more metal than stems. Chromium, supplied to the plants as Cr3+ or Cr6+, was taken up only in the latter case and in limited amounts. In general, walnut was more efficient than maple in the uptake of lead and chromium. The combination of X-ray-based techniques and ICP-OES proved to be a powerful quantitative tool in mapping, with high definition, the sites of metal storage in plant tissues.